289 research outputs found
Television broadcast from space systems: Technology, costs
Broadcast satellite systems are described. The technologies which are unique to both high power broadcast satellites and small TV receive-only earth terminals are also described. A cost assessment of both space and earth segments is included and appendices present both a computer model for satellite cost and the pertinent reported experience with the Japanese BSE
Study of efficient transmission and reception of image-type data using millimeter waves
Evaluation of signal processing and modulation techniques for transmission and reception of image type data via millimeter wave relay satellite
Concepts for 18/30 GHz satellite communication system study. Executive summary
An examination of a multiplicity of interconnected parameters ranging from specific technology details to total system economic costs for satellite communication systems at the 18/30 GHz transmission bands are presented. It was determined that K sub A band systems can incur a small communications outage during very heavy rainfall periods and that reducing the outage to zero would lead to prohibitive system costs. On the other hand, the economics of scale, ie, one spacecraft accommodating 2.5 GHz of bandwidth coupled with multiple beam frequency reuse, leads to very low costs for those users who can tolerate the 5 to 50 hours per year of downtime. A multiple frequency band satellite network can provide the ultimate optimized match to the consumer performance/economics demands
Concepts for 18/30 GHz satellite communication system, volume 1
Concepts for 18/30 GHz satellite communication systems are presented. Major terminal trunking as well as direct-to-user configurations were evaluated. Critical technologies in support of millimeter wave satellite communications were determined
Concepts for 18/30 GHz satellite communication system, volume 1A: Appendix
The following are appended: (1) Propagation phenomena and attenuation models; (2) Models and measurements of rainfall patterns in the U.S.; (3) Millimeter wave propagation experiments; (4) Comparison of the theory and Millimeter wave propagation experiments; (4) Comparison of theory and experiment; (5) A practical rain attenuation model for CONUS; (6) Space diversity; (7) Values of attenuation for selected U.S. cities; and (8) Additional considerations
Long-term treatment with deferiprone enhances left ventricular ejection function when compared to deferoxamine in patients with thalassemia major
Transfusion and iron chelation treatment have significantly reduced morbidity and improved survival of patients with thalassemia major. However, cardiac disease continues to be the most common cause of death.
We report the left-ventricular ejection fraction, determined by echocardiography, in one hundred sixtyeight
patients with thalassemia major followed for at least 5 years who received continuous monotherapy with
deferoxamine (N = 108) or deferiprone (N = 60). The statistical analysis, using the generalized estimating
equations model, indicated that the group treated with deferiprone had a significantly better left-ventricular
ejection fraction than did those treated with deferoxamine (coefficient 0.97; 95% CI 0.37; 1.6, p = 0.002).
The heart may be particularly sensitive to iron-induced mitochondrial damage because of the large number of
mitochondria and its low level of antioxidants. Deferiprone, because of its lower molecular weight, might cross
into heart mitochondria more efficiently, improving their activity and, thereby, myocardial cell function.
Our findings indicate that the long-term administration of deferiprone significantly enhances left-ventricular
function over time in comparison with deferoxamine treatment. However, because of limitations related to
the design of this study, these findings should be confirmed in a prospective, randomized clinical trial
Serial echocardiographic left ventricular ejection fraction measurements: a tool for detecting thalassemia major patients at risk of cardiac death
Cardiac damage remains a major cause of mortality among patients with thalassemia major. The detection of a
lower cardiac magnetic resonance T2* (CMR-T2*) signal has been suggested as a powerful predictor of the subsequent development of heart failure. However, the lack of worldwide availability of CMR-T2* facilities prevents its
widespread use for follow-up evaluations of cardiac function in thalassemia major patients, warranting the need
to assess the utility of other possible procedures.In this setting,the determination of left ventricular ejection fraction
(LVEF)offers an accurate and reproducible method for heart function evaluation. These findings suggest a reduction
in LVEF≥7%, over time, determined by 2-D echocardiography, may be considered a strong predictive tool for the
detection of thalassemia major patients with increased risk of cardiac death. The reduction of LVEF≥7% had higher
(84.76%) predictive value. Finally, Kaplan–Meier survival curves of thalassemia major patients with LVEF≥7%
showed a statistically significant decreased probability of survival for heart disease (p=0.0022).
However, because of limitations related to the study design, such findings should be confirmed in a large
long-term prospective clinical trial
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