bluuebunny/crossref_metadata_2025_split huggingface dataset:
Front propagation in evanescent media
Authors: Büttiker M. , Thomas H. 
Published: April 2022

AbstractWe investigate the time evolution of waves in evanescent media generated by a source within this medium and observed at some distance away from the location of the source. The aim is to find a velocity which describes a causal process and is thus, for a medium with relativistic dispersion, limited by the velocity of light. For a source with a sharp onset in time, the wave function consists of a forerunner generated by the onset of the source, and of a monochromatic front. The forerunner is dominated by a frequency which decreases with time, and the monochromatic front carries the oscillation frequency of the source into the evanescent medium. For a medium with Schrödinger‐like dispersion the velocity of the front is infinite and the monochromatic front propagates with a velocity which is in agreement with the traversal time for tunneling. In the relativistic case the forerunners travel with the velocity of light and the velocity the monochromatic front is smaller than the velocity of light and only for special energies equal to the velocity of light. For sources with a sharp onset, the forerunners are not attenuated and in magnitude far exceed the monochromatic front. This renders the detection of the monochromatic front difficult. To avoid the different behavior of forerunners and monochromatic fronts, sources which are frequency‐band limited can be considered or a short‐time Fourier transform of the field at the observation point can be taken. Both discussions suggest that the traversal time can be determined only up to a factor of 𝒪(1).
Superluminal signal velocity
Authors: Nimtz G. 
Published: April 2022

AbstractIt recently has been demonstrated that signals conveyed by evanescent modes can travel faster than light. In this report some special features of signals are introduced and investigated, for instance the fundamental property that signals are frequency band limited. Evanescent modes are characterized by extraordinary properties: Their energy is negative, they are not directly measurable, and the evanescent region is not causal since the modes traverse this region instantaneously. The study demonstrates the necessity of quantum mechanics in order to understand the superluminal signal velocity of classical evanescent modes.
Electromagnetic simulation of the evanescent mode
Authors: Chen X. , Xiong C. 
Published: April 2022

AbstractThe behaviour of a signal travelling through a piece of evanescent waveguide has been investigated using 3D electromagnetic simulation. The simulation reveals the filtering and resonating features of the evanescent waveguide and explains well most observations in the experiments [1, 2] without using the theory of superluminal signal velocity. However, how to measure and calculate the group velocity on a distorted wave packet remains an open question.
Wave packet tunneling
Authors: Krenzlin H.M. , Budczies J. , Kehr K.W. 
Published: April 2022

AbstractThe tunneling of Gaussian wave packets has been investigated by numerically solving the one‐dimensional Schrödinger equation. The shape of wave packets interacting with a square barrier has been monitored for various values of the barrier width, height and initial width of the wave packet. Compared to the case of free propagation, the maximum of a tunneled wavepacket exhibits a shift, which can be interpreted as an enhanced velocity during tunneling.
Hamiltonian evolution and quantization for extremal black holes
Authors: Kiefer Claus , Louko Jorma 
Published: April 2022

AbstractWe present and contrast two distinct ways of including extremal black holes in a Lorentzian Hamiltonian quantization of spherically symmetric Einstein‐Maxwell theory. First, we formulate the classical Hamiltonian dynamics with boundary conditions appropriate for extremal black holes only. The Hamiltonian contains no surface term at the internal infinity, for reasons related to the vanishing of the extremal hole surface gravity, and quantization yields a vanishing black hole entropy. Second, we give a Hamiltonian quantization that incorporates extremal black holes as a limiting case of nonextremal ones, and examine the classical limit in terms of wave packets. The spreading of the packets, even the ones centered about extremal black holes, is consistent with continuity of the entropy in the extremal limit, and thus with the Bekenstein‐Hawking entropy even for the extremal holes. The discussion takes place throughout within Lorentz‐signature spacetimes.
Atomic interferometry as two‐level particle scattering by a periodic potential
Authors: Bordé Christian J. , Lämmerzahl Claus 
Published: April 2022

AbstractThe beam splitting process of an atomic beam is described by an exactly solvable theory. We use exact plane wave solutions of an atomic two‐level system interacting with laser beams and employ appropriate jump conditions between regions with and without laser beam. The transmission matrix as well as the reflection matrix are given explicitely. Also, the conditions for atom optical analogues of the Borrmann effect and of the pendellösung effect are treated exactly. The high‐energy limit of these phenomena is discussed which is sufficient for many practical purposes.
Nonlinear fluorescence through intermolecular energy transfer and resolution increase in fluorescence microscopy
Authors: Schönle Andreas , Hänninen Pekka E. , Hell Stefan W. 
Published: April 2022

AbstractWe investigate a novel concept to efficiently generate multiphoton induced fluorescence from organic molecules. The concept is based on frustrating the energy transfer between a fluorescent donor and one or more acceptors in conjugated molecules. The nonlinearity is not based on higher order molecular susceptibilities but entirely on their linear properties. Therefore, in contrast to nonresonant multiphoton absorption, this method does not require high local intensities. Likewise, the production of visible fluorescence does not require an infrared excitation wavelength. Hence, when applied to scanning microscopy this property is predicted to increase spatial resolution. Instead of the ∼10 GW/cm2 required in non‐resonant multiphoton excitation, focal intensities ∼10 MW/cm2 are expected to produce an equally strong nonlinear signal. The predicted resolution is up to 30% greater than that of an ideal confocal microscope operating at the same fluorescence wavelength. The resolution improvement over non‐resonant two‐photon absorption microscopes is about two‐fold in all directions.
Potentials in low‐dimensional and semi‐infinite crystals
Authors: Mertins Frank 
Published: April 2022

AbstractFormulas for potentials in low‐dimensional and semi‐infinite lattices are derived, applying Ewald's method. The lattice sums under consideration describe interactions in different physical situations, e.g. point charges in a unit cell, multipoles or centers of van der Waals potentials, and the exchange interaction of Bloch orbitals. New expressions for general low‐dimensional lattice sums are presented together with earlier results in a unified framework. We take care of the convergency problems using a transparent regularization procedure which leads to a well‐defined solution for the electrostatic potential equation. We consider both point charges and more general Gaussian charge distributions. The latter are relevant for the description of realistic systems. For example, the use of Gaussian distributions makes the formulas useful for the quantum chemical description of polymers (modelled by one‐dimensional grids), stacked systems as graphite (approximated by two‐dimensional grids) and surfaces (modelled by semi‐infinite lattices). The potentials are discussed mainly in the frame‐work of classical electrostatics, but are easily applicable to various quantum chemical problems. We also discuss different physical examples. Since they contain only rapidly converging summations, the new formulas presented here are useful for the computational simulation, e.g. of polymers and multipolar or van der Waals potentials of thin films or surfaces.
Electronic Raman scattering and phonon self‐energy effects in the R‐123 system: Signatures of gap and pseudogap
Authors: Bock Andreas 
Published: April 2022

AbstractUsing Raman spectroscopy and transport measurements we investigate thin epitaxial films of Y1—x(Pr, Ca)xBa2Cu3O6+y. We explore the electronic Raman responses in A1g, B1g, and B2g symmetry obtained after subtraction of phononic excitations, and especially, the 2Δ peaks that form out of the electronic background below Tc. We find that the energy of the B1g 2Δ peak, which is a measure of the gap value, increases monotonically with decreasing doping until the peak becomes unresolvable. In contrast, the peak in A1g symmetry follows Tc being still resolvable in the Pr‐doped films. The B2g response is weak and a 2Δ peak is only detected at the highest doping level. As a consequence of strong electron‐phonon coupling, the B1g phonon at ∼340 cm—1 exhibits a pronounced Fano‐type line shape. We use a phenomenological model to describe the line shape that takes into account real and imaginary part of the electronic response. It allows us to obtain the self‐energy corrections and the mass‐enhancement factor λ as a measure of the coupling. In the normal state we find λ = 0.015 around optimal doping and decreasing values with decreasing doping. The electron‐phonon coupling increases strongly below Tc in overdoped samples in which the B1g 2Δ peaks appear in the vicinity of the phonon. Self‐energy effects observed in the superconducting state can only partly be assigned to the redistributing electronic response. Anomalies with respect to frequency, linewidth, and intensity remain. They appear at increasing temperatures with decreasing doping and we provide evidence that they are connected to the presence of the pseudogap. We supplement our study by a comparison with single crystal data and investigate the influence of site‐substitutional disorder on the electronic response and the electron‐phonon interaction.
Persistent current in normal metals
Authors: Mohanty P. 
Published: April 2022

AbstractWe discuss the recent experiments on persistent current in metallic rings in the backdrop of low temperature decoherence. The observed size of the persistent current, typically on the order of the Thouless energy,e/τD, is much larger than the theoretical results, obtained with or without electron interaction. In considering the phenomenology of both decoherence and persistent current, usually observed in similar systems, we argue towards a dynamic role played by decoherence in the generation of a persistent current. A field‐induced phase shift from near‐equilibrium high‐frequency fluctuations– which otherwise gives rise to decoherence–under certain conditions of periodicity and asymmetry due to disorder, is argued to induce a steady state diffusion current on the order ofe/τD, comparable to the observed persistent current.
Temperature and frequency scaling of the quantum Hall effect
Authors: Meisels R. , Kuchar F. , Dybko K. 
Published: April 2022

AbstractThe conductivity of AlGaAs/GaAs heterostructures in the regime of the quantum Hall effect is studied at DC and up to 55 GHz. The results are compared with predictions of the scaling theory. Deviations are attributed to individual impurities in the vicinity of the two‐dimensional electron system.
Critical spectral statistics as the Luttinger liquid of energy levels at a finite temperature
Authors: Kravtsov V.E. 
Published: April 2022

AbstractWe review the recent results on the energy level statistics in disordered conductors near the Anderson localization transition and other critical systems with multifractal eigenstates. We focus on the critical random matrix ensemble (CRMT) suggested by Mirlin and Fyodorov as a possible generic description of the critical parametric spectral statistics (CPSS). We show that in the region of large energy and/or parameter separations and weak multifractality this CRMT is equivalent to the Luttinger liquid of energy levels at a finite temperature with the interaction between the fictitious 1D fermions (energy levels) being dependent on the Dyson symmetry parameter β = 1, 2, 4 and the temperature being proportional to the multifractality exponent η = 1 — D2. We show that the CRMT is the simplest extension of the classical Wigner‐Dyson random matrix ensemble for the case of finite dimensionless conductance g ≫ 1 and suggest the form of the two‐level correlation functions for all the symmetry classes and all energy separations. We argue that these correlation functions coincide with the density correlation functions for the Calogero‐Sutherland model at finite temperatures.
Conductance distribution of disordered quasi one‐dimensional wires
Authors: Wölfle P. , Muttalib K.A. 
Published: April 2022

AbstractWe determine analytically the distribution of conductances of quasi one‐dimensional disordered electron systems, neglecting electron ‐ electron interaction, for all strengths of disorder. We find that in the crossover region between the metallic and insulating regimes, P(g) is highly asymmetric. The average and the variance of P(g) for 〈g〉 ≫ 1 and 〈g〉 ≪ 1 are shown to agree with exact results.
Addition spectra in disordered quantum dots with strongly interacting electrons
Authors: Canali C.M. , Stephan W. 
Published: April 2022

AbstractWe report on numerical simulations of the electron addition spectra in quantum dots weakly coupled to one charge reservoir, and containing a small number (N ≤ 10) of particles. In particular, we investigate the role played by disorder and electron‐electron interaction in creating a surprising feature, known as “electron bunching”, recently observed experimentally. In dots where disorder and on‐site repulsion are both strong, and the direct Coulomb repulsion is short range, we find examples of two electrons entering the dot at very close values of the gate voltage. Whenever such pairing occurs, the first electron involved in the pair appears at the edge of the quantum dot. Furthermore, the tunneling rate of the second electron is much faster than that of the first. We also find that the total spin of the many‐body ground state is partially polarized after the second electron enters the dot. The dependence of the addition spectrum as a function of the magnetic field is discussed.
Hawking radiation from dilaton gravity in 1 + 1 dimensions: a pedagogical review
Authors: Kummer W. , Vassilevich D.V. 
Published: April 2022

AbstractHawking radiation in d = 4 is regarded as a well understood quantum theoretical feature of Black Holes or of other geometric backgrounds with an event horizon. On the other hand, the dilaton theory, emerging after spherical reduction, and generalized dilaton theories only during the last years became the subject of numerous studies which unveiled a surprisingly difficult situation. Recently we have found some solution to the problem of Hawking flux in spherically reduced gravity which has the merit of using a minimal input. It leads to exact cancellation of negative contributions to this radiative flux, encountered in other approaches at infinity, so that our result asymptotically coincides with the one of minimally coupled scalars. The use of an integrated action is avoided — although we have been able to present also that quantity in a closed expression. This short review also summarizes and critically discusses recent activities in this field, including the problem of “conformal frames” for the background and questions which seem to be open in our own approach as well as in others.
Enzyme‐Free Copying of 12 Bases of RNA with Dinucleotides
Authors: Leveau Gabrielle , Pfeffer Daniel , Altaner Bernhard , Kervio Eric , Welsch Franziska , Gerland Ulrich , Richert Clemens 
Published: April 2022

AbstractThe synthesis of complementary strands is the reaction underlying the replication of genetic information. It is likely that the earliest self‐replicating systems used RNA as genetic material. How RNA was copied in the absence of enzymes and what sequences were most likely to have supported replication is not clear. Here we show that mixtures of dinucleotides with C and G as bases copy an RNA sequence of up to 12 nucleotides in dilute aqueous solution. Successful enzyme‐free copying occurred with in situ activation at 4 °C and pH 6.0. Dimers were incorporated in favor of monomers when both competed as reactants, and little misincorporation was detectable in mass spectra. Simulations using experimental rate constants confirmed that mixed C/G sequences are good candidates for successful replication with dimers. Because dimers are intermediates in the synthesis of longer strands, our results support evolutionary scenarios encompassing formation and copying of RNA strands in enzyme‐free fashion.
Bioinspired Design of seco‐Chlorin Photosensitizers to Overcome Phototoxic Effects in Photodynamic Therapy
Authors: Zhu Mengliang , Zhang Hang , Ran Guangliu , Yao Yuhang , Yang Zi‐Shu , Ning Yingying , Yu Yi , Zhang Ruijing , Peng Xin‐Xin , Wu Jiahui , Jiang Zhifan , Zhang Wenkai , Wang Bing‐Wu , Gao Song , Zhang Jun‐Long 
Published: April 2022

AbstractPhotodynamic therapy (PDT) is a non‐invasive treatment modality against a range of cancers and nonmalignant diseases, however one must be aware of the risk of causing phototoxic reactions after treatment. We herein report a bioinspired design of next‐generation photosensitizers (PSs) that not only effectively produce ROS but undergo fast metabolism after treatment to overcome undesirable side effects. We constructed a series of β‐pyrrolic ring‐opening seco‐chlorins, termed beidaphyrin (BP), beidapholactone (BPL), and their zinc(II) derivatives (ZnBP and ZnBPL), featuring intense near‐infrared absorption and effective O2 photosensitization. Irradiation of ZnBPL led to a non‐cytotoxic, metabolizable beidaphodiacetamide (ZnBPD) via in situ generated O2.− but not 1O2, as revealed by mechanistic studies including time‐resolved absorption, kinetics, and isotope labeling. Furthermore, water‐soluble ZnBPL showed an effective therapeutic outcome, fast metabolism, and negligible phototoxic reactions.
Chiral Arene Ligand as Stereocontroller for Asymmetric C−H Activation**
Authors: Liang Hao , Guo Weicong , Li Junxuan , Jiang Jijun , Wang Jun 
Published: April 2022

AbstractDevelopment of chiral ligands is the most fundamental task in metal‐catalyzed asymmetric synthesis. In the last 60 years, various kinds of ligands have been sophisticatedly developed. However, it remains a long‐standing challenge to develop practically useful chiral η6‐arene ligands, thereby seriously hampering the asymmetric synthesis promoted by arene‐metal catalysts. Herein, we report the design and synthesis of a class of readily tunable, C2‐symmetric chiral arene ligands derived from [2.2]paracyclophane. Its ruthenium(II) complexes have been prepared and successfully applied in the enantioselective C−H activation to afford a series of axially chiral isoquinolones (up to 99 % yield and 96 % ee). This study not only lays chemists’ longstanding doubts about whether it is possible to use chiral arene ligands to stereocontrol ruthenium(II)‐catalyzed asymmetric C−H activation, but also opens up a new avenue to achieve asymmetric C−H activation.
Proteoform‐Selective Imaging of Tissues Using Mass Spectrometry**
Authors: Yang Manxi , Hu Hang , Su Pei , Thomas Paul M. , Camarillo Jeannie M. , Greer Joseph B. , Early Bryan P. , Fellers Ryan T. , Kelleher Neil L. , Laskin Julia 
Published: April 2022

AbstractUnraveling the complexity of biological systems relies on the development of new approaches for spatially resolved proteoform‐specific analysis of the proteome. Herein, we employ nanospray desorption electrospray ionization mass spectrometry imaging (nano‐DESI MSI) for the proteoform‐selective imaging of biological tissues. Nano‐DESI generates multiply charged protein ions, which is advantageous for their structural characterization using tandem mass spectrometry (MS/MS) directly on the tissue. Proof‐of‐concept experiments demonstrate that nano‐DESI MSI combined with on‐tissue top‐down proteomics is ideally suited for the proteoform‐selective imaging of tissue sections. Using rat brain tissue as a model system, we provide the first evidence of differential proteoform expression in different regions of the brain.
Mapping Active Site Geometry to Activity in Immobilized Frustrated Lewis Pair Catalysts
Authors: Das Shubhajit , Laplaza Ruben , Blaskovits J. Terence , Corminboeuf Clémence 
Published: April 2022

AbstractThe immobilization of molecular catalysts imposes spatial constraints on their active site. We reveal that in bifunctional catalysis such constraints can also be utilized as an appealing handle to boost intrinsic activity through judicious control of the active site geometry. To demonstrate this, we develop a pragmatic approach, based on nonlinear scaling relationships, to map the spatial arrangements of the acid–base components of frustrated Lewis pairs (FLPs) to their performance in the catalytic hydrogenation of CO2. The resulting activity map shows that fixing the donor–acceptor centers at specific distances and locking them into appropriate orientations leads to an unforeseen many‐fold increase in the catalytic activity of FLPs compared to their unconstrained counterparts.
Photoinduced Chemo‐, Site‐ and Stereoselective α‐C(sp3)−H Functionalization of Sulfides
Authors: Tan Zhenda , Zhu Shibo , Liu Yangbin , Feng Xiaoming 
Published: April 2022

AbstractThe ubiquity of sulfur‐containing molecules in biologically active natural products and pharmaceuticals has long attracted synthetic chemists to develop efficient strategies towards their synthesis. The strategy of direct α‐C(sp3)−H modification of sulfides provides a streamlining access to complex sulfur‐containing molecules. Herein, we report a photoinduced chemo‐, site‐ and stereoselective α‐C(sp3)−H functionalization of sulfides using isatins as the photoredox reagent and coupling partner catalyzed by a chiral gallium(III)‐N,N′‐dioxide complex. The reaction proceeds through a verified single‐electron transfer (SET) mechanism with high efficiency, excellent functional group tolerance, as well as a broad substrate scope. Importantly, this cross‐coupling protocol is highly selective for the direct late‐stage functionalization of methionine‐related peptides, regardless of the inherent structural similarity and complexity of diverse residues.
Enantioselective Synthesis of Spiroketals and Spiroaminals via Gold and Iridium Sequential Catalysis
Authors: Yang Wu‐Lin , Shang Xin‐Yu , Luo Xiaoyan , Deng Wei‐Ping 
Published: April 2022

AbstractThe enantioselective cascade reaction between racemic 2‐(1‐hydroxyallyl)phenols and alkynols/alkynamides was realized by using a gold and iridium sequential catalytic system. In this procedure, the in situ generated exocyclic vinyl ethers or enamides undergo the asymmetric allylation/spiroketalization with π‐ally‐Ir amphiphilic species, which provides an efficient and straightforward access to spiroketals and spiroaminals with excellent enantioselectivities. Moreover, racemic 2‐(1‐hydroxyallyl)anilines were also suitable in this reaction along with a kinetic resolution process, affording enantioenriched spiroaminals and 2‐(1‐hydroxyallyl)anilines in good yields. The synthetic utility of this method has been demonstrated by efficient enantioselective synthesis of the analogue of Paecilospirone.