Accelerated Aging of a Composite Explosive

A given formulation of a composite explosive was submitted to accelerated aging at 293 K, 333 K and 353 K for slightly over a year. Extensive determination of mechanical properties were conducted using an Instron Tester to characterize the aging process of the explosive as a whole. The change of elongation at maximum load can be fitted to a third-order reaction rate giving an enthalpy of activation (Δ Ha) for the aging process of (78 ± 5) kJ/mol. Although the change of stress at maximum load was a function of temperature, it could not be predicted by a simple correlation. Swelling, inverse gas chromatography and N₂O evolution by infrared were applied to the samples aged at 333 K. Swelling measurements show a regular increase with aging of the relative number of cross-linking. Inverse gas chromatography at 373 K in helium indicated a first-order kinetic aging process for every sample, but the rate constant (k) of the samples aged for 0, 30 and 60 days was slightly lower than the one for samples aged for 130, 250 and 375 days. The N₂O evolution measured at 338.5 K in vacuum by infrared absorption indicates an aging process consisting of two consecutive first-order reactions, the second one being ten times slower than the first one. The first stage, which was also studied by inverse gas chromatography, gives rate constants which are about half as large as those measured by chromatography and confirms the changes in behavior from the samples aged for 0, 30 and 60 days to the samples aged for 130, 250 and 375 days. These results are discussed in relation to an aging process by oxidative cross-linking of the binder and degradation of the solid explosive.     

Remote Estimation of Crop Chlorophyll Content Using Spectral Indices Derived From Hyperspectral Data

This paper examines the use of simulated and measured canopy reflectance for chlorophyll estimation over crop canopies. Field spectral measurements were collected over corn and wheat canopies in different intensive field campaigns organized during the growing seasons of 2004 and 2005. They were used to test and evaluate several combined indices for chlorophyll determination using hyperspectral imagery (Compact Airborne Spectrographic Imager). Several index combinations were investigated using both PROSPECT-SAILH canopy simulated spectra and field-measured reflectances. The relationships between leaf chlorophyll content and combined optical indices have shown similar trends for both PROSPECT-SAILH simulated data and ground-measured data sets, which indicates that both spectral measurements and radiative transfer models hold comparable potential for the quantitative retrieval of crop foliar pigments. The data set used has shown that crop type had a clear influence on the establishment of predictive equations as well as on their validation. In addition to generating different predictive equations, corn and wheat data yielded contrasting agreement between estimated and measured chlorophyll contents even for the same predictive algorithm. Among the set of indices tested in this paper, index combinations like modified chlorophyll absorption ratio index/optimized soil-adjusted vegetation index (OSAVI), triangular chlorophyll index/OSAVI, moderate resolution imaging spectrometer terrestrial chlorophyll index/improved soil-adjusted vegetation index (MSAVI), and red-edge model/MSAVI seem to be relatively consistent and more stable as estimators of crop chlorophyll content.     

Microwave signals generated by optical heterodyne betweeninjection-locked semiconductor lasers

Single-mode-laser rate equations with added Langevin noise sources are used to study injection-locked semiconductor lasers. Two slave lasers are frequency-locked on the same or different sidebands of a current-modulated master laser. The optical heterodyne between the two secondary lasers is characterized. It is demonstrated that the frequency stability of the source modulating the master laser is preserved on the sidebands and partially transferred to the slaves. A linear model is first investigated. Static operation conditions and small-signal behavior are then calculated. Direct simulation of the rate equations for each laser is next achieved. This highlights the validity domain and limitations of the linear model. A more complete set of results-such as laser and heterodyne spectra-is also obtained. It is moreover shown that synchronization of the slave laser diodes by optical injection-locking leads to strongly correlated, while not identical, laser fields. Finally, simulation results are compared to experimental data     

Electrochemical behaviour of rapidly solidified and conventionally cast Cu-Ni-Sn alloys

The corrosion behaviour of microcrystalline Cu-Ni-Sn alloys produced by rapid solidification was studied and compared to that of conventionally cast alloys. Due to the great chemical homogeneity provided by rapid solidification, the corrosion resistance of the microcrystalline material was superior to that of conventional material. The former material developed a more uniform and homogeneous barrier layer in 3% NaCl solutions. The electrochemical behaviour of the studied alloys was dependent on the Sn content. The influence of the Ni content on the corrosion performance of both types of materials is also discussed.     

Near-Optimal Signal Preprocessor for Positive Cardiac Arrhythmia Identification

Extremely high reliability of waveform detection is fundamental for computer-assisted identification of cardiac arrhythmias. The problem is formulated in terms of one of the basic aspects in digital signal processing, namely, detection of an unknown deterministic signal in noise. The signal is considered band limited and the noise as Gaussian with zero mean. The theory presented leads to an energy based detector. No a priori assumption is made about the morphology of the waveforms to be detected; only energy thresholding is necessary for event detection. The addition of a linear filter as a front end to the energy detector has resulted in an entire detection process described as suboptimal matched nonlinear filtering. The SNR gain at the input of the energy detector has given performances almost identical to the matched filter. The method has been implemented with an original fast algorithm to allow reasonable execution time for the processing of continuous long-duration signals (1 h). The design of such a fillter is described along with its application to the processing of two simultaneously recorded cardiac signals. The two signals are an auricular electrogram (OEG from an esophageal pill electrode) and an ECG (lead II or III). Systematic evaluation and detection performance results show that the proposed method could be seriously considered as a near-optimal approach to waveform detection, since it is based on proven signal processing theory and is far superior to heuristic methods.     

Increased risk for falling associated with obesity: mathematicalmodeling of postural control

Recent epidemiological studies report that obesity is positively related to fracture incidence. In the present experiment, a model of postural control was used to examine the impact of an abnormal distribution of body fat in the abdominal area upon postural stability. Obese and lightweight humanoids were destabilized by imposing a small initial angular speed from a neutral standing position. To avoid a loss of stability yielding a stepping reaction or a fall, an ankle torque is necessary to counteract the perturbation. Three torque parameters-ankle torque onset, time to peak torque, and muscular ankle torque-were entered in a program to simulate the intrinsic variability of the human postural control system. A loss of stability was detected when the center of pressure exceeded stability margins. The most striking observation is the nonlinear increase of torque needed to stabilize the humanoid when the motor response was chararterized by delayed temporal parameters. The effect was more pronounced when an anterior position of the center of mass was included in the simulations. This suggests that, when submitted to daily postural stresses and perturbations, obese persons (particularly those with an abnormal distribution of body fat in the abdominal area) may be at higher risk of falling than lightweight individuals     

Diversity of Streptococcus thermophilus phages in a large-production cheese factory in Argentina

Phage infections still represent a serious risk to the dairy industry, in which Streptococcus thermophilus is used in starter cultures for the manufacture of yogurt and cheese. The goal of the present study was to analyze the biodiversity of the virulent S. thermophilus phage population in one Argentinean cheese plant. Ten distinct S. thermophilus phages were isolated from cheese whey samples collected in a 2-mo survey. They were then characterized by their morphology, host range, and restriction patterns. These phages were also classified within the 2 main groups of S. thermophilus phages (cos- and pac-type) using a newly adapted multiplex PCR method. Six phages were classified as cos-type phages, whereas the 4 others belonged to the pac-type group. This study illustrates the phage diversity that can be found in one factory that rotates several cultures of S. thermophilus. Limiting the number of starter cultures is likely to reduce phage biodiversity within a fermentation facility.     

Surgical treatment of Wolff-Parkinson-White syndrome: a "retrospectroscopic" view

The surgical treatment of the Wolff-Parkinson-White syndrome made its appearance in 1968 when Dr W. C. Sealy performed the first direct surgical intervention for ablating an accessory connection in a patient with incessant atrioventricular reentrant tachycardia. The surgical approach fell into disfavor in 1990 when catheter ablation using radiofrequency energy was adopted into widespread use. In this presentation, I will attempt to assess the scientific value of the surgical experience using the scholarly tool, the "retrospectroscope," and also to answer the questions, Was it worth it? What was learned? and What was achieved? We conclude that a large body of scientific knowledge and skill was brought to light by this experience and, of even more importance, passed on for best use to the catheter surgeons.     

Storage of trachea for X-ray microanalytical studies of tracheal submucosal glands

Previous studies have suggested that penicillin-resistant pneumococcal isolates (especially those with MIC > 1 microgram/mL) usually are clonally related. To test this hypothesis, the molecular epidemiology of 29 clinical isolates of penicillin-resistant pneumococci (of which 83% were also resistant to either cefotaxime or ceftriaxone) collected in central Taiwan was investigated by pulsed field gel electrophoresis. Twenty-seven distinct patterns were identified. Our results indicate that an increase in penicillin-resistant S. pneumoniae between April 1993 and June 1994 in central Taiwan is not due to the clonal dissemination of a limited number of epidemic strains.