An investigation into the mechanical and tribological properties of plasma electrolytic oxidation and hard-anodized coatings on 6082 aluminum alloy

A ceramic coating on AA6082 aluminum alloy prepared by plasma electrolytic oxidation (PEO) has been studied and compared against a sulphuric acid hard-anodized coating on the same alloy. Surface morphology and microstructures of the coatings have been examined by scanning electron microscopy. X-ray diffraction is used to determine the phase composition of the coatings. The adhesion strength of the coatings has been evaluated using a scratch test method. The coating's mechanical properties such elastic modulus and hardness data have been generated using a dynamic ultra-microhardness tester. Sliding wear tests with different loading rates are performed on the coatings in order to assess their wear resistance. Test results show that the PEO treated samples exhibit significantly better mechanical properties compared to hard anodized samples. The elastic modulus and hardness of the PEO coating are 2-3 times greater than of the hard anodized coating and subsequently, an improved wear resistance of the PEO coating has been achieved. The mechanical properties of the coatings and their relations to their tribological performance are discussed.     

Modeling the conductance and DNA blockade of solid-state nanopores

We present measurements and theoretical modeling of the ionic conductance G of solid-state nanopores with 5-100 nm diameters, with and without DNA inserted into the pore. First, we show that it is essential to include access resistance to describe the conductance, in particular for larger pore diameters. We then present an exact solution for G of an hourglass-shaped pore, which agrees very well with our measurements without any adjustable parameters, and which is an improvement over the cylindrical approximation. Subsequently we discuss the conductance blockade ΔG due to the insertion of a DNA molecule into the pore, which we study experimentally as a function of pore diameter. We find that ΔG decreases with pore diameter, contrary to the predictions of earlier models that forecasted a constant ΔG. We compare three models for ΔG, all of which provide good agreement with our experimental data.     

Electrical properties of conductive Ge nanocrystal thin films fabricated by low temperature in situ growth

Thin films composed of Ge nanocrystals embedded in an amorphous SiO(2) matrix (Ge-NC TFs) were prepared using a low temperature in situ growth method. Unexpected high p-type conductivity was observed in the intrinsic Ge-NC TFs. Unintentional doping from shallow dopants was excluded as a candidate mechanism of hole generation. Instead, the p-type characteristic was attributed to surface state induced hole accumulation in NCs, and the hole conduction was found to be a thermally activated process involving charge hopping from one NC to its nearest neighbor. Theoretical analysis has shown that the density of surface states in Ge-NCs is sufficient to induce adequate holes for measured conductivity. The film conductivity can be improved significantly by post-growth rapid thermal annealing and this effect is explained by a simple thermodynamic model. The impact of impurities on the conduction properties was also studied. Neither compensation nor enhancement in conduction was observed in the Sb- and Ga-doped Ge-NC TFs, respectively. This could be attributed to the fact that these impurities are no longer shallow dopants in NCs and are much less likely to be effectively activated. Finally, the photovoltaic effect of heterojunction diodes employing such Ge-NC TFs was characterized in order to demonstrate its functionality in device implementation.     

MICROBIOLOGICAL PROFILE OF MURCHA STARTERS AND PHYSICO-CHEMICAL CHARACTERISTICS OF POKO, A RICE BASED TRADITIONAL FERMENTED FOOD PRODUCT OF NEPAL

Poko is a traditional rice based fermented food of Nepal prepared using murcha as the starter. The microbiological evaluation of eleven murcha starters showed that the lactic acid bacteria and yeast were dominant at 5×10⁵ to 1.0×10⁹ cfu g^-1 range while fungi were present at 2×10⁵ to 1.0×10⁷ cfu g^-1. Coliforms (1×10² to 1.4×10⁵ cfu g^-1), E. coli (1×10³ cfu g^-1), and. S. aureus (1×10² g^-1) were present in some of the murcha starters. Bacillus cereus was absent in all the starters. The microbial succession during poko fermentation suggested that it was primarily a mixed fermentation of yeasts, molds and lactic acid bacteria. The quality poko product obtained after two days and three days of fermentation at 30°C had a pH, acidity, reducing sugar, total sugar, and alcohol in the range of 3.2-3.0, 1.1-1.3 (% LA), 14.4-15.6 (%), 14.6-18.2 (%) and 1-1.6 (%) respectively. These critical ranges of biochemicals in the poko, due to the fermentation process imparted desirable organoleptic characteristics to the product. Saccharomyces cerevisiae, Candida versatilis, Lactobacillus spp, Pediococcus spp and Rhizopus spp were the dominant microorganisms identified from the poko fermentation. The results suggest that the quality of poko depends upon the microbial flora of the traditional murcha starters.     

HOST DEVELOPERS TO OBJECT TECHNICIANS Transition Strategies for OO Development

A company's decision to study and implement object technologies is just the beginning of a challenging and critical new role for software developers. Text-based, transaction processing-oriented programmers and designers can be retrained to take advantage of the opportunities object-oriented (OO) technology offers.     

Comparative studies on electronic transport due to the reduced dimensionality at the heterojunctions of GaAs/A1xGa(1−x)As and GaxIn(1−x)As/InP systems at low temperatures

Comparative studies on ac/dc mobility due to the reduced dimensionality of spatially confined low dimensional systems, at the heterojunctions of GaAs/A1_xGa_(1−x)As and Ga_xIn_(1−x)As/InP forming quasi-two dimensional (Q2D) and quasi-one dimensional (Q1D) systems have been made. The effect of various low temperature nonphonon scattering mechanisms such as ionized impurity, alloy disorder scattering and surface roughness scattering mechanisms; and phonon scattering mechanisms such as acoustic phonon via deformation potential and piezoelectric scattering mechanisms on the systems has been studied. It is found that the surface roughness scattering mechanism dominates in Q2D system whereas acoustic phonon scattering mechanism dominates in Q1D system due to which the nature and magnitude of the temperature dependent dc/ac mobility curves shows significant variation. Whereas, it is observed that the confinement does not change the nature of the frequency dependent real and imaginary parts of ac mobility curves. However, the mobility is found to be enhanced with effective mass and also due to the confinement, i.e. the mobility for Q1D system is higher than that for Q2D system.     

Enhancing power engineering education through the use of designmodules

This paper describes the main features of four design modules that form part of the curriculum for the final year power engineering students at the Nanyang Technological University, Singapore. Through the use of these modules, the students gain an insight into the various aspects of power engineering-including power electronics and drives-and this will hopefully help them in a better understanding of the practical aspects of power engineering, and therefore make them better engineers in the power industry. The four modules described are Generating Capacity Expansion Planning, Rectifier and DC Motor Control, Power Systems Operations Planning, and Security Enhancement using Optimal Power Flow     

Secure Distributed Key Generation for Discrete-Log Based Cryptosystems

A Distributed Key Generation (DKG) protocol is an essential component of threshold cryptosystems required to initialize the cryptosystem securely and generate its private and public keys. In the case of discrete-log-based (dlog-based) threshold signature schemes (ElGamal and its derivatives), the DKG protocol is further used in the distributed signature generation phase to generate one-time signature randomizers (r = g^k). In this paper we show that a widely used dlog-based DKG protocol suggested by Pedersen does not guarantee a uniformly random distribution of generated keys: we describe an efficient active attacker controlling a small number of parties which successfully biases the values of the generated keys away from uniform. We then present a new DKG protocol for the setting of dlog-based cryptosystems which we prove to satisfy the security requirements from DKG protocols and, in particular, it ensures a uniform distribution of the generated keys. The new protocol can be used as a secure replacement for the many applications of Pedersen's protocol. Motivated by the fact that the new DKG protocol incurs additional communication cost relative to Pedersen's original protocol, we investigate whether the latter can be used in specific applications which require relaxed security properties from the DKG protocol. We answer this question affirmatively by showing that Pedersen's protocol suffices for the secure implementation of certain threshold cryptosystems whose security can be reduced to the hardness of the discrete logarithm problem. In particular, we show Pedersen's DKG to be sufficient for the construction of a threshold Schnorr signature scheme. Finally, we observe an interesting trade-off between security (reductions), computation, and communication that arises when comparing Pedersen's DKG protocol with ours.     

Switching characteristics of an optically controlled GaAs-MESFET

The switching characteristics of an optically controlled Metal Semiconductor Field Effect Transistor (MESFET), popularly known as Optical Field Effect Transistor (OPFET), have been derived analytically. The limitations of the existing model have been overcome in the present model. Calculations are being carried out to examine the effect of illumination on the current-voltage characteristics, drain-to-source capacitance (C_dc), internal gate-to-source capacitance (C_gs), drain-to-source resistance (R_ds), the transconductance (g_m), the input RC time constant and the cutoff frequency (f_T) of a GaAs-MESFET. The variations of these parameters with gate length L_g and the doping concentration N_d have also been studied in dark and illuminated conditions. The results of numerical calculations show that there is an overall decrease in the input RC time constant of the device in the illuminated condition arising from the internal gate-to-source capacitance and the transconductance. The results obtained on the basis of the model show a close agreement with the reported experimental findings. The simple model presented here is fairly accurate and can be used as a basic tool for circuit simulation purposes     

Ancylostoma duodenale is responsible for hookworm infections among pregnant women in the rural plains of Nepal

PURPOSE: To evaluate retrospectively the optimum dosage of irradiation for Kimura's disease. METHODS AND MATERIALS: Twenty patients with Kimura's disease were treated with radiotherapy. The sex ratio was 19 males to 1 female. The mean ages at onset, initial treatment, and radiotherapy were 26.2, 29.5, and 32.2 years, respectively. Radiotherapy was mainly applied for residual or recurrent tumors. The eosinophil count increased by more than 10% in 18 of the 20 patients. In most instances, irradiation was given through a single field with dosages ranging from 20 to 44 Gy. RESULTS: At the completion of radiotherapy, a marked response in tumor size was noted in all cases. The minimum follow-up was 48 months. Local control was obtained in 23 of 31 lesions (74.1%). At dosages of < or =25 Gy, 26-30 Gy, and > 30 Gy, local control was obtained in 2 of 8 (25.0%), 9 of 10 (90.0%), and 12 of 13 sites (92.3%), respectively. CONCLUSIONS: Radiotherapy is an effective treatment for Kimura's disease. This strongly suggests that no surgical procedure other than a biopsy should be carried out. The radiation field should be limited to the lesion and swelling of the adjacent lymph nodes as much as possible, with a optimum dosage of 26-30 Gy regardless of tumor size.