Temporal Aggregation Effects on the Construction of Portfolios of Stocks or Mutual Funds through Optimization Techniques - Some Empirical and Monte Carlo Results

In this paper we test the effects of temporal aggregation (disaggregation) on the efficiency of portfolio construction using the mean variance optimization approach. Using Monte Carlo techniques and empirical data from the Athens Stocks Exchange we confirm that the use of temporally aggregated data effects very seriously the efficiency of the constructed portfolio. Especially as the degree of temporal aggregation increases the application of optimization techniques could lead to different results regarding the percentage of stocks participation, the weights and finally the total portfolio performance.Portfolio Optimization, Stocks; Temporal Aggregation; Stochastic Simulation, The Banking Sector of the Athens Stocks Exchange

Temporal Aggregation and the Akaike and Schwarz Model Selection Criteria. Some Monte Carlo Results

This short paper demonstrates that the use of temporally aggregated data may affect the performance of the well known Akaike and Schwarz model selection criteria. These two criteria are widely used for model selection in linear and nonlinear models. Using Monte Carlo techniques, we find that temporal aggregation could affect seriously the performance of the two aforementioned criteria.

A Note on the Diachronic Behaviour of the OECD Forecasts for Greece

In this short paper a Gamma distributed lags model is used to study the diachronic responses between the actual data and the forecasts supplied by OECD the last 27 years for the case of the Greek Economy. According to our results we verified the potentials of the OECD to improve its forecasts as the size of the foreseeable period decreases. Irrespective of how good are the OECD’s forecasts, there is certainly much room for further improvement.OECD Forecasting Accuracy, Greek Economy, Gamma Distributed Lags Model

Optimal Portfolio Analysis for the Czech Republic, Hungary and Poland During 2001– 2006 Period

This paper examines the strategy of investing in selected East European stock markets: The Czech Republic, Hungary, and Poland. These stocks markets are representative of the emerging stock markets of Eastern Europe and examined from the perspective of an investor who invests solely in the Eastern European markets. International Portfolio investment gradually increased during the late 2000’s in this region. Four portfolio construction techniques were used including the Markowitz mean-variance analysis. The optimal portfolios are evaluated using standard selection criteria and it is shown that possessing a diversified international portfolio which includes some of the aforementioned stock markets is beneficial.Portfolio diversification; Markowitz Mean Variance Frontier; Eastern European Countries.

The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud)

We present new data about the chemical and structural characteristics of bauxite residue (BR) from Greek Al industry, using a combination of microscopic, analytical, and spectroscopic techniques. SEM-EDS indicated a homogeneous dominant “Al-Fe-Ca-Ti-Si-Na-Cr matrix”, appearing at the microscale. The bulk chemical analyses showed considerable levels of Th (111 μg g−1), along with minor U (15 μg g−1), which are responsible for radioactivity (355 and 133 Bq kg−1 for 232Th and 238U, respectively) with a total dose rate of 295 nGy h−1. Leaching experiments, in conjunction with SFICP- MS, using Mediterranean seawater from Greece, indicated significant release of V, depending on S/L ratio, and negligible release of Th at least after 12 months leaching. STEM-EDS/EELS & HR-STEMHAADF study of the leached BR at the nanoscale revealed that the significant immobility of Th4+ is due to its incorporation into an insoluble perovskite-type phase with major composition of Ca0.8Na0.2TiO3 and crystallites observed in nanoscale. The Th LIII-edge EXAFS spectra demonstrated that Th4+ ions, which are hosted in this novel nano-perovskite of BR, occupy Ca2+ sites, rather than Ti4+ sites. That is most likely the reason of no Th release in Mediterranean seawater

Regulation of peripheral blood flow in Complex Regional Pain Syndrome: clinical implication for symptomatic relief and pain management

Background. During the chronic stage of Complex Regional Pain Syndrome (CRPS), impaired microcirculation is related to increased vasoconstriction, tissue hypoxia, and metabolic tissue acidosis in the affected limb. Several mechanisms may be responsible for the ischemia and pain in chronic cold CPRS. Discussion. The diminished blood flow may be caused by either sympathetic dysfunction, hypersensitivity to circulating catecholamines, or endothelial dysfunction. The pain may be of neuropathic, inflammatory, nociceptive, or functional nature, or of mixed origin. Summary. The origin of the pain should be the basis of the symptomatic therapy. Since the difference in temperature between both hands fluctuates over time in cold CRPS, when in doubt, the clinician should prioritize the patient's report of a persistent cold extremity over clinical tests that show no difference. Future research should focus on developing easily applied methods for clinical use to differentiate between central and peripheral blood flow regulation disorders in individual patients

ChatGPT for futures: how large language models can support the development of future scenarios using the Cone of Plausibility

Recently, large language models (LLMs), such as the “Chat Generative Pre-trained Transformer”, commonly known as ChatGPT, are substantially impacting the world of (big) data analytics and artificial intelligence. This paper explores how ChatGPT-4 can be used to support the development of future scenarios using the Cone of Plausibility method. The most recent version ChatGPT 4.0 differs from its predecessors in that it can now access real-time data to generate its responses. This makes it an attractive tool for intelligence analysts, who are faced with the permanent challenge of having to sift through large amounts of data whilst also providing actionable products in a timely manner. Previous versions of ChatGPT were prone to errors such as making up information. But what if, using the right prompts, version 4.0 could become a useful sparring partner for developing future scenarios? In this study, we will ask ChatGPT 4.0 to generate sets of plausible future scenarios for “Russia 2035+” based on previously specified key drivers and assumptions. The LLM’s potential for error is reduced because it is not working with hypotheses that it has generated itself. This could turn ChatGPT into a quick-thinking sparring partner for imagining varieties of future scenarios, supporting out-of-the box thinking and further minimising cognitive biases. To evaluate the reliability and accuracy of the results generated by ChatGPT, we will use the VV&A concept developed by the US Department of Defence. According to this concept, credibility in an intelligence product is rooted in the verification, validation and accreditation of its analysis. This process is routinely followed by every intelligence analyst. We will have found out to which extent and under which circumstances ChatGPT 4.0 can credibly support the development of future scenarios

Evaluating Object-Oriented Designs with Link Analysis

The Hyperlink Induced Topic Search algorithm, which is a method of link analysis, primarily developed for retrieving information from the Web, is extended in this paper, in order to evaluate one aspect of quality in an object-oriented model. Considering the number of discrete messages exchanged between classes, it is possible to identify “God” classes in the system, elements which imply a poorly designed model. The principal eigenvectors of matrices derived from the adjacency matrix of a modified class diagram, are used to identify and quantify heavily loaded portions of an objectoriented design that deviate from the principle of distributed responsibilities. The non-principal eigenvectors are also employed in order to identify possible reusable components in the system. The methodology can be easily automated as illustrated by a Java program that has been developed for this purpose