13C spin-lattice relaxation in natural diamond: Zeeman relaxation in fields of 500 to 5000 G at 300 K due to fixed paramagnetic nitrogen defects

¹³C Spin–lattice relaxation (SLR) times in the laboratory frame have been measured at room temperature as a function of field in the range of 500 to 5000 G on two natural type Ib and Ia diamonds after dynamic nuclear polarization. Each of the diamonds contains two types of fixed paramagnetic centers with overlapping inhomogeneous electron paramagnetic resonance (EPR) lines. EPR techniques have been employed to identify these defects and to determine their concentrations and relaxation times at X-band. Three different nuclear SLR paths, namely that due to electron SLR and two types of three spin processes, are discussed. The one three-spin process (TSP) (type 1) involves a simultaneous transition of two electron spins belonging to the same hyperfine EPR line and a ¹³C spin while the other process (type 2) involves two electron spins belonging to different hyperfine EPR lines and a ¹³C spin. It is shown that the thermal contact between the ¹³C nuclear Zeeman and electron dipole–dipole interaction reservoirs decreases with an increase in field intensity, thus forming a bottleneck in the ¹³C relaxation path due to the type 1 TSP. The contribution of TSP of type 1 dominates that due to electron SLR and the type 2 TSP in relaxing the ¹³C nuclei in type Ib diamond from about 1200 to 5000 G, while for type Ia diamond it dominates from 500 up to about 2200 G. In type Ia diamond over the range 2200 to 5000 G it seems that the type 2 TSP, which involves electrons of neighboring P2 hyperfine lines, dominates that of electron spin–lattice and the type 1 TSP. Over the range 500 to about 1200 G, a field-dependent electron SLR mechanism associated with N3 centers appears to dominate the ¹³C SLR.     

硅基籽晶上化学气相沉积金刚石薄膜及其场发射特性

通过控制电泳沉积(EPD)时间,在硅基片上沉积不同密度的金刚石籽晶。再用热丝化学气相沉积(HFCVD)设备,在硅基籽晶上合成多晶金刚石薄膜。薄膜中通常含有非金刚石相碳成分。用扫描电子显微镜(SEM)和Raman光谱对样品的表面形貌和成分进行了表征,测量了样品的场发射特性。比较并分析了样品的表面形貌和非金刚石成分上的差异对金刚石薄膜场发射特性的影响。     

Optical and Paramagnetic Properties of Synthetic Diamond Single Crystals with a Low Content of Nitrogen

Optical and paramagnetic properties of synthetic diamond single crystals grown by the temperature gradient method in the Fe-Co-C and Fe-Co-Al-C systems using split-sphere high-pressure apparatus have been investigated. For crystals with a high (>5·10¹⁷ cm^–3) nitrogen concentration a good agreement of the concentrations of single substitution nitrogen atoms obtained from EPR, IR, and UV measurements was observed. For crystals with a low ((0.5–5.0)·10¹⁷ cm^–3) nitrogen concentration, there was no correlation between the results of substituting nitrogen concentrations obtained by the methods mentioned. It is shown that this behavior is attributable to the transition of the substituting nitrogen atoms from the paramagnetic neutral to nonparamagnetic positive charge state due to compensation by the boron impurity.     

Szeged index of some nanotubes

The Szeged index is one of the most important topological indices defined in chemistry. In this paper, the Szeged index of the hexagonal triangle graph T(n) and the zig-zag polyhex nanotube TUHC₆[2p,q] are computed.     

Effect of the preparation conditions of Ni-supported shock-wave synthesized nanodiamond catalysts: FT-IR and catalytic considerations

On the basis of the results from the FT-IR, XRD and catalytic studies, a suggestion about the mechanism of surface transformations of Ni-supported detonation-synthesized ultradispersed diamond and the influence of these transformations on the state of the loaded metal have been made. It was proposed that in dependence on the inert or oxidative atmosphere applied for the elimination of the Ni salt precursor, different interactions of the support with the NiO species have taken place that determined the way of their coordination and stability as well as the dispersion of the metal nickel phase formed upon their reduction. The catalytic activity of the latter has been tested in the reaction of toluene hydrogenation.     

Effect of thermal fluctuations on the coarsening dynamics of 2D hexagonal system

The dynamics of ordering in a 2D hexagonal system was investigated through the Cahn-Hilliard-Cook model. At low thermal noise amplitudes, pinning forces acting on grain boundaries dominate the dynamics and the coarsening evolves logarithmically in time. As noise amplitude increases, fluctuations becomes large enough to unlock dislocations located along grain boundaries and the grain boundary motion is driven by curvature. The grain boundary relaxation leads to a grain structure with Lifshitz's configurations. In this case the dynamic is also logarithmic as a consequence of the pinning of triple points.     

The uniaxial brickwork model,exact results,and CVM approximation

A complete phase diagram of the uniaxial brickwork lattice is determined first by using exact results, and then by using the cluster variation method. Both results are in very good agreement, which demonstrates the reliability of the CVM for two-dimensional systems. A well-defined maximum in the exact specific heat and a divergence of the CVM susceptibility provide strong indication for the occurrence of a floating phase.     

Electrochemical Investigation of Ruxolitinib: Sensitive Voltammetric Assay in Drug Product and Human Serum by Using Different Solid Electrodes

Ruxolitinib (RUX), a compound of the pyrrolopyrimidines class with activity as a tyrosine kinase inhibitory drug, is used to treat myelofibrosis. This study is reported for the detailed electrochemical behavior of RUX. The effects of supporting electrolyte, pH, and scanning rate on the peak potentials and currents of RUX were investigated by BDDE and GCE using different voltammetric techniques. Under optimum experimental conditions, calibration curves for RUX were obtained as 4 μM–80 μM and 1 μM–80 μM with a limit of detection (LOD) of 0.517 μM and 0.192 μM by the GCE and BDDE, respectively using DPV.     

On three-dimensional elastic problems of one-dimensional hexagonal quasicrystal bodies

Based on rigorous operator theory, a general solution of the three-dimensional elasticity equations of equilibrium for 1D hexagonal quasicrystals is obtained. The solution is expressed in terms of four quasiharmonic functions, which is very simple and useful. The point phonon (phason) force solution of an infinite 1D hexagonal quasicrystal body is derived, all in terms of elementary functions. They can play an important role in numerical simulations such as boundary element method.     

超细金刚石对应的碳液滴生成时间估算

在爆轰反应区的热密产物流中进行Ｂｒｏｗｎ运动的最初碳原子珠通过任意碰撞在Ｃ－Ｊ面处聚结成碳液滴。这个过程可以近似用胶体理论的快速聚沉动力学来描述。假定在爆轰反应区末端爆轰产物中碳液滴数等于聚沉过程结束时的碳滴数，则在此基础上计算得到的类金刚石碳滴的生成时间在爆轰反应区的时间长度内，实验中得到的超细金刚石的大颗粒（～２０ｎｍ）含有约７．３６１０￣５个原子，其对应反应区内的液态碳滴可以近似处理成严格进行两分子反应的碳的十九级滴，当碳滴所包含的碳原子数达到以上特定值时，爆轰反应过程结束，因此碳滴形成时间能被估算出来。