bluuebunny/crossref_metadata_2025 huggingface dataset:
Shapes of InAs quantum dots on InGaAs∕InP
Authors: Hwang Heedon , Yoon Sukho , Kwon Hyeok , Yoon Euijoon , Kim Hong-Seung , Lee Jeong Yong , Cho Benjamin
Published: December 2004

InAs self-assembled quantum dots were grown on InGaAs lattice-matched on InP by metalorganic chemical vapor deposition. The facet formation on the dot was investigated by atomic force microscopy and transmission electron microscopy. The {136}-faceted InAs dots were elongated along either [13¯0] or [3¯10] to form parallelogram-shaped islands analogous to hut cluster formation in SiGe∕Si quantum dots. Some parallelogram dots also exhibited {110} faceting, presumably on undergoing a shape transition toward dots with facets of higher symmetry.
Ce
3
+
-doped fibers for remote radiation dosimetry
Authors: Vedda A. , Chiodini N. , Di Martino D. , Fasoli M. , Keffer S. , Lauria A. , Martini M. , Moretti F. , Spinolo G. , Nikl M. , Solovieva N. , Brambilla G.
Published: December 2004

A radioluminescent (RL) dosimetric system, based on a SiO2 optical fiber with the core doped by Ce3+ ions as luminescent activators has been investigated. Structural and optical properties of the luminescent fiber have been studied by Raman, refractive index, RL and scintillation time decay measurements, and compared to those obtained on bulk material. The RL response of a composite fiber made of a short portion of active Ce-doped fiber coupled to a long commercial one has been investigated by x-ray irradiation. A linear RL intensity response has been found in the dose rate interval 6×10−3–40mGy∕s together with a good radiation hardness, suggesting possible application in low-dose monitoring.
Cathode priming of a relativistic magnetron
Authors: Jones M. C. , Neculaes V. B. , Lau Y. Y. , Gilgenbach R. M. , White W. M.
Published: December 2004

A cathode priming technique of a relativistic magnetron is analyzed via a three-dimensional particle-in-cell simulation. By imposing a threefold azimuthal variation on the emitting cathode of a six-cavity relativistic magnetron, the electrons are prebunched at birth. This leads to fast startup of the pi mode with three electron spokes. Suppression of unwanted modes during startup is observed in the simulation.
Protein patterning by micromachined silicon embossing on polymer surfaces
Authors: Goustouridis D. , Misiakos K. , Petrou P. S. , Kakabakos S. E.
Published: December 2004

An automated method for creating micron-sized patterns of different proteins is described. Unlike other methods, the process requires no masks, photochemichal reagents, or alignment. The basic tools are a motorized x–y stage, a pneumatic drive, and a micromachined silicon chip with an array of micron scale pyramids. Upon pressing the chip on a plastic slide, inverted pyramids are created on the polymer surface, exposing areas that have no previous coating and can adsorb proteins. The method is suitable for the fast and inexpensive fabrication of dense arrays of different proteins on appropriate substrates.
An organic thin-film transistor of high mobility by dielectric surface modification with organic molecule
Authors: Kim Jong-Moo , Lee Joo-Won , Kim Jai-Kyeong , Ju Byeong-Kwon , Kim Jong-Seung , Lee Yun-Hi , Oh Myung-Hwan
Published: December 2004

Organic thin-film transistors (OTFTs) based on pentacene semiconductor are elaborated on the plastic substrates through a four-level mask process without photolithographic patterning to yield a simple fabrication process. Octadecyltrimethoxysilane (OTMS) as an organic molecule for self-assembled monolayers is deposited on the surface of zirconium oxide dielectric layer. The effect of OTMS interlayer with gate dielectric surface modification on the field effect mobility of OTFTs has been examined and these prototype organic transistors showed excellent electrical characteristics with field effect mobility >0.66cm2∕Vs and Ion∕Ioff>10.5
Sensitivity reduction mechanisms in amorphous selenium photoconductive x-ray image detectors
Authors: Yunus M. , Kabir M. Zahangir , Kasap S. O.
Published: December 2004

Sensitivity reduction in amorphous Se-based photoconductive x-ray image detectors due to previous exposures is studied by Monte Carlo simulation. Collected charge, hence x-ray sensitivity, is calculated by considering deep carrier trapping, taking into account the effects of trap filling, recombination between trapped and drifting carriers and the generation of x-ray induced new deep trap centers. Space charge effects on the electric field, and hence, the effects of electric field on electron hole pair generation and charge transport are also considered. The comparison of the model with the experimental data reveals that the recombination between trapped and oppositely charged drifting carriers and x-ray induced new deep trap centers are mainly responsible for the sensitivity reduction in biased a-Se-based x-ray detectors.
Photoluminescence of GaAs nanowhiskers grown on Si substrate
Authors: Khorenko V. , Regolin I. , Neumann S. , Prost W. , Tegude F.-J. , Wiggers H.
Published: December 2004

GaAs nanowhiskers were grown by metalorganic vapor-phase epitaxy on (111) Si substrates using the vapor-liquid-solid growth mode. The diameter of the nanowhiskers was defined by polydisperse catalytic Au nanoparticles in the range from 5 to 100 nm deposited on the Si substrate from the liquid phase. The low-temperature photoluminescence spectra exhibit a series of unresolved exciton-related transitions shifted to a shorter wavelength due to the quantization effects. Despite some structure defects, relatively high photoluminescence intensity and its linear dependence on the excitation power without saturation confirms the good material quality of fabricated GaAs nanowhiskers.
Effects of intrinsic layer thickness on solar cell parameters of organic p-i-n heterojunction photovoltaic cells
Authors: Taima Tetsuya , Chikamatsu Masayuki , Yoshida Yuji , Saito Kazuhiro , Yase Kiyoshi
Published: December 2004

We fabricated organic p-i-n heterojunction photovoltaic cells of a zinc phthalocyanine (ZnPc)∕1:1 codeposition (ZnPc:C60)∕C60 structure. We investigated the effects of the intrinsic (i-) layer thickness on the photovoltaic properties. The thickness was changed from 0 nm (=p-n heterojunction) to 50 nm (=alli-layer) with the total thickness of 50 nm. While the short-circuit photocurrent increased with increasing the thickness, the fill factor showed the opposite tendency. Therefore, the power conversion efficiency showed a maximum (1.5%) at the thickness of 10 nm under air mass 1.5 global solar conditions. Device simulation based on idealized equivalent circuit of a solar cell demonstrates that the i-layer thickness is concerned in the series resistance of the cells.
Time-resolved photoluminescence in Mobil Composition of Matter-48
Authors: Liu Y. L. , Lee W. Z. , Shen J. L. , Lee Y. C. , Cheng P. W. , Cheng C. F.
Published: December 2004

Dynamical properties of Mobil Composition of Matter (MCM)-48 were studied by time-resolved photoluminescence (PL). The PL intensity exhibits a clear nonexponential profile, which can be fitted by a stretched exponential function. In the temperature range from 50to300K, the PL decay lifetime becomes thermally activated by a characteristic energy of 25meV, which is suggested to be an indication of the phonon-assisted nonradiative process. A model is proposed to explain the relaxation behavior of the PL in MCM-48.
Nanoparticle-based microelectromechanical systems fabricated on plastic
Authors: Wilhelm Eric J. , Neltner Brian T. , Jacobson Joseph M.
Published: December 2004

In this letter, we demonstrate the additive fabrication of electrostatic actuators on polyimide plastic by offset liquid embossing. They are formed by printing a nanoparticle colloid of gold on a polyimide substrate and then under-etching the polyimide through patterned etch holes. Residual stresses in the released gold films cause the films to bend away from the substrate. These films can then be electrostatically attracted toward the substrate and used to modulate light. The actuators range in size from 45to100μm and are controlled by electric fields of approximately 2V∕μm, allowing switching at several hundred cycles per second.
Epitaxial growth and surface modeling of ZnO on c-plane Al2O3
Authors: Murphy T. E. , Walavalkar S. , Phillips J. D.
Published: December 2004

The growth of ZnO on c-plane sapphire by molecular beam epitaxy is presented for varying ratios of zinc and oxygen flux. Reflection high energy electron diffraction patterns during epitaxial growth suggest clear differences in the evolution of surface morphology for differing Zn flux. Atomic force microscope images indicate sizable hexagonal features in the surface morphology for Zn-rich material. A stochastic growth model is presented to represent the experimental ZnO surface, where differences in adatom lateral diffusion length are suspected to be the cause of the differing surface morphology.
Measuring multimodal size distributions of aquatic colloids at trace concentrations
Authors: Walther C. , Cho H. R. , Fanghänel Th.
Published: December 2004

Many applications in research as well as industry require a highly sensitive detection of particulate matter in water or process liquids. We present a technique to measure the distribution of colloid sizes between 20 and 100nm in situ at ultratrace concentrations. The method is based on laser-induced breakdown detection, which has been applied for trace detection of colloids and determination of the weighted mean size. Using a refined method of data evaluation, we are now able to measure the number density of inorganic colloids in six size classes between 20 and 100nm simultaneously below ppb concentration.
In situ formation of two amorphous phases by liquid phase separation in Y–Ti–Al–Co alloy
Authors: Park B. J. , Chang H. J. , Kim D. H. , Kim W. T.
Published: December 2004

The Y28Ti28Al24Co20 alloy undergoes metastable liquid phase separation in the under-cooled liquid state and subsequently solidifies into two different Y-rich and Ti-rich amorphous phases. Secondary phase separation occurs due to the supersaturation of the primary separated liquids as the temperature decreases. Depending on the degree of local undercooling, a wide range of length scale of the microstructure is observed. The characteristic length scale of the two amorphous phases is ∼250nm near the air side of the ribbon, and ∼25nm near the wheel side of the ribbon.
Chemical depth profile of passive oxide on stainless steel
Authors: Kim D. H. , Lee H. H. , Kim S. S. , Kang H. C. , Noh D. Y. , Kim H. , Sinha S. K.
Published: December 2004

The chemical depth profile of the passive oxides formed on a stainless-steel surface (type 430, Fe–16.3%Cr) in pH 8.4 borate solution was obtained quantitatively by in situ anomalous x-ray reflectivity. The passive film consists of a Cr oxide inner layer and a Fe∕Cr oxide outer layer. The absence of Fe oxide underneath Cr oxide indicates that Cr oxide provides the passivity in stainless steel by inhibiting oxygen anion diffusion. The oxide grows by limited metallic cation transfer. The passivity breaks down in transpassive regime due to the oxidation of the Cr oxide to a soluble oxide.
High-pressure deuterium annealing for improving the reliability characteristics of silicon–oxide–nitride–oxide–silicon nonvolatile memory devices
Authors: Choi Sangmoo , Jang Man , Park Hokyung , Hwang Hyunsang , Jeon Sanghun , Kim Juhyung , Kim Chungwoo
Published: December 2004

We report the effects of high-pressure deuterium postmetallization annealing on the reliability characteristics of silicon–oxide–nitride–oxide–silicon nonvolatile memory devices. Compared with the control samples annealed in a conventional forming gas ambient (H2∕N2=4%∕96%), the samples annealed in a high-pressure (10 atm) pure deuterium ambient show improved endurance and retention characteristics without the degradation of program/erase (P/E) speed. In addition, the high-pressure deuterium-annealed samples show a significantly reduced charge loss rate for the electron-stored state and the hole-stored state, before and after the P/E cycles. The improved reliability of the high-pressure deuterium-annealed samples can be explained by the significantly decreased interface trap density and the large kinetic isotope effect of deuterium, which reduces the generation of the interface trap density under the stress of the P/E cycles.
Nanoscale chemical sensor based on organic thin-film transistors
Authors: Wang Liang , Fine Daniel , Dodabalapur Ananth
Published: December 2004

Nanoscale organic thin-film transistors were fabricated to investigate their chemical sensing properties. The use of a four-terminal geometry ensures that the sensor active area is truly nanoscale, and eliminates undesirable spreading currents. The sensor response was markedly different in nanoscale sensors compared to large-area sensors for the same analyte–semiconductor combination. The chemical sensing mechanisms in both microscale and nanoscale transistors are briefly discussed.
Transformed material coefficients for single-domain 0.67Pb(Mg1∕3Nb2∕3)O3–0.33PbTiO3 single crystals under differently defined coordinate systems
Authors: Zhang Rui , Cao Wenwu
Published: December 2004

Due to the confusion in choosing coordinate systems, there occurred some misrepresentations/calculations of effective material properties of 0.67Pb(Mg1∕3Nb2∕3)O3–0.33PbTiO3 single crystals based on its single-domain data. This letter is to clarify these confusions by providing proper data set for each of the currently used coordinate systems.
Weak localization thickness measurements of Si:P delta-layers
Authors: Sullivan D. F. , Kane B. E. , Thompson P. E.
Published: December 2004

We report on our results for the characterization of Si:P delta-layers grown by low temperature molecular beam epitaxy. Our data show that the effective thickness of a delta-layer can be obtained through a weak localization analysis of electrical transport measurements performed in perpendicular and parallel magnetic fields. An estimate of the diffusivity of phosphorus in silicon is obtained by applying this method to several samples annealed at 850°C for intervals of 0–15min. With further refinements, this may prove to be the most precise method of measuring delta-layer widths developed to date, including that of secondary ion mass spectrometry analysis.
Near-field second-harmonic imaging of thin ferromagnetic films
Authors: Dickson W. , Takahashi S. , Pollard R. , Zayats A. V.
Published: December 2004

The principles of magnetic domain image formation in second-harmonic near-field microscopy have been investigated in the case of in-plane magnetic anisotropy. Due to the electromagnetic interaction between a probe and a surface, magnetic contrast can be achieved by observing near-field intensity variations of the SH light for both polarizations of the fundamental light in the longitudinal and transverse illumination configurations without polarization analysis. Domains in thin ferromagnetic films of Ni and Co exhibiting in-plane magnetization have been imaged using the developed approach.
Charge controlled, fixed optic axis analog (“v-shaped”) switching of a bent-core ferroelectric liquid crystal
Authors: O’Callaghan Michael J. , Wand Michael D. , Walker Christopher M. , Nakata Michi
Published: December 2004

Recently discovered anticlinic ferroelectric liquid crystals (FLCs) offer a mode of fast fixed-optic-axis electro-optic modulation useful for a variety of applications. In addition, the high spontaneous polarization of a member of this class of FLCs (∼500–600nC∕cm2) suggests that it is a good candidate for electrostatically controlled thresholdless analog switching, whereas conventional SmC* FLCs have a binary response. Using a simple charge control drive circuit, we have found that this FLC is in fact capable of hysteresis-free analog switching. An optical model suggests that this class of FLCs might be engineered to have a much larger electro-optic effect than seen in this example.
Gate-induced crossover from unconventional metals to Fermi liquids in multiwalled carbon nanotubes
Authors: Kanbara Takayoshi , Iwasa Tatsuya , Tsukagoshi Kazuhito , Aoyagi Yoshinobu , Iwasa Yoshihiro
Published: December 2004

We observed an ambipolar behavior in multiwalled carbon nanotubes in a backgate configuration, which allowed us to perform systematic inspection of the low-temperature transport properties against gate voltage. The results revealed that a power-law temperature-dependent conductance, which is a sign of an unconventional metallic state, disappears when a high gate voltage is applied, and conductance becomes temperature independent, indicating a normal Fermi liquid state. This demonstrates a field effect tuning of electronic states in nanoscaled materials.
Uncovering the hidden ground state of green fluorescent protein
Authors: Kennis John T. M. , Larsen Delmar S. , van Stokkum Ivo H. M. , Vengris Mikas , van Thor Jasper J. , van Grondelle Rienk
Published: December 2004

The fluorescence properties of GFP are strongly influenced by the protonation states of its chromophore and nearby amino acid side chains. In the ground state, the GFP chromophore is neutral and absorbs in the near UV. Upon excitation, the chromophore is deprotonated, and the resulting anionic chromophore emits its green fluorescence. So far, only excited-state intermediates have been observed in the GFP photocycle. We have used ultrafast multipulse control spectroscopy to prepare and directly observe GFP's hidden anionic ground-state intermediates as an integral part of the photocycle. Combined with dispersed multichannel detection and advanced global analysis techniques, the existence of two distinct anionic ground-state intermediates, I
1
and I
2
, has been unveiled. I
1
and I
2
absorb at 500 and 497 nm, respectively, and interconvert on a picosecond timescale. The I
2
intermediate has a lifetime of 400 ps, corresponding to a proton back-transfer process that regenerates the neutral ground state. Hydrogen/deuterium exchange of the protein leads to a significant increase of the I
1
and I
2
lifetimes, indicating that proton motion underlies their dynamics. We thus have assessed the complete chain of reaction intermediates and associated timescales that constitute the photocycle of GFP. Many elementary processes in biology rely on proton transfers that are limited by slow diffusional events, which seriously precludes their characterization. We have resolved the true reaction rate of a proton transfer in the molecular ground state of GFP, and our results may thus aid in the development of a generic understanding of proton transfer in biology.
An ecological approach to preventing human infection: Vaccinating wild mouse reservoirs intervenes in the Lyme disease cycle
Authors: Tsao Jean I. , Wootton J. Timothy , Bunikis Jonas , Luna Maria Gabriela , Fish Durland , Barbour Alan G.
Published: December 2004

Many pathogens, such as the agents of West Nile encephalitis and plague, are maintained in nature by animal reservoirs and transmitted to humans by arthropod vectors. Efforts to reduce disease incidence usually rely on vector control or immunization of humans. Lyme disease, for which no human vaccine is currently available, is a commonly reported vector-borne disease in North America and Europe. In a recently developed, ecological approach to disease prevention, we intervened in the natural cycle of the Lyme disease agent (Borrelia burgdorferi) by immunizing wild white-footed mice (Peromyscus leucopus), a reservoir host species, with either a recombinant antigen of the pathogen, outer surface protein A, or a negative control antigen in a repeated field experiment with paired experimental and control grids stratified by site. Outer surface protein A vaccination significantly reduced the prevalence ofB. burgdorferiin nymphal blacklegged ticks (Ixodes scapularis) collected at the sites the following year in both experiments. The magnitude of the vaccine's effect at a given site correlated with the tick infection prevalence found on the control grid, which in turn correlated with mouse density. These data, as well as differences in the population structures ofB. burgdorferiin sympatric ticks and mice, indicated that nonmouse hosts contributed more to infecting ticks than previously expected. Thus, where nonmouse hosts play a large role in infection dynamics, vaccination should be directed at additional species.
Global network analysis of phenotypic effects: Protein networks and toxicity modulation in
Saccharomyces cerevisiae
Authors: Said Maya R. , Begley Thomas J. , Oppenheim Alan V. , Lauffenburger Douglas A. , Samson Leona D.
Published: December 2004

Using genome-wide information to understand holistically how cells function is a major challenge of the postgenomic era. Recent efforts to understand molecular pathway operation from a global perspective have lacked experimental data on phenotypic context, so insights concerning biologically relevant network characteristics of key genes or proteins have remained largely speculative. Here, we present a global network investigation of the genotype/phenotype data set we developed for the recovery of the yeast
Saccharomyces cerevisiae
from exposure to DNA-damaging agents, enabling explicit study of how protein–protein interaction network characteristics may be associated with phenotypic functional effects. We show that toxicity-modulating proteins have similar topological properties as essential proteins, suggesting that cells initiate highly coordinated responses to damage similar to those needed for vital cellular functions. We also identify toxicologically important protein complexes, pathways, and modules. These results have potential implications for understanding toxicity-modulating processes relevant to a number of human diseases, including cancer and aging.
Systemic delivery of antisense oligoribonucleotide restores dystrophin expression in body-wide skeletal muscles
Authors: Lu Qi Long , Rabinowitz Adam , Chen Yun Chao , Yokota Toshifumi , Yin HaiFang , Alter Julia , Jadoon Atif , Bou-Gharios George , Partridge Terence
Published: December 2004

Antisense oligonucleotide-mediated alternative splicing has great potential for treatment of Duchenne muscular dystrophy (DMD) caused by mutations within nonessential regions of the dystrophin gene. We have recently shown in the dystrophic
mdx
mouse that exon 23, bearing a nonsense mutation, can be skipped after intramuscular injection of a specific 2′-
O
-methyl phosphorothioate antisense oligoribonucleotide (2OMeAO). This skipping created a shortened, but in-frame, transcript that is translated to produce near-normal levels of dystrophin expression. This expression, in turn, led to improved muscle function. However, because DMD affects muscles body-wide, effective treatment requires dystrophin induction ideally in all muscles. Here, we show that systemic delivery of specific 2OMeAOs, together with the triblock copolymer F127, induced dystrophin expression in all skeletal muscles but not in cardiac muscle of the
mdx
dystrophic mice. The highest dystrophin expression was detected in diaphragm, gastrocnemius, and intercostal muscles. Large numbers of fibers with near-normal level of dystrophin were observed in focal areas. Three injections of 2OMeAOs at weekly intervals enhanced the levels of dystrophin. Dystrophin mRNA lacking the targeted exon 23 remained detectable 2 weeks after injection. No evidence of tissue damage was detected after 2OMeAO and F127 treatment either by serum analysis or histological examination of liver, kidney, lung, and muscles. The simplicity and safety of the antisense protocol provide a realistic prospect for treatment of the majority of DMD mutations. We conclude that a significant therapeutic effect may be achieved by further optimization in dose and regime of administration of antisense oligonucleotide.
Density matters: The semiconservative replication of DNA
Authors: Hanawalt Philip C.
Published: December 2004

The semiconservative mode of DNA replication was originally documented through the classic density labeling experiments of Matthew Meselson and Franklin W. Stahl, as communicated to PNAS by Max Delbrück in May 1958. The ultimate value of their novel approach has extended far beyond the initial implications from that elegant study, through more than four decades of research on DNA replication, recombination, and repair. I provide here a short historical commentary and then an account of some developments in the field of DNA replication, which closely followed the Meselson–Stahl experiment. These developments include the application of density labeling to discover the repair replication of damaged DNA, a “nonconservative” mode of synthesis in which faulty sections of DNA are replaced.
Lentivirus-based genetic manipulations of cortical neurons and their optical and electrophysiological monitoring
in vivo
Authors: Dittgen Tanjew , Nimmerjahn Axel , Komai Shoji , Licznerski Pawel , Waters Jack , Margrie Troy W. , Helmchen Fritjof , Denk Winfried , Brecht Michael , Osten Pavel
Published: December 2004

It is becoming increasingly clear that single cortical neurons encode complex and behaviorally relevant signals, but efficient means to study gene functions in small networks and single neurons
in vivo
are still lacking. Here, we establish a method for genetic manipulation and subsequent phenotypic analysis of individual cortical neurons
in vivo
. First, lentiviral vectors are used for neuron-specific gene delivery from α-calcium/calmodulin-dependent protein kinase II or Synapsin I promoters, optionally in combination with gene knockdown by means of U6 promoter-driven expression of short-interfering RNAs. Second, the phenotypic analysis at the level of single cortical cells is carried out by using two-photon microscopy-based techniques: high-resolution two-photon time-lapse imaging is used to monitor structural dynamics of dendritic spines and axonal projections, whereas cellular response properties are analyzed electrophysiologically by two-photon microscopydirected whole-cell recordings. This approach is ideally suited for analysis of gene functions in individual neurons in the intact brain.
Juvenile zebra finches can use multiple strategies to learn the same song
Authors: Liu Wan-chun , Gardner Timothy J. , Nottebohm Fernando
Published: December 2004

Does the ontogeny of vocal imitation follow a set program that, given a target sound, unfolds in a predictable manner, or is it more like problem solving, with many possible solutions? We report that juvenile male zebra finches,
Taeniopygia guttata
, can master their imitation of the same song in various ways; these developmental trajectories are sensitive to the social setting in which the bird grows up. A variety of vocal developmental trajectories have also been described in infants. Are these many ways to learn unique to the vocal domain or a hallmark of advanced brain function?
Directed migration of neural stem cells to sites of CNS injury by the stromal cell-derived factor 1α/CXC chemokine receptor 4 pathway
Authors: Imitola Jaime , Raddassi Khadir , Park Kook In , Mueller Franz-Josef , Nieto Marta , Teng Yang D. , Frenkel Dan , Li Jianxue , Sidman Richard L. , Walsh Christopher A. , Snyder Evan Y. , Khoury Samia J.
Published: December 2004

Migration toward pathology is the first critical step in stem cell engagement during regeneration. Neural stem cells (NSCs) migrate through the parenchyma along nonstereotypical routes in a precise directed manner across great distances to injury sites in the CNS, where they might engage niches harboring local transiently expressed reparative signals. The molecular mechanisms for NSC mobilization have not been identified. Because NSCs seem to home similarly to pathologic sites derived from disparate etiologies, we hypothesized that the inflammatory response itself, a characteristic common to all, guides the behavior of potentially reparative cells. As proof of concept, we show that human NSCs migratein vivo(including from the contralateral hemisphere) toward an infarcted area (a representative CNS injury), where local astrocytes and endothelium up-regulate the inflammatory chemoattractant stromal cell-derived factor 1α (SDF-1α). NSCs express CXC chemokine receptor 4 (CXCR4), the cognate receptor for SDF-1α. Exposure of SDF-1α to quiescent NSCs enhances proliferation, promotes chain migration and transmigration, and activates intracellular molecular pathways mediating engagement. CXCR4 blockade abrogates their pathology-directed chain migration, a developmentally relevant mode of tangential migration that, if recapitulated, could explain homing along nonstereotypical paths. Our data implicate SDF-1α/CXCR4, representative of the inflammatory milieu characterizing many pathologies, as a pathway that activates NSC molecular programs during injury and suggest that inflammation may be viewed not simply as playing an adverse role but also as providing stimuli that recruit cells with a regenerative homeostasis-promoting capacity. CXCR4 expression within germinal zones suggests that NSC homing after injury and migration during development may invoke similar mechanisms.
Gene expression profiles of epithelial cells microscopically isolated from a breast-invasive ductal carcinoma and a nodal metastasis
Authors: Zucchi I. , Mento E. , Kuznetsov V. A. , Scotti M. , Valsecchi V. , Simionati B. , Vicinanza E. , Valle G. , Pilotti S. , Reinbold R. , Vezzoni P. , Albertini A. , Dulbecco R.
Published: December 2004

Expression profiles of breast carcinomas are difficult to interpret when they are obtained from tissue
in toto
, which may contain a large proportion of non-cancer cells. To avoid this problem, we microscopically isolated cells from a primary invasive ductal carcinoma of the breast and from an axillary node harboring a metastatic breast carcinoma, to obtain pure populations of carcinoma cells (≈500) and used them for serial analysis of gene expression. The expression profiles generated from both populations of cells were compared with the profile of a disease-free mammary epithelium. We showed that the expression profiles obtained are exclusive of carcinoma cells with no contribution of non-epithelial cells. From a total of 16,939 unique tags analyzed, we detected 559 statistically significant changes in gene expression; some of these genes have not been previously associated with breast cancer. We observed that many of the down-regulated genes are the same in both cancers, whereas the up-regulated genes are completely different, suggesting that the down-regulation of a set of genes may be the basic mechanism of cancer formation, while the up-regulation may characterize and possibly control the state of evolution of individual cancers. The results obtained may help in characterizing the neoplastic process of breast cancer.
N
-ethylmaleimide-sensitive factor is required for the synaptic incorporation and removal of AMPA receptors during cerebellar long-term depression
Authors: Steinberg Jordan P. , Huganir Richard L. , Linden David J.
Published: December 2004

Cerebellar long-term depression (LTD) is a persistent attenuation of synaptic transmission at the parallel fiber–Purkinje cell synapse mediated by the removal of GluR2 subunit-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. The removal of AMPA receptors requires protein kinase C phosphorylation of the GluR2 subunit within its carboxyl-terminal PSD-95/Discs Large/Zona Occludens-1 (PDZ) ligand and binding of the PDZ domain-containing protein, PICK1. The sequence of the GluR2 subunit is similar to that of the GluR3 and GluR4c subunits, which also contain PDZ ligands and protein kinase C consensus sites. Although GluR3 and GluR4c are also expressed in Purkinje cells, we have previously shown that cerebellar LTD is absent in GluR2
–/–
mice, suggesting that these subunits are unable to substitute functionally for GluR2. Here, we examine the apparent difference in the regulation of these AMPA receptor subunits by attempting to rescue LTD in GluR2
–/–
Purkinje cells with WT and mutant GluR2 and GluR3 subunits. Our results show that the selective interaction of the GluR2 subunit with the
N
-ethylmaleimide-sensitive factor protein is required for synaptic, but not extrasynaptic, incorporation of AMPA receptors as well as for their competence to undergo LTD. In addition, perfusion of a synthetic peptide that acutely disrupts the interaction of GluR2 with
N
-ethylmaleimide-sensitive factor selectively depletes GluR2-containing receptors from synapses and occludes LTD. These findings demonstrate that interaction of AMPA receptors with
N
-ethylmaleimide-sensitive factor plays a critical role in incorporation of AMPA receptors into synapses and for their subsequent removal during cerebellar LTD.
Regulation of a protein phosphatase cascade allows convergent dopamine and glutamate signals to activate ERK in the striatum
Authors: Valjent Emmanuel , Pascoli Vincent , Svenningsson Per , Paul Surojit , Enslen Hervé , Corvol Jean-Christophe , Stipanovich Alexandre , Caboche Jocelyne , Lombroso Paul J. , Nairn Angus C. , Greengard Paul , Hervé Denis , Girault Jean-Antoine
Published: December 2004

Many drugs of abuse exert their addictive effects by increasing extracellular dopamine in the nucleus accumbens, where they likely alter the plasticity of corticostriatal glutamatergic transmission. This mechanism implies key molecular alterations in neurons in which both dopamine and glutamate inputs are activated. Extracellular signal-regulated kinase (ERK), an enzyme important for long-term synaptic plasticity, is a good candidate for playing such a role. Here, we show in mouse that
d
-amphetamine activates ERK in a subset of medium-size spiny neurons of the dorsal striatum and nucleus accumbens, through the combined action of glutamate NMDA and D1-dopamine receptors. Activation of ERK by
d
-amphetamine or by widely abused drugs, including cocaine, nicotine, morphine, and Δ
9
-tetrahydrocannabinol was absent in mice lacking dopamine- and cAMP-regulated phosphoprotein of
M
r
32,000 (DARPP-32). The effects of
d
-amphetamine or cocaine on ERK activation in the striatum, but not in the prefrontal cortex, were prevented by point mutation of Thr-34, a DARPP-32 residue specifically involved in protein phosphatase-1 inhibition. Regulation by DARPP-32 occurred both upstream of ERK and at the level of striatal-enriched tyrosine phosphatase (STEP). Blockade of the ERK pathway or mutation of DARPP-32 altered locomotor sensitization induced by a single injection of psychostimulants, demonstrating the functional relevance of this regulation. Thus, activation of ERK, by a multilevel protein phosphatase-controlled mechanism, functions as a detector of coincidence of dopamine and glutamate signals converging on medium-size striatal neurons and is critical for long-lasting effects of drugs of abuse.
Surface-enhanced Raman scattering on tunable plasmonic nanoparticle substrates
Authors: Jackson J. B. , Halas N. J.
Published: December 2004

Au and Ag nanoshells are investigated as substrates for surface-enhanced Raman scattering (SERS). We find that SERS enhancements on nanoshell films are dramatically different from those observed on colloidal aggregates, specifically that the Raman enhancement follows the plasmon resonance of the individual nanoparticles. Comparative finite difference time domain calculations of fields at the surface of smooth and roughened nanoshells reveal that surface roughness contributes only slightly to the total enhancement. SERS enhancements as large as 2.5 × 10
10
on Ag nanoshell films for the nonresonant molecule
p
-mercaptoaniline are measured.
Nanoscale waviness of low-angle grain boundaries
Authors: Johnson Craig L. , Hÿtch Martin J. , Buseck Peter R.
Published: December 2004

Low-angle grain boundaries (LAGBs) are ubiquitous in natural and man-made materials and profoundly affect many of their mechanical, chemical, and electrical properties. The properties of LAGBs are understood in terms of their constituent dislocations that accommodate the small misorientations between grains. Discrete dislocations result in a heterogeneous local structure along the boundary. In this article, we report the lattice rotation across a LAGB in olivine (Mg
1.8
Fe
0.2
SiO
4
) measured at the nanometer scale by using quantitative high-resolution transmission electron microscopy. The analysis reveals a grain boundary that is corrugated. Elastic calculations show that this waviness is independent of the host material and thus a general feature of LAGBs. Based on our observations and analysis, we provide equations for the boundary position, local curvature, and the lattice rotation field for any LAGB. These results provide the basis for a reexamination of grain-boundary properties in materials such as high-temperature superconductors, nanocrystalline materials, and naturally deformed minerals.
RETRACTED: Vitamin C conjugates of genotoxic lipid peroxidation products: Structural characterization and detection in human plasma
Authors: Sowell John , Frei Balz , Stevens Jan F.
Published: December 2004

α,β-Unsaturated aldehydes such as 4-hydroxy-2-nonenal (HNE) and other electrophilic lipid peroxidation (LPO) products may contribute to the pathogenesis of cancer, cardiovascular diseases, and other age-related diseases by cytotoxic, genotoxic, and proinflammatory mechanisms. The notion that vitamin C (ascorbic acid) acts as a biological antioxidant has been challenged recently by an
in vitro
study showing that ascorbic acid promotes, rather than inhibits, the formation of genotoxic LPO products from the lipid hydroperoxide, hydroperoxy octadecadienoic acid [Lee, S. H., Oe, T. & Blair, I. A. (2001)
Science
292, 2083–2086]. Here, we demonstrate that ascorbic acid acts as a nucleophile and forms Michael-type conjugates with electrophilic LPO products. Several ascorbyl-LPO product conjugates, resulting from the interaction of ascorbic acid with hydroperoxy octadecadienoic acid
in vitro
, were identified by tandem MS, including ascorbyl conjugates of HNE, 4-oxo-2-nonenal, and presumably, 12-oxo-9-hydroxy-10-dodecenoic acid. The same ascorbyl-LPO product conjugates were detected in human plasma. The concentration of the ascorbyl-HNE conjugate in plasma from 11 healthy subjects was found to be 1.30 ± 0.74 μM (mean ± SD). Our data identify ascorbylation (vitamin C conjugation) as a previously unrecognized, biologically relevant pathway for the elimination of electrophilic LPO products, and have implications for the prevention and treatment of chronic inflammatory diseases, as well as the development of novel biomarkers of oxidative stress.
Splicing of U12-type introns deposits an exon junction complex competent to induce nonsense-mediated mRNA decay
Authors: Hirose Tetsuro , Shu Mei-Di , Steitz Joan A.
Published: December 2004

Metazoan cells have two pathways for intron removal involving the U2- and U12-type spliceosomes, which contain mostly nonoverlapping sets of small nuclear ribonucleoproteins. We show that
in vitro
splicing of a U12-type intron assembles an exon junction complex (EJC) that is comparably positioned and contains many of the same components as that deposited by the U2-type spliceosome. The presence of a U12-type intron downstream of a premature termination codon within an open reading frame (ORF) induces nonsense-mediated decay of the mRNA
in vivo
. These findings suggest a common pathway for EJC assembly by the two spliceosomes and highlight the evolutionary age of the EJC and its downstream functions in gene expression.
Heterozygosity for
Lmna
deficiency eliminates the progeria-like phenotypes in
Zmpste24
-deficient mice
Authors: Fong Loren G. , Ng Jennifer K. , Meta Margarita , Coté Nathan , Yang Shao H. , Stewart Colin L. , Sullivan Terry , Burghardt Andrew , Majumdar Sharmila , Reue Karen , Bergo Martin O. , Young Stephen G.
Published: December 2004

Zmpste24 is a metalloproteinase required for the processing of prelamin A to lamin A, a structural component of the nuclear lamina.
Zmpste24
deficiency results in the accumulation of prelamin A within cells, a complete loss of mature lamin A, and misshapen nuclear envelopes.
Zmpste24
-deficient (
Zmpste24
–/–
) mice exhibit retarded growth, alopecia, micrognathia, dental abnormalities, osteolytic lesions in bones, and osteoporosis, which are phenotypes shared with Hutchinson–Gilford progeria syndrome, a human disease caused by the synthesis of a mutant prelamin A that cannot undergo processing to lamin A.
Zmpste24
–/–
mice also develop muscle weakness. We hypothesized that prelamin A might be toxic and that its accumulation in
Zmpste24
–/–
mice is responsible for all of the disease phenotypes. We further hypothesized that
Zmpste24
–/–
mice with half-normal levels of prelamin A (
Zmpste24
–/–
mice with one
Lmna
knockout allele) would be subjected to less toxicity and be protected from disease. Thus, we bred and analyzed
Zmpste24
–/–
Lmna
+/–
mice. As expected, prelamin A levels in
Zmpste24
–/–
Lmna
+/–
cells were significantly reduced.
Zmpste24
–/–
Lmna
+/–
mice were entirely normal, lacking all disease phenotypes, and misshapen nuclei were less frequent in
Zmpste24
–/–
Lmna
+/–
cells than in
Zmpste24
–/–
cells. These data suggest that prelamin A is toxic and that reducing its levels by as little as 50% provides striking protection from disease.
Relationships between physical and chemical characteristics of dipterocarp seeds
Authors: Nakagawa Michiko , Nakashizuka Tohru
Published: December 2004

The physical and chemical seed characteristics of 11 dipterocarp species (fourDipterocarpus, twoDryobalanopsand fiveShoreaspecies) were quantified to examine variations among species. We measured dry weight, pericarp thickness and concentrations of nitrogen, total phenol, condensed tannin, lignin, lipid, starch and total sugar. Although there was low intraspecific variation among parent trees, each species had unique characteristics. We found significant correlations between chemical defensive compounds (i.e. lignin and total phenol) and nitrogen concentration. However, these relationships were no longer significant when an outlier was removed. Fruiting frequency was not significantly correlated with any chemical compound. Seeds ofShoreaspecies had a higher concentration of lipid than seeds ofDipterocarpus. The implications of variation in the physical and chemical characteristics of dipterocarp seeds are discussed.
Ecophysiology of deep simple epicotyl morphophysiological dormancy in seeds of Gagea lutea (Liliaceae)
Authors: Kondo T. , Miura T. , Okubo N. , Shimada M. , Baskin C. , Baskin J.
Published: December 2004

The effects of temperature on embryo growth, radicle emergence and cotyledon emergence of Gagea lutea (Liliaceae), a perennial herb widely distributed in Europe, eastern Siberia, the Kurile Islands, Sakhalin and the Far East, were monitored outdoors and in laboratory tests. In Japan, this species inhabits open secondary grasslands and deciduous forests. Seeds with an underdeveloped embryo are dispersed in late May/early June in Hokkaido. The embryo elongates in autumn, and the radicle emerges from the seed in mid-October to mid-November, at temperatures of about 15/4°C. However, cotyledons do not emerge until April, after seeds with an emerged radicle are covered with snow (near 0°C) for about 4 months. In laboratory experiments, temperatures of 25/15°C or 20/10°C followed by 5–10°C were required for embryo growth and radicle emergence. Rate and percentage of cotyledon emergence were promoted by keeping seeds with an emerged radicle under snow. The optimum temperature for cotyledon emergence after 81 d under snow was 15/5°C. Thus, G. lutea has deep simple epicotyl morphophysiological dormancy, and this is the first report of epicotyl dormancy in the genus.
Germination ecophysiology of the western North American species Osmorhiza depauperata (Apiaceae): implications of preadaptation and phylogenetic niche conservatism in seed dormancy evolution
Authors: Walck Jeffrey L. , Hidayati Siti N.
Published: December 2004

Requirements for dormancy break and embryo growth were determined for seeds of the western North American species, Osmorhiza depauperata. Seeds were collected in August 2001 from Sandia Crest (3200 m elevation) and Las Huertas (2300 m), New Mexico (USA). Embryos in fresh seeds were c. 0.6 mm long, and they had to grow to c. 9–10 mm before the radicle emerged from the mericarp. Embryo growth occurred at low temperatures (1 and 5°C), and seeds germinated to high percentages at 1°C during 32 weeks of incubation in the light. No seeds germinated at 5, 15/6, 20/10, 25/15 or 30/15°C during 32 weeks of incubation. Although a 4–18 week warm-temperature (25/15°C) pretreatment increased germination rates at 1°C, it was unnecessary for a high percentage of seeds to germinate. Gibberellic acid (GA3, 10–1000 mg l–1) did not substitute for cold stratification. Seeds from the low-elevation population contained larger embryos and required less time to germinate than those from the high-elevation population. O. depauperata seeds have deep complex morphophysiological dormancy (MPD), which is similar to two other western North American congeners and an Asian congener, but different from two eastern North American congeners. Results from this study suggest that: (1) phylogenetic niche conservatism has played a role in the persistence of deep complex MPD in the three western North American species of Osmorhiza; and (2) the stimulatory effect from a warm pretreatment in species needing only cold stratification for dormancy break is a preadaptation that initiated the development of an absolute warm requirement in species needing both warm and cold stratification.
On criteria to use in studies of seed evolution
Authors: Nikolaeva M.G.
Published: December 2004

A critical analysis of different criteria used in investigating seed diversity was made. It is concluded that the most promising way to understand the evolution of seeds is to study not only their morphological features, as used by most workers in the field, but also the physiological diversity of seeds in connection with the taxonomic system of plants, together with their ecological and geographical peculiarities.
Soybean galactinol synthase forms fagopyritol B1 but not galactopinitols: substrate feeding of isolated embryos and heterologous expression
Authors: Obendorf Ralph L. , Odorcic Silvia , Ueda Takashi , Coseo Mark P. , Vassallo Elizabeth
Published: December 2004

Soybean (Glycine max(L.) Merrill) seeds accumulate sucrose, raffinose, stachyose and lesser amounts of galactopinitol A, galactopinitol B and fagopyritol B1 in axis and cotyledon tissues as part of the seed maturation process. Somatic embryos appear to be deficient in D-pinitol and galactopinitols, indicating a lack of synthesis by embryo tissuesin vitro. Isolated immature soybean zygotic embryos were fedmyo-inositol, D-pinitol, D-chiro-inositol and sucrose, individually and in combination, to evaluate the role of substrate availability on galactosyl cyclitol accumulation during precocious maturation. Feedingmyo-inositol transiently doubled galactinol accumulation with little effect on other soluble carbohydrates. Feeding D-pinitol increased free D-pinitol 8-fold, galactopinitol A 4.5-fold and galactopinitol B 4.2-fold. Stachyose concentration was 2-fold higher in cotyledons after feeding D-pinitol than after feeding D-chiro-inositol. Feeding D-chiro-inositol increased fagopyritol B1 17-fold in the axis and 7-fold in the cotyledons, but did not increase other soluble carbohydrates. Feeding D-pinitol and D-chiro-inositol together reduced uptake of D-chiro-inositol and steady-state accumulation of galactinol and galactopinitols by 50%, compared to feeding D-pinitol alone. Increasing sucrose concentration from 0 to 200 mM had no effect. Recombinant soybean galactinol synthase, heterologously expressed inEscherichia coli, catalysed the synthesis of fagopyritol B1 and galactinol, but not galactopinitols. These results were consistent with the following interpretations: D-pinitol and D-chiro-inositol were transported from maternal tissues and not synthesized in the embryo, D-chiro-inositol uptake into embryos may be reduced by D-pinitol, fagopyritol B1 was synthesized by galactinol synthase while galactopinitols were not, and fagopyritol B1 and galactopinitols accumulated in response to the supply of free D-chiro-inositol and D-pinitol to embryos.