26,792 research outputs found
A Handheld low-mass, impact instrument to measure nondestructive firmness of fruit
A portable, handheld impact firmness sensor was designed for nondestructive measurement of fruit firmness while the fruit remain attached to the tree or for use in other remote locations where the use of a benchtop instrument would be impractical. The instrument design was based on the low-mass, constant velocity, impact-type measurement concept. Validation tests of the handheld sensor using `Bartlett' pears from orchards in California and Washington showed excellent agreement (r2 = 0.92 and 0.96, respectively) with both ASAE Standard method S368.2 for determining the apparent modulus of intact fruit and the impact firmness scores from a commercial benchtop impact firmness instrument
Tycho Brahe's supernova: light from centuries past
The light curve of SN 1572 is described in the terms used nowadays to
characterize SNeIa. By assembling the records of the observations done in
1572--74 and evaluating their uncertainties, it is possible to recover the
light curve and the color evolution of this supernova. It is found that, within
the SNe Ia family, the event should have been a SNIa with a normal rate of
decline, its stretch factor being {\it s} 0.9. Visual light curve near
maximum, late--time decline and the color evolution sustain this conclusion.
After correcting for extinction, the luminosity of this supernova is found to
be M --19.58 --5 log (D/3.5 kpc) 0.42.Comment: 28 pages, 3 figures, 3 tables. submitted to ApJ (Main Journal
Chaos around Holographic Regge Trajectories
Using methods of Hamiltonian dynamical systems, we show analytically that a
dynamical system connected to the classical spinning string solution
holographically dual to the principal Regge trajectory is non-integrable. The
Regge trajectories themselves form an integrable island in the total phase
space of the dynamical system. Our argument applies to any gravity background
dual to confining field theories and we verify it explicitly in various
supergravity backgrounds: Klebanov-Strassler, Maldacena-Nunez, Witten QCD and
the AdS soliton. Having established non-integrability for this general class of
supergravity backgrounds, we show explicitly by direct computation of the
Poincare sections and the largest Lyapunov exponent, that such strings have
chaotic motion.Comment: 28 pages, 5 figures. V3: Minor changes complying to referee's
suggestions. Typos correcte
Transition between Two Oscillation Modes
A model for the symmetric coupling of two self-oscillators is presented. The
nonlinearities cause the system to vibrate in two modes of different
symmetries. The transition between these two regimes of oscillation can occur
by two different scenarios. This might model the release of vortices behind
circular cylinders with a possible transition from a symmetric to an
antisymmetric Benard-von Karman vortex street.Comment: 12 pages, 0 figure
Features of the Extension of a Statistical Measure of Complexity to Continuous Systems
We discuss some aspects of the extension to continuous systems of a
statistical measure of complexity introduced by Lopez-Ruiz, Mancini and Calbet
(LMC) [Phys. Lett. A 209 (1995) 321]. In general, the extension of a magnitude
from the discrete to the continuous case is not a trivial process and requires
some choice. In the present study, several possibilities appear available. One
of them is examined in detail. Some interesting properties desirable for any
magnitude of complexity are discovered on this particular extension.Comment: 22 pages, 0 figure
Four-year trajectories of episodic memory decline in mid-late life by living arrangements: a cross-national comparison between China and England
BACKGROUND: There is mixed evidence on the association between living arrangements and mid-late life cognition, which may be due to distinct familial arrangements and preferences between populations. To address such heterogeneity, we assessed these associations in China and England.
METHODS: Four-year trajectories of episodic memory scores (0â20, word recall test) by living arrangements (living with partner only, living with partner and children/grandchildren, living with no partner but with children/grandchildren, and living alone) were estimated using latent growth curve modelling for men and women aged 50+ from China (n=12 801) and England (n=10 964).
RESULTS: After adjusting for baseline socioeconomic, health behaviours and health covariates, worse baseline memory was found in Chinese adults living with no partner but with children/grandchildren and in Chinese women living with partner and children/grandchildren, compared with those living with partner only. Better baseline memory was associated with living alone in English women. A faster memory decline was found in Chinese men living with no partner but with children/grandchildren (â0.122 word/year, 95% CI â0.213 to â0.031), as well as in English women living with children/grandchildren with (â0.114, 95% CI â0.180 to â0.049) or without (â0.118, 95% CI â0.209 to â0.026) a partner, and those living alone (â0.075, 95% CI â0.127 to â0.024). No differences at baseline nor over follow-up were found between English men in different living arrangements.
CONCLUSIONS: Overall, our findings did not confirm the protective effects of co-residence with children/grandchildren, nor the detrimental effects of living alone on mid-late life cognition in China and England
Scattering of scalar perturbations with cosmological constant in low-energy and high-energy regimes
We study the absorption and scattering of massless scalar waves propagating
in spherically symmetric spacetimes with dynamical cosmological constant both
in low-energy and high-energy zones. In the former low-energy regime, we solve
analytically the Regge-Wheeler wave equation and obtain an analytic absorption
probability expression which varies with , where is the
central mass and is cosmological constant. The low-energy absorption
probability, which is in the range of , increases monotonically
with increase in . In the latter high-energy regime, the scalar
particles adopt their geometric optics limit value. The trajectory equation
with effective potential emerges and the analytic high-energy greybody factor,
which is relevant with the area of classically accessible regime, also
increases monotonically with increase in , as long is less
than or of the order of . In this high-energy case, the null cosmological
constant result reduces to the Schwarzschild value .Comment: 12 pages, 6 figure
Block Copolymer at Nano-Patterned Surfaces
We present numerical calculations of lamellar phases of block copolymers at
patterned surfaces. We model symmetric di-block copolymer films forming
lamellar phases and the effect of geometrical and chemical surface patterning
on the alignment and orientation of lamellar phases. The calculations are done
within self-consistent field theory (SCFT), where the semi-implicit relaxation
scheme is used to solve the diffusion equation. Two specific set-ups, motivated
by recent experiments, are investigated. In the first, the film is placed on
top of a surface imprinted with long chemical stripes. The stripes interact
more favorably with one of the two blocks and induce a perpendicular
orientation in a large range of system parameters. However, the system is found
to be sensitive to its initial conditions, and sometimes gets trapped into a
metastable mixed state composed of domains in parallel and perpendicular
orientations. In a second set-up, we study the film structure and orientation
when it is pressed against a hard grooved mold. The mold surface prefers one of
the two components and this set-up is found to be superior for inducing a
perfect perpendicular lamellar orientation for a wide range of system
parameters
Clebsch-Gordan and 6j-coefficients for rank two quantum groups
We calculate (q-deformed) Clebsch-Gordan and 6j-coefficients for rank two
quantum groups. We explain in detail how such calculations are done, which
should allow the reader to perform similar calculations in other cases.
Moreover, we tabulate the q-Clebsch-Gordan and 6j-coefficients explicitly, as
well as some other topological data associated with theories corresponding to
rank-two quantum groups. Finally, we collect some useful properties of the
fusion rules of particular conformal field theories.Comment: 43 pages. v2: minor changes and added references. For mathematica
notebooks containing the various q-CG and 6j symbols, see
http://arxiv.org/src/1004.5456/an
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