Design of experiment for the optimisation of deep reactive ion etching of silicon inserts for micro-fabrication

The following paper describes a design of experiments investigation of the deep reactive of pillar structures on a silicon wafer. The etched wafers would subsequently be used as masters for the fabrication of nickel mould inserts for microinjection moulding. Undercuts occur when the pillar base has a smaller cross-section than the apex of the pillar. They therefore affect tolerances of the subsequent nickel mould, its strength and its de-mouldability from the silicon form. The response measured in these experiments was the degree of undercut of micro-scale (10 μm x 10 μm x 40 μm, 5 μm x 5 μm x 40 μm and 2 μm x 2 μm x 40 μm) The literature suggests that gas pressure, platen power, gas flow rate, phase switching times and mask size can all affect the degree of undercut. After examination of this literature, and of manufacturers guidelines, three parameters were selected for experimental testing: platen power, C 4F 8 gas flow rate during the passivation phase and switching times. Switching times was found to be the only statistically significant parameter for both 10x10 μm and 5x5 μm pillars. The 2x2 μm pillars were not successfully replicated and could therefore not undergo statistical evaluation

Statistical Properties of Interacting Bose Gases in Quasi-2D Harmonic Traps

The analytical probability distribution of the quasi-2D (and purely 2D) ideal and interacting Bose gas are investigated by using a canonical ensemble approach. Using the analytical probability distribution of the condensate, the statistical properties such as the mean occupation number and particle number fluctuations of the condensate are calculated. Researches show that there is a continuous crossover of the statistical properties from a quasi-2D to a purely 2D ideal or interacting gases. Different from the case of a 3D Bose gas, the interaction between atoms changes in a deep way the nature of the particle number fluctuations.Comment: RevTex, 10pages, 4 figures, E-mail: [email protected]

The role of surface conditions in nucleate boiling

Nucleation from a single cavity has been stuied indicating that cavity gemtry is aportant in two ways. The mouth diameter determines the superheat nmeded to initiate boiling and its shape determines its stability one boiling has begun. Contact angle is shown to be important in bubble nucleation primarity thrugh its effect on cavity stability. Contact angle measurements made on "clean" and paraffin coated stainIess steel murftces with water shcw that the contact angle varies between 20 and 110* for tenperatures from 20[degree] to 170[degree] C. On the basis of single cavity nucleation theory, it is proposed to characterie the gross nucleation properties of a given surface for all fnds under all conditions with a single group having the dmnions of length. Finally, it is shown experimentally that this characterization is adequate by boiling water, methmnol and ethanol different copper surfaces finished with 3/0 emry, and showing that the number of active centers per unit area is a function of this variable alone.Office of Naval Research DSR Projec

Slug flow

Introduction: When two phases flow concurrently in a pipe, they can distribute themselves in a number of different configurations. The gas could be uniformly dispersed throughout the liquid in the form of small bubbles. There could be large gas bubbles almost filling the tube. There could be an annulus of liquid and core of vapor with or without drops of liquid in it. The interface could be smooth or wavy. When one describes how the phases are distributed, one is specifying the flow regime. Such a description is necessary before any mathematical model can be constructed which will predict a quantity such as pressure drop It is naive to expect that a single mathematical model would adequately encompass all possible two-phase flow regimes, even for a single geometric configuration. Therefore, we shall begin by saying that for this work the results that have been obtained and the conclusions that have been drawn apply only to fully developed slug flow in a round vertical pipe. Slug flow is characterized by large bubblesalmost filling the tubewhich are separated by slugs of liquid. The nose of the bubble is rounded and the tail generally flat. One may or may not find small bubbles in the slug following the large bubble. A number of typical slug flow bubbles are pictured in Figures 4-10. Bubbles very similar to these have been studied by Dumistrescu (1), and Davis and Taylor (2). Both these references consider the same problem. How rapidly will a closed tube full of liquid empty when the bottom is suddenly opened to the atmosphere. The approach used by both authors is to assume that the asymptotic rise velocity (for large times) can be calculated from potential flow theory. The boundary condition at the pipe wall is that the velocity is axial. At the bubble boundary it is assumed that the pressure is constant, The problem is then to find the shape of the bobble that would satisfy the constant pressure boundary condition.(cont.) This was done approximately and in both cases the comparison with experiment was satisfactory though the deviations became large for small tubes. The work of Davis and Taylor, and Dumitrescu served as the starting point for this investigation. The boundary condition at the bubble wall for large bubbles, constant pressure, was still valid to an excellent approximation and the finiteness of the slug flow bubbles did not appear to make much difference in their rise velocity. In the next section, the fluctuation period, the mean density, and the pressure drop will be expressed in terms of the pipe area, the Taylor bubble rise velocity and the flow rates of the two phases. In subsequent sections the observations rade of bubble shape, length and velocity will be described and then a comparison of computed and measured pressure drops given.Office of Naval Research DSR Projec

Nucleoside and oligonucleotide approaches towards potential HIV chemotherapies

The use of oligonucleotides directed against the mRNA of HIV promises site-specific inhibition of viral replication. In this work, the effect of aralkyl substituents on oligonucleotide duplex stability was studied using model oligonucleotide sequences in an attempt to improve targeting of oligonucleotides to viral mRNA. Arakyl-substituted oligonucleotides were made by solid phase synthesis using either the appropriate aralkyl-substituted phosphoramidite or by post-synthetic substitution of a pentafluorophenoxy substituent by N-methylphenethylamine. The presence of phenethyl or benzoyl substituents invariably resulted in thermodynamic destabilisation of all duplexes studied. The methods which were developed for the synthesis of nucleoside intermediates for oligonucleotide applications were also used to prepare a series of nucleoside analogues derived from uridine, 2'-deoxyuridine and AZT. Crystal structures of six compounds were successfully determined. Anti-HIV activity was observed for most compounds in the series although none were without cytotoxicity. The most active compound of the series was the ribose nucleoside; 1-β-D-erythro-pentofuranosyl-4-pentafluorophenoxy-pyrimidine-2(1H)-one 95, derived directly from uridine. The same series of compounds also displayed very modest anti-cancer activity. To enable synthesis of prooligonucleotides and analogues for possible antisense applications, the properties of a new Silyl-Linked Controlled Pore Glass solid support were investigated. Synthesis of the sequences d(Tp)7T, d(Tps)7T and the base-sensitive d(Tp)3(CBzp)2(Tp)2T was achieved using the silyl-linked solid support in a fluoride-induced cleavage/deprotection strategy

UK investment in intangible assets: Report for NESTA

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Spillovers from R&D and other intangible investment: evidence from UK industries

02.12.14 KB. Re-submitted with updated version of paper

UK Innovation Index: productivity and growth in UK industries

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