2,541 research outputs found
Impact of natural climate change and historical land use on landscape development in the Atlantic Forest of Rio de Janeiro, Brazil.
Climate variations and historical land use had a major impact on landscape development in the Brazilian Atlantic Forest (Mata Atlântica). In southeast Brazil, rainforest expanded under warm-humid climate conditions in the late Holocene, but have been dramatically reduced in historical times. Nevertheless, the numerous remaining forest fragments are of outstanding biological richness. In our research in the Atlantic Forest of Rio de Janeiro we aim at the reconstruction of the late Quaternary landscape evolution and an assessment of human impact on landscapes and rainforests. In this context, special focus is given on (a) effects of climate variations on vegetation cover, soil development, and geomorphological processes, and (b) spatial and temporal land use and landscape degradation patterns. In this paper we present some new results of our interdisciplinary research in the Serra dos Órgãos mountain range, state of Rio de Janeiro
Deleterious mutations predicted in the sorghum (\u3ci\u3eSorghum bicolor\u3c/i\u3e) \u3ci\u3eMaturity\u3c/i\u3e (\u3ci\u3eMa\u3c/i\u3e) and \u3ci\u3eDwarf\u3c/i\u3e (\u3ci\u3eDw\u3c/i\u3e) genes from whole‑genome resequencing
In sorghum [Sorghum bicolor (L.) Moench] the Maturity (Ma1, Ma2, Ma3, Ma4, Ma5, Ma6) and Dwarf (Dw1, Dw2, Dw3, Dw4) loci, encode genes controlling flowering time and plant height, respectively, which are critical for designing sorghum ideotypes for a maturity timeframe and a harvest method. Publicly available whole-genome resequencing data from 860 sorghum accessions was analyzed in silico to identify genomic variants at 8 of these loci (Ma1, Ma2, Ma3, Ma5, Ma6, Dw1, Dw2, Dw3) to identify novel loss of function alleles and previously characterized ones in sorghum germplasm. From~ 33 million SNPs and~ 4.4 million InDels, 1445 gene variants were identified within these 8 genes then evaluated for predicted effect on the corresponding encoded proteins, which included newly identified mutations (4 nonsense, 15 frameshift, 28 missense). Likewise, most accessions analyzed contained predicted loss of function alleles (425 ma1, 22 ma2, 40 ma3, 74 ma5, 414 ma6, 289 dw1, 268 dw2 and 45 dw3) at multiple loci, but 146 and 463 accessions had no predicted ma or dw mutant alleles, respectively. The ma and dw alleles within these sorghum accessions represent a valuable source for manipulating flowering time and plant height to develop the full range of sorghum types: grain, sweet and forage/biomass
A survey of energy loss calculations for heavy ions between 1 and 100 keV
The original Lindhard-Scharff-Schi{\o}tt (LSS) theory and the more recent
Tilinin theory for calculating the nuclear and electronic stopping powers of
slow heavy ions are compared with predictions from the SRIM code by Ziegler.
While little discrepancies are present for the nuclear contribution to the
energy loss, large differences are found in the electronic one. When full ion
recoil cascade simulations are tested against the elastic neutron scattering
data available in the literature, it can be concluded that the LSS theory is
the more accurate.Comment: Presented at the 10th International Symposium on Radiation Physics,
17-22 September, 2006, Coimbra, Portugal; style corrections, small change to
fig.
Time Optimal Control in Spin Systems
In this paper, we study the design of pulse sequences for NMR spectroscopy as
a problem of time optimal control of the unitary propagator. Radio frequency
pulses are used in coherent spectroscopy to implement a unitary transfer of
state. Pulse sequences that accomplish a desired transfer should be as short as
possible in order to minimize the effects of relaxation and to optimize the
sensitivity of the experiments. Here, we give an analytical characterization of
such time optimal pulse sequences applicable to coherence transfer experiments
in multiple-spin systems. We have adopted a general mathematical formulation,
and present many of our results in this setting, mindful of the fact that new
structures in optimal pulse design are constantly arising. Moreover, the
general proofs are no more difficult than the specific problems of current
interest. From a general control theory perspective, the problems we want to
study have the following character. Suppose we are given a controllable right
invariant system on a compact Lie group, what is the minimum time required to
steer the system from some initial point to a specified final point? In NMR
spectroscopy and quantum computing, this translates to, what is the minimum
time required to produce a unitary propagator? We also give an analytical
characterization of maximum achievable transfer in a given time for the two
spin system.Comment: 20 Pages, 3 figure
Encarando a atrocidade: a vergonha e sua ausência (Portuguese translation of Facing Atrocity - Translators: Azambuja, Martini & Sattler)
Neste artigo, concentro-me sobre quatro variedades possíveis de ausência da vergonha. Minha esperança é a de que a reflexão sobre essas variedades possa, de alguma maneira, nos dar uma imagem mais completa acerca do papel que a vergonha desempenha sobre nosso caráter moral e nas discussões a respeito da atrocidade. Observo que a vergonha que emerge de uma exposição à atrocidade pode em parte constituir aquilo que nos leva a identificar oevento como atroz. Prossigo então argumentando que quando a vergonha está ausente, esta ausência pode servir para nos cegar para a atrocidade que está à nossa frente, e que é nossa tarefa tentar evitar. Sentir vergonha faz parte de ver a atrocidade pelo que ela é de uma maneira apropriada emocionalmente engajada. Ela é, portanto, uma parte vital de ser humano, e sua ausência em certos casos é uma insuficiência demasiadamente humana de humanidade
A Carbon Nanofilament-Bead Necklace
Carbon nanofilaments with carbon beads grown on their surfaces were successfully synthesized reproducibly by a floating catalyst CVD method. The nanofilaments hosting the pearl-like structures typically show an average diameter of about 60 nm, which mostly consists of low-ordered graphite layers. The beads with diameter range 150−450 nm are composed of hundreds of crumpled and random graphite layers. The mechanism for the formation of these beaded nanofilaments is ascribed to two nucleation processes of the pyrolytic carbon deposition, arising from a temperature gradient between different parts of the reaction chamber. Furthermore, the Raman scattering properties of the beaded nanofilaments have been measured, as well as their confocal Raman G-line images. The Raman spectra reveal that that the trunks of the nanofilaments have better graphitic properties than the beads, which is consistent with the HRTEM analysis. The beaded nanofilaments are expected to have high potential applications in composites, which should exhibit both particle- and fiber-reinforcing functions for the host matrixes
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Data assurance in opaque computations
The chess endgame is increasingly being seen through the lens of, and therefore effectively defined by, a data ‘model’ of itself. It is vital that such models are clearly faithful to the reality they purport to represent. This paper examines that issue and systems engineering responses to it, using the chess endgame as the exemplar scenario. A structured survey has been carried out of the intrinsic challenges and complexity of creating endgame data by reviewing the past pattern of errors during work in progress, surfacing in publications and occurring after the data was generated. Specific measures are proposed to counter observed classes of error-risk, including a preliminary survey of techniques for using state-of-the-art verification tools to generate EGTs that are correct by construction. The approach may be applied generically beyond the game domain
Rearrangement of cluster structure during fission processes
Results of molecular dynamics simulations of fission reactions and are presented. Dependence
of the fission barriers on isomer structure of the parent cluster is analyzed.
It is demonstrated that the energy necessary for removing homothetic groups of
atoms from the parent cluster is largely independent of the isomer form of the
parent cluster. Importance of rearrangement of the cluster structure during the
fission process is elucidated. This rearrangement may include transition to
another isomer state of the parent cluster before actual separation of the
daughter fragments begins and/or forming a "neck" between the separating
fragments
Charge-Induced Fragmentation of Sodium Clusters
The fission of highly charged sodium clusters with fissilities X>1 is studied
by {\em ab initio} molecular dynamics. Na_{24}^{4+} is found to undergo
predominantly sequential Na_{3}^{+} emission on a time scale of 1 ps, while
Na_{24}^{Q+} (5 \leq Q \leq 8) undergoes multifragmentation on a time scale
\geq 0.1 ps, with Na^{+} increasingly the dominant fragment as Q increases. All
singly-charged fragments Na_{n}^{+} up to size n=6 are observed. The observed
fragment spectrum is, within statistical error, independent of the temperature
T of the parent cluster for T \leq 1500 K. These findings are consistent with
and explain recent trends observed experimentally.Comment: To appear in Physical Review Letter
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