Couple Stress in a Semi Infinite Medium under the Action of a Dynamic Pressure on the Boundary

Effect of couple-stresses on elastic stress distribution has been investigated in a semi-infinite medium under the action of a dynamic pressure on the boundary. As a particular example this pressure has been assumed to be a pulse of pressure moving uniformly along the boundary. It is found that the effect of couple-stress on shear stresses is predominant on the boundary surface

Rotating light, OAM paradox and relativistic complex scalar field

Recent studies show that the angular momentum, both spin and orbital, of rotating light beams possesses counter-intuitive characteristics. We present a new approach to the question of orbital angular momentum of light based on the complex massless scalar field representation of light. The covariant equation for the scalar field is treated in rotating system using the general relativistic framework. First we show the equivalence of the U(1) gauge current for the scalar field with the Poynting vector continuity equation for paraxial light, and then apply the formalism to the calculation of the orbital angular momentum of rotating light beams. If the difference between the co-, contra-, and physical quantities is properly accounted for there does not result any paradox in the orbital angular momentum of rotating light. An artificial analogue of the paradoxical situation could be constructed but it is wrong within the present formalism. It is shown that the orbital angular momentum of rotating beam comprising of modes with opposite azimuthal indices corresponds to that of rigid rotation. A short review on the electromagnetism in noninertial systems is presented to motivate a fully covariant Maxwell field approach in rotating system to address the rotating light phenomenon.Comment: No figure

A Novice Approach of Designing CMOS Based Switchable Filters for ASP Applications

A switchable filter can be designed and fabricated with the desired range and parameters, materials say quartz substrate for RF MEMS based applications. The mathematical modeling of the resonators using the desired characteristics of the capacitive coupled filters can be implemented with low insertion loss. In order to design this filter, one can employ a PIN diode along with a semi-lumped resonator. This PIN diode has been used so as it performs the function of electronic switching i.e. the activating and deactivating the filter circuit action without any compromise in the overall performance of the circuit. These filters circuit are designed and implemented in a way so that it can accommodate the external quality factor in order to ensure a good impedance match at each band of operation. The most dominant parameters and characteristics of the second order switchable filter realization. In this work, the author has put an effort to discuss the most desired parameters of the various switchable filters. In these filter circuits, CMOS devices has been used to design because of their well accepted features i.e. low power loss and requirement of low input signal for operation in addition to other ones. The performance of the proposed CMOS based switchable filters has been discussed with its simulated results that have been carried out by using pSpice software with 0.18 micron technology. The insertion loss of this circuit is with the acceptable limits i.e. 2.9 dB and a tenability within two desired frequencies

Magnonic Crystal with Two-Dimensional Periodicity as a Waveguide for Spin Waves

We describe a simple method of including dissipation in the spin wave band structure of a periodic ferromagnetic composite, by solving the Landau-Lifshitz equation for the magnetization with the Gilbert damping term. We use this approach to calculate the band structure of square and triangular arrays of Ni nanocylinders embedded in an Fe host. The results show that there are certain bands and special directions in the Brillouin zone where the spin wave lifetime is increased by more than an order of magnitude above its average value. Thus, it may be possible to generate spin waves in such composites decay especially slowly, and propagate especially large distances, for certain frequencies and directions in ${\bf k}$-space.Comment: 13 pages, 4 figures, submitted to Phys Rev

Supercritical Water Gasification: Practical Design Strategies and Operational Challenges for Lab-Scale, Continuous Flow Reactors

Optimizing an industrial-scale supercritical water gasification process requires detailed knowledge of chemical reaction pathways, rates, and product yields. Laboratory-scale reactors are employed to develop this knowledge base. The rationale behind designs and component selection of continuous flow, laboratory-scale supercritical water gasification reactors is analyzed. Some design challenges have standard solutions, such as pressurization and preheating, but issues with solid precipitation and feedstock pretreatment still present open questions. Strategies for reactant mixing must be evaluated on a system-by-system basis, depending on feedstock and experimental goals, as mixing can affect product yields, char formation, and reaction pathways. In-situ Raman spectroscopic monitoring of reaction chemistry promises to further fundamental knowledge of gasification and decrease experimentation time. High-temperature, high-pressure spectroscopy in supercritical water conditions is performed, however, long-term operation flow cell operation is challenging. Comparison of Raman spectra for decomposition of formic acid in the supercritical region and cold section of the reactor demonstrates the difficulty in performing quantitative spectroscopy in the hot zone. Future designs and optimization of SCWG reactors should consider well-established solutions for pressurization, heating, and process monitoring, and effective strategies for mixing and solids handling for long-term reactor operation and data collection

En-route to the fission-fusion reaction mechanism: a status update on laser-driven heavy ion acceleration

The fission-fusion reaction mechanism was proposed in order to generate extremely neutron-rich nuclei close to the waiting point N = 126 of the rapid neutron capture nucleosynthesis process (r-process). The production of such isotopes and the measurement of their nuclear properties would fundamentally help to increase the understanding of the nucleosynthesis of the heaviest elements in the universe. Major prerequisite for the realization of this new reaction scheme is the development of laser-based acceleration of ultra-dense heavy ion bunches in the mass range of A = 200 and above. In this paper, we review the status of laser-driven heavy ion acceleration in the light of the fission-fusion reaction mechanism. We present results from our latest experiment on heavy ion acceleration, including a new milestone with laser-accelerated heavy ion energies exceeding 5 MeV/u

Valence band spectroscopy in V-grooved quantum wires

We present a combined theoretical and experimental study of the anisotropy in the optical absorption of V-shaped quantum wires. By means of realistic band structure calculations for these structures, we show that detailed information on the heavy- and light-hole states can be singled out from the anisotropy spectra {\em independently of the electron confinement}, thus allowing accurate valence band spectroscopy.Comment: To be published in Appl. Phys. Lett. (8 pages in REVTeX, two postscipt figures