Increasing the pump-up rate to polarize He gas using spin-exchange optical pumping method

In recent years, polarized ³He gas has increasingly been used as neutron polarizers and polarization analyzers. Two of the leading methods to polarize the ³He gas are the spin-exchange optical pumping (SEOP) method and the meta-stable exchange optical pumping (MEOP) method. At present, the SEOP setup is comparatively compact due to the fact that it does not require the sophisticated compressor system used in the MEOP method. The temperature and the laser power available determine the speed, at which the SEOP method polarizes the ³He gas. For the quantity of gas typically used in neutron scattering work, this speed is independent of the quantity of the gas required, whereas the polarizing time using the MEOP method is proportional to the quantity of gas required. Currently, using the SEOP method to polarize several bar-liters of ³He to 70% polarization would require 20−40 h. This is an order of magnitude longer than the MEOP method for the same quantity of gas and polarization. It would therefore be advantageous to speed up the SEOP process. In this article, we analyze the requirements for temperature, laser power, and the type of alkali used in order to shorten the time required to polarize ³He gas using the SEOP method.     

Cucurbit[7]uril Disrupts Aggregate Formation Between Rhodamine B Dyes Covalently Attached to Glass Substrates

Dye aggregation is detrimental to the performance of high optical density dye-doped photonic materials. To overcome this challenge, the ability of cucurbit[7]uril (CB7) as a molecular host to disrupt aggregate formation on glass substrates was examined. Rhodamine B was covalently attached to glass slides by initially coating the surface with azidohexylsiloxane followed by copper-catalyzed “click” triazole formation with rhodamine B propargyl ester. The absorption and emission spectra of rhodamine B coated slides in water indicated diverse heterogeneous properties as surface dye density varied. Fluorescence quenching due to dye aggregation was evident at high surface dye density. Addition of aqueous cucurbit[7]uril (CB7) to the surface-tethered dyes perturbed the spectra to reveal a considerable reduction in heterogeneity, which suggested that the presence of a surface in close proximity does not significantly impair CB7’s ability to complex with tethered rhodamine B.     

Central neurocytoma: typical magnetic resonance spectroscopy findings and atypical ventricular dissemination

PURPOSE: Central neurocytomas (CNCs) are rare neuronal tumors that have a favorable prognosis and lower rate of recurrence compared with other intraventricular neoplasms. Although it may be difficult to distinguish CNC on conventional neuroimaging, typical MR spectroscopy (MRS) features have been reported. We describe the MRI and MRS features of CNC. MATERIALS AND METHODS: Eight patients with CNC were reviewed. Three patients underwent presurgical in vivo single-voxel MRS at short echo time (TE, 35 ms) and multi-voxel MR spectroscopic imaging at long TE (144 ms). The surgically resected tumor specimen of one of these patients was also studied ex vivo using high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance. RESULTS: All eight tumors were located in the lateral ventricles. In six patients, CNC extended into the third ventricle, and in two patients the tumor showed further contiguous intraventricular dissemination into the fourth ventricle. In all three patients who underwent MRS, a characteristic metabolite peak was detected at 3.55 parts per million (ppm) at both long and short TE. HRMAS confirmed the presence of elevated glycine (Gly) at 3.55 ppm, without increase in the concentration of myo-inositol found at the same chemical shift. Elevated choline (at 3.2 ppm) was also seen in all three patients. CONCLUSION: On MRS, CNCs have a typical appearance with a metabolite peak at 3.55 ppm due to increased Gly, and this feature may be helpful in presurgical diagnosis. Although they are rare benign intraventricular tumors, in atypical cases, CNCs can show extensive intraventricular dissemination into the fourth ventricle.     

Analysis ofK→3Π decays in chiral perturbation theory

Using the recently proposed higher-order chiral Lagrangians determined from the integration of nontopological chiral anomalies, we calculate corrections to the current-algebra analysis ofK→3Π decay amplitudes expanded in powers of the Dalitz variables. Effects of quartic-derivative weak chiral Lagrangians are determined through the use of short-distance effective weak Hamiltonian and the factorization method. We find that (1) the constant and linear terms in the amplitude for ΔI=1/2K→3Π are in excellent agreement with experiment; the previous discrepancy of (20–35)% between current algebra and data is thus accounted for by the higher-order effective Lagrangians, (2) the penguin interaction does not play an essential role in the ΔI=1/2 rule, for otherwise it will lead to a large disagreement for the constant and linear terms, (3) one of the two quadratic terms in the ΔI=1/2 process, which arise from the quartic chiral Lagrangians, is in accord with data within experimental errors, while the other is off by four standard deviations, (4) the linear term in the ΔI=3/2 transitions is in good agreement with experiment and contributions from quadratic terms are sizable.     

Phase behaviour of colloid-polymer mixtures

Summary We review the phase behaviour of mixtures of colloids and non-adsorbing polymers. The exclusion of polymer molecules from overlapping ?depletion zones? between two neighbouring colloidal particles results in an unbalanced osmotic pressure pushing the particles together. This depletion potential is separately tunable in range and depth. Theory predicts that the resulting phase behaviour is sensitive to ξ=r _g/R, the ratio of the radius of gyration of a polymer molecule, to the radius of the colloid. At large ξ, a stable colloidalliquid phase becomes possible. This has been confirmed by recent experiments. The formation of non-equilibrium ?transient gel? states when the size ratio is small (≈0.08) is also introduced briefly. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

带有相依重尾冲击的Poisson噪音过程尾的一致渐近性质

本文考虑了带有某种相依重尾冲击的Poisson噪音过程尾的一致渐近性质.当冲击是二元上尾渐近独立的非负随机变量具有长尾和控制变化尾分布且噪音函数具有正的上下界时,得到了过程尾概率的一致渐近公式.进而,当冲击具有连续的一致变化尾分布时,去除了噪音函数具有正的下界的限制.对于噪音函数不一定具有正的上界的情形,当冲击具有两两负象限相依结构时,也得到了一致渐近性结果.     

Hybrid Plasma – Prospects for Application in Medicine and Biology

Russian Physics Journal - Different schemes and designs of generators of low-temperature hybrid plasma produced by simultaneous ionization of plasma-generating medium by an electron beam with...