Modeling power and intermodulation behavior of microwave transistors with unified small‐signal/large‐signal neural network models

This article presents a detailed procedure to learn a nonlinear model and its derivatives to as many orders as desired with multilayer perceptron (MLP) neural networks. A modular neural network modeling a nonlinear function and its derivatives is introduced. The method has been used for the extraction of the large‐signal model of a power MESFET device, modeling the nonlinear relationship of drain‐source current I_ds as well as gate and drain charge Q_g and Q_d with respect to intrinsic voltages V_gs and V_ds over the whole operational bias region. The neural models have been implemented into a user‐defined nonlinear model of a commercial microwave simulator to predict output power performance as well as intermodulation distortion. The accuracy of the device model is verified by harmonic load‐pull measurements. This neural network approach has demonstrated to predict nonlinear behavior with enough accuracy even if based only on first‐order derivative information. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 276–284, 2003.     

Inhibitory properties of the regulatory domains of human protein kinase Calpha and mouse protein kinase Cepsilon

Two fusion proteins in which the regulatory domains of human protein kinase Calpha (Ralpha; amino acids 1-270) or mouse protein kinase Cepsilon (Repsilon; amino acids 1-385) were linked in frame with glutathione S-transferase (GST) were examined for their abilities to inhibit the catalytic activities of protein kinase Calpha (PKCalpha) and other protein kinases in vitro. Both GST-Ralpha and GST-Repsilon but not GST itself potently inhibited the activities of lipid-activated rat brain PKCalpha. In contrast, the fusion proteins had little or no inhibitory effect on the activities of the Ser/Thr protein kinases cAMP-dependent protein kinase, cGMP-dependent protein kinase, casein kinase II, myosin light chain kinase, and mitogen activated protein kinase or on the src Tyr kinase. GST-Ralpha and GST-Repsilon, on a molar basis, were 100-200-fold more potent inhibitors of PKCalpha activity than was the pseudosubstrate peptide PKC19-36. In addition, a GST-Ralpha fusion protein in which the first 32 amino acids of Ralpha were deleted (including the pseudosubstrate sequence from amino acids 19-31) was an effective competitive inhibitor of PKCalpha activity. The three GST-R fusion proteins also inhibited protamine-activated PKCalpha and proteolytically activated PKCalpha (PKM), two lipid-independent forms of PKCalpha; however, the IC50 values for inhibition were 1 order of magnitude greater than the IC50 values obtained in the presence of lipid. These results suggest that part of the inhibitory effect of the GST-R fusion proteins on lipid-activated PKCalpha may have resulted from sequestration of lipid activators. Nonetheless, as evidenced by their abilities to inhibit the lipid-independent forms of the enzyme, the GST-R fusion proteins also inhibited PKCalpha catalytic activity through direct interactions. These data indicate that the R domains of PKCalpha and PKCepsilon are specific inhibitors of protein kinase Calpha activity and suggest that regions of the R domain outside the pseudosubstrate sequence contribute to autoinhibition of the enzyme.     

Low-dose intravenous calcitriol treatment of secondary hyperparathyroidism in hemodialysis patients. Italian Group for the Study of Intravenous Calcitriol

Intravenous calcitriol is known to directly suppress PTH secretion and release. We evaluated the effect of four months of treatment with low-dose intravenous calcitriol on PTH levels in 83 hemodialysis patients. The criteria for including patients in the study were a serum PTH levels at least four times the normal limit, a serum total calcium less than 10 mg/dl and good control of the serum phosphorus level. All patients underwent standard bicarbonate or acetate dialysis; dialysate calcium level was maintained at the usual 3.5 mEq/liter concentration. Initial calcitriol dose was 0.87 +/- 0.02 (SEM) micrograms (0.015 micrograms/kg body wt) thrice weekly at the end of dialysis, and it was reduced in case of hypercalcemia or elevated calcium-phosphate product. Seven out of 83 patients dropped out during treatment. Among the 76 patients who completed the study, 58 (76%) showed a highly significant decrease of intact PTH levels (average reduction 48%) and of alkaline phosphatase levels after four months of therapy. Total serum calcium increased slightly but significantly in the responder group but remained unchanged in the non-responders. No significant changes in ionized calcium levels could be detected, even in responders. Treatment was well tolerated by patients, but 60% of them had transient episodes of hyperphosphatemia. Mean serum phosphate was 4.95 mg/dl at the beginning of the study. It increased significantly after four months of treatment in patients who showed a decrease of PTH levels, although it remained within acceptable limits, below 5.5 mg/dl. Twenty-eight of 76 patients (37%) reduced the dose of calcitriol because their calcium-phosphate products exceeded 60.(ABSTRACT TRUNCATED AT 250 WORDS)     

Age-related changes in the tiger salamander retina

Tiger salamanders have been used in visual science because of the large size of their cells and the ease of preparation and maintenance of in vitro retinal preparations. We have found that salamanders over 27 cm in length show a variety of visual abnormalities. Compared to smaller animals (15-23 cm), large animals exhibited a decrease in visual responses determined by tests of the optomotor reflex. Small animals responded correctly an average of 84.5% of the time in visual testing at three light levels compared to an average of 68.4% for the large animals with the poorest visual performance at the lowest level of illumination. In addition, large animals contained (i) histological degeneration of the outer retina, in particular, loss and disruption of outer segments and abnormalities of the retinal pigmented epithelium, (ii) loss of cells, including photoreceptors, by apoptosis as evaluated with the TUNEL technique, and (iii) an increase in the number of macrophages and lymphocytes within the retina as determined by morphological examination. These histological changes were present in all large animals and all quadrants of their retinas. In contrast, small animals showed virtually no retinal degeneration, no TUNEL-positive cells, and few immune-like cells in the retina. Since large animals are also older animals. the visual changes are age-related. Loss of visual function and histological degeneration in the outer retina also typify aged human eyes. Thus, we propose that large salamanders serve as an animal model for age-related retinal degeneration. In addition to providing a source of aging retina that is readily accessible to experimental manipulation, the salamander provides a pigmented retina with a mixed (2:1, rod:cone) population of photoreceptors, similar to the degeneration-prone parafoveal region of the human eye.     

Experimental performances of 5 GHz harmonic-manipulated highefficiency microwave power amplifiers

The measured performances of 5 GHz single-stage power amplifiers are presented. The amplifying stages were designed using a recently proposed high efficiency design methodology. Improvements in terms of power-added efficiency of 12, 29 and 43% as compared to standard design approaches have been obtained     

3D projection of the LuGre friction model adapted to varying normal forces

Multibody System Dynamics - In this paper, we develop an adaptation of the LuGre friction model so as to allow the development of the friction force and its application in any directions on systems...     

Parasitic effects of the metallic towers on the characteristics of the broadcast antennas

In this article, we use a tool NEC (Numerical Electromagnetic Code) to model antenna on top of a tower structure. Simulation results for the parasitic effect of the tower on characteristics of broadcast DVB‐T (Digital Video Broadcasting Terrestrial) antenna such as input impedance, return loss, gain, front‐to‐back ratio and radiation patterns are reported. In addition, the effect of a nearby tower on antenna characteristics is studied. A 3D tower and broadband antenna in the UHF (470‐862) MHz band are constructed. The antenna works for both digital and analog TV with return loss (RL) ≥ 10 dB, fractional bandwidth of 87% and gain of 12.3 dBi at center frequency. The effective radiated power is calculated by mounting the antenna at each face of the tower to give a satisfactory coverage to a region around the antenna.     

Asymmetrical Doherty power architecture with an integrated driver stage in the auxiliary branch

This contribution presents the analysis, design and characterization of a high gain Doherty power amplifier implementing an integrated Driver stage in the Auxiliary branch. Guidelines and design equations are demonstrated, fulfilling the full integration of the whole new architecture. The development of a microwave monolithic integrated circuit prototype based on TriQuint GaN technology for 7 GHz applications is reported. 10.5 dB of Gain, 38.1 dBm of saturated output power and 42% of efficiency at 7 dB of output back‐off have been demonstrated by experimental results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:498–507, 2014.     

Neural network modeling of microwave FETs based on third‐order distortion characterization

A new method for characterization of HEMT distortion parameters, which extracts the coefficents of a Taylor series expansion of I_ds(V_gs, V_ds), including all cross‐terms, is developed from low‐frequency harmonic measurements. The extracted parameters will be used either in a Volterra series model around a fixed bias point for 3^rd‐order characterization of small‐signal I_ds nonlinearity, or in a large‐signal model of I_ds characteristic, where its partial derivatives are locally characterized up to the 3^rd order in the whole bias region, using a novel neural‐network representation. The two models are verified by one‐tone and two‐tone intermodulation distortion (IMD) tests on a PHEMT device. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

An ontological framework for media analysis and mining

Advances in tools and technologies for digital media production and analysis have assured the availability of larger and larger amount of data which carry a huge amount of information for solving specific application tasks. This development has stressed the need for advanced systems that are not limited to media storage and management but include also their intelligent representation and retrieval. In this paper, we report current results of an ontological framework under development for mining media data, thus offering the possibility of storing, retrieving, analyzing and investigating media to discover novel knowledge relevant to strategic application processes.