Geminate and nongeminate recombination of triplet excitons formed by singlet fission.

We report the simultaneous observation of geminate and nongeminate triplet-triplet annihilation in a solution-processable small molecule TIPS-tetracene undergoing singlet exciton fission. Using optically detected magnetic resonance, we identify recombination of triplet pairs directly following singlet fission, as well as recombination of triplet excitons undergoing bimolecular triplet-triplet annihilation. We show that the two processes give rise to distinct magnetic resonance spectra, and estimate the interaction between geminate triplet excitons to be 60 neV.EPSRC [grant no. EP/J017361/1 and EP/G060738/1]. E. Oppenheimer Foundation and St. Catherine's College, Cambridge. NSF [CMMI- 1255494].This is the author accepted manuscript. The final version is available at http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.238701

Comments on filament-disintegration and its relation to other aspects of solar activity

Studies of ‘disparitions brusques’ in solar cycles 19 and 20 (to 1969) indicate that such events occur frequently. Approximately 30% of all large filaments in these cycles disintegrated in the course of their transit across the solar disk. ‘Major’ flares occurred with above average frequency on the last day on which 141 large disappearing filaments were observed (1958–60; 1966–69). Relationships between a disintegrating filament on July 10–11, 1959, a prior major flare, a newly formed spot, and concomitant growth of Hα plage are presented. Observation of prior descending prominence material apparently directed towards the location of the flare of 1959 July 15 d 19 h 23 m is reported. The development of the filament-associated flare of February 13, 1967 is described.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43723/1/11207_2004_Article_BF00148100.pd

Svestka's Research: Then and Now

Zdenek Svestka's research work influenced many fields of solar physics, especially in the area of flare research. In this article I take five of the areas that particularly interested him and assess them in a "then and now" style. His insights in each case were quite sound, although of course in the modern era we have learned things that he could not readily have envisioned. His own views about his research life have been published recently in this journal, to which he contributed so much, and his memoir contains much additional scientific and personal information (Svestka, 2010).Comment: Invited review for "Solar and Stellar Flares," a conference in honour of Prof. Zden\v{e}k \v{S}vestka, Prague, June 23-27, 2014. This is a contribution to a Topical Issue in Solar Physics, based on the presentations at this meeting (Editors Lyndsay Fletcher and Petr Heinzel

Control of Centrin Stability by Aurora A

Aurora A is an oncogenic serine/threonine kinase which can cause cell transformation and centrosome amplification when over-expressed. Human breast tumors show excess Aurora A and phospho-centrin in amplified centrosomes. Here, we show that Aurora A mediates the phosphorylation of and localizes with centrin at the centrosome, with both proteins reaching maximum abundance from prophase through metaphase, followed by their precipitous loss in late stages of mitosis. Over-expression of Aurora A results in excess phospho-centrin and centrosome amplification. In contrast, centrosome amplification is not seen in cells over-expressing Aurora A in the presence of a recombinant centrin mutant lacking the serine phosphorylation site at residue 170. Expression of a kinase dead Aurora A results in a decrease in mitotic index and abrogation of centrin phosphorylation. Finally, a recombinant centrin mutation that mimics centrin phosphorylation increases centrin's stability against APC/C-mediated proteasomal degradation. Taken together, these results suggest that the stability of centrin is regulated in part by Aurora A, and that excess phosphorylated centrin may promote centrosome amplification in cancer

Study of the post-flare loops on 29 July 1973

We present revised values of temperature and density for the flare loops of 29 July 1973 and compare the revised parameters with those obtained aboard the SMM for the two-ribbon flare of 21 May 1980. The 21 May flare occurred in a developed sunspot group; the 29 July event was a spotless two-ribbon flare. We find that the loops in the spotless flare extended higher (by a factor of 1.4–2.2), were less dense (by a factor of 5 or more in the first hour of development), were generally hotter, and the whole loop system decayed much slower than in the spotted flare (i.e. staying at higher temperature for a longer time). We also align the hot X-ray loops of the 29 July flare with the bright Hα ribbons and show that the Hα emission is brightest at the places where the spatial density of the hot elementary loops is enhanced.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43753/1/11207_2004_Article_BF00151609.pd

Dynamism in the solar core

Recent results of a mixed shell model heated asymmetrically by transient increases in nuclear burning indicate the transient generation of small hot spots inside the Sun somewhere between 0.1 and 0.2 solar radii. These hot bubbles are followed by a nonlinear differential equation system with finite amplitude non-homologous perturbations which is solved in a solar model. Our results show the possibility of a direct connection between the dynamic phenomena of the solar core and the atmospheric activity. Namely, an initial heating about DQ_0 ~ 10^{31}-10^{37} ergs can be enough for a bubble to reach the outer convective zone. Our calculations show that a hot bubble can arrive into subphotospheric regions with DQ_final ~ 10^{28} - 10^{34} ergs with a high speed, up to 10 km s-1, approaching the local sound speed. We point out that the developing sonic boom transforms the shock front into accelerated particle beam injected upwards into the top of loop carried out by the hot bubble above its forefront traveling from the solar interior. As a result, a new perspective arises to explain flare energetics. We show that the particle beams generated by energetic deep-origin hot bubbles in the subphotospheric layers have masses, energies, and chemical compositions in the observed range of solar chromospheric and coronal flares. It is shown how the emergence of a hot bubble into subphotospheric regions offers a natural mechanism that can generate both the eruption leading to the flare and the observed coronal magnetic topology for reconnection. We show a list of long-standing problems of solar physics that our model explains. We present some predictions for observations, some of which are planned to be realized in the near future.Comment: 44 pages, 20 figure

Variability of bone preservation in a confined environment: the case of the catacomb of Sts Peter and Marcellinus (Rome, Italy)

Most of the studies investigating the diagenetic trajectory of fossil bones focus on open-air sites and very little work have been published in confined environments such as catacombs. While the stable thermal history of catacombs should favor bone preservation, the accumulation of corpses over a short period of time could favor their destruction. The aim of this study is to describe the diagenetic trajectory of 128 human bone samples coming from six different burial chambers of the catacomb of Sts Peter and Marcellinus (SSPM, Rome, Italy). A multi-proxy approach was undertaken to provide an assessment of the molecular preservation as well as a direct record of the isotopic composition itself. Collagen yield, carbon and nitrogen abundances, C:N ratio, FT-IR based collagen and carbonate contents and crystallinity index, radiocarbon dating and stable isotope analysis of bone collagen and carbonate indicate that both the mineral and the organic fractions are impacted by diagenesis to various degrees, and that bones originating from the small burial chambers are more affected than those coming from the large ones. While some of the bones were strongly recrystallized, the impact of bone diagenesis on the stable isotope values of bone carbonate was limited. Comparison with contemporary sites from the Latium showed that conditions prevailing in catacombs seem overall to favor, rather than disadvantage bone preservation

Variability of bone preservation in a confined environment: The case of the catacomb of Sts Peter and Marcellinus (Rome, Italy)

Most of the studies investigating the diagenetic trajectory of fossil bones focus on open-air sites and very little work have been published in confined environments such as catacombs. While the stable thermal history of catacombs should favor bone preservation, the accumulation of corpses over a short period of time could favor their destruction. The aim of this study is to describe the diagenetic trajectory of 128 human bone samples coming from six different burial chambers of the catacomb of Sts Peter and Marcellinus (SSPM, Rome, Italy). A multi-proxy approach was undertaken to provide an assessment of the molecular preservation as well as a direct record of the isotopic composition itself. Collagen yield, carbon and nitrogen abundances, C:N ratio, FT-IR based collagen and carbonate contents and crystallinity index, radiocarbon dating and stable isotope analysis of bone collagen and carbonate indicate that both the mineral and the organic fractions are impacted by diagenesis to various degrees, and that bones originating from the small burial chambers are more affected than those coming from the large ones. While some of the bones were strongly recrystallized, the impact of bone diagenesis on the stable isotope values of bone carbonate was limited. Comparison with contemporary sites from the Latium showed that conditions prevailing in catacombs seem overall to favor, rather than disadvantage bone preservation.info:eu-repo/semantics/publishe