150 research outputs found
Excitations of attractive 1-D bosons: Binding vs. fermionization
The stationary states of few bosons in a one-dimensional harmonic trap are
investigated throughout the crossover from weak to strongly attractive
interactions. For sufficient attraction, three different classes of states
emerge: (i) N-body bound states, (ii) bound states of smaller fragments, and
(iii) gas-like states that fermionize, that is, map to ideal fermions in the
limit of infinite attraction. The two-body correlations and momentum spectra
characteristic of the three classes are discussed, and the results are
illustrated using the soluble two-particle model.Comment: 7 pages, 5 figure
Binding between two-component bosons in one dimension
We investigate the ground state of one-dimensional few-atom Bose-Bose
mixtures under harmonic confinement throughout the crossover from weak to
strong inter-species attraction. The calculations are based on the numerically
exact multi-configurational time-dependent Hartree method. For repulsive
components we detail the condition for the formation of a molecular
Tonks-Girardeau gas in the regime of intermediate inter-species interactions,
and the formation of a molecular condensate for stronger coupling. Beyond a
critical inter-species attraction, the system collapses to an overall bound
state. Different pathways emerge for unequal particle numbers and intra-species
interactions. In particular, for mixtures with one attractive component, this
species can be viewed as an effective potential dimple in the trap center for
the other, repulsive component.Comment: 10 pages, 10 figure
Hypothermia protects human neurons
Background and Aims: Hypothermia provides neuroprotection after cardiac arrest, hypoxic-ischemic encephalopathy, and in animal models of ischemic stroke. However, as drug development for stroke has been beset by translational failure, we sought additional evidence that hypothermia protects human neurons against ischemic injury.
Methods: Human embryonic stem cells were cultured and differentiated to provide a source of neurons expressing β III tubulin, microtubule-associated protein 2, and the Neuronal Nuclei antigen. Oxygen deprivation, oxygen-glucose deprivation, and H2O2 -induced oxidative stress were used to induce relevant injury.
Results: Hypothermia to 33°C protected these human neurons against H2O2 -induced oxidative stress reducing lactate dehydrogenase release and Terminal deoxynucleotidyl transferase dUTP nick end labeling-staining by 53% (P≤0·0001; 95% confidence interval 34·8-71·04) and 42% (P≤0·0001; 95% confidence interval 27·5-56·6), respectively, after 24 h in culture. Hypothermia provided similar protection against oxygen-glucose deprivation (42%, P≤0·001, 95% confidence interval 18·3-71·3 and 26%, P≤0·001; 95% confidence interval 12·4-52·2, respectively) but provided no protection against oxygen deprivation alone. Protection (21%) persisted against H2O2 -induced oxidative stress even when hypothermia was initiated six-hours after onset of injury (P≤0·05; 95% confidence interval 0·57-43·1).
Conclusion: We conclude that hypothermia protects stem cell-derived human neurons against insults relevant to stroke over a clinically relevant time frame. Protection against H2O2 -induced injury and combined oxygen and glucose deprivation but not against oxygen deprivation alone suggests an interaction in which protection benefits from reduction in available glucose under some but not all circumstances
Rotating Shallow Water Dynamics: Extra Invariant and the Formation of Zonal Jets
We show that rotating shallow water dynamics possesses an approximate
(adiabatic-type) positive quadratic invariant, which exists not only at
mid-latitudes (where its analogue in the quasigeostrophic equation has been
previously investigated), but near the equator as well (where the
quasigeostrophic equation is inapplicable). Deriving the extra invariant, we
find "small denominators" of two kinds: (1) due to the triad resonances (as in
the case of the quasigeostrophic equation) and (2) due to the equatorial limit,
when the Rossby radius of deformation becomes infinite. We show that the "small
denominators" of both kinds can be canceled. The presence of the extra
invariant can lead to the generation of zonal jets. We find that this tendency
should be especially pronounced near the equator. Similar invariant occurs in
magnetically confined fusion plasmas and can lead to the emergence of zonal
flows.Comment: 29 pages, 4 figure
Microscopic observation of magnon bound states and their dynamics
More than eighty years ago, H. Bethe pointed out the existence of bound
states of elementary spin waves in one-dimensional quantum magnets. To date,
identifying signatures of such magnon bound states has remained a subject of
intense theoretical research while their detection has proved challenging for
experiments. Ultracold atoms offer an ideal setting to reveal such bound states
by tracking the spin dynamics after a local quantum quench with single-spin and
single-site resolution. Here we report on the direct observation of two-magnon
bound states using in-situ correlation measurements in a one-dimensional
Heisenberg spin chain realized with ultracold bosonic atoms in an optical
lattice. We observe the quantum walk of free and bound magnon states through
time-resolved measurements of the two spin impurities. The increased effective
mass of the compound magnon state results in slower spin dynamics as compared
to single magnon excitations. In our measurements, we also determine the decay
time of bound magnons, which is most likely limited by scattering on thermal
fluctuations in the system. Our results open a new pathway for studying
fundamental properties of quantum magnets and, more generally, properties of
interacting impurities in quantum many-body systems.Comment: 8 pages, 7 figure
Stem cell transplantation in traumatic spinal cord injury:a systematic review and meta-analysis of animal studies
Spinal cord injury (SCI) is a devastating condition that causes substantial morbidity and mortality and for which no treatments are available. Stem cells offer some promise in the restoration of neurological function. We used systematic review, meta-analysis, and meta-regression to study the impact of stem cell biology and experimental design on motor and sensory outcomes following stem cell treatments in animal models of SCI. One hundred and fifty-six publications using 45 different stem cell preparations met our prespecified inclusion criteria. Only one publication used autologous stem cells. Overall, allogeneic stem cell treatment appears to improve both motor (effect size, 27.2%; 95% Confidence Interval [CI], 25.0%-29.4%; 312 comparisons in 5,628 animals) and sensory (effect size, 26.3%; 95% CI, 7.9%-44.7%; 23 comparisons in 473 animals) outcome. For sensory outcome, most heterogeneity between experiments was accounted for by facets of stem cell biology. Differentiation before implantation and intravenous route of delivery favoured better outcome. Stem cell implantation did not appear to improve sensory outcome in female animals and appeared to be enhanced by isoflurane anaesthesia. Biological plausibility was supported by the presence of a dose-response relationship. For motor outcome, facets of stem cell biology had little detectable effect. Instead most heterogeneity could be explained by the experimental modelling and the outcome measure used. The location of injury, method of injury induction, and presence of immunosuppression all had an impact. Reporting of measures to reduce bias was higher than has been seen in other neuroscience domains but were still suboptimal. Motor outcomes studies that did not report the blinded assessment of outcome gave inflated estimates of efficacy. Extensive recent preclinical literature suggests that stem-cell-based therapies may offer promise, however the impact of compromised internal validity and publication bias mean that efficacy is likely to be somewhat lower than reported here
Starting laminar plumes: Comparison of laboratory and numerical modeling
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94953/1/ggge1631.pd
High‐resolution models of subduction zones: Implications for mineral dehydration reactions and the transport of water into the deep mantle
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95127/1/ggge196.pd
Modeling Stochasticity and Variability in Gene Regulatory Networks
Modeling stochasticity in gene regulatory networks is an important and
complex problem in molecular systems biology. To elucidate intrinsic noise,
several modeling strategies such as the Gillespie algorithm have been used
successfully. This paper contributes an approach as an alternative to these
classical settings. Within the discrete paradigm, where genes, proteins, and
other molecular components of gene regulatory networks are modeled as discrete
variables and are assigned as logical rules describing their regulation through
interactions with other components. Stochasticity is modeled at the biological
function level under the assumption that even if the expression levels of the
input nodes of an update rule guarantee activation or degradation there is a
probability that the process will not occur due to stochastic effects. This
approach allows a finer analysis of discrete models and provides a natural
setup for cell population simulations to study cell-to-cell variability. We
applied our methods to two of the most studied regulatory networks, the outcome
of lambda phage infection of bacteria and the p53-mdm2 complex.Comment: 23 pages, 8 figure
High spatial and temporal resolution retrospective cine cardiovascular magnetic resonance from shortened free breathing real-time acquisitions
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