127 research outputs found
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 BiSrCaCuO under Tilted Fields
Vortex phase diagram under tilted fields from the axis in
BiSrCaCuO is studied by local magnetization
hysteresis measurements using Hall probes. When the field is applied at large
angles from the axis, an anomaly () other than the well-known
peak effect () are found at fields below . The angular dependence of
the field is nonmonotonic and clearly different from that of
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
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