Irreducibility testing over local fields

The purpose of this paper is to describe a method to determine whether a bivariate polynomial with rational coefficients is irreducible when regarded as an element in , the ring of polynomials with coefficients from the field of Laurent series in with rational coefficients. This is achieved by computing certain associated Puiseux expansions, and as a result, a polynomial-time complexity bound for the number of bit operations required to perform this irreducibility test is computed.

     

The Gravitational Field of a Radiating and Contracting Spherically-Symmetric Body with Heat Flow

A model of a highly idealized spherically symmetric object radiating away its mass with constant luminosity is presented. The body starts at t = – with both infinite mass and radius and contracts to a point at t = 0 without forming an event horizon. Its material particles are moving non-geodesically and shearfree while transporting heat to the surface. Unlike in some radiating star models of a similar type, all physically required conditions are satisfied in this model.     

Higher-Order Corrections to the Effective Gravitational Action from Noether Symmetry Approach

Higher-order corrections of the Einstein–Hilbert action of general relativity can be recovered by imposing the existence of a Noether symmetry to a class of theories of gravity where the Ricci scalar R and its d'Alembertian R are present. In several cases, it is possible to get exact cosmological solutions or, at least, to simplify the dynamics by recovering constants of motion. The main result is that a Noether vector seems to rule the presence of higher-order corrections of gravity.     

Evidence of red cell alignment in the magnetic field of an NMR spectrometer based on the diffusion tensor of water

The alignment of human erythrocytes in aqueous suspensions in the magnetic field B(0) (called the z-direction) of an NMR spectrometer was shown by calculating the diffusion tensor for water in the sample. The diffusion was measured using a pulsed-field-gradient spin-echo NMR method. The extent of diffusion anisotropy for water was exemplified by the values of the apparent diffusion coefficients with erythrocytes of normal shape and volume: for a typical experiment the values for the x-, y-, and z-directions were (6.88 +/- 0.17) x 10(-10), (7.07 +/- 0.17) x 10(-10), and (10.20 +/- 0.17) x 10(-10) m(2) s(-1), respectively. Cells in hypo- and hyperosmotic media were also studied and they too showed the anisotropy of the apparent diffusion coefficients but the extents were different. A new method of data analysis was developed using the Standard Add-On Packages in a Mathematica program. The experimental findings support evidence of erythrocyte alignment that was previously obtained with a high-field-gradient q-space method.     

Anisotropic diffusion in a nematic liquid crystal- An electric field PFG NMR approach

The access to self-diffusion coefficients in anisotropic systems such as thermotropic liquid crystals by means of PFG NMR is complicated by strong dipolar interactions. Additionally, problems arise due to the immediate orientation of low-molar-mass nematic liquid crystals in an external field. The director orientation can be changed by the application of an additional electric field. This can be exploited in order to reduce the dipolar interaction to such an extent that the NMR linewidths change from a solid-state to a liquid-like situation enabling PFG NMR experiments.     

Electron paramagnetic resonance imaging using magnetic-field-gradient spinning

A novel X-band CW EPR imaging has been developed using magnetic-field-gradient (MFG) spinning to obtain spatial distributions of electron paramagnetic species. Spinning MFG EPR imaging for 65 projection spectra required just 55 s while conventional imaging took 11 min 40 s, that is, the acquisition time for the new system is one order of magnitude shorter than that for conventional EPR imaging. Spinning MFG EPR imaging allows one to measure reconstructed images in an interactive manner where resolution and condition can be changed quickly.     

电子成像均匀约束磁场的产生及测试分析

为增加离子与原子碰撞成像系统中探测电子的立体角，设计了一约束电子的复合型亥姆霍兹线圈装置.对复合型亥姆霍兹线圈的磁场分布进行了理论计算和分析，并对制作的复合型亥姆赫兹线圈产生的磁场进行了实验测量，得出磁场的均匀性好于±0.6%. 关键词： 亥姆霍兹线圈 磁场分布 磁场均匀性     

Taub-NUT时空视界附近自旋场的热力学量

利用Wentzel-Kramers-Brillouin近似计算了Taub-NUT时空事件视界附近自旋为1/2，1，3/2，2等无质量场的熵密度、压强和能量密度.结果表明，自旋场附近的热力学量不仅具有与平直时空相同的主导项，还多了两项自旋依赖的附加项. 关键词： Taub-NUT时空 自旋场 热力学量     

极性分子型电流变液

电流变液在电场作用下软硬连续可调的奇特性质具有广泛和重要的应用价值。传统电流变液是基于颗粒极化产生的相互作用,根据介电理论预测,其剪切屈服强度的上限约为10kPa。电流变液被发明50年来,阻碍其应用的主要原因是剪切强度低。近年来发明的"极性分子型电流变液"是一类新型电流变液,其屈服强度比传统电流变液大一个数量级以上,且与电场强度呈线性关系,这一点和传统电流变液中的平方关系也明显不同。文章作者提出了极性分子在颗粒间强局域电场中的取向并与极化电荷作用的模型,成功地解释了观察到的实验现象。根据这一原理,有可能制备出屈服强度高达MPa的电流变液。     

碳纳米管的变温场发射

考察了温度变化对沉积在钨丝针尖上的碳纳米管场发射的影响，发现碳纳米管场发射电流随温度升高而增大，场发射电流的稳定性基本没有变化. 多根碳纳米管的场发射特性随温度变化出现偏离Fowler-Nordheim理论的现象，这种现象可能来自碳纳米管的不均匀性.