10,723 research outputs found
Organosolv pretreatment of Sitka spruce wood: conversion of hemicelluloses to ethyl glycosides
A range of organosolv pretreatments, using ethanol:water mixtures with dilute sulphuric acid, were applied to Sitka spruce sawdust with the aim of generating useful co-products as well as improving saccharification yield. The most efficient of the pretreatment conditions, resulting in subsequent saccharification yields of up to 86%, converted a large part of the hemicellulose sugars to their ethyl glycosides as identified by GC/MS. These conditions also reduced conversion of pentoses to furfural, the ethyl glycosides being more stable to dehydration than the parent pentoses. Through comparison with the behaviour of model compounds under the same reaction conditions it was shown that the anomeric composition of the products was consistent with a predominant transglycosylation reaction mechanism, rather than hydrolysis followed by glycosylation. The ethyl glycosides have potential as intermediates in the sustainable production of high-value chemicals
Isolation of high quality lignin as a by-product from ammonia percolation pretreatment of poplar wood
A two-step process combining percolation-mode ammonia pretreatment of poplar sawdust with mild organosolv purification of the extracted lignin produced high quality, high purity lignin in up to 31% yield and 50% recovery. The uncondensed fraction of the isolated lignin was up to 34%, close to that the native lignin (40%). Less lignin was recovered after pretreatment in batch mode, apparently due to condensation during the longer residence time of the solubilised lignin at elevated temperature. The lignin recovery was directly correlated with its molecular weight and its nitrogen content. Low nitrogen incorporation, observed at high ammonia concentration, may be explained by limited homolytic cleavage of -O-4 bonds. Ammonia concentrations from 15% to 25% (w/w) gave similar results in terms of lignin structure, yield and recovery
New Method to Calculate Electrical Forces Acting on a Sphere in an Electrorheological Fluid
We describe a method to calculate the electrical force acting on a sphere in
a suspension of dielectric spheres in a host with a different dielectric
constant, under the assumption that a spatially uniform electric field is
applied. The method uses a spectral representation for the total electrostatic
energy of the composite. The force is expressed as a certain gradient of this
energy, which can be expressed in a closed analytic form rather than evaluated
as a numerical derivative. The method is applicable even when both the spheres
and the host have frequency-dependent dielectric functions and nonzero
conductivities, provided the system is in the quasistatic regime. In principle,
it includes all multipolar contributions to the force, and it can be used to
calculate multi-body as well as pairwise forces. We also present several
numerical examples, including host fluids with finite conductivities. The force
between spheres approaches the dipole-dipole limit, as expected, at large
separations, but departs drastically from that limit when the spheres are
nearly in contact. The force may also change sign as a function of frequency
when the host is a slightly conducting fluid.Comment: 29 pages, 8 figures, Accepted for Publication in Physical Review
Representing Structural Information of Helical Charge Distributions in Cylindrical Coordinates
Structural information in the local electric field produced by helical charge
distributions, such as dissolved DNA, is revealed in a straightforward manner
employing cylindrical coordinates. Comparison of structure factors derived in
terms of cylindrical and helical coordinates is made. A simple coordinate
transformation serves to relate the Green function in cylindrical and helical
coordinates. We also compare the electric field on the central axis of a single
helix as calculated in both systems.Comment: 11 pages in plain LaTex, no figures. Accepted for publication in PRE
March, 199
Extended 1D Method for Coherent Synchrotron Radiation including Shielding
Coherent Synchrotron Radiation can severely limit the performance of
accelerators designed for high brightness and short bunch length. Examples
include light sources based on ERLs or FELs, and bunch compressors for linear
colliders. In order to better simulate Coherent Synchrotron Radiation, the
established 1-dimensional formalism is extended to work at lower energies, at
shorter bunch lengths, and for an arbitrary configuration of multiple bends.
Wide vacuum chambers are simulated by means of vertical image charges. This
formalism has been implemented in the general beam dynamics code "Bmad" and its
results are here compared to analytical approximations, to numerical solutions
of the Maxwell equations, and to the simulation code "elegant"
Comparison of Different Minimal Velocity Thresholds to Establish Deadlift One Repetition Maximum
The aim of this study was to compare the actual deadlift one repetition maximum (1RM)
and the deadlift 1RM predicted from individualised load-velocity profiles. Twelve moderately
resistance-trained men participated in three deadlift sessions. During the first, 1RM was assessed;
during the second, load-velocity profiles were recorded with six loads (65% to 90% 1RM) using
a linear position transducer recording at 1000 Hz; and during the third, minimal velocity thresholds
(MVT) were recorded from the velocity of the last repetition during sets to volitional fatigue with 70%
and 80% 1RM with a linear position transducer recording at 1000 Hz. Regression was then used to
generate individualised load-velocity profiles and the MVT was used as a cut-off value from which
to predict deadlift 1RM. In general, velocity reliability was poor to moderate. More importantly,
predicted deadlift 1RMs were significantly and meaningfully less than actual deadlift 1RMs (p < 0.05,
d = 1.03–1.75). The main practical application that should be taken from the results of this study is that
individualized load-velocity profiles should not be used to predict deadlift 1RM. Practitioners should
not use this method in combination with the application of MVT obtained from the last repetition of
sets to volitional fatigue
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