bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of the projectile's velocity and diameter on the amorphization of silicon by electrosprayed nanodroplets
Authors: Saiz Fernan , Borrajo-Pelaez Rafael , Gamero-Castaño Manuel
Published: July 2013

The hypervelocity impact of electrosprayed nanodroplets on single-crystal silicon amorphizes a thin layer of the target. Molecular Dynamics simulations have shown that the amorphization results from the melting of the material surrounding the impact interface, followed by an ultrafast quenching that prevents recrystallization. This article extends this previous work to study the role of the projectile's diameter and velocity on the amorphization phenomena and compares the simulation results with experimental measurements of a bombarded silicon target. In the range of projectile diameter and impact velocity studied (diameter between 5 and 30 nm, and velocity between 1 and 6 km/s), the projectile velocity plays a more relevant role than its diameter. A significant amorphous layer begins to develop at a velocity near 3 km/s, its thickness rapidly increasing with velocity until it plateaus at about 4 km/s. The reduction of the melting temperature with pressure combined with the conversion of kinetic energy into thermal energy are responsible for the melting of silicon starting at an impact velocity of 3 km/s. Once the conditions inducing amorphization are reached, the volume of the generated amorphous phase scales linearly with both the kinetic energy and the volume of the projectile.
The role of non-equilibrium charge carriers in thermoelectric cooling
Authors: Gurevich Yu. G. , Velázquez-Pérez J. E.
Published: July 2013

This paper is devoted to the analysis of thermoelectric cooling phenomena in semiconductors containing potential barriers (p-n-junction). The formulation of an adequate self-consistent theoretical model describing the effect is presented. The role of the recombination rate in lineal approximation of the electric current leads to a new formulation of the set of equations describing the Peltier effect that is discussed in detail. The importance of re-distribution of non-equilibrium charge carriers, which has been ignored in most of the publications on this subject, is also shown. Moreover, it is proved that the conventional theory of thermoelectric cooling, which does not take into account the influence of non-equilibrium charge carriers, is not correct in general. In the present work, it is demonstrated that the Peltier effect strongly depends on the recombination rate. In particular, it is shown that the sign of the Peltier effect changes with the value of the recombination rate.
Co-existence of magnetocaloric effect and magnetoresistance in Co substituted La0.67Sr0.33MnO3 at room temperature
Authors: Reshmi C. P. , Savitha Pillai S. , Vasundhara M. , Raji G. R. , Suresh K. G. , Raama Varma Manoj
Published: July 2013

Magnetization (M), Magnetocaloric effect (MCE), and Magnetoresistance (MR) in Co substituted La0.67Sr0.33Mn1−xCoxO3 (x = 0.03, 0.05, and 0.1) samples have been investigated. All the studied samples were crystallized into a single phase rhombohedral structure with R3¯c space group. The Curie temperature (TC) is found to decrease with the increase of Co content and for the composition x = 0.1, a cluster glass-like nature is observed. Temperature variation of magnetic entropy change (ΔSM) shows a positive peak at TC for the composition x = 0.1 with ΔSM = 3.1 J/kg K and relative cooling power, RCP = 155 J/kg at a magnetic field of 50 kOe. Again, the critical analysis of the paramagnetic to ferromagnetic transition and the scaling behaviour of field dependence of MCE for x = 0.1 composition is also reported. Furthermore, the temperature dependence of electrical resistivity under the magnetic fields up to 50 kOe is reported along with the values of 20% enhancement in MR at room temperature for the Co substituted samples.
Ferroeletric like characteristics in redox active polymer of 5,10,15,20 tetra(4-hydroxyphenyl)-porphyrin at room temperature
Authors: Koiry S. P. , Celestin M. E. , Ratnadurai R. , Veerender P. , Majumder C. , Krishnan S. , Stefanakos E. , Goswami Y. , Aswal D. K. , Bhansali Shekhar
Published: July 2013

We report ferroelectric behaviors in electrochemically polymerized 5,10,15,20 tetra(4-hydroxyphenyl)-porphyrin. The ferroelectric behaviors are due to conformational changes that occur during the reduction and oxidation of the polymer under electric field. The conformational changes were studied by in situ Raman spectroscopy and frequency response analysis. The present findings will open up an alternative route for organic ferroelectrics which is presently in urgent need of approaches and materials.
Double oxide deposition and etching nanolithography for wafer-scale nanopatterning with high-aspect-ratio using photolithography
Authors: Seo Jungho , Cho Hanchul , Lee Ju-kyung , Lee Jinyoung , Busnaina Ahmed , Lee HeaYeon
Published: July 2013

We report a nanolithography technique for the high aspect-ratio nanostructure manufacturing using DODE (double oxide deposition and etching) process. Conventional microfabrication processes are integrated to manufacture nanostructure arrays with sub-100 nm of linewidth. This lithography method is developed to overcome resolution limits of photolithography. High aspect-ratio nanostructures with sub-100 nm of lindewidth were fabricated on wafer-scale substrate without nanolithography techniques. The DODE lithography process presented enabled to pave a way to overcome limitations of nanolithography processes and allowed to manufacture large-scale nanostructures using photolithography and thin film deposition and dry etching processes.
Atomic-scale study of topological vortex-like domain pattern in multiferroic hexagonal manganites
Authors: Yu Yi , Zhang Xiaozhong , Zhao Y. G. , Jiang Ning , Yu Rong , Wang J. W. , Fan C. , Sun X. F. , Zhu Jing
Published: July 2013

Using CS-corrected transmission electron microscopy, we demonstrate the atomic details of a topological vortex-like domain pattern in multiferroic hexagonal manganite YMnO3. The domain configuration shown here is confirmed to be different from a real vortex. The vortex-related issue is discussed and understanding of the vortex-like domain pattern is improved. Moreover, atomic configurations of the interlocked domain walls are revealed with the help of atomistic simulation and insights into the domain wall structure are obtained. The present study can throw further light on understanding of structure-property relation in multiferroic hexagonal manganites.
Photorefractive effect at 775 nm in doped lithium niobate crystals
Authors: Nava G. , Minzioni P. , Cristiani I. , Argiolas N. , Bazzan M. , Ciampolillo M. V. , Pozza G. , Sada C. , Degiorgio V.
Published: July 2013

The photorefractive effect induced by 775-nm laser light on doped lithium niobate crystals is investigated by the direct observation in the far field of the transmitted-beam distortion as a function of time. Measurements performed at various Zr-doping concentrations and different light intensities show that the 775-nm light beam induces a steady-state photorefractive effect comparable to that of 532-nm light, but the observed build-up time of the photovoltaic field is longer by three-orders of magnitude. The 775-nm photorefractivity of lithium niobate crystals doped with 3 mol. % ZrO2 or with 5.5 mol. % MgO is found to be negligible.
Effect of electron energy distribution functions on plasma generated vacuum ultraviolet in a diffusion plasma excited by a microwave surface wave
Authors: Zhao J. P. , Chen L. , Funk M. , Sundararajan R. , Nozawa T. , Samukawa S.
Published: July 2013

Plasma generated vacuum ultraviolet (VUV) in diffusion plasma excited by a microwave surface wave has been studied by using dielectric-based VUV sensors. Evolution of plasma VUV in the diffusion plasma as a function of the distance from the power coupling surface is investigated. Experimental results have indicated that the energy and spatial distributions of plasma VUV are mainly controlled by the energy distribution functions of the plasma electrons, i.e., electron energy distribution functions (EEDFs). The study implies that by designing EEDF of plasma, one could be able to tailor plasma VUV in different applications such as in dielectric etching or photo resist smoothing.
Characterization of local charge distribution of polyethylene terephthalate film and influence as a graphene substrate
Authors: Park Won-Hwa , Hwan Noh Seok , Ho Joo Min , Hyeong Kim Tae , Park Wonbae , Jung Myunghee , Moon Jin-San , Ho Park Kyu
Published: July 2013

We examine local electrostatic force distribution of polyethylene terephthalate (PET) film surface before and after transferring graphene in order to compare the influence of local electrostatic interaction between graphene and PET film in terms of the sheet resistance value of deposited graphene. By using the electrical modulation of amplitude in a tapping mode AFM tip, we can obtain the distinguished electrostatic force amplitude mapping of graphene. We determine that different electrostatic attractive interactions between Au-coated tip and bare PET are present and the observed difference can affect the graphene formation and electrical performance, which correlates with the sheet resistance difference.
Simultaneous determination of position and mass in the cantilever sensor using transfer function method
Authors: Kim Deokman , Hong Seongkyeol , Jang Jaesung , Park Junhong
Published: July 2013

We present the simultaneous measurement of mass and position of micro-beads attached to the cantilever-based mass sensors using the transfer function method. 10 μm diameter micro-beads were placed on micro-cantilevers and the cantilevers were excited by lead-zirconate-titanate through low-pass filtered random voltages. The cantilever vibration was measured via a laser Doppler vibrometer before and after applying the beads. From the measured transfer function, the bead position was identified using its influence on the cantilever kinetic energy. The bead mass was then obtained by analyzing the wave propagation near the beads. The predicted position and mass agreed well with actual values.
Surface and core contribution to 1/f-noise in InAs nanowire metal-oxide-semiconductor field-effect transistors
Authors: Persson K.-M. , Malm B. G. , Wernersson L.-E.
Published: July 2013

By measuring 1/f-noise in wrap-gated InAs nanowire metal-oxide-semiconductor field-effect transistors with transport dominating, controllably, in either an inner, core channel, or an outer, surface channel, it is possible to accurately evaluate the material quality related Hooge-parameter, αH, with reduced interference from the surface properties. The devices show low values of αH ∼ 4 × 10−5. At forward bias, where the data suggest that the 1/f-noise is dominated by the contribution from the high-k interface, devices show low values of normalized noise spectral density.
Improved injection efficiency in 290 nm light emitting diodes with Al(Ga)N electron blocking heterostructure
Authors: Kolbe T. , Mehnke F. , Guttmann M. , Kuhn C. , Rass J. , Wernicke T. , Kneissl M.
Published: July 2013

The effect of different Al(Ga)N electron blocking heterostructures (EBH) on the emission spectra and light output power of 290 nm light emitting diodes (LEDs) has been investigated. The carrier injection and internal quantum efficiency of the LEDs is simulated and compared to electroluminescence measurements. The highest light output power has been found for LEDs with an Mg-doped AlN/Al0.7Ga0.3N EBH with an AlN layer thickness >3 nm. The output power of these LEDs was 8.5-times higher compared to LEDs without EBH. This effect is attributed to an improved carrier injection and confinement which prevents electron leakage into the p-doped region of the LED with a simultaneously enhanced hole injection into the active region.
Carrier density dependences of anisotropic optical properties in closely stacked InAs/GaAs one-dimensional quantum dot superlattices
Authors: Kotani Teruhisa , Lugli Paolo , Hamaguchi Chihiro
Published: July 2013

We theoretically study the carrier density dependences of optical properties of closely stacked InAs/GaAs one-dimensional quantum dot superlattices based on the eight-band k·p theory. We find that the phonon assisted carrier injection into the ground state of both conduction and valence minibands is possible for small interdot spacings. We also predict that optical gain and spontaneous emission spectra show strongly anisotropic characters and can be controlled between [001]-, [110]-, [11¯0]-polarization by injected carrier densities as well as interdot spacing. Our findings reveal interesting possibilities of quantum dot-based optoelectronic devices applications.
Deformation mechanisms of irradiated metallic nanofoams
Authors: Zepeda-Ruiz L. A. , Martinez E. , Caro M. , Fu E. G. , Caro A.
Published: July 2013

It was recently proposed that within a particular window in the parameter space of temperature, ion energy, dose rate, and filament diameter, nanoscale metallic foams could show radiation tolerance [Bringa et al., Nano Lett. 12, 3351 (2012)]. Outside this window, damage appears in the form of vacancy-related stacking fault tetrahedra (SFT), with no effects due to interstitials [Fu et al., Appl. Phys. Lett. 101, 191607 (2012)]. These SFT could be natural sources of dislocations within the ligaments composing the foam and determine their mechanical response. We employ molecular dynamics simulations of cylindrical ligaments containing an SFT to obtain an atomic-level picture of their deformation behavior under compression. We find that plastic deformation originates at the edges of the SFT, at lower stress than needed to create dislocations at the surface. Our results predict that nanoscale foams soften under irradiation, a prediction not yet tested experimentally.
Anomalous and spin Hall effects in a magnetic tunnel junction with Rashba spin-orbit coupling
Authors: Vedyayev A. V. , Titova M. S. , Ryzhanova N. V. , Zhuravlev M. Ye. , Tsymbal E. Y.
Published: July 2013

Anomalous and spin Hall effects are investigated theoretically for a magnetic tunnel junction where the applied voltage produces a Rashba spin-orbit coupling within the tunneling barrier layer. The ferromagnetic electrodes are the source of the spin-polarized current. The tunneling electrons experience a spin-orbit coupling inside the barrier due to the applied electrical field. Charge and spin Hall currents are calculated as functions of the position inside the barrier and the angle between the magnetizations of the electrodes. We find that both charge and spin Hall currents are located inside the barrier near the interfaces. The dependence of the currents on magnetic configuration of the magnetic tunnel junction makes possible the manipulation by the Hall currents via rotation of the magnetization of the electrodes.
Inelastic spin depolarization spectroscopy in silicon
Authors: Li Jing , Appelbaum Ian
Published: July 2013

In ballistic injection spin transport devices, a tunnel junction emitter bias voltage determines the energy at which spin-polarized hot electrons cross a Schottky barrier into the conduction band of a semiconductor collector. Fast energy relaxation via phonon emission restores equilibrium for subsequent transport at the band edge. Through an analysis incorporating voltage-dependent measurement of magnetocurrent polarization in silicon spin transport devices along with magnetic-tunnel- and spin-valve-transistor configurations, the contribution to total spin depolarization caused by this inelastic scattering in the presence of spin-orbit interaction is quantified. From the shape of this spectroscopy, it is found that all measured spin depolarization can be accounted for solely by considering spin relaxation during bulk transport in quasi-equilibrium near the conduction band edge; the relaxation of initial spin state is irrelevant to the spin-dependent device characteristics.
Major enhancement of the thermoelectric performance in Pr/Nb-doped SrTiO3 under strain
Authors: Amin B. , Singh N. , Tritt T. M. , Alshareef H. N. , Schwingenschlögl U.
Published: July 2013

The electronic structure and thermoelectric properties of strained (biaxially and uniaxially) Sr0.95Pr0.05TiO3 and SrTi0.95Nb0.05O3 are investigated in the temperature range from 300 K to 1200 K. Substitutions of Pr at the Sr site and Nb at the Ti site generate n-type doping and thus improve the thermoelectric performance as compared to pristine SrTiO3. Further enhancement is achieved by the application of strain, for example, of the Seebeck coefficient by 21% for Sr0.95Pr0.05TiO3 and 10% for SrTi0.95Nb0.05O3 at room temperature in the case of 5% biaxial strain. At 1200 K, we predict figures of merit of 0.58 and 0.55 for 2.5% biaxially strained Sr0.95Pr0.05TiO3 and SrTi0.95Nb0.05O3, respectively, which are the highest values reported for rare earth doped SrTiO3.
Passive optical enhancement of laser-microwave synchronization
Authors: Gliserin A. , Walbran M. , Baum P.
Published: July 2013

Thermal noise is a fundamental limitation for synchronizing microwaves to high-power lasers of low repetition rate. Here, we describe an optical enhancement scheme that concentrates the output power of a fast photodiode into a narrow range of harmonics around a microwave frequency. The scheme is entirely passive and requires no feedback or lock. Using a 5-MHz laser and a microwave at 6.2 GHz, we demonstrate an enhancement of optical-to-microwave conversion by a factor of 4000. The uncorrelated noise on time scales up to 8 min amounts to less than 4 fs, with laser pulses intense enough for pump-probe experiments of structural dynamics.
The symbiotic rumen microbiome and cattle performance: a brief review
Authors: Bath C. , Morrison M. , Ross E. M. , Hayes B. J. , Cocks B. G.
Published: July 2013

The rumen of the dairy cow contains a rich and diverse collection of microbes that during feed digestion produce significant quantities of methane gas and ammonia, both of which contribute to greenhouse gas emissions. Strategies to redirect rumen carbon and nitrogen metabolism away from these products provide opportunities for significant productivity improvements in livestock systems not only by improving nutrient retention, but also by reducing greenhouse gas emissions. In order to develop these strategies, a greater knowledge of the diversity of the microbes within their rumen and their genomic capability is required. Many have used several techniques to study the rumen microbes, and the technology continues to improve. Among them include researchers at the Department of Primary Industries Victoria (DPI Vic) and the Dairy Futures Cooperative Research Centre (CRC) who are addressing the issue of regulation of methane emissions in dairy cattle, while scientists in Queensland and New South Wales, as part of the most recent Beef CRC program, focus on beef cattle. In this brief review, we examine how the techniques used in rumen microbial ecology have changed, and how technology improvements continue to allow us to examine the rumen microbiota of cattle and other ruminants, so as to better understand and possibly select animals with superior traits, leading to improvements in feed efficiency, methane emissions and nitrogen retention.
Determinants of plant establishment success in a multispecies introduction experiment with native and alien species
Authors: Kempel Anne , Chrobock Thomas , Fischer Markus , Rohr Rudolf Philippe , van Kleunen Mark
Published: July 2013

Determinants of plant establishment and invasion are a key issue in ecology and evolution. Although establishment success varies substantially among species, the importance of species traits and extrinsic factors as determinants of establishment in existing communities has remained difficult to prove in observational studies because they can be confounded and mask each other. Therefore, we conducted a large multispecies field experiment to disentangle the relative importance of extrinsic factors vs. species characteristics for the establishment success of plants in grasslands. We introduced 48 alien and 45 native plant species at different seed numbers into multiple grassland sites with or without experimental soil disturbance and related their establishment success to species traits assessed in five independent multispecies greenhouse experiments. High propagule pressure and high seed mass were the most important factors increasing establishment success in the very beginning of the experiment. However, after 3 y, propagule pressure became less important, and species traits related to biotic interactions (including herbivore resistance and responses to shading and competition) became the most important drivers of success or failure. The relative importance of different traits was environment-dependent and changed over time. Our approach of combining a multispecies introduction experiment in the field with trait data from independent multispecies experiments in the greenhouse allowed us to detect the relative importance of species traits for early establishment and provided evidence that species traits—fine-tuned by environmental factors—determine success or failure of alien and native plants in temperate grasslands.
Metabolic modeling of species interaction in the human microbiome elucidates community-level assembly rules
Authors: Levy Roie , Borenstein Elhanan
Published: July 2013

The human microbiome plays a key role in human health and is associated with numerous diseases. Metagenomic-based studies are now generating valuable information about the composition of the microbiome in health and in disease, demonstrating nonneutral assembly processes and complex co-occurrence patterns. However, the underlying ecological forces that structure the microbiome are still unclear. Specifically, compositional studies alone with no information about mechanisms of interaction, potential competition, or syntrophy, cannot clearly distinguish habitat-filtering and species assortment assembly processes. To address this challenge, we introduce a computational framework, integrating metagenomic-based compositional data with genome-scale metabolic modeling of species interaction. We use
in silico
metabolic network models to predict levels of competition and complementarity among 154 microbiome species and compare predicted interaction measures to species co-occurrence. Applying this approach to two large-scale datasets describing the composition of the gut microbiome, we find that species tend to co-occur across individuals more frequently with species with which they strongly compete, suggesting that microbiome assembly is dominated by habitat filtering. Moreover, species’ partners and excluders exhibit distinct metabolic interaction levels. Importantly, we show that these trends cannot be explained by phylogeny alone and hold across multiple taxonomic levels. Interestingly, controlling for host health does not change the observed patterns, indicating that the axes along which species are filtered are not fully defined by macroecological host states. The approach presented here lays the foundation for a reverse-ecology framework for addressing key questions concerning the assembly of host-associated communities and for informing clinical efforts to manipulate the microbiome.
Characterization of the nitric oxide reductase from
Thermus thermophilus
Authors: Schurig-Briccio Lici A. , Venkatakrishnan Padmaja , Hemp James , Bricio Carlos , Berenguer José , Gennis Robert B.
Published: July 2013

Nitrous oxide (N
2
O) is a powerful greenhouse gas implicated in climate change. The dominant source of atmospheric N
2
O is incomplete biological dentrification, and the enzymes responsible for the release of N
2
O are NO reductases. It was recently reported that ambient emissions of N
2
O from the Great Boiling Spring in the United States Great Basin are high, and attributed to incomplete denitrification by
Thermus thermophilus
and related bacterial species [Hedlund BP, et al. (2011)
Geobiology
9(6)471–480]. In the present work, we have isolated and characterized the NO reductase (NOR) from
T. thermophilus
. The enzyme is a member of the cNOR family of enzymes and belongs to a phylogenetic clade that is distinct from previously examined cNORs. Like other characterized cNORs, the
T. thermophilus
cNOR consists of two subunits, NorB and NorC, and contains a one heme
c
, one Ca
2+
, a low-spin heme
b
, and an active site consisting of a high-spin heme
b
and Fe
B
. The roles of conserved residues within the cNOR family were investigated by site-directed mutagenesis. The most important and unexpected result is that the glutamic acid ligand to Fe
B
is not essential for function. The E211A mutant retains 68% of wild-type activity. Mutagenesis data and the pattern of conserved residues suggest that there is probably not a single pathway for proton delivery from the periplasm to the active site that is shared by all cNORs, and that there may be multiple pathways within the
T. thermophilus
cNOR.
Acoustophoretic contactless transport and handling of matter in air
Authors: Foresti Daniele , Nabavi Majid , Klingauf Mirko , Ferrari Aldo , Poulikakos Dimos
Published: July 2013

Levitation and controlled motion of matter in air have a wealth of potential applications ranging from materials processing to biochemistry and pharmaceuticals. We present a unique acoustophoretic concept for the contactless transport and handling of matter in air. Spatiotemporal modulation of the levitation acoustic field allows continuous planar transport and processing of multiple objects, from near-spherical (volume of 0.1–10 μL) to wire-like, without being limited by the acoustic wavelength. The independence of the handling principle from special material properties (magnetic, optical, or electrical) is illustrated with a wide palette of application experiments, such as contactless droplet coalescence and mixing, solid–liquid encapsulation, absorption, dissolution, and DNA transfection. More than a century after the pioneering work of Lord Rayleigh on acoustic radiation pressure, a path-breaking concept is proposed to harvest the significant benefits of acoustic levitation in air.
Visualizing the substrate-, superoxo-, alkylperoxo-, and product-bound states at the nonheme Fe(II) site of homogentisate dioxygenase
Authors: Jeoung Jae-Hun , Bommer Martin , Lin Tzong-Yuan , Dobbek Holger
Published: July 2013

Homogentisate 1,2-dioxygenase (HGDO) uses a mononuclear nonheme Fe
2+
to catalyze the oxidative ring cleavage in the degradation of Tyr and Phe by producing maleylacetoacetate from homogentisate (2,5-dihydroxyphenylacetate). Here, we report three crystal structures of HGDO, revealing five different steps in its reaction cycle at 1.7–1.98 Å resolution. The resting state structure displays an octahedral coordination for Fe
2+
with two histidine residues (His331 and His367), a bidentate carboxylate ligand (Glu337), and two water molecules. Homogentisate binds as a monodentate ligand to Fe
2+
, and its interaction with Tyr346 invokes the folding of a loop over the active site, effectively shielding it from solvent. Binding of homogentisate is driven by enthalpy and is entropically disfavored as shown by anoxic isothermal titration calorimetry. Three different reaction cycle intermediates have been trapped in different HGDO subunits of a single crystal showing the influence of crystal packing interactions on the course of enzymatic reactions. The observed superoxo:semiquinone-, alkylperoxo-, and product-bound intermediates have been resolved in a crystal grown anoxically with homogentisate, which was subsequently incubated with dioxygen. We demonstrate that, despite different folds, active site architectures, and Fe
2+
coordination, extradiol dioxygenases can proceed through the same principal reaction intermediates to catalyze the O
2
-dependent cleavage of aromatic rings. Thus, convergent evolution of nonhomologous enzymes using the 2-His-1-carboxylate facial triad motif developed different solutions to stabilize closely related intermediates in unlike environments.
Digital instability of a confined elastic meniscus
Authors: Biggins John S. , Saintyves Baudouin , Wei Zhiyan , Bouchaud Elisabeth , Mahadevan L.
Published: July 2013

Thin soft elastic layers serving as joints between relatively rigid bodies may function as sealants, thermal, electrical, or mechanical insulators, bearings, or adhesives. When such a joint is stressed, even though perfect adhesion is maintained, the exposed free meniscus in the thin elastic layer becomes unstable, leading to the formation of spatially periodic digits of air that invade the elastic layer, reminiscent of viscous fingering in a thin fluid layer. However, the elastic instability is reversible and rate-independent, disappearing when the joint is unstressed. We use theory, experiments, and numerical simulations to show that the transition to the digital state is sudden (first-order), the wavelength and amplitude of the fingers are proportional to the thickness of the elastic layer, and the required separation to trigger the instability is inversely proportional to the in-plane dimension of the layer. Our study reveals the energetic origin of this instability and has implications for the strength of polymeric adhesives; it also suggests a method for patterning thin films reversibly with any arrangement of localized fingers in a digital elastic memory, which we confirm experimentally.
Gene expression profiles in febrile children with defined viral and bacterial infection
Authors: Hu Xinran , Yu Jinsheng , Crosby Seth D. , Storch Gregory A.
Published: July 2013

Viral infections are common causes of fever without an apparent source in young children. Despite absence of bacterial infection, many febrile children are treated with antibiotics. Virus and bacteria interact with different pattern recognition receptors in circulating blood leukocytes, triggering specific host transcriptional programs mediating immune response. Therefore, unique transcriptional signatures may be defined that discriminate viral from bacterial causes of fever without an apparent source. Gene expression microarray analyses were conducted on blood samples from 30 febrile children positive for adenovirus, human herpesvirus 6, or enterovirus infection or with acute bacterial infection and 22 afebrile controls. Blood leukocyte transcriptional profiles clearly distinguished virus-positive febrile children from both virus-negative afebrile controls and afebrile children with the same viruses present in the febrile children. Virus-specific gene expression profiles could be defined. The IFN signaling pathway was uniquely activated in febrile children with viral infection, whereas the integrin signaling pathway was uniquely activated in children with bacterial infection. Transcriptional profiles classified febrile children with viral or bacterial infection with better accuracy than white blood cell count in the blood. Similarly accurate classification was shown with data from an independent study using different microarray platforms. Our results support the paradigm of using host response to define the etiology of childhood infections. This approach could be an important supplement to highly sensitive tests that detect the presence of a possible pathogen but do not address its pathogenic role in the patient being evaluated.
Control of a four-color sensing photoreceptor by a two-color sensing photoreceptor reveals complex light regulation in cyanobacteria
Authors: Bussell Adam N. , Kehoe David M.
Published: July 2013

Photoreceptors are biologically important for sensing changes in the color and intensity of ambient light and, for photosynthetic organisms, processing this light information to optimize food production through photosynthesis. Cyanobacteria are an evolutionarily and ecologically important prokaryotic group of oxygenic photosynthesizers that contain cyanobacteriochrome (CBCR) photoreceptors, whose family members sense nearly the entire visible spectrum of light colors. Some cyanobacteria contain 12 to 15 different CBCRs, and many family members contain multiple light-sensing domains. However, the complex interactions that must be occurring within and between these photoreceptors remain unexplored. Here we describe the regulation and photobiology of a unique CBCR called IflA (
i
nfluenced by
f
ar-red
l
ight), demonstrating that a second CBCR called RcaE strongly regulates IflA abundance and that IflA uses two distinct photosensory domains to respond to four different light colors: blue, green, red, and far-red. The absorption of red or far-red light by one domain affects the conformation of the other domain, and the rate of relaxation of one of these domains is influenced by the conformation of the other. Deletion of
iflA
results in delayed growth at low cell density, suggesting that IflA accelerates growth under this condition, apparently by sensing the ratio of red to far-red light in the environment. The types of complex photobiological interactions described here, both between unrelated CBCR family members and within photosensory domains of a single CBCR, may be advantageous for species using these photoreceptors in aquatic environments, where light color ratios are influenced by many biotic and abiotic factors.
Induction of human cardiomyocyte-like cells from fibroblasts by defined factors
Authors: Wada Rie , Muraoka Naoto , Inagawa Kohei , Yamakawa Hiroyuki , Miyamoto Kazutaka , Sadahiro Taketaro , Umei Tomohiko , Kaneda Ruri , Suzuki Tomoyuki , Kamiya Kaichiro , Tohyama Shugo , Yuasa Shinsuke , Kokaji Kiyokazu , Aeba Ryo , Yozu Ryohei , Yamagishi Hiroyuki , Kitamura Toshio , Fukuda Keiichi , Ieda Masaki
Published: July 2013

Heart disease remains a leading cause of death worldwide. Owing to the limited regenerative capacity of heart tissue, cardiac regenerative therapy has emerged as an attractive approach. Direct reprogramming of human cardiac fibroblasts (HCFs) into cardiomyocytes may hold great potential for this purpose. We reported previously that induced cardiomyocyte-like cells (iCMs) can be directly generated from mouse cardiac fibroblasts in vitro and vivo by transduction of three transcription factors: Gata4, Mef2c, and Tbx5, collectively termed GMT. In the present study, we sought to determine whether human fibroblasts also could be converted to iCMs by defined factors. Our initial finding that GMT was not sufficient for cardiac induction in HCFs prompted us to screen for additional factors to promote cardiac reprogramming by analyzing multiple cardiac-specific gene induction with quantitative RT-PCR. The addition of Mesp1 and Myocd to GMT up-regulated a broader spectrum of cardiac genes in HCFs more efficiently compared with GMT alone. The HCFs and human dermal fibroblasts transduced with GMT, Mesp1, and Myocd (GMTMM) changed the cell morphology from a spindle shape to a rod-like or polygonal shape, expressed multiple cardiac-specific proteins, increased a broad range of cardiac genes and concomitantly suppressed fibroblast genes, and exhibited spontaneous Ca
2+
oscillations. Moreover, the cells matured to exhibit action potentials and contract synchronously in coculture with murine cardiomyocytes. A 5-ethynyl-2′-deoxyuridine assay revealed that the iCMs thus generated do not pass through a mitotic cell state. These findings demonstrate that human fibroblasts can be directly converted to iCMs by defined factors, which may facilitate future applications in regenerative medicine.
Twelve previously unknown phage genera are ubiquitous in global oceans
Authors: Holmfeldt Karin , Solonenko Natalie , Shah Manesh , Corrier Kristen , Riemann Lasse , VerBerkmoes Nathan C. , Sullivan Matthew B.
Published: July 2013

Viruses are fundamental to ecosystems ranging from oceans to humans, yet our ability to study them is bottlenecked by the lack of ecologically relevant isolates, resulting in “unknowns” dominating culture-independent surveys. Here we present genomes from 31 phages infecting multiple strains of the aquatic bacterium
Cellulophaga baltica
(
Bacteroidetes
) to provide data for an underrepresented and environmentally abundant bacterial lineage. Comparative genomics delineated 12 phage groups that (
i
) each represent a new genus, and (
ii
) represent one novel and four well-known viral families. This diversity contrasts the few well-studied marine phage systems, but parallels the diversity of phages infecting human-associated bacteria. Although all 12
Cellulophaga
phages represent new genera, the podoviruses and icosahedral, nontailed ssDNA phages were exceptional, with genomes up to twice as large as those previously observed for each phage type. Structural novelty was also substantial, requiring experimental phage proteomics to identify 83% of the structural proteins. The presence of uncommon nucleotide metabolism genes in four genera likely underscores the importance of scavenging nutrient-rich molecules as previously seen for phages in marine environments. Metagenomic recruitment analyses suggest that these particular
Cellulophaga
phages are rare and may represent a first glimpse into the phage side of the rare biosphere. However, these analyses also revealed that these phage genera are widespread, occurring in 94% of 137 investigated metagenomes. Together, this diverse and novel collection of phages identifies a small but ubiquitous fraction of unknown marine viral diversity and provides numerous environmentally relevant phage–host systems for experimental hypothesis testing.
Neural crest and Schwann cell progenitor-derived melanocytes are two spatially segregated populations similarly regulated by Foxd3
Authors: Nitzan Erez , Pfaltzgraff Elise R. , Labosky Patricia A. , Kalcheim Chaya
Published: July 2013

Skin melanocytes arise from two sources: either directly from neural crest progenitors or indirectly from neural crest-derived Schwann cell precursors after colonization of peripheral nerves. The relationship between these two melanocyte populations and the factors controlling their specification remains poorly understood. Direct lineage tracing reveals that neural crest and Schwann cell progenitor-derived melanocytes are differentially restricted to the epaxial and hypaxial body domains, respectively. Furthermore, although both populations are initially part of the Foxd3 lineage, hypaxial melanocytes lose Foxd3 at late stages upon separation from the nerve, whereas we recently found that epaxial melanocytes segregate earlier from Foxd3-positive neural progenitors while still residing in the dorsal neural tube. Gain- and loss-of-function experiments in avians and mice, respectively, reveal that Foxd3 is both sufficient and necessary for regulating the balance between melanocyte and Schwann cell development. In addition, Foxd3 is also sufficient to regulate the switch between neuronal and glial fates in sensory ganglia. Together, we propose that differential fate acquisition of neural crest-derived cells depends on their progressive segregation from the Foxd3-positive lineage.
Cranial irradiation compromises neuronal architecture in the hippocampus
Authors: Parihar Vipan Kumar , Limoli Charles L.
Published: July 2013

Cranial irradiation is used routinely for the treatment of nearly all brain tumors, but may lead to progressive and debilitating impairments of cognitive function. Changes in synaptic plasticity underlie many neurodegenerative conditions that correlate to specific structural alterations in neurons that are believed to be morphologic determinants of learning and memory. To determine whether changes in dendritic architecture might underlie the neurocognitive sequelae found after irradiation, we investigated the impact of cranial irradiation (1 and 10 Gy) on a range of micromorphometric parameters in mice 10 and 30 d following exposure. Our data revealed significant reductions in dendritic complexity, where dendritic branching, length, and area were routinely reduced (>50%) in a dose-dependent manner. At these same doses and times we found significant reductions in the number (20–35%) and density (40–70%) of dendritic spines on hippocampal neurons of the dentate gyrus. Interestingly, immature filopodia showed the greatest sensitivity to irradiation compared with more mature spine morphologies, with reductions of 43% and 73% found 30 d after 1 and 10 Gy, respectively. Analysis of granule-cell neurons spanning the subfields of the dentate gyrus revealed significant reductions in synaptophysin expression at presynaptic sites in the dentate hilus, and significant increases in postsynaptic density protein (PSD-95) were found along dendrites in the granule cell and molecular layers. These findings are unique in demonstrating dose-responsive changes in dendritic complexity, synaptic protein levels, spine density and morphology, alterations induced in hippocampal neurons by irradiation that persist for at least 1 mo, and that resemble similar types of changes found in many neurodegenerative conditions.
Pomalidomide is nonteratogenic in chicken and zebrafish embryos and nonneurotoxic in vitro
Authors: Mahony Chris , Erskine Lynda , Niven Jennifer , Greig Nigel H. , Figg William Douglas , Vargesson Neil
Published: July 2013

Thalidomide and its analog, Lenalidomide, are in current use clinically for treatment of multiple myeloma, complications of leprosy and cancers. An additional analog, Pomalidomide, has recently been licensed for treatment of multiple myeloma, and is purported to be clinically more potent than either Thalidomide or Lenalidomide. Using a combination of zebrafish and chicken embryos together with in vitro assays we have determined the relative anti-inflammatory activity of each compound. We demonstrate that in vivo embryonic assays Pomalidomide is a significantly more potent anti-inflammatory agent than either Thalidomide or Lenalidomide. We tested the effect of Pomalidomide and Lenalidomide on angiogenesis, teratogenesis, and neurite outgrowth, known detrimental effects of Thalidomide. We found that Pomalidomide, displays a high degree of cell specificity, and has no detectable teratogenic, antiangiogenic or neurotoxic effects at potent anti-inflammatory concentrations. This is in marked contrast to Thalidomide and Lenalidomide, which had detrimental effects on blood vessels, nerves, and embryonic development at anti-inflammatory concentrations. This work has implications for Pomalidomide as a treatment for conditions Thalidomide and Lenalidomide treat currently.
Oxygen-sensitive mitochondrial accumulation of cystathionine β-synthase mediated by Lon protease
Authors: Teng Huajian , Wu Bo , Zhao Kexin , Yang Guangdong , Wu Lingyun , Wang Rui
Published: July 2013

Oxygen-sensitive accumulation and degradation, two opposite but intrinsically linked events, of heme proteins in mitochondria affect mitochondrial functions, including bioenergetics and oxygen-sensing processes. Cystathionine β-synthase (CBS) contains a prosthetic heme group and catalyzes the production of hydrogen sulfide in mammalian cells. Here we show that CBS proteins were present in liver mitochondria at a low level under normoxia conditions. Ischemia/hypoxia increased the accumulation of CBS proteins in mitochondria. The normalization of oxygen partial pressure accelerated the degradation of CBS proteins. Lon protease, a major degradation enzyme in mitochondrial matrix, recognized and degraded mitochondrial CBS by specifically targeting at the oxygenated heme group of CBS proteins. The accumulation of CBS in mitochondria increased hydrogen sulfide production, which prevented Ca
2+
-mediated cytochrome
c
release from mitochondria and decreased reactive oxygen species generation. Mitochondrial accumulation of heme oxygenase-1, another heme protein, was also regulated by oxygen level and Lon protease in the same mechanism as for CBS. Our findings provide a fundamental and general mechanism for oxygen-sensitive regulation of mitochondrial functions by linking oxygenation level to the accumulation/degradation of mitochondrial heme proteins.
The deoxynucleotide triphosphohydrolase SAMHD1 is a major regulator of DNA precursor pools in mammalian cells
Authors: Franzolin Elisa , Pontarin Giovanna , Rampazzo Chiara , Miazzi Cristina , Ferraro Paola , Palumbo Elisa , Reichard Peter , Bianchi Vera
Published: July 2013

Sterile alpha motif and HD-domain containing protein 1 (SAMHD1) is a triphosphohydrolase converting deoxynucleoside triphosphates (dNTPs) to deoxynucleosides. The enzyme was recently identified as a component of the human innate immune system that restricts HIV-1 infection by removing dNTPs required for viral DNA synthesis. SAMHD1 has deep evolutionary roots and is ubiquitous in human organs. Here we identify a general function of SAMHD1 in the regulation of dNTP pools in cultured human cells. The protein was nuclear and variably expressed during the cell cycle, maximally during quiescence and minimally during S-phase. Treatment of lung or skin fibroblasts with specific siRNAs resulted in the disappearence of SAMHD1 accompanied by loss of the cell-cycle regulation of dNTP pool sizes and dNTP imbalance. Cells accumulated in G1 phase with oversized pools and stopped growing. Following removal of the siRNA, the pools were normalized and cell growth restarted, but only after SAMHD1 had reappeared. In quiescent cultures SAMHD1 down-regulation leads to a marked expansion of dNTP pools. In all cases the largest effect was on dGTP, the preferred substrate of SAMHD1. Ribonucleotide reductase, responsible for the de novo synthesis of dNTPs, is a cytosolic enzyme maximally induced in S-phase cells. Thus, in mammalian cells the cell cycle regulation of the two main enzymes controlling dNTP pool sizes is adjusted to the requirements of DNA replication. Synthesis by the reductase peaks during S-phase, and catabolism by SAMHD1 is maximal during G1 phase when large dNTP pools would prevent cells from preparing for a new round of DNA replication.
Funciones socio-discursivas de las alternancias de gallego y español en la realización bilingüe de cotilleo
Authors: Acuña Ferreira Virginia
Published: July 2013

Este artículo aborda el papel de las alternancias gallego/español en la realización bilingüe de cotilleo. Tras reseñar estudios sobre este género discursivo procedentes de distintas disciplinas, repaso la historia del contacto gallego/español en Galicia y analizo tres fragmentos de cotilleo en una conversación “natural”, que incluyen alternancias en estas lenguas. En mis conclusiones resalto las funciones discursivas y sociolingüísticas que desempeñan estos usos bilingües: su papel en la estructuración del discurso y en el refuerzo de los vínculos interpersonales entre las participantes a través de su cooperación en la construcción de un estilo bilingüe de cotilleo. En este estilo, el uso de gallego tiende a centrarse en las zonas centrales del discurso, en las que se reconstruyen los hechos, actuando como recurso dramatizador y de evaluación implícita; en cambio, el español tiende a localizarse en las zonas periféricas del discurso, es decir, en la aportación inicial de datos de contextualización, contribuyendo a realzar la función dramatizadora del gallego, así como en la conclusión, en la que los comportamientos representados son evaluados explícitamente desde una perspectiva moral.
Malvinas: politics, territory and internationalism
Authors: Munck Ronaldo
Published: July 2013

The reverberations of the 1982 Falklands/Malvinas war in the South Atlantic are still being felt today. British Prime Minister David Cameron accuses Argentina of acting in a colonialist manner. Argentina has stepped up the diplomatic offensive around decolonization and has obtained considerable regional support. From an ‘Argentinian inter-nationalist’ perspective, this article carries out a brief historical analysis to then outline some of the main elements of the current situation. While recognising the critical importance of the geo-strategy in explaining the ongoing conflict in the South Atlantic, the emphasis here is more on the political dimension, especially in relation to emerging positions in Argentina seeking to transcend the dominant nationalist territorial position on the Malvinas.