High-speed, high-frequency ultrasound, \u3ci\u3ein utero\u3c/i\u3e vector-flow imaging of mouse embryos

Real-time imaging of the embryonic murine cardiovascular system is challenging due to the small size of the mouse embryo and rapid heart rate. High-frequency, linear-array ultrasound systems designed for small-animal imaging provide high-frame-rate and Doppler modes but are limited in regards to the field of view that can be imaged at fine-temporal and -spatial resolution. Here, a plane-wave imaging method was used to obtain high-speed image data from in utero mouse embryos and multi-angle, vector-flow algorithms were applied to the data to provide information on blood flow patterns in major organs. An 18-MHz linear array was used to acquire plane-wave data at absolute frame rates ≥10 kHz using a set of fixed transmission angles. After beamforming, vector-flow processing and image compounding, effective frame rates were on the order of 2 kHz. Data were acquired from the embryonic liver, heart and umbilical cord. Vector-flow results clearly revealed the complex nature of blood-flow patterns in the embryo with fine-temporal and -spatial resolution

Estimating the number of components of a multicomponent nonstationary signal using the short-term time-frequency Rényi entropy

This article proposes a method for estimating the local number of signals components using the short term Rényi entropy of signals in the time-frequency plane. (Additional details can be found in the comprehensive book on Time-Frequency Signal Analysis and Processing (see http://www.elsevier.com/locate/isbn/0080443354). In addition, the most recent upgrade of the original software package that calculates Time-Frequency Distributions and Instantaneous Frequency estimators can be downloaded from the web site: www.time-frequency.net. This was the first software developed in the field, and it was first released publicly in 1987 at the 1st ISSPA conference held in Brisbane, Australia, and then continuously updated).The time-frequency Rényi entropy provides a measure of complexity of a nonstationary multicomponent signal in the time-frequency plane. When the complexity of a signal corresponds to the number of its components, then this information is measured as the Rényi entropy of the time-frequency distribution (TFD) of the signal. This article presents a solution to the problem of detecting the number of components that are present in short-time interval of the signal TFD, using the short-term Rényi entropy. The method is automatic and it does not require a prior information about the signal. The algorithm is applied on both synthetic and real data, using a quadratic separable kernel TFD. The results confirm that the short-term Rényi entropy can be an effective tool for estimating the local number of components present in the signal. The key aspect of selecting a suitable TFD is also discussed

Seeing sound: a new way to illustrate auditory objects and their neural correlates

This thesis develops a new method for time-frequency signal processing and examines the relevance of the new representation in studies of neural coding in songbirds. The method groups together associated regions of the time-frequency plane into objects defined by time-frequency contours. By combining information about structurally stable contour shapes over multiple time-scales and angles, a signal decomposition is produced that distributes resolution adaptively. As a result, distinct signal components are represented in their own most parsimonious forms.  Next, through neural recordings in singing birds, it was found that activity in song premotor cortex is significantly correlated with the objects defined by this new representation of sound. In this process, an automated way of finding sub-syllable acoustic transitions in birdsongs was first developed, and then increased spiking probability was found at the boundaries of these acoustic transitions. Finally, a new approach to study auditory cortical sequence processing more generally is proposed. In this approach, songbirds were trained to discriminate Morse-code-like sequences of clicks, and the neural correlates of this behavior were examined in primary and secondary auditory cortex. It was found that a distinct transformation of auditory responses to the sequences of clicks exists as information transferred from primary to secondary auditory areas. Neurons in secondary auditory areas respond asynchronously and selectively -- in a manner that depends on the temporal context of the click. This transformation from a temporal to a spatial representation of sound provides a possible basis for the songbird's natural ability to discriminate complex temporal sequences

Planck 2013 results. II. Low Frequency Instrument data processing

We describe the data processing pipeline of the Planck Low Frequency Instrument (LFI) data processing centre (DPC) to create and characterize full-sky maps based on the first 15.5 months of operations at 30, 44, and 70 GHz. In particular, we discuss the various steps involved in reducing the data, from telemetry packets through to the production of cleaned, calibrated timelines and calibrated frequency maps. Data are continuously calibrated using the modulation induced on the mean temperature of the cosmic microwave background radiation by the proper motion of the spacecraft. Sky signals other than the dipole are removed by an iterative procedure based on simultaneous fitting of calibration parameters and sky maps. Noise properties are estimated from time-ordered data after the sky signal has been removed, using a generalized least squares map-making algorithm. A destriping code (Madam) is employed to combine radiometric data and pointing information into sky maps, minimizing the variance of correlated noise. Noise covariance matrices, required to compute statistical uncertainties on LFI and Planck products, are also produced. Main beams are estimated down to the ≈−20 dB level using Jupiter transits, which are also used for the geometrical calibration of the focal plane

The effects of transducer cross-axis sensitivity in modal analysis

Experimental modal analysis is highly dependent on the quality of the frequency response functions (FRFs) used to extract the mode shapes and other modal parameters. Therefore, the key to success in experimental modal analysis is to obtain FRFs which contain accurate and reliable information;In spite of manufacturers\u27 efforts to minimize the cross-axis sensitivity of their transducers, most transducers used to measure the response of the structure have a primary sensing axis and a perpendicular plane which contains a direction of maximum cross-axis sensitivity. Due to the cross-axis sensitivity, the measured signals are contaminated and this contamination can lead to serious errors in the measured FRFs as well as the resulting modal analysis. It was found that the contamination is not random in nature but is systematically accumulated in the measured FRF, and that the amount of cross-axis measurement error depends on the components of the motion to be measured relative to the primary sensing direction as well as the cross-axis plane;This cross-axis sensitivity error can be compensated for in either the time domain or the frequency domain. The method employed is dependent on the data acquisition and data processing system being used. Accurate calibration for the cross-axis sensitivities should be done using the same compensation process. Both compensated and uncompensated frequency response functions are used to show the effect of cross-axis sensitivity on the modal analysis results obtained for a simple structure

Influence of Intrinsic Trapping on The Performance Characteristics of ZnO-Bi 2

The lumped parameter/complex plane analysis technique reveals several contributions to the ac small-signal terminal immittance of the ZnO-Bi2O3 based varistors' grain-boundary response. The terminal capacitance constitutes multiple trapping phenomena, a barrier layer contribution, and a resonance effect in the frequency range 10-2 ≤ f ≤ 109 Hz. A trapping response near to ∼105 Hz (∼10-6 s), observed via the loss-peak and a distinct depressed semicircular relaxation in the complex capacitance plane, is common to all well-formed (exhibiting good performance for applications) devices regardless of the composition recipe and processing route. This trapping is attributed to possible formation of ionized intrinsic or native defects, and believed to be predominant within the electric field falling regions across the microstructural grain-boundary electrical barriers. The nature of rapidity of this intrinsic trapping and the corresponding degree of uniformity/non-uniformity can be utilized in conjunction with relevant information on other competing trapping phenomena to assess an overall performance of these devices. The constituting elements, responsible for the average relaxation time of the intrinsic trapping, indicate some sort of possible surge arrester (i.e., suppressor/absorber) applications criteria in the power systems' protection. The factors related to materials' history, composition recipe, and processing variables influence or modify relative magnitudes and increase or decrease the visibility of the constituting elements without distorting devices' generic dielectric behavior

2D cross-hole MMR - survey design and sensitivity analysis for cross-hole applications of the magnetometric resistivity method

The magnetometric resistivity (MMR) method measures low-level (typically < 1nT) magnetic fields associated with a low-frequency (1 - 20 Hz) electric current impressed into the ground to determine the subsurface resistivity structure. As a step towards the implementation of MMR for cross-hole imaging, in this Ph.D. thesis several aspects of survey design for near-surface applications are discussed. In numerical, laboratory and field studies the potential of MMR for advanced structural characterization and process monitoring at the field scale is assessed. The 2D cross-hole setup considers borehole measurements of the magnetic field as response to borehole current injection; in this case the magnetic field has only one non-zero component (perpendicular to the imaging plane – B$_{y}$). Optimal survey parameters are inferred from numerical studies regarding signal strength, source-generated noise level and resolving power. Modeling of MMR responses over 2D conductivity structures was performed using a newly developed 2.5D FE program MMRMod. It could be proven that current injection via vertical dipoles provides superior signal-to-noise ratio compared to other transmitter configurations. Analyzing resolving power in terms of sensitivity distribution reveals that dipole configurations reflect confined subsurface volumes, advantageous for tomographic surveys and that transmitter-receiver combinations exceeding an offset equal to the borehole separation do not contribute significantly to the overall crosshole resolution. With the assistance of laboratory testing two concepts for solving two major difficulties inherent in cross-hole MMR field surveying are derived: the correction for the arbitrary borehole sensor orientation and the correction for parasitic correlated noise fields induced by the measurement system itself. The (latter) measurement method with phase switching is thereby first-time successfully applied to the processing of MMR data. In addition, the proposed data processing procedure includes modern lock-in-technique and has proven to be an appropriate tool for an effective information extraction from the measured magnetic fields. Finally, cross-hole MMR data were collected during a water infiltration experiment at the Gorgonzola test site. Acquisition and processing are accomplished according to the developed tomographic measurement approach involving multiple-offset transmitter-receiver arrangements and repeated measurements with time (time-lapse mode). Data, obtained during initially conducted background measurement, are qualitatively validated based on two different conductivity models, one of which is obtained from the inversion of independently collected ERT data. Importantly, the comparison of field data with predicted model curves suggests better resolvability of contrasts by MMR than by ERT. Moreover, the analysis of time-lapse measurements reveals a clear spatiotemporal dependence of the anomalous MMRresponse (MMR response with respect to background value) based upon the water saturation