proton-proton chain reaction

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Proton-proton chain reaction

proton-proton chain reaction

(p-p chain) A series of nuclear fusion reactions by which energy can be generated in the dense cores of stars. The overall effect of the chain reaction is the conversion of hydrogen nuclei to helium nuclei with the release of an immense amount of energy. The energy maintains the core temperature, some of it flowing to the stellar surface. The p-p chain is an efficient energy source even at core temperatures of only 15 million K; it is therefore believed to be the major source of energy in the Sun and in all main-sequence stars that are cooler (less massive) than the Sun. The carbon cycle predominates in the hotter, somewhat more massive stars.

The sequence of steps of the p-p chain is shown in the illustration, with the principal sequence outlined heavily in black. The possible chains occur simultaneously but in what is thought to be 99.75% of the reactions, the sequence begins with two hydrogen nuclei (i.e. protons) combining to emit a positron and a neutrino and forming a nucleus of deuterium. The deuterium then combines with a proton to yield a nucleus of helium–3 and a photon. About 95% of the helium–3 nuclei will combine together to give helium–4, liberating two protons. Overall, each cycle thus converts four protons into one helium–4 nucleus with the release of energy. High collision speeds (plus a quantum-mechanical process known as tunneling) are required for the protons to fuse, since they have to overcome the mutual repulsion arising from their positive charge.

References in periodicals archive ?
" [...] eu vejo produtivo, apesar de nao ter adesao e a gente sempre tem os mesmos participantes [...]" (Pp1); "[...] nao participaram muitas pessoas, vieram em torno de 8 a 11 pessoas somente, sendo que ha mais de 300 hipertensos [...]" (Pe2).
To minimize the possible influence in the validity and reliability values of the PP1 data, the same bicycle and SRM power meter were used in all testing conditions.
Interestingly, the impact tensile strength of PP1PE1B increased to 27 kJ/[m.sup.2], which is almost twice the value of PP1PE1 and 10% more than unmodified PP1. Chodak et al., showed that peroxide initiated crosslinking of PP/LDPE-blends in presence of hydroquinone increases impact strength and gel content.
And CTD's mechanism of action in the human body mainly reflects in that it can inhibit the activity of PP1 and PP2A in kinds of cancer cells, so it affects apoptosis.
In addition to the stress-inducible GADD34-PP1 complex, CReP (constitutive repressor of eIF2[alpha] phosphorylation, also known as PPP1R15B) forms a complex with PP1 that constitutively dephosphorylates eIF2[alpha] [38].
Both protein phosphatases 2A and PP1 have been shown to associate with and dephosphorylate neurofilament proteins [21].
Walter Yin, the latest addition to the Freebiumsultants family, will join as a Manager of the Logistics Department and will have executive oversight of PP1.
Plants also contain phosphatases PP1 and PP2A and, when in contact with MCs, may suffer adverse effects due to the inhibition of these enzymes.
Metabolism of cyclic nucleotides and membrane phospholipids and activation of different protein kinases and phosphatases, particularly MAPKs, PKC, CaMKII, and protein phosphatase 1 (PP1) as well as endogenous enzymatic regulators, are the key biochemical steps and pathways we have evidenced.
Because recombinant HDAC6 binds directly to the protein phosphatase 1 (PP1) catalytic subunit, TSA disrupts endogenous HDAC6-PP1 complexes and activates PP1 (Brush et al., 2004).