A High-Precision Quasi-optical Polarizer for Zeeman Splitting Observations

A series of grooved dielectric quarter-wave plates was made for radio astronomical Zeeman splitting observations at millimeter wavelengths. To meet the stringent requirements on reflection and polarization purity, a design method was formulated based on optimization of multiple reflections. The method solves the problem of achieving low reflections for both polarization components while attaining high purity of circular polarization. Several plates have been manufactured, tested, and used successfully for astronomical observations.     

Segmentation of retinal blood vessels by combining the detection of centerlines and morphological reconstruction

This paper presents an automated method for the segmentation of the vascular network in retinal images. The algorithm starts with the extraction of vessel centerlines, which are used as guidelines for the subsequent vessel filling phase. For this purpose, the outputs of four directional differential operators are processed in order to select connected sets of candidate points to be further classified as centerline pixels using vessel derived features. The final segmentation is obtained using an iterative region growing method that integrates the contents of several binary images resulting from vessel width dependent morphological filters. Our approach was tested on two publicly available databases and its results are compared with recently published methods. The results demonstrate that our algorithm outperforms other solutions and approximates the average accuracy of a human observer without a significant degradation of sensitivity and specificity.     

Comparing the growth of a molecular semiconductor on amorphous and semi-crystalline polycarbonate substrates

Polymeric substrates are of importance in plastic electronics. However, polymeric surfaces can exhibit different morphologies depending on whether they are amorphous or semi-crystalline. This work focuses on the impact of the surface structure of bisphenol A polycarbonate substrates on the nucleation and growth of a p-type semi-conductor, namely zinc phthalocyanine (ZnPc). ZnPc films were deposited under high vacuum at different substrate temperatures on oriented semi-crystalline as well as amorphous substrates of PC. The oriented substrates of PC were prepared by a method combining mechanical rubbing and solvent induced crystallization: the substrates show a periodic and regular alternation of oriented crystalline lamellae. Grazing incidence X-ray diffraction shows that the crystalline lamellae of PC have a preferential (a, c) contact plane. Moreover, the substrates show a bilayer structure made of a 60 nm-thick semi-crystalline overlayer atop an amorphous underlayer. UV–vis spectroscopy shows that the polymorphism of the ZnPc films is not modified by the surface structure of the PC substrate (amorphous versus semi-crystalline). However, the statistical analysis of domain size and density versus substrate temperature T_s evidences different apparent activation energies of the growth mechanism. High Resolution Transmission Electron Microscopy suggests that twinning along a (2 ?1 0) plane accounts for the bifurcations of the in-plane b-axis direction of the ZnPc nanocrystals. On oriented substrates of PC, such bifurcations are partly suppressed by the nanocorrugation of the surface, resulting in larger apparent domain sizes and unidirectional in-plane orientation.     

Particle-based simulation of the interaction between fluid and knitwear

We present a particle-based method to simulate and visualize the interaction of knitwear with fluids. The knitwear is modeled using spring-mass systems and the fluid is modeled using the smoothed particle hydrodynamics method. Two-way coupling is achieved by considering surface tension, capillary, and interparticle forces between the fluid and knitwear. The simulation of fluid and knitwear particles is performed on the graphics processing unit. Photorealistic rendering of knitwear and fluid is achieved by using a hardware-accelerated rasterization-based rendering technique. Our method is able to simulate and visualize the macro- and microstructure of free-form knitwear and reflective and refractive characteristics of the fluid surface.     

Quantitative evaluation of three calibration methods for 3-D freehand ultrasound

In this paper, three different calibration methods for three-dimensional (3-D) freehand ultrasound (US) are evaluated. Calibration is the process of estimating the rigid transformation from US image coordinates to the coordinate system of the tracking sensor mounted onto the probe. Calibration accuracy has an important impact on quantitative studies. Geometrical precision can also be crucial in many interventions and surgery. The proposed evaluation framework relies on a single point phantom and a 3-D US phantom which mimics the US characteristics of human liver. Four quality measures are used: 3-D point localization criterion, distance and volume measurements, and shape based criterion. Results show that during the acquisition procedure, volumetric measurements and shapes of the reconstructed object depend on probe motion used, particularly fan motions for which errors are larger. It is also shown that accurate calibration is essential to obtain reliable quantitative information.     

Antenna Array Designs for OFDM WLAN Indoor Transmission

Wireless local area networks (WLAN??s) based on the 802.11 standards are ubiquitous. However, the popularity of WLAN??s has made interference between WLAN users an issue. Spatial division multiple access (SDMA) is one way to orthogonalize these users and reduce interference. The contribution of this paper is to use real antenna array prototypes to determine the best array design for implementing indoor SDMA. Two SDMA antenna array prototypes are constructed and used to collect propagation measurements in an indoor environment. The propagation data is then incorporated into an SDMA orthogonal frequency division multiplexing (OFDM) analysis. This approach is able to very accurately predict how the two array designs will influence SDMA-OFDM performance in the indoor environment where the measurements are collected. The results indicate that the compact sectorized antenna array prototype performs better than the linear array prototype for in-room communication and that the reverse is true for inter-room communication.     

On‐the‐Spot Immobilization of Quantum Dots,Graphene Oxide,and Proteins via Hydrophobins

Class I hydrophobin Vmh2, a peculiar surface active and versatile fungal protein, is known to self‐assemble into chemically stable amphiphilic films, to be able to change wettability of surfaces, and to strongly adsorb other proteins. Herein, a fast, highly homogeneous and efficient glass functionalization by spontaneous self‐assembling of Vmh2 at liquid–solid interfaces is achieved (in 2 min). The Vmh2‐coated glass slides are proven to immobilize not only proteins but also nanomaterials such as graphene oxide (GO) and quantum dots (QDs). As models, bovine serum albumin labeled with Alexa 555 fluorophore, anti‐immunoglobulin G antibodies, and cadmium telluride QDs are patterned in a microarray fashion in order to demonstrate functionality, reproducibility, and versatility of the proposed substrate. Additionally, a GO layer is effectively and homogeneously self‐assembled onto the studied functionalized surface. This approach offers a quick and simple alternative to immobilize nanomaterials and proteins, which is appealing for new bioanalytical and nanobioenabled applications.     

Superparamagnetic Twist‐Type Actuators with Shape‐Independent Magnetic Properties and Surface Functionalization for Advanced Biomedical Applications

Directed nanoparticle self‐organization and two‐photon polymerization are combined to enable three‐dimensional soft‐magnetic microactuators with complex shapes and shape‐independent magnetic properties. Based on the proposed approach, single and double twist‐type swimming microrobots with programmed magnetic anisotropy are demonstrated, and their swimming properties in DI‐water are characterized. The fabricated devices are actuated using weak rotating magnetic fields and are capable of performing wobble‐free corkscrew propulsion. Single twist‐type actuators possess an increase in surface area in excess of 150% over helical actuators with similar feature size without compromising the forward velocity of over one body length per second. A generic and facile combination of glycine grafting and subsequent protein immobilization exploits the actuator's increased surface area, providing for a swimming microrobotic platform with enhanced load capacity desirable for future biomedical applications. Successful surface modification is confirmed by FITC fluorescence.