Acoustic phonon growth rate in undoped graphene due to external temperature gradient

2020 ◽  
Author(s):  
Subhana Nafees ◽  
Meenhaz Ansari ◽  
SSZ Ashraf
Keyword(s):  
Growth Rate ◽  
Temperature Gradient ◽  
Acoustic Phonon ◽  
External Temperature

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 Macrodefects in Cubic Silicon Carbide Crystals

2010 ◽  
Vol 645-648 ◽  
pp. 375-378 ◽  
Author(s):  
Valdas Jokubavicius ◽  
Justinas Palisaitis ◽  
Remigijus Vasiliauskas ◽  
Rositza Yakimova ◽  
Mikael Syväjärvi
Keyword(s):  
Growth Rate ◽  
Silicon Carbide ◽  
Crystal Growth ◽  
High Temperature ◽  
Temperature Gradient ◽  
Early Stage ◽  
Growth Conditions ◽  
Temperature Ramp ◽  
Cubic Silicon Carbide ◽  
Sublimation Growth

Different sublimation growth conditions of 3C-SiC approaching a bulk process have been investigated with the focus on appearance of macrodefects. The growth rate of 3C-SiC crystals grown on 6H-SiC varied from 380 to 460 μm/h with the thickness of the crystals from 190 to 230 μm, respectively. The formation of macrodefects with void character was revealed at the early stage of 3C-SiC crystal growth. The highest concentration of macrodefects appears in the vicinity of the domain in samples grown under high temperature gradient and fastest temperature ramp up. The formation of macrodefects was related to carbon deficiency which appear due to high Si/C ratio which is used to enable formation of the 3C-SiC polytype.

Morphological Characteristics of W-Nanowires after Selective Etching

2014 ◽  
Vol 1004-1005 ◽  
pp. 24-27
Author(s):  
Wen Jia Wang ◽  
Zhi Long Zhao ◽  
Ming Tang ◽  
Jian Jun Gao
Keyword(s):  
Growth Rate ◽  
Temperature Gradient ◽  
Directional Solidification ◽  
Morphological Characteristics ◽  
Selective Dissolution ◽  
Stability Diagram ◽  
Selective Etching ◽  
Directionally Solidified ◽  
Solidification Furnace ◽  
Nial Matrix

An eutectic NiAl–1.5 at.% W alloy prepared by using directionally solidified (DS)was employed as a source for producing W-nanowires. Several growth rate of 8,15,25/s was respectively used at a temperature gradient of ~240 K/cm in a Bridgman-type directional solidification furnace. A combined stability diagram was applied to predict proper conditions for the selective dissolution of NiAl matrix to get W-wires. Etching in a mixture of HCl:H2O2released parallel aligned W-nanowires with a wire diameter of ~500 nm. Different morphologies, such as nanobelts, lotus-shaped, conical of W-nanowires are obtained at the different conditions.

Growth rate and surface morphology of 4H–SiC crystals grown from Si–Cr–C and Si–Cr–Al–C solutions under various temperature gradient conditions

2014 ◽  
Vol 401 ◽  
pp. 681-685 ◽  
Author(s):  
Takeshi Mitani ◽  
Naoyoshi Komatsu ◽  
Tetsuo Takahashi ◽  
Tomohisa Kato ◽  
Kuniharu Fujii ◽  
...  
Keyword(s):  
Growth Rate ◽  
Temperature Gradient ◽  
Surface Morphology

Morphology of TiC Reinforced Ni-Cr-Mo Composite Coatings Prepared by CO2 Laser

2013 ◽  
Vol 664 ◽  
pp. 551-556
Author(s):  
Guang Yang ◽  
Zong De Liu ◽  
Yong Tian Wang ◽  
Rong Juan Yang
Keyword(s):  
Carbon Dioxide ◽  
Growth Rate ◽  
Temperature Gradient ◽  
Electron Probe ◽  
Composite Coatings ◽  
X Ray ◽  
Solid Interface ◽  
Reinforced Composite ◽  
The Individual

Carbon dioxide (CO2) laser was applied to fabricate TiC reinforced composite coatings. Different microstructures of ceramic phases were observed by SEM. The main phases of coatings were detected by XRD, while the individual one was examined by electron probe X-ray microanalysis .The effect of composition of binder phases on morphology was explained by the ratio of the temperature gradient in front of the liquid/ solid interface to the growth rate.

On the stability of vertical double-diffusive interfaces. Part 2. Two parallel interfaces

1994 ◽  
Vol 267 ◽  
pp. 251-273 ◽  
Author(s):  
I. A. Eltayeb ◽  
D. E. Loper
Keyword(s):  
Growth Rate ◽  
Thermal Diffusivity ◽  
Temperature Gradient ◽  
Prandtl Number ◽  
Clear Pattern ◽  
Stable Temperature ◽  
Infinite Extent ◽  
The Stability ◽  
Double Diffusive

This is the second part of a three-part study of the stability of vertically oriented double-diffusive interfaces having an imposed vertical stable temperature gradient. In this study, flow is forced within a fluid of infinite extent by a prescribed excess of compositionally buoyant material between two parallel interfaces. Compositional diffusivity is ignored while thermal diffusivity and viscosity are finite. The stability of the interfaces is analysed first in the limit that they are close together (compared with the salt-finger lengthscale), then for general spacing. Attention is focused on whether the preferred mode of instability is varicose or sinuous and whether its wavevector is vertical or oblique.The interfaces are found to be unstable for some wavenumber for all values of the Prandtl number and interface spacing. The preferred mode of instability for closely spaced interfaces is varicose and vertical for Prandtl number less than about 9, sinuous oblique for Prandtl number between 9 and 15 and sinuous vertical for larger Prandtl number. For general spacing each of the four possible modes of instability is preferred for some range of Prandtl number and interface separation, with no clear pattern of preference, except that the sinuous oblique mode is preferred for widely separated interfaces. The growth rate of the preferred mode is largest for interfaces having separations of from 1 to 3 salt-finger lengths.

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.

Effect of Ni70Mn25Co5 or Fe55Ni29Co16 on the Growth of Type-II a Large Diamonds with Al as Nitrogen Getter

2011 ◽  
Vol 266 ◽  
pp. 89-92
Author(s):  
Shang Sheng Li ◽  
Ning Luo ◽  
Xiao Lei Li ◽  
Tai Chao Su ◽  
You Mou Zhou ◽  
...  
Keyword(s):  
Growth Rate ◽  
High Pressure ◽  
High Temperature ◽  
Temperature Gradient ◽  
Nitrogen Concentration ◽  
Type Ii ◽  
High Quality ◽  
Quality Type ◽  
Temperature Gradient Method ◽  
Large Diamond

With adopting Al as the nitrogen getter in Ni70Mn25Co5 or Fe55Ni29Co16 catalyst, High-quality type-Ⅱa large diamonds have been grown under the conditions of about 5.5GPa and 1580K by using the temperature gradient method. While Al(2.0wt%) is added in the Fe55Ni29Co16, the nitrogen concentration(Nc) in the diamond is less than 1ppm. While Al(4.0wt%) is added in the Ni70Mn25Co5, the Nc in the diamond is highly arrived at 48ppm. The different of solubility of nitrogen in both catalyst at high pressure and high temperature is the basic reason of the different effect of eliminating nitrogen of Al. It can be shown in experamentals that Al is a less efficient nitrogen getter in Ni70Mn25Co5 than in Fe55Ni29Co16. While Al(2.0wt%) is added in the Fe55Ni29Co16, the high-quality type-Ⅱa large diamond, in which nitrogen is less than 1ppm and which the size was arrived at 3.3mm, had grown by decreasing the growth rate of diamond.

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