13,427 research outputs found
External loading determines specific ECM genes regulation
Bio artificial matrices embedded with cells are simulated in bioreactors to
facilitate ECM production. As cells attach, they
develop forces, which are dependent on cell type
and matrix stiffness. External forces (i.e strain),
however, are critical for tissue homeostasis and
elicit specific cellular responses, such as gene
expression and protein production. Collagen Type
I is a widely used scaffold in Tissue engineering.
The aim of this study was to study the mechanical
and molecular responses, of different cell types to
increasing collagen substrate stiffness
Activation of Long Descending Propriospinal Neurons in Cat Spinal Cord
Isolated mammalian spinal cord has been shown capable of generating locomotor activity. Propriospinal systems assumed to coordinate fore- and hindlimb activity are poorly understood. This study characterizes the long descending propriospinal (LDP) neurons in terms of the location of the somas and their peripheral inputs by direct neuronal recording. Anatomical studies using axonal retrograde transport of horseradish peroxidase from the lumbar to the cervical spinal cord as a tracer first described these neurons. Two hundred and thirty-one LDP neurons were identified in electrophysiological experiments. Of these, 123 responded to natural stimulation, and about 50% of the others were activated only by electrical stimulation. The majority of cells were located in laminae VII and VIII in agreement with anatomical data. The most effective stimuli were mechanical stimulation of skin, deep pressure to subcutaneous tissues, and paw joint movement. Bot excitatory and inhibitory responses were observed
On the high coherence of kilo-Hz Quasi-Periodic Oscillations
We have carried out a systematic study of the properties of the kilo-Hertz
quasi-periodic oscillations (QPO) observed in the X-ray emission of the neutron
star low-mass X-ray binary 4U1608-52, using archival data obtained with the
Rossi X-ray Timing Explorer. We have investigated the quality factor, Q, of the
oscillations (defined as the ratio of the frequency of the QPO peak to its full
width at half maximum). In order to minimise the effect of long-term frequency
drifts, power spectra were computed over the shortest times permitted by the
data statistics. We show that the high Q of ~200 reported by Berger et al.
(1996) for the lower frequency kilo-Hz QPO in one of their observations is by
no means exceptional, as we observe a mean Q value in excess of 150 in 14 out
of the 21 observations analysed and Q can remain above 200 for thousands of
seconds. The frequency of the QPO varies over the wide range 560--890 Hz and we
find a systematic trend for the coherence time of the QPO, estimated as tau=Q
/(pi nu), to increase with the frequency, up to a maximum level at ~ 800 Hz,
beyond which it appears to decrease, at frequencies where the QPO weakens.
There is a more complex relationship between tau and the QPO root mean squared
amplitude (RMS), in which positive and negative correlations can be found. A
higher-frequency QPO, revealed by correcting for the frequency drift of the
560-890 Hz one, has a much lower Q (~10) which does not follow the same
pattern. We discuss these results in the framework of competing QPO models and
show that those involving clumps orbiting within or above the accretion disk
are ruled out.Comment: Accepted for publication in MNRAS, 8 pages, 6 figures, 3 Table
Populations of Pear Thrips, \u3ci\u3eTaeniothrips Inconsequens\u3c/i\u3e (Thysanoptera: Thripidae) in Sugar Maple Stands in Vermont: 1989-2005
Development of an effective IPM strategy for pear thrips, Taeniothrips inconsequens (Uzel) (Thysanoptera: Thripidae), a pest of sugar maple, Acer saccharum Marshall, demands an understanding of their population fluctuations over time. Pear thrips populations were monitored using a standardized soil sampling method every fall from 1989 â 2005 in 14 counties of Vermont (U.S.). Data from individual sites were combined into north, central and south regions. High numbers of thrips emerged from soil sampled in 1989, 1990, 1993 and 2001, particularly in the north region (Washington, Lamoille, and Franklin counties). The central and south regions had lower pear thrips populations over all years. These results provide, for the first time, fundamental knowledge of pear thrips populations across a wide geographical area of Vermont and will assist in the design of suitable control strategies for pear thrips in the future
The problem of shot selection in basketball
In basketball, every time the offense produces a shot opportunity the player
with the ball must decide whether the shot is worth taking. In this paper, I
explore the question of when a team should shoot and when they should pass up
the shot by considering a simple theoretical model of the shot selection
process, in which the quality of shot opportunities generated by the offense is
assumed to fall randomly within a uniform distribution. I derive an answer to
the question "how likely must the shot be to go in before the player should
take it?", and show that this "lower cutoff" for shot quality depends
crucially on the number of shot opportunities remaining (say, before the
shot clock expires), with larger demanding that only higher-quality shots
should be taken. The function is also derived in the presence of a
finite turnover rate and used to predict the shooting rate of an
optimal-shooting team as a function of time. This prediction is compared to
observed shooting rates from the National Basketball Association (NBA), and the
comparison suggests that NBA players tend to wait too long before shooting and
undervalue the probability of committing a turnover.Comment: 7 pages, 2 figures; comparison to NBA data adde
Development of Ground-testable Phase Fresnel Lenses in Silicon
Diffractive/refractive optics, such as Phase Fresnel Lenses (PFL's), offer
the potential to achieve excellent imaging performance in the x-ray and
gamma-ray photon regimes. In principle, the angular resolution obtained with
these devices can be diffraction limited. Furthermore, improvements in signal
sensitivity can be achieved as virtually the entire flux incident on a lens can
be concentrated onto a small detector area. In order to verify experimentally
the imaging performance, we have fabricated PFL's in silicon using gray-scale
lithography to produce the required Fresnel profile. These devices are to be
evaluated in the recently constructed 600-meter x-ray interferometry testbed at
NASA/GSFC. Profile measurements of the Fresnel structures in fabricated PFL's
have been performed and have been used to obtain initial characterization of
the expected PFL imaging efficiencies.Comment: Presented at GammaWave05: "Focusing Telescopes in Nuclear
Astrophysics", Bonifacio, Corsica, September 2005, to be published in
Experimental Astronomy, 8 pages, 3 figure
Effect of thermal exposure, forming, and welding on high-temperature, dispersion-strengthened aluminum alloy: Al-8Fe-1V-2Si
The feasibility of applying conventional hot forming and welding methods to high temperature aluminum alloy, Al-8Fe-1V-2Si (FVS812), for structural applications and the effect of thermal exposure on mechanical properties were determined. FVS812 (AA8009) sheet exhibited good hot forming and resistance welding characteristics. It was brake formed to 90 deg bends (0.5T bend radius) at temperatures greater than or equal to 390 C (730 F), indicating the feasibility of fabricating basic shapes, such as angles and zees. Hot forming of simple contoured-flanged parts was demonstrated. Resistance spot welds with good static and fatigue strength at room and elevated temperatures were readily produced. Extended vacuum degassing during billet fabrication reduced porosity in fusion and resistance welds. However, electron beam welding was not possible because of extreme degassing during welding, and gas-tungsten-arc welds were not acceptable because of severely degraded mechanical properties. The FVS812 alloy exhibited excellent high temperature strength stability after thermal exposures up to 315 C (600 F) for 1000 h. Extended billet degassing appeared to generally improve tensile ductility, fatigue strength, and notch toughness. But the effects of billet degassing and thermal exposure on properties need to be further clarified. The manufacture of zee-stiffened, riveted, and resistance-spot-welded compression panels was demonstrated
Troubles with Bayesianism: An introduction to the psychological immune system
A Bayesian mind is, at its core, a rational mind. Bayesianism is thus well-suited to predict and explain mental processes that best exemplify our ability to be rational. However, evidence from belief acquisition and change appears to show that we do not acquire and update information in a Bayesian way. Instead, the principles of belief acquisition and updating seem grounded in maintaining a psychological immune system rather than in approximating
a Bayesian processor
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