The design of a tool-tip mounted cMUT (capacitive micromachined ultrasonic transducer) micro-array for near field imaging of the retina is undertaken. For intra-vitreal applications, a uniformly excited N×N transducer array is limited to a size of 2mm × 2mm. The physical parameters of the array are constrained by the imaging requirements of a 2 μm resolution and a distance of 400 μm from the retinal surface. The mechanical and electrical parameters of the cMUT are calculated using a combination of the Mason equivalent circuit model and finite element techniques. Optimal transmit power and receive sensitivity for this imaging application are obtained by coupling the transducer model to a pseudo-spectral wave propagation model. The pseudo-spectral method is used to calculate the frequency dependent attenuation of the transmitted acoustic pulse through the vitreous and retinal media. The subsequent reflected wavefront is used to optimize the array transmit power and sensitivity.

An alternative technique for modeling MESFET's for calculation of intermodulation responses is presented. This algorithm not only characterizes the I/V characteristics of the device, but also the derivatives are accurately modeled. The method proposed utilizes a feed-forward neural network using the back-propagation method with the Levenberg-Marquardt (LM) algorithm. The advantage of this technique is that it can be used for both MESFET and HEMT devices. Furthermore, the need to extract fitting parameters is not required. This approach is truly independent of device process and technology, and can therefore be applicable to FET devices from SiC, GaN, GaAs and InP. Excellent agreement is observed between the neural network model and measured I/V data and I/V derivatives up to the 8th order. The I/V derivative evaluation was performed in Agilent's Advance Design Systems.

MOTIVATION: With the generation of a wealth of information, detailing cellular components, their functions and interactions, there is a growing need for the development of new computational tools capable of interpreting these data within spatial and dynamic contexts. Here, we introduce Cell++, a novel stochastic simulation environment with the capacity to study a wide variety of biochemical processes within a spatial context. RESULTS: Focusing on three case studies, we highlight the potential impact of spatial organization in the evolution and engineering of signaling and metabolic pathways. In addition to altering signaling and metabolic efficiency, simulations also demonstrated features consistent with the phenomenon of metabolic channeling. AVAILABILITY: Cell++ is licensed under the GNU general public license (GPL) and has been successfully implemented under Linux and IRIX operating systems. Source code together with a simple tutorial is available at http://www.compsysbio.org/CellSim/.

This investigation features a low-cost (<$100) 1.413-GHz handheld microwave radiometer for use in educating students about microwave radiometry. The microwave radiometer presented is a conventional Dicke radiometer, but fabricated on low-cost printed-circuit board (PCB) material using inexpensive commercial off-the-shelf (COTS) parts. The instrument antenna is a rectangular horn fed by a stacked-patch probe-fed element. With a total weight of just about 2 kg (4 lbs) and a targeted overall cost of under US$100, the handheld radiometer presents several educational potentials in Earth and Sun science applications: primarily as a handy scientific tool for surface soil moisture measurements, and secondarily as a miniature solar radio telescope.