Search PubMed⌕ Search

Biomedical subjects

A Hirsch

Publications and source records attributed to A Hirsch.

At least 37 records · Page 2Linked to original sources
PubMed2001

Measurement of inclusive antiprotons from Au+Au collisions at square root of s(NN) = 130 GeV.

We report the first measurement of inclusive antiproton production at midrapidity in Au+Au collisions at square root of s(NN) = 130 GeV by the STAR experiment at RHIC. The antiproton transverse mass distributions in the measured transverse momentum range of 0.25<p( perpendicular)<0.95 GeV/c are found to fall less steeply for more central collisions. The extrapolated antiproton rapidity density is found to scale approximately with the negative hadron multiplicity density.

Journal Article↗
PubMed2001

Model-independent source imaging using two-pion correlations in (2 to 8)a GeV Au+Au collisions.

We report a particle source imaging analysis based on two-pion correlations in high multiplicity Au+Au collisions at beam energies between 2A and 8A GeV. We apply the imaging technique introduced by Brown and Danielewicz, which allows a model-independent extraction of source functions with useful accuracy out to relative pion separations of about 20 fm. The extracted source functions have Gaussian shapes. Values of source functions at zero separation are almost constant across the energy range under study. Imaging results are found to be consistent with conventional source parameters obtained from a multidimensional Hanburg-Brown-Twiss analysis.

Journal Article↗
PubMed2001

Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at square root of (sNN) = 130 GeV.

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1.

Journal Article↗
PubMed2001

Pion Interferometry of square root of (s(NN)) =130 GeV Au + Au collisions at RHIC.

Two-pion correlation functions in Au+Au collisions at square root of [s(NN)] = 130 GeV have been measured by the STAR (solenoidal tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The Hanbury Brown-Twiss parameters display a weak energy dependence over a broad range in square root of [s(NN)].

Journal Article↗
PubMed2001

Midrapidity antiproton-to-proton ratio from Au+Au collisions at sqrt [s(NN)]=130 GeV.

We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4<p(t)<1.0 GeV/c, the ratio is essentially independent of either transverse momentum or rapidity, with an average of 0.65+/-0.01((stat))+/-0.07((syst)) for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the p-p pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.

Journal Article↗
PubMed2001

BN-doped fullerenes: an NICS characterization.

Heterofullerenes C(58)(BN), C(54)(BN)(3), C(48)(BN)(6), and C(12)(BN)(24) and their hexaanions as well as the C(58)(BN) dimer have been investigated by ab initio calculations. On the basis of the computed nucleus independent chemical shifts (NICS) at the cage center and also at the center of individual rings, BN-doped fullerenes C(58)(BN), C(54)(BN)(3), and C(48)(BN)(6) are slightly more aromatic than C(60), whereas the corresponding hexaanions are significantly less aromatic than C(60)(6)(-). The predicted NICS values may be useful for the identification of the heterofullerenes through their endohedral (3)He NMR chemical shifts. Compared to C(60), the dimerization of C(58)(BN) is calculated to be more exothermic by 16 kcal/mol.

Journal Article↗
PubMed2001

Electrophoretic behavior of a highly water-soluble dendro[60]fullerene.

The aim of the present study was to develop an analytical method for measuring amounts of a dendro[60]fullerene (DF) which is a highly water-soluble [60]fullerene derivative. We tried to define a straightforward methodology using capillary zone electrophoresis, a method which, to our knowledge, has not yet been used to that purpose. Preliminary assays showed that DF has almost the same mobility than the electroosmotic flow (EOF) but in the opposite direction. Attempts were carried out to reduce the EOF and positive results were obtained by adding hydroxypropylcellulose to the background electrolyte. In order to define optimal operating conditions, a Taguchi experimental plan was used to study simultaneously the effects of the main parameters that are pH, ionic strength, methanol amount and hydroxypropylcellulose concentration. Two parameters are of the utmost importance as to their effect on the migration time and separation efficiecy: pH and ionic strength whose actions are opposite.

Carbon↗
PubMed2001

Increased brain and atrial natriuretic peptides in patients with chronic right ventricular pressure overload: correlation between plasma neurohormones and right ventricular dysfunction.

OBJECTIVE: To evaluate the role of plasma neurohormones in the diagnosis of asymptomatic or minimally symptomatic right ventricular dysfunction. SETTING: Tertiary cardiovascular referral centre. METHODS: Plasma brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) concentrations were measured in 21 asymptomatic or minimally symptomatic patients with chronic right ventricular pressure overload caused by congenital heart disease, and in seven healthy volunteers. Right ventricular ejection fraction was determined using magnetic resonance imaging. RESULTS: Right ventricular ejection fraction in the volunteers was higher than in the patients (69.0 (8.2)% v 58.0(12.0)%, respectively; p < 0.006). Left ventricular ejection fraction was 72.3(7.8)% in volunteers and 68.1(11.0)% in patients (NS). There was a significant difference between patients and volunteers in the plasma concentrations of BNP (5.3 (3.5) v 2.3 (1.7) pmol/l, respectively; p < 0.009) and ANP (7.3 (4.5) v 3.6 (1.4) pmol/l; p < 0.05). In both patients and volunteers, mean plasma ANP was higher than mean plasma BNP. Right ventricular ejection fraction was inversely correlated with BNP and ANP (respectively, r = 0.65; p < 0.0002 and r = 0.61; p < 0.002). There was no correlation between left ventricular ejection fraction and BNP (r = 0.2; NS) or ANP (r = 0.52; NS). Similarly, no correlation was shown between the level of right ventricular systolic pressure and either plasma BNP (r = 0.20) or plasma ANP (r = 0.07). CONCLUSIONS: There was a significant inverse correlation between right ventricular ejection fraction and the plasma neurohormones BNP and ANP in asymptomatic or minimally symptomatic patients with right ventricular pressure overload and congenital heart disease. Monitoring changes in BNP and ANP may provide quantitative follow up of right ventricular dysfunction in these patients.

Adult↗
PubMed2001

Root coverage and pocket reduction as combined surgical procedures.

BACKGROUND: One of the main objectives of periodontal reconstructive surgery is the coverage of exposed roots due to gingival recession. A large variety of mucogingival grafting procedures are available that give highly predictable and esthetically acceptable results when treating intact root surfaces. However, these procedures call for a second surgery site in the palate. The present study examines a series of cases in which connective tissue, obtained from the tuberosity during pocket reduction procedures in the posterior region of the maxilla, was used for root coverage. METHODS: Forty-four teeth from 25 patients with gingival recession of 3.30 +/- 0.14 mm (mean +/- SEM) were treated with subepithelial connective tissue grafts using connective tissue obtained from the tuberosity area during pocket reduction procedures in the posterior region of the maxilla. RESULTS: The mean root coverage recession after treatment was 0.16 +/- 0.06 mm, with effectiveness of coverage at 95.0% +/- 1.84 and a predictability of 84.1%. Periodontal probing depth reduction at the donor site was 4.08 +/- 0.24 mm. CONCLUSIONS: These results indicate that the subepithelial connective tissue graft obtained from the tuberosity area during pocket reduction procedures in the posterior region of the maxilla provides a very predictable and esthetic root coverage without the need for a second surgical site.

Adult↗
PubMed2001

Increased brain natriuretic peptide as a marker for right ventricular dysfunction in acute pulmonary embolism.

Right ventricular (RV) function is of major prognostic significance in patients with acute pulmonary embolism (PE). The aim of the present study was to evaluate the role of neurohormone plasma brain natriuretic peptide (BNP) in assessing RV function in patients with acute PE. BNP levels were measured in 16 consecutive patients with acute PE as diagnosed by high probability lung scintigraphy or pulmonary angiography. Twelve healthy age-matched volunteers served as controls. All 16 patients underwent standard echocardiography and blood tests during the first hour of presentation. In the patient group, survival was studied for a period of 30 days. Plasma BNP levels in patients with acute PE were higher than in controls (7.2 [95% CI 0.4 to 144.6] versus 1.4[95% CI 0.4 to 4.6] pmol/L, p = 0.0008). Plasma BNP was significantly higher in 5 patients with RV dysfunction compared to II patients with normal RV function (40.2 [95% CI 7.5 to 214.9] versus 3.3 [95% CI 0.4 to 24.9] pmol/L, p = 0.0003). RV systolic pressure was not significantly correlated with BNP (r = 0.42, p = ns). In conclusion, plasma BNP neurohormone levels might be of clinical importance as a supplementary tool for assessment of RV function in patients with acute PE.

Acute Disease↗
PubMed2000

Synthesis, cyclic voltammetry, and photophysical properties of a bridged o-phenylenediamine-C(60) dyad.

The synthesis, complete spectroscopic characterization, cyclic voltammetry, and photophysical measurements of a new o-phenylenediamine-C(60) dyad are described. By using a tether strategy, only a single regioisomer was obtained. Cyclic voltammetry measurements indicate that the two electroactive groups do not interact in their singlet ground states. Photophysical investigations reveal a rapid photoinduced electron transfer between the singlet excited state of the fullerene acceptor and the o-phenylenediamine donor, yielding a charge-separated radical pair.

Journal Article↗
PubMed2000

Electrochemical studies of seven regioisomers of Tris

Seven of the possible 46 constitutional isomers of tris[di(ethoxycarbonyl)methano[60]fullerene have been isolated and their electrochemical properties studied in CH(2)Cl(2). A two-electron controlled potential electrolysis of each of these isomers results in competing retro-Bingel and isomerization reactions with preferential loss of one or two of the addends. PM3 and AM1 computational studies indicate that while the reactivity of neutral precursors is kinetically controlled, charging of the neutral species with two electrons results in an umpolung of reactivity and introduction of thermodynamic control. Lowering the electrolysis temperature increases the proportion of isomerization, and a new tris-isomer never obtained before via synthetic methods has been isolated.

Journal Article↗
PubMed2000

Reactions of e(-)(aq), CO(2)(*)(-), HO(*), O(2)(*)(-) and O(2)((1)delta(g)) with a dendro[60]fullerene and C(60)[C(COOH)(2)](n) (n = 2-6).

Using pulse radiolysis and laser flash photolysis, we have investigated the reactions of the deleterious species, e(-)(aq), HO&z.rad;, O(2)(*)(-) and O(2)((1)Delta(g)) with 10 water-soluble cyclopropyl-fused C(60) derivatives including a mono-adduct dendro[60]fullerene (d) and C(60) derivatives based on C(60)[C(COOH)(2)](n=2-6), some of which are known to be neuroprotective in vivo. The rate constants for reactions of e(-)(aq) and HO&z.rad; lie in the range 0.5-3.3 x 10(10) M(-1) s(-1). The d and bis-adduct monoanion radicals display sharp absorption peaks around 1000 nm (epsilon = 7 000-11 500 M(-1) cm(-1)); the anions of the tris-, tetra-, and penta-adduct derivatives have broader, weaker absorptions. The monohydroxylated radicals have their most intense absorption maxima around 390-440 nm (epsilon = 1000-3000 M(-1) cm(-1)). The anion and hydroxylated radical absorption spectra display a blue-shift as the number of addends increases. The radical anions react with oxygen (k approximately 10(7)-10(9) M(-1) s(-1)). The reaction of O(2)(*)(-) with the C(60) derivatives does not occur via an electron transfer. The rate constants for singlet oxygen reaction with the dendrofullerene and eee-derivative in D(2)O at pH 7.4 are k approximately 7 x 10(7) and approximately 2 x 10(7) M(-1) s(-1) respectively, in contrast to approximately 1.2 x 10(5) M(-1) s(-1) for the reaction with C(60) in C(6)D(6). The large acceleration of the rates for electron reduction and singlet oxygen reactions in water is due to a solvophobic process.

Carbon↗
PubMed2000

Sideward flow in Au+Au collisions between 2A and 8A GeV

Using the large acceptance Time Projection Chamber of experiment E895 at Brookhaven, measurements of collective sideward flow in Au+Au collisions at beam energies of 2A, 4A, 6A, and 8A GeV are presented in the form of in-plane transverse momentum and the first Fourier coefficient of azimuthal anisotropy v(1). These measurements indicate a smooth variation of sideward flow as a function of beam energy. The data are compared with four nuclear transport models which have an orientation towards this energy range. All four exhibit some qualitative trends similar to those found in the data, although none show a consistent pattern of agreement within experimental uncertainties.

Journal Article↗