A simple molecular theory for photo-induced smectic phase

The response of liquid crystals to light is very important for applications of liquid crystals in display and memory devices. Recently experiments have been carried out on liquid crystals doped with photoactive azo compounds. It is seen that UV rays incident on such systems can lower the nematic isotropic transition temperature T _NI . Also, in some mixtures, a photo-induced smectic phase is observed. This is attributed to the change in the trans (longer) isomer to cis (shorter) isomer of the photoactive dopant. We have earlier developed a molecular mean-field model assuming the medium to consist of inter-converting anti-parallel and parallel pairs to explain the molecular origin of “two lengths”. The model was used to explain double re-entrance, the effect of electric field on T _NI , etc. This model is modified to include the change of trans to cis isomer which is equivalent to an increase of fraction of parallel (shorter) pairs. The calculated phase diagram with respect to incident UV radiation energy shows an induced smectic phase. This is in qualitative agreement with experimental trends.     

A simple precision phase calibrator

A circuit is described which produces two square wave outputs with precise phase differences between them. The range of phase differences which may be selected is from 0° to 360° in increments of 22·5°. However, any increment given by 180°/n, where n is an integer, can be achieved by a suitable choise of circuit components. The device is intended as a means of checking the calibration of phase meters or even for actually calibrating such meters.     

A design for a nonreciprocal phase shifter

A design is described for a nonreciprocal phase shifter, which is the key element in the constitution of a Mach-Zehnder interferometric isolator consisting of a magneto-optical channel waveguide. A four-layered structure waveguide is dealt with in which a cover layer having a larger refractive index than that of the film is placed on the magneto-optic thin film; it is revealed that the phase shifter length can be shortened by up to 6 mm at the 1.15 m wavelength, which is half the length of a nonreciprocal phase shifter constructed of a three-layered waveguide without a large refractive index cover layer. Two types of channel waveguides are investigated: a rib waveguide and a strip-loaded waveguide; they are found to have the same phase shifter length for the optimum condition.     

A geometry optimization framework for photonic crystal design

The performance of photonic crystal devices can depend strongly on their geometry. Alas, their fundamental physics offers relatively little by way of pointers in terms of optimum shapes, so numerical design search techniques must be used in an attempt to determine high performance layouts. We discuss strategies for solving this type of optimization problem, the main challenge of which is the conflict between the enormous size of the space of potentially useful designs and the relatively high computational cost of evaluating the performance of putative shapes. The optimization technique proposed here operates over increasing levels of fidelity, both in terms of the resolution of its non-parametric shape definition and in terms of the resolution of the numerical analysis of the performance of putative designs. This is a generic method, potentially applicable to any type of electromagnetic device shape design problem. We also consider a methodology for assessing the robustness of the optima generated through this process, investigating the impact of manufacturing errors on their performance. As an illustration, we apply this technology to the design of a two-dimensional photonic crystal structure; the result features a large complete band gap structure and a topology that is different from previously published designs.     

A simple scheme for the design of solvent-suppression pulses

Excitation sculpting was first introduced as a way to efficiently suppress solvent signals. It requires a pulse sequence that acts as a null pulse at the solvent-resonance frequency and as an inversion pulse everywhere else. In this article, it is shown that such a goal can be achieved starting with "top-hat" inversion shaped pulses such as I-BURP-2 or gaussian cascade G3. The result is a Globally Antisymmetric Selective Pulse, or GASP. Numerical optimization was used to extend the performance of such pulses. Multifrequency signal suppression was shown to be possible through application of successive excitation sculpting modules.     

A simple thermal phase stabilizer for real-time optical fibre holographic interferometry

An optical fibre interferometer can be made to phase-stabilize by simply attaching a short length of one arm of the interferometer to a straight copper track and heating the track with an electric current. This feedback thermal stabilization scheme works well even for relatively short fibre lengths and there is no need to treat or unjacket the fibre. A fibre-optic Michelson interferometer stabilized by this method successfully provided object and reference beams for real-time holographic interferometric measurements of the distortion of heated test objects.     

A simple method for phase wraps elimination or reduction in spatial fringe patterns

In this paper, we propose a simple method for processing a 2D wrapped phase map that contains a spatial carrier signal in order to completely eliminate, or greatly reduce, the number of phase wraps in the image. The 2D Fourier transform of the wrapped phase map is calculated. Then the spectrum is shifted to the origin in frequency space. After that, the inverse 2D Fourier transform is computed. Finally, a four-quadrant arctangent function is used to calculate the angle of the complex array that was produced by the inverse 2D Fourier transform. This produces a phase map with a smaller number of 2π phase jumps than the original phase map. In some cases, all of the phase wraps are eliminated and there is therefore no need to unwrap the resultant phase map. The reduction of the number of 2π phase jumps can reduce the execution time and improve the noise performance of some phase unwrapping algorithms such as the Flynn method. The validation of the proposed algorithm is demonstrated experimentally and also via computer-simulation.     

动态电路冲激响应初始值的一种简易求法

给出了求解动态电路冲激响应初始值和动态奇异电路响应初始值的一种简易方法.在电路换路后,其电容电压或电感电流的初始状态一般不产生跃变,但有时也可能产生跃变,当一时难于确定时,可先将电路化为其s域模型,并将0-值带进换路后的电路模型,再应用拉氏变换的初值定理,即可在s域解决t域响应的初始状态0 值的问题.该方法广泛适用于各种电路.     

Simplex optimization method for illumination design

A modified simplex optimization method is developed for the design of illumination systems. The simplex method is a judicious choice for illumination optimization because of its robustness and convergence properties. To optimize the simplex method, its four parameters are adjusted dependent on the dimensionality of the space to converge with fewer iterations. This work is presented for the end game, when the optimizer is converging on a local optimum rather than searching for it. Up to a 37% reduction in the number of computations is realized. An example using a compound parabolic concentrator is compared between the standard and the modified simplex methods, providing over 22% improvement in the end game.     

Structural optimization design for large mirror

The system design must be started from the concept with low cost and high performance. In this point, the topological shape of the structure is very important in the view of the structural rigidities and light-weight design.In this paper, the optimization methodology is presented in the design stage of the large optical mirror. We obtain the optimal layout through the topology optimization and then design the details through the size or shape optimization for structural rigidity.     

A comparison between different optimization criteria for tuned mass dampers design

Tuned mass sampers (TMDs) are widely used strategies for vibration control in many engineering applications, so that many TMD optimization criteria have been proposed till now. However, they normally consider only TMD stiffness and damping as design variables and assume that the tuned mass is a pre-selected value. In this work a more complete approach is proposed and then also TMD mass ratio is optimized. A standard single degree of freedom system is investigated to evaluate TMD protection efficiency in case of excitation at the support. More precisely, this model is used to develop two different optimizations criteria which minimize the main system displacement or the inertial acceleration. Different environmental conditions described by various characterizations of the input, here modelled by a stationary filtered stochastic process, are considered. Results show that all solutions obtained considering also the mass of the TMD as design variable are more efficient if compared with those obtained without it. However, in many cases these solutions are inappropriate because the optimal TMD mass is greater than real admissible values in practical technical applications for civil and mechanical engineering. Anyway, one can deduce that there are some interesting indications for applications in some actual contexts. In fact, the results show that there are some ranges of environmental parameters ranges where results attained by the displacement criterion are compatible with real applications requiring some percent of main system mass. Finally, the present research gives promising indications for complete TMD optimization application in emerging technical contexts, as micromechanical devices and nano resonant beams.     

Constraining the initial phase in water-fat separation

An algorithm is described for use in chemical shift-based water-fat separation to constrain the phase of both species to be equal at an echo time of zero. This constraint is physically reasonable since the initial phase should be a property of the excitation pulse and receiver coil only. The advantages of phase constrained water-fat separation, namely, improved noise performance and/or reduced data requirements (fewer echos), are demonstrated in simulations and experiments.     

OTF-based optimization criteria for automatic optical design

Optimization techniques for lens design require that some criterion, or figure of merit, is chosen to describe the performance of the optical system. This study is concerned with systems where the true criterion is the diffraction optical transfer function (OTF). Recent investigations [1] have shown that the geometrical approximation to the diffraction OTF is a valid criterion for OTF optimization for all practical ranges of aberration size and spatial frequency. This paper gives details of these investigations, and compares the geometric criterion with other optimization criteria. It will be shown that in most cases the geometric criterion is markedly superior.     

A simple statistical modeling of random phase reference in holographic memory

We present a simple modeling of random phase reference in holographic memory. The proposed model is analyzed by a statistical approach. Improvement on selectivity using random phase reference is shown in comparison with uniform phase plane wave reference and Gaussian beam reference. This simple and efficient model provides a physical insight and is verified by some experiments.     

Materials design and optimization for thin-film microbatteries

Considerable effort has been invested in developing thin-film solid microbatteries as possible integrated components in microelectronics. Advances have been made particularly in the engineering of lithium/amorphous inorganic electrolyte/layered compound cells fabricated using various evaporation techniques. The main features of these cells are influenced by the characteristics of the fast ionic conductor and the insertion compound layers which are discussed in detail in this work. Design and optimization of lithium-microbattery components are discussed. Different electrochemical systems using lithium borate-glass films as solid electrolytes have been fabricated and characterized. Thin-film active cathodic materials include transition-metal dichalcogenides such as TiS₂, MoS₂, non-transition-metal chalcogenides such as InSe and transition-metal oxides such as MoO₃, V₂O₅, V₆O₁₃ films. Particular attention is paid to the structural and transport properties of these materials and their behaviour in electrochemical lithium cells are presented. Thermodynamics and kinetics are studied as functions of the growth conditions of thin-film components. The physical properties are discussed in relation to the electrochemical cell behavior and battery performance. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994.     

A simple design method of negative refractive index metamaterials

We propose a very simple design method of negative refractive index (NRI) materials that can overcome some drawbacks of conventional resonant-type NRI materials. The proposed NRI materials consist of single or double metallic patterns printed on a dielectric substrate. Our metamaterials (MTMs) show two properties that are different from other types of MTMs in obtaining effective negative values of permittivity (ε) and permeability (μ) simultaneously; the geometrical outlines of the metallic patterns are not confined within any specific shape, and the metallic patterns are printed on only one side of the dielectric substrate. Therefore, they are very easy to design and fabricate using common printed circuit board (PCB) technology according to the appropriate application. Excellent agreement between the experiment and prediction data ensures the validity of our design approach.     

A simple method to design non-collision relative orbits for close spacecraft formation flying

A set of linearized relative motion equations of spacecraft flying on unperturbed elliptical orbits are specialized for particular cases, where the leader orbit is circular or equatorial. Based on these extended equations, we are able to analyze the relative motion regulation between a pair of spacecraft flying on arbitrary unperturbed orbits with the same semi-major axis in close formation. Given the initial orbital elements of the leader, this paper presents a simple way to design initial relative orbital elements of close spacecraft with the same semi-major axis, thus preventing collision under non-perturbed conditions. Considering the mean influence of J₂ perturbation, namely secular J₂ perturbation, we derive the mean derivatives of orbital element differences, and then expand them to first order. Thus the first order expansion of orbital element differences can be added to the relative motion equations for further analysis. For a pair of spacecraft that will never collide under non-perturbed situations, we present a simple method to determine whether a collision will occur when J₂ perturbation is considered. Examples are given to prove the validity of the extended relative motion equations and to illustrate how the methods presented can be used. The simple method for designing initial relative orbital elements proposed here could be helpful to the preliminary design of the relative orbital elements between spacecraft in a close formation, when collision avoidance is necessary.     

A simple method to detect audible echoes in room acoustical design

A simple method to detect audible echoes is proposed as an objective criterion for room acoustics. This method evaluates the perceptibility of sound reflections that are generated by an impulsive sound source and identifies from reflectograms harmful reflections perceived as echoes. Particularly with this method, the masking effect of reverberation is taken into consideration, which cannot be treated sufficiently by the existing objective criteria. The applicability to room acoustical design is verified by evaluating the impulse responses measured in real halls where audible echoes occurred. It is shown that the proposed method detects audible echoes at an accuracy of more than 90% and would be suitable for practical use.