497 research outputs found
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
A System Performance Based Comparison of Sparse Regular and Irregular Antenna Arrays for Millimeter-Wave Multi-User MIMO Base Stations
A system-level study was conducted that evaluated the system performance of various dense and sparse antenna array configurations for application in millimeter-wave multi-user multiple-input multiple-output base stations. The performance was evaluated by investigating the probability that a user experiences an outage when a zero-forcing pre-coder is used in a random line of sight scenario. This paper shows that the outage probability significantly decreased when irregular sparse arrays were used rather than regular sparse or regular dense arrays. A re-configurable linear array was designed and realized as a demonstrator. It used 3D-printed aluminum box horn antenna elements that had wide scanning range in the azimuthal plane and a small scanning range in the elevation plane. For the demonstrator, it was shown that the outage probability was reduced from 3.85% to 0.64% by moving from a sparse regularly spaced array to a sparse randomly spaced array. This amounted to an improvement of a factor of six. The sparse topology allowed for the usage of large antenna elements that had an increased gain and still achieved wide-angle scanning, while reducing mutual coupling to a minimu
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
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