We have developed membrane distributed Bragg reflector (DBR) lasers on thermally oxidized Si substrate (SiO2/Si substrate) to evaluate the parameters of the on-Si lasers we have been developing. The lasers have InGaAsP-based multi-quantum wells (MQWs) grown on InP substrate. We used direct bonding to transfer this active epitaxial layer to SiO2/Si substrate, followed by epitaxial growth of InP to fabricate a buried-heterostructure (BH) on Si. The lateral p-i-n structure was formed by thermal diffusion of Zn and ion implantation of Si. For the purpose of evaluating laser parameters such as internal quantum efficiency and internal loss, we fabricated long-cavity lasers that have 200- to 600-µm-long active regions. The fabricated DBR lasers exhibit threshold currents of 1.7, 2.1, 2.8, and 3.7mA for active-region lengths of 200, 300, 400, and 600µm, respectively. The differential quantum efficiency also depends on active-region length. In addition, the laser characteristics depend on the distance between active region and p-doped region. We evaluated the internal loss to be 10.2cm-1 and internal quantum efficiency to be 32.4% with appropriate doping profile.

In the present paper, we consider fully asynchronous parallelism in membrane computing, and propose two asynchronous P systems for the satisfiability (SAT) and Hamiltonian cycle problem. We first propose an asynchronous P system that solves SAT with n variables and m clauses, and show that the proposed P system computes SAT in O(mn2n) sequential steps or O(mn) parallel steps using O(mn) kinds of objects. We next propose an asynchronous P system that solves the Hamiltonian cycle problem with n nodes, and show that the proposed P system computes the problem in O(n!) sequential steps or O(n2) parallel steps using O(n2) kinds of objects.

Carbon nanotubes (CNTs) have generated great interest within the many areas of nanotechnology due to their superior and outstanding physical properties. However effective dispersion in many solvents has imposed limitations upon the use of CNTs in a number of novel applications. Functionalization presents a solution for CNTs to be more soluble which make them integrate well into any organic, inorganic or biological systems. CNTs can be easily functionalized using cyclodextrin (CD) treatment. The CD modification of carbon nanotubes is both simple and effective. It requires no prolonged heating, filtration and washing which can severely damage the small diameter nanotubes. The formation of surface functional groups and changes of nanotubes structures of functionalized carbon nanotubes (f-CNTs) were monitored by Fourier transform infrared spectroscopy (FTIR), Thermo gravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM), respectively. From the TGA results, the amount of weight loss of the f-CNTs in varying ratios indicated the amount of CD that was functionalized. It was also noted that the FTIR spectra showed the presence of functional groups associated with CD in the f-CNTs. As a result, the cyclodextrin groups were found to be possibly adsorbed at the surface of the nanotubes walls. The f-CNTs showed substantial solubility in N-methyl-2-pyrrolidone (NMP) which helps in a better distribution of the CNTs in the mixed matrix membrane (MMM) prepared. Hence, the influence of the f-CNTs in the polymer matrix will give rise to enhanced physical properties of the MMM suitable for applications in gas separations.

This letter reports a high-performance Ka-band equilateral triangular microstrip patch (ETMP) antenna suspended on a thin dielectric membrane. The membrane is released using a silicon bulk-micromachining technique. A set of closed-form expressions to calculate the resonant frequency of the proposed antenna on the micromachined substrate is also presented. The measured performance of the antenna structure is verified using the finite element method (FEM) based Agilent High Frequency Structure Simulator (version 5.5). The fabricated antenna exhibited a wide -10 dB return loss bandwidth of 1.2 GHz at 35.4 GHz. The measured antenna cross-polarization level is less than -15 dB in both the E- and H-planes.

A fully integrated broadband distributed frequency tripler, periodically loaded with HBV devices, has been designed and fabricated and has demonstrated the generation of a broad range of output frequencies of up to 570 GHz. Key to the design is the principle that the entire frequency tripler circuit is produced monolithically and incorporates novel HBV devices electrically and mechanically interconnected by a thin low-loss SU-8 membrane. With the device fabrication approach used, the novel HBV devices are able to produce a higher capacitance-voltage swing ratio whilst simultaneously minimizing the device series and contact resistances to achieve the optimum conversion efficiency. The entire concept of this work was to design a cost effective fully integrated waveguide package, with the frequency tripler circuit mounted at the E-plane of a micromachined waveguide which was constructed with stepped height and width to prevent the propagation of higher order modes inside the waveguide sections. The micromachined waveguide sections exhibit high dimensional accuracy and a good surface finish which is necessary for the efficient propagation of high frequency signals. The frequency tripler circuit and the accompanying micromachined waveguide sections are mounted in a specifically designed metal test fixture to form a compact and cost-effective subcomponent with great commercial potential for broadband harmonic generation of up to terahertz frequencies. This paper presents the design methodology and techniques used to produce the frequency tripler package, together with some initial measurement results.

A microwave variable delay line using a membrane impregnated with liquid crystal was newly fabricated. By employing the membrane impregnated with liquid crystal to the liquid crystal layer of the delay line, the phase-shift response becomes fast independently of the liquid crystal thickness. Experimental results show that the phase-shift response time of 33 ms, which is two orders of magnitude faster than that of a conventional one, is obtained. The new delay line also exhibits a 270-degree phase-shift and non-dispersive delay characteristics over a wide microwave-frequency range, although a higher control voltage is needed. It is also clarified that the phase-shift characteristics to the control voltage depend on the pore size of the membrane. This membrane impregnated with liquid crystal also enables us to make the variable delay line thin and flexible.

A black membrane is a biological-membrane analogue, i.e. a phospholipid bilayer membrane, artificially formed on an orifice immersed in water. It is used to investigate the properties of the membrane itself and channels embedded therein. In this paper, microfabrication techniques are applied to fabricate the orifice, and a glass substrate is isotropically etched to define the orifice geometry. The periphery of the orifice was patterned with aminosilane to anchor the membrane. The remainder part was coated with fluorosilane to make the surface hydrophobic and to prevent adsorption of channel-forming molecules. We demonstrated experimentally that a stable and reproducible membrane is easily obtainable using the orifice.

Responses in the Nagumo neural circuit to pulse-train stimulation are studied using the time sequence, phase diagram, Poincare section, return map, firing rate, Lyapunov number and bifurcation diagram. For the mono-stable neuron with an equilibrium point deeper than the maximal point of a tunnel diode curve, main responses are periodic or all-or-none and chaotic responses are rarely observed. For the neuron with an equilibrium point located near the maximal point, the response to one input pulse oscillates after the undershoot and responses to pulse-trains make complex bifurcation structure in the threshold diagram. The ranges of periodic responses are stratified in the diagram. There exist broad regions of chaotic responses and chaos is not a special response of the Nagumo circuit, but it often comes out. The results are different from those obtained from Hodgkin-Huxley equations and the BVP model.

This paper describes the higher-order moment analysis of superposed Markov jumping processes. A superposed Markov jumping process is defined as a linear superposition of a finite number of piecewise constant real valued stochastic process whose value changes are associated with state transitions in an underlying descrete state continuous time Markov process. Some phenomena are modeled well by the process such as membrane current fluctuations observed at bio-membranes or load fluctuations in electrical power systems. Theoretical formula of the moment function of any order k is derived and the parameter estimation problem utilizing higher-order moment functions is discussed. A new method of estimating the kinetic parameters of membrane current fluctuations is proposed as a possible application.

Bifurcations of the periodic solutions of the space-clamped Hodgkin-Huxley equations for the muscle membrane are studied regarding the chloride conductance as a parameter. A limit cycle appears at a Hopf bifurcation and disappears at a homoclinic orbit. With high sodium permeability, a subcritical period doubling bifurcation occurs before it disappears.