3,046 research outputs found
Noble metal penetrating cortical stimulating electrode array: preliminary results
Journal ArticleElectrical stimulation of the visual cortex causes subjects to see spots of light (phosphenes) in their visual fields. We have developed arrays of penetrating electrodes which may from the basis of a visual prosthesis centered around electrical stimulation of the visual cortex. These arrays have been constructed of inert materials, and have been implanted into cats to test array insertability and biocompatibility. Tests to determine electrode wire insertion force have also been performed. Preliminary acute histological results have shown little cortical damage due to the implants
Phase diagram for a Bose-Einstein condensate moving in an optical lattice
The stability of superfluid currents in a system of ultracold bosons was
studied using a moving optical lattice. Superfluid currents in a very weak
lattice become unstable when their momentum exceeds 0.5 recoil momentum.
Superfluidity vanishes already for zero momentum as the lattice deep reaches
the Mott insulator(MI) phase transition. We study the phase diagram for the
disappearance of superfluidity as a function of momentum and lattice depth
between these two limits. Our phase boundary extrapolates to the critical
lattice depth for the superfluid-to-MI transition with 2% precision. When a
one-dimensional gas was loaded into a moving optical lattice a sudden
broadening of the transition between stable and unstable phases was observed.Comment: 4 figure
Continuous and Pulsed Quantum Zeno Effect
Continuous and pulsed quantum Zeno effects were observed using a Rb
Bose-Einstein condensate(BEC). Oscillations between two ground hyperfine states
of a magnetically trapped condensate, externally driven at a transition rate
, were suppressed by destructively measuring the population in one of
the states with resonant light. The suppression of the transition rate in the
two level system was quantified for pulsed measurements with a time interval
between pulses and continuous measurements with a scattering rate
. We observe that the continuous measurements exhibit the same
suppression in the transition rate as the pulsed measurements when
, in agreement with the predicted value of 4.
Increasing the measurement rate suppressed the transition rate down to
.Comment: 5 pages, 4 figure
Imaging the Mott Insulator Shells using Atomic Clock Shifts
Microwave spectroscopy was used to probe the superfluid-Mott Insulator
transition of a Bose-Einstein condensate in a 3D optical lattice. Using density
dependent transition frequency shifts we were able to spectroscopically
distinguish sites with different occupation numbers, and to directly image
sites with occupation number n=1 to n=5 revealing the shell structure of the
Mott Insulator phase. We use this spectroscopy to determine the onsite
interaction and lifetime for individual shells
Atom trapping with a thin magnetic film
We have created a Rb Bose-Einstein condensate in a magnetic trapping
potential produced by a hard disk platter written with a periodic pattern. Cold
atoms were loaded from an optical dipole trap and then cooled to BEC on the
surface with radiofrequency evaporation. Fragmentation of the atomic cloud due
to imperfections in the magnetic structure was observed at distances closer
than 40 m from the surface. Attempts to use the disk as an atom mirror
showed dispersive effects after reflection.Comment: 4 pages, 5 figure
The Stability of Double White Dwarf Binaries Undergoing Direct Impact Accretion
We present numerical simulations of dynamically unstable mass transfer in a
double white dwarf binary with initial mass ratio, q = 0.4. The binary
components are approximated as polytropes of index n = 3/2 and the initially
synchronously rotating, semi-detached equilibrium binary is evolved
hydrodynamically with the gravitational potential being computed through the
solution of Poisson's equation. Upon initiating deep contact in our baseline
simulation, the mass transfer rate grows by more than an order of magnitude
over approximately ten orbits, as would be expected for dynamically unstable
mass transfer. However, the mass transfer rate then reaches a peak value, the
binary expands and the mass transfer event subsides. The binary must therefore
have crossed the critical mass ratio for stability against dynamical mass
transfer. Despite the initial loss of orbital angular momentum into the spin of
the accreting star, we find that the accretor's spin saturates and angular
momentum is returned to the orbit more efficiently than has been previously
suspected for binaries in the direct impact accretion mode. To explore this
surprising result, we directly measure the critical mass ratio for stability by
imposing artificial angular momentum loss at various rates to drive the binary
to an equilibrium mass transfer rate. For one of these driven evolutions, we
attain equilibrium mass transfer and deduce that effectively q_crit has evolved
to approximately 2/3. Despite the absence of a fully developed disk, tidal
interactions appear effective in returning excess spin angular momentum to the
orbit.Comment: 27 pages, 6 figures. Please see
http://www.phys.lsu.edu/faculty/tohline/astroph/mftd07/ for animations and
full resolution figures. Accepted for publication in the Astrophysical
Journa
Viral etiology of hospitalized acute lower respiratory infections in children under 5 years of age – a systematic review and meta-analysis
Aim To estimate the proportional contribution of influenza
viruses (IV), parainfluenza viruses (PIV), adenoviruses (AV),
and coronaviruses (CV) to the burden of severe acute lower
respiratory infections (ALRI).
Methods The review of the literature followed PRISMA
guidelines. We included studies of hospitalized children
aged 0-4 years with confirmed ALRI published between
1995 and 2011. A total of 51 studies were included in the
final review, comprising 56 091 hospitalized ALRI episodes.
Results IV was detected in 3.0% (2.2%-4.0%) of all hospitalized
ALRI cases, PIV in 2.7% (1.9%-3.7%), and AV in 5.8%
(3.4%-9.1%). CV are technically difficult to culture, and they
were detected in 4.8% of all hospitalized ALRI patients in
one study. When respiratory syncytial virus (RSV) and less
common viruses were included, at least one virus was detected
in 50.4% (40.0%-60.7%) of all hospitalized severe
ALRI episodes. Moreover, 21.9% (17.7%-26.4%) of these viral
ALRI were mixed, including more than one viral pathogen.
Among all severe ALRI with confirmed viral etiology,
IV accounted for 7.0% (5.5%-8.7%), PIV for 5.8% (4.1%-7.7%),
and AV for 8.8% (5.3%-13.0%). CV was found in 10.6% of
virus-positive pneumonia patients in one study.
Conclusions This article provides the most comprehensive
analysis of the contribution of four viral causes to
severe ALRI to date. Our results can be used in further
cost-effectiveness analyses of vaccine development and
implementation for a number of respiratory viruses
Genetic study of congenital bile-duct dilatation identifies de novo and inherited variants in functionally related genes
Background:
Congenital dilatation of the bile-duct (CDD) is a rare, mostly sporadic, disorder that results in bile retention with severe associated complications. CDD affects mainly Asians. To our knowledge, no genetic study has ever been conducted.
Methods:
We aim to identify genetic risk factors by a “trio-based” exome-sequencing approach, whereby 31 CDD probands and their unaffected parents were exome-sequenced. Seven-hundred controls from the local population were used to detect gene-sets significantly enriched with rare variants in CDD patients.
Results:
Twenty-one predicted damaging de novo variants (DNVs; 4 protein truncating and 17 missense) were identified in several evolutionarily constrained genes (p < 0.01). Six genes carrying DNVs were associated with human developmental disorders involving epithelial, connective or bone morphologies (PXDN, RTEL1, ANKRD11, MAP2K1, CYLD, ACAN) and four linked with cholangio- and hepatocellular carcinomas (PIK3CA, TLN1 CYLD, MAP2K1). Importantly, CDD patients have an excess of DNVs in cancer-related genes (p < 0.025). Thirteen genes were recurrently mutated at different sites, forming compound heterozygotes or functionally related complexes within patients.
Conclusions:
Our data supports a strong genetic basis for CDD and show that CDD is not only genetically heterogeneous but also non-monogenic, requiring mutations in more than one genes for the disease to develop. The data is consistent with the rarity and sporadic presentation of CDD
Quantitative trait loci controlling agronomic and biochemical traits in \u3ci\u3eCannabis sativa\u3c/i\u3e
Understanding the genetic basis of complex traits is a fundamental goal of evolutionary genetics. Yet, the genetics controlling complex traits in many important species such as hemp (Cannabis sativa) remain poorly investigated. Because hemp’s change in legal status with the 2014 and 2018 U.S. Federal Farm Bills, interest in the genetics controlling its numerous agriculturally important traits has steadily increased. To better understand the genetics of agriculturally important traits in hemp, we developed an F2 population by crossing two phenotypically distinct hemp cultivars (Carmagnola and USO31). Using whole-genome sequencing, we mapped quantitative trait loci (QTL) associated with variation in numerous agronomic and biochemical traits. A total of 69 loci associated with agronomic (34) and biochemical (35) trait variation were identified. We found that most QTL co-localized, suggesting that the phenotypic distinctions between Carmagnola and USO31 are largely controlled by a small number of loci. We identified TINY and olivetol synthase as candidate genes underlying colocalized QTL clusters for agronomic and biochemical traits, respectively. We functionally validated the olivetol synthase candidate by expressing the alleles in yeast. Gas chromatography-mass spectrometry assays of extracts from these yeast colonies suggest that the USO31 olivetol synthase is functionally less active and potentially explains why USO31 produces lower cannabinoids compared to Carmagnola. Overall, our results help modernize the genomic understanding of complex traits in hemp
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Biases in the perceived timing of perisaccadic perceptual and motor events
Subjects typically experience the temporal interval immediately following a saccade as longer than a comparable control interval. One explanation of this effect is that the brain antedates the perceptual onset of a saccade target to around the time of saccade initiation. This could explain the apparent continuity of visual perception across eye movements. Thisantedating account was tested in three experiments in which subjects made saccades of differing extents and then judged either the duration or the temporal order of key events. Postsaccadic stimuli underwent subjective temporal lengthening and had early perceived onsets. A temporally advanced awareness of saccade completion was also found, independently of antedating effects. These results provide convergent evidence supporting antedating and differentiating it from other temporal biases
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