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Search Results: 1 - 10 of 401423 matches for " M. Spacek "
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The Model of the Low Rate Telemetry Communication System for Matlab-Simulink
J. Spacek,M. Kasal
Radioengineering , 2012,
Abstract: This article is dedicated to the model of low rate telemetry system, which has been developed for Matlab-Simulink environment. The purpose of this model is a research of the low rate telemetry transmission reliability in those cases where the modulation scheme carrier-subcarrier is used. This modulation scheme is widely used in case of the interplanetary spacecrafts. The main purpose of the model is a research of the effects of AWGN and phase noise especially for very low value of Eb/N0. Effects can be evaluated for the whole transmission system or for its components parts. The model described is very versatile and it can be easily modified or expanded.
The Low Rate Telemetry Transmission Simulator
J. Spacek,M. Kasal
Radioengineering , 2007,
Abstract: The presented paper is dedicated to the low rate telemetry transmission simulator. The basic concept of the system uses the carrier (DSB) and subcarrier (BPSK). The research is focused on the AWGN and carrier phase noise influence. Presented system can be extended with the described carrier phase noise model. In this paper, some issues related to the described model are also discussed. For example, the relation between bit error rate for uncoded bit stream and bit stream with differential coding, which is used in the model. Authors prove the using of Costas loops for very low energy per bit to noise power spectral density ratio. The influence of additive white Gaussian noise and phase noise is also investigated.
Internal and external dynamics of antihydrogen in electric and magnetic fields of arbitrary orientation
Michal Spacek,Vojtech Petracek
Physics , 2012,
Abstract: We have studied the motion of antihydrogen atoms in electric and magnetic fields of arbitrary orientation. Our aim was to find an exact model of external (centre-of-charge) and internal dynamics which would allow us to describe antihydrogen motion in a realistic way. After analysing the kinematics of the charge exchange reaction producing antihydrogen and of antihydrogen deexcitation, we discuss the dynamics in cases of special fields configurations. Finally, we propose an expression for the force acting on an antihydrogen atom when the field configuration is arbitrary. The general formula -- when reduced in the special field configurations -- matches the results which we obtained independently before. The focus is both on the centre of charge dynamics and on the accurate internal quantum characteristics.
Trichoptera Kirby (Insecta) immature fauna from Rio das Almas Basin and Rio Paran?, Goiás State, Brazil, with new records for some genera
Barbosa, Felipe Francisco;Godoy, Bruno Spacek;Oliveira, Leandro Gon?alves;
Biota Neotropica , 2011, DOI: 10.1590/S1676-06032011000400001
Abstract: this paper deals with the trichoptera immature fauna collected in 101 streams in rio das almas basin during august-october 2008 and in rio paran?, iaciara-go municipality, on august 2003, using kick-nets with 0.025 m2 of opening and 2 mm mesh. we record four new genera for goiás state, expanding records of genera from 33 to 37 and contributing to the trichoptera fauna knowledge in central brazil.
Development and evaluation of a clinical algorithm to monitor patients on antiretrovirals in resource-limited settings using adherence, clinical and CD4 cell count criteria
Meya David,Spacek Lisa A,Tibenderana Hilda,John Laurence
Journal of the International AIDS Society , 2009, DOI: 10.1186/1758-2652-12-3
Abstract: Background Routine viral load monitoring of patients on antiretroviral therapy (ART) is not affordable in most resource-limited settings. Methods A cross-sectional study of 496 Ugandans established on ART was performed at the Infectious Diseases Institute, Kampala, Uganda. Adherence, clinical and laboratory parameters were assessed for their relationship with viral failure by multivariate logistic regression. A clinical algorithm using targeted viral load testing was constructed to identify patients for second-line ART. This algorithm was compared with the World Health Organization (WHO) guidelines, which use clinical and immunological criteria to identify failure in the absence of viral load testing. Results Forty-nine (10%) had a viral load of >400 copies/mL and 39 (8%) had a viral load of >1000 copies/mL. An algorithm combining adherence failure (interruption >2 days) and CD4 failure (30% fall from peak) had a sensitivity of 67% for a viral load of >1000 copies/mL, a specificity of 82%, and identified 22% of patients for viral load testing. Sensitivity of the WHO-based algorithm was 31%, specificity was 87%, and would result in 14% of those with viral suppression (<400 copies/mL) being switched inappropriately to second-line ART. Conclusion Algorithms using adherence, clinical and CD4 criteria may better allocate viral load testing, reduce the number of patients continued on failing ART, and limit the development of resistance.
Mosquitoes (Diptera, Culicidae) inhabiting foliar tanks of Guzmania brasiliensis Ule (Bromeliaceae) in central Amazonia, Brazil
Torreias, Sharlene Roberta da Silva;Ferreira-Keppler, Ruth Leila;Godoy, Bruno Spacek;Hamada, Neusa;
Revista Brasileira de Entomologia , 2010, DOI: 10.1590/S0085-56262010000400013
Abstract: mosquitoes in the family culicidae develop their immature forms in different environments depending on various circumstances. this study represents the first contribution to the ecological knowledge of culicids living in the bromeliad g. brasiliensis. the objectives of the study were to compare the culicidae fauna of bromeliads in two seasonal periods, analyzing their abundance, richness and the influence of ph, conductivity and water volume, on the populations. sampling was done at reserva adolpho ducke, manaus, amazonas, brazil between 2003 and 2005. six samplings were done in the rainy season and six in the dry season. on each sampling day, six terrestrial and six epiphytic bromeliads, totaling 144 sampling units, were retrieved. a total of 444 immature mosquitoes were collected, distributed in the following species: culex (microculex) stonei lane & whitman, culex (microculex) chryselatus dyar & knab, culex (microculex) sp., wyeomyia (hystatomyia) autocratica dyar & knab and wyeomyia (hystatomyia) splendida bonne-wepster & bonne. the relationship between abundance of culicidae and sampling period was not significant, although abundance was higher in the dry period. there were significant correlations between water volume and the abundance (p = 0.003) and richness (p = 0.001) of culicids. the ph was positively related to the occurrence of the species wy. autocratica (p= 0.010) and wy. splendida (p= 0.006), demonstrating the influence of this factor in the structuring of bromeliad-inhabiting communities.
A Catalog of Stellar Evolution Profiles and the Effects of Variable Composition on Habitable Systems
Amanda Truitt,Patrick A. Young,Alexander Spacek,Luke Probst,Jeremy Dietrich
Physics , 2015, DOI: 10.1088/0004-637X/804/2/145
Abstract: We present stellar evolution models for 0.5 - 1.2 \Msol at scaled metallicities of 0.1 - 1.5 Z\sol and O/Fe values of 0.44 - 2.28 O/Fe\sol. The time dependent evolution of habitable zone boundaries are calculated for each stellar evolution track based on stellar mass, effective temperature, and luminosity parameterizations. The rate of change of stellar surface quantities and the surrounding habitable zone position are strong functions of all three quantities explored. The range of orbits that remain continuously habitable, or habitable for at least 2 Gyr, are provided. The results show that the detailed chemical characterization of exoplanet host stars and a consideration of their evolutionary history are necessary to assess the likelihood that a planet found in the instantaneous habitable zone has had sufficient time to develop a biosphere capable of producing detectable biosignatures. This model grid is designed for use by the astrobiology and exoplanet communities to efficiently characterize the time evolution of host stars and their habitable zones for planetary candidates of interest.
Total lymphocyte count of 1200 is not a sensitive predictor of CD4 lymphocyte count among patients with HIV disease in Kampala, Uganda
Moses R Kamya, Fred C Semitala, Thomas C Quinn, Allan Ronald, Denise Nyama-Meya, Harriet Mayanja-Kizza, Elly T Katabira, Lisa A Spacek
African Health Sciences , 2004,
Abstract: Introduction: Total Lymphocyte Count (TLC) has been found to be an inexpensive and useful marker for staging disease, predicting progression to AIDS and death and monitoring response to ART. However, the correlation between TLC and CD4 has not been consistent. Access to HAART is expanding in Kampala, Uganda, yet there are no published data evaluating the utility of TLC as inexpensive surrogate marker of CD4 cell count to help guide therapeutic decisions. Objective: To evaluate clinical illnesses and total lymphocyte count (TLC) as surrogate markers of the CD4 cell count in HIV infected persons being considered for ART. Methods: A total of 131 patients were enrolled and evaluated by clinical assessment, TLC and CD4 count. Clinical illnesses and TLC dichotomized at various cut-point values were used to determine the sensitivity, specificity, and positive and negative predictive values (PPV and NPV) for the diagnosis of CD4 count <200 cells/mm3 among 100 participants fulfilling criteria for WHO clinical stage 2 and 3. Results: A strong correlation was observed between TLC and CD4 (r = 0.73, p<0.0001). For all clinical syndromes, except pulmonary tuberculosis, the positive predictive values (PPV) for a CD4 count <200 cells/mm3 were high (>80%) but the negative predictive values (NPV) were low. Using the WHO recommended TLC cut-off of 1200 cells/mm3 to diagnose a CD4 less than 200 cells/mm3, the PPV was 100%, and the NPV was 32%. Conclusion: Our data showed a good correlation between TLC and CD4 cell count. However, the WHO recommended TLC cut-off of 1200 did not identify the majority of WHO stage 2 and 3 patients with CD4 counts less than 200 cells/mm3. A more rational use of TLC counts is to treat all patients with WHO stage 2 and 3 who have a TLC <1200 and to limit CD4 counts to patients who are symptomatic but have TLC of >1200. Key Words: CD4 cell count, total lymphocyte count, clinical algorithm, antiretroviral therapy, resource limited settings African Health Sciences Vol.4(2) 2004: 94-101
Prospects for measuring the gravitational free-fall of antihydrogen with emulsion detectors
AEgIS Collaboration,S. Aghion,O. Ahlén,C. Amsler,A. Ariga,T. Ariga,A. S. Belov,G. Bonomi,P. Br?unig,J. Bremer,R. S. Brusa,L. Cabaret,C. Canali,R. Caravita,F. Castelli,G. Cerchiari,S. Cialdi,D. Comparat,G. Consolati,J. H. Derking,S. Di Domizio,L. Di Noto,M. Doser,A. Dudarev,A. Ereditato,R. Ferragut,A. Fontana,P. Genova,M. Giammarchi,A. Gligorova,S. N. Gninenko,S. Haider,J. Harasimovicz,S. D. Hogan,T. Huse,E. Jordan,L. V. J?rgensen,T. Kaltenbacher,J. Kawada,A. Kellerbauer,M. Kimura,A. Knecht,D. Krasnicky,V. Lagomarsino,A. Magnani,S. Mariazzi,V. A. Matveev,F. Moia,G. Nebbia,P. Nédélec,M. K. Oberthaler,N. Pacifico,V. Petrácek,C. Pistillo,F. Prelz,M. Prevedelli,C. Regenfus,C. Riccardi,O. R?hne,A. Rotondi,H. Sandaker,P. Scampoli,A. Sosa,J. Storey,M. A. Subieta Vasquez,M. Spacek,G. Testera,D. Trezzi,R. Vaccarone,C. P. Welsch,S. Zavatarelli
Physics , 2013, DOI: 10.1088/1748-0221/8/08/P08013
Abstract: The main goal of the AEgIS experiment at CERN is to test the weak equivalence principle for antimatter. AEgIS will measure the free-fall of an antihydrogen beam traversing a moir\'e deflectometer. The goal is to determine the gravitational acceleration g for antihydrogen with an initial relative accuracy of 1% by using an emulsion detector combined with a silicon micro-strip detector to measure the time of flight. Nuclear emulsions can measure the annihilation vertex of antihydrogen atoms with a precision of about 1 - 2 microns r.m.s. We present here results for emulsion detectors operated in vacuum using low energy antiprotons from the CERN antiproton decelerator. We compare with Monte Carlo simulations, and discuss the impact on the AEgIS project.
Study of Duct Characteristics Deduced from Low Latitude Ground Observations of Day-Time Whistler at Jammu  [PDF]
M. Altaf, M. M. Ahmad
International Journal of Astronomy and Astrophysics (IJAA) , 2013, DOI: 10.4236/ijaa.2013.33032
Abstract:

Propagation characteristics of low latitude whistler duct characteristics have been investigated based on day-time measurements at Jammu. The morphogical characteristics of low latitude whistlers are discussed and compared with characteristics of middle and high latitude whistlers. The Max. electron density (Nm) at the height of the ionosphere obtained from whistler dispersion comes out to be higher than that of the background which is in accordance with the characteristics of whistler duct. The equivalent width is found to be close to the satellite observations and the characteristics of whistler duct in low latitude ionosphere are similar to those in middle and high latitude ionosphere. The width of ducts estimated from the diffuseness of the whistler track observed during magnetic storm is found to lie in the range of 50 - 200 Km.

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