bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface potential study of amorphous In–Ga–Zn–O thin film transistors
Authors: Chen C. , Kanicki J.
Published: December 2010

In this paper, we report on surface potentiometry in the channel region of operating amorphous In–Ga–Zn–O thin film transistors by scanning kelvin probe microscopy. Important parameters including the field-effect mobility and source/drain contact resistance are extracted from the channel potential profile. We find that the channel potential as a function of gate/drain bias can be described by the standard metal oxide semiconductor field effect transistor (MOSFET) equation incorporated with two nonideal factors: the gate-voltage-dependent field-effect mobility and the source/drain contact resistance.
Origin of low temperature memory and aging effects in spin glass like La0.7Ca0.3MnO3 nanomanganite
Authors: Karmakar Shilpi , Chaudhuri B. K. , Chan C. L. , Yang H. D.
Published: December 2010

Interesting low temperature memory phenomena have been observed from equilibrium and out of equilibrium magnetic measurements on the La0.7Ca0.3MnO3 nanomanganite system. The observed phenomenon were screened for atomic spin glass (SG), super spin glass (SSG), cluster glass (CG), and superparamagnetic behavior. The results evidences of SG like behavior at low temperature (<40 K) in this manganite system consisting of ferromagnetic nanoparticles. In the temperature region between 40 K and the ferromagnetic Curie point TC∼217 K, a ferromagnetic CG state develops with a relatively weaker interparticle interaction than that of the low temperature SG phase. The dynamic magnetization shows aging, chaos and memory effects. Moreover, we have also noticed asymmetric response in magnetic relaxation in response to positive and negative temperature cycling protocols. The origin and nature of the low-temperature SG state in this system is discussed within the framework of hierarchical organization of metastable states. The results show existence of various time and length scales in the system, which can be explained by considering the nanoparticles with grain boundary spin disorder and the presence of noncompact ferromagnetic clusters.
Effects of solution-grown CdS on Cu(InGa)Se2 grain boundaries
Authors: Lei C. , Duch M. , Robertson I. M. , Rockett A.
Published: December 2010

Complete Cu(In,Ga)Se2 (CIGS) solar cells in which the collecting heterojunctions were formed by chemical bath deposition of CdS were analyzed by transmission electron microscopy and energy dispersive spectroscopy. The CIGS was produced at 400 or 580 °C as either single layers or in a two-step bilayer process. The compositions of grain boundaries were found to be the same as the grains before CdS deposition except in the low temperature-deposited bilayer but after CdS was formed the grain boundaries were found to be anion deficient with some evidence of Cu loss from the CIGS and residual Cu found in the CdS in most cases. The results are consistent with n-type doping of the surface of the CIGS and wrapping of the junction around the grains. In bilayer films the grain boundaries were found to be more open containing many voids and this facilitated penetration of the CdS into the boundaries.
Self-resonant modes in Josephson junctions with a phase discontinuity
Authors: Nappi C. , Adamo M. , Sarnelli E. , Goldobin E.
Published: December 2010

We extend the theory of self-resonances in short Josephson junctions to the case of a piecewise constant critical current density and a κ discontinuity in the Josephson phase. We calculate the amplitude of the self-resonances as a function of applied magnetic field by using an extension of the approach introduced by Kulik for conventional Josephson junctions (I. O. Kulik, JETP Lett. 2, 84 (1965)). The theory given here agrees with existing experiments on superconducting–insulator–ferromagnet–superconductor 0–π Josephson junctions. The results are relevant to the characterization of all modern 0–π junctions as well as 0–κ junctions with artificially created phase discontinuities: high-temperature grain boundary junctions, junctions with a ferromagnetic barrier, and junctions with current injectors.
Superconductor-insulator transitions of quench-condensed films
Authors: Goldman A. M.
Published: December 2010

The superconductor-insulator transitions of quench-condensed ultrathin films of metals are simple examples of continuous quantum phase transitions. Quantum phase transitions differ from thermal phase transitions in that they occur at zero temperature when the ground state of a system is changed in response to a variation of an external parameter of the Hamiltonian. In superconductor-insulator transitions, this control parameter is usually a parallel or perpendicular magnetic field, disorder, or charge density. Quantum phase transitions are studied through measurements, at nonzero temperature, of physical behavior influenced by the quantum fluctuations associated with the transition. Here we focus on the results of transport and magnetotransport measurements of disordered quench-condensed films of metals that are effectively two-dimensional. Open questions relating to the nature of the very puzzling insulating regime and whether there are several different types of superconductor-insulator transitions determined by material properties will be discussed.
Experimental study on dielectric barrier discharge actuators operating in pulse mode
Authors: Kotsonis M. , Veldhuis L.
Published: December 2010

An experimental investigation is performed on the operation of dielectric barrier discharge plasma actuators used as manipulators of secondary and unsteady flow structures such as boundary layer instabilities or shedding vortices. The actuators are tested mainly in pulse mode. High sample rate hot-wire measurements of the induced velocity field downstream of the actuator are taken for the cases of pulse actuation in still air as well as in a laminar boundary layer. Complementary voltage and current measurements are taken to calculate power consumption. Additionally, a study on the influence of the pulse frequency and duty cycle of actuation is performed. Results show the effectiveness of plasma actuators in inducing fluctuating components of velocity when operated in pulse mode. Spectral analysis reveals the connection between the actuator driving signal and the induced flowfield. The magnitude as well as the consistency of the resulting fluctuating field are dependent on both the duty cycle and the pulse frequency. An empirical operational envelope based on phenomenological observations is proposed, for the use of the actuators at specific flow and operational conditions given in the paper.
Nature of the negative thermal expansion in antiperovskite compound Mn3ZnN
Authors: Qu B. Y. , Pan B. C.
Published: December 2010

The magnetic structures of Mn3ZnN compound are theoretically studied, from which a new magnetic ground state (MGS) structure of Mn3ZnN is predicted. Comparison of the calculated volumes between different magnetic structures shows that the Mn3ZnN compound experiences a volume expansion from the high-temperature paramagnetic phase to the low-temperature antiferromagnetic phase Γ5g, and a volume contraction from the Γ5g phase to the MGS phase, in excellent agreement with the observation in experiment. Analysis of the exchange parameters between ions shows that the spin coupling between the Mn ions is responsible for the sudden expansion and contraction of the Mn3ZnN volume. Furthermore, we find that the existed N vacancies in the compound significantly lower the energy of Γ5g. When the concentration of N vacancies is large enough, Γ5g may become the ground state for the defective Mn3ZnN compound. This may be used to explain the experimental observation that the sudden change in volume of Mn3ZnN at about 127 K did not appear [Kim et al., Phys. Rev. B 68, 172402 (2003)].
Mechanism of optical degradation in microstructured InGaN light-emitting diodes
Authors: Li Z. L. , Li K. H. , Choi H. W.
Published: December 2010

While the enhancement of light extraction efficiency from microstructured InGaN light-emitting diodes (μLED) has been firmly established, there is concern over the effect of microstructuring on the device lifetimes. A study on the electrical characteristics and reliability of μLED arrays has been carried out. Despite improved optical performance, expanded device sidewalls served to accelerate the rate of optical degradation, adversely affect the lifetimes of devices. Through current-voltage plots and noise spectrum measurements, vertical current conduction along the plasma-damaged sidewalls was identified as the key degradation mechanism.
Nanosize effects in Eu doped La0.67Ca0.33MnO3 perovskite
Authors: Sree D. Roja , Cholleti Shravan Kumar , Fard Soheila Ghasemi , Reddy Ch. Gopal , Reddy P. Yadagiri , Reddy K. Rama , Turpu Goverdhan Reddy
Published: December 2010

Electrical, magnetic and Mössbauer measurements have been carried out on La0.67−xEuxCa0.33MnO3 (x=0.21 and 0.29) for a comparative study of different grain size materials. The samples have been prepared through sol–gel method and sintered at 700, 800, and 900 °C to achieve nanosized materials. All the prepared samples are found to be single phase having orthorhombic structure. The particle sizes are estimated through x-ray diffraction (XRD) by using the Debye–Scherrer’s formulae and these sizes are further confirmed by transmission electron microscopy (TEM) images. E151u Mössbauer studies reveal that Eu is in 3+ charge state. The isomer shift and full width at half maximum (FWHM) of the Mössbauer peak decrease with the increase in particle size. Reduction in the grain size leads to drastic increase in electrical resistivity in all the samples. The typical metal–insulator transition (MIT) observed in x=0.21 bulk sample disappears with decrease in grain size while an external magnetic field of 8T restores the MIT. For x=0.29, the sample with the lowest grain size does not show a field induced MIT whereas the samples with higher grain sizes show the field induced MIT. Hysteresis in field cooled cooling and warming cycles of magnetization measurements of x=0.21 system suggests that the decrease in grain size induces strong competition between the FM and AFM interaction. Interestingly, the combined effect of chemical pressure induced due to the additional rare earth doping and smaller grain size leads to a more stable AFM phase in x=0.29 system where no such hysteresis is observed in field cooled cooling and warming cycles of magnetization measurements.
A model for the self-pulsing regime of microhollow cathode discharges
Authors: Chabert P. , Lazzaroni C. , Rousseau A.
Published: December 2010

Microhollow cathode discharges may operate in different regimes depending of the discharge current. They are subject to relaxation oscillations in the so-called self-pulsing regime in which the discharge oscillates between two quasiequilibria: at low current it remains confined in the microhole whereas it expands on the cathode backside during short high-current pulses. A model based on a nonlinear discharge resistance is proposed to describe the phenomenon. The analysis of the dynamics reveals that the current pulse rises in an extremely short time while the characteristic (longer) decay time is imposed by the resistance when the discharge is expanded outside the hole. It is shown how the nonlinear discharge resistance may be inferred from the experimental current-voltage signals.
Demonstration of AlGaN/GaN high-electron-mobility transistors on 100 mm diameter Si(111) by plasma-assisted molecular beam epitaxy
Authors: Radhakrishnan K. , Dharmarasu N. , Sun Z. , Arulkumaran S. , Ng G. I.
Published: December 2010

AlGaN/GaN high-electron-mobility transistor structures grown on 100 mm high-resistivity Si(111) substrates using plasma-assisted molecular beam epitaxy are reported. The two-dimensional electron gas (2DEG) formation in the heterostructures was realized by the growth optimization of two-step low temperature and high temperature AlN layers and GaN buffer layer. High-electron mobility of 1100 cm2/V s with a sheet carrier density of 9×1012 cm−2 was achieved. The presence of 2DEG in the AlGaN/GaN interface was confirmed by temperature dependent Hall measurements and capacitance-voltage carrier profiling. The fabricated 1.5 μm gate length high electron mobility transistor exhibited a maximum drain current density of 530 mA/mm and a peak extrinsic transconductance of 156 mS/mm.
Reduced leakage current in Josephson tunnel junctions with codeposited barriers
Authors: Welander Paul B. , McArdle Timothy J. , Eckstein James N.
Published: December 2010

Josephson junctions were fabricated using two different methods of barrier formation. The trilayers employed were Nb/Al–AlOx/Nb on sapphire, where the first two layers were epitaxial. The oxide barrier was formed either by exposing the Al surface to O2 or by codepositing Al in an O2 background. The codeposition process yielded tunnel junctions that showed the theoretically predicted subgap current and no measurable shunt conductance. In contrast, devices with barriers formed by thermal oxidation showed a small shunt conductance in addition to the predicted subgap current.
Capturing ultrafast structural evolutions with a single pulse of MeV electrons: Radio frequency streak camera based electron diffraction
Authors: Musumeci P. , Moody J. T. , Scoby C. M. , Gutierrez M. S. , Westfall M. , Li R. K.
Published: December 2010

In this paper we report on the experimental demonstration of using relativistic electron diffraction and an radiofrequency deflecting cavity to capture in a single shot the entire time-history of the ultrafast laser-induced heating and melting of a single crystal gold sample. By recording the time variation in the Bragg peaks on the streak image of a 16 ps long electron beam it is possible to reconstruct with 400 fs temporal resolution the evolution of the sample structure induced by a 35 mJ/cm2 400 nm laser pump pulse.
Superconducting properties of a two-dimensional doped semiconductor
Authors: Loktev V. M. , Turkowski V.
Published: December 2010

This is a study of the superconducting properties of a two-dimensional model with an additional (insulating) gap Δins that depends on temperature and doping. In particular, we study the doping dependence of the Berezinskii–Kosterlitz–Thouless critical temperature Tc and the superconducting pseudogap temperature TcMF for different values of Δins by taking hydrodynamic fluctuations of the superconducting order parameter into account. We show that the gap Δins affects the values of the superconducting gap and the temperatures Tc and TcMF within the range of carrier densities where the Δins approaches zero. In particular, the derivatives of these quantities have a jump in this region. We discuss the possible relevance of these results to high-temperature superconductors.
Effect of relative humidity on contact angle and particle deposition morphology of an evaporating colloidal drop
Authors: Chhasatia Viral H. , Joshi Abhijit S. , Sun Ying
Published: December 2010

The deposition behavior of inkjet-printed aqueous colloidal drops on a glass substrate has been investigated by using fluorescence microscopy and a high resolution goniometer. Real-time side-view images of a pinned colloidal drop show that the contact angle during evaporation is a function of the relative humidity (RH). The RH also affects the extent to which the drop is able to spread after impacting a substrate, the evaporation rate at the drop surface, and the evaporatively driven flow inside the drop that drives the suspended particles toward the contact line. Results show that the particle deposition area and pattern change significantly with the RH.
Enhanced stability of hydrogen atoms at the graphene/graphane interface of nanoribbons
Authors: Ao Z. M. , Hernández-Nieves A. D. , Peeters F. M. , Li S.
Published: December 2010

The thermal stability of graphene/graphane nanoribbons (GGNRs) is investigated using density functional theory. It is found that the energy barriers for the diffusion of hydrogen atoms on the zigzag and armchair interfaces of GGNRs are 2.86 and 3.17 eV, respectively, while the diffusion barrier of an isolated H atom on pristine graphene was only ∼0.3 eV. These results unambiguously demonstrate that the thermal stability of GGNRs can be enhanced significantly by increasing the hydrogen diffusion barriers through graphene/graphane interface engineering. This may provide new insights for viable applications of GGNRs.
Role of Ru nano-dots embedded in TiO2 thin films for improving the resistive switching behavior
Authors: Yoon Jung Ho , Kim Kyung Min , Lee Min Hwan , Kim Seong Keun , Kim Gun Hwan , Song Seul Ji , Seok Jun Yeong , Hwang Cheol Seong
Published: December 2010

Ru nano-dots were embedded in a Pt/TiO2/Pt resistive switching cell to improve the uniformity of the switching parameters. The TiO2 film grown on the Ru nano-dots had a rutile structure locally whereas other parts of the TiO2 film had an anatase structure. The rutile-structured TiO2 formed conducting filaments easily and their rupture was much more uniform than the randomized ones in anatase TiO2. This largely improved the resistance uniformity at the reading voltage during the repeated resistance switching events. The improvement was also attributed to the high leakage current of the pristine sample at the reading voltage.
Evolution of ion-acoustic solitary waves in Maxwellian dusty plasmas
Authors: Das G. C. , Choudhury Balen , Bora M. P.
Published: December 2010

The nonlinear wave phenomena in the vicinity of Korteweg–de Vries (KdV) equation have been derived to study the salient features of solitons in a complex plasma consisting of Maxwellian electrons, ions, and cold dust with the effect of dust charge fluctuation. The reductive perturbation method has been applied to the dynamical system causeway and the derived KdV equation predicts different natures of solitons in complex plasma. The dynamics of the soliton propagation in the considered plasma constituents in ionospheric auroral regions exhibits rarefactive solitons, which is an interesting feature. The dust charge fluctuation by the increasing impact of electrons leads the nonlinear effect to be tending to zero. Because of which, the formation of a narrow solitary wave packet with the generation of high energy becomes possible and results in the phenomena of soliton radiation. In order to probe this further, we derive a modified KdV equation to study soliton propagation which, in turn, indicates the possibility of the shock formation in solitary waves.
Homogenization of two-dimensional anisotropic dissipative photonic crystal
Authors: Carbonell J. , Cervera F. , Sánchez-Dehesa J. , Arriaga J. , Gumen L. , Krokhin A.
Published: December 2010

We present the theoretical and experimental study of the effective permittivity of photonic crystal (PC) of parallel rods in the long-wavelength limit. Considering low-absorbing materials, we obtain analytical formulas for the imaginary part of the permittivity for the dielectric tensor. For the H-polarized mode propagating in a low-loss PC with rectangular symmetry we predict stronger azimuthal anisotropy for the imaginary part of permittivity than that for the real part. Measurements of microwave transmission through a PC of FR4 rods support the proposed theory. The obtained results may be used for optimization and tailoring of electromagnetic losses in artificial periodic structures.
Novel type of amplitude spiral wave in a two-layer system
Authors: Gao Jihua , Xie Lingling , Nie Haichun , Zhan Meng
Published: December 2010

Interaction of spiral waves in a two-layer system described by a model of coupled complex Ginzburg–Landau equations with negative-feedback couplings ε1 and ε2 is studied. Synchronization of two spiral waves can be broadly found if ε1+ε2 is sufficiently large. Prior to the synchronization, under the condition of strongly asymmetric coupling (|ε1−ε2|⪢0), a novel type of spiral wave, amplitude spiral wave, exists in the driven system. The pattern of amplitude spiral wave shows the spiral in the amplitude and without a singularity point (tip), compared to usual spiral waves known for phase with amplitude uniform far away from tips and rotating around tips.
An evaluation of spatial and temporal patterns of lightning- and human-caused forest fires in Alberta, Canada, 1980 - 2007
Authors: Wang Yonghe , Anderson Kerry R.
Published: December 2010

We used the K-function and kernel estimation methods to evaluate the spatial and temporal patterns of ignition locations of lightning- and human-caused forest fires in Alberta, Canada. Although both of these fire types have spatial patterns of cluster distribution, quantitative measures for evaluating the patterns in the province are lacking. Our results revealed annual differences in the spatial patterns between the two fire types, whereby fires caused by humans tended to be more clustered and had more complex spatial patterns than those caused by lightning. Spatial interactions of cluster and inhibition existed between the two fire types. Human-caused fires in the period 2003–07 were highly concentrated in the southern parts of the province, indicating the existence of an interaction between space and time. Kernel analysis confirmed the observation that in northern Alberta, lightning-caused fires were more likely to occur than human-caused fires; the opposite was true in southern Alberta. This study provided useful spatial information that is not obvious or cannot be inferred from visual examination of raw data. Such quantitative knowledge could lead to the development of fire-response and fire-suppression strategies appropriate to specific regions within the province.
Peak detection in sediment - charcoal records: impacts of alternative data analysis methods on fire-history interpretations
Authors: Higuera Philip E. , Gavin Daniel G. , Bartlein Patrick J. , Hallett Douglas J.
Published: December 2010

Over the past several decades, high-resolution sediment–charcoal records have been increasingly used to reconstruct local fire history. Data analysis methods usually involve a decomposition that detrends a charcoal series and then applies a threshold value to isolate individual peaks, which are interpreted as fire episodes. Despite the proliferation of these studies, methods have evolved largely in the absence of a thorough statistical framework. We describe eight alternative decomposition models (four detrending methods used with two threshold-determination methods) and evaluate their sensitivity to a set of known parameters integrated into simulated charcoal records. Results indicate that the combination of a globally defined threshold with specific detrending methods can produce strongly biased results, depending on whether or not variance in a charcoal record is stationary through time. These biases are largely eliminated by using a locally defined threshold, which adapts to changes in variability throughout a charcoal record. Applying the alternative decomposition methods on three previously published charcoal records largely supports our conclusions from simulated records. We also present a minimum-count test for empirical records, which reduces the likelihood of false positives when charcoal counts are low. We conclude by discussing how to evaluate when peak detection methods are warranted with a given sediment–charcoal record.
The effects of surficial deposit - drainage combinations on spatial variations of fire cycles in the boreal forest of eastern Canada
Authors: Mansuy Nicolas , Gauthier Sylvie , Robitaille André , Bergeron Yves
Published: December 2010

Spatial variations in the fire cycle of a large territory (190 000 km2) located in the boreal forest of eastern Canada were assessed using random sampling points. Our main objective was to determine if regions characterised by a large proportion of dry surficial deposit–drainage (SDD) burn more frequently than regions with a smaller proportion. Through a regionalisation of the landscape units, we analysed the effects of SDD on spatial variations of the fire cycle. A discriminant analysis involving the SDD and other physical variables (precipitation, temperature, aridity index, water bodies, elevation and slope) made it possible to identify a combination of variables characterising each region. A considerable variation in fire cycle was observed among the different SDD types (from 144 to 425 years) and between regions (from 90 to 715 years). Through the discriminant analysis, this study suggests that a combination of possible climatic top-down (precipitation R2 = 0.727, aridity index R2 = 0.663 and temperature R2 = 0.574) and bottom-up factors (xeric undifferentiated till R2 = 0.819 and humid undifferentiated till R2 = 0.691) could explain this variation at the regional scale. Implications of those results for forest protection against fire and regional development are briefly discussed.
Spatial pattern analyses of post-fire residual stands in the black spruce boreal forest of western Quebec
Authors: Madoui Amar , Leduc Alain , Gauthier Sylvie , Bergeron Yves
Published: December 2010

In this study, we characterised the composition and configuration of post-fire residual habitats belonging to two physiographic zones of the black spruce–moss domain in western Quebec. Thirty-three large fires (2000–52 000 ha) were selected and extracted on classified Landsat satellite imagery. The results show that a minimum of 2% and a maximum of 22% of burned areas escaped fire, with an overall average of 10.4%. The many forest patches that partially or entirely escaped fire formed residual habitats (RHs). It was found that although the area of RHs follows a linear relationship with fire size, their proportion appears relatively constant. Spatial analyses showed that the fires could be separated into two groups depending on the physiographic zones (East-Canadian Shield v. West-Clay Belt Lowlands). Fires in the west zone generate less RHs and appear to be associated with more extreme weather conditions. In most cases there was no association with water or wetlands; in some fires the presence of RHs is associated with the proximity of water bodies. The failure to find an association between RHs and wetlands suggests that this type of environment is part of the fuel. Coniferous woodland with moss appears particularly overrepresented within RHs. Our results suggest that the local and regional physiographic conditions strongly influence the creation of RHs; therefore, it is important to consider those differences when applying ecosystem-based management.
Water, climate change, and sustainability in the southwest
Authors: MacDonald Glen M.
Published: December 2010

The current Southwest drought is exceptional for its high temperatures and arguably the most severe in history. Coincidentally, there has been an increase in forest and woodland mortality due to fires and pathogenic outbreaks. Although the high temperatures and aridity are consistent with projected impacts of greenhouse warming, it is unclear whether the drought can be attributed to increased greenhouse gasses or is a product of natural climatic variability. Climate models indicate that the 21st century will be increasingly arid and droughts more severe and prolonged. Forest and woodland mortality due to fires and pathogens will increase. Demography and food security dictate that water demand in the Southwest will remain appreciable. If projected population growth is twinned with suburb-centered development, domestic demands will intensify. Meeting domestic demands through transference from agriculture presents concerns for rural sustainability and food security. Environmental concerns will limit additional transference from rivers. It is unlikely that traditional supply-side solutions such as more dams will securely meet demands at current per-capita levels. Significant savings in domestic usage can be realized through decreased applications of potable water to landscaping, but this is a small fraction of total regional water use, which is dominated by agriculture. Technical innovations, policy measures, and market-based solutions that increase supply and decrease water demand are all needed. Meeting 21st-century sustainability challenges in the Southwest will also require planning, cooperation, and integration that surpass 20th-century efforts in terms of geographic scope, jurisdictional breadth, multisectoral engagement, and the length of planning timelines.
Vulnerability assessment of climate-induced water shortage in Phoenix
Authors: Gober Patricia , Kirkwood Craig W.
Published: December 2010

Global warming has profound consequences for the climate of the American Southwest and its overallocated water supplies. This paper uses simulation modeling and the principles of decision making under uncertainty to translate climate information into tools for vulnerability assessment and urban climate adaptation. A dynamic simulation model, WaterSim, is used to explore future water-shortage conditions in Phoenix. Results indicate that policy action will be needed to attain water sustainability in 2030, even without reductions in river flows caused by climate change. Challenging but feasible changes in lifestyle and slower rates of population growth would allow the region to avoid shortage conditions and achieve groundwater sustainability under all but the most dire climate scenarios. Changes in lifestyle involve more native desert landscaping and fewer pools in addition to slower growth and higher urban densities. There is not a single most likely or optimal future for Phoenix. Urban climate adaptation involves using science-based models to anticipate water shortage and manage climate risk.
A 1,200-year perspective of 21st century drought in southwestern North America
Authors: Woodhouse Connie A. , Meko David M. , MacDonald Glen M. , Stahle Dave W. , Cook Edward R.
Published: December 2010

A key feature of anticipated 21st century droughts in Southwest North America is the concurrence of elevated temperatures and increased aridity. Instrumental records and paleoclimatic evidence for past prolonged drought in the Southwest that coincide with elevated temperatures can be assessed to provide insights on temperature-drought relations and to develop worst-case scenarios for the future. In particular, during the medieval period, ∼AD 900–1300, the Northern Hemisphere experienced temperatures warmer than all but the most recent decades. Paleoclimatic and model data indicate increased temperatures in western North America of approximately 1 °C over the long-term mean. This was a period of extensive and persistent aridity over western North America. Paleoclimatic evidence suggests drought in the mid-12th century far exceeded the severity, duration, and extent of subsequent droughts. The driest decade of this drought was anomalously warm, though not as warm as the late 20th and early 21st centuries. The convergence of prolonged warming and arid conditions suggests the mid-12th century may serve as a conservative analogue for severe droughts that might occur in the future. The severity, extent, and persistence of the 12th century drought that occurred under natural climate variability, have important implications for water resource management. The causes of past and future drought will not be identical but warm droughts, inferred from paleoclimatic records, demonstrate the plausibility of extensive, severe droughts, provide a long-term perspective on the ongoing drought conditions in the Southwest, and suggest the need for regional sustainability planning for the future.
Global value chains and agrifood standards: Challenges and possibilities for smallholders in developing countries
Authors: Lee Joonkoo , Gereffi Gary , Beauvais Janet
Published: December 2010

The rise of private food standards has brought forth an ongoing debate about whether they work as a barrier for smallholders and hinder poverty reduction in developing countries. This paper uses a global value chain approach to explain the relationship between value chain structure and agrifood safety and quality standards and to discuss the challenges and possibilities this entails for the upgrading of smallholders. It maps four potential value chain scenarios depending on the degree of concentration in the markets for agrifood supply (farmers and manufacturers) and demand (supermarkets and other food retailers) and discusses the impact of lead firms and key intermediaries on smallholders in different chain situations. Each scenario is illustrated with case examples. Theoretical and policy issues are discussed, along with proposals for future research in terms of industry structure, private governance, and sustainable value chains.
Arabidopsis
BRCA2 and RAD51 proteins are specifically involved in defense gene transcription during plant immune responses
Authors: Wang Shui , Durrant Wendy E. , Song Junqi , Spivey Natalie W. , Dong Xinnian
Published: December 2010

Systemic acquired resistance (SAR) is a plant immune response associated with both transcriptional reprogramming and increased homologous DNA recombination (HR). SNI1 is a negative regulator of SAR and HR, as indicated by the increased basal expression of defense genes and HR in
sni1
. We found that the
sni1
phenotypes are rescued by mutations in
BREAST CANCER 2
(
BRCA2
). In humans, BRCA2 is a mediator of RAD51 in pairing of homologous DNA. Mutations in
BRCA2
cause predisposition to breast/ovarian cancers; however, the role of the BRCA2–RAD51 complex in transcriptional regulation remains unclear. In
Arabidopsis
, both
brca2
and
rad51
were found to be hypersusceptible not only to genotoxic substances, but also to pathogen infections. A whole-genome microarray analysis showed that downstream of NPR1, BRCA2A is a major regulator of defense-related gene transcription. ChIP demonstrated that RAD51 is specifically recruited to the promoters of defense genes during SAR. This recruitment is dependent on the SAR signal salicylic acid (SA) and on the function of BRCA2. This study provides the molecular evidence showing that the BRCA2–RAD51 complex, known for its function in HR, also plays a direct and specific role in transcription regulation during plant immune responses.
A high-resolution human contact network for infectious disease transmission
Authors: Salathé Marcel , Kazandjieva Maria , Lee Jung Woo , Levis Philip , Feldman Marcus W. , Jones James H.
Published: December 2010

The most frequent infectious diseases in humans—and those with the highest potential for rapid pandemic spread—are usually transmitted via droplets during close proximity interactions (CPIs). Despite the importance of this transmission route, very little is known about the dynamic patterns of CPIs. Using wireless sensor network technology, we obtained high-resolution data of CPIs during a typical day at an American high school, permitting the reconstruction of the social network relevant for infectious disease transmission. At 94% coverage, we collected 762,868 CPIs at a maximal distance of 3 m among 788 individuals. The data revealed a high-density network with typical small-world properties and a relatively homogeneous distribution of both interaction time and interaction partners among subjects. Computer simulations of the spread of an influenza-like disease on the weighted contact graph are in good agreement with absentee data during the most recent influenza season. Analysis of targeted immunization strategies suggested that contact network data are required to design strategies that are significantly more effective than random immunization. Immunization strategies based on contact network data were most effective at high vaccination coverage.
Attenuation of innate immunity by cytomegalovirus IL-10 establishes a long-term deficit of adaptive antiviral immunity
Authors: Chang W. L. William , Barry Peter A.
Published: December 2010

Human cytomegalovirus (HCMV) and many other pathogens exploit the IL-10 pathway, as part of their infectious cycle, either through their own encoded IL-10 (hcmvIL-10 for HCMV) or manipulation of the cellular IL-10 signaling cascade. Based on the in vitro demonstrations of its pleiotropic and cell type-dependent modulatory nature, hcmvIL-10 could profoundly attenuate host immunity, facilitating the establishment and maintenance of a persistent infection in an immune-competent host. To investigate the impact of extrinsic IL-10 on the induction and maintenance of antiviral immune responses in vivo, rhesus macaques were inoculated with variants of rhesus cytomegalovirus (RhCMV) either expressing or lacking the RhCMV ortholog of hcmvIL-10 (rhcmvIL-10). The results show that rhcmvIL-10 alters the earliest host responses to viral antigens by dampening the magnitude and specificity of innate effector cells to primary RhCMV infection. In addition, there is a commensurate reduction in the quality and quantity of early and long-term, RhCMV-specific adaptive immune responses. These findings provide a mechanistic basis of how early interactions between a newly infected host and HCMV could shape the long-term virus–host balance, which may facilitate the development of new prevention and intervention strategies for HCMV.
Mechanism of tungsten-dependent acetylene hydratase from quantum chemical calculations
Authors: Liao Rong-Zhen , Yu Jian-Guo , Himo Fahmi
Published: December 2010

Acetylene hydratase is a tungsten-dependent enzyme that catalyzes the nonredox hydration of acetylene to acetaldehyde. Density functional theory calculations are used to elucidate the reaction mechanism of this enzyme with a large model of the active site devised on the basis of the native X-ray crystal structure. Based on the calculations, we propose a new mechanism in which the acetylene substrate first displaces the W-coordinated water molecule, and then undergoes a nucleophilic attack by the water molecule assisted by an ionized Asp13 residue at the active site. This is followed by proton transfer from Asp13 to the newly formed vinyl anion intermediate. In the subsequent isomerization, Asp13 shuttles a proton from the hydroxyl group of the vinyl alcohol to the α-carbon. Asp13 is thus a key player in the mechanism, but also W is directly involved in the reaction by binding and activating acetylene and providing electrostatic stabilization to the transition states and intermediates. Several other mechanisms are also considered but the energetic barriers are found to be very high, ruling out these possibilities.
There’s plenty of time for evolution
Authors: Wilf Herbert S. , Ewens Warren J.
Published: December 2010

Objections to Darwinian evolution are often based on the time required to carry out the necessary mutations. Seemingly, exponential numbers of mutations are needed. We show that such estimates ignore the effects of natural selection, and that the numbers of necessary mutations are thereby reduced to about
K
 log 
L
, rather than
K

L

, where
L
is the length of the genomic “word,” and
K
is the number of possible “letters” that can occupy any position in the word. The required theory makes contact with the theory of radix-exchange sorting in theoretical computer science, and the asymptotic analysis of certain sums that occur there.
Chemical generation of bispecific antibodies
Authors: Doppalapudi Venkata R. , Huang Jie , Liu Dingguo , Jin Ping , Liu Bin , Li Lingna , Desharnais Joel , Hagen Crystal , Levin Nancy J. , Shields Michael J. , Parish Michelle , Murphy Robert E. , Del Rosario Joselyn , Oates Bryan D. , Lai Jing-Yu , Matin Marla J. , Ainekulu Zemeda , Bhat Abhijit , Bradshaw Curt W. , Woodnutt Gary , Lerner Richard A. , Lappe Rodney W.
Published: December 2010

Bispecific antibodies (BsAbs) are regarded as promising therapeutic agents due to their ability to simultaneously bind two different antigens. Several bispecific modalities have been developed, but their utility is limited due to problems with stability and manufacturing complexity. Here we report a versatile technology, based on a scaffold antibody and pharmacophore peptide heterodimers, that enables rapid generation and chemical optimization of bispecific antibodies, which are termed bispecific CovX-Bodies. Two different peptides are joined together using a branched azetidinone linker and fused to the scaffold antibody under mild conditions in a site-specific manner. Whereas the pharmacophores are responsible for functional activities, the antibody scaffold imparts long half-life and Ig-like distribution. The pharmacophores can be chemically optimized or replaced with other pharmacophores to generate optimized or unique bispecific antibodies. As a prototype, we developed a bispecific antibody that binds both vascular endothelial growth factor (VEGF) and angiopoietin-2 (Ang2) simultaneously, inhibits their function, shows efficacy in tumor xenograft studies, and greatly augments the antitumor effects of standard chemotherapy. This unique antiangiogenic bispecific antibody is in phase-1 clinical trials.
L3MBTL1 polycomb protein, a candidate tumor suppressor in del(20q12) myeloid disorders, is essential for genome stability
Authors: Gurvich Nadia , Perna Fabiana , Farina Andrea , Voza Francesca , Menendez Silvia , Hurwitz Jerard , Nimer Stephen D.
Published: December 2010

The
l3mbtl1
gene is located on the long arm of chromosome 20 (q12), within a region commonly deleted in several myeloid malignancies. L3MBTL1 is a human homolog of the Drosophila polycomb L(3)MBT tumor suppressor protein and thus a candidate tumor suppressor in del(20q12) myeloid disorders. We used the loss-of-function approach to explore the possible tumor suppressive mechanism of L3MBTL1 and found that depletion of L3MBTL1 from human cells causes replicative stress, DNA breaks, activation of the DNA damage response, and genomic instability. L3MBTL1 interacts with Cdc45, MCM2-7 and PCNA, components of the DNA replication machinery, and is required for normal replication fork progression, suggesting that L3MBTL1 causes DNA damage, at least in part, by perturbing DNA replication. An activated DNA damage response and genomic instability are common features in tumorigenesis and a consequence of overexpression of many oncogenes. We propose that the loss of L3MBTL1 contributes to the development of 20q
−
hematopoietic malignancies by inducing replicative stress, DNA damage, and genomic instability.
Ethnic Consciousness in the British Isles
Authors: Nichols Patricia C.
Published: December 2010

La etna konscio en Britaj Insuloj: demandoj por la lingvoplanado
La lingvoplanado okazas ne nur en disvolvigantaj landoj, sed ankau en jam evoluintaj, tamcn pri aliaj lingvoproblemoj. Post la normigo de grava, grandplimulta lingvo, kiel la angla en la Britaj Insuloj, okazas du cefaj lingvaj problemoj rilate al etnoj. Unue, indiĝenaj minoritatoj volas restarigi au reteni lingvojn, kiuj simbolas la etnan identon; due, enmigrintoj devas lerni la lingvon au lingvovarion de la plimulto.
Estas malfacile difini la terminon etno en la Britaj Insuloj. Nek la (jam delonge inter-miksiĝinta) kelta raso, nek la religio, nek la lingvo nun povas esti difinilo. La keltaj lingvoj estas tamen parolataj en izolitaj regionoj kaj elektitaj kiel signifaj indikiloj kaj konserviloj de la naciaj identoj de Skotlando, Irlando kaj Kimrujo, kvankam la grandaj plimultoj tie jam parolas la anglan kiel la unuan lingvon, kiel faras ec la propagand-antoj de la keltaj lingvoj.
La lingvaj situacioj en la tri lokoj evoluis malsame. En Irlando la movado por restarigi la gaelan mildigis sian postulon al nura 'konservo' . En Skotlando la ekzisto de du etnaj lingvoj, la skotgaela kaj la anglaparenca skota, obstaklis la etnolingvan movadon. Nur en Kimrujo iom prosperas, kaj kulture kaj politike, la etna lingvo.
La historioj de la keltaj lingvoj instruas kelkajn lecionojn. Literatura tradicio. religia uzado, normigo kaj amasmedia uzado helpas vivadigi lingvon. Monsparoj ce lingvo-protektado povas konduki al multkostaj protcstoj. Eĉ ĉe mortaj lingvoj, oficialaj simbolaj agoj povas kontentigi etnajn grupojn.
La enmigrintoj, kiuj havas la plej gravajn lingvoproblemojn en Britujo, estas la karib-anoj kaj la sudazianoj. Ili spertas problemojn cefe en la lernejoj, kiuj ekde 1963 klopodas sistemece pliefikigi la metodojn por instrui la anglan al ili sed faras nenion por konservi kompetentojn pri aliaj lingvoj. Tion faras iugrade sudazianaj asocioj. Car la karibanoj plejparte parolas iun variaĵon de la angla, la lernejoj kutimas supozi, ke ili ne havas lingvoproblemojn, kaj traktas ilin same kiel anglojn. Sed la lingvaj kaj aliaj diferencoj kauzas, ke ili multe superproporcie plenigas la klasojn de lern-problemuloj. La lernejoj agnoskas la lingvajn problemojn de la sudazianoj, car ili estas komplete alilingvaj, sed ne konsideras altrudon de la angla kiel diskriminacion au mal-avantagigon. La sudazianoj, pli organizitaj kaj tradicie pli skrib- kaj leg-direktitaj ol la karibanoj, ankaŭ pli sukcesas. Surbaze de la limigitaj informoj sajnas, ke modera en-kalkuligado de lingvokondutaj diferencoj ce samlingvaj enmigrintoj faciligus ties edukigon.
Penoj por konservi la lingvojn de naciaj malplimultoj kaj de enmigrintoj povus utili ne nur al tiuj grupoj mem, sed ankaŭ al la evoluo de kunlabora, kulture rica socio.
Language Skills and Earnings Inequalities
Authors: Lacroix Robert , Vaillancourt François
Published: December 2010

RESUME
Attributs linguistiques et revenus de travail: Problèmes de mesurement et explications économiques
L'effet des attributs linguistiques sur les revenus de travail doit être mesuré à l'aide des méthodes d'analyse multivariée plutôt qu'en utilisant des tableaux croisés et ce car cette dernière méthode associe aux attributs linguistiques des effets résultants de d'autres déterminants du revenu. Pour utiliser l'analyse multivariée on doit modéliser le processus de détermination de revenu. Ceci peut être fait à l'aide de la théorie économique qui peut expliquer les écarts de revenus entre groupes linguistiques. Nous faisons appel à des données sur les revenus de travail de 1973 des diplômés universitaires du Québec pour appuyer notre argumentation. Nous montrons que les résultats tirés des tableaux croisés different fortement de ceux de l'analyse multivariée et qu'un cadre d'analyse offre/demande fournit des prédictions qui se vérifient dans le cas de l'anglais et du français au Québec.
RESUMO
Lingvoscioj kaj enspezaj malegalecoj: Problemoj de mezurado kaj ekonomia eksplikado
Mezurante la efikon de lingvoscioj al salajroj, oni pli guste uzu analizon plurvariantan ol kructabelan, car la kructabela misatribuas al la lingvoscio salajrajn efïkojn kiuj rezultas de aliaj influoj. Por uzi la plurvariantan analizon oni devas modeli la procezon de salajro-kaúzado. Oni povas tion fari per la teorio ekonomia, kiu povas ekspliki lingvo-rilatajn malegalecojn de salajroj. Ni uzas statistikojn pri la salajroj en 1973 de universitat-diplomitoj en Kebekio por apogi ci-tiujn asertojn. Ni montras ke kructabelaj kaj plurvariantaj rezultoj tre malsimilas kaj ke analiza bazo de ofertado kaj mendado donas konfirmeblajn prognozojn pri la angla kaj franca lingvoj in Kebekio.