214,806 research outputs found
An introduction to free higher-spin fields (TOPCITE: 130 citazioni su SPIRES HEP)
No full textIn this article we begin by reviewing the (Fang-)Fronsdal construction and the nonlocal
geometric equations with unconstrained gauge fields and parameters built by Francia
and the senior author from the higher-spin curvatures of de Wit and Freedman. We
then turn to the triplet structure of totally symmetric tensors that emerges from free
String Field Theory in the α′ → 0 limit and to its generalization to (A)dS backgrounds,
and conclude with a discussion of a simple local compensator form of the field equations
that displays the unconstrained gauge symmetry of the non-local equations
How Demanding Should Equality of Opportunity Be, and How Much Have We Achieved?
No full textIn this paper we provide an application-oriented characterization of a class of distance functions monotonically related to the Euclidean distance in terms of some general properties of distance functions between real-valued vectors. Our analysis hinges upon two fundamental properties of distance functions that we call “value-sensitivity” and “order- sensitivity”. We show how these two general properties, combined with natural monotonicity considerations, lead to characterization results that single out several versions of Euclidean distance from the wide class of separable distance functions. We then discuss and motivate our results in two different and apparently unrelated application areas — mobility measurement and spatial voting theory — and propose our characterization as a test for deciding whether Euclidean distance (or some suitable variant) should be used in your favourite application context
A uniqueness result for the continuity equation in two dimensions
No full textWe characterize the autonomous, divergence-free vector fields on the plane such that the Cauchy problem for the continuity equation admits a unique bounded solution (in the weak sense) for every bounded initial datum; the characterization is given in terms of a property of Sard type for the potential associated to .
As a corollary we obtain uniqueness under the assumption that the curl of is a measure. This result can be extended to certain non- autonomous vector fields with bounded divergence
Combination Service for Time-variable Gravity Fields (COST-G) — operations
No full textWith the release of the combined GRACE monthly gravity field time-series COST-G RL01 the Combination Service for Time-variable Gravity fields (COST-G) of the International Association of Geodesy (IAG) became operational in July 2019. We present the COST-G RL01 time-series and provide validation in terms of orbit fit, ice mass trends, lake altimetry and sea level budget. We identify weak points in the combined monthly gravity fields and discuss possible improvements of the combination strategy for future combinations. While COST-G RL01 is based on sets of re-processed GRACE monthly gravity fields, COST-G also provides combinations of monthly Swarm high-low satellite-to-satellite tracking (hl-SST) gravity fields on an operational basis with a latency of 3 months. Combinations of GRACE-FO monthly gravity fields are in the process of operationalization. We provide a status report and first results of GRACE-FO combinations. Combined GRACE, Swarm and GRACE-FO gravity fields complement each other to provide a long-term time-series of mass variation in the system Earth
Extensive Evaluation of Force Fields for G-Quadruplexes
No full textG-Quadruplexes (GQs), folded by guanine-rich nucleic acid sequences, involve in gene expression processes and closely associated with the formation of tumors. So far, GQ has drawn widespread attention for its notable application of serving as potential anti-cancer target. Recently, theoretical studies for GQs have achieved significant progress, most of which are inseparable from molecular dynamics (MD) simulation. As a necessary tool to explore dynamics behavior of molecules, MD simulations strictly depend on force field parameters, which is a sticking point to obtain accurate results. Currently, many force fields for nucleic acids have been developed, but none of them have been accepted widely for GQs. In this paper, we selected five popular force fields, which are parmbsc0, parmbsc1, OL15, Drude2017 and AMOEBANUC17, and conducted explicit-solvent MD simulations on two DNA GQs respectively. We evaluated these force fields from many aspects in detail. Meanwhile, we compared conformational energy using quantum chemistry calculations. With the comprehensive evaluation, Drude2017 achieved better description for GQs, which we suggest that using Drude2017 force field should be taken into account first when investigating GQs by MD simulation.</p
Precise orbit determination based on COST-G time-variable gravity fields
No full textThe Combination Service for Time-variable Gravity fields (COST-G) provides monthly gravity fields, combined from the individual solutions of the COST-G analysis centers and additional partner analysis centers derived from GRACE/GRACE-FO inter-satellite GPS and K-band ranging data. The Precise Orbit Determination (POD) of Earth observation satellites in Low Earth Orbits (LEO) relies on accurate and up-to-date information on the Earthâ?Ts gravity field and its time-variations. We study POD results of the Sentinel-2B, -3B and -6A satellites based either on the monthly COST-G combinations, available with a latency of 2-3 months, or on Fitted Signal Models (FSM) derived on the basis of the COST-G time-series of monthly gravity fields, which allow for the prediction of secular and seasonal gravity variations over several months and therefore may be used in operational LEO POD. Special focus is put on the fit interval of the FSM and the impact of episodic events, e.g. the massive ice melt in Greenland in the summer of 2019, on the performance of the gravity-predictions for POD
Tukey g-and-h Random Fields
No full textWe propose a new class of trans-Gaussian random fields named Tukey g-and-h (TGH) random fields to model non-Gaussian spatial data. The proposed TGH random fields have extremely flexible marginal distributions, possibly skewed and/or heavy-tailed, and, therefore, have a wide range of applications. The special formulation of the TGH random field enables an automatic search for the most suitable transformation for the dataset of interest while estimating model parameters. Asymptotic properties of the maximum likelihood estimator and the probabilistic properties of the TGH random fields are investigated. An efficient estimation procedure, based on maximum approximated likelihood, is proposed and an extreme spatial outlier detection algorithm is formulated. Kriging and probabilistic prediction with TGH random fields are developed along with prediction confidence intervals. The predictive performance of TGH random fields is demonstrated through extensive simulation studies and an application to a dataset of total precipitation in the south east of the United States
Anomalous Phenomena in Solid Dielectrics under High Electric Fields (Keynote)
No full textSolid dielectrics have been used extensively in electrical and electronic industries. In the power industry, ultra high voltage transmission and cost saving of power equipment often result in that the dielectrics are operating under high electric fields. On the other hand, reduction in size for modern electronic systems also requires that the dielectrics operate reliably under high electric fields. It is therefore imperative to understand the response of dielectric materials to the high electric fields. In addition to high conduction current, power loss and potential breakdown, it has been observed over the years there are several anomalous phenomena occurred under high electric fields. These are surface potential cross-over phenomenon in corona charged dielectrics, discharging current flowing in the same direction as charging current, space charge fast decaying and transient space charge limited current. In the present paper all these phenomena have been experimentally demonstrated but most importantly a bipolar charge injection model has been used to understand the observed phenomena under high dc fields. Preliminary simulations based the model reveal that the presence of bipolar charges is the key to explain these anomalous phenomena
On -natural conformal vector fields on unit tangent bundles
No full textsummary:We study conformal and Killing vector fields on the unit tangent bundle, over a Riemannian manifold, equipped with an arbitrary pseudo-Riemannian -natural metric. We characterize the conformal and Killing conditions for classical lifts of vector fields and we give a full classification of conformal fiber-preserving vector fields on the unit tangent bundle endowed with an arbitrary pseudo-Riemannian Kaluza-Klein type metric
- …
