Barium-Functionalized Multiwalled Carbon Nanotube Yarns As Low-Work-Function Thermionic Cathodes

Barium-functionalized multiwalled carbon nanotube yarns were fabricated by drawing and twisting multiwalled carbon nanotube forests through a solution containing barium nitrate. After heat activation under vacuum, the functionalized yarns were enriched in barium oxide due to the high surface-to-volume ratio of the nanotubes. The cathodes exhibited good thermionic properties, with a work function as low as 1.73-2.06 eV and thermionic current density that exceeded 185 mA/cm(2) in a field of 850 V/5 mm at 1317 K. The barium-functionalized yarns had high tensile strength of up to 420 MPa and retained strength of similar to 250 MPa after a 2 h activation process. (C) 2008 American Institute of Physics.

Semi-weight function method on computation of stress intensity factors in dissimilar materials

Semi-weight function method is developed to solve the plane problem of two bonded dissimilar materials containing a crack along the bond. From equilibrium equation, stress and strain relationship, conditions of continuity across interface and free crack surface, the stress and displacement fields were obtained. The eigenvalue of these fields is lambda. Semi-weight functions were obtained as virtual displacement and stress fields with eigenvalue-lambda. Integral expression of fracture parameters, K-I and K-II, were obtained from reciprocal work theorem with semi-weight functions and approximate displacement and stress values on any integral path around crack tip. The calculation results of applications show that the semi-weight function method is a simple, convenient and high precision calculation method.

Semi-gas kinetics model for performance modeling of flowing chemical oxygen-iodine lasers (COIL)

A semi-gas kinetics (SGK) model for performance analyses of flowing chemical oxygen-iodine laser (COIL) is presented. In this model, the oxygen-iodine reaction gas flow is treated as a continuous medium, and the effect of thermal motions of particles of different laser energy levels on the performances of the COIL is included and the velocity distribution function equations are solved by using the double-parameter perturbational method. For a premixed flow, effects of different chemical reaction systems, different gain saturation models and temperature, pressure, yield of excited oxygen, iodine concentration and frequency-shift on the performances of the COIL are computed, and the calculated output power agrees well with the experimental data. The results indicate that the power extraction of the SGK model considering 21 reactions is close to those when only the reversible pumping reaction is considered, while different gain saturation models and adjustable parameters greatly affect the output power, the optimal threshold gain range, and the length of power extraction.

Synchronization of modified Chua's circuit with x vertical bar x vertical bar function

This paper considers the chaos synchronization of the modified Chua's circuit with x vertical bar x vertical bar function. We firstly show that a couple of the modified Chua systems with different parameters and initial conditions can be synchronized using active control when the values of parameters both in drive system and response system are known aforehand. Furthermore, based on Lyapunov stability theory we propose an adaptive active control approach to make the states of two identical Chua systems with unknown constant parameters asymptotically synchronized. Moreover the designed controller is independent of those unknown parameters. Numerical simulations are given to validate the proposed synchronization approach.

Microstructure and nanomechanical properties of the wing membrane of dragonfly

Detailed investigations on the microstructure and the mechanical properties of the wing membrane of the dragonfly were carried out. It was found that in the direction of the thickness the membrane was divided into three layers rather than as traditionally considered as a single entity, and on the surfaces the membrane displayed a random distribution rough microstructure that was composed of numerous nanometer scale columns coated by the cuticle wax secreted. The characteristics of the surfaces were accurately measured and a statistical radial distribution function of the columns was presented to describe the structural properties of the surfaces. Based on the surface microstructure, the mechanical properties of the membranes taken separately from the wings of living and dead dragonflies were investigated by the nanoindentation technique. The Young's moduli obtained here are approximately two times greater than the previous result, and the reasons that yield the difference are discussed. (C) 2007 Elsevier B.V. All rights reserved.

Effects of preceding crop and weed control method on weeds and common bean (Phaseoulus vulgaris L.) yield in a no-tillage cropping system

En 1994, se inició un trabajo de investigación el cual se continuo durante tres años, con el objetivo de evaluar el efecto de cultivos antecesores y métodos de control de malezas sobre el rendimiento frijol común ( P h a s e o l u s vulgaris L.) y la dinámica de las malezas. El frijol y los cultivos antecesores fueron sembrados en sistema de cero labranza. Las secuencias de cultivos estudiadas fueron: maíz (Zea mays L), seguido de frijol y frijol seguido de frijol. Se analizaron tres ciclos de los cultivos (1994, 1995 y 1996). La secuencia de cultivo que produjo el máximo rendimiento fue maíz seguido de frijol en 1994, así como también el promedio de rendimiento a través de los años. Por otro lado, los mayores valores de vainas por planta y semillas por vaina se obtuvieron cuando el frijol antecedió al frijol en 1994. Parcelas con controles de malezas mecánico y químico obtuvieron menores densidades y peso seco de malezas y mejores rendimientos que aquellas parcelas en las cuales se controlo la maleza a través de cobertura muerta.

Self-consistent kinetic modeling of electron distribution function in a low-pressure inductively coupled plasma

Based upon the spatially inhomogeneous Boltzmann equation in two-term approximation coupled with electromagnetic and fluid model analysis for the recently developed inductively coupled plasma sources, a self-consistent electron kinetic model is developed. The electron distribution function, spatial distributions of the electron density and ionization rate are calculated and discussed.

Quantum and variational monte-carlo interaction potentials for li2 (x1-sigma-g+)

Optimized trial functions are used in quantum Monte Carlo and variational Monte Carlo calculations of the Li₂(X ¹Σ⁺_g) potential curve. The trial functions used are a product of a Slater determinant of molecular orbitals multiplied by correlation functions of electron—nuclear and electron—electron separation. The parameters of the determinant and correlation functions are optimized simultaneously by reducing the deviations of the local energy E_L (E_L  Ψ⁻¹_THΨ_T, where Ψ_T denotes a trial function) over a fixed sample. At the equilibrium separation, the variational Monte Carlo and quantum Monte Carlo methods recover 68% and 98% of the correlation energy, respectively. At other points on the curves, these methods yield similar accuracies.

Optimization of tried wave-function in quantum monte-carlo method

A method for optimizing tried wave functions in quantum Monte Carlo method has been found and used to calculate the energies of molecules, such as H-2, Li-2, H-3+, H-3 and H-4. Good results were obtained.