Magnetic Properties and Metastable States in Spin-Crossover Transition of Co-Fe Prussian Blue Analogues

The combination of spin transitions and magnetic ordering provides an interesting structure of phase transitions in Prussian blue analogues (PBAs). To understand the structure of stable and metastable states of Co-Fe PBA, it is necessary to clarify free energy as a function of magnetization and the fraction of the high-temperature component. Including the magnetic interaction between high-temperature states, we study the magnetic phase transition of Co-Fe PBA in addition to spin transitions. Here, we take into account the degeneracy changes due to charge transfer between Co and Fe atoms accompanying the spin transition. In this study, the charge transfer between Co and Fe atoms is explicitly taken into account and also the ferrimagnetic structure of Co-Fe PBAs is expressed in the proper way. First, we found systematic changes in the structures of stable and metastable states as functions of system parameters using mean field theory. In particular, the existence of a metastable magnetic-ordered high-temperature state is confirmed at temperatures lower than that of the hysteresis region of spin transitions. Second, we found that the magnetic interaction causes complex ordering processes of a spin transition and a magnetic phase transition. The effect of a magnetic field on the phase structure is also investigated and we found metamagnetic magnetization processes. Finally, the dynamical properties of this metastable state are studied by Monte Carlo method.Comment: 17 pages, 11 figures, to be published in J. Phys. Soc. Japan; Fig. 1 replace

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

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

Realization of the mean-field universality class in spin-crossover materials

In spin-crossover materials, the volume of a molecule changes depending on whether it is in the high-spin (HS) or low-spin (LS) state. This change causes distortion of the lattice. Elastic interactions among these distortions play an important role for the cooperative properties of spin-transition phenomena. We find that the critical behavior caused by this elastic interaction belongs to the mean-field universality class, in which the critical exponents for the spontaneous magnetization and the susceptibility are $\beta = 1/2$ and $\gamma = 1$, respectively. Furthermore, the spin-spin correlation function is a constant at long distances, and it does not show an exponential decay in contrast to short-range models. The value of the correlation function at long distances shows different size-dependences: $O(1/N)$, $O(1/\sqrt{N})$, and constant for temperatures above, at, and below the critical temperature, respectively. The model does not exhibit clusters, even near the critical point. We also found that cluster growth is suppressed in the present model and that there is no critical opalescence in the coexistence region. During the relaxation process from a metastable state at the end of a hysteresis loop, nucleation phenomena are not observed, and spatially uniform configurations are maintained during the change of the fraction of HS and LS. These characteristics of the mean-field model are expected to be found not only in spin-crossover materials, but also generally in systems where elastic distortion mediates the interaction among local states.Comment: 13 pages, 16 figure

Detection of pathological myopia by PAMELA with texture-based features through an SVM approach

10.1260/2040-2295.1.1.1Journal of Healthcare Engineering111-1

Minyak Atsiri Jahe Gajah Sebagai Pestisida Nabati Bagi Kutu Kebul Menggunakan Metode Destilasi Uap

Komoditas pertanian menjadi sumber ekonomi yang menjanjikan bagi petani adalah tanaman cabai, tanaman cabai juga sangat dibutuhakan bagi kebutuhan baik rumah tangga sebagai penambah cita rasa bagi makanan yang dikonsumsi, namun seringkali komoditas ini terancam gagal panen diakibatkan terserang hama. Hama yang sering muncul sebagai hewan penggangu (Hemiptera: Aleyrodidae). Hama kutu kebul ini dapat menginfeksi tanaman cabai sehingga terjangkit penyakit nekrosis atau pengeringan batang yang relatif cepat dikarenakan kekurangan air, daun lebih cepat menguning, luas daun mengecil karena kekurangan nutrisi. Hama kutu kebul dapat dimusnahkan dengan mengunakan pestisida nabati atau organik. Pestisida nabati atau organik yang dapat digunakan untuk mengatasi hama kutu kebul adalah ekstak minyak atsiri dari tanaman Jahe. Tanaman temu-temuan mengandung senyawa metabolit sekunder yang dapat digunakan sebagai antioksidan, penurunan aktifitas lokomotor (anti kejang), anti tumor, anti bakteri, dan salah satu fungsi yang menunjang penelitian ini adalah dapat digunkan sebagai pestisida nabati bagi hama tanaman. Senyawa yang dapat dijadikan sebagai pestisida nabati adalah senyawa zingiberane yang merupakan komponen utama dan sebagai penentu kualitas minyak atsiri (Rt 29,375), Limonen (Rt 11,680), dan 1,8-Cineole (Rt 14,832). Pengaruh ketiga senyawa tersebut adalah sebagai agen pembesami hama kutu kebul dengan cara merusak sistem reproduksi sehingga terganggu proses reproduksi, merusak sistem pencernaan dan merusak sistem pertahanan diri hama kutu kebul.Komoditas pertanian menjadi sumber ekonomi yang menjanjikan bagi petani adalah tanaman cabai, tanaman cabai juga sangat dibutuhakan bagi kebutuhan baik rumah tangga sebagai penambah cita rasa bagi makanan yang dikonsumsi, namun seringkali komoditas ini terancam gagal panen diakibatkan terserang hama. Hama yang sering muncul sebagai hewan penggangu (Hemiptera: Aleyrodidae). Hama kutu kebul ini dapat menginfeksi tanaman cabai sehingga terjangkit penyakit nekrosis atau pengeringan batang yang relatif cepat dikarenakan kekurangan air, daun lebih cepat menguning, luas daun mengecil karena kekurangan nutrisi. Hama kutu kebul dapat dimusnahkan dengan mengunakan pestisida nabati atau organik. Pestisida nabati atau organik yang dapat digunakan untuk mengatasi hama kutu kebul adalah ekstak minyak atsiri dari tanaman Jahe. Tanaman temu-temuan mengandung senyawa metabolit sekunder yang dapat digunakan sebagai antioksidan, penurunan aktifitas lokomotor (anti kejang), anti tumor, anti bakteri, dan salah satu fungsi yang menunjang penelitian ini adalah dapat digunkan sebagai pestisida nabati bagi hama tanaman. Senyawa yang dapat dijadikan sebagai pestisida nabati adalah senyawa zingiberane yang merupakan komponen utama dan sebagai penentu kualitas minyak atsiri (Rt 29,375), Limonen (Rt 11,680), dan 1,8-Cineole (Rt 14,832). Pengaruh ketiga senyawa tersebut adalah sebagai agen pembesami hama kutu kebul dengan cara merusak sistem reproduksi sehingga terganggu proses reproduksi, merusak sistem pencernaan dan merusak sistem pertahanan diri hama kutu kebul

Early effects of oral administration of lafutidine with mosapride compared with lafutidine alone on intragastric pH values

<p>Abstract</p> <p>Background</p> <p>The ideal medication for treatment of acid related diseases should have a rapid onset of action to promote hemostasis and resolution of symptoms. The aim of our study was to investigate the inhibitory effects on gastric acid secretion after a single oral administrations of lafutidine, is a newly synthesized H2-receptor antagonist, with mosapride 5 mg or lafutidine alone.</p> <p>Methods</p> <p>Ten <it>Helicobacter pylori </it>negative male subjects participated in this randomized, two-way crossover study. Intragastric pH was monitored continuously for 4 hours after a single oral administration of lafutidine 10 mg or lafutidine 10 mg with mosapride 5 mg (the lafutidine being administrated one hour after the mosapride). Each administration was separated by a 7-day washout period.</p> <p>Results</p> <p>The average pH during the 4-hour period after administration of lafutidine 10 mg with mosapride 5 mg was higher than after lafutidine 10 mg alone (median: 5.25 versus 4.58, respectively; <it>p </it>= 0.0318). During the 3–4 hour study period, lafutidine 10 mg with mosapride 5 mg provided a higher pH, compared to lafutidine 10 mg alone (median: 7.28 versus 6.42; <it>p </it>= 0.0208).</p> <p>Conclusion</p> <p>In <it>H. pylori </it>negative healthy male subjects, an oral dose of lafutidine 10 mg with mosapride 5 mg more rapidly increased intragastric pH than lafutidine 10 mg alone.</p

Sigmoidally hydrochromic molecular porous crystal with rotatable dendrons

Vapochromic behaviour of porous crystals is beneficial for facile and rapid detection of gaseous molecules without electricity. Toward this end, tailored molecular designs have been established for metal–organic, covalent-bonded and hydrogen-bonded frameworks. Here, we explore the hydrochromic chemistry of a van der Waals (VDW) porous crystal. The VDW porous crystal VPC-1 is formed from a novel aromatic dendrimer having a dibenzophenazine core and multibranched carbazole dendrons. Although the constituent molecules are connected via VDW forces, VPC-1 maintains its structural integrity even after desolvation. VPC-1 exhibits reversible colour changes upon uptake/release of water molecules due to the charge transfer character of the constituent dendrimer. Detailed structural analyses reveal that the outermost carbazole units alone are mobile in the crystal and twist simultaneously in response to water vapour. Thermodynamic analysis suggests that the sigmoidal water sorption is induced by the affinity alternation of the pore surface from hydrophobic to hydrophilic.journal articl

Low-temperature gas from marine shales: wet gas to dry gas over experimental time

Marine shales exhibit unusual behavior at low temperatures under anoxic gas flow. They generate catalytic gas 300° below thermal cracking temperatures, discontinuously in aperiodic episodes, and lose these properties on exposure to trace amounts of oxygen. Here we report a surprising reversal in hydrocarbon generation. Heavy hydrocarbons are formed before light hydrocarbons resulting in wet gas at the onset of generation grading to dryer gas over time. The effect is moderate under gas flow and substantial in closed reactions. In sequential closed reactions at 100°C, gas from a Cretaceous Mowry shale progresses from predominately heavy hydrocarbons (66% C5, 2% C1) to predominantly light hydrocarbons (56% C1, 8% C5), the opposite of that expected from desorption of preexisting hydrocarbons. Differences in catalyst substrate composition explain these dynamics. Gas flow should carry heavier hydrocarbons to catalytic sites, in contrast to static conditions where catalytic sites are limited to in-place hydrocarbons. In-place hydrocarbons and their products should become lighter with conversion thus generating lighter hydrocarbon over time, consistent with our experimental results