1,099 research outputs found
Photoinduced time-resolved electrodynamics of superconducting metals and alloys
The photoexcited state in superconducting metals and alloys was studied via
pump-probe spectroscopy. A pulsed Ti:sapphire laser was used to create the
non-equilibrium state and the far-infrared pulses of a synchrotron storage
ring, to which the laser is synchronized, measured the changes in the material
optical properties. Both the time- and frequency- dependent photoinduced
spectra of Pb, Nb, NbN, Nb{0.5}Ti{0.5}N, and Pb{0.75}Bi{0.25} superconducting
thin films were measured in the low-fluence regime. The time dependent data
establish the regions where the relaxation rate is dominated either by the
phonon escape time (phonon bottleneck effect) or by the intrinsic quasiparticle
recombination time. The photoinduced spectra measure directly the reduction of
the superconducting gap due to an excess number of quasiparticles created by
the short laser pulses. This gap shift allows us to establish the temperature
range over which the low fluence approximation is valid.Comment: 12 pages with 10 figure
Bibliometrics to assess the productivity and impact of medical research
Background: Bibliometrics is the use of statistical and mathematical analysis to assess research production and quality. These metrics provide important insights into the quality and impact of research by applying standardised metrics. However, there are inherent limitations in their application.
Objective: We aimed to review existing bibliometric indices and assess their comparative utility in the assessment of medical researchers. We specifically aimed to evaluate the utility of the h-index in identifying young or developing medical researchers with future research potential.
Method: We conducted a focussed literature review on commonly used bibliometrics. To explore the utility of these metrics we then used them to evaluate a sample of researchers from a South African medical school faculty. Researchers were ranked with the following metrics: number of publications; h-index; citations per paper; citations per paper per year; and m-index. The h-index, citations and publication counts were drawn from ResearchGate and, if not available, from Google Scholar. The top 20 researchers, based on publication count, were then analysed further.
Results: We identified 145 researchers for analysis of which 37 were excluded due to an inability to obtain additional information. Higher time-dependent metrics (publication count, citation count, h-index) were directly proportional to years since first publication. Indices that corrected for time, such as the m-index, provided more insight and better discrimination in identifying younger researchers with greater research potential.
Conclusion: Bibliometrics have utility as part of the assessment of academic output but may be subject to time-dependent bias. Research quality is best measured using the h-index, g-index and m-index. The h-index is limited by being time dependent and field specific and overlooks highly cited papers. Bibliometrics that account for time, such as the m-index, should be considered in the early identification of young researchers, ideally accompanied by critical peer review
Dynamic Resonance of Light in Fabry-Perot Cavities
The dynamics of light in Fabry-Perot cavities with varying length and input
laser frequency are analyzed and the exact condition for resonance is derived.
This dynamic resonance depends on the light transit time in the cavity and the
Doppler effect due to the mirror motions. The response of the cavity to length
variations is very different from its response to laser frequency variations.
If the frequency of these variations is equal to multiples of the cavity free
spectral range, the response to length is maximized while the response to the
laser frequency is zero. Implications of these results for the detection of
gravitational waves using kilometer-scale Fabry-Perot cavities are discussed
Natriuretic peptide-directed medical therapy: a systematic review
Abstract
Natriuretic peptides (NP) are strongly associated with perioperative cardiovascular events. However, in patients with raised NP, it remains unknown whether treatment to reduce NP levels prior to surgery results in better perioperative outcomes. In this systematic review and meta-analysis, we investigate NP-directed medical therapy in non-surgical patients to provide guidance for NP-directed medical therapy in surgical patients. The protocol was registered with PROSPERO (CRD42017051468). The database search included MEDLINE (PubMed), CINAHL (EBSCO host), EMBASE (EBSCO host), ProQuest, Web of Science, and Cochrane database. The primary outcome was to determine whether NP-directed medical therapy is effective in reducing NP levels within 6 months, compared to standard of care. The secondary outcome was to determine whether reducing NP levels is associated with decreased mortality. Full texts of 18 trials were reviewed. NP-directed medical therapy showed no significant difference compared to standard care in decreasing NP levels (standardized mean difference − 0.04 (− 0.16, 0.07)), but was associated with a 6-month (relative risk (RR) 0.82 (95% confidence interval (CI) 0.68–0.99)) reduction in mortality
Small optic suspensions for Advanced LIGO input optics and other precision optical experiments
We report on the design and performance of small optic suspensions developed
to suppress seismic motion of out-of-cavity optics in the Input Optics
subsystem of the Advanced LIGO interferometric gravitational wave detector.
These compact single stage suspensions provide isolation in all six degrees of
freedom of the optic, local sensing and actuation in three of them, and passive
damping for the other three
Parallel phase modulation scheme for interferometric gravitational-wave detectors
Advanced LIGO (aLIGO) requires multiple frequency sidebands to disentangle all of the main interferometer’s length signals. This paper presents the results of a risk reduction experiment to produce two sets of frequency sidebands in parallel, avoiding mixed ‘sidebands on sidebands’. Two phase modulation frequencies are applied to separate Electro-Optic Modulators (EOMs), with one EOM in each of the two arms of a Mach-Zehnder interferometer. In this system the Mach-Zehnder’s arm lengths are stabilized to reduce relative intensity noise in the recombined carrier beam by feeding a corrective control signal back to the Rubidium Titanyl Phosphate (RTP) EOM crystals to drive the optical path length difference to zero. This setup’s use of the RTP crystals as length actuators provides enough bandwidth in the feedback to meet arm length stability requirements for aLIGO
Characterization of thermal effects in the Enhanced LIGO Input Optics
We present the design and performance of the LIGO Input Optics subsystem as
implemented for the sixth science run of the LIGO interferometers. The Initial
LIGO Input Optics experienced thermal side effects when operating with 7 W
input power. We designed, built, and implemented improved versions of the Input
Optics for Enhanced LIGO, an incremental upgrade to the Initial LIGO
interferometers, designed to run with 30 W input power. At four times the power
of Initial LIGO, the Enhanced LIGO Input Optics demonstrated improved
performance including better optical isolation, less thermal drift, minimal
thermal lensing and higher optical efficiency. The success of the Input Optics
design fosters confidence for its ability to perform well in Advanced LIGO
Sub-nanosecond, time-resolved, broadband infrared spectroscopy using synchrotron radiation
A facility for sub-nanosecond time-resolved (pump-probe) infrared
spectroscopy has been developed at the National Synchrotron Light Source of
Brookhaven National Laboratory. A mode-locked Ti:sapphire laser produces 2 ps
duration, tunable near-IR pump pulses synchronized to probe pulses from a
synchrotron storage ring. The facility is unique on account of the broadband
infrared from the synchrotron, which allows the entire spectral range from 2
cm-1 (0.25 meV) to 20,000 cm-1 (2.5 eV) to be probed. A temporal resolution of
200 ps, limited by the infrared synchrotron-pulse duration, is achieved. A
maximum time delay of 170 ns is available without gating the infrared detector.
To illustrate the performance of the facility, a measurement of electron-hole
recombination dynamics for an HgCdTe semiconductor film in the far- and mid
infrared range is presented.Comment: 11 pages with 9 figures include
Renormalized Energies of Superfluorescent Bursts from an Electron-Hole Magneto-plasma with High Gain in InGaAs Quantum Wells
We study light emission properties of a population-inverted 2D electron-hole
plasma in a quantizing magnetic field. We observe a series of superfluorescent
bursts, discrete both in time and energy, corresponding to the cooperative
recombination of electron-hole pairs from different Landau levels. The emission
energies are strongly renormalized due to many-body interactions among the
photogenerated carriers, exhibiting red-shifts as large as 20 meV at 15 T.
However, the magnetic field dependence of the lowest Landau level emission line
remains excitonic at all magnetic fields. Interestingly, our time-resolved
measurements show that this lowest-energy burst occurs only after all upper
states become empty, suggesting that this excitonic stability is related to the
`hidden symmetry' of 2D magneto-excitons expected in the magnetic quantum
limit.Comment: 5 pages, 4 figure
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