Hearing protector attenuation: A perspective view

The design, performance and evaluation of hearing protectors are matters of substantial current interest. The specific scientific questions which command attention include the accuracy of the shift in free field hearing threshold as a measure of protection, the relationship between physical measurements of sound attenuation with real heads and psycho-physical methods of measurement, the relationship between physical measurements with real and artificial heads, the acoustical behaviour of hearing protectors and the factors which limit their performance, and the relationship between hearing protector attenuation and speech intelligibility. These questions have received considerable attention during the past twenty years but are not yet fully answered.     

Stochastic quantization: A review

The present status of the work on the application of the stochastic quantization procedure is reviewed. A compact mathematical introduction to the basic notions of random processes such as Markov processes, Martingales and Fokker-Planck equations is presented. The stochastic quantization procedure is explained in much detail and it is found to possess remarkable features which can not be achieved within the conventional framework of quantum theory. This admits us to give systematic analyses of irreversible quantum dynamics of dissipative systems and the vacuum tunneling phenomena in non-Abelian gauge theory     

Lorentz matrices: A review

This is an expository review of the Lorentz transformation, which is a change of coordinates used by one inertial observer to those used by another one. The transformation can be represented by a four-by-four matrix, the Lorentz matrix or the Minkowski-Lorentz matrix. The most familiar, or special, case has thex axis of both observers parallel to their relative velocity. A more general transformation drops this constraint. But then a seeming paradox arises when there are three observers, and this has led to a challenge to the self-consistency of the special theory of relativity. It is shown here that this challenge is based on a misunderstanding. The properties of the more general Lorentz transformation are reviewed consistently in terms of the matrix approach, which the author believes is now the easiest approach to understand. The spectral analysis of the Lorentz matrix is also discussed. Several checks are included to make assurance double sure.     

Image enhancement: A review

We first describe the basic linear and non-linear mathematical operations underlying most image enhancement techniques, and compare the hardware available for carrying out these operations which includes digital computers, optical set-ups and special electro-optical devices. Then we give a brief account of the commonly used image enhancement techniques, such as contrast enhancement, crispening, noise elimination, and inverse filtering. Finally, we mention some examples of image enhancement in the biomedical area.This work was supported principally by the National Institutes of Health (Grants 1 P01 GM-14940-02 and 1 P01 GM-15006-02), and in part by the Joint Services Electronics Program (Contract DA 28-043-AMC-02536 (E)).     

Quantum groups: A review

The recent development of quantum groups is summarized from the point of view of quantum physics. The emphasis is on the ideas, concepts, and motivation of these new developments.Invited paper at the Quantum Structures 92 Conference, Castiglioncello, Italy, September 21–26, 1992.     

Josephson-effect samplers: A review

Studies on Josephson samplers are reviewed. The dynamic properties of Josephson junctions used as sensitive comparators in the samplers are analyzed. A theory in terms of which the time resolution and sensitivity of Josephson comparators can be estimated is put forward, and analytical formulas for the limiting characteristics of the samplers are derived. The performance of Josephson samplers based on high-temperature superconductors is discussed. It is shown that samplers with a subpicosecond resolution and nanoampere sensitivity are a feasibility.     

EPR and Bell's theorem: A critical review

The argument of Einstein, Podolsky, and Rosen is reviewed with attention to logical structure and character of assumptions. Bohr's reply is discussed. Bell's contribution is formulated without use of hidden variables, and efforts to equate hidden variables to realism are critically examined. An alternative derivation of nonlocality that makes no use of hidden variables, microrealism, counterfactual definiteness, or any other assumption alien to orthodox quantum thinking is described in detail, with particular attention to the quartet or broken-square question.     

Nanolithography in microelectronics: A review

The current status of basic photolithographic techniques allowing researchers to achieve results that seemed to be unrealistic even a short time ago is reviewed. For example, advanced DUV photolithography makes it possible to exactly reproduce IC elements 25 times smaller in size than the wavelength of an excimer laser used as a lithographic tool. Approaches owing to which optical lithography has pushed far beyond the Rayleigh-Abbe diffraction limit are considered. Among them are optical proximity correction, introduction of an artificial phase shift, immersion, double exposure, double patterning, and others. The prospects for further advancement of photolithography into the nanometer range are analyzed, and the capabilities of photolithography are compared with those of electronolithography, EUV lithography, and soft X-ray lithography     

Synthesis of diamond: A review

The formation of the diamond phase of carbon under extreme static and dynamic conditions is considered.     

Black hole images: A review

In recent years, unprecedented progress has been achieved regarding black holes’ observation through the electromagnetic channel. The images of the supermassive black holes M87*and Sgr A*released by the Event Horizon Telescope(EHT) Collaboration provided direct visual evidence for their existence, which has stimulated further studies on various aspects of the compact celestial objects. Moreover, the information stored in these images provides a new way to understand the pertinent physical proces...     

The waveguide laser: A review

The present article reviews the fundamental physical principles essential to an understanding of waveguide gas and liquid lasers, and the current technological state of these devices. At the present time, waveguide laser transitions span the visible through submillimeter regions of the wavelength spectrum. The introduction discusses the many applications of waveguide lasers and the wide variety of laser configurations that are possible. Section 1 summarizes the properties of modes in hollow dielectric waveguides of circular, rectangular, and planar cross section. Section 2 considers various approaches to optical feedback including internal and external mirror Fabry-Perot type resonators, hollow waveguide distributed feedback structures, and ring-resonant configurations. Section 3 discusses those aspects of molecular kinetic and laser theory pertinent to the design and optimization of waveguide gas lasers such as the scaling laws for discharge-excited gas lasers, molecular models useful in maximizing the oscillation bandwidth, the effects of gas flow rate, and the physics of optically-pumped far-infrared lasers. Finally, a review of the waveguide gas and liquid lasers reported to date is given in Section 4.     

Stimulated emission spectroscopy: A review

This paper reviews some new spectroscopic techniques, broadly defined under the title of stimulated emission spectroscopy, which add to the information on activated crystals obtained by conventional luminescence and absorption techniques. Emphasis is placed on studies of the Stark structure of levels, and of the electron-phonon interaction. Experiments are included on lasers with dispersive resonators (prisms etc.), lasers with combined active media, and with photon injection. Also covered are high temperature (up to ~ 1000° K) spectroscopic analyses of stimulated emission, and multiplication and selfmultiplication (lasers based on non-linear crystals). Analysis of the temperature broadening and shifting of lines can be used to determine the effective Debye temperature for a given activator and a given medium. The kinetic studies have made possible estimation of the non-radiative de-activation time. Other measurements reveal the symmetry of activator centres through magneto-optical investigations. Spectroscopic analysis of the output of phonon lasers yields information on the phonon states of the crystal-matrix.     

Dark energy: A brief review

The problem of dark energy is briefly reviewed in both theoretical and observational aspects. In the theoretical aspect, dark energy scenarios are classified into symmetry, anthropie principle, tuning mechanism, modified gravity, quantum cosmology, holographic principle, back-reaction and phenomenologieal types. In the observational aspect, we introduce cosmic probes, dark energy related projects, observational constraints on theoretical models and model independent reconstructions.     

Quantum vortex strings: A review

The quantum worldsheet dynamics of vortex strings contains information about the 4d non-Abelian gauge theory in which the string lives. Here I tell this story. The string worldsheet theory is typically some variant of the CP^N-1 sigma-model, describing the orientation of the string in a U(N) gauge group. Qualitative parallels between 2d sigma-models and 4d non-Abelian gauge theories have been known since the 1970s. The vortex string provides a quantitative link between the two. In 4d theories with N=2 supersymmetry, the exact BPS spectrum of the worldsheet coincides with the bulk spectrum in 4d. Moreover, by tuning parameters, the CP^N-1 sigma-model can be coaxed to flow to an interacting conformal fixed point which is related to the 4d Argyres-Douglas fixed point. For theories with N=1 supersymmetry, the worldsheet theory suffers dynamical supersymmetry breaking and, more interestingly, supersymmetry restoration, in a way which captures the physics of Seiberg’s quantum deformed moduli space.     

Surface electromagnetic waves: A review

From the beginning of the 20th century, researchers have been interested in surface electromagnetic waves guided by planar interfaces of dissimilar mediums. Much initial research on surface‐plasmon waves and surface‐plasmon‐polariton waves stemmed from theoretical curiosity, but the development of new experimental techniques propelled commercial exploitation for optical sensors of chemical and biological species. Additional surface waves called Dyakonov waves, Tamm waves, and Dyakonov–Tamm waves have emerged during the last 25 years. Experimental observation of Dyakonov waves was reported only in 2009, but the rapid development of experimental apparatus during the 1990s suggests that theoretical predictions will soon be evaluated experimentally, leading to further development of optical detection systems and optical circuitry.     

HgCdTe avalanche photodiodes: A review

This paper presents a comprehensive review of fundamental issues, device architectures, technology development and applications of HgCdTe based avalanche photodiodes (APD). High gain, above 5×10³, a low excess noise factor close to unity, THz gain-bandwidth product, and fast response in the range of pico-seconds has been achieved by electron-initiated avalanche multiplication for SWIR, MWIR, and LWIR detector applications involving low optical signals. Detector arrays with good element-to-element uniformity have been fabricated paving the way for fabrication of HgCdTe-APD FPAs.     

Quasi-two-dimensional organic superconductors: A review

Quasi-two-dimensional organic superconductors are reviewed. These systems exhibit many interesting phenomena, including reduced dimensionality, strong electron - electron and electron - phonon interactions and the proximity of antiferromagnetism, insulator states and superconductivity. Moreover, it has been possible to measure the electronic bands of many of the organics in great detail, in contrast to the situation in other well-known systems in which similar phenomena occur. The crystal structure and normal-state properties of the organics are described before the experimental evidence is presented for and against exotic superconductivity mediated by antiferromagnetic fluctuations. Finally, three instances of field-induced unconventional superconductivity are described.