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We numerically and experimentally investigate collective resonant responses of coherent metasurfaces consisting of planar random-flip asymmetrically split rings. The collective narrow band response becomes broader and eventually disappears with increasing the percentage of flipped split rings. The exploited physical mechanism is the degraded collective response due to random microscopic multipole excitation. Our study provides a method to construct random metasurfaces and is helpful to have an insight into their underlying physics. [ABSTRACT FROM AUTHOR]

2D lateral heterostructures possess atomically sharp lateral interfaces, while understanding of their ultrafast photocarrier dynamics from a spatiotemporal viewpoint is rather elusive. In this study, we have investigated the spatiotemporal evolution of photocarrier dynamics across the 1D lateral interface of a WS2–ReS2 2D lateral heterostructure utilizing femtosecond laser pump–probe. The nontrivial band offset across the 1D lateral interface markedly mediates the spatiotemporal photocarrier transfer and transport processes. Subsequently, a hole accumulation region on the WS2 side and an electron accumulation region (1DEG) on the ReS2 side have been spatially identified by correlating ultrafast photocarrier signals. The measured width of the unilateral depletion region is 1360 ± 160 nm. Our work has provided substantial insights into mediated photocarrier dynamics in the 2D lateral heterostructure, which will benefit explorations in 2D interfacial physics and 2D lateral optoelectronic devices. [ABSTRACT FROM AUTHOR]

This Tutorial focuses on the physics of layered compounds under high pressure. We have chosen h-BN and III–VI layered materials as representative materials. h-BN layers are strictly two-dimensional. Layers in III–VI compounds are more complex, and subtle details in their structural behavior play an important role in the evolution of high pressure properties. They are also interesting because they contain a different number of layers in their primitive unit cell and/or have a different ionic character. We begin describing the structural evolution. We discuss the experimental challenges encountered as well as the main findings related to intra- and interlayer compressibility, polytype influence, and geometrical modifications induced by pressure inside the layers. We then describe lattice vibrations. The origin of the modes is reviewed, paying attention to the relationships between atom motions in different layers. We discuss the convenience of redefining the Grüneisen parameter and describe the behavior of rigid layer modes, soft modes, and Davidov pairs. The last section is devoted to the electronic properties. We show that the changes observed when passing from a single layer to a three-dimensional BN are qualitatively similar to those induced by high pressure. The pressure behavior of electronic transitions in III–VI layered compounds is very rich, revealing the subtle balance between intra- and inter-layer interactions. Finally, we take advantage of high pressure studies to explain the formation of the Mexican hat type of valence band at ambient conditions in single layers of InSe and GaSe, but not in three-dimensional compounds. [ABSTRACT FROM AUTHOR]

Electron spin relaxation is, on many occasions, considered an elephant in the room that challenges the idea of a radical-pair compass, a leading hypothesis for the navigation of migratory avian species. It has been widely recognized that an effective radical-pair magnetoreceptor requires a relaxation time that is long enough for an external magnetic field as weak as the geomagnetic field to significantly modify the coherent spin dynamics. However, previous studies proposed that certain spin relaxation, far quicker than the radical recombination reactions, could enhance, rather than degrade, the directional sensitivity of a radical-pair magnetoreceptor. Here, I investigate relaxation effects on the singlet–triplet interconversion of a model radical pair and find that the enhancement effect originates from population relaxation over a period of several microseconds as a result of efficient spin decoherence. Insights into the truncated spin systems shed light on the physics behind them. I further investigate the possibilities of such enhancement in cryptochrome-based magnetoreception, in which electron hopping takes place between tryptophan residues. [ABSTRACT FROM AUTHOR]

Attempts to understand the molecular structure of water were first made well over a century ago. Looking back at the various attempts, it is illuminating to see how these were conditioned by the state of knowledge of chemistry and physics at the time and the experimental and theoretical tools then available. Progress in the intervening years has been facilitated by not only conceptual and theoretical advances in physics and chemistry but also the development of experimental techniques and instrumentation. Exploitation of powerful computational methods in interpreting what at first sight may seem impenetrable experimental data has led us to the consistent and detailed picture we have today of not only the structure of liquid water itself and how it changes with temperature and pressure but also its interactions with other molecules, in particular those relevant to water's role in important chemical and biological processes. Much remains to be done in the latter areas, but the experimental and computational techniques that now enable us to do what might reasonably be termed "liquid state crystallography" have opened the door to make possible further advances. Consequently, we now have the tools to explore further the role of water in those processes that underpin life itself—the very prospect that inspired Bernal to develop his ideas on the structure of liquids in general and of water in particular. [ABSTRACT FROM AUTHOR]

This Perspective focuses on experimental and theoretical aspects of positron annihilation spectroscopy. This set of methods is highly suitable for identifying and quantifying vacancy-type defects in semiconductors and also allows for analyzing their physics characteristics. We present selected examples from the past decade, where the methods have been used for obtaining timely and useful insights into the defect-controlled phenomenon in narrow-gap (Ge, GaSb) and wide-gap (III-nitride, oxide) semiconductors. We also discuss possible future developments that may allow more detailed studies in novel semiconductor materials and devices with ever more complex lattice structures. [ABSTRACT FROM AUTHOR]

This Perspective focuses on the several overlaps between quantum algorithms and Monte Carlo methods in the domains of physics and chemistry. We will analyze the challenges and possibilities of integrating established quantum Monte Carlo solutions into quantum algorithms. These include refined energy estimators, parameter optimization, real and imaginary-time dynamics, and variational circuits. Conversely, we will review new ideas for utilizing quantum hardware to accelerate the sampling in statistical classical models, with applications in physics, chemistry, optimization, and machine learning. This review aims to be accessible to both communities and intends to foster further algorithmic developments at the intersection of quantum computing and Monte Carlo methods. Most of the works discussed in this Perspective have emerged within the last two years, indicating a rapidly growing interest in this promising area of research. [ABSTRACT FROM AUTHOR]

In this note, we give a self-contained presentation of the POAV2 theory developed by Haddon to study the alignment of π-orbitals along a non-planar molecule. The classical POAV theory is purely geometric instead of the POAV2 which includes more physics in the computations. We compare the results obtained from the POAV2 and POAV theory. We prove that the difference between the two quantities is in most of the cases negligible. As a consequence, the POAV theory is sufficient for most of the purposes concerning the description of the local π-system of a molecule. [ABSTRACT FROM AUTHOR]

The photovoltaic signal is an important characteristic of photodetectors, including but not limited to those that are based on p–n or p–i–n photodiodes. In an open-circuit configuration, pulsed excitation of the detector with ultrafast (femto or nanosecond) pulses leads to a photovoltaic signal that decays slowly (micro-second time scale). If the physics in the detector is dominated by the recombination of the photo-excited charge carriers, one expects the signal to decay without changing its sign. However, some experiments using short-pulse excitation have found that photovoltaic signals can undergo a sign change as a function of time following excitation, with positive signals immediately following the excitation, turning to negative signals several microseconds later. Here, we study various physical effects (density, temperature, electrostriction, pressure, photostriction, and bandgap renormalization) and determine their effect on photovoltaic signals. If, following ultrafast excitation, the carrier density and temperature are increased, and during relaxation the system reaches a state sufficiently close to the quasi-thermal equilibrium in which the carrier density is still elevated, but smaller than the intrinsic thermal equilibrium density at the elevated temperature, then the signal can become negative. [ABSTRACT FROM AUTHOR]

Unlike popular multiband antenna array radiation based on either electric or magnetic surface currents, the use of mutually interleaved and tightly coupled electric and magnetic currents results in an aperture-reuse space-efficient multiband radiating surface for highly integrated antenna-frontend architecture and spatial power combining design scenarios. In this work, slot and dipole modes corresponding to magnetic and electric currents are effectively interleaved and excited in a surface to develop a space-efficient dual-wideband aperture-shared radiating surface. In this case, due to an effective reuse of the antenna aperture over both frequency bands, a high aperture-reuse efficiency is achieved. First, we devise a planar magneto-electric (ME)-dipole-alike antenna and analyze it in both the frequency and time domain. The antenna is then studied by the characteristic mode theory and the findings are validated using full-wave simulations. The developed planar ME-dipole-alike antenna is used to realize a dual-wideband radiating surface in which electric and magnetic currents are mutually coupled and interlaced, which is excited by properly oriented and distributed sources on the antenna's surface. Eventually, a highly isolated dual-wideband prototype was developed and fabricated using a cost-effective multi-layer Printed Circuit Board (PCB) process that operates in the Ku-band with both impedance and gain bandwidth of approximately 42% and in the Ka-band with respective impedance and gain bandwidth of 29% and 16.32%. [ABSTRACT FROM AUTHOR]

The ab initio path integral Monte Carlo (PIMC) method is one of the most successful methods in statistical physics, quantum chemistry and related fields, but its application to quantum degenerate Fermi systems is severely hampered by an exponential computational bottleneck: the notorious fermion sign problem. Very recently, Xiong and Xiong [J. Chem. Phys. 157, 094112 (2022)] have suggested to partially circumvent the sign problem by carrying out simulations of fictitious systems guided by an interpolating continuous variable ξ ∈ [−1, 1], with the physical Fermi- and Bose-statistics corresponding to ξ = −1 and ξ = 1. It has been proposed that information about the fermionic limit might be obtained by calculations within the bosonic sector ξ > 0 combined with an extrapolation throughout the fermionic sector ξ < 0, essentially bypassing the sign problem. Here, we show how the inclusion of the artificial parameter ξ can be interpreted as an effective penalty on the formation of permutation cycles in the PIMC simulation. We demonstrate that the proposed extrapolation method breaks down for moderate to high quantum degeneracy. Instead, the method constitutes a valuable tool for the description of large Fermi-systems of weak quantum degeneracy. This is demonstrated for electrons in a 2D harmonic trap and for the uniform electron gas (UEG), where we find excellent agreement (∼ 0.5 %) with exact configuration PIMC results in the high-density regime while attaining a speed-up exceeding 11 orders of magnitude. Finally, we extend the idea beyond the energy and analyze the radial density distribution (2D trap), as well as the static structure factor and imaginary-time density–density correlation function (UEG). [ABSTRACT FROM AUTHOR]

A real-space method using generating integers is used to determine possible commensurate lattice Moiré patterns for a bilayer of two equal hexagonal lattices, which can in principle be extended to lattice mismatched bilayers. These Moiré patterns can be classified by a pair of relatively prime integers (n , m) , wherein a rotation θ (n , m) of the top hexagonal lattice maps its lattice vector (n , m) to (m , n) of the bottom lattice. Within this formulation, the area of the commensurate supercell is proportional to (n 2 + m 2 + n m) and the number of coincident lattice sites per supercell is given by (n − m) 2. Taking bilayer boron nitride (BN) as an example, we present how to systematically generate Moiré patterns and explore the differences in local chemistry in the interstitial region by impurity intercalation. Systematic calculations of the properties of intercalated 3d transition metals were performed in an h-BN (4 , 3) bilayer, corresponding to a rotation of 9.43 degrees. These calculations reveal that local symmetry in the intercalated region significantly affect the energetics and magnetization of the intercalated species. These results highlight that Moiré pattern physics is not limited to optoelectronic/electronic phenomena, such as interfacial exciton formation or magic angle superconductivity, but it also produces chemical and magnetic atomic site selectivity, which may play important roles in adsorption, catalysis, or quantum information. [ABSTRACT FROM AUTHOR]

The mechanism for microwave absorption in a film has previously been numerically verified from the theoretical formula for RL and attributed to angular and amplitude effects with a simple geometrical representation from energy conservation unique to the film. Starting from the case where |RL| = 0, using basic transmission-line theory and mathematics, it is confirmed theoretically here that the mechanism for absorption mechanism in a film, responsible for the minima of the reflection loss RL/dB, is best explained by wave cancelation theory rather than by impedance matching theory. This theoretical proof also reveals that the mechanisms for a film and material are different. The flaws of neglecting the phase effects of interfaces in a film in quarter-wavelength theory are also quantitatively discussed from transmission-line theory. Contrary to the theory held currently, the reported minima of RL/dB originate from phase effects in the film rather than from the resonance peaks for the intrinsic frequencies of a material. [ABSTRACT FROM AUTHOR]

In Part I of this work published previously, it was proved from the transmission-line theory that impedance matching (IM) theory should be replaced by wave cancellation theory, film is different from the material, and the phase effects from interfaces should be considered in quarter wavelength theory. In this Part, it is shown that energy penetration for a film cannot be defined and IM is flawed because it cannot be proved theoretically or shown to be consistent with experimental data. The multi-absorption peaks in a film originate from wave cancellation under the constraint of energy conservation rather than from the resonances from the material. [ABSTRACT FROM AUTHOR]

With its momentum transfer, light is a primary tool for manipulating microscale objects in various research fields, including physics, chemistry, and biology. Optical force fields, also known as energy landscapes, play a crucial role in manipulating micro- and nano-sized objects, enabling the sorting of mixed micro-sized particles. This study investigates the effect of time-varying periodic optical fields created by a structured light illumination technique on the diffusion motion of micro-sized colloidal particles suspended in a liquid. A simulation code is developed to calculate the optical force acting on particles due to any time-varying optical force field. Simulations are performed to produce trajectories of particles of different sizes suspended in a liquid for different illumination patterns. The results show that the average velocities of the particles depend on the projected optical pattern parameters and that mixtures of particles of different sizes can be separated using time-varying sequential patterns, thereby improving particle separation resolution. [ABSTRACT FROM AUTHOR]

Large contact angle hysteresis surfaces were the topic of a contribution in Ref. [19]. They address the relation between vapor of a liquid, a finite contact angle, and a possible wetting transition at saturation vapor pressure. In Ref. [15], the authors apply surfaces with low contact angle hysteresis to the evaporation of drops of salt solutions. Low contact angle hysteresis implies that contact lines or sessile drops move without much resistance. [Extracted from the article]

A general, self-consistent scheme for analyzing cellular electroporation for bio-medical applications is developed to probe realistic biological shapes and different length scales ranging from nanometers to hundreds of micrometers. The COMSOL Multiphysics suite is used with suitable embellishments to incorporate the details of the electroporation (EP) process and the inherent internal physics. The results are obtained for the voltage pulse driven electroporation for a Jurkat cell with mitochondria (as an example organelle) where spatial dimensions on the order of a few nanometers become important, to hundreds of cells (with Bacillus as an example) where collective effects and mutual interactions can dominate. Thus, scalable computing to generalized geometries with the ability to include complex organelles is made available. The results obtained for mitochondrial EP in Jurkat cells compare well with available data. In addition, quantitative predictions of field attenuation and shielding in Bacillus clusters are made, which point to highly nonuniform field distributions and a strong need to engineer novel electrode designs. [ABSTRACT FROM AUTHOR]

Power law distributions are widely observed in chemical physics, geophysics, biology, and beyond. The independent variable x of these distributions has an obligatory lower bound and, in many cases, also an upper bound. Estimating these bounds from sample data is notoriously difficult, with a recent method involving O(N3) operations, where N denotes sample size. Here I develop an approach for estimating the lower and upper bounds that involve O(N) operations. The approach centers on calculating the mean values, x ̂ min and x ̂ max , of the smallest x and the largest x in N-point samples. A fit of x ̂ min or x ̂ max as a function of N yields the estimate for the lower or upper bound. Application to synthetic data demonstrates the accuracy and reliability of this approach. [ABSTRACT FROM AUTHOR]

In two recent papers [A. D. Becke, J. Chem. Phys. 156, 214101 (2022) and A. D. Becke, J. Chem. Phys. 157, 234102 (2022)], we compared two Kohn–Sham density functionals based on physical modeling and theory with the best density-functional power-series fits in the literature. The best error statistics reported to date for a hybrid functional on the general main-group thermochemistry, kinetics, and noncovalent interactions (GMTKN55) chemical database of Goerigk et al. [Phys. Chem. Chem. Phys. 19, 32184 (2017)] were obtained. In the present work, additional second-order perturbation-theory terms are considered. The result is a 12-parameter double-hybrid density functional with the lowest GMTKN55 WTMAD2 "weighted total mean absolute deviation" error (1.76 kcal/mol) yet seen for any hybrid or double-hybrid density-functional approximation. We call it "DH23." [ABSTRACT FROM AUTHOR]

Fast Radio Bursts (FRBs) are energetic phenomena that have significant implications for understanding fundamental physics and the Universe. Recent observations of FRB 121102, FRB 20220912A, and FRB 20201124A by the Five-hundred-meter Aperture Spherical Telescope showed high-burst rates and distinctive energy distribution and temporal properties. In this study, we examine these observations to investigate the scale invariance of the waiting times between bursts for intervals longer than approximately 1 s. Our analysis revealed a unified scaling law for these longer intervals, which is similar to the behaviour of solar flares. This discovery inspires us to suggest a dual analogy of the FRB scenario across the entire time intervals: with earthquake dynamics at subsecond scales and with solar flare dynamics beyond the one-second threshold. This threshold potentially aligns with the dynamic time-scale of neutron star crusts, offering insight of the occurrence of FRBs into the internal processes of neutron stars. [ABSTRACT FROM AUTHOR]

Can new cosmic physics be uncovered through tensions amongst data sets? Tensions in parameter determinations amongst different types of cosmological observation, especially the 'Hubble tension' between probes of the expansion rate, have been invoked as possible indicators of new physics, requiring extension of the ΛCDM paradigm to resolve. Within a fully Bayesian framework, we show that the standard tension metric gives only part of the updating of model probabilities, supplying a data co-dependence term that must be combined with the Bayes factors of individual data sets. This shows that, on its own, a reduction of data set tension under an extension to ΛCDM is insufficient to demonstrate that the extended model is favoured. Any analysis that claims evidence for new physics solely on the basis of alleviating data set tensions should be considered incomplete and suspect. We describe the implications of our results for the interpretation of the Hubble tension. [ABSTRACT FROM AUTHOR]

Involving students in laboratory and inquiry-based activities can help them understand the concepts of physics. However the learning process should not only focus on the concepts. Moreover, the advantages of using virtual or physical labs are still under examination. The purpose of this study is to analyse which of the two modes (virtual or physical) is the most effective for high-school students, in terms of conceptual understanding and attitudes. The criteria for this comparison are (a) the contribution of these two modes to the improvement of conceptual understanding and (b) the students' attitudes towards both modes of laboratory. The participants were high-school students of 3rd grade in two different groups. For the purpose of the study, four educational scenarios were created: two in the field of Mechanics and two in that of Electricity. The study revealed no statistically significant difference regarding students' experimenting in either lab mode. Moreover, students' attitudes towards both virtual and physical labs were similarly positive. We assume that these results may contribute to a broader perspective on choosing the lab mode when designing activities, given the fact that both the understanding and attitudes of the students are similar in the cases examined. Thus, the final choice of modality should be based on other factors, such as the adequacy of equipment, the educational conditions (e.g. distance education) and the specific learning goals set by the teacher. [ABSTRACT FROM AUTHOR]

Open science is receiving widespread attention globally, and preprinting offers an important way to implement open science practices in scholarly publishing. To develop a systematic understanding of researchers' adoption of and attitudes toward preprinting, we conducted a survey of authors of research papers published in 2021 and early 2022. Our survey results show that the United States and Europe led the way in the adoption of preprinting. The United States and European respondents reported a higher familiarity with and a stronger commitment to preprinting than their colleagues elsewhere in the world. The adoption of preprinting is much stronger in physics and astronomy as well as mathematics and computer science than in other research areas. Respondents identified free accessibility of preprints and acceleration of research communication as the most important benefits of preprinting. Low reliability and credibility of preprints, sharing results before peer review and premature media coverage are the most significant concerns about preprinting, emphasized in particular by respondents in the life and health sciences. According to respondents, the most crucial strategies to encourage preprinting are integrating preprinting into journal submission workflows and providing recognition for posting preprints. [ABSTRACT FROM AUTHOR]

Parallel compressive super-resolution imaging has attracted increasing attention in recent years. However, the super-resolution quality depends on modulation masks and reconstruction algorithms. A deep-learning method provides an efficient solution, but in wide field-of-view (FOV) scenarios, the differences between optical transfer functions (OTFs) of each pixel increase the system complexity and limit its practical application. This study proposed a wide FOV parallel compressive super-resolution imaging approach based on a physics-enhanced network. First, the network and modulation masks of an arbitrary 128 × 128-pixel region were trained; then, the trained network was fine-tuned for the rest of the 128 × 128-pixel regions in the entire wide FOV, which effectively eliminated the OTF variability. Numerical simulations and practical experiments demonstrated that through the proposed approach, super-resolution images of 1020 × 1500 pixels can be reconstructed from 272 × 400-pixel low-resolution measurements using only three designed masks, with the resolution enhanced 3.75 × 3.75 times and the peak signal-to-noise ratio improved by 89.4% compared to the results of the previous compressed sensing algorithm. Besides, the training time was dramatically reduced by 95.5-fold compared with the traditional training strategy for each region alone. This approach decreases the imaging complexity of wide FOV and achieves the high-quality super-resolution reconstruction under few trained masks, thus we believe it can promote rapid imaging for super-resolution and a wide FOV ranging from infrared to terahertz. [ABSTRACT FROM AUTHOR]

Although solar fuels photocatalysis offers the promise of converting carbon dioxide directly with sunlight as commercially scalable solutions have remained elusive over the past few decades, despite significant advancements in photocatalysis band‐gap engineering and atomic site activity. The primary challenge lies not in the discovery of new catalyst materials, which are abundant, but in overcoming the bottlenecks related to material‐photoreactor synergy. These factors include achieving photogeneration and charge‐carrier recombination at reactive sites, utilizing high mass transfer efficiency supports, maximizing solar collection, and achieving uniform light distribution within a reactor. Addressing this multi‐dimensional problem necessitates harnessing machine learning techniques to analyze real‐world data from photoreactors and material properties. In this perspective, the challenges are outlined associated with each bottleneck factor, review relevant data analysis studies, and assess the requirements for developing a comprehensive solution that can unlock the full potential of solar fuels photocatalysis technology. Physics‐informed machine learning (or Physics Neural Networks) may be the key to advancing this important area from disparate data towards optimal reactor solutions. [ABSTRACT FROM AUTHOR]

This paper discusses the relevance of using physical situations to introduce the concept of angles at elementary school. We compare the effectiveness of two geometry teaching sequences. In the first one (physical sequence), the pupils learned the angle concept by experimenting on the playground (i.e. mesospace) and then modelling the situation. In the second one (paper-and-pencil sequence), the pupils worked solely in the space of a sheet of paper (i.e. microspace). In both sequences, pupils compared areas of space delineated by an angle between two directions. Pupils in two Grade 3 classes were exposed to one of the two teaching sequences. The unfolding of these sequences was videotaped and analyzed, and the pupils were tested individually, before and after teaching, to measure each sequence's effectiveness. Results showed that both sequences are effective to grasp the angle concept: Most pupils overcame the common erroneous conception of comparing angles' sides' lengths instead of angle openness. The comparison of areas of space delineated by an angle between two infinite directions, which is the two sequences' common core, seems to be the key factor underlying angle conceptualization. This paper ends with a discussion of these results' teaching implications and the merits of each sequence. [ABSTRACT FROM AUTHOR]

Electrolyte gating technology has been widely used as an effective tool to study novel physics at complex oxide surfaces and interfaces. Certain emergent phenomena reported in electro-gated SrTiO3 (STO) surfaces are particularly interesting. Here, we report on the disparate electron transport behaviors of electrolyte-gated STO (001) and (110) oriented surfaces. In contrast to the anomalous transport from an insulating state to a Kondo-like state and then metallic states on the (001) surface, with increasing carrier density, the (110) surface always behaves as an insulating state. A comparison study suggests that the oxygen vacancies and localized Ti3+ ions on the (001) surface are scatter carriers, but no such defects are found on the (110) surface. This suggests that these surfaces are intrinsically insulating, and the observed anomalous effects are likely induced by the Ti3+ ions and oxygen vacancies introduced during electrolyte gating. This work sheds light on complicated phenomena in electrolyte-gated STO-based systems. [ABSTRACT FROM AUTHOR]

Stretching a segment of a polymer beyond its contour length makes its (primarily backbone) bonds more dissociatively labile, which enables polymer mechanochemistry. Integrating some backbone bonds into suitably designed molecular moieties yields mechanistically and kinetically diverse chemistry, which is becoming increasingly exploitable. Examples include, most prominently, attempts to improve mechanical properties of bulk polymers, as well as prospective applications in drug delivery and synthesis. This review aims to highlight an emerging effort to apply the concepts and experimental tools of mechanochemistry to fundamental physical questions in soft matter. A succinct summary of the state‐of‐the‐knowledge of the field, with emphasis on foundational concepts and generalizable observations, is followed by analysis of 3 recent examples of mechanochemistry yielding molecular‐level details of elastomer failure, macromolecular chain dynamics in elongational flows and kinetic allostery. We conclude with reasons to assume that the highlighted approaches are generalizable to a broader range of physical problems than considered to date. [ABSTRACT FROM AUTHOR]