Loss Imbalance Research Articles

Active Clamping Circuit With Status Feedback for Series-Connected HV-IGBTs

Active clamping circuits can effectively suppress the voltage imbalance between series-connected insulated-gate bipolar transistors (IGBTs). However, while the active clamping circuit is conducting, extra current is injected into the gate of the IGBT, the gate voltage increases, and the IGBT operates in the active region. Therefore, long time conduction and frequent actions of the active clamping circuit will lead to extremely high switching loss of the IGBT with high collector-emitter voltage and serious switching loss imbalance between the series-connected IGBTs, which imperils the efficiency and safety of the system, particularly in the applications of high-voltage IGBT (HV-IGBT) series connection. In this paper, a novel active clamping circuit with status feedback is proposed for series-connected HV-IGBTs. A high-speed status feedback subcircuit is designed for transforming the operation status of an active clamping circuit into optical signal and feeding it back to the control system. According to the feedback signals, the microcontroller regulates the switching-on time and switching-off time of the series-connected HV-IGBTs' drive signals timely in order to implement voltage balancing and, thus, to restrain the actions of active clamping circuits. By applying this voltage balancing method to the HV-IGBT series connection circuit, the voltage balancing performance is expected to improve, and high switching loss and serious switching loss imbalance are expected to be suppressed. Experimental results verify the validity and superiorities of the proposed voltage balancing circuit and control strategy.

Weight Loss and Homeostatic Imbalance of Leptin and Ghrelin Levels in Lean Older Adults

Weight Loss and Homeostatic Imbalance of Leptin and Ghrelin Levels in Lean Older Adults

Subwavelength grating Fourier‐transform interferometer array in silicon‐on‐insulator

AbstractA planar waveguide Fourier‐transform spectrometer with densely arrayed Mach‐Zehnder interferometers is demonstrated. Subwavelength gratings are used to produce an optical path difference without waveguide bends. The fabricated device comprises of an array of 32 Mach‐Zehnder interferometers, which produce a spatial interferogram without any moving parts, yielding a spectral resolution of 50 pm and a free‐spectral range of 0.78 nm. As a result of similar propagation losses in subwavelength grating waveguides and conventional strip waveguides, loss imbalance is minimized and high interferometic extinction ratio of −25 to −30 dB is obtained. Furthermore, phase and amplitude errors arising from normal fabrication variation are compensated by the spectral retrieval process using calibration measurements.

A 3‐dB Quadrature WLP Coupler for 60 GHz Applications

ABSTRACTA 60 GHz tandem coupler using offset broadside coupled lines is proposed in a WLP (Wafer Level Packaging) technology. The fabricated coupler has a core chip area of 750 μm × 385 μm (0.288 mm2). The measured results show an insertion loss of 0.44 dB, an amplitude imbalance of 0.03 dB and a phase difference of 87.6° at 60 GHz. Also the measurement shows an insertion loss of less than 0.67 dB, an amplitude imbalance of less than 0.31 dB, a phase error of less than 3.7°, an isolation of more than 29.7 dB and a return loss of more than 27.9 dB at the input ant coupled ports and more than 14.3 dB at the direct and isolated ports over the frequency band of 57-66 GHz, covering 60 GHz band both in Japan and US. To the best of our knowledge the proposed coupler achieves the lowest ever reported insertion loss and amplitude imbalance for a 3-dB coupler on a silicon substrate. With its superior performance and lower cost compared to the CMOS counterparts, the proposed coupler is a suitable candidate for low-cost high-performance millimeter-wave systems.

A Planar Dual 180<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula> Hybrid Using Multicoupled Line Sections

A novel planar dual 180° hybrid using multicoupled line technology is presented. The proposed structure adopts the power divider and two types of multicoupled lines to improve the return loss and isolation at the balance outputs of a traditional dual Marchand balun. The proposed hybrid allows output ports to be located arbitrarily, which eliminates the complex layout while the dual 180° hybrid applied to balanced radio frequency circuits. This hybrid is designed and implemented on an FR-4 printed circuit board at 2.4 GHz. The measured return loss is lower than -19.7 dB, and the isolation between the two-pair balanced output ports are lower than -28.2 dB from 2.2 to 2.7 GHz. The measured insertion loss and phase imbalance between the two-pair balanced output ports are lower than 8.7 dB and 4.5°, respectively, at the operating frequency of 2.1-2.9 GHz.

Investigation of emission location in top-emitting green organic light-emitting devices by optical analysis

A series of top-emitting organic light-emitting devices with different thicknesses of carrier transporting layers (N,N′-di(1-naphtyl)-N,N′-diphenylbenzidine, tris(8-hyroxyquinloine) aluminum (Alq 3)) and emitting layer (EML, 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)-doped Alq 3) were fabricated. C545T-doped Alq 3 was found to bring about double recombination peaks in EML. As the distance between EML and reflective anode was increased, the outcoupling efficiency greatly deviated from optically-simulated values due to charge imbalance in EML and optical loss at the EML/Alq 3 interface. The device with 30 nm of EML exhibited maximized outcoupling efficiency and further increase of EML thickness brought about decrease in efficiency due to decrease in hole–electron recombination at the EML/Alq 3 interface.

Distortion Correction in a High-Resolution Time-Stretch ADC Scalable to Continuous Time

Distortions caused by system components and by fundamental physical phenomena can limit the performance of photonic time-stretch ADCs. Here we use a combination of time-stretch linearization & equalization, DC-offset subtraction, and operation in a linear propagation regime to improve the signal-to-noise-and-distortion ratio by 17 dB for a 2-channel time-stretch ADC testbed and therein obtain noise-limited performance of 6-7 ENOB over a 10-GHz RF input bandwidth. Time-stretch linearization & equalization corrects for dispersion mismatches among testbed components by applying time-shifts calculated from component group delays to output ADC samples. DC-offset subtraction removes static errors due to insertion loss imbalances and Mach-Zehnder modulator bias offsets. If optical power levels are too high, nonlinear fiber propagation lowers the frequencies of dispersion-induced nulls in the RF transfer function and causes higher-order signal distortions. The 2-channel testbed can be directly scaled to a practical continuous-time system with the addition of more sub-aperture wavelength channels (total of 13 channels and 42 nm of optical bandwidth for a 90 MHz laser repetition rate). Adaptive online and fixed pre-calibrated stitching methods are demonstrated for joining data from one wavelength channel to the next.

The Transcriptome of Nrf2−/− Mice Provides Evidence for Impaired Cell Cycle Progression in the Development of Cigarette Smoke–Induced Emphysematous Changes

Cigarette smoke (CS) imposes a strong oxidative burden on exposed tissues resulting in a severely disturbed oxidant/antioxidant balance, which in the context of chronic exposure is assumed to be a key contributor to CS-related diseases. Because of its emerging central role in orchestrating the general cellular antioxidant response, the pathway leading to the activation of the transcription factor Nrf2 has received mounting attention over the past decade in investigations aimed at elucidating CS-induced pathophysiological mechanisms. To comprehensively characterize the impact of Nrf2 in acute and subchronic smoking scenarios, Nrf2(-/-) mice and their wild-type (wt) ICR littermates were exposed to either ambient air (sham exposure) or one of three doses of CS for up to 5 months, with two postexposure endpoints of 1 and 13 days. The lungs of the mice were monitored for transcriptomic changes on a genome-wide level, which confirmed an impaired expression of antioxidant and phase 2-related genes in CS-exposed Nrf2(-/-) mice. Importantly, in comparison to wt mice, an attenuated cell cycle/mitotic response and intensified stress gene expression pattern were observed in exposed Nrf2(-/-) mice, which was paralleled by clear dose-dependent effects on alveolar destruction and impaired lung function. In contrast, the inflammation-related transcriptional response and scores for various bronchioalveolar inflammation parameters were qualitatively and quantitatively similar in CS-exposed mice of both genotypes. Taken together, these results confirm the protective nature of Nrf2 in oxidative stress scenarios and suggest that the enhanced emphysematous phenotype exhibited by CS-exposed Nrf2(-/-) mice is more likely caused by an imbalance in cell loss and regeneration than by increased inflammation.

Balanced BPSK modulator for Ka‐band communication systems

AbstractThis article details the design of balanced PSK modulator using integrated finline coplanar line hybrid junction. The PSK signal output is in suspended stripline with incident wave carrier in unilateral symmetric finline. Schottky barrier diodes MA4E2037 from M/ACom has been used for modulation. The balanced configuration offers high isolation between the carrier input port and the modulated carrier output port and thus the pulse width variations and amplitude deviations are suppressed. An insertion loss imbalance of ±1.5 dB with an average loss of 2.5 dB in the two switching states has been achieved over 37.0 to 38.0 GHz against the estimated loss of 2.0 dB. The phase imbalance is ±10° with phase switching from 165° to 185°. As the PSK output signal is in suspended stripline, two BPSK Modulators can easily be combined together to work as QPSK modulator for point to point millimeter wave radio links. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3046–3049, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22910

Design and Fabrication of Ultra-Wideband Baluns Embedded in Multilayer Liquid Crystal Polymer Flex

In this paper, we present the design and fabrication of ultra-wideband (UWB) baluns embedded in multilayer liquid crystal polymer (LCP) flex. Fabrication techniques are demonstrated for processing these commercially available LCP thin-films by standard PCB equipments. Variations in the LCP thin-film thickness are characterized and compared before and after lamination. Results show good dimensional stability of the material, a critical factor in controlling the line impedances and performance of the balun. Electrical results of these baluns show bandwidths exceeding 3.1-10.6 GHz with less than 1 dB insertion loss, and amplitude and phase imbalance less than 1.2 dB and 2deg, respectively. These baluns are ideal for applications in UWB communication systems specified by the IEEE 802.15.3a standard.

Integrated Balanced BPSK Modulator for Millimeter Wave Systems

This paper details the design of integrated balanced PSK modulator using finline coplanar line hybrid junction. The PSK signal output is in suspended stripline with incident wave carrier in finline. Schottky barrier Diode MA4E2037 has been used for modulation. The balanced configuration offers high isolation between the carrier input port and the modulated carrier output port and thus the pulse width variations and amplitude deviations are suppressed. An insertion loss imbalance of±1.5 dB with an average loss of 2 dB in the two switching states has been achieved over 38.9 to 40 GHz. The phase imbalance is±10 degrees with phase switching from 180 to 199 degrees As the PSK output signal is in suspended stripline, two BPSK modulators can be easily combined together to work as QPSK modulator.

Non-Linear Growth of Trapped Particle Modes in Linearly Stable, Current-Carrying Plasmas – A Fundamental Process in Plasma Turbulence and Anomalous Transport

The two-stream instability as a fundamental process in a current-carrying plasma is reconsidered. Its well-established linear version, based on kinetic Landau theory, predicts a threshold for the drift velocity between both species below which the plasma should be stable. We report on simulations which, however, show that a plasma as a non-linearly responding medium can be destabilized well below this threshold. Responsible for this unexpected behaviour are coherent, electrostatic, trapped particle structures such as phase space vortices or holes which can grow non-linearly out of thermal noise receiving their energy from the net imbalance of loss of electron kinetic energy and gain of ion kinetic energy. The birth of predominantly zero-energy holes is shown numerically being associated with initial, non-topological fluctuations. The latter are not subject to Landau damping, as they lie outside the realm of linear wave theory. For a pair plasma a typical scenario is presented, which encompasses several regimes such as non-linear growth of multiple holes, saturation and fully developed structural turbulence as well as an asymptotic approach to a new collisionless equilibrium. During the transient, structural state the plasma transport appears to be highly anomalous.

Calcium absorption measurements in normal subjects in determining calcium deposition during prolonged hypokinesia and with and without calcium loading

Measuring calcium (Ca) absorption, Ca balance and Ca level in serum,feces and urine during HK (hypokinesia) with and without Ca loading, the aim of this study was to disclose if prolonged HK could reduce Ca deposition more with or without Ca load contributing to greater Ca imbalance. Studies were conducted during 30-days pre-HK and 364-days HK. Forty male normal volunteers 23.7+/-6.0 years of age were chosen as subjects. They were divided into four groups: unloaded active control subjects (UACS), unloaded hypokinetic subjects (UHKS), loaded active control subjects (LACS), loaded hypokinetic subjects (LHKS). All hypokinetic subjects were walking average distances of 0.5+/-0.2 km day(-1), and active control subjects were running average distances of 6.6+/-1.2 km day(-1). LACS and LHKS were loaded with 1.3 mmol calcium lactate/kg body wt. Before Ca load, fecal Ca loss, urinary Ca and phosphate (P) losses, Ca imbalance, serum ionized calcium (CaI), P and total Ca (Ca(t)) levels increased significantly. (P < 0.05) with time, and serum intact parathyroid hormone (iPTH), 1.25 dihydroxyvitamin D (1.25(OH)2D3) levels and Ca absorption, decreased significantly (P < 0.05) with time in LHKS and UHKS compared with their pre-HK values and their respective active controls (LACS and UACS). After Ca load, however, Ca absorption, serum iPTH and 1.25 (OH)2D3 levels decreased significantly (P < 0.05) more with time, while fecal Ca loss, urinary Ca and P excretion and Ca imbalance increased significantly (P < 0.05) more with time in LHKS than UHKS. Conversely, before and after Ca load, fecal Ca excretion, urinary P and Ca loss, serum CaI, P, Ca, iPTH and 1.25 (OH)2D3 levels, Ca absorption and Ca balance did not change in LACS and UACS compared with their pre-HK values. The greater Ca losses with than without Ca load have shown that the more Ca is consumed the more Ca is eliminated during HK and Ca imbalance. The significant increase of Ca loss with Ca imbalance demonstrated reduced Ca deposition. Dissociation between Ca loss and Ca imbalance demonstrated reduced Ca deposition as the mechanism of Ca imbalance development during HK.

Fluid balance measurements in disclosing fluid deposition during prolonged hypokinesia in healthy subjects.

Measuring fluid absorption and fluid homeostasis, the aim of this study was to establish if hypokinesia (HK) could depress fluid deposition and thus contribute to the development of fluid depletion. Studies were performed during 30 days pre-HK period and during 364 days HK period. Twenty healthy male individuals 24.0 +/- 6.6 years of age were chosen as subjects. They were equally divided into two groups: active control subjects (ACS) and hypokinetic subjects (HKS). All HKS were walking average distances of 0.7 +/- 0.2 km x day(-1) for 364 days, while all ACS were running average distances of 8.5 +/- 1.2 km x day(-1) for 364 days. Water imbalance, whole blood hemoglobin (Hb) and hematocrit (Hct), plasma protein, plasma osmolality, urinary and plasma sodium (Na+) and potassium (K+) levels and fluid loss increased significantly (p < 0.05), while fluid absorption, fluid consumption, glomerular filtration rate (GFR), and renal blood flow (RBF) reduced significantly (p < 0.05) in HKS compared with their pre-HK values and their respective active controls (ACS). Conversely, water balance, whole blood Hb and Hct, plasma protein, plasma osmolality, fluid absorption, GFR, RBF, urinary and plasma Na+ and K+ levels, fluid consumption and fluid loss did not change in ACS compared with their pre-HK control values. Significant increase of fluid loss with fluid imbalance may demonstrate decreased fluid deposition. Dissociation between fluid loss and fluid imbalance may demonstrate decreased fluid deposition as the mechanism of development of fluid depletion. It was concluded that fluid imbalance and the significant increase of Hb, Hct, plasma protein, plasma osmolality, urinary and plasma Na+ and K+ levels may demonstrate the presence of fluid depletion during prolonged HK in humans.

Design issues of a multimode interference-based 3-dB splitter.

We have investigated important issues such as the power loss, the loss imbalance the fabrication tolerances, and the wavelength dependence for the design of a multimode interference-based 3-dB splitter on deeply etched InP waveguides under general, restricted, and symmetric interference mechanisms. For this investigation, we used the finite-element-based beam propagation approach. Results are presented.

Serum fatty acid imbalance in bone loss: example with periodontal disease

Among the numerous factors of bone remodelling, the local action of arachidonic acid metabolites together with cytokines, is particularly important, especially that of prostaglandin PGE2. It has been suggested that the alveolar bone destruction in periodontal disease and osteoporosis can be treated by reducing the ratio of arachidonic acid in phospholipids, which would diminish prostaglandin production. The aim of this study was to evaluate the main serum polyunsaturated fatty acids and a possible alteration in the level of arachidonic acid in patients suffering from periodontal bone loss. Of the 105 patients who participated the study, 78 were suffering from periodontal bone loss and 27 served as a control group. The fatty acids were measured in serum by gas-chromatography. The results showed that the level of fatty acids of the n-6 pathway was higher in our patients with bone loss than in the control group, whereas the reverse was observed with fatty acids of the n-3 pathway. In conclusion, our patients' bone losses are linked with an imbalance between n-6 and n-3 fatty acids, which seems to justify a diet increase in 20- and 22-carbon fatty acids.

Two-output-port fast tunable filter with low lossand low loss variation for 32 wavelength channels

A fast tunable filter with two output ports for 32 WDM channels is proposed. By using only the centre port in wavelength routers with larger free spectral range for the wavelength multi/demultiplexer, low loss and low loss imbalance can be achieved with a reduced number of optical gates. Channel selection is demonstrated for 100 GHz-spaced 32 channel selection.

Digitally tunable optical filters using arrayed-waveguide grating (AWG) multiplexers and optical switches

Two novel configurations for digitally tunable optical filters based on arrayed-waveguide grating (AWG) multiplexers are described in detail with emphasis on the connection of the AWG multiplexer and optical switches. Performance comparisons show that conventional configurations are disadvantaged by the switch size required and loss imbalance among the optical frequency-division-multiplexed (FDM) channels; the proposed configurations require only O(/spl radic/(N)) switch elements to select one of N FDM channels, and the loss imbalance is lower by up to 75% in decibel.

Loss-imbalance equalization in arrayed waveguide-grating (AWG) multiplexer cascades

How to connect arrayed-waveguide-grating (AWG) multiplexers in cascade is discussed with the goal of equalizing the loss imbalance among frequency-division-multiplexed (FDM) channels. This paper proposes to average the FDM-channel loss over the cascaded multiplexers by shifting port connections between each adjacent multiplexer. A simulation predicts that, in a cascade of M periodic N/spl times/N multiplexers, shifting the connections by N/M reduces the loss imbalance from M/spl Delta//spl alpha/ to /spl Delta//spl alpha//M where /spl Delta//spl alpha/ [dB] denotes the loss imbalance per multiplexer. This improvement will extend the cascadable node number in all-optical FDM networks. The prediction is confirmed experimentally in an optical add-drop filter (M=2) constructed with a silica-based AWG 16/spl times/16 multiplexer; the largest loss difference among 15 FDM channels is reduced from 5.0 dB to 1.5 dB. This paper also reports that imperfect multiplexer periodicity due to waveguide dispersion restricts the equalizable frequency bandwidth to less than several free spectral ranges (FSR's).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hypothalamic homeothermy across the ultradian sleep cycle.

In the ambient thermal zone for the vasomotor regulation of body temperature hypothalamic temperature changes across the states of the ultradian sleep cycle are the result of state-dependent heat production-heat loss imbalances affecting the temperature of the arterial blood perfusing the brain. However, the changes in arterial blood temperature are efficiently buffered, at a low energetic cost, by the thermal inertia of the mass of body water. Thus, the oscillations in hypothalamic temperature are maintained within a width of a few tenths of a degree and are so small as to be subliminal as thermal feedback stimuli for thermoregulatory responses. This passive hypothalamic homeothermy would support the hypothesis that a phylogenetic pressure was operative early on in mammals in order to limit the duration of the ultradian sleep cycle so as to fit the thermal inertia of the different masses of body water in mammals of different sizes.