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G David

Publications and source records attributed to G David.

At least 55 records · Page 3Linked to original sources
PubMed2003

Further evidence for the dynamic stability of intracranial saccular aneurysms.

It has long been thought that intracranial saccular aneurysms enlarge and rupture because of mechanical instabilities. Recent nonlinear analyses suggest, however, that at least certain sub-classes of aneurysms do not exhibit quasi-static limit point instabilities or dynamic instabilities in response to periodic loading, and consequently, that the natural history of these lesions is likely governed by growth and remodeling processes. In this paper, we present additional results that support the finding that one particular sub-class of saccular aneurysms is dynamically stable. Specifically, we extended recent results of Shah and Humphrey, which are based on the assumption that some saccular aneurysms can be modeled as spherical elastic membranes surrounded by a viscous cerebrospinal fluid, to account for a viscohyperelastic behavior of the aneurysm. It is shown that inclusion of a "short-term" viscoelastic contribution to the mechanical behavior of an aneurysm serves to increase its dynamic stability against various disturbances.

Aneurysm, Ruptured↗
PubMed2003

Late onset Ommaya reservoir infection due to Staphylococcus aureus: case report and review of Ommaya Infections.

The Ommaya reservoir system has been used for the treatment of chronic central nervous system infections and intracranial tumors for more than three decades. The majority of reported Ommaya reservoir infections occur proximate to the time the device is accessed. A review of the literature reveals that late onset of reservoir infection is quite rare. We report a case of Ommaya reservoir infection due to Staphylococcus aureus that was diagnosed seven years after its insertion and usage for intracerebral non-Hodgkin's lymphoma and review the literature on the microbiology and management of Ommaya reservoir infections.

Adolescent↗
PubMed2002

Flow measurements via two-particle azimuthal correlations in Au + Au collisions at sqrt [s(NN)]=130 GeV.

Two-particle azimuthal correlation functions are presented for charged hadrons produced in Au+Au collisions at the Relativistic Heavy Ion Collider (sqrt [s(NN)]=130 GeV). The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values (v2) show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone epsilon, the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low p(T). A breakdown of this epsilon scaling is observed for charged hadrons with pT >1.0 GeV/c.

Journal Article↗
PubMed2002

Measurement of Lambda and Lambda(macro) particles in Au+Au collisions at the square root of S(NN) = 130 GeV.

We present results on the measurement of Lambda and Lambda(macro) production in Au+Au collisions at square root of (S (NN) = 130 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The Lambda;/Lambda ratios are constant as a function of p(T) and the number of participants. The measured net Lambda density is significantly larger than predicted by models based on hadronic strings (e.g., HIJING) but in approximate agreement with models which include the gluon-junction mechanism.

Journal Article↗
PubMed2002

Net charge fluctuations in Au + Au interactions at sqrt[s(NN)]=130 GeV.

Data from Au + Au interactions at sqrt[s(NN)]=130 GeV, obtained with the PHENIX detector at the Relativistic Heavy-Ion Collider, are used to investigate local net charge fluctuations among particles produced near midrapidity. According to recent suggestions, such fluctuations may carry information from the quark-gluon plasma. This analysis shows that the fluctuations are dominated by a stochastic distribution of particles, but are also sensitive to other effects, like global charge conservation and resonance decays.

Journal Article↗
PubMed2002

Centrality dependence of pi(+/-), K(+/-), p, and (-)p production from sqrt[s(NN)] = 130 GeV Au + Au collisions at RHIC.

Identified pi(+/-), K(+/-), p, and (-)p transverse momentum spectra at midrapidity in sqrt[s(NN)] = 130 GeV Au+Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. Within errors, all midrapidity particle yields per participant are found to be increasing with the number of participating nucleons. There is an indication that K(+/-), p, and (-)p yields per participant increase faster than the pi(+/-) yields. In central collisions at high transverse momenta (p(T) > or =2 GeV/c), (-)p and p yields are comparable to the pi(+/-) yields.

Journal Article↗
PubMed2002

Transverse-mass dependence of two-pion correlations in Au+Au collisions at square root[s(NN)] = 130 GeV.

Two-pion correlations in square root[s(NN)] = 130 GeV Au+Au collisions at RHIC have been measured over a broad range of pair transverse momentum k(T) by the PHENIX experiment at RHIC. The k(T) dependent transverse radii are similar to results from heavy-ion collisions at square root[s(NN)] = 4.1, 4.9, and 17.3 GeV, whereas the longitudinal radius increases monotonically with beam energy. The ratio of the outwards to sidewards transverse radii (R(out)/R(side)) is consistent with unity and independent of k(T).

Journal Article↗
PubMed2002

Measurement of single electrons and implications for charm production in Au+Au collisions at square root[s(NN)] = 130 GeV.

Transverse momentum spectra of electrons from Au+Au collisions at square root[s(NN)] = 130 GeV have been measured at midrapidity by the PHENIX experiment at the Relativistic Heavy Ion Collider. The spectra show an excess above the background from photon conversions and light hadron decays. The electron signal is consistent with that expected from semileptonic decays of charm. The yield of the electron signal dN(e)/dy for p(T) > 0.8 GeV/c is 0.025+/-0.004(stat)+/-0.010(syst) in central collisions, and the corresponding charm cross section is 380+/-60(stat)+/-200(syst) microb per binary nucleon-nucleon collision.

Journal Article↗
PubMed2002

Transscleral Coulomb-controlled iontophoresis of methylprednisolone into the rabbit eye: influence of duration of treatment, current intensity and drug concentration on ocular tissue and fluid levels.

The major problems associated with the use of corticosteroids for the treatment of ocular diseases are their poor intraocular penetration to the posterior segment when administered locally and their secondary side effects when given systemically. To circumvent these problems more efficient methods and techniques of local delivery are being developed. The purposes of this study were: (1) to investigate the pharmacokinetics of intraocular penetration of hemisuccinate methyl prednisolone (HMP) after its delivery using the transscleral Coulomb controlled iontophoresis (CCI) system applied to the eye or after intravenous (i.v.) injection in the rabbit, (2) to test the safety of the CCI system for the treated eyes and (3) to compare the pharmacokinetic profiles of HMP intraocular distribution after CCI delivery to i.v. injection. For each parameter evaluated, six rabbit eyes were used. For the CCI system, two concentrations of HMP (62.5 and 150mg ml(-1)), various intensities of current and duration of treatment were analyzed. In rabbits serving as controls the HMP was infused in the CCI device but without applied electric current. For the i.v. delivery, HMP at 10mg kg(-1)as a 62.5mg ml(-1)solution was used. The rabbits were observed clinically for evidence of ocular toxicity. At various time points after the administration of drug, rabbits were killed and intraocular fluids and tissues were sampled for methylprednisolone (MP) concentrations by high pressure liquid chromatography (HPLC). Histology examinations were performed on six eyes of each group. Among groups that received CCI, the concentrations of MP increased in all ocular tissues and fluids in relation to the intensities of current used (0.4, 1.0 and 2.0mA/0.5cm(2)) and its duration (4 and 10min). Sustained and highest levels of MP were achieved in the choroid and the retina of rabbit eyes treated with the highest current and 10min duration of CCI. No clinical toxicity or histological lesions were observed following CCI. Negligible amounts of MP were found in ocular tissues in the CCI control group without application of current. Compared to i.v. administration, CCI achieved higher and more sustained tissue concentrations with negligible systemic absorption. These data demonstrate that high levels of MP can be safely achieved in intraocular tissues and fluids of the rabbit eye, using CCI. With this system, intraocular tissues levels of MP are higher than those achieved after i.v. injection. Furthermore, if needed, the drug levels achieved with CCI can be modulated as a function of current intensity and duration of treatment. CCI could therefore be used as an alternative method for the delivery of high levels of MP to the intraocular tissues of both the anterior and posterior segments.

Animals↗
PubMed2002

Low-background gamma spectrometry for environmental radioactivity.

Development and performance of a low-background gamma-ray spectrometer are described. The spectrometer consists of a 131% efficient Ge detector in U-type configuration. The passive shielding consists of ultrapure lead of 6" thickness. A top muon guard is used as an active shielding. The spectrometer and shielding are positioned inside a steel room made of 6"-thick pre-World War II iron. The steel room is located underground with 33 m of water-equivalent overburden. The total integrated background rate in the energy range 50-2,700 keV was measured at 0.068 counts per second per 100 cm3 Ge volume. The spectrometer serves as a reference instrument for low-level and highly accurate environmental radioactivity measurements. One specific application of 228Ra determination in drinking water is described. With a 1 l water sample, 1-step chemical procedure, and 1,000 min counting time, a detection limit Ld = 20 mBq/l (0.55 pCi/l) was reached, which meets the EPA mandated limit of 1 pCi/l. Methods of upgrading the spectrometer as well as the predicted improvements in 228Ra detection, including direct counting of water without chemical processing, are discussed.

Journal Article↗
PubMed2002

The osteodystrophy of mucolipidosis type III and the effects of intravenous pamidronate treatment.

Mucolipidosis type III (ML III; McKusick 252600) is a rare lysosomal storage disease in which skeletal involvement is prominent, in particular the destruction of vertebral bodies and the femoral heads. We describe studies in two siblings with ML III that suggest the presence of a distinct metabolic bone disorder. Biochemical indices of bone turnover were increased, and transiliac bone biopsy demonstrated both trabecular osteopenia and marked subperiosteal bone resorption. Intravenous pamidronate treatment given monthly for a year was well tolerated and produced dramatic clinical effects, with reduction in bone pain and improvements in mobility, despite incomplete suppression of bone resorption as assessed by biochemical, radiographic and histological criteria. Bisphosphonate therapy may have an important role in the management of bone pain in ML III, as it does in the related lysosomal disorder of Gaucher disease.

Absorptiometry, Photon↗
PubMed2002

[Legislative framework of embryo research].

The French bioethics law promulgated in 1994 and still in force prohibits nearly all forms of research on the human embryo. However, the concept of the patient-embryo developed in this discussion demonstrates that it is medically mandatory to proceed with such research. The project presented by the government in accordance with the obligatory revision of the 1994 law which was adopted by the Parliament in January 2002 accepts the principle of research on the embryo and embryo cells. An Agency for embryology, human reproduction, and human genetics (APEGH) will be in charge of controlling these activities.

Adult↗
PubMed2001

Suppression of hadrons with large transverse momentum in central Au+Au collisions at root square[s(NN)] = 130 GeV.

Transverse momentum spectra for charged hadrons and for neutral pions in the range 1 GeV/c<p(T)<5 GeV/c have been measured by the PHENIX experiment at RHIC in Au+Au collisions at root square[s(NN)] = 130 GeV. At high p(T) the spectra from peripheral nuclear collisions are consistent with scaling the spectra from p+p collisions by the average number of binary nucleon-nucleon collisions. The spectra from central collisions are significantly suppressed when compared to the binary-scaled p+p expectation, and also when compared to similarly binary-scaled peripheral collisions, indicating a novel nuclear-medium effect in central nuclear collisions at RHIC energies.

Journal Article↗
PubMed2001

Membrane heparan sulfate proteoglycan-supported FGF2-FGFR1 signaling: evidence in support of the "cooperative end structures" model.

Fibroblast growth factor 2 (FGF2)-initiated FGF receptor (FGFR)-signaling requires the assistance of heparin/heparan sulfate. Here, we evaluated the effects of different heparan sulfate proteoglycan (HSPG)-expressing cell lines and HSPGs derived from these cells on FGF2-induced FGFR1-phosphorylation in heparan sulfate-negative BaF3 cells. HSPGs supplied in membrane-associated form, by presenting cells, were all effective promotors of FGF2-initiated FGFR1 phosphorylation, independently of their nature (syndecan/glypican) or cellular origin (human lung fibroblasts, transfected Namalwa cells, or transfected K562 cells). A treatment with heparitinase initially stimulated, but finally completely inhibited, the activity of these presenting cells. In comparison, equivalent amounts of soluble HSPGs, obtained by trypsinization of these cells or by immunopurification from cell extracts, did not promote FGF2-induced FGFR1-phosphorylation, yet removal of the less anionic species or a further treatment with heparitinase converted these soluble fractions into potent activators of FGF2/FGFR1 signaling. Extrapolating from current structural models, we suggest that FGFR dimerization and autophosphorylation is supported by cooperative "heparin-like end structures," and that cell surface association and concentration compensate for the relative scarcity of such end structures in native HSPGs. In this model, "proteolytic" shedding of heparan sulfate would act as a diluting, down-regulatory mechanism, while "heparanolytic" shedding might act as an up-regulatory mechanism, by increasing the concentration of these end structures.

Fibroblast Growth Factor 2↗
PubMed2001

Measurement of the midrapidity transverse energy distribution from square root of [(s)NN] = 130 GeV Au + Au collisions at RHIC.

The first measurement of energy produced transverse to the beam direction at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory is presented. The midrapidity transverse energy density per participating nucleon rises steadily with the number of participants, closely paralleling the rise in charged-particle density, such that / remains relatively constant as a function of centrality. The energy density calculated via Bjorken's prescription for the 2% most central Au+Au collisions at square root[s(NN)] = 130 GeV is at least epsilon(Bj) = 4.6 GeV/fm(3), which is a factor of 1.6 larger than found at sqrt[s(NN)] = 17.2 GeV ( Pb+Pb at CERN).

Journal Article↗
PubMed2001

Centrality dependence of charged particle multiplicity in Au-Au collisions at square root of (s)NN = 130 GeV.

We present results for the charged-particle multiplicity distribution at midrapidity in Au-Au collisions at square root of [s(NN)] = 130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find dN(ch)/d eta(vertical line eta = 0) = 622+/-1(stat)+/-41(syst). The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.

Journal Article↗