3,060 research outputs found
Low-Threshold Surface-Passivated Photonic Crystal Nanocavity Laser
The efficiency and operating range of a photonic crystal laser is improved by
passivating the InGaAs quantum well (QW) gain medium and GaAs membrane using an
(NH4)S treatment. The passivated laser shows a four-fold reduction in
nonradiative surface recombination rate, resulting in a four-fold reduction in
lasing threshold. A three-level carrier dynamics model explains the results and
shows that lasing threshold is as much determined by surface recombination
losses as by the cavity quality factor (Q). Surface passivation therefore
appears crucial in operating such lasers under practical conditions.Comment: 3 pages, 2 figure
Time-resolved lasing action from single and coupled photonic crystal nanocavity array lasers emitting in the telecom-band
We measure the lasing dynamics of single and coupled photonic crystal
nanocavity array lasers fabricated in the indium gallium arsenide phosphide
material system. Under short optical excitation, single cavity lasers produce
pulses as fast as 11 ps (FWHM), while coupled cavity lasers show significantly
longer lasing duration which is not explained by a simple rate equations model.
A Finite Difference Time Domain simulation including carrier gain and diffusion
suggests that asynchronous lasing across the nanocavity array extends the
laser's pulse duration.Comment: 4 pages, 4 figure
Winter Habitat Selection of Cutthroat Trout (\u3cem\u3eOncorhynchus clarki\u3c/em\u3e) in a Large Regulated River
Microhabitat use by cutthroat trout and macrohabitat use by both cutthroat and rainbow trout were studied i n the Green River below Flaming Gorge Dam during the winters of 1988 and 1989. Microhabitat parameters used by cutthroat trout, such as focal velocity, depth, and fish elevation, differed significantly in eddies, runs, and riffles. Mean focal velocities in runs were 0.79 body lengths/seconds (bl/s), in riffles 0.66 bl/s, and in eddies 0.24 bl/s. Cutthroat trout size also varied significantly with macrohabitat; larger fish were found in riffles.
Macrohabitat use by cutthroat trout and rainbow trout differed significantly among species, macrohabitat types, and months. Both rainbow trout and cutthroat trout macrohabitat use shifted from lower velocity habitats during winter to faster velocity habitats in summer. Cutthroat trout and rainbow trout used macrohabitats at seasonally differing rates. Riffles were never selected in proportion to their abundance, especially during high winter discharges. Cutthroat trout implanted with radiotransmitters exhibited little movement during diel monitoring and did not change their occupation of macrohabitats
Measuring unsteady pressure on rotating compressor blades
Miniature semiconductor strain gage pressure transducers mounted in several arrangements were studied. Both surface mountings and recessed flush mountings were tested. Test parameters included mounting arrangement, blade material, temperature, local strain in the acceleration normal to the transducer diaphragm, centripetal acceleration, and pressure. Test results show no failures of transducers or mountings and indicate an uncertainty of unsteady pressure measurement of approximately + or - 6 percent + 0.1 kPa for a typical application. Two configurations were used on a rotating fan flutter program. Examples of transducer data and correction factors are presented
Terahertz Room-Temperature Photonic Crystal Nanocavity Laser
We describe an efficient surface-passivated photonic crystal nanocavity
laser, demonstrating room-temperature operation with 3-ps total pulse duration
(detector response limited) and low-temperature operation with
ultra-low-threshold near 9uW.Comment: 6 pages, 3 figure
Global atmospheric sampling program
Automated instruments were installed on a commercial B-747 aircraft, during the program, to obtain baseline data and to monitor key atmospheric constituents associated with emissions of aircraft engines in order to determine if aircraft are contributing to pollution of the upper atmosphere. Data thus acquired on a global basis over the commercial air routes for 5 to 10 years will be analyzed. Ozone measurements in the 29,000 to 45,000 foot altitude were expanded over what has been available from ozonesondes. Limited aerosol composition measurements from filter samples show low levels of sulfates and nitrates in the upper troposphere. Recently installed instruments for measurement of carbon monoxide and condensation nuclei are beginning to return data
117 THE ASSOCIATION BETWEEN SYNOVIAL FLUID LEVELS OF AGGRECAN ARGS FRAGMENTS AND RADIOGRAPHIC PROGRESSION OF KNEE OSTEOARTHRITIS
ABSTRACT: INTRODUCTION: Aggrecanase cleavage at the 392Glu-393Ala bond in the interglobular domain (IGD) of aggrecan, releasing N-terminal 393ARGS fragments, is an early key event in arthritis and joint injuries. We determined whether synovial fluid (SF) levels of ARGS-aggrecan distinguish subjects with progressive radiographic knee osteoarthritis (ROA) from those with stable or no ROA. METHODS: We studied 141 subjects who, at examination A, had been given meniscectomies an average of 18 years earlier (range, 15 to 22 years). Seventeen individuals without surgery, and without known injury to the menisci or cruciate ligaments, were used as references. At examinations A and B, with a mean follow-up time of 7.5 years, we obtained SF and standing tibiofemoral and skyline patellofemoral radiographs. SF ARGS-aggrecan was measured with an electrochemiluminescence immunoassay, and we graded radiographs according to the OARSI atlas. The association between SF ARGS levels at examination A and progression of radiographic features of knee OA between examinations A and B was assessed by using logistic regression adjusted for age, gender, body mass index, and time between examinations, and stratified by ROA status at examination A. RESULTS: We found a weak negative association between SF ARGS concentrations and loss of joint space: the likelihood of progression of radiographic joint space narrowing decreased 0.9 times per picomole per milliliter increase in ARGS (odds ratio (OR) 0.89; 95% confidence interval (CI), 0.79 to 0.996). In subjects with and without preexisting ROA at examination A, the association was OR, 0.96; 0.81 to 1.13; and 0.77; 0.62 to 0.95, respectively. Average levels of SF ARGS 18 years after meniscectomy were no different from those of reference subjects and were not correlated to radiographic status at examination A. CONCLUSIONS: In subjects with previous knee meniscectomy but without ROA, levels of SF ARGS-aggrecan were weakly and inversely associated with increased loss of joint space over a period of 7.5 years
Quantum dots in photonic crystal cavities
During the past two decades, the development of micro- and nano-fabrication technologies
has positively impacted multiple areas of science and engineering. In the photonics community,
these technologies had numerous early adopters, which led to photonic devices that
exhibit features at the nano-scale and operate at the most fundamental level of light–matter
interaction [28, 39, 18, 29]. One of the leading platforms for these types of devices is
based on gallium arsenide (GaAs) planar photonic crystals (PC) with embedded indium
arsenide (InAs) quantum dots (QDs). The PC architecture is advantageous because it
enables monolithic fabrication of photonic networks for efficient routing of light signals
of the chip [26]. At the same time, PC devices have low loss and ultra-small optical
mode volumes, which enable strong light–matter interactions. The InAs quantum dots
are well suited for quantum photonic applications because they have excellent quantum
efficiencies, large dipole moments, and a variety of quantum states that can be optically
controlled [24, 3]
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