119 research outputs found
Under Review: Shop Class as Soulcraft: An Inquiry Into the Value of Work
Author Crawford argues for the revival of teaching the skills of tool, machine, and material use in the schools. He points to the decline in our knowledge of the artifacts of our culture and the resulting loss of self-determination. The teaching of manual competence has also provided a method of learning that is well suited to many students who are otherwise disenchanted with school
Microscopic picture of aging in SiO2
We investigate the aging dynamics of amorphous SiO2 via molecular dynamics
simulations of a quench from a high temperature T_i to a lower temperature T_f.
We obtain a microscopic picture of aging dynamics by analyzing single particle
trajectories, identifying jump events when a particle escapes the cage formed
by its neighbors, and by determining how these jumps depend on the waiting time
t_w, the time elapsed since the temperature quench to T_f. We find that the
only t_w-dependent microscopic quantity is the number of jumping particles per
unit time, which decreases with age. Similar to previous studies for fragile
glass formers, we show here for the strong glass former SiO2 that neither the
distribution of jump lengths nor the distribution of times spent in the cage
are t_w-dependent. We conclude that the microscopic aging dynamics is
surprisingly similar for fragile and strong glass formers.Comment: 4 pages, 7 figure
Genome-Wide Association and Genomic Prediction for Host Response to Porcine Reproductive and Respiratory Syndrome Virus Infection
Host genetics has been shown to play a role in porcine reproductive and respiratory syndrome (PRRS), which is the most economically important disease in the swine industry. A region on Sus scrofa chromosome (SSC) 4 has been previously reported to have a strong association with serum viremia and weight gain in pigs experimentally infected with the PRRS virus (PRRSV). The objective here was to identify haplotypes associated with the favorable phenotype, investigate additional genomic regions associated with host response to PRRSV, and to determine the predictive ability of genomic estimated breeding values (GEBV) based on the SSC4 region and based on the rest of the genome. Phenotypic data and 60 K SNP genotypes from eight trials of ~200 pigs from different commercial crosses were used to address these objectives. Across the eight trials, heritability estimates were 0.44 and 0.29 for viral load (VL, area under the curve of log-transformed serum viremia from 0 to 21 days post infection) and weight gain to 42 days post infection (WG), respectively. Genomic regions associated with VL were identified on chromosomes 4, X, and 1. Genomic regions associated with WG were identified on chromosomes 4, 5, and 7. Apart from the SSC4 region, the regions associated with these two traits each explained less than 3% of the genetic variance. Due to the strong linkage disequilibrium in the SSC4 region, only 19 unique haplotypes were identified across all populations, of which four were associated with the favorable phenotype. Through cross-validation, accuracies of EBV based on the SSC4 region were high (0.55), while the rest of the genome had little predictive ability across populations (0.09). Traits associated with response to PRRSV infection in growing pigs are largely controlled by genomic regions with relatively small effects, with the exception of SSC4. Accuracies of EBV based on the SSC4 region were high compared to the rest of the genome. These results show that selection for the SSC4 region could potentially reduce the effects of PRRS in growing pigs, ultimately reducing the economic impact of this disease
Genomics of heat stress in chickens
Global climate change, increasing human population and improved economic status in populous developing countries are causing an expansion of poultry production under hot ambient temperatures. High environmental temperatures have a negative impact on productivity and health in poultry. There is evidence for a substantial genetic component to the bird’s response to high temperature, including single genes of major effect as well as complex multigenic control. Therefore, it is feasible and desirable to identify such genes and genomic regions, and to breed chickens that can adapt to high temperatures. Contemporary genomic approaches will yield insight into the genetic mechanisms that contribute to a bird’s ability to cope with a hot environment
Studies of an array of PbF2 Cherenkov crystals with large-area SiPM readout
The electromagnetic calorimeter for the new muon (g-2) experiment at Fermilab
will consist of arrays of PbF2 Cherenkov crystals read out by large-area
silicon photo-multiplier (SiPM) sensors. We report here on measurements and
simulations using 2.0 -- 4.5 GeV electrons with a 28-element prototype array.
All data were obtained using fast waveform digitizers to accurately capture
signal pulse shapes versus energy, impact position, angle, and crystal
wrapping. The SiPMs were gain matched using a laser-based calibration system,
which also provided a stabilization procedure that allowed gain correction to a
level of 1e-4 per hour. After accounting for longitudinal fluctuation losses,
those crystals wrapped in a white, diffusive wrapping exhibited an energy
resolution sigma/E of (3.4 +- 0.1) % per sqrt(E/GeV), while those wrapped in a
black, absorptive wrapping had (4.6 +- 0.3) % per sqrt(E/GeV). The
white-wrapped crystals---having nearly twice the total light
collection---display a generally wider and impact-position-dependent pulse
shape owing to the dynamics of the light propagation, in comparison to the
black-wrapped crystals, which have a narrower pulse shape that is insensitive
to impact position.Comment: 14 pages, 19 figures, accepted to Nucl.Instrum.Meth. A. In v2, edited
Figures 14,15, and 17 for clarity, improved explanation of energy resolution
systematics, added reference to SiP
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