Electronic structure of GaAs1-xNx alloy by soft-X-ray absorption and emission: Origin of the reduced optical efficiency

The local electronic structure of N atoms in a diluted GaAs1-xNx (x=3%) alloy, in view of applications in optoelectronics, is determined for the first time using soft-X-ray absorption (SXA) and emission (SXE). Deviations from crystalline GaN, in particular in the conduction band, are dramatic. Employing the orbital character and elemental specificity of the SXE/SXA spectroscopies, we identify a charge transfer from the N atoms at the valence band maximum, reducing the overlap with the wavefunction in conduction band minimum, as the main factor limiting the optical efficiency of GaAs1-xNx alloys. Moreover, a k-conserving process of resonant inelastic x-ray scattering involving the L1 derived valence and conduction states is discovered.Comment: 3 pages, physica status solidi (Rapid Research Notes), in pres

Predictive markers of abdominal aortic stiffness measured by echo-tracking in subjects with varying insulin sensitivity.

Arterial stiffness is influenced by advancing age and vascular disease and is an independent risk factor for cardiovascular events and death. Using ultrasound measurements, arterial stiffness in a specific arterial segment can be assessed. The aim of this observational study was to explore the prospective and cross-sectional associations between arterial stiffness measured by ultrasound locally in the abdominal aorta and cardiovascular risk factors/markers including insulin resistance measured by the homeostatic model assessment-insulin resistance (HOMA-IR), lipids and abdominal obesity. This study includes 335 subjects from Malmö, Sweden, examined in 1991-1994 and again at follow-up in 1998-2000 (mean age 64 years, 42% men). Ultrasound measurement of the abdominal aorta was performed at follow-up investigation. In the female subgroup, there was a positive association between HOMA-IR at baseline and abdominal aortic stiffness at follow-up (β=0.18, P=0.03) and a negative association between high-density lipoprotein and aortic stiffness (β=-0.23, P=0.005), independently of classical cardiovascular risk factors. These associations were not found among men. The results suggest a greater or different role of impaired glucose metabolism in the pathophysiology of arterial stiffness in women than in men.Journal of Human Hypertension advance online publication, 2 January 2014; doi:10.1038/jhh.2013.126

The planet search programme at the ESO CES and HARPS. IV. The search for Jupiter analogues around solar-like stars

In 1992 we began a precision radial velocity (RV) survey for planets around solar-like stars with the Coude Echelle Spectrograph and the Long Camera (CES LC) at the 1.4 m telescope in La Silla (Chile). We have continued the survey with the upgraded CES Very Long Camera (VLC) and HARPS, both at the 3.6 m telescope, until 2007. The observations for 31 stars cover a time span of up to 15 years and the RV precision permit a search for Jupiter analogues. We perform a joint analysis for variability, trends, periodicities, and Keplerian orbits and compute detection limits. Moreover, the HARPS RVs are analysed for correlations with activity indicators (CaII H&K and CCF shape). We achieve a long-term RV precision of 15 m/s (CES+LC, 1992-1998), 9 m/s (CES+VLC, 1999-2006), and 2.8 m/s (HARPS, 2003-2009, including archive data), resp. This enables us to confirm the known planets around Iota Hor, HR 506, and HR 3259. A steady RV trend for Eps Ind A can be explained by a planetary companion. On the other hand, we find previously reported trends to be smaller for Beta Hyi and not present for Alp Men. The candidate planet Eps Eri b was not detected despite our better precision. Also the planet announced for HR 4523 cannot be confirmed. Long-term trends in several of our stars are compatible with known stellar companions. We provide a spectroscopic orbital solution for the binary HR 2400 and refined solutions for the planets around HR 506 and Iota Hor. For some other stars the variations could be attributed to stellar activity. The occurrence of two Jupiter-mass planets in our sample is in line with the estimate of 10% for the frequency of giant planets with periods smaller than 10 yr around solar-like stars. We have not detected a Jupiter analogue, while the detections limits for circular orbits indicate at 5 AU a sensitivity for minimum mass of at least 1 M_Jup (2 M_Jup) for 13% (61%) of the stars.Comment: 63 pages, 24 figures (+33 online figures), 13 Tables, accepted for publication in A&A (2012-11-13

Electron effective mass in Al0.72_{0.72}Ga0.28_{0.28}N alloys determined by mid-infrared optical Hall effect

The effective electron mass parameter in Si-doped Al$_{0.72}$Ga$_{0.28}$N is determined to be $m^\ast=(0.336\pm0.020)\,m_0$ from mid-infrared optical Hall effect measurements. No significant anisotropy of the effective electron mass parameter is found supporting theoretical predictions. Assuming a linear change of the effective electron mass with the Al content in AlGaN alloys and $m^\ast=0.232\,m_0$ for GaN, an average effective electron mass of $m^\ast=0.376\,m_0$ can be extrapolated for AlN. The analysis of mid-infrared spectroscopic ellipsometry measurements further confirms the two phonon mode behavior of the E$_1$(TO) and one phonon mode behavior of the A$_1$(LO) phonon mode in high-Al-content AlGaN alloys as seen in previous Raman scattering studies

Boosting parallel perceptrons for label noise reduction in classification problems

The final publication is available at Springer via http://dx.doi.org/10.1007/11499305_60Proceedings of First International Work-Conference on the Interplay Between Natural and Artificial Computation, IWINAC 2005, Las Palmas, Canary Islands, Spain, June 15-18, 2005Boosting combines an ensemble of weak learners to construct a new weighted classifier that is often more accurate than any of its components. The construction of such learners, whose training sets depend on the performance of the previous members of the ensemble, is carried out by successively focusing on those patterns harder to classify. This fact deteriorates boosting’s results when dealing with malicious noise as, for instance, mislabeled training examples. In order to detect and avoid those noisy examples during the learning process, we propose the use of Parallel Perceptrons. Among other things, these novel machines allow to naturally define margins for hidden unit activations. We shall use these margins to detect which patterns may have an incorrect label and also which are safe, in the sense of being well represented in the training sample by many other similar patterns. As candidates for being noisy examples we shall reduce the weights of the former ones, and as a support for the overall detection procedure we shall augment the weights of the latter ones.With partial support of Spain’s CICyT, TIC 01–572, TIN 2004–0767

The tensor part of the Skyrme energy density functional. I. Spherical nuclei

We perform a systematic study of the impact of the J^2 tensor term in the Skyrme energy functional on properties of spherical nuclei. In the Skyrme energy functional, the tensor terms originate both from zero-range central and tensor forces. We build a set of 36 parameterizations, which covers a wide range of the parameter space of the isoscalar and isovector tensor term coupling constants, with a fit protocol very similar to that of the successful SLy parameterizations. We analyze the impact of the tensor terms on a large variety of observables in spherical mean-field calculations, such as the spin-orbit splittings and single-particle spectra of doubly-magic nuclei, the evolution of spin-orbit splittings along chains of semi-magic nuclei, mass residuals of spherical nuclei, and known anomalies of charge radii. Our main conclusion is that the currently used central and spin-orbit parts of the Skyrme energy density functional are not flexible enough to allow for the presence of large tensor terms.Comment: 38 pages, 36 figures; Minor correction

Federating distributed clinical data for the prediction of adverse hypotensive events

The ability to predict adverse hypotensive events, where a patient's arterial blood pressure drops to abnormally low (and dangerous) levels, would be of major benefit to the fields of primary and secondary health care, and especially to the traumatic brain injury domain. A wealth of data exist in health care systems providing information on the major health indicators of patients in hospitals (blood pressure, temperature, heart rate, etc.). It is believed that if enough of these data could be drawn together and analysed in a systematic way, then a system could be built that will trigger an alarm predicting the onset of a hypotensive event over a useful time scale, e.g. half an hour in advance. In such circumstances, avoidance measures can be taken to prevent such events arising. This is the basis for the Avert-IT project (http://www.avert-it.org), a collaborative EU-funded project involving the construction of a hypotension alarm system exploiting Bayesian neural networks using techniques of data federation to bring together the relevant information for study and system development