6,307 research outputs found
Control of magnetism in singlet-triplet superconducting heterostructures
We analyze the magnetization at the interface between singlet and triplet
superconductors and show that its direction and dependence on the phase
difference across the junction are strongly tied to the structure of the
triplet order parameter as well as to the pairing interactions. We consider
equal spin helical, opposite spin chiral, and mixed symmetry pairing on the
triplet side and show that the magnetization vanishes at only in the
first case, follows approximately a behavior for the second, and
shows higher harmonics for the last configuration. We trace the origin of the
magnetization to the magnetic structure of the Andreev bound states near the
interface, and provide a symmetry-based explanation of the results. Our
findings can be used to control the magnetization in superconducting
heterostructures and to test symmetries of spin-triplet superconductors.Comment: 5 pages, 3 figure
How Can the Stages of Peck's Community-Making Model be Identified and Predicted for a Collegiate Basketball Team Over the Course of Consecutive Seasons?
The purpose of this study was to explore how Peck's (1987) stages of Community-Making could be identified and predicted for a collegiate basketball team over the course of consecutive seasons by exploring Cohesion, Flow, and athletic performance. The study utilized a repeated measures longitudinal survey design with the members of a Division I collegiate level female basketball team (N = 13) during the athletic seasons of 1999/2000 and 2000/2001. Participants completed both the Group Environment Questionnaire (Carron, Brawley, & Widmeyer, 2002) and the Flow State Scale -2 (Jackson & Eklund, 2003) pre and post competition at several times over the course of the athletic seasons, respectively. Furthermore, athletic performance statistics were collected for the athletic seasons. The data in this study was analyzed using descriptive data analysis, trend graphs, correlational analyses, and regression analysis by way of discriminant analysis. The researcher examined the data analyses and looked for evidence of the stages of Community-Making over the course of the season via the constructs of Cohesion, Flow, and athletic performance. Given the constructs of Flow State, Cohesion, and performance, the researcher determined that the team experienced the stage of Emptiness/Community during the nine-game winning streak. Attributable to the literature (Peck, 1987) regarding the characteristics of a group in Pseudo-Community, the team for this study most likely experienced a stage of Pseudo-Community during the first four games of the season. Considering the dynamic and recursive nature of an athletic season, the researcher determined that the team may have in fact experienced a stage of Chaos both concurrently and subsequent to Pseudo-Community. In effect, it was determined that the team experienced an optimal experience during the nine-game winning streak. Due to data limitations and the sample size it was not possible to predict what would occur for a second season. However, a three stage model of team development was proposed contiguous the team's nine-game winning streak. There is a great deal that is not fully understood about the concept of team development, but suggestions are made for further research into this fascinating phenomenon
Power computation for the triboelectric nanogenerator
We consider, from a mathematical perspective, the power generated by a
contact-mode triboelectric nanogenerator, an energy harvesting device that has
been well studied recently. We encapsulate the behaviour of the device in a
differential equation, which although linear and of first order, has periodic
coefficients, leading to some interesting mathematical problems. In studying
these, we derive approximate forms for the mean power generated and the current
waveforms, and describe a procedure for computing the Fourier coefficients for
the current, enabling us to show how the power is distributed over the
harmonics. Comparisons with accurate numerics validate our analysis
The Universal Rotation Curve of Spiral Galaxies. II The Dark Matter Distribution out to the Virial Radius
In the current LambdaCDM cosmological scenario, N-body simulations provide us
with a Universal mass profile, and consequently a Universal equilibrium
circular velocity of the virialized objects, as galaxies. In this paper we
obtain, by combining kinematical data of their inner regions with global
observational properties, the Universal Rotation Curve (URC) of disk galaxies
and the corresponding mass distribution out to their virial radius. This curve
extends the results of Paper I, concerning the inner luminous regions of Sb-Im
spirals, out to the edge of the galaxy halos.Comment: In press on MNRAS. 10 pages, 8 figures. The Mathematica code for the
figures is available at: http://www.novicosmo.org/salucci.asp Corrected typo
Coexistence of ferromagnetism and singlet superconductivity via kinetic exchange
We propose a novel mechanism for the coexistence of metallic ferromagnetism
and singlet superconductivity assuming that the magnetic instability is due to
kinetic exchange. Within this scenario, the unpaired electrons which contribute
to the magnetization have a positive feedback on the gain of the kinetic energy
in the coexisting phase by undressing the effective mass of the carriers
involved into the pairing. The evolution of the magnetization and pairing
amplitude, and the phase diagram are first analyzed for a generic kinetic
exchange model and then are determined within a specific case with spin
dependent bond-charge occupation.Comment: 4 pages, 2 figure
X-Ray Observations of Black Widow Pulsars
We describe the first X-ray observations of five short orbital period ( day), -ray emitting, binary millisecond pulsars. Four of these, PSRs
J0023+0923, J11243653, J1810+1744, and J22561024 are `black-widow'
pulsars, with degenerate companions of mass , three of which
exhibit radio eclipses. The fifth source, PSR J2215+5135, is an eclipsing
`redback' with a near Roche-lobe filling 0.2 solar mass non-degenerate
companion. Data were taken using the \textit{Chandra X-Ray Observatory} and
covered a full binary orbit for each pulsar. Two pulsars, PSRs J2215+5135 and
J22561024, show significant orbital variability while PSR J11243653 shows
marginal orbital variability. The lightcurves for these three pulsars have
X-ray flux minima coinciding with the phases of the radio eclipses. This
phenomenon is consistent with an intrabinary shock emission interpretation for
the X-rays. The other two pulsars, PSRs J0023+0923 and J1810+1744, are fainter
and do not demonstrate variability at a level we can detect in these data. All
five spectra are fit with three separate models: a power-law model, a blackbody
model, and a combined model with both power-law and blackbody components. The
preferred spectral fits yield power-law indices that range from 1.3 to 3.2 and
blackbody temperatures in the hundreds of eV. The spectrum for PSR J2215+5135
shows a significant hard X-ray component, with a large number of counts above 2
keV, which is additional evidence for the presence of intrabinary shock
emission and is similar to what has been detected in the low-mass X-ray binary
to millisecond pulsar transition object PSR J1023+0038.Comment: 8 pages, 6 figures, 2 tables, submitted to Ap
An Overview of Poly(lactic-co-glycolic) Acid (PLGA)-Based Biomaterials for Bone Tissue Engineering
Poly(lactic-co-glycolic) acid (PLGA) has attracted considerable interest as a base material for biomedical applications due to its: (i) biocompatibility; (ii) tailored biodegradation rate (depending on the molecular weight and copolymer ratio); (iii) approval for clinical use in humans by the U.S. Food and Drug Administration (FDA); (iv) potential to modify surface properties to provide better interaction with biological materials; and (v) suitability for export to countries and cultures where implantation of animal-derived products is unpopular. This paper critically reviews the scientific challenge of manufacturing PLGA-based materials with suitable properties and shapes for specific biomedical applications, with special emphasis on bone tissue engineering. The analysis of the state of the art in the field reveals the presence of current innovative techniques for scaffolds and material manufacturing that are currently opening the way to prepare biomimetic PLGA substrates able to modulate cell interaction for improved substitution, restoration, or enhancement of bone tissue function
A constant dark matter halo surface density in galaxies
We confirm and extend the recent finding that the central surface density
r_0*rho_0 galaxy dark matter halos, where r_0 and rho_0 are the halo core
radius and central density, is nearly constant and independent of galaxy
luminosity. Based on the co-added rotation curves of about 1000 spiral
galaxies, mass models of individual dwarf irregular and spiral galaxies of late
and early types with high-quality rotation curves and, galaxy-galaxy weak
lensing signals from a sample of spiral and elliptical galaxies, we find that
log(r_0*rho_0) = 2.15 +- 0.2, in units of log(Msol/pc^2). We also show that the
observed kinematics of Local Group dwarf spheroidal galaxies are consistent
with this value. Our results are obtained for galactic systems spanning over 14
magnitudes, belonging to different Hubble Types, and whose mass profiles have
been determined by several independent methods. In the same objects, the
approximate constancy of rho_0*r_0 is in sharp contrast to the systematical
variations, by several orders of magnitude, of galaxy properties, including
rho_0 and central stellar surface density.Comment: Accepted for publication in MNRAS. 9 pages, 4 figure
Bifurcation curves of subharmonic solutions
We revisit a problem considered by Chow and Hale on the existence of
subharmonic solutions for perturbed systems. In the analytic setting, under
more general (weaker) conditions, we prove their results on the existence of
bifurcation curves from the nonexistence to the existence of subharmonic
solutions. In particular our results apply also when one has degeneracy to
first order -- i.e. when the subharmonic Melnikov function vanishes
identically. Moreover we can deal as well with the case in which degeneracy
persists to arbitrarily high orders, in the sense that suitable generalisations
to higher orders of the subharmonic Melnikov function are also identically
zero. In general the bifurcation curves are not analytic, and even when they
are smooth they can form cusps at the origin: we say in this case that the
curves are degenerate as the corresponding tangent lines coincide. The
technique we use is completely different from that of Chow and Hale, and it is
essentially based on rigorous perturbation theory.Comment: 29 pages, 2 figure
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