A new laser Doppler flowmeter prototype for depth dependent monitoring of skin microcirculation

Laser Doppler flowmetry (LDF) is now commonly used in clinical research to monitor microvascular blood flow. However, the dependence of the LDF signal on the microvascular architecture is still unknown. That is why we propose a new laser Doppler flowmeter for depth dependent monitoring of skin microvascular perfusion. This new laser Doppler flowmeter combines for the first time, in a device, several wavelengths and different spaced detection optical fibres. The calibration of the new apparatus is herein presented together with in vivo validation. Two in vivo validation tests are performed. In the first test, signals collected in the ventral side of the forearm are analyzed; in the second test, signals collected in the ventral side of the forearm are compared with signals collected in the hand palm. There are good indicators that show that different wavelengths and fibre distances probe different skin perfusion layers. However, multiple scattering may affect the results, namely the ones obtained with the larger fibre distance. To clearly understand the wavelength effect in LDF measurements, other tests have to be performed.     

Geometric Modeling of Mechanical Parts and Processes

Geometry plays a crucial role in nearly all design and production activities in the discrete goods industries. Curiously, these industries' primary means for specifying geometry—two-dimensional graphics—has not changed significantly for more than a century. Dramatic changes are likely to occur in the next decade, however, because the deficiencies of current methods are retarding the progress of automation and are stimulating the development of new, computationally oriented schemes for handling mechanical geometry.     

Fabrication of polystyrene latex nanostructures by nanomanipulation and thermal processing

The capability to fabricate nanoscale structures is a fundamental step toward realizing the promise and potential of nanotechnology. We report on precise manipulation and thermal processing using 100-nm polystyrene latex nanoparticles. This approach is illustrated by fabricating a three-dimensional nanostructure by using an AFM tip to position nanoparticles and then thermally processing to "sinter" the particles to form a contiguous, stable structure. We suggest that this is a general approach, but the use of polystyrene latex particles offers an advantage of low-temperature processing. Use of polystyrene latex also extends the range of materials for which we have demonstrated manipulation and suggests applications including fluorescent doping and electrically conducting polymers.     

Clipping and Signal Determinism: Two Algorithms Requiring Validation

Two algorithms are proposed for recovering signals subjected to bandpass clipping and related types of nonlinear transformations. Both are based on contraction mapping principles and both seem to work experimentally, but neither has been validated formally. The conditions on signal determinism suggested by the algorithms have interesting practical implications.     

Expected Values of Functions of Quantized Random Variables

The computation of expected values of functions of quantized random variables is treated by sampling theory methods, as an extension of Widrow's work on the statistical theory of quantization. It is shown that such expected values can often be evaluated readily when conditions analogous to Nyquist sampling constraints are satisfied. An example-computation of the autocorrelation of a phase-quantized angle-modulated signal-is provided to illustrate the use of the theory. Other potential areas of application are suggested.     

Compensation of Scanner Creep and Hysteresis for AFM Nanomanipulation

Nanomanipulation with atomic force microscopes (AFMs) for nanoparticles with overall sizes on the order of 10 nm has been hampered in the past by the large spatial uncertainties encountered in tip positioning. This paper addresses the compensation of nonlinear effects of creep and hysteresis on the piezo scanners which drive most AFMs. Creep and hysteresis are modeled as the superposition of fundamental operators, and their inverse model is obtained by using the inversion properties of the Prandtl-Ishlinskii operator. Identification of the parameters in the forward model is achieved by a novel method that uses the topography of the sample and does not require position sensors. The identified parameters are used to compute the inverse model, which in turn serves to drive the AFM in an open-loop, feedforward scheme. Experimental results show that this approach effectively reduces the spatial uncertainties associated with creep and hysteresis, and supports automated, computer-controlled manipulation operations that otherwise would fail.     

CAD/CAM for nanoscale self-assembly

IEEE Computer Graphics and Applications has a long tradition of addressing CAD/CAM problems, a tradition that extends even beyond the well-known special issue on solid modeling. Here, we discuss the conversion of a standard representation for a solid object (for example, a boundary representation) into a set of complex message-passing instructions for manufacturing the object by a distributed system-a swarm of robots. Nanotechnology is currently hampered by a lack of manufacturing processes capable of both high throughput and high resolution. Direct-writing systems such as electron beam or scanning-probe microscopy are serial and slow but achieve high resolution, whereas various lithographic techniques are parallel and fast but typically have resolutions on the order of the tens of nanometers. Self-assembly, that is, the spontaneous assembly of components into the desired structures, is a promising concept that might lead to a revolution in nanomanufacturing.