Two solid phases of pyrimidin‐1‐ium hydrogen chloranilate monohydrate determined at 225 and 120 K

The crystal structures of two solid phases of the title compound, C₄H₅N₂⁺·C₆HCl₂O₄⁻·H₂O, have been determined at 225 and 120 K. In the high‐temperature phase, stable above 198 K, the transition temperature of which has been determined by ³⁵Cl nuclear quadrupole resonance and differential thermal analysis measurements, the three components are held together by O—H...O, N...H...O, C—H...O and C—H...Cl hydrogen bonds, forming a centrosymmetric 2+2+2 aggregate. In the N...H...O hydrogen bond formed between the pyrimidin‐1‐ium cation and the water molecule, the H atom is disordered over two positions, resulting in two states, viz. pyrimidin‐1‐ium–water and pyrimidine–oxonium. In the low‐temperature phase, the title compound crystallizes in the same monoclinic space group and has a similar molecular packing, but the 2+2+2 aggregate loses the centrosymmetry, resulting in a doubling of the unit cell and two crystallographically independent molecules for each component in the asymmetric unit. The H atom in one N...H...O hydrogen bond between the pyrimidin‐1‐ium cation and the water molecule is disordered, while the H atom in the other hydrogen bond is found to be ordered at the N‐atom site with a long N—H distance [1.10 (3) Å].     

Robust empirical optimization is almost the same as mean–variance optimization

We formulate a distributionally robust optimization problem where the deviation of the alternative distribution is controlled by a $?$-divergence penalty in the objective, and show that a large class of these problems are essentially equivalent to a mean–variance problem. We also show that while a “small amount of robustness” always reduces the in-sample expected reward, the reduction in the variance, which is a measure of sensitivity to model misspecification, is an order of magnitude larger.     

Carboxylations of alkali metal phenoxides with carbon dioxide

The reaction mechanism of the Kolbe-Schmitt reaction of phenol and 2-naphthol has been investigated. An alkali metal phenoxide-CO2 complex is not an intermediate that can be easily transformed into a carboxylic acid, such as salicylic acid (SA) and p-hydroxybenzoic acid (pHBA). A direct carboxylation of phenoxide with CO2 takes place even at room temperature, and is competitive with the formation of the CO2 complex. The resulting complex decomposes thermally (above ca. 100 degrees C) to phenoxide, which then undergoes further competitive reactions. Experiments using a carbon-13 labeled complex support a mechanism of direct carboxylation, and not the mechanism via a CO2 complex. The reactivity, C-13 NMR and MOPAC/PM3 calculations suggest a new carbonate-like structure for the CO2 complex.     

Contact angle hysteresis in carbon fibers studied by wetting force measurements

The surface free energy of polyacrylonitrile carbon fibers was investigated by using the Wilhelmy technique. The difference in surface free energy between immersion and emersion was observed for the carbon fiber pyrolyzed at 2500 °C.In contrast, the hysteresis disappeared with repyrolyzation of the carbon fibers at 3000 °C. Auger electron spectroscopic analysis indicated that the surface of the latter carbon fiber (repyrolyzed at 3000 °C) consisted of the basal planes of graphite. Rough surface topography of the carbon fiber repyrolyzed at 3000 °C, as observed by scanning electron microscope, did not affect the hysteresis. Therefore, the contact angle hysteresis was attributed to the chemical adsorbants on the activation sites of the fiber surfaces, as detected by Auger electron spectroscopy.     

The first and second derivative matrices in the random phase approximation scheme by using the Lagrangian technique

We have presented the explicit formulas for first and second derivatives of A and B matrices, appearing in the random phase approximation (RPA), with the aid of Lagrangian technique. Owing to the 2n + 1 rule, the Lagrangian approach is more efficient than the conventional approach to evaluate the higher‐order matrix elements. We have confirmed the validity of our formulation by demonstrating the geometry optimization of the first‐excited singlet states of formaldehyde, ethylene, and 1‐amino‐3‐propenal molecules. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Drawing behavior and characteristics of laser‐drawn polypropylene fibers

Drawing behavior, flow drawing, and neck drawing, was studied for isotacticpolypropylene fibers in CO₂ laser drawing system, and the fiber structure and the mechanical properties of drawn fibers were analyzed. For a certain laser power, flow drawing of polypropylene (PP) was possible up to draw ratio (DR) 19.5. Though the drawing stress was very low, the flow‐drawn PP fiber exhibited oriented crystal structure and improved mechanical properties. On the other hand, neck‐drawing was accomplished from DR 4 to 12, with significant increase in drawing stress that enhanced the development of fiber structure and mechanical properties. Unlike PET, the drawing stress depends not only on the DR, but on irradiated laser power also. The 10–12 times neck‐drawn fibers were highly fibrillated. The fibers having tensile strength 910 MPa, initial modulus 11 GPa, and dynamic modulus 14 GPa were obtained by single‐step laser drawing system. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 398–408, 2006     

Brittle fracture and spinnability of viscous materials

Ohne Zusammenfassung     

An example for activation analysis by low-level radioisotope neutron soruce

A 1 Ci Pu−Be neutron source and a low-background beta-spectrometer were used to activate and to measure the beta-rays of low-activity. The main characteristics of this method can be given as follow: The determined S/N ratio increases because the background beta-rays are lower than the gamma-rays. For example, the sensitivity obtained for quantitative analysis of sulphur in silicon is 100 ppm in case of S/N=1.0.     

An admissible form of an inelastic constitutive equation—I. General theory

From the viewpoint of irreversible thermodynamics an admissible form of rate-type constitutive equation of inelastic materials is given. The displacement gradient tensor F referred to the temporarily fixed reference frame which coincides with the Euler frame at the instant of the reference time is decomposed linearly into elastic and inelastic parts so that the procedure of formulation is simplified and clarified. The inelastic deformation rate is directly related to the internal production rate of entropy. The existence of an inelastic potential of the usual sense is not assumed, though the result can be understood to include the conventional flow theory based on an inelastic potential. An example of an elastoviscoplastic constitutive equation is given and some properties of yield surfaces are discussed.