Analog computation using quantum-dot cell network

A novel analog-computation system using a quantum-dot cell network is proposed to solve complex problems. Analog computation is a promising method for solving a mathematical problem by using a physical system analogous to the problem. We designed a novel quantum-dot cell consisting of three-stacked. quantum dots and constructed a cell network utilizing the nearest-neighbor interactions between the cells. We then mapped a graph 3-colorability problem onto the network so that the single-electron configuration of the network in the ground state corresponded to one of the solutions. We calculated the ground state of the cell network and found solutions to the problems. The results demonstrate that analog computation is a promising approach for solving complex problems.

Microphotoluminescence investigation of InAs quantum dot active region in 1.3 mu m vertical cavity surface emitting laser structure

Microphotoluminescence (mu-PL) investigation has been performed at room temperature on InAs quantum dot (QD) vertical cavity surface emitting laser (VCSEL) structure in order to characterize the QD epitaxial structure which was designed for 1.3 mu m wave band emission. Actual and precise QD emission spectra including distinct ground state (GS) and excited state (ES) transition peaks are obtained by an edge-excitation and edge-emission (EEEE) mu-PL configuration. Conventional photoluminescence methods for QD-VCSELs structure analysis are compared and discussed, which indicate the EEEE mu-PL is a useful tool to determine the optical features of the QD active region in an as-grown VCSEL structure. Some experimental results have been compared with simulation results obtained with the aid of the plane-wave admittance method. After adjustment of epitaxial growth according to EEEE mu-PL measurement results, QD-VCSEL structure wafer with QD GS transition wavelength of 1300 nm and lasing wavelength of 1301 nm was obtained.

Measurement of the inelastic branch of the O-14(alpha, p)F-17 reaction: Implications for explosive burning in novae and x-ray bursters

A measurement of the inelastic component of the key astrophysical resonance in the 14O(α,p)17F reaction for burning and breakout from hot carbon-nitrogen-oxygen (CNO) cycles is reported. The inelastic component is found to be comparable to the ground-state branch and will enhance the 14O(α,p)17F reaction rate. The current results for the reaction rate confirm that the 14O(α,p)17F reaction is unlikely to contribute substantially to burning and breakout from the CNO cycles under novae conditions. The reaction can, however, contribute strongly to the breakout from the hot CNO cycles under the more extreme conditions found in x-ray bursters.

Projected shell model description for high-spin states in neutron-rich Fe isotopes

A systematic study of neutron-rich even-even Fe isotopes with a neutron number from 32 to 42 is carried out by using the projected shell model. Calculations are performed up to the spin I=20 state. Irregularities found in the yrast spectra and in B (E2) values are discussed in terms of neutron excitations to the high-j orbital g(9/2). Furthermore, the neutron two-quasiparticle structure of a low-K negative-parity band and the proton two-quasiparticle structure of a high-K positive-parity band are predicted to exist near the yrast region. Our study reveals a soft nature for the ground state of N approximate to 40 isotopes and emphasizes the important role of the neutron g(9/2) orbital in determining the structure properties for both low- and high-spin states in these nuclei.

Possible magnetic and antimagnetic rotations in Dy-144

High spin states of Dy-144 have been studied through in-beam gamma-ray spectroscopy by using the reaction Mo-92(Fe-56,2p2n). It has been found that the continuation of the ground-state band forks into three Delta I=2 bands above the 8(+) state. This forking has been attributed to the alignments of pi h(11/2)(2) or nu h(11/2)(-2) configurations with the help of the systematics in neighboring nuclei. Additionally a negative-parity sideband of Delta I=2 cascades has been observed to start from the 5((-)) state and continue to a dipole band above the (13(-)) state through another negative-parity sideband of Delta I=2 cascades in between. These structures have been discussed from the viewpoint of a competition between "Magnetic Rotation" and "Anti-magnetic Rotation" based on a classical particles-plus-rotor model.

Entrance-channel dependence of isospin effects on double n/p ratio in HIC

Within the hadronic transport model IBUU04, we investigate the effect of density-dependent symmetry energy on double neutron/proton (n/p) ratio of free nucleons in heavy ion collisions by taking four isotopic Sn+Sn reaction systems. Especially the entrance-channel asymmetry and impact-parameter dependence of the effect of symmetry energy are discussed. It is found that in both central and semi-central collisions the sensitivity of the double n/p ratio to the density-dependent symmetry energy is more pronounced in neutron-richer systems. Our results also indicate clearly that the effect of symmetry energy is stronger in central collisions than that in semi-central collisions.

Investigation of ion-atom collision dynamics through imaging techniques

The principle and technique details of recoil ion momentum imaging are discussed and summarized. The recoil ion momentum spectroscopy built at the Institute of Modern Physics (Lanzhou) is presented. The first results obtained at the setup are analyzed. For 30 keV He2+ on He collision, it is found that the capture of single electron occurs dominantly into the first excited states, and the related scattering angle results show that the ground state capture occurs at large impact parameters, while the capture into excited states occurs at small impact parameters. The results manifest the collision dynamics for the sub-femto-second process can be studied through the techniques uniquely. Finally, the future possibilities of applications of the recoil ion momentum spectroscopy in other fields are outlined.

Studies on the exotic structure of Al-23

The longitudinal momentum distribution (P-//) of fragments after one-proton removal from Al-23 and reaction cross sections (sigma(R)) for Al-23,Al-24 on carbon target at 74A MeV have been measured simultaneously. An enhancement in sigma(R) is observed for Al-23 compaxed with Al-24. The full width at half maximum of the P-// distribution for Mg-22 fragments has been determined to be 232 +/- 28 MeV/c. Analysis of P-// using the Few-Body Glauber Model indicates a dominant d-wave configuration for the valence proton in the ground state of Al-23. The exotic structure in Al-23 is discussed.

Identification of a new band and its signature inversion in Re-174

High spin states in Re-174 are investigated via the Sm-152(Al-27, 5n gamma)Re-174 reaction and gamma-gamma coincidence relationships are analysed carefully. A new band is identified due to its spectroscopic connection with the known pi 1/2(-)[541] circle times nu 1/2(-)[521] band. This band is proposed to be the ground-state band built on the pi 1/2(-)[541] circle times nu 5/2(-)[512] configuration in view of the low-lying intrinsic states in the neighbouring odd-mass nuclei. It is of particular interesting that the new band exhibits a phenomenon of low-spin signature inversion, providing a new situation for theoretical investigations.

Properties and structure of N = Z nuclei within relativistic mean field theory

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the proper-ties and structure of N=Z nuclei from Z=20 to Z=48. Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-squaxe (rms) radii of charge and neutron, and shell gaps have been calculated. The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38-42. The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43. The evolution of shell gaps with proton number Z can be clearly observed. Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region. In addition, we found that the Coulomb interaction is not strong enough to breakdown the shell structure of protons in the current region.

Theoretical study on electron impact excitation of highly charged Ne-like ions

The electron impact excitation (EIE) cross sections from the ground state to all of the 2s(2)2p(5)3l and 2s2p(6)3l(l=s, p, d) states along the Ne-like isoelectronic sequence of ions (Z = 50-57) have been calculated by using the multiconfiguration Dirac-Fock package GRASP92 and the fully relativistic distorted-wave program REIE06. In the calculations, the relativistic effects and electron correlation effects are considered systematically. Based on those calculations, the EIE cross sections along the Ne-like isoelectronic sequence of ions for different incident electron energies are discussed, and some important conclusions are drawn. We also study the influence of the correlation effects on the values of the 3C/3D line-intensity ratio [3C: (2p(1/2)3d(3/2))(1) -> 2s(2)2p(6) S-1(0), 3D: (2p(3/2)3d(5/2))(1) -> 2s(2)2p(6) S-1(0)] along the Ne-like sequence. A comparison is made between the present results and previous theoretical calculations and experimental results for the EIE cross sections in Ba-46 (+) ions, and a good agreement is obtained.

Experimental investigation of transfer ionization mechanism in slow He2+ -He collisions

The processes of transfer ionization in He2+ -He collisions at energies ranging from 20 to 40 keV have been studied experimentally by means of cold target recoil ions momentum spectroscopy. From the longitudinal momentum spectra of recoil ions, different mechanisms of transfer ionization have been obtained. The results show that one of the electrons of helium atom being captured into the ground state of projectile ion He2+ and the other one emitted to the continuum state of projectile or target are the dominant mechanisms of transfer ionization. The autoionization cross section of projectile after two-electron capture into a double excited state is small. Transfer ionization for one target electron capture into ground state and the other one into the continuum of projectile mainly occurs at large impact parameter collisions.

Neutron-Proton Asymmetry Dependence of Spectroscopic Factors in Ar Isotopes

Spectroscopic factors have been extracted for proton-rich Ar-34 and neutron-rich Ar-46 using the (p, d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton-rich nucleus Ar-34 compared to that of Ar-46. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutronproton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements.

Can the nuclear symmetry potential at supra-saturation densities be negative?

In the framework of an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, for the central Au-197 + Au-197 reaction at an incident beam energy of 400 MeV/nucleon, the effect of nuclear symmetry potential at supra-saturation densities on the preequilibrium clusters emission is studied. It is found that for the positive symmetry potential at supra-saturation densities the neutron-to-proton ratio of lighter clusters with mass number A less than or similar to 3 [(n/p)(A less than or similar to 3)] is larger than that of the heavier clusters with mass number A > 3 [(n/p)(A>3)], whereas for the negative symmetry potential at supra-saturation densities the (n/p)(A less than or similar to 3) is smaller than the (n/p)(A>3). This may be considered as a probe of the negative symmetry potential at supra-saturation densities.