The Amorphous-Crystal Interface in Silicon: a Tight-Binding Simulation

The structural features of the interface between the cystalline and amorphous phases of Si solid are studied in simulations based on a combination of empirical interatomic potentials and a nonorthogonal tight-binding model. The tight-binding Hamiltonian was created and tested for the types of structures and distortions anticipated to occur at this interface. The simulations indicate the presence of a number of interesting features near the interface. The features that may lead to crystallization upon heating include chains with some defects, most prominently dimers similar to those on the Si(001) 2x1 reconstructed free surface. Within the amorphous region order is lost over very short distances. By examining six different samples with two interfaces each, we find the energy of the amorphous-crystal interface to be 0.49 +/- 0.05 J/m^2Comment: Submitted to Phys. Rev.

Analytical and finite-element study of optimal strain distribution in various beam shapes for energy harvesting applications

Due to the increasing demand for harvesting energy from environmental vibration, for use in self-powered electronic applications, cantilever-based vibration energy harvesting has attracted great interest from various parties and become one of the most common approaches to convert redundant mechanical energy into electrical energy. As the output voltage produces from a piezoelectric material depends greatly on the geometric shape and the size of the beam, there is a need to model and compare the performance of cantilever beams of differing geometries. This paper presents the study of strain distribution in various shapes of cantilever beams, including a convex and concave edge profile elliptical beams that have been overseen in most of the prior literature. Both analytical and finite element models are derived and the resultant strain distributions in the beam are computed based on MATLAB solver and ANSYS finite element analysis tools. An optimum geometry for a vibration-based energy harvester system is verified. Lastly, experimental results comparing the power density for a triangular and rectangular piezoelectric beams are also presented to validate the finding of the study and the claim as suggested in the literature is verified

Kinematic Self-Similar Cylindrically Symmetric Solutions

This paper is devoted to find out cylindrically symmetric kinematic self-similar perfect fluid and dust solutions. We study the cylindrically symmetric solutions which admit kinematic self-similar vectors of second, zeroth and infinite kinds, not only for the tilted fluid case but also for the parallel and orthogonal cases. It is found that the parallel case gives contradiction both in perfect fluid and dust cases. The orthogonal perfect fluid case yields a vacuum solution while the orthogonal dust case gives contradiction. It is worth mentioning that the tilted case provides solution both for the perfect as well as dust cases.Comment: 22 pages, accepted for publication in Int. J. of Mod. Phys.

Beberapa Metode Pengambilan Ektoparasit Pada Burung Merpati Pos (Columba Livia Gmelen)

JANITA AZIZ & M. AMIR. 1988.Some ectoparasites collecting methods of racing pigeon (Columba livia Gmelin). Berita Biologi 3(8):382 - 385.Extraction of ectoparasites of living racing pigeons was done using modified "Fait Isle".The insectisides used for the extraction were pyrethrum,caumaphos and chloroform.The number of acarines extracted during the night was higher than that during the day.In addition insecticides spraying treatment extracted more acarines than fumigation.From the 3 kinds of insecticides used,chloroform proved to kill more acarines than the other two insecticides

Kinematic Self-Similar Plane Symmetric Solutions

This paper is devoted to classify the most general plane symmetric spacetimes according to kinematic self-similar perfect fluid and dust solutions. We provide a classification of the kinematic self-similarity of the first, second, zeroth and infinite kinds with different equations of state, where the self-similar vector is not only tilted but also orthogonal and parallel to the fluid flow. This scheme of classification yields twenty four plane symmetric kinematic self-similar solutions. Some of these solutions turn out to be vacuum. These solutions can be matched with the already classified plane symmetric solutions under particular coordinate transformations. As a result, these reduce to sixteen independent plane symmetric kinematic self-similar solutions.Comment: 29 pages, accepted for publication in Classical Quantum Gravit

Ferromagnetic Ga₁ˍₓ Mnₓ As produced by ion implantation and pulsed-laser melting

We demonstrate the formation of ferromagneticGa₁ˍₓMnₓAsfilms by Mn ion implantation into GaAs followed by pulsed-laser melting. Irradiation with a single excimer laser pulse results in the epitaxial regrowth of the implanted layer with Mn substitutional fraction up to 80% and effective Curie temperature up to 29 K for samples with a maximum Mn concentration of x≈0.03. A remanent magnetization persisting above 85 K has been observed for samples with x≈0.10, in which 40% of the Mn resides on substitutional lattice sites. We find that the ferromagnetism in Ga₁ˍₓMnₓAs is rather robust to the presence of structural defects.The work at the Lawrence Berkeley National Laboratory was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. The work at Harvard was supported by NASA Grant No. NAG8-1680. One of the authors ~M.A.S.! acknowledges support from an NSF Graduate Research Fellowship

Quantitative Analysis of DoS Attacks and Client Puzzles in IoT Systems

Denial of Service (DoS) attacks constitute a major security threat to today's Internet. This challenge is especially pertinent to the Internet of Things (IoT) as devices have less computing power, memory and security mechanisms to mitigate DoS attacks. This paper presents a model that mimics the unique characteristics of a network of IoT devices, including components of the system implementing `Crypto Puzzles' - a DoS mitigation technique. We created an imitation of a DoS attack on the system, and conducted a quantitative analysis to simulate the impact such an attack may potentially exert upon the system, assessing the trade off between security and throughput in the IoT system. We model this through stochastic model checking in PRISM and provide evidence that supports this as a valuable method to compare the efficiency of different implementations of IoT systems, exemplified by a case study

Progress in Monte Carlo calculations of Fermi systems: normal liquid 3He

The application of the diffusion Monte Carlo method to a strongly interacting Fermi system as normal liquid $^3$He is explored. We show that the fixed-node method together with the released-node technique and a systematic method to analytically improve the nodal surface constitute an efficient strategy to improve the calculation up to a desired accuracy. This methodology shows unambiguously that backflow correlations, when properly optimized, are enough to generate an equation of state of liquid $^3$He in excellent agreement with experimental data from equilibrium up to freezing.Comment: 14 pages, 3 eps figure

Toxoplasmosis: Serious disease during pregnancy

Toxoplasmosis is an infection caused by Toxoplasma gondii that leads to abortion or hydrocephalus during pregnancy.One hundered and twenty two aborted women were selected for this study. Serum samples were collected form Al-Kadhmia and Kamal Al-Samari Hospitals,and laboratories around Baghdad, and tested for specific IgG and IgM anti-toxoplasma antibodies to confirm toxoplasmosis in those women by using ELISA test.The result recorded that 51(41.8%) women had antibodies against Toxoplasma gondii, 25(59.5%) women were positive for IgG, and 17(40.5%) women were positive forIgM, while 9(17.6%)women were positive for both