Direct Constraints Research Articles

Real-time planning and collision avoidance control method based on deep reinforcement learning

Real time planning and collision avoidance is an important part of the motion planning for USVs, its core is to design effective planning and collision avoidance methods. This paper proposes a real-time planning and collision avoidance method based on deep reinforcement learning for USVs in complex environments. Firstly, a novel reward function is designed, which transforms the collision avoidance problem into a deep reinforcement learning strategy solution problem that includes distance, direction, speed, and GOLREGs constraints, it ensures the smooth and safe operation of the USV. Secondly, inefficient exploration and exploitation methods make it difficult for intelligent agents to discover key information in the environment, high value experience is obtained through the designed layered sampling exploration mechanism in this article, the intelligent agent learns effective control strategies through this mechanism, which accelerates the convergence of the strategies and reduces the waste of computing resources. Finally, a real-time collision avoidance simulation platform for the USV is established, and experimental results of different exploration mechanisms are compared, the efficiency of the layered sampling exploration mechanism has been verified. The simulation scenarios from easy to difficult are designed, and the results indicate that the USV can complete real-time planning and collision avoidance tasks in complex environments.

Deep Reinforcement Learning With a Stage Incentive Mechanism of Dense Reward for Robotic Trajectory Planning

To improve the efficiency of deep reinforcement learning (DRL)-based methods for robot manipulator trajectory planning in random working environments, we present three dense reward functions. These rewards differ from the traditional sparse reward. First, a posture reward function is proposed to speed up the learning process with a more reasonable trajectory by modeling the distance and direction constraints, which can reduce the blindness of exploration. Second, a stride reward function is proposed to improve the stability of the learning process by modeling the distance and movement distance of joint constraints. Finally, in order to further improve learning efficiency, we are inspired by the cognitive process of human behavior and propose a stage incentive mechanism, including a hard-stage incentive reward function and a soft-stage incentive reward function. Extensive experiments show that the soft-stage incentive reward function is able to improve the convergence rate, get higher mean reward and lower standard deviation after convergence.

The Type II-P Supernova 2019mhm and Constraints on its Progenitor System

We present pre- and postexplosion observations of the Type II-P supernova (SN II-P) 2019mhm located in NGC 6753. Based on optical spectroscopy and photometry, we show that SN 2019mhm exhibits broad lines of hydrogen with a velocity of −8500 ± 200 km s−1 and a 111 ± 2 day extended plateau in its luminosity, typical of the Type II-P subclass. We also fit its late-time bolometric light curve and infer that it initially produced a 56Ni mass of 1.3 × 10−2 ± 5.5 × 10−4 M ⊙. Using imaging from the Wide Field Planetary Camera 2 on the Hubble Space Telescope obtained 19 yr before explosion, we aligned to a postexplosion Wide Field Camera 3 image and demonstrate that there is no detected counterpart to the SN to a limit of >24.53 mag in F814W, corresponding to an absolute magnitude limit of M F814W < −7.7 mag. Comparing to massive-star evolutionary tracks, we determine that the progenitor star had a maximum zero-age main-sequence mass <17.5 M ⊙, consistent with other SN II-P progenitor stars. SN 2019mhm can be added to the growing population of SNe II-P with both direct constraints on the brightness of their progenitor stars and well-observed SN properties.

Pseudo scalar dark matter in a generic U(1)X model

We consider a U(1)X extension of the Standard Model (SM), where the spontaneous breaking of U(1)X gauge group results in a pseudo scalar particle which is the proposed candidate for dark matter. In the model, we introduce three right-handed neutrinos (RHNs) NRi and two extra scalars Φ, χ, which are SM gauge singlets but charged under U(1)X gauge group. Right-handed neutrinos are required to have the model anomaly free and explain the neutrino oscillation data. The heaviest scalar breaks the U(1)X gauge symmetry and the other extra scalar gives a pseudo scalar DM candidate. A pseudo scalar dark matter (DM) is an interesting candidate as it naturally evades the stringent direct detection bounds due to its coupling structure. We study the phenomenology of this pseudo-scalar DM while considering several theoretical and experimental constraints. We find that in our model, there is a feasible parameter space, which satisfies by the DM lifetime bound, relic and direct detection constraints while respecting the colliders and other bounds.

Robust Multilegged Walking Robots for Interactions With Different Terrains

Abstract This paper explores the kinematic synthesis, design, and pilot experimental testing of a six-legged walking robotic platform able to traverse through different terrains. We aim to develop a structured approach to designing the limb morphology using a relaxed kinematic task with incorporated conditions on foot-environments interaction, specifically contact force direction and curvature constraints, related to maintaining contact. The design approach builds up incrementally starting with studying the basic human leg walking trajectory and then defining a “relaxed” kinematic task. The “relaxed” kinematic task consists only of two contact locations (toe-off and heel-strike) with higher-order motion task specifications compatible with foot-terrain(s) contact and curvature constraints in the vicinity of the two contacts. As the next step, an eight-bar leg image is created based on the “relaxed” kinematic task and incorporated within a six-legged walking robot. Pilot experimental tests explore if the proposed approach results in an adaptable behavior which allows the platform to incorporate different walking foot trajectories and gait styles coupled to each environment. The results suggest that the proposed “relaxed” higher-order motion task combined with the leg morphological properties and feet material allowed the platform to walk stably on the different terrains. Here we would like to note that one of the main advantages of the proposed method in comparison with other existing walking platforms is that the proposed robotic platform has carefully designed limb morphology with incorporated conditions on foot-environment interaction. Additionally, while most of the existing multilegged platforms incorporate one actuator per leg, or per joint, our goal is to explore the possibility of using a single actuator to drive all six legs of the platform. This is a critical step which opens the door for the development of future transformative technology that is largely independent of human control and able to learn about the environment through their own sensory systems.

Resonant scattering between dark matter and baryons: Revised direct detection and CMB limits

Traditional dark matter models, e.g., weakly interacting massive particles (WIMPs), assume dark matter (DM) is weakly coupled to the standard model so that elastic scattering between dark matter and baryons can be described perturbatively by the Born approximation; most direct detection experiments are analyzed according to that assumption. We show that when the fundamental DM-baryon interaction is attractive, dark matter-nucleus scattering is nonperturbative in much of the relevant parameter range. The cross section exhibits rich resonant behavior with a highly nontrivial dependence on atomic mass; furthermore, the extended rather than pointlike nature of nuclei significantly impacts the cross sections and must therefore be properly taken into account. The repulsive case also shows significant departures from perturbative predictions and also requires full numerical calculation. These nonperturbative effects change the boundaries of exclusion regions from existing direct detection, astrophysical and CMB constraints. Near a resonance value of the parameters the typical velocity-independent Yukawa behavior, $\ensuremath{\sigma}\ensuremath{\sim}{v}^{0}$, does not apply. We take the nontrivial velocity dependence into account in our analysis, however it turns out that this more accurate treatment has little impact on limits given current constraints. Correctly treating the extended size of the nucleus and doing an exact integration of the Schr\"odinger equation does have a major impact relative to past analyses based on the Born approximation and naive form factors, so those improvements are essential for interpreting observational constraints. We report the corrected exclusion regions superseding previous limits from XQC, CRESST Surface Run, CMB power spectrum and extensions with Lyman-$\ensuremath{\alpha}$ and Milky Way satellites, and Milky Way gas clouds. Some limits become weaker, by an order of magnitude or more, than previous bounds in the literature which were based on perturbation theory and pointlike sources, while others become stronger. Gaps which open by correct treatment of some particular constraint can sometimes be closed using a different constraint. We also discuss the dependence on mediator mass and give approximate expressions for the velocity dependence near a resonance. Sexaquark ($uuddss$) DM with mass around 2 GeV, which exchanges QCD mesons with baryons, remains unconstrained for most of the parameter space of interest. A statement in the literature that a DM-nucleus cross section larger than ${10}^{\ensuremath{-}25}\text{ }\text{ }{\mathrm{cm}}^{2}$ implies dark matter is composite, is corrected.

Dark matter and neutrino masses in a Portalino-like model

We explore a Portalino-like model of dark matter and neutrino masses in which right-handed neutrino fields connect gauge neutral operators from the Standard Model and Hidden Sector. Neutrino masses are generated via a seesaw-like mechanism that can explain the light active neutrino masses. The model includes a “Portalino” state that connects the two sectors via the neutrino portal. Dark Matter in this model consists of a hidden sector Dirac fermion that dominantly freezes-out via resonant annihilations into other hidden sector states, which ultimately results in a population of Portalinos. Due to small mixing in the extended neutrino sector these Portalinos tend to be cosmologically long lived, decaying into Standard Model particles leading to constraints on the model from Big Bang Nucleosynthesis and measurements of the Cosmic Microwave Background radiation. Combining these limits with direct constraints on the size of the Portalino–neutrino mixing and the assumptions of the model the viable mass ranges for the Portalino states are found to be {0.02}~hbox {eV}lesssim m_n lesssim {6.4}~hbox {eV} or {489}~{hbox {MeV}} lesssim m_n lesssim TeV. Indirect dark matter signals in the form of highly boosted, mono-energetic Portalinos produced in Dark Matter annihilations provide a target for neutrino telescopes.

Dark matter in NMSSM with small [formula omitted] and [formula omitted

The NMSSM provides an excellent dark matter candidate, usually the lightest neutralino (χ̃10) being the lightest supersymmetric particle (LSP), in the universe. It is a mixture of the bino, the neutral wino, the neutral higgsinos, and the singlino. In this work, we investigate the features of the lightest neutralino by concentrating on a specific region of the NMSSM parameter space with small values of both λ and κ, taking into account theoretical and experimental constraints, including relic density, direct and indirect detection constraints. We have found that the LSP dark matter is a singlino-dominated neutralino for most of the sample points of the chosen scenario. Thus, contrary to expectations, the NMSSM is not comparable to the MSSM in terms of dark matter properties as λ and κ are very small. The LSP can also be either higgsino-dominated or bino-dominated in some parameter space. The most important parameters affecting the mass and properties of the LSP are κ, λ/κ, and μeff. Further, we notice that σpSI≈1.02σnSI and σpSD≈0.76σnSD for all the surviving sample points.

Incorporating biological knowledge in analyses of environmental mixtures and health.

A key goal of environmental health research is to assess the risk posed by mixtures of pollutants. As epidemiologic studies of mixtures can be expensive to conduct, it behooves researchers to incorporate prior knowledge about mixtures into their analyses. This work extends the Bayesian multiple index model (BMIM), which assumes the exposure-response function is a nonparametric function of a set of linear combinations of pollutants formed with a set of exposure-specific weights. The framework is attractive because it combines the flexibility of response-surface methods with the interpretability of linear index models. We propose three strategies to incorporate prior toxicological knowledge into construction of indices in a BMIM: (a) imposing directional homogeneity constraints on the weights, (b) structuring index weights by exposure transformations, and (c) placing informative priors on the index weights. We propose a novel prior specification that combines spike-and-slab variable selection with an informative Dirichlet distribution based on relative potency factors often derived from previous toxicological studies. In simulations we show that the proposed priors improve inferences when prior information is correct and can protect against misspecification suffered by naïve toxicological models when prior information is incorrect. Moreover, different strategies may be mixed-and-matched for different indices to suit available information (or lack thereof). We demonstrate the proposed methods on an analysis of data from the National Health and Nutrition Examination Survey and incorporate prior information on relative chemical potencies obtained from toxic equivalency factors available in the literature.

Search for leptophilic dark matter at the LHeC

The Large Hadron electron Collider (LHeC) has been designed to push the field of deep inelastic scattering to the high energy and intensity frontier using an intense electron beam with a proton beam from the High Luminosity–Large Hadron Collider. However, LHeC is also a great laboratory for new physics. In this work, we propose a search for dark matter that couples with leptons. This may yield and signals that can be potentially observed through simple missing-energy cuts that suppress the Standard Model background. Considering direct dark matter detection and LHC constraints, we show that LHeC offers a complementary probe for a weak scale dark matter fermion for masses up to 350 GeV, which reproduces the correct relic density, and has interesting implications for lepton flavor violation.

Implications of MicroBooNE’s low sensitivity to electron antineutrino interactions in the search for the MiniBooNE excess

The MicroBooNE experiment searched for an excess of electron-neutrinos in the Booster Neutrino Beam (BNB), providing direct constraints on $\nu_e$-interpretations of the MiniBooNE low-energy excess (LEE). In this article, we show that if the MiniBooNE LEE is caused instead by an excess of $\overline{\nu}_e$, then liquid argon detectors, such as MicroBooNE, SBND and ICARUS, would have poor sensitivity to it. This is due to a strong suppression of $\overline{\nu}_e -{}^{40}$Ar cross sections in the low-energy region of the excess. The MicroBooNE results are consistent at the $2\sigma$~C.L with a scenario in which the MiniBooNE excess is sourced entirely by $\overline{\nu}_e$ interactions. The opportune location of ANNIE, a Gd-loaded water Cherenkov detector, allows for a direct search for a $\overline{\nu}_e$ flux excess in the BNB using inverse-beta-decay events.

XQC and CSR constraints on strongly interacting dark matter with spin and velocity dependent cross sections

Dark matter that interacts strongly with baryons can avoid the stringent dark matter direct detection constraints, because, like baryons, they are likely to be absorbed when traversing the rocks, leading to a suppressed flux in deep underground labs. Such strongly interacting dark matter, however, can be probed by dark matter experiments or other experiments operated on the ground level or in the atmosphere. In this paper we carry out systematic analysis of two of these experiments, XQC and CSR, to compute the experimental constraints on the strongly interacting dark matter in the following three scenarios: (1) spin-independent and spin-dependent interactions; (2) different velocity dependent cross sections; (3) different dark matter mass fractions. Some of the scenarios are first analyzed in the literature. We find that the XQC exclusion region has some non-trivial dependencies on the various parameters and the limits in the spin-dependent case is quite different from the spin-independent case. A peculiar region in the parameter space, where the XQC constraint disappears, is also found in our Monte Carlo simulations. This occurs in the case where the interaction cross section is proportional to the square of the velocity. We further compare our XQC and CSR limits to other experimental constraints, and find that a large parameter space is allowed by various experiments if the dark matter mass fraction is sufficiently small, fχ ≲ 10-4.

Relic gravitons and high-frequency detectors

Cosmic gravitons are expected in the MHz–GHz regions that are currently unreachable by the operating wide-band interferometers and where various classes of electromechanical detectors have been proposed through the years. The minimal chirp amplitude detectable by these instruments is often set on the basis of the sensitivities reachable by the detectors currently operating in the audio band. By combining the observations of the pulsar timing arrays, the limits from wide-band detectors and the other phenomenological bounds we show that this requirement is far too generous and even misleading since the actual detection of relic gravitons well above the kHz would demand chirp and spectral amplitudes that are ten or even fifteen orders of magnitude smaller than the ones currently achievable in the audio band, for the same classes of stochastic sources. We then examine more closely the potential high-frequency signals and show that the sensitivity in the chirp and spectral amplitudes must be even smaller than the ones suggested by the direct and indirect constraints on the cosmic gravitons. We finally analyze the high-frequency detectors in the framework of Hanbury-Brown Twiss interferometry and argue that they are actually more essential than the ones operating in the audio band (i.e. between few Hz and few kHz) if we want to investigate the quantumness of the relic gravitons and their associated second-order correlation effects. We suggest, in particular, how the statistical properties of thermal and non-thermal gravitons can be distinguished by studying the corresponding second-order interference effects.

Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet

During the first half of their main-sequence lifetimes, stars rapidly lose angular momentum to their magnetized winds, a process known as magnetic braking. Recent observations suggest a substantial decrease in the magnetic braking efficiency when stars reach a critical value of the Rossby number, the stellar rotation period normalized by the convective overturn timescale. Cooler stars have deeper convection zones with longer overturn times, reaching this critical Rossby number at slower rotation rates. The nature and timing of the transition to weakened magnetic braking have previously been constrained by several solar analogs and two slightly hotter stars. In this Letter, we derive the first direct constraints from stars cooler than the Sun. We present new spectropolarimetry of the old G8 dwarf τ Cet from the Large Binocular Telescope, and we reanalyze a published Zeeman Doppler image of the younger G8 star 61 UMa, yielding the large-scale magnetic field strengths and morphologies. We estimate mass-loss rates using archival X-ray observations and inferences from Lyα measurements, and we adopt other stellar properties from asteroseismology and spectral energy distribution fitting. The resulting calculations of the wind braking torque demonstrate that the rate of angular momentum loss drops by a factor of 300 between the ages of these two stars (1.4–9 Gyr), well above theoretical expectations. We summarize the available data to help constrain the value of the critical Rossby number, and we identify a new signature of the long-period detection edge in recent measurements from the Kepler mission.

Direction constraints adaptive extended bidirectional A* algorithm based on random two-dimensional map environments

This paper focuses on the mobile robot path planning problem of optimizing the performance metrics of bidirectional A* algorithm in randomized two-dimensional map environments. An algorithm called direction constraints adaptive extended bidirectional A* (DCAE-BA*), which is an improvement of the traditional target dynamic bidirectional A* algorithm (TTD-BA*), is proposed to improve the performance metrics of the algorithm. Regarding the improvement, we propose the adaptive extension method and the direction-constrained optimal node extension method (DCONE). Simulation experiments were conducted for DCAE-BA*, TTD-BA* and traditional A* algorithm (A*) in a large number of random two-dimensional map environments. The simulation experimental scenarios consider four types of start and end point relative directions and three obstacle proportions to objectively and comprehensively evaluate the performance of the proposed algorithms. The results show that different scenarios have a significant impact on the algorithm performance metrics. Finally, the overall performance of the proposed algorithm is evaluated with a large number of experiments in “random” scenarios, and the results show that DCAE-BA* obtains significantly better search time for all three obstacle proportions, and better path length and number of expanded nodes for 10% and 25% obstacle proportions. The effectiveness of the proposed DCAE-BA* algorithm is demonstrated, which provides an essential reference for the path planning of mobile robots in a random 2D map environment.

A highly efficient computational strategy to model the inverse dynamics of a novel 4-DOF parallel mechanism with direct constraints from the base at two point-contact higher kinematic pairs

A highly efficient computational strategy to model the inverse dynamics of a novel 4-DOF parallel mechanism with direct constraints from the base at two point-contact higher kinematic pairs

Vertical‐Slice Ocean Tomography With Seismic Waves

AbstractSeismically generated sound waves that propagate through the ocean are used to infer temperature anomalies and their vertical structure in the deep East Indian Ocean. These T waves are generated by earthquakes off Sumatra and received by hydrophone stations off Diego Garcia and Cape Leeuwin. Between repeating earthquakes, a T wave's travel time changes in response to temperature anomalies along the wave's path. What part of the water column the travel time is sensitive to depends on the frequency of the wave, so measuring travel time changes at a few low frequencies constrains the vertical structure of the inferred temperature anomalies. These measurements reveal anomalies due to equatorial waves, mesoscale eddies, and decadal warming trends. By providing direct constraints on basin‐scale averages with dense sampling in time, these data complement previous point measurements that alias local and transient temperature anomalies.

Quantum Many-Body Theory from a Solution of the N-Representability Problem.

Here we present a many-body theory based on a solution of the N-representability problem in which the ground-state two-particle reduced density matrix (2-RDM) is determined directly without the many-particle wave function. We derive an equation that re-expresses physical constraints on higher-order RDMs to generate direct constraints on the 2-RDM, which are required for its derivation from an N-particle density matrix, known as N-representability conditions. The approach produces a complete hierarchy of 2-RDM constraints that do not depend explicitly upon the higher RDMs or the wave function. By using the two-particle part of a unitary decomposition of higher-order constraint matrices, we can solve the energy minimization by semidefinite programming in a form where the low-rank structure of these matrices can be potentially exploited. We illustrate by computing the ground-state electronic energy and properties of the H_{8} ring.

Automatic velocity analysis with physics-constrained optimal surface picking

Stacking velocity is generally obtained by picking the energy peaks in velocity semblance which can be time consuming when performed manually. Numerous automatic methods have been proposed for accelerating the velocity picking but often generate physically unreasonable picking results when strong and spatially consistent energy anomalies (due to noise and multiples) appear in the semblance map. We develop a constrained optimal surface picking method to automatically pick a 2D velocity field from a 3D semblance volume with high efficiency and robustness. This method is improved from the 2D dynamic programming algorithm by incorporating vertical physical constraints in the time direction and lateral smoothness constraints in the common-midpoint (CMP) direction. The time-direction physical constraint ensures that the picked velocity is positive when converted to an interval velocity, whereas the CMP-direction smoothness constraint ensures that the picked 2D velocity field is laterally continuous. Tests on the Marmousi-2 model indicate that our constrained optimal surface picking algorithm improves the spatial structure consistency of the picked velocity field and is able to robustly avoid picking the strong and consistent energy features generated in the semblance volume by multiples. We further determine the robustness of our method in a 2D real data example by comparing our automatic picking from a 3D semblance volume with a result that is manually picked from individual 2D semblance slices. The comparison indicates that the general trend of our result is consistent with the manual picking and our result looks geologically more reasonable in detail and generates a better stacking image with improved, focused, and more continuous reflections.

Extremely weak Lg attenuation reveals ancient continental relicts in the South China block

Whether the South China block (SCB) occupied an external or internal position in the Rodinia supercontinent remains controversial. The external model favors an accretion orogenic amalgamation setting, whereas the internal model assumes postcollisional extensional rifting in the Neoproterozoic. Recent geochronological data suggested that the SCB was assembled from several ancient nuclei or microcontinental fragments with various origins and geological histories during the early Neoproterozoic, and supported the external position model for the SCB in Rodinia. However, whether these ancient continental nuclei are hidden in the crust requires direct constraints such as those from seismic tomography. In general, these early ancient continental relicts preserved in the present-day crust tend to be characterized by high strength, high velocity, and weak attenuation. Compared with velocity, seismic attenuation tends to be more sensitive to ancient rigid continental fragments. Here, we constructed a high-resolution broadband crustal Lg attenuation model for the SCB and explored the existence and scale of the ancient continental fragments potentially hidden in the deep crust. Four extremely weak attenuation anomalies in the SCB indicate potential locations of these ancient continental relicts in the crust; one is in the Sichuan basin and the other three are beneath the Cathaysia block. The three ancient continental relicts in the Cathaysia block, which are closely corresponding to early surface lithological records, provide seismic evidence supporting an external position for the SCB in the Rodinia supercontinent.