MOS器件介质击穿的场加速因子

本文介绍了二氧化硅介质击穿场加速因子的计算方法。根据氧化层总电荷量不变(对用相同工艺步骤制造的MOS电容而言)的观察结果,并假定I-V曲线在击穿前由Fowler Nordheim沟道所控制,可得到加速因子的简单表达式。该表达式与文献所报道的由实验得到的加速因子非常吻合。从该表达式也可以看出,加速因子与电场有关,其关系式为加速因子与电场之间成对数关系而不是线性关系,这一点在外推加速测试的结果时尤需注意。     

Niosomal encapsulation of the antitubercular drug, pyrazinamide

It is estimated that more than one-third of the world population is infected with Mycobacterium tuberculosis. Pyrazinamide (PZA) plays a unique role in shortening therapy because it kills a population of semilatent tubercle bacilli residing in an acidic environment. Niosomes are vesicles made up of non-ionic surfactant and exhibit behavior similar to liposomes in vivo. Preparation of PZA niosomes took place using different molar ratios of Span 60 and Span 85, with cholesterol (CH) i.e. Span: CH (1:1) and (4:2). Dicetyl phosphate and stearyl amine were used in preparation of negative and positively charged niosomes, respectively. Free PZA was separated by cooling centrifugation and estimated spectrophotometrically at 268.4 nm. Niosomes were characterized by electron microscopy and differential scanning calorimetry. The highest percentage PZA entrapped was obtained using Span 60 and the molar ratio (4:2:1) negatively charged niosomes. This was followed by the neutral PZA neutral (4:2) Span 60 niosomes. Biological evaluation of selected PZA niosomal formulations took place on guinea pigs infected with M. tuberculosis. The present work is an attempt to target maximum concentration of PZA to the affected site (lungs) and to exclude undesirable side effects and decrease toxicity. Macrophage targeting and overcoming drug resistance is our final goal.     

Assessment of Fenton's reagent and ozonation as pre-treatments for increasing the biodegradability of aqueous diethanolamine solutions from an oil refinery gas sweetening process

The aim of this work was to evaluate the efficiency of three chemical oxidation processes for increasing the biodegradability of aqueous diethanolamine solutions (aqueous DEA solutions), to be used as pre-treatments before a biological process. The raw aqueous DEA solution, sourced from a sour gas sweetening plant at a Mexican oil refinery, was first characterized by standardized physico-chemical methods. Then experiments were conducted on diluted aqueous DEA solutions to test the effects of Fenton's reagent, ozone and ozone-hydrogen peroxide on the removal of some physicochemical parameters of these solutions. Lastly, biodegradability tests based on Dissolved Organic Carbon Die Away OECD301-A, were carried out on a dilution of the raw aqueous DEA solution and on the treated aqueous DEA solutions, produced by applying the best experimental conditions determined during the aforementioned oxidation tests. Experimental results showed that for aqueous DEA solutions treated with Fenton's reagent, the best degradation rate (70%) was obtained at pH 2.8, with Fe(2+) and H(2)O(2) at doses of 1000 and 10,000 mg/L respectively. In the ozone process, the best degradation (60%) was observed in aqueous DEA solution (100 mg COD/L), using 100 mg O(3)/L at pH 5. In the ozone-hydrogen peroxide process, no COD or DOC removals were observed. The diluted spent diethanolamine solution showed its greatest increase in biodegradability after a reaction period of 28 days when treated with Fenton's reagent, but after only 15 days in the case of ozonation.     

Reduced signaling through the hedgehog pathway in the uterine stroma causes deferred implantation and embryonic loss

The role of the hedgehog (HH) signaling pathway in implantation was studied in mice in which the HH signal transducer, smoothened (SMO), was conditionally deleted in the stromal compartment of the uterus, using CRE recombinase expressed through the Amhr2(cre) allele. In Amhr2(cre/+)Smo(null/flox)-mutant mice, Smo mRNA in uterine stroma was reduced 49% compared to that in Amhr2(+/+)Smo(null/flox) control mice, while levels in the luminal epithelium were not different. Litter size was reduced 60% in mutants compared with controls, but ovulation rate and the number of implantation sites on day 7 of pregnancy did not differ. The number of corpora lutea was equivalent to the number of implantation sites, indicating that most ovulations resulted in implanted embryos. However, on days 13 to 15, the rate of embryo resorption was elevated in mutants. In control mice, on day 5, implantation sites were present and blastocysts were well-attached. In contrast, blastocysts were readily flushed from uteri of mutant mice on day 5 and implantation sites were rare. On days 5.5 and 6, implantation sites were present in mutant mice, and by day 6 embryos could not be flushed from the uterus. The weight of implantation sites on day 7 was decreased by 42% in mutant mice, consistent with delayed development. Signaling through SMO in the endometrial stroma is required for optimal timing of implantation, and deferred implantation leads to defective embryo development and subsequent pregnancy loss.     

Risk assessment of the lead intake by consumption of red deer and wild boar meat in Southern Spain

The presence of heavy metals in big game meat may pose a risk to human health. The main objective of this paper is to carry out a risk assessment study (using a probabilistic and point-estimate approach) of lead intake by consumption of red deer and wild boar meat in Southern Spain based on Spanish data collected in the period 2003-2006. In general, the concentration levels found for wild boar meat (mean?=?1291?μg?kg(-1)) were much higher than those observed in red deer meat (mean?=?326?μg?kg(-1)). The results from a point-estimate risk assessment showed that the estimated average intake of lead among different exposure scenarios varied from 0.1 to 6.5 and from 0.3 to 38?μg?kg(-1)?week(-1) for red deer and wild boar meat, respectively; and from 0.3 to 35?μg?kg(-1)?week(-1) for individuals consuming both red deer and wild boar meat, and that the estimated intake of lead by consumption of big game meat differed significantly between hunters and non-hunters, it being higher for hunters. Besides this, results from the probabilistic risk assessment study corroborated the fact that risk is greater in hunter populations, reaching a maximum in individuals consuming only wild boar and both types of meat, with 0.4% and 0.2% of the population above the provisional tolerable weekly intake (PTWI), respectively. Likewise, the hunter populations consuming wild boar and both types of big game meat (red deer and wild boar meat) were exposed to the maximum lead level (56?μg?kg(-1)?week(-1)), which corresponded approximately to 224% of the PTWI. Further data and studies will be needed to give a complete risk estimation in which it will be crucial to consider the contribution to the lead intake level of other foods in the diet of both population groups.     

PMF analysis of wide-range particle size spectra collected on a major highway

Particle number concentration data have been collected on a very busy road in central London (Marylebone Road). Continuous size distributions from 15 nm to 10 μm diameter, collected over 21 days, were analyzed using positive matrix factorization which identified 10 factors, five of which were observed to make major contributions (greater than 8%) to either the total number or volume of particulate matter. The sources associated with each factor were identified from the size distribution, directional association, diurnal variation and their relationship to meteorological pollution and traffic volume variables. The factors related to the emissions on Marylebone Road accounted for 40.5% of particle volume and 71.9% of particle number. These comprised nucleation mode exhaust particles (3.6% of total volume and 27.4% of total number), solid mode exhaust particles (18.8% of total volume and 38.0% of total number), brake dust (13.7% of total volume and 1.7% of total number and resuspension (4.4% of total volume and 4.8% of total number). Another six factors were associated with the urban background accounting for 59.5% of total volume and 28.2% of total particle number count. The method is extremely successful at separating the components of on-road emissions including brake wear and resuspension.     

Adsorption and surface complexation study of L-DOPA on Rutile (α-TiO₂) in NaCl solutions

Dihydroxyphenylalanine (DOPA) and similar molecules are of considerable interest in studies of bioadhesion to minerals, solar cells involving titanium dioxide, and biomedical imaging. However, the extent and mechanisms of DOPA adsorption on oxides in salt solutions are unknown. We report measurements of DOPA adsorption on well-characterized rutile (α-TiO?) particles over a range of pH, ionic strength, and surface coverage as well as a surface complexation model analysis establishing the stoichiometry, model surface speciation, and thermodynamic equilibrium constants, which permits predictions in more complex systems. DOPA forms two surface species on rutile, the proportions of which vary strongly with pH but weakly with ionic strength and surface loading. At pH < 4.5 a species involving four attachment points ("lying down") is important, whereas at pH > 4.5 a species involving only two attachment points via the phenolic oxygens ("standing up") predominates. Based on evidence of strong attachment of DOPA to titanium dioxide from single molecule AFM (Lee, H. et al., Proc. Natl. Acad. Sci.2006, 103, 12999-12003) and studies of catechol adsorption, one or more of the DOPA attachments for each species is inner-sphere, the others are likely to be H-bonds.