Generalized thermodynamics and Fokker-Planck equations. Applications to stellar dynamics, two-dimensional turbulence and Jupiter's great red spot

We introduce a new set of generalized Fokker-Planck equations that conserve energy and mass and increase a generalized entropy until a maximum entropy state is reached. The concept of generalized entropies is rigorously justified for continuous Hamiltonian systems undergoing violent relaxation. Tsallis entropies are just a special case of this generalized thermodynamics. Application of these results to stellar dynamics, vortex dynamics and Jupiter's great red spot are proposed. Our prime result is a novel relaxation equation that should offer an easily implementable parametrization of geophysical turbulence. This relaxation equation depends on a single key parameter related to the skewness of the fine-grained vorticity distribution. Usual parametrizations (including a single turbulent viscosity) correspond to the infinite temperature limit of our model. They forget a fundamental systematic drift that acts against diffusion as in Brownian theory. Our generalized Fokker-Planck equations may have applications in other fields of physics such as chemotaxis for bacterial populations. We propose the idea of a classification of generalized entropies in classes of equivalence and provide an aesthetic connexion between topics (vortices, stars, bacteries,...) which were previously disconnected.Comment: Submitted to Phys. Rev.

Corporate Diversification in China: Causes and Consequences

We examine the diversification patterns of almost all publicly listed non-financial companies in China during the 2001 to 2005 period. More than 70 percent of the firms in our sample are diversified. We document that patterns of diversification strongly depend on firms' political connections. Former local bureaucrats are more likely than other CEOs to enter multiple industries. This effect is particularly pronounced in state-owned enterprises (SOEs) that operate in weak institutional environments. These companies are particularly prone to entering low-growth, low-profitability, and unrelated industries. Consequently, the performance effects of diversification differ sharply across SOEs and private firms. While the latter earn a premium from diversifying their operations, SOEs do not. Our results are consistent with the view that provincial and local governments push Chinese SOEs into unattractive sectors of the economy and that politically connected CEOs use their relationships to build corporate empires.Corporate Diversification, Institutions, China

Removal of heat-formed coating from a titanium alloy using high pressure waterjet: Influence of machining parameters on surface texture and residual stress

© 2015 Elsevier B.V. All rights reserved. Titanium alloys are widely used in the aerospace and medical industries owing to their high strength to weight ratio and outstanding corrosion resistance. A problem for titanium or titanium alloys is the existence of a hard, brittle and oxygen-enriched layer on the surface (so called alpha case). This is usually formed during hot forming processes or after long-term service at elevated temperatures in an open-air environment. With the development of waterjet systems, high pressure waterjet has shown its capability for the removal of such hard and difficult-to-machine coatings. Waterjet machining is usually associated with a surface roughening, which is unwanted for most of aerospace applications, but is beneficial for medical application where fixation is required (e.g. metal orthopedic implants). A potential benefit of waterjet material removal is that the process may introduce compressive residual stress to the machined surface and subsurface layers. In this study, Ti-6Al-4V with an alpha case layer was subjected to plain waterjet impact over a range of parametric conditions, to fully remove the alpha case layer. The resulting surfaces were then analyzed to demonstrate the influence of process parameters on both surface roughness and residual stress measured using X-ray diffraction (XRD)

Vertical Integration, Institutional Determinants and Impact: Evidence from China

Where legal systems and market forces enforce contracts inadequately, vertical integration can circumvent these transaction difficulties. But, such environments often also feature highly interventionist government, and even corruption. Vertical integration might then enhance returns to political rent-seeking aimed at securing and extending market power. Thus, where political rent seeking is minimal, vertical integration should add to firm value and economy performance; but where political rent seeking is substantial, firm value might rise as economy performance decays. China offers a suitable background for empirical examination of these issues because her legal and market institutions are generally weak, but nonetheless exhibit substantial province-level variation. Vertical integration is more common where legal institutions are weaker and where regional governments are of lower quality or more interventionist. In such provinces, firms led by insiders with political connections are more likely to be vertically integrated. Vertical integration is negatively associated with firm value if the top corporate insider is politically connected, but weakly positively associated with public share valuations if the politically connected firm is independently audited. Finally, provinces whose vertical integrated firms tend to have politically unconnected CEOs exhibit elevated per capita GDP growth, while provinces whose vertically integrated firms tend to have political insiders as CEOs exhibit depressed per capita GDP growth.

CP violation in Bd,s→l+l−B_{d,s} \to l^+l^- in the model III 2HDM

We have calculated the Wilson coefficients $C_{10}, C_{Q_i}$ (i=1,2) in the $\bar{MS}$ renormalization scheme in the model III 2HDM. Using the obtained Wilson coefficients, we have analyzed the CP violation in decays $B^0_q\to l^+l^-$ (q=d,s) in the model. The CP asymmetry, $A_{CP}$, depends on the parameters of models and $A_{CP}$ in $B_d\to l^+l^-$ can be as large as 40% and 35% for $l=\tau$ and $l=\mu$ respectively. It can reach 4% for $B^0_s$ decays. Because in SM CP violation is smaller than or equal to O($10^{-3}$) which is unobservably small, an observation of CP asymmetry in the decays $B^0_q \to l^+l^- (q=d,s)$ would unambiguously signal the existence of new physics.Comment: revtex4, 16 pages, 7 figure

Open/Closed String Duality for Topological Gravity with Matter

The exact FZZT brane partition function for topological gravity with matter is computed using the dual two-matrix model. We show how the effective theory of open strings on a stack of FZZT branes is described by the generalized Kontsevich matrix integral, extending the earlier result for pure topological gravity. Using the well-known relation between the Kontsevich integral and a certain shift in the closed-string background, we conclude that these models exhibit open/closed string duality explicitly. Just as in pure topological gravity, the unphysical sheets of the classical FZZT moduli space are eliminated in the exact answer. Instead, they contribute small, nonperturbative corrections to the exact answer through Stokes' phenomenon.Comment: 23 pages, 1 figure, harvma

Double Scaling Limits and Twisted Non-Critical Superstrings

We consider double-scaling limits of multicut solutions of certain one matrix models that are related to Calabi-Yau singularities of type A and the respective topological B model via the Dijkgraaf-Vafa correspondence. These double-scaling limits naturally lead to a bosonic string with c $\leq$ 1. We argue that this non-critical string is given by the topologically twisted non-critical superstring background which provides the dual description of the double-scaled little string theory at the Calabi-Yau singularity. The algorithms developed recently to solve a generic multicut matrix model by means of the loop equations allow to show that the scaling of the higher genus terms in the matrix model free energy matches the expected behaviour in the topological B-model. This result applies to a generic matrix model singularity and the relative double-scaling limit. We use these techniques to explicitly evaluate the free energy at genus one and genus two.Comment: 32 pages, 3 figure

Bounds on the mass of the b' quark, revisited

Recent results from the DELPHI collaboration led us to review the present bounds on the b' quark mass. We use all available experimental data for m_b' > 96 GeV to constrain the b' quark mass as a function of the Cabibbo-Kobayashi-Maskawa elements in a sequential four generations model. We find that there is still room for a b' with a mass larger than 96 GeV.Comment: 9 pages and 7 figures. REVTEX

B_s --> mu+ mu- decay in the R-parity violating minimal supergravity

We study B_s --> mu+ mu- in the context of the R-parity violating minimal supergravity in the high tan beta regime. We find that the lowest value of the branching ratio can go well below the present LHCb sensitivity and hence B_s --> mu+ mu- can even be invisible to the LHC. We also find that the present upper bound on Br(B_s --> mu+ mu-) puts strong constraint on the minimal supergravity parameter space. The constraints become more severe if the upper bound is close to its standard model prediction.Comment: 18 pages, 10 figures; version to be published in European Physical Journal