5,843 research outputs found

    How Barred is the NIR Nearby Universe? An analysis using 2MASS

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    We determine a firm lower limit to the bar fraction of 0.58 in the nearby universe using J+H+Ks-band images for 134 spirals from 2MASS. With a mean deprojected semi-major axis of 5.1 kpc, and a mean deprojected ellipticity of 0.45 this local bar sample lays the ground work for studies on bar formation and evolution at high redshift.Comment: In the proceedings "Penetrating Bars through Masks of Cosmic Dust: The Hubble Tuning Fork strikes a New Note

    Design, construction and evaluation of a 3D printed electrochemical flow cell for the synthesis of magnetite nanoparticles

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    A 3D-printed prototype of an electrochemical flow cell for the synthesis of superparamagnetic magnetite nanoparticles of medium size between 15 and 30 nm was constructed and its performance was evaluated. The cell consists of a series of rectangular channels in a parallel electrode arrangement. Electrolyte flows through the channels as the electric current is supplied to the system and a combination of electrochemical and chemical reactions create the appropriate conditions for magnetite precipitation. Different electric configurations were evaluated and both energy and production efficiencies were calculated to determine the best configuration. Different flow and current values were also investigated, and all the materials were analyzed by X-ray diffraction, transmission electron microscopy, Mossbauer spectroscopy and magnetization curve measurements to determine their effect on particle morphology, composition and magnetic behavior. The best results were obtained for a parallel monopolar configuration, with 100 mA (3 mA cm−2) passing in each two electrodes and a flow value of 30 mL min−1, yielding an energy efficiency of 5.9 kJ g−1 and a production rate of 12.1 mg min−1, approximately 6 times higher than the 100 mL standard cell previously used. Magnetic saturation was 77.3 emu g−1, slightly lower than the bulk material (92–100 emu g−1)The authors gratefully acknowledge the scholarship for doctoral studies of Gerardo Ivan Lozano Gutierrez granted by the National Council of Science and Technology of Mexico (CONACyT). The authors are also grateful to the Ministry of Economy and Competitiveness for the project MAT2015-67557-C2-2-P. Support for a sabbatical leave for NCS from the National Council of Science and Technology of Mexico and Exportadora de Postes S.A. de C.V. are greatly appreciate

    Cation distribution of cobalt ferrite electrosynthesized nanoparticles: A methodological comparison

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    Final publication at http://doi.org/10.1016/j.jallcom.2017.12.342, © 2017 Elsevier B.V.The present work seeks to analyse the structural and magnetic properties of cobalt ferrite nanoparticles obtained by electrochemical synthesis by high-resolution transmission electronic microscopy (HRTEM), X-ray absorption spectroscopy (XAS), Mössbauer spectroscopy (MS), neutron diffraction (ND) and SQUID magnetometer. The cationic distribution is analyzed by different techniques. The inversion degree determined by the most accurate measurements was 0.73(1), and the formula for the nanoparticles therefore was (↑Co 0.27 Fe 0.73 )[↓Co 0.73 Fe 1.27 ]O 4 . The magnetic moment found from DC and Mössbauer spectroscopy measurements was 3.8(3) μB, and the coercivity was 7870 Oe at 100 K.This work is supported by the MINECO/FEDER Project MAT2015-67557-C2-2-

    Ground-State Electromagnetic Moments of Calcium Isotopes

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    High-resolution bunched-beam collinear laser spectroscopy was used to measure the optical hyperfine spectra of the 43−51^{43-51}Ca isotopes. The ground state magnetic moments of 49,51^{49,51}Ca and quadrupole moments of 47,49,51^{47,49,51}Ca were measured for the first time, and the 51^{51}Ca ground state spin I=3/2I=3/2 was determined in a model-independent way. Our results provide a critical test of modern nuclear theories based on shell-model calculations using phenomenological as well as microscopic interactions. The results for the neutron-rich isotopes are in excellent agreement with predictions using interactions derived from chiral effective field theory including three-nucleon forces, while lighter isotopes illustrate the presence of particle-hole excitations of the 40^{40}Ca core in their ground state.Comment: Accepted as a Rapid Communication in Physical Review

    Comparison of different methodologies for obtaining nickel nanoferrites

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    Nickel nanoferrites were obtained by means of four different synthetic wet-routes: co-precipitation (CP), sonochemistry (SC), sonoelectrochemistry (SE) and electrochemistry (E). The influence of the synthesis method on the structural and magnetic properties of nickel ferrite nanoparticles is studied. Although similar experimental conditions such as temperature, pH and time of synthesis were used, a strong dependence of composition and microstructure on the synthesis procedure is found, as electron microscopy, X-ray diffraction and Mössbauer spectroscopy studies reveal. Whereas by means of the CP and SC methods particles of a small size around 5–10 nm, respectively, and composed by different phases are obtained, the electrochemical routes (E and SE) allow obtaining monodisperse nanoparticles, with sizes ranging from 30 to 40 nm, and very close to stoichiometry. Magnetic characterization evidences a superparamagnetic behavior for samples obtained by CP and SC methods, whereas the electrochemical route leads to ferromagnetic ferrite nanoparticles

    Parental Involvement Among Collegiate Student-Athletes: An Analysis Across NCAA Divisions

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    Despite emerging evidence of a link between parental involvement and student-athletes’ (SA) experiences, and the desire for educational programming for parents of these SAs, previous research has been limited to the Division I level. This has prevented the ability to inform, develop, and deliver parent programming across the NCAA’s diverse membership. The present study was designed to descriptively assess SA reports of parental involvement (i.e., support, contact, academic engagement, athletic engagement) across NCAA Division I, II, and III member institutions and examine the potential impact of this involvement on SAs’ experiences (i.e., academic self-efficacy, athletic satisfaction, well-being, individuation). Participants were 455 SAs (53% female; 81% Caucasian; Mage = 19.81, SD = 1.65) from DI (30%), DII (37%), and DIII (33%) institutions, who completed an online survey with items assessing parental involvement and SA experiences. Regarding academic classification, 32% were freshmen, 24% sophomores, 22% juniors, and 22% seniors. Results provide novel evidence for an absence of division-wide differences in average levels of involvement and no variability in links between involvement and SA experiences across divisions. Results complement and extend previous research by offering a clearer understanding of differential associations between involvement and SAs’ experiences regardless of division, notably that involvement bolstered well-being but also strongly detracted from individuation. Findings highlight the importance of developing programs to promote positive and developmentally-appropriate parental involvement across the spectrum of intercollegiate athletics, especially given the absence of evidence-based resources presently offered by the NCAA

    Secure Geographic Routing in Ad Hoc and Wireless Sensor Networks

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    Security in sensor networks is one of the most relevant research topics in resource constrained wireless devices and networks. Several attacks can be suffered in ad hoc and wireless sensor networks (WSN), which are highly susceptible to attacks, due to the limited resources of the nodes. In this paper, we propose innovative and lightweight localization techniques that allow for intrusion identification and isolation schemes and provide accurate location information. This information is used by our routing protocol which additionally incorporates a distributed trust model to prevent several routing attacks to the network. We finally evaluate our algorithms for accurate localization and for secure routing which have been implemented and tested in real ad hoc and wireless sensor networks

    Architectures for Future Media Internet

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    Among the major reasons for the success of the Internet have been the simple networking architecture and the IP interoperation layer. However, the traffic model has recently changed. More and more applications (e.g. peerto-peer, content delivery networks) target on the content that they deliver rather than on the addresses of the servers who (originally) published/hosted that content. This trend has motivated a number of content-oriented networking studies. In this paper we summarize some the most important approache

    The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS

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    The influence of haemoglobin genotype on the response to iron supplementation was studied in a randomized, double blind, placebo-controlled trial involving 497 multigravid pregnant women from a rural area of The Gambia. Women were randomly allocated to receive either oral iron (60mg elemental iron per day) or placebo. At 36 weeks of pregnancy, women who had received oral iron during pregnancy had higher mean haemoglobin, packed cell volume, plasma iron and ferritin levels than did women who received placebo. Iron supplementation of pregnant women with the AA haemoglobin genotype also resulted in increases in the packed cell volume (PCV) and haemoglobin level measured after delivery, and in the birth weight of the infant. However, in AS women PCV and haemoglobin level at delivery were lower in the supplemented group and supplementation was also associated with reduced birth weights. In malaria endemic areas, pregnant women with the haemoglobin genotype AS may not benefit from iron supplementation during pregnanc
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