Protons chains

The pair-correlation function for the segmental dynamics of a chain is observed if some protonated chains are dissolved in a deuterated matrix. The scattering experiment then observes the result of the interfering partial waves originating from the different monomers of the same chain. The lower part of Fig. 4 displays results of the pair-correlation function on a PDMS melt (Mw = 1.5 x 105, Mw/Mw = 1.1) containing 12% protonated polymers of the same molecular weight. Again, the data are plotted versus the Rouse variable. 

Recently it also became possible to observe directly the incoherent cross section of a protonated chain. As eluded to in Sect. 2.2, incoherent scattering... 

The single chain dynamics of one given block or of one chain in a diblock copolymer melt is observed if a matched deuterated diblock is mixed with a small amount of labelled diblocks, where the label could be a protonated a or b block or a protonated chain. In terms of the dynamic RPA such a system is a four-component polymer mixture. It is characterized by four different relaxation modes A1-A4 which - depending on the contrast conditions - appear with... 

The emission of a helium nucleus in the final stage regenerates the initial carbon-12. The latter thus plays the role of a catalyst. The overall result is the fusion of four protons into a helium nucleus. At high temperatures, this cycle dominates over the proton-proton chain. Indeed thermal agitation facilitates penetration of the relatively high electrical barrier between proton and carbon nucleus. Whatever hydrogen fusion mechanism is prevalent, the star s mass determines the rate at which it consumes its nuclear fuel, and hence also its lifetime. The higher its mass, the more quickly it bums. 

Hydrogen fusion via either the proton-proton chain or the CNO cycle in the centre of stars comes to an end when most of the hydrogen has been transformed into helium. Helium fusion produces two elements essential to life, namely carbon and oxygen. In fact, carbon constitutes 18% of our bodies, and oxygen 65%, whilst the fractions of these same elements in solar material are just 0.39% and 0.85%, respectively. Only hydrogen and helium are more abundant in the Sun. 

The addition of water causes the formation of a coagulated phase of PBT solutions in any of the solvents named above (of course, the amount of water tolerated varies with the solvent, with the PPA solvent being the most tolerant toward water) (4). In very dilute solutions, the water causes enhanced depolarized scattering, interpreted to be the result of the formation of aggregates in which the rodlike chains are in parallel arrays (10). In more concentrated solutions, a gel phase is created (11,12). In either case, the electronic absorption spectra is altered from that characteristic of the protonated chain to that characteristic of the deprotonated, dry polymer (10). In the following we will report observations on this phase transition. 

Transfer of a P-proton from the propagating carbocation is the most important chain-breaking reaction. It occurs readily because much of the positive charge of the cationic propagating center resides not on carbon, but on the P-hydrogens because of hyperconjugation. Monomer, counterion or any other basic species in the reaction mixture can abstract a P-proton. Chain transfer to monomer involves transfer of a P-proton to monomer with the formation of terminal unsaturation in the polymer. 

The nuclear reaction that finally stabilizes the structure of the protostar is the fusion of two protons to form a deuterium atom, a positron, and a neutrino (1 H(p,p+v)2D). This reaction becomes important at a temperature of a few million degrees. The newly produced deuterium then bums to 3He, which in turn bums to 4He in the proton-proton chain. The proton-proton chain is the main source of nuclear energy in the Sun. With the initiation of hydrogen burning... 

In first generation stars, those that consist almost entirely of hydrogen and helium, and in stars of later generations where the core temperature is less than 20 million degrees (M < M ), hydrogen bums to helium via the proton-proton chains. The simplest chain, and the one activated at the lowest temperature ( 5 million degrees), is called PPI. Three reactions are involved. In the first step, two protons fuse to form a 2He atom, which immediately emits a positron (P1) to form a deuterium atom and a neutrino [ H(p,P v)2D]. This reaction is very slow and controls the rate of the PPI chain. Deuterium then quickly combines with a proton to form 3He (2D(p,y)3He), and two 3He nuclei combine to form 4He and two hydrogen atoms [3He(3He,2p)4He]. 

V. 1. Lim. Structural principles of die globular organisation of proton chains. A stereochemical theory rf globular protein secondary structure. J. MoL BioL 88 857-872(1974). 

As we discussed, numerous neutrinos are produced by the proton-proton chain in the Sun. However, neutrinos interact only very weakly with matter. Every second over 100 billion neutrinos from the Sun pass through every square inch of our bodies and virtually none of them interact with us. Because neutrinos interact so weakly with matter, detecting them is very difficult. For example, in the first solar neutrino detection experiment, scientist Ray Davis used 100,000 gallons of cleaning fluid (for the chlorine the fluid contained) in a detector located in a South Dakota gold mine. Davis expected to detect on average of 1.8 solar neutrinos per day. Instead, Davis s observed rate has consistently been much lower than this. Also, the long-term rate, plotted as a function of time, shows an anticorrelation between neutrino rate and sunspot activity. 

Hydrogen burning and helium production. Hydrogen burns in the core of a star to form 4He through either the proton-proton chain reaction, which takes place at 5 X 106 K or at higher temperatures (> 20 X 106 K) through the carbon cycle (the C-N-O cycle) in which carbon acts as a nuclear catalyst in the production of He. This process is also known as the quiescent burning phase of a star and is a slow process which takes billions of years and covers much of the life of a star. Our sun is currently in this phase. 

Hydrogen burning occurs in two key reaction sequences, the PP (or proton-proton) chains and the CNO (Carbon-Nitrogen-Oxygen) bi-cycle. Both sequences were first understood by Hans Bethe and his collaborators in the 1930s, for which work Bethe won the Nobel Prize in 1967 (5). 

TABLE 17.1. The proton-proton chain for He formation about 90% of the solar energy production... 

Schematic diagram of the proton-proton chain in stellar nucleosynthesis. [Attributed to Borb, reproduced from http //en. wikipedia.org/wiki/Proton%E2 %80%93proton chain reaction (accessed October 17, 2013).]...

Calculatetheamount of energy released during each step of the proton-proton chain. 

The complete proton-proton chain with all its branches. This chain is the main source of energy in the stars of mass comparable to that of the Sun... 

Hydrogen Burning Proton-Proton Chain, CNO-Cycle.641... 

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