1,721,019 research outputs found
A nonlinear elastic description of cell preferential orientations over a stretched substrate
Full text linkThe active response of cells to mechanical cues due to their interaction with the environment has been of increasing interest, since it is involved in many physiological phenomena, pathologies, and in tissue engineering. In particular, several experiments have shown that, if a substrate with overlying cells is cyclically stretched, they will reorient to reach a well-defined angle between their major axis and the main stretching direction. Recent experimental findings, also supported by a linear elastic model, indicated that the minimization of an elastic energy might drive this reorientation process. Motivated by the fact that a similar behaviour is observed even for high strains, in this paper we address the problem in the framework of finite elasticity, in order to study the presence of nonlinear effects. We find that, for a very large class of constitutive orthotropic models and with very general assumptions, there is a single linear relationship between a parameter describing the biaxial deformation and cos^(2) theta(eq), where theta(eq) is the orientation angle of the cell, with the slope of the line depending on a specific combination of four parameters that characterize the nonlinear constitutive equation. We also study the effect of introducing a further dependence of the energy on the anisotropic invariants related to the square of the Cauchy-Green strain tensor. This leads to departures from the linear relationship mentioned above, that are again critically compared with experimental data
Choosing the minimum order size in large-scale retail trade distribution
No full textOne of the main issues characterizing the large-scale retail trade (LSRT) distribution is the relatively high transportation costs compared to profit margins. The complexity of non-integrated supply chains worsens this problem because the actors – wholesalers, third-party logistics providers and retailers – may reasonably have different and conflicting aims. Furthermore, due to the numerous operational field-specific peculiarities, it is not possible to straightforwardly apply those consolidated operations management models which have been conceived in other industrial contests. Among these, the classical models for defining the appropriate order size to minimize transportation costs seem not to be appropriate for the LSRT context. In this paper we propose an approach to compute the minimum order size for a network of retailers supplied by a single wholesaler, to obtain an overall transportation costs optimization through the increase of trucks saturation. Taking cue from literature review on optimization techniques in LSRT supply chain and logistics, and highlighting the context-specific constraints, we propose an heuristic approach which has been validated on the case of an Italian LSRT company
Cell orientation under stretch: Stability of a linear viscoelastic model
Full text linkThe sensitivity of cells to alterations in the microenvironment and in particular to external mechanical stimuli is significant in many biological and physiological circumstances. In this regard, experimental assays demonstrated that, when a monolayer of cells cultured on an elastic substrate is subject to an external cyclic stretch with a sufficiently high frequency, a reorganization of actin stress fibres and focal adhesions happens in order to reach a stable equilibrium orientation, characterized by a precise angle between the cell major axis and the largest strain direction. To examine the frequency effect on the orientation dynamics, we propose a linear viscoelastic model that describes the coupled evolution of the cellular stress and the orientation angle. We find that cell orientation oscillates tending to an angle that is predicted by the minimization of a very general orthotropic elastic energy, as confirmed by a bifurcation analysis. Moreover, simulations show that the speed of convergence towards the predicted equilibrium orientation presents a changeover related to the viscous–elastic transition for viscoelastic materials. In particular, when the imposed oscillation period is lower than the characteristic turnover rate of the cytoskeleton and of adhesion molecules such as integrins, reorientation is significantly faster
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Quantifying the impact of ERP malfunctioning in a manufacturing plant
No full textEnterprise Resource Planning system (ERP) benefits for manufacturing companies have been praised for years and companies have become increasingly dependent on these IT tools. However, any malfunctions or temporary unavailability of the ERP can significantly affect the company business. The ERP obsolescence invokes the critical decision on whether to update, upgrade or substitute it. When these operations require significant investments, a timely evaluation of the advantages and disadvantages is needed. In this paper, we present a methodology to quantify the economic loss caused by the malfunctioning of an ERP supporting a manufacturing plant. The research took cue from a real case of a world-famous multinational company of the automotive industry. In this case, the maintenance contract supporting the previous system expired and the company experienced significant inconveniences by delaying the introduction of a new ERP. Hence, the main functional features of an ERP in a production plant processes are listed, and the potential hindrances due to the information system malfunctioning are classified in four critical macro-categories: production planning, manufacturing operations management, materials management, warehousing and inventory control. The contribution of the paper resides in classification of the main operational losses due to ERP malfunction in a generic manufacturing site, on top of proposing possible criteria for estimating the related economic losses, based on the issues faced during the real-world scenario
Risk Assessment framework for delivery process: A delivery features perspective to optimize efforts in the assessment phase
No full textOne of the main issues faced in supply chain risk management is the lack of a tool for evaluating the risk profile and for identifying which risks require mitigation. The complexity of modern supply chains worsens this issue, mostly in delivery and distribution processes, since these significantly vary according to the delivered product, the distribution channel and the target market. Indeed, these features influence so deeply the risk profile of a company that their effect has an impact on each single delivery. This paper proposes a framework aiming to provide risk managers with a tool that can reduce evaluation effort while helping in focusing the efforts on the assessment and mitigation of critical aspects. Starting from a literature review of supply chain risk taxonomies and through mapping the connection between risk classes and features of the supply chain downstream flows, the framework defines which risks are relevant for a given scenario and how to perform an efficient assessment phase. Finally, to validate the framework and to highlight potential gaps between the outcomes and company managers' perception, a real-world scenario is proposed
Exploring the time features of recognition memory for music in the semantic and episodic systems: An ERP study
No full textPrevious studies Olivetti Belardinelli 2005; Olivetti Belardinelli et al. 1999, 2000) have shown that musical memory relies on different memory systems according to music characteristics (tonality is recollected by means of semantic memory, salience – defined as redundancy of melodic and/or rhythmic parameters – by means of episodic memory), and that such systems recruit different cerebral districts. Nevertheless the time course of such process is still relatively unknown. The aim of this study was to explore the temporal dynamics of musical memory in the semantic and episodic systems. 20 healthy (10 males) right-handed non-musicians participated in this study. Stimuli were 72 short musical themes composed for experimental purposes and employed in our previous studies. They had variable durations (6,5-12,5 s) and were administered in random order with an ISI of 5 s. Stimuli were divided into two different version of a “study lists” (36 stimuli) and two related “test lists” (72 stimuli). Subjects were asked to attentively listen to one “study list”. After 15-20 min. they started the EEG session (electrodes in Fz, Cz, Pz, F7, F8, T3, T4, T5, T6), where they were administered the related “test list” and had to perform a recognition task, pressing a different button whether, according to Tulving’s model (1972): 1) they recognized the melody as previously heard (Remember response); 2) the melody evoked in them a sense of familiarity (Know response); 3) they could not recognize the melody at all (X response). Half of the subjects were asked to press the button as soon as they could decide among the three kinds of response, half of them were instead required to press the button as soon as the musical excerpt was expired. In both cases the analysis concerned the 1000 ms. preceding and following the button press
Mechanics-Based Models to Predict the Alignment of Cells on a Cyclically Stretched Substrate
Full text linkAs pointed out by numerous experiments, the cell cytoskeleton appears to be responsive to external mechanical stimuli. In particular, experimental evidence demonstrates that a population of cells adhering to a substrate which is deformed periodically, for instance to mimic the heartbeat, responds to the strain by reorienting their stress fibres and focal adhesions. At the end of such a process, the cell achieves a specific orientation with respect to the strain direction, and such orientation depends on the characteristics of the external strain. The increasing interest in understanding mechanotransduction phenomena led to a growing attention to the cell realignment behaviour, both from the experimental and from the modelling point of view. Indeed, the contribution of mathematical models turns out to be very important to elucidate some relevant mechanisms and to suggest possible improvements in experimental assays. In this Chapter, we present an overview of mechanics-based mathematical models that have been proposed to describe cell reorientation and we highlight connections among the different research contributions within this field
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