Timothy N. Miller

RFI suppression for ultra wideband radar

An estimate-and-subtract algorithm is presented for the real-time digital suppression of radio frequency interference (RFI) in ultrawideband (UWB) synthetic aperture radar (SAR) systems used for foliage- and ground-penetrating imaging. The algorithm separately processes fixed- and variable-frequency interferers. Excision of estimated targets greatly reduces bias in RFI estimates, thereby reducing target energy loss and sidelobe levels in SAR imagery. Performance is demonstrated on data collected with the Army Research Laboratorys UWB rail SAR.

Booster: Reactive core acceleration for mitigating the effects of process variation and application imbalance in low-voltage chips

Lowering supply voltage is one of the most effective techniques for reducing microprocessor power consumption. Unfortunately, at low voltages, chips are very sensitive to process variation, which can lead to large differences in the maximum frequency achieved by individual cores. This paper presents Booster, a simple, low-overhead framework for dynamically rebalancing performance heterogeneity caused by process variation and application imbalance. The Booster CMP includes two power supply rails set at two very low but different voltages. Each core can be dynamically assigned to either of the two rails using a gating circuit. This allows cores to quickly switch between two different frequencies. An on-chip governor controls the timing of the switching and the time spent on each rail. The governor manages a “boost budget” that dictates how many cores can be sped up (depending on the power constraints) at any given time. We present two implementations of Booster: Booster VAR, which virtually eliminates the effects of core-to-core frequency variation in near-threshold CMPs, and Booster SYNC, which additionally reduces the effects of imbalance in multithreaded applications. Evaluation using PARSEC and SPLASH2 benchmarks running on a simulated 32-core system shows an average performance improvement of 11% for Booster VAR and 23% for Booster SYNC.

VRSync: characterizing and eliminating synchronization-induced voltage emergencies in many-core processors

Power consumption is a primary concern for microprocessor designers. Lowering the supply voltage of processors is one of the most effective techniques for improving their energy efficiency. Unfortunately, low-voltage operation faces multiple challenges going forward. One such challenge is increased sensitivity to voltage fluctuations, which can trigger so-called “voltage emergencies” that can lead to errors. These fluctuations are caused by abrupt changes in power demand, triggered by processor activity variation as a function of workload. This paper examines the effects of voltage fluctuations on future many-core processors. With the increase in the number of cores in a chip, the effects of chip-wide activity fluctuation - such as that caused by global synchronization in multithreaded applications - overshadow the effects of core-level workload variability. Starting from this observation, we developed VRSync, a novel synchronization methodology that uses emergency-aware scheduling policies that reduce the slope of load fluctuations, eliminating emergencies. We show that VRSync is very effective at eliminating emergencies, allowing voltage guardbands to be significantly lowered, which reduces energy consumption by an average of 33%.

The Classification Systems of Stress Fractures: A Systematic Review

Abstract Background: Stress fractures of the upper and lower extremity are troublesome overuse injuries in athletes and nonathletes alike. These injuries have a broad spectrum of severity and prognosis. We performed a systematic search of the literature, which revealed multiple classification systems; however, we did not uncover a general system that offered both validated radiographic and clinical parameters. Methods: A literature search was conducted using Ovid/Medline, Embase, and the Cochrane Library, with publication dates ranging from 1960 to December 2009. Inclusion criteria included all studies and review articles regarding stress or fatigue fractures and their classification. Results: Forty-three studies and/or articles were identified for this review. Of these articles, 27 classification systems were referenced. Sixteen of the systems were applicable to any injury location, and 1 applied to specific bones (femoral neck, tibia, tarsal navicular, pars interarticularis, and fifth metatarsal). Four classification systems were referenced more often than others. Of the classification systems, 11 were based on radiographs alone, while the other 16 used a variety of radiographic modalities, including radiographs, bone scans, computed tomography, ultrasound, and magnetic resonance imaging. Conclusion: There are many different stress fracture classification systems in the literature. These systems employ various imaging modalities, but few include clinical parameters. Many are site specific. Of those that are widely applicable, no general classification system has been shown to be reproducible, easily accessible, safe, inexpensive, and clinically relevant. A gold standard classification system for describing stress fractures has yet to be determined.

The comprehensive description of stress fractures: a new classification system.

BACKGROUND Stress fractures represent a fatigue failure of bone, occurring with a spectrum of severity of structural injury, and healing potential varies by location. There is no comprehensive classification system for stress fractures incorporating both clinical and radiographic characteristics of the injury that is applicable to all bones. We introduce a system that is reproducible, generalizable, easy to use, and clinically relevant, with three descriptors: fracture grade, fracture location, and imaging modality. METHODS After a review of current classification systems, a five-tier system was proposed to determine fracture grade: Grade I indicated asymptomatic stress reaction on imaging, Grade II indicated pain with no fracture line, Grade III indicated non-displaced fracture, Grade IV indicated displaced fracture, and Grade V indicated nonunion. Example cases of each grade with clinical vignettes and images were prepared to test the interobserver and intraobserver reliability of the system by the test and retest evaluation among fifteen clinicians. A questionnaire and recall test assessed the ease of use, clinical applicability, and recall accuracy. RESULTS Test and retest analysis showed that the system had almost perfect agreement in intraobserver reliability with a kappa value of 0.81. The overall intraobserver reliability showed almost perfect agreement with a kappa value of 0.81. Almost perfect agreement with a kappa value of 0.83 was also produced when these responses were compared with our assessment. The overall interobserver reliability had substantial agreement with a kappa value of 0.78. The reliability of the group compared with that of the answer key was almost perfect with a kappa value of 0.83. The recall test showed an overall accuracy of 97.3%. Of the fifteen evaluators who completed questionnaires, fourteen (93.3%) said that the system would be easily remembered, would facilitate communication among colleagues, and would be useful in clinical practice. CONCLUSIONS The proposed stress fracture classification system is clinically relevant, easily applied, and generalizable, and has excellent interobserver and intraobserver reliability.

Mitigating the Effects of Process Variation in Ultra-low Voltage Chip Multiprocessors using Dual Supply Voltages and Half-Speed Units

Energy efficiency is a primary concern for microprocessor designers. One very effective approach to improving processor energy efficiency is to lower its supply voltage to very near to the transistor threshold voltage. This reduces power consumption dramatically, improving energy efficiency by an order of magnitude. Low voltage operation, however, increases the effects of parameter variation resulting in significant frequency heterogeneity between (and within) otherwise identical cores. This heterogeneity severely limits the maximum frequency of the entire CMP. We present a combination of techniques aimed at reducing the effects of variation on the performance and energy efficiency of near-threshold, many-core CMPs. Dual Voltage Rail (DVR), mitigates core-to-core variation with a dual-rail power delivery system that allows post-manufacturing assignment of different supply voltages to individual cores. This speeds up slow cores by assigning them to a higher voltage and saves power on fast cores by assigning them to a lower voltage. Half-Speed Unit (HSU) mitigates within-core variation by halving the frequency of select functional blocks with the goal of boosting the frequency of individual cores, thus raising the frequency ceiling for the entire CMP. Together, these variation-reduction techniques result in almost 50% improvement in CMP performance for the same power consumption over a mix of workloads.

Flexible Error Protection for Energy Efficient Reliable Architectures

Technology scaling is having an increasingly detrimental effect on microprocessor reliability, with increased variability and higher susceptibility to errors. At the same time, as integration of chip multiprocessors increases, power consumption is becoming a significant bottleneck that could threaten their growth. To deal with these competing trends, energy-efficient solutions are needed to deal with reliability problems. This paper presents a reliable multicore architecture that provides targeted error protection by adapting to the characteristics of individual cores and workloads, with the goal of providing reliability with minimum energy. The user can specify an acceptable reliability target for each chip, core, or application. The system then adjusts a range of parameters, including replication and supply voltage, to meet that reliability goal. In this multicore architecture, each core consists of a pair of pipelines that can run independently (running separate threads) or in concert (running the same thread and verifying results). Redundancy is enabled selectively, at functional unit granularity. The architecture also employs timing speculation for mitigation of variation-induced timing errors and to reduce the power overhead of error protection. On-line control based on machine learning dynamically adjusts multiple parameters to minimize energy consumption. Evaluation shows that dynamic adaptation of voltage and redundancy can reduce the energy delay product of a CMP by 30 − 60% compared to static dual modular redundancy.

Arthroscopic evaluation and treatment of biceps brachii long head tendon injuries: A survey of the MOON shoulder group

Context: Injuries to the biceps brachii long head tendon commonly occur in conjunction with tears in the rotator cuff and glenoid labrum. Consensus on treatment of varying levels of severity is undetermined. Settings and Design: We surveyed members of the Multicenter Orthopedic Outcomes Network (MOON) Shoulder Group, to determine a consensus on arthroscopic grading and treatment. Aims: We hypothesized that the Lafosse classification system would show a high level of inter- and intraobserver agreement regarding grading/treatment. Materials and Methods: Arthroscopic videos of 30 patients determined to have biceps brachii long head tendon injuries were viewed by 13 surgeons. The surgeons graded the severity of the injury macrostructure based on the Lafosse classification system and chose from a list of treatment options. Four months later the same surgeons viewed the same videos and repeated the survey. Statistical Analysis Used: Analysis with weighted and non-weighted Kappa values was performed to determine intra- and interobserver reliability for severity grading and to determine the preferred treatments for each level of severity. Results: Intraobserver reliability testing for the Lafosse system showed substantial agreement after two rounds (81.28%, K=0.7006). Interobserver testing demonstrated substantial agreement for Grade 0 (K=0.7152), fair agreement for Grade 1 (K=0.3803), and moderate agreement for Grade 2 (K=0.5156). Combined responses recommended no surgical treatment for 95.4% of the lesions classified as grade 0 (62/65). No surgical treatment was recommended for Grade 1 lesions in 24.1% of the cases (35/145), debridement in 38.6% (56/145), and tenotomy or tenodesis in 37.2% (54/145). Evaluators preferred tenotomy or tenodesis for 98.3% of the Grade 2 lesions (177/180). Conclusions: Analysis of the Lafosse system indicated substantial intraobserver reliability for all grades. As Grades 1 and 2 showed only fair and moderate agreement, a need for a reliable grading system still exists. Grade 2 lesions should be treated with tenotomy or tenodesis. A preferred treatment for Grade 1 lesions could not be determined given the high variability of responses. Higher-powered surveys may help determine the ideal treatment of Grade 1 injuries.

Nyami: a synthesizable GPU architectural model for general-purpose and graphics-specific workloads

Graphics processing units (GPUs) continue to grow in popularity for general-purpose, highly parallel, high-throughput systems. This has forced GPU vendors to increase their focus on general purpose workloads, sometimes at the expense of the graphics-specific workloads. Using GPUs for general-purpose computation is a departure from the driving forces behind programmable GPUs that were focused on a narrow subset of graphics rendering operations. Rather than focus on purely graphics-related or general-purpose use, we have designed and modeled an architecture that optimizes for both simultaneously to efficiently handle all GPU workloads. In this paper, we present Nyami, a co-optimized GPU architecture and simulation model with an open-source implementation written in Verilog. This approach allows us to more easily explore the GPU design space in a synthesizable, cycle-precise, modular environment. An instruction-precise functional simulator is provided for co-simulation and verification. Overall, we assume a GPU may be used as a general-purpose GPU (GPGPU) or a graphics engine and account for this in the architectures construction and in the options and modules selectable for synthesis and simulation. To demonstrate Nyamis viability as a GPU research platform, we exploit its flexibility and modularity to explore the impact of a set of architectural decisions. These include sensitivity to cache size and associativity, barrel and switch-on-stall multithreaded instruction scheduling, and software vs. hardware implementations of rasterization. Through these experiments, we gain insight into commonly accepted GPU architecture decisions, adapt the architecture accordingly, and give examples of the intended use as a GPU research tool.

Evaluation of High-Strength Orthopedic Sutures: A Head-to-Head Comparison

The goal of this study was to determine whether a difference in cycles to failure or mode of failure would be observed among specimens of 3 high-strength suture materials, and whether different suture configurations would affect knot security. Ten representative specimens of Ethibond (Ethicon, Inc, Somerville, New Jersey), FiberWire (Arthrex, Inc, Naples, Florida), MaxBraid (Biomet, Inc, Warsaw, Indiana), and Orthocord (DePuy Orthopaedics, Warsaw, Indiana) were tied in 6 different knot configurations commonly used in orthopedic procedures. Each specimen was cyclically loaded between 9 and 180 N at a rate of 1 Hz until the specimen failed or reached a maximum of 3500 cycles. Each suture material was subjected to tensile loading until failure at a rate of 1.25 mm/s. The 3 most secure knots all included the 3 reverse half-hitch on alternating posts (3-RHAP) configuration. All specimens tied with these 3 knot types failed by suture rupture. All knots using the overhand with 3 of the same half-hitches on the same post (O-3SHSP) configuration failed by knot slippage regardless of suture material. When the 3 strongest knots were combined, FiberWire resisted a significantly greater number of fatigue cycles than Orthocord or MaxBraid. In the single load to failure tests, Orthocord, FiberWire, and MaxBraid all had significantly higher ultimate strength than Ethibond. Knots using the 3-RHAP configuration provide security superior to that of those without this configuration. All 3 high-strength sutures tested outperformed Ethibond in single load to failure testing, with FiberWire resisting the greatest number of cycles. Postoperative strength and reliability of a soft tissue repair is inherently dependent on the properties of the suture materials used.