bluuebunny/crossref_metadata_2025 huggingface dataset:
The Enigma of Ignatius of Antioch
Authors: BRENT ALLEN
Published: June 2006

If we affirm against recent criticism the authenticity of the Middle Recension of the Ignatian letters, we are nevertheless left with the enigma of Ignatius' relations with Polycarp. This paper explains that enigma in terms of two distinct cultural worlds of early second-century Christianity that come together in the meeting of these two church leaders. Ignatius was the first great missionary bishop who reinterpreted church order, the eucharist and martyrdom against the backcloth of the Second Sophistic in Asia Minor, with its pagan processions, cult and embassies that celebrated the social order of the Greek city state in relation to imperial power. Much of Ignatius' iconography was alien to Polycarp, though the latter was finally to canonise both him and his writings by focusing on his impressively enacted refutation of Docetism through his portrayal of his forthcoming martyrdom.
Computing minimal models, stable models and answer sets
Authors: LONC ZBIGNIEW , TRUSZCZYŃSKI MIROSŁAW
Published: June 2006

We propose and study algorithms to compute minimal models, stable models and answer sets of $t$-CNF theories, and normal and disjunctive $t$-programs. We are especially interested in algorithms with non-trivial worst-case performance bounds. The bulk of the paper is concerned with the classes of 2- and 3-CNF theories, and normal and disjunctive 2- and 3-programs, for which we obtain significantly stronger results than those implied by our general considerations. We show that one can find all minimal models of 2-CNF theories and all answer sets of disjunctive 2-programs in time $O(m1\mbox{.}4422\mbox{..}^n)$. Our main results concern computing stable models of normal 3-programs, minimal models of 3-CNF theories and answer sets of disjunctive 3-programs. We design algorithms that run in time $O(m1\mbox{.}6701\mbox{..}^n)$, in the case of the first problem, and in time $O(mn^2 2\mbox{.}2782\mbox{..}^n)$, in the case of the latter two. All these bounds improve by exponential factors the best algorithms known previously. We also obtain closely related upper bounds on the number of minimal models, stable models and answer sets a $t$-CNF theory, a normal $t$-program or a disjunctive $t$-program may have.
Latitudinal variation of the solar He I 58.4 nm irradiance from the optical observation of the interplanetary He I emission
Authors: Yamazaki A. , Yoshikawa I. , Shiomi K. , Takizawa Y. , Miyake W. , Nakamura M.
Published: June 2006

The Extreme Ultraviolet (XUV) scanner on board the Planet‐B spacecraft observed the He I 58.4‐nm emission of the local interstellar gas in interplanetary space during solar maximum. The spacecraft was in an interplanetary orbit with a perihelion of 1 AU and an aphelion of 1.5 AU and encountered the helium focusing cone at a longitude different from the position of the Earth during March and April of 2000. Numerical simulations of the XUV observation were carried out based on a hot model of the interstellar gas (Wu and Judge, 1979) and an empirical solar flux model (SOLAR2000) (Tobiska et al., 2000). In comparison with the XUV observations, we obtain an ionization rate of (2.3 ± 0.27) × 10−7/s and a line width of 0.0098 ± 0.0014 nm, corresponding to a velocity of 50 ± 7.2 km/s. However, the distribution of the interplanetary He I intensity indicates that the solar He I irradiance has an anisotropy in longitude and latitude. From the comparison between the XUV observation and alternative simulations with an anisotropy in the solar He I irradiance and with no anisotropy in the total ionization rate, the He I flux ratio toward the pole to within the ecliptic plane is estimated to be 0.61 ± 0.24. Therefore it is suggested that the ionization rate of helium atoms has similar anisotropies as the solar He I flux. Since the relationship between anisotropies of the ionization rate and the helium density is not linear, a three‐dimensional and time‐dependent approach is required for full understanding on the helium distribution in interplanetary space.
The 17–22 October (1999) solar‐interplanetary‐geomagnetic event: Very intense geomagnetic storm associated with a pressure balance between interplanetary coronal mass ejection and a high‐speed stream
Authors: Dal Lago Alisson , Gonzalez Walter D. , Balmaceda Laura A. , Vieira Luis E. A. , Echer Ezequiel , Guarnieri Fernando L. , Santos Jean , da Silva Marlos R. , de Lucas Aline , Clua de Gonzalez Alicia L. , Schwenn Ranier , Schuch Nelson J.
Published: June 2006

Using observations from the Advanced Composition Explorer (ACE) magnetic field and plasma experiments, we investigate the magnetic, thermal, and dynamic pressure balance in the border of a high‐speed stream (HSS) and an average‐speed interplanetary coronal mass ejection (ICME) observed on 21–22 October (1999). We believe that the HSS compressed the ICME and intensified its internal southward magnetic field, resulting in a very intense geomagnetic storm, with peak Dst of −237 nT. In solar cycle 23 this was the only event, out of 18 very intense geomagnetic storms, i.e., peak Dst < −200 nT, which was caused by such a mechanism. We also address the solar origin of this very intense geomagnetic storm, using combined solar data from three different sources: a ground‐based source, coronal hole maps from the National Solar Observatory (NSO) at Kitt Peak, and two satellite‐based sources, eruption activity from the Extreme Ultraviolet Imaging Telescope (EIT) and coronal mass ejection observations from the Large Angle and Spectrometric Coronagraph (LASCO), both aboard the Solar and Heliospheric Observatory (SOHO). A coronal hole is evident just beside (to the east of) the active region from which an average‐speed coronal mass ejection lifted off on 17–18 October (1999). This was the only possible solar origin of the 21–22 October interplanetary geomagnetic event.
A 12,000 year record of explosive volcanism in the Siple Dome Ice Core, West Antarctica
Authors: Kurbatov A. V. , Zielinski G. A. , Dunbar N. W. , Mayewski P. A. , Meyerson E. A. , Sneed S. B. , Taylor K. C.
Published: June 2006

Air mass trajectories in the Southern Hemisphere provide a mechanism for transport to and deposition of volcanic products on the Antarctic ice sheet from local volcanoes and from tropical and subtropical volcanic centers. This study extends the detailed record of Antarctic, South American, and equatorial volcanism over the last 12,000 years using continuous glaciochemical series developed from the Siple Dome A (SDMA) ice core, West Antarctica. The largest volcanic sulfate spike (280 μg/L) occurs at 5881 B.C.E. Other large signals with unknown sources are observed around 325 B.C.E. (270 μg/L) and 2818 B.C.E. (191 μg/L). Ages of several large equatorial or Southern Hemisphere volcanic eruptions are synchronous with many sulfate peaks detected in the SDMA volcanic ice chemistry record. The microprobe “fingerprinting” of glass shards in the SDMA core points to the following Antarctic volcanic centers as sources of tephra found in the SDMA core: Balenny Island, Pleiades, Mount Berlin, Mount Takahe, and Mount Melbourne as well as Mount Hudson and possibly Mount Burney volcanoes of South America. Identified volcanic sources provide an insight into the poorly resolved transport history of volcanic products from source volcanoes to the West Antarctic ice sheet.
Atmospheric radiative forcing at the surface derived from aircraft irradiance and spectral optical depth measurements
Authors: Bush Brett C. , Valero Francisco P. J. , Pope Shelly K.
Published: June 2006

In this paper we report atmospheric radiative forcing, radiative forcing efficiency, and fractional forcing efficiency by aerosols determined from airborne measurements performed during the Indian Ocean Experiment (INDOEX) and the Asian Pacific Regional Characterization Experiment (ACE‐Asia). The atmospheric radiative forcing at the surface is calculated in the visible spectral region (400–700 nm) using near‐surface observations from the National Center for Atmospheric Research (NCAR) C‐130 aircraft. A total‐direct‐diffuse radiometer (TDDR) with seven spectral bands spanning 400 to 700 nm is used to determine irradiances at the surface as well as spectral (in all seven channels including a narrowband channel at 500 nm, τ500) and broadband (400–700 nm) aerosol optical depths. For INDOEX, using observations in the Arabian Sea, the visible surface forcing efficiencies range from about −74 to −120 W m−2 τ500−1, and the corresponding fractional forcing efficiencies range from about −14 to −30% τ500−1. These forcing values in the Arabian Sea are higher than those derived in a previous study using measurements at a surface site located at the Kaashidhoo Climate Observatory (KCO). During ACE‐Asia, the aerosol forcing and forcing efficiency at the surface are slightly lower than those during INDOEX and range from about −54 to −110 W m−2 τ500−1 and −11 to −23% τ500−1, respectively. These values are consistent with similar measurements made at the surface site at Gosan, Jeju, Republic of Korea. Diurnal forcing efficiencies are also estimated for the aircraft measurements giving a range of −23 to −54 W m−2 τ500−1 for INDOEX and −19 to −37 W m−2 τ500−1 for ACE‐Asia. Forcing efficiencies are determined using broadband aerosol optical depths and reflect small differences (related to changing aerosol characteristics) relative to those values obtained using narrowband quantities.
Is a shutdown of the thermohaline circulation irreversible?
Authors: Yin Jianjun , Schlesinger Michael E. , Andronova Natasha G. , Malyshev Sergey , Li Bin
Published: June 2006

The Atlantic thermohaline circulation (THC) plays a vital role in explaining past abrupt climate changes and in maintaining the current climate. Its remarkable nonlinear dynamics, first demonstrated by H. M. Stommel, have been supported by various types of climate models. This has led to severe concerns that global warming may shut down the THC irreversibly, with consequent catastrophic climate changes, particularly for Europe. Here we use an uncoupled ocean general circulation model (OGCM) and a coupled atmosphere‐ocean general circulation model (AOGCM) to investigate the nonlinear response of the THC to freshwater perturbations in the northern North Atlantic. We find that the THC shuts down irreversibly in the uncoupled OGCM simulations but reversibly in the coupled AOGCM simulations. This occurs because of different feedback processes operating in the uncoupled OGCM and AOGCM. The reversal of the THC in the uncoupled OGCM tends to stabilize the “off” mode of the THC by decreasing the mean salinity of the Atlantic, whereas a crucial negative feedback in the AOGCM helps the THC recover. This negative feedback results from complex air‐sea interactions, and its operation needs the full participation of the atmosphere. Thus given the more realistic simulation by the AOGCM, the irreversible shutdown of the THC caused by freshwater addition appears to be an artifact of the uncoupled OGCM rather than a likely outcome of global warming.
Evaluation of split‐window and dual‐angle correction methods for land surface temperature retrieval from Envisat/Advanced Along Track Scanning Radiometer (AATSR) data
Authors: Coll César , Caselles Vicente , Galve Joan M. , Valor Enric , Niclòs Raquel , Sánchez Juan M.
Published: June 2006

Land surface temperature (LST) can be derived from thermal infrared remote sensing data provided that atmospheric and emissivity effects are corrected for. In this paper, two correction methods were evaluated using a database of ground LST measurements and concurrent Envisat/Advanced Along Track Scanning Radiometer (AATSR) data. They were the split‐window (SW) method, which uses two channels at 11 and 12 μm, and the dual‐angle (DA) method, using one single channel (11 μm) at two observation angles (close to nadir and around 55° forward). The ground LST measurements were performed in a large, flat, and thermally homogeneous area of rice fields during the summers of 2002–2005, when the crop showed full vegetation cover. A total of 23 concurrences of ground measurements and AATSR data were obtained. Results showed that the SW algorithms worked satisfactorily provided that the characteristics of the area are correctly prescribed, either through the classification of the land cover type and vegetation cover fraction or with the surface emissivity. In this case the AATSR‐derived LSTs agreed with the ground LSTs within ±1.0°C for all the data of the comparison, with negligible average bias and a standard deviation of 0.5°C. The DA algorithms were less accurate than the SW algorithms for the data used in this study, yielding standard deviations of 1.0°C.
Titan imagery with Keck adaptive optics during and after probe entry
Authors: de Pater Imke , Ádámkovics Máte , Bouchez Antonin H. , Brown Michael E. , Gibbard Seran G. , Marchis Franck , Roe Henry G. , Schaller Emily L. , Young Eliot
Published: June 2006

We present adaptive optics data from the Keck telescope, taken while the Huygens probe descended through Titan's atmosphere and on the days following touchdown. No probe entry signal was detected. Our observations span a solar phase angle range from 0.05° up to 0.8°, with the Sun in the west. Contrary to expectations, the east side of Titan's stratosphere was usually brightest. Compiling images obtained with Keck and Gemini over the past few years reveals that the east‐west asymmetry can be explained by a combination of the solar phase angle effect and an enhancement in the haze density on Titan's morning hemisphere. While stratospheric haze was prominent over the northern hemisphere, tropospheric haze dominated the south, from the south pole up to latitudes of ∼45°S. At 2.1 μm this haze forms a polar cap, while at 1.22 μm it appears in the form of a collar at 60°S. A few small clouds were usually present near the south pole, at altitudes of 30–40 km. Our narrowband J,H,K images of Titan's surface compare extremely well with that obtained by Cassini ISS, down to the small‐scale features. The surface contrast between dark and bright areas may be larger at 2 μm than at 1.6 and 1.3 μm, which would imply that the dark areas may be covered by a coarser‐grained frost than the bright regions and/or that there is additional 2 μm absorption there.
Mauna Loa volcano is not a methane source: Implications for Mars
Authors: Ryan Steven , Dlugokencky Edward J. , Tans Pieter P. , Trudeau Michael E.
Published: June 2006

Thirteen years of continuous atmospheric carbon dioxide and methane measurements at the Mauna Loa Observatory in Hawaii are used to determine the methane emission rate from the summit of Mauna Loa volcano. We find no measurable methane emissions coming from the summit area, with a 95% confidence upper limit of 9 t CH4 yr−1. Recent studies have detected 10 ppb CH4 in the Martian atmosphere, requiring emissions of about 300 t CH4 yr−1. Volcanic activity has been suggested as a source of abiogenic CH4 on Mars, either by magmatic degassing or reactions in hydrothermal fluids heated by a magma intrusion. The most recent lava flows on Mars (2 My ago) are on the Tharsis shield volcanoes, which may still be active. If Mauna Loa is a valid terrestrial analog, our findings suggest that volcanic activity is not a significant source of methane to the Martian atmosphere.
Positron Emission Tomography Displacement Sensitivity: Predicting Binding Potential Change for Positron Emission Tomography Tracers Based on Their Kinetic Characteristics
Authors: Morris Evan D , Yoder Karmen K
Published: June 2006

There is great interest in positron emission tomography (PET) as a noninvasive assay of fluctuations in synaptic neurotransmitter levels, but questions remain regarding the optimal choice of tracer for such a task. A mathematical method is proposed for predicting the utility of any PET tracer as a detector of changes in the concentration of an endogenous competitor via displacement of the tracer (a.k.a., its ‘vulnerability’ to competition). The method is based on earlier theoretical work by Endres and Carson and by the authors. A tracer-specific predictor, the PET Displacement Sensitivity (PDS), is calculated from compartmental model simulations of the uptake and retention of dopaminergic radiotracers in the presence of transient elevations of dopamine (DA). The PDS predicts the change in binding potential (Δ BP) for a given change in receptor occupancy because of binding by the endogenous competitor. Simulations were performed using estimates of tracer kinetic parameters derived from the literature. For D2/D3 tracers, the calculated PDS indices suggest a rank order for sensitivity to displacement by DA as follows: raclopride (highest sensitivity), followed by fallypride, FESP, FLB, NMSP, and epidepride (lowest). Although the PDS takes into account the affinity constant for the tracer at the binding site, its predictive value cannot be matched by either a single equilibrium constant, or by any one rate constant of the model. Values for Δ BP have been derived from published studies that employed comparable displacement paradigms with amphetamine and a D2/D3 tracer. The values are in good agreement with the PDS-predicted rank order of sensitivity to displacement.
Complex microcalorimeter models and their application to position-sensitive detectors
Authors: Figueroa-Feliciano Enectali
Published: June 2006

We present a general formalism for calculating the linear response, noise spectrum, and energy resolution of complex calorimeters. Using this formalism calorimeters with arbitrary numbers of distinct linked heat capacity systems and/or coupled thermometers can be analyzed. We use this formalism to derive the theoretical resolution of an imaging microcalorimeter called a position- sensitive transition-edge sensor.
Thermal and rheological properties of carbon nanotube-in-oil dispersions
Authors: Yang Ying , Grulke Eric A. , Zhang Z. George , Wu Gefei
Published: June 2006

Prior work on asymmetric thermally conducting nanoparticle dispersions has shown that it is possible to raise the thermal conductivity of low thermal conductivity liquids at modest volume fractions of nanoparticles. Stable and reproducible nanotube dispersions require careful control of the dispersant chemistry as well as an understanding of their response to input energy. This paper addresses the effects of dispersant concentration, dispersing energy, and nanoparticle loading on thermal conductivity and steady shear viscosity of nanotube-in-oil dispersions. The thermal conductivity and viscosity of these dispersions correlate with each other and vary with the size of large scale agglomerates, or clustered nanoparticles, in the fluids. Fluids with large scale agglomerates have high thermal conductivities. Dispersion energy, applied by sonication, can decrease agglomerate size, but also breaks the nanotubes, decreasing both the thermal conductivity and viscosity of nanotube dispersions. Developing practical heat transfer fluids containing nanoparticles may require a balance between the thermal conductivity and viscosity of the dispersions.
Improvement of luminous efficacy in plasma display panels by a counter-type electrode configuration with a large gap
Authors: Hur Min , Kim Jae Rok , Yi Jeong Doo , Cho Yoon Hyoung , Song Su Bin , Park Jun Yong , Lee Han Yong
Published: June 2006

The discharge characteristics of plasma display panel with coplanar and counter-type electrode configurations are compared using the numerical modeling and experiment with respect to real and macrocells, respectively. Numerical analysis shows that the ultraviolet (UV) efficiency and driving voltage of counter type at a gap distance of 230μm are located at similar levels to those of coplanar type at a gap distance of 60μm. The UV efficiency for counter type is enhanced with the rise of xenon fraction and gap distance, between which the large gap operation is more advantageous to high UV efficiency. The measured temporal evolution of infrared emission reveals that the cathode layer plays an important role in forming the discharge current after the gas breakdown. It is found from the time-averaged visible and infrared emissions for the counter type that as the gap distance becomes larger, the positive column region increases but the sheath regime remains almost unchanged. On the other hand, the variation of gap distance gives a little influence on the average discharge current at the same applied voltage. The UV efficiency is thus greatly improved with the gap distance. When the gap becomes double, the UV efficiency is improved by 75%, which is well agreed with the results predicted in the numerical modeling.
Passive optical diagnostic of Xe-propelled Hall thrusters. I. Emission cross sections
Authors: Chiu Yu-hui , Austin Brad L. , Williams Skip , Dressler Rainer A. , Karabadzhak George F.
Published: June 2006

This paper presents a set of xenon apparent emission excitation cross sections for emission lines that have diagnostic value in the analysis of Xe-propelled Hall thruster plasmas. Emission cross sections are presented for three excitation processes involving ground-state xenon atoms: e−+Xe, Xe++Xe, and Xe2++Xe. The cross sections are derived from luminescence spectra produced at single-collision conditions. Apparent emission excitation cross sections are tabulated for 12 visible and 8 near-infrared lines for electron energies ranging from 10to70eV. In case of the near-infrared lines, radiation trapping effects are accounted for by measuring the detailed pressure dependence of the apparent emission cross sections and extrapolating to zero pressure. A semiempirical expression for the pressure dependence is derived that allows zero-pressure extrapolation from threshold to 70eV. Ion-induced cross sections are reported for the same emission lines at an energy per unit charge E∕q of 300eV, chosen for typical Hall thruster operating voltages. Radiation trapping effects are negligible for the ion emission excitation cross sections between 0.1 and 2.0mTorr in the present luminescence experiment.
Theoretical properties of the N vacancy in p-type GaN(Mg,H) at elevated temperatures
Authors: Myers S. M. , Wright A. F. , Sanati M. , Estreicher S. K.
Published: June 2006

The elevated-temperature properties of the N vacancy in Mg-doped, p-type GaN containing H were modeled using atomic-configuration energies and phonon densities of states obtained with density-functional theory. This study encompassed both equilibrium thermodynamics and the rates of diffusion and reaction processes and included the influences of a number of bound complexes involving the vacancy, the Mg dopant, and H. A comparison was made with published experimental information. Our results indicate that N vacancies extensively compensate Mg acceptors at higher doping levels.
Flame spread through cracks of PBX 9501 (a composite octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine-based explosive)
Authors: Berghout H. Laine , Son Steven F. , Hill Larry G. , Asay Blaine W.
Published: June 2006

Recent experiments involving combustion of PBX 9501 [a plastic-bonded high explosive composed of 95% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) by weight in a plasticized, estane-based binder] under confined conditions underscore the importance of cracks and flaws in reaction violence. The presence of a small void space or alternative escape path for combustion gases at the closed end of a crack drastically alters combustion violence. In the case of a true closed-ended crack, where gases can only escape by exiting the open end of the crack, luminous combustion spreads through the closed crack at relatively low rates in the range of a few meters per second, regardless of the pressure external to the slot. Hence, external pressure determines whether reaction can progress into the restricted dimensions of the slot, but it does not necessarily determine the dynamics of the flame’s progress in the slot. When an alternative combustion-gas escape path is available at the closed end of the slot, luminous combustion spreads through the crack at hundreds of meters per second. Additionally, combustion in cracks of confined PBX 9501 materials exhibits oscillatory behavior with a frequency of about 1000Hz for the experimental configuration used. This oscillatory behavior resembles combustion instabilities observed in rocket motors and may arise from similar processes. We also report on preliminary experiments involving 19.1cm long slots in confined PBX 9501, which have produced very high flame-propagation rates of 1500m∕s.
A transmission electron microscopy study of defects formed through the capping layer of self-assembled InAs∕GaAs quantum dot samples
Authors: Sears K. , Wong-Leung J. , Tan H. H. , Jagadish C.
Published: June 2006

Plan-view and cross-sectional transmission electron microscopy have been used for a detailed study of the defects formed in capped InAs∕GaAs quantum dot (QD) samples. Three main types of defects, V-shaped defects, single stacking faults, and stacking fault pyramids, were found to form under growth conditions that led to either very large, indium enriched, or coalesced islands. All three types of defects originate at the buried quantum dot layer and then travel through the GaAs cap to the surface on the {111} planes. The V-shaped defects were the most common and typically consisted of two pairs of closely spaced 60° Shockley partials with a ⟨211⟩ line direction. The two pairs originate together at the buried QD layer and then travel in “opposite” directions on different {111} planes. The second type of defect is the single stacking fault which consists of a single pair of partial dislocations separated by an ≈50nm wide stacking fault. Finally, both complete and incomplete stacking fault pyramids were observed. In the case of the complete stacking fault pyramid the bounding dislocations along the [110], [11¯0], [101¯], and [101] directions were identified as stair rods. A possible mechanism for the stacking fault pyramid formation, which can also account for the creation of incomplete stacking fault pyramids, is presented.
Effect of CO on NO and N2O conversions in nonthermal argon plasma
Authors: Zhao Gui-Bing , Argyle Morris D. , Radosz Maciej
Published: June 2006

200 – 600 ppm of CO inhibit NO conversion in nonthermal Ar plasma, but do not produce N2O. However, 1.01% of CO has no effect on NO conversion, but produces N2O. In general, N2O conversion in Ar plasma decreases with increasing CO concentration. These experimental results cannot be explained by charge transfer reactions of Ar+. Selectivity analysis of all excited states of Ar possibly contributing to NOx conversion without and with CO suggests that only Ar(P23) contributes to NOx conversion and CO dissociation. A kinetic model of 43 reactions is required to model NO conversion or N2O conversion in Ar without CO, whereas 81 reactions are required to model NO conversion and N2O conversion in Ar with CO. At constant gas pressure, a single set of model parameters can predict NO conversion or N2O conversion without and with CO. All experimental results can be explained using a reaction mechanism in which excited neutral states of Ar are the only active species, which supports the conclusion that cations have a negligible impact on these nonthermal plasma reactions.
Equivalent retarder-rotator approach to on-state twisted nematic liquid crystal displays
Authors: Durán Vicente , Lancis Jesús , Tajahuerce Enrique , Jaroszewicz Zbigniew
Published: June 2006

Polarization properties of a twisted nematic liquid crystal cell are fully characterized by an equivalent optical system that consists of a retarder wave plate and a rotator. In this paper we show that this result is of interest to optimize the light-modulation capabilities of a voltage-addressed liquid crystal display (LCD). We provide two examples. First, we demonstrate a calibration method that can be carried out by a standard polarimetric technique with a high degree of precision. Second, we propose an optical device to generate a family of equiazimuth polarization states by adding a quarter-wave plate to the LCD. We find that the design procedure is best described in geometrical terms on the Poincaré sphere by use of the equivalent model. Finally, laboratory results corresponding to a commercial LCD are presented.
Effects of metal-doped indium-tin-oxide buffer layers in organic light-emitting devices
Authors: Chen T.-H. , Wu T. J. , Chen J. Y. , Liou Y.
Published: June 2006

Organic light-emitting devices were fabricated by using different metal (V, Zr, Hf)-doped indium-tin-oxide (ITO) buffer layers on an ITO anode. The metal-doped ITO buffer layers were 15nm thick with different metal concentrations. Both resistivity and work function of the ITO buffer layer were manipulated by these metal dopants. Different effects on the devices, such as reduced turn-on voltage, improved luminance, and enhanced current efficiency, were investigated. A low turn-on voltage was observed for devices with small work function and resistivity. The lowest turn-on voltage (3V) was found on a device with a V-doped ITO buffer layer. The devices usually have a similar current density (J)-voltage (V) characteristics, but not the luminance-J or the current efficiency-J characteristics when the ITO buffer layers have the same work function. The devices with the Hf-doped ITO buffer layers show the best luminance performance among those considered. At 100mA∕cm2, a luminance of 15,000cd∕m2, and a current efficiency of 15cd∕A have been achieved. The balance between the carrier concentration and the energy barrier for the hole injection is possibly responsible for such performance.
Ferroelectric thin films phase diagrams with self-polarized phase and electret state
Authors: Glinchuk Maya D. , Morozovska Anna N. , Eliseev Eugene A.
Published: June 2006

We calculated the three components of polarization in phenomenological theory framework by consideration of three Euler-Lagrange equations allowing for mismatch effect and influence of misfit dislocations, surface piezoelectric effect caused by broken symmetry on the film surface, surface tension, and depolarization field. The equations were solved with the help of variational method proposed earlier [M. D. Glinchuk et al., Physica B 332, 356 (2002)]. This approach leads to the free energy in the form of algebraic expression for different powers of polarization components with the coefficients dependent on film thickness, misfit strain, temperature, etc. The odd powers of polarization related to built-in electric field normal to the surface originated from misfit strain and piezoelectricity in the vicinity of the surface which appeared in the free energy expansion. The obtained free energy opens the way for the calculation of the ferroelectric film properties by conventional procedure of minimization. As an example we calculated phase diagrams of PbZr0.5Ti0.5O3 [PZT(50∕50)] compressive- or tensile-strained films. The temperature behavior of pyroelectric coefficient and dielectric permittivity lead to the forecast of the electretlike polar state, i.e., existence of pyroelectricity below the critical thickness of ferroelectric-paraelectric phase transitions. The mismatch-induced electric field was shown to be the physical nature of the self-polarization phenomenon in ferroelectric thin films.
Sensitive detector for a passive terahertz imager
Authors: Kleinschmidt P. , Giblin S. , Tzalenchuk A. , Hashiba H. , Antonov V. , Komiyama S.
Published: June 2006

We report progress in developing a sensitive detector for terahertz radiation, based on a semiconductor quantum dot (QD) capacitively coupled to a metallic single electron transistor (SET). A charge polarization of the QD induced by the absorption of individual photons is detected by the voltage-biased SET. We investigate the sensitivity of the detector to broadband radiation, over a range of QD barrier heights, and find that there is a measurable photo-signal over wide range of gate voltages defining the QD. This is an improvement on previous designs of terahertz detector based on the QD/SET principle, and makes the new detector a candidate for use in an imaging device.
Evolution of 1∕fα noise during electromigration stressing of metal film: Spectral signature of electromigration process
Authors: Bora Achyut , Raychaudhuri A. K.
Published: June 2006

In this paper we report a systematic study of low-frequency 1∕fα resistance fluctuation in a metal film at different stages of electromigration. The resistance fluctuation (noise) measurement was carried out in presence of a dc electromigration stressing current. We observe that in addition to the increase in the spectral power SV(f), the frequency dependence of the spectral power changes as the electromigration process progresses and the exponent α starts to change from 1 to higher value closer to 1.5. We interpret this change in α as arising due to an additional contribution to the spectral power with a 1∕f3∕2 component, which starts to contribute as the electromigration process progresses. This additional component SV(f)∼1∕f3∕2 has been suggested to originate from long range diffusion that would accompany any electromigration process. The experimental observation finds support in a model simulation, where we also find that the enhancement of noise during electromigration stressing is accompanied by a change in spectral power frequency dependence.
Ferroelectricity in intergrowth Bi3TiNbO9–Bi4Ti3O12 ceramics
Authors: Yi Z. G. , Wang Y. , Li Y. X. , Yin Q. R.
Published: June 2006

Monophase intergrowth Bi3TiNbO9–Bi4Ti3O12 (BTN-BIT) ceramics were synthesized by solid-state reaction method. In the temperature dependence of dielectric permittivity, two anomalies appeared at 945 and 1114K, respectively. The ferroelectric hysteresis loop measurement revealed that the 2Pr is 20μC∕cm2, nearly as twice as that of the BTN ceramic. The crystal structure analysis indicated that the enhanced octahedral distortion along the a axis is the main contribution to the ferroelectricity of BTN-BIT. The increased 2Pr for the BTN-BIT ceramics is ascribed to its larger Ps than that of the BTN and easier domain switching under electric field than that of the BIT.
Flat panel displays for ubiquitous product applications and related impurity doping technologies
Authors: Suzuki Toshiharu
Published: June 2006

Various kinds of flat panel displays such as liquid crystal displays (LCDs), plasma display panels and organic light emitting diode (OLED) displays are briefly evaluated from the perspective of applicability to ubiquitous products. It is clarified that the LCDs and OLED displays are suitable for realizing mobile electronic products with a high quality display, since these displays can use active devices on the backplanes to form active matrix displays and can integrate peripheral circuits of the displays and functional circuits of mobile electronics for a ubiquitous era. It is clarified further that the low temperature polycrystalline silicon (LTPS) thin film transistor (TFT) is the most promising active device for the backplane of such active matrix displays because the LTPS TFT has the possibility to enhance its performance without raising the cost. The low temperature poly-Si TFT fabrication process is introduced, and its key technologies such as crystallization, gate oxide formation, and impurity doping are surveyed. As the property of polycrystalline silicon (poly-Si) influences not only the TFT performance itself but also the efficiency of impurity doping and the integrity of the gate oxide, the crystallinity of the poly-Si is reviewed. After that, the history of the development and the state of the art in impurity doping technology and its issues are addressed in detail. Finally, foreseeing the application of LTPS TFT, the realization of OLED displays, and the progress of LTPS TFT for integrating higher functional circuits for ubiquitous applications, the requirements for impurity doping in such progress are addressed. In particular, the single grain silicon technology and the scaling down of the TFT size, which are thought to be highly effective to enhance the performance of TFTs, and issues of impurity doping technology relating to them are discussed.
Extending ion-track lithography to the low-energy ion regime
Authors: Musket R. G.
Published: June 2006

Ion tracking and ion-track lithography have been performed almost exclusively using ions with energies near or above the maximum in electronic stopping, which occurs at ∼1MeV∕amu. In this paper, ion-track lithography using ions with energies well below this maximum is discussed. The results of etching ion tracks created in polycarbonate films by ions with energies just above the anticipated threshold for creating etchable latent tracks with cylindrical geometry have been examined. Low-energy neon and argon ions with 18–60keV∕amu and fluences of ∼108cm−2 were used to examine the limits for producing useful, etchable tracks in polycarbonate films. By concentrating on the early stages of etching (i.e., ∼20nm<scanning electron microscopy hole diameter <∼100nm), the energy deposition calculated for the incident ion was correlated with the creation of etchable tracks. The experimental results are discussed with regard to the energy losses of the ions in the polycarbonate films and to the formation of continuous latent tracks through the entire thickness of the films. The probability distributions for large-angle scattering events were calculated to assess their importance as a function of ion energy. All these results have significant implications with respect to the threshold for formation of etchable tracks and to the use of low-energy ions for lithographic applications of ion tracking.
Temporal response and first order volume changes during grating formation in photopolymers
Authors: Kelly John V. , Gleeson Michael R. , Close Ciara E. , O’Neill Feidhlim T. , Sheridan John T. , Gallego Sergi , Neipp Cristian
Published: June 2006

We examine the evolution of the refractive index modulation when recording gratings in an acrylamide based photopolymer. A nonlocal diffusion model is used to predict theoretically the grating evolution. The model has been developed to account for both nonlocal spatial and temporal effects in the medium, which can be attributed to polymer chain growth. Previously it was assumed that the temporal effect of chain growth could be neglected. However, temporal effects due to chain growth and monomer diffusion are shown to be significant, particularly over short recording periods where dark field amplification is observed. The diffusion model is solved using a finite-difference technique to predict the evolution of the monomer and polymer concentrations throughout grating recording. Using independently measured refractive index values for each component of the recording medium, the Lorentz-Lorenz relation is used to determine the corresponding refractive index modulation. The corresponding diffraction efficiency is then determined using rigorous coupled wave analysis. The diffraction efficiency curves are presented for gratings recorded using short exposure times, monitored in real time, both during and after recording. The effect of volume shrinkage of polymer on grating evolution is also examined. Both the nonlocal temporal response of the material and monomer diffusion are shown to influence refractive index modulation postexposure.
Synthetic melanin films: Assembling mechanisms, scaling behavior, and structural properties
Authors: Lorite Gabriela S. , Coluci Vitor R. , da Silva Maria Ivonete N. , Dezidério Shirlei N. , Graeff Carlos Frederico O. , Galvão Douglas S. , Cotta Mônica A.
Published: June 2006

In this work we report on the surface characterization of melanin thin films prepared using both water-based and organic solvent-based melanin syntheses. Atomic force microscopy (AFM) analysis of these films suggests that the organic solvent synthesis provides relatively planar basic melanin structures; these basic structures generate surface steps with height in the range of 2–3nm and small tendency to form larger aggregates. The scaling properties obtained from the AFM data were used to infer the assembling mechanisms of these thin films which depend on the solvent used for melanin synthesis. The behavior observed in organic solvent-based melanin suggests a diffusion-limited aggregation process. Thus films with good adhesion to the substrate and smoother morphologies than water-prepared melanin films are obtained. Electronic structure calculations using a conductorlike screening model were also performed in order to elucidate the microscopic processes of thin film formation. Our results suggest that the agglomerates observed in hydrated samples originate from reaction with water at specific locations on the surface most likely defects on the planar structure.
Low temperature synthesis and optical properties of small-diameter ZnO nanorods
Authors: Lv Yuzhen , Guo Lin , Xu Huibin , Ding Lu , Yang Chunlei , Wang Jiannong , Ge Weikun , Yang Shihe , Wu Ziyu
Published: June 2006

Small-diameter ZnO nanorods (∼10nm) with lengths of 80–100nm were synthesized by a simple solution route at low temperature (61.2°C). X-ray diffraction and high-resolution transmission electron microscopy analyses confirmed that the nanorods are hexagonal single crystals with a growth direction along [001]. Room temperature photoluminescence (PL) measurement showed a strong ultraviolet (UV) emission peak at 382nm with weak deep level emission. Quantum confinement effect in the ZnO nanorods was clearly revealed by low temperature PL. The complex origin of the UV peak has been discussed based on the temperature-dependent photoluminescence measurements.
Comparison of crystallization kinetics in a-Si∕Cu and a-Si∕Al bilayer recording films under thermal annealing and pulsed laser irradiation
Authors: Her Yung-Chiun , Chen Chih-Wei , Wu Chun-Lin
Published: June 2006

Under thermal annealing, the crystallization temperatures of a-Si in a-Si∕Cu and a-Si∕Al bilayer recording films were significantly reduced to around 485 and 357°C, respectively, and the activation energies for crystallization were reduced to about 3.3eV. The formation of Cu3Si phase prior to crystallization of a-Si was found to occur at around 175°C in a-Si∕Cu, while no Al silicide was observed in a-Si∕Al before crystallization of a-Si. The reaction exponents for a-Si∕Cu and a-Si∕Al were determined to be around 1.8 and 1.6, respectively, corresponding to a crystallization process in which grain growth occurs with nucleation, and the nucleation rate decreases with the progress of grain growth. Under pulsed laser irradiation, the precipitation of Cu3Si phases and crystallization of a-Si were observed in a-Si∕Cu, while the crystallization and reamorphization of a-Si took place sequentially in a-Si∕Al. The reaction exponents for a-Si∕Cu and a-Si∕Al, determined to be about 2.0 and 2.2, respectively, are slightly higher than those under thermal annealing, indicating that the crystallization processes of a-Si∕Cu and a-Si∕Al under pulsed laser irradiation are similar to those under thermal annealing. However, the decrease of nucleation rate with the progress of grain growth is slower. At the same time, the activation energies for crystallization of a-Si∕Cu and a-Si∕Al, estimated to be about 0.18 and 0.22eV, respectively, are nearly an order of magnitude lower than those under thermal annealing. This may be explained by the explosive crystallization of a-Si by mechanical impact, with a high power pulsed laser.
Strain-stabilized solid phase epitaxy of Si–Ge on Si
Authors: Sage Jennifer F. , Barvosa-Carter William , Aziz Michael J.
Published: June 2006

We compare solid phase epitaxial growth of amorphous Si–Ge alloys created by Ge ion implantation into Si with and without the imposition of 0.5GPa of externally applied biaxial tensile stress. External loading stabilizes the growth front against roughening, resulting in a doubling of the maximum reported Ge concentration for stable growth to 14at.%. The externally applied stress appears to superpose with the intrinsic compositional stress and indicates a threshold of approximately 0.6GPa for interface breakdown. This principle is expected to be applicable to expanding the composition range for stable growth of other semiconductor alloy combinations by other growth techniques.
Optical properties of SnO2 nanoparticles and nanorods synthesized by solvothermal process
Authors: Das Soumen , Kar Soumitra , Chaudhuri Subhadra
Published: June 2006

Phase pure rutile SnO2 nanoparticles and nanorods were prepared by solvothermal technique. The diameters of the nanoparticles were in the range of 5–10nm while the length and width of the nanorods were within 100–200nm and ∼50nm, respectively. The crystal structure, morphology, and sizes of the SnO2 nanocrystals were determined by x-ray diffraction and transmission electron microscopy. Optical properties of the products were explored by Fourier transform infrared spectroscopy, optical absorption, photoluminescence, and Raman studies. Size dependent blueshift of the optical band gap of the nanocrystals was observed due to quantum confinement. The photoluminescence spectra showed broad UV emission. The influence of the particle size and the morphology of the SnO2 nanocrystals on the vibration band in the Raman scattering was studied.
Planar spin valves fabricated on manganite epitaxial thin films
Authors: Pallecchi I. , Bellingeri E. , Canu G. , Caviglia A. , Siri A. S. , Marré D.
Published: June 2006

We fabricate micrometric constrictions in manganite epitaxial thin films by atomic force microscope local anodization. We demonstrate the possibility of realizing planar spin valve devices, exhibiting hysteretic transport behavior as a function of the external magnetic field, associated with magnetic domains orientation. We also observe nonlinear current-voltage characteristics which become increasingly linear in external field and we attribute this crossover to the disappearance of energy barriers of domain walls at the constriction.
Thermically tuned nematic guide
Authors: Corella-Madueño Adalberto , Reyes Juan Adrián
Published: June 2006

We consider a cylindrical fiber with a liquid crystal core satisfying homeotropic weak anchoring boundary conditions. We find the different textures of the nematic inside the cylinder obtained by changing the temperature. We calculate exactly the spatial distribution of the transverse magnetic modes in the guide as a function of temperature of the system by using a numerical scheme.
Growth optimization and structural analysis for ferromagnetic Mn-doped ZnO layers deposited by radio frequency magnetron sputtering
Authors: Abouzaid M. , Ruterana P. , Liu C. , Morkoç H.
Published: June 2006

The effect of the deposition temperature on the crystalline quality of (Zn,Mn)O is investigated in thin films prepared by radio frequency magnetron sputtering on c-plane sapphire and GaN substrates. The layers are made of a 0.5μm Mn-doped layer towards the surface on top of a 150nm pure ZnO buffer. Depending on the deposition temperature, the layers can exhibit a columnar structure; the adjacent domains are rotated from one another by 90°, putting [101¯0] and [11¯20] directions face to face. At high Mn concentration the columnar structure is blurred by the formation of Mn rich precipitates. Only one variety of domains is observed at an optimal deposition temperature of 500°C: they are slightly rotated around the [0001] axis (mosaic growth) and bounded by threading dislocations.