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Search Results: 1 - 10 of 402043 matches for " J. B. Betts "
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Content Disputes in Wikipedia Reflect Geopolitical Instability
Gordana Apic, Matthew J. Betts, Robert B. Russell
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0020902
Abstract: Indicators that rank countries according socioeconomic measurements are important tools for regional development and political reform. Those currently in widespread use are sometimes criticized for a lack of reproducibility or the inability to compare values over time, necessitating simple, fast and systematic measures. Here, we applied the ‘guilt by association’ principle often used in biological networks to the information network within the online encyclopedia Wikipedia to create an indicator quantifying the degree to which pages linked to a country are disputed by contributors. The indicator correlates with metrics of governance, political or economic stability about as well as they correlate with each other, and though faster and simpler, it is remarkably stable over time despite constant changes in the underlying disputes. For some countries, changes over a four year period appear to correlate with world events related to conflicts or economic problems.
Solving the Unbalanced Assignment Problem: Simpler Is Better  [PDF]
Nathan Betts, Francis J. Vasko
American Journal of Operations Research (AJOR) , 2016, DOI: 10.4236/ajor.2016.64028
Abstract: Recently, Yadaiah and Haragopal published in the American Journal of Operations Research a new approach to solving the unbalanced assignment problem. They also provide a numerical example which they solve with their approach and get a cost of 1550 which they claim is optimum. This approach might be of interest; however, their approach does not guarantee the optimal solution. In this short paper, we will show that solving this same example from the Yadaiah and Haragopal paper by using a simple textbook formulation to balance the problem and then solve it with the classic Hungarian method of Kuhn yields the true optimal solution with a cost of 1520.
The influence of vegetation on the ITCZ and South Asian monsoon in HadCM3
M. P. McCarthy, J. Sanjay, B. B. B. Booth, K. Krishna Kumar,R. A. Betts
Earth System Dynamics (ESD) & Discussions (ESDD) , 2012, DOI: 10.5194/esd-3-87-2012
Abstract: The role of global vegetation on the large-scale tropical circulation is examined in the version 3 Hadley Centre climate model (HadCM3). Alternative representations of global vegetation cover from observations and a dynamic global vegetation model (DGVM) were used as the land-cover component for a number of HadCM3 experiments under a nominal present day climate state, and compared to the simulations using the standard land cover map of HadCM3. The alternative vegetation covers result in a large scale cooling of the Northern Hemisphere extra-tropics relative to the HadCM3 standard, resulting in a southward shift in the location of the inter-tropical convergence zone (ITCZ). A significant reduction in Indian monsoon precipitation is also found, which is related to a weakening of the South Asian monsoon circulation, broadly consistent with documented mechanisms relating to temperature and snow perturbations in the Northern Hemisphere extra-tropics in winter and spring, delaying the onset of the monsoon. The role of the Northern Hemisphere extra-tropics on tropical climate is demonstrated, with an additional representation of vegetation cover based on DGVM simulated changes in Northern Hemisphere vegetation from the end of the 21st Century. This experiment shows that through similar processes the simulated extra-tropical vegetation changes in the future contribute to a strengthening of the South Asian monsoon in this model. These findings provide renewed motivation to give careful consideration to the role of global scale vegetation feedbacks when looking at climate change, and its impact on the tropical circulation and South Asian monsoon in the latest generation of Earth System models.
A Mesoproterozoic continental flood rhyolite province, the Gawler Ranges, Australia: the end member example of the Large Igneous Province clan
M. J. Pankhurst, B. F. Schaefer, P. G. Betts, N. Phillips,M. Hand
Solid Earth (SE) & Discussions (SED) , 2011, DOI: 10.5194/se-2-25-2011
Abstract: Rhyolite and dacite lavas of the Mesoproterozoic upper Gawler Range Volcanics (GRV) (>30 000 km3 preserved), South Australia, represent the remnants of one of the most voluminous felsic magmatic events preserved on Earth. Geophysical interpretation suggests eruption from a central cluster of feeder vents which supplied large-scale lobate flows >100 km in length. Pigeonite inversion thermometers indicate eruption temperatures of 950–1100 °C. The lavas are A-type in composition (e.g. high Ga/Al ratios) and characterised by elevated primary halogen concentrations (~1600 ppm fluorine, ~400 ppm chlorine). These depolymerised the magma such that temperature-composition-volatile non-Arrhenian melt viscosity modelling suggests they had viscosities of <3.5 log η (Pa s). These physicochemical properties have led to the emplacement of a Large Rhyolite Province, which has affinities in emplacement style to Large Basaltic Provinces. The low viscosity of these felsic magmas has produced a unique igneous system on a scale which is either not present or poorly preserved elsewhere on the planet. The Gawler Range Volcanic Province represents the erupted portion of the felsic end member of the family of voluminous, rapidly emplaced terrestrial magmatic provinces.
A mesoproterozoic continental flood rhyolite province, the Gawler Ranges, Australia: the end member example of the Large Igneous Province clan
M. J. Pankhurst,B. F. Schaefer,P. G. Betts,N. Phillips
Solid Earth Discussions , 2010, DOI: 10.5194/sed-2-251-2010
Abstract: Rhyolite and dacite lavas of the Mesoproterozoic upper Gawler Range Volcanics (GRV) (>30 000 km3 preserved), South Australia, represent the remnants of one of the most voluminous felsic magmatic events preserved on Earth. Geophysical interpretation suggests eruption from a central cluster of feeder vents which supplied large-scale lobate flows >100 km in length. Pigeonite inversion thermometers indicate eruption temperatures of 950–1100 °C. The lavas are A-type in composition (e.g. high Ga/Al ratios) and characterised by elevated primary halogen concentrations (~1600 ppm Fluorine, ~400 ppm Chlorine). These depolymerised the magma such that temperature-composition-volatile non-Arrhenian melt viscosity modelling suggests they had viscosities of <3.5 log η (Pa s). These physicochemical properties have led to the emplacement of a Large Rhyolite Province, which has affinities in emplacement style to Large Basaltic Provinces. The low viscosity of these felsic magmas has produced a unique igneous system on a scale which is either not present or poorly preserved elsewhere on the planet. The Gawler Range Volcanic Province represents the erupted portion of the felsic end member of the family of voluminous, rapidly emplaced terrestrial magmatic provinces.
Quantum Phase Transition in the Normal State of High-Tc Cuprates at Optimum Doping
F. F. Balakirev,J. B. Betts,A. Migliori,I. Tsukada,Yoichi Ando,G. S. Boebinger
Physics , 2007, DOI: 10.1103/PhysRevLett.102.017004
Abstract: By using a 60 T magnetic field to suppress superconductivity in La2-pSrpCuO4, (LSCO) we reveal an anomalous peak in the Hall number, located at optimum doping and developing at temperatures below the zero-field superconducting transition temperature, Tc. The anomaly bears a striking resemblance to observations in Bi2Sr2-xLaxCuO6+delta (BSLCO) [F. F. Balakirev et al., Nature (London) 424, 912 (2003)], suggesting a normal state phenomenology common to the cuprates that underlies the high-temperature superconducting phase. The peak is ascribed to the transformation of the "Fermi arcs" into a conventional FS, the signature of a Fermi surface reconstruction associated with a quantum phase transition (QPT) near optimum doping and co-incident with the collapse of the pseudogap state.
Unconventional Transition from Metallic to Insulating Resistivity in the Spin-ladder Compound (Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$
F. F. Balakirev,J. B. Betts,G. S. Boebinger,N. Motoyama,H. Eisaki,S. Uchida
Physics , 1998,
Abstract: Spin-ladder compounds make interesting analogs of the high-temperature superconductors, because they contain layers of nearly one-dimensional "ladders" consisting of a square array of copper and oxygen atoms. Increasing the number of legs in the ladders provides a step-wise approach toward the two-dimensional copper-oxygen plane, that structure believed to be a key to high temperature superconductivity. Short-range spin correlations in ladders have been predicted to lead to formation of hole pairs favorable for superconductivity, once enough holes are introduced onto the ladders by doping. Indeed, superconductivity has been discovered in the two-leg ladder compound (Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$ under high pressure. Here we show that charge transport in the non-superconducting state of (Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$ shares three distinct regimes in common with high-temperature superconductors, including an unexplained insulating behavior at low temperatures in which the resistivity increases as the logarithm of the temperature. These observations suggest that the logarithmic divergence arises from a new localization mechanism common to the ladder compounds and the high-temperature superconductors, which may arise from nearly one-dimensional charge transport in the presence of a spin gap.
Metal-to-Insulator Crossover in the Low-Temperature Normal State of Bi_{2}Sr_{2-x}La_{x}CuO_{6+δ}
S. Ono,Yoichi Ando,T. Murayama,F. F. Balakirev,J. B. Betts,G. S. Boebinger
Physics , 2000, DOI: 10.1103/PhysRevLett.85.638
Abstract: We measure the normal-state in-plane resistivity of La-doped Bi-2201 single crystals at low temperatures by suppressing superconductivity with 60-T pulsed magnetic fields. With decreasing hole doping, we observe a crossover from a metallic to insulating behavior in the low-temperature normal state. This crossover is estimated to occur near 1/8 doping, well inside the underdoped regime, and not at optimum doping as reported for other cuprates. The insulating regime is marked by a logarithmic temperature dependence of the resistivity over two decades of temperature, suggesting that a peculiar charge localization is common to the cuprates.
Examination of the c-axis resistivity of Bi_{2}Sr_{2-x}La_xCuO_{6+δ} in magnetic fields up to 58 T
S. Ono,Yoichi Ando,F. F. Balakirev,J. B. Betts,G. S. Boebinger
Physics , 2004, DOI: 10.1103/PhysRevB.70.224521
Abstract: We measure the magnetic-field dependence of the c-axis resistivity, \rho_c(H), in a series of Bi_{2}Sr_{2-x}La_xCuO_{6+\delta} (BSLCO) single crystals for a wide range of doping using pulsed magnetic fields up to 58 T. The behavior of \rho_c(H) is examined in light of the recent determination of the upper critical field H_{c2} for this material using Nernst effect measurements. We find that the peak in \rho_c(H) shows up at a field H_p that is much lower than H_{c2} and there is no discernable feature in \rho_c(H) at H_{c2}. Intriguingly, H_p shows a doping dependence similar to that of T_c, and there is an approximate relation k_{B}T_c \simeq {1/2}g\mu_{B}H_p. Moreover, we show that the data for the lowest-T_c sample can be used to estimate the pseudogap closing field H_{pg}, but the method to estimate H_{pg} proposed by Shibauchi {\it et al.} [Phys. Rev. Lett. {\bf 86}, 5763 (2001)] must be modified to apply to the BSLCO system.
Experimental electronic heat capacities of $α-$ and $δ-$Plutonium; heavy-fermion physics in an element
J. C. Lashley,J. Singleton,A. Migliori,J. B. Betts,R. A. Fisher,J. L. Smith,R. J. McQueeney
Physics , 2003, DOI: 10.1103/PhysRevLett.91.205901
Abstract: We have measured the heat capacities of $\delta-$Pu$_{0.95}$Al$_{0.05}$ and $\alpha-$Pu over the temperature range 2-303 K. The availability of data below 10 K plus an estimate of the phonon contribution to the heat capacity based on recent neutron-scattering experiments on the same sample enable us to make a reliable deduction of the electronic contribution to the heat capacity of $\delta-$Pu$_{0.95}$Al$_{0.05}$; we find $\gamma = 64 \pm 3$ mJK$^{-2}$mol$^{-1}$ as $T \to 0$. This is a factor $\sim 4$ larger than that of any element, and large enough for $\delta-$Pu$_{0.95}$Al$_{0.05}$ to be classed as a heavy-fermion system. By contrast, $\gamma = 17 \pm 1$ mJK$^{-2}$mol$^{-1}$ in $\alpha-$Pu. Two distinct anomalies are seen in the electronic contribution to the heat capacity of $\delta-$Pu$_{0.95}$Al$_{0.05}$, one or both of which may be associated with the formation of the $\alpha'-$ martensitic phase. We suggest that the large $\gamma$-value of $\delta-$Pu$_{0.95}$Al$_{0.05}$ may be caused by proximity to a quantum-critical point.
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