A Field-Induced Re-Entrant Novel Phase and A Ferroelectric-Magnetic Order Coupling in HoMnO3

A re-entrant novel phase has been observed in the hexagonal ferroelectric HoMnO3 in the presence of magnetic fields, in the temperature ranges defined by the plateau of the dielectric constant anomaly. The dielectric plateau evolves with fields from a narrow sharp dielectric peak at the Mn-spin rotation transition at 32.8 K in zero magnetic field. Such a field-induced dielectric plateau anomaly appears both in the temperature sweep at a constant field and in the field sweep at a constant temperature without detectable hysteresis. This is attributed to the indirect coupling between the ferroelectric and antiferromagnetic orders, arising from an antiferromagnetic domain wall effect, where the magnetic order parameter of the Mn subsystem has to change sign across the ferroelectric domain wall in the compound, that influences the ferroelectric domains via a local magnetostrictive effect

Phonons and Magnetic Excitations in Mott-Insulator LaTiO3_3

The polarized Raman spectra of stoichiometric LaTiO$_3$ (T$_N = 150$ K) were measured between 6 and 300 K. In contrast to earlier report on half-metallic LaTiO$_{3.02}$, neither strong background scattering, nor Fano shape of the Raman lines was observed. The high frequency phonon line at 655 cm$^{-1}$ exhibits anomalous softening below T$_N$: a signature for structural rearrangement. The assignment of the Raman lines was done by comparison to the calculations of lattice dynamics and the nature of structural changes upon magnetic ordering are discussed. The broad Raman band, which appears in the antiferromagnetic phase, is assigned to two-magnon scattering. The estimated superexchange constant $J = 15.4\pm0.5$ meV is in excellent agreement with the result of neutron scattering studies.Comment: 4 pages, 5 figure

Синтез та циклофункціоналізація (1,3-тіазолідин-2-іліден)кетонів

Aim. To develop a new approach to the design of (1,3-thiazolidin-2-ylidene)ketones and expansion of their synthetic potential as convenient building blocks in the reactions of [3+2]- and [3+3]-cyclization.Results and discussion. Еlectrophilic intramolecular cyclization (EIC) of N-allythioamides of β-ketoacids using phosphoric acid or iodine is a convenient synthetic method to obtain new (5-methyl- and 5-iodomethyl-1,3-thiazolidine-2-ylidene)ketones. Cyclization of ketones with maleic anhydride leads to derivatives of 2,3-dihydropyrrolo[2,1-b][1,3]thiazole. [3+3]-Cyclocondensation with methyl propiolate and dimethyl acetylenedicarboxylate results in formation of the functionalized [1,3]thiazolo[3,2-a]pyridine derivatives.Experimental part. (5-Methyl- and 5-iodomethyl-1,3-thiazolidin-2-ylidene)ketones were synthesized from N-allylthioamides using phosphoric acid or iodine in chloroform. (1,3-Thiazolidin-2-ylidene)ketones react with maleic anhydride, methyl acetylenecarboxylate or dimethyl acetylenedicarboxylate resulting in a 2,3-dihydropyrrolo[2,1-b][1,3]thiazole-5(6H)-one and 2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyridine derivatives.Conclusions. A convenient method of [5-methyl- and 5-iodomethyl-1,3-thiazolidin-2-ylidene]ketones preparation based on the EIC of N-allylthioamides of β-ketoacids has been developed using phosphoric acid and iodine. The (1,3-thiazolidin-2-ylidene)ketones synthesized can be useful in cyclization reactions leading to functional pyrrolo[2,1-b][1,3]thiazole and [1,3]thiazolo[3,2-a]pyridine derivatives.Цель работы – разработка нового подхода к конструированию (1,3-тиазолидин-2-илиден)кетонов и расширение их синтетического потенциала как удобных структурных блоков в реакциях [3+2]- и [3+3]-циклизации.Результаты и их обсуждение. Показано, что электрофильная внутримолекулярная циклизация (ЭВЦ) N-аллилтиоамидов β-кетокислот, инициированная фосфорной кислотой или йодом, является удобным методом синтеза новых (5-метил- и 5-йодметил-1,3-тиазолидин-2-илиден)кетонов. Их циклизацией с малеиновым ангидридом получены новые производные 2,3-дигидропирроло[2,1-b][1,3]тиазола, а с метиловыми эфирами ацетиленмоно- и дикарбоновой кислот – функциональные производные [1,3]тиазоло[3,2-a]пиридина.Экспериментальная часть. Действием на N-аллилтиоамиды фосфорной кислоты или йода в хлороформе синтезированы (5-метил- и 5-йодметил-1,3-тиазолидин-2-илиден)кетоны, которые реагируют с малеиновым ангидридом, метилацетиленкарбоксилатом или диметилацетилендикарбоксилатом с образованием производных 2,3-дигидропирроло[2,1-b][1,3]тиазол-5(6H)-она и 2,3-дигидро-5H-[1,3]тиазоло[3,2-a]пиридина. Выводы. Разработан удобный метод получения [5-метил- и 5-йодметил-1,3-тиазолидин-2-илиден]кетонов, основанный на ЭВЦ N-аллилтиоамидов β-кетокислот под действием фосфорной кислоты и йода. Синтезированные (1,3-тиазолидин-2-илиден)кетоны могут быть использованы в реакциях циклизации, которые приводят к функциональным производных пирроло[2,1-b][1,3]тиазола и [1,3]тиазоло[3,2-a]пиридина.Мета роботи – розробка нового підходу до конструювання (1,3-тіазолідин-2-іліден)кетонів та розширення їх синтетичного потенціалу як зручних структурних блоків у реакціях [3+2]- та [3+3]-циклізації.Результати та їх обговорення. Показано, що електрофільна внутрішньомолекулярна циклізація (ЕВЦ) N-алілтіоамідів β-кетокислот ініційована фосфорною кислотою або йодом є зручним методом синтезу нових (5-метил- та 5-йодометил-1,3-тіазолідин-2-іліден)кетонів. Їх циклізацією із малеїновим ангідридом отримані похідні 2,3-дигідропіроло[2,1-b][1,3]тіазолу. Взаємодія з метиловими естерами ацетиленмоно- та дикарбонової кислот за схемою [3+3]-циклоконденсації приводить до анелювання піридинового ядра та одержання функціональних похідних [1,3]тіазоло[3,2-a]піридину. Експериментальна частина. Дією на N-алілтіоаміди фосфорної кислоти або йоду в хлороформі синтезовані (5-метил- та 5-йодометил-1,3-тіазолідин-2-іліден)кетони, які реагують із малеїновим ангідридом, метилацетиленкарбоксилатом або диметилацетилендикарбоксилатом з утворенням похідних 2,3-дигідропіроло[2,1-b][1,3]тіазол-5(6H)-ону та 2,3-дигідро-5H-[1,3]тіазоло[3,2-a]піридину. Висновки. Розроблено зручний метод одержання [5-метил- та 5-йодометил-1,3-тіазолідин-2-іліден]кетонів, що ґрунтується на ЕВЦ N-алілтіоамідів β-кетокислот під дією фосфорної кислоти та йоду. Синтезовані (1,3-тіазолідин-2-іліден)кетони можуть бути використані в реакціях циклізації, які приводять до функціональних похідних піроло[2,1-b][1,3]тіазолу та [1,3]тіазоло[3,2-a]піридину

Lattice dynamical probe of charge order and antipolar bilayer stacking in LuFe2O4

We investigated the infrared response of LuFe2O4 through the series of charge, magnetic, and structural transitions. All vibrational modes couple strongly to the charge order, whereas the LuO zone-folding modes are also sensitive to magnetic order and structural distortion. The dramatic splitting of the LuO2 layer mode is attributed to charge-rich/poor proximity effects and its temperature dependence reveals the antipolar nature of the W layer pattern

Cracking cryptic species: external characters to distinguish two recently recognized banded newt species (Ommatotriton ophryticus and O. nesterovi)

Animal science

The Near East as a cradle of biodiversity: a phylogeography of banded newts (genus Ommatotriton) reveals extensive inter- and intraspecific genetic differentiation

The banded newt (genus Ommatotriton) is widely distributed in the Near East (Anatolia, Caucasus and the Levant) - an understudied region from the perspective of phylogeography. The genus is polytypic, but the number of species included and the phylogenetic relationships between them are not settled. We sequenced two mitochondrial and two nuclear DNA markers throughout the range of Ommatotriton. For mtDNA we constructed phylogenetic trees, estimated divergence times using fossil calibration, and investigated changes in effective population size with Bayesian skyline plots and mismatch analyses. For nuDNA we constructed phylogenetic trees and haplotype networks. Species trees were constructed for all markers and nuDNA only. Species distribution models were projected on current and Last Glacial Maximum climate layers. We confirm the presence of three Ommatotriton species: O. nesterovi, O. ophryticus and O. vittatus. These species are genetically distinct and their most recent common ancestor was dated at ∼25Ma (Oligocene). No evidence of recent gene flow between species was found. The species show deep intraspecific genetic divergence, represented by geographically structured clades, with crown nodes of species dated ∼8-13Ma (Miocene to Early Quaternary); evidence of long-term in situ evolution and survival in multiple glacial refugia. While a species tree based on nuDNA suggested a sister species relationship between O. vittatus and O. ophryticus, when mtDNA was included, phylogenetic relationships were unresolved, and we refrain from accepting a particular phylogenetic hypothesis at this stage. While species distribution models suggest reduced and fragmented ranges during the Last Glacial Maximum, we found no evidence for strong population bottlenecks. We discuss our results in the light of other phylogeographic studies from the Near East. Our study underlines the important role of the Near East in generating and sustaining biodiversity

Interaction in the Systems with Tl(І), Hg(ІІ), Pb(ІІ), Si(IV).

Методами РФА та ДТА досліджено фазові рівноваги у квазіпотрійних системах Tl2Х–{Hg, Pb}X–SiX2 (X – S, Se). Установлено існування нових тетрарних еквімолярних сполук. Методом порошку розшифровано кристалічну структуру Tl2HgSiSe4 (ПГ I-42m) та Tl2PbSiS4 (ПГ P21/a). The phase equilibria of the quasi-ternary systems Tl 2Х–{Hg, Pb}X–SiX2 (X – S, Se) were investigated by X-ray phase analyse and DTA. New quaternary phases with equil ratio components were found in these systems. Crystal structures of Tl2HgSiSe4 (S. G. I-42m) and Tl2PbSiS4 (S. G. P21/a) were determinated by X-ray powder diffraction

Kinetic Inductance and Penetration Depth of Thin Superconducting Films Measured by THz Pulse Spectroscopy

We measure the transmission of THz pulses through thin films of YBCO at temperatures between 10K and 300K. The pulses possess a useable bandwidth extending from 0.1 -- 1.5 THz (3.3 cm^-1 -- 50 cm^-1). Below T_c we observe pulse reshaping caused by the kinetic inductance of the superconducting charge carriers. From transmission data, we extract values of the London penetration depth as a function of temperature, and find that it agrees well with a functional form (\lambda(0)/\lambda(T))^2 = 1 - (T/T_c)^{\alpha}, where \lambda(0) = 148 nm, and \alpha = 2. *****Figures available upon request*****Comment: 7 Pages, LaTe

Hole concentration and phonon renormalization in Ca-doped YBa_2Cu_3O_y (6.76 < y < 7.00)

In order to access the overdoped regime of the YBa_2Cu_3O_y phase diagram, 2% Ca is substituted for Y in YBa_2Cu_3O_y (y = 7.00,6.93,6.88,6.76). Raman scattering studies have been carried out on these four single crystals. Measurements of the superconductivity-induced renormalization in frequency (Delta \omega) and linewidth (\Delta 2\gamma) of the 340 cm^{-1} B_{1g} phonon demonstrate that the magnitude of the renormalization is directly related to the hole concentration (p), and not simply the oxygen content. The changes in \Delta \omega with p imply that the superconducting gap (\Delta_{max}) decreases monotonically with increasing hole concentration in the overdoped regime, and \Delta \omega falls to zero in the underdoped regime. The linewidth renormalization \Delta 2\gamma is negative in the underdoped regime, crossing over at optimal doping to a positive value in the overdoped state.Comment: 18 pages; 5 figures; submitted to Phys. Rev. B Oct. 24, 2002 (BX8292