cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
Gravitational-wave polarizations in generic linear massive gravity and generic higher-curvature gravity
Creators: name: Tachinami, Tomoya
name: Tonosaki, Shinpei
name: Sendouda, Yuuiti
Publisher: name: arXiv
Year: 2021
Subjects: subject: General Relativity and Quantum Cosmology (gr-qc)
subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: We study the polarizations of gravitational waves (GWs) in two classes of extended gravity theories. First, we formulate the polarizations in linear massive gravity (MG) with generic mass terms of non-Fierz-Pauli type by identifying all the independent variables that obey Klein-Gordon-type equations. The dynamical degrees of freedom (dofs) in the generic MG consist of spin-2 and spin-0 modes, the former breaking down into two tensor (helicity-2), two vector (helicity-1) and one scalar (helicity-0) components, while the latter just corresponding to a scalar. We find convenient ways of decomposing the two scalar modes of each spin into distinct linear combinations of the transverse and longitudinal polarizations with coefficients directly expressed by the mass parameters, thereby serving as a useful tool in measuring the masses of GWs. Then we analyze the linear perturbations of generic higher-curvature gravity (HCG) whose Lagrangian is an arbitrary polynomial of the Riemann tensor. On a flat background, the linear dynamical dofs in this theory are identified as massless spin-2, massive spin-2, and massive spin-0 modes. As its massive part encompasses the identical structure to the generic MG, GWs in the generic HCG provide six massive polarizations on top of the ordinary two massless modes. In parallel to MG, we find convenient representations for the scalar-polarization modes directly connected to the parameters of HCG. In this analysis, we employ two distinct methods; One takes full advantage of the partial equivalence between the generic HCG and MG at the linear level, whereas the other relies upon a gauge-invariant formalism. We confirm that the two results agree. We also discuss methods to determine the theory parameters by GW-polarization measurements. Our method does not require measuring the propagation speeds or the details of the waveforms of the GWs. [Abridged]
description: 19 pages, no figures, references added, published in Phys. Rev. D
Ο Αναστάσιμος Κανών του Ιωάννου του Δαμασκηνού
Creators: name: Γαλούνης, Κωνσταντίνος Αλέξανδρου
Publisher: name: Aristotle University of Thessaloniki
Year: 2018
Subjects: Αναστάσιμος Κανών
Ιωάννης Δαμασκηνός
Φιλολογική και θεολογική προσέγγιση του Αναστάσιμου Κανόνος
Anastasimos Canon
John Damascene
Philological and theological examination of Anastasimos Canon.

description: Η παρούσα διπλωματική εργασία είχε ως στόχο την εξέταση του Αναστάσιμου Κανόνος του Ιωάννου του Δαμασκηνού. Προς επίτευξη του στόχου αυτού, στο Α’ κεφάλαιο παρατέθηκε ο εν λόγω κανών και έγινε η φιλολογική προσέγγισή του. Συγκεκριμένα, πραγματοποιήθηκε η απόδοσή του στη νεοελληνική γλώσσα καθώς κι η ετυμολογία σημαντικών λέξεων, προκειμένου να γίνει κατανοητό το βαθύτερο νόημα ορισμένων χωρίων. Έπειτα, στο Β’ κεφάλαιο ακολούθησε η θεολογική προσέγγισή του. Προτού ,όμως, προχωρήσουμε στη μελέτη του Αναστάσιμου Κανόνος, απαραίτητη κρίθηκε η ύπαρξη εισαγωγής, εντός της οποίας δόθηκαν χρήσιμες πληροφορίες για τους εκκλησιαστικούς ύμνους και ειδικότερα για το υμνολογικό είδος των κανόνων. Παράλληλα, στον πρόλογο έγινε αναφορά στον σπουδαίο υμνογράφο του εξεταζόμενου κανόνος, ήτοι στον Ιωάννη τον Δαμασκηνό, ο οποίος αποτελεί μια σπουδαία μορφή της Εκκλησίας
description: The aim of the present thesis was to examine the Anastasimos Canon of John Damascene. In the 1st chapter of our research the Canon was cited and was examined philologically. Specifically, we translated it to Modern Greek and we presented the etymology of some important words in order to be understood the deeper meaning of some abstracts. In the 2nd chapter we examined Anastasimos Canon theologically. Moreover, we found necessary to give some useful information in the introduction about the hymns and especially about a kind of them, the Canon. Moreover, we referred to John Damascene, who undoubtedly is a special figure of Church
description: Σε συνεργασία με το τμήμα Κοινωνικής Θεολογίας (Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών)
Strategic Delegation under Cost Asymmetry
Creators: name: Delbono, Flavio
name: Lambertini, Luca
name: Marattin, Luigi
Publisher: name: Alma Mater Studiorum - Università di Bologna
Year: 2015
Subjects: SECS-P/01 Economia politica

description: We revisit the two-stage duopoly game with strategic delegation and asymmetric technologies of Sen and Stamatopoulos (2015). We show that their conclusions are misled by the restrictive assumption that the extent of delegation to managers is restricted to a binary set. Allowing for a continuous set of delegation incentives, we prove that the delegation stage is a prisoners�dilemma, the unique subgame perfect equilibrium entailing both fi�rms hiring managers. At equilibrium,
the more efficient �firm makes higher profi�ts.
A single espresso, please! Rationalizing espresso price dispersion across Italian cities
Creators: name: Delbono, Flavio
name: Dipoppa, Gemma
name: Lambertini, Luca
name: Reggiani, Carlo
Publisher: name: Alma Mater Studiorum - Università di Bologna
Year: 2015
Subjects: SECS-P/01 Economia politica

description: This paper aims at providing an explanation of the observed espresso price dispersion across major Italian cities. The empirical evidence suggests a positive relationships between the average espresso price in a city and the number of coffee shops (normalized for the adult population) operating in that city. This finding is shown to be robust after controlling for GDP per capita and consumers.price index. We provide an interpretation of the empirical findings relying on a model of price competition delivering a continuum of Nash equilibria, where firms adjust the mark-up to offset the negative effect of any increase in their number.
On a relation between Liouville field theory and a two component scalar field theory passing through the random walk
Creators: name: Ferrari, Franco
name: Paturej, Jaroslaw
Publisher: name: arXiv
Year: 2006
Subjects: subject: Mathematical Physics (math-ph)
subject: Statistical Mechanics (cond-mat.stat-mech)
subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: In this work it is proposed a transformation which is useful in order to simplify non-polynomial potentials given in the form of an exponential. As an application, it is shown that the quantum Liouville field theory may be mapped into a field theory with a polynomial interaction between two scalar fields and a massive vector field.
description: 15 pages, 4 figures, LaTeX + RevTeX 4. With respect to the previous version an appendix has been added to provide an alternative proof of Eq. (31). Title and abstract have been changed
TALABALARDA OMMAVIY SPORT TADBIRLARINI TASHKIL QILISH VA O'TKAZISH KOMPETENSIYASINI RIVOJLANTIRISHNING ILMIY-NAZARIY ASOSLARI
Creators: name: Anorqulov Baxtiyor Norqul o'g'li Guliston davlat universiteti "Sport turlarini o'qitish uslubiyati" kafedrasi o'qituvchisi
Publisher: name: Zenodo
Year: 2024

description: Ushbu maqolada talabalarda ommaviy sport tadbirlarini tashkil etish va o'tkazish kompetensiyalarini rivojlantirishning ilmiy-nazariy asoslari ko'rib chiqiladi. Adabiyotlar tahlili asosida ommaviy sport tadbirlarining ahamiyati, talabalar kompetensiyalarini rivojlantirish yo'llari va bu jarayondagi muammolar tahlil qilinadi. Maqolada kompetensiyalarni rivojlantirishning samarali usullari va yondashuvlari taklif etiladi.

Kalit so'zlar: talabalar, ommaviy sport tadbirlari, kompetensiya, rivojlantirish, ilmiy-nazariy asoslar
Η εμπειρία ενηλίκων γυναικών που βίωσαν αδερφική απώλεια κατά την παιδική και εφηβική ηλικία: Μια ερμηνευτική -φαινομενολογική ανάλυση
Creators: name: Τυμπανίδου, Βασιλική Σωτηρία Γεωργίου
Publisher: name: Aristotle University of Thessaloniki
Year: 2018
Subjects: Αδέρφια
Αδερφική Απώλεια
Αδερφικός θρήνος
Siblings
Siblings’ Loss
Siblings’ bereavement

description: Στόχος της παρούσας έρευνας είναι να διερευνήσει την εμπειρία ενήλικων, πλέον, ατόμων που έχασαν αδερφό ή αδερφή κατά την παιδική ή εφηβική ηλικία. Πιο συγκεκριμένα, το ερευνητικό ενδιαφέρον εστιάστηκε στην κατανόηση του υποκειμενικού βιώματος της αδερφικής απώλειας και πώς ο κάθε συμμετέχοντας διαχειρίστηκε την απώλεια αυτή μέσα στο πέρασμα του χρόνου. Επίσης, διερευνήθηκε η θέση που φαίνεται να κατέχει αυτή η πρώιμη εμπειρία της αδερφικής απώλειας στην ζωή των συμμετεχόντων στο παρόν. Ακολουθήθηκε μια ποιοτική προσέγγιση και το δείγμα αποτέλεσαν πέντε (5) ενήλικες γυναίκες, που είχαν βιώσει αδερφική απώλεια κατά την παιδική και εφηβική τους ηλικία. Τα δεδομένα συλλέχθηκαν μέσα από ημι- δομημένες συνεντεύξεις και η ανάλυση έγινε με τη μέθοδο της ερμηνευτικής φαινομενολογίας (Interpretative Phenomenological Analysis, IPA). Τα αποτελέσματα που προέκυψαν και συζητούνται σε σχέση με τη σχετική βιβλιογραφία είναι τα εξής: α) Απώλεια και στάση απέναντι στην ζωή, β) Απώλεια και εαυτός, γ) Απώλεια και σχέση με τους άλλους, δ) Η απώλεια στο σήμερα, ε) Ενοχή, στ) Νοηματοδότηση.
description: The aim of this research is to investigate the experience of adults who have lost a sibling during their childhood or adolescence. The research focused on understanding the personal experience of sibling loss and bereavement and the way each participant has coped with this loss across his life, from the moment of the death up to this day. A qualitative design was used and the analysis was based on the Interpretative Phenomenological Analysis (IPA). Semi- structured interviews were conducted with five (5) adult women, who have experienced sibling loss during their childhood or adolescence. Results revealed the following six themes: a) Loss and perception of life, b) Loss and Self, c) Loss and relationships with others, d) The loss at the present, e) Guilt, f) Need for meaning. The findings of the present study were discussed in reference to previous data.
Telecommuting: a municipal government perspective
Creators: name: Robertson, Judith Irene
Publisher: name: University of British Columbia
Year: 2009

description: Telecommuting has been defined in several ways. For the purpose of this paper, telecommuting (also known as teleworking) is defined as the concept of employees performing some portion of their regular work activities from a remote location, while receiving their regular salary and benefits. This remote work location is typically a satellite office, a neighbourhood office or the employee’s home. Most telecommuting occurs on a part-time basis, one to three days per week. Not every job nor every worker is suitable to telecommute. Although the actual number of telecommuters is unknown, it has been estimated that approximately 7.6 million Americans were telecommuters in 1993 -- 6.1% of the total American workforce. If even a slightly smaller proportion of telecommuters is applied to the Canadian workforce (i.e. 5.75%), there are at least 738,150 Canadian telecommuters. While being influenced by many factors, telecommuting has risen in prominence primarily due to transformations in telecommunications and information technology, the nature of work, the workers, the workplace, urban highway congestion and in some jurisdictions, environmental legislation. Encouraging the establishment of telework centres and home-based telecommuting can increase employment opportunities within the community. Reducing the number of daily trips to a central work place may reduce transportation infrastructure costs (construction and maintenance) and have a positive effect on the environment (improved air quality and energy conservation). With more people staying within their neighbourhood to work, a greater sense of community can result. Telecommuting deserves serious attention on the part of municipalities because it can deliver large benefits in economic, environmental and social terms. This paper is designed to inform, stimulate discussion, and aid in the review of out-dated municipal regulations and procedures as they pertain to telecommuting.
Κίνητρα χρήσης και κοινωνικές ομάδες στο Facebook: Κατανάλωση ειδησεογραφικού περιεχομένου και ψευδείς ειδήσεις
Creators: name: Κωστοπούλου, Ιωάννα Μιχαήλ
Publisher: name: Aristotle University of Thessaloniki
Year: 2018
Subjects: Μέσα Κοινωνικής Δικτύωσης
Κοινωνικές Ομάδες
Κοινωνική Ταυτότητα
Ψευδείς Ειδήσεις
Facebook
Social Media
Social Groups
Social Identity
Fake News

description: Η παρούσα διπλωματική εργασία αποτελεί μια ολοκληρωμένη μελέτη των μέσων κοινωνικής δικτύωσης και συγκεκριμένα των κινήτρων χρήσης και των κοινωνικών ομάδων στο Facebook. Αποτελεί, ακόμη, μελέτη που αφορά στο νεοσύστατο φαινόμενο των ψευδών ειδήσεων. Σε πρώτο επίπεδο, με γνώμονα την διεθνή βιβλιογραφία, εξετάζονται τα social media, τα κίνητρα χρήσης τους και η κοινωνική ταυτότητα Εξετάζεται ακόμη το φαινόμενο των fake news στα social media και η επιρροή τους στη σύγχρονη δημοσιογραφία. Τέλος, μελετάται ενδελεχώς το Facebook, τα κίνητρα χρήσης του, οι κοινότητές του, αλλά και η ύπαρξη των fake news σε αυτό. Αμέσως μετά ακολουθεί εμπειρική μελέτη μέσα από την οποία αναλύονται μια σειρά ερωτήσεων για το Facebook, την παραγωγή και κατανάλωση ειδησεογραφικού περιεχομένου, καθώς και την αντίληψη ύπαρξης ψευδών ειδήσεων. Από τα στοιχεία της έρευνας, στην οποία πήραν μέρος 400 συμμετέχοντες, χρήστες του Facebook, προέκυψαν σημαντικά ευρήματα, τα οποία παρέχουν χρήσιμες κατευθύνσεις για μελλοντική έρευνα.
description: The current thesis is a comprehensive study of the social media tools, namely the usage motivations and social groups on Facebook. It is also a study of the newly created phenomenon of false news. At a first level, social media, motivation for use, and social identity are examined in the light of international bibliography. Furthermore, the phenomenon of fake news in social media and its influence on modern journalism is being examined. Finally, Facebook, its motives for use, its communities and the existence of fake news on it are thoroughly studied. Immediately after, an empirical study follows, which analyzes a series of questions about Facebook, the production and consumption of news content, and the perception of false news’ existence. Significant findings emerged from the data of the research, in which 400 Facebook users took part, providing useful guidance for future research.
Unitary invariants of qubit systems
Creators: name: Toumazet, Frederic
name: Luque, Jean-Gabriel
name: Thibon, Jean-Yves
Publisher: name: arXiv
Year: 2006
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: We give an algorithm allowing to construct bases of local unitary invariants of pure k-qubit states from the knowledge of polynomial covariants of the group of invertible local filtering operations. The simplest invariants obtained in this way are explicited and compared to various known entanglement measures. Complete sets of generators are obtained for up to four qubits, and the structure of the invariant algebras is discussed in detail.
description: 19 pages, 1 figure
Η πολιτική της ρωμαϊκής αυτοκρατορίας έναντι των χριστιανών κατά τον 3ο αιώνα
Creators: name: Αλεξιάδη, Μαρία-Ελένη Χρήστου
Publisher: name: Aristotle University of Thessaloniki
Year: 2018
Subjects: Ρωμαϊκή αυτοκρατορία
Χριστιανοί
Διωγμοί
Roman Empire
Christians
Persecutions

description: Σκοπός της παρούσας διατριβής ήταν η εξέταση της πολιτικής των Ρωμαίων αυτοκρατόρων που έδρασαν κατά τη διάρκεια του 3ου αιώνα απέναντι στους χριστιανούς. Ειδικότερα, στο κύριο μέρος της εργασίας μελετήθηκαν οι αιτίες που ώθησαν τον εκάστοτε αυτοκράτορα να υιοθετήσει μία συγκεκριμένη πολιτική απέναντί τους καθώς και οι συνέπειες που είχε η τελευταία. Επιπλέον, παρατέθηκαν μαρτυρίες προσώπων που έζησαν την περίοδο των διωγμών και παρουσιάστηκαν οι ποινές, τα βασανιστήρια και οι τρόποι θανάτωσης των χριστιανών. Ταυτόχρονα, προκειμένου να κατανοηθούν πληρέστερα οι παράγοντες που παρακίνησαν τους αυτοκράτορες να υιοθετήσουν μία συγκεκριμένη στάση απέναντι στους πιστούς του χριστιανισμού, κρίθηκε ωφέλιμο να παρουσιαστούν κάποια στοιχεία της προσωπικότητάς τους, της γενικότερης πολιτικής τους και της κατάστασης στην οποία βρισκόταν κάθε φορά το ρωμαϊκό κράτος. Δε θα μπορούσαμε όμως να είχαμε περάσει στο κύριο μέρος της εργασίας, δίχως να γίνει λόγος στην εισαγωγή για τη θέση των χριστιανών στην αυτοκρατορία κατά τους δύο πρώτους αιώνες μ.Χ. Παράλληλα, δεν παραλείψαμε να μελετήσουμε τον τρόπο αντιμετώπισής τους από τον λαό και τους λόγιους αλλά και να παραθέσουμε ορισμένα στοιχεία για τη ρωμαϊκή θρησκεία.
description: The aim of the present thesis was the examination of the Roman emperors’ policy against Christians during the 3rd century. Specifically, in the main part of the research they were studied the causes that moved each one of the emperors to act with particular way each time and the consequences of these actions. Furthermore, witnesses were cited by people who lived during the period of the persecutions and the sentences were presented, the torturing and the way Christians were killed. At the same time, in order to become fully understood the factors that pushed the emperors to adopt a specific stand against the faithful to Christianity, it proved beneficial to show some information about their personality, their general policy and the situation in which the roman state is always present. We would not be able to move on to the main part of this piece of work, without talking in the introduction about the position of Christians in the Empire during the first two centuries A.D. Alongside, we didn’t skip to study the way the people and the scholars dealt with them and also to put some information about the roman religion.
description: Σε συνεργασία με: Κοινωνικής Θεολογίας (Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών)
Electronic structure of Diluted Magnetic Semiconductors $Ga_{1-x}Mn_{x}N$ and $Ga_{1-x}Cr_{x}N$
Creators: name: Tandon, Nandan
name: Das, G P
name: Kshirsagar, Anjali
Publisher: name: arXiv
Year: 2006
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: We have undertaken a study of diluted magnetic semiconductors $Ga_{1-x}Mn_{x}N$ and $Ga_{1-x}Cr_{x}N$ with $x=0.0625, 0.125$, using the all electron linearized augmented plane wave method (LAPW) for different configurations of Mn as well as Cr. We study four possible configurations of the impurity in the wurtzite GaN structure to predict energetically most favorable structure within the 32 atom supercell and conclude that the near-neighbor configuration has the lowest energy. We have also analyzed the ferro-magnetic as well as anti-ferromagnetic configurations of the impurity atoms. The density of states as well as bandstructure indicate half metallic state for all the systems. $T_c$ has also been estimated for the above systems.
description: 12 pages, 14 figures, 2 tables
Euler characteristics of Teichmüller curves in genus two
Creators: name: Bainbridge, Matt
Publisher: name: arXiv
Year: 2006
Subjects: subject: Geometric Topology (math.GT)
subject: Algebraic Geometry (math.AG)
subject: FOS: Mathematics
subject: 32G15

description: We calculate the Euler characteristics of all of the Teichmuller curves in the moduli space of genus two Riemann surfaces which are generated by holomorphic one-forms with a single double zero. These curves can all be embedded in Hilbert modular surfaces and our main result is that the Euler characteristic of a Teichmuller curve is proportional to the Euler characteristic of the Hilbert modular surface on which it lies. The idea is to use techniques from algebraic geometry to calculate the fundamental classes of these Teichmuller curves in certain compactifications of the Hilbert modular surfaces. This is done by defining meromorphic sections of line bundles over Hilbert modular surfaces which vanish along these Teichmuller curves. We apply these results to calculate the Siegel-Veech constants for counting closed billiards paths in certain L-shaped polygons. We also calculate the Lyapunov exponents of the Kontsevich-Zorich cocycle for any ergodic, SL_2(R)-invariant measure on the moduli space of Abelian differentials in genus two (previously calculated in unpublished work of Kontsevich and Zorich).
description: 178 pages, 14 figures
CHIME/FRB Catalog 1 results: statistical cross-correlations with large-scale structure
Creators: name: Rafiei-Ravandi, Masoud
name: Smith, Kendrick M.
name: Li, Dongzi
name: Masui, Kiyoshi W.
name: Josephy, Alexander
name: Dobbs, Matt
name: Lang, Dustin
name: Bhardwaj, Mohit
name: Patel, Chitrang
name: Bandura, Kevin
name: Berger, Sabrina
name: Boyle, P. J.
name: Brar, Charanjot
name: Breitman, Daniela
name: Cassanelli, Tomas
name: Chawla, Pragya
name: Dong, Fengqiu Adam
name: Fonseca, Emmanuel
name: Gaensler, B. M.
name: Giri, Utkarsh
name: Good, Deborah C.
name: Halpern, Mark
name: Kaczmarek, Jane
name: Kaspi, Victoria M.
name: Leung, Calvin
name: Lin, Hsiu-Hsien
name: Mena-Parra, Juan
name: Meyers, B. W.
name: Michilli, D.
name: Münchmeyer, Moritz
name: Ng, Cherry
name: Petroff, Emily
name: Pleunis, Ziggy
name: Rahman, Mubdi
name: Sanghavi, Pranav
name: Scholz, Paul
name: Shin, Kaitlyn
name: Stairs, Ingrid H.
name: Tendulkar, Shriharsh P.
name: Vanderlinde, Keith
name: Zwaniga, Andrew
Publisher: name: arXiv
Year: 2021
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences

description: The CHIME/FRB Project has recently released its first catalog of fast radio bursts (FRBs), containing 492 unique sources. We present results from angular cross-correlations of CHIME/FRB sources with galaxy catalogs. We find a statistically significant ($p$-value $\sim 10^{-4}$, accounting for look-elsewhere factors) cross-correlation between CHIME FRBs and galaxies in the redshift range $0.3 \lesssim z \lesssim 0.5$, in three photometric galaxy surveys: WISE$\times$SCOS, DESI-BGS, and DESI-LRG. The level of cross-correlation is consistent with an order-one fraction of the CHIME FRBs being in the same dark matter halos as survey galaxies in this redshift range. We find statistical evidence for a population of FRBs with large host dispersion measure ($\sim 400$ pc cm$^{-3}$), and show that this can plausibly arise from gas in large halos ($M \sim 10^{14} M_\odot$), for FRBs near the halo center ($r \lesssim 100$ kpc). These results will improve in future CHIME/FRB catalogs, with more FRBs and better angular resolution.
description: 26 pages, 16 figures, published in ApJ
Ανάπτυξη και αξιολόγηση εργαλείου End User Development υποβοήθησης κατασκευής βάσεων γράφων από τελικούς χρήστες
Creators: name: Γκάρλας, Ευριπίδης Ιωάννη
Publisher: name: Aristotle University of Thessaloniki
Year: 2018
Subjects: Περιβάλλον Τελικών Χρηστών
Βάσεις Δεδομένων Γράφων
Ευχρηστία
End User Development
Graph Databases
Ease of use

description: Τα τελευταία χρόνια, στον τομέα της Πληροφορικής, είναι εμφανής η ανάπτυξη ενός νέου μοντέλου βάσεων δεδομένων, αυτό των γράφων. Οι εφαρμογές που κατασκευάζονται για εμπορικούς και όχι μόνο λόγους στηρίζονται σε ένα μεγάλο βαθμό στις βάσεις γράφων. Η εργασία αυτή εξετάζει το κατά πόσο μια εφαρμογή-εργαλείο σε end user development, σκοπός της οποίας είναι η κατασκευή μιας εφαρμογής που στηρίζεται σε βάση δεδομένων γράφων, μπορεί να θεωρηθεί εύχρηστη από τους τελικούς χρήστες. Προκειμένου να εξαχθούν συμπεράσματα και να απαντηθεί το παραπάνω ερώτημα, κατασκευάστηκε εφαρμογή web υποβοήθησης τελικού χρήστη στην κατασκευή βάσης δεδομένων γράφων. Στη συνέχεια, η συγκεκριμένη εφαρμογή εξετάστηκε από τους συμμετέχοντες στην έρευνα τελικούς χρήστες μέσω της επίλυσης κάποιας άσκησης που τους δόθηκε. Επίσης, μέσω των απαντήσεων τους σε ερωτηματολόγιο, μετρήθηκαν μεταβλητές όπως η ευχρηστία και η χρησιμότητα της εφαρμογής, η θέληση των συμμετεχόντων για μάθηση πάνω στην εφαρμογή αλλά και η αντίληψη κινδύνου τους κατά τη χρήση της. Τα συμπεράσματα που προέκυψαν, έδειξαν ότι η εφαρμογή μπορεί να θεωρηθεί σε ένα μεγάλο βαθμό εύχρηστη από τους τελικούς χρήστες , ενώ προέκυψαν και άλλα χρήσιμα συμπεράσματα όπως η συσχέτιση ανάμεσα στο χρόνο τον οποίο χρειάστηκαν οι συμμετέχοντες για την επίλυση της άσκησης με τη θέληση τους για μάθηση.
description: In recent years, in the field of Information Technology, the development of a new database model, that of graphs, is evident. Applications developed for commercial and non-commercial reasons depend on graph databases to a great extent. This paper examines whether an end-user development tool, the purpose of which is to build an application based on a graph database, can be considered as easy to use by end users. In order to draw conclusions and answer the above question, an end-user application was developed to build a graph database. This application was tested by the end users that participated in the research through the resolution of an exercise they were given. Also, through their questionnaire responses, variables such as ease of use and application’s usefulness, participants’ willingness to learn on the application and their perceived risk of using were measured. The resulting findings have shown that the application can be considered to a great extent usable by end users and other useful results have emerged such as the correlation between the time that participants needed to solve the exercise with their willingness to learn.
description: Σε συνεργασία με: Λογιστικής και Χρηματοοικονομικής (Πανεπιστήμιο Μακεδονίας)
Electromagnetic form factors from the fifth dimension
Creators: name: Rodriguez-Gomez, D.
name: Ward, J.
Publisher: name: arXiv
Year: 2008
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: We analyse various $U(1)_{EM}$ form factors of mesons at strong coupling in an $\mathcal{N}=2$ flavored version of $\mathcal{N}=4$ $SYM$ which becomes conformal in the UV. The quark mass breaks the conformal symmetry in the IR and generates a mass gap. In the appropriate limit, the gravity dual is described in terms of probe $D7$-branes in $AdS_5\times S^5$. By studying the $D7$ fluctuations we find the suitable terms in a "meson effective theory" which allow us to compute the desired form factors, namely the $γπρ$ and $γf_0ρ$ transition form factors. At large $q^2$ we find perfect agreement with the naive parton model counting, which is a consequence of the conformal nature of both QCD and our model in the UV. By using the same tools, we can compute the $γ^*γ^*π$ form factor. However this channel is more subtle and comparisons to the QCD result are more involved.
description: 34 pages, 6 figures, pdflatex. References and clarifications added
Χρησικτησία επί Αιγιαλού/Παραλίας/Παλαιού Αιγιαλού και Εθνικό Κτηματολόγιο
Creators: name: Χατζής, Κωνσταντίνος Ιωάννη
Publisher: name: Aristotle University of Thessaloniki
Year: 2018
Subjects: Αιγιαλός
Χρησικτησία
Κτηματολόγιο
Foreshore
Adverse Possession
National Cadastre

description: Σκοπός της διατριβής ήταν η απάντηση στο ερώτημα κατά πόσο ο αιγιαλός, η παραλία και ο παλαιός αιγιαλός είναι πράγματα δεκτικά χρησικτησίας. Ειδικότερα, εξετάστηκαν οι ορισμοί και η νομική φύση των παραπάνω πραγμάτων και αναλύθηκαν τα τεχνικά χαρακτηριστικά χάραξης και αποτύπωσής τους στο πλαίσιο του Εθνικού Κτηματολογίου. Εν συνεχεία, έλαβε χώρα μία θεωρητική αλλά και νομολογιακή προσέγγιση του θεσμού της χρησικτησίας, ενώ πραγματοποιήθηκε και ειδική αναφορά στη θέση της στο Εθνικό Κτηματολόγιο. Τέλος, να σημειωθεί ότι η συνδυαστική προσέγγιση των παραπάνω εννοιών που ακολούθησε και ουσιαστικά η απάντηση στο βασικό ερώτημα της παρούσας εργασίας πραγματοποιήθηκε στο πλαίσιο τόσο του ισχύοντος δικαίου, όσο και των προϋφιστάμενων, συμπεριλαμβανομένου και του οθωμανικού.
description: The aim of the present thesis was answering the question whether the foreshore, the beach and the old foreshore were able to be subject to the statute of the adverse possession. In particular, the definitions as well as the legal nature of the aforementioned things were examined and the technical characteristics of their engraving and surveying in the framework of the National Cadastre were analyzed. Afterwards, a theoretical and a jurisprudential approach of the adverse possession took place, while a reference was made regarding its role in the system of the National Cadastre. Finally, it should be noted that the combinatorial analysis of the aforementioned notions that followed and essentially the answer to the principal question of the present thesis was carried out in the framework of the current legal system, as well as with the previous ones, including the Ottoman one.
Διαδικασία εξυγίανσης και διαδικασία ειδικής διαχείρισης του ν. 4307/2014
Creators: name: Πευκαινάκη, Αννα Νικολάου
Publisher: name: Aristotle University of Thessaloniki
Year: 2018
Subjects: Πτωχευτικές διαδικασίες
Διαδικασία εξυγίανσης
Διαδικασία Ειδικής διαχείρισης
Insolvency procedures
Rehabilitation procedure
Special receivership procedure

description: Αντικείμενο της μεταπτυχιακής εργασίας είναι η μελέτη δύο πτωχευτικών διαδικασιών: της διαδικασίας εξυγίανσης του Πτωχευτικού Κώδικα και της διαδικασίας ειδικής διαχείρισης του ν. 4307/2014. Για κάθε μία γίνεται ανάλυση διαχρονικού δικαίου, αναλυτική παρουσίαση των σταδίων της διαδικασίας και παράθεση σχετικής νομολογίας των ελληνικών δικαστηρίων. Στο τελευταίο μέρος της εργασίας επιχειρείται συγκριτική θεώρηση των δύο διαδικασιών και κριτική της πρακτικής εφαρμογής τους
description: The aim of the present thesis is the study of two insolvency procedures: the rehabilitation procedure of Insolvency Code and the special receivership procedure of Law 4307/2014. The thesis includes review of each procedure’s legislation over time, detailed presentation of their stages and listing of the relevant case-law of greek courts. In the last part of the thesis, comparative study of the two procedures and review of their practical application is attempted
Tetraquarks and Pentaquarks in String Models
Creators: name: Ryskin, M. G.
name: Shabelski, Yu. M.
Publisher: name: arXiv
Year: 2006
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: FOS: Physical sciences

description: We consider the production and decay of multiquark systems in the framework of string models where the hadron structure is determined by valence quarks together with string junctions. We show that the low mass multiquark resonances can be very narrow.
description: 7 pages, 2 figures
Η έννομη θέση του ανηλίκου στην αδικοπραξία» - Η ευθύνη του ανηλίκου, του εποπτεύοντος ανήλικο και η συνδρομή του συντρέχοντος πταίσματος
Creators: name: Μπάτιος, Ευάγγελος Γεωργίου
Publisher: name: Aristotle University of Thessaloniki
Year: 2018
Subjects: Ανήλικος
Καταλογισμός
Συντρέχον πταίσμα
Minor
Imputability
Contributory fault

description: Η παρούσα εργασία πραγματεύεται την ευθύνη του ανηλίκου και των εποπτευόντων αυτόν προσώπων με στόχο να καταδείξει, παραθέτοντας την ελληνική θεωρία αλλά και νομολογία, όλες τις πτυχές της ευθύνης αυτής στο δίκαιο των αδικοπραξιών. Αρχικά παρουσιάστηκαν οι έννοιες της υπαιτιότητας και της ικανότητας προς καταλογισμό. Στη συνέχεια αναφερθήκαμε στην προσωπική αδικοπρακτική ευθύνη του ανηλίκου στο πλαίσιο των άρθρων ΑΚ916 και 917 αλλά και στην ευθύνη αυτού (του ανηλίκου) για εύλογη αποζημίωση από λόγους επιείκειας (ΑΚ918). Ακολούθως, εξετάστηκε το συντρέχον πταίσμα του ανηλίκου (άρθρο ΑΚ300). Τέλος, η ευθύνη του εποπτεύοντος ανήλικο, η οποία ρυθμίζεται στο άρθρο ΑΚ923, ως πυρήνας της εργασίας, εξετάστηκε διεξοδικά, υπό το πρίσμα και της ελληνικής νομολογίας
description: The subject of the present thesis is to establish all the aspects of the liability in tort of minors and the liability of guardians for damage caused by minors by using legal theory and case-law. At first, legal terms, culpability and imputability have been presented. Then, we referred to the liability in tort of minors pursuant to articles CC916 and 917 and also the liability of a minor to reasonable compensation imposed by reasons of equity (Art.918CC). Furthermore, we examined the contributory fault of a minor (Art.300CC). Finally, the liability of guardian for minor’s torts, which is provided for by the Law (Art.923CC) and constitutes the core of this thesis, has been extensively examined, followed by a case-law review
The electronic structure and the phases of BaVS3
Creators: name: Fazekas, P.
name: Penc, K.
name: Radnoczi, K.
name: Barisic, N.
name: Berger, H.
name: Forro, L.
name: Mitrovic, S.
name: Gauzzi, A.
name: Demko, L.
name: Kezsmarki, I.
name: Mihaly, G.
Publisher: name: arXiv
Year: 2007
Subjects: subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: BaVS3 is a moderately correlated d-electron system with a rich phase diagram. To construct the corresponding minimal electronic model, one has to decide which d-states are occupied, and to which extent. The ARPES experiment presented here shows that the behavior of BaVS3 is governed by the coexistence of wide-band (A_1g) and narrow-band (twofold degenerate E) d-electrons. We sketch a lattice fermion model which may serve as a minimal model of BaVS3. This serves foremost for the understanding of the metal-insulator in pure BaVS3 and its absence in some related compounds. The nature of the low temperature magnetic order differs for several systems which may be described in terms of the same electron model. We describe several recent experiments which give information about magnetic order at high pressures. In particular, we discuss field-induced insulator-to-metal transition at slightly subcritical pressures, and an evidence for magnetic order in the high-pressure metallic phase. The phase diagram of Sr-doped BaVS3 is also discussed. The complexity of the phases of BaVS3 arises from the fact that it is simultaneously unstable against several kinds of instabilities.
description: Presented at the International Conference on Magnetism 2006 (Kyoto), 6 pages, 9 figures
Fermionic Zero Modes of Supergravity Cosmic Strings
Creators: name: Brax, Ph.
name: van de Bruck, C.
name: Davis, A. C.
name: Davis, Stephen C.
Publisher: name: arXiv
Year: 2006
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: Recent developments in string theory suggest that cosmic strings could be formed at the end of brane inflation. Supergravity provides a realistic model to study the properties of strings arising in brane inflation. Whilst the properties of cosmic strings in flat space-time have been extensively studied there are significant complications in the presence of gravity. We study the effects of gravitation on cosmic strings arising in supergravity. Fermion zero modes are a common feature of cosmic strings, and generically occur in supersymmetric models. The corresponding massless currents can give rise to stable string loops (vortons). The vorton density in our universe is strongly constrained, allowing many theories with cosmic strings to be ruled out. We investigate the existence of fermion zero modes on cosmic strings in supergravity theories. A general index theorem for the number of zero modes is derived. We show that by including the gravitino, some (but not all) zero modes disappear. This weakens the constraints on cosmic string models. In particular, winding number one cosmic D-strings in models of brane inflation are not subject to vorton constraints. We also discuss the effects of supersymmetry breaking on cosmic D-strings.
description: 33 pages
Mathematical Aspects of the Periodic Law
Creators: name: Restrepo, Guillermo
name: Pachon, Leonardo A.
Publisher: name: arXiv
Year: 2006
Subjects: subject: General Mathematics (math.GM)
subject: FOS: Mathematics

description: We review different studies of the Periodic Law and the set of chemical elements from a mathematical point of view. This discussion covers the first attempts made in the 19th century up to the present day. Mathematics employed to study the periodic system includes number theory, information theory, order theory, set theory and topology. Each theory used shows that it is possible to provide the Periodic Law with a mathematical structure. We also show that it is possible to study the chemical elements taking advantage of their phenomenological properties, and that it is not always necessary to reduce the concept of chemical elements to the quantum atomic concept to be able to find interpretations for the Periodic Law. Finally, a connection is noted between the lengths of the periods of the Periodic Law and the philosophical Pythagorean doctrine.
description: 20 pages, PDF file
Improved final doublet designs for the ILC baseline small crossing angle scheme
Creators: name: Appleby, R.
name: Bambade, P.
Publisher: name: arXiv
Year: 2006
Subjects: subject: Accelerator Physics (physics.acc-ph)
subject: FOS: Physical sciences

description: The ILC baseline consists of two interaction regions, one with a 20mrad crossing angle and the other with a 2mrad crossing angle. It is known that the outgoing beam losses in the final doublet and subsequent extraction line are larger in the 2mrad than in the 20mrad layout. In this work, we exploit NbTi and Nb$_3$Sn superconducting magnet technologies to redesign and optimise the final doublet, with the aim of providing satisfactory outgoing disrupted beam power losses in this region. We present three new final doublet layouts, specifically optimised for the 500 GeV and the 1 TeV machines.
description: 14 pages, 4 figures, 12 tables
Method of reconstructing a moving pulse
Creators: name: Howard, Stephen J.
name: Horton, R. D.
name: Hwang, D. Q.
name: Evans, R. W.
name: Brockington, S. J.
name: Johnson, J.
Publisher: name: arXiv
Year: 2007
Subjects: subject: Data Analysis, Statistics and Probability (physics.data-an)
subject: Fluid Dynamics (physics.flu-dyn)
subject: Plasma Physics (physics.plasm-ph)
subject: FOS: Physical sciences

description: We present a method of analyzing a set of N time signals f_i(t) that consist of local measurements of the same physical observable taken at N sequential locations Z_i along the length of an experimental device. The result is an algorithm for reconstructing an approximation F(z,t) of the field f(z,t) in the inaccessible regions between the points of measurement. We also explore the conditions needed for this approximation to hold, and test the algorithm under a variety of conditions. We apply this method to analyze the magnetic field measurements taken on the Compact Toroid Injection eXperiment (CTIX) plasma accelerator; providing a direct means of visualizing experimental data, quantifying global properties, and benchmarking simulation.
description: 17 pages, 9 figures, some changes in notation since version 1
Full counting statistics for interacting trapped fermions
Creators: name: Smith, Naftali R.
name: Doussal, Pierre Le
name: Majumdar, Satya N.
name: Schehr, Gregory
Publisher: name: arXiv
Year: 2021
Subjects: subject: Statistical Mechanics (cond-mat.stat-mech)
subject: Quantum Gases (cond-mat.quant-gas)
subject: Mathematical Physics (math-ph)
subject: FOS: Physical sciences

description: We study $N$ spinless fermions in their ground state confined by an external potential in one dimension with long range interactions of the general Calogero-Sutherland type. For some choices of the potential this system maps to standard random matrix ensembles for general values of the Dyson index $β$. In the fermion model $β$ controls the strength of the interaction, $β=2$ corresponding to the noninteracting case. We study the quantum fluctuations of the number of fermions ${\cal N}_{\cal D}$ in a domain $\cal{D}$ of macroscopic size in the bulk of the Fermi gas. We predict that for general $β$ the variance of ${\cal N}_{\cal D}$ grows as $A_β \log N + B_β$ for $N \gg 1$ and we obtain a formula for $A_β$ and $B_β$. This is based on an explicit calculation for $β\in\left\{ 1,2,4\right\} $ and on a conjecture that we formulate for general $β$. This conjecture further allows us to obtain a universal formula for the higher cumulants of ${\cal N}_{\cal D}$. Our results for the variance in the microscopic regime are found to be consistent with the predictions of the Luttinger liquid theory with parameter $K = 2/β$, and allow to go beyond. In addition we present families of interacting fermion models in one dimension which, in their ground states, can be mapped onto random matrix models. We obtain the mean fermion density for these models for general interaction parameter $β$. In some cases the fermion density exhibits interesting transitions, for example we obtain a noninteracting fermion formulation of the Gross-Witten-Wadia model.
description: 61 pages, 6 figures
Διαβίβαση δεδομένων προσωπικού χαρακτήρα προς τρίτες χώρες υπό το πλαίσιο του Κανονισμού 2016/679/ΕΚ
Creators: name: Αναγνωστάκη, Νίκη Δημητρίου
Publisher: name: Aristotle University of Thessaloniki
Year: 2018
Subjects: Διαβίβαση προσωπικών δεδομένων σε τρίτες χώρες
Προσωπικά Δεδομένα
Κανονισμός 2016/679/ΕΚ
Transfers of personal data to third countries
Personal Data
Regulation (EU) 2016/679

description: Σκοπός της διπλωματικής εργασίας ήταν η συνοπτική παρουσίαση της πτυχής της Διασυνοριακής Ροής πληροφοριών υπό το πλαίσιο του Κανονισμού 2016/679/ΕΚ. Στο Α’ Μέρος αυτής αναλύθηκε το νομικό πλαίσιο προστασίας των προσωπικών δεδομένων σε μία σύντομη ιστορική αναδρομή και παρουσιάστηκε λεπτομερώς το καθεστώς και η πτυχή της διαβίβασης υπό τον νέο Κανονισμό και αξιολογήθηκαν οι προβλεπόμενοι από αυτόν τρόποι για την διαβίβαση των προσωπικών δεδομένων. Τέλος, πραγματοποιήθηκε μία συγκριτική επισκόπηση του νέου Κανονισμού και της καταργούμενης από αυτόν Οδηγίας 95/46/ΕΚ. Στο Β’ Μέρος καταγράφηκαν οι Συμφωνίες διασυνοριακής διαβίβασης πληροφοριών που έχουν υπογραφεί μεταξύ της ΕΕ – Η.Π.Α. και ΕΕ – Ιαπωνίας, ως μεγαλύτερων εμπορικών εταίρων της Ένωσης, καθώς και το νομοθετικό πλαίσιο προστασίας δεδομένων στις ως άνω χώρες. Τέλος, εξετάστηκαν και οι Συμφωνίες Διαβίβασης Προσωπικών Δεδομένων των Επιβατών (Συμφωνίες PNR)
description: The aim of the present thesis was to summarize the aspect of the cross border flows of personal data under the regulation 2016/679 (EU). In Part A, the legal framework of the protection of personal data was analyzed in a brief historical note and the status and aspect of cross-border flows was presented in detail, under the new regulation as well as the legal ways of a cross border flow provided by the regulation. Finally, a comparative overview between the new Regulation and the repealed Directive 95/46 (EU) was conducted. In part B, the Agreements signed between EU – USA and EU – Japan related to cross border data flows were recorded, as EU’s largest trading partner’s, as well as the legal framework of data protection in the aforementioned countries. Lastly, the Passenger Name Record (PNR) Agreements was also examined
Was the Andromeda Stream Produced by a Disk Galaxy?
Creators: name: Fardal, Mark A.
name: Babul, Arif
name: Guhathakurta, Puragra
name: Gilbert, Karoline M.
name: Dodge, Cara
Publisher: name: arXiv
Year: 2008
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: The halo region of M31 exhibits a startling level of stellar inhomogeneities, the most prominent of which is the "giant southern stream". Our previous analysis indicates that this stream, as well as several other observed features, are products of the tidal disruption of a single satellite galaxy with stellar mass ~10^9 solar masses less than 1 Gyr ago. Here we show that the specific observed morphology of the stream and halo debris favors a cold, rotating, disk-like progenitor over a dynamically hot, non-rotating one. These observed characteristics include the asymmetric distribution of stars along the stream cross-section and its metal-rich core/metal-poor sheath structure. We find that a disk-like progenitor can also give rise to arc-like features on the minor axis at certain orbital phases that resemble the recently discovered minor-axis "streams", even reproducing the lower observed metallicity of these streams. Though interpreted by the discoverers as new, independent tidal streams, our analysis suggests that these minor-axis streams may alternatively arise from the progenitor of the giant southern stream. Overall, our study points the way to a more complete reconstruction of the stream progenitor and its merger with M31, based on the emerging picture that most of the major inhomogeneities observed in the M31 halo share a common origin with the giant stream.
description: 5 pages emulateapj, 3 figures; submitted to ApJL. v2: changed Figure 3 to a bitmap to display better on some PDF readers
Scaling Limits for the Gibbs States on Distance-Regular Graphs with Classical Parameters
Creators: name: Koohestani, Masoumeh
name: Obata, Nobuaki
name: Tanaka, Hajime
Publisher: name: arXiv
Year: 2021
Subjects: subject: Combinatorics (math.CO)
subject: Probability (math.PR)
subject: FOS: Mathematics
subject: 46L53, 60F05, 05E30

description: We determine the possible scaling limits in the quantum central limit theorem with respect to the Gibbs state, for a growing distance-regular graph that has so-called classical parameters with base unequal to one. We also describe explicitly the corresponding weak limits of the normalized spectral distribution of the adjacency matrix. We demonstrate our results with the known infinite families of distance-regular graphs having classical parameters and with unbounded diameter.
PRACTICAL ASPECTS OF ACOUSTIC SOURCE LOCALIZATION USING POLYMER-CARBON BLACK COMPOSITE PHASED ARRAYS
Creators: name: Cullen, Robert
Publisher: name: Digital Repository at the University of Maryland
Year: 2015
Subjects: subject: Acoustics
subject: Mechanical engineering
subject: FOS: Mechanical engineering

description: An array of Carbon Black (CB) filled polyurethane sensors is developed to identify the location and intensity of a single acoustic source. The manufacturing procedure of the proposed array is outlined, in details, and several prototypes are manufactured. Characterization of the viscoelastic and piezo-resistive material properties of different samples of the CB filled polyurethane is carried out using Dynamic, Mechanical, Thermal Analyzer (DMTA) and uni-axial compression testing. The structural, dynamical, and sensing performance characteristics of the array sensor are modeled mathematically using the theory of finite elements and utilizing the well-known localization theories of phased arrays.

The experimental performance characteristics of the proposed array sensor are evaluated in comparison to an array of conventional condenser microphones. The purpose of such an experimental effort is to demonstrate the capabilities and limitations of the proposed array sensor as compared with conventional condenser

microphones. Furthermore, the obtained experimental results are utilized to validate the theoretical predictions of the localization of acoustic sources.

It is envisioned that the proposed CB filled polyurethane array sensor presents a cost effective and viable means for identifying the location and intensity of acoustic sources which can vary from stationary to moving sources in air or underwater. Accordingly, the applications of such an array sensor are only limited by our imagination.
The Local Bubble and Interstellar Material Near the Sun
Creators: name: Frisch, P. C.
Publisher: name: arXiv
Year: 2007
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: The properties of interstellar matter (ISM) at the Sun are regulated by our location with respect to the Local Bubble (LB) void in the ISM. The LB is bounded by associations of massive stars and fossil supernovae that have disrupted natal ISM and driven intermediate velocity ISM into the LB interior void. The Sun is located in such a driven ISM parcel. The Local Fluff has a bulk velocity of 19 km/s in the LSR, and an upwind direction towards the center of the gas and dust ring formed by the Loop I supernova remnant interaction with the LB. When the ram pressure of the LIC is included in the total LIC pressure, and if magnetic thermal and cosmic ray pressures are similar, the LIC appears to be in pressure equilibrium with the local hot bubble plasma.
description: Proceedings of Symposium on the Composition of Matter, honoring Johannes Geiss on the occasion of his 80th birthday. Space Science Reviews (in press)