Transfer Functions For Reconstruction Research Articles

Spatio-temporal changes in ocean conditions and primary production in Baffin Bay and the Labrador Sea

Evaluating and understanding bio-environmental relationships at different spatial and temporal scales is important for accurately assessing marine productivity in relation to oceanographic conditions in changing Arctic ecosystems. In this paper, we compare four different bio-environmental datasets, in order to shed new light on the complex marine ecosystem of the Baffin Bay-Labrador Sea region, as well as the historical links between environmental changes and the ecosystem. Satellite dataset was used to describe the regional distribution of chlorophyll a, sea ice concentration (SIC), sea surface temperature (SST) and sea surface salinity (SSS). Chlorophyll a data were also analysed together with shrimp assessment dataset to examine the relationship between marine pelagic productivity and bottom feeders off the Greenland coast. A microfossil dataset (diatom valves) from 57 surface sediment stations was used to describe diatom concentration and diversity across the study region. It was also used in combination with satellite data from the same sites to analyse species-environment relationships and develop a diatom-based transfer function for reconstructing past changes in SIC, SST and SSS. Subsequently, we applied the diatom transfer function on three short sediment cores from off SW and W Greenland spanning the last few centuries. A monitoring dataset of sea ice observations and instrumental measurements of water temperature and salinity, together with atmospheric data (air temperature and wind conditions) from Greenland, were used to develop a more complete picture of 20th and 21st century changes in ocean-climate conditions. Our comparative analyses show clear spatial distribution patterns of marine phytoplankton and identify key ecological groups linked to oceanic conditions. In addition, we find a significant correlation between the different trophic levels, culminating in a ‘productivity boom’ in 2001 CE. On a longer temporal scale, the transfer function reconstructions reveal a good correlation with the satellite, monitoring and observational trends, as well as a consistent, long-term decrease in sea ice linked to ocean-climate variability.

Minimal stratigraphic evidence for coseismic coastal subsidence during 2000 yr of megathrust earthquakes at the central Cascadia subduction zone

AbstractLithology and microfossil biostratigraphy beneath the marshes of a central Oregon estuary limit geophysical models of Cascadia megathrust rupture during successive earthquakes by ruling out >0.5 m of coseismic coastal subsidence for the past 2000 yr. Although the stratigraphy in cores and outcrops includes as many as 12 peat-mud contacts, like those commonly inferred to record subsidence during megathrust earthquakes, mapping, qualitative diatom analysis, foraminiferal transfer function analysis, and 14C dating of the contacts failed to confirm that any contacts formed through subsidence during great earthquakes. Based on the youngest peat-mud contact’s distinctness, >400 m distribution, ∼0.6 m depth, and overlying probable tsunami deposit, we attribute it to the great 1700 CE Cascadia earthquake and(or) its accompanying tsunami. Minimal changes in diatom assemblages from below the contact to above its probable tsunami deposit suggest that the lower of several foraminiferal transfer function reconstructions of coseismic subsidence across the contact (0.1–0.5 m) is most accurate. The more limited stratigraphic extent and minimal changes in lithology, foraminifera, and(or) diatom assemblages across the other 11 peat-mud contacts are insufficient to distinguish them from contacts formed through small, gradual, or localized changes in tide levels during river floods, storm surges, and gradual sea-level rise. Although no data preclude any contacts from being synchronous with a megathrust earthquake, the evidence is equally consistent with all contacts recording relative sea-level changes below the ∼0.5 m detection threshold for distinguishing coseismic from nonseismic changes.

Head-related Transfer Function Reconstruction with Anthropometric Parameters and the Direction of the Sound Source

An accurate head-related transfer function can improve the subjective auditory localization performance of a particular subject. This paper proposes a deep neural network model for reconstructing the head-related transfer function (HRTF) based on anthropometric parameters and the orientation of the sound source. The proposed model consists of three subnetworks, including a one-dimensional convolutional neural network (1D-CNN) to process anthropometric parameters as input features and another network that takes the sound source position as input to serve as a marker. Finally, the outputs of these two networks are merged together as the input to a third network to estimate the HRTF. An objective method and a subjective method are proposed to evaluate the performance of the proposed method. For the objective evaluation, the root mean square error (RMSE) between the estimated HRTF and the measured HRTF is calculated. The results show that the proposed method performs better than a database matching method and a deep-neural-network-based method. In addition, the results of a sound localization test performed for the subjective evaluation show that the proposed method can localize sound sources with higher accuracy than the KEMAR dummy head HRTF or the DNN-based method. The objective and subjective results all show that the personalized HRTFs obtained using the proposed method perform well in HRTF reconstruction.

Multifunctional flexible sensor array-based damage monitoring for switch rail using passive and active sensing

A passive monitoring technique for switch rails will be very attractive because it does not require extra excitations and can realize large area monitoring. However, complex wheel-rail interactions and sparse sensors will affect the accuracy of local damage identification. In contrast, an active monitoring technique has high local damage quantification ability but has low efficiency for large area monitoring. This study firstly presents a combination of piezoceramic material Lead zirconate titanate (PZT) wafers with accelerometers to configure a multifunctional sensor array that brings together active and passive monitoring mechanisms. The multifunctional sensor arrays are produced in a flexible form, which are adapted to complex geometry and are easy to install. In complementary passive monitoring, each sub area’s health state between 2 accelerometers is represented by reconstructing transfer functions, which are calculated from rail vibrations. The reconstructed transfer function in conjunction with principal component analysis (PCA)-based feature extraction is utilized for estimating the damaged sub area. Then accurate local damage identification can be realized through the active guided waves technique and correlation-based diagnostic imaging in conjunction with singular value decomposition (SVD). Simulation and experimental studies show the proposed mechanisms can identify the damaged sub area and basically extract damage locations with different lengths correctly with the sparse sensor array. Finally, based on a controlled experiment, the causes of the errors are evaluated and analyzed. The proposed mechanism can simplify data analysis, save monitoring time, and decrease the final cost.

Objective and efficient terahertz signal denoising by transfer function reconstruction

As an essential processing step in many disciplines, signal denoising efficiently improves data quality without extra cost. However, it is relatively under-utilized for terahertz spectroscopy. The major technique reported uses wavelet denoising in the time-domain, which has a fuzzy physical meaning and limited performance in low-frequency and water-vapor regions. Here, we work from a new perspective by reconstructing the transfer function to remove noise-induced oscillations. The method is fully objective without a need for defining a threshold. Both reflection imaging and transmission imaging were conducted. The experimental results show that both low- and high-frequency noise and the water-vapor influence were efficiently removed. The spectrum accuracy was also improved, and the image contrast was significantly enhanced. The signal-to-noise ratio of the leaf image was increased up to 10 dB, with the 6 dB bandwidth being extended by over 0.5 THz.

Non‐hydrostatic, Non‐linear Processes in the Surf Zone

AbstractIn the surf zone, non‐hydrostatic processes are either neglected or estimated using linear wave theory. The recent development of technologies capable of directly measuring the free surface elevation, such as 2‐D lidar scanners, allow for a thorough assessment of the validity of such hypotheses. In this study, we use subsurface pressure and lidar data to study the non‐linear and non‐hydrostatic character of surf zone waves. Non‐hydrostatic effects are found important everywhere in the surf zone (from the outer to the inner surf zones). Surface elevation variance, skewness, and asymmetry estimated from the hydrostatic reconstruction are found to significantly underestimate the values obtained from the lidar data. At the wave‐by‐wave scale, this is explained by the underestimation of the wave crest maximal elevations, even in the inner surf zone, where the wave profile around the broken wave face is smoothed. The classic transfer function based on linear wave theory brings only marginal improvements in this regard, compared to the hydrostatic reconstruction. A recently developed non‐linear weakly dispersive reconstruction is found to consistently outperform the hydrostatic or classic transfer function reconstructions over the entire surf zone, with relative errors on the surface elevation variance and skewness around 5% on average. In both the outer and inner surf zones, this method correctly reproduces the steep front of breaking and broken waves and their individual wave height to within 10%. The performance of this irrotational method supports the hypothesis that the flow under broken waves is dominated by irrotational motions.

Identifying the signature of sea-surface properties in dinocyst assemblages: Implications for quantitative palaeoceanographical reconstructions by transfer functions and analogue techniques

Abstract Dinoflagellate cyst (=dinocyst) assemblages are widely used for the reconstruction of multiple oceanographic variables through the application of transfer functions. There is evidence that the number and kind of variables driving compositional changes in dinocyst assemblages vary regionally and that the selection of driving factors and the evaluation of transfer function performances are method-specific and complicated by spatial autocorrelation. Here, we used two new modern datasets from the Northern Hemisphere Atlantic-Arctic and the Northern Hemisphere Pacific oceans to re-evaluate the impact of sea-surface properties in dinocyst assemblages. We determined the dimensionality of the dinocyst ecological response and identified the main drivers for both regions. We calibrated and evaluated transfer function methods for the prediction of these variables and estimated their performances considering spatial autocorrelation. In both datasets, multiple environmental variables mutually and independently affect assemblage compositions, but the number and kind of these variables differ between datasets. We detected spatial autocorrelation, which was often due to environmental similarity, but some variables appeared to reflect geographical closeness, implying that spatial independence between sample sites depends upon the variables. We identified different primary drivers in both areas, highlighting the merit of regional calibrations and the necessity to carry out variable selection for each region separately. The multiple gradients identified imply that potentially multiple parameters could be reconstructed from the same fossil dinocyst assemblages. However, as the multiple gradients reflect geographical structuring, we propose that regional calibrations, even at the expense of generalisation, could improve the reliability and interpretation of transfer function reconstructions.

Grass habitat analysis and phytolith-based quantitative reconstruction of Asian monsoon climate change in the sand-loess transitional zone, northern China

AbstractWe investigated climate niches of grasses at regional scales and quantitatively reconstruct Asian monsoon precipitation at the sand-loess transitional zone in northern China. Our results provide direct evidence that certain grass lineages have been specialized in specific habitats: Pooideae grasses stand out and occupy a much cooler environment than all other subfamilies; Pooideae, Aristidoideae, and Chloridoieae occupy dry environments. Pooideae grasses occupy the coldest and driest environments compared to all other subfamilies, with a mean annual temperature (MAT) and precipitation (MAP) of ~13.6 to ~15.3°C and 224 to ~1674 mm, respectively, at a regional scale. We built a database for grasses and their corresponding climate parameters. Based on this database, past climate parameters at the margin of the Asian summer monsoon since ~70 ka were quantitatively reconstructed by phytolith assemblages. They show that this area was dominated by cold- and dry-adapted grasses since ~70 ka with a MAT and MAP of ~3.3 to ~11.0 °C and ~442 to ~900 mm, respectively, generally consistent with the results of phytolith-based transfer function reconstructions and with the results of previous nearby pollen-based quantitative reconstructions. With the improvement of the species-climate and ecosystem dataset, our database-based method is a promising quantitative reconstruction approach to past climatic change in the monsoon region.

Optical Transfer Function Reconstruction in Incoherent Fourier Ptychography**Supported by the National Natural Science Foundation of China under Grant No 61205144, the Research Project of National University of Defense Technology under Grant No JC13-07-01, and the Key Laboratory of High Power Laser and Physics of Chinese Academy of Sciences.

An optical transfer function (OTF) reconstruction model is first embedded into incoherent Fourier ptychography (IFP). The leading result is a proposed algorithm that can recover both the super-resolution image and the OTF of an imaging system with unknown aberrations simultaneously. This model overcomes the difficult problem of OTF estimation that the previous IFP faces. The effectiveness of this algorithm is demonstrated by numerical simulations, and the superior reconstruction is presented. We believe that the reported algorithm can extend the original IFP for more complex conditions and may provide a solution by using structured light for characterization of optical systems' aberrations.

Oxygen stable isotopes during the Last Glacial Maximum climate: perspectives from data–model (<i>i</i>LOVECLIM) comparison

Abstract. We use the fully coupled atmosphere–ocean three-dimensional model of intermediate complexity iLOVECLIM to simulate the climate and oxygen stable isotopic signal during the Last Glacial Maximum (LGM, 21 000 years). By using a model that is able to explicitly simulate the sensor (δ18O), results can be directly compared with data from climatic archives in the different realms. Our results indicate that iLOVECLIM reproduces well the main feature of the LGM climate in the atmospheric and oceanic components. The annual mean δ18O in precipitation shows more depleted values in the northern and southern high latitudes during the LGM. The model reproduces very well the spatial gradient observed in ice core records over the Greenland ice sheet. We observe a general pattern toward more enriched values for continental calcite δ18O in the model at the LGM, in agreement with speleothem data. This can be explained by both a general atmospheric cooling in the tropical and subtropical regions and a reduction in precipitation as confirmed by reconstruction derived from pollens and plant macrofossils. Data–model comparison for sea surface temperature indicates that iLOVECLIM is capable to satisfyingly simulate the change in oceanic surface conditions between the LGM and present. Our data–model comparison for calcite δ18O allows investigating the large discrepancies with respect to glacial temperatures recorded by different microfossil proxies in the North Atlantic region. The results argue for a strong mean annual cooling in the area south of Iceland and Greenland between the LGM and present (> 6 °C), supporting the foraminifera transfer function reconstruction but in disagreement with alkenones and dinocyst reconstructions. The data–model comparison also reveals that large positive calcite δ18O anomaly in the Southern Ocean may be explained by an important cooling, although the driver of this pattern is unclear. We deduce a large positive δ18Osw anomaly for the north Indian Ocean that contrasts with a large negative δ18Osw anomaly in the China Sea between the LGM and the present. This pattern may be linked to changes in the hydrological cycle over these regions. Our simulation of the deep ocean suggests that changes in δ18Osw between the LGM and the present are not spatially homogeneous. This is supported by reconstructions derived from pore fluids in deep-sea sediments. The model underestimates the deep ocean cooling thus biasing the comparison with benthic calcite δ18O data. Nonetheless, our data–model comparison supports a heterogeneous cooling of a few degrees (2–4 °C) in the LGM Ocean.

Early Holocene drought in the Laurentian Great Lakes basin caused hydrologic closure of Georgian Bay

Multiple proxies record aridity in the northern Great Lakes basin ~8,800–8,000 cal (8,000–7,200) BP when water levels fell below outlets in the Michigan, Huron and Georgian Bay basins. Pollen-climate transfer function calculations on radiocarbon-dated pollen profiles from small lakes from Minnesota to eastern Ontario show that a drier climate was sufficient to lower the Great Lakes, in particular Georgian Bay, to closed basins. The best modern climate analog for the early Holocene late Lake Hough stage in the Georgian Bay basin is Black Bass Lake near Brainerd MN. Modern annual precipitation at Brainerd is ~35% lower than at Huntsville ON, in the Georgian Bay catchment; warmer summers and colder, less snowy winters make Brainerd drier than the Georgian Bay snow belt. These values parallel transfer function reconstructions for the early Holocene from pollen records at five small lakes in the Georgian Bay drainage basin. Higher evaporation and evapotranspiration due to greater seasonality during the early Holocene produced a deficit in effective moisture in Georgian Bay that is recorded by the jack/red pine pollen zone that spanned ~8,800–8,200 cal (8,000–7,500) BP. This deficit drove late Lake Hough ~5 m below Lake Stanley in the Huron basin, following diversion of Laurentide Ice sheet meltwater from the Great Lakes basin. The level of Georgian Bay largely depends not on fluvial input from its own drainage basin, but rather from Lake Superior, where the early Holocene moisture deficit was greater. Reconstruction of paleoclimates in Minnesota, northwestern Ontario and Wisconsin produced a closed lake in the Superior basin, which removed the main water input to Georgian Bay. Once the inflow through the St. Marys River was reduced and inflow from other tributary streams was adjusted for isostatic and climatic differences, input was <5% of modern values. Consequent high evaporation rates produced a significant fall in lake level in the Georgian Bay basin and a negative water budget. This reduction in basin supply, together with the high conductivity of stagnant water in late Lake Hough inferred from microfossils in lowstand sediments, peaked at the end of the jack/red pine zone, ~8,300–8,200 (7,450 ± 90) BP. These major hydrologic changes resulting from climate change in the recent geologic past draw attention to possible declines of the Great Lakes under future climates.

Recent sea-level changes in the southern Bay of Biscay: transfer function reconstructions from salt-marshes compared with instrumental data

In order to assess the accuracy and regional significance of salt-marsh reconstructions of former sea level based on foraminiferal transfer functions, we compared the calibration of the foraminiferal assemblages of two salt-marsh cores from two estuaries using the regional transfer function constructed for the southern Bay of Biscay. The foraminifera-based reconstructions were placed into a temporal framework using 137 Cs, heavy metal concentrations, and 210 Pb-derived sediment accumulation rates. The resulting relative sea-level (RSL) curves were compared with the nearest tide-gauge data (Santander). The two RSL trends from core sediments show excellent agreement and are in very good agreement with instrumental data, providing a regional relative sea-level rise of 1.9 mm yr -1 for the 20th century.

Last interglacial (MIS 5e) surface water conditions at the Vøring Plateau (Norwegian Sea), based on dinoflagellate cysts

Sediments from the last interglacial, marine isotope stage 5e (MIS 5e), have been studied for their dinoflagellate cyst content in a core retrieved from the Voring Plateau, Norwegian Sea. Qualitative and quantitative analyses of the data, and comparison with the surface sample and published Holocene data from the core, reveal distinct differences in hydrological surface conditions between the late Holocene and MIS 5e. A higher number of co-dominant, subordinate species in the last interglacial samples suggests there was a more pronounced seasonality of the surface water at this time. This is supported by the significant presence of Bitectatodinium tepikiense, a species that was virtually absent from the area for most of the Holocene. The seasonality signal is further substantiated by transfer-function reconstructions, which also indicates a stronger stratification of the upper water column during MIS 5e. Moreover, the assemblage data clearly show that optimal, fully marine interglacial conditions prevailed only late in MIS 5e (between ca. 117.5 and 116.5 Kya), which is in contrast with the climatic optimum early in the Holocene. Stable oxygen isotope values from planktic foraminifera for this MIS 5e optimum are comparable with the average Holocene values, but are generally ca. 0.3‰ higher than those of the earlier part of the last interglacial (sensu stricto). These higher d18O values are likely to be the result of the enhanced and prolonged influence of Saalian deglacial meltwater, thus corroborating the existence of a quite differently structured sea surface, as suggested by the dinocyst data.

Assessing sea-level data from Connecticut, USA, using a foraminiferal transfer function for tide level

Concerns surrounding possible future climate change, sea level rise, and their potential impacts on coastal environments, have stimulated research seeking to elucidate the relationship between ocean levels and climate at the (sub)century-scale. The need for increasingly precise reconstructions of relative sea-level change has, in-turn, driven the development of new methodologies capable of resolving fine-scale variability within salt-marsh sedimentary sequences. The use of salt-marsh foraminifera as precise indicators of past tide levels has played a central role in this process and is exemplified by a number of detailed studies conducted in Connecticut, USA. In this paper, we apply the most recent methodological advance in the reconstruction of relative sea-levels using salt-marsh foraminifera. We develop a foraminiferal transfer function for tide level, derived from the modern foraminiferal distributions of four Connecticut salt-marshes. In contrast to existing approaches that employ site-specific interpolations of local vertical foraminiferal assemblage zones, this transfer function can provide objective, quantitative and reproducible estimates of palaeomarsh-surface elevation with explicitly stated error terms for marshes throughout Connecticut, irrespective of differences in tidal range. We demonstrate the foraminiferal transfer function approach by employing it to reconstruct changes in palaeomarsh-surface elevation from three cores recovered from Hammock River marsh, Connecticut. The resulting reconstructions, which are precise to ±0.09 m, are tested using an independent dataset from the neighbouring state of Maine, and are used to assess a pivotal record of mean high water (MHW) change from this site. We conclude that the transfer function reconstructions show good general agreement with previous records of palaeomarsh-surface elevation, but with the advantages of quantified error terms and a transparent, reproducible methodology. This replicability will assist in the comparison or combination of local records of MHW change to infer large-scale, regional sea-level variations.

Structure of the upper water column in the northwest North Atlantic: Modern versus Last Glacial Maximum conditions

During the Last Glacial Maximum, the northwestern North Atlantic constituted a major conduit for Labrador and Greenland ice sheet meltwaters. Vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements (δ18O) in planktonic foraminifera. Transfer functions yield temperature and salinity and thus potential density (σθ) for the warmest (August) and coldest (February) months in the photic zone. The δ18O values in different size fractions of epipelagic (Globigerina bulloides) and mesopelagic (Neogloboquadrina pachyderma left‐coiled (Npl)) foraminifera allow us to assess σθ gradients through the pycnocline between surface and intermediate waters, based on the calibration of a σθ versus δ18O relationship from transfer function reconstructions. The size and density of Npl shells provide further constraints on these σθ gradients. The results show the development of a very strong pycnocline during the LGM with a difference of about 3 (summer) to 1.5 (winter) σθ units between surface and underlying waters. They indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow, low‐salinity buoyant layer over the northern North Atlantic. This layer depicted a strong E‐W gradient, with maximum seasonal contrast and minimum absolute σθ values westward.

Reducing Test Time in the High-Volume Production of Analog Circuits using Efficient Test-Vector Generation and Interpolation Techniques

Test cost is one of the main factors determining the profit margin of a device in production. Current test strategies require hundreds of measurements to determine the specifications of a parameter. In this paper, we present an automatic test-vector generation technique that is based on transfer function manipulation and requires only one circuit simulation. The proposed method consists of generating the first set of vectors by applying a derivation technique to the golden transfer function of the circuit under test (CUT). An interpolation technique allows a new transfer function to be constructed based on the first set of test vectors. The difference between the reconstructed transfer function and the golden transfer function is used to select the second set of test vectors. These new test vectors are selected to achieve the best possible fit. Our technique reduces the test vector size to values that at present can be achieved only by using powerful and time-consuming fault simulation tools. As an example, we apply the method to state variable and Chebyshev filters. We also compute the fault coverage in order to demonstrate the effectiveness of this new technique.

Replacing tracheoesophageal voicing sources using LPC synthesis

The feasibility of using the linear predictive coding (LPC) technique to replace the voicing sources of tracheoesophageal speech was explored. Four vowels, [i], [a], [e], [u], and one diphthong [ou], produced by two male and two female tracheoesophageal speakers were analyzed by the LPC autocorrelation method. Normalized prediction error functions were used to choose the algorithm and the control parameters of the analysis. Poles of the vocal tract transfer function were selected from frames whose normalized prediction errors were close to minimum with criteria derived from transfer functions of normally produced vowels. Vowels were synthesized with the reconstructed transfer function and a synthesized excitation input. Results of an identification task indicated that the synthesized vowels were highly intelligible, and the gender of the speaker was better identified from the synthesized vowels than from the original tracheoesophageal vowels.