10,566 research outputs found
The fate of NOx emissions due to nocturnal oxidation at high latitudes: 1-D simulations and sensitivity experiments
The fate of nitrogen oxide pollution during high-latitude winter is controlled by reactions of dinitrogen pentoxide (N2O5) and is highly affected by the competition between heterogeneous atmospheric reactions and deposition to the snowpack. MISTRA (MIcrophysical STRAtus), a 1-D photochemical model, simulated an urban pollution plume from Fairbanks, Alaska to investigate this competition of N2O5 reactions and explore sensitivity to model parameters. It was found that dry deposition of N2O5 made up a significant fraction of N2O5 loss near the snowpack, but reactions on aerosol particles dominated loss of N2O5 over the integrated atmospheric column. Sensitivity experiments found the fate of NOx emissions were most sensitive to NO emission flux, photolysis rates, and ambient temperature. The results indicate a strong sensitivity to urban area density, season and clouds, and temperature, implying a strong sensitivity of the results to urban planning and climate change. Results suggest that secondary formation of particulate (PM2.5) nitrate in the Fairbanks downtown area does not contribute significant mass to the total PM2.5 concentration, but appreciable amounts are formed downwind of downtown due to nocturnal NOx oxidation and subsequent reaction with ammonia on aerosol particles
Employee Response to Compulsory Short-Time Work
This paper reports the results of a survey of over 1500 employees who faced compulsory reductions of 10 percent in hours of work and earnings during the second half of 1985. The workers were asked how they used the free time and how they viewed the program, and their answers were analyzed in relation to their economic and social characteristics. On average, the workers spent 12 percent of the free time in uncompensated work for the company, 43 percent in other work (mostly housework, childcare, and other nonmarket chores), and 45 percent in leisure-time activities such as resting, reading, and hobbies. Ceteris paribus, education and income were positively related to percentage of time spent in company work, and age was negatively related. Time spent in other work rose with the presence of children, especially for women. Employee reaction to the program was generally favorable; married women were most positive and married men least positive. Workers 45 years of age and over were significantly more positive than those 35-44. There was a strong connection between time use and reaction to the program; workers who spent more of their free time working without pay at the company or in home production were much less positive than those who spent more time in leisure activities.
Hydrogen environment embrittlement of astroloy and Udimet 700 (nickel-base) and V-57 (iron-base) superalloys
The sensitivity to hydrogen environment embrittlement of three superalloys was determined. Astroloy forgings were resistant to embrittlement during smooth tensile, notched tensile, and creep testing in 3.5-MN/sq m hydrogen over the range 23 to 760 C. The notched tensile strength of Udimet 700 bar stock in hydrogen at 23 C was only 50 percent of the baseline value in helium. Forgings of V-57 were not significantly embrittled by hydrogen during smooth tensile testing over the range 23 to 675 C; creep and rupture lives of V-57 were degraded by hydrogen. Postcreep tensile ductility of V-57 was reduced by 40 percent after creep exposure in hydrogen
A.B.A. Manual for Conplex Insurance Coverage Litigation: A Prescription for Insurance Nullification
Supersymmetry of Noncompact MQCD-like Membrane Instantons and Heat Kernel Asymptotics
We perform a heat kernel asymptotics analysis of the nonperturbative
superpotential obtained from wrapping of an M2-brane around a supersymmetric
noncompact three-fold embedded in a (noncompact) G_2-manifold as obtained in
[1], the three-fold being the one relevant to domain walls in Witten's MQCD
[2], in the limit of small "zeta", a complex constant that appears in the
Riemann surfaces relevant to defining the boundary conditions for the domain
wall in MQCD. The MQCD-like configuration is interpretable, for small but
non-zero zeta as a noncompact/"large" open membrane instanton, and for
vanishing zeta, as the type IIA D0-brane (for vanishing M-theory cicle radius).
We find that the eta-function Seeley de-Witt coefficients vanish, and we get a
perfect match between the zeta-function Seeley de-Witt coefficients (up to
terms quadratic in zeta) between the Dirac-type operator and one of the two
Laplace-type operators figuring in the superpotential. This is an extremely
strong signature of residual supersymmetry for the nonperturbative
configurations in M-theory considered in this work.Comment: 21 pages, LaTeX; v3: several clarifying remarks added, to appear in
JHE
Integrating Dynamics and Wear Modelling to Predict Railway Wheel Profile Evolution
The aim of the work described was to predict wheel
profile evolution by integrating multi-body dynamics
simulations of a wheelset with a wear model.
The wear modelling approach is based on a wear
index commonly used in rail wear predictions. This
assumes wear is proportional to TÎł, where T is tractive
force and Îł is slip at the wheel/rail interface. Twin disc
testing of rail and wheel materials was carried out to
generate wear coefficients for use in the model.
The modelling code is interfaced with
ADAMS/Rail, which produces multi-body dynamics
simulations of a railway wheelset and contact conditions
at the wheel/rail interface. Simplified theory of rolling
contact is used to discretise the contact patches
produced by ADAMS/Rail and calculate traction and
slip within each.
The wear model combines the simplified theory of
rolling contact, ADAMS/Rail output and the wear
coefficients to predict the wear and hence the change of
wheel profile for given track layouts
The influence of atmosphere on the performance of pure-phase WZ and ZB InAs nanowire transistors
We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs
nanowire transistors in several atmospheres: air, dry pure N and O, and
N bubbled through liquid HO and alcohols to identify whether
phase-related structural/surface differences affect their response. Both WZ and
ZB give poor gate characteristics in dry state. Adsorption of polar species
reduces off-current by 2-3 orders of magnitude, increases on-off ratio and
significantly reduces sub-threshold slope. The key difference is the greater
sensitivity of WZ to low adsorbate level. We attribute this to facet structure
and its influence on the separation between conduction electrons and surface
adsorption sites. We highlight the important role adsorbed species play in
nanowire device characterisation. WZ is commonly thought superior to ZB in InAs
nanowire transistors. We show this is an artefact of the moderate humidity
found in ambient laboratory conditions: WZ and ZB perform equally poorly in the
dry gas limit yet equally well in the wet gas limit. We also highlight the
vital role density-lowering disorder has in improving gate characteristics, be
it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase
nanowires.Comment: Accepted for publication in Nanotechnolog
On the geometry of closed G2-structure
We give an answer to a question posed recently by R.Bryant, namely we show
that a compact 7-dimensional manifold equipped with a G2-structure with closed
fundamental form is Einstein if and only if the Riemannian holonomy of the
induced metric is contained in G2. This could be considered to be a G2 analogue
of the Goldberg conjecture in almost Kahler geometry. The result was
generalized by R.L.Bryant to closed G2-structures with too tightly pinched
Ricci tensor. We extend it in another direction proving that a compact
G2-manifold with closed fundamental form and divergence-free Weyl tensor is a
G2-manifold with parallel fundamental form. We introduce a second symmetric
Ricci-type tensor and show that Einstein conditions applied to the two Ricci
tensors on a closed G2-structure again imply that the induced metric has
holonomy group contained in G2.Comment: 14 pages, the Einstein condition in the assumptions of the Main
theorem is generalized to the assumption that the Weyl tensor is
divergence-free, clarity improved, typos correcte
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