Realistic inversion of diffraction data for an amorphous solid: the case of amorphous silicon

We apply a new method "force enhanced atomic refinement" (FEAR) to create a computer model of amorphous silicon (a-Si), based upon the highly precise X-ray diffraction experiments of Laaziri et al. The logic underlying our calculation is to estimate the structure of a real sample a-Si using experimental data and chemical information included in a non-biased way, starting from random coordinates. The model is in close agreement with experiment and also sits at a suitable minimum energy according to density functional calculations. In agreement with experiments, we find a small concentration of coordination defects that we discuss, including their electronic consequences. The gap states in the FEAR model are delocalized compared to a continuous random network model. The method is more efficient and accurate, in the sense of fitting the diffraction data than conventional melt quench methods. We compute the vibrational density of states and the specific heat, and find that both compare favorably to experiments.Comment: 7 pages and 10 figure

On quantum plasma: a plea for a common sense

The quantum plasma theory has flourished in the past few years without much regard to the physical validity of the formulation or its connection to any real physical system. It is argued here that there is a very limited physical ground for the application of such a theory.Comment: EPL, to be published 201

Rare Asymptomatic Presentation of Omental Mass from Cesarean Stitchline

A case of big oozing lump of unknown origin through a healed cesarean section stitchline, completely asymptomatic at presentation, origin discovered as omentum on exploratory laparotomy came on 10th postoperative day of an uneventful emergency surgery. This rare and silent presentation highlights the need to reconsider the practice of peritoneal nonclosure during cesarean section that has been adopted widely in recent past. It also calls for meticulous dissection and repair of rectus sheath during laparotomy.Keywords: Asymptomatic, cesarean section, peritoneal nonclosure, omental herni

On the L¹ norm of an exponential sum involving the divisor function

In this paper, we obtain bounds on the L¹-norm of the sum ∑_(n≤x)τ(n)e(αn) where τ(n) is the divisor function