Effects of dissolved gas species on ultrasonic degradation of (4-chloro-2-methylphenoxy) acetic acid (MCPA) in aqueous solution

Sonochemical degradation of MCPA ((4-chloro-2-methylphenoxy) acetic acid) in dilute aqueous solutions was studied using ultrasound with a frequency of 500 kHz. The effect of gas atmosphere on MCPA degradation was investigated in nitrogen (N(2)), air (O(2)/N(2)), oxygen (O(2)), argon (Ar) and Ar/O(2) (60/40% v/v) atmospheres. For sonochemical degradation of MCPA in N(2), air (O(2)/N(2)), O(2) and Ar atmospheres, the rate enhancement of MCPA decomposition by sonolysis was found to be more effective in an O(2)-enriched atmosphere compared to Ar atmosphere. It was considered that a higher amount of oxidants was formed in a higher O(2) partial pressure, which accelerated MCPA decomposition in a radical reaction system. On the other hand, both dechlorination and total organic carbon (TOC) removal rates were higher in Ar atmosphere, compared to those in O(2)/N(2) atmosphere. It was found that, MCPA was most effectively decomposed by sonication in Ar/O(2) (60/40% v/v) atmosphere, with higher rates of decomposition, dechlorination and TOC removal.     

Desulfurization reactions on Ni2P(001) and alpha-Mo2C(001) surfaces: complex role of P and C sites

X-ray photoelectron spectroscopy and first-principles density-functional calculations were used to study the interaction of thiophene, H(2)S, and S(2) with Ni(2)P(001), alpha-Mo(2)C(001), and polycrystalline MoC. In general, the reactivity of the surfaces increases following the sequence MoC < Ni(2)P(001) < alpha-Mo(2)C(001). At 300 K, thiophene does not adsorb on MoC. In contrast, Ni(2)P(001) and alpha-Mo(2)C(001) can dissociate the molecule easily. The key to establish a catalytic cycle for desulfurization is in the removal of the decomposition products of thiophene (C(x)H(y) fragments and S) from these surfaces. Our experimental and theoretical studies indicate that the rate-determining step in a hydrodesulfurization (HDS) process is the transformation of adsorbed sulfur into gaseous H(2)S. Ni(2)P is a better catalyst for HDS than Mo(2)C or MoC. The P sites in the phosphide play a complex and important role. First, the formation of Ni-P bonds produces a weak "ligand effect" (minor stabilization of the Ni 3d levels and a small Ni --> P charge transfer) that allows a high activity for the dissociation of thiophene and molecular hydrogen. Second, the number of active Ni sites present in the surface decreases due to an "ensemble effect" of P, which prevents the system from deactivation induced by high coverages of strongly bound S. Third, the P sites are not simple spectators and provide moderate bonding to the products of the decomposition of thiophene and the H adatoms necessary for hydrogenation.     

Tuning characteristic of flashlamp-pumped dye laser with oxygen

The effect of oxygen in the flashlamp-pumped tunable Rhodamine 6G dye laser is experimentally studied. It becomes clear that the laser tuning range is shifted by adding oxygen in the dye solution.     

First-order probability density function of the laser speckle phase

An expression for the first-order probability density function of the laser speckle phase is analytically derived under the assumption that the speckle field obeys a non-circular, complex Gaussian, random process with a certain correlation between the real and imaginary parts of its complex amplitude. The probability density function of the speckle phase is actually evaluated for various cases and shown three-dimensionally as a function of the standard deviation of random object phase variations. The effect of random object phase variations on the probability density function is also investigated in detail.     

Effect of aberrations on off-axis gaussian beams

The effect of aberrations of an optical system on gaussian beams is analyzed. If an incident position of the beams of the optical system does not coincide with the center of its pupil, the beams suffer from aberrations differently in accordance with the various incident positions. The Strehl definition of the beams is studied as a function of the incident position of the beams and the kind of abberations present in the optical system.     

Partially coherent Fresnel diffraction by a slit aperture. II. Axial intensity distributions

The general formula derived in a previous paper is applied to obtain the intensity distribution along the axis normal to a slit aperture in the Fresnel diffraction field when the spatial mutual coherence function of the illumination over the aperture takes three different forms of correlation. It is shown that the axial intensity distribution of Fresnel diffraction by the slit aperture is effectively influenced by the coherence condition across the diffracting aperture.     

Coherent apodization problems

Apodization problems in coherent imagery of removing the edge ringing effect are proposed by considering the edge shifting phenomenon and the passivity of the optical imaging system and are solved by means of the calculus of variations. The resultant pupil functions and corresponding edge image intensity distributions are presented and discussed.     

Berechnung des charakteristischen Verh?ltnisses von Polypropylen, das chemische Inversionen enth?lt (Kopf-Kopf-und Kopf-Schwanz-Einheiten

Ohne Zusammenfassung     

Velocity measurement of a diffuse object by using time-varying speckles

The relation between the velocity of a moving diffuse object and the mean number of integrated speckles in the certain time interval at the far-field plane of the object is obtained. By using this relation based on the first order statistics of integrated speckles, a new method of measuring the velocity of the diffuse object is proposed and experimentally verified. The first order probability density function of time-integrated speckles is also studied from which the validity of the present method is verified.     

Statistical properties of the sum of two partially correlated speckle patterns

The probability density function and average contrast of the sum of two speckle patterns produced with various intensity ratios and correlation conditions have been experimentally investigated. The experimental results are compared with the theoretical ones obtained by Barakat and Goodman. Comparison shows excellent agreement between the experimental and theoretical results.