183 research outputs found

    Melt Electrospinning Designs for Nanofiber Fabrication for Different Applications

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    Nanofibers have been attracting growing attention owing to their outstanding physicochemical and structural properties as well as diverse and intriguing applications. Electrospinning has been known as a simple, flexible, and multipurpose technique for the fabrication of submicro scale fibers. Throughout the last two decades, numerous investigations have focused on the employment of electrospinning techniques to improve the characteristics of fabricated fibers. This review highlights the state of the art of melt electrospinning and clarifies the major categories based on multitemperature control, gas assist, laser melt, coaxial, and needleless designs. In addition, we represent the effect of melt electrospinning process parameters on the properties of produced fibers. Finally, this review summarizes the challenges and obstacles connected to the melt electrospinning technique.Scopu

    Effects of the galactic magnetic field upon large scale anisotropies of extragalactic Cosmic Rays

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    The large scale pattern in the arrival directions of extragalactic cosmic rays that reach the Earth is different from that of the flux arriving to the halo of the Galaxy as a result of the propagation through the galactic magnetic field. Two different effects are relevant in this process: deflections of trajectories and (de)acceleration by the electric field component due to the galactic rotation. The deflection of the cosmic ray trajectories makes the flux intensity arriving to the halo from some direction to appear reaching the Earth from another direction. This applies to any intrinsic anisotropy in the extragalactic distribution or, even in the absence of intrinsic anisotropies, to the dipolar Compton-Getting anisotropy induced when the observer is moving with respect to the cosmic rays rest frame. For an observer moving with the solar system, cosmic rays traveling through far away regions of the Galaxy also experience an electric force coming from the relative motion (due to the rotation of the Galaxy) of the local system in which the field can be considered as being purely magnetic. This produces small changes in the particles momentum that can originate large scale anisotropies even for an isotropic extragalactic flux.Comment: 11 pages, 4 figure

    Relative locality: A deepening of the relativity principle

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    We describe a recently introduced principle of relative locality which we propose governs a regime of quantum gravitational phenomena accessible to experimental investigation. This regime comprises phenomena in which â„Ź\hbar and GNG_N may be neglected, while their ratio, the Planck mass Mp=â„Ź/GNM_p =\sqrt{\hbar / G_N}, is important. We propose that MpM_p governs the scale at which momentum space may have a curved geometry. We find that there are striking consequences for the concept of locality. The description of events in spacetime now depends on the energy used to probe it. But there remains an invariant description of physics in phase space. There is furthermore a reasonable expectation that the geometry of momentum space can be measured experimentally using astrophysical observations.Comment: 8 pages, Latex; this essay was awarded Second Prize in the 2011 Essay Competition of the Gravity Research Foundatio

    On the true nature of renormalizability in Horava-Lifshitz gravity

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    We argue that the true nature of the renormalizability of Horava-Lifshitz gravity lies in the presence of higher order spatial derivatives and not in the anisotropic Lifshitz scaling of space and time. We discuss the possibility of constructing a higher order spatial derivatives model that has the same renormalization properties of Horava-Lifshitz gravity but that does not make use of the Lifshitz scaling. In addition, the state-of-the-art of the Lorentz symmetry restoration in Horava-Lifshitz-type theories of gravitation is reviewed.Comment: Latex file in Revtex style, 5 pages, no figures. v2: references added, version accepted for publication in Foundations of Physic

    The Contribution of Fermi Gamma-Ray Pulsars to the local Flux of Cosmic-Ray Electrons and Positrons

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    We analyze the contribution of gamma-ray pulsars from the first Fermi-Large Area Telescope (LAT) catalogue to the local flux of cosmic-ray electrons and positrons (e+e-). We present new distance estimates for all Fermi gamma-ray pulsars, based on the measured gamma-ray flux and pulse shape. We then estimate the contribution of gamma-ray pulsars to the local e+e- flux, in the context of a simple model for the pulsar e+e- emission. We find that 10 of the Fermi pulsars potentially contribute significantly to the measured e+e- flux in the energy range between 100 GeV and 1 TeV. Of the 10 pulsars, 2 are old EGRET gamma-ray pulsars, 2 pulsars were discovered with radio ephemerides, and 6 were discovered with the Fermi pulsar blind-search campaign. We argue that known radio pulsars fall in regions of parameter space where the e+e- contribution is predicted to be typically much smaller than from those regions where Fermi-LAT pulsars exist. However, comparing the Fermi gamma-ray flux sensitivity to the regions of pulsar parameter space where a significant e+e- contribution is predicted, we find that a few known radio pulsars that have not yet been detected by Fermi can also significantly contribute to the local e+e- flux if (i) they are closer than 2 kpc, and if (ii) they have a characteristic age on the order of one mega-year.Comment: 21 pages, 6 figures, accepted for publication in JCA

    Understanding hadronic gamma-ray emission from supernova remnants

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    We aim to test the plausibility of a theoretical framework in which the gamma-ray emission detected from supernova remnants may be of hadronic origin, i.e., due to the decay of neutral pions produced in nuclear collisions involving relativistic nuclei. In particular, we investigate the effects induced by magnetic field amplification on the expected particle spectra, outlining a phenomenological scenario consistent with both the underlying Physics and the larger and larger amount of observational data provided by the present generation of gamma experiments, which seem to indicate rather steep spectra for the accelerated particles. In addition, in order to study to study how pre-supernova winds might affect the expected emission in this class of sources, the time-dependent gamma-ray luminosity of a remnant with a massive progenitor is worked out. Solid points and limitations of the proposed scenario are finally discussed in a critical way.Comment: 30 pages, 5 figures; Several comments, references and a figure added. Some typos correcte

    Pharmacological, nutritional and antimicrobial uses of Moringa oleifera Lam. leaves in poultry nutrition: An updated knowledge

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    Recently, developing countries have focused on using innovative feed in poultry nutrition. The plant Moringa oleifera is native to India but grows worldwide in tropical and subtropical climates. Moringa is planted on a large scale as it can tolerate severe dry and cold conditions. All parts of this plant can be used for commercial or nutritional purposes, and it has a favorable nutritional profile. Beneficial phytochemicals, minerals, and vitamins are abundant in the leaves. The leaf extracts can be used to treat malnutrition; they also possess anticancer, antioxidant, antidiabetic, antibacterial, and anti-inflammatory properties. Further, moringa contains antinutritional substances, such as trypsin inhibitors, phytates, tannins, oxalates, cyanide, and saponins, which have a harmful effect on mineral and protein metabolism. Previous research suggested that including moringa in chicken diets boosts their growth and productivity. Therefore, this review focuses on the characterization and application of M. oleifera in poultry nutrition and its potential toxicity. Furthermore, we discuss the nutritional content, phytochemicals, and antioxidants of M. oleifera leaf meal and its applicability in poultry rations

    Background Dependent Lorentz Violation: Natural Solutions to the Theoretical Challenges of the OPERA Experiment

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    To explain both the OPERA experiment and all the known phenomenological constraints/observations on Lorentz violation, the Background Dependent Lorentz Violation (BDLV) has been proposed. We study the BDLV in a model independent way, and conjecture that there may exist a "Dream Special Relativity Theory", where all the Standard Model (SM) particles can be subluminal due to the background effects. Assuming that the Lorentz violation on the Earth is much larger than those on the interstellar scale, we automatically escape all the astrophysical constraints on Lorentz violation. For the BDLV from the effective field theory, we present a simple model and discuss the possible solutions to the theoretical challenges of the OPERA experiment such as the Bremsstrahlung effects for muon neutrinos and the pion decays. Also, we address the Lorentz violation constraints from the LEP and KamLAMD experiments. For the BDLV from the Type IIB string theory with D3-branes and D7-branes, we point out that the D3-branes are flavour blind, and all the SM particles are the conventional particles as in the traditional SM when they do not interact with the D3-branes. Thus, we not only can naturally avoid all the known phenomenological constraints on Lorentz violation, but also can naturally explain all the theoretical challenges. Interestingly, the energy dependent photon velocities may be tested at the experiments.Comment: RevTex4, 14 pages, minor corrections, references adde

    Constraining Sources of Ultra High Energy Cosmic Rays Using High Energy Observations with the Fermi Satellite

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    We analyze the conditions that enable acceleration of particles to ultra-high energies, ~10^{20} eV (UHECRs). We show that broad band photon data recently provided by WMAP, ISOCAM, Swift and Fermi satellites, yield constraints on the ability of active galactic nuclei (AGN) to produce UHECRs. The high energy (MeV - GeV) photons are produced by Compton scattering of the emitted low energy photons and the cosmic microwave background or extra-galactic background light. The ratio of the luminosities at high and low photon energies can therefore be used as a probe of the physical conditions in the acceleration site. We find that existing data excludes core regions of nearby radio-loud AGN as possible acceleration sites of UHECR protons. However, we show that giant radio lobes are not excluded. We apply our method to Cen A, and show that acceleration of protons to ~10^{20} eV can only occur at distances >~ 100 kpc from the core.Comment: Extended discussion on former results; Accepted for publication in JCA
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