848 research outputs found
c-axis Josephson Tunneling in Twinned YBCO Crystals
Josephson tunneling between YBCO and Pb with the current flowing along the
c-axis of the YBCO is persumed to come from an s-wave component of the
superconductivity of the YBCO. Experiments on multi-twin samples are not
entirely consistent with this hypothesis. The sign change of the s-wave order
parameter across the N_T twin boundaries should give cancelations, resulting in
a small tunneling current. The actual current is larger than this.
We present a theory of this unexpectedly large current based upon a surface
effect: disorder-induced supression of the d-wave component at the (001)
surface leads to s-wave coherence across the twin boundaries and a non-random
tunneling current. We solve the case of an ordered array of d+s and d-s twins,
and estimate that the twin size at which s-wave surface coherence occurs is
consistent with typical sizes observed in experiments. In this picture, there
is a phase difference of between different surfaces of the material. We
propose a corner junction experiment to test this picture.Comment: 5 pages, 4 eps figure
Electron beam driven alkali metal atom source for loading a magneto-optical trap in a cryogenic environment
We present a versatile and compact electron beam driven source for alkali
metal atoms, which can be implemented in cryostats. With a heat load of less
than 10mW, the heat dissipation normalized to the atoms loaded into the
magneto-optical Trap (MOT), is about a factor 1000 smaller than for a typical
alkali metal dispenser. The measured linear scaling of the MOT loading rate
with electron current observed in the experiments, indicates that electron
stimulated desorption is the corresponding mechanism to release the atoms.Comment: 5 pages, 3 figure
Pointwise estimates for the Bergman kernel of the weighted Fock space
We prove upper pointwise estimates for the Bergman kernel of the weighted
Fock space of entire functions in where is a
subharmonic function with a doubling measure. We derive estimates
for the canonical solution operator to the inhomogeneous Cauchy-Riemann
equation and we characterize the compactness of this operator in terms of
Influence of the Coriolis force in atom interferometry
In a light-pulse atom interferometer, we use a tip-tilt mirror to remove the
influence of the Coriolis force from Earth's rotation and to characterize
configuration space wave packets. For interferometers with large momentum
transfer and large pulse separation time, we improve the contrast by up to 350%
and suppress systematic effects. We also reach what is to our knowledge the
largest spacetime area enclosed in any atom interferometer to date. We discuss
implications for future high performance instruments.Comment: 4 pages, 5 figures, 1 tabl
Current State and Future Directions of Genetics and Genomics of Endophytic Fungi for Bioprospecting Efforts
The bioprospecting of secondary metabolites from endophytic fungi received great attention in the 1990s and 2000s, when the controversy around taxol production from Taxus spp. endophytes was at its height. Since then, hundreds of reports have described the isolation and characterization of putative secondary metabolites from endophytic fungi. However, only very few studies also report the genetic basis for these phenotypic observations. With low sequencing cost and fast sample turnaround, genetics- and genomics-based approaches have risen to become comprehensive approaches to study natural products from a wide-range of organisms, especially to elucidate underlying biosynthetic pathways. However, in the field of fungal endophyte biology, elucidation of biosynthetic pathways is still a major challenge. As a relatively poorly investigated group of microorganisms, even in the light of recent efforts to sequence more fungal genomes, such as the 1000 Fungal Genomes Project at the Joint Genome Institute (JGI), the basis for bioprospecting of enzymes and pathways from endophytic fungi is still rather slim. In this review we want to discuss the current approaches and tools used to associate phenotype and genotype to elucidate biosynthetic pathways of secondary metabolites in endophytic fungi through the lens of bioprospecting. This review will point out the reported successes and shortcomings, and discuss future directions in sampling, and genetics and genomics of endophytic fungi. Identifying responsible biosynthetic genes for the numerous secondary metabolites isolated from endophytic fungi opens the opportunity to explore the genetic potential of producer strains to discover novel secondary metabolites and enhance secondary metabolite production by metabolic engineering resulting in novel and more affordable medicines and food additives
Testing spontaneous localization theories with matter-wave interferometry
We propose to test the theory of continuous spontaneous localization (CSL) in
an all-optical time-domain Talbot-Lau interferometer for clusters with masses
exceeding 1000000 amu. By assessing the relevant environmental decoherence
mechanisms, as well as the growing size of the particles relative to the
grating fringes, we argue that it will be feasible to test the quantum
superposition principle in a mass range excluded by recent estimates of the CSL
effect.Comment: 4 pages, 3 figures; corresponds to published versio
Rapid in vitro prototyping of O-methyltransferases for pathway applications in Escherichia coli
O-Methyltransferases are ubiquitous enzymes involved in biosynthetic pathways for secondary metabolites such as bacterial antibiotics, human catecholamine neurotransmitters, and plant phenylpropanoids. While thousands of putative O-methyltransferases are found in sequence databases, few examples are functionally characterized. From a pathway engineering perspective, however, it is crucial to know the substrate and product ranges of the respective enzymes to fully exploit their catalytic power. In this study, we developed an in vitro prototyping workflow that allowed us to screen ∼30 enzymes against five substrates in 3 days with high reproducibility. We combined in vitro transcription/translation of the genes of interest with a microliter-scale enzymatic assay in 96-well plates. The substrate conversion was indirectly measured by quantifying the consumption of the S-adenosyl-L-methionine co-factor by time-resolved fluorescence resonance energy transfer rather than time-consuming product analysis by chromatography. This workflow allowed us to rapidly prototype thus far uncharacterized O-methyltransferases for future use as biocatalysts
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