Molecular diffusion

Molecular diffusion simply called diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles. Diffusion explains the net flux of molecules from a region of higher concentration to one of lower concentration. Once the concentrations are equal the molecules continue to move, but since there is no concentration gradient the process of molecular diffusion has ceased and is instead governed by the process of self-diffusion, originating from the random motion of the molecules; the result of diffusion is a gradual mixing of material such that the distribution of molecules is uniform. Since the molecules are still in motion, but an equilibrium has been established, the end result of molecular diffusion is called a "dynamic equilibrium". In a phase with uniform temperature, absent external net forces acting on the particles, the diffusion process will result in complete mixing.

Consider two systems. If there is a change in the potential energy of a system. Molecular diffusion is described mathematically using Fick's laws of diffusion. Diffusion is of fundamental importance in many disciplines of physics and biology; some example applications of diffusion: Sintering to produce solid materials Chemical reactor design Catalyst design in chemical industry Steel can be diffused to modify its properties Doping during production of semiconductors. Diffusion is part of the transport phenomena. Of mass transport mechanisms, molecular diffusion is known as a slower one. In cell biology, diffusion is a main form of transport for necessary materials such as amino acids within cells. Diffusion of solvents, such as water, through a semipermeable membrane is classified as osmosis. Metabolism and respiration rely in part upon diffusion in addition to active processes. For example, in the alveoli of mammalian lungs, due to differences in partial pressures across the alveolar-capillary membrane, oxygen diffuses into the blood and carbon dioxide diffuses out.

Lungs contain a large surface area to facilitate this gas exchange process. Fundamentally, two types of diffusion are distinguished: Tracer diffusion and Self-diffusion, a spontaneous mixing of molecules taking place in the absence of concentration gradient; this type of diffusion can be followed using isotopic tracers, hence the name. The tracer diffusion is assumed to be identical to self-diffusion; this diffusion can take place under equilibrium. An excellent method for the measurement of self-diffusion coefficients is pulsed field gradient NMR, where no isotopic tracers are needed. In a so-called NMR spin echo experiment this technique uses the nuclear spin precession phase, allowing to distinguish chemically and physically identical species e.g. in the liquid phase, as for example water molecules within liquid water. The self-diffusion coefficient of water has been experimentally determined with high accuracy and thus serves as a reference value for measurements on other liquids; the self-diffusion coefficient of neat water is: 2.299·10−9 m²·s−1 at 25 °C and 1.261·10−9 m²·s−1 at 4 °C.

Chemical diffusion occurs in a presence of concentration gradient and it results in net transport of mass. This is the process described by the diffusion equation; this diffusion is always a non-equilibrium process, increases the system entropy, brings the system closer to equilibrium. The diffusion coefficients for these two types of diffusion are different because the diffusion coefficient for chemical diffusion is binary and it includes the effects due to the correlation of the movement of the different diffusing species; because chemical diffusion is a net transport process, the system in which it takes place is not an equilibrium system. Many results in classical thermodynamics are not applied to non-equilibrium systems. However, there sometimes occur so-called quasi-steady states, where the diffusion process does not change in time, where classical results may locally apply; as the name suggests, this process is a not a true equilibrium. Non-equilibrium fluid systems can be modeled with Landau-Lifshitz fluctuating hydrodynamics.

In this theoretical framework, diffusion is due to fluctuations whose dimensions range from the molecular scale to the macroscopic scale. Chemical diffusion increases the entropy of a system, i.e. diffusion is a spontaneous and irreversible process. Particles will not spontaneously re-order themselves. Collective diffusion is the diffusion of a large number of particles, most within a solvent. Contrary to brownian motion, the diffusion of a single particle, interactions between particles may have to be considered, unless the particles form an ideal mix with their solvent. In case of an ideal mix, the particle diffusion equation holds true and the diffusion coefficient D the speed of diffusion i


Rolonda was a syndicated daytime talk show that aired from January 17, 1994, to September 17, 1997. It featured Rolonda Watts as the host, was produced by Watts Works Productions in association with King World Productions, was distributed by King World; the program served as a replacement in the majority of the markets carrying the show at launch for The Les Brown Show, a daytime talk show that debuted on September 6, 1993, which went on hiatus in December 1993 due to low ratings, ending its run on January 14, 1994, the Friday before Rolonda's debut. Prior to hosting the show, Watts served as a senior correspondent and weekend anchor for the syndicated daytime newsmagazine series Inside Edition, produced by King World; the program was like many other talk shows at the time, featuring guests who had problems with other guests, wanted to bring them on the show to tell them. Rolanda would try to help them out with their problems. Other topics featured paternity tests, out-of-control teens, other everyday problems.

Towards the end of her show's run, many topics began to go to the extreme as many fights were breaking out, Watts struggled to maintain order on the set. Watts was faced with the claim that this was turning out to be "another Jerry Springer Show"; the opening sequence video used in 1994 both early and late used a sphere-like period symbol drawing out the name'Rolonda' following her smiling for the introduction. In the 1995-1997 seasons, the city of New York was used in vignette scenes of Rolonda connecting with fellow guests in numerous of ways. In the early 1994 intro music composed by David Foster was a slow tempo saxophone theme; the 1995-1997 theme composed by David Foster was an uptempo piano bass and string synthesizer. A solemn version was used for episodes of a serious overtone

USS George Clymer (APA-27)

USS George Clymer was an Arthur Middleton-class attack transport that saw service with the US Navy in four wars - World War II, the Chinese Civil War, the Korean War and the Vietnam War. George Clymer was laid down as African Planet under a Maritime Commission contract 28 October 1940 by Ingalls Shipbuilding of Pascagoula, Mississippi. George Clymer sailed 21 June via Charleston to Norfolk, Virginia where she arrived 30 July for training in Chesapeake Bay, she departed 23 October for French Morocco. After joining Rear Admiral Monroe Kelley's Northern Attack Group off the Moroccan coast 7 November, at midnight 8 November she debarked assault troops on special net-cutting and scouting missions against garrisons at Mehedia and the fortress Kasba. Just before dawn the first wave of troops hit the beach and encountered resistance from the Vichy French. Enemy shore batteries fired on the assembled transports and straddled George Clymer before she opened the range. Hard fighting continued ashore until 11 November.

George Clymer debarked troops, unloaded cargo, treated casualties until 15 November when she sailed to Casablanca to complete offloading cargo. She departed for the United States the 17th. After embarking more than 1,300 Seabees, George Clymer sailed 17 December for the Pacific. One of the first transports to serve in both the Atlantic and Pacific, she reached Nouméa, New Caledonia, 18 January 1943. Redesignated on 1 February, she sailed in convoy 5 February for Guadalcanal, where she arrived the 7th to debark reinforcements and embark casualties and Japanese prisoners of war. During the next 9 months she sailed the Southwest Pacific, carrying cargo and rotating troops from bases in New Zealand, New Caledonia, the New Hebrides, the Fijis to Guadalcanal. On 19 April she evacuated 38 Chinese and Fijian women and children, who had hidden from the Japanese for more than a year, from Guadalcanal and transported them to Nouméa; as flagship of Rear Admiral Theodore Stark Wilkinson's 3rd Amphibious Force, George Clymer departed Guadalcanal 30 October for the invasion of Bougainville.

Closing Cape Torokina 1 November, she disembarked men of the 2nd Marine Raider Battalion before joining other transports in a combined bombardment of enemy positions on Cape Torokina. She returned to Florida Island, 3 November. George Clymer continued troop-carrying and supply runs in the Southwest Pacific until 4 June 1944 when she departed Guadalcanal for the invasion of the Marianas. Steaming via Kwajalein, she operated off Saipan from 17 to 30 June while serving as flagship of Rear Admiral Lawrence Fairfax Reifsnider's Southern Attack Group, she reached Eniwetok 4 July. After debarking assault troops, she served as receiving ship, boat pool tender, medical station for the Southern Transport Group, she remained at Guam until 20 August. Underway again 15 September, George Clymer steamed via Eniwetok and Manus, Admiralties, to the Philippines, where she landed nearly 1,000 troops at Dulag 21 October during the battle of Leyte, she returned to Manus 28 October. Sailing 26 January 1945, she reached Guadalcanal 11 February and for more than a month trained for the invasion of Okinawa.

She departed Carolines, in convoy 27 March. Steaming via Saipan and Pearl Harbor, she arrived San Francisco 9 May. After conversion to a transport squadron and relief amphibious force flagship, she transported 1,200 Seabees to Pearl Harbor from 21 to 27 July. After returning to San Francisco 5 August with wounded veterans embarked, she sailed 12 August for the Philippines, she reached Manila 7 September. Between 3 and 21 October she made a similar voyage from Leyte to Japan. Between 27 November and 28 December she cruised to Guam and Saipan and returned to San Pedro, California with homebound troops. Prior to the Korean War, George Clymer supported various naval operations in the Pacific. From 1 June to 20 August she served at Bikini Atoll as flagship for Transport Division 11 during atomic bomb tests in the Marshall Islands, she conducted training operations along the Pacific coast until 15 December 1947 when she departed San Pedro for the Far East. Arriving Tsingtao, China, 20 January 1948, for more than 6 months she operated along the Chinese coast supporting the Nationalist Chinese troops during the Chinese Civil War.

She departed Tsingtao 5 August. George Clymer returned to San Diego 4 October, during the next 19 months she operated off the coast of Alaska, the West Coast, in Hawaiian waters. After the invasion of South Korea by North Korean troops, she departed Sa