9,049 research outputs found
A mean field approach for string condensed states
We describe a mean field technique for quantum string (or dimer) models.
Unlike traditional mean field approaches, the method is general enough to
include string condensed phases in addition to the usual symmetry breaking
phases. Thus, it can be used to study phases and phases transitions beyond
Landau's symmetry breaking paradigm. We demonstrate the technique with a simple
example: the spin-1 XXZ model on the Kagome lattice. The mean field calculation
predicts a number of phases and phase transitions, including a z=2 deconfined
quantum critical point.Comment: 10 pages + appendix, 15 figure
The gravitational time delay in the field of a slowly moving body with arbitrary multipoles
We calculate the time delay of light in the gravitational field of a slowly
moving body with arbitrary multipoles (mass and spin multipole moments) by the
Time-Transfer-Function (TTF) formalism. The parameters we use, first introduced
by Kopeikin for a gravitational source at rest, make the integration of the TTF
very elegant and simple. Results completely coincide with expressions from the
literature. The results for a moving body (with constant velocity) with
complete multipole-structure are new, according to our knowledge.Comment: 9 pages, no figure
Advanced relativistic VLBI model for geodesy
Our present relativistic part of the geodetic VLBI model for Earthbound
antennas is a consensus model which is considered as a standard for processing
high-precision VLBI observations. It was created as a compromise between a
variety of relativistic VLBI models proposed by different authors as documented
in the IERS Conventions 2010. The accuracy of the consensus model is in the
picosecond range for the group delay but this is not sufficient for current
geodetic pur- poses. This paper provides a fully documented derivation of a new
relativistic model having an accuracy substantially higher than one picosecond
and based upon a well accepted formalism of relativistic celestial mechanics,
astrometry and geodesy. Our new model fully confirms the consensus model at the
picosecond level and in several respects goes to a great extent beyond it. More
specifically, terms related to the acceleration of the geocenter are considered
and kept in the model, the gravitational time-delay due to a massive body
(planet, Sun, etc.) with arbitrary mass and spin-multipole moments is derived
taking into account the motion of the body, and a new formalism for the
time-delay problem of radio sources located at finite distance from VLBI
stations is presented. Thus, the paper presents a substantially elaborated
theoretical justification of the consensus model and its significant extension
that allows researchers to make concrete estimates of the magnitude of residual
terms of this model for any conceivable configuration of the source of light,
massive bodies, and VLBI stations. The largest terms in the relativistic time
delay which can affect the current VLBI observations are from the quadrupole
and the angular momentum of the gravitating bodies that are known from the
literature. These terms should be included in the new geodetic VLBI model for
improving its consistency.Comment: 37 pages, 4 figure
Prevention of the disrupted enamel phenotype in Slc4a4-null mice using explant organ culture maintained in a living host kidney capsule.
Slc4a4-null mice are a model of proximal renal tubular acidosis (pRTA). Slc4a4 encodes the electrogenic sodium base transporter NBCe1 that is involved in transcellular base transport and pH regulation during amelogenesis. Patients with mutations in the SLC4A4 gene and Slc4a4-null mice present with dysplastic enamel, amongst other pathologies. Loss of NBCe1 function leads to local abnormalities in enamel matrix pH regulation. Loss of NBCe1 function also results in systemic acidemic blood pH. Whether local changes in enamel pH and/or a decrease in systemic pH are the cause of the abnormal enamel phenotype is currently unknown. In the present study we addressed this question by explanting fetal wild-type and Slc4a4-null mandibles into healthy host kidney capsules to study enamel formation in the absence of systemic acidemia. Mandibular E11.5 explants from NBCe1-/- mice, maintained in host kidney capsules for 70 days, resulted in teeth with enamel and dentin with morphological and mineralization properties similar to cultured NBCe1+/+ mandibles grown under identical conditions. Ameloblasts express a number of proteins involved in dynamic changes in H+/base transport during amelogenesis. Despite the capacity of ameloblasts to dynamically modulate the local pH of the enamel matrix, at least in the NBCe1-/- mice, the systemic pH also appears to contribute to the enamel phenotype. Extrapolating these data to humans, our findings suggest that in patients with NBCe1 mutations, correction of the systemic metabolic acidosis at a sufficiently early time point may lead to amelioration of enamel abnormalities
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