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High strain rate hardening of metallic cellular metamaterials
Nejc Novak, Matej Vesenjak, Zoran Ren, 2024, izvirni znanstveni članek

Opis: Strain rate hardening caused by the changed deformation mode is a fascinating phenomenon in cellular metamaterials where the material’s stiffness and energy absorption capabilities increase as the strain rate increases. This unique behaviour is attributed to a combination of micro-inertia effects, base material’s strain rate hardening and inertia effects. At high strain rates, the metamaterial’s inertia influences its deformation response, which changes to shock mode. This work briefly presents the geometry and fabrication of different metallic metamaterials. Then, it evaluates their mechanical response at different strain rates, ranging from quasi-static to intermediate dynamic and shock, determined by experimental and computational investigation. The three deformation modes can be separated into two critical loading velocities, unique for each metamaterial, which are also presented and compared in this work for various metamaterials. The investigations show that the deformation mode change in metallic metamaterials depends on their porosity. The critical velocities separating the deformation modes decrease with increasing porosity, i.e., decreased density of the metamaterial results in reduced critical loading velocities. The shock deformation mode in cellular metamaterials is thus attainable at much lower loading velocities than in homogeneous (nonporous) materials.
Ključne besede: metamaterials, cellular structures, high strain rate, experimental testing, computational modelling, compression loading, mechanical properties
Objavljeno v DKUM: 22.05.2024; Ogledov: 156; Prenosov: 6
.pdf Celotno besedilo (3,42 MB)
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Mechanical behaviour of photopolymer cell-size graded triply periodic minimal surface structures at different deformation rates
Yunus Emre Yilmaz, Nejc Novak, Oraib Al-Ketan, Hacer Irem Erten, Ulas Yaman, Anja Mauko, Matej Borovinšek, Miran Ulbin, Matej Vesenjak, Zoran Ren, 2024, izvirni znanstveni članek

Opis: This study investigates how varying cell size affects the mechanical behaviour of photopolymer Triply Periodic Minimal Surfaces (TPMS) under different deformation rates. Diamond, Gyroid, and Primitive TPMS structures with spatially graded cell sizes were tested. Quasi-static experiments measured boundary forces, representing material behaviour, inertia, and deformation mechanisms. Separate studies explored the base material’s behaviour and its response to strain rate, revealing a strength increase with rising strain rate. Ten compression tests identified a critical strain rate of 0.7 s−1 for “Grey Pro” material, indicating a shift in failure susceptibility. X-ray tomography, camera recording, and image correlation techniques observed cell connectivity and non-uniform deformation in TPMS structures. Regions exceeding the critical rate fractured earlier. In Primitive structures, stiffness differences caused collapse after densification of smaller cells at lower rates. The study found increasing collapse initiation stress, plateau stress, densification strain, and specific energy absorption with higher deformation rates below the critical rate for all TPMS structures. However, cell-size graded Primitive structures showed a significant reduction in plateau and specific energy absorption at a 500 mm/min rate.
Ključne besede: cellular materials, triply periodical minimal surface, photopolymer, mechanical properties, strain rate, experimental compressive testing, computer simulations
Objavljeno v DKUM: 22.05.2024; Ogledov: 163; Prenosov: 7
.pdf Celotno besedilo (9,33 MB)
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High strain-rate deformation analysis of open-cell aluminium foam
Anja Mauko, Mustafa Sarıkaya, Mustafa Güden, Isabel Duarte, Matej Borovinšek, Matej Vesenjak, Zoran Ren, 2023, izvirni znanstveni članek

Opis: This study investigated the high-strain rate mechanical properties of open-cell aluminium foam M-pore®. While previous research has examined the response of this type of foam under quasi-static and transitional dynamic loading conditions, there is a lack of knowledge about its behaviour under higher strain rates (transitional and shock loading regimes). To address this gap in understanding, cylindrical open-cell foam specimens were tested using a modified Direct Impact Hopkinson Bar (DIHB) apparatus over a wide range of strain rates, up to 93 m/s. The results showed a strong dependency of the foam's behaviour on the loading rate, with increased plateau stress and changes in deformation front formation and propagation at higher strain rates. The internal structure of the specimens was examined using X-ray micro-computed tomography (mCT). The mCT images were used to build simplified 3D numerical models of analysed aluminium foam specimens that were used in computational simulations of their behaviour under all experimentally tested loading regimes using LS-DYNA software. The overall agreement between the experimental and computational results was good enough to validate the built numerical models capable of correctly simulating the mechanical response of analysed aluminium foam at different loading rates.
Ključne besede: Open-cell aluminium foam, Micro-computed tomography, High-strain rate, Direct impact hopkinson bar, Digital image correlation, Computer simulation
Objavljeno v DKUM: 06.12.2023; Ogledov: 379; Prenosov: 28
.pdf Celotno besedilo (3,28 MB)
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The multi-strain probiotic OMNi-BiOTiC® Active reduces the duration of acute upper respiratory disease in older people : a double-blind, randomised, controlled clinical trial
Maja Strauss, Dušanka Mičetić-Turk, Mateja Lorber, Maja Šikić Pogačar, Anton Koželj, Ksenija Tušek-Bunc, Sabina Fijan, 2023, izvirni znanstveni članek

Opis: Immunosenescence is the adverse change in the human immune function during aging, leaving older people more prone to an increased risk of infections and morbidity. Acute upper respiratory tract infections (URTIs) are very common among older people, often resulting in continued morbidity and mortality. Therefore, approaches, such as consuming probiotics, that shorten the duration or even reduce the incidence of URTIs in older people are being studied. The aim of this study was to determine the effects of a multi-strain probiotic OMNi-BiOTiC® Active, which contains 11 live probiotic strains, on the incidence, duration, and severity of URTIs in older people. In this randomized double-blinded placebo-controlled study, 95 participants, with an average age of 70.9 years in the probiotic group and 69.6 years in the placebo group, were randomly allocated to two groups: 1010 cfu per day of the multi-strain probiotic intervention OMNi-BiOTiC® Active (49) or placebo (46). The incidence of URTIs in older people after 12 weeks supplementation with OMNi-BiOTiC® showed no statistically significant difference between the two groups (p = 0.5244). However, the duration of the URTI infections was statistically significantly different between the groups (p = 0.011). The participants that consumed the probiotic had an average duration of illness of 3.1 ± 1.6 days, whilst participants that received the placebo had symptoms for an average of 6.0 ± 3.8 days (p = 0.011). Statistically significant differences in lymphocyte counts in both groups after supplementation (p = 0.035 for the probiotic group and p = 0.029 for the placebo group) and between both groups were found (p = 0.009). Statistically significant differences in eosinophil (p = 0.002) and basophil counts (p = 0.001) in the probiotic groups before and after supplementation with probiotics were also found. Supplementation with the multi-strain probiotic OMNi-BiOTiC® Active may benefit older people with URTIs. Larger randomised controlled clinical trials are warranted. Clinical Trial Registration; identifier NCT05879393.
Ključne besede: upper respiratory tract infection, URTI, duration of illness, probiotics, multi-strain, older people, immune function
Objavljeno v DKUM: 27.11.2023; Ogledov: 403; Prenosov: 7
.pdf Celotno besedilo (767,38 KB)

Processing of signals produced by strain gauges in testing measurements of the bridges
Boštjan Kovačič, Rok Kamnik, Andrej Štrukelj, Nikolai Ivanovich Vatin, 2015, objavljeni znanstveni prispevek na konferenci

Opis: Practical example of signal processing from strain gauge, inductive transducer and total station measurements are used to illustrate the features of the bridge load testing measurements. FFT provides accurate representation of physical behavior for static and dynamic signals obtained when loading the bridge. As a reference measurement the signal from inductive transducer was taken. A static part of the load test was also geodetically measured and theoretically calculated. The results are comparable.
Ključne besede: bridges, measurements, strain gauge, load test, deformation, strain, signal processing
Objavljeno v DKUM: 12.07.2023; Ogledov: 410; Prenosov: 22
.pdf Celotno besedilo (500,43 KB)
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Strain indicators in the assessment of systolic myocardial function in aboy [!] with hypertrophic cardiomyopathy : a case report
Nadezhda Chernykh, Alla Tarasova, Olga Groznova, 2020, drugi znanstveni članki

Ključne besede: 2D speckle-tracking, strain, hypertrophic cardiomyopathy, early treatment, children
Objavljeno v DKUM: 24.01.2023; Ogledov: 438; Prenosov: 45
.pdf Celotno besedilo (121,67 KB)
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Lifestyle of medical students
Matej Žnidarič, Iza Zavodnik, Lucijan Lučič Šrajer, 2020, izvirni znanstveni članek

Ključne besede: lifestyle, medical students, psychophysical strain, crisis
Objavljeno v DKUM: 24.01.2023; Ogledov: 551; Prenosov: 59
.pdf Celotno besedilo (119,23 KB)
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Questionable research practices : an introductory reflection on causes, patterns and possible responses
Gorazd Meško, Aleksander Koporec Oberčkal, 2010, pregledni znanstveni članek

Opis: Purpose: The purpose of this article is to discuss deviance in science due to increasing pressures on researchers and higher education pedagogues to be more effective and efficient in the ‘academic production’. Design/Methods/Approach: A literature review and reflection. Findings: The authors present a criminological view of deviance in science, discussing the perception of unsuitable scientific and research practices, questionable research practices, ethics and integrity in science, suitable behaviour of researchers in scientific work, and make recommendations for improving the ethics of scientific research in practice. The discussion on deviance in science is based on Merton’s principles of science (1973): the public presentation of knowledge and sharing of ideas, leading to common ownership of scientific discoveries, in which scientists disclaim their intellectual rights to their own insights in exchange for recognition and reputation. An impartial approach and universalism, in which truth is judged by impersonal, universal criteria, rather than based on race, social and economic status, sex, faith, or nationality and other subjective categories is presented and questioned. A non-profit/selfless orientation in which scientists are rewarded for selfless activities, and planned/organized scepticism – that all ideas must be tested, subject to rigorous scientific rules and public disclosure. The authors discuss these principles and connect them with scientific and research practice in Slovenia and abroad. Research limitations/implications: Research results are generalisable as deviance in science occurs in all cultures and have a global impact. Deviance in science is still an under-researched taboo topic and it needs to be discussed. Practical implications: A useful source of information for awareness raising and the improvement of quality of research work. Originality/Value: This paper extends understanding of possible deviance in science and factors related to such practices. The main value of this reflection is to facilitate understanding of factors of deviance in science and trigger a discussion on deviance among scientists.
Ključne besede: science, deviance, research, academic promotion standards, strain
Objavljeno v DKUM: 12.05.2020; Ogledov: 1179; Prenosov: 41
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Work-Home conflict and strain: the role of work-related smartphone use, job insecurity and segmentation preferences
Tjaša Srnko, 2018, magistrsko delo

Opis: Nowadays, through organisational and technological changes, organizations expect availability and work from their employees not just during working hours, but also in their free time. Work can be done from anywhere and at any time, also with the help of smartphones, which is one of the main constructs of the current research. If the employee is working from home on their smartphone, this can have an important contribution to managing work and private life, and also to strain. The individual’s preference of whether to segment his or her work from home also plays an important role in experiencing internal conflicts. As the motivation for work-related smartphone use is not fully clear, job insecurity was additionally explored as a potential predictor. In an online study, conducted in Austria, we collected data from 454 participants of different ages, gender and working backgrounds. For the analysis, multiple moderated regression and mediation analyses were used. Results showed significant relations between work-home interference and strain but no significant results between those constructs while adding work-related smartphone use. Segmentation preferences did not have an influence on the relationship between work-home interference and strain. Job insecurity was revealed to be related to work-related smartphone use and smartphone use to work-home interference. Smartphone use was also found to partially mediate the path from job insecurity to work-home interference. Finally, to prevent negative outcomes of strain, work-home interference and job insecurity, organizations should focus on: providing culture that fits their employees, try to plan availability free time and provide a clear communication.
Ključne besede: Smartphone use, work-home interference, strain, stress, job insecurity, segmentation preferences
Objavljeno v DKUM: 14.01.2019; Ogledov: 1763; Prenosov: 130
.pdf Celotno besedilo (863,72 KB)

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