Method For Making 2-Electron Response Reduced Density Matrices Approximately N-representable

In methods like geminal-based approaches or coupled cluster that are solved using the projected Schr\"odinger equation, direct computation of the 2-electron reduced density matrix (2-RDM) is impractical and one falls back to a 2-RDM based on response theory. However, the 2-RDMs from response theory are not $N$-representable. That is, the response 2-RDM does not correspond to an actual physical $N$-electron wave function. We present a new algorithm for making these non-$N$-representable 2-RDMs approximately $N$-representable, i.e. it has the right symmetry and normalization and it fulfills the $P$-, $Q$- and $G$-conditions. Next to an algorithm which can be applied to any 2-RDM, we have also developed a 2-RDM optimization procedure specifically for seniority-zero 2-RDMs. We aim to find the 2-RDM with the right properties that is the closest (in the sense of the Frobenius norm) to the non-N-representable 2-RDM by minimizing the square norm of the difference between the initial 2-RDM and the targeted 2-RDM under the constraint that the trace is normalized and the 2-RDM, $Q$- and $G$-matrices are positive semidefinite, i.e. their eigenvalues are non-negative. Our method is suitable for fixing non-N-respresentable 2-RDMs which are close to being N-representable. Through the N-representability optimization algorithm we add a small correction to the initial 2-RDM such that it fulfills the most important N-representability conditions.Comment: 13 pages, 8 figure

Charge-state-enhanced ion sputtering of metallic gold nanoislands

Experimental results on the charge-state-dependent sputtering of metallic gold nanoislands are presented. Irradiations with slow highly charged ions of metallic targets were previously considered to show no charge state dependent effects on ion-induced material modification, since these materials possess enough free electrons to dissipate the deposited potential energy before electron-phonon coupling can set in. By reducing the size of the target material down to the nanometer regime and thus enabling a geometric energy confinement, a possibility is demonstrated to erode metallic surfaces by charge state related effects in contrast to regular kinetic sputtering

Towards quantitative Low Energy Ion Scattering on CaSiO3_3 from Comparison to Multiple-Scattering-Resolved Dynamical Binary Collision Approximation Simulations

We perform Low Energy Ion Scattering with 1\,keV He ions on CaSiO$_3$ using a commercial electrostatic detector system and determine the charge fraction of scattered ions from comparison with Binary Collision Approximation simulations. The simulations take dynamical surface changes due to surface cleaning Ar sputtering into account and scattered He particles are separated into single, dual, and multiple scattering trajectories. We find that the charge fraction of single and dual scattered He is about 10 times higher than the one for multiple collisions. Our results show that quantitative concentration profiles can be inferred from this method, if the charge fraction components are determined first

Comparative study regarding the sputtering yield of nanocolumnar tungsten surfaces under Ar+ irradiation

Nanostructured tungsten has been proposed as a promising option for plasma facing materials in future fusion reactors, because compared to conventional tungsten it shows advantages such as a better radiation resistance and, in particular, a retardation of tungsten-fuzz growth. Besides these aspects, the sputtering yield of nanostructured tungsten under ion bombardment is of interest, since it would affect the atomic density of tungsten emitted into the fusion plasma, which leads to radiative heat losses. In this work, we present a multiscale approach for investigating the sputtering yield of nanocolumnar tungsten surfaces under 1 keV and 2 keV Ar irradiation. Our results cover experiments and also computational simulations, which operate either on the basis of the binary collision approximation and ray tracing or use a full molecular dynamics implementation. In our studied case, both computational approaches can predict the sputtering yield of nanocolumnar tungsten surfaces very well. In comparison to flat W, we observe a much reduced dependence on the ion incidence angle, similar as reported for conventional rough surfaces in literature. However, an additional global reduction of the sputtering yield was identified, which can be attributed to geometrical redeposition effects between the separated nanocolumns. These results support the applicability of nanocolumnar tungsten as a first wall coating.Peer reviewe

Wave Mechanics and General Relativity: A Rapprochement

Using exact solutions, we show that it is in principle possible to regard waves and particles as representations of the same underlying geometry, thereby resolving the problem of wave-particle duality

A vacuum double-crystal spectrometer for reference-free highly charged ions X-ray spectroscopy

We have built a vacuum double crystal spectrometer, which coupled to an electron-cyclotron resonance ion source, allows to measure low-energy x-ray transitions in highly-charged ions with accuracies of the order of a few parts per million. We describe in detail the instrument and its performances. Furthermore, we present a few spectra of transitions in Ar$^{14+}$, Ar$^{15+}$ and Ar$^{16+}$. We have developed an ab initio simulation code that allows us to obtain accurate line profiles. It can reproduce experimental spectra with unprecedented accuracy. The quality of the profiles allows the direct determination of line width.Comment: 21 pages; Version

Radio Astronomy

Contains reports on research objectives and eight research projects.National Science Foundation (Grant AST79-25075)National Science Foundation (Grant AST79-20984)National Science Foundation (Grant AST79-19553)U.S. Navy - Office of Naval Research (Contract N00014-80-C-0348)National Aeronautics and Space Administration (Grant NAG2-50)M.I.T. Sloan Fund for Basic ResearchJoint Services Electronics Program (Contract DAAG29-78-C-0020)Joint Services Electronics Program (Contract DAAG29-80-C-0104)National Aeronautics and Space Administration (Grant NAG5-10)National Aeronautics and Space Administration (Contract NAS5-25091)National Aeronautics and Space Administration (Contract NAS5-22929)U.S. Department of Commerce - National Oceanic and Atmospheric Administration (Grant 04-8-MOl-1

Improved X-ray detection and particle identification with avalanche photodiodes

Avalanche photodiodes are commonly used as detectors for low energy x-rays. In this work we report on a fitting technique used to account for different detector responses resulting from photo absorption in the various APD layers. The use of this technique results in an improvement of the energy resolution at 8.2 keV by up to a factor of 2, and corrects the timing information by up to 25 ns to account for space dependent electron drift time. In addition, this waveform analysis is used for particle identification, e.g. to distinguish between x-rays and MeV electrons in our experiment.Comment: 6 pages, 6 figure

Effects of articaine on [3H]noradrenaline release from cortical and spinal cord slices prepared from normal and streptozotocin-induced diabetic rats and compared to lidocaine.

Since a significant proportion of diabetic patients have clinical or subclinical neuropathy, there may be concerns about the use of local anaesthetics. The present study was designed to determine and compare the effects of articaine, a widely used anaesthetic in dental practice, and lidocaine on the resting and axonal stimulation-evoked release of [3H]noradrenaline ([3H]NA) in prefrontal cortex slices and the release of [3H]NA in spinal cord slices prepared from non-diabetic and streptozocin (STZ)-induced diabetic (glucose level=22.03+/-2.31mmol/l) rats. The peak of allodynia was achieved 9 weeks after STZ-treatment. Articaine and lidocaine inhibited the stimulation-evoked release in a concentration-dependent manner and increased the resting release by two to six times. These effects indicate an inhibitory action of these anaesthetics on Na+- and K+-channels. There was no difference in clinically important nerve conduction between non-diabetic and diabetic rats, as measured by the release of transmitter in response to axonal stimulation. The uptake and resting release of NA was significantly higher in the brain slices prepared from diabetic rats, but there were no differences in the spinal cord. For the adverse effects, the effects of articaine on K+ channels (resting release) are more pronounced compared to lidocaine. In this respect, articaine has a thiophene ring with high lipid solubility, which may present potential risks for some patients

Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV

Two-particle angular correlations between unidentified charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum range 0.7 $< p_{\rm{T}, assoc} < p_{\rm{T}, trig} <$ 5.0 GeV/$c$ is examined, to include correlations induced by jets originating from low momen\-tum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range $|\eta|<0.9$. The near-side long-range pseudorapidity correlations observed in high-multiplicity p-Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton--parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p-Pb collisions. Further, the number scales in the intermediate multiplicity region with the number of binary nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/161