High power waveform engineering

For many years industry has considered RF PA design to be a "black art". This perception has been held due to the lack of availability of meaningful information for analysis and design. Due to the emergence of large signal waveform based measurements and increased understanding in the literature, it is now possible to characterise devices and correlate the information for enhanced PA design in terms of efficiency, linearity and/or reliability. This has been well documented and demonstrated using on-wafer devices but where this thesis work begins, little work had been done in expanding this capability to higher more meaningful power levels using packaged devices. This work has successfully addressed both of these limitations and extended visibility of time domain waveform data to higher power levels. Thus, allowing for the uncovering of world record efficiency levels of 77 % (4W output power) for Si LDMOS devices at S band frequencies using waveform engineering based procedures, in this case Class F. A feat previously only reported at L-band frequencies. Other waveform based designs such as inverse Class F and Doherty modes of operation are also successfully demonstrated in this thesis. In both of these cases, voltage related issues affecting reliability were uncovered that merit further consideration in the design process. Waveform engineering was made possible by applying de-embedding the measured current and voltage waveforms to the current generator plane. That is the plane at which the device is free from any device and package parasitics with the current and voltage waveforms seen to be in good agreement with those typically found in literature. These were successfully applied at high power levels (110W) previously not reported. To further demonstrate the relevance of waveform de-embedding, a non-linear charge conservative model based on industry standard modelling techniques was compared against time-domain measurements conducted in several classes of operation. This form of model verification is often overlooked and provides a unique insight into the model's accuracy highlighting new areas of improvement. In most cases the model was shown to be in good agreement with measured data, providing a high level of confidence in the application of waveform engineering principles within the CAD domain. Thus providing the PA designer the facility to apply waveform engineering on both the test bench and within the CAD domain

A view of HIV--infection in Karachi

A prospective study on the prevalence of HIV-l infection in Karachi, Pakistan was conducted over a period of six years (1986-1992). Over 15,000 individualsamples and more than 32,000 donor units of individuals residing in Karachi at the time of sample co llection were tested for HIV-I infection by our screening test EIA which revealed a positivity rate of 0.23% and 0.003% in individual and donor units respectively by Western Blot. We divided patients into four groups A,B,C and D based on the most plausible cause of transmission. The largest number of positive patients belonged to group B, who were of either foreign origin or expatriates or Pakistanis settled abroad. They comprised approximately 67% of the total positive cases and were subjected to testing on strong clinical grounds. In individuals of other groups like group A and D, there was history of travel abroad from time to time. The only positive donor unit (group C) belonged to a person who had been li ving in Middle East for the last 10-12 years. The last group D comprised of samples that wer e directly sent to us without complete history,except for the fact that they had been travelling back and forth. The large majority of patients fell in 20-50 years age group. Despite the limitations of this study, we conclude that the prevalence of HIV is steadily Increasing in our population and so far, we have no been able to find an indigenous case of AIDS in our serie

The Relationship among Directors' Pay, Corporate Governance, and Firm Performance: Evidence from Financial Sector of Pakistan

This research empirically examines the effect of firms' performance and corporate governance attributes on directors' pay. To attain the objective, the data for the period from 2007 to 2014 are retrieved from annual reports of 52 listed financial firms. Return on assets and return on equity are utilized to measure performance. Board size, board independence, board ownership and CEO duality are employed as corporate governance practices. Using the random effect model, the performance has positively related to directors’ pay, but level of significance is sensitive across performance proxies. The board independence has negatively significantly influenced the directors' pay. However, board ownership significantly positively influenced the directors’ pay. Furthermore, board size and CEO duality both have not significantly associated with directors’ pay

Maternal and fetal attachment before birth: Trends in pregnant women of urban Karachi

Background: Maternal-fetal attachment is a multidimensional phenomenon and product of diverse physiological, psychological, and socio-emotional factors. The prenatal period is crucial in forming this bond and further predicts postnatal attachment.Methodology: The present research was conducted using a cross-sectional survey design. Sixty-six participants filled out the survey regarding practices, perceptions, and attitudes toward maternal-fetal attachment after attending an online session on Talking to the Baby in the Womb. Results: Analysis revealed that participants talk to their baby in their tummy. Wondering when the baby starts thinking, feeling, and hearing within also aids in forming a maternal-fetal relationship. A statistically significant difference (p=0.013) was found between HCP and PW in terms of attitude towards feeding the baby and perception of a mother giving up on the baby (p=0.04).Conclusion: The following research allows us to study the differences in the practices between healthcare providers and pregnant women so that interventions can be designed accordingly

The Central Asian Supercourse to Increase Scientific Productivity.

Non

The Central Asian Supercourse to Increase Scientific Productivity

Non

Effect of TiB2 on the Mechanical and Tribological Properties of Marine Grade Aluminum Alloy 5052: An Experimental Investigation

Aluminum Alloy 5052 is one of the excellent corrosion resistant alloys among the Aluminum 5000 series alloys. Despite the favourable corrosion resistance, it exhibits low resistance to wear and perform poorly in various tribological applications.This study attempts to investigate the impact of TiB2 reinforcement on the mechanical and tribological properties of Aluminum Alloy 5052 matrix alloy, fabricated using the stir casting technique. Composites with varying weight percentages (0, 2.5, 5 and 7.5 wt. %)of TiB2 were prepared. Vicker's hardness testing was conducted to assess the effect of TiB2 content on composite hardness.Hardness of composites increased from 65.5 to 85.16 HV in tandem with the TiB2 content depicting a rise of about 30 %. Tribological properties were studied through dry sliding wear tests using a pin-on-disc tribometer, with varying loads (10 N and 50 N)and sliding speeds (1 m/s and 3 m/s). The results demonstrate that the addition of TiB2 significantly improves the wear resistance of the composites,being optimum in composite with 5 wt. % of TiB2. A maximum increase of about 36 % in wear resistance was observed at high load and high-speed conditions corresponding to 5 wt. % TiB2 concentration. FESEM analysis revealed distinct wear modes and the role of TiB2 in changing the wear mechanism from abrasion to delamination. This study underscores the pivotal role of TiB2 in enhancing the mechanical and tribological properties of Aluminum Alloy5052, expanding its application scope, particularly in lightweight engineering applications in general and marine in particular

Millimeter-wave on-wafer large signal characterization system for harmonic source/load pull and waveform measurements

This paper describes a large-signal single-sweep characterization system based on vector network analyzer receivers for on-wafer harmonic load/source pull measurements up to 110 GHz using passive tuners, and waveform measurements up to 100 GHz using an oscilloscope as a phase meter. The calibration and measurement procedures are described and validated with thru structures and on GaAs HEMTs at Ka-band demonstrating the capability to offer an important insight for both technology developers and designers of millimetre-wave transistors and amplifiers