Relaxation of polarized nuclei in superconducting rhodium

Nuclear spin lattice relaxation rates were measured in normal and superconducting (sc) rhodium with nuclear polarizations up to p = 0. 55. This was sufficient to influence the sc state of Rh, whose T(c) and B(c) are exceptionally low. Because B(c)相似文献   

Influence of interparticle interactions on the kinetics of self-assembly and mechanical strength of nanoparticulate aggregates

Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude.     

JT-60U装置温度分布剖面不变性的实验研究

在一系列H模放电条件下，建立了一个旨在研究等离子体温度分布剖面不变性的数据库。介绍了数据库建立过程中要解决的关键问题和所用软件，对等离子体温度分布剖面不变性及芯部约束与边缘参数的关系进行了研究。     

Applications of particle-tracking analysis to the determination of size distributions and concentrations of nanoparticles in environmental, biological and food samples

The manufacture of nanoparticles (NPs) and nanomaterial-based products is rapidly increasing and their possible occurrence in environment, food or biological tissue is becoming of concern for ecological and human health. However, there is a lack of suitable methods to analyze and to characterize NPs in low concentrations in complex matrixes. We compare several particle-tracking methods using video microscopy and a new technique called nanoparticle-tracking analysis (NTA). Video microscopy has been widely applied to investigate particle movement in biological samples, micro-rheology, and velocity profiles in fluids, whilst NTA was devised for determination of size distributions and concentrations in liquid samples. We critically discuss the advantages and the limitations of NTA for such applications.     

Double-spin-flip resonance of rhodium nuclei at positive and negative spin temperatures

Sensitive SQUID-NMR measurements were used to study the mutual interactions in the highly polarized nuclear-spin system of rhodium metal. The dipolar coupling gives rise to a weak double-spin-flip resonance. The observed frequency shifts allow deducing separately the dipolarlike contribution and the isotropic exchange term. For the first time, such measurements were extended to negative absolute temperatures as well. We find an effective dipolar moment 0. 10&mgr;(N) of which about 15% is attributed to a conduction electron mediated pseudodipolar interaction. The isotropic exchange is described by R = -0.9+/-0.1.     

Nuclear ordering in lithium and an upper limit on its ambient pressure superconducting transition temperature

We have discovered spontaneous ordering of nuclear spins in lithium metal by NMR measurements at very low temperatures. In low magnetic fields, B<0.2 mT, the NMR spectra show a pronounced low-frequency anomaly. Also, nonadiabatic response to a slowly varying magnetic field was observed. A rich phase diagram with three different nonparamagnetic regions is proposed. We estimate a critical spin temperature T(c) approximately 350 nK at B=0. We also report the absence of superconductivity in lithium at normal pressure down to T(e) approximately 100 microK (B<10 nT).