Analysis of circuit conditions for optimum intermodulation and gain in bipolar cascomp amplifiers with non-ideal error correction

The cascoded-compensation or ‘Cascomp’ amplifier offers excellent distortion reduction and thermal distortion rejection, but has not seen widespread use because of a limited gain and increased complexity compared with other topologies. The original theory showed that with the addition of an ideal error amplifier the circuit will completely compensate distortion for suitably chosen degeneration and bias values. This research presents a new, rigorous mathematical proof for conditions of compensation. The authors further develop the proof to include the non-idealities of the error amplifier. It is shown that there exists a second bias point, not exposed by the original analysis that offers improved gain while maintaining distortion cancellation. By reducing the error amplifier degeneration resistance, one can increase a Cascomp circuit's overall gain by several dB while maintaining theoretically perfect distortion compensation. A robust bias point is proposed, which takes the advantage of this new theory by optimising circuit values resulting in a comparatively broader and deeper third-order distortion null. The proposed theory is confirmed with simulation and measurement that show agreement within the bounds of process and component error limits

Unified Models of Molecular Emission from Class 0 Protostellar Outflow Sources

Low mass star-forming regions are more complex than the simple spherically symmetric approximation that is often assumed. We apply a more realistic infall/outflow physical model to molecular/continuum observations of three late Class 0 protostellar sources with the aims of (a) proving the applicability of a single physical model for all three sources, and (b) deriving physical parameters for the molecular gas component in each of the sources. We have observed several molecular species in multiple rotational transitions. The observed line profiles were modelled in the context of a dynamical model which incorporates infall and bipolar outflows, using a three dimensional radiative transfer code. This results in constraints on the physical parameters and chemical abundances in each source. Self-consistent fits to each source are obtained. We constrain the characteristics of the molecular gas in the envelopes as well as in the molecular outflows. We find that the molecular gas abundances in the infalling envelope are reduced, presumably due to freeze-out, whilst the abundances in the molecular outflows are enhanced, presumably due to dynamical activity. Despite the fact that the line profiles show significant source-to-source variation, which primarily derives from variations in the outflow viewing angle, the physical parameters of the gas are found to be similar in each core.Comment: MNRAS 12 pages, 16 figure

Reduction of computer usage costs in predicting unsteady aerodynamic loadings caused by control surface motions: Computer program description

A digital computer program was developed to calculate unsteady loadings caused by motions of lifting surfaces with leading edge and trailing edge controls based on the subsonic kernel function approach. The pressure singularities at hinge line and side edges were extracted analytically as a preliminary step to solving the integral equation of collocation. The program calculates generalized aerodynamic forces for user supplied deflection modes. Optional intermediate output includes pressure at an array of points, and sectional generalized forces. From one to six controls on the half span can be accomodated

COMSAT Laboratories' on-board baseband switch development

Work performed at COMSAT Laboratories to develop a prototype on-board baseband switch is summarized. The switch design is modular to accommodate different service types, and the architecture features a high-speed optical ring operating at 1 Gbit/s to route input (up-link) channels to output (down-link) channels. The switch is inherently a packet switch, but can process either circuit-switched or packet-switched traffic. If the traffic arrives at the satellite in a circuit-switched mode, the input processor packetizes it and passes it on to the switch. The main advantage of the packet approach lies in its simplified control structure. Details of the switch architecture and design, and the status of its implementation, are presented

Observation of HCN hyperfine line anomalies towards low- and high-mass star-forming cores

HCN is becoming a popular choice of molecule for studying star formation in both low- and high-mass regions and for other astrophysical sources from comets to high-redshift galaxies. However, a major and often overlooked difficulty with HCN is that it can exhibit non-local thermodynamic equilibrium (non-LTE) behaviour in its hyperfine line structure. Individual hyperfine lines can be strongly boosted or suppressed. In low-mass star-forming cloud observations, this could possibly lead to large errors in the calculation of opacity and excitation temperature, while in massive star-forming clouds, where the hyperfine lines are blended due to turbulent broadening, errors will arise in infall measurements that are based on the separation of the peaks in a self-absorbed profile. The underlying line shape cannot be known for certain if hyperfine anomalies are present. We present a first observational investigation of these anomalies across a range of conditions and transitions by carrying out a survey of low-mass starless cores (in Taurus & Ophiuchus) and high-mass protostellar objects (in the G333 giant molecular cloud) using hydrogen cyanide (HCN) J=1-0 and J=3-2 emission lines. We quantify the degree of anomaly in these two rotational levels by considering ratios of individual hyperfine lines compared to LTE values. We find that all the cores observed show some degree of anomaly while many of the lines are severely anomalous. We conclude that HCN hyperfine anomalies are common in both lines in both low-mass and high-mass protostellar objects, and we discuss the differing hypotheses for the generation of the anomalies. In light of the results, we favour a line overlap effect for the origins of the anomalies. We discuss the implications for the use of HCN as a dynamical tracer and suggest in particular that the J=1-0, F=0-1 hyperfine line should be avoided in quantitative calculations.Comment: 17 pages, 8 figure

Empirical developments in retraction

This study provides current data on key questions about retraction of scientific articles. Findings confirm that the rate of retractions remains low but is increasing. The most commonly cited reason for retraction was research error or inability to reproduce results; the rate from research misconduct is an underestimate, since some retractions necessitated by research misconduct were reported as being due to inability to reproduce. Retraction by parties other than authors is increasing, especially for research misconduct. Although retractions are on average occurring sooner after publication than in the past, citation analysis shows that they are not being recognised by subsequent users of the work. Findings suggest that editors and institutional officials are taking more responsibility for correcting the scientific record but that reasons published in the retraction notice are not always reliable. More aggressive means of notification to the scientific community appear to be necessary

CO abundances in a protostellar cloud: freeze-out and desorption in the envelope and outflow of L483

CO isotopes are able to probe the different components in protostellar clouds. These components, core, envelope and outflow have distinct physical conditions and sometimes more than one component contributes to the observed line profile. In this study we determine how CO isotope abundances are altered by the physical conditions in the different components. We use a 3D molecular line transport code to simulate the emission of four CO isotopomers, 12CO J=2-1, 13CO J=2-1, C18O J=2-1 and C17O J=2-1 from the Class 0/1 object L483, which contains a cold quiescent core, an infalling envelope and a clear outflow. Our models replicate JCMT (James Clerk Maxwell Telescope) line observations with the inclusion of freeze-out, a density profile and infall. Our model profiles of 12CO and 13CO have a large linewidth due to a high velocity jet. These profiles replicate the process of more abundant material being susceptible to a jet. C18O and C17O do not display such a large linewidth as they trace denser quiescent material deep in the cloud.Comment: 9 figures, 13 pages, 2 table

Mass transfer properties of Acacia mangium plantation wood

This study investigated the mass transfer properties (permeability and mass diffusivity) in the longitudinal, radial and tangential directions of plantation-grown Acacia mangium in VinhPhuc province,northeast, Vietnam. These properties will be used to complement a conventional drying model in the future. Measurements of gas and liquid permeability were performed using a Porometer (POROLUXTM1000). Mass diffusivity was determined in a constant humidity and temperature chamber using PVC-CHA vaporimeters. Results showed the gas permeability was significant higher than liquid with the descending order of longitudinal, radial, and tangential directions. The permeability anisotropy ratios from the longitudinal to transverse directions of Acacia mangium were much lower than other published species. However, the obvious anisotropy ratios from radial to tangential for both permeability and diffusivity, is one of concerns as they can exacerbate defects during drying. Besides, the high permeability and diffusivity of Acaciamangium compared to some other species reported compounds its relatively fast drying rate