988 research outputs found
Spectral signature of short attosecond pulse trains
We report experimental measurements of high-order harmonic spectra generated
in Ar using a carrier-envelope-offset (CEO) stabilized 12 fs, 800nm laser field
and a fraction (less than 10%) of its second harmonic. Additional spectral
peaks are observed between the harmonic peaks, which are due to interferences
between multiple pulses in the train. The position of these peaks varies with
the CEO and their number is directly related to the number of pulses in the
train. An analytical model, as well as numerical simulations, support our
interpretation
Intensity Dependence of Laser-Assisted Attosecond Photoionization Spectra
We study experimentally the influence of the intensity of the infrared (IR)
probe field on attosecond pulse train (APT) phase measurements performed with
the RABITT method (Reconstruction of Attosecond Beating by Interference in
Two-Photon Transitions). We find that if a strong IR field is applied, the
attosecond pulses will appear to have lower-than-actual chirp rates. We also
observe the onset of the streaking regime in the breakdown of the weak-field
RABITT conditions. We perform a Fourier-analysis of harmonic and sideband
continuum states and show that the mutual phase relation of the harmonics can
be extracted from higher Fourier components.Comment: preprint to article in Laser Physics Nikolai B. Delone memorial issue
11 pages, 9 figures, published online 15 July 200
Clinical applications of B-type natriuretic peptide (BNP) testing
Many claims have been made in recent years regarding the utility of plasma B-type natriuretic peptide (BNP) concentration measurements in the diagnosis, risk stratification and monitoring of patients with heart failure. This paper summarizes the current evidence and provides guidance for practising clinicians. Overall, plasma BNP testing appears to be of most value in the diagnostic arena, where it is likely to improve the performance of non-specialist physicians in diagnosing heart failure. In clinical practice, BNP testing is best used as a ‘rule out' test for suspected cases of new heart failure in breathless patients presenting to either the outpatient or emergency care settings; it is not a replacement for echocardiography and full cardiological assessment, which will be required for patients with an elevated BNP concentration. Although work is ongoing in establishing the ‘normal' values of BNP, heart failure appears to be highly unlikely below a plasma concentration of 100pg/ml. However, as BNP levels rise with age and are affected by gender, comorbidity and drug therapy, the plasma BNP measurement should not be used in isolation from the clinical contex
Photoemission time-delay measurements and calculations close to the 3s ionization minimum in Ar
We present experimental measurements and theoretical calculations of
photoionization time delays from the and shells in Ar in the photon
energy range of 32-42 eV. The experimental measurements are performed by
interferometry using attosecond pulse trains and the infrared laser used for
their generation. The theoretical approach includes intershell correlation
effects between the 3s and 3p shells within the framework of the random phase
approximation with exchange (RPAE). The connection between single-photon
ionization and the two-color two-photon ionization process used in the
measurement is established using the recently developed asymptotic
approximation for the complex transition amplitudes of laser-assisted
photoionization. We compare and discuss the theoretical and experimental
results especially in the region where strong intershell correlations in the 3s
to kp channel lead to an induced "Cooper" minimum in the 3s ionization
cross-section.Comment: submitted to PR
Full-Duplex Digital Communication on a Single Laser Beam
A proposed free-space optical communication system would operate in a full-duplex mode, using a single constant-power laser beam for transmission and reception of binary signals at both ends of the free-space optical path. The system was conceived for two-way data communication between a ground station and a spacecraft in a low orbit around the Earth. It has been estimated that in this application, a data rate of 10 kb/s could be achieved at a ground-station-to-spacecraft distance of 320 km, using a laser power of only 100 mW. The basic system concept is also applicable to terrestrial free-space optical communications. The system (see figure) would include a diode laser at one end of the link (originally, the ground station) and a liquid-crystal- based retroreflecting modulator at the other end of the link (originally, the spacecraft). At the laser end, the beam to be transmitted would be made to pass through a quarter-wave plate, which would convert its linear polarization to right circular polarization. For transmission of data from the laser end to the retroreflector end, the laser beam would be modulated with subcarrier phase-shift keying (SC-PSK). The transmitted beam would then pass through an aperture- sharing element (ASE) - basically, a mirror with a hole in it, used to separate the paths of the transmitted and received light beams. The transmitted beam would continue outward through a telescope (which, in the original application, would be equipped with a spacecraft-tracking system) that would launch the transmitted beam along the free-space optical path to the retroreflector end
Studies of Diffuse Interstellar Bands. V. Pairwise Correlations of Eight Strong DIBs and Neutral Hydrogen, Molecular Hydrogen, and Color Excess
We establish correlations between equivalent widths of eight diffuse
interstellar bands (DIBs), and examine their correlations with atomic hydrogen,
molecular hydrogen, and EB-V . The DIBs are centered at \lambda\lambda 5780.5,
6204.5, 6283.8, 6196.0, 6613.6, 5705.1, 5797.1, and 5487.7, in decreasing order
of Pearson\^as correlation coefficient with N(H) (here defined as the column
density of neutral hydrogen), ranging from 0.96 to 0.82. We find the equivalent
width of \lambda 5780.5 is better correlated with column densities of H than
with E(B-V) or H2, confirming earlier results based on smaller datasets. We
show the same is true for six of the seven other DIBs presented here. Despite
this similarity, the eight strong DIBs chosen are not well enough correlated
with each other to suggest they come from the same carrier. We further conclude
that these eight DIBs are more likely to be associated with H than with H2, and
hence are not preferentially located in the densest, most UV shielded parts of
interstellar clouds. We suggest they arise from different molecules found in
diffuse H regions with very little H (molecular fraction f<0.01). Of the 133
stars with available data in our study, there are three with significantly
weaker \lambda 5780.5 than our mean H-5780.5 relationship, all of which are in
regions of high radiation fields, as previously noted by Herbig. The
correlations will be useful in deriving interstellar parameters when direct
methods are not available. For instance, with care, the value of N(H) can be
derived from W{\lambda}(5780.5).Comment: Accepted for publication in The Astrophysical Journal; 37 pages, 11
figures, 6 table
A Learning Management System-Based Early Warning System for Academic Advising in Undergraduate Engineering
This chapter describes a design-based research project that developed an early warning system for an undergraduate engineering mentoring program. Using near real-time data from a university’s learning management system, we provided academic advisors with timely and targeted data on students’ academic progress. We discuss the development of the early warning system and detail how academic advisors used it. Our findings point to the value of providing academic advisors with performance data that can be used to direct students to appropriate sources of support.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/107974/1/Krumm_etal_2014_LA.pd
Safety of continuing mineralocorticoid receptor antagonist treatment in patients with heart failure with reduced ejection fraction and severe kidney disease: Data from Swedish Heart Failure Registry
AIMS
Mineralocorticoid receptor antagonists (MRAs) improve outcomes in heart failure with reduced ejection fraction (HFrEF) but remain underused and are often discontinued especially in patients with chronic kidney disease (CKD) due to concerns on renal safety. Therefore, in a real-world HFrEF population we investigated the safety of MRA use, in terms of risk of renal events, any mortality and any hospitalization, across the estimated glomerular filtration rate (eGFR) spectrum including severe CKD.
METHODS AND RESULTS
We analysed patients with HFrEF (ejection fraction <40%), not on dialysis, from the Swedish Heart Failure Registry. We performed multivariable logistic regression models to investigate patient characteristics independently associated with MRA use, and univariable and multivariable Cox regression models to assess the associations between MRA use and outcomes. Of 33 942 patients, 17 489 (51%) received MRA, 32%, 45%, 54%, 54% with eGFR <30, 30-44, 45-59 or ≥60 ml/min/1.73 m , respectively. An eGFR ≥60 ml/min/1.73 m and patient characteristics linked with more severe HF were independently associated with more likely MRA use. In multivariable analyses, MRA use was consistently not associated with a higher risk of renal events (i.e. composite of dialysis/renal death/hospitalization for renal failure or hyperkalaemia) (hazard ratio [HR] 1.04, 95% confidence interval [CI] 0.98-1.10), all-cause death (HR 1.02, 95% CI 0.97-1.08) as well as of all-cause hospitalization (HR 0.99, 95% CI 0.95-1.02) across the eGFR spectrum including also severe CKD.
CONCLUSIONS
The use of MRAs in patients with HFrEF decreased with worse renal function; however their safety profile was demonstrated to be consistent across the entire eGFR spectrum
Development of the human fetal kidney from mid to late gestation in male and female infants
BACKGROUND: During normal human kidney development, nephrogenesis (the formation of nephrons) is complete by term birth, with the majority of nephrons formed late in gestation. The aim of this study was to morphologically examine nephrogenesis in fetal human kidneys from 20 to 41weeks of gestation. METHODS: Kidney samples were obtained at autopsy from 71 infants that died acutely in utero or within 24h after birth. Using image analysis, nephrogenic zone width, the number of glomerular generations, renal corpuscle cross-sectional area and the cellular composition of glomeruli were examined. Kidneys from female and male infants were analysed separately. FINDINGS: The number of glomerular generations formed within the fetal kidneys was directly proportional to gestational age, body weight and kidney weight, with variability between individuals in the ultimate number of generations (8 to 12) and in the timing of the cessation of nephrogenesis (still ongoing at 37weeks gestation in one infant). There was a slight but significant (r2=0.30, P=0.001) increase in renal corpuscle cross-sectional area from mid gestation to term in females, but this was not evident in males. The proportions of podocytes, endothelial and non-epithelial cells within mature glomeruli were stable throughout gestation. INTERPRETATION: These findings highlight spatial and temporal variability in nephrogenesis in the developing human kidney, whereas the relative cellular composition of glomeruli does not appear to be influenced by gestational age.Danica Ryan, Megan R. Sutherland, Tracey J. Flores, Alison L.Kent, Jane E. Dahlstrom,Victor G. Puelles ... et al
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