8,593 research outputs found
Dissipation in Mesoscopic Superconductors with Ac Magnetic Fields
The response of mesoscopic superconductors to an ac magnetic field is
investigated both experimentally and with numerical simulations. We study small
square samples with dimensions of the order of the penetration depth. We obtain
the ac susceptibitity at microwave frequencies as a
function of the dc magnetic field . We find that the dissipation, given
by , has a non monotonous behavior in mesoscopic samples. In the
numerical simulations we obtain that the dissipation increases before the
penetration of vortices and then it decreases abruptly after vortices have
entered the sample. This is verified experimentally, where we find that
has strong oscillations as a function of in small squares of
Pb.Comment: 4 pages, 2 figure
Experimental investigation of dynamical invariants in bipartite entanglement
The non-conservation of entanglement, when two or more particles interact,
sets it apart from other dynamical quantities like energy and momentum. It does
not allow the interpretation of the subtle dynamics of entanglement as a flow
of this quantity between the constituents of the system. Here we show that
adding a third party to a two-particle system may lead to a conservation law
that relates the quantities characterizing the bipartite entanglement between
each of the parties and the other two. We provide an experimental demonstration
of this idea using entangled photons, and generalize it to N-partite GHZ
states
Periastron shift in Weyl class spacetimes
The periastron position advance for geodesic motion in axially symmetric
solutions of the Einstein field equations belonging to the Weyl class of vacuum
solutions is investigated. Explicit examples corresponding to either static
solutions (single Chazy-Curzon, Schwarzschild and a pair of them), or
stationary solution (single rotating Chazy-Curzon and Kerr black hole) are
discussed. The results are then applied to the case of S2-SgrA binary
system of which the periastron position advance will be soon measured with a
great accuracy.Comment: To appear on General Relativity and Gravitation, vol. 37, 200
Neutrino induced threshold production of two pions and N^*(1440) electroweak form factors
We study the threshold production of two pions induced by neutrinos in
nucleon targets. The contribution of nucleon, pion and contact terms are
calculated using a chiral Lagrangian. The contribution of the Roper resonance,
neglected in earlier studies, has also been taken into account. The numerical
results for the cross sections are presented and compared with the available
experimental data. It has been found that in the two pion channels with
and in the final state, the contribution of the
is quite important and could be used to determine the
electroweak transition form factors if experimental data with better statistics
become available in the future.Comment: This version corrects a mistake on the helicity amplitudes sign.
Additional comments on resonance-background relative sign are added. Other
minor corrections. Matches published version. 17 pages, 7 figure
A synbio approach for selection of highly expressed gene variants in Gram-positive bacteria
Abstract Background The market for recombinant proteins is on the rise, and Gram-positive strains are widely exploited for this purpose. Bacillus subtilis is a profitable host for protein production thanks to its ability to secrete large amounts of proteins, and Lactococcus lactis is an attractive production organism with a long history in food fermentation. Results We have developed a synbio approach for increasing gene expression in two Gram-positive bacteria. First of all, the gene of interest was coupled to an antibiotic resistance gene to create a growth-based selection system. We then randomised the translation initiation region (TIR) preceding the gene of interest and selected clones that produced high protein titres, as judged by their ability to survive on high concentrations of antibiotic. Using this approach, we were able to significantly increase production of two industrially relevant proteins; sialidase in B. subtilis and tyrosine ammonia lyase in L. lactis. Conclusion Gram-positive bacteria are widely used to produce industrial enzymes. High titres are necessary to make the production economically feasible. The synbio approach presented here is a simple and inexpensive way to increase protein titres, which can be carried out in any laboratory within a few days. It could also be implemented as a tool for applications beyond TIR libraries, such as screening of synthetic, homologous or domain-shuffled genes
The Bulgeless Seyfert/LINER Galaxy NGC 3367: Disk, Bar, Lopsidedness and Environment
NGC3367 is a nearby isolated active galaxy that shows a radio jet, a strong
bar and evidence of lopsidedness. We present a quantitative analysis of the
stellar and gaseous structure of the galaxy disk and a search for evidence of
recent interaction based on new UBVRI Halpha and JHK images and on archival
Halpha Fabry-Perot and HI VLA data. From a coupled 1D/2D GALFIT bulge/bar/disk
decomposition an (B/D ~ 0.07-0.1) exponential pseudobulge is inferred in all
the observed bands. A NIR estimate of the bar strength = 0.44
places NGC 3367 bar among the strongest ones. The asymmetry properties were
studied using (1) optical and NIR CAS indexes (2) the stellar (NIR) and gaseous
(Halpha, HI) A_1 Fourier mode amplitudes and (3) the HI integrated profile and
HI mean intensity distribution. While the average stellar component shows
asymmetry values close to the average found in the Local Universe for isolated
galaxies, the young stellar component and gas values are largely decoupled
showing significantly larger A_1 mode amplitudes suggesting that the gas has
been recently perturbed. Our search for (1) faint stellar structures in the
outer regions (up to u_R ~ 26 mag arcsec^{-2}), (2) (Halpha) star-forming
satellite galaxies and (3) regions with different colors (stellar populations)
along the disk all failed. Such an absence is interpreted using recent
numerical simulations to constrain a tidal event with an LMC like galaxy to
some dynamical times in the past or to a current very low mass, gas rich
accretion. We conclude that a cold accretion mode (gas and small/dark galaxies)
may be responsible of the nuclear activity and peculiar (young stars and gas)
morphology regardless of the highly isolated environment. Black hole growth in
bulgeless galaxies may be triggered by cosmic smooth mass accretion.Comment: 27 pages, 12 figures, accepted for publication in The Astronomical
Journa
- …