Particle-stabilized oscillating diver: a self-assembled responsive capsule

We report the experimental discovery of a self-assembled capsule, with density set by interfacial glass beads and an internal bubble, that automatically performs regular oscillations up and down a vial in response to a temperature gradient. Similar composites featuring interfacial particles and multiple internal compartments could be the solution to a variety of application challenges.Comment: 7 pages, 3 figure

Growth and calorific approximation in the speckled trout (Salvelinus fontinalis)

From the point of view of energy metabolism, appropriate measures of the rate of oxygen uptake would indicate the energy turnover or the capacity of the organism to perform external work in relation to its size and under the prevalent environmental conditions. Estimates of oxygen uptake when considered in conjunction with growth rate and calorific equivalent of the metabolic rate, would permit estimates of the total energy requirements of the individual. It has long been established, that the calorific equivalent of food consumed corresponds to the heat output plus the heat equivalent of excreta, and that such a measurement of metabolism can be verified also by indirect calorimetric methods based on the gas exchange of the animal

Contested staring: issues and the use of mutual gaze as an on-line measure of social presence

Despite many of the current social presence measures relying heavily on subjective post-test questionnaires, some researchers have identified the value of using on-line, behavioural measures. Gaze, and specifically mutual gaze, is known to be related to social perceptions of an interlocutor, as well as facilitating task performance during an interaction [1, 2, 17]. Second Life allows for the investigation of task- based interaction in a highly controllable social environment, whilst simultaneously allowing measurement of eye movements (using a head-mounted eye-tracker). A paradigm for measuring eye movements of a user during interaction with an avatar or agent is presented. The potential for using this paradigm to investigate the use of mutual gaze as an on- line measure of social presence is discussed

Experimental evidence of shock mitigation in a Hertzian tapered chain

We present an experimental study of the mechanical impulse propagation through a horizontal alignment of elastic spheres of progressively decreasing diameter $\phi_n$, namely a tapered chain. Experimentally, the diameters of spheres which interact via the Hertz potential are selected to keep as close as possible to an exponential decrease, $\phi_{n+1}=(1-q)\phi_n$, where the experimental tapering factor is either $q_1\simeq5.60$~% or $q_2\simeq8.27$~%. In agreement with recent numerical results, an impulse initiated in a monodisperse chain (a chain of identical beads) propagates without shape changes, and progressively transfer its energy and momentum to a propagating tail when it further travels in a tapered chain. As a result, the front pulse of this wave decreases in amplitude and accelerates. Both effects are satisfactorily described by the hard spheres approximation, and basically, the shock mitigation is due to partial transmissions, from one bead to the next, of momentum and energy of the front pulse. In addition when small dissipation is included, a better agreement with experiments is found. A close analysis of the loading part of the experimental pulses demonstrates that the front wave adopts itself a self similar solution as it propagates in the tapered chain. Finally, our results corroborate the capability of these chains to thermalize propagating impulses and thereby act as shock absorbing devices.Comment: ReVTeX, 7 pages with 6 eps, accepted for Phys. Rev. E (Related papers on http://www.supmeca.fr/perso/jobs/

Emulsification in binary liquids containing colloidal particles: a structure-factor analysis

We present a quantitative confocal-microscopy study of the transient and final microstructure of particle-stabilised emulsions formed via demixing in a binary liquid. To this end, we have developed an image-analysis method that relies on structure factors obtained from discrete Fourier transforms of individual frames in confocal image sequences. Radially averaging the squared modulus of these Fourier transforms before peak fitting allows extraction of dominant length scales over the entire temperature range of the quench. Our procedure even yields information just after droplet nucleation, when the (fluorescence) contrast between the two separating phases is scarcely discernable in the images. We find that our emulsions are stabilised on experimental time scales by interfacial particles and that they are likely to have bimodal droplet-size distributions. We attribute the latter to coalescence together with creaming being the main coarsening mechanism during the late stages of emulsification and we support this claim with (direct) confocal-microscopy observations. In addition, our results imply that the observed droplets emerge from particle-promoted nucleation, possibly followed by a free-growth regime. Finally, we argue that creaming strongly affects droplet growth during the early stages of emulsification. Future investigations could clarify the link between quench conditions and resulting microstructure, paving the way for tailor-made particle-stabilised emulsions from binary liquids.Comment: http://iopscience.iop.org/0953-8984/22/45/455102

Role of tyrosine 238 in the active site of Rhodotorula gracilis D-amino acid oxidase - A site-directed mutagenesis study

Y238, one of the very few conserved residues in the active site of d-amino acid oxidases (DAAO), was mutated to phenylalanine and serine in the enzyme from the yeast Rhodotorula gracilis. The mutated proteins are catalytically competent thus eliminating Tyr238 as an active-site acid/base catalyst. Y238F and Y238S mutants exhibit a threefold slower turnover on d-alanine as substrate, which can be attributed to a slower rate of product release relative to the wild-type enzyme (a change of the rate constants for substrate binding was also evident). The Y238 DAAO mutants have spectral properties similar to those of the wild-type enzyme but the degree of stabilization of the flavin semiquinone and the redox properties in the free form of Y238S are different. The binding of the carboxylic acid competitive inhibitors and the substrate d-alanine are changed only slightly, suggesting that the overall substrate binding pocket remains intact. In agreement with data from the pH dependence of ligand binding and with the protein crystal structure, site-directed mutagenesis results emphasize the importance of residue Y238 in controlling access to the active site instead of a role in the substrate/ligand interaction

Economic analysis of fertilizer options for maize production in Tanzania

United States Agency for International Developmen

Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?

Calcitic nanofibres are ubiquitous habits of sec- ondary calcium carbonate (CaCO3 ) accumulations observed in calcareous vadose environments. Despite their widespread occurrence, the origin of these nanofeatures remains enig- matic. Three possible mechanisms fuel the debate: (i) purely physicochemical processes, (ii) mineralization of rod-shaped bacteria, and (iii) crystal precipitation on organic templates. Nanofibres can be either mineral (calcitic) or organic in na- ture. They are very often observed in association with needle fibre calcite (NFC), another typical secondary CaCO3 habit in terrestrial environments. This association has contributed to some confusion between both habits, however they are truly two distinct calcitic features and their recurrent asso- ciation is likely to be an important fact to help understanding the origin of nanofibres. In this paper the different hypotheses that currently exist to explain the origin of calcitic nanofibres are critically reviewed. In addition to this, a new hypothe- sis for the origin of nanofibres is proposed based on the fact that current knowledge attributes a fungal origin to NFC. As this feature and nanofibres are recurrently observed together, a possible fungal origin for nanofibres which are associated with NFC is investigated. Sequential enzymatic digestion of the fungal cell wall of selected fungal species demonstrates that the fungal cell wall can be a source of organic nanofibres. The obtained organic nanofibres show a striking morpho- logical resemblance when compared to their natural coun- terparts, emphasizing a fungal origin for part of the organic nanofibres observed in association with NFC. It is further hy- pothesized that these organic nanofibres may act as templates for calcite nucleation in a biologically influenced mineraliza- tion process, generating calcitic nanofibres. This highlights the possible involvement of fungi in CaCO3 biomineraliza- tion processes, a role still poorly documented. Moreover, on a global scale, the organomineralization of organic nanofi- bres into calcitic nanofibres might be an overlooked process deserving more attention to specify its impact on the biogeo- chemical cycles of both Ca and C

Growth, Structural and Micro hardness studies of KSbF4 and K2SbF5 crystals

Interest in Potassium Fluoro Antimonate crystals has been increased for the last four decades due its superionic conduction and its unusual electro-optic properties. Potassium tetra fluoro antimonate (KSbF4) and Potassium penta fluoro antimonite (K2SbF5) crystals have been grown by slow evaporation method. KSbF4 crystallizes into orthorhombic structure with a space group Pmmn. K2SbF5 belongs to orthorhombic crystal system with a space group Cmcm.nbsp Micro indentation analysis on these crystals indicates that they are moderately softer substances. Both crystals revealed reverse indentation size effect (RISE). Variation of stiffness constant with load has been discussed. Yield strength for KSbF4 and K2SbF5 crystals have been found out as 16.72 and 16.941 MPa respectively.nbs

Landscape natural resources management with soil and water conservation practices

United States Agency for International Developmen