海洋重力传感器伺服回路分析与设计

海洋重力仪是改善舰船惯导系统精度的重要设备，其重力传感器的伺服回路决定着仪器的精度和动态性能。作在介绍零长弹簧海洋重力传感器结构原理的基础上，研究其伺服回路的结构组成和设计方法，分析了其主要环节参数对系统性能的影响，考察了其时域性能，对海洋重力仪的研制具有重要指导作用。     

Chiral Brønsted Acid Directed Iron‐Catalyzed Enantioselective Friedel–Crafts Alkylation of Indoles with β‐Aryl α′‐Hydroxy Enones

A cooperative catalytic system established by the combination of an iron salt and a chiral Brønsted acid has proven to be effective in the asymmetric Friedel–Crafts alkylation of indoles with β‐aryl α′‐hydroxy enones. Good to excellent yields and enatioselectivities were observed for a variety of α′‐hydroxy enones and indoles, particularly for the β‐aryl α′‐hydroxy enones bearing an electron‐withdrawing group at the para position of the phenyl ring (up to 90 % yield and 91 % ee). The proton of the chiral Brønsted acid, the Lewis acid activation site, as well as the inherent basic site for the hydrogen‐bonding interaction of the Brønsted acid are responsible for the high catalytic activities and enantioselectivities of the title reaction. A possible reaction mechanism was proposed. The key catalytic species in the catalytic system, the phosphate salt of Fe^III, which was thought to be responsible for the high activity and good enantioselectivity, was then confirmed by ESIMS studies.     

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.     

Laser induced electronic acceleration process in nano dot

A physical model of the laser induced electron transport in dielectric with small size is discussed. The model assumes that free electrons are originally existent or produced by impact detrapping. The free electrons transporting in low dimensional dielectrics interact with phonons and surface. When the laser electric field strength is high enough, the inelastic electron scattering such as impact ionization and cascade processes will play important roles. A small size effect has been found in electron absorbing laser energy under the conditions that the laser wavelength is in near infrared zone and the material has size in nanometer level. This is a very significative effect to enlighten us on preparing ultrahigh threshold laser films with new nano-structure.     

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.     

高密度平面靶等离子体中激光驱动冲击波加速离子的能谱展宽

本文对超短超强激光脉冲辐照高密度等离子体产生的静电冲击波加速离子的能谱展宽机理进行了数值研究.着重讨论了三种冲击波加速离子的能谱展宽机理:能量沉积到离子中使得冲击波前沿不断减速,被加速离子与背景粒子的碰撞,以及高能离子到达靶背面时受到鞘层场进一步加速.还研究了驱动激光脉冲宽度对冲击波加速离子能谱宽度的影响. 关键词： 激光等离子体 冲击波加速 能谱展宽     

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.