bluuebunny/crossref_metadata_2025 huggingface dataset:
The surface tectonics of mantle lithosphere delamination following ocean lithosphere subduction: Insights from physical‐scaled analogue experiments
Authors: Göğüş Oğuz H. , Pysklywec Russell N. , Corbi Fabio , Faccenna Claudio
Published: May 2011

Many postulated lithospheric removal events occur in regions with an earlier history of subduction, but the relationship between the two processes has not been explored. In this work, we use physical‐scaled analogue experiments to investigate the evolution from ocean lithosphere subduction to collision and possible delamination of the mantle lithosphere from the crust. We test how varying the magnitude of plate convergence alters the behavior of the subduction‐delamination model. Our experiments show that a retreating ocean proplate can evolve to continental mantle lithosphere delamination. Negative surface topography is supported at the delamination hinge, and this migrates back with the peeling lithosphere. With high plate convergence, delamination is suppressed. Rather, the crust and mantle lithosphere split at the collision zone in a form of flake tectonics as oncoming procrust is accreted on top of the retroplate and the promantle lithosphere subducts below. Localized high topography develops at this zone of crustal accretion and thickening. The results suggest that delamination may be a continental continuation of plate retreat and that lithospheric removal is triggered by the transition from one process to another.
Slumping and mass transport deposition in the Nankai fore arc: Evidence from IODP drilling and 3‐D reflection seismic data
Authors: Strasser Michael , Moore Gregory F. , Kimura Gaku , Kopf Achim J. , Underwood Michael B. , Guo Junhua , Screaton Elizabeth J.
Published: May 2011

Multiple lines of evidence exist for a range of sediment mass movement processes within the shallow megasplay fault zone (MSFZ) area and the adjacent slope basin in the outer fore arc of the Nankai subduction zone, Japan. Diagnostic features observed in three‐dimensional reflection seismic data and in cores of the Integrated Ocean Drilling Program (IODP) document a multifarious mass movement history spanning ∼2.87 million years. Various modes and scales of sediment remobilization can be related to the different morphotectonic settings in which they occurred. From this evidence, we decipher the tectonic control on slumping and mass transport deposition in the Nankai fore arc. Three periods of intensified mass wasting coincided with pulses of enhanced activity on the splay fault: (1) an initial phase of juvenile out‐of‐sequence thrusting ∼1.95 to 1.7 Ma, (2) a reactivation phase between ∼1.55 and 1.24 Ma, and (3) at about 1 Ma, during a phase of uplift of the fore‐arc high and motion along the MSFZ. We suggest that slope oversteepening, extensional stress regimes, and lateral transmission of fluid overpressures may have preconditioned the slope sediments to fail. Individual mass‐wasting events may have been triggered by dynamic loading from earthquake waves and/or transient pulses of pore pressure along the splay fault. Overall, our results provide insights into the complicated interplay between tectonic and submarine mass movement processes. We demonstrate that detailed knowledge about the spatial and temporal distribution of submarine mass movements can be integrated into a holistic reconstruction of tectonostratigraphic evolution of accretionary margins.
Making and breaking an island arc: A new perspective from the Oligocene Kyushu‐Palau arc, Philippine Sea
Authors: Ishizuka Osamu , Taylor Rex N. , Yuasa Makoto , Ohara Yasuhiko
Published: May 2011

The Kyushu‐Palau Ridge (KPR) is a 2600 km long remnant island arc that is separated from the active Izu‐Bonin‐Mariana (IBM) arc by a series of spreading and rift basins. We present 40Ar/39Ar ages and geochemical data for the entire length of the Kyushu‐Palau arc as well as for the conjugate arc which is stranded within the IBM fore arc. New 40Ar/39Ar ages indicate that the KPR was active between 25 and 48 Ma, but the majority of the exposed volcanism occurred in the final phase, between 25 and 28 Ma. Rifting of the Kyushu‐Palau arc to form the Shikoku and Parece Vela basins occurred simultaneously along the length of the arc (circa 25 Ma), and at a similar distance from the trench. Unlike the IBM, the KPR has only limited systematic along‐arc geochemical trends. Two geochemical components within the KPR indicate an origin in the suprasubduction mantle. First, EM‐1‐like lavas are identified in a restricted section of the arc, suggesting a localized heterogeneity. Second, EM‐2‐like arc volcanoes formed on juvenile West Philippine Basin crust, potentially reflecting ingress of mantle from the then active EM‐2 province which lies in the west. Another geochemical heterogeneity is found at the KPR–Daito Ridge intersection where the arc developed on preexisting Cretaceous Daito Ridge crust. The geochemical characteristics at this intersection likely result from the involvement of sub–Daito Ridge lithospheric mantle. Subduction flux beneath the KPR generally matches post–45 Ma Eocene/Oligocene lavas in the IBM fore arc, involving fluids and melts derived from altered igneous crust.
Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea
Authors: Cook Mea S. , Keigwin Lloyd D. , Birgel Daniel , Hinrichs Kai‐Uwe
Published: May 2011

There is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period. In this study of two sediment cores from the southeast Bering Sea (700 m and 1467 m water depth), we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor. Within the uncertainty of the radiocarbon age model, the episodes are contemporaneous in the two cores and have similar timing and duration as Dansgaard‐Oeschger events. The episodes are marked by horizons of sediment containing 13C‐depleted authigenic carbonate minerals; 13C‐depleted archaeal and bacterial lipids, which resemble those found in ANME‐1 type anaerobic methane oxidizing microbial consortia; and changes in the abundance and species distribution of benthic foraminifera. The similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region‐wide increase in the upward flux of methane bearing fluids. This study is the first observation outside Santa Barbara Basin of pervasive, repeated methane flux in glacial sediments. However, contrary to the “Clathrate Gun Hypothesis” (Kennett et al., 2003), these coring sites are too deep for methane hydrate destabilization to be the cause, implying that a much larger part of the ocean's sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales. We speculate that pulses of methane in these opal‐rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis. The release could be triggered by seismic shaking on the Aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials.
Simulating the impact of freshwater inputs and deep‐draft icebergs formed during a MIS 6 Barents Ice Sheet collapse
Authors: Green Clare L. , Green J. A. Mattias , Bigg Grant R.
Published: May 2011

An intermediate complexity climate model is used to simulate the collapse of the Barents Ice Sheet during Marine Isotope Stage 6 (MIS 6; 140 ka B.P) with the purpose of investigating whether a mass input of freshwater from the collapse could have affected the convection and deep water formation in the North Atlantic Ocean. Further experiments used a coupled dynamic and thermodynamic iceberg model to determine the effects of deep‐draft icebergs, rather than freshwater alone, on the ocean circulation. The results predict that the collapse of the Barents Ice Sheet had a significant impact on the meridional overturning circulation in both the Atlantic and Pacific oceans. Freshwater fluxes have more of an impact on the Atlantic overturning circulation during the actual release period compared to icebergs, but the bergs induce effects over longer time scales even after the pulse is removed. Freshwater fluxes of 0.15 sverdrup (Sv) and iceberg surges of 0.1 Sv trigger significant changes in the global patterns, particularly in the North Pacific where there is strengthening of the overturning circulation at the expense of that in the North Atlantic, and associated increases in Pacific sea surface temperatures. These results highlight the importance of simulating not only the correct flux but also the form of the freshwater input from ice sheet collapses appropriately.
The role of land use and soils in regulating water flow in small headwater catchments of the Andes
Authors: Roa‐García M. C. , Brown S. , Schreier H. , Lavkulich L. M.
Published: May 2011

Land use changes can have a significant impact on the terrestrial component of the water cycle. This study provides a comparison of three small headwater catchments in the Andean mountains of Colombia with different composition of land use. Several methods were used to quantify differences in the hydrological behavior of these catchments such as flow duration curves, stormflow analysis, and the linear reservoir concept. They were combined with an analysis of the characteristics of soils that contribute to understanding the aggregate catchment hydrological behavior. Andisols, which are soils formed in volcanic areas and with a large capacity to hold water, amplify differences in land use and limit the potential impact of land use management activities (conservation or restoration) on the water regulation function of catchments. Of the three studied catchments, less variability of flows was observed from the catchment with a larger percentage of area in forest, and a slower decrease of flows in the dry season was observed for the catchment with a relatively higher percentage of area in wetlands. Evidence is provided for the infiltration trade‐off hypothesis for tropical environments, which states that after forest removal, soil infiltration rates are smaller and the water losses through quick flow are larger than the gains by reduced evapotranspiration; this is compatible with the results of the application of the linear reservoir concept showing a faster release of water for the least forested catchment.
Compositional modeling of three‐phase flow with gravity using higher‐order finite element methods
Authors: Moortgat Joachim , Sun Shuyu , Firoozabadi Abbas
Published: May 2011

A wide range of applications in subsurface flow involve water, a nonaqueous phase liquid (NAPL) or oil, and a gas phase, such as air or CO2. The numerical simulation of such processes is computationally challenging and requires accurate compositional modeling of three‐phase flow in porous media. In this work, we simulate for the first time three‐phase compositional flow using higher‐order finite element methods. Gravity poses complications in modeling multiphase processes because it drives countercurrent flow among phases. To resolve this issue, we propose a new method for the upwinding of three‐phase mobilities. Numerical examples, related to enhanced oil recovery and carbon sequestration, are presented to illustrate the capabilities of the proposed algorithm. We pay special attention to challenges associated with gravitational instabilities and take into account compressibility and various phase behavior effects, including swelling, viscosity changes, and vaporization. We find that the proposed higher‐order method can capture sharp solution discontinuities, yielding accurate predictions of phase boundaries arising in computational three‐phase flow. This work sets the stage for a broad extension of the higher‐order methods for numerical simulation of three‐phase flow for complex geometries and processes.
Non‐tidal ocean loading effects on geodetic GPS heights
Authors: Williams S. D. P. , Penna N. T.
Published: May 2011

GPS observations used in geophysical studies are not usually corrected for non‐tidal ocean loading (NTOL) displacement. Here we investigate NTOL effects on 3–4 year GPS height time series from 17 sites around the southern North Sea, and compute the NTOL displacement according to two ocean models; the global ECCO model and a high resolution regional model, POLSSM, which covers the northwest European continental shelf. To assess the susceptibility of GPS height estimates to NTOL, reprocessed GIPSY PPP daily solutions are corrected for the resulting displacement, together with atmospheric pressure loading (ATML). We find that the displacements due to NTOL are comparable in size to ATML and the combined correction reduces the variance by 12–22 mm2 (20–30% reduction in RMS). We find that POLSSM outperforms ECCO, with around an 11% greater variance reduction, and hence high resolution models are recommended to correct GPS heights for NTOL.
Evidence for a weakening of tropical surface wind extremes in response to atmospheric warming
Authors: Gastineau Guillaume , Soden Brian J.
Published: May 2011

The changes of extreme winds and its links with precipitation are assessed over the past two decades using daily satellite observations and climate model simulations. Both observations and models indicate a decrease in the frequency of the strongest wind events and an increase in the frequency of light wind events in response to a warming of the tropical oceans. The heaviest precipitation events are found to be more frequent when the tropical oceans warm, but the surface winds associated with these extreme rainfall events weaken. These results add further evidence to suggest that the atmospheric circulation becomes less energetic as the climate warms. It further suggests that the enhancement of the extreme precipitation events is mainly a result of increasing atmospheric water vapor and occurs despite a weakening of the large‐scale circulation, which acts to diminish the mass convergence toward the precipitating zones.
Community profiling and gene expression of fungal assimilatory nitrate reductases in agricultural soil
Authors: Gorfer Markus , Blumhoff Marzena , Klaubauf Sylvia , Urban Alexander , Inselsbacher Erich , Bandian Dragana , Mitter Birgit , Sessitsch Angela , Wanek Wolfgang , Strauss Joseph
Published: May 2011

Although fungi contribute significantly to the microbial biomass in terrestrial ecosystems, little is known about their contribution to biogeochemical nitrogen cycles. Agricultural soils usually contain comparably high amounts of inorganic nitrogen, mainly in the form of nitrate. Many studies focused on bacterial and archaeal turnover of nitrate by nitrification, denitrification and assimilation, whereas the fungal role remained largely neglected. To enable research on the fungal contribution to the biogeochemical nitrogen cycle tools for monitoring the presence and expression of fungal assimilatory nitrate reductase genes were developed. To the ∼100 currently available fungal full-length gene sequences, another 109 partial sequences were added by amplification from individual culture isolates, representing all major orders occurring in agricultural soils. The extended database led to the discovery of new horizontal gene transfer events within the fungal kingdom. The newly developed PCR primers were used to study gene pools and gene expression of fungal nitrate reductases in agricultural soils. The availability of the extended database allowed affiliation of many sequences to known species, genera or families. Energy supply by a carbon source seems to be the major regulator of nitrate reductase gene expression for fungi in agricultural soils, which is in good agreement with the high energy demand of complete reduction of nitrate to ammonium.
Working With Teenagers Who Stutter: Simple Suggestions for a Complex Challenge
Authors: Zebrowski Patricia , Wolf Anthony
Published: May 2011

This paper stems from an invited seminar that we presented at the 2010 ASHA convention in Philadelphia. At that time, we were asked to develop a workshop for speech-language pathologists focused on the treatment of adolescents who stutter and to present an approach that integrated two key areas in stuttering therapy for this population: speech modification and related strategies within the context of adolescent development and experience. We present a philosophy of how to work with teens based on understanding where they are developmentally, psychologically, and socially, and we discuss how to use this philosophy to tailor a therapy approach that fits their needs.
Talking About Stuttering With a Known Person Who Stutters: Impact on Perceptions Towards Stuttering
Authors: Hughes Charles , Gabel Rodney , Palasik Scott
Published: May 2011

The purpose of this study was to explore the extent to which talking about stuttering with a known person who stuttered affected perceptions towards stuttering. A total of 152 participants completed survey items related to demographic information, perceptions of the known person who stutters, and whether or not they discussed stuttering with the person they knew. Finally, participants completed two separate semantic differential scales. The first scale was completed in regard to the person participants knew who stuttered, while the second semantic differential scale was completed regarding a hypothetical “average” person who stuttered. A one-way analysis of variance was conducted for these two semantic differential scales, with the effect of the independent variable of whether participants talked about stuttering with the known person who stuttered. Findings revealed that talking about stuttering with a known person who stuttered did not affect perceptions towards the person or an average person who stuttered. Despite this finding, it should be noted that participants reported relatively positive attitudes towards both the person they knew who stuttered and the average person who stuttered. Future research should continue to explore the benefits of disclosure or discussing stuttering for both people who stutter and listeners.
The Preschool Stuttering Screen for Health Care Professionals
Authors: Donaher Joseph , Deery Christina , Vogel Sarah
Published: May 2011

Healthcare professionals require a thorough understanding of stuttering since they frequently play an important role in the identification and differential diagnosis of stuttering for preschool children. This paper introduces The Preschool Stuttering Screen for Healthcare Professionals (PSSHP) which highlights risk factors identified in the literature as being associated with persistent stuttering. By integrating the results of the checklist with a child’s developmental profile, healthcare professionals can make better-informed, evidence-based decisions for their patients.
Lagrangian coherent structures and the smallest finite-time Lyapunov exponent
Authors: Haller George , Sapsis Themistoklis
Published: May 2011

We point out that local minimizing curves, or troughs, of the smallest finite-time Lyapunov exponent (FTLE) field computed over a time interval [t0, t] and graphed over trajectory positions at time t mark attracting Lagrangian coherent structures (LCSs) at t. For two-dimensional area-preserving flows, we conclude that computing the largest forward-time FTLE field by itself is sufficient for locating both repelling LCSs at t0 and attracting LCSs at t. We illustrate our results on analytic examples, as well as on a two-dimensional experimental velocity field measured near a swimming jellyfish.
Strong reduction of V4+ amount in vanadium oxide/hexadecylamine nanotubes by doping with Co2+ and Ni2+ ions: Electron paramagnetic resonance and magnetic studies
Authors: Saleta M. E. , Troiani H. E. , Ribeiro Guevara S. , Ruano G. , Sánchez R. D. , Malta M. , Torresi R. M.
Published: May 2011

In this work we present a complete characterization and magnetic study of vanadium oxide/hexadecylamine nanotubes (VOx/Hexa NT’s) doped with Co2+ and Ni2+ ions. The morphology of the NT’s has been characterized by transmission electron microscopy, while the metallic elements have been quantified by the instrumental neutron activation analysis technique. The static and dynamic magnetic properties were studied by collecting data of magnetization as a function of magnetic field and temperature and by electron paramagnetic resonance. At difference of the majority reports in the literature, we do not observe magnetic dimers in vanadium oxide nanotubes. Also, we observed that the incorporation of metallic ions (Co2+, S = 3/2 and Ni2+, S = 1) decreases notably the amount of V4+ ions in the system, from 14−16% (nondoped case) to 2%−4%, with respect to the total vanadium atoms (fact corroborated by XPS experiments) anyway preserving the tubular nanostructure. The method to decrease the amount of V4+ in the nanotubes improves considerably their potential technological applications as Li-ion batteries cathodes.
Effects of ultra-low Al alloying In(Al)As layer on the formation and evolution of InAs/GaAs quantum dots
Authors: Zhou X. L. , Chen Y. H. , Li T. F. , Zhou G. Y. , Zhang H. Y. , Ye X. L. , Xu Bo , Wang Z. G.
Published: May 2011

We have introduced ultra-low Al composition at the two-dimensional to three-dimensional transition stage of InAs/GaAs quantum dots (QDs) formation. Two main effects of AlAs on the QDs are revealed: one is to lower the nucleation barrier so as to reduce the critical nucleation thickness of QDs, which is demonstrated by a surface kinetic nucleation model. The other is to facilitate the In atoms migration from wetting layer (WL) to QDs, which holds some signatures such as both increased QDs density and size with increasing AlAs composition, as well as the peak energy red-shift of photoluminescence spectra. The enhanced In atoms migration from WL to QDs is further confirmed via photo-modulated reflectance experiments and energy band calculation, which both demonstrate the reduction of effective WL thickness after AlAs insertion. The observed effects of AlAs on QDs formation and growth evolution could be explained by the Al-alloying effects of InAs wetting layer.
The effect of the electron-phonon coupling on the effective thermal conductivity of metal-nonmetal multilayers
Authors: Ordonez-Miranda J. , Alvarado-Gil J. J. , Yang Ronggui
Published: May 2011

The metal-nonmetal interface plays a critical role in modern electronic and energy conversion devices. For example, metal-nonmetal multilayered structures have recently been proposed as promising materials for solid-state thermionic devices, which could potentially achieve an efficiency that might not be feasible for metals or semiconductors alone. In this work, the effective thermal conductivity of a metal-nonmetal multilayered system (superlattices) is studied using the two-temperature model of heat conduction. By defining the total interfacial thermal resistance, which strongly depends on the electron-phonon coupling factor, it is shown that the thermal conductivity of the system has a simple interpretation as the sum of thermal resistances in series. The role of the electron-phonon coupling and the phonon-phonon interfacial thermal resistance on the total interfacial thermal resistance is discussed. The derived analytical expressions show that the effective thermal conductivity of the multilayered structure is, remarkably, determined by the ratio between the thickness of the metal layers and their intrinsic electron-phonon coupling length. It is demonstrated that the effective thermal conductivity of the metal-nonmetal system can be smaller, equal to, or larger than the thermal conductivity of the nonmetal layer, depending on the length of the metal layer.
The FAST module: An add-on unit for driving commercial scanning probe microscopes at video rate and beyond
Authors: Esch Friedrich , Dri Carlo , Spessot Alessio , Africh Cristina , Cautero Giuseppe , Giuressi Dario , Sergo Rudi , Tommasini Riccardo , Comelli Giovanni
Published: May 2011

We present the design and the performance of the FAST (Fast Acquisition of SPM Timeseries) module, an add-on instrument that can drive commercial scanning probe microscopes (SPM) at and beyond video rate image frequencies. In the design of this module, we adopted and integrated several technical solutions previously proposed by different groups in order to overcome the problems encountered when driving SPMs at high scanning frequencies. The fast probe motion control and signal acquisition are implemented in a way that is totally transparent to the existing control electronics, allowing the user to switch immediately and seamlessly to the fast scanning mode when imaging in the conventional slow mode. The unit provides a completely non-invasive, fast scanning upgrade to common SPM instruments that are not specifically designed for high speed scanning. To test its performance, we used this module to drive a commercial scanning tunneling microscope (STM) system in a quasi-constant height mode to frame rates of 100 Hz and above, demonstrating extremely stable and high resolution imaging capabilities. The module is extremely versatile and its application is not limited to STM setups but can, in principle, be generalized to any scanning probe instrument.
Spin-polarized transport in a full magnetic pn tunnel junction
Authors: Comesaña E. , Aldegunde M. , Garcia-Loureiro A. J.
Published: May 2011

Simulations of the tunneling current as a function of voltage and temperature for a Zener diode where both sides are ferromagnetic have been performed. The current is evaluated as a function of the applied bias, the magnetization, and the temperature on the diode. The tunneling magnetoresistance is also analyzed. Mn doped GaAs parameters were used to simulate a highly asymmetric doped diode, which leads to a large difference on the magnetization values between the p and n sides.
Compact fiber-coupled terahertz spectroscopy system pumped at 800 nm wavelength
Authors: Ellrich Frank , Weinland Tristan , Molter Daniel , Jonuscheit Joachim , Beigang René
Published: May 2011

Photonic terahertz (THz) technology using femtosecond (fs) lasers has a great potential in a wide range of applications, such as non-destructive testing of objects or spectroscopic identification of chemical substances. For industrial purposes, a THz system has to be compact and easily implementable into the particular application. Therefore, fiber-coupled THz systems are the key to a widespread use of THz technology. In order to have flexible THz emitters and detectors near infrared fs light pulses have to be sent through optical fibers of considerable length. As a consequence, the fiber's dispersion has to be compensated for and nonlinear effects in the fiber have to be minimized. A fiber-based THz time-domain spectroscopy system of high stability, flexibility, and portability is presented here.
A piezo-thermal probe for thermomechanical analysis
Authors: Gaitas Angelo , Gianchandani Sachi , Zhu Weibin
Published: May 2011

Thermomechanical analysis (TMA) is widely used to characterize materials and determine transition temperatures and thermal expansion coefficients. Atomic-force microscopy (AFM) microcantilevers have been used for TMA. We have developed a micromachined probe that includes two embedded sensors: one for measuring the mechanical movement of the probe (deflection) and another for providing localized heating. The new probe reduces costs and complexity and allow for portability thereby eliminating the need for an AFM. The sensitivity of the deflection element ((ΔR/R)/deflection) is 0.1 ppm/nm and its gauge factor is 3.24. The melting temperature of naphthalene is measured near 78.5  °C.
Multimodal coherent anti-Stokes Raman spectroscopic imaging with a fiber optical parametric oscillator
Authors: Zhai Yan-Hua , Goulart Christiane , Sharping Jay E. , Wei Huifeng , Chen Su , Tong Weijun , Slipchenko Mikhail N. , Zhang Delong , Cheng Ji-Xin
Published: May 2011

We report on multimodal coherent anti-Stokes Raman scattering (CARS) imaging with a source composed of a femtosecond fiber laser and a photonic crystal fiber (PCF)-based optical parametric oscillator (FOPO). By switching between two PCFs with different zero dispersion wavelengths, a tunable signal beam from the FOPO covering the range from 840 to 930 nm was produced. By combining the femtosecond fiber laser and the FOPO output, simultaneous CARS imaging of a myelin sheath and two-photon excitation fluorescence imaging of a labeled axons in rat spinal cord have been demonstrated at the speed of 20 μs per pixel.
On-demand trajectory control of continuously generated airborne microdroplets
Authors: Ishiwata Tomoki , Sakai Keiji
Published: May 2011

A technique to control the trajectory of in-flight microdroplets is described. The localized electric field generated by a needle electrode applies the dielectrophoretic force to the droplet to deflect its trajectory. Deflection by as much as 0.2 rad can be achieved, sufficient for industrial use. Moreover, highly selective control among droplets in a stream was demonstrated with the electric field modulations of 10 μs, which corresponds to the sorting speed of 105 s−1. In contrast to the conventional electrostatic control, the proposed technique is effective also for insulating liquids, allowing it to be applied to a wider range of materials.
Effects of quantum confinement and shape on band gap of core/shell quantum dots and nanowires
Authors: Gao Faming
Published: May 2011

A quantum confinement model for nanocrystals developed is extended to study for the optical gap shifts in core/shell quantum dots and nanowires. The chemical bond properties and gap shifts in the InP/ZnS, CdSe/CdS, CdSe/ZnS, and CdTe/ZnS core/shell quantum dots are calculated in detail. The calculated band gaps are in excellent agreement with experimental values. The effects of structural taping and twinning on quantum confinement of InP and Si nanowires are elucidated. It is found theoretically that a competition between the positive Kubo energy-gap shift and the negative surface energy shift plays the crucial role in the optical gaps of these nanosystems.
A 2,300-year-long annually resolved record of the South American summer monsoon from the Peruvian Andes
Authors: Bird Broxton W. , Abbott Mark B. , Vuille Mathias , Rodbell Donald T. , Stansell Nathan D. , Rosenmeier Michael F.
Published: May 2011

Decadal and centennial mean state changes in South American summer monsoon (SASM) precipitation during the last 2,300 years are detailed using an annually resolved authigenic calcite record of precipitation
δ
18
O from a varved lake in the Central Peruvian Andes. This unique sediment record shows that
δ
18
O peaked during the Medieval Climate Anomaly (MCA) from A.D. 900 to 1100, providing evidence that the SASM weakened considerably during this period. Minimum
δ
18
O values occurred during the Little Ice Age (LIA) between A.D. 1400 and 1820, reflecting a prolonged intensification of the SASM that was regionally synchronous. After the LIA,
δ
18
O increased rapidly, particularly during the current warm period (CWP; A.D. 1900 to present), indicating a return to reduced SASM precipitation that was more abrupt and sustained than the onset of the MCA. Diminished SASM precipitation during the MCA and CWP tracks reconstructed Northern Hemisphere and North Atlantic warming and a northward displacement of the Intertropical Convergence Zone (ITCZ) over the Atlantic, and likely the Pacific. Intensified SASM precipitation during the LIA follows reconstructed Northern Hemisphere and North Atlantic cooling, El Niño-like warming in the Pacific, and a southward displacement of the ITCZ over both oceans. These results suggest that SASM mean state changes are sensitive to ITCZ variability as mediated by Western Hemisphere tropical sea surface temperatures, particularly in the Atlantic. Continued Northern Hemisphere and North Atlantic warming may therefore help perpetuate the recent reductions in SASM precipitation that characterize the last 100 years, which would negatively impact Andean water resources.
Peptide secondary structure modulates single-walled carbon nanotube fluorescence as a chaperone sensor for nitroaromatics
Authors: Heller Daniel A. , Pratt George W. , Zhang Jingqing , Nair Nitish , Hansborough Adam J. , Boghossian Ardemis A. , Reuel Nigel F. , Barone Paul W. , Strano Michael S.
Published: May 2011

A class of peptides from the bombolitin family, not previously identified for nitroaromatic recognition, allows near-infrared fluorescent single-walled carbon nanotubes to transduce specific changes in their conformation. In response to the binding of specific nitroaromatic species, such peptide–nanotube complexes form a virtual “chaperone sensor,” which reports modulation of the peptide secondary structure via changes in single-walled carbon nanotubes, near-infrared photoluminescence. A split-channel microscope constructed to image quantized spectral wavelength shifts in real time, in response to nitroaromatic adsorption, results in the first single-nanotube imaging of solvatochromic events. The described indirect detection mechanism, as well as an additional exciton quenching-based optical nitroaromatic detection method, illustrate that functionalization of the carbon nanotube surface can result in completely unique sites for recognition, resolvable at the single-molecule level.
Synthesis and characterization of a nanocrystalline diamond aerogel
Authors: Pauzauskie Peter J. , Crowhurst Jonathan C. , Worsley Marcus A. , Laurence Ted A. , Kilcoyne A. L. David , Wang Yinmin , Willey Trevor M. , Visbeck Kenneth S. , Fakra Sirine C. , Evans William J. , Zaug Joseph M. , Satcher Joe H.
Published: May 2011

Aerogel materials have myriad scientific and technological applications due to their large intrinsic surface areas and ultralow densities. However, creating a nanodiamond aerogel matrix has remained an outstanding and intriguing challenge. Here we report the high-pressure, high-temperature synthesis of a diamond aerogel from an amorphous carbon aerogel precursor using a laser-heated diamond anvil cell. Neon is used as a chemically inert, near-hydrostatic pressure medium that prevents collapse of the aerogel under pressure by conformally filling the aerogel’s void volume. Electron and X-ray spectromicroscopy confirm the aerogel morphology and composition of the nanodiamond matrix. Time-resolved photoluminescence measurements of recovered material reveal the formation of both nitrogen- and silicon- vacancy point-defects, suggesting a broad range of applications for this nanocrystalline diamond aerogel.
TGF-β signaling engages an ATM-CHK2-p53–independent RAS-induced senescence and prevents malignant transformation in human mammary epithelial cells
Authors: Cipriano Rocky , Kan Charlene E. , Graham James , Danielpour David , Stampfer Martha , Jackson Mark W.
Published: May 2011

Oncogene-induced senescence (OIS), the proliferative arrest engaged in response to persistent oncogene activation, serves as an important tumor-suppressive barrier. We show here that finite lifespan human mammary epithelial cells (HMEC) undergo a p16/RB- and p53-independent OIS in response to oncogenic RAS that requires TGF-β signaling. Suppression of TGF-β signaling by expression of a dominant-negative TGF-β type II receptor, use of a TGF-β type I receptor inhibitor, or ectopic expression of MYC permitted continued proliferation upon RAS expression. Surprisingly, unlike fibroblasts, shRNA-mediated knockdown of ATM or CHK2 was unable to prevent RAS-mediated OIS, arguing that the DNA damage response is not required for OIS in HMEC. Abrogation of TGF-β signaling not only allowed HMEC lacking p53 to tolerate oncogenic RAS but also conferred the capacity for anchorage-independent growth. Thus, the OIS engaged after dysregulated RAS expression provides an early barrier to malignant progression and is mediated by TGF-β receptor activation in HMEC. Understanding the mechanisms that initiate and maintain OIS in epithelial cells may provide a foundation for future therapies aimed at reengaging this proliferative barrier as a cancer therapy.
Versatile RNA-sensing transcriptional regulators for engineering genetic networks
Authors: Lucks Julius B. , Qi Lei , Mutalik Vivek K. , Wang Denise , Arkin Adam P.
Published: May 2011

The widespread natural ability of RNA to sense small molecules and regulate genes has become an important tool for synthetic biology in applications as diverse as environmental sensing and metabolic engineering. Previous work in RNA synthetic biology has engineered RNA mechanisms that independently regulate multiple targets and integrate regulatory signals. However, intracellular regulatory networks built with these systems have required proteins to propagate regulatory signals. In this work, we remove this requirement and expand the RNA synthetic biology toolkit by engineering three unique features of the plasmid pT181 antisense-RNA-mediated transcription attenuation mechanism. First, because the antisense RNA mechanism relies on RNA-RNA interactions, we show how the specificity of the natural system can be engineered to create variants that independently regulate multiple targets in the same cell. Second, because the pT181 mechanism controls transcription, we show how independently acting variants can be configured in tandem to integrate regulatory signals and perform genetic logic. Finally, because both the input and output of the attenuator is RNA, we show how these variants can be configured to directly propagate RNA regulatory signals by constructing an RNA-meditated transcriptional cascade. The combination of these three features within a single RNA-based regulatory mechanism has the potential to simplify the design and construction of genetic networks by directly propagating signals as RNA molecules.
Pyruvate carboxylase is required for glutamine-independent growth of tumor cells
Authors: Cheng Tzuling , Sudderth Jessica , Yang Chendong , Mullen Andrew R. , Jin Eunsook S. , Matés José M. , DeBerardinis Ralph J.
Published: May 2011

Tumor cells require a constant supply of macromolecular precursors, and interrupting this supply has been proposed as a therapeutic strategy in cancer. Precursors for lipids, nucleic acids, and proteins are generated in the tricarboxylic acid (TCA) cycle and removed from the mitochondria to participate in biosynthetic reactions. Refilling the pool of precursor molecules (anaplerosis) is therefore crucial to maintain cell growth. Many tumor cells use glutamine to feed anaplerosis. Here we studied how “glutamine-addicted” cells react to interruptions of glutamine metabolism. Silencing of glutaminase (GLS), which catalyzes the first step in glutamine-dependent anaplerosis, suppressed but did not eliminate the growth of glioblastoma cells in culture and in vivo. Profiling metabolic fluxes in GLS-suppressed cells revealed induction of a compensatory anaplerotic mechanism catalyzed by pyruvate carboxylase (PC), allowing the cells to use glucose-derived pyruvate rather than glutamine for anaplerosis. Although PC was dispensable when glutamine was available, forcing cells to adapt to low-glutamine conditions rendered them absolutely dependent on PC for growth. Furthermore, in other cell lines, measuring PC activity in nutrient-replete conditions predicted dependence on specific anaplerotic enzymes. Cells with high PC activity were resistant to GLS silencing and did not require glutamine for survival or growth, but displayed suppressed growth when PC was silenced. Thus, PC-mediated, glucose-dependent anaplerosis allows cells to achieve glutamine independence. Induction of PC during chronic suppression of glutamine metabolism may prove to be a mechanism of resistance to therapies targeting glutaminolysis.
Solute diffusion is hindered in the mitochondrial matrix
Authors: Dieteren Cindy E. J. , Gielen Stan C. A. M. , Nijtmans Leo G. J. , Smeitink Jan A. M. , Swarts Herman G. , Brock Roland , Willems Peter H. G. M. , Koopman Werner J. H.
Published: May 2011

Intracellular chemical reactions generally constitute reaction-diffusion systems located inside nanostructured compartments like the cytosol, nucleus, endoplasmic reticulum, Golgi, and mitochondrion. Understanding the properties of such systems requires quantitative information about solute diffusion. Here we present a novel approach that allows determination of the solvent-dependent solute diffusion constant (
D
solvent
) inside cell compartments with an experimentally quantifiable nanostructure. In essence, our method consists of the matching of synthetic fluorescence recovery after photobleaching (FRAP) curves, generated by a mathematical model with a realistic nanostructure, and experimental FRAP data. As a proof of principle, we assessed
D
solvent
of a monomeric fluorescent protein (AcGFP1) and its tandem fusion (AcGFP1
2
) in the mitochondrial matrix of HEK293 cells. Our results demonstrate that diffusion of both proteins is substantially slowed by barriers in the mitochondrial matrix (cristae), suggesting that cells can control the dynamics of biochemical reactions in this compartment by modifying its nanostructure.
Representation and redistribution in federations
Authors: Dragu Tiberiu , Rodden Jonathan
Published: May 2011

Many of the world's most populous democracies are political unions composed of states or provinces that are unequally represented in the national legislature. Scattered empirical studies, most of them focusing on the United States, have discovered that overrepresented states appear to receive larger shares of the national budget. Although this relationship is typically attributed to bargaining advantages associated with greater legislative representation, an important threat to empirical identification stems from the fact that the representation scheme was chosen by the provinces. Thus, it is possible that representation and fiscal transfers are both determined by other characteristics of the provinces in a specific country. To obtain an improved estimate of the relationship between representation and redistribution, we collect and analyze provincial-level data from nine federations over several decades, taking advantage of the historical process through which federations formed and expanded. Controlling for a variety of country- and province-level factors and using a variety of estimation techniques, we show that overrepresented provinces in political unions around the world are rather dramatically favored in the distribution of resources.
Multiple recognition assay reveals prostasomes as promising plasma biomarkers for prostate cancer
Authors: Tavoosidana Gholamreza , Ronquist Gunnar , Darmanis Spyros , Yan Junhong , Carlsson Lena , Wu Di , Conze Tim , Ek Pia , Semjonow Axel , Eltze Elke , Larsson Anders , Landegren Ulf D. , Kamali-Moghaddam Masood
Published: May 2011

Prostasomes are microvesicles (mean diameter, 150 nm) that are produced and secreted by normal and malignant prostate acinar cells. It has been hypothesized that invasive growth of malignant prostate cells may cause these microvesicles, normally released into seminal fluid, to appear in interstitial space and therewith into peripheral circulation. The suitability of prostasomes as blood biomarkers in patients with prostate cancer was tested by using an expanded variant of the proximity ligation assay (PLA). We developed an extremely sensitive and specific assay (4PLA) for detection of complex target structures such as microvesicles in which the target is first captured via an immobilized antibody and subsequently detected by using four other antibodies with attached DNA strands. The requirement for coincident binding by five antibodies to generate an amplifiable reporter results in both increased specificity and sensitivity. The assay successfully detected significantly elevated levels of prostasomes in blood samples from patients with prostate cancer before radical prostatectomy, compared with controls and men with benign biopsy results. The medians for prostasome levels in blood plasma of patients with prostate cancer were 2.5 to sevenfold higher compared with control samples in two independent studies, and the assay also distinguished patients with high and medium prostatectomy Gleason scores (8/9 and 7, respectively) from those with low score (≤6), thus reflecting disease aggressiveness. This approach that enables detection of prostasomes in peripheral blood may be useful for early diagnosis and assessment of prognosis in organ-confined prostate cancer.
Intra- and intermolecular translocation of the bi-domain transcription factor Oct1 characterized by liquid crystal and paramagnetic NMR
Authors: Takayama Yuki , Clore G. Marius
Published: May 2011

The intra- and intermolecular translocation processes whereby the bi-domain transcription factor Oct1 searches for its specific DNA target site have been investigated by residual dipolar coupling (RDC) and paramagnetic relaxation enhancement (PRE) measurements. The RDC data show that the orientation of the POU
S
and POU
HD
domains of Oct1 relative to the long axis of the DNA is the same for specific and nonspecific complexes with DNA. In the context of the specific Oct1-DNA complex, sparsely-populated, spectroscopically “invisible” states reveal their footprints on the PRE profiles observed for the specific complex. Analysis of the PRE data indicates that the POU
HD
domain searches the DNA primarily by rotation-coupled sliding (intramolecular translocation), while the POU
S
domain functions as an antenna to promote intersegment transfer via intermolecular translocation. The latter involves the formation of a bridged intermediate in which the POU
HD
domain is located on the first DNA molecule and the POU
S
domain on the second. The formation of the bridge intermediate promotes the completion of intermolecular translocation of Oct1 via a first order process involving dissociation and association of the POU
HD
domain from one DNA molecule to another. Thus cross-talk between the POU
S
and POU
HD
domains, each fulfilling different and complementary components of the search process ensures efficient sampling of DNA, thereby facilitating the location of specific Oct1 target sites.
Control of mTORC1 signaling by the Opitz syndrome protein MID1
Authors: Liu Enbo , Knutzen Christine A. , Krauss Sybille , Schweiger Susann , Chiang Gary G.
Published: May 2011

Mutations in the
MID1
gene are causally linked to X-linked Opitz BBB/G syndrome (OS), a congenital disorder that primarily affects the formation of diverse ventral midline structures. The MID1 protein has been shown to function as an E3 ligase targeting the catalytic subunit of protein phosphatase 2A (PP2A-C) for ubiquitin-mediated degradation. However, the molecular pathways downstream of the MID1/PP2A axis that are dysregulated in OS and that translate dysfunctional MID1 and elevated levels of PP2A-C into the OS phenotype are poorly understood. Here, we show that perturbations in MID1/PP2A affect mTORC1 signaling. Increased PP2A levels, resulting from proteasome inhibition or depletion of MID1, lead to disruption of the mTOR/Raptor complex and down-regulated mTORC1 signaling. Congruously, cells derived from OS patients that carry MID1 mutations exhibit decreased mTORC1 formation, S6K1 phosphorylation, cell size, and cap-dependent translation, all of which is rescued by expression of wild-type MID1 or an activated mTOR allele. Our findings define mTORC1 signaling as a downstream pathway regulated by the MID1/PP2A axis, suggesting that mTORC1 plays a key role in OS pathogenesis.