PubMed Health⌕ Search

Biomedical subjects

Y Lifshitz

Publications and source records attributed to Y Lifshitz.

At least 19 recordsLinked to original sources
PubMed2005

Structures and energetics of hydrogen-terminated silicon nanowire surfaces.

The analysis and density-functional tight-binding simulations of possible configurations of silicon nanowires (SiNWs) enclosed by low-index surfaces reveal a number of remarkable features. For wires along <100>, <110>, and <111> directions, many low-index facet configurations and cross sections are possible, making their controlled growth difficult. The 112 wires are the most attractive for research and applications because they have only one configuration of enclosing low-index facets with a rectangular cross section, enclosed with the most stable (111) facet and the (110) facet next to it. In general, the stability of the SiNWs is determined by a balance between (1) minimization of the surface energy gamma(111) svr(rectangular)>svr(triangular)]. The energy band gaps follow the order of <100>wires > <112>wires > <111>wires > <110>wires. The results are compared with our recent scanning tunneling microscopy and transmission electron microscopy data.

Journal Article↗
PubMed2004

Visualization of diamond nucleation and growth from energetic species.

The mystery of diamond nucleation by energetic species is resolved via a special deposition scheme. The evolution of the precursor material for diamond nucleation and the development of the nanodiamond crystallites are visualized by high resolution electron microscopy and other spectroscopies. The diamond precipitation and growth are explained in terms of our recently proposed mechanism [Science 297, 1531 (2002)]]: (i) precipitation of sp(3) clusters a small fraction of which are perfect diamond; (ii) growth of diamond crystallites by preferential displacement of amorphous carbon atoms leaving diamond atoms intact. This general scheme is applicable to other materials such as cubic boron nitride.

Journal Article↗
PubMed2002

The mechanism of diamond nucleation from energetic species.

A model for diamond nucleation by energetic species (for example, bias-enhanced nucleation) is proposed. It involves spontaneous bulk nucleation of a diamond embryo cluster in a dense, amorphous carbon hydrogenated matrix; stabilization of the cluster by favorable boundary conditions of nucleation sites and hydrogen termination; and ion bombardment-induced growth through a preferential displacement mechanism. The model is substantiated by density functional tight-binding molecular dynamics simulations and an experimental study of the structure of bias-enhanced and ion beam-nucleated films. The model is also applicable to the nucleation of other materials by energetic species, such as cubic boron nitride.

Journal Article↗
PubMed2001

Nanostructure. Epitaxial diamond polytypes on silicon.

Carbon is unique in the variety of configurations it can adopt with itself and other elements. Here we show how ion beams can be used to nanostructure various diamond polytypes, epitaxially aligning them to a silicon substrate. The ready controllability of ion beams, which are already used to manufacture submicrometre-scale devices, means that our findings should enable new carbon and non-carbon materials to be nanostructured for a host of applications.

Journal Article↗
PubMed2000

A nucleation site and mechanism leading to epitaxial growth of diamond films

A diamond nucleation site responsible for epitaxial growth of diamond on silicon by chemical vapor deposition (CVD) is identified in high-resolution transmission electron microscopic images. Other sites in the same sample leading to polycrystalline growth, but deleterious to epitaxial CVD growth, are also described. A mechanism for the heteroepitaxial growth of diamond is suggested, in which etching of the nondiamond carbon binder exposes and removes nonadherent nanodiamond nuclei, leaving intact only those directly nucleated on the silicon substrate. This work enhances our understanding of diamond nucleation and heteroepitaxial growth and its potential applications.

Journal Article↗
PubMed2000

Higher than expected carrier rates for familial Mediterranean fever in various Jewish ethnic groups.

Familial Mediterranean fever (FMF) is an autosomal recessive disease characterised by recurrent attacks of inflammation of serosal membranes. Amyloidosis leading to renal failure is the most severe complication in untreated patients. In Israel FMF is most frequent among Jews of North African origin. Recently the causative gene (MEFV) has been found and the common mutations characterised. The aim of this study was to investigate the carrier rates of the common MEFV mutations among 400 healthy members of four different ethnic groups (100 in each group) in Israel, and to compare the distribution of the different mutations between FMF carriers and patients. We found a high frequency of carriers among Jews from the various ethnic groups. In North African Jews it was 22%, in Iraqi Jews 39%, in Ashkenazi Jews 21%, and in Iranian Jews 6%. The distribution of the four most common MEFV mutations among healthy individuals (M694V 29%, V726A 16%, M6801 2% and E148Q 53%) was significantly different (P < 0.003) from that found in patients (M694V 84.4%, V726A 9.0%, M6801 0% and E148Q 6.6%). Six healthy asymptomatic individuals were found to carry mutations in both alleles: two homozygotes for E148Q and four compound heterozygotes E148Q/other. These results demonstrate a very high carrier rate among all Jewish ethnic groups. They confirm that mutation E148Q is associated with a milder phenotype, which explains the lower prevalence of FMF among the Ashkenazi and Iraqi Jews. This study raises the question of the need for molecular screening for M694V homozygotes in the Israeli North African Jewish community.

Adult↗
PubMed2000

Role of metal ions in coupling between chemical catalysis and conformational changes in ATP synthase.

Isolated chloroplast ATP synthase (CF0F1) was used for determination of the structure-function relation by measuring the effect of divalent metal ions on the properties of ATPase. Mg2+ ions were more efficient catalysts than Ca2+ ions as indicated by Kcat/Km of 55.2 and 5.4, respectively. Other activity parameters related to binding, such as the Km of MATP and Ki of MADP, indicated a stronger binding in the presence of Mg2+ as seen from a Mg2+/Ca2+ ratio of 2.8 and 3.8, respectively. Strong binding of Ca2+ ions with a Kd of 0.03 +/- 00.6 microM-1 was detected only in the presence of ADP probably because of the positive interactive effect of CaADP as indicated in the inhibition properties. Mg2+ ions were more efficient catalysts also in other forms of the enzyme such as in the thylakoid membrane, in isolated CF0F1 and in CF1. The Mg2+/Ca2+ ratio of Kcat/Km was 5.3, 10.2 and 1.5 for the thylakoid membrane enzyme, the isolated CF0F1 and the soluble CF1 respectively. This indicated that Ca2+ ions became less efficient catalysts in the more intact and integrated enzyme while Mg2+ ions were as efficient in all forms of the enzyme. Unlike Mg2+, Ca2+ ions also did not support proton-coupled ATP synthesis and ATP driven proton pumping. It is suggested that the differences in the ligand structure of these two ions might be the reason for the differential function. An average 0.3 A shorter bond length of octahedral first coordination in Ca2+ ions caused a weaker binding of CaATP than that of MgATP. The effect of differential binding is discussed in relation to the binding of the transition state intermediate and to the rate of product release.

Catalysis↗
PubMed1992

Inhibition of chloroplast CF1-ATPase by vanadate.

Inhibition of ATPase activity by vanadate, having K1/2 of 0.5 mM, was demonstrated in the CF1-ATPase. The Ca(2+)-dependent ATPase activity of the isolated enzyme was inhibited in an allosteric manner by vanadate with a Hill coefficient of 3.19 +/- 0.6. Vanadate also inhibited ATPase and Pi-ATP exchange activities of the chloroplast membrane-bound enzyme. Using 51V NMR it was demonstrated that ATP caused partial release of about 1.87 equivalents while ADP caused additional binding of approximately 1.46 equivalents of vanadate, when added to a solution containing CF1 equilibrated with vanadate. The relevance of these results to a possible involvement of a pentacovalent phosphate as transition state intermediate in the hydrolysis of ATP by CF1-ATPase is discussed.

Adenosine Diphosphate↗
PubMed1992

[Prostatic specific antigen for detection and monitoring of prostatic cancer].

Prostatic specific antigen (PSA) can be detected in normal and benign hypertrophic prostates, as well as in prostatic cancer and its metastases. Since it appears in the serum, this glycoprotein has become an established marker for the detection and monitoring of prostate cancer. Using a radioimmunoassay (CIS--Biointernational, France), we found serum PSA levels higher than 4 ng/ml in 55 of 58 patients with prostatic cancer. The concentrations were proportional to tumor stage: significantly higher in stages C and D than in stages A and B (p less than 0.002). In all 6 cases with occult prostatic carcinoma (stage A), levels were higher than 15 ng/ml. PSA was found to be a good indicator of response to therapy, as well as a marker of tumor progression during follow-up. After radical prostatectomy serum PSA levels decreased to below 1 ng/ml. Following radiotherapy levels returned to normal within 1-6 months in 8 of 11 patients. In 21 of 23 with metastases serum PSA decreased during hormonal treatment. In 3 who responded initially to hormonal therapy, levels increased before clinical manifestation of tumor progression. We conclude that PSA is a sensitive serum marker for the diagnosis of prostatic cancer in cases of metastatic disease of unknown origin, as well as for monitoring the response to treatment of prostatic carcinoma. The use of PSA serum levels for screening for prostatic cancer is still controversial.

Antigens, Neoplasm↗
PubMed1991

Spheroplast-derived membrane vesicles from Rhodobacter capsulatus cells catalyzing nucleotide transport.

Rodobacter capsulatus cells, which were cultured anaerobically in high light intensity, had fewer foldings in the cytoplasmic membrane than those which were grown in lower light intensities. Spheroplast-derived membrane fractions obtained from cells cultured under high light intensity contained a high yield of large right-side-out membrane vesicles. The right-side-out vesicles catalyzed reversible light-induced proton efflux as did intact cells. Nucleotide transport activity was also catalyzed by these membrane vesicles. This activity was indirectly monitored by measurement of photophosphorylation or hydrolysis of externally added diphospho- and triphosphonucleosides. These enzymatic activities occur inside the cytoplasmic membrane of spheroplasts and membrane vesicles and therefore require the transport of the externally added reagents. The indirect measurements of transport were complemented by the demonstration of direct uptake of radiolabeled nucleotides into the membrane vesicles. These data support the suggestion that a nucleotide transporter located in the cytoplasmic membrane of R. capsulatus bacteria mediates these activities.

Adenosine Diphosphate↗
PubMed1989

Nucleotide transport in Rhodobacter capsulatus.

Cytoplasmic membrane vesicles isolated from the gram-negative photosynthetic bacterium Rhodobacter capsulatus catalyzed the transport of nucleotides. No transport occurred in the intact bacteria unless they were pretreated with EDTA. The transport rate was measured by incorporation of radioactive phosphate into externally added ADP or by incorporation of nonradioactive phosphate into added labeled ADP. The catalytic activities which utilized the added ADP were photosynthetic ATP synthesis, Pi-ADP exchange, and adenylate kinase. These activities were shown to occur on the cytoplasmic side of the internal membrane. The products were found in the outer medium. The rate of nucleotide transport across the membranes was comparable to the rate of photophosphorylation. These results indicated that nucleotides can be transported across the cytoplasmic membrane but not across the outer membrane of the native R. capsulatus cell. Therefore, by analogy to the mitochondrial ATP-ADP translocator, the exchange might function as an energy transfer system to the periplasm of these bacteria.

Adenine Nucleotides↗
PubMed1987

Fertility following conservative surgery for tubal pregnancy.

Eighty seven conservative surgical interventions for unruptured tubal pregnancy were performed on 83 patients. Salpingotomy was performed in 66 cases and expression of tubal pregnancy in 21 cases. In this patient group, 76.7% (56 out of 73) experienced intra-uterine pregnancy following surgery and 71.2% (52 out of 73) had a live birth. The recurrence rate of tubal pregnancy was 12.3%. Of the 42 patients with a normal contralateral tube, 36 (85.7%) had an intra-uterine pregnancy, 80.9% had a live birth and 7.1% had a recurrent tubal pregnancy. Sixty percent of the patients who underwent operation on their single tube, had a live birth and 66.6% had an intra-uterine pregnancy; the recurrence of tubal pregnancy in this group was 26.6%. No recurrence of tubal pregnancy was found in the group of patients who underwent expression of tubal gestation. It is suggested that the expression of tubal gestation (milking) is a safe procedure for conserving future fertility, and that the indications for conservative surgical management in patients with unruptured tubal gestation should be broadened to include all patients interested in future pregnancies, regardless of the current state of the contralateral tube.

Adolescent↗