Theoretical study on properties of new isotope (265)Bh

The properties of nuclei belonging to the newly observed a-decay chain starting from (265)Bh have been studied. The axially deformed relativistic mean-field calculation with the force NL-Z2 has been performed in the blocked BCS approximation. Some ground state properties such as binding energies, deformations, spins, and parities, as well as Q-values of the alpha-decay for this decay chain have been calculated and compared with known experimental data. Good agreement is found. The single-particle spectrum of the nucleus (265)Bh is studied and some new magic numbers are found, while the magnitudes of the shell gaps in superheavy nuclei are much smaller than those of nuclei before the actinium region, and the Fermi surfaces are close to the continuum. Thus the superheavy nuclei are usually not stable. The alpha-decay lifetimes in the (265)Bh decay chain are evaluated by different formulae, and compared with experimental data. The methods which give good agreement with the data are selected.

X-ray spectroscopy of hollow argon atoms formed on a beryllium surface

The X-rays induced during interaction of highly charged argon ions with a beryllium surface are reported. It is found that the K shell X-ray yield of single particle during interaction of hydrogen-like argon ions was 3.6 x 10(-3), which is five orders more than that of heliumlike argon ions. Moreover, due to the screening the 2s electron, no K X-ray was emitted during interaction of lithium-like argon ions with the beryllium surface. It is also found that the X-ray spectrum induced by Ar17+ interacting with residual gases is very different from that induced by Ar17+ interacting with the surfaces, that provided an experimental evidence for the existence of the hollow atoms below the surface.

Systematic study of properties of Hs nuclei

The ground-state properties of Hs nuclei are studied in the framework of the relativistic meanfield theory. We find that the more relatively stable isotopes are located on the proton abundant side of the isotopic chain. The last stable nucleus near the proton drip line is probably the (255)Hs nucleus. The alpha-decay half-lives of Hs nuclei are predicted, and together with the evaluation of the spontaneous-fission half-lives it is shown that the nuclei, which are possibly stable against spontaneous fission are (263-274)Hs. This is in coincidence with the larger binding energies per nucleon. If (271-274)Hs can be synthesized and identified, only those nuclei from the upper Z = 118 isotopic chain, which are lighter than the nucleus (294)118, and those nuclei in the corresponding alpha-decay chain lead to Hs nuclei. The most stable unknown Hs nucleus is (268)Hs. The density-dependent delta interaction pairing is used to improve the BCS pairing correction, which results in more reasonable single-particle energy level distributions and nucleon occupation probabilities. It is shown that the properties of nuclei in the superheavy region can be described with this interaction.

Importance of self-consistency in relativistic continuum random-phase approximation calculations

A fully consistent relativistic continuum random phase approximation (RCRPA) is constructed, where the contribution of the continuum spectrum to nuclear excitations is treated exactly by the single-particle Green's function technique. The full consistency of the calculations is achieved that the same effective Lagrangian is adopted for the ground state and the excited states. The negative energy states in the Dirac sea are also included in the single-particle Green's function in the no-sea approximation. The currents from the vector meson and photon exchanges and the Coulomb interaction in RCRPA are treated exactly. The spin-orbit interaction is included naturally in the relativistic frame. Numerical results of the RCRPA are checked with the constrained relativistic mean-field theory. We study the effects of the inconsistency, particularly the currents and Coulomb interaction in various collective multipole excitations.

Relativistic Continuum Random Phase Approximation and Applications I. Formalism

A fully consistent relativistic continuum random phase approximation (RCRPA) is constructed in terms of the Green's function technique. In this method the contribution of the continuum spectrum to nuclear excitations is treated exactly by the single particle Green's function, which includes also the negative states in the Dirac sea in the nose aapproximation. The theoretical formalism of RCRPA and numerical details are presented. The single particle Green's function is calculated numerically by a proper product of regular and irregular solutions of the Dirac equation. The numerical details and the formalism of RCRPA in the momentum representation are presented.

Calibration of an audio-frequency ion trap mass spectrometer

A method for calibration of an audio-frequency (AF) ion trap mass spectrometer is described. The method is proposed to surmount the obstacle that there is a lack of a proper calibrant for mass spectrometers in the mass-to-charge ratio (m/z) range of 10(6) to 10(10). To calibrate such mass spectra, we determine the point of ejection, q(eject), on the stability diagram of the ion trap operated in a mass-selective axial instability mode. This is accomplished by measuring the radial secular frequencies (and therefore, the m/z value) of a single trapped particle using a light scattering method, followed by monitoring the action of particle ejection in real time to obtain the q(eject). A delayed ejection with q(eject) = 0.949 +/- 0.004 is found at a trap driving frequency of Ohm/2pi = 200-600Hz. Theoretical analysis for the origin of the delayed ejection indicates that the delay is predominantly resulted from the existence of multipole components in the fields due to trap imperfections. Inclusion of -3% of the octopole with respect to the basic quadrupole field can satisfactorily account for our observations. An m/z accuracy approaching 0.1% is attainable after proper calibration of the AF ion trap mass spectrometer. (Int J Mass Spectrom 214 (2002) 63-73) (C) 2002 Elsevier Science B.V. All rights reserved.

Biochemical and electron microscopic characterization of the F1F0 ATP Synthase from the hyperthermophilic eubacterium Aquifex aeolicus

The F1F0 ATP synthase has been purified from the hyperthermophilic eubacterium Aquifex aeolicus and characterized. Its subunits have been identified by MALDI-mass spectrometry through peptide mass fingerprinting and MS/MS. It contains the canonical subunits alpha, beta, gamma, delta and epsilon of F-1 and subunits a and c of F-0. Two versions of the b subunit were found, which show a low sequence homology to each other. Most likely they form a heterodimer. An electron microscopic single particle analysis revealed clear structural details, including two stalks connecting F-1 and F-0. In several orientations the central stalk appears to be tilted and/or kinked. It is unclear whether there is a direct connection between the peripheral stalk and the 6 subunit. (c) 2006 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

铂族元素分析方法研究及其在有关地质问题中的应用

Characterization of Platinum Group Elements (PGE) has been applied to earth, space and environmental sciences. However, all these applications are based on a basic prerequisite, i.e. their concentration or ratio in the research objects can be accurately and precisely determined. In fact, development in these related studies is a great challenge to the analytical chemistry of the PGE because their content in the geological sample (non-mineralized) is often extremely low, range from ppt (10~(-12)g/g) to ppt (10~(-9)g/g). Their distribution is highly heterogeneous, usually concentrating in single particle or phase. Therefore, the accurate determination of these elements remains a problem in analytical chemistry and it obstructs the research on geochemistry of PGE. A great effort has been made in scientific community to reliable determining of very low amounts of PGE, which has been focused on to reduce the level of background in used reagents and to solve probable heterogeneity of PGE in samples. Undoubtedly, the fire-assay method is one of the best ways for solving the heterogeneity, as a large amount of sample weight (10-50g) can be hold. This page is mainly aimed at development of the methodology on separation, concentration and determination of the ultra-trace PGE in the rock and peat samples, and then they are applied to study the trace of PGE in ophiolite suite, in Kudi, West Kunlun and Tunguska explosion in 1908. The achievements of the study are summarized as follows: 1. A PGE lab is established in the Laboratory of Lithosphere Tectonic Evolution, IGG, CAS. 2. A modified method of determination of PGE in geological samples using NiS Fire-Assay with inductively coupled plasma-mass spectrometry (ICP-MS) is set up. The technical improvements are made as following: (1) investigating the level of background in used reagents, and finding the contents of Au, Pt and Pd in carbonyl nickel powder are 30, 0.6 and 0.6ng/g, respectively and 0.35, 7.5 and 6.4ng, respectively in other flux, and the contents of Ru, Rh, Os in whole reagents used are very low (below or near the detection limits of ICP-MS); (2) measuring the recoveries of PGE using different collector (Ni+S) and finding 1.5g of carbonyl nickel is effective for recovering the PGE for 15g samples (recoveries are more than 90%), reducing the inherent blank value due to impurities reagents; (3) direct dissolving nickel button in Teflon bomb and using Te-precipitation, so reducing the loss of PGE during preconcentration process and improving the recoveries of PGE (above 60% for Os and 93.6-106.3% for other PGE, using 2g carbonyl nickel); (4) simplifying the procedure of analyzing Osmium; (5)method detection limits are 8.6, 4.8, 43, 2.4, 82pg/g for 15g sample size ofRu, Rh, Pd, Ir, Pt, respectively. 3. An analytical method is set up to determine the content of ultra-trace PGE in peat samples. The method detection limits are 0.06, 0.1, 0.001, 0.001 and 0.002ng/mL for Ru, Rh, Pd, Ir and Pt, respectively. 4. Distinct anomaly of Pd and Os are firstly found in the peat sampling near the Tunguska explosion site, using the analytical method. 5. Applying the method to the study on the origin of Tunguska explosion and making the following conclusions: (1) these excess elements were likely resulted from the Tunguska Cosmic Body (TCB) explosion of 1908. (2) The Tunguska explosive body was composed of materials (solid components) similar to C1 chondrite, and, most probably, a cometary object, which weighed more than 10~7 tons and had a radius of more than 126 m. 6. The analysis method about ultra-trace PGE in rock samples is successfully used in the study on the characteristic of PGE in Kudi ophiolite suite and the following conclusions are made: (1) The difference of the mantle normalization of PGE patterns between dunite, harzburgite and lherzolite in Kudi indicates that they are residual of multi-stage partial melt of the mantle. Their depletion of Ir at a similar degree probably indicates the existence of an upper mantle depleted Ir. (2) With the evolution of the magma produced by the partial melt of the mantle, strong differentiation has been shown between IPGE and PPGE; and the differentiation from pyroxenite to basalt would have been more and more distinct. (3) The magma forming ophiolite in Kudi probably suffered S-saturation process.

On the positivity of the Jansen-He? operator for arbitrary mass

Iantchenko, A.; Jakuba?a-Amundsen, D.H., (2003) 'On the positivity of the Jansen-He? operator for arbitrary mass', Annales of the Institute Henri Poincar? 4 pp.1083-1099 RAE2008

Properties of molecules in tunnel junctions

Molecular tunnel junctions involve studying the behaviour of a single molecule sandwiched between metal leads. When a molecule makes contact with electrodes, it becomes open to the environment which can heavily influence its properties, such as electronegativity and electron transport. While the most common computational approaches remain to be single particle approximations, in this thesis it is shown that a more explicit treatment of electron interactions can be required. By studying an open atomic chain junction, it is found that including electron correlations corrects the strong lead-molecule interaction seen by the ΔSCF approximation, and has an impact on junction I − V properties. The need for an accurate description of electronegativity is highlighted by studying a correlated model of hexatriene-di-thiol with a systematically varied correlation parameter and comparing the results to various electronic structure treatments. The results indicating an overestimation of the band gap and underestimation of charge transfer in the Hartree-Fock regime is equivalent to not treating electron-electron correlations. While in the opposite limit, over-compensating for electron-electron interaction leads to underestimated band gap and too high an electron current as seen in DFT/LDA treatment. It is emphasised in this thesis that correcting electronegativity is equivalent to maximising the overlap of the approximate density matrix to the exact reduced density matrix found at the exact many-body solution. In this work, the complex absorbing potential (CAP) formalism which allows for the inclusion metal electrodes into explicit wavefunction many-body formalisms is further developed. The CAP methodology is applied to study the electron state lifetimes and shifts as the junction is made open.

Nanoscale electronic properties of conjugated polymers and nanocrystals

The objective of this thesis is the exploration and characterisation of the nanoscale electronic properties of conjugated polymers and nanocrystals. In Chapter 2, the first application of conducting-probe atomic force microscopy (CP-AFM)-based displacement-voltage (z-V) spectroscopy to local measurement of electronic properties of conjugated polymer thin films is reported. Charge injection thresholds along with corresponding single particle gap and exciton binding energies are determined for a poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] thin film. By performing measurements across a grid of locations on the film, a series of exciton binding energy distributions are identified. The variation in measured exciton binding energies is in contrast to the smoothness of the film suggesting that the variation may be attributable to differences in the nano-environment of the polymer molecules within the film at each measurement location. In Chapter 3, the CP-AFM-based z-V spectroscopy method is extended for the first time to local, room temperature measurements of the Coulomb blockade voltage thresholds arising from sequential single electron charging of 28 kDa Au nanocrystal arrays. The fluid-like properties of the nanocrystal arrays enable reproducible formation of nanoscale probe-array-substrate junctions, allowing the influence of background charge on the electronic properties of the array to be identified. CP-AFM also allows complementary topography and phase data to be acquired before and after spectroscopy measurements, enabling comparison of local array morphology with local measurements of the Coulomb blockade thresholds. In Chapter 4, melt-assisted template wetting is applied for the first time to massively parallel fabrication of poly-(3-hexylthiophene) nanowires. The structural characteristics of the wires are first presented. Two-terminal electrical measurements of individual nanowires, utilising a CP-AFM tip as the source electrode, are then used to obtain the intrinsic nanowire resistivity and the total nanowire-electrode contact resistance subsequently allowing single nanowire hole mobility and mean nanowire-electrode barrier height values to be estimated. In Chapter 5, solution-assisted template wetting is used for fabrication of fluorene-dithiophene co-polymer nanowires. The structural characteristics of these wires are also presented. Two-terminal electrical measurements of individual nanowires indicate barrier formation at the nanowire-electrode interfaces and measured resistivity values suggest doping of the nanowires, possibly due to air exposure. The first report of single conjugated polymer nanowires as ultra-miniature photodetectors is presented, with single wire devices yielding external quantum efficiencies ~ 0.1 % and responsivities ~ 0.4 mA/W under monochromatic illumination.

Dilute nitride semiconductors : band structure, scattering and high field transport

The substitution of a small fraction x of nitrogen atoms, for the group V elements in conventional III-V semiconductors such as GaAs and GaSb strongly perturbs the conduction band of the host semiconductor. In this thesis we investigate the effects of nitrogen states on the band dispersion, carrier scattering and mobility of dilute nitride alloys. In the supercell model we solve the single particle Hamiltonian for a very large supercell containing randomly placed nitrogen. This model predicts a gap in the density of states of GaNxAs1−x, where this gap is filled in the Green’s function model. Therefore we develop a self-consistent Green’s function (SCGF) approach, which provides excellent agreement with supercell calculations and reveals a gap in the DOS, in contrast with the results of previous non-self-consistent Green’s function calculations. However, including the distribution of N states destroys this gap, as seen in experiment. We then examine the high field transport of carriers by solving the steadystate Boltzmann transport equation and find that it is necessary to include the full distribution of N levels in order to account for the small, low-field mobility and the absence of a negative differential velocity regime observed experimentally with increasing x. Overall the results account well for a wide range of experimental data. We also investigate the band structure, scattering and mobility of carriers by finding the poles of the SCGF, which gives lower carrier mobility for GaNxAs1−x, compared to those already calculated, in better agreement with experiments. The calculated optical absorption spectra for InyGa1−yNxAs1−x and GaNxSb1−x using the SCGF agree well with the experimental data, confirming the validity of this approach to study the band structure of these materials.

Latest development of the combinatorial model of nuclear level densities

The combinatorial model of nuclear level densities has now reached a level of accuracy comparable to that of the best global analytical expressions without suffering from the limits imposed by the statistical hypothesis on which the latter expressions rely. In particular, it provides, naturally, non-Gaussian spin distribution as well as non-equipartition of parities which are known to have an impact on cross section predictions at low energies [1, 2, 3]. Our previous global models developed in Refs. [1, 2] suffered from deficiencies, in particular in the way the collective effects - both vibrational and rotational - were treated. We have recently improved this treatment using simultaneously the single-particle levels and collective properties predicted by a newly derived Gogny interaction [4], therefore enabling a microscopic description of energy-dependent shell, pairing and deformation effects. In addition for deformed nuclei, the transition to sphericity is coherently taken into account on the basis of a temperature-dependent Hartree-Fock calculation which provides at each temperature the structure properties needed to build the level densities. This new method is described and shown to give promising results with respect to available experimental data.

Displacement of particles in microfluidics by laser-generated tandem bubbles.

The dynamic interaction between laser-generated tandem bubble and individual polystyrene particles of 2 and 10 μm in diameter is studied in a microfluidic channel (25 μm height) by high-speed imaging and particle image velocimetry. The asymmetric collapse of the tandem bubble produces a pair of microjets and associated long-lasting vortices that can propel a single particle to a maximum velocity of 1.4 m∕s in 30 μs after the bubble collapse with a resultant directional displacement up to 60 μm in 150 μs. This method may be useful for high-throughput cell sorting in microfluidic devices.

Pittsburgh air quality study overview

Ambient sampling for the Pittsburgh Air Quality Study (PAQS) was conducted from July 2001 to September 2002. The study was designed (1) to characterize particulate matter (PM) by examination of size, surface area, and volume distribution, chemical composition as a function of size and on a single particle basis, morphology, and temporal and spatial variability in the Pittsburgh region; (2) to quantify the impact of the various sources (transportation, power plants, biogenic sources, etc.) on the aerosol concentrations in the area; and (3) to develop and evaluate the next generation of atmospheric aerosol monitoring and modeling techniques. The PAQS objectives, study design, site descriptions and routine and intensive measurements are presented. Special study days are highlighted, including those associated with elevated concentrations of daily average PM2.5 mass. Monthly average and diurnal patterns in aerosol number concentration, and aerosol nitrate, sulfate, elemental carbon, and organic carbon concentrations, light scattering as well as gas-phase ozone, nitrogen oxides, and carbon monoxide are discussed with emphasis on the processes affecting them. Preliminary findings reveal day-to-day variability in aerosol mass and composition, but consistencies in seasonal average diurnal profiles and concentrations. For example, the seasonal average variations in the diurnal PM2.5 mass were predominately driven by the sulfate component. © 2004 Elsevier Ltd. All rights reserved.