1,288 research outputs found
Determination of two-body potentials from n-body spectra
We show how the two-body potential may be uniquely determined from n-body
spectra where the hypercentral approximation is valid. We illustrate this by
considering an harmonic oscillator potential which has been altered by changing
the energy or normalisation constant of the ground state of the n-body system
and finding how this modifies the two-body potential. It is shown that with
increasing number of particles the spectrum must be known more precisely to
obtain the two-body potential to the same degree of accuracy.Comment: 13 pages of text (LATEX), 3 figures (not included, available from
authors), NIKHEF-93-P
Propiedades biológicas de matrices porosas y no porosas de PCL/PFIP
Actualmente existe un alto interés en el estudio de polímeros sintéticos biodegradables para su aplicación como andamiajes biocompatibles en distintas áreas de ingeniería de tejidos. Poli(e-caprolactona) (PCL) y poli(diisopropilfumarato) (PDIPF) han demostrado ser buenos sustratos para la adhesión, el crecimiento y la diferenciación de dos líneas de células osteoblásticas, MC3T3E1 derivadas de células de calvaria ratón y UMR106 osteosarcoma de rata, sugiriendo que estos polímeros pueden ser útiles en la regeneración de tejido óseo. Para obtener un material con buenas propiedades mecánicas y una tasa de degradación intermedia entre ambos homopolímeros se ha preparado una mezcla de PCL y PDIPF compatibilizada por ultrasonido de alta intensidad. Esta mezcla ha demostrado poseer mejores propiedades mecánicas y mayor biocompatibilidad que los homopolímeros correspondientes.
El objetivo de este trabajo es evaluar la actividad de células UMR106 frente a matrices porosas y no porosas de la mezcla de PCL-PFIP compatibilizadas. Las matrices porosas se obtuvieron mediante electrospraying de una solución de la mezcla en cloroformo. Las matrices no porosas se obtuvieron por casting de una solución en cloroformo. Las películas obtenidas se evaluaron por SEM y microscopia óptica, usando el software “Image J” para caracterizarlas morfológicamente. En ambas matrices se realizaron ensayos de adhesión (a 1h), proliferación (a 24 h) y actividad de Fosfatasa Alcalina (ALP) (a 24 y 48 h, control:
superficie de placa de cultivo).
La técnica de electrospraying permitió la obtención de matrices porosas formadas por microgotas tal como se observa mediante SEM. La adhesión y proliferación y la actividad de ALP de las células crecidas sobre las películas aumento significativamente sobre la matriz porosa respecto a la matriz no porosa. El aumento del área superficial proporcionada por la estructura porosa incrementó los marcadores de actividad celular
Qac genes and biocide tolerance in clinical veterinary methicillin-resistant and methicillin-susceptible Staphylococcus aureus and Staphylococcus pseudintermedius
Qac genes are associated with increased tolerance to quaternary ammonium compounds and other cationic biocides such as chlorhexidine. This study aimed to determine whether qac genes and increased biocide tolerance were present in 125 clinical methicillin-resistant and susceptible veterinary staphylococci. A total of 125 methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant and -susceptible Staphylococcus pseudintermedius (MRSP and MSSP) from three archived Australian veterinary staphylococci collections underwent whole genome sequencing, multilocus sequence typing and qac gene screening. Two MRSA isolates (12%) harboured qacA/B genes; both isolates were ST8 from horses. QacJ, qacG and smr genes were identified in 28/90 (31%) MRSP and 1/18 (6%) MSSP isolates. ST71 MRSP was significantly more likely to harbour qac genes than other MRSP clones (p < 0.05). A random subset of 31 isolates underwent minimum bactericidal concentration (MBC) testing against F10SCTM (benzalkonium chloride and biguanide), and HexaconTM (chlorhexidine gluconate), with and without the addition of bovine serum albumin (BSA) as an in vitro substitute for organic matter contamination. Qac genes were not associated with increased phenotypic biocide tolerance but biocide efficacy was significantly affected by the presence of BSA. In the absence of BSA, all MBC values were well below the recommended usage concentration. When BSA was present, regardless of qac gene presence, 50% of MRSA and 43% of MRSP had an F10SCTM MBC above the recommended concentration for general disinfection. Qac genes did not confer increased in vitro biocide tolerance to veterinary staphylococci. Organic matter contamination must be minimized to ensure the efficacy of biocides against MRSA and MRSP
Proximal ischemia is a frequent cause of exercise-induced pain in patients with a normal ankle to brachial index at rest
BACKGROUND: Excluding a vascular origin of exercise-related pain is often difficult in clinical practice. Recent papers have underlined the frequent association of concurrent lumbar spine degenerative disease and peripheral arterial disease. Furthermore, even when suspected, isolated exercise-induced proximal ischemia is difficult to diagnose. Measurement of transcutaneous oxygen pressure (tcpO2) is an interesting and accurate method to differentiate proximal (buttock) from distal (calf) regional blood flow impairment (RBFI) during exercise. OBJECTIVES: We searched for isolated proximal-without-distal RBFI as a possible cause of claudication, in patients with borderline (ABI-b: 0.91 - 0.99) or normal (ABI-n: 1.00 to 1.40) ankle to brachial index at rest. STUDY DESIGN: Retrospective cohort design study. We analyzed patients referred to our laboratory with symptom limiting claudication and an ankle brachial index within normal limits. SETTING: University-based exercise-investigation center. METHODS: Over a 12-year period, we identified 463 patients referred to our laboratory that had their lowest resting ABI between 0.90 and 1.40. The tcpO2 on chest, buttocks, and calves were recorded during treadmill walking tests (3.2 km/h, 10% slope) in 220 ABI-b and 243 ABI-n unique consecutive patients complaining of limiting claudication (each patient\u27s ABI was the lowest of the 2 legs). Limiting claudication was defined as the reported inability to walk 1 kilometer without stopping. A DROP index (limb tcpO2-changes minus chest tcpO2-changes from rest) below -15 mmHg was used to indicate a positive result (i.e. exercise-induced RBFI). RESULTS: Treadmill exercise showed evidence for proximal or distal RBFI, of at least one side, in 128 out of 220 patients (58.2%) and in 86 out of 243 (35.4%) patients with ABI-b and ABI-n, respectively. Isolated proximal-without-distal RBFI was found in 32 out of the 128 (25.0 %) positive tests in ABI-b and 32 out of the 86 (37.2%) positive tests in ABI-n patients. LIMITATIONS: Study limitations include the absence of systematic follow-up of diagnosed patients and absence of systematic search for cardio-respiratory co-morbid conditions. CONCLUSION: Isolated proximal-without distal RBFI is found in approximately one out of 7 patients complaining of symptom limiting claudication with a borderline or normal resting ABI. Exercise-tcpO2 may help to discriminate patients with arterial claudication that could benefit from invasive vascular investigations and procedures
Finite Size and Current Effects on IV Characteristics of Josephson Junction Arrays
The effects of finite size and of finite current on the current-voltage
characteristics of Josephson junction arrays is studied both theoretically and
by numerical simulations. The cross-over from non-linear to linear behavior at
low temperature is shown to be a finite size effect and the non-linear behavior
at higher temperature, , is shown to be a finite current effect.
These are argued to result from competition between the three length scales
characterizing the system. The importance of boundary effects is discussed and
it is shown that these may dominate the behavior in small arrays.Comment: 5 pages, figures included, to appear in PR
Boundary Effects on Dynamic Behavior of Josephson-Junction Arrays
The boundary effects on the current-voltage characteristics in
two-dimensional arrays of resistively shunted Josephson junctions are examined.
In particular, we consider both the conventional boundary conditions (CBC) and
the fluctuating twist boundary conditions (FTBC), and make comparison of the
obtained results. It is observed that the CBC, which have been widely adopted
in existing simulations, may give a problem in scaling, arising from rather
large boundary effects; the FTBC in general turn out to be effective in
reducing the finite-size effects, yielding results with good scaling behavior.
To resolve the discrepancy between the two boundary conditions, we propose that
the proper scaling in the CBC should be performed with the boundary data
discarded: This is shown to give results which indeed scale well and are the
same as those from the FTBC.Comment: RevTex, Final version to appear in Phys. Rev.
Complexification of Gauge Theories
For the case of a first-class constrained system with an equivariant momentum
map, we study the conditions under which the double process of reducing to the
constraint surface and dividing out by the group of gauge transformations
is equivalent to the single process of dividing out the initial phase space by
the complexification of . For the particular case of a phase space
action that is the lift of a configuration space action, conditions are found
under which, in finite dimensions, the physical phase space of a gauge system
with first-class constraints is diffeomorphic to a manifold imbedded in the
physical configuration space of the complexified gauge system. Similar
conditions are shown to hold in the infinite-dimensional example of Yang-Mills
theories. As a physical application we discuss the adequateness of using
holomorphic Wilson loop variables as (generalized) global coordinates on the
physical phase space of Yang-Mills theory.Comment: 25pp., LaTeX, Syracuse SU-GP-93/6-2, Lisbon DF/IST 6.9
Surface and capillary transitions in an associating binary mixture model
We investigate the phase diagram of a two-component associating fluid mixture
in the presence of selectively adsorbing substrates. The mixture is
characterized by a bulk phase diagram which displays peculiar features such as
closed loops of immiscibility. The presence of the substrates may interfere the
physical mechanism involved in the appearance of these phase diagrams, leading
to an enhanced tendency to phase separate below the lower critical solution
point. Three different cases are considered: a planar solid surface in contact
with a bulk fluid, while the other two represent two models of porous systems,
namely a slit and an array on infinitely long parallel cylinders. We confirm
that surface transitions, as well as capillary transitions for a large
area/volume ratio, are stabilized in the one-phase region. Applicability of our
results to experiments reported in the literature is discussed.Comment: 12 two-column pages, 12 figures, accepted for publication in Physical
Review E; corrected versio
LA IMPORTANCIA DE LA DIDÁCTICA EN LA FORMACIÓN DEL PROFESORADO DE CIENCIAS NATURALES
Beginning from a long historical loss of identity of Didactic as a discipline and in consequence, the lack of its presence in the curriculum of teachers, in particular those of natural sciences, considering the critical checking-up, theoretical contributions and investigation in the last decades, Didactic has been reoriented as a discipline which has as object of study and reflection on the practice of teaching in particular context.Luego de un largo proceso histórico signado por la pérdida de identidad de la Didáctica como disciplina -y, en consecuencia de la falta de presencia de la misma en los planes de estudio de los profesorados, en particular de los de Ciencias Naturales-, y a partir de las revisiones críticas, desde aportes teóricos e investigativos en las últimas décadas, la Didáctica se ha reorientado como la disciplina que tiene por objeto el estudio y reflexión sobre las prácticas de la enseñanza en los contextos particulares que las significan
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