The construction and testing of a macro-econometric forecasting model for the Greek economy

This thesis concerns the construction and testing of an annual forecasting econometric model for the Greek economy between 1954 and 1977. The economic structure has been broken down into several subsectors and statistical analysis has been employed to determine the main factors explaining the relationships in each subsector. The work is divided into ten chapters. After a brief introduction giving the background of the Greek economy in outline, the second chapter describes the statistical procedures employed and some of the problems encountered in econometric work, with their suggested solutions. A detailed description of the factor analysis technique is given, as this technique has been extensively employed in the Two Stage Least Squares (TSLS) and reduced form estimations. The Chapters 3-9 deal with the particular subsectors of the economy, i.e. consumption expenditure (Chapter 3), the effect of wealth on consumption (Chapter 4), the determination of investment (Chapter 5), employment, taxes (Chapter 6), international transactions (Chapter 7), wages and prices (Chapter 8) and the financial sector (Chapter 9). Each subsector has been examined in the context of economic theory and specific models have been tested to determine functions which explain the relationships in the various subsectors satisfactorily. In the last chapter all subsectors are brought together to estimate the reduced form of the structure, both as a simultaneous system and blockwise. The technique of factor analysis was employed. Orthogonal and oblique rotation of the factors were used in order to determine their differences, if any, and which one tracks the data better, in simulations within the sample period. The selected reduced form was used to generate forecasts and also to test the properties of some multipliers. A summary of the results of the whole work is finally given

The construction and testing of a macro-econometric forecasting model for the Greek economy

This thesis concerns the construction and testing of an annual forecasting econometric model for the Greek economy between 1954 and 1977. The economic structure has been broken down into several subsectors and statistical analysis has been employed to determine the main factors explaining the relationships in each subsector. The work is divided into ten chapters. After a brief introduction giving the background of the Greek economy in outline, the second chapter describes the statistical procedures employed and some of the problems encountered in econometric work, with their suggested solutions. A detailed description of the factor analysis technique is given, as this technique has been extensively employed in the Two Stage Least Squares (TSLS) and reduced form estimations. The Chapters 3-9 deal with the particular subsectors of the economy, i.e. consumption expenditure (Chapter 3), the effect of wealth on consumption (Chapter 4), the determination of investment (Chapter 5), employment, taxes (Chapter 6), international transactions (Chapter 7), wages and prices (Chapter 8) and the financial sector (Chapter 9). Each subsector has been examined in the context of economic theory and specific models have been tested to determine functions which explain the relationships in the various subsectors satisfactorily. In the last chapter all subsectors are brought together to estimate the reduced form of the structure, both as a simultaneous system and blockwise. The technique of factor analysis was employed. Orthogonal and oblique rotation of the factors were used in order to determine their differences, if any, and which one tracks the data better, in simulations within the sample period. The selected reduced form was used to generate forecasts and also to test the properties of some multipliers. A summary of the results of the whole work is finally given

Complex dynamics in nanoscale phase separated supercooled liquids

The relaxation properties of supercooled AsxS100−x liquids are investigated using a combination of infrared photon correlation spectroscopy and topological constraint theory. Results reveal two channels of relaxation for sulfur-rich compositions that manifest by an unusual profile in the density-density autocorrelation function involving two typical timescales. This indicates a reduced temperature-dependent dynamics for one of the channels associated with a sulfur-rich segregated nanoscale phase that furthermore displays a low liquid fragility. Conversely, the dynamics of the emerging cross-linked As-S network is associated with a growth of the glass transition temperature with As content. These results can be quantitatively understood from topological constraint theory applied to a phase separated network for which a dedicated constraint enumeration must be achieved. The vanishing of this peculiar behavior occurs close to the reported isostatic reversibility window observed at the glass transition

High frequency dynamics in a monatomic glass

The high frequency dynamics of glassy Selenium has been studied by Inelastic X-ray Scattering at beamline BL35XU (SPring-8). The high quality of the data allows one to pinpoint the existence of a dispersing acoustic mode for wavevectors ($Q$) of $1.5<Q<12.5$ nm$^{-1}$, helping to clarify a previous contradiction between experimental and numerical results. The sound velocity shows a positive dispersion, exceeding the hydrodynamic value by $\approx$ 10% at $Q<3.5$ nm$^{-1}$. The $Q^2$ dependence of the sound attenuation $\Gamma(Q)$, reported for other glasses, is found to be the low-$Q$ limit of a more general $\Gamma(Q) \propto \Omega(Q)^2$ law which applies also to the higher $Q$ region, where $\Omega(Q)\propto Q$ no longer holds.Comment: Phys. Rev. Lett. (Accepted

On the origin of the λ\lambda-transition in liquid Sulphur

Developing a novel experimental technique, we applied photon correlation spectroscopy using infrared radiation in liquid Sulphur around $T_\lambda$, i.e. in the temperature range where an abrupt increase in viscosity by four orders of magnitude is observed upon heating within few degrees. This allowed us - overcoming photo-induced and absorption effects at visible wavelengths - to reveal a chain relaxation process with characteristic time in the ms range. These results do rehabilitate the validity of the Maxwell relation in Sulphur from an apparent failure, allowing rationalizing the mechanical and thermodynamic behavior of this system within a viscoelastic scenario.Comment: 5 pages, 4 eps figures, accepted in Phys. Rev. Let

Dynamics of proteins: Light scattering study of dilute and dense colloidal suspensions of eye lens homogenates

We report a dynamic light scattering study on protein suspensions of bovine lens homogenates at conditions (pH and ionic strength) similar to the physiological ones. Light scattering data were collected at two temperatures, 20 oC and 37 oC, over a wide range of concentrations from the very dilute limit up to the dense regime approaching to the physiological lens concentration. A comparison with experimental data from intact bovine lenses was advanced revealing differences between dispersions and lenses at similar concentrations. In the dilute regime two scattering entities were detected and identified with the long-time, self-diffusion modes of alpha-crystallins and their aggregates, which naturally exist in lens nucleus. Self-diffusion coefficients are temperature insensitive, whereas the collective diffusion coefficient depends strongly on temperature revealing a reduction of the net repulsive interparticle forces with lowering temperature. While there are no rigorous theoretical approaches on particle diffusion properties for multi-component, non-ideal hard-sphere, polydispersed systems, as the suspensions studied here, a discussion of the volume fraction dependence of the long-time, self-diffusion coefficient in the context of existing theoretical approaches was undertaken. This study is purported to provide some insight into the complex light scattering pattern of intact lenses and the interactions between the constituent proteins that are responsible for lens transparency. This would lead to understand basic mechanisms of specific protein interactions that lead to lens opacification (cataract) under pathological conditions.Comment: To appear in J. Chem. Phy

Effect of cluster size of chalcogenide glass nanocolloidal solutions on the surface morphology of spin-coated amorphous films

Amorphous chalcogenide thin film deposition can be achieved by a spin-coating technique from proper solutions of the corresponding glass. Films produced in this way exhibit certain grain texture, which is presumably related to the cluster size in solution. This paper deals with the search of such a correlation between grain size of surface morphology of as-deposited spin-coated As33S67 chalcogenide thin films and cluster size of the glass in butylamine solutions. Optical absorption spectroscopy and dynamic light scattering were employed to study optical properties and cluster size distributions in the solutions at various glass concentrations. Atomic force microscopy is used to study the surface morphology of the surface of as-deposited and thermally stabilized spin-coated films. Dynamic light scattering revealed a concentration dependence of cluster size in solution. Spectral-dependence dynamic light scattering studies showed an interesting athermal photo-aggregation effect in the liquid state.Comment: 15 pages, 8 figure

Stress distribution and the fragility of supercooled melts

We formulate a minimal ansatz for local stress distribution in a solid that includes the possibility of strongly anharmonic short-length motions. We discover a broken-symmetry metastable phase that exhibits an aperiodic, frozen-in stress distribution. This aperiodic metastable phase is characterized by many distinct, nearly degenerate configurations. The activated transitions between the configurations are mapped onto the dynamics of a long range classical Heisenberg model with 6-component spins and anisotropic couplings. We argue the metastable phase corresponds to a deeply supercooled non-polymeric, non-metallic liquid, and further establish an order parameter for the glass-to-crystal transition. The spin model itself exhibits a continuous range of behaviors between two limits corresponding to frozen-in shear and uniform compression/dilation respectively. The two regimes are separated by a continuous transition controlled by the anisotropy in the spin-spin interaction, which is directly related to the Poisson ratio $\sigma$ of the material. The latter ratio and the ultra-violet cutoff of the theory determine the liquid configurational entropy. Our results suggest that liquid's fragility depends on the Poisson ratio in a non-monotonic way. The present ansatz provides a microscopic framework for computing the configurational entropy and relaxational spectrum of specific substances.Comment: 11 pages, 5 figures, Final version published in J Phys Chem

EXPERIMENTAL STUDY ON THE EFFECTIVENESS OF AN ENERGY DISSIPATION CONFIGURATION IN AN OPEN CHANNEL OF STEEP SLOPE

Στην παρούσα εργασία μελετάται πειραματικά η ροή σε σήραγγα υπό συνθήκες ελεύθερης επιφάνειας και έντονης κλίσης πυθμένα 1:10. Διερευνάται η δυνατότητα μείωσης της ταχύτητας ροής μέσω συνδυασμού κατακόρυφων, πλευρικών στοιχείων τραχύτητας και λεκανών καταστροφής ενέργειας με οδοντώσεις. Η μελετώμενη διάταξη στηρίζεται στην ύπαρξη επαναλαμβανομένων τμημάτων (modules) εντός των οποίων επιτυγχάνεται επαναληψιμότητα της ροής. Η αποτελεσματικότητα του σχεδιασμού διερευνήθηκε σε υδραυλικό ομοίωμα κλίμακας 1:12,5 που βασίσθηκε σε συνθήκες δυναμικής ομοιότητας κατά Froude για χαρακτηριστικές τιμές παροχής. Η επεξεργασία των μετρήσεων έδειξε ότι με κατάλληλη διάταξη πλευρικών στοιχείων τραχύτητας και διαμόρφωση της λεκάνης καταστροφής ενέργειας ελέγχεται η τιμή της ταχύτητας, ικανοποιείται η απαίτηση μεγίστου βάθους ροής σε σχέση με τις διαστάσεις της σήραγγας και επιτυγχάνεται επαναληψιμότητα της ροής σε κάθε module.The free-surface flow in a tunnel of steep bed slope 1:10 is studied experimentally. The effectiveness of vertical roughness elements on the side walls and energy dissipation basins with blocks is investigated, with the aim to reduce flow velocity in the tunnel. The design is based on the concept of repeated modules in order to achieve flow repeatability. The scale of the physical model was 1:12.5 under Froude similarity conditions. The analysis of measurements indicates that a suitable arrangement of vertical roughness elements on the side walls and a suitable design of the energy dissipation basin can control the flow velocity magnitude, satisfy the maximum flow depth requirement with respect to the tunnel dimensions, and achieve flow repeatability in each modul