Biomedical subjects

V Werner

Publications and source records attributed to V Werner.

17 recordsLinked to original sources

PubMed2006

Identification of mixed-symmetry states in an odd-mass nearly spherical nucleus.

The low-spin structure of 93Nb has been studied using the (n,n'gamma) reaction at neutron energies ranging from 1.5 to 3 MeV and the 94Zr(p,2ngamma)93Nb reaction at bombarding energies from 11.5 to 19 MeV. States at 1779.7 and 1840.6 keV, respectively, are proposed as mixed-symmetry states associated with the pi2p(1/2)-1x(2(1),MS+,94Mo) coupling. These assignments are derived from the observed M1 and E2 transition strengths to the 2p(1/2)-1x(2(1)+,94Mo) symmetric one-phonon states, energy systematics, spins and parities, and comparison with shell model calculations.

Journal Article↗

PubMed2005

Decay of 1+ states as a new probe of the structure of 0+ shape isomers.

The nuclides 98Mo and 100Mo have been studied in photon-scattering experiments by using bremsstrahlung produced from electron beams with kinetic energies from 3.2 to 3.8 MeV. Six electromagnetic dipole transitions in 98Mo and 19 in 100Mo were observed for the first time in the energy range from 2 to 4 MeV. A specific feature in the two nuclides is the de-excitation of one state with spin J = 1 to the 0+ ground state as well as to the first excited 0+ state, which cannot be explained in standard models. We present a model that allows us to deduce the mixing coefficients for the two 0+ shape-isomeric states from the experimental ratio of the transition strengths from the J = 1 state to the 0+ ground state and to the 0+ excited state.

Journal Article↗

PubMed2004

Alternative interpretation of sharply rising E0 strengths in transitional regions.

It is shown that strong 0(+)(2)-->0(+)(1) E0 transitions provide a clear signature of phase transitional behavior in finite nuclei. Calculations using the interacting-boson approximation (IBA) show that these transition strengths exhibit a dramatic and robust increase in spherical-deformed shape transition regions, that this rise matches well the existing data, that the predictions of these E0 transitions remain large in deformed nuclei, that they arise from the specific d-boson coherence in the wave functions, and do not necessarily require the explicit mixing of normal and intruder configurations from different IBA spaces.

Journal Article↗

PubMed2002

Triple point of nuclear deformations.

We show that the second-order phase transition between spherical and deformed shapes of atomic nuclei is an isolated point following from the Landau theory of phase transitions. This point can occur only at the junction of two or more first-order phase transitions which explains why it is associated with one special type of structure and requires the recently proposed first-order phase transition between prolate and oblate nuclear shapes. Finally, we suggest the first empirical example of a nucleus located at the isolated triple-point.

Journal Article↗

PubMed2001

Quantum phase transition for gamma-soft nuclei.

We examine a quantum phase transition in gamma-soft nuclei, where the O(6) limit is simultaneously a dynamical symmetry of the U(6) group of the interacting boson model and a critical point of a prolate-oblate phase transition. This is the only example of phase transitional behavior that can be described analytically for a finite s,d boson system.

Journal Article↗

PubMed1985

Role of beta-lactamases and outer membrane proteins in multiple beta-lactam resistance of Enterobacter cloacae.

The chromosomal beta-lactamase and outer membrane proteins of Enterobacter cloacae were examined to determine their relative contributions to multiple antibiotic resistance in this organism. Mutants altered in beta-lactamase expression, whether derived in the laboratory or recovered from patients treated with one of the new beta-lactam antibiotics, were found to have no detectable alterations in outer membrane proteins. Derepression of beta-lactamase in these mutants was associated with high-level resistance to multiple beta-lactam antibiotics, while loss of inducible beta-lactamase (i.e., production of basal enzyme levels only) was associated with acquisition of susceptibility to many beta-lactam antibiotics, including cephalothin. In contrast, alteration in outer membrane proteins was associated with only moderate-level resistance to beta-lactam antibiotics. However, this included resistance to such drugs as amdinocillin and Sch 34343, which were unaffected by derepression of beta-lactamase. Resistance to chloramphenicol and tetracycline also accompanied changes in outer membrane proteins. Although the outer membrane proteins of various strains of E. cloacae were similar, there did appear to be some major strain-to-strain variations. Thus, it appears that alterations in both beta-lactamase and outer membrane proteins can affect the susceptibility of E. cloacae to many antibiotics. However, alterations in beta-lactamase alone are sufficient to produce high-level multiple beta-lactam resistance in this organism.

Anti-Bacterial Agents↗

PubMed1984

Selection of multiple antibiotic resistance by quinolones, beta-lactams, and aminoglycosides with special reference to cross-resistance between unrelated drug classes.

The ability of three quinolones, two beta-lactams, and one aminoglycoside to select resistant mutants was examined in tests with 30 isolates of commonly encountered nosocomial pathogens. Ciprofloxacin and norfloxacin, two new quinolone derivatives, were no more likely to select resistant mutants than amikacin, whereas nalidixic acid, an older quinolone derivative, was the most likely of the six drugs examined to select resistant mutants. Mutational frequencies of 10(-7) to 10(-8) were observed in most instances. In general, the mutants were 8 to 16 times less susceptible to the drug used for selection. Although most quinolone-selected mutants were cross-resistant only to other drugs within this class, certain mutants of Klebsiella pneumoniae selected by nalidixic acid, ciprofloxacin, or norfloxacin were also less susceptible to beta-lactam antibiotics. This unusual pattern of multiple drug resistance was associated with changes in outer membrane proteins of the organism. Multiple drug resistance was also observed in beta-lactam-selected mutants of Enterobacter cloacae and Pseudomonas aeruginosa (beta-lactams), amikacin-selected mutants of Providencia stuartii and P. aeruginosa (aminoglycosides), and beta-lactam- or amikacin-selected mutants of Serratia marcescens (beta-lactams plus aminoglycosides). These results underscore the need to examine carefully the frequency with which resistance to any new antibiotic develops, as well as the patterns of multiple drug resistance which may occur simultaneously.

Amikacin↗

PubMed1982