5,173 research outputs found
Divergent roles of CprK paralogues from Desulfitobacterium hafniense in activating gene expression
Gene duplication and horizontal gene transfer play an important role in the evolution of prokaryotic genomes. We have investigated the role of three CprK paralogues from the cAMP receptor protein-fumarate and nitrate reduction regulator (CRP-FNR) family of transcriptional regulators that are encoded in the genome of Desulfitobacterium hafniense DCB-2 and possibly regulate expression of genes involved in the energy-conserving terminal reduction of organohalides (halorespiration). The results from in vivo and in vitro promoter probe assays show that two regulators (CprK1 and CprK2) have an at least partially overlapping effector specificity, with preference for ortho-chlorophenols, while meta-chlorophenols proved to be effectors for CprK4. The presence of a potential transposase-encoding gene in the vicinity of the cprK genes indicates that their redundancy is probably caused by mobile genetic elements. The CprK paralogues activated transcription from promoters containing a 14 bp inverted repeat (dehalobox) that closely resembles the FNR-box. We found a strong negative correlation between the rate of transcriptional activation and the number of nuclecitide changes from the optimal dehalobox sequence (TTAAT-N-4-ATTAA). Transcription was initiated by CprK4 from a promoter that is situated upstream of a gene encoding a methyl-accepting chemotaxis protein. This might be the first indication of taxis of an anaerobic bacterium to halogenated aromatic compounds
A Risk Comparison of Ordinary Least Squares vs Ridge Regression
We compare the risk of ridge regression to a simple variant of ordinary least
squares, in which one simply projects the data onto a finite dimensional
subspace (as specified by a Principal Component Analysis) and then performs an
ordinary (un-regularized) least squares regression in this subspace. This note
shows that the risk of this ordinary least squares method is within a constant
factor (namely 4) of the risk of ridge regression.Comment: Appearing in JMLR 14, June 201
Thermodynamic Properties of Generalized Exclusion Statistics
We analytically calculate some thermodynamic quantities of an ideal -on
gas obeying generalized exclusion statistics. We show that the specific heat of
a -on gas () vanishes linearly in any dimension as when
the particle number is conserved and exhibits an interesting dual symmetry that
relates the particle-statistics at to the hole-statistics at at low
temperatures. We derive the complete solution for the cluster coefficients
as a function of Haldane's statistical interaction in
dimensions. We also find that the cluster coefficients and the virial
coefficients are exactly mirror symmetric (=odd) or antisymmetric
(=even) about . In two dimensions, we completely determine the closed
forms about the cluster and the virial coefficients of the generalized
exclusion statistics, which exactly agree with the virial coefficients of an
anyon gas of linear energies. We show that the -on gas with zero chemical
potential shows thermodynamic properties similar to the photon statistics. We
discuss some physical implications of our results.Comment: 24 pages, Revtex, Corrected typo
Transition from phase to generalized synchronization in time-delay systems
The notion of phase synchronization in time-delay systems, exhibiting highly
non-phase-coherent attractors, has not been realized yet even though it has
been well studied in chaotic dynamical systems without delay. We report the
identification of phase synchronization in coupled nonidentical piece-wise
linear and in coupled Mackey-Glass time-delay systems with highly
non-phase-coherent regimes. We show that there is a transition from
non-synchronized behavior to phase and then to generalized synchronization as a
function of coupling strength. We have introduced a transformation to capture
the phase of the non-phase coherent attractors, which works equally well for
both the time-delay systems. The instantaneous phases of the above coupled
systems calculated from the transformed attractors satisfy both the phase and
mean frequency locking conditions. These transitions are also characterized in
terms of recurrence based indices, namely generalized autocorrelation function
, correlation of probability of recurrence (CPR), joint probability of
recurrence (JPR) and similarity of probability of recurrence (SPR). We have
quantified the different synchronization regimes in terms of these indices. The
existence of phase synchronization is also characterized by typical transitions
in the Lyapunov exponents of the coupled time-delay systems.Comment: Accepted for publication in CHAO
Mobile phone dependence, social support and impulsivity in Chinese university students
This study examined the frequency of mobile phone dependence in Chinese university students and explored its association with social support and impulsivity. Altogether, 909 university students were consecutively recruited from a large university in China. Mobile phone use, mobile phone dependence, impulsivity, and social support were measured with standardized instruments. The frequency of possible mobile phone use and mobile phone dependence was 78.3% and 7.4%, respectively. Multinomial logistic regression analyses revealed that compared with no mobile phone dependence, possible mobile phone dependence was significantly associated with being male (p = 0.04, OR = 0.7, 95% CI: 0.4–0.98), excessive mobile phone use (p \u3c 0.001, OR = 1.2, 95% CI: 1.09–1.2), and impulsivity (p \u3c 0.001, OR = 1.05, 95% CI: 1.03–1.06), while mobile phone dependence was associated with length of weekly phone use (p = 0.01, OR = 2.5, 95% CI: 1.2–5.0), excessive mobile phone use (p \u3c 0.001, OR = 1.3, 95% CI: 1.2–1.4), and impulsivity (p \u3c 0.001, OR = 1.08, 95% CI: 1.05–1.1). The frequency of possible mobile phone dependence and mobile phone dependence was high in this sample of Chinese university students. A significant positive association with impulsivity was found, but not with social support
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