50—SOME EXPERIMENTS ON THE FRICTION OF COTTON FIBRES

Some experiments on various aspects of the friction of cotton fibres are discussed in the light of their relevance to the processing of cotton. The topics covered include the friction of raw cotton, friction in fibre blends, fibre friction during twisiting, and friction in chemically treated fibres.     

Performance Comparison of Likelihood, Hard-Limited, and Linear Combining Receivers for FH-MFSK Mobile Radio--Base-to-Mobile Transmission

The performances of three receivers, namely, the hardlimited, the linear, and the maximum-likelihood combiners for the detection of frequency-hopped multilevel frequency-shift keyed signals transmitted from mobiles to base have been reported earlier [11]. Only the hard-limited combiner has been analyzed with respect to base-to-mobile link [1]. Here, we give new results on the performance of the likelihood and the linear combining receivers operating at the mobiles. Whereas it is possible to find exactly the union bound on the probability of bit error for a linear combiner, for a likelihood receiver, bounding and approximation techniques such as simple Chernoff bound and saddle point integration were employed. We also observe the asymptotic (SNR rightarrow infty) equivalence of the hard-limited and the likelihood receivers. This, together with the approximate error estimates at finite SNR, leads us to believe that the likelihood receiver is only marginally superior to a hard-limited combiner. As expected, the linear combiner performs poorly.     

Reaction mechanisms for the limited reversibility of Li-O2 chemistry in organic carbonate electrolytes

The Li-O₂ chemistry in nonaqueous liquid carbonate electrolytes and the underlying reason for its limited reversibility was systematically investigated. X-ray diffraction data showed that regardless of discharge depth lithium alkylcarbonates (lithium propylenedicarbonate (LPDC), or lithium ethylenedicarbonate (LEDC), with other related derivatives) and lithium carbonate (Li₂CO₃) are constantly the main discharge products, while lithium peroxide (Li₂O₂) or lithium oxide (Li₂O) is hardly detected. These lithium alkylcarbonates are generated from the reductive decomposition of the corresponding carbonate solvents initiated by the attack of superoxide radical anions. More significantly, in situ gas chromatography/mass spectroscopy analysis revealed that Li₂CO₃ and Li₂O cannot be oxidized even when charged to 4.6 V vs. Li/Li⁺, while LPDC, LEDC and Li₂O₂ are readily oxidized, with CO₂ and CO released from LPDC and LEDC and O₂ evolved from Li₂O₂. Therefore, the apparent reversibility of Li-O₂ chemistry in an organic carbonate-based electrolyte is actually an unsustainable process that consists of (1) the formation of lithium alkylcarbonates through the reductive decomposition of carbonate solvents during discharging and (2) the subsequent oxidation of these same alkylcarbonates during charging. Therefore, a stable electrolyte that does not lead to an irreversible by-product formation during discharging and charging is necessary for truly rechargeable Li-O₂ batteries.     

Performance-Enhanced Bolometric Terahertz Detectors Based on V<Subscript>2</Subscript>O<Subscript>5</Subscript> for 15 to 30 THz

Terahertz (THz) radiation perception using uncooled detectors are gaining importance due to the increasing demands in the areas of military, space, and industrial, medical, and surveillance applications. In spite of the efforts of researchers to fill the THz gap, there exists a need for detectors in the range between 15 THz and 30 THz. In this paper, we discuss the development of bolometric detectors whose performance is enhanced by an optical immersion technique and their characterization in the aforesaid range of frequencies. These detectors are characterized by high specific detectivity (D*) of 1.28?×?10⁹ cmHz^1/2 W^?1 and high radiometric resolution (noise-equivalent temperature difference?=?26 mK) and are fast enough for bolometric detectors (time constant?=?1.7 ms), which make them suitable for spectroscopic and imaging applications.     

Synthesis of phenetidine-based telechelics and subsequent reactions with water-based curing reagents

The development of soluble telechelics based on aniline are highly desirable due to numerous applications that are possible, especially in the coatings and adhesive industry. Control of molecular length and ease of synthesis lends o-ethoxyaniline to be an ideal candidate for the synthesis of amino-terminated telechelic oligomers. Combined with the higher solubility and reactivity, curing of these functionally reactive oligomers has been accomplished using aqueous formaldehyde, as well as water-dispersed epoxy resins. Spectroscopic studies have been done to characterize the prepolymers, as well as the cured materials. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1811–1817, 1998     

Inhibitors of the salicylate synthase (MbtI) from Mycobacterium tuberculosis discovered by high-throughput screening

A simple steady‐state kinetic high‐throughput assay was developed for the salicylate synthase MbtI from Mycobacterium tuberculosis, which catalyzes the first committed step of mycobactin biosynthesis. The mycobactins are small‐molecule iron chelators produced by M. tuberculosis, and their biosynthesis has been identified as a promising target for the development of new antitubercular agents. The assay was miniaturized to a 384‐well plate format and high‐throughput screening was performed at the National Screening Laboratory for the Regional Centers of Excellence in Biodefense and Emerging Infectious Diseases (NSRB). Three classes of compounds were identified comprising the benzisothiazolones (class I), diarylsulfones (class II), and benzimidazole‐2‐thiones (class III). Each of these compound series was further pursued to investigate their biochemical mechanism and structure–activity relationships. Benzimidazole‐2‐thione 4 emerged as the most promising inhibitor owing to its potent reversible inhibition.     

Using solidification parameters to predict porosity distributions in alloy castings

Quality criteria used in the computer-aided design and analysis of casting processes typically relate geometric, thermal, or solidification parameters to structural features such as centerline shrinkage and microporosity. Quality criteria for the prediction of porosity in castings have been used successfully in steel, but the application of criteria functions to nonferrous alloys has been less successful. Recent work suggests that the dominating mechanism that determines the amount and distribution of porosity in castings is strongly dependent on the solidification mode of the alloy and the solidification conditions. Accordingly, casting processes and alloy types are divided into four groups, and a different set of criteria functions are obtained for each group.     

Use of tanninsulfonic acid in the synthesis of water‐dispersible polyaniline

Polyaniline was synthesized in the presence of tanninsulfonic acid to yield a product tanninsulfonic acid‐doped polyaniline (TANI‐PANI) that is water‐dispersible. Several samples ranging from 0 to 70% tanninsulfonate (TS) were prepared. These samples were then evaluated for differences in dispersibility, particle size, and conductivity. As the percent of TS in the samples was increased, the water‐dispersibility of the TANI‐PANI also increased. The particle size of the samples as well as the conductivity of the samples decreased with increasing percentages of TS in the samples. After extensive washings, however, the conductivity remained fairly constant (～0.5 S/cm) regardless of the amount of TS in the samples. Additionally, elemental analysis, TGA, and IR data were used to demonstrate that the TS may be grafted to polyaniline during the synthesis of TANI‐PANI. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2113–2119, 2007     

Alkylation of naphthalene with alcohols over mesoporous MCM-41

Mesoporous MCM-41 is found to promote alkylation of naphthalene by alcohols. In addition to the preferred branched side chain productsn-alkylated product is also observed in the case of propylation of naphthalene.     

Thermal decomposition as route for silver nanoparticles

Single crystalline silver nanoparticles have been synthesized by thermal decomposition of silver oxalate in water and in ethylene glycol. Polyvinyl alcohol (PVA) was employed as a capping agent. The particles were spherical in shape with size below 10 nm. The chemical reduction of silver oxalate by PVA was also observed. Increase of the polymer concentration led to a decrease in the size of Ag particles. Ag nanoparticle was not formed in the absence of PVA. Antibacterial activity of the Ag colloid was studied by disc diffusion method.