Ray-tracing and physical-optics analysis of the aperture efficiency in a radio telescope

The performance of telescope systems working at microwave or visible-IR wavelengths is typically described in terms of different parameters according to the wavelength range. Most commercial ray-tracing packages have been specifically designed for use with visible-IR systems and thus, though very flexible and sophisticated, do not provide the appropriate parameters to fully describe microwave antennas and to compare with specifications. We demonstrate that the Strehl ratio is equal to the phase efficiency when the apodization factor is taken into account. The phase efficiency is the most critical contribution to the aperture efficiency of an antenna and the most difficult parameter to optimize during the telescope design. The equivalence between the Strehl ratio and the phase efficiency gives the designer/user of the telescope the opportunity to use the faster commercial ray-tracing software to optimize the design. We also discuss the results of several tests performed to check the validity of this relationship that we carried out using a ray-tracing software, ZEMAX, and a full Physical Optics software, GRASP9.3, applied to three different telescope designs that span a factor of approximately 10 in terms of D/lambda. The maximum measured discrepancy between phase efficiency and Strehl ratio varies between approximately 0.4% and 1.9% up to an offset angle of >40 beams, depending on the optical configuration, but it is always less than 0.5% where the Strehl ratio is >0.95.     

Quercetin‐induced apoptotic cascade in cancer cells: Antioxidant versus estrogen receptor α‐dependent mechanisms

The flavonol quercetin, especially abundant in apple, wine, and onions, is reported to have anti‐proliferative effects in many cancer cell lines. Antioxidant or pro‐oxidant activities and kinase inhibition have been proposed as molecular mechanisms for these effects. In addition, an estrogenic activity has been observed but, at the present, it is poorly understood whether this latter activity plays a role in the quercetin‐induced anti‐proliferative effects. Here, we studied the molecular mechanisms of quercetin committed to the generation of an apoptotic cascade in cancer cells devoid or containing transfected estrogen receptor α (ERα; i.e., human cervix epitheloid carcinoma HeLa cells). Although none of tested quercetin concentrations increase reactive oxygen species (ROS) generation in HeLa cells, quercetin stimulation prevents the H₂O₂‐induced ROS production both in the presence and in the absence of ERα. However, this flavonoid induces the activation of p38/MAPK, leading to the pro‐apoptotic caspase‐3 activation and to the poly(ADP‐ribose) polymerase cleavage only in the presence of ERα. Notably, no down‐regulation of survival kinases (i.e., AKT and ERK) was reported. Taken together, these findings suggest that quercetin results in HeLa cell death through an ERα‐dependent mechanism involving caspase‐ and p38 kinase activation. These findings indicate new potential chemopreventive actions of flavonoids on cancer growth.     

Correcting secondary mirror surface errors in Noto 32 m radiotelescope using the 'active' primary mirror

Some results are presented of a successful attempt to correct the surface manufacturing errors on the secondary mirror of the Noto 32 m radiotelescope by means of a new primary mirror, the shape of which is controlled by 244 electromechanical actuators. During a 43 GHz Jupiter observation, the technique yielded a 22% gain increase.     

Basic Element for Square Kilometer Array Training (BEST): Evaluation of the Antenna Noise Temperature

In this paper, a rigorous procedure for calculating the antenna noise temperature is described, and applied to the antenna of BEST-1 (basic element for SKA training - version 1), which represents one of the SKA (square kilometer array) demonstrators. The SKA will be a new-generation radio telescope, with a collecting area 50 times larger than the area of today's largest radio telescope. BEST is the Italian reduced-scale SKA demonstrator, based on the re-instrumentation of about 8000 m² of the Northern Cross radio telescope, built with cylindrical parabolic antennas. In order to perform the antenna-temperature analysis, an electromagnetic tool to accurately evaluate the antenna pattern in the whole space surrounding the antenna itself is required. We used the commercial software GRASP8, developed by TICRA, to characterize reflector antennas. The antenna temperature was evaluated using the guideline adopted by the Antenna Task Force of the SKA world consortium. For BEST-1 at 408 MHz, we found an antenna temperature equal to 30 K in the zenith direction and 60 K at the horizon. The numerical results have been verified through several celestial calibration radio sources.     

An ultrasonic method for measuring tissue displacement: technicaldetails and validation for measuring myocardial thickening

We have developed a method for measuring myocardial thickening from a single ultrasonic transducer attached to the epicardium. Displacement of the underlying myocardial tissue is measured by following the phase of the echoes within a sample volume range-gated across the myocardium. The output is in the form of an analog signal. To verify the accuracy, resolution, and limitations of the system, we derived the equations relating the position of a reflector to the phase of its echo and compared the system output in vitro to a known input using a single moving target and a random distribution of scatterers, and in vivo to that of an ultrasonic transit-time dimension gauge. The results demonstrate that the 10 MHz system can accurately follow the motion of single or multiple targets with a resolution of 0.02 mm. In 25 dogs myocardial thickening measured with the displacement system compared favorably in both waveform and magnitude with thickening measured by the two-crystal transit-time method. Applications for the displacement method include: quantification of regional ventricular function in animal models of cardiovascular diseases, measurement of endocardial to epicardial differences in the deformation of regional myocardium during the cardiac cycle, and evaluation of regional cardiac function in patients during and after corrective cardiac surgery.     

A time-domain physical optics heuristic approach to passiveintermodulation scattering

Passive intermodulation (PIM) is a phenomenon which often arises at junctions between different materials. This may be a major issue in tightly packed antenna farms as those typically present on communication satellites. Here, an heuristic nonlinear extension to the time-domain physical optics (TD-PO) is proposed, to take into account electromagnetic scattering at intermodulated frequencies when such a junction is illuminated by two impinging electromagnetic fields at different frequencies. Simulation results are compared with measures to validate the model     

Prevention and treatment of hypoglycaemia unawareness in type 1 diabetes mellitus

Unawareness of hypoglycaemia (reduced ability/failure to recognize hypoglycaemia symptoms at the physiological threshold of 3.0 mmol/l) occurs frequently in type 1 diabetes mellitus, and patients are then at risk for severe hypoglycaemia. Unawareness of hypoglycaemia is the result of earlier frequent episodes of hypoglycaemia (iatrogenic). Likewise, a history of hypoglycaemia induces unawareness, while meticulous prevention of hypoglycaemia can reverse hypoglycaemia unawareness. Therefore, it is essential that insulin therapy regimens for type 1 diabetes mellitus be designed not only to maintain near-normoglycaemia, but also to minimize hypoglycaemia. Such a goal is feasible as long as (1) a rational plan of insulin therapy is adopted, including appropriate use of the short-acting insulin analogue lispro, (2) blood glucose is properly monitored, (3) blood glucose targets are individualized, and (4) education programs are widely implemented.