Composites of hydroxyapatite and bisphosphonate: properties and alveolar bone response

A composite was made by adsorption of the bisphosphonate [(3-dimethylamino-1-hydroxypropylidene)-1,1-bisphosphonate; dimethyl-APD] into an hydroxyapatite (HA) tube. Adsorbed dimethyl-APD did not change the bulk properties of the HA tube but the surface properties were altered. The amount of 0.1 mmol/L dimethyl-APD adsorbed into the HA tube was 0.78 ( ± 0.20) g after 4 weeks. The composite tube of HA and dimethyl-APD placed after extraction of teeth in the premolar regions of dogs were biocompatible, stable and bonded strongly and intimately to the alveolar bone. Although there was no bone resorption around the composite tubes, no conclusion can be drawn yet from this study as far as local inhibition of alveolar bone resorption is concerned.     

Optimization of correlated multi-response quality engineering by the upside-down normal loss function

Most of the published literature on robust design is basically concerned with a single response. However, the reality is that common industrial problems usually involve several quality characteristics, which are often correlated. Traditional approaches to multidimensional quality do not offer much information on how much better or worse a process is when finding optimal settings. Köksoy and Fan [Engineering Optimization 44 (8): 935–945] pointed out that the upside-down normal loss function provides a more reasonable risk assessment to the losses of being off-target in product engineering research. However, they only consider the single-response case. This article generalizes their idea to more than one response under possible correlations and co-movement effects of responses on the process loss. The response surface methodology has been adapted, estimating the expected multivariate upside-down normal loss function of a multidimensional system to find the optimal control factor settings of a given problem. The procedure and its merits are illustrated through an example.     

Probabilistic calibration of discrete element simulations using the sequential quasi-Monte Carlo filter

The calibration of discrete element method (DEM) simulations is typically accomplished in a trial-and-error manner. It generally lacks objectivity and is filled with uncertainties. To deal with these issues, the sequential quasi-Monte Carlo (SQMC) filter is employed as a novel approach to calibrating the DEM models of granular materials. Within the sequential Bayesian framework, the posterior probability density functions (PDFs) of micromechanical parameters, conditioned to the experimentally obtained stress–strain behavior of granular soils, are approximated by independent model trajectories. In this work, two different contact laws are employed in DEM simulations and a granular soil specimen is modeled as polydisperse packing using various numbers of spherical grains. Knowing the evolution of physical states of the material, the proposed probabilistic calibration method can recursively update the posterior PDFs in a five-dimensional parameter space based on the Bayes’ rule. Both the identified parameters and posterior PDFs are analyzed to understand the effect of grain configuration and loading conditions. Numerical predictions using parameter sets with the highest posterior probabilities agree well with the experimental results. The advantage of the SQMC filter lies in the estimation of posterior PDFs, from which the robustness of the selected contact laws, the uncertainties of the micromechanical parameters and their interactions are all analyzed. The micro–macro correlations, which are byproducts of the probabilistic calibration, are extracted to provide insights into the multiscale mechanics of dense granular materials.     

Selective toxicity of hydroxyl-rich carbon nanodots for cancer research

Nano Research - The toxicity of nanoparticles in a biological system is an integration of effects arising from surface functionality, particle size, ionic dissolution, etc. This complexity suggests...     

Mid-IR real-time monitoring of the carbocationic polymerization of isobutylene and styrene

The in-situ monitoring of the living carbocationic polymerization of isobutylene (IB) and styrene (St) with a fiber optic Attenuated Total Reflection (ATR) probe in the mid-IR "fingerprint" range is reported here for the first time. Monomer consumption was followed by the disappearance of the C=C stretching for both IB and St, and the C−H bending of the CH₃-group in IB. The formation of polyisobutylene (PIB) was also monitored by tracing the asymmetrical doublet characteristic of C−H bending of the t-butyl groups of the PIB. Conversion measurements by conventional off-line gravimetry correlated well with the new technique. Received: 27 August 1997/Revised version: 2 November 1997/Accepted: 20 November 1997     

Optical acceptance function of modified compound parabolic concentrators with linear corrugated reflectors

For reflective cylindrical concentrators the acceptance function, as determined in the meridian plane, remains constant for more oblique planes of incidence. However, if the reflective surface has a linear corrugated structure, it is possible to increase the acceptance in the meridian plane at the expense of reduced acceptance at a more oblique incidence. A ray-tracing study has been performed on the optical properties of troughlike compound parabolic concentrators (CPC's) with linear corrugated reflectors. Calculations of angular acceptance for a modified CPC with concentration C = x is presented. A possible application of this new concentrator is as a secondary concentrator for tracking parabolic troughs.     

New aspects of transversal1H-NMR relaxation in natural rubber vulcanizates

Summary Structure and dynamics of unfilled and carbon black filled natural rubber vulcanizates were investigated by means of transversal¹H-NMR-relaxation. A simple theoretical model including different motions in polymer network was extended by the discussion of an anisotropy parameter of segmental motion not only for the intercrosslink chains but also for the dangling ends. It makes characterization of the filling state of the network possible to approximate. The effect of increasing correlation times _f of the fast anisotropic local motion with reduction of the molecular mass of intercrosslink chains which was observed, but not cleared up in previous investigation is evidently smaller by using this modified model in accordance with the expectation of a local motion. The determined values of M_c are in good agreement with the results of fits by using the unmodified relaxation function.¹³C-NMR-spectra and stress-strain-experiments are leading in most cases to similar results, especially for M_c.     

Russian doll type cryogenic traps: improved design and isotope separation effects

An improved cryogenic trap for removing micromole quantities of condensables from gas mixtures is described. It is based on the so-called Russian doll design, with which extraordinary trapping efficiencies at flow rates of up to 10 L/min are obtained. The active element consists of one or more nested glass fiber thimbles. Despite the large fiber area, quantitative retrieval of condensed CO(2) is obtained. The new design is demountable and incorporates a heat exchange section; trapping efficiency depends little on the level of coolant, as has been tested for CO(2). When fractionation is induced by incomplete trapping, a small isotopic enrichment in (13)C occurs. It also has been discovered that when He is used as carrier gas, a gas chromatographic effect for CO occurs in Russian doll traps, accompanied by a large isotope separation, in which the elution sequence corresponds to the vapor pressure ratios of the isotopomers.     

Stability under vacuum of silicon trap detectors and their use as transfer instruments in cryogenic radiometry

The stability of the responsivity of trap detectors under vacuum has been studied by means of a special chamber designed for the test of photodetectors at low pressure. The first experiments at a wavelength of 647 nm show that the responsivity variations are smaller than the uncertainties of the measurements, approximately 3 parts in 10(5), when the detector operates successively in air, under vacuum, and then again in air. Calculations based on experiments with single windowless photodiodes indicate that the change in trap responsivity that is due to vacuum effects should be smaller than 1 part in 10(5), at least in the visible part of the wavelength range. This stability makes trap detectors suitable for cryogenic radiometry when one uses transfer detectors under vacuum.