327 research outputs found
Synthesis and antibacterial effects of cobalt–cellulose magnetic nanocomposites
© The Royal Society of Chemistry. Green synthesis is employed to prepare cobalt/cellulose nanocomposites with cubic (α-cobalt) cobalt as a main component with antibacterial and magnetic properties. An in situ reduction of aqueous solutions of cobalt ions on a model cellulose substrate surface using hydrogen gas affords spherical, cellulose-stabilised cobalt nanoclusters with magnetic properties and an average diameter of 7 nm that are distributed evenly over the surface of the cellulose fibres. These cobalt/cellulose nanocomposites exhibit good antibacterial action against opportunistic pathogens both Gram-positive (S. aureus) and Gram-negative (E. coli, A. baumannii and P. aeruginosa), with zones of inhibition up to 15 mm, thereby encouraging the deployment of these advanced materials for the treatment of wastewater or within medical dressings. This method of preparation is compared with the analogous in situ reduction of cobalt ions on a cellulose surface using sodium borohydride as reducing agent
Mexican Cartel Tactical Note #20: RPG-29 Anti-Armor Munitions
Note—Up until recently, weapons that provide for armor and bunker defeat capability at the levels that the RPG-29 is capable of, have not been seen in the hands of the Mexican cartels. The fact that they have successfully obtained them—and the origin and mechanism by which they were obtained should be of extreme concern to everyone
Oxidative Dissolution of Lithium and Manganese from Lithium Manganospinel (LiMn 2 O 4 ): Towards Climate-Smart Processes for Critical Metal Recycling
This work reports the oxidative breakdown of the LiMn2O4 structure using alkaline hypochlorite, as a method for recovering both lithium and manganese species. The heterogeneous dissolution rate for this process is monitored through the formation of the permanganate ion. It is found that reaction occurs under activation control, with a barrier that matches that for electron hopping within the spinel. Moreover, this activation barrier is smaller than those observed for typical conventional methods of recovery of lithium or manganese from LiMn2O4; accordingly, the new process is suggested to be climate-smart, despite the low, single-pass, recovery efficiency that results from slow surface kinetics
Evaporative Mass Loss Measurement as a Quality Control Tool for Quality Assurance in the Manufacture of Inks Suitable for High Speed (≥60 m/min) Printing
In any manufacturing environment, it is always important to be able to embrace a culture of traceability of any non-conformed product. For the case of ink manufacture, operator confusion, leading to the mixing-up of solvents, or connecting the incorrect solvent drum to solvent lines, can lead to disastrous consequences that are not trivial for a quality control/quality assurance team to unravel. Accordingly, simple methods for assessing whether the correct solvents were added in the correct ratios to products empower this QA/QC requirement. In this paper, we examine the use of a trivial measurement of evaporative mass loss as a protocol for validating the conformance of manufactured ink to specification. Inspired by the transport-limit that occurs at ultramicroelectrodes in electrochemistry, we develop theory to analyse evaporation rate measurements, and illustrate how vaporisation at the liquid | gas interface is dominated by a diffusion anisotropy, owing to natural convection for organic solvents, manufactured resins and commercialised inks that have been used, inter alia, for the underground transport tickets in the cities of London and Paris. We further demonstrate that the use of incorrect solvents is readily seen through evaporation rate transients, thereby enabling this measurement for human factor mitigation during the ink manufacture process
Linking mineralisation process and sedimentary product in terrestrial carbonates using a solution thermodynamic approach
Determining the processes which generate terrestrial carbonate deposits
(tufas, travertines and to a lesser extent associated chemical sediments such
as calcretes and speleothems) is a long-standing problem. Precipitation of
mineral products from solution reflects a complex combination of biological,
equilibrium and kinetic processes, and the different morphologies of
carbonate sediment produced by different processes have yet to be clearly
demarked. Building on the groundbreaking work of previous authors, we propose
that the underlying control on the processes leading to the deposition of
these products can be most parsimoniously understood from the thermodynamic
properties of their source solutions. Here, we report initial observations of
the differences in product generated from spring and lake systems spanning a
range of temperature–supersaturation space. We find that at high
supersaturation, biological influences are masked by high rates of
physico-chemical precipitation, and sedimentary products from these settings
infrequently exhibit classic "biomediated" fabrics such as clotted micrite.
Likewise, at high temperature (>40 °C) exclusion of vascular
plants and complex/diverse biofilms can significantly inhibit the magnitude
of biomediated precipitation, again impeding the likelihood of encountering
the "bio-type" fabrics.
<br></br>
Conversely, despite the clear division in product between extensive tufa
facies associations and less spatially extensive deposits such as oncoid
beds, no clear division can be identified between these systems in
temperature–supersaturation space. We reiterate the conclusion of previous
authors, which demonstrate that this division cannot be made on the basis of
physico-chemical characteristics of the solution alone. We further provide a
new case study of this division from two adjacent systems in the UK, where
tufa-like deposition continuous on a metre scale is happening at a site with
lower supersaturation than other sites exhibiting only discontinuous
(oncoidal) deposition. However, a strong microbiological division is
demonstrated between these sites on the basis of suspended bacterial cell
distribution, which reach a prominent maximum where tufa-like deposits are
forming.
<br></br>
We conclude that at high supersaturation, the thermodynamic properties of
solutions provide a highly satisfactory means of linking process and product,
raising the opportunity of identifying water characteristics from
sedimentological/petrological characteristics of ancient deposits. At low
supersaturation, we recommend that future research focuses on
geomicrobiological processes rather than the more traditional, inorganic
solution chemistry approach dominant in the past
Microstructure from ferroelastic transitions using strain pseudospin clock models in two and three dimensions: a local mean-field analysis
We show how microstructure can arise in first-order ferroelastic structural
transitions, in two and three spatial dimensions, through a local meanfield
approximation of their pseudospin hamiltonians, that include anisotropic
elastic interactions. Such transitions have symmetry-selected physical strains
as their -component order parameters, with Landau free energies that
have a single zero-strain 'austenite' minimum at high temperatures, and
spontaneous-strain 'martensite' minima of structural variants at low
temperatures. In a reduced description, the strains at Landau minima induce
temperature-dependent, clock-like hamiltonians, with
-component strain-pseudospin vectors pointing to
discrete values (including zero). We study elastic texturing in five such
first-order structural transitions through a local meanfield approximation of
their pseudospin hamiltonians, that include the powerlaw interactions. As a
prototype, we consider the two-variant square/rectangle transition, with a
one-component, pseudospin taking values of , as in a
generalized Blume-Capel model. We then consider transitions with two-component
() pseudospins: the equilateral to centred-rectangle ();
the square to oblique polygon (); the triangle to oblique ()
transitions; and finally the 3D cubic to tetragonal transition (). The
local meanfield solutions in 2D and 3D yield oriented domain-walls patterns as
from continuous-variable strain dynamics, showing the discrete-variable models
capture the essential ferroelastic texturings. Other related hamiltonians
illustrate that structural-transitions in materials science can be the source
of interesting spin models in statistical mechanics.Comment: 15 pages, 9 figure
Effects of O2, Ar, and H2 gases on the field-emission properties of single-walled and multiwalled carbon nanotubes
In this article, the authors compare the effects of O2, Ar, and H2 gases on the field-emission (FE) properties of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs)
Synthesis and antimicrobial effects of highly dispersed, cellulose-stabilized silver/cellulose nanocomposites
Small, spherical silver nanoclusters were synthesised on the surface of paper as a model cellulosic fibre substrate by a standard chemical reduction method. The concentration of the silver nanoclusters on the substrate surface is roughly proportional to the initial silver salt concentration. However, there is a noticeable degree of nanocluster aggregation to larger agglomerates. The addition of small amounts of α-cellulose, carboxymethyl cellulose or aminocellulose during the synthesis of the silver/cellulose nanocomposites suppresses this aggregation and significantly increases the concentration of the silver nanoclusters on the surface of the fibres of cellulose. These small, surface-stabilised silver nanoclusters, with the desired size and morphology, deposited from aqueous solutions on the surface of cellulosic cotton fibres, show enhanced antibacterial activity against MRSA compared to that of the corresponding silver/cotton nanocomposites prepared in the absence of a cellulosic surface stabiliser
Superparaelectric phase in the ensemble of non-interacting ferroelectric nanoparticles
For the first time we predict the conditions of superparaelectric phase
appearance in the ensemble of non-interacting spherical ferroelectric
nanoparticles. The superparaelectricity in nanoparticle was defined by analogy
with superparamagnetism, obtained earlier in small nanoparticles made of
paramagnetic material. Calculations of correlation radius, energetic barriers
of polarization reorientation and polarization response to external electric
field, were performed within Landau-Ginzburg phenomenological approach for
perovskites Pb(Zr,Ti)O3, BiFeO3 and uniaxial ferroelectrics rochelle salt and
triglycine sulfate.Comment: 28 pages, 7 figures, 3 Appendices, to be submitted to Phys. Rev.
Scaled free energies, power-law potentials, strain pseudospins and quasi-universality for first-order structural transitions
We consider ferroelastic first-order phase transitions with
order-parameter strains entering Landau free energies as invariant polynomials,
that have structural-variant Landau minima. The total free energy
includes (seemingly innocuous) harmonic terms, in the {\it
non}-order-parameter strains. Four 3D transitions are considered,
tetragonal/orthorhombic, cubic/tetragonal, cubic/trigonal and
cubic/orthorhombic unit-cell distortions, with respectively, and 2; and and 6. Five 2D transitions are also considered, as
simpler examples. Following Barsch and Krumhansl, we scale the free energy to
absorb most material-dependent elastic coefficients into an overall prefactor,
by scaling in an overall elastic energy density; a dimensionless temperature
variable; and the spontaneous-strain magnitude at transition .
To leading order in the scaled Landau minima become
material-independent, in a kind of 'quasi-universality'. The scaled minima in
-dimensional order-parameter space, fall at the centre and at the
corners, of a transition-specific polyhedron inscribed in a sphere, whose
radius is unity at transition. The `polyhedra' for the four 3D transitions are
respectively, a line, a triangle, a tetrahedron, and a hexagon. We minimize the
terms harmonic in the non-order-parameter strains, by substituting
solutions of the 'no dislocation' St Venant compatibility constraints, and
explicitly obtain powerlaw anisotropic, order-parameter interactions, for all
transitions. In a reduced discrete-variable description, the competing minima
of the Landau free energies induce unit-magnitude pseudospin vectors, with values, pointing to the polyhedra corners and the (zero-value) center.Comment: submitted to PR
- …