Searches for transient astrophysical sources often reveal unexpected classes of objects that are useful physical laboratories. In a recent survey for pulsars and fast transients, we have uncovered ...four millisecond-duration radio transients all more than 40° from the Galactic plane. The bursts' properties indicate that they are of celestial rather than terrestrial origin. Host galaxy and intergalactic medium models suggest that they have cosmological redshifts of 0.5 to 1 and distances of up to 3 gigaparsecs. No temporally coincident x-or gamma-ray signature was identified in association with the bursts. Characterization of the source population and identification of host galaxies offers an opportunity to determine the baryonic content of the universe.
The origins and development of the arid and highly seasonal steppe-desert biome in Central Asia, the largest of its kind in the world, remain largely unconstrained by existing records. It is unclear ...how Cenozoic climatic, geological, and biological forces, acting at diverse spatial and temporal scales, shaped Central Asian ecosystems through time. Our synthesis shows that the Central Asian steppe-desert has existed since at least Eocene times but experienced no less than two regime shifts, one at the Eocene-Oligocene Transition and one in the mid-Miocene. These shifts separated three successive "stable states," each characterized by unique floral and faunal structures. Past responses to disturbance in the Asian steppe-desert imply that modern ecosystems are unlikely to recover their present structures and diversity if forced into a new regime. This is of concern for Asian steppes today, which are being modified for human use and lost to desertification at unprecedented rates.
The number of subduction zones that facilitated the northward translation of the Anatolide‐Tauride continental terrane derived from Gondwana to the southern margin of Eurasia at the longitude of ...western Turkey is debated. We hypothesized that if two north dipping subduction zones facilitated incipient collision in western Turkey, a late Cretaceous arc would have formed within the Neotethys and along the southern margin of Eurasia. To determine if an island arc formed within the Neotethys we investigated the sedimentary record of the Central Sakarya basin, which was deposited along the southern margin of Eurasia from 85 to 45 million years ago. Detrital zircon deposited within the lower levels of the Central Sakarya basin (the Değirmenözü Formation) are associated with south to north‐directed paleocurrents and exhibit a unimodal late Cretaceous age peak sourced from isotopically juvenile mantle melts. Zircon maximum depositional ages from the Değirmenözü Formation cluster between 95 and 90 Ma and are 5–10 Myr older than biostratigraphic depositional ages. Between 95 and 80 Ma, a 12‐unit shift from mantle to crustal derived εHf values occurs in the overlying Yenipazar Formation. We explain the absence of Paleozoic, Eurasian‐sourced detrital zircon, the rapid shift from mantle to crustal derived εHf values, and lag time in terms of passive margin subduction within an isolated intra‐oceanic subduction zone, whose island arc was reworked from south to north into the Central Sakarya basin during incipient collision. Thus, widely outcropping late Cretaceous plutonic rocks within Eurasia must have belonged to an additional convergent margin.
Key Points
We leveraged the isotopic signature of subducted passive margin to test incipient collision models in northwest Turkey
Passive margin subduction resulted in the development of an isolated intra‐oceanic basin
Two north dipping subduction zones facilitated incipient collision in the region
Debate persists concerning the timing and geodynamics of intercontinental collision, style of syncollisional deformation, and development of topography and fold‐and‐thrust belts along the ...>1,700‐km‐long İzmir‐Ankara‐Erzincan suture zone (İAESZ) in Turkey. Resolving this debate is a necessary precursor to evaluating the integrity of convergent margin models and kinematic, topographic, and biogeographic reconstructions of the Mediterranean domain. Geodynamic models argue either for a synchronous or diachronous collision during either the Late Cretaceous and/or Eocene, followed by Eocene slab breakoff and postcollisional magmatism.
We investigate the collision chronology in western Anatolia as recorded in the sedimentary archives of the 90‐km‐long Sarıcakaya Basin perched at shallow structural levels along the İAESZ. Based on new zircon U‐Pb geochronology and depositional environment and sedimentary provenance results, we demonstrate that the Sarıcakaya Basin is an Eocene sedimentary basin with sediment sourced from both the İAESZ and Söğüt Thrust fault to the south and north, respectively, and formed primarily by flexural loading from north‐south shortening along the syncollisional Söğüt Thrust. Our results refine the timing of collision between the Anatolides and Pontide terranes in western Anatolia to Maastrichtian‐Middle Paleocene and Early Eocene crustal shortening and basin formation. Furthermore, we demonstrate contemporaneous collision, deformation, and magmatism across the İAESZ, supporting synchronous collision models. We show that regional postcollisional magmatism can be explained by renewed underthrusting instead of slab breakoff. This new İAESZ chronology provides additional constraints for kinematic, geodynamic, and biogeographic reconstructions of the Mediterranean domain.
Plain Language Summary
The timeline of continent‐continent collisions and the creation of topography, volcanic activity, and thrust faults in Anatolia (Turkey) are highly debated. Continent‐continent collision occurs when oceanic crust between two continental plates has been entirely consumed back into the Earth's interior along a subduction zone. Previous work in western Anatolia suggests that 66–60 million years ago continent‐continent collision was followed by catastrophic rupturing of the sinking oceanic crust, a process known as slab breakoff. Numerical models and field observations demonstrate that slab breakoff is followed by rebound and surface uplift of the overriding plate producing local extension and interrupting sedimentation. By studying a syncollisional sedimentary basin, we determined the sedimentary infill is 52–48 million years old and sourced from both continents, indicating collision must have occurred prior to 52 million years ago. This timing validates previous predictions of synchronous collision across western and central Turkey. Furthermore, the timing of basin infill directly overlaps with the timing of proposed slab breakoff. Our observations and data contradict predictions of the slab breakoff model making breakoff an unlikely candidate. Instead, we propose continued shortening and collision as the cause for the co‐occurrence of sedimentary basin formation, deformation, and volcanism observed throughout western Turkey.
Key Points
The Sarıcakaya Basin is an Eocene sedimentary basin formed by flexural loading from the syncollisional Sogut Thrust fault
Sarıcakaya Basin magmatism and deformation chronology are similar to central Anatolia, supporting synchronous collision across Anatolia
Eocene thrust loading, sedimentation, and convergence in the Sarıcakaya Basin contradict previous interpretations of Eocene slab breakoff
Dental agenesis is the most common developmental anomaly in humans and is frequently associated with several other oral abnormalities. Whereas the incidence of missing teeth may vary considerably ...depending on dentition, gender, and demographic or geographic profiles, distinct patterns of agenesis have been detected in the permanent dentition. These frequently involve the last teeth of a class to develop (I2, P2, M3) suggesting a possible link with evolutionary trends. Hypodontia can either occur as an isolated condition (non‐syndromic hypodontia) involving one (80% of cases), a few (less than 10%) or many teeth (less than 1%), or can be associated with a systemic condition or syndrome (syndromic hypodontia), essentially reflecting the genetically and phenotypically heterogeneity of the condition. Based on our present knowledge of genes and transcription factors that are involved in tooth development, it is assumed that different phenotypic forms are caused by different genes involving different interacting molecular pathways, providing an explanation not only for the wide variety in agenesis patterns but also for associations of dental agenesis with other oral anomalies. At present, the list of genes involved in human non‐syndromic hypodontia includes not only those encoding a signaling molecule (TGFA) and transcription factors (MSX1 and PAX9) that play critical roles during early craniofacial development, but also genes coding for a protein involved in canonical Wnt signaling (AXIN2), and a transmembrane receptor of fibroblast growth factors (FGFR1). Our objective was to review the current literature on the molecular mechanisms that are responsible for selective dental agenesis in humans and to present a detailed overview of syndromes with hypodontia and their causative genes. These new perspectives and future challenges in the field of identification of possible candidate genes involved in dental agenesis are discussed.
We have used millisecond pulsars (MSPs) from the southern High Time Resolution Universe (HTRU) intermediate latitude survey area to simulate the distribution and total population of MSPs in the ...Galaxy. Our model makes use of the scalefactor method, which estimates the ratio of the total number of MSPs in the Galaxy to the known sample. Using our best-fitting value for the z-height, z = 500 pc, we find an underlying population of MSPs of 8.3(±4.2) × 104 sources down to a limiting luminosity of L
min = 0.1 mJy kpc2 and a luminosity distribution with a steep slope of d log N/d log L = −1.45 ± 0.14. However, at the low end of the luminosity distribution, the uncertainties introduced by small number statistics are large. By omitting very low luminosity pulsars, we find a Galactic population above L
min = 0.2 mJy kpc2 of only 3.0(±0.7) × 104 MSPs. We have also simulated pulsars with periods shorter than any known MSP, and estimate the maximum number of sub-MSPs in the Galaxy to be 7.8(±5.0) × 104 pulsars at L = 0.1 mJy kpc2. In addition, we estimate that the high and low latitude parts of the southern HTRU survey will detect 68 and 42 MSPs, respectively, including 78 new discoveries. Pulsar luminosity, and hence flux density, is an important input parameter in the model. Some of the published flux densities for the pulsars in our sample do not agree with the observed flux densities from our data set, and we have instead calculated average luminosities from archival data from the Parkes Telescope. We found many luminosities to be very different than their catalogue values, leading to very different population estimates. Large variations in flux density highlight the importance of including scintillation effects in MSP population studies.
We report on the discovery of four millisecond pulsars (MSPs) in the High Time Resolution Universe (HTRU) pulsar survey being conducted at the Parkes 64 m radio telescope. All four MSPs are in binary ...systems and are likely to have white dwarf companions. In addition, we present updated timing solutions for 12 previously published HTRU MSPs, revealing new observational parameters such as five proper motion measurements and significant temporal dispersion measure variations in PSR J1017−7156. We discuss the case of PSR J1801−3210, which shows no significant period derivative Ṗ after four years of timing data. Our best-fitting solution shows a Ṗ of the order of 10−23, an extremely small number compared to that of a typical MSP. However, it is likely that the pulsar lies beyond the Galactic Centre, and an unremarkable intrinsic Ṗ is reduced to close to zero by the Galactic potential acceleration. Furthermore, we highlight the potential to employ PSR J1801−3210 in the strong equivalence principle test due to its wide and circular orbit. In a broader comparison with the known MSP population, we suggest a correlation between higher mass functions and the presence of eclipses in 'very low mass binary pulsars', implying that eclipses are observed in systems with high orbital inclinations. We also suggest that the distribution of the total mass of binary systems is inversely related to the Galactic height distribution. Finally, we report on the first detection of PSRs J1543−5149 and J1811−2404 as gamma-ray pulsars.
Since the divertor for ITER has been designed to operate in a partially detached mode on the basis of SOLPS calculations, the understanding of the physics of detachment is crucial. The results of ...SOLPS calculations with fluid and Monte-Carlo neutrals; with pure deuterium and with carbon impurities; with and without drifts; with horizontal and vertical targets; and with and without ELMs will be presented. In addition, the possible role of fast electrons which can be expected to strongly modify the ionization rates without much affecting the recombination rates, will be investigated. Calculations with SOLPS indicate a strong enhancement of the ionization rate in the inner divertor leg by the fast electrons, followed by an enhanced volume recombination of these ions giving rise to an enhanced “volume recycling”. This can then increase the volumetric losses in the inner divertor region.
•We study the depositional history of the fossiliferous Orhaniye Basin, Anatolia.•The Orhaniye Basin initially developed as a forearc basin during the Maastrichtian.•The Orhaniye Basin evolved into a ...foreland basin between the Paleocene and 44Ma.•Our dating indicates faunal endemism in Anatolia for most of the early Paleogene.
Located along the İzmir-Ankara-Erzincan Suture (IAES), the Maastrichtian - Paleogene Orhaniye Basin has yielded a highly enigmatic -yet poorly dated- Paleogene mammal fauna, the endemic character of which has suggested high faunal provincialism associated with paleogeographic isolation of the Anatolian landmass during the early Cenozoic. Despite its biogeographic significance, the tectono-stratigraphic history of the Orhaniye Basin has been poorly documented. Here, we combine sedimentary, magnetostratigraphic, and geochronological data to infer the chronology and depositional history of the Orhaniye Basin. We then assess how our new data and interpretations for the Orhaniye Basin impact (1) the timing and mechanisms of seaway closure along the IAES and (2) the biogeographic evolution of Anatolia.
Our results show that the Orhaniye Basin initially developed as a forearc basin during the Maastrichtian, before shifting to a retroarc foreland basin setting sometime between the early Paleocene and 44Ma. This chronology supports a two-step scenario for the assemblage of the central Anatolian landmass, with incipient collision during the Paleocene – Early Eocene and final seaway retreat along the IAES during the earliest Late Eocene after the last marine incursion into the foreland basin. Our dating for the Orhaniye mammal fauna (44–43Ma) indicates the persistence of faunal endemism in northern Anatolia until at least the late Lutetian despite the advanced stage of IAES closure. The tectonic evolution of dispersal corridors linking northern Anatolia with adjacent parts of Eurasia was not directly associated with IAES closure and consecutive uplifts, but rather with the build-up of continental bridges on the margins of Anatolia, in the Alpine and Tibetan-Himalayan orogens.
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