Some Remarks on the Spectral Theory and Commutativity of Unbounded Normal Operators

In this paper we give a development of the spectral theory and commutativity properties of unbounded normal operators in the style of Kadison and Ringrose.     

Modelling banking sector stability with multicriteria approaches

Banking crises can be damaging for the economy, and as the recent experience has shown, nowadays they can spread rapidly across the globe with contagious effects. Therefore, the assessment of the stability of a county’s banking sector is important for regulators, depositors, investors and the general public. In the present study, we propose the development of classification models that assign the banking sectors of various countries in three classes, labelled “low stability”, “medium stability”, and “high stability”. The models are developed using three multicriteria decision aid techniques, which are well-suited to ordinal classification problems. We use a sample of 114 banking sectors (i.e., countries), and a set of criteria that includes indicators of the macroeconomic, institutional and regulatory environment, as well as basic characteristics of the banking and financial sector. The models are developed and tested using a tenfold cross-validation approach and they are benchmarked against models developed with discriminant analysis and logistic regression.     

A note on upper bounds for forecast-value-added relative to naïve forecasts

In forecast value added analysis, the accuracy of relatively sophisticated forecasting methods is compared to that of naïve 1 forecasts to see whether the extra costs and effort of implementing them are justified. In this note, we derive a ratio that indicates the upper bound of a forecasting method’s accuracy relative to naïve 1 forecasts when the mean squared error is used to measure one-period-ahead accuracy. The ratio is applicable when a series is stationary or when its first differences are stationary. Formulae for the ratio are presented for several exemplar time series processes.     

Natural disasters and economic growth: a quantile on quantile approach

Annals of Operations Research - Natural disasters have caused over a million of deaths and $3 trillion in economic losses during the last 20 years. However, theoretical and empirical...     

Handedness enantioselection of carbon nanotubes using helical assemblies of flavin mononucleotide

In order to truly unlock advanced applications of single-walled carbon nanotubes (SWNTs), one needs to separate them according to both chirality and handedness. Here we show that the chiral d-ribityl phosphate chain of flavin mononucleotide (FMN) induces a right-handed helix that enriches the left-handed SWNTs for all suspended (n,m) species. Such enantioselectivity stems from the sp(3) hybridization of the N atom anchoring the sugar moiety to the flavin ring. This produces two FMN conformations (syn and anti) analogous to DNA. Electrostatic interactions between the neighboring uracil moiety and the 2'-OH group of the side chain provide greater stability to the anti-FMN conformation that leads to a right-handed FMN helix. The right-handed twist that the FMN helix imposes to the underlying nanotube, similar to "Indian burn", causes diameter dilation of only the left-handed SWNTs, whose improved intermolecular interactions with the overlaying FMN helix, impart enantioselection.     

Forecast combinations for intermittent demand

Intermittent demand is characterised by infrequent demand arrivals, where many periods have zero demand, coupled with varied demand sizes. The dual source of variation renders forecasting for intermittent demand a very challenging task. Many researchers have focused on the development of specialised methods for intermittent demand. However, apart from a case study on hierarchical forecasting, the effects of combining, which is a standard practice for regular demand, have not been investigated. This paper empirically explores the efficiency of forecast combinations in the intermittent demand context. We examine both method and temporal combinations of forecasts. The first are based on combinations of different methods on the same time series, while the latter use combinations of forecasts produced on different views of the time series, based on temporal aggregation. Temporal combinations of single or multiple methods are investigated, leading to a new time-series classification, which leads to model selection and combination. Results suggest that appropriate combinations lead to improved forecasting performance over single methods, as well as simplifying the forecasting process by limiting the need for manual selection of methods or hyper-parameters of good performing benchmarks. This has direct implications for intermittent demand forecasting in practice.     

Redox-assisted asymmetric ostwald ripening of CdSe dots to rods

The redox-assisted asymmetric Ostwald ripening of dots to rods was observed upon annealing a concentrated dispersion of CdSe nanocrystals (NCs) containing 0.1 M CdCl2 in 3-amino-1-propanol (APOL)/H2O (v/v = 9/1) at 135 degrees C. Transmission electron microscopic investigation, along with UV-vis and photoluminescence results, revealed that, while the length of these NCs increased upon annealing, their diameter remained constant. The surface oxidation of NC Se atoms to SeO2 and its subsequent dissolution into the basic APOL/H2O mixture as SeO32- was found instrumental for such dot-to-rod transformation. The amine-assisted SeO2 reduction to Se0 (as confirmed by X-ray photoelectron spectroscopy and X-ray diffraction results) provides the Se source for further NC growth. The preferential growth along the c-axis leads to the formation of rods with zinc blende CdSe structure at its growing ends, due to the low-temperature growth conditions.     

Passive targeted energy transfers and strong modal interactions in the dynamics of a thin plate with strongly nonlinear attachments

We study targeted energy transfers (TETs) and nonlinear modal interactions attachments occurring in the dynamics of a thin cantilever plate on an elastic foundation with strongly nonlinear lightweight attachments of different configurations in a more complicated system towards industrial applications. We examine two types of shock excitations that excite a subset of plate modes, and systematically study, nonlinear modal interactions and passive broadband targeted energy transfer phenomena occurring between the plate and the attachments. The following attachment configurations are considered: (i) a single ungrounded, strongly (essentially) nonlinear single-degree-of-freedom (SDOF) attachment—termed nonlinear energy sink (NES); (ii) a set of two SDOF NESs attached at different points of the plate; and (iii) a single multi-degree-of-freedom (MDOF) NES with multiple essential stiffness nonlinearities. We perform parametric studies by varying the parameters and locations of the NESs, in order to optimize passive TETs from the plate modes to the attachments, and we showed that the optimal position for the NES attachments are at the antinodes of the linear modes of the plate. The parametric study of the damping coefficient of the SDOF NES showed that TETs decreasing with lower values of the coefficient and moreover we showed that the threshold of maximum energy level of the system with strong TETs occured in discrete models is by far beyond the limits of the engineering design of the continua. We examine in detail the underlying dynamical mechanisms influencing TETs by means of empirical mode decomposition (EMD) in combination with wavelet transforms. This integrated approach enables us to systematically study the strong modal interactions occurring between the essentially nonlinear NESs and different plate modes, and to detect the dominant resonance captures between the plate modes and the NESs that cause the observed TETs. Moreover, we perform comparative studies of the performance of different types of NESs and of the linear tuned mass dampers (TMDs) attached to the plate instead of the NESs. Finally, the efficacy of using this type of essentially nonlinear attachments as passive absorbers of broadband vibration energy is discussed.     

Numerical analysis of the electrical and optical behaviour of a pulsed nitrogen laser through time-dependent resistances and inductances

Received: 28 September 1996     

Multicriteria decision support methodologies for auditing decisions: The case of qualified audit reports in the UK

All UK companies are required by company law to prepare financial statements that must comply with law and accounting standards. With the exception of very small companies, financial accounts must then be audited by UK registered auditors who must express an opinion on whether these statements are free from material misstatements, and have been prepared in accordance with legislation and relevant accounting standards (unqualified opinion) or not (qualified opinion). The objective of the present study is to explore the potentials of developing multicriteria decision aid models for reproducing, as accurately as possible, the auditors’ opinion on the financial statements of the firms. A sample of 625 company audited years with qualified statements and 625 ones with unqualified financial statements over the period 1998–2003 from 823 manufacturing private and public companies is being used in contrast to most of the previous works in the UK that have mainly focused on very small or very large public companies. Furthermore, the models are being developed and tested using the walk-forward approach as opposed to previous studies that employ simple holdout tests or resampling techniques. Discriminant analysis and logit analysis are also used for comparison purposes. The out-of-time and out-of-sample testing results indicate that the two multicriteria decision aid techniques achieve almost equal classification accuracies and are both more efficient than discriminant and logit analysis.