8,772 research outputs found
Quantal Consequences of Perturbations Which Destroy Structurally Unstable Orbits in Chaotic Billiards
Non-generic contributions to the quantal level-density from parallel segments
in billiards are investigated. These contributions are due to the existence of
marginally stable families of periodic orbits, which are structurally unstable,
in the sense that small perturbations, such as a slight tilt of one of the
segments, destroy them completely. We investigate the effects of such
perturbation on the corresponding quantum spectra, and demonstrate them for the
stadium billiard
Finding cool subdwarfs using a V-J reduced proper-motion diagram: Stellar parameters for 91 candidates
We present the results of a search for cool subdwarfs for which our
candidates were drawn from a V-J reduced proper-motion diagram constructed by
Salim & Gould (2002). Kinematic (U, V, and W) and self-consistent stellar
parameters (Teff, log g, [Fe/H], and V_t) are derived for 91 candidate
subdwarfs based on high resolution spectra. The observed stars span 3900K <
Teff < 6200K and -2.63 < [Fe/H] < 0.25 including only 3 giants (log g < 4.0).
Of the sample, 77 stars have MgH lines present in their spectra. With more than
56% of our candidate subdwarfs having [Fe/H] < -1.5, we show that the V-J
reduced proper-motion diagram readily identifies metal-poor stars.Comment: PASP (in press
Hierarchy of QM SUSYs on a Bounded Domain
We systematically formulate a hierarchy of isospectral Hamiltonians in
one-dimensional supersymmetric quantum mechanics on an interval and on a
circle, in which two successive Hamiltonians form N=2 supersymmetry. We find
that boundary conditions compatible with supersymmetry are severely restricted.
In the case of an interval, a hierarchy of, at most, three isospectral
Hamiltonians is possible with unique boundary conditions, while in the case of
a circle an infinite tower of isospectral Hamiltonians can be constructed with
two-parameter family of boundary conditions.Comment: 15 pages, 3 figure
Renormalization Group Analysis of a Quivering String Model of Posture Control
Scaling concepts and renormalization group (RG) methods are applied to a
simple linear model of human posture control consisting of a trembling or
quivering string subject to damping and restoring forces. The string is driven
by uncorrelated white Gaussian noise intended to model the corrections of the
physiological control system. We find that adding a weak quadratic nonlinearity
to the posture control model opens up a rich and complicated phase space
(representing the dynamics) with various non-trivial fixed points and basins of
attraction. The transition from diffusive to saturated regimes of the linear
model is understood as a crossover phenomenon, and the robustness of the linear
model with respect to weak non-linearities is confirmed. Correlations in
posture fluctuations are obtained in both the time and space domain. There is
an attractive fixed point identified with falling. The scaling of the
correlations in the front-back displacement, which can be measured in the
laboratory, is predicted for both the large-separation (along the string) and
long-time regimes of posture control.Comment: 20 pages, 13 figures, RevTeX, accepted for publication in PR
Gradient catastrophe and flutter in vortex filament dynamics
Gradient catastrophe and flutter instability in the motion of vortex filament
within the localized induction approximation are analyzed. It is shown that the
origin if this phenomenon is in the gradient catastrophe for the dispersionless
Da Rios system which describes motion of filament with slow varying curvature
and torsion. Geometrically this catastrophe manifests as a rapid oscillation of
a filament curve in a point that resembles the flutter of airfoils.
Analytically it is the elliptic umbilic singularity in the terminology of the
catastrophe theory. It is demonstrated that its double scaling regularization
is governed by the Painlev\'e-I equation.Comment: 11 pages, 3 figures, typos corrected, references adde
Повседневность первобытного человека
Seven samples of Siluro-Devonian sedimentary rocks from the Cantabrian and Central Iberian zones of the Iberian
Variscan belt have been investigated for provenance and contain four main age populations in variable relative proportion:
Ediacaran–Cryogenian (c. 0.55–0.8Ga), Tonian–Stenian (0.85–1.2Ga), Palaeoproterozoic (c. 1.8–2.2Ga) and Archaean (c.
2.5–3.3Ga). Five samples contain very minor Palaeozoic (Cambrian) zircons and six samples contain minor but significant
zircons of Middle and Early Mesoproterozoic (Ectasian–Calymmian, 1.6–1.8) age. These data highlight the transition from
an arc environment to a stable platform following the opening of the Rheic Ocean. Variations in detrital zircon populations
in Middle–Late Devonian times reflect the onset of Variscan convergence between Laurussia and Gondwana. The presence
of a high proportion of zircons of Tonian–Stenian age in Devonian sedimentary rocks may be interpreted as (1) the existence
of a large Tonian–Stenian arc terrane exposed in the NE African realm (in or around the Arabian–Nubian Shield), (2) the
participation, from the Ordovician time, of a more easterly alongshore provenance of Tonian–Stenian zircons, and (3) an
increase in the relative proportion of Tonian–Stenian zircons with respect to the Ediacaran–Cryogenian population owing to
the drift of the Avalonian–Cadomian ribbon continent, or the progressive burial of Ediacaran–Cryogenian rocks coeval with
the denudation of older source rocks from the craton interior
Detection and imaging in strongly backscattering randomly layered media
Abstract. Echoes from small reflectors buried in heavy clutter are weak and difficult to distinguish from the medium backscatter. Detection and imaging with sensor arrays in such media requires filtering out the unwanted backscatter and enhancing the echoes from the reflectors that we wish to locate. We consider a filtering and detection approach based on the singular value decomposition of the local cosine transform of the array response matrix. The algorithm is general and can be used for detection and imaging in heavy clutter, but its analysis depends on the model of the cluttered medium. This paper is concerned with the analysis of the algorithm in finely layered random media. We obtain a detailed characterization of the singular values of the transformed array response matrix and justify the systematic approach of the filtering algorithm for detecting and refining the time windows that contain the echoes that are useful in imaging
Minimal lepton flavor violating realizations of minimal seesaw models
We study the implications of the global U(1)R symmetry present in minimal
lepton flavor violating implementations of the seesaw mechanism for neutrino
masses. In the context of minimal type I seesaw scenarios with a slightly
broken U(1)R, we show that, depending on the R-charge assignments, two classes
of generic models can be identified. Models where the right-handed neutrino
masses and the lepton number breaking scale are decoupled, and models where the
parameters that slightly break the U(1)R induce a suppression in the light
neutrino mass matrix. We show that within the first class of models,
contributions of right-handed neutrinos to charged lepton flavor violating
processes are severely suppressed. Within the second class of models we study
the charged lepton flavor violating phenomenology in detail, focusing on mu to
e gamma, mu to 3e and mu to e conversion in nuclei. We show that sizable
contributions to these processes are naturally obtained for right-handed
neutrino masses at the TeV scale. We then discuss the interplay with the
effects of the right-handed neutrino interactions on primordial B - L
asymmetries, finding that sizable right-handed neutrino contributions to
charged lepton flavor violating processes are incompatible with the requirement
of generating (or even preserving preexisting) B - L asymmetries consistent
with the observed baryon asymmetry of the Universe.Comment: 21 pages, 4 figures; version 2: Discussion on possible generic models
extended, typos corrected, references added. Version matches publication in
JHE
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