10,803 research outputs found
Universal reduction of pressure between charged surfaces by long-wavelength surface charge modulation
We predict theoretically that long-wavelength surface charge modulations
universally reduce the pressure between the charged surfaces with counterions
compared with the case of uniformly charged surfaces with the same average
surface charge density. The physical origin of this effect is the fact that
surface charge modulations always lead to enhanced counterion localization near
the surfaces, and hence, fewer charges at the midplane. We confirm the last
prediction with Monte Carlo simulations.Comment: 8 pages 1 figure, Europhys. Lett., in pres
Production of exotic charmonium in interactions at hadronic colliders
In this paper we investigate the Exotic Charmonium (EC) production in interactions present in proton-proton, proton-nucleus and
nucleus-nucleus collisions at the CERN Large Hadron Collider (LHC) energies as
well as for the proposed energies of the Future Circular Collider (FCC). Our
results demonstrate that the experimental study of these processes is feasible
and can be used to constrain the theoretical decay widths and shed some light
on the configuration of the considered multiquark states.Comment: 7 pages, 2 figures, 3 tables. v2: Revised version published in
Physical Review
Arterial spin labelling: initial experience, clinical impact and difficulties
RESUMO
O arterial spin labeling (ASL) é uma técnica de perfusão por ressonância magnética (RM) que usa os protões das moléculas de água
do sangue arterial como marcador endógeno. As suas principais vantagens residem no facto de ser um método não invasivo, rápido
e que dispensa a administração de contraste. Actualmente os seus resultados são reprodutíveis de modo robusto, o que o torna uma
ferramenta cada vez mais utilizada na prática clínica. O objectivo deste trabalho é apresentar a nossa experiência inicial com o ASL,
salientando os aspectos técnicos, as principais solicitações clínicas, os resultados obtidos e as dificuldades experimentadas.
Métodos: Foi efectuada uma revisão dos exames realizados durante um período de oito meses, usando uma técnica de ASL pulsado,
num aparelho de 3T. A avaliação dos mapas de perfusão foi realizada de modo qualitativo.
Resultados: As principais indicações clínicas para a realização de ASL foram epilepsia, doenças neuro-degenerativas e tumores
intra-parenquimatosos. Embora o ASL não tenha sido, em nenhum dos casos, a principal ferramenta diagnóstica, contribuiu, por
vezes, com dados fisiológicos importantes para o diagnóstico e para a orientação terapêutica. Salientam-se os casos de doentes com
múltiplas crises epilépticas nos quais foi possível identificar focos de hiperperfusão pós-ictal (cujos resultados foram concordantes com
o SPECT). Destacam-se ainda casos de doenças neuro-degenerativas nos quais o ASL identificou áreas de hipoperfusão típicas das
respectivas entidades nosológicas. As principais dificuldades estiveram relacionadas com o carácter qualitativo da avaliação e com a
valorização clínica dos achados.
Conclusão: O estudo da perfusão cerebral por ASL tem um potencial diagnóstico importante. Com este trabalho mostramos que, com
uma aquisição rápida e pós-processamento simples, pode facilmente integrar os estudos de RM de rotina. Abstract
Arterial spin labelling (ASL) is a MR perfusion technique that uses protons from water molecules of the arterial blood as an endogenous
tracer. It is fast, non-invasive and does not require gadolinium administration. Due to the increasing robustness of the results, it is becoming
an important clinical tool.
In this article we present our initial experience with ASL, highlighting some technical aspects, the main clinical applications, some
achieved results and most important difficulties.
Methods: Review of the examinations performed during eight months, using a pulsating ASL technique in a 3T machine. Perfusion
maps were evaluated qualitatively.
Results: The most frequent clinical applications were epilepsy, neurodegenerative disorders and tumours. Although perfusion data
from ASL had never been crucial for diagnosis, it still provided substantial information. We highlight two epileptic patients who had had
recent seizures, in which ASL depicted distinct post-ictal hyperperfusion areas (with the results being confirmed by SPECT studies).
The impact was also remarkable in patients with neurodegenerative disorders in which ASL depicted hypoperfusion areas, typical of
each nosological entity. The main difficulties were related to the lack of quantitative evaluation and to the clinical interpretation of the
results obtained.
Conclusion: ASL perfusion studies have a great potential in several clinical conditions. In this article we show that, with a fast acquisition
and easy post-processing, it can integrate routine MRI examinations
Canalizing Kauffman networks: non-ergodicity and its effect on their critical behavior
Boolean Networks have been used to study numerous phenomena, including gene
regulation, neural networks, social interactions, and biological evolution.
Here, we propose a general method for determining the critical behavior of
Boolean systems built from arbitrary ensembles of Boolean functions. In
particular, we solve the critical condition for systems of units operating
according to canalizing functions and present strong numerical evidence that
our approach correctly predicts the phase transition from order to chaos in
such systems.Comment: to be published in PR
Collaboration networks from a large CV database: dynamics, topology and bonus impact
Understanding the dynamics of research production and collaboration may
reveal better strategies for scientific careers, academic institutions and
funding agencies. Here we propose the use of a large and multidisciplinar
database of scientific curricula in Brazil, namely, the Lattes Platform, to
study patterns of scientific production and collaboration. In this database,
detailed information about publications and researchers are made available by
themselves so that coauthorship is unambiguous and individuals can be evaluated
by scientific productivity, geographical location and field of expertise. Our
results show that the collaboration network is growing exponentially for the
last three decades, with a distribution of number of collaborators per
researcher that approaches a power-law as the network gets older. Moreover,
both the distributions of number of collaborators and production per researcher
obey power-law behaviors, regardless of the geographical location or field,
suggesting that the same universal mechanism might be responsible for network
growth and productivity.We also show that the collaboration network under
investigation displays a typical assortative mixing behavior, where teeming
researchers (i.e., with high degree) tend to collaborate with others alike.
Finally, our analysis reveals that the distinctive collaboration profile of
researchers awarded with governmental scholarships suggests a strong bonus
impact on their productivity.Comment: 8 pages, 8 figure
Note on the point-splitting procedure to evaluate vacuum fluctuation in certain cylindrically symmetric backgrounds
We revisit two-point function approaches used to study vacuum fluctuation in
wedge-shaped regions and conical backgrounds. Appearance of divergent integrals
is discussed and circumvented. The issue is considered in the context of a
massless scalar field in cosmic string spacetime.Comment: REVTeX file, 7 page
Chemical control of stem-end rot on mango fruits in the San Francisco river Valley.
The objective of this study was to assess the efficacy of some fungicides in reducing the incidence of stem-end rot when applied after flowering onset
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