ALBERT

Description: Magnetic field-induced dissipation-free state in superconducting nanostructures Nature Communications 4, 1437 (2013). doi:10.1038/ncomms2437 Authors: R. Córdoba, T. I. Baturina, J. Sesé, A. Yu Mironov, J. M. De Teresa, M. R. Ibarra, D. A. Nasimov, A. K. Gutakovskii, A. V. Latyshev, I. Guillamón, H. Suderow, S. Vieira, M. R. Baklanov, J. J. Palacios & V. M. Vinokur

Description: Despite broad interest in determining the topographic and climatic histories of mountain ranges, the evolution of California’s Sierra Nevada remains actively debated. Prior stable isotope–based studies of the Sierra Nevada have relied primarily on hydrogen isotopes in kaolinite, hydrated volcanic glass, and leaf n -alkanes. Here, we reconstruct the temperature and elevation of the early Eocene Sierra Nevada using the oxygen isotope composition of kaolinitized granite clasts from the ancestral Yuba and American Rivers that drained the windward (Pacific) flank of the Sierra Nevada. First, we evaluated the possible contributions of hydrogen isotope exchange in kaolinite by direct comparison with oxygen isotope measurements. Next, we utilized differences in the hydrogen and oxygen isotope fractionation in kaolinite to constrain early Eocene midlatitude weathering temperatures. Oxygen isotope geochemistry of in situ kaolinites indicates upstream (eastward) depletion of 18 O in the northern Sierra Nevada. The 18 O values, ranging from 11.4 to 14.4 at the easternmost localities, correspond to paleoelevations as high as 2400 m when simulating the orographic precipitation of moisture from a Pacific source using Eocene boundary conditions. This result is consistent with prior hydrogen isotope studies of the northern Sierra, but oxygen isotope–based paleoelevation estimates are systematically ~500–1000 m higher than those from hydrogen-based estimates from the same samples. Kaolinite geothermometry from 16 samples produced early Eocene weathering temperatures of 13.0–36.7 °C, with an average of 23.2 ± 6.4 °C (1). These kaolinite temperature reconstructions are in general agreement with paleofloral and geochemical constraints from Eocene California localities and climate model simulations. Our results confirm prior hydrogen isotope–based paleoelevation estimates and further substantiate the existence of a hot and high Eocene Sierra Nevada.

Description: Widespread late Pleistocene lake systems of the Basin and Range Province indicate substantially greater moisture availability during glacial periods relative to modern times, but the climatic factors that drive changes in lake levels are poorly constrained. To better constrain these climatic factors, we present a new lacustrine paleoclimate record and precipitation estimates for Lake Surprise, a closed basin lake in northeastern California. We combine a detailed analysis of lake hydrography and constitutive relationships describing the water balance to determine the influence of precipitation, evaporation, temperature, and seasonal insolation on past lake levels. At its maximum extent, during the last deglaciation, Lake Surprise covered 1366 km 2 (36%) of the terminally draining Surprise Valley watershed. Using paired radiocarbon and 230 Th-U analyses, we dated shoreline tufa deposits from wave-cut lake terraces in Surprise Valley, California, to determine the hydrography of the most recent lake cycle. This new lake hydrograph places the highest lake level 176 m above the present-day playa at 15.19 ± 0.18 calibrated ka ( 14 C age). This significantly postdates the Last Glacial Maximum (LGM), when Lake Surprise stood at only moderate levels, 65–99 m above modern playa, similar to nearby Lake Lahontan. To evaluate the climatic factors associated with lake-level changes, we use an oxygen isotope mass balance model combined with an analysis of predictions from the Paleoclimate Model Intercomparison Project 3 (PMIP3) climate model ensemble. Our isotope mass balance model predicts minimal precipitation increases of only 2%–18% during the LGM relative to modern, compared to an ~75% increase in precipitation during the 15.19 ka highstand. LGM PMIP3 climate model simulations corroborate these findings, simulating an average precipitation increase of only 6.5% relative to modern, accompanied by a 28% decrease in total evaporation driven by a 7 °C decrease in mean annual temperature. LGM PMIP3 climate model simulations also suggest a seasonal decoupling of runoff and precipitation, with peak runoff shifting to the late spring–early summer from the late winter–early spring. Our coupled analyses suggest that moderate lake levels during the LGM were a result of reduced evaporation driven by reduced summer insolation and temperatures, not by increased precipitation. Reduced evaporation primed Basin and Range lake systems, particularly smaller, isolated basins such as Surprise Valley, to respond rapidly to increased precipitation during late-Heinrich Stadial 1 (HS1). Post-LGM highstands were potentially driven by increased rainfall during HS1 brought by latitudinally extensive and strengthened midlatitude westerly storm tracks, the effects of which are recorded in the region’s lacustrine and glacial records. These results suggest that seasonal insolation and reduced temperatures have been underinvestigated as long-term drivers of moisture availability in the western United States.

Description: In recent years, the use of wireless sensor networks has been increasing. Localization is a fundamental problem in wireless sensor networks (WSNs), since location information is essential for diverse applications such as tracking, quality network coverage, health, and energy efficiency. In this paper performance of localization algorithms such as range-free, range-based, and fuzzy-based decision is evaluated. We introduce a modification of an algorithm by providing weights to the correlation matrix to improve correctness. In all the cases the accuracy, precision, and computational complexity are evaluated as performance metrics. Location algorithms are evaluated using two scenarios, a first stage where all nodes are randomly distributed in a given area and a second scenario where four APs (access points) are placed on fixed positions and unknown nodes are randomly distributed within the sensing area. The received signal strength (RSS) is used to estimate the position of a node of interest. In the simulation results we show how our modified algorithm improves localization. On the other hand, we also have acceptable accuracy using distance-based algorithms, but they are more complex computationally.

Description: The Late Cretaceous (late Campanian to Maastrichtian) was characterized by a variable greenhouse climate, with evidence for cooling and/or glaciation and warming events. Most of these climatic signals are derived from marine records, and knowledge of the terrestrial climate, especially in the mid-latitudes, is limited due to fragmentary geological records on continents. Here we report mid-latitude terrestrial stable oxygen and carbon isotope data from pedogenic carbonates in the nearly continuous Late Cretaceous age SK-1 core drilled in the Songliao Basin, northeastern China. Our data indicate a punctuated, mid-latitude terrestrial climate in the Late Cretaceous. We interpret the negative excursion of pedogenic carbonate 18 O in the early Maastrichtian to be the result of decreasing temperature and/or strengthened westerlies during global cooling and possible glaciation, providing valuable mid-latitude terrestrial evidence for this event. The negative 13 C isotopic excursion ca. 66 Ma is modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate in the latest Cretaceous. Our continuous stable isotopic records in the Songliao Basin are in accordance with previously published global Late Cretaceous records of climate variability from marine and terrestrial regions, and demonstrate the sensitivity of mid-latitude terrestrial climate in a greenhouse world.

Description: There remains substantial debate concerning the relative roles of tectonics and global climate in driving the evolution of climate in Central Asia. Today, interior Asia—including the Taklamakan, Gobi, and Ordos Deserts—is exceptionally arid and is surrounded by distinct rainfall boundaries, such as those generated by the Asian monsoon systems to the east and south and those generated by high topography to the north and west. Determining how and why these boundaries have varied over the Neogene is hindered by the lack of a single proxy that can be broadly applied through space and time. We construct isoscapes of pedogenic carbonate 13 C ( 13 C c ) over the Neogene in Asia by combining a compilation of 2236 published measurements with new data from three localities in northern Central Asia. Pedogenic carbonate 13 C records local aridity—excepting localities impacted by C 4 grasslands and during large changes in atmospheric p CO 2 —through variations in soil respiration, depth of carbonate formation, and the effect of water stress on plant 13 C. Together, these effects reflect changes in both primary productivity and mean annual precipitation. Throughout the Neogene, we find consistent and exceptionally high 13 C c in interior Asia with a ring of lower 13 C c that demarcates higher precipitation. This persistent ring of lower 13 C c corresponds in the south and east with the influence of the Asian monsoon systems; in the west and north, it reflects both orographic rainfall due to uplift of the Tian Shan and to moisture delivery by the mid-latitude westerlies. Finally, 13 C c and, hence, aridity increases regionally in the latest Neogene, reflecting the effects of Northern Hemisphere glaciation and cooling. This widespread "de-greening" would have increased regional albedo and modified basin-scale water balances, resulting in greater dust fluxes due to reduced vegetative cover and precipitation.