Measurement of the Low-temperature Loss Tangent of High-resistivity Silicon with a High Q-factor Superconducting Resonator

In this letter, we present the direct loss tangent measurement of a high-resistivity intrinsic (100) silicon wafer in the temperature range from ~ 70 mK to 1 K, approaching the quantum regime. The measurement was performed using a technique that takes advantage of a high quality factor superconducting niobium resonator and allows to directly measure the loss tangent of insulating materials with high level of accuracy and precision. We report silicon loss tangent values at the lowest temperature and for electric field amplitudes comparable to those found in planar transmon devices one order of magnitude larger than what was previously estimated. In addition, we discover a non-monotonic trend of the loss tangent as a function of temperature that we describe by means of a phenomenological model based on variable range hopping conduction between localized states around the Fermi energy. We also observe that the dissipation increases as a function of the electric field and that this behavior can be qualitatively described by the variable range hopping conduction mechanism as well. This study lays the foundations for a novel approach to investigate the loss mechanisms and accurately estimate the loss tangent in insulating materials in the quantum regime, leading to a better understanding of coherence in quantum devices

Direct phasing by binary integer programming

Article dans revue scientifique avec comité de lecture.In the absence of phase information, a variety of electron-density distributions is consistent with the observed magnitudes. This ambiguity may be reduced significantly if the distribution values are restricted to 0 or 1, i.e. when the object of search is an envelope rather than a continuous electron-density distribution. The binarizing in both real (the grid-point density values) and reciprocal (the phases) spaces allows the usual structure-factor equations to be replaced by a system of linear inequalities with binary unknowns. A special computer procedure is applied to obtain several sets of values, which satisfy or almost satisfy these inequalities. The averaging of the found phase sets allows the final map to be calculated. The approach was tested with calculated and experimental data for a known protein structure. The size of the grid for the envelope calculation is at the moment the major limitation of the approach. Nevertheless, even for a very small grid, some structure information can be extracted and used as a starting point for further phase improvement or as a way to solve the molecular replacement problem

Spatial memory deficits initiated by agroclavine injection or olfactory bulbectomy in rats are characterized by different levels of long-term potentiation expression in the hippocampus

Aim: To clarify whether long-term potentiation (LTP) is the mechanism underpinning mnemonic processes. Mathrials and methods: We studied LTP in hippocampal slices from rats whose spatial memory deficit was produced by either olfactory bulbectomy (OBX) or pretreatment with an ergot alkaloid, agroclavine. OBX is accompanied by cholinergic system inhibition whereas agroclavine predominantly activates dopaminergic mediation. The both have been shown to be involved in learning/memory and LTP mechanisms. Results: In OBX- vs. sham-operated rat, we have revealed significant reduction of LTP in hippocampal CA1 region. In contrast, no LTP differences in agroclavine- vs. vehicle-treated rats were observed. Conclusions: These results demonstrate that LTP expression in the hippocampus is dependent on the origin of spatial memory impairment. Furthermore, they suggest that pharmacological and neurodegenerative models of AD might be useful approach for discovery of both AD mechanisms and mixed pathology dementias

A solution of the coincidence problem based on the recent galactic core black hole mass density increase

A mechanism capable to provide a natural solution to two major cosmological problems, i.e. the cosmic acceleration and the coincidence problem, is proposed. A specific brane-bulk energy exchange mechanism produces a total dark pressure, arising when adding all normal to the brane negative pressures in the interior of galactic core black holes. This astrophysically produced negative dark pressure explains cosmic acceleration and why the dark energy today is of the same order to the matter density for a wide range of the involved parameters. An exciting result of the analysis is that the recent rise of the galactic core black hole mass density causes the recent passage from cosmic deceleration to acceleration. Finally, it is worth mentioning that this work corrects a wide spread fallacy among brane cosmologists, i.e. that escaping gravitons result to positive dark pressure.Comment: 14 pages, 3 figure

Strings on Bubbling Geometries

We study gauge theory operators which take the form of a product of a trace with a Schur polynomial, and their string theory duals. These states represent strings excited on bubbling AdS geometries which are dual to the Schur polynomials. These geometries generically take the form of multiple annuli in the phase space plane. We study the coherent state wavefunction of the lattice, which labels the trace part of the operator, for a general Young tableau and their dual description on the droplet plane with a general concentric ring pattern. In addition we identify a density matrix over the coherent states on all the geometries within a fixed constraint. This density matrix may be used to calculate the entropy of a given ensemble of operators. We finally recover the BMN string spectrum along the geodesic near any circle from the ansatz of the coherent state wavefunction.Comment: 41 pages, 12 figures, published version in JHE

Dipole-Deformed Bound States and Heterotic Kodaira Surfaces

We study a particular N = 1 confining gauge theory with fundamental flavors realised as seven branes in the background of wrapped five branes on a rigid two-cycle of a non-trivial global geometry. In parts of the moduli space, the five branes form bound states with the seven branes. We show that in this regime the local supergravity solution is surprisingly tractable, even though the background topology is non-trivial. New effects such as dipole deformations may be studied in detail, including the full backreactions. Performing the dipole deformations in other ways leads to different warped local geometries. In the dual heterotic picture, which is locally given by a C* fibration over a Kodaira surface, we study details of the geometry and the construction of bundles. We also point out the existence of certain exotic bundles in our framework.Comment: 40 pages, 3 .eps figures, Harvma

Microscopic Formulation of Black Holes in String Theory

In this Report we review the microscopic formulation of the five dimensional black hole of type IIB string theory in terms of the D1-D5 brane system. The emphasis here is more on the brane dynamics than on supergravity solutions. We show how the low energy brane dynamics, combined with crucial inputs from AdS/CFT correspondence, leads to a derivation of black hole thermodynamics and the rate of Hawking radiation. Our approach requires a detailed exposition of the gauge theory and conformal field theory of the D1-D5 system. We also discuss some applications of the AdS/CFT correspondence in the context of black hole formation in three dimensions by thermal transition and by collision of point particles.Comment: (v2) To appear in Physics Reports; 168 pages, 4 figures. References and clarifications adde

Gauge-Gravity Dualities, Dipoles and New Non-Kahler Manifolds

In this work we explore many directions in the framework of gauge-gravity dualities. In type IIB theory we give an explicit derivation of the local metric for five branes wrapped on rigid two-cycles. Our derivation involves various interplays between warp factors, dualities and fluxes and the final result confirms our earlier predictions. We also find a novel dipole-like deformation of the background due to an inherent orientifold projection in the full global geometry. The supergravity solution for this deformation takes into account various things like the presence of a non-trivial background topology and fluxes as well as branes. Considering these, we manage to calculate the precise local solution using equations of motion. We also show that this dipole-like deformation has the desired property of decoupling the Kaluza-Klein modes from the IR gauge theory. Finally, for the heterotic theory we find new non-Kahler complex manifolds that partake in the full gauge-gravity dualities and study the mathematical structures of these manifolds including the torsion classes, Betti numbers and other topological data.Comment: Harvmac, 80 pages, 4 .eps figures; v2: Some typos corrected and new references added; v3: More typos corrected and references updated. Final version to appear in Nucl. Phys.

Target highlights in CASP14 : Analysis of models by structure providers

Abstract The biological and functional significance of selected CASP14 targets are described by the authors of the structures. The authors highlight the most relevant features of the target proteins and discuss how well these features were reproduced in the respective submitted predictions. The overall ability to predict three-dimensional structures of proteins has improved remarkably in CASP14, and many difficult targets were modelled with impressive accuracy. For the first time in the history of CASP, the experimentalists not only highlighted that computational models can accurately reproduce the most critical structural features observed in their targets, but also envisaged that models could serve as a guidance for further studies of biologically-relevant properties of proteins. This article is protected by copyright. All rights reserved.Peer reviewe

Structural Biology of Human H3K9 Methyltransferases

SET domain methyltransferases deposit methyl marks on specific histone tail lysine residues and play a major role in epigenetic regulation of gene transcription. We solved the structures of the catalytic domains of GLP, G9a, Suv39H2 and PRDM2, four of the eight known human H3K9 methyltransferases in their apo conformation or in complex with the methyl donating cofactor, and peptide substrates. We analyzed the structural determinants for methylation state specificity, and designed a G9a mutant able to tri-methylate H3K9. We show that the I-SET domain acts as a rigid docking platform, while induced-fit of the Post-SET domain is necessary to achieve a catalytically competent conformation. We also propose a model where long-range electrostatics bring enzyme and histone substrate together, while the presence of an arginine upstream of the target lysine is critical for binding and specificity. Enhanced version: This article can also be viewed as an enhanced version in which the text of the article is integrated with interactive 3D representations and animated transitions. Please note that a web plugin is required to access this enhanced functionality. Instructions for the installation and use of the web plugin are available i