1,885 research outputs found
Air fluorescence detection of large air showers below the horizon
In the interest of exploring the cosmic ray spectrum at energies greater than 10 to the 18th power eV, where flux rates at the Earth's surface drop below 100 yr(-1) km(-2) sr(-1), cosmic ray physicists have been forced to construct ever larger detectors in order to collect useful amounts of data in reasonable lengths of time. At present, the ultimate example of this trend is the Fly's Eye system in Utah, which uses the atmosphere around an array of skyward-looking photomultiplier tubes. The air acts as a scintillator to give detecting areas as large as 5000 square kilometers sr (for highest energy events). This experiment has revealed structure (and a possible cutoff) in the ultra-high energy region above 10 o the 19th power eV. The success of the Fly's Eye experiment provides impetus for continuing the development of larger detectors to make accessible even higher energies. However, due to the rapidly falling flux, a tenfold increase in observable energy would call for a hundredfold increase in the detecting area. But, the cost of expanding the Fly's Eye detecting area will approximately scale linearly with area. It is for these reasons that the authors have proposed a new approach to using the atmosphere as a scintillator; one which will require fewer photomultipliers, less hardware (thus being less extensive), yet will provide position and shower size information
An Experiment In Collaborative Spreadsheet Development
To study the extent to which group development can reduce spreadsheet errors, an experiment compared error rates in spreadsheet development by subjects working alone (monads) and by subjects working in groups of three (triads). Impressively, triads made 78% fewer errors than monads. However, this was not as large a reduction as nominal group analysis suggests was possible. Members of triads were satisfied with group development. However, triads whose work went most smoothly, whose members were most satisfied with group interactions, and that had the loosest leadership structure were significantly more likely to make errors than other triads
Rheology of Ring Polymer Melts: From Linear Contaminants to Ring/Linear Blends
Ring polymers remain a major challenge to our current understanding of
polymer dynamics. Experimental results are difficult to interpret because of
the uncertainty in the purity and dispersity of the sample. Using both
equilibrium and non-equilibrium molecular dynamics simulations we have
systematically investigated the structure, dynamics and rheology of perfectly
controlled ring/linear polymer blends with chains of such length and
flexibility that the number of entanglements is up to about 14 per chain, which
is comparable to experimental systems examined in the literature. The smallest
concentration at which linear contaminants increase the zero-shear viscosity of
a ring polymer melt of these chain lengths by 10% is approximately one-fifth of
their overlap concentration. When the two architectures are present in equal
amounts the viscosity of the blend is approximately twice as large as that of
the pure linear melt. At this concentration the diffusion coefficient of the
rings is found to decrease dramatically, while the static and dynamic
properties of the linear polymers are mostly unaffected. Our results are
supported by a primitive path analysis.Comment: 5 pages, 4 figures, accepted by PR
Chronic antibiotic use during adulthood and weight change in the Sister Study
Background/Objectives: Antibiotic use in early life has been associated with weight gain in several populations. However, associations between chronic antibiotic use and weight among adults in the general population are unknown. Subjects/Methods: The NIEHS Sister Study is a longitudinal cohort of sisters of women with breast cancer. We examined associations between chronic antibiotic use (>= 3 months) during the fourth decade of life (30-39 years) and subsequent obesity at enrollment (mean age = 55) via logistic regression. We also examined associations between chronic antibiotic use in the 5 years and 12 months prior to enrollment and weight gain after enrollment in linear mixed models. Models were adjusted for race/ethnicity, education, urban/rural status, age, and smoking. Results: In adjusted analyses (n = 50,237), chronic penicillin use during the 4 th decade of life was associated with obesity at enrollment (OR 2.00, 95% CI 1.40, 2.87), and use in the 5 years prior to enrollment was associated with increased BMI change after enrollment (beta 1.00 95% CI 0.01, 2.00). Use of bactericidals (OR 1.71, 95% CI 1.29, 2.26) during the 4 th decade of life was also associated with obesity at enrollment. Associations for penicillins and bactericidals were consistent across indications for use. Bacteriostatic use in the 5 years prior to enrollment was associated with a reduction in BMI after enrollment (beta -0.52, 95% CI -1.04, 0.00), and tetracycline use during the 4 th decade of life was associated with reduced odds of obesity at enrollment (OR 0.72, 95% CI 0.56, 0.92). However, these inverse associations were only present for those who reported taking antibiotics for skin purposes. Cephalosporins, macrolides, quinolones, and sulfonamides were not associated with BMI change over time. Conclusions: Chronic use of antibiotics during adulthood may have long-lasting impacts on BMI. Associations may differ by antibiotic class, and confounding by indication may be important for some antibiotic classes.Intramural Research Program of the NIH, National Institute of Environmental Sciences [Z01ES044005]; NIEHS [T32ES007018, K99ES028743]; NIHOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Modified Chaplygin Gas and Constraints on its B parameter from CDM and UDME Cosmological models
We study Modified Chaplygin Gas (MCG) as a candidate for dark energy and
predict the values of parameters of the gas for a physically viable
cosmological model. The equation of state of MCG () involves three parameters: , and . The
permitted values of these parameters are determined with the help of
dimensionless age parameter () and Data. Specifically we
study the allowed ranges of values of B parameter in terms of and
( is defined in terms of the constants in the theory). We
explore the constraints of the parameters in Cold Dark Matter(CDM) model and
UDME(Unified Dark Matter Energy) model respectively.Comment: 5 pages, 10 fig
The Impact of Atmospheric Fluctuations on Degree-scale Imaging of the Cosmic Microwave Background
Fluctuations in the brightness of the Earth's atmosphere originating from
water vapor are an important source of noise for ground-based instruments
attempting to measure anisotropy in the Cosmic Microwave Background. This paper
presents a model for the atmospheric fluctuations and derives simple
expressions to predict the contribution of the atmosphere to experimental
measurements. Data from the South Pole and from the Atacama Desert in Chile,
two of the driest places on Earth, are used to assess the level of fluctuations
at each site.Comment: 29 pages, 7 figures, 1 table, appears in The Astrophysical Journa
Molecular Dynamics Simulation Study of Nonconcatenated Ring Polymers in a Melt: I. Statics
Molecular dynamics simulations were conducted to investigate the structural
properties of melts of nonconcatenated ring polymers and compared to melts of
linear polymers. The longest rings were composed of N=1600 monomers per chain
which corresponds to roughly 57 entanglement lengths for comparable linear
polymers. For the rings, the radius of gyration squared was found to scale as N
to the 4/5 power for an intermediate regime and N to the 2/3 power for the
larger rings indicating an overall conformation of a crumpled globule. However,
almost all beads of the rings are "surface beads" interacting with beads of
other rings, a result also in agreement with a primitive path analysis
performed in the following paper (DOI: 10.1063/1.3587138). Details of the
internal conformational properties of the ring and linear polymers as well as
their packing are analyzed and compared to current theoretical models.Comment: 15 pages, 14 figure
Modulator noise suppression in the LISA Time-Delay Interferometric combinations
We previously showed how the measurements of some eighteen time series of
relative frequency or phase shifts could be combined (1) to cancel the phase
noise of the lasers, (2) to cancel the Doppler fluctuations due to non-inertial
motions of the six optical benches, and (3) to remove the phase noise of the
onboard reference oscillators required to track the photodetector fringes, all
the while preserving signals from passinggravitational waves. Here we analyze
the effect of the additional noise due to the optical modulators used for
removing the phase fluctuations of the onboard reference oscillators. We use a
recently measured noise spectrum of an individual modulator to quantify the
contribution of modulator noise to the first and second-generation Time-Delay
Interferometric (TDI) combinations as a function of the modulation frequency.
We show that modulator noise can be made smaller than the expected proof-mass
acceleration and optical-path noises if the modulation frequencies are larger
than MHz in the case of the unequal-arm Michelson TDI combination
, GHz for the Sagnac TDI combination , and
MHz for the symmetrical Sagnac TDI combination . These
modulation frequencies are substantially smaller than previously estimated and
may lead to less stringent requirements on the LISA's oscillator noise
calibration subsystem.Comment: 17 pages, 5 figures. Submitted to: Phys. Rev. D 1
Accelerating the Production and Application of Evidence for Public Health System Improvement: the Search for New Frontiers
The new journal Frontiers in Public Health Services and Systems Research provides a platform for rapidly and widely communicating emerging findings and lessons learned from studies of public health services and delivery systems
- …