Microdroplet generation in gaseous and liquid environments

As trends in biology, chemistry, medicine and manufacturing have pushed macroscopic processes onto the micro scale, droplet generation has been a key factor in allowing these methods to translate. For both surface-based liquid-in-gas generation and lab-on-a-chip-based liquid-in-liquid generation, the ability to create small monodisperse liquid droplets is critically important in constructing reliable and practical devices. This article reviews liquid microdroplet generation in gaseous and liquid environments, covering the general characteristics of generators and the specific methods and technologies used for generation. Furthermore, this study compiles the issues encountered when operating generators, and the measurements and instrumentation used to characterize generated droplets. Applications of droplet generation in printing, analysis, synthesis and manufacturing are also discussed.     

Optimal interval of periodic polarity reversal under automated control for maximizing hydrogen production in microbial electrolysis cells

Microbial electrolysis cells (MECs) are a promising approach for producing hydrogen gas from low-grade substrates with low energy consumption. However, pH increase in a cathode due to proton reduction and thus the need for buffering this pH increase remains a challenge for MEC operation. In this study, a previously reported operational strategy for pH buffer - periodic polarity reversal (PPR) was further studied by developing and applying an automatically control system. The effect of PPR interval on the hydrogen production was investigated and the optimal PPR interval was determined. With an optimal PPR interval of 40 min, the MEC had a significantly low pH increase rate of 0.0085 min^?1 in its cathodes, and this resulted in the highest current density of 1.58 ± 0.02 A m^?2, Coulombic efficiency of 130.3 ± 1.8%, hydrogen production rate of 1.65 ± 0.01 m³ H₂ m^?3d^?1, overall hydrogen recovery of 75.9 ± 0.4%, and energy efficiency relative to the substrate input of 140.8 ± 1.4%. Further analysis suggested that this optimal value of PPR interval was affected by both reaction time and hydrogen supply. When the PPR interval increased from 10 min to 40 min, a longer reaction time helped produce more protons and thus generated a stronger buffer capacity. Beyond 40 min, the mass transfer of the dissolved hydrogen gas could become a limiting factor, leading to a weaker buffer capacity with a longer PPR interval. Those findings have provided an effective pH control strategy with a convenient control system for maximizing hydrogen production in MECs.     

Articulated hybrid mobile robot mechanism with compounded mobility and manipulation and on-board wireless sensor/actuator control interfaces

This paper presents the development of a remotely operated mobile robot system with a hybrid mechanism whereby the locomotion platform and manipulator arm are designed as one entity to support both locomotion and manipulation interchangeably. The mechanical design is briefly described as well as the dynamic simulations used to analyze the robot mobility and functionality. As part of the development, this paper mainly focuses on a new generalized control hardware architecture based on embedded on-board wireless communication network between the robot’s subsystems. This approach results in a modular control hardware architecture since no wire connections are used between the actuators and sensors in each of the mobile robot subsystems and also provides operational fault-tolerance. The effectiveness of this approach is experimentally demonstrated and validated by implementing it in the hybrid mobile robot system. The new control hardware architecture and mechanical design demonstrate the qualitative and quantitative performance improvements of the mobile robot in terms of the new locomotion and manipulation capabilities it provides. Experimental results are presented to demonstrate new operative tasks that the robot was able to accomplish, such as traversing challenging obstacles, and manipulating objects of various capacities; functions often required in various challenging applications, such as search and rescue missions, hazardous site inspections, and planetary explorations.     

Nonlinear Modeling and Control of a Unicycle

A unicycle system is composed of a unicycle and a rider. This system is inherently unstable, but together with a skilled rider can be autonomously controlled and stabilized. A dynamical investigation, a control design and a numerical solution of a nonlinear unicycle autonomous model are presented. The use of a nonlinear model for the control design is shown in this paper to be of great importance. A three-rigid-body physical model was selected for the dynamical study of the system. In a linearized model important physical characteristics of the unicycle system disappear (e.g. interactions between the longitudinal and lateral systems are being neglected), and therefore it is not recommended to be used for the control design. A nonlinear control law, which replaces the rider in stabilizing the model, was derived in the present work, using a nonlinear unicycle model. A simulation study shows good performance of this controller. Time spectral element methods are developed and used for integrating the nonlinear equations of motion. The approach employs the time discontinuous Galerkin method which leads to A-stable high order accurate time integration schemes.     

Optical and electrooptical analysis of GaAs inverted rib phase modulators grown by vapor phase epitaxy

We present experimental and theoretical analysis of GaAs homojunction Schottky barrier phase modulators. The waveguide structures-inverted rib-were grown using the vapor-phase-epitaxy chloride process. These structures are attractive because perfectly planar devices can be realized. Besides that, single-mode operation and low losses can be achieved. The optical (propagation losses, dispersion curves), electrical (electrical field distribution, breakdown voltages) and electrooptical (modulation efficiency) parameters have been calculated using numerical two-dimensional methods. In order to optimize the modulator, various waveguide structures as well as n+ (i.e., substrate) and n- (i.e., waveguide) dopings have been considered in the modeling. Experimental results fit well with the calculated ones. A modulation efficiency of 2.3° . V^-1. mm^-1has been measured. For a completely optimized structure, an efficiency of 4° . V^-1. mm^-1is expected.     

Mechanically based models: Adaptive refinement for B‐spline finite element

This article presents two new methods for adaptive refinement of a B‐spline finite element solution within an integrated mechanically based computer aided engineering system. The proposed techniques for adaptively refining a B‐spline finite element solution are a local variant of np‐refinement and a local variant of h‐refinement. The key component in the np‐refinement is the linear co‐ordinate transformation introduced into the refined element. The transformation is constructed in such a way that the transformed nodal configuration of the refined element is identical to the nodal configuration of the neighbour elements. Therefore, the assembly proceeds as with classic finite elements, while the solution approximation conforms exactly along the inter‐element boundaries. For the h‐refinement, this transformation is introduced into a construction that merges the super element from the finite element world with the hierarchical B‐spline representation from the computational geometry. In the scope of developing sculptured surfaces, the proposed approach supports C⁰ as well as the Hermite B‐spline C¹ continuous shapes. For sculptured solids, C⁰ continuity only is considered in this article. The feasibility of the proposed methods in the scope of the geometric design is demonstrated by several examples of creating sculptured surfaces and volumetric solids. Numerical performance of the methods is demonstrated for a test case of the two‐dimensional Poisson equation. Copyright © 2003 John Wiley & Sons, Ltd.     

Proposal for novel FEL operation

It is shown that free-electron-laser (FEL) operation in a novel wiggler, proposed in a previous paper by the author (1990), is possible. A single-particle approach is used to derive the small-signal gain equation at the fundamental harmonic in this configuration for sufficiently small a_ω. The small-signal gain curve has the same shape as that of the ordinary linearly polarized FEL, but the expressions for the resonance parameter and for the multiplying coefficient in the small-signal gain equation are different. The maximum value of the small-signal gain is proportional to the cube of the interaction region length in the present case, as in the ordinary linearly polarized FEL, but the maximum value of the small-signal gain is greater than that of the ordinary linearly polarized FEL for large enough surface current density     

Vertical currents in microstrip antennas

An analysis of the radiation characteristics of a vertical current inside a dielectric-layer over ground is carried out. The general solution for the fields is given for the case of a vertical current which is independent of the vertical (z) coordinate. An "equivalence-principle" for the replacement of the vertical current by an appropriate surface current is presented. Expressions for the complex input power and for the power which goes into the lowest order transverse magnetic (TM)-type surface-wave mode are derived. In addition, graphs for the case of a short vertical dipole inside a dielectric-layer over ground for the radiation pattern, radiation resistance, and surface-wave resistance are presented. The calculations described above can be applied to the analysis of vertical feeds and short circuits in microstrip antennas.     

Interference of azide in assays of carbohydrates

The effect of sodium azide at concentrations of 0.02% on three carbohydrate assay methods was investigated: it reduced the sensitivity of the phenol-sulfuric acid method for aldoses by 30–35%; the m-hydroxydiphenyl and orcinol methods for galacturonic acid became insensitive. At this level of azide the sensitivity of the orcinol method for neutral sugar, but not for galacturonic acid, could be partially restored by increasing the amount of orcinol in the reaction mixture. The antimicrobial agent thimerosal did not interfere with the phenol-sulfuric acid or m-hydroxybiphenyl methods; with the orcinol method it interfered with the determination of galacturonic acid. This latter problem can be overcome by measuring the absorbance at longer wavelengths or correcting the measurements by an appropriate blank value.     

On the nature of the free edge stress singularity in composite laminated plates

The variational-asymptotic formulation for the edge layer problem is implemented by mixed-hybrid finite elements. This approach is used to analyse the stress singularity at the free edge in composite laminates. Results indicate that the stress singularity (as r → 0) is very closely approximated by log r instead of r^?α.