Spectral flow as a map between N=(2,0)-models

The space of $(2,0)$ models is of particular interest among all heterotic-string models because it includes the models with the minimal $SO(10)$ unification structure, which is well motivated by the Standard Model of particle physics data. The fermionic $\mathbb{Z}_2\times \mathbb{Z}_2$ heterotic-string models revealed the existence of a new symmetry in the space of string configurations under the exchange of spinors and vectors of the $SO(10)$ GUT group, dubbed spinor-vector duality. Such symmetries are important for the understanding of the landscape of string vacua and ultimately for the possible operation of a dynamical vacuum selection mechanism in string theory. In this paper we generalize this idea to arbitrary internal rational Conformal Field Theories (RCFTs). We explain how the spectral flow operator normally acting within a general $(2,2)$ theory can be used as a map between $(2,0)$ models. We describe the details, give an example and propose more simple currents that can be used in a similar way.Comment: 14 pages, v2: minor changes, added one referenc

Deep Supported Excavation in Difficult Ground Conditions in the City of Patras, Greece — Measured vs. Predicted Behavior

The technical characteristics of a deep supported excavation project using anchored diaphragm walls and the measured (by inclinometers) behavior of the soil retaining system are presented. The measured behavior is then compared with the predicted behavior using a finite element model of the excavation. The comparison shows a good agreement in a location where the soil profile is well defined. However, differences in the magnitude of the displacements were observed when the information on the soil profile was incomplete due to the variability of the deposits on site

Site Dependent Ground Response for the City of Patras, Greece

Results of a preliminary study of seismic ground response at different sites of the coastal city of Patras, in Southern Greece, are presented. At each site equivalent linear 1-D response analyses were conducted by using the finite element program LUSH 2. Values of dynamic properties of soils were obtained from either cross-hole tests or empirical correlations. The \u27rigid base\u27 excitation was selected as to best simulate the expected bedrock motions in Patras from local and distant earthquakes. The results of the analyses indicate a strong differentiation of seismic site response when moving from the coastal region of the city to the inland area. Peak surface accelerations were found to vary from 0.10 g in the coastal region to 0.50 g in the inland area, whereas the corresponding values of spectral acceleration ranged from 0.30 g to 2.0 g. Strong motion records obtained in the city during the July 14, 1993 MS = 5.4 Patras earthquake are in agreement with the results of this study. It is concluded that a systematic microzonation study of Patras would contribute to the seismic protection of the city

Hierarchical forecasts for Australian domestic tourism

In this paper we explore the hierarchical nature of tourism demand time series and produce short-term forecasts for Australian domestic tourism. The data and forecasts are organized in a hierarchy based on disaggregating the data for different geographical regions and for different purposes of travel. We consider five approaches to hierarchical forecasting: two variations of the top-down approach, the bottom-up method, a newly proposed top-down approach where top-level forecasts are disaggregated according to forecasted proportions of lower level series, and a recently proposed optimal combination approach. Our forecast performance evaluation shows that the top-down approach based on forecast proportions and the optimal combination method perform best for the tourism hierarchies we consider. By applying these methods, we produce detailed forecasts for the Australian domestic tourism market.Australia, exponential smoothing, hierarchical forecasting, innovations state space models, optimal combination forecasts, top-down method, tourism demand.

Optimal combination forecasts for hierarchical time series

In many applications, there are multiple time series that are hierarchically organized and can be aggregated at several different levels in groups based on products, geography or some other features. We call these "hierarchical time series". They are commonly forecast using either a "bottom-up" or a "top-down" method. In this paper we propose a new approach to hierarchical forecasting which provides optimal forecasts that are better than forecasts produced by either a top-down or a bottom-up approach. Our method is based on independently forecasting all series at all levels of the hierarchy and then using a regression model to optimally combine and reconcile these forecasts. The resulting revised forecasts add up appropriately across the hierarchy, are unbiased and have minimum variance amongst all combination forecasts under some simple assumptions. We show in a simulation study that our method performs well compared to the top-down approach and the bottom-up method. It also allows us to construct prediction intervals for the resultant forecasts. Finally, we apply the method to forecasting Australian tourism demand where the data are disaggregated by purpose of visit and geographical region.Bottom-up forecasting, combining forecasts, GLS regression, hierarchical forecasting, Moore-Penrose inverse, reconciling forecasts, top-down forecasting.

Heterotic free fermionic and symmetric toroidal orbifold models

Free fermionic models and symmetric heterotic toroidal orbifolds both constitute exact backgrounds that can be used effectively for phenomenological explorations within string theory. Even though it is widely believed that for Z2xZ2 orbifolds the two descriptions should be equivalent, a detailed dictionary between both formulations is still lacking. This paper aims to fill this gap: We give a detailed account of how the input data of both descriptions can be related to each other. In particular, we show that the generalized GSO phases of the free fermionic model correspond to generalized torsion phases used in orbifold model building. We illustrate our translation methods by providing free fermionic realizations for all Z2xZ2 orbifold geometries in six dimensions.Comment: 1+49 pages latex, minor revisions and references adde

Creep Effects on Low-Amplitude Modulus of Clays

The investigation considered effects of on-going or previous drained creep on the low amplitude dynamic shear modulus of normally consolidated artificial and natural clay soils. Resonant column tests using the Hardin and Hall devices determined the low-amplitude shear modulus. Results indicated that the strain-rate of on-going creep determined the kind of effect on shear modulus. High strain-rates produced reduced values whereas low strain-rates slightly increased values of modulus, compared to the no-creep values. Previous creep produced higher values of modulus, when the clay was tested under after-creep isotropic confinement. The rate of secondary increase of shear modulus was not affected by the drained creep action. The behaviors of the remolded kaolinite clay and the undisturbed natural clay were remarkably similar

Topography Effects in the Athens 1999 Earthquake: The Case of Hotel Dekelia

The effects of surface topography on the seismic ground response of the site of Hotel DEKELIA, which partially collapsed in the Athens 1999 earthquake, is studied by the finite element method. The hotel site is located at the crest of a 40m high bank of a stream crossing the area. 2-D and I-D analyses of seismic ground response were conducted using five accelerograms recorded in past earthquakes (including the Athens 1999 earthquake) as input motion. Geotechnical data for the site were obtained from the results of a geotechnical investigation conducted at the hotel site whereas a VSO vs. depth profile was estimated by using the SASW method. The ground response analyses were conducted by assuming both equivalent-linear and truly non-linear soil behavior. The results indicate that surface topography has the potential of amplifying the peak horizontal accelerations and the maximum spectral accelerations (for period values ranging from 0.35sec to 0.50 sec) at the hotel site by up to 35% and loo%, respectively. It was also found that the local soil conditions at the site may have amplified significantly the input motion. It is concluded that the combined effects of surface topography and local soil conditions may have contributed to the partial collapse of the hotel