bluuebunny/crossref_metadata_2025 huggingface dataset:
Personalauswahl zwischen Psychotechnik und Charakteranalyse
Authors: Petri Stefan
Published: December 2004

Zusammenfassung. Der Beitrag zeichnet nach einer kurzen Darstellung der Institutionalisierung der Militärpsychologie in Deutschland die schrittweise Veränderung ihrer Grundsätze bei der Ausarbeitung von Personalauswahlmethoden nach. Dabei wird die These vertreten, dass bei der Entwicklung der psychologischen Verfahren für die Auswahl von Offiziersanwärtern die Ausgestaltung der Methoden den Rahmenbedingungen der damaligen Personalpolitik der Reichswehr angepasst war und zudem inhaltlich und der Form nach den Bedürfnissen und Strukturen der militärischen Entscheidungsfindung folgte. Das kann erklären, warum sich die Einführung wissenschaftlicher Verfahren bei der Personalauslese, die eindeutig einen Bruch mit den überkommenen Traditionen der militärischen Elitenrekrutierung darstellte, dennoch zunächst stabilisierend auf die soziale Komposition des Offizierskorps auswirken konnte. Diese änderte sich erst mit dem massiven personellen Ausbau der Wehrmacht ab 1935. Die Auswirkungen der Militärpsychologie als wichtigstem Praxisfeld in den 1930er und 1940er Jahren auf die akademische Psychologie lässt darüber hinaus ein Verständnis der Angewandten Psychologie als simpler Übertragung grundwissenschaftlicher Erkenntnisse auf praktische Probleme zunehmend problematischer erscheinen.
Global control of merging by the interplanetary magnetic field: Cluster observations of dawnside flank magnetopause reconnection
Authors: Eriksson S. , Elkington S. R. , Phan T. D. , Petrinec S. M. , Rème H. , Dunlop M. W. , Wiltberger M. , Balogh A. , Ergun R. E. , André M.
Published: December 2004

Detailed Cluster observations of flank magnetopause reconnection are presented for two events on the Northern and the Southern Hemispheric dawnside flanks when the interplanetary magnetic field (IMF) clock angle = arctan(By/Bz) is within ∼45° of the equatorial plane. The event selection is based on the relative proximity between the Cluster spacecraft 1 position and the predicted magnetospheric sash where antiparallel merging is expected to develop. MHD simulations performed for the two events indicate that the Cluster spacecraft were passing through the MHD sash region in the Northern Hemisphere on 30 June 2001, while crossing the magnetopause equatorward of the Southern Hemispheric sash on 29 May 2001. Accelerated and decelerated plasma flows relative to the magnetosheath velocity were detected by Cluster on both occasions. The Walén test confirms that the observed ΔV is directly correlated with the predicted magnetic field rotation ΔB/ with the expected direction of the normal magnetic field and so we interpret them as speed changes due to magnetic reconnection. The observed directions of ΔV compare very well with the location of the simulated MHD sash relative to Cluster. The magnetic field shear in the locally tangential plane of the magnetopause ranges between 171° and 177° for the 30 June event in good agreement with antiparallel merging at the MHD sash. The corresponding local field shear for the 29 May event is only 144°, either suggesting a component merging site in the direction of the sash or indicating that Cluster is farther away from the location where the neutral line was initially formed as compared with the 30 June event. A comparison between the projected regions of antiparallel and component merging onto the magnetopause and the quasi‐steady direction of plasma acceleration detected by Cluster on 29 May and 30 June support the view that the IMF controls the expected global location of magnetic reconnection at limited regions of the magnetopause. This is in contrast to randomly distributed merging sites over the dayside magnetopause that in principle could generate accelerated flows away from the observed directions of ΔV.
Hydraulic tests in highly permeable aquifers
Authors: Butler James J. , Zhan Xiaoyong
Published: December 2004

A semianalytical solution is presented for a mathematical model describing the flow of groundwater in response to a slug or pumping test in a highly permeable, confined aquifer. This solution, which is appropriate for wells of any degree of penetration and incorporates inertial mechanisms at both the test and observation wells, can be used to gain new insights into hydraulic tests in highly permeable settings. The oscillatory character of slug‐ and pumping‐induced responses will vary considerably across a site, even in an essentially homogeneous formation, when wells of different radii, depths, and screen lengths are used. Thus variations in the oscillatory character of responses do not necessarily indicate variations in hydraulic conductivity (K). Existing models for slug tests in partially penetrating wells in high‐K aquifers neglect the storage properties of the media. That assumption, however, appears reasonable for a wide range of common conditions. Unlike in less permeable formations, drawdown at an observation well in a high‐K aquifer will be affected by head losses in the pumping well. Those losses, which affect the form of the pumping‐induced oscillations, can be difficult to characterize. Thus analyses of observation‐well drawdown should utilize data from the period after the oscillations have dissipated whenever possible. Although inertial mechanisms can have a large impact on early‐time drawdown, that impact decreases rapidly with duration of pumping and distance to the observation well. Conventional methods that do not consider inertial mechanisms should therefore be viable options for the analysis of drawdown data at moderate to large times.
Invasion of ice through rigid anisotropic porous media
Authors: Swainson I. P. , Schulson E. M.
Published: December 2004

Crystallographic textures are presented of ice formed in situ by directional cooling of saturated porous rocks. The observations of texture demonstrate that pore invasion, and not repeated nucleation, dominates the freezing process in these rocks. This implies that microscopic advance of crystallographically coherent ice occurs through the pore network. The textures are governed by the permeability of the pore network and not by the direction of bulk heat flow. The anisotropy of permeability provides a mechanism for grain competition during ice growth, as crystals with fast growth directions aligned favorably to the maximum permeability are favored.
Thermal activation of As implanted in bulk Si and separation by implanted oxygen
Authors: Dalponte M. , Boudinov H. , Goncharova L. V. , Starodub D. , Garfunkel E. , Gustafsson T.
Published: December 2004

We have studied arsenic (As) diffusion and its electrical activation in two different types of silicon substrates: bulk Si and separation by implanted oxygen (SIMOX) wafers. Both substrates were implanted with a dose of 5×1014cm−2 As+ at 20keV. The samples were annealed and physical characterization was performed with secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry, and medium energy ion scattering. The electrical properties of the film were extracted by Hall measurements. The SIMS results showed a lower dopant outdiffusion loss to the atmosphere during annealing in the SIMOX samples. The electrical results for the SIMOX samples were also superior to those of bulk Si due to the higher dopant retention, likely the result of a higher concentration of vacancies, which in turn increases the relative fraction of As which is activated (in substitutional sites). The net effect was a higher sheet carrier concentration and lower sheet resistance in the SIMOX samples. The implantation damage removal was superior in SIMOX samples compared to bulk Si ones.
A comparison of plasma-activated N2∕O2 and N2O∕O2 mixtures for use in ZnO:N synthesis by chemical vapor deposition
Authors: Barnes T. M. , Leaf J. , Hand S. , Fry C. , Wolden C. A.
Published: December 2004

A high-vacuum plasma-assisted chemical-vapor deposition system was used to systematically study ZnO:N thin film synthesis. Nitrogen doping was achieved by mixing either N2O or N2 with O2 in a high-density inductively coupled plasma (ICP) source. In situ diagnostics showed that the ICP composition was predominantly a function of the elemental oxygen to nitrogen ratio, and relatively insensitive to the choice of N2 or N2O as the molecular precursor. Nitrogen incorporation was measured by both x-ray photoelectron spectroscopy and secondary ion mass spectrometry and was found to increase monotonically with both N2O and N2 addition. Nitrogen doping was correlated with systematic shifts in the lattice spacing, electrical conductivity, and optical absorption. Quantitative comparisons between film properties and gas composition suggest that atomic nitrogen is the primary precursor for doping in this system.
Boron-enhanced blistering and exfoliation in hydrogen-implanted SrTiO3
Authors: Lee Jung-Kun , Averitt Richard D. , Nastasi Michael
Published: December 2004

The blistering behavior and the exfoliation of SrTiO3 single crystals were investigated using co-implantation with boron and hydrogen. In contrast to H-only-implantation, co-implantation of B+ with 1×1015ions∕cm2 at 80kV and H+ with 5×1016ions∕cm2 at 40kV caused a vigorous blistering and a complete exfoliation during the annealing process. A comparison of the blistering depth and the hydrogen distribution in the co-implanted samples revealed that the exfoliation did not occur in the regions of maximum hydrogen concentration or maximum hydrogen-related radiation damage. It occurred at the crossover of the boron distribution profile and hydrogen distribution profile. With the aid of an elastic recoil detection and the Rutherford backscattering spectroscopy in the channeling mode, the preimplanted boron was found to facilitate the long-range H movement into the B-implanted region, resulting in the chemical interaction between B and H. A bond analysis obtained from the Fourier transform infrared-attenuated total reflection spectroscopy showed that B–H interactions resulted in the formation of boron hydride. It is proposed that the boron hydride formation and decomposition upon annealing provided the needed gas pressure for the complete exfoliation of B+H co-implanted SrTiO3 crystals.
Magnetic patterning using ion irradiation for highly ordered CoPt alloys with perpendicular anisotropy
Authors: Abes M. , Venuat J. , Muller D. , Carvalho A. , Schmerber G. , Beaurepaire E. , Dinia A. , Pierron-Bohnes V.
Published: December 2004

We used a combination of ion irradiation and e-beam lithography to magnetically pattern an ordered CoPt alloy with strong perpendicular magnetic anisotropy. Ion irradiation disorders the alloy and strongly reduces the magnetic anisotropy. Magnetic force microscopy showed a regular array of 1μm2 square dots with perpendicular anisotropy separated by 1 μm large ranges with in-plane anisotropy. This is further confirmed by magnetic measurements, which showed that arrays protected by a 200 nm Pt layer present the same coercive field and the same perpendicular anisotropy as before irradiation. This is promising for applications in magnetic recording technologies.
Conjugated polymer∕molten salt blends: The relationship between morphology and electrical aging
Authors: Habrard F. , Ouisse T. , Stephan O. , Armand M. , Stark M. , Huant S. , Dubard E. , Chevrier J.
Published: December 2004

Mixing molten salts with luminescent conjugated polymers provides the ability to lower the current threshold of organic electroluminescence (EL) devices. However, this process generally results in unwanted premature electrical aging. We used dynamic atomic force microscopy (AFM) in the electric force detection regime to study the phase microseparation occurring in the salt-polymer blend. We found that in the spin-coated layers, the molten salt most often forms discotic, roughly self-organized sub-microdomains. Their size and density strongly depend on the polymer side chains and overall molecular weight, on the molten salt nature, and on their respective concentrations in solution. We show that the diode current is injected into the vicinity of the interface between the salt and polymer domains, since it is proportional to the perimeter of the salt domains per surface unit, as estimated from the AFM images. The electrical aging is attributed to the degradation of the interface between the polymer and salt domains. This is further corroborated by a number of electrical data.
Unusual thermoelectric behavior of packed crystalline granular metals
Authors: Ausloos M. , Pȩkala M. , Latuch J. , Mucha J. , Vanderbemden Ph. , Vertruyen B. , Cloots R.
Published: December 2004

Loosely packed granular materials are intensively studied nowadays. Electrical and thermal transport properties should reflect the granular structure, as well as intrinsic properties. We have compacted crystalline CaAl-based metallic grains and studied the electrical resistivity and the thermoelectric power as a function of temperature (T) from 15to300K. Both properties show three regimes as a function of temperature. It should be pointed out: (i) The electrical resistivity continuously decreases between 15 and 235K, (ii) with various dependencies, e.g., ≃T−3∕4 at low T, while (iii) the thermoelectric power (TEP) is positive, (iv) shows a bump near 60K, and (v) presents a rather unusual square root of temperature dependence at low temperature. It is argued that these three regimes indicate a competition between geometric and thermal processes—for which a theory seems to be missing in the case of TEP. The microchemical analysis results are also reported, indicating a complex microstructure inherent to the phase diagram peritectic intricacies of this binary alloy.
A time-resolved Langmuir double-probe method for the investigation of pulsed magnetron discharges
Authors: Welzel Th. , Dunger Th. , Kupfer H. , Richter F.
Published: December 2004

Langmuir probes are important means for the characterization of plasma discharges. For measurements in plasmas used for the deposition of thin films, the Langmuir double probe is especially suited. With the increasing popularity of pulsed deposition discharges, there is also an increasing need for time-resolved characterization methods. For Langmuir probes, several single-probe approaches to time-resolved measurements are reported but very few for the double probe. We present a time-resolved Langmuir double-probe technique, which is applied to a pulsed magnetron discharge at several 100 kHz used for MgO deposition. The investigations show that a proper treatment of the current measurement is necessary to obtain reliable results. In doing so, a characteristic time dependence of the charge-carrier density during the “pulse on” time containing maximum values of almost 2∙1011cm−3 was found. This characteristic time dependence varies with the pulse frequency and the duty cycle. A similar time dependence of the electron temperature is only observed when the probe is placed near the magnesium target.
Strain relaxation of GeSi/Si(001) heterostructures grown by low-temperature molecular-beam epitaxy
Authors: Bolkhovityanov Yu. B. , Deryabin A. S. , Gutakovskii A. K. , Revenko M. A. , Sokolov L. V.
Published: December 2004

Plastic relaxation in GexSi1−x∕Si(001) heterostructures with x=0.18–0.62, grown at temperatures of 300–600 °C with the use of a low-temperature (350 °C) Si buffer layer, is considered. It is shown that the use of low-temperature Si and low temperature of growth of GeSi films decreases the density of threading dislocations to the value of 105–106cm−2 in heterostructures with a germanium content x<¯0.3, whereas the density of the threading dislocations in heterostructures with a higher content of Ge remains at the level of ∼108cm−2 and higher. By means of transmission electron microscopy, it is shown that the origination of dislocation half-loops from the surface in the case of a high content of germanium in the film is the main reason for the high density of threading dislocations. Growing of GeSi films with a two-step change in composition is considered. The fact that the density of the threading dislocations in the first step of the film is significantly higher than that in the substrate is noted. Because of their presence, the real thickness of insertion of misfit dislocations into the second step of the film is in ten times less than for the first layer. With an allowance for this effect, almost complete plastic relaxation of the second and further heterostructure steps can be reached at low temperatures and at a smaller thickness of GeSi films. It is concluded that the main factors of low-temperature epitaxy of GeSi, which reduce the density of the threading dislocations in heterostructures are (i) a decrease in the initial threading dislocation density and (ii) an increase in the rate of expansion of dislocation loops, which facilitates plastic relaxation with a smaller number of threading dislocations.
Electroactive fluorinate-based polymers: Ferroelectric and dielectric properties
Authors: Yu Zhi , Ang Chen
Published: December 2004

The dielectric, ferroelectric, and electroactive strain behavior of poly(vinylidene fluoride-trifluoroethylene) copolymers and poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymers is studied in a wide temperature and frequency range. The dielectric response from two dielectric polarization processes, modes A(A′) and B, and the dielectric-background contribution can be identified for these polymers by using the Cole-Cole plot method. Therefore physically reasonable parameters are obtained by fitting the relaxation time to the Vogel-Fulcher relation. On the other hand, the dielectric relaxation step and high strain decrease simultaneously with decreasing temperature; this indicates that the dielectric relaxation process and high strain behavior are strongly correlated. The electron-irradiation effect in copolymers and the monomer effect in terpolymers are discussed.
Coupling effects of the flow and electric fields in electrostatic precipitators
Authors: Zamankhan Parsa , Ahmadi Goodarz , Fan Fa-Gung
Published: December 2004

In this study the variations of the velocity and electric fields in electrohydrodynamic (EHD) flows in a positive single-wire electrostatic precipitator are studied. The fully coupled systems of electrical and hydrodynamical governing equations are solved for both laminar and turbulent flow conditions. Particular attention is given to the flow-electric field coupling effects and the variation of the electrical potential and charge distribution induced by the gas flow field. The presented results show that the effects of airflow on electrical potential and charge density become noticeable at high cross-flow velocities. The electrical conditions in an electrostatic precipitator that was used in an earlier experimental study are also simulated. It is shown that the computational model predictions are in good agreement with the experimental data. A series of parametric studies for a range of parameters for the EHD flows in the single-wire precipitator are performed and the corresponding flow and electric fields are presented. An example of extension of the model to multiwire precipitator is also presented.
Optical properties of correlation-induced paramagnetic FeAl alloy
Authors: Rhee Joo Yull
Published: December 2004

The first-principles electronic-structure calculations of FeAl alloy using the density-functional theory within the local-(spin)-density approximation (LDA) cannot correctly predict the paramagnetic ground state even when using the generalized-gradient approximation (GGA), while the application of the LDA+U method can correctly predict the paramagnetic ground state. Therefore, the FeAl alloy is believed to have a correlation-induced paramagnetic ground state. The electronic structures and optical-conductivity (OC) spectrum of the equiatomic FeAl alloy were calculated using a full-potential linearized-augmented-plane-wave method within the GGA with and without the inclusion of the LDA+U method. The calculated OC spectrum without the LDA+U method does not agree well with the experimental one, while the application of the LDA+U method markedly improves the agreement between the experimental and calculated spectra. The application of the LDA+U method redistributes the Feeg and t2g bands near the Fermi level and this redistribution causes the difference between the OC spectra calculated with a simple GGA and the LDA+U method.
Relation between exchange coupling and enhanced coercivity in the free layer of a patterned magnetic tunnel junction
Authors: Kim CheolGi , Kim Chong-Oh , Tsunoda Masakiyo , Takahashi Migaku , Stobiecki Tomasz
Published: December 2004

A magneto-optical Kerr effect system with a spatial resolution of 2μm was used to measure the local M-H loops for the free layer of a magnetic tunnel junction with a structure of Ta∕Cu∕Ta∕NiFe∕Cu∕Mn75Ir25∕Co70Fe30∕Al2O3∕Co70Fe30∕Ta to investigate the exchange bias field HE and the coercivity HC for the free layer. The HE and HC measured along the direction of the free layer varied symmetrically with respect to the junction center. The measurements indicate that the enhanced HC correlated with HE, and HE could be reasonably explained by using an “orange-peel-type” coupling based on variations in the thickness of the pinned layer along the direction of the free layer. The variation in HE along the pinned-layer’s direction could be ascribed to that of the free-layer’s thickness, and the increase in HE at the junction edge along the pinned layer was due to a decrease in the thickness of the free layer near the edge. However, the nearly constant HC along the pinned layer indicates that the thickness of the free layer can be excluded from the mechanism for enhancing HC, which is a unique difference in the parameters involved in HE and HC, and in the mechanism for enhancing HC.
Columnar tilt and vortex stress in superconducting thin films of NdBa2Cu3O7−δ: Magnetization critical current-density measurements
Authors: Khatua Sanghamitra , Mishra P. K. , Kumar Ravi , Kundaliya D. C. , Buddhikot D. , Pinto R. , Malik S. K.
Published: December 2004

C -axis-oriented NdBa2Cu3O7−δ thin films (thickness ∼2000Å) on LaAlO3 substrates have been prepared and irradiated with Ag+14 (200MeV) ions at different inclinations (θd=0°, 15°, 30°, and 45°) to the c axis. Magnetization-field hysteresis loops have been obtained on pristine and irradiated thin films at two different temperatures in applied magnetic fields up to 5T. Estimates of the critical current density Jc(H,θ) and the volume pinning force Fp(H,θ) from the magnetization data reveal a strong dependence on track inclination. An increase and a subsequent saturation in Fp(H,θ), instead of the usual Gaussian peak around the equivalent matching field, Bϕ, is observed. It is suggested that this dependence of Jc (or Fp) on θd is a consequence of the effective modification of vortex pinning by tilted columnar defects.
Controlled growth of O-polar ZnO epitaxial film by oxygen radical preconditioning of sapphire substrate
Authors: Mei Z. X. , Wang Y. , Du X. L. , Ying M. J. , Zeng Z. Q. , Zheng H. , Jia J. F. , Xue Q. K. , Zhang Z.
Published: December 2004

Oxygen radicals pregrowth treatment and surface nitridation were used to eliminate Zn-polar inversion domains and control the growth of single-domain O-polar ZnO film on sapphire (0001) substrate by rf plasma-assisted molecular beam epitaxy. We found that the formation of oxygen-terminated sapphire surface prior to nitridation is crucial for achieving the anion polarity in subsequent AlN and ZnO layers, as demonstrated by formation of the 3×3 surface reconstruction during ZnO growth and ex situ polarity determination. This method, in general, can be applied to growth of other polar films, such as II-VI oxides and III-V nitrides, on sapphire (0001) substrates.
Interface modification in Co∕Ge bilayer using swift heavy ions
Authors: Som T. , Satpati B. , Satyam P. V. , Kabiraj D. , Gupta Ajay , Mishra N. C.
Published: December 2004

We report on interface modification in Co∕Ge bilayer system using 100MeV Au7+ ion irradiation at different temperatures and fluences. Irradiation induced changes occurring across the Co∕Ge interface are studied by Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy. Although Au irradiation at low temperature does not show any interface mixing, formation of a thin (∼3–4nm) Co–Ge alloy layer has been observed after room temperature irradiation to a fluence of 1×1014ionscm−2. This mixing has been discussed on the basis of synergetic effects of nuclear and electronic energy loss processes in the bilayer system.
Constitutive model for polymethyl methacrylate at high pressure
Authors: Menikoff Ralph
Published: December 2004

A constitutive model of polymethyl methacrylate (PMMA) is developed for use in analyzing experiments with a velocity interferometer system for any reflector (VISAR) diagnostic that utilize PMMA as a window material. A thermodynamically consistent, fully three dimensional rate dependent elastic-plastic model is calibrated to data for (i) shock speed, (ii) release wave speed behind shock, (iii) shear stress behind shock, (iv) shear wave speed from static compression and (v) shock wave profiles. The model is intended for the regime of shock experiments; microsecond time scale and stress up to 10 GPa.
Control on the formation of Si nanodots fabricated by thermal annealing/oxidation of hydrogenated amorphous silicon
Authors: Hazra Sukti , Sakata Isao , Yamanaka Mitsuyuki , Suzuki Eiichi
Published: December 2004

We have fabricated silicon nanocrystals with different dimensions by the thermal annealing and thermal oxidation of ultrathin hydrogenated amorphous silicon (a-Si:H) films (2–10nm) deposited by thermal chemical vapor deposition. Dimensions of silicon nanodots are the function of thickness of the ultrathin a-Si:H film. Therefore, we can change the dimensions of silicon nanodots (3–10nm) by varying the a-Si:H film thickness according to our requirements. From our experimental studies, we have drawn a calibration curve of required a-Si:H film thickness against the average dimension of fabricated crystalline grains.
Nanohole-array size dependence of soft x-ray generation enhancement from femtosecond-laser-produced plasma
Authors: Nishikawa Tadashi , Nakano Hidetoshi , Oguri Katsuya , Uesugi Naoshi , Nishio Kazuyuki , Masuda Hideki
Published: December 2004

Nanostructured targets are very attractive for enhancing the intensity of x-ray pulses generated from laser-produced-plasma. In order to clarify the enhancement mechanism, the nanohole-array size dependence of the characteristics of soft x-ray pulse generation from femtosecond-laser-produced plasma was investigated in detail. We found that the highest x-ray intensity can be obtained and the x-ray pulse duration kept relatively short with a nanohole-array alumina target with a 500 nm hole interval and a 450 nm hole diameter. A 40-fold soft x-ray fluence enhancement and a nine-fold soft x-ray pulse peak intensity enhancement can be obtained. The relatively short x-ray pulse duration of 19 ps can be maintained because the target structure has high local density and nanometer-sized spaces. Similar enhancement effects can be expected by using a nanostructured target with wall thickness of less than 100 nm, space size of around a few 100 nm, and nanostructure depth larger than 20 μm.
Nanoscale-SiC doping for enhancing Jc and Hc2 in superconducting MgB2
Authors: Dou S. X. , Braccini V. , Soltanian S. , Klie R. , Zhu Y. , Li S. , Wang X. L. , Larbalestier D.
Published: December 2004

The effect of nanoscale-SiC doping of MgB2 was investigated in comparison with undoped, clean-limit, and Mg-vapor-exposed samples using transport and magnetic measurements. It was found that there are two distinguishable but related mechanisms that control the critical current-density-field Jc(H) behavior: increase of upper critical field Hc2 and improvement of flux pinning. There is a clear correlation between the critical temperature Tc, the resistivity ρ, the residual resistivity ratio RRR=R(300K)∕R(40K), the irreversibility field H*, and the alloying state in the samples. The Hc2 is about the same within the measured field range for both the Mg-vapor-treated and the SiC-doped samples. However, the Jc(H) for the latter is higher than the former in a high-field regime by an order of magnitude. Mg vapor treatment induced intrinsic scattering and contributed to an increase in Hc2. SiC doping, on the other hand, introduced many nanoscale precipitates and disorder at B and Mg sites, provoking an increase of ρ(40K) from 1μΩcm (RRR=15) for the clean-limit sample to 300μΩcm (RRR=1.75) for the SiC-doped sample, leading to significant enhancement of both Hc2 and H* with only a minor effect on Tc. Electron energy-loss spectroscope and transmission electron microscope analysis revealed impurity phases: Mg2Si, MgO, MgB4, BOx, SixByOz, and BC at a scale below 10nm and an extensive domain structure of 2–4-nm domains in the doped sample, which serve as strong pinning centers.
Exchange bias in NiFe∕FeMn∕NiFe trilayers
Authors: Sankaranarayanan V. K. , Yoon S. M. , Kim D. Y. , Kim C. O. , Kim C. G.
Published: December 2004

Ni Fe ∕ Fe Mn ∕ Ni Fe trilayer structure forms an integral part of many conventional and tunneling magnetoresistance spin valve structures with FeMn antiferromagnetic layer. A systematic investigation of the exchange bias variations of the seed and top pinned NiFe layers in the NiFe∕FeMn∕NiFe trilayer structure is reported as a function of thickness of all the three constituting layers, in multilayers prepared by rf magnetron sputtering. X-ray diffraction patterns show the (111) texture for the NiFe and FeMn layers, necessary for the development of antiferromagnetic γ-fcc phase. In thickness variation studies of all the three magnetic layers, seed NiFe layer shows greater bias (150Oe) than the top pinned NiFe layer (80Oe only). The exchange bias shows the expected 1∕t behavior for increasing NiFe layer thickness after initial maxima at low thickness. In the FeMn antiferromagnet layer thickness variation on the other hand, the large bias values attained around 5nm thickness is nearly retained up to a thickness of 25nm and the bias for the top NiFe layer is again substantially lower. The greater bias observed for the seed NiFe layer in all the three thickness variation studies is attributed to its growth over a saturated (111) oriented NiFe seed layer, which induces formation of interfacial FeMn layers with a net parallel spin ordering, in presence of the constant applied field. On the other hand, at the top FeMn∕NiFe surface, the rigid FeMn surface with compensated bulk spin ordering formed already, is not easily biased and reoriented along the top NiFe layer, to develop as much parallel net spins in the antiferromagnetic material, and hence lower bias.
Evaluation of the small-cone variable axis method in the holographic analysis of Kikuchi electron-diffraction data
Authors: Glander G. S.
Published: December 2004

Holographic analysis is a method for directly inverting electron-diffraction data to produce a real-space image of the surface structure. A refinement called the small-cone variable axis method attempts to minimize artifacts and distortions in the image by limiting the data contributing to the inversion to ensure that the atomic scattering factors for the atoms being imaged are relatively uniform. Kikuchi electron-diffraction data from the Si(111)(3×3)R30°−Al surface structure were holographically analyzed with and without the small-cone variable axis method. Although the refinement produced a slight reduction in the background noise and improved the shapes of some atomic images, it had the adverse effect of reducing the intensities of the images of many atoms, with some of the weaker images disappearing entirely. When holographically analyzing Kikuchi electron-diffraction data, the small-cone variable axis method should be used with caution and the resulting images should be compared with images produced without the method to ensure that useful structural information is not being discarded.
Electromigration-induced void grain-boundary interactions: The mean time to failure for copper interconnects with bamboo and near-bamboo structures
Authors: Ogurtani Tarik Omer , Oren Ersin Emre
Published: December 2004

A well-posed moving boundary-value problem, describing the dynamics of curved interfaces and surfaces associated with voids and/or cracks that are interacting with grain boundaries, is obtained. Extensive computer simulations are performed for void configuration evolution during intergranular motion, under the actions of capillary and electromigration forces in thin-film metallic interconnects with bamboo structures. The analysis of experimental data, utilizing the mean time to failure formulas derived in this paper, gives consistent values for the interface diffusion coefficients and enthalpies of voids. 5.85×10−5exp(−0.95eV∕kT)m2s−1 is the value obtained for voids that form in the interior of the copper interconnects avoiding any surface contamination. 1.80×10−4exp(−1.20eV∕kT)m2s−1 is obtained for those voids that nucleate either at triple junctions or at the grain-boundary technical surface intersections (grain-boundary groove), where the chemical impurities such as Si, O, S, and even C are segregated during the metallization and annealing processes and may act as trap centers for hopping vacancies.
Synthesis method for amorphous metallic foam
Authors: Schroers Jan , Veazey Chris , Demetriou Marios D. , Johnson William L.
Published: December 2004

A synthesis method for the production of amorphous metallic foam is introduced. This method utilizes the thermodynamic stability and thermoplastic formability of the supercooled liquid state to produce low-density amorphous metallic foams in dimensions that are not limited to the critical casting thickness. The method consists of three stages: the prefoaming stage, in which a large number of small bubbles are created in the equilibrium liquid under pressure; the quenching stage, in which the liquid prefoam is quenched to its amorphous state; the foam expansion stage, in which the amorphous prefoam is reheated to the supercooled liquid region and is processed under pressures substantially lower than those applied in the prefoaming step. Results from a dynamic model suggest that the foam expansion process is feasible, as the kinetics of bubble expansion in the supercooled liquid region are faster than the kinetics of crystallization. Within the proposed synthesis method, bulk amorphous foam products characterized by bubble volume fractions of as high as 85% are successfully produced.
Photoluminescence of ZnSexTe1−x∕ZnTe multiple-quantum-well structures grown by molecular-beam epitaxy
Authors: Shih Y. T. , Tsai Y. L. , Yuan C. T. , Chen C. Y. , Yang C. S. , Chou W. C.
Published: December 2004

This work investigates photoluminescence (PL) spectra from ZnSexTe1−x∕ZnTe multiple-quantum-well structures grown on GaAs(001) substrates by molecular-beam epitaxy. The PL data reveal that the band alignment of the ZnSexTe1−x∕ZnTe system is type II. The thermal activation energy for quenching the PL intensity was determined from the temperature-dependent PL spectra. The activation energy was found to increase initially and then decrease as the thickness of the ZnSexTe1−x layers decreases from 7to3nm. The temperature-dependent broadening of the PL linewidth was also investigated. The LO-phonon scattering was found to be the dominant broadening mechanism.
Ambient air effects on electrical characteristics of GaP nanowire transistors
Authors: Kang Donghun , Ko Ju-Hue , Bae Eunju , Hyun Jaewoong , Park Wanjun , Kim Byoung-Kye , Kim Ju-Jin , Lee Cheoljin
Published: December 2004

Gallium phosphide (GaP) nanowire transistors were fabricated in back-gated structure, and their electrical characteristics were measured systematically in both air and vacuum. The transistors turn on typically between −5 and −7V in ambient air. However, a large threshold voltage (Vth) shift, ∼10V, toward negative gate bias was observed in vacuum. After the transistors were exposed to air for 48h, Vth returned to the similar value in ambient air, implying a reversible process. The rate of Vth shift slows down when they were exposed to N2 in comparison with that of air. The shift of Vth is believed to be related to the charge transfer from the surface of GaP nanowire to the physically adsorbed OH or oxygen. In addition, the observed Vth shift from the GaP nanowire transistors can be explained by the conventional n-channel depletion mode metal-oxide-semiconductor field-effect transistor.
Interface intermixing and in-plane grain size in aluminum transition-metal bilayers
Authors: Buchanan J. D. R. , Hase T. P. A. , Tanner B. K. , Powell C. J. , Egelhoff W. F.
Published: December 2004

The correlation between grain size and intermixing in sputter-deposited bilayers of the form X∕Al and Al∕X (where X=Ta, W, Ir, and Os) has been investigated by in-plane grazing-incidence x-ray diffraction. We have found no correlation between grain size and intermixing at the interface and our data provide strong evidence against the postulate that the asymmetry in intermixing arises from the Harrison type-C mechanism of fast diffusion along grain boundaries or dislocations.
Electronic properties and superconductivity of low-dimensional carbon structures
Authors: Kulbachinskiı̆ V. A.
Published: December 2004

A review of research on the electronic properties of low-dimensional structures based on various modifications of carbon is presented. The following effects are discussed: the Shubnikov–de Haas effect in graphite intercalation compounds (GICs) of the acceptor type, superconductivity of GICs of the donor type, weak localization and superconductivity of carbon fibers, the negative magnetoresistance of a carbon foil obtained by pressing of exfoliated graphite, and the superconductivity and spectroscopy of new heterofullerides.
Neutral and charged excitons in a CdTe-based quantum well
Authors: Gaj J. A. , Płochocka P. , Radzewicz C. , Kossacki P. , Maślana W. , Cibert J. , Tatarenko S.
Published: December 2004

We present a summary of our spectroscopic studies of the oscillator strength of transitions related to the formation of neutral and positively charged excitons in modulation p-doped CdTe-based quantum wells. The hole concentration was controlled in the range from 1010 to 1011 cm−2. Continuous-wave and time-resolved femtosecond pump–probe absorption measurements were performed. They allowed us to study the interacting system of excitons, trions, and free holes. Characteristic times of the system were determined, such as the trion formation time. A new explanation of so-called oscillator-strength “stealing” has been proposed, in terms of spin-dependent screening. Experimental evidence is presented for optical creation of transient spin polarization in the quantum well.
Statistical strained-tetrahedron model of local ternary zinc blende crystal structures
Authors: Robouch B. V. , Sheregii E. M. , Kisiel A.
Published: December 2004

The statistical strained-tetrahedron model was developed to overcome two common assumptions of previous models: 1) a rigid undistorted ion sublattice of regular tetrahedra throughout all five configurations, and 2) a random ion distribution. These simplifying assumptions restrict the range of applicability of the models to a narrow subset of ternary alloys for which the constituent binaries have equal or quasi-equal values of their lattice constants and standard molar enthalpies of formation (ΔfH0). Beyond these limits the predictions of such models become unreliable, in particular, when the ternary exhibits site occupation preferences. The strained-tetrahedron model, free from rigidity and stochastic limitations, was developed to better describe and understand the local structure of ternary zinc blende crystals, and interpret experimental EXAFS and far-IR spectra. It considers five tetrahedron configurations with the shape and size distortions characteristic of ternary zinc blende alloys, allows nonrandom distributions and, hence, site occupation preferences, conserves coordination numbers, respects stoichiometry, and assumes that next-neighbor values determine preferences beyond next-neighbor. The configuration probabilities have three degrees of freedom. The nineteen inter-ion crystal distances are constrained by tetrahedron structures; to avoid destructive stresses, we assume that the average tetrahedron volumes of both sublattices relax to equal values. The number of distance free-parameters ⩽7. Model estimates, compared to published EXAFS results, validate the model. Knowing the configuration probabilities, one writes the dielectric function for far-infrared absorption or reflection spectra. Constraining assumptions restrict the number of degrees of freedom. Deconvolution of the experimental spectra yields values of the site occupation preference coefficient and/or the specific oscillator strengths. Validation again confirms the model.
Domain shifts in the aquatic vegetation of shallow urban lakes: the relative roles of low light and anoxia in the catastrophic loss of the submerged angiosperm Vallisneria americana
Authors: Morris Kay , Harrison Katherine A. , Bailey Paul C. E. , Boon Paul I.
Published: December 2004

The catastrophic loss of Vallisneria americana from a shallow urban lake in south-eastern Australia following nutrient enrichment has been reported previously. Two experiments are reported here to determine whether light attenuation or shifts in dissolved oxygen were more important in mediating this loss of submerged plants. The first experiment tested the response of dense beds of Vallisneria to different levels of shade in the field. The second tested the effect of (i) shading and (ii) anoxia on the performance of Vallisneria grown in the glasshouse. In the field, plants persisted after 3 months beneath 100% shade cloth, although with significantly reduced biomass (63%). In contrast, plant biomass beneath 70% shade cloth was reduced by only 9%. The field trials indicate that Vallisneria is highly tolerant to severe light attenuation. In the glasshouse, microcosms that were not artificially aerated become anoxic, and all plants died within 24 days in two of the three replicate microcosms. In shaded microcosms that were artificially aerated, plant biomass was reduced by 48% but no plants died. Severe reductions in dissolved oxygen associated with shading were primarily responsible for the rapid loss of Vallisneria, rather than light attenuation alone was concluded from the current study.
Effects of patchy shade on stream water temperature: how quickly do small streams heat and cool?
Authors: Rutherford J. Christopher , Marsh Nicholas A. , Davies Peter M. , Bunn Stuart E.
Published: December 2004

Summer field observations in five 2nd order streams (width 1–2 m, depth 5–15 cm, velocity 5–10 cm s–1) in Western Australia and south-east Queensland showed that daily maximum temperatures changed by ±4°C over distances of 600–960 m (travel time 2–3 h) immediately downstream from 40–70% step changes in riparian shade. There was a strong linear relationship between the rate of change of daily maximum temperature and the change of shade such that downstream from a 100% change of shade the heating/cooling rates are ±4°C h–1 and ±10°C km–1 (upper bound ±6°C h–1 and ±15°C km–1) respectively. These high rates only apply over short distances and travel times because downstream water temperatures adjust to the new level of shade and reach a dynamic equilibrium. Shade was too patchy in the study streams to measure how long water takes to reach equilibrium, however, using an existing computer model, we estimate that this occurs after ~1200 m (travel time 4 h). Further modelling work is desirable to predict equilibrium temperatures under given meteorological, flow and shade conditions. Nevertheless, landowners and regulators can use this information to determine whether the presence/absence of certain lengths of bankside shade are likely to cause desirable/undesirable temperature decreases/increases.
Species composition and molecular phylogeny of the Indo-Pacific teatfish (Echinodermata:Holothuroidea) bêche-de-mer fishery
Authors: Uthicke Sven , O'Hara Tim D. , Byrne Maria
Published: December 2004

Using mtDNA sequences we found that the Indo-Pacific teatfish fishery comprises at least three species, clarifying confusion on the taxonomic status of these commercially important holothurians. Traditional taxonomic characters, including the morphology of skeletal structures, could not be used to differentiate the species. Sequences of the COI gene (529 bp) distinguished three haplotype clusters, corresponding to distinct colour forms and, to some extent, previously described species. The white teatfish, Holothuria fuscogilva, comprises a range of colour morphs and has a wide distribution over the tropical Indo-Pacific region. The large sequence divergence indicates potential for the presence of several cryptic species in the white teatfish complex. In contrast to current taxonomy, we identified two species of black teatfish that appear to be allopatric: H. whitmaei is entirely black and has a Pacific distribution; whereas H. nobilis has white ventro-lateral dots and only occurs in the Indian Ocean. There is evidence for allopatric speciation between the black teatfish species, possibly driven by separation of the oceans and altered current patterns during the Pliocene, resulting in relatively young species with low intraspecific sequence divergence. These results provide insight into speciation in these tropical holothurians and are crucial for their conservation management.
Vi polysaccharide ofSalmonella typhitargets the prohibitin family of molecules in intestinal epithelial cells and suppresses early inflammatory responses
Authors: Sharma Amita , Qadri Ayub
Published: December 2004

Vi capsular polysaccharide (Vi) was first identified as a virulence antigen ofSalmonella typhi, the causative agent of typhoid fever in humans; it rendersS. typhiresistant to phagocytosis and the action of serum complement. However, the role of Vi during the infection of intestinal epithelium withS. typhiis not completely understood. We show here that Vi can interact with a model human intestinal epithelial cell line, Caco-2, through a cell-surface-associated molecular complex containing two major proteins of 30 and 35 kDa and a minor protein of ≈68 kDa. The two major proteins were identified as the putative tumor suppressor molecule, prohibitin, and its closely related homolog, B cell receptor-associated protein 37. These two proteins were enriched in lipid rafts, and Vi readily associated with these membrane microdomains. Engagement of Caco-2 cells with Vi inhibited their ability to produce an inflammatory response upon infection with Vi–S. typhi. Consistent with this effect, infection of Caco-2 cells with Vi+S. typhiproduced less IL-8 compared with Vi–S. typhi. Cells treated with Vi showed reduced extracellular signal-regulated kinase phosphorylation in response to infection with Vi–S. typhior stimulation with phorbol 12-myristate 13-acetate, suggesting that the mitogen-activated protein kinase pathway might be a target for Vi-mediated inhibition of inflammatory responses. These findings reveal a crucial role for Vi in the modulation of early inflammatory responses during infection withS. typhi. This kind of a modulation could play a significant role in the establishment of infection byS. typhi.