Axial anomalies of Lifshitz fermions

We compute the axial anomaly of a Lifshitz fermion theory with anisotropic scaling z = 3 which is minimally coupled to geometry in 3+1 space‐time dimensions. We find that the result is identical to the relativistic case using path integral methods. An independent verification is provided by showing with spectral methods that the η‐invariant of the Dirac and Lifshitz fermion operators in three dimensions are equal. Thus, by the integrated form of the anomaly, the index of the Dirac operator still accounts for the possible breakdown of chiral symmetry in non‐relativistic theories of gravity. We apply this framework to the recently constructed gravitational instanton backgrounds of Hořava–Lifshitz theory and find that the index is non‐zero provided that the space‐time foliation admits leaves with harmonic spinors. Using Hitchin's construction of harmonic spinors on Berger spheres, we obtain explicit results for the index of the fermion operator on all such gravitational instanton backgrounds with SU(2) × U(1) isometry. In contrast to the instantons of Einstein gravity, chiral symmetry breaking becomes possible in the unimodular phase of Hořava–Lifshitz theory arising at λ = 1/3 provided that the volume of space is bounded from below by the ratio of the Ricci to Cotton tensor couplings raised to the third power. Some other aspects of the anomalies in non‐relativistic quantum field theories are also discussed.     

A surprising method for green extraction of essential oil from dry spices: Microwave dry-diffusion and gravity

Without adding any solvent or water, we proposed a novel and green approach for the extraction of secondary metabolites from dried plant materials. This "solvent, water and vapor free" approach based on a simple principle involves the application of microwave irradiation and earth gravity to extract the essential oil from dried caraway seeds. Microwave dry-diffusion and gravity (MDG) has been compared with a conventional technique, hydrodistillation (HD), for the extraction of essential oil from dried caraway seeds. Essential oils isolated by MDG were quantitatively (yield) and qualitatively (aromatic profile) similar to those obtained by HD, but MDG was better than HD in terms of rapidity (45min versus 300min), energy saving, and cleanliness. The present apparatus permits fast and efficient extraction, reduces waste, avoids water and solvent consumption, and allows substantial energy savings.     

超重力场电沉积NiW合金及其耐碱腐蚀性能

在超重力条件下电沉积NiW合金镀层,考察了超重力对NiW合金电沉积过程(各元素分电流、W含量和槽电压等)的影响规律;并利用扫描电子显微镜(SEM)、Tafel技术和电化学阻抗谱(EIS)技术研究了电沉积NiW合金镀层的表面形貌和在NaOH溶液中的抗腐蚀性能,同时通过浸泡实验考察了镀层的稳定性.结果发现,与常重力条件电沉积的NiW合金相比,超重力场电沉积的NiW合金中W含量增加,镀层表面无微裂纹产生;在10%(w)NaOH溶液中镀层自腐蚀电位正移,自腐蚀电流密度减小,腐蚀电阻也由常重力(重力系数G=1)时的865Ω·cm2增大至超重力(G=256)时的2305Ω·cm2;在10%NaOH溶液中浸泡144h后,超重力场电沉积的NiW合金表面无破碎和起皮现象发生.超重力技术在NiW合金电沉积过程中的应用,使镀层的耐碱腐蚀性能得到改善.     

引信用激光与加速度传感器复合定高技术

比较了不同类型的弹载定高体制,提出了脉冲激光与重力加速度传感器复合定高的定距原理,并对测距误差进行深入分析,得出其定高精度。对设计出的原理样机进行了实验测试,平台倾斜角度检测实验的结果表明,静态条件下最大角度误差小于0.3;0~500 m定高测试实验的结果表明,测量平均值与实际值最大误差为2.5 m,并且与目标距离无关。     

Flame spread over solids in buoyant and forced concurrent flows: Model computations and comparison with experiments

A detailed three-dimensional concurrent flame spread model is tested and compared with three sets of experiments. The parameters varied include: gravity, flow velocity, pressure, oxygen mole fraction, and sample width. In buoyant flows (normal and partial gravities), the computed steady spread rate and flame profiles agree favorably with experiment. The predicted extinction limits are lower but can be improved. Comparison in forced concurrent flow in microgravity shows correct trends. The predicted steady spread rates are lower than the experimental ones if the flames are short but higher than the experimental ones if the flames are long. It is believed that the experimental flames may not have fully reached steady state at the end of the 5-s microgravity drops. Longer duration microgravity experiments in future will be needed to substantiate this belief.     

Gravity on a multifractal

Despite their diversity, many of the most prominent candidate theories of quantum gravity share the property to be effectively lower-dimensional at small scales. In particular, dimension two plays a fundamental role in the finiteness of these models of Nature. Thus motivated, we entertain the idea that spacetime is a multifractal with integer dimension 4 at large scales, while it is two-dimensional in the ultraviolet. Consequences for particle physics, gravity and cosmology are discussed.     

Coupling of Brans-Dicke scalar field with Horava-Lifshitz gravity

We look for a Brans-Dicke type generalization of Horava-Lifshitz gravity. It is shown that such a generalization is possible within the detailed balance condition. Classically, the resulting theory reduces in the low energy limit to the usual Brans-Dicke theory with a negative cosmological constant for certain values of parameters. We then consider homogeneous, isotropic cosmology and study the effects of the new terms appearing in the model.     

Cosmological consequences of exponential gravity in Palatini formalism

We investigate cosmological consequences of a class of exponential f(R)$f(R)$ gravity in the Palatini formalism. By using the current largest type Ia Supernova sample along with determinations of the cosmic expansion at intermediary and high-z   we impose tight constraints on the model parameters. Differently from other f(R)$f(R)$ models, we find solutions of transient acceleration, in which the large-scale modification of gravity will drive the Universe to a new decelerated era in the future. We also show that a viable cosmological history with the usual matter-dominated era followed by an accelerating phase is predicted for some intervals of model parameters.     

Correlated stability conjecture revisited

Correlated stability conjecture (CSC) proposed by Gubser and Mitra (2000, 2001)  and  linked the thermodynamic and classical (in)stabilities of black branes. The classical instabilities, whenever occurring, were conjectured to arise as Gregory–Laflamme (GL) instabilities of translationally invariant horizons. In Buchel (2005) [3] it was shown that the thermodynamic instabilities, specifically the negative specific heat, indeed result in the instabilities in the hydrodynamic spectrum of holographically dual plasma excitations. A counter-example of CSC was presented in the context of black branes with scalar hair undergoing a second-order phase transition (Friess et al., 2005 [4]). In this Letter we discuss a related counter-example of CSC conjecture, where a thermodynamically stable translationally invariant horizon has a genuine tachyonic instability. We study the spectrum of quasinormal excitations of a black brane undergoing a continuous phase transition, and explicitly identify the instability. We compute the critical exponents of the critical momenta and the frequency of the unstable fluctuations and identify the dynamical critical exponent of the model.