Chalk (disambiguation)

Chalk may refer to:

Surname

Magnesium carbonate

Magnesium carbonate, MgCO₃ (archaic name magnesia alba), is an inorganic salt that is a white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.

Forms

The most common magnesium carbonate forms are the anhydrous salt called magnesite (MgCO₃) and the di, tri, and pentahydrates known as barringtonite (MgCO₃·2 H₂O), nesquehonite (MgCO₃·3 H₂O), and lansfordite (MgCO₃·5 H₂O), respectively. Some basic forms such as artinite (MgCO₃·Mg(OH)₂·3 H₂O), hydromagnesite (4 MgCO₃·Mg(OH)₂·4 H₂O), and dypingite (4 MgCO₃· Mg(OH)₂·5 H₂O) also occur as minerals.

Magnesite consists of white trigonal crystals. The anhydrous salt is practically insoluble in water, acetone, and ammonia. All forms of magnesium carbonate react in acids. Magnesium carbonate crystallizes in the calcite structure where in Mg²⁺ is surrounded by six oxygen atoms. The dihydrate one has a triclinic structure, while the trihydrate has a monoclinic structure.

References to 'light' and 'heavy' magnesium carbonates actually refer to the magnesium hydroxy carbonates hydromagnesite and dypingite (respectively).

Chalk (military)

In military terminology, a chalk is a group of paratroopers or other soldiers that deploy from a single aircraft. A chalk often corresponds to a platoon-sized unit for air assault operations, or a company-minus-sized organization for airborne operations. For air transport operations, it can consist of up to a company-plus-sized unit. Oftentimes, a load of paratroopers in one aircraft, prepared for a drop, is also referred to as a stick.

The term was first coined in World War II for airborne troops during Operation Overlord, the Allied invasion of Europe. The aircraft flight number was placed on the troops' backs with chalk. It was later used during the Vietnam War, when it was common practice to number with chalk the sides of the helicopters involved in an operation. During the Battle of Mogadishu (1993), the battle plan called for four chalks from the 75th Ranger Regiment to fast rope down from hovering MH-60L Black Hawk helicopters around the target building. The rangers would then create a four-corner defensive perimeter. The plan failed as two of the Black Hawks were shot down, and the assault turned into a forced evacuation.

1 Month 2 Live

One Month to Live, also called 1 Month 2 Live, was a 5-issue limited series comic book produced by Marvel Comics on a weekly basis in 2010. It was written by Rick Remender in collaboration with Stuart Moore, John Ostrander, and Rob Williams. The original concept was devised by Marvel editor Steve Wacker with the premise "What would you do with one month to change the world?" The storyline centers on a protagonist with terminal cancer, in response to Wacker's aunt having been diagnosed with cancer.

The four writers found the experience of writing the story to be especially poignant, as all had personal experiences with cancer—in particular, Remender, whose father survived a bout with cancer in 2008, and Ostrander, whose wife Kim Yale died of cancer in 1997.

Plot

In an accident with toxic waste, Dennis Sykes gains superpowers and an untreatable cancer. With a life expectancy of barely a month, Sykes launches himself on a brief career as a superhero, in an attempt to make a difference in the world while he still can, assisting the Fantastic Four in saving Ego the Living Planet from a cancerous infection and averting Hammerhead's attempt to take control of his neighbourhood. Although use of his powers made his condition worse, Sykes made a positive impression on many heroes with his dedication to doing the right thing, accepting training from Spider-Man and receiving honorary membership with the FF and the Avengers before he finally died of stress from his final battle.

Flux (biology)

In general, flux in biology relates to movement of a substance between compartments. There are several cases where the concept of flux is important.

Flux (metabolism)

Flux, or metabolic flux is the rate of turnover of molecules through a metabolic pathway. Flux is regulated by the enzymes involved in a pathway. Within cells, regulation of flux is vital for all metabolic pathways to regulate the pathway's activity under different conditions. Flux is therefore of great interest in metabolic network modelling, where it is analysed via flux balance analysis.

In this manner, flux is the movement of matter through metabolic networks that are connected by metabolites and cofactors, and is therefore a way of describing the activity of the metabolic network as a whole using a single characteristic.

Metabolic Flux

It is easiest to describe the flux of metabolites through a pathway by considering the reaction steps individually.The flux of the metabolites through each reaction (J) is the rate of the forward reaction (Vf), less that of the reverse reaction (Vr).

J=Vf-Vr

At equilibrium, there is no flux. Furthermore, it is observed that throughout a steady state pathway, the flux is usually determined by the rate determining step of the reaction.