Friction in surface micromachined microengines

Understanding the frictional properties of advanced Micro-Electro- Mechanical Systems (MEMS) is essential in order to develop optimized designs and fabrication processes, as well as to qualify devices for commercial applications. We develop and demonstrate a method to experimentally measure the forces associated with sliding friction of devices rotating on a hub. The method is demonstrated on the rotating output gear of the microengine recently developed at Sandia National Laboratories. In-situ measurements of an engine running at 18300 rpm give a coefficient of friction of 0.5 for radial (normal) forces less than 4 {mu}N. For larger forces the effective coefficient of friction abruptly increases, suggesting a fundamental change in the basic nature of the interaction between the gear and hub. The experimental approach we have developed to measure the frictional forces associated with the microengine is generically applicable to other MEMS devices

Performance tradeoffs for a surface micromachined microengine

An electromechanical model of Sandia`s microengine is developed and applied to quantify critical performance tradeoffs. This is done by determining how forces impact the mechanical response of the engine to different electrical drive signals. To validate the theoretical results, model-based drive signals are used to operate actual engines, where controlled operation is achieved for the following cases: (1) spring forces are dominant, (2) frictional forces are dominant, (3) linear inertial forces are dominant, (4) viscous damping forces are dominant, and (5) inertial load forces are dominant. Significant improvements in engine performance are experimentally demonstrated in the following areas: positional control, start/stop endurance, constant speed endurance, friction load reduction, and rapid actuation of inertial loads

Semiconductor Noise

Contains reports on five research projects

Electrical and Noise Characteristics of Graphene Field-Effect Transistors: Ambient Effects and Noise Sources

We fabricated a large number of single and bilayer graphene transistors and carried out a systematic experimental study of their low-frequency noise characteristics. A special attention was given to determining the dominant noise sources in these devices and the effect of aging on the current-voltage and noise characteristics. The analysis of the noise spectral density dependence on the area of graphene channel showed that the dominant contributions to the low-frequency electronic noise come from the graphene layer itself rather than from the contacts. Aging of graphene transistors due to exposure to ambient for over a month resulted in substantially increased noise attributed to the decreasing mobility of graphene and increasing contact resistance. The noise spectral density in both single and bilayer graphene transistors either increased with deviation from the charge neutrality point or depended weakly on the gate bias. This observation confirms that the low-frequency noise characteristics of graphene transistors are qualitatively different from those of conventional silicon metal-oxide-semiconductor field-effect transistors.Comment: 26 pages with 8 figure

Semiconductor Noise

Contains reports on two research projects

Diversity, competition, extinction: the ecophysics of language change

As early indicated by Charles Darwin, languages behave and change very much like living species. They display high diversity, differentiate in space and time, emerge and disappear. A large body of literature has explored the role of information exchanges and communicative constraints in groups of agents under selective scenarios. These models have been very helpful in providing a rationale on how complex forms of communication emerge under evolutionary pressures. However, other patterns of large-scale organization can be described using mathematical methods ignoring communicative traits. These approaches consider shorter time scales and have been developed by exploiting both theoretical ecology and statistical physics methods. The models are reviewed here and include extinction, invasion, origination, spatial organization, coexistence and diversity as key concepts and are very simple in their defining rules. Such simplicity is used in order to catch the most fundamental laws of organization and those universal ingredients responsible for qualitative traits. The similarities between observed and predicted patterns indicate that an ecological theory of language is emerging, supporting (on a quantitative basis) its ecological nature, although key differences are also present. Here we critically review some recent advances lying and outline their implications and limitations as well as open problems for future research.Comment: 17 Pages. A review on current models from statistical Physics and Theoretical Ecology applied to study language dynamic

Adenocarcinoma arising at ileostomy sites: Two cases and a review of the literature

Total colectomy with ileostomy placement is a treatment for patients with inflammatory bowel disease or familial adenomatous polyposis (FAP). A rare and late complication of this treatment is carcinoma arising at the ileostomy site. We describe two such cases: a 78-year-old male 30 years after subtotal colectomy and ileostomy for FAP, and an 85-year-old male 50 years after colectomy and ileostomy for ulcerative colitis. The long latency period between creation of the ileostomies and development of carcinoma suggests a chronic metaplasia due to an irritating/inflammatory causative factor. Surgical excision of the mass and relocation of the stoma is the mainstay of therapy, with possible benefits from adjuvant chemotherapy. Newly developed lesions at stoma sites should be biopsied to rule out the possibility of this rare ileostomy complication

Citizens without nations

To broach the question of whether citizenship could exist without (or beyond) community, this paper discusses genealogies of citizenship as membership that binds an individual to the community of birth (of the self or a parent). It is birthright as fraternity that blurs the boundary between citizenship and nationality. After briefly discussing recent critical studies on birthright citizenship (whether it is civic or ethnic or blood or soil) by Ayelet Shachar and Jacqueline Stevens, the paper discusses three critical genealogies of the relationship between birthright and citizenship by Max Weber, Hannah Arendt, and Michel Foucault. Although each provides a critical perspective into the question, Weber reduces citizenship to fraternity with nation and Arendt reduces citizenship to fraternity with the state. It is Foucault who illustrates racialization of fraternity as the connection between citizenship and nationality. Yet, since Foucault limits his genealogical investigations to the 18th and 19th centuries, a genealogy of fraternity of what he calls an immense biblical and Greek tradition remains for Derrida to articulate as a question of citizenship

The Depth and Dynamics of Context: Tracing the Sources and Channels of Engagement and Disengagement in Students' Response to Literature

In this article, we analyze one coauthor's 12th-grade English class, focusing on a small group of students who interpreted the character of Gertrude in Hamlet through a body biography, a life-sized human outline that students filled with words and images that represented their understanding of the character. We analyze the body biography production as a function of the social context of activity and then analyze the processes of composition involved in their production. Analysis of the data reveals that (a) the students exhibited different degrees of commitment to and involvement in the group task, (b) the degree of equity in productivity and social relations varied within the group in accordance with these different degrees of engagement, and (c) the inequity in social relations and contributions to the group product belied the degree to which the final interpretive product met the teacher's assessment criteria. We conclude with a reconsideration of the notion of engagement that includes attention to both the immediate social relations within the classroom and the histories of engagement that students bring to class.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Concurrent use of prescription drugs and herbal medicinal products in older adults: A systematic review

This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/), which permits any noncommercial use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.The use of herbal medicinal products (HMPs) is common among older adults. However, little is known about concurrent use with prescription drugs as well as the potential interactions associated with such combinations. Objective Identify and evaluate the literature on concurrent prescription and HMPs use among older adults to assess prevalence, patterns, potential interactions and factors associated with this use. Methods Systematic searches in MEDLINE, PsycINFO, EMBASE, CINAHL, AMED, Web of Science and Cochrane from inception to May 2017 for studies reporting concurrent use of prescription medicines with HMPs in adults (≥65 years). Quality was assessed using the Joanna Briggs Institute checklists. The Evidence for Policy and Practice Information and Co-ordinating Centre (EPPI-Centre) three stage approach to mixed method research was used to synthesise data. Results Twenty-two studies were included. A definition of HMPs or what was considered HMP was frequently missing. Prevalence of concurrent use by older adults varied widely between 5.3% and 88.3%. Prescription medicines most combined with HMPs were antihypertensive drugs, beta blockers, diuretics, antihyperlipidemic agents, anticoagulants, analgesics, antihistamines, antidiabetics, antidepressants and statins. The HMPs most frequently used were: ginkgo, garlic, ginseng, St John’s wort, Echinacea, saw palmetto, evening primrose oil and ginger. Potential risks of bleeding due to use of ginkgo, garlic or ginseng with aspirin or warfarin was the most reported herb-drug interaction. Some data suggests being female, a lower household income and less than high school education were associated with concurrent use. Conclusion Prevalence of concurrent prescription drugs and HMPs use among older adults is substantial and potential interactions have been reported. Knowledge of the extent and manner in which older adults combine prescription drugs will aid healthcare professionals can appropriately identify and manage patients at risk.Peer reviewedFinal Published versio