2,972 research outputs found
Hyperuniformity with no fine tuning in sheared sedimenting suspensions
Particle suspensions, present in many natural and industrial settings,
typically contain aggregates or other microstructures that can complicate
macroscopic flow behaviors and damage processing equipment. Recent work found
that applying uniform periodic shear near a critical transition can reduce
fluctuations in the particle concentration across all length scales, leading to
a hyperuniform state. However, this strategy for homogenization requires fine
tuning of the strain amplitude. Here we show that in a model of sedimenting
particles under periodic shear, there is a well-defined regime at low
sedimentation speed where hyperuniform scaling automatically occurs. Our
simulations and theoretical arguments show that the homogenization extends up
to a finite lengthscale that diverges as the sedimentation speed approaches
zero.Comment: 11 pages, 6 figure
Weak Scale Superstrings
Recent developments in string duality suggest that the string scale may not
be irrevocably tied to the Planck scale. Two explicit but unrealistic examples
are described where the ratio of the string scale to the Planck scale is
arbitrarily small. Solutions which are more realistic may exist in the
intermediate coupling or ``truly strong coupling'' region of the heterotic
string. Weak scale superstrings have dramatic experimental consequences for
both collider physics and cosmology.Comment: harvmac, 14 pages. References added, 3 typos fixed, Comments added at
beginning of section 4 emphasizing flaws of the toy example
Optical Sky Brightness at Cerro Tololo Inter-American Observatory from 1992 to 2006
We present optical UBVRI sky brightness measures from 1992 through 2006. The
data are based on CCD imagery obtained with the CTIO 0.9-m, 1.3-m, and 1.5-m
telescopes. The B- and V-band data are in reasonable agreement with
measurements previously made at Mauna Kea, though on the basis of a small
number of images per year there are discrepancies for the years 1992 through
1994. Our CCD-based data are not significantly different than values obtained
at Cerro Paranal. We find that the yearly averages of V-band sky brightness are
best correlated with the 10.7-cm solar flux taken 5 days prior to the sky
brightness measures. This implies an average speed of 350 km/sec for the solar
wind. While we can measure an enhancement of the night sky levels over La
Serena 10 degrees above the horizon, at elevation angles above 45 degrees we
find no evidence that the night sky brightness at Cerro Tololo is affected by
artificial light of nearby towns and cities.Comment: 24 pages, 5 figures, to be published in the June, 2007, issue of the
Publications of the Astron. Society of the Pacifi
Slinky Inflation
We present a new approach to quintessential inflation, in which both dark
energy and inflation are explained by the evolution of a single scalar field.
We start from a simple scalar potential with both oscillatory and exponential
behavior. We employ the conventional reheating mechanism of new inflation, in
which the scalar decays to light fermions with a decay width that is
proportional to the scalar mass. Because our scalar mass is proportional to the
Hubble rate, this gives adequate reheating at early times while shutting off at
late times to preserve quintessence and satisfy nucleosynthesis constraints.
We discuss a simple model which solves the horizon, flatness, and "why now"
problems. Without any additional tuning of parameters, this model satisfies all
constraints from CMB, large scale structure, and nucleosynthesis. The
predictions for the inflationary spectral indices are n_S = n_T = 1. In this
model we are currently beginning the third cosmic epoch of accelerated
expansion.Comment: 5 pages, 2 color figures, 1 tabl
Desarrollo de conductas antisociales y funcionamiento familiar en estudiantes de nivel secundaria de instituciones educativas públicas de Comas, 2019
La presente investigación titulada Desarrollo de conductas antisociales y funcionamiento
familiar en estudiantes de nivel secundario de instituciones educativas públicas de Comas,
2019, tuvo como objetivo, determinar la relación existente entre el desarrollo de conductas
antisociales y el funcionamiento familiar, a través de una muestra conformada por 343
estudiantes de ambos sexos, con edades oscilantes entre los 11 y 17 años de edad,
pertenecientes a 4 instituciones educativas públicas de nivel secundario, del distrito
mencionado. Se aplicaron instrumentos como el Cuestionario de Conducta Antisocial (CCA) y la Escala de Cohesión y Adaptabilidad Familiar (FACES III). Asimismo, la presente
investigación fue de tipo descriptivo y correlacional, de enfoque cuantitativo, de tipo básica
y de diseño no experimental, dentro de los resultados obtenidos, gracias a la prueba de
normalidad Shapiro - Wilk, se determinó que en la mayoría de los casos, nuestra muestra no
se ajustó a una distribución normal de los datos, motivo por el cual se trabajaron las
correlaciones, mediante el coeficiente de correlación Rho de Spearman, igualmente, los
resultados demostraron que el desarrollo de conductas antisociales se correlaciona de manera
inversa y significativa con el funcionamiento familiar, concluyendo que aquellos individuos
que presenten mayores índices para el desarrollo de conductas antisociales, se encontrarían
vivenciando un funcionamiento familiar que denote disfunción familiar
Anomalies, Dualities, and Topology of D=6 N=1 Superstring Vacua
We consider various aspects of compactifications of the Type I/heterotic
theory on K3. One family of such compactifications includes the
standard embedding of the spin connection in the gauge group, and is on the
same moduli space as the compactification of the heterotic
theory on K3 with instanton numbers (8,16). Another class, which includes an
orbifold of the Type I theory recently constructed by Gimon and Polchinski and
whose field theory limit involves some topological novelties, is on the moduli
space of the heterotic theory on K3 with instanton numbers
(12,12). These connections between and models
can be demonstrated by T duality, and permit a better understanding of
non-perturbative gauge fields in the (12,12) model. In the transformation
between and models, the strong/weak coupling
duality of the (12,12) model is mapped to T duality in the Type
I theory. The gauge and gravitational anomalies in the Type I theory are
canceled by an extension of the Green-Schwarz mechanism.Comment: 48 page
N=3 Warped Compactifications
Orientifolds with three-form flux provide some of the simplest string
examples of warped compactification. In this paper we show that some models of
this type have the unusual feature of D=4, N=3 spacetime supersymmetry. We
discuss their construction and low energy physics. Although the local form of
the moduli space is fully determined by supersymmetry, to find its global form
requires a careful study of the BPS spectrum.Comment: 27 pages, v2: 32pp., RevTeX4, fixed factors, slightly improved
sections 3D and 4B, v3: added referenc
The p110 delta structure: mechanisms for selectivity and potency of new PI(3)K inhibitors.
Deregulation of the phosphoinositide-3-OH kinase (PI(3)K) pathway has been implicated in numerous pathologies including cancer, diabetes, thrombosis, rheumatoid arthritis and asthma. Recently, small-molecule and ATP-competitive PI(3)K inhibitors with a wide range of selectivities have entered clinical development. In order to understand the mechanisms underlying the isoform selectivity of these inhibitors, we developed a new expression strategy that enabled us to determine to our knowledge the first crystal structure of the catalytic subunit of the class IA PI(3)K p110 delta. Structures of this enzyme in complex with a broad panel of isoform- and pan-selective class I PI(3)K inhibitors reveal that selectivity toward p110 delta can be achieved by exploiting its conformational flexibility and the sequence diversity of active site residues that do not contact ATP. We have used these observations to rationalize and synthesize highly selective inhibitors for p110 delta with greatly improved potencies
A first-principles comparison of the electronic properties of MgC_{y}Ni_{3} and ZnC_{y}Ni_{3} alloys
First-principles, density-functional-based electronic structure calculations
are employed to study the changes in the electronic properties of ZnC_{y}Ni_{3}
and MgC_{y}Ni_{3} using the Korringa-Kohn-Rostoker coherent-potential
approximation method in the atomic sphere approximation (KKR-ASA CPA). As a
function of decreasing C at%, we find a steady decrease in the lattice constant
and bulk modulus in either alloys. However, the pressure derivative of the bulk
modulus displays an opposite trend. Following the Debye model, which relates
the pressure derivative of the bulk modulus with the average phonon frequency
of the crystal, it can thus be argued that ZnCNi_{3} and its disordered alloys
posses a different phonon spectra in comparison to its MgCNi_{3} counterparts.
This is further justified by the marked similarity we find in the electronic
structure properties such as the variation in the density of states and the
Hopfield parameters calculated for these alloys. The effects on the equation of
state parameters and the density of states at the Fermi energy, for partial
replacement of Mg by Zn are also discussed.Comment: 19 pages, 15 figure
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