5,281 research outputs found
Estimating Snow Accumulation and Ablation with L-Band Interferometric Synthetic Aperture Radar (InSAR)
Snow is a critical water resource for the western United States and many regions across the globe. However, our ability to accurately measure and monitor changes in snow mass from satellite remote sensing, specifically its water equivalent, remains a challenge. To confront these challenges, NASA initiated the SnowEx program, a multiyear effort to address knowledge gaps in snow remote sensing. During SnowEx 2020, the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) team acquired an L-band interferometric synthetic aperture radar (InSAR) data time series to evaluate the capabilities and limitations of repeat-pass L-band InSAR for tracking changes in snow water equivalent (SWE). The goal was to develop a more comprehensive understanding of where and when L-band InSAR can provide SWE change estimates, allowing the snow community to leverage the upcoming NASA–ISRO (NASA–Indian Space Research Organization) SAR (NISAR) mission. Our study analyzed three InSAR image pairs from the Jemez Mountains, NM, between 12 and 26 February 2020. We developed a snow-focused multi-sensor method that uses UAVSAR InSAR data synergistically with optical fractional snow-covered area (fSCA) information. Combining these two remote sensing datasets allows for atmospheric correction and delineation of snow-covered pixels within the radar swath. For all InSAR pairs, we converted phase change values to SWE change estimates between the three acquisition dates. We then evaluated InSAR-derived retrievals using a combination of fSCA, snow pits, meteorological station data, in situ snow depth sensors, and ground-penetrating radar (GPR). The results of this study show that repeat-pass L-band InSAR is effective for estimating both snow accumulation and ablation with the proper measurement timing, reference phase, and snowpack conditions
Observations of the Optical Counterpart to XTE J1118+480 During Outburst by the ROTSE-I Telescope
The X-ray nova XTE J1118+480 exhibited two outbursts in the early part of
2000. As detected by the Rossi X-ray Timing Explorer (RXTE), the first outburst
began in early January and the second began in early March. Routine imaging of
the northern sky by the Robotic Optical Transient Search Experiment (ROTSE)
shows the optical counterpart to XTE J1118+480 during both outbursts. These
data include over 60 epochs from January to June 2000. A search of the ROTSE
data archives reveal no previous optical outbursts of this source in selected
data between April 1998 and January 2000. While the X-ray to optical flux ratio
of XTE J1118+480 was low during both outbursts, we suggest that they were full
X-ray novae and not mini-outbursts based on comparison with similar sources.
The ROTSE measurements taken during the March 2000 outburst also indicate a
rapid rise in the optical flux that preceded the X-ray emission measured by the
RXTE by approximately 10 days. Using these results, we estimate a pre-outburst
accretion disk inner truncation radius of 1.2 x 10^4 Schwarzschild radii.Comment: 9 pages, 1 table, 2 figure
The effect of weight loss on lameness in obese dogs with osteoarthritis
This paper describes the effect of weight loss on lameness in obese dogs with osteoarthritis (OA). Fourteen obese client-owned dogs with clinical and radiographic signs of OA participated in an open prospective clinical trial. After a screening visit and a visit for collection of baseline data, the dogs were fed a restricted-calorie diet over a study period of 16 weeks that incorporated six follow-up visits. At each visit, body weight and pelvic circumference were measured and severity of lameness was assessed using a numeric rating scale (NRS), a visual analogue scale (VAS) and kinetic gait analysis. This is the first study to assess both subjectively and objectively, the effect of weight loss alone on lameness in obese dogs with OA. The results indicate that body weight reduction causes a significant decrease in lameness from a weight loss of 6.10% onwards. Kinetic gait analysis supported the results from a body weight reduction of 8.85% onwards. These results confirm that weight loss should be presented as an important treatment modality to owners of obese dogs with OA and that noticeable improvement may be seen after modest weight loss in the region of 6.10 – 8.85% body weight
A terminal assessment of stages theory : introducing a dynamic states approach to entrepreneurship
Stages of Growth models were the most frequent theoretical approach to understanding entrepreneurial business growth from 1962 to 2006; they built on the growth imperative and developmental models of that time. An analysis of the universe of such models (N=104) published in the management literature shows no consensus on basic constructs of the approach, nor is there any empirical confirmations of stages theory. However, by changing two propositions of the stages models, a new dynamic states approach is derived. The dynamic states approach has far greater explanatory power than its precursor, and is compatible with leading edge research in entrepreneurship
Perceived Devaluation and STI Testing Uptake among a Cohort of Street-involved Youth in a Canadian Setting
Perceived devaluation has been shown to have adverse effects on the mental and physical health outcomes of people who use drugs. However, the impact of perceived devaluation on sexually transmitted infections (STI) testing uptake among street-involved youth, who face multiple and intersecting stigmas due to their association with drug use and risky sexual practices, has not been fully characterized. Data were obtained between December 2013 and November 2014 from a cohort of street-involved youth who use illicit drugs aged 14–26 in Vancouver, British Columbia. Multivariable generalized estimating equations were constructed to assess the independent relationship between perceived devaluation and STI testing uptake. Among 300 street-involved youth, 87.0% reported a high perceived devaluation score at baseline. In the multivariable analysis, high perceived devaluation was negatively associated with STI testing uptake after adjustment for potential confounders (Adjusted Odds Ratio = 0.38, 95% Confidence Interval 0.15–0.98). Perceived devaluation was high among street-involved youth in our sample and appears to have adverse effects on STI testing uptake. HIV prevention and care programs should be examined and improved to better meet the special needs of street-involved youth in non-stigmatizing ways
Multi-Jet Event Rates in Deep Inelastic Scattering and Determination of the Strong Coupling Constant
Jet event rates in deep inelastic ep scattering at HERA are investigated
applying the modified JADE jet algorithm. The analysis uses data taken with the
H1 detector in 1994 and 1995. The data are corrected for detector and
hadronization effects and then compared with perturbative QCD predictions using
next-to-leading order calculations. The strong coupling constant alpha_S(M_Z^2)
is determined evaluating the jet event rates. Values of alpha_S(Q^2) are
extracted in four different bins of the negative squared momentum
transfer~\qq in the range from 40 GeV2 to 4000 GeV2. A combined fit of the
renormalization group equation to these several alpha_S(Q^2) values results in
alpha_S(M_Z^2) = 0.117+-0.003(stat)+0.009-0.013(syst)+0.006(jet algorithm).Comment: 17 pages, 4 figures, 3 tables, this version to appear in Eur. Phys.
J.; it replaces first posted hep-ex/9807019 which had incorrect figure 4
Multiplicity Structure of the Hadronic Final State in Diffractive Deep-Inelastic Scattering at HERA
The multiplicity structure of the hadronic system X produced in
deep-inelastic processes at HERA of the type ep -> eXY, where Y is a hadronic
system with mass M_Y< 1.6 GeV and where the squared momentum transfer at the pY
vertex, t, is limited to |t|<1 GeV^2, is studied as a function of the invariant
mass M_X of the system X. Results are presented on multiplicity distributions
and multiplicity moments, rapidity spectra and forward-backward correlations in
the centre-of-mass system of X. The data are compared to results in e+e-
annihilation, fixed-target lepton-nucleon collisions, hadro-produced
diffractive final states and to non-diffractive hadron-hadron collisions. The
comparison suggests a production mechanism of virtual photon dissociation which
involves a mixture of partonic states and a significant gluon content. The data
are well described by a model, based on a QCD-Regge analysis of the diffractive
structure function, which assumes a large hard gluonic component of the
colourless exchange at low Q^2. A model with soft colour interactions is also
successful.Comment: 22 pages, 4 figures, submitted to Eur. Phys. J., error in first
submission - omitted bibliograph
Differential (2+1) Jet Event Rates and Determination of alpha_s in Deep Inelastic Scattering at HERA
Events with a (2+1) jet topology in deep-inelastic scattering at HERA are
studied in the kinematic range 200 < Q^2< 10,000 GeV^2. The rate of (2+1) jet
events has been determined with the modified JADE jet algorithm as a function
of the jet resolution parameter and is compared with the predictions of Monte
Carlo models. In addition, the event rate is corrected for both hadronization
and detector effects and is compared with next-to-leading order QCD
calculations. A value of the strong coupling constant of alpha_s(M_Z^2)=
0.118+- 0.002 (stat.)^(+0.007)_(-0.008) (syst.)^(+0.007)_(-0.006) (theory) is
extracted. The systematic error includes uncertainties in the calorimeter
energy calibration, in the description of the data by current Monte Carlo
models, and in the knowledge of the parton densities. The theoretical error is
dominated by the renormalization scale ambiguity.Comment: 25 pages, 6 figures, 3 tables, submitted to Eur. Phys.
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