5,748 research outputs found
On the production of heavy axion-like particles in the accretion disks of gamma-ray bursts
Heavy axion-like particles have been introduced in several scenarios beyond
the Standard Model and their production in some astrophysical systems should be
possible. In this work, we re-examine the possibility that these type of
particles can be generated in the accretion disks of gamma-ray bursts (GRB),
the most powerful events in the universe. If the produced axions decay into
photons or pairs at the correct distances, a fireball is generated. We
calculate the structure transient accretion disks in GRBs (density, temperature
and thickness profiles) taking into account the effect of heavy axion emission
as well as the rest of the relevant standard cooling processes. This allows us
to obtain the values of the coupling constant g_{aN} in order for the axions
not to become trapped, and we can also compute the emitted heavy axion
luminosity from the entire disk. We find that for the couplings within the
ranges found, then the mechanism for powering GRBs based on heavy axion
production and decay becomes an alternative to the standard picture based upon
magnetohydrodynamic processes and neutrino-antineutrino annihilation.
Otherwise, if heavy axions are produced in the disk but their decay to takes
place further away, the mechanism fails. Still, the decay products (gamma rays
or electrons and positrons) should leave observable signatures which are not
observed for different ranges of values of the coupling constants, depending on
the mass of the heavy axionComment: 14 pages, 7 figures. Updated version that matches the one to be
published on Physics Letters
Using cross-functional, cross-firm teams to co-create value: The role of financial measures
Increasingly, the involvement of representatives from all major business
functions in cross-functional, crossfirmteams is being viewed as a means to
develop and maintain profitable business-to-business relationships.However, if
the measurements of the value co-created in these relationships with customers
and suppliers donot incorporate the financial outcomes of joint cross-functional
initiatives, managers can be led to makedecisions that jeopardize the long-term
profitability of the two firms. In this paper, the authors explore
thedifferences in value co-creation when a company is linked to key customers
and key suppliers through crossfunctionalteams and when it is not. Using a case
study approach, the authors measured value co-creation infinancial terms and
describe how managers changed their behaviors toward customers and suppliers
whenthey were able to compare the value that was being co-created in each
relationship. In each pair ofrelationships, one involved cross-functional teams
and the other did not. The results indicate that crossfunctional,cross-firm
involvement leads to increased value co-creation. The research suggests that
marketingscholars and managers should emphasize the use of cross-functional
teams that involve all major functions tomanage relationships with key
customers, and should incorporate financial measures in the evaluation
ofrelationship performance
Lensing Induced Cluster Signatures in Cosmic Microwave Background
We show that clusters of galaxies induce step-like wiggles on top of the
cosmic microwave background (CMB). The direction of the wiggle is parallel to
the large scale gradient of CMB allowing one to isolate the effect from other
small scale fluctuations. The effect is sensitive to the deflection angle
rather than its derivative (shear or magnification) and is thus tracing outer
parts of the cluster with higher sensitivity than some other methods. A typical
amplitude of the effect is where
is the velocity dispersion of the cluster and several
signals extend out to a fraction of a degree. We derive the expressions for the
temperature profile for several simple parameterized cluster models and
identify some degeneracies between parameters. Finally, we discuss how to
separate this signal from other imprints on CMB using custom designed filters.
Detection of this effect is within reach of the next generation of small scale
CMB telescopes and could provide information about the cluster density profile
beyond the virial radius.Comment: 10 pages, 3 figures, submitted to Ap
The interplay between habitat structure and chemical contaminants on biotic responses of benthic organisms
Habitat structure influences the diversity and distribution of organisms, potentially affecting their response to disturbances by either affecting their ‘susceptibility’ or through the provision of resources that can mitigate impacts of disturbances. Chemical disturbances due to contamination are associated with decreases in diversity and functioning of systems and are also likely to increase due to coastal urbanisation. Understanding how habitat structure interacts with contaminants is essential to predict and therefore manage such effects, minimising their consequences to marine systems. Here, we manipulated two structurally different habitats and exposed them to different types of contaminants. The effects of contamination and habitat structure interacted, affecting species richness. More complex experimental habitats were colonized by a greater diversity of organisms than the less complex habitats. These differences disappeared, however, when habitats were exposed to contaminants, suggesting that contaminants can override effects of habitats structure at small spatial scales. These results provide insight into the complex ways that habitat structure and contamination interact and the need to incorporate evidence of biotic responses from individual disturbances to multiple stressors. Such effects need to be taken into account when designing and planning management and conservation strategies to natural systems
Adopting New Zealand Dairy Farm Principles and Practices in Argentina
The dairy sector is important to Argentina because it creates genuine wealth and employment. Milk production at competitive costs is crucial for the endurance of the Argentine dairy sector; therefore the development of competitive dairy farm systems is important for Argentina. New Zealand (hereafter NZ) dairy farm systems are internationally known for their competitiveness without the presence of subsidies. Though Argentine dairy farmers have been attracted to NZ systems for more than 40 years and despite the fact that the NZ knowledge appears to be beneficial to Argentine farms, NZ practices have been rarely adopted. This seemingly fruitless effort in extending this technology shapes the research question of the present study: Can Argentine dairy farmers benefit from adopting New Zealand dairy farm principles and practices? Seven Argentine dairy farmers were selected as case studies because of their awareness of NZ dairy systems; the research data was collected through interviews, farm physical and economic records, and field visits to the farms. Two frameworks were utilized to analyse the qualitative and quantitative data: the Diffusion Theory (Rogers, 2003) and the IFCN network (International Farm Comparison Network www.ifcnnetwork.org), respectively. Ten NZ innovations were defined; they were principles and practices considered typical in NZ dairy farms and not common in Argentine dairy farms. The innovations were related to four areas of the dairy system: pasture management, herd management & genetics, farm structure & organization, and human resources. The seven farmers selected differed in the level of adoption or rejection of the innovations. Results revealed that higher levels of adoption of NZ innovations by a group of Argentine dairy farms were associated with higher levels of Return on Investment; this was mainly due to a higher utilization of the main asset and most limiting production factor of Argentine and New Zealand dairy farms, the land.Argentine dairy farm systems, New Zealand innovations for Argentina, Argentine dairy industry, Argentine dairy systems, diffusion of innovations, adoption of innovations, Livestock Production/Industries,
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