115 research outputs found
Nodal quasiparticle meltdown in ultra-high resolution pump-probe angle-resolved photoemission
High- cuprate superconductors are characterized by a strong
momentum-dependent anisotropy between the low energy excitations along the
Brillouin zone diagonal (nodal direction) and those along the Brillouin zone
face (antinodal direction). Most obvious is the d-wave superconducting gap,
with the largest magnitude found in the antinodal direction and no gap in the
nodal direction. Additionally, while antinodal quasiparticle excitations appear
only below , superconductivity is thought to be indifferent to nodal
excitations as they are regarded robust and insensitive to . Here we
reveal an unexpected tie between nodal quasiparticles and superconductivity
using high resolution time- and angle-resolved photoemission on optimally doped
BiSrCaCuO. We observe a suppression of the nodal
quasiparticle spectral weight following pump laser excitation and measure its
recovery dynamics. This suppression is dramatically enhanced in the
superconducting state. These results reduce the nodal-antinodal dichotomy and
challenge the conventional view of nodal excitation neutrality in
superconductivity.Comment: 7 pages, 3 figure. To be published in Nature Physic
Комплекс машин для производства лука по ресурсосберегающим технологиям
Relevance. The most common and most mastered method of growing onions, used in the middle zone of the Russian Federation, as well as in the northern part of European countries, is the cultivation of turnip onions from onion. It is believed that this method provides 75% of the production of the entire onion harvest. Due to the sharp increase in the prices of energy carriers, fertilizers, pesticides and agricultural machinery, the production of sharp varieties of onions, grown in the crop, has become unprofitable, and marketable products have lost competitiveness due to high costs. Significant changes in the reduction of labor costs can be achieved by improving the technology and technical means for the production of onions, creating conditions for their work. The effectiveness of designs for sowing seeds of onions, onion sets and planting onions-uterus is determined by the uniform distribution of the bulbs by area of nutrition, depth and their embedding.Results. The material presented in the work is devoted to the analysis of designs and some results of studies of a complex of machines for the production of onions developed in the Penza GAU. Актуальность. Самым распространенным и наиболее освоенным способом выращивания лука, применяемым в средней полосе Российской Федерации, а также в северной части европейских стран, является выращивание лука-репки из севка. Считается, что этот способ обеспечивает 75% продукции всего урожая лука. Из-за резкого повышения цен на энергоносители, удобрения, пестициды и сельхозмашины производство репчатого лука острых сортов, выращиваемого в севочной культуре, стало нерентабельным, а товарная продукция потеряла конкурентоспособность из-за высокой себестоимости. Существенных изменений в сокращении затрат труда можно достичь путем совершенствования технологии и технических средств для производства лука, создания условий для их работы. Эффективность конструкций для посева семян лука, лука-севка и посадки лука-матки определяются равномерностью распределения луковиц по площади питания, глубине и их заделки.Результаты. Представленный в работе материал, в основном, посвящен анализу конструкций и некоторых результатов исследований комплекса машин, для производства лука, разработанных в Пензенском ГАУ.
Superconducting Fluctuation and Pseudogap in Disordered Short Coherence Length Superconductor
We investigate the role of disorder on the superconducting (SC) fluctuation
in short coherence length d-wave superconductors. The particular intetest is
focused on the disorder-induced microscopic inhomogeneity of SC fluctuation and
its effect on the pseudogap phenomena. We formulate the self-consistent 1-loop
order theory for the SC fluctuation in inhomogeneous systems and analyze the
disordered -- model. The SC correlation function, electronic DOS and
the critical temperature are estimated. The SC fluctuation is localized like a
nanoscale granular structure when the coherence length is short, namely the
transition temperature is high. This is contrasted to the long coherence length
superconductors where the order parameter is almost uniform in the microscopic
scale. In the former case, the SC fluctuation is enhanced by the disorder in
contrast to the Abrikosov-Gorkov theory. These results are consistent with the
STM, NMR and transport measurements in high- cuprates and illuminate
the essential role of the microscopic inhomogeneity. We calculate the spacial
dependence of DOS around the single impurity and discuss the consistency with
the NMR measurements
Scanning tunneling spectroscopy of high-temperature superconductors
Tunneling spectroscopy played a central role in the experimental verification
of the microscopic theory of superconductivity in the classical
superconductors. Initial attempts to apply the same approach to
high-temperature superconductors were hampered by various problems related to
the complexity of these materials. The use of scanning tunneling
microscopy/spectroscopy (STM/STS) on these compounds allowed to overcome the
main difficulties. This success motivated a rapidly growing scientific
community to apply this technique to high-temperature superconductors. This
paper reviews the experimental highlights obtained over the last decade. We
first recall the crucial efforts to gain control over the technique and to
obtain reproducible results. We then discuss how the STM/STS technique has
contributed to the study of some of the most unusual and remarkable properties
of high-temperature superconductors: the unusual large gap values and the
absence of scaling with the critical temperature; the pseudogap and its
relation to superconductivity; the unprecedented small size of the vortex cores
and its influence on vortex matter; the unexpected electronic properties of the
vortex cores; the combination of atomic resolution and spectroscopy leading to
the observation of periodic local density of states modulations in the
superconducting and pseudogap states, and in the vortex cores.Comment: To appear in RMP; 65 pages, 62 figure
How to detect fluctuating order in the high-temperature superconductors
We discuss fluctuating order in a quantum disordered phase proximate to a
quantum critical point, with particular emphasis on fluctuating stripe order.
Optimal strategies for extracting information concerning such local order from
experiments are derived with emphasis on neutron scattering and scanning
tunneling microscopy. These ideas are tested by application to two model
systems - the exactly solvable one dimensional electron gas with an impurity,
and a weakly-interacting 2D electron gas. We extensively review experiments on
the cuprate high-temperature superconductors which can be analyzed using these
strategies. We adduce evidence that stripe correlations are widespread in the
cuprates. Finally, we compare and contrast the advantages of two limiting
perspectives on the high-temperature superconductor: weak coupling, in which
correlation effects are treated as a perturbation on an underlying metallic
(although renormalized) Fermi liquid state, and strong coupling, in which the
magnetism is associated with well defined localized spins, and stripes are
viewed as a form of micro-phase separation. We present quantitative indicators
that the latter view better accounts for the observed stripe phenomena in the
cuprates.Comment: 43 pages, 11 figures, submitted to RMP; extensively revised and
greatly improved text; one new figure, one new section, two new appendices
and more reference
A Stochastic Model for Microtubule Motors Describes the In Vivo Cytoplasmic Transport of Human Adenovirus
Cytoplasmic transport of organelles, nucleic acids and proteins on microtubules is usually bidirectional with dynein and kinesin motors mediating the delivery of cargoes in the cytoplasm. Here we combine live cell microscopy, single virus tracking and trajectory segmentation to systematically identify the parameters of a stochastic computational model of cargo transport by molecular motors on microtubules. The model parameters are identified using an evolutionary optimization algorithm to minimize the Kullback-Leibler divergence between the in silico and the in vivo run length and velocity distributions of the viruses on microtubules. The present stochastic model suggests that bidirectional transport of human adenoviruses can be explained without explicit motor coordination. The model enables the prediction of the number of motors active on the viral cargo during microtubule-dependent motions as well as the number of motor binding sites, with the protein hexon as the binding site for the motors
Particle-Hole Symmetry Breaking in the Pseudogap State of Bi2201
In conventional superconductors, a gap exists in the energy absorption
spectrum only below the transition temperature (Tc), corresponding to the
energy price to pay for breaking a Cooper pair of electrons. In high-Tc cuprate
superconductors above Tc, an energy gap called the pseudogap exists, and is
controversially attributed either to pre-formed superconducting pairs, which
would exhibit particle-hole symmetry, or to competing phases which would
typically break it. Scanning tunnelling microscopy (STM) studies suggest that
the pseudogap stems from lattice translational symmetry breaking and is
associated with a different characteristic spectrum for adding or removing
electrons (particle-hole asymmetry). However, no signature of either spatial or
energy symmetry breaking of the pseudogap has previously been observed by
angle-resolved photoemission spectroscopy (ARPES). Here we report ARPES data
from Bi2201 which reveals both particle-hole symmetry breaking and dramatic
spectral broadening indicative of spatial symmetry breaking without long range
order, upon crossing through T* into the pseudogap state. This symmetry
breaking is found in the dominant region of the momentum space for the
pseudogap, around the so-called anti-node near the Brillouin zone boundary. Our
finding supports the STM conclusion that the pseudogap state is a
broken-symmetry state that is distinct from homogeneous superconductivity.Comment: Nature Physics advance online publication, 04/04/2010
(doi:10.1038/nphys1632) Author's version of the paper
Transposon based tagging: IRAP, REMAP, and iPBS
Retrotransposons are a major component of virtually all eukaryotic genomes, which makes them useful as molecular markers. Various molecular marker systems have been developed that exploit the ubiquitous nature of these genetic elements and their property of stable integration into dispersed chromosomal loci that are polymorphic within species. To detect polymorphisms for retrotransposon insertions, marker systems generally rely on PCR amplification between the retrotransposon termini and some component of flanking genomic DNA. The main methods of IRAP, REMAP, RBIP, and SSAP all detect the polymorphic sites at which the retrotransposon DNA is integrated into the genome. Marker systems exploiting these methods can be easily developed and are inexpensively deployed in the absence of extensive genome sequence data. Here, we describe protocols for the IRAP, REMAP and iPBS techniques, including methods for PCR amplification with a single primer or with two primers, agarose gel electrophoresis of the product using optimal electrophoresis buffers, we also describe iPBS techniques for the rapid isolation of retrotransposon termini and full-length elements.Peer reviewe
Pigmentation and spectral absorbance in the deep-sea arctic amphipods Eurythenes gryllus and Anonyx sp.
Complex machines for the production of onions on resource-saving technologies
Relevance. The most common and most mastered method of growing onions, used in the middle zone of the Russian Federation, as well as in the northern part of European countries, is the cultivation of turnip onions from onion. It is believed that this method provides 75% of the production of the entire onion harvest. Due to the sharp increase in the prices of energy carriers, fertilizers, pesticides and agricultural machinery, the production of sharp varieties of onions, grown in the crop, has become unprofitable, and marketable products have lost competitiveness due to high costs. Significant changes in the reduction of labor costs can be achieved by improving the technology and technical means for the production of onions, creating conditions for their work. The effectiveness of designs for sowing seeds of onions, onion sets and planting onions-uterus is determined by the uniform distribution of the bulbs by area of nutrition, depth and their embedding.Results. The material presented in the work is devoted to the analysis of designs and some results of studies of a complex of machines for the production of onions developed in the Penza GAU
- …