55,475 research outputs found
Reaction-diffusion with a time-dependent reaction rate: the single-species diffusion-annihilation process
We study the single-species diffusion-annihilation process with a
time-dependent reaction rate, lambda(t)=lambda_0 t^-omega. Scaling arguments
show that there is a critical value of the decay exponent omega_c(d) separating
a reaction-limited regime for omega > omega_c from a diffusion-limited regime
for omega < omega_c. The particle density displays a mean-field,
omega-dependent, decay when the process is reaction limited whereas it behaves
as for a constant reaction rate when the process is diffusion limited. These
results are confirmed by Monte Carlo simulations. They allow us to discuss the
scaling behaviour of coupled diffusion-annihilation processes in terms of
effective time-dependent reaction rates.Comment: 11 pages, 9 figures, minor correction
Geometrical properties of the trans-spherical solutions in higher dimensions
We investigate the geometrical properties of static vacuum -brane
solutions of Einstein gravity in dimensions, which have spherical
symmetry of orthogonal to the -directions and are invariant under
the translation along them. % The solutions are characterized by mass density
and tension densities. % The causal structure of the higher dimensional
solutions is essentially the same as that of the five dimensional ones. Namely,
a naked singularity appears for most solutions except for the Schwarzschild
black -brane and the Kaluza-Klein bubble. % We show that some important
geometric properties such as the area of and the total spatial volume
are characterized only by the three parameters such as the mass density, the
sum of tension densities and the sum of tension density squares rather than
individual tension densities. These geometric properties are analyzed in detail
in this parameter space and are compared with those of 5-dimensional case.Comment: 14 pages, 2 figures, Title change
Empirical Evaluation of the Parallel Distribution Sweeping Framework on Multicore Architectures
In this paper, we perform an empirical evaluation of the Parallel External
Memory (PEM) model in the context of geometric problems. In particular, we
implement the parallel distribution sweeping framework of Ajwani, Sitchinava
and Zeh to solve batched 1-dimensional stabbing max problem. While modern
processors consist of sophisticated memory systems (multiple levels of caches,
set associativity, TLB, prefetching), we empirically show that algorithms
designed in simple models, that focus on minimizing the I/O transfers between
shared memory and single level cache, can lead to efficient software on current
multicore architectures. Our implementation exhibits significantly fewer
accesses to slow DRAM and, therefore, outperforms traditional approaches based
on plane sweep and two-way divide and conquer.Comment: Longer version of ESA'13 pape
Universality of the Kondo effect in quantum dots with ferromagnetic leads
We investigate quantum dots in clean single-wall carbon nanotubes with
ferromagnetic PdNi-leads in the Kondo regime. In most odd Coulomb valleys the
Kondo resonance exhibits a pronounced splitting, which depends on the tunnel
coupling to the leads and an external magnetic field , and only weakly on
gate voltage. Using numerical renormalization group calculations, we
demonstrate that all salient features of the data can be understood using a
simple model for the magnetic properties of the leads. The magnetoconductance
at zero bias and low temperature depends in a universal way on , where is the Kondo temperature and the external field
compensating the splitting.Comment: 4 pages, 4 figure
Metabolic Impacts of Using Nitrogen and Copper-Regulated Promoters to Regulate Gene Expression in Neurospora crassa.
The filamentous fungus Neurospora crassa is a long-studied eukaryotic microbial system amenable to heterologous expression of native and foreign proteins. However, relatively few highly tunable promoters have been developed for this species. In this study, we compare the tcu-1 and nit-6 promoters for controlled expression of a GFP reporter gene in N. crassa. Although the copper-regulated tcu-1 has been previously characterized, this is the first investigation exploring nitrogen-controlled nit-6 for expression of heterologous genes in N. crassa. We determined that fragments corresponding to 1.5-kb fragments upstream of the tcu-1 and nit-6 open reading frames are needed for optimal repression and expression of GFP mRNA and protein. nit-6 was repressed using concentrations of glutamine from 2 to 20 mM and induced in medium containing 0.5-20 mM nitrate as the nitrogen source. Highest levels of expression were achieved within 3 hr of induction for each promoter and GFP mRNA could not be detected within 1 hr after transfer to repressing conditions using the nit-6 promoter. We also performed metabolic profiling experiments using proton NMR to identify changes in metabolite levels under inducing and repressing conditions for each promoter. The results demonstrate that conditions used to regulate tcu-1 do not significantly change the primary metabolome and that the differences between inducing and repressing conditions for nit-6 can be accounted for by growth under nitrate or glutamine as a nitrogen source. Our findings demonstrate that nit-6 is a tunable promoter that joins tcu-1 as a choice for regulation of gene expression in N. crassa
E-participation service in Saudi Arabian e-Government websites: The influencing factors from citizens' perspective
© 2014 The Authors. In keeping pace with the rapid developments in information and communication technology, the Saudi government has invested heavily, in recent years, in the development of e-participation services in e-Government websites with the aim of enhancing citizens' interaction with the government and thereby making the latter more responsive and accountable to citizens' needs. However, despite its significant efforts, a low level of use of the online opportunities by the citizens for interacting with the government is an endemic problem faced by the Saudi government. In contrast, many countries stand in very good positions compared to Saudi Arabia in terms of citizens' rate of adoption of e-participation services. This suggests that there are influencing factors that have a significant impact on citizens' intention to use eparticipation services in e-Government websites in Saudi Arabia. Therefore, this research aims to explore the factors, from a citizen perspective, that affects individuals' intention to use e-participation services in Saudi Arabian e-Government websites. In addressing its objective, this research commenced with a literature investigation which revealed that there are very few previous studies that have specifically examined the antecedents of citizens' intention to use e-participation services. Much of the existing literature on citizens' intention to use e-Government services have focused predominantly on the transactional services. Additionally, most of these studies have concentrated more on validating popular behavioural models in the context of citizens' use of e-services rather than looking at contextual factors that could impact individual's decision to use such services. Therefore, by reviewing different theories and empirical findings, a conceptual framework has been proposed in this study for understanding Saudi citizens' intention to use e-participation. The framework consists of five constructs, including, intention to use e-participation, attitude, trust, website design, and culture. The relationship between these constructs form the basis for the research hypotheses which will be tested using a quantitative research approach. Specifically, a survey will be used for gathering data from a sample of Saudi citizens and statistical methods will be used for analysing the quantitative data generated from the primary research. The findings of this research can assist the Saudi government and governments of other culturally similar countries in developing more effective citizen-centric e-participation services, thus implying that this study has significant practical implications as well
Electroweak Baryogenesis in a Supersymmetric U(1)' Model
We construct an anomaly free supersymmetric U(1)' model with a secluded
U(1)'-breaking sector. We study the one-loop effective potential at finite
temperature, and show that there exists a strong enough first order electroweak
phase transition for electroweak baryogenesis (EWBG) because of the large
trilinear term in the tree-level Higgs potential. Unlike in
the MSSM, the lightest stop can be very heavy. We consider the non-local EWBG
mechanism in the thin wall regime, and find that within uncertainties the
observed baryon number can be generated from the lepton contribution,
with the secluded sector playing an essential role. The chargino and neutralino
contributions and the implications for the Z' mass and electric dipole moments
are briefly discussed.Comment: RevTex, 4 pages, 2 figures, references added, version to appear in
PR
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