Aeroelastic Stability of Rotor Blades Using Finite Element Analysis

The flutter stability of flap bending, lead-lag bending, and torsion of helicopter rotor blades in hover is investigated using a finite element formulation based on Hamilton's principle. The blade is divided into a number of finite elements. Quasi-steady strip theory is used to evaluate the aerodynamic loads. The nonlinear equations of motion are solved for steady-state blade deflections through an iterative procedure. The equations of motion are linearized assuming blade motion to be a small perturbation about the steady deflected shape. The normal mode method based on the coupled rotating natural modes is used to reduce the number of equations in the flutter analysis. First the formulation is applied to single-load-path blades (articulated and hingeless blades). Numerical results show very good agreement with existing results obtained using the modal approach. The second part of the application concerns multiple-load-path blades, i.e. bearingless blades. Numerical results are presented for several analytical models of the bearingless blade. Results are also obtained using an equivalent beam approach wherein a bearingless blade is modelled as a single beam with equivalent properties. Results show the equivalent beam model

"We were treated like adults" - development of a pre-medicine summer school for 16 year olds from deprived socioeconomic backgrounds: action research study

Objective To develop a one week widening access summer school for 16 year old pupils from, non-traditional backgrounds who are considering applying to medical school, and to identify its short term impact and key success factors.Design Action research with partnership schools tit deprived inner-city areas in five overlapping phases: schools liaison, recruitment of pupils and assessment of needs, programme design, programme delivery, and evaluation. The design phase incorporated findings from one-to-one interviews with every pupil, and workshops and focus groups for pupils, Parents, teachers, medical student assistants, NHS staff, and other stakeholders. An in-depth process evaluation of the summer School was undertaken from the perspective of multiple stakeholders using questionnaires, interviews, focus groups, and observation.Participants 40 pupils aged 16 years from socioeconomically deprived and under-represented ethnic Minority groups.Results The summer school was popular with pupils, parents, teachers, and staff. It substantially raised pupils' confidence and motivation to apply to medical school. Critical success factors were identified as an atmosphere of "respect"; a focus on hands-on work in small groups; the input. of medical students as role models; and vision and leadership from senior staff. A particularly popular and effective aspect Of the course was a grand round held Oil the last clay, in which pupils gave group presentations of real cases.Conclusion An action research format allowed us to draw the different stakeholders into a collaborative endeavour characterised by enthusiasm, interpersonal support, and mutual respect. The input from pupils to the programme design ensured high engagement and low drop-out rates. Hands-on activities in small groups and social drama of preparing and giving a grand round presentation were particularly important

Passivity-Based Control of Human-Robotic Networks with Inter-Robot Communication Delays and Experimental Verification

In this paper, we present experimental studies on a cooperative control system for human-robotic networks with inter-robot communication delays. We first design a cooperative controller to be implemented on each robot so that their motion are synchronized to a reference motion desired by a human operator, and then point out that each robot motion ensures passivity. Inter-robot communication channels are then designed via so-called scattering transformation which is a technique to passify the delayed channel. The resulting robotic network is then connected with human operator based on passivity theory. In order to demonstrate the present control architecture, we build an experimental testbed consisting of multiple robots and a tablet. In particular, we analyze the effects of the communication delays on the human operator's behavior

Static dielectric response and Born effective charge of BN nanotubes from {\it ab initio} finite electric field calculations

{\it Ab initio} investigations of the full static dielectric response and Born effective charge of BN nanotubes (BN-NTs) have been performed for the first time using finite electric field method. It is found that the ionic contribution to the static dielectric response of BN-NTs is substantial and also that a pronounced chirality-dependent oscillation is superimposed on the otherwise linear relation between the longitudinal electric polarizability and the tube diameter ($D$), as for a thin dielectric cylinderical shell. In contrast, the transverse dielectric response of the BN-NTs resemble the behavior of a thin (non-ideal) conducting cylindrical shell of a diameter of $D+4$\AA$$, with a screening factor of 2 for the inner electric field. The medium principal component $Z_y^*$ of the Born effective charge corresponding to the transverse atomic displacement tangential to the BN-NT surface, has a pronounced $D$-dependence (but independent of chirality), while the large longitudinal component $Z_z^*$ exhibits a clear chirality dependence (but nearly $D$-independent), suggesting a powerful way to characterize the diameter and chirality of a BN-NT.Comment: submitted to PR

Channel saturation and conductance quantization in single-atom gold constrictions

Notwithstanding the discreteness of metallic constrictions, it is shown that the finite elasticity of stable, single-atom gold constrictions allows for a continuous and reversible change in conductance, thereby enabling observation of channel saturation and conductance quantization. The observed channel saturation and signature for conductance quantization is achieved by superposition of atomic/subatomic-scale oscillations on a retracting/approaching gold tip against a gold substrate of a scanning probe. Results also show that conductance histograms are neither suitable for evaluating the stability of atomic configurations through peak positions or peak height nor appropriate for assessing conductance quantization. A large number of atomic configurations with similar conductance values give rise to peaks in the conductance histogram. The positions of the peaks and counts at each peak can be varied by changing the conditions under which the histograms are made. Histogram counts below 1Go cannot necessarily be assumed to arise from single-atom constrictions

Traumatic Dental Injuries Among 12-15-Year-Old-School Children in Panchkula

Background:: Traumatic dental injury (TDI) in children and adolescents has become one of the most serious dental public health problems. Despite such a high prevalence of dental trauma, very less attention has been paid to TDI, its etiology, and prevention. Objectives:: To determine the prevalence of anterior tooth traumatic dental injuries in 12-15-year-old school children of Panchkula district, India, and to find any correlation with the cause, gender, extent of overbite as well as over-jet, and previous treatment. Patients and Methods:: A multistage sample of 12-15-year-old school children (n = 810) in Panchkula district, Haryana, was selected. The children were screened using WHO criteria for oral examination and a trained dental surgeon examined the children. Those with clinical TDI were examined further for the type of traumatic injuries using Elis classification modified by Holland. Overjet and overbite were recorded. After examination, questions regarding the cause of trauma and its treatment were asked. Data were subjected to statistical analysis using the Chi square and Mantel-Haenszel tests by SPSS version 20.0. Results:: The results showed that out of 810 children, 86 (10.2 %) had TDI. Males had higher prevalence of trauma than females (P < 0.05). The common cause of trauma was fall (51.11%) followed by sports injuries (41.86%). Enamel-dentin fracture without pulpal involvement was the most common type of trauma and the most frequent involved teeth were maxillary central incisors. A significant association was observed between overjet and overbite and trauma. Only 3.5% of the children affected with trauma had received treatment. Conclusions:: The prevalence of traumatic injuries to permanent incisors in 12-15-year-old Panchkula school children was relatively high. TDI was associated with gender, overjet, and lip competence. There was a great unmet treatment need

Graphitic-BN Based Metal-free Molecular Magnets From A First Principle Study

We perform a first principle calculation on the electronic properties of carbon doped graphitic boron nitride graphitic BN. It was found that carbon substitution for either boron or nitrogen atom in graphitic BN can induce spontaneous magnetization. Calculations based on density functional theory with the local spin density approximation on the electronic band structure revealed a spin polarized, dispersionless band near the Fermi energy. Spin density contours showed that the magnetization density originates from the carbon atom. The magnetization can be attributed to the carbon 2p electron. Charge density distribution shows that the carbon atom forms covalent bonds with its three nearest neighbourhood. The spontaneous magnetization survives the curvature effect in BN nanotubes, suggesting the possibility of molecular magnets made from BN. Compared to other theoretical models of light-element or metal-free magnetic materials, the carbon-doped BN are more experimentally accessible and can be potentially useful.Comment: 8 pages, 4 figure