Bacterias y su implicación en el fallo de implantes de Titanio

Peer Reviewe

A reinterpretation of Volcano Ranch lateral distribution measurements to infer the mass composition of cosmic rays

In the course of its operation, the Volcano Ranch array collected data on the lateral distribution of showers produced by cosmic rays at energies above $10^{17}$ {\rm eV}. From these data very precise measurements of the steepness of the lateral distribution function, characterized by the $\eta$ parameter, were made. The current availability of sophisticated hadronic interaction models has prompted a reinterpretation of the measurements. We use the interaction models {\sc qgsjet} and {\sc sibyll} in the {\sc aires} Monte Carlo code to generate showers together with {\sc geant4} to simulate the response of the detectors to ground particles. As part of an effort to estimate the primary mass composition of cosmic rays at this energy range, we present the results of our preliminary analysis of the distribution of $\eta$.Comment: 4 pages, 5 figures Talk presented at the XII International Symposium on Very High Energy Cosmic Ray Interactions, CERN 2002. To be published in Nucl. Phys. B (Proc. Suppl.

Spin transmission through quantum dots with strong spin-orbit interaction

Quantum oscillations of the spin conductance through regular and chaotic 2D quantum dots under the varying Rashba spin orbit interaction and at zero magnetic field have been numerically calculated by summing up the spin evolution matrices for classical transmitting trajectories. Fourier analysis of these oscillations showed power spectra strongly dependent on the dot geometry. For narrow rings the spectra are dominated by a single peak in accordance with previous analytic results. In other geometries the spectra are represented by multiple peaks for regular QD and quasicontinuum for chaotic QD.Comment: 10 pages, 5 figure

Statistical significance of fine structure in the frequency spectrum of Aharonov-Bohm conductance oscillations

We discuss a statistical analysis of Aharonov-Bohm conductance oscillations measured in a two-dimensional ring, in the presence of Rashba spin-orbit interaction. Measurements performed at different values of gate voltage are used to calculate the ensemble-averaged modulus of the Fourier spectrum and, at each frequency, the standard deviation associated to the average. This allows us to prove the statistical significance of a splitting that we observe in the h/e peak of the averaged spectrum. Our work illustrates in detail the role of sample specific effects on the frequency spectrum of Aharonov-Bohm conductance oscillations and it demonstrates how fine structures of a different physical origin can be discriminated from sample specific features.Comment: accepted for publication in PR

Conductance fluctuations in diffusive rings: Berry phase effects and criteria for adiabaticity

We study Berry phase effects on conductance properties of diffusive mesoscopic conductors, which are caused by an electron spin moving through an orientationally inhomogeneous magnetic field. Extending previous work, we start with an exact, i.e. not assuming adiabaticity, calculation of the universal conductance fluctuations in a diffusive ring within the weak localization regime, based on a differential equation which we derive for the diffuson in the presence of Zeeman coupling to a magnetic field texture. We calculate the field strength required for adiabaticity and show that this strength is reduced by the diffusive motion. We demonstrate that not only the phases but also the amplitudes of the h/2e Aharonov-Bohm oscillations are strongly affected by the Berry phase. In particular, we show that these amplitudes are completely suppressed at certain magic tilt angles of the external fields, and thereby provide a useful criterion for experimental searches. We also discuss Berry phase-like effects resulting from spin-orbit interaction in diffusive conductors and derive exact formulas for both magnetoconductance and conductance fluctuations. We discuss the power spectra of the magnetoconductance and the conductance fluctuations for inhomogeneous magnetic fields and for spin-orbit interaction.Comment: 18 pages, 13 figures; minor revisions. To appear in Phys. Rev.

Improved constraints on WIMPs from the International Germanium Experiment IGEX

One IGEX 76Ge double-beta decay detector is currently operating in the Canfranc Underground Laboratory in a search for dark matter WIMPs, through the Ge nuclear recoil produced by the WIMP elastic scattering. A new exclusion plot, has been derived for WIMP-nucleon spin-independent interactions. To obtain this result, 40 days of data from the IGEX detector (energy threshold E \~ 4 keV), recently collected, have been analyzed. These data improve the exclusion limits derived from all the other ionization germanium detectors in the mass region from 20 GeV to 200 GeV, where a WIMP supposedly responsible for the annual modulation effect reported by the DAMA experiment would be located. The new IGEX exclusion contour enters, by the first time, the DAMA region by using only raw data, with no background discrimination, and excludes its upper left part. It is also shown that with a moderate improvement of the detector performances, the DAMA region could be fully explored.Comment: 14 pages, 8 figures, submitted to Physics Letters B (revised version after referee's comments, some figures added

New constraints on WIMPs from the Canfranc IGEX dark matter search

The IGEX Collaboration enriched 76Ge double-beta decay detectors are currently operating in the Canfranc Underground Laboratory with an overburden of 2450 m.w.e. A recent upgrade has made it possible to use them in a search for WIMPs. A new exclusion plot has been derived for WIMP-nucleon spin-independent interaction. To obtain this result, 30 days of data from one IGEX detector, which has an energy threshold of ~4 keV, have been considered. These data improve the exclusion limits derived from other germanium diode experiments in the ~50 GeV DAMA region, and show that with a moderate improvement of the background below 10 keV, the DAMA region may be tested with an additional 1 kg-year of exposure.Comment: 7 pages, 2 figures, submitted to Physics Letter

Optimal Radio Window for the Detection of Ultra-High-Energy Cosmic Rays and Neutrinos off the Moon

When high-energy cosmic rays impinge on a dense dielectric medium, radio waves are produced through the Askaryan effect. We show that at wavelengths comparable to the length of the shower produced by an Ultra-High Energy cosmic ray or neutrino, radio signals are an extremely efficient way to detect these particles. Through an example it is shown that this new approach offers, for the first time, the realistic possibility of measuring UHE neutrino fluxes below the Waxman-Bahcall limit. It is shown that in only one month of observing with the upcoming LOFAR radio telescope, cosmic-ray events can be measured beyond the GZK-limit, at a sensitivity level of two orders of magnitude below the extrapolated values.Comment: Submitted to Astroparticle Physic

Preconceptional cardiovascular health and pregnancy outcomes in women with systemic lupus erythematosus

Objective. To estimate the effects of preconceptional cardiovascular (CV) health, measured by American Heart Association (AHA) guidelines, on pregnancy outcomes in women with systemic lupus erythematosus (SLE). Methods. The study included patients in the Hopkins Lupus Pregnancy Cohort. Body mass index (BMI), total cholesterol, and blood pressure (BP) in the most recent clinic visit prior to conception or first trimester were used to determine CV health (ideal, intermediate, or poor health) based on AHA definitions. Outcomes included preterm birth, gestational age at birth, and small for gestational age (SGA). Multivariable linear and logistic regression models with generalized estimating equations estimated the association of each CV health factor and outcome. Results. The analysis included 309 live births. There were 95 preterm births (31%), and of the 293 pregnancies with birth weights, 18% were SGA. Ideal BMI, total cholesterol, and BP were reported in 56%, 85%, and 51% of pregnancies, respectively. Intermediate BMI was associated with decreased odds of SGA (OR 0.26, 95% CI 0.11-0.63), adjusted for race and prednisone use. Intermediate/poor total cholesterol was associated with increased odds of preterm birth (OR 2.21, 95% CI 1.06-4.62). Intermediate/poor BP was associated with decreased gestational age at birth (β -0.96, 95% CI -1.62 to -0.29). Conclusion. Poor/intermediate preconception CV health affects pregnancy outcomes of preterm birth and SGA infants among women with SLE. Efforts to maintain BMI, total cholesterol, and BP within the recommended ideal range prior to pregnancy is important to improve pregnancy outcomes in women with SLE

Effect of pregnancy on disease flares in patients with systemic lupus erythematosus

Objective: Prior studies found conflicting results about whether lupus is likely to flare during or after pregnancy. Using a large cohort of pregnant and non-pregnant women with lupus, we estimated the effect of pregnancy on disease flares in systemic lupus erythematosus. Methods: Data were collected in the Hopkins Lupus Cohort 1987-2015. Women aged 14-45 years with >1 measurement of disease activity were included. The time-varying exposures were classified as pregnancy, postpartum or non-pregnant/non-postpartum periods. Flares were defined as: (1) change in Physician Global Assessment (PGA)≥1 from previous visit and (2) change in Safety of Estrogens in Lupus National Assessment-Systemic Lupus Erythematosus Disease Activity Index (SELENA-SLEDAI)≥4 from previous visit. A stratified Cox model estimated HRs with bootstrap 95% CIs. Results: There were 1349 patients, including 398 pregnancies in 304 patients. There was an increased rate of flare defined by PGA during pregnancy (HR: 1.59; 95% CI 1.27 to 1.96); however, this effect was modified by hydroxychloroquine (HCQ) use, with the HR of flares in pregnancy compared with non-pregnant/non-postpartum periods estimated to be 1.83 (95% CI 1.34 to 2.45) for patients with no HCQ use and 1.26 (95% CI 0.88 to 1.69) for patients with HCQ use. The risk of flare was similarly elevated among non-HCQ users in the 3 months postpartum, but not for women taking HCQ after delivery. Conclusions: Our study supports and extends previous findings that the incidence of flare is increased during pregnancy and within the 3 months postpartum. Continuing HCQ, however, appeared to mitigate the risk of flare during and after pregnancy