Effective procedure for selective ammonolysis of monosubstituted oxiranes: application to E7389 synthesis

A highly effective procedure is reported to synthesize 1,2-aminoalcohols by regio- and chemo-selective ammonolysis of mono-substituted epoxides. Additive- and concentration-effects were studied, revealing that (1) methanesulfonic acid is most effective among the additives tested and (2) formation of bis-adducts is practically eliminated at [C] ? 40 mM. The optimum condition thus identified was successfully applied to the final step of the synthesis of potent anti-tumor compound E7389.     

First-principles study of the pentacene/Cu(1 1 1) interface: Adsorption states and vacuum level shifts

We have studied the interaction of pentacene with a Cu(1 1 1) surface using density functional theory (DFT) within a generalized gradient approximation (GGA) and the van der Waals density functional [vdW-DF, M. Dion, H. Rydberg, E. Schröder, D.C. Langreth, B.I. Lundqvist, Phys. Rev. Lett. 92 (2004) 246401]. The adsorption energy is accurately predicted by vdW-DF, while the equilibrium distances between pentacene and the metal substrate (Z_C) are overestimated by both GGA and vdW-DF. The work function changes depend significantly on Z_C. The experimental work function change can be successfully reproduced by GGA if the experimentally reported adsorption geometry is used, whereas the magnitude of the work function change is underestimated if calculated adsorption geometries are applied. We examined the IDIS model [H. Vázquez, R. Qszwaldowski, P. Pou, J. Ortega, R. Pérez, F. Flores, A. Kahn, Europhys. Lett. 65 (2004) 802] to compare it with the GGA results. The interface dipoles estimated by the IDIS model fairly agree with the GGA results, provided that the adsorption distance is large. On the other hand, they tend to deviate from the GGA results as the adsorption distance becomes smaller, where back donation from the metal surface to the adsorbate occurs. Our analysis reveals that at experimentally reported metal–organic distance, back donation is significant enough to induce polarization of pentacene molecules perpendicular to the surface, which leads to a reduction of the work function. Thus, at the experimentally reported metal–organic distance, the work function change estimated by a simple IDIS model deviates from that calculated by self-consistent GGA calculations. We also found that at the experimentally reported metal–organic distance, the transferred electrons create weak chemical bonds between pentacene and the Cu(1 1 1) surface, illustrating the reactive nature of pentacene.     

Integrated experiments of fast ignition targets by Gekko-XII and LFEX lasers

Implosion and heating experiments at the Institute of Laser Engineering, Osaka University on Fast Ignition (FI) targets for the FIREX-1 project have been performed with Gekko-XII laser for implosions and LFEX laser for heating. We tried to reduce the prepulse level in the LFEX laser system and have improved the plasma diagnostics to observe the plasma in the harsh hard X-ray environment. A plastic (CD) shell target, 7-μm thick and 500 μm in diameter with a hollow gold cone was used in this experiment to guide the short-pulse laser at the time of the maximum compression. The shell target was imploded with 9 or 12 beams of Gekko-XII laser (527 nm) with energy of 300 J/beam in a 1.5 ns pulse. Two of the four LFEX laser (1053 nm) beams were injected into the inside bottom of the cone with an energy up to 0.7 kJ/beam in a 1.5 ps pulse at the time around the maximum implosion. We have observed neutron enhancement up to 3.5 × 10⁷ with total heating energy of 300 J, which is higher than the yield obtained in the previous experiment in 2002 [R. Kodama et al. Nature 418, 933 (2002)]. We found the estimated heating efficiency is at a level of 10–20%. Fuel heating to 5 keV is expected when the full output of LFEX is used.     

Low-pass filtering effects of viscous sublayer on high Schmidt number mass transfer close to a solid wall

Numerical simulation of high Schmidt number turbulent mass transfer at a solid wall is carried out. Particular attention is paid to the response of the concentration field to the wall-normal velocity fluctuation inside the viscous sublayer. Spatio-temporal correlation shows that the high Schmidt number concentration field becomes insensitive to the wall-normal velocity fluctuation. In addition, there exists a significant time lag in the response of the concentration field to the wall-normal velocity fluctuation. As a result, the instantaneous distribution of the local mass transfer rate is drastically changed. These facts explain why the analogy between the momentum and mass transfer does not hold close to the wall. Based on a one-dimensional advection–diffusion equation, we derive a transfer function connecting the wall-normal velocity and the concentration fluctuations. It is shown that the present model can reproduce the fundamental dynamical features of high Schmidt number concentration field.     

Superconducting Pb island nanostructures studied by scanning tunneling microscopy and spectroscopy

Superconductivity of nanosized Pb-island structures whose radius is 0.8 to 2.5 times their coherence length was studied under magnetic fields using low-temperature scanning tunneling microscopy and spectroscopy. Spatial profiles of superconductivity were obtained by conductance measurements at zero-bias voltage. Critical magnetic fields for vortex penetration and expulsion and for superconductivity breaking were measured for each island. The critical fields depending on the lateral size of the islands and existence of the minimum lateral size for vortex formation were observed.     

High-contrast, high-intensity laser pulse generation using a nonlinear preamplifier in a Ti:sapphire laser system

We report a high-contrast, high-intensity Ti:sapphire chirped-pulse amplification system that incorporates a nonlinear preamplifier based on optical parametric chirped-pulse amplification (OPCPA). By cooling the Ti:sapphire crystal in the final amplifier down to 77 K, the chirped-pulses are amplified to 2.9 J at a 10 Hz repetition rate without a thermal lensing effect. Pulse compression down to 19 fs duration obtained after amplification indicates a peak power of 80 TW. With the OPCPA, the temporal contrast is significantly improved to better than 7x10(-9) in a few picoseconds interval prior to the main laser pulse.     

Characterization of phosphorus-doped homoepitaxial (1 0 0) diamond films grown using high-power-density MWPCVD method with a conventional quartz-tube chamber

Phosphorus-doped n-type homoepitaxial diamond films have been successfully grown at high substrate temperatures (>1000 °C) on high-pressure/high-temperature-synthesized type-Ib single-crystalline diamond (1 0 0) substrates, by using a conventional microwave plasma chemical-vapor-deposition (CVD) system with high power densities. The deposition system employed in this work had an easily exchangeable 36 mm inner-diameter quartz-tube growth chamber. The homoepitaxial diamond films thus grown were characterized by means of Hall-effect measurements with an AC magnetic field, atomic force microscope observations and secondary ion mass spectrometry techniques. The dependences of the substrate temperature (≤1300 °C) and the P/C ratio in the source gas (≤9900 ppm) on the specimen features were investigated. The optimum substrate temperature deduced was ≈1160 °C, which was also applicable to the CVD growth of undoped homoepitaxial diamond layers. The n-type conductions with an activation energy ≈0.6 eV were observed for the specimens with amounts of the P atoms incorporated to ≈1.5 × 10¹⁸ cm⁻³ whereas the doping efficiencies changed from ≈0.06% to ≈0.92% with the growth condition. Possible origins for these results are discussed in relation to the growth mechanism.     

Dcdftbmd: Divide-and-Conquer Density Functional Tight-Binding Program for Huge-System Quantum Mechanical Molecular Dynamics Simulations

Dcdftbmd is a Fortran 90/95 program that enables efficient quantum mechanical molecular dynamics (MD) simulations using divide-and-conquer density functional tight-binding (DC-DFTB) method. Based on the remarkable performance of previous massively parallel DC-DFTB energy and gradient calculations for huge systems, the code has been specialized to MD simulations. Recent implementations and modifications including DFTB extensions, improved computational speed in the DC-DFTB computational steps, algorithms for efficient initial guess charge prediction, and free energy calculations via metadynamics technique have enhanced the capability to obtain atomistic insights in novel applications to nanomaterials and biomolecules. The energy, structure, and other molecular properties are also accessible through the single-point calculation, geometry optimization, and vibrational frequency analysis. The available functionalities are outlined together with efficiency tests and simulation examples. © 2019 Wiley Periodicals, Inc.     

GPU-Accelerated Large-Scale Excited-State Simulation Based on Divide-and-Conquer Time-Dependent Density-Functional Tight-Binding

The present study implemented the divide-and-conquer time-dependent density-functional tight-binding (DC-TDDFTB) code on a graphical processing unit (GPU). The DC method, which is a linear-scaling scheme, divides a total system into several fragments. By separately solving local equations in individual fragments, the DC method could reduce slow central processing unit (CPU)-GPU memory access, as well as computational cost, and avoid shortfalls of GPU memory. Numerical applications confirmed that the present code on GPU significantly accelerated the TDDFTB calculations, while maintaining accuracy. Furthermore, the DC-TDDFTB simulation of 2-acetylindan-1,3-dione displays excited-state intramolecular proton transfer and provides reasonable absorption and fluorescence energies with the corresponding experimental values. © 2019 Wiley Periodicals, Inc.     

Stabilization effects of carboxylate on pyrotechnic compositions including Mg powder in water

Magnesium powder is a common fuel in the field of pyrotechnics. The metal corrodes easily under wet conditions. This can lead to problems such as spontaneous ignition and deterioration of combustion performance when the powder is used in humid areas. For pyrotechnic compositions containing magnesium, harmful stabilizers are often used. In this study, we researched a less harmful replacement for the stabilizer and selected linseed oil, which is used as cooking oil. Experiments were conducted to examine linseed oil’s stabilization effects against magnesium corrosion when it is in contact with an oxidizer under humid conditions by coating magnesium powder and soaking it in aqueous oxidizer solutions. The oxidation of linseed oil led to its polymerization, because of which the stabilizing effect of linseed oil was lost. Stearic acid, which is a saturated fatty acid, was also examined for its stabilizing effects. Melted stearic acid was mixed with magnesium, and coating of stearic acid on magnesium particles was confirmed. The effect of stearic acid coating is more prominent than that of simple mixing of stearic acid with Mg. The stabilization effect of linseed oil and stearic acid coating shows that unharmful organic stabilizers can also be used in pyrotechnic compositions containing Mg.