A 2.7-kW, 29-MHz class-E/F/sub odd/ amplifier with a distributed active transformer

A Class-E/Fodd high power amplifier (PA) using the distributed active transformer (DAT) is demonstrated at 29MHz. The DAT combines the output power from four VDMOS push-pull pairs. The zero voltage switching (ZVS) condition is investigated and modified for the Class-E/Fodd amplifier with a non-ideal output transformer. All lumped elements including the DAT and the transistor package are modeled and optimized to achieve the ZVS condition and the high drain efficiency. The PA exhibits 2.7kW output power with 79% drain efficiency and 18dB gain at 29MHz

Effects of age, sex, context, and lexicality on hyperarticulation of Korean fricatives

Seoul Korean is known for a rare three-way laryngeal contrast among lenis, fortis, and aspirated voiceless stops, which has recently undergone a change in phonetic implementation: whereas older speakers rely more on voice onset time (VOT) to distinguish lenis and aspirated stops, younger speakers rely more on onset fundamental frequency (f 0) in the following vowel. This production difference is reflected in disparate strategies for enhancing the contrast in clear speech, supporting the view that younger and older speakers represent the three laryngeal categories differently in terms of VOT and f 0 targets (Kang & Guion, 2008). In the current study, we used the clear speech paradigm to test for change in the representation of the two-way contrast between fortis (/s*/) and non-fortis (/s/) fricatives. Native Seoul Korean speakers (n = 32), representing two generations and both sexes, were recorded producing the coronal stops and fricatives in different vowel contexts, item types (real vs. nonce words), and speech registers (plain citation vs. clear). We report acoustic data on how the above factors influence production of the fricative contrast and discuss implications for the phonological categorization of non-fortis /s/ as lenis, aspirated, or a hybrid lenis-aspirated category.https://drive.google.com/open?id=0B1_NoAiLQlnkZ2RtdEtuYTlaMkkOthe

Nonlinear Design Technique for High-Power Switching-Mode Oscillators

A simple nonlinear technique for the design of high-efficiency and high-power switching-mode oscillators is presented. It combines existing quasi-nonlinear methods and the use of an auxiliary generator (AG) in harmonic balance. The AG enables the oscillator optimization to achieve high output power and dc-to-RF conversion efficiency without affecting the oscillation frequency. It also imposes a sufficient drive on the transistor to enable the switching-mode operation with high efficiency. Using this AG, constant-power and constant-efficiency contour plots are traced in order to determine the optimum element values. The oscillation startup condition and the steady-state stability are analyzed with the pole-zero identification technique. The influence of the gate bias on the output power, efficiency, and stability is also investigated. A class-E oscillator is demonstrated using the proposed technique. The oscillator exhibits 75 W with 67% efficiency at 410 MHz

Analysis and elimination of hysteresis and noisy precursors in power amplifiers

Power amplifiers (PAs) often exhibit instabilities leading to frequency division by two or oscillations at incommensurate frequencies. This undesired behavior can be detected through a large-signal stability analysis of the solution. However, other commonly observed phenomena are still difficult to predict and eliminate. In this paper, the anomalous behavior observed in a Class-E PA is analyzed in detail. It involves hysteresis in the power-transfer curve, oscillation, and noisy precursors. The precursors are pronounced bumps in the power spectrum due to noise amplification under a small stability margin. The correction of the amplifier performance has required the development of a new technique for the elimination of the hysteresis. Instead of a trial-and-error procedure, this technique, of general application to circuit design, makes use of bifurcation concepts to suppress the hysteresis phenomenon through a single simulation on harmonic-balance software. Another objective has been the investigation of the circuit characteristics that make the noisy precursors observable in practical circuits and a technique has been derived for their elimination from the amplifier output spectrum. All the different techniques have been experimentally validated

Multiplicity Fluctuations in Limited Segments of Momentum Space in Statistical Models

Multiplicity fluctuations in limited segments of momentum space are calculated for a classical pion gas within the statistical model. Results for the grand canonical, canonical, and micro-canonical ensemble are obtained, compared and discussed. We demonstrate that even in the large volume limit correlations between macroscopic subsystems due to energy and momentum conservation persist. Based on the micro-canonical formulation we make qualitative predictions for the rapidity and transverse momentum dependence of multiplicity fluctuations. The resulting effects are of similar magnitude as the predicted enhancement due to a phase transition from a quark-gluon plasma to a hadron gas phase, or due to the critical point of strongly interacting matter, and qualitatively agree with recently published preliminary multiplicity fluctuation data of the NA49 SPS experiment.Comment: 23 pages, 4 figure

Event-by-event fluctuations of the charged particle ratio from non-equilibrium transport theory

The event by event fluctuations of the ratio of positively to negatively charged hadrons are predicted within the UrQMD model. Corrections for finite acceptance and finite net charge are derived. These corrections are relevant to compare experimental data and transport model results to previous predictions. The calculated fluctuations at RHIC and SPS energies are shown to be compatible with a hadron gas. Thus, deviating by a factor of 3 from the predictions for a thermalized quark-gluon plasma.Comment: This paper clarifies the previous predictions of Jeon and Koch (hep-ph/0003168) and addresses issues raised in hep-ph/0006023. 2 Figures, 10pp, uses RevTe

Dijet asymmetry at the Large Hadron Collider

The MARTINI numerical simulation allows for direct comparison of theoretical model calculations and the latest results for dijet asymmetry from the ATLAS and CMS collaborations. In this paper, partons are simulated as undergoing radiative and collisional processes throughout the evolution of central lead-lead collisions at the Large Hadron Collider. Using hydrodynamical background evolution determined by a simulation which fits well with the data on charged particle multiplicities from ALICE and a value of $\alpha_s\approx 0.25-0.3$, the dijet asymmetry is found to be consistent with partonic energy loss in a hot, strongly-interacting medium.Comment: 8 pages, 3 figures. For version 2: ATLAS' latest analysis is included, with some comments and minor changes of wordin