Trust, but Verify: Two-Phase Typing for Dynamic Languages

A key challenge when statically typing so-called dynamic languages is the ubiquity of value-based overloading, where a given function can dynamically reflect upon and behave according to the types of its arguments. Thus, to establish basic types, the analysis must reason precisely about values, but in the presence of higher-order functions and polymorphism, this reasoning itself can require basic types. In this paper we address this chicken-and-egg problem by introducing the framework of two-phased typing. The first "trust" phase performs classical, i.e. flow-, path- and value-insensitive type checking to assign basic types to various program expressions. When the check inevitably runs into "errors" due to value-insensitivity, it wraps problematic expressions with DEAD-casts, which explicate the trust obligations that must be discharged by the second phase. The second phase uses refinement typing, a flow- and path-sensitive analysis, that decorates the first phase's types with logical predicates to track value relationships and thereby verify the casts and establish other correctness properties for dynamically typed languages

Electrical conductivity for Copper Oxide (CuO) nanofluids in the superconducting phase. A generalization of Type II superconductivity hydrodynamics behavior

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Copper oxide superconducting nanofluids exhibit a lot of very interesting technological properties and their behaviour is typical of a two- phase nanofluid. Near the superconductivity trasition temperature, their electrical conductivity is the sum of a normal conductivity component and a flux flow superconducting contribution from the unpinned motion of vortices within the sample. Armed with recent experimental results for regular type II superconductivity nanosamples, we review the corresponding expected behaviour for CuO High Temperature Superconducting (HTSC) systems. The equivalent Navier-Stokes equations that go under the name Ginzburg–Landau equations for the superconducting density are briefly reviewed and their solutions are presented in a clear way for the particular problem. Contribution of fluctuations of the structural vortex lattice, which is a stable solution of the Time Dependent Ginzburg-Landau (TDGL) equations, to the flux flow two -phase conductivity is briefly presented. The corresponding discussion for the two-phase thermal conductivity of a superconducting nanosample is going to be presented in a separate future publication

Οι Επαναστάσεις του 1848 στον Ελληνικό Τύπο: Ιδεολογικές τάσεις και προσλήψεις στην ελληνική δημόσια σφαίρα

Θέμα της παρούσης εργασίας είναι ο τρόπος με τον οποίο αποτυπώθηκαν οι ευρωπαϊκές επαναστάσεις του 1848 στον Ελληνικό Τύπο. Σκοπός της είναι η ανάδειξη των ιδεολογικών τάσεων που υπήρχαν στην ελληνική δημόσια σφαίρα κατά την Οθωνική περίοδο. Ερευνητικές πηγές αποτέλεσαν τα σχετικά με τις επαναστάσεις άρθρα τεσσάρων εφημερίδων των ετών 1848-1849. Πρόκειται για τα Αθηναϊκά έντυπα Αιών, Ελπίς, Συντηρητική και το Ερμουπολίτικο Αίολο, που βρίσκονται ψηφιοποιημένα στη Βιβλιοθήκη της Βουλής των Ελλήνων. Έγινε προσπάθεια οι εφημερίδες να αντιπροσωπεύουν όσο το δυνατόν περισσότερο το ιδεολογικό πολιτικό τοπίο της εποχής. Κατά την εξεταζόμενη περίοδο 1848-49 ο Αιών επρόσκειτο στο Ρωσικό Κόμμα, η Ελπίς στο Αγγλικό Κόμμα, ενώ ο Αίολος και η Συντηρητική στήριζαν τις βασιλικές κυβερνήσεις του Γαλλικού Κόμματος. Οι δυο πρώτες εντάσσονται στο φιλελεύθερο ιδεολογικό στρατόπεδο, ενώ οι δυο τελευταίες στο συντηρητικό. Το πρώτο κεφάλαιο της εργασίας εξετάζει τη σχέση του θεσμού του Τύπου με τον χώρο της δημόσιας σφαίρας. Αρχικά παρουσιάζεται η συγκρότηση και η δομή της δημόσιας σφαίρας, δηλαδή του φαντασιακού κοινού ιδιωτών ατόμων με σκοπό την ανταλλαγή απόψεων και την κριτική των δημοσίων πραγμάτων, στη Δυτική Ευρώπη. Στη συνέχεια επιχειρείται η σκιαγράφηση της ελληνικής δημόσιας σφαίρας κατά την Οθωνική περίοδο και παρουσιάζεται η λειτουργία του Τύπου σε αυτήν, καθώς και η σχέση του με το πολιτικό και κομματικό σύστημα της εποχής. Στο δεύτερο κεφάλαιο παρουσιάζεται η δημοσιογραφική κάλυψη των επαναστατικών γεγονότων του έτους 1848 και γίνεται προσπάθεια ερμηνείας της. Έμφαση δίνεται στην Παρισινή επανάσταση του Φεβρουάριου, την Παρισινή εργατική εξέγερση του Ιούνιου και την αντεπίθεση των δυνάμεων της Αντίδρασης το φθινόπωρο του ίδιου έτους. Το τρίτο κεφάλαιο ασχολείται με την κάλυψη των γεγονότων του έτους 1849. Πέρα από την αντιμετώπιση του Τύπου προς την οριστική ήττα των επαναστατικών δυνάμεων, εξετάζονται ξεχωριστά η διαμάχη των εφημερίδων Αιών και Ελπίς γύρω από τον Ουγγρικό πόλεμο της Ανεξαρτησίας καθώς και η στάση του Τύπου προς τις αναταραχές στα υπό Βρετανική κηδεμονία Ιόνια Νησιά τα έτη 1848-1849. Τέλος, διατυπώνονται συμπεράσματα σχετικά με τη δομή της ελληνικής δημόσιας σφαίρας εκείνης της περιόδου, των ιδεολογικών τάσεων που υπήρχαν σε αυτήν καθώς και τον πολιτικό ιδεολογικό χαρακτήρα των τριών «ξενικών» κομμάτων.The object of this dissertation is the manner in which the European revolutions of 1848 were presented by the Greek Press. The dissertation’s aim is to illustrate the ideological currents present to the Greek public sphere during the Othonian period. The sources of the research were the newspaper articles of the years 1848-1849 regarding the revolutions. These are coming from the Athenian newspapers Aion, Elpis, Sintiritiki and the Ermoupolitan Aiolos, which are founded in the digital newspaper archive of the Greek Parliament’s Library. The attempt was the newspapers to cover as much as possible of the era’s political ideological field. During the years 1848-49 Aion was supporting the Russian Party, Elpis the English Party and Aiolos and Sintiritiki were supporting the French Party’s governments appointed by king Otto. The first two papers were liberal leaning while the rest two were conservative. The first chapter of the dissertation examines the relation between the Press and the public sphere. First, it presents the formation and the structure of the public sphere, i.e. the imagined community of private people with purpose of exchanging opinions and critique public affairs, in Western Europe. Then, an attempt is made of an outline of the Greek public sphere of the Othonian period and the function of the Press in, as well as of the relation between the Press and the political party system of the era. The second chapter presents the coverage of the revolutionary events of the year 1848 and an effort of its assessment is made. The chapter focuses on the French revolution of February1848, the Paris June uprising and the counterattack of the Reactionary forces in the autumn of the same year. The third chapter is concerned with the following year’s events coverage. Besides the attitude of the Press towards the Revolutionary forces’ final defeat, also examined are the dispute between Aion and Elpis for the Hungarian War of Independence and the stance of the newspapers towards the revolts in the British protectorate of the Ionian Islands during 1848-1849. Finally, some conclusions are drawn, regarding the structure of the Othonian period’s Greek public sphere, the ideological currents which occurred in it and the ideological character of the three “foreign” parties

Magnetic pinning of Andreev levels in epitaxial semiconductor-superconductor nanowires

An epitaxial semiconductor-superconductor nanowire is a superconducting system with a complex level structure originating from the hybridization: in addition to a dense set of higher-energy states derived predominantly from the metallic superconducting shell above the bulk gap $\Delta$, there is a small number of lower-energy proximitized states from the semiconducting core that define the induced gap $\Delta^*$. Nanostructures based on such nanowires can furthermore incorporate quantum dots to confine a handful of electrons in order to obtain localized spins for storing and manipulating quantum information. Magnetic properties of these composite devices are complex due to the interplay of exchange interaction, electron correlation effects and the spin-orbit coupling (SOC). We discuss the magnetic field dependence in three devices with different combinations of embedded quantum dots and superconducting islands. For strong fields, they show pinning of excitation energies to a uniform spacing, even if for weak fields they have non-universal properties with clearly different behaviors for even and odd number of confined electrons. We propose a quantum impurity model for hybrid devices that incorporates all relevant effects and solve it. We show that the model accounts for the key observations and permits unambiguous interpretation of phenomena in terms of many-particle states. In particular, we study the replicas of the Yu-Shiba-Rusinov states in the hybrid gap, their collapse and oscillation around zero bias with increasing field, and the strong smoothing effect of the SOC on these oscillations. We conclude that the SOC-induced mixing of many-body states is a generic mechanism for magnetic pinning and that it is likely to be a ubiquitous feature in hybrid semi-super nanowires.Comment: 13 pages, 6 figure

Temperature Induced Shifts of Yu-Shiba-Rusinov Resonances in Nanowire-Based Hybrid Quantum Dots

The strong coupling of a superconductor to a spinful quantum dot results in Yu-Shiba-Rusinov (YSR) discrete subgap excitations. In isolation and at zero temperature, the excitations are $\delta$ resonances. In transport experiments, however, they show as broad differential conductance peaks. We obtain the lineshape of the peaks and their temperature dependence in superconductor-quantum-dot-metal (S-QD-N) nanowire-based devices. Unexpectedly, we find that the peaks shift in energy with temperature, with the shift magnitude and sign depending on ground state parity and bias voltage. Additionally, we empirically find a power-law scaling of the peak area versus temperature. These observations are not explained by current models

Coulombic subgap states

Energy gaps are ubiquitous in the solid state. While in superconductors the Bardeen-Cooper-Schrieffer gap comes from Cooper pairing mediated by the crystal lattice, in Mott insulators the Coulomb gap results instead from electron-electron interactions. These gaps can be populated by subgap states due to various mechanisms. Here we demonstrate the existence of \textit{Coulombic} states, a new type of subgap states arising in a device with an energy gap opened by both Cooper pairing and Coulomb repulsion. The hybrid gap is provided by a superconducting island in Coulomb blockade, while the states arise due to electron transfer between the island and a nearby quantum dot. The Coulomb interaction in the device produces an unusual excitation spectrum exhibiting broken electron-hole energy symmetry, discontinuity of spectral curves, strongly renormalized g-factors and high-degeneracy points. The repercussions of the new states for the search of Majorana states in topological superconducting islands are elucidated.Comment: Supplementary Information available as an ancillary file with this submissio