bluuebunny/crossref_metadata_2025 huggingface dataset:
Stem cells in the adult pancreas and liver
Authors: Burke Zoë D. , Thowfeequ Shifaan , Peran Macarena , Tosh David
Published: May 2007

Stem cells are undifferentiated cells that can self-renew and generate specialized (functional) cell types. The remarkable ability of stem cells to differentiate towards functional cells makes them suitable modalities in cellular therapy (which means treating diseases with the body's own cells). Potential targets for cellular therapy include diabetes and liver failure. However, in order for stem cells to be clinically useful, we must learn to identify them and to regulate their differentiation. We will use the intestine as a classical example of a stem cell compartment, and then examine the evidence for the existence of adult stem cells in two endodermally derived organs: pancreas and liver. We will review the characteristics of the putative stem cells in these tissues and the transcription factors controlling their differentiation towards functional cell types.
A synthetic small molecule, ONO-1301, enhances endogenous growth factor expression and augments angiogenesis in the ischaemic heart
Authors: Nakamura Kazuto , Sata Masataka , Iwata Hiroshi , Sakai Yoshiki , Hirata Yasunobu , Kugiyama Kiyotaka , Nagai Ryozo
Published: May 2007

It has been shown previously that administration of angiogenic growth factors as genes or proteins can augment collateral growth in ischaemic tissues. In the present study, we have investigated the effect of ONO-1301, a synthetic prostacyclin agonist with thromboxane-synthase-inhibitory activity, on expression of endogenous growth factors and angiogenesis. ONO-1301 induced secretion of HGF (hepatocyte growth factor) and VEGF (vascular endothelial growth factor) from cultured normal human dermal fibroblasts in a dose-dependent manner. Dibutyryl cAMP, an analogue of cAMP, and forskolin, an adenylate cyclase activator, mimicked the effect of ONO-1301. Conversely, Rp-cAMP (adenosine 3′,5′-cyclic monophosphorothioate), an inhibitor of cAMP, partially inhibited the effect of ONO-1301, suggesting that cAMP mediated the effect of ONO-1301 in up-regulating the expression of HGF and VEGF, at least in part. ONO-1301 promoted tube-like formation by HUVECs (human umbilical vein endothelial cells) when co-cultured with fibroblasts, and the angiogenic effect of ONO-1301 was abrogated by administration of a neutralizing antibody against HGF or VEGF. To generate a slow-releasing form of ONO-1301, ONO-1301 was mixed with poly(DL-lactic-co-glycolic acid). The slow-releasing form of ONO-1301 was injected directly into the ischaemic myocardium of mice immediately after ligation of the left anterior descending artery. The slow-releasing form of ONO-1301 up-regulated HGF and VEGF expression and increased capillary density in the border zone (342.7±29.7 capillaries/mm2 in controls compared with 557.2±26.7 capillaries/mm2 in treated animals; P<0.01) at 7 days. The slow-releasing form of ONO-1301 ameliorated left ventricular enlargement after 28 days and improved survival rate. In conclusion, our results indicate that ONO-1301 up-regulated endogenous growth factors and promoted angiogenesis in response to acute ischaemia. Therefore ONO-1301 might have a therapeutic potential in treating ischaemic diseases.
Oxidative stress, antioxidant status and DNA damage in patients with impaired glucose regulation and newly diagnosed Type 2 diabetes
Authors: Song Fangfang , Jia Wenbo , Yao Ying , Hu Yafei , Lei Lin , Lin Jie , Sun Xiufa , Liu Liegang
Published: May 2007

Previous studies have postulated the association between oxidative stress and Type 2 diabetes. Considering the long pre-diabetic period with IGR (impaired glucose regulation) and its high risk of developing diabetes, to test this hypothesis, we have investigated oxidative stress pathways and DNA damage in patients with IGR and newly diagnosed Type 2 diabetes. The study population consisted of 92 subjects with NGT (normal glucose tolerance), 78 patients with IGR and 113 patients with newly diagnosed diabetes. Plasma MDA (malondialdehyde) and TAC (total antioxidative capacity) status, erythrocyte GSH content and SOD (superoxide dismutase) activity were determined. A comet assay was employed to evaluate DNA damage. Compared with subjects with NGT, patients with IGR had reduced erythrocyte SOD activity. Patients with diabetes had a higher plasma MDA concentration, but a lower plasma TAC level and erythrocyte SOD activity, than the NGT group. Correlation analysis revealed a strong positive association between IR (insulin resistance) and MDA concentration, but negative correlations with TAC status and SOD activity. With respect to β-cell function, a positive association with TAC status and an inverse correlation with GSH respectively, were observed. The comet assay revealed slight DNA damage in patients with IGR, which was increased in patients with diabetes. Significant correlations were observed between DNA damage and hyperglycaemia, IR and β-cell dysfunction. In conclusion, the results of the present study suggest that hyperglycaemia in an IGR state caused the predominance of oxidative stress over antioxidative defence systems, leading to oxidative DNA damage, which possibly contributed to pancreatic β-cell dysfunction, IR and more pronounced hyperglycaemia. This vicious circle finally induced the deterioration to diabetes.
Effect of crystallographic orientation of Co2MnGe Heusler-alloy film on its surface roughness and ordered structure
Authors: Takeda Y. , Yoshimura S. , Takano M. , Asano H. , Matsui M.
Published: May 2007

The effects of direction and degree of preferred orientation of Co2MnGe film on the surface roughness and the ordered structure were investigated by utilizing various buffer layers and underlayers. Degrees of preferred orientation of Co2MnGe film were estimated by measuring the full width at half maximum (FWHM) of the x-ray diffraction rocking curve for Co2MnGe(400) or Co2MnGe(220) reflections. A high B2 ordered structure and a high saturation magnetization, which is almost the same value as in the case of epitaxial Co2MnGe films, were obtained regardless of the direction and degree of preferred orientation, except in the case of the Co2MnGe films without both buffer layers and underlayers. Also, surface roughness decreased when decreasing the FWHM of x-ray diffraction rocking curve, and the small surface roughness (that is almost the same value as in the case of epitaxial Co2MnGe films) was obtained for Co2MnGe films with the high degree of preferred orientation. A smaller surface roughness was obtained in the case of Co2MnGe films with (110) preferred orientation compared with the Co2MnGe(100) case. The tendencies of change of the surface roughness were explained from the viewpoint of surface energy.
Simple method to incorporate nonparabolicity effects in the Schrödinger equation of a quantum dot
Authors: Gómez-Campos F. M. , Rodríguez-Bolívar S. , Carceller J. E.
Published: May 2007

In this work we formulate the nonparabolic Schrödinger equation for a quantum dot in order to explore the main features of the carriers in these systems. In addition, we present a fast iterative numerical algorithm to solve it, obtaining the energy levels and envelope functions. We also model the electrostatic potential profile in a manner that makes it possible to discuss the effects of stronger confinements on the results. To demonstrate a practical implementation of this algorithm, we carry out an investigation into the effects of nonparabolicity of the valence band on the eigenstates of a Si quantum dot. Finally, we fit our results, using power expressions to relate the energy levels to the size of the cubic quantum dots, thus demonstrating the relevance of nonparabolicity.
Shear flows at the tokamak edge and their interaction with edge-localized modes
Authors: Aydemir A. Y.
Published: May 2007

Shear flows in the scrape-off layer (SOL) and the edge pedestal region of tokamaks are shown to arise naturally out of transport processes in a magnetohydrodynamic model. In quasi-steady-state conditions, collisional resistivity coupled with a simple bootstrap current model necessarily leads to poloidal and toroidal flows, mainly localized to the edge and SOL. The role of these flows in the grad-B drift direction dependence of the power threshold for the L (low) to H (high) transition, and their effect on core rotation, are discussed. Theoretical predictions based on symmetries of the underlying equations, coupled with computational results, are found to be in agreement with observations in Alcator C-Mod [Phys. Plasmas 12, 056111 (2005)]. The effects of these self-consistent flows on linear peeling/ballooning modes and their nonlinear consequences are also examined.
Columnar versus smectic order in systems of charged colloidal rods
Authors: Wensink H. H.
Published: May 2007

We study the stability of inhomogeneous liquid crystalline states in systems of monodisperse, stiff, charged rods. By means of a bifurcation analysis applied to the Onsager free energy for charged rods in strongly nematic states, we investigate nematic-smectic and nematic-columnar instabilities as a function of the Debye screening length κ−1. While the nematic-smectic transition clearly preempts the nematic-columnar one in the regime of strong screening (i.e., small κ−1) a marked stability of hexagonal columnar order is observed at larger screening lengths. The theoretical results are substantiated by Brownian dynamics computer simulation results based on the Yukawa site model. Our connect to experiments on tobacco mosaic virus rods, in particular, but might be relevant for soft rodlike mesogens in strong external directional fields in general.
Infrared spectroscopy of Cu+(H2O)n and Ag+(H2O)n: Coordination and solvation of noble-metal ions
Authors: Iino Takuro , Ohashi Kazuhiko , Inoue Kazuya , Judai Ken , Nishi Nobuyuki , Sekiya Hiroshi
Published: May 2007

M + ( H 2 O ) n and M+(H2O)n∙Ar ions (M=Cu and Ag) are studied for exploring coordination and solvation structures of noble-metal ions. These species are produced in a laser-vaporization cluster source and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region using a triple quadrupole mass spectrometer. Density functional theory calculations are also carried out for analyzing the experimental IR spectra. Partially resolved rotational structure observed in the spectrum of Ag+(H2O)1∙Ar indicates that the complex is quasilinear in an Ar-Ag+-O configuration with the H atoms symmetrically displaced off axis. The spectra of the Ar-tagged M+(H2O)2 are consistent with twofold coordination with a linear O-M+-O arrangement for these ions, which is stabilized by the s-d hybridization in M+. Hydrogen bonding between H2O molecules is absent in Ag+(H2O)3∙Ar but detected in Cu+(H2O)3∙Ar through characteristic changes in the position and intensity of the OH-stretch transitions. The third H2O attaches directly to Ag+ in a tricoordinated form, while it occupies a hydrogen-bonding site in the second shell of the dicoordinated Cu+. The preference of the tricoordination is attributable to the inefficient 5s-4d hybridization in Ag+, in contrast to the extensive 4s-3d hybridization in Cu+ which retains the dicoordination. This is most likely because the s-d energy gap of Ag+ is much larger than that of Cu+. The fourth H2O occupies the second shells of the tricoordinated Ag+ and the dicoordinated Cu+, as extensive hydrogen bonding is observed in M+(H2O)4∙Ar. Interestingly, the Ag+(H2O)4∙Ar ions adopt not only the tricoordinated form but also the dicoordinated forms, which are absent in Ag+(H2O)3∙Ar but revived at n=4. Size dependent variations in the spectra of Cu+(H2O)n for n=5–7 provide evidence for the completion of the second shell at n=6, where the dicoordinated Cu+(H2O)2 subunit is surrounded by four H2O molecules. The gas-phase coordination number of Cu+ is 2 and the resulting linearly coordinated structure acts as the core of further solvation processes.
Effects of band-offset on the carrier lifetime in InAs quantum dots on InP substrates
Authors: Jang Y. D. , Kim N. J. , Lee H. , Lee D. , Pyun S. H. , Jeong W. G. , Jang J. W. , Oh D. K. , Kim Jin Soo
Published: May 2007

The carrier lifetime of an InAs/InGaAsP quantum dot (QD) on an InP substrate is measured to be twice that of an InAs/InAlGaAs QD on the same substrate, although the ground-state energy levels and barrier heights of these QDs are comparable. These differences are interpreted in terms of the smaller conduction band-offset in InAs/InGaAsP QDs compared to InAs/InAlGaAs QDs.
Magnetic properties of CrSb: A first-principle study
Authors: Kahal L. , Zaoui A. , Ferhat M.
Published: May 2007

We present a first-principle study on the magnetic properties of CrSb in the zinc-blende and NiAs structures. To this end we use all electron full-potential linear augmented plane wave method within both the local spin density and generalized gradient approximations. Various physical quantities, such as total and local magnetic moments, are given for different structures and phases. Besides, a detailed analysis of the investigated properties is supported by the calculation of the cohesive energy, band structure, density of states, and specific charge densities. Results mainly show that CrSb is a half-metal ferromagnetic in the zinc-blende structure with a magnetic moment of 3.000μB∕f.u. Its half-metallic gap reaches 0.69eV at the equilibrium volume.
Elastocapillary filling of deformable nanochannels
Authors: van Honschoten J. W. , Escalante M. , Tas N. R. , Jansen H. V. , Elwenspoek M.
Published: May 2007

The capillary filling speed of wetting liquids of varying viscosity and surface tension in hydrophilic nanochannels with an elastic capping layer has been analyzed. The channels, with a height just below 80nm, are suspended by a thin flexible membrane that easily deforms due to the negative pressure which develops behind the moving meniscus. In the elastocapillary filling of the channels, two opposite effects compete: the decreased cross channel sections increase the flow resistance, while the Laplace pressure that acts as the driving force becomes more negative due to the increased meniscus curvature. Although the meniscus position shows a square root of time behavior as described by the Washburn relation, the net result of the induced bending of the membranes is a definite increase of the filling speed. We propose a relatively straightforward model for this elastocapillary process and present experimental results of the filling speed of ethanol, water, cyclohexane, and acetone that are found to be in good agreement with the presented model, for membrane deflections of up to 80% of the original channel height.
A study on the stability of O2 on oxometalloporphyrins by the first principles calculations
Authors: Kubota Yoshiyuki , Escaño Mary Clare Sison , Dy Eben Sy , Nakanishi Hiroshi , Kasai Hideaki
Published: May 2007

The authors investigated the interaction of oxometalloporphyrins (MO(por))—specifically, MoO(por), WO(por), TiO(por), VO(por), and CrO(por)—with O2 by using first principles calculations. MoO(por) and WO(por) undergo reactions with O2; on the other hand, TiO(por), VO(por), and CrO(por) do not. Next, they compared the interaction of MoO(por) and WO(por) with O2. Activation barriers for the reactions of MoO(por) and WO(por) with a side-on O2 are small. For MoO(por)(O2), the activation barrier for the reverse reaction that liberates O2 is also small; however, that for WO(por)(O2) is large. The experimental results that photoirradiation with visible light or heating of MoOVI(tmp)(O2) regenerates MoOVI(tmp) by liberating O2 while WOVI(tmp)(O2) does not [J. Tachibana, T. Imamura, and Y. Sasaki, Bull. Chem. Soc. Jpn. 71, 363 (1998)] are explained by the difference in activation barriers of the reverse reactions. This means that bonds formed between the W atom and O2 are stronger than those between the Mo atom and O2. The bond strengths can be explained by differences in the energy levels between the highest occupied molecular orbital of MoO(por) and WO(por), which are mainly formed from the a orbitals of the central metal atom and π* orbitals of O2.
Ab initio study of spectroscopic constants and anharmonic force field of Ge74Cl2
Authors: Pang Weixiu , Wang Meishan , Yang Chuanlu , Zhang Yongfeng
Published: May 2007

The equilibrium structure, spectroscopy constants, and anharmonic force field of germanium dichloride have been calculated at MP2, B3LYP, and CCSD(T) levels of theory employing two basis sets, cc-pVDZ and cc-pVTZ, respectively. The computed geometries, rotational constants, and vibration-rotation interaction constants, and quartic centrifugal distortion constants are compared with the available experimental data. The harmonic frequencies, anharmonic constants, and cubic and quartic force constants are predicted. The calculated results show that the MP2 results are in excellent agreement with experiment and represent a substantial improvement over the results obtained from B3LYP. The CCSD(T) method is also an advisable choice to study anharmonic force field of molecules.
Binding energy of a hydrogenic donor impurity in a rectangular parallelepiped-shaped quantum dot: Quantum confinement and Stark effects
Authors: Li Shu-Shen , Xia Jian-Bai
Published: May 2007

We calculate the binding energy of a hydrogenic donor impurity in a rectangular parallelepiped-shaped quantum dot (QD) in the framework of effective-mass envelope-function theory using the plane wave basis. The variation of the binding energy with edge length, position of the impurity, and external electric field is studied in detail. A finite potential model is adopted in our calculations. Compared with the infinite potential model [C. I. Mendoza et al., Phys. Rev. B 71, 075330 (2005)], the following results are found: (1) if the impurity is located in the interior of the QD, our results give a smaller binding energy than the infinite potential model; (2) the binding energies are more sensitively dependent on the applied electric field in the finite potential model; (3) the infinite potential model cannot give correct results for a small QD edge length for any location of the impurity in the QD; (4) some degeneracy is lifted when the dot is no longer cubic.
Distortion of bulk-ion distribution function due to nuclear elastic scattering and its effect on T(d,n)He4 reaction rate coefficient in neutral-beam-injected deuterium-tritium plasmas
Authors: Matsuura H. , Nakao Y.
Published: May 2007

An effect of nuclear elastic scattering on the rate coefficient of fusion reaction between field deuteron and triton in the presence of neutral beam injection heating is studied. Without assuming a Maxwellian for bulk-ion distribution function, the Boltzmann-Fokker-Planck (BFP) equations for field (bulk) deuteron, field (bulk) triton, α-particle, and beam deuteron are simultaneously solved in an ITER-like deuterium-tritium thermonuclear plasma [R. Aymar, Fusion Eng. Des. 55, 107 (2001)]. The BFP calculation shows that enhancement of the reaction rate coefficient due to knock-on tail formation in fuel-ion distribution functions becomes appreciable, especially in the case of low-density operations.
Fabrication of comblike nanostructures using self-assembled cluster arrays of molybdenum oxides
Authors: Okada Arifumi , Yoshimura Masamichi , Ueda Kazuyuki
Published: May 2007

Self-assembled cluster arrays formed at the initial stage of Mo(110) oxidation and subsequent fabrication of comblike structures have been studied by scanning tunneling microscopy. After 180L oxygen exposure, large protrusions are arranged as self-assembly along the [1¯13] or [11¯3] direction. The average diameter and height of each protrusion are estimated to be approximately 0.8 and 0.15–0.2nm, which correspond to the sizes of clusters of several atoms. The cluster arrays correspond to the MoO3 nucleation at the antiphase boundaries of the MoO2 surface. After thermal evaporation of the cluster arrays, comblike step structures consisting of narrow branches and trenches are obtained.
Photonic band gaps and planar cavity of two-dimensional eightfold symmetric void-channel photonic quasicrystals
Authors: Zhou Guangyong , Gu Min
Published: May 2007

By using the femtosecond laser induced microexplosion method, high-quality two-dimensional eightfold photonic quasicrystals have been fabricated in a solid transparent polymer material. Multiorder band gaps have been observed in a 25-layer structure with a suppression rate of up to 72% for the fundamental gap. Polarization measurements show that the photonic quasicrystal has a strong anisotropic effect, showing that the transverse electric is the favorite polarization. Fabry-Pérot cavities have been fabricated by removing the central layer of channels. Based on the cavity mode position, the order of the mode and the effective cavity size have been determined.
Optimized thickness of superconducting aluminum electrodes for measurement of spin polarization with MgO tunnel barriers
Authors: Yang Hyunsoo , Yang See-Hun , Parkin Stuart S. P. , Leo Titus , Smith David J.
Published: May 2007

Superconducting tunneling spectroscopy (STS) is one of the most useful techniques for measuring the tunneling spin polarization of magnetic materials, typically carried out using aluminum electrodes. Recent studies using MgO barriers have shown the extreme sensitivity of the spin polarization to annealing at temperatures up to ∼400°C. Here the authors show that by optimizing the thickness of aluminum superconducting electrodes, STS measurements can be carried out even for such high annealing temperatures.
Transition from the strong- to the weak-coupling regime in semiconductor microcavities: Polarization dependence
Authors: Ballarini D. , Amo A. , Viña L. , Sanvitto D. , Skolnick M. S. , Roberts J. S.
Published: May 2007

The dependence on the polariton spin orientation of the transition from the strong- to the weak-coupling regime in InGaAs semiconductor microcavities is experimentally studied by means of time-resolved photoluminescence. Polaritons are nonresonantly excited by circularly polarized pulses and the photoluminescence of the K‖∼0 states is analyzed into its co- and cross-polarized components. The loss of strong coupling with increasing excitation intensity takes place at different powers for polaritons with opposite spin orientation and it is determined by the polariton population of each spin.
“Blueshift” in photoluminescence and photovoltaic spectroscopy of the ion-milling formed n-on-p HgCdTe photodiodes
Authors: Zha F. X. , Shao Jun , Jiang J. , Yang W. Y.
Published: May 2007

Photoluminescence characterization of n-on-p Hg1−xCdxTe photodiodes formed by ion-milling technique shows that the luminescence peak of the n-type conversion region shifts remarkably toward higher energy with an amount of ∼40meV more than that of the p region. The photovoltaic response of the diodes was examined. The origin of the “blueshift” may be ascribed to the Burstein-Moss effect associated with the high electron concentration of the type conversion region.
Al-based Ohmic reflectors with low leakage currents and high reflectance for p-GaN flip-chip processes
Authors: Chae S. W. , Kim D. H. , Kim T. G. , Ko K. Y. , Sung Y. M.
Published: May 2007

The authors report the improvement of InGaN∕GaN light-emitting diodes on Al reflectors, commonly used as n-type GaN contacts. A Cu-doped indium oxide (CIO) (5nm)/indium tin oxide (ITO) (380nm) interlayer was deposited and annealed at 500°C, after which an Al (400nm)∕Ti–W (30nm) layer was sputtered on the ITO interlayer to reflect the light. The reflectance of CIO∕ITO∕Al∕Ti–W was ∼92% at 460nm, higher than that of the popular Ni∕Ag∕Pt scheme, and the forward voltage was 3.2–3.3V, similar to that of the Ni∕Ag∕Pt contact. Furthermore, the mean leakage current of CIO∕ITO∕Al∕Ti–W was 0.12μA, much lower than 0.54μA of Ni∕Ag∕Pt at −5V.
Slow electromagnetic wave guided in subwavelength region along one-dimensional periodically structured metal surface
Authors: Ruan Zhichao , Qiu Min
Published: May 2007

A perfect electric conductor surface with one-dimensional periodic rectangle holes is proposed as a surface-plasmon-like waveguide, where designed surface plasmon modes with very low group velocity are confined in a subwavelength region. It is shown that the half maximum of electric field intensity of the mode can be confined in a 0.20λ×0.10λ subwavelength region on the transversal plane and the group velocity approaches to zeros, where λ is the wavelength in vacuum.
Polarity control of ZnO films on (0001) Al2O3 by Cr-compound intermediate layers
Authors: Park J. S. , Hong S. K. , Minegishi T. , Park S. H. , Im I. H. , Hanada T. , Cho M. W. , Yao T. , Lee J. W. , Lee J. Y.
Published: May 2007

This letter presents a reliable and very easy method for selective growth of polarity controlled ZnO films on (0001) Al2O3 substrates by plasma-assisted molecular-beam epitaxy. Cr-compound intermediate layers are used to control the crystal polarity of ZnO films on (0001) Al2O3. ZnO films grown on rocksalt structure CrN/(0001) Al2O3 shows Zn polarity, while those grown on rhombohedral Cr2O3∕(0001) Al2O3 shows O polarity. Possible interface atomic arrangements for both heterostructures are proposed.
Deformation-induced nanoscale high-temperature phase separation in Co–Fe alloys at room temperature
Authors: Zhang Lai-Chang , Calin Mariana , Paturaud Flora , Mickel Christine , Eckert Jürgen
Published: May 2007

Instead of applying severe plastic deformation, high-temperature heat treatment or high pressure, grain refinement and high-temperature phase separation induced by deformation in single-phase body-centered-cubic (bcc) coarse-grained Co–Fe alloys have been achieved by simple room-temperature compression. The alloys exhibit large plasticity over 140% without fracture. Phase separation from the bcc phase to nanoscale face-centered-cubic Fe and Co phases, which generally occurs at high temperature above ∼1150K, is formed in the deformed samples. The possible mechanisms are shear deformation and deformation-enhanced atomic diffusion rather than the temperature rise during deformation.
Quantum Hall effect at cleaved InSb surfaces and low-temperature annealing effect
Authors: Masutomi Ryuichi , Hio Masayuki , Mochizuki Toshimitsu , Okamoto Tohru
Published: May 2007

The authors have performed low-temperature in-plane magnetotransport measurements on two-dimensional electron systems induced by deposition of Ag at in situ cleaved surfaces of p-type InSb. The quantum Hall effect was observed even at low magnetic fields around 2T. The surface electron density and the electron mobility exhibit strong dependence on the Ag coverage and the annealing temperature in the range of 15–40K. The annealing effect suggests that the surface morphology strongly affects the properties of the two-dimensional electron systems.
The Role of Location in Knowledge Creation and Diffusion: Evidence of Centripetal and Centrifugal Forces in the City of London Financial Services Agglomeration
Authors: Cook Gary A S , Pandit Naresh R , Beaverstock Jonathan V , Taylor Peter J , Pain Kathy
Published: May 2007

In this paper we report on a major empirical study of centripetal and centrifugal forces in the City of London financial services agglomeration. The study sheds light on (1) the manner and magnitude of firm interaction in the agglomeration; (2) the characteristics of the agglomeration that aid the competitiveness of incumbent firms; and (3) the problems associated with agglomeration. In addressing these issues, we use the data to (1) test emerging theory that explains the high productivity and innovation of agglomerations in terms of their ability to generate and diffuse knowledge; and (2) evaluate the ‘end of geography’ thesis.
Investigating Urban Spatial Mismatch Using Job–Housing Indicators to Model Home–Work Separation
Authors: Horner Mark W , Mefford Jessica N
Published: May 2007

During the past four decades a great deal of research has been carried out investigating aspects of the spatial mismatch hypothesis. At its foundation, the notion of spatial mismatch is driven largely by social justice, as some groups are disproportionately disadvantaged by the patterns of metropolitan growth and development. We offer geographical insights into this dimension of spatial mismatch through an exploratory spatial analysis of metropolitan-scale home and work locations. This is achieved by developing a conceptual framework that synthesizes research on spatial mismatch and jobs–housing balance. Following this, a model is employed to detect home–work imbalances, controlling for race, ethnicity, and the mode of commute. The approach is applied to data on the residential and work locations for commuter groups in the Atlanta, GA metropolitan area. The results reveal how potential commute options differ across commuter groups and show that minority home–work alternatives are more spatially constrained.
Performance Measurement in UK Town Centre Management Schemes and US Business Improvement Districts: Comparisons and UK Implications
Authors: Hogg Sophie , Medway Dominic , Warnaby Gary
Published: May 2007

Performance measurement was introduced in the public sector to evaluate the impact of policy intervention. It has been heavily promoted to UK town centre managers in recent years by the government, retailers, and the Association of Town Centre Management (ATCM). Using data from interviews undertaken with UK town centre managers and business improvement district (BID) managers in the USA during 2002–03, the authors compare and contrast performance measurement in terms of concept, design, and use in these two contexts, as well as considering the issue of ‘performance ownership’. Implications for the UK are discussed in the light of the recent introduction of BIDs.
Hollywood, Vancouver, and the World: Employment Relocation and the Emergence of Satellite Production Centers in the Motion-Picture Industry
Authors: Scott Allen J , Pope Naomi E
Published: May 2007

The paper opens with an identification of the phenomenon of employment relocation (runaway production) from Hollywood and the concomitant formation of satellite production centers in other parts of the world. A brief theoretical analysis of this issue is provided, emphasizing the role of scale effects and transactions costs. The empirical record of the decentralization of film-shooting activities from Hollywood over the period from the early 1980s to the early 2000s is reviewed. We describe the effects of these activities on the rise and consolidation of the Vancouver film-production complex, and we engage in a broad discussion of the spatial and economic structure of the complex. We subsequently show that many places in other countries (for example, Australia, New Zealand, Romania, the Czech Republic, Mexico, South Africa, and elsewhere) are now competing strongly with Vancouver for film-shooting activities from Hollywood. We predict that this competition is likely to intensify greatly over the next decade or so, and that the global geography of film-shooting activities will almost certainly become increasingly more variegated as new studio complexes open up around the world.
The Impact of Abolishing Social-Housing Grants on the Compact-City Policy of Dutch Municipalities
Authors: Altes Willem K Korthals
Published: May 2007

Building on previously developed land is a top priority in Dutch compact-city policies. During the 1980s government grants supported building on these locations. In 1990 nonsubsidised housing accounted for only 5% of the housing programme for these inner-city sites. In 1995, as a result of the transformation of the welfare state in the Netherlands, the government abolished grants for the construction of social housing. This had a massive impact on the housing programme; and subsidies, as a proportion of the cost of infrastructure provision, dropped from 68% in 1990 to 30% in 2000. These changes have had a major impact on the role of municipalities and the powers they need to provide new housing on previously developed land. The municipalities' lack of powers and the new market conditions are contributing to the present stagnation of housebuilding in the Netherlands, and both of these factors influence Dutch compact-city policy.
Memory-Making ‘from Below’: Rescaling Remembrance at the Kranji War Memorial and Cemetery, Singapore
Authors: Muzaini Hamzah , Yeoh Brenda
Published: May 2007

Current literature on Commonwealth war cemeteries has tended to analyze these spaces of memory either as loci of ‘personal’ mourning or as symbolic manifestations of ‘imperial’ identities. However, as the number of those directly related to the war dwindles, these memorials as sites of bereavement have become less relevant to a new generation. As former colonies break away from the former British empire, these sites as expressions of a landscape that is ‘for ever England’ may also be losing currency. In this paper we focus upon Kranji War Memorial and Cemetery, a site maintained by the Commonwealth War Graves Commission to honour mainly those sacrificed in Singapore during the Second World War. Specifically, we highlight how Singaporeans have, in recent times, reappropriated the meanings of the site ‘from below’—through the contemporization and extraction of counternarratives—in an attempt to keep the resonance of the site for them. This, we argue, has led to the rescaling of remembrance from the level of the ‘personal’ or ‘imperial’ (which initially kept locals away) to one that is ‘national’ or ‘global’ (thus, salient to locals as well). In doing so we suggest how the readings of the site are bound to scales of commemoration, and how mnemonic practices at such memoryscapes may be contested within and across scales.
Grouping Effects in Flash-Induced Perceptual Fading
Authors: Vergeer Mark L T , van Lier Rob
Published: May 2007

We show that the flash-induced fading effect can be influenced by grouping based on colour and shape similarity. In flash-induced fading, peripherally presented elements perceptually disappear after a flash has been presented around or next to the element(s) (Kanai and Kamitani, 2003 Journal of Cognitive Neuroscience15 664–672). In the present study, two elements (which could either be similar or different in both colour and shape) were presented at an eccentricity of 2.6° from a fixation cross. After 2 s, a short flash (40 ms) was presented around one of the elements. The two elements remained on the screen for 2.5 s after the flash. We found a higher percentage of mutual perceptual disappearance when the two elements were similar in colour or in shape. These results converge with other findings showing that perceptual fading phenomena are influenced by effects of perceptual grouping. This indicates that, besides low-level adaptation, more global processes play a part in perceptual fading as well and should thus be taken into account in giving a full explanation of perceptual fading in general.
Inaccurate Representation of the Ground Surface beyond a Texture Boundary
Authors: Wu Bing , He Zijiang J , Ooi Teng Leng
Published: May 2007

The sequential-surface-integration-process (SSIP) hypothesis was proposed to elucidate how the visual system constructs the ground-surface representation in the intermediate distance range (He et al, 2004 Perception33 789–806). According to the hypothesis, the SSIP constructs an accurate representation of the near ground surface by using reliable near depth cues. The near ground representation then serves as a template for integrating the adjacent surface patch by using the texture gradient information as the predominant depth cue. By sequentially integrating the surface patches from near to far, the visual system obtains the global ground representation. A critical prediction of the SSIP hypothesis is that, when an abrupt texture-gradient change exists between the near and far ground surfaces, the SSIP can no longer accurately represent the far surface. Consequently, the representation of the far surface will be slanted upward toward the frontoparallel plane (owing to the intrinsic bias of the visual system), and the egocentric distance of a target on the far surface will be underestimated. Our previous findings in the real 3-D environment have shown that observers underestimated the target distance across a texture boundary. Here, we used the virtual-reality system to first test distance judgments with a distance-matching task. We created the texture boundary by having virtual grass- and cobblestone-textured patterns abutting on a flat (horizontal) ground surface in experiment 1, and by placing a brick wall to interrupt the continuous texture gradient of a flat grass surface in experiment 2. In both instances, observers underestimated the target distance across the texture boundary, compared to the homogeneous-texture ground surface (control). Second, we tested the proposal that the far surface beyond the texture boundary is perceived as slanted upward. For this, we used a virtual checkerboard-textured ground surface that was interrupted by a texture boundary. We found that not only was the target distance beyond the texture boundary underestimated relative to the homogeneous-texture condition, but the far surface beyond the texture boundary was also perceived as relatively slanted upward (experiment 3). Altogether, our results confirm the predictions of the SSIP hypothesis.
Illusory Bands in Orientation and Spatial Frequency: A Cortical Analog to Mach Bands
Authors: Essock Edward A , Hansen Bruce C , Haun Andrew M
Published: May 2007

Illusory bands at a luminance transition in space (ie an edge) are well known. Here we demonstrate illusory bands of enhanced orientations or spatial frequencies at transitions between higher-contrast and lower-contrast image content along the orientation and spatial-frequency dimensions—the dimensions of cortical spatial coding. We conclude that this illusion is a consequence of cortical-level suppression of units of similar orientations and spatial frequencies and serves to aid texture segmentation while providing efficient neural coding.
Role of Peyer's patches in the induction of
Helicobacter pylori
-induced gastritis
Authors: Nagai Shigenori , Mimuro Hitomi , Yamada Taketo , Baba Yukiko , Moro Kazuyo , Nochi Tomonori , Kiyono Hiroshi , Suzuki Toshihiko , Sasakawa Chihiro , Koyasu Shigeo
Published: May 2007

Helicobacter pylori
is a Gram-negative spiral bacterium that causes gastritis and peptic ulcer and has been implicated in the pathogenesis of gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. Although Th1 immunity is involved in gastritis and the accumulation of
H. pylori
-specific CD4
+
T cells in the
H. pylori
-infected gastric mucosa in human patients, how T cells are primed with
H. pylori
antigens is unknown because no apparent lymphoid tissues are present in the stomach. We demonstrate here that Peyer's patches (PPs) in the small intestine play critical roles in
H. pylori
-induced gastritis; no gastritis is induced in
H. pylori
-infected mice lacking PPs. We also observed that the coccoid form of
H. pylori
is phagocytosed by dendritic cells in PPs. We propose that
H. pylori
converts to the coccoid form in the anaerobic small intestine and stimulates the host immune system through PPs.
A climate-driven switch in plant nitrogen acquisition within tropical forest communities
Authors: Houlton Benjamin Z. , Sigman Daniel M. , Schuur Edward A. G. , Hedin Lars O.
Published: May 2007

The response of tropical forests to climate change will depend on individual plant species' nutritional strategies, which have not been defined in the case of the nitrogen nutrition that is critical to sustaining plant growth and photosynthesis. We used isotope natural abundances to show that a group of tropical plant species with diverse growth strategies (trees and ferns, canopy, and subcanopy) relied on a common pool of inorganic nitrogen, rather than specializing on different nitrogen pools. Moreover, the tropical species we examined changed their dominant nitrogen source abruptly, and in unison, in response to precipitation change. This threshold response indicates a coherent strategy among species to exploit the most available form of nitrogen in soils. The apparent community-wide flexibility in nitrogen uptake suggests that diverse species within tropical forests can physiologically track changes in nitrogen cycling caused by climate change.
Photodynamic molecular beacon as an activatable photosensitizer based on protease-controlled singlet oxygen quenching and activation
Authors: Zheng Gang , Chen Juan , Stefflova Klara , Jarvi Mark , Li Hui , Wilson Brian C.
Published: May 2007

Molecular beacons are FRET-based target-activatable probes. They offer control of fluorescence emission in response to specific cancer targets, thus are useful tools for
in vivo
cancer imaging. Photodynamic therapy (PDT) is a cell-killing process by light activation of a photosensitizer (PS) in the presence of oxygen. The key cytotoxic agent is singlet oxygen (
1
O
2
). By combining these two principles (FRET and PDT), we have introduced a concept of photodynamic molecular beacons (PMB) for controlling the PS's ability to generate
1
O
2
and, ultimately, for controlling its PDT activity. The PMB comprises a disease-specific linker, a PS, and a
1
O
2
quencher, so that the PS's photoactivity is silenced until the linker interacts with a target molecule, such as a tumor-associated protease. Here, we report the full implementation of this concept by synthesizing a matrix metalloproteinase-7 (MMP7)-triggered PMB and achieving not only MMP7-triggered production of
1
O
2
in solution but also MMP7-mediated photodynamic cytotoxicity in cancer cells. Preliminary
in vivo
studies also reveal the MMP7-activated PDT efficacy of this PMB. This study validates the core principle of the PMB concept that selective PDT-induced cell death can be achieved by exerting precise control of the PS's ability to produce
1
O
2
by responding to specific cancer-associated biomarkers. Thus, PDT selectivity will no longer depend solely on how selectively the PS can be delivered to cancer cells. Rather, it will depend on how selective a biomarker is to cancer cells, and how selective the interaction of PMB is to this biomarker.
Matching phylogeny and metabolism in the uncultured marine bacteria, one cell at a time
Authors: Stepanauskas Ramunas , Sieracki Michael E.
Published: May 2007

The identification of predominant microbial taxa with specific metabolic capabilities remains one the biggest challenges in environmental microbiology, because of the limits of current metagenomic and cell culturing methods. We report results from the direct analysis of multiple genes in individual marine bacteria cells, demonstrating the potential for high-throughput metabolic assignment of yet-uncultured taxa. The protocol uses high-speed fluorescence-activated cell sorting, whole-genome multiple displacement amplification (MDA), and subsequent PCR screening. A pilot library of 11 single amplified genomes (SAGs) was constructed from Gulf of Maine bacterioplankton as proof of concept. The library consisted of five flavobacteria, one sphingobacterium, four alphaproteobacteria, and one gammaproteobacterium. Most of the SAGs, apart from alphaproteobacteria, were phylogenetically distant from existing isolates, with 88–97% identity in the 16S rRNA gene sequence. Thus, single-cell MDA provided access to the genomic material of numerically dominant but yet-uncultured taxonomic groups. Two of five flavobacteria in the SAG library contained proteorhodopsin genes, suggesting that flavobacteria are among the major carriers of this photometabolic system. The
puf
M and
nas
A genes were detected in some 100-cell MDA products but not in SAGs, demonstrating that organisms containing bacteriochlorophyll and assimilative nitrate reductase constituted <1% of the sampled bacterioplankton. Compared with metagenomics, the power of our approach lies in the ability to detect metabolic genes in uncultured microorganisms directly, even when the metabolic and phylogenetic markers are located far apart on the chromosome.
Construction and behavior of engineered minichromosomes in maize
Authors: Yu Weichang , Han Fangpu , Gao Zhi , Vega Juan M. , Birchler James A.
Published: May 2007

Engineered minichromosomes were constructed in maize by modifying natural A and supernumerary B chromosomes. By using telomere-mediated chromosomal truncation, it was demonstrated that such an approach is feasible for the generation of minichromosomes of normal A chromosomes by selection of spontaneous polyploid events that compensate for the deficiencies produced. B chromosomes are readily fractionated by biolistic transformation of truncating plasmids. Foreign genes were faithfully expressed from integrations into normal B chromosomes and from truncated miniB chromosomes. Site-specific recombination between the terminal transgene on a miniA chromosome and a terminal site on a normal chromosome was demonstrated. It was also found that the miniA chromosome did not pair with its progenitor chromosomes during meiosis, indicating a useful property for such constructs. The miniB chromosomes are faithfully transmitted from one generation to the next but can be changed in dosage in the presence of normal B chromosomes. This approach for construction of engineered chromosomes can be easily extended to other plant species because it does not rely on cloned centromere sequences, which are species-specific. These platforms will provide avenues for studies on plant chromosome structure and function and for future developments in biotechnology and agriculture.
IL1-receptor accessory protein-like 1 (IL1RAPL1), a protein involved in cognitive functions, regulates N-type Ca
2+
-channel and neurite elongation
Authors: Gambino Frédéric , Pavlowsky Alice , Béglé Aurélie , Dupont Jean-Luc , Bahi Nadia , Courjaret Raphael , Gardette Robert , Hadjkacem Hassen , Skala Henriette , Poulain Bernard , Chelly Jamel , Vitale Nicolas , Humeau Yann
Published: May 2007

Null mutations in the IL1-receptor accessory protein-like 1 gene (
IL1RAPL1
) are responsible for an inherited X-linked form of cognitive impairment. IL1RAPL1 protein physically interacts with neuronal calcium sensor-1 (NCS-1), but the functional impact of the IL1RAPL1/NCS-1 interaction remains unknown. Here, we demonstrate that stable expression of IL1RAPL1 in PC12 cells induces a specific silencing of N-type voltage-gated calcium channels (N-VGCC) activity that explains a secretion deficit observed in these IL1RAPL1 cells. Importantly, this modulation of VGCC activity is mediated by NCS-1. Indeed, a specific loss-of-function of N-VGCC was observed in PC12 cells overexpressing NCS-1, and a total recovery of N-VGCC activity was obtained by a down-regulation of NCS-1 in IL1RAPL1 cells. The functional relevance of the interaction between IL1RAPL1 and NCS-1 was also suggested by the reduction of neurite elongation observed in nerve growth factor (NGF)-treated IL1RAPL1 cells, a phenotype rescued by NCS-1 inactivation. Because both proteins are highly expressed in neurons, these results suggest that IL1RAPL1-related mental retardation could result from a disruption of N-VGCC and/or NCS-1-dependent synaptic and neuronal activities.
“Diminishing returns” in the scaling of functional leaf traits across and within species groups
Authors: Niklas Karl J. , Cobb Edward D. , Niinemets Ülo , Reich Peter B. , Sellin Arne , Shipley Bill , Wright Ian J.
Published: May 2007

More than 5,000 measurements from 1,943 plant species were used to explore the scaling relationships among the foliar surface area and the dry, water, and nitrogen/phosphorus mass of mature individual leaves. Although they differed statistically, the exponents for the relationships among these variables were numerically similar among six species groups (ferns, graminoids, forbs, shrubs, trees, and vines) and within 19 individual species. In general, at least one among the many scaling exponents was <1.0, such that increases in one or more features influencing foliar function (e.g., surface area or living leaf mass) failed to keep pace with increases in mature leaf size. Thus, a general set of scaling relationships exists that negatively affects increases in leaf size. We argue that this set reflects a fundamental property of all plants and helps to explain why annual growth fails to keep pace with increases in total body mass across species.