bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the resonant frequencies of silicon microcantilevers coated with vanadium dioxide films during the insulator-to-metal transition
Authors: Rúa Armando , Fernández Félix E. , Hines Melissa A. , Sepúlveda Nelson
Published: March 2010

Vanadium dioxide (VO2) thin films were grown on silicon microcantilevers and companion test substrates by pulsed laser deposition followed by in situ annealing in an oxidizing atmosphere, with annealing times used to control crystallite sizes. Annealing times of 18 min produced VO2 films with average crystallite sizes of ∼10 nm or less, while those annealed for 35 min had crystallites of average size ∼90 nm, comparable to sample thickness. X-ray diffraction and x-ray photoelectron spectroscopy studies of the samples showed that films with crystallite sizes ∼40 nm or greater consisted of substoichiometric VO2 in its monoclinic phase, with preferential orientation with (011) planes parallel to the sample surface, while finer structured samples had a substantially similar composition, but showed no clear evidence of preferential orientation and were probably partially amorphous. Forced vibration experiments were performed with the cantilevers as they were thermally cycled through the VO2 insulator-to-metal transition (IMT). Very large reversible changes in the resonant frequencies of up to 5% (3.6 kHz) as well as hysteretic behavior were observed, which depend strongly on film crystallite size. The average value of Young’s modulus for VO2 films with crystallite sizes of ∼90 nm was estimated from the mechanical resonance data at room temperature to be ∼120 GPa, but the large tensile stresses which develop between film and substrate through the IMT impede a similar determination for the VO2 tetragonal phase, since the commonly used relationships for cantilever frequencies derived from elasticity theory are not applicable for strongly curved composite beams. The results presented show that VO2 thin films can be useful in novel microscale and nanoscale electromechanical resonators in which effective stiffness can be tuned thermally or optically. This response can provide additional functionality to VO2—based devices which take advantage of other property changes through the IMT.
Short-wavelength infrared second harmonic generation in quantum cascade lasers
Authors: Cho Yong-Hee , Belyanin Alexey
Published: March 2010

We propose an electrically pumped intersubband laser capable of operating at short infrared wavelengths ∼1.5–2.5 μm. Short-wavelength operation is achieved via resonant intracavity second harmonic generation in quantum cascade (QC) lasers based on high band offset heterostructures. This approach overcomes the fundamental problem of intervalley scattering that prohibits direct lasing in QC lasers in this spectral range. The proposed devices can be modulated at a rate exceeding 100 GHz, which may be interesting for a variety of applications. We present detailed calculations of bandstructure design, phase-matched waveguide, and current-output power dependence for the devices based on GaInAs/AlAsSb/InP heterostructures. Accurate position of highly excited subbands is determined by calculating the conduction band (CB) dispersion with the energy-dependent 14-band effective mass, in which matrix elements are adjusted to fit the CB structure obtained with a 30-band k⋅p method. We also discuss the controversial location of lateral valleys, which imposes the limitation on the fundamental laser transition energy.
ONIOM-based QM:QM electronic embedding method using Löwdin atomic charges: Energies and analytic gradients
Authors: Mayhall Nicholas J. , Raghavachari Krishnan , Hratchian Hrant P.
Published: March 2010

In this work, we report a new quantum mechanical:quantum mechanical (QM:QM) method which provides explicit electronic polarization of the high-level region by using the Löwdin atomic charges from the low-level region. This provides an embedding potential which naturally evolves with changes in nuclear geometry. However, this coupling of the high-level and low-level regions introduces complications in the energy gradient evaluation. Following previous work, we derive and implement efficient gradients where a single set of self-consistent field response equations is solved. We provide results for the calculation of deprotonation energies of a hydroxylated spherosiloxane cluster (Si8O12H7OH) and the dissociation energy of a water molecule from a [ZnIm3(H2O)]2+ complex. We find that the Löwdin charge embedding model provides results which are not only an improvement over mechanical embedding (no electronic embedding) but which are also resistant to large overpolarization effects which occur more often with Mulliken charge embedding. Finally, a scaled-Löwdin charge embedding method is also presented which provides a method for fine tuning the extent of electronic polarization.
A connection between HH3 and Korteweg–de Vries with one source
Authors: Zhao Jun-xiao , Conte Robert
Published: March 2010

In the system made of Korteweg–de Vries with one source, we first show by applying the Painlevé test that the two components of the source must have the same potential. We then explain the natural introduction of an additional term in the potential of the source equations while preserving the existence of a Lax pair. This allows us to prove the identity between the traveling-wave reduction and one of the three integrable cases of the cubic Hénon–Heiles Hamiltonian system.
Invited Review Article: Unsteady and pulsating pressure and temperature: A review of experimental techniques
Authors: Nabavi Majid
Published: March 2010

Unsteady flow of liquids and gasses are important in many scientific, engineering, and biological contexts. Measurement of the characteristics of unsteady and pulsating flows is more difficult than that of static flows. Time constants of the sensors must be understood, sampling rates must satisfy basic signal processing criteria and synchronization of the measurements with the flow may be necessary. Because of development of more advanced measurement devices, there has recently been a growing interest in unsteady and pulsating flow measurements and the number of papers in this field has increased in recent years. This paper reviews the current state of the art in sensors and measurement techniques for the characterization of pressure and temperature in unsteady and pulsating flows including an analysis of the advantages and limitations of each technique.
Role of field-effect on c-Si surface passivation by ultrathin (2–20 nm) atomic layer deposited Al2O3
Authors: Terlinden N. M. , Dingemans G. , van de Sanden M. C. M , Kessels W. M. M.
Published: March 2010

Al 2 O 3 synthesized by plasma-assisted atomic layer deposition yields excellent surface passivation of crystalline silicon (c-Si) for films down to ∼5 nm in thickness. Optical second-harmonic generation was employed to distinguish between the influence of field-effect passivation and chemical passivation through the measurement of the electric field in the c-Si space-charge region. It is demonstrated that this electric field—and hence the negative fixed charge density—is virtually unaffected by the Al2O3 thickness between 2 and 20 nm indicating that a decrease in chemical passivation causes the reduced passivation performance for <5 nm thick Al2O3 films.
High-gain integrated inverters based on ZnO metal-semiconductor field-effect transistor technology
Authors: Frenzel H. , Schein F. , Lajn A. , von Wenckstern H. , Grundmann M.
Published: March 2010

We report on the design and fabrication of ZnO-based integrated inverters consisting of normally-on metal-semiconductor field-effect transistors and AgxO Schottky diodes as level shifters. The inverters show high gain values up to 197 at 3 V operating voltage and low uncertainty levels in the range of 0.13 V. The influence of the level shifter and the channel material/thickness on the performance of the inverters has been investigated. Using Zn0.997Mg0.003O for the channel thin film leads to high reproducibility (90%) of the devices. A logic NOR-gate has been implemented showing the possibility to fabricate a complete logic.
Can gas hydrate structures be described using classical simulations?
Authors: Conde Maria M. , Vega Carlos , McBride Carl , Noya Eva G. , Ramírez Rafael , Sesé Luis M.
Published: March 2010

Quantum path-integral simulations of the hydrate solid structures have been performed using the recently proposed TIP4PQ/2005 model. By also performing classical simulations using this model, the impact of the nuclear quantum effects on the hydrates is highlighted; nuclear quantum effects significantly modify the structure, densities, and energies of the hydrates, leading to the conclusion that nuclear quantum effects are important not only when studying the solid phases of water but also when studying the hydrates. To analyze the validity of a classical description of hydrates, a comparison of the results of the TIP4P/2005 model (optimized for classical simulations) with those of TIP4PQ/2005 (optimized for path-integral simulations) was undertaken. A classical description of hydrates is able to correctly predict the densities at temperatures above 150 K and the relative stabilities between the hydrates and ice Ih. The inclusion of nuclear quantum effects does not significantly modify the sequence of phases found in the phase diagram of water at negative pressures, namely, Ih→sII→sH. In fact the transition pressures are little affected by the inclusion of nuclear quantum effects; the phase diagram predictions for hydrates can be performed with reasonable accuracy using classical simulations. However, for a reliable calculation of the densities below 150 K, the sublimation energies, the constant pressure heat capacity, and the radial distribution functions, the incorporation of nuclear quantum effects is indeed required.
The chemical shift of deprotonated water dimer: Ab initio path integral simulation
Authors: Shiga Motoyuki , Suzuki Kimichi , Tachikawa Masanori
Published: March 2010

The H1 NMR chemical shift in deprotonated water dimer H3O2− has been studied by ab initio path integral simulation. The simulation predicts that the isotropic shielding of hydrogen-bonded proton increases as a function of temperature by about 0.003 ppm/K. This change is about an order of magnitude larger than that of the nonhydrogen-bonded proton. It is concluded that this is caused by the significant difference in the quantum distribution of proton at high and low temperatures in the low barrier hydrogen bond.
Periodic anchoring condition for alignment of a short pitch cholesteric liquid crystal in uniform lying helix texture
Authors: Hegde Gurumurthy , Komitov Lachezar
Published: March 2010

Due to flexoelectricity, a cholesteric liquid crystal unidirectionally aligned in a sandwich cell, with its helix lying parallel to the confining cell substrates, exhibit a flexoelectro-optic response when subjected to an electric field applied perpendicular to the helix axis. The clarity of the flexoelectro-optic response is dependent on the quality of the uniformly lying helix texture of the cholesteric which often is difficult to achieve. Herein, a method for alignment of a short pitch cholesteric in such a texture by means of a periodic surface anchoring condition with periodicity matching that of the cholesteric liquid crystal is described.
High-performance CF4 plasma treated polycrystalline silicon thin-film transistors using a high-k Tb2O3 gate dielectric
Authors: Pan Tung-Ming , Li Zhi-Hong
Published: March 2010

In this letter, we have developed a high-k Tb2O3 gate dielectric polycrystalline silicon (poly-Si) thin-film transistors (TFTs) prepared under a CF4 plasma treatment. A high-performance TFT device that has a low threshold voltage of 0.89 V, a high effective carrier mobility of 59.6 cm2/V s, a small subthreshold swing of 212 mV/dec, and a high ION/IOFF current ratio of 8.15×106 can be achieved. This phenomenon is attributed to fluorine atoms into poly-Si films can effectively passivate the trap states near the Tb2O3/poly-Si interface. The fluorine incorporation also enhanced electrical reliability of the Tb2O3 poly-Si TFT. All of these results suggest that the CF4 plasma-treated poly-Si Tb2O3 TFT is a good candidate for high-performance TFTs.
Coupling different levels of resolution in molecular simulations
Authors: Poblete Simón , Praprotnik Matej , Kremer Kurt , Delle Site Luigi
Published: March 2010

Simulation schemes for liquids or strongly fluctuating systems that allow to change the molecular representation in a subvolume of the simulation box while preserving the equilibrium with the surroundings introduce conceptual problems of thermodynamic consistency. In this work we present a general scheme based on thermodynamic arguments which ensures a thermodynamic equilibrium among molecules of different representations. The robustness of the algorithm is tested for two examples, namely, an adaptive resolution simulation, atomistic/coarse grained, for a liquid of tetrahedral molecules, and an adaptive resolution simulation of a binary mixture of tetrahedral molecules and spherical solutes.
The role of polarization on surface plasmon polariton excitation on metallic gratings in the conical mounting
Authors: Romanato F. , Lee K. H. , Ruffato G. , Wong C. C.
Published: March 2010

The polarization effects of surface plasmon polaritons (SPP) in an azimuthally rotated gratings have been investigated. Mixed s and p modes can be excited using the polarization angle of the incident light to optimize the SPP coupling. Experimental results and simulations show which component of polarization is effective for the SPP excitation. The optimum angle direction has been calculated analytically. The SPR tunability by polarization may uncover important features in SPP applications.
Simultaneous measurement of concentrations and velocities of submicron species using multicolor imaging and microparticle image velocimetry
Authors: Yang Jing-Tang , Lai Yu-Hsuan , Fang Wei-Feng , Hsu Miao-Hsing
Published: March 2010

We propose a novel approach to resolve simultaneously the distributions of velocities and concentration of multiple, submicron species in microfluidic devices using microparticle image velocimetry, and particle counting. Both two-dimensional measurement and three-dimensional analysis of flow fields, from the stacked images, are achieved on applying a confocal fluorescence microscope. The displacements of all seeding particles are monitored to determine the overall velocity field, whereas the multicolor particles are counted and analyzed individually for each color to reveal the distributions of concentration and velocity of each species. A particle-counting algorithm is developed to determine quantitatively the spatially resolved concentration. This simultaneous measurement is performed on a typical T-shaped channel to investigate the mixing of fluids. The results are verified with numerical simulation; satisfactory agreement is achieved. This measurement technique possesses reliability appropriate for a powerful tool to analyze multispecies mixing flows, two-phase flows, and biofluids in microfluidic devices.
Polycentric Urban Development: The Case of Hangzhou
Authors: Yue Wenze , Liu Yong , Fan Peilei
Published: March 2010

Despite the advantages of polycentric structure and its rich literature drawn from cities in industialized countries, little attention has been paid to the study of polycentric urban development in developing countries based on land-use information. With Hangzhou used as a case study, the authors investigate polycentric urban development through an analysis of directions of urban expansion, urban–rural gradients, and growth types. The multidisciplinary methodology employed, based on theories and methods in remote sensing, geographic information systems, and landscape ecology, has been proved to be useful in the morphological study of polycentric urban development. It was found that Hangzhou has expanded in different directions at various speeds, shifting to a polycentric urban pattern through radial expansion. Along the main transportation corridors, the values of the mean patch sizes of urban patches displayed multiple peaks, and the landscape-shape index maintained a horizontal trend in urban fringes, reflecting the formation of polycentricity. Further, as edge growth and spontaneous growth accounted for 40%–50% and 30–40% of urban growth, respectively, and infill growth was responsible for only a small proportion of urban growth, it is suggested that dispersed urban patches have been increasingly agglomerated into big ones, especially along road corridors. Hangzhou's polycentric urban development was shaped both by the planning efforts of the government and by market forces. The municipal government guided the polycentric development through drafting and revising master plans, annexing nearby districts, and establishing development zones. Nevertheless, market forces played an increasingly important role in Hangzhou's polycentric development through the implementation of an urban land market, the inflow of migrant workers, and the relocation of industries.
Cognitive Continental Drift: How Attitudes Can Change the Overall Pattern of Cognitive Distances
Authors: Carbon Claus-Christian
Published: March 2010

By the late Carboniferous period, the continents that today make up North America and Europe collided with the southern parts of Gondwana to form the western half of the last super-continent Pangea. From this moment on, North America and Europe have steadily been drifting apart, as was initially described by Alfred Wegener in 1915. In this paper a cognitive counterpart of this continental drift is described—which progresses much faster than the phenomenon of plate tectonics. Distance estimations between cities of Europe and the USA were strongly modulated by an interactive effect of the social attitude towards the Iraq War in 2003 and towards US citizens in general, letting America and Europe drift apart hundreds of kilometers for those who disliked the war but were meanwhile sympathetic to US citizens. Possible implications for the relationship between Europe and the US are discussed and perspectives for a cognitive rapprochement of Europe and the USA are provided.
Floating Choices: A Generational Perspective on Intentions of Rural–Urban Migrants in China
Authors: Yue Zhongshan , Li Shuzhuo , Feldman Marcus W , Du Haifeng
Published: March 2010

Using data from a 2005 survey of rural–urban migrants in Shenzhen, we investigate the intentions of two groups of migrants. We use the birth years from 1970 to 1980 as a reasonable range of dividing lines to separate the two groups. For each year we divide the sample into those born before that year and those born in or after that year. These are referred to as the old generation and the new generation, respectively. Three possible development trajectories are considered: settling in cities, returning home to seek a nonagricultural job, and returning home to farm. We find that members of the new generation have stronger desires to do nonfarm work, and that returning to seek a nonagricultural job has become the most important planned trajectory for this generation. Sharp differences exist between the two generations in the reasons that underlie their intentions. For the old generation, conditions such as age, family responsibility, and type of job are important determinants of intentions, while other conditions such as initial migration motives, social capital, and socioeconomic conditions of origin areas are important for the intentions of the new generation. Thus the new generation is more likely to view migration as a form of investment with the accumulation of human capital and social capital. Those migrants from the old generation who have higher education levels also intend to seek a nonfarm job. However, because of the combined effects of life cycle and the market transition in China, these intentions are not as strong as those of the new generation. We discuss economic and policy implications of our findings.
Innovative Strategies of Agricultural Cooperatives in the Framework of the New Rural Development Paradigms: The Case of the Region of Valencia (Spain)
Authors: Ortiz-Miranda Dionisio , Moreno-Pérez Olga M , Moragues-Faus Ana M
Published: March 2010

With this paper we aim to analyse how new entrepreneurial strategies are emerging in the field of agricultural cooperatives within the Region of Valencia (Spain), and how these strategies are characterised through the lens of the agrarian-based rural development model. Initial results show that these strategies have the potential to strengthen the role of cooperatives in rural economic development as they add value to specific territorial resources, create new ties with other local and nonlocal actors, and diversify the economy of rural areas. Nevertheless, the cooperative (collective) nature of these organisations can also create decision-making and investment problems, as they can divide the interests of their social base.
Gender, Natural Capital, and Migration in the Southern Ecuadorian Andes
Authors: Gray Clark L
Published: March 2010

This paper investigates the roles of gender and natural capital (defined as land and associated environmental services) in out-migration from a rural study area in the southern Ecuadorian Andes. Drawing on original household survey data, I construct and compare multivariate event history models of individual-level, household-level, and community-level influences on the migration of men and women. The results undermine common assumptions that landlessness and environmental degradation universally contribute to out-migration. Instead, men access land resources to facilitate international migration and women are less likely to depart from environmentally marginal communities relative to other areas. These results reflect a significantly gendered migration system in which natural capital plays an important but unexpected role.
Ethno-Religious Categories and Measuring Occupational Attainment in Relation to Education in England and Wales: A Multilevel Analysis
Authors: Johnston Ron , Sirkeci Ibrahim , Khattab Nabil , Modood Tariq
Published: March 2010

It has been suggested that ‘ethnic penalties’ exist in British labour markets, whereby members of ethnic minority groups fail to get into occupations commensurate with their qualifications. Often these analyses of occupational attainment by education treat minority groups as homogeneous, not recognising that in several there is substantial heterogeneity on other criteria, such as religion, which may also influence occupational attainment. We argue that there are significant variations among these ethno-religious minorities regarding their labour-market performance, which is measured using a continuous scale of skill-level distances—a measure of returns to education.
Mouse cystic fibrosis transmembrane conductance regulator forms cAMP-PKA–regulated apical chloride channels in cortical collecting duct
Authors: Lu Ming , Dong Ke , Egan Marie E. , Giebisch Gerhard H. , Boulpaep Emile L. , Hebert Steven C.
Published: March 2010

The cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in many segments of the mammalian nephron, where it may interact with and modulate the activity of a variety of apical membrane proteins, including the renal outer medullary potassium (ROMK) K
+
channel. However, the expression of CFTR in apical cell membranes or its function as a Cl
−
channel in native renal epithelia has not been demonstrated. Here, we establish that CFTR forms protein kinase A (PKA)-activated Cl
−
channels in the apical membrane of principal cells from the cortical collecting duct obtained from mice. These Cl
−
channels were observed in cell-attached apical patches of principal cells after stimulation by forskolin/3-isobutyl-1-methylxanthine. Quiescent Cl
−
channels were present in patches excised from untreated tubules because they could be activated after exposure to Mg-ATP and the catalytic subunit of PKA. The single-channel conductance, kinetics, and anion selectivity of these Cl
−
channels were the same as those of recombinant mouse CFTR channels expressed in
Xenopus laevis
oocytes. The CFTR-specific closed-channel blocker CFTR
inh
-172 abolished apical Cl
−
channel activity in excised patches. Moreover, apical Cl
−
channel activity was completely absent in principal cells from transgenic mice expressing the ΔF508 CFTR mutation but was present and unaltered in ROMK-null mice. We discuss the physiologic implications of open CFTR Cl
−
channels on salt handling by the collecting duct and on the functional CFTR–ROMK interactions in modulating the metabolic ATP-sensing of ROMK.
Hypoxia converts the myogenic action of insulin-like growth factors into mitogenic action by differentially regulating multiple signaling pathways
Authors: Ren Hongxia , Accili Domenico , Duan Cunming
Published: March 2010

Insulin-like growth factors (IGFs) stimulate myoblast proliferation and differentiation. It remains elusive how these mutually exclusive cellular responses are elicited by the same growth factor. Here we report that whereas IGF promotes myoblast differentiation under normoxia, it stimulates proliferation under hypoxia. Hypoxia activates the HIF-1 transcriptional program and knockdown of HIF-1α changes the mitogenic action of IGF into myogenic action under hypoxia. Conversely, overexpression of HIF-1α abolishes the myogenic effect of IGF under normoxia. Under normoxia, IGF activates the Akt-mTOR, p38, and Erk1/2 MAPK pathways. Hypoxia suppresses basal and IGF-induced Akt-mTOR and p38 activity, whereas it enhances and prolongs IGF-induced Erk1/2 activation in a HIF-1–dependent fashion. Activation of Akt-mTOR and p38 promotes myogenesis, and p38 also inhibits proliferation. Activation of Erk stimulates myoblast proliferation but inhibits differentiation. These results suggest that hypoxia converts the myogenic action of IGFs into mitogenic action by differentially regulating multiple signaling pathways via HIF-1-dependent mechanisms. Our findings provide a mechanistic explanation for the paradoxical actions of IGFs during myogenesis and reveal a novel mechanism by which cells sense and integrate growth factor signals and oxygen availability in their microenvironments.
The KaiA protein of the cyanobacterial circadian oscillator is modulated by a redox-active cofactor
Authors: Wood Thammajun L. , Bridwell-Rabb Jennifer , Kim Yong-Ick , Gao Tiyu , Chang Yong-Gang , LiWang Andy , Barondeau David P. , Golden Susan S.
Published: March 2010

The circadian rhythms exhibited in the cyanobacterium
Synechococcus elongatus
are generated by an oscillator comprised of the proteins KaiA, KaiB, and KaiC. An external signal that commonly affects the circadian clock is light. Previously, we reported that the bacteriophytochrome-like protein CikA passes environmental signals to the oscillator by directly binding a quinone and using cellular redox state as a measure of light in this photosynthetic organism. Here, we report that KaiA also binds the quinone analog 2,5-dibromo-3-methyl-6-isopropyl-
p
-benzoquinone (DBMIB), and the oxidized form of DBMIB, but not its reduced form, decreases the stability of KaiA in vivo, causes multimerization in vitro, and blocks KaiA stimulation of KaiC phosphorylation, which is central to circadian oscillation. Our data suggest that KaiA directly senses environmental signals as changes in redox state and modulates the circadian clock.
Global patterns in leaf
13
C discrimination and implications for studies of past and future climate
Authors: Diefendorf Aaron F. , Mueller Kevin E. , Wing Scott. L. , Koch Paul L. , Freeman Katherine H.
Published: March 2010

Fractionation of carbon isotopes by plants during CO
2
uptake and fixation (Δ
leaf
) varies with environmental conditions, but quantitative patterns of Δ
leaf
across environmental gradients at the global scale are lacking. This impedes interpretation of variability in ancient terrestrial organic matter, which encodes climatic and ecological signals. To address this problem, we converted 3,310 published leaf
δ
13
C values into mean Δ
leaf
values for 334 woody plant species at 105 locations (yielding 570 species-site combinations) representing a wide range of environmental conditions. Our analyses reveal a strong positive correlation between Δ
leaf
and mean annual precipitation (MAP; R
2
 = 0.55), mirroring global trends in gross primary production and indicating stomatal constraints on leaf gas-exchange, mediated by water supply, are the dominant control of Δ
leaf
at large spatial scales. Independent of MAP, we show a lesser, negative effect of altitude on Δ
leaf
and minor effects of temperature and latitude. After accounting for these factors, mean Δ
leaf
of evergreen gymnosperms is lower (by 1–2.7‰) than for other woody plant functional types (PFT), likely due to greater leaf-level water-use efficiency. Together, environmental and PFT effects contribute to differences in mean Δ
leaf
of up to 6‰ between biomes. Coupling geologic indicators of ancient precipitation and PFT (or biome) with modern Δ
leaf
patterns has potential to yield more robust reconstructions of atmospheric
δ
13
C values, leading to better constraints on past greenhouse-gas perturbations. Accordingly, we estimate a 4.6‰ decline in the
δ
13
C of atmospheric CO
2
at the onset of the Paleocene-Eocene Thermal Maximum, an abrupt global warming event ∼55.8 Ma.
Iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas
Authors: Trick Charles G. , Bill Brian D. , Cochlan William P. , Wells Mark L. , Trainer Vera L. , Pickell Lisa D.
Published: March 2010

Oceanic high-nitrate, low-chlorophyll environments have been highlighted for potential large-scale iron fertilizations to help mitigate global climate change. Controversy surrounds these initiatives, both in the degree of carbon removal and magnitude of ecosystem impacts. Previous open ocean enrichment experiments have shown that iron additions stimulate growth of the toxigenic diatom genus
Pseudonitzschia
. Most
Pseudonitzschia
species in coastal waters produce the neurotoxin domoic acid (DA), with their blooms causing detrimental marine ecosystem impacts, but oceanic
Pseudonitzschia
species are considered nontoxic. Here we demonstrate that the sparse oceanic
Pseudonitzschia
community at the high-nitrate, low-chlorophyll Ocean Station PAPA (50° N, 145° W) produces approximately 200 pg DA L
−1
in response to iron addition, that DA alters phytoplankton community structure to benefit
Pseudonitzschia
, and that oceanic cell isolates are toxic. Given the negative effects of DA in coastal food webs, these findings raise serious concern over the net benefit and sustainability of large-scale iron fertilizations.
A neural substrate in the human hippocampus for linking successive events
Authors: Paz Rony , Gelbard-Sagiv Hagar , Mukamel Roy , Harel Michal , Malach Rafael , Fried Itzhak
Published: March 2010

Memory formation requires the placement of experienced events in the same order in which they appeared. A large body of evidence from human studies indicates that structures in the medial temporal lobe are critically involved in forming and maintaining such memories, and complementing evidence from lesion and electrophysiological work in animals support these findings. However, it remains unclear how single cells and networks of cells can signal this temporal relationship between events. Here we used recordings from single cells in the human brain obtained while subjects viewed repeated presentations of cinematic episodes. We found that neuronal activity in successive time segments became gradually correlated, and, as a result, activity in a given time window became a faithful predictor of the activity to follow. This correlation emerged rapidly, within two to three presentations of an episode and exceeded both context-independent and pure stimulus-driven correlations. The correlation was specific for hippocampal neurons, did not occur in the amygdala and anterior cingulate cortex, and was found for single cells, cell pairs, and triplets of cells, supporting the notion that cell assemblies code for the temporal relationships between sensory events. Importantly, this neuronal measure of temporal binding successfully predicted subjects’ ability to recall and verbally report the viewed episodes later. Our findings suggest a neuronal substrate for the formation of memory of the temporal order of events.
Notch signaling drives IL-22 secretion in CD4+T cells by stimulating the aryl hydrocarbon receptor
Authors: Alam Muhammad Shamsul , Maekawa Yoichi , Kitamura Akiko , Tanigaki Kenji , Yoshimoto Takayuki , Kishihara Kenji , Yasutomo Koji
Published: March 2010

CD4+helper T (Th) cells differentiate toward distinct effector cell lineages characterized by their distinct cytokine expression patterns and functions. Multiple Th cell populations secrete IL-22 that contributes to both protective and pathological inflammatory responses. Although the differentiation of IL-22-producing Th cells is controlled by the aryl hydrocarbon receptor (AhR), little is known about the regulatory mechanisms inducing physiological stimulators for AhR. Here, we show that Notch signaling enhances IL-22 production by CD4+T cells by a mechanism involving AhR stimulation. Notch-mediated stimulation of CD4+T cells increased the production of IL-22 even in the absence of STAT3. CD4+T cells from RBP-J-deficient mice had little ability to produce IL-22 through T cell receptor-mediated stimulation. RBP-J-deficient mice were highly susceptible to the detrimental immunopathology associated with ConA-induced hepatitis with little IL-22 production by CD4+T cells. Exogenous IL-22 protected RBP-J-deficient mice from ConA-induced hepatitis. Notch signaling promoted production of endogenous stimulators for AhR, which further augmented IL-22 secretion. Our studies identify a Notch–AhR axis that regulates IL-22 expression and fine-tunes immune system control of inflammatory responses.
Polymorphonuclear leukocytes mediate
Staphylococcus aureus
Panton-Valentine leukocidin-induced lung inflammation and injury
Authors: Diep Binh An , Chan Liana , Tattevin Pierre , Kajikawa Osamu , Martin Thomas R. , Basuino Li , Mai Thuy T. , Marbach Helene , Braughton Kevin R. , Whitney Adeline R. , Gardner Donald J. , Fan Xuemo , Tseng Ching W. , Liu George Y. , Badiou Cedric , Etienne Jerome , Lina Gerard , Matthay Michael A. , DeLeo Frank R. , Chambers Henry F.
Published: March 2010

Community-associated methicillin-resistant
Staphylococcus aureus
(CA-MRSA) is epidemic in the United States, even rivaling HIV/AIDS in its public health impact. The pandemic clone USA300, like other CA-MRSA strains, expresses Panton-Valentine leukocidin (PVL), a pore-forming toxin that targets polymorphonuclear leukocytes (PMNs). PVL is thought to play a key role in the pathogenesis of necrotizing pneumonia, but data from rodent infection models are inconclusive. Rodent PMNs are less susceptible than human PMNs to PVL-induced cytolysis, whereas rabbit PMNs, like those of humans, are highly susceptible to PVL-induced cytolysis. This difference in target cell susceptibility could affect results of experimental models. Therefore, we developed a rabbit model of necrotizing pneumonia to compare the virulence of a USA300 wild-type strain with that of isogenic PVL-deletion mutant and -complemented strains. PVL enhanced the capacity of USA300 to cause severe lung necrosis, pulmonary edema, alveolar hemorrhage, hemoptysis, and death, hallmark clinical features of fatal human necrotizing pneumonia. Purified PVL instilled directly into the lung caused lung inflammation and injury by recruiting and lysing PMNs, which damage the lung by releasing cytotoxic granule contents. These findings provide insights into the mechanism of PVL-induced lung injury and inflammation and demonstrate the utility of the rabbit for studying PVL-mediated pathogenesis.
Direct structural insight into the substrate-shuttling mechanism of yeast fatty acid synthase by electron cryomicroscopy
Authors: Gipson Preeti , Mills Deryck J. , Wouts Remco , Grininger Martin , Vonck Janet , Kühlbrandt Werner
Published: March 2010

Yeast fatty acid synthase (FAS) is a 2.6-MDa barrel-shaped multienzyme complex, which carries out cyclic synthesis of fatty acids. By electron cryomicroscopy of single particles we obtained a three-dimensional map of yeast FAS at 5.9-Å resolution. Compared to the crystal structures of fungal FAS, the EM map reveals major differences and new features that indicate a considerably different arrangement of the complex in solution compared to the crystal structures, as well as a high degree of variance inside the barrel. Distinct density regions in the reaction chambers next to each of the catalytic domains fitted the substrate-binding acyl carrier protein (ACP) domain. In each case, this resulted in the expected distance of ∼18 
Å
from the ACP substrate-binding site to the active site of the catalytic domains. The multiple, partially occupied positions of the ACP within the reaction chamber provide direct structural insight into the substrate-shuttling mechanism of fatty acid synthesis in this large cellular machine.
Arabidopsis
dynamin-related proteins DRP2B and DRP1A participate together in clathrin-coated vesicle formation during endocytosis
Authors: Fujimoto Masaru , Arimura Shin-ichi , Ueda Takashi , Takanashi Hideki , Hayashi Yoshikazu , Nakano Akihiko , Tsutsumi Nobuhiro
Published: March 2010

Endocytosis performs a wide range of functions in animals and plants. Clathrin-coated vesicle (CCV) formation is an initial step of endocytosis, and in animal cells is largely achieved by dynamins. However, little is known of its molecular mechanisms in plant cells. To identify dynamin-related proteins (DRPs) involved in endocytic CCV formation in plant cells, we compared the behaviors of two structurally different
Arabidopsis
DRPs, DRP2B and DRP1A, with those of the clathrin light chain (CLC), a marker of CCVs, at the plasma membrane by variable incidence angle fluorescent microscopy (VIAFM). DRP2B shares domain organization with animal dynamins whereas DRP1A is plant-specific. We show that green fluorescent protein (GFP)-tagged DRP2B and DRP1A colocalized with CLC tagged with monomeric Kusabira Orange (mKO) in
Arabidopsis
cultured cells. Time-lapse VIAFM observations suggested that both GFP-DRP2B and GFP-DRP1A appeared and accumulated on the existing mKO-CLC foci and disappeared at the same time as or immediately after the disappearance of mKO-CLC. Moreover, DRP2B and DRP1A colocalized and assembled/disassembled together at the plasma membrane in
Arabidopsis
cells. A yeast two-hybrid assay showed that DRP2B and DRP1A interacted with each other. An inhibitor of clathrin-mediated endocytosis, tyrphostin A23, disturbed the localization of DRP1A, but had little effect on the localization of DRP2B, indicating that DRP1A and DRP2B have different molecular properties. These results suggest that DRP2B and DRP1A participate together in endocytic CCV formation in
Arabidopsis
cells despite the difference of their molecular properties.
A new Lower Pleistocene archeological site in Europe (Vallparadís, Barcelona, Spain)
Authors: Martínez Kenneth , Garcia Joan , Carbonell Eudald , Agustí Jordi , Bahain Jean-Jaques , Blain Hugues-Alexandre , Burjachs Francesc , Cáceres Isabel , Duval Mathieu , Falguères Christophe , Gómez Manuel , Huguet Rosa
Published: March 2010

Here we report the discovery of a new late Lower Pleistocene site named Vallparadís (Barcelona, Spain) that produced a rich archeological and paleontological sequence dated from the upper boundary of the Jaramillo subchron to the early Middle Pleistocene. This deposit contained a main archeological layer with numerous artifacts and a rich macromammalian assemblage, some of which bore cut marks, that could indicate that hominins had access to carcasses. Paleomagnetic analysis, electron spin resonance-uranium series (ESR-US), and the biostratigraphic chronological position of the macro- and micromammal and lithic assemblages of this layer reinforce the proposal that hominins inhabited Europe during the Lower Pleistocene. The archeological sequence provides key information on the successful adaptation of European hominins that preceded the well-known fossil population from Atapuerca and succeeded the finds from Orce basin. Hence, this discovery enables us to close a major chronological gap in the early prehistory of Iberia. According to the information in this paper and the available data from these other sites, we propose that Mediterranean Western Europe was repeatedly and perhaps continuously occupied during the late Matuyama chron.
Information dynamics shape the sexual networks of Internet-mediated prostitution
Authors: Rocha Luis E. C. , Liljeros Fredrik , Holme Petter
Published: March 2010

Like many other social phenomena, prostitution is increasingly coordinated over the Internet. The online behavior affects the offline activity; the reverse is also true. We investigated the reported sexual contacts between 6,624 anonymous escorts and 10,106 sex buyers extracted from an online community from its beginning and six years on. These sexual encounters were also graded and categorized (in terms of the type of sexual activities performed) by the buyers. From the temporal, bipartite network of posts, we found a full feedback loop in which high grades on previous posts affect the future commercial success of the sex worker, and vice versa. We also found a peculiar growth pattern in which the turnover of community members and sex workers causes a sublinear preferential attachment. There is, moreover, a strong geographic influence on network structure—the network is geographically clustered but still close to connected, the contacts consistent with the inverse-square law observed in trading patterns. We also found that the number of sellers scales sublinearly with city size, so this type of prostitution does not, comparatively speaking, benefit much from an increasing concentration of people.
Increased fibrillar amyloid-β burden in normal individuals with a family history of late-onset Alzheimer’s
Authors: Mosconi Lisa , Rinne Juha O. , Tsui Wai H. , Berti Valentina , Li Yi , Wang Huiyu , Murray John , Scheinin Noora , Någren Kjell , Williams Schantel , Glodzik Lidia , De Santi Susan , Vallabhajosula Shankar , de Leon Mony J.
Published: March 2010

Having a parent affected with late-onset Alzheimer's disease (LOAD) is a major risk factor among cognitively normal (NL) individuals. This
11
C-Pittsburgh Compound B (PiB)-PET study examines whether NL individuals with LOAD parents show increased fibrillar amyloid-beta (Aβ) deposition, a hallmark of Alzheimer's disease (AD) pathology and whether there are parent-of-origin effects. Forty-two 50- to 80-year-old NL persons were examined with PiB-PET. These individuals included 14 NL subjects with a maternal family history (FH) of LOAD (FHm), 14 NL subjects with a paternal FH (FHp), and 14 NL subjects with a negative family history of any dementia (FH−). Statistical parametric mapping and automated regions-of-interest were used to compare cerebral-to-cerebellar PiB standardized uptake value ratios, reflecting fibrillar Aβ burden, across groups. FH groups did not differ in age, gender, education, and apolipoprotein E (ApoE) status. NL FHm subjects showed higher PiB retention in AD-affected anterior and posterior cingulate cortex (PCC), precuneus, parietal, temporal, occipital, and frontal cortices, right basal ganglia, and thalamus, compared with FH− and FHp subjects. FHp subjects showed increased PiB retention in the PCC and frontal cortex, intermediate between FHm and FH− subjects. Results remained significant after controlling for age, gender, education, and ApoE status. Children of parents with LOAD, particularly those with affected mothers, have increased fibrillar Aβ load in AD-vulnerable regions compared with controls, perhaps accounting for the known increased risk for AD. Present findings may motivate further research on familial transmission and parent-of-origin effects in LOAD.
Src kinase regulates the integrity and function of the Golgi apparatus via activation of dynamin 2
Authors: Weller Shaun G. , Capitani Mirco , Cao Hong , Micaroni Massimo , Luini Alberto , Sallese Michele , McNiven Mark A.
Published: March 2010

The size and integrity of the Golgi apparatus is maintained via a tightly controlled regulation of membrane traffic using a variety of different signaling and cytoskeletal proteins. We have recently observed that activation of c-Src has profound effects on Golgi structure, leading to dramatically vesiculated cisternae in a variety of cell types. As the large GTPase dynamin (Dyn2) has been implicated in Golgi vesiculation during secretion, we tested whether inhibiting Dyn2 activity by expression of a Dyn2K44A mutant or siRNA knockdown could attenuate active Src-induced Golgi fragmentation. Indeed, these perturbations attenuated fragmentation, and expression of a Dyn2Y(231/597)F mutant protein that cannot be phosphorylated by Src kinase had a similar effect . Finally, we find that Dyn2 is markedly phosphorylated during the transit of VSV-G protein through the TGN whereas expression of the Dyn2Y(231/597)F mutant significantly reduces exit of the nascent protein from this compartment. These findings demonstrate that activation of Dyn2 by Src kinase regulates Golgi integrity and vesiculation during the secretory process.
Targeted deletion of βIII spectrin impairs synaptogenesis and generates ataxic and seizure phenotypes
Authors: Stankewich Michael C. , Gwynn Babette , Ardito Thomas , Ji Lan , Kim Jung , Robledo Raymond F. , Lux Samuel E. , Peters Luanne L. , Morrow Jon S.
Published: March 2010

The spectrin membrane skeleton controls the disposition of selected membrane channels, receptors, and transporters. In the brain βIII spectrin binds directly to the excitatory amino acid transporter (EAAT4), the glutamate receptor delta, and other proteins. Mutations in βIII spectrin link strongly to human spinocerebellar ataxia type 5 (SCA5), correlating with alterations in EAAT4. We have explored the mechanistic basis of this phenotype by targeted gene disruption of
Spnb3
. Mice lacking intact βIII spectrin develop normally. By 6 months they display a mild nonprogressive ataxia. By 1 year most
Spnb3
−/−
animals develop a myoclonic seizure disorder with significant reductions of EAAT4, EAAT1, GluRδ, IP3R, and NCAM140. Other synaptic proteins are normal. The cerebellum displays increased dark Purkinje cells (PC), a thin molecular layer, fewer synapses, a loss of dendritic spines, and a 2-fold expansion of the PC dendrite diameter. Membrane and expanded Golgi profiles fill the PC dendrite and soma, and both regions accumulate EAAT4. Correlating with the seizure disorder are enhanced hippocampal levels of neuropeptide Y and EAAT3 and increased calpain proteolysis of αII spectrin. It appears that βIII spectrin disruption impairs synaptogenesis by disturbing the intracellular pathways selectively regulating protein trafficking to the synapse. The mislocalization of these proteins secondarily disrupts glutamate transport dynamics, leading to seizures, neuronal damage, and compensatory changes in EAAT3 and neuropeptide Y.
Mitotic gene conversion events induced in G1-synchronized yeast cells by gamma rays are similar to spontaneous conversion events
Authors: Lee Phoebe S. , Petes Thomas D.
Published: March 2010

In a previous study, we mapped spontaneous mitotic reciprocal crossovers (RCOs) in a 120-kb interval of chromosome V of
Saccharomyces cerevisiae
. About three-quarters of the crossovers were associated with gene conversion tracts. About 40% of these conversion tracts had the pattern expected as a consequence of repair of a double-stranded DNA break (DSB) of an unreplicated chromosome. We test this hypothesis by examining the crossovers and gene conversion events induced by gamma irradiation in G1- and G2-arrested diploid yeast cells. The gene conversion patterns of G1-irradiated cells (but not G2-irradiated cells) mimic conversion events associated with spontaneous RCOs, confirming our previous conclusion that many spontaneous crossovers are initiated by a DSB on an unreplicated chromosome.