50 nm GaAs mHEMTs and MMICs for ultra-low power distributed sensor network applications

We report well-scaled 50 nm GaAs metamorphic HEMTs (mHEMTs) with DC power consumption in the range 1-150 ΜW/Μ demonstrating f<sub>T</sub> of 30-400 GHz. These metrics enable the realisation of ultra-low power (<500 ΜW) radio transceivers for autonomous distributed sensor network applications

Groundwater seepage landscapes from distant and local sources in experiments and on Mars

© 2014 Author(s). Valleys with theater-shaped heads can form due to the seepage of groundwater and as a result of knickpoint (waterfall) erosion generated by overland flow. This ambiguity in the mechanism of formation hampers the interpretation of such valleys on Mars, particularly since there is limited knowledge of material properties. Moreover, the hydrological implications of a groundwater or surface water origin are important for our understanding of the evolution of surface features on Mars, and a quantification of valley morphologies at the landscape scale may provide diagnostic insights on the formative hydrological conditions. However, flow patterns and the resulting landscapes produced by different sources of groundwater are poorly understood. We aim to improve the understanding of the formation of entire valley landscapes through seepage processes from different groundwater sources that will provide a framework of landscape metrics for the interpretation of such systems. We study groundwater seepage from a distant source of groundwater and from infiltration of local precipitation in a series of sandbox experiments and combine our results with previous experiments and observations of the Martian surface. Key results are that groundwater flow piracy acts on valleys fed by a distant groundwater source and results in a sparsely dissected landscape of many small and a few large valleys. In contrast, valleys fed by a local groundwater source, i.e., nearby infiltration, result in a densely dissected landscape. In addition, valleys fed by a distant groundwater source grow towards that source, while valleys with a local source grow in a broad range of directions and have a strong tendency to bifurcate, particularly on flatter surfaces. We consider these results with respect to two Martian cases: Louros Valles shows properties of seepage by a local source of groundwater and Nirgal Vallis shows evidence of a distant source, which we interpret as groundwater flow from Tharsis

Very high performance 50 nm T-gate III-V HEMTs enabled by robust nanofabrication technologies

In this paper, we review a range of nanofabrication techniques which enable the realization of uniform, high yield, high performance 50 nm T-gate III-V high electron mobility transistors (HEMTs). These technologies have been applied in the fabrication of a range of lattice matched and pseudomorphic InP HEMTs and GaAs metamorphic HEMTs with functional yields in excess of 95%, threshold voltage uniformity of 5 mV, DC transconductance of up to 1600 mS/mm and f/sub T/ of up to 480 GHz. These technologies and device demonstrators are key to enabling a wide range of millimeter-wave imaging and sensing applications beyond 100 GHz, particularly where array-based multi-channel solutions are required

Closure to “Time Development of Scour around a Cylinder in Simulated Tidal Currents”

A Discussion Closure to “Time Development of Scour around a Cylinder in Simulated Tidal Currents

Patches in a side-by-side configuration: a description of the flow and deposition fields

In the last few decades, a lot of research attention has been paid to flow-vegetation interactions. Starting with the description of the flow field around uniform macrophyte stands, research has evolved more recently to the description of flow fields around individual, distinct patches. However, in the field, vegetation patches almost never occur in isolation. As such, patches will influence each other during their development and interacting, complex flow fields can be expected. In this study, two emergent patches of the same diameter (D = 22 cm) and a solid volume fraction of 10% were placed in a side-by-side configuration in a lab flume. The patches were built as an array of wooden cylinders, and the distance between the patches (gap width Delta) was varied between Delta = 0 and 14 cm. Flow measurements were performed by a 3D Vectrino Velocimeter (Nortek AS) at mid-depth of the flow. Deposition experiments of suspended solids were performed for selected gap widths. Directly behind each patch, the wake evolved in a manner identical to that of a single, isolated patch. On the centerline between the patches, the maximum velocity U-max was found to be independent of the gap width Delta. However, the length over which this maximum velocity persists, the potential core L-j, increased linearly as the gap width increased. After the merging of the wakes, the centerline velocity reaches a minimum value U-min. The minimum centerline velocity decreased in magnitude as the gap width decreased. The velocity pattern within the wake is reflected in the deposition patterns. An erosion zone occurs on the centerline between the patches, where the velocity is elevated. Deposition occurs in the low velocity zones directly behind each patch and also downstream of the patches, along the centerline between the patches at the point of local velocity minimum. This downstream deposition zone, a result of the interaction of neighbouring patch wakes, may facilitate the establishment of new vegetation, which may eventually inhibit flow between the upstream patches and facilitate patch merger

Aspects of automation in clinical chemistry

Automation has been employed by laboratories to help them cope with an exponentially rising workload during the last two decades. In this thesis examine some of the objectives behind applications of automation to both the analytical and clerical processes within the laboratory. I consider, in particular the application of Critical Path Analysis to the problem of achieving a major priority of any laboratory - a fast turnround time. For the reasons outlined in Chapter 1, in modern clinical biochemistry (chemical pathology) laboratories, staff and equipment are concentrated into fixed sites with large workloads and considerable managerial problems. Control over the diverse and complex sequences of operations performed in dealing with requests for analyses requires an appreciation of the relationship of one activity to another within each sequence. Once the individual activities which contribute directly to the overall turnround time of requests have been identified, attempts can then be made to reduce the duration of elements of the critical path, in the expectation that the total turnround time will then be shortened. I suggest that Critical Path Analysis, one of a family of related management tools, may be applied to the operations within a clinical biochemistry laboratory. The elements of Critical Path Analysis are described in Chapter 1, and applied to the steps necessary to generate an electrolyte profile. In Chapter 2, Critical Path Analysis is used to study the interrelationships between activities performed during analysis of specimens. It is shown that increased sampling rates can directly affect the critical path and some of the work which has resulted in the development of faster, or more suitable analytical equipment within the author's laboratory is presented. Revised Critical Path networks are then used to demonstrate the effects of implementation of such equipment in the rate limiting areas of analysis. I conclude this Chapter by consideration of automated data acquisition and result calculation, and the amount of time which can be saved by these techniques. The 'fine tuning' of analytical results is examined in Chapter 3. Some of the problems associated with an overloaded manual reporting I system in a large clinical biochemistry laboratory are considered, and the network of activities is described. Critical Path Analysis is again used to illustrate the effects on turnround time of transferring clerical activities to a computer system, and the major gains to be made by installing computer terminals in ward areas, despite problems imposed by consideration of confidentiality at remote sites, and limitations on the data which can be printed at such sites. In Chapter 4, attention is drawn to the existence of a finite lower limit to turnround time beyond which no further improvement can be expected, no matter what developments occur in either speed of analysis or efficiency of clerical record handling. The discussion of Chapter 5 briefly considers the radical changes to the present structure of laboratories which might be necessary to further reduce turnround times in Clinical Biochemistry

Near-Bed Turbulent Kinetic Energy Budget Under a Large-Scale Plunging Breaking Wave Over a Fixed Bar

Hydrodynamics under regular plunging breaking waves over a fixed breaker bar were studied in a large-scale wave flume. A previous paper reported on the outer flow hydrodynamics; the present paper focuses on the turbulence dynamics near the bed (up to 0.10 m from the bed). Velocities were measured with high spatial and temporal resolution using a two component laser Doppler anemometer. The results show that even at close distance from the bed (1 mm), the turbulent kinetic energy (TKE) increases by a factor five between the shoaling, and breaking regions because of invasion of wave breaking turbulence. The sign and phase behavior of the time-dependent Reynolds shear stresses at elevations up to approximately 0.02 m from the bed (roughly twice the elevation of the boundary layer overshoot) are mainly controlled by local bed-shear-generated turbulence, but at higher elevations Reynolds stresses are controlled by wave breaking turbulence. The measurements are subsequently analyzed to investigate the TKE budget at wave-averaged and intrawave time scales. Horizontal and vertical turbulence advection, production, and dissipation are the major terms. A two-dimensional wave-averaged circulation drives advection of wave breaking turbulence through the near-bed layer, resulting in a net downward influx in the bar trough region, followed by seaward advection along the bar's shoreward slope, and an upward outflux above the bar crest. The strongly nonuniform flow across the bar combined with the presence of anisotropic turbulence enhances turbulent production rates near the bed

The OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS): Spectral Maps of the Asteroid Bennu

The OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) is a point spectrometer covering the spectral range of 0.4 to 4.3 microns (25,000-2300 cm-1). Its primary purpose is to map the surface composition of the asteroid Bennu, the target asteroid of the OSIRIS-REx asteroid sample return mission. The information it returns will help guide the selection of the sample site. It will also provide global context for the sample and high spatial resolution spectra that can be related to spatially unresolved terrestrial observations of asteroids. It is a compact, low-mass (17.8 kg), power efficient (8.8 W average), and robust instrument with the sensitivity needed to detect a 5% spectral absorption feature on a very dark surface (3% reflectance) in the inner solar system (0.89-1.35 AU). It, in combination with the other instruments on the OSIRIS-REx Mission, will provide an unprecedented view of an asteroid's surface.Comment: 14 figures, 3 tables, Space Science Reviews, submitte