Charge conservation, entropy current and gravitation Aoki, Sinya; Onogi, Tetsuya; Yokoyama, Shuichi
International journal of modern physics. A, Particles and fields, gravitation, cosmology,
10/2021, Volume:
36, Issue:
29
Journal Article
Peer reviewed
Open access
We propose a new class of vector fields to construct a conserved charge in a general field theory whose energy–momentum tensor is covariantly conserved. We show that there always exists such a vector ...field in a given field theory even without global symmetry. We also argue that the conserved current constructed from the (asymptotically) timelike vector field can be identified with the entropy current of the system. As a piece of evidence we show that the conserved charge defined therefrom satisfies the first law of thermodynamics for an isotropic system with a suitable definition of temperature. We apply our formulation to several gravitational systems such as the expanding universe, Schwarzschild and Banãdos, Teitelboim and Zanelli (BTZ) black holes, and gravitational plane waves. We confirm the conservation of the proposed entropy density under any homogeneous and isotropic expansion of the universe, the precise reproduction of the Bekenstein–Hawking entropy incorporating the first law of thermodynamics, and the existence of gravitational plane wave carrying no charge, respectively. We also comment on the energy conservation during gravitational collapse in simple models.
•Energy saving potential is assessed by energy balance and thermal comfort.•Enthalpy change is used as the result of energy fluxes of a room in hot-humid zones.•Thermal comfort index APMV is proper ...for naturally ventilated buildings.•Steps are given to design a well-performed naturally ventilated building.
This paper examines naturally ventilated buildings in hot and humid summer zones and proposes an air enthalpy-based energy conservation rating method with an emphasis on the combined thermal comfort-ventilation parameters, particularly the impact of humidity and human adaptations on thermal comfort. The new method starts with energy flow analysis to a naturally ventilated room and assessment of thermal comfort accounting for the humidity of the naturally ventilated room as well as the occupants’ adaptability, differing from the PMV models and widely-used adaptive models adopted in existing rating methods. It contributes to designing a well-performed naturally ventilated building by analysing the interplay of climate elements, design features, indoor thermal comfort, and energy consumption for cooling in hot-humid climates. It also gives the access to rate the influence of an estimated energy saving due to natural ventilation on the energy system at a district or national scale. The proposed method is then applied to a naturally ventilated office located in three cities within this particular climatic region of China. The results indicate that natural ventilation is an effective way to improve thermal comfort while maintaining a low cooling energy consumption in hot-humid summer zones. Using natural ventilation could help reduce cooling energy demand by 10–30% compared to not using natural ventilation. Its energy saving potential is strongly affected by the enthalpy of outdoor air, followed by airflow rate. Then, a contrast comparison between the new method based on energy balance and Chinese indoor thermal comfort standard and the conventional method coupling adaptive ASHRAE standard-55 thermal comfort model with sensible heat balance model is carried out. The contrast results validate the considerable impacts of humidity on energy balance analysis and thermal comfort rating. It points out the new method makes improvement of the maximum energy saving potential of naturally ventilated buildings prediction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We present a general procedure to construct the first law of thermodynamics on the apparent horizon and illustrate its validity by examining it in some extended gravity theories. Applying this ...procedure, we can describe the thermodynamics on the apparent horizon in Randall–Sundrum braneworld imbedded in a nontrivial bulk. We discuss the mass-like function which was used to link Friedmann equation to the first law of thermodynamics and obtain its special case which gives the generalized Misner–Sharp mass in Lovelock gravity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Аннотация. В статье предпринята попытка строгой аксиоматизации термодинамики, т. е. построения такого ее изложения, при котором все ее изложение вытекает из нескольких аксиом. При этом оказывается, ...что классическая точка зрения, состоящая в том, что все здание термодинамики может быть построено на пяти началах (так называемые минус первый, нулевой, первый, второй и третий законы термодинамики), не выдерживает критики - количество аксиом существенно больше. Попытка выявить логическую необходимость введения этих аксиом в основания термодинамики и выявление самой их физической сущности (формулировка) и предприняты в данной статье.
We suggest that using the first law of thermodynamics is a convenient method to obtain a correct form of the expansion law of the universe (Padmanabhan,
arXiv:1206.4916
v1 hep-th). We will, then, use ...this idea to obtain the expansion law for a Kodama observer. By using the expansion law for a Kodama observer, we can obtain the dynamic equation of the FRW universe for deformed Horava–Lifshitz gravity. The use of the first law of thermodynamics also leads to a new approach for obtaining the Friedmann equations for f(R) and scalar tensor gravities.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The author has shown previously that the first law of thermodynamics must be modified for materials with negative thermal expansion and for auxetic materials. In this paper, those earlier results ...have been developed and improved and a paradox stemming from the previous findings has been solved. It is shown that in thermodynamic equations, the motive force of the process must be written on the left-hand side and its effect must be written on the right-hand side. Consequently, the first law of thermodynamics for heat exchange and compression has different signs. This result is of importance for the entire field of thermodynamics.
► The first law of thermodynamics for auxetic materials needs modification. ► Equation describing a compression does not follow from equation of heat transfer. ► Motive force of the process must be written on the left-hand side of the equation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Modeling Coandã effect has been a fundamental issue in fluid dynamic research in the XX century. It has lost some interest because of the improvement in CFD, even if it could be still important in ...the area of the preliminary design of aerodynamic devices that benefits of fluid deflection by convex surfaces. An effective model of Coandã effect has not been defined, and fundamental questions are still open. The influence of convective heat exchange on Coandã adhesion of a fluid stream on a convex surface in the presence of a temperature gradient between the fluid and the convex surface is a problem, which affects many practical cases, but it is still marginally approached by scientific literature. This paper aims to start an effective research direction on the effects of convective heat exchange on Coandã effect. It approaches the problem with a set of CFD simulations. It analyses the previous hypotheses, which are based on Prandtl number and evidences the need of a more effective model that accounts also for the Reynolds number.
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DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The tunneling radiation of particles from Born–Infeld anti-de Sitter black holes is studied by using the Parikh–Wilczek method and the emission rate of a particle is calculated. It is shown that the ...emission rate is related to the change of the Bekenstein–Hawking entropy of the black hole and the emission spectrum deviates from the purely thermal spectrum but is consistent with an underlying unitary theory.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In some papers, dependences of the isobaric heat capacity of water versus pressure and temperature were obtained. It is shown that these dependences contradict both the dependence of heat capacity on ...temperature for supercooled water, and an important thermodynamic equation for the dependence of heat capacity on pressure. A possible explanation for this contradiction is proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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