High hydrostatic pressure ESR manostats

Abstract

Two high pressure X-band ESR resonators for sensitive measurements are described. Both systems have 100 kHz internal modulation coils and can cooperate with any standard ESR spectrometer. These cavities operate in two different temperature and pressure ranges: 77–400 K, up to 0.8 GPa and liquid helium temperature range, up to 1 GPa, respectively. Additionally, the cavity operating in the 77–400 K temperature range enables Photo-ESR measurements to be carried out.     

On the Shape and Dimensions of Three-Dimensional Cavities in Supercavitating Flows

The shape of long, trailing cavities behind three-dimensional headforms is discussed. The case of a flat elliptic wing is specifically treated. Three distinct shape regimes are found: quasi-planar, long-flat, spheroidal. These appear in successively higher speed ranges (lower cavitation numbers, ). It is argued that the cavities may be replaced by surrogates in the form of slender ellipsoids. The pressures on these are almost constant and correspond to a cavitation number equal to twice their longitudinal added mass coefficient, k₁. A heuristic theory based on kinetic energy fields is given, relating k₁ to the product of headform drag and cavity length. This theory correlates with an exact theory in the same form given by Garabedian for axi-symmetric cones and also with its extension to planar flows. Results are given here for the shape of the cavity behind an elliptic wing of any aspect ratio, given drag, and cavitation number. Specific formulae are given in the form, = f (C_D/AR), for the transition between the quasi-planar and long-flat regime, and the long-flat and spheroidal regime.     

基于天线辐射理论构建微波混沌腔的随机耦合模型

为了能够快速有效地求解电大复杂腔体(微波混沌腔)的电磁耦合问题, 文中采用统计电磁学方法研究了该类腔体电磁散射的统计特征. 首先, 根据天线辐射理论, 利用电磁场的本征模展开式建立了腔体耦合输入阻抗表达式. 其次, 利用波动混沌理论和概率统计方法进一步推导出了微波混沌腔的随机耦合模型. 该方法简单并且可以直接推导出三维模型. 最后, 构建了一个三维Sinai微波混沌腔并进行数值仿真实验, 其仿真实验结果与随机耦合模型计算结果的统计特征基本一致. 重要的是, 该模型与复杂腔体的细节特征无关, 能够快速有效地预测微波混沌腔的敏感耦合问题. 关键词： 统计电磁学 微波混沌腔 输入阻抗 随机耦合模型     

High-frequency gravitational waves having large spectral densities and their electromagnetic response

Various cosmology models, brane oscillation scenarios, interaction of interstellar plasma with intense electromagnetic radiation, and even high-energy physics experiments （e.g., Large Hadron Collider （LHC）） all predict high frequency gravitational waves （HFGWs, i.e., high-energy gravitons） in the microwave band and higher frequency region, and some of them have large energy densities. Electromagnetic （EM） detection to such HFGWs would be suitable due to very high frequencies and large energy densities of the HFGWs. We review several typical EM detection schemes, i.e., inverse Gertsenshtein effect （G-effect）, coupling of the inverse G effect with a coherent EM wave, coupling of planar superconducting open cavity with a static magnetic field, cylindrical superconducting closed cavity, and the EM sychro-resonance system, and discuss related minimal detectable amplitudes and sensitivities. Furthermore, we give some new ideas and improvement ways enhancing the possibility of measuring the HFGWs. It is shown that there is still a large room for improvement for those schemes to approach and even reach up the requirement of detection of HFGWs expected by the cosmological models and high-energy astrophysical process.     

双光子过程耦合腔系统中光场的量子特性

本文研究了双光子过程原子与耦合腔相互作用系统中腔场的压缩效应和反聚束效应.考虑系统总激发数等于2的情况,利用数值计算方法讨论了腔场间的耦合强度变化和原子与腔场间耦合强度变化对反聚束效应的影响.研究结果表明:腔场不呈现出压缩效应;腔场的反聚束效应与原子与腔场的耦合系数之间,以及与腔场间的耦合系数之间都存在着非线性关系.     

Entanglement of two Jaynes-Cummings atoms in single-excitation space

We study the entanglement dynamics of two atoms coupled to their own Jaynes-Cummings cavities in single-excitation space.Here,we use concurrence to measure atomic entanglement,and consider the Bell-like states to be initial states.Our analysis suggests that collapse and revival take place in entanglement dynamics.The physical mechanism behind entanglement dynamics is periodic information and energy exchange between atoms and light fields.For the initial Bell-like states,evolutionary periodicity of the atomic entanglement can only be found if the ratio of the two atom-cavity coupling strengths is a rational number.Also,whether there is a time translation between two kinds of initial Bel-like state depends on odd versus even numbers of the coupling strength ratio.     

Dynamically tunable multiband plasmon-induced transparency effect based on graphene nanoribbon waveguide coupled with rectangle cavities system

A dynamically tunable multiband plasmon-induced transparency (PIT) effect in a series of rectangle cavities coupled with a graphene nanoribbon waveguide system is investigated theoretically and numerically by tuning the Fermi level of the graphene rectangle cavity. A single-PIT effect is realized using two different methods: one is the direct destructive interference between bright and dark modes, and the other is the indirect coupling through a graphene nanoribbon waveguide. Moreover, dual-PIT effect is obtained by three rectangle cavities side-coupled with a graphene nanoribbon waveguide. Results show that the magnitude of the dual-PIT window can be controlled between 0.21 and 0.74, and the corresponding group index is controlled between 143.2 and 108.6. Furthermore, the triple-PIT effect is achieved by the combination of bright-dark mode coupling and the cavities side-coupled with waveguide mechanism. Thus, sharp PIT windows can be formed, a high transmission is maintained between 0.51 and 0.74, and the corresponding group index is controlled between 161.4 and 115.8. Compared with previously proposed graphene-based PIT effects, the size of the introduced structure is less than 0.5 μm². Particularly, the slow light effect is crucial in the current research. Therefore, a novel approach is introduced toward the realization of optical sensors, optical filters, and slow light and light storage devices with ultra-compact, multiband, and dynamic tunable.     

Photodissociation and photoionization of sodium coated C $_\mathsf{60}$ clusters

At the Prague Asterix Laser System Center (PALS) the Asterix iodine laser delivering up to 700 J/0.5 ns is used as a pump source for X-ray laser experiments and applications. The prepulse technique was applied which is known to improve the neon-like X-ray laser output at the J = 0-1 transition dramatically. Since Zn slab targets were used the operating wavelength was 21.2 nm. A prepulse having up to 20 J precedes the main pulse by 10 ns. The main beam and the prepulse beam are focussed by two different optical systems separately and their foci are superimposed at the target surface. By implementing a half-cavity set-up for double-pass amplification using a Mo/Si multilayer mirror - which can be used for more than 100 shots - the X-ray laser output was more than 10 times stronger than at the single pass in a 30 mm long plasma. Double-pass amplification was observed to be most efficient when the pump pulse duration was at least 150 ps longer than the round trip time ( ≈ 260 ps) in the half-cavity. Under this fundamental condition the X-ray laser reached saturation in the double-pass regime containing approx. 4 mJ energy which has been proved to be enough for future applications. In this contribution, the X-ray laser features like divergence in two dimensions, the beam quality (symmetry), the pointing angle and the integrated intensity giving an estimation of the output energy are investigated over 110 shots. To characterize the stability of the X-ray laser the shot distribution, the mean value and the standard deviation for these parameters are evaluated. For 18 shots in a series - what was achievable during one day - the corresponding values are given, and a statistical analysis carrying out a chi-squared test characterize the Zn X-ray laser as a robust tool suitable for applications. In the future it is planned to allocate X-ray laser beam time to external research groups. Received 17 May 2002 / Received in final form 10 September 2002 Published online 6 November 2002 RID="a" ID="a"e-mail: praeg@fzu.cz     

“Magic Relation” Between the Structures of Coexisting Phases at a First-Order Phase Transition in a Hard Sphere System

In the statistical geometry of a hard sphere system of any number of dimensions, V _o and S _o, the so-called available space and the area of the interface between the available and unavailable space, respectively, can be used as surrogates for chemical potential and pressure. It is shown exactly that, if a first-order transition occurs, the relation dV _o/dS _o=–/2D, where is the diameter of a sphere and D is the dimensionality of the system, must hold for densities in the phase coexistence region. This relation is remarkable in that –/2D is the ratio of the volume to the surface area of a sphere. Also, it is shown that it is possible for the system to have two successive first-order transitions, but that the occurrence of a continuous transition (even in two dimensions) is unlikely. It is argued that this unlikelihood is substantially strengthened by the absence of temperature (except as a trivial factor) as a variable in hard-sphere systems. This suggests that the findings of the KTHNY theory, recent simulations, and colloid experiments (specialized to sticky hard disks) can be extended to true hard disks. The fundamental physics underlying the magic relation is yet to be exposed. The author continues to search for the underlying reason and hopes that the present paper will stimulate others to join the search.     

Hydrophobic interactions and clustering in a porous capsule: option to remove hydrophobic materials from water

The investigation of hydrophobic interactions under confined conditions is of tremendous interdisciplinary interest. It is shown that based on porous capsules of the type {(pentagon)}(12){(linker)}(30) ≡ {(Mo)Mo(5)(12){Mo(2)(ligand)}(30), which exhibit different hydrophobic interiors-achieved by coordinating related ligands to the internal sites of the 30 {Mo(2)} type linkers-there is the option to study systematically interactions with different uptaken/encapsulated hydrophobic molecules like long-chain alcohols as well as to prove the important correlation between the sizes of the related hydrophobic cavities and the option of water encapsulations. The measurements of 1D- and 2D-NMR spectra (e.g. ROESY, NOESY and HSQC) allowed the study of the interactions especially between encapsulated n-hexanol molecules and the hydrophobic interior formed by propionate ligands present in a new synthesized capsule. Future detailed studies will focus on interactions of a variety of hydrophobic species with different deliberately constructed hydrophobic capsule interiors.