Probing the cure of 13C labelled bisphenol A dicyanate ester in carbon fibre reinforced composites using solid state 13C NMR, SEM and FTIR

We report a study of the curing mechanism of ¹³C labelld bisphenol A dicyanate ester in the presence of a electrolytically surface treated XAS carbon fibre using several techniques – solid state ¹³C NMR, scanning electron microscopy (SEM) and diffuse reflectance FTIR. Comparison of the results obtained in pure matrices and solution shows that the resin undergoes the same reaction mechanism in both cases and forms the sym-triazine network structure in the composite. Received: 25 November 1996/Accepted: 23 January 1997     

Influence of bias current and signal power on behaviour of an antireflection-coated laser amplifier

The variation of gain with wavelength of a 1.5 ?m semiconductor-laser amplifier with antireflection-coated facets has been measured over several modes. The internal gain and resonant wavelength were found using a curve- fitting technique and the dependence of these quantities on bias current and signal power was investigated.     

Eliminating spurious modes in finite-element waveguide problems by using divergence-free fields

Spurious solutions in the finite-element analysis of the modes of waveguides and optical fibres are completely eliminated by the use of fields which are exactly divergence-free. Such fields are themselves computed by the finite-element method.     

Effects of a limited nap on night sleep in older subjects.

The night sleep of 16 women (aged 50–60 yrs), which had been preceded by either afternoon naps or no-nap control periods, was assessed by polygraphic and subjective measures. There were 2 nap and 2 non-nap nights. The naps were limited to a 1-hr opportunity. The measures of all Ss, good nappers (more than 20-min sleep on both nap occasions), and Ss with 50-min or more nap time, were separately analyzed. The null hypothesis of a nap effect could not be rejected. It is concluded that within limits, naps may be recommended to offset the common night-time awakenings in older persons. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A study of slotline leaky-wave antennas

The results of an experimental investigation of several millimeter-wave slotline leaky-wave antennas at 94 GHz are given. The experimental results show how variations in the transverse slot geometry affect the radiation pattern. Additionally, slot geometry variations also change the polarization performance of the antenna. The narrow transverse slot array was more sensitive to a perpendicularly (E_y-E_z) polarized electric field than the wide slot case. Also, the change in the effective phase constant along the antenna with changing slot dimensions caused a noticeable shift in the angle of the main beams. However, the beamwidths for all cases remained about the same. A simple model is presented to explain this. For designing an antenna of this form, the effective phase constant, β, can be approximately determined using a numerical analysis of the uniform slot problem. Given β and the operating frequency and the scanning ranges, the element spacing can be determined. The attenuation constant does not change much when the transverse slot widths are varied. If greater sensitivity to an E _y-E_z polarized wave is desired, the transverse slots should be narrow     

Quadrature Vestigial Sideband (QVSB) Data Transmission

The combined use of quadrature modulation and vestigial sideband filtering is investigated as a means of obtaining a spectrally efficient modulation scheme. The name quadrature vestigial sideband (QVSB) aptly describes the new system, whereby two independent data streams are each VSB modulated into the same passband, but on quadrature related carriers. The inherent interference between the quadrature related channels is shown to be of a controlled form, similar to the intersymbol interference (ISI) in partial response (PR) systems. Techniques suitable for "unwinding" the ISI in PR systems are shown to be also applicable to QVSB. Precoding with bit-by-bit, decoding, nonoptimum and optimum probablistic decoding are investigated. The latter method results in only a 1.2 dBE_{b}/N_{0}degradation, atP_{b} = 10^{-5}, compared to coherent binary phase shift keying (BPSK), although up to a fourfold increase in spectral efficiency can be obtained.     

Angiotensin-converting enzyme inhibition and angiotensin II subtype-1 receptor blockade during the progression of left ventricular dysfunction: differential effects on myocyte contractile processes

Inhibition of the angiotensin-converting enzyme (ACE) in the setting of chronic left ventricular (LV) dysfunction has been demonstrated to have beneficial effects on survival and symptoms. However, whether ACE inhibition has direct effects on myocyte contractile processes and if these effects are mediated primarily through the AT1 angiotensin-II receptor subtype remains unclear. The present project examined the relationship between changes in LV and myocyte function and beta adrenergic receptor transduction in four groups of six dogs each: (1) Rapid Pace: LV failure induced by chronic rapid pacing (4 weeks; 216 +/- 2 bpm); (2) Rapid Pace/ACEI: concomitant ACE inhibition (ACEI: fosinopril 30 mg/kg b.i.d.) with chronic pacing; (3) Rapid Pace/AT1 Block: concomitant AT1 Ang-II receptor blockade [Irbesartan: SR 47436(BMS-186295) 30 mg/kg b.i.d.] with chronic pacing; and (4) Control: sham controls. With Rapid Pace, the LV end-diastolic volume increased by 62% and the ejection fraction decreased by 53% from control. With Rapid Pace/ACEI, the LV end-diastolic volume was reduced by 24% and the ejection fraction increased by 26% from Rapid Pace only values. Rapid Pace/AT1 Block did not improve LV geometry or function from Rapid Pace values. Myocyte contractile function decreased by 40% with Rapid Pace and increased from this value by 32% with Rapid Pace/ACEI. Rapid Pace/AT1 Block had no effect on myocyte function when compared with Rapid Pace values. With Rapid Pace/ACEI, beta receptor density and cyclic AMP production were normalized and associated with an improvement in myocyte beta adrenergic response compared with Rapid Pace only. Although Rapid Pace/AT1 also normalized beta receptor density, cyclic AMP production was unchanged and myocyte beta adrenergic response was reduced by 15% compared with Rapid Pace only. ACE inhibition with chronic rapid pacing improved LV and myocyte geometry and function, and normalized beta receptor density and cyclic AMP production. However, AT1 Ang-II receptor blockade with chronic rapid pacing failed to provide similar protective effects on LV and myocyte geometry and function. These unique findings suggest that the effects of ACE inhibition on LV geometry and myocyte contractile processes in the setting of developing LV failure are not primarily caused by modulation of AT1 Ang-II receptor activation.     

Influence of intracrystalline diffusion in shape selective catalytic test reactions

Molecular dynamics simulations are used to measure the self diffusion constant D of linear decane and n-methylnonanes (n = 2, 3, 4, and 5) at a catalytically relevant temperature in seven 10 member ring zeolites. Two general behaviors are observed in D as the branch position is moved towards the center of the alkane chain. For three of the zeolites (MEL, MFI, and MTT), D decreases monotonically as expected based on a consideration of the bulkiness of the different isomers. For the other four, alkane diffusion is considered anamolous as D is not a monotonic function of branch position. For n-methylnonanes in three zeolites D shows a minimum at either n = 2 (FER), 3 (EUO), or 4 (TON). In AEL, D has a local maximum for n = 3. Alkane diffusion is anamolous in these zeolites because they have structural features that provide a unique hindrance to molecular motion along the main diffusion channel. The ability of the zeolite to hinder motion depends on the molecular structure of the isoparaffin, resulting in the anamolous behavior observed. The 10 member ring zeolites selected for this study represent the entire group for which known structures exist and values of the modified constraint index have been published. The diffusion data presented indicates that product shape selectivity may play some part in determining the modified constraint index. This revised version was published online in July 2006 with corrections to the Cover Date.