Cell-surface receptors and proteins on platelet membranes imaged by scanning force microscopy using immunogold contrast enhancement

High resolution scanning force microscope (SFM) images of fibrinogen-exposed platelet membranes are presented. Using ultrasharp carbon tips, we are able to obtain submolecular scale resolution of membrane surface features. Corroboration of SFM results is achieved using low voltage, high resolution scanning electron microscopy (LVHRSEM) to image the same protein molecule that is seen in the SFM. We obtain accurate height dimensions by SFM complemented by accurate lateral dimensions obtained by LVHRSEM. The use of 14- and 5-nm gold labels to identify specific membrane-bound biomolecules and to provide contrast enhancement with the SFM is explored as a useful adjunct to observation of unlabeled material. It is shown that the labels are useful for locating specific protein molecules on platelet membrane surfaces and for assessing the distribution of these molecules using the SFM. Fourteen nm labels are shown to be visible over the membrane corrugation, whereas 5-nm labels appear difficult to resolve using the present SFM instrumental configuration. When using the 5-nm labels, collateral use of LVHRSEM allows one to examine SFM images at submolecular resolution and associate function with the structures imaged after the SFM experiment is completed

Constraining warm dark matter with cosmic shear power spectra

We investigate potential constraints from cosmic shear on the dark matter particle mass, assuming all dark matter is made up of light thermal relic particles. Given the theoretical uncertainties involved in making cosmological predictions in such warm dark matter scenarios we use analytical fits to linear warm dark matter power spectra and compare (i) the halo model using a mass function evaluated from these linear power spectra and (ii) an analytical fit to the non-linear evolution of the linear power spectra. We optimistically ignore the competing effect of baryons for this work. We find approach (ii) to be conservative compared to approach (i). We evaluate cosmological constraints using these methods, marginalising over four other cosmological parameters. Using the more conservative method we find that a Euclid-like weak lensing survey together with constraints from the Planck cosmic microwave background mission primary anisotropies could achieve a lower limit on the particle mass of 2.5 keV.Comment: 26 pages, 9 figures, minor changes to match the version accepted for publication in JCA

Counting BPS states on the Enriques Calabi-Yau

We study topological string amplitudes for the FHSV model using various techniques. This model has a type II realization involving a Calabi-Yau threefold with Enriques fibres, which we call the Enriques Calabi-Yau. By applying heterotic/type IIA duality, we compute the topological amplitudes in the fibre to all genera. It turns out that there are two different ways to do the computation that lead to topological couplings with different BPS content. One of them leads to the standard D0-D2 counting amplitudes, and from the other one we obtain information about bound states of D0-D4-D2 branes on the Enriques fibre. We also study the model using mirror symmetry and the holomorphic anomaly equations. We verify in this way the heterotic results for the D0-D2 generating functional for low genera and find closed expressions for the topological amplitudes on the total space in terms of modular forms, and up to genus four. This model turns out to be much simpler than the generic B-model and might be exactly solvable.Comment: 62 pages, v3: some results at genus 3 corrected, more typos correcte

Limits on the Neutrino Mass and Mixing Angle from Pion and Lepton Decays

Motivated by a recent rather surprising conclusion based on the 1992 PDG data on the pion, kaon and lepton decays that if three generations of neutrinos are assumed to be massive and mixed, the heaviest neutrino, $\nu_3$, could have a mass in the range, 155~\mbox{MeV} \lsim m_3 \lsim 225~\mbox{MeV}, we have analyzed the latest 1995 data on the leptonic decays of pion, $\mu$ and $\tau$ with the assumption that three generations of neutrinos are massive and mixed. It is shown that when the radiative corrections are included and the constraint {}from partial decay widths is imposed, the 1995 data are consistent with three massless neutrinos with no mixing. Various limits on the neutrino mass and mixing angle implied by the 1995 data are presented together with a critique of the previous analysis.Comment: REVTeX file, 20 pages and 10 figures (not included). Revision of the analysis and inclusion of the latest data. The TeX file and the figures (uuencoded, compressed, tarred file) are available at http://fermi.pha.jhu.edu/personnel/fornengo/fornengo.htm

Quantum Hall effect in a p-type heterojunction with a lateral surface quantum dot superlattice

The quantization of Hall conductance in a p-type heterojunction with lateral surface quantum dot superlattice is investigated. The topological properties of the four-component hole wavefunction are studied both in r- and k-spaces. New method of calculation of the Hall conductance in a 2D hole gas described by the Luttinger Hamiltonian and affected by lateral periodic potential is proposed, based on the investigation of four-component wavefunction singularities in k-space. The deviations from the quantization rules for Hofstadter "butterfly" for electrons are found, and the explanation of this effect is proposed. For the case of strong periodic potential the mixing of magnetic subbands is taken into account, and the exchange of the Chern numbers between magnetic subands is discussed.Comment: 12 pages, 5 figures; reported at the 15th Int. Conf. on High Magnetic Fields in Semicond. Phys. (Oxford, UK, 2002

One-pion transitions between heavy baryons in the constituent quark model

Single pion transitions of S wave to S wave, P wave to S wave and P wave to P wave heavy baryons are analyzed in the framework of the Heavy Quark Symmetry limit (HQS). We use a constituent quark model picture for the light diquark system with an underlying SU(2N_{f}) X O(3) symmetry to reduce the number of the HQS coupling factors required to describe these transitions. We also use the quantum theory of angular momentum to rewrite the one-pion transitions constituent quark model results in a more general form using the 6j- and 9j-symbols. We finally estimate the decay rates of some single pion transitions between charm baryon states.Comment: Latex, 33 pages including 2 figures (Postscript). Some typos are corrected with minor changes. Two references were added to the final version which will appear in Phy. Rev.

Isospin splitting in heavy baryons and mesons

A recent general analysis of light-baryon isospin splittings is updated and extended to charmed baryons. The measured $\Sigma_c$ and $\Xi_c$ splittings stand out as being difficult to understand in terms of two-body forces alone. We also discuss heavy-light mesons; though the framework here is necessarily less general, we nevertheless obtain some predictions that are not strongly model-dependent.Comment: 12 pages REVTEX 3, plus 4 uuencoded ps figures, CMU-HEP93-

Vasodilation of rat skeletal muscle arteries by the novel BK channel opener GoSlo is mediated by the simultaneous activation of BK and Kv7 channels

BACKGROUND AND PURPOSE: BK channels play important roles in various physiological and pathophysiological processes and thus have been the target of several drug development programs focused on creating new efficacious BK channel openers, such as the GoSlo-SR compounds. However, the effect of GoSlo-SR compounds on vascular smooth muscle has not been studied. Therefore, we tested the hypothesis that GoSlo-SR compounds dilate arteries exclusively by activating BK channels. EXPERIMENTAL APPROACH: Experiments were performed on rat Gracilis muscle, saphenous, mesenteric and tail arteries using isobaric and isometric myography, sharp microelectrodes, digital droplet PCR and the patch-clamp technique. KEY RESULTS: GoSlo-SR compounds dilated isobaric and relaxed and hyperpolarized isometric vessel preparations and their effects were abolished after (i) functionally eliminating K channels by pre-constriction with 50 mM KCl or (ii) blocking all K channels known to be expressed in vascular smooth muscle. However, these effects were not blocked when BK channels were inhibited. Surprisingly, the K(V)7 channel inhibitor XE991 reduced their effects considerably, but neither K(V)1 nor K(V)2 channel blockers altered the inhibitory effects of GoSlo-SR. However, the combined blockade of BK and K(V)7 channels abolished the GoSlo-SR-induced relaxation. GoSlo-SR compounds also activated K(V)7.4 and K(V)7.5 channels expressed in HEK 293 cells. CONCLUSIONS AND IMPLICATIONS: This study shows that GoSlo-SR-compounds are effective relaxants in vascular smooth muscle and mediate their effects by a combined activation of BK and K(V)7.4/K(V)7.5 channels. Activation of K(V)1, K(V)2 or K(V)7.1 channels or other vasodilator pathways seem not to be involved

Inflationary Perturbations: the Cosmological Schwinger Effect

This pedagogical review aims at presenting the fundamental aspects of the theory of inflationary cosmological perturbations of quantum-mechanical origin. The analogy with the well-known Schwinger effect is discussed in detail and a systematic comparison of the two physical phenomena is carried out. In particular, it is demonstrated that the two underlying formalisms differ only up to an irrelevant canonical transformation. Hence, the basic physical mechanisms at play are similar in both cases and can be reduced to the quantization of a parametric oscillator leading to particle creation due to the interaction with a classical source: pair production in vacuum is therefore equivalent to the appearance of a growing mode for the cosmological fluctuations. The only difference lies in the nature of the source: an electric field in the case of the Schwinger effect and the gravitational field in the case of inflationary perturbations. Although, in the laboratory, it is notoriously difficult to produce an electric field such that pairs extracted from the vacuum can be detected, the gravitational field in the early universe can be strong enough to lead to observable effects that ultimately reveal themselves as temperature fluctuations in the Cosmic Microwave Background. Finally, the question of how quantum cosmological perturbations can be considered as classical is discussed at the end of the article.Comment: 49 pages, 6 figures, to appear in a LNP volume "Inflationary Cosmology

Inflation with Ω≠1\Omega \not = 1

We discuss various models of inflationary universe with $\Omega \not = 1$. A homogeneous universe with $\Omega > 1$ may appear due to creation of the universe "from nothing" in the theories where the effective potential becomes very steep at large $\phi$, or in the theories where the inflaton field $\phi$ nonminimally couples to gravity. Inflation with $\Omega < 1$ generally requires intermediate first order phase transition with the bubble formation, and with a second stage of inflation inside the bubble. It is possible to realize this scenario in the context of a theory of one scalar field, but typically it requires artificially bent effective potentials and/or nonminimal kinetic terms. It is much easier to obtain an open universe in the models involving two scalar fields. However, these models have their own specific problems. We propose three different models of this type which can describe an open homogeneous inflationary universe.Comment: 29 pages, LaTeX, parameters of one of the models are slightly modifie