8,472 research outputs found
Variability of crop calendar stage dates
There are no author-identified significant results in this report
Equilibrium binding energies from fluctuation theorems and force spectroscopy simulations
Brownian dynamics simulations are used to study the detachment of a particle
from a substrate. Although the model is simple and generic, we attempt to map
its energy, length and time scales onto a specific experimental system, namely
a bead that is weakly bound to a cell and then removed by an optical tweezer.
The external driving force arises from the combined optical tweezer and
substrate potentials, and thermal fluctuations are taken into account by a
Brownian force. The Jarzynski equality and Crooks' fluctuation theorem are
applied to obtain the equilibrium free energy difference between the final and
initial states. To this end, we sample non--equilibrium work trajectories for
various tweezer pulling rates. We argue that this methodology should also be
feasible experimentally for the envisioned system. Furthermore, we outline how
the measurement of a whole free energy profile would allow the experimentalist
to retrieve the unknown substrate potential by means of a suitable
deconvolution. The influence of the pulling rate on the accuracy of the results
is investigated, and umbrella sampling is used to obtain the equilibrium
probability of particle escape for a variety of trap potentials.Comment: 21 pages, 11 figures, To appear in Soft Matte
Two-stage fan. 3: Data and performance with rotor tip casing treatment, uniform and distorted inlet flows
A two stage fan with a 1st-stage rotor design tip speed of 1450 ft/sec, a design pressure ratio of 2.8, and corrected flow of 184.2 lbm/sec was tested with axial skewed slots in the casings over the tips of both rotors. The variable stagger stators were set in the nominal positions. Casing treatment improved stall margin by nine percentage points at 70 percent speed but decreased stall margin, efficiency, and flow by small amounts at design speed. Treatment improved first stage performance at low speed only and decreased second stage performance at all operating conditions. Casing treatment did not affect the stall line with tip radially distorted flow but improved stall margin with circumferentially distorted flow. Casing treatment increased the attenuation for both types of inlet flow distortion
Asymmetries in Mars' Exosphere: Implications for X-ray and ENA Imaging
Observations and simulations show that Mars' atmosphere has large seasonal
variations. Total atmospheric density can have an order of magnitude
latitudinal variation at exobase heights. By numerical simulations we show that
these latitude variations in exobase parameters induce asymmetries in the
hydrogen exosphere that propagate to large distances from the planet. We show
that these asymmetries in the exosphere produce asymmetries in the fluxes of
energetic neutral atoms (ENAs) and soft X-rays produced by charge exchange
between the solar wind and exospheric hydrogen. This could be an explanation
for asymmetries that have been observed in ENA and X-ray fluxes at Mars.Comment: Submitted to Space Science Review. v2: Minor changes in text and
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Magnetic properties of Yb2Mo2O7 and Gd2Mo2O7 from rare earth Mossbauer measurements
Using 170-Yb and 155-Gd Mossbauer measurements down to 0.03K, we have
examined the semiconducting pyrochlore Yb2Mo2O7 where the Mo intra-sublattice
interaction is anti-ferromagnetic and the metallic pyrochlore Gd2Mo2O7 where
this interaction is ferromagnetic. Additional information was obtained from
susceptibility, magnetisation and 172-Yb perturbed angular correlation
measurements. The microscopic measurements evidence lattice disorder which is
important in Yb2Mo2O7 and modest in Gd2Mo2O7. Magnetic irreversibilities occur
at 17K in Yb2Mo2O7 and at 75K in Gd2Mo2O7 and below these temperatures the rare
earths carry magnetic moments which are induced through couplings with the Mo
sublattice. In Gd2Mo2O7, we observe the steady state Gd hyperfine populations
at 0.027K are out of thermal equilibrium, indicating that Gd and Mo spin
fluctuations persist at very low temperatures. Frustration is thus operative in
this essentially isotropic pyrochlore where the dominant Mo intra-sublattice
interaction is ferromagnetic.Comment: 9 pages, 9 figure
Motor preparation of spatially and temporally defined movements: Evidence from startle
This article is available open access through the publisher’s website at the link below. Copyright © 2011 the American Physiological Society.Previous research has shown that the preparation of a spatially targeted movement performed at maximal speed is different from that of a temporally constrained movement (Gottlieb et al. 1989b). In the current study, we directly examined preparation differences in temporally vs. spatially defined movements through the use of a startling stimulus and manipulation of the task goals. Participants performed arm extension movements to one of three spatial targets (20°, 40°, 60°) and an arm extension movement of 20° at three movement speeds (slow, moderate, fast). All movements were performed in a blocked, simple reaction time paradigm, with trials involving a startling stimulus (124 dB) interspersed randomly with control trials. As predicted, spatial movements were modulated by agonist duration and timed movements were modulated by agonist rise time. The startling stimulus triggered all movements at short latencies with a compression of the kinematic and electromyogram (EMG) profile such that they were performed faster than control trials. However, temporally constrained movements showed a differential effect of movement compression on startle trials such that the slowest movement showed the greatest temporal compression. The startling stimulus also decreased the relative timing between EMG bursts more for the 20° movement when it was defined by a temporal rather than spatial goal, which we attributed to the disruption of an internal timekeeper for the timed movements. These results confirm that temporally defined movements were prepared in a different manner from spatially defined movements and provide new information pertaining to these preparation differences
Laboratory measurements and theoretical calculations of O_2 A band electric quadrupole transitions
Frequency-stabilized cavity ring-down spectroscopy was utilized to measure electric quadrupole transitions within the ^(16)O_2 A band, b^1Σ^+_g ← X^3Σ^-_g(0,0). We report quantitative measurements (relative uncertainties in intensity measurements from 4.4% to 11%) of nine ultraweak transitions in the ^NO, ^PO, ^RS, and ^TS branches with line intensities ranging from 3×10^(−30) to 2×10^(−29) cm molec.^(−1). A thorough discussion of relevant noise sources and uncertainties in this experiment and other cw-cavity ring-down spectrometers is given. For short-term averaging (t<100 s), we estimate a noise-equivalent absorption of 2.5×10^(−10) cm^(−1) Hz^(−1/2). The detection limit was reduced further by co-adding up to 100 spectra to yield a minimum detectable absorption coefficient equal to 1.8×10^(−11) cm^(−1), corresponding to a line intensity of ~2.5×10^(−31) cm molec.^(−1). We discuss calculations of electric quadrupole line positions based on a simultaneous fit of the ground and upper electronic state energies which have uncertainties <3 MHz, and we present calculations of electric quadrupole matrix elements and line intensities. The electric quadrupole line intensity calculations and measurements agreed on average to 5%, which is comparable to our average experimental uncertainty. The calculated electric quadrupole band intensity was 1.8(1)×10^(−27) cm molec.−1 which is equal to only ~8×10^(−6) of the magnetic dipole band intensity
Modification of photosystem II activity by protein phosphorylation
AbstractPhosphorylation of proteins within pea thylakoid membranes decreases photosystem II (PSII) mediated electron transfer at saturating light intensities which, according to changes in room temperature chlorophyll fluorescence transients, is due to a modification in the electron transfer from QA to QB. However, a previously reported increase in the ability of DCMU to inhibit PS2 electron flow to DCPIP, as a consequence of protein phosphorylation, was not observed, although changes in DCMU efficacy were found to depend upon the redox state of the plastoquinone (PQ) pool
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