224 research outputs found
Towards a Study of the Ne-22(p,gamma)Na-23 Reaction at LUNA
No full textThe 22Ne(p,γ)23Na reaction is a part of the hydrogen burning NeNa cycle. In second-generation stars hydrogen burning may proceed via this cycle. The rate of the 22Ne(p,γ) 23Na reaction depends on the strength of several resonances in the energy range of the LUNA 400 kV accelerator which have never been observed in direct experiments. A related study is under preparation at LUNA
Sliding and abrasive wear behaviour of HVOF- and HVAF-sprayed Cr3C2-NiCr hardmetal coatings
No full textThis paper provides a comprehensive characterisation of HVOF- and HVAF-sprayed Cr3C2-25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems. All coatings contain less Cr3C2 than the feedstock powder, possibly due to the rebound of some Cr3C2-rich particles during high-velocity impact onto the substrate. Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter- and intra-lamellar cohesion, being higher (≥70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch. Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (≈5×10-6 mm3/(Nm)). At 400 °C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from ≈0.7 to ≈0.5. The thermal expansion coefficient of the coatings (11.08×10-6 °C-1 in the 30-400 °C range) is sufficiently close to that of the steel substrate (14.23×10-6 °C-1) to avoid macro-cracking
Tribology of HVOF- and HVAF-sprayed WC-10Co4Cr hardmetal coatings: A comparative assessment
No full textThis paper provides a comprehensive assessment of the sliding and abrasive wear behaviour of WC-10Co4Cr hardmetal coatings, representative of the existing state-of-the-art. A commercial feedstock powder with two different particle size distributions was sprayed onto carbon steel substrates using two HVOF and two HVAF spray processes. Mild wear rates of <10-7mm3/(Nm) and friction coefficients of ≈0.5 were obtained for all samples in ball-on-disk sliding wear tests at room temperature against Al2O3 counterparts. WC-10Co4Cr coatings definitely outperform a reference electrolytic hard chromium coating under these test conditions. Their wear mechanisms include extrusion and removal of the binder matrix, with the formation of a wavy surface morphology, and brittle cracking. The balance of such phenomena is closely related to intra-lamellar features, and rather independent of those properties (e.g. indentation fracture toughness, elastic modulus) which mainly reflect large-scale inter-lamellar cohesion, as quantitatively confirmed by a principal component analysis. Intra-lamellar dissolution of WC into the matrix indeed increases the incidence of brittle cracking, resulting in slightly higher wear rates. At 400°C, some of the hardmetal coatings fail because of the superposition between tensile residual stresses and thermal expansion mismatch stresses (due to the difference between the thermal expansion coefficients of the steel substrate and of the hardmetal coating). Those which do not fail, on account of lower residual stresses, exhibit higher wear rates than at room temperature, due to oxidation of the WC grains.The resistance of the coatings against abrasive wear, assessed by dry sand-rubber wheel testing, is related to inter-lamellar cohesion, as proven by a principal component analysis of the collected dataset. Therefore, coatings deposited from coarse feedstock powders suffer higher wear loss than those obtained from fine powders, as brittle inter-lamellar detachment is caused by their weaker interparticle cohesion, witnessed by their systematically lower fracture toughness as well
The Use of Tetrazine-Norbornene Click Products in Supramolecular Hydrogel Crosslinking and the Design of Dynamic Hydrogels
No full textHerein, the discovery and application of a novel class of supramolecular secondary interactions between the cycloaddition products of the inverse electron-demand Diels Alder (IEDDA) tetrazine-norbornene click reaction is described. First, a direct comparison of the bulk properties of poly(ethylene glycol) (PEG) hydrogels crosslinked with either the radical-mediated thiol-norbornene reaction or the tetrazine-norbornene reaction revealed significant and unexpected differences in the two gels. These differences in the storage moduli, swelling, and susceptibility to hydrolytic degradation of the two gel formulations could not be attributed to differences in crosslink density or crosslinking reaction efficiency. However, molecular dynamics simulations suggested the existence of supramolecular interactions between the tetrazine-norbornene click products (TNCP) which could provide additional physical crosslinking of the network. This was confirmed by the gelation of multi-arm PEG macromers end-functionalized with TNCP in the absence of covalent crosslinking. Unlike other supramolecular crosslinking moieties, TNCP can be synthesized in situ in physiologic conditions with the bio-orthogonal IEDDA reaction without the need for exogenous initiators or adjustment in pH, temperature, or ion concentrations. In situ TNCP installation was then leveraged as a mechanism for bio-orthogonal, controlled gel stiffening in a pre-existing and enzymatically-degradable covalent PEG-peptide network. Pendant TNCP groups demonstrated a concentration-dependent effect on bulk gel modulus, and TNCP installation yielded an approximately 2 kPa increase in shear storage modulus over the course of 4-6 hours. This approach had no effect on the viability of encapsulated cells and the increase in gel stiffness was long-lasting in culture conditions. Finally, TNCP-functionalized gelatin was used to create a shear-thinning, extrudable hydrogel. As in PEG-peptide hydrogels, the installation of pendant TNCP groups in covalently crosslinked gelatin networks increased the bulk shear storage modulus of the gel. Additionally, supramolecular gelatin gels were formed via installation of TNCP along norbornene-functionalized gelatin molecules. These supramolecular gel-TNCP hydrogels exhibited fitness for extrusion, demonstrating both shear thinning and rapid recovery of gel stiffness after shear. In short, this work presents the use of the bio-orthogonal IEDDA tetrazine reaction to synthesize supramolecular interacting domains in situ in hydrogel biomaterials. Future studies will serve to expand the remarkably broad potential applicability of this chemistry
Resarch on children's magazine of Western Trache
No full textYüksek LisansCumhuriyet sonrası Batı Trakya'da yayımlanan dönemin çocuk dergilerini, farklı gazete ve dergi başlığı altında bulunan çocuk ilavelerini bu çalışmamızda tanıtarak incelemeye çalıştık. Batı Trakya'da 1928 sonrası Latin harfleriyle çıkan birçok yayın faaliyeti yanında, çocuk edebiyatına dair eserlerin ilk nüvelerini teşkil eden çocuk dergilerinde bunun en güzel örnekleri verilmiştir. Biz de bu çalışmayla Batı Trakya'da çıkan çocuk dergilerini kapsamlı bir şekilde araştırmamıza dahil ettik. Bu çalışma "Ön Söz", "Giriş", "Sonuç" ve "Kaynakça" dışında iki ana bölümden oluşmaktadır. Giriş kısmı akabinde Batı Trakya'nın tarihsel ve coğrafi yapısıyla, siyasal ve kültürel yapısı hakkında bilgi verdik. Yine Batı Trakya'da geçmişte nihayet bulan ve günümüzde varlığını sürdüren basın faaliyetleri hakkında genel bir çerçeve çizmiş olduk. I. Bölüm'de hem dergilerin tanıtımlarını, güttükleri amaçları, içerik açısından bir incelemesini yapmaya çalıştık, hem de bu dergiler üzerinde çalışma yapmak isteyecek olanlara kolaylık sağlayabilecek bir dizin hazırladık. Biçim bakımından yaptığımız incelemede dergilerin biçim özelliklerini, amacı, yazar kadrosu hakkında bilgi verdik. İçerik incelemesinde ise edebiyat türlerine göre sınıflandırarak incelemeye çalıştık. Bu bölümde yer alan Dizin kısmında da Kronolojik, Yazar Adına Göre (Alfabetik) ve Tematik olarak bir sınıflandırma yaptık. Ayrıca dergilere ait belge niteliğinde olan fotoğrafları Dergilere Ait Belge ve Fotoğraflar başlığı altında bu bölümün sonuna ekledik. Anahtar Kelimeler: Batı Trakya, Çocuk Dergisi, Çocuk Edebiyatı, İncelemeIn this work, I tried to present the journals for children, the sections for children in different newspapers or journals published in Western Thrace region of Greece in Turkish language, after the foundation of the Republic of Turkey. After the Latin alphabet revolution in Turkey in 1928, there were a lot of works published in Western Thrace, including journals for children. At these journals for children, it is possible to see the first examples of children literature in Western Thrace. In this dissertation, I investigated the journals for children published in Western Thrace, adding to my research. Other than the sections of "Preface", "Introduction", "Conclusion" and "Bibliography", this dissertation consists of two main parts. After the introduction part, I gave information about the history, geography, culture and political organisation of Western Thrace. Also, I drew a general picture of different periodically published journals or newspapers, which some of them ceased to exist and others are still continuing to be published. At the first part, I tried to present the journals, explore the goals of them, analyze the content and provide an index to help the future researchers. Regarding my research about the form of journals, I investigated the form, goals, and authors of the journals. On the other hand, in my investigation about the content, I tried to classify them according to the type of literature. At the index section of this part, I classified the literature according to Chronological order, author names (alphabetically) and thematically. I added another section in this part consisting of the photographs of the journals as evidence and named it "Photographs and Documents of the Journals". Key Words: Western Thrace, Children Magazine, Children's Literature, Examinatio
Arthropoda. Jnsecta. Orthoptera. II
No full textTavola XI
Tavola parietale.
Presente sulla tavola in basso a destra il monogramma dell\u27autore: HN (Hinrich Nitsche)
PANARTHROPODA,
Phylum Arthropoda
Subphylum Hexapoda
Classe Insecta
Orthoptera
Caelifera (1, 2, 3) ed Ensifera (7)
4) Uovo
5) Apparato buccale masticatore
6) Esoscheletro con spiracoli delle trache
7) Gryllotalpa, corpo tozzo, zampe anteriori robuste, atte a scavare gallerie, costumi sotterranei.
8 e 9) Organi stridulanti sulle zampe.
10) Ala con venature tracheali
11, 12) particolari di ramificazioni tracheali.Tavola XI
Tavola parietale.
Presente sulla tavola in basso a destra il monogramma dell\u27autore: HN (Hinrich Nitsche)
PANARTHROPODA,
Phylum Arthropoda
Subphylum Hexapoda
Classe Insecta
Orthoptera
Caelifera (1, 2, 3) ed Ensifera (7)
4) Uovo
5) Apparato buccale masticatore
6) Esoscheletro con spiracoli delle trache
7) Gryllotalpa, corpo tozzo, zampe anteriori robuste, atte a scavare gallerie, costumi sotterranei.
8 e 9) Organi stridulanti sulle zampe.
10) Ala con venature tracheali
11, 12) particolari di ramificazioni tracheali.PANARTHROPODA,
Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Orthoptera
Caelifera (1, 2, 3) and Ensifera (7)
4) Egg
5) Chewing mouthparts
6) Exoskeleton with spiracles of tracheae
7) Gryllotalpa: stubby body, sturdy forelegs, designed to dig tunnels, underground costumes.
8 e 9) Stridulating organs on legs.
10) A wing with tracheal veins.
11, 12) Details of tracheal ramification.PANARTHROPODA,
Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Orthoptera
Caelifera (1, 2, 3) and Ensifera (7)
4) Egg
5) Chewing mouthparts
6) Exoskeleton with spiracles of tracheae
7) Gryllotalpa: stubby body, sturdy forelegs, designed to dig tunnels, underground costumes.
8 e 9) Stridulating organs on legs.
10) A wing with tracheal veins.
11, 12) Details of tracheal ramification
Secondary Cosmic Ray Particles Due to GCR Interactions in the Earth's Atmosphere
No full textPrimary GCR interact with the Earth's atmosphere originating atmospheric showers, thus giving rise to fluxes of secondary particles in the atmosphere. Electromagnetic and hadronic interactions interplay in the production of these particles, whose detection is performed by means of complementary techniques in different energy ranges and at different depths in the atmosphere, down to the Earth's surface. Monte Carlo codes are essential calculation tools which can describe the complexity of the physics of these phenomena, thus allowing the analysis of experimental data. However, these codes are affected by important uncertainties, concerning, in particular, hadronic physics at high energy. In this paper we shall report some results concerning inclusive particle fluxes and atmospheric shower properties as obtained using the FLUKA transport and interaction code. Some emphasis will also be given to the validation of the physics models of FLUKA involved in these calculations
Discovery of Extraterrestrial 244Pu in 2 Million Year Old Fossilized Stromatolites
No full textThe rapid neutron capture process ( r -process) is responsible for producing about half of the elements heavier than iron in the Universe through cataclysmic events such as core-collapse supernovae and neutron star mergers (NSMs). Despite extensive research, the exact astrophysical sites of the r -process remain one of the unanswered questions in science. The well-known supernova-produced radioisotope ^60 Fe has been detected in terrestrial reservoirs, providing evidence that material from a nearby supernova reached Earth approximately 2 million years (Ma) ago. Our study reports the detection of ^244 Pu in fossilized stromatolite samples that are 2.0 Ma old, collected from palustrine–lacustrine stratigraphic layers dating back to approximately 5 Ma located at the margins of the present-day Lake Turkana Basin in northern Kenya. We demonstrate that stromatolites can mass-concentrate actinides in the range of 10 ^2 –10 ^3 . Using accelerator mass spectrometry, we isolate ^244 Pu and eliminate the anthropogenic contribution. From our findings, we evaluate a terrestrial fluence between 0.2 and 4.7 × 10 ^3 at cm ^−2 , in relative agreement with previous studies. The detection of the r -process ^244 Pu around 2 Ma ago raises the possibility of a common supernova origin with ^60 Fe; however, alternative scenarios, such as the production of ^244 Pu in NSMs or other cosmic events and its transport to Earth alongside ^60 Fe via interstellar debris, cannot be ruled out, highlighting the need to consider multiple mechanisms for isotopic transport in the cosmos
Genetic Background Influences Arterial Vasomotor Function in Male and Female Mice
No full textCardiovascular disease (CVD) is the leading cause of death worldwide and is typically preceded by atherosclerotic lesion buildup within the arteries. Endothelial dysfunction is a known precursor to the development of atherosclerosis and subsequent progression of heart disease. While diet and environmental factors contribute to the progression of vascular diseases, there also exists a strong genetic component. To study the implication of genetic background on vasomotor and endothelial function, inbred mouse strains with varying degrees of endothelial impairment are often utilized. Previous research by our laboratory and others has reported variation in vasoconstrictor and vasodilator responses across male strains of mice in the thoracic aorta (TA). However, functional data from female populations and in other arteries that are implicated in atherosclerosis have not been elucidated. Also, it is unclear if vasomotor functional differences between sexes and strains are due to nitric oxide (NO)-mediated mechanisms.
The primary purposes of this dissertation research were to: 1) Assess vascular function along the large arterial network in male and female mice with distinct genetic backgrounds. 2) Determine the vasodilatory reliance these strains and arteries have on NO-mediated pathways.
Vasoreactivity to the endothelium-dependent vasodilator ACh varied across strains and throughout the arteries tested with some strains exhibiting artery-specific impairment. Vasoreactivity to the endothelium-independent vasodilator SNP was uniform across all strains and arteries tested other than the maximal dilation (%) in male carotid arteries (CA). Maximal constrictor responses (%) to the ��1 adrenergic agonist phenylephrine (PE) varied across strains and arteries while sensitivity (EC50) did not. Results indicated some concentration-response heterogeneity in the female populations in relation to their male counterparts. Lastly, the most athero-prone strain (B6) relied most heavily upon NO-mediated vasorelaxation, while the least athero-prone strains (NZW, SJL) relied less upon NO for vasorelaxation
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