5,362 research outputs found
Unique Thermal Properties of Clothing Materials.
Cloth wearing seems so natural that everyone is self-deemed knowledgeable and has some expert opinions about it. However, to clearly explain the physics involved, and hence to make predictions for clothing design or selection, it turns out to be quite challenging even for experts. Cloth is a multiphased, porous, and anisotropic material system and usually in multilayers. The human body acts as an internal heat source in a clothing situation, thus forming a temperature gradient between body and ambient. But unlike ordinary engineering heat transfer problems, the sign of this gradient often changes as the ambient temperature varies. The human body also perspires and the sweat evaporates, an effective body cooling process via phase change. To bring all the variables into analysis quickly escalates into a formidable task. This work attempts to unravel the problem from a physics perspective, focusing on a few rarely noticed yet critically important mechanisms involved so as to offer a clearer and more accurate depiction of the principles in clothing thermal comfort
Are there hyperentropic objects ?
By treating the Hawking radiation as a system in thermal equilibrium, Marolf
and R. Sorkin have argued that hyperentropic objects (those violating the
entropy bounds) would be emitted profusely with the radiation, thus opening a
loophole in black hole based arguments for such entropy bounds. We demonstrate,
on kinetic grounds, that hyperentropic objects could only be formed extremely
slowly, and so would be rare in the Hawking radiance, thus contributing
negligibly to its entropy. The arguments based on the generalized second law of
thermodynamics then rule out weakly self-gravitating hyperentropic objects and
a class of strongly self-gravitating ones.Comment: LaTeX, 4 page
Effect of magnetic field on the charge and thermal transport properties of hot and dense QCD matter
We have studied the effect of strong magnetic field on the charge and thermal
transport properties of hot QCD matter at finite chemical potential. For this
purpose, we have calculated the electrical () and thermal
() conductivities using kinetic theory in the relaxation time
approximation, where the interactions are subsumed through the distribution
functions within the quasiparticle model at finite temperature, strong magnetic
field and finite chemical potential. This study helps to understand the impacts
of strong magnetic field and chemical potential on the local equilibrium by the
Knudsen number () through and on the relative behavior between
thermal conductivity and electrical conductivity through the Lorenz number
() in the Wiedemann-Franz law. We have observed that, both
and get increased in the presence of strong magnetic field, and the
additional presence of chemical potential further increases their magnitudes,
where shows decreasing trend with the temperature, opposite
to its increasing behavior in the isotropic medium, whereas increases
slowly with the temperature, contrary to its fast increase in the isotropic
medium. The variation in explains the decrease of the Knudsen number
with the increase of the temperature. However, in the presence of strong
magnetic field and finite chemical potential, gets enhanced and
approaches unity, thus, the system may move slightly away from the equilibrium
state. The Lorenz number ( in the abovementioned
regime of strong magnetic field and finite chemical potential shows linear
enhancement with the temperature and has smaller magnitude than the isotropic
one, thus, it describes the violation of the Wiedemann-Franz law for the hot
and dense QCD matter in the presence of a strong magnetic field.Comment: 29 pages, 6 figure
Asymmetrically Encapsulated vertical ITO/MoS2/Cu2O photodetector with ultra-high sensitivity
Strong light absorption, coupled with moderate carrier transport properties,
makes two-dimensional (2-D) layered transition metal dichalcogenide (TMD)
semiconductors promising candidates for low intensity photodetection
applications. However, the performance of these devices is severely
bottlenecked by slow response with persistent photocurrent due to long lived
charge trapping, and nonreliable characteristics due to undesirable ambience
and substrate effects. Here we demonstrate ultra-high specific detectivity (D*)
of 3.2x10^14 Jones and responsivity (R) of 5.77x10^4 AW-1 at an optical power
density (P_op) of 0.26 Wm-2 and external bias (V_ext) of -0.5 V in an indium
tin oxide (ITO)/MoS2/copper oxide (Cu2O)/Au vertical multi-heterojunction
photodetector exhibiting small carrier transit time. The active MoS2 layer
being encapsulated by carrier collection layers allows us to achieve negligible
trap assisted persistent photocurrent and repeatable characteristics over large
number of cycles. We also achieved a large D*>10^14 Jones at zero external bias
due to the built-in field of the asymmetric photodetector. Benchmarking the
performance against existing reports in literature shows a pathway for
achieving reliable and highly sensitive photodetectors for ultra-low intensity
photodetection applications.Comment: Accepted in Small, Wile
Self-Powered, Highly Sensitive, High Speed Photodetection Using ITO/WSe2/SnSe2 Vertical Heterojunction
Two dimensional transition metal di-chalcogenides (TMDCs) are promising
candidates for ultra-low intensity photodetection. However, the performance of
these photodetectors is usually limited by ambience induced rapid performance
degradation and long lived charge trapping induced slow response with a large
persistent photocurrent when the light source is switched off. Here we
demonstrate an indium tin oxide (ITO)/WSe/SnSe based vertical double
heterojunction photoconductive device where the photo-excited hole is confined
in the double barrier quantum well, whereas the photo-excited electron can be
transferred to either the ITO or the SnSe layer in a controlled manner. The
intrinsically short transit time of the photoelectrons in the vertical double
heterojunction helps us to achieve high responsivity in excess of A/W
and fast transient response time on the order of s. A large built-in
field in the WSe sandwich layer results in photodetection at zero external
bias allowing a self-powered operation mode. The encapsulation from top and
bottom protects the photo-active WSe layer from ambience induced
detrimental effects and substrate induced trapping effects helping us to
achieve repeatable characteristics over many cycles
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