Orientation-dependent pseudomorphic growth of InAs for use in lattice-mismatched mid-infrared photonic structures

In this study, InAs was deposited on GaAs (100) and GaAs (111)B 2 degrees towardssubstrates for the purpose of differentiating the InAs growth mode stemming from strain and then analyzed using in-situ reflection high energy electron diffraction, scanning electron microscopy, Raman spectroscopy, reflectance spectroscopy, and atomic force microscopy. The procession of InAs deposition throughout a range of deposition conditions results in assorted forms of strain relief revealing that, despite lattice mismatch for InAs on GaAs (approximately 7%), InAs does not necessarily result in typical quantum dot/wire formation on (111) surfaces, but instead proceeds two-dimensionally due primarily to the surface orientation

Wandering intellect, intuition and chance in architecture

Improvisation is the art of fabrication with what is at hand. It fosters spontaneous decisions, but it is not random. It becomes a spiritual wandering of intuitive, intellectual, and chance components. Improvisation happens in the process of making art and architecture, and is experienced by wandering through the process using rational, intuitive, and chance components. This phenomenon is expressed in architecture, Abstract Expressionism, and jazz improvisation. These art forms are a synthesis of intellect, intuition, and chance based on culture, environment and memory, which reconstruct our place in the world. Heidegger and Piaget provide the philosophical foundation for this argument. Architecture engages these issues and is a vivid reflection and expression of our environment. The art forms of jazz improvisation and abstract expressionism also exhibit aspects of wandering and gathering. Classical and Avant-Garde literary sources will be used in support of wandering through the intellect by intuition and chance. Through wandering, such as Odysseus in Homer's epic, one's place in in the world is found

Influence of Gluteus Medius Strength on Interlimb Asymmetry in Female Recreational Runners.

PURPOSE: Running-related injuries are most often single-sided and are partially attributed to lower limb movement and loading asymmetries.1 Gluteus Medius (GM) plays a significant role in lower limb alignment, especially in the frontal and transverse planes by its influence on the pelvis and the femur.2 Female runners are more prone to GM weakness which has been proposed to be a risk factor for overuse injuries.3 These strength deficits contribute to abnormal lower limb kinematics and kinetics during dynamic tasks like running and jumping.4 These changes include an increase in peak hip adduction angle (HA), hip internal rotation angle (HI), knee abduction moment (KA) and rearfoot eversion angle (RE).4 Symmetry Angle (SA) is a commonly-used, robust measure of determining symmetry.1 No study has evaluated the role of unilateral GM strength on interlimb asymmetry for HA, HI, KA and RE during running. We hypothesized that female runners with stronger GM would demonstrate decreased interlimb asymmetry for HI, HA, KA and RE during running. METHODS: Thirty healthy female recreational runners (Age: 35.40±10.52 yrs, Height: 1.66±0.06 m, Weight: 61.61±7.31 kg) running at least 10 km per week participated in this study. Isometric GM strength was measured using a handheld dynamometer for the right lower limb and participants were divided into two groups of stronger and weaker. 3D gait analysis was conducted as participants ran on an instrumented treadmill at 2.98 m/s. Peak HA, HI, KA and RE were generated for the bilateral lower extremities and interlimb asymmetry using SA was calculated for all variables. A Shapiro-Wilk test for normality was conducted and it showed that all variables were not normally distributed. Wilcoxon Two-Sample Test was performed to look at differences between the two groups for HA, HI, KA and RE. RESULTS: Female runners with weaker GM demonstrated significantly increased asymmetry for HA (18.80±24.11 vs 12.20±24.11 %, p=0.02), HI (18.47±24.11 vs 12.53±24.11 %, p=0.03), and KA (18.33±24.11 vs 12.67±24.11 %, p=0.04). For RE, the weaker group had greater asymmetry (16.13±24.11 vs 14.87±24.11 %, p=0.35), but the relationship was not significant. CONCLUSIONS: This study suggested that runners with weaker GM on one side exhibited increased interlimb asymmetry during running for certain kinematic and kinetic variables. Future studies should determine how unilateral and bilateral strength deficits contribute to interlimb asymmetry and running biomechanics in healthy and injured runners.https://scholarscompass.vcu.edu/uresposters/1290/thumbnail.jp

Classification of Radar Targets Using Invariant Features

Automatic target recognition ATR using radar commonly relies on modeling a target as a collection of point scattering centers, Features extracted from these scattering centers for input to a target classifier may be constructed that are invariant to translation and rotation, i.e., they are independent of the position and aspect angle of the target in the radar scene. Here an iterative approach for building effective scattering center models is developed, and the shape space of these models is investigated. Experimental results are obtained for three-dimensional scattering centers compressed to nineteen-dimensional feature sets, each consisting of the singular values of the matrix of scattering center locations augmented with the singular values of its second and third order monomial expansions. These feature sets are invariant to translation and rotation and permit the comparison of targets modeled by different numbers of scattering centers. A metric distance metric is used that effectively identifies targets under real world conditions that include noise and obscuration

Using Cross-Eye Techniques to Counter Radio Frequency Agile Monopulse Processing

The purpose of this research was to evaluate how current cross-eye techniques protect an airborne platform versus a pulse-to-pulse Radio Frequency (RF) agile monopulse processing threat and, if necessary, develop a new cross-eye techniques to counter this threat. This research evaluates how both current retrodirective cross-eye techniques and an original technique, namely synchronized cross-eye, hide the true skin return in the time and frequency domain while preserving the necessary phase interferometric effects at the threat radar location. Existing retrodirective cross-eye techniques are inadequate to counter the RF agile threat due to propagation delays. Using modeling and simulation, the research shows that geometrically dependent parameters are virtually constant on a pulse-to-pulse basis. If a low Radar Cross Section source can be deployed and, given that it is illuminated first by the threat radar, cross-eye jamming waveforms at the threat can hide the skin return in time and reproduce the necessary phase interferometric pattern, but small frequency differences between the two jamming sources occur at the threat radar location. Fortunately, these differences can only be detected if the threat employs up-front Doppler processing. Monopulse processing radars are a true threat to airborne platforms. Existing countermeasure techniques may not be able to deal with a monopulse processing radar with random, pulse-to-pulse Radio Frequency (RF) agility. This thesis examines the effects current cross-eye techniques have against RF agile threats and investigates an alternative form of cross-eye, synchronized cross-eye, to counter RF agile threats

Computerized Construction of a Seasonal Flow-Duration Table

Various graphical methods have been developed to handle the statistical data gathered for hydrological studies. Those most familiar are probably the hydrograph, the mass curve, and the flow-duration curve. The first two graphical techniques have been in use for numerous years and as a result, are described in many textbooks. The first published writings dealing with the flow-duration curve are believed to have been released in about 1878. However, the general use of the flow-duration curve started around the year 1915, but as late as 1934 it was felt that many of the fundamental principles of the flow-duration curve were not fully understood by many engineers. Flow-duration curves and tables are statistical devices which show the probability of occurrence of different flows. In actuality, the flow-duration curve or table gives the percentage of time a certain flow is equaled or exceeded. A further discussion on the definition, construction, and uses of the flow-duration table and curve will be presented later in this paper. A series of studies on the seasonal flow characteristics of various river basins in eastern South Dakota have been conducted at South Dakota State University. During the course of these studies of the seasonal variations in stream flow, conducted by Rakness and Chen. It was considered useful to construct the flow-duration curves for the streams being studied. It was shown by Rakness that an annual flow-duration curve or table will not depict the seasonal variations of a stream. That is to say, while a given flow may be equaled or exceeded 50% of the time, the annual flow-duration curve does not indicate when the flow is available. For example, the time when the flow is available is extremely important in the case of irrigation, water supply, fish life propagation, pollution control, or for any other usage where the demand is seasonal. As a result of these studies and the apparent utility of the seasonal flow-duration table, it became apparent that a computer program capable of constructing the seasonal flow-duration table directly from the given records would be an important tool for hydrological studies. This awareness of the need for a computer program to construct the seasonal flow-duration table resulted in the study described in this paper

Spectroscopy studies of straincompensated mid-infrared QCL active regions on misoriented substrates

In this work, we perform spectroscopic studies of AlGaAs/InGaAs quantum cascade laser structures that demonstrate frequency mixing using strain-compensated active regions. Using a three-quantum well design based on diagonal transitions, we incorporate strain in the active region using single and double well configurations on various surface planes (100) and (111). We observe the influence of piezoelectric properties in molecular beam epitaxy grown structures, where the addition of indium in the GaAs matrix increases the band bending in between injector regions and demonstrates a strong dependence on process conditions that include sample preparation, deposition rates, mole fraction, and enhanced surface diffusion lengths. We produced mid-infrared structures under identical deposition conditions that differentiate the role of indium(strain) in intracavity frequency mixing and show evidence that this design can potentially be implemented using other material systems