395 research outputs found
Framework for assessing the quality of quality management programs
A model for assessing the quality of quality management programs is presented in this paper. The role of Strategic Gaps and Knowledge Gaps in evaluating the quality of quality management programs is discussed in this paper. In addition, the paper presents a method for identification of any possible Strategic Gaps and Knowledge Gaps which may exist in organisational quality management processes. The existence of such gaps may adversely affect the expected outcome from the implemented quality management programs. Furthermore, the paper explores the relationship between the perception of the developers or implementers of quality management programs and other related organizational attributes. Finally, the study seeks to identify other management characteristics associated with success or otherwise of quality management programs in HR departments. In so doing, the importance of addressing issues arising from Strategic Gaps and Knowledge Gaps is addressed
Analysis of band-gap formation in squashed arm-chair CNT
The electronic properties of squashed arm-chair carbon nanotubes are modeled
using constraint free density functional tight binding molecular dynamics
simulations. Independent from CNT diameter, squashing path can be divided into
{\it three} regimes. In the first regime, the nanotube deforms with negligible
force. In the second one, there is significantly more resistance to squashing
with the force being nN/per CNT unit cell. In the last regime,
the CNT looses its hexagonal structure resulting in force drop-off followed by
substantial force enhancement upon squashing. We compute the change in band-gap
as a function of squashing and our main results are: (i) A band-gap initially
opens due to interaction between atoms at the top and bottom sides of CNT. The
orbital approximation is successful in modeling the band-gap opening at
this stage. (ii) In the second regime of squashing, large
interaction at the edges becomes important, which can lead to band-gap
oscillation. (iii) Contrary to a common perception, nanotubes with broken
mirror symmetry can have {\it zero} band-gap. (iv) All armchair nanotubes
become metallic in the third regime of squashing. Finally, we discuss both
differences and similarities obtained from the tight binding and density
functional approaches.Comment: 16 pages and 6 figures, To appear in PR
Quantum heat transfer through an atomic wire
We studied the phononic heat transfer through an atomic dielectric wire with
both infinite and finite lengths by using a model Hamiltonian approach. At low
temperature under ballistic transport, the thermal conductance contributed by
each phonon branch of a uniform and harmonic chain cannot exceed the well-known
value which depends linearly on temperature but is material independent. We
predict that this ballistic thermal conductance will exhibit stepwise behavior
as a function of temperature. By performing numerical calculations on a more
realistic system, where a small atomic chain is placed between two reservoirs,
we also found resonance modes, which should also lead to the stepwise behavior
in the thermal conductance.Comment: 14 pages, 2 separate figure
A potential use for the C-band polarimetric SAR parameters to characterise the soil surface over bare agriculture fields
The objective of this study was to analyze the potential of the C-band polarimetric SAR parameters for the soil surface characterization of bare agricultural soils. RADARSAT-2 data and simulations using the Integral Equation Model (IEM) were analyzed to evaluate the polarimetric SAR parameters' sensitivities to the soil moisture and surface roughness. The results showed that the polarimetric parameters in the C-band were not very relevant to the characterization of the soil surface over bare agricultural areas. Low dynamics were often observed between the polarimetric parameters and both the soil moisture content and the soil surface roughness. These low dynamics do not allow for the accurate estimation of the soil parameters, but they could augment the standard inversion approaches to improve the estimation of these soil parameters. The polarimetric parameter alpha_1 could be used to detect very moist soils (>30%), while the anisotropy could be used to separate the smooth soils
Analysis of TerraSAR-X data sensitivity to bare soil moisture, roughness, composition and soil crust
Le comportement du signal radar TerraSAR-X en fonction des paramètres du sol (rugosité, humidité, structure) a été analysé sur des données 2009 et 2010. Les résultats montrent que la sensibilité du signal radar à l'humidité est plus importante pour des faibles incidences (25° en comparaison à 50°). Pour des fortes valeurs d'humidité, le signal TerraSAR-X est plus sensible à la rugosité du sol à forte incidence (50°). La forte résolution spatiale des données TerraSAR-X (1 m) permet de détecter la croûte de battance à l'échelle intra parcellaire. / Soils play a key role in shaping the environment and in risk assessment. We characterized the soils of bare agricultural plots using TerraSAR-X (9.5 GHz) data acquired in 2009 and 2010. We analyzed the behavior of the TerraSAR-X signal for two configurations, HH-25° and HH-50°, with regard to several soil conditions: moisture content, surface roughness, soil composition and soil-surface structure (slaking crust).The TerraSAR-X signal was more sensitive to soil moisture at a low (25°) incidence angle than at a high incidence angle (50°). For high soil moisture (N25%), the TerraSAR-X signal was more sensitive to soil roughness at a high incidence angle (50°) than at a low incidence angle (25°). The high spatial resolution of the TerraSAR-X data (1 m) enabled the soil composition and slaking crust to be analyzed at the within-plot scale based on the radar signal. The two loamy-soil categories that composed our training plots did not differ sufficiently in their percentages of sand and clay to be discriminated by the X-band radar signal.However, the spatial distribution of slaking crust could be detected when soil moisture variation is observed between soil crusted and soil without crust. Indeed, areas covered by slaking crust could have greater soil moisture and consequently a greater backscattering signal than soils without crust
Structure and conductance histogram of atomic-sized Au contacts
Many experiments have shown that the conductance histograms of metallic
atomic-sized contacts exhibit a peak structure, which is characteristic of the
corresponding material. The origin of these peaks still remains as an open
problem. In order to shed some light on this issue, we present a theoretical
analysis of the conductance histograms of Au atomic contacts. We have combined
classical molecular dynamics simulations of the breaking of nanocontacts with
conductance calculations based on a tight-binding model. This combination gives
us access to crucial information such as contact geometries, forces, minimum
cross-section, total conductance and transmission coefficients of the
individual conduction channels. The ensemble of our results suggests that the
low temperature Au conductance histograms are a consequence of a subtle
interplay between mechanical and electrical properties of these nanocontacts.
At variance with other suggestions in the literature, our results indicate that
the peaks in the Au conductance histograms are not a simple consequence of
conductance quantization or the existence of exceptionally stable radii. We
show that the main peak in the histogram close to one quantum of conductance is
due to the formation of single-atom contacts and chains of gold atoms.
Moreover, we present a detailed comparison with experimental results on Au
atomic contacts where the individual channel transmissions have been
determined.Comment: 11 pages, 10 figures, version to be published in Phys. Rev. B. The
paper has been thoroughly revised and several figures have been replaced by
new one
Conductance through a single atom
In this paper we present an analysis of conduction through a single atom between two metal electrodes. Based on ab initio total-energy and electronic-structure calculations, and molecular-dynamics simulations using the embedded-atom model, we show that the conductance through an atom depends on the electronic structure of both the single atom and the metal electrodes, as well as the binding structure between the single atom and the surfaces of the metal electrodes. Our results enable us to interpret experimental results obtained by using a mechanical break junction on atomic-scale wires
Quantum point contact on graphite surface
The conductance through a quantum point contact created by a sharp and hard
metal tip on the graphite surface has features which to our knowledge have not
been encountered so far in metal contacts or in nanowires. In this paper we
first investigate these features which emerge from the strongly directional
bonding and electronic structure of graphite, and provide a theoretical
understanding for the electronic conduction through quantum point contacts. Our
study involves the molecular-dynamics simulations to reveal the variation of
interlayer distances and atomic structure at the proximity of the contact that
evolves by the tip pressing toward the surface. The effects of the elastic
deformation on the electronic structure, state density at the Fermi level, and
crystal potential are analyzed by performing self-consistent-field
pseudopotential calculations within the local-density approximation. It is
found that the metallicity of graphite increases under the uniaxial compressive
strain perpendicular to the basal plane. The quantum point contact is modeled
by a constriction with a realistic potential. The conductance is calculated by
representing the current transporting states in Laue representation, and the
variation of conductance with the evolution of contact is explained by taking
the characteristic features of graphite into account. It is shown that the
sequential puncturing of the layers characterizes the conductance.Comment: LaTeX, 11 pages, 9 figures (included), to be published in Phys. Rev.
B, tentatively scheduled for 15 September 1998 (Volume 58, Number 12
Structure of aluminum atomic chains
First-principles density functional calculations reveal that aluminum can
form planar chains in zigzag and ladder structures. The most stable one has
equilateral triangular geometry with four nearest neighbors; the other stable
zigzag structure has wide bond angle and allows for two nearest neighbors. An
intermediary structure has the ladder geometry and is formed by two strands.
All these planar geometries are, however, more favored energetically than the
linear chain. We found that by going from bulk to a chain the character of
bonding changes and acquires directionality. The conductance of zigzag and
linear chains is 4e^2/h under ideal ballistic conditions.Comment: modified detailed version, one new structure added, 4 figures,
modified figure1, 1 tabl
Multiple Functionality in Nanotube Transistors
Calculations of quantum transport in a carbon nanotube transistor show that
such a device offers unique functionality. It can operate as a ballistic
field-effect transistor, with excellent characteristics even when scaled to 10
nm dimensions. At larger gate voltages, channel inversion leads to resonant
tunneling through an electrostatically defined nanoscale quantum dot. Thus the
transistor becomes a gated resonant tunelling device, with negative
differential resistance at a tunable threshold. For the dimensions considered
here, the device operates in the Coulomb blockade regime, even at room
temperature.Comment: To appear in Phys. Rev. Let
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