Thermal conductivity is the ability of a material to conduct heat. Metals are good at heat conduction. The thermal conductivity of a material is a defining property that aids in the development of effective heating/cooling technologies. A value for thermal conductivity can be determined by measuring the rate at which heat can pass through a material.
Thermal resistivity is the opposite of thermal conductivity. This means not conducting heat much. Materials with high resistivity are called "thermal insulators" and are used in clothing, thermoses, home insulation, and cars to keep people warm or in refrigerators, freezers, and thermoses to keep things cold.
Thermal conductivity is often represented by the Greek letter "kappa", formula_1. The units of thermal conductivity are watts per meter-kelvin. Watts are a measure of power, meters are a measure of length, and kelvins are a measure of temperature. From the units, we can see that thermal conductivity is a measure of how much power moves through a distance due to a temperature difference.
Some great thermal insulators are:
Vacuum, Aerogel, Polyurethane
Some great thermal conductors are:
Silver, Copper, Diamond
Silver is one of the most thermally conductive materials (and is relatively common), and because of this there are some cool experiments you can do with silver that show extremely well how thermal conduction works.
One example is when you put 2 spoons in boiling water, one spoon is steel and the other is silver. When you take the spoons out of the boiling water, the silver spoon is hotter than the steel spoon. The reason for this is that silver conducts heat better than steel. The silver spoon will also cool off faster because of this, as it is better at releasing heat.
Another example of silver's thermal conductivity is to put different materials on ice cubes. An iron washer will just sit on the ice and slowly become colder. A copper penny will melt through the ice cube and become colder faster. A silver coin, spoon, or ring on the ice cube will sink into it almost as though the ice cube were made of thick syrup, and the silver will become ice cold almost instantly. Again, this is because the silver is really good at drawing heat from the air and giving it to the ice cube. Copper is also good at this, but not as much as silver.
Hydride
A hydride is a compound with hydrogen bonded to other elements. Except for a few of the Noble gases, all of the elements in the periodic table can form hydrides. The properties of hydrides can be very different, but some of the hydrides have similar properties.
"Metallic hydrides": compounds with ionic bonding. They are very reactive, making them difficult to dissolve. Most alkali metals and alkaline earth metals form ionic hydrides.
"Metallic" or "Interstitial hydrides": These have metallic properties like good electrical conductivity and thermal conductivity. They are called interstitial because hydrogen can enter the metallic lattice (framework of metal atoms). Metallic hydrides are mostly formed from the metals in the groups 3 to 5 of the periodic table. Some of these are used in the nickel metal-hydride battery.
"Covalent hydrides": These have covalent bonds between hydrogen and the other element. Most of the p-block elements form covalent hydrides. Many of these hydrides are unstable in air or water or when heated. Hydrocarbons are the hydrides of carbon, ammonia is a hydride of nitrogen, and water is a hydride of oxygen.
Horse the Band
Horse the Band is an American hardcore rock band from Lake Forest, California that was started in 1999. They are famous for using video-game style music in their songs.
Hospice
A hospice is a type of medical treatment that helps take care of people who are very sick and have an illness that they will not be able to heal from. Many people staying in hospices have cancer or AIDS. People who stay in hospices are expected to die soon, but sometimes they get better. Hospices are different from other medicinal treatments because they mostly try to make people feel better instead of trying to cure them. Hospice tries to allow people to die with as little pain as possible.
Hospices have doctors, nurses, and other people who go to patients houses, nursing homes and hospitals to talk to people who want to use hospice medicine.
The Hospice movement was started in England in the 1950s by a nurse named Dame Cicely Saunders. The word Dame at the start of her name means that she did such good work starting hospices that the Queen of England made her a female knight.
A different nurse named Florence Wald brought hospice medicine to the United States because she worked with Dame Cicely Saunders and liked what she did.
There are four types of hospice care, and all of them focus on different stages of a patient’s needs.
In-Home Hospice : The first level of hospice care is in-home hospice, which means that hospice staff will come to a patient’s home to provide care. This type of hospice care is typically used in the early stages of hospice, helping patients transition from a hospital to their homes.
Continuous Care : The second level of hospice care is continuous care, which is in-home care with 24/7 support. With constant care, a patient has a member of hospice staff on hand at all times to help assist in symptom management.
In-Patient Hospice : The third level of hospice care is in-patient hospice care. While it’s never a patient’s first choice to be in a hospital, away from the comfort of their home, there are times when symptoms become too much to manage even by continuous in-home care. In-patient hospice allows a patient to be observed by nurses and physicians around the clock, ready at a moment’s notice to treat advanced symptoms and offer expert insights and care. In-patient hospice facilities tend to be calmer and more “home-like” than regular hospital visits to replicate a familiar setting’s comfort.
Respite Care : The fourth and final level of hospice care is respite care. Respite care exists as a sort of hybrid between in-patient and in-home or continuous home care. The point of respite care is primarily to offer relief to caregivers. Especially for those with no medical background, becoming a primary caregiver to a hospice patient can be too physically taxing and emotionally draining. Respite care allows caregivers relief from the responsibility of having a hospice patient in their care for as many as five days and nights to recharge.
Offa of Mercia
Offa was the King of Mercia from 757 until his death in July 796.
Many historians regard Offa as the most powerful Anglo-Saxon king before Alfred the Great. Offa died in 796 and was succeeded by his son, Ecgfrith, who reigned for less than five months before Coenwulf of Mercia became king.
Offa was the son of Thingfrith, a descendant of Eowa of Mercia. Eowa was a king of Mercia who ruled along with his more famous brother Penda of Mercia. In 757 the king of Mercia,Athelbald, was murdered. There was a short civil war between others claiming the throne. An ealdorman named Beornred seized the throne of Mercia but Offa drove him out of Mercia and became king himself that same year. The alliances Athelbald had formed fell apart when Offa came to power. Offa had very little power outside of Mercia for the first several years of his reign.