Nonlinear Characterization of Wideband Microwave Devices and Dispersive Effects in GaN HEMTs

Measurements play a key role in the development of microwave hardware as they allow engineers to test and verify the RF performance on a system, circuit, and component level. Since modern cellular standards employ complex modulation formats with wider signal bandwidths to cope with the growing demand of higher datarates, nonlinear characterization using wideband stimuli is becoming increasingly important. Furthermore, III-N semiconductor technologies such as gallium nitride (GaN) are to a larger extent utilized to enable higher performance in microwave circuits. However, GaN is highly frequency-dispersive due to trapping phenomena and thermal effects. This thesis deals with the development of nonlinear measurement instruments as well as characterization of dispersive effects in GaN high-electron-mobility transistors (HEMTs).A measurement setup for wideband, nonlinear characterization of microwave devices has been designed and verified. The setup allows for simultaneous acquisition of low-frequency and radio-frequency signals from DC up to 4~GHz through the use of wideband signal generators and measurement receivers. This enables measurement scenarios such as multi-band load-pull and large-signal characterization of IQ-mixers, which can give useful insight into how to optimize the performance in a RF transmitter.Electrothermal characterization of GaN devices has been carried out using conventional measurement methods such as pulsed I-V, and it is shown that trapping phenomena and thermal effects due to self-heating or mutual coupling are challenging to separate. Multiple methods must be utilized to fully characterize both the large-signal and small-signal impact on device performance. A new characterization method has been developed, for extraction of thermal transfer functions between mutually coupled devices on e.g. a semiconductor wafer. The method does not require any DC-bias on the measured devices, which can potentially reduce the influence of trapping during characterization of thermal properties in materials

Vector-corrected Nonlinear Multi-port IQ-mixer Characterization using Modulated Signals

In this paper, large-signal operation of IQ-mixers isstudied using a vector-corrected four-port measurement setup with modulated signals as stimuli. The measurement setup presents unique characterization possibilities since it has two ports at low/baseband frequencies and two ports at RF, making it ideal for characterization of frequency-translating devices such as mixers. A commercial upconverting IQ-mixer is studied, with the I and Q input signals residing at incommensurate frequencygrids, enabling separation of the nonlinear distortion generated in the I and Q branches. Frequency-domain and time-domain measurements reveal imbalances between the I and Q branches in terms of conversion gain and nonlinear distortion. It is also shown for the same mixer that operating the I and Q branches concurrently has limited influence on both conversion gain and nonlinear distortion, compared to non-concurrent operation

Fibromodulin Deficiency Reduces Low-Density Lipoprotein Accumulation in Atherosclerotic Plaques in Apolipoprotein E-Null Mice.

OBJECTIVE: The aim of this study was to analyze how an altered collagen structure affects development of atherosclerotic plaques. METHODS AND RESULTS: Fibromodulin-null mice develop an abnormal collagen fibril structure. In apolipoprotein E (ApoE)-null and ApoE/fibromodulin-null mice, a shear stress-modifying carotid artery cast induced formation of atherosclerotic plaques of different phenotypes; inflammatory in low-shear stress regions and fibrous in oscillatory shear stress regions. Electron microscopy showed that collagen fibrils were thicker and more heterogeneous in oscillatory shear stress lesions from ApoE/fibromodulin-null mice. Low-shear stress lesions were smaller in ApoE/fibromodulin-null mice and contained less lipids. Total plaque burden in aortas stained en face with Oil Red O, as well as lipid accumulation in aortic root lesions, was also decreased in ApoE/fibromodulin-null mice. In addition, lipid accumulation in RAW264.7 macrophages cultured on fibromodulin-deficient extracellular matrix was decreased, whereas levels of interleukin-6 and -10 were increased. Our results show that an abnormal plaque collagen fibril structure can influence atherosclerotic plaque development. CONCLUSIONS: The present findings suggest a more complex role for collagen in plaque stability than previously anticipated, in that it may promote lipid-accumulation and inflammation at the same time as it provides mechanical stability

Репродуктивный потенциал и динамика его составляющих за последнее десятилетие

РЕПРОДУКТИВНОСТИ АНАЛИЗЭПИДЕМИОЛОГИЧЕСКИЕ ФАКТОРЫЗДОРОВЬЯ СОСТОЯНИЕДЕМОГРАФИЧЕСКАЯ СТАТИСТИКАРЕПРОДУКЦИ

Енергоощадне зовнішнє освітлення та його вплив на якісні показники електричної енергії

Background: Despite an increasing number of studies on the factors mediating the impact of the economic recession on mental health, research beyond the individual employment status is scarce. Our objectives were to investigate in which ways the mental health of employed and unemployed populations is differently affected by the current economic recession along the educational scale and to examine whether financial strain and social support explain these effects of the crisis. Methods: A repeated cross-sectional study, using two waves of the Andalusian Health Survey in 2007 (pre-crisis) and 2011-2012 (crisis). A population aged between 19 and 64 years was selected. The dependent variable was the Mental Component Summary of the SF-12 questionnaire. We performed Poisson regression models stratified by working status, with period, educational level, financial strain and social support as independent variables. We examined interactions between period and educational level. Age, sex, main earner, cohabitation and partner's working status were considered as covariates. Results: The study included 3210 individuals (1185 women) in 2007 and 3633 individuals (1486 women) in 2011-2012. In working individuals the prevalence of poor mental health increased for secondary and complete primary studies groups during crisis compared to the pre-crisis period, while it decreased significantly in the university study group (PR = 0.76, 95 % CI: 0.58-0.99). However, in unemployed individuals prevalence ratios for poor mental health increased significantly only in the secondary studies group (PR = 1.73, 95 % CI: 1.06-2.83). Financial strain and social support yielded consistent associations with mental health in all subgroups. Only financial strain could partly explain the crisis effect on mental health among the unemployed. Conclusions: Our study supports the finding that current economic recession is associated with poorer mental health differentially according to labour market status and educational level. Those with secondary studies may be at risk in times of economic recession. In connection with this, emerging educational inequalities in mental health among the employed population were observed. Our research also suggests a partial mediating role of financial strain for the effects of crisis on poor mental health among the unemployed. Good social support appears to buffer poor mental health in all subgroups but not specifically during crisis period

Phase diagram of an impurity in the spin-1/2 chain: two channel Kondo effect versus Curie law

We consider a magnetic s=1/2 impurity in the antiferromagnetic spin chain as a function of two coupling parameters: the symmetric coupling of the impurity to two sites in the chain $J_1$ and the coupling between the two sites $J_2$. By using field theory arguments and numerical calculations we can identify all possible fixed points and classify the renormalization flow between them, which leads to a non-trivial phase diagram. Depending on the detailed choice of the two (frustrating) coupling strengths, the stable phases correspond either to a decoupled spin with Curie law behavior or to a non-Fermi liquid fixed point with a logarithmically diverging impurity susceptibility as in the two channel Kondo effect. Our results resolve a controversy about the renormalization flow.Comment: 5 pages in revtex format including 4 embedded figures (using epsf). The latest version in PDF format is available from http://fy.chalmers.se/~eggert/papers/phase-diagram.pd

Prediction of Nonlinear Distortion in Wideband Active Antenna Arrays

In this paper we propose a technique for comprehensive analysis of nonlinear and dynamic characteristics of multi-antenna transmitters (TXs). The analysis technique is enabled by the development of a Volterra series-based dual-input model for power amplifiers (PAs), which is capable of taking into account the joint effects of PA nonlinearity, antenna crosstalk and mismatch for wideband modulated signals. By combining multiple instances of the PA model with linear dynamic antenna simulations we develop the analysis technique. The proposed method allows the prediction of the output signal of every antenna in an arbitrarily sized TX array, as well as the total far-field radiated wave of the TX for any input signal with low computational effort. A 2.12 GHz four-element TX demonstrator based on GaAs PAs is implemented to verify simulation results with measurements. The proposed technique is a powerful tool to study hardware characteristics, as for example the effects of antenna design and element spacing. It can be used in cases where experiments are not feasible, and thus aid the development of next generation wireless systems

О сложности моделирования графиков электрических нагрузок потребителей с кусочно-непрерывными расходными характеристиками

While the social determinants of cardiovascular disease (CVD) are fairly well-known, the determinants of socioeconomic inequalities in CVD are scarcely studied and almost completely based on cross-sectional designs in which the changing circumstances across the life course are not taken into account. The present study seeks to incorporate a life course approach to the social determinants of socioeconomic inequalities in CVD. The specific aims were to 1) examine how income-related inequalities in CVD change over two decades of the mid-late life course, and 2) identify the key social determinants of the inequalities at each time period. The cohort (N = 44,039) comprised all individuals aged 40-60 years in 1990 who during 1990-2010 were enrolled in the county-wide preventive effort :"Västerbotten Intervention Program" (VIP). The cohort was followed over these two decades by Swedish population register data linked within the Umeå SIMSAM Lab micro data infrastructure. First-time hospitalization for CVD and mean earned income were used to calculate the concentration index (C) during four periods of 5-6 years. The C for each period was decomposed by sociodemographic factors, using Wagstaff-type decomposition analysis. Results suggest that inequalities in CVD increase gradually from mid-life to old age; from initially non-significant to particularly marked among the elderly. The decomposition showed that, from middle to old age, educational and employment inequalities underwent a transition from initially dominant to a moderate role in explaining the health inequalities, coupled with an increasing importance of age and a stable role of income. In conclusion, the study illustrates the need for incorporating a dynamic life course perspective into research, policy and practice concerned with equity in health.Errata Social Science &amp; Medicine (2016) 160 p. 128 DOI:10.1016/j.socscimed.2016.05.031</p