3,182 research outputs found

    Estimation accuracy vs. engineering significance of contact parameters for solid dampers

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    Abstract All numerical models of friction-damped bladed arrays require knowledge or information of contact-friction parameters. In the literature, these parameters are typically tuned so that the experimental Frequency Response Function (FRF) of a damped blade matches its numerical counterpart. It is well known that there exist multiple combinations of contact parameters capable of satisfying a given experimental-numerical FRF match. A better approach towards a finer tuning could be based on directly measuring contact forces transmitted between blade platforms through the damper: in this case friction coefficients are estimated through tangential over normal force components during those hysteresis segments which are safely identified as being in a slip condition. This has been applied by these authors to rigid bar (solid) dampers. Unfortunately, the four contact stiffness values (left and right damper-platform contact, normal and tangential) are more than the measurements available in the technique presented by these authors. Therefore, the problem is underdetermined. The purpose of this paper is twofold, i.e., to propose an alternative way to estimate contact stiffness values (i.e. thus solving the under-determinacy mentioned above) and to check the effective significance of such estimates from a practical engineering point of view. The contact parameter estimation technique proposed by these authors produces, for each contact parameter, a best-fit value and an uncertainty band. It will be shown that the uncertainty affecting each contact parameter results in an uncertainty on the equivalent damping and stiffness indicators at blade level which is lower than 5%

    Latest Investigations on Underplatform Damper inner Mechanics

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    Underplatform dampers (UPDs) are widely used as a source of friction damping and are frequently incorporated into compressors and turbines for both aircraft and power-plant applications to mitigate the effects of resonant vibrations on fatigue failure. Due to the nonlinear nature of dry friction, in general dynamic analysis of structures constrained through frictional contacts is difficult, direct time integration with commercial finite element codes may not be a suitable choice given the large computation times. For this reason, ad hoc numerical codes have been developed in the frequency domain. Some authors prefer a separate routine in order to compute contact forces as a function of input displacements, others include the damper in the FE model of the bladed array. All numerical models, however, require knowledge or information of contact -friction parameters, which are established either through direct frictional measurements, done with the help of single contact test arrangements, or by fine tuning the parameters in the numerical model and comparing the experimental response of damped blade against its computed response. The standard approach is to fine-tune and experimentally validate the UPDs models by comparing measured and calculated vibration response of blade pairs. To our knowledge, nobody has ever attempted to directly measure the forces transmitted between the platforms through the damper and the relative damper-platform movement. In the light of recent results from direct measurements on dampers it is evident that a dedicated routine for the damper mechanics is an effective tool to capture those finer details which are essential to an appropriate description of damper behaviour. This was made possible by the successful effort of the present authors to accurately measure the forces transmitted between the platforms through the damper, to connect them with the relative platforms movement and to use the findings for the validation of the numerical model. The cross-comparison between numerical and experimental results allows to gain a clear understanding of all contact events (stick, slip, lift) which take place during the cycle, and on how they influence the damping performance

    Numerical and experimental investigations on underplatform damper mechanics

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    So called under-platform dampers are widely used as a source of friction damping to mitigate resonance in gas turbine blades and avoid service failures. Due to the high computational cost of performing dynamic analysis of structures constrained through frictional contacts, ad hoc numerical codes have been developed in the frequency domain. Whatever the numerical model, it requires knowledge of contact-friction parameters, which are established either through single contact frictional measurements, or by tuning the damper parameters though comparison of the experimental response of damped blade against its computed response or, else, by fine tuning the damper parameters by comparing the measured v. the calculated hysteresis cycle. The last one is these authors’ choice. Equipment and method are described accordingly

    Building a Culture of IL Assessment: Establishing Buy-In for Programmatic Change

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    Slime cells on the surface of Eragrostis seeds maintain a level of moisture around the grain to enhance germination

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    Eragrostis is a cosmopolitan genus of the family Poaceae. Several wild species, including E. pilosa (L.) Beauv., are harvested for food, but the only cultivated crop-species is tef [E. tef (Zucc.) Trotter]. Despite its importance as a staple food and its plasticity to diverse environmental conditions, little is known about the structural and physiological strategies that adapt tef seeds to endure diverse and variable moisture regimes. Here, we report the presence of slime cells, a type of modified epidermal cell, covering the fruit of tef and its wild relative, E. pilosa. The slime produced by Eragrostis belongs to the ‘true' slime type, since it is exclusively composed of pectins. Pectin forms uniform layers on the cell wall inner surface, which are confined by a thin cellulose layer to prevent release into the cell lumen. In the presence of water, pectins quickly hydrate, causing swelling of the slime cells. This is followed by their detachment, which may be controlled by a thin cuticle layer on the fruit surface. The ability of slime to absorb and maintain moisture around the grain is thought to be an adaptive feature for Eragrostis growing in dry habitats. This retention of water by slime may create conditions that are suitable for rapid germinatio

    Erythema multiforme-like irritant contact dermatitis after application of an antiscabies treatment.

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    We describe the case of an irritant contact dermatitis due to an antiscabies treatment in a man who presented to our clinic with an important cutaneous reaction with many hemorrhagic, "target" erythema multiforme-like lesions, as the result of an acute toxic insult of the skin by permethrin 5%. This is a possible, but very uncommon symptom of non-eczematous contact dermatitis and an unusual drug causing the acute hypersensitivity reaction typical of erythema multiforme

    Challenges in IAQ for Indoor Spaces: A Comparison of the Reference Guideline Values of Indoor Air Pollutants from the Governments and International Institutions

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    Since people spend most of their time inside buildings, indoor air quality (IAQ) remains a highlighted topic to ensure in the built environment to improve public health, especially for vulnerable users. To achieve a better indoor environment quality (IEQ), some countries’ governments or regional institutions have developed and published reference guideline values of various air pollutants to prevent the IAQ from becoming adverse to occupants. Beyond guidelines by World Health Organization (WHO), in some countries, there are specific institutional requirements on the IAQ, and others integrated it into the building regulation for the built environment. This paper is based on the literature research, summarized from previously conducted works by the authors, on the chemical reference values of IAQ-related regulations and guidelines published by several Governments or related institutions from various regions around the World. Despite these efforts at standardization and legislation, many indoor air quality monitoring activities conducted in several countries still fall short of the main indications produced. By comparing the reference values of 35 pollutants, both physical and chemical ones, which are proposed in documents from 23 regions included so far, the IAQ research and prevention actions on progress in different regions should be included in monitoring plans with guidelines/reference values in their current state. The outcome of the paper is to define the current trends and suggest some perspectives on the field of interest for improving the indoor air quality of generic spaces at an international level. It becomes evident that, at the global level, IAQ represents a complex political, social, and health challenge, which still suffers from the absence of a systematic and harmonized approach. This is not a new situation; the issue was raised more than 40 years ago, and despite efforts and a pandemic, the situation has not changed

    Can Homes Affect Well-Being? A Scoping Review among Housing Conditions, Indoor Environmental Quality, and Mental Health Outcomes

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    The purpose of the scoping review is to explore the relationship between housing conditions, indoor environmental quality (IEQ), and mental health implications on human well-being. In fact, time spent at home increased due to the recent COVID-19 lockdown period, and social-sanitary emergencies are expected to grow due to the urbanization phenomenon. Thus, the role of the physical environment in which we live, study, and work, has become of crucial importance, as the literature has recently highlighted. This scoping review, conducted on the electronic database Scopus, led to the identification of 366 articles. This, after the screening processes based on the inclusion criteria, led to the final inclusion of 31 papers related specifically to the OECD area. The review allowed the identification of five housing conditions [house type, age, and floor level; housing qualities; household composition; neighborhood; green spaces] that, by influencing the IEQ parameters, had impacts on the mental health outcomes addressed. By synthesizing the contributions of the review, a list of design recommendations has been provided. These will serve as a basis for future researchers, from which to develop measures to reduce inequalities in housing by making them healthier, more resilient, and salutogenic

    Possible regulation of CFTR-chloride channels by membrane-bound phosphatases in pancreatic duct cells

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    AbstractWe have studied CFTR-Cl− channels in non-CF CAPAN-1 and in CFTR-transfected CFPAC-PLJ-CFTR-6 epithelial cells from human pancreas. Theophylline and IBMX induced the opening of cell-attached CFTR-Cl− channels. Theophylline, IBMX and the alkaline phosphatase (AP) inhibitor levamisole enhanced the activity of excised channels and reduced by 70–75% the apical membrane-associated APs activity. Okadaic acid had no effect on APs and channel activities. A polyclonal anti-alkaline phosphatase antibody (which detected apical APs) reduced APs activity and activated quiescent excised chloride channels. These results suggest that CFTR channels may be regulated by membrane-bound phosphatases

    Developing an Information Literacy Assessment Rubric: A Case Study of Collaboration, Process, and Outcomes

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    A team of four librarians at the [Institution Name] ([Institution Initials]) Libraries partnered with the [Institution Initials] Office of Institutional Effectiveness and its Director of Assessment & Accreditation Services for General Education to conduct a campus-wide, exploratory assessment of undergraduate information literacy skills. The project evaluated a selection of graduating, senior-level student papers using a rubric developed as part of the collaboration. This paper describes and discusses the collaborative rubric development and rating process, the practical implications for other librarians seeking to conduct a similar assessment, and the impact the project is having on the library instruction program
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