Single Queue Attended by Alternative Servers with Changeover Times

A single queue is serviced by two servers alternately, in alternate busy periods. A changeover time is required whenever the servers are replaced. In this model, the changeover time of a server is initiated as soon as one server completes the services of the units waiting before him namely at the end of his busy period. It may be noted that the empty state of the system is never reached. A comparison of this model with the model with empty state has been done

Alternate Servers with Set up Times

The paper analyzes a queueing model consisting of a single queue serviced by two servers alternately. A change over time is required when one server is replaced by another. In a busy period, only one server is servicing and when it empties the queue, the second server takes over and thus the two servers work alternately. The actual service after the change over time of the particular server under operation

Structural studies of phosphorus induced dimers on Si(001)

Renewed focus on the P-Si system due to its potential application in quantum computing and self-directed growth of molecular wires, has led us to study structural changes induced by P upon placement on Si(001)-$p(2\times 1)$. Using first-principles density functional theory (DFT) based pseudopotential method, we have performed calculations for P-Si(001) system, starting from an isolated P atom on the surface, and systematically increasing the coverage up to a full monolayer. An isolated P atom can favorably be placed on an {\bf M} site between two atoms of adjacent Si dimers belonging to the same Si dimer row. But being incorporated in the surface is even more energetically beneficial due to the participation of the {\bf M} site as a receptor for the ejected Si. Our calculations show that up to 1/8 monolayer coverage, hetero-dimer structure resulting from replacement of surface Si atoms with P is energetically favorable. Recently observed zig-zag features in STM are found to be consistent with this replacement process. As coverage increases, the hetero-dimers give way to P-P ortho-dimers on the Si dimer rows. This behavior is similar to that of Si-Si d-dimers but are to be contrasted with the Al-Al dimers, which are found between adjacent Si dimers rows and in a para-dimer arrangement. Unlike Al-Si system P-Si does not show any para to ortho transition. For both systems, the surface reconstruction is lifted at about one monolayer coverage. These calculations help us in understanding the experimental data obtained using scanning tunneling microscope.Comment: To appear in PR

The number of privately treated tuberculosis cases in India: an estimation from drug sales data

Background Understanding the amount of tuberculosis managed by the private sector in India is crucial to understanding the true burden of the disease in the country, and thus globally. In the absence of quality surveillance data on privately treated patients, commercial drug sales data offer an empirical foundation for disease burden estimation. Methods We used a large, nationally representative commercial dataset on sales of 189 anti-tuberculosis products available in India to calculate the amount of anti-tuberculosis treatment in the private sector in 2013–14. We corrected estimates using validation studies that audited prescriptions against tuberculosis diagnosis, and estimated uncertainty using Monte Carlo simulation. To address implications for numbers of patients with tuberculosis, we explored varying assumptions for average duration of tuberculosis treatment and accuracy of private diagnosis. Findings There were 17·793 million patient-months (95% credible interval 16·709 million to 19·841 million) of anti-tuberculosis treatment in the private sector in 2014, twice as many as the public sector. If 40–60% of private-sector tuberculosis diagnoses are correct, and if private-sector tuberculosis treatment lasts on average 2–6 months, this implies that 1·19–5·34 million tuberculosis cases were treated in the private sector in 2014 alone. The midpoint of these ranges yields an estimate of 2·2 million cases, two to three times higher than currently assumed. Interpretation India's private sector is treating an enormous number of patients for tuberculosis, appreciably higher than has been previously recognised. Accordingly, there is a re-doubled need to address this burden and to strengthen surveillance. Tuberculosis burden estimates in India and worldwide require revision

Multi-Channel Transport in Disordered Medium under Generic Scattering Conditions

Our study of the evolution of transmission eigenvalues, due to changes in various physical parameters in a disordered region of arbitrary dimensions, results in a generalization of the celebrated DMPK equation. The evolution is shown to be governed by a single complexity parameter which implies a deep level of universality of transport phenomena through a wide range of disordered regions. We also find that the interaction among eigenvalues is of many body type that has important consequences for the statistical behavior of transport properties.Comment: 19 Pages, No Figure

Features of the fluctuation -electromagnetic interaction between a small conducting particle and polarizable medium

For the first time, new important features of the fluctuation electromagnetic interaction between a small conducting particle and a smooth surface of polarizable medium (both dielectric and metallic) are worked out. The particle is characterized by classical electric and magnetic polarizabilities. The temperature dependence and retardation effects are explicitly taken into account. The resulting interaction force between a metallic particle and the surface of metal proves to be determined to great extent by magnetic coupling and reveals specific dependences on distance, temperature, particle radius and material properties of contacting materials. Numerical estimations are given in the case of a Cu particle above a smooth Cu substrate at different particle radius and temperature of the system.Comment: 13 pages, 5 figure

Excited-state spectroscopy using single-spin manipulation in diamond

We use single-spin resonant spectroscopy to study the spin structure in the orbital excited-state of a diamond nitrogen-vacancy center at room temperature. We find that the excited state spin levels have a zero-field splitting that is approximately half of the value of the ground state levels, a g-factor similar to the ground state value, and a hyperfine splitting ~20x larger than in the ground state. In addition, the width of the resonances reflects the electronic lifetime in the excited state. We also show that the spin-splitting can significantly differ between NV centers, likely due to the effects of local strain, which provides a pathway to control over the spin Hamiltonian and may be useful for quantum information processing.Comment: 15 pages, 3 figure

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

Pentagonal nanowires: a first-principles study of atomic and electronic structure

We performed an extensive first-principles study of nanowires in various pentagonal structures by using pseudopotential plane wave method within the density functional theory. Our results show that nanowires of different types of elements, such as alkali, simple, transition and noble metals and inert gas atoms, have a stable structure made from staggered pentagons with a linear chain perpendicular to the planes of the pentagons and passing through their centers. This structure exhibits bond angles close to those in the icosahedral structure. However, silicon is found to be energetically more favorable in the eclipsed pentagonal structure. These quasi one dimensional pentagonal nanowires have higher cohesive energies than many other one dimensional structures and hence may be realized experimentally. The effect of magnetic state are examined by spin-polarized calculations. The origin of the stability are discussed by examining optimized structural parameters, charge density and electronic band structure, and by using analysis based on the empirical Lennard-Jones type interaction. Electronic band structure of pentagonal wires of different elements are discussed and their effects on quantum ballistic conductance are mentioned. It is found that the pentagonal wire of silicon exhibits metallic band structure.Comment: 4 figures, accepted for publication in Phys. Rev.

The determinants of hotels' marketing managers' green marketing behaviour

Little is known about the factors underlying the pro-environmental behaviour of marketing managers. This paper explores the determinants of green marketing practices in the Red Sea hotel sector in Egypt. The research model assesses green marketing practices against the personal and organisational values of the marketing managers, together with a range of organisational and demographic variables expected to influence hotels' environmental behaviour. From a valid sample of 89 marketing managers responsible for 194 hotels, it was found that organisational contextual variables, and in particular targeting Western tourists, being affiliated to an international hotel chain and the marketers' own demographics, including age, academic subject studied and gender, were the best predictors of more proactive green marketing. Personal environmental values did not explain the pro-environmental behaviour of marketers, and the organisational environmental values that had explained part of their ethical behaviour had resulted from voluntarism rather than utilitarian or conformance-based values. Government policies also appeared to be ineffective determinants. The implications for green marketing practices are also discussed. © 2010 Taylor & Francis