An alternative test to check the validity of convergence results

This paper presents a simple method for identifying distributional dynamic properties of economies using the ideas of concordance and discordance. It can be employed to examine the strength and validity of the results of other methods. The method has the advantage of comparing distributions at two points without relying on intermediary data between the two time points. We present results that suggest there is more ‘strong-divergence’ than ‘strong-convergence’ in GDP between countries over the time period 1960-2000 although the distribution exhibits both convergent and divergent characteristics

Overshoot mechanism in transient excitation of THz and Gunn oscillations in wide-bandgap semiconductors

A detailed study of high-field transient and direct-current (DC) transport in GaN-based Gunn diode oscillators is carried out using the commercial simulator Sentaurus Device. Applicability of drift-diffusion (DD) and hydrodynamic (HD) models to high-speed, highfrequency devices is discussed in depth, and the results of the simulations from these models are compared. It is shown, for a highly homogeneous device based on a short (2 μm) supercritically doped (1017 cm-3) GaN specimen, that the DD model is unable to correctly take into account some essential physical effects which determine the operation mode of the device. At the same time, the HD model is ideally suited to solve such problems due to its ability to incorporate non-local effects. We show that the velocity overshoot near the device contacts and space charge injection and extraction play a crucial role in defining the operation mode of highly homogeneous short diodes in both the transient regime and the voltagecontrolled oscillation regime. The transient conduction current responses are fundamentally different in the DD and HD models. The DD current simply repeats the velocity-field (v-F) characteristics, and the sample remains in a completely homogeneous state. In the HD model, the transient current pulse with a full width at half maximum of approximately 0.2 ps is increased about twofold due to the carrier injection (extraction) into (from) the active region and the velocity overshoot. The electron gas is characterized by highly inhomogeneous distributions of the carrier density, the electric field and the electron temperature. The simulation of the DC steady states of the diodes also shows very different results for the two models. The HD model shows the trapped stable anodic domain in the device, while the DD model completely retains all features of the v-F characteristics in a homogeneous gas. Simulation of the voltage-controlled oscillator shows that it operates in the accumulation layer mode generating microwave signals at 0.3 to 0.7 THz. In spite of the fact that the known criterion of a Gunn domain mode n0L > (n0L)0 was satisfied, no Gunn domains were observed. The explanation of this phenomenon is given. © 2012 Momox et al

Field statistics modelling of beat noise in an optical amplifier

The authors present a rigorous and self-contained noise analysis of an optical amplifier based on the statistics of the input source field and the amplified spontaneous emission field of the amplifier. The method enables us to obtain the frequency dependence of the output electrical noise power, which has not been derived in previous studies of optical amplifier noise based on the photon statistics master equation. The authors characterise for the first time the noise of an optical amplifier in combination with a super-fluorescent source, taking into account the frequency dependence of the gain and the presence of optional optical filters

Noise analysis of an amplified fiber-optic recirculating-ring delay line

We present the first theoretical and experimental noise analysis of a fiber-optic recirculating-ring delay line (RDL) including a doped fiber amplifier to compensate for the roundtrip loss. Both thermal-like sources and laser sources are considered. The output source induced noise (signal-signal beat noise), signal-spontaneous (s-sp) beat noise, and spontaneous-spontaneous (sp-sp) beat noise spectra for a thermal-like source are calculated from the autocorrelation function of the output detector current. It is shown that all three electrical beat noise spectra can be expressed as correlations of the output optical signal and ASE spectra. The source-induced noise will normally be the dominating noise source, but in some applications, the other noise terms also will be of importance. We use our theory to define the maximum number of recirculations in an amplified RDL with a pulsed source, where the fundamental noise floor is determined by the sp-sp beat noise

Noise in amplified fibre optic recirculating-ring delay lines

We characterize for the first time the noise in fiber optic recirculating-ring delay lines including doped fiber amplifiers, which are interesting components in many fiber optic sensors because of their enhanced total delay times compared to conventional recirculating-ring delay lines