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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Inlet total pressure loss due to acoustic wall treatment

Experimental determination of the effect of diffuser wall acoustic treatment on inlet total pressure loss. Data were obtained by testing an inlet model with 10 different acoustically treated diffusers differing only in the design of the Helmholtz resonator acoustic treatment. Tests were conducted in a wind tunnel at forward velocities to 41 meters per second for inlet throat Mach numbers of .5 to .8 and angles of attack as high as 50 degrees. Results indicate a pressure loss penalty due to acoustic treatment that increases linearly with the porosity of the acoustic facing sheet. For a surface porosity of 14% the total pressure loss was 21% greater than that for an untreated inlet. The penalty resulting from treatment increased for average throat Mach numbers above approximately .7 where local regions of sonic or supersonic surface flow were encountered. Pressure loss over the treatment was not affected by the presence of noise.

Miller, B. A.↗
NASA NTRS1977

Polarization loss of a satellite - Data collection sensor link

It is noted that the stringent economy of data-collection systems consisting of several widely dispersed satellite-monitored sensor platforms can be partially achieved by using an inexpensive linearly polarized antenna on each platform and that due to Faraday rotation of the ionosphere, the satellite antenna must be circularly polarized to avoid a prohibitive polarization loss. The cumulative probability distribution of polarization loss between a linearly polarized platform antenna and an elliptically polarized satellite antenna is computed for satellite-antenna axial ratios of 3 and 4 dB. The results indicate that a polarization loss of 4.5 dB must be expected for a reliability of 85% and an axial ratio of 3 dB. It is suggested that the conventional assignment of a 3-dB polarization loss to the communication link considered may not insure the required link reliability.

Estep, H.↗
NASA NTRS1978

Neutrino angular momentum loss in rotating stars

We consider how an axisymmetric, uniformly and slowly rotating homogeneous star might be affected by the loss of energy and angular momentum via neutrino emission. For example, these losses can cause a collapsing, rotating star to flatten either faster or slower than would be the case if these losses were not taken fully into account, depending on the efficiency of the angular momentum loss mechanism.

Epstein, R.↗
NASA NTRS1978

Ozone profiles and chemical loss rates in the tropical stratosphere deduced from backscatter ultraviolet measurements

Analysis of data obtained by the backscatter ultraviolet (BUV) experiment on the Atmosphere Explorer E satellite has provided equatorial ozone mixing ratio profiles for equinox and solstice conditions. The combination of these results with a pure oxygen chemical model yields the rate of odd oxygen loss due to the sum of the odd hydrogen, nitrogen, and chlorine cycles. Use of recent mid-latitude stratospheric measurements of HO(x), NO(x), and ClO(x) with the BUV data provides an independent calculation of the catalytic loss. Below 45 km the agreement between the two sets of loss rates is satisfactory. At higher altitudes the odd hydrogen cycle provides far more O(x) loss than can be tolerated by the BUV measurements if the photodissociation of O2 is the only source and has the currently accepted magnitude. The results suggest either a tropical HO(x) concentration smaller than is now believed or the presence of a very large source of odd oxygen in the upper stratosphere and lower mesosphere.

Frederick, J. E.↗
NASA NTRS1978

Prolonged weightlessness and calcium loss in man

Calcium losses occurring in men subjected to weightlessness in orbital space flight for periods of up to twelve weeks were determined, and the data are used to predict the long-term consequences of weightlessness upon the skeletal system. Loss of calcium increased exponentially from about 50 mg/d at the end of the first week to approximately 300 mg/d at the end of 12 weeks. Hypercalciuria reached a constant level within four weeks while fecal calcium losses continued to increase throughout the period of exposure. Calcium losses from the calcaneus were closely correlated with calcium imbalance, but no changes were detected in the mineral mass of the ulna and radius. It is suggested that the demineralization process may not be totally reversible

Rambaut, P. C.↗
NASA NTRS1979

Relation of ultrasonic energy loss factors and constituent properties in unidirectional composites

A model is developed relating composite constituents properties with ultrasonic energy loss factors for longitudinal waves propagating in the principal directions of a unidirectional graphite/epoxy fiber composite. All the constituents are assumed to behave as linear viscoelastic materials with energy dissipation properties defined by loss factors. It is found that by introducing a new constituent called the interface material, the composite and constituent properties can be brought into consistency with simple series and parallel models. An expression relating the composite loss factors to the loss factors of the constituents is derived and its coefficients are evaluated.

Williams, J. H., Jr.↗
NASA NTRS1980

Pulsation and mass loss in Mira variables

The behavior of pulsation in the outer layers of a typical Mira variable was studied in the adiabatic and isothermal limits. A shock wave propagates outward once per period and the radial velocity obtained from observations of hydrogen emission lines is identified with the velocity of gas in the post shock region. In the adiabatic case, mass loss in the form of a steady stellar wind was produced. In the isothermal case, no continuous mass loss was produced but occasional ejection of shells occur. Pulsation introduced into a star undergoing steady mass loss as a result of radiation pressure acting on grains caused the mass loss rate to increase by a factor of approximately 40, while the terminal velocity of the flow was almost unaltered.

Wood, P. R.↗
NASA NTRS1980

Mass loss from warm giants: Magnetic effects

Among warm giant stars, rapid mass loss sets in along a well defined velocity dividing line (VDL). Hot corona also disappear close to the VDL and thermal pressure cannot drive the observed rapid mass loss in these stars. The VDL may be associated with magnetic fields changing from closed to open. Such a change is consistent with the lack of X-rays from late-type giants. A magnetic transition locus based on Pneuman's work on helmet streamer stability agrees well with the empirical VDL. The change from closed to open fields not only makes rapid mass loss possible, but also contributes to energizing the mass loss in the form of discrete bubbles.

Mullan, D. J.↗
NASA NTRS1981

Calculation of atmospheric loss from microwave radiometric noise temperature measurements

Microwave propagation loss in the atmosphere can be inferred from microwave radiometric noise temperature measurements. The relevant equations are given and a derivation and calculation is made assuming various physical models. Comparison is made with the commonly used lumped element atmospheric model (isothermal and uniform loss) and the model with linear temperature and exponential loss distributions. The results are useful for estimating the integral inversion differences due to the model selection. This indicates that the commonly used lumped element atmospheric model is a very good approximation with judicious choice of the effective physical temperature. For the worst case comparison, the lumped element model agrees with the variable parameter model within 0.2 dB up to a propagation loss of 3 dB.

Stelzried, C.↗
NASA NTRS1981

Mass-loss rates from early-type stars

The mass loss rates are derived for a number of unevolved O-type stars and a few WN stars from high dispersion IUE spectra of their P Cygni profiles. When combined with other published mass loss rates, it is found that the relationship between log m and M sub BOL is a broad band rather than a linear relation, suggesting that the line radiation driven wind theory may not be sufficient to explain mass loss. The mass loss rates for the WN stars, while more uncertain, confirm that these stars lose mass about 100 times faster than O-stars.

Conti, P. S.↗
NASA NTRS1980

The effect of solar array voltage patterns on plasma power losses

The use of high-voltage solar arrays in space is discussed in connection with the draining of array power by currents flowing between exposed surfaces through the surrounding plasma. The possibility of reducing the power loss by arranging solar cell strings in repeated small-area modules to eliminate any large areas at high potentials is investigated. It is found that the difference in power loss between modular and linear patterned high-voltage arrays is fairly small. Although the use of modular patterns can reduce the effective mean potential by about 10%, for the type of configuration being considered there is also a 10% increase in sheath area, leading to only a few percent change in total power loss. It is concluded that plasma power loss should not be a primary consideration in designing the physical arrangement of high-voltage arrays.

Mandell, M. J.↗
NASA NTRS1980

Ultrasonic wave propagation loss factor in composite in terms of constituent properties

A model is developed to relate the energy loss factors of ultrasonic longitudinal waves propagating in the principal directions of a unidirectional graphite fiber composite to the composite constituent properties. All the constituents are assumed to behave as linear viscoelastic materials with energy dissipation properties defined by loss factors. It is found that by introducing a new constituent called the interface material, the composite and constituent properties can be brought into consistency with simple series and parallel models. An expression relating the composite loss factors to the loss factors of the constituents is derived and its coefficients are evaluated.

Williams, J. H., Jr.↗
NASA NTRS1981

Mass loss rates from O stars in OB associations

The considered investigation is concerned with an extension of an analysis of the spectra of 31 O type stars observed with the International Ultraviolet Explorer (IUE) satellite to include excited as well as resonant lines. The investigation makes use of the methods developed by Olson (1981). Most of the stars are unevolved cluster members, a group which has not been treated in previous studies. Attention is given to the theory and techniques for mass loss rate determination, the correlation of mass loss with various stellar parameters, and a comparison of the obtained results with the predictions of models. A major consequence of the derived mass loss relationship is that mass loss by stellar winds will affect the evolution of only very luminous (massive) stars. It is, however, emphasized that the obtained relationship is dominated by main-sequence O stars. It is found that the subordinate lines of N IV and O IV are much weaker than what is expected in O stars.

Garmany, C. D.↗
NASA NTRS1981

Mass loss from cool stars

Recently obtained spectroscopic observations indicating mass loss in cool stars are reviewed with analogies to the solar atmosphere. Spectral diagnostics of mass loss are discussed with new theoretical calculations of chromospheric line profiles. A general picture of mass loss from cool stars is developed and related to chromospheric and coronal emissions measured by IUE and the HEAO-2 Observatory. These winds range in characteristics from the hot (10 to the 6th K) and fast wind with low mass loss found in the dwarf stars to the warm (approximately 10 to the 5th K), moderate speed winds present in hybrid luminous supergiants, and the coolest massive winds emerging from the latest type supergiants exhibiting lowest thermal velocities and circumstellar shells. Evidence for stellar surface inhomogeneity and variability of outflow is briefly discussed.

Dupree, A. K.↗
NASA NTRS1981

Observations and theory of mass loss in late-type stars

The presented review is mainly concerned with the ubiquitous mass loss which occurs during most of a star's existence as a cool giant or supergiant. Observations of mass loss are considered, taking into account wind components and kinematics, and the temperature structure of cool winds. Theories of mass loss are examined, giving attention to radiation pressure on dust, radiation pressure in Lyman alpha, and magnetic wave-driven winds. It is pointed out that the study of mass loss from late-type stars appears to be entering a promising new phase. In this phase, the behavior of cool giants and supergiants is considered from a solar perspective, a perspective which contains important implications concerning the nature of solar activity.

Hartmann, L.↗
NASA NTRS1982

Dynamics of weight loss during prolonged spaceflight

Data from three Skylab flights lasting 28, 59, and 84 days are used to study changes in body composition occurring during extended spaceflight. The analysis includes pre- and postflight measurements used to compute lean body mass and body fat losses for an entire mission using previously accepted methods based on total body water, potassium, and density, and also includes the daily metabolic balances in order to provide an estimate of the time course of the changes in water, protein, and fat. The analytical approach is explained and the results presented, including a summary of changes in lean body mass and changes in weight loss and tissue components. It is concluded that little more than half of the weight loss observed during the missions can be attributed to loss in lean body mass, the remainder being derived from fat stores.

Leach, C. S.↗
NASA NTRS1983

A review and summary of cell and module mismatch losses from theoretical and experimental studies

Studies on power loss due to photovoltaic (PV) cell and module parameter mismatch were reviewed. The losses result from the current voltage (I-V) characteristics of cells which vary over a manufactured lot. The peak power and the peak power I-V point vary from cell to cell. The largest parameter variation occurs in the cell photocurrent generation and the most significant loss occurs in series connections since all cells are essentially limited by the lowest photocurrent. Most theoretical studies address only photocurrent variation effects, which consider shunt and series resistance, ideality factor and saturation current to be comparatively insignificant. One study is identified which specifically configured the study of mismatch loss effects. Experimental results consist of estimates based on limited data not taken from specially configured tests.

Lambarski, T. J.↗
NASA NTRS1983

Mass loss rates and anisotropies in the outflows from late-type stars

It has been found that late-type giants and supergiants are losing large amounts of mass. However, it is still not known why these stars lose mass. In connection with the aim to understand this process, it is attempted to establish more accurate mass loss rates in order to consider in detail a popular model for mass loss, taking into account the hypothesis that radiation pressure on grains is important or even controls the mass outflows. This hypothesis can be tested by comparing measurements of the flux from the star, the mass loss rate, and the outflow velocity of the material. The largest uncertainty is related to the mass loss rate. Most models for interpreting the observations of these stars have been for spherically symmetric envelopes. However, highly anisotropic outflows have been observed. It is, therefore, one of the purposes of this investigation to study the importance of the anisotropy in the physical characteristics of the outflow. It is found that anisotropy does not greatly alter the important basic photochemical processes, and that radiation pressure on grains can be important.

Jura, M.↗