Pulse tail suppression in laser diode output by tunable notch filter

Efficient suppression of relaxation oscillations in the output signal from an overdriven gain-switched laser diode was demonstrated. Several quantum-well distributed feedback laser diodes from different manufacturers were used for experimental analysis. A five-fold increase in the peak power was achieved for the tail-free operation. It was found that spectral filtering removed the nonlinearly chirped components resulting in pulse shortening by a factor of three.

Local delivery of the KCa3.1 blocker, TRAM-34, prevents acute angioplasty-induced coronary smooth muscle phenotypic modulation and limits stenosis

Objective-We previously demonstrated that upregulation of intermediate-conductance Ca2+ -activated K+ channels (KCa 3.1) is necessary for mitogen-induced phenotypic modulation in isolated porcine coronary smooth muscle cells (SMCs). The objective of the present study was to determine the role of KCa3.1 in the regulation of coronary SMC phenotypic modulation in vivo using a swine model of postangioplasty restenosis. Methods and Results-Balloon angioplasty was performed on coronary arteries of swine using either noncoated or balloons coated with the specific KCa3.1 blocker TRAM-34. Expression of KCa3.1, c-jun, c-fos, repressor element-1 silencing transcription factor (REST), smooth muscle myosin heavy chain (SMMHC), and myocardin was measured using qRT-PCR in isolated medial cells 2 hours and 2 days postangioplasty. KCa3.1, c-jun, and c-fos mRNA levels were increased 2 hours postangioplasty, whereas REST expression decreased. SMMHC expression was unchanged at 2 hours, but decreased 2 days postangioplasty. Use of TRAM-34 coated balloons prevented KCa3.1 upregulation and REST downregulation at 2 hours, SMMHC and myocardin downregulation at 2 days, and attenuated subsequent restenosis 14 and 28 days postangioplasty. Immunohistochemical analysis demonstrated corresponding changes at the protein level. Conclusion-Blockade of KCa3.1 by delivery of TRAM-34 via balloon catheter prevented smooth muscle phenotypic modulation and limited subsequent restenosis. © 2008 American Heart Association, Inc.

Novel design of FBG-based composite double notch VSB filter for DWDM systems

This paper proposes a novel design of optical filters based on a cascade of tailored fiber Bragg gratings (FBGs) operating in the transmission regime. As an example of the application of the proposed general technique, ultranarrow optical vestigial sideband (VSB) filtering based on two FBGs operating in the transmission regime was examined. This design can be easily implemented by writing FBG-based filters for each wavelengthdivision-multiplexing channel before multiplexing. © 2006 IEEE.

The effect of notch filtering on the waveform of the newborn auditory brainstem response

OBJECTIVE: To identify whether the use of a notch filter significantly affects the morphology or characteristics of the newborn auditory brainstem response (ABR) waveform and so inform future guidance for clinical practice. DESIGN: Waveforms with and without the application of a notch filter were recorded from babies undergoing routine ABR tests at 4000, 1000 and 500 Hz. Any change in response morphology was judged subjectively. Response latency, amplitude, and measurements of response quality and residual noise were noted. An ABR simulator was also used to assess the effect of notch filtering in conditions of low and high mains interference. RESULTS: The use of a notch filter changed waveform morphology for 500 Hz stimuli only in 15% of tests in newborns. Residual noise was lower when 4000 Hz stimuli were used. Response latency, amplitude, and quality were unaffected regardless of stimulus frequency. Tests with the ABR stimulator suggest that these findings can be extended to conditions of high level mains interference. CONCLUSIONS: A notch filter should be avoided when testing at 500 Hz, but at higher frequencies appears to carry no penalty.

Tail-free operation of an overdriven gain-switched DFB laser by spectral filtering

The tail-free operation of an overdriven gain-switched distributed feedback (DFB) laser by spectral filtering was demonstrated. The filtering was realized using a mechanically tunable fiber Bragg grating (FBG). The unfiltered and filtered signals were traced by corresponding oscilloscope. The spectral filtering removed the nonlinearly chirped components resulting in the pulse shortening. The results showed unwanted relaxation in the overdriven DFB laser were supressed by using a steep-edge notch filter.

The influence of non-metallic inclusions upon the properties of linepipe steels

The principal aim of this work was to determine the role of non-metallic inclusions in the process of hydrogen stepwise cracking (SWC). Additionally, the influence of inclusions upon the notch ductility of hydrogen charged (HC) and uncharged (UN) tensile specimens was examined. To obtain a basis for experiment a series of low carbon-manganese steels were prepared by induction melting. In order to produce variations in the composition, morphology, volume fraction, size and distribution of the inclusions the steel chemistry was adjusted prior to casting by additions of deoxidiser and Ca-Si injection. Sections of each ingot were hot rolled. Metallography, image analysis, mechanical tests and hydrogen SWC tests were then carried out. The volume fraction, morphology, and shape of inclusions influenced the tensile ductility of the steels. Marked anisotropy was found in the steels containing type II MnS inclusions at all rolling temperatures, whereas the fully Ca treated steel was isotropic. It was found that several inclusion parameters (projected length PL, mean free distance MFD, nearest-neighbour distance NND) correlated with fracture strain. An increase in inclusion volume fraction and/or the dimension of inclusions on a plane parallel to the plane of fracture led to a decrease in fracture strain. The inclusion parameters did not correlate with the fracture strains for the HC tensile specimens. However, large or clusters of inclusions acted as the principal sites for crack initiation. `Fisheyes' or areas of `flat' fracture were often found on these fracture surfaces. The criteria for SWC initiation was found to be either large inclusions or clusters of inclusions. As the PL of inclusions increased the probability of large SWCs occurring increased. SWC initiation at inclusions was believed to occur at a critical concentration of hydrogen. Factors which assisted the concentration of hydrogen at inclusions were discussed. None of the proposed mechanisms of hydrogen embrittlement could be identified as the single cause of SWC.

Fundamental mechanisms affecting service performance of electroplated plastics

Ten grades of ABS and four grades of polypropylene have been plated with various copper + nickel + chromium coatings and subjected to a variety of tests. In corrosion studies the pre-electroplating sequence and plastics type have been shown to influence performance. One ABS pre-electroplating sequence was consistently associated with better corrosion performance; two factors were responsible for this, namely the more severe nature of the etch and the relatively more noble electroless nickel. Statistical analysis has indicated that order of severity of the corrosion tests was static-mobile-CASS, the latter being the least severe. In mechanical tests two properties of ABS and polypropJylene, ductility and impact strength, have been shown to be adversely affected when electrodeposited layers were applied. The cause of this is due to a complex of factors, the most important of which is the notch sensitivity of the plastics. Peel adhesion has been studied on flat panels and also on ones which had a ridge and a valley moulded into one face. High adhesion peaks occurred on the flat face at regions associated with the ridge and valley. The local moulding conditions induced by the features were responsible for this phenonemon. In the main programme the thermal cycling test was shown to be more likely than the peel adhesion test to give an indication of the service performance of electroplated plastics.

The mechanics of creep crack growth in a Magnox alloy

Magnox AL80 has been used for a study of creep crack propagation. A number of variables have been considered such as specimen geometry,notch root radius, material thickness, creep prestrain and stress level.The work has covered the material behaving under two values of the creep exponent, n=3.5 and n=7, according to the stress level. As well as observing initiation times and crack growth rates, scribed grids have been used to examine the near crack tip strain levels and distributions. It was shown that estimations of COD from notch flank opening can give misleading indications of material behaviour and that a more informative method was to monitor displacements in the material surrounding the crack tip. Strong evidence was found for crack advance being displacement controlled, however it was shown that the COD approach should be considered geometry dependant. The summation of ∈xx and ∈yy provided the most successful description of crack advance as it produced a single value that described propagation in all the cases concidered. The strain distributions indicates that σyy was related to distance from a point ahead of the crack tip by the exponent - (l/n+l) and that σxx is proportional to σyy. The constraint stresses arising in the DEN and CN specimens were evaluated. Initiation time was found to be principally affected by the stress level but was modified by the constraints arising from specimen geometry. Crack growth was found not to obey either the empirical K or σpett relationships but was reviewed in context of the observed strain behaviour.

Ductile fracture mechanisms in a structural steel

Microstructural fracture processes in a BS4360 Grade 50D structural steel with lower sulphur content were studied in smooth tensile specimen tests and Charpy-size bend bar tests. Based on the experimental analysis, an experimental void growth relation with the plastic strain and stress triaxiality and multiplying factor on void growth were determined. Experimental results show that the void growth relation can be reasonably used to estimate the constraint in the specimens containing the notch or crack, also they can be used to evaluate the variations of the stress triaxiality in front of the notch and crack tip under general yielding condition. Side-grooves obviously increase the constraint of the CVN specimens. Strain hardening leads to increasing the stress triaxiality, and decelerating the net void growth. This is especially true for the values of stress triaxiality more than about one. Additionally, the effect of the stress triaxiality on the critical void growth corresponding to the onset of ductile tearing was preliminarily investigated. In this work, a large number of smaller specimens were tested to investigate the ductile-brittle transition behaviour of the structural steel. A void growth rate explanation was suggested for evaluating the temperature transition behaviour. The elastic-plastic fracture tough-ness values based on small specimen tests, such as pre-cracked side-grooved bending specimen and short bar tensile specimen, may give large overestimates of the plane strain fracture toughness.

The effect of thermochemical treatment on the fatigue properties of alloy steels

The effect of thermochemical treatment namely carburising on the fatigue behaviour of one carbon and two alloy steels has been studied in rotating and unidirectional bending. The effect of carbon profile on the unidirect¬ional bending fatigue strength of 63SA14 was assessed, and it was found that single stage carburising with a surface carbon content of 0.8% has resulted in a higher fatigue strength than other types of carbon profiles. Residual stresses and other metallurgical variables arising from different carbon profiles, were also considered. The highest compressive stresses h~e resulted from boost-diffuse-carburising. On the other hand surface decarburisation was associated with tensile residual stresses and a reduced fatigue strength. Retained austenite was found to be detrimental in unidirectional bending fatigue; however its presence in carburised 83SAIS did not seem to influence the rotating bending fatigue strength. Carbide particles in globular and/or intergranular form were detrimental to compressive residual stresses; the unidirectional bending fatigue strength is markedly lowered. The highest fatigue strength was accomplished by vacuum carburising. The absence of internal oxidation was the key factor in the increased fatigue strength; the presence of uniformly distributed fine carbide particles did not upset the superior fatigue strength of vacuum carburised pieces. The effect of mean stress on the fatigue strength of carburised 63SA14 was studied. Increasing the mean stress as would be expected resulted in a decreased fatigue strength. Carburisation showed its advantages at low mean stress, but at high mean stress it offers little advantage over the uncarburised hardened conditions. Notch effect was also studied in unidirectional bending of carburised 080MlS. The general trend showed that the fatigue strength decreases with increasing the stress concentration factor. But different carburising conditions have different effect on notch sensitivity.

Studies on the luminance-related characteristics of the transient pattern reversal electroretinogram

The electroretinogram evoked by reversal pattern stimulation (rPERG) is known to contain both pattern contrast and luminance related components. The retinal mechanisms of the transient rPERGs subserving these functional characteristics are the main concern in the present studies. Considerable attention has been paid to the luminance-related characteristics of the response. The transient PERGs were found to consist of two subsequent processes using low frequency attenuation analysis. The processes overlapped and the individual difference in each process timings formed the major cause for the variations of the negative potential waveform of the transient rPERGs. Attention has been paid to those having ‘notch’ type of variation. Under different contrast levels, the amplitudes of the positive and negative potentials were linearly increased with higher contrast level and the negative potential showed a higher sensitivity to contrast changes and higher contrast gain. Under lower contrast levels, the decreased amplitudes made the difference in the timing course of the positive and negative processes evident, interpreting the appearance of the notch in some cases. Visual adaptation conditions for recording the transient rPERG were discussed. Another effort was to study the large variation of the transient rPERGs (especially the positive potential, P50) in the elderly who’s distant and near visual acuity were normal. It was found that reduction of retinal illumination contributed mostly to the P50 amplitude loss and contrast loss mostly to the negative potential (N95) amplitude loss. Senile miosis was thought to have little effect on the reduction of the retinal illumination, while the changes in the optics of the eye was probably the major cause for it, which interpreted the larger individual variation of the P50 amplitude of the elderly PERGs. Convex defocus affected the transient rPERGs more effectively than concave lenses, especially the N95 amplitude in the elderly. The disability of accommodation and the type and the degree of subjects’ ametropia should be taken into consideration when the elderly rPERGs were analysed.

The effect of innate compliance on the performance of a counterpulsation device

Cardiovascular disease (CVD) continues to be one of the top causes of mortality in the world. World Heart Organization (WHO) reported that in 2004, CVD contributed to almost 30% of death from estimated worldwide death figures of 58 million[1]. Heart failure treatment varies from lifestyle adjustment to heart transplantation; its aims are to reduce HF symptoms, prolong patient survival and minimize risk [2]. One alternative available in the market for HF treatment is Left Ventricular Assist Device (LVAD). Chronic Intermittent Mechanical Support (CIMS) device is a novel (LVAD) heart failure treatment using counterpulsation similar to Intra Aortic Balloon Pumps (IABP). However, the implantation site of the CIMS balloon is in the ascending aorta just distal to aortic valve contrasted with IABP in the descending aorta. Counterpulsation coupled with implantation close to the aortic valve enables comparable flow augmentation with reduced balloon volume. Two prototypes of the CIMS balloon were constructed using rapid prototyping: the straight-body model is a cylindrical tube with a silicone membrane lining with zero expansive compliance. The compliant-body model had a bulging structure that allowed the membrane to expand under native systolic pressure increasing the device’s static compliance to 1.5 mL/mmHg. This study examined the effect of device compliance and vascular compliance on counterpulsating flow augmentation. Both prototypes were tested on a two-element Windkessel model human mock circulatory loop (MCL). The devices were placed just distal to aortic valve and left coronary artery. The MCL mimicked HF with cardiac output of 3 L/min, left ventricular pressure of 85/15 mmHg, aortic pressure of 70/50 mmHg and left coronary artery flow rate of 66 mL/min. The mean arterial pressure (MAP) was calculated to be 57 mmHg. Arterial compliance was set to be1.25 mL/mmHg and 2.5 mL/mmHg. Inflation of the balloon was triggered at the dicrotic notch while deflation was at minimum aortic pressure prior to systole. Important haemodynamics parameters such as left ventricular pressure (LVP), aortic pressure (AoP), cardiac output (CO), left coronary artery flowrate (QcorMean), and dP (Peak aortic diastolic augmentation pressure – AoPmax ) were simultaneously recorded for both non-assisted mode and assisted mode. ANOVA was used to analyse the effect of both factors (balloon and arterial compliance) to flow augmentation. The results showed that for cardiac output and left coronary artery flowrate, there were significant difference between balloon and arterial compliance at p < 0.001. Cardiac output recorded maximum output at 18% for compliant body and stiff arterial compliance. Left coronary artery flowrate also recorded around 20% increase due to compliant body and stiffer arterial compliance. Resistance to blood ejection recorded highest difference for combination of straight body and stiffer arterial compliance. From these results it is clear that both balloon and arterial compliance are statistically significant factors for flow augmentation on peripheral artery and reduction of resistance. Although the result for resistance reduction was different from flow augmentation, these results serves as an important aspect which will influence the future design of the CIMS balloon and its control strategy. References: 1. Mathers C, Boerma T, Fat DM. The Global Burden of disease:2004 update. Geneva: World Heatlh Organization; 2008. 2. Jessup M, Brozena S. Heart Failure. N Engl J Med 2003;348:2007-18.

Fatigue cracking from stress concentration in mild steel

Pulsating; tension fatigue tests have been carried out on edge notched specimens of a mild steel. An electrical potential drop technique was used to determine the number of cycles taken to initiate cracks and the rate at which the cracks grew across the specimen. The results could be described by the range of stress intensity factor, which for crack initiation was modified to take account of the notch root radius. Analysis of elastic stress distributions at cracks and notches and models of plasticity at crack tips are used to discuss the results. Limited evidence in the literature indicates that the fracture mechanics approach may provide a general description of crack initiation and growth in notched specimens, and a simple graphical method of calculating fatigue lives is described. The results are used to illustrate the effects of specimen size and geometry on the fatigue life of notched specimens. The relevance of the work to the assessment of the significance of defects in welds is discussed.

Cleavage initiation in the intercritically reheated coarse-grained heat-affected zone:Part I. Fractographic evidence

Tensile, crack opening displacement (COD), blunt notch, and Charpy impact tests were used to investigate cleavage initiation in the intercritically reheated coarse-grained heat-affected zone (IC CG HAZ) of three steels. The steels were chosen to provide different distributions and morphologies of MA (high-carbon martensite with some retained austenite) particles within the IC CG HAZ structure. Observation of minimum impact toughness values for the IC CG HAZ was found to be associated with a particular microstructure containing a near-connected grain boundary network of blocky MA particles, the MA particles being significantly harder than the internal grain microstructure. The initiation mechanism for this structure was determined to be from a combination of an overlap of residual transformational induced stress fields, due to the formation of the MA particles, between two closely spaced particles and stress concentration effects resulting from debonding of the particles. © 1994 The Minerals, Metals and Materials Society, and ASM International.

Cleavage initiation in the intercritically reheated coarse-grained heat affected zone:Part II. Failure criteria and statistical effects

In part 1 of this article, cleavage initiation in the intercritically reheated coarse-grained heat affected zone (IC CG HAZ) of high-strength low-alloy (HSLA) steels was determined to occur between two closely spaced blocky MA particles. Blunt notch, crack tip opening displacement (CTOD), and precracked Charpy testing were used in this investigation to determine the failure criteria required for cleavage initiation to occur by this mechanism in the IC CG HAZ. It was found that the attainment of a critical level of strain was required in addition to a critical level of stress. This does not occur in the case of high strain rate testing, for example, during precracked Charpy testing. A different cleavage initiation mechanism is then found to operate. The precise fracture criteria and microstructural requirements (described in part I of this article) result in competition between potential cleavage initiation mechanisms in the IC CG HAZ.