Shaping single crystalline BaTiO3nanostructures by focused neon or helium ion milling.

The realization of perovskite oxide nanostructures with controlled shape and dimensions remains a challenge. Here, we investigate the use of helium and neon focused ion beam (FIB) milling in an ion microscope to fabricate BaTiO3nanopillars of sub-500 nm in diameter starting from BaTiO3(001) single crystals. Irradiation of BaTiO3with He ions induces the formation of nanobubbles inside the material, eventually leading to surface swelling and blistering. Ne-FIB is shown to be suitable for milling without inducing surface swelling. The resulting structures are defect-free single crystal nanopillars, which are enveloped, on the top and lateral sidewalls, by a point defect-rich crystalline region and an outer Ne-rich amorphous layer. The amorphous layer can be selectively etched by dipping in diluted HF. The geometry and beam-induced damage of the milled nanopillars depend strongly on the patterning parameters and can be well controlled. Ne ion milling is shown to be an effective method to rapidly prototype BaTiO3crystalline nanostructures.

Adjacent-level arthroplasty following cervical fusion.

OBJECTIVE Adjacent-level disc degeneration following cervical fusion has been well reported. This condition poses a major treatment dilemma when it becomes symptomatic. The potential application of cervical arthroplasty to preserve motion in the affected segment is not well documented, with few studies in the literature. The authors present their initial experience of analyzing clinical and radiological results in such patients who were treated with arthroplasty for new or persistent arm and/or neck symptoms related to neural compression due to adjacent-segment disease after anterior cervical discectomy and fusion (ACDF). METHODS During a 5-year period, 11 patients who had undergone ACDF anterior cervical discectomy and fusion (ACDF) and subsequently developed recurrent neck or arm pain related to adjacent-level cervical disc disease were treated with cervical arthroplasty at the authors' institution. A total of 15 devices were implanted (range of treated levels per patient: 1-3). Clinical evaluation was performed both before and after surgery, using a visual analog scale (VAS) for pain and the Neck Disability Index (NDI). Radiological outcomes were analyzed using pre- and postoperative flexion/extension lateral radiographs measuring Cobb angle (overall C2-7 sagittal alignment), functional spinal unit (FSU) angle, and range of motion (ROM). RESULTS There were no major perioperative complications or device-related failures. Statistically significant results, obtained in all cases, were reflected by an improvement in VAS scores for neck/arm pain and NDI scores for neck pain. Radiologically, statistically significant increases in the overall lordosis (as measured by Cobb angle) and ROM at the treated disc level were observed. Three patients were lost to follow-up within the first year after arthroplasty. In the remaining 8 cases, the duration of follow-up ranged from 1 to 3 years. None of these 8 patients required surgery for the same vertebral level during the follow-up period. CONCLUSIONS Artificial cervical disc replacement in patients who have previously undergone cervical fusion surgery appears to be safe, with encouraging early clinical results based on this small case series, but more data from larger numbers of patients with long-term follow-up are needed. Arthroplasty may provide an additional tool for the management of post-fusion adjacent-level cervical disc disease in carefully selected patients.

Complete anatomic reduction and monosegmental fusion for lumbar spondylolisthesis of Grade II and higher: use of the minimally invasive "rocking" technique.

OBJECTIVE Different surgical approaches have been described for treatment of spondylolisthesis, including in situ fusions, reductions of various degrees, and inclusion of healthy adjacent segments into the fusion construct. To the authors' knowledge, there are only sparse reports describing consistent complete reduction and monosegmental transforaminal lumbar interbody fusion for spondylolisthesis using a minimally invasive technique. The authors assess the efficacy of this technique in the reduction of local deformity and correction of overall sagittal profile in single-level spondylolisthesis. METHODS This cohort study consists of a total of 36 consecutive patients treated over a period of 6 years. Patients with varying grades of lumbar spondylolisthesis (29 Meyerding Grade II and 7 Meyerding Grade III) were treated with operative reduction via minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) in which the "rocking" technique was used. The clinical outcomes were measured using the visual analog scale (VAS) for pain and the Revised Oswestry Disability Index (ODI) for low-back pain/dysfunction. Meyerding grade, pelvic incidence (PI), lumbar lordosis (LL), disc space angle (DSA), pelvic tilt (PT), and sacral slope (SS) were assessed to measure the radiological outcomes. These were reviewed for each patient for a minimum of 2 years. RESULTS At most recent follow-up, 94% of patients were pain free. There were 2 patients (6%) who had moderate pain (which corresponded to higher-grade of listhesis), but all showed an improvement in pain scores (p < 0.05). The mean VAS score improved from 6.5 (SD 1.5) preoperatively to 1.6 (SD 1.3) and the mean ODI score improved from 53.7 (SD 13.1) preoperatively to 22.5 (SD 15.5) at 2-year follow-up. All radiological parameters improved following surgery. Most significant improvement was noted for LL, DSA, and SS. Both LL and SS were found to decrease, while DSA increased postoperatively. PI remained relatively unchanged, while PT showed a mild increase, which was not significant. Good fusion was achieved with implants in situ at 2-year follow-up. A 100% complete reduction of all grades of spondylolisthesis was achieved. The overall sagittal profile improved dramatically. No major perioperative complications were encountered. CONCLUSIONS Minimally invasive monosegmental TLIF for spondylolisthesis reduction using this rocking technique is effective in the treatment of various grades of spondylolisthesis. Consistent complete reduction of the slippage as well as excellent correction of overall sagittal profile can be achieved, and the need for including healthy adjacent segments in the fusion construct can be avoided.

Prediction of failure in notched carbon-fibre-reinforced-polymer laminates under multi-axial loading.

A damage-based finite-element model is used to predict the fracture behaviour of centre-notched quasi-isotropic carbon-fibre-reinforced-polymer laminates under multi-axial loading. Damage within each ply is associated with fibre tension, fibre compression, matrix tension and matrix compression. Inter-ply delamination is modelled by cohesive interfaces using a traction-separation law. Failure envelopes for a notch and a circular hole are predicted for in-plane multi-axial loading and are in good agreement with the observed failure envelopes from a parallel experimental study. The ply-by-ply (and inter-ply) damage evolution and the critical mechanisms of ultimate failure also agree with the observed damage evolution. It is demonstrated that accurate predictions of notched compressive strength are obtained upon employing the band broadening stress for microbuckling, highlighting the importance of this damage mode in compression. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'.

Minimally invasive transforaminal lumbar interbody fusion-indications and clinical experience.

BACKGROUND: Transforaminal lumbar interbody fusion (TLIF) has emerged as one of the common procedures performed by spine surgeons. Back pain and radiculopathy due to degenerative disc disease, spondylolisthesis, or deformity are the usual indications. Minimally invasive surgery (MIS) techniques have proven to be effective in TLIF as they are associated with less blood loss, fewer wound complications and infections, faster recovery, and decreased hospital costs. The novel technique described in this study helps to achieve a circumferential lumbar fusion using a unilateral posterior approach, via a muscle-dilating exposure, thereby minimizing the approach-related morbidity. OBJECTIVES: An overview of the minimally invasive TLIF (MIS-TLIF) procedures including indications, techniques, and clinical experience along with a review of the medical literature is hereby presented. METHODS: All patients who underwent MIS-TLIF for various indications at our institution from 2009 to 2014 were retrospectively reviewed. All patients in this series had low back pain as their predominant symptom, with varying degrees of radicular pain and neurologic symptoms. The data collected retrospectively for analysis were age, gender, previous diagnoses, revision diagnosis, duration of symptoms, levels of fusion, operating time, intraoperative blood loss, clinical and radiographic results after surgery, and complications. Back and leg pain quantified by visual analog scale scores preoperatively, postoperatively, and at the last follow-up were assessed for clinical outcomes. CONCLUSIONS: Our clinical experience along with a review of the medical literature indicates that TLIF can be effectively and safely performed in a minimally invasive fashion for a wide variety of indications.

Silencing TNF-α in macrophages and dendritic cells for arthritis treatment.

OBJECTIVES: Tumour necrosis factor (TNF)-α secreted by macrophages and dendritic cells (DCs) plays a predominant role in arthritis. Our previous studies suggest that a small peptide, RVG-9R (29-aa peptide derived from the rabies virus glycoprotein, fused to 9R residues), can deliver small interfering RNA (siRNA) to macrophages and DCs. We therefore tested whether knockdown of TNF-α expression in macrophages and DCs by RVG-9R/bound siRNA targeting TNF-α reduces the severity of collagen antibody-induced arthritis (CAIA) in mice. METHOD: Arthritis was induced in mice by injecting a combination of antibodies to collagen followed by lipopolysaccharide (LPS) treatment. Mice were also injected with TNF-α siRNA complexed with RVG-9R peptide or an irrelevant peptide RVMAT-9R on days 1, 3, 5, and 7. As a positive control, dexamethasone was injected intravenously. Paw thickness was measured every 2 days and the mice were killed on day 10 for testing synovial TNF-α levels and histological analysis of joints. RESULTS: In control mice, arthritis developed on day 4 and reached its peak between day 7 and day 9. Treatment with siTNF-α bound to RVG-9R, but not to RVMAT-9R, resulted in reducing paw thickness scores to the same level as dexamethasone treatment, associated with reduced TNF-α level in synovial fluid. Histological analysis of joints in the control RVMAT-9R/TNF-α siRNA-treated mice showed marked pannus formation and destruction of cartilage and subchondrial bone, as well as severe infiltration of inflammatory cells into the synovium. By contrast, the joint pathology was markedly reduced in RVG-9R/TNF-α siRNA-treated mice resembling the dexamethasone-treated mice. CONCLUSIONS: Suppression of TNF-α expression in macrophages and DCs by RVG-9R-mediated siRNA delivery could potentially be a clinically viable strategy for treatment of arthritis.

Targeting ribosome biogenesis reinforces ERK-dependent senescence in pancreatic cancer.

Pancreatic adenocarcinomas (PDAC) often possess mutations in K-Ras that stimulate the ERK pathway. Aberrantly high ERK activation triggers oncogene-induced senescence, which halts tumor progression. Here we report that low-grade pancreatic intraepithelial neoplasia displays very high levels of phospho-ERK consistent with a senescence response. However, advanced lesions that have circumvented the senescence barrier exhibit lower phospho-ERK levels. Restoring ERK hyperactivation in PDAC using activated RAF leads to ERK-dependent growth arrest with senescence biomarkers. ERK-dependent senescence in PDAC was characterized by a nucleolar stress response including a selective depletion of nucleolar phosphoproteins and intranucleolar foci containing RNA polymerase I designated as senescence-associated nucleolar foci (SANF). Accordingly, combining ribosome biogenesis inhibitors with ERK hyperactivation reinforced the senescence response in PDAC cells. Notably, comparable mechanisms were observed upon treatment with the platinum-based chemotherapy regimen FOLFIRINOX, currently a first-line treatment option for PDAC. We thus suggest that drugs targeting ribosome biogenesis can improve the senescence anticancer response in pancreatic cancer.

Pancreatic neuroendocrine tumors in patients with tuberous sclerosis complex.

We explored pancreatic neuroendocrine tumors (PanNETs) associated with tuberous sclerosis complex (TSC) to determine their incidence in the TSC population; define their clinical, radiological, and pathological characteristics; and investigate their association with underlying genotypes. Retrospectively reviewed abdominal imaging of 219 patients with TSC, evaluating the incidence, size, and architecture of pancreatic lesions. Pathology records at Massachusetts General Hospital (MGH) were reviewed for all PanNET diagnoses in patients with TSC. Literature was reviewed for TSC-related PanNET cases. Nine patients with TSC were found to have a pancreatic lesion(s) on abdominal imaging and six patients have been diagnosed with a PanNET by pathology at MGH. Twelve cases of TSC-associated PanNETs have been reported in the literature. Of these 18 PanNET cases, one third were cystic, and the average age at resection was 26 years. Germline TSC2 mutations were found in all patients for whom genetic data were available (n = 3). We did not identify pancreatic angiomyolipomas in this series. Our results suggest that PanNETs are the most common pancreatic lesion in patients with TSC. Focal pancreatic mass lesions, solid or cystic, in patients with TSC should be considered possible PanNETs, and resection of the lesion may be clinically indicated.

Free-energy-based framework for early forecasting of stem cell differentiation.

Commitment of stem cells to different lineages is inherently stochastic but regulated by a range of environmental bio/chemo/mechanical cues. Here, we develop an integrated stochastic modelling framework for predicting the differentiation of hMSCs in response to a range of environmental cues, including sizes of adhesive islands, stiffness of substrates and treatment with ROCK inhibitors in both growth and mixed media. The statistical framework analyses the fluctuations of cell morphologies over approximately a 24 h period after seeding the cells in the specific environment and uses the cytoskeletal free-energy distribution to forecast the lineage the hMSCs will commit to. The cytoskeletal free energy which succinctly parametrizes the biochemical state of the cell is shown to capture hMSC commitment over a range of environments while simple morphological factors such as cell shape, tractions on their own are unable to correlate with lineages hMSCs adopt.

Tunable Energy Absorption Characteristics of Architected Honeycombs Enabled via Additive Manufacturing.

Tailoring of material architectures in three-dimensions enabled by additive manufacturing (AM) offers the potential to realize bulk materials with unprecedented properties optimized for location-specific structural and/or functional requirements. Here we report tunable energy absorption characteristics of architected honeycombs enabled via material jetting AM. We realize spatially tailored 3D printed honeycombs (guided by FE studies) by varying the cell wall thickness gradient and evaluate experimentally and numerically the energy absorption characteristics. The measured response of architected honeycombs characterized by local buckling (wrinkling) and progressive failure reveals over 110% increase in specific energy absorption (SEA) with a concomitant energy absorption efficiency of 65%. Design maps are presented that demarcate the regime over which geometric tailoring mitigates deleterious global buckling and collapse. Our analysis indicates that an energy absorption efficiency as high as 90% can be achieved for architected honeycombs, whereas the efficiency of competing microarchitected metamaterials rarely exceeds 50%. The tailoring strategy introduced here is easily realizable in a broad array of AM techniques, making it a viable candidate for developing practical mechanical metamaterials.

Molecular and biotechnological aspects of microbial proteases.

Proteases represent the class of enzymes which occupy a pivotal position with respect to their physiological roles as well as their commercial applications. They perform both degradative and synthetic functions. Since they are physiologically necessary for living organisms, proteases occur ubiquitously in a wide diversity of sources such as plants, animals, and microorganisms. Microbes are an attractive source of proteases owing to the limited space required for their cultivation and their ready susceptibility to genetic manipulation. Proteases are divided into exo- and endopeptidases based on their action at or away from the termini, respectively. They are also classified as serine proteases, aspartic proteases, cysteine proteases, and metalloproteases depending on the nature of the functional group at the active site. Proteases play a critical role in many physiological and pathophysiological processes. Based on their classification, four different types of catalytic mechanisms are operative. Proteases find extensive applications in the food and dairy industries. Alkaline proteases hold a great potential for application in the detergent and leather industries due to the increasing trend to develop environmentally friendly technologies. There is a renaissance of interest in using proteolytic enzymes as targets for developing therapeutic agents. Protease genes from several bacteria, fungi, and viruses have been cloned and sequenced with the prime aims of (i) overproduction of the enzyme by gene amplification, (ii) delineation of the role of the enzyme in pathogenecity, and (iii) alteration in enzyme properties to suit its commercial application. Protein engineering techniques have been exploited to obtain proteases which show unique specificity and/or enhanced stability at high temperature or pH or in the presence of detergents and to understand the structure-function relationships of the enzyme. Protein sequences of acidic, alkaline, and neutral proteases from diverse origins have been analyzed with the aim of studying their evolutionary relationships. Despite the extensive research on several aspects of proteases, there is a paucity of knowledge about the roles that govern the diverse specificity of these enzymes. Deciphering these secrets would enable us to exploit proteases for their applications in biotechnology.

Degradation of the insecticidal toxin produced by Bacillus thuringiensis var. kurstaki by extracellular proteases produced by Chrysosporium sp.

AIMS: Some Cry proteins produced by the soil bacterium Bacillus thuringiensis (Bt) or by transgenic Bt plants persist in agricultural soils for an extended period of time, which may pose a hazard for nontarget soil organisms. The aims of our study were to screen for soil fungi capable of degrading the Cry1Ac toxin and to identify the mechanisms that lead to the inactivation of this protein. METHODS AND RESULTS: Of the eight fungal strains screened, only one, Chrysosporium sp., was found to produce extracellular proteases capable of degrading the 66-kDa Cry1Ac at the N-terminal end of amino acid 125 (alanine). The proteolytic products of the Cry1Ac toxin did not exhibit any insecticidal activity against Helicoverpa armigera, in contrast to its high toxicity exhibited in the native form. CONCLUSIONS: Proteases elaborated by the Chrysosporium sp. degrade the Cry1Ac toxin in a way that it looses its insecticidal activity against H. armigera. SIGNIFICANCE AND IMPACT OF THE STUDY: Chrysosporium sp., a specific soil micro-organism capable of producing proteases that degrade the Cry1Ac toxin into inactive products under controlled conditions is being reported for the first time. Application of this observation needs to be further tested in field conditions.

The homeostatic ensemble for cells.

Cells are quintessential examples of out-of-equilibrium systems, but they maintain a homeostatic state over a timescale of hours to days. As a consequence, the statistics of all observables is remarkably consistent. Here, we develop a statistical mechanics framework for living cells by including the homeostatic constraint that exists over the interphase period of the cell cycle. The consequence is the introduction of the concept of a homeostatic ensemble and an associated homeostatic temperature, along with a formalism for the (dynamic) homeostatic equilibrium that intervenes to allow living cells to evade thermodynamic decay. As a first application, the framework is shown to accurately predict the observed effect of the mechanical environment on the in vitro response of smooth muscle cells. This includes predictions that both the mean values and diversity/variability in the measured values of observables such as cell area, shape and tractions decrease with decreasing stiffness of the environment. Thus, we argue that the observed variabilities are inherent to the entropic nature of the homeostatic equilibrium of cells and not a result of in vitro experimental errors.

Analysis of electro-permeation of hydrogen in metallic alloys.

A reaction-diffusion type modelling framework is presented to analyse both electro-permeation (EP) and thermal desorption spectrometry (TDS) measurements of hydrogen in metallic alloys. It is assumed that the kinetics of hydrogen motion is governed by diffusion through the lattice, along with trapping/detrapping at specific sites such as dislocations, grain boundaries, etc. It is shown that the trapping and detrapping rates are typically much faster than the diffusion rate, and consequently a simplification of the governing equations suffices such that local equilibrium exists between lattice and trapped hydrogen. Using this local equilibrium assumption, we then present an asymptotic analysis of the governing kinetic equation for the EP test. This asymptotic analysis reveals that four regimes of behaviour exist, ranging from negligible trapping to the complete filling of deep traps. The analysis suggests that EP tests should be so-arranged that three regimes of behaviour are spanned, in order to extract the relevant material properties associated with hydrogen transport. The numerical solutions presented in this study support the asymptotic analysis. The hydrogen kinetics framework is also deployed to analyse both EP and TDS tests on the same martensitic steel. The EP measurements all lie in regime I and are thus insufficient to uniquely determine both the trap density and binding energy. Reasonable agreement is obtained between measurements and numerical predictions of TDS tests using parameters estimated from the EP tests. Further improvements in measurements are required to confirm the fidelity of this modelling approach.This article is part of the themed issue 'The challenges of hydrogen and metals'.

NEUDOSE: A CubeSat Mission for Dosimetry of Charged Particles and Neutrons in Low-Earth Orbit.

During space missions, astronauts are exposed to a stream of energetic and highly ionizing radiation particles that can suppress immune system function, increase cancer risks and even induce acute radiation syndrome if the exposure is large enough. As human exploration goals shift from missions in low-Earth orbit (LEO) to long-duration interplanetary missions, radiation protection remains one of the key technological issues that must be resolved. In this work, we introduce the NEUtron DOSimetry & Exploration (NEUDOSE) CubeSat mission, which will provide new measurements of dose and space radiation quality factors to improve the accuracy of cancer risk projections for current and future space missions. The primary objective of the NEUDOSE CubeSat is to map the in situ lineal energy spectra produced by charged particles and neutrons in LEO where most of the preparatory activities for future interplanetary missions are currently taking place. To perform these measurements, the NEUDOSE CubeSat is equipped with the Charged & Neutral Particle Tissue Equivalent Proportional Counter (CNP-TEPC), an advanced radiation monitoring instrument that uses active coincidence techniques to separate the interactions of charged particles and neutrons in real time. The NEUDOSE CubeSat, currently under development at McMaster University, provides a modern approach to test the CNP-TEPC instrument directly in the unique environment of outer space while simultaneously collecting new georeferenced lineal energy spectra of the radiation environment in LEO.

Bone mass in Indian children--relationships to maternal nutritional status and diet during pregnancy: the Pune Maternal Nutrition Study.

CONTEXT/OBJECTIVE: Bone mass is influenced by genetic and environmental factors. Recent studies have highlighted associations between maternal nutritional status during pregnancy and bone mass in the offspring. We hypothesized that maternal calcium intakes and circulating micronutrients during pregnancy are related to bone mass in Indian children. DESIGN/SETTING/PARTICIPANTS/MAIN OUTCOME MEASURES: Nutritional status was measured at 18 and 28 wk gestation in 797 pregnant rural Indian women. Measurements included anthropometry, dietary intakes (24-h recall and food frequency questionnaire), physical workload (questionnaire), and circulating micronutrients (red cell folate and plasma ferritin, vitamin B12, and vitamin C). Six years postnatally, total body and total spine bone mineral content and bone mineral density (BMD) were measured using dual-energy x-ray absorptiometry (DXA) in the children (n = 698 of 762 live births) and both parents. RESULTS: Both parents' DXA measurements were positively correlated with the equivalent measurements in the children (P < 0.001 for all). The strength of these correlations was similar for fathers and mothers. Children of mothers who had a higher frequency of intake of calcium-rich foods during pregnancy (milk, milk products, pulses, non-vegetarian foods, green leafy vegetables, fruit) had higher total and spine bone mineral content and BMD, and children of mothers with higher folate status at 28 wk gestation had higher total and spine BMD, independent of parental size and DXA measurements. CONCLUSIONS: Modifiable maternal nutritional factors may influence bone health in the offspring. Fathers play a role in determining their child's bone mass, possibly through genetic mechanisms or through shared environment.

[Cardiac MR tagging: optimization of sequence parameters and comparison at 1.5 T and 3.0 T in a volunteer study]. / Kardiales MR-Tagging: Parameteroptimierung und Sequenzvergleich bei 1.5 T und 3.0 T an einem Probandenkollektiv.

PURPOSE: The aim of this study was the optimization of a gradient echo (GRE) MR tagging sequence at 3.0 T in comparison to 1.5 T in order to obtain the best image contrast between the myocardium, tag lines and blood signal. Theoretically expected improvements of signal-to-noise (SNR) and contrast-to-noise ratios (CNR) were also calculated. MATERIALS AND METHODS: 14 healthy volunteers (8 male, 6 female; mean age 43.4 +/- 10.3 years) were scanned using a 3.0 T as well as a 1.5 T whole-body system. A GRE flash-2 D tagging sequence was evaluated (midventricular short axis view) by varying the flip angle (8 - 16 degrees ), slice thickness (4 - 8 mm; fixed flip angle 1.5/3.0 T: 12 degrees /8 degrees , tag size 8 mm) and tag size (4 - 8 mm, fixed flip angle 1.5/3.0 T: 12 degrees /8 degrees , slice thickness 6 mm). The field of view, acquisition time and temporal resolution (45 ms) were kept constant. Qualitative and quantitative image analysis was performed by calculating the SNR, CNR (tag) as well as the relative contrast between the myocardium and tag lines (RCMT). RESULTS: Based on individual comparison, the best imaging protocol was found at a slice thickness of 6 mm, tag size of 8 mm, optimized flip angle of 8 degrees (3.0 T) and 12 degrees (1.5 T), respectively. Compared to 1.5 T, a significantly higher overall image score was determined (mean +/- sd; 3.2 +/- 0.2 vs. 2.7 +/- 0.4) and a strong correlation between the CNR (tag) and RCMT for flip angle alpha and the slice thickness was found. A higher field strength resulted in an 80 % increase in the CNR (tag) compared to 1.5 T (mean 10.7/6.1). Furthermore, the SNR was improved by 35 % (mean 20.6/15.3) and the RCMT by 35 % (mean 0.47/0.35). CONCLUSION: Myocardial tagging at 3.0 T has shown superior image quality in comparison to 1.5 T due to a higher baseline SNR and an improved CNR as well as RCMT. The suppressed fading of the tags enables the accessibility to the diastolic phase of the cardiac cycle.

Learning styles of preclinical students in a medical college in western Nepal.

OBJECTIVES: Information on the learning styles of medical students are lacking in medical colleges in Nepal. Learning styles may be associated with student understanding and may predict success in examination. The present study was carried out to obtain information on learning styles and preferences for teaching of fourth semester medical students and note the association, if any, between respondents' personal characteristics and preferences for learning styles and types of teaching. The correlation between preferences for learning styles and types of teaching and performance in the second year university examination was also explored. METHODS: The study was carried out during October 2003 at the Manipal College of Medical Sciences, Pokhara, Nepal using the Approaches and Study Skills Inventory (ASSIST) instrument. Information on the respondents' personal characteristics was collected. Respondents had to indicate their degree of agreement with a set of statements using a modified Likert-type scale. The statements were grouped into three main learning styles and two types of teaching. The median scores among different subgroups of respondents were compared using appropriate non-parametric tests (p<0.05). RESULTS: Ninety-two students (92%) participated; fifty-six were male. Thirty-one respondents were Nepalese, 48 were Indians. Majority were educated in English medium schools. The median scores for deep and surface learning styles were 64 and 49 respectively (maximum score=80). The scores for strategic learning was 75.5 (maximum score=100). There was no clear preference for any particular type of teaching. Indian students used more surface apathetic learning strategies compared to others. There was a negative correlation between surface learning and marks obtained in the final examination. CONCLUSIONS: The students mainly used deep and strategic learning styles. Differences in preference for learning styles and types of teaching were noted according the respondents' personal characteristics. This was a preliminary study and further studies are required.

Discrete dislocation plasticity analysis of loading rate-dependent static friction.

From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent on the size of the contact, but also on the rate of deformation. Moreover, depending on its physical origin, adhesion can also be size and rate dependent, albeit different from plasticity. We present a two-dimensional model that incorporates both discrete dislocation plasticity inside a face-centred cubic crystal and adhesion in the interface to understand the rate dependence of friction caused by micrometre-size asperities. The friction strength is the outcome of the competition between adhesion and discrete dislocation plasticity. As a function of contact size, the friction strength contains two plateaus: at small contact length [Formula: see text], the onset of sliding is fully controlled by adhesion while for large contact length [Formula: see text], the friction strength approaches the size-independent plastic shear yield strength. The transition regime at intermediate contact size is a result of partial de-cohesion and size-dependent dislocation plasticity, and is determined by dislocation properties, interfacial properties as well as by the loading rate.