1,655 research outputs found
Solid-State Quantum Computer Based on Scanning Tunneling Microscopy
We propose a solid-state nuclear spin quantum computer based on application
of scanning tunneling microscopy (STM) and well-developed silicon technology.
It requires the measurement of tunneling current modulation caused by the
Larmor precession of a single electron spin.
Our envisioned STM quantum computer would operate at the high magnetic field
(T) and at low temperature K.Comment: 3pages RevTex including 2 figure
Derivation of Internally-Consistent Thermodynamic Data by the Technique of Mathematical Programming: a Review with Application the System MgO-SiO2-H2O
The problem of deriving an optimal set of thermodynamic properties of minerals from a diverse experimental data base is reviewed and a preferred methodology proposed. Mathematical pro-gramming(MAP) methods extend the linear programming (LIP) approach first presented by Gordon (1973), and make it possible to account for the type of information conveyed, and the uncertainties attending both phase equilibrium data and direct measurements of phase properties. For phase equilibrium data which are (in most cases) characterized by non-normal error distributions across experimental brackets, the midpoint of a bracket is no more probable than other points, and the data are best treated by considering the inequality in the change in Gibbs free energy of reaction at each half-bracket. Direct measurements of phase properties can be assumed to have approximately normal error distributions, and the MAP technique optimizes agreement with these values by using the principles of least squares in the definition of an objective function. The structure of this problem, treatment of uncertainties in various types of experimental data, and method of optimizing final solutions are discussed in some detail. The method is applied to experimental data in the MgO-SiO2-H2O system, where inconsistencies among the data are resolved and an optimal set of thermodynamic properties is presented. The derived standard state entropies and volumes agree with all direct measurements (within their uncertainties), as do enthalpies of formation from the elements except for those of talc (+16 kJ mol−1), anthophyllite (+ 14 kJ mol−1), and brucite (−1 kJ mol−1). Stable phase relations in the system have the topology predicted by Greenwood (1963, 1971), with quartz- and forsterite-absent invariant points at 683 °C-6-4 kb and 797 °C-12 kb respectively, repeating at 552 °C-120 b and 550 °C-55 b. The thermodynamic analysis indicates little remaining flexibility in the phase relations, which, when combined with suitable activity models for solid solution, should allow for accurate determination of the conditions of metamorphism of ultramafic rock
6'-Methoxy Raloxifene-analog enhances mouse bone properties with reduced estrogen receptor binding
Raloxifene (RAL) is an FDA-approved drug used to treat osteoporosis in postmenopausal women. RAL suppresses bone loss primarily through its role as a selective estrogen receptor modulator (SERM). This hormonal estrogen therapy promotes unintended side effects, such as hot flashes and increased thrombosis risk, and prevents the drug from being used in some patient populations at-risk for fracture, including children with bone disorders. It has recently been demonstrated that RAL can have significant positive effects on overall bone mechanical properties by binding to collagen and increasing bone tissue hydration in a cell-independent manner. A Raloxifene-Analog (RAL-A) was synthesized by replacing the 6-hydroxyl substituent with 6-methoxy in effort to reduce the compound's binding affinity for estrogen receptors (ER) while maintaining its collagen-binding ability. It was hypothesized that RAL-A would improve the mechanical integrity of bone in a manner similar to RAL, but with reduced estrogen receptor binding. Molecular assessment showed that while RAL-A did reduce ER binding, downstream ER signaling was not completely abolished. In-vitro, RAL-A performed similarly to RAL and had an identical concentration threshold on osteocyte cell proliferation, differentiation, and function. To assess treatment effect in-vivo, wildtype (WT) and heterozygous (OIM+/-) female mice from the Osteogenesis Imperfecta (OI) murine model were treated with either RAL or RAL-A from 8 weeks to 16 weeks of age. There was an untreated control group for each genotype as well. Bone microarchitecture was assessed using microCT, and mechanical behavior was assessed using 3-point bending. Results indicate that both compounds produced analogous gains in tibial trabecular and cortical microarchitecture. While WT mechanical properties were not drastically altered with either treatment, OIM+/- mechanical properties were significantly enhanced, most notably, in post-yield properties including bone toughness. This proof-of-concept study shows promising results and warrants the exploration of additional analog iterations to further reduce ER binding and improve fracture resistance
Comparison of Recoil-Induced Resonances (RIR) and Collective Atomic Recoil Laser (CARL)
The theories of recoil-induced resonances (RIR) [J. Guo, P. R. Berman, B.
Dubetsky and G. Grynberg, Phys. Rev. A {\bf 46}, 1426 (1992)] and the
collective atomic recoil laser (CARL) [ R. Bonifacio and L. De Salvo, Nucl.
Instrum. Methods A {\bf 341}, 360 (1994)] are compared. Both theories can be
used to derive expressions for the gain experienced by a probe field
interacting with an ensemble of two-level atoms that are simultaneously driven
by a pump field. It is shown that the RIR and CARL formalisms are equivalent.
Differences between the RIR and CARL arise because the theories are typically
applied for different ranges of the parameters appearing in the theory. The RIR
limit considered in this paper is , while the CARL
limit is , where is the magnitude of the
difference of the wave vectors of the pump and probe fields, is the
width of the atomic momentum distribution and is a recoil
frequency. The probe gain for a probe-pump detuning equal to zero is analyzed
in some detail, in order to understand how the gain arises in a system which,
at first glance, might appear to have vanishing gain. Moreover, it is shown
that the calculations, carried out in perturbation theory have a range of
applicability beyond the recoil problem. Experimental possibilities for
observing CARL are discussed.Comment: 16 pages, 1 figure. Submitted to Physical Review
Elastic and Raman scattering of 9.0 and 11.4 MeV photons from Au, Dy and In
Monoenergetic photons between 8.8 and 11.4 MeV were scattered elastically and
in elastically (Raman) from natural targets of Au, Dy and In.15 new cross
sections were measured. Evidence is presented for a slight deformation in the
197Au nucleus, generally believed to be spherical. It is predicted, on the
basis of these measurements, that the Giant Dipole Resonance of Dy is very
similar to that of 160Gd. A narrow isolated resonance at 9.0 MeV is observed in
In.Comment: 31 pages, 11 figure
Adiabaticity Conditions for Volatility Smile in Black-Scholes Pricing Model
Our derivation of the distribution function for future returns is based on
the risk neutral approach which gives a functional dependence for the European
call (put) option price, C(K), given the strike price, K, and the distribution
function of the returns. We derive this distribution function using for C(K) a
Black-Scholes (BS) expression with volatility in the form of a volatility
smile. We show that this approach based on a volatility smile leads to relative
minima for the distribution function ("bad" probabilities) never observed in
real data and, in the worst cases, negative probabilities. We show that these
undesirable effects can be eliminated by requiring "adiabatic" conditions on
the volatility smile
A randomized, placebo-controlled trial of late Na current inhibition (ranolazine) in coronary microvascular dysfunction (CMD): impact on angina and myocardial perfusion reserve.
AimsThe mechanistic basis of the symptoms and signs of myocardial ischaemia in patients without obstructive coronary artery disease (CAD) and evidence of coronary microvascular dysfunction (CMD) is unclear. The aim of this study was to mechanistically test short-term late sodium current inhibition (ranolazine) in such subjects on angina, myocardial perfusion reserve index, and diastolic filling.Materials and resultsRandomized, double-blind, placebo-controlled, crossover, mechanistic trial in subjects with evidence of CMD [invasive coronary reactivity testing or non-invasive cardiac magnetic resonance imaging myocardial perfusion reserve index (MPRI)]. Short-term oral ranolazine 500-1000 mg twice daily for 2 weeks vs. placebo. Angina measured by Seattle Angina Questionnaire (SAQ) and SAQ-7 (co-primaries), diary angina (secondary), stress MPRI, diastolic filling, quality of life (QoL). Of 128 (96% women) subjects, no treatment differences in the outcomes were observed. Peak heart rate was lower during pharmacological stress during ranolazine (-3.55 b.p.m., P < 0.001). The change in SAQ-7 directly correlated with the change in MPRI (correlation 0.25, P = 0.005). The change in MPRI predicted the change in SAQ QoL, adjusted for body mass index (BMI), prior myocardial infarction, and site (P = 0.0032). Low coronary flow reserve (CFR <2.5) subjects improved MPRI (P < 0.0137), SAQ angina frequency (P = 0.027), and SAQ-7 (P = 0.041).ConclusionsIn this mechanistic trial among symptomatic subjects, no obstructive CAD, short-term late sodium current inhibition was not generally effective for SAQ angina. Angina and myocardial perfusion reserve changes were related, supporting the notion that strategies to improve ischaemia should be tested in these subjects.Trial registrationclinicaltrials.gov Identifier: NCT01342029
Struct2Net: a web service to predict protein–protein interactions using a structure-based approach
Struct2Net is a web server for predicting interactions between arbitrary protein pairs using a structure-based approach. Prediction of protein–protein interactions (PPIs) is a central area of interest and successful prediction would provide leads for experiments and drug design; however, the experimental coverage of the PPI interactome remains inadequate. We believe that Struct2Net is the first community-wide resource to provide structure-based PPI predictions that go beyond homology modeling. Also, most web-resources for predicting PPIs currently rely on functional genomic data (e.g. GO annotation, gene expression, cellular localization, etc.). Our structure-based approach is independent of such methods and only requires the sequence information of the proteins being queried. The web service allows multiple querying options, aimed at maximizing flexibility. For the most commonly studied organisms (fly, human and yeast), predictions have been pre-computed and can be retrieved almost instantaneously. For proteins from other species, users have the option of getting a quick-but-approximate result (using orthology over pre-computed results) or having a full-blown computation performed. The web service is freely available at http://struct2net.csail.mit.edu.National Institute of General Medical Sciences (U.S.) (Grant Number 1R01GM081871)Toyota Technological Institute at Chicag
Higher Dimensional Kerr-AdS Black Holes and the AdS/CFT Correspondence
Using the counterterm subtraction technique we calculatehe stress-energy
tensor, action, and other physical quantities for Kerr-AdS black holes in
various dimensions. For Kerr-AdS_5 with both rotation parameters non-zero, we
demonstrate that stress-energy tensor, in the zero mass parameter limit, is
equal to the stress tensor of the weakly coupled four dimensional dual field
theory. As a result, the total energy of the generalKerr-AdS_5 black hole at
zero mass parameter, exactly matches the Casimir energy of the dual field
theory. We show that at high temperature, the general Kerr-AdS_5 and
perturbative field theory stress-energy tensors are equal, up to the usual
factor of 3/4. We also use the counterterm technique to calculate the stress
tensors and actions for Kerr-AdS_6, and Kerr-AdS_7 black holes, with one
rotation parameter, and we display the results. We discuss the conformal
anomalies of the field theories dual to the Kerr-AdS_5 and Kerr-AdS_7
spacetimes. In these two field theories, we show that the rotation parameters
break conformal invariance but not scale invariance, a novel result for a
non-trivial field theory. For Kerr-AdS_7 the conformal anomalies calculated on
the gravity side and the dual (0,2) tensor multiplet theory are equal up to 4/7
factor. We expect that the Casimir energy of the free field theory is the same
as the energy of the Kerr-AdS_7 black hole (with zero mass parameter), up to
that factor.Comment: 18 pages, LaTex (v3: references added. footnote added
Wavelets techniques for pointwise anti-Holderian irregularity
In this paper, we introduce a notion of weak pointwise Holder regularity,
starting from the de nition of the pointwise anti-Holder irregularity. Using
this concept, a weak spectrum of singularities can be de ned as for the usual
pointwise Holder regularity. We build a class of wavelet series satisfying the
multifractal formalism and thus show the optimality of the upper bound. We also
show that the weak spectrum of singularities is disconnected from the casual
one (denoted here strong spectrum of singularities) by exhibiting a
multifractal function made of Davenport series whose weak spectrum di ers from
the strong one
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