18,824 research outputs found
Film breakers prevent migration of aqueous potassium hydroxide in fuel cells
Electrolyte film breakers made from polytetrafluoroethylene are installed in the reactant and water vapor removal outlets of each cell and sealed by elastomers. Use of these devices in the water vapor removal cavity outlets prevents loss of KOH solution through film migration during water removal
Vent subsystem - development plan
Vent subsystem design specifications for use in fuel cell assembl
Shear-stress controlled dynamics of nematic complex fluids
Based on a mesoscopic theory we investigate the non-equilibrium dynamics of a
sheared nematic liquid, with the control parameter being the shear stress
(rather than the usual shear rate, ). To
this end we supplement the equations of motion for the orientational order
parameters by an equation for , which then becomes time-dependent.
Shearing the system from an isotropic state, the stress- controlled flow
properties turn out to be essentially identical to those at fixed .
Pronounced differences when the equilibrium state is nematic. Here, shearing at
controlled yields several non-equilibrium transitions between
different dynamic states, including chaotic regimes. The corresponding
stress-controlled system has only one transition from a regular periodic into a
stationary (shear-aligned) state. The position of this transition in the
- plane turns out to be tunable by the delay
time entering our control scheme for . Moreover, a sudden
change of the control method can {\it stabilize} the chaotic states appearing
at fixed .Comment: 10 pages, 11 figure
Fuel cell module development plan - Activity 145 - 205
Development plan for fuel cell modules consisting of 35 two-cell sections and incorporating static moisture control subsystems as integral part of modul
Superlattices and NiPi structures in new forms of cascade solar cells
The activity in the field of photovoltaic semiconductor superstructures is described. Progress was accomplished in the two principal directions previously defined in our initial proposal, i.e.: (1) Theoretical investigation of the optical properties of superlattices; and (2) New solar cell concepts and device modeling. Although important information concerning the optical constants of superlattices and multiple quantum well structures was obtained from our computer model, most of the theoretical efforts have progressively shifted from the former to the latter aspect of the project because of the discovery of a new kind of photovoltaic device which may exhibit improved performances with respect to conventional solar cells
The diversity of a distributed genome in bacterial populations
The distributed genome hypothesis states that the set of genes in a
population of bacteria is distributed over all individuals that belong to the
specific taxon. It implies that certain genes can be gained and lost from
generation to generation. We use the random genealogy given by a Kingman
coalescent in order to superimpose events of gene gain and loss along ancestral
lines. Gene gains occur at a constant rate along ancestral lines. We assume
that gained genes have never been present in the population before. Gene losses
occur at a rate proportional to the number of genes present along the ancestral
line. In this infinitely many genes model we derive moments for several
statistics within a sample: the average number of genes per individual, the
average number of genes differing between individuals, the number of
incongruent pairs of genes, the total number of different genes in the sample
and the gene frequency spectrum. We demonstrate that the model gives a
reasonable fit with gene frequency data from marine cyanobacteria.Comment: Published in at http://dx.doi.org/10.1214/09-AAP657 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Magnon Heat Conductivity and Mean Free Paths in Two-Leg Spin Ladders: A Model-Independent Determination
The magnon thermal conductivity of the spin ladders
in has been investigated at low doping levels
, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic
defects which define an upper limit for and therefore allow
a clear-cut relation between and to
be established independently of any model. Over a large temperature range we
observe a progressive suppression of with increasing
Zn-content and find in particular that with respect to pure is strongly suppressed even in
the case of tiny impurity densities where ~{\AA}.
This shows unambiguously that large ~{\AA} which
have been reported for and on basis of a kinetic model are in the correct order
of magnitude
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