1 

Fast lowsidelobe synthesis for large planar array antennas utilizing successive fast fourier transforms of the array factor
A new and very fast lowsidelobe pattern synthesis method for planar array antennas with periodic element spacing is described. The basic idea of the method is that since the array factor is related to the element excitations through an inverse Fourier transform, the element excitations can be derived from the array factor through a direct Fourier transform. Starting with an initial set of suitable element excitations the array factor is calculated. After matching the array factor to the prescribed pattern, an updated set of excitations is obtained through a direct Fourier transform performed on the matched array factor. From this updated set, only the samples associated with the aperture are retained, where after a new array factor is calculated. The whole process is repeated until the updated array factor does not violate any longer the pattern requirements. The proposed synthesis method provides significant improvements in terms of performance, computational speed, flexibility, and ease of implementation in software to the methods described in reviewed literature. A number of representative examples are presented to demonstrate the various unique capabilities of the method. The results include sum and difference patterns for circular and elliptical aperture shapes featuring uniform ultra low sidelobes. © 2007 IEEE.

[Abstract]

2 

"True" physical optics for the accurate characterization of antenna radomes and lenses
With the introduction of the "True" Physical Optics, the source in the far field of the canonical structure was not assumed but instead to use the exact dielectric slab's GF's in orde to obtain a more accurate approximation of the PO currents in both the external and the internal sides of the radome. Indeed the PO approximation, consists only in assuming that, for large radii of curvature of the structure, the currents are locally the same as the ones associated to the canonical planar structure that best fits the actual geometry in the point considered.

[Abstract]

3 

Efficient Partitioning of Algorithms for Long Convolutions and their Mapping onto Architectures
We present an efficient approach for the partitioning of algorithms implementing long convolutions. The dependence graph (DG) of a convolution algorithm is locally sequential globally parallel (LSGP) partitioned into smaller, less complex convolution algorithms. The LSGP partitioned DG is mapped onto a signal flow graph (SFG), in which each processor element (PE) performs a small convolution algorithm. The key is then to reduce the complexity of the SFG in two steps: 1. local reduction of complexity: the short Fast Fourier Transform (FFT) is used to perform the small convolution within the PE, 2. global reduction of complexity: the short FFTs within the PEs are relocated to the global level, where redundant short FFT operations are eliminated. The remaining operation within the PEs is now a simple elementwise multiplyadd. After a graph transform, the structure of the SFG kernel is recognized as a set of parallel small convolutions. If we use the short FFT to perform these short convolutions, we come to our final realization of the long convolution algorithm. The computational complexity of this realization is close to the optimum for convolutions, that is, script O sign (N log N). Our approach is thus achieving this N log N  low without having to implement largesize FFTs. We use, instead, small FFT blocks. The advantage is that small FFT transforms are commercially available, and that they can even be implemented in singlechip VLSI architectures. Our final SFG is three dimensional and can be mapped efficiently onto prototype architectures or dedicated VLSI processors. We demonstrate the procedure in the paper by a design example: the implementation of a prototype convolution architecture that we designed for a realtime radar imaging system.

[Abstract]

4 

The penetration depth in modelling natural groundwater flow
In this paper, we present a method that may lead to a better quantitative insight into the relation between the size (horizontal dimensions) of a natural groundwater flow modelling area and the schematization required for a numerical model. The method is based on a decomposition of the spatial variability of the groundwater table into a Fourier series. Each sinusoidal Fourier mode has a specific wavelength that can be considered as a measure of the scale represented by the mode. Modes with small wavelengths correspond to local differences in the groundwater table and modes with large wavelengths correspond to regional differences in the groundwater table. The contribution of each individual Fourier mode to the groundwater flow at a certain depth can be determined. This offers the opportunity to evaluate which details in the variation of the groundwater table should be taken into account in a certain numerical model. A penetration depth is defined and used to determine the depth over which the groundwater flow pattern is significantly influenced by a certain Fourier mode. Such an analysis can be performed for each important Fourier mode in the problem under consideration. This approach results in simple algebraic expressions to assess grid size and the vertical dimension of a numerical model.

[Abstract]

5 

A single Chip Implementation for Fast Convolution of Long Sequences
Usually, long convolutions are computed by programmable DSP boards using long FFTs. Typical operational requirements such as minimum power dissipation, minimum volume and high dynamic range/accuracy, make this solution often inefficient and even unacceptable. In this paper we present a single chip floating point solution for large convolution problems. It is based on an algorithm that maps long convolutions on short FFTs without affecting the optimum complexity O(N log N). The chip contains a highly parallelized short length FFT core enabling us to compute an FFT completely, without external FFT working memory intervention. The FFT core contains a set of fully parallelized radix 2 processing cores based on a hybrid floating point data format. The proposed implementation of the arithmetic blocks is the result of a trade off between maximum accuracy, maximum dynamic range and minimum chip area. The convolution chip will be used in a realtime Synthetic Aperture Radar (SAR) imaging processor developed for onboard aircraft or satellite processing.

[Abstract]

6 

Element failure correction for a large monopulse phased array antenna with active amplitude weighting
Recently a new method is introduced to synthesize low sidelobe patterns for planar array antennas with a periodic element arrangement. The method makes use of the property that for a planar array with periodic spacing of the elements, an inverse Fourier transform relationship exists between the array factor and the element excitations. This property is used in an iterative way to derive the array element excitations from the prescribed array factor. The same method is also able to partially compensate the degradation of the sidelobe and gain performance of array patterns due to element failures. Numerical examples of arrayfailure correction using this method are given for ultralow sidelobe sum and difference patterns of a 5800element circular array where the failed elements are randomly dispersed across the aperture. The tapers in this array are created exclusively by active weighting in the transmit/receive (T/R) modules using variable gain control. © 2007 IEEE.

[Abstract]

7 

Green's function for an infinite slot printed between two homogeneous dielectrics  Part I: Magnetic currents
This sequence of papers presents an analytical closed form for the Green's function of an infinite slot printed between two different homogeneous dielectrics. This first part is devoted to the derivation of the slot magnetic current and to the discussion of the relevant physical implications. The Fourier spectrum of the magnetic current is derived by solving in analytical form, under small width approximation, the integral equation (IE) representing the continuity of the magnetic field trough the slot axis. The accuracy of the result is validated trough a fine meshing Method of Moments. From the consequent spectral expression, a closed form approximation of the leakywave propagation and attenuation constants is derived. An asymptotic expression for the current is also obtained by steepest descent path evaluation of the pertinent spectral integral. Analytical expressions of the quasi static (reactive) contribution is given for both elementary dipole and delta gap excitations. The asymptotic, uniform closed form approximation for the field in every space point will be formulated and discussed in the second part of the paper.

[Abstract]

8 

Detection of a buried wire with two resistively loaded wire antennas
The use of two identical straight thinwire antennas for the detection of a buried wire is analyzed with the aid of numerical calculations. The buried wire is located below an interface between two homogeneous halfspaces. The detection setup, which is formed by a transmitting and a receiving wire, is located above the interface. The transmitter is excited by a pulsed voltage in a small gap. A resistance profile according to Wu and King [1965] has been used to suppress the reflections at the end of the wires. This enhances the visibility of properties of the lower halfspace directly from the time response of the current along the receiving antenna. The problem is solved in several steps. First, the electric field integral equation for the total current along a single thinwire antenna in a homogeneous space is formulated. The result is then used to construct a set of coupled integral equations to describe the currents along all three wires without the resistive load. The integral equations contain the transmitted and reflected fields due to the interface. Next, the set of integral equations is adapted for the resistance profile along the wires of the detection setup. The reflected and transmitted fields in both halfspaces are treated as secondary incident fields in the integral equation for the currents along the wires. In these equations, the response from a pulsed dipole source in the same configuration occurs as a Green's function. The inverse spatial Fourier transformation that occurs in the transmitted and reflected fields is carried out with the aid of a frequency independent, composite Gaussian quadrature rule. The set of coupled integral equations is solved by using the continuoustime discretizedspace approach, where the space discretization is kept fixed for all frequencies. This results in a linear system of equations with a fixed dimension which is solved by the conjugate gradientfast Fourier transform (CGFFT) method. With the aid of a marchingoninfrequency scheme, the system is solved for a number of frequencies. Time domain results are obtained by applying an inverse Fourier transformation. Representative numerical results are presented and discussed.

[Abstract]

9 

Engineering Multirate Convolutions for Radar Imaging
We present a schematic design methodology for multirate convolution systems, based on combined algorithmic development and architecture design. It allows us to map the algebraic specification of a long convolution algorithm directly onto efficient fast convolution hardware based on short FFT processor elements or dedicated VLSI processors. The design methodology exploits the known relationship between multirate filter banks and fast convolution schemes in an implicit manner, and allows the hardware designer to concentrate on typical application specific constraints such as processing speed, processor size and memory utilization. The methodology has proven its usefulness in the design of a convolution processor for realtime onboard synthetic aperture radar imaging

[Abstract]

10 

ProblemMatched Basis Functions for Microstrip Coupled Slot Antennas based on Transmission Line Greens Functions
A general algorithm for the analysis of microstrip coupled leaky wave slot antennas was discussed. The method was based on the construction of physically appealing entire domain Methods of Moments (MoM) basis function that allowed a consistent reduction of the number of unknowns and of total computation time. The basis function obtained were solutions of an integral equation that represented the boundary conditions of a physical problem and had adequate contents of local reactive energy. The procedure could also be used as a matrixcompression technique when the basis function were reviewed as ruling the group of the subdomain unknowns

[Abstract]

11 

ProblemMatched Basis Functions for Microstrip Coupled Slot Arrays based on Transmission Line Green+s Functions (TLGF)
A method is proposed for the analysis of arrays of linear printed antennas. After the formulation of pertinent set of integral equations, the appropriate equivalent currents of the Method of Moments are represented in terms of two sets of entire domain basis functions. These functions synthesize on one side the resonant behavior of the slot, microstrips or dipole and on the other side the field in proximity of the feeding source and of the discontinuities. In order to define these basis functions, canonical geometries are identified, whose Green's functions have been found in semianalytical form. The accuracy and the effectiveness of the method in terms of convergence rate and number of unknowns is demonstrated by comparison with a standard fine meshing fullwave analysis. The method is extremely convenient for large arrays where the details of the feed are very small in terms of the wavelength. Since the proposed solution is independent on the dimensions of these details, it provides a dramatic reduction of the number of unknowns with respect to a standard fine mesh analysis.

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[Abstract]

12 

Quantitative comparison of adhesion in metaltoplastic systems
A peel test device was used to monitor metalpolymer adhesion. This technique showed variations in the resulting force within 1%, and enabled the ranking of many systems. A change in the 50 nmadhesion layer resulted in a variation of the fracture energy by a factor 2.3. A change of the substrate led to a change in adhesion by a factor 40. The peeling results were also combined with attenuated total reflectance Fourier transform infrared measurements to provide qualitative insight of the bonds at the substrate surface. Differences were also visible after surface pretreatment by plasma or sputter etching with different gases, as changes in interaction bonds as well as in adhesion were observed. © 2008 Elsevier B.V. All rights reserved.

[Abstract]

13 

3D postprocessing of prebeamformed RF data in the frequencywavenumber domain
Threedimensional (3D) high resolution beamforming is made more difficult by high data rates. This can be overcome by twostep imaging approaches such as the synthetic aperture beamforming technique. In this technique the first step significantly reduces the data rate by linebased delay and sum, whereas the second stage recombines the data to a high resolution volume image. The second step is implemented using 3D Fast Fourier Transforms and an interpolation step in frequencywavenumber domain. A proof of concept is shown using a scanning 1 MHz focused single element transducer. The resulting volume image had a maximum 6dB point spread function of 3 mm throughout the entire depth of 135 mm. The signaltonoise ratio was improved by 20dB in the far field.

[Abstract]

14 

Bioconversion of red ginseng saponins in the gastrointestinal tract in vitro model studied by highperformance liquid chromatographyhigh resolution Fourier transform ion cyclotron resonance mass spectrometry
article 
2009

Author: 
Kong, H.
·
Wang, M.
·
Venema, K.
·
Maathuis, A.
·
Heijden, R. van der
·
Greef, J. van der
·
Xu, G.
·
Hankemeier, T.

Keywords: 
Biology · Analytical research · Biomedical research · Acidic hydrolysis · Ginsenoside · HPLCFTICRMS · Intestinal bacteria · Metabolism · Metabolite profiling · Panax ginseng · Gastrointestinal model · TIM · Acidic hydrolysis · Ginsenoside · HPLCFTICRMS · Intestinal bacteria · Metabolite profiling · Panax ginseng · Bacteriology · Biochemistry · Biomolecules · Body fluids · Chromatographic analysis · Chromatography · Cyclotron resonance · Cyclotrons · Electron cyclotron resonance · High performance liquid chromatography · High pressure liquid chromatography · Hydrolysis · Ion chromatography · Liquid chromatography · Mass spectrometers · Mass spectrometry · Metabolism · Metabolites · Pharmacodynamics · Plasmas · Resonance · Spectrometers · Spectrometry · Spectrum analysis · Technological forecasting · Thermal insulating materials · Fourier transforms · Chinese medicine · Biological Availability · Biotransformation · Chromatography, High Pressure Liquid · Fourier Analysis · Ginsenosides · Humans · HydrogenIon Concentration · Intestine, Large · Mass Spectrometry · Models, Biological · Panax · Reproducibility of Results · Solid Phase Extraction · Panax ginseng

A highperformance liquid chromatographyhigh resolution Fourier transform ion cyclotron resonance mass spectrometry (HPLCFTICRMS) method was developed to investigate the metabolism of ginsenosides in in vitro models of the gastrointestinal tract. The metabolites were identified by highresolution tandem mass spectrometry. Degradation and bioconversion routes of the different ginsenosides at acidic (gastric) conditions and in the presence of intestinal microbiota were elaborated. Besides hydrolysis (deglycosylation) also hydration reactions occurred at acidic conditions. The results illustrate the value of metabolite profiling by HPLCFTICRMS for understanding of the mechanisms in bioavailability of herbal drugs and their metabolites. © 2008 Elsevier B.V. All rights reserved.

[Abstract]

15 

Quantitative profiling of bile acids in biofluids and tissues based on accurate mass high resolution LCFTMS: Compound class targeting in a metabolomics workflow
article 
2008

Author: 
Bobeldijk, I.
·
Hekman, M.
·
Vries de Weij, J.van der
·
Coulier, L.
·
Ramaker, R.
·
Kleemann, R.
·
Kooistra, T.
·
Rubingh, C.
·
Freidig, A.
·
Verheij, E.

Keywords: 
Analytical research · Accurate mass · Bile acids · Body fluids · High performance liquid chromatography · Metabolomics · Targeted metabolite profiling · Tissues · Acids · Arsenic compounds · Chlorine compounds · Cholesterol · Chromatographic analysis · Complexation · Electrospray ionization · Fourier transforms · High performance liquid chromatography · Histology · Ionization · Ionization of liquids · Liquid chromatography · Liquid phase epitaxy · Liver · Mass spectrometers · Mass spectrometry · Metabolites · Phase separation · Plasmas · Separation · Spectrometers · Spectrometry · Sulfate minerals · Accurate mass · Bile acid synthesis · Bile acids · Biofluids · Biological fluids · Cholesterol homeostasis · Chromatographymass spectrometry · Electro spraying · Fourier Transform Mass Spectrometer · Generic methods · High resolutions · HPLCMS · Human plasmas · Human urine · Linear ion trap · Metabolomics · Mouse liver · Pooled samples · Reversedphase high performance · Sample preparations · Targeted metabolite profiling · Tissues · Body fluids · Bile acid · Glycine · Sulfate · Accuracy · Animal experiment · Animal tissue · Article · Bile acid synthesis · Body fluid · Cholesterol intake · Cholesterol liver level · Controlled study · Electrospray · Fourier transform mass spectrometry · Homeostasis · Human · Liver · Metabolite · Metabolomics · Nonhuman · Priority journal · Quantitative analysis · Reversed phase high performance liquid chromatography · Statistical significance · Tissue · Animals · Bile Acids and Salts · Cholesterol, Dietary · Chromatography, Liquid · Computational Biology · Fourier Analysis · Humans · Liver · Mass Spectrometry · Metabolism · Mice · Reproducibility of Results

We report a sensitive, generic method for quantitative profiling of bile acids and other endogenous metabolites in small quantities of various biological fluids and tissues. The method is based on a straightforward sample preparation, separation by reversedphase high performance liquidchromatography mass spectrometry (HPLCMS) and electrospray ionisation in the negative ionisation mode (ESI). Detection is performed in full scan using the linear ion trap Fourier transform mass spectrometer (LTQFTMS) generating data for many (endogenous) metabolites, not only bile acids. A validation of the method in urine, plasma and liver was performed for 17 bile acids including their taurine, sulfate and glycine conjugates. The method is linear in the 0.011 μM range. The accuracy in human plasma ranges from 74 to 113%, in human urine 77 to 104% and in mouse liver 79 to 140%. The precision ranges from 2 to 20% for pooled samples even in studies with large number of samples (n > 250). The method was successfully applied to a multicompartmental APOE*3Leiden mouse study, the main goal of which was to analyze the effect of increasing dietary cholesterol concentrations on hepatic cholesterol homeostasis and bile acid synthesis. Serum and liver samples from different treatment groups were profiled with the new method. Statistically significant differences between the diet groups were observed regarding total as well as individual bile acid concentrations. © 2008 Elsevier B.V. All rights reserved.

[Abstract]
