A family of thermostable fungal cellulases created by structure-guided recombination

SCHEMA structure-guided recombination of 3 fungal class II cellobiohydrolases (CBH II cellulases) has yielded a collection of highly thermostable CBH II chimeras. Twenty-three of 48 genes sampled from the 6,561 possible chimeric sequences were secreted by the Saccharomyces cerevisiae heterologous host in catalytically active form. Five of these chimeras have half-lives of thermal inactivation at 63°C that are greater than the most stable parent, CBH II enzyme from the thermophilic fungus Humicola insolens, which suggests that this chimera collection contains hundreds of highly stable cellulases. Twenty-five new sequences were designed based on mathematical modeling of the thermostabilities for the first set of chimeras. Ten of these sequences were expressed in active form; all 10 retained more activity than H. insolens CBH II after incubation at 63°C. The total of 15 validated thermostable CBH II enzymes have high sequence diversity, differing from their closest natural homologs at up to 63 amino acid positions. Selected purified thermostable chimeras hydrolyzed phosphoric acid swollen cellulose at temperatures 7 to 15°C higher than the parent enzymes. These chimeras also hydrolyzed as much or more cellulose than the parent CBH II enzymes in long-time cellulose hydrolysis assays and had pH/activity profiles as broad, or broader than, the parent enzymes. Generating this group of diverse, thermostable fungal CBH II chimeras is the first step in building an inventory of stable cellulases from which optimized enzyme mixtures for biomass conversion can be formulated

A single chain analysis of doped quasi one dimensional spin 1 compounds: paramagnetic versus spin 1/2 doping

We present a numerical study of single chain models of doped spin 1 compounds. We use low energy effective one-dimensional models for both the cases of paramagnetic and spin-1/2 doping. In the case of paramagnetic doping, the effective model is equivalent to the bond disordered spin-1/2 chain model recently analyzed by means of real space renormalization group by Hyman and Yang. By means of exact diagonalizations in the XX limit, we confirm the stability of the Haldane phase for weak disorder. Above a critical amount of disorder, the effective model flows to the so called random singlet fixed point. In the case of spin-1/2 doping, we argue that the Haldane phase should be destabilized even for weak disorder. This picture is not in contradiction with existing experimental data. We also discuss the possible occurrence of (unobserved) antiferromagnetically ordered phases.Comment: 13 pages, 7 included figure

Nonmonotonous Magnetic Field Dependence and Scaling of the Thermal Conductivity for Superconductors with Nodes of the Order Parameter

We show that there is a new mechanism for nonmonotonous behavior of magnetic field dependence of the electronic thermal conductivity of clean superconductors with nodes of the order parameter on the Fermi surface. In particular, for unitary scatterers the nonmonotony of relaxation time takes place. Contribution from the intervortex space turns out to be essential for this effect even at low temperatures. Our results are in a qualitative agreement with recent experimental data for superconducting UPt_3. For E_{2u}-type of pairing we find approximately the scaling of the thermal conductivity in clean limit with a single parameter x=T/T_c\sqrt{B_{c2}/B} at low fields and low temperatures, as well as weak low-temperature dependence of the anisotropy ratio K_{zz}/K_{yy} in zero field. For E_{1g}-type of pairing deviations from the scaling are more noticeable and the anisotropy ratio is essentially temperature dependent.Comment: 37 pages, 8 Postscript figures, REVTE

Impact of apolipoprotein E genotype variation on means, variances, and correlations of plasma lipid, lipoprotein, and apolipoprotein traits in octogenarians

The impact of apoliporotein (apo) E genotype variation on means, variances and correlations between plasma lipid traits was studied in male and female octogenarians. Females had significantly higher mean levels of all 10 of the measured plasma lipid traits than males. The subset of concomitants (i.e., age, height, weight, body mass index, glucose and uric acid) that made a statistically significant contribution to interindividual variability was different in males and females for every trait considered. Gender-specific associations between variation in apo E genotype and variation in pariticular measures of lipid metabolism, adjusted for concomitant variation, were observed: in females there were no statistically significant associations while in males the means of the three common apo E genotypes were significantly different for adjusted measures of total cholesterol, low density lipoprotein cholesterol and low density lipoprotin-apo B. The common apo E genotypes were heterogeneous with respect to intragenotypic variance for adjusted logtransformed triglyceride levels in females only. Finally, the three common apo E genotypes were heterogeneous with respect to the correlation between traits, adjusted for concomitant variation, and gender influenced the manner in which the genotypes differed for specific correlations. This study documents that variation in the apo E gene has a significant impact on means, variances and correlations of plasma lipid traits in octogenarians, but the effects are context-, that is, gender- and age-, dependent. © 1995 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38262/1/1320580405_ftp.pd

Neutron and X-ray Scattering Studies of the Lightly-Doped Spin-Peierls System Cu(1-x)Cd(x)GeO3

Single crystals of the lightly-doped spin-Peierls system Cu(1-x)Cd(x)GeO3 have been studied using bulk susceptibility, x-ray diffraction, and inelastic neutron scattering techniques. We investigate the triplet gap in the magnetic excitation spectrum of this quasi-one dimensional quantum antiferromagnet, and its relation to the spin-Peierls dimerisation order parameter. We employ two different theoretical forms to model the inelastic neutron scattering cross section and chi''(Q,omega), and show the sensitivity of the gap energy to the choice of chi''(Q,omega). We find that a finite gap exists at the spin-Peierls phase transition.Comment: 15 Pages, 7 Figures, Submitted to J. Phys. :Condensed Matte

Phase diagram of UPt3_3 in the E1gE_{1g} model

The phase diagram of the unconventional superconductor UPt$_3$ is explained under the long-standing hypothesis that the pair wavefunction belongs to the $E_{1g}$ representation of the point group. The main objection to this theory has been that it disagrees with the experimental phase diagram when a field is applied along the c-axis. By a careful analysis of the free energy this objection is shown to be incorrect. This singlet theory also explains the unusual anisotropy in the upper critical field curves, often thought to indicate a triplet pair function.Comment: 11 pages, Revtex, 2 figures (uuencoded, gzip'ed Postscript

Spin Defects in Spin-Peierls Systems

We examine spin-Peierls systems in the presence of spin defects which are introduced by replacing magnetic ions $Cu^{2+}$ with non-magnetic ones $Zn^{2+}$ in $CuGeO_3$. By using the action for the bosonized Hamiltonian, it is shown directly that the antiferromagnetic state induced by the spin defects coexists with the spin-Peierls states. Further the doping dependences of both transition temperature of spin-Peierls state and the spin gap have been calculated. The transition temperature of the present estimation shows good agreement quantitatively with that observed in Cu_{1-\de} Zn_\de O_3 for the region of the doping rate, \de<0.02.Comment: jpsj style, 11 pages, 2 figure

Thermal Conductivity of superconducting (TMTSF)_2ClO_4: evidence for a nodeless gap

We report on the first measurements of thermal conductivity in the superconducting state of (TMTSF)_2ClO_4. The electronic contribution to heat transport is found to decrease rapidly below T_c, indicating the absence of low-energy electronic excitations. We argue that this result provides strong evidence for a nodeless superconducting gap function but does not exclude a possible unconventional order parameter.Comment: 4 pages including 4 figures, submitted to Phys. Rev. Let

Navigation Patterns in Ederly During Multitasking in Virtual Environnment

Cognitive assessment and screening can be realized with virtual environments (VE). These VE reproduce ecological situation and give an overview of participants difficulties through scoring systems. The most variables used to qualify participants performance are number of errors and time completion. These variables are link to cognition and navigation skill in VEs. We assessed navigation of adult and elderly in a multitasking VE. Navigation patterns were elaborate with diagram to visually detect differences between the two age groups. Elderly have poorer performance than adults