Single and vertically coupled type II quantum dots in a perpendicular magnetic field: exciton groundstate properties

The properties of an exciton in a type II quantum dot are studied under the influence of a perpendicular applied magnetic field. The dot is modelled by a quantum disk with radius $R$, thickness $d$ and the electron is confined in the disk, whereas the hole is located in the barrier. The exciton energy and wavefunctions are calculated using a Hartree-Fock mesh method. We distinguish two different regimes, namely $d<<2R$ (the hole is located at the radial boundary of the disk) and $d>>2R$ (the hole is located above and below the disk), for which angular momentum $(l)$ transitions are predicted with increasing magnetic field. We also considered a system of two vertically coupled dots where now an extra parameter is introduced, namely the interdot distance $d_{z}$. For each $l_{h}$ and for a sufficient large magnetic field, the ground state becomes spontaneous symmetry broken in which the electron and the hole move towards one of the dots. This transition is induced by the Coulomb interaction and leads to a magnetic field induced dipole moment. No such symmetry broken ground states are found for a single dot (and for three vertically coupled symmetric quantum disks). For a system of two vertically coupled truncated cones, which is asymmetric from the start, we still find angular momentum transitions. For a symmetric system of three vertically coupled quantum disks, the system resembles for small $d_{z}$ the pillar-like regime of a single dot, where the hole tends to stay at the radial boundary, which induces angular momentum transitions with increasing magnetic field. For larger $d_{z}$ the hole can sit between the disks and the $l_{h}=0$ state remains the groundstate for the whole $B$-region.Comment: 11 pages, 16 figure

Argon tagging of doubly transition metal doped aluminum clusters: The importance of electronic shielding

The interaction of argon with doubly transition metal doped aluminum clusters, AlnTM2+ (n = 1–18, TM = V, Nb, Co, Rh), is studied experimentally in the gas phase via mass spectrometry. Density functional theory calculations on selected sizes are used to understand the argon affinity of the clusters, which differ depending on the transition metal dopant. The analysis is focused on two pairs of consecutive sizes: Al6,7V2+ and Al4,5Rh2+, the largest of each pair showing a low affinity toward Ar. Another remarkable observation is a pronounced drop in reactivity at n = 14, independent of the dopant element. Analysis of the cluster orbitals shows that this feature is not a consequence of cage formation but is electronic in nature. The mass spectra demonstrate a high similarity between the size-dependent reactivity of the clusters with Ar and H2. Orbital interactions provide an intuitive link between the two and further establish the importance of precursor states in the reactions of the clusters with hydrogen

Nuclear Theory and Science of the Facility for Rare Isotope Beams

The Facility for Rare Isotope Beams (FRIB) will be a world-leading laboratory for the study of nuclear structure, reactions and astrophysics. Experiments with intense beams of rare isotopes produced at FRIB will guide us toward a comprehensive description of nuclei, elucidate the origin of the elements in the cosmos, help provide an understanding of matter in neutron stars, and establish the scientific foundation for innovative applications of nuclear science to society. FRIB will be essential for gaining access to key regions of the nuclear chart, where the measured nuclear properties will challenge established concepts, and highlight shortcomings and needed modifications to current theory. Conversely, nuclear theory will play a critical role in providing the intellectual framework for the science at FRIB, and will provide invaluable guidance to FRIB's experimental programs. This article overviews the broad scope of the FRIB theory effort, which reaches beyond the traditional fields of nuclear structure and reactions, and nuclear astrophysics, to explore exciting interdisciplinary boundaries with other areas. \keywords{Nuclear Structure and Reactions. Nuclear Astrophysics. Fundamental Interactions. High Performance Computing. Rare Isotopes. Radioactive Beams.Comment: 20 pages, 7 figure

Performance of a demand controlled mechanical extract ventilation system for dwellings

The main aim of ventilation is to guarantee a goodindoor air quality, related to the energy consumed forheating and fan(s). Active or passive heat recoverysystems seem to focus on the reduction of heatingconsumption at the expense of fan electricityconsumption and maintenance. In this study, demandcontrolledmechanical extract ventilation systems ofRenson (DCV1 and DCV2), based on natural supply inthe habitable rooms and mechanical extraction in thewet rooms (or even the bedrooms), was analysed forone year by means of multi-zone Contam simulationson a reference detached house and compared withstandard MEV and mechanical extract ventilationsystems with heat recovery (MVHR). To this end, IAQ, total energy consumption,CO2 emissions and total cost of the systems aredetermined. The results show that DCV systems withincreased supply air flow rates or direct mechanicalextract from bedrooms can significantly improve IAQ,while reducing total energy consumption comparedto MEV. Applying DCV reduces primary heatingenergy consumption and yearly fan electricityconsumption at most by 65% to 50% compared toMEV. Total operational energy costs and CO2emissions of DCV are similar when compared toMVHR. Total costs of DCV systems over 15 years aresmaller when compared to MVHR due to lowerinvestment and maintenance costs

One-neutron knockout in the vicinity of the N=32 sub-shell closure: 9Be(57Cr,56Cr+ gamma)X

The one-neutron knockout reaction 9Be(57Cr,56Cr + gamma)X has been measured in inverse kinematics with an intermediate-energy beam. Cross sections to individual states in 56Cr were partially untangled through the detection of the characteristic gamma-ray transitions in coincidence with the reaction residues. The experimental inclusive longitudinal momentum distribution and the yields to individual states are compared to calculations that combine spectroscopic factors from the full fp shell model and nucleon-removal cross sections computed in a few-body eikonal approach.Comment: PRC, in pres

Spectroscopy of the odd-odd fp-shell nucleus 52Sc from secondary fragmentation

The odd-odd fp-shell nucleus 52Sc was investigated using in-beam gamma-ray spectroscopy following secondary fragmentation of a 55V and 57Cr cocktail beam. Aside from the known gamma-ray transition at 674(5)keV, a new decay at E_gamma=212(3) keV was observed. It is attributed to the depopulation of a low-lying excited level. This new state is discussed in the framework of shell-model calculations with the GXPF1, GXPF1A, and KB3G effective interactions. These calculations are found to be fairly robust for the low-lying level scheme of 52Sc irrespective of the choice of the effective interaction. In addition, the frequency of spin values predicted by the shell model is successfully modeled by a spin distribution formulated in a statistical approach with an empirical, energy-independent spin-cutoff parameter.Comment: accepted for publication in PR

An octacoordinated Nb atom in the NbAl₈H₈⁺ cluster

The NbAl8H8+ cluster was formed in a molecular beam and characterized by mass spectrometry and infrared spectroscopy. Density functional theory calculations show the lowest-energy isomer is a high symmetry singlet with the Nb atom placed at the center of a distorted hexagonal Al ring and coordinated by two AlH moieties, therefore exhibiting octacoordination. The unprecedented high-symmetric geometry is attributed to the 20 valence electrons; the central Nb atom adheres to the 18-electron rule and two additional delocalized electrons stabilize the hexagonal ring

Half-life and spin of 60Mn^g

A value of 0.28 +/- 0.02 s has been deduced for the half-life of the ground state of 60Mn, in sharp contrast to the previously adopted value of 51 +/- 6 s. Access to the low-spin 60Mn ground state was accomplished via beta decay of the 0+ 60Cr parent nuclide. New, low-energy states in 60Mn have been identified from beta-delayed gamma-ray spectroscopy. The new, shorter half-life of 60Mn^g is not suggestive of isospin forbidden beta decay, and new spin and parity assignments of 1+ and 4+ have been adopted for the ground and isomeric beta-decaying states, respectively, of 60Mn.Comment: 13 pages, 5 figures, Accepted for publication in Phys. Rev.

Probing the single-particle character of rotational states in 19^{19}F using a short-lived isomeric beam

A beam containing a substantial component of both the $J^{\pi}=5^+$, $T_{1/2}=162$ ns isomeric state of $^{18}$F and its $1^+$, 109.77-min ground state has been utilized to study members of the ground-state rotational band in $^{19}$F through the neutron transfer reaction $(d$,$p)$ in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2$^+$ band-terminating state. The agreement between shell-model calculations, using an interaction constructed within the $sd$ shell, and our experimental results reinforces the idea of a single-particle/collective duality in the descriptions of the structure of atomic nuclei

On radiative corrections for unpolarized electron proton elastic scattering

A statistical analysis of the elastic unpolarized electron proton scattering data shows that, at large momentum transfer, the size and the $\epsilon$ dependence of the radiative corrections, as traditionally calculated and applied, may induce large correlations of the parameters of the Rosenbluth fit, which prevent a correct extraction of the electric proton form factor. Using the electron QED structure (radiation) function approach the cross section of elastic electron-proton scattering in leading and next-to leading approximations is calculated and expressed as a correction to the Born cross section, which is different for the electric and the magnetic contribution. When properly applied to the data, it may give the solution to the problem of the discrepancy of the polarized and unpolarized results on electron proton scattering.Comment: 11 pagex, 5 figure