ROLE OF WATER IN THE KINETIC MODELING OF METHANOL TRANSFORMATION INTO HYDROCARBONS ON HZSM-5 ZEOLITE

The attenuating effect of reaction-medium water (feed and/or reaction product) on the kinetics of the steps of methanol transformation into hydrocarbons on a HZSM-5 zeolite catalyst was studied by means of a kinetic model. In this model, the effect of water was quantified in all the steps of the kinetic scheme by means of a kinetic parameter, which is constant with temperature under the conditions of the MTG process. At low temperature, under conditions in which only methanol dehydration occurs, the kinetics of this reaction is attenuated by the presence of water, and the coefficient that quantifies the attenuation decreases as temperature is increased. In addition to considering the effect of water content in the reaction medium, another innovation of the kinetic model proposed, compared to those proposed in the literature consisting of lumps, is the fact that the higher reactivity of dimethyl ether over methanol is taken into account. A step of cracking of gasoline lump hydrocarbons to produce light olefins (ethene and propene) was also taken into account. The kinetic model proposed was verified by using the results obtained in an integral isothermal fixed bed reactor, in the 573–723 K range, for an ample range of space time values. The results revealed that the effect of water is due to its adsorption on the active sites by competition with the intermediate compounds of the kinetic scheme.     

A fully integrated high IP1dB CMOS SPDT switch using stacked transistors for 2.4 GHz TDD transceiver applications

A transmit/receive (T/R) switch is an essential module of every modern time division duplex (TDD) transceiver circuit. A T/R switch with high power handling capacity in CMOS process is difficult to design due to capacitive coupling of radio frequency signals to the substrate. This paper proposes a single-pole-double-throw (SPDT) T/R switch designed in a standard Silterra 130 nm CMOS process for high-power applications like RFID readers. The results reveal that, in 2.4 GHz ISM band, the proposed switch exhibits a very high input P1dB of 39 dBm with insertion loss of only 0.34 dB and isolation of 40 dB in transmit mode but 1.08 dB insertion loss and 30 dB isolation in receive mode. Stacked thick-oxide triple-well transistors, resistive body floating and negative control voltages are used to achieve such lucrative performance. Moreover, the chip size of the designed switch is only 0.034 mm² as bulky inductors and capacitors are avoided. The Monte-Carlo and corner analyses confirm that the performance of the switch is also quite stable and reliable.     

THE SUBURBANIZATION OF DECLINE: FILTERING,NEIGHBORHOODS, AND HOUSING MARKET DYNAMICS

This study explores how the locations and characteristics of neighborhoods affected the process of housing filtering in the Orlando metropolitan area during the 2000s. The results show that racial composition was an important determinant of filtering down and that the foreclosure rate and income composition of neighborhoods became more important factors during the housing market bust period. The filtering process tended to be more affected by neighborhood attributes than by changes in the housing market, especially during the housing market bust period. As the filtering down process was not sensitive to the neighborhood location itself, suburban areas were also susceptible to filtering down processes like inner city areas. Moreover, there was a high probability of suburban decline through filtering down during the housing market bust period. These results may be the reflection of recent trends of central city rebound and suburban decline in the Sun Belt.     

N-NITROSOPROLINE AND N-NITROSOSARCOSINE IN ESTONIAN FOODSTUFFS

The N-nitrosoamino acids (NNA) N-nitrosoproline (NPRO) and N-nitrososarcosine (NSAR) are precursors of the carcinogenic N-nitrosamines. Methodology using gas chromatography for their determination and data on their contents in 52 food products are presented. Food products consisted of smoked meats (12), smoked (9) and boiled (11) sausage, cheese (10), fish (7) and beer (3). Results showed that NNA formed during processing, particularly in meat, where levels of NPRO were as high as 353μg/kg. The compounds accumulated in the adipose tissue and surface portion of the product. Smoking caused increased formation of NPRO, while the use of liquid smoke minimized it. NPRO in meat products in natural casings was higher than in synthetic ones, and frying of boiled sausage and hams further enchanced NPRO formation. Like meat, smoked cheese and fish showed consistently higher NNA levels than the non-smoked products. These data indicate means of reducing NNA contents in foods by modification of processing techniques .     

Fourier analysis of multi-temporal AVHRR data applied to a land cover classification

A signal processing technique is presented and applied to annual patterns of the Global Vegetation Index (GVI) derived from the Advanced Very High Resolution Radiometer (AVHRR) to examine the frequency distribution of the multi-temporal signal. It is shown that frequencies of the signal are linked to integrated GVI, seasonal variability and subseasonal variability of the land cover type. These characteristics are used to derive a land cover classification.     

Transmission electron microscopy applied to the study of works of art: sample preparation methodology and possible techniques

Technical examination of a work of art is a necessary preliminary stage both for proper conservation/restoration of the work and for purposes of dating and/or authentication. There is a wide variety of methods and procedures, and of these a particularly valuable technique is stratigraphic analysis in view of the data that it furnishes on the composition of the pictorial layers of which a painting is composed. The techniques utilized in this type of analysis to date have been essentially light microscopy and scanning electron microscopy. Transmission electron microscopy can provide new data for characterization of pictorial layers, thanks to the possibility of individually using ultrathin sections of paint sample. This study provides morphological analysis and microanalysis by X-ray energy dispersion, with determination of the crystalline structure of each particle by electron diffraction. The sample preparation method for producing thin sections from the pictorial layers for examination in the TEM is described. This allows the stratigraphic section to be preserved exactly as applied by the artist. The first results from the examination of three microsamples from actual old works of art are presented. The individual components of each strata were successfully identified in all cases.