Hard X-ray lens-less microscopy raises hopes for a non-invasive quantitative imaging, capable of achieving the extreme resolving power demands of nanoscience. However, a limit imposed by the partial ...coherence of third generation synchrotron sources restricts the sample size to the micrometer range. Recently, X-ray ptychography has been demonstrated as a solution for arbitrarily extending the field of view without degrading the resolution. Here we show that ptychography, applied in the Bragg geometry, opens new perspectives for crystalline imaging. The spatial dependence of the three-dimensional Bragg peak intensity is mapped and the entire data subsequently inverted with a Bragg-adapted phase retrieval ptychographical algorithm. We report on the image obtained from an extended crystalline sample, nanostructured from a silicon-on-insulator substrate. The possibility to retrieve, without transverse size restriction, the highly resolved three-dimensional density and displacement field will allow for the unprecedented investigation of a wide variety of crystalline materials, ranging from life science to microelectronics.
► A new multiasperity model is presented to study the contact of rough surfaces. ► Interaction and coalescing effects between asperities are taken into account. ► Results predict linearity between ...contact area and load according to experimental data. ► The slope parameter κ of the area–load relation is almost insensitive to H, N and hrms.
Starting from the multiasperity contact theory, firstly addressed by Greenwood and Williamson 1 and Bush et al. 2, in the present paper we suggest a new methodology to take into account the lateral interaction between the asperities and their coalescing, neglected in the first formulation of the theory. When two opposing rough surfaces approach, the number and the size of the contacts grow, and some contacts spots may merge to form larger contact areas.
This phenomenon is modeled, in this paper, in a simple way replacing the overlapping contact spots with a single ‘appropriate’ equivalent asperity.
The method has been then utilized to analyse the contact between an elastic half-space and a numerically generated self-affine fractal rigid surface. The fractal surface has been generated by employing spectral methods. Results predict linearity between contact area and load and are in good agreement with numerical and experimental investigations.
We present a novel theory of the adhesive contact of linear viscoelastic materials sliding at constant velocity against rough substrates. Despite the non-conservative behaviour of the system, the ...closure equation, needed to calculate the unknown size of the contact area, can be rigorously formulated in the form of a local energy balance. The results highlight three main peculiar features of the contact, which are strictly ascribable to the interplay of adhesion and viscoelasticity. First, a velocity dependent pull-off force is predicted, whose maximum value occurs at intermediate sliding velocity. Second, the energy release rates G1 and G2 at the contact trailing and leading edges respectively, present a non-monotonic dependence on the indenter sliding velocity. Third, the velocity dependence of the hysteretic friction μ is significantly altered and presents a friction peak much more pronounced compared to the adhesiveless viscoelastic case. Theoretical predictions are in very good agreement with existing experimental data.
We study the sliding contact of viscoelastic layers on rigid rough profiles, with two different contact configurations: constrained on the upper boundary, and uniformly loaded on the top.
Results ...show that layer thickness and boundary conditions affect both the average contact quantities and the viscoelastic friction. Interestingly, the latter is strongly influenced by the specific controlled parameter. Under displacement controlled conditions, large differences are observed in the frictional behavior of the two contact configurations. Conversely, in load control, the friction coefficient is almost independent of the specific boundary condition.
Finally, a comparison with a 1D version of the Persson's theory is proposed, finding a good agreement in terms of contact area and friction coefficient dependence on the sliding velocity.
•Boundary conditions effects on viscoelastic layer in sliding contact is investigated.•Under load controlled conditions friction is not affected by boundary conditions.•Persson's theory predictions are in good agreement with the numerical calculations.
In the last decade a high amount of photovoltaic and wind power generators have been connected to the electric grid, introducing operational problems for transmission and distribution system ...operators due to the variability and the non-programmability of solar radiation and wind. The paper concerns an analysis on the benefits in adopting storage systems to reduce the imbalance costs associated to renewable energy sources. An analysis on a photovoltaic system has been performed considering different battery technologies. Discrete-time Markov chains have been used to generate a 20 years' time series of irradiance, that has been used to calculate the PV power production. Markov simulation parameters have been deeply studied in order to optimize them and obtain reliable synthetic data of ground irradiance. This data was then used as input of a hybrid PV and storage model allowing to obtain realistic economic and technical results, improving thus the results respect to the methods based on probabilistic weather simulations. An imbalance tariff has been assumed and its cost has been analysed in relation to the storage system costs. An optimal size for the different battery technology has been investigated considering the reduction of variability of the photovoltaic production and the economic convenience of the hybrid system. The use of Markov chains for the optimization of the battery size can be considered as the major novelty of the proposed approach.
•We considered penalties for unbalanced production due to PV intrinsic variability.•Markov chains have been used systematically for weather simulation.•Mathematical model of the PV power plant and of the batteries in the storage system.•Power flow calculation has been performed when the plant is connected to the network.•Accurate economical analysis took into account: storage system, production, penalties.
The mechanism of detachment of thin films from a flat smooth rigid substrate is investigated. In particular, analytical solutions in closed form are proposed for the double peeling of an elastic tape ...as well as for the axisymmetric peeling of a membrane. We show that in the case of double peeling of an endless elastic tape, a critical value of the pull-off force is found, above which the tape is completely detached from the substrate. In particular, as the detachment process advances, the peeling angle is stabilized on a limiting value, which only depends on the geometry of the tape, its elastic modulus and on the interfacial energy
Δ
γ
. This predicted behavior agrees with the “theory of multiple peeling” and clarifies some aspects of this theory. Moreover, it is also corroborated by experimental results (work in progress) we are carrying out on a standard adhesive tape adhered to a smooth flat poly(methyl methacrylate) surface. In the case of the axisymmetric adhering membrane, a different behavior is observed. In such case, the system is always stable, and the detached area monotonically increases with the peeling force, i.e., the elastic membrane can sustain in principle any applied force. Results are validated by a fully numerical analysis performed with the aid of a finite element commercial software.
•The periodic V-shaped double peeling of elastic films from soft elastic substrate is investigated.•Adhesive strength increases with the substrate compliance.•Initial small detachments can be ...tolerated without unstable peeling taking place.•Enhancement in adhesive strength occurs when the contact is splitted in multiple smaller contacts.•High resistance to detachment is obtained by properly tuning the properties of film and substrate.
In this paper, a periodic configuration of V-shaped double peeling process is investigated. Specifically, an elastic thin film is detached from a soft elastic material by applying multiple concentrated loads periodically distributed with spatial periodicity λ. The original Kendall’s idea is extended to take into account the change in elastic energy occurring in the substrate when the detachment fronts propagate. The symmetric configuration typical of a V-peeling process causes the energy release rate to be sensitive to variations of the elastic energy stored in the soft substrate. This results in an enhancement of the adhesion strength because part of the external work required to trigger the peeling mechanism is converted in substrate elastic energy.
A key role is played by both spatial periodicity λ and elasticity ratio E/Eh, between tape and substrate elastic moduli, in determining the conditions of stable adhesion. Indeed, the presence of multiple peeling fronts determines a modification of the mechanism of interaction, because deformations close to each peeling front are also affected by the stresses related to the other fronts. Results show that the energy release rate depends on the detached length of the tape so that conditions can be established which lead to an increase of the supported load compared to the classical peeling on rigid substrates.
Finally, we also find that for any given value of the load per unit length, an optimum value of the wavelength λ exists that maximizes the tolerance of the system, before unstable propagation of the peeling front can occur.
Continuously variable transmissions (CVT) have been widely used in many different areas such as automotive, robotics, manufacturing and aerospace industry. In CVT drives, a properly designed control ...strategy is needed to ensure the precise control of the speed ratio, and a deep knowledge of the steady-state and transient behavior of the drive is necessary to this purpose. In the framework of belt and chain CVT drives, model-based approaches developed for this purpose are mainly of two types: continuous models and multibody models. Continuous models are much less costly from a computation point of view, while multibody models are usually believed to be more accurate. The aim of this paper is twofold: first the CMM continuum model Carbone G., Mangialardi L., Mantriota G., ASME Journal of Mechanical Design, 127, 103–113 (2005) is compared with a multibody model of the chain-CVT variator. Secondly, the CMM model is proposed for a fast and enhanced characterization of the shifting dynamics of chain CVT. The analysis shows that, except for dynamical effects due to the intermittent contact of the chain pins with the pulleys and caused by the polygonal action of the chain, the CMM and multibody models provide very similar results. Moreover, this study shows, by exploiting the CMM model, that the overall dynamics of the CVT can be described by a relatively simple first order nonlinear differential equation, which can be very easily implemented for CVT real-time control applications. The accuracy of such a simplified approach is then tested against some preliminary shifting experiments under torque load conditions. Results show a very good agreement between theoretical predictions and experimental outcomes, thus making this simplified approach a promising tool to develop advanced real-time control of CVT transmissions for automotive applications.
Disaster citizen science, or the use of scientific principles and methods by "non-professional" scientists or volunteers, may be a promising way to enhance public health emergency preparedness (PHEP) ...and build community resilience. However, little research has focused on understanding this emerging field and its implications for PHEP. To address research gaps, this paper: (1) assesses the state of disaster citizen science by developing an inventory of disaster citizen science projects; (2) identifies different models of disaster citizen science; and (3) assesses their relevance for PHEP.
We searched the English-language peer-reviewed and grey literature for disaster citizen science projects with no time period specified. Following searches, a team of three reviewers applied inclusion/exclusion criteria that defined eligible disasters and citizen science activities. Reviewers extracted the following elements from each project: project name and description; lead and partner entities; geographic setting; start and end dates; type of disaster; disaster phase; citizen science model; and technologies used.
A final set of 209 projects, covering the time period 1953-2017, were included in the inventory. Projects were classified across five citizen science models: distributed or volunteer sensing (n = 19; 9%); contributory (n = 98; 47%); distributed intelligence (n = 52; 25%); collaborative research (n = 32; 15%); and collegial research (n = 8; 4%). Overall, projects were conducted across all disaster phases and most frequently for earthquakes, floods, and hurricanes. Although activities occurred globally, 40% of projects were set in the U.S. Academic, government, technology, and advocacy organizations were the most prevalent lead entities. Although a range of technologies were used, 77% of projects (n = 161) required an internet-connected device. These characteristics varied across citizen science models revealing important implications for applications of disaster citizen science, enhancement of disaster response capabilities, and sustainability of activities over time.
By increasing engagement in research, disaster citizen science may empower communities to take collective action, improve system response capabilities, and generate relevant data to mitigate adverse health impacts. The project inventory established a baseline for future research to capitalize on opportunities, address limitations, and help disaster citizen science achieve its potential.
IntroductionVitamin B12, folic acid and homocysteine play a key role in cellular functioning as part of “one-carbon metabolism”, a biochemical pathway involved in many essential biological processes, ...such as DNA synthesis. Therefore, imbalance involving these micronutrients might impair neurological functioning as well. Vitamin B12 has been implicated in the onset of a wide range of neuropsychiatric symptoms/disorders, like mood disorders, anxiety, hallucinations and delirium. Altered levels have been reported in mood disorders (MDs), but available literature particularly focuses on major depression (MDD), while the information in bipolar disorders (BDs) is still limited.ObjectivesThe present study aimed at assessing vitamin B12, homocysteine and folic acid in bipolar inpatients and detecting any relationship with clinical features or outcome measures.MethodsA total sample of 69 inpatients was selected. Diagnoses of bipolar disorder I (BDI), II (BDII), schizoaffective disorders, and MDD, were assessed according to DSM-5 criteria. The Mini International Neuropsychiatric Interview (MINI), Hamilton Rating Scale for Depression (HRSD), Young Mania Rating Scale (YMRS) and Clinical Global Impression-Severity (CGI) scales were used to complete the psychopathological evaluation. The blood parameters were measured according to common clinical-chemical methods.ResultsAbout 50 % of bipolar patients (34) showed significantly lower vitamin B12, and 14 higher homocysteine levels than normative values. No differences were noted between genders, except for a slightly higher rate of women showing lower homocysteine, phase of illness, intake of psychotropic drugs, or dietary habits. Folic acid levels were normal in most of the sample. Patients with a family history of suicide showed significantly lower levels of vitamin B12.ConclusionsThese results suggest that implementing the assessment of vitamin B12, homocysteine and folic acid in patients with BD in routine clinical practice could be a useful as well as simple, non-invasive and cheap tool. Although other studies are necessary, the present findings that lower levels of vitamin B12 seem typical of patients with a family history of suicide independently from the phase of illness, suggests that they might constitute a possible predictor of this tragic outcome.Disclosure of InterestNone Declared
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