3,672 research outputs found
Analysis of the Movement of Chlamydomonas Flagella: The Function of the Radial-spoke System Is Revealed by Comparison of Wild-type and Mutant Flagella
The mutation uni-1 gives rise to uniflagellate Chlamydomonas cells which rotate around a fixed point in the microscope field, so that the flagellar bending pattern can be photographed easily . This has allowed us to make a detailed analysis of the wild-type flagellar bending pattern and the bending patterns of flagella on several mutant strains. Cells containing uni-1, and recombinants of uni-1 with the suppressor mutations, sup(_pf)-1 and sup(_pf)-3, show the typical asymmetric bending pattern associated with forward swimming in Chlamydomonas,
although sup(_pf)-1 flagella have about one-half the normal beat frequency, apparently as the result of defective function of the outer dynein arms. The pf-17 mutation has been shown to produce nonmotile flagella in which radial spoke heads and five characteristic axonemal
polypeptides are missing. Recombinants containing pf-17 and either sup(_pf)-1 or sup(_pf)-3 have
motile flagella, but still lack radial-spoke heads and the associated polypeptides . The flagellar
bending pattern of these recombinants lacking radial-spoke heads is a nearly symmetric, large
amplitude pattern which is quite unlike the wild-type pattern . However, the presence of an
intact radial-spoke system is not required to convert active sliding into bending and is not
required for bend initiation and bend propagation, since all of these processes are active in the
sup(_pf) pf-17 recombinants. The function of the radial-spoke system appears to be to convert the
symmetric bending pattern displayed by these recombinants into the asymmetric bending
pattern required for efficient swimming, by inhibiting the development of reverse bends during
the recovery phase of the bending cycle
Statistics of quantum transmission in one dimension with broad disorder
We study the statistics of quantum transmission through a one-dimensional
disordered system modelled by a sequence of independent scattering units. Each
unit is characterized by its length and by its action, which is proportional to
the logarithm of the transmission probability through this unit. Unit actions
and lengths are independent random variables, with a common distribution that
is either narrow or broad. This investigation is motivated by results on
disordered systems with non-stationary random potentials whose fluctuations
grow with distance.
In the statistical ensemble at fixed total sample length four phases can be
distinguished, according to the values of the indices characterizing the
distribution of the unit actions and lengths. The sample action, which is
proportional to the logarithm of the conductance across the sample, is found to
obey a fluctuating scaling law, and therefore to be non-self-averaging, in
three of the four phases. According to the values of the two above mentioned
indices, the sample action may typically grow less rapidly than linearly with
the sample length (underlocalization), more rapidly than linearly
(superlocalization), or linearly but with non-trivial sample-to-sample
fluctuations (fluctuating localization).Comment: 26 pages, 4 figures, 1 tabl
Recalibration Methodology to Compensate for Changing Fluid Properties in an Individual Nozzle Direct Injection Systems
Limited advancement of direct injection pesticide application systems has been made in recent years, which has hindered further commercialization of this technology. One approach to solving the lag and mixing issues typically associated with injection-based systems is high-pressure individual nozzle injection. However, accurate monitoring of the chemical concentrate flow rate can pose a challenge due to the high pressure, low flow, and changing viscosities of the fluid. A methodology was developed for recalibrating high-pressure chemical concentrate injectors to compensate for fluid property variations and evaluate the performance of this technique for operating injectors in an open-loop configuration. Specific objectives were to (1) develop a method for continuous recalibration of the chemical concentrate injectors to ensure accurate metering of chemicals of varying viscosities and (2) evaluate the recalibration method for estimating individual injector flow rates from a system of multiple injectors to assess potential errors. Test results indicated that the recalibration method was able to compensate for changes in fluid kinematic viscosity (e.g., from temperature changes and/or product variation). Errors were less than 3.4% for the minimum injector duty cycle (DCi) (at 10%) and dropped 0.2% for the maximum DCi (at 90%) for temperature changes of up to 20°C. While larger temperature changes may be expected, these test results showed that the proposed method could be successfully implemented to meet desired injection rates. Because multiple injectors would be used in commercial deployment of this technology, a method was developed to calculate the desired injector flow rate using initial injector calibration factors. Using this multi-injector recalibration method, errors ranged from 0.23% to 0.66% between predicted and actual flow rates for all three injectors
Recalibration Methodology to Compensate for Changing Fluid Properties in an Individual Nozzle Direct Injection Systems
Limited advancement of direct injection pesticide application systems has been made in recent years, which has hindered further commercialization of this technology. One approach to solving the lag and mixing issues typically associated with injection-based systems is high-pressure individual nozzle injection. However, accurate monitoring of the chemical concentrate flow rate can pose a challenge due to the high pressure, low flow, and changing viscosities of the fluid. A methodology was developed for recalibrating high-pressure chemical concentrate injectors to compensate for fluid property variations and evaluate the performance of this technique for operating injectors in an open-loop configuration. Specific objectives were to (1) develop a method for continuous recalibration of the chemical concentrate injectors to ensure accurate metering of chemicals of varying viscosities and (2) evaluate the recalibration method for estimating individual injector flow rates from a system of multiple injectors to assess potential errors. Test results indicated that the recalibration method was able to compensate for changes in fluid kinematic viscosity (e.g., from temperature changes and/or product variation). Errors were less than 3.4% for the minimum injector duty cycle (DCi) (at 10%) and dropped 0.2% for the maximum DCi (at 90%) for temperature changes of up to 20°C. While larger temperature changes may be expected, these test results showed that the proposed method could be successfully implemented to meet desired injection rates. Because multiple injectors would be used in commercial deployment of this technology, a method was developed to calculate the desired injector flow rate using initial injector calibration factors. Using this multi-injector recalibration method, errors ranged from 0.23% to 0.66% between predicted and actual flow rates for all three injectors
Recalibration Methodology to Compensate for Changing Fluid Properties in an Individual Nozzle Direct Injection Systems
Limited advancement of direct injection pesticide application systems has been made in recent years, which has hindered further commercialization of this technology. One approach to solving the lag and mixing issues typically associated with injection-based systems is high-pressure individual nozzle injection. However, accurate monitoring of the chemical concentrate flow rate can pose a challenge due to the high pressure, low flow, and changing viscosities of the fluid. A methodology was developed for recalibrating high-pressure chemical concentrate injectors to compensate for fluid property variations and evaluate the performance of this technique for operating injectors in an open-loop configuration. Specific objectives were to (1) develop a method for continuous recalibration of the chemical concentrate injectors to ensure accurate metering of chemicals of varying viscosities and (2) evaluate the recalibration method for estimating individual injector flow rates from a system of multiple injectors to assess potential errors. Test results indicated that the recalibration method was able to compensate for changes in fluid kinematic viscosity (e.g., from temperature changes and/or product variation). Errors were less than 3.4% for the minimum injector duty cycle (DCi) (at 10%) and dropped 0.2% for the maximum DCi (at 90%) for temperature changes of up to 20°C. While larger temperature changes may be expected, these test results showed that the proposed method could be successfully implemented to meet desired injection rates. Because multiple injectors would be used in commercial deployment of this technology, a method was developed to calculate the desired injector flow rate using initial injector calibration factors. Using this multi-injector recalibration method, errors ranged from 0.23% to 0.66% between predicted and actual flow rates for all three injectors
The Pulsation Mode and Distance of the Cepheid FF Aquilae
The determination of pulsation mode and distance for field Cepheids is a
complicated problem best resolved by a luminosity estimate. For illustration a
technique based on spectroscopic luminosity discrimination is applied to the
4.47d s-Cepheid FF Aql. Line ratios in high dispersion spectra of the variable
yield values of =-3.40+-0.02 s.e.(+-0.04 s.d.), average effective
temperature Teff=6195+-24 K, and intrinsic color (-)o = +0.506+-0.007,
corresponding to a reddening of E(B-V)=0.25+-0.01, or E(B-V)(B0)=0.26+-0.01.
The skewed light curve, intrinsic color, and luminosity of FF Aql are
consistent with fundamental mode pulsation for a small amplitude classical
Cepheid on the blue side of the instability strip, not a sinusoidal pulsator. A
distance of 413+-14 pc is estimated from the Cepheid's angular diameter in
conjunction with a mean radius of =39.0+-0.7 Rsun inferred from its
luminosity and effective temperature. The dust extinction towards FF Aql is
described by a ratio of total-to-selective extinction of
Rv=Av/E(B-V)=3.16+-0.34 according to the star's apparent distance modulus.Comment: To appear in ApJ
Dynamics at the angle of repose: jamming, bistability, and collapse
When a sandpile relaxes under vibration, it is known that its measured angle
of repose is bistable in a range of values bounded by a material-dependent
maximal angle of stability; thus, at the same angle of repose, a sandpile can
be stationary or avalanching, depending on its history. In the nearly jammed
slow dynamical regime, sandpile collapse to a zero angle of repose can also
occur, as a rare event. We claim here that fluctuations of {\it dilatancy} (or
local density) are the key ingredient that can explain such varied phenomena.
In this work, we model the dynamics of the angle of repose and of the density
fluctuations, in the presence of external noise, by means of coupled stochastic
equations. Among other things, we are able to describe sandpile collapse in
terms of an activated process, where an effective temperature (related to the
density as well as to the external vibration intensity) competes against the
configurational barriers created by the density fluctuations.Comment: 15 pages, 1 figure. Minor changes and update
Height and Pressure Test for Improving Spray Application
Pesticide application in agricultural fields affects a little over a million acres each year (USDA 2012). Current spray application equipment can automatically adjust nozzle flow rates in reaction to speed changes to maintain consistent application rates across the field. Uniform distribution of pesticides from the spray boom is critical to ensure proper crop care while minimizing negative environmental effects. Boom pressure and height are two primary factors that affect proper spray uniformity; however information on the combined effects of these factors are limited. The goal of this study was to provide end users with quantified data regarding the effects of combined nozzle pressure and height variability on spray uniformity for three common spray nozzles. Specific objectives of this project were to 1) determine a suitable operating envelope (i.e., nozzle pressure and height) to meet current performance standards for the nozzles tests, 2) determine errors between theoretical spray distributions (from nozzle manufacturer flow and spacing data) to laboratory patternator data collected at different nozzle pressures, and 3) compare nozzle distribution errors (theoretical versus patternator data) with coefficient of variation (CV), a current spray uniformity performance metric. A laboratory patternator was used to collect nozzle distribution in 25 mm increments across the spray pattern while varying height and pressure for the spray nozzles tested. The operating envelope for different combinations of pressure and height was considered acceptable if the CV values were less than 10%. CV values were compared to root mean squared error (RMSE) for the AIXR 11003 nozzles operated at a height of 51 cm and four operating pressures to evaluate potential differences when accuracy is considered (i.e., RMSE). In some configurations the data exceeded 10% CV resulting in a more constricted operating envelope for each individual nozzle type. The CV values show more variance versus RMSE values. For the AIXR11003, as pressure increased the RMSE decreased in value, meaning the experimental pattern became closer to the ideal pattern as pressure increased. The CV values decreased as pressure increased until a threshold is reached; CV values focus on precision but not accuracy, showing the spray pattern was consistent but not necessarily accurate, indicating the CV disregards the theoretical values and does not indicate error in the values. Thus accuracy of spray pattern distribution may not be considered in the manufacturerâs nozzle report
Reddenings of FGK supergiants and classical Cepheids from spectroscopic data
Accurate and homogeneous atmospheric parameters (Teff, log (g), Vt, [Fe/H])
are derived for 74 FGK non-variable supergiants from high-resolution, high
signal-to-noise ratio, echelle spectra. Extremely high precision for the
inferred effective temperatures (10-40 K) is achieved by using the line-depth
ratio method. The new data are combined with atmospheric values for 164
classical Cepheids, observed at 675 different pulsation phases, taken from our
previously published studies. The derived values are correlated with unreddened
B-V colours compiled from the literature for the investigated stars in order to
obtain an empirical relationship of the form: (B-V)o = 57.984 - 10.3587(log
Teff)^2 + 1.67572(log Teff)^3 - 3.356(log (g)) + 0.0321(Vt) + 0.2615[Fe/H] +
0.8833((log (g))(log Teff)). The expression is used to estimate colour excesses
E(B-V) for individual supergiants and classical Cepheids, with a precision of
+-0.05 mag. for supergiants and Cepheids with n=1-2 spectra, reaching +-0.025
mag. for Cepheids with n>2 spectra, matching uncertainties for the most
sophisticated photometric techniques. The reddening scale is also a close match
to the system of space reddenings for Cepheids. The application range is for
spectral types F0--K0 and luminosity classes I and II.Comment: accepted for publication (MNRAS
- âŠ