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The exact analytical solution for a classical oscillator with time-dependent frequency is explored. We establish that the closed form solution for such an oscillator is possible provided the frequency is complex and obeying some stringent conditions. The complex nature of the frequency very often occurs in several physical problems. Therefore, the present model calculations are of relevant in fundamental and in practical situations. The solution of the classical oscillator of time-dependent complex frequency is used to obtain the solution of its quantum mechanical counterpart. The possibilities of getting the squeezed states and the nonclassical properties of the initial coherent radiation field coupled to the oscillator are discussed.

A new collective effect has been revealed in resonance fluorescence: the side and central components of the triplet in the emission spectrum of an atomic ensemble excited by an intense coherent field are narrowed in the case of the critical number of atoms in the ensemble.

The ionization of an atom by a nonclassical electromagnetic field has been studied by a method developed to obtain results for an arbitrary initial state of the field, including squeezed vacuum with a large average number of photons. Characteristics of the ionization of atomic systems by nonclassical squeezed light have been demonstrated for the first time. In contrast to the case of a coherent field, a significantly smoother decrease in the contributions of different above-threshold channels to ionization has been found. Features of photo-electron spectra in continuum have been revealed for the first time as a significant overlapping of peaks from different ionization channels.

This chapter explores the evolution of comparative and international education. A catch-all for disconnected research about education outside the United States? A coherent field of study, with its own theory and methods? Border crossers, transcending disciplinary boundaries? Two parallel stories capture contending perspectives and academic roles. Rooted in notions of development, one highlights the links between research and foreign aid. The other wrestles with poverty, power, and liberation as it challenges that relationship. Comparative and international education becomes contested terrain, where not only findings but also approaches and methods are at issue, where review and validation require attention to power and authority, and where self-critical scholarship is essential.

Now well into its second decade, the field of computer-supported collaborative learning (CSCL) appears healthy, encompassing a diversity of topics of study, methodologies, and representatives of various research communities. It is an appropriate time to ask: what central questions can integrate our work into a coherent field? This chapter proposes the study of technology affordances for intersubjective meaning making as an integrating research agenda for CSCL. A brief survey of epistemologies of collaborative learning and forms of computer support for that learning characterize the field to be integrated and motivate the proposal. A hybrid of experimental, descriptive, and design methodologies is proposed in support of this agenda. A working definition of intersubjective meaning making as joint composition of interpretations of a dynamically evolving context is provided and used to propose a framework around which dialogue between analytic approaches can take place.

We study the effects of motion for an Unruh-DeWitt detector, modeled as a two-level system, on the amount of coherence extracted, when it interacts with a massless scalar coherent field in 1+1 Minkowski spacetime. We observe that compared to a detector at rest, for certain values of the initial energy of the field and the interaction duration, the amount is larger for both a detector moving with a constant speed or uniform acceleration. This "swelling" of coherence, which becomes more intense for increasing values of velocity or acceleration, is mostly observed for short durations, when the energy of the field is larger compared to that of the detector, and for longer durations but smaller field energies. As a consequence, the rate at which coherence is lost, is sometimes slower for a moving detector than for a detector at rest., 6 pages, 4 figures

Structured fields that are spatially completely coherent have been extensively studied in the context of long-distance optical communication, as the structure in the intensity profile of such fields is used for encoding information. This method of doing optical communication works very well in the absence of turbulence. However, in the presence of turbulence, the intensity structures of such fields start to degrade because of the complete spatial coherence of the field, and this structural degradation increases with the increase in turbulence strength. On the other hand, several theoretical studies have now shown that the structured fields that are spatially only partially coherent are less affected by turbulence. However, to the best of our knowledge, no such experimental demonstration has been reported until now. In this Letter, we experimentally demonstrate the structural robustness of partially coherent fields in the presence of turbulence, and we show that for a given turbulence strength, the structural robustness of a partially coherent field increases as the spatial coherence length of the field is decreased.

It is known that a spatially partially coherent light field produces better imaging contrast compared to a spatially coherent field and that the contrast increases as the spatial coherence length of the field becomes smaller. The transverse spatial coherence length of most spatially partially coherent fields increases upon propagation. As a result, the field produces progressively decreasing image quality at subsequent transverse planes. By controlling the propagation of spatial coherence, we demonstrate enhanced image quality at different transverse planes along the propagation direction through a scattering medium. Using a source with propagation-invariant spatial coherence function, we report experimental observations of imaging different transverse planes with equal contrast over a significant distance. Furthermore, we generate a spatially partially coherent source that can be tailored to have minimum-possible transverse coherence area at the plane of the object to be imaged, and using this source, we demonstrate imaging spatially separated transverse planes with maximum possible image contrast.

While the study of the so-called “little magazines” of modernism at large has grown, in the past few years, into a coherent field with a rich scholarship, it would still benefit from further articu...

We describe how to synthesize stochastic instances of any genuine partially coherent field using complex screens. The primary utility of this work will be in simulating partially coherent beams propagating through random and complex media.

A method is given for evaluating electromagnetic scattering by an irregular surface with spatially-varying impedance. This uses an operator expansion with respect to impedance variation and allows examination of its effects and the resulting modification of the field scattered by the rough surface. For a fixed rough surface and randomly varying impedance, expressions are derived for the scattered field itself, and for the coherent field with respect to impedance variation for both flat and rough surfaces in the form of effective impedance conditions.

Nunez et al. (2019) argue that cognitive science has failed either ``to transition to a mature inter-disciplinary coherent field'' (p. 782) or ``to generate a successful [Lakatosian] research program'' (p. 789). We argue that the former was never the intention of many early researchers within the field, while the latter is an inappropriate criterion by which to judge an entire discipline. However we concur with Nunez et al. (2019) that the individual disciplinary balance within cognitive science has changed over time. Of particular concern is the fact that the use of computational methods appears to be on the wane.

Physical review / D D 99(9), 096007 (2019). doi:10.1103/PhysRevD.99.096007, We study electron-positron pair production by the combination of a strong, constant electric field and a thermal background. We show that this process is similar to dynamically assisted Schwinger pair production, where the strong field is instead assisted by another coherent field, which is weaker but faster. We treat the interaction with the photons from the thermal background perturbatively, while the interaction with the electric field is nonperturbative (i.e., a Furry picture expansion in α). At O(α2) we have ordinary perturbative Breit-Wheeler pair production assisted nonperturbatively by the electric field. Already at this order we recover the same exponential part of the probability as previous studies, which did not expand in α. This means that we do not have to consider higher orders, so our approach allows us to calculate the preexponential part of the probability, which has not been obtained before in this regime. Although the prefactor is in general subdominant compared to the exponential part, in this case it can be important because it scales as α2≪1 and is therefore much smaller than the prefactor at O(α0) (pure Schwinger pair production). We show that, because of the exponential enhancement, O(α2) still gives the dominant contribution for temperatures above a certain threshold, but, because of the small prefactor, the threshold is higher than what the exponential alone would suggest., Published by Inst.189733, Melville, NY

A critical characteristic of migration is that it involves people in all their complexity, and with all their complex needs. Therefore, migration, perhaps more than any other field of international law, is difficult to separate as a body of law from human rights, trade, taxation, investment, health, security, etc. In this brief essay, I will describe two critical, and distinct, linkages that prevent us from cabining migration as a separate field. Both arise in the area of labor migration. Indeed, it is through linkage with other fields of international law, such as trade and investment, that states could establish international legal commitments to liberalize migration.

This article aimed at presenting the scattered econophysics literature as a unified and coherent field through a specific lens imported from philosophy science. More precisely, I used the methodology developed by Imre Lakatos to cover the methodological evolution of econophysics over these last two decades. In this perspective, three co-existing approaches have been identified: statistical econophysics, bottom-up agent based econophysics and top-down agent based econophysics. Although the last is presented here as the last step of the methodological evolution of econophysics, it is worth mentioning that this tradition is still very new. A quick look on the econophysics literature shows that the vast majority of works in this field deal with a strictly statistical approach or a classical bottom-up agent-based modelling. In this context of diversification, the objective (and contribution) of this article is to emphasize the conceptual coherence of econophysics as a unique field of research. With this purpose, I used a theoretical framework coming from philosophy of science to characterize how econophysics evolved by combining a methodological enrichment with the preservation of its core conceptual statements.

A numerical implementation of a method to analyze scattering by randomly located obstacles in a slab geometry is presented. In general, the obstacles can be of arbitrary shape, but, in this first implementation, the obstacles are dielectric spheres. The coherent part of the reflected and transmitted intensity at normal incidence is treated. Excellent agreement with numerical results found in the literature of the effective wave number is obtained. Moreover, comparisons with the results of the Bouguer–Beer (B–B) law are made. The present theory also gives a small reflected coherent field, which is not predicted by the Bouguer–Beer law, and these results are discussed in some detail.

The entropy squeezing properties of different types of moving three-level atoms coupled with a single-mode coherent field are studied. The influences of the moving velocity and initial states of the three-level atom on the entropy squeezing are discussed. The results show that, the entropy squeezing properties of the three-level atom depend on its initial state, moving velocity, and the type. A stationary three-level atom can not obtain a steady entropy squeezing whatever initial conditions are chosen, while a moving three-level atom can achieve a steady and optimal entropy squeezing through choosing higher velocity and appropriate initial state. Our result provides a simple method for preparing squeezing resources with ultra-low quantum noise of the three-level atomic system without additional any complex techniques.

The intrinsic decoherence effect for two qubits interacting with a coherent field, under the dipole-dipole interaction and two-photon resonance, is analytically described. We investigate numerically the population inversion and the quantum coherence. The results show that the generated mixture entropy and the entanglement negativity, can be enhanced and protected by the dipole-dipole interaction and by reducing the initial coherent field intensity. In particular, we find that, the collapses and revivals of the population inversion present high sensitivity to these physical parameters. The nonlinearity of the two-photon processes leads to a generation of a strong two-qubit entanglement. This generated entanglement depends on the initial coherent field intensity, the dipole-dipole interaction and the intrinsic decoherence.

A recent article (Núñez et al., 2019) claims that cognitive science, while starting off as a multidisciplinary enterprise, has “failed to transition to a mature inter‐disciplinary coherent field.” Two indicators reported in support of this claim target one of the two journals of the Cognitive Science Society, Cognitive Science , depicting cognitive science as an increasingly monodisciplinary subfield which is dominated by psychology. With a focus on the society's other journal, Topics in Cognitive Science , the present commentary reveals a greater degree of interdisciplinarity and discusses the relative values of diversity and integration for the field. publishedVersion

Використовуючи метод рентгеноструктурного аналізу було вивчено вплив ударно-вібраційної обробки (УВО) на структурні параметри та фазовий склад сумішей діоксидів кремнію та титану. За допомогою методу трансмісійної електронної мікроскопії (ТЕМ) встановлена зміна морфологічних особливостей нанорозмірних порошків. Методом гальваностатичного циклювання проаналізовано зміну зарядових ємностей літієвих джерел струму (ЛДС) внаслідок УВО основи катодного матеріалу. У даній роботі висвітлена залежність між зміною структурно-морфологічних особливостей, електронної структури та зарядовими ємностями ЛДС. Із порівняння СЕМ та ТЕМ зображень сумішей оксидів титану та кремнію до та після УВО встановлено, що внаслідок УВО відбувається одночасне подрібнення конгломератів вихідних компонент з подальшим рівномірним розподілом частинок оксидів один між одним та утворення нових агломератів з більш щільною структурою. Встановлена агломерація супроводжується зміною параметра гратки с зміною областей когерентного розсіювання кристалічного TiO2 в залежності від концентрації його в суміші. З результатів гальваностатичного циклювання встановлено, що зарядова ємність ЛДС з катодами на основі суміші після УВО є дещо більшою у порівнянні із зарядовою ємністю ЛДС з катодом на основі вихідної суміші. З результатів аналізу встановлено, що збільшення зарядової ємності ЛДС з катодом на основі сумішей після УВО є наслідком перерозподілу Sisd-, Tisd- та Op-валентних електронів та зміни структурно-морфологічних особливостей при утворенні міжатомної взаємодії між наночастинками оксидів. The effect of mechanical treatment at microbraker (MBT) on the structural parameters and phase composition of mixtures of silicon and titanium dioxides was studied using the method of X-ray structural analysis. Transmission electron microscopy (TEM) revealed a change in the morphological features of nanoscale powders. The change in the discharge capacities of lithium power sources (LPS) due to the mechanical treatment of the cathode material base was analyzed by galvanostatic cycling. This paper highlights the relationship between changes in structural and morphological features, electronic structure, and charge capacities of LPS. From the comparison of SEM and TEM images of mixtures of titanium and silicon oxides before and after MBT, it is established that due to MBT, the agglomerates of the initial components are simultaneously crushed with perfect mixing of oxide particles between each other and new agglomerates with a denser structure are formed. The established agglomeration is accompanied by a change in the lattice parameter c with a change in the coherent scattering regions of crystalline TiO2 depending on its concentration in the mixtures. From the results of galvanostatic cycling, it is found that the charge capacity of the LPS with cathodes based on the mixture after treatment is somewhat larger compared to the charge capacity of the LPS with the cathode based on the initial mixture. The results of the analysis show that the increase of the charge capacity of the LPS with the cathode on the basic mixtures after treatment is a consequence of the redistribution of Sisd-, Tisd- and Op-valence electrons and changes of structural-morphological features in the formation of interatomic interaction between oxide particles.