130 research outputs found
Josephson current in a superconductor -- ferromagnet -- superconductor junction with in-plane ferromagnetic domains
We study a diffusive superconductor--ferromagnet--superconductor (SFS)
junction with in-plane ferromagnetic domains. Close to the superconducting
transition temperature, we describe the proximity effect in the junction with
the linearized Usadel equations. We find that properties of such a junction
depend on the size of the domains relative to the magnetic coherence length. In
the case of large domains, the junction exhibits transitions to the
state, similarly to a single-domain SFS junction. In the case of small domains,
the magnetization effectively averages out, and the junction is always in the
zero state, similarly to a superconductor--normal metal--superconductor (SNS)
junction. In both those regimes, the influence of domain walls may be
approximately described as an effective spin-flip scattering. We also study the
inhomogeneous distribution of the local current density in the junction. Close
to the 0-- transitions, the directions of the critical current may be
opposite in the vicinity of the domain wall and in the middle of the domains.Comment: 9 pages, 6 figure
DVB-S2 Experiment over NASA's Space Network
The commercial DVB-S2 standard was successfully demonstrated over NASAs Space Network (SN) and the Tracking Data and Relay Satellite System (TDRSS) during testing conducted September 20-22nd, 2016. This test was a joint effort between NASA Glenn Research Center (GRC) and Goddard Space Flight Center (GSFC) to evaluate the performance of DVB-S2 as an alternative to traditional NASA SN waveforms. Two distinct sets of tests were conducted: one was sourced from the Space Communication and Navigation (SCaN) Testbed, an external payload on the International Space Station, and the other was sourced from GRCs S-band ground station to emulate a Space Network user through TDRSS. In both cases, a commercial off-the-shelf (COTS) receiver made by Newtec was used to receive the signal at White Sands Complex. Using SCaN Testbed, peak data rates of 5.7 Mbps were demonstrated. Peak data rates of 33 Mbps were demonstrated over the GRC S-band ground station through a 10MHz channel over TDRSS, using 32-amplitude phase shift keying (APSK) and a rate 89 low density parity check (LDPC) code. Advanced features of the DVB-S2 standard were evaluated, including variable and adaptive coding and modulation (VCMACM), as well as an adaptive digital pre-distortion (DPD) algorithm. These features provided additional data throughput and increased link performance reliability. This testing has shown that commercial standards are a viable, low-cost alternative for future Space Network users
Generation of Cosmological Seed Magnetic Fields from Inflation with Cutoff
Inflation has the potential to seed the galactic magnetic fields observed
today. However, there is an obstacle to the amplification of the quantum
fluctuations of the electromagnetic field during inflation: namely the
conformal invariance of electromagnetic theory on a conformally flat underlying
geometry. As the existence of a preferred minimal length breaks the conformal
invariance of the background geometry, it is plausible that this effect could
generate some electromagnetic field amplification. We show that this scenario
is equivalent to endowing the photon with a large negative mass during
inflation. This effective mass is negligibly small in a radiation and matter
dominated universe. Depending on the value of the free parameter of the theory,
we show that the seed required by the dynamo mechanism can be generated. We
also show that this mechanism can produce the requisite galactic magnetic field
without resorting to a dynamo mechanism.Comment: Latex, 16 pages, 2 figures, 4 references added, minor corrections;
v4: more references added, boundary term written in a covariant form,
discussion regarding other gauge fields added, submitted to PRD; v5: matched
with the published versio
Josephson current in a superconductor-ferromagnet junction with two non-collinear magnetic domains
We study the Josephson effect in a
superconductor--ferromagnet--superconductor (SFS) junction with ferromagnetic
domains of non-collinear magnetization. As a model for our study we consider a
diffusive junction with two ferromagnetic domains along the junction. The
superconductor is assumed to be close to the critical temperature , and
the linearized Usadel equations predict a sinusoidal current-phase relation. We
find analytically the critical current as a function of domain lengths and of
the angle between the orientations of their magnetizations. As a function of
those parameters, the junction may undergo transitions between 0 and
phases. We find that the presence of domains reduces the range of junction
lengths at which the phase is observed. For the junction with two domains
of the same length, the phase totally disappears as soon as the
misorientation angle exceeds . We further comment on possible
implication of our results for experimentally observable 0-- transitions
in SFS junctions.Comment: 9 pages, 4 figures, minor changes, references adde
Elastic and Raman scattering of 9.0 and 11.4 MeV photons from Au, Dy and In
Monoenergetic photons between 8.8 and 11.4 MeV were scattered elastically and
in elastically (Raman) from natural targets of Au, Dy and In.15 new cross
sections were measured. Evidence is presented for a slight deformation in the
197Au nucleus, generally believed to be spherical. It is predicted, on the
basis of these measurements, that the Giant Dipole Resonance of Dy is very
similar to that of 160Gd. A narrow isolated resonance at 9.0 MeV is observed in
In.Comment: 31 pages, 11 figure
Two-photon final states in peripheral heavy ion collisions
We discuss processes leading to two photon final states in peripheral heavy
ion collisions at RHIC. Due to the large photon luminosity we show that the
continuum subprocess can be observed with a
large number of events. We study this reaction when it is intermediated by a
resonance made of quarks or gluons and discuss its interplay with the continuum
process, verifying that in several cases the resonant process ovewhelms the
continuum one. It is also investigated the possibility of observing a scalar
resonance (the meson) in this process. Assuming for the the
mass and total decay width values recently reported by the E791 Collaboration
we show that RHIC may detect this particle in its two photon decay mode if its
partial photonic decay width is of the order of the ones discussed in the
literature.Comment: 10 pages, 8 figure
Field induced superconductivity with enhanced and tunable paramagnetic limit
We demonstrate that in a superconducting multilayered system with alternating
interlayer coupling a new type of nonuniform superconducting state can be
realized under in-plane magnetic field. The Zeeman effect in this state is
compensated by the energy splitting between bonding and antibonding levels.
Such compensation mechanism at low temperature leads to the field-induced
superconductivity. We discuss the conditions for the experimental observation
of the predicted phenomena.Comment: 5 pages, 4 figures include
On the pion electroproduction amplitude
We analyze amplitudes for the pion electroproduction on proton derived from
Lagrangians based on the local chiral SU(2) x SU(2) symmetries. We show that
such amplitudes do contain information on the nucleon axial form factor F_A in
both soft and hard pion regimes. This result invalidates recent Haberzettl's
claim that the pion electroproduction at threshold cannot be used to extract
any information regarding F_A.Comment: 14 pages, 6 figures, revised version, accepted for publication in
Phys. Rev.
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Coordinated Science Laboratory was formerly known as Control Systems LaboratoryNational Science Foundation / ECS-84-10902 and CCR-87-14565Amoco Foundatio
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