Extraction of protactinium from acid media using Aliquat 336

Solvent extraction studies on protactinium were carried out from hydrofluoric acid, hydrochloric acid, and a mixture of hydrochloric and hydrofluoric acids using Aliquat 336 and ²³¹Pa. The extraction of protactinium from hydrofluoric acid (0.025–10 M) decreased with increasing acid concentration and was less than 10% above 5 M. The extraction from hydrochloric acid (0.5–8 M) started only above 4 M and increased with increasing acid concentration. The extraction of protactinium from a mixture containing hydrochloric acid (0.5–8 M) and 0.03 M hydrofluoric acid decreased with increasing acid concentration reached to a minimum at about 2 M and then increased with increasing acid concentration. At low acidity, extraction of protactinium from hydrofluoric acid was higher compared to hydrochloric acid and the mixture of hydrochloric and hydrofluoric acids. Nitric acid (10 M) and hydrofluoric acid (10 M) were suitable for quantitative recovery of protactinium from organic phase. The extraction of ²³¹Pa from real thorium lean raffinate of thorium–uranium extraction process was studied using optimized extraction conditions.     

Status,ecological services and management of aquatic weeds of floodplain wetlands in India: An overview

Floodplain wetlands of India are biologically rich and productive ecosystems that support unique aquatic flora and fauna. Covering an area of about 0.354 million ha, the floodplain wetlands are a major source of self‐recruiting small indigenous fish (SIF). They offer vast potential for both capture and culture‐based fisheries, securing livelihood and nutrition for a large section of the population. In addition to tremendous anthropogenic pressures and climatic variability, these resources have experienced a significant reduction in their geographical and areal extent. Aquatic macrophytes infestation in Indian floodplain wetlands is posing serious challenges to their ecological and economic functioning. Degradation and shrinkage of these important resources have been observed over the past few decades, attributable to the spread of aquatic weed infestation, warranting urgent attention in regard to their conservation and restoration to address their impending challenges. The present study compiled a total of 530 species under 103 families of aquatic macrophyte, representing four Indian states of the Ganga and Brahmaputra river basin. Among these 530 species, 85 species exhibit medicinal values and 30 species are edible, whereas some other species are used for basketry, cordage, fodder and as dye. Accordingly, the present study reviews the present status of the floodplain wetlands, their common aquatic weeds and their ecological services. It also synthesizes the latest knowledge and discusses the challenging issues of aquatic weed management and their control measures directed to the sustainable management of the aquatic resources.     

Low-Temperature Synthesis of 0.65 PbMg1/3Nb2/3O3–0.35PbTiO3 Ceramics

Nanocrystalline 0.65 PbMg_1/3Nb_2/3O₃–0.35PbTiO₃ powders were synthesized by citrate gel method. The gel was prepared using citrate (titanium and niobium) and nitrate (lead and magnesium) salts. The hard gel obtained after completion of the reaction was treated to get the desired phase. Thermal analysis of the gel was done to optimize the calcination temperature. The calcined powders were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The crystallite size and the effective strain were found to be 50 nm and 0.03584 N, respectively.     

Preparation and characterization of an enzyme electrode based on cholesterol esterase and cholesterol oxidase immobilized onto conducting polypyrrole films

Cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) enzymes were entrapped within polypyrrole (PPy) films on a platinum disc electrode during electrochemical polymerization. The characteristics of the PPy/ChEt/ChOx enzyme electrode thus prepared were investigated as a function of the time, pH, temperature, and concentration of cholesteryl palmitate by a spectrophotometric method. PPy/ChEt/ChOx electrodes can be used for the estimation of cholesteryl palmitate concentrations from 1 to 8 mM, can be used least 10 times, and have a shelf life of about 1 month at 4–10°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3769–3773, 2004     

On Fast and Accurate Detection of Unauthorized Wireless Access Points Using Clock Skews

We explore the use of clock skew of a wireless local area network access point (AP) as its fingerprint to detect unauthorized APs quickly and accurately. The main goal behind using clock skews is to overcome one of the major limitations of existing solutions—the inability to effectively detect Medium Access Control (MAC) address spoofing. We calculate the clock skew of an AP from the IEEE 802.11 Time Synchronization Function (TSF) time stamps sent out in the beacon/probe response frames. We use two different methods for this purpose—one based on linear programming and the other based on least-square fit. We supplement these methods with a heuristic for differentiating original packets from those sent by the fake APs. We collect TSF time stamp data from several APs in three different residential settings. Using our measurement data as well as data obtained from a large conference setting, we find that clock skews remain consistent over time for the same AP but vary significantly across APs. Furthermore, we improve the resolution of received time stamp of the frames and show that with this enhancement, our methodology can find clock skews very quickly, using 50-100 packets in most of the cases. We also discuss and quantify the impact of various external factors including temperature variation, virtualization, clock source selection, and NTP synchronization on clock skews. Our results indicate that the use of clock skews appears to be an efficient and robust method for detecting fake APs in wireless local area networks.     

Rheological behavior of gel‐filled raw natural rubber and styrene‐butadiene rubber with reference to gel‐matrix intermixing

Natural rubber (NR) and styrene‐butadiene rubber (SBR) latex gels were prepared by sulfur prevulcanization technique with varying amounts of curing agent and accelerator systems to generate gradient in crosslink density. These gels were characterized by solvent swelling, dynamic light scattering, atomic force microscopy, and mechanical properties. Crosslinked NR gels were intermixed with neat SBR matrix and vice versa. Rheological behavior of chemically crosslinked gel‐filled NR and SBR was studied by capillary rheometry. Intermixing of crosslinked gels in the rubber matrices resulted in a considerable reduction in apparent shear viscosity and die swell values. This behavior was found to be dependent on several factors like gel concentration in the matrix, crosslink density of the gels, their size, and distribution. The effect of temperature on viscosity was studied extensively following the Arrhenious‐Eyring model. A shear rate‐temperature superposition mastercurve was constructed to predict the melt viscosities of the systems as a function of temperature. The change in die swell values was related to the change in first normal stress difference. The scanning electron photomicrographs of the extrudates revealed that presence of gels markedly improved the surface roughness of the raw rubbers. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Authentication study of volatile flavour compounds composition in Slavonian traditional dry fermented salami “kulen”

Volatiles from famous Slavonian salami “kulen” were isolated by nitrogen purge and steam distillation (NPSD) and analysed, for the first time, by gas chromatography and mass spectrometry (GC and GC–MS). In all, 119 organic compounds were identified that originated from lipid oxidation, amino acid degradation, smoke treatment and added spices with different distribution among NPSD traps. NPSD method enabled comprehensive profiling with almost exclusive distribution of several major compounds in particular trap with little or no interference from abundant lipid constituents in the samples. The major identified flavour important compounds were methylphenols, methoxyphenols, organosulphur compounds (diallyl sulphide, diallyl disulphide, methylallyl disulphide, diallyl trisulphide and methional) and several derivatives of 2-cyclopenten-1-one such as ethyl cyclotene. Non-important flavour constituents such as high-molecular fatty acids, alcohols and aldehydes were also present among abundant compounds. General trends for possible discrimination of “kulen” volatiles profile among other European salami volatiles were noticed (lower amount of terpenes and higher percentages of diallyl sulphide, methoxyphenols, methylphenols and 2-cyclopenten-1-one derivatives).     

A boundary layer analysis for entrance region heat transfer in vertical microchannels within the slip flow regime

A boundary layer integral analysis has been executed to investigate the heat transfer characteristics of natural convection gas flows in symmetrically heated vertical microchannels, under the conditions of large channel aspect ratios, in the slip flow regime. It has been revealed that for low values of Rayleigh number, the entrance region length is only a small fraction of the total channel extent. For higher values of Rayleigh number, however, effects of the developing region are non-trivial, and two counteracting heat transfer mechanisms need to be aptly taken into consideration for interpreting the Nusselt number values. In the present study, the proportionate enhancement in the average Nusselt number with wall-slip effects has been observed to become more prominent for higher values of Knudsen number. However, the relative augmentation in the rate of heat transfer tends to get somewhat arrested for higher values of Rayleigh number, as attributable to the counteracting influences of augmented rates of advective transport and reduced wall-adjacent temperature gradients. For all cases, the boundary layer theory based predictions have been found to agree excellently with the corresponding results obtained from full-scale numerical predictions.     

Attainable regions of reactive distillation. Part II: Single reactant azeotropic systems

In reactive distillation (RD) one can conveniently manipulate the concentration profiles on the reactive stages by exploiting the difference in volatility of the various components. This property of RD can be advantageously used to improve the selectivity toward the desired product in case of series or series parallel reactions, and obtain a performance superior to the network of conventional reactors. In the previous work [Agarwal, V., et al., 2008. Attainable regions of reactive distillation—Part I. Single reactant non-azeotropic systems. Chemical Engineering Science, submitted for publication], we introduced representative unit models of RD to obtain the attainable regions of RD for non-azeotropic systems. In this work, we extend the approach to a system involving single binary azeotrope. Design guidelines have been formulated based on the residue curve maps, to obtain the improved attainable region with the help of these representative RD models either alone or in the form of their network.