Browsing by Author "Lockhart, Thurmon E."

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    Active Noise Reduction Versus Passive Designs in Communication Headsets: Speech Intelligibility and Pilot Performance Effects in an Instrument Flight Simulation
    Valimont, Robert Brian (Virginia Tech, 2006-04-20)
    Researchers have long known that general aviation (GA) aircraft exhibit some of the most intense and potentially damaging sound environments to a pilot's hearing. Yet, another potentially more ominous result of this noise-intense environment is the masking of the radio communications. Radio communications must remain intelligible, as they are imperative to the safe and efficient functioning of the airspace, especially the airspace surrounding our busiest airports, Class B and Class C. However, the high amplitude, low frequency noise dominating the GA cockpit causes an upward spreading of masking with such inference that it renders radio communications almost totally unintelligible, unless the pilot is wearing a communications headset. Even with a headset, some researchers have stated that the noise and masking effects overcome the headset performance and still threaten the pilot's hearing and overall safety while in the aircraft. In reaction to this situation, this experiment sought to investigate the effects which active noise reduction (ANR) headsets have on the permissible exposure levels (PELs), speech intelligibility, workload, and ultimately the pilot's performance inside the cockpit. Eight instrument-rated pilot participants flew through different flight tasks of varying levels and types of workload embedded in four 3.5 hour flight scenarios while wearing four different headsets. The 3.5 hours were considered long duration due the instrument conditions, severe weather conditions, difficult flight tasks, and the fatiguing effects of a high intensity noise environment. The noise intensity and spectrum in the simulator facility were specifically calibrated to mimic those of a Cessna 172. Speech intelligibility of radio communications was modified using the Speech Transmission Index (STI), while measures of flight performance and workload were collected to examine any relationships between workload, speech intelligibility, performance, and type of headset. It is believed that the low frequency attenuation advantages afforded by the ANR headset decreased the signal-to-noise ratio, thereby increasing speech intelligibility for the pilot. This increase may positively affect workload and flight performance. Estimates of subjective preference and comfort were also collected and analyzed for relevant relationships. The results of the experiment supported the above hypotheses. It was found that headsets which incorporate ANR technology do increase speech intelligibility which has a direct inverse influence on workload. For example, an increase in speech intelligibility is seen with a concomitant decrease in pilot workload across all types and levels of workload. Furthermore, flight task performance results show that the pilot's headset can facilitate safer flight performance. However, the factors that influence performance are more numerous and complex than those that affect speech intelligibility or workload. Factors such as the operational performance of the communications system in the headset, in addition to the ANR technology, were determined to be highly influential factors in pilot performance. This study has concluded that the pilot's headset has received much research and design attention as a noise attenuation device. However, it has been almost completely overlooked as a tool which could be used to facilitate the safety and performance of a general aviation flight. More research should focus on identifying and optimizing the headset components which contribute most to the results demonstrated in this experiment. The pilot's headset is a component of the aviation system which could economically improve the safety of the entire system.
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    Activity Recognition Processing in a Self-Contained Wearable System
    Chong, Justin Brandon (Virginia Tech, 2008-09-12)
    Electronic textiles provide an effective platform to contain wearable computing elements, especially components geared towards the application of activity recognition. An activity recogni tion system built into a wearable textile substrate can be utilized in a variety of areas including health monitoring, military applications, entertainment, and fashion. Many of the activity recognition and motion capture systems previously developed have several drawbacks and limitations with regard to their respective designs and implementations. Some such systems are often times expensive, not conducive to mass production, and may be difficult to calibrate. An effective system must also be scalable and should be deployable in a variety of environments and contexts. This thesis presents the design and implementation of a self-contained motion sensing wearable electronic textile system with an emphasis toward the application of activity recognition. The system is developed with scalability and deployability in mind, and as such, utilizes a two-tier hierarchical model combined with a network infrastructure and wireless connectivity. An example prototype system, in the form of a jumpsuit garment, is presented and is constructed from relatively inexpensive components and materials.
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    Age-Related Ankle Strength Degradation and Effects on Slip-Induced Falls
    Khuvasanont, Tanavadee (Virginia Tech, 2002-07-18)
    Each year there is an increasing incidence of slip and fall accidents, especially among the elderly population. Existing evidence has identified several aging effects related to slip and fall accidents, yet, the causes of these accidents with advancing age are still little known. The objective of this research was to investigate the factors influencing the initial phase of unexpected slips and falls in younger and older individuals. More specifically, the relationship between ankle strength, the ankle joint power to transfer the whole body center-of-mass during normal gait, and the likelihood of slip-induced falls was identified. The walking experiment and the ankle strength tests were conducted in the Locomotion Research Laboratory, Virginia Tech. Fourteen old (67-79 years old) and 14 young (19-35 years old) individuals participated in this study (7 male and 7 female for each age group).Within a subsequent 20-minute session of natural walking on a linear track, kinematic and kinetic data were collected synchronously. A slippery surface was introduced to the participant on the purpose of unexpected slip event. The ankle strength tests were performed using a dynamometer. The results indicated that ankle strength degradation in older individuals was related to the outcome of slips (i.e., higher frequency of falls). The results also indicated that older individuals' RCOF was less than their younger counterparts. However, older individuals fell more often than younger individuals. It is concluded that friction demand characteristics may not be a total deterministic factor of fall accidents. Thus, the further research should focus not only on the dynamic of slips, but also on the dynamics of falls.
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    The Age-Related Dynamic Accommodative Characteristics Associated With Light Intensity and Chromaticity
    Shi, Wen (Virginia Tech, 2007-12-04)
    Visual accommodation plays a critical role in one's visual perception and activities of daily living. The age-related accommodation loss poses a greater risk to older adults' safety and independence. Although extensive effort has been made to study the effects of aging on accommodation, the relationship between aging and the dynamic aspects of accommodation is still unknown. Furthermore, since light is the carrier of external stimuli for accommodation, it is of value to assess the influences of light on the age-related accommodation loss. Therefore, a study was conducted to investigate the age-related dynamic accommodative characteristics under various conditions of the intensity and chromaticity of light. To ascertain the effects of aging, ten individuals from each of three age groups (i.e., younger group: 20 to 29 years old, middle-aged group: 40 to 49 years old, and older group: 60 to 69 years old) were recruited, and their dynamic accommodation responses were examined. Laboratory experiments were designed to measure accommodation in a simulated condition where a person must alternate from viewing outside to reading the dashboard while driving. It was hypothesized that the advancing of age will lead to the deterioration of one's dynamic accommodative performance, and light of different intensities and chromaticities will interact with the effects of aging on accommodation. The results of the study supported the above hypotheses. It was found that the advancing of age, the decrease of light intensity, and the change of light chromaticity all led to the alteration of one's dynamic accommodative performance. The present study concluded with a biomechanical and neural model elaborating the mechanism of an accommodation process within the scope of the study.
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    The Age-Related Effects of Visual Input on Multi-Sensory Weighting Process During Locomotion and Unexpected Slip Perturbations
    Jongprasithporn, Manutchanok (Virginia Tech, 2011-09-09)
    Falls are the leading cause of fatal and non-fatal injuries among older adults. Age-related sensory degradation may increase instability and increase the risk of slips and falls in older adults. The integration of three sensory systems (visual, proprioceptive, and vestibular systems) and the respective weighting of each are needed to maintaining balance during unexpected slip-induced falls. The visual system is often thought of as the most important sensory system in playing a major role in stabilizing posture, guiding locomotion and controlling slip response. However, previous studies have focused on the age-related effects of visual input on static postural stability. The age-related effects of visual input associated with locomotion and unexpected slip perturbations (i.e., dynamic tasks) remains unclear. The purpose of this study is to investigate the age-related effects of visual input on multi-sensory processing during locomotion and unexpected slip perturbations. Fifteen young and fifteen old adults were recruited to participate in this study. Motion capture system, force plate, and EMG data were collected during the experiments. Various biomechanical and neuromuscular characteristics were identified to quantify the age-related effects of visual input during locomotion and unexpected slip perturbations. The results indicate that temporary loss of visual input during walking could cause individuals to adopt a more cautious gait strategy to compensate for their physical and neuronal changes as shown in increased double support time and higher co-contraction (i.e., stiffness) of the knee and ankle joints. Older adults also have higher co-contraction at the ankle joint during walking as compared with young adults. Regarding slip-induced falls, temporary loss of visual input causes increased slip distances and response times of upper and lower limbs in both younger and older groups. In terms of kinematics, the combination of age and temporary loss of visual input influenced the perturbed limb. In terms of muscle activation patterns, temporary loss of visual input may increase the proprioceptive gain as shown in early muscle activity onset, increased muscle activation duration, and increased co-contraction at the knee joint. However, stiffness may increase the difficulty to detect a slip event and reduce flexibility and increase slip-induced falls. Although the human body cannot fully compensate for the temporary loss of visual input, the results in this study suggest that the reweighting process increases proprioceptive gain while visual input is unavailable. These findings support the implication of future research in order to understand the potential hazards which could occur while walking and slipping with temporary loss of visual input. The results may also contribute to the design of effective interventions to improve motor learning by applied visual occlusion in slips/falls training to reduce fall risk and enhance safety. The visual occlusion paradigm may assist to increase learning encoded in intrinsic coordination, related to motor performance skill, providing the flexibility required to adapt to complex environments such as slip-induced falls.
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    Aging effect on successful reactive-recovery from unexpected slips: a 3D lower extremity joint moment analysis
    Liu, Jian (Virginia Tech, 2004-09-14)
    The objective of the proposed study was to perform three-dimensional (3D) inverse dynamics analysis to determine lower extremity (ankle, knee and hip) joint moments on previously collected slip perturbation experimental data. In addition, the aging effect on the joint moment generation in both normal walking and reactive-recovery conditions was examined. Dataset collected during previous slip and fall experiments, which were conducted in a typical gait analysis setting, were analyzed in current study. All the participants were subjected to the screening criteria, which defined the successful reactive-recovery (i.e. non-fall trials) based on slip distance, sliding heel velocity, whole body COM velocity, and motion pictures. Nine young and nine old healthy participants, who were identified possessing representative trials, were involved as participants in current study. A local coordinate system was constructed on each joint and each segment of the lower extremity based on available landmarks using the Gram-Schmidt orthogonalization algorithm. 3D inverse dynamics was implemented to obtained lower extremity joint moments. Magnitude and timing of obtained joint moment patterns during stance phase were subjected to one and two-way analysis of covariance (ANCOVA) with walking velocity as covariate. The aging effect and gait condition effect were evaluated. Increases in peak joint moment, peak joint power, and joint moment generation ratio were detected in successful reactive-recovery. Distinct age-related joint moment generation strategy was observed through findings of peak joint moment ratio and joint moment generation rate. The elderly, who were able to reactive recover, were found to be as rapid as their younger counterparts in terms of initiating and developing reactive joint moment. It was concluded that ankle joint was critical in balance recovery while hip joint assumed the major responsibility of balance maintenance of upper body during successful reactive-recovery. Increased demand on muscle strength during balance recovery lead to the distinct joint moment generation strategy adopted by the elderly, and confirmed the necessity of lower extremity strength training. In addition, implementation of 3D joint moment analysis was justified in current study and was suggested in future slip and fall researches.
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    Ambulatory Fall Event Detection with Integrative Ambulatory Measurement (IAM) Framework
    Liu, Jian (Virginia Tech, 2008-08-29)
    Injuries associated with fall accidents pose a significant health problem to society, both in terms of human suffering and economic losses. Existing fall intervention approaches are facing various limitations. This dissertation presented an effort to advance indirect type of injury prevention approach. The overall objective was to develop a new fall event detection algorithm and a new integrative ambulatory measurement (IAM) framework which could further improve the fall detection algorithm's performance in detecting slip-induced backward falls. This type of fall was chosen because slipping contributes to a major portion of fall-related injuries. The new fall detection algorithm was designed to utilize trunk angular kinematics information as measured by Inertial Measurement Units (IMU). Two empirical studies were conducted to demonstrate the utility of the new detection algorithm and the IAM framework in fall event detection. The first study involved a biomechanical analysis of trunk motion features during common Activities of Daily Living (ADLs) and slip-induced falls using an optical motion analysis system. The second study involved collecting laboratory data of common ADLs and slip-induced falls using ambulatory sensors, and evaluating the performance of the new algorithm in fall event detection. Results from the current study indicated that the backward falls were characterized by the unique, simultaneous occurrence of an extremely high trunk extension angular velocity and a slight trunk extension angle. The quadratic form of the two-dimensional discrimination function showed a close-to-ideal overall detection performance (AUC of ROCa = 0.9952). The sensitivity, specificity, and the average response time associated with the specific configuration of the new algorithm were found to be 100%, 95.65%, and 255ms, respectively. The individual calibration significantly improved the response time by 2.4% (6ms). Therefore, it was concluded that slip-induced backward fall was clearly distinguishable from ADLs in the trunk angular phase plot. The new algorithm utilizing a gyroscope and orientation sensor was able to detect backward falls prior to the impact, with a high level of sensitivity and specificity. In addition, individual calibration provided by the IAM framework was able to further enhance the fall detection performance.
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    An Analytical Motion Filter for Humanoid Robots
    Muecke, Karl James (Virginia Tech, 2009-03-31)
    Mimicking human motion with a humanoid robot can prove to be useful for studying gaits, designing better prostheses, or assisting the elderly or disabled. Directly mimicking and implementing a motion of a human on a humanoid robot may not be successful because of the different dynamic characteristics between them, which may cause the robot to fall down due to instability. Using the Zero Moment Point as the stability criteria, this work proposes an Analytical Motion Filter (AMF), which stabilizes a reference motion that can come from human motion capture data, gait synthesis using kinematics, or animation software, while satisfying common constraints. In order to determine how the AMF stabilized a motion, the different kinds of instabilities were identified and classified when examining the reference motions. The different cases of instability gave more insight as to why a particular motion was unstable: the motion was too fast, too slow, or inherently unstable. In order to stabilize the gait two primary methods were utilized: time and spatial scaling. Spatial scaling scaled the COM trajectory down towards a known stable trajectory. Time scaling worked similarly by changing the speed of the motion, but was limited in effectiveness based on the types of instabilities in the motion and the coupling of the spatial directions. Other constraints applied to the AMF and combinations of the different methods produced interesting results that gave more insight into the stability of the gait. The AMF was tested using both simulations and physical experiments using the DARwIn miniature humanoid robot developed by RoMeLa at Virginia Tech as the test platform. The simulations proved successful and provided more insight to understanding instabilities that can occur for different gait generation methods. The physical experiments worked well for non-walking motions, but because of insufficient controllability in the joint actuators of the humanoid robot used for the experiment, the high loads during walking motions prevented them from proper testing. The algorithms used in this work could also be expanded to legged robots or entirely different platforms that depend on stability and can use the ZMP as a stability criterion. One of the primary contributions of this work was showing that an entire reference motion could be stabilized using a single set of closed form solutions and equations. Previous work by others considered optimization functions and numeric schemes to stabilize all or a portion of a gait. Instead, the Analytical Motion Filter gives a direct relationship between the input reference motion and the resulting filtered output motion.
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    Biomechanical adaptations of human gait due to external loads
    Lee, Minhyung (Virginia Tech, 2008-08-01)
    Gait is the method of human locomotion using limbs. Recently, the analysis of human motion, specifically human gait, has received a large amount of research attention. Human gait can contain a wide variety of information that can be used in biometrics, disease diagnosis, injury rehabilitation, and load determination. In this dissertation, the development of a model-based gait analysis technique to classify external loads is presented. Specifically, the effects of external loads on gait are quantified and these effects are then used to classify whether an individual gait pattern is the result of carrying an external load or not. First of all, the reliability of using continuous relative phase as a metric to determine loading condition is quantified by intra-class correlation coefficients (ICC) and the number of required trials is computed. The ICC(2, 1) values showed moderate reliability and 3 trials are sufficient to determine lower body kinematics under two external load conditions. Then, the work was conducted to provide the baseline separability of load carriage conditions into loaded and unloaded categories using several lower body kinematic parameters. Satisfactory classification of subjects into the correct loading condition was achieved by resorting to linear discriminant analysis (LDA). The baseline performance from 4 subjects who were not included in training data sets shows that the use of LDA provides an 88.9% correct classification over two loaded and unloaded walking conditions. Extra weights, however, can be in the form of an external load carried by an individual or excessive body weight carried by an overweight individual. The study now attempts to define the differences in lower body gait patterns caused by either external load carriage, excessive body weight, or a combination of both. It was found significant gait differences due to external load carriage and excessive body weight. Principal Component Analysis (PCA) was also used to analyze the lower body gait patterns for four loading conditions: normal weight unloaded, normal weight loaded, overweight unloaded and overweight loaded. PCA has been shown to be a powerful tool for analyzing complex gait data. In this analysis, it is shown that in order to quantify the effects of external loads for both normal weight and overweight subjects, only two principal components (PCs) are needed. The results in this dissertation suggest that there are gait pattern changes due to external loads, and LDA could be applied successfully to classify the gait patterns with an unknown load condition. Both load carriage and excessive body weight affect lower body kinematics, but it is proved that they are not the same loading conditions. Methods in the current work also give a potential for new medical and clinical ways of investigating gait effects in osteoarthritis patients and/or obese people.
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    Biomechanical analysis of effects of neuromusculoskeletal training for older adults on the likelihood of slip-induced falls
    Kim, Sukwon (Virginia Tech, 2006-02-06)
    Research Objectives The objective of this study was to evaluate if neuromusculoskeletal training (i.e., weight and balance training) for older adults could reduce the likelihood of slip-induced fall accidents. The study focused on evaluating biomechanics among the elderly at pre- and post-training stages during processes associated with slip-induced fall accidents. Motivations: Older adults are at a higher risk of falls due to deficient gait characteristics and postural control, especially when facing unexpected external perturbations such as slippery surfaces. The literature (Alexander et al., 1992; Englander 1996; Hausdorff, 2001; Rizzo 1998) indicates that falls among the elderly over 65 result in enormous economic and personal losses, therefore, the losses must be diminished. The results from this study can provide intervention strategies for researchers, health care individuals, and the elderly and their families in reducing the likelihood of slip-induced falls. Background: More than 25% of older adults fall every year (Sattin, 1992), and older adults and their family members fear their falls and fall-related injuries due to the associated high mortality rate (Jensen, 2003). The Center for Disease Control (CDC) reported in 2003 that emergency departments treated more than 1.6 million seniors due to fall-related injuries and, among them, 373,000 were admitted to the hospital. In 2002, The National Safety Council reported that 14,500 people died due to fall-related accidents, and 60 percent of them were 65 years of age and older. To minimize economic and personal losses, tribometric techniques for assessing shoe/floor interactions, the biomechanical responses in walking on slippery floor surfaces, and postural control were studied. Still, the elderly population is at a high risk of falling, severe enough that it is a major cause of hospitalization (CDC, 2003). Yet reasons for slip-induced fall accidents are not clear. Therefore, mechanisms involving fall accidents must be explored and, further, interventions to minimize fall accidents must be discovered and implemented. The occurrence of falls among the elderly are postulated to result from neuromusculoskeletal aging. The changes in neuromusculoskeletal components with advancing age are commonly accompanied with mobility problems and poor health status contributing to a decreased physical capability such as a reduction in lower extremity strength (Larsson et al., 1979; Lord et al., 1991 and 1994; Murray et al. 1985; Stalberg et al., 1989; Whipple et al. 1987) and insecure and unconfident balance (Manchester et al. 1989; Stelmach and Sirica, 1987; Teasdale et al. 1991; Thelen et al., 1998; Woolacott, 1986) leading to unstable dynamic postural control and poor gait dynamics (Alexander, 1994; Judge, 2003; Lockhart et al., 2003; Wolfson, 2001). Unstable dynamic postural control and poor gait dynamics influence the likelihood of falls among older adults (Guralnik et al.1994; Judge et al.1996; Lockhart et al., 2003; Tinetti et al. 1988). Therefore, in an effort to improve unstable dynamic postural control and poor gait dynamics, strength and balance training have been proposed and implemented. (Campbell et al., 1999; Day et al., 2002; Fiatarone et al., 1994; Neil, 1994; Shepard et al., 1993; Tinetti et al, 1994; Wolfson et al, 1993). Problem Statement: Although the significance of muscle strengthening and balance training in reducing falls for older adults has been addressed previously, most studies (Berg et al., 1992; Duncan et al., 1990; Guralnik et al.,1994; Hageman et al., 1995; Nashner, 1993; Nashner and McCollum, 1985; Nevitt et al., 1989; Overstall et al., 1977; Rikli and Jones, 1999; Tinetti, 1986) have focused on the effect of muscle strengthening and balance training on the static and dynamic postural control such as quite standing, one-leg stand, the sit-to-stand test, the test of precise movement, functional reaching, or the mobility test. Yet, research to evaluate the effectiveness of muscle strengthening and balance training on actual slip-induced fall events was lacking. This study were carried out to evaluate the likelihood of falls at pre- and post stages of training by incorporating and validating the effectiveness of training utilizing actual perturbations commonly associated with slips and falls. Method: 18 older adults participated in the study for 8 weeks: 6 individuals in balance group, 6 individuals in weight group, and 6 individuals in control group (social group). Each group met three times a week and each session lasted for 1 hour. Biomechanical dependent measures and psychosocial dependent measures were evaluated to the effects of training. Results: The results indicated that, overall, training resulted in improvements in biomechanical dependent measures. Further, regular social activities resulted in improvements in proprioception sensory sensitivity and in ankle dorsiflexion muscular strength. Conclusion: Balance training contributed to an improvement in ankle flexibility, whereas, weight training did not contribute to an improvement in ankle flexibility although either weight or balance training played a role in decreasing slip-propensity and the likelihood of slip-induced falls among older adults. An ability to integrate neuro-musculo-skeletal systems was improved by training and was a main contributor in reducing the likelihood of slip-induced falls. Proprioception sensitivity by itself did not play a role in decreasing the likelihood of slip-induced falls. In addition, the exercise training as well as social activities played a role in altering psychosocial behavior (i.e. fear of falling and independency) of older adults. The author concluded that an ability to integrate neuro-musculo-skeletal systems could be improved by either balance or weight training and could be a primary factor contributing to a reduction in the likelihood of slip-induced falls among older adults. In addition, the author concluded that the regular social activities also could contribute to an enhancement in the psychosocial characteristics of older adults.
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    Bipedal Walking for a Full Size Humanoid Robot Utilizing Sinusoidal Feet Trajectories and Its Energy Consumption
    Han, Jea-Kweon (Virginia Tech, 2012-04-24)
    This research effort aims to develop a series of full-sized humanoid robots, and to research a simple but reliable bipedal walking method. Since the debut of Wabot from Waseda University in 1973, several full-sized humanoid robots have been developed around the world that can walk, and run. Although various humanoid robots have successfully demonstrated their capabilities, bipedal walking methods are still one of the main technical challenges that robotics researchers are attempting to solve. It is still challenging because most bipedal walking methods, including ZMP (Zero Moment Point) require not only fast sensor feedback, but also fast and precise control of actuators. For this reason, only a small number of research groups have the ability to create full-sized humanoid robots that can walk and run. However, if we consider this problem from a different standpoint, the development of a full-sized humanoid robot can be simplified as long as the bipedal walking method is easily formulated. Therefore, this research focuses on developing a simple but reliable bipedal walking method. It then presents the designs of two versions of a new class of super lightweight (less than 13 kg), full-sized (taller than 1.4 m) humanoid robots called CHARLI-L (Cognitive Humanoid Autonomous Robot with Learning Intelligence – Lightweight) and CHARLI-2. These robots have unique designs compared to other full- sized humanoid robots. CHARLI-L utilizes spring assisted parallel four-bar linkages with synchronized actuation to achieve the goals of lightweight and low cost. Based on the experience and lesions learned from CHARLI-L, CHARLI-2 uses gear train reduction mechanisms, instead of parallel four-bar linkages, to increase actuation torque at the joints while further reducing weight. Both robots successfully demonstrated untethered bipedal locomotion using an intuitive walking method with sinusoidal foot movement. This walking method is based on the ZMP method. Motion capture tests using six high speed infrared cameras validate the proposed bipedal walking method. Additionally, the total power and energy consumptions during walking are calculated from measured actuator currents.
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    Characterization of a Sea-State Simulator for Ergonomic Studies
    Bateman, David Brenton (Virginia Tech, 2011-03-30)
    With the use of tow-tank experiments, data may be generated for ships of various classes using comprehensive instrumentation. This data gives the ability to determine the response of ships to various sea-state conditions far in advanced of their construction and launch. However, this data does not indicate the effects of those sea-states to the individuals aboard that ship. In order to define these effects a sea-state simulator must be designed and built. Once construction is completed a series of test must be conducted to determine the response of the simulator. This response allows the comparison to actual tow-tank data to determine if the simulator is capable of performing the desired research.
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    Classifying Step and Spin Turns Using Wireless Gyroscopes and Implications for Fall Risk Assessments
    Fino, Peter C.; Frames, Christopher W.; Lockhart, Thurmon E. (MDPI, 2015-05-06)
    Recent studies have reported a greater prevalence of spin turns, which are more unstable than step turns, in older adults compared to young adults in laboratory settings. Currently, turning strategies can only be identified through visual observation, either in-person or through video. This paper presents two unique methods and their combination to remotely monitor turning behavior using three uniaxial gyroscopes. Five young adults performed 90° turns at slow, normal, and fast walking speeds around a variety of obstacles while instrumented with three IMUs (attached on the trunk, left and right shank). Raw data from 360 trials were analyzed. Compared to visual classification, the two IMU methods’ sensitivity/specificity to detecting spin turns were 76.1%/76.7% and 76.1%/84.4%, respectively. When the two methods were combined, the IMU had an overall 86.8% sensitivity and 92.2% specificity, with 89.4%/100% sensitivity/specificity at slow speeds. This combined method can be implemented into wireless fall prevention systems and used to identify increased use of spin turns. This method allows for longitudinal monitoring of turning strategies and allows researchers to test for potential associations between the frequency of spin turns and clinically relevant outcomes (e.g., falls) in non-laboratory settings.
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    Comparing LED Lighting Systems in the Detection and Color Recognition of Roadway Objects
    Terry, Travis N. (Virginia Tech, 2011-05-11)
    This study compared two LED luminaires and their abilities to provide detection distance and color recognition distance of potential roadway hazard. Detection distance is regarded as a metric of visibility. Color recognition distance is a metric for comparing the impact of the (Correlated Color Temperature) CCT of each luminaire and their color contrast impact. Mesopic vision, the mode of vision most commonly used for night driving, was considered in this study. Off-axis objects were presented to participants to assess the peripheral abilities of the luminaires. The impacts of luminance and color contrast were addressed in this study. The experiment was performed on the Virginia Smart Road where standard objects of different colors and pedestrians wearing different colors were detected by drivers of a moving vehicle in a controlled environment. The key difference between the two luminaires was their color temperatures (3500K versus 6000K). The results indicated that neither light source provided a significant benefit over the other although significant interactions were found among object color, age, and lighting level. The results indicate that the luminaires provide similar luminance contrast but their color contrasts depend heavily on the color temperature, the object, and the observer. This study followed the protocol developed by the Mesopic Optimisation of Visual Efficiency (MOVE) consortium developed by the CIE for modeling mesopic visual behavior.
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    Design and Analysis of a Low-Power Low-Voltage Quadrature LO Generation Circuit for Wireless Applications
    Wang, Shen (Virginia Tech, 2012-08-31)
    The competitive market of wireless communication devices demands low power and low cost RF solutions. A quadrature local oscillator (LO) is an essential building block for most transceivers. As the CMOS technology scales deeper into the nanometer regime, design of a low-power low-voltage quadrature LO still poses a challenge for RF designers. This dissertation investigates a new quadrature LO topology featuring a transformer-based voltage controlled oscillator (VCO) stacked with a divide-by-two for low-power low-voltage wireless applications. The transformer-based VCO core adopts the Armstrong VCO configuration to mitigate the small voltage headroom and the noise coupling. The LO operating conditions, including the start-up condition, the oscillation frequency, the voltage swing and the current consumption are derived based upon a linearized small-signal model. Both linear time-invariant (LTI) and linear time-variant (LTV) models are utilized to analyze the phase noise of the proposed LO. The results indicate that the quality factor of the primary coil and the mutual inductance between the primary and the secondary coils play an important role in the trade-off between power and noise. The guidelines for determining the parameters of a transformer are developed. The proposed LO was fabricated in 65 nm CMOS technology and its die size is about 0.28 mm2. The measurement results show that the LO can work at 1 V supply voltage, and its operation is robust to process and temperature variations. In high linearity mode, the LO consumes about 2.6 mW of power typically, and the measured phase noise is -140.3 dBc/Hz at 10 MHz offset frequency. The LO frequency is tunable from 1.35 GHz to 1.75 GHz through a combination of a varactor and an 8-bit switched capacitor bank. The proposed LO compares favorably to the existing reported LOs in terms of the figure of merit (FoM). More importantly, high start-up gain, low power consumption and low voltage operation are achieved simultaneously in the proposed topology. However, it also leads to higher design complexity. The contributions of this work can be summarized as 1) proposal of a new quadrature LO topology that is suitable for low-power low-voltage wireless applications, 2) an in-depth circuit analysis as well as design method development, 3) implementation of a fully integrated LO in 65 nm CMOS technology for GPS applications, 4) demonstration of high performance for the design through measurement results. The possible future improvements include the transformer optimization and the method of circuit analysis.
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    Determination of Normal or Abnormal Gait Using a Two-Dimensional Video Camera
    Smith, Benjamin Andrew (Virginia Tech, 2007-04-06)
    The extraction and analysis of human gait characteristics using image sequences and the subsequent classification of these characteristics are currently an intense area of research. Recently, the focus of this research area has turned to the realm of computer vision as an unobtrusive way of performing this analysis. With such systems becoming more common, a gait analysis system that will quickly and accurately determine if a subject is walking normally becomes more valuable. Such a system could be used as a preprocessing step in a more sophisticated gait analysis system or could be used for rehabilitation purposes. In this thesis a system is proposed which utilizes a novel fusion of spatial computer vision operations as well as motion in order to accurately and efficiently determine if a subject moving through a scene is walking normally or abnormally. Specifically this system will yield a classification of the type of motion being observed, whether it is a human walking normally or some other kind of motion taking place within the frame. Experimental results will show that the system provides accurate detection of normal walking and can distinguish abnormalities as subtle as limping or walking with a straight leg reliably.
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    Developing an Electronic Tool for Cross-Cultural Computer Supported Collaborative Work (CCSCW)
    Vu, Jimmy M. (Virginia Tech, 2004-03-15)
    There is a lack of tools available to support cross-cultural communication and collaboration. Current research is comprised of assessments of the need for better cross-cultural communication tools and discussions of simple guidelines for developing such a tool. Existing programs such as chat or video-conferencing have been altered to be used in a cross-cultural setting, but little data has been gathered on their effectiveness. There is a need, according to the literature in the field of Computer Supported Collaborative Work (CSCW), that cross-cultural tools be developed, researched, and comprehensively studied. The purpose of this research was to show that a simple cross-cultural communication tool can be developed to support electronic cross-cultural collaborations. BlissChat was developed in Virginia Tech's Macroergonomics and Group Decision Systems Laboratory for this purpose. The dependent measures for the study consisted of the time of completion and errors committed. The experimental design was a 2 x 2 between factor design. The factors were divided into a concordant (same language culture) group versus a discordant (different language culture) group. The other independent variable was the environment, whether they used the communication tool BlissChat, or in the ideal setting of face-to- face (FtF). The two culture groups used were Chinese first language speakers and English first language speakers. Participants who used BlissChat were able to perform their tasks as accurately as those who met FtF by not committing significantly more errors (p<0.05), but they did not perform as efficiently. The participants using BlissChat did not perform as efficiently as those meeting FtF (p<0.05). It took participants using BlissChat much longer to perform their task than participants in FtF conditions (p<0.05). The consequence of these outcomes will effect both the current use as well as the future outcomes of CCSCW.
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    Developing and Evaluating New Methods for Assessing Postural Control and Dynamics
    Zhang, Hong Bo (Virginia Tech, 2013-03-15)
    Falls are the leading cause of injuries among older adults (>65) and frequently result in reduced mobility, loss of independence, decreased quality of life, injury, and death.  Extensive research has been conducted regarding postural coordination and control, and other mechanisms/processes involved in maintaining postural stability.  However, there is relatively limited knowledge regarding the patterns of joint coordination, the underlying postural controller, and efficient methods to assess passive and active musculoskeletal properties relevant to balance.  In the current work, three new methods were developed to address these limitations and also to better understand the effects of localized ankle muscle fatigue, gender, and aging on postural coordination and control. First, two methods were used to evaluate postural coordination.  A wavelet coherence approach was developed and applied to assess the level and pattern of coordination between pairs of joints (i.e., ankle-knee, ankle-trunk, and ankle-head).  In addition, the uncontrolled manifold method was implemented for evaluation of potential whole-body coordination control goals.  Clear patterns of intermittent wavelet coherence were evident, indicating that joint coordination is intermittently executed.  Both in-phase and anti-phase coherence were detected over frequencies of 2.5 -- 4.0 Hz.  Shoulder and head kinematics appeared more likely than the whole-body center of mass as control goals for whole body coordination.  Both aging and ankle muscle fatigue led to a reduction of joint coordination. Second, an intermittent sliding mode controller was developed to model quiet upright stance.  In contrast to most previous postural controllers, which assume continuous control, an intermittent controller was considered more consistent with recent evidence on muscle activity and the results of the first study on postural coordination.  The sliding mode controller was able to accurately track kinematics and kinetics, and generated passive and active ankle torques comparable with previous results.  Ankle fatigue led to an increase in active ankle torque especially among young adults and males. Third, a new method was developed to estimate passive and active mechanical properties at the ankle (e.g., stiffness and damping).  This method was inspired from intermittent control theory, and the earlier results noted.  As opposed to conventional methods, this new method is computationally efficient and does not require external mechanical or sensory perturbations.  The method yielded a ratio of passive to active ankle torques consistent with earlier evidence, and larger passive and active ankle torques among males and older adults.  A post-fatigue increase of active ankle torque was estimated, especially among males and young adults. In addition to providing new analytical methods, the noted studies suggest that older adults have decreased joint coordination and increased ankle stiffness.  As a practical implication of this, fall prevention training programs may benefit from seeking to develop appropriate joint coordination strategies and ankle stiffness magnitudes.  To expand on the current work, future research should consider measuring muscle contraction characteristics at multiple joints and in different postures or activities.
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    Dynamic Visual Performance Characteristics of Elderly Drivers
    Raj, Pankaj (Virginia Tech, 2005-08-10)
    The objective of the present study was to understand how the visual and mental processes work in tandem to affect the overall information processing capability of the individual, especially the older population, in a dynamic visual task such as driving. More specifically, our aim was to understand how the different parameters related to display of visual information in an in-vehicle display system and the age of the subject affect the information processing performance. The effects of stimulus distance, target size, display time, bits of information and the age group of the subject (young versus old) on the reading performance (information processing ability) under photopic and scotopic viewing conditions were thoroughly investigated in this study. Fifty-six individuals (28 young, 28 elderly) from the Montgomery County region were tested in the study in a mixed factorial repeated measures design with age as between subjects and the other independent variables as within subjects. The dependent variable was the reading score, i.e., the number of letters correctly identified. Results obtained from this study revealed that all of the independent variables had significant effects on the reading performance of the participants, except ambient illumination. Specifically, age has an important influence on the specific values of the design parameters. Also, these parameters interact among themselves so that one can be used to compensate for the other. These results can be used for developing the most relevant and optimal in-vehicle visual displays for the older population.
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    Dynamical Properties of Postural Control in Obese Community-Dwelling Older Adults
    Frames, Christopher W.; Soangra, Rahul; Lockhart, Thurmon E.; Lach, John; Ha, Dong Sam; Roberto, Karen A.; Lieberman, Abraham (MDPI, 2018-05-24)
    Postural control is a key aspect in preventing falls. The aim of this study was to determine if obesity affected balance in community-dwelling older adults and serve as an indicator of fall risk. The participants were randomly assigned to receive a comprehensive geriatric assessment followed by a longitudinal assessment of their fall history. The standing postural balance was measured for 98 participants with a Body Mass Index (BMI) ranging from 18 to 63 kg/m2, using a force plate and an inertial measurement unit affixed at the sternum. Participants’ fall history was recorded over 2 years and participants with at least one fall in the prior year were classified as fallers. The results suggest that body weight/BMI is an additional risk factor for falling in elderly persons and may be an important marker for fall risk. The linear variables of postural analysis suggest that the obese fallers have significantly higher sway area and sway ranges, along with higher root mean square and standard deviation of time series. Additionally, it was found that obese fallers have lower complexity of anterior-posterior center of pressure time series. Future studies should examine more closely the combined effect of aging and obesity on dynamic balance.