bluuebunny/crossref_metadata_2025 huggingface dataset:
Modified atomic force microscopy cantilever design to facilitate access of higher modes of oscillation
Authors: Sadewasser S. , Villanueva G. , Plaza J. A.
Published: July 2006

The detection of higher modes of oscillation in atomic force microscopy can provide additional information on sample properties. However, the limited bandwidth of the photodiode in the beam deflection detection technique often limits the detectable frequency range. We present a novel cantilever design, which allows lowering the frequency of higher modes of oscillation, maintaining the frequency of the fundamental resonance. Simulations by finite element methods show that the ratio between the second mode and the fundamental resonance frequency can be adjusted between 2 and 10, compared to 6.3 for the regular rectangular cantilever design. Even stronger changes are observed for the third oscillation mode, corresponding to a torsional cantilever oscillation. Cantilevers with modified geometry were fabricated using silicon micromachining processes and subsequently tested, confirming the results from the simulation.
Bifrequency acousto-optic beam splitter
Authors: Kastelik J. C. , Dupont S. , Benaissa H. , Pommeray M.
Published: July 2006

In this article, we present a bifrequency acousto-optic beam splitter used to select independently the two polarization states of an arbitrary polarized input beam with two acoustic carriers. We make use of a dual frequency anisotropic interaction in the crystal, two acoustic waves diffract the optical beam, each frequency being tuned for interaction with only one of the beam polarizations. We explain how this double interaction is made possible by a proper cut of the paratellurite crystal and for a chosen launching angle of the input beam. In the first part we derive the theory underlying the acousto-optic interaction and the design of the paratellurite device. Then we describe our experimental setup, show some experimental results, and discuss them.
Rapid contactless thermometry with submilli-Kelvin resolution
Authors: Coffey T. , Mielke C. H. , Ruminer P. , Migliori A. , Kim D. , Kim K. H. , Moritomo Y.
Published: July 2006

We present a contactless method of detecting small changes in the surface temperature of metallic samples over a short time period. The thermometry method incorporates a contactless heater and simplifies sample preparation requirements for calorimetric measurements. We demonstrate that we can measure small temperature shifts (250μK) in 5ms at midrange temperatures (155K). This method does not serve as a conventional thermometer but as an in situ thermometer useful for narrow temperature ranges, such as the region of a phase transition (often exploited in bolometers). The manganite material Nd0.5Sr0.5MnO3 was chosen as a test material for our experiments because it is a well characterized material where resistivity and magnetization [Kuwakara et al., Science 270, 961 (1995)] and thermal conductivity [Kim et al., American Physical Society March Meeting, W24.009 (2004)] have been previously measured and the material undergoes a metal-insulator transition.
Lens-coupled liquid core waveguide for ultraviolet-visible absorption spectroscopy
Authors: Robles Tony , Paige David , Anastasio Cort
Published: July 2006

We have developed and characterized a modular liquid core waveguide (LCW) assembly for use in a commercial spectrophotometer to measure very low light absorbance values for dilute aqueous solutions in both the ultraviolet and visible wavelengths. The sample cell in this assembly is composed of a ∼1m, pure Teflon® AF 2400 tube that is coupled to the spectrophotometer light path with a quartz lens and windows. Spectrophotometric absorbance measurements of test solutions (e.g., dilute sodium nitrate and hydrogen peroxide) produce clear and distinct spectra that exhibit a lower limit of detection of 3mAU between 240 and 640nm. At absorbances above 10mAU our LCW system produces spectra from multiple independent injections that have a relative standard deviation of less than 10% and average absorbances within 5% of calculated values based on published molar absorptivities.
Optically trapped aqueous droplets for single molecule studies
Authors: Reiner J. E. , Crawford A. M. , Kishore R. B. , Goldner Lori S. , Helmerson K. , Gilson M. K.
Published: July 2006

We demonstrate a technique for creating, manipulating, and combining femtoliter volume chemical containers. The containers are surfactant-stabilized aqueous droplets in a low index-of-refraction fluorocarbon medium. The index-of-refraction mismatch between the container and fluorocarbon is such that individual droplets can be optically trapped by single focus laser beams, i.e., optical tweezers. Here, we trap and manipulate individual droplets, detect the fluorescence from single dye and red fluorescent protein molecules encapsulated in droplets, and observe fluorescence resonance energy transfer from a single dye pair on a deoxyribonucleic acid molecule encapsulated in a droplet.
Gain narrowing and random lasing from dye-doped polymer-dispersed liquid crystals with nanoscale liquid crystal droplets
Authors: Liu Y. J. , Sun X. W. , Elim H. I. , Ji W.
Published: July 2006

Dye-doped polymer-dispersed liquid crystals have been studied for random lasing. The dye-doped polymer-dispersed liquid crystal film was fabricated by photoinitiated polymerization with a collimated 514.5nm Ar+ laser beam. Scanning electron microscopy analysis showed that most liquid crystal droplets in polymer matrix ranged from 20to80nm. Gain narrowing and random lasing from dye-doped polymer dispersed liquid crystals were observed under the excitation of a frequency-doubled Nd:YAG (yttrium aluminum garnet) laser operating at a wavelength of 532nm. The possible mechanism was proposed to explain the random lasing. The threshold of the random lasing was about 25μJ/pulse. The linewidth of the lasing peaks was about 1nm. With the film thickness of 6.5μm, the lasing mode was nearly transverse electric polarized.
In situ electric-field-induced contrast imaging of electronic transport pathways in nanotube-polymer composites
Authors: Jesse Stephen , Guillorn Michael A. , Ivanov Ilia N. , Puretzky Alexander A. , Howe Jane Y. , Britt Phillip F. , Geohegan David B.
Published: July 2006

An electric-field-induced contrast mechanism for scanning electron microscopy is reported which permits the visualization of embedded nanomaterials inside various matrices with high contrast and high definition. The high contrast is proposed to result from localized enhancement of secondary electron emission from the nanomaterials due to electric-field-induced changes in their work functions. By utilizing a stage that allows in situ current-voltage measurements inside a scanning electron microscope, single-walled carbon nanotubes embedded within polymethyl methacrylate films were visualized directly. In addition to the rapid assessment of nanotube dispersion within polymers, electric-field-induced contrast imaging enables the determination of percolation pathways. From the contrast in the images, the relative voltage at all points in the electron micrograph can be determined, providing a new mechanism to understand electronic percolation through nanoscale networks.
Growth of Mg–Al spinel microcrystals on a sapphire surface using a solution-precipitation method
Authors: Liu Che-Ming , Chen Jyh-Chen
Published: July 2006

A solution-precipitation process was used to grow Mg–Al spinel microcrystals at etched pits in a c-axial sapphire single crystal surface. In the proposed innovative growth process, the etched pits function as heterogeneous nucleation points. The quenching and aging treatment causes Mg ions to diffuse into the sapphire crystal, precipitating as microcrystals at the etched pits. We found the precipitated crystals to be (111) Mg–Al spinels with a triangular pyramidal shape.
Accumulator for the production of intense positron pulses
Authors: Cassidy D. B. , Deng S. H. M. , Greaves R. G. , Mills A. P.
Published: July 2006

An intense pulsed positron source has been developed using a buffer gas trap to accumulate large numbers of positrons and create a dense plasma, which may then be bunched and spatially focused. Areal densities of more than 3×1010e+cm−2 have been achieved in a subnanosecond pulse producing an instantaneous positron current of more than 10mA. We describe various aspects of the device including a detection technique specifically developed for use with intense positron pulses. Two applications are also described as well as future experiments such as the formation of positronium molecules and the positronium Bose-Einstein condensate.
Long symmetric high-pressure cell for magnetic measurements in superconducting quantum interference device magnetometer
Authors: Kamenev K. V. , Tancharakorn S. , Robertson N. , Harrison A.
Published: July 2006

We describe a high-pressure cell for magnetic measurements in a magnetic property measurement system superconducting quantum interference device (SQUID) magnetometer. The cell has been developed for studies of weakly magnetic materials and has the operating pressure limit of 1GPa. Its design is focused on reducing the background signal by making the pressure cell symmetric with respect to the sample in order to provide an integrable SQUID response. The use of an externally loaded cylinder has resulted in the increased strength of the cell and in the provision of a larger sample volume. The optimization of the cell’s length has made it possible to use the approximation of an infinitely long cylinder in the whole range of accessible pressures and to apply the Lamé equation for calculating the change in the diameter of the cell as a function of applied pressure. This enabled us to remove a superconductive manometer from the cell and use the diameter-pressure calibration instead. This has further increased the sensitivity of the measurements at low temperatures which is particularly relevant to studies of weakly magnetic materials. The performance of the cell is illustrated by the results of high-pressure measurements on the molecular antiferromagnet [N(C2H5)4][FeCl4].
Field-induced polymer wall formation in a bistable smectic-A liquid crystal display
Authors: Büyüktanir Ebru A. , Gheorghiu Nadina , West John L. , Mitrokhin Maxim , Holter Børre , Glushchenko Anatoliy
Published: July 2006

We developed a composite system to produce robust bistable smectic-A (SmA) liquid crystal based flexible displays by encapsulating the liquid crystal material in a polymer wall structure. While keeping all the intrinsic bistable properties of the SmA material, the field-induced polymer walls bridge the two display substrates and bring significant advantages over the polymer dispersed liquid crystal structure. Here we analyze the performance of an encapsulated pixel and demonstrate superior electro-optical characteristics, high contrast ratio, and excellent sunlight readability.
Strain relaxation in buried SrRuO3 layer in (Ca1−xSrx)(Zr1−xRux)O3∕SrRuO3∕SrTiO3 system
Authors: Kim Soo Gil , Wang Yudi , Chen I-Wei
Published: July 2006

A novel relaxation phenomenon occurs in buried SrRuO3 layers in strained (Ca1−xSrx)(Zr1−xRux)O3∕SrRuO3∕SrTiO3 (001) thin film system. The lightly strained SrRuO3 buried layer is initially clamped by the SrTiO3 substrate. After a heavily strained (Ca1−xSrx)(Zr1−xRux)O3 overlayer is deposited, localized strain relaxation develops in the buried layer. This is manifested by a crosshatch pattern of ⟨100⟩ corrugations on the surface, due to the slip of ⟨110⟩ {110} threading dislocations. The phenomenon can be controlled by tuning the growth kinetics and strain energy of the overlayer.
Orientation dependent ferroelectric properties in samarium doped bismuth titanate thin films grown by the pulsed-laser-ablation method
Authors: Cheng Zhenxiang , Kannan Chinna Venkatasamy , Ozawa Kiyoshi , Kimura Hideo , Wang Xiaolin
Published: July 2006

Samarium doped bismuth titanate thin films with the composition of Bi3.25Sm0.75Ti3O12 and with strong preferred orientations along the c axis and the (117) direction were fabricated on Pt∕TiO2∕SiO2∕Si substrate by pulsed laser ablation. Measurements on Pt∕BSmT∕Pt capacitors showed that the c-axis oriented film had a small remanent polarization (2Pr) of 5μC∕cm2, while the highly (117) oriented film showed a 2Pr value of 54μC∕cm2 at an electrical field of 268kV∕cm and a coercive field Ec of 89kV∕cm. This is different from the sol-gel derived c-axis oriented Bi3.15Sm0.85Ti3O12 film showing a 2Pr value of 49μC∕cm2.
Control of lateral domain spreading in congruent lithium niobate by selective proton exchange
Authors: Grilli S. , Canalias C. , Laurell F. , Ferraro P. , De Natale P.
Published: July 2006

Proton exchange was observed to increase the poling voltage for congruent lithium niobate. Patterned proton exchange was then used to control domain nucleation and inhibit broadening of reversed domains. Periodically proton exchanged samples were used to form domain gratings by electric field poling just using planar electrodes and without need for poling current control. The reversed domain gratings had a duty cycle faithfully reproducing that of the proton exchanged pattern with straight domain walls parallel to the x face, thus demonstrating that high-fidelity reversed domain patterning is possible to obtain by a relatively simple process.
Microfluidic bypass for efficient passive regulation of droplet traffic at a junction
Authors: Cristobal Galder , Benoit Jean-Philippe , Joanicot Mathieu , Ajdari Armand
Published: July 2006

We propose a simple design for microfabricated junctions that allows an equal and regular distribution of droplets between the two outlets of a T junction. It relies on establishing a connection between the two outlets shortly after the junction to provide short-time memory to the device and induce perfect alternation in the choice of the outlet. We experimentally demonstrate the benefits of this simple passive device by a direct comparison to junctions without bypasses.
Direct synthesis and characterization of CdS nanobelts
Authors: Wang Z. Q. , Gong J. F. , Duan J. H. , Huang H. B. , Yang S. G. , Zhao X. N. , Zhang R. , Du Y. W.
Published: July 2006

A method to directly synthesize single crystalline CdS nanobelts has been developed. The advantages of the method in rapid synthesis within several minutes and catalyst free comparing to the previous method propose a potential avenue to the further practical device production and applications. The as-synthesized CdS nanobelts grow along the [100] crystalline direction with usually 500–2000nm in width and about tens to several hundred micrometers in length. Two luminescence peaks around 516 and 758nm in room-temperature photoluminescence spectrum are ascribed to the band-to-band and trap emission, respectively.
Deformation-induced nanostructuring in a Ti–Nb–Ta–In β alloy
Authors: Xu W. , Kim K. B. , Das J. , Calin M. , Rellinghaus B. , Eckert J.
Published: July 2006

Easy deformation-induced nanostructuring was found in a Ti–Nb–Ta–In β alloy with low stability against α″ martensitic transformation. Upon severe plastic deformation at the sample center, the reversible β→α″ martensitic transformation plays a significant role for grain refinement. A possible mechanism is proposed, in which the formation of fine martensite, the interaction among slip dislocations, martensite and twins, and the reversible transition from α″ back to β phase are considered as the main causes leading to pronounced grain refinement to the nanoscale.
Effective modification of indium tin oxide for improved hole injection in organic light-emitting devices
Authors: Di Chong-an , Yu Gui , Liu Yunqi , Xu Xinjun , Song Yabin , Zhu Daoben
Published: July 2006

We demonstrate modification of the indium tin oxide (ITO) surface with an ultrathin layer of hexadecafluorocopper phthalocyanine (F16CuPc) can significantly enhance hole injection as a result of the formation of an interfacial dipole layer. The dipole layer produces a surface potential shift, which reduces the hole injection energy barriers and thus improves the hole injection efficiency. The devices with anode modification exhibit significantly enhanced luminance efficiencies and dramatically decreased operation voltages, compared to devices with the bare ITO anode. The minimum turn-on voltage of 2.6V and the maximum efficiency of 5.1cd∕A are achieved.
Photonic crystal cavity-based micro/nanodisplay for visible lights
Authors: Li Baojun , Cai Xuejuan , Zhang Yao
Published: July 2006

A micro/nanodisplay in a two-dimensional photonic crystal slab has been investigated for visible light applications. By introducing a line-defect waveguide and different point defect resonant cavities, incoming visible lights with different wavelengths can be trapped by the different size cavities and then emitted to the free space when they travel along the line-defect waveguide. Therefore, a colorful surface-emitting display can be achieved on the surface of the photonic crystal slab with all colors ranging from red to violet.
Anti-Stokes photoluminescence in ZnO microcrystal
Authors: Cao Weitao , Du Weimin , Su Fuhai , Li Guohua
Published: July 2006

Low temperature (10K) strong anti-Stokes photoluminescence (ASPL) of ZnO microcrystal excited by low power cw 532nm laser is reported here. Energy upconversion of 1.1eV is obtained in our experiment with no conventional nonlinear effect. Through the study of the normal photoluminescence and temperature dependence of ASPL we conclude that the green band luminescence in ZnO is related to deep donor to valance band transition. Using the two-step two-photon absorption model, we provide a plausible mechanism leading to the ASPL phenomenon in our experiment.
Relaxation of process induced surface stress in amorphous silicon carbide thin films using low energy ion bombardment
Authors: Argyrakis P. , McNabb P. , Snell A. J. , Cheung R.
Published: July 2006

The surface stress in amorphous silicon carbide (a-SiC) thin films has been modified after processing. We show that low energy argon ion bombardment in an inductively coupled plasma reactor causes relaxation of the induced surface stress. Cantilever beams of variable length (25–150μm) have been fabricated and their deflection profiles have been compared before and after ion bombardment using white light interferometry. Our experiments show that the ion bombardment relaxes the stress gradient of the cantilever beams. Both the duration of plasma exposure as well as the bias voltage contribute to relaxing the stress gradient in the a-SiC thin film.
Kinetic details of the nucleation in supercooled liquid metals
Authors: Liu J. , Zhao J. Z. , Hu Z. Q.
Published: July 2006

The kinetic details of the nucleation in a supercooled Ni6Cu4 melt are investigated using molecular dynamics simulation method. It is indicated that the nucleus is a random mixture of a large number of fcc structures and a small number of hcp structures. The growth rate of the nucleus increases linearly with undercooling (ΔT). The results show the microstructure evolution in the supercooled liquid of Ni6Cu4 clearly.
Using infrared laser to enhance field emission of carbon nanotube
Authors: Hwang J. D. , Chen K. F. , Chan L. H. , Chang Y. Y.
Published: July 2006

Infrared laser has been used to irradiate carbon nanotube (CNT) powders and the performance of CNT emitter was enhanced. The CNTs were prepared by conventional electric arc discharge method and laser irradiation was processed by Nd:YAG infrared laser with a wavelength of 1064nm. It was found that the turn-on electric field was significantly decreased for laser treated sample. As compared to the sample of no laser treatment, the emission current density was enhanced by a magnitude of 16.56 for 225J∕cm2 treated plus annealing one. Possible mechanism is discussed here.
Solid phase epitaxy during Ge condensation from amorphous SiGe layer on silicon-on-insulator substrate
Authors: Balakumar S. , Tung C. H. , Lo G. Q. , Kumar R. , Balasubramanian N. , Kwong D. L. , Fei Gao , Lee S. J.
Published: July 2006

We report the solid phase epitaxial growth of silicon germanium (SiGe) layer during condensation/oxidation of sputter deposited amorphous SiGe layer on Si on insulator (SOI). The amorphous SiGe layer was first converted into polycrystalline film by preannealing and high temperature oxidation process. The solid phase epitaxial growth occurs during further oxidation/annealing process of polycrystalline SiGe on the Si on insulator substrate. A final thickness of about 1040Å of single crystalline SiGe is achieved with initial amorphous SiGe and SOI of thickness of 1000 and 740Å, respectively SiGe with 60% Ge concentration was achieved on further condensation followed by cyclic annealing to eliminate the defects formed in the layer.
Enhanced light extraction from circular Bragg grating coupled microcavities
Authors: Su Mark Y. , Mirin Richard P.
Published: July 2006

A sevenfold enhancement of light extraction over a 130nm bandwidth from a semiconductor at room temperature was achieved using circular Bragg gratings (CBGs) etched around the periphery of a vertical-cavity light-emitting structure. The CBG defined an in-plane circular cavity for light trapped in guided modes. Maximum enhancement was observed with CBGs that efficiently coupled circular cavity modes into resonant extracted modes of the vertical cavity. The enhancement factor corresponded to a 41% external efficiency.
Spiral exchange coupling in trilayer magnetic junction mediated by diluted-magnetic-semiconductor thin film
Authors: Lin Chia-Hui , Lin Hsiu-Hau , Hong Tzay-Ming
Published: July 2006

We revisit the noncollinear exchange coupling across the trilayer magnetic junction mediated by the diluted-magnetic-semiconductor thin film. By numerical approaches, we investigate the spiral angle between the ferromagnetic layers extensively in the parameter space. In contrast to previous study, we discovered the important role of spin relaxation, which tends to favor spiral exchange over the oscillatory Ruderman-Kittel-Kasuya-Yosida interaction. Finally, we discuss the physics origins of these two types of magnetic interactions.
Special cantilever geometry for the access of higher oscillation modes in atomic force microscopy
Authors: Sadewasser S. , Villanueva G. , Plaza J. A.
Published: July 2006

Employing higher oscillation modes of microcantilevers promises higher sensitivity when applied as sensors, for example, for mass detection or in atomic force microscopy. Introducing a special cantilever geometry, we show that the relation between the resonance frequencies of the first and second resonance modes can be modified to separate them further or to bring them closer together. In atomic force microscopy the latter is of special interest as the photodiode of the beam deflection detection limits the accessible frequency range. Using finite element simulations, we optimized the design of the modified cantilever geometry for a maximum reduction of the frequency of the second oscillation mode with respect to the first mode. Cantilevers were fabricated by silicon micromachining and subsequently utilized in an ultrahigh vacuum Kelvin probe force microscope imaging the surface potential of C60 on graphite.
Sequence of focused optical vortices generated by a spiral fractal zone plate
Authors: Tao S. H. , Yuan X.-C. , Lin J. , Burge R. E.
Published: July 2006

We propose a method for producing a sequence of focused optical vortices along the propagation direction by using a spiral fractal zone plate. The generated beam possesses the optical vortices embedded at subsidiary foci as well as the major ones of the fractal zone plate. The experimental results are obtained in good agreement with the simulations.
Backward difference frequency generation in an AlGaAs waveguide
Authors: Lanco L. , Ducci S. , Likforman J. P. , Ravaro M. , Filloux P. , Marcadet X. , Leo G. , Berger V.
Published: July 2006

We report on the observation of a noncollinear difference frequency generation at 1.55μm in an AlGaAs multilayer waveguide. In such three-wave-mixing process, which occurs between a transverse pump beam and two counterpropagating guided modes, the phase matching parameter is the angle of incidence of the pump and the peak efficiency is 3.5×10−6W−1. This innovative device is suitable as a tunable, narrow-bandwidth source of counterpropagating twin photons for quantum information.
Photoinduced fluorescence enhancement in CdSe∕ZnS quantum dot monolayers: Influence of substrate
Authors: Uematsu Takafumi , Maenosono Shinya , Yamaguchi Yukio
Published: July 2006

Photoinduced fluorescence enhancement (PFE) of CdSe∕ZnS core/shell quantum dot (QD) films on SiOx substrates was investigated. The fluorescence intensity of the QD film on SiO1.9 was greatly enhanced by continuous irradiation in vacuum, while the same QD film on SiO0.6 showed a small enhancement of the fluorescence intensity. After irradiation, the rate of fluorescence decay of the QD film on SiO0.6 was smaller than that of the QD film on SiO1.9. Our results suggest that the origin of PFE derives from the photoejection of electrons into the substrate, and that the oxygen-excess-related defects work as trap sites for the electrons.
Hydrogen-plasma-induced thermal donors in high resistivity n-type magnetic Czochralski-grown silicon
Authors: Huang Y. L. , Simoen E. , Claeys C. , Rafí J. M. , Clauws P. , Job R. , Fahrner W. R.
Published: July 2006

In this work, the formation of donors in n-type high resistivity magnetic Czochralski-grown silicon wafers, directly exposed to a hydrogen plasma, is investigated by a combination of capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements. C-V analysis demonstrates diffusionlike concentration profiles close to the surface, pointing to the formation of hydrogen-related shallow donors in silicon during the hydrogenation. In addition, oxygen thermal donors are created during a subsequent annealing (20min) performed at 350–450°C, as demonstrated by DLTS. It is shown that the hydrogen-related shallow donors are the dominant donors in as-hydrogenated samples, while hydrogen acts as a catalyst during the formation of oxygen thermal donors in the temperature range of 350–450°C. It is finally shown that the formation of both kinds of donors is Fermi-level dependent.
Structural and electrical properties of HfLaOx films for an amorphous high-k gate insulator
Authors: Yamamoto Y. , Kita K. , Kyuno K. , Toriumi A.
Published: July 2006

Thin HfLaOx films on Si(100) have been investigated as an alternative gate insulator. The introduction of La2O3 into HfO2 causes an increase of crystallization temperature. Furthermore, unlike other Hf-based amorphous materials such as HfSiOx or HfAlOx, the permittivity of HfLaOx keeps a high value (>20). The capacitance-voltage curve of metal oxide semiconductor capacitor using the HfLaOx dielectric film has shown a negligible hysteresis and no frequency dispersion, indicating very small degradations of both interface and bulk properties. In addition, a very low fixed charge density in HfLaOx films is demonstrated from a very small film thickness dependence of the flatband voltage.
Influence of vacuum toroidal field on two-fluid flowing equilibria of helicity-driven spherical torus plasmas
Authors: Kanki T. , Nagata M.
Published: July 2006

Two-fluid flowing equilibrium configurations of a helicity-driven spherical torus (HD-ST) in the realistic confinement region, including a flux conserver and a coaxial helicity source, are numerically determined by means of the combination of the finite difference and the boundary element methods. It is found from the numerical results that electron fluid near the central conductor is tied to a vacuum toroidal field and ion fluid is not. The magnetic configurations change from the high-q HD-ST (safety factor, q>1) with a paramagnetic toroidal field and low-β (volume average β value, ⟨β⟩≈2%) through the helicity-driven spheromak and reversed-field pinch to the ultra-low-q HD-ST (0<q<1) with a diamagnetic toroidal field and high-β (⟨β⟩≈18%) as the vacuum toroidal field at the inner edge regions decreases and reverses the sign. The two-fluid effects are more significant in this equilibrium transition when the ion diamagnetic drift has the same direction as the E×B one.
The Migration–Immigration Link in Canada's Gateway Cities: A Comparative Study of Toronto, Montreal, and Vancouver
Authors: Hou Feng , Bourne Larry S
Published: July 2006

In this paper we explore the links between internal migration and international immigration in Canada's three largest metropolitan areas. In particular, we use a place-specific approach to test the displacement hypothesis that the migration behaviour of the less-well-educated native-born population is sensitive to the inflows of immigrants. Based on analyses of microdata from five consecutive censuses covering the period from 1981 to 2001, we find that the migration–immigration relationships are complex, often subtle, and inconsistent across the three cities. Growth in the immigrant population is correlated with an increased out-migration rate among the less-well-educated native-born population, but only in Toronto and Vancouver. This correlation, however, is not independent of changes in housing prices. We also find no consistent support for an alternative hypothesis that economic restructuring accounts for the net out-migration from immigrant gateway cities.
Challenging the Derived Transport-Demand Thesis: Geographical Issues in Freight Distribution
Authors: Rodrigue Jean-Paul
Published: July 2006

One of the core concepts in transport and economic geography states that transportation is a derived demand, both for passengers and for freight transport alike. This assumption is reflected in the conventional literature which underlines that transport exists because it is the expression of a spatially differentiated function of supply and demand, and is thus considered to be ‘derived’ from other activities. However, recent developments in logistics and supply-chain management underline a paradigm shift in the consideration of freight transport as a derived demand. In many sectors of activity, the functions of production, consumption, and transportation have become embedded to the point that it is difficult to tell them apart. The author investigates the extent to which the concept of derived transport demand is being challenged by supply-chain management strategies. To overcome some of the inadequacies of the conventional perspective, it is suggested that several segments of freight-related activities should be considered as part of an integrated transport demand. Although operationally derived demand still applies to freight distribution, strategically—at the level of global commodity chains—integrated demand appears to be the emerging paradigm that is worth investigating further.
Measuring Workforce Segregation: Religious Composition of Private-Sector Employees at Individual Sites in Northern Ireland
Authors: Shirlow Peter
Published: July 2006

In this paper I examine the scope of publicly available information on the religious composition of employees in private-sector companies in Northern Ireland. I highlight the unavailability of certain types of monitoring data and the impact of data aggregation at company as opposed to site level. Both oversights lead to underestimates of the extent of workplace segregation in Northern Ireland. The ability to provide more-coherent data on workplace segregation, by religion, in Northern Ireland is crucial in terms of advancing equality and other social-justice agendas. I argue that a more-accurate monitoring of religious composition of workplaces is part of an overall need to develop a spatial approach in which the importance of ethnically territorialised spaces in the reproduction of ethnosectarian disputation is understood.
Enabling Global Trade above the Clouds: Restructuring Processes and Information Technology in the Transatlantic Air-Cargo Industry
Authors: Schwarz Guido
Published: July 2006

Neither conventional economic geography nor transport geography have paid sufficient attention to the restructuring of the logistics industry. As anecdotal evidence mounts in the business literature about revolutionary changes taking place in the distributive sectors of the economy, more analysis from a geographic perspective is needed. Among transport modes, air cargo is unique because it is one of the backbones of global trade for many commodities. The author analyzes the transformations affecting the transatlantic (USA–Europe) air-cargo market, focusing on the changing roles of the different types of firms in the industry in performing the functions necessary for the transportation of goods by air and for processing associated information. The importance of information handling, processing, and transmittal has been amplified relative to transportation functions, redefining the interrelationship between the physical space of goods flows and the virtual space of information flows. As a result, functional integration and consolidation have become the dominant processes for future industry development, leading to market concentration and the emergence of growing cargo-hub airports.
Apparent predation of juvenile coho salmon (Oncorhynchus kisutch) by prickly sculpins (Cottus asper) is an artefact of trapping methodology
Authors: Tomaro Londi M.
Published: July 2006

Freshwater sculpins often inhabit the same waterways as juvenile salmonids and may impact the survival of juvenile salmonids through predation on early life-history stages. In the present study, the stomach contents of 2302 individual Cottus asper, a freshwater sculpin, collected from Auke Lake, Alaska, were examined during the boreal summer of 2000 to determine if C. asper are important natural predators of juvenile coho salmon (Oncorhynchus kisutch), and to explore possible trap bias of gear used in preliminary diet studies. The diet of sculpins collected in confining traps was compared with the diet of sculpins collected in nets. Significant predation on pre-smolt coho salmon by trapped sculpins, but none by netted sculpins, was observed. This result provides strong evidence of trap bias in the observed diet of C. asper. The remainder of the diet of trapped sculpins also differed significantly from that of netted sculpins. Significantly more trapped sculpins had eaten plant material and fish, whereas significantly more netted sculpins had consumed molluscs. Finally, sculpin diet was correlated with sculpin size, which may influence predation on other salmonid life-stages. These results expand our understanding of prickly sculpin diet and show that they are not important predators of juvenile coho salmon. These findings also demonstrate the importance of assessing the potential bias of collection gear and sampling techniques.
Organic iron(III) speciation in surface transects across a frontal zone: the Chatham Rise, New Zealand
Authors: Tian Feng , Frew Russell D. , Sander Sylvia , Hunter Keith A. , Ellwood Michael J.
Published: July 2006

Iron (Fe) is a critical nutrient in marine systems and the organic complexation of Fe is a central factor of the marine biogeochemistry of Fe. In the present study, total dissolved Fe and its organic speciation were measured in filtered seawater samples (<0.2 μm) collected along three surface transects across the subtropical (ST) front, east of New Zealand, in austral spring (October 2000). Total dissolved Fe concentrations were low (~0.1 nm) in the subantarctic (SA) waters. The highest Fe concentration (~0.8 nm) was observed at the mixing boundary north of the Subtropical Convergence (STC) and then decreased relatively quickly both southward and northward. Cathodic stripping voltammetry was used to determine Fe speciation. The dissolved Fe(iii) was fully complexed (>99.9%) by natural organic ligands, which were found to occur in excess of the dissolved Fe concentration at 1.29 ± 0.33 nm (equivalent to an excess over Fe of ~1.0 nm), and with a complex stability of

log⁡

K
′

FeL,F
e

3+

-->
K′FeL,Fe3+ = 22.67 ± 0.22. The total ligand concentrations were consistently higher (~0.5 nm) in the ST and STC waters than in the SA waters. Our Fe data imply that the regional currents may be an important vehicle for transporting the elevated Fe across the front.
Development of an age - length structured model of the Hauraki Gulf - Bay of Plenty snapper (Pagrus auratus) population
Authors: Gilbert D. J. , Davies N. M. , McKenzie J. R.
Published: July 2006

The development of a population model in which population state is defined by a matrix of numbers at age and length is described. Functional forms for processes that fitted Hauraki Gulf–Bay of Plenty (New Zealand) snapper (Pagrus auratus) population data were developed. The model was fitted to: commercial and research samples of proportions at age and length, commercial samples of proportions at age, tag–recapture estimates of numbers at length, a catch per unit effort abundance index, and sea surface temperature data. For each age–length element of the state matrix, the model determines a transition vector that gives a distribution of non-negative growth increments. Mean growth is both length- and age–length-dependent, but also varies between years. Annual mean growth and annual year-class strength were both found to be positively related to sea surface temperature, but during different seasons. It was also found that variations in growth between years resulted in moderate and sustained fluctuations in population biomass. Diagnostic tools that were helpful in fitting the age–length data are described, and potentially fruitful model developments are suggested.
Modelling transport of larval New Zealand abalone (Haliotis iris) along an open coast
Authors: Stephens S. A. , Broekhuizen N. , Macdiarmid A. B. , Lundquist C. J. , McLeod L. , Haskew R.
Published: July 2006

The dispersal and transport of larval New Zealand abalone Haliotis iris was simulated using coupled two-dimensional hydrodynamic and Lagrangian particle-trajectory models. The aim was to estimate pelagic larval dispersal potential along the open coast, as a starting point from which basic management questions can be made for this recreationally and commercially important species. Larval dispersal was simulated from representative spawning sites under a range of representative hydrodynamic conditions, including wave-induced circulation cells. Larval presence over near-shore reef habitat declined as the energy of the flow field and corresponding larval dispersal and transport increased. Thus, spawning during high-energy conditions will promote dispersal and transport but reduce successful recruitment on near-shore reefs. This indicates that seeding of the adjacent coast is likely to be sporadic, with existing populations necessarily being somewhat self-recruiting. Results suggest that an ideal management system would ensure that adult populations were maintained at intervals of 10–30 km along the coast to maintain larval supply to areas in between. Dispersal characteristics were specific to the release site, and the simulations suggest that marine reserves can be positioned to accordingly achieve desired functions: for example, optimal choices can be made for seeding areas, recruitment or self-maintaining areas.
Rapid Asia–Europe–North America geographic dispersal of earliest Eocene primate
Teilhardina
during the Paleocene–Eocene Thermal Maximum
Authors: Smith Thierry , Rose Kenneth D. , Gingerich Philip D.
Published: July 2006

True primates appeared suddenly on all three northern continents during the 100,000-yr-duration Paleocene–Eocene Thermal Maximum at the beginning of the Eocene, ≈55.5 mya. The simultaneous or nearly simultaneous appearance of euprimates on northern continents has been difficult to understand because the source area, immediate ancestors, and dispersal routes were all unknown. Now, omomyid haplorhine
Teilhardina
is known on all three continents in association with the carbon isotope excursion marking the Paleocene–Eocene Thermal Maximum. Relative position within the carbon isotope excursion indicates that Asian
Teilhardina asiatica
is oldest, European
Teilhardina belgica
is younger, and North American
Teilhardina brandti
and
Teilhardina americana
are, successively, youngest. Analysis of morphological characteristics of all four species supports an Asian origin and a westward Asia-to-Europe-to-North America dispersal for
Teilhardina
. High-resolution isotope stratigraphy indicates that this dispersal happened in an interval of ≈25,000 yr. Rapid geographic dispersal and morphological character evolution in
Teilhardina
reported here are consistent with rates observed in other contexts.
Influence of sex chromosome constitution on the genomic imprinting of germ cells
Authors: Durcova-Hills Gabriela , Hajkova Petra , Sullivan Stephen , Barton Sheila , Surani M. Azim , McLaren Anne
Published: July 2006

Germ cells in XY male mice establish site-specific methylation on imprinted genes during spermatogenesis, whereas germ cells in XX females establish their imprints in growing oocytes. We showed previously that
in vitro
, sex-specific methylation patterns of pluripotent stem cell lines derived from germ cells were influenced more by the sex chromosome constitution of the cells themselves than by the gender of the embryo from which they had been derived. To see whether the same situation would prevail
in vivo
, we have now determined the methylation status of
H19
expressed from the maternal allele, and the expression and methylation status of a paternally expressed gene
Peg3
, in germ cells from sex-reversed and control embryos. For these imprinted genes, we conclude that the female imprint is a response of the germ cells to undergoing oogenesis, rather than to their XX chromosome constitution. Similarly, both our XY and our sex-reversed XX male germ cells clearly showed a male rather than a female pattern of DNA methylation; here, however, the sex chromosome constitution had a significant effect, with XX male germ cells less methylated than the XY controls.
Sialidase enhances spinal axon outgrowth
in vivo
Authors: Yang Lynda J. S. , Lorenzini Ileana , Vajn Katarina , Mountney Andrea , Schramm Lawrence P. , Schnaar Ronald L.
Published: July 2006

The adult CNS is an inhibitory environment for axon outgrowth, severely limiting recovery from traumatic injury. This limitation is due, in part, to endogenous axon regeneration inhibitors (ARIs) that accumulate at CNS injury sites. ARIs include myelin-associated glycoprotein, Nogo, oligodendrocyte-myelin glycoprotein, and chondroitin sulfate proteoglycans (CSPGs). Some ARIs bind to specific receptors on the axon growth cone to halt outgrowth. Reversing or blocking the actions of ARIs may promote recovery after CNS injury. We report that treatment with sialidase, an enzyme that cleaves one class of axonal receptors for myelin-associated glycoprotein, enhances spinal axon outgrowth into implanted peripheral nerve grafts in a rat model of brachial plexus avulsion, a traumatic injury in which nerve roots are torn from the spinal cord. Repair using peripheral nerve grafts is a promising restorative surgical treatment in humans, although functional improvement remains limited. To model brachial plexus avulsion in the rat, C8 nerve roots were cut flush to the spinal cord and a peroneal nerve graft was inserted into the lateral spinal cord at the lesion site. Infusion of
Clostridium perfringens
sialidase to the injury site markedly increased the number of spinal axons that grew into the graft (2.6-fold). Chondroitinase ABC, an enzyme that cleaves a different ARI (CSPGs), also enhanced axon outgrowth in this model. In contrast, phosphatidylinositol-specific phospholipase C, which cleaves oligodendrocyte-myelin glycoprotein and Nogo receptors, was without benefit. Molecular therapies targeting sialoglycoconjugates and CSPGs may aid functional recovery after brachial plexus avulsion or other nervous system injuries and diseases.
An amphipathic helix targets serum and glucocorticoid-induced kinase 1 to the endoplasmic reticulum-associated ubiquitin-conjugation machinery
Authors: Arteaga Maria Francisca , Wang Lin , Ravid Tommer , Hochstrasser Mark , Canessa Cecilia M.
Published: July 2006

Serum- and glucocorticoid-induced kinase 1 (Sgk1) regulates many ion channels and transporters in epithelial cells and promotes cell survival under stress conditions. In this study we demonstrate that Sgk1 is a short-lived protein regulated by the endoplasmic reticulum (ER)-associated degradation system and subcellular localization to the ER. We identified a hydrophobic motif (residues 18–30) as the signal for ER localization and rapid degradation by the ubiquitin (Ub)/proteasome pathway in both yeast and mammalian cells. Deletion or reduction of hydrophobicity of the motif redistributes Sgk1 to the cytosol and nucleus and markedly increases its half-life. We determined that the Ub-conjugating UBC6 and UBC7 and the Ub ligase HRD1 are the ER-associated Ub enzymes that mediate degradation of Sgk1; thus, Sgk1 has been identified as a cytosolic substrate for mammalian HRD1. Compartmentalization of Sgk1 controls the functional and spatial specificities of Sgk1-mediated signaling pathways, whereas rapid protein turnover provides a means to rapidly adjust Sgk1 abundance in response to different hormonal and external stimuli that increase Sgk1 gene transcription.
Phenotypic plasticity of T cell progenitors upon exposure to Notch ligands
Authors: Krueger Andreas , Garbe Annette I. , von Boehmer Harald
Published: July 2006

Despite many efforts, the nature of thymic immigrants that give rise to T cells has remained obscure, especially since it became known that extrathymic lineage-negative, Sca-1–positive, c-kit high progenitor cells differ from intrathymic early T cell progenitors (ETPs) by functional potential and dependence on Notch signaling. After our observation that intrathymic T cell precursors expressing a human CD25 reporter under control of pre-TCRα regulatory elements almost exclusively have the ETP phenotype, we have analyzed the phenotypic changes of reporter-expressing common lymphoid progenitor (CLP) cells in the bone marrow when cultured on Delta-like 1–expressing stromal cells. We note that these quickly adopt the phenotype of double negative (DN)2 thymocytes with little display of the ETP phenotype. Our data suggest that common lymphoid progenitor (CLP) cells could be responsible for the rapid reconstitution of thymus function after bone marrow transplantation since CLP cells in the blood have the capacity to rapidly enter the thymus and become DN2 thymocytes.
Oxidative stress generated by hemorrhagic shock recruits Toll-like receptor 4 to the plasma membrane in macrophages
Authors: Powers Kinga A. , Szászi Katalin , Khadaroo Rachel G. , Tawadros Patrick S. , Marshall John C. , Kapus András , Rotstein Ori D.
Published: July 2006

Oxidative stress generated by ischemia/reperfusion is known to prime inflammatory cells for increased responsiveness to subsequent stimuli, such as lipopolysaccharide (LPS). The mechanism(s) underlying this effect remains poorly elucidated. These studies show that alveolar macrophages recovered from rodents subjected to hemorrhagic shock/resuscitation expressed increased surface levels of Toll-like receptor 4 (TLR4), an effect inhibited by adding the antioxidant N-acetylcysteine to the resuscitation fluid. Consistent with a role for oxidative stress in this effect, in vitro H2O2 treatment of RAW 264.7 macrophages similarly caused an increase in surface TLR4. The H2O2-induced increase in surface TLR4 was prevented by depleting intracellular calcium or disrupting the cytoskeleton, suggesting the involvement of receptor exocytosis. Further, fluorescent resonance energy transfer between TLR4 and the raft marker GM1 as well as biochemical analysis of the raft components demonstrated that oxidative stress redistributes TLR4 to lipid rafts in the plasma membrane. Preventing the oxidant-induced movement of TLR4 to lipid rafts using methyl-β-cyclodextrin precluded the increased responsiveness of cells to LPS after H2O2 treatment. Collectively, these studies suggest a novel mechanism whereby oxidative stress might prime the responsiveness of cells of the innate immune system.