13,339 research outputs found
CP Violation and Moduli Stabilization in Heterotic Models
The role of moduli stabilization in predictions for CP violation is examined
in the context of four-dimensional effective supergravity models obtained from
the weakly coupled heterotic string. We point out that while stabilization of
compactification moduli has been studied extensively, the determination of
background values for other scalars by dynamical means has not been subjected
to the same degree of scrutiny. These other complex scalars are important
potential sources of CP violation and we show in a simple model how their
background values (including complex phases) may be determined from the
minimization of the supergravity scalar potential, subject to the constraint of
vanishing cosmological constant.Comment: 8 Pages. Based on a talk given at the CP Violation Conference,
University of Michigan, Ann Arbor, November 4-18, 2001, correction to Eq.
(27
Molecular dynamics simulations of the evaporation of particle-laden droplets
We use molecular dynamics simulations to study the evaporation of
particle-laden droplets on a heated surface. The droplets are composed of a
Lennard-Jones fluid containing rigid particles which are spherical sections of
an atomic lattice, and heating is controlled through the temperature of an
atomistic substrate. We observe that sufficiently large (but still nano-sized)
particle-laden drops exhibit contact line pinning, measure the outward fluid
flow field which advects particle to the drop rim, and find that the structure
of the resulting aggregate varies with inter-particle interactions. In
addition, the profile of the evaporative fluid flux is measured with and
without particles present, and is also found to be in qualitative agreement
with earlier theory. The compatibility of simple nanoscale calculations and
micron-scale experiments indicates that molecular simulation may be used to
predict aggregate structure in evaporative growth processes
Observers can always generate nonlocal correlations without aligning measurements by covering all their bases
Quantum theory allows for correlations between the outcomes of distant
measurements that are inconsistent with any locally causal theory, as
demonstrated by the violation of a Bell inequality. Typical demonstrations of
these correlations require careful alignment between the measurements, which
requires distant parties to share a reference frame. Here, we prove, following
a numerical observation by Shadbolt et al., that if two parties share a Bell
state and each party randomly chooses three orthogonal measurements, then the
parties will always violate a Bell inequality. Furthermore, we prove that this
probability is highly robust against local depolarizing noise, in that small
levels of noise only decrease the probability of violating a Bell inequality by
a small amount. We also show that generalizing to N parties increases the
robustness against noise. These results improve on previous ones that only
allowed a high probability of violating a Bell inequality for large numbers of
parties.Comment: 4 pages, 2 figures. v2: updated reference. v3: published versio
A survey of the properties of early-type galaxies
A compilation of the properties of elliptical and early disk galaxies was completed. In addition to material from the literature, such as Infrared Astronomy Satellite (IRAS) fluxes, the compilation includes recent measurements of HI and CO, as well as a review of the x ray properties by Forman and Jones. The data are used to evaluate the gas content of early systems and to search for correlations with x ray emission. The interstellar medium in early-type galaxies is generally dominated by hot interstellar gas (T approx. 10 to the 7th power K; c.f. the review by Fabbiano 1989 and references therein). In addition, a significant fraction of these galaxies show infrared emission (Knapp, et al., 1989), optical emission lines, and visible dust. Sensitive studies in HI and CO of a number of these galaxies have been completed recently, resulting in several detections, particularly of the later types. Researchers wish to understand the connection among these different forms of the interstellar medium, and to examine the theoretical picture of the fate of the hot gas. To do so, they compiled observations of several forms of interstellar matter for a well-defined sample of early-type galaxies. Here they present a statistical analysis of this data base and discuss the implications of the results
Shear flow pumping in open microfluidic systems
We propose to drive open microfluidic systems by shear in a covering fluid
layer, e.g., oil covering water-filled chemical channels. The advantages as
compared to other means of pumping are simpler forcing and prevention of
evaporation of volatile components. We calculate the expected throughput for
straight channels and show that devices can be built with off-the-shelf
technology. Molecular dynamics simulations suggest that this concept is
scalable down to the nanoscale.Comment: 4 pages, 4 figure, submitted to Phys. Rev. Let
A Simple Model for Pulse Profiles from Precessing Pulsars, with Special Application to Relativistic Binary PSR B1913+16
We study the observable pulse profiles that can be generated from precessing
pulsars. A novel coordinate system is defined to aid visualization of the
observing geometry. Using this system we explore the different families of
profiles that can be generated by simple, circularly symmetric beam shapes. An
attempt is then made to fit our model to the observations of relativistic
binary PSR B1913+16. It is found that while qualitatively similar pulse
profiles can be produced, this minimal model is insufficient for an accurate
match to the observational data. Consequently, we confirm that the emission
beam of PSR B1913+16 must deviate from circular symmetry, as first reported by
Weisberg and Taylor. However, the approximate fits obtained suggest that it may
be sufficient to consider only minimal deviations from a circular beam in order
to explain the data. We also comment on the applicability of our analysis
technique to other precessing pulsars, both binary and isolated.Comment: 35 pages and 8 figures. Published versio
Nonnegative subtheories and quasiprobability representations of qubits
Negativity in a quasiprobability representation is typically interpreted as
an indication of nonclassical behavior. However, this does not preclude states
that are non-negative from exhibiting phenomena typically associated with
quantum mechanics - the single qubit stabilizer states have non-negative Wigner
functions and yet play a fundamental role in many quantum information tasks. We
seek to determine what other sets of quantum states and measurements for a
qubit can be non-negative in a quasiprobability representation, and to identify
nontrivial unitary groups that permute the states in such a set. These sets of
states and measurements are analogous to the single qubit stabilizer states. We
show that no quasiprobability representation of a qubit can be non-negative for
more than four bases and that the non-negative bases in any quasiprobability
representation must satisfy certain symmetry constraints. We provide an
exhaustive list of the sets of single qubit bases that are non-negative in some
quasiprobability representation and are also permuted by a nontrivial unitary
group. This list includes two families of three bases that both include the
single qubit stabilizer states as a special case and a family of four bases
whose symmetry group is the Pauli group. For higher dimensions, we prove that
there can be no more than 2^{d^2} states in non-negative bases of a
d-dimensional Hilbert space in any quasiprobability representation.
Furthermore, these bases must satisfy certain symmetry constraints,
corresponding to requiring the bases to be sufficiently complementary to each
other.Comment: 17 pages, 8 figures, comments very welcome; v2 published version.
Note that the statement and proof of Theorem III.2 in the published version
are incorrect (an erratum has been submitted), and this arXiv version (v2)
presents the corrected theorem and proof. The conclusions of the paper are
unaffected by this correctio
Quasinormal Modes and Stability Criterion of Dilatonic Black Hole in 1+1 and 4+1 Dimensions
We study the stability of black holes that are solutions of the dilaton
gravity derived from string-theoretical models in two and five dimensions
against to scalar field perturbations, using the Quasinormal Modes (QNMs)
approach. In order to find the QNMs corresponding to a black hole geometry, we
consider perturbations described by a massive scalar field non-minimally
coupled to gravity. We find that the QNM's frequencies turn out to be pure
imaginary leading to purely damped modes, that is in agreement with the
literature of dilatonic black holes. Our result exhibits the unstable behavior
of the considered geometry against the scalar perturbations. We consider both
the minimal coupling case, i.e., for which the coupling parameter
vanishes, and the case .Comment: sevarl changes, some reference was added, 10 pages, 4 figure
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