1,134 research outputs found
Propriedades físicas e mecânicas de compósitos de cimento reforçados com fibra de curauá (Ananas erectifolius)
O objetivo deste estudo é a caracterização de compósitos cimentícios com reforço de fibras longas de curauá. Estes compósitos são constituídos de matriz cimentícia composta por cimento CP V-ARI, areia, água e superplastificante. A substituição de materiais como o cimento por reforços de materiais naturais como a fibra de curauá se tornam objetos de pesquisa por reduzirem o custo, serem biodegradáveis, gerarem baixa energia em sua produção e possuírem propriedades como baixa densidade e capacidade de isolamento térmico e acústico. Para a produção dos compósitos laminados, foi determinada a influência da fração volumétrica de fibras no compósito em teores de adição de 0%, 5%, 10%, 15% e 20%. Como metodologia moldou-se o compósito em cinco camadas, intercalando três camadas de matriz cimentícia e duas camadas de reforço de fibra de curauá. Os ensaios avaliaram o comportamento físico e mecânico dos compósitos em diferentes dias (7, 28 e 90 dias). Observou-se que o teor de fibra de curauá de 10%, com essa metodologia, apresentou resultados compatíveis à referência com relação à resistência à flexão aos 90 dias, sendo indicado dessa forma a cura dos painéis por 90 dias para aplicação. E a redução na massa específica dos painéis foi possível, de forma significativa, com as adições acima de 10% de fibra de curauá.The objective of this study is the characterization of cementitious composites with reinforcement of long fibers of curauá. These composites consist of a cement matrix composed of CP V-ARI cement, sand, water and superplasticizer. The replacement of materials such as cement with reinforcements of natural materials such as curauá fiber become objects of research because they reduce the cost, are biodegradable, generate low energy in their production and have properties such as low density and thermal and acoustic isolation capacity. For the production of laminated composites, the influence of the volumetric fraction of fibers in the composite was determined at addition levels of 0%, 5%, 10%, 15% and 20%. As a methodology, the composite was molded in five layers, interspersing three layers of cement matrix and two layers of curauá fiber reinforcement. The tests evaluated the physical and mechanical behavior of the composites on different days (7, 28 and 90 days). It was observed that the curauá fiber content of 10%, with this methodology, presented results compatible with the reference in relation to the flexural strength at 90 days, thus indicating the curing of the panels for 90 days for application. And the reduction in the specific mass of the panels was possible, in a significant way, with the additions above 10% of curauá fiber
Error bounds for the large-argument asymptotic expansions of the Hankel and Bessel functions
In this paper, we reconsider the large-argument asymptotic expansions of the
Hankel, Bessel and modified Bessel functions and their derivatives. New
integral representations for the remainder terms of these asymptotic expansions
are found and used to obtain sharp and realistic error bounds. We also give
re-expansions for these remainder terms and provide their error estimates. A
detailed discussion on the sharpness of our error bounds and their relation to
other results in the literature is given. The techniques used in this paper
should also generalize to asymptotic expansions which arise from an application
of the method of steepest descents.Comment: 32 pages, 2 figures, accepted for publication in Acta Applicandae
Mathematica
Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: an international expert proposal for interim standard definitions for acquired resistance
AbstractMany different definitions for multidrug-resistant (MDR), extensively drug-resistant (XDR) and pandrug-resistant (PDR) bacteria are being used in the medical literature to characterize the different patterns of resistance found in healthcare-associated, antimicrobial-resistant bacteria. A group of international experts came together through a joint initiative by the European Centre for Disease Prevention and Control (ECDC) and the Centers for Disease Control and Prevention (CDC), to create a standardized international terminology with which to describe acquired resistance profiles in Staphylococcus aureus, Enterococcus spp., Enterobacteriaceae (other than Salmonella and Shigella), Pseudomonas aeruginosa and Acinetobacter spp., all bacteria often responsible for healthcare-associated infections and prone to multidrug resistance. Epidemiologically significant antimicrobial categories were constructed for each bacterium. Lists of antimicrobial categories proposed for antimicrobial susceptibility testing were created using documents and breakpoints from the Clinical Laboratory Standards Institute (CLSI), the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the United States Food and Drug Administration (FDA). MDR was defined as acquired non-susceptibility to at least one agent in three or more antimicrobial categories, XDR was defined as non-susceptibility to at least one agent in all but two or fewer antimicrobial categories (i.e. bacterial isolates remain susceptible to only one or two categories) and PDR was defined as non-susceptibility to all agents in all antimicrobial categories. To ensure correct application of these definitions, bacterial isolates should be tested against all or nearly all of the antimicrobial agents within the antimicrobial categories and selective reporting and suppression of results should be avoided
Microscopic transition potential: Determination of and coupling constants
A transition potential, based on an effective
quark-quark interaction and a constituent quark cluster model for baryons, is
derived in the Born-Oppenheimer approach. The potential shows significant
differences with respect to those obtained by a direct scaling of the
nucleon-nucleon interaction. From its asymptotic behavior we extract the values
of and coupling constants in a
particular coupling schemeComment: 15 eps figures, Accepted for publication in Phys. Rev.
Elastic electron deuteron scattering with consistent meson exchange and relativistic contributions of leading order
The influence of relativistic contributions to elastic electron deuteron
scattering is studied systematically at low and intermediate momentum transfers
( fm). In a -expansion, all leading order
relativistic -exchange contributions consistent with the Bonn OBEPQ models
are included. In addition, static heavy meson exchange currents including boost
terms and lowest order -currents are considered. Sizeable
effects from the various relativistic two-body contributions, mainly from
-exchange, have been found in form factors, structure functions and the
tensor polarization . Furthermore, static properties, viz. magnetic
dipole and charge quadrupole moments and the mean square charge radius are
evaluated.Comment: 15 pages Latex including 5 figures, final version accepted for
publication in Phys.Rev.C Details of changes: (i) The notation of the curves
in Figs. 1 and 2 have been clarified with respect to left and right panels.
(ii) In Figs. 3 and 4 an experimental point for T_20 has been added and a
corresponding reference [48] (iii) At the end of the text we have added a
paragraph concerning the quality of the Bonn OBEPQ potential
Recovering Joys Law as a Function of Solar Cycle, Hemisphere, and Longitude
Bipolar active regions in both hemispheres tend to be tilted with respect to
the East West equator of the Sun in accordance with Joys law that describes the
average tilt angle as a function of latitude. Mt. Wilson observatory data from
1917 to 1985 are used to analyze the active-region tilt angle as a function of
solar cycle, hemisphere, and longitude, in addition to the more common
dependence on latitude. Our main results are as follows: i) We recommend a
revision of Joys law toward a weaker dependence on latitude (slope of 0.13 to
0.26) and without forcing the tilt to zero at the Equator. ii) We determine
that the hemispheric mean tilt value of active regions varies with each solar
cycle, although the noise from a stochastic process dominates and does not
allow for a determination of the slope of Joys law on an 11-year time scale.
iii) The hemispheric difference in mean tilt angles, 1.1 degrees + 0.27, over
Cycles 16 to 21 was significant to a three-sigma level, with average tilt
angles in the northern and southern hemispheres of 4.7 degrees + 0.26 and 3.6
degrees + 0.27 respectively. iv) Area-weighted mean tilt angles normalized by
latitude for Cycles 15 to 21 anticorrelate with cycle strength for the southern
hemisphere and whole-Sun data, confirming previous results by Dasi-Espuig,
Solanki, Krivova, et al. (2010, Astron. Astrophys. 518, A7). The northern
hemispheric mean tilt angles do not show a dependence on cycle strength. vi)
Mean tilt angles do not show a dependence on longitude for any hemisphere or
cycle. In addition, the standard deviation of the mean tilt is 29 to 31 degrees
for all cycles and hemispheres indicating that the scatter is due to the same
consistent process even if the mean tilt angles vary.Comment: 13 pages, 4 figures, 3 table
Superhard Phases of Simple Substances and Binary Compounds of the B-C-N-O System: from Diamond to the Latest Results (a Review)
The basic known and hypothetic one- and two-element phases of the B-C-N-O
system (both superhard phases having diamond and boron structures and
precursors to synthesize them) are described. The attention has been given to
the structure, basic mechanical properties, and methods to identify and
characterize the materials. For some phases that have been recently described
in the literature the synthesis conditions at high pressures and temperatures
are indicated.Comment: Review on superhard B-C-N-O phase
Professional closure by proxy: the impact of changing educational requirements on class mobility for a cohort of Big 8 partners
Closure events impacting on class mobility may include mechanisms initiated by bodies other than the professional body. The research examines if the introduction of full-time study requirements at universities for aspiring accountants effectively introduced a closure mechanism in the accounting profession. Data was derived from an Oral History study of partners in large firms. The younger partners (born after the Second World War) completed full-time degree study at university, but did not provide evidence of class mobility into the profession. The older cohort, born between 1928 and 1946, completed part-time studies only, few completed a degree, and, in contrast to the younger cohort, shows a perceptible upward movement from lower socio-economic classes into the professional class. This suggests that changing the preferred educational routes for new accountants entering the large chartered accounting (CA) firms compromised the "stepping stone" function of accounting as a portal into the professional class
Isobar Excitations and the Ground State of Nuclei
The influence of isobar components on the ground state properties of
nuclear systems is investigated for nuclear matter as well as finite nuclei.
Many-body wave functions, including isobar configurations, and binding energies
are evaluated employing the framework of the coupled-cluster theory. It is
demonstrated that the effect of isobar configurations depends in a rather
sensitive way on the model used for the baryon-baryon interaction. As examples
for realistic baryon-baryon interactions with explicit inclusion of isobar
channels we use the local () and non-local meson exchange potentials
(Bonn) but also a model recently developed by the Salamanca group,
which is based on a quark picture. The differences obtained for the nuclear
observables are related to the treatment of the interaction, the -exchange
contributions in particular, at high momentum transfers.Comment: 12 pages, including 5 figure
Ru-decorated Pt nanoparticles on N-doped multi-walled carbon nanotubes by atomic layer deposition for direct methanol fuel cells
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