862 research outputs found
The Apparent Fractal Conjecture
This short communication advances the hypothesis that the observed fractal
structure of large-scale distribution of galaxies is due to a geometrical
effect, which arises when observational quantities relevant for the
characterization of a cosmological fractal structure are calculated along the
past light cone. If this hypothesis proves, even partially, correct, most, if
not all, objections raised against fractals in cosmology may be solved. For
instance, under this view the standard cosmology has zero average density, as
predicted by an infinite fractal structure, with, at the same time, the
cosmological principle remaining valid. The theoretical results which suggest
this conjecture are reviewed, as well as possible ways of checking its
validity.Comment: 6 pages, LaTeX. Text unchanged. Two references corrected. Contributed
paper presented at the "South Africa Relativistic Cosmology Conference in
Honour of George F. R. Ellis 60th Birthday"; University of Cape Town,
February 1-5, 199
Mutations in the 23S rRNA gene are associated with clarithromycin resistance in Helicobacter pylori isolates in Brazil
BACKGROUND: Resistance of Helicobacter pylori to clarithromycin has been associated with A2142G and A2143G point mutations in the 23S rRNA gene. Thus, the purpose of the present study was to determine the prevalence of each mutation in 52 clarithromycin-resistant H. pylori strains and to characterize the influence each type of mutation on the MIC. METHODS: The MIC for clarithromycin was determined by the agar dilution method, and the point mutations of H. pylori were detected by PCR followed by restriction fragment length polymorphism. RESULTS: Clarithromycin MICs ranged from 2 to >256 microgram ml(-1 )among the 52 strains included in this study. Both the A2142G and the A2143G mutations were present in 94.2% of clarithromycin-resistant H. pylori strains examined. A relationship was observed between the presence of the A2142G mutation and the highest MIC values (p = 0.01). CONCLUSION: In an H. pylori-infected population, the A2142G mutation may incur to a greater probability of treatment failure if clarithromycin is used
Elastocaloric Effect in Graphene Kirigami
Kirigami, a traditional Japanese art of paper-cutting, has recently been
explored for its elastocaloric effect (ECE) in kirigami-based materials (KMs),
where applying strain induces temperature changes. In this study, we
investigate the ECE in a nanoscale graphene kirigami (GK) monolayer,
representing the thinnest possible KM, to better understand this phenomenon.
Through molecular dynamics simulations, we analyze the temperature change and
coefficient of performance (COP) of the nanoscale GK architecture. Our findings
reveal that while GKs lack the intricate temperature changes observed in
macroscopic KMs, they exhibit a substantial temperature change of approximately
9.32 K (23 times higher than that of macroscopic KMs, which is about 0.4K) for
heating and -3.50 K for cooling. Additionally, they demonstrate reasonable COP
values of approximately 1.57 and 0.62, respectively. It is noteworthy that the
one-atom-thick graphene configuration prevents the occurrence of the complex
temperature distribution observed in macroscopic KMs.Comment: 14 pages, 06 figures, and 01 tabl
Dust content solutions for the Alcubierre warp drive spacetime
The Alcubierre metric is a spacetime geometry where a massive particle inside
a spacetime distortion, called warp bubble, is able to travel at velocities
arbitrarily higher than the velocity of light, a feature known as the warp
drive. This is a consequence of general relativity, which allows global
superluminal velocities but restricts local speeds to subluminal ones as
required by special relativity. In this work we solved the Einstein equations
for the Alcubierre warp drive spacetime geometry considering the dust matter
distribution as source, since the Alcubierre metric was not originally advanced
as a solution of the Einstein equations, but as a spacetime geometry proposed
without a source gravity field. We found out that all Einstein equations
solutions of this geometry containing pressureless dust lead to vacuum
solutions. We also concluded that these solutions connect the Alcubierre metric
to the Burgers equation, which describes shock waves moving through an inviscid
fluid. Our results also indicated that these shock waves behave as plane waves.Comment: 15 pages, 1 figure. LaTeX. Accepted for publication in the European
Physical Journal
Continuidade do La Niña favorece a atual safra de café.
As condições atmosféricas e oceânicas revelam que o fenômeno La Niña continua presente, sendo provável que tais condições persistam até junho, quando tem início o inverno. A partir de julho há igual probabilidade (50%) que as condições de La Niña continuem ou condições ENSO neutras ocorram até setembro, quando tem início a primavera no hemisfério Sul. A partir da segunda quinzena de fevereiro foi observada a redução do volume de chuvas em Minas Gerais. No mês de março, a chuva foi mais concentrada no Triângulo e no Sul de Minas, o que contribuiu para a baixa umidade de água no solo em parte de outras regiões cafeeiras do Estado. Em abril, apesar da melhor distribuição das chuvas no Estado, a umidade do solo continuou baixa principalmente em grande parte da região das Matas de Minas, no Sul de Minas e na região da Chapada de Minas. As consequências de tais condições poderão ser reveladas nas próximas semanas, nos lavadores de café, com a maior presença de grãos vazios e malformados. Diante das condições climáticas reinantes, o produtor deve estar atento ao mercado do café que mantém a tendência de oscilação e alta nos preços. Quem possuir estoques deve ficar atento ao mercado e aproveitar os preços para vender de acordo com sua necessidade. Sabendo que o café é um produto que tem o seu valor de mercado estritamente relacionado com seu aspecto qualitativo, o produtor deve sempre investir em todos os processos que contribuem para a obtenção de um café de qualidade
Sun-Graphyne: A New 2D Carbon Allotrope with Dirac Cones
Due to the success achieved by graphene, several 2D carbon-based allotropes
were theoretically predicted and experimentally synthesized. Here, we propose a
new 2D carbon allotrope named Sun-Graphyne (S-GY). We used density functional
theory and reactive molecular dynamics simulations to investigate its
mechanical, structural, electronic, and optical properties. The results showed
that S-GY exhibits good dynamical and thermal stabilities. Its formation energy
and elastic moduli are -8.57 eV/atom and 262.37 GPa, respectively. S-GY is a
semi-metal and presents two Dirac cones in its band structure. This material is
transparent, and its intense optical activity is limited to the infrared
region. Remarkably, the band structure of S-GY remains practically unchanged at
even moderate strain regimes. As far as we know, this is the first 2D carbon
allotrope to exhibit this behaviour.Comment: 17 pages, and 11 figure
Germinal center architecture disturbance during Plasmodium berghei ANKA infection in CBA mice
<p>Abstract</p> <p>Background</p> <p>Immune responses to malaria blood stage infection are in general defective, with the need for long-term exposure to the parasite to achieve immunity, and with the development of immunopathology states such as cerebral malaria in many cases. One of the potential reasons for the difficulty in developing protective immunity is the poor development of memory responses. In this paper, the potential association of cellular reactivity in lymphoid organs (spleen, lymph nodes and Peyer's patches) with immunity and pathology was evaluated during <it>Plasmodium berghei </it>ANKA infection in CBA mice.</p> <p>Methods</p> <p>CBA mice were infected with 1 × 10<sup>6 </sup><it>P. berghei </it>ANKA-parasitized erythrocytes and killed on days 3, 6–8 and 10 of infection. The spleen, lymph nodes and Peyer's patches were collected, fixed in Carson's formalin, cut in 5 μm sections, mounted in glass slides, stained with Lennert's Giemsa and haematoxylin-eosin and analysed with bright-field microscopy.</p> <p>Results</p> <p>Early (day 3) strong activation of T cells in secondary lymphoid organs was observed and, on days 6–8 of infection, there was overwhelming activation of B cells, with loss of conventional germinal center architecture, intense centroblast activation, proliferation and apoptosis but little differentiation to centrocytes. In the spleen, the marginal zone disappeared and the limits between the disorganized germinal center and the red pulp were blurred. Intense plasmacytogenesis was observed in the T cell zone.</p> <p>Conclusion</p> <p>The observed alterations, especially the germinal center architecture disturbance (GCAD) with poor centrocyte differentiation, suggest that B cell responses during <it>P. berghei </it>ANKA infection in mice are defective, with potential impact on B cell memory responses.</p
Coupled spillway devices and energy dissipation system at St-Marc (France)
The physical modeling tests for the rehabilitation of St-Marc Dam with a PKW are presented. A particular focus is put on the energy dissipation downstream from the PKW. The adopted solution is a leaned “ski-jump gutter” placed at the contact line between the downstream face of the dam and the natural foundation rock. It consists of a cylindrical profile, developed around an inclined axis and closed by a horizontal reach at the end of the structure. The aim of this solution is to guide the flow issued from the PKW to the stilling basin of the left existing spillway. The experimental tests consider various operation conditions which required pressure measurements at different impact zones. Structural design of the PKW is impacted by the fact that the concrete of the dam is subjected to a noteworthy blowing reaction. For that reason, the new structure could not be anchored in the existing dam. Thus, the spillway behaves as a gravity structure
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