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Visualization of facet-dependent pseudo-photocatalytic behavior of TiO2 nanorods for water splitting using In situ liquid cell TEM
We report an investigation of the pseudo-photocatalytic behavior of rutile TiO2 nanorods for water splitting observed with liquid cell transmission electron microscopy (TEM). The electron beam serves as a “light” source to initiate the catalytic reaction and a “water-in-salt” aqueous solution is employed as the electrolyte. The observation reveals that bubbles are generated preferentially residing near the {110} facet of a rutile TiO2 nanorod under a low electron dose rate (9.3–18.6 e-/Å2·s). These bubbles are ascribed to hydrogen gas generated from the pseudo-photocatalytic water splitting. As the electron beam current density increases to 93 e-/Å2 ·s, bubbles are also found at the {001} and {111} facets as well as in the bulk liquid solution, demonstrating the dominant effects of water electrolysis by electron beam under higher dose rates. The facet-dependent pseudo-photocatalytic behavior of rutile TiO2 nanorods is further validated using density functional theory (DFT)calculation. Our work establishes a facile liquid cell TEM setup for the study of pseudo-photocatalytic water splitting and it may also be applied to investigation of other photo-activated phenomena occurring at the solid-liquid interfaces
Free-standing graphene films embedded in epoxy resin with enhanced thermal properties
The poor thermal conductivity of polymer composites has long been a deterrent to their increased use in high-end aerospace or defence applications. This study describes a new approach for the incorporation of graphene in an epoxy resin, through the addition of graphene as free-standing film in the polymeric matrix. The electrical and thermal conductivity of composites embedding two different free-standing graphene films was compared to composites with embedded carbon nanotube buckypapers (CNT-BP). Considerably higher thermal conductivity values than those achieved with conventional dispersing methods of graphene or CNTs in epoxy resins were obtained. The characterisation was complemented with a study of the structure at the microscale by cross-sectional scanning electron microscopy (SEM) images and a thermogravimetric analysis (TGA). The films are preconditioned in order to incorporate them into the composites, and the complete manufacturing process proposed allows the production and processing of these materials in large batches. The high thermal conductivity obtained for the composites opens the way for their use in demanding thermal management applications, such as electronic enclosures or platforms facing critical temperature loads.European Defence Agency tender No 17.ESI.OP.066. Study on the Impact of Graphene on Defence Application
Surface processes and kinetics of CO2 reduction on Pt(100) electrodes of different surface structure in sulfuric acid solutions
The reduction of CO2 on a Pt(100) electrode in CO2 saturated 0.5 M H2SO4 solutions was studied by in situ FTIR reflection spectroscopy and a programmed potential step technique. Different surface structures of Pt(100) electrode were prepared by different treatments including fast potential cycling (200 V s(-1)) for a known time. The Pt(100) surface was characterized by a parameter gamma that designates the relative amplitude of the current peak of hydrogen adsorption on (100) sites distributed on the one-dimensional surface domains to that on the two-dimensional surface domains. The in situ FTIR spectroscopic results demonstrated that the reduction of CO2 on the Pt(100) dominated by two-dimensional surface domains produced only bridge-bonded CO (COB) species, which give rise to IR absorption near 1840 cm(-1). However both bridge- and linear-bonded CO (COL, yielding IR absorption at around 2010 cm(-1)) species are found for CO2 reduction on the Pt(100) dominated by one-dimensional surface domains. The small intensity of the COL and COB bands indicates that coverage by reduced CO2 species (r-CO2. or COL and COB species) is low. The cyclic voltammetric (CV) studies confirmed quantitatively the in situ FTIRS results, and revealed that the r-CO2 species adsorb preferentially on (100) sites distributed on the two-dimensional surface domains. The initial rate of CO2 reduction upsilon (i), i.e., the rate of CO2 reduction on a clean Pt(100) surface, has been determined quantitatively from studies using a programmed potential step technique. It has been demonstrated that the maximum values of upsilon (i)(upsilon (m)(i)) measured on Pt(100) electrodes with different surface structures all appeared at -0.19 V. From analysis of the relationship between upsilon (m)(i) and gamma we have determined that the upsilon (m)(i) of CO2 reduction on (100) sites distributed on the two-dimensional surface domains is 0.53 x 10(-11) mol cm(-2) s(-1) and that on (100) sites distributed on the one-dimensional surface domains is approximately 2.66 x 10(-11) Mol cm(-2) s(-1). Based on in situ FTIRS and electrochemical studies a migration process of the r-CO2 from the one-dimensional surface domains to the two-dimensional surface domains has been proposed to be involved in CO2 reduction. The present study has thrown new light on the electrocatalytic activity of different surface structures of a Pt(100) electrode and the surface processes and kinetics of CO2 reduction
Iris classification based on sparse representations using on-line dictionary learning for large-scale de-duplication applications
De-duplication of biometrics is not scalable when the number of people to be enrolled into the biometric system runs into billions, while creating a unique identity for every person. In this paper, we propose an iris classification based on sparse representation of log-gabor wavelet features using on-line dictionary learning (ODL) for large-scale de-duplication applications. Three different iris classes based on iris fiber structures, namely, stream, flower, jewel and shaker, are used for faster retrieval of identities. Also, an iris adjudication process is illustrated by comparing the matched iris-pair images side-by-side to make the decision on the identification score using color coding. Iris classification and adjudication are included in iris de-duplication architecture to speed-up the identification process and to reduce the identification errors. The efficacy of the proposed classification approach is demonstrated on the standard iris database, UPOL
Initial experience with off-pump left ventricular assist device implantation in single center: retrospective analysis
<p>Abstract</p> <p>Background</p> <p>We hypothesize that implantation of left ventricular assist device through off-pump technique is feasible and has a comparable result to implantation on cardiopulmonary bypass and could improve one-year survival.</p> <p>Methods</p> <p>This retrospective, observational, single-center study was conducted on 29 consecutive patients at our institution who underwent off-pump left ventricular assist device implantation by a single surgeon.</p> <p>Results</p> <p>Twenty-seven procedures were performed successfully using the off-pump technique. The survival rate was 92% at 30 days, 76% at 90 days, and 67% at one year. We compared the one-year survival of different implantation periods, and divided our study into three time intervals (2004-2005, 2006, and 2007). There was a trend in reduction in number of deaths over one year that demonstrated a decrease in death rate from 50% to 17%, as well as improvement in our experience over time. However, this trend is not statistically significant (p = 0.08) due to limited sample size.</p> <p>Conclusions</p> <p>Based upon our findings, off-pump left ventricular assist device implantation is a feasible surgical technique, and combining this technique with improved device technology in the future may provide even greater improvement in patient outcomes.</p
Lightweighting design optimisation for additively manufactured mirrors
Design for additive manufacture (AM; 3D printing) is significantly different than design for subtractive machining. Although there are some limitations on the designs that can be printed, the increase in the AM design-space
removes some of the existing challenges faced by the traditional lightweight mirror designs; for example, sandwich mirrors are just as easy to fabricate as open-back mirrors via AM, and they provide an improvement in
structural rigidity. However, the ability to print a sandwich mirror as a single component does come with extra
considerations; such as orientation upon the build plate and access to remove any temporary support material.
This paper describes the iterations in optimisation applied to the lightweighting of a small, 84 mm diameter
by 20 mm height, spherical concave mirror intended for CubeSat applications. The initial design, which was
fabricated, is discussed in terms of the internal lightweighting design and the design constraints that were
imposed by printing and post-processing. Iterations on the initial design are presented; these include the use of
topology optimisation to minimise the total internal strain energy during mirror polishing and the use of lattices
combined with thickness variation i.e. having a thicker lattice in strategic support locations. To assess the
suitability of each design, finite element analysis is presented to quantify the print-through of the lightweighting
upon the optical surface for a given mass reduction
Additively manufactured mirrors for CubeSats
Additive manufacturing (AM; 3D printing) is a fabrication process that builds an object layer-upon-layer and
promotes the use of structures that would not be possible via subtractive machining. Prototype AM metal mirrors
are increasingly being studied in order to exploit the advantage of the broad AM design-space to develop intricate
lightweight structures that are more optimised for function than traditional open-back mirror lightweighting.
This paper describes a UK Space Agency funded project to design and manufacture a series of lightweighted
AM mirrors to fit within a 3 U CubeSat chassis. Five AM mirrors of identical design will be presented: two in
aluminium (AlSi10Mg), two in nickel phosphorous (NiP) coated AlSi10Mg, and one in titanium (Ti64). For each
material mirror pair, one is hand-polished (including the Ti64) and the other is diamond turned. Metrology
data, surface form error and surface roughness, will be presented to compare and contrast the different materials
and post-processing methods. To assess the presence of porosity, a frequent concern for AM materials, X-ray
computed tomography measurements will be presented to highlight the location and density of pores within the
mirror substrate; methods to mitigate the distribution of pores near the optical surface will be described. As a
metric for success, the AlSi10Mg + NiP and AlSi10Mg mirrors should be suitable in terms of metrology data for
visible and infrared applications respectively
Wall roughness induces asymptotic ultimate turbulence
Turbulence is omnipresent in Nature and technology, governing the transport
of heat, mass, and momentum on multiple scales. For real-world applications of
wall-bounded turbulence, the underlying surfaces are virtually always rough;
yet characterizing and understanding the effects of wall roughness for
turbulence remains a challenge, especially for rotating and thermally driven
turbulence. By combining extensive experiments and numerical simulations, here,
taking as example the paradigmatic Taylor-Couette system (the closed flow
between two independently rotating coaxial cylinders), we show how wall
roughness greatly enhances the overall transport properties and the
corresponding scaling exponents. If only one of the walls is rough, we reveal
that the bulk velocity is slaved to the rough side, due to the much stronger
coupling to that wall by the detaching flow structures. If both walls are
rough, the viscosity dependence is thoroughly eliminated in the boundary layers
and we thus achieve asymptotic ultimate turbulence, i.e. the upper limit of
transport, whose existence had been predicted by Robert Kraichnan in 1962
(Phys. Fluids {\bf 5}, 1374 (1962)) and in which the scalings laws can be
extrapolated to arbitrarily large Reynolds numbers
CO adsorption on electrode of Pt nanoparticles investigated by cyclic voltammetry and in situ FTIR spectroscopy
Pt nanoparticles were prepared by the chemical reduction method. The average diameter of Pt nanoparticles was determined to be 2.5 nm by TEM. The electrochemical properties of Pt nanoparticles were studied by cyclic voltammetry. In comparison with massive Pt, the oxidation current peak of CO adsorbed on Pt nanoparticles is broader. Twin adsorbates of CO on Pt nanoparticles were determined by in situ FTIRS for the first time. It has revealed that the linear and twin-bonded CO can be converted into bridge-bonded CO with the variation of electrode potential. A series of special properties of Pt nanoparticles, such as enhanced IR absorption of CO adsorbates, were also observed
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