Assessing the insulating properties of an ultrathin SrTiO3shell grown around GaAs nanowires with molecular beam epitaxy

We have studied electronic transport in undoped GaAs/SrTiO₃core-shell nanowires standing on their Si substrate with two-tip scanning tunneling microscopy in ultrahigh vacuum. The resistance profile along the nanowires is proportional to the tip separation with resistances per unit length of a few GΩ/μm. Examination of the different transport pathways parallel to the nanowire growth axis reveals that the measured resistance is consistent with a conduction along the interfacial states at the GaAs{110} sidewalls, the 2 nm thick SrTiO₃shell being as much as resistive, despite oxygen deficient growth conditions. The origin of the shell resistivity is discussed in light of the nanowire analysis with transmission electron microscopy and Raman spectroscopy, providing good grounds for the use of SrTiO₃shells as gate insulators.

New beam line for time-of-flight medium energy ion scattering with large area position sensitive detector

A new beam line for medium energy ion mass scattering (MEIS) has been designed and set up at the Ångström laboratory, Uppsala University, Sweden. This MEIS system is based on a time-of-flight (ToF) concept and the electronics for beam chopping relies on a 4 MHz function generator. Repetition rates can be varied between 1 MHz and 63 kHz and pulse widths below 1 ns are typically obtained by including beam bunching. A 6-axis goniometer is used at the target station. Scattering angle and energy of backscattered ions are extracted from a time-resolved and position-sensitive detector. Examples of the performance are given for three kinds of probing ions, (1)H(+), (4)He(+), and (11)B(+). Depth resolution is in the nanometer range and 1 and 2 nm thick Pt layers can easily be resolved. Mass resolution between nearby isotopes can be obtained as illustrated by Ga isotopes in GaAs. Taking advantage of the large size detector, a direct imaging (blocking pattern) of crystal channels are shown for hexagonal, 4H-SiC. The ToF-MEIS system described in this paper is intended for use in semiconductor and thin film areas. For example, depth profiling in the sub nanometer range for device development of contacts and dielectric interfaces. In addition to applied projects, fundamental studies of stopping cross sections in this medium energy range will also be conducted.

A rotatable electron spectrometer for multicoincidence experiments

We have developed a rotatable hemispherical spectrometer with good energy and angular resolution, which can be positioned with the lens axis arbitrarily within a solid angle of 1 pi. The collection angle of the emitted electrons with respect to the polarization axis of the light is set by means of a three-axes goniometer, operating under vacuum. An important requirement for this setup was the possibility to perform coincidences between the electron analyzed by the spectrometer and one or several other particles, such as ions, electrons, or photons. The lens system and the hemispheres have been designed to accommodate such experimental demands, regarding parameters such as the resolving power, the acceptance angle, or the width of the kinetic energy window which can be recorded for a given pass energy. We have chosen to detect the impact position of the electron at the focal plane of the hemispherical analyzer with a delay line detector and a time-to-digital converter as acquisition card rather than using a conventional charge-coupled device camera.

Kinematically complete study of dissociative ionization of by ion impact

We present a kinematically complete study of dissociative ionization of D(2) by 13.6 MeV/u S(15+) ions. The experiment allows us to unravel the competing mechanisms, namely, direct single ionization, autoionization of doubly excited states, ionization excitation, and double ionization, and to analyze the corresponding electron angular distribution from fixed-in-space molecules. The conclusions are supported by theoretical calculations in which the correlated motion of all electrons and nuclei and the interferences between them are described from first principles.

Immunoassays for the detection of nicergoline and its metabolites in human plasma

In order to determine nicergoline pharmacokinetics after oral administration to humans, we have developed two radioimmunoassays, one directed against nicergoline and the other directed against known nicergoline metabolites. The assays were validated according to the recommendations of international regulatory agencies and their limits of quantification were 40 and 10 pg/ml, respectively. In order to further validate the methods, a chromatographic separation of immunoreactive entities was performed with samples from healthy volunteers who were given 15 mg of Sermion (nicergoline orally administered). Chromatographic determination of assay specificity showed that the metabolite radioimmunoassay recognised known nicergoline metabolites but also a new metabolite. Using the antibodies directed against nicergoline, we were unable to detect nicergoline in the human plasma. This suggests that nicergoline is absent in the circulation because of complete metabolism through its first-pass effect.

Psychosocial variables, age, and angiographically-determined coronary artery disease in women

The present study explored the relationship between psychosocial measures and the degree of coronary stenosis in a sample of 59 women between the ages of 39 and 84. Coronary occlusion was correlated with elevated cholesterol and marginally correlated with age and was inversely associated with years of education. Based on hierarchical multiple regression, an interview-based measure of hostility was associated with coronary stenosis after controlling for traditional risk factors, and age moderated the hostility-stenosis relationship. Further, a second regression model suggested that trait anxiety was inversely correlated with degree of occlusion, perhaps because low-anxious women are referred for catheterization later in the course of the disease. Contrary to hypotheses, there was no evidence that repression of interview-based hostility or anxiety predicted coronary occlusion. Given the small sample size, results should be considered preliminary. Future studies should explore the degree to which anxiety and hostility are associated with coronary heart disease (CHD) in larger samples of women and the degree to which age moderates the hostility-occlusion association.

[C virus of Drosophila and dynamics of host population]

Drosophila melanogaster populations are naturally infected by the Drosophila C virus (DCV). Ingestion of this non-hereditary virus early in the life-cycle has a positive effect. Demographic parameters measured on DCV-free and DCV-infected populations of the same genotype enabled us to compute the population growth rates (multiplication rates) by means of matrix models. The DCV-infected sample had a larger growth rate both for low and high larval densities. Since it is not possible to experiment on a mixed population where DCV-free and DCV-infected individuals live together, a model combining competition and contamination was used. Simulations showed that coexistence of free and infected animals can occur. Such a result leads us to question the relation between population growth rate and fitness.

Conjunctivitis in clean room workers. Nursing evaluation and intervention

Conjunctivitis, in the industrial setting, can be attributed to eye contact with contaminated microscope oculars. Establishing a simple, convenient process for cleaning microscope oculars as well as educating employees and their management is important to reduce risk of contamination. Early identification and treatment of an isolated infection by the occupational health nurse and temporary exclusion from microscope work is essential in controlling the spread of infection and preventing a potential epidemic. The occupational health nurse plays a pivotal role in the recognition of and response to workplace health concerns and development of targeted strategies to promote and maintain health in the workplace.

Ocular infections and the industrial use of microscopes

A cluster of ocular infections occurred in one area of a computer fabrication facility that relied on the use of industrial microscopes. A questionnaire was administered to all employees in this area. Microscope oculars were cultured and compared with control microscopes from a nonindustrial setting. Risk of infection was correlated with the number of hours of microscope use per day and subjective indicators of cleanliness. Bacterial cultures confirmed increased colony counts in industrial oculars compared with control oculars. Hygienic practices were instituted similar to those employed in medical settings. No further outbreaks of conjunctivitis have been reported in a 1-year follow-up.

Influence of lipids with branched-chain fatty acids on the physical, morphological and functional properties of Escherichia coli cytoplasmic membrane

Escherichia coli cells (unsaturated fatty acid auxotroph) have been adapted to grow on branched-chain fatty acids. Membrane vesicles were isolated from cells grown on a mixture of branched-chain fatty acids isolated from the lipids of Bacillus subtilis (E. coli (B. subtilis) membranes) and on a pure synthetic anti-isononadecanoic acid (E. coli (aC19) membranes). We have shown, using wide-angle X-ray diffraction and differential scanning calorimetry, that the ordered state of the lipids is perturbed in the case of E. coli (B. subtilis) membranes but is unperturbed in the case of E. coli (aC19) membranes. The perturbation leads to the presence of a large wide-angle X-ray diffraction at 4.25--4.3 A, as opposed to the presence of a sharp 4.2 A reflection in unperturbed systems. We have shown, using freeze-fracture electron microscopy, that a protein segregation exists in the case of E. coli (aC19) membranes (at low temperature the integral membrane proteins aggregate in the membrane domains containing the disordered lipids); we do not observe such segregation in the case of E. coli (B. subtilis) membranes. We conclude that in cases where the branching of the fatty acids introduces a perturbation of the lipid order, the integral membrane proteins can still be accommodated in membrane domains containing the 'perturbed' ordered lipids. Finally, we have determined the rate of beta-galactoside transport in E. coli (aC19) and E. coli (B. subtilis) membranes as a function of temperature. We have shown that, in both cases, the Arrhenius representations display an increased slope in the region of the disorder-to-order transition. We conclude that such an increased slope may have different origins. In the case of E. coli (aC19) membranes, it is the result of the aggregation of the beta-galactoside carriers together with other integral membrane proteins which may lead to the inactivation of the carriers; in the case of E. coli (B. subtilis) membranes, it is the result of the partial immobilisation of the carriers embedded in a lipid environment, of which the fluidity, despite the perturbation of its lipid order, is still much less than that associated with lipids in a totally disordered state.