Fabrication of support structures to prevent SU-8 stiction in high aspect ratio structures

We have previously demonstrated that it is possible to fabricate densely-packed high aspect ratio structures in SU-8 by means of a top-plate support member which stiffens the overall structure and prevents pattern collapse. In this work we have computed the tensile stresses induced in the top-plate structures due to the capillary forces that arise between the columns due to the surface tension of the drying liquid. We have further studied the dynamic behavior of the structure after an instantaneous force. Based on these results, we have shown that the predicted optimal thickness of the top-plate structure is sufficient to maintain structural integrity.     

Effects of Aluminum Concentration on the Oxidation Behaviors of Reactively Sputtered TiAlN Films

Polycrystalline TiAlN films were deposited on a substrate of high-speed steel via a radio-frequency-bias reactive-sputtering process. The effects of aluminum concentration (0–60 at.%) on the high-temperature oxidation behavior of TiAlN films were explored by using in situ thermogravimetric analysis and high-temperature X-ray diffractometry. The composition and distribution of the oxidizing layers over TiAlN films were investigated. Results indicated that the oxidation resistance increased as the aluminum concentration increased. The type and location of oxidizing phases also were dependent on the aluminum concentration. Three major oxides-i.e., Al₂O₃, TiO₂, and TiO-were observed. The thickness of the Al₂O₃ layer increased and the TiO₂ gradually changed to TiO as the aluminum content increased. Thermodynamic calculations were compared to experimental observations, and they showed good agreement.     

Automated class testing using threaded multi-way trees to represent the behaviour of state machines

Extensive test data is required to demonstrate that “few” errors exist in software. If the process of software testing could be carried out automatically, testing efficiency would increase and the cost of software development would be significantly reduced. In this paper, a tool for detecting errors in object oriented classes is proposed. The approach uses a state-based testing method. The method utilises state machines in order to produce threaded multi-way trees, which are referred to as inspection trees. Inspection trees can be used to generate test cases and parse test results files. This allows us to determine whether the classes under test contain errors. The algorithms for the creation of inspection trees and the examination of the test results file using an inspection tree are described in the paper. This revised version was published online in June 2006 with corrections to the Cover Date.     

CHARACTERIZATION OF ZIRCONIA POWDER SYNTHESIZED VIA REVERSE MICROEMULSION PRECIPITATION

A two-reverse-microemulsion precipitation technique was applied to synthesize nanocrystalline tetragonal zirconia using H₂O solution/CTAB/hexanol as the microemulsion system. Two solutions of reverse microemulsion, one containing Zr⁴⁺ aqueous droplets and the other aqueous ammonia droplets with the same water/surfactant ratio, were prepared separately and mixed together to form a slurry of nanosized ZrO₂ precursors, which filled the matrix of the surfactant, CTAB. The precursors were recovered, calcined to form nanocrystalline zirconia powder, and then characterized by using a transmission electron microscope to determine the particle size, a scanning electron microscope to examine the microstructure of the zirconia powder, and an X-ray diffractometer to determine the crystal phase and crystallite size. It is concluded that the primary particle size of the precursor determines the transformation temperature of the precursor and the crystal structure of the calcined zirconia.     

Instrumented tracer for Lagrangian measurements in Rayleigh-Bénard convection

We have developed novel instrumentation for making Lagrangian measurements of temperature in diverse fluid flows. A small neutrally buoyant capsule is equipped with on-board electronics which measures temperature and transmits the data via a wireless radio frequency link to a desktop computer. The device has 80 dB dynamic range, resolving millikelvin changes in temperature with up to 100 ms sampling time. The capabilities of these "smart particles" are demonstrated in turbulent thermal convection in water. We measure temperature variations as the particle is advected by the convective motion and analyze its statistics. Additional use of cameras allow us to track the particle position and to report here the first direct measurement of Lagrangian heat flux transfer in Rayleigh-Bénard convection. The device shows promise for opening new research in a broad variety of fluid systems.     

Preparation of silazane grafted yttria-stabilized zirconia nanocrystals via water/CTAB/hexanol reverse microemulsion

The nanosized precursors of yttria-stabilized zirconia (YSZ) were prepared via a water/CTAB/hexanol reverse microemulsion. The surface hydroxyl groups of the YSZ precursor were substituted by siloxyl groups using HMDS (hexamethydisilazane) as starting material. The untreated and treated YSZ powder were characterized by ultraviolet-visible-near-infrared spectrometer, FT-IR spectrometer, X-ray diffractometer, BET surface-area analyzer, and electron probe microanalysis (EPMA). After HMDS treatment, the amount of Si atom grafted on the nanoparticle surface was about 1 mol%. The crystallite size of the treated powder was smaller and the surface area was larger than the untreated powder.     

Methodology for calculating turn-off transient of photoconductive circuit elements in picosecond optoelectronics

A methodology for calculating the transient following sudden removal of photon or mass-particle excitation is developed for semiconductor devices in which high hole-electron recombination rates, rather than short transit times, yield picosecond response time. We suggest the name photoconductive circuit element (PCE) for these optoelectronic transducers to emphasize their potential application to diverse circuit and system functions. The device consists of a nearly intrinsic active region that contains extremely high concentrations of deep-level states acting as recombination centers. Regions of semiconductors highly doped with shallow donor or acceptor atoms connected to metallic contacts border this active region. In calculating the turnoff transient, we set forth criteria that define nearly ideal ohmic-contact systems and the quasi-neutrality regime of the intrinsic region. If these criteria are met, the turn-off transient becomes a problem in photoconductive decay. For incremental variations in the electron and hole quasi-Fermi voltages much less than the thermal voltage, two characteristic times, assigned to each recombination-center energy level, rather than a single lifetime, describe electron-hole recombination. A computer algorithm accounting for incremental variations within suitably small time intervals then enables calculation of observables that may vary by many orders of magnitude, InP:Fe photoconductive circuit elements containing eight different Fe concentrations, excited by 780 and 600 nm laser-light pulses and 6 MeV electron pulses, showed a (1/e)-fall-time versus Fe-concentration in general accord with results calculated by the methodology. The capture cross sections and the energy distribution of the recombination-center energy levels receive attention. The InP:Fe transducers showed (1/e)-fall-times in the sub- 100-ps regime.     

Effects of Structural Isomers of Spermine on the Higher-Order Structure of DNA and Gene Expression

Polyamines are involved in various biological functions, including cell proliferation, differentiation, gene regulation, etc. Recently, it was found that polyamines exhibit biphasic effects on gene expression: promotion and inhibition at low and high concentrations, respectively. Here, we compared the effects of three naturally occurring tetravalent polyamines, spermine (SPM), thermospermine (TSPM), and N⁴-aminopropylspermidine (BSPD). Based on the single DNA observation with fluorescence microscopy together with measurements by atomic force microscopy revealed that these polyamines induce shrinkage and then compaction of DNA molecules, at low and high concentrations, respectively. We also performed the observation to evaluate the effects of these polyamine isomers on the activity of gene expression by adapting a cell-free luciferase assay. Interestingly, the potency of their effects on the DNA conformation and also on the inhibition of gene expression activity indicates the highest for TSPM among spermine isomers. A numerical evaluation of the strength of the interaction of these polyamines with negatively charged double-strand DNA revealed that this ordering of the potency corresponds to the order of the strength of the attractive interaction between phosphate groups of DNA and positively charged amino groups of the polyamines.     

Distinct p53-mediated G1/S checkpoint responses in two NIH3T3 subclone cells following treatment with DNA-damaging agents

N3T3 and P-3T3 cells, originally isolated from a NIH3T3 cell clone on the basis of their negative and positive transformation by v-Abl, v-Src and Bcr-Abl, were previously found to show distinct cyclin activity changes following 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment, which is anti-mitogenic for N-3T3 cells and mitogenic for P-3T3 cells. We have found in this study that, while the G1/S arrest and cell death induced by serum starvation and TPA treatment in N-3T3 cells did not involve p53-mediated checkpoint or apoptosis, N-3T3 and P-3T3 cells evidently responded differently in these aspects of cell cycle regulation to DNA-damaging agents, methylmethane sulfonate (MMS) and gamma-radiation. In N-3T3 cells, DNA damages elicit cell growth arrest at G1/S transition with concomitant accumulation of p53 and p53-inducible Waf1/Cip1 proteins and also signs of apoptosis such as DNA ladder patterns and apoptotic (subgenomic) peak in flow cytograph. Conversely, P-3T3 cells treated with the DNA-damaging agents showed no cell cycle interruption nor accumulation of p53 or Waf1/Cip1. However, both P-3T3 and N-3T3 cells showed the same p53 protein half-life of 40 min or less, the same wild-type p53 DNA sequence and the same co-immunoprecipitable cellular proteins in complexes with p53, suggesting that an alteration in a signal transduction pathway upstream of p53 might account for the evasion of p53-mediated G1 checkpoint in P-3T3 cells.     

Association of Methylentetraydrofolate Reductase (MTHFR) 677 C > T gene polymorphism and homocysteine levels in psoriasis vulgaris patients from Malaysia: a case-control study

Background  

The methylenetetrahydrofolate reductase (MTHFR) enzyme catalyzes the reduction of 5, 10-methylenetetrahydrofolate to 5-methyltetrahydrofolate and methyl donors. The methyl donors are required for the conversion of homocysteine to methionine. Mutation of MTHFR 677 C > T disrupts its thermostability therefore leads to defective enzyme activities and dysregulation of homocysteine levels.