Performance of large-size superconducting coil in 0.21T MRI system

A high-temperature superconductor (HTS) was used on magnetic resonance imaging (MRI) receiver coils to improve image quality because of its intrinsic low electrical resistivity. Typical HTS coils are surface coils made of HTS thin-film wafers. Their applications are severely limited by the field of view (FOV) of the surface coil configuration, and the improvement in image quality by HTS coil is also reduced as the ratio of sample noise to coil noise increases. Therefore, previous HTS coils are usually used to image small in vitro samples, small animals, or peripheral human anatomies. We used large-size HTS coils (2.5-, 3.5-, and 5.5-in mean diameter) to enhance the FOV and we evaluated their performance through phantom and human MR images. Comparisons were made among HTS surface coils, copper surface coils, and cool copper surface coils in terms of the signal-to-noise ratio (SNR) and sensitivity profile of the images. A theoretical model prediction was also used to compare against the experimental result. We then selected several human body parts, including the wrist, feet, and head, to illustrate the advantage of HTS coil over copper coil when used in human imaging. The results show an SNR gain of 200% for 5.5-in HTS coil versus same size copper coils, while for 2.5- and 3.5-in coils it is 250%. We also address the various factors that affect the performance of large size HTS coils, including the coil-to-sample spacing due to cryogenic probe and the coil-loading effect.     

Antibacterial Surface Coatings from Zinc Oxide Nanoparticles Embedded in Poly(N‐isopropylacrylamide) Hydrogel Surface Layers

Despite multiple research approaches to prevent bacterial colonization on surfaces, device‐associated infections are currently responsible for about 50% of nosocomial infections in Europe and significantly increase health care costs, which demands development of advanced antibacterial surface coatings. Here, novel antimicrobial composite materials incorporating zinc oxide nanoparticles (ZnO NP) into biocompatible poly(N‐isopropylacrylamide) (PNIPAAm) hydrogel layers are prepared by mixing the PNIPAAm prepolymer with ZnO NP, followed by spin‐coating and photocrosslinking. Scanning electron microscopy (SEM) characterization of the composite film morphology reveals a homogeneous distribution of the ZnO NP throughout the film for every applied NP/polymer ratio. The optical properties of the embedded NP are not affected by the matrix as confirmed by UV‐vis spectroscopy. The nanocomposite films exhibit bactericidal behavior towards Escherichia coli (E. coli) for a ZnO concentration as low as ≈0.74 μg cm^?2 (1.33 mmol cm^?3), which is determined by inductively coupled plasma optical emission spectrometry. In contrast, the coatings are found to be non‐cytotoxic towards a mammalian cell line (NIH/3T3) at bactericidal loadings of ZnO over an extended period of seven days. The differential toxicity of the ZnO/hydrogel nanocomposite thin films between bacterial and cellular species qualifies them as promising candidates for novel biomedical device coatings.     

Functional Perovskites – From Epitaxial Films to Nanostructured Arrays

Functional perovskite materials gain increasing significance due to their wide spectrum of attractive properties, including ferroelectric, ferromagnetic, conducting and multiferroic properties. Due to the developments of recent years, materials of this type can conveniently be grown, mainly by pulsed laser deposition, in the form of epitaxial films, multilayers, superlattices, and well‐ordered arrays of nanoislands. These structures allow for investigations of preparation–microstructure–property relations. A wide variation of the properties is possible, determined by strain, composition, defect contents, dimensional effects, and crystallographic orientation. An overview of our corresponding work of recent years is given, particularly focusing on epitaxial films, superlattices and nanoisland arrays of (anti)ferroelectric and multiferroic functional perovskites.     

用无线传感器组成无线传感器网络

物联网的愿景之一是能够测量以前从未测量过的变量。无论应用是监视基础设施老化(例如桥梁、隧道或电力传输线的老化),还是实时提供停车及交通信息,都需要无线传感器网络(WSN)提供与有线网络类似的性能,而且适合实际部署。传感器网络要能够扩展至包含大量无线节点,而且在很多情况下,需要跨越很长的距离。     

Experimental validation of the linear drive train for a total artificial heart system

In industrialized countries cardiovascular diseases are the major cause of death. Beside heart transplants, which are a limited option due to the limited number of available human donor hearts, Total Artificial Hearts (TAHs) are the only therapy available for some patients with terminal heart diseases. For various reasons a total implantable artificial heart is desirable, but also sets restrictions in terms of weight and dimensions due to the limited space in the human thorax. Therefore a precise requirement profile is needed for the drive design to provide sufficient force for the blood pump and to avoid oversizing of the drive and to prevent blood damage by overheating.     

Impact of the gain saturation dynamics in semiconductor optical amplifiers on the characteristics of an analog optical link

We evaluate both theoretically and experimentally the gain saturation dynamics of semiconductor optical amplifiers when inserted into an analog optical link. Its impact in terms of radio frequency response, nonlinearity, and noise is investigated. In particular, the frequency response is shown to be a peculiar high-pass filter exhibiting two characteristic frequencies.     

An Advanced Traffic Engineering Approach Based on the Approximate Invariance of Effective Bandwidths

We present a novel shaping algorithm, called effective bandwidth shaper (EBS), which limits passing data streams' effective bandwidths to a pre-defined upper bound. The shaping algorithm is part of the proposed traffic engineering approach for providing quality of service guarantees to the network users. The traffic engineering approach relies on the property, that effective bandwidths do not change when passing a network node, the so called “invariance property” of effective bandwidths. The algorithm's functionality is verified by application to MPEG video traces. Furthermore, the shaping performance is investigated in different network scenarios with reactive TCP traffic. Our performance studies focus on the dependencies of delays and throughputs upon the number of competing connections, the choice of the space parameter, different TCP protocol variants, and buffer sizes. Moreover we show that the effective bandwidths' invariance when passing a switch, as proven for the case of the many limiting regime (infinitely many sources), holds already for a surprisingly small number of competing flows even in the presence of aggressive TCP traffic.     

Embedded resistors and capacitors for organic-based SOP

System-on-package (SOP) architectures take advantage of compact, high-performance designs to place the maximum amount of functionality on a subsystem that can then be mounted on a lower-cost, lower density interconnect board. Embedding passive components is a key technology in achieving these goals since this enables smaller SOP substrate footprints or, equivalently, higher functional density, along with better power distribution, increased design flexibility and improved reliability. The resulting footprint areas of integrating capacitors will have more of an effect on the layer count of SOP assemblies than will integrating resistors due to the rather low specific capacitances of most embeddable dielectrics, but the situation is improving steadily. It may be necessary to use two different dielectric materials to cover the entire required range. The inherently lower parasitic inductance of embedded capacitors makes them much more useful in decoupling than surface mount capacitors, enabling more robust power distribution and decreased power/ground noise. The key to this performance enhancement in large boards is the use of a thin dielectric to decrease the inductance but, for the smaller SOP substrates, the dielectric constant must also be high to provide sufficient decoupling capacitance in the reduced area.     

Superconducting microwave filter systems for cellular telephone base stations

In the second decade following the discovery of high-temperature superconductivity (HTS), wireless communications has emerged as the earliest large commercial market. The enormous growth of the wireless industry coupled with its increasing technology demands has created a significant opportunity for HTS technology in wireless base stations. These systems combine high-performance HTS RF filters with cryocooled semiconductor preamplifiers to offer enhanced sensitivity to improve signal reception and exceptional selectivity to reject interfering signals. There are now thousands of installed HTS systems and the prospects are good for widespread future deployment. This paper discusses the underlying technologies that support HTS wireless applications, based upon the characteristic microwave properties of HTS thin films and substrates. HTS filter design technology has been under development for a decade and has gained a fair measure of maturity in terms of design tools, simulation techniques, and available topologies. The need for extremely narrow-band filters, highly selective filters, frequency-agile filters, and very compact filter designs has led to many technology advances. On the system level, comparable advances in cryocooler technology and cryopackaging have enabled the development of a broadly deployable technology. We discuss industry trends and the methodologies and results of simulations and real-world measurements of HTS filter systems.     

INFLUENCE OF TEMPERATURE AND SOLVENT ON THE PRECIPITATION OF ASPHALTENES

Asphaltenes has been precipitated from a Kuwait flash residue using different n-alkanes (n-C5 to n-C8) at various temperatures ranging from 4^°C to reflux temperatures of the used precipitants. Structures in the asphaltene fractions has been revealed using U.V. fluorescence spectroscopy, elemental analysis and to some extent 1H-nmr. These analysis shows that asphaltenes precipitated in the same amount but at different temperature and with different solvents have merely the same composition. For all n-alkanes the curves of precipitated amount versus temperature show maxima at about 25^°C, implying a shift in the solubility of the asphaltenes.The impact of alkane chain length on the aggregation of asphaltenes through hydrogen bonds is discussed using the alkane-alcohol system as a model. The asphaltene solubility is discussed with the help of the Scatchard-Hildebrand equation.