46 research outputs found
Anisotropic optical conductivity of the putative Kondo insulator CeRuSn
Kondo insulators and in particular their non-cubic representatives have
remained poorly understood. Here we report on the development of an anisotropic
energy pseudogap in the tetragonal compound CeRuSn employing optical
reflectivity measurements in broad frequency and temperature ranges, and local
density approximation plus dynamical mean field theory calculations. The
calculations provide evidence for a Kondo insulator-like response within the
plane and a more metallic response along the c axis and qualitatively
reproduce the experimental observations, helping to identify their origin
Effects of electronic correlations and disorder on the thermopower of NaxCoO2
For the thermoelectric properties of NaxCoO2, we analyze the effect of local
Coulomb interaction and (disordered) potential differences for Co-sites with
adjacent Na-ion or vacancy. The disorder potential alone increases the
resistivity and reduces the thermopower, while the Coulomb interaction alone
leads only to minor changes compared to the one-particle picture of the local
density approximation. Only combined, these two terms give rise to a
substantial increase of the thermopower: the number of (quasi-)electrons around
the Fermi level is much more suppressed than that of the (quasi-)holes. Hence,
there is a particle-hole imbalance acting in the same direction as a similar
imbalance for the group velocities. Together, this interplay results in a large
positive thermopower. Introducing a thermoelectric spectral density, we located
the energies and momenta regions most relevant for the thermopower and changes
thereof.Comment: 23 pages, 27 figures, accepted at PR
Charge Kondo Effect in Thermoelectric Properties of Lead Telluride doped with Thallium Impurities
We investigate the thermoelectric properties of PbTe doped with a small
concentration of Tl impurities acting as acceptors and described by
Anderson impurities with negative on-site (effective) interaction. The
resulting charge Kondo effect naturally accounts for a number of the low
temperature anomalies in this system, including the unusual doping dependence
of the carrier concentration, the Fermi level pinning and the self-compensation
effect. The Kondo anomalies in the low temperature resistivity at temperatures
and the -dependence of the residual resistivity are
also in good agreement with experiment. Our model also captures the qualitative
aspects of the thermopower at higher temperatures for high
dopings () where transport is expected to be largely dominated by
carriers in the heavy hole band of PbTe.Comment: chapter contributed to 'New Materials for Thermoelectric
Applications: Theory and Experiment' Springer Series: NATO Science for Peace
and Security Series - B: Physics and Biophysics, pp. 67-80, ed. Veljko
Zlati\'c, and Alex Hewson (Editor). ISBN: 978-94-007-4983-2 (2013
Genomic and dietary discontinuities during the Mesolithic and Neolithic in Sicily
Summary Sicily is a key region for understanding the agricultural transition in the Mediterranean, due to its central position. Here, we present genomic and stable isotopic data for 19 prehistoric Sicilians covering the Mesolithic to Bronze Age periods (10,700-4,100 yBP). We find that Early Mesolithic hunter-gatherers (HGs) from Sicily are a highly drifted lineage of the Early Holocene western European HGs, while Late Mesolithic HGs carry ∼20% ancestry related to northern and (south)eastern European HGs, indicating substantial gene flow. Early Neolithic farmers are genetically most similar to farmers from the Balkans and Greece, with only ∼7% ancestry from local Mesolithic HGs. The genetic discontinuities during the Mesolithic and Early Neolithic match changes in material culture and diet. Three outlying individuals dated to ∼8,000 yBP, however, suggest that hunter-gatherers interacted with incoming farmers at Grotta dell’Uzzo, resulting in a mixed economy and diet for a brief interlude at the Mesolithic-Neolithic transition.- Introduction - Results -- Genetically-distinct groups of prehistoric Sicilians -- Genomic and dietary transitions in Sicily during the Mesolithic and Early Neolithic -- Did Sicilian Late Mesolithic foragers adopt some aspects of early farming? - Discussion -- Limitations of the stud
Genomic and dietary transitions during the Mesolithic and Early Neolithic in Sicily
Southern Italy is a key region for understanding the agricultural transition in the Mediterranean due to its central position. We present a genomic transect for 19 prehistoric Sicilians that covers the Early Mesolithic to Early Neolithic period. We find that the Early Mesolithic hunter-gatherers (HGs) are a highly drifted sister lineage to Early Holocene western European HGs, whereas a quarter of the Late Mesolithic HGs ancestry is related to HGs from eastern Europe and the Near East. This indicates substantial gene flow from (south-)eastern Europe between the Early and Late Mesolithic. The Early Neolithic farmers are genetically most similar to those from the Balkan and Greece, and carry only a maximum of ~7% ancestry from Sicilian Mesolithic HGs. Ancestry changes match changes in dietary profile and material culture, except for two individuals who may provide tentative initial evidence that HGs adopted elements of farming in Sicily
Dutch randomized trial comparing standard catheter-directed thrombolysis versus Ultrasound-accElerated Thrombolysis for thromboembolic infrainguinal disease (DUET): design and rationale
Background: The use of thrombolytic therapy in the treatment of thrombosed infrainguinal native arteries and bypass grafts has increased over the years. Main limitation of this treatment modality, however, is the occurrence of bleeding complications. Low intensity ultrasound (US) has been shown to accelerate enzymatic thrombolysis, thereby reducing therapy time. So far, no randomized trials have investigated the application of US-accelerated thrombolysis in the treatment of thrombosed infra-inguinal native arteries or bypass grafts. The DUET study (Dutch randomized trial comparing standard catheter-directed thrombolysis versus Ultrasound-accElerated Thrombolysis for thrombo-embolic infrainguinal disease) is designed to assess whether US-accelerated thrombolysis will reduce therapy time significantly compared with standard catheter-directed thrombolysis.Methods/design: Sixty adult patients with recently (between 1 and 7 weeks) thrombosed infrainguinal native arteries or bypass grafts with acute limb ischemia class I or IIa, according to the Rutherford classification for acute ischemia, will be randomly allocated to either standard thrombolysis (group A) or US-accelerated thrombolysis (group B). Patients will be recruited from 5 teaching hospitals in the Netherlands during a 2-year period. The primary endpoint is the duration of catheter-directed thrombolysis needed for uninterrupted flow in the thrombosed infrainguinal native artery or bypass graft, with outflow through at least 1 crural artery.Discussion: The DUET study is a randomized controlled trial that will provide evidence of whether US-accelerated thrombolysis will significantly reduce therapy time in patients with recently thrombosed infrainguinal native arteries or bypass grafts, without an increase in complications. Trial registration: Current Controlled Trials ISRCTN72676102
Ten millennia of hepatitis B virus evolution
Hepatitis B virus (HBV) has been infecting humans for millennia and remains a global health problem, but its past diversity and dispersal routes are largely unknown. We generated HBV genomic data from 137 Eurasians and Native Americans dated between ~10,500 and ~400 years ago. We date the most recent common ancestor of all HBV lineages to between ~20,000 and 12,000 years ago, with the virus present in European and South American hunter-gatherers during the early Holocene. After the European Neolithic transition, Mesolithic HBV strains were replaced by a lineage likely disseminated by early farmers that prevailed throughout western Eurasia for ~4000 years, declining around the end of the 2nd millennium BCE. The only remnant of this prehistoric HBV diversity is the rare genotype G, which appears to have reemerged during the HIV pandemic