Railway construction cost estimation

196 σ.Σκοπός της εργασίας αυτής είναι η εκτίμηση τους κόστους κατασκευής μιας σύγχρονης σιδηροδρομικής γραμμής καθώς και των λοιπών εγκαταστάσεων που την αποτελούν. Για το σκοπό αυτό προσδιορίζονται και παρουσιάζονται αναλυτικά τα κατασκευαστικά στοιχεία εκείνα που επηρεάζουν τον σχεδιασμό και το κόστος κατασκευής νέων γραμμών. Έπεται η συλλογή στοιχείων κόστους με χρήση αναλυτικών τιμολογίων σιδηροδρομικών εργασιών και βιβλιογραφικών πηγών. Στη συνέχεια αναπτύσσεται μεθοδολογία, η οποία καθοδηγεί τον χρηστή μέσω κριτηρίων και αξιολογήσεων στην επιλογή των διάφορων παραμέτρων σχεδιασμού. Τελικό αποτέλεσμα της εργασίας είναι η διατύπωση του μοντέλου υπολογισμού σε λογιστικό φύλλο περιβάλλοντος Microsoft Excel αυτοματοποιώντας τη διαδικασία εκτίμησης κόστους σιδηροδρομικών έργων.The aim of this thesis is the construction cost estimation of a modern railway line and the rest facilities that compose it. For this purpose the construction elements are defined and presented in detail, that affect the design and construction cost of new lines. With use of detailed railway works invoices and bibliographic sources the costs data collection follows. Then a methodology is developed, guiding the user through criteria and evaluations in the selection of various design parameters. End result of this work is the formulation of the model calculation in a Microsoft Excel spreadsheet which automates the cost estimation process of railway projects.Λάμπρος Κ. Δεληγιάννη

Theory of the vortex matter transformations in high Tc superconductor YBCO

Flux line lattice in type II superconductors undergoes a transition into a "disordered" phase like vortex liquid or vortex glass, due to thermal fluctuations and random quenched disorder. We quantitatively describe the competition between the thermal fluctuations and the disorder using the Ginzburg -- Landau approach. The following T-H phase diagram of YBCO emerges. There are just two distinct thermodynamical phases, the homogeneous and the crystalline one, separated by a single first order transitions line. The line however makes a wiggle near the experimentally claimed critical point at 12T. The "critical point" is reinterpreted as a (noncritical) Kauzmann point in which the latent heat vanishes and the line is parallel to the T axis. The magnetization, the entropy and the specific heat discontinuities at melting compare well with experiments.Comment: 4 pages 3 figure

Finding Inductive Loop Invariants using Large Language Models

Loop invariants are fundamental to reasoning about programs with loops. They establish properties about a given loop's behavior. When they additionally are inductive, they become useful for the task of formal verification that seeks to establish strong mathematical guarantees about program's runtime behavior. The inductiveness ensures that the invariants can be checked locally without consulting the entire program, thus are indispensable artifacts in a formal proof of correctness. Finding inductive loop invariants is an undecidable problem, and despite a long history of research towards practical solutions, it remains far from a solved problem. This paper investigates the capabilities of the Large Language Models (LLMs) in offering a new solution towards this old, yet important problem. To that end, we first curate a dataset of verification problems on programs with loops. Next, we design a prompt for exploiting LLMs, obtaining inductive loop invariants, that are checked for correctness using sound symbolic tools. Finally, we explore the effectiveness of using an efficient combination of a symbolic tool and an LLM on our dataset and compare it against a purely symbolic baseline. Our results demonstrate that LLMs can help improve the state-of-the-art in automated program verification

Disorder Induced Transitions in Layered Coulomb Gases and Superconductors

A 3D layered system of charges with logarithmic interaction parallel to the layers and random dipoles is studied via a novel variational method and an energy rationale which reproduce the known phase diagram for a single layer. Increasing interlayer coupling leads to successive transitions in which charge rods correlated in N>1 neighboring layers are nucleated by weaker disorder. For layered superconductors in the limit of only magnetic interlayer coupling, the method predicts and locates a disorder-induced defect-unbinding transition in the flux lattice. While N=1 charges dominate there, N>1 disorder induced defect rods are predicted for multi-layer superconductors.Comment: 4 pages, 2 figures, RevTe

Vortex Matter Transition in Bi2{}_2Sr2{}_2CaCu2{}_2O8+y{}_{8+y} under Tilted Fields

Vortex phase diagram under tilted fields from the $c$ axis in Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+y}$ is studied by local magnetization hysteresis measurements using Hall probes. When the field is applied at large angles from the $c$ axis, an anomaly ($H_p^\ast$) other than the well-known peak effect ($H_p$) are found at fields below $H_p$. The angular dependence of the field $H_p^\ast$ is nonmonotonic and clearly different from that of $H_p$ and depends on the oxygen content of the crystal. The results suggest existence of a vortex matter transition under tilted fields. Possible mechanisms of the transition are discussed.Comment: Revtex, 4 pages, some corrections are adde

A Bragg glass phase in the vortex lattice of a type II superconductor

Although crystals are usually quite stable, they are sensitive to a disordered environment: even an infinitesimal amount of impurities can lead to the destruction of the crystalline order. The resulting state of matter has been a longstanding puzzle. Until recently it was believed to be an amorphous state in which the crystal would break into crystallites. But a different theory predicts the existence of a novel phase of matter: the so-called Bragg glass, which is a glass and yet nearly as ordered as a perfect crystal. The lattice of vortices that can contain magnetic flux in type II superconductors provide a good system to investigate these ideas. Here we show that neutron diffraction data of the vortex lattice in type II superconductors provides unambiguous evidence for a weak, power-law decay of the crystalline order characteristic of a Bragg glass. The theory also predicts accurately the electrical transport properties of superconductors; it naturally explains the observed phase transition and the dramatic jumps in the critical current associated with the melting of the Bragg glass. Moreover the model explains experiments as diverse as X-ray scattering in disordered liquid crystals and conductivity of electronic crystals.Comment: 9 pages, 4 figure