bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduced chemical sputtering of carbon by silicon doping
Authors: Salonen E. , Nordlund K. , Keinonen J. , Runeberg N. , Wu C. H.
Published: September 2002

Doping is a widely used method to enhance the properties of materials. Despite the recently increased understanding of the mechanisms of chemical erosion by low-energy hydrogen ions, the effect of doping on these types of processes is still not well understood. We study the erosion of Si-doped (0–30 at. %) carbon under 20 eV deuterium irradiation using molecular dynamics simulations. We show that the chemical sputtering of carbon decreases with increasing Si concentration. The reasons for the reduced sputtering yield lie in the longer Si–C interaction lengths and efficient dynamic rebonding of hydrocarbon species.
Micromechanics of actuation of ionic polymer-metal composites
Authors: Nemat-Nasser Sia
Published: September 2002

Ionic polymer-metal composites (IPMCs) consist of a polyelectrolyte membrane (usually, Nafion or Flemion) plated on both faces by a noble metal, and is neutralized with certain counter ions that balance the electrical charge of the anions covalently fixed to the backbone membrane. In the hydrated state (or in the presence of other suitable solvents), the composite is a soft actuator and sensor. Its coupled electrical-chemical-mechanical response depends on: (1) the chemical composition and structure of the backbone ionic polymer; (2) the morphology of the metal electrodes; (3) the nature of the cations; and (4) the level of hydration (solvent saturation). A systematic experimental evaluation of the mechanical response of both metal-plated and bare Nafion and Flemion in various cation forms and various water saturation levels has been performed in the author’s laboratories at the University of California, San Diego. By examining the measured stiffness of the Nafion-based composites and the corresponding bare Nafion, under a variety of conditions, I have sought to develop relations between internal forces and the resulting stiffness and deformation of this class of IPMCs. Based on these and through a comparative study of the effects of various cations on the material’s stiffness and response, I have attempted to identify potential micromechanisms responsible for the observed electromechanical behavior of these materials, model them, and compare the model results with experimental data. A summary of these developments is given in the present work. First, a micromechanical model for the calculation of the Young modulus of the bare Nafion or Flemion in various ion forms and water saturation levels is given. Second, the bare-polymer model is modified to include the effect of the metal plating, and the results are applied to calculate the stiffness of the corresponding IPMCs, as a function of the solvent uptake. Finally, guided by the stiffness modeling and data, the actuation of the Nafion-based IPMCs is micromechanically modeled. Examples of the model results are presented and compared with the measured data.
Design of one-dimensional random surfaces with specified scattering properties
Authors: Méndez E. R. , Garcı́a-Guerrero E. E. , Leskova T. A. , Maradudin A. A. , Muñoz-López J. , Simonsen I.
Published: September 2002

We propose a method for designing a one-dimensional random perfectly conducting surface which, when illuminated by a plane wave, scatters it with a prescribed angular distribution of intensity. The method is applied to the design of a surface that scatters light uniformly within a specified range of scattering angles, and produces no scattering outside this range. It is tested by computer simulations, and a procedure for fabricating such surfaces on photoresist is described.
Enhanced flux pinning in Zr-doped MgB2 bulk superconductors prepared at ambient pressure
Authors: Feng Y. , Zhao Y. , Pradhan A. K. , Cheng C. H. , Yau J. K. F. , Zhou L. , Koshizuka N. , Murakami M.
Published: September 2002

We prepared a series of Mg1−xZrxB2 bulk samples with different x values by the solid-state reaction at ambient pressure and investigated the effects of the Zr doping on phase compositions, microstructure, and flux pinning behavior. The results indicate that the a axis increases with the increase of the Zr doping and the c axis remains unchanged. ZrB2 phases form and a small amount of Zr atoms may substitute Mg in Zr-doped samples. Critical temperature drops with increasing the Zr doping. It is found that critical current density Jc can be significantly enhanced by the Zr doping and the best data are achieved in Mg0.9Zr0.1B2. For this sample, Jc values are remarkably improved to 1.83×106 A/cm2 in the self field and 5.51×105 A/cm2 in 1 T at 20 K. Also, the irreversibility field is increased by the Zr doping. The high density, fine grain size of MgB2, and small ZrB2 particles in Zr-doped samples may be responsible for the enhancement of Jc. Also, the field dependence of Jc at different temperatures was briefly discussed.
Field-induced effects in the relaxor ferroelectric Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 studied by micro-Brillouin scattering
Authors: Ko Jae-Hyeon , Kojima Seiji
Published: September 2002

Field-induced changes of Brillouin scattering spectra in a relaxor-based ferroelectric Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystal have been examined under an electric field oriented along the pseudocubic [001] direction. A complete cycle of the Brillouin shift-electric field loop shows that sound velocities of one longitudinal and two transverse modes are softened during the polarization reversal. In particular, one transverse mode, which corresponds to the (c11−c12)/2 elastic stiffness coefficient, becomes markedly soft from 18.6 to 14 GHz and then restores its initial value at two distinct electric fields. In addition, two peaks have also been observed in the field dependence of the full width at half maximum of this mode. It implies that, at least two kinds of polarization rotation process are involved in the switching process, which seems to be related with the existence of intermediate monoclinic symmetry during the field-induced phase transition from rhombohedral to tetragonal phase.
Lasing from semiconductor microring on the end of an optical fiber
Authors: Corbett B. , Lambkin P. , Wu G. H. , Houlihan J. , Huyet G.
Published: September 2002

Isolated InGaAsP microrings with an outer diameter of 5.8 μm, a width of 1 μm, and a thickness of 0.41 μm were fabricated by epitaxial separation. Individual devices were bonded to multimode optical fiber using Van der Waals forces and optically pumped through the fiber. Lasing around 1505 nm was measured under pulsed and cw pumping at room temperature. The threshold pump power for pulsed operation was estimated to be 38 and 80 μW for cw operation. Multiple radial and azimuthal modes were present due to strong, three-dimensional confinement. Under strong pulsed pumping thermal effects caused the emission wavelength to chirp.
Magnetic phase transitions in the system La1−xBixMnO3+λ
Authors: Troyanchuk I. O. , Mantytskaja O. S. , Szymczak H. , Shvedun M. Yu.
Published: September 2002

The crystal structure and magnetic properties of the La1−xBixMnO3+λ system (0⩽x⩽1;λ⩽0.08) are studied as functions of the oxygen and bismuth contents. In oxidized samples La1−xBixMnO3+λ a phase transition from a ferromagnetic state (rhombohedric phase) to a state of the spin glass type (quasitetragonal phase) is observed with increase of the bismuth concentration. The reduced samples La1−xBixMnO3 are weak ferromagnets down to x⩽0.6 and then transform into a ferromagnetic state. It is supposed that the Bi3+ ions stabilize the dx2−y2 orbitals in the nearest Mn3+ ions whereas the dz2 orbitals of the La3+ ions are stabilized. The orbitally disordered phases and dx2−y2-orbitally ordered phases are ferromagnetic, the dz2-orbitally ordered phases show antiferromagnetic ordering, and the state of the orbital glass type corresponds to a state of the spin glass type.
Unsteady fluid flow and temperature fields in a horizontal enclosure with an adiabatic body
Authors: Ha Man Yeong , Kim In-Kyu , Yoon Hyun Sik , Lee Sangsan
Published: September 2002

A two-dimensional solution for unsteady natural convection in an enclosure with an adiabatic square body is obtained using an accurate and efficient Chevyshev spectral collocation method. A spectral multi-domain methodology is used to handle an adiabatic body located at the center of computational domain. The physical model considered here is that an adiabatic body is located at the center between the bottom hot and top cold walls. In order to see the effects of the presence of an adiabatic body on time-dependent natural convection between the hot and cold walls, we investigated the detail structure of fluid flow and heat transfer as a function of time for different Rayleigh numbers varying in the range of 103 to 106. When Ra=103, streamlines and isotherms reach the steady state without any oscillatory transients, and the flow and temperature distribution around the body in the enclosure shows a four-fold symmetrical pattern. At Ra=4×103, 104, and 105, streamlines and isotherms reach the steady state after starting oscillatory transients, and the flow and temperature fields change their shape from the symmetrical pattern to the nonsymmetrical one as time goes by. When Ra=106, streamlines and isotherms become time-dependent, and the fluid flow and temperature fields also change their shape in a regularly periodic fashion as a function of time.
On the role of Ge in the growth of β-FeSi2 on silicon (100) surfaces
Authors: Zenkevich A. , Gaiduk P. I. , Gunnlaugsson H. P. , Weyer G.
Published: September 2002

The microstructure of β-FeSi2 silicide layers formed with the addition of Ge by pulsed laser deposition at 650 °C on (001) Si substrate has been investigated by transmission electron microscopy and Mössbauer spectroscopy. The Ge atoms are not incorporated in the silicide in noticeable amounts but the addition causes the growth of β-FeSi2 micrograins with a high density of specific twin lamellae, whereas Ge segregates in epitaxial SiGe alloy grains.
Photonic crystals of shape-anisotropic colloidal particles
Authors: Velikov Krassimir P. , van Dillen Teun , Polman Albert , van Blaaderen Alfons
Published: September 2002

Spherical silica (SiO2), zinc sulfide (ZnS), and core-shell particles of these materials undergo substantial anisotropic plastic deformation under high-energy ion irradiation. Individual particles can be turned into oblate or prolate ellipsoids with exact control over the aspect ratio. In this letter, we report on the fabrication and optical characterization of thin three-dimensional photonic crystals of spherical particles, which have been anisotropically deformed into spheroidal oblates by means of ion irradiation. As a result of the collective deformation process, both the unit cell symmetry and the particle form factor have been changed leading to appreciable tunability in the optical properties of the photonic crystal.
High resolution magnetic force microscopy using focused ion beam modified tips
Authors: Phillips G. N. , Siekman M. , Abelmann L. , Lodder J. C.
Published: September 2002

Atomic force microscope tips coated by the thermal evaporation of a magnetic 30 nm thick Co film have been modified by focused ion beam milling with Ga+ ions to produce tips suitable for magnetic force microscopy. Such tips possess a planar magnetic element with high magnetic shape anisotropy, an extremely high aspect ratio of greater than 30:1, and an end radius of less than 25 nm. These tips have been used in a commercial atomic force microscope under ambient conditions to obtain 30 nm resolution magnetic images of an established CoNi/Pt multilayer reference sample.
Optical properties of oxygen precipitates and dislocations in silicon
Authors: Binetti S. , Pizzini S. , Leoni E. , Somaschini R. , Castaldini A. , Cavallini A.
Published: September 2002

Photoluminescence (PL) and deep level transient spectroscopy (DLTS) measurements were used to study the origin of optical emissions in the 0.8–1.0 eV region of selected oxygen precipitated and dislocated silicon samples. It was shown that the D1 band, present in both types of samples, is the convolution of different sub-bands, narrowly spaced between 0.802 and 0.820 eV. The emission at 0.807 eV, assigned in the literature to dislocations, was found only in samples where dislocations were intentionally generated by plastic deformation or induced by the clustering of self-interstitials generated during the growth of oxide precipitates. A comparison of the results of PL, DLTS, and optical DLTS measurements allows the assignment of levels involved in the radiative recombination processes.
Negative differential conductance in the tunnel Schottky contact with two-dimensional channel
Authors: Feiginov Michael N.
Published: September 2002

A semiconductor tunnel structure with negative differential conductance (NDC) is proposed and analyzed theoretically. NDC appears due to tunneling through a Schottky barrier into a quantum well. That can be realized in the structures similar to high electron-mobility transistor (HEMT) with tunneling between the gate and two-dimensional channel. Both diodes (two-terminal devices) and transistors (in particular, HEMTs) with NDC could be realized on the basis of the structures. Such structures could be used for generation of high-frequency radiation. The proposed structure should also have the current–voltage characteristic of N type.
Vertically stacking self-assembled quantum wires
Authors: Mu Xiaodong , Ding Yujie J. , Yang Haeyeon , Salamo Gregory J.
Published: September 2002

Self-assembled InP/InAs/InP quantum wires (QWRs) have been stacked for ten vertical periods and characterized based on photoluminescence (PL) studies. Compared with single-period QWRs, behaviors in the PL spectra and some fundamental effects have been observed. Through the detailed analyses of the PL shapes, linewidths, and polarizations at different pump wavelengths, pump intensities, and sample temperatures, it is evidenced that the wire width and subband energy gradually decrease while the average wire thickness increases from the bottom period to the top one, period by period. Meanwhile, the average wire width gradually decreases. Following these results, growth conditions have been suggested, which can be essential to improving the optical quality of these self-assembled QWRs.
Ordered arrays of vertically correlated GaAs and AlAs quantum wires grown on a GaAs(311)A surface
Authors: Litvinov D. , Rosenauer A. , Gerthsen D. , Ledentsov N. N. , Bimberg D. , Ljubas G. A. , Bolotov V. V. , Volodin V. A. , Efremov M. D. , Preobrazhenskii V. V. , Semyagin B. R. , Soshnikov I. P.
Published: September 2002

We study GaAs–AlAs short-period superlattices (SPSLs) grown on a GaAs(311)A surface using plan-view transmission electron microscopy (TEM). A strong in-plane compositional modulation with a period of 3.2 nm along the [01̄1] direction is revealed by TEM under chemically sensitive imaging conditions and in high-resolution TEM. Our results confirm the formation of highly ordered vertically aligned arrays of GaAs and AlAs quantum wires formed via self-organized growth. Bright photoluminescence (PL) at room temperature in the green and yellow spectral range is observed.
Pyroelectric nanoporous films: Synthesis and properties
Authors: Suyal Ganesh , Seifert Andreas , Setter Nava
Published: September 2002

PbZr x Ti 1−x O 3  (x=0.45) and PbxCa1−xTiO3 (PCT) (x=0.75) porous thin films were deposited on platinized silicon wafers by chemical solution deposition route using a polymer as a volatile phase. The introduction of pores creates a matrix-void composite resulting in a high figure of merit for pyroelectric applications. The figures of merit Fv and Fd for PCT films are shown to be as high as 4.8 and 250 μC/m2 K, respectively.
Stabilization of electrode migration in polymer electroluminescent devices
Authors: Chua Soo-Jin , Ke Lin , Kumar Ramadas Senthil , Zhang Keran
Published: September 2002

A thin 3-nm-thick parylene layer is deposited by chemical vapor deposition at room temperature on the indium tin oxide (ITO) coated glass substrate to form a bilayer anode of an organic light emitting diode. The parylene layer forms a conformal film to cover the spikes present in the ITO film. This parylene film presents a smoother surface to the subsequent organic layers. The parylene film not only reduces the occurrence of dark spots, acting as a barrier for oxygen diffusion from either the ITO or from the atmosphere and stabilizing the migration of the electrodes during electrical stress, but also improves the injection of holes from the anode. By inserting another parylene layer in between the organic and cathode layers, the probability of formation of nonemissive areas is further reduced.
Empirical function for homogeneous water nucleation rates
Authors: Wölk Judith , Strey Reinhard , Heath Christopher H. , Wyslouzil Barbara E.
Published: September 2002

Very recently, Wölk and Strey [J. Phys. Chem. B 105, 11683 (2001)] presented empirical temperature correction functions for calculating homogeneous nucleation rates J of H2O and D2O (1<J/cm−3 s−1<1020) from classical nucleation theory over an extended range of temperature T (200<T/K<310) and supersaturations S (5<S<200). Here, we critically test the correction functions to the Becker–Döring nucleation rate equation JBD against an extensive set of experimental data, and find that the equations distinctly improve the agreement between theory and experiment for very little extra work. The success of the corrected nucleation rate functions is surprising, given that they were developed based on experimental nucleation rates measured in a nucleation pulse chamber over a limited nucleation rate range 105<J/cm−3 s−1<1010, supersaturation range 6<S<22, and temperature range 220<T/K<260.
Blackbody radiation from resistively heated multiwalled carbon nanotubes during field emission
Authors: Sveningsson M. , Jönsson M. , Nerushev O. A. , Rohmund F. , Campbell E. E. B.
Published: September 2002

We report the observation of blackbody radiation from aligned multiwalled carbon nanotubes undergoing field emission. The light intensity correlates with fluctuations in the emission current. The onset of light emission occurs at an emission current of 1 mA/cm2 and corresponds to a temperature on the order of 1550 K. Beyond this critical current irreversible changes occur in the nanotube film. The correlation between light intensity and emission current provides convincing evidence for Joule heating and stable operation for nanotube temperatures up to at least 2000 K and emission current densities on the order of 10 mA/cm2.
Electric-field-induced birefringence in LiNbO3 measured by generalized transmission ellipsometry
Authors: Jellison G. E. , Griffiths C. O. , Holcomb D. E.
Published: September 2002

Transmission generalized ellipsometry has been used to measure electric-field-induced birefringence in LiNbO3. By stepping an imaging lens over the end of an optical fiber attached to the detector, images of the retardation, fast axis, diattenuation, and depolarization can be obtained with a resolution of ∼31 μm. It is shown that the retardation and the fast axis in z-cut LiNbO3 under bias is not constant throughout the material, but can vary as much as a factor of 2. Furthermore, this retardation is a function of the magnitude and duration of the applied voltage.
Terahertz frequency difference from vertically integrated low-temperature-grown GaAs photodetector
Authors: Peytavit E. , Arscott S. , Lippens D. , Mouret G. , Matton S. , Masselin P. , Bocquet R. , Lampin J. F. , Desplanque L. , Mollot F.
Published: September 2002

We report on the development of a photoconductive detector based on low-temperature-grown GaAs which is vertically integrated with terahertz spiral antennas. A non steady-state velocity overshoot effect was expected in the photoresponse with a responsivity of 0.04 A/W at a bias voltage of 8 V. Photomixing experiments using two optical 0.8 μm beating lasers show a 3 dB bandwith of 700 GHz with a radiation power at terahertz frequency of 0.5 μW under 2×30 mW optical pumping.
High-transparency superconductor–insulator–normal- metal–insulator–superconductor Josephson junctions for digital electronics
Authors: Nevirkovets I. P. , Ketterson J. B.
Published: September 2002

Nb / Al / AlO x / Al / AlO x / Al / Nb junctions with critical current densities, jc, up to 38 kA/cm2 were fabricated. A critical voltage of Vc=1.25 mV and small hysteresis (about 6% of the critical current) at 4.2 K were obtained for jc=21 kA/cm2. Also, Nb/Al/AlOx/Al/Nb/Al/NbN junctions with jc=33 kA/cm2 and Vc=0.76 mV were fabricated, where it is suggested that a second tunnel barrier at the Al/NbN interface is present as a result of Al nitridation during NbN deposition.
High-resolution surface charge image achieved by a multiforce sensor based on a quartz tuning fork in electrostatic force microscope
Authors: Wang Zhi-yong , Bao Jian-bin , Zhang Hong-hai , Guo Wen-ming
Published: September 2002

A multiforce sensor was fabricated by attaching a tiny tungsten tip to a tuning fork. By operating an ac modulation bias on the minitip of the needle sensor, we have achieved a dynamic noncontact mode electrostatic force microscope with high spatial resolution. It can utilize the van der Waals force and electrostatic force signals between the microtip and the sample, respectively, to obtain the images of topography and quantitative surface charge density of an open-gate field effect transistor simultaneously.
Evolution and microstructure of shear bands in nanostructured Fe
Authors: Wei Q. , Jia D. , Ramesh K. T. , Ma E.
Published: September 2002

Shear band development in consolidated nanocrystalline and ultrafine-grained Fe has been monitored as a function of overall strain from the onset of plastic deformation. The deformation mechanisms of the grains inside the shear bands, the origin of the inhomogeneous deformation, and the propensity for shear localization in nanostructures are explained based on microstructural information acquired using transmission electron microscopy.
Multiple resonances in microdisk lasers of π-conjugated polymers
Authors: Polson R. C. , Vardeny Z. V. , Chinn D. A.
Published: September 2002

We have fabricated microdisk lasers from π-conjugated polymers that show multiline emission spectrum upon optical excitation. Using Fourier transform analysis, each emission line is assigned integer to an interger Bessel function that helps to estimate the field distribution inside the photoexcited polymer microdisk. We found that the microdisk can sustain two different laser modes with different, though complementary, field distributions and that the index of refraction decreases with increasing excitation intensity.
High-resolution patterning of semiconductors using electron-beam-assisted wet etching
Authors: Richter G. , Schmidt G. , Molenkamp L. W. , Bibus M. , de Boeck J.
Published: September 2002

Chemical wet etching as a lithographic technique often suffers from strong underetching underneath the mask, limiting the achievable size of the structures. We have developed a chemical wet etching technique in which the etching rate and anisotropy of the process is controlled by electron-beam exposure, resulting in structures with lateral dimensions down to 12 nm. Results are shown for (Al,Ga)Sb–InAs quantum-well structures and InAs layers. A possible mechanism is discussed.
Magnetic and electrical properties of Co2MnGa grown on GaAs (001)
Authors: Holmes S. N. , Pepper M.
Published: September 2002

The Heusler alloys are a group of magnetic materials that will form essential components in hybrid, ferromagnet–semiconductor devices that utilize spin injection. We demonstrate that such an alloy, Co2MnGa:GaAs(001) is ferromagnetic at 300 K and has controllable magnetic properties. A weak in-plane uniaxial anisotropy is observed with the easy axis along the [0,−1,1] direction. Metallic rather than semiconducting behavior is observed over a range of wafer thicknesses. The extrapolated bulk resistivity is 20 μΩ cm at 300 K and the residual resistivity ratios range from 1.15 to 1.7 depending on the wafer thickness. An anisotropic magnetoresistance of 6% at 300 K (and 8% at 1.6 K) demonstrates the importance of spin–orbit scattering in these disordered alloys. Several issues are addressed in this letter as to whether the manifestation of the predicted spin-polarized band structure and minority spin band gap can be observed.
Maternal Modulation of Neonatal Immune System Development
Authors: Fagoaga Omar R. , Nehlsen-Cannarella Sandra L.
Published: September 2002

Changes in programming of neonatal immune development were effected through maternal immune modulation (Leishmania major inoculation). In progeny of these dams, immune profiles in both blood and spleen were changed throughout the neonatal period and were pronounced after weaning. White blood cell (WBC) and lymphocyte counts in blood of 45‐day‐old progeny were two‐fold less than control animals. In blood, proportions of B cells were greater, while T helpers, Tc/s and NK cells were less than in controls. In contrast, proportions of splenic B and NK cells were greater than controls. But, proportions of all T and Tc/s cells on d20 and 45 were lower than controls. In blood, absolute numbers of all T, Th naïve and Th memory cells were lower than in controls. In contrast, in the spleen, numbers of NK, T and Th naïve and memory cells were up to 200% greater than in control pups. Cytokine responses of splenic lymphocytes stimulated through CD3 ligation revealed no difference in IL‐4 production. In contrast, IL‐2 and IFNγ were lower on d45 and 5, respectively, in the experimental compared to control mice. These data support the hypothesis that maternal immune events during gestation can modulate the pattern of immune development in offspring.
The ecological status of Lake Laguna de Bay, Philippines
Authors: Tamayo-Zafaralla M. , Santos R. A. V. , Orozco R. P. , Elegado G. C. P.
Published: September 2002

This article assesses the ecological status of Laguna de Bay using available published and unpublished information. The declining fishery productivity of the lake is the most glaring evidence of its stressed ecological state. This loss stems from numerous deleterious factors operating throughout the lake and its drainage basin. Phytoplankton community composition has drastically changed over the years and algal biomass has diminished in the presence of ample supplies of nitrogen and phosphorus. Light limitation due to high siltation rates in the perennially turbid lake whose Secchi depth is only 5 cm might be the primary limitation to photosynthesis. The problem of siltation in the lake is the result of deforestation in the watershed that heightened soil erosion rates. Trophic relationships are inadequately examined in Laguna de Bay, the biggest lake in Southeast Asia. High biological oxygen demand and high heavy metal levels in the lake water, sediments, and biota are evidence of excessive pollution. Heavy metal levels in fish are similar to those found in fish from a smaller nearby lake receiving mine tailings. Collectively, these observations show that Laguna de Bay is an extremely stressed ecosystem needing rehabilitation. The article concludes with a set of recommendations on how to deal with the problem of impairment of lake ecology, namely, the improvement of the hydrological regime, control of the internal loading of fertilizing nutrients, toxic and hazardous chemicals, control of the sources of pollution, a systematic implementation of closed and open seasons to fishing, the establishment of a system for the assessment and evaluation of environmental perturbations, and revitalization and support for local community efforts to safeguard the ecology of the lake.
MAP2 is required for dendrite elongation, PKA anchoring in dendrites, and proper PKA signal transduction
Authors: Harada Akihiro , Teng Junlin , Takei Yosuke , Oguchi Keiko , Hirokawa Nobutaka
Published: September 2002

Microtubule-associated protein 2 (MAP2) is a major component of cross-bridges between microtubules in dendrites, and is known to stabilize microtubules. MAP2 also has a binding domain for the regulatory subunit II of cAMP-dependent protein kinase (PKA). We found that there is reduction in microtubule density in dendrites and a reduction of dendritic length in MAP2-deficient mice. Moreover, there is a significant reduction of various subunits of PKA in dendrites and total amounts of various PKA subunits in hippocampal tissue and cultured neurons. In MAP2-deficient cultured neurons, the induction rate of phosphorylated CREB after forskolin stimulation was much lower than in wild-type neurons. Therefore, MAP2 is an anchoring protein of PKA in dendrites, whose loss leads to reduced amount of dendritic and total PKA and reduced activation of CREB.
Active translocon complexes labeled with GFP–Dad1 diffuse slowly as large polysome arrays in the endoplasmic reticulum
Authors: Nikonov Andrei V. , Snapp Erik , Lippincott-Schwartz Jennifer , Kreibich Gert
Published: September 2002

In the ER, the translocon complex (TC) functions in the translocation and cotranslational modification of proteins made on membrane-bound ribosomes. The oligosaccharyltransferase (OST) complex is associated with the TC, and performs the cotranslational N-glycosylation of nascent polypeptide chains. Here we use a GFP-tagged subunit of the OST complex (GFP–Dad1) that rescues the temperature-sensitive (ts) phenotype of tsBN7 cells, where Dad1 is degraded and N-glycosylation is inhibited, to study the lateral mobility of the TC by FRAP. GFP–Dad1 that is functionally incorporated into TCs diffuses extremely slow, exhibiting an effective diffusion constant (Deff) about seven times lower than that of GFP-tagged ER membrane proteins unhindered in their lateral mobility. Termination of protein synthesis significantly increases the lateral mobility of GFP–Dad1 in the ER membranes, but to a level that is still lower than that of free GFP–Dad1. This suggests that GFP–Dad1 as part of the OST remains associated with inactive TCs. Our findings that TCs assembled into membrane-bound polysomes diffuse slowly within the ER have mechanistic implications for the segregation of the ER into smooth and rough domains.
The 2 micron plasmid purloins the yeast cohesin complex
Authors: Mehta Shwetal , Yang Xian Mei , Chan Clarence S. , Dobson Melanie J. , Jayaram Makkuni , Velmurugan Soundarapandian
Published: September 2002

The yeast 2 micron plasmid achieves high fidelity segregation by coupling its partitioning pathway to that of the chromosomes. Mutations affecting distinct steps of chromosome segregation cause the plasmid to missegregate in tandem with the chromosomes. In the absence of the plasmid stability system, consisting of the Rep1 and Rep2 proteins and the STB DNA, plasmid and chromosome segregations are uncoupled. The Rep proteins, acting in concert, recruit the yeast cohesin complex to the STB locus. The periodicity of cohesin association and dissociation is nearly identical for the plasmid and the chromosomes. The timely disassembly of cohesin is a prerequisite for plasmid segregation. Cohesin-mediated pairing and unpairing likely provides a counting mechanism for evenly partitioning plasmids either in association with or independently of the chromosomes.
Lysosomes and the plasma membrane
Authors: Andrews Norma W.
Published: September 2002

Studies of the cell invasion mechanism of the parasite Trypanosoma cruzi led to a series of novel findings, which revealed a previously unsuspected ability of conventional lysosomes to fuse with the plasma membrane. This regulated exocytic process, previously regarded mostly as a specialization of certain cell types, was recently shown to play an important role in the mechanism by which cells reseal their plasma membrane after injury.
Interaction of A2E with Model Membranes. Implications to the Pathogenesis of Age-related Macular Degeneration
Authors: De Soma , Sakmar Thomas P.
Published: September 2002

Deposition of a fluorophoric material, known as lipofuscin, in retinal pigment epithelium cells has been speculated to be one of the biomarkers of age-related macular degeneration. One of the fluorophores of lipofuscin has been characterized as A2E, a pyridinium bisretinoid. Its cationic nature along with two hydrophobic retinal chains suggests that it can disrupt the membrane integrity by its detergent-like activity and can thus cause cellular damage. With this notion, we studied in detail the interaction between A2E and the model membranes of different lipid compositions using fluorescence steady-state and fluorescence anisotropy measurements. A transition from vesicular to micellar structure occurred upon incorporation of A2E into the lipid bilayer. However, the A2E concentration at which this transition occurred depends on the lipid composition. A lipid mixture containing 10% phosphatidylserine (PS) (close to disc membrane PS content) behaved similarly to a lipid mixture having no PS. In contrast, vesicles containing 20% PS showed significantly different behavior. Membrane solubilization by A2E was also confirmed by vesicle leakage experiments. A2E also showed significant activity in liposome-mediated gene transfection. A lipid formulation containing 40% A2E and a helper lipid showed plasmid DNA transfection efficiency comparable to commercially available transfection reagents with no evidence of cytotoxicity. These results contribute to understanding the mechanism underlying the A2E-induced cellular dysfunction.
Attributions in explanations of risk estimates
Authors: Kahlor LeeAnn , Dunwoody Sharon , Griffin Robert J.
Published: September 2002

In the spring of 1993, nearly 40 percent of Milwaukee-area residents experienced a nationally publicized outbreak of cryptosporidium, a parasite that infested the metropolitan drinking water supply. Using open-ended survey data gathered from 610 adult residents in the wake of that outbreak, this study looks at factors related to the ways in which people make sense of their quantitative personal risk estimates. The concepts of informal reasoning and attribution aided this endeavor. Analysis of open-ended comments about the risk of getting ill from a waterborne parasite indicated that explanations of personal risk were consistent with predictions made by attribution theory. Good outcomes, which included having remained healthy during the outbreak, were associated with a greater likelihood that respondents would attribute causation to themselves, while one specific bad outcome, having experienced the illness, was associated with a greater likelihood that respondents would attribute causation externally. This study also examined predictors of whether respondents employed probabilistic language in those attributions. Analysis indicated that income was positively related to the use of probability-oriented language, while age and race were negatively related to the use of such language (i.e., persons of color and older individuals were less likely to use such language).
Issues in cybersecurity; understanding the potential risks associated with hackers/crackers
Authors: Smith Alan D. , Rupp William T.
Published: September 2002

It is commonplace to say that the 11 September attacks have changed everything. A global revolution is changing business, and business is changing the world. With unsettling speed, two forces are converging; a new generation of business leaders is rewriting the rules of business, and a new breed of fast companies is challenging the corporate status quo. The Internet is an information superhighway, touching almost every aspect of the economy from government agencies, financial institutions, businesses, and professional organizations. With the year 2002 and its increasing number of court cases on Internet‐related issues, the courts are obviously still struggling with the question of intellectual property rights in an open source code environment supporting e‐commerce. By modeling and classifying the risks associated with cybersecurity issues, firms and specific individuals should not become a casualty of this cyberwar, nor become paranoid about the risks ‐‐ be informed and follow common business sense practices, policies, and procedures.
New insights into intracellular lipid binding proteins: The role of buried water
Authors: Lücke Christian , Huang Sinian , Rademacher Martin , Rüterjans Heinz
Published: September 2002

The crystal structures of most intracellular lipid binding proteins (LBPs) show between 5 and 20 internally bound water molecules, depending on the presence or the absence of ligand inside the protein cavity. The structural and functional significance of these waters has been discussed for several LBPs based on studies that used various biophysical techniques. The present work focuses on two very different LBPs, heart‐type fatty acid binding protein (H‐FABP) and ileal lipid binding protein (ILBP). Using high‐resolution nuclear magnetic resonance spectroscopy, certain resonances belonging to side‐chain protons that are located inside the water‐filled lipid binding cavity were observed. In the case of H‐FABP, the pH‐ and temperature‐dependent behavior of selected side‐chain resonances (Ser82 OgH and the imidazole ring protons of His93) indicated an unusually slow exchange with the solvent, implying that the intricate hydrogen‐bonding network of amino‐acid side‐chains and water molecules in the protein interior is very rigid. In addition, holo H‐FABP appeared to display a reversible self‐aggregation at physiological pH. For ILBP, on the other hand, a more solvent‐accessible protein cavity was deduced based on the pH titration behavior of its histidine residues. Comparison with data from other LBPs implies that the evolutionary specialization of LBPs for certain ligand types was not only because of mutations of residues directly involved in ligand binding but also to a refinement of the internal water scaffold.
Characterization of an Enteropathogenic Bovine Calicivirus Representing a Potentially New Calicivirus Genus
Authors: Smiley J. R. , Chang K. O. , Hayes J. , Vinjé J. , Saif L. J.
Published: September 2002

Bovine enteric caliciviruses (BEC) are associated with diarrhea in young calves. The BEC strains detected in Europe form a third genogroup within the genus “Norwalk-like viruses” (NLV) of the familyCaliciviridae. In this report, we present sequence, clinical, and histological data characterizing a novel enteropathogenic BEC strain, NB, detected in fecal specimens from calves in the United States. The complete RNA genome of the NB virus is 7,453 bases long and is organized into two open reading frames (ORFs). ORF-1 is 2,210 amino acids long and encodes a large nonstructural polyprotein contiguous with the major capsid protein (VP1), similar to the lagoviruses and “Sapporo-like viruses” (SLV). The conserved calicivirus motifs were identified in the nonstructural proteins. ORF-2 is located at the 3′ end of the genome and encodes a small basic protein (VP2) of 225 amino acids. The 5′ and 3′ untranslated regions are 74 and 67 bases long, respectively. Among caliciviruses, NB virus shows amino acid identities of 14.1 to 22.6% over the entire ORF-1 nonstructural-protein sequence with NLV, SLV, vesivirus, and lagovirus strains, while the overall sequence identity of the complete NB VP-1 with other caliciviruses is low, varying between 14.6 and 26.7%. Phylogenetic analysis of the complete VP1 protein, including strains from all four calicivirus genera, showed the closest grouping of NB virus to be with viruses in the genusLagovirus, which cause liver infections and systemic hemorrhage in rabbits. In gnotobiotic calves, however, NB virus elicited only diarrhea and intestinal lesions that were most severe in the upper small intestine (duodenum and jejunum), similar to the NLV BEC strains. The tissues of major organs, including the lung, liver, kidney, and spleen, had no visible microscopic lesions.
Nonspecific Nucleoside Triphosphatase P4 of Double-Stranded RNA Bacteriophage φ6 Is Required for Single-Stranded RNA Packaging and Transcription
Authors: Pirttimaa Markus J. , Paatero Anja O. , Frilander Mikko J. , Bamford Dennis H.
Published: September 2002

Bacteriophage φ6 has a segmented double-stranded RNA genome. The genomic single-stranded RNA (ssRNA) precursors are packaged into a preformed protein capsid, the polymerase complex, composed of viral proteins P1, P2, P4, and P7. Packaging of the genomic precursors is an energy-dependent process requiring nucleoside triphosphates. Protein P4, a nonspecific nucleoside triphosphatase, has previously been suggested to be the prime candidate for the viral packaging engine, based on its location at the vertices of the viral capsid and its biochemical characteristics. In this study we were able to obtain stable polymerase complex particles that are completely devoid of P4. Such particles were not able to package ssRNA segments and did not display RNA polymerase (either minus- or plus-strand synthesis) activity. Surprisingly, a mutation in P4, S250Q, which reduced the level of P4 in the particles to about 10% of the wild-type level, did not affect RNA packaging activity or change the kinetics of packaging. Moreover, such particles displayed minus-strand synthesis activity. However, no plus-strand synthesis was observed, suggesting that P4 has a role in the plus-strand synthesis reaction also.
Vesicular Stomatitis Virus Infection Alters the eIF4F Translation Initiation Complex and Causes Dephosphorylation of the eIF4E Binding Protein 4E-BP1
Authors: Connor John H. , Lyles Douglas S.
Published: September 2002

Vesicular stomatitis virus (VSV) modulates protein synthesis in infected cells in a way that allows the translation of its own 5′-capped mRNA but inhibits the translation of host mRNA. Previous data have shown that inactivation of eIF2α is important for VSV-induced inhibition of host protein synthesis. We tested whether there is a role for eIF4F in this inhibition. The multisubunit eIF4F complex is involved in the regulation of protein synthesis via phosphorylation of cap-binding protein eIF4E, a subunit of eIF4F. Translation of host mRNA is significantly reduced under conditions in which eIF4E is dephosphorylated. To determine whether VSV infection alters the eIF4F complex, we analyzed eIF4E phosphorylation and the association of eIF4E with other translation initiation factors, such as eIF4G and the translation inhibitor 4E-BP1. VSV infection of HeLa cells resulted in the dephosphorylation of eIF4E at serine 209 between 3 and 6 h postinfection. This time course corresponded well to that of the inhibition of host protein synthesis induced by VSV infection. Cells infected with a VSV mutant that is delayed in the ability to inhibit host protein synthesis were also delayed in dephosphorylation of eIF4E. In addition to decreasing eIF4E phosphorylation, VSV infection also resulted in the dephosphorylation and activation of eIF4E-binding protein 4E-BP1 between 3 and 6 h postinfection. Analysis of cap-binding complexes showed that VSV infection reduced the association of eIF4E with the eIF4G scaffolding subunit at the same time as its association with 4E-BP1 increased and that these time courses correlated with the dephosphorylation of eIF4E. These changes in the eIF4F complex occurred over the same time period as the onset of viral protein synthesis, suggesting that activation of 4E-BP1 does not inhibit translation of viral mRNAs. In support of this idea, VSV protein synthesis was not affected by the presence of rapamycin, a drug that blocks 4E-BP1 phosphorylation. These data show that VSV infection results in modifications of the eIF4F complex that are correlated with the inhibition of host protein synthesis and that translation of VSV mRNAs occurs despite lowered concentrations of the active cap-binding eIF4F complex. This is the first noted modification of both eIF4E and 4E-BP1 phosphorylation levels among viruses that produce capped mRNA for protein translation.
The NS2 Proteins of Parvovirus Minute Virus of Mice Are Required for Efficient Nuclear Egress of Progeny Virions in Mouse Cells
Authors: Eichwald Virginie , Daeffler Laurent , Klein Michèle , Rommelaere Jean , Salomé Nathalie
Published: September 2002

The small nonstructural NS2 proteins of parvovirus minute virus of mice (MVMp) were previously shown to interact with the nuclear export receptor Crm1. We report here the analysis of two MVM mutant genomic clones generating NS2 proteins that are unable to interact with Crm1 as a result of amino acid substitutions within their nuclear export signal (NES) sequences. Upon transfection of human and mouse cells, the MVM-NES21 and MVM-NES22 mutant genomic clones were proficient in synthesis of the four virus-encoded proteins. While the MVM-NES22 clone was further able to produce infectious mutant virions, no virus could be recovered from cells transfected with the MVM-NES21 clone. Whereas the defect of MVM-NES21 appeared to be complex, the phenotype of MVM-NES22 could be traced back to a novel distinct NS2 function. Infection of mouse cells with the MVM-NES22 mutant led to stronger nuclear retention not only of the NS2 proteins but also of infectious progeny MVM particles. This nuclear sequestration correlated with a severe delay in the release of mutant virions in the medium and with prolonged survival of the infected cell populations compared with wild-type virus-treated cultures. This defect could explain, at least in part, the small size of the plaques generated by the MVM-NES22 mutant when assayed on mouse indicator cells. Altogether, our data indicate that the interaction of MVMp NS2 proteins with the nuclear export receptor Crm1 plays a critical role at a late stage of the parvovirus life cycle involved in release of progeny viruses.
A NOTE ON COMMUTING SQUARES ARISING FROM AUTOMORPHISMS ON SUBFACTORS
Authors: LOI PHAN H.
Published: September 2002

Using an idea due to Popa, we can associate a commuting square of factors to any given finite set of automorphisms acting on an inclusion of factors of finite index. We use this setting to obtain a simple proof of Popa's classification theorem of strongly outer actions of finitely generated discrete strongly amenable groups on a strongly amenable inclusion of type II 1 factors. We also obtain a new complete outer conjugacy invariant for arbitrary automorphisms, which contains the higher obstruction of Kawahigashi and the standard invariant as a special case.
CUTTING AND PASTING OF RIEMANN SURFACES WITH ABELIAN DIFFERENTIALS I
Authors: HASHIMOTO YOSHITAKE , OHBA KIYOSHI
Published: September 2002

We introduce a method of constructing once punctured Riemann surfaces by cutting the complex plane along "line segments" and pasting by "parallel transformations". The advantage of this construction is to give a good visualization of the deformation of complex structures of Riemann surfaces. In fact, given a positive integer g, there appears a family of once punctured Riemann surfaces of genus g which is complete and effectively parametrized at any point. Our construction naturally gives each of the resulting surfaces what we call a Lagrangian lattice Λ, a certain subgroup of the first homology. Furthermore Λ and the puncture determine an Abelian differential ωΛ of the second kind on the Riemann surface. Using Λ and ωΛ we consider the Kodaira–Spencer maps and some extension of the family to obtain any once punctured Riemann surface with a Lagrangian lattice. In particular we describe the moduli space of once punctured elliptic curves with Lagrangian lattices.