797 research outputs found
Radiation can never again dominate Matter in a Vacuum Dominated Universe
We demonstrate that in a vacuum-energy-dominated expansion phase,
surprisingly neither the decay of matter nor matter-antimatter annihilation
into relativistic particles can ever cause radiation to once again dominate
over matter in the future history of the universe.Comment: updated version, as it will appear in Phys. Rev D. Title change, and
some other minor alteration
Ciliary Dysfunction in Polycystic Kidney Disease: An Emerging Model with Polarizing Potential
The majority of different cell types in the human body have a cilium, a thin rod-like structure of uniquely arranged microtubules that are encapsulated by the surface plasma membrane. The cilium originates from a basal body, a mature centriole that has migrated and docked to the cell surface. The non-motile cilia are microtubule-based organelles that are generally considered sensory structures. The purpose of this review is to discuss the practicality of the ciliary hypothesis as a unifying concept for polycystic kidney disease and to review current literature in the field of cilium biology, as it relates to mechanosensation and planar cell polarity. The polycystins and fibrocystin localization at the cilium and other subcellular localizations are discussed, followed by a hypothetical model for the cilium\u27s role in mechanosensing, planar cell polarity, and cystogenesis
Limits on MeV Dark Matter from the Effective Number of Neutrinos
Thermal dark matter that couples more strongly to electrons and photons than
to neutrinos will heat the electron-photon plasma relative to the neutrino
background if it becomes nonrelativistic after the neutrinos decouple from the
thermal background. This results in a reduction in N_eff below the
standard-model value, a result strongly disfavored by current CMB observations.
Taking conservative lower bounds on N_eff and on the decoupling temperature of
the neutrinos, we derive a bound on the dark matter particle mass of m_\chi >
3-9 MeV, depending on the spin and statistics of the particle. For p-wave
annihilation, our limit on the dark matter particle mass is stronger than the
limit derived from distortions to the CMB fluctuation spectrum produced by
annihilations near the epoch of recombination.Comment: 5 pages, 1 figure, discussion added, references added and updated,
labels added to figure, to appear in Phys. Rev.
Stringy Effects During Inflation and Reheating
We consider inflationary cosmology in the context of string compactifications
with multiple throats. In scenarios where the warping differs significantly
between throats, string and Kaluza-Klein physics can generate potentially
observable corrections to the cosmology of inflation and reheating. First we
demonstrate that a very low string scale in the ground state compactification
is incompatible with a high Hubble scale during inflation, and we propose that
the compactification geometry is altered during inflation. In this
configuration, the lowest scale is just above the Hubble scale, which is
compatible with effective field theory but still leads to potentially
observable CMB corrections. Also in the appropriate region of parameter space,
we find that reheating leads to a phase of long open strings in the Standard
Model sector (before the usual radiation-dominated phase). We sketch the
cosmology of the long string phase and we discuss possible observational
consequences.Comment: 33pp, RevTeX4, v2. minor changes, added ref
On the Time-Dependent Analysis of Gamow Decay
Gamow's explanation of the exponential decay law uses complex "eigenvalues"
and exponentially growing "eigenfunctions". This raises the question, how
Gamow's description fits into the quantum mechanical description of nature,
which is based on real eigenvalues and square integrable wave functions.
Observing that the time evolution of any wave function is given by its
expansion in generalized eigenfunctions, we shall answer this question in the
most straightforward manner, which at the same time is accessible to graduate
students and specialists. Moreover the presentation can well be used in physics
lectures to students.Comment: 10 pages, 4 figures; heuristic argument simplified, different example
discussed, calculation of decay rate adde
Ciliary Polycystin-2 Is a Mechanosensitive Calcium Channel Involved in Nitric Oxide Signaling Cascades
Cardiovascular complications such as hypertension are a continuous concern in patients with autosomal dominant polycystic kidney disease (ADPKD). The PKD2 encoding for polycystin-2 is mutated in ≈15% of ADPKD patients. Here, we show that polycystin-2 is localized to the cilia of mouse and human vascular endothelial cells. We demonstrate that the normal expression level and localization of polycystin-2 to cilia is required for the endothelial cilia to sense fluid shear stress through a complex biochemical cascade, involving calcium, calmodulin, Akt/PKB, and protein kinase C. In response to fluid shear stress, mouse endothelial cells with knockdown or knockout of Pkd2 lose the ability to generate nitric oxide (NO). Consistent with mouse data, endothelial cells generated from ADPKD patients do not show polycystin-2 in the cilia and are unable to sense fluid flow. In the isolated artery, we further show that ciliary polycystin-2 responds specifically to shear stress and not to mechanical stretch, a pressurized biomechanical force that involves purinergic receptor activation. We propose a new role for polycystin-2 in transmitting extracellular shear stress to intracellular NO biosynthesis. Thus, aberrant expression or localization of polycystin-2 to cilia could promote high blood pressure because of inability to synthesize NO in response to an increase in shear stress (blood flow)
Geological processes defining the formation of plumasite-type corundum in the Paleoproterozoic Isertoq Terrane, South-East Greenland
Plumasite-type corundum occurrences in the Nattivit area in South-East Greenland offer a unique opportunity to study corundum formation in-situ where pegmatites intruded into metamorphosed lherzolite and dunite of the Archean-Paleoproterozoic continental crust. The Nattivit area, located in the Isertoq Terrane of North Atlantic Craton, forms part of the overriding plate during convergence of the Nagssugtoqidian orogen (1910-1840 Ma). New field observations and elemental and isotopic geochemical analysis provide further insights in the history of crustal convergence, its exhumation and how corundum was formed. The continental crust in the area consists of metamorphosed mafic to ultramafic rocks and tonalite-trondhjemite-granodiorite (TTG) gneisses, where the mafic rocks in the Isertoq Terrane yield a εNd T model age of 3000–2800 Ma. Dunite and lherzolite sills/dikes intruded the mafic rocks before the intrusion of the TTG sheets. The intrusion ages for the TTG obtained from zircon U-Pb geochronology are 2818 ± 8 Ma, 2760 ± 13 Ma to 2667 ± 7 Ma. U-Pb zircon data, zircon textures and Th/U ratios indicate metamorphism occurred at 2698 ± 7 Ma to 2629 ± 11 Ma, 2500–2400 Ma and 1900–1600 Ma. Whole rock geochemical data of mafic to ultramafic rocks show a continental arc affinity, with negative Ta, Nb and positive Pb anomalies. A metasomatic event at 2390 ± 70 Ma partly reset the isotopic signature in the mafic to ultramafic rocks. A marked absence of ages between 2350 and 2100 Ma in the TTG zircon age populations exists, indicating a period with minimal magmatic and/or metamorphic activity. The metamorphic mineral assemblages of the schist, amphibolite, ultramafic rocks and metasomatic reaction zones in ultramafic rocks indicate upper to medium–high amphibolite facies conditions. Kyanite in the metasomatic reaction zones in ultramafic rocks indicate the higher end of the temperature and pressure range above 4.2–10 kbar and 530–800 °C, similar to estimates from dolerite dikes in the Kitak area. The syn-tectonic pegmatites with an intrusion age of 1843 ± 4 Ma formed corundum. The new data indicate that the pegmatite melt/fluid and the geotectonic setting are defining factors for generating plumasite-type corundum
A novel cell immunoassay to measure survival of motor neurons protein in blood cells
BACKGROUND: The motor neuron degenerative disease spinal muscular atrophy (SMA) is the leading genetic cause of infant mortality and is caused by mutations in the survival of motor neurons (SMN) gene that reduce the expression levels of the SMN protein. A major goal of current therapeutic approaches is to increase SMN levels in SMA patients. The purpose of this study was to develop a reliable assay to measure SMN protein levels from peripheral blood samples. METHODS: We developed a novel cell immunoassay to quantitatively measure SMN levels from peripheral blood mononuclear cells (PBMCs) using a single anti-SMN antibody. RESULTS: SMN levels determined by the cell immunoassay are comparable to levels determined by Western blot, but in contrast, the immunoassay does not involve cell lysis, requires a small amount of patient material, and can be done on a large number of samples simultaneously. SMN levels from PBMCs are not influenced by cell type heterogeneity. CONCLUSION: SMN levels measured from total PBMCs provide an important snapshot of SMN protein expression, which should be a useful aid in SMA diagnosis, and a surrogate marker of efficacy of treatment in SMA clinical trials
The Effect of Time Variation in the Higgs Vacuum Expectation Value on the Cosmic Microwave Background
A time variation in the Higgs vacuum expectation value alters the electron
mass and thereby changes the ionization history of the universe. This change
produces a measurable imprint on the pattern of cosmic microwave background
(CMB) fluctuations. The nuclear masses and nuclear binding energies, as well as
the Fermi coupling constant, are also altered, with negligible impact on the
CMB. We calculate the changes in the spectrum of the CMB fluctuations as a
function of the change in the electron mass. We find that future CMB
experiments could be sensitive to |\Delta m_e/m_e| \sim |\Delta G_F/G_F| \sim
10^{-2} - 10^{-3}. However, we also show that a change in the electron mass is
nearly, but not exactly, degenerate with a change in the fine-structure
constant. If both the electron mass and the fine-structure constant are
time-varying, the corresponding CMB limits are much weaker, particularly for l
< 1000.Comment: 6 pages, 3 figures, Fig. 3 modified, other minor correction
Probing Unstable Massive Neutrinos with Current Cosmic Microwave Background Observations
The pattern of anisotropies in the Cosmic Microwave Background depends upon
the masses and lifetimes of the three neutrino species. A neutrino species of
mass greater than 10 eV with lifetime between 10^{13} sec and 10^{17} sec
leaves a very distinct signature (due to the integrated Sachs-Wolfe effect):
the anisotropies at large angles are predicted to be comparable to those on
degree scales. Present data exclude such a possibility and hence this region of
parameter space. For eV, sec, we find
an interesting possibility: the Integrated Sachs Wolfe peak produced by the
decaying neutrino in low- models mimics the acoustic peak expected in
an model.Comment: 5 pages, 4 figure
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