1,212 research outputs found
Distributed computer system enhances productivity for SRB joint optimization
Initial calculations of a redesign of the solid rocket booster joint that failed during the shuttle tragedy showed that the design had a weight penalty associated with it. Optimization techniques were to be applied to determine if there was any way to reduce the weight while keeping the joint opening closed and limiting the stresses. To allow engineers to examine as many alternatives as possible, a system was developed consisting of existing software that coupled structural analysis with optimization which would execute on a network of computer workstations. To increase turnaround, this system took advantage of the parallelism offered by the finite difference technique of computing gradients to allow several workstations to contribute to the solution of the problem simultaneously. The resulting system reduced the amount of time to complete one optimization cycle from two hours to one-half hour with a potential of reducing it to 15 minutes. The current distributed system, which contains numerous extensions, requires one hour turnaround per optimization cycle. This would take four hours for the sequential system
Discrete Fracture Model with Anisotropic Load Sharing
A two-dimensional fracture model where the interaction among elements is
modeled by an anisotropic stress-transfer function is presented. The influence
of anisotropy on the macroscopic properties of the samples is clarified, by
interpolating between several limiting cases of load sharing. Furthermore, the
critical stress and the distribution of failure avalanches are obtained
numerically for different values of the anisotropy parameter and as a
function of the interaction exponent . From numerical results, one can
certainly conclude that the anisotropy does not change the crossover point
in 2D. Hence, in the limit of infinite system size, the crossover
value between local and global load sharing is the same as the one
obtained in the isotropic case. In the case of finite systems, however, for
, the global load sharing behavior is approached very slowly
Dynamical response and confinement of the electrons at the LaAlO3/SrTiO3 interface
With infrared ellipsometry and transport measurements we investigated the
electrons at the interface between LaAlO3 and SrTiO3. We obtained a sheet
carrier density of Ns~5-9x 10E13 cm^-2, an effective mass of m*~3m_e, and a
strongly frequency dependent mobility. The latter are similar as in bulk
SrTi1-xNbxO3 and therefore suggestive of polaronic correlations of the confined
carriers. We also determined the vertical density profile which has a strongly
asymmetric shape with a rapid initial decay over the first 2 nm and a
pronounced tail that extends to about 11 nm.Comment: 4 pages, 3 figures, 1 EPAPS file (3 figures
Enriching gender in PER: A binary past and a complex future
In this article, we draw on previous reports from physics, science education,
and women's studies to propose a more nuanced treatment of gender in physics
education research (PER). A growing body of PER examines gender differences in
participation, performance, and attitudes toward physics. We have three
critiques of this work: (1) it does not question whether the achievements of
men are the most appropriate standard, (2) individual experiences and student
identities are undervalued, and (3) the binary model of gender is not
questioned. Driven by these critiques, we propose a conception of gender that
is more up-to-date with other fields and discuss gender-as-performance as an
extended example. We also discuss work on the intersection of identities [e.g.,
gender with race and ethnicity, socioeconomic status, lesbian, gay, bisexual,
and transgender (LGBT) status], much of which has been conducted outside of
physics. Within PER, some studies examine the intersection of gender and race,
and identify the lack of a single identity as a key challenge of "belonging" in
physics. Acknowledging this complexity enables us to further critique what we
term a binary gender deficit model. This framework, which is implicit in much
of the gender-based PER, casts gender as a fixed binary trait and suggests that
women are deficient in characteristics necessary to succeed. Alternative models
of gender allow a greater range and fluidity of gender identities, and
highlight deficiencies in data that exclude women's experiences. We suggest new
investigations that diverge from this expanded gender framework in PER.Comment: 27 pages, accepted to Phys. Rev. Special Topics - PE
Elementary processes governing the evolution of road networks
Urbanisation is a fundamental phenomenon whose quantitative characterisation
is still inadequate. We report here the empirical analysis of a unique data set
regarding almost 200 years of evolution of the road network in a large area
located north of Milan (Italy). We find that urbanisation is characterised by
the homogenisation of cell shapes, and by the stability throughout time of
high-centrality roads which constitute the backbone of the urban structure,
confirming the importance of historical paths. We show quantitatively that the
growth of the network is governed by two elementary processes: (i)
`densification', corresponding to an increase in the local density of roads
around existing urban centres and (ii) `exploration', whereby new roads trigger
the spatial evolution of the urbanisation front. The empirical identification
of such simple elementary mechanisms suggests the existence of general, simple
properties of urbanisation and opens new directions for its modelling and
quantitative description.Comment: 10 pages, 6 figure
Heart rate variability in association with frequent use of household sprays and scented products in SAPALDIA
Background: Household cleaning products are associated with adverse respiratory health outcomes, but the cardiovascular health effects are largely unknown.Objective: We determined if long-term use of household sprays and scented products at home was associated with reduced heart rate variability (HRV), a marker of autonomic cardiac dysfunction.Methods: We recorded 24-hr electrocardiograms in a cross-sectional survey of 581 Swiss adults, 1, 1-3, or 4-7 days/week, unexposed (reference)] of using cleaning sprays, air freshening sprays, and scented products.Results: Decreases in 24-hr SDNN and TP were observed with frequent use of all product types, but the strongest reductions were associated with air freshening sprays. Compared with unexposed participants, we found that using air freshening sprays 4-7 days/week was associated with 11% [95% confidence interval (CI): -20%, -2%] and 29% (95% CI: -46%, -8%) decreases in 24-hr SDNN and TP, respectively. Inverse associations of 24-SDNN and TP with increased use of cleaning sprays, air freshening sprays, and scented products were observed mainly in participants with obstructive lung disease (p > 0.05 for interactions).Conclusions: In predominantly older adult women, long-term frequent use of household spray and scented products was associated with reduced HRV, which suggests an increased risk of cardiovascular health hazards. People with preexisting pulmonary conditions may be more susceptibl
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