157 research outputs found
Some symmetry properties of spin currents and spin polarizations in multi-terminal mesoscopic spin-orbit coupled systems
We study theoretically some symmetry properties of spin currents and spin
polarizations in multi-terminal mesoscopic spin-orbit coupled systems. Based on
a scattering wave function approach, we show rigorously that in the equilibrium
state no finite spin polarizations can exist in a multi-terminal mesoscopic
spin-orbit coupled system (both in the leads and in the spin-orbit coupled
region) and also no finite equilibrium terminal spin currents can exist. By use
of a typical two-terminal mesoscopic spin-orbit coupled system as the example,
we show explicitly that the nonequilibrium terminal spin currents in a
multi-terminal mesoscopic spin-orbit coupled system are non-conservative in
general. This non-conservation of terminal spin currents is not caused by the
use of an improper definition of spin current but is intrinsic to
spin-dependent transports in mesoscopic spin-orbit coupled systems. We also
show that the nonequilibrium lateral edge spin accumulation induced by a
longitudinal charge current in a thin strip of \textit{finite} length of a
two-dimensional electronic system with intrinsic spin-orbit coupling may be
non-antisymmetric in general, which implies that some cautions may need to be
taken when attributing the occurrence of nonequilibrium lateral edge spin
accumulation induced by a longitudinal charge current in such a system to an
intrinsic spin Hall effect.Comment: 11 pages, 6 figure
Production of dihydroxyacetone from glycerol by engineered Escherichia coli cells co-expressing gldA and nox genes
Glycerol can be converted into more valuable compound dihydroxyacetone by the nicotinamide adenine dinucleotide (NAD+)-dependent glycerol dehydrogenase. However, it is economically prohibitive to produce dihydroxyacetone using purified glycerol dehydrogenase at the expense of a stoichiometric amount of the cofactor NAD+. In this study, Escherichia coli was engineered for dihydroxyacetone production by enhancing its glycerol dehydrogenase activity and introducing NADH oxidase activity. Under optimized conditions, dihydroxyacetone productivity reached 0.13 g/h/g wet cell mass by recombinant E. coli D4 (pET-24b-gldA+nox) cells co-expressing gldA gene from E. coli and nox gene from Enterococcus faecalis. It was interesting to note that exogenous NAD+ greatly improved dihydroxyacetone production for the whole-cell biotransformation process. These results should be useful for the development of advanced bioprocess in terms of glycerol utilization.Keywords: Dihydroxyacetone, Glycerol dehydrogenase, NAD+, whole-cell biotransformation, Escherichia coliAfrican Journal of Biotechnology Vol. 12(27), pp. 4387-439
Non-equilibrium spin polarization effects in spin-orbit coupling system and contacting metallic leads
We study theoretically the current-induced spin polarization effect in a
two-terminal mesoscopic structure which is composed of a semiconductor
two-dimensional electron gas (2DEG) bar with Rashba spin-orbit (SO) interaction
and two attached ideal leads. The nonequilibrium spin density is calculated by
solving the scattering wave functions explicitly within the ballistic transport
regime. We found that for a Rashba SO system the electrical current can induce
spin polarization in the SO system as well as in the ideal leads. The induced
polarization in the 2DEG shows some qualitative features of the intrinsic spin
Hall effect. On the other hand, the nonequilibrium spin density in the ideal
leads, after being averaged in the transversal direction, is independent of the
distance measured from the lead/SO system interface, except in the vicinity of
the interface. Such a lead polarization effect can even be enhanced by the
presence of weak impurity scattering in the SO system and may be detectable in
real experiments.Comment: 6 pages,5 figure
Kinetic magnetoelectric effect in a 2D semiconductor strip due to boundary-confinement induced spin-orbit coupling
In a thin strip of a two-dimensional semiconductor electronic system,
spin-orbit coupling may be induced near both edges of the strip due to the
substantial spatial variation of the confining potential in the boundary
regions. In this paper we show that, in the presence of boundary-confinement
induced spin-orbit coupling, a longitudinal charge current circulating through
a 2D semiconductor strip may cause \textit{strong} non-equilibrium spin
accumulation near both edges of the strip. The spins will be polarized along
the normal of the 2DEG plane but in opposite directions at both edges of the
strip. This phenomenon is essentially a kinetic magnetoelectric effect from the
theoretical points of view, but it manifests in a very similar form as was
conceived in a spin Hall effect.Comment: 7 pages, 4 fig
Engineering NAD+ availability for Escherichia coli whole-cell biocatalysis: A case study for dihydroxyacetone production
Background: Whole-cell redox biocatalysis has been intensively explored for the production of valuable compounds because excellent selectivity is routinely achieved. Although the cellular cofactor level, redox state and the corresponding enzymatic activity are expected to have major effects on the performance of the biocatalysts, our ability remains limited to predict the outcome upon variation of those factors as well as the relationship among them. Results: In order to investigate the effects of cofactor availability on whole-cell redox biocatalysis, we devised recombinant Escherichia coli strains for the production of dihydroxyacetone (DHA) catalyzed by the NAD + -dependent glycerol dehydrogenase (GldA). In this model system, a water-forming NAD + oxidase (NOX) and a NAD + transporter (NTT4) were also co-expressed for cofactor regeneration and extracellular NAD + uptake, respectively. We found that cellular cofactor level, NAD + /NADH ratio and NOX activity were not only strain-dependent, but also growth condition-dependent, leading to significant differences in specific DHA titer among different whole-cell biocatalysts. The host E. coli DH5α had the highest DHA specific titer of 0.81\ua0g/g DCW with the highest NAD + /NADH ratio of 6.7 and NOX activity of 3900 U. The biocatalyst had a higher activity when induced with IPTG at 37\ub0C for 8\ua0h compared with those at 30\ub0C for 8\ua0h and 18\ua0h. When cells were transformed with the ntt4 gene, feeding NAD + during the cell culture stage increased cellular NAD(H) level by 1.44 fold and DHA specific titer by 1.58 fold to 2.13\ua0g/g DCW . Supplementing NAD + during the biotransformation stage was also beneficial to cellular NAD(H) level and DHA production, and the highest DHA productivity reached 0.76\ua0g/g DCW /h. Cellular NAD(H) level, NAD + /NADH ratio, and NOX and GldA activity dropped over time during the biotransformation process.Conclusions: High NAD + /NADH ratio driving by NOX was very important for DHA production. Once cofactor was efficiently cycled, high cellular NAD(H) level was also beneficial for whole-cell redox biocatalysis. Our results indicated that NAD + transporter could be applied to manipulate redox cofactor level for biocatalysis. Moreover, we suggested that genetically designed redox transformation should be carefully profiled for further optimizing whole-cell biocatalysis. \ua9 2013 Zhou et al.; licensee BioMed Central Ltd
Engineering yeast for high-level production of diterpenoid sclareol
The diterpenoid sclareol is an industrially important precursor for alternative sustainable supply of ambergris. However, its current production from plant extraction is neither economical nor environmental-friendly, since it requires laborious and cost-intensive purification procedures and plants cultivation is susceptible to environmental factors. Engineering cell factories for bio-manufacturing can enable sustainable production of natural products. However, stringent metabolic regulation poses challenges to rewire cellular metabolism for overproduction of compounds of interest. Here we used a modular approach to globally rewire the cellular metabolism for improving sclareol production to 11.4 g/L in budding yeast Saccharomyces cerevisiae, the highest reported diterpenoid titer in microbes. Metabolic flux analysis showed that modular balanced metabolism drove the metabolic flux toward the biosynthesis of targeted molecules, and transcriptomic analysis revealed that the expression of central metabolism genes was shaped for a new balanced metabolism, which laid a foundation in extensive metabolic engineering of other microbial species for sustainable bio-production
Effect of Peritoneal Fluid from Endometriosis Patients on Sperm Motion Characteristics and Acrosome Reaction
ABSTRACT: Objective-To determine whether peritoneal fluid from women with endometriosis contributes to infertility by impairing sperm motion and functional characteristics. Methods-Women with endometriosis (n = 20) underwent laparoscopy for infertility or pelvic pain. Patients undergoing tubal ligation served as controls (n = 14). Peritoneal fluid was aspirated from women with endometriosis, or from women undergoing laparoscopic tubal ligation. Sperm motility, motion characteristics and acrosome reaction were assessed following incubation with peritoneal fluid. Results-Sperm motility, motion characteristics, and acrosome reaction did not differ significantly between the two groups after 3, 5, or 24 hours of incubation with peritoneal fluid. Conclusions-Sperm motion or functional characteristics showed no significant impairment when sperm from normal donors were incubated with peritoneal fluid from patients with endometriosis. It is unlikely that peritoneal fluid in these patients contributes to infertility. Int J Fertil 44 (1)
Essential role of protein tyrosine phosphatase 1B in obesity-induced inflammation and peripheral insulin resistance during aging
Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of
insulin signaling and a therapeutic target for type 2 diabetes
(T2DM). In this study, we have evaluated the role of PTP1B in the
development of aging-associated obesity, inflammation, and
peripheral insulin resistance by assessing metabolic parameters at
3 and 16 months in PTP1B) ⁄ ) mice maintained on mixed genetic
background (C57Bl ⁄ 6J · 129Sv ⁄ J). Whereas fat mass and adipocyte
size were increased in wild-type control mice at 16 months, these
parameters did not change with aging in PTP1B) ⁄ ) mice. Increased
levels of pro-inflammatory cytokines, crown-like structures, and
hypoxia-inducible factor (HIF)-1a wereobserved only in adipose tissue
from 16-month-old wild-type mice. Similarly, islet hyperplasia
and hyperinsulinemia were observed in wild-type mice with agingassociated
obesity, but not in PTP1B) ⁄ ) animals. Leanness in 16-
month-old PTP1B) ⁄ ) mice was associated with increased energy
expenditure. Whole-body insulin sensitivity decreased in 16-
month-old control mice; however, studies with the hyperinsulinemic–
euglycemic clamp revealed that PTP1B deficiency prevented
this obesity-related decreased peripheral insulin sensitivity. At a
molecular level, PTP1B expression and enzymatic activity were upregulated
in liver and muscle of 16-month-old wild-type mice as
were the activation of stress kinases and the expression of p53.
Conversely, insulin receptor-mediated Akt ⁄ Foxo1 signaling was
attenuated in these aged control mice. Collectively, these data
implicate PTP1B in the development of inflammation and insulin
resistance associated with obesity during aging and suggest that
inhibition of this phosphatase by therapeutic strategies might protect
against age-dependentT2DMThis work was supported by grants from Ministerio de Ciencia e
Innovación (Spain) SAF2009-08114 and (to A.M.V.), BFU2008-
04901-C03-02 and 03 (to M.R and J.M.C., respectively),
BFU2008-01283 (to M.V), Comunidad de Madrid S2010/BMD-
2423 and Centro de Investigación Biomédica en Red de Diabetes
y Enfermedades Metabólicas Asociadas (CIBERDEM) (Instituto Salud
Carlos III). CBMSO is recipient of institutional aid from Ramón
Areces Foundation. We also acknowledge grants NIH-R01
DK080756, ADA 7-07-RA-80, and NIH U24-DK093000 (to J.K.K.)
and UMass Mouse Phenotyping Center supported by UMass Diabetes
and Endocrinology Research Center Grant (DK32520) and
EFSD/Amylin Programme 2011 grant (to A.M.V.)
Electron pumping in graphene mechanical resonators
The combination of high frequency vibrations and metallic transport in
graphene makes it a unique material for nano-electromechanical devices. In this
letter, we show that graphene-based nano-electromechanical devices are
extremely well suited for charge pumping, due to the sensitivity of its
transport coefficients to perturbations in electrostatic potential and
mechanical deformations, with the potential for novel small scale devices with
useful applications
On a Stochastic Wave Equation Driven by a Non-Gaussian Levy Process
This paper investigates a damped stochastic wave equation driven by a
non-Gaussian Levy noise. The weak solution is proved to exist and be unique.
Moreover we show the existence of a unique invariant measure associated with
the transition semigroup under mild conditions.Comment: 17 page
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