354 research outputs found
Superfluidity of Dense He in Vycor
We calculate properties of a model of He in Vycor using the Path Integral
Monte Carlo method. We find that He forms a distinct layered structure with
a highly localized first layer, a disordered second layer with some atoms
delocalized and able to give rise to the observed superfluid response, and
higher layers nearly perfect crystals. The addition of a single He atom was
enough to bring down the total superfluidity by blocking the exchange in the
second layer. Our results are consistent with the persistent liquid layer model
to explain the observations. Such a model may be relevant to the experiments on
bulk solid He, if there is a fine network of grain boundaries in those
systems.Comment: 4 pages, 4 figure
Frequency of conjugative transfer of plasmid-encoded ISEcp1 - blaCTX-M-15 and aac(6')-lb-cr genes in Enterobacteriaceae at a tertiary care center in Lebanon - role of transferases
<p>Abstract</p> <p>Background</p> <p>The frequency of transfer of genes encoding resistance to antimicrobial agents was determined by conjugation in ESBL-producing and/or fluoroquinolone or aminoglycoside resistant Enterobacteriaceae clinical isolates at a tertiary care center in Lebanon. In addition, the role of <it>tra </it>genes encoding transferases in mediating conjugation was assessed.</p> <p>Methods</p> <p>Conjugation experiments were done on 53 ESBL-producing and/or fluoroquinolone resistant <it>E. coli </it>and <it>K. pneumoniae </it>and ESBL-producing <it>S. sonnei </it>isolates. Antimicrobial susceptibility testing on parent and transconjugant isolates, and PCR amplifications on plasmid extracts of the resistance-encoding genes: <it>bla</it><sub>CTX-M-15 </sub>with the <it>ISEcp1 </it>insertion sequence, the <it>aac(6')-lb-cr </it>and <it>qnr</it>S genes, as well as <it>tra </it>encoding transferases genes were done. Random amplified polymorphic DNA (RAPD) analysis was performed to demonstrate whether conjugative isolates are clonal and whether they are linked epidemiologically to a particular source.</p> <p>Results</p> <p>Antimicrobial susceptibility testing on transconjugants revealed that 26 out of 53 (49%) ESBL-producing <it>Enterobacteriaceae </it>were able to transfer antimicrobial resistance to the recipients. Transfer of high-level resistance to the transconjugants encoded by the <it>bla</it><sub>CTX-M-15 </sub>gene downstream the <it>ISEcp1 </it>insertion sequence against 3rd generation cephalosporins, and of low-level resistance against ciprofloxacin, and variable levels of resistance against aminoglycosides encoded by <it>aac(6')-lb-cr </it>gene, were observed in transconjugants. <it>tra </it>encoding transferase genes were detected exclusively in conjugative isolates.</p> <p>Conclusion</p> <p>In conclusion, the frequency of transfer of antimicrobial resistance in non clonal <it>Enterobacteriaceae </it>at the tertiary care center by conjugation was 49%. Conjugation occurred in isolates expressing the <it>tra </it>encoding transferase genes. Multiple conjugative strains harboring the plasmid encoded antimicrobial resistant genes were circulating in the medical center. Molecular epidemiology analysis showed that conjugative isolates are neither clonal nor linked to a particular site and transfer of antimicrobial resistance is by horizontal transfer of plasmids.</p
Solidification of small para-H2 clusters at zero temperature
We have determined the ground-state energies of para-H clusters at zero
temperature using the diffusion Monte Carlo method. The liquid or solid
character of each cluster is investigated by restricting the phase through the
use of proper importance sampling. Our results show inhomogeneous
crystallization of clusters, with alternating behavior between liquid and solid
phases up to N=55. From there on, all clusters are solid. The ground-state
energies in the range N=13--75 are established and the stable phase of each
cluster is determined. In spite of the small differences observed between the
energy of liquid and solid clusters, the corresponding density profiles are
significantly different, feature that can help to solve ambiguities in the
determination of the specific phase of H clusters.Comment: 17 pages, accepted for publication in J. Phys. Chem.
Correlation between Group B Streptococcal Genotypes, Their Antimicrobial Resistance Profiles, and Virulence Genes among Pregnant Women in Lebanon
The antimicrobial
susceptibility profiles of 76
Streptococcus agalactiae (Group
B Streptococci [GBS]) isolates from vaginal
specimens of pregnant women near term were
correlated to their genotypes generated by
Random Amplified Polymorphic DNA analysis and
their virulence factors encoding genes
cylE, lmb, scpB, rib, and bca
by PCR. Based on the distribution of the
susceptibility patterns, six profiles were
generated. RAPD analysis detected 7 clusters of
genotypes. The cylE gene was
present in 99% of the isolates, the
lmb in 96%,
scpB in 94.7%,
rib in 33%, and
bca in 56.5% of isolates.
The isolates demonstrated a significant
correlation between antimicrobial resistance and
genotype clusters denoting the distribution of
particular clones with different antimicrobial
resistance profiles, entailing the practice of
caution in therapeutic options. All virulence
factors encoding genes were detected in all
seven genotypic clusters with
rib and bca
not coexisting in the same
genome
Thin helium film on a glass substrate
We investigate by Monte Carlo simulations the structure, energetics and
superfluid properties of thin helium-four films (up to four layers) on a glass
substrate, at low temperature. The first adsorbed layer is found to be solid
and "inert", i.e., atoms are localized and do not participate to quantum
exchanges. Additional layers are liquid, with no clear layer separation above
the second one. It is found that a single helium-three impurity resides on the
outmost layer, not significantly further away from the substrate than
helium-four atoms on the same layer.Comment: Six figures, submitted for publication to the Journal of Low
Temperature Physic
Path integral Monte Carlo simulation of charged particles in traps
This chapter is devoted to the computation of equilibrium (thermodynamic)
properties of quantum systems. In particular, we will be interested in the
situation where the interaction between particles is so strong that it cannot
be treated as a small perturbation. For weakly coupled systems many efficient
theoretical and computational techniques do exist. However, for strongly
interacting systems such as nonideal gases or plasmas, strongly correlated
electrons and so on, perturbation methods fail and alternative approaches are
needed. Among them, an extremely successful one is the Monte Carlo (MC) method
which we are going to consider in this chapter.Comment: 18 pages, based on talks on Hareaus school on computational methods,
Greifswald, September 200
Genotypes and serotype distribution of macrolide resistant invasive and non- invasive Streptococcus pneumoniae isolates from Lebanon
<p>Abstract</p> <p>Background</p> <p>This study determined macrolide resistance genotypes in clinical isolates of <it>Streptococcus pneumoniae </it>from multiple medical centers in Lebanon and assessed the serotype distribution in relation to these mechanism(s) of resistance and the source of isolate recovery.</p> <p>Methods</p> <p>Forty four macrolide resistant and 21 macrolide susceptible <it>S. pneumoniae </it>clinical isolates were tested for antimicrobial susceptibility according to CLSI guidelines (2008) and underwent molecular characterization. Serotyping of these isolates was performed by Multiplex PCR-based serotype deduction using CDC protocols. PCR amplification of macrolide resistant <it>erm </it>(encoding methylase) and <it>mef </it>(encoding macrolide efflux pump protein) genes was carried out.</p> <p>Results</p> <p>Among 44 isolates resistant to erythromycin, 35 were resistant to penicillin and 18 to ceftriaxone. Examination of 44 macrolide resistant isolates by PCR showed that 16 isolates harbored the <it>erm</it>(B) gene, 8 isolates harbored the <it>mef </it>gene, and 14 isolates harbored both the <it>erm</it>(B) and <it>mef </it>genes. There was no amplification by PCR of the <it>erm</it>(B) or <it>mef </it>genes in 6 isolates. Seven different capsular serotypes 2, 9V/9A,12F, 14,19A, 19F, and 23, were detected by multiplex PCR serotype deduction in 35 of 44 macrolide resistant isolates, with 19F being the most prevalent serotype. With the exception of serotype 2, all serotypes were invasive. Isolates belonging to the invasive serotypes 14 and 19F harbored both <it>erm</it>(B) and <it>mef </it>genes. Nine of the 44 macrolide resistant isolates were non-serotypable by our protocols.</p> <p>Conclusion</p> <p>Macrolide resistance in <it>S. pneumoniae </it>in Lebanon is mainly through target site modification but is also mediated through efflux pumps, with serotype 19F having dual resistance and being the most prevalent and invasive.</p
Improved Mitochondrial Function with Diet-Induced Increase in Either Docosahexaenoic Acid or Arachidonic Acid in Membrane Phospholipids
Mitochondria can depolarize and trigger cell death through the opening of the mitochondrial permeability transition pore (MPTP). We recently showed that an increase in the long chain n3 polyunsaturated fatty acids (PUFA) docosahexaenoic acid (DHA; 22:6n3) and depletion of the n6 PUFA arachidonic acid (ARA; 20:4n6) in mitochondrial membranes is associated with a greater Ca2+ load required to induce MPTP opening. Here we manipulated mitochondrial phospholipid composition by supplementing the diet with DHA, ARA or combined DHA+ARA in rats for 10 weeks. There were no effects on cardiac function, or respiration of isolated mitochondria. Analysis of mitochondrial phospholipids showed DHA supplementation increased DHA and displaced ARA in mitochondrial membranes, while supplementation with ARA or DHA+ARA increased ARA and depleted linoleic acid (18:2n6). Phospholipid analysis revealed a similar pattern, particularly in cardiolipin. Tetralinoleoyl cardiolipin was depleted by 80% with ARA or DHA+ARA supplementation, with linoleic acid side chains replaced by ARA. Both the DHA and ARA groups had delayed Ca2+-induced MPTP opening, but the DHA+ARA group was similar to the control diet. In conclusion, alterations in mitochondria membrane phospholipid fatty acid composition caused by dietary DHA or ARA was associated with a greater cumulative Ca2+ load required to induced MPTP opening. Further, high levels of tetralinoleoyl cardiolipin were not essential for normal mitochondrial function if replaced with very-long chain n3 or n6 PUFAs
Mucosal CD8 T Cell Responses Are Shaped by Batf3-DC After Foodborne Listeria monocytogenes Infection
While immune responses have been rigorously examined after intravenous Listeria monocytogenes (Lm) infection, less is understood about its dissemination from the intestines or the induction of adaptive immunity after more physiologic models of foodborne infection. Consequently, this study focused on early events in the intestinal mucosa and draining mesenteric lymph nodes (MLN) using foodborne infection of mice with Lm modified to invade murine intestinal epithelium (InlAM Lm). InlAM Lm trafficked intracellularly from the intestines to the MLN and were associated with Batf3-independent dendritic cells (DC) in the lymphatics. Consistent with this, InlAM Lm initially disseminated from the gut to the MLN normally in Batf3–/– mice. Activated migratory DC accumulated in the MLN by 3 days post-infection and surrounded foci of InlAM Lm. At this time Batf3–/– mice displayed reduced InlAM Lm burdens, implicating cDC1 in maximal bacterial accumulation in the MLN. Batf3–/– mice also exhibited profound defects in the induction and gut-homing of InlAM Lm-specific effector CD8 T cells. Restoration of pathogen burden did not rescue antigen-specific CD8 T cell responses in Batf3–/– mice, indicating a critical role for Batf3 in generating anti-InlAM Lm immunity following foodborne infection. Collectively, these data suggest that DC play diverse, dynamic roles in the early events following foodborne InlAM Lm infection and in driving the establishment of intestinal Lm-specific effector T cells.Fil: Imperato, Jessica Nancy. Stony Brook University Renaissance School Of Medicine; Estados UnidosFil: Xu, Daqi. Uconn Health; Estados UnidosFil: Romagnoli, Pablo Alberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigacion Medica Mercedes y Martin Ferreyra. Grupo Vinculado Centro de Investigacion En Medicina Traslacional Severo R. Amuchastegui - Cimetsa | Universidad Nacional de Cordoba. Instituto de Investigacion Medica Mercedes y Martin Ferreyra. Grupo Vinculado Centro de Investigacion En Medicina Traslacional Severo R. Amuchastegui - Cimetsa | Instituto de Investigacion Medica Mercedes y Martin Ferreyra. Instituto de Investigacion Medica Mercedes y Martin Ferreyra. Grupo Vinculado Centro de Investigacion En Medicina Traslacional Severo R. Amuchastegui - Cimetsa.; ArgentinaFil: Qiu, Zhijuan. Stony Brook University Renaissance School Of Medicine; Estados UnidosFil: Perez, Pedro. Stony Brook University Renaissance School Of Medicine; Estados UnidosFil: Khairallah, Camille. Stony Brook University Renaissance School Of Medicine; Estados UnidosFil: Pham, Quynh Mai. Uconn Health; Estados UnidosFil: Andrusaite, Anna. University of Glasgow; Reino UnidoFil: Bravo Blas, Alberto. The Beatson Institute For Cancer Research; Reino UnidoFil: Milling, Simon W. F.. University of Glasgow; Reino UnidoFil: Lefrancois, Leo. Uconn Health; Estados UnidosFil: Khanna, Kamal M.. University of New York; Estados UnidosFil: Puddington, Lynn. Uconn Health; Estados UnidosFil: Sheridan, Brian S.. Stony Brook University Renaissance School Of Medicine; Estados Unido
On the possible "supersolid" character of parahydrogen clusters
We present results of a theoretical study of structural and superfluid
properties of parahydrogen clusters comprising 25, 26 and 27 molecules at low
temperature. The microscopic model utilized here is based on the
Silvera-Goldman pair potential. Numerical results are obtained by means of
Quantum Monte Carlo simulations, making use of the continuous-space Worm
Algorithm. The clusters are superfluid in the low temperature limit, but
display markedly different physical behaviours. For N=25 and 27, superfluidity
at low temperature arises as clusters melt, i.e., become progressively
liquid-like as a result of quantum effects. On the other hand, for N = 26 the
cluster remains rigid and solid-like. We argue that this cluster can be
regarded as a mesoscopic "supersolid". This physical picture is supported by
results of simulations in which a single parahydrogen molecule in the cluster
is isotopically substituted.Comment: 18 pages, 7 figure
- …