Crack Stability and Its Effect on Fracture Toughness of Hot-Pressed Silicon Nitride Beam Specimens

The effect of stable crack extension on fracture toughness test results was determined using single-edge precracked beam specimens. Crack growth stability was examined theoretically for bars loaded in three-point bending under displacement control. The calculations took into account the stiffness of both the specimen and the loading system. The results indicated that the stiffness of the testing system played a major role in crack growth stability. Accordingly, a test system and specimen dimensions were selected which would result in unstable or stable crack extension during the fracture toughness test, depending on the exact test conditions. Hot-pressed silicon nitride bend bars (NC132) were prepared with precracks of different lengths, resulting in specimens with different stiffnesses. The specimens with the shorter precracks and thus higher stiffness broke without stable crack extension, while those with longer cracks, and lower stiffness, broke after some stable crack extension. The fracture toughness values from the unstable tests were 10% higher than those from the stable tests. This difference, albeit small, is systematic and is not considered to be due to material or specimen-to-specimen variation. It is concluded that instability due to the stiffness of test system and specimen must be minimized to ensure some stable crack extension in a fracture toughness test of brittle materials in order to avoid inflated fracture toughness values.     

Orderly stimulation of skeletal muscle motor units with tripolarnerve cuff electrode

An electrical nerve stimulation technique, using single tripolar electrode, was shown to be capable of recruiting motor units according to their size, while allowing simultaneous but independent control of firing rate in the active units. Test paradigms consisting of established fundamental physiological concepts of soleus-gastrocnemius architecture, motor units conduction velocity, firing rate behavior of motor units of different sizes, and their susceptibility to fatigue were employed to validate the technique and demonstrate its utility as a basic and applied research tool.     

Contribution of the fill to the static behaviour of arched masonry structures: theoretical formulation

In the paper, one presents the theoretical set-up of an original formulation aimed at accounting for the contribution of the fill to the structural strength of masonry vaults and arches and at providing an evaluation about its skill of cooperating to stress absorption with the main vaulted resisting structure. Usually the action of components ordinarily regarded as non-structural members is often neglected in static analyses. Actually, it is a common practice to assume a number of elements of vaulted or arched constructions, such as the fill and the buttress, as completely unable to exert any structural action, rather than trying to evaluate their contribution; therefore, those are usually assumed to be a dead weight, unable to contribute to the bearing capacity of the vault. Starting from the consideration that the fill is somehow subject to some pre-compression because of the permanent load, an approach is proposed where the fill is considered to be able to provide a partial absorption of the variable loads with a reduced load transmission onto the main structural members. The procedure leads to more realistic evaluations about the safety assessment of vaulted structures, which are in major agreement with their real behaviour.     

Single edge-crack stress intensity factor solutions

Weight function arguments and a boundary collocation technique are used to re-examine the stress intensity factor solutions to several classic two-dimensional linear elastic single edge-crack configurations. Limits to applicability and the solutions to the three and four-point bend, pure bending, eccentrically loaded tension, and other boundary condition problems are extracted from the solution to the uniformly loaded single edge-cracked configuration. A simple representation of the asymptotic behavior is proposed and a common expression that captures the full range of crack length to specimen width ratio is presented.     

Proprotein Convertase Subtilisin Kexin Type 9 Inhibitors Reduce Platelet Activation Modulating ox-LDL Pathways

Background: Proprotein convertase subtilisin kexin type 9 inhibitors (PCSK9i) lower LDL-cholesterol and slow atherosclerosis preventing cardiovascular events. While it is known that circulating PCSK9 enhances platelet activation (PA) and that PCSK9i reduce it, the underlying mechanism is not still clarified. Methods: In a multicenter before–after study in 80 heterozygous familial hypercholesterolemia (HeFH) patients on treatment with maximum tolerated statin dose ± ezetimibe, PA, soluble-NOX2-derived peptide (sNOX2-dp), and oxidized-LDL (ox-LDL) were measured before and after six months of PCSK9i treatment. In vitro study investigates the effects of plasma from HeFH patients before and after PCK9i on PA in washed platelets (wPLTs) from healthy subjects. Results: Compared to baseline, PCSK9i reduced the serum levels of LDL-c, ox-LDL, Thromboxane (Tx) B2, sNOX2-dp, and PCSK9 (p < 0.001). The decrease of TxB2 correlates with that of ox-LDL, while ox-LDL reduction correlated with PCSK9 and sNOX2-dp delta. In vitro study demonstrated that wPLTs resuspended in plasma from HeFH after PCSK9i treatment induced lower PA and sNOX2-dp release than those obtained using plasma before PCSK9i treatment. This reduction was vanished by adding ox-LDL. ox-LDL-induced PA was blunted by CD36, LOX1, and NOX2 inhibition. Conclusions: PCSK9i treatment reduces PA modulating NOX2 activity and in turn ox-LDL formation in HeFH patients.     

He ION BOMBARDMENT OF C60 FULLERENE: AN FT-IR AND RAMAN STUDY

C₆₀ fullerene films have been bombarded with He⁺ ions at 30 keV at room temperature in vacuum. The structural changes undergone by C₆₀ have been followed by both FT-IR and Raman spectroscopy. Raman spectroscopy was the most useful tool for this scope. It has been clearly discovered that at low radiation dose C₆₀ forms oligomers but at higher radiation doses it is converted into an amorphous carbonaceous matter. The implications of these results on the possible survival of C₆₀ fullerene in the interstellar space have been discussed briefly in connection with the previous results on the effects of various types of electromagnetic radiation over C₆₀.     

Point defects induced in ion irradiated 4H–SiC probed by exciton lines

The defects produced in 4H–SiC epitaxial layers by irradiation with a 200 keV H⁺ ion beam in the fluence range 6.5 × 10¹¹–1.8 × 10¹³ ions/cm² are investigated by Low Temperature Photoluminescence (LTPL–40 K).The defects produced by ion beam irradiation induce the formation of some sharp lines called “alphabet lines” in the photoluminescence spectra in the 425–443 nm range, due to the recombination of excitons at structural defects.From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P₁ lines (e, f, g) and the P₂ lines (a, b, c, d) that exhibit different trends with the ion fluence. The P₁ group normalized yield increases with ion fluence, reaches a maximum at 2.5 × 10¹² ions/cm² and then decreases. The P₂ group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5 × 10¹² ions/cm² and decreases at higher fluence, reaching a value of 50% of the maximum yield.The behaviour of P₁ and P₂ lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.     

He Ion Bombardment of C70 Fullerene: An FT-IR and Raman Study

C₇₀ fullerene films deposited on a silicon substrate have been bombarded with He⁺ ions at 30 keV at room temperature in vacuum. The structural changes undergone by C₇₀ have been followed by both FT-IR and Raman spectroscopy. The results have been compared to the behavior of C₆₀ fullerene and discussed in an astrochemical context. The main conclusion is that C₇₀, contrary to C₆₀, does not form oligomers at low radiation dose but it is directly and gradually degraded to amorphous carbon (carbon black).