Parametric amplification in single-walled carbon nanotube nanoelectromechanical resonators

The low quality factor (Q) of Single-walled carbon nanotube (SWNT) resonators has limited their sensitivity in sensing application. To this end, we employ the technique of parametric amplification by modulating the spring constant of SWNT resonators at twice the resonant frequency, and achieve 10 times Q enhancement. The highest Q obtained at room temperature is around ~700, which is 3-4 times better than previous Q record reported for doubly-clamped SWNT resonators. Furthermore, efficient parametric amplification is found to only occur in the catenary vibration regime. Our results open up the possibility to employ light-weight and high-Q carbon nanotube resonators in single molecule and atomic mass sensing.Comment: 14 pages, 3 figure

Carbon Based Nanoelectromechanical Resonators.

Owing to their light mass and high Young’s modulus, carbon nanotubes (CNTs) and graphene are promising candidates for nanoelectromechanical resonators capable of ultrasmall mass and force sensing. Unfortunately, the mass sensitivity of CNT resonators is impeded by the low quality factor (Q) caused by intrinsic losses. Therefore, one should minimize dissipations or seek an external way to enhance Q in order to overcome the fundamental limits. In this thesis, I first carried out a one-step direct transfer technique to fabricate pristine CNT nanoelectronic devices at ambient temperature. This process technique prevents unwanted contaminations, further reducing surface losses. Using this technique, CNT resonators was fabricated and a fully suspended CNT p-n diode with ideality factor equal to 1 was demonstrated as well. Subsequently, the frequency tuning mechanisms of CNT resonators were investigated in order to study their nonlinear dynamics. Downward frequency tuning caused by capacitive spring softening effect was demonstrated for the first time in CNT resonators adopting a dual-gate configuration. Leveraging the ability to modulate the spring constant, parametric amplification was demonstrated for Q enhancement in CNT resonators. Here, the simplest parametric amplification scheme was implemented by modulating the spring constant of CNTs at twice the resonance frequency through electrostatic gating. Consequently, at least 10 times Q enhancement was demonstrated and Q of 700 at room temperature was the highest record to date. Moreover, parametric amplification shows strong dependence on DC gate voltages, which is believed due to the difference of frequency tunability in different vibrational regimes. Graphene takes advantages over CNTs due to the availability of wafer-scale graphene films synthesized by chemical vapor deposition (CVD) method. Thus, I also examined graphene resonators fabricated from CVD graphene films. Ultra-high frequency (UHV) graphene resonators were demonstrated, and the Qs of graphene resonators are around 100. Future directions of graphene resonators include investigating the potential losses, exploring the origin of nonlinear damping, and demonstrating parametric amplification for Q enhancement.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91487/1/chungwu_1.pd

Palpation of preoperatively inserted indwelling angiocatheter facilitates intraoperative localization of obscure gastrointestinal bleeding of small intestinal origin

SummaryBackgroundPalpation of the indwelling angiographic catheter inserted before operation to localize obscure gastrointestinal bleeding of small intestinal origin during laparotomy has rarely been reported in the literature.PurposeThe purpose of the study is to investigate the role of palpable indwelling angiocatheter inserted before operation in localizing obscure gastrointestinal bleeding of small intestinal origin during laparotomy.MethodsBetween January 2003 and December 2010, seven patients who had a clinical impression of obscure gastrointestinal bleeding of small intestinal origin and angiographic extravasation from the mesenteric artery had an angiocatheter inserted into the distal mesenteric branch. During laparotomy the catheter was palpated to guide subsequent resection of the intestine. The clinical outcomes of these patients were retrospectively reviewed.ResultsDuring laparotomy the retained catheter failed to be palpated in one patient. Six patients underwent segmental resection of intestine under guidance of the palpated catheter. All six patients had positive identification of small bowel bleeding. The yield rate of intraoperative localization was 86% (6 out of 7). Two of the six patients ceased bleeding after operation, but died of underlying disease progression. Four of the six patients had an uneventful postoperative clinical course without recurrent bleeding after a median follow-up period of 25 months.ConclusionPalpation of the indwelling angiographic catheter selectively left before operation is effective for precisely locating obscure gastrointestinal bleeding of small intestinal origin during laparotomy

Metabolic syndrome and abdominal fat are associated with inflammation, but not with clinical outcomes, in peritoneal dialysis patients

BACKGROUND: In the general population, metabolic syndrome (MetS) is correlated with visceral fat and a risk factor for cardiovascular disease (CVD); however, little is known about the significance of abdominal fat and its association with inflammation and medication use in peritoneal dialysis (PD) patients. We investigated the relationship of visceral fat area (VFA) with C-reactive protein (CRP) levels and medication use in PD patients and followed their clinical outcomes. METHODS: In a prospective study from February 2009 to February 2012, we assessed diabetes mellitus (DM) status, clinical and PD-associated characteristics, medication use, CRP levels, components of MetS, and VFA in 183 PD patients. These patients were categorized into 3 groups based on MetS and DM status: non-MetS (group 1, n = 73), MetS (group 2, n = 65), and DM (group 3, n = 45). VFA was evaluated by computed tomography (CT) and corrected for body mass index (BMI). RESULTS: Patients in group 1 had smaller VFAs than patients in groups 2 and 3 (3.2 ± 1.8, 4.6 ± 1.9, and 4.9 ± 2.0 cm(2)/[kg/m(2)], respectively, P < 0.05) and lower CRP levels (0.97 ± 2.31, 1.27 ± 2.57, and 1.11 ± 1.35 mg/dL, respectively, P < 0.05). VFA increased with the number of criteria met for MetS. After adjusting for age, body weight, and sex, CRP and albumin levels functioned as independent positive predictors of VFA; on other hand, the use of renin-angiotensin system blockers was inversely correlated with VFA in PD patients without DM. In the survival analysis, DM patients (group 3) had the poorest survival among the 3 groups, but no significant differences were found between groups 1 and 2. CONCLUSION: This study showed that VFA and MetS are associated with CRP levels but cannot predict survival in PD patients without DM. The complex relationship of nutritional parameters to VFA and MetS may explain these results. The type of antihypertensive medication used was also associated with the VFA. The mechanisms behind these findings warrant further investigation

Investigation of the Mechanical Properties of Nano-Scale Metallic Crystal Structural with Point Defects

It is difficult to know if a nano-structure has similar characteristics with bulk structure properties. Hence, this paper developed atomistic-continuum mechanics (ACM), and used the finite element method (FEM) to transfer an originally discrete atomic structure into an equilibrium continuum model. The purpose of this research is to study the Young's modulus of copper in nano-scale structure under tensile testing and vibration loading. In this approach, the face-centered-cubic (fcc) metal bonds might be able to describe the inter-atomic forces between adjacent atoms. In short, the bond of the atomic lattice could be replaced by the spring element. The mechanical properties are discussed in terms of change in the structural size and the percentage of point defects of copper

Integration of Genetic Programming and TABU Search Mechanism for Automatic Detection of Magnetic Resonance Imaging in Cervical Spondylosis

Cervical spondylosis is a kind of degenerative disease which not only occurs in elder patients. The age distribution of patients is unfortunately decreasing gradually. Magnetic Resonance Imaging (MRI) is the best tool to confirm the cervical spondylosis severity but it requires radiologist to spend a lot of time for image check and interpretation. In this study, we proposed a prediction model to evaluate the cervical spine condition of patients by using MRI data. Furthermore, to ensure the computing efficiency of the proposed model, we adopted a heuristic programming, genetic programming (GP), to build the core of refereeing engine by combining the TABU search (TS) with the evolutionary GP. Finally, to validate the accuracy of the proposed model, we implemented experiments and compared our prediction results with radiologist’s diagnosis to the same MRI image. The experiment found that using clinical indicators to optimize the TABU list in GP+TABU got better fitness than the other two methods and the accuracy rate of our proposed model can achieve 88% on average. We expected the proposed model can help radiologists reduce the interpretation effort and improve the relationship between doctors and patients