The de Haas-van Alphen effect across the metamagnetic transition in Sr3_3Ru2_2O7_7

We report a study of the de Haas-van Alphen (dHvA) effect on the itinerant metamagnet Sr$_3$Ru$_2$O$_7$. Extremely high sample purity allows the observation of dHvA oscillations both above and below the metamagnetic transition field of 7.9 T. The quasiparticle masses are fairly large away from the transition, and are enhanced by up to an extra factor of three as the transition is approached, but the Fermi surface topography change is quite small. The results are qualitatively consistent with a field-induced Stoner transition in which the mass enhancement is the result of critical fluctuations.Comment: 4 pages, 3 figure

First Observation of Quantum Oscillations in the Ferromagnetic Superconductor UCoGe

We succeeded in growing high quality single crystals of the ferromagnetic superconductor UCoGe and measured the magnetoresistance at fields up to 34T. The Shubnikov-de Haas signal was observed for the first time in a U-111 system (UTGe, UTSi, T: transition metal). A small pocket Fermi surface (F~1kT) with large cyclotron effective mass 25m0 was detected at high fields above 22T, implying that UCoGe is a low carrier system accompanyed with heavy quasi-particles. The observed frequency decreases with increasing fields, indicating that the volume of detected Fermi surface changes nonlinearly with field. The cyclotron mass also decreases, which is consistent with the decrease of the A coefficient of resistivity.Comment: 5 pages, 5 figures, accepted for publication in J. Phys. Soc. Jp

High-field magnetization of the 3d heavy-fermion system LiV2_2O4−d_{4-d} (d = 0, 0.08)

Metamagnetic behavior has been observed in LiV2O4 powder sample around 38 T at 4.2 K. On the other hand, magnetization for oxygen deficient LiV2O3.92 shows no indication of metamagnetism up to 40 T, and shows substantially reduced magnetic moment compared to that of LiV2O4. These results suggest that ferromagnetic interaction is strongly enhanced by magnetic fields in LiV2O4, whereas antiferromagnetic interaction is dominant in LiV2O3.92.Comment: 9 pages, 3 figures, to be published in J. Phys.: Condens. Matte

Molecular Evolutionary Analysis of the Influenza A(H1N1)pdm, May–September, 2009: Temporal and Spatial Spreading Profile of the Viruses in Japan

BACKGROUND: In March 2009, pandemic influenza A(H1N1) (A(H1N1)pdm) emerged in Mexico and the United States. In Japan, since the first outbreak of A(H1N1)pdm in Osaka and Hyogo Prefectures occurred in the middle of May 2009, the virus had spread over 16 of 47 prefectures as of June 4, 2009. METHODS/PRINCIPAL FINDINGS: We analyzed all-segment concatenated genome sequences of 75 isolates of A(H1N1)pdm viruses in Japan, and compared them with 163 full-genome sequences in the world. Two analyzing methods, distance-based and Bayesian coalescent MCMC inferences were adopted to elucidate an evolutionary relationship of the viruses in the world and Japan. Regardless of the method, the viruses in the world were classified into four distinct clusters with a few exceptions. Cluster 1 was originated earlier than cluster 2, while cluster 2 was more widely spread around the world. The other two clusters (clusters 1.2 and 1.3) were suggested to be distinct reassortants with different types of segment assortments. The viruses in Japan seemed to be a multiple origin, which were derived from approximately 28 transported cases. Twelve cases were associated with monophyletic groups consisting of Japanese viruses, which were referred to as micro-clade. While most of the micro-clades belonged to the cluster 2, the clade of the first cases of infection in Japan originated from cluster 1.2. Micro-clades of Osaka/Kobe and the Fukuoka cases, both of which were school-wide outbreaks, were eradicated. Time of most recent common ancestor (tMRCA) for each micro-clade demonstrated that some distinct viruses were transmitted in Japan between late May and early June, 2009, and appeared to spread nation-wide throughout summer. CONCLUSIONS: Our results suggest that many viruses were transmitted from abroad in late May 2009 irrespective of preventive actions against the pandemic influenza, and that the influenza A(H1N1)pdm had become a pandemic stage in June 2009 in Japan

High-Field Fermi Surface Properties in the Low Carrier Heavy Fermion Compound URu2Si2

We performed the Shubnikov-de Haas (SdH) experiments of the low carrier heavy fermion compound URu2Si2 at high fields up to 34T and at low temperatures down to 30mK. All main SdH branches named alpha, beta and gamma were observed for all the measured field-directions (H // [001] -> [100], [100] -> [110] and [001] -> [110]), indicating that these are attributed to the closed Fermi surfaces with nearly spherical shapes. Anomalous split of branch alpha was detected for the field along the basal plane, and the split immediately disappears by tilting the field to [001] direction, implying a fingerprint of the hidden order state. High field experiments reveal the complicated field-dependence of the SdH frequencies and the cyclotron masses due to the Zeeman spin-splitting associated with the Fermi surface reconstruction in the hidden order state with small carrier numbers. A new SdH branch named omega with large cyclotron mass of 25m0 was detected at high fields above 23T close to the hidden order instabilities.Comment: 6 pages, 7 figures, accepted for publication in J. Phys. Soc. Jp

Searching for evidence of a global catastrophe in the East African Rift Basin: Did the Toba supereruption alter paleoflora at Gona, Ethiopia?

Approximately 75,500 (+/- 900) years ago, the largest supereruption of the Late Pleistocene occurred in Sumatra, Indonesia. This explosion introduced ~1015 grams of fine ash into the atmosphere, produced ~3000 km3 of magma, and pyroclastic flows carpeted a ~105 km2 radius around the epicenter of the eruption. All flora and fauna within a 350 km radius were annihilated, and the enormous amount of ash that was aerosolized into the atmosphere is thought to have increased the Earth’s average albedo, which is speculated to be a possible catalyst for a period of global cooling. The advent of the Toba supereruption coincides with a period of Anatomically Modern Human (AMH) migration out-of-Africa. While recent studies show that the effects from the “environmental catastrophe” observed in Sumatra likely did not significantly alter the environments of East Africa during this time, there are only two comprehensive studies of cryptotephra (microscopic ash) layers from the Toba volcano in the East African Rift System, only one of which focuses on the variability in vegetation pre- and post-eruption. Additionally, both of those studies are focused on localities in Lake Malawi, records of which are sourced from lacustrine cores. As AMH are terrestrial-based mammals, and only passively interact with lacustrine environments, the question then arises, How did the vegetation in terrestrial areas with AMH activity change pre- and post-Toba supereruption? The answer to this question may lie in the sediments and soils of Gona, Ethiopia, a significant paleoanthropological project area that contains an abundance of Early and Middle-to-Late Pleistocene archaeological and hominin fossil sites, fluvial sediments and soils, and a well-constrained chronostratigraphic record. Yaalu (11° 3\u27 51.55 N, 40° 25\u27 23.12 E), a paleoanthropological site in Gona, has strata that have been dated to 85-70ka. During the 2020 field season, an undergraduate assistant and I will scout the area for an outcrop or series of outcroppings that encompass the full strata. Once a suitable site is located, a step-trench will be dug down-section to reveal the underlying strata. Individual soil horizons will be characterized, and oriented samples that encompass the full scope of the trench will be extracted. Sediment and soil samples will then be examined for evidence of cryptotephra, and phytoliths, silicic imprints of cellular structures from flora, will be extracted and characterized. Phytoliths will be point-counted, and percent relative abundance calculations will be derived from total phytolith count, alongside the starting dry weight. Namely, the tree cover and aridity indexes will be utilized, to see the change in low elevation semi-deciduous forests, and the expansion or contraction of riparian grass communities in the area. This study will allow us to see examine the variability of flora (or lack thereof) at Gona during a critical period of early human development. If phytolith assemblages significantly change, or if the overall concentration of phytoliths decreases at Yaalu post-Toba, then one could infer that the Toba supereruption was a catalyst for, at the very least, minimal change within Gona’s ecosystem

Paleopedology associated with the rise and dispersal of Anatomically Modern Humans at Gona, Ethiopia

Geologists and paleoanthropologists continue to debate the onset, development, and rate of change of out-of-Africa dispersals by Anatomically Modern Humans (AMH). Climatic and environmental variability is often inferred to be the catalysts of these migrations, yet the precise context of these dispersals, including climate effects on local flora and fauna, remains unclear. This study addresses this uncertainty by examining a series of eleven fossilized soils (paleosols) that range in age from the Middle Pleistocene (~570 ka) to present at Gona, Ethiopia, a significant paleoanthropological area that has abundant archaeological and AMH fossil sites. Paleosols provide an ideal archive for reconstructing the localized changes in paleoenvironment and paleoclimate associated with Gona’s archaeological and fossil sites, as they are a reservoir of biogeochemical dynamics related to the surrounding environment. Initial morphological observations from the paleosols of the Yaalu (~80 ka) and Erole (12 ka) fossil sites show the presence of soil carbonate and shrink-swell features indicative of seasonal climate. Bulk geochemical data supports these observations, with the Yaalu paleosols yielding average mean annual precipitation (MAP) and temperature (MAT) values of 723 mm/yr (± 108) and 14.0°C (± 4.4), with Erole paleosols yielding average MAP and MAT values of 832 mm/yr (± 108) and 13.3°C (± 4.4), respectively. These data will continue to be expanded upon and will encompass eight archaeological and fossil localities in eleven different sites. Although these results are preliminary, this growing dataset will compliment more regional-scale paleoenvironmental and paleoclimate records when interpreting the forcings and responses of Out-of-Africa migrations

Evidence of Late Pleistocene and Holocene paleo-Critical Zones at Gona, Ethiopia

The African Humid Period (AHP), spanning a period of approximately 12-5 ka, resulted in Northern and Eastern Africa being wetter than today and had notable impacts on flora, fauna, and humans. Much of the work pertaining to the AHP across Eastern Africa utilizes lacustrine and marine proxies rather than fluvial. Gona, located in the Afar region of Ethiopia, is known for its extensive archaeological and fossil records in fluvial deposits. However, the paleoenvironments of the AHP at Gona have not been investigated. This study uses stratigraphy, geochronology, and paleopedology to reconstruct the Late Pleistocene and AHP paleoenvironments, i.e., paleo-Critical Zones. We examine two paleosols, the Odele and Erole paleosols, located in the Asbole study region of Gona. The Odele paleosol is between the Korina Tuff (\u3c39 ka) and the Kilaitoli Tuff (~25.7 ka) and weathered during late-stage MIS-3 and MIS-2. The Erole paleosol, a relict soil that weathered during the AHP, is ~15 m above the Kilaitoli Tuff and immediately above a calibrated 14C age of 12 ka. Both paleosols formed along paleo-tributaries of the ancestral Awash River, as only matrix-supported gravels are found. The Erole paleosol displays consistently darker Munsell values than the Odele paleosol. Average strain calculations using paleosol geochemistry show a volumetric collapse on the order of 34 ± 4% in the Erole paleosol and little to no dilation/collapse in the Odele paleosol, 0 ± 2%. Calculations of open-system mass transport of elements through the profiles (Tau) show an 18 ± 7% loss of SiO2 and a 69 ± 5% loss of CaO in the Erole paleosol, which are greater than the 2 ± 1% loss of SiO2 and 1 ± 3% loss of CaO in the Odele paleosol. These strain and tau results suggest more intense weathering and elemental loss in the Erole paleosol. These results are consistent with recent paleoclimate reconstructions, and we infer that the collapse and elemental loss in the Erole paleosol are due to a period of increased rainfall during the AHP than the preceding MIS-3 and MIS-2 tim