U.S. Air Force Space Command

Abstract : A new empirical atmospheric density model, Jacchia-Bowman 2008, is developed as an improved revision to the Jacchia-Bowman 2006 model which is based on Jacchia s diffusion equations. Driving solar indices are computed from on-orbit sensor data are used for the solar irradiances in the extreme through far ultraviolet, including x-ray and Lyman-alpha wavelengths. New exospheric temperature equations are developed to represent the thermospheric EUV and FUV heating. New semiannual density equations based on multiple 81-day average solar indices are used to represent the variations in the semiannual density cycle that result from EUV heating. Geomagnetic storm effects are modeled using the Dst index as the driver of global density changes. The model is validated through comparisons with accurate daily density drag data previously computed for numerous satellites in the altitude range of 175 to 1000 km. Model comparisons are computed for the JB2008, JB2006, Jacchia 1970, and NRLMSIS 2000 models. Accelerometer measurements from the CHAMP and GRACE satellites are also used to validate the new geomagnetic storm equations.

Abstract Although there is growing enthusiasm for supply chain management and integrated logistics, much prescriptive writing rests on a flimsy empirical base. Explores the methodological dilemmas which arise in research in logistics practice. Presents three contrasting models of research frameworks. Outlines the experiences of a novel investigation into supply chain integration in the UK carried out in the first half of 1994. Makes recommendations about the use of secondary data, and strategies for future research.

We describe the design and performance of an infrared imaging spectrograph that was first used as an airborne sensor in October, 1995. This instrument, called the spatially-enhanced broadband array spectrograph system (SEBASS), is intended to explore the utility of hyperspectral infrared sensors for remotely identifying solids, liquids, gases, and chemical vapors in the 2 to 14 micrometers 'chemical fingerprint' spectral region. The instrument, which is an extension of an existing non-imaging spectrograph uses two spherical-faced prisms to operate simultaneously in the atmospheric transmission windows found between 2.0 and 5.2 micrometers and between 7.8 and 13.4 micrometers (LWIR). ALthough the SEBASS instrument is designed primarily for use from an aircraft platform, it was used in March 1996 for a tower-based collection.

A new model-based vision (MBV) algorithm is developed to find regions of interest (ROI's) corresponding to masses in digitized mammograms and to classify the masses as malignant/benign. The MBV algorithm is comprised of five modules to structurally identify suspicious ROI's, eliminate false positives, and classify the remaining as malignant or benign. The focus of attention module uses a difference of Gaussians (DoG) filter to highlight suspicious regions in the mammogram. The index module uses tests to reduce the number of nonmalignant regions from 8.39 to 2.36 per full breast image. Size, shape, contrast, and Laws texture features are used to develop the prediction module's mass models. Derivative-based feature saliency techniques are used to determine the best features for classification. Nine features are chosen to define the malignant/benign models. The feature extraction module obtains these features from all suspicious ROI's. The matching module classifies the regions using a multilayer perceptron neural network architecture to obtain an overall classification accuracy of 100% for the segmented malignant masses with a false-positive rate of 1.8 per full breast image. This system has a sensitivity of 92% for locating malignant ROI's. The database contains 272 images (12 b, 100 microm) with 36 malignant and 53 benign mass images. The results demonstrate that the MBV approach provides a structured order of integrating complex stages into a system for radiologists.

Algorithms for designing a mother wavelet /spl psi/(x) such that it matches a signal of interest and such that the family of wavelets {2/sup -(j/2)//spl psi/(2/sup -j/x-k)} forms an orthonormal Riesz basis of L/sup 2/(/spl Rscr/) are developed. The algorithms are based on a closed form solution for finding the scaling function spectrum from the wavelet spectrum. Many applications require wavelets that are matched to a signal of interest. Most current design techniques, however, do not design the wavelet directly. They either build a composite wavelet from a library of previously designed wavelets, modify the bases in an existing multiresolution analysis or design a scaling function that generates a multiresolution analysis with some desired properties. In this paper, two sets of equations are developed that allow us to design the wavelet directly from the signal of interest. Both sets impose bandlimitedness, resulting in closed form solutions. The first set derives expressions for continuous matched wavelet spectrum amplitudes. The second set of equations provides a direct discrete algorithm for calculating close approximations to the optimal complex wavelet spectrum. The discrete solution for the matched wavelet spectrum amplitude is identical to that of the continuous solution at the sampled frequencies. An interesting byproduct of this work is the result that Meyer's spectrum amplitude construction for an orthonormal bandlimited wavelet is not only sufficient but necessary. Specific examples are given which demonstrate the performance of the wavelet matching algorithms for both known orthonormal wavelets and arbitrary signals.

OBJECTIVE: This study examined the prevalence and sources of occupational stress for military personnel and the relationship between work stress and emotional health in the military population. METHODS: Four hundred seventy-two active duty military personnel stationed at F. E. Warren Air Force Base completed a 65-item survey that included items involving reported life events, perceptions about occupational stress, and perceptions about the relationship between work stress and emotional health. RESULTS: These military personnel were significantly more likely to report suffering from job stress than civilian workers (p < 0.001). One-quarter (26%) reported suffering from significant work stress, 15% reported that work stress was causing them significant emotional distress, and 8% reported experiencing work stress that was severe enough to be damaging their emotional health. Generic work stressors were endorsed more frequently than military-specific stressors. CONCLUSIONS: More than one-quarter of this sample of military personnel reported suffering from significant work stress and a significant number of these individuals suffered serious emotional distress. These results support previous research suggesting that work stress may be a significant occupational health hazard in the U.S. military.

Journal Article This New Ocean: A History of Project Mercury. By Loyd S. Swenson, Jr., James M. Grimwood, and Charles C. Alexander. (Washington: Government Printing Office, 1966. xv + 681 pp. Illustrations, notes, appendixes, bibliography, and index. $5.50.) Get access Paul M. Davis Paul M. Davis Air Force Logistics Command Search for other works by this author on: Oxford Academic Google Scholar Journal of American History, Volume 54, Issue 2, September 1967, Pages 455–456, https://doi.org/10.2307/1894882 Published: 01 September 1967

Requirements are the foundation of the software release process. They provide the basis for estimating costs and schedules, as well as developing design and testing specifications. When requirements have been agreed on by both clients and maintenance management, then adding to, deleting from, or modifying those existing requirements during the execution of the software maintenance process impacts the maintenance cost, schedule, and quality of the resulting product. The basic problem is not the changing in itself, but rather the inadequate approaches for dealing with changes in a way that minimizes and communicates the impact to all stakeholders. Using data collected from one organization on 44 software releases spanning seven products, this paper presents two quantitative techniques for dealing with requirements change in a maintenance environment. First, exploratory data analysis helps one to understand the sources, frequency, and types of changes being made. Second, a regression model helps managers communicate the cost and schedule effects of changing requirements to clients and other release stakeholders. These two techniques can help an organization provide a focus for management action during the software maintenance process. Copyright © 1999 John Wiley & Sons, Ltd.

Orbits of launch-vehicle upper stages and spheres were observed by U.S. Air Force Space Command, and the resulting observations were converted by the Space Analysis Office to fitted ballistic coefficients by comparing the observed orbit with an orbit predicted by an atmospheric-drag model. The ballistic coefficients contain signals that result from atmospheric variability not captured by the model as well as signals that correspond to changes in the satellite-drag coefficient. For objects in highly elliptical orbits with perigee altitudes below 200 km a 50% change in ballistic coefficient can be observed. This drastic change is associated with both changes in the energy accommodation coefficient driven by atomic-oxygen adsorption and entry into a transition flow region where a diffuse shock forms ahead of the satellite near perigee. Furthermore, the observed ballistic coefficients for objects in near-circular orbits ( speeds) do not match those of objects in highly eccentric orbits ( speeds near perigee). This difference is attributed to a decrease in adsorption efficiency postulated by previous researchers that is formalized in this work into a semi-empirical model. The model parameters suggest that the average binding energy of atomic oxygen on satellite surfaces is about 5.7 eV.

Long‐term thermospheric neutral density trends near 400 km altitude are analyzed using high accuracy satellite drag measurements over the common time period 1970–2000. Data coverage is over all latitudes and local times and an extensive range of solar and geomagnetic conditions. Densities are compared to empirical models that remove known variations related to solar activity, latitude, local time, day of year and altitude. An average unmodeled secular neutral density decrease of 1.7% per decade is detected. This result is qualitatively consistent with predictions of thermospheric cooling related to anthropogenic causes deduced by theoretical models, and in general agreement with global cooling estimates determined from previous analyses of satellite orbital decay.

Abstract The ability to accurately track and predict satellite locations is of paramount importance to space‐faring nations. In the low Earth orbit satellite environment, atmospheric drag is by far the dominant error associated with orbit propagation. Nowcasts of thermospheric density are routinely accomplished through calibration of semiempirical models using recent data, yet forward predictions degrade quickly as lead time increases. Physics‐based approaches offer a great forecasting potential but one that has yet to be realized due to a lack of robust data assimilation schemes. In an effort to account for the driver/response characteristics of the thermosphere‐ionosphere system, a new data assimilative technique is developed. Abandoning the ensemble Kalman filter framework in favor of a variational technique, iterative model reinitialization is applied self‐consistently to estimate a time history of effective solar and geophysical drivers. The current implementation of this technique, referred to as Iterative Reinitialization, Driver Estimation and Assimilation, works by ingesting neutral mass density measurements from low‐Earth orbiting accelerometers. A long‐term simulation is carried out during 2003, a period consisting of a wide range of solar and geomagnetic activity levels. The new technique is shown to greatly reduce RMS errors of the physics‐based model relative to ingested observations from the Challenging Mini‐Satellite Payload (CHAMP) satellite as well as to an independent validation data set from the Gravity Recovery And Climate Experiment (GRACE) satellite. This work is the first such demonstration of an accurate and robust physics‐based method capable of specifying neutral density during both quiet and disturbed times and offers a promising outlook for improving density forecasting capabilities.

An iterative method based on the conjugate gradient (CG) algorithm is developed for the efficient treatment of equations involving multiple excitations. Examples show that significant time savings can be obtained as compared to treating each excitation individually with the conjugate gradient algorithm. However, these savings are not obtained without the drawback of increased memory requirements to store the additional excitations, residuals, and solutions. The efficiency of this algorithm tends to increase as additional excitations are added.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radiometric measurements during the past decade from the Solar Maximum Mission and Nimbus 7 satellites have shown that the total solar irradiance varies in step with the sun's 11-year magnetic activity cycle. Stellar observations from the Lowell and Mount Wilson observatories now confirm and elaborate this discovery. These measurements show that older stars similar to the sun tend to become brighter as their magnetic activity level increases, just as the sun does during its 11-year activity cycle. Younger stars, however, tend to become fainter as their magnetic activity level increases. This contrasting behavior suggests that the balance between the competing phenomena that influence solar brightness variability has shifted during the sun's lifetime.

The biconjugate gradient (BCG) method for solving linear systems is shown to be more efficient than the conjugate gradient (CG) method for several examples from electromagnetic scattering. A remedy for the occasional stagnation of the algorithm is proposed. The potential flaw in the BCG algorithm may be avoided when encountered by restarting the algorithm with a perturbed estimate of the solution.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The High Accuracy Satellite Drag Model (HASDM) requires satellite ballistic coefficients (B) in order to estimate accurate atmospheric temperature/density corrections. Using satellite tracking data true B values were obtained for over 40 satellites that have been in orbit since 1970. Differential orbit corrections were computed from 1970 to 2001 every 3 days throughout the 31-year period for each satellite. The true B values were computed by averaging the nearly 3200 estimated B values obtained for each satellite. These true B values were validated by comparing the true B values of two spheres with theoretical values based on their known physical dimensions, and by comparing the true B values obtained for pairs of satellites having very similar size, shape, and mass. The estimated B variations for a number of satellites were then averaged over each year from 1970 to 2001, and compared with solar indices plotted for the last three solar cycles.

An important factor in the design of equipment for maximum efficiency of human operation is the design, illumination, and arrangement of visual displays which provide information to the human operator. This report provides a compilation of general human engineering recommendations and presents some of the supporting data which should aid the engineer in providing the most satisfactory visual presentations of information. The report is divided into seven chapters entitled: Mechanical Indicators, Warning Devices, Cathode Ray Tubes and Signal Coding, Printed Materials, Instrument Panel Layout, Lighting, and Visual Detection and Identification. Liberal use is made of pictorial, graphic, and tabular presentations to illustrate the data and design recommendations. A table of contents, subject index, and a selected bibliography are included as an aid to the user.

We show evidence that solar wind density enhancements and pressure pulses can lead to intense low‐energy particle precipitation and an associated, but unexpected, damping of thermospheric density response. Ground‐based indices, used as proxies for thermospheric energy deposition, fail to capture these interactions in forecasting algorithms. Superposed epoch comparison of a group of poorly specified neutral density storms suggests an event‐chain of (1) multi‐hour, pre‐storm solar wind density enhancement, followed by solar wind dynamic pressure pulses that trigger excess low‐energy particle flux to the upper atmosphere; (2) enhanced production of thermospheric Nitric Oxide (NO) by precipitating particles and storm heating; (3) NO infrared cooling and damping of the thermosphere; and (4) mis‐forecast of neutral density. In the control storms, these features are absent or muted. We discuss the roles of solar wind pre‐conditioning and solar cycle dependency in the problem storms. These problem neutral‐density storms reveal an element of “geo‐effectiveness” that highlights competition between hydrodynamic aspects of the solar wind and other interplanetary drivers.

BACKGROUND: Culminating with the events of September 11, 2001, U.S. civilian and military populations are vulnerable to terrorist attacks. Information about the patterns of injuries and their causes inform disaster management planning and can improve structural and architectural design. This report documents the injuries following an estimated 20K bomb at the Khobar Towers military compound in Dhahran, Saudi Arabia. METHODS: US Air Force personnel in the compound at the time of the bombing were evaluated. Data were collected through a mail survey, and a review of military medical records and autopsy reports. Outcome measures included injury types, treatment status, severity, and causes of injuries. RESULTS: The study identified 574 persons who were injured in the bombing; 19 persons died. A total of 420 (73%) persons were injured directly in the blast and 154 (27%) persons were injured during evacuation, search and rescue, during cleanup, or sustained only auditory or inhalation trauma. Sixteen percent of survivors injured directly in the blast were hospitalized; 6% were critical. Soft tissue and foreign body injuries of the lower extremities were the most common injuries among survivors, most often caused by glass. Persons who died suffered extensive, multiple injuries from blunt trauma and one death was caused by glass. CONCLUSIONS: All deaths were immediate and the majority of survivors suffered minor to moderate injuries. Injuries and deaths were consistent with extensive glass damage in the compound and fragmentation of building concrete. Improved building designs and retrofits such as blast-resistant glass and prevention of structural collapse or building fragmentation should be considered in building design and construction in high threat areas.

Lubrication of microelectromechanical systems (MEMS) became very critical as the devices became complex and its reliability began to deteriorate. In this paper, ionic liquids (ILs) with low volatility and high environmental stability were investigated as lubricants for sliding MEMS devices. A method that is based on atomic force microscopy (AFM) with a liquid cell was developed to study friction and wear properties of surfaces lubricated with ILs, having a systematic variation in molecular geometry and chemistry. Six-member pyridinium and five-member imidazolium rings are compared as cations in ethyl methyl pyridinium and ethyl methyl imidazolium ethyl sulfate; influence of short and long alkyl chain lengths on lubrication is studied with butyl methyl pyrrolidinium and hexyl methyl pyrrolidinium bis(trifluro methyl sulfonyl) imide. Formation of a surface-screening cation layer was discovered and linked to low friction and wear of IL-lubricated hydrogenated-silicon (H-Si) substrates. Several promising IL lubricants were identified from the AFM study and were tested in real MEMS motor devices. The friction and wear data obtained for these tests showed good correlation with the failure life span of lubricated MEMS motors. This supports a conclusion that the AFM-liquid-cell technique can be used in screening IL lubricants for MEMS devices.

[Abstract] Atmospheric drag remains the dominant uncertainty for low altitude satellite precision orbit determination . Empirical models are used to estimate satellite drag. Model accuracies have shown little improvement in the past 35 years. A new Ja cchia -Bowman 2006 (JB2006) empirical model has been developed as part of the Air Force Space Command’s High A ccuracy Satellite Drag Model (HASDM) program. Significant new model features of JB2006 are solar indices based on satellite EUV and FUV sensor s and an improved semiannual variation. This new model is compared to historic models vs altitude, latitude, local time , day of year and solar and geomagnetic conditions . Data are from a unique high accuracy set of thermospheric neutral densities with one -day r esolution, obtained from tracking of 38 satellites. The e valuation is carried out for the period 199 7 to 2004 , when the specific solar indices for JB2006 were available . The results provide improved understanding of quantitative relations between current s olar inputs and t he response of the thermosphere . New formulations incorporated into the JB2006 lead to a capability to more accurately specify thermospheric density .