Signatures of the excitonic memory effects in four-wave mixing processes in cavity polaritons

We report the signatures of the exciton correlation effects with finite memory time in frequency domain degenerate four-wave mixing (DFWM) in semiconductor microcavity. By utilizing the polarization selection rules, we discriminate instantaneous, mean field interactions between excitons with the same spins, long-living correlation due to the formation of biexciton state by excitons with opposite spins, and short-memory correlation effects in the continuum of unbound two-exciton states. The DFWM spectra give us the relative contributions of these effects and the upper limit for the time of the exciton-exciton correlation in the unbound two-exciton continuum. The obtained results reveal the basis of the cavity polariton scattering model for the DFWM processes in high-Q GaAs microcavity.Comment: 11 pages, 1 figur

The source of A-type magmas in two contrasting settings: U–Pb, Lu–Hf and Re–Os isotopic constraints

The sources of post-orogenic A-type magmas from two distinct geodynamic settings are compared. The end of the ca. 514–480 Ma Delamerian Orogeny, southeastern South Australia, was marked by ~ 10 Myr of bimodal A-type magmatism, driven by convective removal of thickened lithosphere. Initial Os and Hf isotope ratios record a heterogeneous lithospheric mantle source, with some input from aesthenospheric mantle. Mafic parental melts fractionated to produce the granites. In contrast, initial Os isotope ratios of the A-type magmas that comprise the ca. 1598–1583 Ma Mesoproterozoic Gawler Felsic Large Igneous Province, central South Australia, record a dominant evolved lower crust component. However, initial Hf isotope ratios from these samples are depleted, indicating a mantle source for lithophile elements. This voluminous, bimodal magmatism lasted for ~ 15 Myr, and ended the Wartakan Orogeny. In both cases the homogenisation of chemical (rheological) heterogeneities, inherited from terrain amalgamation and orogenic thickening, strengthened the lithosphere. The contemporaneous fusion of heterogeneous mantle ± crust may represent a common, stabilising influence on the lithospheric column regardless of tectono-magmatic setting

The Large Magellanic Cloud and the Distance Scale

The Magellanic Clouds, especially the Large Magellanic Cloud, are places where multiple distance indicators can be compared with each other in a straight-forward manner at considerable precision. We here review the distances derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing Binaries, and show that the results from these distance indicators generally agree to within their errors, and the distance modulus to the Large Magellanic Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science. From a presentation at the conference The Fundamental Cosmic Distance Scale: State of the Art and the Gaia Perspective, Naples, May 201

Toward an internally consistent astronomical distance scale

Accurate astronomical distance determination is crucial for all fields in astrophysics, from Galactic to cosmological scales. Despite, or perhaps because of, significant efforts to determine accurate distances, using a wide range of methods, tracers, and techniques, an internally consistent astronomical distance framework has not yet been established. We review current efforts to homogenize the Local Group's distance framework, with particular emphasis on the potential of RR Lyrae stars as distance indicators, and attempt to extend this in an internally consistent manner to cosmological distances. Calibration based on Type Ia supernovae and distance determinations based on gravitational lensing represent particularly promising approaches. We provide a positive outlook to improvements to the status quo expected from future surveys, missions, and facilities. Astronomical distance determination has clearly reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press (chapter 8 of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Age

Provenance of the Early Mesoproterozoic Radium Creek Group in the northern Mount Painter Inlier: Correlating isotopic signatures to inform tectonic reconstructions

New in situ zircon LA-ICPMS geochronologic and Hf-isotope data from the Radium Creek Group within the Mount Painter Inlier provide important temporal constraints on the Early Mesoproterozoic palaeogeography of eastern Proterozoic Australia. The entire Radium Creek Group was deposited in a single basin forming phase, and has a maximum depositional age of 1595. ±. 3.7. Ma. Detrital zircon from these metasedimentary rocks have U-Pb age populations at ca. 1595. Ma, 1660-1680. Ma, 1710-1780. Ma, ca. 1850. Ma and ca. 2500. Ma. These grains are characterised by isotopically diverse and evolved sources, and have crystallised within predominantly felsic igneous host-rocks. The relative age spectra and isotopic character has more similarity with the Gawler Craton than the Arunta Block, Curnamona Province or the Mount Isa Inlier. These observations suggest that the Mount Painter Province was adjacent to the Gawler Craton in the Early Mesoproterozoic. Our data supports a coherent South Australian Craton at ca. 1595. Ma and a contiguous continental mass that included the North and South Australian cratons. The Mount Painter Inlier occupied a complex plate tectonic setting in the overriding plate of two convergent margins. © 2014 Elsevier B.V

Astronomical Distance Determination in the Space Age: Secondary Distance Indicators

The formal division of the distance indicators into primary and secondary leads to difficulties in description of methods which can actually be used in two ways: with, and without the support of the other methods for scaling. Thus instead of concentrating on the scaling requirement we concentrate on all methods of distance determination to extragalactic sources which are designated, at least formally, to use for individual sources. Among those, the Supernovae Ia is clearly the leader due to its enormous success in determination of the expansion rate of the Universe. However, new methods are rapidly developing, and there is also a progress in more traditional methods. We give a general overview of the methods but we mostly concentrate on the most recent developments in each field, and future expectations. © 2018, The Author(s)

Lower crustal assimilation in oceanic arcs: Insights from an osmium isotopic study of the Lesser Antilles

We present whole rock 187Os/188Os data for the most mafic lavas along the Lesser Antilles arc (MgO = 5–17 wt.%) and for the subducting basalt and sediments. 187Os/188Os ratios vary from 0.127 to 0.202 in the arc lavas. Inverse correlations between 187Os/188Os and Os concentrations and between 187Os/188Os and indices of differentiation such as MgO suggests that assimilation, rather than source variation, is responsible for the range of Os isotopic variation observed. 87Sr/86Sr, La/Sm and Sr/Th are also modified by assimilation since they all correlate with 187Os/188Os. The assimilant is inferred to have a MORB-like 87Sr/86Sr with high Sr (>700 ppm), low light on middle and heavy rare earth elements (L/M-HREE; La/Sm ∼2.5) and 187Os/188Os > 0.2. Such compositional features are likely to correspond to a plagioclase-rich early-arc cumulate. Given that assimilation affects lavas that were last stored at more than 5 kbar, assimilation must occur in the middle-lower crust. Only a high MgO picrite from Grenada escaped obvious assimilation (MgO = 17% wt.%) and could reflect mantle source composition. It has a very radiogenic 87Sr/86Sr (0.705) but a 187Os/188Os ratio that overlaps the mantle range (0.127). 187Os/188Os and 87Sr/88Sr ratios of the sediments and an altered basalt from the subducting slab vary from 0.18 to 3.52 and 0.708 to 0.714. We therefore suggest that, unlike Sr, no Os from the slab was transferred to the parental magmas. Os may be either retained in the mantle wedge or even returned to the deep mantle in the subducting slab