Quasi-local charges and asymptotic symmetry generators

The quasi-local formulation of conserved charges through the off-shell approach is extended to cover the asymptotic symmetry generators. By introducing identically conserved currents which are appropriate for asymptotic Killing vectors, we show that the asymptotic symmetry generators can be understood as quasi-local charges. We also show that this construction is completely consistent with the on-shell method.Comment: 19 pages; v2 typos fixe

Thermodynamic Volume and the Extended Smarr Relation

We continue to explore the scaling transformation in the reduced action formalism of gravity models. As an extension of our construction, we consider the extended forms of the Smarr relation for various black holes, adopting the cosmological constant as the bulk pressure as in some literatures on black holes. Firstly, by using the quasi-local formalism for charges, we show that, in a general theory of gravity, the volume in the black hole thermodynamics could be defined as the thermodynamic conjugate variable to the bulk pressure in such a way that the first law can be extended consistently. This, so called, thermodynamic volume can be expressed explicitly in terms of the metric and field variables. Then, by using the scaling transformation allowed in the reduced action formulation, we obtain the extended Smarr relation involving the bulk pressure and the thermodynamic volume. In our approach, we do not resort to Euler's homogeneous scaling of charges while incorporating the would-be hairy contribution without any difficulty.Comment: 1+21 pages, plain LaTeX; v2 typo fixed and references adde

Cognitive Theory of War: Why Do Weak States Choose War against Stronger States?

The key question to be addressed in this paper is why weaker states with a slight chance of winning do not avoid war against stronger states. Even though most war theory does offer a few insights about the conditions under which weak states choose war when there is only a slight possibility of winning, explanations based on either emphasis on rationality or ignorance of “interacting structure” of international relations leave many practical remedies unexplained. This paper explains asymmetric conflict on the combination of Prospect theory and Game theory. The interacting game structure of asymmetric conflicts can be summarized. Under the threat of massive retaliation by a strong state, a weak state is forced to choose between war (defection) and withdrawal (cooperation). In asymmetric conflicts, defection (war against a strong state with a slight chance of winning) is a risky gamble, and cooperation is safe choice. In contrast to Expected Utility theory, this paper argues that weak states in a loss frame chooses risky war (defection) against a superior adversary in the hope of recovering from their crisis. This paper follows crisis analyses of other Prospect theorists. The nature and seriousness of the crisis of a weak state are analyzed. The rare occurrence and deviant characteristics of a weak state’s war choice make it suitable to use a qualitative structured analysis. The research hypothesis is applied to three case studies: the Gulf War between Iraq and the United States-led alliance in 1990, the Falkland/Malvinas Island war between Argentina and the United Kingdom in 1982, and the Middle East War between Egypt and Israel in 1973. The implication of this study is that enforcing strategy based on superior capability is not a reasonable means to prevent a weak state in a loss frame from choosing war against superior adversary

Silk as a biomaterial paste for biomimetic composite

Silk is a highly promising biomaterial with unique bio-physicochemical properties, such as excellent mechanical and optical properties, biocompatibility and programmable biodegradability. Among many different types, silk from domesticated silkworm, bombyx mori has received wide attention owing to its availability in virtually unlimited quantities and ease of extraction. In this study, we investigated silkworm silk as a protein glue to realize nacre-like composites. We have employed spin assisted layer-by-layer technique to fabricate ultrathin free-standing biocomposite films. Two different composites have been studied: (i) graphene oxide (GO)/silk and (ii) chitin/silk. From our prior work, it is known that the adsorption of amphiphilic silk on amphiphilic GO flakes is highly sensitive to the pH of the silk solution. In this study, we investigated the influence of pH of the silk solution on the mechanical properties of silk/GO composites. We found that the pH of silk solution has a significant influence on the structure and elastic modulus of the composite films. Over the pH rage studied here (pH4 to pH10), the modulus of composite films could be varied from 8 GPa to 31 GPa. Apart from the relative volume fractions of the two components, our results show that interfacial interaction between protein glue and graphene oxide plays a determining role in the ultimate mechanical properties of the film. Additionally, we fabricated first protein-polysaccharide biocomposite layer-by-layer assembled composite using silk and chitin. Chitin is known for its chemical stability and excellent mechanical properties. However, it is a very difficult material to process due to its poor solubility, requiring strong organic solvent of hexafluoro-2-proponal (HFIP) to dissolve. Despite these difficulties, we have successfully developed a robust fabrication approach to realize chitin-silk biocomposite with different volume fractions of chitin, and demonstrate the release of these film from substrate into freestanding state. We have investigated the mechanical properties of these ultrathin films. The highest elastic modulus of the composite was found to be 6.9 GPa with 0.3% chitin, which is significantly higher than that of the composite film made with chitosan, a highly deacetylate form of chitin. Taken together, our studies provide novel insights into the nanoscale structure and mechanical properties of ultrathin free-standing bionanocomposites fabricated using layer-by-layer assembly