40,091 research outputs found
Persistence of characteristics of an ordered flux line lattice above the second peak in
We report Small Angle Neutron Scattering measurements of the flux lines
lattice (FLL) in . As previously reported, the
scattered intensity decreases strongly when the magnetic field is increased,
but it remains measurable far above the second peak. The direct observation of
Bragg peaks proves that the characteristics of a lattice are still present. No
structural features related to a symmetry breaking, such as a liquid like or an
amorphous state, can be observed. However, the associated scattered intensity
is very low and is difficult to explain. We discuss the coexistence between two
FLL states as a possible interpretation.Comment: accepted for publication in Phys Rev
Foundations of self-consistent particle-rotor models and of self-consistent cranking models
The Kerman-Klein formulation of the equations of motion for a nuclear shell
model and its associated variational principle are reviewed briefly. It is then
applied to the derivation of the self-consistent particle-rotor model and of
the self-consistent cranking model, for both axially symmetric and triaxial
nuclei. Two derivations of the particle-rotor model are given. One of these is
of a form that lends itself to an expansion of the result in powers of the
ratio of single-particle angular momentum to collective angular momentum, that
is essentual to reach the cranking limit. The derivation also requires a
distinct, angular-momentum violating, step. The structure of the result implies
the possibility of tilted-axis cranking for the axial case and full
three-dimensional cranking for the triaxial one. The final equations remain
number conserving. In an appendix, the Kerman-Klein method is developed in more
detail, and the outlines of several algorithms for obtaining solutions of the
associated non-linear formalism are suggested.Comment: 29 page
Upper critical field in {BaKBiO}: magnetotransport versus magnetotunneling
Elastic tunneling is used as a powerful direct tool to determine the upper
critical field in the high- oxide BaKBiO. The
temperature dependence of inferred from the tunneling follows the
Werthamer-Helfand-Hohenberg prediction for type-II superconductors. A
comparison will be made with resistively determined critical field data.Comment: 4 pages incl. 5 figure
Numerical Solution of the Small Dispersion Limit of the Camassa-Holm and Whitham Equations and Multiscale Expansions
The small dispersion limit of solutions to the Camassa-Holm (CH) equation is
characterized by the appearance of a zone of rapid modulated oscillations. An
asymptotic description of these oscillations is given, for short times, by the
one-phase solution to the CH equation, where the branch points of the
corresponding elliptic curve depend on the physical coordinates via the Whitham
equations. We present a conjecture for the phase of the asymptotic solution. A
numerical study of this limit for smooth hump-like initial data provides strong
evidence for the validity of this conjecture. We present a quantitative
numerical comparison between the CH and the asymptotic solution. The dependence
on the small dispersion parameter is studied in the interior and at
the boundaries of the Whitham zone. In the interior of the zone, the difference
between CH and asymptotic solution is of the order , at the trailing
edge of the order and at the leading edge of the order
. For the latter we present a multiscale expansion which
describes the amplitude of the oscillations in terms of the Hastings-McLeod
solution of the Painlev\'e II equation. We show numerically that this
multiscale solution provides an enhanced asymptotic description near the
leading edge.Comment: 25 pages, 15 figure
Quaternionic Diffusion by a Potential Step
In looking for qualitative differences between quaternionic and complex
formulations of quantum physical theories, we provide a detailed discussion of
the behavior of a wave packet in presence of a quaternionic time-independent
potential step. In this paper, we restrict our attention to diffusion
phenomena. For the group velocity of the wave packet moving in the potential
region and for the reflection and transmission times, the study shows a
striking difference between the complex and quaternionic formulations which
could be matter of further theoretical discussions and could represent the
starting point for a possible experimental investigation.Comment: 10 pages, 1 figur
Relativistic Static Thin Disks: The Counter-Rotating Model
A detailed study of the Counter-Rotating Model (CRM) for generic finite
static axially symmetric thin disks with nonzero radial pressure is presented.
We find a general constraint over the counter-rotating tangential velocities
needed to cast the surface energy-momentum tensor of the disk as the
superposition of two counter-rotating perfect fluids. We also found expressions
for the energy density and pressure of the counter-rotating fluids. Then we
shown that, in general, there is not possible to take the two counter-rotating
fluids as circulating along geodesics neither take the two counter-rotating
tangential velocities as equal and opposite. An specific example is studied
where we obtain some CRM with well defined counter-rotating tangential
velocities and stable against radial perturbations. The CRM obtained are in
agree with the strong energy condition, but there are regions of the disks with
negative energy density, in violation of the weak energy condition.Comment: 19 pages, 6 figures. Submitted to Physical Review
Children's syntax is supported by the maturation of BA44 at 4 years, but of the posterior STS at 3 years of age
Within the first years of life, children learn major aspects of their native language. However, the ability to process complex sentence structures, a core faculty in human language called syntax, emerges only slowly. A milestone in syntax acquisition is reached around the age of 4 years, when children learn a variety of syntactic concepts. Here, we ask which maturational changes in the child's brain underlie the emergence of syntactically complex sentence processing around this critical age. We relate markers of cortical brain maturation to 3- and 4-year-olds' sentence processing in contrast to other language abilities. Our results show that distinct cortical brain areas support sentence processing in the two age groups. Sentence production abilities at 3 years were associated with increased surface area in the most posterior part of the left superior temporal sulcus, whereas 4-year-olds showed an association with cortical thickness in the left posterior part of Broca's area, i.e. BA44. The present findings suggest that sentence processing abilities rely on the maturation of distinct cortical regions in 3- compared to 4-year-olds. The observed shift to more mature regions involved in processing syntactically complex sentences may underlie behavioral milestones in syntax acquisition at around 4 years
Children’s syntax is supported by the maturation of BA44 at 4 years, but of the posterior STS at 3 years of age
Nanometer Scale Mapping of the Density of States in an Inhomogeneous Superconductor
Using high speed scanning tunneling spectroscopy, we perform a full mapping
of the quasiparticle density of states (DOS) in single crystals of
BiPbSrCaCuO(2212). The measurements carried out at 5 K showed a complex spatial
pattern of important variations of the local DOS on the nanometer scale.
Superconducting areas are co-existing with regions of a smooth and larger
gap-like DOS structure. The superconducting regions are found to have a minimum
size of about 3 nm. The role of Pb-introduced substitutional disorder in the
observed spatial variations of the local DOS is discussed.Comment: 4 page Letter with 3 figures (2 color figures
Solid helium at high pressure: A path-integral Monte Carlo simulation
Solid helium (3He and 4He) in the hcp and fcc phases has been studied by
path-integral Monte Carlo. Simulations were carried out in the
isothermal-isobaric (NPT) ensemble at pressures up to 52 GPa. This allows one
to study the temperature and pressure dependences of isotopic effects on the
crystal volume and vibrational energy in a wide parameter range. The obtained
equation of state at room temperature agrees with available experimental data.
The kinetic energy, E_k, of solid helium is found to be larger than the
vibrational potential energy, E_p. The ratio E_k/E_p amounts to about 1.4 at
low pressures, and decreases as the applied pressure is raised, converging to
1, as in a harmonic solid. Results of these simulations have been compared with
those yielded by previous path integral simulations in the NVT ensemble. The
validity range of earlier approximations is discussed.Comment: 7 pages, 5 figure
- …