A spin triplet supercurrent through the half-metallic ferromagnet CrO2

In general, conventional superconductivity should not occur in a ferromagnet, though it has been seen in iron under pressure. Moreover, theory predicts that the current is always carried by pairs of electrons in a spin singlet state, so conventional superconductivity decays very rapidly when in contact with a ferromagnet, which normally prohibits the existence of singlet pairs. It has been predicted that this rapid spatial decay would not occur when spin triplet superconductivity could be induced in the ferromagnet. Here we report a Josephson supercurrent through the strong ferromagnet CrO2, from which we infer that it is a spin triplet supercurrent. Our experimental setup is different from those envisaged in the earlier predictions, but we conclude that the underlying physical explanation for our result is a conversion from spin singlet to spin triplets at the interface. The supercurrent can be switched with the direction of the magnetization, analogous to spin valve transistors, and therefore could enable magnetization-controlled Josephson junctions.Comment: 14 pages, including 3 figure

Standstill Electric Charge Generates Magnetostatic Field Under Born-Infeld Electrodynamics

The Abelian Born-Infeld classical non-linear electrodynamic has been used to investigate the electric and magnetostatic fields generated by a point-like electrical charge at rest in an inertial frame. The results show a rich internal structure for the charge. Analytical solutions have also been found. Such findings have been interpreted in terms of vacuum polarization and magnetic-like charges produced by the very high strengths of the electric field considered. Apparently non-linearity is to be accounted for the emergence of an anomalous magnetostatic field suggesting a possible connection to that created by a magnetic dipole composed of two mognetic charges with opposite signals. Consistently in situations where the Born-Infeld field strength parameter is free to become infinite, Maxwell`s regime takes over, the magnetic sector vanishes and the electric field assumes a Coulomb behavior with no trace of a magnetic component. The connection to other monopole solutions, like Dirac`s, t' Hooft`s or Poliakov`s types, are also discussed. Finally some speculative remarks are presented in an attempt to explain such fields.Comment: 11 pages, 3 figures. In this version is update a permanent address of the author L.P.G. De Assis and information on submission publication. Submetted to International Journal of Theoretical Physic

Matrix Black Holes

Four and five dimensional extremal black holes with nonzero entropy have simple presentations in M-theory as gravitational waves bound to configurations of intersecting M-branes. We discuss realizations of these objects in matrix models of M-theory, investigate the properties of zero-brane probes, and propose a measure of their internal density. A scenario for black hole dynamics is presented.Comment: 26 pages, harvmac; a few more references and additional comment

Endogenous PTH Deficiency Impairs Fracture Healing and Impedes the Fracture-Healing Efficacy of Exogenous PTH(1-34)

Although the capacity of exogenous PTH1-34 to enhance the rate of bone repair is well established in animal models, our understanding of the mechanism(s) whereby PTH induces an anabolic response during skeletal repair remains limited. Furthermore it is unknown whether endogenous PTH is required for fracture healing and how the absence of endogenous PTH would influence the fracture-healing capacity of exogenous PTH.Closed mid-diaphyseal femur fractures were created and stabilized with an intramedullary pin in 8-week-old wild-type and Pth null (Pth(-/-)) mice. Mice received daily injections of vehicle or of PTH1-34 (80 µg/kg) for 1-4 weeks post-fracture, and callus tissue properties were analyzed at 1, 2 and 4 weeks post-fracture. Cartilaginous callus areas were reduced at 1 week post-fracture, but were increased at 2 weeks post-fracture in vehicle-treated and PTH-treated Pth(-/-) mice compared to vehicle-treated and PTH-treated wild-type mice respectively. The mineralized callus areas, bony callus areas, osteoblast number and activity, osteoclast number and surface in callus tissues were all reduced in vehicle-treated and PTH-treated Pth(-/-) mice compared to vehicle-treated and PTH-treated wild-type mice, but were increased in PTH-treated wild-type and Pth(-/-) mice compared to vehicle-treated wild-type and Pth(-/-) mice.Absence of endogenous PTH1-84 impedes bone fracture healing. Exogenous PTH1-34 can act in the absence of endogenous PTH but callus formation, including accelerated endochondral bone formation and callus remodeling as well as mechanical strength of the bone are greater when endogenous PTH is present. Results of this study suggest a complementary role for endogenous PTH1-84 and exogenous PTH1-34 in accelerating fracture healing

Coherent coupling between radio frequency, optical, and acoustic waves in piezo-optomechanical circuits

The interaction of optical and mechanical modes in nanoscale optomechanical systems has been widely studied for applications ranging from sensing to quantum information science. Here, we develop a platform for cavity optomechanical circuits in which localized and interacting 1550 nm photons and 2.4 GHz phonons are combined with photonic and phononic waveguides. Working in GaAs facilitates manipulation of the localized mechanical mode either with a radio frequency field through the piezo-electric effect, or optically through the strong photoelastic effect. We use this to demonstrate a novel acoustic wave interference effect, analogous to coherent population trapping in atomic systems, in which the coherent mechanical motion induced by the electrical drive can be completely cancelled out by the optically-driven motion. The ability to manipulate cavity optomechanical systems with equal facility through either photonic or phononic channels enables new device and system architectures for signal transduction between the optical, electrical, and mechanical domains

Joint profiling of DNA methylation and chromatin architecture in single cells.

We report a molecular assay, Methyl-HiC, that can simultaneously capture the chromosome conformation and DNA methylome in a cell. Methyl-HiC reveals coordinated DNA methylation status between distal genomic segments that are in spatial proximity in the nucleus, and delineates heterogeneity of both the chromatin architecture and DNA methylome in a mixed population. It enables simultaneous characterization of cell-type-specific chromatin organization and epigenome in complex tissues

Power-law singularities in string theory and M-theory

We extend the definition of the Szekeres-Iyer power-law singularities to supergravity, string and M-theory backgrounds, and find that are characterized by Kasner type exponents. The near singularity geometries of brane and some intersecting brane backgrounds are investigated and the exponents are computed. The Penrose limits of some of these power-law singularities have profiles $A\sim {\rm u}^{-\gamma}$ for $\gamma\geq 2$. We find the range of the exponents for which $\gamma=2$ and the frequency squares are bounded by 1/4. We propose some qualitative tests for deciding whether a null or timelike spacetime singularity can be resolved within string theory and M-theory based on the near singularity geometry and its Penrose limits.Comment: 32 page

Inverse Modeling for MEG/EEG data

We provide an overview of the state-of-the-art for mathematical methods that are used to reconstruct brain activity from neurophysiological data. After a brief introduction on the mathematics of the forward problem, we discuss standard and recently proposed regularization methods, as well as Monte Carlo techniques for Bayesian inference. We classify the inverse methods based on the underlying source model, and discuss advantages and disadvantages. Finally we describe an application to the pre-surgical evaluation of epileptic patients.Comment: 15 pages, 1 figur

Quantum Measurement Theory in Gravitational-Wave Detectors

The fast progress in improving the sensitivity of the gravitational-wave (GW) detectors, we all have witnessed in the recent years, has propelled the scientific community to the point, when quantum behaviour of such immense measurement devices as kilometer-long interferometers starts to matter. The time, when their sensitivity will be mainly limited by the quantum noise of light is round the corner, and finding the ways to reduce it will become a necessity. Therefore, the primary goal we pursued in this review was to familiarize a broad spectrum of readers with the theory of quantum measurements in the very form it finds application in the area of gravitational-wave detection. We focus on how quantum noise arises in gravitational-wave interferometers and what limitations it imposes on the achievable sensitivity. We start from the very basic concepts and gradually advance to the general linear quantum measurement theory and its application to the calculation of quantum noise in the contemporary and planned interferometric detectors of gravitational radiation of the first and second generation. Special attention is paid to the concept of Standard Quantum Limit and the methods of its surmounting.Comment: 147 pages, 46 figures, 1 table. Published in Living Reviews in Relativit