Theory of Magneto--Acoustic Transport in Modulated Quantum Hall Systems Near ν=1/2\nu=1/2

Motivated by the experimental results of Willett et al [Phys.Rev. Lett., {\bf 78}, 4478 (1997)] we develop a magneto-transport theory for the response of a two dimensional electron gas (2DEG) in the Fractional Quantum Hall Regime near Landau level filling factor $\nu = 1/2$ to the surface acoustic wave (SAW) in the presence of an added periodic density modulation. We assume there exists a Composite Fermion Fermi Surface (CF-FS) at $\nu = 1/2$, and we show that the deformation of the (CF-FS) due to the density modulation can be at the origin of the observed transport anomalies for the experimental conditions. Our analysis is carried out particularly for the non-local case which corresponds to the SAW experiments. We introduce a new model of a deformed CF-FS. The model permits us to explain anomalous features of the response of the modulated 2DEG to the SAW near $\nu = 1/2:$ namely the nonlinear wave vector dependence of the electron conductivity, the appearance of peaks in the SAW velocity shift and attenuation and the anisotropy of the effect, all of which originate from contributions to the conductivity tensor due to the regions of the CF-FS which are flattened by the applied modulation.Comment: 13 pages, 4 figures, the published versio

Composite Fermions and the Fermion-Chern-Simons Theory

The concept of composite fermions, and the related Fermion-Chern-Simons theory, have been powerful tools for understanding quantum Hall systems with a partially full lowest Landau level. We shall review some of the successes of the Fermion-Chern-Simons theory, as well as some limitations and outstanding issues.Comment: 13 pages, including 2 figures. Invited talk at International Symposium, Quantum Hall Effect: Past, Present and Future, Stuttgart, July 2003. Proceedings to appear in Physica

Composite fermions in the Fractional Quantum Hall Effect: Transport at finite wavevector

We consider the conductivity tensor for composite fermions in a close to half-filled Landau band in the temperature regime where the scattering off the potential and the trapped gauge field of random impurities dominates. The Boltzmann equation approach is employed to calculate the quasiclassical transport properties at finite effective magnetic field, wavevector and frequency. We present an exact solution of the kinetic equation for all parameter regimes. Our results allow a consistent description of recently observed surface acoustic wave resonances and other findings.Comment: REVTEX, 4 pages, 1 figur

Effective mass of composite fermion: a phenomenological fit in with anomalous propagation of surface acoustic wave

We calculate the conductivity associated with the anomalous propagation of a surface acoustic wave above a two-dimensional electron gas at $\nu=1/2$. Murthy-Shankar's middle representation is adopted and a contribution to the response functions beyond the random phase approximation has been taken into account. We give a phenomenological fit for the effective mass of composite fermion in with the experimental data of the anomalous propagation of surface acoustic wave at $\nu=1/2$ and find the phenomenological value of the effective mass is several times larger than the theoretical value $m_{th}^*=6\epsilon/e^2l_{1/2}$ derived from the Hartree-Fock approximation. We compare our phenomenologically fitting composite fermion effective mass with those appeared in the measurements of the activation energy and the Shubnikov-de Haas effect and find that our result is fairly reasonable.Comment: 8 pages, 5 figures, the longer version of cond-mat/9801131 with crucial corrections, accepted for publication by PR

The Orbit of the Orphan Stream

We use recent SEGUE spectroscopy and SDSS and SEGUE imaging data to measure the sky position, distance, and radial velocities of stars in the tidal debris stream that is commonly referred to as the "Orphan Stream." We fit orbital parameters to the data, and find a prograde orbit with an apogalacticon, perigalacticon, and eccentricity of 90 kpc, 16.4 kpc and 0.7, respectively. Neither the dwarf galaxy UMa II nor the Complex A gas cloud have velocities consistent with a kinematic association with the Orphan Stream. It is possible that Segue-1 is associated with the Orphan Stream, but no other known Galactic clusters or dwarf galaxies in the Milky Way lie along its orbit. The detected portion of the stream ranges from 19 to 47 kpc from the Sun and is an indicator of the mass interior to these distances. There is a marked increase in the density of Orphan Stream stars near (l,b)=(253,49) deg., which could indicate the presence of the progenitor at the edge of the SDSS data. If this is the progenitor, then the detected portion of the Orphan Stream is a leading tidal tail. We find blue horizontal branch (BHB) stars and F turnoff stars associated with the Orphan Stream. The turnoff color is (g-r)_0=0.22. The BHB stars have a low metallicity of [Fe/H]=-2.1. The orbit is best fit to a halo potential with a halo plus disk mass of about 2.6x10^11 Solar masses, integrated to 60 kpc from the Galactic center. Our best fit is found with a logarithmic halo speed of v_halo=73+/-24 km/s, a disk+bulge mass of M(R< 60 kpc) = 1.3x10^11 Solar masses, and a halo mass of M(R< 60 kpc) = 1.4x10^11 Solar masses. The Orphan Stream is projected to extend to 90 kpc from the Galactic center, and measurements of these distant parts of the stream would be a powerful probe of the mass of the Milky Way (truncated).Comment: 17 Figures, ApJ accepte

Spiritual care: development of a nursing student resource

Background: The growth of international migration and globalization has increasingly diversified patient populations, emphasizing the need for nursing students to provide competent spiritual care. Purpose: To comprehensively understand the teaching and learning strategies used to prepare undergraduate nursing students for spiritual care and the development of an educational resource. Methods: An integrative literature review using deductive data analysis, consultations with Northwestern Polytechnic (NWP) faculty and students, and an environmental scan were conducted. Findings from these three methods informed the development of a student Spiritual Care Quick Reference (SCQR) for clinical and a faculty Spiritual Care Educational Resource (SCER). Results: Development of a SCQR for students and a faculty SCER. Conclusions: No one strategy is best, but any combination of educational strategies (e.g., case studies, discussion, lectures, simulation) can positively impact spiritual care competency within clinical practice. The developed resource can be valuable for faculty to promote the spiritual care competency of undergraduate students

Characterization of fractional-quantum-Hall-effect quasiparticles

Composite fermions in a partially filled quasi-Landau level may be viewed as quasielectrons of the underlying fractional quantum Hall state, suggesting that a quasielectron is simply a dressed electron, as often is true in other interacting electron systems, and as a result has the same intrinsic charge and exchange statistics as an electron. This paper discusses how this result is reconciled with the earlier picture in which quasiparticles are viewed as fractionally-charged fractional-statistics ``solitons". While the two approaches provide the same answers for the long-range interactions between the quasiparticles, the dressed-electron description is more conventional and unifies the view of quasiparticle dynamics in and beyond the fractional quantum Hall regime.Comment: 11 pages, latex, no figure

Habitual intake of flavonoid subclasses and risk of colorectal cancer in two large prospective cohorts

Background: Flavonoids inhibit the growth of colon cancer cells in vitro. In a secondary analysis of a randomized controlled trial, the Polyp Prevention Trial, a higher intake of one sub-class, flavonols, was significantly associated with reduced risk of recurrent advanced adenoma. Most previous prospective studies on colorectal cancer evaluated only a limited number of flavonoid sub-classes and intake ranges, yielding inconsistent results.  Objective: To examine whether higher habitual dietary intakes of flavonoid subclasses (flavonols, flavones, flavanones, flavan-3-ols and anthocyanins) are associated with lower risk of colorectal cancer.  Design: Using data from validated food frequency questionnaires administered every four years and an updated flavonoid food composition database flavonoid intakes were calculated for 42,478 male participants from the Health Professionals Follow-up Study and for 76,364 female participants from the Nurses’ Health Study.  Results: During up to 26 years of follow-up, 2,519 colorectal cancer cases (1,061 in men, 1,458 in women) were documented. Intakes of flavonoid subclasses were not associated with risk of colorectal cancer in either cohort. Pooled multivariable adjusted relative risks (95% confidence interval) comparing the highest with the lowest quintile were 1.04 (0.91, 1.18) for flavonols; 1.01 (0.89, 1.15) for flavones; 0.96 (0.84, 1.10) for flavanones; 1.07 (0.95, 1.21) for flavan-3-ols; and 0.98 (0.81, 1.19) for anthocyanins (all p-values for heterogeneity by sex >0.19). In subsite analyses, flavonoid intake was also not associated with colon or rectal cancer risk.  Conclusion: Our findings do not support the hypothesis that a higher habitual intake of any flavonoid sub-class decreases the risk of colorectal cancer

Multicarrier communication over underwater acoustic channels with nonuniform Doppler shifts

Author Posting. © IEEE, 2008. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 33 (2008): 198-209, doi:10.1109/JOE.2008.920471.Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of the carrier frequency to the signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat the channel as having a common Doppler scaling factor on all propagation paths, and propose a two-step approach to mitigating the Doppler effect: 1) nonuniform Doppler compensation via resampling that converts a "wideband" problem into a "narrowband" problem and 2) high-resolution uniform compensation of the residual Doppler. We focus on zero-padded orthogonal frequency-division multiplexing (OFDM) to minimize the transmission power. Null subcarriers are used to facilitate Doppler compensation, and pilot subcarriers are used for channel estimation. The receiver is based on block-by-block processing, and does not rely on channel dependence across OFDM blocks; thus, it is suitable for fast-varying UWA channels. The data from two shallow-water experiments near Woods Hole, MA, are used to demonstrate the receiver performance. Excellent performance results are obtained even when the transmitter and the receiver are moving at a relative speed of up to 10 kn, at which the Doppler shifts are greater than the OFDM subcarrier spacing. These results suggest that OFDM is a viable option for high-rate communications over wideband UWA channels with nonuniform Doppler shifts.B. Li and S. Zhou are supported by the ONR YIP grant N00014-07-1-0805 and the NSF grant ECCS-0725562. M. Stojanovic is supported by the ONR grant N00014-07-1-0202. L. Freitag is supported by the ONR grants N00014- 02-6-0201 and N00014-07-1-0229. P. Willett is supported by the ONR grant N00014-07-1-0055