806 research outputs found
A novel platform for the production of nonhydroxylated gelatins based on the methylotrophic yeast Hansenula polymorpha
The use of yeast as a host for heterologous expression of proteins that are normally derived from animal tissue is a promising way to ensure defined products that are devoid of potential harmful animal side products. Here we report on the production and secretion of a custom-designed gelatin, Hu3–His8, by the yeast Hansenula polymorpha. We observed that Hu3–His8 was poorly secreted by the heterologous Saccharomyces cerevisiae invertase secretion signal. In contrast, the S. cerevisiae mating factor α prepro sequence efficiently directed secretion into the culture medium. However, at higher copy numbers, intracellular accumulation of Hu3–His8 precursors occurred. Overproduction of Erv29p, a protein required for packaging of the glycosylated pro-α factor into COPII vesicles, did not improve gelatin secretion in the multicopy strain. Previously, H. polymorpha was reported to hydroxylate proline residues in gelatinous sequences. In contrast, we were unable to detect hydroxyprolines in the secreted Hu3–His8. Also, we failed to identify a gene encoding prolyl-4-hydroxylase in the H. polymorpha genome.
Design fabrication and characterization of an in-plane AFM probe with ultra-sharp silicon nitride tip
Scanning rates of the atomic force microscope (AFM) could be significantly \ud
increased by integrating the force sensing probe with microelectromechanical systems (MEMS). We present a micromachining method for batch fabrication of in-plane AFM probes that consist of an ultra-sharp silicon nitride tip on a single \ud
crystal silicon cantilever. Our fabrication method is fully compatible with the silicon-on-insulator (SOI) micromachining allowing a straightforward monolithic integration of the AFM probes with high-aspect-ratio monocrystalline silicon MEMS. Scanning probes with a sharp tip having diameter of less then 10 nm are successfully realized and tested in a commercial AFM set-up demonstrating \ud
feasibility and the large innovation potential of this method
Bear in mind: the role of personal background in semantic animal fluency – The SMART-MR study
ObjectivesSemantic fluency is a prominent neuropsychological task, typically administered within the category ‘animals’. With the increasing development of novel item-level metrics of semantic fluency, a concern around the validity of item-level analyses could be that personal background factors (e.g., hobbies like birdwatching or fishing) may disproportionally influence performance. We analyzed animal fluency performance at the item level and investigated the prevalence of individuals with abundant knowledge in specific classes of animals (e.g., birds, fish, insects) and the relationship of such knowledge with personal background factors and other cognitive tasks (episodic memory and executive functioning).MethodParticipants included 736 Dutch middle-aged to older adults from the SMART-MR cohort (mean age 58 ± 9.4 years, 18% women). Individuals were asked to name as many animals as possible for 2 min. Number of people with abundant animal class knowledge was calculated for the ability to recall a series of minimum ≥5 and up to ≥15 animals within a specific class with at most one interruption by an animal from another class. Subsequent analyses to investigate relationships of abundant class knowledge with sociodemographic characteristics (t-tests and chi-square tests) and cognitive performance (linear regressions) were performed for a cut-off of ≥10 animals within a specific class (90th percentile), with a sensitivity analysis for ≥7 animals (67th percentile).ResultsA total of 416 (56.2%) participants recalled a series of ≥5 animals from a specific class, 245 (33.3%) participants recalled ≥7, 78 (10.6%) participants recalled ≥10, and 8 (1.1%) participants recalled ≥15. Those who recalled a series of at least 10 animals within a class were older, more often men, and more often retired than those who did not. Moreover, they had a higher total score on animal fluency, letter fluency (i.e., executive functioning), and episodic memory tasks compared to those who did not.DiscussionOur results suggest that the benefit of abundant animal class knowledge gained by personal background does not disproportionally influence animal fluency performance as individuals with such knowledge also performed better on other cognitive tasks unrelated to abundant knowledge of animal classes
Resonant Photon-Assisted Tunneling Through a Double Quantum Dot: An Electron Pump From Spatial Rabi Oscillations
The time average of the fully nonlinear current through a double quantum dot,
subject to an arbitrary combination of ac and dc voltages, is calculated
exactly using the Keldysh nonequilibrium Green function technique. When driven
on resonance, the system functions as an efficient electron pump due to Rabi
oscillation between the dots. The pumping current is maximum when the coupling
to the leads equals the Rabi frequency.Comment: 6 pages, REVTEX 3.0, 3 postscript figure
Parity Fluctuations Between Coulomb Blockaded Superconducting Islands
We find that if two superconducting islands of different number parity are
linked by a tunnel junction the unpaired electron in the odd island has a
tendency to tunnel into the even island. This process leads to fluctuations in
time of the number parity of each island, giving rise to a random telegraph
noise spectrum with a characteristic frequency that has an unusual temperature
dependence. This new phenomenon should be observable in a Cooper-pair pump and
similar single-electron tunneling devices.Comment: 4 pages, self-unpacking uuencoded gz-compressed postscript file with
3 figures included; also available at
http://www.lassp.cornell.edu/janko/publications.htm
Many Body Theory of Charge Transfer in Hyperthermal Atomic Scattering
We use the Newns-Anderson Hamiltonian to describe many-body electronic
processes that occur when hyperthermal alkali atoms scatter off metallic
surfaces. Following Brako and Newns, we expand the electronic many-body
wavefunction in the number of particle-hole pairs (we keep terms up to and
including a single particle-hole pair). We extend their earlier work by
including level crossings, excited neutrals and negative ions. The full set of
equations of motion are integrated numerically, without further approximations,
to obtain the many-body amplitudes as a function of time. The velocity and
work-function dependence of final state quantities such as the distribution of
ion charges and excited atomic occupancies are compared with experiment. In
particular, experiments that scatter alkali ions off clean Cu(001) surfaces in
the energy range 5 to 1600 eV constrain the theory quantitatively. The
neutralization probability of Na ions shows a minimum at intermediate
velocity in agreement with the theory. This behavior contrasts with that of
K, which shows ... (7 figures, not included. Figure requests:
[email protected])Comment: 43 pages, plain TeX, BUP-JBM-
Asymptotic tunneling conductance in Luttinger liquids
Conductance through weak constrictions in Luttinger liquids is shown to
vanish with frequency as , where
is a dimensionless parameter characterizing the Luttinger liquid phase, and
and are nonuniversal constants. The first term arises from the ^^
Coulomb blockade' effect and dominates for , whereas the second
results from eliminating high-energy modes and dominates for .Comment: Latex file + one appended postcript figur
N-representability and stationarity in time-dependent density functional theory
To construct an N-representable time-dependent density-functional theory, a
generalization to the time domain of the Levy-Lieb (LL) constrained search
algorithm is required. That the action is only stationary in the Dirac-Frenkel
variational principle eliminates the possibility of basing the search on the
action itself. Instead, we use the norm of the partial functional derivative of
the action in the Hilbert space of the wave functions in place of the energy of
the LL search. The electron densities entering the formalism are
-representable, and the resulting universal action functional has a unique
stationary point in the density at that corresponding to the solution of the
Schr\"{o}dinger equation. The original Runge-Gross (RG) formulation is subsumed
within the new formalism. Concerns in the literature about the meaning of the
functional derivatives and the internal consistency of the RG formulation are
allayed by clarifying the nature of the functional derivatives entering the
formalism.Comment: 9 pages, 0 figures, Phys. Rev. A accepted. Introduction was expanded,
subsections reorganized, appendix and new references adde
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