Dennis Kim

Modal Parameter Tuning of an Axisymmetric Resonator via Mass Perturbation

This paper reports the permanent frequency mismatch reduction of the primary wineglass modes in a planar axisymmetric resonator by strategic mass loading. The resonator consists of a set of concentric rings that are affixed to neighboring rings by a staggered system of spokes. The outer layers of spokes are targets for mass deposition. This paper develops modified ring equations that guide the mass perturbation process, and despite the fact that the deposited mass and deposition locations are quantized, it is possible to systematically reduce the frequency difference of the wineglass modes to effective degeneracy such that two modes cannot be distinguished in a frequency response plot. Results on five resonators are reported with nominal wineglass modes near 14 kHz, quality factors of 50k, and frequency mismatches exceeding 30 Hz in some cases, but with postperturbation mismatches smaller than 80 mHz. Furthermore, it is also shown that the quality factors remain unchanged.

Spectral Analysis of Vibratory Gyro Noise

This paper presents analysis of the noise spectra of closed-loop mode-matched vibratory gyros. Closed-form expressions for the noise-equivalent angular rate spectrum as well as the integrated angular rate (angle) variance are derived to explore the effects of modal frequency mismatch, closed-loop bandwidth, and the spectra of noise sources appearing at the sensors input and output. It is shown that noise sources located at the output of the sensors electromechanical transfer function create angle white noise in the closed-loop sensor. The angle white noise dominates the integrated rate behavior until it crosses the angle random walk asymptote at integration times exceeding the sensors open-loop time constant. Even though the closed-loop sensor asymptotically recovers the angle random walk figure associated with the mode-matched open-loop sensor, the results can be used to quantify the larger integrated rate variance that is produced as a consequence of extending the sensors bandwidth through feedback. A parameter, called the effective bandwidth, is introduced to capture the relative importance of the input noise versus output noise in determining the noise-equivalent rate spectrum. It is shown that the rate noise spectrum is robust to frequency mismatch as long as it does not exceed the effective bandwidth parameter. Empirical data obtained with a high performance MEMS vibratory gyro shows excellent agreement with the model predictions for a variety of sensor configurations including frequency-matched, frequency-mismatched, modified bandwidth, and manipulated input noise intensity cases.

Ventilator-associated pneumonia in severe traumatic brain injury: the clinical significance of admission chest computed tomography findings.

BACKGROUND Ventilator-associated pneumonia (VAP) in severe traumatic brain injury (STBI) is a significant morbidity. Bilateral dependent consolidation (BDC) can be seen on admission chest computed tomography (CCT) in STBI. We hypothesize that this finding may be associated with VAP. MATERIALS AND METHODS We retrospectively studied patients who sustained STBI after blunt injury and survived >48 h, who were admitted over a 40-mo period. We defined STBI as an admission Glasgow Coma Scale Score ≤ 8. We identified VAP by an elevated white blood cell count, a new infiltrate on chest x-ray, and a positive respiratory culture in a ventilated patient. Variables included demographics, injury, admission CCT, and culture data. We compared BDC-positive and BDC-negative patients. RESULTS There were 33 cases of VAP in 94 study patients (35.1%), in whom the incidence of intracranial pressure (ICP) monitoring (66.7% versus 39.3%; P = 0.011) was significantly increased. Ventilator-associated pneumonia was significantly increased in the 28 patients (29.8%) in the BDC-positive group (16 [57.1%] versus 17 (25.6%); P = 0.004). Bilateral dependent consolidation independently predicted VAP. In the 33 VAP cases, gram-negative organisms were present in 27 patients (81.8%), with a predominance of Enterobacteriaceae (16 patients [48.5%]). Culture results did not significantly differ between the early (<4 d) versus late or BDC-positive versus BDC-negative VAP groups. CONCLUSIONS Ventilator-associated pneumonia is common after STBI, and BDC is independently associated; however, there is no predilection for specific organisms. Admission CCT findings may prove useful in identifying a group of STBI patients at higher risk for VAP.

Association of Admission Laboratory Values and the Timing of Endoscopic Retrograde Cholangiopancreatography With Clinical Outcomes in Acute Cholangitis

Importance Acute cholangitis (AC), particularly severe AC, has historically required urgent endoscopic decompression, although the timing of decompression is controversial. We previously identified 2 admission risk factors for adverse outcomes in AC: total bilirubin level greater than 10 mg/dL and white blood cell count greater than 20 000 cells/µL. Objectives To validate previously identified prognostic factors in AC, evaluate the effect of timing of endoscopic retrograde cholangiopancreatography on clinical outcomes, and compare recent experience with AC vs an historical cohort. Design, Setting, and Participants A retrospective analysis (2008-2015) of patients with AC (validation cohort, n = 196) was conducted at 2 academic medical centers to validate predictors of adverse outcome. Timing of endoscopic retrograde cholangiopancreatography and outcome were stratified by severity using the Tokyo Guidelines for acute cholangitis diagnosis. Outcomes for the validation cohort were compared with the derivation cohort (1995-2005; n = 114). Data analysis was conducted from July 1, 2015, to September 9, 2015. Main Outcomes and Measures Death and a composite outcome of death or organ failure. Results The median age of patients in the derivation cohort was 54 years (interquartile range, 40-65 years) and in the validation cohort was 59 years (45-67 years). Multivariate logistic regression analysis of the validation cohort confirmed white blood cell count of more than 20 000 cells/µL (odds ratio, 3.4; 95% CI, 1.2-9.5; P = .02) and total bilirubin level of more than 10 mg/dL (odds ratio, 5.4; 95% CI, 1.8-16.4; P = .003) as independent risk factors for poor outcomes. In the validation cohort, timing of endoscopic retrograde cholangiopancreatography was not significantly different between those with and without an adverse outcome, even when stratified by AC severity (moderate: median, 0.6 hours [interquartile range (IQR), 0.5-0.9] vs 1.7 hours [IQR, 0.7-18.0] and severe: median, 10.6 hours [IQR, 1.2-35.1] vs 25.5 hours [IQR, 15.5-58.5] for those with and without adverse events, respectively). Patients in the validation cohort had a shorter hospital length of stay (median, 7 days [IQR, 4-10 days] vs 9 days [IQR, 5-16 days]) and lower rate of intensive care unit admission (26% vs 82%), despite a higher rate of severe cholangitis (n = 131 [67%] vs n = 29 [25%]). There were no significant differences in the composite outcome between the validation and derivation cohorts (22 [18.6%] vs 44 [22.4%]; P = .47). Adjusted analysis demonstrated decreased mortality in the validation cohort (odds ratio, 0.3; 95% CI, 0.1-0.7; P = .01). Conclusions and Relevance White blood cell count greater than 20 000 cells/µL and total bilirubin level greater than 10 mg/dL are independent prognostic factors for adverse outcomes in AC. Consideration should be given to include these criteria in the Tokyo Guidelines severity assessment. Timing of endoscopic retrograde cholangiopancreatography does not appear to affect clinical outcomes in these patients. Management of AC has improved with time, with an overall shorter hospital length of stay, lower rate of intensive care unit admission, and a decreased adjusted mortality, demonstrating improvements in care efficiency and delivery.

Tuning of MEMS Gyroscope using Evolutionary Algorithm and &#8220; switched drive-angle&#8221; method

We propose a tuning method for micro-electro-mechanical systems (MEMS) gyroscopes based on evolutionary computation that has the capacity to efficiently increase the sensitivity of MEMS gyroscopes through tuning and, furthermore, to find the optimally tuned configuration for this state of increased sensitivity. We present the results of an experiment to determine the speed and efficiency of an evolutionary algorithm applied to electrostatic tuning of MEMS micro gyros. The MEMS gyro used in this experiment is a Pyrex post resonator gyro (PRG) in a closed-loop control system. A measure of the quality of tuning is given by the difference in resonant frequencies, or frequency split, for the two orthogonal rocking axes. The current implementation of the closed-loop platform is able to measure and attain a relative stability in the sub-millihertz range, leading to a reduction of the frequency split to less than 100 mHz

Reading Habits of General Surgery Residents and Association With American Board of Surgery In-Training Examination Performance

IMPORTANCE Few large-scale studies have quantified and characterized the study habits of surgery residents. However, studies have shown an association between American Board of Surgery In-Training Examination (ABSITE) scores and subsequent success on the American Board of Surgery Qualifying and Certifying examinations. OBJECTIVES To identify the quantity of studying, the approach taken when studying, the role that ABSITE preparation plays in resident reading, and factors associated with ABSITE performance. DESIGN, SETTING, AND PARTICIPANTS An anonymous 39-item questionnaire including demographic information, past performance on standardized examinations, reading habits, and study sources during the time leading up to the 2014 ABSITE and opinions pertaining to the importance of the ABSITE was administered August 1, 2014, to August 25, 2014, to 371 surgery residents in 15 residency programs nationwide. MAIN OUTCOMES AND MEASURES Scores from the 2014 ABSITE. RESULTS A total of 273 residents (73.6%) responded to the survey. Seven respondents did not provide their January 2014 ABSITE score, leaving 266 for statistical analysis. Most respondents were male (162 of 266 [60.9%]), with a mean (SD) age of 29.8 (2.6) years. The median number of minutes spent studying per month was 240 (interquartile range, 120-600 minutes) for patient care or clinical duties and 120 for the ABSITE (interquartile range, 30-360 minutes). One hundred sixty-four of 266 respondents (61.7%) reported reading consistently throughout the year for patient care or clinical duties. With respect to ABSITE preparation, 72 of 266 residents (27.1%) reported reading consistently throughout the year, while 247 of 266 residents (92.9%) reported preparing between 1 and 8 weeks prior to the examination. Univariate analysis (with results reported as effect on median ABSITE percentile scores [95% CIs]) identified the following factors as positively correlated with ABSITE scores: prior United States Medical Licensing Examination (USMLE) 1 and 2 scores (per 1-point increase: USMLE 1, 0.1 [0.02-0.14], P = .03; USMLE 2, 0.3 [0.19-0.44], P < .001), prior Medical College Admission Test (MCAT) scores (per 1-point increase, 1.2 [1.3-2.0]; P = .002), high opinion of ABSITE significance (P < .001), surgical textbook use (11 [6-16]; P = .02), daily studying (13 [4-23]; P = .02), and high satisfaction with study materials (P < .001). On multivariable analysis, USMLE 2 score (per 1-point increase, 0.4 [0.2-0.6]; P < .001), MCAT score (0.6 [0.2-1.0]; P = .003), opinion of ABSITE significance (9.2 [6.9-11.6]; P < .001), and having an equal focus on patient care and ABSITE preparation during study (6.1 [0.6-11.5]; P = .03) were identified as positive predictors of ABSITE performance. CONCLUSIONS AND RELEVANCE Most residents reported reading consistently for patient care throughout the year. Daily studying and textbook use were associated with higher ABSITE scores on univariate analysis. Scores on the USMLE 2 and MCAT, as well as resident attitude regarding the importance of the ABSITE results, were independent predictors of ABSITE performance.

Dissecting Tuned MEMS Vibratory Gyros

Vibratory rate sensors exploit coriolis force coupling terms that exist between two lightly damped modes when the equations of motion are written in a sensor-fixed coordinate system. Feedback plays a central role in the function of these sensors because one mode is driven at its natural frequency to a target amplitude, despite the fact that the natural frequency may drift or disturbances may be present that would otherwise cause the response amplitude to change. This excitation loop is present in all vibratory rate sensors. The highest performance vibratory gyros, however, employ a force-to-rebalance controller that attenuates the motion of the second mode. In this case, two closed-loop signals are demodulated in order to estimate the angular rate of rotation of the sensor. This chapter explains in detail the advantages of operating high quality factor vibratory gyros in a “tuned” configuration in which the modal frequencies of both modes are equal. In high Q resonators, however, the bandwidth of the sensor is too low to be useful for the vast majority of applications and so a force-to-rebalance controller is necessary to increase the sensor bandwidth. We address some common misconceptions concerning the use of feedback and unequivocally show that the force-to-rebalance controller does not degrade the signal-to-noise ratio for frequencies below the mechanical bandwidth of the resonances. As a consequence of this property, the estimated change in angle of the gyro, that is the integrated estimated angular rate, employing force-to-rebalance feedback asymptotically approaches the optimum noise characteristics associated with the open-loop gyro. The analysis is complemented by experiments conducted with the Disk Resonator Gyro (DRG). Tuned sensor dynamics are of paramount importance so we present a systematic method that efficiently determines the biasing voltages that are necessary for tuning the DRG. This approach has been successfully applied to other vibratory gyro prototypes, but its most attractive feature is the fact that it lends itself to automation and, thus, is suited to a production environment. The zero rate bias and quadrature terms are also derived from a generic sensor model, and it is shown that aside from the dynamics of the sensor’s resonator, there are two critical dynamic elements in vibratory gyros that can impact the stability of the zero rate bias. Any change in phase of these dynamic elements will mix the zero rate bias and quadrature signals so as to produce a change in the apparent rate bias and, thus, these elements are a source of low-frequency drift in the rate signal.

A MEM vibratory gyro with mode-matching achieved by resonator mass loading

This paper presents preliminary performance results for a vibratory rate gyro based on a novel MEM resonator whose design facilitates frequency mismatch reduction via mass loading. A model-based systematic tuning algorithm was implemented to reduce the n=2 modal frequency mismatch without impacting the quality factors. Mass loading the resonator eliminates the need for electrostatic tuning and only a single bias voltage to the resonator is required for operation as a rate sensor. Force-to-rebalance operation with a 10Hz bandwidth yielded a minimum rate bias instability of 0.11deg/hr and an estimated angle random walk of 0.02 deg/root-hr. A decrease in rate noise was also demonstrated as the sensors cross-channel coupling was reduced by aligning the forcer/pick-off frame with the anti-nodes of the modes.

Tailored Etch Profiles for Wafer-Level Frequency Tuning of Axisymmetric Resonators

This paper reports a wafer-level technique for the systematic elimination of the modal frequency difference between a nominally degenerate pair of modes in an axisymmetric resonator design. A targeted etch process is developed in which masking resist and a conformal layer are ablated at specific sites on the resonator thereby exposing the underlying silicon and enabling site-specific mass removal by SiDRIE. A model of the perturbed resonator dynamics guides the selection of the ablation sites so that the subsequent timed etch reduces the modal frequency differences by a prescribed amount. This wafer-level process is demonstrated on seven resonators whose modal frequency differences are reduced below 100 mHz from initial splits as large as 15 Hz for a pair of modes with 13.5 kHz nominal frequencies. [2016-0208]

Association Between Hyponatremia and Complicated Appendicitis

PACIFIC COAST SURGICAL ASSOCIATION Association Between Hyponatremia and Complicated Appendicitis Complicated appendicitis is associated with worse outcomes among patients with acute appendicitis.1 Preoperative identification of patients with a perforated or gangrenous appendicitis may have important clinical implications regarding the timing of surgery and the suitability for nonoperative management strategies. The objective of this study was to identify clinical variables associated with the presence of complicated appendicitis.