Isomorphous Fe Substituted ZSM-5 for Methane Dehydroaromatization

Shale gas has become an abundant source of natural gas in recent years; methane is one of its major chemical components. Meanwhile, benzene, which is applied into the manufacturing of complex chemicals, is an important chemical intermediate in petrochemical industry. Direct methane dehydroaromatization (DHA) under non-oxidative condition is an alternative approach to convert methane into benzene. The reaction mechanism is generally considered a synergistic result of metal sites and Bronsted acid sites of HZSM-5. Here, methane is activated by metal site while zeolite provides the shape-selective environment and the diffusion channel for reactive molecules. Among different bi-functional catalysts, Mo/HZSM-5 is the most studied catalyst for this reaction due to its strong catalytic performance. However, coke formation driven by thermodynamics will ultimately lead to catalyst deactivation. This problem is exacerbated by the fact that the catalyst regeneration for Mo/ZSM-5 is relatively lengthy and uneconomical due to its loss of activity after burn-off. Recent reports suggested that atomically dispersed iron on silica can have high conversion of methane to higher hydrocarbon and can potentially suppress coke formation. Our group previously found that highly dispersed iron on ZSM-5, H-(Fe)ZSM-5, also shows high benzene selectivity and reduced coke formation. However, severe coke formation still result from secondary reactions of product on Bronsted acid site of ZSM-5. The purpose of this research is to study how catalytic performance and coke formation are influenced by the catalyst structure of H-(Fe)ZSM-5 and how this structure can be affected by the ZSM-5 synthesis. Specifically, the impact of hydrothermal time, hydrolysis time and template ratio in ZSM-5 synthesis were investigated since these parameters can have influence on both crystallinity and particle size. It is found that both of these structural parameters can have significant influence on catalytic performance. In addition, we found that passivation of external Bronsted acid sites can improve catalyst stability by reducing coke formation but simultaneously also decreases the reactivity. Overall, we developed a well-defined catalyst with high selectivity (~86%) in DHA by optimizing only synthetic parameters without applying any post-treatment

Structured Meta-Mirrors for Beam Spatial Filtering

The work presents optical spatial filtering in reflection based on translationally invariant meta-mirrors. The meta-structure is generated by a thin grating presenting a transverse modulation of the refraction index on the sub-micron scale located in front of a mirror. We analyze the angular spectrum of the reflected waves for different types of structured meta-mirrors as well as the filtering effects of these meta-structures in reflected beams. The comparison between FDTD simulations of full Maxwell equations and different approximated models allows to determine the filtering contribution from the structured cavity and from Mie resonances associated to elements generating the grating.Peer ReviewedPostprint (author's final draft

EFFECT OF ATTACHlNG STRING DAMPERS ON VIBRATION CHARACTERISTICS OF A TENNIS RACKET

The "damper", a small device attached to the tennis racket string-bed, is commonly used by tennis players with little scientific support for its functions. The purpose of this study was to clarify the effect of damper attachment on racket vibration characteristics. Two accelerometers attached at different locations were used to measure racket handle and string-bed vibration patterns with and without a damper. Ball-racket impacts were controlled by releasing the ball abve the racket for producing consistent impact intensity at four different locations. Although amplitudes of spring-bed acceleration could be reduced by the damper, vibration on the racket handle was not affected by the damper

Flat focusing in reflection from a chirped dielectric mirror with a defect layer

Recently, the principle of flat focusing based on one-dimensionally chirped dielectric mirrors has been proposed and experimentally demonstrated. The flat chirped mirror causes anomalous diffraction of the beam during reflection, opposite to the normal diffraction in free space propagation. The anomalous diffraction compensates the normal diffraction of the beam resulting in focusing after reflection. For a better focusing performance and for a larger near-field focal distance, a stronger anomalous diffraction is required. We show that the anomalous diffraction can be enhanced by introducing a defect layer in the chirped mirror, as the structure becomes similar to a Gires-Tournois interferometer. The focal distance can be substantially increased due to the defect layer. In our specific structure, the focal distance shows an increase from 19 to 39 mu m, numerically.Peer ReviewedPostprint (author's final draft

Criterion of Incipient Re-Suspension of Deposition by Density Currents

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Secretory Carcinoma: A Silent Mass Increasing in the Parotid Gland

BACKGROUND: Secretory carcinoma (SC) of the salivary gland, also known as mammary analog secretory carcinoma, is a rare tumor in the parotid gland. This kind of tumor is characterized by generally indolent clinical behavior and expression of a break in the ETV6 gene. CASE REPORT: We present a unique case of secretory carcinoma and show its favorable prognoses. CONCLUSION: Secretory carcinoma of the salivary gland is a low-grade carcinoma with a favorable prognosis. It has low regional lymph node and distant metastasis potential. Due to the possibility of misdiagnosis, immunohistochemical studies and FISH are suggested. The most effective treatment is complete surgical excision with negative surgical margins

Nonlinear photoacoustic microscopy via a loss modulation technique: from detection to imaging

In order to achieve high-resolution deep-tissue imaging, multi-photon fluorescence microscopy and photoacoustic tomography had been proposed in the past two decades. However, combining the advantages of these two imaging systems to achieve optical-spatial resolution with an ultrasonic-penetration depth is still a field with challenges. In this paper, we investigate the detection of the two-photon photoacoustic ultrasound, and first demonstrate background-free two-photon photoacoustic imaging in a phantom sample. To generate the background-free two-photon photoacoustic signals, we used a high-repetition rate femtosecond laser to induce narrowband excitation. Combining a loss modulation technique, we successfully created a beating on the light intensity, which not only provides pure sinusoidal modulation, but also ensures the spectrum sensitivity and frequency selectivity. By using the lock-in detection, the power dependency experiment validates our methodology to frequency-select the source of the nonlinearity. This ensures our capability of measuring the background-free two-photon photoacoustic waves by detecting the 2nd order beating signal directly. Furthermore, by mixing the nanoparticles and fluorescence dyes as contrast agents, the two-photon photoacoustic signal was found to be enhanced and detected. In the end, we demonstrate subsurface two-photon photoacoustic bio-imaging based on the optical scanning mechanism inside phantom samples