Electro-optic transparent frequency conversion of a continuous light wave based on multistage phase modulation

Frequency conversion of a continuous light wave based on multistage phase modulation has been investigated both analytically and numerically. The proposed frequency-conversion process consists of three stages: (i) phase modulation and chirp compression to generate a pulse train, (ii) Doppler shift of the pulse center frequency in a second phase modulation, and (iii) demodulation of the pulse train. By controlling the modulation power we can select the destination frequency from an equally spaced grid separated by the modulation frequency. A conversion efficiency of approximately 40% has been numerically confirmed with respect to a destination frequency of +/- 50 channels. Carrier frequency conversion of an analog data stream is numerically demonstrated.     

Influence of relative humidity on fracture toughness of rock: Implications for subcritical crack growth

Information relating to the fracture toughness of geomaterials is critical to our understanding of tensile fracturing, and in particular in geological and rock engineering projects that are subjected to elevated moisture levels. In this study, we conducted a comprehensive set of fracture toughness tests on a suite of key rock types in air under different relative humidities and at constant temperature in order to investigate the influence of relative humidity on fracture toughness. Three sandstones and two igneous rocks were chosen for this purpose. We show that the value of fracture toughness decreases with increasing relative humidity. In addition, we find that the decrease in fracture toughness was more significant when the expansive clay such as smectite was included in rock. Since smectite is prone to expanding in the presence of water, the strength and thus crack growth resistance decrease when relative humidity is high. Therefore, we interpret the decreasing fracture toughness upon the degradation of expansive clays with increasing water content. It was also shown that the decrease of the fracture toughness with increasing humidity is less significant than the concomitant decrease in the measured value of the subcritical stress intensity factor. This was likely as a result of stress corrosion having little influence on the fracture toughness. We conclude that crack growth in rock is affected by humidity, and that clay content is an important contributing factor to changes in fracture toughness and subcritical stress intensity factor.     

Interfacial electron transfer dynamics in dye-modified graphene oxide nanosheets studied by single-molecule fluorescence spectroscopy

Graphene oxide (GO) nanosheets have received a great deal of attention for a wide range of applications from optoelectronic devices to biological sensors. We now report a mechanistic study of the interfacial electron transfer (ET) processes between organic dye molecule, 9-phenyl-2,3,7-trihydroxy-6-fluorone (PF), and nanometre-sized GO sheets using ensemble-averaged and single-molecule spectroscopies. The ET dynamics was characterized by the direct observation of the PF radical cation during the laser flash photolysis, and its reaction rate was determined to be ~10(11) s(-1). The single-molecule fluorescence spectroscopy was utilized to clarify the heterogeneous nature of the interfacial ET within individual composites. Their fluorescence lifetimes and spectra were found to vary from composite to composite, possibly due to the different local structures and molecular interactions. The autocorrelation analysis of fluorescence intensity trajectories also revealed the temporal fluctuation of the ET reactivity.     

Folding dynamics of cytochrome C using pulse radiolysis

Pulse radiolysis is a powerful method to realize real-time observation of various redox processes, which induces various structural and functional changes occurring in biological systems. However, its application has been mainly limited to studies of the redox reactions of rather smaller biological systems such as DNA because of an undesired reaction due to various free radicals generated by pulse radiolysis. For application of pulse radiolysis to generate plenty of redox reactions of biological systems, selective redox reactions induced by electron pulses have to be developed. In this study, we report that in the presence of the high concentration of the denaturant, guanidine HCl (GdHCl), the selective reduction of the oxidized cytochrome c (Cyt c) takes place in time scales of a few microseconds by the electron transfer from the guanidine radical that is formed by the fast reaction of e(aq)(-) with GdHCl, consequently leading to folding kinetics of Cyt c. By providing insight into the folding dynamics of Cyt c, we show that the pulse radiolysis technique can be used to track the folding dynamics of various biomolecules in the presence of a denaturant including GdHCl.     

Active Site Models for the Cu(A) Site of Peptidylglycine α-Hydroxylating Monooxygenase and Dopamine β-Monooxygenase

A mononuclear copper(II) superoxo species has been invoked as the key reactive intermediate in aliphatic substrate hydroxylation by copper monooxygenases such as peptidylglycine α-hydroxylating monooxygenase (PHM), dopamine β-monooxygenase (DβM), and tyramine β-monooxygenase (TβM). We have recently developed a mononuclear copper(II) end-on superoxo complex using a N-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane tridentate ligand, the structure of which is similar to the four-coordinate distorted tetrahedral geometry of the copper-dioxygen adduct found in the oxy-form of PHM (Prigge, S. T.; Eipper, B. A.; Mains, R. E.; Amzel, L. M. Science2004, 304, 864-867). In this study, structures and physicochemical properties as well as reactivity of the copper(I) and copper(II) complexes supported by a series of tridentate ligands having the same N-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane framework have been examined in detail to shed light on the chemistry dictated in the active sites of mononuclear copper monooxygenases. The ligand exhibits unique feature to stabilize the copper(I) complexes in a T-shape geometry and the copper(II) complexes in a distorted tetrahedral geometry. Low temperature oxygenation of the copper(I) complexes generated the mononuclear copper(II) end-on superoxo complexes, the structure and spin state of which have been further characterized by density functional theory (DFT) calculations. Detailed kinetic analysis on the O(2)-adduct formation reaction gave the kinetic and thermodynamic parameters providing mechanistic insights into the association and dissociation processes of O(2) to the copper complexes. The copper(II) end-on superoxo complex thus generated gradually decomposed to induce aliphatic ligand hydroxylation. Kinetic and DFT studies on the decomposition reaction have suggested that C-H bond abstraction occurs unimolecularly from the superoxo complex with subsequent rebound of the copper hydroperoxo species to generate the oxygenated product. The present results have indicated that a superoxo species having a four-coordinate distorted tetrahedral geometry could be reactive enough to induce the direct C-H bond activation of aliphatic substrates in the enzymatic systems.     

Application of sol-gel derived silica films containing a methyl radical to a slab laser

Films were prepared by dipping slab laser glass into an acid alcoholic solution of tetraethoxysilane and methyltriethoxysilane. Methyltriethoxysilane introduces methyl radicals into the silica film. By introducing methyl radicals and choosing the best mixing ratio, durable, pinhole free films with a low refractive index of 1.38 at 1.054 μm were obtained.

The slab laser, coated with this film had a 1.83 times higher output energy in comparison with an uncoated slab.     

A study on the effect of the source line profile in atomic magneto-optical rotation spectroscopy (AMORS), using a Zeeman-shifted hollow cathode lamp

Summary Using a magnetized hollow cathode lamp as a Zeeman-shifted light source, the effects of the source line profile on the intensity of rotatory radiation and the calibration curve were studied for AMORS (atomic magneto-optical rotation spectroscopy). With the alteration of the source line profile, an increase in the intensity of rotatory radiation by about max. 40% was found. The rollover of the calibration curve could be avoided by selecting the strengths of the magnetic fields applied to the atomizer and the hollow cathode lamp.

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Untersuchung der Wirkung des Linienprofils der Lichtquelle in der magneto-optischen Atomrotations-Spektroskopie (AMORS) mit Hilfe einer Hohlkathodenlampe mit Zeeman-Verschiebung

Zusammenfassung Mit Hilfe einer magnetisierten Hohlkathodenlampe als Lichtquelle mit Zeeman-Verschiebung wurden die Wirkungen des Linienprofils der Lichtquelle auf die Intensität der Rotationsstrahlung und auf die Eichkurve untersucht. Mit Änderung des Linienprofils ergab sich eine Intensitätssteigerung der Rotationsstrahlung bis zu 40%. Abweichungen der Eichkurve konnten durch geeignete Wahl der magnetischen Feldstärken am Atomizer und der Hohlkathodenlampe vermieden werden.

     

Diels-alder reactions of cyclohexadienes derived from decarboxylation of photo[4 + 2]cycloadducts between 4,6-dimethyl-2-pyrone and cyclic olefins

Labile photo [4 + 2] adducts between 4,6-dimethyl-2-pyrone and cyclic olefins reacted with second olefins to give cross adducts, and with acetylenes to afford both bis-adducts and benzene derivatives with the concurrent decarboxylation, respectively. The reaction mechanism of the latter was considered.     

Effect of oxygen on the formation and decay of stilbene radical cation during the resonant two-photon ionization

Formation and decay of radical cations of trans-stilbene and p-substituted trans-stilbenes (S.+) during the resonant two-photon ionization (TPI) of S in acetonitrile in the presence and absence of O(2) have been studied with laser flash photolysis using a XeCl excimer laser (308 nm, fwhm 25 ns). The transient absorption spectra of S.+ were observed with a peak around 470-490 nm. The formation quantum yield of S.+ (0.06-0.29) increased with decreasing oxidation potential (E(ox)) and increasing fluorescence lifetime (tau(f)) of S, except for trans-4-methoxystilbene which has the lowest E(ox) and longer tau(f) among S. The considerable low yield and fast decay in a few tens of nanoseconds time scale were observed for trans-4-methoxystilbene.+ in the presence of O(2), but not for other S.+ . It is suggested that formation of the ground-state complex between trans-4-methoxystilbene and O(2) and the distonic character of trans-4-methoxystilbene.+ with separation and localization of the positive charge on the oxygen of the p-methoxyl group and an unpaired electron on the beta-olefinic carbon are responsible for the fast reaction of trans-4-methoxystilbene.+ with O(2) or superoxide anion, leading to the considerable low yield and fast decay of trans-4-methoxystilbene.+ . The mechanism based on the transient absorption measurement of S.+ during the TPI is consistent with the relatively high oxidation efficiency of trans-4-methoxystilbene among S based on the product analysis during the photoinduced electron transfer in the presence of a photosensitizer such as 9,10-dicyanoanthracene and O(2) in acetonitrile.