4,093 research outputs found
Circular strings, wormholes and minimum size
The quantization of circular strings in an anti-de Sitter background
spacetime is performed, obtaining a discrete spectrum for the string mass. A
comparison with a four-dimensional homogeneous and isotropic spacetime coupled
to a conformal scalar field shows that the string radius and the scale factor
have the same classical solutions and that the quantum theories of these two
models are formally equivalent. However, the physically relevant observables of
these two systems have different spectra, although they are related to each
other by a specific one-to-one transformation. We finally obtain a discrete
spectrum for the spacetime size of both systems, which presents a nonvanishing
lower bound.Comment: 11 pages, LaTeX2e, minor change
Dominant negative phenotype of Bacillus thuringiensis Cry1Ab, Cry11Aa and Cry4Ba mutants suggest hetero-oligomer formation among different Cry toxins.
Background - Bacillus thuringiensis Cry toxins are used worldwide in the control of different insect pests important in agriculture or in human health. The Cry proteins are pore-forming toxins that affect the midgut cell of target insects. It was shown that non-toxic Cry1Ab helix a-4 mutants had a dominant negative (DN) phenotype inhibiting the toxicity of wildtype Cry1Ab when used in equimolar or sub-stoichiometric ratios (1:1, 0.5:1, mutant:wt) indicating that oligomer formation is a key step in toxicity of Cry toxins. Methodology/Principal Findings - The DN Cry1Ab-D136N/T143D mutant that is able to block toxicity of Cry1Ab toxin, was used to analyze its capacity to block the activity against Manduca sexta larvae of other Cry1 toxins, such as Cry1Aa, Cry1Ac, Cry1Ca, Cry1Da, Cry1Ea and Cry1Fa. Cry1Ab-DN mutant inhibited toxicity of Cry1Aa, Cry1Ac and Cry1Fa. In addition, we isolated mutants in helix a-4 of Cry4Ba and Cry11Aa, and demonstrate that Cry4Ba-E159K and Cry11Aa-V142D are inactive and completely block the toxicity against Aedes aegypti of both wildtype toxins, when used at sub-stoichiometric ratios, confirming a DN phenotype. As controls we analyzed Cry1Ab-R99A or Cry11Aa-E97A mutants that are located in helix a-3 and are affected in toxin oligomerization. These mutants do not show a DN phenotype but were able to block toxicity when used in 10:1 or 100:1 ratios (mutant:wt) probably by competition of binding with toxin receptors. Conclusions/Significance - We show that DN phenotype can be observed among different Cry toxins suggesting that may interact in vivo forming hetero-oligomers. The DN phenotype cannot be observed in mutants affected in oligomerization, suggesting that this step is important to inhibit toxicity of other toxin
Quantificação dos horizontes húmicos e dinâmica da decomposição de material foliar em solos florestais.
Estudos sobre o balanço entre o carbono estocado na biomassa e o perdido por meio da composição, visando a quantificação do acúmulo líquido de carbono de um sistema florestal.bitstream/CNPS-2009-09/11577/1/comtec21_2003_quantificacao.pd
A Robust Intelligent Tutoring System for the Integration of People with Intellectual Disabilities into Social and Work Environments
New 9.9-GHz methanol masers
The Australia Telescope Compact Array (ATCA) has been used to make the first
extensive search for the class I methanol masers at 9.9 GHz. In total, 48
regions of high-mass star formation were observed. In addition to masers in
W33-Met (G12.80-0.19) and G343.12-0.06 (IRAS 16547-4247) which have already
been reported in the literature, two new 9.9-GHz masers have been found towards
G331.13-0.24 and G19.61-0.23. We have determined absolute positions (accurate
to roughly a second of arc) for all the detected masers and suggest that some
class I masers may be associated with shocks driven into molecular clouds by
expanding HII regions. Our observations also imply that the evolutionary stage
of a high-mass star forming region when the class I masers are present can
outlast the stage when the class II masers at 6.7 GHz are detectable, and
overlaps significantly with the stage when OH masers are active.Comment: accepted for publication in MNRAS, 14 pages, 3 figures, 4 table
Correlation of the HPV genotype with the degree of dysplasia in patients with cervicouter cancer in the General Hospital Naval of high specialty
Background: Cervical-uterine cancer (CaCu) is the second leading cause of death in women worldwide and the first in developing countries. It has been correlated to human papillomavirus (HPV) genotype with cancerous lesions reported in histopathological studies, which tells us about the prognosis of the patients. Objective of present study was to correlate the genotype of HPV to the histopathological result evaluated in these patients at the Naval Hospital of High Specialty.Methods: A total of 316 women attended at the Naval General High Marine Hospital from 2015 to 2016 with HPV diagnosis were included, the histopathological report was correlated with the HPV genotype determined by the chain reaction of the polymerase (PCR). Statistical tests were applied for Smirnov and Kolmogorov, Chi square, OR, Anova-Kruskal Wallis. Data were processed using the SPSS software version 19 and a P <0.05 was taken as statistical significance.Results: The mean age was 36.0±10.2. The detection of cervical cancer was reported in 3.8% and stage CIN III 2.5%; the highest proportion of patients were in the CIN I stage (51.3%), while the CIN II was 9.2%, and up to 30.7% were classified as HPV infection; only 2.5% were normal. The types of HPV prevalent by PCR were those at high risk different from 16 and 18 with a rate of 34.8%, then 16 at 5.1% and 18 at 0.3%. More than half of the cases (54.4%) were negative for the serotypes analyzed. In general terms, CaCu and CIN III were observed in 15% of the type 16, 0% in type 18, 25% in other high risk and 60% in negative PCR.Conclusions: In this study, we obtained essential data that tells us that this population could be treated with low-risk HPV types associated with CaCu
B-Function Expression in the Flower Center Underlies the Homeotic Phenotype of Lacandonia schismatica (Triuridaceae)
Spontaneous homeotic transformations have been described in natural populations of both plants and animals, but little is known about the molecular-genetic mechanisms underlying these processes in plants. In the ABC model of floral organ identity in Arabidopsis thaliana, the B- and C-functions are necessary for stamen morphogenesis, and C alone is required for carpel identity. We provide ABC model-based molecular-genetic evidence that explains the unique inside-out homeotic floral organ arrangement of the monocotyledonous mycoheterotroph species Lacandonia schismatica (Triuridaceae) from Mexico. Whereas a quarter million flowering plant species bear central carpels surrounded by stamens, L. schismatica stamens occur in the center of the flower and are surrounded by carpels. The simplest explanation for this is that the B-function is displaced toward the flower center. Our analyses of the spatio-temporal pattern of B- and C-function gene expression are consistent with this hypothesis. The hypothesis is further supported by conservation between the B-function genes of L. schismatica and Arabidopsis, as the former are able to rescue stamens in Arabidopsis transgenic complementation lines, and Ls-AP3 and Ls-PI are able to interact with each other and with the corresponding Arabidopsis B-function proteins in yeast. Thus, relatively simple molecular modifications may underlie important morphological shifts in natural populations of extant plant taxa
Morphologies of Ultracompact HII Regions in W49A and Sgr B2: Prevalence of Shells and a Modified Classification Scheme
We have used Very Large Array (VLA) observations of the massive star forming
regions W49A and Sgr B2, obtained with resolutions from 2\farcs0 to 0\farcs04,
to classify the morphologies of nearly 100 ultracompact HII regions. These high
resolution, multi-frequency, multi-configuration VLA observations motivate
several modifications of the existing morphological classification scheme for
UC HII regions. In this work, we describe the modified morphology scheme and
the criteria used in source classification. In particular, we drop the
``core-halo'' classification, add a ``bipolar'' classification, and change the
shell classification to ``shell-like''. We tally the percentage of each
morphology found in the Sgr B2 and W49A regions and find broad agreement with
the Galactic plane surveys in the distribution of morphologies for most types.
However, we find that nearly a third of the sources in these regions are
shell-like, which is a higher percentage by nearly a factor of ten than found
in the surveys of Galactic plane star forming regions by Wood & Churchwell
(1989a) and Kurtz et al. (1994). This difference may be due to physical
differences in the environments of these two extreme star forming regions.
Alternatively, differences in observational technique may be responsible.Comment: 10 pages, 1 figure, 1 table, to appear in The Astrophysical Journal
Letter
Two massive star-forming regions at early evolutionary stages
We report sensitive ATCA radio-continuum observations toward IRAS 15596-5301
and 16272-4837, two luminous objects (> 2x10^4 Lsun) thought to represent
massive star-forming regions in early stages of evolution (due to previously
undetected radio emission at the 1-sigma level of 2 mJy per beam). Also
reported are 1.2-millimeter continuum and a series of molecular-line
observations made with the SEST telescope. For IRAS 15596-5301, the
observations reveal the presence of three distinct compact radio-continuum
sources associated with a dense molecular core. We suggest that this core
contains a cluster of B stars which are exciting compact HII regions that are
in pressure equilibrium with the dense molecular surroundings. No radio
continuum emission was detected from IRAS 16272-4837 (3-sigma limit of 0.2
mJy). However, a dense molecular core has been detected. The high luminosity
and lack of radio emission from this massive core suggests that it hosts an
embedded young massive protostar that is still undergoing an intense accretion
phase. This scenario is supported by the observed characteristics of the line
profiles and the presence of a bipolar outflow detected from observations of
the SiO emission. We suggest that IRAS 16272-4837 is a bona fide massive star-
forming region in a very early evolutionary stage, being the precursor of an
ultra compact HII region.Comment: 25 pages, 9 figures, accepted for publication in The Astrophysical
Journa
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