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The largest source of commercial natural rubber (NR) latex for industrial use comes from the Hevea brasiliensis trees. The major usage of NR latex is in glove manufacturing, particularly medical gloves and devices for diverse applications in the healthcare sector. An account on the colloidal properties of fresh field latex and the technical latex feedstock produced from it is described. The importance of the nonrubber constituents (proteins and lipids) associated with the rubber core in biosynthesis of the rubber molecules in rubber particles, and the nanostructure of the surface layer surrounding the core will be highlighted. The basic principle of latex thin film formation and its relevance to prerequisites for barrier material in infection control will be elaborated. The basic science behind latex compounding, the unique purpose of prevulcanization, and the many interfacial phenomena associated with the glove dipping process will be unraveled. Medical gloves are the first-line defense against healthcare-associated infections.

High-quality epitaxial Fe 3 Si films (1 0 0) were grown on the GaAs (1 0 0) surface using molecular beam epitaxy (MBE). High-resolution X-ray diffraction analysis using an X-ray energy of 12.38 keV from synchrotron radiation gave a narrow rocking curve of ∼0.014° for the Fe 3 Si (0 0 6) reflection, with a lattice mismatch between the film and GaAs of ∼0.25% in the normal direction. Square-shaped M–H loops with a typical moment of 660 emu/cm 3 at 10 K and the easy axis along [1 0 0] were obtained for films grown at a substrate temperature ( T s ) of 150 °C, and the M–H loops at low fields show fine features for films grown at a T s of 200–300 °C. A two-step growth procedure with the initial growth at 150 °C and subsequently ramping to 250 °C was applied to minimize the interfacial reactions, thus to achieve abrupt interfaces.

Aim: To identify novel microbial inhibitors of protein phosphatase 1 (PP1). Methods and Results: 750 actinomycetes and 408 microfungi were isolated from Sabah forest soils and screened for production of potential PP1 inhibitors using an in vivo screening system, in which candidate inhibitors were identified through mimicking the properties of PP1-deficient yeast cells. Acetone extracts of two fungi, H9318 (Penicillium) and H9978 (non-Penicillium) identified in this way showed inhibitory activity towards both mammalian PP1 and PP2A in an in vitro phosphatase assay, while extract from H7520 (Streptomyces) inhibited PP2A but not PP1. Consistently, using a drug-induced haploinsufficiency test, strains with either reduced PP1 or PP2A function were hypersensitive to H9318 and H9978 extracts whereas only the latter strain showed hypersensitivity to H7250 extract. H9318 extract was fractionated using RP-HPLC into two active peaks (S1 and S2). A yeast strain with reduced PP1 function showed hypersensitivity to fraction S2 whereas a strain with reduced PP2A function was hypersensitive to fraction S1. However, S1 and S2 inhibited both PP1 and PP2A activities to a similar extent. Conclusion: Three candidate PP inhibitors have been identified. Significance and Impact of the Study : Further development may generate useful research tools and ultimately therapeutic agents.

Surface modification of natural rubber (NR) latex films by argon plasma treatment, as well as by UV-induced graft copolymerization of the plasma-pretreated films with either acrylamide (AAm) or 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFA), have been carried out to impart new surface properties, such as hydrophilicity or hydrophobicity, on NR latex films. X-ray photoelectron spectroscopy was used to investigate the chemical composition of the modified film surfaces. The peroxide functionalities resulting from surface reaction with air after the Ar plasma treatment greatly facilitated the subsequent UV-induced graft copolymerization. In general, higher monomer concentration, longer UV graft copolymerization time, and longer plasma pretreatment time led to higher graft yield. Contact angle measurements revealed that the hydrophilicity of the NR film surface was considerably enhanced by the plasma treatment and the subsequent graft copolymerization with AAm. On the other hand, water contact angle as large as 109° was achieved for rubber surface graft-copolymerized with HFA. Atomic force microscopic images indicated that surface modification by graft copolymerization had also resulted in a substantial reduction in the surface roughness of the NR latex films.

The proposed scheme relates to a technique called "local nonlinear feedback loop (LNFL)" for stabilization of oversampling sigma-delta modulators (SDMs). SDM stabilized by the LNFL technique avoids the instability limitation without overall signal-to-noise ratio (SNR) degradation, because the LNFL technique keeps the input dynamic range within proper bounds (-/spl Delta//2, /spl Delta//2) absolutely to prevent integrators from overload, whether the critical integrator in SDM enters the unstable region or not. Unlike conventional methods, the nonlinear compensative operation in the proposed technique does not increase the quantization noise proportionally to cause the overall SNR degradation in the meanwhile. Besides, the proposed algorithm can be applied to various configurations of oversampling SDMs, such as single-loop and multiple-loop structures, for high stability and low-power very large scale integration applications.

Natural rubber (NR) latex film chlorinated by chlorine gas generated in situ from acidified hypochlorite solution at room temperature was characterised by FTIR-ATR, SEM-EDX and contact angle techniques. Chlorinated and oxygenated structures were found on the film surface after chlorination. The level of surface chlorination increased with chlorination durat-ion and chlorine dosage. The hydrophilicity of the surface improved after chlorination. However, cracking of the surface was noted and the surface mean roughness, Ra of the chlorinated surface increased with extent of chlorination. The thickness of the chlorinated layer on the NR latex film was found to be less than 10 μm. Severe cracking of the film surface at high chlorine dosage and extended reaction time was evident. Surface roughening and hardening both would result in a reduction in the adhesive friction of the chlorinated surface against a substrate. Chlorination accelerated the oxidative chain scission of the rubber molecules, especially at elevated temperature, with the attendant introduction of conjugated C=C double bonds into and increase in number and concentration of oxygenated structures of the rubber molecules. Discoloration and poor heat resistance proper-ties of chlorinated NR latex film are perhaps the results of these effects.

The effect of metal cations, both nonhydrolyzable and hydrolyzable, on the zeta potential of palm olein emulsions stabilized by the nonionic emulsifier, polyoxyethylene nonyl phenyl ether, was investigated as a function of pH and cation concentrations, respectively. The oil drops were found to be negatively charged in the presence of simple mono- and divalent cations. Charge reversal of the oil drops was observed when hydrolyzable cations (Zn2+, Cu2+, Fe3+, and Al3+) were used and the behavior is strongly dependent on the type of cation, its concentration, and the pH of the dispersion. The results are discussed in terms of current theories of electrophoresis and adsorption-precipitation at interfaces. The chemical free energies of adsorption of the cations were calculated. Copyright 1999 Academic Press.

Tin tailings slurries from two ex-mining ponds were coagulated by mono-, di- and trivalent metallic cations. The optimum concentration for coagulation and the aggregate size of these slurries were monitored for each cation. Both the constituent clay mineral and the pore fluid compositions of the slurry have a strong influence on its coagulation behaviour. The interaction of these with various ionic species, formed by ion exchange processes of the clay minerals and the hydrolysis reaction of the metallic cations in solution, enhanced this behaviour further. This observation was supported by electrophoretic mobility data of the clay slurry in the presence of these cations measured as a function of dispersion pH and cation concentration.

Methods have been developed recently for the preparation of monodisperse ellipsoidal polystyrene particles which also allow the axial ratio to be varied. Electrophoretic examination of these particles raised the possibility of a non-uniform surface charge distribution. Heterocoagulation of small spherical cationic particles onto the surface of the anionic ellipsoidal particles has been used to explore this possibility.

Interpretation of 16S rRNA sequences is a difficult problem faced by clinical microbiologists and technicians. In this study, we evaluated the updated 16SpathDB 2.0 database, using 689 16S rRNA sequences from 689 complete genomes of medically important bacteria. Among these 689 16S rRNA sequences, none was wrongly identified, with 35.8% reported as a single bacterial species having >98% identity with the query sequence (category 1), 63.9% reported as more than 1 bacterial species having >98% identity with the query sequence (category 2), 0.3% reported to the genus level (category 3), and none reported as no match (category 4). For the 16S rRNA sequences of non-duplicated bacterial species reported as category 1 or 2, the percentage of bacterial species reported as category 1 was significantly higher for anaerobic Gram-positive/Gram-negative bacteria than aerobic/facultative anaerobic Gram-positive/Gram-negative bacteria. 16SpathDB 2.0 is a user-friendly and accurate database for 16S rRNA sequence interpretation in clinical laboratories.

Palm oil-in-water emulsions prepared using various ethoxylated nonionic emulsifiers were studied with respect to the effect of concentration and type of the selected emulsifiers, and the emulsification process itself on the properties of the emulsions obtained. The stability of the emulsion during storage was monitored. The physical properties were characterized by particle size analysis, turbidity, interfacial tension, and electrophoretic mobility measurements. Results show that emulsion stability was strongly dependent upon the types of palm oil and emulsifier used and their concentrations. Stable emulsions with minimal creaming at room temperature for up to 6 months can be prepared with the right choice of emulsifier and under the correct conditions of emulsification. The influence of the interfacial layer of emulsifier on emulsion stability is discussed.

Fresh natural rubber latex particles are stabilized by adsorbed proteins and phospholipids while those for high-ammonia latex concentrate are stabilized mainly by adsorbed long-chain fatty acid soaps, the hydrolysis products of phospholipids. The structure of this surface layer surrounding the latex particles is analyzed using the electrophoresis model of Ohshima and Kondo. Good agreement between theoretical and observed electrophoretic mobility was found, except at very low ionic strength. The results were consistent with a model of an uncharged bared polyisoprene latex particle coated by a charged mixed layer of long-chain fatty acid soaps, proteins, and polypeptides of finite thickness in matured latex concentrate. This surface layer is ion-penetrable and its resistance to liquid flow changes with time on prolonged hydrolysis.

The profound influence of the hydrolytic behaviour of ions of heavy metals such as Cu, Zn, Pb, Cd, Mn and Ni on the electrophoretic mobility of colloidal clay taken from slurries from ponds from former tin mines was studied. The strong adsorption of soluble hydrolysed species and insoluble metallic hydroxide on the clay surface leads to a reduction in the surface charge of the clay particles and eventually to charge reversal. The results show that the shape of the mobility-pH curves was completely different from those for simple cations. Generally, at concentrations greater than 10−4 mol dm−3 and pH>6, the metal ions hydrolyse extensively to form positively charged mononuclear and polynuclear species which could become adsorbed and reverse the charge of the clay particles. At higher pH, a second reversal, back to negatively charged surface, occurred owing to the formation of insoluble metal hydroxide. At very low concentration of metal ions, two constant (negative) mobility regions were observed: one under acidic pH and the other under alkaline pH. The hydrolysis was influenced by the presence of particulates in the systems.

A scarlet fever outbreak occurred in Hong Kong in 2011. The majority of cases resulted in the isolation of Streptococcus pyogenes emm12 with multiple antibiotic resistances. Phylogenetic analysis of 22 emm12 scarlet fever outbreak isolates, 7 temporally and geographically matched emm12 non–scarlet fever isolates, and 18 emm12 strains isolated during 2005–2010 indicated the outbreak was multiclonal. Genome sequencing of 2 nonclonal scarlet fever isolates (HKU16 and HKU30), coupled with diagnostic polymerase chain reaction assays, identified 2 mobile genetic elements distributed across the major lineages: a 64.9-kb integrative and conjugative element encoding tetracycline and macrolide resistance and a 46.4-kb prophage encoding superantigens SSA and SpeC and the DNase Spd1. Phenotypic comparison of HKU16 and HKU30 with the S. pyogenes M1T1 strain 5448 revealed that HKU16 displays increased adherence to HEp-2 human epithelial cells, whereas HKU16, HKU30, and 5448 exhibit equivalent resistance to neutrophils and virulence in a humanized plasminogen murine model. However, in contrast to M1T1, the virulence of HKU16 and HKU30 was not associated with covRS mutation. The multiclonal nature of the emm12 scarlet fever isolates suggests that factors such as mobile genetic elements, environmental factors, and host immune status may have contributed to the 2011 scarlet fever outbreak.

The particulates of tin tailings slurries sampled from three ex-mining ponds (MN, PN and SH) were mainly clay minerals with some silt and sand particles. The general physical properties of these particulates such as particle size distribution, solids contents and surface area were determined as a function of slime depth and grid position within the ponds. An explanation of the trend observed in terms of the geological origin and formation of the slimes through natural weathering process was attempted. In addition, the particulate nature of the clay minerals was characterized with respect to particle morphology using electron microscopy and clay mineralogy by X-ray diffraction. Analysis on the amorphous and organic contents of the slimes was also included. SH slime with a high amorphous content was acidic in nature whereas PN slime containing about 8% montmorillonite was the most stable colloidally. The stability of these slime dispersions was explained in the light of current theory on lyophobic colloidal dispersions in relation to the clay mineral and chemical compositions of the slime samples. In view of the highly variable particle size and morphology, and considerable variations in exact compositional characteristics of the clay slurries from pond to pond, it is clear that such physicochemical characterization of the slurries is essential in understanding the dewatering behaviour of the slimes and thus important in the subsequent design of an efficient reclamation method most suitable for the pond in question. Because the settling behaviour of the slurry is controlled by colloidal clay, the importance of clay mineralogy in mining waste characterization cannot be overemphasized.

Background: Laribacter hongkongensis is associated with community-acquired gastroenteritis and traveler's diarrhea and it can reside in human, fish, frogs and water. In this study, we performed an in-depth annotation of the genes in its genome related to adaptation to the various environmental niches.Results: L. hongkongensis possessed genes for DNA repair and recombination, basal transcription, alternative σ-factors and 109 putative transcription factors, allowing DNA repair and global changes in gene expression in response to different environmental stresses. For acid stress, it possessed a urease gene cassette and two arc gene clusters. For alkaline stress, it possessed six CDSs for transporters of the monovalent cation/proton antiporter-2 and NhaC Na +:H + antiporter families. For heavy metals acquisition and tolerance, it possessed CDSs for iron and nickel transport and efflux pumps for other metals. For temperature stress, it possessed genes related to chaperones and chaperonins, heat shock proteins and cold shock proteins. For osmotic stress, 25 CDSs were observed, mostly related to regulators for potassium ion, proline and glutamate transport. For oxidative and UV light stress, genes for oxidant-resistant dehydratase, superoxide scavenging, hydrogen peroxide scavenging, exclusion and export of redox-cycling antibiotics, redox balancing, DNA repair, reduction of disulfide bonds, limitation of iron availability and reduction of iron-sulfur clusters are present. For starvation, it possessed phosphorus and, despite being asaccharolytic, carbon starvation-related CDSs.Conclusions: The L. hongkongensis genome possessed a high variety of genes for adaptation to acid, alkaline, temperature, osmotic, oxidative, UV light and starvation stresses and acquisition of and tolerance to heavy metals. © 2011 Lau et al; licensee BioMed Central Ltd., published_or_final_version

Tin tailing slimes from three ex-mining ponds located in different parts of Malaysia and with different clay compositions were studied. Pengkalan slime contained about 8% of montmorillonite clay; Serendah (SH) slime had a high content of amorphous materials (24%) while the main constituents of all samples were kaolinite and illite with a small amount of organic materials and microorganisms as exemplified by Malim Nawar slime. The surface nature of the clay minerals in these slimes was characterised using the particle microelectrophoresis technique. The electrokinetic behaviour of the slime basically followed that of kaolinite but differences due to compositional variations were evident. This is especially so for the SH slime where the amorphous materials present completely modified the surface property of the kaolinite. The magnitude of the electrophoretic mobility depended strongly upon the exchangeable cations associated with the clay particles and pore fluid chemistry of the slime samples. The evaluation of the isoelectric point of the edges of clay particles by the electrokinetic method is discussed. The importance of understanding the charged surfaces of the clay minerals in the slimes in relation to the design of an efficient dewatering programme is briefly discussed.

Based on conventional active queue management (AQM), random early detection (RED) and modified random early detection (MRED) algorithms, progressive random early detection (PRED) algorithm improved by the progressive adjustment method is proposed. It regulates the packet dropping probability progressively by comparing the instantaneous queue size with the progressive maximum queue threshold parameters. Experimental results show PRED's flexibility makes itself achieve higher transmission throughput and lower end-to-end average delay for various network topologies.

H.264/AVC is the latest block-based video coding standard from MPEG and VCEG. It not only provides efficient video coding at various bit rates, but also uses some new error resilience tools. Flexible macroblock ordering (FMO) is one of the new error resilience tools involved in H.264/AVC. Here, we present a novel algorithm, wavelet-based flexible macroblock ordering (WFMO), to adaptively allocate macro blocks into four slice groups based on Discrete Wavelet Transform (DWT), and then adopt unequal error protection to enhance the robustness of the packet carrying the slice group of importance and psychovisual sensitivity Simulations show the proposed WFMO can partition the psychovisiually sensitive slice groups efficiently and keep better subjective video quality under poor network condition.

Linear prediction coding (LPC) technique for speech processing is the key part of speech codec. In this paper, forward volume normalizer (FVN) is proposed to keep the stationary characteristic of the speech signal fed to the encoder and to enhance the accuracy of LPC analysis under nonstationary speech condition. According to the measurement of ITU-T P.862 Perceptual Evaluation of Speech Quality (PESQ) equipment, the experimental results show the degradation of the subjective speech quality from nonstationary speech signal can be somewhat removed by the proposed Forward Volume Normalizer at the pre-stage of speech codec.

Based on the former "Local Nonlinear Feedback Loop (LNFL)" technique for stabilization of oversampling Sigma-Delta Modulator (SDM), an improved technique called "Sub-bit Nonlinear Feedback Loop (SNFL)" is proposed to further raise the stability. The SNFL technique not only avoids the instability limitation of high-order SDM without SNR degradation like the former LNFL technique, but also suppresses the output swing range of the critical integrator more effectively than the former LNFL technique. This is because the stabilization scheme of the SNFL technique can achieve to restrict the key signal within sub-bit swing range (- \Delta /4, \Delta/4) or less, while the LNFL technique only can restrict the key signal within integer-bit swing range (- \Delta /2, \Delta/2). The simulation verifies that both stability and dynamic range of SDM is improved by the proposed SNFL technique more than by the former LNFL technique.

The key performance index related to RF circuit design for a portfolio of varactor structures, N+/Nwell MOS varactor (N+/NW MOSVAR). P+/Pwell MOSVAR (P+/PW MOSVAR) and junction varactor (JVAC) were studied using advanced 0.18/spl mu/m to 90nm RF-CMOS technologies. The engineering and trade-offs for quality factor (Q-factor), tuning ratio (TR = C/sub max/ / C/sub min/), capacitance mismatch and flicker noise for different device structure, geometry size, operation and process conditions were compared to provide a comprehensive guideline for selecting varactor structures and dimensions during advanced RFIC design.

For characterizing the frequency and power response of the SiGe HBT devices, the HBT devices with different base and collector contact configuration structure have been fabricated by using the 0.18 /spl mu/m high-speed SiGe BiCMOS technologies. In this work, we investigated three different types of layout with the same emitter area A/sub E/=0.3/spl times/10.16 /spl mu/m/sup 2/, including single base and single collector contact, double base and single collector contacts, and double base and double collector contacts. Regarding the maximum output power and cutoff frequency (f/sub T/), the double bases and double collectors structure is the optimized layout, which provides a 6.4 dBm maximum output power and a PAE of 40 % at 2.4 GHz. It also leads to achieve a higher cutoff frequency due to the reduction of contact resistances.

The platform-based implementation of the IP phone featuring a low-power System-On-Chip (SOC) processor is described in the paper. And, the feasibility of the low-power SOC processor is also evaluated. The prototype of our developed IP phone has been successfully completed and tested for several months. The testing results obviously show that the IP phone embedding a low-power SOC processor still operates well even with less power consumption. Therefore, it verifies the low-power SOC processor is eligible to be applied to high-performance and cost-efficient IP phone implementation.

Based on the MASH (multistage noise shaping) architecture, an improved architecture-uni-MASH which employs the time-division concept for architecture and circuit reuse is proposed. Uni-MASH retains robust stability and high-ordered noise shaping factor of MASH's virtues. Besides, the following additional advantages of uni-MASH are verified by computer simulation: (1) Uni-MASH has smaller chip area than MASH. (2) Uni-MASH reduces the gain mismatch effects between each SDM stage.

A modified transcutaneous electric nerve stimulator (TENS) stimulation waveform was implemented in an experimental prototype unit. The new stimulation waveform was developed to increase electrical power transfer to human tissue. This waveform differs from those generated in traditional TENS in both shape and spectral content. A pilot study of skin impedance using TENS electrodes was performed. The gain and phase of skin impedance were measured, and the results were consistent with a first order system across the entire subject population. Individual skin impedance profiles did not vary significantly with respect to skin preparation, texture, or moisture. Bode plots were made of data from inter-electrode measurements on subjects with both prepared and unprepared skin. Results revealed that electrode-to-electrode surface resistance can be modeled as a first order low pass filter. The new stimulation waveform was developed to provide more energy within the resistive portion of the skin impedance profile. This spectral shaping increases real power transfer to the skin by spectrally matching the waveform to the resistive frequency range of the skin. The distributed spectral energies for the new prototype waveform and a traditional TENS device stimulation waveform were multiplied by the skin impedance to provide a theoretical measurement of effective power transfer. This effective power transfer ratio was calculated for the two waveforms. The prototype waveform showed a 80% theoretical effective power transfer increase over the traditional waveform. An assessment of TENS function was done in a pilot test with chronic TENS users. The results showed that a spectrally matched waveform is more electrically efficient, allows more stimulation amplitude without causing irritation, is more comfortable in the long term, causes minimal nerve stimulation, and does not induce erratic skeletal muscle quiver.

The proposed scheme relates to techniques called "local nonlinear feedback loop (LNFL)" and "enhanced-LNFL" for stabilization of oversampling sigma-delta modulators. SDM stabilized by LNFL or enhanced-LNFL techniques avoids the instability limitation without SNR degradation. Besides, both proposed approaches to suppress the signal's swing range can be applied to various configurations of SDMs, such as multiple-loop and single-loop structures, for high stability and low power VLSI applications.

A microprocessor based TENS device is developed which utilizes a spatial procedure in the administration of electrical fields to actively interfere with pain signals reaching the brain. This unusual design also has the advantage of requiring the frequency characteristics of the electrical waveform produced to be optimally tuned to the mechanical impedance properties of the skin/tissue. Hence a much more efficient procedure for the transfer of electrical energy from the TENS device to the human tissue is provided. Data are presented involving patients from the Dayton VA Medical Center in Ohio, USA being tested with this new microprocessor system compared to the treatment obtained via a traditional stimulator.

In rats anesthetized with urethane, intraperitoneal administration of a water-soluble organogermanium compound 2-carboxyethyl germanium sesquioxide (Ge-132) produced a dose-related reduction in either the mean arterial pressure or the heart rate. Both hypotension and bradycardia responses induced by Ge-132 injection were significantly inhibited by pretreatment of the animals with either spinal transection or bilateral vagotomy. The data indicate that Ge-132 induces both hypotension and bradycardia by promoting an activation of the parasympathetic efferent mechanisms and an inhibition of the sympathetic efferent mechanisms. On the other hand, following intraperitoneal injection of Ge-132, increased grooming and head swaying (as shown by an enhancement in fine movements monitored by an electronic activity counter) were provoked. Furthermore, the amphet-amine-induced enhancement in fine movements was potentiated by pretreatment of the animals with Ge-132. Thus, it appears that Ge-132 acts through the catecholaminergic mechanisms in the brain to induce locomotor stimulation in rats.

Seventy-one Neurospora cultures were isolated from Oncom tahu based on soybean residues in the Jakarta-Bogor and from Oncom based on peanut presscake in the Lembang-Bandung regions of West Java. They were heterothallic and had 8-ascospore per ascus. In crosses with authentic reference cultures of three known heterothallic species, Neurospora intermedia, N. crassa and N. sitophila, only crosses with N. intemedia produced abundant viable black ascospores and few inviable white ones. This meiotic sterility test of hybrids identified the Oncom cultures as N. intermedia Tai and not N. sitophilia as previously assumed. However, all the Oncom isolates except one (H2118) differed from wild N. intermedia collected from remains of burnt vegetation. The Oncom cultures with the proposed varietal status as N. intermedia var. oncomensis had bright yellow and large macroconidia in contrast to wild N. intermedia and H2118 with pink and small macroconidia. Some of the Oncom cultures showed degeneration towards poor mycelial growth and loss of conidiation on repeated vegetative subculturing.

Relations entre les proprietes rheologiques d'une part, ou les proprietes mecaniques dynamiques d'autre part et la distribution des masses moleculaires

When very low-level activities are measured in the presence of high background, the required counting times are very long. Non-statistical background fluctuations over these long counting times increase the uncertainties in the net counts. In addition, it becomes difficult to estimate these uncertainties. Subdividing the long counting times into several short intervals, with alternating measurements of background counts and gross counts, is expected to improve the situation. In this paper, the concept of lower limit of detection is reviewed and the nature of difficulty introduced by the non-statistical background fluctuations is discussed. The improvement expected from subdividing the counting times into short intervals is tested by doing an experimental study with a shielded 3″ × 3″ NaI(Tl) detector.

This paper deals with measurements of atmospheric concentrations of short-lived radon and thoron daughters from the activity collected on a filter through which air is sampled, giving rise to a mixture of α, β and γ-ray activities. Generalized equations suitable for a weighted regression analysis are presented. A theoretical framework is developed and methods of calibrating the system are proposed. Equality of the half lives of RaA and ThC″ needs special attention.

A simple and convenient method of transport of serum in the form of protein disc on water resistant medium is described. The method was used to study the stability of thyroxine (T4), cortisol, thyroid stimulating hormone (TSH), parathormone (PTH) and insulin. The mean recoveries of these hormones were between 98 and 100%. The standard deviations of duplicates of assays for protein disc samples were comparable to that of serum samples except in assays using enzyme immunoassay techniques. The correlation coefficients of the results between the serum and protein disc samples were satisfactory ranging from 0.86–0.99. The proposed method could be used for interlaboratory referral of serum.

The effect of serum. methanol/water, and detergents on the dissociation of the antigens thyroxin (T4) and triiodothyronine (T3) from immobilized antibody was investigated by an antigen binding technique and scanning electron microscopy. The antibody coatings immobilized on the different polymeric substrates showed varying degrees of denaturation and desorption due to detergents but were unaffected by a 60 40 (by volume) mixture of methanol/water after various washington procedures. The factors influencing the dissociation and its relevance to recycling immunoassay are discussed. It was found that nonspecific binding of serum proteins to the antibody coatings wa a major caused of deterioration in antibody binding capacity.

Separation of palm oil mill effluent into various particulate fractions from the soluble constituents was achieved by high-speed centrifugation. The particulates were found to account for only 1.7–2.6% (w/w) of the effluent. These particulates were shown to be the colloidal rod-like particles of macrofibrils, raphide particles and plant cell debris, the last being the major component. Together they contributed slightly less than 50% to the pollutant level of the effluent. Anaerobic digestion of the palm oil mill effluent resulted in a 96% reduction in BOD and 87% reduction in suspended solids. The plant cell debris was completely removed whereas the raphide particles seemed intact after the anaerobic treatment. The anaerobic process also caused a decrease in particle size and number of the colloidal macrofibrils.

The effectiveness of chemical flocculation and dissolved air flotation process as applied to the secondary treatment of the anaerobically digested liquor of palm oil mill effluent (POME) was investigated and compared. Results indicated that the dissolved air flotation method was more efficient than chemical flocculation in an all round removal of pollutants from the digested liquor. Even though both methods were able to achieve a 97% removal of the suspended solids of the digested liquor, the removal of soluble matter of inorganic and organic origins was far from satisfactory. This is in general agreement with the recognised view of the superior efficiency of biological methods over physico-chemical methods in treating soluble substances. An explanation of the observed behaviour of the digested liquor in the presence of aluminium salt and polymeric flocculant in terms of the solution chemistry of polyelectrolyte and hydrolysable metallic cations was attempted.

The fractionation of palm oil mill effluent (POME) into free oil drops, and soluble and particulate fractions delineated the distribution of chemical constituents among the fractions. About 30% of the total solvent-extractable oil in POME existed as free oil droplets; the rest was almost completelt associated with the particulate fraction. The acid-insoluble lignin to α-cellulose ratio of the particulate fraction was relatively high. The soluble fraction was found to contain all the dissolved minerals and soluble carbohydrates. The level of proteins in the soluble fraction was, however, low. The major portion of the nitrogen (and hence the proteins) of POME appeared to be associated with the particulates. A discussion, in the light of the present results, on some problems likely to be encountered in the utilisation or treatment of POME, was attempted. Additional data on the chemical constituents of the sludge from the clarification station were also included for discussion.

Variation of solid-phase antibody concentration could give rise to poor intra- and interassay precision. A new method to detect this variation is reported. Pooled sera with thyroxine (T4) values at the low, medium, and high ranges were assayed in duplicate using anti-T4-coated polystyrene beads. The antigen-antibody complexes were dissociated with methanol-water mixture and the antibodies re-used for subsequent T4 assays in which the same beads were used with the same set of standards and pooled sera. A second set of assays using randomised beads after each assay-wash cycle were also carried out. The variations in weights and surface structures of the beads were also studied. The variation of T4 results of group methods using polyethylene glycol in an external quality control program was also compared with that of covalently linked solid-phase particulate antibody methods over 2 periods. The experimental results showed that there was bead-to-bead variation of antibody concentration which could give rise to poor precision. Rigorous control of the immobilised antibody concentration could further improve the assay performance.