bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature- and field-dependent critical currents in [(Bi,Pb)2Sr2Ca2Cu3Ox]0.07(La0.7Sr0.3MnO3)0.03 thick films grown on LaAlO3 substrates
Authors: Paredes Omar , Morán Oswaldo , Baca Eval
Published: January 2013

La0.7Sr0.3MnO3 (LSMO) nanoparticles were embedded in (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) thick films, which were grown by simple melting-quenching-annealing (MQA) method on (001)-oriented LaAlO3 (LAO) substrates. The nominal composition of the composite-like hybrid system was (Bi2223)1−x(LSMO)x with x = 0.03. The constituent elements, Bi2223 and LSMO, were prepared separately by standard solid state reaction and Pechini's method, respectively. The analysis of the X-ray diffraction patterns suggested a polycrystalline growth mode of the thick films on the LAO substrates. From electric transport measurements, the superconducting onset temperature and the superconducting critical temperature (ρ = 0) ended up being 105 and 62 K, respectively. The flux pinning energy U was determined using the Anderson-Kim model. The value of U was compared with those obtained for similar samples with concentrations x = 0.01 and x = 0.05. Current-voltage characteristics were recorded at different temperatures in order to analyze the behavior of the superconducting current (Ic) of the films. A dramatic drop of Ic was observed at ∼20 K. This seems to be linked to the presence of flux creep acting as dissipation factors attributed to LSMO nanoparticles. Isothermal magnetization loops recorded at T < Tc and T > Tc showed clear diamagnetic and ferromagnetic signals, which verify the multifunctional character of the system. Based on the isothermal M(H)-loops recorded at 5, 20, and 40 K and taking Kim's model into account, the dependence of superconducting current density (Jc), and the volume pinning force (Fp) on the magnetic field were calculated. The dependence Jc(B) at 5 K showed an exponential-type behavior, which is described by an empirical equation. This empirical equation considers the maximum value of Fp, which may be scaled with the Kramer's expression for Fp. From this scaling procedure, diverse exponents, associated with different pinning mechanisms, were determined. The drastic fall of Jc(B) at T > 20 K is discussed by considering the decreasing of the lower critical field (Hc1), penetration field (Hp), irreversible magnetic field (Hirr), and magnetization maximum (Mmax) with increasing in the LSMO particle content.
Magnetoelectric coupling driven by inverse magnetostriction in multiferroic BiMn3Mn4O12
Authors: Gauzzi A. , Rousse G. , Mezzadri F. , Calestani G. L. , André G. , Bourée F. , Calicchio M. , Gilioli E. , Cabassi R. , Bolzoni F. , Prodi A. , Bordet P. , Marezio M.
Published: January 2013

Inserting both polar A and magnetic B ions in a same crystalline phase, such as A = Bi3+, B = Fe3+ or Mn3+ in simple perovskites ABO3, has been successful in achieving multiferroic properties with large ferroelectric and magnetic orders. However, modest magnetoelectric couplings have been hitherto reported, thus preventing any application for future electronics. By means of neutron diffraction, we found a large uniform C-type modulation of an E-type antiferromagnetic structure of the Mn3+ ions in the quadruple perovskite BiMn3Mn4O12. A symmetry analysis indicates that this modulation is induced by the internal strain created by the polar Bi3+ ion, which gives evidence of a large magnetoelectric coupling driven by inverse magnetostriction. This modulation is indeed absent in the isomorphic and isovalent compound LaMn3Mn4O12 containing the nonpolar La3+ ion. Our analysis indicates that this coupling mechanism is effective owing to the symmetry-limited structural distortions and inhomogeneities characteristic of the quadruple perovskite structure, thus preventing the release of the strain. We conclude that internal strain is a key control parameter to achieve large magnetoelectric couplings in proper ferroelectrics.
Performance of graphene thermal photon detectors
Authors: McKitterick Christopher B. , Prober Daniel E. , Karasik Boris S.
Published: January 2013

We analyze the performance of graphene microstructures as thermal photon detectors and deduce the range of parameters that define a linear response. The saturation effects of a graphene thermal detector that operates beyond the linear range are described in detail for a single-photon detector (calorimeter). We compute the effect of operating beyond this linear range and find that sensitive detection occurs for such non-linear operation. We identify the optimum conditions and find that single-photon detection at terahertz frequencies should be feasible.
Optimal switching using coherent control
Authors: Trøst Kristensen Philip , Heuck Mikkel , Mørk Jesper
Published: January 2013

We introduce a general framework for the analysis of coherent control in coupled optical cavity-waveguide systems. Within this framework, we use an analytically solvable model, which is validated by independent numerical calculations, to investigate switching in a micro cavity and demonstrate that the switching time, in general, is not limited by the cavity lifetime. Therefore, the total energy required for switching is a more relevant figure of merit than the switching speed, and for a particular two-pulse switching scheme we use calculus of variations to optimize the switching in terms of input energy.
First-principles study of elastic properties of cubic Cr1−xAlxN alloys
Authors: Zhou Liangcai , Holec David , Mayrhofer Paul H.
Published: January 2013

The elastic properties of paramagnetic cubic B1 (c-) Cr1−xAlxN ternary alloys are studied using stress-strain and energy-strain methods within the framework of density functional theory. A strong compositional dependence of the elastic properties is predicted. Young's modulus, E, and shear modulus, G, exhibit the same compositional trends as experimentally measured hardness values (i.e., increasing with Al content), while bulk modulus, B, remains almost constant. The isotropic elastic response in the c-Cr1−xAlxN is predicted for concentrations around x = 0.50. Brittle behavior and directional bonding characteristics are predominant in the c-Cr1−xAlxN coatings in the whole composition range and become more pronounced with increasing Al content.
High-performance thermoelectric mineral Cu12−xNixSb4S13 tetrahedrite
Authors: Suekuni Koichiro , Tsuruta Kojiro , Kunii Masaru , Nishiate Hirotaka , Nishibori Eiji , Maki Sachiko , Ohta Michihiro , Yamamoto Atsushi , Koyano Mikio
Published: January 2013

X-ray structural analysis and high-temperature thermoelectric properties measurements are performed on polycrystalline samples of artificial mineral Cu12−xNixSb4S13 tetrahedrite. Analysis of the atomic displacement parameter manifests low-energy vibration of Cu(2) out of CuS3 triangle plane. The vibration results in low lattice thermal conductivity of less than 0.5 W K−1 m−1. By tuning of the Ni composition x and decrease of electronic thermal conductivity, dimensionless thermoelectric figure of merit for x = 1.5 achieves 0.7 at 665 K, which is a considerably high value among p-type Pb-free sulfides. Because the tetrahedrite is an environmentally friendly material, it constitutes a good thermoelectric material for use in support of a sustainable society.
Development of a surface plasmon resonance and nanomechanical biosensing hybrid platform for multiparametric reading
Authors: Alvarez Mar , Fariña David , Escuela Alfonso M. , Sendra Jose Ramón , Lechuga Laura M.
Published: January 2013

We have developed a hybrid platform that combines two well-known biosensing technologies based on quite different transducer principles: surface plasmon resonance and nanomechanical sensing. The new system allows the simultaneous and real-time detection of two independent parameters, refractive index change (Δn), and surface stress change (Δσ) when a biomolecular interaction takes place. Both parameters have a direct relation with the mass coverage of the sensor surface. The core of the platform is a common fluid cell, where the solution arrives to both sensor areas at the same time and under the same conditions (temperature, velocity, diffusion, etc.).The main objective of this integration is to achieve a better understanding of the physical behaviour of the transducers during sensing, increasing the information obtained in real time in one single experiment. The potential of the hybrid platform is demonstrated by the detection of DNA hybridization.
Evidence of current free double layer in high density helicon discharge
Authors: Ganguli A. , Sahu B. B. , Tarey R. D.
Published: January 2013

This paper investigates the formation of double layer (DL) in helicon plasmas. In the experiment, argon plasma production is using the excitation of m = −1 helicon mode with magnetic mirror field with high mirror ratio of ∼1:1.7. We have specifically used the radio frequency compensated Langmuir probe (LP) to measure the relevant plasma parameters simultaneously so as to investigate the details about the plasma production. The DL, which consists of both warm and bulk populations towards higher potential region and only dense bulk plasmas towards the lower potential region downstream the antenna, is present in the transition region. LP measurements also show an abrupt fall of density along with a potential drop of about 20 V and e ΔVpk Te≈12 within a few cm. The potential drop is equal to the difference of the electron temperatures between the two plasma regions forming the DL, which is present in the plateau region of mirror, unlike in several prior studies on the DL formation in the region of strong gradients in the magnetic field. The DL is strong, current-free, electric double-layer with estimated thickness of about 10 Debye lengths.
Increasing the K-shell yield of line radiation in Z-pinch implosions using alloyed Al/Mg wire-arrays
Authors: Delong Xiao , Ning Ding , Chuang Xue , Jun Huang , Yang Zhang , Cheng Ning , Shunkai Sun
Published: January 2013

The variation of the K-shell yield of pure aluminum wire-array Z-pinch implosions with load parameters is discussed. The mechanism and the efficiency of increasing the K-shell yield using alloyed Al/Mg wire-arrays are numerically investigated. It has been shown that the maximum K-shell yield from a pure aluminum wire-array Z-pinch implosion can be obtained at an optimal load mass for a given generator and at a fixed initial wire-array radius. This optimal load mass is determined by the load energy coupling with the generator, the capability of Z-pinch plasmas to emit the K-shell radiation, and the self absorption of K-shell lines. For different generators, the optimal load mass increases as the drive current increases, and the line absorption limits the further increase of K-shell radiation. The coupled energy per ion is likely decreasing with increased mass, so the plasma might not be able to ionize into the K-shell. Also, the ability of the plasma to radiatively cool can increase with mass, thus, making it difficult for the plasma to ionize into and remain in the K-shell during the stagnation phase of the implosion. Alloyed Al/Mg wire-arrays were thus suggested to be used to decrease the opacity of K-shell lines and to increase the overall K-shell yield. In this paper, we show that using alloyed Al/Mg wire-arrays will decrease the opacity and increase the K-shell yield remarkably if the plasma is optically thick. We will also show that the efficiency of increasing the K-shell yield with alloyed Al/Mg wire-arrays cannot increase indefinitely. The ratio of K-shell yield from an alloyed Al/Mg wire-array to that from a pure aluminum wire-array reaches a limit. For example, we show that when the mass share of magnesium is 10% then this limit is 1.2, and for a 50% mass share, the limit is 1.3.
Electrically tunable molecular doping of graphene
Authors: Singh A. K. , Uddin M. A. , Tolson J. T. , Maire-Afeli H. , Sbrockey N. , Tompa G. S. , Spencer M. G. , Vogt T. , Sudarshan T. S. , Koley G.
Published: January 2013

Electrical tunability of molecular doping of graphene has been investigated using back-gated field effect transistors. Variation of the gate voltage from positive to negative values resulted in reduced p-type doping by NO2, which decreased below detection limit at −45 V. A reverse trend was observed for NH3, where its n-type doping increased with more negative gate voltage, becoming undetectable at 5 V. Our results indicate that adsorption induced molecular doping of graphene could not be detected when the Fermi level coincides with the adsorption induced defect states, which yields NO2 acceptor energy level of ∼320 meV below the Dirac point.
Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes
Authors: Verma Jai , Kandaswamy Prem Kumar , Protasenko Vladimir , Verma Amit , Grace Xing Huili , Jena Debdeep
Published: January 2013

We demonstrate a GaN quantum dot ultraviolet light-emitting diode that uses tunnel injection of carriers through AlN barriers into the active region. The quantum dot heterostructure is grown by molecular beam epitaxy on AlN templates. The large lattice mismatch between GaN and AlN favors the formation of GaN quantum dots in the Stranski-Krastanov growth mode. Carrier injection by tunneling can mitigate losses incurred in hot-carrier injection in light emitting heterostructures. To achieve tunnel injection, relatively low composition AlGaN is used for n- and p-type layers to simultaneously take advantage of effective band alignment and efficient doping. The small height of the quantum dots results in short-wavelength emission and are simultaneously an effective tool to fight the reduction of oscillator strength from quantum-confined Stark effect due to polarization fields. The strong quantum confinement results in room-temperature electroluminescence peaks at 261 and 340 nm, well above the 365 nm bandgap of bulk GaN. The demonstration opens the doorway to exploit many varied features of quantum dot physics to realize high-efficiency short-wavelength light sources.
Volmer-Weber growth of AlSb on Si(111)
Authors: Proessdorf A. , Hanke M. , Jenichen B. , Braun W. , Riechert H.
Published: January 2013

AlSb is grown by molecular beam epitaxy. The evolution and the relaxation of the deposited AlSb layer is investigated by synchrotron-based in situ grazing incidence x-ray diffraction (GID), and the analysis of the real space distribution is performed by atomic force microscopy. AlSb forms islands with (111)A polarity and {110} surface orientations with different side facets following the Volmer-Weber growth mode. GID investigations reveal facet rods originating from AlSb{110} islands. It is shown that a concentration of only 0.7% AlSb{110} oriented domains influences the diffraction pattern in such a way that additional crystal truncation rods parallel to the surface appear.
Plasma turbulence in the scrape-off layer of tokamak devices
Authors: Ricci Paolo , Rogers B. N.
Published: January 2013

Plasma turbulence is explored in the scrape-off layer of tokamak devices using three-dimensional global two-fluid simulations. Two transport regimes are discussed: one in which the turbulent fluctuations saturate nonlinearly due to the Kelvin-Helmholtz instability, and another in which the fluctuations saturate due to a local flattening of the plasma gradients and associated removal of the linear instability drive. Focusing on the latter regime, analytical estimates of the cross-field transport and plasma profile gradients are obtained that display Bohm-scaling diffusion properties.
Time-and-space resolved comparison of plasma expansion velocities in high-power diodes with velvet cathodes
Authors: Yang Jie , Shu Ting , Fan Yuwei
Published: January 2013

Time-and-space resolved comparison of the expansion velocities of plasmas in the planar diode with cathodes made of carbon velvet and polymer velvet has been performed. The diode was powered by a 200 kV, 110 ns pulse, and the peak current density was nearly 477 A/cm2. A four-channel high speed framing camera (HSFC) was used to observe the formation and subsequent movement of the cathode plasmas. More accurate and valuable information about the two-dimensional (radial and axial) velocity components of the cathode plasmas was also acquired by utilizing the digital image processing methods. Additionally, the perveance model based on the Child-Langmuir law was used to calculate the expansion velocities of the diode plasmas from voltage and current profiles. Results from the two diagnostics were compared. Comparing the average values of the radial and axial velocity components indicated that the former was much larger than the latter during the initial period of the current. It was also found that the radial velocity of the carbon velvet cathode (190 cm/μs) was much larger than that (90 cm/μs) of the polymer velvet cathode. Moreover, the average values of both the radial and axial velocity components of the carbon velvet cathode were typically in the range of 2.5 ± 1.5 cm/μs, which were smaller than that of the polymer velvet cathode during the current flattop. These results, together with the comparison of calculated values from the perveance model, indicated that the diode with carbon velvet cathode was more robust as compared with the polymer velvet cathode for the same electron current densities.
All solution processed, nanowire enhanced ultraviolet photodetectors
Authors: Afal Aysegul , Coskun Sahin , Emrah Unalan Husnu
Published: January 2013

We report on the fabrication and characterization of transparent and fully solution processed, nanowire based ultraviolet (UV) photodetectors with high responsivity. For this purpose, UV sensitive zinc oxide (ZnO) nanowires were grown hydrothermally on transparent electrodes formed by spray coated network of silver (Ag) nanowires. Fabricated UV photodetectors showed short recovery time, around 4 s, with a decent on/off ratio of 2600. Effect of in-situ annealing and nanowire length was investigated. Our design provides a simple and cost effective approach for the fabrication of high performance UV photodetectors.
Full compensation of oxygen vacancies in EuTiO3 (001) epitaxial thin film stabilized by a SrTiO3 surface protection layer
Authors: Shimamoto K. , Hatabayashi K. , Hirose Y. , Nakao S. , Fukumura T. , Hasegawa T.
Published: January 2013

We fabricated highly insulating EuTiO3 (001) epitaxial thin films capped with SrTiO3 protection layers on SrTiO3 (001) substrates by combining pulsed laser deposition and post-annealing processes. The epitaxial SrTiO3 protection layer played a significant role in compensation of oxygen vacancies in the EuTiO3 thin films by preventing excess oxidation of the films and by “locking” the EuTiO3 perovskite structure in an epitaxial manner from the top during the air-annealing process. The obtained EuTiO3 thin films demonstrated an antiferromagnetic transition at 5.4 K, quantum paraelectricity down to ∼25 K, and a magnetoelectric coupling comparable to that of bulk EuTiO3.
Defect enhanced funneling of diffusion current in silicon
Authors: Azimi S. , Dang Z. Y. , Song J. , Breese M. B. H. , Vittone E. , Forneris J.
Published: January 2013

We report a current transport mechanism observed during electrochemical anodization of ion irradiated p-type silicon, in which a hole diffusion current is highly funneled along the gradient of modified doping profile towards the maximum ion induced defect density, dominating the total current flowing and hence the anodization behaviour. This study is characterized within the context of electrochemical anodization but relevant to other fields where any residual defect density may result in similar effects, which may adversely affect performance, such as in wafer gettering or satellite-based microelectronics. Increased photoluminescence intensity from localized buried regions of porous silicon is also shown.
Two-color femtosecond strobe lighting of coherent acoustic phonons emitted by quantum dots
Authors: Péronne Emmanuel , Charron Eric , Vincent Serge , Sauvage Sébastien , Lemaître Aristide , Perrin Bernard , Jusserand Bernard
Published: January 2013

The transient acoustic pulse emitted by a single InAs quantum dots layer was measured depending on the pump wavelength. By tuning the pump wavelength through the transition energies of the GaAs barrier, the wetting layer and the quantum dots themselves, the acoustic phonon emission is shown to be strongly correlated to the electronic structure of the quantum dots layer system. The contributions of the wetting layer and the quantum dots to the acoustic signal were clearly identified and quantified by comparing different regions of the same sample containing or not quantum dots.
Analysis of perturbations in the lateral far-field of blue InGaN laser diodes
Authors: Kopp F. , Lell A. , Eichler C. , Schwarz U. T. , Strauss U.
Published: January 2013

The origin of perturbations in the Gaussian-shaped lateral far-field of blue InGaN laser diodes is explored. Near-field measurements reveal that small stray light intensity peaks beside the ridge waveguide exist. In order to prove quantitatively the impact of this stray light on the far field, an exemplary beam propagation method simulation is performed. Moreover, laser cuts as a chip technological process to block stray light from the out-couple facet are presented. These laser cuts result in a significant improvement of the lateral far-field.
Rice cultivar responses to elevated CO2 at two free-air CO2 enrichment (FACE) sites in Japan
Authors: Hasegawa Toshihiro , Sakai Hidemitsu , Tokida Takeshi , Nakamura Hirofumi , Zhu Chunwu , Usui Yasuhiro , Yoshimoto Mayumi , Fukuoka Minehiko , Wakatsuki Hitomi , Katayanagi Nobuko , Matsunami Toshinori , Kaneta Yoshihiro , Sato Takashi , Takakai Fumiaki , Sameshima Ryoji , Okada Masumi , Mae Tadahiko , Makino Amane
Published: January 2013

There is some evidence that rice cultivars respond differently to elevated CO2 concentrations ([CO2]), but [CO2] × cultivar interaction has never been tested under open-field conditions across different sites. Here, we report on trials conducted at free-air CO2 enrichment (FACE) facilities at two sites in Japan, Shizukuishi (2007 and 2008) and Tsukuba (2010). The average growing-season air temperature was more than 5°C warmer at Tsukuba than at Shizukuishi. For four cultivars tested at both sites, the [CO2] × cultivar interaction was significant for brown rice yield, but there was no significant interaction with site-year. Higher-yielding cultivars with a large sink size showed a greater [CO2] response. The Tsukuba FACE experiment, which included eight cultivars, revealed a wider range of yield enhancement (3–36%) than the multi-site experiment. All of the tested yield components contributed to this enhancement, but there was a highly significant [CO2] × cultivar interaction for percentage of ripened spikelets. These results suggest that a large sink is a prerequisite for higher productivity under elevated [CO2], but that improving carbon allocation by increasing grain setting may also be a practical way of increasing the yield response to elevated [CO2].
Daily prolactin pulse inhibits the corpus luteum during lactational quiescence in the marsupial, Macropus eugenii
Authors: Hinds L. A. , Tyndale-Biscoe C. H.
Published: January 2013

The corpus luteum (CL) of the tammar wallaby is inhibited by prolactin during lactation and seasonal quiescence. In seasonal quiescence a daily transient pulse of prolactin (PRL) of less than 2 h duration is sufficient to maintain inhibition. We investigated whether the same inhibition applies in lactation and, if so, how. Our results show that inhibition of the CL during lactation is maintained by a transient pulse of prolactin once a day. They also show that the minimum time without a PRL pulse for the CL to escape inhibition is more than 48 h and less than 72 h. Nevertheless, some animals had a longer refractory period than 72 h, which was reflected in a longer interval to the progesterone peak and birth. These results support the previous conclusion that PRL exercises its effect on a rate-limiting step in progesterone synthesis and secretion rate from the CL, which precedes any increase in its mass. Therefore, we conclude that the role of PRL is to act as a luteostatic agent, an effect that is in marked contrast to its luteotrophic effect in many eutherian species, including rodents.
Microarray analysis of mRNA from cumulus cells following in vivo or in vitro maturation of mouse cumulus–oocyte complexes
Authors: Kind Karen L. , Banwell Kelly M. , Gebhardt Kathryn M. , Macpherson Anne , Gauld Ashley , Russell Darryl L. , Thompson Jeremy G.
Published: January 2013

The IVM of mammalian cumulus–oocyte complexes (COCs) yields reduced oocyte developmental competence compared with oocytes matured in vivo. Altered cumulus cell function during IVM is implicated as one cause for this difference. We have conducted a microarray analysis of cumulus cell mRNA following IVM or in vivo maturation (IVV). Mouse COCs were sourced from ovaries of 21-day-old CBAB6F1 mice 46 h after equine chorionic gonadotrophin (5 IU, i.p.) or from oviducts following treatment with 5 IU eCG (61 h) and 5 IU human chorionic gonadotrophin (13 h). IVM was performed in α-Minimal Essential Medium with 50 mIU FSH for 17 h. Three independent RNA samples were assessed using the Affymetrix Gene Chip Mouse Genome 430 2.0 array (Affymetrix, Santa Clara, CA, USA). In total, 1593 genes were differentially expressed, with 811 genes upregulated and 782 genes downregulated in IVM compared with IVV cumulus cells; selected genes were validated by real-time reverse transcription–polymerase chain reaction (RT-PCR). Surprisingly, haemoglobin α (Hba-a1) was highly expressed in IVV relative to IVM cumulus cells, which was verified by both RT-PCR and western blot analysis. Because haemoglobin regulates O2 and/or nitric oxide availability, we postulate that it may contribute to regulation of these gases during the ovulatory period in vivo. These data will provide a useful resource to determine differences in cumulus cell function that are possibly linked to oocyte competence.
Effects of fire on cation content in water: a laboratory simulation study
Authors: Cancelo-González J. , Rial-Rivas M. E. , Díaz-Fierros F.
Published: January 2013

Laboratory experiments were carried out to explore the effect of thermal shocks (as occur during fire) and simulated rainfall events on cation leaching dynamics in an organic rich Leptic Umbrisol soil. The soil samples were collected in the field using specially designed lysimeter boxes that allow sampling and application of thermal shock treatments and simulated rainfall while keeping the soil structure unaltered. The soil temperature during the thermal shocks and degree-hours of accumulated heat were determined, and cation (Na+, K+, Ca2+ and Mg2+) leaching was measured in surface runoff (0-cm depth) and subsurface flow (12-cm depth) samples collected from the lysimeter boxes. Important differences were found in cation leaching in relation to thermal shock: monovalent cation leaching from the soil above 200°C (68 degree-hours) and divalent cations leaching above 220°C (195 degree-hours) was higher than that seen in other treatments. In general, the amount of cations leached increased with the severity of the thermal shock; however, under moderate conditions, there was a decrease in cation leaching, mainly of monovalent ions. The exchangeable cation losses by leaching in the intense heat treatments were ~80%.
Long prereproductive selection and divergence by depth in a Caribbean candelabrum coral
Authors: Prada Carlos , Hellberg Michael E.
Published: January 2013

Long-lived corals, the foundation of modern reefs, often follow ecological gradients, so that populations or sister species segregate by habitat. Adaptive divergence maintains sympatric congeners after secondary contact or may even generate species by natural selection in the face of gene flow. Such ecological divergence, initially between alternative phenotypes within populations, may be aided by immigrant inviability, especially when a long period separates larval dispersal and the onset of reproduction, during which selection can sort lineages to match different habitats. Here, we evaluate the strength of one ecological factor (depth) to isolate populations by comparing the genes and morphologies of pairs of depth-segregated populations of the candelabrum coral
Eunicea flexuosa
across the Caribbean.
Eunicea
is endemic to the Caribbean and all sister species co-occur.
Eunicea flexuosa
is widespread both geographically and across reef habitats. Our genetic analysis revealed two depth-segregated lineages. Field survivorship data, combined with estimates of selection coefficients based on transplant experiments, suggest that selection is strong enough to segregate these two lineages. Genetic exchange between the Shallow and Deep lineages occurred either immediately after divergence or the two have diverged with gene flow. Migration occurs asymmetrically from the Shallow to Deep lineage. Limited recruitment to reproductive age, even under weak annual selection advantage, is sufficient to generate habitat segregation because of the cumulative prolonged prereproductive selection. Ecological factors associated with depth can act as filters generating strong barriers to gene flow, altering morphologies, and contributing to the potential for speciation in the sea.
WISP2 regulates preadipocyte commitment and PPARγ activation by BMP4
Authors: Hammarstedt Ann , Hedjazifar Shahram , Jenndahl Lachmi , Gogg Silvia , Grünberg John , Gustafson Birgit , Klimcakova Eva , Stich Vladimir , Langin Dominique , Laakso Markku , Smith Ulf
Published: January 2013

Inability to recruit new adipose cells following weight gain leads to inappropriate enlargement of existing cells (hypertrophic obesity) associated with inflammation and a dysfunctional adipose tissue. We found increased expression of WNT1 inducible signaling pathway protein 2 (WISP2) and other markers of WNT activation in human abdominal s.c. adipose tissue characterized by hypertrophic obesity combined with increased visceral fat accumulation and insulin resistance. WISP2 activation in the s.c. adipose tissue, but not in visceral fat, identified the metabolic syndrome in equally obese individuals. WISP2 is a novel adipokine, highly expressed and secreted by adipose precursor cells. Knocking down WISP2 induced spontaneous differentiation of 3T3-L1 and human preadipocytes and allowed NIH 3T3 fibroblasts to become committed to the adipose lineage by bone morphogenetic protein 4 (BMP4). WISP2 forms a cytosolic complex with the peroxisome proliferator-activated receptor γ (PPARγ) transcriptional activator zinc finger protein 423 (Zfp423), and this complex is dissociated by BMP4 in a SMAD-dependent manner, thereby allowing Zfp423 to enter the nucleus, activate PPARγ, and commit the cells to the adipose lineage. The importance of intracellular Wisp2 protein for BMP4-induced adipogenic commitment and PPARγ activation was verified by expressing a mutant Wisp2 protein lacking the endoplasmic reticulum signal and secretion sequence. Secreted Wnt/Wisp2 also inhibits differentiation and PPARγ activation, albeit not through Zfp423 nuclear translocation. Thus adipogenic commitment and differentiation is regulated by the cross-talk between BMP4 and canonical WNT signaling and where WISP2 plays a key role. Furthermore, they link WISP2 with hypertrophic obesity and the metabolic syndrome.
Microbiome of the upper troposphere: Species composition and prevalence, effects of tropical storms, and atmospheric implications
Authors: DeLeon-Rodriguez Natasha , Lathem Terry L. , Rodriguez-R Luis M. , Barazesh James M. , Anderson Bruce E. , Beyersdorf Andreas J. , Ziemba Luke D. , Bergin Michael , Nenes Athanasios , Konstantinidis Konstantinos T.
Published: January 2013

The composition and prevalence of microorganisms in the middle-to-upper troposphere (8–15 km altitude) and their role in aerosol-cloud-precipitation interactions represent important, unresolved questions for biological and atmospheric science. In particular, airborne microorganisms above the oceans remain essentially uncharacterized, as most work to date is restricted to samples taken near the Earth’s surface. Here we report on the microbiome of low- and high-altitude air masses sampled onboard the National Aeronautics and Space Administration DC-8 platform during the 2010 Genesis and Rapid Intensification Processes campaign in the Caribbean Sea. The samples were collected in cloudy and cloud-free air masses before, during, and after two major tropical hurricanes, Earl and Karl. Quantitative PCR and microscopy revealed that viable bacterial cells represented on average around 20% of the total particles in the 0.25- to 1-μm diameter range and were at least an order of magnitude more abundant than fungal cells, suggesting that bacteria represent an important and underestimated fraction of micrometer-sized atmospheric aerosols. The samples from the two hurricanes were characterized by significantly different bacterial communities, revealing that hurricanes aerosolize a large amount of new cells. Nonetheless, 17 bacterial taxa, including taxa that are known to use C1–C4 carbon compounds present in the atmosphere, were found in all samples, indicating that these organisms possess traits that allow survival in the troposphere. The findings presented here suggest that the microbiome is a dynamic and underappreciated aspect of the upper troposphere with potentially important impacts on the hydrological cycle, clouds, and climate.
Activity-based probes for rhomboid proteases discovered in a mass spectrometry-based assay
Authors: Vosyka Oliver , Vinothkumar Kutti R. , Wolf Eliane V. , Brouwer Arwin J. , Liskamp Rob M. J. , Verhelst Steven H. L.
Published: January 2013

Rhomboid proteases are evolutionary conserved intramembrane serine proteases. Because of their emerging role in many important biological pathways, rhomboids are potential drug targets. Unfortunately, few chemical tools are available for their study. Here, we describe a mass spectrometry-based assay to measure rhomboid substrate cleavage and inhibition. We have identified isocoumarin inhibitors and developed activity-based probes for rhomboid proteases. The probes can distinguish between active and inactive rhomboids due to covalent, reversible binding of the active-site serine and stable modification of a histidine residue. Finally, the structure of an isocoumarin-based inhibitor with
Escherichia coli
rhomboid GlpG uncovers an unusual mode of binding at the active site and suggests that the interactions between the 3-substituent on the isocoumarin inhibitor and hydrophobic residues on the protease reflect S′ subsite binding. Overall, these probes represent valuable tools for rhomboid study, and the structural insights may facilitate future inhibitor design.
DNA and virus particle vaccination protects against acquisition and confers control of viremia upon heterologous simian immunodeficiency virus challenge
Authors: Patel Vainav , Jalah Rashmi , Kulkarni Viraj , Valentin Antonio , Rosati Margherita , Alicea Candido , von Gegerfelt Agneta , Huang Wensheng , Guan Yongjun , Keele Brandon F. , Bess Julian W. , Piatak Michael , Lifson Jeffrey D. , Williams William T. , Shen Xiaoying , Tomaras Georgia D. , Amara Rama R. , Robinson Harriet L. , Johnson Welkin , Broderick Kate E. , Sardesai Niranjan Y. , Venzon David J. , Hirsch Vanessa M. , Felber Barbara K. , Pavlakis George N.
Published: January 2013

We have previously shown that macaques vaccinated with DNA vectors expressing SIVmac239 antigens developed potent immune responses able to reduce viremia upon high-dose SIVmac251 challenge. To further improve vaccine-induced immunity and protection, we combined the SIVmac239 DNA vaccine with protein immunization using inactivated SIVmac239 viral particles as protein source. Twenty-six weeks after the last vaccination, the animals were challenged intrarectally at weekly intervals with a titrated dose of the heterologous SIVsmE660. Two of DNA-protein coimmunized macaques did not become infected after 14 challenges, but all controls were infected by 11 challenges. Vaccinated macaques showed modest protection from SIVsmE660 acquisition compared with naïve controls (
P
= 0.050; stratified for TRIM5α genotype). Vaccinees had significantly lower peak (1.6 log,
P
= 0.0048) and chronic phase viremia (
P
= 0.044), with 73% of the vaccinees suppressing viral replication to levels below assay detection during the 40-wk follow-up. Vaccine-induced immune responses associated significantly with virus control: binding antibody titers and the presence of rectal IgG to SIVsmE660 Env correlated with delayed SIVsmE660 acquisition; SIV-specific cytotoxic T cells, prechallenge CD4
+
effector memory, and postchallenge CD8
+
transitional memory cells correlated with control of viremia. Thus, SIVmac239 DNA and protein-based vaccine protocols were able to achieve high, persistent, broad, and effective cellular and humoral immune responses able to delay heterologous SIVsmE660 infection and to provide long-term control of viremia. These studies support a role of DNA and protein-based vaccines for development of an efficacious HIV/AIDS vaccine.
Arachidonoyl-phosphatidylcholine oscillates during the cell cycle and counteracts proliferation by suppressing Akt membrane binding
Authors: Koeberle Andreas , Shindou Hideo , Koeberle Solveigh C. , Laufer Stefan A. , Shimizu Takao , Werz Oliver
Published: January 2013

The activity of protein kinase B (Akt)—a major kinase promoting cell proliferation and survival—oscillates during the cell cycle. To investigate whether membrane phospholipids may regulate Akt phosphorylation and thus activity, we monitored the lipid profile of nocodazole-synchronized mouse NIH 3T3 fibroblasts during the cell cycle by liquid chromatography electrospray ionization tandem mass spectrometry (LC-MS/MS). The proportion ofsn-2-arachidonoyl-phosphatidylcholine (20:4-PC) inversely correlated with Akt activity. Increasing the cellular ratio of 20:4-PC by supplementation of 20:4-PC to the cell culture medium diminished Akt [serine (Ser)473] phosphorylation. Saturated and monounsaturated phosphatidylcholines, used as control had no effect; 20:4-PC reduced cell proliferation relative to controls, interfered with S-phase transition, and suppressed Akt downstream signaling and cyclin expression like LY294002, which is a specific inhibitor of the phosphatidylinositol-3-kinase/Akt pathway. Additive effects of 20:4-PC and LY294002 were not observed, underlining the critical role of Akt for 20:4-PC signaling; 20:4-PC suppressed Akt membrane translocation as shown by immunofluorescence microscopy but left the concentration of the anchor lipid phosphatidylinositol-3,4,5-trisphosphate unchanged. An in vitro binding assay suggests that 20:4-PC attenuates the interaction of Akt with its membrane binding site. We conclude that 20:4-PC oscillates during the cell cycle and delays cell cycle progression by inhibiting Akt membrane binding.
Membrane invaginations facilitate reversible water flux driving tunable iridescence in a dynamic biophotonic system
Authors: DeMartini Daniel G. , Krogstad Daniel V. , Morse Daniel E.
Published: January 2013

Squids have used their tunable iridescence for camouflage and communication for millions of years; materials scientists have more recently looked to them for inspiration to develop new “biologically inspired” adaptive optics. Iridocyte cells produce iridescence through constructive interference of light with intracellular Bragg reflectors. The cell’s dynamic control over the apparent lattice constant and dielectric contrast of these multilayer stacks yields the corresponding optical control of brightness and color across the visible spectrum. Here, we resolve remaining uncertainties in iridocyte cell structure and determine how this unusual morphology enables the cell’s tunable reflectance. We show that the plasma membrane periodically invaginates deep into the iridocyte to form a potential Bragg reflector consisting of an array of narrow, parallel channels that segregate the resulting high refractive index, cytoplasmic protein-containing lamellae from the low-index channels that are continuous with the extracellular space. In response to control by a neurotransmitter, the iridocytes reversibly imbibe or expel water commensurate with changes in reflection intensity and wavelength. These results allow us to propose a comprehensive mechanism of adaptive iridescence in these cells from stimulation to color production. Applications of these findings may contribute to the development of unique classes of tunable photonic materials.
Molecular basis of antibiotic multiresistance transfer in
Staphylococcus aureus
Authors: Edwards Jonathan S. , Betts Laurie , Frazier Monica L. , Pollet Rebecca M. , Kwong Stephen M. , Walton William G. , Ballentine W. Keith , Huang Julianne J. , Habibi Sohrab , Del Campo Mark , Meier Jordan L. , Dervan Peter. B. , Firth Neville , Redinbo Matthew R.
Published: January 2013

Multidrug-resistant
Staphylococcus aureus
infections pose a significant threat to human health. Antibiotic resistance is most commonly propagated by conjugative plasmids like pLW1043, the first vancomycin-resistant
S. aureus
vector identified in humans. We present the molecular basis for resistance transmission by the nicking enzyme in
S. aureus
(NES), which is essential for conjugative transfer. NES initiates and terminates the transfer of plasmids that variously confer resistance to a range of drugs, including vancomycin, gentamicin, and mupirocin. The NES N-terminal relaxase–DNA complex crystal structure reveals unique protein–DNA contacts essential in vitro and for conjugation in
S. aureus
. Using this structural information, we designed a DNA minor groove-targeted polyamide that inhibits NES with low micromolar efficacy. The crystal structure of the 341-residue C-terminal region outlines a unique architecture; in vitro and cell-based studies further establish that it is essential for conjugation and regulates the activity of the N-terminal relaxase. This conclusion is supported by a small-angle X-ray scattering structure of a full-length, 665-residue NES–DNA complex. Together, these data reveal the structural basis for antibiotic multiresistance acquisition by
S
.
aureus
and suggest novel strategies for therapeutic intervention.
Genomic dosage effects on heterosis in triploid maize
Authors: Yao Hong , Dogra Gray Anjali , Auger Donald L. , Birchler James A.
Published: January 2013

The genetic basis of hybrid vigor or heterosis has been debated for more than a century. A popular hypothesis to explain this phenomenon is that there are different slightly deleterious recessive homozygous alleles in the two parents and that these alleles are complemented in the hybrid so that the biomass and fertility exceed both parents. To address the complementation hypothesis in a direct manner, heterosis was examined in diploid inbreds and reciprocal hybrids and compared with matched triploid inbred derivatives and two types of triploid hybrids that differ in the number of genomes from the different parents. Complementation of recessive mutations would occur equally in the two types of triploid hybrids predicting that, if this complementation were the sole basis of the heterotic response, the two types of triploid hybrids would be equivalent for hybrid vigor. However, the reciprocal diploid hybrids were similar for six of nine measured traits, but the two types of triploid hybrids differed significantly for eight of the same traits. Importantly, the triploid hybrids differed in the level of high-parent heterosis relative to the derived triploid inbreds. Also, the differences observed between the reciprocal triploid hybrids correlated strongly with differences observed between the inbreds, either at the diploid or triploid level, in a manner explicable by genome dosage rather than parent of origin effects. The findings of this study suggest that a major component of heterosis is a mechanism that is modulated by dosage-sensitive factors that involves allelic diversity across the genome.
Shp2 plays a crucial role in cell structural orientation and force polarity in response to matrix rigidity
Authors: Lee Hsiao-Hui , Lee Hsin-Chang , Chou Chih-Chiang , Hur Sung Sik , Osterday Katie , del Álamo Juan C. , Lasheras Juan C. , Chien Shu
Published: January 2013

Cells can sense and respond to physical properties of their surrounding extracellular matrix. We have demonstrated here that tyrosine phosphatase Shp2 plays an essential role in the response of mouse embryonic fibroblasts to matrix rigidity. On rigid surfaces, large focal adhesions (FAs) and anisotropically oriented stress fibers are formed, whereas cells plated on compliant substrates form numerous small FAs and radially oriented stress fibers. As a result, traction force is increased and organized to promote cell spreading and elongation on rigid substrates. Shp2-deficient cells do not exhibit the stiffness-dependent increase in FA size and polarized stress fibers nor the intracellular tension and cell shape change. These results indicate the involvement of Shp2 in regulating the FAs and the cytoskeleton for force maintenance and organization. The defect of FA maturation in Shp2-deficient cells was rescued by expressing Y722F Rho-associated protein kinase II (ROCKII), suggesting that ROCKII is the molecular target of Shp2 in FAs for the FA maturation. Thus, Shp2 serves as a key mediator in FAs for the regulation of structural organization and force orientation of mouse embyonic fibroblasts in determining their mechanical polarity in response to matrix rigidity.
Stick-slip friction and wear of articular joints
Authors: Lee Dong Woog , Banquy Xavier , Israelachvili Jacob N.
Published: January 2013

Significance

The goal of this study was to use the Surface Forces Apparatus to examine the effects of slip-stick friction on cartilage surface morphology under different loading and sliding conditions. Different load and speed regimes were represented using friction maps that separated regimes of smooth and stick-slip sliding. The finding of this work is that damage generally occurs within the stick-slip regimes and is not directly related to the friction coefficient. Prolonged exposure of cartilage surfaces to stick-slip sliding resulted in a significant increase of surface roughness, indicative of severe morphological changes (damage) of the cartilage surfaces.
Role for the obesity-related
FTO
gene in the cellular sensing of amino acids
Authors: Gulati Pawan , Cheung Man Ka , Antrobus Robin , Church Chris D. , Harding Heather P. , Tung Yi-Chun Loraine , Rimmington Debra , Ma Marcella , Ron David , Lehner Paul J. , Ashcroft Frances M. , Cox Roger D. , Coll Anthony P. , O’Rahilly Stephen , Yeo Giles S. H.
Published: January 2013

SNPs in the first intron of
FTO
(
fat mass and obesity associated
) are strongly associated with human obesity. While it is not yet formally established that this effect is mediated through the actions of the FTO protein itself, loss of function mutations in
FTO
or its murine homologue
Fto
result in severe growth retardation, and mice globally overexpressing FTO are obese. The mechanisms through which FTO influences growth and body composition are unknown. We describe a role for FTO in the coupling of amino acid levels to mammalian target of rapamycin complex 1 signaling. These findings suggest that FTO may influence body composition through playing a role in cellular nutrient sensing.