203 research outputs found
Crystal structures and proton dynamics in potassium and cesium hydrogen bistrifluoroacetate salts with strong symmetric hydrogen bonds
The crystal structures of potassium and cesium bistrifluoroacetates were
determined at room temperature and at 20 K and 14 K, respectively, with the
single crystal neutron diffraction technique. The crystals belong to the I2/a
and A2/a monoclinic space groups, respectively, and there is no visible phase
transition. For both crystals, the trifluoroacetate entities form dimers linked
by very short hydrogen bonds lying across a centre of inversion. Any proton
disorder or double minimum potential can be rejected. The inelastic neutron
scattering spectral profiles in the OH stretching region between 500 and 1000
cm^{-1} previously published [Fillaux and Tomkinson, Chem. Phys. 158 (1991)
113] are reanalyzed. The best fitting potential has the major characteristics
already reported for potassium hydrogen maleate [Fillaux et al. Chem. Phys. 244
(1999) 387]. It is composed of a narrow well containing the ground state and a
shallow upper part corresponding to dissociation of the hydrogen bond.Comment: 31 pages, 7 figure
The High-Flux Backscattering Spectrometer at the NIST Center for Neutron Research
We describe the design and current performance of the high-flux
backscattering spectrometer located at the NIST Center for Neutron Research.
The design incorporates several state-of-the-art neutron optical devices to
achieve the highest flux on sample possible while maintaining an energy
resolution of less than 1mueV. Foremost among these is a novel phase-space
transformation chopper that significantly reduces the mismatch between the beam
divergences of the primary and secondary parts of the instrument. This resolves
a long-standing problem of backscattering spectrometers, and produces a
relative gain in neutron flux of 4.2. A high-speed Doppler-driven monochromator
system has been built that is capable of achieving energy transfers of up to
+-50mueV, thereby extending the dynamic range of this type of spectrometer by
more than a factor of two over that of other reactor-based backscattering
instruments
Tunneling of quantum rotobreathers
We analyze the quantum properties of a system consisting of two nonlinearly
coupled pendula. This non-integrable system exhibits two different symmetries:
a permutational symmetry (permutation of the pendula) and another one related
to the reversal of the total momentum of the system. Each of these symmetries
is responsible for the existence of two kinds of quasi-degenerated states. At
sufficiently high energy, pairs of symmetry-related states glue together to
form quadruplets. We show that, starting from the anti-continuous limit,
particular quadruplets allow us to construct quantum states whose properties
are very similar to those of classical rotobreathers. By diagonalizing
numerically the quantum Hamiltonian, we investigate their properties and show
that such states are able to store the main part of the total energy on one of
the pendula. Contrary to the classical situation, the coupling between pendula
necessarily introduces a periodic exchange of energy between them with a
frequency which is proportional to the energy splitting between
quasi-degenerated states related to the permutation symmetry. This splitting
may remain very small as the coupling strength increases and is a decreasing
function of the pair energy. The energy may be therefore stored in one pendulum
during a time period very long as compared to the inverse of the internal
rotobreather frequency.Comment: 20 pages, 11 figures, REVTeX4 styl
Toxocariasis: a silent threat with a progressive public health impact
Background: Toxocariasis is a neglected parasitic zoonosis that afflicts millions of the pediatric and adolescent populations worldwide, especially in impoverished communities. This disease is caused by infection with the larvae of Toxocara canis and T. cati, the most ubiquitous intestinal nematode parasite in dogs and cats, respectively. In this article, recent advances in the epidemiology, clinical presentation, diagnosis and pharmacotherapies that have been used in the treatment of toxocariasis are reviewed.
Main text: Over the past two decades, we have come far in our understanding of the biology and epidemiology of toxocariasis. However, lack of laboratory infrastructure in some countries, lack of uniform case definitions and limited surveillance infrastructure are some of the challenges that hindered the estimation of global disease burden. Toxocariasis encompasses four clinical forms: visceral, ocular, covert and neural. Incorrect or misdiagnosis of any of these disabling conditions can result in severe health consequences and considerable medical care spending. Fortunately, multiple diagnostic modalities are available, which if effectively used together with the administration of appropriate pharmacologic therapies, can minimize any unnecessary patient morbidity.
Conclusions: Although progress has been made in the management of toxocariasis patients, there remains much work to be done. Implementation of new technologies and better understanding of the pathogenesis of toxocariasis can identify new diagnostic biomarkers, which may help in increasing diagnostic accuracy. Also, further clinical research breakthroughs are needed to develop better ways to effectively control and prevent this serious disease
Cost-Effectiveness Analysis of Diagnostic Options for Pneumocystis Pneumonia (PCP)
Diagnosis of Pneumocystis jirovecii pneumonia (PCP) is challenging, particularly in developing countries. Highly sensitive diagnostic methods are costly, while less expensive methods often lack sensitivity or specificity. Cost-effectiveness comparisons of the various diagnostic options have not been presented.We compared cost-effectiveness, as measured by cost per life-years gained and proportion of patients successfully diagnosed and treated, of 33 PCP diagnostic options, involving combinations of specimen collection methods [oral washes, induced and expectorated sputum, and bronchoalveolar lavage (BAL)] and laboratory diagnostic procedures [various staining procedures or polymerase chain reactions (PCR)], or clinical diagnosis with chest x-ray alone. Our analyses were conducted from the perspective of the government payer among ambulatory, HIV-infected patients with symptoms of pneumonia presenting to HIV clinics and hospitals in South Africa. Costing data were obtained from the National Institutes of Communicable Diseases in South Africa. At 50% disease prevalence, diagnostic procedures involving expectorated sputum with any PCR method, or induced sputum with nested or real-time PCR, were all highly cost-effective, successfully treating 77-90% of patients at 189-232 per life-year gained. A relatively cost-effective diagnostic procedure that did not require PCR was Toluidine Blue O staining of induced sputum (109 per life-year gained) compared with several molecular diagnostic options.For diagnosis of PCP, use of PCR technologies, when combined with less-invasive patient specimens such as expectorated or induced sputum, represent more cost-effective options than any diagnostic procedure using BAL, or chest x-ray alone
FREQUENCY OF ANTI- Toxocara spp. ANTIBODIES IN INDIVIDUALS ATTENDED BY THE CENTRO DE SALUD FAMILIAR AND ENVIRONMENTAL CONTAMINATION WITH Toxocara canis EGGS IN DOG FECES, IN THE COASTAL NIEBLA TOWN, CHILE
High prevalence of oxacillinases in clinical multidrug-resistant Acinetobacter baumannii isolates from the Tshwane region, South Africa – an update
BACKGROUND : Acinetobacter baumannii is an important hospital-acquired pathogen in healthcare facilities that
frequently causes bacteraemia and ventilator-associated pneumonia in intensive care units. Acinetobacter baumannii
can be isolated from various sites in the hospital environment like medical equipment, bed linen, medical personnel
and indwelling catheters. It is difficult to treat A. baumannii infections because of their highly resistant antimicrobial
profiles. The purpose of this study was to determine the prevalence of β-lactamase genes in multidrug-resistant (MDR)
clinical A. baumannii isolates using Multiplex-PCR (M-PCR) assays.
METHODS : One hundred MDR A. baumannii isolates were collected from the diagnostic division of the Department of
Medical Microbiology after routine analysis of the submitted specimens. All collected isolates were identified and tested
for susceptibility using the VITEK 2® system (bioMérieux, France). Six isolates were excluded from this study because the
isolates were incorrectly identified as A. baumannii with the VITEK 2® system (bioMérieux, France). Molecular tests, namely
M-PCR assays, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were performed. MLST
analyses were performed on representative isolates from the four major pulsotypes (≥5 isolates with 80 % similarity) and
selective isolates from each minor pulsotype.
RESULTS : All the A. baumannii isolates showed 100 % resistance to ampicillin, amoxicillin, cefuroxime, cefuroximine axetil,
cefoxitin, cefotaxime and nitrofurantoin. Seven percent of the isolates were resistant to amikacin. Two percent of the
isolates were classified as having intermediate susceptibility to tigecycline. A. baumannii isolates showed an antibiotic
resistance profile of 67 % and higher to antibiotics, such as ceftazidime, cefepime, imipenem, meropenem, gentamicin,
ciprofloxacin and trimethoprim/sulfamethoxazole. None of the isolates were resistant to colistin. The M-PCR assays
showed that 99 % of the isolates contained the OXA-51 gene and 77 % contained the OXA-23 gene. None of the
isolates contained the GES, GIM, IMP, KPC, NDM, OXA-24, OXA-58, PER, SIM, SPM, VEB and VIM genes. Representative A.
baumannii isolates were grouped into five existing sequence types (ST): ST106, ST258, ST339, ST502, ST758 and ST848.
Isolates belonging to the pan-European clonal lineages I and II (EUI and EUII) were identified.
CONCLUSION : The high prevalence of MDR A. baumannii isolates has a severe impact on available treatment choices and
this in return impacts on treatment outcomes in the studied healthcare facilities. The most dominant ST among the
collected isolates was ST758, member of the EUI group. The presence of the OXA-23 gene was not restricted to a
specific ST. Continuous research and surveillance is necessary to monitor the circulating β-lactamase genes in clinical
settings to guide infection control policies in order to try and curb the spread of this bacterium.ML was supported by a
National Research Foundation (NRF) grant. The MALDI-TOF analysis is based on
research supported in part by the National Research Foundation (NRF) of South
Africa (Grant specific unique reference number (UID) 74426).http://www.biomedcentral.com/bmcinfectdis/am201
Growth And The Growth Hormone-Insulin Like Growth Factor 1 Axis In Children With Chronic Inflammation:Current Evidence, Gaps In Knowledge And Future Directions
Growth failure is frequently encountered in children with chronic inflammatory conditions like juvenile idiopathic arthritis, inflammatory bowel disease and cystic fibrosis. Delayed puberty and attenuated pubertal growth spurt is often seen during adolescence. The underlying inflammatory state mediated by pro-inflammatory cytokines, prolonged use of glucocorticoid and suboptimal nutrition contribute to growth failure and pubertal abnormalities. These factors can impair growth by their effects on the growth hormone-insulin like growth factor axis and also directly at the level of the growth plate via alterations in chondrogenesis and local growth factor signaling. Recent studies on the impact of cytokines and glucocorticoid on the growth plate studies further advanced our understanding of growth failure in chronic disease and provided a biological rationale of growth promotion. Targeting cytokines using biologic therapy may lead to improvement of growth in some of these children but approximately one third continue to grow slowly. There is increasing evidence that the use of relatively high dose recombinant human growth hormone may lead to partial catch up growth in chronic inflammatory conditions, although long term follow-up data is currently limited. In this review, we comprehensively review the growth abnormalities in children with juvenile idiopathic arthritis, inflammatory bowel disease and cystic fibrosis, systemic abnormalities of the growth hormone-insulin like growth factor axis and growth plate perturbations. We also systematically reviewed all the current published studies of recombinant human growth hormone in these conditions and discuss the role of recombinant human insulin like growth factor-1
Evidence of macroscopically entangled protons in a mixed isotope crystal of KHpD1-pCO3
We examine whether protons and deuterons in the crystal of
KHDCO at 300 K are particles or matter waves. The neutron
scattering function measured over a broad range of reciprocal space reveals the
enhanced diffraction pattern anticipated for antisymmetrized macroscopic states
for protons (fermions). These features exclude a statistical distribution of
protons and deuterons. Raman spectra are consistent with a mixture of KHCO
and KDCO sublattices whose isomorphous structures are independent of the
isotope content. We propose a theoretical framework for decoherence-free proton
and deuteron states
The impact of vibrational spectroscopy with neutrons on our view of quantum dynamics in hydrogen bonds and proton transfer
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