bluuebunny/crossref_metadata_2025 huggingface dataset:
Planetary (Rossby) waves and inertia–gravity (Poincaré) waves in a barotropic ocean over a sphere
Authors: Paldor Nathan , De-Leon Yair , Shamir Ofer
Published: June 2013

The construction of approximate Schrödinger eigenvalue equations for planetary (Rossby) waves and for inertia–gravity (Poincaré) waves on an ocean-covered rotating sphere yields highly accurate estimates of the phase speeds and meridional variation of these waves. The results are applicable to fast rotating spheres such as Earth where the speed of barotropic gravity waves is smaller than twice the tangential speed on the equator of the rotating sphere. The implication of these new results is that the phase speed of Rossby waves in a barotropic ocean that covers an Earth-like planet is independent of the speed of gravity waves for sufficiently large zonal wavenumber and (meridional) mode number. For Poincaré waves our results demonstrate that the dispersion relation is linear, (so the waves are non-dispersive and the phase speed is independent of the wavenumber), except when the zonal wavenumber and the (meridional) mode number are both near 1.
COMPLEMENT OF THE ZERO DIVISOR GRAPH OF A LATTICE
Authors: JOSHI VINAYAK , KHISTE ANAGHA
Published: June 2013

In this paper, we determine when $\mathop{({\Gamma }_{I} (L))}\nolimits ^{c} $, the complement of the zero divisor graph ${\Gamma }_{I} (L)$ with respect to a semiprime ideal $I$ of a lattice $L$, is connected and also determine its diameter, radius, centre and girth. Further, a form of Beck’s conjecture is proved for ${\Gamma }_{I} (L)$ when $\omega (\mathop{({\Gamma }_{I} (L))}\nolimits ^{c} )\lt \infty $.
THE CONLEY ATTRACTORS OF AN ITERATED FUNCTION SYSTEM
Authors: BARNSLEY MICHAEL F. , VINCE ANDREW
Published: June 2013

We investigate the topological and metric properties of attractors of an iterated function system (IFS) whose functions may not be contractive. We focus, in particular, on invertible IFSs of finitely many maps on a compact metric space. We rely on ideas of Kieninger [Iterated Function Systems on Compact Hausdorff Spaces (Shaker, Aachen, 2002)] and McGehee and Wiandt [‘Conley decomposition for closed relations’, Differ. Equ. Appl. 12 (2006), 1–47] restricted to what is, in many ways, a simpler setting, but focused on a special type of attractor, namely point-fibred invariant sets. This allows us to give short proofs of some of the key ideas.
Giant cell reparative granuloma of the temporal bone successfully resected with preservation of hearing
Authors: Takata Y , Hidaka H , Ishida K , Kobayashi T
Published: June 2013

Objective:

To describe a case of giant cell reparative granuloma of the temporal bone which extended into the middle-ear cavity, and which was successfully treated surgically via a transmastoid approach, with hearing preservation.

Case:

A 37-year-old man presented with a one-year history of right-sided hearing loss, complicated by a three-month history of otalgia and a sensation of aural fullness. Computed tomography and magnetic resonance imaging demonstrated an osteolytic tumour lesion in the right temporal bone. The diagnosis was confirmed by biopsy from the mastoid lesion.

Investigation and intervention:

Pure-tone audiometry, computed tomography and magnetic resonance imaging were conducted, followed by total resection.

Result:

The giant cell reparative granuloma of the temporal bone was completely resected, with preservation of hearing.

Conclusion:

Although this patient's giant cell reparative granuloma of the temporal bone extended into the middle-ear cavity, total resection was achieved, with preservation of hearing. To the best of our knowledge, hearing preservation following resection of giant cell reparative granuloma of the temporal bone has not previously been reported.
Comparison of the crop speciesBrassica napusand wildB. rapa: characteristics relevant for building up a persistent seed bank in the soil
Authors: de Jong Tom J. , Tudela Isanta Maria , Hesse Elze
Published: June 2013

Can seed characters be used for predicting the presence of a persistent seed bank in the field? We address this question using ten cultivars of the cropBrassica napus, ten feralB. napusaccessions originating from seeds collected in the field and nine accessions of the closely related ruderal speciesBrassica rapa. When buried for a year in the field, seeds of the wildB. rapadisplayed, as expected, much higher survival fractions than those of domesticatedB. napusat two different locations in The Netherlands. Compared toB. napus, B. rapaproduces relatively small seeds with high levels of aliphatic glucosinolates and a thick seed coat. However, within each species none of these characters correlated with seed survival in the soil. At low temperatures,B. rapaseeds had lower and more variable germination fractions than those ofB. napus; a small fraction (4.6%) of theB. rapaseeds showed primary dormancy. Rather surprisingly,B. napusdisplayed genetic differences in germination at low temperature, and germination fractions at 5°C correlated negatively with seed survival in the soil. Our comparisons between and within the two species suggest that foregoing germination at low temperatures is an important character for developing a persistent seed bank. We discuss our results in light of environmental risk assessment of genetically modifiedB. napus.
Freiman Homomorphisms of Random Subsets of
Authors: PONTIVEROS GONZALO FIZ
Published: June 2013

Given a set $A\subset\mathbb{Z}_{N}$, we say that a function $f\colon A \to \mathbb{Z}_{N}$ is a Freiman homomorphism if f(a)+f(b)=f(c)+f(d) whenever a,b,c,d ∈ A satisfy a+b=c+d. This notion was introduced by Freiman in the 1970s, and plays an important role in the field of additive combinatorics. We say that A is linear if the only Freiman homomorphisms are functions of the form f(x) = ax+b.

Suppose the elements of A are chosen independently at random, each with probability p. We shall look at the following question: For which values of p=p(N) is A linear with high probability as N → ∞? We show that if p=(2logN − ω(N))1/3N−2/3, where ω(N) → ∞ as N → ∞, then A is not linear with high probability, whereas if p=N−1/2+ε for any ε>0 then A is linear with high probability.
NEW PERSPECTIVES ON DEPRECIATION SHOCKS AS A SOURCE OF BUSINESS CYCLE FLUCTUATIONS
Authors: Furlanetto Francesco , Seneca Martin
Published: June 2013

In this paper we study the transmission of capital depreciation shocks. The existing literature in the real business cycle tradition has concluded that these shocks are irrelevant to business cycle fluctuations. We show that they are potentially important drivers of aggregate fluctuations in a new Keynesian model. Nominal rigidities and some persistence in the shock process are the key ingredients that generate co-movement across real variables.
Large-signal characterization of DDR silicon IMPATTs operating up to 0.5 THz
Authors: Acharyya Aritra , Chakraborty Jit , Das Kausik , Datta Subir , De Pritam , Banerjee Suranjana , Banerjee J.P.
Published: June 2013

Large-signal (L-S) characterization of double-drift region (DDR) impact avalanche transit time (IMPATT) devices based on silicon designed to operate at different millimeter-wave (mm-wave) and terahertz (THz) frequencies up to 0.5 THz is carried out in this paper using an L-S simulation method developed by the authors based on non-sinusoidal voltage excitation (NSVE) model. L-S simulation results show that the device is capable of delivering peak RF power of 657.64 mW with 8.25% conversion efficiency at 94 GHz for 50% voltage modulation; whereas RF power output and efficiency reduce to 89.61 mW and 2.22% respectively at 0.5 THz for same voltage modulation. Effect of parasitic series resistance on the L-S properties of DDR Si IMPATTs is also investigated, which shows that the decrease in RF power output and conversion efficiency of the device due to series resistance is more pronounced at higher frequencies especially at the THz regime. The NSVE L-S simulation results are compared with well established double-iterative field maximum (DEFM) small-signal (S-S) simulation results and finally both are compared with the experimental results. The comparative study shows that the proposed NSVE L-S simulation results are in closer agreement with experimental results as compared to those of DEFM S-S simulation.
A Short History of English Literature
Authors: Nayar Pramod K.
Published: June 2013

A History of English Literature is a comprehensive survey, in chronological fashion, of the major periods, authors and movements from Chaucer to the present. Written for undergraduate and postgraduate students in South Asian universities, this History locates authors, genres and developments within their social, political and historical contexts. Informed by contemporary literary and cultural theory, this account also prepares the student for further explorations in particular genres and periods in English literature.
Primary sensory cortices contain distinguishable spatial patterns of activity for each sense
Authors: Liang M. , Mouraux A. , Hu L. , Iannetti G.D.
Published: June 2013

Whether primary sensory cortices are essentially multisensory or whether they respond to only one sense is an emerging debate in neuroscience. Here we use a multivariate pattern analysis of functional magnetic resonance imaging data in humans to demonstrate that simple and isolated stimuli of one sense elicit distinguishable spatial patterns of neuronal responses, not only in their corresponding primary sensory cortex, but in other primary sensory cortices. These results indicate that primary sensory cortices, traditionally regarded as unisensory, contain unique signatures of other senses and, thereby, prompt a reconsideration of how sensory information is coded in the human brain.
Hydrodynamic instabilities provide a generic route to spontaneous biomimetic oscillations in chemomechanically active filaments
Authors: Laskar Abhrajit , Singh Rajeev , Ghose Somdeb , Jayaraman Gayathri , Kumar P. B. Sunil , Adhikari R.
Published: June 2013

Non-equilibrium processes which convert chemical energy into mechanical motion enable the motility of organisms. Bundles of inextensible filaments driven by energy transduction of molecular motors form essential components of micron-scale motility engines like cilia and flagella. The mimicry of cilia-like motion in recent experiments on synthetic active filaments supports the idea that generic physical mechanisms may be sufficient to generate such motion. Here we show, theoretically, that the competition between the destabilising effect of hydrodynamic interactions induced by force-free and torque-free chemomechanically active flows and the stabilising effect of nonlinear elasticity, provides a generic route to spontaneous oscillations in active filaments. These oscillations, reminiscent of prokaryotic and eukaryotic flagellar motion, are obtained without having to invoke structural complexity or biochemical regulation. This minimality implies that biomimetic oscillations, previously observed only in complex bundles of active filaments, can be replicated in simple chains of generic chemomechanically active beads.
Low‐complexity multi‐standard variable length coding decoder using tree‐based partition and classification
Authors: Lo Chia‐Cheng , Hsu Chia‐Wei , Shieh Ming‐Der
Published: June 2013

MPEG‐2 and H.264/AVC use variable length coding (VLC) to remove statistical redundancy. Representing the codeword table efficiently is thus an important issue to reduce hardware complexity, especially for multi‐standard applications. In this study, the VLC tree is decomposed using sub‐tree classification. The proposed algorithm reduces the amount of storage required for codewords. The proposed MPEG‐2/H.264 VLC decoder has 11.9 K gates when synthesised to operate at 180 MHz. The gate count is 20% lower than the sum of gate count of individual H.264 and MPEG‐2 VLC decoders.
Superolateral Dislocation of Bilateral Intact Condyles—An Unusual Presentation: Report of a Case and Review of Literature
Authors: Singh Virendra , Gupta Pranav , Khatana Shruti , Bhagol Amrish
Published: June 2013

Dislocation of the mandibular condyle is the clinical condition of the condyle head being displaced out of the glenoid fossa but still remaining within the joint capsule. However, the anatomy of the mandibular condyle, glenoid fossa, and zygomatic arch usually prevent the dislocation of intact condyles out of the glenoid fossa whenever the mandible is subjected to high impact. Complete dislocation of the mandibular condyle from the glenoid fossa can be classified into four groups: anterior, posterior, lateral, and superior dislocation. All the groups except anterior dislocation are rare. Superolateral dislocation of the intact mandibular condyle occurs very rarely. We report a case of lateral dislocation of bilateral intact condyles associated with left parasymphysis fracture. The purpose of this report is to review all of the available English literature on this dislocation and discuss the possible causative mechanism and diagnostic features, as well as clinical management.
Effect of dimethylaluminumhydride-derived aluminum oxynitride passivation layer on the interface chemistry and band alignment of HfTiO-InGaAs gate stacks
Authors: He Gang , Deng Bin , Chen Hanshuang , Chen Xiaoshuang , Lv Jianguo , Ma Yongqing , Sun Zhaoqi
Published: June 2013

In this letter, the reduction and removal of surface native oxide from as-received InGaAs surface by using dimethylaluminumhydride-derived aluminum oxynitride (AlON) passivation layer prior to HfTiO deposition is proposed to solve Fermi level pinning issue. It has been revealed that complete consumption of native oxides of AsOx and GaOx at the InGaAs surface, but no effect to InOx, has been realized after metalorganic chemical vapor deposition AlON at 300 °C. X-ray photoelectron spectroscopy observations of HfTiO/InGaAs gate stacks demonstrate that introducing AlON layer can suppress the regrowth of native oxide at the interface. In addition, the dependence of the valence band spectra of HfTiO/InGaAs gate stacks on AlON passivation layer has been discussed in detail.
Quantum defects at the critical charge
Authors: Katriel Jacob , Gaigalas Gediminas , Puchalski Mariusz
Published: June 2013

The quantum defect is an empirically introduced notion that has allowed convenient interpolations of spectral data along atomic isoelectronic sequences and their extrapolation with respect to the principal quantum number. Both yield valuable spectral information, the latter providing estimates of low-energy-electron elastic scattering phase shifts as well. We examine a recently proposed conjecture concerning the extrapolated value of the quantum defect along an isoelectronic sequence: If the binding energy of the outermost electron vanishes in the singly negative ion, then its asymptotic quantum defect is an integer whose value is equal to the number of occupied shells with the same orbital angular momentum. This behavior is associated with the fact, established by means of appropriate electronic structure calculations, that—asymptotically—the outermost orbital becomes an infinitely diffuse hydrogen-like orbital. In most cases explored the asymptotic behavior can be ascertained by analysis of spectral data along the appropriate isoelectronic sequence, but in some cases the approach to the asymptotic value takes place over a very narrow range of nuclear charge in the vicinity of that of the negative ion.
Experimental study of anti-resonant behavior of material parameters in periodic and aperiodic composite materials
Authors: Alitalo Pekka , Culhaoglu Ali E. , Simovski Constantin R. , Tretyakov Sergei A.
Published: June 2013

In the literature on composite materials with extreme or unusual electromagnetic properties (so-called metamaterials), it is common to retrieve the effective material parameters from the scattering parameters (complex reflection and transmission coefficients) of the metamaterial layer. Most often, this retrieval is done by using the well-known Nicolson-Ross-Weir method or its modifications. It is commonly known that one of the two effective parameters of many metamaterials retrieved in this way (either effective permittivity or permeability) exhibits the so-called anti-resonance, which is a nonphysical feature. This effect has been understood as a manifestation of spatial dispersion in the sample. Many previous works have either claimed or assumed that the anti-resonance is an effect caused by the periodicity of the composite material. To our knowledge, this claim was never supported by comparisons of periodical and random samples. In some other works, it has been theoretically shown that the anti-resonance of the retrieved material parameters can be avoided, e.g., by the introduction of additional surface parameters into the retrieval procedure. If it is so, the anti-resonance has nothing to do with the internal periodicity of the bulk medium. In the present work, we numerically and experimentally investigate the question if the internal periodicity of metamaterial layers is essential for the appearance of anti-resonances in extracted material parameters. We show that it is not so. Therefore, our result is in favor of the theory which treats the anti-resonance as a deficiency of the Nicolson-Ross-Weir retrieval procedure applied to spatially dispersive media.
Origin of giant permittivity and high-temperature dielectric anomaly behavior in Na0.5Y0.5Cu3Ti4O12 ceramics
Authors: Liang Pengfei , Li Yanyan , Zhao Yuqing , Wei Lingling , Yang Zupei
Published: June 2013

Na0.5Y0.5Cu3Ti4O12 ceramics prepared by the conventional solid-state reaction method under various sintering conditions were found to exhibit a giant dielectric constant over 10 000 around room temperature. Two electrical responses were observed in the combined modulus and impedance plots, indicating the presence of Maxwell-Wagner relaxation. The contributions of semiconducting grains and insulating grain boundaries (corresponding to high-frequency and low-frequency electrical response, respectively) played important roles in the dielectric properties of Na0.5Y0.5Cu3Ti4O12 ceramics. The correlations between grain boundaries resistance and low frequency dielectric loss, grains resistance and the position of dielectric loss peak were addressed. Mixed-valent structures of Cu2+/Cu3+ and Ti3+/Ti4+ had been determined using X-ray photoelectron spectroscopy. Electron hopping between Cu2+ and Cu3+ and electron transport in Ti3+–O–Ti4+ paths were proposed as the origin of the semiconducting nature of Na0.5Y0.5Cu3Ti4O12 ceramics. In particular, high-temperature dielectric anomaly behavior was investigated in detail. A dielectric peak exhibiting relaxor-like behavior was observed around 200 °C, which was linked with the formation of oxygen vacancies. Based on the electric modulus results, this behavior was explored in the light of the defect formation and explained in terms of a competition process depending on the combinational contribution to polarization between n- and p-type carriers rather than a relaxation process.
Reduction of structural defects in thick 4H-SiC epitaxial layers grown on 4° off-axis substrates
Authors: Yazdanfar M. , Ivanov I. G. , Pedersen H. , Kordina O. , Janzén E.
Published: June 2013

By carefully controlling the surface chemistry of the chemical vapor deposition process for silicon carbide (SiC), 100 μm thick epitaxial layers with excellent morphology were grown on 4° off-axis SiC substrates at growth rates exceeding 100 μm/h. In order to reduce the formation of step bunching and structural defects, mainly triangular defects, the effect of varying parameters such as growth temperature, C/Si ratio, Cl/Si ratio, Si/H2 ratio, and in situ pre-growth surface etching time are studied. It was found that an in-situ pre growth etch at growth temperature and pressure using 0.6% HCl in hydrogen for 12 min reduced the structural defects by etching preferentially on surface damages of the substrate surface. By then applying a slightly lower growth temperature of 1575 °C, a C/Si ratio of 0.8, and a Cl/Si ratio of 5, 100 μm thick, step-bunch free epitaxial layer with a minimum triangular defect density and excellent morphology could be grown, thus enabling SiC power device structures to be grown on 4° off axis SiC substrates.
Very high channel conductivity in ultra-thin channel N-polar GaN/(AlN, InAlN, AlGaN) high electron mobility hetero-junctions grown by metalorganic chemical vapor deposition
Authors: Lu Jing , Denninghoff Dan , Yeluri Ramya , Lal Shalini , Gupta Geetak , Laurent Matthew , Keller Stacia , DenBaars Steven P. , Mishra Umesh K.
Published: June 2013

Different back barrier designs comprising of AlN, AlGaN, and InAlN layers are investigated for ultra-thin GaN channel N-polar high-electron-mobility-transistors grown by metalorganic chemical vapor deposition. A combinational back barrier with both AlGaN and InAlN materials is proposed. The dependence of channel conductivity on channel thickness is investigated for different back barrier designs. The study demonstrated that the back barrier design of AlN/InAlN/AlGaN is capable of retaining high channel conductivity for ultra-scaled channel thicknesses. For devices with 5-nm-thick channel, a sheet resistance of ∼230 Ω/◻ and mobility ∼1400 cm2/V-s are achieved when measured parallel to the multi-step direction of the epi-surface.
Resonance line shape, strain and electric potential distributions of composite magnetoelectric sensors
Authors: Gerken Martina
Published: June 2013

Multiferroic composite magnetoelectric (ME) sensors are based on the elastic coupling of a magnetostrictive phase and a piezoelectric phase. A deformation of the magnetostrictive phase causes strain in the piezoelectric phase and thus an induced voltage. Such sensors may be applied both for static as well as for dynamic magnetic field measurements. Particularly high sensitivities are achieved for operation at a mechanical resonance. Here, the resonance line shape of layered (2-2 composite) cantilever ME sensors at the first bending-mode resonance is investigated theoretically. Finite element method (FEM) simulations using a linear material model reveal an asymmetric resonance profile and a zero-response frequency for the ME coefficient. Frequency-dependent strain and electric potential distributions inside the magnetoelectric composite are studied for the case of a magnetostrictive-piezoelectric bilayer. It is demonstrated that a positive or a negative voltage may be induced across the piezoelectric layer depending on the position of the neutral plane. The frequency-dependent induced electric potential is investigated for structured cantilevers that exhibit magnetostriction only at specific positions. For static operation an induced voltage is obtained locally at positions with magnetostriction. In addition to this direct effect a resonance-assisted effect is observed for dynamic operation. Magnetostriction in a limited area of the cantilever causes a global vibration of the cantilever. Thus, deformation of the piezoelectric layer and an induced electric potential also occur in areas of the cantilever without magnetostriction. The direct and the resonance-assisted pathway may induce voltages of equal or of opposite sign. The net induced voltage results from the superposition of the two effects. As the resonance-assisted induced voltage changes sign upon passing the resonance frequency, while the direct component is constant, an asymmetric line shape and a zero-response frequency result for the ME coefficient. The zero-response oscillator frequency may be below or above the resonance frequency. The calculated FEM resonance line shapes are fitted successfully to a superposition function of a constant component and a resonant component with a Lorentzian line shape. Equivalence of the superposition function line shape to a Fano resonance profile is derived for frequencies around the resonance. Fano resonances are ubiquitous in physics occurring due to the constructive and destructive quantum interference of two different scattering pathways, e.g., for photons or electrons. The superposition fit parameters describing the resonance line shape are calculated as a function of the cantilever substrate thickness. The inclusion of loss by adjustment of the damping parameter is discussed. The results derived here also are applicable to higher order modes or longitudinal resonance modes.
Two-dimensional electron gas generated by La-doping at SrTiO3(001) surface: A first-principles study
Authors: Li Yun , Yu Jaejun
Published: June 2013

We carried out first-principles calculations to study the electronic properties of SrO-terminated and TiO2-terminated SrTiO3(001) surfaces with La-doping at the surface. We find that an intrinsic lower-lying state at the SrO-terminated surface can accommodate a two-dimensional electron gas (2DEG). By introducing La-doping at the SrO-terminated surface the energy position of the surface state and the 2DEG density can be tuned by changing the doping concentration. The higher the La-doping concentration, the lower the lower-lying state and the higher the 2DEG density. This 2DEG has a small effective mass and hopefully shows a high mobility.
Examination of the wind speed limit function in the Rothermel surface fire spread model
Authors: Andrews Patricia L. , Cruz Miguel G. , Rothermel Richard C.
Published: June 2013

The Rothermel surface fire spread model includes a wind speed limit, above which predicted rate of spread is constant. Complete derivation of the wind limit as a function of reaction intensity is given, along with an alternate result based on a changed assumption. Evidence indicates that both the original and the revised wind limits are too restrictive. Wind limit is based in part on data collected on the 7 February 1967 Tasmanian grassland fires. A reanalysis of the data indicates that these fires might not have been spreading in fully cured continuous grasslands, as assumed. In addition, more recent grassfire data do not support the wind speed limit. The authors recommend that, in place of the current wind limit, rate of spread be limited to effective midflame wind speed. The Rothermel model is the foundation of many wildland fire modelling systems. Imposition of the wind limit can significantly affect results and potentially influence fire and fuel management decisions.
Techniques for optimising long-term, large-scale capture–mark–resighting raptor studies: climb hard, band fast
Authors: Hurley Victor G. , White John G. , Cooke Raylene
Published: June 2013

Context
Efficiency of large-scale capture–mark–recapture (CMR) studies can be improved by developing accurate methods for predicting the window of opportunity in which banding can occur.

Aims
This research aimed to investigate potential efficiency improvements in a long-term CMR raptor study. The research focussed on: (1) developing selection processes for adopting CMR protocols; (2) testing methods for increasing the number of nestlings successfully banded; and (3) assessing the efficacy of visual identification (VID) bands for collecting re-sight data.

Methods
Ten selection criteria were developed into a robust CMR-technique selection process and used to assess marking techniques commonly applied to birds. Optimising banding effort by predicting banding dates using two different techniques a priori and a posteriori were tested against a traditional approach to the timing of banding. The cost (in time) to collect resight data at an active nest site was also measured.

Key results
The CMR selection criteria and parameters provided a transparent selection process and scored metal VID bands the highest for the study design. This provided individual recognition of marked birds up to the expected life-span of 14 years. Both techniques for predicting banding dates improved the proportion of whole clutches banded by 40%. The average time to identify both peregrine falcon adults of a breeding pair wearing VID bands was 30 min.

Conclusions
The two methods described here for predicting preferred banding dates are of particular value as efficient approaches to banding large numbers of nestlings are key to the success of CMR studies. All of the methods developed in this research can be applied to CMR studies of almost any bird species with a predictable seasonal breeding system.

Implications
Optimisation and cost effectiveness of CMR studies for seasonal breeding birds can be significantly improved by accurately predicting the window of opportunity in which banding of nestlings can be carried out, and also utilising VID colour bands for rapid collection of recapture data.
Osmotic stress does not trigger brevetoxin production in the dinoflagellateKarenia brevis
Authors: Sunda William G. , Burleson Cheska , Hardison D. Ransom , Morey Jeanine S. , Wang Zhihong , Wolny Jennifer , Corcoran Alina A. , Flewelling Leanne J. , Van Dolah Frances M.
Published: June 2013

With the global proliferation of toxic harmful algal bloom species, there is a need to identify the environmental and biological factors that regulate toxin production. One such species,Karenia brevis, forms nearly annual blooms that threaten coastal regions throughout the Gulf of Mexico. This dinoflagellate produces brevetoxins, which are potent neurotoxins that cause neurotoxic shellfish poisoning and respiratory illness in humans, as well as massive fish kills. A recent publication reported that a rapid decrease in salinity increased cellular toxin quotas inK. brevisand hypothesized that brevetoxins serve a role in osmoregulation. This finding implied that salinity shifts could significantly alter the toxic effects of blooms. We repeated the original experiments separately in three different laboratories and found no evidence for increased brevetoxin production in response to low-salinity stress in any of the eightK. brevisstrains we tested, including three used in the original study. Thus, we find no support for an osmoregulatory function of brevetoxins. The original publication also stated that there was no known cellular function for brevetoxins. However, there is increasing evidence that brevetoxins promote survival of the dinoflagellates by deterring grazing by zooplankton. Whether they have other as-yet-unidentified cellular functions is currently unknown.
SlmA forms a higher-order structure on DNA that inhibits cytokinetic Z-ring formation over the nucleoid
Authors: Tonthat Nam K. , Milam Sara L. , Chinnam Nagababu , Whitfill Travis , Margolin William , Schumacher Maria A.
Published: June 2013

The spatial and temporal control of Filamenting temperature sensitive mutant Z (FtsZ) Z-ring formation is crucial for proper cell division in bacteria. In
Escherichia coli
, the synthetic lethal with a defective Min system (SlmA) protein helps mediate nucleoid occlusion, which prevents chromosome fragmentation by binding FtsZ and inhibiting Z-ring formation over the nucleoid. However, to perform its function, SlmA must be bound to the nucleoid. To deduce the basis for this chromosomal requirement, we performed biochemical, cellular, and structural studies. Strikingly, structures show that SlmA dramatically distorts DNA, allowing it to bind as an orientated dimer-of-dimers. Biochemical data indicate that SlmA dimer-of-dimers can spread along the DNA. Combined structural and biochemical data suggest that this DNA-activated SlmA oligomerization would prevent FtsZ protofilament propagation and bundling. Bioinformatic analyses localize SlmA DNA sites near membrane-tethered chromosomal regions, and cellular studies show that SlmA inhibits FtsZ reservoirs from forming membrane-tethered Z rings. Thus, our combined data indicate that SlmA DNA helps block Z-ring formation over chromosomal DNA by forming higher-order protein-nucleic acid complexes that disable FtsZ filaments from coalescing into proper structures needed for Z-ring creation.
Strain history dependence of the nonlinear stress response of fibrin and collagen networks
Authors: Münster Stefan , Jawerth Louise M. , Leslie Beverly A. , Weitz Jeffrey I. , Fabry Ben , Weitz David A.
Published: June 2013

We show that the nonlinear mechanical response of networks formed from un–cross-linked fibrin or collagen type I continually changes in response to repeated large-strain loading. We demonstrate that this dynamic evolution of the mechanical response arises from a shift of a characteristic nonlinear stress–strain relationship to higher strains. Therefore, the imposed loading does not weaken the underlying matrices but instead delays the occurrence of the strain stiffening. Using confocal microscopy, we present direct evidence that this behavior results from persistent lengthening of individual fibers caused by an interplay between fiber stretching and fiber buckling when the networks are repeatedly strained. Moreover, we show that covalent cross-linking of fibrin or collagen inhibits the shift of the nonlinear material response, suggesting that the molecular origin of individual fiber lengthening may be slip of monomers within the fibers. Thus, a fibrous architecture in combination with constituents that exhibit internal plasticity creates a material whose mechanical response adapts to external loading conditions. This design principle may be useful to engineer novel materials with this capability.
Justice- and fairness-related behaviors in nonhuman primates
Authors: Brosnan Sarah F.
Published: June 2013

A distinctive feature across human societies is our interest in justice and fairness. People will sometimes invest in extremely costly behavior to achieve fair outcomes for themselves and others. Why do people care so much about justice? One way to address this is comparatively, exploring behaviors related to justice and fairness in other species. In this paper, I review work exploring responses to inequity, prosocial behavior, and other relevant behaviors in nonhuman primates in an effort to understand both the potential evolutionary function of these behaviors and the social and ecological reasons for the individual differences in behavior. I also consider how these behaviors relate to human behavior, particularly in the case of experimental studies using games derived from experimental economics to compare nonhuman primates’ responses to those of humans in similar experimental conditions. These results emphasize the importance of a comparative approach to better understand the function and diversity of human behavior.
Making lasting memories: Remembering the significant
Authors: McGaugh James L.
Published: June 2013

Although forgetting is the common fate of most of our experiences, much evidence indicates that emotional arousal enhances the storage of memories, thus serving to create, selectively, lasting memories of our more important experiences. The neurobiological systems mediating emotional arousal and memory are very closely linked. The adrenal stress hormones epinephrine and corticosterone released by emotional arousal regulate the consolidation of long-term memory. The amygdala plays a critical role in mediating these stress hormone influences. The release of norepinephrine in the amygdala and the activation of noradrenergic receptors are essential for stress hormone-induced memory enhancement. The findings of both animal and human studies provide compelling evidence that stress-induced activation of the amygdala and its interactions with other brain regions involved in processing memory play a critical role in ensuring that emotionally significant experiences are well-remembered. Recent research has determined that some human subjects have highly superior autobiographic memory of their daily experiences and that there are structural differences in the brains of these subjects compared with the brains of subjects who do not have such memory. Understanding of neurobiological bases of such exceptional memory may provide additional insights into the processes underlying the selectivity of memory.
Affiliation, empathy, and the origins of theory of mind
Authors: Seyfarth Robert M. , Cheney Dorothy L.
Published: June 2013

To understand the evolution of a Theory of Mind, we need to understand the selective factors that might have jumpstarted its initial evolution. We argue that a subconscious, reflexive appreciation of others’ intentions, emotions, and perspectives is at the roots of even the most complex forms of Theory of Mind and that these abilities may have evolved because natural selection has favored individuals that are motivated to empathize with others and attend to their social interactions. These skills are adaptive because they are essential to forming strong, enduring social bonds, which in turn enhance reproductive success. We first review evidence from both humans and other animals indicating that reflexive and reflective mental state attributions are inextricably linked and play a crucial role in promoting affiliative social bonds. We next describe results from free-ranging female baboons showing that individuals who show high rates of affiliative behavior form stronger social bonds with other females. These bonds, in turn, are linked to fitness. We then provide data from three different types of social challenges (male immigration, changes in grooming behavior after the death of a close relative, and responses during playback experiments), suggesting that females who manifest high rates of affiliative behavior may also be more motivated to anticipate challenges, react adaptively to setbacks, and respond appropriately to social interactions.
Similarity in form and function of the hippocampus in rodents, monkeys, and humans
Authors: Clark Robert E. , Squire Larry R.
Published: June 2013

We begin by describing an historical scientific debate in which the fundamental idea that species are related by evolutionary descent was challenged. The challenge was based on supposed neuroanatomical differences between humans and other primates with respect to a structure known then as the hippocampus minor. The debate took place in the early 1860s, just after the publication of Darwin’s famous book. We then recount the difficult road that was traveled to develop an animal model of human memory impairment, a matter that also turned on questions about similarities and differences between humans and other primates. We then describe how the insight that there are multiple memory systems helped to secure the animal model and how the animal model was ultimately used to identify the neuroanatomy of long-term declarative memory (sometimes termed explicit memory). Finally, we describe a challenge to the animal model and to cross-species comparisons by considering the case of the concurrent discrimination task, drawing on findings from humans and monkeys. We suggest that analysis of such cases, based on the understanding that there are multiple memory systems with different properties, has served to emphasize the similarities in memory function across mammalian species.
Impact of contour on aesthetic judgments and approach-avoidance decisions in architecture
Authors: Vartanian Oshin , Navarrete Gorka , Chatterjee Anjan , Fich Lars Brorson , Leder Helmut , Modroño Cristián , Nadal Marcos , Rostrup Nicolai , Skov Martin
Published: June 2013

On average, we urban dwellers spend about 90% of our time indoors, and share the intuition that the physical features of the places we live and work in influence how we feel and act. However, there is surprisingly little research on how architecture impacts behavior, much less on how it influences brain function. To begin closing this gap, we conducted a functional magnetic resonance imaging study to examine how systematic variation in contour impacts aesthetic judgments and approach-avoidance decisions, outcome measures of interest to both architects and users of spaces alike. As predicted, participants were more likely to judge spaces as beautiful if they were curvilinear than rectilinear. Neuroanatomically, when contemplating beauty, curvilinear contour activated the anterior cingulate cortex exclusively, a region strongly responsive to the reward properties and emotional salience of objects. Complementing this finding, pleasantness—the valence dimension of the affect circumplex—accounted for nearly 60% of the variance in beauty ratings. Furthermore, activation in a distributed brain network known to underlie the aesthetic evaluation of different types of visual stimuli covaried with beauty ratings. In contrast, contour did not affect approach-avoidance decisions, although curvilinear spaces activated the visual cortex. The results suggest that the well-established effect of contour on aesthetic preference can be extended to architecture. Furthermore, the combination of our behavioral and neural evidence underscores the role of emotion in our preference for curvilinear objects in this domain.
Structure and superorganization of acetylcholine receptor–rapsyn complexes
Authors: Zuber Benoît , Unwin Nigel
Published: June 2013

The scaffolding protein at the neuromuscular junction, rapsyn, enables clustering of nicotinic acetylcholine receptors in high concentration and is critical for muscle function. Patients with insufficient receptor clustering suffer from muscle weakness. However, the detailed organization of the receptor–rapsyn network is poorly understood: it is unclear whether rapsyn first forms a wide meshwork to which receptors can subsequently dock or whether it only forms short bridges linking receptors together to make a large cluster. Furthermore, the number of rapsyn-binding sites per receptor (a heteropentamer) has been controversial. Here, we show by cryoelectron tomography and subtomogram averaging of
Torpedo
postsynaptic membrane that receptors are connected by up to three rapsyn bridges, the minimum number required to form a 2D network. Half of the receptors belong to rapsyn-connected groups comprising between two and fourteen receptors. Our results provide a structural basis for explaining the stability and low diffusion of receptors within clusters.
Identification of transferrin receptor 1 as a hepatitis C virus entry factor
Authors: Martin Danyelle N. , Uprichard Susan L.
Published: June 2013

Hepatitis C virus (HCV) is a liver tropic pathogen that affects ∼170 million people worldwide and causes liver pathologies including fibrosis, cirrhosis, steatosis, iron overload, and hepatocellular carcinoma. As part of a project initially directed at understanding how HCV may disrupt cellular iron homeostasis, we found that HCV alters expression of the iron uptake receptor transferrin receptor 1 (TfR1). After further investigation, we found that TfR1 mediates HCV entry. Specifically, functional studies showed that TfR1 knockdown and antibody blocking inhibit HCV cell culture (HCVcc) infection. Blocking cell surface TfR1 also inhibited HCV pseudoparticle (HCVpp) infection, demonstrating that TfR1 acts at the level of HCV glycoprotein-dependent entry. Likewise, a TfR1 small-molecule inhibitor that causes internalization of surface TfR1 resulted in a decrease in HCVcc and HCVpp infection. In kinetic studies, TfR1 antibody blocking lost its inhibitory activity after anti-CD81 blocking, suggesting that TfR1 acts during HCV entry at a postbinding step after CD81. In contrast, viral spread assays indicated that HCV cell-to-cell spread is less dependent on TfR1. Interestingly, silencing of the TfR1 trafficking protein, a TfR-1 specific adaptor protein required for TfR1 internalization, also inhibited HCVcc infection. On the basis of these results, we conclude that TfR1 plays a role in HCV infection at the level of glycoprotein-mediated entry, acts after CD81, and possibly is involved in HCV particle internalization.
Conserved microRNA pathway regulates developmental timing of retinal neurogenesis
Authors: La Torre Anna , Georgi Sean , Reh Thomas A.
Published: June 2013

Significance

The sequential generation of different types of neurons and glia is a fundamental property of neurogenesis, but little is known about the mechanisms controlling this phenomenon. Conditional deletion of Dicer prevents progenitors from progressing in their competence to generate late cell types, indefinitely generating early cell types. We now elucidate the molecular mechanism for this phenomenon. Three microRNAs, let-7, microRNA-125, and microRNA-9, serve as key regulators of the early to late developmental transition in retinal progenitors. These results show how progenitor temporal identity is controlled, a finding that will impact efforts to generate specific neural types from pluripotent stem cells.
Evidence for glycoprotein transport into complex plastids
Authors: Peschke Madeleine , Moog Daniel , Klingl Andreas , Maier Uwe G. , Hempel Franziska
Published: June 2013

Diatoms are microalgae that possess so-called “complex plastids,” which evolved by secondary endosymbiosis and are surrounded by four membranes. Thus, in contrast to primary plastids, which are surrounded by only two membranes, nucleus-encoded proteins of complex plastids face additional barriers, i.e., during evolution, mechanisms had to evolve to transport preproteins across all four membranes. This study reveals that there exist glycoproteins not only in primary but also in complex plastids, making transport issues even more complicated, as most translocation machineries are not believed to be able to transport bulky proteins. We show that plastidal reporter proteins with artificial N-glycosylation sites are indeed glycosylated during transport into the complex plastid of the diatom
Phaeodactylum tricornutum
. Additionally, we identified five endogenous glycoproteins, which are transported into different compartments of the complex plastid. These proteins get N-glycosylated during transport across the outermost plastid membrane and thereafter are transported across the second, third, and fourth plastid membranes in the case of stromal proteins. The results of this study provide insights into the evolutionary pressure on translocation mechanisms and pose unique questions on the operating mode of well-known transport machineries like the translocons of the outer/inner chloroplast membranes (Toc/Tic).
Concepts and implications of altruism bias and pathological altruism
Authors: Oakley Barbara A.
Published: June 2013

The profound benefits of altruism in modern society are self-evident. However, the potential hurtful aspects of altruism have gone largely unrecognized in scientific inquiry. This is despite the fact that virtually all forms of altruism are associated with tradeoffs—some of enormous importance and sensitivity—and notwithstanding that examples of pathologies of altruism abound. Presented here are the mechanistic bases and potential ramifications of pathological altruism, that is, altruism in which attempts to promote the welfare of others instead result in unanticipated harm. A basic conceptual approach toward the quantification of altruism bias is presented. Guardian systems and their over arching importance in the evolution of cooperation are also discussed. Concepts of pathological altruism, altruism bias, and guardian systems may help open many new, potentially useful lines of inquiry and provide a framework to begin moving toward a more mature, scientifically informed understanding of altruism and cooperative behavior.
Dynamics of brain networks in the aesthetic appreciation
Authors: Cela-Conde Camilo J. , García-Prieto Juan , Ramasco José J. , Mirasso Claudio R. , Bajo Ricardo , Munar Enric , Flexas Albert , del-Pozo Francisco , Maestú Fernando
Published: June 2013

Neuroimage experiments have been essential for identifying active brain networks. During cognitive tasks as in, e.g., aesthetic appreciation, such networks include regions that belong to the default mode network (DMN). Theoretically, DMN activity should be interrupted during cognitive tasks demanding attention, as is the case for aesthetic appreciation. Analyzing the functional connectivity dynamics along three temporal windows and two conditions, beautiful and not beautiful stimuli, here we report experimental support for the hypothesis that aesthetic appreciation relies on the activation of two different networks, an initial aesthetic network and a delayed aesthetic network, engaged within distinct time frames. Activation of the DMN might correspond mainly to the delayed aesthetic network. We discuss adaptive and evolutionary explanations for the relationships existing between the DMN and aesthetic networks and offer unique inputs to debates on the mind/brain interaction.