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PubMed2004

Atomic force microscopic corroboration of bond aging for adhesion of Streptococcus thermophilus to solid substrata.

Initial bacterial adhesion is considered to be reversible, but over time the adhesive bond between a bacterium and a substratum surface may strengthen, turning the process into an irreversible state. Microbial desorption has been studied in situ in controlled flow devices as a function of the organisms resident time on the surface (J. Colloid Interface Sci. 164 (1994) 355). It appeared that desorption of Streptococcus thermophilus decreased strongly within approximately 50 s after initial adhesion due to bond aging. In this paper, bond aging between the S. thermophilus cell surface and the silicon nitride tip of an AFM (atomic force microscope) is corroborated microscopically and related to the macroscopic, residence time-dependent desorption of the organism under flow. AFM indicated bond strengthening between the tip and the cell surface within 100 s of contact, which is on the same order of magnitude as bond aging inferred from residence time-dependent desorption. Comparison of the interaction energies derived from AFM and macroscopic desorption indicate that bond strengthening arises as a result of multiple attachments of extracellular polymeric substances to a substratum surface.

Bacterial Adhesion↗

PubMed2006

Flux stabilization of silicon nitride microsieves by backpulsing and surface modification with PEG moieties.

The influence of the surface properties of chemically modified silicon nitride microsieves on the filtration of protein solutions and defatted milk is described in this research. Prior to membrane filtrations, an antifouling polymer based on poly(ethylene glycol), poly(TMSMA-r-PEGMA) was synthesized and applied on silicon-based surfaces like silicon, silicon nitride, and glass. The ability of such coating to repel proteins like bovine serum albumin (BSA) was confirmed by ellipsometry and confocal fluorescence microscopy. In BSA and skimmed milk filtrations no differences could be seen between unmodified and PEG-coated membranes (decreasing permeability in time). On the other hand, reduced fouling was observed with PEG-modified microsieves in combination with backpulsing and air sparging.

Air Pollutants, Occupational↗

PubMed2006

Preparation, structure and thermal stability of onium- and amino-functionalized silicas for the use as catalysts supports.

We explored and compared several synthetic methods of grafting silica with strong (alkyltriphenylphosphonium, tetralkylammonium, propylpyridinium and dialkylimidazolium) and weak (gamma-aminopropyl, gamma-(N-imidazolyl)propyl) anion-exchanging groups starting with commercially available chloroalkyl- and gamma-aminopropylsilanes. Structure of the intermediate and final materials was investigated by elemental analysis, titration, 13C, 29Si, 31P MAS NMR, DRIFT, and TPD MS. The derivatives of alkyltriphenylphosphonium, propylpyridinium and dialkylimidazolium cation can be prepared with satisfactory quaternisation yields (ca. 30-100%) via the nucleophilic substitution of gamma-chloropropyl groups either in the silane or in chloropropylsilica, resulting in bonded phases with moderate densities: 0.2-1.0 group nm(-2) (onium salts) and 0.2-1.5 group nm(-2) (amines). Parallel one-pot end-capping/hydrophobization can be done if a mixture of target silane with end-capping reagent or gamma-chloropropylsilane is used. The grafted layer is highly stable at the level of Si-C bonds and decomposes at ca. 400 degrees C, while the onium functions begin to decompose at ca. 250 degrees C, lowering the thermal stability of materials. Thus, anion-exchanging silicas can be envisaged for the use as catalyst supports at moderate temperatures.

Catalysis↗

PubMed2006

Adsorption of mixtures of nonionic sugar-based surfactants with other surfactants at solid/liquid interfaces II. Adsorption of n-dodecyl-beta-D-maltoside with a cationic surfactant and a nonionic ethoxylated surfactant on solids.

Synergy and antagonism between sugar-based surfactants, a group of environmentally benign surfactants, and cationic surfactants and nonionic ethoxylated surfactants have been investigated in this study with solids which adsorbs only one or other when presented alone. Sugar-based n-dodecyl-beta-D-maltoside (DM) does not adsorb on silica by itself. However, in mixtures with cationic dodecyltrimethylammonium bromide (DTAB) and nonionic nonylphenol ethoxylated decyl ether (NP-10), DM adsorbs on silica through hydrophobic interactions. In contrast, although DM does adsorb on alumina, the presence of NP-10 reduces the adsorption of DM as well as that of the total surfactant adsorption. Such synergistic/antagonistic effects of sugar-based n-dodecyl-beta-D-maltoside (DM) in mixtures with other surfactants at solid/liquid interfaces were systematically investigated and some general rules on synergy/antagonism in mixed surfactant systems are identified. These results have implications for designing surfactant combinations for controlled adsorption or prevention of adsorption.

Adsorption↗

PubMed2006

Performance of a stratified sand filter in removal of chemical oxygen demand, total suspended solids and ammonia nitrogen from high-strength wastewaters.

A stratified sand filter column, operated in recirculation mode and treating synthetic effluent resembling high-strength dairy wastewaters was studied over a 342-d duration. The aim of this paper was to examine the organic, total suspended solids (TSS) and nutrient removal rates of the sand filter, operated in recirculation mode, under incrementally increasing hydraulic and organic loading rates and to propose a field filter-sizing criterion. Best performance was obtained at a system hydraulic loading rate of 10 L m(-2) d(-1); a higher system hydraulic loading rate (of 13.4 L m(-2) d(-1)) caused surface ponding. The system hydraulic loading rate of 10 L m(-2) d(-1) gave a filter chemical oxygen demand (COD), TSS, and total kjeldahl nitrogen (TKN) loading rate of 14, 3.7, and 2.1 g m(-2) d(-1), respectively, and produced consistent COD and TSS removals of greater than 99%, and an effluent NO(3)-N concentration of 42 mg L(-1) (accounting for an 86% reduction in total nitrogen (Tot-N)). As the proportional surface area requirement for the sand filter described in this study is less than the recommended surface area requirement of a free-water surface (FWS) wetland treating an effluent of similar quality, it could provide an economic and sustainable alternative to conventional wetland treatment.

Dairying↗

PubMed2006

Simultaneous uptake of ammonium and phosphate ions by compounds prepared from paper sludge ash.

Al-containing CaO-SiO(2)-H(2)O phases were prepared by hydrothermal treatment of mixtures of paper sludge ash (PSA) with various silica and calcia sources and their properties were determined with particular reference to the simultaneous uptake of ammonium and phosphate ions, which are implicated in the eutrophication of lakes and ponds. After examination of various silica and calcia sources, Ca(OH)(2) and SiO(2) sol were selected as the most appropriate starting materials. Dry milling was found to be superior to wet milling in avoiding contamination from the milling media during mixing. Nine samples with three different Ca/Si ratios and Al(2)O(3) contents were prepared with various mass ratios of Ca(OH)(2), PSA and SiO(2). The chemical compositions of the hydrothermal products of these mixtures moved towards the tieline of CaSiO(3)-PSA, with respect to the starting compositions. The major phase formed in all samples was poorly crystalline C-S-H(I), with hydroxysodalite also formed in the Al-containing mixtures. All the products showed a capacity for the simultaneous uptake of ammonium and phosphate ions. The saturated sorption capacities calculated from the Langmuir equation ranged from 0.9 to 2.4mmol/g for the ammonium ion and from 3.3 to 5.2mmol/g for the phosphate ion. Since the sorption capacities for both ions increased with increasing Ca contents of the product, substitution of Ca(2+) for NH(4)(+) and the formation of calcium phosphate phases such as apatite and brushite by precipitation are thought to be the main sorption mechanisms.

Adsorption↗

PubMed2006

Modification of the method of thread manufacture improves stroke induction rate and reduces mortality after thread-occlusion of the middle cerebral artery in young or aged rats.

Improving models of human stroke by the use of aged animals has been advocated; however the commonly used rat middle cerebral artery thread-occlusion model has produced suboptimal stroke induction and excess mortality in aged rats. We report the development of a modified method for silicone-coating the tip of occluding threads which produces a malleable silicone-coated tip which is firmly bonded and of highly consistent diameter, and overcomes problems of thread insertion through the narrowed carotid canal found in aged animals. Comparison of stroke outcomes and mortality were made between these threads and heat-treated poly-L-lysine coated threads. The rate of successful stroke induction in aged rats was significantly improved (from 14% to 86%). Similarly, mortality fell from 21-31% to 3-7% or less in both young and old rats with or without diabetes and hypertension. An occluding thread tip diameter of 0.35-0.38 mm was optimal for induction of mid-sized strokes in both young and old rats. This method of thread manufacture overcomes problems of inconsistency of diameter and bonding of the silicone-coated tip, and these threads produce significant improvements in stroke induction by MCA occlusion, particularly in aged animals and those with co-morbidities.

Aging↗

PubMed2006

Prototype of a silicon nitride ceramic-based miniplate osteofixation system for the midface.

OBJECTIVE: The favorable properties of silicon nitride (Si3N4) ceramics, such as high mean strength level and fracture toughness, suggest biomedical use as an implant material. Minor reservations about the biocompatibility of Si3N4 ceramics were cleared up by previous in vitro and in vivo investigations. STUDY DESIGN AND SETTING: A Si3N4 prototype minifixation system was manufactured and implanted for osteosynthesis of artificial frontal bone defects in 3 minipigs. After 3 months, histological sections, computed tomography (CT) scans, and magnetic resonance imaging (MRI) scans were obtained. Finite element modeling (FEM) was used to simulate stresses and strains on Si3N4 miniplates and screws to calculate survival probabilities. RESULTS: Si3N4 miniplates and screws showed satisfying intraoperative workability. There was no implant loss, displacement, or fracture. Bone healing was complete in all animals. The formation of new bone was observed in direct contact to the implants. The implants showed no artifacts on CT and MRI scanning. FEM simulation confirmed the mechanical reliability of the screws, whereas simulated plate geometries regarding pullout forces at maximum load showed limited safety in a bending situation. CONCLUSIONS: Si3N4 ceramics show a good biocompatibility outcome both in vitro and in vivo. In ENT surgery, this ceramic may serve as a biomaterial for osteosynthesis (eg, of the midface including reconstruction the floor of the orbit and the skull base). To our knowledge, this is the first introduction of a ceramic-based miniplate-osteofixation system. Advantages compared with titanium are no risk of implantation to bone with mucosal attachment, no need for explantation, and no interference with radiologic imaging. Disadvantages include the impossibility of individual bending of the miniplates.

Animals↗

PubMed2004

Ground-state potential energy function of SiCl+.

Vibration-rotational (infrared) spectra belonging to four isotopomers of SiCl+ molecular ion in the ground X1Sigma+ electronic state (in total 152 transitions of the fundamental and hot bands up to nu=6) have been reduced to the parameters of the Born-Oppenheimer potential, which is represented in the form of the generalized potential energy function. The dimensionless standard error of the fit is 0.95. The obtained potential is most accurate presently available.

Cations, Monovalent↗

PubMed2005

Gyromagnetic factor of Cr4+ ions in forsterite.

The average value of g factor (i.e., g ) of Cr4+ ions in forsterite (Mg2SiO4) is calculated with the cubic symmetry approximation from the complete high-order perturbation formula of g factor for 3d2 ion in cubic tetrahedral cluster. In the formula, the contribution to g factor from the charge-transfer mechanism (which is neglected in the crystal-field theory) is considered in addition to that from the widely used crystal-field mechanism. From the calculations, the reasonable observed value of g is suggested (note: the experimental values of g by various authors are scattered) and the important contribution of charge-transfer mechanism to g factor can be found.

Chromium↗

PubMed2005

1,2-Dibromoethyl-trichlorosilane (CH2BrCHBrSiCl3): conformational structure and vibrational properties by gas-phase electron diffraction, infrared and Raman spectroscopy, and ab initio molecular orbital and density functional theory calculations.

The molecular structure and conformational properties of 1,2-dibromoethyl-trichlorosilane (CH2BrCHBrSiCl3) have been investigated using gas-phase electron diffraction (GED) data recorded at a temperature of 100 degrees C, together with ab initio molecular orbital (MO) and density functional theory (DFT) calculations, infrared (IR) and Raman spectroscopy in the liquid and solid phases, and normal coordinate analysis (NCA). The molecule exists in the gas- and liquid phases as a mixture of three conformers, gauche(-) [G(-)], with a refined torsion angle phi(BrCCBr)=-71(6) degrees, anti [A], with a torsion angle phi(BrCCBr) approximately -170 degrees , and gauche(+) [G(+)], with a torsion angle phi(BrCCBr) approximately +70 degrees . The second torsion angle of importance, the rotation about the CSi bond, has been refined to a value of +175(13) degrees . Torsion angles were only refined for the more abundant G(-) conformer. In the solid phase, only the G(-) conformer was observed. The temperature-dependent Raman spectra have provided an estimate of the relative conformational entropies, DeltaS. The obtained composition from GED refinements was (%) G(-)/A/G(+)=64(27)/23(13)/13(18) (values with estimated 2sigma uncertainties), giving a conformational stability order in agreement with both the Raman enthalpy measurements and the ab initio MO and DFT calculations using the 6-311G(d) basis set and scaled zero-point energies. Relevant structural parameter values obtained from the GED refinements (with the ab initio HF values used as constraints) were as follows (G(-) values with estimated 2sigma uncertainties): bond lengths (r(g)):r(C-C)=1.501(18)A, r(SiC)=1.865(15)A, r(CBr)=1.965(8)A (average), r(SiCl)=2.028(3)A (average). Bond angles ( anglealpha):angleCCSi=114.1(33) degrees , angleC1C2Br=114.0(21) degrees , angleCSiCl=109.6(7) degrees (average). Experimental IR/Raman and obtained vibrational wavenumbers based on both the unscaled, fixed-scaled as well as the scale-refined quantum-mechanical force fields [HF/6-311G(d)] are presented. The results are discussed and compared with some similar molecules from the literature.

Electrons↗

PubMed2005

Characterization of kaolinite of the Baten El-Ghoul region/south Jordan by infrared spectroscopy.

The infrared spectra (3700-500 cm-1) have been recorded for kaolinite obtained from the Baten El-Ghoul region/south Jordan. The spectra were recorded for raw and dried samples, using KBr disk and nujol methods. The vibrational assignments of the basic fundamental modes were proposed, which were supported by the spectra obtained from the two methods used. The results obtained were compared with other related studies.

Bromides↗

PubMed2005

Electronic states of Ga(3)Si, GaSi(3), and their ions.

The equilibrium geometries and electronic states of Ga(3)Si, GaSi(3), and their ions are investigated using the complete active space self-consistent-field (CASSCF) and DFT(B3LYP)/CCSD(T) techniques. The (2)B(1), (3)B(1), and (1)A(1) states in C(2v) symmetry with a planar quadrilateral geometry are found to be the ground states of Ga(3)Si, Ga(3)Si(+), and Ga(3)Si(-), respectively. On the other hand, the ground states of GaSi(3), GaSi(3)(-) are also predicted to undergo Jahn-Teller distortion to the (2)A'' and (1)A' states in C(s) with a distorted triangular pyramid geometry, respectively, whereas that of GaSi(3)(+) is found to be the (1)A(1) state in C(3v) with symmetric triangular pyramid structure. Binding energies, electron affinities, ionization energies of Ga(3)Si and GaSi(3) are computed at the CCSD(T)/QCISD(T) level and discussed.

Electrochemistry↗

PubMed2004

Three-dimensional modelling of micromachined-ultrasonic-transducer arrays operating in water.

We report on the 3-D modelling of periodic arrays of capacitive micromachined ultrasonic transducers (cMUTs) operating in fluid. Specific developments have been performed to model biperiodic transducer arrays and to take into account radiation into any stratified media at the front-side as well as the back-side of the device. The model is based on a periodic finite-element-analysis/boundary-element-method (FEA/BEM). It is applied to micromachined ultrasonic transducers (MUTs), based on silicon-nitride-circular-membrane arrays on a silicon substrate, and operating in water. The spectrum characteristics of MUTs excited in phase are investigated, showing that very-large-band emission is achievable as previously demonstrated by many authors. However, other contributions are also found, depending on the excitation conditions, that do not radiate in the fluid. These contributions are identified as guided modes that could generate significant cross-talk effects. The origin and the nature of these modes is analyzed to gain insight in the actual operation of MUTs.

Equipment Design↗

PubMed2005

Non-destructive testing of ceramic balls using high frequency ultrasonic resonance spectroscopy.

Although ceramic balls are used more and more for bearings in the aerospace and space industries, defects in this type of ceramic material could be dangerous, particularly if such defects are located close to the surface. In this paper, we propose a non-destructive testing method for silicon nitride balls, based on ultrasonic resonance spectroscopy. Through the theoretical study of their elastic vibrations, it is possible to characterize the balls using a vibration mode that is similar to surface wave propagation. The proposed methodology can both excite spheroidal vibrations in the ceramic balls and detect such vibrations over a large frequency range. Studying their resonance spectrums allows the balls' elastic parameters be characterized. Ours is an original method that can quickly estimate the velocity of surface waves using high frequency resonances, which permits surface and sub-surface areas to be tested specifically. Two applications are described in this paper. Both use velocity measurements to achieve their different goals, the first to differentiate between flawless balls from different manufacturing processes, and the second to detect small defects, such as cracks. Our method is rapid and permits the entire ceramic ball to be tested in an industrial context.

Ceramics↗

PubMed2006

Bulk-wave and guided-wave photoacoustic evaluation of the mechanical properties of aluminum/silicon nitride double-layer thin films.

The development of devices made of micro- and nano-structured thin film materials has resulted in the need for advanced measurement techniques to characterize their mechanical properties. Photoacoustic techniques, which use pulsed laser irradiation to nondestructively induce very high frequency ultrasound in a test object via rapid thermal expansion, are suitable for nondestructive and non-contact evaluation of thin films. In this paper, we compare two photoacoustic techniques to characterize the mechanical parameters of edge-supported aluminum and silicon nitride double-layer thin films. The elastic properties and residual stresses in such films affect their mechanical performance. In a first set of experiments, a femtosecond transient pump-probe technique is used to investigate the Young's moduli of the aluminum and silicon nitride layers by launching ultra-high frequency bulk acoustic waves in the films. The measured transient signals are compared with simulated transient thermoelastic signals in multi-layer structures, and the elastic moduli are determined. Independent pump-probe tests on silicon substrate-supported region and unsupported region are in good agreement. In a second set of experiments, dispersion curves of the A(0) mode of the Lamb waves that propagate along the unsupported films are measured using a broadband photoacoustic guided-wave method. The residual stresses and flexural rigidities for the same set of double-layer membranes are determined from these dispersion curves. Comparisons of the results obtained by the two photoacoustic techniques are made and discussed.

Acoustics↗

PubMed2005

Ozone decomposition of 2-methylisoborneol (MIB) in adsorption phase on high silica zeolites with preventing bromate formation.

This work elucidates the applicability of our newly developed adsorptive ozonation process for the decomposition of 2-methylisoborneol (MIB), a typical taste and odor chemical, without the formation of possibly carcinogenic bromate ions. First, zeolite adsorbents were screened for their ability to adsorb MIB with a batch-type adsorption experimental apparatus and a flow-type decomposition experimental apparatus included an adsorbent-packed column. The USY zeolite with the highest silica to alumina ratio (SiO(2)/Al(2)O(3) molar ratio=70) showed the best performance as an adsorbent. Using this adsorbent, an ozonation experiment on an MIB solution including bromide ions was performed under various retention times using the flow-type apparatus. As a result, sufficient decomposition of MIB was achieved with preventing bromate formation.

Adsorption↗

PubMed1997

Adherence of oral streptococci to an immobilized antimicrobial agent.

An antimicrobial agent, 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride, was immobilized on silica. Interaction between the material (termed) OAIS) and various oral bacterial species were then studied. Seven species of Streptococcus and two Actinomyces were investigated for their ability to adhere to this biomaterial. Cell-surface hydrophobicity and zeta-potential were examined as well. Analysis of extracted hydrophobic proteins which adhered to OAIS revealed that the adherence of these micro-organisms was closely related to the hydrophobicity of their cell surfaces. The results of zeta-potential assays indicated that negative charge on the cell surface inhibited adherence to OAIS. Gel electrophoresis revealed that OAIS could absorb cell-surface hydrophobic proteins from all bacterial species tested. Preadsorption of hydrophobic components on the cell surface inhibited adherence of the Strep. mutans strain to OAIS in a dose-dependent manner. The results indicate that OAIS adsorption of these oral bacteria was dependent on the degree of hydrophobicity of their surfaces. A major component of this adherence was hydrophobic cell-surface proteins.

Absorption↗