4,346 research outputs found
Resonant Tunneling through double-bended Graphene Nanoribbons
We investigate theoretically resonant tunneling through double-bended
graphene nanoribbon structures, i.e., armchair-edged graphene nanoribbons
(AGNRs) in between two semi-infinite zigzag graphene nanoribbon (ZGNR) leads.
Our numerical results demonstrate that the resonant tunneling can be tuned
dramatically by the Fermi energy and the length and/or widths of the AGNR for
both the metallic and semiconductor-like AGNRs. The structure can also be use
to control the valley polarization of the tunneling currents and could be
useful for potential application in valleytronics devices.Comment: 4 pages, 4 figure
The Limiting Distribution of Decoherent Quantum Random Walks
The behaviors of one-dimensional quantum random walks are strikingly
different from those of classical ones. However, when decoherence is involved,
the limiting distributions take on many classical features over time. In this
paper, we study the decoherence on both position and ``coin'' spaces of the
particle. We propose a new analytical approach to investigate these phenomena
and obtain the generating functions which encode all the features of these
walks. Specifically, from these generating functions, we find exact analytic
expressions of several moments for the time and noise dependence of position.
Moreover, the limiting position distributions of decoherent quantum random
walks are shown to be Gaussian in an analytical manner. These results
explicitly describe the relationship between the system and the level of
decoherence.Comment: 38 pages. 3 figures. Based on a Ph.D. thesis at Temple Universit
Prostate cancer screening in Europe and Asia
Prostate cancer (PCa) is the second most common cancer among men worldwide and even ranks first in Europe. Although Asia is known as the region with the lowest PCa incidence, it has been rising rapidly over the last 20 years mostly due to the introduction of prostate-specific antigen (PSA) testing. Randomized PCa screening studies in Europe show a mortality reduction in favor of PSA-based screening but coincide with high proportions of unnecessary biopsies, overdiagnosis and subsequent overtreatment. Conclusive data on the value of PSA-based screening and hence the balance between harms and benefits in Asia is still lacking. Because of known racial variations, Asian countries should not directly apply the European screening models. Like in the western world also in Asia, new predictive markers, tools and risk stratification strategies hold great potential to improve the early detection of PCa and to reduce the worldwide existing negative aspects of PSA-based PCa screening
Comparison of clinically significant prostate cancer detection by MRI cognitive biopsy and in-bore MRI-targeted biopsy for naïve biopsy patients
Background: Multiparametric magnetic resonance imaging (mpMRI) targeted prostate biopsy increases the diagnostic accuracy of clinically significant prostate cancer (PCa). Currently there is no consensus on which type of MRI-targeted biopsy performs better in a given setting. In this study, we aimed to compare the detection rate of (clinically significant) PCa by MRI cognitive targeted biopsy (COG) and in-bore MRI-targeted biopsy (IB) techniques for naïve prostate biopsy patients in China. Methods: Our study included 85 men from Beijing United Family Hospital and Clinics and 88 men from Beijing Hospital, National Center of Gerontology. All men had no history of prostate biopsy, undergoing mpMRI scan due to elevated PSA and/or abnormal DRE. The men in Beijing United Family Hospital group received COG plus systematic biopsy. The men in Beijing Hospital group only received IB. Results: The median age in COG and IB group was 63.0 years and 70.0 years (P<0.01). The median PSA was 7.4 and 6.8 ng/mL in COG and IB group respectively (P=0.124). The detection rate of PCa was 36.5% by COG and 52.3% by IB (P=0.037). The detection rate of clinically significant PCa (Gleason score ≥7) was 23.5% and 29.5% by COG and IB (P=0.371) respectively. In COG group, combination biopsy (COG + systematic biopsy) achieved improved PCa (42.4%) and clinically s
Low energy physical properties of high-Tc superconducting Cu oxides: A comparison between the resonating valence bond and experiments
In a recent review by Anderson and coworkers\cite{Vanilla}, it was pointed
out that an early resonating valence bond (RVB) theory is able to explain a
number of unusual properties of high temperature superconducting (SC)
Cu-oxides. Here we extend previous calculations \cite{anderson87,FC
Zhang,Randeria} to study more systematically low energy physical properties of
the plain vanilla d-wave RVB state, and to compare results with the available
experiments. We use a renormalized mean field theory combined with variational
Monte Carlo and power Lanczos methods to study the RVB state of an extended
model in a square lattice with parameters suitable for the hole doped
Cu-oxides. The physical observable quantities we study include the specific
heat, the linear residual thermal conductivity, the in-plane magnetic
penetration depth, the quasiparticle energy at the antinode , the
superconducting energy gap, the quasiparticle spectra and the Drude weight. The
traits of nodes (including , the Fermi velocity and the velocity
along Fermi surface ), as well as the SC order parameter are also
studied. Comparisons of the theory and the experiments in cuprates show an
overall qualitative agreement, especially on their doping dependences.Comment: 12 pages, 14 figures, 1 tabl
Binding energies and electronic structures of adsorbed titanium chains on carbon nanotubes
We have studied the binding energies and electronic structures of metal (Ti,
Al, Au) chains adsorbed on single-wall carbon nanotubes (SWNT) using first
principles methods. Our calculations have shown that titanium is much more
favored energetically over gold and aluminum to form a continuous chain on a
variety of SWNTs. The interaction between titanium and carbon nanotube
significantly modifies the electronic structures around Fermi energy for both
zigzag and armchair tubes. The delocalized 3d electrons from the titanium chain
generate additional states in the band gap regions of the semiconducting tubes,
transforming them into metals.Comment: 4 pages, 3 figure
Nonclassical crystallization of amorphous iron nanoparticles by radio frequency methods
Amorphousironnanoparticles were synthesized using an aqueous reduction in iron(II) sulfate with sodium borohydride and sodium citrate. Various radio frequency (rf) exposure times were investigated in order to determine trends in nonclassical crystallization. RF times from 15 to 300 s revealed an increase in crystallite size from 5 to 60 nm, as determined by powde rx-ray diffraction. Also, solvent optimization revealed that ethanol produced the largest trends for increasing crystallite size without total oxidation of the samples. Magnetic characterization by room temperature vibrating sample magnetometry and high resolution transmission microscopy was performed to verify magnetic properties and particle morphology
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