6,569 research outputs found
The predictability of advection-dominated flux-transport solar dynamo models
Space weather is a matter of practical importance in our modern society.
Predictions of forecoming solar cycles mean amplitude and duration are
currently being made based on flux-transport numerical models of the solar
dynamo. Interested in the forecast horizon of such studies, we quantify the
predictability window of a representative, advection-dominated, flux-transport
dynamo model by investigating its sensitivity to initial conditions and control
parameters through a perturbation analysis. We measure the rate associated with
the exponential growth of an initial perturbation of the model trajectory,
which yields a characteristic time scale known as the e-folding time .
The e-folding time is shown to decrease with the strength of the
-effect, and to increase with the magnitude of the imposed meridional
circulation. Comparing the e-folding time with the solar cycle periodicity, we
obtain an average estimate for equal to 2.76 solar cycle durations.
From a practical point of view, the perturbations analysed in this work can be
interpreted as uncertainties affecting either the observations or the physical
model itself. After reviewing these, we discuss their implications for solar
cycle prediction.Comment: 33 pages, 12 figure
Path integral quantization of scalar fluctuations above a kink
We quantize scalar fluctuations in 1+1 dimensions above a classical
background kink. The properties of the effective action for the corresponding
classical field are studied with an exact functional method, alternative to
exact Wilsonian renormalization, where the running parameter is a bare mass,
and the regulator of the quantum theory is fixed. We extend this approach, in
an appendix, to a Yukawa interaction in higher dimension.Comment: Comments adde
A mean-field Babcock-Leighton solar dynamo model with long-term variability
Dynamo models relying on the Babcock-Leighton mechanism are successful in
reproducing most of the solar magnetic field dynamical characteristics.
However, considering that such models operate only above a lower magnetic field
threshold, they do not provide an appropriate magnetic field regeneration
process characterizing a self-sustainable dynamo. In this work we consider the
existence of an additional \alpha-effect to the Babcock-Leighton scenario in a
mean-field axisymmetric kinematic numerical model. Both poloidal field
regeneration mechanisms are treated with two different strength-limiting
factors. Apart from the solar anti-symmetric parity behavior, the main solar
features are reproduced: cyclic polarity reversals, mid-latitudinal equatorward
migration of strong toroidal field, poleward migration of polar surface radial
fields, and the quadrature phase shift between both. Long-term variability of
the solutions exhibits lengthy periods of minimum activity followed by
posterior recovery, akin to the observed Maunder Minimum. Based on the analysis
of the residual activity during periods of minimum activity, we suggest that
these are caused by a predominance of the \alpha-effect over the
Babcock-Leighton mechanism in regenerating the poloidal field.Comment: 21 pages, 6 figure
NGC1277: a massive compact relic galaxy in the nearby Universe
As early as 10 Gyr ago, galaxies with more than 10^11 Msun in stars already
existed. While most of these massive galaxies must have subsequently
transformed through on-going star formation and mergers with other galaxies, a
small fraction (<0.1%) may have survived untouched till today. Searches for
such relic galaxies, useful windows to explore the early Universe, have been
inconclusive to date: galaxies with masses and sizes like those observed at
high redshift (M*>10^11 Msun; Re<1.5 kpc) have been found in the local
Universe, but their stars are far too young for the galaxy to be a relic
galaxy. This paper explores the first case of a nearby galaxy, NGC1277 (in the
Perseus cluster at a distance of 73 Mpc), which fulfills all the criteria to be
considered a relic galaxy. Using deep optical spectroscopy, we derive the star
formation history along the structure of the galaxy: the stellar populations
are uniformly old (>10 Gyr) with no evidence for more recent star formation
episodes. The metallicity of their stars is super-solar ([Fe/H]=0.20+-0.04) and
alpha enriched ([alpha/Fe]=0.4+-0.1). This suggests a very short formation time
scale for the bulk of stars of this galaxy. This object also rotates very fast
(Vrot~300 km/s) and has a large velocity dispersion (sigma>300 km/s). NGC1277
will allow future explorations in full detail of properties such as the
structure, internal dynamics, metallicity, dust content and initial mass
function at around 10-12 Gyr back in time when the first massive galaxies were
built.Comment: 4 figures; Accepted for publication at ApJ Letter
Antecedentes da Adoção da Computação em Nuvem: Efeitos da Infraestrutura, Investimento e Porte
Cloud computing, a peculiar form of storage and of making information available, has attracted much interest for its potential to significantly alter required investment in information technology infrastructure. As a paradox, while organizations can benefit from the possibility of implementing cloud computing, decision makers are faced with the dilemma arising from the possibility that competitors will have access to previously scarce or unique resources, essentially sources of competitive advantage. The question that arises is whether cloud computing increases the complexity of investment decisions or, in contrast, simplifies the analysis by allowing resources to be released for investment in other skills required by the business. This research investigates what antecedents are associated with the decision to undertake cloud computing and evaluates the effects existing IT infrastructure and the size and amount of investments have in this decision. Analysis of secondary data was used to develop a structural model, which is accompanied by explanations of the relationships uncovered. This paper's contributions include a theoretical explanation of the quandary related to IT investments within this context and the decision to adopt cloud computing and, additionally, the presentation of some managerial implications of these findings. Research limitations and suggestions for changes in future studies are also presented
Replication of Internet Privacy Concerns in the Mobile Banking Context
This study is a conceptual replication of the work of Hong and Thong (2013), who developed the Internet Privacy Concerns scale to measure individuals’ concerns regarding how personal information is handled by websites. We adapt the wording of the original survey items to the context of mobile banking and follow the same procedures to assess the scale. The replication results reinforce the stability and applicability of the scale over the years and in different scenarios. In contrast with the original study, however, we detect a high correlation between the Control and Awareness dimensions, suggesting the design of an additional second-order dimension that we label “exposure management” (individuals’ consciousness about existing controls that mitigate the risks of personal data loss)
Genomic mechanisms for cold tolerance and production of exopolysaccharides in the Arctic cyanobacterium Phormidesmis priestleyi BC1401
BACKGROUND: Cyanobacteria are major primary producers in extreme cold ecosystems. Many lineages of cyanobacteria thrive in these harsh environments, but it is not fully understood how they survive in these conditions and whether they have evolved specific mechanisms of cold adaptation. Phormidesmis priestleyi is a cyanobacterium found throughout the cold biosphere (Arctic, Antarctic and alpine habitats). Genome sequencing of P. priestleyi BC1401, an isolate from a cryoconite hole on the Greenland Ice Sheet, has allowed for the examination of genes involved in cold shock response and production of extracellular polymeric substances (EPS). EPSs likely enable cyanobacteria to buffer the effects of extreme cold and by identifying mechanisms for EPS production in P. priestleyi BC1401 this study lays the way for investigating transcription and regulation of EPS production in an ecologically important cold tolerant cyanobacterium. RESULTS: We sequenced the draft genome of P. priestleyi BC1401 and implemented a new de Bruijn graph visualisation approach combined with BLAST analysis to separate cyanobacterial contigs from a simple metagenome generated from non-axenic cultures. Comparison of known cold adaptation genes in P. priestleyi BC1401 with three relatives from other environments revealed no clear differences between lineages. Genes involved in EPS biosynthesis were identified from the Wzy- and ABC-dependent pathways. The numbers of genes involved in cell wall and membrane biogenesis in P. priestleyi BC1401 were typical relative to the genome size. A gene cluster implicated in biofilm formation was found homologous to the Wps system, although the intracellular signalling pathways by which this could be regulated remain unclear. CONCLUSIONS: Results show that the genomic characteristics and complement of known cold shock genes in P. priestleyi BC1401 are comparable to related lineages from a wide variety of habitats, although as yet uncharacterised cold shock genes in this organism may still exist. EPS production by P. priestleyi BC1401 likely contributes to its ability to survive efficiently in cold environments, yet this mechanism is widely distributed throughout the cyanobacterial phylum. Discovering how these EPS related mechanisms are regulated may help explain why P. priestleyi BC1401 is so successful in cold environments where related lineages are not. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12864-016-2846-4) contains supplementary material, which is available to authorized users
Photonic nano-structures on (111) oriented diamond
We demonstrate the fabrication of single-crystalline diamond nanopillars on a
(111)-oriented chemical vapor deposited diamond substrate. This crystal
orientation offers optimal coupling of nitrogen-vacancy (NV) center emission to
the nanopillar mode and is thus advantageous over previous approaches. We
characterize single native NV centers in these nanopillars and find one of the
highest reported saturated fluorescence count rates in single crystalline
diamond in excess of 10 counts per second. We show that our
nano-fabrication procedure conserves the preferential alignment as well as the
spin coherence of the NVs in our structures. Our results will enable a new
generation of highly sensitive probes for NV magnetometry and pave the way
toward photonic crystals with optimal orientation of the NV center's emission
dipole.Comment: 4 pages original manuscript, 3 pages supplementary materia
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