280 research outputs found
High Efficiency Transmitter Architecture for Nano-satellites
No full textThe fast growing interest in nano-satellite development and the use of nano-satellite for complex missions has led to an increase in the downlink data-rate. The availability of free bands (amateur frequency bands: VHF and UHF) is getting limited and more challenging to do the frequency coordination. This can be attributed to the surge in number of nano-satellite being launched. There has been 430% increase in the number of satellites launched in 2013 compared to 2012. This trend has led the nano-satellite developers to start looking into higher frequency bands and S-band has been a popular choice. But, going by the trend, frequency coordination in the S-band can also get challenging. Thus, there is a need to develop a nano-satellite transmitter that uses spectrally efficient modulation scheme, at the same time it has to be power efficient and be compatible with some of the existing communication standards. This work deals with developing the requirements on a nano-satellite transmitter based on mission case study, look at the need for efficiency and linearity enhancement technique for the transmitter, select the most appropriate architecture for nano-satellite application and show a proof of concept using a prototype. Using system engineering approach the efficiency and linearity enhancement technique that was chosen was LINC architecture. ADS simulations were performed to understand different configurations of LINC and finally, measurements were performed on the chosen configuration to characterize its efficiency and linearity. 16-QAM, 16-APSK, 32-QAM, 32-APSK and 64-QAM modulation schemes were implemented and tested. The best EVM was obtained for 16-APSK with 20 degrees compensation stub in the Chireix combiner which was 0.27% and the best efficiency was obtained for 16-APSK modulation scheme which was implemented without any compensation stubs. Based on the lessons learnt during simulations and measurements, recommendations are provided to improve the LINC configuration and improve the reliability of the measurement setup.ElectronicsMicroelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
A characterization of t/s-diagnosability and sequential t-diagnosability in designs
Get PDFThis publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. As such, it is in the public domain, and under the provisions of Title 17, United States Code, Section 105, may not be copyrighted.IEEE Transactions on Computers, C-39, October 1990, pp. 1298-1304A multiprocessing system is t/s diagnosable if all faulty processors can be identified to within s processors provided there are no more than t faculty processors. A characterization theorem of Karunanithi and Medman for t/s diagnosability in certain special cases of systems called designs is extended to the entire class of D designs. We show that for large...
Imaging of Calcium in <i>Drosophila</i> Larval Motor Nerve Terminals
No full text Karunanithi, Shanker, John Georgiou, Milton P. Charlton, and Harold L. Atwood. Imaging of calcium in Drosophila larval motor nerve terminals. J. Neurophysiol. 78: 3465–3467, 1997. Calcium measurements in the presynaptic terminal are essential in the investigation of mechanisms underlying neurotransmitter release. To enhance the genetic analysis of secretory mechanisms, we have developed Ca2+ imaging techniques for Drosophila larval motor nerve terminals. We studied Ca2+ signals in “big” (type Ib) and “small” (type Is) boutons that innervate ventral longitudinal muscles 6 and 7 in each abdominal segment of Canton-S (CS)-strain 3rd instar larvae. The indicator fluo-3 in conjunction with confocal microscopy was used to detect stimulus-dependent changes in [Ca2+]i. The Ca2+ signals were reliable and reproducible, and the resting fluorescence remained constant throughout the experiments. The Ca2+ signals increased with stimulus frequency from 5 to 20 Hz for both bouton types. No significant differences in the Ca2+ signals were seen between the two bouton types at 5 and 20 Hz, but there was a difference at 10 Hz. The decay of the Ca2+ signal was more prolonged after 20-Hz stimulation than after 5 and 10 Hz. At the single-synapse level, the secretory efficacy of Is synapses is greater than that of Ib synapses, but our data show that factors other than differences in Ca2+ entry may govern the strength of synaptic transmission. </jats:p
Assessment of bone mineral density by DXA and the trabecular microarchitecture of the calcaneum by texture analysis in pre- and postmenopausal women in the evaluation of osteoporosis
No full textThe in vivo evaluation of trabecular bone structure could be useful in the diagnosis of osteoporosis for the characterization of therapeutic response and understanding the role of parameters other than bone mineral density (BMD) in defining skeletal status. This study was made to evaluate changes taking place in the trabecular architecture of bone with age and menopausal status in women. The findings are compared with the femoral neck bone as well as the trochantar bone mineral density determined by dual energy X-ray absorptiometry (DXA), which is a standard reference test for evaluation of osteoporosis. Seventy females were recruited for the study, 25 pre-menopausal (mean age ± SD: 39.4 ± 3.8) and 45 postmenopausal (mean age ± SD: 57.9 ± 7.9) women. The right femoral neck bone mineral density was measured for them by dual energy X-ray absorptiometry (DXA). For the same individuals, lateral view radiographs of the right calcaneum were taken as well. The radiographs were digitized and the region of interest (ROI) of 256 x 256 pixels was selected, the run-length matrix was computed for calculating seven parameters [Table 1] and the two-dimensional fast Fourier transform of the image was calculated. Using the FFT, the power spectral density (PSD) was derived and the root mean square (RMS) value was determined. Our results confirm that age has a significant influence on the texture of the trabecular bone and bone mineral density
HERMES Radio: Energy and Spectral Efficient Transmitter architectures for small satellites
No full textAs the complexity of nanosatellite missions have increased over time, the data generated on-board nanosatellites have increased multiple folds. As a result, there is a need to downlink large amounts of data. Multiple nanosatellite missions have started using spectral efficient modulation schemes recommended in DVB.S2 and DVB.S2X to make the best use of the available spectrum. One of the main challenges in adopting higher order modulation schemes is to power-efficiently upconvert and amplify the baseband signals. All the lost efficiency in converting the DC power to the RF output is dissipated as heat and the relatively small thermal mass of nanosatellites poses thermal management challenges. As a first step to addressing the challenge of improving the power efficiency of the communication module, optimization techniques to improve the Peak to Average Power Ratio (PAPR) of the modulation schemes (16/32-APSK) are discussed in this paper. The PAPR of 16-APSK reduces by ~2 dB by incorporating filtering techniques discussed in this paper. Further, a well-known efficiency and linearity enhancement technique; Out-phasing/LINC (Linear Amplification using Non-linear Components) is discussed. As a variant of the out-phasing architecture, a novel approach is proposed using two circularly polarized antenna to transmit the constant envelope signals in opposite polarizations and signal combining is performed at the receiver. Simulations results are used to demonstrate how higher efficiencies can be achieved using the proposed architecture.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic
A Framework for Designing and Testing the Digital Signal Processing unit of a Pulsar Based Navigation System
No full textNavigation systems using pulsar signals have been of great interest ever since the discovery of pulsars in 1967 and various studies were carried out ever since to determine the feasibility of such systems. The successful working of a navigation system using pulsar would mean that spacecraft can maneuver through the deep space with very little help from earth. Another notable aspect of this navigation mechanism is that pulsar signals are available throughout the cosmos, so this sys- tem could be used for a wide range of orbital configurations such as Low Earth Orbits (LEO), Medium Earth Orbit (MEO), Geosta- tionary Orbits (GEO) and Interplanetary orbits enabling a universal navigation system. In this thesis, a software framework has been developed to replicate the environmental setup for a pulsar navigation system. This frame- work can be used to design a high level system design of the pulsar signal processing unit which will be a part of the navigation system. The framework can be used to generate pulsar templates as it can process the raw data from a receiver. The generated templates will be used in the final navigation system in the stages of correlation and detection. The software framework was developed using a very novel system design approach using SystemC-AMS, which consists of C++ classes that felicitate high level system design involving analog and mixed signals. The design approach, implementation, results and limitations of this framework is also presented. Based on the conclusions derived from the framework, a road-map is provided for future development.Embedded SystemsMicroelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Examining an Australian physical activity and nutrition intervention using RE-AIM
No full textTranslating evidence-based interventions into community practice is vital to health promotion. This study used the RE-AIM framework to evaluate the larger dissemination of the ManUp intervention, an intervention which utilized interactiveweb-based technologies to improve the physical activity and nutrition behaviors of residents in Central Queensland, Australia. Data were collected for each RE-AIM measure (Reach, Effectiveness, Adoption, Implementation, Maintenance) using (i) computer-assisted telephone interview survey (N = 312) with adults (18 years and over) from Central Queensland, (ii) interviews with key stakeholders from local organizations (n = 12) and (iii) examination of project-related statistics and findings. In terms of Reach, 47% of participants were aware of the intervention; Effectiveness, there were no significant differences between physical activity and healthy nutrition levels in those aware and unaware; Adoption, 73 participants registered for the intervention and 25% of organizations adopted some part of the intervention; Implementation, 26% of participants initially logged onto the website, 29 and 17% started the web-based physical activity and nutrition challenges, 33% of organizations implemented the intervention, 42% considered implementation and 25% reported difficulties; Maintenance, an average of 0.57 logins and 1.35 entries per week during the 12 week dissemination and 0.27 logins and 0.63 entries per week during the 9-month follow-up were achieved, 22 and 0% of participants completed the web-based physical activity and nutrition challenges and 33.3% of organizations intended to continue utilizing components of the intervention. While this intervention demonstrated good reach, effectiveness, adoption and implementation warrant further investigation.Cristina M. Caperchione, Mitch Duncan, Gregory S. Kolt, Corneel Vandelanotte, Richard R. Rosenkranz, Anthony Maeder, Manny Noakes, Mohan Karunanithi and W. Kerry Mummer
A STUDY ON NON-LINEAR SINGULAR SYSTEMS FROM FLUID DYNAMICS USING LEAPFROG METHOD
No full text<p>This paper deals with the non- Linear singular system from fluid dynamics. The results (approximate solutions) obtained using single-term Haar wavelet series and Leapfrog methods are compared with the exact solutions of the non-Linear singular system from fluid dynamics. It is found that the solution obtained using Leapfrog method is closer to the original solution of the non-Linear singular system from fluid dynamics. The high accuracy and the wide applicability of Leapfrog method approach will be demonstrated with numerical examples.</p>
Regularity of solutions of Sobolev type semilinear integrodifferential equations in Banach spaces
No full textIn this article, we prove the existence of mild and classical solutions of Sobolev type semilinear integrodifferential equations of the form
d/dt [Ex(t) = A[x(t) + ∫t0 F(t - s)x(s)ds] + ƒ(t, x(t))
in Banach spaces. The results are obtained by using the Banach contraction mapping principle and resolvent operator. An application is provided to illustrate the theory.Mathematic
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