Strategic delegation in a sequential model with multiple stages

We analyze strategic delegation in a Stackelberg model with an arbitrary number, n, of firms. We show that the n-1 last movers delegate their production decisions to managers whereas the first mover does not. Equilibrium incentive rates are increasing in the order with which managers select quantities. Letting u_i^* denote the equilibrium payoff of the firm whose manager moves in the i-th place, we show that u_n^*>u_{n-1}^*>...>u_2^*>u_1^*. We also compare the delegation outcome of our game with that of a Cournot oligopoly and show that the late (early) moving firms choose higher (lower) incentive rates than the Cournot firms.Comment: To appear in International Game Theory Review (IGTR), Vol. 13, No. 3 (2011) 1-1

Stacking classifiers for anti-spam filtering of e-mail

We evaluate empirically a scheme for combining classifiers, known as stacked generalization, in the context of anti-spam filtering, a novel cost-sensitive application of text categorization. Unsolicited commercial e-mail, or "spam", floods mailboxes, causing frustration, wasting bandwidth, and exposing minors to unsuitable content. Using a public corpus, we show that stacking can improve the efficiency of automatically induced anti-spam filters, and that such filters can be used in real-life applications

Generation of Coherent Structures After Cosmic Inflation

We investigate the nonlinear dynamics of hybrid inflation models, which are characterized by two real scalar fields interacting quadratically. We start by solving numerically the coupled Klein-Gordon equations in static Minkowski spacetime, searching for possible coherent structures. We find long-lived, localized configurations, which we identify as a new kind of oscillon. We demonstrate that these two-field oscillons allow for "excited" states with much longer lifetimes than those found in previous studies of single-field oscillons. We then solve the coupled field equations in an expanding Friedmann-Robertson-Walker spacetime, finding that as the field responsible for inflating the Universe rolls down to oscillate about its minimum, it triggers the formation of long-lived two-field oscillons, which can contribute up to 20% of the total energy density of the Universe. We show that these oscillons emerge for a wide range of parameters consistent with WMAP 7-year data. These objects contain total energy of about 25*10^20 GeV, localized in a region of approximate radius 6*10^-26 cm. We argue that these structures could have played a key role during the reheating of the Universe.Comment: 12 pages, 10 .pdf figures, uses RevTex4; v2: expanded discussion in section IV, accepted for publication in Phys.Rev. D. Results remain the sam

Geomorphological reconnaissance of the Psathopyrgos and Rion-Patras Fault zones (Achaia, NW Peloponnesus).

Στην εργασία αυτή συζητώνται γεωμορφολογικές παρατηρήσεις κατά μήκος των ενεργών ρηξιγενών ζωνών Ψαθοιτύργου και Ρίου-Πατρών (ΒΑ τμήμα). Οι ρηξιγενείς ζώνες αυτές αντιστοιχούν σε ρηξιγενή μέτωπα περισσότερο ή λιγότερο πολύπλοκης μορφολογίας. Τα γεωμορφολογικά χαρακτηριστικά των μετώπων δίδουν πληροφορίες για την γεωμετρία των ζωνών αυτών, συμπληρωματικές των ήδη υπαρχόντων δεδομένων από γεωλογικές έρευνες. Στοχεύοντας στην αναγνώριση θέσεων δυνητικά κατάλληλων για γεωμορφολογικές και γεωλογικές έρευνες για την εκτίμηση των ρυθμών ολίσθησης ρηγμάτων αυτών των ζωνών κατά το Ολόκαινο, περιγράφονται περιπτώσεις ρηγματωμένων ολοκαινικών γεωμορφών και σχετιζόμενων με αυτές επιφανειακών αποθέσεων. Επι πλέον, συζητώνται τα προβλήματα ανεύρεσης θέσεων κατάλληλων για γεωλογικές/γεωμορφολογικές έρευνες γαι τον χρονικό προσδιορισμό πρόσφατων σεισμικών διαρήξεων (παλαιοσεισμολογία), προβλήματα που οφείλονται τόσο σε ανθρώπινες επεμβάσεις, όσο και σε φυσικές γεωμορφολογικές διεργασίες.In this communication we discuss reconnaissance geomorphological observations along the active Psathopyrgos and Rion-Patras (NE part) fault zones. These fault zones correspond to more or less complex rangefronts, the geomorphic characteristics of which provide hints on the details of the fault zone geometries, adding to the existing geological data in the bibliography. Aiming at the identification of locations suitable or potentially suitable for geomorphological and geological studies for the determination of fault slip rates in the Holocene, we describe cases of faulted Holocene landforms and associated surficial deposits. We also discuss problems involved in finding locations suitable for geological (paleoseismological) studies for the determination of the timing of recent earthquake ruptures, problems due to both man-made and natural causes

Long-Lived Time-Dependent Remnants During Cosmological Symmetry Breaking: From Inflation to the Electroweak Scale

Through a detailed numerical investigation in three spatial dimensions, we demonstrate that long-lived time-dependent field configurations emerge dynamically during symmetry breaking in an expanding de Sitter spacetime. We investigate two situations: a single scalar field with a double-well potential and the bosonic sector of an SU(2) non-Abelian Higgs model. For the single scalar, we show that large-amplitude oscillon configurations emerge spontaneously and persist to contribute about 1.2% of the energy density of the universe. We also show that for a range of parameters, oscillon lifetimes are enhanced by the expansion and that this effect is a result of parametric resonance. For the SU(2) case, we see about 4% of the final energy density in oscillons.Comment: 10 pages, RevTex4, 6 figures; v2: expanded SU(2) model section, added 2 figures, added one section, improved overall presentation and updated references, accepted for publication in Phys. Rev. D. Results remain the sam

Aging of bone marrow mesenchymal stromal cells: Hematopoiesis disturbances and potential role in the development of hematologic cancers

Aging of bone marrow is a complex process that is involved in the development of many diseases, including hematologic cancers. The results obtained in this field of research, year after year, underline the important role of cross-talk between hematopoietic stem cells and their close environment. In bone marrow, mesenchymal stromal cells (MSCs) are a major player in cell-to-cell communication, presenting a wide range of functionalities, sometimes opposite, depending on the environmental conditions. Although these cells are actively studied for their therapeutic properties, their role in tumor progression remains unclear. One of the reasons for this is that the aging of MSCs has a direct impact on their behavior and on hematopoiesis. In addition, tumor progression is accompanied by dynamic remodeling of the bone marrow niche that may interfere with MSC functions. The present review presents the main features of MSC senescence in bone marrow and their implications in hematologic cancer progression

Learning to Filter Spam E-Mail: A Comparison of a Naive Bayesian and a Memory-Based Approach

We investigate the performance of two machine learning algorithms in the context of anti-spam filtering. The increasing volume of unsolicited bulk e-mail (spam) has generated a need for reliable anti-spam filters. Filters of this type have so far been based mostly on keyword patterns that are constructed by hand and perform poorly. The Naive Bayesian classifier has recently been suggested as an effective method to construct automatically anti-spam filters with superior performance. We investigate thoroughly the performance of the Naive Bayesian filter on a publicly available corpus, contributing towards standard benchmarks. At the same time, we compare the performance of the Naive Bayesian filter to an alternative memory-based learning approach, after introducing suitable cost-sensitive evaluation measures. Both methods achieve very accurate spam filtering, outperforming clearly the keyword-based filter of a widely used e-mail reader

Information Content of Spontaneous Symmetry Breaking

We propose a measure of order in the context of nonequilibrium field theory and argue that this measure, which we call relative configurational entropy (RCE), may be used to quantify the emergence of coherent low-entropy configurations, such as time-dependent or time-independent topological and nontopological spatially-extended structures. As an illustration, we investigate the nonequilibrium dynamics of spontaneous symmetry-breaking in three spatial dimensions. In particular, we focus on a model where a real scalar field, prepared initially in a symmetric thermal state, is quenched to a broken-symmetric state. For a certain range of initial temperatures, spatially-localized, long-lived structures known as oscillons emerge in synchrony and remain until the field reaches equilibrium again. We show that the RCE correlates with the number-density of oscillons, thus offering a quantitative measure of the emergence of nonperturbative spatiotemporal patterns that can be generalized to a variety of physical systems.Comment: LaTeX, 9 pages, 5 figures, 1 tabl

Predicting Ground Subsidence Induced by Pumping Combining Space Measurements and Geotechnical Modeling: Application in the Thessaly Region, Greece

Space technology is a new technology that provides cost-effective measurements of past displacement data. Based on these displacement measurements, within the framework of the European Space Agency’s GMES Terrafirma Project, an improved geotechnical design approach is proposed combining geotechnical modelling and space measurements to predict ground subsidence induced by the lowering of the water table. Then the proposed methodology is applied to predict future displacement at the Thessaly plain - Carla region, Greece due to excessive pumping