Search results for "CTAB"
showing 10 items of 231 documents
Limits and Criticalities of Predictions and Forecasting in Complex Social and Economic Scenarios: A Cybernetics Key
2014
Predictions play a key role in assuring the status of “rationality” in decisions. Nevertheless, in the field of social sciences and economics, predictions fail to correctly depict the oncoming scenarios. Why is it so difficult to achieve quantitative prediction of social and economic systems? Can science provide reliable predictions of social and economic paths that can be used to implement effective interventions? As in the notorious “El Farol bar problem” depicted by Brian Arthur (Am Econ Rev 84:406–411, 1994), the validity of predictive models is more a social issue than a matter of good mathematics. Predictability in social systems is due to limited knowledge of society and human behavi…
Human brain mechanisms of pain perception and regulation in health and disease
2005
Context: The perception of pain due to an acute injury or in clinical pain states undergoes substantial processing at supraspinal levels. Supraspinal, brain mechanisms are increasingly recognized as playing a major role in the representation and modulation of pain experience. These neural mechanisms may then contribute to interindividual variations and disabilities associated with chronic pain conditions. Objective: To systematically review the literature regarding how activity in diverse brain regions creates and modulates the experience of acute and chronic pain states, emphasizing the contribution of various imaging techniques to emerging concepts. Data Sources: MEDLINE and PRE-MEDLINE s…
Natural Organic Compounds in Soil Solution: Potential Role as Soil Quality Indicators
2013
This review focuses on the chemical nature of that fraction of already dissolved organic matter into soil solution, or extracted by mild extractants, which is truly readily available for microbial activity and, consequently, more sensitive than total soil organic matter to changes in management and/or environmental conditions. In particular, we deal with low molecular weight compounds such as monosaccharides, amino sugars and amino acids. Soil sampling strategy and extraction procedure, prior to analyses, are crucial to make comparable results among laboratories. Although soil management and climatic conditions may cause large variability, extractable organic C and N may indicate the amount…
Waves to Weather: Exploring the Limits of Predictability of Weather
2021
AbstractPrediction of weather is a main goal of atmospheric science. Its importance to society is growing continuously due to factors such as vulnerability to natural disasters, the move to renewable energy sources, and the risks of climate change. But prediction is also a major scientific challenge due to the inherently limited predictability of a chaotic atmosphere, and has led to a revolution in forecasting methods as we have moved to probabilistic prediction. These changes provide the motivation for Waves to Weather (W2W), a major national research program in Germany with three main university partners in Munich, Mainz, and Karlsruhe. We are currently in the second 4-yr phase of our pla…
SECULAR MEAN REVERSION AND LONG-RUN PREDICTABILITY OF THE STOCK MARKET
2016
Empirical financial literature documents the evidence of mean reversion in stock prices and the absence of out-of-sample return predictability over periods shorter than 10 years. The goal of this paper is to test the random walk hypothesis in stock prices and return predictability over periods longer than 10 years. Specifically, using 141 years of data, this paper begins by performing formal tests of the random walk hypothesis in the prices of the real S&P Composite Index over increasing time horizons up to 40 years. Even though our results cannot support the conventional wisdom which says that the stock market is safer for long-term investors, our findings speak in favor of the mean revers…
Forecasting the size premium over different time horizons
2013
Abstract In this paper, we provide evidence that the small stock premium is predictable both in-sample and out-of-sample through the use of a set of lagged macroeconomic variables. We find that it is possible to forecast the size premium over time horizons that range from one month to one year. We demonstrate that the predictability of the size premium allows a portfolio manager to generate an economically and statistically significant active alpha.
The Limits to Volatility Predictability: Quantifying Forecast Accuracy Across Horizons
2018
Volatility forecasting is crucial for portfolio management, risk management, and pricing of derivative securities. Still, little is known about how far ahead one can forecast volatility. First, in this paper we introduce the notions of the spot and forward predicted volatilities and propose to describe the term structure of volatility predictability by the spot and forward forecast accuracy curves. Then, by employing a few popular time-series volatility models, we perform a comprehensive empirical study on the horizon of volatility predictability. Our results suggest that, whereas the spot volatility can be predicted over horizons that extend to 35 weeks, the horizon of the forward volatili…
The predictability of international terrorism: A time‐series analysis
1988
Abstract The study examines the predictability of international terrorism in terms of the existence of trends, seasonality, and periodicity of terrorist events. The data base used was the RAND Corporation's Chronology of International Terrorism. It contains the attributes of every case of international terrorism from 1968 to 1986 (n = 5,589). The authors applied Box‐Jenkins models for a time‐series analysis of the occurrence of terrorist events as well as their victimization rates. The analysis revealed that occurrence of terrorist events is far from being random: There is a clear trend and an almost constant periodicity of one month that can be best described by a first‐order moving averag…
Closed-loop bandwidth impact on MVSA for rotor broken bar diagnosis in IRFOC double squirrel cage induction motor drives
2013
This paper investigates the detectability of rotor broken bars in indirect rotor flux oriented control (IRFOC) for variable speed double cage induction motor drives, using vibration signature analysis techniques. The Impact of the closed loop control system cannot be neglected when the detection of rotor asymmetries in the machine is based on the signature analysis of electrical or mechanical variables. Therefore, the investigation of rotor fault components for different bandwidths of closed-loop regulators is necessary to evaluate its relevance in the above listed variables. This paper investigates the impact of the control system on relevance of the fault components computed from axial an…
Biochar based remediation of water and soil contaminated by phenanthrene and pentachlorophenol
2017
Abstract Phenanthrene (Phe) and pentachlorophenol (PCP) are classified as persistent organic pollutants and represent serious concern for the environment as they are toxic and ubiquitous. Biochar based remediation is an emerging technology used in water and soil contamination. In this study we used poplar (BP) and conifer (BC) biochars to remediate water and soil contaminated by Phe and PCP. BP and BC were able to remove completely either Phe or PCP from contaminated water within one to three days. When biochar was confined in a porous membrane, BC and BP maintained their sorption efficiency for several remediation cycles. However, in these conditions BC allowed faster Phe removal. In soil …