135 research outputs found
Improved predictions of coral bleaching using seasonal baselines and higher spatial resolution
Coral bleaching spread across the southern Great Barrier Reef in January 2006, after sea temperatures reached climatological summer maxima 2 months before normal. Current satellite-derived warning systems were unable to detect severe bleaching conditions in the region because of their use of a constant thermal threshold (summer maximum monthly mean) and low spatial resolution (50 km). Here it is shown that such problems can be ameliorated if the thermal threshold is adjusted for seasonal variation and a 4-km spatial resolution is used. We develop a seasonally and spatially improved thermal threshold for coral bleaching on the basis of a weekly climatology of sea surface temperatures extending from austral spring to late summer, and apply the method to two case-study sites. At both sites, and in particular at the nearshore site that was undetected by the 50-km satellite product, the seasonally adjusted thermal threshold produced a greatly improved consistency between accumulated heating and bleaching severity. The application of thermal stress algorithms that reflect the long-term mean pattern in seasonal variation allows coral bleaching to be forecast with higher precision
Analysis of the intraspinal calcium dynamics and its implications on the plasticity of spiking neurons
The influx of calcium ions into the dendritic spines through the
N-metyl-D-aspartate (NMDA) channels is believed to be the primary trigger for
various forms of synaptic plasticity. In this paper, the authors calculate
analytically the mean values of the calcium transients elicited by a spiking
neuron undergoing a simple model of ionic currents and back-propagating action
potentials. The relative variability of these transients, due to the stochastic
nature of synaptic transmission, is further considered using a simple Markov
model of NMDA receptos. One finds that both the mean value and the variability
depend on the timing between pre- and postsynaptic action-potentials. These
results could have implications on the expected form of synaptic-plasticity
curve and can form a basis for a unified theory of spike time-dependent, and
rate based plasticity.Comment: 14 pages, 10 figures. A few changes in section IV and addition of a
new figur
Probing top flavour-changing neutral scalar couplings at the CERN LHC
Top decays into a light Higgs boson and an up or charm quark can reach
detectable levels in Standard Model extensions with two Higgs doublets or with
new exotic quarks, and in the Minimal Supersymmetric Standard Model. Using both
a standard and a neural network analysis we show that the CERN Large Hadron
Collider will give 3 sigma evidence of decays with Br(t -> Hc) >= 6.5 10^-5 or
set a limit Br(t -> Hc) <= 4.5 10^-5 with a 95% confidence level if these
decays are not observed. We also consider limits obtained from single top
production associated with a neutral Higgs boson.Comment: Uses elsart.cls. 16 pages, 9 PS figures. Some comments and references
added. Final version to appear in PL
Symmetries and Elasticity of Nematic Gels
A nematic liquid-crystal gel is a macroscopically homogeneous elastic medium
with the rotational symmetry of a nematic liquid crystal. In this paper, we
develop a general approach to the study of these gels that incorporates all
underlying symmetries. After reviewing traditional elasticity and clarifying
the role of broken rotational symmetries in both the reference space of points
in the undistorted medium and the target space into which these points are
mapped, we explore the unusual properties of nematic gels from a number of
perspectives. We show how symmetries of nematic gels formed via spontaneous
symmetry breaking from an isotropic gel enforce soft elastic response
characterized by the vanishing of a shear modulus and the vanishing of stress
up to a critical value of strain along certain directions. We also study the
phase transition from isotropic to nematic gels. In addition to being fully
consistent with approaches to nematic gels based on rubber elasticity, our
description has the important advantages of being independent of a microscopic
model, of emphasizing and clarifying the role of broken symmetries in
determining elastic response, and of permitting easy incorporation of spatial
variations, thermal fluctuations, and gel heterogeneity, thereby allowing a
full statistical-mechanical treatment of these novel materials.Comment: 21 pages, 4 eps figure
Solitosynthesis of Q-balls
We study the formation of Q-balls in the early universe, concentrating on
potentials with a cubic or quartic attractive interaction. Large Q-balls can
form via solitosynthesis, a process of gradual charge accretion, provided some
primordial charge assymetry and initial ``seed'' Q-balls exist. We find that
such seeds are possible in theories in which the attractive interaction is of
the form , with a light ``Higgs'' mass. Condensate formation
and fragmentation is only possible for masses in the sub-eV range;
these Q-balls may survive untill present.Comment: 9 pages, 1 figur
Satellite-Detected Fluorescence Reveals Global Physiology of Ocean Phytoplankton
Phytoplankton photosynthesis links global ocean biology and climate-driven fluctuations in the physical environment. These interactions are largely expressed through changes in phytoplankton physiology, but physiological status has proven extremely challenging to characterize globally. Phytoplankton fluorescence does provide a rich source of physiological information long exploited in laboratory and field studies, and is now observed from space. Here we evaluate the physiological underpinnings of global variations in satellite-based phytoplankton chlorophyll fluorescence. The three dominant factors influencing fluorescence distributions are chlorophyll concentration, pigment packaging effects on light absorption, and light-dependent energy-quenching processes. After accounting for these three factors, resultant global distributions of quenching-corrected fluorescence quantum yields reveal a striking consistency with anticipated patterns of iron availability. High fluorescence quantum yields are typically found in low iron waters, while low quantum yields dominate regions where other environmental factors are most limiting to phytoplankton growth. Specific properties of photosynthetic membranes are discussed that provide a mechanistic view linking iron stress to satellite-detected fluorescence. Our results present satellite-based fluorescence as a valuable tool for evaluating nutrient stress predictions in ocean ecosystem models and give the first synoptic observational evidence that iron plays an important role in seasonal phytoplankton dynamics of the Indian Ocean. Satellite fluorescence may also provide a path for monitoring climate-phytoplankton physiology interactions and improving descriptions of phytoplankton light use efficiencies in ocean productivity models
Rapid And Durable Responses With The Syk/Jak Inhibitor Cerdulatinib In A Phase 2 Study In Relapsed/Refractory Follicular Lymphoma—Alone Or In Combination With Rituximab
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149541/1/hon30_2629.pd
Moon Shadow by Cosmic Rays under the Influence of Geomagnetic Field and Search for Antiprotons at Multi-TeV Energies
We have observed the shadowing of galactic cosmic ray flux in the direction
of the moon, the so-called moon shadow, using the Tibet-III air shower array
operating at Yangbajing (4300 m a.s.l.) in Tibet since 1999. Almost all cosmic
rays are positively charged; for that reason, they are bent by the geomagnetic
field, thereby shifting the moon shadow westward. The cosmic rays will also
produce an additional shadow in the eastward direction of the moon if cosmic
rays contain negatively charged particles, such as antiprotons, with some
fraction. We selected 1.5 x10^{10} air shower events with energy beyond about 3
TeV from the dataset observed by the Tibet-III air shower array and detected
the moon shadow at level. The center of the moon was detected
in the direction away from the apparent center of the moon by 0.23 to
the west. Based on these data and a full Monte Carlo simulation, we searched
for the existence of the shadow produced by antiprotons at the multi-TeV energy
region. No evidence of the existence of antiprotons was found in this energy
region. We obtained the 90% confidence level upper limit of the flux ratio of
antiprotons to protons as 7% at multi-TeV energies.Comment: 13pages,4figures; Accepted for publication in Astroparticle Physic
Particle density fluctuations
Event-by-event fluctuations in the multiplicities of charged particles and
photons at SPS energies are discussed. Fluctuations are studied by controlling
the centrality of the reaction and rapidity acceptance of the detectors.
Results are also presented on the event-by-event study of correlations between
the multiplicity of charged particles and photons to search for DCC-like
signals.Comment: Talk presented at Quark Matter 2002, Nantes, Franc
Low energy atmospheric muon neutrinos in MACRO
We present the measurement of two event samples induced by atmospheric
of average energy . In the first sample,
the neutrino interacts inside the MACRO detector producing an upward-going muon
leaving the apparatus. The ratio of the number of observed to expected events
is with an angular
distribution similar to that expected from the Bartol atmospheric neutrino
flux. The second is a mixed sample of internally produced downward-going muons
and externally produced upward-going muons stopping inside the detector. These
two subsamples are selected by topological criteria; the lack of timing
information makes it impossible to distinguish stopping from downgoing muons.
The ratio of the number of observed to expected events is . Using the ratio of the two subsamples (for
which most theoretical uncertainties cancel) we can test the pathlength
dependence of the oscillation hypothesis. The probability of agreement with the
no-oscillation hypothesis is 5% .
The deviations of our observations from the expectations has a preferred
interpretation in terms of oscillations with maximal mixing and
. These parameters are in agreement
with our results from upward throughgoing muons, induced by of much
higher energies.Comment: 7 pages, 6 figures. Submitted to Phys. Lett.
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