A New Multiple Access Technique For Use With Satellite Networks

The Multiple Access Discrete Address System described is particularly applicable to future digital modulation systems. A high degree of efficiency is achieved using methods which provide the advantages of time division without the critical dependence on precise timing characteristic of more conventional techniques. A performance comparison with current fm/fdm is provided. In communicating through a satellite repeater, a modulation technique must be selected to serve two separate functions. The first is the address function which must permit the receiver to separate the desired signal from other transmis-- sions simultaneously using a given repeater. The second function is to transfer a message between two users. This presentation relates to the first function and describes a Multiple Access Discrete Address System that has unique features, particularly applicable to future digital communications networks . In a sense, a satellite communications link is nothing more than a microwave circuit with an unattended repeater. One of the prime differences, however, is that due to the high cost of the satellite a number of circuits must use the same repeating amplifier. It is also a characteristic that the satellite is severely power limited. This power limitation at the present time is not a technological limit, but results from the sharing of frequency band with ground-based systems and international agreements covering satellite radiated power. The multiple users combined with the power limit places constraints on the system and is the fundamental reason for the presence of a multiple access problem. It may also be observed that in any communications network it is necessary for the receiver to be able to select a particular transmission of interest from the multiple signals that it has access to; hence, the requirement for discrete addressing

The Relationship Between Teacher Perceptions Of Professional Learning Communities And Student Achievement

A significant challenge facing public schools is the need to increase student achievement while having student gains enhanced through growth models. Teaching strategies/methods have evolved over the years from an island approach where the teacher was alone in his/her classroom and responsible for students progressing to a broader yet more specific approach to teacher professional development in order to enhance student learning. Districts, schools, and individual teachers have long valued professional development and professional learning. These educational professional learning opportunities collectively give the district, school, and individual teachers a community at work in which a collective focus and commitment to improving practice has long been understood to assist students increase their academic achievement (DuFour, DuFour, & Eaker, 2008). DuFour, DuFour, Eaker, & Many (2010) argue one of the key components of a professional learning community is a results-oriented focus which is characterized by the outcome rather than the strategies to get there. Too often, education professionals focus on the process and activities of what teachers do rather than the evidence of their students\u27 outcomes based on teaching and learning. Hord (2004) furthers the point by arguing that Professional Learning Communities (PLCs) show improvement of student achievement results through such communities in schools. In Madison County Schools, Madison County, KY, there are multiple opportunities for teachers to develop professionally as individuals, team members, schools, and collectively as a district. These professional learning opportunities are well planned and documented in professional growth plans, comprehensive school improvement plans, and district improvement plans in order to fulfill requirements such as local Certified Evaluation Plans (CEP) and The Kentucky Framework for Teaching (Danielson 2012). All Madison County Schools, specifically the five middle schools, use Professional Learning Communities (PLCs) to further develop and enhance teaching with the overarching purpose of supporting greater student achievement. This study utilized the five Madison County middle schools\u27 and district-level data to assess the relationship between teacher perception of Professional Learning Communities and how well students achieve at each specific schools and district-wide. The characteristics evaluated included teachers\u27 perception of professional learning through PLCs along with actual student data specific to the teacher. Prior research focused primarily on individual predictors of variance on student achievement, while this study combines all of the predictors for observation on predictors of variance

Use of alkoxides in the preparation of low-expansion reconstructed TiO2-SiO2 glasses

Reconstructed TiO2-SiO2 glasses were prepared by impregnating porous glass with solutions containing titanium tetraisopropoxide Ti(OC3H7)4, converting the alkoxide in the pores to titania, and consolidating the porous structure. The final glasses contained from about 6 to 11 wt% TiO2. On subjecting them to treatments in an oxy/gas flame (term for pure oxygen combustion) or a high-temperature furnace it was possible to obtain clear glasses with thermal expansion coefficients ranging from -0.2 to +0.3 · 10^-6/K. Reconstructed glasses containing about 7 wt% TiO2 were thermally stable, showing no significant change in expansion after 10 h heating in air at 970 °C. However, glasses with higher TiO2 contents were not thermally stable when reheated. X-ray analyses revealed that they contained rutile, a high-expansion phase that readily accounts for the increase in expansion observed after reheating. Water permeation studies of alkoxide-impregnated porous glass showed that the rate of penetration of water, and hence the rate of hydrolysis of the alkoxide, is diffusion-controlled. Reactions that are likely to occur in the impregnated porous glass on hydrolysis and on heating are discussed

Dehydroxylation and nitriding of porous glass by means of water-soluble nitrogen-containing organic compounds

Hydroxyl groups in reconstructed 96 % SiO2 glass are effectively removed by impregnating porous glass in an aqueous solution containing organic compounds that are thermally decomposable to produce reactive gaseous nitrogen species prior to consolidation of the porous structure in a nonoxidizing atmosphere. Infrared measurements show that glasses that have been impregnated in the porous state with urea, guanidine hydrochloride, or guanidine carbonate have essentially zero water content and furthermore contain nitrogen at sites normally occupied by oxygen atoms. Amide groups are absent in final glasses that have been prepared from porous glass containing high concentrations of guanidine hydrochloride, suggesting removal of hydrogen from such groups by interaction with chloride ions at elevated temperatures. The annealing points of such final glasses are markedly higher than those of untreated glasses

Chlorine treatment of nitrided porous glass

Nitrided reconstructed 96 % SiO2 glasses prepared from ammonia-treated porous glass have a tendeney to reboil on heating to the high temperatures required for lampworking. This problem can be eliminated by subjecting the nitrided porous glass to chlorine at elevated temperatures prior to pore closure. Infrared measurements of the final glasses show that =NH groups are absent in the chlorine-treated glasses. Possible reactions that account for the removal of hydrogens from amide groups are presented. The role of subjecting the nitrided porous glass to a hot acid wash is also discussed

Chemical and physical characterization of porous materials prepared by leaching glasses in the system Na2O-Al2O3-B2O3-F

The leachability of glasses in the system Na2O-Al2O3-B2O3-F with Al2O3 contents of about 50 wt% was investigated. It was found necessary to heat-treat the glasses at temperatures that assure not only phase separation but also formation of microcrystalline phases to prevent crumbling, swelling, and excessive restructuring of the glasses on leaching in hot dilute acetic acid solutions or hot distilled water. Chemical analysis showed that the leached glasses contain up to 96 wt% Al2O3 , based on ignited weight. Leaching rate studies show that the removal of the nonaluminous constituents by the hot leachant is diffusion-controlled. The surface areas and pore sizes of the alumina-rich porous skeleton that results on leaching are from ≈ 80 to ≈ 250 m2/g and from ≈ 6 to ≈ 15 nm, depending on heat treatment and leaching conditions. Visual examination and x-ray diffraction studies show that the heat treatment of the base glass induces phase separation and leads to the formation of crystalline phases such as Na3AlF6 and Na2Al2B2O7. The increases in density and thermal expansion of the base glasses with fluoride content on subsequent heat treatment are chiefly due to the formation of such crystalline phases

Recent Light Satellite Missions and Accomplishments in the DOD Space Test Program

Over the past 27 years, the US Air Force, as executive agent for the Department of Defense (DOD) Space Test Program, has flown approximately 325 space experiments for the Army, Navy, Air Force, and other DOD agencies not authorized their own means of spaceflight. These experiments have made significant contributions to the improvement of military technology and operations. This paper will include a brief review of the program overall status, various experiment capabilities being tested and the use of these experiment results in military activities. The paper\u27s major theme will concentrate on three specific lightsat spacecraft from the broad range of test vehicles used by the Space Test program. These lightsats are currently undergoing testing or are actively manifested for spaceflight. The discussion of each host lightsat and its accompanying experiment will include experiment objective, lightsat design criteria, and status/results to date. Lightsats addressed include: 1) Space Test Experiments Platform (STEP). This standard STP lightsat bus has successfully carried its initial experiment, a Technology for Autonomous Operational Survivability (TAOS) payload and is programmed to perform three additional missions; Mission 1 (P90-1) which will carry four experiments, Mission 2 (P91-2) which will carry the Signal Identification Experiment (SIDEX), and Mission 3 (P92-2) which will carry five experiments. 2) Radar Calibration Satellite (RADCAL). Flying in a polar circular orbit it will primarily serve to calibrate over 50 worldwide C-Band radars used in launch and tracking missions. In addition, it will host three secondary experiments. 3) Advanced Photovoltaic and Electronic Experiment (APEX). This Pegasus-launched lightsat is hosting three experiments addressing: space power diagnostics, cosmic ray upset, and thin film ferroelectrics. The paper will conclude with a brief discussion of planned future light sat hosted experiment

Thermal dehydroxylation of porous glass

The thermal removal of hydroxyl groups from porous glass tubing depends on both temperature and time. The general relationship between these two parameters and the residual hydroxyl content in 96 % SiO2 (by weight) reconstructed glass was determined by subjecting porous glass tubes to various temperatures in vacuum and in dry air. The temperature for maximum removal of water decreases as the hold time increases. The optimum temperatures result from a balance in rates of water diffusion and glass sintering which retards diffusion. Increasing the total pressure of the atmosphere surrounding the porous glass during the degassing cycle decreases the net degassing rate. The role of other factors such as composition of the porous glass and pore structure are briefly mentioned