407 research outputs found
Experimental Constraints on the Pairing State of the Cuprate Superconductors: an Emerging Consensus
We present a critical discussion of recent experimental probes of the pairing
state of the high temperature superconductors, focusing primarily, but not
exclusively, on \Yba, where the best data currently exist. Penetration depth
measurements near \Tc\ give no indication of an extra transition, indicating
that the pairing state is a one-dimensional representation of the crystal
symmetry. Penetration depth measurements at low temperatures provide strong
evidence for a change in sign of the gap function over the Fermi surface.
Quantum mechanical phase interference experiments generally confirm this and in
addition show that the nodal positions are consistent with a \dx2y2\ pairing
state. This pairing state is consistent with photoemission measurements of the
gap function, Raman scattering, the effect on \Tc\ of impurities, and many
other data (reviewed by two of us previously) which indicate the presence of
low lying excitations in the superconducting state. We also discuss evidence
that apparently does not fit in with a \dx2y2\ pairing state, and we describe
possible alternative scenarios.Comment: 81 pages, macro package (modified version of uiucmac.tex) included in
submission, figures NOT available (but not essential
Optical nanolithography using a scanning near-field probe with an integrated light source
An ultracompact near-field optical probe is described that is based on a single, integrated assembly consisting of a gallium nitride (GaN) light-emitting diode (LED), a microlens, and a cantilever assembly containing a hollow pyramidal probe with a subwavelength aperture at its apex. The LED emits ultraviolet light and may be used as a light source for near-field photolithographic exposure. Using this simple device compatible with many commercial atomic force microscope systems, it is possible to form nanostructures in photoresist with a resolution of 35 nm, corresponding to λ/10. © 2008 American Institute of Physics
A classical statistical model for distributions of escape events in swept-bias Josephson junctions
We have developed a model for experiments in which the bias current applied
to a Josephson junction is slowly increased from zero until the junction
switches from its superconducting zero-voltage state, and the bias value at
which this occurs is recorded. Repetition of such measurements yields
experimentally determined probability distributions for the bias current at the
moment of escape. Our model provides an explanation for available data on the
temperature dependence of these escape peaks. When applied microwaves are
included we observe an additional peak in the escape distributions and
demonstrate that this peak matches experimental observations. The results
suggest that experimentally observed switching distributions, with and without
applied microwaves, can be understood within classical mechanics and may not
exhibit phenomena that demand an exclusively quantum mechanical interpretation.Comment: Eight pages, eight figure
Growth and Nutrient Uptake by Soybean Plants in Nutrient Solutions of Graded Concentrations
Design Development Test and Evaluation (DDT and E) Considerations for Safe and Reliable Human Rated Spacecraft Systems
A team directed by the NASA Engineering and Safety Center (NESC) collected methodologies for how best to develop safe and reliable human rated systems and how to identify the drivers that provide the basis for assessing safety and reliability. The team also identified techniques, methodologies, and best practices to assure that NASA can develop safe and reliable human rated systems. The results are drawn from a wide variety of resources, from experts involved with the space program since its inception to the best-practices espoused in contemporary engineering doctrine. This report focuses on safety and reliability considerations and does not duplicate or update any existing references. Neither does it intend to replace existing standards and policy
Protracted Reproduction in Sunfish: the Temporal Dimension in Fish Recruitment Revisited
Understanding how life histories influence reproductive success under uncertain conditions is necessary to predict population dynamics. For many organisms, protracted reproduction may increase expected offspring recruitment in variable environments, requiring that temporal patterns of reproduction be considered when developing management or conservation strategies. We explored the interrelationships among birth date, production of embryos on nests, survival of larvae to the open-water stage, and survival of juveniles through the first fall and winter of life for bluegill and pumpkinseed sunfish (Lepomis macrochirus and L. gibbosus) in Lake Opinicon, Ontario, during May 1998 through May 1999. Age-0 sunfish were sampled with nesting surveys for embryos, surface tows for free-swimming larvae, and seining/trawling for juveniles. Age of juveniles (days post swim-up) was quantified using otoliths. The abundance of embryos on nests and the density of open-water larvae were unrelated across all dates and sites. Although 40% of larvae had appeared in the open water by 12 June, most juveniles sampled in the fall were produced after that time, suggesting that high mortality of early produced larvae occurred. Larval survival to the juvenile stage was generally unrelated to the abundance of edible zooplankton taxa during swim-up from nests. Larval survival was often highest at temperatures \u3e23.5°C. Fall length of age-0 sunfish increased with increasing age. Both age-specific length and mean lengths shifted positively between October 1998 and May 1999, suggesting that growth of all individuals and perhaps selective mortality of small juveniles occurred. Although early reproduction may increase sizes reached by fall and thereby improve overwinter survival, early hatched larvae are subject to variable environmental factors that may reduce survival. Late-hatched larvae may reach relatively smaller sizes by fall, but have higher survival probabilities during this life stage. Protracted reproduction appears to be a response to variable environmental factors influencing growth and survival across multiple life stages. As such, all reproducing adults, rather than those perceived to produce offspring during typically favorable times, must be protected from exploitation or other human-induced perturbations
Anomalous Thermostat and Intraband Discrete Breathers
We investigate the dynamics of a macroscopic system which consists of an
anharmonic subsystem embedded in an arbitrary harmonic lattice, including
quenched disorder. Elimination of the harmonic degrees of freedom leads to a
nonlinear Langevin equation for the anharmonic coordinates. For zero
temperature, we prove that the support of the Fourier transform of the memory
kernel and of the time averaged velocity-velocity correlations functions of the
anharmonic system can not overlap. As a consequence, the asymptotic solutions
can be constant, periodic,quasiperiodic or almost periodic, and possibly weakly
chaotic. For a sinusoidal trajectory with frequency we find that the
energy transferred to the harmonic system up to time is proportional
to . If equals one of the phonon frequencies ,
it is . We prove that there is a full measure set such that for
in this set it is , i.e. there is no energy dissipation.
Under certain conditions there exists a zero measure set such that for (0 \leq
\alpha < 1)(1 <\alpha \leq 2)\Omega\Omega\mathcal{C}(k)\Omega\in\mathcal{C}(k)t$.Comment: Physica D in prin
Sulfur Deficiency of Sugar Beets
Sulfur deficiency of sugar beets (Beta Vulgaris L.) was first reported in
1941 by Tolman and Stoker (10) in beets grown for seed in the Willamette Valley
of Oregon. The symptoms were described as retarded growth, yellow color,
breakdown of leaf tissue, lack of flowering, and increased susceptibility to
disease. Since then sulfur deficiency of this crop has been reported in California
(11) and Sweden (5). Sulfur deficiency of sugar beets decreases seed
yield (10) as well as the yield and percent of sugar in the roots (5). A review
of the sulfur requirements of sugar, fiber and oil crops has been published (8)
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