scholarly journals Amplification and Attenuation of Acoustic Phonons in Graphenelike Silicene

2021 ◽  
Vol 9 (12) ◽  
pp. 1594-1597
Author(s):  
Kasala Suresha
Keyword(s):  
Temperature Gradient ◽  
Physical Properties ◽  
Dirac Fermions ◽  
Acoustic Phonons ◽  
External Temperature ◽  
Electronic Dispersion

Abstract: Because of unique physical properties, graphene, a 2D honeycomb arrangement of carbon atoms, has attracted tremendous attention. Silicene, the graphene equivalent for silicon, could follow this trend, opening new perspectives for applications, especially due to its compatibility with Si-based electronics. Silicene has been theoretically predicted as a buckled honeycomb arrangement of Si atoms and having an electronic dispersion resembling that of relativistic Dirac fermions. We calculate theoretically in this article, the amplification and attenuation of acoustic phonons due to an external temperature gradient in Silicene at temperature ࢀ= 77K in the hypersound regime. The dependence of normalized amplification or attenuation on the frequency wasnumerically evaluated. It is observed from our calculations that when the temperature gradient is zero, absorption of acoustic phonons occurs and when temperature gradient is greater than zero, absorption switches to amplification of acoustic phonons. Keywords: Silicene, Amplification, Attenuation, Acoustic phonons, Temperature gradient.

scholarly journals Vapor flux and recrystallization during dry snow metamorphism under a steady temperature gradient as observed by time-lapse micro-tomography

2012 ◽  
Vol 6 (5) ◽  
pp. 1141-1155 ◽  
Author(s):  
B. R. Pinzer ◽  
M. Schneebeli ◽  
T. U. Kaempfer
Keyword(s):  
Temperature Gradient ◽  
Physical Properties ◽  
Time Lapse ◽  
Phase Changes ◽  
External Temperature ◽  
Vapor Flux ◽  
Snow Metamorphism ◽  
Diffusion Enhancement ◽  
Micro Tomography ◽  
Snow Microstructure

Abstract. Dry snow metamorphism under an external temperature gradient is the most common type of recrystallization of snow on the ground. The changes in snow microstructure modify the physical properties of snow, and therefore an understanding of this process is essential for many disciplines, from modeling the effects of snow on climate to assessing avalanche risk. We directly imaged the microstructural changes in snow during temperature gradient metamorphism (TGM) under a constant gradient of 50 K m−1, using in situ time-lapse X-ray micro-tomography. This novel and non-destructive technique directly reveals the amount of ice that sublimates and is deposited during metamorphism, in addition to the exact locations of these phase changes. We calculated the average time that an ice volume stayed in place before it sublimated and found a characteristic residence time of 2–3 days. This means that most of the ice changes its phase from solid to vapor and back many times in a seasonal snowpack where similar temperature conditions can be found. Consistent with such a short timescale, we observed a mass turnover of up to 60% of the total ice mass per day. The concept of hand-to-hand transport for the water vapor flux describes the observed changes very well. However, we did not find evidence for a macroscopic vapor diffusion enhancement. The picture of {temperature gradient metamorphism} produced by directly observing the changing microstructure sheds light on the micro-physical processes and could help to improve models that predict the physical properties of snow.

scholarly journals Vapor flux and recrystallization during dry snow metamorphism under a steady temperature gradient as observed by time-lapse micro-tomography

2012 ◽  
Vol 6 (3) ◽  
pp. 1673-1714 ◽  
Author(s):  
B. R. Pinzer ◽  
M. Schneebeli ◽  
T. U. Kaempfer
Keyword(s):  
Temperature Gradient ◽  
Physical Properties ◽  
Time Lapse ◽  
Steady Temperature ◽  
Data Set ◽  
External Temperature ◽  
Vapor Flux ◽  
Snow Metamorphism ◽  
Micro Tomography

Abstract. Dry snow metamorphism under an external temperature gradient is the most common type of recrystallization of snow on the ground. The changes in snow microstructure modify the physical properties of snow, and therefore an understanding of this process is essential for many disciplines, from modeling the effects of snow on climate to assessing avalanche risk. We directly imaged the microstructural changes in snow during metamorphism under a steady temperature gradient (STGM) of 50 K m−1, using in situ time-lapse X-ray micro-tomography. This novel and non-destructive technique directly reveals the amount of ice that sublimates and is deposited during metamorphism, and in addition the exact locations of these phase changes. From the four-dimensional data set, we calculated the average time that an ice volume stayed in place before it sublimated, and found a characteristic residence time of 2–3 days. This means that most of the ice changes its phase from solid to vapor and back many times in a seasonal snow pack, where similar temperature conditions can be found. Consistent with such a short timescale, we observed a mass turnover of up to 60 % of the total ice mass per day. The concept of hand-to-hand transport for the water vapor flux describes the observed changes very well. However, we did not find evidence for a macroscopic vapor diffusion enhancement. The picture of STGM that is produced by directly observing the microstructure of snow in situ sheds light on the micro-physical processes and could help to improve models that predict the physical properties of snow.

scholarly journals Study of a temperature gradient metamorphism of snow from 3-D images: time evolution of microstructures, physical properties and their associated anisotropy

2014 ◽  
Vol 8 (6) ◽  
pp. 2255-2274 ◽  
Author(s):  
N. Calonne ◽  
F. Flin ◽  
C. Geindreau ◽  
B. Lesaffre ◽  
S. Rolland du Roscoat
Keyword(s):  
Temperature Gradient ◽  
Physical Properties ◽  
Time Evolution ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Large Set ◽  
Correlation Lengths ◽  
Snow Properties ◽  
Cold Room ◽  
Anisotropy Coefficients

Abstract. We carried out a study to monitor the time evolution of microstructural and physical properties of snow during temperature gradient metamorphism: a snow slab was subjected to a constant temperature gradient in the vertical direction for 3 weeks in a cold room, and regularly sampled in order to obtain a series of three-dimensional (3-D) images using X-ray microtomography. A large set of properties was then computed from this series of 3-D images: density, specific surface area, correlation lengths, mean and Gaussian curvature distributions, air and ice tortuosities, effective thermal conductivity, and intrinsic permeability. Whenever possible, specific attention was paid to assess these properties along the vertical and horizontal directions, and an anisotropy coefficient defined as the ratio of the vertical over the horizontal values was deduced. The time evolution of these properties, as well as their anisotropy coefficients, was investigated, showing the development of a strong anisotropic behavior during the experiment. Most of the computed physical properties of snow were then compared with two analytical estimates (self-consistent estimates and dilute beds of spheroids) based on the snow density, and the size and anisotropy of the microstructure through the correlation lengths. These models, which require only basic microstructural information, offer rather good estimates of the properties and anisotropy coefficients for our experiment without any fitting parameters. Our results highlight the interplay between the microstructure and physical properties, showing that the physical properties of snow subjected to a temperature gradient cannot be described accurately using only isotropic parameters such as the density and require more refined information. Furthermore, this study constitutes a detailed database on the evolution of snow properties under a temperature gradient, which can be used as a guideline and a validation tool for snow metamorphism models at the micro- or macroscale.

X-ray diffraction method for determination of interplanar spacing and temperature distribution in crystals under an external temperature gradient

2015 ◽  
Vol 48 (3) ◽  
pp. 853-856 ◽  
Author(s):  
V. R. Kocharyan ◽  
A. S. Gogolev ◽  
A. E. Movsisyan ◽  
A. H. Beybutyan ◽  
S. G. Khlopuzyan ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Temperature Gradient ◽  
Single Crystal ◽  
Interplanar Spacing ◽  
Diffraction Method ◽  
X Ray Diffraction ◽  
External Temperature ◽  
X Ray ◽  
Spacing Distribution

An X-ray diffraction method is developed for the determination of the distribution of temperature and interplanar spacing in a single-crystal plate. In particular, the temperature and the interplanar spacing differences in two different parts of a quartz single crystal of X-cut are experimentally determined depending on the value of the temperature gradient applied perpendicularly to the reflecting atomic planes (10\bar 11). The temperature distribution along the direction perpendicular to the reflecting atomic planes (10\bar 11) and the interplanar spacing distribution of atomic planes (10\bar 11) are determined as well.

On the thermocapillary motion of partially engulfed compound drops

2009 ◽  
Vol 626 ◽  
pp. 263-289 ◽  
Author(s):  
L. ROSENFELD ◽  
O. M. LAVRENTEVA ◽  
A. NIR
Keyword(s):  
Temperature Gradient ◽  
Volume Ratio ◽  
Thermal Conductivity Ratio ◽  
External Temperature ◽  
Interfacial Tensions ◽  
Thermocapillary Motion ◽  
Physical Conditions ◽  
Thermal Fields ◽  
Induced Motion ◽  
Compound Drops

In this work the thermocapillary-induced motion of partially engulfed compound drops is considered. This phenomenon occurs in many natural and technological processes in which heat is exchanged between such hybrid drops and the medium around them through the interfaces. Two types of thermal fields and the resulting motions are studied; flow induced by an external temperature gradient and spontaneous thermocapillary motion. For the first flow type, it was found that, in general, the motion is induced in the direction of the temperature gradient. However, under certain physical conditions and drops' configuration a motion against the temperature gradient may be observed. In the second case, spontaneous thermocapillary motion, the compound drop moves due to surface tension gradients which result from the geometric non-uniformity of the system. Results are presented for several parameters such as configuration of the compound drop, viscosity, thermal conductivity ratio, the dependence of the various interfacial tensions on temperature and the volume ratio of the phases within the drop.

scholarly journals Study of a temperature gradient metamorphism of snow from 3-D images: time evolution of microstructures, physical properties and their associated anisotropy

2014 ◽  
Vol 8 (1) ◽  
pp. 1407-1451 ◽  
Author(s):  
N. Calonne ◽  
F. Flin ◽  
C. Geindreau ◽  
B. Lesaffre ◽  
S. Rolland du Roscoat
Keyword(s):  
Temperature Gradient ◽  
Physical Properties ◽  
Time Evolution ◽  
Analytical Models ◽  
Correlation Lengths ◽  
Snow Properties ◽  
Cold Room ◽  
Macro Scale ◽  
Validation Tool ◽  
Anisotropy Coefficients

Abstract. We carried out a study to monitor the time evolution of microstructural and physical properties of snow during a temperature gradient metamorphism: a snow slab was subjected to a constant temperature gradient along the vertical during three weeks in a cold-room, and regularly sampled in order to obtain a set of 3-D images using X-ray microtomography. A large panel of properties was then computed from this series of 3-D images: density, specific surface area, correlation length, mean and Gaussian curvature distributions, air and ice tortuosities, effective thermal conductivity, and intrinsic permeability. Whenever possible, a specific attention was paid to assess these properties along the vertical and horizontal directions, and an anisotropy coefficient defined as the ratio of the vertical over the horizontal values was deduced. The time evolution of these properties, as well as their anisotropy coefficients, was investigated, showing the development of a strong anisotropic behavior during the experiment. Most of the computed physical properties of snow were then compared with two analytical models (Self consistent estimates and Dilutes bed of spheroids) based on the snow density, and the size and anisotropy of the grains through the correlation lengths. These models, which require only basic microstructural information, offer rather good estimates of the properties and anisotropy coefficients for our experiment without any fitting parameters. Our results highlight the interplay between the microstructure and physical properties, showing that the physical properties of snow subjected to a temperature gradient cannot be described accurately using only isotropic parameters such as the density and require more refined information. Furthermore, this study constitutes a detailed database on the evolution of snow properties under a temperature gradient, which can be used as a guideline and a validation tool for snow metamorphism models at the micro or macro scale.

scholarly journals Pastato termofizinių savybių modeliavimas naudojant „Simulink“

2008 ◽  
Vol 42 (43) ◽  
pp. 121-127
Author(s):  
Antanas Mikuckas ◽  
Irena Mikuckienė ◽  
Egidijus Kazanavičius ◽  
Jonas Čeponis
Keyword(s):  
Physical Properties ◽  
Heating System ◽  
External Temperature ◽  
Thermal Transients ◽  
Geometrical Characteristics ◽  
Time Period ◽  
Building Components ◽  
Residential House ◽  
Heating Energy Consumption ◽  
Thermo Physical Properties

Šildant pastatus ne tik užtikrinamas komfortas, bet ir energetiškai teršiama aplinka, o gaminant kurą teršiama atmosfera. Šildymui mažiau sunaudojant energijos sutaupoma lėšų ir mažinama tarša. Pasiūlytas pastato šiluminio balanso modelis leidžia įvertinti įvairių veiksnių (atitvarų šiluminė varža, oro infiltracijos greitis, katilo galingumas, šildymo sistemos valdymo algoritmai ir t. t.) įtaką pastato šildymui sunaudojamos energijos kiekiui. Pateikiami modeliavimo rezultatai.Modeling thermo-physical properties of building using “Simulik”Antanas Mikuckas, Irena Mikuckienė, Egidijus Kazanavičius, Jonas Čeponis SummaryVarious models are used to study heat dynamics in buildings for evaluating heating energy consumption. This paper deals with model allowing to simulate thermal transients depending on the geometrical characteristics and thermo-physical properties of building components (exterior walls, internal partitions ceilings, floors and windows), external temperature variations and properties of heating system. The results for residential house are shown. The heat consumption for a specified time period was calculated. The heating energy conservation methods are analyzed and compared.

Superconductivity in the two-dimensional nonbenzenoid biphenylene sheet with Dirac cone

2D Materials ◽  
2021 ◽  
Author(s):  
Yanfeng Ge ◽  
Zhicui Wang ◽  
Xing Wang ◽  
Wenhui Wan ◽  
Yong Liu
Keyword(s):  
Physical Properties ◽  
Fermi Level ◽  
Superconducting Devices ◽  
Dirac Fermions ◽  
Two Dimensional ◽  
Dirac Cone ◽  
Electronic Density ◽  
Strongly Coupled ◽  
Rotational Vibration ◽  
Electronic Doping

Abstract During the past decade, two-dimensional materials have attracted much attention in superconductivity due to their feasible physical properties and easy chemical modifications. Herein, we use a recently literature reported novel biphenylene sheet (BP sheet) for investigating superconductivity-related physical properties. The electronic states of BP sheet that appeared near the Fermi level are composed of pz orbital of carbon due to sp2 hybridization. Also, an anisotropic Dirac cone is formed just above the Fermi level by crossing two bands comprised of different carbon atoms. One of the two bands is quasi-flat thus leading to a peak of electronic density of states above the Fermi level. In addition, the rotational-vibration phonon mode of the six-membered carbon ring is strongly coupled with electrons. The electron-phonon coupling induces the superconductivity of 6.2 K in BP sheet. Furthermore, both small uniaxial strains and electronic doping can take the Dirac cone and high electronic density of state close to the Fermi level and further raise the superconducting critical temperature to 27.4 K and 21.5 K, respectively. The obtained result suggests that BP sheet with Dirac fermions and superconductivity can be a potential material for the development of future superconducting devices.

Computational Analysis of Laminar Natural Convection in Rectangular Enclosures of Different Aspect Ratios With Different Heating Conditions

2012 ◽  
Author(s):  
Mosfequr Rahman ◽  
Charles Walker ◽  
Gustavo Molina ◽  
Valentin Soloiu
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Temperature Gradient ◽  
Aspect Ratio ◽  
Heat Generation ◽  
Internal Heat ◽  
Internal Heat Generation ◽  
External Temperature ◽  
Aspect Ratios

Natural convection in rectangular enclosures is found in many real-world engineering applications. Included in these applications are the energy efficient design of buildings, operation and safety of nuclear reactors, solar collector design, passive energy storage, heat transfer across multi-pane windows, thermo-electric refrigeration and heating devices, and the design-for-mitigation of optical distortion in large-scale laser systems. A common industrial application of natural convection is free air cooling without the aid of fans and can happen on small scales such as computer chips to large scale process equipment. The enclosure phenomena can loosely be organized into two large classes: (1) horizontal enclosures heated from below and (2) vertical enclosures heated from the side. In addition to temperature gradient convection strength within the enclosure can vary due to the existence of heat sources with different strength. Numerical simulations are conducted for free convective flow of air with or without internal heat generation in two-dimensional rectangular enclosures of different aspect ratios. The objective of this numerical study is to investigate the effects of external temperature gradient, internal heat generation and aspect ratio (AR) of enclosure (ratio of the length of the isothermal walls to their separation distance), in free convective laminar flow of a fluid. Two-dimensional rectangular enclosures of different aspect ratio (1, 2, 4, 6, 8, and 10) with two adiabatic side walls and isothermal bottom (hot) and top (cold) walls are considered for the first configuration. Whereas for the second configuration, two adiabatic top and bottom walls, isothermal left side (cold) and right side (hot) walls are considered. Two principal parameters considered for the flow of fluid are the external Rayleigh number, RaE, which represents the effect due to the differential heating of the isothermal walls, and the internal Rayleigh number, RaI, which represents the strength of the internal heat generation. The effect of external temperature gradient and aspect ratio on natural convection has been observed by varying the value of external Rayleigh number (RaE) equal to 2×104, 2×105, and 2×106 and keeping the internal Rayleigh number constant (RaI = 2×105). Similarly, the effect of internal heat generation and aspect ratio on natural convection has been observed by varying the value of internal Rayleigh number (RaI) equal to 2×104, 2×105, and 2×106 and keeping the external Rayleigh number constant (RaE = 2×105). Significant changes in flow patterns and isotherms have been observed for all cases. Also the variation of average heat flux ratio (convective heat flux/corresponding conduction heat flux) along the hot and cold walls, and the convection strength have been calculated for all cases. It is found that the aspect ratio has a significant effect in fluid flow and heat transfer in the enclosures. The average heat flux ratio and the strength of convection increase with aspect ratio as the enclosure shape changes square (AR = 1) to shallow (AR > 1).

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