ShantanuT01/DACTYL-Pretraining huggingface dataset:
Point cloud based retrieval for place recognition is still a challenging problem due to drastic appearance and illumination changes of scenes in changing environments. Existing deep learning based global descriptors for the retrieval task usually consume a large amount of computation resources (e.g., memory), which may not be suitable for the cases of limited hardware resources. In this paper, we develop an efficient point cloud learning network (EPC-Net) to form a global descriptor for visual place recognition, which can obtain good performance and reduce computation memory and inference time. First, we propose a lightweight but effective neural network module, called ProxyConv, to aggregate the local geometric features of point clouds. We leverage the spatial adjacent matrix and proxy points to simplify the original edge convolution for lower memory consumption. Then, we design a lightweight grouped VLAD network (G-VLAD) to form global descriptors for retrieval. Compared with the original VLAD network, we propose a grouped fully connected (GFC) layer to decompose the high-dimensional vectors into a group of low-dimensional vectors, which can reduce the number of parameters of the network and maintain the discrimination of the feature vector. Finally, to further reduce the inference time, we develop a simple version of EPC-Net, called EPC-Net-L, which consists of two ProxyConv modules and one max pooling layer to aggregate global descriptors. By distilling the knowledge from EPC-Net, EPC-Net-L can obtain discriminative global descriptors for retrieval. Extensive experiments on the Oxford dataset and three in-house datasets demonstrate that our proposed method can achieve state-of-the-art performance with lower parameters, FLOPs, and runtime per frame.
In the present work we report a study on the viscous extended holographic Ricci dark energy (EHRDE) model under the assumption of existence of bulk viscosity in the linear barotropic fluid and the EHRDE in the framework of standard Eckart theory of relativistic irreversible thermodynamics and it has been observed that the non-equilibrium bulk viscous pressure is significantly smaller than the local equilibrium pressure. We have studied the equation of state (EoS) parameter and observed that the EoS behaves like "quintom" and is consistent with the constraints set by observational data sets from SNLS3, BAO and Planck + WMAP9 + WiggleZ measurements in the reference S. Kumar and L. Xu, \emph{Phys. Lett. B},\textbf{737}, 244 (2014). Analysis of statefinder parameters has shown the possibility of attainment of $\Lambda$CDM phase under current model and at the same time it has been pointed out that the for $z=0$ i.e. current universe, the statefinder pair is different from that of $\Lambda$CDM and the $\Lambda$CDM can be attained in a later stage of the universe. An analysis of stability has shown that although the viscous EHRDE along with viscous barotropic is classically unstable in the present epoch, it can lead to a stable universe in very late stage. Considering an universe enveloped by event horizon we have observed validity of generalized second law of thermodynamics.
We present a novel reconfigurable metal-oxide-semiconductor multi-gate transistor that can host a quadruple quantum dot in silicon. The device consist of an industrial quadruple-gate silicon nanowire field-effect transistor. Exploiting the corner effect, we study the versatility of the structure in the single quantum dot and the serial double quantum dot regimes and extract the relevant capacitance parameters. We address the fabrication variability of the quadruple-gate approach which, paired with improved silicon fabrication techniques, makes the corner state quantum dot approach a promising candidate for a scalable quantum information architecture.
Pairing properties of even-even superheavy N=184 isotones are studied within the Skyrme-Hartree-Fock+BCS approach. In the particle-hole channel we take the Skyrme energy density functional SLy4, while in the particle-particle channel we employ the seniority pairing force and zero-range delta-interactions with different forms of density dependence. We conclude that the calculated static fission trajectories weakly depend on the specific form of the delta-pairing interaction. We also investigate the impact of triaxiality on the inner fission barrier and find a rather strong Z dependence of the effect.
Parametric downconversion (PDC) in semiconductor Bragg-reflection waveguides (BRW) is routinely exploited for photon-pair generation in the telecommunication range. Contrary to many conventional PDC sources, BRWs offer possibilities to create spectrally broadband but nevertheless indistinguishable photon pairs in orthogonal polarizations that simultaneously incorporate high frequency entanglement. We explore the characteristics of co-propagating twin beams created in a type-II ridge BRW. Our PDC source is bright and efficient, which serves as a benchmark of its performance and justifies its exploitation for further use in quantum photonics. We then examine the coalescence of the twin beams and investigate the effect of their inevitable multi-photon contributions on the observed photon bunching. Our results show that BRWs have a great potential for producing broadband indistinguishable photon pairs as well as multi-photon states.
In this paper we examine the subset of Farey fractions of order Q consisting of those fractions whose denominators are odd. In particular, we consider the frequencies of values of numerators of differences of consecutive elements in this set. After proving an asymptotic result for these frequencies, we use estimates coming from incomplete Kloosterman sums to generalize our result to subintervals of [0,1].
The recent progress in the localized covariant density functional constrained by the relativistic Hartree-Fock theory is briefly presented by taking the Gamow-Teller resonance in 90Zr as an example. It is shown that the constraints introduced by the Fock terms into the particle-hole residual interactions are straight forward and robust.
Electron tunneling is associated with light emission. In order to elucidate its generating mechanism, we provide a novel experimental ansatz that employs fixed-distance epitaxial graphene as metallic electrodes. In contrast to previous experiments, this permits an unobscured light spread from the tunnel junction, enabling both a reliable calibration of the visible to infrared emission spectrum and a detailed analysis of the dependence of the parameters involved. In an open, non-resonant geometry, the emitted light is perfectly characterized by a Planck spectrum. In an electromagnetically resonant environment, resonant radiation is added to the thermal spectrum, both being strictly proportional in intensity. In full agreement with a simple heat conduction model, we provide evidence that in both cases the light emission stems from a hot electronic subsystem in interaction with its linear electromagnetic environment. These very clear results should resolve any ambiguity about the mechanism of light emission in nano contacts.
We study various aspects of black holes and gravitational collapse in Einstein-Yang-Mills theory under the assumption of spherical symmetry. Numerical evolution on hyperboloidal surfaces extending to future null infinity is used. We begin by constructing colored and Reissner-Nordstrom black holes on surfaces of constant mean curvature and analyze their perturbations. These linearly perturbed black holes are then evolved into the nonlinear regime and the masses of the final Schwarzschild black holes are computed as a function of the initial horizon radius. We compare with an information-theoretic bound on the lifetime of unstable hairy black holes derived by Hod. Finally we study critical phenomena in gravitational collapse at the threshold between different Yang-Mills vacuum states of the final Schwarzschild black holes, where the n=1 colored black hole forms the critical solution. The work of Choptuik et al. (1999) is extended by using a family of initial data that includes another region in parameter space where the colored black hole with the opposite sign of the Yang-Mills potential forms the critical solution. We investigate the boundary between the two regions and discover that the Reissner-Nordstrom solution appears as a new approximate codimension-two attractor.
We report on the experimental demonstration and electrical characterization of N = 7 armchair graphene nanoribbon (7-AGNR) field effect transistors. The back-gated transistors are fabricated from atomically precise and highly aligned 7-AGNRs, synthesized with a bottom-up approach. The large area transfer process holds the promise of scalable device fabrication with atomically precise nanoribbons. The channels of the FETs are approximately 30 times longer than the average nanoribbon length of 30 nm to 40 nm. The density of the GNRs is high, so that transport can be assumed well-above the percolation threshold. The long channel transistors exhibit a maximum I$_{ON}$/I$_{OFF}$ current ratio of 87.5.
In this paper, we report results for the wave packet dynamics in a class of quasiperiodic chains consisting of two types of weakly coupled clusters. The dynamics are studied by means of the return probability and the mean square displacement. The wave packets show anomalous diffusion in a stepwise process of fast expansion followed by time intervals of confined wave packet width. Applying perturbation theory, where the coupling parameter v is treated as perturbation, the properties of the eigenstates of the system are investigated and related to the structure of the chains. The results show the appearance of non-localized states only in sufficiently high orders of the perturbation expansions. Further, we compare these results to the exact solutions obtained by numerical diagonalization. This shows that eigenstates spread across the entire chain for v>0, while in the limit v->0 ergodicity is broken and eigenstates only spread across clusters of the same type, in contradistinction to trivial localization for v=0. Caused by this ergodicity breaking, the wave packet dynamics change significantly in the presence of an impurity offering the possibility to control its long-term dynamics.
In this work, we observe the rigidity percolation phenomena in a fast ion conducting, conditional glass forming system (AgI)75-x-(Ag2O)25-(MoO3)x. To find out where, why and how the rigidity percolation phenomenon occurs within the range of 20 < x < 37.5, calorimetry and photoelectron spectroscopy experiments are performed. The temperature dependence of heat capacity (normalized) at glass transition temperature (Tg), exhibits fluctuations for samples with higher AgI concentration. This specific quality attributes to fragile glass. The wide range of composition accommodates both the fragile and strong glasses, and therefore a fragility threshold. The heat capacity (absolute) values, at Tg when plotted over the whole range of compositions, exhibits an abrupt sign shift, from negative to positive, revealing the fragility threshold. The appearance of negative heat capacity has been corroborated with the thermodynamic behavior of nanoclusters. This technique has been identified as a novel method to recognize the existence of nanoclusters in this type of glasses. The photoelectron spectroscopy study shows the formation of essential covalent structural units, [- Mo - O - Ag - O -] and complex molybdenum oxides in the positive heat capacity region. Finally, the non-reversing enthalpy profile has been studied over the whole composition range. The global, square well minima sandwiched between floppy and stress rigid region has been identified to be the intermediate phase, within the range 32.25 < x < 35.
The magnetic field of a sunspot guides magnetohydrodynamic waves toward higher atmospheric layers. In the upper photosphere and lower chromosphere, wave modes with periods longer than the acoustic cut-off period become evanescent. The cut-off period essentially changes due to the atmospheric properties, e.g., increases for larger zenith inclinations of the magnetic field. In this work, we aim at introducing a novel technique of reconstructing the magnetic field inclination on the basis of the dominating wave periods in the sunspot chromosphere and upper photosphere. On 2013 August 21st, we observed an isolated, circular sunspot (NOAA11823) for 58 min in a purely spectroscopic multi-wavelength mode with the Interferometric Bidimensional Spectro-polarimeter (IBIS) at the Dunn Solar Telescope. By means of a wavelet power analysis, we retrieved the dominating wave periods and reconstructed the zenith inclinations in the chromosphere and upper photosphere. The results are in good agreement with the lower photospheric HMI magnetograms. The sunspot's magnetic field in the chromosphere inclines from almost vertical (0$^{\circ}$) in the umbra to around 60$^{\circ}$ in the outer penumbra. With increasing altitude in the sunspot atmosphere, the magnetic field of the penumbra becomes less inclined. We conclude that the reconstruction of the magnetic field topology on the basis of sunspot oscillations yields consistent and conclusive results. The technique opens up a new possibility to infer the magnetic field inclination in the solar chromosphere.
In this paper we study number fields which are Euclidean with respect to a function different from the absolute value of the norm. We also show that the Euclidean minimum with respect to weighted norms may be irrational and not isolated.
Carbon monoxide (CO) is one of the primary coolants of gas and an easily accessible tracer of molecular gas in spiral galaxies but it is unclear if CO plays a similar role in metal poor dwarfs. We carried out a deep observation with IRAM 30 m to search for CO emission by targeting the brightest far-IR peak in a nearby extremely metal poor galaxy, Sextans A, with 7% Solar metallicity. A weak CO J=1-0 emission is seen, which is already faint enough to place a strong constraint on the conversion factor (a_CO) from the CO luminosity to the molecular gas mass that is derived from the spatially resolved dust mass map. The a_CO is at least seven hundred times the Milky Way value. This indicates that CO emission is exceedingly weak in extremely metal poor galaxies, challenging its role as a coolant in these galaxies.
We have used images and spectra of the Sloan Digital Sky Survey to examine the host galaxies of 519 nearby supernovae. The colors at the sites of the explosions, as well as chemical abundances, and specific star formation rates of the host galaxies provide circumstantial evidence on the origin of each supernova type. We examine separately SN II, SN IIn, SN IIb, SN Ib, SN Ic, and SN Ic with broad lines (SN Ic-BL). For host galaxies that have multiple spectroscopic fibers, we select the fiber with host radial offset most similar to that of the SN. Type Ic SN explode at small host offsets, and their hosts have exceptionally strongly star-forming, metal-rich, and dusty stellar populations near their centers. The SN Ic-BL and SN IIb explode in exceptionally blue locations, and, in our sample, we find that the host spectra for SN Ic-BL show lower average oxygen abundances than those for SN Ic. SN IIb host fiber spectra are also more metal-poor than those for SN Ib, although a significant difference exists for only one of two strong-line diagnostics. SN Ic-BL host galaxy emission lines show strong central specific star formation rates. In contrast, we find no strong evidence for different environments for SN IIn compared to the sites of SN II. Because our supernova sample is constructed from a variety of sources, there is always a risk that sampling methods can produce misleading results. We have separated the supernovae discovered by targeted surveys from those discovered by galaxy-impartial searches to examine these questions and show that our results do not depend sensitively on the discovery technique.
We investigate the gluon transverse momentum dependent correlators as Fourier transform of matrix elements of nonlocal operator combinations. At the operator level these correlators include both field strength operators and gauge links bridging the nonlocality. In contrast to the collinear PDFs, the gauge links are no longer unique for transverse momentum dependent PDFs (TMDs) and also Wilson loops lead to nontrivial effects. We look at gluon TMDs for unpolarized, vector and tensor polarized targets. In particular a single Wilson loop operators become important when one considers the small-x limit of gluon TMDs.
We have systematically studied the S-wave pseudoscalar meson and heavy vector meson scattering lengths to the third order with the chiral perturbation theory, which will be helpful to reveal their strong interaction. For comparison, we have presented the numerical results of the scattering lengths (1) in the framework of the heavy meson chiral perturbation theory and (2) in the framework of the infrared regularization. The chiral expansion converges well in some channels.
As an alternative way of describing the cosmological velocity field, we discuss the evolution of rotational invariants constructed from the velocity gradient tensor. Compared with the traditional divergence-vorticity decomposition, these invariants, defined as coefficients of characteristic equation of the velocity gradient tensor, enable a complete classification of all possible flow patterns in the dark-matter comoving frame, including both potential and vortical flows. We show that this tool, first introduced in turbulence two decades ago, proves to be very useful in understanding the evolution of the cosmic web structure, and in classifying its morphology. Before shell-crossing, different categories of potential flow are highly associated with cosmic web structure, because of the coherent evolution of density and velocity. This correspondence is even preserved at some level when vorticity is generated after shell-crossing. The evolution from the potential to vortical flow can be traced continuously by these invariants. With the help of this tool, we show that the vorticity is generated in a particular way that is highly correlated with the large-scale structure. This includes a distinct spatial distribution and different types of alignment between cosmic web and vorticity direction for various vortical flows. Incorporating shell-crossing into closed dynamical systems is highly non-trivial, but we propose a possible statistical explanation for some of these phenomena relating to the internal structure of the three-dimensional invariants space.
Dynamical interactions in binary systems are thought to play a major role in the formation of extreme horizontal branch stars (EHBs) in the Galactic field. However, it is still unclear if the same mechanisms are at work in globular clusters, where EHBs are predominantly single stars. Here we report on the discovery of a unique close binary system (period ~1.61 days) in the globular cluster NGC6752, comprising an EHB and a main-sequence companion of 0.63+-0.05 Msun. Such a system has no counterpart among nearly two hundred known EHB binaries in the Galactic field. Its discovery suggests that either field studies are incomplete, missing this type of systems possibly because of selection effects, or that a particular EHB formation mechanism is active in clusters but not in the field.
We give a recipe relating holomorphic quantities in supersymmetric field theory to their descendants in non-supersymmetric Z_2 orbifold field theories. This recipe, consistent with a recent proposal of Strassler, gives exact results for bifermion condensates, domain wall tensions and gauge coupling constants in the planar limit of the orbifold theories.
We are interested in predator-prey dynamics on infinite trees, which can informally be seen as particular two-type branching processes where individuals may die (or be infected) only after their parent dies (or is infected). We study two types of such dynamics: the chase-escape process, introduced by Kordzakhia with a variant by Bordenave, and the birth-and-assassination process, introduced by Aldous & Krebs. We exhibit a coupling between these processes and branching random walks starting from a random point and killed at the barrier 0. This sheds new light on the chase-escape and birth-and-assassination processes, which allows us to recover by probabilistic means previously known results and also to obtain new results. For instance, we find the asymptotic behavior of tail of the number of infected individuals in both the subcritical and critical regimes for the chase-escape process, and show that the birth-and-assassination process ends almost surely at criticality.
Though most fermionic Mott insulators order at low temperatures, ordering is ancillary to their insulating behaviour. Our emphasis here is on disentangling ordering from the intrinsic strongly correlated physics of a doped half-filled band. To this end, we focus on the 2D Hubbard model. Because the charge gap arises from on-site correlations, we implement a non-perturbative approach which incorporates local physics. Crucial to this method is a self-consistent two-site dynamical cluster expansion which builds in the nearest-neighbour energy scale, $J$.   At half-filling, we find that the spectral function possesses a gap of order $U$ and is devoid of any coherent quasi-particle peaks. In the doped case, we find that the Fermi surface exceeds the Luttinger volume. Additionally in the underdoped regime, we find that a pseudogap opens in the single particle density of states.The pseudogap closes above optimal doping and hence our proposal is not inconsistent with that of Loram. In analogy with the Mott gap and antiferromagnetism, we propose that ordering may also accompany the formation of a pseudogap. We suggest a current pattern within a 1-band model that preserves translational but breaks time-reversal symmetry along the canonical x and y axes but not along $x=\pm y$ that is consistent with the experimental observations. Finally, we show that the Hall coefficient in a doped Mott insulator must change sign at a doping level $x<1/3$. The sign change is tied to a termination of strong correlation physics in the doped Mott state.
We show that there is a tradeoff between the useful key distribution bit rate and the total length of deployed fiber in tree-type passive optical networks for BB84 quantum key distribution applications. A two stage splitting architecture where one splitting is carried in the central office and a second in the outside plant and figure of merit to account for the tradeoff are proposed. We find that there is an optimum solution for the splitting ratios of both stages in the case of Photon Number Splitting (PNS) attacks and Decoy State transmission. We then analyze the effects of the different relevant physical parameters of the PON on the optimum solution.
The strong maximum principle is a remarkable characterization of parabolic equations, which is expected to be partly inherited by fractional diffusion equations. Based on the corresponding weak maximum principle, in this paper we establish a strong maximum principle for time-fractional diffusion equations with Caputo derivatives, which is slightly weaker than that for the parabolic case. As a direct application, we give a uniqueness result for a related inverse source problem on the determination of the temporal component of the inhomogeneous term.