Element gain drifts as an imaging dynamic range limitation in PAF-based interferometers

Interferometry with phased-array feeds (PAFs) presents new calibration challenges in comparison with single-pixel feeds. In particular, temporal instability of the compound beam patterns due to element gain drifts (EGDs) can produce calibration artefacts in interferometric images. To translate imaging dynamic range requirements into PAF hardware and calibration requirements, we must learn to relate EGD levels to imaging artefact levels. We present a MeqTrees-based simulations framework that addresses this problem, and apply it to the APERTIF prototype currently in development for the WSRT.Comment: 4 pages, 3 figures, poster presentation at the XXX URSI General Assembly and Scientific Symposium (Istanbul, Turkey, August 13-20, 2011

Numerical Results for the System Noise Temperature of an Aperture Array Tile and Comparison with Measurements

The purpose of this report is to document the noise performance of a complex beamforming array antenna system and to characterize the recently developed noise measurement facility called THACO, which was developed at ASTRON. The receiver system includes the array antenna of strongly coupled 144 TSA elements, 144 Low Noise Amplifiers (LNAs) (Tmin =35-40K) and the data recording/storing facilities of the initial test station that allow for off-line digital beamforming. The primary goal of this study is to compare the measured receiver noise temperatures with the simulated values for several practical beamformers, and to predict the associated receiver noise coupling contribution, antenna thermal noise and ground noise pick-up (due to the back radiation).Comment: ASTRON repor

Conceptualization of the experience of the individual in the educational space in the light of scientific rationality as a problem of professional identity in global and sociocultural dynamics

As a problem, professional identity associated with the educational space is investigated from the position of belonging to professional groups. The contradictory state of education in the modern world actualizes the problem of identity in the educational space from the perspective of classical modern European rationality with its focus on the scientific forms of cognition, knowledge. The current situation in the world educational space is developed in the ambiguity of the idea of the world, which is expressed in the crisis of universalism and cognitive integrity: the place of rational knowledge in culture is replaced by mythic ideas. The way of thinking exists independently of the individual. The transfer of thinking is a learning task. However, at the present stage, with a sharp increase in the amount of information reported, the emphasis is on formalizing of the educational process, rather than constructivizing. The teacher’s responsibility as a carrier of scientific rationality, which primarily defines the universal meaning of human activity in the transmission of social experience and knowledge, is growing. The level of education of a person is a measure of implementation of the possibility of his/her formation, taking into account the dichotomous nature of the individual's socialization and professional identity based on it. Such a holistic perception of the world will allow gaining a deep understanding of the essence of things, fitting science into the cultural context of modernity

Radiation methods in the diagnosis of primary and recurrent malignant ovarian struma: A case report

We provide a rare clinical and diagnostic observation of primary and recurring malignant ovarian struma. Malignant struma of the right ovary was detected 2 years after surgical treatment of primary benign struma of the left ovary. Six months later, the patient was diagnosed with a disease relapse, visualized exclusively according to radioisotope research methods. In the fourth year of anticancer treatment, ultrasonography revealed recurring foci along the peritoneum. According to the ultrasound data on the pelvic peritoneum and the projection of the removed right ovary, multiple solid nodes with high blood flow were visualized. Peak systolic velocity ranged from 2 to 9 cm/s in minor lesions from 4 to 12 mm, with an RI max of 0.53. For 4 years, the patient underwent radioiodine therapy with 131I with an activity of 6.0 GBq; the patients condition during the treatment was satisfactory

The concept of violence in the philosophy of Aristotle

The idea that the concept of 'violence' was part and is still viewed as part of a broad philosophical category may seem strange. However, the problem is resolved by referring to the concept of 'force,' which is lost in modern philosophy. The exception was the works in which we find some “traces” of this concept, including the works of Aristotle, which need to be free from modernizing interpretation

An Axi-Symmetric Segmented Composite SKA Dish Design: Performance and Production Analysis

A concept of an axi-symmetric dish as antenna reflector for the next generation radio telescope - the Square Kilometre Array (SKA) - is presented. The reflector is based on the use of novel thermoplastic composite material (reinforced with carbon fibre) in the context of the telescope design with wide band single pixel feeds. The baseline of this design represents an array of 100's to 1000's reflector antennas of 15-m diameter and covers frequencies from <1 to 10 GHz. The purpose of our study is the analysis of the production cost of the dish and its performance in combination with a realistic wideband feed (such as the 'Eleven Antenna' feed) over a wide frequency band and a range of elevation angles. The presented initial simulation results inidicate the potential of the proposed dish concept for low-cost and mass production and demonstrate sensitivity comparable to that of the presently considered off-set Gregorian reflector antenna with the same projected aperture area. We expect this observation to be independent of the choice of the feed, as several other single-pixel wideband feeds (that have been reported in the literature) have similar beamwidth and phase center location, both being rather constant with frequency.Comment: Invited paper for the Asia-Pacific Microwave Conference 2011 (APMC 2011), Melbourne, 5-8 Dec., Australia, 201

Performance of Polarimetric Beamformers for Phased Array Radio Telescopes

Abstract The results of four recently introduced beamforming schemes for phased array systems are discussed, each of which is capable to provide high sensitivity and accurate polarimetric performance of array-based radio telescopes. Ideally, a radio polarimeter should recover the actual polarization state of the celestial source, and thus compensate for unwanted polarization degradation effects which are intrinsic to the instrument. In this paper, we compare the proposed beamforming schemes through an example of a practical phased array system (APERTIF prototype) and demonstrate that the optimal beamformer, the max-SLNR beamformer, the eigenvector beamformer, and the bi-scalar beamformer are sensitivity equivalent but lead to different polarization state solutions, some of which are sub-optimal

Migration Processes Modeling with Cellular Automation

Abstract. The problem of interregional migration flows modeling is being studied. The conjecture that modeling household migration behavior at local level in view of community interactions and using cellular automata results in adequate forecasting of interregional migration flows has been numerically confirmed. A computer program was developed in order to implement the cellular automaton suggested in this study, which models interregional migration flows. Cellular automaton program was tested on Primorsky krai migration flows statistical data; a short-term forecast of the region migration flows was obtained

APERTIF, a focal plane array for the WSRT

In this paper we describe a focal plane array (FPA) prototype, based on Vivaldi elements, developed for the Westerbork Synthesis Radio Telescope (WSRT) to increase its instantaneous field of view by a factor 25 and double its current bandwidth. This prototype is the first step in a project that has the ambition to equip most of the WSRT antennas with FPAs to improve the survey speed of the telescope. Examples of scientific applications are surveys of the northern sky in polarised continuum and HI emission, and efficient searches for pulsars and transients.Comment: 7 pages, 6 figures. Presented at "The Evolution of Galaxies through the Neutral Hydrogen Window", Feb 1-3, 2008, Arecibo Observatory, Puerto Rico. High resolution versions of figures available in jpg-forma