1,345 research outputs found
Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy
We have recorded dose-fractionated electron cryo-microscope images of thin
films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on
a Falcon~II direct electron detector using 300 keV electrons. We observe Thon
rings \cite{Thon1966} in both the power spectrum of the summed frames and the
sum of power spectra from the individual frames. The Thon rings from amorphous
carbon images are always more visible in the power spectrum of the summed
frames whereas those of amorphous ice are more visible in the sum of power
spectra from the individual frames. This difference indicates that while
pre-irradiated carbon behaves like a solid during the exposure, amorphous ice
behaves like a fluid with the individual water molecules undergoing
beam-induced motion. Using the measured variation in the power spectra
amplitude with number of electrons per image we deduce that water molecules are
randomly displaced by mean squared distance of 1.1 \AA for every
incident 300 keV e/\AA. The induced motion leads to an optimal
exposure with 300 keV electrons of 4.0 e/\AA per image with which to
see Thon rings centred around the strong 3.7{\AA} scattering peak from
amorphous ice. The beam-induced movement of the water molecules generates
pseudo-Brownian motion of embedded macromolecules. The resulting blurring of
single particle images contributes an additional term, on top of that from
radiation damage, to the minimum achievable B-factor for macromolecular
structure determination.Comment: 11 pages, 6 figures, Supplementary information 6 pages with 5 figure
A New Symmetry for QED
We demonstrate that QED exhibits a previously unobserved symmetry. Some
consequences are discussed.Comment: 9 pages, MZ-TH/93-02, DIAS-STP-93-0
Efficacy of a four-week uphill sprint training intervention in field hockey players
Current evidence increasingly suggests that very short, supra-maximal bouts of exercise can have significant health and performance benefits. The majority of research conducted in the area however, uses laboratory-based protocols, which can lack ecological validity. The purpose of this study was to examine the effects of a high intensity sprint-training programme on hockey related performance measures. 14 semi-professional hockey players completed either a 4-week high intensity training (HIT) intervention, consisting of a total of six sessions HIT, which progressively increased in volume (n=7), or followed their normal training programme (Con; n=7). Straight-line sprint speed with and without a hockey stick and ball, and slalom sprint speed, with and without a hockey stick and ball were used as performance indicators. Maximal sprint speed over 22.9m was also assessed. Upon completion of the four-week intervention, straight-line sprint speed improved significantly in the HIT group (~3%), with no change in performance for the Con group. Slalom sprint speed, both with and without a hockey ball was not significantly different following the training programme in either group. Maximal sprint speed improved significantly (12.1%) in the HIT group, but there was no significant performance change in the Con group. The findings of this study indicate that a short period of HIT can significantly improve hockey related performance measures, and could be beneficial to athletes and coaches in field settings
The Impact of Full and Half-day Head Start Programs on Kindergarten Readiness
The 2013-2014 school year brought mandated school readiness screenings to 173 school districts across the state of Kentucky. According to the Governor’s Task Force on early childhood development and education (2012), school readiness is defined as: each child enters school ready to engage in and benefit from early learning experiences that best promote the child’s success. To assess whether students were school ready the use of the Brigance© Screens III was implemented across the state. This study investigated the impact of enrollment in half and full-day Head Start programs on kindergarten readiness for students in Kentucky as measured by the Brigance© Screens III. The Brigance© scores were analyzed using the composite score and subdomain scores which are reported as ready, not ready, or ready with supports. A multivariate analysis of variance, or MANOVA, was utilized to examine if there was a significant difference in full or half-day readiness outcomes
Comparison of optimal performance at 300keV of three direct electron detectors for use in low dose electron microscopy
Low dose electron imaging applications such as electron cryo-microscopy are now benefitting from the improved performance and flexibility of recently introduced electron imaging detectors in which electrons are directly incident on backthinned CMOS sensors. There are currently three commercially available detectors of this type: the Direct Electron DE-20, the FEI Falcon II and the Gatan K2 Summit. These have different characteristics and so it is important to compare their imaging properties carefully with a view to optimise how each is used. Results at 300 keV for both the modulation transfer function (MTF) and the detective quantum efficiency (DQE) are presented. Of these, the DQE is the most important in the study of radiation sensitive samples where detector performance is crucial. We find that all three detectors have a better DQE than film. The K2 Summit has the best DQE at low spatial frequencies but with increasing spatial frequency its DQE falls below that of the Falcon II
From head to tail it's a 2 way street for neuro-immune communication
Animals need to be able to rapidly and effectively respond to changes in their external and internal environment. To achieve this the nervous and immune systems need to coordinate their responses, integrating multiple cues including presence of potential pathogens, and availability of food. In our recent study we demonstrate that signaling by sensory neurons in the head using the classical neurotransmitter serotonin can negatively regulate the rectal epithelial immune response upon infection of C. elegans with the naturally occurring bacterial pathogen Microbacterium nematophilum (M. nematophilum). The complicated nature of the mammalian brain and immune system has made it difficult to identify the molecular mechanisms mediating these interactions. With its simple, well described, nervous system and a rapidly growing understanding of its immune system, C. elegans has emerged as an excellent model to study the mechanisms by which animals recognize pathogens and coordinate behavioral and cellular immune responses to infection
Quantumness in decoherent quantum walk using measurement-induced disturbance
The classicalization of a decoherent discrete-time quantum walk on a line or
an n-cycle can be demonstrated in various ways that do not necessarily provide
a geometry-independent description. For example, the position probability
distribution becomes increasingly Gaussian, with a concomitant fall in the
standard deviation, in the former case, but not in the latter. As another
example, each step of the quantum walk on a line may be subjected to an
arbitrary phase gate, without affecting the position probability distribution,
no matter whether the walk is noiseless or noisy. This symmetry, which is
absent in the case of noiseless cyclic walk, but is restored in the presence of
sufficient noise, serves as an indicator of classicalization, but only in the
cyclic case. Here we show that the degree of quantum correlations between the
coin and position degrees of freedom, quantified by a measure based on the
disturbance induced by local measurements (Luo, Phys. Rev. A 77, 022301
(2008)), provides a suitable measure of classicalization across both type of
walks. Applying this measure to compare the two walks, we find that cyclic
quantum walks tend to classicalize faster than quantum walks on a line because
of more efficient phase randomization due to the self-interference of the two
counter-rotating waves. We model noise as acting on the coin, and given by the
squeezed generalized amplitude damping (SGAD) channel, which generalizes the
generalized amplitude damping channel.Comment: 8 pages with 8 figures, Published versio
The Glue Around Quarks and the Interquark Potential
The quarks of quark models cannot be identified with the quarks of the QCD
Lagrangian. We review the restrictions that gauge field theories place on any
description of physical (colour) charges. A method to construct charged
particles is presented. The solutions are applied to a variety of applications.
Their Green's functions are shown to be free of infra-red divergences to all
orders in perturbation theory. The interquark potential is analysed and it is
shown that the interaction responsible for anti-screening results from the
force between two separately gauge invariant constituent quarks. A fundamental
limit on the applicability of quark models is identified.Comment: 4 pages, LaTeX, talk given at Montpellier meeting QCD9
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