Magnetic structure and spin dynamics of quasi-one-dimensional spin-chain antiferromagnet BaCo2V2O8

We report a neutron diffraction and muon spin relaxation muSR study of static and dynamical magnetic properties of BaCo2V2O8, a quasi-one-dimensional spin-chain system. A proposed model for the antiferromagnetic structure includes: a propagation vector k_AF = (0, 0, 1), independent of external magnetic fields for fields below a critical value H_c(T). The ordered moments, of 2.18 \mu_B per Co ion, are aligned along the crystallographic c-axis. Within the screw chains, along the c axis, the moments are arranged antiferromagnetically. In the basal planes the spins are arranged ferromagnetically (forming zig-zags paths) along one of the axis and antiferromagnetically along the other. The temperature dependence of the sub-lattice magnetization is consistent with the expectations of the 3D Ising model. A similar behavior is observed for the internal static fields at different muon stopping sites. Muon time spectra measured at weak longitudinal fields and temperatures much higher than T_N can be well described using a single muon site with an exponential muon spin relaxation that gradually changes into an stretched exponential on approaching T_N. The temperature-induced changes of the relaxation suggest that the Co fluctuations dramatically slow down and the system becomes less homogeneous as it approaches the antiferromagnetic state.Comment: 7 pages, 9 figure

キソク コウシ マンガン サンカブツ ノ ソウブンリ オヨビ スピン デンカ キドウ セイレツ ノ カクジキ キョウメイ オヨビ μSR ニヨル ケンキュウ

Nuclear magnetic resonance and μSR measurements have been made to study the phase separation, spin, charge and orbital ordering in A-site ordered manganese oxides. In the antiferromagnetic YBaMn2O6, the magnetic moments of Mn4+ and Mn3+ ions are estimated to be 3.0 μB and 3.6 μB from the observed NMR spectra at 295 MHz and 320 MHz, respectively, which agree with the expected spins S=3/2 and S=2 of Mn4+ and Mn3+ ions, respectively. In the μSR experimental results in YBaMn2O6, the intensity of positrons shows the typical time decay of a single exponential function in the paramagnetic phase and the oscillation in the antiferromagnetic phase, which indicates that the antiferromagnetic phase in YBaMn2O6 is similar to the ordinary antiferromagnetic phase. 55Mn NMR spectra in LaBaMn2O6 at low temperature consists of the signals from both ferromagnetic and antiferromagnetic phases, which gives the evidence for the coexistence of the ferromagnetic and antiferromagnetic phases in the ground state in LaBaMn2O6 from the microscopic point of view. In the μSR experimental results in LaBaMn2O6, the intensity of positrons shows the typical time decay of a single exponential function in the paramagnetic phase but still shows no oscillation in the ferromagnetic phase, which indicates that the ferromagnetic phase in LaBaMn2O6 is very different from the ordinary ferromagnetic phase. On the contrary, in the coexisting antiferromagnetic phase in the ground state the intensity of positrons shows the typical time decay of oscillation due to the internal field, which indicates that the coexisting antiferromagnetic phase in LaBaMn2O6 is similar to the ordinary antiferromagnetic phase. These results may be concerned with the fact that the antiferromagnetic phase is created in the ferromagnetic phase

Carotenoid composition and carotenogenic gene expression during Ipomoea petal development

Japanese morning glory (Ipomoea nil) is a representative plant lacking a yellow-flowered cultivar, although a few wild Ipomoea species contain carotenoids in their petals such as Ipomoea sp. (yellow petals) and I. obscura (pale-yellow petals). In the present study, carotenoid composition and the expression patterns of carotenogenic genes during petal development were compared among I. nil, I. obscura, and Ipomoea sp. to identify the factors regulating carotenoid accumulation in Ipomoea plant petals. In the early stage, the carotenoid composition in petals of all the Ipomoea plants tested was the same as in the leaves mainly showing lutein, violaxanthin, and β-carotene (chloroplast-type carotenoids). However, in fully opened flowers, chloroplast-type carotenoids were entirely absent in I. nil, whereas they were present in trace amounts in the free form in I. obscura. At the late stage of petal development in Ipomoea sp., the majority of carotenoids were β-cryptoxanthin, zeaxanthin, and β-carotene (chromoplast-type carotenoids). In addition, most of them were present in the esterified form. Carotenogenic gene expression was notably lower in I. nil than in Ipomoea sp. In particular, β-ring hydroxylase (CHYB) was considerably suppressed in petals of both I. nil and I. obscura. The CHYB expression was found to be significantly high in the petals of Ipomoea sp. during the synthesis of chromoplast-type carotenoids. The expression levels of carotenoid cleavage genes (CCD1 and CCD4) were not correlated with the amount of carotenoids in petals. These results suggest that both I. obscura and I. nil lack the ability to synthesize chromoplast-type carotenoids because of the transcriptional down-regulation of carotenogenic genes. CHYB, an enzyme that catalyses the addition of a hydroxyl residue required for esterification, was found to be a key enzyme for the accumulation of chromoplast-type carotenoids in petals

Process intensification for post combustion CO₂ capture with chemical absorption: a critical review

The concentration of CO₂ in the atmosphere is increasing rapidly. CO₂ emissions may have an impact on global climate change. Effective CO₂ emission abatement strategies such as carbon capture and storage (CCS) are required to combat this trend. Compared with pre-combustion carbon capture and oxy-fuel carbon capture approaches, post-combustion CO₂ capture (PCC) using solvent process is one of the most mature carbon capture technologies. There are two main barriers for the PCC process using solvent to be commercially deployed: (a) high capital cost; (b) high thermal efficiency penalty due to solvent regeneration. Applying process intensification (PI) technology into PCC with solvent process has the potential to significantly reduce capital costs compared with conventional technology using packed columns. This paper intends to evaluate different PI technologies for their suitability in PCC process. The study shows that rotating packed bed (RPB) absorber/stripper has attracted much interest due to its high mass transfer capability. Currently experimental studies on CO₂ capture using RPB are based on standalone absorber or stripper. Therefore a schematic process flow diagram of intensified PCC process is proposed so as to motivate other researches for possible optimal design, operation and control. To intensify heat transfer in reboiler, spinning disc technology is recommended. To replace cross heat exchanger in conventional PCC (with packed column) process, printed circuit heat exchanger will be preferred. Solvent selection for conventional PCC process has been studied extensively. However, it needs more studies for solvent selection in intensified PCC process. The authors also predicted research challenges in intensified PCC process and potential new breakthrough from different aspects

Castleman Disease Presenting with Jaundice: A Case with the Multicentric Hyaline Vascular Variant

Castleman disease (CD) is a rare lymphoproliferative disorder of unknown etiology with different clinical manifestations. A previous healthy 50 year-old man was hospitalized for right upper quadrant (RUQ) abdominal pain. He had jaundice and a 1 cm-sized lymph node in the right supraclavicular area. Pancreas and biliary computed tomography (CT) showed masses at the right renal hilum and peripancreatic areas. Positron emission tomography (PET) showed widespread systemic lymphadenopathy. Excisional biopsy of the right supraclavicular node revealed a hyaline vascular variant of CD. Corticosteroid therapy was started and the extent of disease decreased. We here report a case of multicentric CD, the hyaline vascular variant, presenting with jaundice, diagnosed by excisional biopsy and successfully treated with corticosteroids

Observing Supermassive Black Holes across cosmic time: from phenomenology to physics

In the last decade, a combination of high sensitivity, high spatial resolution observations and of coordinated multi-wavelength surveys has revolutionized our view of extra-galactic black hole (BH) astrophysics. We now know that supermassive black holes reside in the nuclei of almost every galaxy, grow over cosmological times by accreting matter, interact and merge with each other, and in the process liberate enormous amounts of energy that influence dramatically the evolution of the surrounding gas and stars, providing a powerful self-regulatory mechanism for galaxy formation. The different energetic phenomena associated to growing black holes and Active Galactic Nuclei (AGN), their cosmological evolution and the observational techniques used to unveil them, are the subject of this chapter. In particular, I will focus my attention on the connection between the theory of high-energy astrophysical processes giving rise to the observed emission in AGN, the observable imprints they leave at different wavelengths, and the methods used to uncover them in a statistically robust way. I will show how such a combined effort of theorists and observers have led us to unveil most of the SMBH growth over a large fraction of the age of the Universe, but that nagging uncertainties remain, preventing us from fully understating the exact role of black holes in the complex process of galaxy and large-scale structure formation, assembly and evolution.Comment: 46 pages, 21 figures. This review article appears as a chapter in the book: "Astrophysical Black Holes", Haardt, F., Gorini, V., Moschella, U and Treves A. (Eds), 2015, Springer International Publishing AG, Cha