390 research outputs found
Structure of Metastable States in Phase Transitions with High-Spin Low-Spin Degree of Freedom
Difference of degeneracy of the low-spin (LS) and high-spin (HS) states
causes interesting entropy effects on spin-crossover phase transitions and
charge transfer phase transitions in materials composed of the spin-crossover
atoms. Mechanisms of the spin-crossover (SC) phase transitions have been
studied by using Wajnflasz model, where the degeneracy of the spin states (HS
or LS) is taken into account and cooperative natures of the spin-crossover
phase transitions have been well described. Recently, a charge transfer (CT)
phase transition due to electron hopping between LS and HS sites has been
studied by using a generalized Wajnflasz model. In the both systems of SC and
CT, the systems have a high temperature structure (HT) and a low temperature
structure (LT), and the change between them can be a smooth crossover or a
discontinuous first order phase transition depending on the parameters of the
systems. Although apparently the standard SC system and the CT system are very
different, it is shown that both models are equivalent under a certain
transformation of variables. In both systems, the structure of metastable state
at low temperatures is a matter of interest. We study temperature dependence of
fraction of HT systematically in a unified model, and find several structures
of equilibrium and metastable states of the model as functions of system
parameters. In particular, we find a reentrant type metastable branch of HT in
a low temperature region, which would play an important role to study the
photo-irradiated processes of related materials.Comment: 19 pages, 11 figure
Status of ECR ion sources at JAERI
At the Takasaki site of Japan Atomic Energy Research Institute, four ECR ion sources were purchased or developed so far. This paper will report their performance, modification and status. The outlines for each source are as follows; 1. OCTOPUS purchased from IBA s.a. has been in use with a cyclotron since 1990. The gas feed system was modified to change gas species within 10 minutes to avoid impurity ions in the cocktail beam acceleration technique of the cyclotron. 2. ECR-18 with 18-GHz microwave has a solenoid coil between a pair of mirror coils to change mirror ratio in a wide range. A bump between mirror peaks in the original axial field distribution was removed by halving the solenoid length. The performance in generating high charge state ions was significantly improved as a result. 3. HYPERNANOGAN was purchased from PANTECHNIK s.a. and installed in the cyclotron system this year. Test operation was successfully made with generation of Ar, Pb and Ta ions. 4. MINI ECR is a full permanent magnet source with 10 GHz microwave. As a result of modifications for vacuum and the application of a bias probe, 40 microA of Ar4+ beam was obtained, for example. Using this source, a new technique was developed to vaporize very refractory materials into plasma by fluorinating them with SF6 plasma. The source is in use for a 400 kV ion implantor since last year
Bulk and surface switching in Mn-Fe-based Prussian Blue Analogues
Many Prussian Blue Analogues are known to show a thermally induced phase
transition close to room temperature and a reversible, photo-induced phase
transition at low temperatures. This work reports on magnetic measurements,
X-ray photoemission and Raman spectroscopy on a particular class of these
molecular heterobimetallic systems, specifically on
Rb0.81Mn[Fe(CN)6]0.95_1.24H2O, Rb0.97Mn[Fe(CN)6]0.98_1.03H2O and
Rb0.70Cu0.22Mn0.78[Fe(CN)6]0.86_2.05H2O, to investigate these transition
phenomena both in the bulk of the material and at the sample surface. Results
indicate a high degree of charge transfer in the bulk, while a substantially
reduced conversion is found at the sample surface, even in case of a near
perfect (Rb:Mn:Fe=1:1:1) stoichiometry. Thus, the intrinsic incompleteness of
the charge transfer transition in these materials is found to be primarily due
to surface reconstruction. Substitution of a large fraction of charge transfer
active Mn ions by charge transfer inactive Cu ions leads to a proportional
conversion reduction with respect to the maximum conversion that is still
stoichiometrically possible and shows the charge transfer capability of metal
centers to be quite robust upon inclusion of a neighboring impurity.
Additionally, a 532 nm photo-induced metastable state, reminiscent of the high
temperature Fe(III)Mn(II) ground state, is found at temperatures 50-100 K. The
efficiency of photo-excitation to the metastable state is found to be maximized
around 90 K. The photo-induced state is observed to relax to the low
temperature Fe(II)Mn(III) ground state at a temperature of approximately 123 K.Comment: 12 pages, 8 figure
Electrospinning of poly (ether sulfone) and evaluation of the filtration efficiency
To produce high heat-resistant air filter, filtration properties of poly (ether sulfone) (PES) made by various electrospinning conditions were evaluated. The PES webs of 0.4-1.1 mu m average diameter fiber were obtained from 35-40 wt% PES / N,N- Dimethylacetamide (DMAc) solution. The diameter profile of electrospun PES web was clearly affected by PES concentration of the spinning dope and feeding rate of the dope, while the take-up speed effects little. The needle-collector distance affects the diameter profile for higher feeding rate conditions. The pore size of these webs was 1.3-5.6 mu m, which was decided not only average fiber diameter but also fiber diameter variation. Both filtration efficiency and pressure loss were dropped steeply at about 3.0 mu m of pore size. For the web having a pore size of 3.2 mu m, the pressure loss decrease to 215 Pa, while the filtration efficiency for 0.3 mu m particle kept 99.9998 %, which satisfied the HEPA requirement.ArticleSen'i Gakakishi. 63(12): 307-312 (2007)journal articl
Novel mechanism of photoinduced reversible phase transitions in molecule-based magnets
A novel microscopic mechanism of bi-directional structural changes is
proposed for the photo-induced magnetic phase transition in Co-Fe Prussian blue
analogues on the basis of ab initio quantum chemical cluster calculations. It
is shown that the local potential energies of various spin states of Co are
sensitive to the number of nearest neighbor Fe vacancies. As a result, the
forward and backward structural changes are most readily initiated by
excitation of different local regions by different photons. This mechanism
suggests an effective strategy to realize photoinduced reversible phase
transitions in a general system consisting of two local components.Comment: 4 pages, LaTex, 3 figures, to appear in Phys. Rev. Let
Online wide-angle X-ray diffraction/small-angle X-ray scattering measurements for the CO2-laser-heated drawing of poly(ethylene terephthalate) fiber
This is a preprint of an article published in JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS. Vol 43(9): 1090-1099 (2005).ArticleJOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS. 43(9): 1090-1099 (2005)journal articl
Electronic structure study by means of X-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet
The electronic structure of the single molecule magnet system
M[Fe(L)2]3*4CHCl3 (M=Fe,Cr; L=CH3N(CH2CH2O)2) has been studied using X-ray
photoelectron spectroscopy, X-ray absorption spectroscopy, soft X-ray emission
spectroscopy, and density functional calculations. There is good agreement
between theoretical calculations and experimental data. The valence band mainly
consists of three bands between 2 eV and 30 eV. Both theory and experiments
show that the top of the valence band is dominated by the hybridization between
Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe
in the molecule is most likely in the 2+ charge state. Its neighboring atoms
(O,N) exhibit a magnetic polarisation yielding effective spin S=5/2 per iron
atom, giving a high spin state molecule with a total S=5 effective spin for the
case of M = Fe.Comment: Fig.2 replaced as it will appear in J. Chem. Phy
Fiber structure development in PS/PET sea-island conjugated fiber during continuous laser drawing
The effect of draw ratio, molecular weight, and sea-island conjugated spinning with a polystyrene component on the fiber structure development of PET during laser drawing was analyzed by in-situ measurements with a 0.1 ms time resolution using an ultra-high luminance X-ray beam generated from a synchrotron equipped with an undulator. The fiber temperature increased from 120 °C to 160–220 °C during the structure development process. By drawing the higher molecular weight PET to a higher draw ratio, a larger amount of fibrillar smectic mesophase formed just after the onset of necking, and a more highly oriented crystal formed after the extinction of the smectic mesophase. Accordingly, fibers with higher strength and higher thermal shrinkage stress were obtained. On the other hand, by conjugated spinning with a PS component, the fiber temperature increased along with an increase in the drawing stress, but the stress applied to the PET component should have decreased. The amount of smectic mesophase formed by the conjugated-spinning process was drastically decreased, and no crystallization induction time was observed, unlike the other cases. Crystallization, particularly the growth of a lamellar crystal, was also promoted. Moreover, a higher Young's modulus, a higher yield stress, and a higher shrinkage stress were observed for the conjugated-spun and drawn fibers. Therefore, the fibrillar smectic mesophase seems to block the formation of the lamellar crystal. Furthermore, the resultant fibrillar structure tends to result in a higher strength, but a relatively lower modulus and yield strength of the fiber.ArticlePOLYMER. 79:37-46 (2015)journal articl
Effect of melt spinning conditions on the fiber structure development of polyethylene terephthalate
The effects of spinning conditions on fiber properties are not well explained by the fiber structures because the birefringence, crystallinity, and SAXS patterns are often similar. In this study, the effects on the fiber structure development of polyethylene terephthalate after necking was analyzed by simultaneous WAXD/SAXS measurements. An X-shaped SAXS pattern was observed for all fibers drawn at the minimum draw ratio. In contrast, by drawing under a drawing stress of 100 MPa, the strong diffraction of the smectic phase and an obviously larger long period less than 1 ms after necking were observed for fibers spun at 500-1500 m/min, while almost no smectic phase was observed for fibers spun at 2000 m/min. A higher crystallization rate and clear draw ratio dependence of crystallization rate were also observed for the fiber spun at 2000 m/min. The clear differences in structure development can explain their differences in tensile strength and thermal shrinkage. (C) 2017 Elsevier Ltd. All rights reserved.ArticlePOLYMER.116:367-377(2017)journal articl
Effect of draw ratio on fiber structure development of polyethylene terephthalate
Fiber properties are decided by its structure, and the structure are mainly formed in the fiber drawing process. In this study, the effects of the draw ratio on the fiber structure development of polyethylene terephthalate after continuous neck-drawing were investigated using simultaneous WAXD/SAXS measurements. Low-oriented amorphous as-spun fibers were drawn to a draw ratio of 3.0-4.5, at which the fiber can be stably neck drawn. WAXD and SAXS images were obtained up to 2.0 ms when the structure was mainly developed. The smectic (0010) diffraction intensity and long period increased with increasing draw ratio up to 4.2, and a larger (0010) diffraction d-spacing was observed at a draw ratio of 4.5. The results suggest that more fibrillar structures were formed with increasing draw ratio up to 4.2, and more constrained molecular bundles were formed at a draw ratio of 4.5. A larger amount of constrained fibrillar structures can bear a greater tensile force in tensile tests, therefore the drawn fibers have higher tensile strengths. (C) 2017 Elsevier Ltd. All rights reserved.ArticlePOLYMER.116:357-366(2017)journal articl
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