103 research outputs found
Anisotropy in nanocellular polymers promoted by the addition of needleâlike sepiolites
This work presents a new strategy for obtaining nanocellular materials with high anisotropy ratios by means of the addition of needleâlike nanoparticles. Nanocellular polymers are of great interest due to their outstanding properties, whereas anisotropic structures allow the realization of improved thermal and mechanical properties in certain directions. Nanocomposites based on poly(methyl methacrylate) (PMMA) with nanometric sepiolites are generated by extrusion. From the extruded filaments, cellular materials are produced using a twoâstep gas dissolution foaming method. The effect of adding various types and contents of sepiolites is investigated. As a result of the extrusion process, the needleâlike sepiolites are aligned in the machine direction in the solid nanocomposites. Regarding the cellular materials, the addition of sepiolites allows one to obtain anisotropic nanocellular polymers with cell sizes of 150 to 420ânm and cell nucleation densities of 1013â1014 nucleiâcmâ3 and presenting anisotropy ratios ranging from 1.38 to 2.15, the extrusion direction being the direction of the anisotropy. To explain the appearance of anisotropy, a mechanism based on cell coalescence is proposed and discussed. In addition, it is shown that it is possible to control the anisotropy ratio of the PMMA/sepiolite nanocellular polymers by changing the amount of wellâdispersed sepiolites in the solid nanocomposites
Mechanical Properties of PMMA-Sepiolite Nanocellular Materials with a Bimodal Cellular Structure
Bimodal cellular poly(methyl methacrylate) with micron and nano sized (300 to
500 nm) cells with up to 5 weight percent of sepiolite nanoparticles and
porosity from 50 weight percent to 75 weight percent are produced by solid
state foaming. Uniaxial compression tests are performed to measure the effect
of sepiolite concentration on the elastic modulus and the yield strength of the
solid and cellular nanocomposites. Single edge notch bend tests are conducted
to relate the fracture toughness of the solid and cellular nanocomposites to
sepiolite concentration. The relative modulus is independent of sepiolite
content to within material scatter when considering the complete porosity
range. In contrast, a mild enhancement of the relative modulus is observed by
the addition of sepiolite particles for the foamed nanocomposites with a
porosity close to 50 percent. The relative compressive strength of the cellular
nanocomposites mildly decreases as a function of sepiolite concentration. A
strong enhancement of the relative fracture toughness by the addition of
sepiolites is observed. The enhancement of the relative fracture toughness and
the relative modulus (at 50 percent porosity) can be attributed to an improved
dispersion of the particles due to foaming and the migration of micron sized
aggregates from the solid phase to the microcellular pores during foaming
Single-mode Bragg gratings in tapered few-modes and multimode fibers
We propose the implementation of fiber Bragg gratings in tapered few-modes, and multimode fibers to accomplish single-mode operation by reducing the core diameter while preserving the core-cladding structure. Gratings present a single reflection band and the device show low insertion losses after the taper fabrication and the fiber Bragg gratings inscription. The excitation of high order odd-modes in the core of the fiber has been identified as the main loss mechanism; it can be prevented by means of symmetric illumination of the fibers. We also demonstrate the excitation of high order cladding modes (cladding-air modes) along the taper transitions; these modes can be removed without a significant increment of the insertion loss
Neutrino-nucleus cross sections for oscillation experiments
Neutrino oscillations physics is entered in the precision era. In this
context accelerator-based neutrino experiments need a reduction of systematic
errors to the level of a few percent. Today one of the most important sources
of systematic errors are neutrino-nucleus cross sections which in the
hundreds-MeV to few-GeV energy region are known with a precision not exceeding
20%. In this article we review the present experimental and theoretical
knowledge of the neutrino-nucleus interaction physics. After introducing
neutrino oscillation physics and accelerator-based neutrino experiments, we
overview general aspects of the neutrino-nucleus cross sections, both
theoretical and experimental views. Then we focus on these quantities in
different reaction channels. We start with the quasielastic and
quasielastic-like cross section, putting a special emphasis on multinucleon
emission channel which attracted a lot of attention in the last few years. We
review the main aspects of the different microscopic models for this channel by
discussing analogies and differences among them.The discussion is always driven
by a comparison with the experimental data. We then consider the one pion
production channel where data-theory agreement remains very unsatisfactory. We
describe how to interpret pion data, then we analyze in particular the puzzle
related to the impossibility of theoretical models and Monte Carlo to
simultaneously describe MiniBooNE and MINERvA experimental results. Inclusive
cross sections are also discussed, as well as the comparison between the
and cross sections, relevant for the CP violation
experiments. The impact of the nuclear effects on the reconstruction of
neutrino energy and on the determination of the neutrino oscillation parameters
is reviewed. A window to the future is finally opened by discussing projects
and efforts in future detectors, beams, and analysis
Beyond efficacy in water containers: Temephos and household entomological indices in six studies between 2005 and 2013 in Managua, Nicaragua
Entrepreneursâ mental health and well-being:A review and research agenda
Interest in entrepreneursâ mental health and well-being (MWB) is growing in recognition of the role of MWB in entrepreneursâ decision making, motivation, and action. Yet relevant knowledge is dispersed across disciplines, which makes what we currently understand about entrepreneursâ MWB unclear. In this systematic review I integrate insights from 144 empirical studies. These studies show that research is focused on three research questions: (1) Do different types of entrepreneurs differ in their MWB? What are the (2) antecedents and (3) consequences of entrepreneursâ MWB? The review systematizes evidence on known antecedents and consequences of entrepreneursâ MWB but also reveals overlooked and undertheorized sources and outcomes of entrepreneursâ MWB. The review provides a mapping and framework that advance research on entrepreneursâ MWB and help to position entrepreneursâ MWB more centrally in management and entrepreneurship research. It calls for researchers to go beyond applying models developed for employees to understand entrepreneurs. Instead, the findings point the way to developing a dedicated theory of entrepreneurial work and MWB that is dynamic, socialized, and open to considering context and acknowledges variability and fluidity across entrepreneursâ life domains, as well as the centrality of work for entrepreneursâ identity
A High Accurate Approximation for a Galactic Newtonian Nonlinear Model Validated by Employing Observational Data
This article proposes Perturbation Method (PM) to solve nonlinear problems. As case study PM is employed to provide a detailed study of a nonlinear galactic model. Our approach is rather elementary and seeks to explain as much detail as possible the material of this work.In particular our solution gives rise qualitatively, to the known flat rotation curves. In fact, we compare the numerical solution and the obtained approximation by employing observational data proving the validity and high accuracy of the model under study
Anaplasma phagocytophilum Ats-1 Is Imported into Host Cell Mitochondria and Interferes with Apoptosis Induction
Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis, infects human neutrophils and inhibits mitochondria-mediated apoptosis. Bacterial factors involved in this process are unknown. In the present study, we screened a genomic DNA library of A. phagocytophilum for effectors of the type IV secretion system by a bacterial two-hybrid system, using A. phagocytophilum VirD4 as bait. A hypothetical protein was identified as a putative effector, hereby named Anaplasma translocated substrate 1 (Ats-1). Using triple immunofluorescence labeling and Western blot analysis of infected cells, including human neutrophils, we determined that Ats-1 is abundantly expressed by A. phagocytophilum, translocated across the inclusion membrane, localized in the host cell mitochondria, and cleaved. Ectopically expressed Ats-1 targeted mitochondria in an N-terminal 17 residue-dependent manner, localized in matrix or at the inner membrane, and was cleaved as native protein, which required residues 55â57. In vitro-translated Ats-1 was imported in a receptor-dependent manner into isolated mitochondria. Ats-1 inhibited etoposide-induced cytochrome c release from mitochondria, PARP cleavage, and apoptosis in mammalian cells, as well as Bax-induced yeast apoptosis. Ats-1(55â57) had significantly reduced anti-apoptotic activity. Bax redistribution was inhibited in both etoposide-induced and Bax-induced apoptosis by Ats-1. Taken together, Ats-1 is the first example of a bacterial protein that traverses five membranes and prevents apoptosis at the mitochondria
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