Real-time measurement of temporal waveforms of a terahertz pulse using a probe pulse with a tilted pulse front

We propose a novel method that uses a femtosecond pulse with a tilted pulse front as a probe pulse to perform real-time measurement of temporal waveforms of a terahertz pulse. This method can operate on a single shot in principle. Real-time measurement of the terahertz pulse was achieved using the dynamic subtraction method with a synchronized high-speed complimentary metal-oxide semiconductor sensor. A time window of 2.6 ps was achieved. This value agrees well with results that were calculated theoretically and measured by an interferometric inverted field autocorrelator.     

Simultaneous thermogravimetry - mass spectrometry for a solid oxide fuel cell cathode: (La0.7Sr0.3)0.9MnO3

A SOFC cathode related perovskite material, (La_0.7Sr_0.3)_0.9MnO₃, has been investigated by simultaneous thermogravimetry - mass spectrometry from room temperature to 1770 K. Water, carbon dioxide and oxygen were detected by mass spectrometry. Water and carbon dioxide evolution can be interpreted by assuming that prior to the thermogravimetry-mass spectrometry measurement about 0.5 % of the lanthanum component had reacted with carbon dioxide and water to form La₂(CO₃)₃*8H₂O, which dehydrated and decomposed via La₂O₂CO₃ into La₂O₃ and evolving H₂O and CO₂ during the present experiment. The observation that the lanthanum strontium manganite emitted oxygen in two stages can be ascribed to the two different oxygen sites in the perovskite lattice, that is, the oxygen excess and deficient regions.     

Magnetic structure of V5S8

The magnetic structure of V₅S₈ has been investigated by neutron diffraction at low temperature. Two single crystals (sample 1 and sample 2) grown by the same procedure gave considerably different results. Sample 1 was found to have an incommensurate structure, while sample 2 was found to have simple collinear antiferromagnetic structure consistent with magnetic measurements. Although the positions of the magnetic diffraction peaks of sample 1 were close to those of sample 2, the neutron intensity behavior was quite different and the detailed structure could not be determined in the case of sample 1. In both samples, the magnitude of the moments was evaluated to be much larger than the value estimated from NMR.     

Photoisomerization of bis(trifluoromethyl)thiophenes

The photolysis of 2,3-bis(trifluoromethyl)thiophene gave an equilibrium mixture of 2,3- and 3,4-bis(trifluoromethyl)Dewar thiophenes, while that of 2,5-bis(trifluoromethyl)thiophene gave 2,4-bis(trifluoromethyl)-thiophene, which seemed to be formed through an intermediate other than the Dewar form.     

(2H)2-2C type superstructure of TiS1.62, determined by high-resolution electron microscopy

A superstructure of TiS_1.62 is determined by 100 kV high-resolution electron microscopy, in which the arrangement of metal vacancies is obtained from structure images. The crystal has monoclinic symmetry (pseudo-hexagonal) with lattice parameters a = 11.9, b = 6.85, c = 11.5Å, β = 90°. The space group is considered as $\text{F2}\text{m}$. Metal vacancies are confined to every second metal layer and ordered within the partly filled metal layer, resulting in formation of a (2H)₂2C type of superstructure. The ordered metal vacancy layers are arranged in 2C-type stacking sequence along the c axis, while sulfur atoms are arranged in 2H-type stacking sequence along the c axis.     

Behavior of vanadium dioxide single crystals synthesized under the various oxygen partial pressures at 1500 K

The effects of nonstoichiometry upon the behavior of vanadium dioxide single crystals in the vicinity of the semiconductor/metal transition temperature (T_c) were experimentally investigated. According to the electrical and thermal measurements, more stoichiometric vanadium dioxide exhibited the less electrical conductivity gap, the larger thermal and electrical hysteresis, and the lower transition temperature than the increased nonstoichiometric one near transition. Infrared absorptions and X-ray observations indicated the local and overall lattice distortion in the nonstoichiometric crystal due to the existence of V⁵⁺ ions. Furthermore, an intermediate phase between the low-temperature monoclinic and the high-temperature tetragonal phases was found in the nonstoichiometric VO₂. On the other hand, no evidence for this intermediate phase was found in the stoichiometric one. Finally, some comparisons and discussions of our present data with the previously published ones were made.     

Studies on the synthesis of compounds related to adenosine-3',5'-cyclic phosphate. VI. Synthesis and cardiac effects of N6,N6,2'-O-trialkyl-, N6,2'-O-dialkyl-, and 2'-O-alkyladenosine-3',5'-cyclic phosphates

The alkylation of adenosine-3',5'-cyclic phosphate (cAMP, 1) with alkyl bromides was investigated and various new alkylated cAMP derivatives, N6,N6,2'-O-trialkyl cAMPs (2), N6,2'-O-dialkyl cAMPs (3) and 2'-O-alkyl cAMPs (4), were prepared by a one step reaction without the introduction of a protecting group into 1. Compounds (2) were synthesized from 1 by treatment with alkyl bromides in the presence of NaH or potassium tert-butoxide in dimethyl sulfoxide. Compounds (3) were also synthesized from 1 under conditions similar to those of the synthesis of 2 except for the use of MeONa as a base. Compounds (4) were prepared from 1 by treatment with alkyl bromides in the presence of 18-crown-6 in dioxane-aqueous KOH solution. N6,2'-O-Dibenzyl cAMP (3e) was obtained from 1 by the same method as the preparation of 4. These new alkylated derivatives were evaluated for cardiotonic activity in vitro. Some of them showed weak positive inotropic effects and strong negative chronotropic effects. Thus, the presence of the 2'-hydroxyl group seemed to be essential for the appearance of potent positive inotropic activity caused by cAMP derivatives.     

Formation and metabolism of pungent principle of Capsicum fruits. XV. Microdetermination of capsaicin by high-performance liquid chromatography with electrochemical detection

A new, highly sensitive method for quantitative separation and determination of capsaicin and dihydrocapsaicin by high-performance liquid chromatography with electrochemical detection is elaborated. The method employs a Cosmosil 5Ph column eluted with 100 mM potassium dihydrogenphosphate containing 45% acetonitrile (pH 5.0) at a flow-rate of 1.0 ml/min, and an electrochemical detector (at a potential of +750 mV versus the Ag/AgCl electrode). The detection limits for both capsaicin and dihydrocapsaicin were 12 pg (39 fmol) at a signal-to-noise ratio of 3:1. By applying this method, the biological half-life of capsaicin in the rat was investigated.