2,553 research outputs found
Temporal frequency of radio emissions for the April 25, 1984 flare
The National Geophysical Data Center archives data of the solar-terrestrial environment. The USAF Radio Solar Telescope Network (RSTN) data allow performance of time series analysis to determine temporal oscillations as low as three seconds. The X13/3B flare which erupted in region 4474 (S12E43) on the 24 to 25 of April 1984, was selected. The soft X-rays, 1 to 8 A, remained above X-levels for 50 minutes and the radio emissions measured at Learmonth Solar Observatory reached a maximum of 3.15 x 10 to the 5th power SFUs at 410 MHz at 0000UT. A power spectral analysis of the fixed frequency RSTN data from Learmonth shows possible quasi-periodic fluctuations in the range two to ten seconds. Repetition rates or quasi-periodicities, in the case of the power spectral analysis, generally showed the same trends as the average solar radio flux at 245 and 8800 MHz. The quasi-periodicities at 1415 MHz showed no such trends
Energy Dissipation in Interstellar Cloud Collisions
We present a study of the kinetic energy dissipation in interstellar cloud
collisions. The main aim is to understand the dependence of the elasticity
(defined as the ratio of the final to the initial kinetic energy of the clouds)
on the velocity and mass ratio of the colliding clouds, magnetic field
strength, and gas metallicity for head-on collisions. The problem has been
studied both analytically and via numerical simulations. We have derived handy
analytical relationships that well approximate the analogous numerical results.
The main findings of this work are: (i) the kinetic energy dissipation in cloud
collisions is minimum (i.e. the collision elasticity is maximum) for a cloud
relative velocity ; (ii) the above minimum value is
proportional , where is the metallicity and is the cloud
size: the larger is the more dissipative (i.e. inelastic) the
collision will be; (iii) in general, we find that the energy dissipation
decreases when the magnetic field strength, and mass ratio of the clouds are
increased and the metallicity is decreased, respectively. We briefly discuss
the relevance of this study to the global structure of the interstellar medium
and to galaxy formation and evolution.Comment: 16 pages, aasms LaTeX, 7 figures. ApJ, accepte
License prices for financially constrained firms
It is often alleged that high auction prices inhibit service deployment. We investigate this claim under the extreme case of financially constrained bidders. If demand is just slightly elastic, auctions maximize consumer surplus if consumer surplus is a convex function of quantity (a common assumption), or if consumer surplus is concave and the proportion of expenditure spent on deployment is greater than one over the elasticity of demand. The latter condition appears to be true for most of the large telecom auctions in the US and Europe. Thus, even if high auction prices inhibit service deployment, auctions appear to be optimal from the consumers’ point of view
Closed-Form Bayesian Inferences for the Logit Model via Polynomial Expansions
Articles in Marketing and choice literatures have demonstrated the need for
incorporating person-level heterogeneity into behavioral models (e.g., logit
models for multiple binary outcomes as studied here). However, the logit
likelihood extended with a population distribution of heterogeneity doesn't
yield closed-form inferences, and therefore numerical integration techniques
are relied upon (e.g., MCMC methods).
We present here an alternative, closed-form Bayesian inferences for the logit
model, which we obtain by approximating the logit likelihood via a polynomial
expansion, and then positing a distribution of heterogeneity from a flexible
family that is now conjugate and integrable. For problems where the response
coefficients are independent, choosing the Gamma distribution leads to rapidly
convergent closed-form expansions; if there are correlations among the
coefficients one can still obtain rapidly convergent closed-form expansions by
positing a distribution of heterogeneity from a Multivariate Gamma
distribution. The solution then comes from the moment generating function of
the Multivariate Gamma distribution or in general from the multivariate
heterogeneity distribution assumed.
Closed-form Bayesian inferences, derivatives (useful for elasticity
calculations), population distribution parameter estimates (useful for
summarization) and starting values (useful for complicated algorithms) are
hence directly available. Two simulation studies demonstrate the efficacy of
our approach.Comment: 30 pages, 2 figures, corrected some typos. Appears in Quantitative
Marketing and Economics vol 4 (2006), no. 2, 173--20
Employment Expectations and Gross Flows by Type of Work Contract
There is growing interest in understanding firms’ temporary and permanent employment practices and how institutional changes shape them. Using data on Spanish establishments, we examine: (a) how employers adjust temporary and permanent job and worker flows to prior employment expectations, and (b) how the 1994 and 1997 labour reforms promoting permanent employment affected establishments’ employment practices. Generally, establishments’ prior employment expectations are realized through changes in all job and worker flows. However, establishments uniquely rely on temporary hires as a buffer to confront diminishing long-run employment expectations. None of the reforms significantly affected establishments’ net temporary or permanent employment flows.http://deepblue.lib.umich.edu/bitstream/2027.42/40032/3/wp646.pd
Software Citation Implementation Challenges
The main output of the FORCE11 Software Citation working group
(https://www.force11.org/group/software-citation-working-group) was a paper on
software citation principles (https://doi.org/10.7717/peerj-cs.86) published in
September 2016. This paper laid out a set of six high-level principles for
software citation (importance, credit and attribution, unique identification,
persistence, accessibility, and specificity) and discussed how they could be
used to implement software citation in the scholarly community. In a series of
talks and other activities, we have promoted software citation using these
increasingly accepted principles. At the time the initial paper was published,
we also provided guidance and examples on how to make software citable, though
we now realize there are unresolved problems with that guidance. The purpose of
this document is to provide an explanation of current issues impacting
scholarly attribution of research software, organize updated implementation
guidance, and identify where best practices and solutions are still needed
Regressor and random-effects dependencies in multilevel models
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72623/1/j.0039-0402.2003.00254.x.pd
A randomized, phase 2 trial of docetaxel with or without PX-866, an irreversible oral phosphatidylinositol 3-kinase inhibitor, in patients with relapsed or metastatic head and neck squamous cell cancer
INTRODUCTION: The phosphotidylinositol-3 kinase (PI3K)/serine-threonine kinase (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is frequently altered in head and neck squamous cell cancer (HNSCC). PX-866 is an oral, irreversible, pan-isoform inhibitor of PI3K. Preclinical models revealed synergy with docetaxel and a phase 1 trial demonstrated tolerability of this combination. This randomized phase 2 study evaluated PX-866 combined with docetaxel in patients with advanced, refractory HNSCC. METHODS: Patients with locally advanced, recurrent or metastatic HNSCC who had received at least one and no more than two prior systemic treatment regimens were randomized (1:1) to a combination of docetaxel (75mg/m(2) IV every 21days) with or without PX-866 (8mg PO daily; Arms A and B, respectively). The primary endpoint was progression free survival (PFS). Secondary endpoints included objective response rate (RR), overall survival (OS), toxicity, and correlation of biomarker analyses with efficacy outcomes. RESULTS: 85 patients were enrolled. There was a non-significant improvement in response rate in the combination arm (14% vs. 5%; P=0.13). Median PFS was 92days in Arm A and 82days in Arm B (P=0.42). There was no difference in OS between the two arms (263 vs. 195days; P=0.62). Grade 3 or higher adverse events were infrequent, but more common in the combination arm with respect to diarrhea (17% vs. 2%), nausea (7% vs. 0%), and febrile neutropenia (21% vs. 5%); grade 3 or higher anemia was more frequent in arm B (7% vs. 27%). PIK3CA mutations or PTEN loss were infrequently observed. CONCLUSION: The addition of PX-866 to docetaxel did not improve PFS, RR, or OS in patients with advanced, refractory HNSCC without molecular pre-selection
Diabetes mellitus in centenarians
OBJECTIVES: Describe prevalence of diabetes mellitus among centenarians. DESIGN: Cross-sectional, population-based. SETTING: 44 counties in northern Georgia. PARTICIPANTS: 244 centenarians (aged 98-108, 15.8% men, 20.5% African-American, 38.0% community-dwelling) from the Georgia Centenarian Study (2001-2009). MEASUREMENTS: Nonfasting blood samples assessed HbA(1c) and relevant clinical parameters. Demographic, diagnosis, and diabetes complications covariates were assessed. RESULTS: 12.5% of centenarians were known to have diabetes. Diabetes was more prevalent among African-Americans (27.7%) than Whites (8.6%, p=.0002). There were no differences between men (16.7%) and women (11.7%, p=.414), centenarians living in the community (10.2%) or facilities (13.9%, p=.540). Diabetes was more prevalent among overweight/obese (23.1%) than non-overweight (7.1%, p=.002) centenarians. Anemia (78.6% versus 48.3%, p=.004) and hypertension (79.3% versus 58.6%, p=.041) were more prevalent among centenarians with diabetes than without and centenarians with diabetes took more nonhypoglycemic medications(8.6 versus 7.0, p=.023). No centenarians with hemoglobin A1c < 6.5% had random serum glucose levels above 200 mg/dl. Diabetes was not associated with 12 month all-cause mortality, visual impairment, amputations, cardiovascular disease or neuropathy. 37% of centenarians reported onset before age 80 (survivors), 47% between 80 and 97 years (delayers) and 15% age 98 or older (escapers). CONCLUSION: Diabetes is a risk factor for cardiovascular disease and mortality, but is seen in persons who live into very old age. Aside from higher rates of anemia and use of more medications, few clinical correlates of diabetes were observed in centenarians
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