Article about science 3

Necessity is famously the mother of invention, and there is no more pressing necessity than war. One other desideratum of warfare is surprise. And Ukraine, in its fight with its Russian invaders, has been good at invention and surprise, both separately and in combination.

One particular surprise was something that was washed ashore in September on the Crimean coastline near Sevastopol, the site of a naval base that is the home port of Russia’s Black Sea fleet. A photograph of it suggests something that looks like a large version of a hobbyist’s remote-controlled model boat. The cameras amidships and on the bow indicated that it may have been on a spying mission.

Intriguing. But then, late in October, came the sting. A fleet of the things, accompanied by aerial drones, attacked the Black Sea fleet at anchor. In the Ukrainian version of subsequent events, three vessels were hit and damaged, including the fleet’s replacement flag-ship, Admiral Makarov, the previous incumbent of that role, Moskva, having, in the words of a Ukrainian wag, been “promoted to submarine” by a more conventional attack using anti-ship missiles.

Is this the start of a new form of naval warfare? The world’s most serious naval powers—America, China, Britain, Israel and so on—have been experimenting with so-called Uncrewed Surface Vessels for about a decade. But these have mostly been missile- or gun-carrying boats rigged to operate under remote control. Kamikaze craft have been the province of irregular forces, such as the Houthi and Hamas.

The inventive military boffins of Ukraine have changed that. They have shown the effectiveness of fleets of kamikaze marine drones, unencumbered by human crew who might balk at running the gauntlet of machinegun fire that was directed at the drones when they were on their final attack run, which was gleefully posted online by Ukraine’s exceptionally effective propagandists.

https://www.economist.com/newsletters/simply-science?

Article about engineering 2

Numerical study and experimental validation of the size effect of smooth and mode I cracked semi-circular bend specimens

Scientific Reports volume 13, Article number: 7570 (2023) Cite this article

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Abstract

The edge-cracked semi-circular bend (SCB) specimen subjected to three-point bending loading is used in many applications to measure the fracture behavior of quasi-brittle materials. The main objective of the present work was to study the effect of the crack length to SCB specimen radius ratio (a/R), span to specimen diameter ratio (S/D), and specimen size on its flexural and mode I crack growth behavior. The contour integral method was implemented using the 3-D finite element method to determine the mode I stress intensity factor. In addition, high-strength concrete specimens were experimentally studied to validate the numerical results. The results show that the maximum compression stress is not sensitive to the S/D value, while the tensile stress is very sensitive. The value of S/D is the main parameter controlling the crack driving force (i.e., the crack mouth opening displacement (CMOD) and the normalized stress intensity factor, YI). For the same S/D, the SCB specimen diameter value change has a marginal effect on CMOD and YI. The specimen with S/D = 0.8 showed that it is the most compatible specimen with three-point bending test conditions, regardless of the SCB specimen size. A good agreement between the numerical and experimental results was achieved.

Introduction

The edge-cracked semi-circular bend (SCB) specimen under three-point bending loading is used to measure the material fracture behavior of rock materials, concrete, asphalt mixtures, and biomaterials1,2,3,4,5. The main advantage of using the SCB specimen is that it can easily be taken from the cores of any material6. Furthermore, it has a simple geometry and test procedure for calculating mixed mode I–II fracture toughness7,8,9. Arsalan et al.10 recently improved the SCB specimen to obtain a ductile adhesive’s mixed-mode fracture behavior with a considerable fracture process zone ahead of the crack tip. The mixed-mode SIF is a function of the crack length ratio a/R. Its orientation concerns the loading direction and the distance between the supports11,12, as shown in Fig. 1. Crack length appears to be a more significant factor than the specimen thickness on the SIF13. Furthermore, the SIFs become very sensitive at the large crack length to SCB specimen radius ratio (a/R) values8.

https://www.nature.com/articles/s41598-023-34201-z

Article about spiders 1

Spiders

Spiders are arachnids, a class of arthropods that also includes scorpions, mites, and ticks. There are more than 45,000 known species of spiders, found in habitats all over the world. There’s a spider with a cartoonish butt, spiders that can jump on demand, and cannibal spiders that look like pelicans.

Spiders range in size from the tiny Samoan moss spider, which is .011 inch long, to the massive Goliath birdeater, a tarantula with a leg span of almost a foot.

Harmful spiders?

For most people, the thought of spiders conjures up images of tarantulas, wolf spiders, and other (seemingly) fearsome creatures. Though all spiders have venom to one degree or another, only a handful are dangerous to humans. Those include the black widow and the brown recluse, both found in the United States.

The vast majority of spiders are harmless and serve a critical purpose: controlling insect populations that could otherwise devastate crops. Without spiders to eat pests harmful to agriculture, it’s thought that our food supply would be put at risk.

How spiders eat and hunt

Most species are carnivorous, either trapping flies and other insects in their webs, or hunting them down. They can’t swallow their food as is, though—spiders inject their prey with digestive fluids, then suck out the liquefied remains.

Though not all spiders build webs, every species produces silk. They use the strong, flexible protein fiber for many different purposes: to climb (think Spider Man), to tether themselves for safety in case of a fall, to create egg sacs, to wrap up prey, to make nests, and more.

Most spider species have eight eyes, though some have six. Despite all of those eyes, though, many don’t see very well. A notable exception is the jumping spider, which can see more colors than humans can. Using filters that sit in front of cells in their eyes, the day-hunting jumping spider can see in the red spectrum, green spectrum, and in UV light.

https://www.nationalgeographic.com/animals/invertebrates/facts/spiders

My memoir

The death of my girlfriend Gwen Stacy

Gwen Stacy, my girlfriend, and I met while we were both studying as undergraduates at ESU. My aunt, May, was in the hospital at the time and I felt worried and ignored her advances, and my aunt felt bad about my estrangement. We felt attracted to each other and we fall in love. When Gwen found out that I was Spider-Man, She was surprised, But supported me at all times and was there for me because she loved me.

One day, I was fighting with the Green Goblin, and he drops Gwen through the top of a clock tower. I tried to save her by throwing my web and catching her, but a sudden stop snapped her neck and she died. I was wracked with guilt after being able to save her fatal fall. For months after her death, I was dull and inconsolable, ceasing to be Spider-Man entirely.