Technische Universität Darmstadt

About: Technische Universität Darmstadt is a education organization based out in Darmstadt, Germany. It is known for research contribution in the topics: Computer science & Context (language use). The organization has 17316 authors who have published 40619 publications receiving 937916 citations. The organization is also known as: Darmstadt University of Technology & University of Darmstadt.

Large-scale nuclear structure calculations for spin-dependent WIMP scattering with chiral effective field theory currents

Abstract: We perform state-of-the-art large-scale shell-model calculations of the structure factors for elastic spin-dependent WIMP scattering off $^{129,131}\mathrm{Xe}$, $^{127}\mathrm{I}$, $^{73}\mathrm{Ge}$, $^{19}\mathrm{F}$, $^{23}\mathrm{Na}$, $^{27}\mathrm{Al}$, and $^{29}\mathrm{Si}$. This comprehensive survey covers the nonzero-spin nuclei relevant to direct dark matter detection. We include a pedagogical presentation of the formalism necessary to describe elastic and inelastic WIMP-nucleus scattering. The valence spaces and nuclear interactions employed have been previously used in nuclear structure calculations for these mass regions and yield a good spectroscopic description of these isotopes. We use spin-dependent WIMP-nucleus currents based on chiral effective field theory at the one-body level and including the leading long-range two-body currents due to pion exchange, which are predicted in chiral effective field theory. Results for all structure factors are provided with theoretical error bands due to the nuclear uncertainties of WIMP currents in nuclei.

Equation-of-state dependence of the gravitational-wave signal from the ring-down phase of neutron-star mergers

Abstract: Neutron star (NS) merger simulations are conducted for 38 representative microphysical descriptions of high-density matter in order to explore the equation-of-state (EoS) dependence of the postmerger ring-down phase. The formation of a deformed, oscillating, differentially rotating very massive NS is the typical outcome of the coalescence of two stars with $1.35{M}_{\ensuremath{\bigodot}}$ for most candidate EoSs. The oscillations of this object imprint a pronounced peak in the gravitational wave (GW) spectra, which is used to characterize the emission for a given model. The peak frequency of this postmerger GW signal correlates very well with the radii of nonrotating NSs, and thus allows us to constrain the high-density EoS by a GW detection. In the case of $1.35\mathrm{\text{\ensuremath{-}}}1.35{M}_{\ensuremath{\bigodot}}$ mergers the peak frequency scales particularly well with the radius of an NS with $1.6{M}_{\ensuremath{\bigodot}}$, where the maximum deviation from this correlation is only 60 m for fully microphysical EoSs which are compatible with NS observations. Combined with the uncertainty in the determination of the peak frequency it appears likely that a GW detection can measure the radius of a $1.6{M}_{\ensuremath{\bigodot}}$ NS with an accuracy of about 100--200 m. We also uncover relations of the peak frequency with the radii of nonrotating NSs with $1.35{M}_{\ensuremath{\bigodot}}$ or $1.8{M}_{\ensuremath{\bigodot}}$, with the radius or the central energy density of the maximum-mass Tolman-Oppenheimer-Volkoff configuration, and with the pressure or sound speed at a fiducial rest mass density of about twice the nuclear saturation density. Furthermore, it is found that a determination of the dominant postmerger GW frequency can provide an upper limit for the maximum mass of nonrotating NSs. The effect of variations of the binary setup are investigated and corresponding functional dependences between the peak frequency and radii of nonrotating NSs are derived. With higher total binary masses, correlations are tighter for radii of nonrotating NSs with higher masses. The prospects for a detection of the postmerger GW signal and a determination of the dominant GW frequency are estimated to be in the range of 0.015--1.2 events per year with the upcoming Advanced Laser Interferometer Gravitational Wave Observatory detector.

Virtual machine support for dynamic join points

Abstract: A widespread implementation approach for the join point mechanism of aspect-oriented languages is to instrument areas in code that match the static part of pointcut designators, inserting dynamic checks for that part of matching that depends on run-time conditions, if needed. For performance reasons, such dynamic checks should be avoided whenever possible. One way to do so is to postpone weaving of advice calls until run-time, when conditions determining the emergence of join points hold. This calls for fluid code---code that adapts itself to the join point emergence at run-time, and suggests that AOP concepts should be integrated into the execution model underlying a VM. In this paper, we present first steps toward such an integration in Steamloom, an extension of IBM's Jikes Research Virtual Machine. Steamloom is fairly restricted, but our initial experimental results indicate that aspect-aware VMs and fluid code are promising w.r.t performance. While the focus in this paper is on performance, there are other advantages of aspect-aware VMs to be investigated in the future.

Global spatial distribution of natural riverine silica inputs to the coastal zone

Abstract: . Silica, SiO2, in dissolved (DSi) and particulate (PSi) form, is both a major product of continental weathering as well as an essential nutrient in terrestrial and aquatic systems. Here we present estimates of the spatial distribution of riverine silica fluxes under natural conditions, i.e. without human influence, to ~140 segments of the global coastal zone. Focussing on the construction of the DSi budget, natural DSi concentration is multiplied with discharge of rivers for each segment for documented basins and segments. Segments with no documentation available are estimated using clustered information based mainly on considerations of local lithology, climate, and lake retention. We approximate fluxes of particulate silica in various forms (PSi) from fluxes of suspended matter, calculated from existing models. Results have been established for silica fluxes, concentrations and yields for drainage basins of the different continents, oceans basins as well as coastal segment basins. For the continental surfaces actually draining into the oceans (exorheic regions, representing 114.7 million (M) km2), 371 M t y−1 of DSi and 8835 M t y−1 of PSi are transported, corresponding to a mean concentration of 9.5 mg l−1 and 226 mg l−1, and to a mean yield of 3.3 t km−2 y−1 and 77 t km−2 y−1, respectively. DSi yields exceeding 6.6 t km−2 y−1, i.e. >2× the global average, represent 17.4% of the global continental ice-free exorheic area but correspond to 56.0% of DSi fluxes. Pacific catchments hold most of the hyper-active areas (>5× global average), suggesting a close connection between tectonic activity and DSi fluxes resulting from silicate weathering. The macro-filters of regional and marginal seas intercept 33% and 46% of the total dissolved and particulate silica fluxes. The mass of DSi received from rivers per unit square area of various oceans ranges over more than one order of magnitude. When expressed per unit volume and when individual regional seas are considered this figure ranges over two to three orders of magnitude, an illustration of the heterogeneity of the land to sea connection.