bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and prototype of parallel, wire‐actuated robots with a constraining linkage
Authors: Mroz Geoff , Notash Leila
Published: November 2004

Currently, wire‐actuated robots are not used extensively in industry, but they are gaining more attention due to advantages they possess. Low weight, cost, and power consumption are features that make wire‐controlled robots worth researching. This article investigates the designs of two different, 4 degrees of freedom parallel, wire‐actuated robots so that a prototype of one of these can be built. A design methodology is developed and presented. The process will be beneficial to those working on designing and prototyping a new robot or modifying an existing robot. Stability of both designs is considered first to ensure that the robots are able to exert and withstand end effector forces in different positions throughout their respective workspaces. The stiffness and strength of the materials used in the designs is also investigated using finite element analysis. © 2004 Wiley Periodicals, Inc.
Non‐parametric estimation of the odds ratios for continuous exposures using generalized additive models with an unknown link function
Authors: Cadarso‐Suárez Carmen , Roca‐Pardiñas Javier , Figueiras Adolfo , González‐Manteiga Wenceslao
Published: November 2004

The generalized additive, model (GAM) is a powerful and widely used tool that allows researchers to fit, non‐parametrically, the effect of continuous predictors on a transformation of the mean response variable. Such a transformation is given by a so‐called link function, and in GAMs this link function is assumed to be known. Nevertheless, if an incorrect choice is made for the link, the resulting GAM is misspecified and the results obtained may be misleading. In this paper, we propose a modified version of the local scoring algorithm that allows for the non‐parametric estimation of the link function, by using local linear kernel smoothers. To better understand the effect that each covariate produces on the outcome, results are expressed in terms of the non‐parametric odds ratio (OR) curves. Bootstrap techniques were used to correct the bias in the OR estimation and to construct pointwise confidence intervals. A simulation study was carried out to assess the behaviour of the resulting estimates. The proposed methodology was illustrated using data from the AIDS Register of Galicia (NW Spain), with a view to assessing the effect of the CD4 lymphocyte count on the probability of being AIDS‐diagnosed via Tuberculosis (TB). This application shows how the link's flexibility makes it possible to obtain OR curve estimates that are less sensitive to the presence of outliers and unusual values that are often present in the extremes of the covariate distributions. Copyright © 2004 John Wiley & Sons, Ltd.
What to do with a Corpse?: Physical Reality and the Fictional World in the Shakespearean Theatre
Authors: ICHIKAWA MARIKO
Published: November 2004

In the Shakespearean theatre, the removal of dead bodies from the stage was a theatrical necessity, owing to the absence of a curtain between the stage and the auditorium. Despite the many non-realistic conventions accepted in the theatre, the disposal of corpses had to be carried out in such a way as not to disrupt the reality of the fictional world. An analysis of certain kinds of intriguing situations, such as suicide scenes, reveals how efficiently Shakespeare and his contemporaries utilized the stage hangings, the upper gallery, and the stage trap so as to avoid the necessity of bringing on bearers for the corpses at the ends of the scenes. Only at the end of the play, when the logic of the fictional world stops functioning, could the spectacle of a corpse getting up and leaving the stage have been accepted by the audience.
Dances About Spain: Censorship at the Federal Theatre Project
Authors: COOPER ELIZABETH
Published: November 2004

In 1939 the Chicago and New York City dance units of the Works Progress Administration's Federal Theatre Project premiered two works inspired by the events of the Spanish Civil War. This paper offers an examination of the conflicts that arose in presenting dances about a war in which the US government adopted a position of neutrality, but about which many artists took a profoundly partisan stance. Further, this research unveils how internal censorship at the Federal Theatre Project affected the creation and presentation of these dances as well as ways in which the choreographers (Ruth Page/Bentley Stone and Helen Tamiris) subverted requests for alterations to their scenarios and choreography.
The Entertaining Mr. Orton: How Joe Orton's Plays Can Outgrow the ‘Swinging Sixties’
Authors: STREIT LINDA
Published: November 2004

This re-examination of the plays of 1960s farceur Joe Orton reveals that his plays can survive the passage of time as well as cultural displacement. Orton's skill lies in using the medium of the theatre to create a liminal situation, whereby all the signs and subtexts can crystallize into accessible images, which are explored here from a semiotic perspective. Orton's scrupulous understanding of genre and plot construction enables him to pay lip-service to a specific genre, as he simultaneously mocks modern realistic theatre conventions; the one-room settings are examined for their metonymic function, and the props and costume are considered from the semiotic perspective of vectorization. This fresh approach to Joe Orton elucidates how the plays have their own intrinsic dramatic merit, independent of their original 1960s context: Orton plays games with his audiences, and game-playing is a universal pastime.
Can We Live as One Family? Rethinking the Two Koreas' Kinship in John Hoon's Kang Tek-koo
Authors: KIM SUK-YOUNG
Published: November 2004

John Hoon's play, Kang Tek-koo, tells the story of the unexpected encounter between two half-brothers, one South Korean and the other North Korean, in Russia after the collapse of the Soviet Union. In the play, the conventional tragic scene of the reunion of the family members separated by the Korean War is dealt with in a resilient comic spirit from the perspective of a younger generation of South Koreans. This article examines the production of Kang Tek-koo by the South Korean company Apple Theatre, which took place in 2001 – a time when the fluid dynamics of globalization were encompassing Korea, and the transnational flow of media, people, and ideology opened up the possibility for North and South Koreans to interact and search for a common language, culture, home and nationhood.
Investigating the Lake Bosumtwi impact structure: Insight from numerical modeling
Authors: Artemieva Natalia , Karp Tobias , Milkereit Bernd
Published: November 2004

The current topography of the Lake Bosumtwi crater and some of its structural dimensions have been determined by geophysical methods. We combine these data with sophisticated numerical models to evaluate the cratering process itself (for example, melt and tektite generation) as well as to test the modeling code. The geophysical maps show some asymmetry in plan view, with the main anomaly north of the crater center. The simulations of the early stage show asymmetric patterns only in ejecta and tektite distributions, while the late stage is modeled for the vertical impact without any asymmetry. We estimate the projectile size from scaling laws and then, varying material properties, reproduce a crater, which is similar to the Bosumtwi, but too deep. Bulking allows us to reconcile differences between the model results and the observed topography. Shock melt estimates are in good agreement with the Bosumtwi magnetic signature. Modeled distribution of tektites assumes an impact angle of 30°–45° and an impact direction from the N‐NE. The combination of numerical models and field evidence not only provides necessary information for upcoming scientific drilling of the structure but also suggests interesting and well‐suited drill sites. Besides the central uplift and the annular moat with a suggested thick breccia cover, drilling at the location of the geophysical anomalies and comparison of downrange and transversal locations will provide new insight into preimpact and impact‐induced asymmetries.
Icelandic analogs to Martian flood lavas
Authors: Keszthelyi Laszlo , Thordarson Thorvaldur , McEwen Alfred , Haack Henning , Guilbaud Marie‐Noelle , Self Stephen , Rossi Matti J.
Published: November 2004

We report on new field observations from Icelandic lava flows that have the same surface morphology as many Martian flood lava flows. The Martian flood lavas are characterized by a platy‐ridged surface morphology whose formation is not well understood. The examples on Mars include some of the most pristine lava on the planet and flows >1500 km long. The surfaces of the flows are characterized by (1) ridges tens of meters tall and wide and hundreds of meters long, (2) plates hundreds of meters to kilometers across that are bounded by ridges, (3) smooth surfaces broken into polygons several meters across and bowed up slightly in the center, (4) parallel grooves 1–10 km long cut into the flow surface by flow past obstacles, and (5) inflated pahoehoe margins. The Icelandic examples we examined (the 1783–1784 Laki Flow Field, the Búrfells Lava Flow Field by Lake Myvatn, and a lava flow from Krafla Volcano) have all these surface characteristics. When examined in detail, we find that the surfaces of the Icelandic examples are composed primarily of disrupted pahoehoe. In some cases the breccia consists of simple slabs of pahoehoe lava; in other cases it is a thick layer dominated by contorted fragments of pahoehoe lobes. Our field observations lead us to conclude that these breccias are formed by the disruption of an initial pahoehoe surface by a large flux of liquid lava within the flow. In the case of Laki, the lava flux was provided by surges in the erupted effusion rate. At Búrfells it appears that the rapid flow came from the sudden breaching of the margins of a large ponded lava flow. Using the observations from Iceland, we have improved our earlier thermal modeling of the Martian flood lavas. We now conclude that these platy‐ridged lava flows may have been quite thermally efficient, allowing the flow to extend for >100 km under a disrupted crust that was carried on top of the flow.
The heat flux and the temperature gradient in the lower atmosphere
Authors: Higgins Chad W. , Parlange Marc B. , Meneveau Charles
Published: November 2004

Most parameterizations used in Large Eddy Simulations of the atmospheric boundary layer are based on the assumption that subgrid‐scale fluxes are aligned against spatial gradients of transported quantities (down‐gradient closures). Based on field experiments, we determine the distribution and most probable relative orientations of the subgrid‐scale (SGS) heat flux relative to parameterizations based on the temperature gradient. We show that, under neutral and unstable atmospheric stability, the SGS heat flux most likely lies within the geometric span of the so called mixed tensor eddy diffusivity model.
Miocene changes in bottom current regime recorded in continental rise sediments on the Pacific margin of the Antarctic Peninsula
Authors: Hernández‐Molina F. J. , Larter R. D. , Rebesco M. , Maldonado A.
Published: November 2004

A Fossil Mounded Sedimentary Body (MB) has been identified in the Miocene sedimentary record on the central continental rise west of Adelaide Island, Antarctic Peninsula, using multichannel seismic reflection profiles. The MB has an elongated NE trend away from a group of seamounts, and it developed between two troughs. We interpret it as a patch drift plastered against the NE (lee) side of an obstacle. The MB's depositional patterns provide the first clear evidence of Early Miocene bottom current activity on the central rise, and they suggest that flow was towards the NE, probably as part of the Antarctic Circumpolar Current. This segment of the rise is, however, presently affected by a SW‐flowing branch of Lower Circumpolar Deep Water. The change in bottom water flow took place during the Middle or Late Miocene, and we suggest that it is probably indicative of more widespread palaeoceanographic changes during this period.
Parameters of solar wind electron heat‐flux pitch‐angle distributions and IMF topologies
Authors: Feuerstein W. M. , Larson D. E. , Luhmann J. G. , Lin R. P. , Kahler S. W. , Crooker N. U.
Published: November 2004

Pitch‐angle distributions (PADs) of solar wind heat‐flux (HF) electrons are used as a proxy for interplanetary magnetic field (IMF) topology. Unidirectional PADs yield IMF solar polarities, and bidirectional electron (BDE) PADs are interpreted as signatures of closed fields. A general perception exists that the directionalities are easily distinguished, clearly defining open and closed IMFs. We quantify PADs with the ratios of the HF parallel and anti‐parallel to the IMF to that perpendicular to the IMF plotting these parameters against each other in a directionality distribution for six years of electron data from the 3DP experiment on the Wind satellite. This bimodal plot clearly shows the unidirectional populations, but shows no evidence for a separate bidirectional HF population. A similar plot of magnetic clouds is double‐banded with no evidence of a bifurcation between bidirectional and unidirectional regimes. In conclusion, this basic parameterization shows no distinction between open and closed field topologies.
Atmospheric evolution of organic aerosol
Authors: Molina M. J. , Ivanov A. V. , Trakhtenberg S. , Molina L. T.
Published: November 2004

We report here results of an experimental study of the OH‐initiated oxidation of solid organics in the presence of O2, NOx and H2O, using two kinds of self‐assembled organic monolayers (alkane and aromatic), paraffin and pyrene films as proxies for organic aerosol. We show that the OH‐initiated oxidation of the alkane surfaces leads to rapid volatilization. The gas‐phase products detected include HO2, H2O2, CO, CO2, HCO, CH2O, CH3CHO, CH3OH, and HCOOH. We conclude that volatilization is at least as efficient as wet deposition as a removal process for aliphatic particulates, whereas aromatic particulates show higher stability towards volatilization.
Decadal oscillation of spring rain in northern Taiwan
Authors: Hung Chih‐wen , Hsu Huang‐Hsiung , Lu Mong‐Ming
Published: November 2004

This study found that the spring (February–April) rainfall in northern Taiwan has fluctuated concurrently with the Pacific Decadal Oscillation (PDO) since the early 20th century. It is proposed that this fluctuation in spring rain is induced by the tropical sea surface temperature (SST) anomaly embedded in the PDO, which has been known to oscillate in opposite phase to the SST in the extra‐tropical North Pacific. When the PDO index is positive (negative), the SST over the tropical Central‐Eastern Pacific is warmer (colder) than normal, and a low‐level anti‐cyclonic (cyclonic) anomalous flow is induced over the Philippine Sea. This anomalous anti‐cyclonic (cyclonic) flow results in southwesterly (northeasterly) anomalous winds to the east of Taiwan and enhances (reduces) the trough extending southwestward from southern Japan to northern Taiwan. As a consequence, more (less) spring rain occurs in northern Taiwan during the positive (negative) PDO phases.
Magnetic turbulence in the plasma sheet
Authors: Vörös Z. , Baumjohann W. , Nakamura R. , Volwerk M. , Runov A. , Zhang T. L. , Eichelberger H. U. , Treumann R. , Georgescu E. , Balogh A. , Klecker B. , Réme H.
Published: November 2004

Small‐scale magnetic turbulence observed by the Cluster spacecraft in the plasma sheet is investigated by means of a wavelet estimator suitable for detecting distinct scaling characteristics even in noisy measurements. The spectral estimators used for this purpose are affected by a frequency‐dependent bias. The variances of the wavelet coefficients, however, match the power‐law shaped spectra, which makes the wavelet estimator essentially unbiased. These scaling characteristics of the magnetic field data appear to be essentially nonsteady and intermittent. The scaling properties of bursty bulk flow (BBF) and non‐BBF associated magnetic fluctuations are analyzed with the aim of understanding processes of energy transfer between scales. Small‐scale (∼0.08–0.3 s) magnetic fluctuations having the same scaling index α ∼ 2.6 as the large‐scale (∼0.7–5 s) magnetic fluctuations occur during BBF‐associated periods. During non‐BBF associated periods the energy transfer to small scales is absent, and the large‐scale scaling index α ∼ 1.7 is closer to Kraichnan or Iroshnikov‐Kraichnan scalings. The anisotropy characteristics of magnetic fluctuations show both scale‐dependent and scale‐independent behavior. The former can be partly explained in terms of the Goldreich‐Sridhar model of MHD turbulence, which leads to the picture of Alfvénic turbulence parallel and of eddy turbulence perpendicular to the mean magnetic field direction. Nonetheless, other physical mechanisms, such as transverse magnetic structures, velocity shears, or boundary effects can contribute to the anisotropy characteristics of plasma sheet turbulence. The scale‐independent features are related to anisotropy characteristics which occur during a period of magnetic reconnection and fast tailward flow.
Generation of cold O+ beams observed in the tail lobe by weak fast shocks in the polar magnetosphere
Authors: Lin C. C. , Wu B. H. , Lee L. C. , Chao J. K.
Published: November 2004

Observations of cold O+ beams (COBs) in the lobe/mantle region of Earth's magnetotail showed that O+ ions originating from the ionosphere can stream into the distant tail (40–200 RE). These O+ ions have a high parallel streaming energy (∼1–20 keV) and low perpendicular thermal energy (∼70–210 eV) in the distant tail. In this paper, we propose that the nonadiabatic shock heating of O+ ions in the polar magnetosphere and the subsequent adiabatic evolution of ion velocity can lead to the occurrence of COBs in the tail lobe. The heating and acceleration of heavy O+ ions by fast shocks are studied by a theoretical analysis and hybrid simulations. It is found that after the passing of fast shock, heavy ions gain a gyration speed Vg ≃ MAVAsin(θ2 − θ1)/cosθ1, where MA is the upstream Alfvén Mach number, VA is upstream Alfvén speed, and θ1 (θ2) is upstream (downstream) shock normal angle. After heating, the adiabatic evolution in the tail lobe can transfer a major part of perpendicular thermal energy T⊥ to the observed parallel streaming energy W∥. We have found that weak fast shocks in the polar magnetosphere with MA ≃ 1.05–1.2 can lead to the observed streaming energy associated with COBs. Weak fast shocks in the magnetosphere can be generated by the interaction of interplanetary shocks/discontinuities with Earth's magnetosphere. Escaping ionospheric O+ ions can gain enough energy from shock heating to account for observations of COBs in the tail lobe. For example, the ion heating by a shock with MA ∼ 1.11 at a radial distance of rs = 6.5 RE can lead to COBs with O+ streaming energy W∥ ∼ 5 keV and perpendicular thermal energy T⊥ ∼ 220 eV observed at x = 185 RE.
Midlatitude ionospheric plasma temperature climatology and empirical model based on Saint Santin incoherent scatter radar data from 1966 to 1987
Authors: Zhang Shun‐Rong , Holt John M. , Zalucha Angela M. , Amory‐Mazaudier Christine
Published: November 2004

Ionospheric plasma temperature variations have recently been studied based on incoherent scatter radar (ISR) observations at a lower midlatitude site, Shigaraki, in East Asia [Otsuka et al., 1998] and Millstone Hill, a typical subauroral midlatitude site in North America [Zhang and Holt, 2004]. The French Saint Santin ISR, with a geographic latitude slightly higher but an apex latitude 14° lower than Millstone, collected bistatic and quadristatic measurements for over two solar cycles beginning in September 1965. A database of these data, containing observations between 1966 and 1987, has been used in this study in order to establish the midlatitude ionospheric climatology, in particular that of the upper atmosphere thermal status, as well as empirical models for space weather applications. This paper presents, in comparison with the Millstone Hill results, variations of ion and electron temperatures (Ti and Te) with solar activity, season, time of the day, and altitude. The F2 region Te at St. Santin is found to be lower than at Millstone between March and July, when the St. Santin electron density Ne is relatively higher. The midday Te below 300 km increases with F10.7, as at Millstone Hill. Above 300 km it tends to decrease with F10.7 at St. Santin, while it increases in summer at Millstone Hill. Ti between 250 and 350 km peaks midway between spring and summer. We have also created St. Santin ionospheric models for Ne, Te, and Ti using a bin‐fit technique similar to that used for the Millstone Hill models. Comparisons with corresponding IRI predications indicate good agreement in Ti at high solar activity, and above the F2 peak, Te from the IRI tends to be higher than both the St. Santin and Millstone Hill models.
Statistics of solar microwave radio burst spectra with implications for operations of microwave radio systems
Authors: Nita Gelu M. , Gary Dale E. , Lanzerotti Louis J.
Published: November 2004

Analysis of 412 solar radio burst events in the microwave range [1.2–18] GHz that were measured at the New Jersey Institute of Technology Owens Valley Solar Array over 2 years (2001–2002) during the peak of the 23rd solar cycle is conducted in the context of the possible interference of such bursts with radio‐receiving and radar systems that operate at these frequencies. It is found that there is a small probability for solar interference for systems operating at a frequency ν > 2.6 GHz and with a typical noise floor, but the probability increases significantly at lower frequencies. The probability is greater for more sensitive systems operating with higher gain, but the likelihood of interference can be partially ameliorated by an increase in the operating frequency. Finally, our statistics indicate that it could be beneficial for radio and radar systems operating below 2.6 GHz to employ an adaptable mode wherein, if the prediction of solar activity suggested the possible occurrence of a large radio burst, system operators could switch operations to a less susceptible frequency band above 2.6 GHz.
Room temperature photo-oxidation of NH4F-prepared H–Si(111)(1×1) and Hx–Si(100)
Authors: Morse Kathleen A. , Pianetta Piero
Published: November 2004

This work discusses the room temperature photo-oxidation of hydrogen-passivated silicon surfaces. Specifically, photoemission spectroscopy is used to investigate how the factors present in cleanrooms, including ultraviolet (UV) light, oxygen (O2), and water (H2O), lead to the photo-oxidation of the hydrogen-passivated silicon surface. Results indicate that both the H–Si(111)(1×1) and Hx–Si(100) surfaces oxidize when exposed to UV light in the presence of O2 only, H2O only, or humid air (both O2 and H2O). We propose that UV light assists in the photo-oxidation of the hydrogen-terminated silicon surfaces by cleaving the H–Si surface bond. This process generates silicon surface radicals that can then be scavenged by either O2 to form peroxyl radicals (Si–O–O∙) or by H2O to form silanols (Si–OH). Results also show that photo-oxidation is most significant when the surface is exposed to both O2 and H2O in the presence of UV light. Results from the humid air photo-oxidation experiments indicate that after the H–Si surface bond is cleaved by UV light, H2O reacts with the generated silicon surface radical to form a silanol. This is followed by a subsequent step involving UV light and O2.
Epitaxial growth and characterization of stoichiometric LiNbO3 films prepared by the sol-gel method
Authors: Takahashi Makoto , Otowa Ryouhei , Mori Hidekazu , Sato Shoji , Nishiwaki Akira , Wakita Koichi , Ohnishi Naoyuki , Yagi Touru , Uchida Tetsuo
Published: November 2004

After stoichiometric LiNbO3 thick films were deposited on z-cut LiNbO3 substrates using the sol-gel method from a precursor solution containing various polyvinyl alcohol (PVA) concentrations, their characteristics were investigated. The film thickness increased linearly with the increase in PVA and precursor concentrations. The orientation relationships between films and substrates were determined by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and the results showed that (006) oriented LiNbO3 epitaxial layers with parallel epitaxial relationships could be grown on a z-cut LiNbO3 substrate. The refractive indexes of the films were n0=2.28±0.02 and ne=2.19±0.02 at a wavelength of 632.8nm, and their transmission loss was 0.50±0.04dB∕cm.
Influence of interface-related anisotropy on magnetic properties of Fe- and Co-based thin films and patterned structures
Authors: Kazakova O. , Hanson M. , Yu A. C. C.
Published: November 2004

In this work, the influence of interfaces and microstructure on the magnetic properties of Fe- and Co-based thin films and patterned submicron structures was investigated. For this purpose, we studied arrays of circular and elliptical elements with identical lateral dimension, down to 150nm, made from Fe∕Co multilayer and FeCo alloy films with the same chemical composition (75at.%Co) and thickness, t=20nm. The samples were investigated by magnetic force microscopy and alternating gradient force magnetometry techniques. We show that the average magnetic moment meff of the material depends strongly on the local environment of Fe and Co atoms. Whereas the FeCo alloy film yields meff=1.96μB in good agreement with the bulk value; a significant enhancement is observed in the Fe∕Co multilayer with meff=2.8±0.3μB. In arrays of patterned elements, both the local distribution of magnetic moments and the processes of magnetization reversal were found to depend on the presence of interfaces as well as the microstructure and magnetocrystalline anisotropy of the initial films. The experiments indicate a higher stability of the zero-field single domain (SD) elements of the alloy, whereas the patterns of the multilayers are characterized by the development of a simpler quasi-SD structure during magnetization reversal. We demonstrate that the Fe25Co75 elliptical elements may change their magnetization direction by the coherent rotation of moments, whereas this process should be excluded in the Fe2∕Co6 ellipses. The influence of all these parameters on the magnetic behavior and energy balance is discussed.
Effect of interstitial oxygen on the crystal structure and magnetic properties of Ni nanoparticles
Authors: Roy Aparna , Srinivas V. , Ram S. , De Toro J. A. , Riveiro J. M.
Published: November 2004

The structure and magnetic properties of fine Ni nanoparticles (∼65nm diameter) having a spontaneous surface oxide layer have been studied. The particles were prepared by the chemical reduction of nickel ions in an aqueous medium, with sodium borohydride as the reducing agent. X-ray diffraction (XRD), transmission electron microscopy, and magnetization measurements (M-H plots and field cooled∕zero field cooled curves) have been used for characterizing the samples. No detectable change is observed in the M-H curves or in the XRD patterns of the “as prepared” sample and the sample annealed in air at 573K. We have indexed both these patterns as Ni in a tetragonal crystal structure with lattice parameters a=0.4905nm, c=0.5330nm and a=0.4890nm, c=0.5310nm for the “as prepared” and 573K annealed sample, respectively. This is a new report about the formation of Ni in a modified crystal structure. The M-H curves of both the samples show a clear hysteretic behavior but do not saturate, thereby suggesting the existence of both ferromagnetic and paramagnetic components in the magnetization. Large coercivity values ≈123Oe as compared to 6Oe in bulk Ni have been obtained. The magnetization results have been analyzed in correlation with X-ray diffraction and microstructure and satisfactorily explained on the basis of a core-shell model, where we consider each particle as a magnetically heterogeneous system consisting of a ferromagnetic core of Ni and an antiferromagnetic∕paramagnetic shell of NiO.
Laser-induced generation of micrometer-sized luminescent patterns on rare-earth-doped amorphous films
Authors: Zanatta A. R. , Ribeiro C. T. M.
Published: November 2004

Room-temperature photoluminescence has been achieved from rare-earth-doped amorphous (a-) GeN films. The samples were prepared by the radio-frequency-sputtering method, and light emission from the rare-earth (RE) centers was obtained after irradiating the films with a highly focused laser beam. As a result of this laser annealing procedure, almost circular holes with approximately 1-μm diameter were produced on the surface of the a-GeN films. The area nearby these holes correspond to crystalline Ge and coincide with the regions, where relatively strong RE-related luminescence takes place. These laser-annealed areas can be easily and conveniently managed in order to generate different microscopic luminescent patterns. Depending on the RE ion employed, visible and near-infrared light emission were obtained from the patterns so produced. The development of these micrometer-sized luminescent centers, as well as their probable mechanisms of excitation-recombination, will be presented and discussed. The importance of the current experimental results to future technological applications such as microdevices, for example, will also be outlined.
High-resolution observation by double-biprism electron holography
Authors: Harada Ken , Tonomura Akira , Matsuda Tsuyoshi , Akashi Tetsuya , Togawa Yoshihiko
Published: November 2004

High-resolution electron holography has been achieved by using a double-biprism interferometer implemented on a 1MV field emission electron microscope. The interferometer was installed behind the first magnifying lens to narrow carrier fringes and thus enabled complete separation of sideband Fourier spectrum from center band in reconstruction process. Holograms of Au fine particles and single-crystalline thin films with the finest fringe spacing of 4.2pm were recorded and reconstructed. The overall holography system including the reconstruction process performed well for holograms in which carrier fringes had a spacing of around 10pm. High-resolution lattice images of the amplitude and phase were clearly reconstructed without mixing of the center band and sideband information. Additionally, entire holograms were recorded without Fresnel fringes normally generated by the filament electrode of the biprism, and the holograms were thus reconstructed without the artifacts caused by Fresnel fringes.
Nonlinear optical properties and surface-plasmon enhanced optical limiting in Ag–Cu nanoclusters co-doped in SiO2 Sol-Gel films
Authors: Kiran P. Prem , Shivakiran Bhaktha B. N. , Rao D. Narayana , De Goutam
Published: November 2004

The nonlinear optical properties and the role of the surface-plasmon resonance (SPR) on optical limiting (OL) properties of Ag–Cu nanoclusters co-doped in SiO2 matrix prepared using the sol-gel technique with a Cu∕Ag molar ratio of 1, 2 and 3, respectively, are presented. The studies were made using the second harmonic of high-power nanosecond and picosecond Nd:YAG lasers. These films show a self-defocusing nonlinearity with both nanosecond and picosecond pulses and a good nonlinear absorption behavior with the nanosecond pulse excitation. The nonlinear refractive index decreased with decreasing particle size, whereas the nonlinear absorption increased with an increase in Cu concentration. The observed nonlinear absorption is explained by taking into account the cumulative effect of both the intraband and interband mechanisms. The excitation near the SPR of Cu resulted in an enhanced OL behavior with increasing Cu concentration. No such concentration dependence is observed when the excitation is near the SPR of Ag, however, the limiting threshold is reduced approximately 10–17 times. Excitation at wavelengths far below the SPR of Ag and Cu has not shown any OL behavior. The major contribution toward OL is observed to be from the interband absorption and from a possible energy transfer within the higher unoccupied states of Cu and Ag. Although nonlinear scattering is observed at higher intensities, its contribution is found to be much less than that of the nonlinear absorption assisted by an energy transfer.
Micro-photoluminescence characterization of local electronic states in a (110) GaAs quantum well fabricated by cleaved-edge overgrowth
Authors: Oh Ji-Won , Yoshita Masahiro , Hayamizu Yuhei , Akiyama Hidefumi , Pfeiffer Loren N. , West Ken W.
Published: November 2004

Local electronic states due to characteristic surface islands and pits formed on an atomically flat (110) GaAs interface of a quantum well fabricated by a cleaved-edge-overgrowth method with high-temperature growth-interrupt annealing are characterized by micro-photoluminescence (PL) imaging and spectroscopy. With the overall observation of the 6-nm-thick (110) quantum well with the area of 6.8-μm width and 3-mm length, we found local PL signals due to isolated 2- or 3-monolayer (ML) islands, isolated 1-ML pits, and 1-ML islands and pits formed along the cleavage atomic-step lines, and gradual change of the states across the full range of the sample.
Chemical stresses in boundary layer diffusion
Authors: Lin Hung-Yi , Ko Sun-Chien , Lee Sanboh
Published: November 2004

Chemical stresses induced in the boundary layer of a B∕A∕B sandwiched slab during diffusion were analyzed. Both the cases of constant surface concentration source and instantaneous surface concentration source were considered. The diffusivity of diffusant is much greater in the central layer than the outer layers. The concentration of diffusant in the sandwiched slab was obtained using the Laplace-Fourier transformation technique. Assuming that the stresses developed in the outer layers were negligibly small during the boundary layer diffusion, the stresses developed in the central layer were determined based on the Moutier cycle theorem. Numerical results were performed to illustrate the effect of diffusivity ratio of diffusant in the central layer to that in the outer layers and of specimen size on stress variation.
Characterization of bulk microdefects in Ge single crystals
Authors: Poelman D. , De Gryse O. , De Roo N. , Janssens O. , Clauws P. , Bras W. , Dolbnya I. P. , Romandic I.
Published: November 2004

The work reported here concerns the characterization of bulk microdefects in germanium single-crystal wafers. From comparison with the case of silicon, it is expected that bulk microdefects are formed due to diffusion and interaction of self-interstitials and vacancies during Czochralski growth, solely dependent on the growth parameters. Unfortunately, several of the defect characterization methods, which can be used for silicon, fail in the case of germanium due to its lower band gap. Therefore, the possibilities of two alternative techniques, x-ray topography and small-angle x-ray scattering, respectively, were investigated. The results, combined with a characterization of the material surface using scanning laser reflectometry, indicate that in Ge, the same kind of intrinsic growth-related defects exist, as in Si.
Microstructure of epitaxial MnAs films on GaAs(001): An in situ x-ray study
Authors: Jenichen B. , Satapathy D. , Braun W. , Däweritz L. , Ploog K. H.
Published: November 2004

We present an analysis of thin MnAs films on GaAs(001) by the x-ray grazing incidence diffraction during molecular-beam epitaxy and immediately after deposition near the growth temperature. Separate MnAs peaks are detected for average thicknesses starting from ≈1 monolayer, indicating the formation of a relaxed MnAs lattice. The variation of the position and shape of the MnAs peaks during growth yields the time dependence of relaxation and island sizes. The MnAs domains of different orientations are detected and their amount is analyzed quantitatively. A line broadening due to the size and strain effects is observed. Both the effects are separated for each of the main directions along the interface. The lateral domain sizes of 10–40nm and strain values of 0.2%–0.6% are found in the MnAs films. We find that the positions of the misfit dislocations at the interface are correlated.
Third order nonlinearities in Ge-As-Se-based glasses for telecommunications applications
Authors: Gopinath Juliet T. , Soljačić Marin , Ippen Erich P. , Fuflyigin Vladimir N. , King Wesley A. , Shurgalin Max
Published: November 2004

We have studied the third order optical nonlinearities of Ge-As-Se-based glasses. The glasses have high melting and glass transition temperatures that offer the potential for integration with traditional compound oxide glasses into highly nonlinear, high-index-contrast fibers. We used z-scan and femtosecond pump-probe techniques to measure the nonlinear refractive index and two-photon absorption coefficient of the glasses at telecommunication wavelengths. Nonlinearities as high as ∼900× that of silica were measured at 1540nm in Ge35As15Se50 with a glass transition temperature of 380°C.
Optical and electronic characteristics of single walled carbon nanotubes and silicon nanoclusters by tetrahertz spectroscopy
Authors: Altan Hakan , Huang Feng , Federici John F. , Lan Aidong , Grebel Haim
Published: November 2004

We have conducted visible pump-THz (THz—terahertz) probe measurements on single wall carbon nanotubes deposited on quartz substrates. Our results suggest that the photoexcited nanotubes exhibit localized transport due to Lorentz-type photoinduced localized states from 0.2 to 0.7 THz. Upon modeling the THz transmission through the photoexcited layer with an effective dielectric constant given by Maxwell-Garnett theory we found that the data are best fit by a broad Lorentz state at 0.5 THz. These experiments were repeated for ion-implanted, 3–4 nm Si nanoclusters in quartz for which a similar behavior was observed.
Ultrabroadband single-mode long-period fiber gratings using high-order cladding modes
Authors: Dangui Vinayak , Digonnet Michel J. F. , Kino Gordon S.
Published: November 2004

We demonstrate analytically that long-period fiber gratings operating near the maximum of a cladding mode's phase-matching curve can be designed to exhibit far broader bandwidths (around 800nm) than reported to date, at any center wavelength and with any peak attenuation. In a given fiber, the center wavelength and attenuation are controlled independently by properly selecting the grating period and length, respectively, Extremely large bandwidths are obtained by increasing the grating index perturbation, by increasing the fiber core radius, and∕or optimizing the numerical aperture. Implemented with a mechanically induced grating, this concept produced a 1465nm filter with a record 10dB bandwidth of 360nm.
Transport properties of undoped and NH3-doped polycrystalline SnO2 with low background electron concentrations
Authors: Korotkov R. Y. , Farran A. J. E. , Culp T. , Russo D. , Roger C.
Published: November 2004

A series of polycrystalline 1 μm thick SnO2 films were deposited onto borosilicate glass substrates by atmospheric pressure chemical vapor deposition. Unintentionally doped as-grown SnO2 layers had electron concentrations and mobility of 2–4×1017cm−3 and 25–30cm2∕Vs, respectively. Potential barriers and trap concentrations were calculated to be 30 meV and 2.3×1012cm−2, respectively. Upon N2∕vacuum annealing at 670 K for 15–20 min, the potential barrier height decreased to 8 meV and the electron mobility increased to 58cm2∕Vs. When doped with ammonia, the mobility of as-grown samples decreased to 0.5cm2∕Vs. The magnitude of the potential barriers varied, with ammonia doping, from 175 to 31 meV with trap densities of 4.7–1.2×1012cm−3, respectively. Upon vacuum∕N2 annealing at 670 K for 20 min, the electron mobilities of ammonia doped films recovered to 50–71cm2∕Vs, whereas the height of the potential barriers decreased to 3–4 meV with trap concentrations of 8–9×1011cm−2. The observed changes in the electrical properties are well described by a double back-to-back Schottky barrier model.
Temperature dependent photoreflectance and photoluminescence characterization of GaInNAs∕GaAs single quantum well structures
Authors: Chen T. H. , Huang Y. S. , Lin D. Y. , Tiong K. K.
Published: November 2004

Ga 0.69 In 0.31 N x As 1 − x ∕ GaAs single quantum well (SQW) structures with three different nitrogen compositions ( x=0%, 0.6%, and 0.9%) have been characterized, as functions of temperature in the range 10–300K, by the techniques of photoreflectance (PR) and photoluminescence (PL). In PR spectra, clear Franz-Keldysh oscillations (FKOs) above the GaAs band edge and the various excitonic transitions originating from the QW region have been observed. The built-in electric field in the SQW has been determined from FKOs and found to increase with N concentration. The PR signal has been found to decrease for nitrogen incorporated samples when the temperature was lowered due to a weakening of the modulation efficiency induced by carrier localization. A careful analysis of PR and PL spectra has led to the identification of various excitonic transitions, mnH(L), between the mth conduction band state and the nth heavy (light)-hole band state. The anomalous temperature dependent 11H transition energy and linewidth observed in the PL spectra have been explained as originating from the localized states as a result of nitrogen incorporation. The temperature dependence analysis yields information on the parameters that describe the temperature variations of the interband transitions.
Self-consistent energy balance simulations of hole dynamics in SiGe∕SiTHz quantum cascade structures
Authors: Ikonić Z. , Harrison P. , Kelsall R. W.
Published: November 2004

Analysis of hole transport in cascaded p-Si∕SiGe quantum well structures is performed using self-consistent rate equations simulations. The hole subband structure is calculated using the 6×6k·p model, and then used to find carrier relaxation rates due to the alloy disorder, acoustic, and optical phonon scattering, as well as hole-hole scattering. The simulation accounts for the in-plane k-space anisotropy of both the hole subband structure and the scattering rates. Results are presented for prototype THzSi∕SiGe quantum cascade structures.
Effect of La substitution on phase transitions in lead zirconate stannate titanate (55∕35∕10) ceramics
Authors: Chan Wai-Hung , Xu Z. , Hung T. F. , Chen Haydn
Published: November 2004

Investigations of the structure-property relationships in Pb1−3x∕2Lax(Zr0.55Sn0.35Ti0.10)O3. (PLZST100x∕55∕35∕10) have been performed for x between 0 and 0.08 by means of x-ray diffraction, electron microscopy, polarization, and dielectric studies. Factors affecting the phase stability were determined. The base composition PLZST0∕55∕35∕10 was ferroelectric (FE) at room temperature and transformed into an incommensurate antiferroelectric (AFEin) state on heating. Evidence was presented that low La addition could destabilize the FE state and PLZST2∕55∕35∕10 became AFEin at room temperature, which transformed to a multicell cubic state and then to a paraelectric (PE) phase upon heating. Further increase of La content enhanced the stability of the AFEin state at room temperature. Moreover, addition of La could also broaden the AFEin-PE phase transition temperature region and decrease its maximal dielectric constant εmax′.
Enhanced dielectric properties of Ba1−xSrxTiO3 thin film grown on La1−xSrxMnO3 bottom layer
Authors: Miao Jun , Chen Weiran , Zhao Li , Chen Bin , Yang Hao , Peng Wei , Zhu Xiaohong , Xu Bo , Cao Lixin , Qiu Xianggang , Zhao Bairu
Published: November 2004

The Ba0.7Sr0.3TiO3(BST)∕La0.67Sr0.33MnO3(LSMO) heterostructure has been fabricated by pulsed-laser deposition on (001) SrTiO3 single crystal substrate. The crystallization and surface morphology of the heterostructure have been characterized by x-ray diffraction and atomic force microscopy. The composition distribution along the depth of the heterostructure is analyzed by Auger electron spectroscopy. It is founded that the LSMO bottom layer shows a marked effect on the dielectric properties of the BST films. Comparing with BST∕YBCO (YBCO—YBa2Cu3O7) heterostructure grown by similar process, the dielectric loss exhibits much lower and less frequency dispersive, especially in the high frequency region. The loss tangent at 100kHz is about 0.012 and the figure of merit factor is about 25 under the condition of 200kV∕cm. Ferroelectric hysteresis measurement shows that the remanent polarization and coercive field of the heterostructure are 3.4μC∕cm2 and 39kV∕cm, respectively. These parameters are all better than BST∕YBCO heterostructure. The good surface morphology and the element diffusion between BST and LSMO layers may be suggested to be responsible for the above-improved parameters of BST∕LSMO heterostructure.
ABAB organization of Ge∕Si(001) islands in multiplanes grown with low pressure chemical vapor deposition
Authors: Kermarrec O. , Campidelli Y. , Bensahel D.
Published: November 2004

Encapsulation of Ge∕Si(001) islands with Si and SiGe, and growth of Ge island multiplanes in low pressure chemical vapor deposition is presented. Differences from similar structures grown with other epitaxy techniques were found. Encapsulation with pure silicon results in a highly faceted silicon surface, consisting of pyramids, whereas capping with silicon-germanium results in smoother surfaces. Both capping materials keep the aspect ratio of the underlying capped islands unchanged. Then, Ge island multiplanes are grown, and the role of the silicon spacer thickness on island organization is emphasized. A dramatic transition in island self-organization is observed. Whereas usual vertical alignment occurs for thin spacers, this alignment is rapidly lost when the spacer thickness increases. Following a transient regime of oblique alignment, the Ge island planes organize in a stable staggered (ABAB) vertical sequence, in which the island distribution is very reproducible. The ABAB vertical organization is accompanied by a surface organization, jointly producing a tetragonal centered lattice of Ge islands in the silicon matrix. The faceted silicon spacer surface is believed to play the key role in the self-organization transition.
Structural and transport properties of CuSc1−xMgxO2+y delafossites
Authors: Kykyneshi R. , Nielsen B. C. , Tate J. , Li J. , Sleight A. W.
Published: November 2004

Transport and structural properties of Mg-doped and O-intercalated sintered powders and polycrystalline films of CuSc1−xMgxO2+y are reported. Substitution of Mg for Sc systematically increases the p-type conductivity in CuSc1−xMgxO2 sintered powders, producing a maximum conductivity of 0.015S∕cm at x≈0.06. A similar level of conductivity is observed in transparent polycrystalline CuSc1−xMgxO2 films at the same doping level. Mg doping causes no significant increase in optical absorption at this level. Intercalation of oxygen into the delafossite structure leads to a much larger increase in p-type conductivity. In powders, the maximum conductivity is 0.5S∕cm at y=0.23 and x=0.05. In oxygen-intercalated films, the maximum conductivity was 25S∕cm, with the transparent films gradually darkening as oxygen is incorporated. Oxygen intercalation increases the a-axis lattice parameter of the delafossite structure in both films and powders, with a much smaller effect on the c-axis parameter. Two distinct phases with y≈0 and y≈0.5 are observed in x-ray diffraction of powders. In films intermediate values of y are observed, often in combination with a distinct y=0 phase. The absorption properties of the powder samples indicate introduction of defects into the 2H polymorph of CuScO2 and CuSc1−xMgxO2 compared to the 3R polymorph.