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Absorption Properties Of Type-Ii Inas/Inassb Superlattices Measured By Spectroscopic Ellipsometry, P T. Webster, N A. Riordan, S Liu, E H. Steenbergen, R A. Synowicki, Y H. Zhang, S R. Johnson
Absorption Properties Of Type-Ii Inas/Inassb Superlattices Measured By Spectroscopic Ellipsometry, P T. Webster, N A. Riordan, S Liu, E H. Steenbergen, R A. Synowicki, Y H. Zhang, S R. Johnson
U.S. Air Force Research
Strain-balanced InAs/InAsSb superlattices offer access to the mid- to long-wavelength infrared region with what is essentially a ternary material system at the GaSb lattice constant. The absorption coefficients of InAs/InAsSb superlattices grown by molecular beam epitaxy on (100)-oriented GaSb substrates are measured at room temperature over the 30 to 800 meV photon energy range using spectroscopic ellipsometry, and the miniband structure of each superlattice is calculated using a Kronig-Penney model. The InAs/InAsSb conduction band offset is used as a fitting parameter to align the calculated superlattice ground state transition energy to the measured absorption onset at room temperature and to …
Cavity Ignition In Supersonic Flow By Spark Discharge And Pulse Detonation, Timothy M. Ombrello, Campbell D. Carter, Chung-Jen Tam, Kuang-Yu Hsu
Cavity Ignition In Supersonic Flow By Spark Discharge And Pulse Detonation, Timothy M. Ombrello, Campbell D. Carter, Chung-Jen Tam, Kuang-Yu Hsu
U.S. Air Force Research
Ignition of an ethylene fueled cavity in a supersonic flow was achieved through the application of two energy deposition techniques: a spark discharge and pulse detonator (PD). High-frequency shadowgraph and chemiluminescence imaging showed that the spark discharge ignition was passive with the ignition kernel and ensuing flame propagation following the cavity flowfield. The PD produced a high-pressure and temperature exhaust that allowed for ignition at lower tunnel temperatures and pressures than the spark discharge, but also caused significant disruption to the cavity flowfield dynamics. Under certain cavity fueling conditions a multiple regime ignition process occurred with the PD that led …
Autoignition Behavior Of Synthetic Alternative Jet Fuels: An Examination Of Chemical Composition Effects On Ignition Delays At Low To Intermediate Temperatures, Daniel Valco, Gerald Gentz, Casey Allen, Meredith Colket, Tim Edwards, Sandeep Gowdagiri, Matthew A. Oehlschlaeger, Elisa Toulson, Tonghun Lee
Autoignition Behavior Of Synthetic Alternative Jet Fuels: An Examination Of Chemical Composition Effects On Ignition Delays At Low To Intermediate Temperatures, Daniel Valco, Gerald Gentz, Casey Allen, Meredith Colket, Tim Edwards, Sandeep Gowdagiri, Matthew A. Oehlschlaeger, Elisa Toulson, Tonghun Lee
U.S. Air Force Research
The autoignition characteristics of military aviation fuels (JP-5 and JP-8), proposed camelina-derived hydroprocessed renewable jet fuel replacements (HRJ-8 and HRJ-5), Fischer–Tropsch fuels (Shell and Sasol), three Sasol isoparaffinic solvents, as well as 50/50 volumetric blends of the alternative fuels with the conventional fuels are examined. Experiments were conducted in a rapid compression machine and shock tube at compressed temperatures of 625 K ≤ Tc ≤ 1000 K, a compressed pressure of 20 bar, and under stoichiometric and lean conditions. Several implicit properties of the alternative fuels prompted a study of the influence of chemical composition on autoignition, including the influence …
State-Space Representation Of The Unsteady Aerodynamics Of Flapping Flight, Haithem E. Taha, Muhammad R. Hajj, Philip S. Beran
State-Space Representation Of The Unsteady Aerodynamics Of Flapping Flight, Haithem E. Taha, Muhammad R. Hajj, Philip S. Beran
U.S. Air Force Research
A state-space formulation for the aerodynamics of flapping flight is presented. The Duhamel's principle, applied in linear unsteady flows, is extended to non-conventional lift curves to capture the LEV contribution. The aspect ratio effects on the empirical formulae used to predict the static lift due to a stabilized Leading Edge Vortex (LEV) are provided. The unsteady lift due to arbitrary wing motion is generated using the static lift curve. Then, state-space representation for the unsteady lift is derived. The proposed model is validated through a comparison with direct numerical simulations of Navier-Stokes on hovering insects. A comparison with quasi-steady models …
Airmen With Mild Traumatic Brain Injury (Mtbi) At Increased Risk For Subsequent Mishaps, Casserly R. Whitehead, Timothy S. Webb, Timothy S. Wells, Kari L. Hunter
Airmen With Mild Traumatic Brain Injury (Mtbi) At Increased Risk For Subsequent Mishaps, Casserly R. Whitehead, Timothy S. Webb, Timothy S. Wells, Kari L. Hunter
U.S. Air Force Research
Background: Little is known regarding long-term performance decrements associated with mild Traumatic Brain Injury (mTBI). The goal of this study was to determine if individuals with an mTBI may be at increased risk for subsequent mishaps. Methods: Cox proportional hazards modeling was utilized to calculate hazard ratios for 518,958 active duty U.S. Air Force service members (Airmen) while controlling for varying lengths of followup and potentially confounding variables. Two non-mTBI comparison groups were used; the second being a subset of the original, both without head injuries two years prior to study entrance. Results: Hazard ratios indicate that the causes of …
Optimal Thickness Distributions Of Aeroelastic Flapping Shells, Bret Stanford, Philip Beran
Optimal Thickness Distributions Of Aeroelastic Flapping Shells, Bret Stanford, Philip Beran
U.S. Air Force Research
The severe weight limitations of flapping wing micro air vehicles necessitates the use of thin flexible wings, which in turn requires an aeroelastic modeling tool for proper numerical characterization. Furthermore, due to the unconventional nature of these vehicles, wing design guidelines for thrust and/or power considerations are not generally available; numerical design optimization then becomes a valuable tool. This work couples a nonlinear shell model to an unsteady vortex lattice solver, and then computes analytical design gradients: the derivative of aerodynamic force/power quantities with respect to a large vector of thickness variables. Gradient-based optimization is then used to locate the …
Direct Ignition And S-Curve Transition By In Situ Nano-Second Pulsed Discharge In Methane/Oxygen/Helium Counterflow Flame, Wenting Sun, Sang Hee Won, Timothy Ombrello, Campbell Carter, Yiguang Ju
Direct Ignition And S-Curve Transition By In Situ Nano-Second Pulsed Discharge In Methane/Oxygen/Helium Counterflow Flame, Wenting Sun, Sang Hee Won, Timothy Ombrello, Campbell Carter, Yiguang Ju
U.S. Air Force Research
A well-defined plasma assisted combustion system with novel in situ discharge in a counterflow diffusion flame was developed to study the direct coupling kinetic effect of non-equilibrium plasma on flame ignition and extinction. A uniform discharge was generated between the burner nozzles by placing porous metal electrodes at the nozzle exits. The ignition and extinction characteristics of CH4/O2/He diffusion flames were investigated by measuring excited OH* and OH PLIF, at constant strain rates and O2 mole fraction on the oxidizer side while changing the fuel mole fraction. It was found that ignition and extinction occurred with an abrupt change of …
Reducing Uncertainty In Fatigue Life Limits Of Turbine Engine Alloys, J M. Larson, S K. Jha, C J. Szczepanski, M J. Caton, R John, A H. Rosenberger, D J. Buchanan, P J. Golden, J R. Jira
Reducing Uncertainty In Fatigue Life Limits Of Turbine Engine Alloys, J M. Larson, S K. Jha, C J. Szczepanski, M J. Caton, R John, A H. Rosenberger, D J. Buchanan, P J. Golden, J R. Jira
U.S. Air Force Research
In probabilistic design of materials for fracture-critical components in modern military turbine engines, a typical maximum design target risk (DTR) is 5 X 10-8 component failures/engine flight hour. This metric underscores the essential role of safety in a design process that simultaneously strives to achieve performance, efficiency, reliability, and affordability throughout the life cycle of the engine. Traditionally, the design and life management approaches for engine materials have typically relied on extensive testing programs to produce large databases of fatigue data, from which statistically based life limits are derived by extrapolation from the mean fatigue behavior. However, we …
Direct Flutter And Limit Cycle Computations Of Highly Flexible Wings For Efficient Analysis And Optimization, Bret Stanford, Philip Beran
Direct Flutter And Limit Cycle Computations Of Highly Flexible Wings For Efficient Analysis And Optimization, Bret Stanford, Philip Beran
U.S. Air Force Research
The usefulness of flutter as a design metric is diluted for wings with destabilizing (softening) nonlinearities, as a stable high-amplitude limit cycle (subcritical) may exist for flight speeds well below the flutter point. It is thus desired to design aeroelastic structures such that the post-flutter behavior is as benign (i.e., supercritical) as possible, among the other constraints commonly considered in the optimization process. In order to account for these metrics in an accurate and efficient manner, direct tools are utilized to first locate the Hopf-point (flutter speed), and then to obtain a nonlinear perturbation solution via the method of multiple …
Stability And Power Optimality In Time-Periodic Flapping Wing Structures, Bret Stanford, Philip Beran, Richard Snyder, Mayuresh Patil
Stability And Power Optimality In Time-Periodic Flapping Wing Structures, Bret Stanford, Philip Beran, Richard Snyder, Mayuresh Patil
U.S. Air Force Research
This paper investigates the nonlinear dynamics of a vehicle with two flexible flapping wings. The body dynamics and the wings' deformation are monolithically grouped into a single system of equations, with aerodynamics accounted for by a quasi-steady blade element method. A periodic shooting method is then used to locate closed orbits of this non-autonomous system, and Floquet multipliers assess the linearized stability about the nonlinear orbit. This framework is then exposed to a gradient based optimizer, in order to quantify the role of wing planform variables, wing structure variables, and kinematic actuation variables in obtaining vehicles with superior open-loop stability …
Geochemical Evaluation Of High Sulfate Levels In Ponca Creek, Northeastern Nebraska, Jon C. Atkinson
Geochemical Evaluation Of High Sulfate Levels In Ponca Creek, Northeastern Nebraska, Jon C. Atkinson
U.S. Air Force Research
Most surface water and shallow groundwater occurring in northeastern Nebraska are of the calcium bicarbonate type, with minor concentrations (e.g., 10–200 mg/L) of sulfate (SO4). Examination of historical water quality data (major cations and anions) for Ponca Creek, a predominantly ephemeral streamin northeastern Nebraska, revealed that SO4 concentrations ranged from about 110 to almost 1000mg/L and contribute to a calcium sulfate hydrochemical facies. Consequently, most SO4 concentrations were above the U.S. Environmental Protection Agency secondary maximum contaminant level in drinking water of 250 mg/L. Sulfate concentrations for the same period for a nearby stream, Verdigre Creek, …
Focusing Of Longitudinal Ultrasonic Waves In Air With An Aperiodic Flat Lens, John T. Welter, Shamachary Sathish, Daniel Christensen, Philip Brodrick, Jason D. Heebl, Matthew Cherry
Focusing Of Longitudinal Ultrasonic Waves In Air With An Aperiodic Flat Lens, John T. Welter, Shamachary Sathish, Daniel Christensen, Philip Brodrick, Jason D. Heebl, Matthew Cherry
U.S. Air Force Research
Modeling and experimental results of an ultrasonic aperiodic flat lens for use in air are presented. Predictive modeling of the lens is performed using a hybrid genetic-greedy algorithm constrained to a linear structure. The optimized design parameters are used to fabricate a lens. A method combining a fiber-disk arrangement and scanning laser vibrometer measurements is developed to characterize the acoustic field distribution generated by the lens. The focal spot size is determined to be 0.88 of the incident wavelength of 8090 kHz at a distance of 2.5 mm from the lens. Theoretically computed field distributions, optimized frequency of operation, and …
A Location Analysis Approach For Military Maintenance Scheduling With Geographically Dispersed Service Areas, Dale L. Overholts Ii, John E. Bell, Marvin A. Arostegui
A Location Analysis Approach For Military Maintenance Scheduling With Geographically Dispersed Service Areas, Dale L. Overholts Ii, John E. Bell, Marvin A. Arostegui
U.S. Air Force Research
This research uses a two-stage maximal covering location problem (MCLP) model to develop Intercontinental ballistic missile (ICBM) maintenance schedules for the US Air Force. Solutions are compared to actual missile maintenance activities accomplished at F. E. Warren Air Force Base (AFB), Wyoming in May 2005. Sensitivity analysis is performed to determine the impact of altering security response times and the number of security patrol are as on the quality of daily maintenance schedules and personnel usage. Results indicate marked improvement over traditional Air Force scheduling methods. In addition, sensitivity analysis identifies the levels at which the quality and quantity of …
Selecting And Conserving Lands For Biodiversity: The Role Of Remote Sensing, John Wiens, Robert Sutter, Mark Anderson, Jon Blanchard, Analie Barnett, Naikoa Aguilar-Amuchastegui, Chadwick Avery, Stephen Laine
Selecting And Conserving Lands For Biodiversity: The Role Of Remote Sensing, John Wiens, Robert Sutter, Mark Anderson, Jon Blanchard, Analie Barnett, Naikoa Aguilar-Amuchastegui, Chadwick Avery, Stephen Laine
U.S. Air Force Research
A major focus of conservation is on protecting areas to ensure the persistence of biological diversity. Because such areas may be large, not easily accessible, subject to change, and sensitive to the surrounding landscape, remote sensing can be a valuable tool in establishing and managing protected areas. We describe three case studies to illustrate how remote sensing can contribute to setting priorities for conservation actions, monitoring the status of conservation targets, and evaluating the effectiveness of conservation strategies. In the Connecticut River watershed, remote sensing has been used to assess flood regimes and identify key areas of floodplain forests and …
United States Air Force Posture Statement 2009, U.S. Air Force
United States Air Force Posture Statement 2009, U.S. Air Force
U.S. Air Force Research
Today, the United States faces a spectrum of challenges to our national security and global interests. As an integral member of the Joint team, America’s Air Force provides the critical capabilities of Global Vigilance, Global Reach, and Global Power. The United States Air Force is 'All In" today’s Joint fight. At the same time, our investments in new capabilities will ensure we are ready for tomorrow’s challenges. The mission of the United States Air Force is to "fly, fight, and win…in air, space and cyberspace"—as an integral member of the Joint …
Perchlorate In Wet Deposition Across North America, Srinath Rajagopalan, Todd A. Anderson, Stephen Cox, Greg Harvey, Qiuqiong Cheng, W. Andrew Jackson
Perchlorate In Wet Deposition Across North America, Srinath Rajagopalan, Todd A. Anderson, Stephen Cox, Greg Harvey, Qiuqiong Cheng, W. Andrew Jackson
U.S. Air Force Research
Natural perchlorate is believed to be of atmospheric origin, yet no systematic study has been conducted to evaluate perchlorate deposition rate and possible seasonal or spatial variations. This study evaluated perchlorate concentrations in weekly composite wet deposition samples acquired through the National Atmospheric DepositionProgramfrom 26 sites across the continental United States, Alaska, and Puerto Rico for a 1-3 year period. Perchlorate concentrations varied from /L to a high of 102 ng/L with a mean of 14.1±13.5 ng/L for the 1578 total samples. The annual perchlorate flux by site ranged from a low of 12.5 (TX) to 157 mg/ha-year (NE) and …
United States Air Force Posture Statement 2008, U.S. Air Force
United States Air Force Posture Statement 2008, U.S. Air Force
U.S. Air Force Research
The United States Air Force provides the Nation with a powerful deterrent force in times of peace, and it sets the conditions for Joint and Coalition victory in times of war. For over seventeen years, since Operation DESERT SHIELD, the United States Air Force has been engaged in continuous combat operations. Our Airmen have maintained constant watch, deployed continuously, engaged America’s adversaries directly, responded to human crises around the world, and provided the Global Vigilance, Global Reach, and Global Power to secure our Nation.
The 2008 Strategy For United States Air Force Intelligence, Surveillance And Reconnaissance, U.S. Air Force
The 2008 Strategy For United States Air Force Intelligence, Surveillance And Reconnaissance, U.S. Air Force
U.S. Air Force Research
Since the inception of the Air Force, our Nation has asked us to create aerospace forces that no adversary could "out gun" under any circumstances. For over six decades we have answered that call. Now the Nation demands that we also create a set of capabilities that no adversary can "out smart" in the future. This strategy outlines our response in the realm of Intelligence, Surveillance and Reconnaissance (ISR).
This is a new document that specifies why and how our Air Force will provide the capacity and capability for full spectrum ISR. It provides the foundation for enabling our air …
An Integer Programming Approach To Support The Us Air Force’S Air Mobility Network, Corbin G. Koepke, Andrew P. Armacost, Cynthia Barnhart, Stephan E. Kolitz
An Integer Programming Approach To Support The Us Air Force’S Air Mobility Network, Corbin G. Koepke, Andrew P. Armacost, Cynthia Barnhart, Stephan E. Kolitz
U.S. Air Force Research
The United States Air Force’s air mobility command is responsible for creating a schedule and executing that schedule for a large-scale air mobility network that encompasses aircraft with prioritized missions. Aerial ports (airports) can process or park a maximum number of aircraft, called the maximum on ground (MOG). As the schedule changes due to disruptions, such as equipment failure or weather, the MOG constraint can cause the new schedule to be infeasible. Traditionally, re-planning the channel route schedule to adhere to MOG constraints has been a manual process that usually stops after the first feasible set of changes is found, …
The Complete Management Of Extremity Vascular Injury In A Local Population: A Wartime Report From The 332nd Expeditionary Medical Group/Air Force Theater Hospital, Balad Air Base, Iraq, Michael A. Peck, W. Darrin Clouse, Mitchell W. Cox, Andrew N. Bowser, Jonathan L. Eliason, Donald H. Jenkins, David L. Smith, Todd E. Rasmussen
The Complete Management Of Extremity Vascular Injury In A Local Population: A Wartime Report From The 332nd Expeditionary Medical Group/Air Force Theater Hospital, Balad Air Base, Iraq, Michael A. Peck, W. Darrin Clouse, Mitchell W. Cox, Andrew N. Bowser, Jonathan L. Eliason, Donald H. Jenkins, David L. Smith, Todd E. Rasmussen
U.S. Air Force Research
Background: Although the management of vascular injury in coalition forces during Operation Iraqi Freedom has been described, there are no reports on the in-theater treatment of wartime vascular injury in the local population. This study reports the complete management of extremity vascular injury in a local wartime population and illustrates the unique aspects of this cohort and management strategy.
Methods: From September 1, 2004, to August 31, 2006, all vascular injuries treated at the Air Force Theater Hospital (AFTH) in Balad, Iraq, were registered. Those in non-coalition troops were identified and retrospectively reviewed.
Results: During the study …
Electrical Control Of The Thermodiffusive Instability In Premixed Propane–Air Flames, D. L. Wisman, S. D. Marcum, B. N. Ganguly
Electrical Control Of The Thermodiffusive Instability In Premixed Propane–Air Flames, D. L. Wisman, S. D. Marcum, B. N. Ganguly
U.S. Air Force Research
This work focuses upon the effects of DC electric fields on the stability of downward propagating atmospheric pressure premixed propane–air flames under experimental conditions that provide close coupling of the electric field to the flame. With the appropriate electrode geometry, modest applied voltages are shown to drive a stable conical flame first into a wrinkled-laminar flamelet geometry, and then further toward either a highly unstable distributed flamelet regime or a collective oscillation of the flame front. Applied potentials up through +5 kV over a 40-mm gap encompassing the flame front have been used to force the above transition sequence in …
United States Air Force Posture Statement 2007, U.S. Air Force
United States Air Force Posture Statement 2007, U.S. Air Force
U.S. Air Force Research
Our 2007 Posture Statement articulates the major elements required to fulfill our mission. It reaffirms our commitment to focus our energies on the Global War on Terror; to develop and care for our Airmen and their families; and to recapitalize and modernize our aging aircraft, spacecraft and equipment.
Impact Of Phlebotomine Sand Flies On U.S. Military Operations At Tallil Air Base, Iraq: 3. Evaluation Of Surveillance Devices For The Collection Of Adult Sand Flies, Douglas A. Burkett, Ronald Knight, James A. Dennett, Van Sherwood, Edgar Rowton, Russell E. Coleman
Impact Of Phlebotomine Sand Flies On U.S. Military Operations At Tallil Air Base, Iraq: 3. Evaluation Of Surveillance Devices For The Collection Of Adult Sand Flies, Douglas A. Burkett, Ronald Knight, James A. Dennett, Van Sherwood, Edgar Rowton, Russell E. Coleman
U.S. Air Force Research
We evaluated the effectiveness of commercially available light traps and sticky traps baited with chemical light sticks for the collection of phlebotomine sand flies. Evaluations were conducted at Tallil Air Base, Iraq, in 2003. In an initial study, a Centers for Disease Control and Prevention (CDC)-style trap with UV bulb collected significantly more sand flies than did an up-draft CDC trap, a standard down-draft CDC trap (STD-CDC), or a sticky strap with a green chemical light stick. In a subsequent study, we found that the addition of chemical light sticks to sticky traps resulted in a significant increase in the …
United States Air Force Posture Statement 2006, U.S. Air Force
United States Air Force Posture Statement 2006, U.S. Air Force
U.S. Air Force Research
Over a century ago, America crossed the threshold of powered flight and gave wings to the world. Soon military leaders realized the implications of this development, and warfare was changed forever. America was fortunate to have "Great Captains" with the vision to imagine the possibilities of air and space power - Airmen like Billy Mitchell, Frank Andrews, Hap Arnold, Ira Eaker, Jimmy Doolittle, Bennie Schriever. They have given us a proud heritage of courage, excellence and innovation. In so doing, they also give us a sense of perspective and a way to understand the Air Force's future.
Basic Materials Research Programs At The U.S. Air Force Office Of Scientific Research, Herbert C. Carlson, K. C. Goretta
Basic Materials Research Programs At The U.S. Air Force Office Of Scientific Research, Herbert C. Carlson, K. C. Goretta
U.S. Air Force Research
The Air Force Office of Scientific Research (AFOSR) annually sponsors approximately 5000 research scientists at 1000 universities and laboratories, generating about 10,000 Ph.D. graduates per decade, all expected to publish their basic research findings in peer-reviewed journals. After a brief introduction of the nature of AFOSR’s support to basic research in the U.S. and international scientific communities, work it supports at the frontiers of materials science is highlighted. One focused research theme that drives our investment is the MEANS program. It begins with the end in mind; materials are designed with practicable manufacture as an explicit initial goal. AFOSR’s broad …
Field-Scale Demonstration Of Induced Biogeochemical Reductive Dechlorination At Dover Air Force Base, Dover, Delaware, Lonnie G. Kennedy, Jess W. Everett, Erica Becvar, Donald Defeo
Field-Scale Demonstration Of Induced Biogeochemical Reductive Dechlorination At Dover Air Force Base, Dover, Delaware, Lonnie G. Kennedy, Jess W. Everett, Erica Becvar, Donald Defeo
U.S. Air Force Research
Biogeochemical reductive dechlorination (BiRD) is a new remediation approach for chlorinated aliphatic hydrocarbons (CAHs). The approach stimulates common sulfate-reducing soil bacteria, facilitating the geochemical conversion of native iron minerals into iron sulfides. Iron sulfides have the ability to chemically reduce many common CAH compounds including PCE, TCE, DCE, similar to zero valent iron (Fe0). Results of a field test at Dover Air Force Base, Dover, Delaware, are given in this paper. BiRD was stimulated by direct injection of Epson salt (MgSO4·7H2O) and sodium (L) lactate (NaC3H5O3) in five …
Perchlorate Toxicity And Risk Assessment, David R. Mattie, Joan Strawson, Jay Zhao
Perchlorate Toxicity And Risk Assessment, David R. Mattie, Joan Strawson, Jay Zhao
U.S. Air Force Research
Ammonium perchlorate is the oxidizer ingredient in solid propellant mixtures for rockets, missiles and munitions such as Titan, Minuteman, Peacekeeper, Hawk, Polaris and the Space Shuttle. Perchlorate salts may also be used in medicine, matches, munitions and pyrotechnics (illuminating and signaling flares, colored and white smoke generators, tracers, incendiary delays, fuses, photo-flash compounds and fireworks). Perchlorate is also found in lubricating oils, finished leather, fabric fixer, dyes, electroplating, aluminum refining, manufacture of rubber, paint and enamel production, as an additive in cattle feed, in magnesium batteries and as a component of automobile air bag inflators.'
Atomic Force Microscope Tip Spontaneous Retraction From Dielectric Surfaces Under Applied Electrostatic Potential, S. F. Lyuksyutov, P. B. Paramonov, O. V. Mayevska, M. A. Reagan, E. Sancaktar, R. A. Vaia, S. Juhl
Atomic Force Microscope Tip Spontaneous Retraction From Dielectric Surfaces Under Applied Electrostatic Potential, S. F. Lyuksyutov, P. B. Paramonov, O. V. Mayevska, M. A. Reagan, E. Sancaktar, R. A. Vaia, S. Juhl
U.S. Air Force Research
A time-resolved method for tip’ retraction at µs-scale away from dielectric surfaces has been developed. Analysis of the forces in the system comprising AFM tip, water meniscus, and polymer film suggests that an electrostatic repulsion of the tip from the surface in the double-layered (water and polymer) system, and water condensation in the tip–surface junction are the dominant factors enabling the mechanical work for tip retraction. Nanostructures of 5–80nm height are formed in polymeric surfaces as a result. This interesting physical phenomenon could be used for nanostructures patterning in polymeric materials at enhanced aspect ratio.
Force Protection Using Composite Sandwich Structures, R. L. Sierakowski, M. L. Hughes
Force Protection Using Composite Sandwich Structures, R. L. Sierakowski, M. L. Hughes
U.S. Air Force Research
In the recent past, advances have been made in the attempt to utilize composite materials as components in protective structures such as those employed by the Air Force to secure critical military assets. In such applications, where lightweight materials that exhibit large levels of energy absorption and high strength/stiffness characteristics are desirable, composite sandwich constructions offer an attractive solution.
In an attempt to evaluate the suitability of certain sandwich structures for use in force protection applications, several sandwich constructions with somewhat novel core materials were identified. A group of thermoplastic core materials have been developed that possess features of both …
Atomic Force Microscopy Of Bacillus Spore Surface Morphology, Ruth A. Zolock, Guangming Li, Charles Bleckmann, Larry Burggraf, Douglas C. Fuller
Atomic Force Microscopy Of Bacillus Spore Surface Morphology, Ruth A. Zolock, Guangming Li, Charles Bleckmann, Larry Burggraf, Douglas C. Fuller
U.S. Air Force Research
Bacillus spore surface morphology was imaged with atomic force microscopy (AFM) to determine if characteristic surface features could be used to distinguish between four closely related species; Bacillus anthracis Sterne strain, Bacillus thuringiensis var. kurstaki, Bacillus cereus strain 569, and Bacillus globigii var. niger. AFM surface height images showed an irregular topography across the curved upper surface of the spores. Phase images showed a superficial grain structure with different levels of phase contrast and significant differences in average surface morphologies among the four species. Although spores of the same species showed similarities, there was significant variability within each …