55,224 research outputs found
Z_2 Topological Insulators in Ultracold Atomic Gases
We describe how optical dressing can be used to generate bandstructures for
ultracold atoms with non-trivial Z_2 topological order. Time reversal symmetry
is preserved by simple conditions on the optical fields. We first show how to
construct optical lattices that give rise to Z_2 topological insulators in two
dimensions. We then describe a general method for the construction of
three-dimensional Z_2 topological insulators. A central feature of our approach
is a new way to understand Z_2 topological insulators starting from the
nearly-free electron limit
Exact Groundstates of Rotating Bose Gases close to a Feshbach Resonance
We study the groundstates of rotating Bose gases when interactions are
affected by a nearby Feshbach resonance. We show that exact groundstates at
high angular momentum can be found analytically for a general and realistic
model for the resonant interactions. We identify parameter regimes where the
exact groundstates are exotic fractional quantum Hall states, the excitations
of which obey non-abelian exchange statistics.Comment: 4 page
Underwater space suit pressure control regulator
A device is reported for regulating the pneumatic pressure in a ventilated space suit relative to the pressure imposed on the suit when being worn by a person underwater to simulate space environment for testing and experimentation. A box unit located on the chest area of the suit comprises connections for suit air supply and return lines and carries a regulator valve that stabilizes the air pressure differential between the inside and outside of the suit. The valve and suit pressure is controlled by the suit occupant and the valve includes a mechanism for quickly dumping the suit pressure in case of emergency. Pressure monitoring and relief devices are also included in the box unit
Operation of a haynes alloy no. 25 forced circulation loop to study the effects of hydrogen in a simulated sunflower system
Haynes alloy forced circulation mercury loop for studying hydrogen effects in working fluid of Rankine cycle Sunflower solar power syste
Seasonal dynamics of soil respiration and nitrogen mineralization in chronically warmed and fertilized soils
Although numerous studies have examined the individual effects of increased temperatures and N deposition on soil biogeochemical cycling, few have considered how these disturbances interact to impact soil C and N dynamics. Likewise, many have not assessed season-specific responses to warming and N inputs despite seasonal variability in soil processes. We studied interactions among season, warming, and N additions on soil respiration and N mineralization at the Soil Warming × Nitrogen Addition Study at the Harvard Forest. Of particular interest were wintertime fluxes of C and N typically excluded from investigations of soils and global change. Soils were warmed to 5°C above ambient, and N was applied at a rate of 5 g m−2 y−1. Soil respiration and N mineralization were sampled over two years between 2007 and 2009 and showed strong seasonal patterns that mirrored changes in soil temperature. Winter fluxes of C and N contributed between 2 and 17% to the total annual flux. Net N mineralization increased in response to the experimental manipulations across all seasons, and was 8% higher in fertilized plots and 83% higher in warmed plots over the duration of the study. Soil respiration showed a more season-specific response. Nitrogen additions enhanced soil respiration by 14%, but this increase was significant only in summer and fall. Likewise, warming increased soil respiration by 44% over the whole study period, but the effect of warming was most pronounced in spring and fall. The only interaction between warming × N additions took place in autumn, when N availability likely diminished the positive effect of warming on soil respiration. Our results suggest that winter measurements of C and N are necessary to accurately describe winter biogeochemical processes. In addition, season-specific responses to the experimental treatments suggest that some components of the belowground community may be more susceptible to warming and N additions than others. Seasonal changes in the abiotic environment may have also interacted with the experimental manipulations to evoke biogeochemical responses at certain times of year
Spin 1 inversion: a Majorana tensor force for deuteron alpha scattering
We demonstrate, for the first time, successful S-matrix to potential
inversion for spin one projectiles with non-diagonal yielding a
interaction. The method is a generalization of the
iterative-perturbative, IP, method. We present a test case indicating the
degree of uniqueness of the potential. The method is adapted, using established
procedures, into direct observable to potential inversion, fitting ,
, , and for d + alpha scattering over
a range of energies near 10 MeV. The interaction which we find is
very different from that proposed elsewhere, both real and imaginary parts
being very different for odd and even parity channels.Comment: 7 pages Revtex, 4 ps figure
Rescue of splicing-mediated intron loss maximizes expression in lentiviral vectors containing the human ubiquitin C promoter.
Lentiviral vectors almost universally use heterologous internal promoters to express transgenes. One of the most commonly used promoter fragments is a 1.2-kb sequence from the human ubiquitin C (UBC) gene, encompassing the promoter, some enhancers, first exon, first intron and a small part of the second exon of UBC. Because splicing can occur after transcription of the vector genome during vector production, we investigated whether the intron within the UBC promoter fragment is faithfully transmitted to target cells. Genetic analysis revealed that more than 80% of proviral forms lack the intron of the UBC promoter. The human elongation factor 1 alpha (EEF1A1) promoter fragment intron was not lost during lentiviral packaging, and this difference between the UBC and EEF1A1 promoter introns was conferred by promoter exonic sequences. UBC promoter intron loss caused a 4-fold reduction in transgene expression. Movement of the expression cassette to the opposite strand prevented intron loss and restored full expression. This increase in expression was mostly due to non-classical enhancer activity within the intron, and movement of putative intronic enhancer sequences to multiple promoter-proximal sites actually repressed expression. Reversal of the UBC promoter also prevented intron loss and restored full expression in bidirectional lentiviral vectors
Topological Kondo effect with Majorana fermions
The Kondo effect is a striking consequence of the coupling of itinerant
electrons to a quantum spin with degenerate energy levels. While degeneracies
are commonly thought to arise from symmetries or fine-tuning of parameters, the
recent emergence of Majorana fermions has brought to the fore an entirely
different possibility: a "topological degeneracy" which arises from the
nonlocal character of Majorana fermions. Here we show that nonlocal quantum
spins formed from these degrees of freedom give rise to a novel "topological
Kondo effect". This leads to a robust non-Fermi liquid behavior, known to be
difficult to achieve in the conventional Kondo context. Focusing on mesoscopic
superconductor devices, we predict several unique transport signatures of this
Kondo effect, which would demonstrate the non-local quantum dynamics of
Majorana fermions, and validate their potential for topological quantum
computation
Local majority dynamics on preferential attachment graphs
Suppose in a graph vertices can be either red or blue. Let be odd. At
each time step, each vertex in polls random neighbours and takes
the majority colour. If it doesn't have neighbours, it simply polls all of
them, or all less one if the degree of is even. We study this protocol on
the preferential attachment model of Albert and Barab\'asi, which gives rise to
a degree distribution that has roughly power-law ,
as well as generalisations which give exponents larger than . The setting is
as follows: Initially each vertex of is red independently with probability
, and is otherwise blue. We show that if is
sufficiently biased away from , then with high probability,
consensus is reached on the initial global majority within
steps. Here is the number of vertices and is the minimum of
and (or if is even), being the number of edges each new
vertex adds in the preferential attachment generative process. Additionally,
our analysis reduces the required bias of for graphs of a given degree
sequence studied by the first author (which includes, e.g., random regular
graphs)
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