First order plus frequency dependent delay modeling : new perspective or mathematical curiosity?

The first-order-plus-dead-time model (FOPDT) is a popular simplified representation of higher order dynamics. However, a well known drawback is the rapid decrease of the frequency response accuracy with increasing process order. This especially applies to the higher frequency range. Literature offers solutions by extending this three parameter model with more parameters. Here, a fractional dead time is proposed. As such, a Frequency-Dependent Delay (FDD) is introduced, which offers a better approximation. As the fractional-order term introduces nonlinear coupling between the phase and the magnitude of the process, the fitting of the function becomes an iterative process, so a constrained multi-objective optimization is needed. This novel model, first-order-plus-frequency-dependent-delay or FOPFDD is fitted on a real electrical ladder network of resistors and capacitors of four and eight parts. The classic model, which is clearly a special case of the new model, is outperformed in the entire bandwidth

Technological-Knowledge Dynamics in Lab-Equipment Models of Quality Ladders

The Perpetual Inventory Model (PIM) assumes that, in each period, an arbitrary constant fraction of technological-knowledge stock is lost. By connecting the aggregate resource constraint with firms’ market value, we give a theoretical background to the PIM by showing that the technological-knowledge accumulation follows a dynamic process with an endogenous depreciation rate, which remains stable in steady state. Moreover, we relate different concepts of technological-knowledge used in the literature.endogenous growth, endogenous depreciation rate, Perpetual Inventory Model, technological-knowledge dynamics

Dispersion of Ordered Stripe Phases in the Cuprates

A phase separation model is presented for the stripe phase of the cuprates, which allows the doping dependence of the photoemission spectra to be calculated. The idealized limit of a well-ordered array of magnetic and charged stripes is analyzed, including effects of long-range Coulomb repulsion. Remarkably, down to the limit of two-cell wide stripes, the dispersion can be interpreted as essentially a superposition of the two end-phase dispersions, with superposed minigaps associated with the lattice periodicity. The largest minigap falls near the Fermi level; it can be enhanced by proximity to a (bulk) Van Hove singularity. The calculated spectra are dominated by two features -- this charge stripe minigap plus the magnetic stripe Hubbard gap. There is a strong correlation between these two features and the experimental photoemission results of a two-peak dispersion in La$_{2-x}$Sr$_x$CuO$_4$, and the peak-dip-hump spectra in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. The differences are suggestive of the role of increasing stripe fluctuations. The 1/8 anomaly is associated with a quantum critical point, here expressed as a percolation-like crossover. A model is proposed for the limiting minority magnetic phase as an isolated two-leg ladder.Comment: 24 pages, 26 PS figure

What Does Subjective Socioeconomic Status Measure and Why Does it Predict Health So Well?

Socioeconomic status (SES) is robustly associated with myriad health outcomes. Each step up in SES is associated with improved health, a phenomenon known as the SES-health gradient (Adler et al., 2014). The SES-health gradient is found when SES is measured via objective indicators, or when SES is measured subjectively such as with the MacArthur Scale of Subjective Social Status (i.e., MacArthur ladder). Despite widespread usage of subjective measures of SES in health research, there are quite different interpretations of what these measures represent. In the present research we work from two competing interpretations to investigate how subjective SES and associated health measures are related to economic circumstances and non-economic social status. In a series of three correlational studies (N = 1,310) we investigated the associations between the MacArthur ladder, social status, and economic circumstances and their respective roles in the subjective SES-health gradient. We find evidence that economic circumstances and social status are distinct constructs that are both uniquely associated with the MacArthur ladder. Social status and economic circumstances also both explained the association between the MacArthur ladder and health and well-being measures. Our findings suggest that subjective SES (as measured by the MacArthur ladder) and the associated subSES-health gradient are explainable via both social status and economic circumstances.Master of Art

Falls from height : risk perception of ladder users within the UK construction industry

Accidents involving falls from portable ladders occur at a rate of forty per week in the construction industry. Ladders are so common that they are taken for granted and the perceived risks are often under-estimated. The purpose of this study was to analyse the risk perception of operatives using portable ladders, and to develop and test a ladder-use training aid. The research used a quantitative, within-subjects survey, consisting of three structured questionnaires administered to four hundred respondents attending construction related training programmes. The surveys used images of actual ladder-use situations, and were carried out in two stages; the first stage measured the level of risk perception and sensation seeking before any training had taken place, and the second measured any change in the level of risk perception following the use of the ladder training-aid. Initial pre-training results revealed that operatives over-estimated the risks from high-level ladder use situations, and underestimated the risks from low-level ladder use situations. Post-training results showed an improvement in risk perception, especially for low-level situations. It was concluded that risk perception varies both with the individual and their level of experience, and that the training-aid had a positive impact on the improvement of ladder-use risk perception. Keywords: Falls, ladder, risk perception, training aid