5,178 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
Ontogeny of Hemidactylus (Gekkota, Squamata) with emphasis on the limbs
Squamate reptiles constitute a major component of the world's terrestrial vertebrate diversity, encompassing many morphotypes related to ecological specialization. Specifically, Gekkota, the sister clade to most other squamates, have highly specialized autopodia, which have been linked to their ecological plasticity. In this study, a developmental staging table of the gecko Hemidactylus, housed at the Museum fur Naturkunde, is established. Twelve post-ovipositional stages are erected, monitoring morphological embryological transitions in eye, ear, nose, heart, limbs, pharyngeal arches, and skin structures. Ecomorphological specializations in the limbs include multiple paraphalanges, hypothesized to aid in supporting the strong muscles, that are situated adjacent to metacarpal and phalangeal heads. Furthermore, some phalanges are highly reduced in manual digits III and IV and pedal digits III, IV, and V. Development, composition, and growth of limb elements is characterized in detail via mu CT, histochemistry, and bone histological analysis. Using known life history data from two individuals, we found an average lamellar bone accretion rate in the humeral diaphysis comparable to that of varanids. Various adult individuals also showed moderate to extensive remodeling features in their long bone cortices, indicating that these animals experience a highly dynamic bone homeostasis during their growth, similar to some other medium-sized to large squamates. This study of in-ovo development of the gecko Hemidactylus and its ecomorphological specializations in the adult autopodia, enlarges our knowledge of morphological trait evolution and of limb diversity within the vertebrate phylum.Peer reviewe
Ni(0) catalysed homo-coupling reactions: a novel route towards the synthesis of multinuclear ruthenium polypyridine complexes featuring made-to-order properties.
A new synthetic procedure for the efficient preparation of dinuclear ruthenium(II) polypyridyl complexes is reported. The compounds
synthesised are [(bpy)2Ru(BPBT)Ru(bpy)2](PF6)2 and [(bpy)2Ru(BPZBT)Ru(bpy)2](PF6)2 (bpys2,29-bipyridine; H2BPBTs5,59-
bis(pyridin-2-yl)-3,39-bis(1,2,4-triazole); H2BPZBTs5,59-bis(pyrazin-2-yl)-3,39-bis(1,2,4-triazole). Electrochemical experiments show
that the two dinuclear systems investigated exhibit pH switchable intercomponent interactions
Production of Entangled X-rays through Nonlinear Double Compton Scattering
An accessible source for the production of entangled x-rays is crucial for
the field of high-energy quantum optics. Here, we present a detailed analysis
of the entanglement and polarisation of the two photons emitted by an electron
in an intense laser wave (nonlinear double Compton scattering), by working
within the framework of strong-field QED. By identifying a contribution to the
emission probability stemming from the electron being on-shell or off-shell
between the two photons emissions, we show that the entangled photons are
generated via the off-shell contribution, which can be distinguished from those
emitted via the on-shell channel by a polarisation measurement. We also provide
an intuitive picture to explain the entanglement and propose an experiment to
produce and isolate entangled x-rays.Comment: Contains an article and Supplemental Materia
Synthesis and characterisation of ruthenium complexes containing a pendent catechol ring
A series of [Ru(bipy)âL]âș and [Ru(phen)âL]âș complexes where L is 2-[5-(3,4-dimethoxyphenyl)-4H-1,2,4-triazol-3-yl]pyridine (HL1) and 4-(5-pyridin-2-yl-4H-1,2,4-triazol-3-yl)benzene-1,2-diol (HL2) are reported. The compounds obtained have been characterised using X-ray crystallography, NMR, UV/Vis and emission spectroscopies. Partial deuteriation is used to determine the nature of the emitting state and to simplify the NMR spectra. The acid-base properties of the compounds are also investigated. The electronic structures of [Ru(bipy)âL1]âș and Ru(bipy)âHL1]ÂČâș are examined using ZINDO. Electro and spectroelectrochemical studies on [Ru(bipy)â(L2)]âș suggest that proton transfer between the catechol and triazole moieties on L2 takes place upon oxidation of the L2 ligand
Salivary microRNAs: Diagnostic markers of mild traumatic brain injury in contact-sport
Concussion is difficult to diagnose, particularly when symptoms are atypical or late in presenting. An accurate and timely initial assessment is crucial for clinical management. Cerebral spinal fluid (CSF) and blood markers of traumatic brain injury show promising results but their clinical applicability in concussion has significant limitations. In the study, we explored saliva as a new source of biomarkers of concussion. Saliva samples of concussed players were collected after 48â72 h from concussion and analyzed by high-throughput technologies. A discovery group of 10 concussed rugby professional and semiprofessional athletes and 10 non-concussed matched controls was used for the analysis of 92 inflammatory proteins by the Proseek-Multiplex-Inflammation technology. In addition, saliva samples of 6 concussed and 6 non-concussed athletes were used to screen 800 human microRNAs (miRNAs) by the Nanostring Technology. The results were then validated by RT-qPCR in an enlarged cohort (validation group) comprising 22 concussed athletes. Results showed, no significant variations of the 65 inflammatory proteins detected in saliva between groups but 5 microRNAs, miR-27b-3p (p = 0.016), let-7i-5p (p = 0.001), miR-142-3p (p = 0.008), miR-107 (p = 0.028), miR-135b-5p (p = 0.017) significantly upregulated in concussed athletes. Univariate ROC curve analysis showed that the differentially expressed miRNAs could be considered good classifiers of concussion. Further analyses showed significant correlation between these microRNAs and Reaction Time component of the ImPACT concussion assessment tool. In addition, biocomputation analysis predicted the involvement of these microRNAs in important biological processes that might be related to trauma, such as response to hypoxia, cell death, neurogenesis, axon repair and myelination. Ease of access and non-invasiveness of saliva samples make these biomarkers particularly suitable for concussion assessment
An Application of the Three-Step Test-Interview (TSTI) in the Validation of the Relational Depth Frequency Scale
The main objective of this study is to evaluate the utility of a new qualitative scale development methodologyâThree-Step Test-Interview (TSTI)âin its first application in the validation of a psychotherapy scale: The Relational Depth Frequency Scale (RDFS). The TSTI is a cognitive pretesting method designed to uncover potential problems in scale construction. The RDFS is a six-item unidimensional scale of in-depth therapeutic relating, designed for use in large-scale outcome studies. Following the creation of an item pool and âexpert ratings,â a purposive sample of four therapists and four clients (five females, three males, mean age: 49 years) was recruited to take part in the TSTI with the view to refine the original 36-item RDFS prior to psychometric exploration. Structured observations pointed to problems in test-takersâ patterns of responses in relation to theoretical knowledge of the relational depth construct. Issues uncovered and addressed included some misinterpretations of instructions and items, redundant content, double-barreled items, and test-takersâ reactions to intimate content wording. The method supported the refinement of the RDFS including amendment to its instructions and the removal of problematic items. TSTI results produced knowledge on the scale which could not be captured with statistical methods
âBreaking up is hard to doâ: the formation and resolution of sister chromatid intertwines
The absolute necessity to resolve every intertwine between the two strands of the DNA double helix provides a massive challenge to the cellular processes that duplicate and segregate chromosomes. Although the overwhelming majority of intertwines between the parental DNA strands are resolved during DNA replication, there are numerous chromosomal contexts where some intertwining is maintained into mitosis. These mitotic sister chromatid intertwines (SCIs) can be found as; short regions of unreplicated DNA, fully replicated and intertwined sister chromatidsâcommonly referred to as DNA catenationâand as sister chromatid linkages generated by homologous recombination-associated processes. Several overlapping mechanisms, including intra-chromosomal compaction, topoisomerase action and Holliday junction resolvases, ensure that all SCIs are removed before they can prevent normal chromosome segregation. Here, I discuss why some DNA intertwines persist into mitosis and review our current knowledge of the SCI resolution mechanisms that are employed in both prokaryotes and eukaryotes, including how deregulating SCI formation during DNA replication or disrupting the resolution processes may contribute to aneuploidy in cancer
Time dependence of the electron and positron components of the cosmic radiation measured by the PAMELA experiment between July 2006 and December 2015
Cosmic-ray electrons and positrons are a unique probe of the propagation of
cosmic rays as well as of the nature and distribution of particle sources in
our Galaxy. Recent measurements of these particles are challenging our basic
understanding of the mechanisms of production, acceleration and propagation of
cosmic rays. Particularly striking are the differences between the low energy
results collected by the space-borne PAMELA and AMS-02 experiments and older
measurements pointing to sign-charge dependence of the solar modulation of
cosmic-ray spectra. The PAMELA experiment has been measuring the time variation
of the positron and electron intensity at Earth from July 2006 to December 2015
covering the period for the minimum of solar cycle 23 (2006-2009) till the
middle of the maximum of solar cycle 24, through the polarity reversal of the
heliospheric magnetic field which took place between 2013 and 2014. The
positron to electron ratio measured in this time period clearly shows a
sign-charge dependence of the solar modulation introduced by particle drifts.
These results provide the first clear and continuous observation of how drift
effects on solar modulation have unfolded with time from solar minimum to solar
maximum and their dependence on the particle rigidity and the cyclic polarity
of the solar magnetic field.Comment: 11 pages, 2 figure
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