11,761 research outputs found
Modulation of galactic protons in the heliosphere during the unusual solar minimum of 2006 to 2009
The last solar minimum activity period, and the consequent minimum modulation
conditions for cosmic rays, was unusual. The highest levels of galactic protons
were recorded at Earth in late 2009 in contrast to expectations. Proton spectra
observed for 2006 to 2009 from the PAMELA cosmic ray detector on-board the
Resurs-DK1 satellite are presented together with the solutions of a
comprehensive numerical model for the solar modulation of cosmic rays. The
model is used to determine what mechanisms were mainly responsible for the
modulation of protons during this period, and why the observed spectrum for
2009 was the highest ever recorded. From mid-2006 until December 2009 we find
that the spectra became significantly softer because increasingly more low
energy protons had reached Earth. To simulate this effect, the rigidity
dependence of the diffusion coefficients had to decrease significantly below ~3
GeV. The modulation minimum period of 2009 can thus be described as relatively
more "diffusion dominated" than previous solar minima. However, we illustrate
that drifts still had played a significant role but that the observable
modulation effects were not as well correlated with the waviness of the
heliospheric current sheet as before. Protons still experienced global gradient
and curvature drifts as the heliospheric magnetic field had decreased
significantly until the end of 2009, in contrast to the moderate decreases
observed during previous minimum periods. We conclude that all modulation
processes contributed to the observed increases in the proton spectra for this
period, exhibiting an intriguing interplay of these major mechanisms
Semiclassical limit for Schr\"odinger equations with magnetic field and Hartree-type nonlinearities
The semi-classical regime of standing wave solutions of a Schr\"odinger
equation in presence of non-constant electric and magnetic potentials is
studied in the case of non-local nonlinearities of Hartree type. It is show
that there exists a family of solutions having multiple concentration regions
which are located around the minimum points of the electric potential.Comment: 34 page
The Tangled Nature model as an evolving quasi-species model
We show that the Tangled Nature model can be interpreted as a general
formulation of the quasi-species model by Eigen et al. in a frequency dependent
fitness landscape. We present a detailed theoretical derivation of the mutation
threshold, consistent with the simulation results, that provides a valuable
insight into how the microscopic dynamics of the model determine the observed
macroscopic phenomena published previously. The dynamics of the Tangled Nature
model is defined on the microevolutionary time scale via reproduction, with
heredity, variation, and natural selection. Each organism reproduces with a
rate that is linked to the individuals' genetic sequence and depends on the
composition of the population in genotype space. Thus the microevolutionary
dynamics of the fitness landscape is regulated by, and regulates, the evolution
of the species by means of the mutual interactions. At low mutation rate, the
macro evolutionary pattern mimics the fossil data: periods of stasis, where the
population is concentrated in a network of coexisting species, is interrupted
by bursts of activity. As the mutation rate increases, the duration and the
frequency of bursts increases. Eventually, when the mutation rate reaches a
certain threshold, the population is spread evenly throughout the genotype
space showing that natural selection only leads to multiple distinct species if
adaptation is allowed time to cause fixation.Comment: Paper submitted to Journal of Physics A. 13 pages, 4 figure
Measuring knowledge, attitudes and behavior of nurses in medication management. Cross-cultural comparisons in Italy and Malta
Medication errors are one of the most common causes of negative events affecting patient safety all over the world. Scientific literature divides the factors that contribute to the occurrence of harmful events into factors related to the characteristics of the healthcare workers and factors related to the organization of the drug management process. The aim of the study was to examine the knowledge, attitudes and behaviours related to medication errors among Italian and Maltese nurses
New insights into Chlamydiae persistence: an energy metabolism strategy?
Chlamydiaceae is a family of obligate intracellular bacteria generally considered energy parasites. Several studies have suggested that Chlamydiae are capable of independently producing energy and, more importantly, several genes involved in the energy metabolism are up-regulated during the persistent state. Thus, it has been suggested that chlamydial persistence could be a complex and flexible metabolic strategy designed to favor a lengthy survival in the host cell by evading the immune response. In conclusion, more detailed studies on the shift in the chlamydial energy metabolism, from the active to the persistent form, may be helpful in future to determine whether chlamydial persistence observed in vitro does occur in vivo and whether chronic sequelae of chlamydial diseases may be related to the persistence
Time-space focused intrusion of genetically unrelated arc magmas in the early Paleozoic Ross-Delamerian Orogen (Morozumi Range, Antarctica)
The growth of continental crust in accretionary orogenic belts takes place through repeated cycles of subduction–
accretion of rock units fromcontinental and oceanic magmatic arcs, supra-subduction zone backarcs and forearcs
loaded with continent-derived materials. An ancient example relevant to magmatic arc accretion models is
represented by the remnants of the Cambrian–Ordovician Ross Orogen in the Morozumi Range, Victoria Land
(Antarctica). There, late Neoproterozoic phyllites host an intrusive complex which preserves a remarkably
uncommon record of genetically unrelated magma pulses emplaced under a variable stress regime in a short
time span: (1) a dominant K-feldspar–phyric granite, (2) fine-grained dioritic stocks and dykes, (3) a
peraluminous granite; and (4) a tonalitic–granodioritic dyke swarm. Laserprobe U–Pb zircon dates cluster at
late Cambrian times for all these units, yet they carry differential cargoes of relict cores. Unique geochemical–
isotopic signatures for both the less evolved magmas (diorite and dyke tonalite) and the most acidic ones (granite
and peraluminous granite) indicate that each one of them originated from distinct sources at depth. Additionally,
field relationships and chemical evolutionary trends testify for a variety of shallow level open-system processes,
such as magma mingling/mixing between diorite and main granite magmas, as well as progressive incorporation
of the host schists by the dyke tonalite magma. In summary, crustal growth in the Morozumi intrusive complex
was contributed by fresh mantle magma issuing from the metasomatised mantle wedge, while the production
of othermelts did recycle different crustal portions/layers: the main granite derived fromGrenville-age granulitic
lower crust; the peraluminous granite from late Proterozoic upper crust, and the tonalite magmas derived from
subduction erosion-enriched subarc mantle and evolved by ingestion of local metasedimentary rocks. Overall,
the Morozumi intrusive complex yields evidence for emplacement in the same site at the same time of magmas
issuing fromdifferent sources that are usually found at a different depth in the arc lithospheric section. A likely scenario
to activate this specific mechanism of melt production is a subduction zone affected by subduction erosion
Hardware prototyping and validation of a W-ΔDOR digital signal processor
Microwave tracking, usually performed by on ground processing of the signals coming from a spacecraft, represents a crucial aspect in every deep-space mission. Various noise sources, including receiver noise, affect these signals, limiting the accuracy of the radiometric measurements obtained from the radio link. There are several methods used for spacecraft tracking, including the Delta-Differential One-Way Ranging (ΔDOR) technique. In the past years, European Space Agency (ESA) missions relied on a narrowband ΔDOR system for navigation in the cruise phase. To limit the adverse effect of nonlinearities in the receiving chain, an innovative wideband approach to ΔDOR measurements has recently been proposed. This work presents the hardware implementation of a new version of the ESA X/Ka Deep Space Transponder based on the new tracking technique named Wideband ΔDOR (W-ΔDOR). The architecture of the new transponder guarantees backward compatibility with narrowband ΔDOR
Protective role of carbonic anhydrases III and VII in cellular defense mechanisms upon redox unbalance
Under oxidative stress conditions, several constitutive cellular defense systems are activated, which involve both enzymatic systems
and molecules with antioxidant properties such as glutathione and vitamins. In addition, proteins containing reactive sulfhydryl
groups may eventually undergo reversible redox modifications whose products act as protective shields able to avoid further
permanent molecular oxidative damage either in stressful conditions or under pathological circumstances. After the recovery of
normal redox conditions, the reduced state of protein sulfhydryl groups is restored. In this context, carbonic anhydrases (CAs)
III and VII, which are human metalloenzymes catalyzing the reversible hydration of carbon dioxide to bicarbonate and proton,
have been identified to play an antioxidant role in cells where oxidative damage occurs. Both proteins are mainly localized in
tissues characterized by a high rate of oxygen consumption, and contain on their molecular surface two reactive cysteine
residues eventually undergoing S-glutathionylation. Here, we will provide an overview on the molecular and functional features
of these proteins highlighting their implications into molecular processes occurring during oxidative stress conditions
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