Investigation of ortho↔para hydrogen conversion by collisions with neutrons

Liquid hydrogen (LH) is constituted by para hydrogen (pH) and ortho hydrogen (oH) molecules. We analyzed the neutron scattering cross sections for pH→oH, pH→pH, oH→pH, and oH→oH reactions in LH. Results show that incident neutron energy lower than 14.7 meV is not sufficient to achieve pH→oH conversion. As energy increases, the cross section of pH→oH reaction increases sharply. If incident neutron energy is larger than 30 meV, branching fraction of pH molecules being converted into oH molecules upon inelastic scattering with the neutrons approaches 100%. As for the opposite process, branching fraction of oH→pH conversion is 10%–20% when incident neutron energy is lower than 30 meV. This conversion fraction oscillates with increasing incident neutron energy, eventually stabilizing at 30%. Based on the cross sections of the four reaction channels, we calculated the corresponding conversion rates based on a reactor cold neutron source model. There is 0.12% pH molecules of LH moderator would be converted to oH for one month operation . If neutron flux increased by 2 orders of magnitude, more than 10% pH would be transformed into oH, which means relative conversion rate of pH→oH induced by neutron inelastic scattering is not negligible.     

Adiabatic photo-steering theory in topological insulators

Feasible external control of material properties is a crucial issue in condensed matter physics. A new approach to achieving this aim, named adiabatic photo-steering, is reviewed. The core principle of this scheme is that several material constants are effectively turned into externally tunable variables by irradiation of monochromatic laser light. Two-dimensional topological insulators are selected as the optimal systems that exhibit a prominent change in their properties following the application of this method. Two specific examples of photo-steered quantum phenomena, which reflect topological aspects of the electronic systems at hand, are presented. One is the integer quantum Hall effect described by the Haldane model, and the other is the quantum spin Hall effect described by the Kane–Mele model. The topological quantities associated with these phenomena are the conventional Chern number and spin Chern number, respectively. A recent interesting idea, time-reversal symmetry breaking via a temporary periodic external stimulation, is also discussed.     

New exact solutions of the coupled sine-Gordon equations in nonlinear optics using the modified Kudryashov method

The main aim of this article is studying the coupled sine-Gordon equations in nonlinear optics, which describe the propagation of an optical pulse in fibre waveguide. New exact solutions of the coupled sine-Gordon equations have been derived through the use of the well-organized modified Kudryashov method.     

大型冷冻机组净化回收系统的改造设计

文中阐述了某大型冷冻机组的净化回收系统的设计改造。实施技术改造措施后,提高了原冷冻机运行可靠性和制冷剂F-11回收率,为企业创造了可观的经济效益,同时大幅减少制冷剂F-11的排放,对保护生态环境有重要意义。     

The Analogy between Light and Sound in the History of Optics from the Ancient Greeks to Isaac Newton. Part 1

Analogies between hearing and seeing already existed in ancient Greek theories of perception. The present paper follows the evolution of such analogies until the rise of 17th century optics, with due regard to the diversity of their origins and nature but with particular emphasis on their bearing on the physical concepts of light and sound. Whereas the old Greek analogies were only side effects of the unifying concepts of perception, the analogies of the 17th century played an important role in constructing optical theories by imitation of acoustic theories, or vice versa. This transition depended on several factors including the changing relations between optics, music, mathematics, and physics, the diversity of early modern concepts of sound, and the rise of a new physics based on experimentation and mechanical explanation.     

Superconducting toroidal combined-function magnet for a compact ion beam cancer therapy gantry

A superconducting, combined-function, 5 T, 90°, toroidal magnet with a large bore is described in this paper. This magnet is designed to be the last and most difficult part of a compact superconducting magnet-based carbon gantry optics for ion beam cancer therapy. The relatively small size of this toroidal magnet allows for a gantry the size of which is smaller or at least comparable to that of a proton gantry. The gantry design places the toroidal magnet between the scanning magnets and the patient, that is the scanning magnets are placed midway through the gantry. By optimizing the coil winding configuration of this magnet, near point-to-parallel optics is achieved between the scanning magnets and the patient; while at the same time there is only a small distortion of the beam-shape when scanning. We show that the origin of the beam-shape distortion is the strong sextupole components, whose effects are greatly pronounced when the beam is widely steered in the magnet. A method to correct such an undesirable effect is suggested and demonstrated by a numerical particle tracking through the calculated three-dimensional magnetic field.     

能动主镜的风载变形研究

风载引起的主镜变形是大口径望远镜必须考虑的问题.针对类似于Subaru望远镜的薄镜面能动光学系统,采用固定点力反馈控制方法对风载进行校正,本文引入了压强模式的概念,提取出风载产生的镜面变形的大部分信息,并据此对固定点力反馈控制方法进行了研究,得到如下结论:风载产生的镜面变形主要是平移、倾斜、像散和离焦等低阶像差;相同系...     

高真空多层绝热低温容器整体热分析及试验验证

对35 m'高真空多层绝热低温容器在满载液氧的状态下进行热分析,得到标准状态下该容器漏热量的分布范围及相应的静态蒸发率分布,分析了导热和辐射漏热在总漏热的比重.将计算结果和静态蒸发率试验进行对比,结果符合较好,说明计算的准确性和有效性.进而分析了冷态下玻璃钢支承件和罐体的接触情况.结果可为高真空多层绝热低温容器的设计、...     

大型LNG储罐关键技术

论述了大型LNG储罐的建造标准、罐体材料、罐体设计、焊接、绝热、施工。指出9Ni钢强度、韧性需改进,可尝试细化晶粒、提高纯净度、添加合金元素等方法。9Ni钢焊接不当易造成电弧磁偏吹、焊接裂纹及焊接接头低温韧性差,可通过选用合适的焊材、减小弧坑、控制焊接线能量来改善。针对储罐的特殊结构及绝热要求,应进行详细的结构设计及计算,选用合适的绝热材料及施工方案。为尽快提升我国大型LNG储罐建造水平,制定相关标准十分必要。     

热处理工艺对高强度含铜9Ni钢组织和性能的影晌

随着液化天然气（LNG）储罐朝着大型化发展,在不增加容器壁厚的情况下,必须提高钢板强度。在传统9Ni钢中添加Cu,通过析出强化,使其强度水平得到显著提高。提出一种新型含1．25％Cu（质量分数）9Ni钢。试验钢经过控轧直接淬火（DQ）;研究了DO材料分别经过1）QLT（奥氏体（γ）单相区淬火（Q）＋两相区（α＋γ）淬火...