562 research outputs found
Tuning of magnetic and electronic states by control of oxygen content in lanthanum strontium cobaltites
We report on the magnetic, resistive, and structural studies of perovskite
LaSrCoO. By using the relation of synthesis
temperature and oxygen partial pressure to oxygen stoichiometry obtained from
thermogravimetric analysis, we have synthesized a series of samples with
precisely controlled . These samples show three structural
phases at , , , and two-phase
behavior for other oxygen contents. The stoichiometric material with
is a cubic ferromagnetic metal with the Curie temperature K. The increase of to 0.15 is followed by a linear decrease of
to 160 K and a metal-insulator transition near the
boundary of the cubic structure range. Further increase of results in
formation of a tetragonal phase for
and a brownmillerite phase for . At low
temperatures, these are weak ferromagnetic insulators (canted antiferromagnets)
with magnetic transitions at and 120 K, respectively. At
higher temperatures, the phase is -type
antiferromagnetic between 230 K and 360 K. Low temperature magnetic
properties of this system for can be described in terms of a
mixture of Co ions in the low-spin state and Co ions in the
intermediate-spin state and a possible spin transition of Co to the
intermediate-spin state above . For , there appears to
be a combination of Co and Co ions, both in the high-spin state
with dominating antiferromagnetic interactions.Comment: RevTeX, 9 pages, 7 figures, to be published in Physical Review
Dynamic nuclear polarization enhanced solid-state NMR studies of surface modification of gamma-alumina
Dynamic nuclear polarization (DNP) gives large (>100-fold) signal enhancements in solid-state NMR spectra via the transfer of spin polarization from unpaired electrons from radicals implanted in the sample. This means that the detailed information about local molecular environment available for bulk samples from solid-state NMR spectroscopy can now be obtained for dilute species, such as sites on the surfaces of catalysts and catalyst supports. In this paper we describe a DNP-enhanced solid-state NMR study of the widely used catalyst gamma-alumina which is often modified at the surface by the incorporation of alkaline earth oxides in order to control the availability of catalytically active penta-coordinate surface Al sites. DNP-enhanced 27Al solid-state NMR allows surface sites in gamma-alumina to be observed and their 27Al NMR parameters measured. In addition changes in the availability of different surface sites can be detected after incorporation of BaO
Pengaruh Penyuluhan Bahaya Gunung Berapi Terhadap Kesiapsiagaan Siswa SMP Kristen Kakaskasen Kota Tomohon Menghadapi Bencana Gunung Berapi
ABSRACT: Volcano is one of the frequent disasters in Indonesia. Volcanic eruptions can cause many casualties and losses, Tomohon city has two active volcanoes that require coordinated disaster preparedness. Christian junior high school is the one of which always affected when the volcano erupted because just 3 miles from mount lokon, mount Lokon whereas the impact area within 5 miles. Purpose to analyze Effect Of Volcano Hazards Counseling To Students Preparedness Of Christian Junior High School Kakaskasen Tomohon City To Be Up Against Volcano Disaster. Samples in this research were 60 respondents using probability sampling techniques. Design of the research is one group pre test-post test and data collected from respondents using questionnaire. Research result obtained P value 0,00 with t value is 23,78 and t table 2,002. Conclusion shows there is Effect Of Volcano Hazards Counseling To Students Preparedness Of Christian Junior High School Kakaskasen Tomohon City To Be Up Against Volcano Disaster. Suggestion for further research are expected to further investigate the other factors that can increase preparedness
Ion exchange and binding in selenium remediation materials using DNP-enhanced solid-state NMR spectroscopy
Selenate-loaded selenium water remediation materials based on polymer fibres have been investigated by dynamic nuclear polarization (DNP) enhanced solid-state NMR. For carbon-13 a significant reduction in experiment time is obtained with DNP even when compared with conventional carbon-13 NMR spectra recorded using larger samples. For the selenium remediation materials studied here this reduction allows efficient acquisition of {1H}-77Se heteronuclear correlation spectra which give information about the nature of the binding of the remediated selenate ions with the grafted side chains which provide the required ion exchange functionality
Electrochemical synthesis of polyaniline/metal-based anodes and their use in microbial fuel cell
A limited number of metals may be suitable as bioanode material: noble metals, such as gold and platinum, could be the optimum choice being electrochemically inert in the operational potential window of the bioelectrochemical system. However, high costs limit their wide scale application. Even though its antimicrobial nature, copper is being considered as a promising alternative anode material, due to its high conductivity, that allows minimising the electrode material costs. Literature research indicated that high-performing electrochemically active biofilms may be grown on this metal. In the present work, gold and copper substrates have been coated by a conductive polymer (PANI), using a layer – by – layer procedure: surface grafting by reduction of 4-nitrobenzendiazonium salt was followed by reduction of nitro- to amino-groups; PANI was electrodeposited on this under-layer. The synthesized anodes were tested as working electrodes (WE) in a microbial fuel cell fed with anaerobic sludge and acetate; to assess the growth of the biofilm on the WE surface, the trend of the bioelectrocatalytic current of acetate oxidation was monitored over time. Cyclic voltammetries reveal the presence of typical redox couples related to the presence of electroactive microorganisms on the electrode surface. Preliminary data show bioelectrochemical activity on polyaniline-coated metal surfaces
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