Biomedical subjects

A Ron

Publications and source records attributed to A Ron.

At least 19 recordsLinked to original sources

PubMed2002

Hydrodynamic flow of ions and atoms in partially ionized plasmas.

We have derived the hydrodynamic equations of motion for a partially ionized plasma, when the ionized component and the neutral components have different flow velocities and kinetic temperatures. Starting from the kinetic equations for a gas of ions and a gas of atoms we have considered various processes of encounters between the two species: self-collisions, interspecies collisions, ionization, recombination, and charge exchange. Our results were obtained by developing a general approach for the hydrodynamics of a gas in a binary mixture, in particular when the components drift with respect to each other. This was applied to a partially ionized plasma, when the neutral-species gas and the charged-species gas have separate velocities. We have further suggested a generalized version of the relaxation time approximation and obtained the contributions of the interspecies encounters to the transport equations.

Journal Article↗

PubMed2001

Plasma dynamics in capillary discharge soft x-ray lasers.

The dynamics and stability of collapsing gas columns, generated by a fast capillary discharge setup, are studied for obtaining soft x-ray amplification in highly ionized ions. Electron temperature and density measurements at the peak of the compression stage are used for tuning the discharge parameters. Once the needed conditions were achieved, strong amplification of the 3s-3p transition in Ne-like Ar ions at 469 A is observed. A gain coefficient of >0.75 cm(-1) and a beam divergence of <5 mrad are measured along plasma columns of <150 microm diameter and up to 165 mm length.

Journal Article↗

PubMed2000

[Cortical blindness following coronary angiography].

Cortical blindness has been occasionally reported as a complication after cerebral angiography, but is rare after coronary angiography. The contrast agent is believed to be responsible for the sudden development of blindness. Although the exact mechanism is unknown, it appears that the contrast agent disrupts the blood brain barrier, mostly in the occipital areas. We report a 77-year-old man who suddenly developed transient, bilateral cortical blindness 4 hours after coronary angiography. Using contrast enhancement, the CT scan showed typical, symmetrical involvement of both occipital lobes. There were no other neurological deficits. Vision and CT findings returned to normal within 48 hours.

Aged↗

PubMed2000

Negatively charged quantum well polaritons in a GaAs/AlAs microcavity: An analog of atoms in a cavity

The negatively charged exciton (X-) is observed to strongly couple with the microcavity- (MC-)confined photons in a GaAs quantum well containing a two-dimensional electron gas with 0<n(e)</=3x10(10) cm(-2). This strong coupling results in a formation of charged polaritons. The coupling strength is found to depend on sqrt[n(e)], in analogy to two-level atoms in a cavity. The analysis of the reflection and photoluminescence spectra shows that X- is strongly admixed with the neutral exciton via their coupling with the MC photons. The linewidth dependence on n(e) indicates that electron-polariton scattering is effective.

Journal Article↗

PubMed1999

Cell pairing and methylation in Tetrahymena thermophila are altered by exogenous homocysteine.

Homocysteine is causally associated with birth defects such as spina bifida, and with premature vascular disease. We have investigated the effects of homocysteine on a cell-cell interaction in a fundamental eukaryotic system, the free-living ciliate Tetrahymena. Exogenously added homocysteine inhibits cell pairing in a dose-dependent manner. These effects are exacerbated by adenosine, which by itself has little demonstrable influence on pairing. S-adenosylhomocysteine (SAH) is a product of the reaction between adenosine and homocysteine, and is an inhibitor of methyl transferases. We therefore predicted that protein methylation would be significantly inhibited by homocysteine. A direct test of that hypothesis involved a demonstration that incorporation of an isotopically labeled methyl group from methionine into proteins was significantly reduced by homocysteine. The undermethylated proteins are of low molecular weight, and might correspond to known methylatable signaling proteins. We show that vanadate, an inhibitor of protein phosphatase, also inhibits cell pairing, and that the effects of vanadate and homocysteine are additive. This is the first demonstration that methylation and possibly phosphorylation play a regulatory role in cell-cell interactions in ciliates.

Animals↗

PubMed1999

NGOs in community health insurance schemes: examples from Guatemala and the Philippines.

In poor rural communities, access to basic health care is often severely limited by inadequate supply as well as financial barriers to seeking care. National policies may introduce social health insurance, but these are likely to begin with the salaried public and private sector workers while the informal sector population may be the last to be covered. Community initiatives to generate health care financing require a complex development process. This paper covers attempts to develop such schemes in rural populations in Guatemala and the Philippines through non-government organizations and notes the major factors which have contributed to unequal progress in the two schemes. The scheme of the Association por Salud de Barillas (ASSABA) in Guatemala was not sufficiently established as an administrative body at the conceptual stage and there was no clear national policy on health care financing. By the time the necessary action was taken, local conflicts hindered progress. In the Philippines, the ORT Health Plus Scheme (OHPS) was implemented during the period of legislation of a national health insurance act. The appraisal after three years of operation shows that OPHS has made health care affordable and accessible to the target population, composed mainly of low and often unstable income families in rural areas. The major success factors are probably the administrative structure provided by a cooperative and controls in the delivery system and in expenditures, through the salaried primary health care team, referral process and the capitation agreement for hospital-based services. The proliferation of such schemes could benefit from national guidelines, a formal accreditation process and an umbrella organization to provide assistance in design, training and information services, involving government, non-government and academic institutions as an integral part of the development process.

Accreditation↗

PubMed1999

The reform of the rural cooperative medical system in the People's Republic of China: interim experience in 14 pilot counties.

During the 1960's and 1970's the Chinese government encouraged the 'rural cooperative medical systems' (RCMS), in order to ensure access to basic health care among the rural population. There was a break in the development of the RCMS in the early 1980's, as a consequence of market economic reforms. These reforms involved a shift from a communal to a household production system. As a result the collective way of financing rural health care was more or less abandoned. However, the government of the People's Republic of China was aware of the need to provide social protection against health care expenses. In March 1994 the government initiated a project to reestablish the RCMS. This project was implemented on a pilot basis in 14 counties of seven provinces. The reestablishment of the RCMS would be guided by the basic principles of health insurance. In October 1995, a first mid-term evaluation of the RCMS Project was held. One of the major research questions concerned the extent to which the RCMS had reduced the risk of paying health care bills that would otherwise be a burden on families. This article addresses this question and assesses the results obtained after two years of RCMS experimental work. A general finding is that the population structure by occupation and income varies, and that the RCMS has adapted itself to this variety. It is also confirmed that the burden of health care costs on families was reduced, more so in some counties than in others, but this reduction has been modest. The research results indicate that there is ample room for improvement. The outlook is hopeful, however. At the national level, there is now systematic thinking about RCMS. The current RCMS work is also having a considerable influence on other counties that are keen to reestablish the RCMS.

China↗

PubMed1998

Prediction of successful induction of labor: comparison of transvaginal ultrasonography and the Bishop score.

OBJECTIVE: To determine whether transvaginal ultrasonography of the cervix before induction of labor is a better predictor of successful induction than the Bishop score. STUDY DESIGN: Eighty-six consecutive patients scheduled for induction of labor underwent digital cervical examination followed by transvaginal ultrasonography to measure cervical length and to determine the presence of wedging. Patients were induced with either oxytocin or intracervical prostaglandin E2 gel followed by oxytocin when required. The agent for induction was selected on the basis of the digital examination. The primary outcome criteria were successful induction and the duration of labor. RESULTS: Successful induction and the duration of labor were significantly associated with the Bishop score and cervical length. Cervical wedging was associated only with successful induction. However, in a logistic regression model that included these parameters as independent variables, only the Bishop score and parity were significantly correlated with successful induction and the duration of labor. CONCLUSIONS: Transvaginal ultrasonographic evaluation of the cervix before induction of labor does not improve the prediction of cervical inducibility obtained by the Bishop score.

Adult↗

PubMed1996