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Search Results: 1 - 10 of 527963 matches for " D. M. Siegel "
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Excitation of non-radial stellar oscillations by gravitational waves: a first model
D. M. Siegel,M. Roth
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17240.x
Abstract: The excitation of solar and solar-like g modes in non-relativistic stars by arbitrary external gravitational wave fields is studied starting from the full field equations of general relativity. We develop a formalism that yields the mean-square amplitudes and surface velocities of global normal modes excited in such a way. The isotropic elastic sphere model of a star is adopted to demonstrate this formalism and for calculative simplicity. It is shown that gravitational waves solely couple to quadrupolar spheroidal eigenmodes and that normal modes are only sensitive to the spherical component of the gravitational waves having the same azimuthal order. The mean-square amplitudes in case of stationary external gravitational waves are given by a simple expression, a product of a factor depending on the resonant properties of the star and the power spectral density of the gravitational waves' spherical accelerations. Both mean-square amplitudes and surface velocities show a characteristic R^8-dependence (effective R^2-dependence) on the radius of the star. This finding increases the relevance of this excitation mechanism in case of stars larger than the Sun.
Excitation of stellar oscillations by gravitational waves: hydrodynamic model and numerical results for the Sun
D. M. Siegel,M. Roth
Physics , 2011, DOI: 10.1088/0004-637X/729/2/137
Abstract: Starting from a general relativistic framework a hydrodynamic formalism is derived that yields the mean-square amplitudes and rms surface velocities of normal modes of non-relativistic stars excited by arbitrary gravitational wave (GW) radiation. In particular, stationary GW fields are considered and the resulting formulae are evaluated for two general types of GW radiation: radiation from a particular astrophysical source (e.g., a binary system) and a stochastic background of gravitational waves (SBGW). Expected sources and signal strengths for both types of GW radiation are reviewed and discussed. Numerical results for the Sun show that low-order quadrupolar g modes are excited more strongly than p modes by orders of magnitude. Maximal rms surface velocities in the case of excitation by astrophysical sources are found to be v {\le} 10^(-8) mm/s, assuming GW strain amplitudes of h {\le} 10^(-20). It is shown that current models for an SBGW produced by cosmic strings, with Omega_GW ~ 10^(-8)-10^(-5) in the frequency range of solar g modes, are able to produce maximal solar g-mode rms surface velocities of 10^(-5)-10^(-3) mm/s. This result lies close to or within the amplitude range of 10^(-3)-1 mm/s expected from excitation by turbulent convection, which is currently considered to be responsible for stellar g-mode excitation. It is concluded that studying g-mode observations of stars other than the Sun, in which excitation by GWs could be even more effective due to different stellar structures, might provide a new method to either detect GWs or to deduce a significant direct upper limit on an SBGW at intermediate frequencies between the pulsar bound and the bounds from interferometric detectors on Earth.
Defect controlled vortex generation in current-carrying narrow superconducting strips
D. Yu. Vodolazov,K. Ilin,M. Merker,M. Siegel
Physics , 2015,
Abstract: We experimentally study effect of single circular hole on the critical current $I_c$ of narrow superconducting strip with width $W$ much smaller than Pearl penetration depth $\Lambda$. We found nonmonotonous dependence of $I_c$ on the location of a hole across the strip and a weak dependence of $I_c$ on radius of hole has been found in case of hole with $\xi \ll R \ll W$ ($\xi$ is a superconducting coherence length) which is placed in the center of strip. The observed effects are caused by competition of two mechanisms of destruction of superconductivity - the entrance of vortex via edge of the strip and the nucleation of the vortex-antivortex pair near the hole. The mechanisms are clearly distinguishable by difference in dependence of $I_c$ on weak magnetic field.
Haptenation: Chemical Reactivity and Protein Binding
Itai Chipinda,Justin M. Hettick,Paul D. Siegel
Journal of Allergy , 2011, DOI: 10.1155/2011/839682
Abstract: Low molecular weight chemical (LMW) allergens are commonly referred to as haptens. Haptens must complex with proteins to be recognized by the immune system. The majority of occupationally related haptens are reactive, electrophilic chemicals, or are metabolized to reactive metabolites that form covalent bonds with nucleophilic centers on proteins. Nonelectrophilic protein binding may occur through disulfide exchange, coordinate covalent binding onto metal ions on metalloproteins or of metal allergens, themselves, to the major histocompatibility complex. Recent chemical reactivity kinetic studies suggest that the rate of protein binding is a major determinant of allergenic potency; however, electrophilic strength does not seem to predict the ability of a hapten to skew the response between Th1 and Th2. Modern proteomic mass spectrometry methods that allow detailed delineation of potential differences in protein binding sites may be valuable in predicting if a chemical will stimulate an immediate or delayed hypersensitivity. Chemical aspects related to both reactivity and protein-specific binding are discussed. 1. Introduction The term, “hapten,” was coined by Landsteiner and Jacobs [1] and is derived from the Greek “hapten”, meaning “to fasten.” Haptens are low molecular weight (LMW; <1000 daltons) chemicals that must bind to a carrier molecule to be antigenic. The carrier is usually an endogenous or exogenous protein to which the LMW chemical is covalently bound. The hapten hypothesis was originally proposed to explain both humoral and cellular immune responses to LMW chemicals observed by Landsteiner and Jacobs [1] in their research. The absolute requirement for covalent binding of a hapten to a protein for immune recognition in the development of all drug/LMW chemical allergies has been challenged in recent years [2], but substantial evidence exists for this to be a prominent mechanism through which chemicals and drugs or their metabolites become antigenic. The role of chemical reactivity has been proposed to be one of the major determinants in allergic contact dermatitis (ACD). Over the years, extensive databases containing representative chemicals that are skin sensitizers have been published [3–5]. In the context of occupational health, predictive toxicology, and ensuring overall safety of manufactured products, it is important that skin sensitization potential of new and existing chemicals be assessed. The use of guinea pigs has been the experimental model of choice in evaluating the skin sensitization potential of chemicals [6, 7] until about a
Suppression of dissipation in Nb thin films with triangular antidot arrays by random removal of pinning sites
M. Kemmler,D. Bothner,K. Ilin,M. Siegel,R. Kleiner,D. Koelle
Physics , 2008, DOI: 10.1103/PhysRevB.79.184509
Abstract: The depinning current Ic versus applied magnetic field B close to the transition temperature Tc of Nb thin films with randomly diluted triangular arrays of antidots is investigated. % Our experiments confirm essential features in Ic(B) as predicted by Reichhardt and Olson Reichhardt [Phys.Rev. B 76, 094512 (2007)]. % We show that, by introducing disorder into periodic pinning arrays, Ic can be enhanced. % In particular, for arrays with fixed density n_p of antidots, an increase in dilution Pd induces an increase in Ic and decrease of the flux-flow voltage for B>Bp=n_p Phi_0.
Detection Efficiency of a Spiral-Nanowire Superconducting Single-Photon Detector
D. Henrich,L. Rehm,S. D?rner,M. Hofherr,K. Ilin,A. Semenov,M. Siegel
Physics , 2012,
Abstract: We investigate the detection efficiency of a spiral layout of a Superconducting Nanowire Single-Photon Detector (SNSPD). The design is less susceptible to the critical current reduction in sharp turns of the nanowire than the conventional meander design. Detector samples with different nanowire width from 300 to 100 nm are patterned from a 4 nm thick NbN film deposited on sapphire substrates. The critical current IC at 4.2 K for spiral, meander, and simple bridge structures is measured and compared. On the 100 nm wide samples, the detection efficiency is measured in the wavelength range 400-1700 nm and the cut-off wavelength of the hot-spot plateau is determined. In the optical range, the spiral detector reaches a detection efficiency of 27.6%, which is ~1.5 times the value of the meander. In the infrared range the detection efficiency is more than doubled.
High efficiency deterministic Josephson Vortex Ratchet
M. Beck,E. Goldobin,M. Neuhaus,M. Siegel,R. Kleiner,D. Koelle
Physics , 2005, DOI: 10.1103/PhysRevLett.95.090603
Abstract: We investigate experimentally a Josephson vortex ratchet -- a fluxon in an asymmetric periodic potential driven by a deterministic force with zero time average. The highly asymmetric periodic potential is created in an underdamped annular long Josephson junction by means of a current injector providing efficiency of the device up to 91%. We measured the ratchet effect for driving forces with different spectral content. For monochromatic high-frequency drive the rectified voltage becomes quantized. At high driving frequencies we also observe chaos, sub-harmonic dynamics and voltage reversal due to the inertial mass of a fluxon.
Commensurability effects in superconducting Nb films with quasiperiodic pinning arrays
M. Kemmler,C. Guerlich,A. Sterck,H. Poehler,M. Neuhaus,M. Siegel,R. Kleiner,D. Koelle
Physics , 2006, DOI: 10.1103/PhysRevLett.97.147003
Abstract: We study experimentally the critical depinning current Ic versus applied magnetic field B in Nb thin films which contain 2D arrays of circular antidots placed on the nodes of quasiperiodic (QP) fivefold Penrose lattices. Close to the transition temperature Tc we observe matching of the vortex lattice with the QP pinning array, confirming essential features in the Ic(B) patterns as predicted by Misko et al. [Phys. Rev. Lett, vol.95, 177007 (2005)]. We find a significant enhancement in Ic(B) for QP pinning arrays in comparison to Ic in samples with randomly distributed antidots or no antidots.
Deterministic Josephson Vortex Ratchet with a load
M. Knufinke,K. Ilin,M. Siegel,D. Koelle,R. Kleiner,E. Goldobin
Physics , 2011, DOI: 10.1103/PhysRevE.85.011122
Abstract: We investigate experimentally a deterministic underdamped Josephson vortex ratchet -- a fluxon-particle moving along a Josephson junction in an asymmetric periodic potential. By applying a sinusoidal driving current one can compel the vortex to move in a certain direction, producing average dc voltage across the junction. Being in such a rectification regime we also load the ratchet, i.e., apply an additional dc bias current I_dc (counterforce) which tilts the potential so that the fluxon climbs uphill due to the ratchet effect. The value of the bias current at which the fluxon stops climbing up defines the strength of the ratchet effect and is determined experimentally. This allows us to estimate the loading capability of the ratchet, the output power and efficiency. For the quasi-static regime we present a simple model which delivers simple analytic expressions for the above mentioned figures of merit.
Non-ideal artificial phase discontinuity in long Josephson 0-kappa-junctions
T. Gaber,E. Goldobin,A. Sterck,R. Kleiner,D. Koelle,M. Siegel,M. Neuhaus
Physics , 2004, DOI: 10.1103/PhysRevB.72.054522
Abstract: We investigate the creation of an arbitrary $\kappa$-discontinuity of the Josephson phase in a long Nb-AlO_x-Nb Josephson junction (LJJ) using a pair of tiny current injectors, and study the formation of fractional vortices formed at this discontinuity. The current I_inj, flowing from one injector to the other, creates a phase discontinuity kappa ~ I_inj. The calibration of injectors is discussed in detail. The small but finite size of injectors leads to some deviations of the properties of such a 0-kappa-LJJ from the properties of a LJJ with an ideal kappa-discontinuity. These experimentally observed deviations in the dependence of the critical current on I_inj$ and magnetic field can be well reproduced by numerical simulation assuming a finite injector size. The physical origin of these deviations is discussed.
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