707 research outputs found
Microstructure, magneto-transport and magnetic properties of Gd-doped magnetron-sputtered amorphous carbon
The magnetic rare earth element gadolinium (Gd) was doped into thin films of
amorphous carbon (hydrogenated \textit{a}-C:H, or hydrogen-free \textit{a}-C)
using magnetron co-sputtering. The Gd acted as a magnetic as well as an
electrical dopant, resulting in an enormous negative magnetoresistance below a
temperature (). Hydrogen was introduced to control the amorphous carbon
bonding structure. High-resolution electron microscopy, ion-beam analysis and
Raman spectroscopy were used to characterize the influence of Gd doping on the
\textit{a-}GdC(:H) film morphology, composition, density and
bonding. The films were largely amorphous and homogeneous up to =22.0 at.%.
As the Gd doping increased, the -bonded carbon atoms evolved from
carbon chains to 6-member graphitic rings. Incorporation of H opened up the
graphitic rings and stabilized a -rich carbon-chain random network. The
transport properties not only depended on Gd doping, but were also very
sensitive to the ordering. Magnetic properties, such as the spin-glass
freezing temperature and susceptibility, scaled with the Gd concentration.Comment: 9 figure
Influence of layer microstructure on the double nucleation process in Cu/Mg multilayers
9 pĂĄginas, 9 figuras, 3 tablas.-- et al.We have investigated by differential scanning calorimetry the thermal evolution of Cu/Mg multilayers with different modulation lengths, ranging from 7/28âtoâ30/120ânm. The Cu and Mg layers were grown by sequential evaporation in an electron beam deposition system. The phase identification and layer microstructure were determined by cross-section transmission electron microscopy, Rutherford backscattering, and scanning electron microscopy with focused ion beam for sample preparation. Upon heating, the intermetallic CuMg2 forms at the interfaces until coalescence is reached and thickens through a diffusion-limited process. Cross-section transmission electron microscopy observations show a distinct microstructure at the top and bottom of the as-prepared Mg layers, while no significant differences were seen in the Cu layers. We show that this effect is responsible for the observed asymmetry in the nucleation process between the Cu on Mg and the Mg on Cu interfaces. By modeling the calorimetric data we determine the role of both interfaces in the nucleation and lateral growth stages. We also show that vertical growth proceeds by grain development of the product phase, increasing significantly the roughness of the interfaces.The financial support by Project No. MAT2004-04761 granted by the Spanish Ministry of Education and 2005SGR00201 granted by the DirecciĂł General de Recerca of the Generalitat of Catalonia is acknowledged. One of the authors (J.L.L.) acknowledges the financial support from the Hungarian National Science Fund (OTKA043437).Peer reviewe
Application of Pulsed Field Gel Electrophoresis to Determine Îł-ray-induced Double-strand Breaks in Yeast Chromosomal Molecules
The frequency of DNA double-strand breaks (dsb) was determined in yeast cells exposed to Îł-rays under anoxic conditions. Genomic DNA of treated cells was separated by pulsed field gel electrophoresis, and two different approaches for the evaluation of the gels were employed: (1) The DNA mass distribution profile obtained by electrophoresis was compared to computed profiles, and the number of DSB per unit length was then derived in terms of a fitting procedure; (2) hybridization of selected chromosomes was performed, and a comparison of the hybridization signals in treated and untreated samples was then used to derive the frequency of dsb
Abrupt global events in the Earth's history: a physics perspective
The timeline of the Earth's history reveals quasi-periodicity of the
geological record over the last 542 Myr, on timescales close, in the order of
magnitude, to 1 Myr. What is the origin of this quasi-periodicity? What is the
nature of the global events that define the boundaries of the geological time
scale? I propose that a single mechanism is responsible for all three types of
such events: mass extinctions, geomagnetic polarity reversals, and sea-level
fluctuations. The mechanism is fast, and involves a significant energy release.
The mechanism is unlikely to have astronomical causes, both because of the
energies involved, and because it acts quasi-periodically. It must then be
sought within the Earth itself. And it must be capable of reversing the Earth's
magnetic field. The last requirement makes it incompatible with the consensus
model of the origin of the geomagnetic field - the hydromagnetic dynamo
operating in the Earth's fluid core. In the second part of the paper, I show
that a vast amount of seemingly unconnected geophysical and geological data can
be understood in a unified way if the source of the Earth's main magnetic field
is a ~200-km-thick lithosphere, repeatedly magnetized as a result of
methane-driven oceanic eruptions, which produce ocean flow capable of dynamo
action. The eruptions are driven by the interplay of buoyancy forces and
exsolution of dissolved gas, which accumulates in the oceanic water masses
prone to stagnation and anoxia. Polarity reversals, mass extinctions, and
sequence boundaries are consequences of these eruptions. Unlike the consensus
model of geomagnetism, this scenario is consistent with the paleomagnetic data
showing that "directional changes during a [geomagnetic polarity] reversal can
be astonishingly fast, possibly occurring as a nearly instantaneous jump from
one inclined dipolar state to another in the opposite hemisphere".Comment: Final journal version. New title, significant changes. Supersedes v.
Heterogenized Pyridine-Substituted Cobalt(II) Phthalocyanine Yields Reduction of CO2 by Tuning the Electron Affinity of the Co Center
Conversion of CO2 to reduced products is a promising route to alleviate irreversible climate change. Here we report the synthesis of a Co-based phthalocyanine with pyridine moieties (CoPc-Pyr), which is supported on a carbon electrode and shows Faradaic efficiency âŒ90% for CO at 490 mV of overpotential (-0.6 V vs reversible hydrogen electrode (RHE)). In addition, its catalytic activity at -0.7 V versus RHE surpasses other Co-based molecular and metal-organic framework catalysts for CO2 reduction at this bias. Density functional theory calculations show that pyridine moieties enhance CO2 adsorption and electron affinity of the Co center by an inductive effect, thus lowering the overpotential necessary for CO2 conversion. Our study shows that CoPc-Pyr reduces CO2 at lower overpotential and with higher activity than noble metal electrodes, such as silver
Steering hyper-giants' traffic at scale
Large content providers, known as hyper-giants, are responsible for sending the majority of the content traffic to consumers. These hyper-giants operate highly distributed infrastructures to cope with the ever-increasing demand for online content. To achieve 40 commercial-grade performance of Web applications, enhanced end-user experience, improved reliability, and scaled network capacity, hyper-giants are increasingly interconnecting with eyeball networks at multiple locations. This poses new challenges for both (1) the eyeball networks having to perform complex inbound traffic engineering, and (2) hyper-giants having to map end-user requests to appropriate servers. We report on our multi-year experience in designing, building, rolling-out, and operating the first-ever large scale system, the Flow Director, which enables automated cooperation between one of the largest eyeball networks and a leading hyper-giant. We use empirical data collected at the eyeball network to evaluate its impact over two years of operation. We find very high compliance of the hyper-giant to the Flow Directorâs recommendations, resulting in (1) close to optimal user-server mapping, and (2) 15% reduction of the hyper-giantâs traffic overhead on the ISPâs long-haul links, i.e., benefits for both parties and end-users alike.EC/H2020/679158/EU/Resolving the Tussle in the Internet: Mapping, Architecture, and Policy Making/ResolutioNe
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