Transfer Function Technique Research Articles

Mid-Brunhes century-scale diatom sea surface temperature and sea ice records from the Atlantic sector of the Southern Ocean (ODP Leg 177, sites 1093, 1094 and core PS2089-2)

Diatom assemblages from ODP Leg 177 sites 1093, 1094 and core PS2089-2, from the present Antarctic sea ice free zone and close to the Polar Front, were analyzed in order to reconstruct the climate development around the Mid-Brunhes Event 400 000 yr ago, as reflected by summer sea surface temperature (SSST) and sea ice distribution. Dense sample spacing allows a mean temporal resolution during Marine Isotope Stage (MIS) 11 (423–362 ka) of 300–400 yr. SSST values were estimated from diatom assemblages using a transfer function technique. The distribution pattern of sea ice diatoms indicates that the present-day ice free Antarctic Zone was seasonally covered by sea ice during the cold MIS 12 and MIS 10. These glacial periods are characterized by sea ice fluctuations with a periodicity of 3 and 1.85 kyr, suggesting the occurrence of Dansgaard–Oeschger-style millennial-scale oscillations in the Atlantic sector of the Southern Ocean during the glacial stages MIS 12 and MIS 10. Termination V (MIS 12/11) is characterized by a distinct temperature increase of 4–6°C, intersected especially at the southern site 1094 and core PS2089-2 by two distinct cooling events reminiscent of the Younger Dryas, which are associated with a northward shift of the winter sea ice edge in the Antarctic Zone. The SSST record is characterized by distinct temperature intervals bounded by stepwise, rapid changes. Maximum temperatures were reached during Termination V and the early MIS 11, exceeding modern values by 2°C over a period of 8 kyr. This pattern indicates a very early response of the Southern Ocean to global climate on Milankovitch-driven climate variability. The SSST optimum is marked by millennial-scale temperature oscillations with an amplitude of ca. 1°C and periodicities of ca. 1.85 and 1.47 kyr, probably reflecting changes in the ocean circulation system. The SSSTs during the MIS 11 temperature optimum do not exceed values obtained from other interglacial optima such as the early periods of MIS 5 or MIS 1 from the Antarctic Zone. However, the total duration of the warmest period was distinctly longer than observed from other interglacials. The comparison of the South Atlantic climate record with a high-resolution record from ODP Leg 162, site 980 from the North Atlantic shows a strong conformity in the climate development during the studied time interval.

Late Quaternary sea-surface temperature variations in the southeast Atlantic: a planktic foraminifer faunal record of the past 600 000 yr (IMAGES II MD962085)

A high-resolution (∼4–5cm/kyr) giant piston core record (MD962085) retrieved during an IMAGES II-NAUSICAA cruise from the continental slope of the southeast Atlantic Ocean reveals striking variations in planktonic foraminifer faunal abundances and sea-surface temperatures (SST) during the past 600 000 yr. The location and high-quality sedimentary record of the core provide a good opportunity to assess the variability of the Benguela Current system and associated important features of the ocean-climate system in the southeast Atlantic. The planktonic foraminifer faunal abundances of the core are dominated by three assemblages: (1) Neogloboquadrina pachyderma (right coiling)+ Neogloboquadrina dutertrei, (2) Globigerina bulloides, and (3) Globorotalia inflata. The assemblage of N. pachyderma (right coiling)+ N. dutertrei shows distinctive abundance changes which are nearly in-phase with glacial–interglacial variations. The high abundances of this assemblage are associated with major glacial conditions, possibly representing low SST/high nutrient level conditions in the southwestern Africa margin. In contrast, the G. bulloides and G. inflata assemblages show greater high-frequency abundance change patterns, which are not parallel to the glacial–interglacial changes. These patterns may indicate rapid oceanic frontal movements from the south, and a rapid change in the intensity of the Benguela upwelling system from the east. A single episode of maximum abundances of a polar water species N. pachyderma (left coiling) occurred in the beginning of stage 9 (∼340–330 kyr). The event of the maximum occurrence of this species shown in this record may indicate instability in the Benguela coastal upwelling, or the Antarctic polar front zone position. A winter season SST estimate using transfer function techniques for this record shows primarily glacial–interglacial variations. The SST is maximal during the transitions from the major glacial to interglacial stages (Terminations I, II, IV, V), and is associated with the abundance maxima of a warm water species indicator Globigerinoides ruber. Cross-spectral analyses of the SST record and the SPECMAP stack reveal statistically significant concentrations of variance and coherencies in three major orbital frequency bands. The SST precedes changes in the global ice volume in all orbital frequency bands, indicating a dominant southern Hemispheric climate effect over the Benguela Current region in the southeast Atlantic.

A necessary condition for pole assignment by constant output feedback

In this paper we shall investigate the pole assignment problem by constant output feedback using transfer function techniques. In particular, a necessary condition is given for the existence of constant output feedback which assigns the eigenvalues of closed-loop system to any desired positions.

Late quaternary upper-water column structure in upwelling areas of the South China Sea

Based on a quantitative analysis of planktonic foraminifera in two gravity cores (17928 and 17954), the history of the upper-water structure of the eastern and western slopes of the South China Sea (SCS) over the last 220 Ka was reconstructed using the transfer function technique. Our results show that lower sea surface temperature (SST) and shallower depth of thermocline (DOT) exist at Core 17928, off Luzon, in the glacial periods; on the contrary, the same situation turned up in the interglacial at Core 17954, off Vietnam. These changes of the upper-water column structure in the two areas are induced by coastal up-welling, which in turn is driven by monsoons, namely, winter monsoon leads to upwelling at the eastern slope, and summer monsoon gives birth to upwelling on the western slope. Moreover, the intensity of upwellings is also closely related to the evolution of the East Asian monsoon. Therefore, we assume that the changes of the upwelling in the two sites indicate strengthenning of winter and summer monsoon during the glacial and interglacial periods, respectively.

An in situ transfer function technique for the assessment of the acoustic absorption of materials in buildings

A method for measuring the absorption properties of materials in situ at mid to high frequencies is proposed. It is an adapted version of the well known free-field two-microphone transfer function technique to in situ conditions. The novel features of the method are presented: noise-immune acquisition technique, proper time windowing — both windowing strategy and window choice — practical geometrical transducer setup at oblique incidence. A rigorous study of measurement conditioning as a function of incidence is given using the conformal mapping technique. Experimental results are ultimately provided in realistic in situ conditions showing the viability of the method with comparison to standing wave tube measurements.

Less Adrenergic Response to Mental Task During Verapamil Compared to Amlodipine Treatment in Hypertensive Subjects

We compared the effects of amlodipine and verapamil slow release on autonomic responses to a 5-min mental arithmetic test (MST) in patients with mild to moderate hypertension. Twenty subjects received 8 weeks of verapamil slow release 240 mg or amlodipine 10 mg in a double-blind crossover design, both after 4 weeks' placebo. Heart rate (HR) and blood pressure (BP) were continuously monitored. Venous plasma catecholamines were analysed by a radioenzymatic assay. Baroreflex sensitivity (BRS) was estimated with the transfer function technique. Calculations of the area under the curve (AUC) were used to estimate average HR, BP and catecholamine concentrations. The reactivity to MST was estimated as percent change from the basal AUC. A paired t

Millennial‐scale sea surface temperature variability in the western tropical North Atlantic from planktonic foraminiferal census counts

Planktonic foraminiferal census counts are used to construct high‐resolution sea surface temperature (SST) and subsurface (thermocline) temperature records at a core site in the Tobago Basin, Lesser Antilles. The record is used to document climatic variability at this tropical site in comparison to middle‐ and high‐latitude sites and to test current concepts of cross‐equatorial heat transports as a major player in interhemispheric climate variability. Temperatures are estimated using transfer function and modern analog techniques. Glacial‐maximum cooling of 2.5°'3°C is indicated; maximum cooling by 4°C is inferred for isotope stage 3. The SST record displays millennial‐scale variability with temperature jumps of up to 3°C and closely tracks the structure of ice‐core Dansgaard/Oeschger cycles. SST variations in part of the record run opposite to the SST evolution at high northern latitude sites, pointing to thermohaline circulation and marine heat transport as an important factor driving SST in the tropical and high‐latitude Atlantic, both on orbital and suborbital timescales.

Ocean forecasting in narrow shelf seas: application to the Spanish coasts

The continental shelf surrounding the Spanish coast is very narrow. This is of great importance when studying the wave and surge dynamics in the region and contrasts with other well-studied regions like the North Sea, both in the physics and in the modelling techniques applied to obtain predictions of waves and sea surface elevation at the coastline. This paper describes those differences and presents the approach to the problem implemented in the wave and surge prediction system operational at Clima Marı́timo (CM). The narrowness of the Spanish continental shelf requires very high resolution grids to be applied to localised regions near the coast. The usual configuration of a local system nested to a global system (e.g. grids covering the North Sea nested to the European Centre for Medium Range Weather Forecasting global model) cannot be used in this case. Interpolation and coarse grid errors from boundary conditions provided by a global grid very near the coast will not be corrected by a small-scale local application. It was found that self-contained systems, solving in the same run the basin and local scales by means of variable grid spacing techniques, were the optimal solution. Some new techniques were developed in the process (two-way nesting for the wave generation model, a transfer function technique for the wave spectra) and implemented in the system. Although some of these developments have been already published [Gómez, M., Carretero, J.C., 1997. A two-way nesting procedure for the WAM model: application to the Spanish coast. J. Offshore Mech. Arctic Eng. 119 (February 1997).], the final set-up of both systems is presented here for the first time. Both systems are regularly verified with experimental data from the Spanish network of buoy and tide gauges. Results from this intercomparison are discussed in this paper. The PROMISE Spanish Coast Data Set was used to carry out much of the work presented here (i.e. the forcing and validation of the surge prediction system). This is a collection of physical oceanographic and meteorological data in the Bay of Biscay during stormy periods from November 1995 to March 1996.

The determination of the acoustic properties of sound sources actively controlled in a square duct

This study is to present the determination of the acoustic properties of sound sources actively controlled in a square duct. Therefore, the measurement of sound source reflection coefficient using transfer function technique, the related prediction on sound source impedance and the comparison of the predicted source impedance as described with that of the measurement by using Helmholtz resonator technique are all included in this study. The result of this study, clearly shows that the reflection coefficient of sound source is very dependent on the acoustic frequency involved, and the predicted source impedance by using transfer function method agrees fairly well with that measured by using Helmholtz resonator method.

Bounds on the a priori index crossover probabilities for trellis-based channel codes

This paper derives truncated union bounds on the a priori index crossover probabilities p(j|i) that result when an n-bit data index i is convolutionally encoded, transmitted over a noisy channel, and decoded with the Viterbi algorithm, giving received index j. The bounds are derived with a modified transfer function technique, using n-stage state transition matrices with symbolic labels. The technique is easily automated with commercial symbolic algebra packages. Bounds are obtained for convolutional and trellis-coded modulation (TCM) codes, over binary symmetric and additive white Gaussian noise (AWGN) channels. A joint source channel coding example demonstrates that the bounds on p(j|i) developed in this paper can give a 13-dB accuracy improvement in end-to-end signal-to-noise ratio (SNR) predictions, when compared to predictions based on bounds on the delivered bit error probability P/sub b/.

Statistical downscaling of general circulation model output: A comparison of methods

A range of different statistical downscaling models was calibrated using both observed and general circulation model (GCM) generated daily precipitation time series and intercompared. The GCM used was the U.K. Meteorological Office, Hadley Centre's coupled ocean/atmosphere model (HadCM2) forced by combined CO2 and sulfate aerosol changes. Climate model results for 1980–1999 (present) and 2080–2099 (future) were used, for six regions across the United States. The downscaling methods compared were different weather generator techniques (the standard “WGEN” method, and a method based on spell‐length durations), two different methods using grid point vorticity data as an atmospheric predictor variable (B‐Circ and C‐Circ), and two variations of an artificial neural network (ANN) transfer function technique using circulation data and circulation plus temperature data as predictor variables. Comparisons of results were facilitated by using standard sets of observed and GCM‐derived predictor variables and by using a standard suite of diagnostic statistics. Significant differences in the level of skill were found among the downscaling methods. The weather generation techniques, which are able to fit a number of daily precipitation statistics exactly, yielded the smallest differences between observed and simulated daily precipitation. The ANN methods performed poorly because of a failure to simulate wet‐day occurrence statistics adequately. Changes in precipitation between the present and future scenarios produced by the statistical downscaling methods were generally smaller than those produced directly by the GCM. Changes in daily precipitation produced by the GCM between 1980–1999 and 2080–2099 were therefore judged not to be due primarily to changes in atmospheric circulation. In the light of these results and detailed model comparisons, suggestions for future research and model refinements are presented.

Assessment of sea surface temperature variations in the central North Atlantic using the alkenone unsaturation index (U 37k′)

A high resolution record of U 37 k′ -derived SST estimations has been obtained in a core from the central North Atlantic Ocean (SU90/08, 43°30′N, 30°24′W) spanning a time period of 280 ky. The general trend of the U 37 k′ profile parallels closely the δ 180 signal and represent an independent confirmation that the SST variations in the glacial-interglacial time scales are correlated with the northern ice sheets evolution. In contrast to the CLIMAP (1984) conclusions based on the foraminiferal transfer function technique, the SST during the last interglacial period (LIP, isotopic stage 5.5) are 2–3°C warmer than during the Holocene. This result is in good agreement with many studies based in coastal and continental records that strongly suggest warmer climatic conditions over North America and Europe. Finally, the SST estimates during the last glacial maximum (LGM, 18 ky bp) where 4.5°C cooler than during the previous glacial period (PGP, stage 6). We argue that this difference is caused by a northward position of the polar front during the PGP in the Central North Atlantic.

In situ absorption measurements using a transfer function technique and MLS

The transfer function (or two-microphone) technique is a tool for measuring materials absorption related parameters as impedance or absorption coefficients. But this method is laboratory bound in its original form due to free field assumption and practical issues. It is shown that after proper modifications the transfer function technique can be used successfully in noisy and reverberating fields and work well at low frequency even in small measurement rooms, becoming therefore a really in situ measurement technique. A wide frequency range implementation is presented, based on a two-channel MLS measurement system, ‘‘energy ratio invariant’’ time windowing, a basic specular reflection propagation model with spherical decoupling, and a particular geometrical configuration. The measurement method is tested on a wide range of absorbers. For impedance measurements using infinite surface propagation models the uniqueness of the inversion procedure is investigated using the conformal mapping technique. In addition, faster inversion and model computation routines are proposed. Measurement results obtained under realistic in situ conditions are provided and compared with reference methods.

A technological solution to the testing and data reduction of single fibre fragmentation tests

Abstract The single fibre fragmentation test was first introduced in 1965 for measuring interfacial adhesion in fibre reinforced composites. However, this test is still far from a routine test and no suitable testing standard exists. Consequently, this method is hardly used by research laboratories of the reinforcing fibre manufacturers, composite fabricators and other standardisation organisations. The main reasons for the failure of the fragmentation test to establish as a standard quality control tool are the time consuming manual testing procedures and the poor confidence in the data reduction techniques used for calculating the interfacial adhesion parameter. An integrated machine, software and data reduction approach has been developed for the fragmentation test. The new approach allows the stoppage of the fragmentation test at pre-defined strains and digitisation of the whole embedded fibre length using a microscope attached with a video-camera and Sun work-station. Subsequently, the fragment and associated debond lengths are measured using a Visual Basic program in a semi-automatic process. The problems associated with the huge amount of computer graphics data and compatibility of different graphics formats have been sorted out. This leads to substantial savings in the time required for the fragmentation test. Using this integrated machine and software approach, the single fibre fragmentation test has been carried out on carbon fibre samples with well-defined interfaces. The results were analysed using the conventional Kelly–Tyson model and the cumulative stress transfer function (CSTF) technique, at different applied strains. It has been shown that the CSTF technique can be used for assessing the fibre-matrix adhesion from the single fibre fragmentation test at any applied strain before or after the saturation of the fragmentation process, thus eliminating the need for specially formulated resin for the fragmentation test.

Determination of Acoustical Impedance of Absorbing Surfaces by Two-Microphone Transfer Function Techniques: Measurement In-Situ

In the fourth and final of a series of papers on the measurement of acoustical impedance of absorbing surfaces using the two-microphone transfer function technique, the application of the technique to the measurement of a suspended ceiling and to soft grassland is described. Real materials often exhibit extended reaction, and detailed experimental data is currently difficult to obtain for such samples. But for precise sound field predictions, accurate acoustical data is required. The suspended ceiling tiles investigated are extended reaction panels and measurements are performed in-situ. Consequently, no restrictions on the sample area, edge conditions, or homogeneity are applied. Comparisons with theoretical models are presented. These investigations indicate that the panel absorber can be described by its surface impedance, and that the two-microphone transfer function technique can be used to successfully measure this characteristic in-situ. The surface impedance of soft grassland is also successfully measured using both normal and oblique incident sound. These measurements are compared with theoretical models, which are then used to obtain information concerning the structure of the ground, without invasive sampling.

Sliding Mode Control for a Robot Scara

The variable structure systems (VSS) theory has been developed many years ago, and it has been proved that it's well suited for robotics arms where the robust performances are most important in spite of the presence of parametric variations and disturbances. A practical realization of a robust controller using VSS is described in this paper. The important issue in the design of VSS is to avoid the chattering caused by the switched input. This problem is solved by introducing the continuous control input instead of switched input. To this end, a PID corrector which can be timed on line, is used. This paper shows the benefits of using such controller associated to VSS to eliminate the chattering. At the end, the robustness of the control against input disturbance and payload variations is demonstrated. In this study the controller design is obtained by combining classical transfer function techniques, sliding mode systems ideas and PID control. The interest of the overall controller is in its potential to combine the good transient performance and the steady state properties of the VSS-PID control. The PID boundary layer provides adaptive tracking quality even under changing process parameters. The above mentioned techniques are applied to the regulation (point to point) control of a robot SCARA with the three degree of freedom. In this work, experimental results obtained by applying the VSS-PID control law to real manipulator are given.

Determination of Acoustical Impedance of Absorbing Surfaces by Two-Microphone Transfer Function Techniques: Effect of Absorption Mechanism

In the third of a series of papers on the measurement of acoustical impedance of absorbing surfaces using the two-microphone transfer function technique, the influence of surface absorption mechanism upon the measured impedance is described. The results from measurements of the impedance of bulk reactors are compared with values obtained from theoretical models. Materials investigated are an inhomogeneous polyurethane foam, a distributed resonance absorber, and a twin layer foam. This paper also investigates how the measurement technique behaves with samples which are bulk reacting and have surface roughness. A rough surfaced polyurethane foam sample is used. The results indicate that at frequencies for which the surface irregularities are small in comparison to the wavelength, the material can be accurately characterised by the acoustical impedance acting at an effective plane. For higher frequencies it is thought that the measuring technique becomes inaccurate due to scattering of sound by the surface roughness, and the consequent breakdown of the sound field prediction methods.

Speech intelligibility in Grady Gammage Memorial Auditorium

‘‘The most important function of sound in theater is to ensure audience comfort in perceiving audio component of a performance’’ [Bracewell, Sound Design of Theater (1993)]. Background research has unveiled poor speech intelligibility at the Gammage Auditorium. This study aims to map speech intelligibility in different seating areas and measure the factors causing poor speech intelligibility. The instrument used to collect data will be the Techron TEF System 12 analyzer. This instrument uses modulation transfer function (MTF) and speech transmission index (STI) techniques. This is based on RASTI techniques by measuring the reduction of signal modulation in an acoustic transmission path [Keele, Jr. (1988)]. MTF is a measure of how well the amplitude modulation of a signal is preserved when a signal is sent from one point to another. The measurement modulations at different frequencies are converted to a single value that indicates the speech intelligibility in the auditorium. This single value is STI. Measurements are also provided on data for signal-to-noise ratio and RT60. A separate measurement of background noise level would indicate poor speech intelligibility due to excessive reverberation or background noise.

Determination of Acoustical Impedance of Absorbing Surfaces by Two-Microphone Transfer Function Techniques: Geometrical and Measurement Errors

In the second of a series of papers on the measurement of acoustical impedance of absorbing surfaces in-situ, geometrical and measurement errors for the two microphone transfer function technique are detailed. The effects of finite sample area on the impedance measured are considered, and experimental results show that for edge effects to be negligible, the minimum dimension of a sample should be two wavelengths. The method also becomes inaccurate when the transfer function tends to unity. This is shown to occur at low frequencies, but more importantly, at higher frequencies when an integral number of half wavelengths exists between the path length differences to the microphones. The results of the error analysis show that great care should be taken in determining the precise locations of the microphones. In particular, care should be taken in the alignment of the microphones with respect to the normal to the sample, since errors due to the alignment of the probe combine features of errors not only in the microphone positions, but also in the source location and the angle of sound incidence. In comparison with typical errors in the experimental geometry, errors due to the precision of typical transfer function estimates are very small.

Faunal and alkenone reconstructions of subtropical North Atlantic surface hydrography and paleotemperature over the last 28 kyr

Two techniques for estimating past variations in sea surface temperature (SST) have been used to investigate climatic change in Biogeochemical Oceanic Flux Study (BOFS) core 31K (19°N, 20°W) from the eastern subtropical Atlantic. High‐resolution SST records for the last 28 kyr have been produced using planktonic foraminiferal assemblages, based on the Imbrie‐Kipp transfer function technique, and the UK′37 index derived from abundances of C37 alkenones biosynthesized by prymnesiophyte algae. Modern observations suggest that these indices reflect particular hydrographic conditions in the upper ocean: the UK′37 index corresponds to the temperature at the time of maximum coccolith productivity, typically late spring‐early summer in the study area today, whereas the faunal transfer function is calibrated for seasonal maximum and minimum temperatures. In general, the faunal and biomarker paleotemperature records display comparable SST variations during the last glacial and deglacial, but although the overall trends are similar, differences exist in the magnitude and timing of these temperature changes. Most notably, the faunal Twarm and UK′37 SST estimates diverge by 3°C between 8 ka and 6 ka, and this offset persists through the late Holocene. This difference cannot be adequately explained by uncertainties associated with either the calibration data sets or fluctuating preservation levels. We therefore propose that the deviation in SST estimates is linked to a switch in the seasonal timing of maximum coccolith production from the summer in the glacial ocean to the late spring‐early summer in the modern ocean. Our results suggest that a dual approach to SST estimation based on faunal and biomarker proxies can provide a valuable means of evaluating mixed layer and productivity changes associated with the movement of oceanographic frontal zones during the late Quaternary.