bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrafast gain and index dynamics of quantum dash structures emitting at 1.55μm
Authors: van der Poel M. , Mørk J. , Somers A. , Forchel A. , Reithmaier J. P. , Eisenstein G.
Published: August 2006

The authors systematically characterize the ultrafast gain and index recovery of a quantum dash semiconductor optical amplifier after it has amplified a strong femtosecond pulse. The results show a recovery dominated by a fast time constant of 1.4ps with an ultimate recovery taking place on a 150ps time scale. The results are distinctly different from the recovery of quantum dot amplifiers and reflect the special density of states of the quantum-wire-like dashes.
Effects of radial strain on the desorption of hydrogen from the surface of palladium-doped carbon nanotubes
Authors: Guo Z. H. , Yan X. H. , Yang Y. R.
Published: August 2006

By using the first-principles method, the authors study the strain effects on hydrogen desorption on the surface of single-walled carbon nanotubes (SWCNTs). It is found that hydrogen chemisorbed on the surface of carbon nanotubes doped with Pd can be released under large radial strain, for the desorbed hydrogen atoms are molecularly bound by Pd atoms with several tenths of an eV. The method of desorption for the chemisorbed hydrogen can be expected to release the residual hydrogen on the surface of SWCNTs.
Giant magnetoelectric effect in Metglas/polyvinylidene-fluoride laminates
Authors: Zhai Junyi , Dong Shuxiang , Xing Zengping , Li Jiefang , Viehland D.
Published: August 2006

Here, the authors report thin (<100μm) and flexible magnetoelectric (ME) composites consisting of Metglas (high-μ magnetostriction) and polyvinylidene-fluoride (piezopolymer) layers laminated together. Both unimorph and three-layer configurations have been studied. The authors find that these ME laminates (i) require dc magnetic biases as low as 8Oe to (ii) induce giant ME voltage coefficients of 7.2V∕cmOe at low frequencies, and up to 310V∕cmOe under resonant drive.
Origin of clear ferromagnetism for p-type GaN implanted with Fe+ (5 and 10at.%)
Authors: Shon Yoon , Lee Sejoon , Jeon H. C. , Park Y. S. , Kim D. Y. , Kang T. W. , Kim Jin Soak , Kim Eun Kyu , Fu D. J. , Fan X. J. , Park Y. J. , Baik J. M. , Lee J. L.
Published: August 2006

The systematic enhancement of ferromagnetic hysteresis loops for GaN implanted with high doses of Fe (5→10at.%) takes place with an increase in the annealing temperature from 700to850°C. The trends of magnetic properties coincide with the results of the increased full width at half maximum of triple axis diffraction for GaN (0002), including the appearance of GaFeN, the enhanced Fe-related photoluminescence transitions, and the systematic increase in sizes of symmetric spin ferromagnetic domains GaFeN in atomic force microscopy and magnetic force microscopy.
Giant oxidation related relief of Al-rich layers on cleaved mirrors of GaSb∕Ga0.1Al0.9SbAs∕GaInAsSb laser structures
Authors: Dementyev P. A. , Dunaevskii M. S. , Ankudinov A. V. , Makarenko I. V. , Petrov V. N. , Titkov A. N. , Baranov A. N. , Yarekha D. A. , Laiho R.
Published: August 2006

Oxidation kinetics of Al-rich layers in ambient room conditions is investigated on cleaved mirrors of GaSb∕Ga1−xAlxAsSb (x=0.9–0.93) laser heterostructure. The measurements performed by atomic force microscopy demonstrate intensive growth of native oxide during the first two months with further saturation of the oxide thickness to about 1μm. In studies of the oxide cross section using additional cleavages perpendicular to the laser mirror, the volume of the oxidized part of the Al-rich layer is found to expand through elevations on the heterostructure mirror so that the height of the elevations reaches one-third of the total thickness of the oxide.
Negative strain rate sensitivity in ultrahigh-strength nanocrystalline tantalum
Authors: Wang Y. M. , Hodge A. M. , Bythrow P. M. , Barbee T. W. , Hamza A. V.
Published: August 2006

Nanocrystalline tantalum prepared through direct current magnetron sputtering exhibits a negative strain rate sensitivity behavior under nanoindentation; i.e., the hardness value of nanocrystalline tantalum decreases with increasing indentation loading rates. High resolution transmission electron microscopy reveals a beta- to alpha-phase transformation underneath the indents, suggesting that the pseudohexagonal to body-centered cubic structural transformation in nanocrystalline tantalum is likely pressure induced. Evidence of shear banding was documented along the edge of indents, consistent with the negative strain rate sensitivity observed.
Photocurrent response wavelength up to 1.1μm from photovoltaic cells based on narrow-band-gap conjugated polymer and fullerene derivative
Authors: Xia Yangjun , Wang Li , Deng Xianyu , Li Dongyun , Zhu Xuhui , Cao Yong
Published: August 2006

An extremely narrow-band-gap conjugated polymer poly(5,7-bis(4-decanyl-2-thienyl)thieno[3,4-b]diathiazole-thiophene-2,5) (PDDTT) (Eg≈1.01eV) was synthesized by Stille coupling reaction, which absorbs the light from 330–1220nm in solid thin film and shows good solution processibility. The polymeric photovoltaic cells based on PDDTT/[6,6]-phenyl-C61-butyric acid methyl ester blend show the short circuit density of 0.83mA∕cm2, open current voltage of 0.35V, and photocurrent spectra response from 330to1100nm under AM 1.5 simulator (100mW∕cm2).
Percolation transition and colossal magnetoresistive effects in a complex network
Authors: Ju Sheng , Cai Tian-Yi , Guo Guang-Yu , Li Zhen-Ya
Published: August 2006

Recent experiments have shown the intrinsic topology complexity in self-organized manganites. The coexistence of short- and long-range forces and the diversity of many competing phases have challenged present electronic models based on regular lattices. The challenge is approached here by invoking the concept of small-world network, whose topology interpolates between regular lattices and random graphs. Magnetic phase transition and percolation transition in these complex networks are studied via Monte Carlo simulations and finite-size scaling analyses. The observed ramified percolative fractals, signified field-induced percolation transition, and enhanced colossal magnetoresistive effects agree with experiments well.
Wavelength-tunable and high-temperature lasing in ZnMgO nanoneedles
Authors: Yang H. Y. , Lau S. P. , Yu S. F. , Tanemura M. , Okita T. , Hatano H. , Teng K. S. , Wilks S. P.
Published: August 2006

Zn 1 − x Mg x O nanoneedles were prepared by an ion-beam technique on Zn1−xMgxO thin films with Mg contents of up to 21at.%. The photoluminescence emission energies of the Zn1−xMgxO nanoneedles measured at room temperature increased monotonically with Mg contents and it reached 3.6eV when x=0.21. Random laser action was observed in the Zn1−xMgxO nanoneedles with x⩽0.1 at temperature ranging from 300to470K under 355nm optical excitation. The characteristic temperature of the Zn1−xMgxO nanoneedles was determined to be 84K. The high-temperature lasing of the Zn1−xMgxO nanoneedles are attributed to the high crystal quality of the nanoneedles, enhancement of oscillator strength in nanostructures, and a self-compensation mechanism in random laser cavities.
Enhancement of electron injection in polymer light-emitting diodes with a supramolecular insulating nanolayer on the bottom cathode
Authors: Cho Jeong Ho , Lee Hwa Sung , Jang Yunseok , Lee Yongkyun , Kwon Soon Kab , Jang Jin , Cho Kilwon
Published: August 2006

With the aim of enhancing the electron injection of a polymer light-emitting diode (PLED), a supramolecular insulating nanolayer that reacts with the cathode (Ag) was inserted between the bottom cathode and the emitting material. The PLED threshold voltage (for 1cd∕m2) was found to decrease from 5.6to4.2V as a result of the introduction of the nanolayer. Synchrotron radiation photoelectron spectroscopy results show that inserting the supramolecular insulating nanolayer results in a decrease in the work function of about 0.7eV. This reduction lowers the electron injection barrier and produces an increase in the luminance.
Strong upconversion from Er3Al5O12 ceramic powders prepared by low temperature direct combustion synthesis
Authors: Maciel Glauco S. , Rakov Nikifor , Fokine Michael , Carvalho Isabel C. S. , Pinheiro Carlos B.
Published: August 2006

Crystalline ceramic powders of Er3Al5O12 were obtained by low temperature direct combustion synthesis. Irradiating the sample with a low-power continuous-wave infrared (1.48μm) diode laser led to ultraviolet, violet, blue, green, and red (380, 410, 456, 495, 525, 550, and 660nm) emissions. The strong upconversion luminescence appeared to the eyes as an intense green color. The presence of efficient four- and three-photon frequency upconversion processes makes this material an excellent candidate for use in photonic devices based on upconverter phosphors.
Highly efficient white organic light emitting diodes comprising an interlayer to separate fluorescent and phosphorescent regions
Authors: Schwartz Gregor , Fehse Karsten , Pfeiffer Martin , Walzer Karsten , Leo Karl
Published: August 2006

White organic light emitting diodes combining the phosphorescent green and orange-red emitting systems fac tris(2-phenylpyridine) iridium doped 4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA) and iridium(III)bis(2-methyldibenzo-[f,h]quinoxaline)(acetylacetonate) doped N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine with the blue fluorescent dye 2,2′,7,7′-tetrakis(2,2-diphenylvinyl)spiro-9,9′-bifluorene (Spiro-DPVBi) are presented. By introducing a thin layer of coevaporated TCTA and 2,2′,2″ (1,3,5-benzenetriyl) tris-[1-phenyl-1H-benzimidazole] between the phosphorescent and the fluorescent region, both singlet and triplet excitons are confined efficiently, whereas charge carriers still pass easily this interlayer. Furthermore, the interlayer suppresses Dexter transfer of the phosphorescent excitons to the nonradiative triplet state of Spiro-DPVBi. Best devices reach a current efficiency of 16.3cd∕A at 100cd∕m2 and a color rendering index of 85 at warm white CIE chromaticity coordinates of (0.47, 0.42). Due to the use of electrically doped charge transport layers, 100cd∕m2 are obtained at 2.95V with a power efficiency of 17.4lm∕W.
Revisiting the Region: ‘Ordinary’ and ‘Exceptional’ Regions in the Work of Hilda Ormsby 1917–1940
Authors: Maddrell Avril
Published: August 2006

Increased interest in and recognition of the value of the region and particularly the ‘ordinary region’ as opposed to more-glamorous ‘exceptional regions’ encourages us to reexplore the nature and purpose of what could be described as the first methodological blueprint of modern British geographical enquiry. Received histories of geography which give the impression of the production of geographical knowledge as a (near) universal male domain and the post-1960s critique of the regional approach as descriptive and nonhermeneutical have combined to make invisible the geographical work of most women (and some men) working in British universities in the first half of the 20th century. Despite this, insights can clearly be gained from biographical studies of both ‘ordinary’ geographers like Hilda Ormsby and the epistemology of the ‘ordinary region’. This allows for a richer and more-nuanced critical historiography of geography, but there is also a potentially fruitful reciprocity in conversation between that history of geographical ideas and explorations of economic alterity. Regional studies which may have been dismissed as ‘merely descriptive’ can be found to articulate detailed accounts of local socioeconomic practices giving evidence of the historical grounding for current economic standing, including complex and sometimes resistant interaction with dominant modes of economic ‘success’.
Employer Perceptions of Skills Deficiencies in the UK Labour Market: A Subregional Analysis
Authors: Watson Duncan , Johnson Steve , Webb Robert
Published: August 2006

Past research on labour-market skills shortages indicates that employers report skills shortages or hard-to-fill vacancies for a variety of different reasons. Nevertheless, there is some consensus that skills-shortages analysis needs to examine such shortages within the context of the local labour market in order to understand the labour-market dynamics and structural factors that affect the propensity for unemployed people to fill ‘skills shortage’ vacancies. The traditional approach has been to utilise qualitative analysis and case studies. In contrast, in this paper we undertake a multivariate probit analysis of employer perceptions of skills shortages utilising a subregional dataset from a survey of Dorset employers undertaken in 1998. On a general level, we demonstrate the complexity involved in attempting to measure skills problems using the responses of employers to standard surveys. The key findings of the probit analysis are that: firm size is a significant determinant in skills-deficiency perception, growing firms have a higher skills-shortage perception, and reported perceptions of skills deficiencies vary significantly according to the position of the respondent in the organisation. This reinforces the message that great care needs to be taken when analysing measures of skills deficiencies that are derived solely from employer surveys at national or subregional level.
Transnationalism and Migrants' Imaginings of Citizenship
Authors: Leitner Helga , Ehrkamp Patricia
Published: August 2006

Recent academic debates on transnationalism, immigration, and citizenship have largely ignored migrants' perspectives on citizenship. On the basis of ethnographic research in Germany and the United States between 1998 and 2001, we examine the values and meanings contemporary migrants assign to national citizenship and their citizenship practices. We argue that dominant discourses of liberal democratic citizenship and migrants' situated subject positions condition and mediate in complex ways their imaginings and practices of citizenship. We discuss how and why migrants' perspectives conform in significant ways across these two countries, while also varying among migrants. National citizenship remains meaningful in their struggle for mobility across borders, for equal protection under the law, and for equal access to social and political rights. However, migrants are also aware of the discrepancy between promises of equity and fairness associated with liberal democratic citizenship and the reality in which even naturalized migrants experience discrimination. Issues of belonging to and identification with the national community render national citizenship complicated for migrants as they negotiate multiple identities and allegiances, with varying outcomes. Differences among migrants notwithstanding, the majority can and do identify with multiple communities, and desire to participate and become members in more than one national community, suggesting that migrants challenge conceptions of bounded national citizenship. This does not entail, however, a deterritorialization of citizenship and identities.
Transnationalism, Gender, and Civic Participation: Canadian Case Studies of Hong Kong Immigrants
Authors: Preston Valerie , Kobayashi Audrey , Man Guida
Published: August 2006

It is widely claimed that recent migration trends show increasing levels of transnational activity, but there is a need for a more detailed understanding of the relationship between transnationalism and citizenship participation, particularly from a gendered perspective. A study of immigrants from Hong Kong to Vancouver and Toronto, the largest group of immigrants to Canada in the period 1989 to 1997, shows that, although migration occurred in a context of anticipated political instability around reunification with the People's Republic of China, the most significant justification for emigration was to further the interests of the family, particularly children's education. Gender differences are subtle, but women tend to focus more strongly on family considerations, whereas men are somewhat more concerned with economic and political issues. Transnational activities focus around ties of family and friendship, rather than around political or economic ties. Women and men both seek formal rights of citizenship, and are beginning to express a desire for more participation in Canadian society. Contrary to theories of hypermobility among Hong Kong emigrants, transnationalism and citizenship participation are seen as a basis for settlement. Gendered approaches to transnationalism need to understand how the concept of citizenship, and citizenship participation, develops as a result of wider social relations that are structured differently for women and men.
Immigration Policies, State Discourses on Foreigners, and the Politics of Identity in Switzerland
Authors: Riaño Yvonne , Wastl-Walter Doris
Published: August 2006

The role of state discourses in the construction of ‘otherness’ and in the production of inequality has become a major issue during a time of increasing changes in migration flows, of an increased presence of nationalist parties, and of increasingly restrictive immigration policies in Europe. In this paper we examine historical shifts in the representation of foreigners within Swiss state discourses and the effects of these shifts on the integration of immigrants into Swiss society. As state discourses regarding foreigners significantly changed after the First World War, the emphasis of immigration policies shifted from a facilitating to a constraining approach. Überfremdung, the notion that excessive numbers of foreigners can threaten Swiss identity, emerged as one of the most influential discourses in Switzerland and provided the foundation for a quantitative and qualitative strategy of defence against the immigration, settlement, and naturalisation of foreigners. In recent years, however, an agreement on freedom of movement between Switzerland and the European Union has been struck, and immigration policies have once again adopted a facilitating stance. As this applies only to citizens of the European Union, a stratified system of immigrant rights has been continued and perpetuated. At the same time, right-wing parties, which have recently risen to power, have successfully used Überfremdung propaganda to persuade Swiss populations to vote against the relaxation of conditions for the naturalisation of foreigners, thus ensuring that immigrants will be excluded from access to citizenship rights over generations. The politics of immigration in Switzerland is above all a politics of national identity.
The Canadian Hispanic Day Parade, or How Latin American Immigrants Practise (Sub)Urban Citizenship in Toronto
Authors: Veronis Luisa
Published: August 2006

In this paper I explore immigrants' notions and practices of citizenship, and how these contribute to the citizenship debate. In order to achieve this, I examine Latin American immigrants' struggle for belonging in Toronto by looking at the Canadian Hispanic Day Parade. This multicultural celebration of ethnic diversity takes place in a marginalized suburban neighbourhood of the city, and I argue that Latin Americans use it to affirm the existence of a Latin American identity and community in Toronto. But, while the parade serves to contest dominant representations of immigrants, visible minorities, and the disadvantaged, it also reveals how forms of community mobilization can internalize neoliberal social relations and even promote a neoliberal agenda. The aim of the paper is to reflect upon the political potential of ethnic celebrations, as well as the constraints and complexities of immigrant citizenship practice within the contemporary context of Canadian multiculturalism and neoliberalism.
“We Turks are No Germans”: Assimilation Discourses and the Dialectical Construction of Identities in Germany
Authors: Ehrkamp Patricia
Published: August 2006

In this paper I examine the ways in which politicians, media, and native residents formulate assimilation discourses—that is, expectations for immigrants to adapt to prevailing norms and cultures—and the effects that such discourses have on social relations in immigrant-receiving societies. Archival and ethnographic research in Germany illustrates that assimilation discourses are central in the dialectical process of identity construction in which native-born Germans and immigrants from Turkey construct their respective ‘other’, and thereby themselves. I pay particular attention to the effects of assimilation discourses in negotiations over belonging and culture at multiple scales in Germany—from the national to the neighborhood level. Space figures prominently in these negotiations, as the spaces that immigrants occupy and create often become the focus of debates about difference, otherness, and the unassimilability of migrants in Germany.
An Efficient, Eco-Friendly, One-Pot Protocol for the Synthesis of 2-Oxazolines Promoted by Ionic Liquid/Indium Chloride
Authors: Kamakshi R. , Reddy Boreddy S. R.
Published: August 2006

2-Oxazolines have been synthesized using a solventless ionic liquid melt in good yields at ambient temperatures. The efficiency of various Lewis acid catalysts for the same reaction has been compared. The effectiveness of different alkyl chains in the ionic liquids for the synthesis of oxazolines has been studied and a butylmethylimidazolinium chloride/indium chloride melt has been found to be the best media for promoting the reaction.
Synthesis and Biological Activity of Allosteric Modulators of GABAB Receptors, Part 1. N-(Phenylpropyl)-1-arylethylamines
Authors: Kerr David I. B. , Ong Jennifer , Perkins Michael V. , Prager Rolf H. , Puspawati Ni Made
Published: August 2006

A series of 15 analogues of fendiline, and 34 derivatives of N-(3-phenylpropyl)-1-arylethylamine have been prepared for evaluation as positive allosteric modulators of GABAB receptors. The most active (EC50, 10 nM) was N-(3,3-diphenylpropyl)-1-(3-chloro-4-methoxyphenyl)ethylamine 6g.
Synthesis, Characterization, and Photophysics of a New Trinuclear Mercury(II) Complex of 1,3,5-Triethynylbenzene
Authors: Liu Li , Wong Wai-Yeung , Ho Cheuk-Lam
Published: August 2006

A new trinuclear mercury(ii) complex of 1,3,5-triethynylbenzene [(MeHgC≡C)3(1,3,5-C6H3)] 1 was prepared in good yield by Hagihara’s dehydrohalogenation reaction of HgMeCl with [(HC≡C)3(1,3,5-C6H3)] under ambient conditions. This trimercury triacetylide complex’s structure was confirmed by common spectroscopic techniques and its photophysical properties were examined and compared with the isolobal gold(i) congener [{(PPh3)AuC≡C}3(1,3,5-C6H3)] 2. Our investigations indicate that the organic triplet emissions can be harvested by the heavy-atom effect of mercury which enables efficient intersystem crossing from the S1 singlet excited state to the T1 triplet excited state. The influence of Hg and Au centres on the phosphorescence efficiency and evolution of the lowest electronic singlet and triplet excited states is critically characterized. Both complexes 1 and 2 possess high-energy triplet states of 2.77–2.82 eV, in which the order of intersystem crossing rate follows the order Au > Hg.
Synthesis and Characterization of α,β-Unsaturated Hydroximoyl Chlorides and Hydroximates
Authors: Johnson James E. , Lu Ling , Dai Houquan , Canseco Diana C. , Small Krista M. , Dolliver Debra D. , Fronczek Frank R.
Published: August 2006

New α,β-unsaturated hydroximoyl chlorides (PhC(Cl)=CHC(Cl)=NOCH3) and hydroximates (PhC(OCH3)=CHC(OCH3)=NOCH3) were prepared. The ZZ-isomer of PhC(Cl)=CHC(Cl)=NOCH3 was prepared in four steps from ethyl benzoylacetate. Ultraviolet irradiation of the ZZ-isomer gives a mixture of all four possible isomers. Sodium methoxide was reacted with these isomers to determine the configuration about the carbon–carbon double bond for each. The Z-isomers reacted with sodium methoxide to give the corresponding alkyne by elimination whereas the E-isomers gave the substitution product. The configuration about the carbon–nitrogen double bond was determined from the 1H NMR chemical shift of the NOCH3 group.
Enantioselective Friedel - Crafts Reactions of Aromatic Amines with Ethyl Glyoxylate in Pyridinium-Based Ionic Liquids
Authors: Malhotra Sanjay V. , Xiao Ying
Published: August 2006

The Friedel–Crafts reactions of aromatic amines with ethyl glyoxylate in pyridinium-based ionic liquids (ILs) are investigated using 2,2′-dihydroxy-1,1′-binaphthyl (BINOL) metal complexes as chiral catalysts. Reaction parameters such as the catalyst–IL compositions, reactant compositions, reaction time, and reaction temperature are studied. High yields and excellent enantioselectivities are achieved under the relatively mild conditions. The ILs can also be recycled and reused as opposed to traditional solvent systems.
Precise adaptation in bacterial chemotaxis through “assistance neighborhoods”
Authors: Endres Robert G. , Wingreen Ned S.
Published: August 2006

The chemotaxis network in
Escherichia coli
is remarkable for its sensitivity to small relative changes in the concentrations of multiple chemical signals over a broad range of ambient concentrations. Key to this sensitivity is an adaptation system that relies on methylation and demethylation (or deamidation) of specific modification sites of the chemoreceptors by the enzymes CheR and CheB, respectively. It was recently discovered that these enzymes can access five to seven receptors when tethered to a particular receptor. We show that these “assistance neighborhoods” are necessary for precise adaptation in a model for signaling by clusters of chemoreceptors. In agreement with experiment, model clusters composed of receptors of different types exhibit high sensitivity and precise adaptation over a wide range of chemical concentrations and the response of adapted clusters to addition/removal of attractant scales with free-energy change. We predict two limits of precise adaptation at large attractant concentrations: Either receptors reach full methylation and turn off, or receptors become saturated and cease to respond to attractant but retain their adapted activity.
A proteomic study of
Methylobacterium extorquens
reveals a response regulator essential for epiphytic growth
Authors: Gourion Benjamin , Rossignol Michel , Vorholt Julia A.
Published: August 2006

Aerial plant surfaces are colonized by diverse bacteria such as the ubiquitous
Methylobacterium
spp. The specific physiological traits as well as the underlying regulatory mechanisms for bacterial plant colonization are largely unknown. The purpose of this study was to identify proteins produced specifically in the phyllosphere by comparing the proteome of
Methylobacterium extorquens
colonizing the leaves either with that of bacteria colonizing the roots or with that of bacteria growing on synthetic medium. We identified 45 proteins that were more abundant in
M. extorquens
present on plant surfaces as compared with bacteria growing on synthetic medium, including 9 proteins that were more abundant on leaves compared with roots. Among the proteins induced during epiphytic growth, we found enzymes involved in methanol utilization, prominent stress proteins, and proteins of unknown function. In addition, we detected a previously undescribed type of two-domain response regulator, named PhyR, that consists of an N-terminal sigma factor (RpoE)-like domain and a C-terminal receiver domain and is predicted to be present in essentially all
Alphaproteobacteria
. The importance of PhyR was demonstrated through phenotypic tests of a deletion mutant strain shown to be deficient in plant colonization. Among PhyR-regulated gene products, we found a number of general stress proteins and, in particular, proteins known to be involved in the oxidative stress response such as KatE, SodA, AhpC, Ohr, Trx, and Dps. The PhyR-regulated gene products partially overlap with the bacterial
in planta
-induced proteome, suggesting that PhyR is a key regulator for adaptation to epiphytic life of
M. extorquens
.
Structure of archaeal translational initiation factor 2 βγ–GDP reveals significant conformational change of the β-subunit and switch 1 region
Authors: Sokabe Masaaki , Yao Min , Sakai Naoki , Toya Shingo , Tanaka Isao
Published: August 2006

Archaeal/eukaryotic initiation factor 2 (a/eIF2) consists of α-, β-, and γ-subunits and delivers initiator methionine tRNA (Met-tRNA
i
) to a small ribosomal subunit in a GTP-dependent manner. The structures of the aIF2βγ (archaeal initiation factor 2 βγ) heterodimeric complex in the apo and GDP forms were analyzed at 2.8- and 3.4-Å resolution, respectively. The results showed that the N-terminal helix and the central helix–turn–helix domain of the β-subunit bind to the G domain of the γ-subunit but are distant from domains 2 and 3, to which the α-subunit and Met-tRNA
i
bind. This result is consistent with most of the previous analyses of eukaryotic factors, and thus indicates that the binding mode is essentially conserved among a/eIF2. Comparison with the uncomplexed structure showed significant differences between the two forms of the β-subunit, particularly the C-terminal zinc-binding domain, which does not interact with the γ-subunit and was suggested previously to be involved in GTP hydrolysis. Furthermore, the switch 1 region in the γ-subunit, which is shown to be responsible for Met-tRNA
i
binding by mutational analysis, is moved away from the nucleotide through the interaction with highly conserved R87 in the β-subunit. These results implicate that conformational change of the β-subunit facilitates GTP hydrolysis by inducing the conformational change of the switch 1 region toward the off state.
Multifunctionality and mechanical origins: Ballistic jaw propulsion in trap-jaw ants
Authors: Patek S. N. , Baio J. E. , Fisher B. L. , Suarez A. V.
Published: August 2006

Extreme animal movements are usually associated with a single, high-performance behavior. However, the remarkably rapid mandible strikes of the trap-jaw ant,
Odontomachus bauri
, can yield multiple functional outcomes. Here we investigate the biomechanics of mandible strikes in
O. bauri
and find that the extreme mandible movements serve two distinct functions: predation and propulsion. During predatory strikes,
O. bauri
mandibles close at speeds ranging from 35 to 64 m·s
−1
within an average duration of 0.13 ms, far surpassing the speeds of other documented ballistic predatory appendages in the animal kingdom. The high speeds of the mandibles assist in capturing prey, while the extreme accelerations result in instantaneous mandible strike forces that can exceed 300 times the ant’s body weight. Consequently, an
O. bauri
mandible strike directed against the substrate produces sufficient propulsive power to launch the ant into the air. Changing head orientation and strike surfaces allow
O. bauri
to use the trap-jaw mechanism to capture prey, eject intruders, or jump to safety. This use of a single, simple mechanical system to generate a suite of profoundly different behavioral functions offers insights into the morphological origins of novelties in feeding and locomotion.
Human cytomegalovirus-encoded chemokine receptor US28 promotes tumorigenesis
Authors: Maussang David , Verzijl Dennis , van Walsum Marijke , Leurs Rob , Holl Jens , Pleskoff Olivier , Michel Detlef , van Dongen Guus A. M. S. , Smit Martine J.
Published: August 2006

Human cytomegalovirus (HCMV) is a widely spread herpesvirus, suggested to play a role in tumor progression. US28, a chemokine receptor encoded by HCMV, binds a broad spectrum of chemokines and constitutively activates various pathways linked to proliferation. Our studies reveal that expression of US28 induces a proangiogenic and transformed phenotype by up-regulating the expression of vascular endothelial growth factor and enhancing cell growth and cell cycle progression. US28-expressing cells promote tumorigenesis when injected into nude mice. The G protein-uncoupled constitutively inactive mutant of US28, induces delayed and attenuated tumor formation, indicating the importance of constitutive receptor activity in the early onset of tumor development. Importantly, also in glioblastoma cells infected with the newly isolated clinical HCMV strain Titan, US28 was shown to be involved in the HCMV-induced angiogenic phenotype. Hence, the constitutively activated chemokine receptor US28 might act as a viral oncogene and enhance and/or promote HCMV-associated tumor progression.
Overexpressing a NAM, ATAF, and CUC (NAC) transcription factor enhances drought resistance and salt tolerance in rice
Authors: Hu Honghong , Dai Mingqiu , Yao Jialing , Xiao Benze , Li Xianghua , Zhang Qifa , Xiong Lizhong
Published: August 2006

Drought and salinity are major abiotic stresses to crop production. Here, we show that overexpression of stress responsive gene
SNAC1
(
STRESS-RESPONSIVE NAC 1
) significantly enhances drought resistance in transgenic rice (22–34% higher seed setting than control) in the field under severe drought stress conditions at the reproductive stage while showing no phenotypic changes or yield penalty. The transgenic rice also shows significantly improved drought resistance and salt tolerance at the vegetative stage. Compared with WT, the transgenic rice are more sensitive to abscisic acid and lose water more slowly by closing more stomatal pores, yet display no significant difference in the rate of photosynthesis.
SNAC1
is induced predominantly in guard cells by drought and encodes a NAM, ATAF, and CUC (NAC) transcription factor with transactivation activity. DNA chip analysis revealed that a large number of stress-related genes were up-regulated in the
SNAC1
-overexpressing rice plants. Our data suggest that
SNAC1
holds promising utility in improving drought and salinity tolerance in rice.
Coactosin-like protein supports 5-lipoxygenase enzyme activity and up-regulates leukotriene A4production
Authors: Rakonjac Marija , Fischer Lutz , Provost Patrick , Werz Oliver , Steinhilber Dieter , Samuelsson Bengt , Rådmark Olof
Published: August 2006

Regulation of 5-lipoxygenase (5LO) activity is a key determinant for the biosynthesis of proinflammatory leukotrienes. Coactosin-like protein (CLP) is an F-actin-binding protein that can also bind 5LO. Here, we report that CLP can up-regulate and modulate 5LO activity [formation of 5(S)-hydroperoxy-6-trans-8,11,14-cis-eicosatetraenoic acid (5-HPETE)], 5(S)-hydroxy-6-trans-8,11,14-cis-eicosatetraenoic acid (5-HETE), and 5(S)-trans-5,6-oxido-7,9-trans-11,14-cis-eicosatetraenoic acid (LTA4)in vitro. Three findings are presented. First, CLP up-regulates Ca2+-induced 5LO activity, in the absence of phosphatidylcholine (membrane). Apparently, CLP can function as a scaffold for 5LO, similar to membranes. Second, CLP gives a considerable (3-fold) increase in the amount of LTA4formed by 5LO, when present together with phosphatidylcholine. Third, CLP increases the ratio of 5-HETE/5-HPETE. These effects require protein interaction by Trp residues in ligand-binding loops of the 5LO β-sandwich; both binding and stimulatory effects of CLP were abolished for the mutant 5LO-W13/75/102A. In polymorphonuclear leukocytes stimulated with Ca2+ionophore, both CLP and 5LO associated with the nucleus, whereas in resting cells, CLP and 5LO were cytosolic. These findings establish CLP as a factor relevant for 5LO product formation. Functioning as a 5LO scaffold, CLP may provide a basis for the formation of 5-HETE in the cytosol of different cell types. Furthermore, in stimulated cells, CLP appears to function in a complex together with 5LO and membranes, increasing the capacity of 5LO for leukotriene biosynthesis.
Structural basis for the inhibition of insulin-like growth factors by insulin-like growth factor-binding proteins
Authors: Sitar Tomasz , Popowicz Grzegorz M. , Siwanowicz Igor , Huber Robert , Holak Tad A.
Published: August 2006

Insulin-like growth factor-binding proteins (IGFBPs) control bioavailability, activity, and distribution of insulin-like growth factor (IGF)1 and -2 through high-affinity IGFBP/IGF complexes. IGF-binding sites are found on N- and C-terminal fragments of IGFBPs, the two conserved domains of IGFBPs. The relative contributions of these domains to IGFBP/IGF complexation has been difficult to analyze, in part, because of the lack of appropriate three-dimensional structures. To analyze the effects of N- and C-terminal domain interactions, we determined several x-ray structures: first, of a ternary complex of N- and C-terminal domain fragments of IGFBP4 and IGF1 and second, of a “hybrid” ternary complex using the C-terminal domain fragment of IGFBP1 instead of IGFBP4. We also solved the binary complex of the N-terminal domains of IGFBP4 and IGF1, again to analyze C- and N-terminal domain interactions by comparison with the ternary complexes. The structures reveal the mechanisms of IGF signaling regulation via IGFBP binding. This finding supports research into the design of IGFBP variants as therapeutic IGF inhibitors for diseases of IGF disregulation. In IGFBP4, residues 1–38 form a rigid disulphide bond ladder-like structure, and the first five N-terminal residues bind to IGF and partially mask IGF residues responsible for the type 1 IGF receptor binding. A high-affinity IGF1-binding site is located in a globular structure between residues 39 and 82. Although the C-terminal domains do not form stable binary complexes with either IGF1 or the N-terminal domain of IGFBP4, in the ternary complex, the C-terminal domain contacts both and contributes to blocking of the IGF1 receptor-binding region of IGF1.
Alveolar epithelial cell mesenchymal transition develops
in vivo
during pulmonary fibrosis and is regulated by the extracellular matrix
Authors: Kim Kevin K. , Kugler Matthias C. , Wolters Paul J. , Robillard Liliane , Galvez Michael G. , Brumwell Alexis N. , Sheppard Dean , Chapman Harold A.
Published: August 2006

Mechanisms leading to fibroblast accumulation during pulmonary fibrogenesis remain unclear. Although there is
in vitro
evidence of lung alveolar epithelial-to-mesenchymal transition (EMT), whether EMT occurs within the lung is currently unknown. Biopsies from fibrotic human lungs demonstrate epithelial cells with mesenchymal features, suggesting EMT. To more definitively test the capacity of alveolar epithelial cells for EMT, mice expressing β-galactosidase (β-gal) exclusively in lung epithelial cells were generated, and their fates were followed in an established model of pulmonary fibrosis, overexpression of active TGF-β1. β-gal-positive cells expressing mesenchymal markers accumulated within 3 weeks of
in vivo
TGF-β1 expression. The increase in vimentin-positive cells within injured lungs was nearly all β-gal-positive, indicating epithelial cells as the main source of mesenchymal expansion in this model.
Ex vivo
, primary alveolar epithelial cells cultured on provisional matrix components, fibronectin or fibrin, undergo robust EMT via integrin-dependent activation of endogenous latent TGF-β1. In contrast, primary cells cultured on laminin/collagen mixtures do not activate the TGF-β1 pathway and, if exposed to active TGF-β1, undergo apoptosis rather than EMT. These data reveal alveolar epithelial cells as progenitors for fibroblasts
in vivo
and implicate the provisional extracellular matrix as a key regulator of epithelial transdifferentiation during fibrogenesis.
Scale-invariant structure of strongly conserved sequence in genomic intersections and alignments
Authors: Salerno William , Havlak Paul , Miller Jonathan
Published: August 2006

A power-law distribution of the
length
of perfectly conserved sequence from mouse/human whole-genome intersection and alignment is exhibited. Spatial correlations of these elements within the mouse genome are studied. It is argued that these power-law distributions and correlations are comprised in part by functional noncoding sequence and ought to be accounted for in estimating the statistical significance of apparent sequence conservation. These
inter
-genomic correlations of conservation are placed in the context of previously observed
intra
-genomic correlations, and their possible origins and consequences are discussed.
Local subplasma membrane Ca
2+
signals detected by a tethered Ca
2+
sensor
Authors: Lee Moo Yeol , Song Hong , Nakai Junichi , Ohkura Masamichi , Kotlikoff Michael I. , Kinsey Stephen P. , Golovina Vera A. , Blaustein Mordecai P.
Published: August 2006

Accumulating evidence indicates that plasma membrane (PM) microdomains and the subjacent “junctional” sarcoplasmic/endoplasmic reticulum (jS/ER) constitute specialized Ca
2+
signaling complexes in many cell types. We examined the possibility that some Ca
2+
signals arising in the junctional space between the PM and jS/ER may represent cross-talk between the PM and jS/ER. The Ca
2+
sensor protein, GCaMP2, was targeted to different PM domains by constructing genes for fusion proteins with either the α1 or α2 isoform of the Na
+
pump catalytic (α) subunit. These fusion proteins were expressed in primary cultured mouse brain astrocytes and arterial smooth muscle cells. Immunocytochemistry demonstrated that α2(f)GCaMP2, like native Na
+
pumps with α2-subunits, sorted to PM domains that colocalized with subjacent S/ER; α1(f)GCaMP2, like Na
+
pumps with α1-subunits, was more uniformly distributed. The GCaMP2 moieties in both constructs were tethered just beneath the PM. Both constructs detected global Ca
2+
signals evoked by serotonin (in arterial smooth muscle cells) and ATP, and by store-operated Ca
2+
channel-mediated Ca
2+
entry after S/ER unloading with cyclopiazonic acid (in Ca
2+
-free medium). When cytosolic Ca
2+
diffusion was markedly restricted with EGTA, however, only α2(f)GCaMP2 detected the local, store-operated Ca
2+
channel-mediated Ca
2+
entry signal. Thus, α1 Na
+
pumps are apparently excluded from the PM microdomains occupied by α2 Na
2+
pumps. The jS/ER and adjacent PM may communicate by Ca
2+
signals that are confined to the tiny junctional space between the two membranes. Similar methods may be useful for studying localized Ca
2+
signals in other subPM microdomains and signals associated with other organelles.
Just a Phase?: Integrating Conflict Dynamics Over Time
Authors: Diehl Paul F.
Published: August 2006

Most international conflict research focuses on behavior within a given phase or stage of conflict. Little consideration is given to how actions in one phase affect the dynamics of conflict behavior in subsequent phases. This article postulates several different phases of conflict, gives a numerical overview of past research on those phases, and identifies and assesses several different approaches to integrating those phases, including selection effects, rational choice, path dependency, learning, and issue-centered approaches.
Modeling Middle East Security: A Formal Assessment of Regional Responses to the Iraq War
Authors: Snider Lewis W. , Strakes Jason E.
Published: August 2006

This investigation applies an expected utility (EU) analysis to assess the impact of the 2003 U.S. intervention in Iraq on the security perceptions of states in the Persian Gulf region, and to determine how shifts in the distribution of preferences among self-interested actors might influence the formation of coalitions in the Middle East. The outcome suggests that concerns for an incumbent leader's political survival may create a set of values that prevents states from forming coalitions in response to a commonly perceived threat. Of particular interest is the finding that while challengers such as Iran may not forge an anti-U.S. coalition, by maintaining its current position Tehran could foreclose bargaining opportunities that would result in an outcome more favorable to the U.S.
The Determinants of China's Defense Expenditure Before and After Transition
Authors: Bing-Fu Chen , Zhao Liming
Published: August 2006

This paper examines the determinants of China's defense expenditure over the period 1960—1999, and two sub-samples before and after transition for 1960—1980 and 1981— 1999, applying official Chinese data and SIPRI Yearbook data. An empirical econometric model is set up on the basis of standard neo-classical theory. The empirical results suggest that earlier defense expenditure, changes in the strategy environment, and GDP are major determinants of China's defense expenditure on the long run. For the split periods, the national security environment, economic factor, and earlier defense expenditure are the main determining factors prior to 1981, but earlier defense expenditure is the main determinant after 1981 (when official Chinese data are used). The impact of Taiwanese military spending on Mainland China's demand for defense expenditure was not statistically significant.
Exploring Operationalizations of Political Relevance
Authors: Bennett D. Scott
Published: August 2006

During the past decade, researchers have commonly employed one of two sets of interstate dyads as the population of cases in quantitative analyses of international conflict, choosing to examine either “all dyads” or “politically relevant dyads.” The main argument against using the “all dyads” set is that it includes many dyads where there is no chance of conflict, and so analysts using this set are examining many pairs of states in which the hypotheses in question are irrelevant. The criticism of politically relevant dyads is that this set does not capture 15% to 20% of the actual conflicts that occur. In this paper I examine the current operationalization of “political relevance” to see whether the operationalization can be slightly modified and encompass all actual conflicts. If it could be, then use of the modified politically relevant dyad case subset might be more appropriate or have advantages over what is currently employed. I conclude that while it is possible to improve upon current operationalizations of political relevance (in terms of capturing conflicts), it is difficult to reach a 100% capture rate. It is also clear from the analysis that the various politically relevant operationalizations do better at capturing wars than militarized interstate disputes (MIDs), and do better at capturing the actions of MID and war originators than MID and war joiners.
Effect of carbon nanomaterials on calcium carbonate crystallization
Authors: Anderson Robin E. , Barron Andrew R.
Published: August 2006

The addition of the water-soluble carbon nanomaterials, fullerenol (C60(OH)n), hydroxylated single walled carbon nanotubes (HO-SWNTs) and isophthalic acid functionalized-SWNTs (IPA-SWNTs), alter the morphology and crystal phase of CaCO3 precipitates form aqueous solution. CaCO3 precipitation in the presence of C60(OH)n results in the formation of spherical features, 5-pointed flower shaped clusters, and triangular crystals as opposed to the usual rhombic crystals. In addition, the meta-stable vaterite phase is observed with the addition of C60(OH)n. The effect on crystal growth of the C60(OH)n is not a simple function of the pH of the solution, although it may be due to reactivity of the hydroxyl groups. Precipitation with water-soluble HO-SWNT and IPA-SWNTs produces CaCO3 coated SWNTs with the CaCO3 being amorphous rather than crystalline.
Hydrogen bonding interaction between ethyl methacrylate and alcohols in non-polar solvents: an FTIR study
Authors: Dharmalingam K. , Ramachandran K. , Sivagurunathan P.
Published: August 2006

The association between ethyl methacrylate and n-butanol, s-butanol and t-butanol in non-polar solvents viz. n-heptane, CCl4, and benzene has been investigated by means of FTIR spectroscopy. The most likely association complex between alcohol and acrylic ester is 1:1 stoichiometric complex through the free hydroxyl group of alcohol and the carbonyl group of ester. The formation constant of the 1:1 complexes has been calculated using Nash method. It is shown that the strength of the hydrogen bond (C==O:HO) in the various systems studied depend on the acidity of the R-OH proton and the steric factor of the alkyl group of the alkyl alcohol and also on the solvents used. The solvent effect on the formation of hydrogen bond equilibria is discussed in terms of specific interaction between the solute and solvent.