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From May 2010 to September 2010, researchers of the US Army Engineer Research and Development Center and Mississippi State University evaluated the performance of different warm-mix asphalt (WMA) mixtures for their use for airfield pavements. The performance of mixtures produced using different WMA technologies was compared to the performance of the same mixtures produced at hot-mix asphalt (HMA) temperatures. Studied were permanent deformation, durability, non-load associated cracking, moisture damage, and workability. Evaluated were Evotherm 3G, Sasobit , and foamed asphalt. Two aggregates, crushed chert gravel and crushed limestone, were used. The base binder was PG 67-22 from a single refinery. Three reclaimed-asphalt pavement (RAP) contents were used (0, 25, and 50%) to study the incorporation of higher percentages of RAP in WMA than allowed in HMA. Results indicated WMA is a viable product for airfield pavement surface mixtures. However, rutting from traffic and moisture-damage susceptibility must be addressed. Adding RAP to the mix could help, but also could reduce low-temperature performance and durability. Findings suggest WMA with RAP is less susceptible to low-temperature performance problems than HMA with RAP. However, it s not possible to translate the lab results for durability or workability to field performance. Two engineering technical letters (ETLs) and a guide specification were developed from this study. The first, ETL 11-3, was published in August 2011 and provides general information and guidance. The second ETL and the guide specification, both under review, provide more specific guidance on design and construction of airfield pavements using WMA., The original document contains color images. Prepared in collaboration with Mississippi State University, Dept. of Civil and Environmental Engineering, Mississippi State, MS.

In designing flexible pavements for military airfields, minimum thicknesses of surface and base courses are given in the Unified Facilities Criteria (UFC) in tabular form based on the aircraft type, traffic area, and base California Bearing Ratio (CBR). With the development of larger and heavier aircraft, the minimum thickness requirements were simply adjusted upward through an empirical approach. In this report, the U.S. Army Engineer Research and Development Center (ERDC) research team proposes a rational methodology for determining minimum thicknesses for airfield pavements. The proposed procedure considers aircraft wheel loads, tire pressure, load repetitions, and the CBR of both base and subbase layers. In addition to presenting the methodology for determining layer minimum thicknesses from a structural standpoint, the manuscript briefly presents an examination of the effects of construction methods and materials on minimum thickness. Construction equipment and asphalt material characteristics directly influence the thickness of asphalt layer that can be constructed and its performance when subjected to traffic and the environment., The original document contains color images.

Ultra high molecular weight (UHMW) polyethylene panels for aircraft arresting systems have been used in the United States for approximately 15 years to provide better resistance to erosion of the pavement surface under arresting cables. When concrete or asphalt is used directly under the cables, the pavement surface becomes heavily damaged during a short period of time, requiring that the damaged area be removed and patched. A research project was awarded to the U.S. Army Engineer Research and Development Center by the Air Force Civil Engineer Support Agency at Tyndall Air Force Base to inspect a number of polyethylene panels throughout the United States and Europe and to recommend ways to improve performance of the panels and the pavement materials and joint sealants adjacent to the panels. Generally, the UHMW panels have provided much-improved performance, but some changes are needed to improve the overall performance. Several problems have occurred, including warping of the panels, loss of bond between the sealant and the panels, and damage to the adjacent pavement surface when traffic passes over the joint between the panels and the pavement. Items that need improvement include reducing the amount of warping, improving the bond between the sealant and panels, and improving the performance of the asphalt and concrete mixtures adjacent to the panels., The original document contains color images.

An evaluation of aged asphalt concrete (AC) was performed during the period March August 2007 at Polk Army Airfield (Fort Polk, LA), Redstone Army Airfield (Huntsville, AL), Simmons Army Airfield (Fort Bragg, NC), and Forney Army Airfield (Fort Leonard Wood, MO) to develop a method for predicting the performance of aged AC surfaces in situ. This research project was an extension of an investigation that was conducted in fiscal year 2006. Similar test procedures were followed for both projects. A portable seismic pavement analyzer was used on the in situ AC pavements to determine the pavement modulus. The aged AC samples obtained from the military airfields were brought to the U.S. Army Engineer Research and Development Center for laboratory testing. Dynamic shear rheometer tests were conducted on the asphalt binder samples, indirect tensile strength tests were run on core samples, and beam fatigue tests were performed on beam samples. The results from this study were used to develop adjustments to the current Department of Defense fatigue criterion to improve fatigue life predictions for aged AC surfaces. Also, the results of this investigation were used to develop fatigue criteria to be used when evaluating AC pavements in the field., The original document contains color images.

The low-frequency power spectrum has been measured for ErAs:InAlGaAs diodes and shows at least a ten-times reduction of 1/f noise compared to traditional Al Schottky diodes on the same semiconductor material. These junctions are grown by molecular beam epitaxy, preventing oxidation and other contamination at the junction. The major noise source for these devices is attributed to the sidewalls and not the junction itself. Low-frequency oscillations have also been observed and associated with a deep trap level estimated to be similar to 200 meV below the conduction band edge by the comparison of diodes with different InAlGaAs compositions and confirmed by deep level transient spectroscopy. This deep level could be associated to erbium incorporation in the depletion region.

The low-frequency power spectrum has been measured for ErAs:InAlGaAs diodes and shows at least a ten-times reduction of 1/f noise compared to traditional Al Schottky diodes on the same semiconductor material. These junctions are grown by molecular beam epitaxy, preventing oxidation and other contamination at the junction. The major noise source for these devices is attributed to the sidewalls and not the junction itself. Low-frequency oscillations have also been observed and associated with a deep trap level estimated to be similar to 200 meV below the conduction band edge by the comparison of diodes with different InAlGaAs compositions and confirmed by deep level transient spectroscopy. This deep level could be associated to erbium incorporation in the depletion region.

In contrast to traditional metal-semiconductor (i.e., Schottky) junctions, molecular beam epitaxy (MBE)-grown ErAs:InAlGaAs heterojunctions have recently been shown to provide highly "engineerable" electrical rectification characteristics through the tuning of the Schottky barrier height, while maintaining the very low specific capacitance. This letter reports an approximate 10x improvement in the low-frequency noise performance by using MBE-grown ErAs as the Schottky contact instead of evaporated aluminum. The low-frequency noise power spectrum of ErAs devices has been observed to have a 1/f(1.0) frequency dependence. Constant-current bias-dependent measurements have shown a 1.8 power law dependence of the noise spectral density on dc current. (c) 2006 American Institute of Physics.

We demonstrate a molecular beam epitaxy growth technique to create intentionally textured interfaces between semimetallic ErAs and GaAs that result in interface orientations that are different from the substrate. To grow the textured interfaces, ErAs is deposited on (100) GaAs and islands form in an island growth mode. Enough GaAs is then deposited to fill the space between islands with semiconductor. More ErAs is deposited on the ErAs/GaAs surface and the new ErAs islands are thought to nucleate on the exposed top surface of the partially covered islands. The process is repeated to "stack" the islands. By quadratically increasing the amount of ErAs deposited in each repetition, the islands form into cones/pyramids that coalesce into a complete film with an intentionally roughened interface. Compared to a smooth interface between ErAs and GaAs, the Schottky barrier height between textured ErAs and n-GaAs can be reduced from similar to 0.81 to similar to 0.52 eV, and the Schottky barrier height between ErAs and p-GaAs can be increased from similar to 0.38 to similar to 0.63 eV. (c) 2006 American Vacuum Society.

An investigation of the optical transmission properties of semimetallic ErAs films grown by molecular beam epitaxy reveals a maximum in transmission around 1.55 mu m. The semitransparent window extends from similar to 1.5 to 2.3 mu m. These films were found to have resistivities less than 7x10(-5) Omega cm and permit similar to 85% transmission for a 150 nm film and similar to 97% transmission for a 15 nm film with respect to a GaAs substrate at 1.55 mu m. These results suggest that ErAs may be a useful material for applications requiring transparent contacts from 1.5 to 2.3 mu m. Polycrystalline films of ErAs were grown on sapphire substrates to investigate optical properties of ErAs in the visible region. (c) 2006 American Institute of Physics.

We demonstrate a molecular beam epitaxy growth technique to create intentionally textured interfaces between semimetallic ErAs and GaAs that result in interface orientations that are different from the substrate. To grow the textured interfaces, ErAs is deposited on (100) GaAs and islands form in an island growth mode. Enough GaAs is then deposited to fill the space between islands with semiconductor. More ErAs is deposited on the ErAs/GaAs surface and the new ErAs islands are thought to nucleate on the exposed top surface of the partially covered islands. The process is repeated to "stack" the islands. By quadratically increasing the amount of ErAs deposited in each repetition, the islands form into cones/pyramids that coalesce into a complete film with an intentionally roughened interface. Compared to a smooth interface between ErAs and GaAs, the Schottky barrier height between textured ErAs and n-GaAs can be reduced from similar to 0.81 to similar to 0.52 eV, and the Schottky barrier height between ErAs and p-GaAs can be increased from similar to 0.38 to similar to 0.63 eV. (c) 2006 American Vacuum Society.

In contrast to traditional metal-semiconductor (i.e., Schottky) junctions, molecular beam epitaxy (MBE)-grown ErAs:InAlGaAs heterojunctions have recently been shown to provide highly "engineerable" electrical rectification characteristics through the tuning of the Schottky barrier height, while maintaining the very low specific capacitance. This letter reports an approximate 10x improvement in the low-frequency noise performance by using MBE-grown ErAs as the Schottky contact instead of evaporated aluminum. The low-frequency noise power spectrum of ErAs devices has been observed to have a 1/f(1.0) frequency dependence. Constant-current bias-dependent measurements have shown a 1.8 power law dependence of the noise spectral density on dc current. (c) 2006 American Institute of Physics.

An investigation of the optical transmission properties of semimetallic ErAs films grown by molecular beam epitaxy reveals a maximum in transmission around 1.55 mu m. The semitransparent window extends from similar to 1.5 to 2.3 mu m. These films were found to have resistivities less than 7x10(-5) Omega cm and permit similar to 85% transmission for a 150 nm film and similar to 97% transmission for a 15 nm film with respect to a GaAs substrate at 1.55 mu m. These results suggest that ErAs may be a useful material for applications requiring transparent contacts from 1.5 to 2.3 mu m. Polycrystalline films of ErAs were grown on sapphire substrates to investigate optical properties of ErAs in the visible region. (c) 2006 American Institute of Physics.

We demonstrate subpicosecond photocarrier lifetimes at 1.55 mum in GaSb/ErSb nanoparticle superlattices grown by molecular beam epitaxy. Pump-probe measurements were made with a 1.55 mum mode-locked laser in transmission geometry to determine the photocarrier lifetime. The lifetime is found to be dependent on the size of the ErSb particles, amount of ErSb, and the distance between layers of particles. Through manipulation of these three parameters the photocarrier lifetime can be tuned down to less than 300 fs, the temporal limit of our experiment. (C) 2004 American Institute of Physics.

We demonstrate subpicosecond photocarrier lifetimes at 1.55 mum in GaSb/ErSb nanoparticle superlattices grown by molecular beam epitaxy. Pump-probe measurements were made with a 1.55 mum mode-locked laser in transmission geometry to determine the photocarrier lifetime. The lifetime is found to be dependent on the size of the ErSb particles, amount of ErSb, and the distance between layers of particles. Through manipulation of these three parameters the photocarrier lifetime can be tuned down to less than 300 fs, the temporal limit of our experiment. (C) 2004 American Institute of Physics.

This STTR Phase I effort entailed two separate tasks, each focusing on a different aspect of the bioparticle remote detection problem: (1) the phenomenology of absorption by Bacillus subtillis (BC) in the THz region between 300 and 500 GHz; and (2) the design, construction, and tabletop demonstration of a differential-absorption radar (DAR) transceiver suitable as a remote sensor in Phase II. Both tasks met with significant success. The primary objective of the phenomenology effort was to measure the THz transmission through BC with the highest possible accuracy using a vector network analyzer. Previously, measurements made at the University of Virginia displayed two possible absorption resonances in this region centered at 327 and 421 GHz, respectively. In the Phase I measurements, there was no evidence for the 327 GHz resonance. But there was distinct evidence for the 421 GHz resonance that appeared both in vector-network-analyzer and in differential-absorption-radar measurements. Two promising signatures were observed in the Phase 1 effort, one around 425 GHz and the other around 445 CHz. The primary objective of the transceiver development effort was to construct and show the feasibility of a differential absorption radar operating between roughly 420 and 450 GHz. To meet the requirement of field portability, an all-solid-state, cryogen-free, transceiver was assembled using a harmonic multiplier chain for the transmitter and a hot electron bolometer for the receiver. The hot electron bolometer is operated at 4.2 K in a compact, closed-cycle refrigerator. In the first bench-top DAR demonstration, the BC absorption signature centered around 425 GHz was detected and shown to have curvature very close to that obtained by vector network analysis. This is considered to represent a proof-of-concept for the proposed biparticle DAR approach. (15 figures), The original document contains color images. All DTIC reproductions will be in black and white. Topic no. ARMY02-T002.

This article surveys recent progress in the development of high-power microwave and millimeter-wave solid-state sources using spatial power-combining techniques. Several promising topologies are discussed, and four technology demonstrations are presented that have emerged from recent research in academia and industry. We also include a brief discussion of potential applications and systems insertion issues.

This article surveys recent progress in the development of high-power microwave and millimeter-wave solid-state sources using spatial power-combining techniques. Several promising topologies are discussed, and four technology demonstrations are presented that have emerged from recent research in academia and industry. We also include a brief discussion of potential applications and systems insertion issues.

A compact, narrow-linewidth, tunable source of THz radiation has been developed for spectroscopy and other high-resolution applications. Distributed-Bragg-reflector (DBR) diode lasers at 850 nm are used to pump a low-temperature-grown GaAs photomixer. Resonant optical feedback is employed to stabilize the center frequencies and narrow the linewidths of the DBR lasers. The heterodyne linewidth full-width at half-maximum of two optically locked DBR lasers is 50 kHz on the 20 ms time scale and 2 MHz over 10 s; free-running DBR lasers have linewidths of 40 and 90 MHz on such time scales. This instrument has been used to obtain rotational spectra of acetonitrile (CH3CN) at 313 GHz. Detection limits of 1 × 10^–4 Hz^1/2 (noise/total power) have been achieved, with the noise floor dominated by the detector's noise equivalent power.

A compact, narrow-linewidth, tunable source of THz radiation has been developed for spectroscopy and other high-resolution applications. Distributed-Bragg-reflector (DBR) diode lasers at 850 nm are used to pump a low-temperature-grown GaAs photomixer. Resonant optical feedback is employed to stabilize the center frequencies and narrow the linewidths of the DBR lasers. The heterodyne linewidth full-width at half-maximum of two optically locked DBR lasers is 50 kHz on the 20 ms time scale and 2 MHz over 10 s; free-running DBR lasers have linewidths of 40 and 90 MHz on such time scales. This instrument has been used to obtain rotational spectra of acetonitrile (CH3CN) at 313 GHz. Detection limits of 1 × 10^–4 Hz^1/2 (noise/total power) have been achieved, with the noise floor dominated by the detector's noise equivalent power.

This report summarizes two technical approaches aimed at developing three dimensional photonic crystals having wider stop bands than conventional crystals. The first approach is a composite photonic crystal made by stacking monoperiodic sections of a (111) oriented fcc crystal. Because of its similarity to heteroepitaxial structures made from semiconductors having different band gaps, we call it a photonic crystal heterostructure. By making a discrete change in the lattice constant between adjacent monoperiodic sections, the net stop band width can be increased well beyond that of a given section. In a stack of three different sections each having one fcc repeat unit, a stop band was measured between approximately 17 and 26 0Hz which gradually increased in depth with frequency. The second approach is a metallodielectric photonic crystal fabricated by placing metal spheres at each lattice site of a dielectric face centered cubic structure. The resulting sample displays an electromagnetic stop band spanning approximately one octave. The lower frequency edge of the stop band is consistent with the Mie condition for the metallic spheres, and the center frequency of the stop band depends on the periodicity of the lattice and the support dielectric material. For example, a sample having a cubic lattice constant of 1.65 cm, 3/3-inch-diameter chrome spheres at each atomic core, and Teflon support dielectric displayed a lower band edge of approximately 5.2 GHz, an upper band edge of about 12.8 GHz, and a maximum rejection at the center of the band of roughly 20 dB.

The goal of this two-year program was to create two new sources for ultrafast electronic circuits. Two technical approaches were pursued. The first was a cw optoelectronic photomixer using low- temperature-grown (LTG) GaAs as the active material. Prior to this research, little work had been done on cw photomixers at millimeter-wave (i.e., f> 30 GHz) or higher frequencies. The primary limitation was the lack of a suitably fast photoconductive material. LTG GaAs is a promising material for this application because of its short photoconductive lifetime and robust electrical properties. Through the research carried out on this program, the photomixer was developed into a very useful source for frequencies above 1006Hz. The second approach was an electronic pulse generator using a resonant-tunneling diode (RTD) as the active device. The basis for this generator was the high switching speed of the (RTD) when connected to a low-impedance transmission line. Previous work had produced single high-speed switching events in RTDs, but the switching d not heen made self- induced and repetitive. In this effort self-generated pulse trains were produced having a pulse width of approximately 25ps, a repetition rate up to 36Hz, and a pulse amplitude of approximately 0.5 V. One attractive feature of the RTh pulse generator is that it can be modified to generate several useful types of pulse waveforms, such as the impulse function and square waves.

Single frequency microwave radiometry has been used to detect and estimate oil slick thicknesses. Because only a single sampling point is used, estimates of oil thickness can become ambiguous. MIT Lincoln Laboratory proposed the concept of using a frequency scanning radiometer to sample multiple points across a frequency band, thus resolving the problem of ambiguities in oil thickness estimation. A laboratory-prototype FSR capable of scanning over Ka-band (26 -40GHz) was designed, built, and tested. The FSR was used in laboratory proof-of-principle testing to (1) measure uniform thickness oil layers under various ambient weather conditions (day, night, clear, cloudy, drizzle, and snow) and different oil types, and (2) measure the phenomenology of non-uniform thickness oil layers and emulsions. Comparisons of measured data sets with theoretical predictions demonstrated that the expected response of oil is consistent regardless of oil type or ambient weather condition. Comparisons of uniform oil layer measurements and non-uniform measurements with theoretical predictions indicate that the radiometric brightness temperature (TB) of the oil above that of water is a function of the percentage of that thickness of oil within the antenna field-of-view. Water/oil emulsions were measured and have a higher TB than a uniform layer of pure oil at the same thickness. Recommendations for FSR modifications and improvements, as well as future collection work are included. -BKA

A low-temperature-grown GaAs interdigitated-electrode photomixer is used to generate coherent power at microwave frequencies. An output power of 200 microwatts ( - 7 dBm) is generated by pumping the photomixer with two 70-mW modes of a Ti:Al 203 laser, separated in frequency by 200 MHz. This represents an optical-to-microwave conversion efficiency of 0.14%, which is within 50% of a prediction based on optical-heterodyne theory. When two lasers are used and the frequency of one is tuned with respect to the other, the output frequency of the photomixer increases smoothly and the output power is nearly constant up to 20 GHz. At higher frequencies the power decays because of parasitic capacitance.

Over the three-year course of this program, several issues in the device physics of resonant-tunneling diodes (RTDs) have been investigated, including the small-signal admittance, the shot noise, and the transport through multiple-quantum well structures. A large quantum-well inductance has been measured in the negative-differential-resistance region (NDR), but not in the positive-differential-resistance (PDR) region. The microwave shot-noise has been found to be suppressed relative to normal shot-noise in the PDR region, but enhanced in the NDR region. Triple-well RTDs have displayed a much wider NDR region in voltage than conventional single-well RTDs. Several new RTD material systems have been demonstrated including Type-II InAS/AlSb and Type-I GaSb/AlSb, the first of which has yielded excellent properties for high-speed device applications. Studies of highly lattice mismatched InAs/AlSb RTDs on GaAs substrates have proven that the RTD characteristics are insensitive to a high density of dislocations. Finally, these results have been incorporated into the design of RTDs in high-frequency oscillators and high-speed switches. The InGaAs/AlAs RTD has been optimized for application in a quasioptical fundamental-frequency oscillator operating above 200 GHz. The same material system has been used to make a low-power RTD load for heterojunction field- effect and bipolar transistors in high-performance digital integrated circuits.

This report covers a study of the effects of broadening the specifications for JP-4 and JP-8, by increasing the freeze point, decreasing the smoke point, and extending the end point on minimizing costs and maximizing fuel availability. The study considered the impact on the engines and airframes. It was concluded that the specification maximum allowable freeze point of JP-4 or JP-8 could not be increased without degrading aircraft system performance and safety on the basis of criteria available to this study. Increases in availability were predicted for JP-4 of up to 9% and for JP-8 between 41% and 62%. A fuel price analysis was performed based on prices through 1978. Price changes subsequent to the analysis have been so rapid and so unbalanced between products that predictions cannot be made of price changes resulting from specification changes. (Author), Prepared in cooperation with Union Oil Co. of California, Union Science and Technology Div., and Pratt and Whitney Aircraft Group, Government Products Div.

Recycling of aged asphalt concrete pavements has been demonstrated to be cost-effective and to reduce the demand for natural resources such as aggregate and asphalt. Because of the advantages derived when using recycled materials, the capability to predict long-term performance is needed so that optimum benefits can be obtained. This study was undertaken to evaluate the laboratory performance to recycled asphalt concrete mixtures and to compare these results to those measured for conventional asphalt concrete mixtures. Results of this study indicated a satisfactory comparison between laboratory performance of recycled mixtures and conventional mixtures. Fatigue analysis indicated that conventional mixtures would provide the greatest fatigue resistance in thick asphalt concrete layers at lower temperatures, while the recycled mixtures would provide the greatest fatigue resistance in thin asphalt layers at higher temperatures. Water susceptability was shown to be related more to aggregate type than to mixture type. The data show that recycled mixtures prepared with the recycling agent produced mixtures with the lowest durability and poorest low temperature performance when compared with the recycled mixtures prepared with AC-5 or compared with the conventional mixtures.

compiled and surveyed under the direction of the Commissioners by James Slade ; H.M. Wightman, surveyor ; E.R. Brown, del., "This plan also includes portions of the adjacent territory in the cities of Boston and Roxbury and the town of Brookline.", Shows property owners and selected buildings of interest., "Dec. 31st, 1861.", Oriented with north toward the upper right., Shows radial distance from City Hall.

Shortly after construction fat spots began to appear throughout the project on a 3 inch hot mix asphalt (HMA) overlay of an existing PCC pavement. The fat spots appeared to occur at end of truck loads. After time the fat spots developed into potholes and the asphalt appeared to be stripped from the aggregate at the bottom of the potholes. Some rutting and shoving also developed at these fat spots. The objective of this study was to evaluate the HMA and to determine potential causes of these fat spots. The test plan included a visual inspection of the pavement and obtaining core samples from fat spots, adjacent to fat spots and from random locations throughout the project. Rut depth, measurements were also obtained. The cores were tested for asphalt content, gradation, void content and slag content. Several of the asphalt mix layers were split in half (resulting in top and bottom halves) and the asphalt content and gradation of each half compared. The asphalt cement from several cores were recovered and the viscosity and penetration determined. The results of this study indicated that the most likely cause of the fat spots was contamination of the HMA with some solvent (likely diesel) during the placement operation. (22 p.)