Nanodiamond landmarks for subcellular multimodal optical and electron imaging.

There is a growing need for biolabels that can be used in both optical and electron microscopies, are non-cytotoxic, and do not photobleach. Such biolabels could enable targeted nanoscale imaging of sub-cellular structures, and help to establish correlations between conjugation-delivered biomolecules and function. Here we demonstrate a sub-cellular multi-modal imaging methodology that enables localization of inert particulate probes, consisting of nanodiamonds having fluorescent nitrogen-vacancy centers. These are functionalized to target specific structures, and are observable by both optical and electron microscopies. Nanodiamonds targeted to the nuclear pore complex are rapidly localized in electron-microscopy diffraction mode to enable "zooming-in" to regions of interest for detailed structural investigations. Optical microscopies reveal nanodiamonds for in-vitro tracking or uptake-confirmation. The approach is general, works down to the single nanodiamond level, and can leverage the unique capabilities of nanodiamonds, such as biocompatibility, sensitive magnetometry, and gene and drug delivery

Assessment by finite element analysis of the impact of osteoporosis and osteoarthritis on hip resurfacing

Hip resurfacing is proposed as an alternative to total hip replacement (THR) for treatment of osteoarthritis (OA), especially for younger, heavier and more active sufferers. There is however, concern with regards to the incidence of post operative femoral neck fractures. We have investigated, with finite element models, the changes in stress and strain in the femoral neck following hip resurfacing. We have included several different bone material property values representing normal, elderly, osteoarthritic and osteoporotic bone. We have also modelled two different hip implant orientations. We have shown that hip resurfacing may increase the magnitude of stress and strain in the femoral neck, especially in osteoporotic bone. We have also shown that the superolateral offset associated with the valgus orientation, not the valgus orientation itself, may be what reduces the stress and strain in the neck and leads to lower incidence of fracture

Forward Signal Propagation Learning

We propose a new learning algorithm for propagating a learning signal and updating neural network parameters via a forward pass, as an alternative to backpropagation. In forward signal propagation learning (sigprop), there is only the forward path for learning and inference, so there are no additional structural or computational constraints on learning, such as feedback connectivity, weight transport, or a backward pass, which exist under backpropagation. Sigprop enables global supervised learning with only a forward path. This is ideal for parallel training of layers or modules. In biology, this explains how neurons without feedback connections can still receive a global learning signal. In hardware, this provides an approach for global supervised learning without backward connectivity. Sigprop by design has better compatibility with models of learning in the brain and in hardware than backpropagation and alternative approaches to relaxing learning constraints. We also demonstrate that sigprop is more efficient in time and memory than they are. To further explain the behavior of sigprop, we provide evidence that sigprop provides useful learning signals in context to backpropagation. To further support relevance to biological and hardware learning, we use sigprop to train continuous time neural networks with Hebbian updates and train spiking neural networks without surrogate functions

Design and performance of ropes for climbing and sailing

Ropes are an important part of the equipment used by climbers, mountaineers, and sailors. On first inspection, most modern polymer ropes appear similar, and it might be assumed that their designs, construction, and properties are governed by the same requirements. In reality, the properties required of climbing ropes are dominated by the requirement that they effectively absorb and dissipate the energy of the falling climber, in a manner that it does not transmit more than a critical amount of force to his body. This requirement is met by the use of ropes with relatively low longitudinal stiffness. In contrast, most sailing ropes require high stiffness values to maximize their effectiveness and enable sailors to control sails and equipment precisely. These conflicting requirements led to the use of different classes of materials and different construction methods for the two sports. This paper reviews in detail the use of ropes, the properties required, manufacturing techniques and materials utilized, and the effect of service conditions on the performance of ropes. A survey of research that has been carried out in the field reveals what progress has been made in the development of these essential components and identifies where further work may yield benefits in the future

Electrical transport and optical studies of ferromagnetic Cobalt doped ZnO nanoparticles exhibiting a metal-insulator transition

The observed correlation of oxygen vacancies and room temperature ferromagnetic ordering in Co doped ZnO1-o nanoparticles reported earlier (Naeem et al Nanotechnology 17, 2675-2680) has been further explored by transport and optical measurements. In these particles room temperature ferromagnetic ordering had been observed to occur only after annealing in forming gas. In the current work the optical properties have been studied by diffuse reflection spectroscopy in the UV-Vis region and the band gap of the Co doped compositions has been found to decrease with Co addition. Reflections minima are observed at the energies characteristic of Co+2 d-d (tethrahedral symmetry) crystal field transitions, further establishing the presence of Co in substitutional sites. Electrical transport measurements on palletized samples of the nanoparticles show that the effect of a forming gas is to strongly decrease the resistivity with increasing Co concentration. For the air annealed and non-ferromagnetic samples the variation in the resistivity as a function of Co content are opposite to those observed in the particles prepared in forming gas. The ferromagnetic samples exhibit an apparent change from insulator to metal with increasing temperatures for T>380K and this change becomes more pronounced with increasing Co content. The magnetic and resistive behaviors are correlated by considering the model by Calderon et al [M. J. Calderon and S. D. Sarma, Annals of Physics 2007 (Accepted doi: 10.1016/j.aop.2007.01.010] where the ferromagnetism changes from being mediated by polarons in the low temperature insulating region to being mediated by the carriers released from the weakly bound states in the higher temperature metallic region.Comment: 7 pages, 6 figure

Infrared band intensities of 1,2-dibromoethane in solutions: Electrostatic effect and influence of hydrogen bonding on the conformational equilibrium

The conformational equilibrium of 1,2-dibromoethane (DBE) in various media (vapor phase, liquid, and solutions in n-hexane, carbon tetrachloride, toluene, carbon disulfide, bromoform, acetone, nitromethane, deuterated acetonitrile and deuterated dimethylsulfoxide) has been studied by IR absorption spectra. The enthalpy differences between trans (t) and gauche (g) conformers (ΔHo) were determined from the dependencies of 1n(It/Ig) upon T-1, where It and Ig are the integrated intensities of the bands, belonging to different conformers. The values RT · 1n(It/Ig) and (R · 1n (It/Ig) + ΔHo/T) obtained at 296 K were used as measures of the free enthalpy (ΔGo) and entropy differences of the conformers (ΔSo) respectively, when considering their changes with solvent. To minimize the errors due to solvent and temperature effects on the IR-band absorption coefficients, four different band pairs of trans and gauche conformers were investigated. Good correlations between ΔGo, ΔHo and the function of dielectric permitivity of the medium (0.5 -( -1)/(2 + 1))1/2 were observed for all solvents except toluene. Significant changes of ΔSo with the media have been found: they cover more than 1.5 cal mol-1 K-1 when going from the vapor phase to polar solvents. The ΔSo values correlate with ΔHo ones (compensation effect); the slope of the dependence (ΔΔSo/ΔΔHo) = (1.0 ± 0.3) · 10-3 K-1 is close to those determined earlier for 1,2-dichloro- and bromofluoro-ethanes, trans-1,2-dichlorocyclohexane and o-iodophenol. The overall integrated intensities in the CH2-stretching (αA/B(str), 3200-2700, cm-1) and deformational (αA/B(def), 1550-1300, cm-1) regions were measured for neat DBE and its solutions in CCl4, CD3CN and (CD3)2SO. The αA/B(str) value noticeably increases when going from CCl4 to proton acceptor solvents, while the αA/B(def) does not depend on the solvent. These results are interpreted within the framework of the formation of weak hydrogen bonds between CH2-groups of DBE and proton acceptor groups of the solvents. The enthalpies of specific interaction of DBE with CD3CN and (CD3)2SO were estimated using the 'intensity rule'. These values are about 1 kcal mol-1. Nevertheless, poor correlation between ΔHo, ΔGo and basicity parameters of the solvents indicate the minor effect of the H-bond formation on the conformational equilibrium of DBE

Au-Decorated Ce-Ti Mixed Oxides for Efficient CO Preferential Photooxidation

We investigated the photocatalytic behavior of gold nanoparticles supported on CeO2-TiO2 nanostructured matrixes in the CO preferential oxidation in H2-rich stream (photo-CO-PROX), by modifying the electronic band structure of ceria through addition of titania and making it more suitable for interacting with free electrons excited in gold nanoparticles through surface plasmon resonance. CeO2 samples with different TiO2 concentrations (0-20 wt %) were prepared through a slow coprecipitation method in alkaline conditions. The synthetic route is surfactant-free and environmentally friendly. Au nanoparticles (<1.0 wt % loading) were deposited on the surface of the CeO2-TiO2 oxides by deposition-precipitation. A benchmarking sample was also considered, prepared by standard fast coprecipitation, to assess how a peculiar morphology can affect the photocatalytic behavior. The samples appeared organized in a hierarchical needle-like structure, with different morphologies depending on the Ti content and preparation method, with homogeneously distributed Au nanoparticles decorating the Ce-Ti mixed oxides. The morphology influences the preferential photooxidation of CO to CO2 in excess of H2 under simulated solar light irradiation at room temperature and atmospheric pressure. The Au/CeO2-TiO2 systems exhibit much higher activity compared to a benchmark sample with a non-organized structure. The most efficient sample exhibited CO conversions of 52.9 and 80.2%, and CO2 selectivities equal to 95.3 and 59.4%, in the dark and under simulated sunlight, respectively. A clear morphology-functionality correlation was found in our systematic analysis, with CO conversion maximized for a TiO2 content equal to 15 wt %. The outcomes of this study are significant advancements toward the development of an effective strategy for exploitation of hydrogen as a viable clean fuel in stationary, automotive, and portable power generators