24,925 research outputs found
Families of exact solutions of a 2D gravity model minimally coupled to electrodynamics
Three families of exact solutions for 2-dimensional gravity minimally coupled
to electrodynamics are obtained in the context of theory. It is
shown, by supersymmetric formalism of quantum mechanics, that the quantum
dynamics of a neutral bosonic particle on static backgrounds with both varying
curvature and electric field is exactly solvable.Comment: 13 pages, LaTeX, to be published in JM
Non-Langevin behaviour of the uncompensated magnetisation in nanoparticles of artificial ferritin
The magnetic behaviour of nanoparticles of antiferromagnetic ferritin has
been investigated by 57Fe Mossbauer absorption spectroscopy and magnetisation
measurements, in the temperature range 2.5K-250K and with magnetic fields up to
7T. Samples containing nanoparticles with an average number of Fe atoms ranging
from 400 to 2500 were studied. The value of the anisotropy energy per unit
volume was determined and found to be in the range 3-6 10**5 ergs/cm3, which is
a value typical for ferric oxides. By comparing the results of the two
experimental methods at large field, we show that, contratry to what is
currently assumed, the uncompensated magnetisation of the feritin cores in the
superparamagnetic regime does not follow a Langevin law. For magnetic fields
below the spin-flop field, we propose an approximate law for the field and
temperature variation of the uncompensated magnetisation which has so far never
been applied in antiferromagnetic systems. This approach should more generally
hold for randomly oriented antiferro- magnetic nanoparticles systems with weak
uncompensated moments.Comment: 11 pages, 11 figure
Variation in the Thyrotropic Activity of Human Chorionic Gonadotropin in Chinese Hamster Ovary Cells Arises from Differential Expression of the Human Thyrotropin Receptor and Microheterogeneity of the Hormone.
The role of hCG as a stimulator of the human thyroid has been a subject of controversy, because discrepant results have been obtained in different in vitro assays. In an attempt to explain the variation observed in the thyroid response to hCG, we investigated the ability of hCG and that of its isoforms and glycosylation variants to inhibit [125I]bovine (b) TSH binding and stimulate adenylate cyclase in two clones, JP09 and JP26, of Chinese hamster ovary cells stably transfected with the human TSH receptor (hTSHr). The two clones differed with respect to the number of hTSHr expressed per cell (34,000 in JP09 and 2,000 in JP26 cells). Both responded extremely well to bTSH; the cAMP response to 0.001 IU/L bTSH was distinguishable from basal values. Interestingly, JP09 cells were readily stimulated by hCG (20-100 mg/L; 0.52-2.6 x 10(-6) mol/L) to release cAMP, whereas JP26 cells showed little if any response. Also, cAMP stimulation produced by asialo-hCG was 12-fold in JP09 cells and only 4-fold in JP26 cells compared to 45- and 67-fold stimulations by bTSH, respectively. Stimulation by asialo-hCG was approximately 30% that of bTSH in JP09 cells, but less than 6% in JP26 cells. When assessing the thyrotropic activity of the microheterogeneous isoforms of hCG, more alkaline pI forms were found to be more active than those of a more acidic pI regardless of whether they were derived from normal or molar pregnancy urine. Further studies with hCG, asialo-hCG, asialoagalacto-hCG, and deglycosylated hCG revealed that removal of sialic acid caused a marked increase in both its affinity for hTSHr and its cAMP-releasing potency, whereas removal of further carbohydrate, although it slightly enhanced receptor binding, was detrimental to adenylate cyclase activation. In conclusion, differences in hTSHr expression may cause a variation in the cAMP response to hCG or its glycosylation variants, as does the microheterogeneity of the hormone itself. These mechanisms may be responsible at least in part for the divergent responses of different cell types to hCG and render interpretation of the physiological meaning of the data obtained in recombinant receptor systems difficult
Flavor Mass and Mixing and S_3 Symmetry -- An S_3 Invariant Model Reasonable to All --
We assume that weak bases of flavors (u, c)_{L,R}, (d,s)_{L,R}, (e, \mu)
_{L,R}, (\nu_e, \nu_\mu)_{L,R} are the S_3 doublet and t_{L,R}, b_{L,R},
\tau_{L,R}, {\nu_\tau}_{L,R} are the S_3 singlet and further there are S_3
doublet Higgs (H_D^1, H_D^2) and S_3 singlet Higgs H_S. We suggest an S_3
invariant Yukawa interaction, in which masses caused from the interaction of
S_3 singlet flavors and Higgs is very large and masses caused from interactions
of S_3 doublet flavors and Higgs are very small, and the vacuum expectation
value _0 is rather small compared to the _0. In this model,
we can explain the quark sector mass hierarchy, flavor mixing V_{CKM} and
measure of CP violation naturally. The leptonic sector mass hierarchy and
flavor mixing described by V_{MNS} having one-maximal and one-large mixing
character can also be explained naturally with no other symmetry restriction.
In our model, an origin of Cabibbo angle is the ratio \lambda=_0
/_0 and an origin of CP violation is the phase of H_D^1.Comment: 16 page
Study of a soft lander/support module for Mars missions. Volume 3 - Appendixes Final summary report
Soft lander support module for Mars missions - lunar module radar evaluation and vernier phase simulatio
Statistical Mechanics of Relativistic One-Dimensional Self-Gravitating Systems
We consider the statistical mechanics of a general relativistic
one-dimensional self-gravitating system. The system consists of -particles
coupled to lineal gravity and can be considered as a model of
relativistically interacting sheets of uniform mass. The partition function and
one-particle distitrubion functions are computed to leading order in
where is the speed of light; as results for the
non-relativistic one-dimensional self-gravitating system are recovered. We find
that relativistic effects generally cause both position and momentum
distribution functions to become more sharply peaked, and that the temperature
of a relativistic gas is smaller than its non-relativistic counterpart at the
same fixed energy. We consider the large-N limit of our results and compare
this to the non-relativistic case.Comment: latex, 60 pages, 22 figure
Collective treatment of High Energy Thresholds in SUSY - GUTs
Supersymmetric GUTs are the most natural extension of the Standard model
unifying electroweak and strong forces. Despite their indubitable virtues,
among these the gauge coupling unification and the quantization of the electric
charge, one of their shortcomings is the large number of parameters used to
describe the high energy thresholds (HET), which are hard to handle. We present
a new method according to which the effects of the HET, in any GUT model, can
be described by fewer parameters that are randomly produced from the original
set of the parameters of the model. In this way, regions favoured by the
experimental data are easier to locate, avoiding a detailed and time consuming
exploration of the parameter space, which is multidimensional even in the most
economic unifying schemes. To check the efficiency of this method, we directly
apply it to a SUSY SO(10) GUT model in which the doublet-triplet splitting is
realized through the Dimopoulos-Wilczek mechanism. We show that the demand of
gauge coupling unification, in conjunction with precision data, locates regions
of the parameter space in which values of the strong coupling \astrong are
within the experimental limits, along with a suppressed nucleon decay, mediated
by a higgsino driven dimension five operators, yielding lifetimes that are
comfortably above the current experimental bounds. These regions open up for
values of the SUSY breaking parameters m_0, M_1/2 < 1 TeV being therefore
accessible to LHC.Comment: 21 pages, 8 figures, UA-NPPS/BSM-10/02 (added
A simple SO(10) GUT in five dimensions
A simple supersymmetric SO(10) GUT in five dimensions is considered. The
fifth dimension is compactified on the orbifold
possessing two inequivalent fixed points. In our setup, all matter and Higgs
multiplets reside on one brane (PS brane) where the original SO(10) gauge group
is broken down to the Pati-Salam (PS) gauge group, SU(4)_c \timesSU(2)_L
\times SU(2), by the orbifold boundary condition, while only the SO(10)
gauge multiplet resides in the bulk. The further breaking of the PS symmetry to
the Standard Model gauge group is realized by Higgs multiplets on the PS brane
as usual in four dimensional models. Proton decay is fully suppressed. In our
simple setup, the gauge coupling unification is realized after incorporating
threshold corrections of Kaluza-Klein modes. When supersymmetry is assumed to
be broken on the other brane, supersymmetry breaking is transmitted to the PS
brane through the gaugino mediation with the bulk gauge multiplet.Comment: 12 pages, 1 figure, some errors have been corrected (no change in
conclusions
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