Porous polycrystalline silicon: a new material for MEMS

A new technique for the fabrication of thin patterned layers of porous polycrystalline silicon (polysilicon) and surface micromachined structures is presented. First, a multilayer structure of polysilicon between two layers of low-stress silicon nitride is prepared on a wafer of silicon. Electrochemical anodization with an external cathode takes place in an RF solution. A window in the outer nitride layer provides contact between the polysilicon and the HF solution; the polysilicon layer contacts the substrate through openings in the lower silicon nitride layer (remote from the upper windows). Porous polysilicon growth in the lateral direction is found at rates as high as 15 μm min^-1 in 12M (25%, wgt) HF to be controlled by surface-reaction kinetics. A change in morphology occurs when either the anodic potential is raised or the HF concentration is decreased, causing the polysilicon to be electropolished. The etch front advances proportionally to the square root of time as expected for a mass-transport-controlled process. Similar behavior is observed in HF anodic reactions of single-crystal silicon. Dissolution of the polysilicon layer is confirmed using profilometry and scanning electron microscopy. Enclosed cavities (chambers surrounded by porous plugs) are formed by alternating between pore formation and uniform dissolution. Porous polysilicon also forms over a broad-area layer of polycrystalline silicon that has been deposited without overcoating the silicon wafer with a thin film of silicon nitride. The resulting porous layer may be useful for gas-absorption purposes in ultrasonic sensors     

Analogue placement using guided enumeration

In this paper a new efficient approach to the placement problem of analogue circuits is presented. In the design of analogue circuits, strong interaction between humans and automatic tools is crucial to obtain good results. Hence there is a strong need for fast algorithms to support an interactive and incremental design style. In the design process, usually many geometric constraints such as symmetry or matching requirements are introduced by the designer to obtain a placement that fulfils all electrical requirements. Most state-of-the-art analogue placement tools employ simulated annealing algorithms and map geometric constraints into the cost function of the annealing algorithm; thus they have to search the whole design space. In our approach an initial global placement is computed establishing neighbourhood relations between all modules. Afterwards the design space is reduced to placements that fulfil these neighbourhood relations and user-specified geometrical constraints. the reduced design space is fully enumerated to find the optimal solution. the implemented tool achieves typical CPU times of a few seconds for designs of about 40 modules, making it an excellent choice for an interactive design process. Two examples are presented: (i) a high-speed CMOS comparator lay-out is compared with lay-outs published in other papers and (ii) a BiCMOS bandpass amplifier lay-out that has to be embedded into a mixed-signal chip is compared with the manual lay-out of a fabricated chip. We achieved the smallest lay-out size published for the comparator while fulfilling all required constraints. For the amplifier the synthesized lay-out is very similar to the manual one and about the same size.     

Animal performance and fleece characteristics of Angora goats maintained on western and southern Texas rangeland

Two hundred castrated male Angora goats (18 mo of age) were divided equally between rangeland sites in the oak savannah of the Edwards Plateau (EP) and the mixed-brush shrublands of the South Texas Plains (STP) for 5 yr to study influence of environment and age on body weight (BW), mohair production, and mohair fiber characteristics. Goats were grazed on rangeland typical of the respective regions and were given typical management that included shearing in February and July or August of each year. Shorn goats were weighed and individual fleeces were measured for grease weight (GFW), clean yield (CMFP), average fiber diameter (AFD), and proportion of medullated fibers, med (MFP) and kemp (KFP). Rainfall and maximum and minimum temperatures were recorded daily at each site. The AFD (P = .01) and its associated SD (P < .001) and kemp levels (P = .03) were all higher at the STP than at the EP site (39.4 vs 37.9 microns, 10.4 vs 11.1 microns, and .80 vs .68%, respectively). Angora goats at EP weighed less (38.1 vs 41.7 kg, P = .03), and sheared less (1.90 vs 2.22 kg, P = .01), finer (36.4 vs 39.3 microns, P < .001), and less kempy (.52 vs .84%, P < .001) mohair at the February shearing than at the August shearing. No seasonal differences in body weight or in mohair production or quality were apparent at STP. The proportions of total variation in grease mohair production (30.6%), CMFP (22.2%), and AFD (15.7%) due to year effects were two to three times greater at STP than at EP. In contrast, year effects were responsible for only a small proportion (2.2 to 4.6%) of the variation in medullated fibers. The effects of rainfall accumulation within specific 6-mo growing periods were positive for BW, GFW, CFW, AFD, SD of AFD and MFP and negative for CMFP and KFP. Only the rainfall effects on SD of AFD and medullated fibers were significant (P < .05). The effects of age were positive for BW (P < .001), CMFP (P = .046), AFD (P < .001), MFP (P = .014), and KFP (P = .084) and negative for GFW (P = .046) and CFW (P = .107). This study documents influence of environment and age of goats on body weight, mohair production, and fiber characteristics.     

Prophylactic and therapeutic efficacy of an avian antitoxin in ricin intoxication

This study was designed to demonstrate the efficacy in animals of a ricin antitoxin consisting of purified avian antibodies. Antitoxins consisting of avian antibodies have significant advantages when compared to conventional mammalian (e.g. horse) antibodies; (a) avian antibodies do not fix human complement, eliminating associated inflammatory reactions, and, (b) avian antibodies can be manufactured more economically. Ricin toxoid was injected into laying hens followed by collection of eggs bearing hyperimmune immunoglobulin. Immunoglobulin was extracted from yolks and purified by immunoaffinity chromatography. In a mouse model for toxin neutralization it was shown that immunoaffinity purified ricin antibodies could prevent ricin lethality. Furthermore, it was shown that passive antibody treatment leads to active ricin immunization in animals given lethal ricin doses. Highly purified avian antibodies, as developed in this study, should offer enhanced clinical effectiveness, greater safety, and reduced manufacturing costs when compared to other technologies.     

Genes and regulatory sites of the "host-takeover module" in the terminal redundancy of Bacillus subtilis bacteriophage SPO1

Members of the CYP2F gene subfamily are selectively expressed in lung tissues and have been implicated as important catalysts in the formation of reactive intermediates from several pneumotoxic chemicals. Human CYP2F1 bioactivates 3-methylindole (3MI), while mouse CYP2F2 bioactivates naphthalene. Although 3MI is a potent pneumotoxin in ruminants and rodents, the participation of cytochrome P450s from the 2F subfamily in 3MI bioactivation has not been fully defined. To test the hypothesis that a goat lung 2F homologue uniquely catalyzes the dehydrogenation of 3MI to the putative electrophile 3-methylene-indolenine, the CYP2F3 cDNA was cloned from a goat lung cDNA library and expressed in Escherichia coli. The predicted amino acid sequence of CYP2F3 possessed 82% identity to both human CYP2F1 and mouse CYP2F2. CYP2F3 was mutated at the 5' end, expressed in E. coli, and shown to have a molecular mass of 50 kDa. The reconstituted enzyme uniquely catalyzed only the dehydrogenation of 3MI to form 3-methylene-indolenine, an electrophilic intermediate, without detectable formation of other products, thus demonstrating highly unusual selectivity for dehydrogenation rather than hydroxylation of a substrate. Immunoinhibition studies demonstrated that about 20% of the production of the intermediate in goat lung microsomal samples was produced by CYP2F3. The CYP2F3 enzyme had a specific activity that was similar to that of human cDNA-expressed CYP2F1. CYP2F3 also stereoselectively catalyzed the formation of the 1R,2S-oxide from naphthalene; this stereoisomer is the putative pneumotoxin. The enzyme, however, lacked catalytic activity with other common P450 substrates including 7-ethoxycoumarin, a substrate for CYP2F1, indicating that the substrate selectivity of CYP2F3 appears to be high.     

Biological control of Botrytis cinerea growth on apples stored under modified atmospheres

The combined effect of modified-atmosphere packaging and the application of a bacterial antagonist (Erwinia sp.) on Botrytis cinerea growth on apples (cv. 'Golden Delicious') was investigated. Inoculated apples were stored in polyethylene bags at 5 degrees C. The initial gas composition in each bag was set according to a central composite experimental design involving five levels of O2 (1 to 15%) and CO2 (0 to 15%). Control samples under ambient conditions were also included. Without the antagonist, measurements of mold colony diameter over time showed that O2 had no effect on the growth of B. cinerea, while increased CO2 levels delayed its growth by about 4 days. Application of the antagonist resulted in a significant interaction between O2 and CO2. At low O2 levels, CO2 had no effect on mold growth, but at high O2, CO2 enhanced mold growth. O2 and the antagonist worked synergistically to reduce mold growth by about 6 days at low levels of CO2. However, at high CO2 levels, O2 had no effect. The strongest antagonistic effect was observed under ambient conditions. Overall, results showed that high CO2 atmospheres can slow the growth of B. cinerea and that Erwinia sp. was an effective antagonist against B. cinerea growth on apples, particularly under ambient conditions.     

A double-blind, controlled comparison of the novel antipsychotic olanzapine versus haloperidol or placebo on anxious and depressive symptoms accompanying schizophrenia

BACKGROUND: Depressive symptoms are a common feature of schizophrenia and may represent a core part of the illness. Where present, it has been associated with greater overall morbidity and mortality. Monotherapy with conventional dopamine antagonists may either worsen or bestow a limited therapeutic benefit. Accordingly the use of adjunctive thymoleptics has been explored. In contrast, olanzapine (OLZ), an atypical antipsychotic agent, offers a distinctive and pleotropic pharmacology suggestive of a broader efficacy profile than conventional neuroleptic agents. METHODS: In a 6-week placebo- and haloperidol (HAL)-controlled trial with 335 randomized subjects with chronic schizophrenia in an acute exacerbation, three fixed dose ranges of OLZ (5, 10, or 15 +/- 2.5 mg) were evaluated versus HAL (10-20 mg) or placebo. RESULTS: Baseline to endpoint change in the Brief Psychiatric Rating Scale including the anxiety-depression cluster (items 1, 2, 5, 9) was analyzed. Two dose ranges of OLZ (10 +/- 2.5, 15 +/- 2.5) were superior to placebo (p < 05) in improving mood status, whereas HAL was not. CONCLUSION: Contributions from a more selective mesolimbic dopaminergic profile, D1 or D4 activity, the release of dopamine/norepinephrine in the prefrontal cortex, and/or serotonin 5-HT2A,C antagonism may explain the differential benefit seen with OLZ in the treatment of comorbid anxious and depressive symptoms in schizophrenia.