Internal Wavelengths Research Articles

A Seasonal Harmonic Model for Internal Tide Amplitude Prediction

AbstractWe present an empirical model of the seasonal variability of the internal tide using seasonal harmonics to modulate the amplitude of the fundamental tidal constituents. Internal tide data, from both long‐term, in‐situ moorings and a mesoscale‐resolving and internal tide‐resolving ocean model, are used to demonstrate the performance of the seasonal harmonic model for the Indo‐Australian Basin region. The seasonal model describes up to 15% more of the observed (baroclinic) sea surface height variance than a fixed‐amplitude harmonic model at the mooring sites. The ocean model results demonstrate that the study region, which includes the Australian North West Shelf (NWS), Timor Sea, and southern Indonesian Islands, is dominated by standing wave interference patterns due to the presence of multiple generation sites. The seasonal harmonic model reveals that temporal shifts in the standing wave patterns coincide with seasonal variations in density stratification. This shift is particularly evident within distances of 2–3 internal wave lengths from strong generation sites. The fraction of the variance of the internal tide signal explained by seasonal modulations is largest in standing wave node regions, contributing to differences in predictive skill of the seasonal harmonic model at two moorings separated by only 38 km. Output of the harmonic model also demonstrates that the seasonally evolving internal tide propagating southward from Lombok Strait had a small amplitude in October when shear from the Indonesian Throughflow was strongest.

Modelling Internal Tides in the Strait of Canso

ABSTRACT A three-dimensional regional circulation model is used to investigate the internal M2 tide structure in the Strait of Canso located in eastern Nova Scotia, Canada. The embayment, an active shipping port, was found to have M2 baroclinic velocities occasionally reaching 0.15 m s−1 and typically faster than the barotropic tide. An internal tide spatial structure develops, characterized by the first vertical mode, and highly sensitive to the details of stratification. A region near the mouth of the Strait, with a strong cross-bathymetry barotropic flow was identified as the main generating site. The regular “canyon-like” features of the Strait concentrate the energy towards the bottom and head and, under favourable conditions, reflect energy from the head, forming a standing wave. The modelling study found that, although some internal tide is generated year-round, only summer stratification conditions were favourable for standing wave development because of both increased internal energy levels and longer wavelengths capable of transporting the energy farther up the Strait. A balanced internal energy budget for the area highlights a tendency towards local dissipation and enhanced mixing rates. Persistent convection cells and upwelling zones suggest possible impacts on biological activity, sediment, and oil spill dynamics in the region. The findings are validated with current meter and water level observations.

Response of small sharks to nonlinear internal waves

AbstractPlankton and nekton may respond passively or actively to large‐amplitude, nonlinear internal waves (NLIW), with periods and wavelengths on the order of minutes and hundreds of meters, and the NLIW can cause direct or indirect changes in distribution. NLIW are ubiquitous in the coastal ocean, but understanding the influence of NLIW on organism response and distribution is challenging, because of NLIW unpredictability, short temporal and spatial scales, and the difficulty in resolving the biological response. Measurements of currents, temperature, and shark acoustic traces in Massachusetts Bay were used to evaluate the short‐term response of individuals as well as the mean effects on the distribution of an aggregation of small sharks, Squalus acanthias. In two NLIW events, we detected 527 and 3240 shark traces. Individuals moved up and down in response to the currents associated with the sinking and rising of the thermocline. However, mean distribution deepened during one of the events, suggesting that organisms did not merely move in concert with the thermocline oscillation, but that sharks instead might have responded actively. Measurements of vertical currents and shark's depth change during one of the NLIW events indicate that with downward currents (sinking of the thermocline), the sharks tend to react passively. However, in response to the fastest upward currents, sharks appeared to swim down, supporting an active response in the rising phase of the wave. NLIW and other high‐frequency processes can have a profound influence on the distribution of pelagic organisms, yet their ecological consequences remain largely unaccounted for.

Internal Solitary Waves in the Andaman Sea: New Insights from SAR Imagery

The Andaman Sea in the Indian Ocean has been a classical study region for Internal Solitary Waves (ISWs) for several decades. Papers such as Osborne and Burch (1980) usually describe mode-1 packets of ISWs propagating eastwards, separated by distances of around 100 km. In this paper, we report on shorter period solitary-like waves that are consistent with a mode-2 vertical structure, which are observed along the Ten Degree Channel, and propagate side-by-side the usual large mode-1 solitary wave packets. The mode-2 waves are identified in TerraSAR-X images because of their distinct surface signatures, which are reversed when compared to those that are typical of mode-1 ISWs in the ocean. These newly observed regularly-spaced packets of ISW-like waves are characterized by average separations of roughly 30 km, which are far from the nominal mode-1 or even the mode-2 internal tidal wavelengths. On some occasions, five consecutive and regularly spaced mode-2 ISW-like wave envelopes were observed simultaneously in the same TerraSAR-X image. This fact points to a tidal generation mechanism somewhere in the west shallow ridges, south of the Nicobar Islands. Furthermore, it implies that unusually long-lived mode-2 waves can be found throughout the majority of the fortnightly tidal cycle. Ray tracing techniques are used to identify internal tidal beams as a possible explanation for the generation of the mode-2 solitary-like waves when the internal tidal beam interacts with the ocean pycnocline. Linear theory suggests that resonant coupling with long internal waves of higher-mode could explain the longevity of the mode-2 waves, which propagate for more than 100 km. Owing to their small-scale dimensions, the mode-2 waves may have been overlooked in previous remote sensing images. The enhanced radiometric resolution of the TerraSAR-X, alongside its wide coverage and detailed spatial resolutions, make it an ideal observational tool for the present study.

Acoustic mode based internal tide tomography from the PhilSea 2009 experiment

The Philippine Sea 2009 experiment transmitted low frequency broadband sound pulses to a mode resolving array located at 185 km. The entire experiment was conducted over a period of one month, during which, most of the transmissions took place every 5 min, and the rest every 3 h. This talk estimates the travel times of the mode pulses and inverts them for the internal tide induced sound speed variability across the propagation path. A first order perturbation theory approach models mode travel times as range-averaged function of the sound speeds. Depending on the propagation distance, the contributions from some internal tide wavelengths are enhanced while others suppressed in the mode travel times. The talk shows the month-long time-series of the mode peak arrival times and estimates a spectrum for the observations. The presentation then derives an expression to relate the spectral components of the mode arrival times in terms of the internal tide spatial wavenumbers. The magnitude of the arrival time spectral components at the tide frequencies are used to invert for the respective internal tides across the propagation path. The tomographic inverse for the internal tides are compared with CTD measurements at the receiver and the source arrays.

Silicon‐Modified Rare‐Earth Transitions—A New Route to Near‐ and Mid‐IR Photonics

Silicon underpins microelectronics but lacks the photonic capability needed for next‐generation systems and currently relies on a highly undesirable hybridization of separate discrete devices using direct band gap semiconductors. Rare‐earth (RE) implantation is a promising approach to bestow photonic capability to silicon but is limited to internal RE transition wavelengths. Reported here is the first observation of direct optical transitions from the silicon band edge to internal f‐levels of implanted REs (Ce, Eu, and Yb); this overturns previously held assumptions about the alignment of RE levels to the silicon band gap. The photoluminescence lines are massively redshifted to several technologically useful wavelengths and modeling of their splitting indicates that they must originate from the REs. Eu‐implanted silicon devices display a greatly enhanced electroluminescence efficiency of 8%. Also observed is the first crystal field splitting in Ce luminescence. Mid‐IR silicon photodetectors with specific detectivities comparable to existing state‐of‐the‐art mid‐IR detectors are demonstrated.

Dynamic response of density-stratified fluid in a submarine rectangular trench

Interfacial waves under various wave conditions are numerically and experimentally investigated within a submarine rectangular trench. The three-dimensional numerical model Truchas is employed to trace the free surface and the interfacial motion using the volume of fluid method. The free surface and interfacial motion are measured using a CCD camera to validate the model. Both the numerical and experimental results show two types of interfacial motion, namely, partial standing wave patterns and traveling wave patterns. The numerical model is then employed to study the mechanisms of the different modes of interfacial motions (partial standing/traveling waves) and their corresponding amplification factors (external/internal modes). It is shown that the partial standing wave patterns are easily generated when the motion of the surface waves is 180° out of phase at the two sides of the trench. However, the existence of partial standing wave patterns does not mean partial standing internal waves occur. The partial standing internal waves are triggered as internal wave wavelengths reach resonant condition. Furthermore, the ratio of the interface wave height to the surface wave height decreases with wave nonlinearity, suggesting that the nonlinear effect may significantly change the interfacial wave motion. Finally, it is found that the excited pairs of counter-rotating vortices around the interfacial wave can induce a large velocity in the lower layer for the internal mode, indicating that bottom erosion can be enhanced in this manner.

Number of tunable wavelength converters and internal wavelengths needed for cost‐effective design of asynchronous optical packet switching system with shared or output fibre delay line buffer

Optical packet switching (OPS) is being considered as one of the switching technologies for a future optical internet. For contention resolution in an optical packet switching (OPS) system, the wavelength dimension is generally used in combination with a fibre delay line (FDL) buffer. In this study, the authors propose to reduce the number of tunable wavelength converters (TWCs) by sharing TWCs for cost-effective design of an asynchronous OPS system with a shared or an output FDL buffer. Asynchronous and variable-length packets are considered in the OPS system design. To investigate the number of TWCs needed for the OPS system, an algorithm is proposed, which searches for an available TWC and an unused internal wavelength, as well as an outgoing channel. This algorithm is applied to an OPS system with a shared or an output FDL buffer. Also, the number of internal wavelengths (i.e. the conversion range of the TWC) needed for an asynchronous OPS system is presented for cost reduction of the OPS system.

Internal Solitary Waves in the Brazilian SE Continental Shelf: Observations by Synthetic Aperture Radar

We present an analysis of internal solitary waves (ISWs) on the SE Brazilian continental shelf using a set of Envisat/ASAR satellite images. For the 17-month observation period, 467 ISW packets were detected. Most of observed solitons were associated to 4–6 ms-1 wind. The number of ISW packets shows a seasonal signal with a peak in summer, with higher concentration in the outer shelf in all seasons, followed by midshelf during the summer. Propagation direction of ISWs was predominantly onshore with packets separated by typical M2 internal tide wavelengths (~10–40 km). The highest values of the barotropic tidal forcing F are concentrated at the shelf break between 200 and 500 m isobaths. These characteristics suggest that ISWs are formed from nonlinear disintegration of internal tides generated at the shelf break that propagate shoreward as interfacial internal waves. No significant change in the number of ISWs from spring to neap tides was observed in spite of significant tidal current variation (60%). Even not being a region of strong tides, this study shows that ISWs are a frequent and widespread feature, possibly playing a significant dynamic role, affecting biological production, sediment dispersion, and transport.

An Optical Packet Switch with a Limited Number of TWCs and Internal Wavelengths for the Hybrid Buffer

A hybrid buffer structured optical packet switch and its scheduling algorithm are presented for a limited number of tunable wavelength convertors (TWCs) and internal wavelengths. The hybrid buffer consists of the fiber delay line (FDL) buffer and the electronic buffer. With the proposed algorithm, it could lead realizable packet loss reduction that the LAUC-VF algorithm with only the FDL buffer does not reach. Also, we optimized the number of TWCs and internal wavelengths of the hybrid buffer structured OPS. For the fully shared TWC structure, the optimum number of TWCs and internal wavelengths to guarantee minimum packet loss is evaluated to prevent resource waste under the hybrid buffer.

Space borne SAR observations of oceanic internal waves in North Bay of Bengal

Sea surface manifestations of internal waves (IW) in the shallow continental shelf waters of North Bay of Bengal have been observed in almost all seasons imaged by Synthetic Aperture Radar (SAR) images of ERS1/2 and Envisat ASAR missions during the period 1993–2004. Shoreward propagating short-period IW packets are observed particularly in summer stratified coastal waters Off Chilka region. In summer waters, prominent short-period shoreward propagating internal waves of consecutive imageries of ERS-1/2 SAR (12th and 13th April 1996) are studied. On 4th October 2003, Envisat ASAR imaged strong surface manifestations of huge internal wave group wavelengths and those propagations were discussed in detail. In the research, we also made an attempt for temporal distribution of IW signatures on SAR in North Bay of Bengal.

Improving the High-Performance Inductively Coupled Plasma Optical Emission Spectrometry Methodology through Exact Matching

Exact matching is investigated as a means of improving high-performance inductively coupled plasma optical emission spectrometry (HP-ICP-OES), a technique developed at the National Institute of Standards and Technology (NIST) to enable elemental determinations with relative expanded uncertainty of approximately 0.2% expressed at 95% confidence. "Exact matching" refers to the very careful matching of analyte mass fractions, internal standard mass fractions, and matrix compositions among the calibration and unknown sample solutions prepared for an analysis. Computer spreadsheet modeling results and laboratory data involving 16 pairs of analyte and internal standard wavelengths show that exact matching of analyte and internal standard mass fractions mitigates imprecision and bias that can be caused by even subtle nonlinearity in the ICP-OES instrument response. Laboratory experiments also demonstrate matrix effects caused by small variations in acid composition and by mass fractions of Na less than 4 mg kg(-1), emphasizing the need for exact matching of matrix compositions. HP-ICP-OES analyses performed at NIST with and without exact matching illustrate that exact matching enables relative expanded uncertainties to be halved to approximately 0.1%.

A QoS optical packet switching system: architectural design and experimental demonstration [Topics in Optical Communications

Optical packet switching has been considered a prominent paradigm for future WDM networks to efficiently support a multitude of applications with diverse quality of service requirements. In this article we present the architectural design and experimental demonstration of a 10 Gb/s QoS optical packet switching system (QOPSS) for WDM networks. It embodies a set of many-to-one space switches, each of which handles the switching solely for a cluster of wavelengths. With the cluster-based optical switch design, QOPSS trades off limited statistical multiplexing gains for higher system scalability. By many-to-one, multiple packets that are carried by different internal wavelengths are scheduled to switch to the same output port but receive different delays afterward. QOPSS adopts downsized feed-forward optical buffers, yielding drastic reduction in packet loss probability in an economical manner. Significantly, through using four-wave-mixing wavelength converters at the output section, QOPSS permits optical packet preemption, thus achieving effectual QoS differentiation. The article presents both simulation and experimental testbed results to demonstrate the feasibility and superior packet loss/QoS performance of the system.

Pseudo-Banyan Optical WDM Packet Switching System With Near-Optimal Packet Scheduling

We present a novel pseudo-Banyan optical packet switching system (SBOPSS) for optical wavelength division multiplexing (WDM) networks. The system includes a group of pseudo-Banyan space switches together with single-stage downsized fiber-delay-line-based optical buffers. SBOPSS is scalable, with the result that each pseudo-Banyan space switch performs packet switching only for a cluster of wavelengths. The downsized optical buffers that are shared by output ports via the use of a small number of internal wavelengths result in efficient reduction in packet loss. Essentially, SBOPSS employs a packet scheduling algorithm, referred to as the parallel and incremental packet scheduler (PIPS). Given a set of newly arriving packets per time slot, PIPS determines a maximum number of valid paths (packets) to be scheduled with the current buffers’ state taken into account. The algorithm aims at maximizing the system throughput subject to satisfying three constraints, which are switch-contention free, buffer-contention free, and sequential delivery. Significantly, we prove that PIPS is incremental in the sense that the computed-path sets are monotonically nondecreasing over time. We then propose a hardware parallel system architecture for the implementation of PIPS. As is shown, PIPS achieves a near-optimal solution with an exceptionally low computational complexity, O(∣P∣×log2(NMW)), where P is the newly-arriving-packet set, N the number of input ports, and M and W the numbers of internal and external wavelengths, respectively. From simulation results that pit the PIPS algorithm against four other algorithms, we show that PIPS outperforms these algorithms on both system throughput and computational complexity.

Determination of trace elements in liquid aspartame sweeteners by ICP OES and ICP-MS following acid digestion

In order to determine inorganic constituents and contaminants in liquid aspartame sweeteners, different brands of this product were analyzed by ICP OES and ICP-MS. The samples were submitted to acid digestion and parameters such as internal standardization and wavelengths, in the case of ICP OES, and a recovery test were evaluated. The analytes studied were As, Ca, Cd, Co, Cu, K, Fe, Mg, Mn, Na, Ni, Pb, Se and Zn. Since there is not a certified reference material for sweeteners, the accuracy of the proposed method was evaluated by recovery tests and the values were in the range of 90–110% for the majority of the analytes. The detection limits for the elements determined by ICP OES were in the range 0.01 (Mn)– 2.0 (K) µg g−1 while those determined by ICP-MS were 0.001 µg g−1 for all the elements except Mn and As (0.002 µg g−1). The relative standard deviations were below 12% for ICP OES and below 14% for ICP-MS determinations. The mean concentration of the elements detected by ICP OES (Ca, Fe, K, Mg, Na, and Zn) varied according to the brand. The other analytes, were determined by ICP-MS. For these elements, a significant variation in their concentrations was also found for different samples, except for Co and Ni. The use of both multielemental techniques allowed the evaluation of the inorganic composition and the rapid determination of several elements in aspartame sweeteners, with adequate accuracy.

Whistler propagation in nonsymmetrical density channels

We present results from a study of whistler propagation in plasma density channels extended along Earth's geomagnetic field and localized across it. Our study is focused on whistler guiding by channels with a nonsymmetrical density profile across the channel. Such profiles are typical for density inhomogeneities observed on/near the plasmapause formed in the Earth's magnetosphere during strong geomagnetic storms/substorms. Considering these density channels as a combination of high‐density and low‐density ducts, we analyze leakage of the electromagnetic energy from these ducts depending on various parameters of the system. Our results indicate that a whistler with a frequency less than half of the local electron gyrofrequency can propagate along a nonsymmetrical duct with a homogeneous central part, without any leakage, when the width of the duct is equal to an integral multiple of each of the two internal perpendicular wavelengths. We also show that a homogeneous ducting region is not necessary; a low‐frequency whistler can be guided along a region of appropriate density within a monotonic density gradient. This finding makes our results particularly relevant for the interpretation of intense whistler dynamics recorded in a number of satellite observations near/on the plasmapause where strong transverse density gradients are observed.

Optimization of Tunable Wavelength Converters and Internal Wavelengths in the Optical Packet Switch with Shared FDL Buffer

In an effort to reduce switch cost, we present the optimum numbers of tunable wavelength converters (TWCs) and internal wavelengths required for contention resolution of asynchronous and variable length packets, in the optical packet switch (OPS) with the shared fiber delay line (FDL) buffer. To optimize TWCs and internal wavelengths related to OPS design cost, we proposed a scheduling algorithm for the limited TWCs and internal wavelengths. For three TWC alternatives (not shared, partially shared, and fully shared cases), the optimum numbers of TWCs and internal wavelengths to guarantee minimum packet loss are evaluated to prevent resource waste. Under a given load, TWCs and internal wavelengths could be significantly reduced, guaranteeing the same packet loss as the performance of an OPS with full TWCs and internal wavelengths.

Two- and three-dimensional numerical models of internal tide generation at a continental slope

Some numerical models of internal tide generation at a continental slope are two-dimensional where the along-slope variation is neglected. The energy flux carried by internal tides computed using such two-dimensional models is often underestimated, compared with three-dimensional simulations of the same region, by a factor of 10 or more. The reason for this difference is investigated using both numerical and analytical models. It is shown that in numerical models, it is not the lack of the along-shelf forcing but the use of sponge or radiating conditions at the cross-shelf boundaries that leads to the severe underestimate of the offshore flux. To obtain realistic estimates of energy flux a three-dimensional model with an along-shelf scale of at least 5 internal tide wave lengths at the depth of maximum forcing is necessary.

Precision and Noise in Inductively Coupled Plasma Atomic Emission Spectroscopy with Charge-Injection Device Detection

An inductively coupled plasma (ICP)-echelle optical system coupled with a charge-injection device (CID) detector was evaluated for precision and noise. Simultaneous collection of analyte wavelengths and simultaneous background correction have invalidated underlying assumptions in some traditional models. Signal flicker noise, a major limitation in single-channel detection, was eliminated by the time correlation of analyte and internal standard wavelengths. Once flicker noise was eliminated, most fluctuation was found to be caused by slight wavelength shifts along the axis of the detector, rather than by the theoretically predicted signal shot noise. This fluctuation can be corrected by increasing center subarray sizes or by employing well-matched internal standard lines. In either case, precision of 0.3 to 0.18% relative standard deviation (RSD) was achieved over a time span of 7 h. Background flicker noise was also eliminated by simultaneous background correction, demonstrating a multichannel advantage of ICP detection using charge-transfer devices. In this work, theoretical expressions were developed to incorporate major sources of noise based on the specific readout characteristics of an array detector. These expressions match experimental data extremely well for measurement of relative standard deviation in background (RSDB) and detection limits. These data have then been compared to the single-channel case, which describes photomultiplier tube (PMT) detection, as well as the theoretical limit dictated by background shot noise.

The /spl lambda/-scheduler: A multiwavelength scheduling switch

We propose a new multiwavelength almost all-optical switch architecture called the /spl lambda/-scheduler that uses wavelength division multiplexing (WDM) internally to fold the switch architecture in both the space and time domains to reduce the hardware complexity and to improve the signal characteristics through the switch. The /spl lambda/-scheduler preserves the packet order for a given input-output pair, is consistent with virtual circuit switching, and when combined with appropriate connection and flow control protocols, provides lossless communication for bursty (or nonconstant rate) traffic, provided the traffic satisfies certain smoothness properties. The /spl lambda/-scheduler uses novel scheduling and wavelength assignment algorithms, in conjunction with a series of feed-forward delay blocks, to avoid packet collisions within the switch or at the switch outputs. We present two implementations of the /spl lambda/-scheduler when the number of internal wavelengths k equal the number of inputs (and outputs) N to the switch. In the compressed /spl lambda/-scheduler, the N internal wavelengths are used to fold the architecture in the time domain, which reduces the total number of delay blocks for the switch by 2N log N. In the collapsed /spl lambda/-scheduler, the N internal wavelengths are used to fold the architecture in the space domain, which reduces the number of delay blocks and total fiber length used for delays by a factor of N. We examine the insertion loss for both /spl lambda/-scheduler implementations and discuss the trade-offs between the reduction in overall component count and the improvement in the signal characteristics.