Dark-matter decays and Milky Way satellite galaxies

We consider constraints on a phenomenological dark-matter model consisting of two nearly degenerate particle species using observed properties of the Milky Way satellite galaxy population. The two parameters of this model, assuming the particle masses are >~ GeV, are v_k, the recoil speed of the daughter particle, and tau, the lifetime of the parent particle. The satellite constraint that spans the widest range of v_k is the number of satellites that have a mass within 300 pc M300 > 5 x 10^6 solar masses, although constraints based on M300 in the classical dwarfs and the overall velocity function are competitive for v_k >~ 50 km/s. In general, we find that tau <~ 30 Gyr is ruled out for 20 km/s <~ v_k <~ 200 km/s, although we find that the limits on tau for fixed v_k can change constraints by a factor of ~3 depending on the star-formation histories of the satellites. We advocate using the distribution of M300 in Milky Way satellites determined by next-generation all-sky surveys and follow-up spectroscopy as a probe of dark-matter properties.Comment: 17 pages, 9 figures, submitted to Phys. Rev.

Initial comparisons of modular-sized, integrated utility systems and conventional systems for several building types

The results of a study of the application of a modular integrated utility system to six typical building types are compared with the application of a conventional utility system to the same facilities. The effects of varying the size and climatic location of the buildings and the size of the powerplants are presented. Construction details of the six building types (garden apartments, a high rise office building, high rise apartments, a shopping center, a high school, and a hospital) and typical site and floor plans are provided. The environmental effects, the unit size determination, and the market potential are discussed. The cost effectiveness of the various design options is not considered

Ensemble versus individual system in quantum optics

Modern techniques allow experiments on a single atom or system, with new phenomena and new challenges for the theoretician. We discuss what quantum mechanics has to say about a single system. The quantum jump approach as well as the role of quantum trajectories are outlined and a rather sophisticated example is given.Comment: Fundamental problems in quantum theory workshop, invited lecture. 11 pages Latex + 7 figures. To appear in Fortschr. d. Physi

Information disclosure of social media users: Does control over personal information, user awareness and security notices matter?

Purpose – The purpose of this paper is to bridge the gap in the existing literature by exploring the antecedents of information disclosure of social media users. In particular, the paper investigates the link between information disclosure, control over personal information, user awareness and security notices in the social context, all of which are shown to be different from existing studies in e-commerce environments. Design/methodology/approach – The authors collected and analysed data from 514 social network users. The model is estimated using ordinary least squares and robust standard errors are estimated using the Huber-White sandwich estimators. Findings – The results show that in social networking contexts, control over personal information is negatively and statistically associated with information disclosure. However, both user awareness and security notices have a positive statistical effect on information disclosure. Originality/value – Whilst research on issues of individual information privacy in e-commerce is plentiful, the area of social networking and privacy protection remains under-explored. This paper provides a useful model for analysing information disclosure behaviour on social networks. The authors discuss the practical implications of the findings for actors in social media interactions

Topologically Alice Strings and Monopoles

Symmetry breaking can produce ``Alice'' strings, which alter scattered charges and carry monopole number and charge when twisted into loops. Alice behavior arises algebraically, when strings obstruct unbroken symmetries -- a fragile criterion. We give a topological criterion, compelling Alice behavior or deforming it away. Our criterion, that \pi_o(H) acts nontrivially on \pi_1(H), links topologically Alice strings to topological monopoles. We twist topologically Alice loops to form monopoles. We show that Alice strings of condensed matter systems (nematic liquid crystals, helium 3A, and related non-chiral Bose condensates and amorphous chiral superconductors) are topologically Alice, and support fundamental monopole charge when twisted into loops. Thus they might be observed indirectly, not as strings, but as loop-like point defects. We describe other models, showing Alice strings failing our topological criterion; and twisted Alice loops supporting deposited, but not fundamental, monopole number.Comment: 2 figures; this paper consolidates preprints hep-th/0304161 and hep-th/0304162, to appear in Phys. Rev.

The connection between the host halo and the satellite galaxies of the Milky Way

Many properties of the Milky Way's dark matter halo, including its mass assembly history, concentration, and subhalo population, remain poorly constrained. We explore the connection between these properties of the Milky Way and its satellite galaxy population, especially the implication of the presence of the Magellanic Clouds for the properties of the Milky Way halo. Using a suite of high-resolution $N$-body simulations of Milky Way-mass halos with a fixed final Mvir ~ 10^{12.1}Msun, we find that the presence of Magellanic Cloud-like satellites strongly correlates with the assembly history, concentration, and subhalo population of the host halo, such that Milky Way-mass systems with Magellanic Clouds have lower concentration, more rapid recent accretion, and more massive subhalos than typical halos of the same mass. Using a flexible semi-analytic galaxy formation model that is tuned to reproduce the stellar mass function of the classical dwarf galaxies of the Milky Way with Markov-Chain Monte-Carlo, we show that adopting host halos with different mass-assembly histories and concentrations can lead to different best-fit models for galaxy-formation physics, especially for the strength of feedback. These biases arise because the presence of the Magellanic Clouds boosts the overall population of high-mass subhalos, thus requiring a different stellar-mass-to-halo-mass ratio to match the data. These biases also lead to significant differences in the mass--metallicity relation, the kinematics of low-mass satellites, the number counts of small satellites associated with the Magellanic Clouds, and the stellar mass of Milky Way itself. Observations of these galaxy properties can thus provide useful constraints on the properties of the Milky Way halo.Comment: 20 pages, 12 figures, accepted for publication in ApJ. A new section on the effect of host halo mass-assembly history on the central galaxy stellar mass is adde

The importance of preventive feedback: inference from observations of the stellar masses and metallicities of Milky Way dwarf galaxies

Dwarf galaxies are known to have remarkably low star formation efficiency due to strong feedback. Adopting the dwarf galaxies of the Milky Way as a laboratory, we explore a flexible semi-analytic galaxy formation model to understand how the feedback processes shape the satellite galaxies of the Milky Way. Using Markov-Chain Monte-Carlo, we exhaustively search a large parameter space of the model and rigorously show that the general wisdom of strong outflows as the primary feedback mechanism cannot simultaneously explain the stellar mass function and the mass--metallicity relation of the Milky Way satellites. An extended model that assumes that a fraction of baryons is prevented from collapsing into low-mass halos in the first place can be accurately constrained to simultaneously reproduce those observations. The inference suggests that two different physical mechanisms are needed to explain the two different data sets. In particular, moderate outflows with weak halo mass dependence are needed to explain the mass--metallicity relation, and prevention of baryons falling into shallow gravitational potentials of low-mass halos (e.g. "pre-heating") is needed to explain the low stellar mass fraction for a given subhalo mass.Comment: 14 pages, 4 figures, accepted for publication in Ap

Individual information security, user behaviour and cyber victimisation: An empirical study of social networking users

While extant literature on privacy in social networks is plentiful, issues pertaining to information security remain largely unexplored. This paper empirically examines the relationship between online victimisation and users' activity and perceptions of personal information security on social networking services (SNS). Based on a survey of active users, we explore how behavioural patterns on social networks, personal characteristics and technical efficacy of users impact the risk of facing online victimisation. Our results suggest that users with high-risk propensity are more likely to become victims of cybercrime, whereas those with high perceptions of their ability to control information shared on SNS are less likely to become victims. The study shows that there is a negative and statistically significant association between multipurpose dominant SNS (e.g. Facebook, Google +) usage and victimisation. However, activity on the SNS for knowledge exchange (e.g. LinkedIn, Blogger) has a positive and statistically significant association with online victimisation. Our results have implications for practice as they inform the social media industry that protection of individual information security on SNS cannot be left entirely to the user. The importance of user awareness in the context of social technologies plays an important role in preventing victimisation, and social networking services should provide adequate controls to protect personal information

A New Method for Calculating Arrival Distribution of Ultra-High Energy Cosmic Rays above 10^19 eV with Modifications by the Galactic Magnetic Field

We present a new method for calculating arrival distribution of UHECRs including modifications by the galactic magnetic field. We perform numerical simulations of UHE anti-protons, which are injected isotropically at the earth, in the Galaxy and record the directions of velocities at the earth and outside the Galaxy for all of the trajectories. We then select some of them so that the resultant mapping of the velocity directions outside the Galaxy of the selected trajectories corresponds to a given source location scenario, applying Liouville's theorem. We also consider energy loss processes of UHE protons in the intergalactic space. Applying this method to our source location scenario which is adopted in our recent study and can explain the AGASA observation above 4 \times 10^{19} eV, we calculate the arrival distribution of UHECRs including lower energy (E>10^19 eV) ones. We find that our source model can reproduce the large-scale isotropy and the small-scale anisotropy on UHECR arrival distribution above 10^19 eV observed by the AGASA. We also demonstrate the UHECR arrival distribution above 10^19 eV with the event number expected by future experiments in the next few years. The interesting feature of the resultant arrival distribution is the arrangement of the clustered events in the order of their energies, reflecting the directions of the galactic magnetic field. This is also pointed out by Alvarez-Muniz et al.(2002). This feature will allow us to obtain some kind of information about the composition of UHECRs and the magnetic field with increasing amount of data.Comment: 10 pages, 8 figures, to appear in the Astrophysical Journa