Interface Energy Measurement of MgO and ZnO: Understanding the Thermodynamic Stability of Nanoparticles

Nanomaterials have triggered excitement in both fundamental science and technological applications in several fields However, the same characteristic high interface area that is responsible for their unique properties causes unconventional instability, often leading to local collapsing during application Thermodynamically, this can be attributed to an increased contribution of the interface to the free energy, activating phenomena such as sintering and grain growth The lack of reliable interface energy data has restricted the development of conceptual models to allow the control of nanoparticle stability on a thermodynamic basis. Here we introduce a novel and accessible methodology to measure interface energy of nanoparticles exploiting the heat released during sintering to establish a quantitative relation between the solid solid and solid vapor interface energies. We exploited this method in MgO and ZnO nanoparticles and determined that the ratio between the solid solid and solid vapor interface energy is 11 for MgO and 0.7 for ZnO. We then discuss that this ratio is responsible for a thermodynamic metastable state that may prevent collapsing of nanoparticles and, therefore, may be used as a tool to design long-term stable nanoparticles.

Interface excess and polymorphic stability of nanosized zirconia-magnesia

Controlling the phase stability of ZrO2 nanoparticles is of major importance in the development of new ZrO2-based nanotechnologies. Because of the fact that in nanoparticles the surface accounts for a larger fraction of the total atoms, the relative phase stability can be controlled throughout the surface composition, which can be toned by surface excess of one of the components of the system., The objective of this work is to delineate a relationship between surface excess (or solid solution) of MgO relative to ZrO2 and the polymorphic stability of (ZrO2)(1-x) - (MgO), nanopowders, where 0.0 <= x <= 0.6. The nanopowders were prepared by a liquid precursor method at 500 degrees C and characterized by N-2 adsorption (BET), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), and Raman spectroscopy. For pure ZrO2 samples, both tetragonal and monoclinic polymorphs were detected, as expected considering the literature. For MgO molar fractions varying from 0.05 to 0.10, extensive solid solution could not be detected, and a ZrO2 surface energy reduction, caused by Mg surface excess detected by XPS, promoted tetragonal polymorph thermodynamic stabilization with relation to monoclinic. For MgO molar fractions higher than 0.10 and up to 0.40, Mg solid solution could be detected and induced cubic phase stabilization. MgO periclase was observed only at x = 0.6. A discussion based on the relationship between the surface excess, surface energy, and polymorph stability is presented.

Performance analysis of a single-user MISO ultra-wideband time reversal system with DFE

This paper presents an analysis of the performance of a baseband multiple-input single-output (MISO) time reversal ultra-wideband system (TR-UWB) incorporating a symbol spaced decision feedback equalizer (DFE). A semi-analytical performance analysis based on a Gaussian approach is considered, which matched well with simulation results, even for the DFE case. The channel model adopted is based on the IEEE 802.15.3a model, considering correlated shadowing across antenna elements. In order to provide a more realistic analysis, channel estimation errors are considered for the design of the TR filter. A guideline for the choice of equalizer length is provided. The results show that the system`s performance improves with an increase in the number of transmit antennas and when a symbol spaced equalizer is used with a relatively small number of taps compared to the number of resolvable paths in the channel impulse response. Moreover, it is possible to conclude that due to the time reversal scheme, the error propagation in the DFE does not play a role in the system`s performance.

Jointly multi-user detection and channel estimation with genetic algorithm

This work aims at proposing the use of the evolutionary computation methodology in order to jointly solve the multiuser channel estimation (MuChE) and detection problems at its maximum-likelihood, both related to the direct sequence code division multiple access (DS/CDMA). The effectiveness of the proposed heuristic approach is proven by comparing performance and complexity merit figures with that obtained by traditional methods found in literature. Simulation results considering genetic algorithm (GA) applied to multipath, DS/CDMA and MuChE and multi-user detection (MuD) show that the proposed genetic algorithm multi-user channel estimation (GAMuChE) yields a normalized mean square error estimation (nMSE) inferior to 11%, under slowly varying multipath fading channels, large range of Doppler frequencies and medium system load, it exhibits lower complexity when compared to both maximum likelihood multi-user channel estimation (MLMuChE) and gradient descent method (GrdDsc). A near-optimum multi-user detector (MuD) based on the genetic algorithm (GAMuD), also proposed in this work, provides a significant reduction in the computational complexity when compared to the optimum multi-user detector (OMuD). In addition, the complexity of the GAMuChE and GAMuD algorithms were (jointly) analyzed in terms of number of operations necessary to reach the convergence, and compared to other jointly MuChE and MuD strategies. The joint GAMuChE-GAMuD scheme can be regarded as a promising alternative for implementing third-generation (3G) and fourth-generation (4G) wireless systems in the near future. Copyright (C) 2010 John Wiley & Sons, Ltd.

Construction and Evaluation of an Opto-Coupled Potentiostat with a PC/PDA Interface

The design, construction, and characterization of a portable opto-coupled potentiostat are presented. The potentiostat is battery-powered, managed by a microcontroller, which implements cyclic voltammetry (CV) using suitable sensor electrodes. Its opto-coupling permits a wide range of current measurements, varying from mA to nA. Two software interfaces were developed to perform the CV measurement: a virtual instrument for a personal computer (PC) and a C-base interface for personal digital assistant (PDA). The potentiostat has been evaluated by detection of potassium ferrocyanide in KCl medium, both with macro and microelectrodes. There was good agreement between the instrumental results and those from commercial equipment.

User guide for shock and blast simulation with the OctVCE code (version 3.5+), Department of Mechanical Engineering Report 2007/13

OctVCE is a cartesian cell CFD code produced especially for numerical simulations of shock and blast wave interactions with complex geometries. Virtual Cell Embedding (VCE) was chosen as its cartesian cell kernel as it is simple to code and sufficient for practical engineering design problems. This also makes the code much more ‘user-friendly’ than structured grid approaches as the gridding process is done automatically. The CFD methodology relies on a finite-volume formulation of the unsteady Euler equations and is solved using a standard explicit Godonov (MUSCL) scheme. Both octree-based adaptive mesh refinement and shared-memory parallel processing capability have also been incorporated. For further details on the theory behind the code, see the companion report 2007/12.

When oceans meet: a teleost shows secondary intergradation at an Indian-Pacific interface

The Indo-West Pacific is characterized by extraordinary marine species diversity. The evolutionary mechanisms responsible for generating this diversity remain puzzling, but are often linked to Pleistocene sea level fluctuations. The impact of these sea level changes on the population genetic architecture of the estuarine fish Lates calcarifer are investigated via a natural experiment in a region of the Indo-West Pacific known to have undergone considerable change during the Pleistocene. L. calcarifer, a coastline-restricted catadromous teleost, provides an excellent model for studying the effects of sea level change as its habitat requirements potentially make it sensitive to the region's physical history. Evidence was found for a large phylogenetic break (4% mtDNA control region; 0.47% ATPase 6 and 8) either side of the Torres Strait, which separates the Western Pacific and Indian Oceans, although some mixing of the clades was evident. This suggests clinal secondary introgression of the clades via contemporary gene flow. Further, populations on Australia's east coast appear to have passed through a bottleneck. This was linked to the historical drying of the Great Barrier Reef coastal lagoon, which resulted in a significant loss of habitat and forced retreat into isolated refugia. These results suggest that historical eustatic changes have left a significant imprint on the molecular diversity within marine species as well as among them in the Indo-West Pacific.

Observation of a cubic phase in mesoporous silicate films grown at the air/water interface

X-Ray diffraction is reported from mesoporous silicate films grown at the air/water interface. The films were studied both as powdered films, and oriented on silicon or mica sheets. At early stages of growth we observe Bragg diffraction from a highly ordered cubic phase, with both long and short d-spacing peaks. We have assigned this as a discontinuous micellar Pm3n phase in which the silica is partly ordered. Later films retain only the known hexagonal p6m peaks and have lost any order both at short d-spacings and the longer d-spacing Bragg peaks characteristic of the cubic structure. The silica framework is considerably expanded from that in bulk amorphous silica, average Si Si distances are some 30% greater. Incorporation of glycerol or polyethylene glycol preserves the earlier cubic structure. To be consistent with earlier, in situ, X-ray and neutron reflectivity data we infer that both structures are produced after a phase transition from a less-ordered him structure late in the induction phase. The structural relations between the film Pm3n and p6m phase(s) and the known bulk SBA-1 and MCM-41 phases are briefly discussed.

Synthesis of silica films at the air/water interface: Effect of template chain length and ionic strength

We have grown surfactant-templated silicate films at the air-water interface using n-alkyltrimethylammonium bromide and chloride in an acid synthesis with tetraethyl orthosilicate as the silicate source. The films have been grown with and without added salt (sodium chloride, sodium bromide) and with n-alkyl chain lengths from 12 to 18, the growth process being monitored by X-ray reflectometry. Glassy, hexagonal, and lamellar structures have been produced in ways that are predictable from the pure surfactant-water phase diagrams. The synthesis appears to proceed initially through an induction period characterized by the accumulation of silica-coated spherical micelles near the surface. All syntheses, except those involving C(12)TACl, show a sudden transformation of the spherical micellar phase to a hexagonal phase. This occurs when the gradually increasing ionic strength and/or changing ethanol concentration is sufficient to change the position of boundaries within the phase diagram. A possible mechanism for this to occur may be to induce a sphere to rod transition in the micellar structure. This transformation, as predicted from the surfactant-water phase diagram, can be induced by addition of salts and is slower for chloride than bromide counteranions. The hexagonal materials change in cell dimension as the chain length is changed in a way consistent with theoretical model predictions. All the materials have sufficiently flexible silica frameworks that phase interconversion is observed both from glassy to hexagonal and from hexagonal, to lamellar and vice versa in those surfactant systems where multiple phases are found to exist.

Effect of removing user fees on attendance for curative and preventive primary health care services in rural South Africa

User fees are used to recover costs and discourage unnecessary attendance at primary care clinics in many developing countries. In South Africa, user fees for children aged under 6 yea rs and pregnant women were removed in 1994, and in 1997 all user fees at all primary health care clinics were abolished. The intention of these policy changes was to improve access to health services for previously disadvantaged communities. We investigated the impact of these changes on clinic attendance patterns in Hlabisa health district. Average quarterly new registrations and total attendances for preventive services (antenatal care, immunization, growth monitoring) and curative services (treatment of ailments) at a mobile primary health care unit were studied from 1992 to 1998. Regression analysis was undertaken to assess whether trends were statistically significant. There was a sustained increase in new registrations (P = 0.0001) and total attendances (P = 0.0001)for curative services, and a fall in new registrations (P = 0.01) and total attendances for immunization and growth monitoring (P = 0.0002) over the study period. The upturn in demand for curative services started at the time of the first policy change. The decreases in antenatal registrations (P = 0.07) and attendances (P = 0.09) were not statistically significant The number of new registrations for immunization and growth monitoring increased following the first policy change but declined thereafter. We found no evidence that the second policy change influenced underlying trends. The removal of user fees improved access to curative services but this may have happened at the expense of some preventive services. Governments should remain vigilant about the effects of new health policies in order to ensure that objectives are being met.

Structure development in octadecyl trimethylammonium templated silicate films grown at the air/water interface

The mechanism of growth of silicate films at the air/liquid interface has been investigated in situ by a series of grazing incidence diffraction experiments using a 20 x 25 cm(2) imaging plate as the detector. C(18)TAX (X = Br- or Cl-) has been used as the film templating surfactant. The formation of a layered phase, prior to growth of the hexagonal mesophase in C(18)TABr templated films. has been seen. This layered structure has a significantly shorter d spacing compared to the final hexagonal film (43 versus 48 Angstrom, respectively). The correlation lengths associated with the development of the hexagonal in-plane diffraction spots are much longer in-plane than perpendicular to the air/liquid interface (300 Angstrom versus 50 Angstrom). This implies that the film forms via the growth or aggregation of islands that are initially only a micelle or two thick. which then grow down into the solution.

Ecological interface design for pasteurizer II: A process description of semantic mapping

Ecological interface design (EID) is proving to be a promising approach to the design of interfaces for complex dynamic systems. Although the principles of EID and examples of its effective use are widely available, few readily available examples exist of how the individual displays that constitute an ecological interface are developed. This paper presents the semantic mapping process within EID in the context of prior theoretical work in this area. The semantic mapping process that was used in developing an ecological interface for the Pasteurizer II microworld is outlined, and the results of an evaluation of the ecological interface against a more conventional interface are briefly presented. Subjective reports indicate features of the ecological interface that made it particularly valuable for participants. Finally, we outline the steps of an analytic process for using EID. The findings presented here can be applied in the design of ecological interfaces or of configural displays for dynamic processes.

Structural development of silicated films self-assembled at the air-water interface

The development of structure perpendicular to and in the plane of the interface has been studied for mesoporous silicate films self-assembled at the air/water interface. The use of constrained X-ray and neutron specular reflectometry has enabled a detailed study of the structural development perpendicular to the interface during the pre-growth phase. Off-specular neutron reflectometry and grazing incidence X-ray diffraction has enabled the in-plane structure to be probed with excellent time resolution. The growth mechanism under the surfactant to silicate source ratios used in this work is clearly due to the self-assembly of micellar and molecular species at the air/liquid interface, resulting in the formation of a planar mesoporous film that is tens of microns thick. (C) 2003 Elsevier Science B.V. All rights reserved.

Rat osseous plate alkaline phosphatase as Langmuir monolayer - An infrared study at the air-water interface

A glycosylphosphatidylinositol (GPI)-anchored enzyme (rat osseous plate alkaline phosphatase-OAP) was studied as monolayer (pure and mixed with lipids) at the air-water interface. Surface pressure and surface potential-area isotherms showed that the enzyme forms a stable monolayer and exhibits a liquid-expanded state even at surface pressure as high as 30 mN m(-1). Isotherms for mixed dimyristoylphosphatidic acid (DMPA)-OAP monolayer showed the absence of a liquid-expanded/liquid-condensed phase transition as observed for pure DMPA monolayer. In both cases, pure or mixed monolayer, the enzyme preserves its native conformation under compression at the air-water interface as observed from in situ p-polarized light Fourier transform-infrared reflection-absorption spectroscopic (FT-IRRAS) measurements. Changes in orientation and conformation of the enzyme due to the presence or absence of DMPA, as well as due to the surface compression, are discussed. (C) 2008 Published by Elsevier Inc.

Jacobsen catalyst immobilized on chitosan membrane as interface catalyst in organic/aqueous system for alkene oxidation

The Jacobsen catalyst, Mn(salen), was immobilized in chitosan membrane. The obtained Mn(salen)-Chit was characterized by thermogravimetric analysis (TC), differential thermal analysis (DTA), differential scanning calorimetry (DSC), infrared spectroscopy (FT-IR), degree of N-acetylation by (1)H NMR, and UV-vis spectroscopy. The UV-vis absorption spectrum of the encapsulated catalyst displayed the typical bands of the Jacobsen catalyst, and the FT-IR presented an absorption band characteristic of the imines present in the Jacobsen catalyst. The chitosan membranes were available, in a biphasic system, as a catalytic barrier between two different phases: an organic substrate phase (cyclooctene or styrene) and an aqueous solution of either m-CPBA, t-BuOOH or H(2)O(2), and dismissing the need for phase transfer agents and leading to better product yields compared with the catalyst in homogeneous medium. This new catalyst did not leach from the support and was reused many times, leading to high turnover frequencies. (C) 2009 Elsevier B.V. All rights reserved.