4,832 research outputs found
Structural Responses of Quasi-2D Colloid Fluids to Excitations Elicited by Nonequilibrium Perturbations
We investigate the response of a dense monodisperse quasi-two-dimensional
(q2D) colloid suspension when a particle is dragged by a constant velocity
optical trap. Consistent with microrheological studies of other geometries, the
perturbation induces a leading density wave and trailing wake, and we use
Stokesian Dynamics (SD) simulations to parse direct colloid-colloid and
hydrodynamic interactions. We go on to analyze the underlying individual
particle-particle collisions in the experimental images. The displacements of
particles form chains reminiscent of stress propagation in sheared granular
materials. From these data, we can reconstruct steady-state dipolar flow
patterns that were predicted for dilute suspensions and previously observed in
granular analogs to our system. The decay of this field differs, however, from
point Stokeslet calculations, indicating that the finite size of the colloids
is important. Moreover, there is a pronounced angular dependence that
corresponds to the surrounding colloid structure, which evolves in response to
the perturbation. Put together, our results show that the response of the
complex fluid is highly anisotropic owing to the fact that the effects of the
perturbation propagate through the structured medium via chains of
colloid-colloid collisions
Quantum Phase Diffusion in a Small Underdamped Josephson Junction
Quantum phase diffusion in a small underdamped Nb/AlO/Nb junction (
0.4 m) is demonstrated in a wide temperature range of 25-140 mK where
macroscopic quantum tunneling (MQT) is the dominant escape mechanism. We
propose a two-step transition model to describe the switching process in which
the escape rate out of the potential well and the transition rate from phase
diffusion to the running state are considered. The transition rate extracted
from the experimental switching current distribution follows the predicted
Arrhenius law in the thermal regime but is greatly enhanced when MQT becomes
dominant.Comment: 4 pages, 4 figures, 1 tabl
The DNA Helicase Activity of BLM Is Necessary for the Correction of the Genomic Instability of Bloom Syndrome Cells
Bloom syndrome (BS) is a rare autosomal recessive disorder characterized by growth deficiency, immunodeficiency, genomic instability, and the early development of cancers of many types. BLM, the protein encoded by BLM, the gene mutated in BS, is localized in nuclear foci and absent from BS cells. BLM encodes a DNA helicase, and proteins from three missense alleles lack displacement activity. BLM transfected into BS cells reduces the frequency of sister chromatid exchanges and restores BLM in the nucleus. Missense alleles fail to reduce the sister chromatid exchanges in transfected BS cells or restore the normal nuclear pattern. BLM complements a phenotype of a Saccharomyces cerevisiae sgs1 top3 strain, and the missense alleles do not. This work demonstrates the importance of the enzymatic activity of BLM for its function and nuclear localization pattern
Classification of a supersolid: Trial wavefunctions, Symmetry breakings and Excitation spectra
A state of matter is characterized by its symmetry breaking and elementary
excitations.
A supersolid is a state which breaks both translational symmetry and internal
symmetry.
Here, we review some past and recent works in phenomenological
Ginsburg-Landau theories, ground state trial wavefunctions and microscopic
numerical calculations. We also write down a new effective supersolid
Hamiltonian on a lattice.
The eigenstates of the Hamiltonian contains both the ground state
wavefunction and all the excited states (supersolidon) wavefunctions. We
contrast various kinds of supersolids in both continuous systems and on
lattices, both condensed matter and cold atom systems. We provide additional
new insights in studying their order parameters, symmetry breaking patterns,
the excitation spectra and detection methods.Comment: REVTEX4, 19 pages, 3 figure
Laboratory and Field Assessments of Prey-Mediated Effects of Transgenic Bt Rice on Ummeliata insecticeps (Araneida: Linyphiidae)
One major concern regarding the release of Bt rice is its potential impact through tritrophic interactions on nontarget arthropods, especially natural enemies. We studied the effects of two Bt transgenic rice varieties, TT9- 3 and KMD1, expressing Cry1Ab/Cry1Ac and Cry1Ab, respectively, on a predatory ground spider [Ummeliata insecticeps (Bösenberg et Strand)] supplied with Bt rice-fed brown planthopper [Nilaparvata lugens (Stål)] nymphs. Although immunoassays confirmed that U. insecticeps ingested Bt insecticidal protein when supplied with Bt rice-fed N. lugens, no negative effects were found on its survival and development. Furthermore, the fecundity of U. insecticeps fed prey reared on Bt rice was not significantly different from that of those fed prey reared on non-Bt rice. A 3-yr field trial indicated that Bt rice did not significantly affect the population density of U. insecticeps in comparison with non-Bt rice. In conclusion, the Bt rice lines tested in this study had no adverse effects on the survival, developmental time, or fecundity of U. insecticeps in the laboratory or on population dynamics in the fiel
Impacts of Six Bt Rice Lines on Nontarget Rice Feeding Thrips Under Laboratory and Field Conditions
Nontarget impacts of six transgenic Bt rice lines (expressing the Cry1Ab or Cry1Ab/Cry1Ac protein) on the thrips, Stenchaetothrips biformis (Bagnall), attacking the rice seedling and tillering stages, were evaluated under laboratory and field conditions. Laboratory results showed relatively longer larval, pupal development and preoviposition durations of S. biformis. Although it had a shorter oviposition period, female adult longevity and less total laid eggs were found when fed on some tested Bt rice in comparison to non-Bt controls. S. biformis population dynamics in Bt and non-Bt plots were monitored using the plastic bag and beat plate methods. In the field, the temporal patterns of S. biformis population changes were similar between tested Bt rice lines and their respective control; however, the total number of S. biformis individuals collected from the Bt plots were significantly less or the same, varying from variety to variety, compared with those from the non-Bt plots. ELISA results showed that the Bt insecticidal protein could be transferred from Bt rice to the thrips, and the concentrations of the protein in rice leaves and thrips were not significantly correlated with some important biological parameters of the thrip. In addition, the potential effects of Bt rice on the abundance of S. biformis candidate predators are also discussed. In conclusion, our results show that the six Bt rice lines assessed may be less preferable host plants to S. biformis at the individual and population levels in comparison to the non-Bt rice plant
Quantum and classical resonant escapes of a strongly-driven Josephson junction
The properties of phase escape in a dc SQUID at 25 mK, which is well below
quantum-to-classical crossover temperature , in the presence of strong
resonant ac driving have been investigated. The SQUID contains two
Nb/Al-AlO/Nb tunnel junctions with Josephson inductance much larger than
the loop inductance so it can be viewed as a single junction having adjustable
critical current. We find that with increasing microwave power and at
certain frequencies and /2, the single primary peak in the
switching current distribution, \textrm{which is the result of macroscopic
quantum tunneling of the phase across the junction}, first shifts toward lower
bias current and then a resonant peak develops. These results are explained
by quantum resonant phase escape involving single and two photons with
microwave-suppressed potential barrier. As further increases, the primary
peak gradually disappears and the resonant peak grows into a single one while
shifting further to lower . At certain , a second resonant peak appears,
which can locate at very low depending on the value of . Analysis
based on the classical equation of motion shows that such resonant peak can
arise from the resonant escape of the phase particle with extremely large
oscillation amplitude resulting from bifurcation of the nonlinear system. Our
experimental result and theoretical analysis demonstrate that at ,
escape of the phase particle could be dominated by classical process, such as
dynamical bifurcation of nonlinear systems under strong ac driving.Comment: 10 pages, 9 figures, 1 tabl
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