Characterizing rare fluctuations in soft particulate flows.

Soft particulate media include a wide range of systems involving athermal dissipative particles both in non-living and biological materials. Characterization of flows of particulate media is of great practical and theoretical importance. A fascinating feature of these systems is the existence of a critical rigidity transition in the dense regime dominated by highly intermittent fluctuations that severely affects the flow properties. Here, we unveil the underlying mechanisms of rare fluctuations in soft particulate flows. We find that rare fluctuations have different origins above and below the critical jamming density and become suppressed near the jamming transition. We then conjecture a time-independent local fluctuation relation, which we verify numerically, and that gives rise to an effective temperature. We discuss similarities and differences between our proposed effective temperature with the conventional kinetic temperature in the system by means of a universal scaling collapse.Soft particulate flows such as granular media are prone to fluctuations like jamming and avalanches. Here Rahbari et al. consider the statistics of rare fluctuations to identify an effective temperature which, unlike previous ones, is valid for packing fractions both near and far from the jamming point.

Impact of microphysics on the growth of one-dimensional breath figures.

Droplet patterns condensing on solid substrates (breath figures) tend to evolve into a self-similar regime, characterized by a bimodal droplet size distribution. The distributions comprise a bell-shaped peak of monodisperse large droplets and a broad range of smaller droplets. The size distribution of the latter follows a scaling law characterized by a nontrivial polydispersity exponent. We present here a numerical model for three-dimensional droplets on a one-dimensional substrate (fiber) that accounts for droplet nucleation, growth, and merging. The polydispersity exponent retrieved using this model is not universal. Rather it depends on the microscopic details of droplet nucleation and merging. In addition, its values consistently differ from the theoretical prediction by Blackman and Brochard [Phys. Rev. Lett. 84, 4409 (2000)]. Possible causes of this discrepancy are pointed out.

Arrest stress of uniformly sheared wet granular matter.

We conduct extensive independent numerical experiments considering frictionless disks without internal degrees of freedom (rotation, etc.) in two dimensions. We report here that for a large range of the packing fractions below random-close packing, all components of the stress tensor of wet granular materials remain finite in the limit of zero shear rate. This is direct evidence for a fluid-to-solid arrest transition. The offset value of the shear stress characterizes plastic deformation of the arrested state which corresponds to dynamic yield stress of the system. Based on an analytical line of argument, we propose that the mean number of capillary bridges per particle, ν, follows a nontrivial dependence on the packing fraction, ϕ, and the capillary energy, ɛ. Most noticeably, we show that ν is a generic and universal quantity which does not depend on the driving protocol. Using this universal quantity, we calculate the arrest stress, σ(a), analytically based on a balance of the energy injection rate due to the external force driving the flow and the dissipation rate accounting for the rupture of capillary bridges. The resulting prediction of σ(a) is a nonlinear function of the packing fraction, ϕ, and the capillary energy, ɛ. This formula provides an excellent, parameter-free prediction of the numerical data. Corrections to the theory for small and large packing fractions are connected to the emergence of shear bands and of contributions to the stress from repulsive particle interactions, respectively.

The effect of mutations near the T1 copper site on the biochemical characteristics of the small laccase from Streptomyces coelicolor A3(2).

Bacterial laccases show low activities but can be of biotechnological interest due to industrially suitable characteristics such as thermostability and tolerance to alkaline pH. In this study, three separate mutations (M298F, V290N and V290A) were introduced at or near the T1 copper site of the small laccase (SLAC) from Streptomyces coelicolor A3(2) and biochemical properties were assessed in comparison with the native enzyme. The mutation, V290N showed approximately double the activity of SLAC when ABTS was used as substrate while the specific activity of SLAC-M298F was 4-5 times higher than that of SLAC when the assays were performed at ≥70°C. There was no significant difference in activity with 2,6-dimethoxyphenol (2,6-DMP); however, there was a significant shift in the optimal pH from pH 9.5 (SLAC) to 7.5 (SLAC-V290N). Optimal temperature for activity was not significantly altered but thermostability was reduced in all three mutants. The substrate range of the mutant variants remained largely unchanged, with the exception of SLAC-M298F which was unable to oxidise veratryl alcohol. Interestingly, the "typical" laccase inhibitor, sodium azide, had no significant inhibitory effect on the activity of SLAC-M298F, which also exhibited increased resistance to inhibition by sulfhydryl compounds. SLAC-V290N showed higher catalytic efficiency for 2,6-DMP (kcat/Km=2.226mM(-1)s(-1)) and ABTS (kcat/Km=1.874mM(-1)s(-1)) compared to SLAC (kcat/Km=1.615mM(-1)s(-1) for 2,6-DMP and kcat/Km=1.611mM(-1)s(-1) for ABTS). This study has shown that three ligands that are closely associated with the T1 copper in SLAC play a key role in maintaining enzymatic activity. Whilst the introduction of mutations at these sites negated favourable characteristics such as thermostability, several favourable effects were observed. This study has also extended the knowledge base on the biochemical characteristics of SLAC, and its suitability as a template for engineering with the aim of widening its potential range of industrial applications.

Resting state functional magnetic resonance imaging reveals distinct brain activity in heavy cannabis users - a multi-voxel pattern analysis.

Chronic cannabis use can cause cognitive, perceptual and personality alterations, which are believed to be associated with regional brain changes and possible changes in connectivity between functional regions. This study aims to identify the changes from resting state functional magnetic resonance imaging scans. A two-level multi-voxel pattern analysis was proposed to classify male cannabis users from normal controls. The first level analysis works on a voxel basis and identifies clusters for the input of a second level analysis, which works on the functional connectivity between these regions. We found distinct clusters for male cannabis users in the middle frontal gyrus, precentral gyrus, superior frontal gyrus, posterior cingulate cortex, cerebellum and some other regions. Based on the functional connectivity of these clusters, a high overall accuracy rate of 84-88% in classification accuracy was achieved. High correlations were also found between the overall classification accuracy and Barrett Barrett Impulsiveness Scale factor scores of attention and motor. Our result suggests regional differences in the brains of male cannabis users that span from the cerebellum to the prefrontal cortex, which are associated with differences in functional connectivity.

Network representations of nonequilibrium steady states: Cycle decompositions, symmetries, and dominant paths.

Nonequilibrium steady states of Markov processes give rise to nontrivial cyclic probability fluxes. Cycle decompositions of the steady state offer an effective description of such fluxes. Here we present an iterative cycle decomposition exhibiting a natural dynamics on the space of cycles that satisfies detailed balance. Expectation values of observables can be expressed as cycle "averages," resembling the cycle representation of expectation values in dynamical systems. We illustrate our approach in terms of an analogy to a simple model of mass transit dynamics. Symmetries are reflected in our approach by a reduction of the minimal number of cycles needed in the decomposition. These features are demonstrated by discussing a variant of an asymmetric exclusion process. Intriguingly, a continuous change of dominant flow paths in the network results in a change of the structure of cycles as well as in discontinuous jumps in cycle weights.

Fluidization of wet granulates under shear.

Small amounts of a wetting liquid render sand a stiff and moldable material. The cohesive forces between the sand grains are caused by capillary bridges at the points of contact. Due to the finite strength of these bridges wet sand undergoes a transition from an arrested (i.e., solidified) to a fluidized state under an externally applied shear force. The transition between these two dynamic states is studied in a MD-type simulation of a two-dimensional assembly of bidisperse frictionless disks under the action of a cosine force profile. In addition to soft core repulsion the disks interact through a hysteretic and short ranged attractive force modeling the effect of the capillary bridges. In this model the transition between the fluidized and the arrested state is discontinuous and hysteretic. The parameter dependence of the critical force for solidification is modeled by combining theoretical arguments with a detailed numerical exploration of the transition. We address a range of densities from slightly below close packing until slightly above densities where the system approaches a shear-banded state. Differences and similarities of the transition in wet granulates to the jamming transition are also addressed.

Phase separation under ultraslow cooling: Onset of nucleation.

We discuss the interplay between a slow continuous drift of temperature, which induces continuous phase separation, and the nonlinear diffusion term in the phi(4)-model for phase separation of a binary mixture. This leads to a bound for the stability of diffusive demixing. It is demonstrated that the same findings apply in other models, except for slight modifications of the bound. In practice stable diffusive demixing can only be achieved when special precautions are taken in experiments on real mixtures. Therefore, the recent observations on complex dynamical behavior in such systems should be considered as a new challenge for understanding generic features of phase-separating systems.

[Severe encephalitis without correlate in MRI]. / Schwerste Enzephalitiden ohne Korrelat im MRT.

Encephalitis could be a life-threatening disease depending on localisation and infectious agent. Neuroimaging, especially MRI, is an important component in the diagnosis. The recent investigations demonstrate that diffusion abnormalities are the first and sensitive signs of viral encephalitis. We describe five patients with severe encephalitis with normal MR imaging. Three of five patients were intermittently mechanically ventilated, two of these longer than 4 weeks. The other two patients suffered from a severe psychosyndrome with seriously limited ability to communicate throughout 6 weeks. At the time of first MRI examination all patients were noticeably ill. Four of five patients had at least one follow-up MRI. The MRI examinations included FLAIR sequences and DWI in four of five patients. Contrast-enhancement was detectable in none of our patients. Follow-up examinations revealed that symptoms of encephalitis were noticeably or completely regressive.

[Combined simulation training: a new concept and workshop is useful for crisis management in gastrointestinal endoscopy]. / Kombiniertes Simulationstraining: Ein neues Kurskonzept trainiert und verbessert das Krisenmanagement der gastroenterologischen Endoskopie.

INTRODUCTION: Crisis management as well as realistic emergency situations can be trained in the new developed simulation workshop "Gastrointestinal Endoscopy and Crisis Resource Management" by combining a full-scale simulator and the Erlanger Endoscopy Trainer. The aim of the current study was to evaluate the efficiency of the newly developed simulation workshop. METHODS: Endoscopists with more than 12 months experience can train their endoscopic skills and crisis resource management with the help of different simulators. In addition, two different scenarios (GI bleeding with significant blood loss and sedation overdoses) embedded in a realistic surrounding (emergency room) have to be managed by the participants. Vital parameters, endoscopic skills, as well as personal interactions were recorded and graded. RESULTS: 100 participants took part in the newly developed workshop (between June and December 2003). The participants showed a significantly better endoscopic performance and a significantly better crisis management after the standardized training program. CONCLUSIONS: Simulation training plays an essential role in aviation and minimizes the risk for human errors. In the current study it is clearly shown that simulation training is also useful in gastrointestinal endoscopy. The newly developed workshop may thus be of crucial importance to improve personal crisis management. Simulation also leads to an improvement of endoscopic and emergency skills. Accordingly, simulation training should be recommended or offered as an education option in gastrointestinal endoscopy.

Coarse-grained entropy and information dimension of dynamical systems: The driven Lorentz gas.

We study the resolution dependence of the steady-state saturation values of coarse-grained entropies characterizing general dynamical systems. For dissipative maps they are proportional to the information codimension of the chaotic attractor. Thus, they provide a highly accurate method for determining the information dimension and related characteristics of the dynamical system. This general result is demonstrated for the field-driven Lorentz gas. In the discussion, we take the results on the resolution dependence of the entropy as the starting point to revisit different approaches to define thermodynamic entropy production for transport processes in dynamical systems, and discuss the role of local equilibrium in this enterprise.

Heat and cold-induced male sterility in Drosophila buzzatii: genetic variation among populations for the duration of sterility.

Here we studied three phenotypic traits in Drosophila buzzatii that are strongly effected by temperature, and are expected to be closely associated with fitness in nature. The traits measured were thermal threshold of male sterility, time for males to gain fertility when reared at a sterility-inducing temperature and transferred to 25 degrees C on eclosion and survival after development. The last two traits were measured under four temperature regimes, constant 12 degrees C, 25 degrees C, 31 degrees C, and fluctuating 25 degrees C (18 h) and 38 degrees C (6 h). We looked for genetic variation in these traits and relations among them in four lines of D. buzzatii originating from Argentina and Tenerife. The thermal threshold of heat-induced male sterility was found to lie within the range of 30.0-31.0 degrees C. When measuring the time for males to gain fertility, males reared at a nonstressful temperature (25 degrees C) were fertile 58-67 h after emergence with only minor differences among lines. When reared constant 31 degrees C, males were fertile 174-225 h after hatching. The Argentinean lines were significantly faster in recovering from sterility than were the lines from Tenerife. When reared in a fluctuating temperature regime, differences among lines increased, dividing the lines into three significantly different groups, with a sterility period of 135-215 h. When reared at 12 degrees C from the pupal stage, males were fertile after 106-130 h with significant difference in the variance but not in the mean duration of sterility. Significant differences in viability were found among development temperatures, but not among lines, and viability and the duration of sterility seem to be genetically independent.

Phase separation in binary fluid mixtures with continuously ramped temperature.

We consider the demixing of a binary fluid mixture, under gravity, which is steadily driven into a two-phase region by slowly ramping the temperature. We assume, as a first approximation, that the system remains spatially isothermal, and we examine the interplay of two competing nonlinearities. One of these arises because the supersaturation is greatest far from the meniscus, creating inversions of the density which can lead to fluid motion; although isothermal, this is somewhat like the Bénard problem (a single-phase fluid heated from below). The other is the intrinsic diffusive instability which results either in nucleation or in spinodal decomposition at large supersaturations. Experimental results on a simple binary mixture show interesting oscillations in heat capacity and optical properties, for a wide range of ramp parameters. We argue that these oscillations arise under conditions where both nonlinearities are important.

Multibaker map for shear flow and viscous heating.

A consistent description of shear flow and the accompanying viscous heating as well as the associated entropy balance is given in the framework of a deterministic dynamical system. The laminar shear flow is modeled by a Hamiltonian multibaker map which drives velocity and temperature fields. In the appropriate macroscopic limit one recovers the Navier-Stokes and heat conduction equations along with the associated entropy balance. This indicates that results of nonequilibrium thermodynamics can be described by means of an abstract, sufficiently chaotic, and mixing dynamics. A thermostating algorithm can also be incorporated into this framework.

Antigen contacts by Ni-reactive TCR: typical alphass chain cooperation versus alpha chain-dominated specificity.

VB17(+) TCR dominate in Ni-driven T cell cultures from highly Ni-sensitized patients. Using transfection of TCR from three CD4(+), VB17(+), Ni-specific human T cell clones, we studied their Ni-MHC contacts by site-directed TCR mutation and combination of alpha and ss chains between different TCR. All three TCR exhibited N-nucleotide-determined Arg-Asp motifs in their CDR3-ss sequences. Two of them were specifically restricted to HLA-DR13, while the third one accepted a variety of HLA-DR alleles. The highly similar alpha or ss chains of the DR13-restricted TCR were interchangable without loss of specificity, but alpha or ss chains of other TCR were not tolerated. Mutations of their Arg-Asp motif revealed loss of reactivity upon exchanging Asp for Glu or Ala and of Arg for Ala but not of Arg for Lys or the Ni binding His. Reactivity was also destroyed by mutation of alpha chain position 51, proposed as a general contact site for MHC. Hence, in these two TCR the Arg-Asp motif is clearly involved in contacting Ni-MHC complexes, and close cooperation between alpha and ss chain is required. In contrast, the third TCR retained Ni reactivity upon mutation of alpha chain position 51 or of its ss chain Arg-Asp motif, which rather affected the pattern of DR cross-restriction. Moreover, its alpha chain paired with various ss chains from other, even mouse TCR, irrespective of their specificity, retaining Ni reactivity as well as promiscuous HLA-DR restriction. This preponderance of an alpha chain in defining specificity indicates fundamental differences in Ni interactions of individual TCR and implies that ss chain similarities may not necessarily result from antigen selection.

Thermodynamic cross effects from dynamical systems

We give a thermodynamically consistent description of simultaneous heat and particle transport, as well as of the associated cross effects, in the framework of a chaotic dynamical system, a generalized multibaker map. Besides the density, a second field with appropriate source terms is included in order to mimic, after coarse graining, a spatial temperature distribution and its time evolution. An expression is derived for the irreversible entropy production in a steady state, as the average of the growth rate of the relative density, a unique combination of the two fields.

Multibaker map for thermodynamic cross effects in dynamical systems

A consistent description of simultaneous heat and particle transport, including cross effects, and the associated entropy balance is given in the framework of a deterministic dynamical system. This is achieved by a multibaker map where, in addition to the phase-space density of the multibaker, a second field with appropriate source terms is included in order to mimic a spatial temperature distribution and its time evolution. Conditions are given to ensure consistency in an appropriately defined continuum limit with the thermodynamic entropy balance. They leave as the only free parameter of the model the entropy flux let directly into the surroundings. If it vanishes in the bulk, the transport properties of the model are described by the thermodynamic transport equations. Another choice leads to a uniform temperature distribution. It represents transport problems treated by means of a thermostating algorithm, similar to the one considered in nonequilibrium molecular dynamics.

Fluctuation theorems for entropy production in open systems

We derive a fluctuation theorem to describe entropy fluctuations in steady states of systems with density gradients due to open boundaries. The fluctuations are related to the growth rate of the phase-space density, instead of the phase-space contraction rate. Explicit derivations are presented for a multibaker map, but the arguments are rather general, and should hold for a much wider class of dynamical systems. A comparison with recent results for stochastic systems is also given.

Subcellular compartmentalization of activation and desensitization of responses mediated by NK2 neurokinin receptors.

A functional fluorescent neurokinin NK2 receptor was constructed by joining enhanced green fluorescent protein to the amino-terminal end of the rat NK2 receptor and was expressed in human embryonic kidney cells. On cell suspensions, the binding of fluorescent Bodipy-labeled neurokinin A results in a saturatable and reversible decrease of NK2 receptor fluorescence via fluorescence resonance energy transfer. This can be quantified for nM to microM agonist concentrations and monitored in parallel with intracellular calcium responses. On single cells, receptor site occupancy and local agonist concentration can be determined in real time from the decrease in receptor fluorescence. Simultaneous measurement of intracellular calcium responses and agonist binding reveals that partial receptor site occupancy is sufficient to desensitize cellular response to a second agonist application to the same membrane area. Subsequent stimulation of a distal membrane area leads to a second response to agonist, provided that it had not been exposed to agonist during the first application. Together with persistent translocation of fluorescent protein kinase C to the membrane area exposed to agonist, the present data support that not only homologous desensitization but also heterologous desensitization of NK2 receptors is compartmentalized to discrete membrane domains.