An Exceptionally Narrow Band-Gap (∼4 eV) Silicate Predicted in the Cubic Perovskite Structure: BaSiO₃

The electronic structures of 35 <i>A</i>²⁺<i>B</i>⁴⁺O₃ ternary cubic perovskite oxides, including their hypothetical chemical compositions, were calculated by a hybrid functional method with the expectation that peculiar electronic structures and unique carrier transport properties suitable for semiconductor applications would be hidden in high-symmetry cubic perovskite oxides. We found unique electronic structures of Si-based oxides (<i>A</i> = Mg, Ca, Sr, and Ba, and <i>B</i> = Si). In particular, the unreported cubic BaSiO₃ has a very narrow band gap (4.1 eV) compared with conventional nontransition-metal silicates (e.g., ∼9 eV for SiO₂ and the calculated value of 7.3 eV for orthorhombic BaSiO₃) and a small electron effective mass (0.3<i>m</i>₀, where <i>m</i>₀ is the free electron rest mass). The narrow band gap is ascribed to the nonbonding state of Si 3s and the weakened Madelung potential. The existence of the predicted cubic perovskite structure of BaSiO₃ was experimentally verified by applying a high pressure of 141 GPa. The present finding indicates that it could be possible to develop a new transparent oxide semiconductor of earth abundant silicates if the symmetry of its crystal structure is appropriately chosen. Cubic BaSiO₃ is a candidate for high-performance oxide semiconductors if this phase can be stabilized at room temperature and ambient pressure

Results of the blood examinations.

<p>a: SBO indicates small bowel obstruction</p><p>WBC: white blood cell; Plt: platelet; ALP: alkaline phosphatase; LDH: lactic dehydrogenase; CK: creatine phosphokinase; CRP: C-reactive protein; LA: lactic acid; I-FABP: intestinal fatty acid-binding protein.</p

Postperovskite Phase Transition of ZnGeO₃: Comparative Crystal Chemistry of Postperovskite Phase Transition from Germanate Perovskites

The postperovskite phase of ZnGeO₃ was confirmed by laser heating experiments of the perovskite phase under 110–130 GPa at high temperature. Ab initio calculations indicated that the phase transition occurs at 133 GPa at 0 K. This postperovskite transition pressure is significantly higher than those reported for other germanates, such as MnGeO₃ and MgGeO₃. The comparative crystal chemistry of the perovskite-to-postperovskite transition suggests that a relatively elongated <i>b</i>-axis in the low-pressure range resulted in the delay in the transition to the postperovskite phase. Similar to most GdFeO₃-type perovskites that transform to the CaIrO₃-type postperovskite phase, ZnGeO₃ perovskite eventually transformed to the CaIrO₃-type postperovskite phase at a critical rotational angle of the GeO₆ octahedron. The formation of the postperovskite structure at a very low critical rotational angle for MnGeO₃ suggests that relatively large divalent cations likely break down the corner-sharing GeO₆ frameworks without a large rotation of GeO₆ to form the postperovskite phase

Flow diagram of the patients included in this study.

<p>Forty-seven of 281 patients with acute abdomen were diagnosed with bowel obstruction. Ten patients with large bowel obstruction were excluded, and finally 37 patients with small bowel obstruction (SBO) were included in this study. According to the findings of enhanced computed tomography, they were divided into the two groups, those with strangulated bowel obstruction or those with simple bowel obstruction.</p

Clinical characteristics (n = 37).

<p>a: CT indicates computed tomography</p><p>b: SBO indicates small bowel obstruction</p

Receiver operating characteristics curves showing diagnostic performance for strangulated small bowel obstruction.

<p>Areas under the curve (95% confidence intervals) for each marker are as follows: intestinal fatty acid-binding protein (I-FABP), 0.854 (0.685- 0.941); lactic acid, 0.735 (0.524– 0.894); white blood cell (WBC) count, 0.664 (0.443–0.805); alkaline phosphatase (ALP), 0.640 (0.442–0.799). The cut-off level of I-FABP concentration at which the Youden index exhibited a maximum value was 6.5 ng/ml.</p

Univariate analysis of biomedical markers predicting strangulated small bowel obstruction.

<p>WBC: white blood cell; Plt: platelet; ALP: alkaline phosphatase; LDH: lactic dehydrogenase; CK: creatine phosphokinase; CRP: C-reactive protein; LA: lactic acid; I-FABP: intestinal fatty acid-binding protein.</p

Results of the multiple logistic regression analysis.

<p>WBC: white blood cell; LA: lactic acid; I-FABP: intestinal fatty acid-binding protein.</p

Comparison of the diagnostic usefulness of the blood biochemical markers for predicting strangulated small bowel obstruction.

<p>Numbers in parentheses represent 95% confidence intervals.</p>a<p>ROC indicates receivor operating characteristics.</p>b<p>PPV indicates the positive predictive value.</p>c<p>NPV indicates the negative predictive value.</p><p>WBC: white blood cell; Plt: platelet; ALP: alkaline phosphatase; LDH: lactic dehydrogenase;</p><p>CK:creatine phosphokinase; CRP: C-reactive protein; LA:lactic acid; I-FABP: intestinal fatty acid-binding protein</p

A Pressure Induced Structural Dichotomy in Isostructural Bis-1,2,3-thiaselenazolyl Radical Dimers

The pressure dependence of the crystal and molecular structure of the bis-1,2,3-thiaselenazolyl radical dimer [<b>1b</b>]₂ has been investigated over the range 0–11 GPa by powder diffraction methods using synchrotron radiation and diamond anvil cell techniques. At ambient pressure, the dimer consists of a pair of radicals linked by a hypervalent 4-center 6-electron S---Se–Se---S σ-bond in an essentially coplanar arrangement. The dimers are packed in cross-braced slipped π-stack arrays running along the <i>x</i>-direction of the monoclinic (space group <i>P</i>2₁/<i>c</i>) unit cell. Pressurization to 11 GPa causes the unit cell dimensions <i>a</i> and <i>c</i> to undergo a slow but uniform compression, while the <i>b</i>-axis is slightly elongated. There is virtually no change in the molecular structure or in the slipped π-stack crystal architecture. This behavior is in marked contrast to that of the isostructural radical dimer [<b>1a</b>]₂, where the basal fluorine is replaced by hydrogen. Pressurization of this latter material induces a phase change near 4–5 GPa, characterized by a sharp contraction in <i>a</i> and <i>c</i>, and a correspondingly large increase in <i>b</i>. At the molecular level, the transition is associated with a buckling of the σ-bonded dimer to a more conventional π-bonded arrangement. Geometry optimized DFT band structure calculations on [<b>1b</b>]₂ replicate the observed structural changes and indicate that compression widens both the valence and conduction bands but does not induce band gap closure until >13 GPa. This result is consistent with the measured thermal activation energy for conduction <i>E</i>_act, which indicates that a metallic state requires pressures > 10 GPa