This document discusses multiscale modelling of urban climate. It proposes coupling global, mesoscale, and microscale models to account for climate effects that occur over different spatial and temporal scales, from months down to seconds and from kilometers to meters. The approach uses a global model to provide boundary conditions to a mesoscale model with hundreds of meter resolution, and couples this with an urban canopy model to capture local temperature and wind fields at smaller scales important for building energy use and pedestrian comfort. Governing equations for mass, momentum, energy, turbulence, and radiation are presented for the mesoscale and canopy models.
(1) The document discusses physics concepts related to magnetic fields, sound waves, orbital motion, heat transfer, electrostatics, and nuclear reactions.
(2) Multiple choice questions with one or more correct answers assess concepts like magnetic fields from current-carrying conductors and solenoids, Doppler effect of sound waves, orbital angular momentum and wavelength transitions in hydrogen-like atoms, heat absorption rates as a function of temperature, and electrostatic fields between overlapping charged spheres.
(3) Paragraph questions provide contexts for circular motion down an inclined plane with friction, step-up and step-down power transmission using transformers, and nuclear binding energy and the conditions for nuclear fusion and fission reactions.
Internal multiple attenuation using inverse scattering: Results from prestack...Arthur Weglein
The attenuation of internal multiples in a multidimensional
earth is an important and longstanding problem in exploration
seismics. In this paper we report the results of applying
an attenuation algorithm based on the inverse scattering
series to synthetic prestack data sets generated in on
and two dimensional earth models. The attenuation algorithm
requires no information about the subsurface structure
or the velocity field. However, detailed information about
the source wavelet is a prerequisite. An attractive feature of:
the attenuation algorithm is the preservation of the amplitude
(and phase) of primary events in the data; thus allowing for
subsequent AVO and other true amplitude processing.
This document summarizes a study measuring the transverse beam emittance at the Energy Selection System (ESS) of the KIRAMS-430 superconducting cyclotron. The researchers used a quadrupole variation method, where they varied the magnetic strength of a quadrupole magnet and measured the resulting beam size at a beam profile monitor. They analyzed the measurements using both linear matrix formalism and particle tracking simulations. The results from both analysis methods were consistent with emittances calculated from Monte Carlo simulations within the measurement uncertainties. The study demonstrated the feasibility of using the quadrupole variation method to characterize the beam quality at the ESS ion beamline.
The document discusses the calculation of vacuum polarization corrections to the energy levels of hydrogen atom. It presents numerical calculations of the one-photon vacuum polarization corrections to the 1s, 2s, 2p, 3s, 3p and 3d energy levels of hydrogen using the Uehling potential. The contribution of this correction decreases with increasing principal quantum number n and orbital quantum number l. It also calculates the relativistic effects on the 1s, 2s, 2p1/2 and 2p3/2 levels using Dirac wave functions. The results show the vacuum polarization effect is largest near the nucleus and decreases with n.
This document discusses the electromagnetic modeling of large planar arrays using the Scale Changing Technique (SCT). SCT decomposes planar structures into hierarchical scales to reduce computational requirements. It expresses fields on orthogonal modes and computes scale-changing networks between domains to model coupling. The document presents applications of SCT to modeling infinite and finite reflectarrays, characterizing coupling in non-uniform arrays, and simulating 2D arrays under plane wave and horn excitation. SCT was shown to efficiently model multiscale arrays and characterize coupling while avoiding issues of conventional full-wave solvers.
Comparison of Different Absorbing Boundary Conditions for GPR Simulation by t...IJMER
This paper compares three boundary conditions, i.e. transmitting boundary condition, Sarma
absorbing boundary condition and the uniaxial complete matched layerabsorbing boundary condition for
simulation of ground penetrating radar (GPR) by the time domain finite element (FEM) method. The
formulations of the three boundary conditions for the FEM method are described. Their effectiveness in
absorbing the incident electromagnetic waves are evaluated by the reflection coefficient on the boundary
of a simple GPR model.The results demonstrate that UPML boundary condition can yield a reflection
coefficient smaller than -50 dB, which is -20 dB smaller than other two boundary conditions.
Electronic bands structure and gap in mid-infrared detector InAs/GaSb type II...IJERA Editor
We present here theoretical study of the electronic bands structure E (d1) of InAs (d1=25 Å)/GaSb (d2=25 Å) type
II superlattice at 4.2 K performed in the envelope function formalism. We study the effect of d1 and the offset ,
between heavy holes bands edges of InAs and GaSb, on the band gap Eg (), at the center of the first Brillouin
zone, and the semiconductor-to-semimetal transition. Eg (, T) decreases from 288.7 meV at 4.2 K to 230 meV
at 300K. In the investigated temperature range, the cut-off wavelength 4.3 m ≤ c ≤ 5.4 m situates this sample
as mid-wavelength infrared detector (MWIR). Our results are in good agreement with the experimental data
realized by C. Cervera et al.
(1) The document discusses physics concepts related to magnetic fields, sound waves, orbital motion, heat transfer, electrostatics, and nuclear reactions.
(2) Multiple choice questions with one or more correct answers assess concepts like magnetic fields from current-carrying conductors and solenoids, Doppler effect of sound waves, orbital angular momentum and wavelength transitions in hydrogen-like atoms, heat absorption rates as a function of temperature, and electrostatic fields between overlapping charged spheres.
(3) Paragraph questions provide contexts for circular motion down an inclined plane with friction, step-up and step-down power transmission using transformers, and nuclear binding energy and the conditions for nuclear fusion and fission reactions.
Internal multiple attenuation using inverse scattering: Results from prestack...Arthur Weglein
The attenuation of internal multiples in a multidimensional
earth is an important and longstanding problem in exploration
seismics. In this paper we report the results of applying
an attenuation algorithm based on the inverse scattering
series to synthetic prestack data sets generated in on
and two dimensional earth models. The attenuation algorithm
requires no information about the subsurface structure
or the velocity field. However, detailed information about
the source wavelet is a prerequisite. An attractive feature of:
the attenuation algorithm is the preservation of the amplitude
(and phase) of primary events in the data; thus allowing for
subsequent AVO and other true amplitude processing.
This document summarizes a study measuring the transverse beam emittance at the Energy Selection System (ESS) of the KIRAMS-430 superconducting cyclotron. The researchers used a quadrupole variation method, where they varied the magnetic strength of a quadrupole magnet and measured the resulting beam size at a beam profile monitor. They analyzed the measurements using both linear matrix formalism and particle tracking simulations. The results from both analysis methods were consistent with emittances calculated from Monte Carlo simulations within the measurement uncertainties. The study demonstrated the feasibility of using the quadrupole variation method to characterize the beam quality at the ESS ion beamline.
The document discusses the calculation of vacuum polarization corrections to the energy levels of hydrogen atom. It presents numerical calculations of the one-photon vacuum polarization corrections to the 1s, 2s, 2p, 3s, 3p and 3d energy levels of hydrogen using the Uehling potential. The contribution of this correction decreases with increasing principal quantum number n and orbital quantum number l. It also calculates the relativistic effects on the 1s, 2s, 2p1/2 and 2p3/2 levels using Dirac wave functions. The results show the vacuum polarization effect is largest near the nucleus and decreases with n.
This document discusses the electromagnetic modeling of large planar arrays using the Scale Changing Technique (SCT). SCT decomposes planar structures into hierarchical scales to reduce computational requirements. It expresses fields on orthogonal modes and computes scale-changing networks between domains to model coupling. The document presents applications of SCT to modeling infinite and finite reflectarrays, characterizing coupling in non-uniform arrays, and simulating 2D arrays under plane wave and horn excitation. SCT was shown to efficiently model multiscale arrays and characterize coupling while avoiding issues of conventional full-wave solvers.
Comparison of Different Absorbing Boundary Conditions for GPR Simulation by t...IJMER
This paper compares three boundary conditions, i.e. transmitting boundary condition, Sarma
absorbing boundary condition and the uniaxial complete matched layerabsorbing boundary condition for
simulation of ground penetrating radar (GPR) by the time domain finite element (FEM) method. The
formulations of the three boundary conditions for the FEM method are described. Their effectiveness in
absorbing the incident electromagnetic waves are evaluated by the reflection coefficient on the boundary
of a simple GPR model.The results demonstrate that UPML boundary condition can yield a reflection
coefficient smaller than -50 dB, which is -20 dB smaller than other two boundary conditions.
Electronic bands structure and gap in mid-infrared detector InAs/GaSb type II...IJERA Editor
We present here theoretical study of the electronic bands structure E (d1) of InAs (d1=25 Å)/GaSb (d2=25 Å) type
II superlattice at 4.2 K performed in the envelope function formalism. We study the effect of d1 and the offset ,
between heavy holes bands edges of InAs and GaSb, on the band gap Eg (), at the center of the first Brillouin
zone, and the semiconductor-to-semimetal transition. Eg (, T) decreases from 288.7 meV at 4.2 K to 230 meV
at 300K. In the investigated temperature range, the cut-off wavelength 4.3 m ≤ c ≤ 5.4 m situates this sample
as mid-wavelength infrared detector (MWIR). Our results are in good agreement with the experimental data
realized by C. Cervera et al.
The enhancement of sub-barrier fusion has been interpreted due to coupling between the relative motion and other degrees of freedom. The coupling gives rise to the distribution of fusion barriers and passage over the lowest barrier which is responsible for fusion enhancement at energies below the barrier. There are several orders of magnitude could be considered due to the tunneling through the barrier. The barrier height could be deduced from the measured cross section data for different energies, as well as using many empirical forms for incomplete and complete fusion of two massive nuclei. Firstly, we present a formula for barrier height (ODEFF) and check, over wide ranges of interacting pairs the percentage agreement with those calculated or measured values for all pairs within ZP ZT ≤ 3000. Secondly, the more recently measured excitation functions are studied using four models of nuclear forces, indicating that most of them can be used for wide energy range while the others failed to do so .We refer this notice to the theory deducing the model . For this, the 14 undertaken pairs recover the range18 ≤ ZP ZT ≤ 1320
This document contains:
1) Instructions for a past IB exam paper that requires answering all questions from Section A and one from Section B within 75 minutes.
2) Three sample questions from Section A about physics concepts including motion in a magnetic field, forces on a rotating ball, and energy transfers.
3) Details for three optional questions in Section B, two involving multiple parts about topics in physics and one in chemistry.
Analytical approach of ordinary frozen wavesAmélia Moreira
This document describes analytical work on frozen waves (FWs) and their potential application in optical trapping and micromanipulation. FWs are constructed from a superposition of Bessel beams with different longitudinal wave numbers that can generate a predetermined longitudinal intensity profile. The generalized Lorenz-Mie theory and integral localized approximation are used to derive expressions for the beam-shape coefficients that describe FWs and allow calculation of their optical properties. Examples of FW intensity profiles are shown to agree with previous works. Optical forces exerted by FWs on spherical particles are also calculated.
This document summarizes an approach for classifying seafloor textures in high resolution sonar images using multiscale discriminant analysis. The approach extracts statistical parameters from wavelet decompositions of the sonar images at multiple scales. A discriminant analysis is then used to reduce the feature space and generate an optimal subspace for classification. The method was tested on real sonar images containing speckle noise and showed improved classification of seabed textures like pebbles, dunes, ridges and sand.
2012 NPhysics - Sculpting oscillators with light within a nonlinear quantum f...Guilherme Tosi
This document summarizes research on sculpting oscillating quantum fluids of light within a nonlinear polariton condensate. Key points:
1) The researchers were able to directly image stable quantum oscillator wavefunctions of polariton condensates in real space using a simple optical microscope.
2) By injecting polaritons at two spatially separated points, an effective potential was created that trapped the polaritons into quantized energy levels resembling a simple harmonic oscillator.
3) Varying the pump properties in real time allowed controlling the shape and energy levels of the potential, demonstrating potential for integrated polariton-based quantum devices.
1607.07566 strain-controlled spin splitting in the conduction band ofmonolaye...MUHAMMADANSHORY5
1) The document discusses how applying biaxial strain can effectively control and tune the substantial spin splitting bands observed in the conduction band minimum (CBM) of monolayer WS2.
2) First-principles density functional theory calculations show that these spin splitting bands induce spin textures with fully out-of-plane spin polarization in opposite directions between the K and Q points.
3) The study clarifies that strain plays a significant role in the spin-orbit coupling of monolayer WS2, with implications for designing future spintronics devices.
As recent and future galaxy surveys map the large-scale structure of the universe with unprecedented pace and precision, it is worthwhile to consider innovative data analysis methods beyond traditional Gaussian 2-point statistics to extract more cosmological information from those datasets. Such efforts are often plagued by substantially increased complexity of the analysis. Hoping to improve this, I will present simple, nearly optimal methods to measure 3-point statistics as easily as 2-point statistics, by cross-correlating the mass density with specific quadratic fields [arXiv:1411.6595]. Inspired by these results, I will argue that BAO reconstructions already combine 2-point statistics with certain 3- and 4-point functions automatically [arXiv:1508.06972]. I will present several new Eulerian and Lagrangian reconstruction algorithms and discuss their performance in simulations.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Modeling the transport of charge carriers in the active devices diode submicr...IJERA Editor
A Monte Carlo simulation program was developed to simulate the movement of electrons in a submicron GaInP diode three dimensional (3D) with 0.1 microns-long active layer. The algorithm couples a standard Monte Carlo particle simulator for the Boltzmann equation with a 3D Poisson solver. Thus a series of hits for a specific MC submicron diode (GaInP), with an active layer (n = 2x1015cm-3) of length 0.1μm surrounded by two regions doped with n = 5x1017cm-3, are presented. The lattice temperature is 300K and the anode voltage Va is 1V. The analysis also showed that the average drift velocity to the electrons in the channel is about 5x106 cm/sec
1) Researchers designed novel antennas using coordinate transformation to manipulate electromagnetic waves, including a directive antenna, beam-steerable antenna, and quasi-isotropic antenna.
2) Specifically, an ultra-directive antenna was designed by transforming a cylindrical space into a rectangular one, stretching a radiating source into an extended coherent radiator.
3) The antenna was fabricated using metamaterials constructed from layers of split-ring resonators and electric LC resonators to achieve the required electromagnetic parameters for the transformation. Measurements showed the antenna transformed an omnidirectional radiation pattern into a highly directive emission with a 13 degree half-power beamwidth.
Segmentation Based Multilevel Wide Band Compression for SAR Images Using Coif...CSCJournals
Synthetic aperture radar (SAR) data represents a significant resource of information for a large variety of researchers. Thus, there is a strong interest in developing data encoding and decoding algorithms which can obtain higher compression ratios while keeping image quality to an acceptable level. In this work, results of different wavelet-based image compression and segmentation based wavelet image compression are assessed through controlled experiments on synthetic SAR images. The effects of dissimilar wavelet functions, number of decompositions are examined in order to find optimal family for SAR images. The choice of optimal wavelets in segmentation based wavelet image compression is coiflet for low frequency and high frequency component. The results presented here is a good reference for SAR application developers to choose the wavelet families and also it concludes that wavelets transform is rapid, robust and reliable tool for SAR image compression. Numerical results confirm the potency of this approach.
1) The document discusses the motion of a projectile in a constant gravitational field under the influence of a retarding force proportional to its velocity.
2) It expresses the time of flight and time of fall/rise of the projectile as functions of the constant of resistance per unit mass of the projectile.
3) It proves that the time of fall is always greater than the time of rise, except when the constant of resistance is zero, where they are equal.
Optimal energy management and storage sizing for electric vehiclesPower System Operation
This document summarizes an approach to optimally manage power sharing between the battery and supercapacitor in a hybrid energy storage system for electric vehicles. It formulates the problem as an infinite horizon dynamic program and solves it using linear programming with basis function approximation. Numerical results show the suboptimal policy from this approach can closely approximate the optimal policy given a sufficient number of basis functions.
This document discusses the seismic safety assessment of rockfill dams. It presents an alternative approach to assessing slope stability under earthquake loading that is based on full dynamic time domain analysis, rather than the standard quasi-static method. The document describes the finite element model of a rockfill dam case study, including geometry, material properties, and applied static and earthquake loading. It notes that full dynamic analysis can better account for dynamic effects on slope stability compared to the quasi-static method.
A general theoretical design of semiconductor nanostructures withAlexander Decker
This document presents a theoretical design for semiconductor nanostructures with equispaced energy levels, specifically for quantum wells in semiconductor ternary alloys. The procedure maps the envelope function Schrodinger equation for a realistic quantum well into an effective-mass Schrodinger equation with a linear harmonic oscillator potential through coordinate transformation. This allows the electron effective mass and potential to be obtained, providing signatures for the equispaced energy levels in quantum wells of semiconductor ternary alloys. Preliminary results are presented for ternary alloy quantum wells, with the goal of generalizing previous studies and obtaining solutions that depict the signatures for equispaced energy levels.
1) A bar magnet falling through a copper pipe reaches a terminal velocity due to eddy currents induced in the pipe walls from the changing magnetic field.
2) By equating the loss of potential energy to energy dissipated through Joule heating, an expression for terminal velocity as a function of magnet and pipe properties is derived.
3) Only considering the magnetic dipole contribution results in an estimated copper conductivity around 40% lower than published values, showing higher order effects are needed.
TWO DIMENSIONAL MODELING OF NONUNIFORMLY DOPED MESFET UNDER ILLUMINATIONVLSICS Design
A two dimensional numerical model of an optically gated GaAs MESFET with non uniform channel doping has been developed. This is done to characterize the device as a photo detector. First photo induced voltage (Vop) at the Schottky gate is calculated for estimating the channel profile. Then Poisson’s equation for the device is solved numerically under dark and illumination condition. The paper aims at developing the MESFET 2-D model under illumination using Monte Carlo Finite Difference method. The results discuss about the optical potential developed in the device, variation of channel potential under different biasing and illumination and also about electric fields along X and Y directions. The Cgs under different illumination is also calculated. It has been observed from the results that the characteristics of the device are strongly influenced by the incident optical illumination.
El documento describe las principales técnicas de compresión de datos utilizadas en la televisión digital, incluyendo MPEG-2 y MPEG-4 para video, MPEG y AC-3 para audio, y la transmisión de datos. Explica cómo la transformada discreta del coseno es fundamental para la compresión de video y los diferentes tipos de frames que usa MPEG-2. También cubre el estándar chino AVS y las ventajas del sistema Dolby AC-3 para audio multicanal.
The Airbus A380 is the world's largest passenger airliner. It has a double-deck design with space for over 500 passengers. The upper deck extends the entire length of the aircraft. Airbus began developing the A380 in 2000 to compete with the Boeing 747. Major structural sections are built across Europe and assembled in France. The A380 completed its first flight in 2005 and entered commercial service with Singapore Airlines in 2007. Several airlines now use the A380, with Emirates having the most on order.
This document summarizes research comparing the effects of complex urban geometries versus simplified representations in mesoscale modeling. It tests the hypothesis that cities can be accurately modeled as regular arrays of cubes or canopies. The document describes simulations of drag forces, shortwave radiation exchange, and wind flow for a real urban geometry compared to simplified representations of long canopies and cubes while keeping total built volume equal. Results show differences in drag, radiation absorption on walls and ground, and velocity fields between the real and simplified geometries.
This document contains a collection of links related to App Inventor and programming. It includes links to photos of early App Inventor workshops in Japan, documentation on the Squeak programming language, news articles about App Inventor moving to MIT, the main App Inventor website, Japanese blogs discussing App Inventor, and the App Inventor Japan Google group. The links provide resources for learning about and using App Inventor, a visual programming tool for building Android apps.
The enhancement of sub-barrier fusion has been interpreted due to coupling between the relative motion and other degrees of freedom. The coupling gives rise to the distribution of fusion barriers and passage over the lowest barrier which is responsible for fusion enhancement at energies below the barrier. There are several orders of magnitude could be considered due to the tunneling through the barrier. The barrier height could be deduced from the measured cross section data for different energies, as well as using many empirical forms for incomplete and complete fusion of two massive nuclei. Firstly, we present a formula for barrier height (ODEFF) and check, over wide ranges of interacting pairs the percentage agreement with those calculated or measured values for all pairs within ZP ZT ≤ 3000. Secondly, the more recently measured excitation functions are studied using four models of nuclear forces, indicating that most of them can be used for wide energy range while the others failed to do so .We refer this notice to the theory deducing the model . For this, the 14 undertaken pairs recover the range18 ≤ ZP ZT ≤ 1320
This document contains:
1) Instructions for a past IB exam paper that requires answering all questions from Section A and one from Section B within 75 minutes.
2) Three sample questions from Section A about physics concepts including motion in a magnetic field, forces on a rotating ball, and energy transfers.
3) Details for three optional questions in Section B, two involving multiple parts about topics in physics and one in chemistry.
Analytical approach of ordinary frozen wavesAmélia Moreira
This document describes analytical work on frozen waves (FWs) and their potential application in optical trapping and micromanipulation. FWs are constructed from a superposition of Bessel beams with different longitudinal wave numbers that can generate a predetermined longitudinal intensity profile. The generalized Lorenz-Mie theory and integral localized approximation are used to derive expressions for the beam-shape coefficients that describe FWs and allow calculation of their optical properties. Examples of FW intensity profiles are shown to agree with previous works. Optical forces exerted by FWs on spherical particles are also calculated.
This document summarizes an approach for classifying seafloor textures in high resolution sonar images using multiscale discriminant analysis. The approach extracts statistical parameters from wavelet decompositions of the sonar images at multiple scales. A discriminant analysis is then used to reduce the feature space and generate an optimal subspace for classification. The method was tested on real sonar images containing speckle noise and showed improved classification of seabed textures like pebbles, dunes, ridges and sand.
2012 NPhysics - Sculpting oscillators with light within a nonlinear quantum f...Guilherme Tosi
This document summarizes research on sculpting oscillating quantum fluids of light within a nonlinear polariton condensate. Key points:
1) The researchers were able to directly image stable quantum oscillator wavefunctions of polariton condensates in real space using a simple optical microscope.
2) By injecting polaritons at two spatially separated points, an effective potential was created that trapped the polaritons into quantized energy levels resembling a simple harmonic oscillator.
3) Varying the pump properties in real time allowed controlling the shape and energy levels of the potential, demonstrating potential for integrated polariton-based quantum devices.
1607.07566 strain-controlled spin splitting in the conduction band ofmonolaye...MUHAMMADANSHORY5
1) The document discusses how applying biaxial strain can effectively control and tune the substantial spin splitting bands observed in the conduction band minimum (CBM) of monolayer WS2.
2) First-principles density functional theory calculations show that these spin splitting bands induce spin textures with fully out-of-plane spin polarization in opposite directions between the K and Q points.
3) The study clarifies that strain plays a significant role in the spin-orbit coupling of monolayer WS2, with implications for designing future spintronics devices.
As recent and future galaxy surveys map the large-scale structure of the universe with unprecedented pace and precision, it is worthwhile to consider innovative data analysis methods beyond traditional Gaussian 2-point statistics to extract more cosmological information from those datasets. Such efforts are often plagued by substantially increased complexity of the analysis. Hoping to improve this, I will present simple, nearly optimal methods to measure 3-point statistics as easily as 2-point statistics, by cross-correlating the mass density with specific quadratic fields [arXiv:1411.6595]. Inspired by these results, I will argue that BAO reconstructions already combine 2-point statistics with certain 3- and 4-point functions automatically [arXiv:1508.06972]. I will present several new Eulerian and Lagrangian reconstruction algorithms and discuss their performance in simulations.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Modeling the transport of charge carriers in the active devices diode submicr...IJERA Editor
A Monte Carlo simulation program was developed to simulate the movement of electrons in a submicron GaInP diode three dimensional (3D) with 0.1 microns-long active layer. The algorithm couples a standard Monte Carlo particle simulator for the Boltzmann equation with a 3D Poisson solver. Thus a series of hits for a specific MC submicron diode (GaInP), with an active layer (n = 2x1015cm-3) of length 0.1μm surrounded by two regions doped with n = 5x1017cm-3, are presented. The lattice temperature is 300K and the anode voltage Va is 1V. The analysis also showed that the average drift velocity to the electrons in the channel is about 5x106 cm/sec
1) Researchers designed novel antennas using coordinate transformation to manipulate electromagnetic waves, including a directive antenna, beam-steerable antenna, and quasi-isotropic antenna.
2) Specifically, an ultra-directive antenna was designed by transforming a cylindrical space into a rectangular one, stretching a radiating source into an extended coherent radiator.
3) The antenna was fabricated using metamaterials constructed from layers of split-ring resonators and electric LC resonators to achieve the required electromagnetic parameters for the transformation. Measurements showed the antenna transformed an omnidirectional radiation pattern into a highly directive emission with a 13 degree half-power beamwidth.
Segmentation Based Multilevel Wide Band Compression for SAR Images Using Coif...CSCJournals
Synthetic aperture radar (SAR) data represents a significant resource of information for a large variety of researchers. Thus, there is a strong interest in developing data encoding and decoding algorithms which can obtain higher compression ratios while keeping image quality to an acceptable level. In this work, results of different wavelet-based image compression and segmentation based wavelet image compression are assessed through controlled experiments on synthetic SAR images. The effects of dissimilar wavelet functions, number of decompositions are examined in order to find optimal family for SAR images. The choice of optimal wavelets in segmentation based wavelet image compression is coiflet for low frequency and high frequency component. The results presented here is a good reference for SAR application developers to choose the wavelet families and also it concludes that wavelets transform is rapid, robust and reliable tool for SAR image compression. Numerical results confirm the potency of this approach.
1) The document discusses the motion of a projectile in a constant gravitational field under the influence of a retarding force proportional to its velocity.
2) It expresses the time of flight and time of fall/rise of the projectile as functions of the constant of resistance per unit mass of the projectile.
3) It proves that the time of fall is always greater than the time of rise, except when the constant of resistance is zero, where they are equal.
Optimal energy management and storage sizing for electric vehiclesPower System Operation
This document summarizes an approach to optimally manage power sharing between the battery and supercapacitor in a hybrid energy storage system for electric vehicles. It formulates the problem as an infinite horizon dynamic program and solves it using linear programming with basis function approximation. Numerical results show the suboptimal policy from this approach can closely approximate the optimal policy given a sufficient number of basis functions.
This document discusses the seismic safety assessment of rockfill dams. It presents an alternative approach to assessing slope stability under earthquake loading that is based on full dynamic time domain analysis, rather than the standard quasi-static method. The document describes the finite element model of a rockfill dam case study, including geometry, material properties, and applied static and earthquake loading. It notes that full dynamic analysis can better account for dynamic effects on slope stability compared to the quasi-static method.
A general theoretical design of semiconductor nanostructures withAlexander Decker
This document presents a theoretical design for semiconductor nanostructures with equispaced energy levels, specifically for quantum wells in semiconductor ternary alloys. The procedure maps the envelope function Schrodinger equation for a realistic quantum well into an effective-mass Schrodinger equation with a linear harmonic oscillator potential through coordinate transformation. This allows the electron effective mass and potential to be obtained, providing signatures for the equispaced energy levels in quantum wells of semiconductor ternary alloys. Preliminary results are presented for ternary alloy quantum wells, with the goal of generalizing previous studies and obtaining solutions that depict the signatures for equispaced energy levels.
1) A bar magnet falling through a copper pipe reaches a terminal velocity due to eddy currents induced in the pipe walls from the changing magnetic field.
2) By equating the loss of potential energy to energy dissipated through Joule heating, an expression for terminal velocity as a function of magnet and pipe properties is derived.
3) Only considering the magnetic dipole contribution results in an estimated copper conductivity around 40% lower than published values, showing higher order effects are needed.
TWO DIMENSIONAL MODELING OF NONUNIFORMLY DOPED MESFET UNDER ILLUMINATIONVLSICS Design
A two dimensional numerical model of an optically gated GaAs MESFET with non uniform channel doping has been developed. This is done to characterize the device as a photo detector. First photo induced voltage (Vop) at the Schottky gate is calculated for estimating the channel profile. Then Poisson’s equation for the device is solved numerically under dark and illumination condition. The paper aims at developing the MESFET 2-D model under illumination using Monte Carlo Finite Difference method. The results discuss about the optical potential developed in the device, variation of channel potential under different biasing and illumination and also about electric fields along X and Y directions. The Cgs under different illumination is also calculated. It has been observed from the results that the characteristics of the device are strongly influenced by the incident optical illumination.
El documento describe las principales técnicas de compresión de datos utilizadas en la televisión digital, incluyendo MPEG-2 y MPEG-4 para video, MPEG y AC-3 para audio, y la transmisión de datos. Explica cómo la transformada discreta del coseno es fundamental para la compresión de video y los diferentes tipos de frames que usa MPEG-2. También cubre el estándar chino AVS y las ventajas del sistema Dolby AC-3 para audio multicanal.
The Airbus A380 is the world's largest passenger airliner. It has a double-deck design with space for over 500 passengers. The upper deck extends the entire length of the aircraft. Airbus began developing the A380 in 2000 to compete with the Boeing 747. Major structural sections are built across Europe and assembled in France. The A380 completed its first flight in 2005 and entered commercial service with Singapore Airlines in 2007. Several airlines now use the A380, with Emirates having the most on order.
This document summarizes research comparing the effects of complex urban geometries versus simplified representations in mesoscale modeling. It tests the hypothesis that cities can be accurately modeled as regular arrays of cubes or canopies. The document describes simulations of drag forces, shortwave radiation exchange, and wind flow for a real urban geometry compared to simplified representations of long canopies and cubes while keeping total built volume equal. Results show differences in drag, radiation absorption on walls and ground, and velocity fields between the real and simplified geometries.
This document contains a collection of links related to App Inventor and programming. It includes links to photos of early App Inventor workshops in Japan, documentation on the Squeak programming language, news articles about App Inventor moving to MIT, the main App Inventor website, Japanese blogs discussing App Inventor, and the App Inventor Japan Google group. The links provide resources for learning about and using App Inventor, a visual programming tool for building Android apps.
This Ruby script opens an Excel file, iterates through each cell in the used range of the active sheet, prints the cell name and age, closes the book and quits the Excel application. It then takes the data, converts it to a YAML format and saves it to a file. Finally, it loads the YAML file and saves each person object to the database.
Este artigo investiga as causas e efeitos do estresse no corpo e na mente humanos. Discute que a prática de atividades físicas e yoga podem ajudar a prevenir e controlar o estresse de forma eficaz, promovendo o bem-estar psicofísico e melhorando a qualidade de vida sob diversos aspectos. O artigo também descreve os sintomas físicos e mentais do estresse e como o yoga, ao complementar a atividade física, pode tratar e prevenir o estresse de maneira mais efetiva.
This document summarizes a study that compares the effects of complex urban geometries versus simplified geometries on mesoscale modeling. Specifically, it examines the impacts on spatially averaged drag forces, velocities, turbulent kinetic energy, and shortwave radiation exchange. The study uses an Immersed Boundary Technique to compute velocity fields and a Simplified Radiosity Algorithm to compute radiative exchanges. Results show that while total solar radiation entering complex and simplified domains is the same, the distribution of radiation absorbed by roofs, walls, and ground surfaces differs between the geometries.
Atmosphere Clouds Model Algorithm for Solving Optimal Reactive Power Dispatch...ijeei-iaes
In this paper, a new method, called Atmosphere Clouds Model (ACM) algorithm, used for solving optimal reactive power dispatch problem. ACM stochastic optimization algorithm stimulated from the behavior of cloud in the natural earth. ACM replicate the generation behavior, shift behavior and extend behavior of cloud. The projected (ACM) algorithm has been tested on standard IEEE 30 bus test system and simulation results shows clearly about the superior performance of the proposed algorithm in plummeting the real power loss.
CitySim is micro-simulation software for comprehensively modeling and optimizing resource flows in urban planning. It simulates buildings' energy flows using a thermal circuit model and considers embodied energy and water/waste flows. CitySim couples with a transportation model to account for all key urban resource flows. This allows testing planning interventions to improve sustainability. Current work focuses on extending CitySim's modeling capabilities and optimizing urban resource flows using evolutionary algorithms.
This document discusses a new multi-scale modeling approach for simulating urban climate. It involves coupling macro, meso, and micro-scale models. Freely available macro-scale model results are input into a meso-model with grid sizes representing the city. This meso-model interpolates the results to finer scales representing the city boundaries. An urban canopy model is used to account for building energy exchanges. A new immersed boundary approach allows micro-scale fluid simulations using a simple grid for any complex geometry. This coupled multi-scale model can predict city-scale temperature, wind, and pressure fields accounting for both building-scale and larger topographical effects.
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This document summarizes a numerical study of airflow over an Ahmed body using RANS turbulence models. It finds that the k-ε-v2 model more accurately predicts separation and reattachment compared to other models. The study simulates flow over an Ahmed body with a 35 degree rear angle using various turbulence models and investigates the effects of grid layout and differencing schemes on the results. Numerical results agree well with experimental data on the wake structure and turbulent kinetic energy distribution behind the body.
Physical processes in the earth system are modeled with mathematical representations called parameterizations. This talk will describe some of the conceptual approaches and mathematics used do describe physical parameterizations focusing on cloud parameterizations. This includes tracing physical laws to discrete representations in coarse scale models. Clouds illustrate several of the complexities and techniques common to many physical parameterizations. This includes the problem of different scales, sub-grid scale variability. Discussions of mathematical methods for dealing with the sub-grid scale will be discussed. In-exactness or indeterminate problems for both weather and climate will be discussed, including the problems of indeterminate parameterizations, and inexact initial conditions. Different mathematical methods, including the use of stochastic methods, will be described and discussed, with examples from contemporary earth system models.
Thin Film Pressure Estimation of Argon and Water using LAMMPSCSCJournals
In this work, we investigate the pressure and density characteristics of water film when simulated using the emerging technique called many body dissipative particle dynamics method. This work also layout the methodology of estimating local pressure from LAMMPS simulation using Harasima scheme. Using the triangular shaped cloud interpolation function, pressure and density are estimated at local bins and compared with the experimental database. Our results show good agreement for the molecular dynamics results of the argon system, while the many body dissipative particle model fails to simulate the water properties at room temperature. In its current form, the many body dissipative particle method cannot be used for accurate liquid vapor interfacial simulations and heat transfer studies.
This document summarizes a research article about a capacitance-to-digital converter (CDC) designed for capacitive MEMS sensors. The CDC uses a two-step process: 1) A switched-capacitor preamplifier converts the capacitance to a voltage. 2) A self-oscillated noise-shaping integrating dual-slope converter digitizes the output into a multi-bit digital stream by using time resolution rather than amplitude resolution. Experimental results on a prototype show the CDC achieves 17-bit resolution while consuming 146 μA from a 1.5V power supply, allowing pressure sensing at 1 Pa resolution.
Use of mesoscale modeling to increase the reliability of wind resource assess...Jean-Claude Meteodyn
During wind farm design phase, the wind direction distribution is a crucial information for wind turbine layout optimization. However, in complex terrains, the wind rose at hub height of the wind turbines can be quite different from met mast measurement.The study shows that in complex terrains, the use of mesoscale modeling provides a complement to met mast measurement. It allows to better determine the turbine-specific wind rose and to reduce the uncertainty in wind resource assessment. The coupling of mesoscale and CFD model allows to produce high resolution wind map, by taking into account both mesoscale and microscale terrain effects.
This document discusses atmospheric chemistry models and their use in quantifying atmospheric concentrations and fluxes. Global 3D models divide the atmosphere into grid boxes and use the continuity equation to track species concentrations over time, accounting for transport, chemistry, emissions and deposition. Transport is parameterized using turbulence and convection schemes. Chemistry is solved using operator splitting and implicit methods. Models are evaluated and improved using atmospheric observations from satellites, aircraft and surface sites through data assimilation techniques like inverse modeling. Examples are given of various applications of the GEOS-CHEM global model.
Optical Absoprtion of Thin Film SemiconductorsEnrico Castro
This document analyzes the optical properties of several thin film semiconductors. It characterizes the transmittance, reflectance, and absorption of CdS films deposited at different times, as well as Sb-S-Se films deposited at different temperatures. Key results include the absorption coefficient, transmission and reflection percentages in different wavelength regions, and estimates of photon flux and potential short circuit current density for each film based on their bandgaps. Optical properties were measured using UV-VIS spectroscopy to understand how effectively the materials could absorb light.
This study implements a Bayesian statistical framework to calibrate the SCOPE process-based simulator for simulating gross primary production (GPP) and top-of-canopy reflectance at a spruce flux tower site in the Czech Republic. Markov chain Monte Carlo simulation is used to quantify the uncertainty in SCOPE input parameters by comparing simulated and measured reflectance and GPP data. The results show the posterior parameter distributions have lower uncertainty than the prior distributions. Simulated half-hourly GPP over the growing season using maximum a posteriori parameter estimates matches the measured data. Future work will estimate seasonal parameter variations to improve GPP simulation accuracy.
Narayan Shrestha [ACCURACY OF X-BAND LOCAL AREA WEATHER RADAR (LAWR) OF LEUVE...Narayan Shrestha
This document summarizes the accuracy of rainfall estimates from an X-band Local Area Weather Radar (LAWR) installed in Leuven, Belgium and its application for hydrological modelling of the 48.17 km2 Molenbeek/Parkbeek catchment. Different adjustment techniques including range dependent adjustment, mean field bias adjustment, and Brandes spatial adjustment were applied to raw radar data, improving the mean absolute error by 47% and root mean square error by 45% compared to original radar estimates. Two rainfall-runoff models, VHM and NAM, were used to simulate streamflow in the catchment, showing similar performance and greater accuracy simulating more uniform winter storms than summer storms.
3 d single gaas co axial nanowire solar cell for nanopillar-array photovoltai...ijcsa
Nanopillar array photovoltaics give unique advantages over today’s planar thin films in the areas of
optical properties and carrier collection, arising from their 3D geometry. The choice of the material
system, however, is essential in order to gain the advantage of the large surface/interface area associated
with nanopillars. Therefore, a well known Si and GaAs material are used in the design and studied in this
nanowire application. This work calculates and analyses the performance of the coaxial GaAs nanowire
and compared with that of Si nanowire using a semi-classical method. The current-voltage characteristics
are investigated for both under dark and AM1.5G illumination. It is found that GaAs nanowire gives almost
double efficiency with its counterpart Si nanowire. Their TCAD simulations can be validated reasonably
with that of published experimental result.
The SpaceDrive Project - First Results on EMDrive and Mach-Effect ThrustersSérgio Sacani
Propellantless propulsion is believed to be the best option for interstellar travel. However, photon rockets or solar sails have thrusts so low that maybe only nano-scaled spacecraft may reach the next star within our lifetime using very high-power laser beams. Following into the footsteps of earlier breakthrough propulsion programs, we are investigating different concepts based on non-classical/revolutionary propulsion ideas that claim to be at least an order of magnitude more efficient in producing thrust compared to photon rockets. Our intention is to develop an excellent research infrastructure to test new ideas and measure thrusts and/or artefacts with high confidence to determine if a concept works and if it does how to scale it up. At present, we are focusing on two possible revolutionary concepts: The EMDrive and the Mach-Effect Thruster. The first concept uses microwaves in a truncated cone-shaped cavity that is claimed to produce thrust. Although it is not clear on which theoretical basis this can work, several experimental tests have been reported in the literature, which warrants a closer examination. The second concept is believed to generate mass fluctuations in a piezo-crystal stack that creates non-zero time-averaged thrusts. Here we are reporting first results of our improved thrust balance as well as EMDrive and Mach-Effect thruster models. Special attention is given to the investigation and identification of error sources that cause false thrust signals. Our results show that the magnetic interaction from not sufficiently shielded cables or thrusters are a major factor that needs to be taken into account for proper μN thrust measurements for these type of devices.
Toward overcoming the concept of effective stiffness and damping in the dynam...Alessandro Palmeri
In the current state-of-practice, the time-domain dynamic analysis of structures incorporating viscoelastic members is generally carried out through the Modal Strain Energy (MSE) method, or other procedures somehow based on the quite simplistic idea of substituting the actual viscoelastically damped structure with an equivalent system featuring a pure viscous damping.
This crude approximation in civil engineering applications is very often encouraged by manufacturers of the viscoelastic devices themselves, whose interest is to simplify as much as possible the design procedures for structures embedding their products. As an example, elastomeric seismic isolators are generally advertised and sold with a table listing the equivalent values of elastic stiffness and viscous damping ratio for different amplitudes of vibration. Unfortunately, many experimental and analytical studies confirm that the real dynamic behaviour of such devices is much more complicated, and cannot be bend to the interests of manufacturers and designers.
Despite the advances in the field made in the last two decades, two well-established beliefs continue to underpin use and abuse of the concepts of effective stiffness and damping for viscoelastically damped structures: first, MSE method and similar procedures are unconditionally assumed to provide good approximations, which are acceptable for design purposes; second, the implementation of more refined approaches is thought to be computationally too expensive, and hence suitable just for a few very important constructions.
In this presentation, as a further contribution to overcome these popular beliefs, a novel time-domain numerical scheme of dynamic analysis is proposed and numerically validated. After a brief review of the LPA (Laguerre’s Polynomial Approximation) technique for one-dimensional viscoelastic members of known relaxation function, the state-space equations of motion for linear structures with viscoelastic components are derived in the modal space. Aimed at making the proposed approach more general, the distribution of the viscoelastic components is allowed to be non-proportional to mass and elastic stiffness, in so removing the most severe limitation of previous formulations. Then, a cascade scheme is derived by decoupling in each time step traditional state variables (i.e. modal displacements and velocities) and additional internal variables. The joint use of modal analysis and improved cascade scheme permits to reduce the size of the problem and to keep low the computational burden. The illustrative application to the small-amplitude vibration of a cable beam made of different viscoelastic materials demonstrates the versatility of the proposed approach. The numerical results confirm a superior accuracy with respect to the classical MSE method, whose underestimate in the low-frequency range can be as large as 75%.
A Land Data Assimilation System Utilizing Low Frequency Passive Microwave Rem...drboon
To address the gap in bridging global and smaller modelling scales, downscaling approaches have been reported as an appropriate solution. Downscaling on its own is not wholly adequate in the quest to produce local phenomena, and in this paper we use a physical downscaling method combined with data assimilation strategies, to obtain physically consistent land surface condition prediction. Using data assimilation strategies, it has been demonstrated that by minimizing a cost function, a solution utilizing imperfect models and observation data including observation errors is feasible. We demonstrate that by assimilating lower frequency passive microwave brightness temperature data using a validated theoretical radiative transfer model, we can obtain very good predictions that agree well with observed conditions.
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MULTISCALE MODELLING OF URBAN CLIMATE
1. Eleventh International IBPSA Conference
Glasgow, Scotland
July 27-30, 2009
MULTISCALE MODELLING OF URBAN CLIMATE
Adil Rasheed1 and Darren Robinson1
1
Solar Energy and Building Physics Laboratory,
Ecole Polytechnique Fédérale de Lausanne,
Station 18, CH-1015 Lausanne, Switzerland.
represented by an urban canopy model. Such a model
ABSTRACT would improve the accuracy of energy predictions
Climate Modelling is a complex task. One of the from both building and urban resource flow
most important reasons is the presence of a large simulation software.
variety of spatio-temporal scales. There are climatic
changes that take place over a time period of a few
months and then there are gusts which might last
only a few seconds. Similarly there can be a strong
influence on the weather of a city due to the presence
of a large water body like a sea or of a mountain
having a dimension of a few tens or hundreds of
kilometres and then there can be a local influence due
to the presence of urban structures like buildings and
canopies having dimensions of the order of a few
meters only. It is not computationally tractable to
handle all of these scales in a single climate model.
However, we can solve this issue by an integration of
a global, meso and micro scale model capable of
handling each of the different scales of interest. In Figure 1 Multiscale Modelling approach
this paper we describe in detail one such approach, But when investigating natural ventilation strategies
along with some sample results demonstrating the for buildings or the comfort of pedestrians in a city, it
capabilities of this tool. is also important to account for the local temperature
INTRODUCTION and velocity field in an accurate way; which depends
on local as well as on large scale phenomenon. For
Due to differences in radiation exchange, surface this we couple our mesoscale predictions with a
thermophysical properties, anthropogenic gains and microscale solver. With this one-directional coupling
evaporative sinks as well as reduced mean air high level models may be regarded as pre-processors
velocity, the mean air temperature in cities tends to to the lower level ones. This opens the possibility of
be higher than in the immediate rural surroundings. being able to couple microclimate models with pre-
But due to inertial differences the magnitude of this computed mesoclimate results, which could be made
heat island effect (which may also be negative) varies available from internet sites. Our modelling
with the time of day. Accounting for this complexity methodologies are presented along with some sample
requires a detailed numerical model. Another results in the following sections.
problem arises because of the diverse time and length
scales involved in atmospheric flow. The length scale MODELS
for example can vary from a few meters (buildings)
Mesoscale Model
to a few kilometers (mountains). It is almost
impossible to resolve all these scales in a single A Global Model developed by NCEP (National
model with the presently available computational Center for Environmental Prediction) having a
power. resolution of 270km x 270 km forces our Mesoscale
Model (MM) having a resolution ranging from a few
A way to overcome this problem is to couple
hundred meters to a few kilometres. The MM solves
different models capable of resolving different scales.
equations 1 to 6 (below) on a structured terrain
As shown in Figure 1 in our approach we use a
following grid using a finite volume approach.
global numerical model having a resolution of a few
Turbulence is modelled using a one equation model
hundred kilometers to provide boundary conditions
suggested by Bougeault and Lacarrere (1989)
to a mesoscale model having a resolution of a few
hundred meters. The exchanges of mass, momentum
and energy with the urban texture are implicitly
- 505 -
2. Governing Equations ∂A
W ′A′ = − K z …(5)
Mass Conservation equation: This simply states that, ∂z
in any arbitrarily chosen control volume in the K z = C k lk E 3 / 2 …(6)
atmosphere, the mass of air is always conserved.
Furthermore since the wind speed encountered in the
The radiation (both longwave and short wave) model
atmosphere is never comparable to the speed of
of Schayes (1982) is used along with the possibility
sound we can further make an assumption that the
to switch to the Simplified Radiosity Algorithm
fluid is incompressible. Putting this mathematically
described later in this paper.
we have that:
∂ρU i Urban Canopy Model
=0 ...(1)
∂xi In the previous section we described our mesoscale
Momentum Conservation Equation model which typically has a resolution of a few
This simply states that, for any arbitrarily chosen hundred metres. In order to resolve the scales smaller
control volume in the atmosphere, the rate of change than this grid a one-dimensional Urban Canopy
of momentum of the packet of air is equal to the Model (UCM) has been developed. The governing
resultant of the total force acting on that volume. equations (7,8,9) of the UCM for predicting the
Mathematically, this can be represented as follows: velocity, temperature and turbulent kinetic energy
… (2) profiles inside the canopy is obtained by a spatial
∂ρU ∂p ∂U U ∂U ′W ′ θ −θ
=− − − −ρ gδ i 3 − 2ε ijk Ω j (U − U kG ) + Dui
i j
∂t
i
∂xi ∂x j
i
∂z θ0
0
averaging of the equations which form the basis of
the mesoscale model. This averaging assumes
In Equation 2, the term on the left hand side is the
periodicity in the occurrence of urban structures. A
rate of change of momentum. The first term on the
building is represented by a block of specified width,
right hand side is the gradient of pressure. The
breadth and height while the street is represented by
second is the advection term, the third term arises
its width and orientation (Figure 2).
due to turbulence, the fourth term is the result of
buoyancy and the fifth term is the corialis force that
results from the rotation of the earth, while the last
term is the source or sink of momentum. This can be
used to account for the drag or shear forces due to
buildings encountered in a city.
Energy Conservation Equation
The energy conservation principle states that for a
particular control volume the imbalance in energy
input and output leads to a change in the internal
energy of the air in that volume.
R /C
∂ρθ ∂ρθ U i ∂ρθ ′W ′ 1 ⎡ p0 ⎤ ∂Rl
p
…(3) Figure 2: Geometries handled in the UCM
=− − −− +D
Cp ⎢ p ⎥
θ
∂t ∂xi ∂z ⎣ ⎦ ∂z
The drag forces offered by the rectangular cuboids
In Equation 3, the LHS is the rate of change of the have been taken to be proportional to the square of
internal energy of the air packet. The first two terms the local velocity field and the turbulent and
on the RHS are the advection and the turbulent dispersive fluxes (which arise due to the spatial
transportation of potential temperature respectively averaging) have been combined (because they are
The third term on the RHS represents the radiative similar for B/W > 1). At the lower boundary both the
heating of the packet of air, while the last term horizontal velocity components are taken as zero.
represents the source or sink of the energy equation. The upper boundary condition is applied at 3.4 times
the height of the cube. Constant values are applied at
Turbulent Kinetic Energy Equation the upper end by the MM. For the energy equation a
∂ρ E ∂U E ∂ E′W ′ ⎡⎛ ∂U ⎞2 ⎛ ∂U y ⎞2 ⎤ g ∂θ E3/ 2
=− i − + ρ K z ⎢⎜ x ⎟ + ⎜ ⎟ ⎥ − ρ Kz − ρCε + DE constant heat flux is given at the ground surface and
∂t ∂xi ∂z ⎢⎝ ∂z ⎠ ⎝ ∂z ⎠ ⎥ θ0
⎣ ⎦
∂z lε
…(4) at the top boundary the temperature is supplied by the
The LHS of the Equation 4 is the rate of change of MM.
turbulent kinetic energy. The first, second, third,
fourth, fifth and sixth terms on the RHS correspond
∂u 1 ∂ ⎛ ∂u ⎞
to the advection, turbulent transportation, shear = ⎜ K zu Λ ⎟ − a1Cd u u + v
2 2 … (7)
production, buoyancy production, dissipation and ∂t Λ ∂zc ⎝ ∂zc ⎠
additional sources of turbulent kinetic energy.
∂v 1 ∂ ⎛ ∂v ⎞
= ⎜ K zv Λ ⎟ − a2Cd v u + v
2 2 …(8)
The turbulence terms in all of the above equations are ∂t Λ ∂zc ⎝ ∂zc ⎠
modelled as Equation 5 and 6: ∂θ 1 ∂ ⎛ ∂θ ⎞
= ⎜ K zθ Λ ⎟ − Qθ …(9)
∂t Λ ∂zc ⎝ ∂zc ⎠
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3. B1 Pb ( z ) vertical profiles of velocities and temperature which
a1 = ...(10)
are then used to compute the effects of drag forces,
( B1 + W1 )( B2 + W2 ) − B1 B2 Pb ( z )
shear forces and the convective exchange of energy
B2 Pb ( z )
a2 = ..(11) between the building and its surroundings. These are
( B1 + W1 )( B2 + W2 ) − B1 B2 Pb ( z ) called the sources of momentum and energy at the
Urban Canopy scale. They can be further modified
⎛ B1 B2 ⎞
Λ = 1− ⎜ ⎟ Pb ( z ) ...(12) using a Building Energy Model to include the effects
⎝ ( B1 + W1 )( B2 + W2 ) ⎠ of air-conditioning. These UCM sources are then
2 2
interpolated back to the Mesoscale grid thus
⎛ ∂u ⎞ ⎛ ∂v ⎞ Sm 2
3/
providing the sources of the respective equations at
K zu = K zv = K zθ = L2 ⎜ ⎟ +⎜ ⎟ the mesoscale.
⎝ ∂zc ⎠ ⎝ ∂zc ⎠ C
...(13) Microscale Model
A complete derivation of the expression of Kzu can be As stated earlier the mesoscale model gives the
found in Gambo (1978). The length scale L is given velocity and temperature profile at a resolution of a
by Watanabe and Kondo (1990) and was derived few hundred meters. However, one might be
from considerations of a forest canopy: interested in a more detailed profile of these
quantities to evaluate natural ventilation potential or
pedestrian comfort. To achieve this, a high-resolution
2κ 3
L ( zc ) = (1 − exp(−η ) ) ...(14) numerical computational model is used which
ca combines fluid dynamics calculations with the
caz ; thermodynamic processes taking place at the walls
η= ...(15)
2κ 2 and roof surfaces encountered in a city. To use a
purely conventional CFD approach to simulate air
and above the canopy we use an interpolation
flow around complex geometries encountered in a
formula after Blackadar (1968):
city one is normally left with no option but to use an
unstructured mesh (Figure 4(a)). But unstructured
κ zc ...(16) grid generation is a time consuming process and also
L ( zc ) ≤
κz the numerical methods for solving the conservation
1+
L0 equations with unstructured meshes suffer from
stability and convergence issues. In contrast a
which interpolates between two limits L ~ kz , at z Cartesian mesh (Figure 4(b)) is very easy to generate
= 0 and L = Lo as L → ∞ . In this study we have
and efficient numerical algorithms are available to
significantly reduce the computational time.
used a value of Lo = 70m. However, it is not straightforward to fit Cartesian
grids to complex geometries and doing so invariably
creates a great many redundant cells. As a
compromise we use a solution which combines
numerical stability with the possibility of creating
grids for complex geometries, called immersed
boundaries.
Figure 3: Modelling of the urban element (a) Unstructured Mesh
The source term appearing in the energy equation of
the UCM is the amount of energy exchanged with the
urban elements. To estimate this, a one dimensional
conduction equation is solved for walls, roofs and
ground (Figure 3) by assuming a fixed temperature
inside the building and 2m below the ground. At the
other surface (in contact with the air) a time
dependent heat flux (due to radiation) is applied as
the boundary condition. The UCM computes the (b) Structured mesh
Figure 4: Different types of mesh
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4. In this approach the simulation around complex the sky contribution matrix. This matrix is then
geometries is conducted using a non body conformal simply multiplied by the radiance of each sky patch
cartesian grid in which the fluid solid interface is to obtain the incident energy at each surface.
represented by a surface grid, but the Cartesian Similarly, the sun view factors are used to obtain the
volume is generated with no regard to this surface direct contribution matrix. Finally, the view factors
grid. Thus the solid boundary would cut through the between surfaces are combined with the relative
Cartesian volume grid. Because the grid doesn’t angle between the surfaces to obtain the surface
conform to the solid boundary, incorporating the contribution matrix. This matrix allows for
boundary conditions requires us to modify the computation of the contribution due to reflection.
equations in the vicinity of the boundary. Assuming Further details including results from extensive
that such a modification is possible (of course it is) validation tests can be found in Robinson (2004)
the modified governing equations would then be
discretized using a finite difference, finite volume or MODEL CALIBRATION
a finite element technique without resorting to To demonstrate the capabilities of our Multiscale
coordinate transformation or complex discretization Model we have chosen the city of Basel. Basel is
operators. When compared with unstructured grid located at the border with Germany and France, at a
methods, the Cartesian grid-based IB method retains latitude and longitude of 47° 00' North and 8° 00'
the advantage of being amenable to powerful line- East, respectively.
iterative techniques and geometric multigrid
methods, which can also lead to lower per-grid-point To conduct a realistic simulation, input data such as
operation counts. the topography and land use are required.
Immersed Boundary Approach in an Urban Furthermore, to force the effects of the scales larger
Context: This new algorithm as against the than those handled by the mesoscale model
conventional CFD approach offers us the possibility appropriate meteorological data are required as
of simulating large domains. In principle constructing boundary conditions. Fortunately, these data are
urban geometry with a 3-D modeling tool is trivial available on the internet to be used by the scientific
and quick and such geometries can be readily community. However, before using them in the
converted into a STL (sterio lithography file) format simulations these data have to be processed. Below
which holds information about the solid-liquid we explain briefly how the various input data are
interface (in our case the building-atmosphere obtained and processed.
interface). The file is parsed to find out the solid and Meteorological Data
fluid zones. The flow equation is solved only in the
As noted earlier the scales that are comparable to the
fluid zone, so that in the solid zone the flow
grid size are resolved by the model. However, scales
equations are switched off. The air flowing over the
that are bigger than the domain or lie outside of the
buildings are treated as phase one and the buildings
domain can't be parameterized or resolved. Their
are treated as phase two. The Specific heat capacity,
effects are captured in the mesoscale model using a
conductivity and density of the two phases are
procedure called nesting (Figure 5(a) and 5(b)) via
specified for each building and the air separately. The
boundary conditions. The effects of oceans and
amount of solar radiation as well as the
mountains are taken into account by a Global model
anthropogenic heat generated due to human activities
like NCEP (National Center for Environmental
can be looked upon as heat sources which might vary
predictions). The data (velocity, humidity,
with time. The methodology to compute the solar
temperature, pressure) from this global model is
radiation is explained in the next section. The
available via a web portal cdc.no.gov (2008).
boundary conditions of velocity and temperature are
forced through the interpolation of results from Moreover, the global model has a resolution of
mesoscale simulations on to the microscale grid, with 270km X 270km whereas we require the velocities,
care being taken to impose mass conservation over temperature and humidity to be interpolated to a grid
the full domain. having a resolution of just 1m X 1km. For this we
first construct a domain with a resolution of 15 X 15
Simplified Radiosity Algorithm: In order to
km and assuming it to be 100% rural. We then run a
implement the SRA (Simplified Radiosity
simulation to generate an output file. This output file
Algorithm) for the calculation of longwave and
is then used to force another smaller domain with a
shortwave exchange in urban context, the view
higher resolution. We thus interpolate in a few steps
factors from each surface to a descretized sky vault,
from the global model to the mesoscale model
the sun to each surface and from surface to surface
domain.
are required. The view factors are computed by
rendering the scene from different points (sun Landuse
positions or the centroids of the triangles resulting
A major aim of this project is to study the interaction
from surface tessellization). The view factors of the
between the climate of a region and the urban
sky are used with the cosine of the angle of incidence
texture. It has been well established through various
between the surfaces and the sky patches to obtain
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5. field experiments and numerical simulations that the
urban texture significantly affects the urban
microclimate. Relevant simulations of the urban
climate are therefore only possible when we input the
correct landuse data into the model. This data is
obtained from another web portal. The Global
Vegetation Monitoring Unit of the European
Commission Joint Research Centre, provides for the
year 2000 a harmonized land cover database over the
whole globe. From this data we can determine the
fraction of artificial surfaces. In Figure 6(a) one can
see the graphical representation of the data obtained
from the net and in Figure 6 (b) the processed result
in the format required by the mesoscale model. (b) Interpolated land usedata
Figure 6: Interpolation of land use data
Topography
A mesoscale domain may range from a few
kilometers to a few hundred of kilometers. Over such
a large expanse the topography may vary
significantly. Such variations can be taken into
account by downloaded topological data from the
website edc.usgs.gov (2008). This data is expressed
as a global digital elevation model (DEM) with a
horizontal grid spacing of 30 arcs seconds
(approximately 1km). In our case we have
(a) Raw downloaded data downloaded the topography of Europe. In Figure 7(a)
below one can see the graphical interpretation of the
raw data downloaded from the website. This data is
then processed (see Figure 7(a)) to extract the
topographical information for the domain we want to
simulate.
(b) Interpolated data
Figure 5: Interpolation of meteorological data
(a) Downloaded topography
(b) Interpolated topography
(a) Downloaded land use data Figure 7: Interpolation of topography
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6. 3-D geometry simplified geometry match those of the actual city.
Here we describe a method, which not only
The final data requirement of our multiscale
eliminates the need of time-consuming field survey
modeling methodology relates to the geometry of
but also reduces a complex representation of a city to
buildings as input to microscale simulations. For this
an “equivalent” simplified representation. To
we produce an abstracted form of buildings’
accomplish this we choose a mesoscale cell and
geometry using the NURB (Non-Uniform Rational
download a Google image of its ariel view. The view
BSpline) based 3-D modelling software Rhinoceros.
is then used to create a three dimensional model. The
For this an aerial view of the city is obtained from
SRA is used to compute the distribution of radiation
Google Earth image (Figure 8(a)). The corresponding
on different types of surface (roofs, grounds and
2D geometry is sketched (Figure 8(b)) using
walls) while the IB technique is used to compute drag
Rhinoceros. The resultant polygons are then
and spatially averaged quantities (velocity and
vertically extruded according to the building heights
turbulent kinetic energy profiles) for the same
estimated from visual surveys.
domain. We then search for a simplified
representation (consisting of a regular array of cubes)
which has similar characteristics as the complex one.
Figure 9 presents an example to demonstrate the
concept.
(a) Complex
(a) Google image
(b) Sketched geometry using Rhino
Figure 8: 3-D geometry for microscale simulation (b) Simplified
Figure 9: Equivalent Simplified Geometry
Simplified geometry fitting
The inputs to the mesoscale model, which include
street width, building width, building density and a
statistical representation of the buildings’ heights, are
generally obtained through quantitative field surveys
(which are very slow and time consuming to
perform) or qualitative estimates. But in performing
this geometric abstraction there is no way to ensure
that the total built surfaces and volumes of the
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7. In both the geometric representations of Figure 9 the Microscale Result
total built surfaces, built volume, the distribution of
In Figure 10 we present results relating to the district
shortwave radiation amongst different surfaces and
of Matthäus in Basel. For this the boundary
the average velocity profile are similar. Thus the
conditions have been forced on the microclimate
complex representation shown in Figure 9(a) can be
model using the results of the mesoscale model. The
replaced by the simplified representation shown in
ambient temperature tends to be higher in the regions
Figure 9(b) and can be used in a mesoscale
where the velocity is lower (Figure 11(b)); the more a
simulation.
packet of air circulates around a built structure the
RESULTS more time it has to exchange energy with the
buildings, thus becoming warmer. As can be
Mesoscale Results
observed in Figure 11(a) streams of air flowing
In Figure 10(a) we have assumed a hypothetical through the city attain a higher temperature compared
situation where the whole of Basel and its to the stream that avoids contact with built surfaces.
surrounding area is 100% rural, implying no urban
structures.
In Figure 10(b) we have presented the impact of
introducing a simplified urban representation of the
city; the result corresponding to midday at a height of
5meters above the ground. Here one can clearly see a
rise in temperature in and around the city. This can
be attributed to the increased absorption of radiation
by the urban structures, to the change in surface
thermophysical properties and a damping of air flow
in the city. The UHI intensity is around 5-6C which
can have a significant impact on energy demands for
cooling or heating.
(a) Streamlines and velocity vectors
(a) Rural (b) Temperature and velocity profiles along a line
stretching from one end of the domain to the other
along the direction of flow.
Figure 11: Microscale Simulation Results
CONCLUSIONS
In this paper we describe a new solution to handling
the range of time and length scales which influence
urban climate predictions in a computationally
tractable way. This involve the use of results from a
global meteorological model to force the boundary
conditions of a mesoscale model, in which a model
(b) Urban of the urban canopy is embedded. These mesoscale
Figure 10: Temperature profiles for rural and predictions may then be used to force the boundary
urban simulations for the city of Basel conditions of a local microscale model, so that good
quality local urban climate predictions may be
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8. achieved whilst accounting for large scale climatic REFERENCES
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ACKNOWLEDGEMENTS
Blackadar, A. (1968). The vertical distribution of
The financial support received for this work from
national research programme 54 of the Swiss wind and turbulent exchange in neutral
National Science Foundation is gratefully atmosphere. Jounal of Geophysics, 4:3085{3102
acknowledged. Gambo, K. (1978). Notes on the turbulence closure
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Dθ Source term for the energy equation tml
E Turbulent Kinetic Energy http://www-tem.jrc.it/glc2000
E ′ Fluctuation in turbulent kinetic energy http://edc.usgs.gov/products/elevation/gtopo30/gtopo
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U x , U y Horizontal Mesoscale Velocites
g acceleration due to gravity
Cε , Ck Constants
lε Dissipative length scale
lk Length scale
DE Source term for the turbulent kinetic energy
u , v Horiontal velocities in the canopy
zc vertical distance in the canopy
K zu , K zv , K zθ diffusivity
Cd constant
B1 , B2 , W1 , W2
Pb ( z ) probability of having a building of height z
κ von karman constant
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