Sol-gel Preparation and Preliminary in vitro Evaluation of Fluorapatite／Hydroxyapatite Solid Solution Films

Fluorapatite/hydroxyapatite solid solution has better biological properties than other apatites, especially used as films or coatings. In this work, sol-gel preparation and in vitro behavior of fluorapatite/hydroxyapatite solid solution films on titanium alloy were investigated. Ca(NO3)2-4H20 and PO(OH)x(OEt)3-x were selected as precursors, and hexafluorophosphoric acid (HPFo) was used as a fluorine containing reagent. The Ca and P precursors were mixed with HPFo to keep the Ca/P molar ratio 1.67. The mixtures refluxed for 12 h were used as dipping sols for the preparation of the films. The phase of the films obtained at 600℃ was apatite. The F contents in the films increased with the concentrations of HPF6 in the dipping sols. The solid solution films were shown to have better stability than hydroxyapatite films, and a reasonably good bioactivity in the in vitro evaluation.     

Short-term frequency stability of clock generators for multigigahertz rapid-single-flux quantum digital circuits

Superconducting digital systems based on Josephson junctions have generally used a synchronous timing strategy. A master clock signal is used to delimit a data window during which the system changes state and data is transferred from one block to the next. The temporal stability of the clock signal has a profound effect on the performance of rapid single flux quantum (RSFQ) digital systems. In particular, short-term clock fluctuations, or clock jitter, can degrade system performance due to the hazard of timing constraint violations. The successful development of large-scale RSFQ digital systems will require highly stable multigigahertz on-chip clock sources. To meet this need, methods for characterizing and measuring the short-term stability of such sources are required. We identify the relevant figure of merit to characterize and compare various clocks: the cycle-to-cycle standard deviation of the clock periods. We present experimental techniques for the measurement of this figure of merit and apply them to the measurement of jitter in a clock generator used often in RSFQ systems, the ring oscillator. High-frequency phase noise measurements found the jitter of a 9.6-GHz clock to be in the range from 0.6% to 0.36% of the clock period. The measured values of clock jitter fell within the 95% confidence interval of our stochastic circuit simulations. This was sufficient evidence to conclude that thermal noise from the resistors in the circuit may be the dominant source of jitter in the ring oscillator.     

Creep of PVDF monofilament sutures: service performance prediction from short-term tests

Isothermal short-term creep of poly (vinylidene fluoride) (PVDF) monofilament sutures was determined at several temperatures between 10 and 90 °C under the stress of 10 MPa. Long term service performance was predicted for 10 decades of time. The compliance master curve as a function of time fits a hyperbolic sine equation. The temperature shift factor as a function of the temperature a_T (T) is accurately represented by a general equation based on free volume. A simple relationship between the two parameters of the equation is explored. The viscoelasticity of PVDF is also seen in dynamic mechanical analysis performed at the frequency of 1 Hz. The origin of the viscoelastic character well present in the deformability of the PVDF in service is due to the occurrence of the α_c relaxation that is active at ∼50 °C (E″ peak at 1 Hz).     

Defect-free sintering of two material powder injection molded components Part II Model

A defect-free, two-material component can be obtained via co-sintering by suitably altering the powder characteristics or compositions, as demonstrated in Part I. In this paper, a model to ascertain the suitability of material systems to be co-sintered without defects such as delamination or interface pores is presented. The model is based on the management of the stress induced due to the difference in shrinkage and an analysis of the in situ strength of the weaker material during sintering. Tool steel in combination with stainless steel admixed with boron and Fe-2Ni admixed with boron are two systems used to validate the model. The predictions of the model are in good agreement with the observations.     

Cost estimates to guide pre-selection of processes

A process is a method of shaping, joining or surface-treating a material. Process selection has three steps. The first is to identify from the ‘menu’ of all available processes, the subset, which can give a chosen material the desired shape with the desired detail, precision and finish. The second is to choose, from among these, the ones that will do so at the lowest cost. The final step is to investigate the most promising processes in depth, exploring considerations such as availability, in-house experience, safety and environmental issues. The first two steps can be thought of as process pre-selection. Components have to be assembled and finished to create products. Here too, the ability to rank by cost, however crudely, helps guide pre-selection. Cost models are reviewed from the perspective of material and process selection. An approximate model is useful provided it has generality—that is, it must allow comparison of very different processes. Many approaches fail in this. One that works, based on resource consumption, is developed here and its use for selection is illustrated. It has been implemented as part of a tool that allows rapid pre-selection from a database of 112 processes.     

Ionizing-Radiation Response of the GaAs/(Al, Ga)As PHEMT: A Comparison of Gamma- and X-ray Results

An experiment is reported on the effect of ⁶⁰Co gamma rays or 45-keV x-ray photons on the GaAs/(Al, Ga)As PHEMT. It is shown that x-ray treatment can improve the dc performance of the device in some cases. This finding is attributed in part to the annealing or modification of DX centers.     

4/spl times/10 GHz mode-locked multiple-wavelength fiber laser

We demonstrate a four-wavelength 10-GHz mode-locked erbium-doped fiber laser, with wavelength spacings of 3.5-5 nm. Nearly transform-limited Gaussian pulses of 11- to 14-ps duration are measured and all wavelengths are synchronous.     

Optimization of a photopolymerizable holographic recording material based on polyvinylalcohol using angular responses

Acrylamide-based holographic recording materials have significant advantages and the composition of these materials has been optimized in terms of energetic sensitivity and diffraction efficiency. As a result, diffraction gratings with an efficiency of almost 80% for energetic exposures of 35 mJ/cm² and a spatial frequency of 1000 lines/mm in photosensitive films 65 μm thick have been obtained. In this paper we present the effects of intensity, thickness, and variation in the concentration of each component by studying the angular responses of the diffraction gratings recorded in each composition.