862 research outputs found
Crystallization Kinetics of Colloidal Spheres under Stationary Shear Flow
A systematic experimental study of dispersions of charged colloidal spheres
is presented on the effect of steady shear flow on nucleation and
crystal-growth rates. In addition, the non-equilibrium phase diagram as far as
the melting line is concerned is measured. Shear flow is found to strongly
affect induction times, crystal growth rates and the location of the melting
line. The main findings are that (i) the crystal growth rate for a given
concentration exhibits a maximum as a function of the shear rate, (ii) contrary
to the monotonous increase of the growth rate with increasing concentration in
the absence of flow, a maximum of the crystal growth rate as a function of
concentration is observed for sheared systems, and (iii) the induction time for
a given concentration exhibits a maximum as a function of the shear rate. These
findings will be partly explained on a qualitative level.Comment: 17 pages, 10 figures, accepted in Langmui
Accumulation of 125I-labelled thiouracil and propylthiouracil in murine melanotic melanomas.
We have shown that thioamides are incorporated as false precursors into melanin during its synthesis. To be clinically useful in the diagnosis or therapy of melanotic melanomas, they would have to be tagged with an appropriate isotope or possibly a cytotoxic moiety. 125I-Thiouracil (125I-TU) is here shown to be accumulated in the melanin of melanotic melanomas transplanted into mice in a similar way as is 14C-thiouracil (14C-TU). 125I-TU gives tumour/liver and tumour/muscle ratios up to 22 and 778 respectively, at 4 days after administration. 125I-TU is accumulated by melanoma cells in vitro more effectively than 14C-TU (125I-TU/14C-TU, 2.7), while the in vivo accumulation into melanomas is slightly lower for 125I-TU as compared to 14C-TU (125I-TU/14C-TU, 0.35). This appears to be due to a partial deiodination (less than 14% of the dose within 4 days) and probably a more rapid excretion of 125I-TU or its metabolite(s). The accumulation of radioactivity in the thyroid can essentially be eliminated by pretreatment with potassium iodide and/or thyroxine. 125I-Propylthiouracil is also accumulated in melanotic melanoma cells in vivo and in vitro, but at a lower level than in 125I-TU and 14C-TU
Learning from where âeyeâ remotely look or point: impact on number line estimation error in adults.
In this paper we present an investigation into the use of visual cues during number
line estimation, and their influence on cognitive processes for reducing number
line estimation error. Participants completed a 0-1000 number line estimation task
pre and post a brief intervention in which they observed static-visual or dynamicvisual
cues (control, anchor, gaze cursor, mouse cursor) and also made estimation
marks to test effective number-target estimation. Results indicated that a
significant pre-test to post-test reduction in estimation error was present for
dynamic visual cues of modelled eye-gaze and mouse-cursor. However, there was
no significant performance difference between pre and post-test for the control or
static anchor conditions. Findings are discussed in relation to the extent to which
anchor points alone are meaningful in promoting successful segmentation of the
number line, and whether dynamic cues promote the utility of these locations in
reducing error through attentional guidance
Design and development of a low-cost mask-type eye tracker to collect quality fixation measurements in the sport domain
The aim of the study was to build a low-cost mask-type eye tracker with accuracy and precision levels similar to those reported for commercial eye tracking devices. To this end, head-mounted hardware was designed and developed, while open-source software was modified for digital image capture, manipulation, and fixation analysis. An image recognition application was also included with different lighting scenarios. Moreover, parallax and viewing perspective errors were controlled to ensure the quality of data collection. The device was wireless and lightweight (99âg) to allow for natural movement and avoid participant discomfort. After calibration of a 9-target monocular grid, spatial accuracy and precision of the eye tracker was evaluated by 30 participants, at four different lighting setups, both before and after a climbing task. Validity tests showed high levels of accuracy in all conditions as evidenced by a systematic error for a 13-target grid of <0.5°. The reliability tests also showed consistent measurements with no differences in accuracy recorded between participants, lighting conditions, and visual behaviors for the pre- versus post-climbing task. These results suggest that the present eye tracker reports spatial accuracy similar to other commercial systems with levels of high quality. Altogether, this innovative user interface is suitable for research purposes and/or performance analysis in physical activity and sport-related activities. Also, features of this mask-type eye tracking system make it a suitable perceptual user interface to investigate humanâcomputer interactions in a large number of other research fields including psychology, education, marketing, transportation, and medicine
Nematic-Isotropic Spinodal Decomposition Kinetics of Rod-like Viruses
We investigate spinodal decomposition kinetics of an initially nematic
dispersion of rod-like viruses (fd virus). Quench experiments are performed
from a flow-stabilized homogeneous nematic state at high shear rate into the
two-phase isotropic-nematic coexistence region at zero shear rate. We present
experimental evidence that spinodal decomposition is driven by orientational
diffusion, in accordance with a very recent theory.Comment: 17 pages, 6 figures, accepted in Phys. Rev.
Does Social Presence or the Potential for Interaction reduce Social Gaze in Online Social Scenarios? Introducing the "Live Lab" paradigm.
Research has shown that peopleâs gaze is biased away from faces in the real-world but
towards them when they are viewed onscreen. Non-equivalent stimulus conditions may have
represented a confound in this research however, as participants viewed onscreen stimuli as
pre-recordings where interaction was not possible, compared to real-world stimuli which
were viewed in real-time where interaction was possible. We assessed the independent
contributions of online social presence and ability for interaction on social gaze by
developing the âlive labâ paradigm. Participants in three groups (N = 132) viewed a
confederate either as a) a live webcam stream where interaction was not possible (one-way),
b) a live webcam stream where an interaction was possible (two-way) or c) as a prerecording.
Potential for interaction, rather than online social presence, was the primary
influence on gaze behaviour: Participants in the pre-recorded and one-way conditions looked
more to the face than those in the two-way condition, particularly when the confederate made
âeye contactâ. Fixation durations to the face were shorter when the scene was viewed live,
particularly during a bid for eye contact
Our findings support the dual function of gaze, but suggest that online social presence alone
is not sufficient to activate social norms of civil inattention. Implications for the
reinterpretation of previous research are discussed
Grad-seq guides the discovery of ProQ as a major small RNA-binding protein
The functional annotation of transcriptomes and identification of noncoding RNA (ncRNA) classes has been greatly facilitated by the advent of next-generation RNA sequencing which, by reading the nucleotide order of transcripts, theoretically allows the rapid profiling of all transcripts in a cell. However, primary sequence per se is a poor predictor of function, as ncRNAs dramatically vary in length and structure and often lack identifiable motifs. Therefore, to visualize an informative RNA landscape of organisms with potentially new RNA biology that are emerging from microbiome and environmental studies requires the use of more functionally relevant criteria. One such criterion is the association of RNAs with functionally important cognate RNA-binding proteins. Here we analyze the full ensemble of cellular RNAs using gradient profiling by sequencing (Grad-seq) in the bacterial pathogen Salmonella enterica, partitioning its coding and noncoding transcripts based on their network of RNAâprotein interactions. In addition to capturing established RNA classes based on their biochemical profiles, the Grad-seq approach enabled the discovery of an overlooked large collective of structured small RNAs that form stable complexes with the conserved protein ProQ. We show that ProQ is an abundant RNA-binding protein with a wide range of ligands and a global influence on Salmonella gene expression. Given its generic ability to chart a functional RNA landscape irrespective of transcript length and sequence diversity, Grad-seq promises to define functional RNA classes and major RNA-binding proteins in both model species and genetically intractable organisms
Pupil dilation as an implicit measure of appetitive Pavlovian learning
Appetitive Pavlovian conditioning is a learning mechanism of fundamental biological and pathophysiological significance. Nonetheless, its exploration in humans remains sparse, which is partly attributed to the lack of an established psychophysiological parameter that aptly represents conditioned responding. This study evaluated pupil diameter and other ocular response measures (gaze dwelling time, blink duration and count) as indices of conditioning. Additionally, a learning model was used to infer participants' learning progress on the basis of their pupil dilation. Twenty-nine healthy volunteers completed an appetitive differential delay conditioning paradigm with a primary reward, while the ocular response measures along with other psychophysiological (heart rate, electrodermal activity, postauricular and eyeblink reflex) and behavioral (ratings, contingency awareness) parameters were obtained to examine the relation among different measures. A significantly stronger increase in pupil diameter, longer gaze duration and shorter eyeblink duration was observed in response to the reward-predicting cue compared to the control cue. The Pearce-Hall attention model best predicted the trial-by-trial pupil diameter. This conditioned response was corroborated by a pronounced heart rate deceleration to the reward-predicting cue, while no conditioning effect was observed in the electrodermal activity or startle responses. There was no discernible correlation between the psychophysiological response measures. These results highlight the potential value of ocular response measures as sensitive indices for representing appetitive conditioning
Exploring the nature of visual fixations on other pedestrians
How we look at other people may affect conclusions drawn about the effect of changes in lighting when this task needs to be done after dark. This paper reports further analysis of the distance and duration of fixation on other pedestrians, updating a previous review by considering a greater number of fixations and by examining the influence on these of other characteristics such as the relative direction of travel. This analysis provides further support for a tendency to fixate others at a distance of 15 m and for a duration of 500 ms
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