Sediment dynamics on a steep, megatidal, mixed sand–gravel–cobble beach

Results are presented from a pilot study of shore-face sediment dynamics on a steep, poorly sorted, coarse-grained, megatidal beach at the head of the Bay of Fundy, Nova Scotia, Canada. The experiment involved the first field deployment of a prototype wideband, pulse-coherent, bistatic acoustic Doppler profiling system. Measurements of the vertical structure of flow and turbulence above a sloping bed, as well as bed material velocity, demonstrate the capabilities of this instrument vis-à-vis studies of nearshore sediment dynamics at the field scale. The second focus of the paper is the unexpected observation that the surficial sediment median diameter, across the lower two-thirds of the intertidal zone, underwent a pronounced decrease when wave forcing was more energetic, compared to values observed during calmer conditions. The explanation for this result appears to involve the formation – in wave-dominated conditions – of metre-scale wavelength, 20 cm high ripples on the rising tide, which are then planed flat by the swash and/or the shore break on the subsequent ebb

Bias in mean velocities and noise in variances and covariances measured using a multistatic acoustic profiler: The Nortek Vectrino Profiler

This paper compiles the technical characteristics and operating principles of the Nortek Vectrino Profiler and reviews previously reported user experiences. A series of experiments are then presented that investigate instrument behaviour and performance, with a particular focus on variations within the profile. First, controlled tests investigate the sensitivity of acoustic amplitude (and Signal-to-Noise Ratio, SNR) and pulse-to-pulse correlation coefficient, R2, to seeding concentration and cell geometry. Second, a novel methodology that systematically shifts profiling cells through a single absolute vertical position investigates the sensitivity of mean velocities, SNR and noise to: (a). emitted sound intensity and the presence (or absence) of acoustic seeding; and (b). varying flow rates under ideal acoustic seeding conditions. A new solution is derived to quantify the noise affecting the two orthogonal tristatic systems of the Vectrino Profiler and its contribution to components of the Reynolds stress tensor. Results suggest that for the Vectrino Profiler: 1. optimum acoustic seeding concentrations are ~3,000 to 6,000 mg L-1; 2. mean velocity magnitudes are biased by variable amounts in proximal cells but are consistently underestimated in distal cells; 3. noise varies parabolically with a minimum around the "sweet spot", 50 mm below the transceiver; 4. the receiver beams only intersect at the sweet spot and diverge nearer to and further from the transceiver. This divergence significantly reduces the size of the sampled area away from the sweet spot, reducing data quality; 5. the most reliable velocity data will normally be collected in the region between approximately 43 and 61 mm below the transceiver

Rain-induced turbulence and air-sea gas transfer

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): C07009, doi:10.1029/2008JC005008.Results from a rain and gas exchange experiment (Bio2 RainX III) at the Biosphere 2 Center demonstrate that turbulence controls the enhancement of the air-sea gas transfer rate (or velocity) k during rainfall, even though profiles of the turbulent dissipation rate ɛ are strongly influenced by near-surface stratification. The gas transfer rate scales with ɛ inline equation for a range of rain rates with broad drop size distributions. The hydrodynamic measurements elucidate the mechanisms responsible for the rain-enhanced k results using SF6 tracer evasion and active controlled flux technique. High-resolution k and turbulence results highlight the causal relationship between rainfall, turbulence, stratification, and air-sea gas exchange. Profiles of ɛ beneath the air-sea interface during rainfall, measured for the first time during a gas exchange experiment, yielded discrete values as high as 10−2 W kg−1. Stratification modifies and traps the turbulence near the surface, affecting the enhancement of the transfer velocity and also diminishing the vertical mixing of mass transported to the air-water interface. Although the kinetic energy flux is an integral measure of the turbulent input to the system during rain events, ɛ is the most robust response to all the modifications and transformations to the turbulent state that follows. The Craig-Banner turbulence model, modified for rain instead of breaking wave turbulence, successfully predicts the near-surface dissipation profile at the onset of the rain event before stratification plays a dominant role. This result is important for predictive modeling of k as it allows inferring the surface value of ɛ fundamental to gas transfer.This work was funded by a generous grant from the David and Lucile Packard Foundation and the Lamont-Doherty Earth Observatory Climate Center. Additional funding was provided by the National Science Foundation (OCE-05-26677) and the Office of Naval Research Young Investigator Program (N00014-04-1-0621)

Restoration of biogeomorphic systems by creating windows of opportunity to support natural establishment processes

In degraded landscapes, recolonization by pioneer vegetation is often halted by the presence of persistent environmental stress. When natural expansion does occur, it is commonly due to the momentary alleviation of a key environmental variable previously limiting new growth. Thus, studying the circumstances in which expansion occurs can inspire new restoration techniques, wherein vegetation establishment is provoked by emulating natural events through artificial means. Using the salt-marsh pioneer zone on tidal flats as a biogeomorphic model system, we explore how locally raised sediment bed forms, which are the result of natural (bio)geomorphic processes, enhance seedling establishment in an observational study. We then conduct a manipulative experiment designed to emulate these facilitative conditions in order to enable establishment on an uncolonized tidal flat. Here, we attempt to generate raised growth-promoting sediment bed forms using porous artificial structures. Flume experiments demonstrate how these structures produce a sheltered hydrodynamic environment in which suspended sediment and seeds preferentially settle. The application of these structures in the field led to the formation of stable, raised sediment platforms and the spontaneous recruitment of salt-marsh pioneers in the following growing season. These recruits were composed primarily of the annual pioneering Salicornia genus, with densities of up to 140 individuals/m2 within the structures, a 60-fold increase over ambient densities. Lower abundances of five other perennial species were found within structures that did not appear elsewhere in the pioneer zone. Furthermore, recruits grew to be on average three times greater in mass inside of the structures than in the neighboring ambient environment. The success of this restoration design may be attributed to the combination of three factors: (1) enhanced seed retention, (2) suppressed mortality, and (3) accelerated growth rates on the elevated surfaces generated by the artificial structures. We argue that restoration approaches similar to the one shown here, wherein the conditions for natural establishment are actively mimicked to promote vegetation development, may serve as promising tools in many biogeomorphic ecosystems, ranging from coastal to arid ecosystems

Using micro-bubbles as acoustic targets for large scale fluid flow experiments

There are many times when it is useful to operate or test acoustic profiling and velocity sensors in laboratory facilities. Unfortunately, the often clean, clear water in such facilities provides little or no backscatter for these instruments to operate. Additional scatterers may be introduced in some cases but this can be unpractical in large facilities or may introduce volumes of particulate matter that are unacceptable. In this note, we describe the use of the Dissolved Air Floatation (DAF) method for creating large quantities of microscopic bubbles to serve as acoustic targets. The advantage of the approach is that it is comparatively inexpensive and does not contaminate the water in any way. A limitation of the approach is that bubbles rise through the water and therefore must be continuously produced. The method is demonstrated in the Institute of Ocean Technology - Ice Tank facility which is 12 m wide, 3 m deep, and 90 m long. In this tank, a large plume of bubbles could be injected at mid-depth and would collectively rise to the surface at a speed of 5 to 10 cm s-1. The rise speed for individual 100 \u3bcm bubbles expected from a DAF system is about 1 cm s-1 so it is likely that bubble residence time could be increased by dispersing the bubbles through the water column. \ua9 2011 IEEE.Peer reviewed: YesNRC publication: Ye

Recent developments in panel level packaging

Panel Level packaging (PLP) is one of the latest packaging trends in microelectronics. Besides technology developments towards heterogeneous integration also larger substrates formats are targeted. Fan-out Wafer Level manufacturing is currently done on wafer level up to 12”/300 mm and 330 mm diameter respectively. For higher productivity and therewith lower costs, larger form factors are introduced. Instead of following the wafer level roadmaps to 450 mm, panel level packaging might be the next big step. Upscaling of technology when moving from wafer to panel level as well as the use or adaptation of existing large area tools and materials as e.g. from Printed Circuit Board (PCB) or Liquid Crystal Display (LCD) manufacturing is not possible. Additionally, the missing standardization in sizes is another challenge. Considered panel dimensions ranges from 300x300 mm 2 to 457x610 mm 3 or 510x515 mm 2 up to 600x600 mm 2 or even larger. The paper will describe recent developments along the process chain including materials for carrier selection, encapsulation and redistribution layer as well as the related process and equipment options. Especially the redistribution layer (RDL) application offers a variety of technology options. In addition, main challenges as warpage, die shift and panel handling in PLP will be discussed. However, for industrialization also the understanding of the cost structure and cost opportunities are important - also referring to the different technology options. Therefore, a highly granular cost model is introduced and application scenarios are presented