bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared absorption from OH− ions adjacent to lithium acceptors in hydrothermally grown ZnO
Authors: Halliburton L. E. , Wang Lijun , Bai Lihua , Garces N. Y. , Giles N. C. , Callahan M. J. , Wang Buguo
Published: December 2004

An intense infrared absorption band has been observed in a hydrothermally grown ZnO crystal. At 12K, the band peaks near 3577.3cm−1 and has a half width of 0.40cm−1, and at 300K, the band peaks at 3547cm−1 and has a half width of 41.3cm−1. This absorption band is highly polarized, with its maximum intensity occurring when the electric field of the measuring light is parallel to the c axis of the crystal. Photoinduced electron-paramagnetic-resonance experiments show that the crystal contains lithium acceptors (i.e., lithium ions occupying zinc sites). Lithium and OH− ions are present in the crystal because lithium carbonate, sodium hydroxide, and potassium hydroxide are used as solvents during the hydrothermal growth. In the as-grown crystal, some of the lithium acceptors will have an OH− ion located at an adjacent axial oxygen site (to serve as a passivator), and we assign the 3577.3-cm−1 band observed at 12K to these neutral complexes. Our results illustrate the role of hydrogen as a charge compensator for singly ionized acceptors in ZnO.
Soft x-ray resonant magneto-optical Kerr effect as a depth-sensitive probe of magnetic heterogeneity: Its application to resolve helical spin structures using linear p polarization
Authors: Lee Ki-Suk , Kim Sang-Koog , Kortright J. B.
Published: December 2004

We have calculated the soft x-ray resonant Kerr intensities as a function of the incident grazing angle of linearly p-polarized waves from the model spin structures, where the chirality (handedness) of the spin spirals (twist in depth) in a magnetic layer and the periodicity of a unit spiral are designed to vary. Variations in the chirality and the periodicity lead to noticeable changes in the Kerr intensity versus the grazing angle, which is due not only to a large sensitivity of the Kerr intensity of the linear p polarization to both the magnitude and direction of the transverse components of magnetizations, but also to a large dependence of the depth sensitivity on the grazing angle at the resonance regions. The measurement and analysis of the specular Kerr intensity are relatively straightforward in determining the inhomogeneous spin structures in depth, compared to those of the Kerr rotation and ellipticity. This is proven to be a convenient and useful probe to determine the handedness of spin spiral structures, as well as to resolve the detailed magnetic heterostructures in depth in ultrathin-layered films.
Solvent-enhanced dye diffusion in polymer thin films for polymer light-emitting diode application
Authors: Graves-Abe Troy , Pschenitzka Florian , Jin H. Z. , Bollman Brent , Sturm J. C. , Register R. A.
Published: December 2004

The method of solvent-enhanced dye diffusion for patterning full-color (red, green, and blue) polymer light-emitting diode displays was investigated in detail. After local dry transfer of dye onto a device polymer film, the dye remains on the surface of the polymer layer and must be diffused into the polymer for efficient emission. Exposure of the polymer to solvent vapor at room temperature increases the dye-diffusion coefficient by many orders of magnitude, allowing rapid diffusion of the dye into the film without a long, high-temperature anneal that can degrade the polymer. The increase in diffusion is due to absorption of the solvent vapor into the polymer film, which increases the polymer thickness and decreases its effective glass transition temperature Tg,eff. Measurements of the polymer in solvent vapor indicate that its thickness varies roughly linearly with pressure and inversely with temperature, with thickness increases as large as 15% often observed. A model based on Flory-Huggins theory is used to describe these results. The diffusion of the dye into the polymer was evaluated by photoluminescence and secondary-ion mass spectroscopy. This dye-diffusion increase is largest for high solvent-vapor partial pressures and, most surprisingly, is larger at lower temperatures than at higher temperatures. This anomalous temperature dependence is due to the increased solvent-vapor absorption and consequent reduction in the effective glass-transition temperature at lower temperatures.
“Migration energy” for impurity diffusion in crystalline solids: A closer look
Authors: Ramanarayanan Panchapakesan , Srinivasan Balaji , Cho Kyeongjae , Clemens Bruce M.
Published: December 2004

Point defect mediated diffusion of impurities in crystalline materials involves a sequence of several processes, which are repeated in varying combinations a multiple number of times. The concept of “activation energy” has been borrowed from simple chemical reactions, where the reactants are postulated to form an activated complex before decomposing into products. While ideas such as the smallest rate (or the rates of a select few “important” processes) being the rate determining step and hence the overall activation energy may be applicable in the case of chemical reactions that are sequential, such ideas are shown to be too simplistic to be applicable to describe diffusion in the crystalline phase. In this paper, we present a systematic scheme to arrive at the macroscopic activation energy in terms of the energy barriers for the constituent microscopic processes. We apply this scheme to the case of vacancy mediated diffusion of impurities in a diamond lattice. We present results of numerical verification of the scheme performed by kinetic Monte Carlo simulations based on the energy barriers obtained using the density functional theory within the local density approximation. We then present observations on the dependence of the macroscopic “migration energy” on the energy barriers for the constituent microscopic processes. As an illustration of how the energy barriers for the microscopic processes can be affected, we present first principles calculation of the effect of biaxial strain on these energy barriers.
A positron lifetime study of lanthanum and niobium doped Pb(Zr0.6Ti0.4)O3
Authors: Gottschalk S. , Hahn H. , Balogh A. G. , Puff W. , Kungl H. , Hoffmann M. J.
Published: December 2004

A study of vacancy-related defects in lanthanum and niobium doped PbZr0.6Ti0.4O3 with dopant concentrations of 0–6 and 0–4mol%, respectively has been performed using positron annihilation spectroscopy X-ray diffraction, and photoelectron spectroscopy. Positron lifetime as well as coincidence annihilation radiation Doppler line broadening measurements were carried out. It was found that the samples exhibit vacancylike defects that act as positron traps. Two main defect lifetime components were found in both sample sets one at ≈150ps and one at ≈300ps. These defect trapping sites can be attributed to single oxygen vacancies and A-site vacancies, respectively. Doppler line broadening measurements, however, do not show significant changes as a function of dopant concentrations in terms of shape S and wing W parameters.
Dielectric properties of Pb(Zn1∕3Ta2∕3)O3-modified Pb(Mg1∕3Nb2∕3)O3-PbTiO3 perovskite ceramics
Authors: Kim Jee-Su , Kim Nam-Kyoung
Published: December 2004

Perovskite solid solutions of 0.2Pb(Zn1∕3Ta2∕3)O3-0.8Pb[(Mg1∕3Nb2∕3),Ti]O3 were synthesized and characterized. Developed structures and the crystallographic symmetries as well as the lattice parameters were investigated. Weak-field dielectric constant and loss values of the ceramics were measured as functions of composition, temperature, and frequency. The dielectric constant spectra in the paraelectric temperature region were also analyzed in terms of diffuseness in the phase transition modes. The results were compared with other substituents of Pb(Mg1∕3Ta2∕3)O3, Pb(Mg1∕3Nb2∕3)O3, as well as Pb(Zn1∕3Nb2∕3)O3.
Low dark current and blue enhanced a-Si:H∕a-SiC:H heterojunction n-i-δi-p photodiode for imaging applications
Authors: Servati Peyman , Vygranenko Yuri , Nathan Arokia , Morrison Scott , Madan Arun
Published: December 2004

This paper presents an a-Si:H∕a-SiC:H heterojunction n-i-δi-p photodiode with low dark current and enhanced short wavelength responsivity suitable for low-level light detection applications. Junction properties and carrier transport are investigated in terms of current-voltage characteristics, photocurrent transient measurements, and spectral photoresponse. It is demonstrated that introduction of a thin (∼40Å) undoped a-SiC:H buffer (δi) at the p-i interface significantly reduces the reverse dark current and recombination losses at this interface. A dark current density of ∼10pA∕cm2 at reverse bias of 1V is achieved for the n-i-δi-p structure, in which the p-type a-SiC:H window layer and the undoped δi buffer layer have a band gap of 2eV.
Enhanced charge separation in chlorophyll a solar cell by gold nanoparticles
Authors: Barazzouk Saïd , Hotchandani Surat
Published: December 2004

An efficient organic photoelectrochemical cell based on chlorophyll a (Chla) and gold nanoparticles is constructed. The enhanced performance of this cell is due to the beneficial role of gold nanoparticles in accepting and shuttling the photogenerated electrons in Chla to the collecting electrode. This produces a long-distance charge-separated state, resulting into an enhancement in charge separation efficiency.
Conversion of p-type to n-type diamond by exposure to a deuterium plasma
Authors: Kalish R. , Saguy C. , Cytermann C. , Chevallier J. , Teukam Z. , Jomard F. , Kociniewski T. , Ballutaud D. , Butler J. E. , Baron C. , Deneuville A.
Published: December 2004

The lack of a shallow donor in diamond with reasonable room temperature conductivity has been a major obstacle, until now, for the realization of many diamond based electronic devices. Most recently it has been shown that exposure of p-type (B doped) homoepitaxial diamond layers to a deuterium plasma can result in the formation of n-type diamond with a shallow donor state (Ea=0.34eV) and high room temperature mobility (430cm2∕Vs) [Z. Teukam et al., Nat. Mater. 2, 482 (2003); C. Saguy et al., Diamond Relat. Mater. 13, 700 (2004)]. Experimental results, based on the comparison of secondary ion mass spectrometry profiles of B and D and Hall effect measurements at different temperatures are presented. They confirm the previous speculation that some deuterium related complex is responsible for the donor activity in diamond. These donors are shown to be formed in a two-step process. First, deuterium diffuses into the entire B containing layer rather slowly, being trapped by the boron acceptors and passivating them. Once all B have formed complexes, further exposure to a D plasma results in the formation of a layer that contains about twice as many D atoms as the B content. This step is the one that gives rise to the excellent n-type features observed. The most recent theoretical attempts to explain the donor state by simulations of various boron-hydrogen complexes in diamond are reviewed.
The study of mass transport of acetone in polycarbonate
Authors: Ouyang Hao , Wu Ming-Tsang , Ouyang Wen
Published: December 2004

The mechanism of mass transport and associated crystallization in polycarbonate (PC) were studied. Based on Harmon’s model for case I (or Fickian), case II (or swelling), and anomalous transport, the data of the initial period of mass uptake were analyzed. Due to the initially small dimensional variation of the PC and the initially small amount of crystallization, the influence of crystallinity on the mass transport can be ignored. The diffusivity in case I and the velocity in case II both followed the Arrhenius relationship. Case II dominated the transport process as the activation energy of case II is lower than that of case I. This finding was further verified by measuring the movement of diffusion fronts with a carefully selected observation coordinate. A distinct transport front was identified from the measurements of optical microscope and the microhardness. This investigation addresses more complicated microstructures of PC during mass transport.
Highly disordered intergrowths in Sr2FeMoO6
Authors: Liao X. Z. , Sharma A. , Wei M. , MacManus-Driscoll J. L. , Branford W. , Cohen L. F. , Bugoslavsky Y. , Zhu Y. T. , Peterson D. E. , Jiang Y. B. , Xu H. F.
Published: December 2004

Two Sr2FeMoO6 samples, synthesized under different conditions and showing very different magnetotransport properties, were analyzed using transmission electron microscopy. The different magnetoresistive behaviors observed in the two samples coincide with the formation of different amounts of striped areas intergrown in the samples. The striped areas are comprised of a disordered and cation deficient phase, SrFe1−x−yMox−zO3−δ. The sample magnetization and magnetoresistance values decrease significantly with an increased presence of the striped phase. The striped phase was promoted by typical reducing formation conditions for Sr2FeMoO6 in Ar-1% H2 gas.
Physical mechanism for orientation dependence of ferroelectric fatigue in Pb(Zn1∕3Nb2∕3)O3-5%PbTiO3 crystals
Authors: Lee Jung-Kun , Yi Jae Yun , Hong Kug-Sun
Published: December 2004

The underlying phenomenology of the crystallographic orientation dependence on ferroelectric fatigue behavior was investigated in rhombohedral Pb(Zn1∕3Nb2∕3)O3-5%PbTiO3 (PZN-5PT) crystals. It was recently found that an electric field (E field) application along the ⟨001⟩ direction of PZN-5PT crystal did not induce the fatigue to 105cycles of bipolar electric field cycling (switching), while the ferroelectric fatigue became evident from 103cycles of polarization switching along the ⟨111⟩ direction. In this study, the dependence of ferroelectric fatigue on the crystal orientation is explained by changes in internal stress, switching mechanisms, and domain configuration. The magnitude of the in-plane tensile strain was a maximum during a domain switching in ⟨111⟩ oriented crystals, resulting in the suppressed motion of domain boundaries in ⟨111⟩ oriented crystals. In addition to the stress, differences in domain switching mechanisms and domain boundary density for ⟨001⟩ and ⟨111⟩ oriented crystals contributed to the orientation dependence of ferroelectric fatigue. Sideways domain growth became dominant and domain width increased when the E field was applied along the ⟨111⟩ direction. Sideways domain growth of ⟨111⟩ oriented crystal swept oxygen vacancies of the domains during the consecutive switching process, leading to the effective accumulation of oxygen vacancies at the domain boundaries. Smaller domain boundary densities found in ⟨111⟩ oriented crystals, in comparison to ⟨100⟩ oriented crystals, also contributed to the increase in the density of accumulated oxygen vacancies at domain boundaries after sweeping oxygen vacancies of the domains, due to the impact of increased E-field cycling and cumulative switching. High in-plane tensile stress and a high concentration of oxygen vacancies at the domain boundaries due to sideways growth and small domain boundary density were suggested to pin the movement of domain boundaries and enhance the fatigue in ⟨111⟩ oriented crystals.
Derivation of the switch-on parameters in the dual channel double heterostructure optoelectronic switch
Authors: Taylor G. W. , Opper H. , Cai J. , Garber B. , Basilica R.
Published: December 2004

The switching mechanism in the dual channel double heterostructure optoelectronic switch is investigated using a mathematically precise definition to describe the conditions at the transition between the off state and negative resistance regions on the thyristor I–V curve. Analytical expressions of quantum well density, voltage, and current parameters at switching are found for both three terminal electrical injection and optical input. Agreement is found to be within 2% of full numerical simulation. Using derivatives of the analytic functions to determine the various current gains, the classic thyristor switching equations due to avalanching are found to be inaccurate and that instead switching is more appropriately determined by the rate of change of charge populations in the control regions compared to the other charges in the device. This analysis is supported by measurements of three terminal thyristor operation of the thyristor device.
Prism coupling technique investigation of elasto-optical properties of thin polymer films
Authors: Ay Feridun , Kocabas Askin , Kocabas Coskun , Aydinli Atilla , Agan Sedat
Published: December 2004

The use of thin polymer films in optical planar integrated optical circuits is rapidly increasing. Much interest, therefore, has been devoted to characterizing the optical and mechanical properties of thin polymer films. This study focuses on measuring the elasto-optical properties of three different polymers; polystyrene, polymethyl-methacrylate, and benzocyclobutane. The out-of-plane elastic modulus, refractive index, film thickness, and birefringence of thin polymer films were determined by means of the prism coupling technique. The effect of the applied stress on the refractive index and birefringence of the films was investigated. Three-dimensional finite element method analysis was used so as to obtain the principal stresses for each polymer system, and combining them with the stress dependent refractive index measurements, the elasto-optic coefficients of the polymer films were determined. It was found that the applied stress in the out-of-plane direction of the thin films investigated leads to negative elasto-optic coefficients, as observed for all the three thin polymer films.
Determination of strain localization in aluminum alloys using laser-induced photoelectron emission
Authors: Cai M. , Langford S. C. , Levine L. E. , Dickinson J. T.
Published: December 2004

Uniaxial tensile deformation of oxidized aluminum produces low work-function patches of fresh metal which can be probed by measurements of photoelectron emission during exposure to ultraviolet light. We report measurements of photoelectron emission during uniaxial testing of polycrystalline Al(1200), Al–Mn(3003), Al–Mg(5052), and Al–Mg–Si(6061) alloys where the broad face of the gauge section is exposed to pulsed excimer laser radiation (248nm). We show that strain localization alters the distribution of fresh surface metal produced by subsequent deformation. The transition from more homogenous deformation to the principally localized deformation associated with shear bands is associated with a discontinuity in the growth rate of photoelectron intensities versus time. At this transition, the rate of fresh metal production along the illuminated portion of gauge section decreases. In all four materials, the strain at the discontinuity is somewhat below the strain given by the Considère criterion, consistent with the role of microstructural effects in strain localization. We suggest that these photoelectron measurements constrain quantitative models of strain localization.
Metastable boron active concentrations in Si using flash assisted solid phase epitaxy
Authors: Jain S. H. , Griffin P. B. , Plummer J. D. , Mccoy S. , Gelpey J. , Selinger T. , Downey D. F.
Published: December 2004

There has been considerable interest recently, in the formation of the source drain junctions of metal oxide semiconductor transistors using solid phase epitaxy (SPE) to activate the dopants rather than a traditional high temperature anneal. Previous studies have shown that this method results in high dopant activation as well as shallow junctions (due to the small thermal budget). In this we study the effect the temperature of SPE regrowth has on the boron activation. We find that boron activation has a monotonically increasing dependence on the temperature. Significantly, we show that by carrying out the SPE regrowth at temperatures above 1050°C, it is possible to obtain active concentrations well above the electrical solubility limits.
Wormhole liquid crystal display modes
Authors: Inaba M. , Okada H. , Onnagawa H.
Published: December 2004

Wormhole liquid crystal display modes are proposed. Micron-sized and randomly arranged holes on upper and lower electrodes are formed in order to deform a liquid crystal alignment. By optimizing cell thickness, the calculation of director profiles and transmittance based on Frank’s continuum theory and Jones matrix are carried out and the maximum transmittance is compared with experimental results. Good transmittance versus voltage characteristics was obtained regardless of the sign of the dielectric anisotropy. From optical microscopy, radial and spherical domains were found at the electrode holes. The position of these domains was randomly arranged and its shape was that of a half-cut droplet. Electro-optical response and viewing angle characteristics have also been evaluated.
Small angle light scattering and clusters of thermal donors in Si
Authors: Kraitchinskii A. , Kras’ko M. , Neimash V. , Shpinar L. , Tishchenko V. , Voitovich V. , Goushcha A. O. , Metzler R. A.
Published: December 2004

This paper reports the application of small angle light scattering technique for characterization of Si samples with clusters of thermal donors. The observed dependencies of the intensity of scattered light on the period of thermal treatment of studied samples are interpreted by a model involving the multiple light scattering events. The study shows the effect of increased oxygen concentration at places where relatively small clusters of thermal donors are formed. This offers an explanation for the “small diffusion coefficient of oxygen” paradox arising during modeling of the formation kinetics of thermal donors in silicon.
Modulated whistler wave packets associated with density perturbations
Authors: Kourakis I. , Shukla P. K.
Published: December 2004

The parametric interaction between large amplitude whistlers and ponderomotively driven quasistationary density perturbations in plasmas is considered. A cubic nonlinear Schrödinger equation is derived and then solved analytically to show the occurrence of modulational instability as well as the existence of bright and dark envelope solitons, which are referred to as whistlerons. Explicit whistleron profiles are presented and the relevance to space and laboratory plasmas is discussed.
Enhanced light extraction efficiency from organic light emitting diodes by insertion of a two-dimensional photonic crystal structure
Authors: Do Young Rag , Kim Yoon-Chang , Song Young-Woo , Lee Yong-Hee
Published: December 2004

We studied the characteristics of organic light emitting diode (OLED) devices containing two-dimensional (2D) SiO2∕SiNx photonic crystal (PC) layers. The finite-difference time-domain (FDTD) method was employed for the design and analysis of the PC OLED. Based on the design parameters derived from the FDTD calculations, a 2D PC layer was introduced on the glass substrate of a typical OLED structure by two-step irradiated hologram lithography and reactive ion etching. Experiments showed that incorporation of the PC layer improved the light extraction efficiency by over 50% compared to the conventional OLED, without noticeable degradation in electrical characteristics, under typical operating conditions. This improvement originates from the liberation of the photons trapped in the high-index guiding layers.
Dynamic switching in tilted and conventional perpendicular recording media
Authors: Gao Kai-Zhong , Bertram H. Neal
Published: December 2004

The single-particle energy surface model is utilized to study the switching field limit and the magnetization ringing in the dynamic reversal process. A simple analysis of magnetization ringing is shown and a method to reduce magnetization ringing in dynamic switching is suggested. We show that for the applied field smaller than the grain anisotropy field, the magnetization ringing is reduced with decreasing applied field magnitude. The energy surface model also predicts that for high data rate magnetic recording, the dynamic switching field may be well below the Stoner–Wohlfarth value. The magnetic write width can be much larger than the physical write pole width in perpendicular magnetic recording systems.
Transient and ac electrical transport under forward and reverse bias conditions in aluminum/porous silicon∕p-cSi structures
Authors: Theodoropoulou M. , Karahaliou P. K. , Krontiras C. A. , Georga S. N. , Xanthopoulos N. , Pisanias M. N. , Tsamis C. , Nassiopoulou A. G.
Published: December 2004

Dielectric impedance measurements as well as transient current–voltage (I–V) characteristics under conditions of forward and reverse bias are reported in aluminum/porous silicon (PS)∕p-cSi structures at different temperatures. Under reverse bias conditions, the electrical conduction of the structures can be modeled by a simple equivalent circuit of two parallel RC networks in series combination, representing a bulk and a junction region. The bulk conduction is ohmic. From the detailed analysis of the PS/cSi junction, the carrier concentration NA and the depletion layer width W are evaluated at each temperature. The elapsed time t0 from the onset of the square pulse, at which the transition from the dominant bulk resistance to junction conduction takes place, is a function of temperature. As the temperature decreases, conduction due to bulk resistance dominates over junction conduction. On the other, hand forward conduction is dominated from the bulk. Two conduction mechanisms are present. As the time proceeds, Poole–Frenkel conduction follows an ohmic conduction. The time after the onset of the square voltage pulse, at which this turnover takes place, is a function of temperature.
Pressure-sensitive dissipation in elastomers and its implications for the detonation of plastic explosives
Authors: Knauss Wolfgang G. , Sundaram Sairam
Published: December 2004

The role of binder deformation and the associated energy dissipation on the detonation sensitivity of plastically bonded explosives is considered by accounting for dilatation-sensitive viscoelastic shear response. Following the observation that pressurization can prolong the relaxation and retardation times of a viscoelastic elastomer tremendously, the implications of this phenomenon are considered for a thin layer of a model elastomer, sheared between two blocks of octahydro-1,3,5,7- tetranitro-1,3,5,7-tetrazocine under deformation rates typical in detonation scenarios. The consequences of concurrent pressurization on heat generation are examined using small deformation as well as finite deformation analyses. While a dilatation-insensitive viscoelastic behavior generates notable temperature increases, they are insufficient to cause ignition of the explosive. However, taking into account the increased dissipation associated with the pressure-induced changes in the intrinsic time scale and viscosity of the elastomer leads to temperature rises on the order of 1000°C, which are consistent with “hot spots” held responsible for the initiation of detonation in the adjacent explosive grains.
Analytical k∙p method: Anisotropic optical matrix elements in (11N)-oriented quantum wells
Authors: Chen Chun-Nan
Published: December 2004

This paper develops a k∙p method with analytical expressions to investigate the optical anisotropy of (11N)-oriented In0.53Ga0.47As∕InP quantum wells. The proposed method is not only more straightforward than the conventional k∙p method, but also more efficient. The present results reveal that in-plane anisotropy is associated with low-symmetry crystal microstructures. Hence, of the various (11N)-oriented quantum wells considered in the present study, the low-symmetry (110) sample exhibits the most obvious anisotropy, while the high-symmetry (001) and (111) samples exhibit isotropy.
Impedance magnetocardiography: Experiments and modeling
Authors: Claycomb J. R. , Vajrala V. , Nawarathna D. , Miller J. H.
Published: December 2004

We report on impedance magnetocardiography studies using high-Tc superconducting quantum interference device (SQUID) magnetometers in a partially shielded environment. The SQUID detects magnetic-field variations due to impedance changes in the thorax at 15kHz. SQUID measurements are compared to impedance magnetocardiograms recorded at 100kHz using a copper pickup coil. An electromagnetic finite element model is used to simulate the distribution of ac during the cardiac cycle.
Continuous or catastrophic solid–liquid transition in jammed systems
Authors: Coussot P. , Roussel N. , Jarny S. , Chanson H.
Published: December 2004

Pasty materials encountered in industry and in earth science are intermediate between solids and liquids either in terms of their internal structure (disordered but jammed) or from a mechanical point of view. Our results indicate that the apparent behavior of a particulate system (soils, suspensions, clays, etc.) can range from liquid-like to soil or solid-like depending on the relative importance of the energy supplied to it and its “state of jamming” which evolves in time, and the transition from one state to another may appear either continuous or catastrophic.
Discrete breather modes associated with vertical dust grain oscillations in dusty plasma crystals
Authors: Kourakis I. , Shukla P. K.
Published: December 2004

Accounting for the lattice discreteness and the sheath electric field nonlinearity in dusty plasma crystals, it is demonstrated that highly localized structures (discrete breathers) involving vertical (transverse, off-plane) oscillations of charged dust grains may exist in a dust lattice. These structures correspond to either extremely localized bright breather excitations (pulses) or dark excitations composed of dips/voids. Explicit criteria for selecting different breather modes are presented.
Corrected Article: “Experimental observation of nonspherically-decaying radiation from a rotating superluminal source” [J. Appl. Phys. 96, 4614 (2004)]
Authors: Ardavan A. , Hayes W. , Singleton J. , Ardavan H. , Fopma J. , Halliday D.
Published: December 2004

We describe the experimental implementation of a superluminal (i.e., faster than light in vacuo) polarization current distribution that both oscillates and undergoes centripetal acceleration. Theoretical treatments predict that the radiation emitted by each volume element of the superluminally moving distribution pattern will comprise a Čerenkov-like envelope with two sheets that meet along a cusp. Correspondingly, the emission from the experimental machine is found to be tightly beamed in both the azimuthal and polar directions. The beaming is frequency independent and has a sharply defined and unchanging geometry determined only by the speed and path of the moving distribution pattern, i.e., by the parameters governing the structure of the Čerenkov-like envelopes. In addition, over a restricted range of angles, we detect the presence of cusps in the emitted radiation. These, which are due to the focusing of wave fronts on a propagating space curve, result in the reception, during a short time period, of radiation emitted over a considerably longer period of (retarded) source time. The intensity of the radiation at these angles was observed to decline more slowly with increasing distance from the source than would the emission from a conventional antenna. The angular distribution of the emitted radiation and the properties associated with the cusps are in good quantitative agreement with theoretical models of superluminal sources once the effect of reflections from the earth’s surface are taken into account. In particular, the prediction that the beaming and the slow decay should extend into the far zone has been tested to several hundred Fresnel distances (Rayleigh ranges). The excellent agreement between the theoretical calculations and the data suggests that the apparatus achieves precise and reproducible control of the polarization current and that similar machines could be of general interest for studying and utilizing the novel effects associated with superluminal electrodynamics.
Dark Matter and the Tully–Fisher Law
Authors: Freeman Ken C.
Published: December 2004

I discuss the origin of the Tully–Fisher law in the context of the observed scaling laws for dark halos.
Temporal and spatial distribution and abundance of blue swimmer crab (Portunus pelagicus) larvae in a temperate gulf
Authors: Bryars Simon R. , Havenhand Jon. N.
Published: December 2004

A plankton-sampling programme for blue swimmer crab (Portunus pelagicus) larvae was conducted in the temperate waters of Gulf St Vincent, South Australia, to investigate: (1) if larval hatching is seasonal; (2) if larvae are restricted to surface waters; (3) if larvae are hatched offshore; and (4) if larval development occurs offshore. The temporal and spatial distribution and abundance of larvae indicated that hatching and zoeal development occur mainly in deeper offshore waters during the warmer months of November to March, and that zoeal development occurs in a range of depths from the neuston to at least 14 m. Although peaks in abundance usually occurred in the upper 3 m, zoeae were distributed throughout the water column, with the majority occurring in sub-surface waters below 1 m depth. There was no evidence for a daylight ontogenetic or tidal vertical migration in the four zoeal stages. Limited sampling revealed no evidence for a diurnal vertical migration in stage-1 zoea. Although the seasonal and inshore-offshore patterns of hatching observed in the study were typical for a portunid species, the broad vertical distribution differed from that observed for P. pelagicus in previous studies.
Functional specialization within a vesicle tethering complex
Authors: Wiederkehr Andreas , De Craene Johan-Owen , Ferro-Novick Susan , Novick Peter
Published: December 2004

The exocyst is an octameric protein complex required to tether secretory vesicles to exocytic sites and to retain ER tubules at the apical tip of budded cells. Unlike the other five exocyst genes, SEC3, SEC5, and EXO70 are not essential for growth or secretion when either the upstream activator rab, Sec4p, or the downstream SNARE-binding component, Sec1p, are overproduced. Analysis of the suppressed sec3Δ, sec5Δ, and exo70Δ strains demonstrates that the corresponding proteins confer differential effects on vesicle targeting and ER inheritance. Sec3p and Sec5p are more critical than Exo70p for ER inheritance. Although nonessential under these conditions, Sec3p, Sec5p, and Exo70p are still important for tethering, as in their absence the exocyst is only partially assembled. Sec1p overproduction results in increased SNARE complex levels, indicating a role in assembly or stabilization of SNARE complexes. Furthermore, a fraction of Sec1p can be coprecipitated with the exoycst. Our results suggest that Sec1p couples exocyst-mediated vesicle tethering with SNARE-mediated docking and fusion.
Ameloblastin is a cell adhesion molecule required for maintaining the differentiation state of ameloblasts
Authors: Fukumoto Satoshi , Kiba Takayoshi , Hall Bradford , Iehara Noriyuki , Nakamura Takashi , Longenecker Glenn , Krebsbach Paul H. , Nanci Antonio , Kulkarni Ashok B. , Yamada Yoshihiko
Published: December 2004

Tooth morphogenesis results from reciprocal interactions between oral epithelium and ectomesenchyme culminating in the formation of mineralized tissues, enamel, and dentin. During this process, epithelial cells differentiate into enamel-secreting ameloblasts. Ameloblastin, an enamel matrix protein, is expressed by differentiating ameloblasts. Here, we report the creation of ameloblastin-null mice, which developed severe enamel hypoplasia. In mutant tooth, the dental epithelium differentiated into enamel-secreting ameloblasts, but the cells were detached from the matrix and subsequently lost cell polarity, resumed proliferation, and formed multicell layers. Expression of Msx2, p27, and p75 were deregulated in mutant ameloblasts, the phenotypes of which were reversed to undifferentiated epithelium. We found that recombinant ameloblastin adhered specifically to ameloblasts and inhibited cell proliferation. The mutant mice developed an odontogenic tumor of dental epithelium origin. Thus, ameloblastin is a cell adhesion molecule essential for amelogenesis, and it plays a role in maintaining the differentiation state of secretory stage ameloblasts by binding to ameloblasts and inhibiting proliferation.
Apoptotic Cells with Oxidation-specific Epitopes Are Immunogenic and Proinflammatory
Authors: Chang Mi-Kyung , Binder Christoph J. , Miller Yury I. , Subbanagounder Ganesamoorthy , Silverman Gregg J. , Berliner Judith A. , Witztum Joseph L.
Published: December 2004

Oxidation of low density lipoprotein (LDL) generates a variety of oxidatively modified lipids and lipid-protein adducts that are immunogenic and proinflammatory, which in turn contribute to atherogenesis. Cells undergoing apoptosis also display oxidized moieties on their surface membranes, as determined by binding of oxidation-specific monoclonal antibodies. In the present paper, we demonstrated by mass spectrometry that in comparison with viable cells, membranes of cells undergoing apoptosis contain increased levels of biologically active oxidized phospholipids (OxPLs). Indeed, immunization of mice with syngeneic apoptotic cells induced high autoantibody titers to various oxidation-specific epitopes of oxidized LDL, including OxPLs containing phosphorylcholine, whereas immunization with viable thymocytes, primary necrotic thymocytes, or phosphate-buffered saline did not. Reciprocally, these antisera specifically bound to apoptotic cells through the recognition of oxidation-specific epitopes. Moreover, splenocyte cultures from mice immunized with apoptotic cells spontaneously released significant levels of T helper cell (Th) 1 and Th2 cytokines, whereas splenocytes from controls yielded only low levels. Finally, we demonstrated that the OxPLs of apoptotic cells activated endothelial cells to induce monocyte adhesion, a proinflammatory response that was abrogated by an antibody specific to oxidized phosphatidylcholine. These results suggest that apoptotic cell death generates oxidatively modified moieties, which can induce autoimmune responses and a local inflammatory response by recruiting monocytes via monocyte–endothelial cell interaction.
Crucial Role for Ecto-5′-Nucleotidase (CD73) in Vascular Leakage during Hypoxia
Authors: Thompson Linda F. , Eltzschig Holger K. , Ibla Juan C. , Van De Wiele C. Justin , Resta Regina , Morote-Garcia Julio C. , Colgan Sean P.
Published: December 2004

Extracellular adenosine has been widely implicated in adaptive responses to hypoxia. The generation of extracellular adenosine involves phosphohydrolysis of adenine nucleotide intermediates, and is regulated by the terminal enzymatic step catalyzed by ecto-5′-nucleotidase (CD73). Guided by previous work indicating that hypoxia-induced vascular leakage is, at least in part, controlled by adenosine, we generated mice with a targeted disruption of the third coding exon of Cd73 to test the hypothesis that CD73-generated extracellular adenosine functions in an innate protective pathway for hypoxia-induced vascular leakage. Cd73−/− mice bred and gained weight normally, and appeared to have an intact immune system. However, vascular leakage was significantly increased in multiple organs, and after subjection to normobaric hypoxia (8% O2), Cd73−/− mice manifested fulminant vascular leakage, particularly prevalent in the lung. Histological examination of lungs from hypoxic Cd73−/− mice revealed perivascular interstitial edema associated with inflammatory infiltrates surrounding larger pulmonary vessels. Vascular leakage secondary to hypoxia was reversed in part by adenosine receptor agonists or reconstitution with soluble 5′-nucleotidase. Together, our studies identify CD73 as a critical mediator of vascular leakage in vivo.
The ETS Transcription Factor Spi-B Is Required for Human Plasmacytoid Dendritic Cell Development
Authors: Schotte Remko , Nagasawa Maho , Weijer Kees , Spits Hergen , Blom Bianca
Published: December 2004

A number of transcription factors that act as molecular switches for hematopoietic lineage decisions have been identified. We recently described the ETS transcription factor Spi-B to be exclusively expressed in plasmacytoid dendritic cells (pDCs), but not in myeloid DCs. To assess whether Spi-B is required for pDC development we used an RNA interference knock down approach to specifically silence Spi-B protein synthesis in CD34+ precursor cells. We observed that a knock down of Spi-B mRNA strongly inhibited the ability of CD34+ precursor cells to develop into pDCs in both in vitro assays as well as in vivo upon injection into recombination activating gene 2−/− γ common−/− mice. The observed effects were restricted to the pDC lineage as the differentiation of pro–B cells and CD14+ myeloid cells was not inhibited but slightly elevated by Spi-B knock down. Knock down of the related ETS factor PU.1 also inhibited in vitro development of CD34+ cells into pDCs. However, in contrast to Spi-B, PU.1 knock down inhibited B cell and myeloid cell development as well. These results identify Spi-B as a key regulator of human pDC development.
Solution structure of the rhodanese homology domain At4g01050(175–295) from Arabidopsis thaliana
Authors: Pantoja‐Uceda David , López‐Méndez Blanca , Koshiba Seizo , Inoue Makoto , Kigawa Takanori , Terada Takaho , Shirouzu Mikako , Tanaka Akiko , Seki Motoaki , Shinozaki Kazuo , Yokoyama Shigeyuki , Güntert Peter
Published: December 2004

The three‐dimensional structure of the rhodanese homology domain At4g01050(175–195) from Arabidopsis thaliana has been determined by solution nuclear magnetic resonance methods based on 3043 upper distance limits derived from NOE intensities measured in three‐dimensional NOESY spectra. The structure shows a backbone root mean square deviation to the mean coordinates of 0.43 Å for the structured residues 7–125. The fold consists of a central parallel β‐sheet with five strands in the order 1–5–4–2–3 and arranged in the conventional counterclockwise twist, and helices packing against each side of the β‐sheet. Comparison with the sequences of other proteins with a rhodanese homology domain in Arabidopsis thaliana indicated residues that could play an important role in the scaffold of the rhodanese homology domain. Finally, a three‐dimensional structure comparison of the present noncatalytic rhodanese homology domain with the noncatalytic rhodanese domains of sulfurtransferases from other organisms discloses differences in the length and conformation of loops that could throw light on the role of the noncatalytic rhodanese domain in sulfurtransferases.
Marginalized Binary Mixed‐Effects Models with Covariate‐Dependent Random Effects and Likelihood Inference
Authors: Wang Zengri , Louis Thomas A.
Published: December 2004

SummaryMarginal models and conditional mixed‐effects models are commonly used for clustered binary data. However, regression parameters and predictions in nonlinear mixed‐effects models usually do not have a direct marginal interpretation, because the conditional functional form does not carry over to the margin. Because both marginal and conditional inferences are of interest, a unified approach is attractive. To this end, we investigate a parameterization of generalized linear mixed models with a structured random‐intercept distribution that matches the conditional and marginal shapes. We model the marginal mean of response distribution and select the distribution of the random intercept to produce the match and also to model covariate‐dependent random effects. We discuss the relation between this approach and some existing models and compare the approaches on two datasets.
Joint Modeling of Longitudinal and Survival Data via a Common Frailty
Authors: Ratcliffe Sarah J. , Guo Wensheng , Ten Have Thomas R.
Published: December 2004

SummaryWe develop a joint model for the analysis of longitudinal and survival data in the presence of data clustering. We use a mixed effects model for the repeated measures that incorporates both subject‐ and cluster‐level random effects, with subjects nested within clusters. A Cox frailty model is used for the survival model in order to accommodate the clustering. We then link the two responses via the common cluster‐level random effects, or frailties. This model allows us to simultaneously evaluate the effect of covariates on the two types of responses, while accounting for both the relationship between the responses and data clustering. The model was motivated by a study of end‐stage renal disease patients undergoing hemodialysis, where we wished to evaluate the effect of iron treatment on both the patients' hemoglobin levels and survival times, with the patients clustered by enrollment site.
A Smooth Test of Goodness‐of‐Fit for Growth Curves and Monotonic Nonlinear Regression Models
Authors: Ducharme Gilles R. , Fontez Bénédicte
Published: December 2004

Summary We propose a goodness‐of‐fit test for growth curves based on an adaptation of the data‐driven smooth test paradigm. It is simple to apply and can assess the fit of a model to a set of growth experiences. A simulation study shows that for small samples, the test holds its level. Moreover, its power is found to be generally greater than existing tests. The article concludes by revisiting the long‐standing problem of validating a model for the growth of human stature.
Measurement Error in Covariates in the Marginal Hazards Model for Multivariate Failure Time Data
Authors: Greene Wendy F. , Cai Jianwen
Published: December 2004

SummaryWe consider measurement error in covariates in the marginal hazards model for multivariate failure time data. We explore the bias implications of normal additive measurement error without assuming a distribution for the underlying true covariate. To correct measurement‐error‐induced bias in the regression coefficient of the marginal model, we propose to apply the SIMEX procedure and demonstrate its large and small sample properties for both known and estimated measurement error variance. We illustrate this method using the Lipid Research Clinics Coronary Primary Prevention Trial data with total cholesterol as the covariate measured with error and time until angina and time until nonfatal myocardial infarction as the correlated outcomes of interest.
Evaluation of Community‐Intervention Trials via Generalized Linear Mixed Models
Authors: Yasui Yutaka , Feng Ziding , Diehr Paula , McLerran Dale , Beresford Shirley A. A. , McCulloch Charles E.
Published: December 2004

Summary In community‐intervention trials, communities, rather than individuals, are randomized to experimental arms. Generalized linear mixed models offer a flexible parametric framework for the evaluation of community‐intervention trials, incorporating both systematic and random variations at the community and individual levels. We propose here a simple two‐stage inference method for generalized linear mixed models, specifically tailored to the analysis of community‐intervention trials. In the first stage, community‐specific random effects are estimated from individual‐level data, adjusting for the effects of individual‐level covariates. This reduces the model approximately to a linear mixed model with the unit of analysis being community. Because the number of communities is typically small in community‐intervention studies, we apply the small‐sample inference method of Kenward and Roger (1997, Biometrics53, 983–997) to the linear mixed model of second stage. We show by simulation that, under typical settings of community‐intervention studies, the proposed approach improves the inference on the intervention‐effect parameter uniformly over both the linearized mixed‐effect approach and the adaptive Gaussian quadrature approach for generalized linear mixed models. This work is motivated by a series of large randomized trials that test community interventions for promoting cancer preventive lifestyles and behaviors.
Binomial‐Type Ordinary Differential Equations of the Third Order
Authors: Sobolevsky S.
Published: December 2004

The complete Painlevé classification of the binomial ordinary differential equations of the third order is built. Eight classes of equations with Painlevé property are obtained. All of these equations are solved in terms of elementary functions and known Painlevé transcendents.