Alumina-supported catalysts for propane oxidative dehydrogenation from mixed VXM(6−X)O19 (M=W, Mo) hexametalate precursors

γ-Al₂O₃ supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium–tungsten and vanadium–molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW₅O₁₉⁵⁻, V₂W₄O₁₉⁴⁻, VMo₅O₁₉⁵⁻ and V₂Mo₄O₁₉⁴⁻) from aqueous solutions. The isopolyanion solutions were characterized by UV-Vis and ⁵¹V NMR spectroscopy. Vanadium, vanadium–tungsten and vanadium–molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state ⁵¹V NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VO_x/γ-Al₂O₃ was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on the γ-Al₂O₃ surface.     

The cationic polymerization of α-methylstyrene in liquid sulfur dioxide initiated by the HI/I2 system

The polymerization of α-methylstyrene (αMeSty) initiated by HI/I₂ or HI in the presence of liquid sulfur dioxide has been investigated. The number-average molecular weight increased with the monomer concentration for reactions initiated by the HI/I₂ system. I₂ also participates in the initiation process, increasing the number-average polymer chain at higher monomer concentration. HI alone is also able to initiate the polymerization of αMeSty in the presence of SO₂. With this initiator, transfer reaction can be minimized in systems containing low amount of SO₂. Received: 19 December 1996/Revised: 27 January 1997/Accepted 29 January 1997     

A new framework for understanding educational digital library use: re-examining digital divides in U.S. schools

Despite their decade of deployment, educational digital libraries have not achieved sustained use in elementary and secondary schools in the United States. Barriers to accessing the Internet and computers have been widely targeted by myriad initiatives, but efforts aimed at bridging this first-level “digital divide” have not led to increased use of the Internet and digital library resources in U.S. classrooms. In fact, such programs have revealed additional divides that affect educators’ use. This paper examines the additional digital divide levels and proposes a new framework for understanding technology innovation in schools that can improve development and outreach approaches by digital library developers.     

An equation of state formulation of the thermodynamic properties of R134a (1,1,1,2-tetrafluoroethane)

New correlations for the thermodynamics properties of R134a are presented. A classical equation for the molar Helmholtz energy is used with temperature and density as the independent variables. The equation is accurate for both the liquid and vapour phases at pressures up to 70 Pa, and for a temperature range from the triple point to 450 K. Temperatures are given on the new International Temperature Scale of 1990 (ITS 90). The equation was developed by using experimental data for pressure-volume-temperature (PVT) properties, isochoric heat capacity, second virial coefficients, speed of sound and coexistence properties. Comparisons with experimental data and with two other equations of state are given. Ancillary equations representing the saturated liquid and vapour densities and the vapour pressure are also presented.     

Evaluation of thermal and mechanical properties of rubber compositions based on SBR extended with safe oils

The extender oil usually employed in compositions of rubbers based on styrene and butadiene (SBR) 1712 is the distilled aromatic extract (DAE). In this work, this oil was substituted by oils with low levels of polycyclic aromatic hydrocarbons (PAHs): treated residual aromatic extract (TRAE) and two naphthenic oils from different suppliers (HN1 and HN2). This substitution was performed in response to REACH Regulation (EC No. 1907/2006 European Parliament and the Council of December 18, 2006, Annex XVII), which state that the sum of individual PAHs should be below 10 mg/kg and the levels of benzo (a) pyrene (BaP) should not exceed 1 mg/kg. Infrared spectroscopy was employed to characterize the structure of crude oils and respective SBR compositions. Thermal properties of the materials were evaluated by thermogravimetry and differential scanning calorimetry. Mechanical properties as tension tests, hardness, abrasion resistance, and resilience were also determined. The final results showed that it is possible to replace the extender oil DAE for any of the oils tested, specially the naphthenic HN1, without any loss of the properties evaluated in this study for the SBR compositions. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Increasing X-ray image interpretation competency of cargo security screeners

X-ray screening of containers and unit load devices in the area of cargo shipping is becoming an essential and common feature at ports and airports all over the world. The detection of prohibited items in X-ray images is a challenging task for screening officers as they need to know which items are prohibited and what they look like in X-ray images. The main aim of this study was to investigate whether X-ray image interpretation competency of cargo security screeners can be increased by computer-based training. More specifically, effects of training were investigated by conducting tests before training started and after approximately three months of training. Moreover, it was examined whether viewing X-ray images in pseudo color would lead to a better detection performance compared to when X-ray images are shown in greyscale. Recurrent computer-based training resulted in large performance increases after three months. No significant difference in detection performance could be found for tests when using X-ray images in greyscale vs. pseudo color.     

Absence of sterol biosynthesis in oyster tissue culture

An oyster heart tissue culture was used to investigate the ability of the American oyster (Crassostrea virginica) to synthesize sterols from [¹⁴C]acetate. Lipids were extracted from cultured oyster heart cells and no label was found in the purified fatty acid fraction, 90% of which was located in the saturated and monounsaturated fractions. Although these results cannot rule out the possibility of sterol synthesis in other oyster tissues, this and previous evidence are in support of the hypothesis that the American oyster is unable to synthesize sterols.     

Dietary arachidonic acid reduces fatty liver,increases diet consumption and weight gain in ethanol-fed rats

We fed young male Sprague-Dawley rats for 4 wk ad libitum liquid diets containing 34% of the calories as ethanol and 35% as fat with (AA+) and without (AA−) arachidonic acid (20∶4). Additional rats in the control groups were fed similar diets made isocaloric with dextrose with (CA+) and without (CA−) 20∶4. The liver triglyceride (TG) content of rats in the AA+ group was reduced ca. 3-fold over that of rats in the AA-group. The diet consumption and body wts of rats in the AA+ group were significantly greater than those of rats fed alcohol without the 20∶4 supplement (AA−). Also livers from rats in the AA+ group were as large as those from rats in control groups (CA+, CA−) and ca. twice as large as those from rats in the AA-group. The fatty acid composition of liver TG in rats fed the alcohol diet was similar to that of dietary fat. Levels of 20∶4 and docosatetraenoic acid (22∶4) in liver TG fatty acids from rats fed diets without arachidonate (AA−, CA−) were low (trace to 1.6%). After ingestion of arachidonic acid, 20∶4 increased to ca. 10% and 22∶4 to ca. 5%. The content of liver phospholipids was higher in livers of rats fed ethanol (AA−) than in those of controls (CA−). Presented at the ISF/AOCS World Congress, April 27-May 1, 1980, New York City.     

Sigma流量计在市政排水管网的成功应用

美国内珀维尔市通过安装准确耐用的流量计,消除了传感器的漂移,为流量监测系统提供了可靠的数据。通过这些可靠的流量和液位数据,能够分析市政排水管网的状态,判断入流和渗漏问题,优化对市政排水管网的维护和管理,执行最优的污水管道修复策略,最终减少因入流和渗漏问题对污水处理厂造成的流量冲击。     

Guiding collaborative revision of science explanations

International Journal of Computer-Supported Collaborative Learning - This paper illustrates how the combination of teacher and computer guidance can strengthen collaborative revision and identifies...