ShantanuT01/DACTYL-Pretraining huggingface dataset:
The large variety of 2D materials and their co-integration in van der Waals (vdW) heterostructures enable innovative device engineering. In addition, their atomically-thin nature promotes the design of artificial materials by proximity effects that originate from short-range interactions. Such a designer approach is particularly compelling for spintronics, which typically harnesses functionalities from thin layers of magnetic and non-magnetic materials and the interfaces between them. Here, we overview recent progress on 2D spintronics and opto-spintronics using vdW heterostructures. After an introduction to the forefront of spin transport research, we highlight the unique spin-related phenomena arising from spin-orbit and magnetic proximity effects. We further describe the ability to create multi-functional hybrid heterostructures based on vdW materials, combining spin, valley and excitonic degrees of freedom. We end with an outlook on perspectives and challenges for the design and production of ultra-compact all-2D spin devices and their potential applications in conventional and quantum technologies.
We present a scheme for scalable quantum information processing (QIP) with atomic ensembles and flying photons. Using the Rydberg blockade, we encode the qubits in the collective atomic states, which could be manipulated fast and easily due to the enhanced interaction, in comparison to the single-atom case. We demonstrate that our proposed gating could be applied to generation of two-dimensional cluster states for measurement-based quantum computation. Moreover, the atomic ensembles also function as quantum repeaters useful for long distance quantum state transfer. We show the possibility of our scheme to work in bad cavity or in weak coupling regime, which could much relax the experimental requirement. The efficient coherent operations on the ensemble qubits enable our scheme to be switchable between quantum computation and quantum communication using atomic ensembles.
Fix a prime number p and choose, once and for all, an embedding of the algebraic closure of Q into Qp. Let k and N be integers, and suppose N is not divisible by p. If f is a modular form of weight k, level N, and trivial character which is an eigenform for the p-th Hecke operator Tp, we define the slope of f to be the p-adic valuation of the eigenvalue of Tp. This paper reports on computations that suggest that there is quite a lot of structure to the set of slopes for eigenforms of varying weight k. In particular, we find that the slopes are often smaller than expected, that they are almost always integers, that there is evidence of a connection between fractional slopes and slopes which are "bigger than usual", and that there are some hints of a connection to the theory of theta-cycles.
Very high precision seismic space missions such as CoRoT and Kepler provide the means for testing the modelling of transport processes in stellar interiors. For some stars, such as $\delta$ Scuti $\gamma$ Doradus and Be stars, for instance, the observed pulsation spectra are modified by rotation to such an extent that it prevents any fruitful interpretation. Our aim is to characterise acoustic pulsation spectra of realistic stellar models in order to be able to interpret asteroseismic data from such stars. The 2-dimensional oscillation code ACOR, which treats rotation in a non-perturbative manner, is used to study pulsation spectra of highly distorted evolved models of stars. 2D models of stars are obtained by a self-consistent method which distorts spherically averaged stellar models a posteriori, at any stage of evolution, and for any type of rotation law. Four types of modes are calculated in a very dense frequency spectrum, among which are island modes. The regularity of the island modes spectrum is confirmed and yields a new set of quantum numbers, with which an \'echelle diagram can be built. Mixed gravito-acoustic modes are calculated in rapidly rotating models for the first time.
We present Spitzer IRAC images of the HH 111 outflow, that show a wealth of condensations/knots in both jet and counterjet. Studying the positional distribution of these knots, we find very suggestive evidence of a mirror symmetric pattern in the jet/counterjet flow. We model this pattern as the result of an orbital motion of the jet source around a binary companion. From a fit of an analytic, ballistic model to the observed path of the HH 111 system, we find that the motion in a binary with two approx. 1 Msolar stars (one of them being the HH 111 source), in a circular orbit with a separation of approx. 186 AU would produce the mirror symmetric pattern seen in the outflow.
The ongoing surveys of galaxies and those for the next generation of telescopes will demand the execution of high-CPU consuming machine codes for recovering detailed star formation histories (SFHs) and hence age-metallicity relationships (AMRs). We present here an expeditive method which provides quick-look AMRs on the basis of representative ages and metallicities obtained from colour-magnitude diagram (CMD) analyses. We have tested its perfomance by generating synthetic CMDs for a wide variety of galaxy SFHs. The representative AMRs turn out to be reliable down to a magnitude limit with a photometric completeness factor higher than $\sim$ 85 per cent, and trace the chemical evolution history for any stellar population (represented by a mean age and an intrinsic age spread) with a total mass within ~ 40 per cent of the more massive stellar population in the galaxy.
The illumination of a single-layer transition metal dichalcogenide with an elliptically-polarized light beam is shown to give rise to a differential rate of inter-band carrier excitation between the valence and conduction states around the valley edges, $ K $ and $ K^{'} $. This rate with a linear dependence on the beam ellipticity and inverse of the optical gap manifests as an asymmetric Fermi distribution between the valleys or a non-equilibrium population which under an external field and a Berry curvature induced anomalous velocity results in an externally tunable finite valley Hall current. Surface imperfections that influence the excitation rates are included through the self-consistent Born approximation. Additionally, we show that circular dichroism in the vicinity of the valley edges also exhibits an ellipticity dependence.
In this paper we show that graphene surface plasmons can be excited when an electromagnetic wave packet impinges on a single metal slit covered with graphene. The excitation of the plasmons localized over the slit is revealed by characteristic peaks in the absorption spectrum. It is shown that the position of the peaks can be tuned either by the graphene doping level or by the dielectric function of the material filling the slit. The whole system forms the basis for a plasmonic sensor when the slit is filled with an analyte.
We define 2-decompositions of ribbon graphs, which generalise 2-sums and tensor products of graphs. We give formulae for the Bollobas-Riordan polynomial of such a 2-decomposition, and derive the classical Brylawski formula for the Tutte polynomial of a tensor product as a (very) special case. This study was initially motivated from knot theory, and we include an application of our formulae to mutation in knot diagrams.
We define a quasar-galaxy mixing diagram using the slopes of their spectral energy distributions (SEDs) from 1\mu m to 3000\AA\ and from 1\mu m to 3\mu m in the rest frame. The mixing diagram can easily distinguish among quasar-dominated, galaxy-dominated and reddening-dominated SED shapes. By studying the position of the 413 XMM selected Type 1 AGN in the wide-field "Cosmic Evolution Survey" (COSMOS) in the mixing diagram, we find that a combination of the Elvis et al. (1994, hereafter E94) quasar SED with various contributions from galaxy emission and some dust reddening is remarkably effective in describing the SED shape from 0.3-3\mu m for large ranges of redshift, luminosity, black hole mass and Eddington ratio of type 1 AGN. In particular, the location in the mixing diagram of the highest luminosity AGN is very close (within 1\sigma) to that of the E94 SED. The mixing diagram can also be used to estimate the host galaxy fraction and reddening in quasar. We also show examples of some outliers which might be AGN in different evolutionary stages compared to the majority of AGN in the quasar-host galaxy co-evolution cycle.
Related to a conjecture of Tom Wolff, we solve a singular Neumann problem for a linearized p-Laplace equation in the unit disk.
Stellar population models to predict the H Balmer and HeI lines in absorption are presented. Models are computed for burst and continuous star formation. It is found that the Balmer and HeI line profiles are sensitive to the age, except during the first 4 Myr of the evolution, when the equivalent widths of these lines are constant. The comparison of these lines with the corresponding nebular emission lines indicates that Hd and the higher-order terms of the Balmer series and HeI (3819, 4026, 4388 and 4922) in absorption are very good age-indicators of starbursts. Models are applied to date the super-star cluster B in NGC 1569.
We present a new sample of bright galaxy pairs extracted applying an objective selection code to UZC catalog.The sample is volume limited to M$_{zw}$ = -18.9 +5 log ${\it h}$ and contains 89 galaxy pairs.We analyze the kinematical, morphological and photometrical properties of galaxies belonging to this sample. We show that velocity separation, $| \Delta v_{r} |$, between pair members is significantly lower in spiral type (S+S) pairs than in early-type (E+E) and mixed (E+S) pairs.This indicates that truly isolated galaxy pairs are more likely to be found among S+S pairs. We show that ellipticals are rare and underluminous in B and that late spirals (T $\ge$ 4) are overluminous. We confirm that the formation of bright ellipticals is a phenomenon linked to group/cluster environment, while galaxy-galaxy interaction may enhance blue luminosity of disk galaxies through SF phenomena. This last statement is supported by the presence of strong FIR emission from early spirals in this sample and by the high frequency of AGN/SB phenomenon, revealed mainly in pairs of low relative radial velocity separation and showing signs of interaction.
Using the Green function method, binding effects on produced eta-mesons in the two-stage reaction \gamma + A \to N + \eta + (A-1) \to N + (\pi N) + (A-2) are studied. The energy spectrum of the correlated pi-N pairs which arise from decays of etas inside the nucleus is strongly affected by an attractive eta-nucleus optical potential. Its resonant behavior gives a clear signal of formating intermediate eta-mesic nuclei.
Future observations of the cosmic microwave background (CMB) polarization are expected to set an improved upper bound on the tensor-to-scalar ratio of $r\lesssim 0.03$. Recently, we showed that small field models of inflation can produce a significant primordial gravitational wave signal. We constructed viable small field models that predict a value of $r$ as high as $0.01$. Models that predict higher values of $r$ are more tightly constrained and lead to larger field excursions. This leads to an increase in tuning of the potential parameters and requires higher levels of error control in the numerical analysis. Here, we present viable small field models which predict $r=0.03$. We further find the most likely candidate among these models which fit the most recent Planck data while predicting $r= 0.03$. We thus demonstrate that this class of small field models is an alternative to the class of large field models. The BICEP3 experiment and the Euclid and SPHEREx missions are expected to provide experimental evidence to support or refute our predictions.
The dependence of the turnover frequency on the linear size is presented for a sample of GPS and CSS radio sources derived from complete samples. The dependence of the luminosity of the emission at the peak frequency with the linear size and the peak frequency is also presented for the galaxies in the sample. The luminosity of the smaller sources evolve strongly with the linear size. Optical depth effects have been included to the 3D model for the radio source of Kaiser (2000) to study the spectral turnover. Using this model, the observed trend can be explained by synchrotron self absorption. The observed trend in the peak-frequency -- linear-size plane is not affected by the luminosity evolution of the sources.
Solutions of the wave equation in a space-time containing a thin cosmic string are examined in the context of non-linear generalised functions. Existence and uniqueness of solutions to the wave equation in the Colombeau algebra G is established for a conical space-time and this solution is shown to be associated to a distributional solution. A concept of generalised hyperbolicity, based on test fields, can be defined for such singular space-times and it is shown that a conical space-time is G-hyperbolic.
Many real networks have cliques as their constitutional units. Here we present a family of scale-free network model consist of cliques, which is established by a simple recursive algorithm. We investigate the networks both analytically and numerically. The obtained analytical solution shows that the networks follow a power-law degree distribution, with degree exponent continuously tuned between 2 and 3, coinciding with the empirically found results. The exact expression of clustering coefficient is also provided for the networks. Furthermore, the investigation of the average path length reveals that the networks possess small-world feature.
I review the current knowledge of high-energy emission from extragalctic jets. First I discuss gamma-ray emission from blazars, which provides us numerous precious information on the innermost portions of the relativistic jets. I describe the constraints on the dynamics of the jet from the subpc to the pc scale provided by recent VLBI studies of TeV sources, together with the modelling of the emission from the blazar jet. Finally I discuss high energy emission from large scale jets as seen by Chandra and I report on the expected gamma-ray emission from large-scale regions of jets.
$\alpha$ decay is treated microscopically, where the unstable mother nucleus and residual daughter nucleus are described using HFB wave functions, obtained with the Skyrme effective interaction. From these wave functions the amplitude for forming $\alpha$ particles in the mother nucleus is computed. Two different Skyrme parametrizations with different pairing properties are compared, and we find good agreement with experiment for relative decay rates in both cases. The absolute values of the decay rates are under-estimated.
The Epoch of Reionization (EoR)---when neutral hydrogen in the intergalactic medium was systematically ionized---is a period in our Universe's history that is currently poorly understood. However, a key prediction of most models is a correlation between the density and ionization field during the EoR. This has consequences for the 21cm power spectrum. Here, we propose a parametrization for the density-ionization correlation and study the dependence of the 21cm power spectrum on this parameterization. We use this formalism to forecast the ability of current and future observations to constrain these correlations. We find that upper limits on the dimensionless power spectrum at redshifts $7.5 < z < 8.5$ using $k$ bins between $0.1\,\textrm{Mpc}^{-1} < k < 0.75\,\textrm{Mpc}^{-1}$ with error bars at the level of $\sim\!\!20\,\textrm{mK}^2$ about our fiducial model would rule out uncorrelated reionization at $99\%$ credibility. Beyond upper limits, we find that at its full sensitivity, the Hydrogen Epoch of Reionization Array (HERA) will be able to place strong constraints on the sign and magnitude of density-ionization correlations.
In this paper we give a classification of the asymptotic expansion of the $q$-expansion of reciprocals of Eisenstein series $E_k$ of weight $k$ for the modular group $\func{SL}_2(\mathbb{Z})$. For $k \geq 12$ even, this extends results of Hardy and Ramanujan, and Berndt, Bialek and Yee, utilizing the Circle Method on the one hand, and results of Petersson, and Bringmann and Kane, developing a theory of meromorphic Poincar{\'e} series on the other. We follow a uniform approach, based on the zeros of the Eisenstein series with the largest imaginary part. These special zeros provide information on the singularities of the Fourier expansion of $1/E_k(z)$ with respect to $q = e^{2 \pi i z}$.
The main purpose of this master thesis is to study the $LS$-sequences of points introduced by Carbone in \cite{Carbone} and find two generalizations of them to the unit square. Here we also present a new algorithm proposed by the same author in \cite{Carbone2} and we implement it in order to have a graphical description of these sequences. Chapter 1 includes a collection of results concerning the uniform ditribution theory and the discrepancy (we refer to \cite{Drmota_Tichy} and \cite{Kuipers_Niederreiter} for a complete survey on the matter). In Chapter 2 we focuse our attention on the $LS$-sequences of partitions and of points in the unit interval, giving particular attention to the ordering of the points "\`{a} la van der Corput \rq\rq and finding a way to compute them related to the digit expansion of natural numbers in base $L+S$. In Chapter 3 we move on the unit square where we find two generalizations of the $LS$-sequences following the historical development of the van der Corput sequence in the multidimensional case. This is the reason why we call the first sequence $LS$- sequence of points \`{a} la van der Corput-Hammersley and the second one $LS$-sequence \`{a} la Halton.
We report a high-resolution neutron diffraction study on the orbitally-degenerate spin-1/2 hexagonal antiferromagnet AgNiO2. A structural transition to a tripled unit cell with expanded and contracted NiO6 octahedra indicates root(3) x root(3) charge order on the Ni triangular lattice. This suggests charge order as a possible mechanism of lifting the orbital degeneracy in the presence of charge fluctuations, as an alternative to Jahn-Teller distortions. A novel magnetic ground state is observed at base temperatures with the electron-rich S = 1 Ni sites arranged in alternating ferromagnetic rows on a triangular lattice, surrounded by a honeycomb network of non-magnetic and metallic Ni ions. We also report first-principles band-structure calculations that explain microscopically the origin of these phenomena.
Using a recently introduced 5D Riemann flat metric, we investigate the possibility of introducing dissipation in the dynamics of the inflaton field on an effective 4D FRW metric, in the framework of the STM theory of gravity.
We describe an infinite set of smooth projective threefolds that have equivalent derived categories but are not isomorphic, contrary to a conjecture of Kawamata. These arise as blow-ups of $\mathbb P^3$ at various configurations of 8 points, which are related by Cremona transformations.
We investigate the spectral properties of the UV ($\lambda\lambda$2650-3050 \AA) and optical ($\lambda\lambda$4000-5500 \AA) Fe II emission features in a sample of 293 type 1 active galactic nuclei (AGNs) from Sloan Digital Sky Survey (SDSS) database. We explore different correlations between their emission line properties, as well as the correlations with the other emission lines from the spectral range. We find several interesting correlations and we can outline the most interesting results as follows. (i) There is a kinematical connection between the UV and optical Fe II lines, indicating that the UV and optical Fe II lines originate from the outer part of the broad line region, so-called intermediate line region; (ii) The unexplained anticorrelations of the optical Fe II (EW Fe II$_{opt}$) versus EW [O III] 5007 \AA\ and EW Fe II$_{opt}$ versus FWHM Hbeta have not been detected for the UV Fe II lines; (iii) The significant averaged redshift in the UV Fe II lines, which is not present in optical Fe II, indicates an inflow in the UV Fe II emitting clouds, and probably their asymmetric distribution. (iv) Also, we confirm the anticorrelation between the intensity ratio of the optical and UV Fe II lines and FWHM of Hbeta, and we find the anticorrelations of this ratio with the widths of Mg II 2800 \AA, optical Fe II and UV Fe II. This indicates a very important role for the column density and microturbulence in the emitting gas. We discuss the starburst activity in high-density regions of young AGNs as a possible explanation of the detected optical Fe II correlations and intensity line ratios of the UV and optical Fe II lines.
We define graded, quasi-coherent $\mathcal{O}_S$-algebras over a given base derived scheme $S$, and show that these are equivalent to derived $\mathbb{G}_{m,S}$-schemes which are affine over $S$. We then use this $\mathbb{G}_{m,S}$-action to define the projective spectrum $\mathrm{Proj} (\mathcal{B})$ of a graded algebra $\mathcal{B}$ as a quotient stack, show that $\mathrm{Proj} (\mathcal{B})$ is representable by a derived scheme over $S$, and describe the functor of points of $\mathrm{Proj} (\mathcal{B})$ in terms of line bundles. The theory of graded algebras and projective spectra is then used to define the blow-up of a closed immersion of derived schemes. Our construction will coincide with the existing one for the quasi-smooth case. The construction is done by generalizing the extended Rees algebra to the derived setting, using Weil restrictions. We close by also generalizing the deformation to the normal cone to the derived setting.
Using MOPED we determine non-parametrically the star-formation and metallicity history of over 37,000 high-quality galaxy spectra from the Sloan Digital Sky Survey (SDSS) early data release. We use the entire spectral range, rather than concentrating on specific features, and we estimate the complete star formation history without prior assumptions about its form (by constructing so-called `population boxes'). The main results of this initial study are that the star formation rate in SDSS galaxies has been in decline for ~6 Gyr; a metallicity distribution for star-forming gas which is peaked ~3 Gyr ago at about solar metallicity, inconsistent with closed-box models, but consistent with infall models. We also determine the infall rate of gas in SDSS and show that it has been significant for the last 3 Gyr. We investigate errors using a Monte-Carlo Markov Chain algorithm. Further, we demonstrate that recovering star formation and metallicity histories for such a large sample becomes intractable without data compression methods, particularly the exploration of the likelihood surface. By exploring the whole likelihood surface we show that age-metallicity degeneracies are not as severe as by using only a few spectral features. We find that 65% of galaxies contain a significant old population (with an age of at least 8 Gyr), including recent starburst galaxies, and that over 97% have some stars older than 2 Gyr. It is the first time that the past star formation history has been determined from the fossil record of the present-day spectra of galaxies.