ShantanuT01/DACTYL-Pretraining huggingface dataset:
In this note, we explicitly compute the vacuum expectation value of the commutator of scalar fields in a d-dimensional conformal field theory on the cylinder. We find from explicit calculations that we need smearing not only in space but also in time to have finite commutators except for those of free scalar operators. Thus the equal time commutators of the scalar fields are not well-defined for a non-free conformal field theory, even if which is defined from the Lagrangian. We also have the commutator for a conformal field theory on Minkowski space, instead of the cylinder, by taking the small distance limit. For the conformal field theory on Minkowski space, the above statements are also applied.
Quantum correlations between two free spinless dissipative distinguishable particles (interacting with a thermal bath) are studied analytically using the quantum master equation and tools of quantum information. Bath-induced coherence and correlations in an infinite-dimensional Hilbert space are shown. We show that for temperature T > 0 the time-evolution of the reduced density matrix cannot be written as the direct product of two independent particles. We have found a time-scale that characterizes the time when the bath-induced coherence is maximum before being wiped out by dissipation (purity, relative entropy, spatial dispersion, and mirror correlations are studied). The Wigner function associated to the Wannier lattice (where the dissipative quantum walks move) is studied as an indirect measure of the induced correlations among particles. We have supported the quantum character of the correlations by analyzing the geometric quantum discord.
Z' exclusion limits and errors of Z' model measurements are compared for different reactions at future linear colliders. The influence of the c.m. energy, integrated luminosity, beam polarization and systematic errors is discussed. The sensitivity to a Z' depends only on the product Ls and not on the integrated luminosity and the c.m. energy separately.
We have employed the GMRT and the VLA to map the Lockman Hole. At 610 and 1,400 MHz, we reach noise levels of 15 and 6 uJy/beam, respectively, with well-matched resolutions (~5"). At this depth we obtained reliable detections for about half of the known submm galaxies (SMGs) in the field. For radio-identified SMGs, which are typically at z ~ 2, we measure a mean radio spectral index of alpha = -0.75 +/- 0.06 and standard deviation of 0.29, between rest-frame ~1.8 and ~4.2 GHz. The slope of their continuum emission is indistinguishable from that of local star-forming galaxies and suggests that extended optically-thin synchrotron emission dominates the radio output of SMGs. Cooling effects by synchrotron emission and Inverse Compton scattering off the CMB do not seem to affect their radio SEDs. For those SMGs judged by Spitzer mid-IR colours and spectroscopy to host obscured AGN, we find a clear deviation from the rest of the sample - they typically have steeper radio spectral indices, alpha ~< -1.0. These findings suggest these mid-IR-/AGN-selected SMGs may have an intrinsically different injection mechanism for relativistic particles, or they might reside in denser environments. This work provides a reliable spectral template for the estimation of far-IR/radio photometric redshifts, and will enable accurate statistical K-corrections for the large samples of SMGs expected with SCUBA-2 and Herschel.
In the standard cosmological model, the dimming of distant Type Ia supernovae is explained by invoking the existence of repulsive `dark energy' which is causing the Hubble expansion to accelerate. However this may be an artifact of interpreting the data in an (oversimplified) homogeneous model universe. In the simplest inhomogeneous model which fits the SNe Ia Hubble diagram without dark energy, we are located close to the centre of a void modelled by a Lema\'itre-Tolman-Bondi metric. It has been claimed that such models cannot fit the CMB and other cosmological data. This is however based on the assumption of a scale-free spectrum for the primordial density perturbation. An alternative physically motivated form for the spectrum enables a good fit to both SNe Ia (Constitution/Union2) and CMB (WMAP 7-yr) data, and to the locally measured Hubble parameter. Constraints from baryon acoustic oscillations and primordial nucleosynthesis are also satisfied.
We review some of the properties of chameleon theories. Chameleon fields are gravitationally coupled to matter and evade gravitational tests thanks to two fundamental properties. The first one is the density dependence of the chameleon mass. In most cases, in a dense environment, chameleons are massive enough to induce a short ranged fifth force. In other cases, non-linear effects imply the existence of a thin shell effect shielding compact bodies from each other and leading to an irrelevant fifth force. We also mention how a natural extension of chameleon theories can play a role to solve the PVLAS versus CAST discrepancy.
Broken symmetry is the essence of exotic properties in condensed matters. Tungsten ditelluride, WTe$_2$, exceptionally takes a non-centrosymmetric crystal structure in the family of transition metal dichalcogenides, and exhibits novel properties$^{1-4}$, such as the nonsaturating magnetoresistance$^1$ and ferroelectric-like behavior$^4$. Herein, using the first-principles calculation, we show that unique layer stacking in WTe$_2$ generates surface dipoles with different strengths on the top and bottom surfaces in few-layer WTe$_2$. This leads to a layer-dependence for electron/hole carrier ratio and the carrier compensation responsible for the unusual magnetoresistance. The surface dipoles are tunable and switchable using the interlayer shear displacement. This could explain the ferroelectric-like behavior recently observed in atomically thin WTe$_2$ films$^4$. In addition, we reveal that exfoliation of the surface layer flips the out-of-plane spin textures. The presented results will aid in the deeper understanding, manipulation, and further exploration of the physical properties of WTe$_2$ and related atom-layered materials, for applications in electronics and spintronic devices.
Automatic parsing of anatomical objects in X-ray images is critical to many clinical applications in particular towards image-guided invention and workflow automation. Existing deep network models require a large amount of labeled data. However, obtaining accurate pixel-wise labeling in X-ray images relies heavily on skilled clinicians due to the large overlaps of anatomy and the complex texture patterns. On the other hand, organs in 3D CT scans preserve clearer structures as well as sharper boundaries and thus can be easily delineated. In this paper, we propose a novel model framework for learning automatic X-ray image parsing from labeled CT scans. Specifically, a Dense Image-to-Image network (DI2I) for multi-organ segmentation is first trained on X-ray like Digitally Reconstructed Radiographs (DRRs) rendered from 3D CT volumes. Then we introduce a Task Driven Generative Adversarial Network (TD-GAN) architecture to achieve simultaneous style transfer and parsing for unseen real X-ray images. TD-GAN consists of a modified cycle-GAN substructure for pixel-to-pixel translation between DRRs and X-ray images and an added module leveraging the pre-trained DI2I to enforce segmentation consistency. The TD-GAN framework is general and can be easily adapted to other learning tasks. In the numerical experiments, we validate the proposed model on 815 DRRs and 153 topograms. While the vanilla DI2I without any adaptation fails completely on segmenting the topograms, the proposed model does not require any topogram labels and is able to provide a promising average dice of 85% which achieves the same level accuracy of supervised training (88%).
We conduct photoluminescence microscopy that is sensitive to both electron and nuclear spin polarization to investigate the changes that occur in the magnetic ordering in the vicinity of the first integer quantum Hall state in a GaAs 2D electron system (2DES). We observe a discontinuity in the electron spin polarization and nuclear spin longitudinal relaxation time which heralds a spontaneous transition to a phase of magnetic skyrmions. We image in real space the spin phase domains that coexist at this transition, and observe hysteresis in their formation as a function of the 2DES's chemical potential. Based on measurements in a tilted magnetic field orientation, we found that the transition is protected by an energy gap containing the Zeeman energy, and conclude that the skyrmions here have formed as an ensemble.
Suspended graphene membrane presents a particular structure with fundamental interests and applications in nanomechanics, thermal transport and optoelectronics. Till now, the commonly used geometries are still quite simple and limited to the microscale. We propose here to overcome this problem by making nanostructures in suspended epitaxial bilayer graphene on a large scale and with a large variety of geometries. We also demonstrate a new hybrid thin film of SiC-graphene with an impressive robustness. Since the mechanics and thermal dissipation of a suspended graphene membrane are strongly related to its own geometry, we have in addition focused on thermal transport and strain engineering experiments. Micro-Raman spectroscopy mapping was successfully performed for various geometries with intrinsic properties measurements at the nanoscale. Our engineering of graphene geometry has permitted to reduce the thermal transport, release and modulate the strain in our structures.
From next generation gas turbines to scavenging waste heat from car exhausts, finding new materials with ultra-low thermal conductivity ($\kappa$) has the potential to lead to large gains in device efficiency. Crystal structures with inherently low $\kappa$ are consequently desirable, but candidate materials are rare and often difficult to make. Using first principles calculations and inelastic neutron scattering we have studied the pyrochlore La$_2$Zr$_2$O$_7$ which has been proposed as a next generation thermal barrier. We find that there is a highly anharmonic, approximately flat, vibrational mode associated with the kagome planes. Our results suggest that this mode is responsible for the low thermal conductivity observed in the pyrochlores and that kagome compounds will be a fruitful place to search for other low $\kappa$ materials.
The low frequency (110--180 MHz) capabilities of the Westerbork Synthesis Radio Telescope (WSRT) are used to characterise a large collection of single pulses from three low magnetic field pulsars. Using the Pulsar Machine II (PuMa-II) to acquire and coherently dedisperse the pulsar signals, we examine whether the bright pulses observed in these pulsars are related to the classical giant pulse emission. Giant pulses are reported from PSR B1112$+$50 and bright pulses from the PSRs B1133$+$16 and B0031$-$07. These pulsars also exhibit large intensity modulations observed as rapid changes in the single pulse intensity. Evidence of global magnetospheric effects is provided by our detection of bright double pulses in PSRs B0031$-$07 and B1133$+$16. Using the multi-frequency observations, we accurately determine the dispersion measures (4.844$\pm$0.002 for B1133$+$16 and 9.1750$\pm$0.0001 for B1112$+$50), derive the radio emission height in PSR B1133$+$16 and report on the properties of subpulse drift modes in these pulsars. We also find that these pulsars show a much larger intensity modulation at low sky frequencies resulting in narrow and bright emissions.
Prior highly-tuned image parsing models are usually studied in a certain domain with a specific set of semantic labels and can hardly be adapted into other scenarios (e.g., sharing discrepant label granularity) without extensive re-training. Learning a single universal parsing model by unifying label annotations from different domains or at various levels of granularity is a crucial but rarely addressed topic. This poses many fundamental learning challenges, e.g., discovering underlying semantic structures among different label granularity or mining label correlation across relevant tasks. To address these challenges, we propose a graph reasoning and transfer learning framework, named "Graphonomy", which incorporates human knowledge and label taxonomy into the intermediate graph representation learning beyond local convolutions. In particular, Graphonomy learns the global and structured semantic coherency in multiple domains via semantic-aware graph reasoning and transfer, enforcing the mutual benefits of the parsing across domains (e.g., different datasets or co-related tasks). The Graphonomy includes two iterated modules: Intra-Graph Reasoning and Inter-Graph Transfer modules. The former extracts the semantic graph in each domain to improve the feature representation learning by propagating information with the graph; the latter exploits the dependencies among the graphs from different domains for bidirectional knowledge transfer. We apply Graphonomy to two relevant but different image understanding research topics: human parsing and panoptic segmentation, and show Graphonomy can handle both of them well via a standard pipeline against current state-of-the-art approaches. Moreover, some extra benefit of our framework is demonstrated, e.g., generating the human parsing at various levels of granularity by unifying annotations across different datasets.
The Muskat problem involves filtration of two incompressible fluids throughout a porous medium. In this paper we shall discuss in 3-D the relevance of the Rayleigh-Taylor condition, and the topology of the initial interface, in order to prove its local existence in Sobolev spaces.
The measurement of the spin frequency in accreting millisecond X-ray pulsars (AMXPs) is strongly affected by the presence of an unmodeled component in the pulse arrival times called 'timing noise'. We show that it is possible to attribute much of this timing noise to a pulse phase offset that varies in correlation with X-ray flux, such that noise in flux translates into timing noise. This could explain many of the pulse frequency variations previously interpreted in terms of true spin up or spin down, and would bias measured spin frequencies. Spin frequencies improved under this hypothesis are reported for six AMXPs. The effect would most easily be accounted for by an accretion rate dependent hot spot location.
Mixed modes seen in evolved stars carry information on their deeper layers that can place stringent constraints on their physics and on their global properties (mass, age, etc...). In this study, we present a method to identify and measure all oscillatory mode characteristics (frequency, height, width). Analyzing four subgiants stars, we present the first measure of the effect of the degree of mixture on the l=1 mixed modes characteristics. We also show that some stars have measurable l=2 mixed modes and discuss the interest of their measure to constrain the deeper layers of stars.
We study the primitive divisors of the terms of $(\Delta_n)_{n \geq 1}$, where $\Delta_n=N_{K/ \mathbb{Q}}(u^n-1)$ for $K$ a real quadratic field, and $u>1$ a unit element of its ring of integers. The methods used allow us to find the terms of the sequence that do not have a primitive prime divisor.
We report on tunneling measurements that reveal for the first time the evolution of the quasi-particle state density across the bandwidth controlled Mott metal to insulator transition in the rare earth perovskite nickelates. In this, a canonical class of transition metal oxides, we study in particular two materials close to the T=0 metal-insulator transition: NdNiO3 , an antiferromagnetic insulator, and LaNiO3, a correlated metal. We measure a sharp gap in NdNiO3, which has an insulating ground state, of ~ 30 meV. Remarkably, metallic LaNiO3 exhibits a pseudogap of the same order that presages the metal insulator transition. The smallness of both the gap and pseudogap suggests they arise from a common origin: proximity to a quantum critical point at or near the T=0 metal-insulator transition. It also supports theoretical models of the quantum phase transition in terms of spin and charge instabilities of an itinerant Fermi surface.
Thermoelectric properties of single crystal Ta2PdSe6 is investigated by means of transport measurements, and a density functional calculation. We found a giant Peltier conductivity of 100 Acm-1K-1 at 10 K and successfully explained it by means of conventional semiconductor theory. We concluded that an uncompensated semimetal, high mobility, and heavy effective mass are responsible for the giant Peltier conductivity. Our finding opens a new ground in the field of thermoelectrics to explore much better semimetals for a new possible application such as an electric current generator for a superconducting magnet.
We present a compendium of disk galaxy scaling relations and a detailed characterization of their intrinsic scatter. Observed scaling relations are typically characterized by their slope, intercept, and scatter; however, these parameters are a mixture of observational errors and astrophysical processes. We introduce a novel Bayesian framework for computing the intrinsic scatter of scaling relations that accounts for nonlinear error propagation and covariant uncertainties. Bayesian intrinsic scatters are ~25percent more accurate than those obtained with a first-order classical method, which systematically underestimates the true intrinsic scatter. Structural galaxy scaling relations based on velocity (V23.5), size (R23.5), luminosity (L23.5), colour (g-z), central stellar surface density (Sigma1), stellar mass (M*), dynamical mass (Mdyn), stellar angular momentum (j*), and dynamical angular momentum (jdyn), are examined to demonstrate the power and importance of the Bayesian formalism. Our analysis is based on a diverse selection of over 1000 late-type galaxies from the Photometry and Rotation Curve Observations from Extragalactic Surveys compilation with deep optical photometry and extended rotation curves. We determine the tightest relation for each parameter by intrinsic orthogonal scatter, finding M*-V23.5, R23.5-j*, and L23.5-jdyn to be especially tight. The scatter of the R23.5-L23.5, V23.5-(g-z), and R23.5-jdyn relations is mostly intrinsic, making them ideal for galaxy formation and evolutionary studies. Our code to compute the Bayesian intrinsic scatter of any scaling relation is also presented. We quantify the correlated nature of many uncertainties in galaxy scaling relations and scrutinize the uncertain nature of disk inclination corrections and their effect on scatter estimates.
We prove that the maximum determinant of an $n \times n $ matrix, with entries in $\{0,1\}$ and at most $n+k$ non-zero entries, is at most $2^{k/3}$, which is best possible when $k$ is a multiple of 3. This result solves a conjecture of Bruhn and Rautenbach. We also obtain an upper bound on the number of perfect matchings in $C_4$-free bipartite graphs based on the number of edges, which, in the sparse case, improves on the classical Bregman's inequality for permanents. This bound is tight, as equality is achieved by the graph formed by vertex disjoint union of 6-vertex cycles.
We measure the strength, frequency, and timescale of tidally triggered star formation at redshift z=0.08-0.38 in a spectroscopically complete sample of galaxy pairs drawn from the magnitude-limited redshift survey of 9,825 Smithsonian Hectospec Lensing Survey (SHELS) galaxies with R<20.3. To examine the evidence for tidal triggering, we identify a volume-limited sample of major (|\Delta M_R|<1.75, corresponding to mass ratio >1/5) pair galaxies with $M_R < -20.8 in the redshift range z=0.08-0.31. The size and completeness of the spectroscopic survey allows us to focus on regions of low local density. The spectrophotometric calibration enables the use of the 4000 Ang break (D_n4000), the H\alpha specific star formation rate (SSFR_{H\alpha}), and population models to characterize the galaxies. We show that D_n4000 is a useful population classification tool; it closely tracks the identification of emission line galaxies. The sample of major pair galaxies in regions of low local density with low D_n4000 demonstrates the expected anti-correlation between pair-wise projected separation and a set of star formation indicators explored in previous studies. We measure the frequency of triggered star formation by comparing the SSFR_{H\alpha} in the volume-limited sample in regions of low local density: 32 +/-7% of the major pair galaxies have SSFR_{H\alpha} at least double the median rate of the unpaired field galaxies. Comparison of stellar population models for pair and for unpaired field galaxies implies a timescale for triggered star formation of ~300-400 Myr.
The Tarleton Observatory's 0.8m telescope and CCD photometer were used to obtain 1298 observations of the short period eclipsing binary star MW And. The observations were obtained in Johnson's BVR filters. The light curves show that MW And is an eclipsing binary star with a period of 0.26376886 days. Further analysis showed that the period of MW And is changing at the rate of 0.17sec/year. The photometric solutions were obtained using the 2015 version of the Wilson-Devinney model. The solutions show that MW And is an eclipsing binary star of W UMa type. Our analysis suggests that the system has a light curve of W-subtype contact system. Its spectral type of K0/K1, as estimated from its color, places it in the Zero-Age contact zone of the period-spectral diagram. Luminosity from the solutions indicate that it is a double-line spectroscopic system and therefore, spectroscopic observations are recommended for further detail study.
Exact analytical expressions for the $\Delta S=1$ coupling $\im G_E$ in terms of observable spectral functions are given. This coupling determines the size of the $\Delta I=3/2$ contribution to $\epsilon'$. We show analytically how the scheme-dependence and scale dependences vanish to all orders in $1/N_c$ and NLO in $\alpha_S$ explicitly both for $Q_7$ and $Q_8$.   Numerical results are derived for both $Q_7$ and $Q_8$ from the $\tau$-data and known results on the scalar spectral functions. In particular we study the effect of all higher dimension operators.   The coefficients of the leading operators in the OPE of the needed correlators are derived to NLO in $\alpha_S$.
We review the current status of the understanding how the accretion onto the central black hole proceeds in Active Galaxies. Standard accretion disk is a key element in all relatively bright active galaxies like Seyferts and quasars, although it is not present in very low luminosity sources, like Sgr A*. However, the standard disk does not explain the broad band spectrum, so the disk has to be supplemented with a number of additional components, and our deeper understanding of these components is still far from being complete. These additional elements are: compact hard X-ray corona, inner hot flow, warm corona, disk wind and the Broad Line Region, and finally dusty/molecular torus. All these elements seem to be needed in various proportions, depending predominantly on the Eddington ratio of a given source. These elements also interact with each other which is not yet fully taken into account.
We consider a class of nonlocal generalized perimeters which includes fractional perimeters and Riesz type potentials. We prove a general isoperimetric inequality for such functionals, and we discuss some applications. In particular we prove existence of an isoperimetric profile, under suitable assumptions on the interaction kernel.