Predicting cortical bone adaptation to axial loading in the mouse tibia

The development of predictive mathematical models can contribute to a deeper understanding of the specific stages of bone mechanobiology and the process by which bone adapts to mechanical forces. The objective of this work was to predict, with spatial accuracy, cortical bone adaptation to mechanical load, in order to better understand the mechanical cues that might be driving adaptation. The axial tibial loading model was used to trigger cortical bone adaptation in C57BL/6 mice and provide relevant biological and biomechanical information. A method for mapping cortical thickness in the mouse tibia diaphysis was developed, allowing for a thorough spatial description of where bone adaptation occurs. Poroelastic finite-element (FE) models were used to determine the structural response of the tibia upon axial loading and interstitial fluid velocity as the mechanical stimulus. FE models were coupled with mechanobiological governing equations, which accounted for non-static loads and assumed that bone responds instantly to local mechanical cues in an on–off manner. The presented formulation was able to simulate the areas of adaptation and accurately reproduce the distributions of cortical thickening observed in the experimental data with a statistically significant positive correlation (Kendall's τ rank coefficient τ = 0.51, p < 0.001). This work demonstrates that computational models can spatially predict cortical bone mechanoadaptation to a time variant stimulus. Such models could be used in the design of more efficient loading protocols and drug therapies that target the relevant physiological mechanisms

Assessing Preservice Teachers’ Presentation Capabilities: Contrasting the Modes of Communication with the Constructed Impression

A research-based understanding of how to develop and assess classroom presentation skills is vital for the effective development of pre-service teacher communication capabilities. This paper identifies and compares two different models of assessing pre-service teachers’ presentation performance – one based on the Modes of Communication (voice, body language, words, and alignment between those elements) and another based on features of the Constructed Impression of the communication acts (confidence, clarity, engagement and appropriateness). The Modes of Communication and the Constructed Impression of 164 pre-service teacher presentations were rated. The Constructed Impression model provided a better fit to data, while averaging of Modes of Communication elements offered more accurate prediction of overall score. All elements in both models made a significant contribution to the overall perception of communication performance. The study also reports on the relative contribution of voice, body language, words and alignment to the perceived confidence, clarity, engagement and appropriateness of the pre-service teacher presentations. Implications for developing pre-service teachers’ presentation capabilities are also discussed

Ultrathin Oxide Films by Atomic Layer Deposition on Graphene

In this paper, a method is presented to create and characterize mechanically robust, free standing, ultrathin, oxide films with controlled, nanometer-scale thickness using Atomic Layer Deposition (ALD) on graphene. Aluminum oxide films were deposited onto suspended graphene membranes using ALD. Subsequent etching of the graphene left pure aluminum oxide films only a few atoms in thickness. A pressurized blister test was used to determine that these ultrathin films have a Young's modulus of 154 \pm 13 GPa. This Young's modulus is comparable to much thicker alumina ALD films. This behavior indicates that these ultrathin two-dimensional films have excellent mechanical integrity. The films are also impermeable to standard gases suggesting they are pinhole-free. These continuous ultrathin films are expected to enable new applications in fields such as thin film coatings, membranes and flexible electronics.Comment: Nano Letters (just accepted

Thermal atomic layer etching of germanium-rich SiGe using an oxidation and "conversion-etch" mechanism

The thermal atomic layer etching (ALE) of germanium-rich SiGe was demonstrated using an oxidation and "conversion-etch" mechanism with oxygen (O-2) or ozone (O-3), hydrofluoric acid (HF), and trimethylaluminum [TMA, Al(CH3)(3)] as the reactants. The crystalline germanium-rich SiGe film was prepared using physical vapor deposition and had a composition of Si0.15Ge0.85. In situ spectroscopic ellipsometry was employed to monitor the thickness of both the SiGe film and the surface oxide layer on the SiGe film during thermal ALE. Using a reactant sequence of O-2-HF-TMA, the etch rate of the SiGe film increased progressively with temperatures from 225 to 290 degrees C. At 290 degrees C, the SiGe film thickness decreased linearly at a rate of 0.57 angstrom /cycle with a surface oxide thickness of 18-19 angstrom. This etch rate was obtained using reactant pressures of 25, 0.2, and 0.4Torr and doses of 1.5, 1.0, and 1.0s for O-2, HF, and TMA, respectively. The TMA and HF reactions were self-limiting and the O-2 reaction was reasonably self-limiting at 290 degrees C. Using an O-3-HF-TMA reaction sequence, the SiGe ALE etch rate was 0.42 angstrom /cycle at 290 degrees C. This etch rate was obtained using reactant pressures of 15, 0.2, and 0.4Torr and dose times of 0.5, 1.0, and 1.0s for O-3, HF, and TMA, respectively. The O-3, TMA, and HF reactions were all self-limiting at 290 degrees C. Atomic force microscopy images revealed that thermal ALE with the O-2-HF-TMA or O-3-HF-TMA reaction sequences did not roughen the surface of the SiGe film. The SiGe film was etched selectively compared with Si or Si3N4 at 290 degrees C using an O-2-HF-TMA reaction sequence. The etch rate for the SiGe film was >10 times faster than Si(100) or Si3N4 that was prepared using low-pressure chemical vapor deposition. This selectivity for the SiGe film will be useful to fabricate Si nanowires and nanosheets using SiGe as the sacrificial layer.Peer reviewe

Geodesics for Efficient Creation and Propagation of Order along Ising Spin Chains

Experiments in coherent nuclear and electron magnetic resonance, and optical spectroscopy correspond to control of quantum mechanical ensembles, guiding them from initial to final target states by unitary transformations. The control inputs (pulse sequences) that accomplish these unitary transformations should take as little time as possible so as to minimize the effects of relaxation and decoherence and to optimize the sensitivity of the experiments. Here we give efficient syntheses of various unitary transformations on Ising spin chains of arbitrary length. The efficient realization of the unitary transformations presented here is obtained by computing geodesics on a sphere under a special metric. We show that contrary to the conventional belief, it is possible to propagate a spin order along an Ising spin chain with coupling strength J (in units of Hz), significantly faster than 1/(2J) per step. The methods presented here are expected to be useful for immediate and future applications involving control of spin dynamics in coherent spectroscopy and quantum information processing

Time Optimal Control in Spin Systems

In this paper, we study the design of pulse sequences for NMR spectroscopy as a problem of time optimal control of the unitary propagator. Radio frequency pulses are used in coherent spectroscopy to implement a unitary transfer of state. Pulse sequences that accomplish a desired transfer should be as short as possible in order to minimize the effects of relaxation and to optimize the sensitivity of the experiments. Here, we give an analytical characterization of such time optimal pulse sequences applicable to coherence transfer experiments in multiple-spin systems. We have adopted a general mathematical formulation, and present many of our results in this setting, mindful of the fact that new structures in optimal pulse design are constantly arising. Moreover, the general proofs are no more difficult than the specific problems of current interest. From a general control theory perspective, the problems we want to study have the following character. Suppose we are given a controllable right invariant system on a compact Lie group, what is the minimum time required to steer the system from some initial point to a specified final point? In NMR spectroscopy and quantum computing, this translates to, what is the minimum time required to produce a unitary propagator? We also give an analytical characterization of maximum achievable transfer in a given time for the two spin system.Comment: 20 Pages, 3 figure

What has finite element analysis taught us about diabetic foot disease and its management?:a systematic review

Over the past two decades finite element (FE) analysis has become a popular tool for researchers seeking to simulate the biomechanics of the healthy and diabetic foot. The primary aims of these simulations have been to improve our understanding of the foot's complicated mechanical loading in health and disease and to inform interventions designed to prevent plantar ulceration, a major complication of diabetes. This article provides a systematic review and summary of the findings from FE analysis-based computational simulations of the diabetic foot.A systematic literature search was carried out and 31 relevant articles were identified covering three primary themes: methodological aspects relevant to modelling the diabetic foot; investigations of the pathomechanics of the diabetic foot; and simulation-based design of interventions to reduce ulceration risk.Methodological studies illustrated appropriate use of FE analysis for simulation of foot mechanics, incorporating nonlinear tissue mechanics, contact and rigid body movements. FE studies of pathomechanics have provided estimates of internal soft tissue stresses, and suggest that such stresses may often be considerably larger than those measured at the plantar surface and are proportionally greater in the diabetic foot compared to controls. FE analysis allowed evaluation of insole performance and development of new insole designs, footwear and corrective surgery to effectively provide intervention strategies. The technique also presents the opportunity to simulate the effect of changes associated with the diabetic foot on non-mechanical factors such as blood supply to local tissues.While significant advancement in diabetic foot research has been made possible by the use of FE analysis, translational utility of this powerful tool for routine clinical care at the patient level requires adoption of cost-effective (both in terms of labour and computation) and reliable approaches with clear clinical validity for decision making

Alopecia areata is characterized by dysregulation in systemic type 17 and type 2 cytokines, which may contribute to disease‐associated psychological morbidity

Background: Alopecia areata (AA) is a common autoimmune disease, causing patchy hair loss that can progress to involve the entire scalp (totalis) or body (universalis). CD8+NKG2D+ T cells dominate hair follicle pathogenesis, but the specific mechanisms driving hair loss are not fully understood. Objectives To provide a detailed insight into the systemic cytokine signature associated with AA, and assess the association between cytokines and depression. Methods: Multiplex analysis of plasma cytokines from AA patients, psoriatic arthritis (PsA) patients and healthy controls. We also assessed incidence of depression and anxiety using the Hospital Anxiety and Depression Scale. Results: Our analysis identified a systemic inflammatory signature associated with AA, characterised by elevated levels of IL-17A, IL-17F, IL-21 and IL-23 indicative of a type 17 immune response. Circulating levels of the type 2 cytokines IL-33, IL-31 and IL-17E/25 are also significantly increased in AA. In comparison to PsA, AA was associated with higher levels of IL-17F, IL-17E and IL-23. We hypothesised that circulating inflammatory cytokines may contribute to wider comorbidities associated with AA. We assessed psychiatric comorbidity in AA using the Hospital Anxiety and Depression Scale and found that 18% and 51% of people with AA experienced symptoms of depression and anxiety, respectively. Using linear regression modelling, we identified that levels of IL-22 and IL-17E are positively and significantly associated with depression. Conclusion: Our data highlight changes in both type 17 and 2 cytokines, suggesting that complex systemic cytokine profiles may contribute both to the pathogenesis of AA and to the associated depression