720 research outputs found
Strain Modulated Electronic Properties of Ge Nanowires - A First Principles Study
We used density-functional theory based first principles simulations to study
the effects of uniaxial strain and quantum confinement on the electronic
properties of germanium nanowires along the [110] direction, such as the energy
gap and the effective masses of the electron and hole. The diameters of the
nanowires being studied are up to 50 {\AA}. As shown in our calculations, the
Ge [110] nanowires possess a direct band gap, in contrast to the nature of an
indirect band gap in bulk. We discovered that the band gap and the effective
masses of charge carries can be modulated by applying uniaxial strain to the
nanowires. These strain modulations are size-dependent. For a smaller wire (~
12 {\AA}), the band gap is almost a linear function of strain; compressive
strain increases the gap while tensile strain reduces the gap. For a larger
wire (20 {\AA} - 50 {\AA}), the variation of the band gap with respect to
strain shows nearly parabolic behavior: compressive strain beyond -1% also
reduces the gap. In addition, our studies showed that strain affects effective
masses of the electron and hole very differently. The effective mass of the
hole increases with a tensile strain while the effective mass of the electron
increases with a compressive strain. Our results suggested both strain and size
can be used to tune the band structures of nanowires, which may help in design
of future nano-electronic devices. We also discussed our results by applying
the tight-binding model.Comment: 1 table, 8 figure
Implementing quantum gates through scattering between a static and a flying qubit
We investigate whether a two-qubit quantum gate can be implemented in a
scattering process involving a flying and a static qubit. To this end, we focus
on a paradigmatic setup made out of a mobile particle and a quantum impurity,
whose respective spin degrees of freedom couple to each other during a
one-dimensional scattering process. Once a condition for the occurrence of
quantum gates is derived in terms of spin-dependent transmission coefficients,
we show that this can be actually fulfilled through the insertion of an
additional narrow potential barrier. An interesting observation is that under
resonance conditions the above enables a gate only for isotropic Heisenberg
(exchange) interactions and fails for an XY interaction. We show the existence
of parameter regimes for which gates able to establish a maximum amount of
entanglement can be implemented. The gates are found to be robust to variations
of the optimal parameters.Comment: 7 pages, 3 figure
Repairing a shield tunnel damaged by secondary grouting.
This paper reports on a repair work which has recently been conducted for a metro tunnel in Hefei city, China. The tunnel has been originally constructed using shield method where synchronous grouting was used to fill the gaps between the tunnel segments and soil. Following a regular maintenance inspection of the tunnel, several leakage issues were identified between three stations. Secondary grouting was adopted as a solution to block the tunnel leakage, however, shortly after the start of grouting work, the track and track bed were found to be unevenly uplifted with significant cracks in the tunnel’s segments. The paper describes and discusses key aspects of this case study including ground conditions, leakages patterns of the tunnel, recorded volumes and injection pressure of the secondary grouting, as well as survey data of track displacement and segment cracks. The investigation confirmed that the situation was caused by an inappropriate implementation of the secondary grouting, particularly by high grouting pressure (significantly higher than the geostatic pressure), large volumes of injected grout, and poor selection of grouting locations. Ground Penetrating Radar (GPR) was conducted to inspect the tunnel conditions before commencing the structural repair work, which revealed that there were no voids under the track bed of the affected zone. The study presents simplified strategies used to repair the damage while maintaining minimum disturbance to the affected segments
The potential of a solid-state fermentation supplement to augment white lupin (Lupinus albus) meal incorporation in diets for farmed common carp (Cyprinus carpio)
A 10-week feeding trial was conducted to evaluate the effects of partially substituting soya protein concentrate (SPC), with white lupin (Lupinus albus) meal in carp (Cyprinus carpio) diets. This study further investigated the dietary inclusion of a solid-state fermentation (SSF) product of Aspergillus niger in tandem with SPC replacement. Six experimental diets were produced to be isonitrogenous (42%), isolipdic (8%) and isoenergetic (19 MJ kg−1). Four diets were formulated to have 12.5 and 25% substitution of SPC using lupin meal, and with and without a supplement of 0.1% of SSF. An additional two diets were designed to serve as a basal reference with no SPC replacement, but one supplemented with 0.1% SSF inclusion. The results of this study showed that SPC can be replaced with up to 25% white lupin meal in carp diets, without reduction of growth performance, feed utilisation, body composition, gut integrity or health. The addition of SSF to the test diets enhanced growth performance (specific growth rate, P < 0.05) and nutrient utilisation (e.g. feed conversion ratio and protein efficiency ratio, P < 0.05)
A multiband envelope function model for quantum transport in a tunneling diode
We present a simple model for electron transport in semiconductor devices
that exhibit tunneling between the conduction and valence bands. The model is
derived within the usual Bloch-Wannier formalism by a k-expansion, and is
formulated in terms of a set of coupled equations for the electron envelope
functions. Its connection with other models present in literature is discussed.
As an application we consider the case of a Resonant Interband Tunneling Diode,
demonstrating the ability of the model to reproduce the expected behaviour of
the current as a function of the applied voltageComment: 8 pages, 4 figure
Entanglement Controlled Single-Electron Transmittivity
We consider a system consisting of single electrons moving along a 1D wire in
the presence of two magnetic impurities. Such system shows strong analogies
with a Fabry - Perot interferometer in which the impurities play the role of
two mirrors with a quantum degree of freedom: the spin. We have analysed the
electron transmittivity of the wire in the presence of entanglement between the
impurity spins. The main result of our analysis is that, for suitable values of
the electron momentum, there are two maximally entangled state of the impurity
spins the first of which makes the wire transparent whatever the electron spin
state while the other strongly inhibits the electron transmittivity. Such
predicted striking effect is experimentally observable with present day
technology.Comment: Published version (6 figures
Cardio-thoracic ratio is stable, reproducible and has potential as a screening tool for HIV-1 related cardiac disorders in resource poor settings
BACKGROUND: Cardiovascular disorders are common in HIV-1 infected persons in Africa and presentation is often insidious. Development of screening algorithms for cardiovascular disorders appropriate to a resource-constrained setting could facilitate timely referral. Cardiothoracic ratio (CTR) on chest radiograph (CXR) has been suggested as a potential screening tool but little is known about its reproducibility and stability. Our primary aim was to evaluate the stability and the inter-observer variability of CTR in HIV-1 infected outpatients. We further evaluated the prevalence of cardiomegaly (CTR≥0.5) and its relationship with other risk factors in this population. METHODOLOGY: HIV-1 infected participants were identified during screening for a tuberculosis vaccine trial in Khayelitsha, South Africa between August 2011 and April 2012. Participants had a digital posterior-anterior CXR performed as well as history, examination and baseline observations. CXRs were viewed using OsiriX software and CTR calculated using digital callipers. RESULTS: 450 HIV-1-infected adults were evaluated, median age 34 years (IQR 30-40) with a CD4 count 566/mm 3 (IQR 443-724), 70% on antiretroviral therapy (ART). The prevalence of cardiomegaly was 12.7% (95% C.I. 9.6%-15.8%). CTR was calculated by a 2 nd reader for 113 participants, measurements were highly correlated r = 0.95 (95% C.I. 0.93-0.97) and agreement of cardiomegaly substantial κ = 0.78 (95% C.I 0.61-0.95). CXR were repeated in 51 participants at 4-12 weeks, CTR measurements between the 2 time points were highly correlated r = 0.77 (95% C.I 0.68-0.88) and agreement of cardiomegaly excellent κ = 0.92 (95% C.I. 0.77-1). Participants with cardiomegaly had a higher median BMI (31.3; IQR 27.4-37.4) versus 26.9; IQR 23.2-32.4); p<0.0001) and median systolic blood pressure (130; IQR 121-141 versus 125; IQR 117-135; p = 0.01). CONCLUSION: CTR is a robust measurement, stable over time with substantial inter-observer agreement. A prospective study evaluating utility of CXR to identify cardiovascular disorder in this population is warranted
The HI content of the Eridanus group of galaxies
The HI content of galaxies in the Eridanus group is studied using the GMRT
observations and the HIPASS data. A significant HI deficiency up to a factor of
2-3 is observed in galaxies in the high galaxy density regions. The HI
deficiency in galaxies is observed to be directly correlated with the local
projected galaxy density, and inversely correlated with the line-of-sight
radial velocity. Furthermore, galaxies with larger optical diameters are
predominantly in the lower galaxy density regions. It is suggested that the HI
deficiency in Eridanus is due to tidal interactions. In some galaxies,
evidences of tidal interactions are seen. An important implication is that
significant evolution of galaxies can take place in the group environment. In
the hierarchical way of formation of clusters via mergers of groups, a fraction
of the observed HI deficiency in clusters could have originated in groups. The
co-existence of S0's and severely HI deficient galaxies in the Eridanus group
suggests that galaxy harassment is likely to be an effective mechanism for
transforming spirals to S0's.Comment: 21 pages; Accepted for publication in Journal of Astroph. & Astron.
March, 200
Southern GEMS groups II: HI distribution, mass functions and HI deficient galaxies
We investigate the neutral hydrogen (HI) content of sixteen groups for which
we have multi-wavelength data including X-ray observations. Wide-field imaging
of the groups was obtained with the 20-cm multibeam system on the 64-m Parkes
telescope. We have detected ten previously uncatalogued HI sources, one of
which has no visible optical counterpart. We examine the HI properties of the
groups, compared to their X-ray characteristics, finding that those groups with
a higher X-ray temperature and luminosity contain less HI per galaxy. The HI
content of a group depends on its morphological make-up, with those groups
dominated by early-type galaxies containing the least total HI. We determined
the expected HI for the spiral galaxies in the groups, and found that a number
of the galaxies were HI deficient. The HI deficient spirals were found both in
groups with and without a hot intra-group medium. The HI deficient galaxies
were not necessarily found at the centre of the groups, however, we did find
that two thirds of HI deficient galaxies were found within about 1 Mpc from the
group centre, indicating that the group environment is affecting the gas-loss
from these galaxies. We determined the HI mass function for a composite sample
of 15 groups, and found that it is significantly flatter than the field HI mass
function. We also find a lack of high HI-mass galaxies in groups. One possible
cause of this effect is the tidal stripping of HI gas from spiral galaxies as
they are pre-processed in groups.Comment: accepted for publication in MNRAS, 26 pages, 13 Figures, 2 Appendice
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