bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and current-voltage characterization of a ferroelectric lead zirconate titanate/AlGaN∕GaN field effect transistor
Authors: Kang Youn-Seon , Fan Qian , Xiao Bo , Alivov Ya. I. , Xie Jinqiao , Onojima Norio , Cho Sang-Jun , Moon Yong-Tae , Lee Hosun , Johnstone D. , Morkoç Hadis , Park Young-Soo
Published: March 2006

We demonstrated ferroelectric field effect transistors (FFETs) with hysteretic I-V characteristics in a modulation-doped field effect transistors (MODFET) AlGaN∕GaN platform with ferroelectric Pb(Zr,Ti)O3 between a GaN channel and a gate metal. The pinch-off voltage was about 6–7V comparable to that of conventional Schottky gate MODFET. Counterclockwise hysteresis appeared in the transfer characteristics with a drain current shift of ∼5mA for zero gate-to-source voltage. This direction is opposite and much more pronounced than the defect induced clockwise hysteresis in conventional devices, which suggests that the key factor contributing to the counterclockwise hysteresis of the FFET is the ferroelectric switching effect of the lead zirconate titanate gate.
Broadband 6μm<λ<8μm superluminescent quantum cascade light-emitting diodes
Authors: Zibik E. A. , Ng W. H. , Revin D. G. , Wilson L. R. , Cockburn J. W. , Groom K. M. , Hopkinson M.
Published: March 2006

Midinfrared emission from intersubband superluminescent light-emitting diodes is reported. We have obtained broadband emission spectra at around 7μm with a full width at half maximum of ∼2μm, using quantum-cascade-laser active regions designed to emit at 11 different wavelengths simultaneously. By introducing additional mirror loss in the Fabry–Perot resonator using just a single cleaved facet, with the other mirror formed by wet etching, the laser threshold current is significantly increased and superlinear light-current characteristics are observed. Optical peak powers of several tens of μW are measured at low temperatures.
Electromechanical coupling factors of single-domain 0.67Pb(Mg1∕3Nb2∕3)O3–0.33PbTiO3 single-crystal thin films
Authors: Wasa K. , Ito S. , Nakamura K. , Matsunaga T. , Kanno I. , Suzuki T. , Okino H. , Yamamoto T. , Seo S. H. , Noh D. Y.
Published: March 2006

Thin films of single c-domain/single-crystal (1−x)Pb(Mg1∕3Nb2∕3)O3−xPbTiO3 (PMN-PT) with x≅0.33 near a morphotropic boundary composition were heteroepitaxially grown on (110)SRO∕(001)Pt∕(001)MgO substrates. The heteroepitaxial growth was achieved by rf-magnetron sputtering at the substrate temperature of 600°C. After the sputtering deposition, the substrates were rapidly cooled from 600°C to room temperature by atmospheric air gas at a cooling rate of 100°C∕min. The rapid cooling process enhanced the heteroepitaxial growth of the single c-domain/single crystal PMN-PT thin films. Their electromechanical coupling factor kt measured by a resonance spectrum method was 45% at resonant frequency of 1.3GHz with phase velocity of 5500 to 6000m∕s for the film thickness of 2.3μm. The d33 and d31 were 194pC∕N and −104pC∕N, respectively. The observed kt,d33, and d31 were almost the same to the bulk single-crystal values. The present PMN-PT thin films are applicable for a fabrication of GHz planar bulk acoustic wave transducers.
Enhanced fatigue-endurance of ferroelectric Pb1−xSrx(Zr0.52Ti0.48)O3 thin films prepared by sol-gel method
Authors: Wang Y. , Shao Q. Y. , Liu J.-M.
Published: March 2006

The polarization fatigue behaviors of ferroelectric Pb1−xSrx(Zr0.52Ti0.48)O3 (PSZT) thin films deposited on Pt-coated silicon wafers are investigated. Significantly enhanced fatigue endurance with increasing Sr doping and decreasing temperature is observed, and the almost fatigue-free performance up to 1010 switching cycles for PSZT (x=0.2) thin films at room temperature is identified. The dc-conductivity measurements suggest almost 20 times decreasing of the oxygen vacancy density as the Sr doping increases from x=0 to x=0.2. It is believed that the Sr-doping enhances the stability of oxygen ions and suppresses oxygen vacancies, consequently resulting in the improved fatigue endurance.
An approximate method to estimate ac loss in tape-wound superconducting coils
Authors: Claassen J. H.
Published: March 2006

An approach to estimate the hysteretic loss in a coil wound with superconducting tape is presented. The loss depends on magnetic fields in the superconductor at peak coil current. For a given total current, the fields depend on how the current is distributed across the tape width. The loss is calculated as a function of a single parameter characterizing a range of plausible current distributions. The minimum should represent an upper bound to the actual loss. Results are presented for a specific pancake coil example, both isolated and incorporated as part of an assembly of stacked, identical coils.
Structural order effect in visible photoluminescence properties of nanocrystalline Si:H thin films
Authors: Chen H. , Shen W. Z. , Wei W. S.
Published: March 2006

We report room-temperature visible photoluminescence (PL) properties of highly ordered hydrogenated nanocrystalline Si(nc-Si:H) with good electrical performance. The PL profiles can be well reproduced by the model of Islam and Kumar [J. Appl. Phys. 93, 1753 (2003)], incorporating the effects of quantum confinement and localized surface states, as well as a log-normal crystallite size distribution. Raman, PL, and electrical results consistently reveal that improvement of structural order within nc-Si:H is beneficial to enhance the PL efficiency. Owing to adequate order, strong visible PL and high electron mobility can coexist in nc-Si:H, which may provide possibilities in Si-based optoelectronics.
The formation characteristics of closed-loop random cavities inside highly disordered ZnO polycrystalline thin films
Authors: Yu S. F. , Li H. D. , Abiyasa A. P. , Leong Eunice S. P. , Lau S. P.
Published: March 2006

The formation characteristics of closed-loop random cavities inside highly disordered ZnO films with and without rib waveguide structure are investigated. The size dependence of the random cavities inside the random media on temperature and pump intensity profile is studied by applying Fourier transform to the corresponding lasing spectra. Simple rate equation analysis has revealed that the formation of the random cavities depends mainly on the profile of the optical gain, which is a function of the pump intensity profile and carrier diffusion length of the random media.
Site of Er ions in silica layers codoped with Si nanoclusters and Er
Authors: Pellegrino P. , Garrido B. , Arbiol J. , Garcia C. , Lebour Y. , Morante J. R.
Published: March 2006

Silica layers implanted with Si and Er ions to various doses and annealed at 950°C have been investigated by means of energy-filtered transmission electron microscopy (EFTEM) and high annular angle dark field (HAADF). EFTEM analysis reveals Si nanoclusters (Si-nc) with an average size around 3nm for high Si content (15at.%) whereas no clusters can be imaged for the lowest Si excess (5at.%). Raman scattering supports that amorphous Si precipitates are present in all the samples. Moreover, the filtered images show that Er ions appear preferentially located outside the Si-nc. HAADF analysis confirms that the Er atoms form agglomerations of 5–10nm size when the Er concentration exceeds 1×1020cm−3. This observation correlates well with the reduction of the Er population excitable by Si nanoclusters, in the best case corresponding to 10% of the total. A suitable tuning of the annealing drastically reduces this deleterious effect.
Determination of grain boundary stiffness from molecular dynamics simulation
Authors: Zhang Hao , Du Danxu , Srolovitz David J. , Mendelev Mikhail I.
Published: March 2006

We report the quantitative prediction of grain boundary stiffness as a function of boundary inclination using molecular dynamics simulations in a series of Σ5 [001] tilt grain boundaries. The grain boundary stiffness exhibits a large anisotropy, which is of the same order of magnitude as that of the grain boundary mobility. Surprisingly, these two anisotropies nearly cancel, leaving the reduced mobility (product of the stiffness and boundary mobility) nearly isotropic.
Ultrafast carrier dynamics in InxGa1−xN (0001) epilayers: Effects of high fluence excitation
Authors: Lioudakis Emmanouil , Othonos Andreas , Dimakis Emmanouil , Iliopoulos Eleftherios , Georgakilas Alexandros
Published: March 2006

Ultrafast carrier dynamics in InxGa1−xN (0001) epilayers were investigated, using femtosecond transient differential transmission and reflection measurements for x=0.07, 0.15, and 0.33, over a fluence range of 1–12mJ∕cm2. Stimulated emission as well as band gap renormalization play a crucial role in the dynamics of the photogenerated carriers. Threshold fluence leading to saturation of the differential reflectivity and transmission signals related to the In mole fraction has been observed, which is attributed to band gap renormalization, Auger process, and carrier recombination through In-rich nanoclusters. Furthermore, coherent acoustic phonon oscillations have also been observed in the In0.15Ga0.85N at high fluence excitation.
Study of the dielectric function of hexagonal InN: Impact of indium clusters and of native oxide
Authors: Losurdo Maria , Bruno Giovanni , Kim Tong-Ho , Choi Soojeong , Brown April
Published: March 2006

The complex dielectric function of hexagonal InN has been determined in the 0.72–6.50eV photon energy range using spectroscopic ellipsometry. The InN films have been synthesized using molecular beam epitaxy on Si-face 6H-SiC(0001) substrates. The fundamental band gap E0 and higher energy interband critical points have been identified at room temperature. The impact of indium clusters and of the InN native oxide on the dielectric function is discussed.
Syntheses and vibrational spectra of some tris(alkanethiolato)mercurate(II) complexes, and crystal structure of the Hexakis(methanethiolato)dimercurate(II) dianion
Authors: Bowmaker GA , Dance IG , Dobson BC , Rogers DA
Published: March 2006

The complexes [cation]
[Hg(SR)3](R = Me, cation = Et4N+; R = But,
cation = Et4N+, Bu4N+, [N(Ph3P)2]+)
have been prepared. The crystal structure of the methanethiolate
complex shows that it contains centrosymmetric dinuclear
anions [(MeS)2Hg(�-SMe)2Hg(SMe)2]2- with distorted tetrahedral
geometry about the mercury atoms. Vibrational
spectroscopic evidence suggests that this complex dissociates on dissolution in
ethanol to give mononuclear [Hg(SMe)3]-
species. The ButS- complexes appear to
exist as mononuclear [Hg(SBut)3]-
species both in the solid state and in solution. The metal-sulfur stretching
frequencies are assigned for all of the complexes studied, and the vibrational spectra are discussed in terms of the
structures of the complex anions involved. Crystal data for [(C2H5)4N]2Hg2(SCH3)6
: a 8.656(5), b gS130(6), c 12.368(8) �;
α 102.16(4), β 105.51(4), γ 105.29(4)�; space group P1, Z 1, R
0.034, Rw 0.042.
The endo- and exo-1,7,7-Trimethylbicyclo[2.2.1]heptan-2-amines (Bornan-2-amines) and their acetamides
Authors: Carman RM , Greenfield KL
Published: March 2006

Melting points provide a
poor method for differentiation between the exo and endo N-(bornan-2-yl)- acetamides, and have led to errors by previous workers.
Spectral differences leading to unambiguous assignment are discussed in this
paper. Trapping of the bornan-2-yl carbenium ion with
acetonitrile leads to exo products.
Phylogenetic relationships within the genus Atopobathynella Schminke (Bathynellacea:Parabathynellidae)
Authors: Cho Joo-Lae , Humphreys W. F. , Lee Sang-Don
Published: March 2006

The present study attempts to reconstruct the phylogenetic relationships among species of Atopobathynella Schminke, 1973 in order to elucidate their distributional patterns and to seek a mechanism for the worldwide colonisation of the limnic interstitial by the Parabathynellidae. We describe six new Atopobathynella recently discovered in Western Australia: A. gascoyneensis, sp. nov., A. hinzeae, sp. nov., A. schminkei, sp. nov., A. wattsi, sp. nov., A. readi, sp. nov. and A. glenayleensis, sp. nov. The phylogenetic relationships among these species and four previously known species in the genus are assessed using 28 morphological characters. The analysis yielded two most parsimonious trees 71 steps long with consistency index 0.5070, retention index 0.5270, and rescaled consistency index 0.2672. One of these trees supports the grouping of A. readi, sp. nov. + (((A. wattsi, sp. nov. + A. glenaylensis, sp. nov.) + (A. hospitalis Schminke, 1973 (A. gascoyneensis, sp. nov. (A. schminkei, sp. nov. + A. hinzeae, sp. nov.)))) + (A. valdiviana (Noodt, 1964) (A. compagana Schminke, 1973 + A. chelifera Schminke, 1973))). We discuss the monophyly of Atopobathynella and its phylogenetic position within the family Parabathynellidae. The results of the phylogenetic analysis and the biogeographical data suggest that the ancestors of Atopobathynella colonized groundwater via limnic surface water.
An overview of the phylogeny of the families Lafoeidae and Hebellidae (Hydrozoa:Leptothecata): their composition and classification
Authors: Marques Antonio C. , Peña Cantero Alvaro L. , Migotto Alvaro E.
Published: March 2006

A cladistic analysis of the genera of the family ‘Lafoeidae’ was performed in order to investigate suprageneric classifications and the boundaries of the family, as well as to organise the available morphological data and discuss the possible evolution of some morphological characters. Our results suggest that the former ‘Lafoeidae’ must be separated into two families: the Hebellidae and the Lafoeidae (including the subfamilies Lafoeinae and Zygophylacinae).
A morphometric analysis of mygalomorph spider carapace shape and its efficacy as a phylogenetic character (Araneae)
Authors: Bond Jason E. , Beamer David A.
Published: March 2006

Shape features are often used as characters in cladistic analyses, yet states of these characters are seldom delineated in an objective, repeatable fashion. Carapace shape is one such character that is often used in analyses of mygalomorph spider relationships. For example, most analyses have used cephalic region morphology (e.g. steeply arched v. flat or sloping) as a key feature that delineates some major clades. In practice, carapace shapes at the extremes are relatively easy to identify; however, intermediate carapace shapes have proven to be much more difficult to objectively score in one of three shape categories. In this study, carapace shape is used as an exemplar characteristic to evaluate the utility of shape features in phylogenetic analyses and to evaluate our ability to effectively score discrete character states. Carapaces from 178 spider specimens sampled across 13 of the 15 nominal mygalomorph families were digitally photographed and their outlines were traced and pseudo-landmarks plotted. An elliptical Fourier analysis was then employed in an attempt to both delineate and assess character states. It is concluded that landmark analyses are inappropriate for carapace shape delineation as a result of difficulties in scoring precision and, thus, outline analyses are the preferred method given the morphology. Carapace shape is not a very useful character for broad-level systematic studies of mygalomorph relationships owing to the variable nature of the feature and our inability to detect discrete discernable shapes.
The expression of the clock protein PER2 in the limbic forebrain is modulated by the estrous cycle
Authors: Perrin Jennifer S. , Segall Lauren A. , Harbour Valerie L. , Woodside Barbara , Amir Shimon
Published: March 2006

Daily behavioral and physiological rhythms are linked to circadian oscillations of clock genes in the brain and periphery that are synchronized by the master clock in the suprachiasmatic nucleus. In addition, there are a number of inputs that can influence circadian oscillations in clock gene expression in a tissue-specific manner. Here we identify an influence on the circadian oscillation of the clock protein PER2, endogenous changes in ovarian steroids, within two nuclei of the limbic forebrain: the oval nucleus of the bed nucleus of the stria terminalis and central nucleus of the amygdala. We show that the daily rhythm of PER2 expression within these nuclei but not in the suprachiasmatic nucleus, dentate gyrus, or basolateral amygdala is blunted in the metestrus and diestrus phases of the estrus cycle. The blunting of the PER2 rhythm at these phases of the cycle is abolished by ovariectomy and restored by phasic estrogen replacement suggesting that fluctuations in estrogen levels or their sequelae are necessary to produce these effects. The finding that fluctuations in ovarian hormones have area-specific effects on clock gene expression in the brain introduces a new level of organizational complexity in the control of circadian rhythms of behavior and physiology.
The Relationship between Proliferating Cell Nuclear Antigen Expression and Histomorphometrical Alterations in Cyclosporin A-Induced Gingival Overgrowth in Rats
Authors: Cetinkaya Burcu Ozkan , Acikgoz Gokhan , Aydin Oguz , Korkmaz Adnan , Keles Gonca Cayir
Published: March 2006

The aim of this study was to investigate the relationship between Proliferating Cell Nuclear Antigen (PCNA) expression and histomorphometrical alterations in cyclosporin A (CsA)-induced gingival overgrowth with or without microbial dental plaque accumulation. Forty male Wistar rats were equally divided into 4 groups; Group I (control); Group II (CsA); Group III (ligature); Group IV (ligature and CsA). After 8 weeks of experimental period, rats were subsequently decapitated and mandibular molars were dissected. Gingival overgrowth was determined by measuring depth of the gingival sulcus, then the mandible were decalcified and serial sections were obtained for histomorphometric and immunohistochemical analysis. Histomorphometric analysis included the measurement of epithelial thickness; immunohistochemical analysis included the assessment of PCNA expression in the oral and sulcular epithelium of buccal and lingual gingiva. Epithelial thickness and PCNA expression were significantly increased in buccal oral epithelium of Group II ( p < 0.05) and in all regions in Group IV ( p < 0.05) compared to control group. Also gingival overgrowth was more prominent in Group IV in comparison to Group II. These results indicate that CsA-induced gingival alterations are closely accociated with increased epithelial proliferative activity, and dental plaque accumulation seems not to be an essential but to be an aggrevating factor for the progression of the lesion.
Spontaneous and Irradiation-Induced Tumor Susceptibility in Brca2 Germline Mutant Mice and Cooperative Effects with a p53 Germline Mutation
Authors: McAllister Kimberly A. , Houle Christopher D. , Malphurs Jason , Ward Toni , Collins N. Keith , Gersch William , Wharey Laura , Seely John C. , Betz Laura , Bennett L. Michelle , Wiseman Roger W. , Davis Barbara J.
Published: March 2006

Mutations in both p53 and BRCA2 are commonly seen together in human tumors suggesting that the loss of both genes enhances tumor development. To elucidate this interaction in an animal model, mice lacking the carboxy terminal domain of Brca2 were crossed with p53 heterozygous mice. Females from this intercross were then irradiated with an acute dose of 5 Gy ionizing radiation at 5 weeks of age and compared to nonirradiated controls. We found decreased survival and timing of tumor onsets, and significantly higher overall tumor incidences and prevalence of particular tumors, including stomach tumors and squamous cell carcinomas, associated with the homozygous loss of Brca2, independent of p53 status. The addition of a p53 mutation had a further impact on overall survival, incidence of osteosarcomas and stomach tumors, and tumor latency. The spectrum of tumors observed for this Brca2 germline mouse model suggest that it faithfully recapitulates some human disease phenotypes associated with BRCA2 loss. In addition, these findings include extensive in vivo data demonstrating that germline Brca2 and p53 mutations cooperatively affect animal survivals, tumor susceptibilities, and tumor onsets.
Ireland’s National Innovation System: An Exploratory Study of Supporting Institutions and Dynamic Actors
Authors: Pontikakis Dimitrios , McDonnell Thomas , Geoghegan Will
Published: March 2006

This paper begins with a brief look at the literature on national innovation systems (NIS). Building on the NIS approach, we present a simple conceptual framework. National innovative competence is dependent on the presence of dynamic STI actors, operating within the confines of compatible institutions. We distinguish the roles played by different STI actors and argue that heterogeneous actors engage in innovation for different reasons. Collaborative innovation is not always a natural consequence of engagement in innovation but is characterised by a distinct set of considerations. The latter part of the paper is concerned with the application of this conceptual framework to the case of Ireland. We identify the institutions pertaining to Ireland’s current innovative performance. An outline of STI actors according to their role in the system is then presented. In turn we outline the various contributions of Irish STI actors and explore their motives for engaging in innovation and collaborative innovation.
Policy Initiative Dilemmas Surrounding Media Convergence: A Cross National Perspective
1
Authors: Menon Siddhartha
Published: March 2006

The discourse surrounding convergence of mass media content and infrastructures has been fraught with extravagant expectations and rhetoric. This article utilizes a cross‐national perspective and focuses on regulatory aspects of the media convergence issue in order to explore the disconnect between the hype and realities of convergence. Three research questions characterize the relevant existing policy initiatives, identify obstacles to convergence and in comparativist terms ascertain which policy models have been relatively more effective. This paper adopts a case study structure integrating convergence policy models in the US, South Africa, Japan and India.
English Spelling Reform
Authors: Carter James B.
Published: March 2006

Knowledge is the wealth of nations, and language is the main social technology by which knowledge is communicated. An efficient orthography is therefore of great importance. English, as the principal international language of the early twenty‐first century, has much to offer the world, but its spelling is archaic and dysfunctional. Technically, the reform of English spelling would not be difficult, but there are very major political obstacles in the way. The benefits of spelling reform would greatly exceed the costs, and a ‘Big bang’ approach to reform is required. The present article outlines a technical solution and the way in which reform could be implemented.
Roger Backhouse on the Study of Dissent
Authors: Samuels Warren J.
Published: March 2006

Roger Backhouse (Backhouse 2004) has provided both an insightful deconstruction of dissent and a suggested terminology to deal with subtle distinctions within the domain of dissent, especially regarding the status of heterodoxy. There is more to be said, largely in expansion of his analyses—placing his analyses in a larger context. Section I summarizes Backhouse's position and Section II presents my own thoughts.
Lymphocytes: not useless after all
Authors: Clayton Julie
Published: March 2006

Half a century ago, an immunologist named N. Avrion Mitchison showed that lymphocytes—then thought to be useless—triggered tumor rejection in mice.
On invariant distances on asymptotic Teichmüller spaces
Authors: Miyachi Hideki
Published: March 2006

In this paper, we will establish that any invariant distance on asymptotic Teichmüller space is a complete distance.
Compact composition operators not in the Schatten classes
Authors: Jones Matthew
Published: March 2006

We provide a direct construction of the mapping

φ
\varphi

given by Tom Carroll and Carl Cowen in ‘Compact composition operators not in the Schatten classes’ (1991, in J. Operator Theory 26).
The inner amenability of the generalized Thompson group
Authors: Picioroaga Gabriel
Published: March 2006

In this paper we prove that the general version

F
(
N
)

F(N)

of the Thompson group is inner amenable. As a consequence we generalize a result of P. Jolissaint. To do so, we prove first that

F
(
N
)

F(N)

together with a normal subgroup are i.c.c (infinite conjugacy classes) groups. Then, we investigate the relative McDuff property out of which we extract property

Γ
\Gamma

for the group von Neumann algebras involved. By a result of E. G. Effros,

F
(
N
)

F(N)

follows inner amenable.
Unique continuation for the system of elasticity in the plane
Authors: Escauriaza L.
Published: March 2006

We prove the strong unique continuation property for the Lamé system of elastostatics in the plane,

∇
⋅

(
μ

(
∇
u
+
∇

u
t

)

)

+
∇

(
λ
∇
⋅
u
)

=
0

\nabla \cdot \left (\mu \left (\nabla u+\nabla u^t \right ) \right )+\nabla \left (\lambda \nabla \cdot u\right )=0

, with variable Lamé coefficients

μ
\mu

,

λ
\lambda

, when

μ
\mu

is Lipschitz and

λ
\lambda

is measurable.
The groupoid algebra of an eigenvalue pattern
Authors: Tsang Kin-Wai
Published: March 2006

The eigenvalue pattern of a *-homomorphism between two matrix algebras over commutative C∗^*-algebras is a generalization of the Gelfand map in the commutative case. We give a systematic formulation of abstract eigenvalue pattern and extend the classical results by using a technique involving the groupoid algebras of eigenvalue patterns. In the case with matrix algebras over the one-dimensional circle, we characterize all the *-homomorphisms up to unitary equivalence by their eigenvalue patterns. Moreover, this technique has an application to recent classification theorems of C∗^*-algebras proved by the present author.
Contractible subgraphs and Morita equivalence of graph 𝐶*-algebras
Authors: Crisp Tyrone , Gow Daniel
Published: March 2006

In this paper we describe an operation on directed graphs which produces a graph with fewer vertices, such that the

C
∗

C^*

-algebra of the new graph is Morita equivalent to that of the original graph. We unify and generalize several related constructions, notably delays and desingularizations of directed graphs.
Spectrum of bilateral shifts with operator-valued weights
Authors: Bourhim A.
Published: March 2006

We describe the spectrum of bilateral operator-weighted shifts.
𝖫^{2}-summand vectors in Banach spaces
Authors: Aizpuru Antonio , Garcia-Pacheco Francisco
Published: March 2006

The aim of this paper is to study the set

L

X

2

\mathsf {L} _{X}^{\mathtt {2}}

of all

L

2

\mathsf {L}^{\mathtt {2}}

-summand vectors of a real Banach space

X
X

. We provide a characterization of

L

2

\mathsf {L}^{\mathtt { 2}}

-summand vectors in smooth real Banach spaces and a general decomposition theorem which shows that every real Banach space can be decomposed as an

L

2

\mathsf {L}^{\mathtt {2}}

-sum of a Hilbert space and a Banach space without nontrivial

L

2

\mathsf {L}^{\mathtt {2}}

-summand vectors. As a consequence, we generalize some results and we obtain intrinsic characterizations of real Hilbert spaces.
A note about the shape of attractors of discrete semidynamical systems
Authors: Morón Manuel , del Portal Francisco
Published: March 2006

We state in a short way a result that improves one of the main theorems in a paper of M. Gobbino concerning the topological properties that the phase space induces in an attractor of a discrete dynamical system.
The ESCRT-III Subunit hVps24 Is Required for Degradation but Not Silencing of the Epidermal Growth Factor Receptor
Authors: Bache Kristi G. , Stuffers Susanne , Malerød Lene , Slagsvold Thomas , Raiborg Camilla , Lechardeur Delphine , Wälchli Sébastien , Lukacs Gergely L. , Brech Andreas , Stenmark Harald
Published: March 2006

The endosomal sorting complexes required for transport, ESCRT-I, -II, and -III, are thought to mediate the biogenesis of multivesicular endosomes (MVEs) and endosomal sorting of ubiquitinated membrane proteins. Here, we have compared the importance of the ESCRT-I subunit tumor susceptibility gene 101 (Tsg101) and the ESCRT-III subunit hVps24/CHMP3 for endosomal functions and receptor signaling. Like Tsg101, endogenous hVps24 localized mainly to late endosomes. Depletion of hVps24 by siRNA showed that this ESCRT subunit, like Tsg101, is important for degradation of the epidermal growth factor (EGF) receptor (EGFR) and for transport of the receptor from early endosomes to lysosomes. Surprisingly, however, whereas depletion of Tsg101 caused sustained EGF activation of the mitogen-activated protein kinase pathway, depletion of hVps24 had no such effect. Moreover, depletion of Tsg101 but not of hVps24 caused a major fraction of internalized EGF to accumulate in nonacidified endosomes. Electron microscopy of hVps24-depleted cells showed an accumulation of EGFRs in MVEs that were significantly smaller than those in control cells, probably because of an impaired fusion with lyso-bisphosphatidic acid-positive late endosomes/lysosomes. Together, our results reveal functional differences between ESCRT-I and ESCRT-III in degradative protein trafficking and indicate that degradation of the EGFR is not required for termination of its signaling.
The levansucrase and inulosucrase enzymes of Lactobacillus reuteri 121 catalyse processive and non-processive transglycosylation reactions
Authors: Ozimek Lukasz K. , Kralj Slavko , van der Maarel Marc J. E. C. , Dijkhuizen Lubbert
Published: March 2006

Bacterial fructosyltransferase (FTF) enzymes synthesize fructan polymers from sucrose. FTFs catalyse two different reactions, depending on the nature of the acceptor, resulting in: (i) transglycosylation, when the growing fructan chain (polymerization), or mono- and oligosaccharides (oligosaccharide synthesis), are used as the acceptor substrate; (ii) hydrolysis, when water is used as the acceptor. Lactobacillus reuteri 121 levansucrase (Lev) and inulosucrase (Inu) enzymes are closely related at the amino acid sequence level (86 % similarity). Also, the eight amino acid residues known to be involved in catalysis and/or sucrose binding are completely conserved. Nevertheless, these enzymes differ markedly in their reaction and product specificities, i.e. in β(2→6)- versus β(2→1)-glycosidic-bond specificity (resulting in levan and inulin synthesis, respectively), and in the ratio of hydrolysis versus transglycosylation activities [resulting in glucose and fructooligosaccharides (FOSs)/polymer synthesis, respectively]. The authors report a detailed characterization of the transglycosylation reaction products synthesized by the Lb. reuteri 121 Lev and Inu enzymes from sucrose and related oligosaccharide substrates. Lev mainly converted sucrose into a large levan polymer (processive reaction), whereas Inu synthesized mainly a broad range of FOSs of the inulin type (non-processive reaction). Interestingly, the two FTF enzymes were also able to utilize various inulin-type FOSs (1-kestose, 1,1-nystose and 1,1,1-kestopentaose) as substrates, catalysing a disproportionation reaction; to the best of our knowledge, this has not been reported for bacterial FTF enzymes. Based on these data, a model is proposed for the organization of the sugar-binding subsites in the two Lb. reuteri 121 FTF enzymes. This model also explains the catalytic mechanism of the enzymes, and differences in their product specificities.
Bacillus subtilis EzrA and FtsL synergistically regulate FtsZ ring dynamics during cell division
Authors: Kawai Yoshikazu , Ogasawara Naotake
Published: March 2006

Previous work has shown that the Bacillus subtilis EzrA protein directly inhibits FtsZ ring assembly, which is required for normal cell division, and that loss of EzrA results in hyperstabilization of the FtsZ polymer in vivo. Here, it was found that in ezrA-disrupted cells, artificial expression of YneA, which suppresses cell division during the SOS response, and disruption of noc (yyaA), which acts as an effector of nucleoid occlusion, resulted in accumulation of multiple non-constricting FtsZ rings, inhibition of cell division, and synthetic lethality. Overexpression of the essential cell division protein FtsL suppressed the effect of ezrA disruption. FtsL overexpression recovered the delayed FtsZ ring constriction seen in ezrA-disrupted wild-type cells. Conversely, the absence of EzrA caused lethality in cells producing a lower amount of FtsL than wild-type cells. It has previously been reported that FtsL is recruited to the division site during the later stages of cell division, although its exact role is currently unknown. The results of this study suggest that FtsL and EzrA synergistically regulate the FtsZ ring constriction in B. subtilis. Interestingly, FtsL overexpression also suppressed the cell division inhibition due to YneA expression or Noc inactivation in ezrA-disrupted cells.
Exploitation of a β-lactamase reporter gene fusion in the carbapenem antibiotic production operon to study adaptive evolution in Erwinia carotovora
Authors: Bowden Steven D. , Salmond George P. C.
Published: March 2006

Erwinia carotovorasubsp.carotovorastrain ATTn10 produces theβ-lactam antibiotic 1-carbapen-2-em-3-carboxylic acid (carbapenem) by expressing thecarABCDEFGHoperon. Mutants exhibiting increased carbapenem gene transcription were positively selected using an engineered strain with a functionalβ-lactamase translational fusion incarH, the last gene of the operon. However, spontaneous ampicillin-resistant mutants were isolated even when transcription ofcarH : : blaMwas blocked by a strongly polar mutation incarE. The mechanism of resistance was shown to be due to cryptic IS10elements transposing upstream ofcarH : : blaM, thereby providing new promoters enablingcarH : : blaMtranscription. Southern blots showed that IS10was present in multicopy in ATTn10. In addition, a Tn10genetic remnant was discovered. The results offer insights into the genetic archaeology of strain ATTn10 and highlight the powerful impacts of cryptic IS elements in bacterial adaptive evolution.
The role of a gene cluster for trehalose metabolism in dehydration tolerance of the filamentous cyanobacterium Anabaena sp. PCC 7120
Authors: Higo Akiyoshi , Katoh Hiroshi , Ohmori Kazuko , Ikeuchi Masahiko , Ohmori Masayuki
Published: March 2006

Expression of the genes for trehalose synthesis (mtsandmth, encoding maltooligosyl trehalose synthase and hydrolase) and trehalose hydrolysis (treH) inAnabaenasp. PCC 7120 was up-regulated markedly upon dehydration. However, the amount of trehalose accumulated during dehydration was small, whereas a large amount of sucrose was accumulated. Northern blotting analysis revealed that these genes were transcribed as an operon. Gene disruption ofmthresulted in a decrease in the trehalose level and in tolerance during dehydration. In contrast, gene disruption oftreHresulted in an increase in both the amount of trehalose and tolerance. These results suggest that trehalose is important for the dehydration tolerance of this cyanobacterium. The amount of trehalose accumulated during dehydration was small, corresponding to 0·05–0·1 % of dry weight, suggesting that trehalose did not stabilize proteins and membranes directly during dehydration. To reveal the role of trehalose, the expression profiles of the wild-type strain and gene disruptants during dehydration were compared by using oligomeric DNA microarray. It was found that the expression of two genes, one of which encodes a cofactor of a chaperone DnaK, correlated with trehalose content, suggesting that a chaperone system induced by trehalose is important for the dehydration tolerance ofAnabaenasp. PCC 7120.
Identification of a Spiroplasma citri hydrophilic protein associated with insect transmissibility
Authors: Killiny Nabil , Batailler Brigitte , Foissac Xavier , Saillard Colette
Published: March 2006

With the aim of identifyingSpiroplasma citriproteins involved in transmission by the leafhopperCirculifer haematoceps, protein maps of four transmissible and four non-transmissible strains were compared. Total cell lysates of strains were analysed by two-dimensional gel electrophoresis using commercially available immobilized pH gradients (IPGs) covering a pH range of 4–7. Approximately 530 protein spots were visualized by silver staining and the resulting protein spot patterns for the eight strains were found to be highly similar. However, comparison using PDQuest 2-D analysis software revealed two trains of protein spots that were present only in the four transmissible strains. Using MALDI-TOF (matrix-assisted laser desorption/ionization time-of-flight) mass spectrometry and a nearly completeS. citriprotein database, established during the still-ongoingS. citriGII-3-3X genome project, the sequences of both proteins were deduced. One of these proteins was identified in the general databases as adhesion-related protein (P89) involved in the attachment ofS. citrito gut cells of the insect vector. The second protein, with an apparent molecular mass of 32 kDa deduced from the electrophoretic mobility, could not be assigned to a known protein and was named P32. The P32-encoding gene (714 bp) was carried by a large plasmid of 35·3 kbp present in transmissible strains and missing in non-transmissible strains. PCR products with primers designed from thep32gene were obtained only with genomic DNA isolated from transmissible strains. Therefore, P32 has a putative role in the transmission process and it could be considered as a marker forS. citrileafhopper transmissibility. Functional complementation of a non-transmissible strain with thep32gene did not restore the transmissible phenotype, despite the expression of P32 in the complemented strain. Electron microscopic observations of salivary glands of leafhoppers infected with the complemented strain revealed a close contact between spiroplasmas and the plasmalemma of the insect cells. This further suggests that P32 protein contributes to the association ofS. citriwith host membranes.
Identification of a transposable genomic island of Paracoccus pantotrophus DSM 11072 by its transposition to a novel entrapment vector pMMB2
Authors: Mikosa Malgorzata , Sochacka-Pietal Marta , Baj Jadwiga , Bartosik Dariusz
Published: March 2006

A novel shuttle entrapment vector, pMMB2, was used to identify a large transposable element, TnPpa1 (44·3 kb), of Paracoccus pantotrophus DSM 11072. TnPpa1 has a composite structure with divergently oriented copies of a cryptic transposon, Tn3434 (Tn3 family), located at both termini. The core region of the element contains a large set of putative genes, whose products show similarity to enzymes involved in central intermediary metabolism (e.g. tricarboxylic acid cycle or 2-methylcitrate cycle), transporters, transcriptional regulators and conserved proteins of unknown function. A 4·2 kb DNA segment of TnPpa1 is homologous to a region of chromosome cII of Rhodobacter sphaeroides 2.4.1, which exemplifies the mosaic structure of this element. TnPpa1 is bordered by 5 bp long directly repeated sequences and is located within a mega-sized replicon, pWKS5, in the DSM 11072 genome. Spontaneous inversion of the core region of TnPpa1 was detected in the host genome. Analysis of the distribution of TnPpa1 in three other strains of P. pantotrophus revealed that this element was present exclusively within DSM 11072, which suggests its relatively recent acquisition by lateral transfer. The identification of TnPpa1 (which may be considered a transposable genomic island) provides evidence for the transposition and lateral transfer of large DNA segments of chromosomal origin (carrying various housekeeping genes), which may have a great impact on the evolution of bacterial genomes.
Biofilm formation by mycoplasma species and its role in environmental persistence and survival
Authors: McAuliffe Laura , Ellis Richard J. , Miles Katie , Ayling Roger D. , Nicholas Robin A. J.
Published: March 2006

Although mycoplasmas possess a very limited genome, little is known about their virulence mechanisms and methods of persistence in the host. Examination of a wide range of mycoplasma species found considerable variation in their ability to form a biofilm.Mycoplasma putrefaciens,M. cottewii,M. yeatsii,M. agalactiaeandM. bovisproduced prolific biofilms. Conversely, the highly pathogenic mycoplasma and causative agent of contagious bovine pleuropneumonia,Mycoplasma mycoidessubsp.mycoidesSC, was unable to produce a biofilm. Biofilms were found to be considerably more resistant to stress, including heat and desiccation, than planktonic cells. A link between the biofilm phenotype and genotype as determined by molecular typing was found forM. bovis. Analysis of biofilms using fluorescent staining combined with confocal microscopy demonstrated that mycoplasma biofilms formed a highly differentiated structure with stacks and channels. Biofilm formation may indicate that mycoplasmas are capable of surviving in the environment.
The MAP kinase signal transduction network in Candida albicans
Authors: Monge R. Alonso , Román E. , Nombela C. , Pla J.
Published: March 2006

MAP (mitogen-activated protein) kinase-mediated pathways are key elements in sensing and transmitting the response of cells to environmental conditions by the sequential action of phosphorylation events. In the fungal pathogenCandida albicans, different routes have been identified by genetic analysis, and especially by the phenotypic characterization of mutants altered in the Mkc1, Cek1/2 and Hog1 MAP kinases. The cell integrity (orMKC1-mediated) pathway is primarily involved in the biogenesis of the cell wall. The HOG pathway participates in the response to osmotic stress while the Cek1 pathway mediates mating and filamentation. Their actual functions are, however, much broader and Mkc1 senses several types of stress, while Hog1 is also responsive to other stress conditions and participates in two morphogenetic programmes: filamentation and chlamydospore formation. Furthermore, it has been recently shown that Cek1 participates in a putative pathway involved in the construction of the cell wall and which seems to be operative under basal conditions. As these stimuli are frequently encountered in the human host, they provide a reasonable explanation for the significant reduction in pathogenicity that several signal transduction mutants show in certain animal models of virulence. MAPK pathways therefore represent an attractive multienzymic system for which novel antifungal therapy could be designed.
An orphan DNA (cytosine-5-)-methyltransferase in Vibrio cholerae
Authors: Banerjee Sanjib , Chowdhury Rukhsana
Published: March 2006

5-Methyl cytosine (m5C) was detected in genomic DNA of the enteric pathogen Vibrio cholerae by HPLC analysis and immunoblotting with m5C-specific antibody. Although cleavage with the restriction endonuclease EcoRII revealed the absence of a Dcm homologue in V. cholerae, analysis of the genome sequence indicated the presence of a gene, designated in this study as vchM, which encodes a DNA (cytosine-5-)-methyltransferase (m5C-MTase) designated M.Vch. M.Vch is not associated with a restriction endonuclease or a mismatch very short patch repair (Vsr)-like endonuclease and is hence an ‘orphan’ or solitary MTase, although analysis of a phylogenetic tree indicated that related cytosine MTases are all components of restriction-modification systems. M.Vch recognizes and methylates the first 5′ C in the degenerate sequence 5′-RCCGGY-3′. RT-PCR analysis suggested that vchM gene expression is increased during the stationary phase of growth. During stationary phase, the spontaneous mutation frequency in the V. cholerae wild-type strain was significantly higher than in the corresponding vchM mutant strain, suggesting that the presence of M.Vch and the absence of a very short patch (VSP) repair-like system imposes upon V. cholerae a mutator phenotype.
The response of Escherichia coli to exposure to the biocide polyhexamethylene biguanide
Authors: Allen Michael J. , White Graham F. , Morby Andrew P.
Published: March 2006

The global response ofEscherichia colito the broad-spectrum biocide polyhexamethylene biguanide (PHMB) was investigated using transcriptional profiling. The transcriptional analyses were validated by direct determination of the PHMB-tolerance phenotypes of derivatives ofE. coliMG1655 carrying either insertionally inactivated genes and/or plasmids expressing the cognate open reading frames from a heterologous promoter in the corresponding chromosomally inactivated strains. The results showed that a wide range of genes was altered in transcriptional activity and that all of the corresponding knockout strains subsequently challenged with biocide were altered in tolerance. Of particular interest was the induction of therhsgenes and the implication of enzymes involved in the repair/binding of nucleic acids in the generation of tolerance, suggesting a novel dimension in the mechanism of action of PHMB based on its interaction with nucleic acids.
Subtractive hybridization and optical mapping of the enterotoxigenic Escherichia coli H10407 chromosome: isolation of unique sequences and demonstration of significant similarity to the chromosome of E. coli K-12
Authors: Chen Qing , Savarino Stephen J. , Venkatesan Malabi M.
Published: March 2006

Enterotoxigenic Escherichia coli (ETEC) is a primary cause of diarrhoea in infants in developing countries and in travellers to endemic regions. While several virulence genes have been identified on ETEC plasmids, little is known about the ETEC chromosome, although it is expected to share significant homology in backbone sequences with E. coli K-12. In the absence of genomic sequence information, the subtractive hybridization method and the more recently described optical mapping technique were carried out to determine the degree of genomic variation between virulent ETEC strain H10407 and the non-pathogenic E. coli K-12 strain MG1655. In one round of PCR-based suppression subtractive hybridization, 153 fragments representing sequences unique to strain H10407 were identified. blast searches indicated that few unique sequences showed homology to known pathogenicity island genes identified in related E. coli pathogens. A total of 65 fragments contained sequences that were either linked to hypothetical proteins or showed no homology to any known sequence in the database. The remaining sequences were either phage or prophage related or displayed homology to classifiable genes that function in various aspects of bacterial metabolism. The 153 unique sequences showed variable distribution across different ETEC strains including ETEC strain B7A, which is attenuated in virulence and lacked several H10407-specific sequences. Restriction-enzyme-based optical maps of strain H10407 were compared to in silico restriction maps of strain MG1655 and related E. coli pathogens. The 5·1 Mb ETEC chromosome was ∼500 kb greater in length than the chromosome of E. coli K-12, collinear with it and indicated several discrete regions where insertions and/or deletions had occurred relative to the chromosome of strain MG1655. No major inversions, transpositions or gross rearrangements were observed on the ETEC chromosome. Based on comparisons with known genomic sequences and related optical-map-based restriction site similarity, the sequence of the H10407 chromosome is expected to demonstrate ∼96 % identity with that of E. coli K-12.