128 research outputs found
Measurement of the Transverse Spin Transfer Coefficient D_nn(0˚) for (p,n) Reactions at 160 MeV
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Spin Transfer Measurements for (p,n) Reactions at Intermediate Energy
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Measurements of Gamow-Teller Strength Distributions in Masses 13 and 15
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Excitation of Giant Spin-Isospin Multipole Vibrations in 54,56-Fe and 58,60-Ni
This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit
Toward a Quantization of Null Dust Collapse
Spherically symmetric, null dust clouds, like their time-like counterparts,
may collapse classically into black holes or naked singularities depending on
their initial conditions. We consider the Hamiltonian dynamics of the collapse
of an arbitrary distribution of null dust, expressed in terms of the physical
radius, , the null coordinates, for a collapsing cloud or for an
expanding cloud, the mass function, , of the null matter, and their
conjugate momenta. This description is obtained from the ADM description by a
Kucha\v{r}-type canonical transformation. The constraints are linear in the
canonical momenta and Dirac's constraint quantization program is implemented.
Explicit solutions the constraints are obtained for both expanding and
contracting null dust clouds with arbitrary mass functions.Comment: 10 pages, 2 figures (eps), RevTeX4. The last two sections have been
revised and corrected. To appear in Phys. Rev.
Spin injection into a ballistic semiconductor microstructure
A theory of spin injection across a ballistic
ferromagnet-semiconductor-ferromagnet junction is developed for the Boltzmann
regime. Spin injection coefficient is suppressed by the Sharvin
resistance of the semiconductor , where is the
Fermi-surface cross-section. It competes with the diffusion resistances of the
ferromagnets , and in the absence of contact
barriers. Efficient spin injection can be ensured by contact barriers. Explicit
formulae for the junction resistance and the spin-valve effect are presented.Comment: 5 pages, 2 column REVTeX. Explicit prescription relating the results
of the ballistic and diffusive theories of spin injection is added. To this
end, some notations are changed. Three references added, typos correcte
Row-switched states in two-dimensional underdamped Josephson junction arrays
When magnetic flux moves across layered or granular superconductor
structures, the passage of vortices can take place along channels which develop
finite voltage, while the rest of the material remains in the zero-voltage
state. We present analytical studies of an example of such mixed dynamics: the
row-switched (RS) states in underdamped two-dimensional Josephson arrays,
driven by a uniform DC current under external magnetic field but neglecting
self-fields. The governing equations are cast into a compact
differential-algebraic system which describes the dynamics of an assembly of
Josephson oscillators coupled through the mesh current. We carry out a formal
perturbation expansion, and obtain the DC and AC spatial distributions of the
junction phases and induced circulating currents. We also estimate the interval
of the driving current in which a given RS state is stable. All these
analytical predictions compare well with our numerics. We then combine these
results to deduce the parameter region (in the damping coefficient versus
magnetic field plane) where RS states can exist.Comment: latex, 48 pages, 15 figs using psfi
Coherent spin valve phenomena and electrical spin injection in ferromagnetic/semiconductor/ferromagnetic junctions
Coherent quantum transport in ferromagnetic/ semiconductor/ ferromagnetic
junctions is studied theoretically within the Landauer framework of ballistic
transport. We show that quantum coherence can have unexpected implications for
spin injection and that some intuitive spintronic concepts which are founded in
semi-classical physics no longer apply: A quantum spin-valve (QSV) effect
occurs even in the absence of a net spin polarized current flowing through the
device, unlike in the classical regime. The converse effect also arises, i.e. a
zero spin-valve signal for a non-vanishing spin-current. We introduce new
criteria useful for analyzing quantum and classical spin transport phenomena
and the relationships between them. The effects on QSV behavior of
spin-dependent electron transmission at the interfaces, interface Schottky
barriers, Rashba spin-orbit coupling and temperature, are systematically
investigated. While the signature of the QSV is found to be sensitive to
temperature, interestingly, that of its converse is not. We argue that the QSV
phenomenon can have important implications for the interpretation of
spin-injection in quantum spintronic experiments with spin-valve geometries.Comment: 15 pages including 11 figures. To appear in PR
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
Observation of Scaling Violations in Scaled Momentum Distributions at HERA
Charged particle production has been measured in deep inelastic scattering
(DIS) events over a large range of and using the ZEUS detector. The
evolution of the scaled momentum, , with in the range 10 to 1280
, has been investigated in the current fragmentation region of the Breit
frame. The results show clear evidence, in a single experiment, for scaling
violations in scaled momenta as a function of .Comment: 21 pages including 4 figures, to be published in Physics Letters B.
Two references adde
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