3,302 research outputs found
Quantum Phase Tomography of a Strongly Driven Qubit
The interference between repeated Landau-Zener transitions in a qubit swept
through an avoided level crossing results in Stueckelberg oscillations in qubit
magnetization. The resulting oscillatory patterns are a hallmark of the
coherent strongly-driven regime in qubits, quantum dots and other two-level
systems. The two-dimensional Fourier transforms of these patterns are found to
exhibit a family of one-dimensional curves in Fourier space, in agreement with
recent observations in a superconducting qubit. We interpret these images in
terms of time evolution of the quantum phase of qubit state and show that they
can be used to probe dephasing mechanisms in the qubit.Comment: 5 pgs, 4 fg
Anomalously Weak Dynamical Friction in Halos
A bar rotating in a pressure-supported halo generally loses angular momentum
and slows down due to dynamical friction. Valenzuela & Klypin report a
counter-example of a bar that rotates in a dense halo with little friction for
several Gyr, and argue that their result invalidates the claim by Debattista &
Sellwood that fast bars in real galaxies require a low halo density. We show
that it is possible for friction to cease for a while should the pattern speed
of the bar fluctuate upward. The reduced friction is due to an anomalous
gradient in the phase-space density of particles at the principal resonance
created by the earlier evolution. The result obtained by Valenzuela & Klypin is
probably an artifact of their adaptive mesh refinement method, but anyway could
not persist in a real galaxy. The conclusion by Debattista & Sellwood still
stands.Comment: To appear in "Island Universes - Structure and Evolution of Disk
Galaxies" ed. R. S. de Jong, 8 pages, 4 figures, .cls and .sty files include
Optical Response for the d-density wave model
We have calculated the optical conductivity and the Raman response for the
d-density wave model, proposed as a possible explanation for the pseudogap seen
in high Tc cuprates. The total optical spectral weight remains approximately
constant on opening of the pseudogap for fixed temperature. This occurs because
there is a transfer of weight from the Drude peak to interband transitions
across the pseudogap. The interband peak in the optical conductivity is
prominent but becomes progressively reduced with increasing temperature, with
impurity scattering, which distributes it over a larger energy range, and with
ineleastic scattering which can also shift its position, making it difficult to
have a direct determination of the value of the pseudogap. Corresponding
structure is seen in the optical scattering rate, but not necessarily at the
same energies as in the conductivity.Comment: 14 pages, 15 figures, final revised version published in PR
Collective motional resonances and instabilities of an electron cloud stored in a Penning trap
We have experimentally investigated the behavior of an electron cloud confined in a Penning trap at weak superimposed magnetic fields. Exciting the motional frequencies of the electrons by an external drive field we found the axial mode split into two components which were identified as center-of-mass and individual electron oscillations. When the trapping potential was varied, rapid electron loss appeared at numerous values of the applied voltage. They are determined by the relation n z ω z + n m ω m =ω c . ω z ,ω m ,ω c are the axial, magnetron, and cyclotron frequency of the trapped electrons, respectively. The reason for this loss is attributed to higher order contributions to the ideal quadrupole trapping potential
Advection Drives Nitrate Past the Microphytobenthos in Intertidal Sands, Fueling Deeper Denitrification
Nitrification rates are low in permeable intertidal sand flats such that the water column is the primary source of nitrate to the sediment. During tidal inundation, nitrate is supplied to the pore space by advection rather than diffusion, relieving the microorganisms that reside in the sand from nitrate limitation and supporting higher denitrification rates than those observed under diffusive transport. Sand flats are also home to an abundant community of benthic photosynthetic microorganisms, the microphytobenthos (MPB). Diatoms are an important component of the MPB that can take up and store high concentrations of nitrate within their cells, giving them the potential to alter nitrate availability in the surrounding porewater. We tested whether nitrate uptake by the MPB near the sediment surface decreases its availability to denitrifiers along deeper porewater flow paths. In laboratory experiments, we used NOx (nitrate + nitrite) microbiosensors to confirm that, in the spring, net NOx consumption in the zone of MPB photosynthetic activity was stimulated by light. The maximum potential denitrification rate, measured at high spatial resolution using microsensors with acetylene and nitrate added, occurred below 1.4 cm, much deeper than light-induced NOx uptake (0.13 cm). Therefore, the shallower MPB had the potential to decrease NOx supply to the deeper sediments and limit denitrification. However, when applying a realistic downward advective flow to sediment from our study site, NOx always reached the depths of maximum denitrification potential, regardless of light availability or season. We conclude that during tidal inundation porewater advection overwhelms any influence of shallow NOx uptake by the MPB and drives water column NOx to the depths of maximum denitrification potential
Controllable chirality-induced geometrical Hall effect in a frustrated highly-correlated metal
A current of electrons traversing a landscape of localized spins possessing
non-coplanar magnetic order gains a geometrical (Berry) phase which can lead to
a Hall voltage independent of the spin-orbit coupling within the material--a
geometrical Hall effect. We show that the highly-correlated metal UCu5
possesses an unusually large controllable geometrical Hall effect at T<1.2K due
to its frustration-induced magnetic order. The magnitude of the Hall response
exceeds 20% of the \nu=1 quantum Hall effect per atomic layer, which translates
into an effective magnetic field of several hundred Tesla acting on the
electrons. The existence of such a large geometric Hall response in UCu5 opens
a new field of inquiry into the importance of the role of frustration in
highly-correlated electron materials.Comment: article and supplemental informatio
Comparative Genomics Analysis of a New Exiguobacterium Strain from Salar de Huasco Reveals a Repertoire of Stress-Related Genes and Arsenic Resistance
Indexación: Web of Science; Scopus.The Atacama Desert hosts diverse ecosystems including salt flats and shallow Andean lakes. Several heavy metals are found in the Atacama Desert, and microorganisms growing in this environment show varying levels of resistance/tolerance to copper, tellurium, and arsenic, among others. Herein, we report the genome sequence and comparative genomic analysis of a new Exiguobacterium strain, sp. SH31, isolated from an altiplanic shallow athalassohaline lake. Exiguobacterium sp. SH31 belongs to the phylogenetic Group II and its closest relative is Exiguobacterium sp. S17, isolated from the Argentinian Altiplano (95% average nucleotide identity). Strain SH31 encodes a wide repertoire of proteins required for cadmium, copper, mercury, tellurium, chromium, and arsenic resistance. Of the 34 Exiguobacterium genomes that were inspected, only isolates SH31 and S17 encode the arsenic efflux pump Acr3. Strain SH31 was able to grow in up to 10 mM arsenite and 100 mM arsenate, indicating that it is arsenic resistant. Further, expression of the ars operon and acr3 was strongly induced in response to both toxics, suggesting that the arsenic efflux pump Acr3 mediates arsenic resistance in Exiguobacterium sp. SH31.http://journal.frontiersin.org/article/10.3389/fmicb.2017.00456/ful
Evaluating the capacity of human gut microorganisms to colonize the zebrafish larvae (Danio rerio)
Indexación: Scopus.In this study we evaluated if zebrafish larvae can be colonized by human gut microorganisms. We tested two strategies: (1) through transplantation of a human fecal microbiota and (2) by successively transplanting aerotolerant anaerobic microorganisms, similar to the colonization in the human intestine during early life. We used conventionally raised zebrafish larvae harboring their own aerobic microbiota to improve the colonization of anaerobic microorganisms. The results showed with the fecal transplant, that some members of the human gut microbiota were transferred to larvae. Bacillus, Roseburia, Prevotella, Oscillospira, one unclassified genus of the family Ruminococcaceae and Enterobacteriaceae were detected in 3 days post fertilization (dpf) larvae; however only Bacillus persisted to 7 dpf. Successive inoculation of Lactobacillus, Bifidobacterium and Clostridioides did not improve their colonization, compared to individual inoculation of each bacterial species. Interestingly, the sporulating bacteria Bacillus clausii and Clostridioides difficile were the most persistent microorganisms. Their endospores persisted at least 5 days after inoculating 3 dpf larvae. However, when 5 dpf larvae were inoculated, the proportion of vegetative cells in larvae increased, revealing proliferation of the inoculated bacteria and better colonization of the host. In conclusion, these results suggest that it is feasible to colonize zebrafish larvae with some human bacteria, such as C. difficile and Bacillus and open an interesting area to study interactions between these microorganisms and the host. © 2018 Valenzuela, Caruffo, Herrera, Medina, Coronado, Feijóo, Muñoz, Garrido, Troncoso, Figueroa, Toro, Reyes-Jara, Magne and Navarrete.https://www.frontiersin.org/articles/10.3389/fmicb.2018.01032/ful
Calculation of minor hysteresis loops under metastable to stable transformations in vortex matter
We present a model in which metastable supercooled phase and stable
equilibrium phase of vortex matter coexist in different regions of a sample.
Minor hysteresis loops are calculated with the simple assumption of the two
phases of vortex matter having field-independent critical current densities. We
use our earlier published ideas that the free energy barrier separating the
metastable and stable phases reduces as the magnetic induction moves farther
from the first order phase transition line, and that metastable to stable
transformations occur in local regions of the sample when the local energy
dissipation exceeds a critical value. Previously reported anomalous features in
minor hysteresis loops are reproduced, and calculated field profiles are
presented.Comment: 9pages, 7 figure
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