Quantum railroads and directed localization at the juncture of quantum Hall systems

The integer quantum Hall effect (QHE) and one-dimensional Anderson localization (AL) are limiting special cases of a more general phenomenon, directed localization (DL), predicted to occur in disordered one-dimensional wave guides called "quantum railroads" (QRR). Here we explain the surprising results of recent measurements by Kang et al. [Nature 403, 59 (2000)] of electron transfer between edges of two-dimensional electron systems and identify experimental evidence of QRR's in the general, but until now entirely theoretical, DL regime that unifies the QHE and AL. We propose direct experimental tests of our theory.Comment: 11 pages revtex + 3 jpeg figures, to appear in Phys. Rev.

Magnetic Properties of a Quantum Ferrimagnet: NiCu(pba)(D_2O)_3 . 2D_2O

We report the results of magnetic measurements on a powder sample of NiCu(pba)(D_2O)_3 \cdot 2D_2O$(pba=1,3-propylenebis(oxamato)) which is one of the prototypical examples of an$S$=1/2 and 1 ferrimagnetic chain. Susceptibility($\chi$) shows a monotonous increase with decreasing temperature (T) and reaches a maximum at about 7 K. In the plot of$\chi T$versus$T$, the experimental data exhibit a broad minimum and are fit to the$\chi T$curve calculated for the ferrimagnetic Heisenberg chain composed of S=1/2 and 1. From this fit, we have evaluated the nearest-neighbor exchange constant$J/k_B=121 K$, the g-values of Ni$^{2+}$and Cu$^{2+}$,$g_{Ni}$=2.22 and$g_{Cu}$=2.09, respectively. Applied external field dependence of$\chi T$ at low temperatures is reproduced fairly well by the calculation for the same ferrimagnetic model.Comment: 7pages, 4 postscript figures, usues REVTEX. appear in J. Phys. Soc. Jpn vol 67 No.7 (1998

CD40 Ligand Expression is Defective in a Subset of Patients with Common Variable Immunodeficiency.

Common variable immunodeficiency (CVI) is characterized by hypogammaglobulinemia and recurrent bacterial infections due to failure of CVI B cells to differentiate in vivo into immunoglobulin-secreting plasma cells. We hypothesized that T-cell dysfunction resulting in abnormal contact-mediated B-cell activation may play a prominent role in the failure of CVI B cells to produce specific antibody. We have previously shown that B-cell proliferation and IgE production after stimulation with anti-CD40 and interleukin (IL) 4 were normal in 22 CVI patients evaluated, indicating that CVI B cells respond to signals delivered via CD40. Here we report that CD40 ligand (gp39) mRNA expression by activated lymphocytes from CVI patients (n = 31) as a group was significantly depressed (P \u3c 0.0001) compared with normal controls (n = 32). gp39 mRNA expression by activated lymphocytes from 13 CVI patients fell below the normal control range. T-cell surface expression of functional gp39 protein was correspondingly low in those patients with gp39 mRNA levels below normal control range and normal in patients with gp39 mRNA levels within normal control range. In CVI patients as a group, gp39 mRNA levels correlated with IL-2 mRNA levels (P \u3c 0.002, r = 0.6) and production (P \u3c 0.001, r = 0.7) but not with gene expression or production of other lymphokines evaluated, suggesting an as-yet-undetermined association between gp39 and IL-2 gene regulation. Of the 13 patients whose activated T cells exhibited gp39 mRNA expression below the normal control range, 2 had normal T-cell-derived lymphokine production, whereas the remaining 11 exhibited broader T-cell dysfunction, resulting in IL-2 deficiency, and in some patients deficient production of other lymphokines as well, reflecting a heterogeneity in the underlying mechanisms leading to depressed gp39 expression in these patients. The observation that both gene and surface expression of gp39 by activated T cells is depressed in a subgroup of CVI patients suggests that inefficient signaling via CD40 may be responsible, in part, for failure of B-cell differentiation in these patients

Gauge Dependence of Mass and Condensate in Chirally Asymmetric Phase of Quenched QED3

We study three dimensional quenched Quantum Electrodynamics in the bare vertex approximation. We investigate the gauge dependence of the dynamically generated Euclidean mass of the fermion and the chiral condensate for a wide range of values of the covariant gauge parameter $\xi$. We find that (i) away from $\xi=0$, gauge dependence of the said quantities is considerably reduced without resorting to sophisticated vertex {\em ansatze}, (ii) wavefunction renormalization plays an important role in restoring gauge invariance and (iii) the Ward-Green-Takahashi identity seems to increase the gauge dependence when used in conjunction with some simplifying assumptions. In the Landau gauge, we also verify that our results are in agreement with those based upon dimensional regularization scheme within the numerical accuracy available.Comment: 14 pages, 11 figures, uses revte

Gauged Nambu-Jona-Lasinio model with extra dimensions

We investigate phase structure of the D (> 4)-dimensional gauged Nambu-Jona-Lasinio (NJL) model with $\delta(=D-4)$ extra dimensions compactified on TeV scale, based on the improved ladder Schwinger-Dyson (SD) equation in the bulk. We assume that the bulk running gauge coupling in the SD equation for the SU(N_c) gauge theory with N_f massless flavors is given by the truncated Kaluza-Klein effective theory and hence has a nontrivial ultraviolet fixed point (UVFP). We find the critical line in the parameter space of two couplings, the gauge coupling and the four-fermion coupling, which is similar to that of the gauged NJL model with fixed (walking) gauge coupling in four dimensions. It is shown that in the presence of such walking gauge interactions the four-fermion interactions become ``nontrivial'' even in higher dimensions, similarly to the four-dimensional gauged NJL model. Such a nontriviality holds only in the restricted region of the critical line (``nontrivial window'') with the gauge coupling larger than a non-vanishing value (``marginal triviality (MT)'' point), in contrast to the four-dimensional case where such a nontriviality holds for all regions of the critical line except for the pure NJL point. In the nontrivial window the renormalized effective potential yields a nontrivial interaction which is conformal invariant. The exisitence of the nontrivial window implies ``cutoff insensitivity'' of the physics prediction in spite of the ultraviolet dominance of the dynamics. In the formal limit D -> 4, the nontrivial window coincides with the known condition of the nontriviality of the four-dimensional gauged NJL model, $9/(2N_c) < N_f - N_c < 9/2 N_c$.Comment: 34 pages, 6 figures, references added, to appear in Phys.Rev.D. The title is changed in PR

Ballistic spin-polarized transport and Rashba spin precession in semiconductor nanowires

We present numerical calculations of the ballistic spin-transport properties of quasi-one-dimensional wires in the presence of the spin-orbit (Rashba) interaction. A tight-binding analog of the Rashba Hamiltonian which models the Rashba effect is used. By varying the robustness of the Rashba coupling and the width of the wire, weak and strong coupling regimes are identified. Perfect electron spin-modulation is found for the former regime, regardless of the incident Fermi energy and mode number. In the latter however, the spin-conductance has a strong energy dependence due to a nontrivial subband intermixing induced by the strong Rashba coupling. This would imply a strong suppression of the spin-modulation at higher temperatures and source-drain voltages. The results may be of relevance for the implementation of quasi-one-dimensional spin transistor devices.Comment: 19 pages (incl. 9 figures). To be published in PR

Chiral Symmetry Breaking in Quenched Massive Strong-Coupling QED4_4

We present results from a study of subtractive renormalization of the fermion propagator Dyson-Schwinger equation (DSE) in massive strong-coupling quenched QED$_4$. Results are compared for three different fermion-photon proper vertex {\it Ans\"{a}tze\/}: bare $\gamma^\mu$, minimal Ball-Chiu, and Curtis-Pennington. The procedure is straightforward to implement and numerically stable. This is the first study in which this technique is used and it should prove useful in future DSE studies, whenever renormalization is required in numerical work.Comment: REVTEX 3.0, 15 pages plus 7 uuencoded PostScript figure

The detection of neutrino interactions in the emulsion/lead target of the OPERA experiment

The OPERA neutrino detector in the underground Gran Sasso Laboratory (LNGS) was designed to perform the first detection of neutrino oscillations in appearance mode through the study of $\nu_\mu\to\nu_\tau$ oscillations. The apparatus consists of an emulsion/lead target complemented by electronic detectors and it is placed in the high energy long-baseline CERN to LNGS beam (CNGS) 730 km away from the neutrino source. Runs with CNGS neutrinos were successfully carried out in 2007 and 2008 with the detector fully operational with its related facilities for the emulsion handling and analysis. After a brief description of the beam and of the experimental setup we report on the collection, reconstruction and analysis procedures of first samples of neutrino interaction events

Emulsion sheet doublets as interface trackers for the OPERA experiment

New methods for efficient and unambiguous interconnection between electronic counters and target units based on nuclear photographic emulsion films have been developed. The application to the OPERA experiment, that aims at detecting oscillations between mu neutrino and tau neutrino in the CNGS neutrino beam, is reported in this paper. In order to reduce background due to latent tracks collected before installation in the detector, on-site large-scale treatments of the emulsions ("refreshing") have been applied. Changeable Sheet (CSd) packages, each made of a doublet of emulsion films, have been designed, assembled and coupled to the OPERA target units ("ECC bricks"). A device has been built to print X-ray spots for accurate interconnection both within the CSd and between the CSd and the related ECC brick. Sample emulsion films have been extensively scanned with state-of-the-art automated optical microscopes. Efficient track-matching and powerful background rejection have been achieved in tests with electronically tagged penetrating muons. Further improvement of in-doublet film alignment was obtained by matching the pattern of low-energy electron tracks. The commissioning of the overall OPERA alignment procedure is in progress.Comment: 19 pages, 19 figure

Measurement of the atmospheric muon charge ratio with the OPERA detector

The OPERA detector at the Gran Sasso underground laboratory (LNGS) was used to measure the atmospheric muon charge ratio in the TeV energy region. We analyzed 403069 atmospheric muons corresponding to 113.4 days of livetime during the 2008 CNGS run. We computed separately the muon charge ratio for single and for multiple muon events in order to select different energy regions of the primary cosmic ray spectrum and to test the charge ratio dependence on the primary composition. The measured charge ratio values were corrected taking into account the charge-misidentification errors. Data have also been grouped in five bins of the "vertical surface energy". A fit to a simplified model of muon production in the atmosphere allowed the determination of the pion and kaon charge ratios weighted by the cosmic ray energy spectrum.Comment: 14 pages, 10 figure