180 research outputs found
Limits to solar cycle predictability: Cross-equatorial flux plumes
Within the Babcock-Leighton framework for the solar dynamo, the strength of a
cycle is expected to depend on the strength of the dipole moment or net
hemispheric flux during the preceding minimum, which depends on how much flux
was present in each hemisphere at the start of the previous cycle and how much
net magnetic flux was transported across the equator during the cycle. Some of
this transport is associated with the random walk of magnetic flux tubes
subject to granular and supergranular buffeting, some of it is due to the
advection caused by systematic cross-equatorial flows such as those associated
with the inflows into active regions, and some crosses the equator during the
emergence process.
We aim to determine how much of the cross-equatorial transport is due to
small-scale disorganized motions (treated as diffusion) compared with other
processes such as emergence flux across the equator. We measure the
cross-equatorial flux transport using Kitt Peak synoptic magnetograms,
estimating both the total and diffusive fluxes. Occasionally a large sunspot
group, with a large tilt angle emerges crossing the equator, with flux from the
two polarities in opposite hemispheres. The largest of these events carry a
substantial amount of flux across the equator (compared to the magnetic flux
near the poles). We call such events cross-equatorial flux plumes. There are
very few such large events during a cycle, which introduces an uncertainty into
the determination of the amount of magnetic flux transported across the equator
in any particular cycle. As the amount of flux which crosses the equator
determines the amount of net flux in each hemisphere, it follows that the
cross-equatorial plumes introduce an uncertainty in the prediction of the net
flux in each hemisphere. This leads to an uncertainty in predictions of the
strength of the following cycle.Comment: A&A, accepte
Magnetic flux generation and transport in cool stars
The Sun and other cool stars harbouring outer convection zones manifest
magnetic activity in their atmospheres. The connection between this activity
and the properties of a deep-seated dynamo generating the magnetic flux is not
well understood. By employing physical models, we study the spatial and
temporal characteristics of the observable surface field for various stellar
parameters. We combine models for magnetic flux generation, buoyancy
instability, and transport, which encompass the entire convection zone. The
model components are: (1) a thin-layer alpha-Omega dynamo at the base of the
convection zone; (2) buoyancy instabilities and the rise of flux tubes through
the convection zone in 3D, which provides a physically consistent determination
of emergence latitudes and tilt angles; and (3) horizontal flux transport at
the surface. For solar-type stars and rotation periods longer than about 10
days, the latitudinal dynamo waves generated by the deep-seated alpha-Omega
dynamo are faithfully reflected by the surface distribution of magnetic flux.
For rotation periods of the order of two days, however, Coriolis acceleration
of rising flux loops leads to surface flux emergence at much higher latitudes
than the dynamo waves at the bottom of the convection zone reach. A similar
result is found for a K0V star with a rotation period of two days. In the case
of a rapidly rotating K1 subgiant, overlapping dynamo waves lead to noisy
activity cycles and mixed-polarity fields at high latitudes.Comment: 14 pages, 14 figures. Accepted for publication in Astronomy &
Astrophysic
Generalized four-point characterization method for resistive and capacitive contacts
In this paper, a four-point characterization method is developed for
resistive samples connected to either resistive or capacitive contacts.
Provided the circuit equivalent of the complete measurement system is known
including coaxial cable and connector capacitances as well as source output and
amplifier input impedances, a frequency range and capacitive scaling factor can
be determined, whereby four-point characterization can be performed. The
technique is demonstrated with a discrete element test sample over a wide
frequency range using lock-in measurement techniques from 1 Hz - 100 kHz. The
data fit well with a circuit simulation of the entire measurement system. A
high impedance preamplifier input stage gives best results, since lock-in input
impedances may differ from manufacturer specifications. The analysis presented
here establishes the utility of capacitive contacts for four-point
characterizations at low frequency.Comment: 21 pages, 10 figure
Cost analysis and related factors in patients with traumatic hand injury
The aim of this study was to measure the direct and indirect costs and factors influencing these costs in patients presenting following traumatic hand injury. We assessed patients aged 18-65 years who were in work. Hand injury severity and functional status were assessed. Direct costs, including medical care expenses, and indirect costs, including lost productivity, were calculated. Seventy-nine patients of a mean age of 32 years were included. The mean direct cost for each patient was 1891 (53% of total cost). Injury severity, time to return to work, and hospitalization time were the main parameters of increased total cost in a linear regression analysis. © The Author(s) 2012
Observing and modelling the young solar analogue EK Draconis: starspot distribution, elemental abundances, and evolutionary status
Observations and modelling of stars with near-solar masses in their early
phases of evolution is critical for a better understanding of how dynamos of
solar-type stars evolve. We examine the chemical composition and the spot
distribution of the pre-main-sequence solar analogue EK Dra. Using spectra from
the HERMES Spectrograph (La Palma), we obtain the abundances of 23 elements
with respect to the solar ones, which lead to a , with
significant overabundance of Li and Ba. The s-process elements Sr, Y, and Ce
are marginally overabundant, while Co, Ni, Cu, Zn are marginally deficient
compared to solar abundances. The overabundance of Ba is most likely due to the
assumption of depth-independent microturbulent velocity. Li abundance is
consistent with the age and the other abundances may indicate distinct initial
conditions of the pre-stellar nebula. We estimate a mass of 1.04 and
an age of \,Myr using various spectroscopic and photometric
indicators. We study the surface distribution of dark spots, using 17 spectra
collected during 15 nights using the CAFE Spectrograph (Calar Alto). We also
conduct flux emergence and transport (FEAT) simulations for EK Dra's parameters
and produce 15-day-averaged synoptic maps of the likely starspot distributions.
Using Doppler imaging, we reconstruct the surface brightness distributions for
the observed spectra and FEAT simulations, which show overall agreement for
polar and mid-latitude spots, while in the simulations there is a lack of
low-latitude spots compared to the observed image. We find indications that
cross-equatorial extensions of mid-latitude spots can be artefacts of the less
visible southern-hemisphere activity.Comment: 15 pages, 16 figures, accepted for publication in MNRAS; corrections
in Abstract and Introductio
Brand elevation in supply chains
In the last decades supply chain management has been explored from different perspectives fueling a myriad of research in the field. Although the literature on supply chain management (SCM) is vast, major gaps requiring scientific exploration still exist. Among these, interaction of branding and supply chain concepts clearly stands out. The aim of this paper is to investigate the power of brand in supply chains by taking literature devoted to supply chain management into consideration, relationship marketing and brand management. This paper explores the power of brand in terms of SCM and it defines the concept of “brand elevation in supply chain”. The objectives of this study are thus twofold: identifying “brand elevation in supply chain” concept and proposing a conceptual model associated to the power of brand in supply chains
Enhanced topical delivery of dexamethasone by β-cyclodextrin decorated thermoresponsive nanogels
Highly hydrophilic, responsive nanogels are attractive as potential systems for the topical delivery of bioactives encapsulated in their three-dimensional polymeric scaffold. Yet, these drug carrier systems suffer from drawbacks for efficient delivery of hydrophobic drugs. Addressing this, β-cyclodextrin (βCD) could be successfully introduced into the drug carrier systems by exploiting its unique affinity toward dexamethasone (DXM) as well as its role as topical penetration enhancer. The properties of βCD could be combined with those of thermoresponsive nanogels (tNGs) based on dendritic polyglycerol (dPG) as a crosslinker and linear thermoresponsive polyglycerol (tPG) inducing responsiveness to temperature changes. Electron paramagnetic resonance (EPR) studies localized the drug within the hydrophobic cavity of βCD by differences in its mobility and environmental polarity. In fact, the fabricated carriers combining a particulate delivery system with a conventional penetration enhancer, resulted in an efficient delivery of DXM to the epidermis and the dermis of human skin ex vivo (enhancement compared to commercial DXM cream: ∼2.5 fold in epidermis, ∼30 fold in dermis). Furthermore, DXM encapsulated in βCD tNGs applied to skin equivalents downregulated the expression of proinflammatory thymic stromal lymphopoietin (TSLP) and outperformed a commercially available DXM cream
Surface flux evolution constraints for flux transport dynamos
The surface flux transport (SFT) model of solar magnetic fields involves
empirically well-constrained velocity and magnetic fields. The basic evolution
of the Sun's large-scale surface magnetic field is well described by this
model. The azimuthally averaged evolution of the SFT model can be compared to
the surface evolution of the flux transport dynamo (FTD), and the evolution of
the SFT model can be used to constrain several near-surface properties of the
FTD model.
We compared the results of the FTD model with different upper boundary
conditions and diffusivity profiles against the results of the SFT model. Among
the ingredients of the FTD model, downward pumping of magnetic flux, related to
a positive diffusivity gradient, has a significant effect in slowing down the
diffusive radial transport of magnetic flux through the solar surface. Provided
the pumping was strong enough to give rise to a downflow of a magnetic Reynolds
number of 5 in the near-surface boundary layer, the FTD using a vertical
boundary condition matches the SFT model based on the average velocities above
the boundary layer. The FTD model with a potential field were unable to match
the SFT results.Comment: Accepted for A&
Gas and seismicity within the Istanbul seismic gap
Understanding micro-seismicity is a critical question for earthquake hazard assessment. Since the devastating earthquakes of Izmit and Duzce in 1999, the seismicity along the submerged section of North Anatolian Fault within the Sea of Marmara (comprising the “Istanbul seismic gap”) has been extensively studied in order to infer its mechanical behaviour (creeping vs locked). So far, the seismicity has been interpreted only in terms of being tectonic-driven, although the Main Marmara Fault (MMF) is known to strike across multiple hydrocarbon gas sources. Here, we show that a large number of the aftershocks that followed the M 5.1 earthquake of July, 25th 2011 in the western Sea of Marmara, occurred within a zone of gas overpressuring in the 1.5–5 km depth range, from where pressurized gas is expected to migrate along the MMF, up to the surface sediment layers. Hence, gas-related processes should also be considered for a complete interpretation of the micro-seismicity (~M < 3) within the Istanbul offshore domain
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