Turbulent jet interaction with a long rise-time pressure signature

A sonic boom signature with a long rise time has the ability to reduce the sonic boom, but it does not necessarily minimize the sonic boom at the ground level because of the real atmospheric turbulence. In this study, an effect of the turbulence on a long rise-time pressure signature was experimentally investigated in a ballistic range facility. To compare the effects of the turbulence on the long and short rise-time pressure signatures, a cone-cylinder projectile that simultaneously produces these pressure signatures was designed. The pressure waves interacted with a turbulent field generated by a circular nozzle. The turbulence effects were evaluated using flow diagnostic techniques: high-speed schlieren photography, a point-diffraction interferometer, and a pressure measurement. In spite of the fact that the long and short rise-time pressure signatures simultaneously travel through the turbulent field, the turbulence effects do not give the same contribution to these overpressures. Regarding the long rise-time pressure signature, the overpressure fluctuation due to the turbulence interaction is almost uniform, and a standard deviation 1.5 times greater than that of the no-turbulence case is observed. By contrast, a short rise-time pressure signature which passed through the same turbulent field is strongly affected by the turbulence. A standard deviation increases by a factor of 14 because of the turbulence interaction. Additionally, there is a non-correlation between the overpressure fluctuations of the long and short rise-time pressure signatures. These results deduce that the length of the rise time is important to the turbulence effects such as the shock focusing/diffracting.     

Characterization of cross-linking structure in terephthalate polyesters formed through material recycling process by pyrolysis-gas chromatography in the presence of organic alkali

Typical terephthalate polyesters such as poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) were characterized by pyrolysis-gas chromatography (Py-GC) in the presence of tetramethylammonium hydroxide in terms of the cross-linking structure formed during their material recycling. In the pyrograms of PBT and PET thermally treated at 270 °C for 1 h, which were prepared as model polymers containing cross-linking structures, an additional peak was commonly observed as well as the main reactive pyrolysis products for the original polyesters such as dimethyl terephthalate. Based on the observed spectra obtained by Py-GC/mass spectrometry and Py-GC/Fourier transform infrared spectrometry measurements, this peak was assigned to the product reflecting a biphenyl-type cross-linking structure. Furthermore, in the pyrograms of kneaded PBT and PET samples also at 270 °C for a total of 1 h, which were prepared to simulate material recycling, the same peak for the cross-linking structure was also observed, although its intensity was slightly lower than that in the samples thermally treated in air. This fact verified that the biphenyl-type cross-linking structure would be considerably formed during the recycling of PBT and PET, which might in turn contribute to the deteriorated properties of the recycled materials from waste polyesters. Moreover, difference in the formation of the cross-linking between PBT and PET is discussed on the basis of the observed results.     

Dynamic-to-Static Planar Chirality Conversion in Pillar[5]arenes Regulated by Guest Solvents or Amplified by Crystallization

Controlling dynamic chirality and memorizing the controlled chirality are important. Chirality memory has mainly been achieved using noncovalent interactions. However, in many cases, the memorized chirality arising from noncovalent interactions is erased by changing the conditions such as the solvent and temperature. In this study, the dynamic planar chirality of pillar[5]arenes was successfully converted into static planar chirality by introducing bulky groups through covalent bonds. Before introducing the bulky groups, pillar[5]arene with stereogenic carbon atoms at both rims existed as a pair of diastereomers, and thus showed planar chiral inversion that was dependent on the chain length of the guest solvent. The pS and pR forms, regulated by guest solvents, were both diastereomerically memorized by introducing bulky groups. Furthermore, the diastereomeric excess was amplified by crystallization of the pillar[5]arene. The subsequent introduction of bulky groups yielded pillar[5]arene with an excellent diastereomeric excess (95 % de).     

Variation in the chromatographic,material, and chemical characteristics of methacrylate‐based polymer monoliths during photoinitiated low‐temperature polymerization

Both the separation behavior and the structure of a polymer monolith column depends on both the reaction solution composition and the polymerization conditions. In photoinitiated low‐temperature polymerization, polymerization temperature, irradiation intensity, and polymerization time were key factors to control the monolith characteristics. In this study, the effect of polymerization time on the chromatographic, material, and chemical characteristics of poly(butyl methacrylate‐co‐ethylene dimethacrylate) monoliths was studied using pyrolysis‐gas chromatography, Raman spectroscopy, inverse size exclusion chromatography, scanning electron microscopy, and chromatographic methods. Both butyl methacrylate and ethylene dimethacrylate monomers were incorporated into the monolith as the polymerization time increased, and it resulted in increases in both the flow resistance (decrease in both permeability and total/through pore porosities) and retention factors. The longer polymerization time led to lower relative amounts of free methacrylate functional groups in the monolith, i.e. cross‐linking was enhanced. The increase of the polymerization time from 8 to 12 min significantly reduced the separation efficiency for the retained analyte, whereas an increase in the fraction of the mesoporosity was observed.     

Sub-5-fs real-time spectroscopy of transition states in bacteriorhodopsin during retinal isomerization

By using a sub-5-fs visible laser pulse, we have made the first observation of the vibrational spectra of the transition state during trans-cis isomerization in the retinal chromophore of bacteriorhodopsin (bR(S68). No instant isomerization of the retinal occurs in spite of electron promotion from the bonding pi-orbital to the anti-bonding pi*-orbital. The difference between the in-plane and out-of-plane vibrational frequencies (about 1150-1250 and 900-1000 cm(-1), respectively) is reduced during the first time period. The vibrational spectra after this period became very broad and weak and are ascribed to a "silent state." The silent state lasts for 700-900 fs until the chromophore isomerizes to the cis-C13 = C14 conformation. The frequency of the C = C stretching mode was modulated by the torsion mode of the C13 = C14 double bond with a period of 200 fs. The modulation was clearly observed for four to five periods. Using the empirical equation for the relation between bond length and stretching frequency, we determined the transitional C = C bond length with about 0.01 angstroms accuracy during the torsion motion around the double bond with 1-fs time resolution.     

Facile synthesis of ZnS-AgInS2 solid solution nanoparticles for a color-adjustable luminophore

Nanoparticles of ZnS-AgInS2 solid solution (ZAIS) were synthesized by the thermal decomposition of (AgIn)xZn2(1-x)(S2CN(C2H5)2)4 precursors in a hot oleylamine solution. X-ray powder diffraction analyses revealed that the resulting nanoparticle powders were not a mixture of ZnS and AgInS2 but a ZnS-AgInS2 solid solution in which the fraction of ZnS was enlarged with a decrease in the value of x, that is, an increase in the content of Zn2+ in the precursors used. The energy gap of ZAIS nanoparticles could be controlled by the composition of solid solution. Intense emission was observed at room temperature, regardless of the kind of the particles, the peak wavelength of PL being blue-shifted from 720 to 540 nm with a decrease in the value of x. The highest quantum yield of ca. 24% was obtained for nanoparticles prepared with x = 0.86, which was much higher than the quantum yields reported for I-III-VI2-based semiconductor nanoparticles, such as CuInS2 and ZnS-CuInS2 solid solution.     

Effect of electropolymerization duration on the structure and performance of polypyrrole/graphene nanoplatelet counter electrode for dye-sensitized solar cells

Journal of Solid State Electrochemistry - Despite their potential for use as a low-cost energy-conversion device, dye-sensitized solar cells (DSSCs) have not been widely utilized because they apply...     

Photocatalytic syntheses of azoxybenzene by visible light irradiation of silica-coated cadmium sulfide nanocomposites

Photoirradiation (lambda= 436 nm) of a deaerated 2-propanol aqueous solution containing nitrobenzene and rhodium-loaded silica-coated cadmium sulfide nanoparticles produced azoxybenzene with relatively high selectivity (68%), the photocatalytic activity being enhanced with a decrease in the size of the semiconductor particle core.     

Total synthesis of (-)-brevisin: a concise synthesis of a new marine polycyclic ether

The first and highly efficient total synthesis of (-)-brevisin has been achieved. The title compound was synthesized in only 29 steps (longest linear sequence) from commercially available starting materials. The synthesis provided over 70 mg of a marine polycyclic ether compound.