Microwave Performance of AlGaN/GaN High-Electron-Mobility Transistors on Si/SiO2/Poly-SiC Substrates

The radiofrequency (RF) performance of AlGaN/GaN high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) on Si-on-poly-SiC (SopSiC) substrates formed by the Smart-Cut^TM process is reported. This provides a low-cost, high-thermal-conductivity substrate for power applications. HEMTs with a 0.5 μm gate length show cutoff frequencies (f _T) of 18 to 27 GHz for gate-to-drain distances of 3 to 32 μm and a maximum frequency of oscillation (f _max) of 43 to 47 GHz. The f _max values are slightly lower than comparable devices on sapphire, SiC or Si alone. This approach looks promising for applications requiring cheap large-area substrates and better thermal management than provided by pure Si substrates alone.     

Enhanced heat exchanger design for hydrogen storage using high-pressure metal hydride – Part 2. Experimental results

Hydrogen storage systems utilizing high-pressure metal hydrides (HPMHs) require a highly effective heat exchanger to remove the large amounts of heat released once the hydrogen is charged into the system. Aside from removing the heat, the heat exchanger must be able to accomplish this task in an acceptably short period of time. A near-term target for this ‘fill-time’ is less than 5 min. In this two-part study, a new class of heat exchangers is proposed for automobile hydrogen storage systems. The first part discussed the design methodology and a 2-D computational model that was constructed to explore the thermal and kinetic behavior of the metal hydride. This paper discusses the experimental setup and testing of a prototype heat exchanger using Ti_1.1CrMn as HPMH storage material. Tests were performed to examine the influence of pressurization profile, coolant flow rate and coolant temperature on metal hydride temperature and reaction rate. The experimental data are compared with predictions of the 2-D model to validate the model, calculate reaction progress and determine fill time. The prototype heat exchanger successfully achieved a fill time of 4 min 40 s with a combination of fast pressurization and low coolant temperature. A parameter termed non-dimensional conductance (NDC) is shown to be an effective tool in designing HPMH heat exchangers and estimating fill times achievable with a particular design.     

Safety approach in the EU test blanket systems design

This paper reveals the safety strategy and approach developed and followed in the design of the two EU TBS describing its objectives, components and implementation. Addressing the safety in the early stage of the conceptual design of nuclear facilities is a well recognized international practice and industrial project-level requirement for the successful completion of the licensing process within expected project cost and schedule. The impact of the early development of the safety approach, its implementation and monitoring in the design of nuclear device like the TBS is not limited to the safety assessment and licensing activities only. Safety approach plays indispensible role in reducing the overall project risk. It infiltrates the entire design process through the unavoidable interfaces between the design features and its safety level. In reality the entire process of the TBS development, design, technological demonstration and implementation is affected by the project team safety culture.     

A replication framework for program‐to‐program interaction across unreliable networks and its implementation in a servlet container

We propose a service replication framework for unreliable networks. The service exhibits the same consistency guarantees about the order of execution of operation requests as its non‐replicated implementation. Such guarantees are preserved in spite of server replica failure or network failure (either between server replicas or between a client and a server replica), and irrespective of when the failure occurs. Moreover, the service guarantees that in the case when a client sends an ‘update’ request multiple times, there is no risk that the request be executed multiple times. No hypotheses about the timing retransmission policy of clients are made, e.g. the very same request might even arrive at different server replicas simultaneously. All of these features make the proposed framework particularly suitable for interaction between remote programs, a scenario that is gaining increasing importance. We discuss a prototype implementation of our replication framework based on Tomcat, a very popular Java‐based Web server. The prototype comes into two flavors: replication of HTTP client session data and replication of a counter accessed as a Web service. Copyright © 2005 John Wiley & Sons, Ltd.     

1D-photonic crystals prepared from the amorphous chalcogenide films

We describe the preparation and optical properties of the 15-layer chalcogenide dielectric mirrors with the first order stop bands in near infrared range. The high refractive index Sb–Se and low refractive index Ge–S layers were deposited on silicon and glass substrates using thermal evaporation method. To centre the stop bands of the prepared chalcogenide mirrors at 1.55 μm, the layer thicknesses, d(Sb–Se) = 117 and d(Ge–S) = 183 nm, were calculated from the quarter wave stack condition. The optical reflectivity measurements revealed the total reflection from the 15-layer chalcogenide mirrors in the range of 1,400–1,600 nm for the unpolarized light with normal incidence. The effect of annealing on the optical properties of the prepared chalcogenide mirrors was studied as well. Using spectral ellipsometry, we examined the angular dependence of the multilayers reflectivity for the light with s- and p-polarization. The preparation of the dielectric mirrors for near infrared region from chalcogenide films seems to be possible exploiting good optical quality of chalcogenide films and their simple deposition.     

Surface modification of hydrogels based on poly(2-hydroxyethyl methacrylate) with extracellular matrix proteins

Infrared attenuated total reflection spectroscopy was used for in situ observation of the deposition of collagen I on poly(2-hydroxyethyl methacrylate-co-methacrylic acid, 2.9%) hydrogels and subsequent attachment of laminin or fibronectin on the collagen surface. While there was no adsorption of collagen dissolved in an acid solution on the hydrogel surface, it deposited on the surface at pH 6.5. The collagen layers with attached laminin or fibronectin were stable on hydrogel surface in physiological solution. The modification with collagen and particularly with collagen and laminin or fibronectin allowed the adhesion and growth of mesenchymal stromal cells and astrocytes on the hydrogel surface.     

Theoretical and experimental study of the effects of spray inclination on two-phase spray cooling and critical heat flux

Experiments were conducted with PF-5052 liquid sprays impacting a 1.0 × 1.0 cm² heated test surface at different inclination angles, flow rates, and subcoolings. Inclination angle had no noticeable effect on the single-phase or two-phase regions of the boiling curve. Maximum CHF was always achieved with the spray impinging normal to the test surface; increasing angle of inclination away from the normal decreased CHF appreciably. Video analysis showed inclined sprays produced lateral liquid film flow towards the farthest downstream region of the test surface. The film liquid provided partial resistance to dryout despite the weak volumetric spray flux in the downstream region. A new theoretical model of the spray’s impact area and volumetric flux proves this decrease is the result of a sharp reduction in the fraction of the test surface area that is directly impacted by the spray. Combining the model and video results with a previous point-based CHF correlation for normal sprays is shown to accurately predict the effects of orientation angle on CHF for different nozzles and operating conditions.     

Evaluation of stability and functionality of BaCe1-xlnxO3-s electrolyte in a wider range of indium concentration

The properties of BaCei-xInxO3-δ(x=0.05,0.10,0.15,0.20,0.25,0.30,0.35,and 0.40)as proton conducting electrolyte are examined.The dense electrolyte is formed aft...     

Microstructure of Ni-Based Self-Fluxing Alloy Coating (PartⅠ)

The microstructure of a Ni-based self-fluxing alloy coating produced by an oxygen-acetylene flame spraying Ni-16.5Cr-3.3B-4.7Si-4. 4Fe-0. 8C system alloy powder onto a common steel substrate was investigated by microanalysis methods. The phases in the coating were observed by SEM and determined by XEDS X-Ray energy spectrum and X-Ray diffraction patterns. Meanwhile, some molecular formulas were calculated.