Spatial distribution of local tunneling conductivity due to interference and Coulomb interaction effects for deep and shallow impurities on semiconductor surfaces

Spatial distribution of local tunneling conductivity was investigated for deep and shallow impurities on semiconductor surfaces. Non-equilibrium Coulomb interaction and interference effects were taken into account and analyzed theoretically with the help of Keldysh formalism. Two models were investigated: mean field self-consistent approach for shallow impurity state and Hubbard-{I} model for deep impurity state. We have found that not only above the impurity but also at the distances comparable to the lattice period both effects interference between direct and resonant tunneling channels and on-site Coulomb repulsion of localized electrons strongly modifies form of tunneling conductivity measured by the scanning tunneling microscopy/spectroscopy (STM/STS).Comment: 5 pages, 3 figure

Orientational ordering in monolayers of ortho–para hydrogen

We discuss orientational ordering in monolayers of solid hydrogen in view of recent experimental findings in NMR studies of (ortho)c–(para)₁–c-hydrogen mixtures on boron nitride substrate. Analysis of the temperature-concentration behavior for the observed NMR frequency splitting is given on the basis of a two-dimensional (J = 1)c–(J = 0)₁–c-rotor model with the quadrupolar coupling constant Г₀ = (0.50 ± 0.03) K and the crystalline field amplitude V₀ = (0.70 ± 0.10) K derived from experiment. The two distinct para-rotational short-range ordered structures are described in terms of the local alignment and orientation of the polar principal axis, and are shown to be due to the interplay between the positive and negative crystalline fields. It is shown that the local structures observed below the 2D site-percolation threshold cp = 0.72 are rather different from the ferromagnetic-type para-rotational ordering suggested earlier by Harris and Berlinsky

NMR studies of methane and hydrogen in microporous materials

We review the results of nuclear magnetic resonance studies of the molecular dynamics of the quantum gases HD and CH₄ adsorbed in the cages of microporous structures. Measurements of the variation of the nuclear spinlattice and nuclear spin-spin relaxation times with temperature provide detailed information about the translational and rotational dynamics of the adsorbed molecules over a wide temperature range

Through the combining glass

Reflective optical combiners like beam splitters and two way mirrors are used in AR to overlap digital contents on the users' hands or bodies. Augmentations are usually unidirectional, either reflecting virtual contents on the user's body (Situated Augmented Reality) or augmenting user's reflections with digital contents (AR mirrors). But many other novel possibilities remain unexplored. For example, users' hands, reflected inside a museum AR cabinet, can allow visitors to interact with the artifacts exhibited. Projecting on the user's hands as their reflection cuts through the objects can be used to reveal objects' internals. Augmentations from both sides are blended by the combiner, so they are consistently seen by any number of users, independently of their location or, even, the side of the combiner through which they are looking. This paper explores the potential of optical combiners to merge the space in front and behind them. We present this design space, identify novel augmentations/interaction opportunities and explore the design space using three prototypes

Design and performance of the ADMX SQUID-based microwave receiver

The Axion Dark Matter eXperiment (ADMX) was designed to detect ultra-weakly interacting relic axion particles by searching for their conversion to microwave photons in a resonant cavity positioned in a strong magnetic field. Given the extremely low expected axion-photon conversion power we have designed, built and operated a microwave receiver based on a Superconducting QUantum Interference Device (SQUID). We describe the ADMX receiver in detail as well as the analysis of narrow band microwave signals. We demonstrate the sustained use of a SQUID amplifier operating between 812 and 860 MHz with a noise temperature of 1 K. The receiver has a noise equivalent power of 1.1x10^-24 W/sqrt(Hz) in the band of operation for an integration time of 1.8x10^3 s.Comment: 8 pages, 12 figures, Submitted to Nuclear Inst. and Methods in Physics Research,

Requests On E-Mail: a Cross-Cultural Comparison

This study investigates differences in request e-mails written in English by Chinese English learners and native American English speakers The results show that while Chinese English learners treat e-mail communications like either formal letters or telephone conversations, native American English speakers regard e-mail communications as closer to written memos It was also found that although the native American English speakers structure their e-mail request messages in a rather direct sequence, the linguistic forms they employ to express their requests are more indirect In contrast, the Chinese English learners structure their request messages in an indirect sequence, but the linguistic forms they use to realize their requests are more direct Given this contrast, it is not surprising that some of the request samples written by Chinese English learners were judged as very impolite by the native English speaking evaluators in this study The findings of this study thus demonstrate the importance of studying requests within the overall discourse in which they occur. Studying only the linguistic forms used in phrasing the request itself, as in the studies conducted by Blum-Kulka et al (1989), cannot provide us with a full picture of the cultural differences inherent in making requestsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69055/2/10.1177_003368829802900206.pd

Extended search for the invisible axion with the axion dark matter experiment

This Letter reports on a cavity haloscope search for dark matter axions in the Galactic halo in the mass range 2.81–3.31μeV. This search utilizes the combination of a low-noise Josephson parametric amplifier and a large-cavity haloscope to achieve unprecedented sensitivity across this mass range. This search excludes the full range of axion-photon coupling values predicted in benchmark models of the invisible axion that solve the strong CP problem of quantum chromodynamics

Photoproduction of D∗±D^{*\pm} mesons associated with a leading neutron

The photoproduction of $D^{*\pm} (2010)$ mesons associated with a leading neutron has been observed with the ZEUS detector in $ep$ collisions at HERA using an integrated luminosity of 80 pb$^{-1}$. The neutron carries a large fraction, {$x_L>0.2$}, of the incoming proton beam energy and is detected at very small production angles, {$\theta_n<0.8$ mrad}, an indication of peripheral scattering. The $D^*$ meson is centrally produced with pseudorapidity {$|\eta| 1.9$ GeV}, which is large compared to the average transverse momentum of the neutron of 0.22 GeV. The ratio of neutron-tagged to inclusive $D^*$ production is $8.85\pm 0.93({\rm stat.})^{+0.48}_{-0.61}({\rm syst.})\%$ in the photon-proton center-of-mass energy range {$130 <W<280$ GeV}. The data suggest that the presence of a hard scale enhances the fraction of events with a leading neutron in the final state.Comment: 28 pages, 4 figures, 2 table

Measurement of dijet photoproduction for events with a leading neutron at HERA

Differential cross sections for dijet photoproduction and this process in association with a leading neutron, e+ + p -> e+ + jet + jet + X (+ n), have been measured with the ZEUS detector at HERA using an integrated luminosity of 40 pb-1. The fraction of dijet events with a leading neutron was studied as a function of different jet and event variables. Single- and double-differential cross sections are presented as a function of the longitudinal fraction of the proton momentum carried by the leading neutron, xL, and of its transverse momentum squared, pT^2. The dijet data are compared to inclusive DIS and photoproduction results; they are all consistent with a simple pion-exchange model. The neutron yield as a function of xL was found to depend only on the fraction of the proton beam energy going into the forward region, independent of the hard process. No firm conclusion can be drawn on the presence of rescattering effects.Comment: 40 pages, 18 figure