41,887 research outputs found
Power Corrections in Charmless B Decays
In this paper, we focus on the role of power corrections in QCD
factorization(QCDF) method in charmless two-body nonleptonic meson decays.
We use the ratio of the branching fraction of to
that of , for which the theoretical uncertainties are
greatly reduced, to show clearly that the power corrections in charmless B
decays are probably large. With other similar ratios considered, for example,
for the decay, it is very likely that, among various
sources of power corrections, annihilation topology plays an indispensable role
at least for penguin dominated channels. We also consider some
selective ratios of direct CP asymmetries. Among these, we find that, if power
corrections other than the chirally enhanced power corrections and annihilation
topology were negligible, QCDF would predict the direct CP asymmetry of to be about 3 times larger than that of ,
with opposite sign. Experimentally any significant deviation from this
prediction would suggest either new physics or possibly the importance of
long-distance rescattering effects.Comment: references and note added, to appear in Phys. Rev.
Cosmology with Varying Constants
The idea of possible time or space variations of the `fundamental' constants
of nature, although not new, is only now beginning to be actively considered by
large numbers of researchers in the particle physics, cosmology and
astrophysics communities. This revival is mostly due to the claims of possible
detection of such variations, in various different contexts and by several
groups. Here, I present the current theoretical motivations and expectations
for such variations, review the current observational status, and discuss the
impact of a possible confirmation of these results in our views of cosmology
and physics as a whole.Comment: 14 pages, no figures. Essay to appear in Phil. Trans. Roy. Soc. Lond.
A Triennial Series (Christmas 2002 Issue
Nodeless superconductivity in the noncentrosymmetric MoRhN superconductor: a SR study
The noncentrosymmetric superconductor MoRhN, with K,
adopts a -Mn-type structure (space group 432), similar to that of
MoAlC. Its bulk superconductivity was characterized by magnetization
and heat-capacity measurements, while its microscopic electronic properties
were investigated by means of muon-spin rotation and relaxation (SR). The
low-temperature superfluid density, measured via transverse-field (TF)-SR,
evidences a fully-gapped superconducting state with , very close to 1.76 - the BCS gap value for
the weak coupling case, and a magnetic penetration depth nm.
The absence of spontaneous magnetic fields below the onset of
superconductivity, as determined by zero-field (ZF)-SR measurements, hints
at a preserved time-reversal symmetry in the superconducting state. Both TF-and
ZF-SR results evidence a spin-singlet pairing in MoRhN.Comment: 5 figures and 5 pages. Accepted for publication as a Rapid
Communication in Phys. Rev.
An integrated social media communication view on content marketing by South African non-profit sectors
Background: Organisations widely adopt social media to communicate with stakeholders, yet research into content marketing in the South African non-profit sector is sparse. It is concerned with consistently producing valuable and relevant content for social media. As it is generally associated with the field of marketing, limited research exists from a communication perspective. This perceived gap in taking a communication stance prompted this investigation into the ways in which these organisations attend to social media content aspects. Objectives: The research objective was to acquire a broad understanding of content marketing on social media, unique to South African non-profit organisations. Key areas that were uncovered and statistically verified in an earlier quantitative study and how these are attended to in real life were explored. Method: A qualitative approach was used to obtain in-depth insights into the use of content marketing. Semi-structured interviews were used as data collection method to explore non-profit sector’s approaches to social media communication, and to determine whether their efforts could be regarded as being integrated. Results: The findings yielded valuable insights into the ways that non-profit sectors in South Africa practise social media communication. The benefits of using social media for communication is acknowledged, yet vital aspects such as sourcing content, considering stakeholders’ needs and demographics communication, using available planning tools and recognising employees as internal ambassadors are not considered. Conclusion: The findings of this study highlight several key areas and topics that organisations should consider an integrated social media communication approach as alternative for content marketing in the non-profit secto
On the Approximability and Hardness of the Minimum Connected Dominating Set with Routing Cost Constraint
In the problem of minimum connected dominating set with routing cost
constraint, we are given a graph , and the goal is to find the
smallest connected dominating set of such that, for any two
non-adjacent vertices and in , the number of internal nodes on the
shortest path between and in the subgraph of induced by is at most times that in . For general graphs, the only
known previous approximability result is an -approximation algorithm
() for by Ding et al. For any constant , we
give an -approximation
algorithm. When , we give an -approximation
algorithm. Finally, we prove that, when , unless , for any constant , the problem admits no
polynomial-time -approximation algorithm, improving
upon the bound by Du et al. (albeit under a stronger hardness
assumption)
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