518 research outputs found
Flat deformation of a spacetime admitting two Killing fields
It is shown that given an analytic Lorentzian metric on a 4-manifold, ,
which admits two Killing vector fields, then it exists a local deformation law
, where is a 2-dimensional projector, such that is
flat and admits the same Killing vectors. We also characterize the particular
case when the projector coincides with the quotient metric. We apply some
of our results to general stationary axisymmetric spacetime
Site-Specific Integration of Foreign DNA into Minimal Bacterial and Human Target Sequences Mediated by a Conjugative Relaxase
This is an open-access article distributed under the terms of the Creative Commons Attribution License.[Background]: Bacterial conjugation is a mechanism for horizontal DNA transfer between bacteria which requires cell to cell contact, usually mediated by self-transmissible plasmids. A protein known as relaxase is responsible for the processing of DNA during bacterial conjugation. TrwC, the relaxase of conjugative plasmid R388, is also able to catalyze site-specific integration of the transferred DNA into a copy of its target, the origin of transfer (oriT), present in a recipient plasmid. This reaction confers TrwC a high biotechnological potential as a tool for genomic engineering.
[Methodology/Principal Findings]: We have characterized this reaction by conjugal mobilization of a suicide plasmid to a recipient cell with an oriT-containing plasmid, selecting for the cointegrates. Proteins TrwA and IHF enhanced integration frequency. TrwC could also catalyze integration when it is expressed from the recipient cell. Both Y18 and Y26 catalytic tyrosil residues were essential to perform the reaction, while TrwC DNA helicase activity was dispensable. The target DNA could be reduced to 17 bp encompassing TrwC nicking and binding sites. Two human genomic sequences resembling the 17 bp segment were accepted as targets for TrwC-mediated site-specific integration. TrwC could also integrate the incoming DNA molecule into an oriT copy present in the recipient chromosome.
[Conclusions/Significance]: The results support a model for TrwC-mediated site-specific integration. This reaction may allow R388 to integrate into the genome of non-permissive hosts upon conjugative transfer. Also, the ability to act on target sequences present in the human genome underscores the biotechnological potential of conjugative relaxase TrwC as a site-specific integrase for genomic modification of human cells.This work was supported by grant BIO2008-00133 from the Spanish Ministry of Science and Innovation to ML. CGP was a recipient of a predoctoral fellowship from the University of Cantabria, Spain.Peer reviewe
Flat deformation theorem and symmetries in spacetime
The \emph{flat deformation theorem} states that given a semi-Riemannian
analytic metric on a manifold, locally there always exists a two-form ,
a scalar function , and an arbitrarily prescribed scalar constraint
depending on the point of the manifold and on and , say , such that the \emph{deformed metric} is
semi-Riemannian and flat. In this paper we first show that the above result
implies that every (Lorentzian analytic) metric may be written in the
\emph{extended Kerr-Schild form}, namely where is flat and are two null covectors such that
; next we show how the symmetries of are connected to those of
, more precisely; we show that if the original metric admits a
Conformal Killing vector (including Killing vectors and homotheties), then the
deformation may be carried out in a way such that the flat deformed metric
`inherits' that symmetry.Comment: 30 pages, 0 figure
A translocation motif in relaxase TrwC specifically affects recruitment by its conjugative type IV secretion system
Type IV secretion system (T4SS) substrates are recruited through a translocation signal that is poorly defined for conjugative relaxases. The relaxase TrwC of plasmid R388 is translocated by its cognate conjugative T4SS, and it can also be translocated by the VirB/D4 T4SS of Bartonella henselae, causing DNA transfer to human cells. In this work, we constructed a series of TrwC variants and assayed them for DNA transfer to bacteria and human cells to compare recruitment requirements by both T4SSs. Comparison with other reported relaxase translocation signals allowed us to determine two putative translocation sequence (TS) motifs, TS1 and TS2. Mutations affecting TS1 drastically affected conjugation frequencies, while mutations affecting either motif had only a mild effect on DNA transfer rates through the VirB/D4 T4SS of B. henselae. These results indicate that a single substrate can be recruited by two different T4SSs through different signals. The C terminus affected DNA transfer rates through both T4SSs tested, but no specific sequence requirement was detected. The addition of a Bartonella intracellular delivery (BID) domain, the translocation signal for the Bartonella VirB/D4 T4SS, increased DNA transfer up to 4% of infected human cells, providing an excellent tool for DNA delivery to specific cell types. We show that the R388 coupling protein TrwB is also required for this high-efficiency TrwC-BID translocation. Other elements apart from the coupling protein may also be involved in substrate recognition by T4SSs
Short and Longer-term Psychological Consequences of Operation Cast Lead: documentation from a Mental Health program in the Gaza Strip
<p>Abstract</p> <p>Background</p> <p>There is growing recognition of the psychological impact of adversity associated with armed conflict on exposed civilian populations. Yet there is a paucity of evidence on the value of mental health programs in these contexts, and of the chronology of psychological sequelae, especially in prolonged conflicts with repeated cycles of extreme violence. Here, we describe changes in the psychological profile of new patients in a mental health program after the military offensive Cast Lead, in the context of the prolonged armed conflict involving the Gaza Strip.</p> <p>Methods</p> <p>This study analyses routinely collected program data from a Médecins Sans Frontières mental health program in the Gaza Strip spanning 2007–2011. Data consist of socio-demographic as well as clinical baseline and follow-up data on new patients entering the program. Comparisons were made through Chi square and Fisher’s exact tests, univariate and multivariate logistic and linear regression.</p> <p>Results</p> <p>PTSD, depression and other anxiety disorders were the most frequent psychopathologies, with 21% having multiple diagnoses. With a median of nine sessions, clinical improvement was recorded for 83% (1122/1357), and more common for those with separation anxiety, acute and posttraumatic disorders as principal diagnosis (855/1005), compared to depression (141/183, p<0.01). Noted changes proximal to Operation Cast Lead were: a doubling in patient case load with a broader socio-economic background, shorter interval from an identified traumatic event to seeking care, and a rise in diagnoses of acute and posttraumatic stress disorders. Sustained changes included: high case load, more distal triggering events, and increase in diagnoses of other anxiety disorders (especially for children 15 years and younger) and depression (especially for patients 16 years and older).</p> <p>Conclusion</p> <p>Evolving changes in patient volume, diagnoses and recall period to triggering events suggest a lengthy and durable effect of an intensified exposure to violence in a context of prolonged conflict. Our findings suggest that mental health related humanitarian relief in protracted conflicts might need to prepare for an increase in patients with changing profiles over an extended period following an acute flare-up in violence.</p
On the motion of a classical charged particle
We show that the Lorentz-Dirac equation is not an unavoidable consequence of
energy-momentum conservation for a point charge. What follows solely from
conservation laws is a less restrictive equation already obtained by Honig and
Szamosi. The latter is not properly an equation of motion because, as it
contains an extra scalar variable, it does not determine the future evolution
of the charge. We show that a supplementary constitutive relation can be added
so that the motion is determined and free from the troubles that are customary
in Lorentz-Dirac equation, i. e. preacceleration and runaways
On the degrees of freedom of a semi-Riemannian metric
A semi-Riemannian metric in a n-manifold has n(n-1)/2 degrees of freedom,
i.e. as many as the number of components of a differential 2-form. We prove
that any semi-Riemannian metric can be obtained as a deformation of a constant
curvature metric, this deformation being parametrized by a 2-for
Development of Silicon PhotoMultipliers at FBK-irst
We report on the development of Silicon PhotoMultipliers (SiPM) at the Fondazione Bruno Kessler (FBK)-irst (Trento, Italy) in the framework of a collaboration with INFN. Device geometry and technology are resumed, and selected
results from the characterization of SiPM prototypes from three production batches are reported, including static, dynamic, and noise properties, as well as photodetection efficiency
Reference frames and rigid motions in relativity: Applications
The concept of rigid reference frame and of constricted spatial metric, given
in the previous work [\emph{Class. Quantum Grav.} {\bf 21}, 3067,(2004)] are
here applied to some specific space-times: In particular, the rigid rotating
disc with constant angular velocity in Minkowski space-time is analyzed, a new
approach to the Ehrenfest paradox is given as well as a new explanation of the
Sagnac effect. Finally the anisotropy of the speed of light and its measurable
consequences in a reference frame co-moving with the Earth are discussed.Comment: 13 pages, 1 figur
A bacterial-based algorithm to simulate complex adaptive systems
Following a bacterial-based modeling approach, we want to model and analyze the impact of both decentralization and heterogeneity on group behavior and collective learning. Inspired by bacterial conjugation, we have defined an artificial society in which agents' strategies adapt to changes in resources location, allowing migration and survival in a dynamic sugarscape-like scenario. To study the impact of these variables we have simulated a scenario in which resources are limited and localized. We also have defined three constraints in genetic information processing (inhibition of plasmid conjugation, inhibition of plasmid reproduction and inhibition of plasmid mutation). Our results affirmed the hypothesis that efficiency of group adaptation to dynamic environments is better when societies are varied and distributed than when they are homogeneous and centralized
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