10,462 research outputs found
Tracking and Data Relay Satellite System (TDRSS)
The DSN (Deep Space Network) mission support requirements for the Tracking and Data Relay Satellite System (TDRSS) are summarized. The TDRSS consists of four identical satellites in geosynchronous orbits (35,800 km) and a dedicated ground station. The payload of each satellite is a telecommunications service system that relays communication signals between low earth-orbiting user spacecraft and the TDRSS ground terminal. Mission objectives are outlined and the DSN support requirements are defined through the presentation of tables and narratives describing the spacecraft flight profile; DSN support coverage; frequency assignments; support parameters for telemetry, command and support systems; and tracking support responsibility
Sensitivity of the photo-physical properties of organometallic complexes to small chemical changes
We investigate an effective model Hamiltonian for organometallic complexes
that are widely used in optoelectronic devices. The two most important
parameters in the model are , the effective exchange interaction between the
and orbitals of the ligands, and , the renormalized
energy gap between the highest occupied orbitals on the metal and on the
ligand. We find that the degree of metal-to-ligand charge transfer (MLCT)
character of the lowest triplet state is strongly dependent on the ratio
. is purely a property of the complex and can be
changed significantly by even small variations in the complex's chemistry, such
as replacing substituents on the ligands. We find that that small changes in
can cause large changes in the properties of the complex,
including the lifetime of the triplet state and the probability of injected
charges (electrons and holes) forming triplet excitations. These results give
some insight into the observed large changes in the photophysical properties of
organometallic complexes caused by small changes in the ligands.Comment: Accepted for publication in J. Chem. Phys. 14 pages, 9 figures,
Supplementary Info: 15 pages, 17 figure
Propagation properties of Rossby waves for latitudinal β-plane variations of <I>f</I> and zonal variations of the shallow water speed
Using the shallow water equations for a rotating layer of fluid, the wave and dispersion equations for Rossby waves
are developed for the cases of both the standard β-plane approximation for the latitudinal variation of the
Coriolis parameter <I>f</I> and a zonal variation of the shallow water speed. It is well known that the wave normal diagram for the
standard (mid-latitude) Rossby wave on a β-plane is a circle in wave number (<I>k</I><sub>y</sub>,<I>k</I><sub>x</sub>) space, whose
centre is displaced −β/2 ω units along the negative <I>k</I><sub>x</sub> axis, and whose radius is less than this displacement, which means that phase
propagation is entirely westward. This form of anisotropy (arising from the
latitudinal <I>y</I> variation of <I>f</I>), combined with the highly dispersive nature of the wave, gives rise to a group
velocity diagram which permits eastward as well as westward propagation. It is shown that the group velocity
diagram is an ellipse, whose centre is displaced westward, and whose major and minor axes give the
maximum westward, eastward and northward (southward) group speeds as functions of the frequency and a parameter
<I>m</I> which measures the ratio of the low frequency-long wavelength Rossby wave speed to the shallow water speed. We
believe these properties of group velocity diagram have not been elucidated in this way before. We present a
similar derivation of the wave normal diagram and its associated group velocity curve for the case of a zonal
(<I>x</I>) variation of the shallow water speed, which may arise when the depth of an ocean varies zonally from a
continental shelf
Use of thermal infrared and colour infrared imagery to detect crop moisture stress
The author has identified the following significant results. In the presence of variable plant cover (primarily percent cover) and variable available water content, the remotely sensed apparent temperatures correlate closely with plant cover and poorly with soil water. To the extent that plant cover is not systematically related to available soil water, available water in the root zone values may not be reliably predicted from the thermal infrared data. On the other hand, if plant cover is uniform and the soil surface is shown in a minor way, the thermal data indicate plant stress and consequently available water in the soil profile
Studies of auroral X-ray imaging from high altitude spacecraft
Results of a study of techniques for imaging the aurora from a high altitude satellite at X-ray wavelengths are summarized. The X-ray observations allow the straightforward derivation of the primary auroral X-ray spectrum and can be made at all local times, day and night. Five candidate imaging systems are identified: X-ray telescope, multiple pinhole camera, coded aperture, rastered collimator, and imaging collimator. Examples of each are specified, subject to common weight and size limits which allow them to be intercompared. The imaging ability of each system is tested using a wide variety of sample spectra which are based on previous satellite observations. The study shows that the pinhole camera and coded aperture are both good auroral imaging systems. The two collimated detectors are significantly less sensitive. The X-ray telescope provides better image quality than the other systems in almost all cases, but a limitation to energies below about 4 keV prevents this system from providing the spectra data essential to deriving electron spectra, energy input to the atmosphere, and atmospheric densities and conductivities. The orbit selection requires a tradeoff between spatial resolution and duty cycle
To boldly gulp: standard metabolic rate and boldness have context-dependent influences on risk-taking to breathe air in a catfish
The African sharptooth catfish Clarias gariepinus has bimodal respiration, it has a suprabranchial air-breathing organ alongside substantial gills. We used automated bimodal respirometry to reveal that undisturbed juvenile catfish (N=29) breathed air continuously in normoxia, with a marked diurnal cycle. Air breathing and routine metabolic rate (RMR) increased in darkness when, in the wild, this nocturnal predator forages. Aquatic hypoxia (20% air saturation) greatly increased overall reliance on air breathing. We investigated whether two measures of risk taking to breathe air, namely absolute rates of aerial O2 uptake (ṀO2,air) and the percentage of RMR obtained from air (%ṀO2,air), were influenced by individual standard metabolic rate (SMR) and boldness. In particular, whether any influence varied with resource availability (normoxia versus hypoxia) or relative fear of predation (day versus night). Individual SMR, derived from respirometry, had an overall positive influence on ṀO2,air across all contexts but a positive influence on %ṀO2,air only in hypoxia. Thus, a pervasive effect of SMR on air breathing became most acute in hypoxia, when individuals with higher O2 demand took proportionally more risks. Boldness was estimated as time required to resume air breathing after a fearful stimulus in daylight normoxia (Tres). Although Tres had no overall influence on ṀO2,air or %ṀO2,air, there was a negative relationship between Tres and %ṀO2,air in daylight, in normoxia and hypoxia. There were two Tres response groups, ‘bold’ phenotypes with Tres below 75 min (N=13) which, in daylight, breathed proportionally more air than ‘shy’ phenotypes with Tres above 115 min (N=16). Therefore, individual boldness influenced air breathing when fear of predation was high. Thus, individual energy demand and personality did not have parallel influences on the emergent tendency to take risks to obtain a resource; their influences varied in strength with context
Trying to Help without getting in their Faces: Public Library Staff Descriptions of Providing Consumer Health Information
Several recent studies have analyzed users\u27 descriptions of the reference transaction, but little research has analyzed library staff members\u27 accounts of reference encounters. This article builds on the work of Marie Radford and the authors of the library visit studies by examining library staff members\u27 descriptions of providing consumer health reference services. WE conclude that an in-depth study of staff members\u27 accounts can provide insight into the different ways that library staff members and users construct problems in the reference encounter and can therefore suggest potential solutions
Benchmarking leakage from water reticulation systems in South Africa
A project to assess the levels of leakage in 30 water utilities throughout South Africa was initiated by the Water Research Commission. The BENCHLEAK software was used to evaluate the water utilities and performance indicators calculated by the model were used to compare levels of non-revenue water. Results showed that utilities ranked differently according to the different indicators, and that the South African results are similar to world norms. Feed back from the water utilities showed that some of the data requested were confusing and required clarity. The number of service connections, apparent losses and length of pipe between the street edge and the meter were looked at in more detail.
Standard drawings were developed to assist water utilities in determining their number of service connections. A table is presented to assess the apparent losses of each water utility in a more pragmatic way. Water SA Vol. 30 (5) 2005: pp.25-3
‘Handle with care’: literature, archaeology, slavery
This article examines the relationship between literary and bioarchaeological approaches to slavery, and investigates how the methods and priorities of each discipline might inform each other in understanding what it was like to be enslaved. Both bioarchaeologists and creative writers have attempted to access the inner lives of enslaved people, yet there has been little interaction between these disciplines. This paper offers an account of an interdisciplinary research project which brought together a literary scholar, two archaeological scientists and seven creative writers to explore how writing might not only communicate a history primarily understood through archaeological evidence, but could itself inform approaches to that evidence. We discuss two key themes which emerged from the project as ways of opening up, rather than claiming, the past: Conversation and Caring. These are themes which were also crucial to the success of the interdisciplinary process, as it was only through attention to our relationships with each other that we were ultimately able to begin to reassess the nature of material in each of our disciplines.AHR
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