Thoughts about next-generation (S)TEM instruments in science

Different aspects of desirable developments in (scanning) transmission electron microscopes are discussed. Topics are the issues with closed data and control channels, the fixed optical design, and the layout of the sample environment. A solution concept to some of these issues on the basis of current technology and already demonstrated concepts is presented and future possibilities in in situ and multi-dimensional microscopy with the new concept are laid out.     

Polarization Mode Dispersion in High-Speed Optical Communication Systems

Abstract

We review the research progress concerning some fundamental issues related to polarization-mode dispersion (PMD) in high-speed fiber-optic transmission systems. We pay particular attention to issues such as the PMD-induced pulse broadening, PMD measurement and emulation, as well as PMD compensation. An electrical equalization technique based on a transversal filter and an optical technique based on a nonlinear chirped fiber Bragg gratings for PMD compensation will be discussed.     

Strangeness enhancement

Highly effective conversion of kinetic energy into abundant particle multiplicity is the remarkable feature discovered in high energy heavy ion collisions. This short and pedagogic review addresses topical issues related to the understanding of this phenomenon, originating in the creation of the deconfined quark–gluon plasma phase. I consider in depth the apparently simple, yet sometimes misunderstood, intricate issues: a) statistical hadro-chemistry, chemical parameters, b) strange flavor chemical equilibration in quark–gluon plasma, and c) particle yields and sudden hadronization, in the historic perspective of work and competition with my friend József Zimányi.     

CZTS‐based materials and interfaces and their effects on the performance of thin film solar cells

Cu₂ZnSnS₄ (CZTS) and its related materials such as Cu₂ZnSnSe₄ (CZTSe) and Cu₂ZnSn(S,Se)₄ (CZTSSe) have attracted considerable attention as an absorber material for thin film solar cells due to the non‐toxicity, elemental abundance, and large production capacity of their constituents. Despite the similarities between CZTS‐based materials and Cu(In,Ga)Se₂(CIGS), the record efficiency of CZTS‐based solar cells remains significantly lower than that of CIGS solar cells. Considering that the difference between the two lies in the choice of the absorber material, the cause of the lower efficiency of CZTS‐based solar cells can be isolated to the issues associated with CZTS‐based materials and their related interfaces. Herein, these issues and the work done to understand and resolve them is reviewed. Unlike existing review papers, every unique region of CZTS‐based solar cells that contributes to its lower efficiency, namely: (1) the bulk of the absorber, (2) the grain boundaries of the absorber, (3) the absorber/buffer layer interface, and (4) the absorber/back contact interface are surveyed. This review also intends to identify the major unresolved issues and the potential improvement approaches of realizing sizable improvements in the solar cells' efficiency, thus providing a guide as to where research efforts should be focused. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

A clustering-driven medium access control protocol for WDM star networks

Channel assignment and nodes’ service order are two key issues that have to be addressed when designing medium access control (MAC) protocols for WDM star networks. Traditional scheduling techniques consider either channel assignment or nodes’ service order issues. Furthermore, they make use of information such as data channels or receivers’ availability, without combining it with senders’ demands. This paper introduces a novel approach to message scheduling algorithms for WDM star networks, which is driven by clustering techniques. The proposed clustering driven-minimum scheduling latency (CD-MSL) scheme combines all the aforementioned information to create groups of similar source nodes on the basis of the destination nodes of their messages, aiming at rearranging nodes’ service order and improving network performance. Extensive simulation results are presented, which indicate that the proposed clustering-driven scheme leads to a significantly higher throughput-delay performance, in comparison to conventional scheduling algorithms.     

Spacecraft charging, an update

Twenty years after the landmark SCATHA program, spacecraft charging and its associated effects continue to be major issues for Earth-orbiting spacecraft. Since the time of SCATHA, spacecraft charging investigations were focused primarily on surface effects and spacecraft external surface design issues. Today, however, a significant proportion of spacecraft anomalies are believed to be caused by internal charging effects (charging and ESD events internal to the spacecraft Faraday cage envelope). This review will, following a brief summary of the state of the art in surface charging, concentrate on the problems introduced by penetrating electrons (“internal charging”) and related processes (buried charge and deep dielectric charging). With the advent of tethered spacecraft and the deployment of the International Space Station, low altitude charging has taken on a new significance as well. These and issues tied to the dense, low altitude plasma environment and the auroral zone will also be briefly reviewed     

Particle creation,classicality and related issues in quantum field theory: I. Formalism and toy models

The quantum theory of a harmonic oscillator with a time dependent frequency arises in several important physical problems, especially in the study of quantum field theory in an external background. While the mathematics of this system is straightforward, several conceptual issues arise in such a study. We present a general formalism to address some of the conceptual issues like the emergence of classicality, definition of particle content, back reaction etc. In particular, we parameterize the wave function in terms of a complex number (which we call excitation parameter) and express all physically relevant quantities in terms it. Many of the notions—like those of particle number density, effective Lagrangian etc., which are usually defined using asymptotic in–out states—are generalized as time-dependent concepts and we show that these generalized definitions lead to useful and reasonable results. Having developed the general formalism we apply it to several examples. Exact analytic expressions are found for a particular toy model and approximate analytic solutions are obtained in the extreme cases of adiabatic and highly non-adiabatic evolution. We then work out the exact results numerically for a variety of models and compare them with the analytic results and approximations. The formalism is useful in addressing the question of emergence of classicality of the quantum state, its relation to particle production and to clarify several conceptual issues related to this. In Paper II which is a sequel to this, the formalism will be applied to analyze the corresponding issues in the context of quantum field theory in background cosmological models and electric fields.     

Issues relating to the use of a 61.5 dB conversion factor when comparing airborne and underwater anthroprogenic noise levels

Although a considerable amount of the current underwater acoustics literature deals with the proper documentation and analysis of underwater anthropogenic noise levels, mistakes and misconceptions can occur when attempts are made (often by non-experts) to make these data accessible for legislators, journalists and the public. This is because it is difficult for humans to assess qualitatively underwater sound level and quality. It can even be difficult for researchers to judge whether a given underwater sound should be classified as “loud” or “soft”. Many practitioners have suggested that the difference between airborne and underwater sound can be accounted for by applying a 61.5 dB comparison factor (in an attempt to compensate for the different acoustic impedances, and dB reference level conventions, which characterize acoustics in air and water). Whilst use of such a factor is preferable to use of none (which has led to misleading comparisons between levels in-air and water) nevertheless its existence could confer a false sense of security that the comparison is sound, whereas in fact, depending on the details of the comparison, a range of other issues would have to be rigorously taken in to account. Those issues include the perception of sound and annoyance underwater, and the problematic issue of making comparisons across species. This paper does not offer solutions to those issues, but rather outlines the thinking behind the 61.5 dB comparison factor, and shows the intriguing results of it blind application in some interesting example scenarios.     

Progress of Aluminum Gallium Indium Phosphide Red Laser Diodes and Beyond

Abstract

High-quality aluminum gallium indium phosphide epitaxial layers for red laser diodes have been grown by the metal organic chemical vapor deposition method. The layers have some issues, such as narrowing of the band gap, low p-carrier concentration, difficulty in epitaxial growth for quantum well structures, and generating of high-density hillocks. The issues have been successfully solved by introducing (100) substrates with misorientaion toward the [011] direction. High performance transverse-mode stabilized lasers are achieved by introducing the substrates, novel strain-compensated multiple-quantum well structures, which can add large strain to the wells, and low-loss optical cavity. This article also describes their applications.     

Scaling and self-similarity in Pb<Subscript>1-x</Subscript>Fe<Subscript>x</Subscript>S nanoparticle films

This paper addresses the issues of scaling and self-similarity in typical nanoparticle films. The role played by microscopic processes contributing to growth on these issues is probed. While we perform this investigation for a specific system viz., Pb_1-xFe_xS nanoparticle films for clarity of the procedures, the analysis is general and can be applied to a variety of systems obtained using different deposition techniques.     

‘You caught me off guard’: Probing the futures of complex engineered nanomaterials

This paper applies principles and methods from the framework of anticipatory governance to the case of what the National Research Council calls “complex engineered nanomaterials” (CENM). This framework does not aim to generate crystal ball visions or definitive answers, but rather provides guidance for uncovering, understanding, and addressing social, ethical, environmental, and policy issues that stem from emerging technologies. Thus, in anticipation of increased CENM research, CENM products, and their different governance challenges, we aim to lay the groundwork for the anticipatory governance of CENMs by mapping out what—according to the engineers and scientists, we interviewed who are working at the research level of these CENMs—will be the main issues and themes that we need to pay attention to in the near future. The structured interviews focused on three groups of questions: (1) potential and/or actual applications and/or products from the participant’s research; (2) environmental health and safety issues pertaining to both the participant’s research and CENMs generally; and (3) the future of CENMs. Without a foundational understanding to build on, social scientists, policymakers, and regulatory agencies will be at a loss about how to govern CENMs before they are widely implemented in society.     

Low frequency vibroacoustic investigation of wooden T-junctions

In this paper, an experimental investigation on the influence of glue on the low frequency vibroacoustic performance (up to 200 Hz) of wooden T-junctions is presented along with a discussion of modelling issues related to the junctions. The mock-ups studied represent cut-outs of full size timber floor assemblies typically used in Sweden. Their dynamic performance was first studied experimentally by means of modal analysis. Moreover, finite element (FE) simulations of the T-junctions were carried out to establish reliable prediction tools, using the measurement data as calibration input. Modelling issues were addressed to investigate the influence of different features that must be taken into account when simulating the connections as part of larger structures. Guidelines for modelling these type of connections, when developing low frequency FE predictive tools, are presented here.     

Hopf term,fractional spin and soliton operators in the O(3) non-linear sigma model

We re-examine three issues, the Hopf term, fractional spin and the soliton operators, in the 2+1 dimensional O(3) non-linear sigma model based on the adjoint orbit parametrization (AOP) introduced earlier. It is shown that the Hopf term is well defined for configurations of any soliton charge Q if we adopt a time-independent boundary condition at spatial infinity. We then develop the Hamiltonian formulation of the model in the AOP and thereby argue that the well-known Q² formula for fractional spin holds only for a restricted class of configurations. Operators that create states of given classical configurations of any soliton number in the (physical) Hilbert space are constructed. Our results clarify some of the points that are crucial for the above three topological issues and yet have remained obscure in the literature.     

Foreword

We introduce the main issues related to the new cosmological advances coming from observations of the Cosmic Microwave Background (CMB). These issues are then detailed in the following articles of this special CMB volume. To cite this article: F.-X. Désert, C. R. Physique 4 (2003).     

Contents of the following issues of Opticheskiĭ Zhurnal (Journal of Optical Technology)

Chronicle

Contents of the following issues of Opticheskiĭ Zhurnal (Journal of Optical Technology)     

Alien Attack: A Non-Pharmaceutical Complement for ADHD Treatment

Mental health issues are among the most common health issues nowadays, with attention-deficit hyperactivity disorder (ADHD) being the most common neurobehavioral disorder affecting children and adolescents. ADHD is a heterogeneous disease affecting patients in various cognitive domains that play a key role in daily life, academic development, and social abilities. Furthermore, ADHD affects not only patients but also their families and their whole environment. Although the main treatment is based on pharmacotherapy, combined therapies including cognitive training and psychological therapy are often recommended. In this paper, we propose a user-centered application called Alien Attack for cognitive training of children with ADHD, based on working memory, inhibitory control, and reaction-time tasks, to be used as a non-pharmacological complement for ADHD treatment in order to potentiate the patients’ executive functions (EFs) and promote some beneficial effects of therapy.     

Contents of the following issues of Opticheski? Zhurnal (Journal of Optical Technology)

Chronicle

Contents of the following issues of Opticheskiĭ Zhurnal (Journal of Optical Technology)     

Contents of the following issues of Opticheskiĭ Zhurnal (Journal of optical technology)

Chronicle

Contents of the following issues of Opticheskiĭ Zhurnal (Journal of optical technology)     

Material considerations for third generation infrared photon detectors

In the paper, issues associated with the development and exploitation of materials used in fabrication of third generation infrared photon detectors are discussed. In this class of detectors two main competitors, HgCdTe photodiodes and quantum well photoconductors are considered. The performance figures of merit of state-of-the-art HgCdTe and QWIP focal plane arrays (FPAs) are similar because the main limitations come from the readout circuits. The metallurgical issues of the epitaxial layers such as uniformity and number of defected elements are the serious problems in the case of long wavelength infrared (LWIR) and very LWIR (VLWIR) HgCdTe FPAs. It is predicted that superlattice based InAs/GaInSb system grown on GaSb substrate seems to be an alternative to HgCdTe with good spatial uniformity and an ability to span cutoff wavelength from 3 to 25 μm. In this context the material properties of type II superlattices are considered more in detail.     

Precision X-ray optics for fundamental interactions in atomic physics,resolving discrepancies in the X-ray regime

Reliable knowledge of the complex X-ray form factor (Re(f) and f) is required for many fields including crystallography, medical diagnosis and XAFS studies. However, there are discrepancies between theory and theory, experiment and experiment and theory and experiment of 10% and more, over central X-ray energies. Discrepancies exist for most elements, despite claimed experimental accuracies of 1%. This paper summarises the current variation between experimental and theoretical results, and outlines key issues for obtaining experimental accuracies of 1% in critical wavelength ranges for selected elements to address these issues. This paper critically surveys available experimental data for attenuation coefficients and suggests a procedure for obtaining significantly higher accuracy measurements in the future.