bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen dissociation and diffusion on Ni- and Ti-doped Mg(0001) surfaces
Authors: Pozzo M. , Alfè D. , Amieiro A. , French S. , Pratt A.
Published: March 2008

It is well-known, both theoretically and experimentally, that alloying MgH2 with transition elements can significantly improve the thermodynamic and kinetic properties for H2 desorption, as well as the H2 intake by Mg bulk. Here, we present a density functional theory investigation of hydrogen dissociation and surface diffusion over a Ni-doped surface and compare the findings to previously investigated Ti-doped Mg(0001) and pure Mg(0001) surfaces. Our results show that the energy barrier for hydrogen dissociation on the pure Mg(0001) surface is high, while it is small/null when Ni∕Ti are added to the surface as dopants. We find that the binding energy of the two H atoms near the dissociation site is high on Ti, effectively impeding diffusion away from the Ti site. By contrast, we find that on Ni, the energy barrier for diffusion is much reduced. Therefore, although both Ti and Ni promote H2 dissociation, only Ni appears to be a good catalyst for Mg hydrogenation, allowing diffusion away from the catalytic sites. Experimental results corroborate these theoretical findings, i.e., faster hydrogenation of the Ni-doped Mg sample as opposed to the reference Mg- or Ti-doped Mg.
Cationic ordering and role of A-site ion in manganese-based double perovskites
Authors: Singh M. P. , Truong K. D. , Laverdière J. , Charpentier S. , Jandl S. , Fournier P.
Published: March 2008

We present the details of growth parameters which promote the cationic ordering in multiferroic A2CoMnO6 (A=La or Bi) thin films grown on SrTiO3 (001). Our study manifest that well-ordered Co∕Mn states can be achieved at relatively high temperature and oxygen partial pressure. Structural, magnetic, and magnetodielectric properties of these films are studied. The importance and influence of Co∕Mn ordering and the role of A-type cations on the physical properties of A2CoMnO6 films are elucidated.
Characterization of high-density patterned media fabricated by a new anodizing process
Authors: Yasui Nobuhiro , Ichihara Sigeru , Nakamura Takashi , Imada Aya , Saito Tatsuya , Ohashi Yoshihiro , Den Tohru , Miura Kenji , Muraoka Hiroaki
Published: March 2008

Patterned media with dots of 65nm period (153Gdots∕in.2) and 25nm period (1.03Tdots∕in.2) fabricated by a new anodizing process were investigated. Write/read characteristics were successfully measured with a specific patterned marker providing an accessing method to the narrow patterned area of 10×10μm2. The read-back signals were obtained by a spin stand with a flying head and a static tester with a contact head. Although 1 dot resolution was not achieved in the flying write/read measurement for the media with 25nm period (1.03Tdots∕in.2), it was achieved in the contact write/read measurement.
Cation engineering of Cu-ferrite films deposited by alternating target laser ablation deposition
Authors: Yang Aria , Chen Zhaohui , Islam Shaheen M. , Vittoria Carmine , Harris V. G.
Published: March 2008

Epitaxial copper ferrite thin films were deposited on MgO substrates by the alternating target laser ablation deposition method. A series of films was studied to explore the impact of oxygen operating pressure, substrate temperature, and the ratio of laser shots incident on each target upon the magnetic, structural, and atomic structural properties. The highest saturation magnetization, 2800G, was achieved at a 90mTorr oxygen pressure and at 650°C for the substrate temperature. This value is 65% higher than the room temperature magnetization for bulk equilibrium samples. The inversion parameter was measured by extended x-ray absorption fine structure analysis. The sample having the highest saturation magnetization had a corresponding inversion parameter (percentage of Cu ion octahedral site occupancy) of 51.5% compared with the bulk value of 85%.
On defect interactions in axially loaded single-walled carbon nanotubes
Authors: Huq A. M. A. , Goh K. L. , Zhou Z. R. , Liao K.
Published: March 2008

Despite the unparalleled mechanical properties of carbon nanotubes (CNTs), experiments have revealed large scattering which could be attributed to structural defects. How two neighboring defects may interact and influence the mechanical properties of CNTs is still unclear. Here, interactions between a Stone-Wales (SW) defect pair in axially loaded single-walled carbon nanotubes (SWCNTs) are systematically studied using molecular mechanics. The defect-defect interaction is quantified by the bond with the highest energy, E, which varies in magnitude with respect to the interdefect distance, D. Defect pairs, corresponding to combinations of two types of SW defects (namely, the SW defect of A and B modes) with a different relative orientation angle, ϕ, embedded in SWCNTs of different size and chirality were studied. It is shown from the results that, in general, E varies according to defect pair, and converges to a constant at large D. It is found that the magnitude of E is regulated by the type of defect pair, and the profile of E vs D is modulated by ϕ. In addition, E is also influenced by the tube size and chirality. From all of the cases studied, the largest indifference length, D0, beyond which two neighboring defects do not feel the existence of each other, is found to be approximately 30 Å.
Spin injection into ferromagnetic Co2MnAl by optical absorption in GaAs
Authors: Isber Samih , Park Young Ju , Moodera Jagadeesh S. , Heiman Don
Published: March 2008

Spin-oriented electrons were injected into ferromagnetic Co2MnAl by optical absorption in GaAs. Schottky diode heterostructures were fabricated by molecular beam epitaxy growth of the Heusler ferromagnet Co2MnAl epitaxially on GaAs. The GaAs was illuminated near the bandgap at room temperature by circularly polarized light with 1.45eV. Spin-polarized photocurrent was observed for forward biased conditions. A barrier height of 0.6eV was found from I-V and photoemission experiments.
Ultrahigh performance three-dimensional electromagnetic relativistic kinetic plasma simulation
Authors: Bowers K. J. , Albright B. J. , Yin L. , Bergen B. , Kwan T. J. T.
Published: March 2008

The algorithms, implementation details, and applications of VPIC, a state-of-the-art first principles 3D electromagnetic relativistic kinetic particle-in-cell code, are discussed. Unlike most codes, VPIC is designed to minimize data motion, as, due to physical limitations (including the speed of light!), moving data between and even within modern microprocessors is more time consuming than performing computations. As a result, VPIC has achieved unprecedented levels of performance. For example, VPIC can perform ∼0.17 billion cold particles pushed and charge conserving accumulated per second per processor on IBM’s Cell microprocessor—equivalent to sustaining Los Alamos’s planned Roadrunner supercomputer at ∼0.56 petaflop (quadrillion floating point operations per second). VPIC has enabled previously intractable simulations in numerous areas of plasma physics, including magnetic reconnection and laser plasma interactions; next generation supercomputers like Roadrunner will enable further advances.
Tailoring the magnetization reversal of elliptical dots using exchange bias (invited)
Authors: Sort J. , Buchanan K. S. , Pearson J. E. , Hoffmann A. , Menéndez E. , Salazar-Alvarez G. , Baró M. D. , Miron M. , Rodmacq B. , Dieny B. , Nogués J.
Published: March 2008

Exchange bias effects have been studied in elliptical dots composed of ferromagnetic Ni80Fe20–antiferromagnetic Ir20Mn80 bilayers. The magnetization reversal mechanisms and magnetic configurations have been investigated by magneto-optic Kerr effect and magnetic force microscopy. Although the obtained bias fields in these dots are relatively small, the magnetization reversal is found to be influenced by the ferromagnetic–antiferromagnetic coupling. Namely, for some off-axis angles of measurement, the magnetization reversal mechanism of the Ni80Fe20–Ir20Mn80 ellipses depends on whether exchange bias is induced along the minor or major axis of the ellipses. Hence, exchange bias is shown to be an effective means for tailoring the magnetization reversal of elliptical dots after sample fabrication.
Angular dependence of magnetization reversal in exchange-biased Co∕Pt multilayer with perpendicular magnetic anisotropy
Authors: Nie Y. , Lin W. W. , Huang M. , Xie K. X. , Du J. , Sang H. , Xiao G.
Published: March 2008

The magnetization reversal in exchange-biased (Co∕Pt)5∕Co∕FeMn multilayer with perpendicular magnetic anisotropy has been studied depending on the angle between an applied field and the easy axis (the normal of the film plane). The results show different characters from that in most in-plane exchange bias systems. In a large angular range, the magnetization rotates first toward the adjacent direction of easy axis for both descending and ascending branches because perpendicular magnetic anisotropy is much larger than unidirectional exchange anisotropy. With increasing the angle from 0° to 90°, the magnitude of the exchange bias field decreases, but the coercivity increases due to domain nucleation and propagation included in the magnetization reversal process. The angular dependence of magnetization reversal shows no hysteresis between clockwise and counterclockwise rotations.
Formation mechanism of self-organized voids in dielectrics induced by tightly focused femtosecond laser pulses
Authors: Song Juan , Wang Xinshun , Hu Xiao , Dai Ye , Qiu Jianrong , Cheng Ya , Xu Zhizhan
Published: March 2008

In this paper, we briefly summarize two typical morphology characteristics of the self-organized void array induced in bulk of fused silica glass by a tightly focused femtosecond laser beam, such as the key role of high numerical aperture in the void array formation and the concentric-circle-like structure indicated by the top view of the void array. By adopting a physical model which combines the nonlinear propagation of femtosecond laser pulses with the spherical aberration effect (SA) at the interface of two mediums of different refractive indices, reasonable agreements between the simulation results and the experimental results are obtained. By comparing the fluence distributions of the case with both SA and nonlinear effects included and the case with only consideration of SA, we suggest that spherical aberration, which results from the refractive index mismatch between air and fused silica glass, is the main reason for the formation of the self-organized void array.
Curving monolithic silicon for nonplanar focal plane array applications
Authors: Dinyari Rostam , Rim Seung-Bum , Huang Kevin , Catrysse Peter B. , Peumans Peter
Published: March 2008

Despite progress in the performance of image sensors, comparatively little work has focused on overcoming the limitations of planar image sensor arrays. We present a technique to construct curved monolithic silicon structures that can be processed using standard silicon processing prior to curving. The process relies on microstructuring of a monolithic silicon die using a deep reactive ion etch process. This technique can be used to build curved integrated circuits such as image sensors for more compact cameras with improved optical performance.
Carrier transport mechanisms of Pnp AlGaN∕GaN heterojunction bipolar transistors
Authors: Kumakura Kazuhide , Makimoto Toshiki
Published: March 2008

We fabricated Pnp AlGaN∕GaN heterojunction bipolar transistors (HBTs) with various base widths WB and investigated their common-emitter current-voltage characteristics at room temperature to clarify their carrier transport mechanisms. The current gain β increased as WB decreased. The maximum current gain βmax was 40 in a HBT with a WB of 30nm. HBTs with different base widths exhibited almost the same tendency for β to increase with increasing the collector current IC, indicating that the carrier transport mechanism is the same in all the n-GaN base layers. With a low IC, recombination in the emitter-base depletion region is the dominant carrier transport mechanism. β was less affected when IC was high, and the carrier transport was dominated by the minority hole diffusion in the neutral base layer. The minority hole diffusion length obtained from the HBT characteristics agrees well with previous results obtained with electron beam induced current measurements, also indicating that βmax was determined by the minority hole diffusion length in the n-GaN base layer.
Development of a compact optical system for microarray scanning using a DVD pickup head
Authors: Shimomura T. , Izawa C. , Matsui T.
Published: March 2008

We present a compact optical system using a commercially available DVD pickup head for microarray scanning. Our instrument successfully provides a low-cost, compact, and simple microarray scanning optical system in comparison to conventional ones due to the use of small-sized optical components and the implementation of a simple autofocusing system using an embedded voice coil motor. The performance of this system was validated by using a microarray slide with spots of fluorescent dyes. It was confirmed that our optical head performed satisfactorily and was suitable for practical use in microarray scanners. This result provides evidence of the superiority of our microarray scanning optical system over conventional ones because of its space-saving properties and cost effectiveness.
Numerical analysis of the production profile of H atoms and subsequent H− ions in large negative ion sources
Authors: Takado N. , Tobari H. , Inoue T. , Hanatani J. , Hatayama A. , Hanada M. , Kashiwagi M. , Sakamoto K.
Published: March 2008

The production and transport processes of H0 atoms are numerically simulated using a three-dimensional Monte Carlo transport code. The code is applied to the large JAEA 10ampere negative ion source under the Cs-seeded condition to obtain a spatial distribution of surface-produced H− ions. In this analysis, the amount of H0 atoms produced through dissociation processes of H2 molecules is calculated from the electron temperature and density obtained by Langmuir probe measurements. The high-energy tail of electrons, which greatly affects H0 atom production, is taken into account by fitting a single-probe characteristic as a two-temperature Maxwellian distribution. In the H0 atom transport process, the energy relaxation of the H0 atoms, which affects the surface H− ion production rate, is taken into account. The result indicates that the surface H− ion production is enhanced near the high-electron-temperature region where H0 atom production is localized.
Large surface enhanced Raman scattering enhancements from fracture surfaces of nanoporous gold
Authors: Qian L. H. , Inoue A. , Chen M. W.
Published: March 2008

We report the improved surface enhanced Raman scattering (SERS) of mechanically ruptured nanoporous gold. The SERS intensities of rhodamine 6G and crystal violet 10B molecules from the fracture surfaces of nanoporous gold are about one order of magnitude higher than those from the as-prepared samples. Microstructural characterization reveals that the fracture surfaces contain numerous sharp protrusions with 5–10nm apexes, produced by localized plastic deformation of gold ligaments during failure. The large SERS enhancements from the fracture surfaces are most likely associated with the intensified electromagnetic fields around the nanosized protrusions and the electromagnetic interaction between the protrusions.
Luminescence readout of nanoparticle phase state
Authors: Denisyuk A. I. , Jonsson F. , MacDonald K. F. , Zheludev N. I. , García de Abajo F. J.
Published: March 2008

We report that the phase state of bistable gallium nanoparticles, controlled by optical or electron beam excitations, can be identified via measurements of their cathodoluminescent emission, thus offering an innovative conceptual basis for the development of high density nonvolatile phase-change memories. Changes of up to 20% in visible emission intensity are observed following low-fluence optical or electron beam induced phase switching in a monolayer of 60nm particles.
Subwavelength focusing of surface acoustic waves generated by an annular interdigital transducer
Authors: Laude Vincent , Gérard Davy , Khelfaoui Naima , Jerez-Hanckes Carlos F. , Benchabane Sarah , Khelif Abdelkrim
Published: March 2008

We propose and demonstrate experimentally the concept of the annular interdigital transducer that focuses acoustic waves on the surface of a piezoelectric material to a single, diffraction-limited spot. The shape of the transducing fingers follows the wave surface. Experiments conducted on lithium niobate substrates evidence that the generated surface waves converge to the center of the transducer, producing a spot that shows a large concentration of acoustic energy. This concept is of practical significance to design new intense microacoustic sources, for instance for enhanced acousto-optical interactions.
Stochastic Coulomb blockade in coupled asymmetric silicon dots formed by pattern-dependent oxidation
Authors: Manoharan M. , Tsuchiya Yoshishige , Oda Shunri , Mizuta Hiroshi
Published: March 2008

This paper reports the observation of stochastic Coulomb blockade for the coupled silicon dots. The device was fabricated from the highly doped dual recess structured silicon channel by means of stress induced pattern-dependent oxidation. Sparsely placed Coulomb oscillation characteristics were observed from the transport characteristics at a low temperature and these irregularities decreased linearly as temperature increased. These characteristics were interpreted as the stochastic Coulomb blockade effect, which occurs due to the mismatch between individual dots in the energy spectrum ladder of the serially connected dots.
Influence of surface ligands on saturation magnetization of FePt nanoparticles
Authors: Tanaka Yasushi , Saita Soichiro , Maenosono Shinya
Published: March 2008

The influence of organic ligands on the saturation magnetization (MS) of chemically disordered face-centered-cubic (fcc) FePt nanoparticles (NPs) was investigated. By increasing the basicity and/or surface coverage of ligands, the MS of fcc-phase FePt NPs decreases due to an increase in electron donation from the ligand to the Fe d bands. FePt NPs capped with 1-octanethiol or 1-dodecanethiol show larger MS than as-synthesized NPs capped with oleic acid due to a thinning of the nonmagnetic shell.
Multifunctional carbon nanotube networks for fuel cells
Authors: Kaempgen M. , Lebert M. , Nicoloso N. , Roth S.
Published: March 2008

A single walled carbon nanotube (SWCNT) network is functionalized in different ways to achieve a multifunctional electrode. This electrode material is used as light and thin gas diffusion electrodes in fuel cells. In contrast to any previous work, no other carbon material is part of the electrode. We demonstrate that the performance of such all-SWCNT gas diffusion electrodes is comparable to that of regular electrodes which are based on amorphous carbon. This allows the entire replacement of these regular carbon electrodes by such multifunctionalized SWCNT networks. This way, extremely thin and light gas diffusion electrodes are realized, potentially fulfilling the demands of light-weight power supplies.
Outcomes of the search for new perennial and salt tolerant pasture plants for southern Australia
Authors: Dear B. S. , Reed K.F. M. , Craig A. D.
Published: March 2008

The potential adaptation of a range of perennial pasture species to recharge environments in southern Australia is reviewed based on their performance in 20 field nurseries in a nationally coordinated project. Species were also evaluated for their suitability to discharge sites where salt and waterlogging are major restraints. Species are ranked according to their potential to be incorporated into farming systems and the scope for further breeding and selection.
Medicago sativa L. (lucerne) was the most persistent of the perennial legumes across a diversity of recharge environments. Lotus corniculatus L. (birdsfoot trefoil) showed the most promise on soils prone to waterlogging. Other legumes that showed potential included Cullen australasicum (Schltdl.) J.W. Grimes (tall verbine) and Lotononis bainesii Baker (lotononis). The herb Chicoriyum intybus L. was superior to M. sativa on more acid soils.
Phalaris aquatica L. (phalaris) and summer dormant cultivars of Dactylis glomerata L. (cocksfoot), Festuca arundinacea L. (tall fescue) and Lolium perenne L. (perennial ryegrass) were among the most persistent and productive of the perennial grasses. Further exploitation of temperate perennial grass germplasm with increased summer dormancy should be a priority to increase the role of these grass species in lower rainfall, summer-dry environments. Although difficult to establish, the indigenous grasses Austrodanthonia caespitosa (Gaudich.) H.P. Linder (wallaby grass) and A. richardsonii (Cashmore) H.P. Linder were persistent and showed good recruitment. They should be a priority for low rainfall, low input environments.
Other grasses that showed promise were Chloris gayana Kunth (Rhodes grass), Secale montanum Guss. (mountain rye), Microlaena stipoides (Labill.) R. Br. (weeping grass), Ehrhata calcycina Sm. (veldt grass) and Bromus stamineus E. Desv. (grazing brome).
For discharge environments, Melilotus siculus (Turra) Vitman ex B.D. Jacks. was one of the most salt tolerant legumes and should be a priority for further development. Medicago polymorpha L. (burr medic) appears underutilised in discharge environments. Increasing the waterlogging tolerance of this moderately salt tolerant species would further enhance its potential. Trifolium michelianum Savi. (balansa clover) owed its success in discharge areas more to ‘salt avoidance’ rather than salt tolerance per se. Melilotus sulcatus Desf., T. tomentosum L. and Lotus tenuis Waldst. & Kit. ex Willd. also had traits that may prove advantageous for discharge environments.
Within the pasture grasses, Puccinellia ciliata Bor (pucinellia) was superior at sites prone to waterlogging whereas T. ponticum performed better in moderately drained saline sites.
Heat stress causes inhibition of the
de novo
synthesis of antenna proteins and photobleaching in cultured
Symbiodinium
Authors: Takahashi Shunichi , Whitney Spencer , Itoh Shigeru , Maruyama Tadashi , Badger Murray
Published: March 2008

Coral bleaching, caused by heat stress, is accompanied by the light-induced loss of photosynthetic pigments in
in situ
symbiotic dinoflagellate algae (
Symbiodinium
spp.). However, the molecular mechanisms responsible for pigment loss are poorly understood. Here, we show that moderate heat stress causes photobleaching through inhibition of the
de novo
synthesis of intrinsic light-harvesting antennae [chlorophyll
a
–chlorophyll
c
2
–peridinin–protein complexes (acpPC)] in cultured
Symbiodinium
algae and that two Clade A
Symbiodinium
species showing different thermal sensitivities of photobleaching also show differential sensitivity of this key protein synthesis process. Photoinhibition of photosystem II (PSII) and subsequent photobleaching were observed at temperatures of >31°C in cultured
Symbiodinium
CS-73 cells grown at 25–34°C, but not in cultures of the more thermally tolerant control
Symbiodinium
species OTcH-1. We found that bleaching in CS-73 is associated with loss of acpPC, which is a major antennae protein in
Symbiodinium
. In addition, the thermally induced loss of this protein is light-dependent, but does not coincide directly with PSII photoinhibition and is not caused by stimulated degradation of acpPC. In cells treated at 34°C over 24 h, the steady-state
acpPC
mRNA pool was modestly reduced, by ≈30%, whereas the corresponding synthesis rate of acpPC was diminished by >80%. Our results suggest that photobleaching in
Symbiodinium
is consequentially linked to the relative susceptibility of PSII to photoinhibition during thermal stress and occurs, at least partially, because of the loss of acpPC via undefined mechanism(s) that hamper the
de novo
synthesis of acpPC primarily at the translational processing step.
RelB is the NF-κB subunit downstream of NIK responsible for osteoclast differentiation
Authors: Vaira Sergio , Johnson Trevor , Hirbe Angela C. , Alhawagri Muhammad , Anwisye Imani , Sammut Benedicte , O'Neal Julie , Zou Wei , Weilbaecher Katherine N. , Faccio Roberta , Novack Deborah Veis
Published: March 2008

NF-κB inducing kinase (NIK) is required for osteoclastogenesis in response to pathologic stimuli, and its loss leads to functional blockade of both alternative and classical NF-κB caused by cytoplasmic retention by p100. We now show that deletion of p100 restores the capacity of NIK-deficient osteoclast (OC) precursors to differentiate and normalizes RelB and p65 signaling. Differentiation of
NIK
−/− precursors is also restored by overexpression of RelB, but not p65. Additionally,
RelB
−/− precursors fail to form OCs in culture, and this defect is rescued by re-expression of RelB, but not by overexpression of p65. To further support the role of RelB in OCs, we challenged
RelB
−/− mice with TNF-α
in vivo
and found a diminished osteoclastogenic response. We then examined tumor-induced osteolysis in both
RelB
−/− and
NIK
−/− mice by using the B16 melanoma model. Growth of tumor cells in the bone marrow was similar to WT controls, but the absence of either RelB or NIK completely blocked the tumor-induced loss of trabecular bone. Thus, the alternative NF-κB pathway, culminating in activation of RelB, has a key and specific role in the differentiation of OCs that cannot be compensated for by p65.
Structural inference of native and partially folded RNA by high-throughput contact mapping
Authors: Das Rhiju , Kudaravalli Madhuri , Jonikas Magdalena , Laederach Alain , Fong Robert , Schwans Jason P. , Baker David , Piccirilli Joseph A. , Altman Russ B. , Herschlag Daniel
Published: March 2008

The biological behaviors of ribozymes, riboswitches, and numerous other functional RNA molecules are critically dependent on their tertiary folding and their ability to sample multiple functional states. The conformational heterogeneity and partially folded nature of most of these states has rendered their characterization by high-resolution structural approaches difficult or even intractable. Here we introduce a method to rapidly infer the tertiary helical arrangements of large RNA molecules in their native and non-native solution states. Multiplexed hydroxyl radical (·OH) cleavage analysis (MOHCA) enables the high-throughput detection of numerous pairs of contacting residues via random incorporation of radical cleavage agents followed by two-dimensional gel electrophoresis. We validated this technology by recapitulating the unfolded and native states of a well studied model RNA, the P4–P6 domain of the
Tetrahymena
ribozyme, at subhelical resolution. We then applied MOHCA to a recently discovered third state of the P4–P6 RNA that is stabilized by high concentrations of monovalent salt and whose partial order precludes conventional techniques for structure determination. The three-dimensional portrait of a compact, non-native RNA state reveals a well ordered subset of native tertiary contacts, in contrast to the dynamic but otherwise similar molten globule states of proteins. With its applicability to nearly any solution state, we expect MOHCA to be a powerful tool for illuminating the many functional structures of large RNA molecules and RNA/protein complexes.
The maturing architecture of the brain's default network
Authors: Fair Damien A. , Cohen Alexander L. , Dosenbach Nico U. F. , Church Jessica A. , Miezin Francis M. , Barch Deanna M. , Raichle Marcus E. , Petersen Steven E. , Schlaggar Bradley L.
Published: March 2008

In recent years, the brain's “default network,” a set of regions characterized by decreased neural activity during goal-oriented tasks, has generated a significant amount of interest, as well as controversy. Much of the discussion has focused on the relationship of these regions to a “default mode” of brain function. In early studies, investigators suggested that, the brain's default mode supports “self-referential” or “introspective” mental activity. Subsequently, regions of the default network have been more specifically related to the “internal narrative,” the “autobiographical self,” “stimulus independent thought,” “mentalizing,” and most recently “self-projection.” However, the extant literature on the function of the default network is limited to adults, i.e., after the system has reached maturity. We hypothesized that further insight into the network's functioning could be achieved by characterizing its development. In the current study, we used resting-state functional connectivity MRI (rs-fcMRI) to characterize the development of the brain's default network. We found that the default regions are only sparsely functionally connected at early school age (7–9 years old); over development, these regions integrate into a cohesive, interconnected network.
From rhetoric to reality: advancing literacy by cross‐curricular means
Authors: Alexander Joy , Jarman Ruth , McClune Billy , Walsh Patrick
Published: March 2008

Cross‐curricularity, literacy and critical literacy are currently promoted as components of a curriculum appropriate for the twenty‐first century. The first two, in particular, are prescribed elements of classroom experience in Northern Ireland, which is the immediate context of this article, but also more widely in the UK. Teachers are implementing cross‐curricular and interdisciplinary initiatives, but rhetorical imperatives can translate into superficial realities. The reasons for this are explored, as are the reasons why interdisciplinary studies, literacy across the curriculum and critical literacy are deemed to be of significance for education at the present time. The ‘Making Science: Making News’ project is described, in which Key Stage 3 science and English classes worked together, with input from a research scientist and a journalist, to produce articles on space science which were published in local newspapers. The outcomes of the project are discussed from the perspectives of both teachers and learners. It is argued that this project is an example of genuine interdisciplinary activity; that it went beyond literacy skills to a deeper development of scientific discourse; and that, through its media connection, there was potential for building an ongoing awareness in pupils of critical literacy and scientific literacy.
Dread and passion: primary and secondary teachers' views on teaching the arts1
Authors: Wilson Graeme B. , MacDonald Raymond A.R. , Byrne Charles , Ewing Sandra , Sheridan Marion
Published: March 2008

This article reports on a study of the views of Scottish teachers concerning the delivery of arts subjects within the 5–14 curriculum. Data were gathered through focus group interviews with primary, secondary and primary head teachers, and a questionnaire survey of 232 teachers in 10 Scottish LEAs. Research issues included the balance of the curriculum; assessment; the specialist knowledge required to teach each subject with confidence; how the arts were valued by parents and schools; and the benefits which may accrue to pupils and the school through participation in the arts. This article compares findings from primary teachers with those from secondary teachers. While differences were apparent in terms of confidence with teaching and assessing the arts, and how they felt arts subjects were valued, all participants strongly endorsed the benefits of arts education, particularly in terms of pupils' personal development. The implications of these findings are discussed in relation to current literature.
Asymptotics of matrix integrals and tensor invariants of compact Lie groups
Authors: Stolz Michael , Tate Tatsuya
Published: March 2008

In this paper we give an asymptotic formula for a matrix integral which plays a crucial role in the approach of Diaconis et al. to random matrix eigenvalues. The choice of parameter for the asymptotic analysis is motivated by an invariant-theoretic interpretation of this type of integral. For arbitrary regular irreducible representations of arbitrary connected semisimple compact Lie groups, we obtain an asymptotic formula for the trace of permutation operators on the space of tensor invariants, thus extending a result of Biane on the dimension of these spaces.
Spectral dominance and commuting chains
Authors: Hoai Bich , Johnson Charles , Spitkovsky Ilya
Published: March 2008

A positive semidefinite (PSD) operator

A
A

“spectrally dominates” a PSD operator

B
B

if

A
t

−

B
t

A^t-B^t

is PSD for all

t
>
0

t>0

. We (i) give a new characterization of spectral dominance in finite dimensions in terms of a monotonic chain of intermediate, pairwise commuting operators and (ii) determine for which pairs

A
,
B

A,B

spectral dominance persists under the taking of arbitrary compressions. Earlier results about spectral dominance are proven (in finite dimensions) in new ways, and several corollary observations are made.
Groups with a character of large degree
Authors: Snyder Noah
Published: March 2008

Let

G
G

be a finite group of order

n
n

and

V
V

a simple

C

[
G
]

\mathbb {C}[G]

-module of dimension

d
d

. For some nonnegative number

e
e

, we have

n
=
d
(
d
+
e
)

n=d(d+e)

. If

e
e

is small, then the character of

V
V

has unusually large degree. We fix

e
e

and attempt to classify such groups. For

e
≤
3

e \leq 3

we give a complete classification. For any other fixed

e
e

we show that there are only finitely many examples.
Asymptotic cones and Assouad-Nagata dimension
Authors: Dydak J. , Higes J.
Published: March 2008

We prove that the dimension of any asymptotic cone over a metric space

(
X
,
ρ
)

(X,\rho )

does not exceed the asymptotic Assouad-Nagata dimension

asdim

A
N

⁡
(
X
)

\operatorname {asdim}_{AN}(X)

of

X
X

. This improves a result of Dranishnikov and Smith (2007), who showed

dim
⁡
(
Y
)
≤

asdim

A
N

⁡
(
X
)

\dim (Y)\leq \operatorname {asdim}_{AN}(X)

for all separable subsets

Y
Y

of special asymptotic cones

Cone
ω

⁡
(
X
)

\operatorname {Cone}_\omega (X)

, where

ω
\omega

is an exponential ultrafilter on natural numbers. We also show that the Assouad-Nagata dimension of the discrete Heisenberg group equals its asymptotic dimension.
On exceptional eigenvalues of the Laplacian for Γ₀(𝑁)
Authors: Li Xian-Jin
Published: March 2008

An explicit Dirichlet series is obtained, which represents an analytic function of

s
s

in the half-plane

ℜ
s
>
1

/

2

\Re s>1/2

except for having simple poles at points

s

j

s_{j}

that correspond to exceptional eigenvalues

λ

j

\lambda _{j}

of the non-Euclidean Laplacian for Hecke congruence subgroups

Γ

0

(
N
)

\Gamma _{0}(N)

by the relation

λ

j

=

s

j

(
1
−

s

j

)

\lambda _{j}=s_{j}(1-s_{j})

for

j
=
1
,
2
,
⋯
,
S

j=1,2,\cdots , S

. Coefficients of the Dirichlet series involve all class numbers

h

d

h_{d}

of real quadratic number fields. But, only the terms with

h

d

≫

d

1

/

2
−
ϵ

h_{d}\gg d^{1/2-\epsilon }

for sufficiently large discriminants

d
d

contribute to the residues

m

j

/

2

m_{j}/2

of the Dirichlet series at the poles

s

j

s_{j}

, where

m

j

m_{j}

is the multiplicity of the eigenvalue

λ

j

\lambda _{j}

for

j
=
1
,
2
,
⋯
,
S

j=1,2,\cdots , S

. This may indicate (I’m not able to prove yet) that the multiplicity of exceptional eigenvalues can be arbitrarily large. On the other hand, by density theorem the multiplicity of exceptional eigenvalues is bounded above by a constant depending only on

N
N

.
A Weierstrass type representation for minimal surfaces in Sol
Authors: Inoguchi Jun-ichi , Lee Sungwook
Published: March 2008

The normal Gauss map of a minimal surface in the model space

S
o
l

\mathrm {Sol}

of solvegeometry is a harmonic map with respect to a certain singular Riemannian metric on the extended complex plane.
Spectral mapping theorem for linear hyperbolic systems
Authors: Lichtner Mark
Published: March 2008

We show high frequency resolvent and spectral estimates and prove the spectral mapping theorem for linear hyperbolic systems in one space dimension.
𝐻*-algebras and quantization of para-Hermitian spaces
Authors: van Dijk Gerrit , Pevzner Michael
Published: March 2008

In the present note we describe a family of

H
∗

H^*

-algebra structures on the set

L
2

(
X
)

L^2(X)

of square integrable functions on a rank-one para-Hermitian symmetric space

X
X

.
Free submodules for the central representation in the cohomology of Lie algebras
Authors: Cairns Grant , Jessup Barry
Published: March 2008

If

Z
Z

is the centre of the Lie algebra

L
L

, its cohomology

H
∗

(
L
)

H^*(L)

is naturally a module over the exterior algebra

Λ
Z

\Lambda Z

. Under suitable hypotheses on

L
L

, motivated by recent work by Pouseele and Tirao, we find free summands in

H
∗

(
L
)

H^*(L)

for this module structure, thus establishing the Toral Rank Conjecture for a new class of Lie algebras.
Dirichlet-Neumann-impedance boundary value problems arising in rectangular wedge diffraction problems
Authors: Castro L. , Kapanadze D.
Published: March 2008

Boundary value problems originated by the diffraction of an electromagnetic (or acoustic) wave by a rectangular wedge with faces of possible different kinds are analyzed in a Sobolev space framework. The boundary value problems satisfy the Helmholtz equation in the interior (Lipschitz) wedge domain, and are also subject to different combinations of boundary conditions on the faces of the wedge. Namely, the following types of boundary conditions will be under study: Dirichlet-Dirichlet, Neumann-Neumann, Neumann-Dirichlet, Impedance-Dirichlet, and Impedance-Neumann. Potential theory (combined with an appropriate use of extension operators) leads to the reduction of the boundary value problems to integral equations of Fredholm type. Thus, the consideration of single and double layer potentials together with certain reflection operators originate pseudo-differential operators which allow the proof of existence and uniqueness results for the boundary value problems initially posed. Furthermore, explicit solutions are given for all the problems under consideration, and regularity results are obtained for these solutions.
All dihedral division algebras of degree five are cyclic
Authors: Matzri Eliyahu
Published: March 2008

In 1982 Rowen and Saltman proved that every division algebra which is split by a dihedral extension of degree

2
n

2n

of the center,

n
n

odd, is in fact cyclic. The proof requires roots of unity of order

n
n

in the center. We show that for

n
=
5

n=5

, this assumption can be removed. It then follows that

5

Br
⁡
(
F
)

{}_{5\!\!\!\:}\operatorname {Br}(F)

, the

5
5

-torsion part of the Brauer group, is generated by cyclic algebras, generalizing a result of Merkurjev (1983) on the

2
2

and

3
3

torsion parts.
A new approach to relatively nonexpansive mappings
Authors: Espínola Rafa
Published: March 2008

In this paper we study the nonexpansivity of the so-called relatively nonexpansive mappings. A relatively nonexpansive mapping with respect to a pair of subsets

(
A
,
B
)

(A,B)

of a Banach space

X
X

is a mapping defined from

A
∪
B

A\cup B

into

X
X

such that

‖
T
x
−
T
y
‖
≤
‖
x
−
y
‖

\|Tx-Ty\|\le \|x-y\|

for

x
∈
A

x\in A

and

y
∈
B

y\in B

. These mappings were recently considered in a paper by Eldred et al. (Proximinal normal structure and relatively nonexpansive mappings, Studia Math. 171 (3) (2005), 283-293) to obtain a generalization of Kirk’s Fixed Point Theorem. In this work we show that, for certain proximinal pairs

(
A
,
B
)

(A,B)

, there exists a natural semimetric for which any relatively nonexpansive mapping with respect to

(
A
,
B
)

(A,B)

is nonexpansive. This fact will be used to improve one of the two main results from the aforementioned paper by Eldred et al. At that time we will also obtain several consequences regarding the strong continuity properties of relatively nonexpansive mappings and the relation between the two main results from the same work.
Non-Gaussian upper estimates for heat kernels on spaces of homogeneous type
Authors: Yang Dachun , Zhou Yuan
Published: March 2008

The authors extend non-Gaussian upper estimates on the positive real axis to a certain sector of

C

\mathbb {C}

including the positive real axis for heat kernels on spaces of homogeneous type, which are known to be holomorphic in that sector.
Bifurcation of homoclinics of Hamiltonian systems
Authors: Pejsachowicz Jacobo
Published: March 2008

We obtain sufficient conditions for bifurcation of homoclinic trajectories of nonautonomous Hamiltonian vector fields parametrized by a circle, together with estimates for the number of bifurcation points in terms of the Maslov index of the asymptotic stable and unstable bundles of the linearization at the stationary branch.
The complex Hessian equation with infinite Dirichlet boundary value
Authors: Xiang Ni , Yang Xiao-Ping
Published: March 2008

The existence and nonexistence of the

Γ
\Gamma

-subharmonic solutions for the complex Hessian equations with infinite Dirichlet boundary value are proved in the certain bounded domain in

C
n

C^n

. We calculate the k-Hessian of the radially symmetric function and use radial functions to construct various barrier functions in this paper. Moreover, it is shown that the growth rate conditions are nearly optimal.
On the decay properties of solutions to a class of Schrödinger equations
Authors: Dawson L. , McGahagan H. , Ponce G.
Published: March 2008

We construct a local in time, exponentially decaying solution of the one-dimensional variable coefficient Schrödinger equation by solving a nonstandard boundary value problem. A main ingredient in the proof is a new commutator estimate involving the projections

P
±

P_\pm

onto the positive and negative frequencies.
Splitting criterion for reflexive sheaves
Authors: Abe Takuro , Yoshinaga Masahiko
Published: March 2008

We give a criterion for a reflexive sheaf to split into a direct sum of line bundles.
On a congruence of Blichfeldt concerning the order of finite groups
Authors: Chillag David
Published: March 2008

We show that if

G
G

is a finite group,

C
C

a conjugacy class of

G
G

and

d
=

|
C
|

d=\left \vert C\right \vert

,

d

2

,

d

3

,
…
,

d

m

d_{2},d_{3},\ldots ,d_{m}

are the distinct elements in the multiset
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="StartSet StartFraction StartAbsoluteValue upper C EndAbsoluteValue chi left-parenthesis upper C right-parenthesis Over chi left-parenthesis 1 right-parenthesis EndFraction vertical-bar chi element-of normal upper I normal r normal r left-parenthesis upper G right-parenthesis EndSet">

{

|
C
|

χ
(
C
)

χ
(
1
)

 

|

 
χ
∈

I
r
r

(
G
)
}

\left \{ \frac {\left \vert C\right \vert \chi (C)} {\chi (1)}\ |\ \chi \in \mathrm {Irr}(G)\right \}

(here

χ
(
C
)

\chi (C)

is the value of

χ
\chi

on any element of

C
C

), then
\[
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="StartAbsoluteValue upper G slash mathematical left-angle upper C mathematical right-angle EndAbsoluteValue dot left-parenthesis d minus d 2 right-parenthesis left-parenthesis d minus d 3 right-parenthesis midline-horizontal-ellipsis left-parenthesis d minus d Subscript m Baseline right-parenthesis identical-to 0 mod StartAbsoluteValue upper G EndAbsoluteValue period">

|
G

/

⟨
C
⟩

|

⋅

(
d
−

d

2

)

(
d
−

d

3

)

⋯

(
d
−

d

m

)

≡
0
 
mod
⁡
 

|
G
|

.

\left \vert G/\left \langle C\right \rangle \right \vert \cdot \left ( d-d_{2}\right ) \left ( d-d_{3}\right ) \cdots \left ( d-d_{m}\right ) \equiv 0\ \operatorname {mod}\ \left \vert G\right \vert .

\]
This is a dual to a generalization of a theorem of Blichfeldt stating that if

G
G

is a finite group,

θ
\theta

a generalized character and

d
=
θ
(
1
)
,

d

2

,

d

3

,
…
,

d

m

d=\theta (1),d_{2},d_{3},\ldots ,d_{m}

are the distinct values of

θ
\theta

, then
\[
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="StartAbsoluteValue kernel left-parenthesis theta right-parenthesis EndAbsoluteValue left-parenthesis d minus d 2 right-parenthesis left-parenthesis d minus d 3 right-parenthesis midline-horizontal-ellipsis left-parenthesis d minus d Subscript m Baseline right-parenthesis identical-to 0 mod StartAbsoluteValue upper G EndAbsoluteValue period">

|
ker
⁡
(
θ
)
|

(
d
−

d

2

)

(
d
−

d

3

)

⋯

(
d
−

d

m

)

≡
0
 
mod
⁡
 

|
G
|

.

\left \vert \ker (\theta )\right \vert \left ( d-d_{2}\right ) \left ( d-d_{3}\right ) \cdots \left ( d-d_{m}\right ) \equiv 0\ \operatorname {mod} \ \left \vert G\right \vert .

\]
We also observe that

d
=
θ
(
1
)

d=\theta (1)

in Blichfeldt’s congruence can be replaced, with a minor adjustment, by any rational value of

θ
\theta

. A similar change can be done to the first congruence above.
Collagen Fibril Flow and Tissue Translocation Coupled to Fibroblast Migration in 3D Collagen Matrices
Authors: Miron-Mendoza Miguel , Seemann Joachim , Grinnell Frederick
Published: March 2008

In nested collagen matrices, human fibroblasts migrate from cell-containing dermal equivalents into surrounding cell-free outer matrices. Time-lapse microscopy showed that in addition to cell migration, collagen fibril flow occurred in the outer matrix toward the interface with the dermal equivalent. Features of this flow suggested that it depends on the same cell motile machinery that normally results in cell migration. Collagen fibril flow was capable of producing large-scale tissue translocation as shown by closure of a ∼1-mm gap between paired dermal equivalents in floating, nested collagen matrices. Our findings demonstrate that when fibroblasts interact with collagen matrices, tractional force exerted by the cells can couple to matrix translocation as well as to cell migration.
Cleavage of Mcd1 by Caspase-like Protease Esp1 Promotes Apoptosis in Budding Yeast
Authors: Yang Hui , Ren Qun , Zhang Zhaojie
Published: March 2008

Over the last decade, yeast has been used successfully as a model system for studying the molecular mechanism of apoptotic cell death. Here, we report that Mcd1, the yeast homology of human cohesin Rad21, plays an important role in hydrogen peroxide-induced apoptosis in yeast. On induction of cell death, Mcd1 is cleaved and the C-terminal fragment is translocated from nucleus into mitochondria, causing the decrease of mitochondrial membrane potential and the amplification of cell death in a cytochrome c-dependent manner. We further demonstrate that the caspase-like protease Esp1 has dual functions and that it is responsible for the cleavage of Mcd1 during the hydrogen peroxide-induced apoptosis. When apoptosis is induced, Esp1 is released from the anaphase inhibitor Pds1. The activated Esp1 acts as caspase-like protease for the cleavage of Mcd1, which enhances the cell death via its translocation from nucleus to mitochondria.