45,841 research outputs found
Consequences of Content Diversity for Online Public Spaces for Local Communities
While there is significant potential for social technologies to strengthen local communities, creating viable online spaces for them remains difficult. Maintaining a reliable content stream is challenging for local communities with their bounded emphases and limited population of potential contributors. Some systems focus on specific information types (e.g. restaurant, events). Others allow many different information types. This paper reports our findings about the consequences of content diversity from a study of neighborhood-oriented Facebook groups. The findings raise questions about the viability of designs for local online communities that focus narrowly on single topics, goals, and audiences
One-dimensional relativistic dissipative system with constant force and its quantization
For a relativistic particle under a constant force and a linear velocity
dissipation force, a constant of motion is found. Problems are shown for
getting the Hamiltoninan of this system. Thus, the quantization of this system
is carried out through the constant of motion and using the quantization of the
velocity variable. The dissipative relativistic quantum bouncer is outlined
within this quantization approach.Comment: 11 pages, no figure
CP violation in semileptonic tau lepton decays
The leading order contribution to the direct CP asymmetry in tau^{+/-} ->
K^{+/-} pi^0 nu_{tau} decay rates is evaluated within the Standard Model. The
weak phase required for CP violation is introduced through an interesting
mechanism involving second order weak interactions, which is also responsible
for tiny violations of the Delta S= Delta Q rule in K_{l3} decays. The
calculated CP asymmetry turns out to be of order 10^{-12}, leaving a large
window for studying effects of non-standard sources of CP violation in this
observable.Comment: 5 pages, 3 figures, version published in Phys.Rev.
Structures and Stabilities of Doubly-charged (MgO)nMg2+ (n=1-29) Cluster Ions
Ab initio perturbed ion plus polarization calculations are reported for
doubly-charged nonstoichiometric (MgO)nMg2+ (n=1-29) cluster ions. We consider
a large number of isomers with full relaxations of the geometries, and add the
correlation correction to the Hartree-Fock energies for all cluster sizes. The
polarization contribution is included at a semiempirical level also for all
cluster sizes. Comparison is made with theoretical results for neutral (MgO)n
clusters and singly-charged alkali-halide cluster ions. Our method is also
compared to phenomenological pair potential models in order to asses their
reliability for calculations on small ionic systems. The large
coordination-dependent polarizabilities of oxide anions favor the formation of
surface sites, and thus bulklike structures begin to dominate only after n=24.
The relative stabilities of the cluster ions against evaporation of a MgO
molecule show variations that are in excellent agreement with the experimental
abundance spectra.Comment: Final version accepted in Journal of Chemical Physics; 8 pages plus 8
figures (6 GIFs and 2 PSs). The main difference with respect to the original
submission is the inclusion of coordination-dependent polarizabilities for
oxide anions. That results in substantial changes in the result
Radiative corrections of to decays
The electromagnetic radiative corrections to the ( is a vector meson and a charged
lepton) decay rates are evaluated using the cutoff method to regularize virtual
corrections and incorporating intermediate resonance states in the real-photon
amplitude to extend the region of validity of the soft-photon approximation.
The electromagnetic and weak form factors of hadrons are assumed to vary
smoothly over the energies of virtual and real photons under consideration. The
cutoff dependence of radiative corrections upon the scale that
separates the long- and short-distance regimes is found to be mild and is
considered as an uncertainty of the calculation. Owing to partial cancellations
of electromagnetic corrections evaluated over the three- and four-body regions
of phase space, the photon-inclusive corrected rates are found to be dominated
by the short-distance contribution. These corrections will be relevant for a
precise determination of the quark mixing angles by testing isospin
symmetry when measurements of semileptonic rates of charged and neutral
mesons at the few percent level become available. For completeness, we also
provide numerical values of radiative corrections in the three-body region of
the Dalitz plot distributions of these decays.Comment: Further comments and two references adde
Energy consumption, income and CO2 emissions in Latin America
I describe and compare the environment policies of European Union and of 12 Latin Americans economies. For this, I use common statistical methods, such as non-parametric tests, convergence analysis (Beta and Sigma) and panel data, in order to verify the hypothesis that emissions and energy use in Latin America has been increasing since the mid-20th century. The statistical tests used confirm the proposed hypothesis. I also rely upon the Environmental Kuznets Curve- whereby economies that are at the growth stage are more focused on achieving the latter than they are on environmental concerns and those which have already achieved growth focus more on environmental concerns-to take an alternative approach by introducing the role of economic growth in the evolution of energy consumption and emissions. This chapter reaches the conclusion that energy consumption and pollutant emissions in LA, in per capita terms, are converging. This suggests that the initial levels of the variables help to explain why some countries have increased emissions (in this case, energy consumption) to a greater extent than other economies in the region. Evidence of convergence is also found, as well as a monotonic relationship between the level of pollution and the level of development (consistent with the Environmental Kuznets Curve).Energy Consumption, emissions, Latin America, Convergence
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