Symmetry dictated universal helicity redistribution of Dirac fermions in transport

Helicity is a fundamental property of Dirac fermions. Yet, how it changes in transport processes remains largely mysterious. We uncover, theoretically, the rule of spinor state transformation and consequently universal helicity redistribution in two cases of transport through potentials of electrostatic and mass types, respectively. The former is dictated by Lorentz boost and its complex counterpart in Klein tunneling regime. The latter is governed by an abstract rotation group we identified, which reduces to SO(2) when acting on the plane of effective mass and momentum. This endows an extra structure foliating the Hilbert space of Dirac spinors, establishes miraculously a unified yet latent connection between helicity, Klein tunneling, and Lorentz boost. Our results thus deepen the understanding of relativistic quantum transport, and may open a new window for exotic helicity-based physics and applications in mesoscopic systems.Comment: 6 pages, 4 figure

Production of proton-rich nuclei around Z=84-90 in fusion-evaporation reactions

Within the framework of the dinuclear system model, production cross sections of proton-rich nuclei with charged numbers of Z=84-90 are investigated systematically. Possible combinations with the $^{28}$Si, $^{32}$S, $^{40}$Ar bombarding the target nuclides $^{165}$Ho, $^{169}$Tm, $^{170-174}$Yb, $^{175,176}$Lu, $^{174,176-180}$Hf and $^{181}$Ta are analyzed thoroughly. The optimal excitation energies and evaporation channels are proposed to produce the proton-rich nuclei. The systems are feasible to be constructed in experiments. It is found that the neutron shell closure of N=126 is of importance during the evaporation of neutrons. The experimental excitation functions in the $^{40}$Ar induced reactions can be nicely reproduced. The charged particle evaporation is comparable with neutrons in cooling the excited proton-rich nuclei, in particular for the channels with $\alpha$ and proton evaporation. The production cross section increases with the mass asymmetry of colliding systems because of the decrease of the inner fusion barrier. The channels with pure neutron evaporation depend on the isotopic targets. But it is different for the channels with charged particles and more sensitive to the odd-even effect.Comment: 15 pages, 10 figures. arXiv admin note: text overlap with arXiv:0803.1117, arXiv:0707.258

Retrieval of Optical Constant and Particle Size Distribution of Particulate Media Using the PSO-Based Neural Network Algorithm

An improved neural network algorithm was proposed and applied to the inverse radiative problems. A multi-strategy particle swarm optimization was applied to improve the performance of the back propagation multi-layer feed-forward neural network algorithm. Three commonly used particle size distribution (PSD) functions in a one-dimensional particle system were retrieved using the proposed algorithm. In addition, the optical constant was also estimated, and the measurement errors were considered. Results show that the proposed algorithm can be applied to the retrieval of PSDs and optical constant even with measurement errors. Finally, the proposed algorithm was applied to the simultaneous estimation of the PSDs and optical constant using the multi-wavelength and multi-thickness method

Methyl 9H-carbazole-9-acetate

The title compound, C15H13NO2, was synthesized by N-alkyl­ation of methyl bromo­acetate with 9H-carbazole. The carbazole ring system is essentially planar (mean atomic deviation = 0.0346 Å) and makes a dihedral angle of 86.5 (7)° with the methyl acetate group. Weak inter­molecular C—H⋯O hydrogen bonding is present in the crystal structure

Trinitrophenol Reactive T-Cell Hybridomas Recognize Antigens That Require Antigen Processing

Protein antigens must be taken up, processed, and displayed on the surface of antigen-presenting cells in association with major histocompatibility complex molecules before they can be recognized by T cells. Whether recognition of the haptens used to study allergic contact hypersensitivity in murine models similarly requires processing has not been determined. We analyzed whether presentation of trinitrophenol to trinitrophenol reactive T-cell hybridomas requires antigen processing by studying the effects of inhibitors of antigen processing and presentation on tile ability of a syngeneic B-cell tumor (A20) to present trinitrophenol to a series of interleukin-2 producing, trinitrophenol specific, major histocompatibility complex class II-restricted T-cell hybridomas.The ability of trinitrophenol modified A20 cells to stimulate the hybridomas was completely inhibited by rnonoclonal, anti-trinitrophenol, or anti-Ia antibodies and was significantly reduced by paraformaldehyde fixation immediately after trinitrophenol modification. Trinitrophenol-modified A20 cultured at 37°C for 2h prior to fixation was significantly more effective at stimulating the hybridomas than trinitrophenol-modified A20 to present trinitrophenol was inhibited by chloroquine. Paraformaldehyde fixation and chloroquine treatment had similar effects on the ability of trinitrophenol modified lymph node dendritic cells to stimulate the trinitrophenol specific hybridomas. Paraformaldehyde fixation and chloroquine treatment had similar effects on the ability of A20 cells to present ovalbumin to ovalbumin-specific hybridomas as they had on the ability of trinitrophenol modified A20 cells to present trinitrophenol to the trinitrophenol specific hybridomas. One of seven T-cell hybridomas responded to trinitrophenol modified ovalbumin but not other trinitrophenol modified proteins. These results suggest that, at least in part, T cells in the contact hypersensitivity response to trinitrophenol recognize antigens that require processing and that trinitrophenol modified proteins can be recognized