ShantanuT01/DACTYL-Pretraining huggingface dataset:
Owing to our dependance on spaceborne technology, an awareness of disturbances in the near-Earth space environment is proving to be increasingly crucial. Earth-directed Coronal mass ejections (CMEs) emanating from the Sun are the primary drivers of space weather disturbances. Studies of CMEs, their kinematics, and their near-Earth effects are therefore gaining in importance.   The effect of CMEs near the Earth is often manifested as transient decreases in galactic cosmic ray intensity, which are called Forbush decreases (FDs). In this thesis we probe the structure of CMEs and their associated shocks using FD observations by the GRAPES-3 muon telescope at Ooty. We have established that the cumulative diffusion of galactic cosmic rays into the CME is the dominant mechanism for causing FDs (Chapter 3).   This diffusion takes place through a turbulent sheath region between the CME and the shock. One of our main results concerns the turbulence level in this region. We have quantitatively established that cross-field diffusion aided by magnetic field turbulence accounts for the observed lag between the FD and the magnetic field enhancement of the sheath region (Chapter 4 ).   We have also investigated the nature of the driving forces acting on CMEs in this thesis. Using CME data from the SECCHI coronagraphs aboard STEREO sapcecraft, we have found evidence for the non-force-free nature of the magnetic field configuration inside these CMEs, which is the basis for the (often-invoked) Lorentz self-force driving (Chapter 5).   Taken together the work presented in this thesis is a comprehensive attempt to characterise CME propagation from typical coronagraph fields of view to the Earth.
We make a semiclassical analysis of thermal pair creations of quasiparticles at various filling factors in quantum Hall systems. It is argued that the gap energy is reduced considerably by the Coulomb potential made by impurities. It is also shown that a tunneling process becomes important at low temperature and at strong magnetic field. We fit typical experimental data excellently based on our semiclassical results of the gap energy.
A new formulation of the subject equation is presented. Several parametric and semi-parametric solutions are derived. The parametric solution for a=-1 was originally presented in 1972, but never published. A computer-generated version was found by Zajta and published in 1983. The pencil-and-paper version is presented for the record, along with many other examples, including eight coincidental triplet solutions.
Derivative expansion and large-$D$ expansion are two perturbation techniques, which are used to generate dynamical black-brane solutions to Einstein's equations in presence of negative cosmological constant. In this note we have compared these two techniques and established the equivalence of the gravity solutions generated by these two different techniques in appropriate regime of parameter space up to first non-trivial order in both the perturbation parameters for Einstein-Maxwell systems, generalizing the earlier works of [arXiv:1807.05058], [arXiv:1902.00854] for non-charged systems. An one-to-one map between dynamical black-brane geometry and AdS space, which also exists at finite number of dimensions, has also been established.
In this note we give a new bound for large sieve with characters to power moduli which improves in some range of the parameters the previous bounds of Baier/Zhao and Halupczok.
The onset of a solar eruption is formulated here as either a magnetic catastrophe or as an instability. Both start with the same equation of force balance governing the underlying equilibria. Using a toroidal flux rope in an external bipolar or quadrupolar field as a model for the current-carrying flux, we demonstrate the occurrence of a fold catastrophe by loss of equilibrium for several representative evolutionary sequences in the stable domain of parameter space. We verify that this catastrophe and the torus instability occur at the same point; they are thus equivalent descriptions for the onset condition of solar eruptions.
Let $\bar{P}$ be a sequence of length $2n$ in which each element of $\{1,2,...,n\}$ occurs twice. Let $P'$ be a closed curve in a closed surface $S$ having $n$ points of simple auto-intersections, inducing a 4-regular graph embedded in $S$ which is 2-face colorable. If the sequence of auto-intersections along $P'$ is given by $\bar{P}$, we say that is a {\em $P'$ 2-face colorable solution for the Gauss Code $\bar{P}$ on surface $S$} or a {\em lacet for $\bar{P}$ on $S$}. In this paper we present a necessary and sufficient condition yielding these solutions when $S$ is Klein bottle. The condition take the form of a system of $m$ linear equations in $2n$ variables over $\Z_2$, where $m \le n(n-1)/2$. Our solution generalize solutions for the projective plane and on the sphere. In a strong way, the Klein bottle is an extremal case admitting an affine linear solution: we show that the similar problem on the torus and on surfaces of higher connectivity are modelled by a quadratic system of equations.
A weighted U-statistic based on a random sample X_1,...,X_n has the form U_n=\sum_{1\le i,j\le n}w_{i-j}K(X_i,X_j), where K is a fixed symmetric measurable function and the w_i are symmetric weights. A large class of statistics can be expressed as weighted U-statistics or variations thereof.   This paper establishes the asymptotic normality of U_n when the sample observations come from a nonlinear time series and linear processes.
We analyze vacuum Killing Initial Data on characteristic Cauchy surfaces. A general theorem on existence of Killing vectors in the domain of dependence is proved, and some special cases are analyzed in detail, including the case of bifurcate Killing horizons.
Because of thermal expansion and residual interactions, hot nuclear fragments produced in multifragmentation reactions may have lower nucleon density than the equilibrium density of cold nuclei. In terms of liquid-drop model this effect can be taken into account by reducing the bulk energy of fragments. We study the influence of this change on fragment yields and isotope distributions within the framework of the statistical multifragmentation model. Similarities and differences with previously discussed modifications of symmetry and surface energies of nuclei are analyzed.
Thue equations and their relative and inhomogeneous extensions are well known in the literature. There exist methods, usually tedious methods, for the complete resolution of these equations. On the other hand our experiences show that such equations usually do not have extremely large solutions. Therefore in several applications it is useful to have a fast algorithm to calculate the "small" solutions of these equations. Under "small" solutions we mean the solutions, say, with absolute values or sizes $\leq 10^{100}$. Such algorithms were formerly constructed for Thue equations, relative Thue equations. The relative and inhomogeneous Thue equations have applications in solving index form equations and certain resultant form equations. It is also known that certain "totally real" relative Thue equations can be reduced to absolute Thue equations (equations over $\Bbb Z$).   As a common generalization of the above results, in our paper we develop a fast algorithm for calculating "small" solutions (say with sizes $\leq 10^{100}$) of inhomogeneous relative Thue equations, more exactly of certain inequalities that generalize those equations. We shall show that in the "totally real" case these can similarly be reduced to absolute inhomogeneous Thue inequalities. We also give an application to solving certain resultant equations in the relative case.
We report the discovery of an unusual object near the spiral galaxy IC 2497, discovered by visual inspection of the Sloan Digital Sky Survey (SDSS) as part of the Galaxy Zoo project. The object, known as Hanny's Voorwerp, is bright in the SDSS g band due to unusually strong OIII 4959-5007 emission lines. We present the results of the first targeted observations of the object in the optical, UV and X-ray, which show that the object contains highly ionized gas. Although the line ratios are similar to extended emission-line regions near luminous AGN, the source of this ionization is not apparent. The emission-line properties, and lack of x-ray emission from IC 2497, suggest either a highly obscured AGN with a novel geometry arranged to allow photoionization of the object but not the galaxy's own circumnuclear gas, or, as we argue, the first detection of a quasar light echo. In this case, either the luminosity of the central source has decreased dramatically or else the obscuration in the system has increased within 10^5 years. This object may thus represent the first direct probe of quasar history on these timescales.
We analyse the damping by radiation reaction and by Compton drag of strong, superluminal electromagnetic waves in the context of pulsar winds. The associated radiation signature is found by estimating the efficiency and the characteristic radiation frequencies. Applying these estimates to the gamma-ray binary containing PSR B1259-63, we show that the GeV flare observed by Fermi-LAT can be understood as inverse Compton emission by particles scattering photons from the companion star, if the pulsar wind termination shock acquires a precursor of superluminal waves roughly 30 days after periastron. This constrains the mass-loading factor of the wind $\mu=L/\dot{N}mc^2$ (where $L$ is the luminosity and $\dot{N}$ the rate of loss of electrons and positrons) to be roughly $6\times 10^4$.
The linear polarization images of the jet in the giant elliptical galaxy M87 have previously been observed with Very Long Baseline Array at 7 mm. They exhibit a complex polarization structure surrounding the optically thick and compact subparsec-scale core. However, given the low level of linear polarization in the core, it is required to verify that this complex structure does not originate from residual instrumental polarization signals in the data. We have performed a new analysis of the same data sets observed in four epochs by using the Generalized Polarization CALibration pipeline (GPCAL). This novel instrumental polarization calibration pipeline overcomes the limitations of LPCAL, a conventional calibration tool used in the previous M87 studies. The resulting images show a compact linear polarization structure with its peak nearly coincident with the total intensity peak, which is significantly different from the results of previous studies. The core linear polarization is characterized as fractional polarization of $\sim0.2-0.6$% and polarization angles of $\sim66-92^\circ$, showing moderate variability. We demonstrate that, based on tests with synthetic data sets, LPCAL using calibrators having complex polarization structures cannot achieve sufficient calibration accuracy to obtain the true polarization image of M87 due to a breakdown of the "similarity approximation". We find that GPCAL obtains more accurate D-terms than LPCAL by using observed closure traces of calibrators that are insensitive to both antenna gain and polarization leakage corruptions. This study suggests that polarization imaging of very weakly polarized sources has become possible with the advanced instrumental polarization calibration techniques.
This chapter presents an overview of the properties of a Bose-Einstein condensate (BEC) trapped in a periodic potential. This system has attracted a wide interest in the last years, and a few excellent reviews of the field have already appeared in the literature (see, for instance, [1-3] and references therein). For this reason, and because of the huge amount of published results, we do not pretend here to be comprehensive, but we will be content to provide a flavor of the richness of this subject, together with some useful references. On the other hand, there are good reasons for our effort. Probably, the most significant is that BEC in periodic potentials is a truly interdisciplinary problem, with obvious connections with electrons in crystal lattices, polarons and photons in optical fibers. Moreover, the BEC experimentalists have reached such a high level of accuracy to create in the lab, so to speak, paradigmatic Hamiltonians, which were first introduced as idealized theoretical models to study, among others, dynamical instabilities or quantum phase transitions.
Influence of the fourth generation, if ever exists, on the experimentally measurable quantities such as invariant dilepton mass distribution, lepton forward-backward asymmetry, and the ratio (Gamma_L/Gamma_T) of the decay widths when K* meson is longitudinally and transversally polarized, is studied. Using the experimental results on the branching ratios for the (B -> X_s) gamma and semileptonic (B -> X_c l nu) decays, the two possible solutions of the 4x4 Cabibbo-Kobayashi-Maskawa factor (V_{t's} V_{t^'b}) are obtained as a function of the t'-quark mass. It is observed that the results for the above-mentioned physical quantities are essentially different from the standard model predictions only for one solution of the CKM factor. In this case the above-mentioned physical quantities can serve as efficient tools in search of the fourth generation. The other solution yields almost identical results with the SM.
The effective chiral Lagrangian of the strong and electromagnetic interactions of the pseudoscalar mesons at low energies depends on a set of low energy constants. We determine the contributions to the electromagnetic coupling constants at order $O(e^2 p^2)$, which arise from resonances within a photon loop. We give some implications of our results, in particular we discuss in detail the effects on the corrections to Dashen's theorem.
Without pretending to any rigour, we find a general expression of the electrostatic self-energy in static black holes with spherical symmetry. We determine the entropy bound of a charged object by assuming the existence of thermodynamics for these black holes. By combining these two results, we show that the entropy bound does not depend on the considered black hole.
Supersonic flows in the interstellar medium (ISM) are believed to be a key driver of the molecular cloud formation and evolution. Among molecular clouds' properties, the ratio between the solenoidal and compressive modes of turbulence plays important roles in determining the star formation efficiency. We use numerical simulations of supersonic converging flows of the warm neutral medium (WNM) resolving the thermal instability to calculate the early phase of molecular cloud formation, and investigate the turbulence structure and the density probability distribution function (density PDF) of the multiphase ISM. We find that both the solenoidal and compressive modes have their power spectrum similar to the Kolmogorov spectrum. The solenoidal (compressive) modes account for >~80% (<~20%) of the total turbulence power. When we consider both the cold neutral medium (CNM) and the thermally unstable neutral medium (UNM) up to T <~ 400 K, the density PDF follows the log-normal distribution whose width sigma_s is well explained by the known relation from the isothermal turbulence as sigma_s = ln(1 + b^2 * M^2) (where b is the parameter representing the turbulence mode ratio and M is the turbulent Mach number). The density PDF of the CNM component alone (T <= 50 K), however, exhibits a narrower sigma_s by a factor of ~ 2. These results suggest that observational estimations of b based on the CNM density PDF requires the internal turbulence within each CNM clump but not the inter-clump relative velocity, the latter of which is instead powered by the WNM/UNM turbulence.
This paper studies the plane constrained shear problem for single crystals having one active slip system and subjected to loading in both directions within the small strain thermodynamic dislocation theory proposed by Le (2018). The numerical solution of the boundary value problem shows the combined isotropic and kinematic work hardening, the sensitivity of the stress-strain curves to temperature and strain rate, the Bauschinger effect, and the size effect.
We show that the law of the overall supremum $\bar{X}_t=\sup_{s\le t}X_s$ of a L\'evy process $X$ before the deterministic time $t$ is equivalent to the average occupation measure $\mu_t(dx)=\int_0^t\p(X_s\in dx)\,ds$, whenever 0 is regular for both open halflines $(-\infty,0)$ and $(0,\infty)$. In this case, $\p(\bar{X}_t\in dx)$ is absolutely continuous for some (and hence for all) $t>0$, if and only if the resolvent measure of $X$ is absolutely continuous. We also study the cases where 0 is not regular for one of the halflines $(-\infty,0)$ or $(0,\infty)$. Then we give absolute continuity criterions for the laws of $(\bar{X}_t,X_t)$, $(g_t,\bar{X}_t)$ and $(g_t,\bar{X}_t,X_t)$, where $g_t$ is the time at which the supremum occurs before $t$. The proofs of these results use an expression of the joint law $\p(g_t\in ds,X_t\in dx,\bar{X}_t\in dy)$ in terms of the entrance law of the excursion measure of the reflected process at the supremum and that of the reflected process at the infimum. As an application, this law is made (partly) explicit in some particular instances.
Going down to the limit of ultrathin films holds promise for a new generation of devices such as ferroelectric tunnel junctions or resistive memories. However, these length scales also make the devices sensitive to parasitic effects related to miniaturization, and a better understanding of what happens as size is reduced is of practical importance for the future development of these devices.   As the experimental advances in materials preparation and characterization have come together with great progress in theoretical modeling of ferroelectrics, both theorists and experimentalists can finally probe the same length and time scales. This allows realtime feedback between theory and experiment, with new discoveries now routinely made both in the laboratory and on the computer. Throughout this chapter, we will highlight the recent advances in density functional theory based modeling and the role it played in our understanding of ultrathin ferroelectrics. We will begin with a brief introduction to ferroelectricity and ferroelectric oxides, followed by an overview of the major theoretical developments. We will then discuss some of the subtleties of ferroelectricity in perovskite oxides, before turning our attention to the main subject of the chapter -- ferroelectricity in ultrathin films. We will discuss in detail the influence of the mechanical, electrical and chemical boundary conditions on the stability of the polar state in a parallel plate capacitor geometry, introducing the notion of depolarization fields that tend to destabilize ferroelectricity. We will look at other ways in which a thin ferroelectric can preserve its polar state, focusing on ferroelectric domains and domain walls. Finally, we will briefly discuss artificially layered ferroelectrics and the potential they hold as tailor-made materials for electronic applications.
We present a detailed study of the magnetic properties of low-temperature-molecular-beam-epitaxy grown Ge:Mn dilute magnetic semiconductor films. We find strong indications for a frozen state of Ge_{1-x}Mn_{x}, with freezing temperatures of T_f=12K and T_f=15K for samples with x=0.04 and x=0.2, respectively, determined from the difference between field-cooled and zero-field-cooled magnetization. For Ge_{0.96}Mn_{0.04}, ac susceptibility measurements show a peak around T_f, with the peak position T'_f shifting as a function of the driving frequency f by Delta T_f' / [T_f' Delta log f] ~ 0.06, whereas for sample Ge_{0.8}Mn_{0.2} a more complicated behavior is observed. Furthermore, both samples exhibit relaxation effects of the magnetization after switching the magnitude of the external magnetic field below T_f which are in qualitative agreement with the field- and zero-field-cooled magnetization measurements. These findings consistently show that Ge:Mn exhibits a frozen magnetic state at low temperatures and that it is not a conventional ferromagnet.
This paper studies a spatial queueing system on a circle, polled at random locations by a myopic server that can only observe customers in a bounded neighborhood. The server operates according to a greedy policy, always serving the nearest customer in its neighborhood, and leaving the system unchanged at polling instants where the neighborhood is empty. This system is modeled as a measure-valued random process, which is shown to be positive recurrent under a natural stability condition that does not depend on the server's scan range. When the interpolling times are light-tailed, the stable system is shown to be geometrically ergodic. The steady-state behavior of the system is briefly discussed using numerical simulations and a heuristic light-traffic approximation.
Very light gravitino scenario m_{3/2} < 16 eV is very interesting, since there is no cosmological problem. However in such a scenario, stability of the vacuum is an important issue. Recently, Yonekura and one of the authors RS have investigated the parameter space of a low scale gauge mediation with a perturbatively stable vacuum and found that there are severe upper bound on the gaugino masses. In this paper, we show that such a model can be completely excluded/discovered at very early stage of the LHC run.
Conformal theories in a d dimensional spacetime may be expressed as manifestly conformal theories in a d+2 dimensional conformal space as first proposed by Dirac. The reduction to d dimensions goes via the d+1 dimensional hypercone in the conformal space. Here we give a rather extensive expose of such theories. We review and extend the theory of spinning conformal particles. We give a precise and geometrical formulation of manifestly conformal fields for which we give a consistent action principle. The requirement of invariance under special gauge transformations off the hypercone plays a fundamental role here. Maxwell's theory and linear conformal gravity are derived in the conformal space and are treated in detail. Finally, we propose a consistent coordinate invariant action principle in the conformal space and give an action that should correspond to conformal gravity.
The global boundedness and asymptotic behavior are investigated for the solutions of a nonlocal time fractional reaction-diffusion equation (NTFRDE)   $$ \frac{\partial^{\alpha }u}{\partial t^{\alpha }}=\Delta u+\mu u^{2}(1-kJ*u)-\gamma u, \qquad(x,t)\in\mathbb{R}^{N}\times(0,+\infty)$$ with $0<\alpha <1,\beta, \mu ,k>0,N\leq 2$ and $u(x,0)=u_{0}(x)$. Under appropriate assumptions on $J$ and the property of time fractional derivative, it is proved that for any nonnegative and bounded initial conditions, the problem has a global bounded classical solution if $k^{*}=0$ for $N=1$ or $k^{*}=(\mu C^{2}_{GN}+1)\eta^{-1}$ for $N=2$, where $C_{GN}$ is the constant in Gagliardo-Nirenberg inequality. With further assumptions on the initial datum, for small $\mu$ values, the solution is shown to converge to $0$ exponentially or locally uniformly as $t \rightarrow \infty$, which is referred as the Allee effect in sense of Caputo derivative. Moreover, under the condition of $J \equiv 1$, it is proved that the nonlinear NTFRDE has a global bounded solution in any dimensional space with the nonlinear diffusion terms $\Delta u^{m}\, (2-\frac{2}{N}< m\leq 3)$.