333 research outputs found
Direct measurement of swimming and diving kinematics of giant Atlantic bluefin tuna (Thunnus thynnus)
Tunas possess a range of physiological and mechanical adaptations geared towards high-performance swimming that are of considerable interest to physiologists, ecologists and engineers. Advances in biologging have provided significant improvements in understanding tuna migrations and vertical movement patterns, yet our understanding of the locomotion and swimming mechanics of these fish under natural conditions is limited. We equipped Atlantic bluefin tuna (Thunnus thynnus) with motion-sensitive tags and video cameras to quantify the gaits and kinematics used by wild fish. Our data reveal significant variety in the locomotory kinematics of Atlantic bluefin tuna, ranging from continuous locomotion to two types of intermittent locomotion. The tuna sustained swimming speeds in excess of 1.5 m s−1 (0.6 body lengths s−1), while beating their tail at a frequency of approximately 1 Hz. While diving, some descents were entirely composed of passive glides, with slower descent rates featuring more gliding, while ascents were primarily composed of active swimming. The observed swimming behaviour of Atlantic bluefin tuna is consistent with theoretical models predicting such intermittent locomotion to result in mechanical and physiological advantages. Our results confirm that Atlantic bluefin tuna possess behavioural specializations to increase their locomotory performance, which together with their unique physiology improve their capacity to use pelagic and mesopelagic habitats
New physics, the cosmic ray spectrum knee, and cross section measurements
We explore the possibility that a new physics interaction can provide an
explanation for the knee just above GeV in the cosmic ray spectrum. We
model the new physics modifications to the total proton-proton cross section
with an incoherent term that allows for missing energy above the scale of new
physics. We add the constraint that the new physics must also be consistent
with published cross section measurements, using cosmic ray observations,
an order of magnitude and more above the knee. We find that the rise in cross
section required at energies above the knee is radical. The increase in cross
section suggests that it may be more appropriate to treat the scattering
process in the black disc limit at such high energies. In this case there may
be no clean separation between the standard model and new physics contributions
to the total cross section. We model the missing energy in this limit and find
a good fit to the Tibet III cosmic ray flux data. We comment on testing the new
physics proposal for the cosmic ray knee at the Large Hadron Collider.Comment: 17 pages, 4 figure
Destabilization of dark states and optical spectroscopy in Zeeman-degenerate atomic systems
We present a general discussion of the techniques of destabilizing dark
states in laser-driven atoms with either a magnetic field or modulated laser
polarization. We show that the photon scattering rate is maximized at a
particular evolution rate of the dark state. We also find that the atomic
resonance curve is significantly broadened when the evolution rate is far from
this optimum value. These results are illustrated with detailed examples of
destabilizing dark states in some commonly-trapped ions and supported by
insights derived from numerical calculations and simple theoretical models.Comment: 14 pages, 10 figure
Rings and bars: unmasking secular evolution of galaxies
Secular evolution gradually shapes galaxies by internal processes, in
contrast to early cosmological evolution which is more rapid. An important
driver of secular evolution is the flow of gas from the disk into the central
regions, often under the influence of a bar. In this paper, we review several
new observational results on bars and nuclear rings in galaxies. They show that
these components are intimately linked to each other, and to the properties of
their host galaxy. We briefly discuss how upcoming observations, e.g., imaging
from the Spitzer Survey of Stellar Structure in Galaxies (S4G), will lead to
significant further advances in this area of research.Comment: Invited review at "Galaxies and their Masks", celebrating Ken
Freeman's 70-th birthday, Sossusvlei, Namibia, April 2010. To be published by
Springer, New York, editors D.L. Block, K.C. Freeman, & I. Puerari; minor
change
Phase transition between synchronous and asynchronous updating algorithms
We update a one-dimensional chain of Ising spins of length with
algorithms which are parameterized by the probability for a certain site to
get updated in one time step. The result of the update event itself is
determined by the energy change due to the local change in the configuration.
In this way we interpolate between the Metropolis algorithm at zero temperature
for of the order of 1/L and for large , and a synchronous deterministic
updating procedure for . As function of we observe a phase transition
between the stationary states to which the algorithm drives the system. These
are non-absorbing stationary states with antiferromagnetic domains for ,
and absorbing states with ferromagnetic domains for . This means
that above this transition the stationary states have lost any remnants to the
ferromagnetic Ising interaction. A measurement of the critical exponents shows
that this transition belongs to the universality class of parity conservation.Comment: 5 pages, 3 figure
RGDS peptides immobilized on titanium alloy stimulate bone cell attachment, differentiation and confer resistance to apoptosis
A major cause of implant failure in skeletal tissues is failure of osseointegration, often due to lack of adhesion of cells to the titanium (Ti) alloy interface. Since arginine- glycine-aspartic acid (RGD)-containing peptides have been shown to regulate osteoblast adhesion, we tested the hypothesis that, bound to a Ti surface, these peptides would promote osteoblasts differentiation, while at the same time inhibit apoptosis. RGDS and RGES (control) peptides were covalently linked to Ti discs using an APTS linker. While the grafting of both RGDS and RGES significantly increased Ti surface roughness, contact angle analysis showed that APTS significantly increased the surface hydrophobicity; when the peptides were tethered to Ti, this was reduced. To evaluate attachment, MC3T3-E1 osteoblast cells were grown on these discs. Significantly more cells attached to the Ti-grafted RGDS then the Ti-grafted RGES control. Furthermore, expression of the osteoblasts phenotype was significantly enhanced on the Ti-grafted RGDS surface. When cells attached to the Ti-grafted RGDS were challenged with staurosporine, an apoptogen, there was significant inhibition of apoptosis; in contrast, osteoblasts adherent to the Ti-grafted RGES were killed. It is concluded that RGD-containing peptides covalently bonded to Ti promotes osteoblasts attachment and survival with minimal changes to the surface of the alloy. Therefore, such modifications to Ti would have the potential to promote osseointegration in vivo
Soft and hard tissue assessment of immediate implant placement: a case series
Objectives : The aim of this prospective study was to evaluate clinically and radiographically the success and esthetic result of immediate implant placement at the time of extraction. Material and methods : Twelve patients with 14 titanium screw-shaped implants (13–16 mm length and 4.3 or 5 mm diameters) were placed in the extraction sockets. Defects after implant placement were recorded, and then filled up with deproteinized bovine bone mineral, bioabsorbable collagen membrane, and absorbable pins. The defect was again re-evaluated at second-stage surgery. Clinical and radiographic parameters of the peri-implant conditions were assessed at the moment of prosthesis placement and at 1-year follow-up. Results : The cumulative implant survival and success rate was 100% after a 1-year observation period. Analysis of the esthetic result showed that the mean pink esthetic score (PES) was 11.1 (SD 1.35) at 1-year follow-up. At 1 year, 64.3% papillae had a score of 2 and the remaining 35.7% score 3 according to the Jemt (1997) papillary index. Optimal value of width of the keratinized mucosa was recorded in 13 (92.9%) implant cases in both periods of follow-up. At 1-year follow-up, the linear distance between implant-shoulder to the bone peaks remains stable with a mean of 2.62±0.2 mm at the mesial and 2.9±0.58 mm at the distal aspect. Conclusion : Careful evaluation of potential extraction sites before immediate implant installation promotes optimal implant esthetics. To cite this article: Juodzbalys G, Wang H-L. Soft and hard tissue assessment of immediate implant placement: a case series. Clin. Oral Impl. Res. 18 , 2007; 237–243 doi:10.1111/j.1600-0501.2006.01312.xPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74957/1/j.1600-0501.2006.01312.x.pd
Projection Postulate and Atomic Quantum Zeno Effect
The projection postulate has been used to predict a slow-down of the time
evolution of the state of a system under rapidly repeated measurements, and
ultimately a freezing of the state. To test this so-called quantum Zeno effect
an experiment was performed by Itano et al. (Phys. Rev. A 41, 2295 (1990)) in
which an atomic-level measurement was realized by means of a short laser pulse.
The relevance of the results has given rise to controversies in the literature.
In particular the projection postulate and its applicability in this experiment
have been cast into doubt. In this paper we show analytically that for a wide
range of parameters such a short laser pulse acts as an effective level
measurement to which the usual projection postulate applies with high accuracy.
The corrections to the ideal reductions and their accumulation over n pulses
are calculated. Our conclusion is that the projection postulate is an excellent
pragmatic tool for a quick and simple understanding of the slow-down of time
evolution in experiments of this type. However, corrections have to be
included, and an actual freezing does not seem possible because of the finite
duration of measurements.Comment: 25 pages, LaTeX, no figures; to appear in Phys. Rev.
Ramond-Ramond Fields, Fractional Branes and Orbifold Differential K-Theory
We study D-branes and Ramond-Ramond fields on global orbifolds of Type II
string theory with vanishing H-flux using methods of equivariant K-theory and
K-homology. We illustrate how Bredon equivariant cohomology naturally realizes
stringy orbifold cohomology. We emphasize its role as the correct cohomological
tool which captures known features of the low-energy effective field theory,
and which provides new consistency conditions for fractional D-branes and
Ramond-Ramond fields on orbifolds. We use an equivariant Chern character from
equivariant K-theory to Bredon cohomology to define new Ramond-Ramond couplings
of D-branes which generalize previous examples. We propose a definition for
groups of differential characters associated to equivariant K-theory. We derive
a Dirac quantization rule for Ramond-Ramond fluxes, and study flat
Ramond-Ramond potentials on orbifolds.Comment: 46 pages; v2: typos correcte
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