Ising model on self-avoiding walk chains

The phase transitions of nearest-neighbour interacting Ising models on self-avoiding walk (SAW) chains on square and triangular lattices have been studied using Monte Carlo technique. To estimate the transition temperature (T _c) bounds, the average number of nearest-neighbours (Z _eff) of spins on SAWs have been determined using the computer simulation results, and the percolation thresholds (p _c) for site dilution on SAWs have been determined using Monte Carlo methods. We find, for SAWs on square and triangular lattices respectively,Z _eff=2.330 and 3.005 (which compare very well with our previous theoretically estimated values) andp _c=0.022±0.003 and 0.045±0.005. When put in Bethe-Peierls approximations, the above values ofZ _eff givekT _c/J<1.06 and 1.65 for Ising models on SAWs on square and triangular lattices respectively, while, using the semi-empirical relation connecting the Ising modelT _c's andp _c's for the same lattices, we findkT _c/J0.57 and 0.78 for the respective models. Using the computer simulation results for the shortest connecting path lengths in SAWs on both kinds of lattices, and integrating the spin correlations on them, we find the susceptibility exponent =1.024±0.007, for the model on SAWs on two dimensional lattices.     

Immobilization of cellulase using polyurethane foam

Cellulase was covalently immobilized using a hydrophilic polyurethane foam (Hypol®FHP 2002). Compared to the free enzyme, immobilized cellulase showed a dramatic decrease (7.5-fold) in the Michaelis constant for carboxymethylcellulose. The immobilized enzyme also had a broader and more basic pH optimum (pH 5.5–6.0), a greater stability under heat-denaturing or liquid nitrogen-freezing conditions, and was relatively more efficient in utilizing insoluble cellulose substrates. High molecular weight compounds (Blue Dextran) could move throughout the foam matrix, indicating permeability to insoluble celluloses; activity could be further improved 2.4-fold after powdering, foams under liquid nitrogen. The improved kinetic and stability features of the immobilized cellulase combined with advantageous properties of the polyurethane foam (resistance to enzymatic degradation, plasticity of shape and size) suggest that this mechanism of cellulase immobilization has high potential for application in the industrial degradation of celluloses.     

Complexation of Ni, Cu, Zn, and Cd by DOC in some metal-impacted freshwater lakes: a comparison of approaches using electrochemical determination of free-metal-ion and labile complexes and a computer speciation model, WHAM V and VI

Complexation of Ni(II), Cu(II), Zn(II), and Cd(II) by dissolved organic carbon (DOC) in some freshwater lakes in Rouyn-Noranda, Québec, Canada, where they were impacted by effluents from a nearby copper smelter, was measured by kinetic and equilibrium methods using cathodic and anodic stripping voltammetry. The measured free-metal-ion and labile metal-complex concentrations were compared with the predictions made by a widely-used computer speciation model, the Windermere Humic Aqueous Model (WHAM): WHAM V and its improved version WHAM VI. If it is assumed that 65% of the DOC is “active”, i.e. behaving as isolated humic substances such as fulvic acid, both versions of WHAM are able to predict the labile and free-metal-ion concentrations of Ni, Zn, and Cd reasonably well; however, both underestimate the free-copper-ion concentration by one to two orders of magnitude. WHAM VI is generally better than or equal to WHAM V for successfully predicting most of the free-metal-ion concentrations. The modelled competition by Al(III) and Fe(III) in the lake surface waters showed that in most cases Cu(II) was most affected by this competition. WHAM VI predicts a larger effect from the Al(III) and Fe(III) competition than does WHAM V.     

STUDIES ON HUMAN LENS: I. ORIGIN AND DEVELOPMENT OF FLUORESCENT PIGMENTS

Abstract
Fluorescence spectra of normal mature human lenses have been measured and at least eight species with distinct emission characteristics identified. To determine the specific photochemical and photophysical processes responsible for the origin and development of these fluorophores, emission behavior of the products generated by successive irradiation of young human lenses (3–6 y old) as well as of L-tryptophan solution have been systematically monitored. Fluorescent products that resulted from this irradiation were comparable to many of the fluorophores detected in aged lenses, indicating that light plays a major role in the development of these pigments. In addition to photogenerated species, there are other compounds in human lenses, presumably advanced glycosylated end products, with marked fluorescence properties.
Several oxidation products of tryptophan including N -formylkynurenine or its derivatives, β-carboline or its derivatives, and anthranilic acid have been identified in the mature human lens. The development of several photoproducts also was attributed to endogenous ascorbate-mediated Maillard reaction products, which undergo photoconversion by the visible light. Although some of these chromophores could act as photosensitaizers, the sensitizing efficiency of many are low. Conversely, the near-UV filtering capability of these colored compounds conceivably could protect the vitreous and retina from development of any photochemical lesion.     

MONITORING LIGHT-INDUCED CHANGES IN ISOLATED, INTACT EYE LENSES

Fluorescence spectral changes occurring upon irradiation with 300 nm light have been monitored in situ in isolated, intact, whole lenses from the eyes of several species. The findings corroborate observations on other individual constituent protein molecules in the solution state, and also reveal features attributable to the supramolecular protein assembly that exists in the whole lens. Irradiation of the lens with 300 nm light causes red shifts in the tryptophan emission spectrum, suggesting alterations in the protein packing in the lens. Intermolecular energy transfer from tryptophan to one of the photoproducts, presumably N-formylkynurenine (N-FK), occurs in the condensed-phase sample. The N-FK formed is photodegraded efficiently in the lens, indicating that the photodynamic effects of endogenous N-FK might not be as severe as has been thought. Species variation in the photoevents are evident, particularly in avian lenses that contain the variant δ-crystallin as the core protein. The photoinduced changes in the near-UV circular dichroism of δ-crystallin (which is α-helical, as opposed to the β-sheet structure of α-, β-, and -γ-crystallins), isolated from chicken lenses, are remarkably different from other crystallins. Irradiation of δ-crystallin leads to a drastic reduction of circular dichroism intensity in the 250–300 nm region, whereas no changes are seen in the peptide absorption band.     

Hybrid electron cyclotron resonance-radio-frequency plasma etching of III–V semiconductors in Cl2-based discharges. Part I: GaAs and related compounds

A systematic study has been performed of the dry etching characteristics of GaAs, Al_0.3Ga_0.7As, and GaSb in chlorine-based electron cyclotron resonance (ECR) discharges. The gas mixtures investigated were CCl₂F₂/O₂, CHCl₂F/O₂, and PCl₃. The etching rates of all three materials increase rapidly with applied RF power, while the addition of the microwave power at moderate levels (150 W) increases the etch rates by 20–80%. In the microwave discharges, the etch rates decrease with increasing pressure, but at 1 m Torr it is possible to obtain usable rates for self-bias voltages 100 V. Of the Freon-based mixtures, CHCl₂F provides the least degradation of optical (photoluminescence) and electrical (diode ideality factors and Schottky barrier heights) properties of GaAs as a result of dry etching. Smooth surface morphologies are obtained on all three materials provided the microwave power is limited to 200 W. Above this power, there is surface roughening evident with all of the gas mixtures investigated.     

Immobilization of amyloglucosidase using two forms of polyurethane polymer

Amyloglucosidase was covalently immobilized using two hydrophilic prepolymers: Hypol FHP 2002 (creates foams) and Hypol FHP 8190H (creates gels). The foamable prepolymer was superior as a support for enzyme immobilization. The percent activity immobilized in the polyurethane foams was 25 +/- 1.5%. Large substrates (greater than 200,000 daltons in mol wt) were hydrolyzed as effectively as smaller ones by the immobilized enzyme. The Km value of the foam-immobilized enzyme increased from 0.76 mg/mL (free) to 0.86 mg/mL (immobilized), whereas the Vmax dropped from 90.9 (free) to 12.4 nmol glucose/min/mL (immobilized). The long-term (2 mo) storage stability of amyloglucosidase was enhanced by immobilization in foams (70% activity retained; free enzyme only retained 50%). Immobilization also improved the enzyme stability to various denaturing agents (sodium chloride, urea, and ethanol). The immobilized enzyme exhibited increased stability compared to the free enzyme at high temperatures (95 degrees C). Both glycogen and starch could be utilized by the immobilized enzyme, indicating that this technique could prove useful for starch hydrolysis.     

Synthesis, structure and properties of delocalized transition metal chelates: Diazoketiminato chelates of Co(III) and Pt(II)

The reactions of HL 1 [where HL is 1N-(2-pyridyl-2-methyl)-2-arylazoaniline and is formulated as ArN = NC₆H₄N(H)(CH₂C₅H₄N); Ar = C₆H₅ (for HL¹) or p-MeC₆H₄ (for HL²) or p-ClC₆H₄ (for HL³)] with K₂PtCl₄ and Co(ClO₄)₃ · 6H₂O afforded the (L)PtCl and [(L)₂Co]ClO₄ complexes, respectively. The HL ligands bind the platinum(II) and cobalt(III) centres in a tridentate (N,N,N) fashion, forming new diazoketiminato chelates upon dissociating the amino proton. The X-ray structures of (L³)PtCl and [(L³)₂Co]ClO₄ were determined. Redox properties of the new complexes have been examined.     

Flat periodic representations ofU q (G)

We give explicit expression of flat periodic representations, when they exist, of the quantum analogues of simple Lie algebras and their affine extensions for a parameter of deformationq equal to a root of unity. By flat periodic, we mean that these representations have no highest weight and that all the weights have multiplicity 1.