1,829 research outputs found
Near-infrared spectroscopy study of tourniquet-induced forearm ischaemia in patients with coronary artery disease
Near-Infrared Spectroscopy (NIR) can be employed to monitor local changes in haemodynamics and oxygenation of human tissues. A preliminary study has been performed in order to evaluate the NIRS transmittance response to induced forearm ischaemia in patients with coronary artery disease (CAD). The population consists in 40 patients with cardiovascular risk factors and angiographically documented CAD, compared to a group of 13 normal subjects. By inflating and subsequently deflating a cuff placed around the patient arm, an ischaemia has been induced and released, and the patients have been observed until recovery of the basal conditions. A custom LAIRS spectrometer (IRIS) has been used to collect the backscattered light intensities from the patient forearm throughout the ischaemic and the recovery phase. The time dependence of the near-infrared transmittance on the control group is consistent with the available literature. On the contrary, the magnitude and dynamics of the NIRS signal on the CAD patients show deviations from the documented normal behavior, which can be tentatively attributed to abnormal vessel stiffness. These preliminary results, while validating the performance of the IRIS spectrometer, are strongly conducive towards the applicability of the NIRS technique to ischaemia analysis and to endothelial dysfunction characterization in CAD patients with cardiovascular risk factors.Publisher PD
19F nuclear spin relaxation and spin diffusion effects in the single ion magnet LiYF4:Ho3+
Temperature and magnetic field dependences of the 19F nuclear spin-lattice
relaxation in a single crystal of LiYF4 doped with holmium are described by an
approach based on a detailed consideration of the magnetic dipole-dipole
interactions between nuclei and impurity paramagnetic ions and nuclear spin
diffusion processes. The observed non-exponential long time recovery of the
nuclear magnetization after saturation at intermediate temperatures is in
agreement with predictions of the spin-diffusion theory in a case of the
diffusion limited relaxation. At avoided level crossings in the spectrum of
electron-nuclear states of the Ho3+ ion, rates of nuclear spin-lattice
relaxation increase due to quasi-resonant energy exchange between nuclei and
paramagnetic ions, in contrast to the predominant role played by electronic
cross-relaxation processes in the low-frequency ac-susceptibility.Comment: 27 pages total, 5 figures, accepted for publication, Eur. Phys. J.
Transesterificação de óleo de soja com diversos catalisadores alcalinos.
Amostras de óleo de soja neutralizado e seco foram transesterificadas com etanol comercial a 99,5% na presença de quantidades equivalentes de hidróxido, metóxido, etóxido e gliceróxido de sódio como catalisadores. Com o uso dos três alcóxidos obteve-se a separação do glicerol formado durante a reação, o que não ocorreu com o uso de hidróxido de sódio. O rendimento de sódio, como catalisador na transesterificação, apresenta vantagens econômicas e tecnológicas quando comparado com o hidróxido de sódio.bitstream/item/65433/1/CTAA-DOCUMENTOS-12-TRANSESTERIFICACAO-DE-OLEO-DE-SOJA-COM-DIVERSOS-CATALISADORES-ALCALINOS-FL-021.pd
Fast response and temporal coherent oscillations in small-world networks
We have investigated the role that different connectivity regimes play in the dynamics of a network of Hodgkin-Huxley neurons by computer simulations. The different connectivity topologies exhibit the following features: random topologies give rise to fast system response yet are unable to produce coherent oscillations in the average activity of the network; on the other hand, regular topologies give rise to coherent oscillations, but in a temporal scale that is not in accordance with fast signal processing. Finally, small-world topologies, which fall between random and regular ones, take advantage of the best features of both, giving rise to fast system response with coherent oscillations.We acknowledge G. Laurent, A. Bäcker, M. Bazhenov,
M. Rabinovich, and H. Abarbanel for insightful discussions.
We thank the Dirección General de Enseñanza
Superior e Investigación Científica for financial support
(PB97-1448), the CAM for financial support to L. F. L.,
and the CCCFC (UAM) for the use of computation
resources
Network analysis identifies weak and strong links in a metapopulation system
The identification of key populations shaping the structure and connectivity of metapopulation systems is a major challenge in population ecology. The use of molecular markers in the theoretical framework of population genetics has allowed great advances in this field, but the prime question of quantifying the role of each population in the system remains unresolved. Furthermore, the use and interpretation of classical methods are still bounded by the need for a priori information and underlying assumptions that are seldom respected in natural systems. Network theory was applied to map the genetic structure in a metapopulation system by using microsatellite data from populations of a threatened seagrass, Posidonia oceanica, across its whole geographical range. The network approach, free from a priori assumptions and from the usual underlying hypotheses required for the interpretation of classical analyses, allows both the straightforward characterization of hierarchical population structure and the detection of populations acting as hubs critical for relaying gene flow or sustaining the metapopulation system. This development opens perspectives in ecology and evolution in general, particularly in areas such as conservation biology and epidemiology, where targeting specific populations is crucial
The importance of ultrasound findings in the study of anal pain
ABSTRACT
Objective: endoanal ultrasonography can detect organic causes
of anal pain without pathology on physical examination. The
aim of this study is to evaluate the importance of endoanal ultrasonography
in the diagnosis and therapeutic management of idiopathic
and functional anal pain.
Material and methods: retrospective study, between 15
March 2005 and 15 June 2008, of all patients with proctalgia
and normal examination or with alterations not responsible for
anal pain at proctologic exam that have undergone an endoanal
ultrasonography.
Results: a total of 90 patients were analyzed, with a mean
age of 50.5 years, 58% were female. Twenty-three patients had
functional anal pain clinic criteria. Endoanal ultrasonography revealed
alterations in 49% of patients. The primary findings were
changes in sphincters in 14 patients, followed by anal sepsis in 12
patients, anal fissure in 10 patients, perirectal lesions in 6 patients
and ulcer of the anal canal in 2 patients. Of the patients with
sphincter defects, 5 patients had criteria of chronic anal pain. In
this group of patients, no differences were found in manometric
and defecographic results between the different ultrasound abnormalities.
Conclusions: the endoanal ultrasonography detected occult
organic lesions to proctologic examination, in half the patients
with anal pain. Ultrasound abnormalities were found in 22% of
patients with functional anal pain. However, there was no correlation
between ultrasound findings and physiological studies, and
therefore could not find etiological or pathogenic factors of functional
anal pain
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