7,362 research outputs found
Characterisation of novel biomass degradation enzymes from the genome of <i>Cellulomonas fimi</i>
Recent analyses of genome sequences belonging to cellulolytic bacteria have revealed many genes potentially coding for cellulosic biomass degradation enzymes. Annotation of these genes however, is based on few biochemically characterised examples. Here we present a simple strategy based on BioBricks for the rapid screening of candidate genes expressed in Escherichia coli. As proof of principle we identified over 70 putative biomass degrading genes from bacterium Cellulomonas fimi, expressing a subset of these in BioBrick format. Six novel genes showed activity in E. coli. Four interesting enzymes were characterised further. α-l-arabinofuranosidase AfsB, β-xylosidases BxyF and BxyH and multi-functional β-cellobiosidase/xylosidase XynF were partially purified to determine their optimum pH, temperature and kinetic parameters. One of these enzymes, BxyH, was unexpectedly found to be highly active at strong alkaline pH and at temperatures as high as 100 °C. This report demonstrates a simple method of quickly screening and characterising putative genes as BioBricks
Gate-Controlled Electron Spin Resonance in a GaAs/AlGaAs Heterostructure
The electron spin resonance (ESR) of two-dimensional electrons is
investigated in a gated GaAs/AlGaAs heterostructure. We found that the ESR
resonance frequency can be turned by means of a gate voltage. The front and
back gates of the heterostructure produce opposite g-factor shift, suggesting
that electron g-factor is being electrostatically controlled by shifting the
equilibrium position of the electron wave function from one epitaxial layer to
another with different g-factors
Spin Relaxation in a Quantum Dot due to Nyquist Noise
We calculate electron and nuclear spin relaxation rates in a quantum dot due
to the combined action of Nyquist noise and electron-nuclei hyperfine or
spin-orbit interactions. The relaxation rate is linear in the resistance of the
gate circuit and, in the case of spin-orbit interaction, it depends essentially
on the orientations of both the static magnetic field and the fluctuating
electric field, as well as on the ratio between Rashba and Dresselhaus
interaction constants. We provide numerical estimates of the relaxation rate
for typical system parameters, compare our results with other, previously
discussed mechanisms, and show that the Nyquist mechanism can have an
appreciable effect for experimentally relevant systems.Comment: v2: New discussion of arbitrary gate setups (1 new figure), more
Comments on experiments; 6 pages, 4 figure
Viscous Effects on Impact Probes in a Subsonic Rarified Gas Flow
The problem of time response of pressure gaging systems used with low density flows has been discussed in Ref ]4, and the effect of outgassing on pressure magnitudes was indicated in the same reference. Briefly, gases or vapors adhering to the internal walls of the pressure gaging system behave like gas sources and produce a pressure rise in the gage system which has no relation to the external flow. The effect can also occur in the reverse direction, with "in-gassing" or the action of an effective sink in the gage system as gases entering through the probe orifice are adsorbed to the walls. For given surface conditions, the magnitude of the pressure error to be expected due to out-gassing depends on the dimensions of the probe system. In the present tests, it was desirable to use the smallest possible probe to yield the lowest possible Reynolds number. The lower limit on size was fixed by outgassing effects, evaluated by the following procedure. 2.0 PROCEDURE The pumping system was adjusted to give a pressure, measured at the reservoir, of 9 microns Hg with no flow into the wind tunnel. The upstream metering valve was then opened and the air flow rate adjusted to give a pressure of 100 microns in the reservoir under steady flow conditions, The pressure read by one of the impact tubes, inserted into the flow, was measured. The upstream metering valve was then closed rapid)y, and the reservoir pressure, p0, and the impact probe pressure, Pj, were measured simultaneously at definite time intervals. Another probe was inserted into the flow and the procedure repeated, until the pressure-time data had been obtained for each probe investigated. The results for a series of tests Involving probe Nos.l, 2 and 3 are shown on HYD 2616 300 RESULTS From HYD 2616, It is clear that the smallest probe (No.3) requires the longest time to reach equilibrium. After a sufficient time has elapsed (about 180 seconds), this probe read the same, within the accuracy of measurement, as the other two, When a similar experiment was performed utilizing a probe which was one-half the size of probe No.2, it indicated a pressure, after 180 seconds, which was almost 10 microns Hg higher than the other probes. Accordingly, only probe Nos. 1, 2, 3 and 4 were employed in the experiments, and a time of at least 180 seconds was allowed to elapse between a change of setting and the reading of the instruments
Is there a renormalization of the 1D conductance in Luttinger Liquid model?
Properties of 1D transport strongly depend on the proper choice of boundary
conditions. It has been frequently stated that the Luttinger Liquid (LL)
conductance is renormalized by the interaction as . To
contest this result I develop a model of 1D LL wire with the interaction
switching off at the infinities. Its solution shows that there is no
renormalization of the universal conductance while the electrons have a free
behavior in the source and drain reservoirs.Comment: 5 pages, RevTex 2.0, attempted repair of tex error
Some Phenomenology of Intersecting D-Brane Models
We present some phenomenology of a new class of intersecting D-brane models.
Soft SUSY breaking terms for these models are calculated in the u - moduli
dominant SUSY breaking approach (in type IIA). In this case, the dependence of
the soft terms on the Yukawas and Wilson lines drops out. These soft terms have
a different pattern compared to the usual heterotic string models.
Phenomenological implications for dark matter are discussed.Comment: 29 pages, 1 figure, References adde
Spectroscopy of a Cooper-Pair box in the Autler-Townes configuration
A theoretical spectroscopic analysis of a microwave driven superconducting
charge qubit (Cooper-pair box coupled) to an RLC oscillator model is performed.
By treating the oscillator as a probe through the backreaction effect of the
qubit on the oscillator circuit, we extract frequency splitting features
analogous to the Autler-Townes effect from quantum optics, thereby extending
the analogies between superconducting and quantum optical phenomenology. These
features are found in a frequency band that avoids the need for high frequency
measurement systems and therefore may be of use in qubit characterization and
coupling schemes. In addition we find this frequency band can be adjusted to
suit an experimental frequency regime by changing the oscillator frequency.Comment: 13 pages, 7 figures. v2: Revised version after referee comments.
Accepted for publication by Physical Review
Spin texture on the Fermi surface of tensile strained HgTe
We present ab initio and k.p calculations of the spin texture on the Fermi
surface of tensile strained HgTe, which is obtained by stretching the
zincblende lattice along the (111) axis. Tensile strained HgTe is a semimetal
with pointlike accidental degeneracies between a mirror symmetry protected
twofold degenerate band and two nondegenerate bands near the Fermi level. The
Fermi surface consists of two ellipsoids which contact at the point where the
Fermi level crosses the twofold degenerate band along the (111) axis. However,
the spin texture of occupied states indicates that neither ellipsoid carries a
compensating Chern number. Consequently, the spin texture is locked in the
plane perpendicular to the (111) axis, exhibits a nonzero winding number in
that plane, and changes winding number from one end of the Fermi ellipsoids to
the other. The change in the winding of the spin texture suggests the existence
of singular points. An ordered alloy of HgTe with ZnTe has the same effect as
stretching the zincblende lattice in the (111) direction. We present ab initio
calculations of ordered Hg_xZn_1-xTe that confirm the existence of a spin
texture locked in a 2D plane on the Fermi surface with different winding
numbers on either end.Comment: 8 pages, 8 figure
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