ShantanuT01/DACTYL-Pretraining huggingface dataset:
In this paper we show a Zariski pair of sextics which is not a degeneration of the original example given by Zariski. This is the first example of this kind known. The two curves of the pair have a trivial Alexander polynomial. The difference in the topology of their complements can only be detected via finer invariants or techniques. In our case the generic braid monodromies, the fundamental groups, the characteristic varieties and the existence of dihedral coverings of $\PP^2$ ramified along them can be used to distinguish the two sextics. Our intention is not only to use different methods and give a general description of them but also to bring together different perspectives of the same problem.
We construct algebraic families of exotic affine 3-spheres, that is, smooth affine threefolds diffeomorphic to a non-degenerate smooth complex affine quadric of dimension 3 but non algebraically isomorphic to it. We show in particular that for every smooth topologically contractible affine surface S with trivial automorphism group, there exists a canonical smooth family of pairwise non isomorphic exotic affine 3-spheres parametrized by the closed points of S.
Studying the GRBs' gamma-ray spectra may reveal some physical information of Gamma-ray Bursts. The Fermi satellite observed more than two thousand GRBs. The FERMIGBRST catalog contains GRB parameters (peak energy, spectral indices, intensity) estimated for both the total emission (fluence), and the emission during the interval of the peak flux. We found a relationship with linear discriminant analysis between the spectral categories and the model independent physical data. We compared the Swift and Fermi spectral types. We found a connection between the Fermi fluence spectra and the Swift spectra but the result of the peak flux spectra can be disputable. We found that those GRBs which were observed by both Swift and Fermi can similarly discriminate as the complete Fermi sample. We concluded that the common observation probably did not mean any trace of selection effects in the spectral behavior of GRBs.
In this work we present an application of the lambda-phi^4 field theoretical model to the adsorption of atoms and molecules on metallic surfaces - the electrochemical deposition. The usual approach to this system consists in the computational simulation using Monte Carlo techniques of an effective lattice-gas Hamiltonian. We construct an effective model towards a comparison between the lattice-gas Hamiltonian and the discrete version of the lambda-phi^4 Hamiltonian, obtaining the relationships between the model parameters and electrochemical quantities. The lambda-phi^4 model is studied in the mean field approximation, and the results are fitted and compared to numerical simulated and experimental data.
Recently there is trend to study topological properties in one-dimensional(1D) periodic systems. Concepts such as Zak phase are considered as topological invariants that characterize the bulk bands. The bulk 1D systems are classified to topologically nontrivial and trivial phases according to the value of the so-called topological invariant. The existence of edge states or interface states is viewed as a hallmark of the topological nontriviality of the 1D systems. In this work we demonstrate the so-called topological properties in 1D systems are not topological by showing they are description-dependent: the same system can be both topological and trivial depending on how we describe the system. We demonstrate that Zak phase and other related concepts are not topological invariants by showing they depend on the choice of gauge, especially on the choice of unit cell. We show, for the same bulk system, edge states or interface states can be both present and absent depending the choices of boundaries. So the existence of localized states in 1D system is only a boundary property.
Optical spectroscopy has been combined with computational and theoretical techniques to show how the spin dynamics in the model multiferroic BiFeO3 responds to the application of hydrostatic pressure and its corresponding series of structural phase transitions from R3c to the Pnma phases. As pressure increases, multiple spin excitations associated with non-collinear cycloidal magnetism collapse into two excitations, which show jump discontinuities at some of the ensuing crystal phase transitions. Effective Hamiltonian approach provides information on the electrical polarization and structural changes of the oxygen octahedra through the successive structural phases. The extracted parameters are then used in a Ginzburg-Landau model to reproduce the evolution with pressure of the spin waves excitations observed at low energy and we demonstrate that the structural phases and the magnetic anisotropy drive and control the spin excitations.
This is an article commissioned by the Spanish Physics Magazine ("Revista Espa\~nola de F\'isica") for the Centennial Anniversary of the discovery of General Relativity. The article reviews experimental and observational efforts to test Einstein's theory of General Relativity in a variety of scenarios (from the Solar System to binary pulsars, from the Sag A* to binary black hole and neutron star coalescences).
Hawking evaporation of photons in a variable-mass Kerr space-time is investigated by using a method of the generalized tortoise coordinate transformation. The blackbody radiant spectrum of photons displays a new spin-rotation coupling effect obviously dependent on different helicity states of photons.
We use the Millennium simulation to show that halo clustering varies significantly with cosmic web type. Halos are classified as node, filament, sheet and void halos based on the eigenvalue decomposition of the velocity shear tensor. The velocity field is sampled by the peculiar velocities of a fixed number of neighbouring halos and spatial derivatives are computed using a kernel borrowed from smoothed particle hydrodynamics. The classification scheme is used to examine the clustering of halos as a function of web type for halos with masses larger than $10^{11}$. We find that node halos show positive bias, filament halos show negligible bias, and void and sheet halos are anti-biased independent of halo mass. Our findings suggest that the mass dependence of halo clustering is rooted in the composition of web types as a function of halo mass. The substantial fraction of node type halos for halo masses $\gtrsim 2\times10^{13}\,h^{-1}\rm M_\odot$ leads to positive bias. Filament type halos prevail at intermediate masses, $10^{12} - 10^{13}\,h^{-1}\rm M_\odot$, resulting in unbiased clustering. The large contribution of sheet type halos at low halo masses $\lesssim 10^{12}\,h^{-1}\rm M_\odot$ generates anti-biasing.
HS0705+6700 (also identified as V470 Cam) is a short period (2.3 h) post common envelope detached eclipsing sdB binary system which exhibits transit time variations (TTVs) of a cyclical nature. We report a further 25 timings of light minima and show that our new TTVs support and extend this cyclical pattern to 1.6 periods. We examine possible causes of the observed TTVs and confirm that the presence of a third, and possibly a fourth, body could provide an elegant explanation of these cyclical variations. However other non-circumbinary mechanisms, e.g. Applegate magnetic dynamo effects, will remain possible contenders until sufficient data has been accumulated to demonstrate that the periodicity of the TTVs is time independent.
Experimental results for adhesive contacts on substrates coated with elastomeric thin films have recently been obtained by C. Tardivat and L. L\'{e}ger (J. Adhesion Sci. Technol. 15 1055-1078 (2001)) by the so-called JKR test, which provides both adhesion energy and elastic modulus. These data show that on substrates coated with thin films the adhesion and effective elastic modulus of the sphere depend upon the film thickness. In keeping with the experimental conditions, we try to interpret these data using a simple model (E. Barthel and A. Perriot, J. Phys. D 40, 1059-1067 (2007)) in the thin film limit, ie when the film thickness is small compared to the contact radius. Although the film does impact the local crack tip stress field, we show that no effect on the macroscopic contact variables is expected for the adhesion to coated substrates in such confined geometries. The deviations from the experimental results are ascribed to the idealized contact boundary conditions assumed in the model.
We theoretically study the coupling of Bose-Einstein condensed atoms to the mechanical oscillations of a nanoscale cantilever with a magnetic tip. This is an experimentally viable hybrid quantum system which allows one to explore the interface of quantum optics and condensed matter physics. We propose an experiment where easily detectable atomic spin-flips are induced by the cantilever motion. This can be used to probe thermal oscillations of the cantilever with the atoms. At low cantilever temperatures, as realized in recent experiments, the backaction of the atoms onto the cantilever is significant and the system represents a mechanical analog of cavity quantum electrodynamics. With high but realistic cantilever quality factors, the strong coupling regime can be reached, either with single atoms or collectively with Bose-Einstein condensates. We discuss an implementation on an atom chip.
We consider an incompressible non-isothermal fluid flow with non-linear slip boundary conditions governed by Tresca's friction law. We assume that the stress tensor is given as $\sigma = 2 \mu\bigl( \theta, u, | D(u) |) |D(u) |^{p-2} D(u) - \pi {\rm Id}$ where $\theta$ is the temperature, $\pi$ is the pressure, $u$ is the velocity and $D(u)$ is the strain rate tensor of the fluid while $p$ is a real parameter. The problem is thus given by the $p$-Laplacian Stokes system with subdifferential type boundary conditions coupled to a $L^1$ elliptic equation describing the heat conduction in the fluid. We establish first an existence result for a family of approximate coupled problems where the $L^1$ coupling term in the heat equation is replaced by a bounded one depending on a parameter $0<\delta <<1$, by using a fixed point technique. Then we pass to the limit as $\delta$ tends to zero and we prove the existence of a solution $(u, \pi, \theta)$ to our original coupled problem in Banach spaces depending on $p$ for any $p > 3/2$.
Infrared Detectors based on a Quantum Cascade have been proposed to suppress the dark current which is identified as a limiting factor in Quantum Well Infrared Photodetectors. Those detectors have been mostly designed for the 3-5um and 8-12um range of wavelength. For detector operating in the THz range a complete change of regime of transport is expected since the photon energy is lower than the Longitudinal Optical (LO) phonon energy. Using a two dimensional code of transport we have identified Interface Roughness (IR) as the key interaction in such a structure. We have used scanning transmission electron microscopy (STEM) to evaluate the IR parameters (magnitude of the roughness and mean distance between defects) instead of the classical mobility measurements. Finally, we used these parameters to study their influence on the resistance of the device.
An experimental study on the interaction of heavy, highly charged, and energetic ions (52 MeV Ni^13+) with pure H2O, pure CO2 and mixed H2O:CO2 astrophysical ice analogs is presented. This analysis aims to simulate the chemical and the physicochemical interactions induced by heavy cosmic rays inside dense and cold astrophysical environments such as molecular clouds or protostellar clouds. The measurements were performed at the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds in Caen, France). The gas samples were deposited onto a CsI substrate at 13 K. In-situ analysis was performed by a Fourier transform infrared (FTIR) spectrometer at different fluences. Radiolysis yields of the produced species were quantified. The dissociation cross sections of pure H2O and CO2 ices are 1.1 and 1.9E-13 cm^2, respectively. In the case of mixed H2O:CO2 (10:1) the dissociation cross sections of both species are about 1E-13 cm^2. The measured sputtering yield of pure CO2 ice is 2.2E4 molec/ion. After a fluence of 2-3E12 ions/cm^2 the CO2/CO ratio becomes roughly constant (~0.1), independent of the of initial CO2/H2O ratio. A similar behavior is observed for the H2O2/H2O ratio which stabilizes at 0.01, independent of the initial H2O column density or relative abundance.
The thermoelectric power, $S(T)$, of the heavy fermions YbT$_{2}$Zn$_{20}$ ($T$ = Fe, Ru, Os, Ir, Rh, and Co) has been measured to characterize their strong electronic correlations. A large, negative, local minimum in $S(T)$ with approximately -70 $\mu$V/K is found for all compounds. From the observed local minimum, the energy scales associated with both the Kondo temperature and the crystalline electric field splitting are deduced and compared to previous specific heat measurements. At low temperatures, $S(T)$ follows a linear temperature dependence, $S(T)$ = $\alpha T$, with an enhanced value of $\alpha$ which is characteristic for a heavy fermion state. In the zero temperature limit, the enhanced $\alpha$ value strongly correlates with the electronic specific heat coefficient, $C(T)/T$, due to the large density of states at the Fermi level.
Recently it was demonstrated, both theoretically and experimentally, how to separate a particle from its spin, or any other property, a phenomenon known as the "Quantum Cheshire Cat". We present two novel gedanken experiments, based on the quantum Zeno effect, suggesting a dynamical process thorough which this curious phenomenon occurs. We analyze, for the first time, a quantum current consisting of spin without mass. Thus, the quantum variables of pre- and post-selected particles are understood to be involved in various interactions, even in the absence of their owners. This current is shown to provide a local explanation for seemingly nonlocal interactions.
The formation of a hydroxylated native oxide layer on Si(001) under wet conditions is studied by means of first principles molecular dynamics simulations. Water molecules are found to adsorb and dissociate on the oxidised surface leading to rupture of Si-O bonds and producing reactive sites for attack by dissolved dioxygen or hydrogen peroxide molecules. Tensile strain is found to enhance the driving force for the dissociative adsorption of water, suggesting that similar reactions could be responsible for environmentally-driven sub-critical crack propagation in silicon.
We prove that the normalized Poincar\'e bundle on the moduli space of stable rank $r$ vector bundles with a fixed determinant on a smooth projective curve $X$ induces a family of nef vector bundles on the moduli space. Two applications follow. We show that when the genus of $X$ is large, the derived category of $X$ is embedded into the derived category of the moduli space for arbitrary rank and coprime degree, which extends the results of Narasimhan, Fonarev-Kuznetsov, and Belmans-Mukhopadhyay. As the second application, we construct a family of ACM bundles on the moduli space. A key ingredient of our proof is the investigation of birational geometry of the moduli spaces of parabolic bundles.
A newly developed fast molecular-dynamics method is applied to BaTiO3 ferroelectric thin-film capacitors with short-circuited electrodes or under applied voltage. The molecular-dynamics simulations based on a first-principles effective Hamiltonian clarify that dead layers (or passive layers) between ferroelectrics and electrodes markedly affect the properties of capacitors, and predict that the system is unable to hop between a uniformly polarized ferroelectric structure and a striped ferroelectric domain structure at low temperatures. Simulations of hysteresis loops of thin-film capacitors are also performed, and their dependence on film thickness, epitaxial constraints, and electrodes are discussed.
We construct two families of harmonic Maass Hecke eigenforms. This construction answers a question of Mazur about the existence of an "eigencurve-type" object in the world of harmonic Maass forms. Using these families, we construct $p$-adic harmonic Maass forms in the sense of Serre.
The Planck Collaboration has shown that the number of clusters as a function of their mass and redshift is an extremely powerful tool for cosmological analyses. However, the true cluster mass is not directly measurable. Among the possible approaches, clusters mass could be related to different observables via self similar scaling law. These observables are related to the baryonic components of which a cluster is composed. However, the theoretical relations that allow the use of these proxies often are affected by observational and physical biases, which impacts on the determination of the cluster mass. Fortunately, cosmological simulations are an extremely powerful tool to assess these problems. We present our calibration of the scaling relation between mass and velocity dispersion of galaxy members from the study of the simulated clusters of \THP{} project with mass above $10^{13} M_\odot$. In order to investigate the presence of a redshift dependence, we analyzed 16 different redshifts between $z = 0$ and $z = 2$. Finally, we investigated the impact of different AGN feedback models.
We investigate intensity oscillations observed simultaneously in the quiet chromosphere and in the corona, above an enhanced network area at the boundary of an equatorial coronal hole. A Fourier analysis is applied to a sequence of images observed in the 171 A and 1600 A passbands of TRACE. Four interesting features above the magnetic network are further investigated by using a wavelet analysis. Our results reveal that, in both the 171 A and 1600 A passbands, oscillations above the magnetic network show a lack of power at high frequencies (5.0-8.3 mHz), and a significant power at low (1.3-2.0 mHz) and intermediate frequencies (2.6-4.0 mHz). The global 5-min oscillation is clearly present in the 4 analyzed features when seen in the 1600 A passband, and is also found with enhanced power in feature 1 (leg of a large coronal loop) and feature 2 (legs of a coronal bright point loop) when seen in the 171 A passband. Two features above an enhanced network element (feature 3 and feature 4) show repeated propagating behaviors with a dominant period of 10 min and 5 min, respectively. We suggest these oscillations are likely to be slow magneto-acoustic waves propagating along inclined magnetic field lines, from the lower solar atmosphere into the corona. The energy flux carried by these waves is estimated of the order of 40 erg cm\^{-2} s\^{-1} for the 171 A passband and is far lower than the energy required to heat the quiet corona. For the 1600 A passband, the energy flux is about 1.4*10^6 erg cm\^{-2} s\^{-1}, which is about one third of the required energy budget for the chromosphere.
Perturbation theory is an indispensable tool for studying the cosmic large-scale structure, and establishing its limits is therefore of utmost importance. One crucial limitation of perturbation theory is shell-crossing, which is the instance when cold-dark-matter trajectories intersect for the first time. We investigate Lagrangian perturbation theory (LPT) at very high orders in the vicinity of the first shell-crossing for random initial data in a realistic three-dimensional Universe. For this we have numerically implemented the all-order recursion relations for the matter trajectories, from which the convergence of the LPT series at shell-crossing is established. Convergence studies performed up to the 40th order reveal the nature of the convergence-limiting singularities. These singularities are not the well-known density singularities at shell-crossing but occur at later times when LPT already ceased to provide physically meaningful results.
The successful assembly of heterostructures consisting of several layers of different 2D materials in arbitrary order by exploiting van der Waals forces has truly been a game changer in the field of low dimensional physics. For instance, the encapsulation of graphene or MoS2 between atomically flat hexagonal boron nitride (hBN) layers with strong affinity and graphitic gates that screen charge impurity disorder provided access to a plethora of interesting physical phenomena by drastically boosting the device quality. The encapsulation is accompanied by a self-cleansing effect at the interfaces. The otherwise predominant charged impurity disorder is minimized and random strain fluctuations ultimately constitute the main source of residual disorder. Despite these advances, the fabricated heterostructures still vary notably in their performance. While some achieve record mobilities, others only possess mediocre quality. Here, we report a reliable method to improve fully completed van der Waals heterostructure devices with a straightforward post-processing surface treatment based on thermal annealing and contact mode AFM. The impact is demonstrated by comparing magnetotransport measurements before and after the AFM treatment on one and the same device as well as on a larger set of treated and untreated devices to collect device statistics. Both the low temperature properties as well as the room temperature electrical characteristics, as relevant for applications, improve on average substantially. We surmise that the main beneficial effect arises from reducing nanometer scale corrugations at the interfaces, i.e. the detrimental impact of random strain fluctuations.
We present a morphological and physical analysis of a Giant Molecular Cloud (GMC) using the carbon monoxide isotopologues ($^{12}$CO, $^{13}$CO, C$^{18}$O $^{3}P_{2}\rightarrow$ $^{3}P_{1}$) survey of the Galactic Plane (Mopra CO Southern Galactic Plane Survey), supplemented with neutral carbon maps from the HEAT telescope in Antarctica. The giant molecular cloud structure (hereinafter the ring) covers the sky region $332^\circ$ < $\ell$ < $333^\circ$ and $\mathit{b}$ = $\pm 0.5^\circ$ (hereinafter the G332 region). The mass of the ring and its distance are determined to be respectively ~2$\times10^{5}\mathrm{M_{\odot}}$ and ~3.7 kpc from Sun. The dark molecular gas fraction, estimated from the $^{13}$CO and [CI] lines, is $\sim17\%$ for a CO T$_{\mathrm{ex}}$ between [10,20 K]. Comparing the [CI] integrated intensity and N(H$_{2}$) traced by $^{13}$CO and $^{12}$CO, we define an X$\mathrm{_{CI}^{809}}$ factor, analogous to the usual X$_{\mathrm{co}}$, through the [CI] line. X$\mathrm{_{CI}^{809}}$ ranges between [1.8,2.0]$\times10^{21}\mathrm{cm}^{-2}\mathrm{K}^{-1}\mathrm{km}^{-1}\mathrm{s}$. We examined local variation in X$_{\mathrm{co}}$ and T$_{\mathrm{ex}}$ across the cloud, and find in regions where the star formation activity is not in an advanced state, an increase in the mean and dispersion of the X$_{\mathrm{co}}$ factor as the excitation temperature decreases. We present a catalogue of C$^{18}$O clumps within the cloud. The star formation (SF) activity ongoing in the cloud shows a correlation with T$_{\mathrm{ex}}$, [CI] and CO emissions, and anti-correlation with X$_{\mathrm{co}}$, suggesting a North-South spatial gradient in the SF activity. We propose a method to disentangle dust emission across the Galaxy, using HI and $^{13}$CO data. We describe Virtual Reality (VR) and Augmented Reality (AR) data visualisation techniques for the analysis of radio astronomy data.