bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation and experimental characterization of polymer/carbon nanotubes composites for strain sensor applications
Authors: De Vivo B. , Lamberti P. , Spinelli G. , Tucci V. , Vertuccio L. , Vittoria V.
Published: August 2014

In this paper, a numerical model is presented in order to analyze the electrical characteristics of polymer composites filled by carbon nanotubes (CNTs) subject to tensile stress and investigate the possible usage of such materials as innovative sensors for small values of strain. The simulated mechano-electrical response of the nanocomposite is obtained through a multi-step approach which, through different modeling stages, provides a simple and effective tool for material analysis and design. In particular, at first, the morphological structures of the composites are numerically simulated by adopting a previously presented model based on a Monte Carlo procedure in which uniform distributions of the CNTs, approximated as of solid cylinders and ensuring some physical constraints, are dispersed inside a cubic volume representing the polymer matrix. Second, a geometrical analysis allows to obtain the percolation paths detected in the simulated structures. Suitable electrical networks composed by resistors and capacitors associated to the complex charge transport and polarization mechanisms occurring in the percolation paths are then identified. Finally, the variations of these circuit parameters, which are differently affected by the mechanical stresses applied to the composites, are considered to analyze the electromechanical characteristics of the composites and hence their performances as stress sensors. The proposed approach is used to investigate the impact on the electro-mechanical response of some physical properties of the base materials, such as the type of carbon nanotube, the height of energy barrier of polymer resin, as well as characteristics of the composite, i.e., the volume fraction of the filler. The tunneling effect between neighboring nanotubes is found to play a dominant role in determining the composite sensitivity to mechanical stresses. The simulation results are also compared with the experimental data obtained by performing stress tests on samples of a multi walled CNT filled composite based on poly (ε-caprolactone), a polymer which is of interest for its biocompatibility. Model simulations and measured data show generally satisfactory agreement, confirming the effectiveness of the proposed approach to account for the impact of the interactions between CNTs and the insulating resin on the electromechanical response of the composite.
Compositional dependence of optical critical point parameters in pseudomorphic GeSn alloys
Authors: D'Costa Vijay Richard , Wang Wei , Zhou Qian , Chan Taw Kuei , Osipowicz Thomas , Tok Eng Soon , Yeo Yee-Chia
Published: August 2014

Spectroscopic ellipsometry was used to investigate the optical response of pseudomorphic Ge1−xSnx (0 ≤ x ≤ 0.17) alloys grown directly on Ge (100) by molecular beam epitaxy. A detailed compositional study of amplitudes, broadenings, energies, and phase angles associated with critical points E1, E1 + Δ1, E0′, and E2 of GeSn alloys was carried out using a derivative analysis. The results can be understood in terms of the electronic bandstructure of Ge or relaxed GeSn alloys with the following differences. First, broadening parameters in pseudomorphic alloys are found to have lower values compared to relaxed alloys indicating lower dislocation density in our pseudomorphic alloys relative to relaxed alloys. Second, the amplitudes of E1 and E1 + Δ1 are enhanced and reduced, respectively, with respect to relaxed GeSn alloys, and the trends are captured using the k.p method as a biaxial stress induced effect. Third, phase angles are lower than Ge for all the critical points suggesting reduction of excitonic effects in GeSn with respect to Ge.
Optical properties of Pr-doped BaY2F8
Authors: Andrade Adriano B. , de Mello Ana C. S. , Rezende Marcos V. dos S. , Baldochi Sonia L. , Valerio Mário E. G.
Published: August 2014

Crystalline samples of Pr-doped BaY2F8 (BaYF) were prepared by zone melting technique. The pure phase obtained was identified by X-ray diffraction measurement. Optical absorption result was evaluated and it showed that the formation of the absorption bands can be connected to color centers generated by radiation in the matrix. Radioluminescence emission measurements after excitation by X-ray showed that the material exhibited components responsible for long lasting phosphorescence. Short decay times were also evaluated, the measurements showed a fast component around 70 ns associated to the 4f15d1 → 4f2 transition of the Pr3+ ion. The Thermoluminescence (TL) results indicate the presence of two trapping centers.
On the possibility of the multiple inductively coupled plasma and helicon plasma sources for large-area processes
Authors: Lee Jin-Won , Lee Yun-Seong , Chang Hong-Young , An Sang-Hyuk
Published: August 2014

In this study, we attempted to determine the possibility of multiple inductively coupled plasma (ICP) and helicon plasma sources for large-area processes. Experiments were performed with the one and two coils to measure plasma and electrical parameters, and a circuit simulation was performed to measure the current at each coil in the 2-coil experiment. Based on the result, we could determine the possibility of multiple ICP sources due to a direct change of impedance due to current and saturation of impedance due to the skin-depth effect. However, a helicon plasma source is difficult to adapt to the multiple sources due to the consistent change of real impedance due to mode transition and the low uniformity of the B-field confinement. As a result, it is expected that ICP can be adapted to multiple sources for large-area processes.
Comparative analysis of hole transport in compressively strained InSb and Ge quantum well heterostructures
Authors: Agrawal Ashish , Barth Michael , Madan Himanshu , Lee Yi-Jing , Lin You-Ru , Wu Cheng-Hsien , Ko Chih-Hsin , Wann Clement H. , Loubychev Dmitri , Liu Amy , Fastenau Joel , Lindemuth Jeff , Datta Suman
Published: August 2014

Compressively strained InSb (s-InSb) and Ge (s-Ge) quantum well heterostructures are experimentally studied, with emphasis on understanding and comparing hole transport in these two-dimensional confined heterostructures. Magnetotransport measurements and bandstructure calculations indicate 2.5× lower effective mass for s-InSb compared to s-Ge quantum well at 1.9 × 1012 cm–2. Advantage of strain-induced m* reduction is negated by higher phonon scattering, degrading hole transport at room temperature in s-InSb quantum well compared to s-Ge heterostructure. Consequently, effective injection velocity is superior in s-Ge compared to s-InSb. These results suggest s-Ge quantum well heterostructure is more favorable and promising p-channel candidate compared to s-InSb for future technology node.
Fluorescence excitation enhancement by Bloch surface wave in all-polymer one-dimensional photonic structure
Authors: Fornasari L. , Floris F. , Patrini M. , Canazza G. , Guizzetti G. , Comoretto D. , Marabelli F.
Published: August 2014

We demonstrate photoluminescence excitation enhancement in an all-polymer flexible one-dimensional photonic crystal structure capped with a fluorescent organic ultrathin film. When optical matching conditions between the excitation beam and the Bloch Surface Wave mode supported by the photonic structure are achieved, a ten times enhancement of the photoluminescence is observed. We notice that in these systems luminescence signal reinforcement is achieved by increasing the pump efficiency with no need of spectral resonance to the emission of the chosen fluorophore. All these features make these systems suitable candidates for easy, flexible, and cheap fluorescent sensing.
Excitation cross section of erbium-doped GaN waveguides under 980 nm optical pumping
Authors: Hui R. , Xie R. , Feng I.-W. , Sun Z. Y. , Lin J. Y. , Jiang H. X.
Published: August 2014

Excitation cross section of erbium-doped GaN waveguides is measured to be approximately 2.2×10−21cm2 at 980 nm pumping wavelength. This cross section value is found relatively insensitive to the crystalline quality of epilayers. However, spontaneous emission carrier lifetimes in these waveguides are directly related to both the crystalline quality and the optical loss, and thus can be used as a material quality indicator.
Improvement of the recoverable energy storage density and efficiency by utilizing the linear dielectric response in ferroelectric capacitors
Authors: Peng Bin , Xie Zhenkun , Yue Zhenxing , Li Longtu
Published: August 2014

The recoverable energy storage performance of 400 nm undoped and 4 mol. % Nb-doped PbZr0.4Ti0.6O3 ferroelectric capacitors was studied. The DC dielectric strength improved from 1351 kV/cm (undoped) to 1878 kV/cm (Nb-doped), and the latter capacitors had high recoverable energy storage density up to 20 J/cm3 with efficiency of 70%, benefiting mainly from the linear dielectric response. This study suggests that donor doping is an effective way to improve the dielectric strength and illustrates the significant role of the linear dielectric response in ferroelectrics for high power applications.
Mapping near-field localization in plasmonic optical nanoantennas with 10 nm spatial resolution
Authors: Kiesow Karissa I. , Dhuey Scott , Habteyes Terefe G.
Published: August 2014

Quantifying the near-field localization in plasmonic optical nanoantennas is fundamentally important to understand and optimize the design and fabrication of nanostructures for various applications. Here, the near-field localization in optical gap nanoantennas that are in resonance or near-resonance with 633 nm excitation wavelength is directly visualized in real space with 10 nm spatial resolutions, mapping the amplitude and phase characteristics of the in-plane and out-of-plane vector components selectively. While large field amplitude is observed in the gap for the in-plane component, the narrow gaps that are not resolved in the topographic image have been clearly observed in the optical images when the out-of-plane component is mapped, suggesting that the lateral optical resolution can surpass the radius of curvature of the probing tip. The effects of various structural parameters and metallic adhesion layer on the extent of field localization have been discussed, providing important insight in designing and fabricating plasmonic optical devices.
Mechanical confinement for improved energy storage density in BNT-BT-KNN lead-free ceramic capacitors
Authors: Chauhan Aditya , Patel Satyanarayan , Vaish Rahul
Published: August 2014

With the advent of modern power electronics, embedded circuits and non-conventional energy harvesting, the need for high performance capacitors is bound to become indispensible. The current state-of-art employs ferroelectric ceramics and linear dielectrics for solid state capacitance. However, lead-free ferroelectric ceramics propose to offer significant improvement in the field of electrical energy storage owing to their high discharge efficiency and energy storage density. In this regards, the authors have investigated the effects of compressive stress as a means of improving the energy storage density of lead-free ferroelectric ceramics. The energy storage density of 0.91(Bi0.5Na0.5)TiO3-0.07BaTiO3-0.02(K0.5Na0.5)NbO3 ferroelectric bulk ceramic was analyzed as a function of varying levels of compressive stress and operational temperature .It was observed that a peak energy density of 387 mJ.cm-3 was obtained at 100 MPa applied stress (25oC). While a maximum energy density of 568 mJ.cm-3 was obtained for the same stress at 80oC. These values are indicative of a significant, 25% and 84%, improvement in the value of stored energy compared to an unloaded material. Additionally, material's discharge efficiency has also been discussed as a function of operational parameters. The observed phenomenon has been explained on the basis of field induced structural transition and competitive domain switching theory.
Surface potential calculation and drain current model for junctionless double-gate polysilicon TFTs
Authors: Deng W. , Ma X. , Huang J.
Published: August 2014

Surface potential is a key parameter in evaluating the DC property of thin-film transistors (TFTs). In this paper, for the junctionless symmetric double-gate polysilicon TFTs, a physical-based explicit calculation to surface potential has been derived. Incorporating impurity concentration, mobile charge and trap density into Poisson's equation, a closed form of band bending as a function of gate voltage is obtained and demonstrated as an accurate and computationally efficient solution. Based on surface potential, a drain current model for long-channel devices is provided in explicit forms. Furthermore, it is verified successfully by comparisons with both 2D numerical simulation and experimental data in different operation regions.
Over 7% magnetic field-induced strain in a Ni-Mn-Ga five-layered martensite
Authors: Pagounis E. , Chulist R. , Szczerba M. J. , Laufenberg M.
Published: August 2014

A Ni-Mn-Ga single crystal with a modulated five-layered martensite structure is reported, demonstrating giant magnetic field induced strain (MFIS) of 7.1% at room temperature and of 6% at temperatures close to the austenite transformation (TA = 71 °C). The room temperature MFIS clearly exceeds the best results of around 6% measured earlier in 10M martensites. The larger MFIS is connected to the huge (>1%) change in the lattice distortion of the 10M structure, obtained within a narrow temperature interval of 47 K, which has been previously observed only during intermartensitic transformation. The present material shall effectively reduce the size of magnetic shape memory actuators.
Color-Dependent Motion Illusions in Stationary Images and Their Phenomenal Dimorphism
Authors: Kitaoka Akiyoshi
Published: August 2014

The color-dependent motion illusion in stationary images—a special type of the Fraser–Wilcox illusion—is introduced and discussed. The direction of illusory motion changes depending on whether the image is of high or low luminance and whether the room is bright or dark. This dimorphism of illusion was confirmed by surveys. It is suggested that two different spatial arrangements of color can produce the motion illusion. One is a spatial arrangement where long- and short-wavelength color regions sandwich a darker strip; the other is where the same color regions sandwich a brighter strip.
A robust nanoscale experimental quantification of fracture energy in a bilayer material system
Authors: Lau Denvid , Broderick Kurt , Buehler Markus J. , Büyüköztürk Oral
Published: August 2014

Significance

Accurate measurement of interfacial properties is critical any time two materials are bonded—in composites, tooth crowns, or when biomaterials are attached to the human body. Yet, in spite of this importance, reliable methods to measure interfacial properties between dissimilar materials remain elusive. Here we present an experimental method for robust characterization of organic–inorganic interfaces. Combining theory, experiment, and molecular simulation, we show that debonding between layers of materials can be controlled through residual stresses in a deposited metallic layer. We validate the method and show that moisture degrades the bonding between epoxy and silica, a technologically important interface. This may enable us to design more durable concrete composites that could be used to innovate our nation's aging infrastructure.
Predicting the outcomes of treatment to eradicate the latent reservoir for HIV-1
Authors: Hill Alison L. , Rosenbloom Daniel I. S. , Fu Feng , Nowak Martin A. , Siliciano Robert F.
Published: August 2014

Significance

HIV infection cannot be cured by current antiretroviral drugs, due to the presence of long-lived latently infected cells. New antilatency drugs are being tested in clinical trials, but major unknowns remain. It is unclear how much latent virus must be eliminated for a cure, which remains difficult to answer empirically due to few case studies and limited sensitivity of viral reservoir assays. In this paper, we introduce a mathematical model of HIV dynamics to calculate the likelihood and timing of viral rebound following antilatency treatment. We derive predictions for the required efficacy of antilatency drugs, and demonstrate that rebound times may be highly variable and occur after years of remission. These results will aid in designing and interpreting HIV cure studies.
Antioxidant Capacity of Water‐Extractable Arabinoxylan from Commercial Barley, Wheat, and Wheat Fractions
Authors: Malunga Lovemore Nkhata , Beta Trust
Published: August 2014

The objective of this research was to analyze the antioxidant capacity directly of water‐extractable nonstarch polysaccharides (NSP) and feruloylated arabinoxylans (WEAX) following their characterization. NSP were isolated from barley, wheat, and wheat fractions (germ, bran, and aleurone). WEAX were extracted only from wheat fractions. Antioxidant capacity of NSP measured with the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH), 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid (ABTS), and oxygen radical absorbance capacity (ORAC) assays was 24.0–99.0, 40.0–122.0, and 140.0–286.0μM Trolox equivalents (TE)/g, respectively. The antioxidant capacity of WEAX was 75.7–84.0, 58.0–105.0, and 110.0–235.0μM TE/g for those three assays. DPPH and ABTS were highly correlated to xylose content (R2 = 0.85), degree of substitution (R2 = −0.99), total phenolic acids (R2 = >0.73), total phenolic content (TPC) (R2 = >0.78), and ferulic acid content (R2 = >0.86). ORAC was only influenced by TPC (R2 = 0.63). By taking yield and antioxidant capacity into account, NSP would provide about 0.4–4.2, 0.6–5.1, and 2.8–12.0μM TE/g of flour of radical scavenging activity as measured by DPPH, ABTS, and ORAC, respectively, compared with WEAX (0.4–1.0, 0.3–1.3, and 0.6–2.8μM TE/g). Our results suggest that NSP or WEAX may play a role in protection against free radicals in a food matrix and likely in the gastrointestinal tract.
Evaluation of the Ryegrass Stem Rust Model STEMRUST_G and Its Implementation as a Decision Aid
Authors: Pfender W. F. , Coop L. B. , Seguin S. G. , Mellbye M. E. , Gingrich G. A. , Silberstein T. B.
Published: August 2014

STEMRUST_G, a simulation model for epidemics of stem rust in perennial ryegrass grown to maturity as a seed crop, was validated for use as a heuristic tool and as a decision aid for disease management with fungicides. Multistage validation had been used in model creation by incorporating previously validated submodels for infection, latent period duration, sporulation, fungicide effects, and plant growth. Validation of the complete model was by comparison of model output with observed disease severities in 35 epidemics at nine location-years in the Pacific Northwest of the United States. We judge the model acceptable for its purposes, based on several tests. Graphs of modeled disease progress were generally congruent with plotted disease severity observations. There was negligible average bias in the 570 modeled-versus-observed comparisons across all data, although there was large variance in size of the deviances. Modeled severities were accurate in >80% of the comparisons, where accuracy is defined as the modeled value being within twice the 95% confidence interval of the observed value, within ± 1 day of the observation date. An interactive website was created to produce disease estimates by running STEMRUST_G with user-supplied disease scouting information and automated daily weather data inputs from field sites. The model and decision aid supplement disease managers' information by estimating the level of latent (invisible) and expressed disease since the last scouting observation, given season-long weather conditions up to the present, and it estimates effects of fungicides on epidemic development. In additional large-plot experiments conducted in grower fields, the decision aid produced disease management outcomes (management cost and seed yield) as good as or better than the growers' standard practice. In future, STEMRUST_G could be modified to create similar models and decision aids for stem rust of wheat and barley, after additional experiments to determine appropriate parameters for the disease in these small-grain hosts.
The Analgesic Effects of Proximal, Distal, or No Sciatic Nerve Block on Posterior Knee Pain after Total Knee Arthroplasty
Authors: Abdallah Faraj W. , Chan Vincent W. S. , Gandhi Rajiv , Koshkin Arkadiy , Abbas Sherif , Brull Richard
Published: August 2014

Background:

The analgesic efficacy of sciatic nerve block (SNB) after total knee arthroplasty (TKA) is unclear. Proximal and distal SNB are each reported to provide posterior knee analgesia, whereas others suggest that posterior knee pain is not important after TKA. This prospective, randomized, double-blind, parallel-arm, placebo-controlled trial examined whether proximal or distal SNB provides superior analgesia in the posterior knee compared with no SNB after TKA.

Methods:

Sixty patients undergoing TKA were randomized to single-shot SNB using either the infragluteal (Proximal group) or popliteal (Distal group) technique, or no SNB (Placebo group). All patients received spinal anesthesia and continuous-femoral nerve blockade. A blinded observer assessed posterior and anterior knee pain at 2, 4, 6, 8, 12, and 24 h postoperatively. The primary outcome was moderate-to-severe posterior knee pain at 4 h postoperatively; secondary outcomes included SNB procedural time, needle passes, and discomfort.

Results:

Fifty-three patients were analyzed. The proportion of patients (Proximal:Distal:Placebo) who experienced moderate-to-severe posterior knee pain was 18%:22%:89% (P < 0.00001) at 2 h, 24%:28%:72% (P < 0.01) at 4 h, and 12%:17%:78% (P = 0.00003) at 6 h postoperatively. For the anterior knee, the proportion of patients reporting moderate-to-severe pain was 6%:11%:44% (P = 0.02) at 2 h, 6%:6%:39% (P = 0.012) at 4 h, and 12%:6%:44% (P = 0.017) at 6 h postoperatively. Moderate-to-severe pain did not differ between groups beyond 6 h. Both proximal and distal SNB reduced rest pain in the posterior and anterior knee up to 8 h postoperatively compared with no SNB. The popliteal technique required shorter procedural time, fewer needle passes, and produced less discomfort.

Conclusion:

Proximal and distal SNB each reduce posterior and anterior knee pain after TKA compared with no SNB.
Factors Affecting the Nonlinear Force Versus Distraction Height Curves in an In Vitro C5–C6 Anterior Cervical Distraction Model
Authors: Wen Junxiang , Xu Jianwei , Li Lijun , Yang Mingjie , Pan Jie , Chen Deyu , Jia Lianshun , Tan Jun
Published: August 2014

Study Design:

In vitro biomechanical study of cervical intervertebral distraction.

Objective:

To investigate the forces required for distraction to different heights in an in vitro C5–C6 anterior cervical distraction model, focusing on the influence of the intervertebral disk, posterior longitudinal ligament (PLL), and ligamentum flavum (LF).

Summary of Background Data:

No previous studies have reported on the forces required for distraction to various heights or the factors resisting distraction in anterior cervical discectomy and fusion.

Materials and Methods:

Anterior cervical distraction at C5–C6 was performed in 6 cadaveric specimens using a biomechanical testing machine, under 4 conditions: A, before disk removal; B, after disk removal; C, after disk and PLL removal; and D, after disk and PLL removal and cutting of the LF. Distraction was performed from 0 to 10 mm at a constant velocity (5 mm/min). Force and distraction height were recorded automatically.

Results:

The force required increased with distraction height under all 4 conditions. There was a sudden increase in force required at 6–7 mm under conditions B and C, but not D. Under condition A, distraction to 5 mm required a force of 268.3±38.87 N. Under conditions B and C, distraction to 6 mm required <15 N, and further distraction required dramatically increased force, with distraction to 10 mm requiring 115.4±10.67 and 68.4±9.67 N, respectively. Under condition D, no marked increase in force was recorded.

Conclusions:

Distraction of the intervertebral space was much easier after disk removal. An intact LF caused a sudden marked increase in the force required for distraction, possibly indicating the point at which the LF was fully stretched. This increase in resistance may help to determine the optimal distraction height to avoid stress to the endplate spacer.
Angiosarcoma of the Eyelid With Superimposed Enterobacter Infection
Authors: Hamill Eric B. , Agrawal Megha , Diwan A Hafeez , Winthrop Kevin L. , Marx Douglas P.
Published: August 2014

Angiosarcoma is a rare, aggressive, malignant endothelial neoplasm with a variable clinical presentation. The authors describe a case of angiosarcoma involving the eyelid that was complicated by a superimposed Enterobacter infection. Following positive cultures for E. aerogenes and multiple biopsies suspicious but not definitive for angiosarcoma, a final biopsy was consistent with angiosarcoma.
Friedrich Ernst Peter Hirzebruch. 17 October 1927 — 27 May 2012
Authors: Atiyah Sir Michael
Published: August 2014

Friedrich Hirzebruch was the outstanding mathematician of postwar Germany, who made Bonn a great international mathematical centre.
Mechanistic adaptability of cancer cells strongly affects anti-migratory drug efficacy
Authors: Sun Wei , Lim Chwee Teck , Kurniawan Nicholas Agung
Published: August 2014

Cancer metastasis involves the dissemination of cancer cells from the primary tumour site and is responsible for the majority of solid tumour-related mortality. Screening of anti-metastasis drugs often includes functional assays that examine cancer cell invasion inside a three-dimensional hydrogel that mimics the extracellular matrix (ECM). Here, we built a mechanically tuneable collagen hydrogel model to recapitulate cancer spreading into heterogeneous tumour stroma and monitored the three-dimensional invasion of highly malignant breast cancer cells, MDA-MB-231. Migration assays were carried out in the presence and the absence of drugs affecting four typical molecular mechanisms involved in cell migration, as well as under five ECMs with different biophysical properties. Strikingly, the effects of the drugs were observed to vary strongly with matrix mechanics and microarchitecture, despite the little dependence of the inherent cancer cell migration on the ECM condition. Specifically, cytoskeletal contractility-targeting drugs reduced migration speed in sparse gels, whereas migration in dense gels was retarded effectively by inhibiting proteolysis. The results corroborate the ability of cancer cells to switch their multiple invasion mechanisms depending on ECM condition, thus suggesting the importance of factoring in the biophysical properties of the ECM in anti-metastasis drug screenings.
Interaction of a screw dislocation with a nano-sized, arbitrarily shaped inhomogeneity with interface stresses under anti-plane deformations
Authors: Wang Xu , Schiavone Peter
Published: August 2014

We propose an elegant and concise general method for the solution of a problem involving the interaction of a screw dislocation and a nano-sized, arbitrarily shaped, elastic inhomogeneity in which the contribution of interface/surface elasticity is incorporated using a version of the Gurtin–Murdoch model. The analytic function inside the arbitrarily shaped inhomogeneity is represented in the form of a Faber series. The real periodic function arising from the contribution of the surface mechanics is then expanded as a Fourier series. The resulting system of linear algebraic equations is solved through the use of simple matrix algebra. When the elastic inhomogeneity represents a hole, our solution method simplifies considerably. Furthermore, we undertake an analytical investigation of the challenging problem of a screw dislocation interacting with two closely spaced nano-sized holes of arbitrary shape in the presence of surface stresses. Our solutions quite clearly demonstrate that the induced elastic fields and image force acting on the dislocation are indeed size-dependent.
Convective stability of carbon sequestration in anisotropic porous media
Authors: Hill A. A. , Morad M. R.
Published: August 2014

The stability of convection in an anisotropic porous medium, where the solute concentration is assumed to decay via a first-order chemical reaction, is studied. This is a simplified model for the interactions between carbon dioxide and brine in underground aquifers; the instability of which is essential in reducing reservoir mixing times. The key purpose of this paper is to explore the role porous media anisotropy plays in convective instabilities. It is shown that varying the ratio of horizontal to vertical solutal diffusivites does not significantly affect the behaviour of the instability. This is also the case for changes of permeability when the diffusion rate dominates the solute reaction rate. However, interestingly, when the solute reaction rate dominates the diffusion rate a change in the permeability of the porous material does have a substantial effect on the instability of the system. The region of potential subcritical instabilities is shown to be negligible, which further supports the novel instability behaviour.
Be meek or be bold? A colony-level behavioural syndrome in ants
Authors: Bengston S. E. , Dornhaus A.
Published: August 2014

Consistent individual variation in animal behaviour is nearly ubiquitous and has important ecological and evolutionary implications. Additionally, suites of behavioural traits are often correlated, forming behavioural syndromes in both humans and other species. Such syndromes are often described by testing for variation in traits across commonly described dimensions (e.g. aggression and neophobia), independent of whether this variation is ecologically relevant to the focal species. Here, we use a variety of ecologically relevant behavioural traits to test for a colony-level behavioural syndrome in rock ants (
Temnothorax rugatulus
). Specifically, we combine field and laboratory assays to measure foraging effort, how colonies respond to different types of resources, activity level, response to threat and aggression level. We find evidence for a colony level syndrome that suggests colonies consistently differ in coping style—some are more risk-prone, whereas others are more risk-averse. Additionally, by collecting data across the North American range of this species, we show that environmental variation may affect how different populations maintain consistent variation in colony behaviour.
Senescence or selective disappearance? Age trajectories of body mass in wild and captive populations of a small-bodied primate
Authors: Hämäläinen Anni , Dammhahn Melanie , Aujard Fabienne , Eberle Manfred , Hardy Isabelle , Kappeler Peter M. , Perret Martine , Schliehe-Diecks Susanne , Kraus Cornelia
Published: August 2014

Classic theories of ageing consider extrinsic mortality (EM) a major factor in shaping longevity and ageing, yet most studies of functional ageing focus on species with low EM. This bias may cause overestimation of the influence of senescent declines in performance over condition-dependent mortality on demographic processes across taxa. To simultaneously investigate the roles of functional senescence (FS) and intrinsic, extrinsic and condition-dependent mortality in a species with a high predation risk in nature, we compared age trajectories of body mass (BM) in wild and captive grey mouse lemurs (
Microcebus murinus
) using longitudinal data (853 individuals followed through adulthood). We found evidence of non-random mortality in both settings. In captivity, the oldest animals showed senescence in their ability to regain lost BM, whereas no evidence of FS was found in the wild. Overall, captive animals lived longer, but a reversed sex bias in lifespan was observed between wild and captive populations. We suggest that even moderately condition-dependent EM may lead to negligible FS in the wild. While high EM may act to reduce the average lifespan, this evolutionary process may be counteracted by the increased fitness of the long-lived, high-quality individuals.
The geomagnetic environment in which sea turtle eggs incubate affects subsequent magnetic navigation behaviour of hatchlings
Authors: Fuxjager Matthew J. , Davidoff Kyla R. , Mangiamele Lisa A. , Lohmann Kenneth J.
Published: August 2014

Loggerhead sea turtle hatchlings (Caretta caretta) use regional magnetic fields as open-ocean navigational markers during trans-oceanic migrations. Little is known, however, about the ontogeny of this behaviour. As a first step towards investigating whether the magnetic environment in which hatchlings develop affects subsequent magnetic orientation behaviour, eggs deposited by nesting female loggerheads were permitted to developin situeither in the natural ambient magnetic field or in a magnetic field distorted by magnets placed around the nest. In orientation experiments, hatchlings that developed in the normal ambient field oriented approximately south when exposed to a field that exists near the northern coast of Portugal, a direction consistent with their migratory route in the northeastern Atlantic. By contrast, hatchlings that developed in a distorted magnetic field had orientation indistinguishable from random when tested in the same north Portugal field. No differences existed between the two groups in orientation assays involving responses to orbital movements of waves or sea-finding, neither of which involves magnetic field perception. These findings, to our knowledge, demonstrate for the first time that the magnetic environment present during early development can influence the magnetic orientation behaviour of a neonatal migratory animal.
Evolution of positive and negative density-dependent dispersal
Authors: Rodrigues António M. M. , Johnstone Rufus A.
Published: August 2014

Understanding the evolution of density-dependent dispersal strategies has been a major challenge for evolutionary ecologists. Some existing models suggest that selection should favour positive and others negative density-dependence in dispersal. Here, we develop a general model that shows how and why selection may shift from positive to negative density-dependence in response to key ecological factors, in particular the temporal stability of the environment. We find that in temporally stable environments, particularly with low dispersal costs and large group sizes, habitat heterogeneity selects for negative density-dependent dispersal, whereas in temporally variable environments, particularly with high dispersal costs and small group sizes, habitat heterogeneity selects for positive density-dependent dispersal. This shift reflects the changing balance between the greater competition for breeding opportunities in more productive patches, versus the greater long-term value of offspring that establish themselves there, the latter being very sensitive to the temporal stability of the environment. In general, dispersal of individuals out of low-density patches is much more sensitive to habitat heterogeneity than is dispersal out of high-density patches.
The evolution of scarab beetles tracks the sequential rise of angiosperms and mammals
Authors: Ahrens Dirk , Schwarzer Julia , Vogler Alfried P.
Published: August 2014

Extant terrestrial biodiversity arguably is driven by the evolutionary success of angiosperm plants, but the evolutionary mechanisms and timescales of angiosperm-dependent radiations remain poorly understood. The Scarabaeoidea is a diverse lineage of predominantly plant- and dung-feeding beetles. Here, we present a phylogenetic analysis of Scarabaeoidea based on four DNA markers for a taxonomically comprehensive set of specimens and link it to recently described fossil evidence. The phylogeny strongly supports multiple origins of coprophagy, phytophagy and anthophagy. The ingroup-based fossil calibration of the tree widely confirmed a Jurassic origin of the Scarabaeoidea crown group. The crown groups of phytophagous lineages began to radiate first (Pleurostict scarabs: 108 Ma; Glaphyridae between 101 Ma), followed by the later diversification of coprophagous lineages (crown-group age Scarabaeinae: 76 Ma; Aphodiinae: 50 Ma). Pollen feeding arose even later, at maximally 62 Ma in the oldest anthophagous lineage. The clear time lag between the origins of herbivores and coprophages suggests an evolutionary path driven by the angiosperms that first favoured the herbivore fauna (mammals and insects) followed by the secondary radiation of the dung feeders. This finding makes it less likely that extant dung beetle lineages initially fed on dinosaur excrements, as often hypothesized.
In Silico Design of Self-Optimizing Integrated Metabolic and Gene Regulatory Networks
Authors: Maarleveld Timo R. , Ng Bennett K. , Sauro Herbert M. , Kim Kyung Hyuk
Published: August 2014

Biological organisms acclimatize to varying environmental conditions via active self-regulation of internal gene regulatory networks, metabolic networks, and protein signaling networks. While much work has been done to elucidate the topologies of individual networks in isolation, understanding of inter-network regulatory mechanisms remains limited. This shortcoming is of particular relevance to synthetic biology. Synthetic biological circuits tend to lose their engineered functionality over generational time, primarily due to the deleterious stress that they exert on their host organisms. To reduce this stress (and thus minimize loss of functionality) synthetic circuits must be sensitive to the health of the host organism. Development of integrated regulatory systems is therefore essential to robust synthetic biological systems. The aim of this study was to develop integrated gene-regulatory and metabolic networks which self-optimize in response to varying environmental conditions. We performedin silicoevolution to develop such networks using a two-step approach: (1) We optimized metabolic networks given a constrained amount of available enzyme. Here, we found that a proportional relationship between flux control coefficients and enzyme mass holds in all linear sub-networks of branched networks, except those sub-networks which contain allosteric regulators. Network optimization was performed by iteratively redistributing enzyme until flux through the network was maximized. Optimization was performed for a range of boundary metabolite conditions to develop a profile of optimal enzyme distributions as a function of environmental conditions. (2) We generated and evolved randomized gene regulatory networks to modulate the enzymes of a target metabolic pathway. The objective of the gene regulatory networks was to produce the optimal distribution of metabolic network enzymes given specific boundary metabolite conditions of the target network. Competitive evolutionary algorithms were applied to optimize the specific structures and kinetic parameters of the gene regulatory networks. With this method, we demonstrate the possibility of algorithmic development of integrated adaptive gene and metabolic regulatory networks which dynamically self-optimize in response to changing environmental conditions.
Cell fate inclination within 2-cell and 4-cell mouse embryos revealed by single-cell RNA sequencing
Authors: Biase Fernando H. , Cao Xiaoyi , Zhong Sheng
Published: August 2014

It remains an open question when and how the first cell fate decision is made in mammals. Using deep single-cell RNA-seq of matched sister blastomeres, we report highly reproducible inter-blastomere differences among 10 2-cell and five 4-cell mouse embryos. Inter-blastomere gene expression differences dominated between-embryo differences and noise, and were sufficient to cluster sister blastomeres into distinct groups. Dozens of protein-coding genes exhibited reproducible bimodal expression in sister blastomeres, which cannot be explained by random fluctuations. The protein expression of one gene out of four of these bimodal genes tested, Gadd45a, exhibited clear inter-blastomeric contrasts. We traced some of the bimodal mRNA expressions to embryonic genome activation, and others to blastomere-specific RNA depletion. Inter-blastomere differences created coexpression gene networks that were much stronger and larger than those that can possibly be created by random noise. The highly correlated gene pairs at the 4-cell stage overlapped with those showing the same directions of differential expression between inner cell mass (ICM) and trophectoderm (TE). These data substantiate the hypothesis of inter-blastomere differences in 2- and 4-cell mouse embryos, and associate these differences with ICM/TE differences.
Leaf Vein Length per Unit Area Is Not Intrinsically Dependent on Image Magnification: Avoiding Measurement Artifacts for Accuracy and Precision
Authors: Sack Lawren , Caringella Marissa , Scoffoni Christine , Mason Chase , Rawls Michael , Markesteijn Lars , Poorter Lourens
Published: August 2014

Leaf vein length per unit leaf area (VLA; also known as vein density) is an important determinant of water and sugar transport, photosynthetic function, and biomechanical support. A range of software methods are in use to visualize and measure vein systems in cleared leaf images; typically, users locate veins by digital tracing, but recent articles introduced software by which users can locate veins using thresholding (i.e. based on the contrasting of veins in the image). Based on the use of this method, a recent study argued against the existence of a fixed VLA value for a given leaf, proposing instead that VLA increases with the magnification of the image due to intrinsic properties of the vein system, and recommended that future measurements use a common, low image magnification for measurements. We tested these claims with new measurements using the software LEAFGUI in comparison with digital tracing using ImageJ software. We found that the apparent increase of VLA with magnification was an artifact of (1) using low-quality and low-magnification images and (2) errors in the algorithms of LEAFGUI. Given the use of images of sufficient magnification and quality, and analysis with error-free software, the VLA can be measured precisely and accurately. These findings point to important principles for improving the quantity and quality of important information gathered from leaf vein systems.
High-dynamic-range coherent diffractive imaging: ptychography using the mixed-mode pixel array detector
Authors: Giewekemeyer Klaus , Philipp Hugh T. , Wilke Robin N. , Aquila Andrew , Osterhoff Markus , Tate Mark W. , Shanks Katherine S. , Zozulya Alexey V. , Salditt Tim , Gruner Sol M. , Mancuso Adrian P.
Published: August 2014

Coherent (X-ray) diffractive imaging (CDI) is an increasingly popular form of X-ray microscopy, mainly due to its potential to produce high-resolution images and the lack of an objective lens between the sample and its corresponding imaging detector. One challenge, however, is that very high dynamic range diffraction data must be collected to produce both quantitative and high-resolution images. In this work, hard X-ray ptychographic coherent diffractive imaging has been performed at the P10 beamline of the PETRA III synchrotron to demonstrate the potential of a very wide dynamic range imaging X-ray detector (the Mixed-Mode Pixel Array Detector, or MM-PAD). The detector is capable of single photon detection, detecting fluxes exceeding 1 × 1088-keV photons pixel−1s−1, and framing at 1 kHz. A ptychographic reconstruction was performed using a peak focal intensity on the order of 1 × 1010 photons µm−2s−1within an area of approximately 325 nm × 603 nm. This was done without need of a beam stop and with a very modest attenuation, while `still' images of the empty beam far-field intensity were recorded without any attenuation. The treatment of the detector frames and CDI methodology for reconstruction of non-sensitive detector regions, partially also extending the active detector area, are described.
A prominent stepwise advance of the tree line in north‐east Finland
Authors: Aakala Tuomas , Hari Pertti , Dengel Sigrid , Newberry Sarah L. , Mizunuma Toshie , Grace John
Published: August 2014

The elevational limit of trees (henceforth, the ‘tree line’) is widely considered to be a sensitive indicator of environmental change. Here, we document the 20th century tree line advance and increase in the tree population at the tree line ecotone, along a Pinus sylvestris‐dominated slope in north‐eastern Finland, in conditions where growth and recruitment have generally been linked to temperature variation.

Using tree recruitment ages (growth to 1.3 m height) along an elevational transect, we compared recruitment to variation in environmental conditions associated with tree line dynamics, seed and cone crops, and reindeer densities. We further investigated the relationships among temperature and tree‐level growth variables.

Results show the existence of a former tree line at approximately 400 m a.s.l. and an advance of trees that began in the 1920s and reached the top of the fell (at 470 m a.s.l.) in the 1980s. During this time, the population density of P. sylvestris increased from 4 to 468 trees within the 5.6 ha study plot. Needle and shoot lengths were positively related to air temperature but recruitment was not.

Average rate of P. sylvestris advance over the 20th century was consistent with earlier studies, but the temporal patterns of both upslope advance and population density increase were unexpected: both were characterized by a strongly stepwise pattern, culminating in a rapid advance and density increase in the 1970–1980s, and returning to low levels in the 1990s.

Despite a positive relationship between growth and temperature variables at the tree level, climatic variables, or seed and cone crops were inconsistent with recruitment patterns. For most part of the 20th century, the increase corresponded to the gradual atmospheric CO2 increase, but of the variables screened only the changes in reindeer densities coincided with the stepwise pattern.

Synthesis. Our results confirmed the connection between tree‐level processes and temperature variability as expected from earlier studies. However, recruitment was not correlated with any of the environmental variables. Our findings point towards complex tree line dynamics, in which biotic agents may play a major role in mediating tree line response to environmental change.
The Effect of Teaching Parliamentary Studies on Students' Knowledge and Attitudes: A Pilot Study
Authors: Cowley Philip , Stuart Mark
Published: August 2014

The Westminster Parliament has recently invested considerable resource in developing a series of ‘Parliamentary Studies’ modules throughout British universities. But what difference does the teaching of Parliament make to students' understanding of the institution? In this pilot study, the results of a series of questions about the institution (both factual and attitudinal) which are asked at the beginning of the module are compared with the results of the same questions asked towards the end of teaching. Increases in levels of both knowledge and support are discovered.