Shell structure in neutron-rich Ca and Ni nuclei under semi-realistic mean fields

Shell structure in the neutron-rich Ca and Ni nuclei is investigated by the spherical Hartree-Fock calculations with the semi-realistic $NN$ interactions. Specific ingredients of the effective interaction, particularly the tensor force, often play a key role in the $Z$ dependence of the neutron shell structure. Such examples are found in N=32 and N=40; N=32 becomes magic or submagic in $^{52}$Ca while its magicity is broken in $^{60}$Ni, and N=40 is submagic (though not magic) in $^{68}$Ni but not in $^{60}$Ca. Comments are given on the doubly magic nature of $^{78}$Ni. We point out that the loose binding can lead to a submagic number N=58 in $^{86}$Ni, assisted by the weak pair coupling.Comment: 14 pages including 5 figures, to appear in Physical Review C (Rapid Communication

Parity Dependence of Nuclear Level Densities

A simple formula for the ratio of the number of odd- and even-parity states as a function of temperature is derived. This formula is used to calculate the ratio of level densities of opposite parities as a function of excitation energy. We test the formula with quantum Monte Carlo shell model calculations in the $(pf+g_{9/2})$-shell. The formula describes well the transition from low excitation energies where a single parity dominates to high excitations where the two densities are equal.Comment: 14 pages, 4 eps figures included, RevTe

Quantum number projection at finite temperature via thermofield dynamics

Applying the thermo field dynamics, we reformulate exact quantum number projection in the finite-temperature Hartree-Fock-Bogoliubov theory. Explicit formulae are derived for the simultaneous projection of particle number and angular momentum, in parallel to the zero-temperature case. We also propose a practical method for the variation-after-projection calculation, by approximating entropy without conflict with the Peierls inequality. The quantum number projection in the finite-temperature mean-field theory will be useful to study effects of quantum fluctuations associated with the conservation laws on thermal properties of nuclei.Comment: 27 pages, using revtex4, to be published in PR

Total and Parity-Projected Level Densities of Iron-Region Nuclei in the Auxiliary Fields Monte Carlo Shell Model

We use the auxiliary-fields Monte Carlo method for the shell model in the complete $(pf+0g_{9/2})$-shell to calculate level densities. We introduce parity projection techniques which enable us to calculate the parity dependence of the level density. Results are presented for $^{56}$Fe, where the calculated total level density is found to be in remarkable agreement with the experimental level density. The parity-projected densities are well described by a backshifted Bethe formula, but with significant dependence of the single-particle level-density and backshift parameters on parity. We compare our exact results with those of the thermal Hartree-Fock approximation.Comment: 14 pages, 3 Postscript figures included, RevTe

Conductance of graphene nanoribbon junctions and the tight binding model

Planar carbon-based electronic devices, including metal/semiconductor junctions, transistors and interconnects, can now be formed from patterned sheets of graphene. Most simulations of charge transport within graphene-based electronic devices assume an energy band structure based on a nearest-neighbour tight binding analysis. In this paper, the energy band structure and conductance of graphene nanoribbons and metal/semiconductor junctions are obtained using a third nearest-neighbour tight binding analysis in conjunction with an efficient nonequilibrium Green’s function formalism. We find significant differences in both the energy band structure and conductance obtained with the two approximations

A Scintillating Fiber Tracker With SiPM Readout

We present a prototype for the first tracking detector consisting of 250 micron thin scintillating fibers and silicon photomultiplier (SiPM) arrays. The detector has a modular design, each module consists of a mechanical support structure of 10mm Rohacell foam between two 100 micron thin carbon fiber skins. Five layers of scintillating fibers are glued to both top and bottom of the support structure. SiPM arrays with a channel pitch of 250 micron are placed in front of the fibers. We show the results of the first module prototype using multiclad fibers of types Bicron BCF-20 and Kuraray SCSF-81M that were read out by novel 32-channel SiPM arrays from FBK-irst/INFN Perugia as well as 32-channel SiPM arrays produced by Hamamatsu. A spatial resolution of 88 micron +/- 6 micron at an average yield of 10 detected photons per minimal ionizig particle has been achieved.Comment: 5 pages, 7 figures, submitted as proceedings to the 11th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD08

Kaon decay interferometry as meson dynamics probes

We discuss the time dependent interferences between $K_L$ and $K_S$ in the decays in $3\pi$ and $\pi\pi\gamma$, to be studied at interferometry machines such as the $\phi$-factory and LEAR. We emphasize the possibilities and the advantages of using interferences, in comparison with width measurements, to obtain information both on $CP$ conserving and $CP$ violating amplitudes. Comparison with present data and suggestions for future experiments are made.Comment: 15 pages, in RevTex, Report INFNNA-IV-93-31, UTS-DFT-93-2

Appearance of Flat Bands and Edge States in Boron-Carbon-Nitride Nanoribbons

Presence of flat bands and edge states at the Fermi level in graphene nanoribbons with zigzag edges is one of the most interesting and attracting properties of nanocarbon materials but it is believed that they are quite fragile states and disappear when B and N atoms are doped at around the edges. In this paper, we theoretically investigate electronic and magnetic properties of boron-carbon-nitride (BCN) nanoribbons with zigzag edges where the outermost C atoms on the edges are alternately replaced with B and N atoms using the first principles calculations. We show that BCN nanoribbons have the flat bands and edge states at the Fermi level in both H_2 rich and poor environments. The flat bands are similar to those at graphene nanoribbons with zigzag edges, but the distributions of charge and spin densities are different between them. A tight binding model and the Hubbard model analysis show that the difference in the distribution of charge and spin densities is caused by the different site energies of B and N atoms compared with C atoms.Comment: 5 pages; 3 figure

Strong rescattering in K-> 3pi decays and low-energy meson dynamics

We present a consistent analysis of final state interactions in ${K\rightarrow 3\pi}$ decays in the framework of Chiral Perturbation Theory. The result is that the kinematical dependence of the rescattering phases cannot be neglected. The possibility of extracting the phase shifts from future $K_S-K_L$ interference experiments is also analyzed.Comment: 14 pages in RevTex, 3 figures in postscrip

Photo-Thermoelectric Effect at a Graphene Interface Junction

We investigate the optoelectronic response of a graphene interface junction, formed with bilayer and single-layer graphene, by photocurrent (PC) microscopy. We measure the polarity and amplitude of the PC while varying the Fermi level by tuning a gate voltage. These measurements show that the generation of PC is by a photo-thermoelectric effect. The PC displays a factor of ~10 increase at the cryogenic temperature as compared to room temperature. Assuming the thermoelectric power has a linear dependence on the temperature, the inferred graphene thermal conductivity from temperature dependent measurements has a T^{1.5} dependence below ~100 K, which agrees with recent theoretical predictions