The Firms Speak: What the World Business Environment Survey Tells Us about Constraints on Private Sector Development

This chapter summarizes the salient results of the World Business Environment Survey (WBES). It shows that important dimensions of the climate for business operation and investment can be measured, analyzed, and compared across countries, and that governance is key to the business environment and investment climate. The survey findings suggest that key policy, institutional, and governance indicators affect the growth of a firm's sales and investment and the extent to which firms operate in the unofficial economy. Further, the paper provides empirical support for some commonly held notions, while challenging others. It suggests a link between taxation, financing, and corruption on the one hand, and growth and investment on the other, and it highlights the costs to economies where the state is captured by a narrow set of private interests.

Para to Ortho transition of metallic dimers on Si(001)

Extensive electronic structure calculations are performed to obtain the stable geometries of metals like Al, Ga and In on the Si(001) surface at 0.5 ML and 1 ML coverages. Our results coupled with previous theoretical findings explain the recent experimental data in a comprehensive fashion. At low coverages, as shown by previous works, `Para' dimers give the lowest energy structure. With increasing coverage beyond 0.5 ML, `Ortho' dimers become part of low energy configurations leading toward a `Para' to `Ortho' transition at 1 ML coverage. For In mixed staggered dimers (`Ortho' and `Para') give the lowest energy configuration. For Ga, mixed dimers are non-staggered, while for Al `Para' to `Ortho' transition of dimers is complete. Thus at intermediate coverages between 0.5 and 1 ML, the `Ortho' and `Para' dimers may coexist on the surface. Consequently, this may be an explanation of the fact that the experimental observations can be successfully interpreted using either orientation. A supported zigzag structure at 0.5 ML, which resembles ${\rm (CH)_x}$, does not undergo a dimerization transition, and hence stays semi-metallic. Also, unlike ${\rm (CH)_x}$ the soliton formation is ruled out for this structure.Comment: 8 pages, 6 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

Dark linear seesaw mechanism

We propose a minimal model where a dark sector, odd under a $\mathcal{Z}_2$ discrete symmetry, is the seed of lepton number violation in the neutrino sector at the loop level, in the context of the linear seesaw mechanism. Neutrino mass suppression stems from a naturally small scalar potential coupling which breaks the lepton number symmetry softly. The fact that we consider (dark) Dirac vector-like neutral leptons, prevents the appearance of other mass terms that could contribute to neutrino masses via alternative mechanisms. We study the dark-matter phenomenology of the model, focusing on the case in which the stable particle is the lightest neutral scalar arising from the dark scalar sector. Prospects for testing our framework with the results of current and future lepton flavour violation searches are also discussed.Comment: 13 LaTeX pages, 3 figure

Unusual Higgs or Supersymmetry from Natural Electroweak Symmetry Breaking

This review provides an elementary discussion of electroweak symmetry breaking in the minimal and the next-to-minimal supersymmetric models with the focus on the fine-tuning problem -- the tension between natural electroweak symmetry breaking and the direct search limit on the Higgs boson mass. Two generic solutions of the fine-tuning problem are discussed in detail: models with unusual Higgs decays; and models with unusual pattern of soft supersymmetry breaking parameters.Comment: 23 pages, 6 figures; invited review by MPL

A novel multiplex PCR system for the detection of virulence associated genes of E. coli O157:H7 from food system

In view of the importance E. coli serotype 0157:H7 in human diseases, an easy and quick system is desirable to detect toxin producing strains. In this report, we describe standardization of a novel multiplex Polymerase Chain Reaction (mPCR) assay for simultaneous detection of four important genes associated with the organism E. coli 0157:H7 viz., stx 1, stx 2, eae A, hly A along with an internal amplification control (IAC). The mPCR method developed in the present study is sensitive enough to detect cells as low as 103 CFU ml-1 or g-1 of the food samples. The E. coli 0157:H7 strains having been identified to contain the gene in the mPCR were unequivocally detected positive for the serological and conventional culture method.  As E. coli 0157:H7 is qualified as biowarfare agent; this mPCR system is of immense help in detecting them during emergencies of biological war and suspected outbreaks.&nbsp

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.

Electroweak symmetry breaking in supersymmetric models with heavy scalar superpartners

We propose a novel mechanism of electroweak symmetry breaking in supersymmetric models, as the one recently discussed by Birkedal, Chacko and Gaillard, in which the Standard Model Higgs doublet is a pseudo-Goldstone boson of some global symmetry. The Higgs mass parameter is generated at one loop level by two different, moderately fine-tuned sources of the global symmetry breaking. The mechanism works for scalar superpartner masses of order 10 TeV, but gauginos can be light. The scale at which supersymmetry breaking is mediated to the visible sector has to be low, of order 100 TeV. Fine-tuning in the scalar potential is at least two orders of magnitude smaller than in the MSSM with similar soft scalar masses. The physical Higgs boson mass is (for $\tan\beta\gg1$) in the range 120-135 GeV.Comment: 17 pages, no figures, LaTe

Measuring the W-t-b Interaction at the ILC

The large top quark mass suggests that the top plays a pivotal role in Electroweak symmetry-breaking dynamics and, as a result, may have modified couplings to Electroweak bosons. Hadron colliders can provide measurements of these couplings at the ~10% level, and one of the early expected triumphs of the International Linear Collider is to reduce these uncertainties to the per cent level. In this article, we propose the first direct measurement of the Standard Model W-t-b coupling at the ILC, from measurements of t tbar-like signals below the t tbar production threshold. We estimate that the ILC with 100 fb^{-1} can measure a combination of the coupling and top width to high precision, and when combined with a direct measurement of the top width from the above-threshold scan, results in a model-independent measurement of the W-t-b interaction of the order of ~ 3%

Helicopter tail rotor thrust and main rotor wake coupling in crosswind flight

The tail rotor of a helicopter with a single main rotor configuration can experience a significant reduction in thrust when the aircraft operates in crosswind flight. Brown’s vorticity transport model has been used to simulate a main rotor and tail rotor system translating at a sideslip angle that causes the tail rotor to interact with the main rotor tip vortices as they propagate downstream at the lateral extremities of the wake. The tail rotor is shown to exhibit a distinct directionally dependent mode during which tail rotors that are configured so that the blades travel forward at the top of the disk develop less thrust than tail rotors with the reverse sense of rotation. The range of flight speeds over which this mode exists is shown to vary considerably with the vertical location of the tail rotor. At low flight speeds, the directionally dependent mode occurs because the tail rotor is immersed within not only the downwash from the main rotor but also the rotational flow associated with clusters of largely disorganized vorticity within the main rotor wake. At higher flight speeds, however, the tail rotor is immersed within a coherent supervortex that strongly influences the velocity field surrounding the tail rotor