512 research outputs found
A general computer model for predicting the performance of gas sorption refrigerators
Projected performance requirements for cryogenic spacecraft sensor cooling systems which demand higher reliability and longer lifetimes are outlined. The gas/solid sorption refrigerator is viewed as a potential solution to cryogenic cooling needs. A software model of an entire gas sorption refrigerator system was developed. The numerical model, evaluates almost any combination and order of refrigerator components and any sorbent-sorbate pair or which the sorption isotherm data are available. Parametric curves for predicting system performance were generated for two types of refrigerators, a LaNi5-H2 absorption cooler and a Charcoal-N2 adsorption cooler. It is found that precooling temperature and heat exchanger effectiveness affect the refrigerator performance. It is indicated that gas sorption refrigerators are feasible for a number of space applications
Promoting a Growth Mindset in CS1: Does One Size Fit All? A Pilot Study
This paper describes a pilot intervention conducted in CS1, in theacademic year of 2016-2017. The intervention was based on thework of Dweck, promoting a growth Mindset in an effort to in-crease performance in introductory programming. The study alsoexamined data from a previous year (as a control group) to compareand contrast the results. Multiple factors related to programmingperformance were recorded with the control and treatment group,which were measured at multiple intervals throughout the course,to monitor changes as the pilot intervention was implemented.This study found a significant increase in programming perfor-mance when the intervention was deployed. However, althoughperformance increased for the treatment group, the average Mindsetdid not significantly change towards a growth Mindset (replicatingthe findings of Cutts et al, 2010). To further explore this finding,a preliminary deeper investigation using k-means clustering wascarried out. The investigation found that the intervention promoteda growth Mindset for some student profiles and a fixed Mindset forothers. This finding is important for educators considering interven-tion development or implementation of Mindset, and demonstratesthat a Mindset intervention may not be suitable for all learners
Measuring the Primordial Deuterium Abundance During the Cosmic Dark Ages
We discuss how measurements of fluctuations in the absorption of cosmic
microwave background (CMB) photons by neutral gas during the cosmic dark ages,
at redshifts z ~ 7--200, could reveal the primordial deuterium abundance of the
Universe. The strength of the cross-correlation of brightness-temperature
fluctuations due to resonant absorption of CMB photons in the 21-cm line of
neutral hydrogen with those due to resonant absorption of CMB photons in the
92-cm line of neutral deuterium is proportional to the fossil deuterium to
hydrogen ratio [D/H] fixed during big bang nucleosynthesis (BBN). Although
technically challenging, this measurement could provide the cleanest possible
determination of [D/H], free from contamination by structure formation
processes at lower redshifts, and has the potential to improve BBN constraints
to the baryon density of the Universe \Omega_{b} h^2. We also present our
results for the thermal spin-change cross-section for deuterium-hydrogen
scattering, which may be useful in a more general context than we describe
here.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Cosmological Signatures of Interacting Neutrinos
We investigate signatures of neutrino scattering in the Cosmic Microwave
Background (CMB) and matter power spectra, and the extent to which present
cosmological data can distinguish between a free streaming or tightly coupled
fluid of neutrinos. If neutrinos have strong non-standard interactions, for
example, through the coupling of neutrinos to a light boson, they may be kept
in equilibrium until late times. We show how the power spectra for these models
differ from more conventional neutrino scenarios, and use CMB and large scale
structure data to constrain these models. CMB polarization data improves the
constraints on the number of massless neutrinos, while the Lyman--
power spectrum improves the limits on the neutrino mass. Neutrino mass limits
depend strongly on whether some or all of the neutrino species interact and
annihilate. The present data can accommodate a number of tightly-coupled
relativistic degrees of freedom, and none of the interacting-neutrino scenarios
considered are ruled out by current data -- although considerations regarding
the age of the Universe disfavor a model with three annihilating neutrinos with
very large neutrino masses.Comment: 17 pages, 14 figures, minor changes and references added, published
in Phys. Rev.
Polarizing Bubble Collisions
We predict the polarization of cosmic microwave background (CMB) photons that
results from a cosmic bubble collision. The polarization is purely E-mode,
symmetric around the axis pointing towards the collision bubble, and has
several salient features in its radial dependence that can help distinguish it
from a more conventional explanation for unusually cold or hot features in the
CMB sky. The anomalous "cold spot" detected by the Wilkinson Microwave
Anisotropy Probe (WMAP) satellite is a candidate for a feature produced by such
a collision, and the Planck satellite and other proposed surveys will measure
the polarization on it in the near future. The detection of such a collision
would provide compelling evidence for the string theory landscape.Comment: Published version. 15 pages, 8 figure
Blood spots as an alternative to whole blood collection and the effect of a small monetary incentive to increase participation in genetic association studies
<p>Abstract</p> <p>Background</p> <p>Collection of buccal cells from saliva for DNA extraction offers a less invasive and convenient alternative to venipuncture blood collection that may increase participation in genetic epidemiologic studies. However, dried blood spot collection, which is also a convenient method, offers a means of collecting peripheral blood samples from which analytes in addition to DNA can be obtained.</p> <p>Methods</p> <p>To determine if offering blood spot collection would increase participation in genetic epidemiologic studies, we conducted a study of collecting dried blood spot cards by mail from a sample of female cancer cases (n = 134) and controls (n = 256) who were previously selected for a breast cancer genetics study and declined to provide a venipuncture blood sample. Participants were also randomized to receive either a 2.00 incentive vs. 26% for no incentive, p = 0.6), it was significantly associated with participation among the breast cancer cases (48% vs. 27%, respectively, p = 0.01). There did not appear to be any bias in response since no differences between cases and controls and incentive groups were observed when examining several demographic, work history and radiation exposure variables.</p> <p>Conclusion</p> <p>This study demonstrates that collection of dried blood spot cards in addition to venipuncture blood samples may be a feasible method to increase participation in genetic case-control studies.</p
Chronic wasting disease prions are not transmissible to transgenic mice overexpressing human prion protein
Chronic wasting disease (CWD) is a prion disease that affects free-ranging and captive cervids, including mule deer, white-tailed deer, Rocky Mountain elk and moose. CWD-infected cervids have been reported in 14 USA states, two Canadian provinces and in South Korea. The possibility of a zoonotic transmission of CWD prions via diet is of particular concern in North America where hunting of cervids is a popular sport. To investigate the potential public health risks posed by CWD prions, we have investigated whether intracerebral inoculation of brain and spinal cord from CWD-infected mule deer transmits prion infection to transgenic mice overexpressing human prion protein with methionine or valine at polymorphic residue 129. These transgenic mice have been utilized in extensive transmission studies of human and animal prion disease and are susceptible to BSE and vCJD prions, allowing comparison with CWD. Here, we show that these mice proved entirely resistant to infection with mule deer CWD prions arguing that the transmission barrier associated with this prion strain/host combination is greater than that observed with classical BSE prions. However, it is possible that CWD may be caused by multiple prion strains. Further studies will be required to evaluate the transmission properties of distinct cervid prion strains as they are characterized
The Quintessential CMB, Past & Future
The past, present and future of cosmic microwave background (CMB) anisotropy
research is discussed, with emphasis on the Boomerang and Maxima balloon
experiments. These data are combined with large scale structure (LSS)
information and high redshift supernova (SN1) observations to explore the
inflation-based cosmic structure formation paradigm. Here we primarily focus on
a simplified inflation parameter set, {omega_b,omega_{cdm},Omega_{tot},
Omega_Q,w_Q, n_s,tau_C, sigma_8}. After marginalizing over the other cosmic and
experimental variables, we find the current CMB+LSS+SN1 data gives
Omega_{tot}=1.04\pm 0.05, consistent with (non-baroque) inflation theory.
Restricting to Omega_{tot}=1, we find a nearly scale invariant spectrum, n_s
=1.03 \pm 0.07. The CDM density, omega_{cdm}=0.17\pm 0.02, is in the expected
range, but the baryon density, omega_b=0.030\pm 0.004, is slightly larger than
the current nucleosynthesis estimate. Substantial dark energy is inferred,
Omega_Q\approx 0.68\pm 0.05, and CMB+LSS Omega_Q values are compatible with the
independent SN1 estimates. The dark energy equation of state, parameterized by
a quintessence-field pressure-to-density ratio w_Q, is not well determined by
CMB+LSS (w_Q<-0.3 at 95%CL), but when combined with SN1 the resulting w_Q<-0.7
limit is quite consistent with the w_Q=-1 cosmological constant case. Though
forecasts of statistical errors on parameters for current and future
experiments are rosy, rooting out systematic errors will define the true
progress.Comment: 14 pages, 3 figs., in Proc. CAPP-2000 (AIP), CITA-2000-6
CMB Analysis of Boomerang & Maxima & the Cosmic Parameters {Omega_tot,Omega_b h^2,Omega_cdm h^2,Omega_Lambda,n_s}
We show how estimates of parameters characterizing inflation-based theories
of structure formation localized over the past year when large scale structure
(LSS) information from galaxy and cluster surveys was combined with the rapidly
developing cosmic microwave background (CMB) data, especially from the recent
Boomerang and Maxima balloon experiments. All current CMB data plus a
relatively weak prior probability on the Hubble constant, age and LSS points to
little mean curvature (Omega_{tot} = 1.08\pm 0.06) and nearly scale invariant
initial fluctuations (n_s =1.03\pm 0.08), both predictions of (non-baroque)
inflation theory. We emphasize the role that degeneracy among parameters in the
L_{pk} = 212\pm 7 position of the (first acoustic) peak plays in defining the
range upon marginalization over other variables. Though the CDM
density is in the expected range (\Omega_{cdm}h^2=0.17\pm 0.02), the baryon
density Omega_bh^2=0.030\pm 0.005 is somewhat above the independent 0.019\pm
0.002 nucleosynthesis estimate. CMB+LSS gives independent evidence for dark
energy (Omega_\Lambda=0.66\pm 0.06) at the same level as from supernova (SN1)
observations, with a phenomenological quintessence equation of state limited by
SN1+CMB+LSS to w_Q<-0.7 cf. the w_Q=-1 cosmological constant case.Comment: 11 pages, 3 figs., in Proc. IAU Symposium 201 (PASP), CITA-2000-6
A status report on the observability of cosmic bubble collisions
In the picture of eternal inflation as driven by a scalar potential with
multiple minima, our observable universe resides inside one of many bubbles
formed from transitions out of a false vacuum. These bubbles necessarily
collide, upsetting the homogeneity and isotropy of our bubble interior, and
possibly leading to detectable signatures in the observable portion of our
bubble, potentially in the Cosmic Microwave Background or other precision
cosmological probes. This constitutes a direct experimental test of eternal
inflation and the landscape of string theory vacua. Assessing this possibility
roughly splits into answering three questions: What happens in a generic bubble
collision? What observational effects might be expected? How likely are we to
observe a collision? In this review we report the current progress on each of
these questions, improve upon a few of the existing results, and attempt to lay
out directions for future work.Comment: Review article; comments very welcome. 24 pages + 4 appendices; 19
color figures. (Revised version adds two figures, minor edits.
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