7,464 research outputs found
Existence of nodal solutions for Dirac equations with singular nonlinearities
We prove, by a shooting method, the existence of infinitely many solutions of
the form of the nonlinear Dirac
equation {equation*} i\underset{\mu=0}{\overset{3}{\sum}} \gamma^\mu
\partial_\mu \psi- m\psi - F(\bar{\psi}\psi)\psi = 0 {equation*} where
is compactly supported and \[F(x) = \{{array}{ll}
p|x|^{p-1} & \text{if} |x|>0 0 & \text{if} x=0 {array}.] with
under some restrictions on the parameters and We study also the
behavior of the solutions as tends to zero to establish the link between
these equations and the M.I.T. bag model ones
Constraining short-range spin-dependent forces with polarized He
We have searched for a short-range spin-dependent interaction using the spin
relaxation of hyperpolarized He. Such a new interaction would be mediated
by a hypothetical light scalar boson with \CP-violating couplings to the
neutron. The walls of the He cell would generate a pseudomagnetic field and
induce an extra depolarization channel. We did not see any anomalous spin
relaxation and we report the limit for interaction ranges between
and : , where () are the (pseudo)scalar coupling
constant, improving the previous best limit by 1 order of magnitude
Search for a new short-range spin-dependent force with polarized Helium 3
Measuring the depolarization rate of a He hyperpolarized gas is a
sensitive method to probe hypothetical short-range spin-dependent forces. A
dedicated experiment is being set up at the Institute Laue Langevin in Grenoble
to improve the sensitivity. We presented the status of the experiment at the
10th PATRAS Workshop on Axions, WIMPs and WISPs.Comment: Presented at the 10th PATRAS Workshop on Axions, WIMPs and WISP
Self-management of context-aware overlay ambient networks
Ambient Networks (ANs) are dynamically changing and heterogeneous as they consist of potentially large numbers of independent, heterogeneous mobile nodes, with spontaneous topologies that can logically interact with each other to share a common control space, known as the Ambient Control Space. ANs are also flexible i.e. they can compose and decompose dynamically and automatically, for supporting the deployment of cross-domain (new) services. Thus, the AN architecture must be sophisticatedly designed to support such high level of dynamicity, heterogeneity and flexibility. We advocate the use of service specific overlay networks in ANs, that are created on-demand according to specific service requirements, to deliver, and to automatically adapt services to the dynamically changing user and network context. This paper presents a self-management approach to create, configure, adapt, contextualise, and finally teardown service specific overlay networks
Ferromagnetism and interlayer exchange coupling in short period (Ga,Mn)As/GaAs superlattices
Magnetic properties of (Ga,Mn)As/GaAs superlattices are investigated. The
structures contain magnetic (Ga,Mn)As layers, separated by thin layers of
non-magnetic GaAs spacer. The short period GaMnAs/GaAs
superlattices exhibit a paramagnetic-to-ferromagnetic phase transition close to
60K, for thicknesses of (Ga,Mn)As down to 23 \AA. For
GaMnAs/GaAs superlattices of similar dimensions, the Curie
temperature associated with the ferromagnetic transition is found to oscillate
with the thickness of non magnetic spacer. The observed oscillations are
related to an interlayer exchange interaction mediated by the polarized holes
of the (Ga,Mn)As layers.Comment: REVTeX 4 style; 4 pages, 2 figure
Modelling the dynamics of turbulent floods
Consider the dynamics of turbulent flow in rivers, estuaries and floods. Based on the widely used k-epsilon model for turbulence, we use the techniques of centre manifold theory to derive dynamical models for the evolution of the water depth and of vertically averaged flow velocity and turbulent parameters. This new model for the shallow water dynamics of turbulent flow: resolves the vertical structure of the flow and the turbulence; includes interaction between turbulence and long waves; and gives a rational alternative to classical models for turbulent environmental flows
WIYN Open Cluster Study. XXXVIII. Stellar Radial Velocities in the Young Open Cluster M35 (NGC 2168)
We present 5201 radial-velocity measurements of 1144 stars, as part of an
ongoing study of the young (150 Myr) open cluster M35 (NGC 2168). We have
observed M35 since 1997, using the Hydra Multi-Object Spectrograph on the WIYN
3.5m telescope. Our stellar sample covers main-sequence stars over a magnitude
range of 13.0<V<16.5 (1.6 - 0.8 Msun) and extends spatially to a radius of 30
arcminutes (7 pc in projection at a distance of 805 pc or 4 core radii). Due to
its youth, M35 provides a sample of late-type stars with a range of rotation
periods. Therefore, we analyze the radial-velocity measurement precision as a
function of the projected rotational velocity. For narrow-lined stars (v sin i
< 10 km/s), the radial velocities have a precision of 0.5 km/s, which degrades
to 1.0 km/s for stars with v sin i = 50 km/s. The radial-velocity distribution
shows a well-defined cluster peak with a central velocity of -8.16 +/- 0.05
km/s, permitting a clean separation of the cluster and field stars. For stars
with >=3 measurements, we derive radial-velocity membership probabilities and
identify radial-velocity variables, finding 360 cluster members, 55 of which
show significant radial- velocity variability. Using these cluster members, we
construct a color-magnitude diagram for our stellar sample cleaned of field
star contamination. We also compare the spatial distribution of the single and
binary cluster members, finding no evidence for mass segregation in our stellar
sample. Accounting for measurement precision, we place an upper limit on the
radial-velocity dispersion of the cluster of 0.81 +/- 0.08 km/s. After
correcting for undetected binaries, we derive a true radial-velocity dispersion
of 0.65 +/- 0.10 km/s.Comment: accepted for publication in A
Grain-boundary grooving and agglomeration of alloy thin films with a slow-diffusing species
We present a general phase-field model for grain-boundary grooving and
agglomeration of polycrystalline alloy thin films. In particular, we study the
effects of slow-diffusing species on grooving rate. As the groove grows, the
slow species becomes concentrated near the groove tip so that further grooving
is limited by the rate at which it diffuses away from the tip. At early times
the dominant diffusion path is along the boundary, while at late times it is
parallel to the substrate. This change in path strongly affects the
time-dependence of grain boundary grooving and increases the time to
agglomeration. The present model provides a tool for agglomeration-resistant
thin film alloy design. keywords: phase-field, thermal grooving, diffusion,
kinetics, metal silicidesComment: 4 pages, 6 figure
Effect of lattice mismatch-induced strains on coupled diffusive and displacive phase transformations
Materials which can undergo slow diffusive transformations as well as fast
displacive transformations are studied using the phase-field method. The model
captures the essential features of the time-temperature-transformation (TTT)
diagrams, continuous cooling transformation (CCT) diagrams, and microstructure
formation of these alloys. In some materials systems there can exist an
intrinsic volume change associated with these transformations. We show that
these coherency strains can stabilize mixed microstructures (such as retained
austenite-martensite and pearlite-martensite mixtures) by an interplay between
diffusive and displacive mechanisms, which can alter TTT and CCT diagrams.
Depending on the conditions there can be competitive or cooperative nucleation
of the two kinds of phases. The model also shows that small differences in
volume changes can have noticeable effects on the early stages of martensite
formation and on the resulting microstructures.
-- Long version of cond-mat/0605577
-- Keywords: Ginzburg-Landau, martensite, pearlite, spinodal decomposition,
shape memory, microstructures, TTT diagram, CCT diagram, elastic compatibilityComment: 10 pages, 13 figures, long version of cond-mat/0605577. Physical
Review B, to appear in volume 75 (2007
- …