7,844 research outputs found
High pressure transport study of non-Fermi liquid behaviour in U2Pt2In and U3Ni3Sn4
The strongly correlated metals U2Pt2In and U3Ni3Sn4 show pronounced non-Fermi
liquid (NFL) phenomena at ambient pressure. Here we review single-crystal
electrical resistivity measurements under pressure (p <= 1.8 GPa) conducted to
investigate the stability of the NFL phase. For tetragonal U2Pt2In (I||a) we
observe a rapid recovery of the Fermi-liquid T^2-term with pressure. The
Fermi-liquid temperature varies as T_FL ~ p-p_c, where p_c= 0 is a critical
pressure. The analysis within the magnetotransport theory of Rosch provides
evidence for the location of U2Pt2In at a zero pressure antiferromagnetic
quantum critical point (QCP). In the case of cubic U3Ni3Sn4 we find T_FL ~
(p-p_c)^1/2. The analysis provides evidence for an antiferromagnetic QCP in
U3Ni3Sn4 at a negative pressure p_c= -0.04+-0.04 GPa.Comment: 6 pages (4 figures); to appear in Proc. of Int. Conf. PPHMF-IV (20-25
Oct. 2001, Santa Fe
Towards F1 Hybrid Seed Potato Breeding
Compared to other major food crops, progress in potato yield as the result of breeding efforts is very slow. Genetic gains cannot be fixed in potato due to obligatory out-breeding. Overcoming inbreeding depression using diploid self-compatible clones should enable to replace the current method of out-breeding and clonal propagation into an F1 hybrid system with true seeds. This idea is not new, but has long been considered unrealistic. Severe inbreeding depression and self-incompatibility in diploid germplasm have hitherto blocked the development of inbred lines. Back-crossing with a homozygous progenitor with the Sli gene which inhibits gametophytic self-incompatibility gave self-compatible offspring from elite material from our diploid breeding programme. We demonstrate that homozygous fixation of donor alleles is possible, with simultaneous improvement of tuber shape and tuber size grading of the recipient inbred line. These results provide proof of principle for F1 hybrid potato breeding. The technical and economic perspectives are unprecedented as these will enable the development of new products with combinations of useful traits for all stakeholders in the potato chain. In addition, the hybrid’s seeds are produced by crossings, rendering the production and voluminous transport of potato seed tubers redundant as it can be replaced by direct sowing or the use of healthy mini-tubers, raised in greenhouses
Inflation with a graceful exit and entrance driven by Hawking radiation
We present a model for cosmological inflation which has a natural "turn on"
and a natural "turn off" mechanism. In our model inflation is driven by the
Hawking-like radiation that occurs in Friedman-Robertson-Walker (FRW)
space-time. This Hawking-like radiation results in an effective negative
pressure "fluid" which leads to a rapid period of expansion in the very early
Universe. As the Universe expands the FRW Hawking temperature decreases and the
inflationary expansion turns off and makes a natural transition to the power
law expansion of a radiation dominated universe. The "turn on" mechanism is
more speculative, but is based on the common hypothesis that in a quantum
theory of gravity at very high temperatures/high densities Hawking radiation
will stop. Applying this speculation to the very early Universe implies that
the Hawking-like radiation of the FRW space-time will be turned off and
therefore the inflation driven by this radiation will turn off.Comment: 19 pages, 2 figures revtex, matches PRD published versio
Microwave-induced excess quasiparticles in superconducting resonators measured through correlated conductivity fluctuations
We have measured the number of quasiparticles and their lifetime in aluminium
superconducting microwave resonators. The number of excess quasiparticles below
160 mK decreases from 72 to 17 m with a 6 dB decrease of the
microwave power. The quasiparticle lifetime increases accordingly from 1.4 to
3.5 ms. These properties of the superconductor were measured through the
spectrum of correlated fluctuations in the quasiparticle system and condensate
of the superconductor, which show up in the resonator amplitude and phase
respectively. Because uncorrelated noise sources vanish, fluctuations in the
superconductor can be studied with a sensitivity close to the vacuum noise
On Kink-Dynamics of Stacked-Josephson Junctions
Dynamics of a fluxon in a stack of coupled long Josephson junctions is studied numericallv. Based on the numerical simulations, we show that the dependence of the propagation velocity c on the external bias current γ is determined by the ratio of the critical currents of thc two junctions J
Bounding the Hubble flow in terms of the w parameter
The last decade has seen increasing efforts to circumscribe and bound the
cosmological Hubble flow in terms of model-independent constraints on the
cosmological fluid - such as, for instance, the classical energy conditions of
general relativity. Quite a bit can certainly be said in this regard, but much
more refined bounds can be obtained by placing more precise constraints (either
theoretical or observational) on the cosmological fluid. In particular, the use
of the w-parameter (w=p/rho) has become increasingly common as a surrogate for
trying to say something about the cosmological equation of state. Herein we
explore the extent to which a constraint on the w-parameter leads to useful and
nontrivial constraints on the Hubble flow, in terms of constraints on density
rho(z), Hubble parameter H(z), density parameter Omega(z), cosmological
distances d(z), and lookback time T(z). In contrast to other partial results in
the literature, we carry out the computations for arbitrary values of the space
curvature k in [-1,0,+1], equivalently for arbitrary Omega_0 <= 1.Comment: 15 page
Fluctuations in the electron system of a superconductor exposed to a photon flux
We report on fluctuations in the electron system, Cooper pairs and
quasiparticles, of a superconducting aluminium film. The superconductor is
exposed to pair-breaking photons (1.54 THz), which are coupled through an
antenna. The change in the complex conductivity of the superconductor upon a
change in the quasiparticle number is read out by a microwave resonator. A
large range in radiation power can be chosen by carefully filtering the
radiation from a blackbody source. We identify two regimes. At high radiation
power, fluctuations in the electron system caused by the random arrival rate of
the photons are resolved, giving a straightforward measure of the optical
efficiency (48%). At low radiation power fluctuations are dominated by excess
quasiparticles, the number of which is measured through their recombination
lifetime
Higher dimensional thin-shell wormholes in Einstein-Yang-Mills-Gauss-Bonnet gravity
We present thin-shell wormhole solutions in Einstein-Yang-Mills-Gauss-Bonnet
(EYMGB) theory in higher dimensions d\geq5. Exact black hole solutions are
employed for this purpose where the radius of thin-shell lies outside the event
horizon. For some reasons the cases d=5 and d>5 are treated separately. The
surface energy-momentum of the thin-shell creates surface pressures to resist
against collapse and rendering stable wormholes possible. We test the stability
of the wormholes against spherical perturbations through a linear
energy-pressure relation and plot stability regions. Apart from this restricted
stability we investigate the possibility of normal (i.e. non-exotic) matter
which satisfies the energy conditions. For negative values of the Gauss-Bonnet
(GB) parameter we obtain such physical wormholes.Comment: 9 pages, 6 figures. Dedicated to the memory of Rev. Ibrahim Eken
(1927-2010) of Turke
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