p‐Type Optoelectronic and Transparent Conducting Oxide Properties of Delafossite CuAl1/2Fe1/2O2

CuAl_1/2Fe_1/2O₂ delafossite was prepared using a solid‐state reaction method to investigate its optical and electronic transport properties. CuAl_1/2Fe_1/2O₂ formed a hexagonal delafossite structure with an Rm space group. The positive Seebeck coefficient and the direct optical gap of 3.6 eV confirmed that the CuAl_1/2Fe_1/2O₂ delafossite in a p‐type transparent conducting oxide. The fluorescence emission at 390 nm (green emission) confirmed that CuAl_1/2Fe_1/2O₂ has a direct transition band gap. Thermogravimetric analysis indicated a weight loss of 1.2%, caused by the intercalation of O atoms, which produced hole carriers from the different ionic radii at the B sites. The electric conductivity at room temperature was thermally activated, as predicted by the small‐polaron hopping mechanism, with an activation energy of 75 meV and a charge transport energy of 61 meV. CuAl_1/2Fe_1/2O₂ delafossite exhibited p‐type optoelectronic behavior and is a transparent conducting oxide, which may be crucial in the p‐type photonic and electrode industries.     

Lactulose fermentation and lactose absorption in Chilean patients with liver cirrhosis: importance for hepatic encephalopathy therapy

BACKGROUND: There has been controversy concerning the indications for coronary artery surgery in the elderly, particularly in countries where health resources are restricted. AIMS: To assess the results of coronary artery bypass grafting (CABG) in a large group of elderly subjects with regard to initial risks and long term follow-up. METHODS: Ninety-six consecutive patients aged 70 years or older underwent isolated CABG between January 1981 and December 1985. Long term follow-up was obtained in 94 (98%). RESULTS: The mean age was 71.6 years (70-78) and mean duration of follow-up 73 months. Seventy (73%) were male. In 80 cases the myocardial score was > 10. In 22 of 90 who had left ventricular angiography the ejection fraction was < 50%. Hospital survival was 96% and the five year survival 77%. It was not influenced by gender, myocardial score, ejection fraction or age at the time of operation. The status of survivors was reviewed in 1991. Of the 55 long term survivors 35 (64%) were free of angina. Eight (15%) and ten (18%) were in the Canadian Cardiovascular Society Angina classes 1 and 2 respectively. Seventeen patients (31%) had symptoms of heart failure with 14 (25%) in NYHA class 2 and 3 (5%) in class 3. Eight patients (15%) had survived a cerebrovascular event during follow-up. There were 35 late deaths (37%). Sixteen of these were cardiac, 18 due to other causes and one unknown.     

Dispersion of gold dodecanethiolate in a silsesquioxane film with pendant dodecyl chains: from photoluminescent materials to gold nanocomposites

Photoluminescence of Au(I)-dodecane thiolate (Au(I)-DDT) and its thermal reduction to metallic gold have been extensively reported in the literature. However, the incorporation of this salt to a polymeric matrix to produce photoluminescent materials or gold nanocomposites by thermal reduction is a difficult task due to the insolubility of Au(I)-DDT. In this study it is shown that a silsesquioxane with pendant dodecyl chains can be a convenient host of Au(I)-DDT. The presence of dodecyl chains in both compounds and the in situ generation of the salt in the solution of the silsesquioxane precursor enabled to obtain a uniform dispersion of Au(I)-DDT in the silsesquioxane matrix. Flexible films were generated, exhibiting characteristic photoluminescent properties before thermal treatment and a uniform dispersion of gold nanoparticles after heating at 150 °C for different periods of time.     

Photoinduced degradation of α-Si:H/μc-Si:H tandem photoconvertes at elevated temperatures

Photoinduced degradation of tandem photoconverters with the structure α-Si:H/μc-Si:H and initial efficiency of 10.5% at temperatures of 298, 328, and 353 K is experimentally studied. It has been found that, at a temperature of 298 K, the efficiency of the photoconverters decreases by 1.0–1.2% during long light exposure, while an increase in temperature to 328 K leads to a decrease in efficiency to 0.2%; at a temperature of 353 K, no degradation is observed. To explain these results, a modified H-collision model was used. Thermal-activation energy has been determined for the process that hampers the growth of dangling (ruptured) bonds in the i-α-Si:H layer.     

Reduction of the level of the radiation effect on space SA photoconverters with the use of solar radiation concentrators

The capabilities of the solar radiation concentrators as means of space solar array (SA) photoconverter protection from radiation are considered. The concentrator screening effect with respect to protons and electrons is qualitatively evaluated. It is shown that this effect for SAs with linear lens concentrators is several times larger than that in the case of trough-type mirror concentrating systems.     

Characterization of Imprinted Microbeads Synthesized via Minisuspension Polymerization

The properties of MIPs synthesized by minisuspension polymerization are studied. The template is cyclododecyl 2,4‐dihydroxybenzoate ( 1 ), which behaves as good mimic of the estrogenic mycotoxin zearalenone. 2‐DAEM and EGDMA are used as functional and crosslinker monomers, respectively. The synthesized particles are characterized by optical and electronic microscopy, N₂ sorption measurements, and FT‐IR spectroscopy. The molecular recognition capability of MIPs is evaluated by comparing the adsorption Freundlich isotherms of MIPs to those of the corresponding non‐imprinted polymers. It is concluded that MSP is an attractive alternative for molecular imprinting because it is easy to apply and produces high yield of spherical particles of “tunable” size with acceptable molecular recognition capabilities.

     

Thermoelectric properties of Cu1−xPtxFeO2 (0.0 ≤ x ≤ 0.05) delafossite-type transition oxide

The samples of Cu_1−xPt_xFeO₂ (0 ≤ x ≤ 0.05) delafossite were synthesized by solid state reaction method for studying thermoelectric properties. The properties of Seebeck coefficient, electrical conductivity and thermal conductivity were measured in the high temperature ranging from 300 to 960 K. The results of Seebeck coefficient, electrical conductivity and power factor were increased with increasing Pt substitution and temperature. The thermal conductivity was decreased from 5.8 to 3.5 W/mK with increasing the temperature from 300 to 960 K. An important results, the highest value of power factor and ZT is 2.0 × 10⁻⁴ W/mK² and 0.05, respectively, for x = 0.05 at 960 K.     

The effect of phase transition of crednerite/delafossite CuMn1−xCrxO2 on optical,thermal, and power factor properties

This study aims to investigate the effect of the phase transition of CuMn_1−xCr_xO₂ compound on the Jahn–Teller effect which in turn affects the optical, thermal, and thermoelectric power factor properties. The CuMn_1−xCr_xO₂ samples were synthesized by a solid-state reaction method. The ab initio computation was applied to evaluate the electronic and optical properties in order to confirm the experiment data. The appearance of the phase transition from crednerite CuMnO₂ to delafossite CuCrO₂ was confirmed by X-ray diffraction (XRD) and the ab initio computation through displaying the mixed crednerite/delafossite phase; and, the existence of the Jahn–Teller effect was confirmed by the X-ray photoelectron spectroscopy (XPS) technique exhibiting the occurrence of mixed-state Mn³⁺/Mn⁴⁺ ions. The results obtained from XRD, XPS, and the ab initio computation implied the decrease of the Jahn–Teller behavior with increased x content under the influence of the phase transition from the crednerite phase to the delafossite phase of CuMn_1−xCr_xO₂. Surprisingly, the Jahn–Teller distortion reduction caused an increase in the energy gap of the optical property, electrical resistivity, and activation energy in thermally activated band conduction. The effect suffered the specific heat behavior by being separated into two groups of crednerite and delafossite, and enhanced the small polaron behavior by increasing the activation energy of thermally activated band conduction. The phase transition reduced the results of thermal conductivity, thermopower, and thermoelectric power factor properties. In other words, the effect of the phase transition from the crednerite CuMnO₂ phase to the delafossite CuCrO₂ phase on CuMn_1−xCr_xO₂ compound reduced the Jahn–Teller effect with increased Cr content which in turn caused changes in the optical, thermal, and thermoelectric power factor properties. The effect of the phase transition is advantageous for the improvement of material properties.     

Selective charge transfer in donor/acceptor systems bridged by Tröger base derivatives

Recently, unusual charge transfer properties of two triarylamines bridged through an aliphatic bridge (Tröger base) have been reported. The donor/acceptor couple was shown to have an important electronic coupling between its centers for the hole transfer, although in the absence of a π linker. In contrast, we here show, by combining first principles calculations with experimental studies, that the bridge has a practically null role in coupling the electron transfer. This sharp contrast might present an interesting potential in the design of molecular devices.