bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recent Advances onα‐Azidoketones and Esters in the Synthesis ofN‐Heterocycles
Authors: Borkotoky Lodsna , Maurya Ram Awatar 
Published: May 2022

AbstractOrganic azides have been proven to possess versatile reactivity that is utilized to synthesize a large number of molecular scaffolds. Among the azides,α‐azidoketones and esters have been widely explored to synthesize numerous high valuedN‐heterocycles. The enhanced acidity of the methylene hydrogen atoms by adjacent carbonyl or ester groups of α‐azidoketones and esters largely attributes to their unique chemical behaviour. It has been mostly utilized in two ways: a) the azides have been directly treated with other reagents in a basic medium and b) they are converted intoα‐azidovinylketones and esters through Knoevenagel condensation with aldehydes and subsequently treated with various reagents to access nitrogen heterocycles. This review provides a general outlook and concise report onα‐azidoketones and esters towards the synthesis of variousN‐heterocycles such as pyrroles, indoles, pyrazoles, imidazoles, triazoles, pyridines, pyrimidine, pyrazine and many others.
Different approaches to the study of the gravitational radiation emitted by astrophysical sources
Authors: Ferrari Valeria 
Published: May 2022

AbstractStars and black holes are sources of gravitational radiation in many phases of their life, and the signals they emit exhibit features that are characteristic of the generating process. Emitted since the beginning of star formation, these signals also contribute to create a stochastic background of gravitational waves. We shall show how the spectral properties of this background can be estimated in terms of the energy spectrum of each single event and of the star formation rate history, which is now deducible from astronomical observations. We shall further discuss the process of scattering of masses by stars and black holes, showing that, unlike black holes, stars emit signals that carry a clear signature of the nature of the source.
Tails of the density of states of two‐dimensional Dirac fermions
Authors: Villain‐Guillot S. , Jug G. , Ziegler K. 
Published: May 2022

AbstractThe density of states of Dirac fermions with a random mass on a two‐dimensional lattice is considered. We give the explicit asymptotic form of the single‐electron density of states as a function of both energy and (average) Dirac mass, in the regime where all states are localized. We make use of a weak‐disorder expansion in the parameter g/m2, where g is the strength of disorder and m the average Dirac mass for the case in which the evaluation of the (supersymmetric) integrals corresponds to non‐uniform solutions of the saddle point equation. The resulting density of states has tails which deviate from the typical pure Gaussian form by an analytic prefactor.
Numerical Relativity in 3+1 Dimensions
Authors: Brügmann B. 
Published: May 2022

AbstractNumerical relativity is finally approaching a state where the evolution of rather general (3+1)‐dimensional data sets can be computed in order to solve the Einstein equations. After a general introduction, three topics of current interest are briefly reviewed: binary black hole mergers, the evolution of strong gravitational waves, and shift conditions for neutron star binaries.
Rotating bodies as boundary value problems
Authors: Neugebauer G. 
Published: May 2022

AbstractThere are physically interesting particular cases in which the treatment of the matter region of rotating bodies may be replaced by the formulation of boundary values along the surface of the body. In this way, rotating black holes and rotating disks of dust (“galaxies”)are described by boundary value problems which can be solved by means of the so‐called Inverse Scattering Method. Physical properties of the solutions and consequences of the approach are discussed. Among other things, the balance problem for two black holes can be tackled.
The binary black‐hole dynamics at the third post‐Newtonian order in the orbital motion
Authors: Jaranowski P. , Schäfer G. 
Published: May 2022

AbstractThe orbital dynamics of the binary point‐mass systems is ambiguous at the third post‐Newtonian order of approximation. The static ambiguity is known to be related to the difference between the Brill‐Lindquist solution and the Misner‐Lindquist solution of the time‐symmetric conformally flat initial value problem for binary black holes.The kinetic ambiguity is noticed to violate in general the standard relation between the center‐of‐mass velocity and the total linear momentum as demanded by global Lorentz invariance.
Factor structure of the Tomimatsu‐Sato solutions and their recurrence relations
Authors: Hoenselaers C. 
Published: May 2022

AbstractWe consider stationary axisymmetric vacuum solutions of Einstein's equations for which the Ernst potential is rational in prolate spheroidal coordinates. Extending an earlier study we show that there are several new expressions which are factorizable. In particular, we concentrate on the Tomimatsu‐Sato solutions and their recurrence relations. Various continuum limits of the recurrence relations will be discussed.
Coupled Brownian motors on a tilted washboard
Authors: Van den Broeck C. , Bena I. , Reimann P. , Lehmann J. 
Published: May 2022

AbstractWe consider globally coupled particles, each of them governed by a deterministic relaxation dynamics in a critically tilted washboard potential, but without a preferential spatial direction for the coupled system as a whole. For weak‐to‐moderate coupling we observe a spontaneous breaking of the system intrinsic symmetry which entails a spontaneous collective transport via a ratchet effect, possibly with a superimposed oscillatory long time behavior. For strong coupling, spontaneous symmetry breaking and spontaneous directed current are ruled out, whereas a negative mobility in response to an externally applied force is recovered.
Classical and quantum transport in deterministic Hamiltonian ratchets
Authors: Dittrich T. , Ketzmerick R. , Otto M.‐F. , Schanz H. 
Published: May 2022

AbstractWe study directed transport in classical and quantum area‐preserving maps, periodic in space and momentum. On the classical level, we show that a sum rule excludes directed transport of the entire phase space, leaving only the possibility of transport in (dynamically defined) subsets, such as regular islands or chaotic areas. As a working example, we construct a mapping with a mixed phase space where both the regular and the chaotic components support directed currents, but with opposite sign. The corresponding quantum system shows transport of similar strength, associated to the same subsets of phase space as in the classical map.
Kramers turnover theory for bridges
Authors: Hershkovitz Eli , Pollak Eli 
Published: May 2022

AbstractThe bridge length dependence of the classical transfer rate from donor to acceptor is studied for symmetric bridged systems. The reaction rate is shown to be factorizable into an escape rate from the donor well and a transmission factor through the bridge. As expected for a diffusing particle this transmission factor is inversely proportional to the bridge length, for long bridges. The Pollak‐Grabert‐Hänggi turnover theory is shown to be applicable for all friction strengths and bridge lengths studied in this paper.
The single electron transistor and artificial atoms
Authors: Kastner M.A. 
Published: May 2022

AbstractModern techniques of lithography make it possible to confine electrons to sufficiently small dimensions that the quantization of both their charge and their energy are easily observable. When such confined electrons are allowed to tunnel to metallic leads a single electron transistor (SET) is created. This transistor turns on and off again every time one electron is added to the isolated region. Whereas we can understand conventional transistors using classical concepts, the SET is quantum mechanical in an essential way. In fact, there is a close analogy between the confined electrons inside an SET and an atom. In this review, the physics underlying the operation of SETs is explained, a brief history of its invention is presented, and issues of current interest are discussed.
Atom optics: Old ideas, current technology, and new results
Authors: Pritchard D.E. , Cronin A.D. , Gupta S. , Kokorowski D.A. 
Published: May 2022

AbstractAtom optics is the coherent manipulation of the atomic matter waves originally postulated by the developers of quantum mechanics. These pioneers also proposed the use of stimulated light forces to manipulate particles. These ideas have been combined with current technology to produce the field of atom optics. This, in turn, has shed new light on old quantum problems like the which way problem and the origins of quantum decoherence. Bose Einstein condensates combine naturally with atom optics to produce new results such as the coherent amplification of matter waves. This review of atom optics traces these connections.
Quantum architecture of novel solids
Authors: Zunger A. 
Published: May 2022

AbstractThe current status of our understanding of Quantum Mechanics is that if one specifies the chemical formula of a compound (e.g., CuAu, or GaAs, or NiPt) it is still impossible to predict if this material is a superconductor or not, but it is now possible to predict its crystal structure. This is a nontrivial accomplishment for there are as many as 2N possible structures for a binary compound. This article reviews this classic question of structural chemistry and condensed matter physics: How can one figure out which of the astronomic number of possible crystal structures is selected by Nature?
Scale invariance in the causal approach to renormalization theory
Authors: Grigore Dan R. 
Published: May 2022

AbstractThe dilation invariance is studied in the framework of Epstein‐Glaser approach to renormalization theory. Some analogues of the Callan‐Symanzik equations are found and they are applied to the scalar field theory and to Yang‐Mills models. We find the interesting result that, if all fields of the theory have zero masses, then from purely cohomological consideration, one can obtain the anomalous terms of logarithmic type.
Operator product expansion in local causal perturbation theory
Authors: Prange Dirk 
Published: May 2022

AbstractWe derive an operator product expansion in φ4‐theory for the time ordered product of two interacting fields in the Bogoliubov‐Epstein‐Glaser approach. Our result relies on the definition of an appropriate bilocal time ordered product as a generalization of the local time ordered products given by Epstein‐Glaser.
Universal Relationship of Time and Frequency in Photonic Tunnelling
Authors: Haibel A. , Nimtz G. 
Published: May 2022

AbstractTunnelling transit time for frustrated total internal reflection (FTIR) in a double‐prism experiment was measured using microwave radiation. We have found that the transit time is of the same order of magnitude as the corresponding transit time measured either in an undersized waveguide (evanescent modes) or in a photonic lattice. Moreover we have established that in all such experiments the tunnelling transit time is approximately equal to the reciprocal (1/f) of the corresponding frequency of radiation.
Some remarks on the Bel‐Robinson tensor
Authors: Garecki Janusz 
Published: May 2022

AbstractIn this paper we present our point of view on the correct physical interpretation of the Bel‐Robinson tensor within the framework of standard General Relativity (GR), i.e., within the framework of GR without supplementary elements like an arbitrary vector field, a distinguished tetrad field or a second metric. We show that this tensor arises as a consequence of the Bianchi identities and, in a natural manner, it is linked to the difference of the canonical gravitational energy‐momentum as calculated in normal coordinates in a small vicinity of their origin P and in the origin P.
Size of three‐dimensional objects measured by means of photoemission electron microscopy
Authors: Nepijko S.A. , Sedov N.N. , Schmidt O. , Fecher G.H. , Schönhense G. 
Published: May 2022

AbstractPb particles on a Si(111) substrate were investigated using a photoemission electron microscope (PEEM). The electrons have been excited by a linearly polarised femtosecond laser beam with a wavelength of λ = 400 nm. The PEEM images exhibit an unusually high contrast. They arise due to photoemission being of a nontrivial nature because the photon energy is lower than the work function of the sample. It may be caused by the following processes: two‐ or multi‐photon absorption, tunnel‐photoeffect induced by a strong lowering of the potential barrier owing to enhancement of the electrical field of the powerful incident light wave on a rough surface, generation of second harmonic with its following absorption, or electron gas heating. Images obtained with orthogonal directions of the photon polarisation were compared to estimate the shape of different Pb particles. The size of the islands was determined by two methods, either from the shape of the spatial brightness distribution or from the area under the curve of this distribution.
Irreducible Freedman‐Townsend vertex and Hamiltonian BRST cohomology
Authors: Bizdadea C. , Cioroianu E.M. , Saliu S.O. 
Published: May 2022

AbstractThe irreducible Freedman‐Townsend vertex is derived by means of the Hamiltonian deformation procedure based on local BRST cohomology.
The statistical mechanics of topological polymers: a field theorist point of view
Authors: Ferrari Franco 
Published: May 2022

AbstractThis is a self‐contained introduction to polymer physics and to the application of field theoretical techniques to the statistical mechanics of polymer systems. Of course, since polymer physics is a highly interdisciplinary subject, involving different disciplines like knot theory, field theory, statistical mechanics and some notions of bio‐chemistry and chemistry, it is not possible to cover all these topics in a single review. Particular emphasis is given here to the problem of describing the fluctuations of topologically linked polymers in a solution from a microscopical point of view. Some recent advances in this direction are presented. Another purpose of this work is to serve as a guide for whoever would like to apply the methods of field theory to polymers. To ease reading, technical terms have been quoted in boldface characters at the points in which their meaning is explained.
New hierarchy for the Liouville equation, irreversibility and Fokker‐Planck‐like structures
Authors: Alvarez‐Estrada R.F. 
Published: May 2022

AbstractThe issue of irreversibility is revisited for a closed system formed by N classical non‐relativistic particles inside a volume Ω, interacting through two‐body potentials, for large N and Ω. The classical phase‐space distribution function f, multiplied by suitable Hermite polynomials and integrated over all momenta, yields new moments. The Liouville equation and the initial distribution fin imply a new non‐equilibrium linear infinite hierarchy for the moments. That hierarchy differs from the BBGKY one for distribution functions and displays some suggestive Fokker‐Planck‐like structures. A physically motivated ansatz for fin (which introduces statistical assumptions), used by previous authors, is chosen. All moments of order n ≥ n0 are expressed in terms of those of order n0 — 1 and of fin. The properties of the Fokker‐Planck‐like structures (hermiticity, non‐negative eigenvalues) allow for implementing a natural long‐time approximation in the hierarchy, so as to introduce relaxation to equilibrium and irreversibility, consistently with the hydrodynamical balance equations. Further (more restrictive) assumptions and approximations lead to new irreversible models, generalizing non‐trivially the Fokker‐Planck equation. They are described through a truncated hierarchy of linear equations for moments of order n ≤ n0 — 1 (n0 being finite). The connections with Brownian particle dynamics and Fluid Dynamics are analyzed, for consistency.
Power spectrum of fluctuations in self‐gravitating systems in a statistical thermodynamics approach
Authors: Granovskii Y.I. , Stelmach J. 
Published: May 2022

AbstractFor the description of a self‐gravitating system, a closed formula is found for the power spectrum of the density fluctuations within a statistical thermodynamics approach. A key point of the calculation is the evaluation of the statistical integral describing a system of “particles” interacting gravitationally in a canonical ensemble. The power spectrum turns out to have a smoothed step‐like form. A characteristic length separates two classes of distance regimes and thus t wo phases. The almost flat part of the spectrum for small wave vectors means that there is no distinguished scale of fluctuations in the self‐gravitating system for distances larger than some characteristic length.
Spatial optical (2+1)‐dimensional scalar‐ and vector‐solitons in saturable nonlinear media
Authors: Weilnau C. , Ahles M. , Petter J. , Träger D. , Schröder J. , Denz C. 
Published: May 2022

Abstract(2+1)‐dimensional optical spatial solitons have become a major field of research in nonlinear physics throughout the last decade due to their potential in adaptive optical communication technologies. With the help of photorefractive crystals that supply the required type of nonlinearity for soliton generation, we are able to demonstrate experimentally the formation, the
dynamic properties, and especially the interaction of solitary waves, which were so far only known from general soliton theory. Among the complex interaction scenarios of scalar solitons, we reveal a distinct behavior denoted as anomalous interaction, which is unique in soliton‐supporting systems. Further on, we realize highly parallel, light‐induced waveguide configurations based on photorefractive screening solitons that give rise to technical applications towards waveguide couplers and dividers as well as all‐optical information processing devices where light is controlled by light itself. Finally, we demonstrate the generation, stability and propagation dynamics of multi‐component or vector solitons, multipole transverse optical structures bearing a complex geometry. In analogy to the particle‐light dualism of scalar solitons, various types of vector solitons can ‐ in a broader sense ‐ be interpreted as molecules of light.
The metal‐insulator transitions of VO2: A band theoretical approach
Authors: Eyert V. 
Published: May 2022

AbstractThe results of first principles electronic structure calculations for the metallic rutile and the insulating monoclinic phase of vanadium dioxide are presented. In addition, the insulating phase is investigated for the first time. The density functional calculations allow for a consistent understanding of all three phases. In the rutile phase metallic conductivity is carried by metal orbitals, which fall into the one‐dimensional band, and the isotropically dispersing bands. Hybridization of both types of bands is weak. In the phase splitting of the band due to metal‐metal dimerization and upshift of the bands due to increased p‐d overlap lead to an effective separation of both types of bands. Despite incomplete opening of the optical band gap due to the shortcomings of the local density approximation, the metal‐insulator transition can be understood as a Peierls‐like instability of the band in an embedding background of electrons. In the phase, the metal‐insulator transition arises as a combined embedded Peierls‐like and antiferromagnetic instability. The results for VO2 fit into the general scenario of an instability of the rutile‐type transition‐metal dioxides at the beginning of the d series towards dimerization or antiferromagnetic ordering within the characteristic metal chains. This scenario was successfully applied before to MoO2 and NbO2. In the compounds, the and bands can be completely separated, which leads to the observed metal‐insulator transitions.
Quantum Hall effect in intentionally disordered two‐dimensional electron systems
Authors: Buth K. , Merkt U. 
Published: May 2022

AbstractIn this work intentionally disordered two‐dimensional electron systems in modulation doped GaAs/GaAlAs heterostructures are studied by magnetotransport experiments. The disorder is provided by a δ‐doped layer of negatively charged beryllium acceptors. In low magnetic fields a strong negative magnetoresistance is observed that can be ascribed to magnetic‐field‐induced delocalization. At increased magnetic fields the quantum Hall effect exhibits broad Hall plateaus whose centers are shifted to higher magnetic fields, i.e. lower filling factors. This shift can be explained by an asymmetric density of states. Consistently, the transition into the insulating state of quantum Hall droplets in high magnetic fields occurs at critical filling factors around νc=0.4, i.e. well below the value 1/2 that is expected for symmetric disorder potentials. The insulator transition is characterized by the divergence of both the longitudinal resistance as well as the Hall resistance. This is contrary to other experiments which observe a finite Hall resistance in the insulating regime and has not been observed previously. According to recent theoretical studies the divergence of the Hall resistance points to quantum coherent transport via tunneling between quantum Hall droplets. The magnetotransport experiments are supplemented by simulations of potential landscapes for random and correlated distributions of repulsive scatterers, which enable the determination of percolation thresholds, densities of states, and oscillator strengths for far‐infrared excitations. These simulations reveal that the strong shift of the Hall plateaus and the observed critical filling factor for the insulator transition in high magnetic fields require an asymmetric density of states that can only be generated by a strongly correlated beryllium distribution. Cyclotron resonance on the same samples also indicates the possibility of correlations between the beryllium acceptors.
Spin polarization transitions in the FQHE
Authors: Mariani E. , Mazzarello R. , Sassetti M. , Kramer B. 
Published: May 2022

AbstractThe spin polarization of the FQHE ground states at fixed filling factors is analyzed within a composite fermion model. As a function of the perpendicular magnetic field several cross‐overs between differently polarized ground states are predicted, in agreement with recent experimental investigations. The magnetic field and temperature scalings of the polarization, as well as the magnetic field dependence of the spin‐flip gap are studied.
Precise Modulation of Triple‐Phase Boundaries towards a Highly Functional Exsolved Catalyst for Dry Reforming of Methane under a Dilution‐Free System
Authors: Oh Jinkyung , Joo Sangwook , Lim Chaesung , Kim Hyung Jun , Ciucci Francesco , Wang Jian‐Qiang , Han Jeong Woo , Kim Guntae 
Published: May 2022

AbstractDry reforming of methane (DRM) has been emerging as a viable solution to achieving carbon neutrality enhanced by the Paris Agreement as it converts the greenhouse gases of CO2 and CH4 into industrially useful syngas. However, there have been limited studies on the DRM catalyst under mild operating conditions with a high dilution gas ratio due to their deactivation from carbon coking and metal sintering. Herein, we apply the triple‐phase boundary (TPB) concept to DRM catalyst via exsolution phenomenon that can secure elongated TPB by controlling the Fe‐doping ratio in perovskite oxide. Remarkably, the exsolved catalyst with prolongated TPB shows exceptional CO2 and CH4 conversion rates of 95.9 % and 91.6 %, respectively, stable for 1000 hours under a dilution‐free system. DFT calculations confirm that the Lewis acid of support and Lewis base of metal at the TPB promote the adsorption of reactants, resulting in lowering the overall CO2 dissociation and CH4 dehydrogenation energy.