ShantanuT01/DACTYL-Pretraining huggingface dataset:
We have studied magnetotransport properties of a high-mobility two-dimensional electron system subject to weak electric fields. At low magnetic field $B$, the differential resistivity acquires a correction $\delta r \propto -\lambda^2 j^2/B^2$, where $\lambda$ is the Dingle factor and $j$ is the current density, in agreement with theoretical predictions. At higher magnetic fields, however, $\delta r$ becomes $B$-independent, $\delta r \propto -j^2$. While the observed change in behavior can be attributed to a crossover from overlapping to separated Landau levels, full understanding of this behavior remains a subject of future theories.
Some theoretical aspects of 3-flavour (3f) neutrino oscillations are reviewed. These include: general properties of 3f oscillation probabilities; matter effects in \nu_\mu \leftrightarrow \nu_\tau oscillations; 3f effects in oscillations of solar, atmospheric, reactor and supernova neutrinos and in accelerator long-baseline experiments; CP and T violation in neutrino oscillations in vacuum and in matter, and the problem of U_{e3}.
We have constructed a photoionization model, using the 3-D Monte Carlo code MOCASSIN for one of the hydrogen-deficient knots (J3) of the born-again planetary nebula Abell 30. The model consists of spherical knots, comprising a cold, dense, hydrogen-deficient core with very high metal abundances. The inner core is surrounded by a less dense hydrogen-deficient and metal-enriched gas envelope, with less extreme abundances. The envelope of the knot might have been formed by the mixing of the knot material with the surrounding nebular gas. This bi-chemistry, bi-density model did not produce enough heating to match the fluxes of the collisionally excited emission lines (CELs) and of the optical recombination lines (ORLs) observed in the spectrum of the knot. We therefore included heating by photoelectric emission from dust grains in the thermal equilibrium calculations, and found that dust-to-gas ratios of 0.077 and 0.107 by mass for the central core and the envelope of the knot, respectively, are sufficient to fit the spectrum. Surprisingly, photoelectric emission from grains is the dominant source of heating in the hot envelope of the knot, while heating by photoionization of helium and heavy elements dominates in the cold core. The chemical abundances inferred from our modelling indicate, in agreement with the empirical analysis of Wesson et al. (2003), that the C/O ratio in the two regions of the knot is less than unity, contrary to theoretical predictions for born-again nebulae.
We present a new survey strategy to discover and study high redshift Type Ia supernovae (SNe Ia) using the Hubble Space Telescope (HST). By targeting massive galaxy clusters at 0.9<z<1.5, we obtain a twofold improvement in the efficiency of finding SNe compared to an HST field survey and a factor of three improvement in the total yield of SN detections in relatively dust-free red-sequence galaxies. In total, sixteen SNe were discovered at z>0.95, nine of which were in galaxy clusters. This strategy provides a SN sample that can be used to decouple the effects of host galaxy extinction and intrinsic color in high redshift SNe, thereby reducing one of the largest systematic uncertainties in SN cosmology.
Typical two-path interferometers are intensity-balanced because this maximizes the visibility of their interference patterns. Unbalancing the interferometer can be advised when back action on the object whose position is monitored is to be reduced. Variations of the intensity splitting ratios in two-path interferometers are analyzed in order to determine optimal interferometric performance while minimizing back action: it turns out that homodyning-like schemes perform best.
In this talk we briefly describe some basic elements of chiral perturbation theory, $\chi PT$, and how the implementation of unitarity and other novel elements lead to a better expansion of the $T$ matrix for meson meson and meson baryon interactions. Applications are then done to the $ \pi \pi $ interaction in nuclear matter in the scalar and vector channels, antikaons in nuclei and $K^-$ atoms, and how the $\phi$ meson properties are changed in a nuclear medium.
The study of exotic nuclei around 132Sn is a subject of current experimental and theoretical interest. Experimental information for nuclei in the vicinity of 132Sn, which have been long inaccessible to spectroscopic studies, is now available thanks to new advanced facilities and techniques. The experimental data which have been now become available for these neutron-rich nuclei may suggest a modification in the shell structure. They are, in fact, somewhat different from what one might expect by extrapolating the existing results for N<82, and as a possible explanation a change in the single-proton level scheme has been suggested. The latter would be caused by a more diffuse nuclear surface, and could be seen as a precursor of major effects which should show up at larger neutron excess. New data offer therefore the opportunity to test the shell model and look for a possible evolution of shell structure when going toward neutron drip line. This is stimulating shell-model studies in this region. Here, we present an overview of recent shell-model studies of 132Sn neighbors, focusing attention on those calculations employing realistic effective interactions.
A stochastic model with a continuum of economic agents often involves shocks at both macro and micro levels. This can be formalized by a continuum of random variables that are conditionally independent given the macro level shocks. Based on the framework of a Fubini extension, the results on the exact law of large numbers and its converse for a con- tinuum of independent random variables in [14] are extended to the setting with conditional independence given general macro states. As an illustrative application, it is shown that any ex ante efficient allocation in an asymmetric information economy with general aggre- gate uncertainty has a (utility) equivalent allocation that is incentive compatible, which generalizes the corresponding results in [15] to the case with infinitely many states.
A Monte Carlo scheme to sample the screening potential H(r) of Yukawa plasmas notably at short distances is presented. This scheme is based on an importance sampling technique. Comparisons with former results for the Coulombic one-component plasma are given. Our Monte Carlo simulations yield an accurate estimate of H(r) as well for short range and long range interparticle distances.
The role of null-point reconnection in a 3D numerical MHD model of solar emerging flux is investigated. The model consists of a twisted magnetic flux tube rising through a stratified convection zone and atmosphere to interact and reconnect with a horizontal overlying magnetic field in the atmosphere. Null points appear as the reconnection begins and persist throughout the rest of the emergence, where they can be found mostly in the model photosphere and transition region, forming two loose clusters on either side of the emerging flux tube. Up to 26 nulls are present at any one time, and tracking in time shows that there is a total of 305 overall, despite the initial simplicity of the magnetic field configuration. We find evidence for the reality of the nulls in terms of their methods of creation and destruction, their balance of signs, their long lifetimes, and their geometrical stability. We then show that due to the low parallel electric fields associated with the nulls, null-point reconnection is not the main type of magnetic reconnection involved in the interaction of the newly emerged flux with the overlying field. However, the large number of nulls implies that the topological structure of the magnetic field must be very complex and the importance of reconnection along separators or separatrix surfaces for flux emergence cannot be ruled out.
Cosmic Ray Ensembles (CRE) are yet not observed groups of cosmic rays with a common primary interaction vertex or the same parent particle. One of the processes capable of initiating identifiable CRE is an interaction of an ultra-high energy (UHE) photon with the solar magnetic field which results in an electron pair production and the subsequent synchrotron radiation. The resultant electromagnetic cascade forms a very characteristic line-like front of a very small width ($\sim$ meters), stretching from tens of thousands to even many millions of kilometers. In this contribution we present the results of applying a toy model to simulate detections of such CRE at the ground level with an array of ideal detectors of different dimensions. The adopted approach allows us to assess the CRE detection feasibility for a specific configuration of a detector array. The process of initiation and propagation of an electromagnetic cascade originated from an UHE photon passing near the Sun, as well as the resultant particle distribution on ground, were simulated using the CORSIKA program with the PRESHOWER option, both modified accordingly. The studied scenario results in photons forming a cascade that extends even over tens of millions of kilometers when it arrives at the top of the Earth's atmosphere, and the photon energies span practically the whole cosmic ray energy spectrum. The topology of the signal consists of very extended CRE shapes, and the characteristic, very much elongated disk-shape of the particle distribution on ground illustrates the potential for identification of CRE of this type.
These are the handouts of an undergraduate minicourse at the Universit\`a di Bari, in the context of the 2017 INdAM Intensive Period "Contemporary Research in elliptic PDEs and related topics". Without any intention to serve as a throughout epitome to the subject, we hope that these notes can be of some help for a very initial introduction to a fascinating field of classical and modern research.
Theoretical expectations concerning the low $x$ and low $Q^2$ behaviour of $g_1$ are summarized and compared with the recent SMC data.
Exotic nuclear structures such as bubbles and tori are analyzed through semiclassical extended Thomas-Fermi calculations with the Skyrme force SkM$^*$. The variational equations for neutron and proton densities are solved fully self-consistently in spherical (bubbles) and cylindrical (tori) symmetries. The possible existence of bubble configurations in some astrophysical scenarios is discussed. The stability of toroidal structures against change of quadrupole moment is studied. A global minimum of the energy is found in heavy
Recently, the image of a Schwarzschild black hole with an accretion disk has been revisited, and it showed that the "photon ring", defined as highly bent light rays that intersect the disk plane more than twice, is extremely narrow and makes a negligible contribution to the total brightness. In this paper, we investigate the observational appearance of an optically and geometrically thin accretion disk around a hairy black hole in an Einstein-Maxwell-scalar model. Intriguingly, we find that in a certain parameter regime, due to an extra maximum or an "ankle-like" structure in the effective potential for photons, the photon ring can be remarkably wide, thus making a notable contribution to the flux of the observed image. In particular, there appears a wide and bright annulus, which comprises multiple concentric bright thin rings with different luminosity, in the high resolution image.
We review the nucleon's polarized structure functions from the viewpoint of gauge invariant, nonlocal light-cone operators in QCD. We discuss a systematic treatment of the polarized structure functions and the corresponding parton distribution functions. We also address a question of what information on the structure of Nature will be obtained from the future polarized experiments.   From this point of view, we will discuss the W gamma production at RHIC polarized experiment.
We provide a description of deformed $N=Z$ nuclei in a formalism of $\alpha$-like quartets. Quartets are constructed variationally by resorting to the use of proper intrinsic states. Various types of intrinsic states are introduced which generate different sets of quartets for a given nucleus. Energy spectra are generated via configuration-iteraction calculations in the spaces built with these quartets. The approach has been applied to $^{24}$Mg and $^{28}$Si in the $sd$ shell and to $^{48}$Cr in the $pf$ shell. In all cases a good description of the low-lying spectra has been achieved. As a peculiarity of the approach, a close correspondence is observed between the various sets of quartets employed and the occurrence of well defined band-like structures in the spectra of the systems under study.
We prove the exponential convergence to the equilibrium, quantified by R\'enyi divergence, of the solution of the Fokker-Planck equation with drift given by the gradient of a strictly convex potential. This extends the classical exponential decay result on the relative entropy for the same equation.
For integers $n\geq r$, we treat the $r$th largest of a sample of size $n$ as an $\mathbb{R}^\infty$-valued stochastic process in $r$ which we denote $\mathbf{M}^{(r)}$. We show that the sequence regarded in this way satisfies the Markov property. We go on to study the asymptotic behaviour of $\mathbf{M}^{(r)}$ as $r\to\infty$, and, borrowing from classical extreme value theory, show that left-tail domain of attraction conditions on the underlying distribution of the sample guarantee weak limits for both the range of $\mathbf{M}^{(r)}$ and $\mathbf{M}^{(r)}$ itself, after norming and centering. In continuous time, an analogous process $\mathbf{Y}^{(r)}r$ based on a two-dimensional Poisson process on $\mathbb{R}_+\times \mathbb{R}$ is treated similarly, but we find that the continuous time problems have a distinctive additional feature: there are always infinitely many points below the $r$th highest point up to time $t$ for any $t>0$. This necessitates a different approach to the asymptotics in this case.
We present an interpretation of the phenomenological relations between the spectral peak, isotropic luminosity and duration of long gamma ray bursts that have been discovered by Amati et al., Ghirlanda et al., Firmani et al., and Liang & Zhang. In our proposed model, a jet undergoes internal dissipation which prevents its bulk Lorentz factor from exceeding 1/theta (theta being the jet opening angle) until it escapes from the core of its progenitor star, at a radius of order 1e10 cm; dissipation may continue at larger radii. The dissipated radiation will be partially thermalized, and we identify its thermal peak (Doppler boosted by the outflow) with E_pk. The radiation comes, in effect, from within the jet photosphere. The non-thermal, high energy part of the GRB emission arises from Comptonization of this radiation by relativistic electrons and positrons outside the effective photosphere. This model can account naturally not only for the surprisingly small scatter in the various claimed correlations, but also for the normalization, as well as the slopes. It then has further implications for the jet energy, the limiting jet Lorentz factor, and the relation of the energy, opening angle and burst duration to the mass and radius of the stellar stellar progenitor. The observed relation between pulse width and photon frequency can be reproduced by inverse-Compton emission at ~ 1e14 cm from the engine, but there are significant constraints on the energy distribution and isotropy of the radiating particles.
Negative superhumps are believed to arise in cataclysmic variable systems when the accretion disk is tilted with respect to the orbital plane. Slow retrograde precession of the line-of-nodes results in a signal---the negative superhump---with a period slightly less than the orbital period. Previous studies have shown that tilted disks exhibit negative superhumps, but a consensus on how a disk initially tilts has not been reached. Analytical work by Lai suggests that a magnetic field on the primary can lead to a tilt instability in a disk when the dipole moment is offset in angle from the spin axis of the primary and when the primary's spin axis is, itself, not aligned with the angular momentum axis of the binary orbit. However, Lai did not apply his work to the formation of negative superhumps. In this paper, we add Lai's model to an existing smoothed particle hydrodynamics code. Using this code, we demonstrate the emergence of negative superhumps in the "light curve" for a range of magnetic dipole moments. We show that the period deficits calculated from these negative superhumps match those in simulations using manually tilted disks. When positive superhumps appear ($q \lesssim 0.33$), we show that the period excesses calculated from these signals are also consistent with previous results. Using examples, we show that the disks are tilted, though the tilt varies periodically, and that they precess in the retrograde direction. The magnetic fields found to lead to the emergence of negative superhumps lie in the kilogauss regime.
We report on a chiral effective field theory calculation of Compton scattering from the proton. Our calculation includes pions, nucleons, and the Delta(1232) as explicit degrees of freedom. It uses the "delta expansion", and so implements the hierarchy of scales m_pi < M_Delta-M_N < Lambda_chi. In this expansion the power counting in the vicinity of the Delta peak changes, and resummation of the loop graphs associated with the Delta width is indicated.   We have computed the nucleon Compton amplitude in the delta expansion up to N3LO for photon energies of the order of m_pi. This is the first order at which the proton Compton scattering amplitudes receive contributions from contact operators which encode contributions to the spin-independent polarisabilities from states with energies of the order of Lambda_chi. We fit the coefficients of these two operators to the experimental proton Compton data that has been taken in the relevant photon-energy domain, and are in a position to extract new results for the proton polarisabilities alpha and beta.
Very recently, J 1128+5925 was found to show strong intraday variability at radio wavelengths and may be a new source with annual modulation of the timescale of its radio variability. Therefore, its radio variability can be best explained via interstellar scintillation. Here we present the properties of its optical variability for the first time after a monitoring program in 2007 May. Our observations indicate that in this period J 1128+5925 only showed trivial optical variability on internight timescale, and did not show any clear intranight variability. This behavior is quite different from its strong radio intraday variability. Either this object was in a quiescent state in optical in this period, or it is intrinsically not so active in optical as it is in radio regimes.
A perturbation theory of the static response of insulating crystals to homogeneous electric fields, that combines the modern theory of polarization (MTP) with the variation-perturbation framework is developed, at unrestricted order of perturbation. First, we address conceptual issues related to the definition of such a perturbative approach. In particular, in our definition of an electric-field-dependent energy functional for periodic systems, the position operator appearing in the perturbation term is replaced by a Berry-phase expression, along the lines of the MTP. Moreover, due to the unbound nature of the perturbation, a regularization of the Berry-phase expression for the polarization is needed in order to define a numerically-stable variational procedure. Regularization is achieved by means of discretization, which can be performed either before or after the perturbation expansion. We compare the two possibilities and apply them to a model tight-binding Hamiltonian. Lowest-order as well as generic formulas are presented for the derivatives of the total energy, the normalization condition, the eigenequation, and the Lagrange parameters.
X-ray observations of supernova remnants (SNRs) allow us to investigate the chemical inhomogeneity of ejecta, offering unique insight into the nucleosynthesis in supernova explosions. Here we present detailed imaging and spectroscopic studies of the "Fe knot" located along the eastern rim of the Type Ia SNR Tycho (SN 1572) using Suzaku and Chandra long-exposure data. Surprisingly, the Suzaku spectrum of this knot shows no emission from Cr, Mn, or Ni, which is unusual for the Fe-rich regions in this SNR. Within the framework of the canonical delayed-detonation models for SN Ia, the observed mass ratios M_Cr/M_Fe < 0.023, M_Mn/M_Fe < 0.012, and M_Ni/M_Fe < 0.029 (at 90% confidence) can only be achieved for a peak temperature of (5.3-5.7) x 10^9 K and a neutron excess of < 2.0 x 10^-3. These constraints rule out the deep, dense core of a Chandrasekhar-mass white dwarf as the origin of the Fe knot, and favors either incomplete Si burning or the alpha-rich freeze-out regime, probably close to their boundary. An explosive He burning regime is a possible alternative, although this hypothesis is in conflict with the main properties of this SNR.
We investigated the thermoelectric transport properties of EuNi2P2 and EuIr2Si2 in order to evaluate the relevance of Kondo interaction and valence fluctuations in these materials. While the thermal conductivities behave conventionally, the thermopower curves exhibit large values with pronounced maxima as typically observed in Ce- and Yb-based heavy-fermion materials. However, neither the positions of these maxima nor the absolute thermopower values at low temperature are in line with the heavy-fermion scenario and the moderately enhanced effective charge carrier masses. Instead, we may relate the thermopower in our materials to the temperature-dependent Eu valence by taking into account changes in the chemical potential. Our analysis confirms that valence fluctuations play an important role in EuNi2P2 and EuIr2Si2.
Comparison results are given for time-inhomogeneous Markov processes with respect to function classes induced stochastic orderings. The main result states comparison of two processes, provided that the comparability of their infinitesimal generators as well as an invariance property of one process is assumed. The corresponding proof is based on a representation result for the solutions of inhomogeneous evolution problems in Banach spaces, which extends previously known results from the literature. Based on this representation, an ordering result for Markov processes induced by bounded and unbounded function classes is established. We give various applications to time-inhomogeneous diffusions, to processes with independent increments and to L\'evy driven diffusion processes.
We perform first-principles calculations of electron transport across a nickel-graphene interface. Four different geometries are considered, where the contact area, graphene and nickel surface orientations and the passivation of the terminating graphene edge are varied. We find covalent bond formation between the graphene layer and the nickel surface, in agreement with other theoretical studies. We calculate the energy-dependent electron transmission for the four systems and find that the systems have very similar edge contact resistance, independent of the contact area between nickel and graphene, and in excellent agreement with recent experimental data. A simple model where graphene is bonded with a metal surface shows that the results are generic for covalently bonded graphene, and the minimum attainable edge contact resistance is twice the ideal edge quantum contact resistance of graphene.