The new compounds ANb2PSe10, where A = K, Rb and Cs, form from polyselenophosphate flux reactions and crystallize in the noncentrosymmetric space group Pc. They feature infinite one-dimensional 1/∞[Nb2PSe10–] chains separated by alkali cations. The chains consist of [Nb2(Se2)2]4+ clusters bridged by a diselenide and a [PSe4]3– group. The chains pack differently depending on which alkali cation is present in the lattice. As a result, the analogs are not isostructural with respect to each other, and each has a different unit cell. The reaction chemistry involving a multitude of reaction conditions and their respective products is discussed. Other products from these reactions include NbSe3 and Nb2Se9 in both crystalline and microfibrous morphologies. The ANb2PSe10 compounds are stable to oxidation in ambient air but decompose when heated above 350 °C. Their band gaps were measured to be 1.1–1.2 eV and the resistivity of the K analog at room temperature was measured at 4.5 Ω·cm. Nonlinear optical second harmonic generation measurements were done on the Rb analog yielding a χ2 of ∼7 pm/V and showing phase matching behavior.
The objective of this study was to assess the capability of T2-weighted magnetic resonance imaging (T2W-MRI) and the additional diagnostic value of dynamic contrast-enhanced MRI (DCE-MRI) using multitransmit 3 T in the localization of bladder cancer.This prospective study was approved by the local institutional review board. Thirty-six patients were included in the study and provided informed consent. Magnetic resonance imaging scans were performed with T2W-MRI and DCE-MRI on a 3-T multitransmit system. Two observers (with 12 and 25 years of experience) independently interpreted T2W-MRI before DCE-MRI data (maps of pharmacokinetic parameters) to localize bladder tumors. The pathological examination of cystectomy bladder specimens was used as a reference criteria standard. The McNemar test was performed to evaluate the differences in sensitivity, specificity, and accuracy. Scores of κ were calculated to assess interobserver agreement.The sensitivity, specificity, and accuracy of the localization with T2W-MRI alone were 81% (29/36), 63% (5/8), and 77% (34/44) for observer 1 and 72% (26/36), 63% (5/8), and 70% (31/44) for observer 2. With additional DCE-MRI available, these values were 92% (33/36), 75% (6/8), and 89% (39/44) for observer 1 and 92% (33/36), 63% (5/8), and 86% (38/44) for observer 2. Dynamic contrast-enhanced MRI significantly (P<0.01) improved the sensitivity and accuracy for observer 2. For the 23 patients treated with chemotherapy, DCE-MRI also significantly (P<0.02) improved the sensitivity and accuracy of bladder cancer localization with T2W-MRI alone for observer 2. Scores of κ were 0.63 for T2W-MRI alone and 0.78 for additional DCE-MRI. Of 7 subcentimeter malignant tumors, 4 (57%) were identified on T2W images and 6 (86%) were identified on DCE maps. Of 11 malignant tumors within the bladder wall thickening, 6 (55%) were found on T2W images and 10 (91%) were found on DCE maps.Compared with conventional T2W-MRI alone, the addition of DCE-MRI improved interobserver agreement as well as the localization of small malignant tumors and those within bladder wall thickening.
Two new lithium-containing diamond-like semiconductors, Li2ZnGeSe4 and Li2ZnSnSe4, have been prepared by high-temperature, solid-state synthesis. Single crystal X-ray diffraction reveals that both compounds adopt the wurtz-kesterite structure type, crystallizing in the noncentrosymmetric space group Pn. X-ray powder diffraction coupled with Rietveld refinement indicates the high degree of phase purity in which the materials are prepared. Both compounds display optical bandgaps around 1.8 eV, wide optical transparency windows from 0.7 to 25 μm and type-I phase matched second harmonic generation starting at 2500 nm and persisting deeper into the infrared. Using the Kurtz powder method, the second-order nonlinear optical coefficient, χ((2)), was estimated to be 19 and 23 pm V(-1) for Li2ZnGeSe4 and Li2ZnSnSe4, respectively. Using a 1064 nm incident laser beam with a pulse width (τ) of 30 ps both compounds exhibit a laser damage threshold of 0.3 GW cm(-2), which is higher than that of the AgGaSe2 reference material measured under identical conditions. Differential thermal analysis shows that the title compounds are stable up to 684 and 736 °C, respectively. These properties collectively demonstrate that Li2ZnGeSe4 and Li2ZnSnSe4 have great potential for applications in tunable laser systems, especially in the infrared and even up to the terahertz regime. Electronic structure calculations using a plane-wave pseudopotential method within density functional theory provide insight regarding the nature of the bandgap and bonding.
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