Early detection of ageing in solder joints through laser probe thermal analysis of the peltier effect

We have recently developed an optical contactless method for testing the quality of solder joints during accelerated thermal cycling ageing processes.¹ The method was based upon the measurement of the dynamic thermal behaviour of the joint to short bursts of Joule heating. It has proved to be efficient in revealing the formation of cracks at the lead-solder interface. We present a method to evaluate ageing at a much earlier stage in the cycling process. We have observed in earlier work,¹ that before cracks appear, structural changes occur in the solder at the lead-solder interface. The thermal response of the solder joint is recorded over time to a Peltier heat perturbation produced by flowing a current pulse through the interface where structural changes occur. The key point in this method is to discriminate the Peltier effect from the Joule thermal response because both effects generate heat. The variation of the early Peltier response in the thermal cycling ageing tests is seen as a quantitative signature of the structural changes in the lead-solder interface.     

Effect of air gap on cylindrical dielectric resonator antenna operating in TM/sub 01/ mode

The results of a numerical study on the effect of an air gap on the input impedance and resonance frequency of a cylindrical dielectric resonator (CDR) antenna operating in the TM/sub 01/ mode as a function of dielectric constant are presented. The CDR resides on a conducting ground plane and is excited by a coaxial probe through the bottom of the ground plane. Some of the numerical results are validated experimentally.<>     

L-arginine reduces kidney collagen accumulation and N-epsilon-(carboxymethyl)lysine in the aging NMRI-mouse

BACKGROUND: The aging process leads to glomerular basement membrane (GBM) thickening due to increased collagen accumulation. This mechanism can be explained by the nonenzymatic glycosylation hypothesis of collagen aging. We have published the positive effect of L-arginine on glucose-mediated cross-linking, and if the nonenzymatic glycosylation hypothesis of aging holds, the pharmacological effect of L-arginine on glucose-mediated cross-links in the aging Hannover NMRI mouse can be expected. METHODS: Animals were given L-arginine 50 mg/kg body weight/day orally and compared to a control group without treatment. RESULTS: Electron microscopical measurement of the GBM thickness showed significant differences between controls (4920 +/- 1680 A) and the experimental group (2345 +/- 815 A). Determination of the total kidney collagen content based upon 4-trans hydroxyproline revealed 13.9 +/- 3.9 mg/100 mg kidney weight (kw) in the untreated group versus 7.9 +/- 4.2 mg/100 mg kw in the treated group. For solubility studies based upon hydroxyproline determination, collagen was eluted by pepsin digestion. This revealed 18.7 +/- 3.9 mg/100 mg kw in the controls versus 7.8 +/- 4.8 mg/100 mg kw in the treated group. HPLC analysis of N-epsilon-(carboxymethyl)lysine (CML) showed in the treated group (1.847 +/- 0.247 nM/microM hydroxyproline) significantly lower concentrations than in the untreated group (3.399 +/- 0.349 nM/microM hydroxyproline). On sodium dodecyl sulfate (SDS) polyacrylamidegel electrophoresis, the eluates of the treated animals showed less high molecular weight material than their untreated mates. CONCLUSIONS: We cannot discriminate between the probable mechanisms of cross-linking but we clearly can state that L-arginine reduces cross-linking and collagen accumulation in aging collagen type IV accompanied and strongly associated with decreased CML content.     

Flow dynamics or ‘quaking’ in gravity discharge from silos

This paper reviews the characteristics of pulsating or cyclic flow of bulk solids during gravity discharge in bins and silos. The dynamic load phenomenon is often referred to as “silo quaking” and is influenced by various factors related to the type of flow pattern developed in the bin and the flow properties of the bulk material. Of particular relevance is the influence of ‘slip-stick’ during shear flow, and the velocity at critical sections in the silo during discharge. An overview of recent and current research on this subject is presented.     

Applications of ultrashort pulse propagation in Bragg gratings forwavelength-division multiplexing and code-division multiple access

We discuss theoretical and experimental studies on the propagation of ultrashort pulses through fiber Bragg gratings. We also consider several applications in optical communications to be found by combining ultrashort pulses and fiber Bragg gratings: a multiwavelength source for wavelength-division-multiplexed systems and a means for implementing optical code-division multiple access     

Optical characterization of low-temperature-grown GaAs forultrafast all-optical switching devices

Low-temperature-grown GaAs (LT-GaAs) is a promising material for all-optical switching devices due to its outstanding optical characteristics. In this paper, we outline a simplified model we have developed to describe the dynamics of the carriers in this material. We also report the results of a series of measurements that we have performed to characterize the optical properties of the material. Specifically, we present the first measurements of the two-photon absorption coefficient and the refractive index changes as a function of the growth and annealing temperatures in LT-GaAs. Finally, we show how our model can be used to optimize the material for applications in all-optical switching     

Monitoring Proteolysis During Cheddar Cheese Ripening Using Two-Dimensional Gel Electrophoresis

A 2-D gel electrophoretic method, consisting of isoelectric focusing and alkaline urea-PAGE was used to monitor proteolysis during ripening (180d, 5°C and 8°C) of full- and reduced-fat Cheddar cheese. The method enabled quantifying changes in levels of peptides in cheese with good spot-resolution. Results can complement those from other analyses, especially those for determining low MW peptides. Notable effects were found for cheese composition and ripening temperature on gel pattern and on relative levels of selected proteolysis products. In both cheese varieties, most peptides reached a maximum during the first 3 ripening months and gradually disappeared as ripening advanced.     

Two distinct DNA ligase activities in mitotic extracts of the yeast Saccharomyces cerevisiae

Four biochemically distinct DNA ligases have been identified in mammalian cells. One of these enzymes, DNA ligase I, is functionally homologous to the DNA ligase encoded by the Saccharomyces cerevisiae CDC9 gene. Cdc9 DNA ligase has been assumed to be the only species of DNA ligase in this organism. In the present study we have identified a second DNA ligase activity in mitotic extracts of S. cerevisiae with chromatographic properties different from Cdc9 DNA ligase, which is the major DNA joining activity. This minor DNA joining activity, which contributes 5-10% of the total cellular DNA joining activity, forms a 90 kDa enzyme-adenylate intermediate which, unlike the Cdc9 enzyme-adenylate intermediate, reacts with an oligo (pdT)/poly (rA) substrate. The levels of the minor DNA joining activity are not altered by mutation or by overexpression of the CDC9 gene. Furthermore, the 90 kDa polypeptide is not recognized by a Cdc9 antiserum. Since this minor species does not appear to be a modified form of Cdc9 DNA ligase, it has been designated as S. cerevisiae DNA ligase II. Based on the similarities in polynucleotide substrate specificity, this enzyme may be the functional homolog of mammalian DNA ligase III or IV.