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Illuminating a water solution with a focused continuous wave laser produces a strong local heating of the liquid that leads to the nucleation of bubbles, also known as thermocavitation. During the growth of the bubble, the surrounding liquid is expelled from the constraining microfluidic channel through a nozzle, creating a jet. The characteristics of the resulting liquid jet were imaged using ultra-fast imaging techniques. Here, we provide a phenomenological description of the jet shapes and velocities and compare them with a boundary integral numerical model. We define the parameter regime, varying jet speed, taper geometry, and liquid volume for optimal printing, injection, and spray applications. These results are important for the design of energy-efficient needle-free jet injectors based on microfluidic thermocavitation. [ABSTRACT FROM AUTHOR]

Interest in micro-optical components for applications ranging from telecommunications to life sciences has driven the need for accessible, low-cost fabrication techniques. Many microlens fabrication processes are unsuitable for applications requiring 100% fill factor, apertures ~1000 [micro]m with high numerical aperture, and scalability to large areas (e.g., tens of centimeters to meters) with millions of lenses. We report on a flexible, low-cost mold fabrication technique that utilizes a combination of milling and microforging. The technique involves first performing a rough cut with a ball-end mill. Final shape and sag height are then achieved by pressing a sphere of equal diameter into the milled divot. Using this process, we have fabricated molds for rectangular arrays of 1-10,000 lenses with apertures of 25-1600 [micro]m, sag heights of 3-130 [micro]m, interlens spacings of 250-2000 [micro]m, and fill factors up to 100%. Mold profiles have a roughness and figure error of 68 nm and 354 nm, respectively, for 100% fill factor, 1000 [micro]m aperture lenses. The required forging force was modeled as a modified open-die forging process and experimentally verified to increase nearly linearly with surface area. The optical performance of lens arrays injection molded from microforged molds was characterized by imaging the point spread function and was found to be in the range of theoretical values. The process can be easily adapted to lenticular arrays as well. Limitations include milling machine range and accuracy. OCIS codes: 220.4000, 120.4610, 120.6660, 120.6650.

We have developed an instrument for monitoring real-time PCR using fluorescence anisotropy, enabling an assay chemistry in which the fluorescence from a labeled primer elucidates amplification. The instrument holds the sample temperature constant to within [+ or -] 0.03[degrees]C during measurement in the extension phase of each PCR cycle and achieves 0.116 mP FA resolution. Primer conjugation with Alexa-Fluor 488, when compared with other fluorophores, is shown to provide the greatest FA range between primer and product. Comparable reproducibility and linearity of the crossing point for a range of target copy numbers is observed between the FA-based assay run in our instrument and the SYBR green assay run in commercial instrumentation. Reproducibility is also consistent with Poisson-distributed experimental error in aliquoting starting copies, a theoretical limit to instrument/ assay performance.

Wire electrical discharge machining (EDM), with a complementary chemical etching process, is explored and assessed as a method for developing microelectrode array assemblies for intracortically recording brain activity. Assembly processes based on these methods are highlighted, and results showing neural activity successfully recorded from the brain of a mouse using an EDM-based device are presented. Several structures relevant to the fabrication of microelectrode arrays are also offered in order to demonstrate the capabilities of EDM. Index Terms--Brain-machine interface, electrical discharge machining (EDM), intracortical recording, microelectrode array, neural implant.

In holography and speckle interferometry the measurement range is generally limited by the greatest number of fringes that can be resolved in a single image. As a result these techniques have been generally confined to small displacement measurement applications. In the case of out-of-plane measurements one can overcome this limitation by simply adding incremental measurements at individual detector pixels. In the case of in-plane measurements, however, summing incremental measurements is not a straightforward procedure since the interference pattern moves laterally across the detector as the material deforms. We describe a modeling technique based on finite elements which solves this problem. In combination with a full field method such as holography or speckle interferometry, it provides a very sensitive measurement technique with dense spatial sampling and large dynamic range. Experimental results of speckle interferometry operating in transmission to measure in-plane displacements of biological membranes are presented, where total material displacements are of the order of millimeters. The results also demonstrate how the finite strain tensor is calculated analytically from the data at any point on the material. Key words: Speckle, interferometry, finite elements, membranes.

This paper describes an apparatus designed to study large mechanical deformations in biological membranes. The task of mechanically characterizing biological membranes is challenging because of the anisotropic and nonlinear nature of their material properties. The apparatus described here is well suited to the task because it uses speckle interferometry to measure in-plane displacements in a distributed fashion and has multiple degrees of freedom in the applied stress mechanism. In this way few a priori assumptions or restrictions are imposed on the applied stress and strain fields. The interferometer operates in transmission mode to increase the light efficiency of the system since the sample biological membranes are translucent and reflect little light. The experimental results confirm that the strain fields in the biological membranes that are generated in the experiments are highly nonuniform and cannot be properly estimated from a small number of point measurements. Key words: Speckle, interferometry, membranes, mechanical testing.

The physical properties of a porous medium impregnated by a liquid or vapor are dictated in part by the spatial distribution of these phases within the solid host matrix and by physicochemical interactions at the solid-liquid-vapor boundaries. We report on a novel 3-D imaging technique based on the high spatial resolution and chemical specificity of the confocal Raman microscope, which allows for the first time the in situ study and visualization of these processes. Images showing the topology of immiscible liquids (trichloroethylene-water) in a natural porous sandstone demonstrate the potential of the technique and reveal a rich variety of interfacial phenomena.

We present a robust method of phase unwrapping that was designed for use on noisy phase images with arbitrary fringe patterns. The method proceeds by first identifying distinct regions between fringe boundaries in an image and then phase shifting the regions with respect to one another by multiples of 2[Pi] to unwrap the phase. Image pixels are segmented between interfringe and fringe boundary areas by fitting a plane model using least squares to overlapping domains centered on all pixels. The method is tolerant of fringe gradient degradation caused by noise, filtering artifacts, and finite instrumentation bandwidth. Key words: Phase unwrapping, interferometry, speckle, holography, moire.

A microfabrication technology capable of electrodepositing truly three-dimensional metal structures is introduced. Micrometer-scale nickel structures including a multicoiled helical spring have been fabricated. Electrodeposition is localized by placing a sharp-tipped electrode in a plating solution, near a substrate, and applying a voltage. Structures are built by moving the electrode appropriately with respect to the substrate. Vertical deposition rates of 6 [[micro]meter]/s are observed, two orders of magnitude greater than those of conventional electrodeposition. The theory of mass transport to a region of localized field is discussed, and a model of deposition profile is presented. The process can potentially produce submicrometer feature sizes using a range of materials including pure metals, alloys, and polymers.

Traditional approaches in confocal microscopy have focused on techniques to generate volumetric intensity or phase images of an object. In these different imaging modes the scattered optical-field properties depend on local refractive index and absorption, properties not unique to a given material. We report here on a confocal microscope that uses Raman scattered light to generate volumetric chemical images of a material. We designed and built a prototype instrument, called a confocal scanning laser Raman microscope, that combines a confocal scanning laser microscope with a Fourier-transform-Raman spectrometer. The high depth and lateral spatial resolution of the confocal optics design define a volume element from which the Raman scattered light is collected, and the spectrometer analyzes its spectral content. The sample is scanned through the microscope probe volume, and a chemical image is generated based on the content of the Raman spectrum extracted from each scan position in the sample. The results include instrument characterization measurements and examples of confocal chemical imaging. Key words: Confocal chemical imaging, confocal scanning Fourier-transform-Raman microscope, confocal Raman microspectrometer.

The theory underlying a new method for the identification of time-varying systems is described. The method uses singular value decomposition to obtain least-squares estimates of time-varying impulse response functions from an ensemble of input-output realizations. No a priori assumptions regarding the system structure or form of the time-variation are required and there are few restrictions on the input signal. Simulation studies, using a model of time-varying joint dynamics, show that the method can track rapid changes in system dynamics accurately and is robust in the presence of output noise. An application of the method is demonstrated by using it to track dynamic ankle stiffness during a rapid, voluntary, isometric contraction. During the transient phase of the contraction, low-frequency ankle stiffness gain decreased in a manner which could not be described with the second-order model of joint dynamics often used under stationary conditions.