755 research outputs found
Photoelectric Fields and Band Gap in Doped Lithium Niobate Crystals
Photorefractive effect was researched and band gap was determined in nominally pure congruent and stoichiometric lithium niobate crystals, and in a series of congruent LiNbO3 crystals doped by Mg, Zn, B, Gd, Y, Er cations, and LiNbO3 single crystals with double doping Mg:Gd, Mg:Fe, Mg:Y, Mg:Ta by photoinduced light scattering and optical spectroscopy methods.
Keywords: lithium niobate single crystal, doping, photorefractive effect, photoinduced light scattering, optical spectroscopy, band ga
A model for studying the hemostatic consumption or destruction of platelets
A fundamental issue in understanding homeostasis of the hematopoietic system is to what extent intrinsic and extrinsic factors regulate cell fate. We recently revisited this issue for the case of blood platelets and concluded that platelet life span is largely regulated by internal factors, in contrast to the long-held view that accumulated damage from the environment triggers clearance. However, it is known that in humans there is an ongoing fixed requirement for platelets to maintain hemostasis and prevent bleeding; hence a proportion of platelets may be consumed in such processes before the end of their natural life span. Whether it is possible to detect this random loss of platelets in normal individuals at steady-state is unknown. To address this question, we have developed a mathematical model that independently incorporates age-independent random loss and age-dependent natural senescent clearance. By fitting to population survival curves, we illustrate the application of the model in quantifying the fixed requirement for platelets to maintain hemostasis in mice, and discuss the relationship with previous work in humans. Our results suggest a higher requirement for platelets in mice than in humans, however experimental uncertainty in the data limits our ability to constrain this quantity. We then explored the relationship between experimental uncertainty and parameter constraint using simulated data. We conclude that in order to provide useful constraint on the random loss fraction the standard error in the mean of the data must be reduced substantially, either through improving experimental uncertainty or increasing the number of experimental replicates to impractical levels. Finally we find that parameter constraint is improved at higher values of the random loss fraction; thus the model find utility in situations where the random loss fraction is expected to be high, for example during active bleeding or some types of thrombocytopenia.Mark R. Dowling, Emma C. Josefsson, Katya J. Henley, Benjamin T. Kile, Philip D. Hodgki
Measurement of the Gluino Mass via Cascade Decays for SPS 1a
If R-parity conserving supersymmetry is realised with masses below the TeV
scale, sparticles will be produced and decay in cascades at the LHC. In the
case of a neutral LSP, which will not be detected, decay chains cannot be fully
reconstructed, complicating the mass determination of the new particles. In
this paper we extend the method of obtaining masses from kinematical endpoints
to include a gluino at the head of a five-sparticle decay chain. This
represents a non-trivial extension of the corresponding method for the squark
decay chain. We calculate the endpoints of the new distributions and assess
their applicability by examining the theoretical distributions for a variety of
mass scenarios. The precision with which the gluino mass can be determined by
this method is investigated for the mSUGRA point SPS 1a. Finally we estimate
the improvement obtained from adding a Linear Collider measurement of the LSP
mass.Comment: 40 pages; extended discussion of error
In vivo measurement of somatodendritic release of dopamine in the ventral tegmental area
The ventral tegmental area (VTA), the locus of mesolimbic dopamine cell bodies, contains dopamine. Experiments in brain slices have demonstrated that VTA dopamine can be released by local electrical stimulation. Measurements with both push-pull cannula and microdialysis in intact animals have also obtained evidence for releasable dopamine. Here we demonstrate that dopamine release in the VTA can be evoked by remote stimulations of the medial forebrain bundle (MFB) in the anesthetized rat. In initial experiments, the MFB was electrically stimulated while a carbon-fiber electrode was lowered to the VTA, with recording by fast-scan cyclic voltammetry. While release was not observed with the carbon fiber 4 to 6 mm below dura, a voltammetric response was observed a t 6-8 mm below dura, but the voltammogram was poorly defined. At lower depths, in the VTA, dopamine release was evoked. Immunohistochemistry experiments with antibodies for tyrosine hydroxylase (TH) confirmed that dopamine processes were primarily found below 8 mm. Similarly, tissue content determined by liquid chromatography revealed serotonin but not dopamine dorsal to 8 mm with both dopamine and serotonin at lower depths. Evaluation of the VTA signal by pharmacological means showed that it increased with inhibitors of dopamine uptake, but release was not altered by D2 agents. Dopamine release in the VTA was frequency dependent and could be exhausted by stimulations longer than 5 s. Thus, VTA dopamine release can be evoked in vivo by remote stimulations and it resembles release in terminal regions, possessing a similar uptake mechanism and a finite releasable storage pool
Forurensningssituasjonen i Mjøsa med tilløpselver 2012
Denne rapporten gir en kortfattet oversikt over de viktigste resultatene fra overvĂĽkingen i VannomrĂĽde Mjøsa i 2012. Undersøkelsene er utført pĂĽ oppdrag fra Vassdragsforbundet for Mjøsa med tilløpselver. OvervĂĽkingen omfatter fysiske, kjemiske og biologiske forhold i Mjøsas hovedvannmasser, hygieniske forhold, konsentrasjoner og transport av nĂŚringsstoffer i de seks største tilløpselvene samt i utløpselva Vorma. Videre er biologiske forhold i utvalgte tilløpselver undersøkt. Ă
rsrapporten for 2012 gir en fyldigere presentasjon av müledata og vurderinger. Data presenteres ogsü fortløpende gjennom NIVAs overvükingsverktøy Aquamonitor.Vassdragsforbundet for Mjøsa med tilløpselve
Gravitational Perturbations of a Six Dimensional Self-Tuning Model
We investigate gravitational perturbations in a compact six-dimensional
self-tuning brane model. We specifically look for analytic solutions to the
perturbed Einstein equations that correspond in four-dimensions to massless or
approximately massless scalars coupled to matter on the brane. The presence of
such modes with gravitational couplings would be phenomenologically
unacceptable. The most general solution for all such modes is obtained, but it
is found that they are all eliminated by the boundary conditions. Our main
result is that to linear order in perturbation theory this model does not
contain any light scalars. We speculate that this model does not self-tune.Comment: CALT-68-2478, 15 pages; added references, clarified comments about
fine-tuning in this mode
Combined analysis of solar neutrino and solar irradiance data: further evidence for variability of the solar neutrino flux and its implications concerning the solar core
A search for any particular feature in any single solar neutrino dataset is
unlikely to establish variability of the solar neutrino flux since the count
rates are very low. It helps to combine datasets, and in this article we
examine data from both the Homestake and GALLEX experiments. These show
evidence of modulation with a frequency of 11.85 yr-1, which could be
indicative of rotational modulation originating in the solar core. We find that
precisely the same frequency is prominent in power spectrum analyses of the
ACRIM irradiance data for both the Homestake and GALLEX time intervals. These
results suggest that the solar core is inhomogeneous and rotates with sidereal
frequency 12.85 yr-1. We find, by Monte Carlo calculations, that the
probability that the neutrino data would by chance match the irradiance data in
this way is only 2 parts in 10,000. This rotation rate is significantly lower
than that of the inner radiative zone (13.97 yr-1) as recently inferred from
analysis of Super-Kamiokande data, suggesting that there may be a second, inner
tachocline separating the core from the radiative zone. This opens up the
possibility that there may be an inner dynamo that could produce a strong
internal magnetic field and a second solar cycle.Comment: 22 pages, 9 tables, 10 figure
A Mouse Model of Harlequin Ichthyosis Delineates a Key Role for Abca12 in Lipid Homeostasis
Harlequin Ichthyosis (HI) is a severe and often lethal hyperkeratotic skin disease caused by mutations in the ABCA12 transport protein. In keratinocytes, ABCA12 is thought to regulate the transfer of lipids into small intracellular trafficking vesicles known as lamellar bodies. However, the nature and scope of this regulation remains unclear. As part of an original recessive mouse ENU mutagenesis screen, we have identified and characterised an animal model of HI and showed that it displays many of the hallmarks of the disease including hyperkeratosis, loss of barrier function, and defects in lipid homeostasis. We have used this model to follow disease progression in utero and present evidence that loss of Abca12 function leads to premature differentiation of basal keratinocytes. A comprehensive analysis of lipid levels in mutant epidermis demonstrated profound defects in lipid homeostasis, illustrating for the first time the extent to which Abca12 plays a pivotal role in maintaining lipid balance in the skin. To further investigate the scope of Abca12's activity, we have utilised cells from the mutant mouse to ascribe direct transport functions to the protein and, in doing so, we demonstrate activities independent of its role in lamellar body function. These cells have severely impaired lipid efflux leading to intracellular accumulation of neutral lipids. Furthermore, we identify Abca12 as a mediator of Abca1-regulated cellular cholesterol efflux, a finding that may have significant implications for other diseases of lipid metabolism and homeostasis, including atherosclerosis
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