Fundamental analysis of the failure of polymer-based fiber reinforced composites

A mathematical model is described which will permit predictions of the strength of fiber reinforced composites containing known flaws to be made from the basic properties of their constituents. The approach was to embed a local heterogeneous region (LHR) surrounding the crack tip into an anisotropic elastic continuum. The model should (1) permit an explicit analysis of the micromechanical processes involved in the fracture process, and (2) remain simple enough to be useful in practical computations. Computations for arbitrary flaw size and orientation under arbitrary applied load combinations were performed from unidirectional composites with linear elastic-brittle constituent behavior. The mechanical properties were nominally those of graphite epoxy. With the rupture properties arbitrarily varied to test the capability of the model to reflect real fracture modes in fiber composites, it was shown that fiber breakage, matrix crazing, crack bridging, matrix-fiber debonding, and axial splitting can all occur during a period of (gradually) increasing load prior to catastrophic fracture. The computations reveal qualitatively the sequential nature of the stable crack process that precedes fracture

Fracturing highly disordered materials

We investigate the role of disorder on the fracturing process of heterogeneous materials by means of a two-dimensional fuse network model. Our results in the extreme disorder limit reveal that the backbone of the fracture at collapse, namely the subset of the largest fracture that effectively halts the global current, has a fractal dimension of $1.22 \pm 0.01$. This exponent value is compatible with the universality class of several other physical models, including optimal paths under strong disorder, disordered polymers, watersheds and optimal path cracks on uncorrelated substrates, hulls of explosive percolation clusters, and strands of invasion percolation fronts. Moreover, we find that the fractal dimension of the largest fracture under extreme disorder, $d_f=1.86 \pm 0.01$, is outside the statistical error bar of standard percolation. This discrepancy is due to the appearance of trapped regions or cavities of all sizes that remain intact till the entire collapse of the fuse network, but are always accessible in the case of standard percolation. Finally, we quantify the role of disorder on the structure of the largest cluster, as well as on the backbone of the fracture, in terms of a distinctive transition from weak to strong disorder characterized by a new crossover exponent.Comment: 5 pages, 4 figure

Mitochondrial Function in Alzheimer’s Disease: Focus on Astrocytes

The brain is one of the most energy-requiring organs in the human body. Mitochondria not only generate this energy, but are centrally involved critical cellular functions including maintenance of calcium homeostasis, synthesis of biomolecules, and cell signaling. Even though neurons and astrocytes preferentially use different energy substrates and metabolic pathways, these two cell types are intricately linked in their energy metabolism. Recently it has become clear that astrocytes have a key role in the regulation and support of the neuronal mitochondrial quality control, yet several questions remain unanswered to fully understand the mechanisms of mitochondrial function, transport, turnover and degradation in astrocytes. Alzheimer’s disease is the most common neurodegenerative disorder, the exact mechanisms of which remain incompletely understood. The fact that astrocytic mitochondrial dysfunction is an early event in the pathogenesis of Alzheimer’s disease suggests that more research on mitochondrial function and impairment is required in the hopes of disease alleviation in the future

Financial attractiveness of wood production in smallholder plantations of Central Vietnam in the context of developing carbon markets

In Vietnam, fast-growing Acacia hybrid dominates commercial smallholdings and is largely managed in short rotations for pulpwood. However, increasing demand for logwood implies growing Acacia hybrid in longer rotations. One way of encouraging smallholders to prolong the rotation would be payments for aboveground carbon storage. Thus, this study evaluated the financial attractiveness of shifting from pulpwood to logwood production, with and without hypothetical carbon payments of $5,$10 and $20 tCO(2)e ha(-1). The data were drawn from smallholder interviews, a plantation inventory and a market study. The growth models for a 5-year pulpwood regime and various logwood regimes used for financial modelling were developed in CO2FIX simulation software. With a financially optimal rotation length of 9-10 years, the study finds that growing Acacia hybrid for logwood is much more profitable than growing it for pulpwood. However, due to thinning in logwood regime, a financially optimal logwood regime stores only 15-16% more carbon than a 5-year pulpwood regime. Consequently, carbon payments at any of the three price levels would not shift the financially optimal rotation length. The study concluded that carbon payments alone are unlikely to be an effective means to encourage smallholders in central Vietnam to prolong the rotation.Peer reviewe

Mitä voimme oppia maailmalla järjestetyistä perusturvaan liittyvistä kokeista? : Katsaus kenttäkoeasetelmiin

Tämän työpaperin tarkoituksena on esitellä ulkomailla tehtyjä tai suunnitteilla olevia perustulokokeita, jotka voivat olla hyödyksi Suomessa vireillä olevan perustulokokeilun valmistelu-työssä. Kuvailemme myös muita kenttäkokeita, joiden koeasetelmista voidaan Suomessakin ottaa oppia. Käymme lisäksi läpi perustulokokeiden vaikutusten arvioimisen kannalta keskeistä taloustieteellistä teoriaa. Lähteinä olemme käyttäneet akateemisia tutkimusjulkaisuja. Tämä on rajannut tarkastelusta pois kokeet tai kokeilut, joista ei ole tehty kunnollisia selvityksiä tai analyysejä. Alankomaissa suunnitteilla olevien kokeiden tiedot perustuvat niitä valmistelevien tutkijoiden haastatteluihin. Kuvailemme työpaperissa lyhyesti, minkälaisia eri kokeet ovat olleet ja minkälaisia tuloksia niistä on saatu. Näihin havaintoihin perustuen olemme valmistelleet listan keskeisimmistä opeista, jotka kannattaa huomioida suomalaisen perustulokenttäkokeen valmistelussa. Nämä opit on jaettu kolmeen aihealueeseen: tutkimuskysymykset, koeasetelma ja tulosten arvioiminen. Yksi olennaisimmista tutkimuskysymyksistä perustulokokeessa on selvittää, miten ilman tiukkoja ehtoja ja tulorajoja myönnettävä rahaetuus vaikuttaa työn tarjontaan. Sitä olisi hyvä tutkia erilaisilla perustulotason ja veroasteiden yhdistelmillä, jotta voidaan ymmärtää sekä tulo- että substituutiovaikutuksia. Subjektiivisen hyvinvoinnin ja stressitasojen mittaaminen voi auttaa havaitsemaan perustulon vaikutuksia herkemmin ja yksilöllisemmin kuin pelkän työn tarjonnan tarkastelu. Siksi myös niitä tulisi seurata kokeessa. Laadullisesti hyvän koeasetelman edellytyksenä on riittävän iso otoskoko, joka mahdollistaa eri ihmisryhmien tarkemman tarkastelun. Koehenkilöt tulee valita arpomalla ja vapaaehtoisten käyttöä koehenkilöinä tulisi välttää. Koska tietylle alueelle rajautuva koe vähentää tulosten yleistettävyyttä, olisi valtakunnallinen koe suotuisin vaihtoehto. Kokeen on kestettävä myös riittävän pitkään, jotta käyttäytymisvaikutuksia ehditään havaita. Tulosten arviointiin liittyen suosittelemme, että kokeiltavan ohjelman arviointi otetaan huomioon jo suunnittelu- ja toteutusvaiheessa. Tuloksia arvioitaessa oikean ajankohdan valitseminen aineistosta on yhtä lailla tärkeää. Lisäksi kokeen aineiston avoimuus parantaa tutkimuksen laatua. Mikään aiemmin suoritetuista perustulokokeista ei pysty antamaan suoraan vastauksia, miten perustulon käyttöönotto vaikuttaisi ihmisten käyttäytymiseen Suomessa, koska ne on tehty Suomen nykytilasta poikkeavissa olosuhteissa. Muista kokeista voidaan kuitenkin ammentaa ideoita siihen, miten perustulokokeilu Suomessa kannattaisi toteuttaa

Increased iron content in the heart of the Fmr1 knockout mouse

Peer reviewe

Tannins, flavonoids and stilbenes in extracts of African savanna woodland trees Terminalia brownii, Terminalia laxiflora and Anogeissus leiocarpus showing promising antibacterial potential

Terminalia laxiflora, Terminalia brownii and Anogeissus leiocarpus are used as decoctions, macerations, infusions and fumigations in East and West African traditional medicine for treatment of infectious diseases and their symptoms. Using this ethnopharmacological information as a guideline for our research and owing to the fact that these species have not been subjected to in depth antibacterial and phytochemical studies, thirty-nine extracts of various polarities of the stem bark, stem wood and roots were studied for growth inhibitory effects against the human pathogenic bacteria Staphylococcus epidermidis, Staphylococcus aureus, Micrococcus luteus and Pseudomonas aeruginosa. Our results indicate that the studied species contain antibacterial compounds of a wide range of polarities. All polar root extracts of T. laxiflora and various polar extracts of T. brownii roots, including hot water decoctions, gave broad-spectrum antibacterial effects and low MIC values of 39 mu g/ml. The main ellagitannins in an ethyl acetate extract of the root of T. laxiflora were found to be corilagin and its derivative and punicalagin. A methanol extract of the roots of T. brownii contained methyl-(S)-flavogallonate and its derivative as the main identified ellagitannins. Moreover, both Terminalia species were found to contain ellagic acid xylopyranoside and methyl ellagic acid xyloside and pure ellagic acid was present in T. brownii. Pure punicalagin did not give as low MIC as an ethyl acetate extract of the roots of T. laxiflora, containing punicalagin as one of its main compounds, although this ellagitannin totally inhibited the growth of S. aureus at 125 mu g/ml and P. aeruginosa at 500 mu g/ml. Similarly, pure ellagic and gallic acid gave higher MIC values than the methanolic root extract of T. brownii against S. aureus and P. aeruginosa. Moreover, a Sephadex LH-20 fraction of the methanolic extract of the roots of T. brownii, enrichedwithmethyl-(S)-flavogallonate and its isomer, gave higher MIC values than the crude methanolic extract. These results suggest that the polyphenols in the extracts might act synergistically with each other. A methanolic soxhlet extract of the roots of A. leiocarpus, containing ampelopsin, aromadendrin, taxifolin, pinosylvin and 4'-methylpinosylvin gave a low MIC value of 39 mu g/ml against all bacterial strains used in this investigation. Our results demonstrate that the roots, stem bark and stem wood of T. brownii, T. laxiflora and A. leiocarpus are rich sources of (new) antimicrobial compounds and justify the uses of these plants for treatment of infections in African traditional medicine.Peer reviewe

Systemic Inflammation Induced Changes in Protein Expression of ABC Transporters and Ionotropic Glutamate Receptor Subunit 1 in the Cerebral Cortex of Familial Alzheimer`s Disease Mouse Model

Alzheimer's disease (AD) is an incurable disease, with complex pathophysiology and a myriad of proteins involved in its development. In this study, we applied quantitative targeted absolute proteomic analysis for investigation of changes in potential AD drug targets, biomarkers, and transporters in cerebral cortices of lipopolysaccharide (LPS)-induced neuroinflammation mouse model, familial AD mice (APdE9) with and without LPS treatment as compared to age-matched wild type (WT) mice. The ABCB1, ABCG2 and GluN1 protein expression ratios between LPS treated APdE9 and WT control mice were 0.58 (95% CI 0.44-0.72), 0.65 (95% CI 0.53-0.77) and 0.61 (95% CI 0.52-0.69), respectively. The protein expression levels of other proteins such as MGLL, COX-2, CytC, ABCC1, ABCC4, SLC2A1 and SLC7A5 did not differ between the study groups. Overall, the study revealed that systemic inflammation can alter ABCB1 and ABCG2 protein expression in brain in AD, which can affect intra-brain drug distribution and play a role in AD development. Moreover, the inflammatory insult caused by peripheral infection in AD may be important factor triggering changes in GluN1 protein expression. However, more studies need to be performed in order to confirm these findings. The quantitative information about the expression of selected proteins provides important knowledge, which may help in the optimal use of the mouse models in AD drug development and better translation of preclinical data to humans. (c) 2021 American Pharmacists Association. Published by Elsevier Inc. All rights reserved.Peer reviewe