bluuebunny/crossref_metadata_2025 huggingface dataset:
2H NMR studies of glycerol dynamics in protein matrices
Authors: Herbers C. R. , Sauer D. , Vogel M.
Published: March 2012

We use 2H NMR spectroscopy to investigate the rotational motion of glycerol molecules in matrices provided by the connective tissue proteins elastin and collagen. Analyzing spin-lattice relaxation, line-shape properties, and stimulated-echo decays, we determine the rates and geometries of the motion as a function of temperature and composition. It is found that embedding glycerol in an elastin matrix leads to a mild slowdown of glycerol reorientation at low temperatures and glycerol concentrations, while the effect vanishes at ambient temperatures or high solvent content. Furthermore, it is observed that the nonexponential character of the rotational correlation functions is much more prominent in the elastin matrix than in the bulk liquid. Results from spin-lattice relaxation and line shape measurements indicate that, in the mixed systems, the strong nonexponentiality is in large part due to the existence of distributions of correlation times, which are broader on the long-time flank and, hence, more symmetric than in the neat system. Stimulated-echo analysis of slow glycerol dynamics reveals that, when elastin is added, the mechanism for the reorientation crosses over from small-angle jump dynamics to large-angle jump dynamics and the geometry of the motion changes from isotropic to anisotropic. The results are discussed against the background of present and previous findings for glycerol and water dynamics in various protein matrices and compared with observations for other dynamically highly asymmetric mixtures so as to ascertain in which way the viscous freezing of a fast component in the matrix of a slow component differs from the glassy slowdown in neat supercooled liquids.
Ion condensation behavior and dynamics of water molecules surrounding the sodium poly(methacrylic acid) chain in water: A molecular dynamics study
Authors: Chung Yung-Ting , Huang Ching-I
Published: March 2012

All-atom molecular dynamics simulations are used to study the condensation behavior of monovalent (Na+) and multivalent (Ca2+) salt counterions associated with the co-ions (Cl−) surrounding the charged poly(methacrylic acid) (PMAA) chain in water. The study is extended to the influences on chain conformation, local arrangement, and dynamics of water in the highly diluted aqueous solutions. We find that even when the salt ions are monovalent, they attract more than one charged monomer and act as a bridging agent within the chain, as the multivalent salt ions. In principle, the salt ions bridge between not only the “non-adjacent” but also the “adjacent” charged monomers, leading to a more coil-like and a locally stretched conformation, respectively. With an increase in the salt concentration, the amount of coiled-type condensed ions increase and reach a maximum when the chain conformation becomes the most collapsed; whereas, the stretched-type shows an opposite trend. Our results show that the attractive interactions through the condensed salt ions between the non-adjacent monomers are responsible for the conformational collapse. When the salt concentration increases high enough, a significant increase for the stretched-type condensed ions makes an expansion effect on the chain. These stretched-type salt ions, followed by the adsorption of the co-ions and water molecules, tend to form a multilayer organization outside surrounding the PMAA chain. Thus, the expansion degree of the chain conformation is greatly limited. When only the monovalent Na+ ions are present in the solutions, water molecules are primarily adsorbed into either the condensed Na+ ions or the COO− groups. These adsorbed water molecules form hydrogen bonds with each other and enhance the local bridging behavior associated with the Na+ condensation on the resultant chain conformation. With an increase in the amount of multivalent Ca2+ salt ions, more water molecules are bonded directly with the condensed Ca2+ ions. In this case, only the condensed Ca2+ ions provide a strong bridging effect within the polymer chain. We observe a significant shift towards a higher frequency of the oxygen vibration spectrum and only a slight shift towards a higher frequency of the hydrogen spectrum for the water molecules associated with the ion condensation.
Multilayered graphene anode for blue phosphorescent organic light emitting diodes
Authors: Hwang Joohyun , Kyw Choi Hong , Moon Jaehyun , Yong Kim Taek , Shin Jin-Wook , Woong Joo Chul , Han Jun-Han , Cho Doo-Hee , Woo Huh Jin , Choi Sung-Yool , Lee Jeong-Ik , Yong Chu Hye
Published: March 2012

In this work, we report on blue organic light emitting devices (OLEDs), which have multilayered graphene as its anode. Our graphene films have been grown catalytically and transferred to the support. The fabricated blue OLEDs with graphene anode showed outstanding external quantum efficiency of 15.6% and power efficiency of 24.1 lm/W at 1000 cd/m2. Weak oxygen plasma treatments on graphene film surfaces improved the injection property between the anode and hole injection layer.
Sub-diffraction-limit semiconductor resonators operating on the fundamental magnetic resonance
Authors: Strupiechonski E. , Xu G. , Brekenfeld M. , Todorov Y. , Isac N. , Andrews A. M. , Klang P. , Sirtori C. , Strasser G. , Degiron A. , Colombelli R.
Published: March 2012

We demonstrate semiconductor terahertz (THz) resonators with sub-wavelength dimensions in all three dimensions of space. The maximum confinement is obtained for resonators with a diameter of 13 μm, which operate at a wavelength of ≈272 μm. This corresponds to a λeff/6 confinement, where λeff is the wavelength inside the material (or λ/20, if the free space wavelength is considered). These highly sub-wavelength devices operate on the fundamental magnetic resonance, which corresponds to the fundamental oscillation mode of split-ring resonators and is usually inactive in purely optical resonators. In this respect, these resonators are another step towards the hybridization of optics and electronics at THz frequencies. As a proof of principle for cavity quantum electrodynamics experiments, we apply these resonators to THz intersubband polaritons.
Alignment layers with variable anchoring strengths from Polyvinyl Alcohol
Authors: Cui Yue , Zola Rafael S. , Yang Young-Cheol , Yang Deng-Ke
Published: March 2012

In the study of polyvinyl alcohol (PVA) alignment layers for liquid crystal devices, we found that the anchoring strength can be greatly varied by changing the alignment film thickness. Both the polar and azimuthal anchoring strengths increased with increasing film thickness; however, they had different film thickness dependences. It was also noticed that the quartic term in the expansion of the Rapini-Papoular anchoring energy was important for describing the polar anchoring. In the experiment, solid PVA was dissolved in a thinner and spin-coated on glass substrates to create alignment layers. The substrates were assembled to make electrically-controlled birefringence liquid crystal cells. The polar anchoring strength of the alignment layer was measured using the high field method and the azimuthal anchoring strength using the twist angle method.
Spatial and spectral performance of a chromotomosynthetic hyperspectral imaging system
Authors: Bostick Randall L. , Perram Glen P.
Published: March 2012

The spatial and spectral resolutions achievable by a prototype rotating prism chromotomosynthetic imaging (CTI) system operating in the visible spectrum are described. The instrument creates hyperspectral imagery by collecting a set of 2D images with each spectrally projected at a different rotation angle of the prism. Mathematical reconstruction techniques that have been well tested in the field of medical physics are used to reconstruct the data to produce the 3D hyperspectral image. The instrument operates with a 100 mm focusing lens in the spectral range of 400–900 nm with a field of view of 71.6 mrad and angular resolution of 0.8–1.6 μrad. The spectral resolution is 0.6 nm at the shortest wavelengths, degrading to over 10 nm at the longest wavelengths. Measurements using a point-like target show that performance is limited by chromatic aberration. The system model is slightly inaccurate due to poor estimation of detector spatial resolution, this is corrected based on results improving model performance. As with traditional dispersion technology, calibration of the transformed wavelength axis is required, though with this technology calibration improves both spectral and spatial resolution. While this prototype does not operate at high speeds, components exist which will allow for CTI systems to generate hyperspectral video imagery at rates greater than 100 Hz.
Direct measurement of the spectral transfer function of a laser based anemometer
Authors: Angelou Nikolas , Mann Jakob , Sjöholm Mikael , Courtney Michael
Published: March 2012

The effect of a continuous-wave (cw) laser based anemometer's probe volume on the measurement of wind turbulence is studied in this paper. Wind speed time series acquired by both a remote sensing cw laser anemometer, whose line-of-sight was aligned with the wind direction, and by a reference sensor (sonic anemometer) located in the same direction, were used. The spectral transfer function, which describes the attenuation of the power spectral density of the wind speed turbulence, was calculated and found to be in good agreement with the theoretical exponential function, which is based on the properties of the probe volume of a focused Gaussian laser beam. Parameters such as fluctuations of the wind direction, as well as the overestimation of the laser Doppler spectrum threshold, were found to affect the calculation of the spectral transfer function by introducing high frequency noise.
Investigation of micro/nanoring formation by protein solution evaporation inside confined microwells
Authors: Lo Kuo-Feng , Juang Yi-Je
Published: March 2012

In this study, fabrication of the micro/nanoring-like structures was accomplished via solution evaporation inside the microwells. A phenomenological mechanism for the evaporation process inside the microconfinement was proposed, which is different from that for evaporation of a droplet on a substrate in the ambient condition where either the coffee-ring effect or the Marangoni effect is observed. Moreover, reasoning about how the solvent evaporates from the microwells was also provided. It was found that the normalized height of the deposited structure was approximately proportional to the solution concentration.
Design and evaluation of an imaging spectrophotometer incorporating a uniform light source
Authors: Noble S. D. , Brown R. B. , Crowe T. G.
Published: March 2012

Accounting for light that is diffusely scattered from a surface is one of the practical challenges in reflectance measurement. Integrating spheres are commonly used for this purpose in point measurements of reflectance and transmittance. This solution is not directly applicable to a spectral imaging application for which diffuse reflectance measurements are desired. In this paper, an imaging spectrophotometer design is presented that employs a uniform light source to provide diffuse illumination. This creates the inverse measurement geometry to the directional illumination/diffuse reflectance mode typically used for point measurements. The final system had a spectral range between 400 and 1000 nm with a 5.2 nm resolution, a field of view of approximately 0.5 m by 0.5 m, and millimeter spatial resolution. Testing results indicate illumination uniformity typically exceeding 95% and reflectance precision better than 1.7%.
Disordered surface structure of an ultra-thin tin oxide film on Rh(100)
Authors: Zenkyu R. , Tajima D. , Yuhara J.
Published: March 2012

The composition and structure of an ultra-thin tin oxide film on Rh(100), prepared by the deposition of a submonolayer of tin followed by annealing in an O2 atmosphere, were examined by a combination of low-energy electron diffraction (LEED), Auger electron spectroscopy, X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), and ab initio calculations based on density functional theory (DFT). Although the LEED pattern exhibited c(2 × 8) spots clearly, a uniform periodicity of the c(2 × 8) unit cell was not observed in the STM images. The bright dots that were observed periodically in the STM image were similar to those of the ultra-thin Sn2O3 film on Rh(111) and formed a zigzag arrangement with the numerous point and line defects. The XPS study revealed that the Sn 3d5/2 peak of the tin oxide film on Rh(100) showed a metallic state as well as an oxide state that was between the SnO2 and SnO states. The structural models, which were based on the Sn2O3 structure on Rh(111), were determined using DFT total energy calculations. The simulated STM images of the two slightly different honeycomb-chain models well reproduced the zigzag arrangement in the STM image. The STM image and XPS spectrum were interpreted using a combination of the two models.
Analysis of efficiency droop in nitride light-emitting diodes by the reduced effective volume of InGaN active material
Authors: Ryu Han-Youl , Shin Dong-Soo , Shim Jong-In
Published: March 2012

In InGaN quantum wells (QWs), effective active volume can be greatly reduced due to carrier localization in In-rich region and inhomogeneous carrier distribution. The authors investigate the efficiency droop of InGaN-based light-emitting diodes (LEDs) based on the carrier rate equation including the influence of the reduced effective active volume. It is found that efficiency droop characteristics can be modeled well without employing a large Auger recombination coefficient by assuming that only a small portion of the QWs is effectively used as active region. The presented model is expected to provide insight into the realization of droop-free operation in nitride LEDs.
Optical coupling of surface plasmons between graphene sheets
Authors: Wang Bing , Zhang Xiang , Yuan Xiaocong , Teng Jinghua
Published: March 2012

In this letter, we theoretically investigate the coupling of far-infrared surface plasmon polaritons (SPPs) between spatially separated graphene sheets. By using the finite-difference frequency-domain method, we numerically illustrate the SPP propagation and modulation in the graphene sheets. The coupling of SPPs is employed to design zero insertion loss optical splitters, 1 × 2 digital optical spatial switches, and ultra-compact Mach-Zehnder interferometers with the arm length far below the diffraction limit. The study provides an effective way in designing graphene based high-speed and ultra-compact optoelectronic devices.
Optical characterization of band-edge property of In6S7 compound
Authors: Ho Ching-Hwa , Wang Yi-Ping , Huang Ying-Sheng
Published: March 2012

The evaluation of band gap, exciton, and electronic structure of an energy compound is crucial and essential. We report direct optical evidence of band gap, band-edge exciton, and white-light photoelectric conversion for a solar-energy material In6S7 herein. The direct gap of In6S7 is determined to be 0.93 eV. The value is extremely suitable for absorption of full sunlight spectrum extension to near infrared region.
Hexagonal and pentagonal shapes of self-catalyzed one-dimensional GaAs nanostructures: Shape dependence of the phase evolutions
Authors: Heon Kim Young , Woo Park Dong , Jun Lee Sang , Kim KwangMoo , Chang Park Yun
Published: March 2012

Hexagonal and pentagonal shapes of one-dimensional (1-D) nanostructures were observed at the growth of GaAs by molecular beam epitaxy method without catalyst aid. We report on the phase evolution dependence on the shapes of 1-D GaAs nanostructures. The hexagonal-shaped nanostructures showed a transition region composed of twin boundaries and stacking faults during the phase transition from a zinc-blende (ZB) structure to a wurtzite (WZ) structure. On the other hand, the pentagonal-shaped nanostructures appeared to have an abrupt transition from a ZB structure to a WZ structure and to be elongated along 〈112¯〉 directions of a ZB structure.
Electron-nuclei spin coupling in GaAs—Free versus localized electrons
Authors: Huang J. , Chen Y. S. , Ludwig A. , Reuter D. , Wieck A. D. , Bacher G.
Published: March 2012

We report on an experimental evidence of a significantly different dynamic nuclear polarization (DNP) for localized and itinerant electrons in n-GaAs. Optically injected spin-polarized electrons are used to generate dynamic nuclear polarization via electron-nucleus hyperfine interaction. Using time resolved Kerr rotation measurements for probing the transient Overhauser field, the DNP time constants for itinerant and localized electrons are extracted to be 10 min and less than 1 min, respectively. This is attributed to a rapid DNP occurring in the vicinity of the donors followed by a delayed nuclear spin polarization in between the donor sites.
Absolute calibration of optical tweezers including aberrations
Authors: Dutra R. S. , Viana N. B. , Maia Neto P. A. , Nussenzveig H. M.
Published: March 2012

We extend a previous proposal for absolute calibration of optical tweezers by including optical setup aberrations into the first-principles theory, with no fitting parameters. Astigmatism, the dominant term, is determined from images of the focused laser spot. Correcting it can substantially increase stiffness. Comparison with experimental results yields agreement within error bars for a broad range of bead sizes and trap heights, as well as different polarizations. Absolute calibration is established as a reliable and practical method for applications and design of optical tweezers systems.
Fast vapor phase growth of SiO2 nanowires via surface-flow on Ag core/SiO2 shell structure
Authors: Gao Lei , Ji Ailing , Lu Nianpeng , Li Chaorong , Cao Zexian
Published: March 2012

Uniform, millimeter-long SiO2 nanowires were grown from co-evaporation of Ag2O and SiO powders. The ‘frozen’ growth scenario by cooling enables revelation of the vapor-liquid-solid mechanism here in action, which is generally inaccessible due to the high temperature and high pressure condition. Ag core/SiO2 shell preformed in the vapor and wetting the substrate will expose its liquid Ag-core to catalyze nanowire growth, at a rate over 10 nm/s, via viscous flow of the encasing SiO2 layer which precipitates through a liquid neck zone. This method is characteristic of high-yield of catalytic seeds free from overgrowth or consuming, easy control of wire thickness by vapor pressure adjustment, enhanced rooting ability since catalyst deposition on substrate becomes dispensable, etc. Also spinning growth of nanowires observed in many other circumstances can be explained by the viscous flow mechanism.
Analyzing the propagating waves in the two-dimensional photonic crystal by the decoupled internal-field expansion method
Authors: Pei Ting-Hang , Huang Yang-Tung
Published: March 2012

We propose the decoupled internal-field expansion (IFE) method to discuss refractions in the photonic crystal (PhC). This method decouples the full wave in the PhC and classifies them into two categories including the forward-propagating and backward-propagating waves denoted by the index n. A triangular-PhC case is demonstrated and both positive and negative refractions are discussed by this method. The incident angle of 10° results in the positive refracted wave with the refracted angle about 8°, which approximately corresponds to the forward wave of n=0 order. The negative refracted waves, which exist in the left and right edge regions, propagate almost parallel to the interfaces between the PhC and outside media. Meanwhile, due to the interaction between the negative refracted wave and the nearest few rows of air cylinders, the reflected wave and another weaker negative refracted wave are created. Finally, the weaker negative refracted waves from both edge regions interfere with each other in the middle region. It is found out that the negative refracted waves in edge regions as well as the interfered wave in the middle region can be constructed by two n=-1 forward and backward waves. On the other hand, the positive refracted wave is composed of the n=0 forward wave dressed other n≠0 forward waves, the propagation angle is affected by these dressed waves, especially near the edge region. Finally, another case proves this point of view explicitly.
Livestock mobility in arid and semiarid Australia: escaping variability in space
Authors: McAllister R. R. J.
Published: March 2012

Livestock mobility is practised by pastoralists to cope with some of the variability and unpredictability of limited forage resources and because a diverse portfolio of strategies is needed to manage risk. The global trend towards rangeland privatisation, fragmentation and land-use intensification is eroding many of the institutions that have traditionally facilitated pastoral mobility. While Australia’s pastoral industry was developed as a European private-property system, livestock mobility has recently been increasing, indicating an important response to variability regardless of a nation’s wealth or development. This paper discusses how opportunistic movements of livestock over large scales by trading grazing rights between enterprises are effective but imperfect. Knowledge about the trustworthiness of individuals and local environments is often limited and poorly monitored. There is scope for policy to support mobility by targeting these institutional failures. The Australian system of trading grazing rights can inform efforts to maintain spatial flexibility in the industrial era.
Habitat characteristics may override climatic influences on ant assemblage composition: a study using a 300-km climatic gradient
Authors: Yates Michelle L. , Gibb Heloise , Andrew Nigel R.
Published: March 2012

We assessed the relative importance of a variety of climatic and habitat variables in structuring ant communities along a 300-km climatic gradient. Sampling was conducted in semiarid, transitional and cool temperate climatic zones in New South wales, Australia. Ants were sampled at three paired sites of two habitats (pastures and conservation ‘remnants’) in each of the climatic zones (herein referred to as ‘zones’) using pitfall traps. Remnants represented original open forests, while pastures were a mix of grassland vegetation and cleared woodland. We tested the effects of habitat type, region (representing different climatic zones) and environmental variables on assemblages using distance-based similarity measures (Permanova and Permdisp) and canonical analysis of principal coordinates. Assemblage composition differed between habitats and zones, but we found no interaction effects. Assemblage dispersion (between-site heterogeneity) differed between habitats but not among zones. Pasture habitats supported more homogeneous assemblages than remnant habitats. Our findings suggest that habitat type, and structure, homogenise assemblages in pastures, thus overriding the effects of local climate apparent in remnants. As remnants are isolated within the biologically homogeneous pastures, movement of unique species between remnants in response to climate changes may be limited, thus landscape connectivity is likely to be important in reducing species loss.
Optimal portfolio design to reduce climate-related conservation uncertainty in the Prairie Pothole Region
Authors: Ando Amy W. , Mallory Mindy L.
Published: March 2012

Climate change is likely to alter the spatial distributions of species and habitat types but the nature of such change is uncertain. Thus, climate change makes it difficult to implement standard conservation planning paradigms. Previous work has suggested some approaches to cope with such uncertainty but has not harnessed all of the benefits of risk diversification. We adapt Modern Portfolio Theory (MPT) to optimal spatial targeting of conservation activity, using wetland habitat conservation in the Prairie Pothole Region (PPR) as an example. This approach finds the allocations of conservation activity among subregions of the planning area that maximize the expected conservation returns for a given level of uncertainty or minimize uncertainty for a given expected level of returns. We find that using MPT instead of simple diversification in the PPR can achieve a value of the conservation objective per dollar spent that is 15% higher for the same level of risk. MPT-based portfolios can also have 21% less uncertainty over benefits or 6% greater expected benefits than the current portfolio of PPR conservation. Total benefits from conservation investment are higher if returns are defined in terms of benefit–cost ratios rather than benefits alone. MPT-guided diversification can work to reduce the climate-change–induced uncertainty of future ecosystem-service benefits from many land policy and investment initiatives, especially when outcomes are negatively correlated between subregions of a planning area.
Superoxide dismutase is dispensable for normal animal lifespan
Authors: Van Raamsdonk Jeremy Michael , Hekimi Siegfried
Published: March 2012

Reactive oxygen species (ROS) are toxic oxygen-containing molecules that can damage multiple components of the cell and have been proposed to be the primary cause of aging. The antioxidant enzyme superoxide dismutase (SOD) is the only eukaryotic enzyme capable of detoxifying superoxide, one type of ROS. The fact that SOD is present in all aerobic organisms raises the question as to whether SOD is absolutely required for animal life and whether the loss of SOD activity will result in decreased lifespan. Here we use the genetic model organism
Caenorhabditis elegans
to generate an animal that completely lacks SOD activity (
sod-12345
worms). We show that
sod-12345
worms are viable and exhibit a normal lifespan, despite markedly increased sensitivity to multiple stresses. This is in stark contrast to what is observed in other genetic model organisms where the loss of a single
sod
gene can result in severely decreased survival. Investigating the mechanism underlying the normal lifespan of
sod-12345
worms reveals that their longevity results from a balance between the prosurvival signaling and the toxicity of superoxide. Overall, our results demonstrate that SOD activity is dispensable for normal animal lifespan but is required to survive acute stresses. Moreover, our findings indicate that maintaining normal stress resistance is not crucial to the rate of aging.
Dual functions of the Hsm3 protein in chaperoning and scaffolding regulatory particle subunits during the proteasome assembly
Authors: Barrault Marie-Bénédicte , Richet Nicolas , Godard Chloe , Murciano Brice , Le Tallec Benoît , Rousseau Erwann , Legrand Pierre , Charbonnier Jean-Baptiste , Le Du Marie-Hélène , Guérois Raphaël , Ochsenbein Françoise , Peyroche Anne
Published: March 2012

The 26S proteasome, a molecular machine responsible for regulated protein degradation, consists of a proteolytic core particle (20S CP) associated with 19S regulatory particles (19S RPs) subdivided into base and lid subcomplexes. The assembly of 19S RP base subcomplex is mediated by multiple dedicated chaperones. Among these, Hsm3 is important for normal growth and directly targets the carboxyl-terminal (C-terminal) domain of Rpt1 of the Rpt1–Rpt2–Rpn1 assembly intermediate. Here, we report crystal structures of the yeast Hsm3 chaperone free and bound to the C-terminal domain of Rpt1. Unexpectedly, the structure of the complex suggests that within the Hsm3–Rpt1–Rpt2 module, Hsm3 also contacts Rpt2. We show that in both yeast and mammals, Hsm3 actually directly binds the AAA domain of Rpt2. The Hsm3 C-terminal region involved in this interaction is required in vivo for base assembly, although it is dispensable for binding Rpt1. Although Rpt1 and Rpt2 exhibit weak affinity for each other, Hsm3 unexpectedly acts as an essential matchmaker for the Rpt1-Rpt2-Rpn1 assembly by bridging both Rpt1 and Rpt2. In addition, we provide structural and biochemical evidence on how Hsm3/S5b may regulate the 19S RP association to the 20S CP proteasome. Our data point out the diverse functions of assembly chaperones.
Mixotrophic basis of Atlantic oligotrophic ecosystems
Authors: Hartmann Manuela , Grob Carolina , Tarran Glen A. , Martin Adrian P. , Burkill Peter H. , Scanlan David J. , Zubkov Mikhail V.
Published: March 2012

Oligotrophic subtropical gyres are the largest oceanic ecosystems, covering >40% of the Earth's surface. Unicellular cyanobacteria and the smallest algae (plastidic protists) dominate CO
2
fixation in these ecosystems, competing for dissolved inorganic nutrients. Here we present direct evidence from the surface mixed layer of the subtropical gyres and adjacent equatorial and temperate regions of the Atlantic Ocean, collected on three Atlantic Meridional Transect cruises on consecutive years, that bacterioplankton are fed on by plastidic and aplastidic protists at comparable rates. Rates of bacterivory were similar in the light and dark. Furthermore, because of their higher abundance, it is the plastidic protists, rather than the aplastidic forms, that control bacterivory in these waters. These findings change our basic understanding of food web function in the open ocean, because plastidic protists should now be considered as the main bacterivores as well as the main CO
2
fixers in the oligotrophic gyres.
Structural and mechanistic insights into the activation of Stromal interaction molecule 1 (STIM1)
Authors: Yang Xue , Jin Hao , Cai Xiangyu , Li Siwei , Shen Yuequan
Published: March 2012

Calcium influx through the Ca
2+
release-activated Ca
2+
(CRAC) channel is an essential process in many types of cells. Upon store depletion, the calcium sensor in the endoplasmic reticulum, STIM1, activates Orai1, a CRAC channel in the plasma membrane. We have determined the structures of SOAR from
Homo sapiens
(hSOAR), which is part of STIM1 and is capable of constitutively activating Orai1, and the entire coiled coil region of STIM1 from
Caenorhabditis elegans
(ceSTIM1-CCR) in an inactive state. Our studies reveal that the formation of a SOAR dimer is necessary to activate the Orai1 channel. Mutations that disrupt SOAR dimerization or remove the cluster of positive residues abolish STIM1 activation of Orai1. We identified a possible inhibitory helix within the structure of ceSTIM1-CCR that tightly interacts with SOAR. Functional studies suggest that the inhibitory helix may keep the C-terminus of STIM1 in an inactive state. Our data allowed us to propose a model for STIM1 activation.
Calcium and pH-dependent packing and release of the gel-forming MUC2 mucin
Authors: Ambort Daniel , Johansson Malin E. V. , Gustafsson Jenny K. , Nilsson Harriet E. , Ermund Anna , Johansson Bengt R. , Koeck Philip J. B. , Hebert Hans , Hansson Gunnar C.
Published: March 2012

MUC2, the major colonic mucin, forms large polymers by N-terminal trimerization and C-terminal dimerization. Although the assembly process for MUC2 is established, it is not known how MUC2 is packed in the regulated secretory granulae of the goblet cell. When the N-terminal VWD1-D2-D′D3 domains (MUC2-N) were expressed in a goblet-like cell line, the protein was stored together with full-length MUC2. By mimicking the pH and calcium conditions of the secretory pathway we analyzed purified MUC2-N by gel filtration, density gradient centrifugation, and transmission electron microscopy. At pH 7.4 the MUC2-N trimer eluted as a single peak by gel filtration. At pH 6.2 with Ca
2+
it formed large aggregates that did not enter the gel filtration column but were made visible after density gradient centrifugation. Electron microscopy studies revealed that the aggregates were composed of rings also observed in secretory granulae of colon tissue sections. The MUC2-N aggregates were dissolved by removing Ca
2+
and raising pH. After release from goblet cells, the unfolded full-length MUC2 formed stratified layers. These findings suggest a model for mucin packing in the granulae and the mechanism for mucin release, unfolding, and expansion.
Interaction with plant transcription factors can mediate nuclear import of phytochrome B
Authors: Pfeiffer Anne , Nagel Marie-Kristin , Popp Claudia , Wüst Florian , Bindics János , Viczián András , Hiltbrunner Andreas , Nagy Ferenc , Kunkel Tim , Schäfer Eberhard
Published: March 2012

Phytochromes (phy) are red/far-red–absorbing photoreceptors that regulate the adaption of plant growth and development to changes in ambient light conditions. The nuclear transport of the phytochromes upon light activation is regarded as a key step in phytochrome signaling. Although nuclear import of phyA is regulated by the transport facilitators far red elongated hypocotyl 1 (FHY1) and fhy1-like, an intrinsic nuclear localization signal was proposed to be involved in the nuclear accumulation of phyB. We recently showed that nuclear import of phytochromes can be analyzed in a cell-free system consisting of isolated nuclei of the unicellular green algae
Acetabularia acetabulum
. We now show that this system is also versatile to elucidate the mechanism of the nuclear transport of phyB. We tested the nuclear transport characteristics of full-length phyB as well as N- and C-terminal phyB fragments in vitro and showed that the nuclear import of phyB can be facilitated by phytochrome-interacting factor 3 (PIF3). In vivo measurements of phyB nuclear accumulation in the absence of PIF1, -3, -4, and -5 indicate that these PIFs are the major transport facilitators during the first hours of deetiolation. Under prolonged irradiations additional factors might be responsible for phyB nuclear transport in the plant.
Sex, puberty, and the timing of sleep EEG measured adolescent brain maturation
Authors: Campbell Ian G. , Grimm Kevin J. , de Bie Evan , Feinberg Irwin
Published: March 2012

The steep adolescent decline in the slow wave (delta, 1–4 Hz) electroencephalogram (EEG) of nonrapid eye movement (NREM) sleep is a dramatic maturational change in brain electrophysiology thought to be driven by cortical synaptic pruning. A perennial question is whether this change in brain electrophysiology is related to sexual maturation. Applying Gompertz growth models to longitudinal data spanning ages 9–18 y, we found that the timing of the delta decline was significantly (
P
< 0.0001) linked to timing of pubertal maturation. This timing relation remained significant when sex differences in the timing of the delta decline were statistically controlled. Sex differences and the relation to the timing of puberty jointly explained 67% of the between-subject variance in the timing of the delta decline. These data provide a demonstration of a temporal relation between puberty and an electrophysiological marker of adolescent brain development. They can guide research into whether the neuroendocrine events of puberty are mechanistically linked to cortical maturation or whether, instead, the two maturational processes are parallel but independent programs of human ontogenesis.
Mutant induced pluripotent stem cell lines recapitulate aspects of TDP-43 proteinopathies and reveal cell-specific vulnerability
Authors: Bilican Bilada , Serio Andrea , Barmada Sami J. , Nishimura Agnes Lumi , Sullivan Gareth J. , Carrasco Monica , Phatnani Hemali P. , Puddifoot Clare A. , Story David , Fletcher Judy , Park In-Hyun , Friedman Brad A. , Daley George Q. , Wyllie David J. A. , Hardingham Giles E. , Wilmut Ian , Finkbeiner Steven , Maniatis Tom , Shaw Christopher E. , Chandran Siddharthan
Published: March 2012

Transactive response DNA-binding (TDP-43) protein is the dominant disease protein in amyotrophic lateral sclerosis (ALS) and a subgroup of frontotemporal lobar degeneration (FTLD-TDP). Identification of mutations in the gene encoding TDP-43 (
TARDBP
) in familial ALS confirms a mechanistic link between misaccumulation of TDP-43 and neurodegeneration and provides an opportunity to study TDP-43 proteinopathies in human neurons generated from patient fibroblasts by using induced pluripotent stem cells (iPSCs). Here, we report the generation of iPSCs that carry the TDP-43 M337V mutation and their differentiation into neurons and functional motor neurons. Mutant neurons had elevated levels of soluble and detergent-resistant TDP-43 protein, decreased survival in longitudinal studies, and increased vulnerability to antagonism of the PI3K pathway. We conclude that expression of physiological levels of TDP-43 in human neurons is sufficient to reveal a mutation-specific cell-autonomous phenotype and strongly supports this approach for the study of disease mechanisms and for drug screening.
Regulation of cell cycle progression by forkhead transcription factor FOXO3 through its binding partner DNA replication factor Cdt1
Authors: Zhang Yiru , Xing Yuqian , Zhang Lei , Mei Yang , Yamamoto Kazuo , Mak Tak W. , You Han
Published: March 2012

To ensure genome stability, DNA must be replicated once and only once during each cell cycle. Cdt1 is tightly regulated to make sure that cells do not rereplicate their DNA. Multiple regulatory mechanisms operate to ensure degradation of Cdt1 in S phase. However, little is known about the positive regulators of Cdt1 under physiological conditions. Here we identify FOXO3 as a binding partner of Cdt1. FOXO3 forms a protein complex with Cdt1, which in turn blocks its interaction with DDB1 and PCNA. Conversely, FOXO3 depletion facilitated the proteolysis of Cdt1 in unperturbed cells. Intriguingly, FOXO3 deficiency resulted in impaired S-phase entry and reduced cell proliferation. We provide data that FOXO3 knockdown mimics Cdt1 down-regulation and affects G1/S transitions. Our results demonstrate a unique role of FOXO3 in binding to Cdt1 and maintaining its level required for cell cycle progression.
Disclosing the in vivo organization of a viral histone-like protein in
Bacillus subtilis
mediated by its capacity to recognize the viral genome
Authors: Holguera Isabel , Ballesteros-Plaza David , Muñoz-Espín Daniel , Salas Margarita
Published: March 2012

Organization of replicating prokaryotic genomes requires architectural elements that, similarly to eukaryotic systems, induce topological changes such as DNA supercoiling. Bacteriophage ϕ29 protein p6 has been described as a histone-like protein that compacts the viral genome by forming a nucleoprotein complex and plays a key role in the initiation of protein-primed DNA replication. In this work, we analyze the subcellular localization of protein p6 by immunofluorescence microscopy and show that, at early infection stages, it localizes in a peripheral helix-like configuration. Later, at middle infection stages, protein p6 is recruited to the bacterial nucleoid. This migrating process is shown to depend on the synthesis of components of the ϕ29 DNA replication machinery (i.e., terminal protein and DNA polymerase) needed for the replication of viral DNA, which is required to recruit the bulk of protein p6. Importantly, the double-stranded DNA-binding capacity of protein p6 is essential for its relocalization at the nucleoid. Altogether, the results disclose the in vivo organization of a viral histone-like protein in bacteria.
Chemical and Electrical Approaches to Sedation of Hybrid Striped Bass: Induction, Recovery, and Physiological Responses to Sedation
Authors: Trushenski Jesse T. , Bowker James D. , Gause Brian R. , Mulligan Bonnie L.
Published: March 2012

Currently, in the United States, there are few sedatives available to fisheries professionals that are safe, effective, and practical. Chemical sedatives, including tricaine methanesulfonate (MS‐222), carbon dioxide (CO2), benzocaine, and eugenol may be used to sedate fish, though none of these compounds are currently approved by the U.S. Food and Drug Administration as immediate‐release fish sedatives. Another option is the use of electricity to temporarily immobilize fish. Few studies have assessed the efficacy of these options for immediate‐release sedation in side‐by‐side comparisons. We evaluated the use of MS‐222 (150 mg/L), CO2 (∼400 mg/L), benzocaine (150 mg/L), eugenol (60 mg/L), and a commercially available electrosedation unit (30 Hz pulsed DC, 60 V, 25% duty cycle, 3‐s exposures) to induce hybrid striped bass (white bass Morone chrysops × striped bass M. saxatilis; 510 ± 12 g [mean ± SE]) to stage IV anesthesia or sedation. Induction times were shortest (0.2 ± 0.1 min) when electrosedation was used and longest (2.5 ± 0.1 min) when CO2 was used; the induction times for the other chemical sedatives varied (<2 min). Recovery times were longest for eugenol (5.2 ± 0.4 min postinduction) and benzocaine (4.0 ± 0.4 min); however, the difference in recovery time between these two treatments was not significant or between recovery times for benzocaine and the remaining sedatives (∼3–4 min). Physiological responses varied but were consistent with the generalized stress response. Circulating levels of cortisol, glucose, and lactate increased after sedation, and though response magnitude and duration varied somewhat among these variables, these changes were resolved within 6 h. Changes in plasma osmolality and hematocrit were less overt and varied less among the sedatives. Electrosedation may be a suitable tool for quickly sedating hybrid striped bass; however, all of the sedatives evaluated were effective at the doses and strengths used and some may be better suited to certain applications than to others.
Comparing Economic Values of Trout Anglers and Nontrout Anglers in Colorado's Stocked Public Reservoirs
Authors: Loomis John , Ng Kawa
Published: March 2012

Trout are often popular target species for anglers worldwide and have been the most commonly stocked game fish species in the USA. Using survey data collected at Colorado's stocked public reservoirs in 2009, we found that trout anglers’ net economic benefits were more than twice those of anglers fishing for species other than trout. Values estimated from the travel cost method produced angler-day consumer surpluses (willingness to pay [WTP]) of US$191.60 for trout anglers and $61.68 for nontrout anglers. Based on the contingent valuation method, the mean WTP was $196.48 for trout anglers and $73.84 for nontrout anglers, while the median WTP was $164.53 for trout anglers and $56.78 for nontrout anglers. Thus, the relative values of fishing for trout versus fishing for other species are robust to nonmarket valuation methods, and the two valuation methods show convergent validity.

Received August 31, 2010; accepted November 11, 2011
Tracks of the third wave: democracy theory, democratisation and the dilemma of political succession in Africa
Authors: Nwosu Bernard
                      Ugochukwu
Published: March 2012

The sweep of the third-wave moment of democratic impulses through Africa saw mass movements against authoritarian rule and the demand for liberalisation of political spaces. Ruling-group compromises and promises of democratisation diluted the fervour of this demand. Conservative interests captured the process by creating formal institutions of political competition but without corresponding necessary conditions for democracy. They set up regimes of political succession that rendered the political field a closed space. National trends in succession are linked to the discursive paradigm that underpins third-wave democratisation. Selected studies of succession in African states indicate trends towards illegitimate and unpopular self-succession, hereditary trends, the appointment of proxies and only a few instances of emerging liberal democratic regimes. The dominance of perverse third-wave trajectories in Africa points to the inadequacy of the minimalist epistemology upon which the idea of the third wave is based.

[Traces de la troisième vague: la théorie de la démocratie, la démocratisation et le dilemme de la succession politique en Afrique]. La marche de la troisième vague d'impulsions démocratiques à travers l'Afrique a engendré des mouvements de masse contre le régime autoritaire et la demande de libéralisation des espaces politiques. Des compromis de la classe dirigeante et des promesses de démocratisation ont dilué la ferveur de cette demande. Des intérêts conservateurs ont capturé le processus en créant des institutions formelles de compétition politique, mais sans les conditions correspondantes nécessaires à la démocratie. Ils mettent en place des régimes de succession politique qui ont rendu le champ politique un espace clos. Les tendances nationales de succession sont liées au paradigme discursif qui sous-tend la troisième vague de démocratisation. Les études sélectionnées de succession dans les états africains indiquent une tendance à la succession illégitime et impopulaire de soi-même, les tendances héréditaires, la nomination des mandataires et quelques cas seulement de nouveaux régimes de démocratie libérale. La prédominance des trajectoires perverses de la troisième vague en Afrique souligne l'insuffisance de l'épistémologie minimaliste sur lequel l'idée de la troisième vague est fondée.

Mots-clés: troisième vague; démocratization; procédure; substantive; succession; élection
Rubbishing: a wrong approach to Eritrea/Ethiopia union
Authors: Weldehaimanot Simon , Kesete Semere
Published: March 2012

As part of a revisionist discourse, it has been contended that the core of Eritrea's political, cultural and economic identity is based on colonial premises and these three premises are false. As a result, Eritrea is in a dilemma. It is further contended that Eritrea's future lies in seeking unity with Ethiopia. This article is a rejoinder to the contention. It shows the truthfulness of the premises and argues that, save for the prevalent dictatorship, it was and it still is a correct decision for Eritreans to opt for an independent Eritrea. Avoiding the old talk, this rejoinder recommends that as sovereign states, Eritrea and Ethiopia should govern their relations by principles of civilised nations.

[Rejeter: une mauvaise approche de l'union érythréenne/éthiopienne]. Dans le cadre d'un discours révisionniste, il a été soutenu que le noyau de l'identité politique, culturelle et économique de l'Érythrée est basé sur des prémisses coloniales et que ces trois prémisses sont fausses. En conséquence, l'Erythrée se trouve dans un dilemme. Il est aussi soutenu que l'avenir de l'Erythrée se situe dans la poursuite de l'unité avec l'Éthiopie. Cet article est une réponse à cet argument. Il montre la véracité des prémisses et affirme que, sauf pour la dictature courante, c'était et c'est encore une bonne décision pour les Erythréens d'avoir opté pour une Érythrée indépendante. Eviter les discours anciens, cette réponse recommande que l'Érythrée et l'Éthiopie, comme états souverains, devraient régir leurs relations par des principes des nations civilisées.

Mots-clés: Érythrée; Éthiopie; sécession; indépendance; ghedli; économie politique