Compact surfaces with no Bonnet mate

This note gives sufficient conditions (isothermic or totally nonisothermic) for an immersion of a compact surface to have no Bonnet mate.Comment: 7 pages, LaTeX2

Closed trajectories of a particle model on null curves in anti-de Sitter 3-space

We study the existence of closed trajectories of a particle model on null curves in anti-de Sitter 3-space defined by a functional which is linear in the curvature of the particle path. Explicit expressions for the trajectories are found and the existence of infinitely many closed trajectories is proved.Comment: 12 pages, 1 figur

Theory and Practice of Metro Network Design

Most transit networks are designed empirically. For bus net­works this process 1s often satisfactory because bus routes and networks are very dependent on local conditions, and they can be easily modified, allowing easy corrections of problems which line design may cause in operations. However, with transit systems which have extensive infrastructure, most typically metro lines and networks, corrections are ex­tremely difficult to make. Develop­ment of an optimal network and avoidance of design features which result in operational pro­blems are therefore of great im­portance. Yet, the experiences from the design and operation of such large older metro systems as London, Moscow, New York, Pan\u27s and Tokyo, or from numerous recently built medium-size metro systems, such as Hong Kong, San Francisco, Sao Paulo and Washington, remain largely unknown to the designers of new metro networks. This paper presents a theoretical analysis of transit lines and networks and its applications. The focus is on network geometry and operational characteristics. The basic design and operational elements, such as geometric forms of lines, headways, schedules, etc., are discussed in general terms, valid for any mode; however, the main focus is on metro systems because of the par­ticular importance of these analyses for fixed, permanent systems

Role and Organization of Transfers in Transit Networks

Passenger transfers among transit lines involve certain resistance , because they cause some delay and require passenger orientation and walking between vehicles on different lines. Therefore it is sometimes believed that transfers are undesirable and that they should be avoided whenever possible. The fact is, however, that transit networks with many transfer opportunities offer passengers much greater selection of travel paths than networks with disconnected lines which involve no transferring. In addition, the more transferring is performed, the greater is network efficiency, because each line can be designed optimally for its physical conditions, volume and character of demand. Consequently, when transfers are planned correctly, the resistance for passengers can be easily outweighed by the benefits transfers bring with respect to line alignments, schedules and, eventually, in better services offered. Passenger transfers among lines thus represent an important element of transit travel

Excursion Sets and Non-Gaussian Void Statistics

Primordial non-Gaussianity (NG) affects the large scale structure (LSS) of the universe by leaving an imprint on the distribution of matter at late times. Much attention has been focused on using the distribution of collapsed objects (i.e. dark matter halos and the galaxies and galaxy clusters that reside in them) to probe primordial NG. An equally interesting and complementary probe however is the abundance of extended underdense regions or voids in the LSS. The calculation of the abundance of voids using the excursion set formalism in the presence of primordial NG is subject to the same technical issues as the one for halos, which were discussed e.g. in arXiv:1005.1203. However, unlike the excursion set problem for halos which involved random walks in the presence of one barrier $\delta_c$, the void excursion set problem involves two barriers $\delta_v$ and $\delta_c$. This leads to a new complication introduced by what is called the "void-in-cloud" effect discussed in the literature, which is unique to the case of voids. We explore a path integral approach which allows us to carefully account for all these issues, leading to a rigorous derivation of the effects of primordial NG on void abundances. The void-in-cloud issue in particular makes the calculation conceptually rather different from the one for halos. However, we show that its final effect can be described by a simple yet accurate approximation. Our final void abundance function is valid on larger scales than the expressions of other authors, while being broadly in agreement with those expressions on smaller scales.Comment: 28 pages (18+appendices), 7 figures; v2 -- minor changes in sec 3.2, version published in PR

Videogame Addiction Scale for Children: Psychometric Properties and Gamer Profiles in the Italian Context

Given the few studies examining the evaluation of screening tools for videogame addiction among children aged 12 years and under, the present study analyzed (i) the psychometric properties (factorial structure, reliability indices and criterion validity) of the Italian version of the Videogame Addiction Scale for Children (VASC) and (ii) its construct validity using a person-centered approach. Two studies were carried out. In study 1, 728 participants completed a survey including demographic information, questions concerning the amount of time spent in playing videogames, and the Italian version of the VASC. In study 2, 1008 participants completed a survey comprising demographic information, the Italian version of the VASC, the Big Five Questionnaire for Children, and the social dimension subscale of the Multidimensional Self-Concept Scale. Findings supported (i) the four-dimensional first-order factor structure, (ii) full scalar invariance across age groups and partial scalar equivalence across gender, and (iii) reliability and criterion validity of the VASC. The construct validity of the VASC was confirmed by the identification of two distinct profiles (high videogame players vs. low videogame players) and their specific patterns of associations with personality traits and social self-concept. Interaction effects of gender × profiles on personality traits were evidenced. Overall, the findings provided validity for the use of the Italian version of the VASC and extending the body of literature on videogame addiction

Halo statistics in non-Gaussian cosmologies: the collapsed fraction, conditional mass function, and halo bias from the path-integral excursion set method

Characterizing the level of primordial non-Gaussianity (PNG) in the initial conditions for structure formation is one of the most promising ways to test inflation and differentiate among different scenarios. The scale-dependent imprint of PNG on the large-scale clustering of galaxies and quasars has already been used to place significant constraints on the level of PNG in our observed Universe. Such measurements depend upon an accurate and robust theory of how PNG affects the bias of galactic halos relative to the underlying matter density field. We improve upon previous work by employing a more general analytical method - the path-integral extension of the excursion set formalism - which is able to account for the non-Markovianity caused by PNG in the random-walk model used to identify halos in the initial density field. This non-Markovianity encodes information about environmental effects on halo formation which have so far not been taken into account in analytical bias calculations. We compute both scale-dependent and -independent corrections to the halo bias, along the way presenting an expression for the conditional collapsed fraction for the first time, and a new expression for the conditional halo mass function. To leading order in our perturbative calculation, we recover the halo bias results of Desjacques et. al. (2011), including the new scale-dependent correction reported there. However, we show that the non-Markovian dynamics from PNG can lead to marked differences in halo bias when next-to-leading order terms are included. We quantify these differences here. [abridged]Comment: Accepted for publication in MNRAS. Includes minor revisions recommended by referee, slightly revised notation for clarity, and corrected typo