Determination of elastic and viscoplastic material properties obtained from indentation tests using a combined finite element analysis and optimization approach

Conventional indentation tests do not provide an accurate estimation of viscoplastic material properties. In this work, a combined finite element analysis and optimization approach is developed for the determination of elastic–plastic and creep material properties using only a single indentation loading–unloading curve based on a two-layer viscoplasticity model. Utilizing the indentation loading–unloading curve obtained from a finite element-simulated experiment with a spherical and a conical indenter, a set of six key material properties (Young’s modulus, yield stress, work hardening exponent and three creep parameters) can be determined. Non-linear optimization algorithms are used with different sets of initial material properties, leading to good agreements with the numerically simulated target loading–unloading curves

Adsorption-induced conversion of the carbon nanotube field effect transistor from ambipolar to unipolar behavior

We investigate ambipolar to unipolar transition by the effect of ambient air on the carbon nanotube field-effect transistor. A unipolar transport property of the double-walled nanotube field-effect transistor and its conversion from ambipolar behavior are observed. We suggest that adsorptions of oxygen molecules, whose lowest-unoccupied-molecular-orbital state is around the midgap of the carbon nanotube, could suppress the electron channel formation and, consequently, result in the unipolar transport behavior.open343

A comparison of surgical outcomes between endoscopic and robotically assisted thyroidectomy: the authors’ initial experience

Background: The gasless, transaxillary endoscopic thyroidectomy (GTET) offers a distinct advantage over the conventional open operation by leaving no visible neck scar, and in an attempt to improve its ergonomics and surgical outcomes, the robotically assisted thyroidectomy (RAT) was introduced. The RAT uses the same endoscopic route as the GTET but with the assistance of the da Vinci S robotic system. Excellent results for RAT have been reported, but it remains unclear whether RAT offers any potential benefits over GTET. Methods: From June to December 2009, 46 patients underwent endoscopic thyroidectomy. Of these patients, 39 had surgery without the robot (GTET) and 7 had surgery with the robot (RAT). Demographics, surgical indications, operative findings, and postoperative outcomes were compared between the two groups. All the patients were followed up for at least 6 months after surgery. Results: Patient demographics, surgical indications, and extent of resection were similar between the two groups. The median total procedure time was significantly longer for RAT (149 min) than for GTET (100 min; p = 0.018), but the contralateral recurrent laryngeal nerve was more likely to identified in RAT (100%) than in GTET (42.9%; p = 0.070). On the average, GTET needed one more surgical assistant than RAT (1 vs. 0; ppublished_or_final_versionSpringer Open Choice, 21 Feb 201

Waking up the gut in critically ill patients

Multiorgan failure frequently develops in critically ill patients. While therapeutic efforts in such patients are often focused on the lungs, on the cardiovascular system as well as on the kidneys, it is important to also consider the functional alterations in gut motility and hormone secretion. Given the central regulatory functions of many gut hormones, such as glucagon-like peptide 1, glucagon-like peptide 2, ghrelin and others, exogenous supplementation of some of these factors may be beneficial under conditions of critical illness. From a pragmatic point of view, the most feasible way towards a restoration of gut hormone secretion in critically ill patients is to provide enteral nutritional supply as soon as possible