Loss-resilient Coding of Texture and Depth for Free-viewpoint Video Conferencing

Free-viewpoint video conferencing allows a participant to observe the remote 3D scene from any freely chosen viewpoint. An intermediate virtual viewpoint image is commonly synthesized using two pairs of transmitted texture and depth maps from two neighboring captured viewpoints via depth-image-based rendering (DIBR). To maintain high quality of synthesized images, it is imperative to contain the adverse effects of network packet losses that may arise during texture and depth video transmission. Towards this end, we develop an integrated approach that exploits the representation redundancy inherent in the multiple streamed videos a voxel in the 3D scene visible to two captured views is sampled and coded twice in the two views. In particular, at the receiver we first develop an error concealment strategy that adaptively blends corresponding pixels in the two captured views during DIBR, so that pixels from the more reliable transmitted view are weighted more heavily. We then couple it with a sender-side optimization of reference picture selection (RPS) during real-time video coding, so that blocks containing samples of voxels that are visible in both views are more error-resiliently coded in one view only, given adaptive blending will erase errors in the other view. Further, synthesized view distortion sensitivities to texture versus depth errors are analyzed, so that relative importance of texture and depth code blocks can be computed for system-wide RPS optimization. Experimental results show that the proposed scheme can outperform the use of a traditional feedback channel by up to 0.82 dB on average at 8% packet loss rate, and by as much as 3 dB for particular frames

A biomechanical approach to prevent falls in ergonomic settings

Introduction: Fall-related injuries are exceptionally prevalent in occupational settings. While endangering the workers’ health, falls cause poor productivity and increased economic burden in the workplace. Hence, identifying these threats and training workers to achieve proper postural control is crucial. Purpose: Study 1: To investigate the ankle joint kinematics in unexpected and expected trip responses during single-tasking (ST), dual-tasking (DT), and triple-tasking (TT), before and after a physically fatiguing exercise. Study 2: To investigate the impact of virtual heights, DT, and training on static postural stability and cognitive processing. Methods: Study 1: Twenty collegiate volunteers (10 males and females, one left leg dominant, age 20.35 plus-minus 1.04 years, height 174.83 plus-minus 9.03 cm, mass 73.88 plus-minus 15.55 kg) were recruited. Ankle joint kinematics were recorded while treadmill walking during normal gait (NG), unexpected trip (UT), and expected trip (ET) perturbations with DT and physical fatigue. Study 2: Twenty-eight collegiate volunteers (14 males and females; all right leg dominant; age 20.48 plus-minus 1.26 years; height 172.67 plus-minus 6.66 cm; mass 69.52 plus-minus 13.78 kg; body mass index 23.32 plus-minus 3.54 kg/m2) were recruited. They were exposed to different virtual environments (VEs) over three days with and without DT. Postural sway parameters, lower extremity muscle activity, heart rate, and subjective anxiety parameters were collected. Results: Study 1: Greater maximum ankle angles were observed during UT compared to NG, MDT compared to ST, and TT compared to ST, while greater minimum ankle angles were observed during ET compared to NG and during post-fatigue compared to pre-fatigue. Study 2: Greater postural decrements and poor cognitive processing were observed in high altitudes and DT. Discussion & conclusions: Study 1: Trip recovery responses are different between during DT, TT, and fatigue. Study 2: Static postural stability deteriorates at higher virtual altitudes and with DT, while it improves with a two-day training. Virtual height exposure reduces cognitive performance. Importance: The findings of these studies will provide insights into the biomechanics of falls in ergonomic settings and aid in designing functional and convenient fall prevention programs

A Predictive Model of Nuclear Power Plant Crew Decision-Making and Performance in a Dynamic Simulation Environment

The safe operation of complex systems such as nuclear power plants requires close coordination between the human operators and plant systems. In order to maintain an adequate level of safety following an accident or other off-normal event, the operators often are called upon to perform complex tasks during dynamic situations with incomplete information. The safety of such complex systems can be greatly improved if the conditions that could lead operators to make poor decisions and commit erroneous actions during these situations can be predicted and mitigated. The primary goal of this research project was the development and validation of a cognitive model capable of simulating nuclear plant operator decision-making during accident conditions. Dynamic probabilistic risk assessment methods can improve the prediction of human error events by providing rich contextual information and an explicit consideration of feedback arising from man-machine interactions. The Accident Dynamics Simulator paired with the Information, Decision, and Action in a Crew context cognitive model (ADS-IDAC) shows promise for predicting situational contexts that might lead to human error events, particularly knowledge driven errors of commission. ADS-IDAC generates a discrete dynamic event tree (DDET) by applying simple branching rules that reflect variations in crew responses to plant events and system status changes. Branches can be generated to simulate slow or fast procedure execution speed, skipping of procedure steps, reliance on memorized information, activation of mental beliefs, variations in control inputs, and equipment failures. Complex operator mental models of plant behavior that guide crew actions can be represented within the ADS-IDAC mental belief framework and used to identify situational contexts that may lead to human error events. This research increased the capabilities of ADS-IDAC in several key areas. The ADS-IDAC computer code was improved to support additional branching events and provide a better representation of the IDAC cognitive model. An operator decision-making engine capable of responding to dynamic changes in situational context was implemented. The IDAC human performance model was fully integrated with a detailed nuclear plant model in order to realistically simulate plant accident scenarios. Finally, the improved ADS-IDAC model was calibrated, validated, and updated using actual nuclear plant crew performance data. This research led to the following general conclusions: (1) A relatively small number of branching rules are capable of efficiently capturing a wide spectrum of crew-to-crew variabilities. (2) Compared to traditional static risk assessment methods, ADS-IDAC can provide a more realistic and integrated assessment of human error events by directly determining the effect of operator behaviors on plant thermal hydraulic parameters. (3) The ADS-IDAC approach provides an efficient framework for capturing actual operator performance data such as timing of operator actions, mental models, and decision-making activities

Balance Recovery Response in Community-Dwelling Adults with Unilateral Transtibial Amputation and the Potential Benefits of a Weight-Shifting Balance Training Intervention

Previous studies have shown that individuals with various physical, sensory and neuromuscular impairments are at higher risks of falls. Individuals with unilateral transtibial amputation (UTTA) suffered from all these impairments, and tripping not surprisingly caused a considerable number of falls in this population. To study falls, researchers have to put participants in a well-protected environment and reproduce tripping fall scenarios. Furthermore, the perturbation delivery needs to be precise in terms of temporo-spatial timing. These features would ensure the quality of responses elicited and reproducibility of the results. Thus, in Chapter 2, we developed a treadmill-based perturbation delivery protocol and confirmed that by referencing ground reaction force, the system was able to consistently and precisely deliver perturbations in early stance phase to elicit tripping falls.Because tripping usually arrests only one side of the limb, individuals with UTTA may respond differently when encountering trips with their prosthetic versus non- prosthetic limb. Understanding the biomechanical differences in fall recovery response between these two tripping conditions will facilitate ideas for patient-specific intervention targeting tripping fall prevention. Therefore, in Chapter 3, we utilized the protocol developed in Chapter 2 to deliver destabilizing perturbations to the participants in order to examine the limb-to-limb differences during fall recovery. We found that while the gross fall recovery strategies (i.e. the stepping response) were similar, there existed key biomechanical differences. Perturbation during a static standing condition was typically arrested with the perturbed limb making the recovery step. Dynamic perturbation condition was recovered with the contralateral (non-perturbed) limb making the first recovery step followed by the ipsilateral limb making the reciprocal second recovery step. We observed that certain defined response times were longer when the recover step was executed by the prosthetic limb in both static and dynamic perturbation conditions, suggesting the impaired sensory detection or motor execution of the prosthetic limb. Currently, clinical practitioners are encouraged to include balance training in post amputation rehabilitation. A balance training that focuses on weight-shifting may prepare individuals with lower limb loss the essential ability to make successful recovery step when encountering destabilizing scenarios. However, it is currently unknown if a training program focusing solely on balance control can improve fall recovery response. Hence, in Chapter 4, we examined the effects of a 2-day weight-shifting balance training using protocols developed in Chapters 2 and 3. We found that certain biomechanical variables relevant to weight-shifting and weight-bearing during fall recovery were altered by the training. For instance, the duration for unloading the prosthetic limb before taking the recovery step during static perturbation condition were improved after training. Another example was that when the prosthetic limb was perturbed, the duration of the first recovery step increased; meanwhile, when the non-prosthetic limb was perturbed, the duration of the second recovery step increased. These two durations were the non- prosthetic limb executing the recovery step in which the prosthetic limb providing the stance support, and the stance time increased. Overall, our findings suggest that sensorimotor deficits related to UTTA may lead to longer duration of step time when the prosthetic limb executed the recovery step. This is a promising direction to intervene in the future. Our balance training protocol appears to improve components that were related to participants’ weight-shifting ability. Whilst for altering the global fall recovery responses, we concluded that a more perturbation-based approach may be required and should be investigated in the future

Gettysburg: Our College\u27s Magazine Winter 2015

Table of Contents: From the President Janet Morgan Riggs \u2777 Scholarship Expands Access to STEM Fields (Diane Allwardt Trobaugh \u2767) Office Hours: Prof. Florence Ramond Jurney Budding Entrepreneur Helps Buyers Find Sellers (Wei Xiong \u2715, Prof. Cliff Presser) Board of Trustees Appoints Two (James Banks Jr. \u2780, Troy Datcher \u2790) The 411: Lauren Wise Bright \u2790 Bullets Play LAX for Turkey and Thailand (Jake Adoni \u2716, Reed Barbe \u2716, Bijan Firouzan \u2715) The Changing Future of Farming (Enzo Pinga \u2711) Frank Arbogast \u2716 Creating a Culture of Success Beth O\u27Boyle \u2798 Coach Credits Current and Past Bullets for NCAA Bid (Matt Garrett) Lincoln Trophy and F&M History Media Notes Conversations No Major No Problem: Gettysburg Grads Find Liberal Arts Education is Perfect Preparation for Careers in Communications Nikki Rhoads Contemporary Impressions (Geoffrey Jackson \u2791) Connecting the Dots: How a Dead African Rhino is a Threat to U.S. National Security (Prof. Shirley Anne Warshaw, Keith J. Masback \u2787) Better Fuel for the Fire: Improving Global Health One Hearth at a Time (Brady Luceno \u2708, Prof. Lisa Portmess) What Students Do (Prof. Steve Siviy) What Makes Gettysburg Great (Prof. William D. Bowman) Work That Makes a Difference (Benjamin Constable \u2713) Class Notes Life Unexpected Kathryn Rossetter \u2773https://cupola.gettysburg.edu/gburgmag/1003/thumbnail.jp

Identifying Gait Deficits in Stroke Patients Using Inertial Sensors

Falls remain a significant problem for stroke patients. Tripping, the main cause of falls, occurs when there is insufficient clearance between the foot and ground. Based on an individual’s gait deficits, different joint angles and coordination patterns are necessary to achieve adequate foot clearance during walking. However, gait deficits are typically only quantified in a research or clinical setting, and it would be helpful to use wearable devices – such as accelerometers – to quantify gait disorders in real-world situations. Therefore, the objective of this project was to understand gait characteristics that influence the risk of tripping, and to detect these characteristics using accelerometers. Thirty-five participants with a range of walking abilities performed normal walking and attempted to avoid tripping on an unexpected object while gait characteristics were quantified using motion capture techniques and accelerometers. Multiple regression was used to identify the relationship between joint coordination and foot clearance, and multiple analysis of variance was used to determine characteristics of gait that differ between demographic groups, as well as those that enable obstacle avoidance. Machine learning techniques were employed to detect joint angles and the risk of tripping from patterns in accelerometer signals. Measures of foot clearance that represent toe height throughout swing instead of at a single time point are more sensitive to changes in joint coordination, with hip-knee coordination during midswing having the greatest effect. Participants with a history of falls or stroke perform worse than older non-fallers and young adults on many factors related to falls risk, however, there are no differences in the ability to avoid an unexpected obstacle between these groups. Individuals with an inability to avoid an obstacle have lower scores on functional evaluations, exhibit limited sagittal plane joint range of motion during swing, and adopt a conservative walking strategy. Machine learning processes can be used to predict knee range of motion and classify individuals at risk for tripping based on an ankle-worn accelerometer. This work is significant because a portable device that detects gait characteristics relevant to the risk of tripping without expensive motion capture technology may reduce the risk of falls for stroke patients

Intra Coding Strategy for Video Error Resiliency: Behavioral Analysis

One challenge in video transmission is to deal with packet loss. Since the compressed video streams are sensitive to data loss, the error resiliency of the encoded video becomes important. When video data is lost and retransmission is not possible, the missed data should be concealed. But loss concealment causes distortion in the lossy frame which also propagates into the next frames even if their data are received correctly. One promising solution to mitigate this error propagation is intra coding. There are three approaches for intra coding: intra coding of a number of blocks selected randomly or regularly, intra coding of some specific blocks selected by an appropriate cost function, or intra coding of a whole frame. But Intra coding reduces the compression ratio; therefore, there exists a trade-off between bitrate and error resiliency achieved by intra coding. In this paper, we study and show the best strategy for getting the best rate-distortion performance. Considering the error propagation, an objective function is formulated, and with some approximations, this objective function is simplified and solved. The solution demonstrates that periodical I-frame coding is preferred over coding only a number of blocks as intra mode in P-frames. Through examination of various test sequences, it is shown that the best intra frame period depends on the coding bitrate as well as the packet loss rate. We then propose a scheme to estimate this period from curve fitting of the experimental results, and show that our proposed scheme outperforms other methods of intra coding especially for higher loss rates and coding bitrates

Bridging the gap between pupping and molting phenology: behavioral and ecological drivers in Weddell seals

Thesis (Ph.D.) University of Alaska Fairbanks, 2018In Antarctica, the narrow window of favorable conditions constrains the life history phenology of female Weddell seals (Leptonychotes weddellii) such that pupping, breeding, foraging, and molting occur in quick succession during summer; however, the carry-over effects from one life history event to another are unclear. In this dissertation, I characterize the phenological links between molting and pupping, and evaluate feeding behavior and ice dynamics as mechanistic drivers. First, I review the contributions of natural and sexual selection to the evolution of molting strategies in the contexts of energetics, habitat, function, and physiology. Many polar birds and mammals adhere to an analogous biannual molting strategy wherein the thin, brown summer feathers/fur are replaced with thick, white winter feathers/fur. Polar pinnipeds are an exception to the biannual molting paradigm; most rely on blubber for insulation and exhibit a single molt per year. Second, I describe the duration and timing of the Weddell seal molt based on data from 4,000 unique individuals. In adult females, I found that successful reproduction delays the molt by approximately two weeks relative to non-reproductive individuals. Using time-depth recorder data from 59 Weddell seals at the crucial time between pupping and molting, I report a striking mid-summer shallowing of seal dive depths that appears to follow a vertical migration of fishes during the summer phytoplankton bloom. The seals experience higher foraging success during this vertical shift in the prey distribution, which allows them to re-gain mass quickly before the molt. Across four years of study, later ice break-out resulted in later seal dive shallowing and later molt. In combination, the data presented in this dissertation suggest that molting, foraging, and pupping phenology are linked in Weddell seals and are affected by ice break-out timing.National Science Foundation Graduate Research Fellowship Program Grant No. DGE-124278