Quantifying and characterizing contemporary riparian sedimentation

Fluvial processes of erosion, sediment transport and deposition determine the changing form and sedimentary structure of naturally adjusting riparian zones. Riparian sediment storage has both scientific and management importance in relation to: (i) the quantities of sediment that are involved; (ii) the quality of the sediment; and (iii) the dispersal of biological materials, notably the vegetation propagules that are transported and deposited in association with the sediment. After discussing the significance of riparian sedimentation processes, this paper reviews methods for quantifying contemporary sediment deposition within water bodies and their margins. Methods for investigating contemporary riparian sedimentation are given particular emphasis, and the extent to which different methods provide comparable estimates and have been used to support the analysis of different physical and chemical properties of the sediment are outlined. The importance of the following are stressed: (i) selecting a sampling method that is suited to the sedimentation environment; (ii) incorporating careful cross‐calibration if measurements from different methods are to be combined; and (iii) replicating measurements to give more robust estimates if small traps are employed. It is concluded that artificial turf mats provide a useful design of sediment trap across a range of environmental conditions because: (i) their surface roughness reduces problems of sediment removal by flood waters or rainfall; (ii) their pliability permits installation on irregular surfaces; (iii) they can be securely attached to the ground with metal pins to resist high shear stresses from river flows; (iv) they are robust and light and so easily manipulated in the field and laboratory; (v) it is possible to fully recover the deposited sediment to accurately determine the amount of sediment deposited and to support a range of other analyses. Results are presented to illustrate how artificial turf mats can be used to estimate the quantity and quality of deposited sediment and to explore the associated deposition of viable seeds. This provides one example of the important hydroecological role of riparian sedimentation processes and of the potential for the development of innovative, interdisciplinary research on riparian sediment dynamics. Copyright © 2003 John Wiley & Sons, Ltd.     

Measurement and modeling of self-heating in SOI nMOSFET's

Self-heating in SOI nMOSFET's is measured and modeled. Temperature rises in excess of 100 K are observed for SOI devices under static operating conditions. The measured temperature rise agrees well with the predictions of an analytical model and is a function of the silicon thickness, buried oxide thickness, and channel-metal contact separation. Under dynamic circuit conditions, the channel temperatures are much lower than predicted from the static power dissipation. This work provides the foundation for the extraction of device modeling parameters for dynamic operation (at constant temperature) from static device characterization data (where temperature varies widely). Self-heating does not greatly reduce the electromigration reliability of SOI circuits, but might influence SOI device design, e.g., requiring a thinner buried oxide layer for particular applications and scaled geometries     

Thermal conductivity of doped polysilicon layers

The thermal conductivities of doped polysilicon layers depend on grain size and on the concentration and type of dopant atoms. Previous studies showed that layer processing conditions strongly influence the thermal conductivity, but the effects of grain size and dopant concentration were not investigated in detail. The current study provides thermal conductivity measurements for low-pressure chemical-vapor deposition (LPCVD) polysilicon layers of thickness near 1 μm doped with boron and phosphorus at concentrations between 2.0×10¹⁸ cm^-3 and 4.1×10¹⁹ cm^-3 for temperatures from 20 K to 320 K. The data show strongly reduced thermal conductivity values at all temperatures compared to similarly doped single-crystal silicon layers, which indicates that grain boundary scattering dominates the thermal resistance. A thermal conductivity model based on the Boltzmann transport equation reveals that phonon transmission through the grains is high, which accounts for the large phonon mean free paths at low temperatures. Algebraic expressions relating thermal conductivity to grain size and dopant concentration are provided for room temperature. The present results are important for the design of MEMS devices in which heat transfer in polysilicon is important     

Micromachined jets for liquid impingement cooling of VLSI chips

Two-phase microjet impingement cooling is a potential solution for removing heat from high-power VLSI chips. Arrays of microjets promise to achieve more uniform chip temperatures and very high heat transfer coefficients. This paper presents the design and fabrication of single-jets and multijet arrays with circular orifice diameters ranging from 40 to 76 /spl mu/m, as well as integrated heater and temperature sensor test devices. The performance of the microjet heat sinks is studied using the integrated heater device as well as an industry standard 1 cm/sup 2/ thermal test chip. For single-phase, the silicon temperature distribution data are consistent with a model accounting for silicon conduction and fluid advection using convection coefficients in the range from 0.072 to 4.4 W/cm/sup 2/K. For two-phase, the experimental results show a heat removal of up to 90 W on a 1 cm/sup 2/ heated area using a four-jet array with 76 /spl mu/m diameter orifices at a flowrate of 8 ml/min with a temperature rise of 100/spl deg/C. The data indicate convection coefficients are not significantly different from coefficients for pool boiling, which motivates future work on optimizing flowrates and flow regimes. These microjet heat sinks are intended for eventual integration into a closed-loop electroosmotically pumped cooling system.     

Impact of nanotube density and alignment on the elastic modulus near the top and base surfaces of aligned multi-walled carbon nanotube films

The mechanical compliance of vertically aligned carbon nanotube (VACNT) films renders them promising as interface materials that can accommodate thermal expansion mismatch. Here we study the relationship between the detailed morphology and elastic modulus of multi-walled VACNT films with thicknesses ranging from 98 to 1300 μm. A systematic analysis of scanning electron micrographs reveals variations in nanotube alignment and density among samples and within different regions of a given film. Nanoindentation of both top and bottom film surfaces using an atomic force microscope with spherical indenters with radii between 15 and 25 μm provides evidence of the modulus differences. The top surface is shown to have a higher modulus than the base, with out-of-plane modulus values of 1.0–2.8 MPa (top) and 0.2–1.4 MPa (base). The indentation data and microstructural information obtained from electron microscopy are interpreted together using an open cell foam model to account for differences in nanotube alignment and density, which are generally lower at the base and yield predictions that are consistent with the modulus data trends. This work shows that microstructure analysis complements property measurements to improve our understanding of nanostructured materials.     

Convectively driven polymerase chain reaction thermal cycler

We have fabricated a low-cost disposable polymerase chain reaction thermal chamber that uses buoyancy forces to move the sample solution between the different temperatures necessary for amplification. Three-dimensional, unsteady finite element modeling and a simpler 1-D steady-state model are used together with digital particle image velocimetry data to characterize the flow within the device. Biological samples have been amplified using this novel thermal chamber. Time for amplification is less than 30 min. More importantly, an analysis of the energy consumption shows significant improvements over current technology.     

Pathologic prognostic factors for patients with breast carcinoma. Which factors are important

Current technologies can identify subsets of patients who are at greater risk for developing recurrent carcinoma. This article presents conventional and generally accepted pathologic features of breast carcinoma that allow breast carcinoma patients to be placed into low-risk or high-risk categories for recurrence-free or overall survival. Also, the role of flow cytometry, estrogen-progesterone receptor measurement, tumor angiogenesis, and selection oncoprotein expression, such as c-erbB2, are reviewed.