983 research outputs found
Multiple Andreev Reflection and Giant Excess Noise in Diffusive Superconductor/Normal-Metal/Superconductor Junctions
We have studied superconductor/normal metal/superconductor (SNS) junctions
consisting of short Au or Cu wires between Nb or Al banks. The Nb based
junctions display inherent electron heating effects induced by the high thermal
resistance of the NS boundaries. The Al based junctions show in addition
subharmonic gap structures in the differential conductance dI/dV and a
pronounced peak in the excess noise at very low voltages V. We suggest that the
noise peak is caused by fluctuations of the supercurrent at the onset of
Josephson coupling between the superconducting banks. At intermediate
temperatures where the supercurrent is suppressed a noise contribution ~1/V
remains, which may be interpreted as shot noise originating from large multiple
charges.Comment: 7 pages, 7 figures, extended versio
Delay-dependent amplification of a probe pulse via stimulated Rayleigh scattering
Stimulated Rayleigh scattering of pump and probe light pulses of close
carrier frequencies is considered. A nonzero time delay between the two pulses
is shown to give rise to amplification of the delayed (probe) pulse accompanied
by attenuation of the pump, both on resonance and off resonance. In either
case, phase-matching effects are shown to provide a sufficiently large gain,
which can exceed significantly direct one-photon-absorption losses
Two-dimensional array of diffusive SNS junctions with high-transparent interfaces
We report the first comparative study of the properties of two-dimensional
arrays and single superconducting film - normal wire - superconducting film
(SNS) junctions. The NS interfaces of our SNS junctions are really high
transparent, for superconducting and normal metal parts are made from the same
material (superconducting polycrystalline PtSi film). We have found that the
two-dimensional arrays reveal some novel features: (i) the significant
narrowing of the zero bias anomaly (ZBA) in comparison with single SNS
junctions, (ii) the appearance of subharmonic energy gap structure (SGS), with
up to n=16 (eV=\pm 2\Delta/n), with some numbers being lost, (iii) the
transition from 2D logarithmic weak localization behavior to metallic one. Our
experiments show that coherent phenomena governed by the Andreev reflection are
not only maintained over the macroscopic scale but manifest novel pronounced
effects as well. The behavior of the ZBA and SGS in 2D array of SNS junctions
strongly suggests that the development of a novel theoretical approach is
needed which would self-consistently take into account the distribution of the
currents, the potentials, and the superconducting order parameter.Comment: RevTex, 5 pages, 5 figure
Impaired photoprotection in Phaeodactylum tricornutum KEA3 mutants reveals the proton regulatory circuit of diatoms light acclimation
International audienceDiatoms are successful phytoplankton clades able to acclimate to changing environmental conditions, including e.g. variable light intensity. Diatoms are outstanding at dissipating light energy exceeding the maximum photosynthetic electron transfer (PET) capacity via the nonphotochemical quenching (NPQ) process. While the molecular effectors of NPQ as well as the involvement of the proton motive force (PMF) in its regulation are known, the regulators of the PET/PMF relationship remain unidentified in diatoms. We generated mutants of the H /K antiporter KEA3 in the model diatom . Loss of KEA3 activity affects the PET/PMF coupling and NPQ responses at the onset of illumination, during transients and in steady-state conditions. Thus, this antiporter is a main regulator of the PET/PMF coupling. Consistent with this conclusion, a parsimonious model including only two free components, KEA3 and the diadinoxanthin de-epoxidase, describes most of the feedback loops between PET and NPQ. This simple regulatory system allows for efficient responses to fast (minutes) or slow (e.g. diel) changes in light environment, thanks to the presence of a regulatory calcium ion (Ca )-binding domain in KEA3 modulating its activity. This circuit is likely tuned by the NPQ-effector proteins, LHCXs, providing diatoms with the required flexibility to thrive in different ocean provinces
InAs nanowire hot-electron Josephson transistor
At a superconductor (S)-normal metal (N) junction pairing correlations can
"leak-out" into the N region. This proximity effect [1, 2] modifies the system
transport properties and can lead to supercurrent flow in SNS junctions [3].
Recent experimental works showed the potential of semiconductor nanowires (NWs)
as building blocks for nanometre-scale devices [4-7], also in combination with
superconducting elements [8-12]. Here, we demonstrate an InAs NW Josephson
transistor where supercurrent is controlled by hot-quasiparticle injection from
normal-metal electrodes. Operational principle is based on the modification of
NW electron-energy distribution [13-20] that can yield reduced dissipation and
high-switching speed. We shall argue that exploitation of this principle with
heterostructured semiconductor NWs opens the way to a host of
out-of-equilibrium hybrid-nanodevice concepts [7, 21].Comment: 6 pages, 6 color figure
An Integrated Modeling Approach for Predicting Process Maps of Residual Stress and Distortion in a Laser Weld: A Combined CFD–FE Methodology
Laser welding has become an important joining methodology within a number of industries for the structural joining of metallic parts. It offers a high power density welding capability which is desirable for deep weld sections, but is equally suited to performing thinner welded joints with sensible amendments to key process variables. However, as with any welding process, the introduction of severe thermal gradients at the weld line will inevitably lead to process-induced residual stress formation and distortions. Finite element (FE) predictions for weld simulation have been made within academia and industrial research for a number of years, although given the fluid nature of the molten weld pool, FE methodologies have limited capabilities. An improvement upon this established method would be to incorporate a computational fluid dynamics (CFD) model formulation prior to the FE model, to predict the weld pool shape and fluid flow, such that details can be fed into FE from CFD as a starting condition. The key outputs of residual stress and distortions predicted by the FE model can then be monitored against the process variables input to the model. Further, a link between the thermal results and the microstructural properties is of interest. Therefore, an empirical relationship between lamellar spacing and the cooling rate was developed and used to make predictions about the lamellar spacing for welds of different process parameters. Processing parameter combinations that lead to regions of high residual stress formation and high distortion have been determined, and the impact of processing parameters upon the predicted lamellar spacing has been presented
Marker-assisted introgression of the salinity tolerance locus Saltol in temperate japonica rice
Background Rice is one of the most salt sensitive crops at seedling, early vegetative and reproductive stages. Varieties
with salinity tolerance at seedling stage promote an efficient growth at early stages in salt affected soils, leading
to healthy vegetative growth that protects crop yield. Saltol major QTL confers capacity to young rice plants growing
under salt condition by maintaining a low Na+/
K+ molar ratio in the shoots.
Results Marker-assisted backcross (MABC) procedure was adopted to transfer Saltol locus conferring salt tolerance
at seedling stage from donor indica IR64-Saltol to two temperate japonica varieties, Vialone Nano and Onice. Forward
and background selections were accomplished using polymorphic KASP markers and a final evaluation of genetic
background recovery of the selected lines was conducted using 15,580 SNP markers obtained from Genotyping by
Sequencing. Three MABC generations followed by two selfing, allowed the identification of introgression lines achieving
a recovery of the recurrent parent (RP) genome up to 100% (based on KASP markers) or 98.97% (based on GBS).
Lines with highest RP genome recovery (RPGR) were evaluated for agronomical-phenological traits in field under nonsalinized
conditions. VN1, VN4, O1 lines were selected considering the agronomic evaluations and the RPGR% results
as the most interesting for commercial exploitation. A physiological characterization was conducted by evaluating
salt tolerance under hydroponic conditions. The selected lines showed lower standard evaluation system (SES) scores:
62% of VN4, and 57% of O1 plants reaching SES 3 or SES 5 respectively, while only 40% of Vialone Nano and 25% of
Onice plants recorded scores from 3 to 5, respectively. VN1, VN4 and O1 showed a reduced electrolyte leakage values,
and limited negative effects on relative water content and shoot/root fresh weight ratio.
Conclusion The Saltol locus was successfully transferred to two elite varieties by MABC in a time frame of three years.
The application of background selection until BC3F3
allowed the selection of lines with a RPGR up to 98.97%. Physiological
evaluations for the selected lines indicate an improved salinity tolerance at seedling stage. The results supported
the effectiveness of the Saltol locus in temperate japonica and of the MABC procedure for recovering of the RP
favorable traits
Algebraic Cryptanalysis of Curry and Flurry using Correlated Messages
In \cite{BPW}, Buchmann, Pyshkin and Weinmann have described two families of
Feistel and SPN block ciphers called Flurry and Curry
respectively. These two families of ciphers are fully parametrizable and have
a sound design strategy against basic statistical attacks; i.e. linear and
differential attacks. The encryption process can be easily described by a set
of algebraic equations. These ciphers are then targets of choices for
algebraic attacks. In particular, the key recovery problem has been reduced to
changing the order of a Groebner basis \cite{BPW,BPWext}. This attack -
although being more efficient than linear and differential attacks - remains
quite limited. The purpose of this paper is to overcome this limitation by
using a small number of suitably chosen pairs of message/ciphertext for
improving algebraic attacks. It turns out that this approach permits to go one
step further in the (algebraic) cryptanalysis of Flurry and
\textbf{Curry}. To explain the behavior of our attack, we have established an
interesting connection between algebraic attacks and high order differential
cryptanalysis \cite{Lai}. From extensive experiments, we estimate that our
approach, that we can call an ``algebraic-high order
differential cryptanalysis, is polynomial when the Sbox is a power function.
As a proof of concept, we have been able to break Flurry -- up to
rounds -- in few hours
- …