STING RAY

Some AStingray-related fatalities (in humans) are extremely rare, partly because a stingray's venom, while extraordinarily painful, isn't usually deadly -- unless the initial strike is to the chest or abdominal area.

Australian bull ray, estimated to weigh about 220 pounds. Australian bull rays can be up to 4 feet wide and 8 feet long -- all stingrays use the same attack mechanism regardless of size. The mechanism is called a sting, up to 8 inches long in a bull ray, located near the base of the tail. The sting contains a sharp spine with serrated edges, or barbs, that face the body of the fish. There is a venom gland at the base of the spine and a membrane-like sheath that covers the entire sting mechanism.

When a stingray attacks, it needs to be facing its victim, because all it does is flip its long tail upward over its body so it strikes whatever is in front of it. The ray doesn't have direct control over the sting mechanism, only over the tail. In most cases, when the sting enters a person's body, the pressure causes the protective sheath to tear. When the sheath tears, the sharp, serrated edges of the spine sink in and venom flows into the wound.

A stingray's venom is not necessarily fatal, but it hurts a lot. It's composed of the enzymes 5-nucleotidase and phosphodiesterase and the neurotransmitter serotonin. Serotonin causes smooth muscle to severely contract, and it is this component that makes the venom so painful. The enzymes cause tissue and cell death. If the venom is introduced into an area like the ankle, it can usually be treated. Heat breaks down stingray venom and limits the amount of damage it can do. If not treated quickly enough, amputation might be necessary. But if the venom enters the abdomen or chest cavity, the resulting tissue death can be fatal because of the major organs located in the vicinity. If the spike enters the heart the results are fatal.

While a stingray's venom can do serious damage, the most destructive part of the sting mechanism can actually be the barbs on the spine. The sharp tip of the sting enters a person pretty smoothly, but its exit is roughly equivalent to backing up over those "severe tire damage" blades. Remember that the points of the barbs are facing the stingray. Even if venom weren't involved at all, pulling the spike out of a human's chest or abdomen could be enough to cause death from the massive tearing of tissue that results.

Defrosting a windshield

What's the best way to defrost ice froma windshield:

What's better Cold Air or Warm Air?

If you can't alter the air's humidity, warm air will definitely heat up your window faster and defrost it faster than cold air. The only problem with using hot air is that rapid heating can cause stresses on the window and its frame because the temperature will rise somewhat unevenly and lead to uneven expansion. Such stress can actually break the window, "On coldest days in winter, if you turn up the heat full blast to defrost the windshield and the outside of the window still are covered with ice, after about 10 minutes of heating, the windshield will "pop" and a fracture the winshield.

About the humidity caveat: if you can blow dry air across your windshield, that will defrost it faster than just about anything else, even if that air is cold. The water molecules on your windshield are constantly shifting back and forth between the solid phase (ice) and the gaseous phase (steam or water vapor). Heating the ice will help more water molecules leave the ice for the water vapor, but dropping the density of the water vapor will reduce the number of water molecules leaving the water vapor for the ice. Either way, the ice decreases and the water vapor increases. Since you car's air condition begins drying the air much soon after you start the car than its heater begins warming the air, many modern cars concentrate first on drying the air rather than on heating it.

Diesel vs Gas Engines

What is the difference between spark ignition engines and diesel engines?

Just before burning their fuels, both engines compress air inside a sealed cylinder. This compression process adds energy to the air and causes its temperature to skyrocket.

In a spark ignition engine, the air that's being compressed already contains fuel so this rising temperature is a potential problem. If the fuel and air ignite spontaneously, the engine will "knock" and won't operate at maximum efficiency. The fuel and air mixture is expected to wait until it's ignited at the proper instant by the spark plug. That's why gasoline is formulated to resist ignition below a certain temperature.
The higher the "octane" of the gasoline, the higher its certified ignition temperature. Virtually all modern cars operate properly with regular gasoline. Nonetheless, people frequently put high-octane (high-test or premium) gasoline in their cars under the mistaken impression that their cars will be better for it. If your car doesn't knock significantly with regular gasoline, use regular gasoline.

A diesel engine doesn't have spark ignition. Instead, it uses the high temperature caused by extreme compression to ignite its fuel. It compresses pure air to high temperature and pressure, and then injects fuel into this air. Timed to arrive at the proper instant, the fuel bursts into flames and burns quickly in the superheated compressed air. In contrast to gasoline, diesel fuel is formulated to ignite easily as soon as it enters hot air.

How a Relay Works

Relay construction are amazingly simple devices. There are four parts in every relay:
Electromagnet, Armature that can be attracted by the electromagnet, spring and a set of electrical contacts The following figure shows these four parts in action:

The relay consists of two separate and completely independent circuits. The first is at the bottom and drives the electromagnet. In this circuit, a switch is controlling power to the electromagnet. When the switch is on, the electromagnet is on, and it attracts the armature. The armature is acting as a switch in the second circuit. When the electromagnet is energize, the armature completes the second circuit and the light is on. When the electromagnet is not energize, the spring pulls the armature away and the circuit is not complete. In that case the light is dark

When you purchase relays, you generally have control over several variables:

1) The voltage and current that is needed to activate the armature
2) The maximum voltage and current that can run through the armature and the
armature contacts
3) The number of armatures (generally one or two)
4) The number of contacts for the armature (generally one or two)
5) Whether the contact (if only one contact is provided) is normally open (NO) or normally
closed (NC)