Passively harmonically mode-locked vertical-external-cavity surface-emitting laser emitting 1.1 ps pulses at 147 GHz repetition rate

Coupled-cavity passive harmonic mode-locking of a quantum well based vertical-external-cavity surface-emitting laser has been demonstrated, yielding an output pulse train of 1.5 ps pulses at a repetition rate of 80 GHz and with an average power of 80 mW. Harmonic mode-locking results from coupling between the main laser cavity and a cavity formed within the substrate of the saturable absorber structure. Mode-locking on the second harmonic of the substrate cavity allows a train of 1.1 ps pulses to be generated at a repetition rate of 147 GHz with 40 mW average power. © 2010 American Institute of Physics.

The Stability of a Vertical Single-Walled Carbon Nanotube Under Its Own Weight

It has been reported recently that single carbon nanotubes were attached to AFM tips to act as nanotweezers. In order to investigate its stability, a vertical single-walled carbon nanotube (SWCNT) under its own weight is studied in this paper. The lower end of the carbon nanotube is clamped. Firstly the governing dimensionless numbers are derived by dimensional analysis. Then the theoretical analysis based on an elastic column model is carried out. Two ratios, I.e., the ratio of half wall thickness to radius (t=R) and the ratio of gravity to elastic resilience ($\rho$gR=E), and their influences on the ratio of critical length to radius are discussed. It is found that the relationship between the critical ratio of altitude to radius and ratio of half thickness to radius is approximately linear. As the dimensionless number $\rho$gR=E increases, the compressive force per unit length (weight) becomes larger, thus critical ratio of altitude to radius must become smaller to maintain stability. At last the critical length of SWCNT is calculated. The results of this paper will be helpful for the stability design of nanotweezers-like nanostructures.

On the mechanism of the formation of horizontal cracks in a vertical column of saturated sand

Extended horizontal cracks have! been observed experimentally in a vertical column of saturated sand when a flow of water is forced to percolate upward through it. This paper provides a theory for this phenomenon. It will be shown that the presence of inhomogeneity in permeability along the length of the column is essential for such cracks to develop. It will also be shown that small initial inhomogeneity may be magnified through the transport of the finer component of the sand by percolation. Under certain conditions liquefaction takes place at a section of the sand column causing a crack to initiate and grow there. This theory is found to be in good qualitative agreement with the experimental findings.

An In-Situ Observation On Initial Aggregation Process Of Colloidal Particles Near Three-Phase Contact Line Of Air, Water And Vertical Substrate

The self-assembling process near the three-phase contact line of air, water and vertical substrate is widely used to produce various kinds of nanostructured materials and devices. We perform an in-situ observation on the self-assembling process in the vicinity of the three phase contact line. Three kinds of aggregations, i.e. particle-particle aggregation, particle-chain aggregation and chain-chain aggregation, in the initial stage of vertical deposition process are revealed by our experiments. It is found that the particle particle aggregation and the particle-chain aggregation can be qualitatively explained by the theory of the capillary immersion force and mirror image force, while the chain-chain aggregation leaves an opening question for the further studies. The present study may provide more deep insight into the self-assembling process of colloidal particles.

Role Of Vertical Component Of Surface Tension Of The Droplet On The Elastic Deformation Of Pdms Membrane

Poly(dimethylsiloxane) (PDMS) has been widely used in lab-on-a-chip and micro- total analysis systems (mu-TAS), thus wetting and electrowetting behaviors of PDMS are of great importance in these devices. PDMS is a kind of soft polymer material, so the elastic deformation of PDMS membrane by a droplet cannot be neglected due to the vertical component of the interfacial tension between the liquid and vapor, and this vertical component of liquid-vapor surface tension is also balanced by the stress distribution within the PDMS membrane. Such elastic deformation and stress distribution not only affect the exact measurement of contact angle, but also have influence on the micro-fluidic behavior of the devices. Using ANSYS code, we simulated numerically the elastic deformation and stress distribution of PDMS membrane on a rigid substrate due to the liquid-vapor surface tension. It is found that the vertical elastic deformation of the PDMS membrane is on the order of several tens of nanometers due to the application of a droplet with a diameter of 2.31 mm, which is no longer negligible for lab-on-a-chip and mu-TAS. The vertical elastic deformation increases with the thickness of the PDMS membrane, and there exists a saturated membrane thickness, regarded as a semi-infinite membrane thickness, and the vertical elastic deformation reaches a limiting value when the membrane thickness is equal to or thicker than such saturated thickness. (C) Koninklijke Brill NV, Leiden, 2008.

Reconstructing The Vertical Distribution Of The Aeolian Saltation Mass Flux Based On The Probability Distribution Of Lift-Off Velocity

The probability distribution of lift-off velocity of the saltating grains is a bridge to linking microscopic and macroscopic research of aeolian sand transport. The lift-off parameters of saltating grains (i.e., the horizontal and vertical lift-off velocities, resultant lift-off velocity, and lift-off angle) in a wind tunnel are measured by using a Phase Doppler Particle Analyzer (PDPA). The experimental results show that the probability distribution of horizontal lift-off velocity of saltating particles on a bed surface is a normal function, and that of vertical lift-off velocity is an exponential function. The probability distribution of resultant lift-off velocity of saltating grains can be expressed as a log-normal function, and that of lift-off angle complies with an exponential function. A numerical model for the vertical distribution of aeolian mass flux based on the probability distribution of lift-off velocity is established. The simulation gives a sand mass flux distribution which is consistent with the field data of Namikas (Namikas, S.L., 2003. Field measurement and numerical modelling of acolian mass flux distributions on a sandy beach, Sedimentology 50, 303-326). Therefore, these findings are helpful to further understand the probability characteristics of lift-off grains in aeolian sand transport. (c) 2007 Elsevier B.V. All rights reserved.

Hydrodynamic interaction between two vertical cylinders in water waves

The hydrodynamic interaction between two vertical cylinders in water waves is investigated based on the linearized potential flow theory. One of the two cylinders is fixed at the bottom while the other is articulated at the bottom and oscillates with small amplitudes in the direction of the incident wave. Both the diffracted wave and the radiation wave are studied in the present paper. A simple analytical expression for the velocity potential on the surface of each cylinder is obtained by means of Graf's addition theorem. The wave-excited forces and moments on the cylinders, the added masses and the radiation damping coefficients of the oscillating cylinder are all expressed explicitly in series form. The coefficients of the series are determined by solving algebraic equations. Several numerical examples are given to illustrate the effects of various parameters, such as the separation distance, the relative size of the cylinders, and the incident angle, on the first-order and steady second-order forces, the added masses and radiation-damping coefficients as well as the response of the oscillating cylinder.

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.

Análisis del flujo de la comunicación interna formal (Vertical-Horizontal) en la estructura organizativa de la Facultad de Desarrollo Rural (UNA-FDR) I semestre 2014

La comunicación representa un papel fundamental en las organizaciones, para alcanzar la eficacia y la eficiencia a través de los medios que se utilizan para trasmitir mensajes e información. Por ello la investigación desarrollada muestra un análisis del flujo de la comunicación interna formal en la estructura organizativa de la Facultad de Desarrollo Rural, con la objeto de realizar propuestas que permitan mejorar las relaciones humanas en el campo laboral de los distintos niveles jerárquicos, como también mejorar la eficacia y eficiencia de la comunicación formal y valorar los medios de comunicación utilizados. La investigación desarrollada es no experimental de tipo descriptivo, la selección de la muestra se realizó de forma razonada por conveniencia, definiendo criterios de selección. La recolección de los datos se realizó mediante la técnica de la entrevista dirigida a autoridades y la encuesta a docentes y estudiantes. Los principales hallazgos encontrados evidencian que: Las autoridades, docentes y estudiantes manifiestan que se desarrolla un proceso de comunicación eficaz y eficiente garantizando las tareas y actividades en tiempo y forma haciendo uso de los medios de comunicación adecuados para la transmisión de mensajes e información. Los medios orales y escritos utilizados por las autoridades docentes y estudiantes les han permitido ser eficientes. Los medios de comunicación utilizados con mayor frecuencia en los diferentes niveles jerárquicos son el correo electrónico personal, comunicación espontánea y las cartas.