3,532 research outputs found
Neutronic Analysis on Potential Accident Tolerant Fuel-Cladding Combination USi-FeCrAl
Neutronic performance is investigated for a potential accident tolerant fuel
(ATF),which consists of USi fuel and FeCrAl cladding. In comparison
with current UO-Zr system, FeCrAl has a better oxidation resistance but a
larger thermal neutron absorption cross section. USi has a higher
thermal conductivity and a higher uranium density, which can compensate the
reactivity suppressed by FeCrAl. Based on neutronic investigations, a possible
USi-FeCrAl fuel-cladding systemis taken into consideration. Fundamental
properties of the suggested fuel-cladding combination are investigated in a
fuel assembly.These properties include moderator and fuel temperature
coefficients, control rods worth, radial power distribution (in a fuel rod),
and different void reactivity coefficients. The present work proves that the
new combination has less reactivity variation during its service lifetime.
Although, compared with the current system, it has a little larger deviation on
power distribution and a little less negative temperature coefficient and void
reactivity coefficient and its control rods worth is less important, variations
of these parameters are less important during the service lifetime of fuel.
Hence, USi-FeCrAl system is a potential ATF candidate from a neutronic
view
The stability of mRNA influences the temporal order of the induction of genes encoding inflammatory molecules
The inflammatory response plays out over time in a reproducible and organized way after an initiating stimulus. Here we show that genes activated in cultured mouse fibroblasts in response to the cytokine tumor necrosis factor could be categorized into roughly three groups, each with different induction kinetics. Although differences in transcription were important in determining the grouping of these genes, differences in mRNA stability also exerted a strong influence on the temporal order of gene expression, in some cases overriding that of transcriptional control elements. Transcripts of mRNA expressed early had abundant AU-rich elements in their 3' untranslated regions, whereas those expressed later had fewer. Thus, mRNA stability and transcriptional control, two intrinsic characteristics of genes, control the kinetics of gene expression induced by proinflammatory cytokines
Throughput Analysis of CSMA Wireless Networks with Finite Offered-load
This paper proposes an approximate method, equivalent access intensity (EAI),
for the throughput analysis of CSMA wireless networks in which links have
finite offered-load and their MAC-layer transmit buffers may be empty from time
to time. Different from prior works that mainly considered the saturated
network, we take into account in our analysis the impacts of empty transmit
buffers on the interactions and dependencies among links in the network that is
more common in practice. It is known that the empty transmit buffer incurs
extra waiting time for a link to compete for the channel airtime usage, since
when it has no packet waiting for transmission, the link will not perform
channel competition. The basic idea behind EAI is that this extra waiting time
can be mapped to an equivalent "longer" backoff countdown time for the
unsaturated link, yielding a lower link access intensity that is defined as the
mean packet transmission time divided by the mean backoff countdown time. That
is, we can compute the "equivalent access intensity" of an unsaturated link to
incorporate the effects of the empty transmit buffer on its behavior of channel
competition. Then, prior saturated ideal CSMA network (ICN) model can be
adopted for link throughput computation. Specifically, we propose an iterative
algorithm, "Compute-and-Compare", to identify which links are unsaturated under
current offered-load and protocol settings, compute their "equivalent access
intensities" and calculate link throughputs. Simulation shows that our
algorithm has high accuracy under various offered-load and protocol settings.
We believe the ability to identify unsaturated links and compute links
throughputs as established in this paper will serve an important first step
toward the design and optimization of general CSMA wireless networks with
offered-load control.Comment: 6 pages. arXiv admin note: text overlap with arXiv:1007.5255 by other
author
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