Bonding interactions between ligand-decorated colloidal particles

<p>We study the interactions between particles that form reversible bonds. Theoretically, we find that the mean association constant between a pair of such particles can be well approximated by a double exponential function of the individual bond free energy when at least one of the following conditions holds: (i) when the individual bond strength is sufficiently weak and (ii) when the bond-forming ligands are randomly (Poisson) distributed among the particles in the system. In experiments with ligand-grafted colloidal particles, randomness in both the number of the ligands per colloid and the spatial distribution on the colloid is inherent to common fabrication techniques. We theoretically investigate the effect of quenched disordered ligand positions on interaction heterogeneity. Furthermore, we perform Monte Carlo simulations of colloidal particles decorated with mobile, quenched disordered, or uniformly distributed ligands to investigate the extent to which the mean association constant is a good approximation for the magnitude of the effective interactions in such systems, and to define the limits of applicability of the double exponential expression. We find that for large enough particles (100 nm–1 µm in diameter) at usual experimental parameters, the simple analytical expression provides a good description of the inter-particle interactions. The theory is finally extended beyond dimeric bonds to general multimeric complexes.</p

The effect of exercise-induced elevation in core temperature on cold-induced vasodilatation response in toes

Cold-induced vasodilatation (CIVD) has been proposed as a potential protective mechanism against cold injuries during exposure of extremities to a cold environment. The purpose of this study was to evaluate the effect of exercise and the associated elevation in core temperature on toe skin temperatures during immersion of the foot in cold (8°C) water. Subjects (N = 8) participated in two trials. In one, they conducted an incremental exercise to exhaustion (exercise) on a cycle ergometer, which was followed by immersion of the right foot in 8°C water. In the second trial (control), immersion of the foot in cold water was not preceded by exercise. Upon completion of the exercise in the exercise trial, and at the onset of the immersion of the foot in cold water, tympanic temperature was 0.6°C (P &lt; 0.01) higher than pre-exercise levels. There was a significant increase (P &lt; 0.05) in the number of CIVD waves, but not their amplitudes, in the exercise trial compared to the control trial. A CIVD response occurred in 57.5% of all toes in the exercise trial, and in only 27.5% in the control trial. Additionally, 50% of subjects exhibited CIVD in at least one toe in the control trial, and 87.5% during the exercise trial. It is concluded that exercise, and particularly the associated elevation in core temperature, enhances the frequency of the toe CIVD responses, and can therefore potentially act as a protective mechanism against cold injury. © Springer-Verlag 2009

The trainability and contralateral response of cold-induced vasodilatation in the fingers following repeated cold exposure

Cold-induced vasodilatation (CIVD) is proposed to be a protective response to prevent cold injuries in the extremities during cold exposure, but the laboratory-based trainability of CIVD responses in the hand remains equivocal. Therefore, we investigated the thermal response across the fingers with repeated local cold exposure of the whole hand, along with the transferability of acclimation to the fingers of the contralateral hand. Nine healthy subjects immersed their right hand up to the styloid process in 8°C water for 30 min daily for 13 days. The left hand was immersed on days 1 and 13. Skin temperature was recorded on the pads of the five fingertips and the dorsal surface of the hand. The presence of CIVD, defined as an increase in finger skin temperature of 0.5°C at any time during cooling, occurred in 98.5% of the 585 (9 subjects × 5 sites × 13 trials) measurements. Seven distinct patterns of thermal responses were evident, including plateaus in finger temperature and superimposed waves. The number (N) of CIVD waves decreased in all digits of the right hand over the acclimation period (P = 0.02), from average (SD) values ranging from 2.7 (1.7) to 3 (1.4) in different digits on day 1, to 1.9 (0.9) and 2.2 (0.7) on day 13. Average (SD) finger skin temperature (Tavg) ranged from 11.8 (1.4)°C in finger 5 to 12.7 (2.8)°C in finger 3 on day 1, and then decreased significantly (P &amp;lt; 0.001) over the course of the training immersions, attaining values ranging from 10.8 (0.9)°C in finger 4 to 10.9 (0.9)°C in finger 2 on day 13. In the contralateral hand, N was reduced from 2.5 to 1.5 (P &amp;lt; 0.01) and Tavg by ∼2°C (P &amp;lt; 0.01). No changes were observed in thermal sensation or comfort of the hand over the acclimation. We conclude that, under conditions of whole-hand immersion in cold water, CIVD is not trainable and may lead to systemic attenuation of thermal responses to local cooling. © Springer-Verlag 2008

The right delay: Detecting specific spike patterns with STDP and axonal conduction delays

Item does not contain fulltextAxonal conduction delays should not be ignored in simulations of spiking neural networks. Here it is shown that by using axonal conduction delays, neurons can display sensitivity to a specific spatio-temporal spike pattern. By using delays that complement the firing times in a pattern, spikes can arrive simultaneously at an output neuron, giving it a high chance of firing in response to that pattern. An unsupervised learning mechanism called spike-timing-dependent plasticity then increases the weights for connections used in the pattern, and decreases the others. This allows for an attunement of output neurons to specific activity patterns, based on temporal aspects of axonal conductivity.ICANNGA 10 - 10th international conference, ICANNGA 2010, Ljubljana, Slovenia, April 14-16, 201

Nanoparticle organization in sandwiched polymer brushes.

The organization of nanoparticles inside grafted polymer layers is governed by the interplay of polymer-induced entropic interactions and the action of externally applied fields. Earlier work had shown that strong external forces can drive the formation of colloidal structures in polymer brushes. Here we show that external fields are not essential to obtain such colloidal patterns: we report Monte Carlo and molecular dynamics simulations that demonstrate that ordered structures can be achieved by compressing a "sandwich" of two grafted polymer layers, or by squeezing a coated nanotube, with nanoparticles in between. We show that the pattern formation can be efficiently controlled by the applied pressure, while the characteristic length-scale, that is, the typical width of the patterns, is sensitive to the length of the polymers. Based on the results of the simulations, we derive an approximate equation of state for nanosandwiches