bluuebunny/crossref_metadata_2025 huggingface dataset:
Passivation of air-exposed AlGaAs using low frequency plasma-enhanced chemical vapor deposition of silicon nitride
Authors: Jaouad A. , Aimez V.
Published: September 2006

The authors report on the development of a simple passivation technique of air-exposed AlxGa1−xAs using (NH4)2S treatment and low frequency plasma-enhanced chemical vapor deposition of silicon nitride. Metal-insulator-semiconductor capacitors were fabricated on p-AlxGa1−xAs substrates and characterized using capacitance-voltage and conductance-frequency measurements. Modulation of the surface potential is observed and unpinning of Fermi level is demonstrated. The minimum interface state density as estimated using conductance method is in the order of (2–3)×1012cm−2eV−1. The passivation potential of the low frequency plasma may be explained by the high level of hydrogen bombardment of the substrate.
Shear-driven magnetic reconnection in viscous resistive incompressible plasmas
Authors: Litvinenko Yuri E.
Published: September 2006

Planar magnetic reconnection, driven by shear flows in viscous resistive incompressible plasmas, is analyzed. Time-dependent profiles of the flow velocity and the reconnecting magnetic field are computed by solving the magnetohydrodynamic equations for disturbances of a magnetostatic configuration. The resulting asymptotic profiles for large times are characterized by boundary layers, formed at the boundaries of the region, rather than by a localized reconnecting current sheet within the region. Analysis of steady viscoresistive solutions confirms that a smooth solution, reached by a dynamically evolving system, must be nonlocalized. The results imply that at least two-dimensional shear flows are required for driving magnetic reconnection in viscous resistive plasmas.
Defect generation at SiO2∕Si interfaces by low pressure chemical vapor deposition of silicon nitride
Authors: Jin Hao , Weber K. J. , Smith P. J.
Published: September 2006

Low pressure chemical vapor deposition of Si3N4 on oxidized Si (111) surfaces causes a change in the properties of the dominant interface defect, the Pb center, observed by electron paramagnetic resonance. The change in the signature of the Pb center is consistent with the formation of an oxynitride layer at the interface, which could be formed during the initial stages of nitride layer deposition. Photoconductivity decay measurements show a concomitant increase in the minority carrier recombination rate at the Si surface. The modified Si surface shows a worse thermal stability than the as-oxidized Si surface.
Scanning transmission x-ray microscopy of isolated multiwall carbon nanotubes
Authors: Felten A. , Hody H. , Bittencourt C. , Pireaux J.-J. , Hernández Cruz D. , Hitchcock A. P.
Published: September 2006

Scanning transmission x-ray microscopy (STXM) has been used to study isolated carbon nanotubes for the first time. STXM and transmission electron microscopy were applied to the same type of nanotubes, providing unique information about their composition, and electronic and structural properties. The carbon 1s near-edge x-ray absorption fine structure spectra show significant differences between multiwall carbon nanotube and carbon nanoparticle contaminants. Pristine and acid treated multiwall carbon nanotubes were also compared, highlighting the potential of the technique to differentiate surface functional groups at the nanoscale.
Dosimetric characteristics of LiF:Mg,Cu,Si thermoluminescent materials
Authors: Lee J. I. , Yang J. S. , Kim J. L. , Pradhan A. S. , Lee J. D. , Chung K. S. , Choe H. S.
Published: September 2006

Dosimetric characteristics of LiF:Mg,Cu,Si thermoluminescent (TL) material developed at KAERI have been investigated and compared with those of commercially available LiF:Mg,Cu,P (GR-200A). LiF:Mg,Cu,Si thermoluminescence dosimeter (TLD) can be heated up to 573K without any loss of TL sensitivity or any change in the glow curve structure. High-temperature glow peak in LiF:Mg,Cu,Si is significantly lower than that in GR-200A, consequently the residual signal is only 0.025%, which is about 35 times less than that of GR-200A. The TL sensitivity of the LiF:Mg,Cu,Si TLD is about 55 and 1.1 times higher than those of the LiF:Mg,Ti (TLD-100) and GR-200A, respectively.
Point contact Andreev reflection by nanoindentation of polymethyl methacrylate
Authors: Clifford E. , Coey J. M. D.
Published: September 2006

A versatile technique for performing spin polarization measurements via point contact Andreev reflection has been developed. This technique involves depositing a superconductor (lead) onto a thin film of the material to be studied through a nanohole formed in a layer of photoresist, using an atomic force microscope as a nanoindenter. Copper and nickel were used to demonstrate the method. The polarizations of CrO2 and Co2MnSi were also measured, the former giving a value of 95%, as expected, and the latter giving 20%, which was surprisingly low for a candidate half metal.
A comparison of ultrarelativistic electron- and positron-bunch propagation in plasmas
Authors: Zhou C. T. , He X. T. , Yu M. Y.
Published: September 2006

Beam-driven acceleration of electrons and positrons by the electric field of the plasma wakefield is considered in detail using a self-consistent relativistic cylindrical particle-in-cell code with implicit electromagnetic solver. The plasma characteristics, such as the particle motion, the density, the temperatures, the wake fields, and the energies and their transfer, are investigated. Strong local energization and heating of the plasma electrons are observed. Small groups of ions in the wake can also attain temperatures higher than the secondary ionization potential of lithium vapor. It is verified that an electron bunch indeed excites a wakefield of higher energy than a positron bunch, which, in fact, behaves like a negative charge plasma bunch because of the suck-in of background plasma electrons.
Sol-gel derived multiferroic BiFeO3 ceramics with large polarization and weak ferromagnetism
Authors: Chen F. , Zhang Q. F. , Li J. H. , Qi Y. J. , Lu C. J. , Chen X. B. , Ren X. M. , Zhao Y.
Published: September 2006

Insulating BiFeO3 ceramics of single perovskite phase were prepared by rapid sintering using sol-gel derived fine powders. The ceramics are dense and consist of grains of 2–6μm in diameter. Their leakage current density remains lower than 3.02×10−4A∕cm2 under the poling field below 119kV∕cm. The main conduction mechanism from 15to119kV∕cm is space-charge-limited current relating to oxygen vacancies. The ceramics exhibit a saturated ferroelectric hysteresis loop with a large remanent polarization (2Pr=56μC∕cm2) under the applied field of 180kV∕cm. Weak ferromagnetism with remanent magnetization of 1.5×10−5μB∕Fe is observed at 10K.
Molecular conductance measurements through printed Au nanodots
Authors: Jiang W. , Garfunkel E. , Zhitenev N. , Abusch-Magder D. , Tennant D. , Bao Z.
Published: September 2006

Gold pads with ∼100nm diameter are imprinted on self-assembled monolayers of alkane dithiols of different lengths using nanotransfer printing. The pads are contacted by conductive atomic force microscope tips, and electron transport was measured as a function of force. Atomic scale topography at the metal-molecule interface is essential to describe the conductance-stress relationship. A finite force (1–10nN) deforms devices resulting in two competing effects: (a) a larger contact area and (b) deformation of the interfacial bonds and∕or tilting of the molecules. The estimated conductance of molecules is significantly smaller than results suggested in previous experiments and calculations.
A generalization of the charge equilibration method for nonmetallic materials
Authors: Nistor Razvan A. , Polihronov Jeliazko G. , Müser Martin H. , Mosey Nicholas J.
Published: September 2006

Assigning effective atomic charges that properly reproduce the electrostatic fields of molecules is a crucial step in the construction of accurate interatomic potentials. We propose a new approach to calculate these charges, which as previous approaches are, is based on the idea of charge equilibration. However, we only allow charge to flow between covalently bonded neighbors by using the concept of so-called split charges. The semiempirical fit parameters in our approach do not only reflect atomic properties (electronegativity and atomic hardness) but also bond-dependent properties. The new method contains two popular but hitherto disjunct approaches as limiting cases. We apply our methodology to a set of molecules containing the elements silicon, carbon, oxygen, and hydrogen. Effective charges derived from electrostatic potential surfaces can be predicted more than twice as accurately as with previous works, at the expense of one additional fit parameter per bond type controlling the polarizability between two bonded atoms. Additional bond-type parameters can be introduced, but barely improve the results. An increase in accuracy of only 30% over existing techniques is achieved when predicting Mulliken charges. However, this could be improved with additional bond-type parameters.
Dynamic atomic force microscopy operation based on high flexure modes of the cantilever
Authors: Girard P. , Ramonda M. , Arinero R.
Published: September 2006

We show the interest of the high flexure modes of vibration for amplitude-controlled atomic force microscopy (AFM). In connection with AFM working conditions, we define the stabilization time threshold of the oscillating sensor. We show experimentally that, in both air and vacuum, the stabilization time decreases appreciably when the order of the flexure mode of the cantilever increases. Under ambient conditions, this increases the possible scan speeds by about one order of magnitude. Under vacuum and using standard sensors, the amplitude-controlled conditions are satisfied for harmonics equal to or higher than the second. Morphology imaging is then obtained. Thus, high flexure mode AFM easily extends the well known amplitude-controlled operations from ambient to vacuum environment, which allows new AFM applications.
Effect of electromagnetic environment on the dielectric resonance in the ferroelectric-ferromagnetic composite
Authors: Bai Yang , Zhou Ji , Sun Yu , Li Bo , Yue Zhenxing , Gui Zhilun , Li Longtu
Published: September 2006

The influence of electromagnetic environment on resonance character of dielectrics was studied in the ferroelectric-ferromagnetic composite. The magnetic phase induces inhomogeneous electromagnetic environment, which will baffle the motion of charged particles in neighboring ferroelectric grains. The influence is not strong enough to change the dielectric properties of composite except for its dielectric resonance character. With the rise of permeability or proportion of magnetic phase, the dielectric resonance peak turns wider and smoother. The dielectric response tends to transit from resonance to relaxation. The electromagnetic interaction between components will prevent the resonance character for the equilibrium of the system.
High mobility n-type thin-film transistors based on N,N′-ditridecyl perylene diimide with thermal treatments
Authors: Tatemichi Shuhei , Ichikawa Musubu , Koyama Toshiki , Taniguchi Yoshio
Published: September 2006

The authors demonstrated that N,N′-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) thin-film transistors (TFTs) exhibited high field-effect electron mobility of 2.1cm2∕Vs by just annealing at an adequate temperature (140°C) after the TFT fabrications. While PTCDI-C13 formed c-axis oriented thin films, the thermal treatments improved crystallinity of the thin films as revealed by x-ray diffraction. The thermal treatment also affected thin-film morphologies; the morphologies changed from oval ball-like grains to flat and large tilelike grains, which had molecular height steps and whose size reached several micrometers.
Tunable threshold voltage and flatband voltage in pentacene field effect transistors
Authors: Wang Annie , Kymissis Ioannis , Bulović Vladimir , Akinwande Akintunde I.
Published: September 2006

Charged interface states are introduced by UV-ozone treatment of a polymer gate dielectric, parylene, prior to deposition of the organic semiconductor, pentacene, thereby modifying the organic field effect transistor (OFET) operation from enhancement to depletion mode. Quasistatic capacitance-voltage measurements and the corresponding current-voltage characteristics show that the threshold voltage VT and flatband voltage VFB can be shifted by over +50V, depending on the ozone exposure time. This work demonstrates that careful control of the semiconductor-insulator interface state densities is essential to VT and VFB control and the fabrication of reliable OFET integrated circuits.
Effective work function modulation by controlled dielectric monolayer deposition
Authors: Pantisano L. , Schram T. , O’Sullivan B. , Conard T. , De Gendt S. , Groeseneken G. , Zimmerman P. , Akheyar A. , Heyns M. M. , Shamuilla S. , Afanas’ev V. V. , Stesmans A.
Published: September 2006

It is shown that the interface between gate dielectric and metal electrode critically determines the effective work function and hence metal oxide semiconductor field effect transistor threshold voltage. Electrostatic potential at the interface is perturbed by a polarization layer and this can be engineered at a monolayer level. It is demonstrated that the interface polarization layer can be modified by carefully depositing both dielectric and metal gate materials followed by a high temperature treatment offering a route to work function control.
Interlayer exchange coupling in Fe∕MgO∕Fe magnetic tunnel junctions
Authors: Katayama T. , Yuasa S. , Velev J. , Zhuravlev M. Ye. , Jaswal S. S. , Tsymbal E. Y.
Published: September 2006

Interlayer exchange coupling (IEC) in fully epitaxial Fe∕MgO∕Fe(001) tunnel junctions with wedge-shaped MgO layers is measured at room temperature from the unidirectional shift of the Kerr hysteresis loop. It is found that the IEC is antiferromagnetic for small MgO thickness but changes sign at 0.8nm. Ab initio calculations of IEC show that this behavior can be explained by the presence of O vacancies in the MgO barrier which makes IEC antiferromagnetic for thin barriers. With increasing MgO thickness the resonance contribution to IEC from localized defect states is reduced resulting in the ferromagnetic coupling typical for perfect MgO barriers.
Plasma lens and plume divergence in the Hall thruster
Authors: Fruchtman A. , Cohen-Zur A.
Published: September 2006

The effect of magnetic field curvature on the plume divergence in the Hall thruster is analyzed. The two-dimensional plasma flow and electric field are determined self-consistently within the paraxial approximation in this plasma lens, a nearly axial electric field perpendicular to the curved magnetic field lines. The ion radial velocity along the thruster is described analytically. The authors suggest positioning the ionization layer near the zero of the magnetic field in a reversing-direction field configuration for a minimal beam divergence. They also show that an additional emitting electrode can reduce plume divergence.
Enhancement of diffraction of dye-doped polymer film assisted with nematic liquid crystals
Authors: Kuo Chie-Tong , Huang Shuan-Yu
Published: September 2006

The dynamic behavior of surface relief grating of dye-doped polymer film has been under investigation. The enhancement of the first-order diffraction efficiency for dye-doped polymer film can be demonstrated through the use of nematic liquid crystals as the interface. The larger surface modulation of relief grating measured by the atomic force microscopy is consistent with the enhancement of the first-order diffraction efficiency. The time evolution of diffraction efficiency for dye-doped polymer film in contact with nematic liquid crystals shows the pattern of rise-decay-rise to a stable level. The decay of diffraction efficiency is temperature dependent. The pump-probe transmission experiment confirms that the decay of diffraction efficiency is attributed to the inhomogeneous orientation of nematic liquid crystals due to photothermal fluctuation.
Transmission electron microscopy characterization and sculpting of sub-1nm Si–O–C freestanding nanowires grown by electron beam induced deposition
Authors: Frabboni S. , Gazzadi G. C. , Spessot A.
Published: September 2006

The authors present a transmission electron microscopy characterization and sculpting of freestanding Si–O–C nanowires, fabricated by electron beam induced deposition from a tetraethylorthosilicate precursor, in a dual beam system. Electron energy loss spectroscopy and near edge structure analyses performed on as deposited wires show the formation of amorphous silicon dioxide with extra oxygen and carbon content. Subsequent electron beam sculpting by 200keV transmission electron microscope irradiation decreases carbon and oxygen contents leaving the silicon oxidation state unchanged and narrows Si–O–C wire width to less than 1nm.
Real-time three-dimensional surface measurement by color encoded light projection
Authors: Chen S. Y. , Li Y. F. , Guan Q. , Xiao G.
Published: September 2006

Existing noncontact methods for surface measurement suffer from the disadvantages of poor reliability, low scanning speed, or high cost. The authors present a method for real-time three-dimensional data acquisition by a color-coded vision sensor composed of common components. The authors use a digital projector controlled by computer to generate desired color light patterns. The unique indexing of the light codes is a key problem and is solved in this study so that surface perception can be performed with only local pattern analysis of the neighbor color codes in a single image. Experimental examples and performance analysis are provided.
Magnetic properties of epitaxial CrN films
Authors: Ney A. , Rajaram R. , Parkin S. S. P. , Kammermeier T. , Dhar S.
Published: September 2006

The authors have investigated the structural and magnetic properties of CrN films grown on MgO(001) and sapphire(0001) by rf-plasma-assisted molecular beam epitaxy. CrN∕MgO(001) exhibits a better epitaxial quality than CrN/sapphire(0001). The CrN∕MgO film shows clear paramagnetic behavior at low temperatures, whereas CrN/sapphire exhibits a ferromagneticlike response with an order temperature above room temperature which resembles the magnetic behavior found in Cr-doped dilute magnetic semiconductors. Keeping in mind that bulk CrN exhibits antiferromagnetic behavior, the dramatically different magnetic behaviors found in epitaxial CrN films grown on MgO and sapphire demonstrate the importance of epitaxial constraints in determining their magnetic properties.
Compositional and structural changes in LiNbO3 following deep He+ ion implantation for film exfoliation
Authors: Roth Ryan M. , Djukic Djordje , Lee Yoo Seung , Osgood Richard M. , Bakhru Sasha , Laulicht Bryan , Dunn Kathleen , Bakhru Hassaram , Wu Liqi , Huang Mengbing
Published: September 2006

The physical mechanism of He-ion-based exfoliation in Z-cut LiNbO3 is investigated. Rutherford backscattering/channeling, nuclear-reaction analysis, and transmission electron microscopy are used to examine the compositional and structural changes caused by deep ion implantation followed by thermal annealing. Lattice disruption, He-bubble formation, and Li depletion are observed in the implantation region, as well as the onset of exfoliation. The implications of these observations for the crystal ion slicing method are discussed.
Pentacene: PTCDI-C13H27 molecular blends efficiently harvest light for solar cell applications
Authors: Pandey Ajay K. , Dabos-Seignon Sylvie , Nunzi Jean-Michel
Published: September 2006

Solar cells exhibiting efficient photon harvesting are built from molecular blends of pentacene: PTCDI-C13H27. Absorption of the composition spans the whole visible spectrum with an onset at 730nm. External quantum efficiency approaches unity at the peak absorption of pentacene. A 2.0% power conversion efficiency is obtained under 80mWcm−2 AM 1.5 illumination, with 8.6mAcm−2 short-circuit current. The comparison with bilayer devices suggests directions of improvement in conversion efficiency such as controlled growth of the blend layers.
Extrinsic paramagnetic Meissner effect in multiphase indium-tin alloys
Authors: Chu Shaoyan , Schwartz Adam J. , Massalski Thaddeus B. , Laughlin David E.
Published: September 2006

The authors report the observation of a paramagnetic Meissner effect (PME) in a two-phase In–Sn alloy in which the phases become superconducting at different temperatures. This observation has been tested and confirmed by constructing an artificial In–Sn sample in which one phase was deliberately encapsulated in another. The authors conclude that PME is extrinsic, rather than intrinsic, and thus describe it as an extrinsic paramagnetic Meissner effect (EPME). It is expected to occur in multiple-phase samples where more than one phase is superconducting and where a suitable microstructural phase distribution is developed. In such samples EPME can be produced at will.
Monolayer protection for eletrochemical migration control in silver nanocomposite
Authors: Li Yi , Wong C. P.
Published: September 2006

The authors introduced an effective approach of using monolayer-protected silver nanoparticles to reduce silver migration for electronic device interconnect applications. Formation of surface complex between the carboxylate anion and surface silver ion reduces the solubility and diffusivity significantly of migration components and therefore contributes to effective migration control. A fundamental understanding of the mechanism of silver migration control was conducted by studying the current-voltage relationships of the nanocomposites with a migration model. The control of silver migration enables the application of the silver composites in fine pitch and high performance electronic device interconnects.
Secondary lymphoid tissue chemokine (SLC/CCL21)/CCR7 signaling regulates fibrocytes in renal fibrosis
Authors: Sakai Norihiko , Wada Takashi , Yokoyama Hitoshi , Lipp Martin , Ueha Satoshi , Matsushima Kouji , Kaneko Shuichi
Published: September 2006

Fibrocytes are a distinct population of bloodborne cells that share markers of leukocytes as well as mesenchymal cells. We hypothesized that CCR7-positive fibrocytes migrate into the kidney in response to secondary lymphoid tissue chemokine (SLC/CCL21) and contribute to renal fibrosis. To investigate this hypothesis, renal fibrosis was induced by unilateral ureteral obstruction in mice. A considerable number of fibrocytes dual-positive for CD45 and type I collagen (ColI) or CD34 and ColI infiltrated the interstitium, reaching a peak on day 7. Most fibrocytes were positive for CCR7, and CCL21/CCR7 blockade reduced the number of infiltrating fibrocytes. CCL21 and MECA79 dual-positive vessels were also detected in the interstitium. The blockade of CCL21/CCR7 signaling by anti-CCL21 antibodies reduced renal fibrosis, which was confirmed by a decrease in fibrosis in CCR7-null mice with concomitant reduction in renal transcripts of pro α1 chain of ColI and TGF-β1. The number of F4/80-positive macrophages decreased along with renal transcripts of monocyte chemoattractant protein 1 (MCP-1/CCL2) after the blockade of CCL21/CCR7 signaling. These findings suggest that CCR7-positive fibrocytes infiltrate the kidney via CCL21-positive vessels, thereby contributing to the pathogenesis of renal fibrosis. Thus, the CCL21/CCR7 signaling of fibrocytes may provide therapeutic targets for combating renal fibrosis.
Progesterone blocks estrogen-induced DNA synthesis through the inhibition of replication licensing
Authors: Pan Haiyan , Deng Yan , Pollard Jeffrey W.
Published: September 2006

In the uterus, progesterone (P
4
) acts early in G
1
as a physiological inhibitor of estradiol-17β (E
2
)-induced epithelial cell proliferation. Gene expression profiling of uterine epithelial cell RNA isolated 3 h after hormonal treatment of ovariectomized mice revealed the co-coordinate down-regulation by P
4
of >20 genes whose functions are associated with DNA replication. This group included all of the minichromosome maintenance (MCM) proteins that are required for DNA replication licensing. E
2
regulated loading of these MCM proteins onto chromatin in parallel with its induction of DNA synthesis. E
2
caused this chromatin loading by retention of MCM proteins in the nucleus and through the induction of the loading factor Cdt1, which is necessary for the MCM heterohexamer to bind to the origin of DNA replication. P
4
dramatically reduced the binding of the MCMs to chromatin by a number of mechanisms. First, MCM mRNA and protein abundance was down-regulated. Second, P
4
inhibited the E
2
induction of Cdt1. Third, P
4
treatment sequestered the normally nuclear MCM proteins into the cytoplasm. This reduced MCM binding resulted in the complete inhibition of E
2
-induced DNA synthesis by P
4
. These data reveal mechanisms not only for female sex steroid hormone action but also in the regulation of DNA replication licensing.
Cross-protective immunity can account for the alternating epidemic pattern of dengue virus serotypes circulating in Bangkok
Authors: Adams B. , Holmes E. C. , Zhang C. , Mammen M. P. , Nimmannitya S. , Kalayanarooj S. , Boots M.
Published: September 2006

Dengue virus, the causative agent of dengue fever and its more serious manifestation dengue hemorrhagic fever, is widespread throughout tropical and subtropical regions. The virus exists as four distinct serotypes, all of which have cocirculated in Bangkok for several decades with epidemic outbreaks occurring every 8–10 years. We analyze time-series data of monthly infection incidence, revealing a distinctive pattern with epidemics of serotypes 1, 2, and 3 occurring at approximately the same time and an isolated epidemic of serotype 4 occurring in the intervening years. Phylogenetic analysis of virus samples collected over the same period shows that clade replacement events are linked to the epidemic cycle and indicates that there is an interserotypic immune reaction. Using an epidemic model with stochastic seasonal forcing showing 8- to 10-year epidemic oscillations, we demonstrate that moderate cross-protective immunity gives rise to persistent out-of-phase oscillations similar to those observed in the data, but that strong or weak cross-protection or cross-enhancement only produces in-phase patterns. This behavior suggests that the epidemic pattern observed in Bangkok is the result of cross-protective immunity and may be significantly altered by changes in the interserotypic immune reaction.
Crocidolite asbestos and SV40 are cocarcinogens in human mesothelial cells and in causing mesothelioma in hamsters
Authors: Kroczynska Barbara , Cutrone Rochelle , Bocchetta Maurizio , Yang Haining , Elmishad Amira G. , Vacek Pamela , Ramos-Nino Maria , Mossman Brooke T. , Pass Harvey I. , Carbone Michele
Published: September 2006

Only a fraction of subjects exposed to asbestos develop malignant mesothelioma (MM), suggesting that additional factors may render some individuals more susceptible. We tested the hypothesis that asbestos and Simian virus (SV40) are cocarcinogens. Asbestos and SV40 in combination had a costimulatory effect in inducing ERK1/2 phosphorylation and activator protein-1 (AP-1) activity in both primary Syrian hamster mesothelial cells (SHM) and primary human mesothelial cells (HM). Ap-1 activity caused the expression and activation of matrix metalloprotease (MMP)-1 and MMP-9, which in turn led to cell invasion. Experiments using siRNA and chemical inhibitors confirmed the specificity of these results. The same effects were observed in HM and SHM. Experiments in hamsters showed strong cocarcinogenesis between asbestos and SV40: SV40 did not cause MM, asbestos caused MM in 20% of hamsters, and asbestos and SV40 together caused MM in 90% of hamsters. Significantly lower amounts of asbestos were sufficient to cause MM in animals infected with SV40. Our results indicate that mineral fibers and viruses can be cocarcinogens and suggest that lower amounts of asbestos may be sufficient to cause MM in individuals infected with SV40.
Identification of
Clostridium difficile
toxin B cardiotoxicity using a zebrafish embryo model of intoxication
Authors: Hamm Elaine E. , Voth Daniel E. , Ballard Jimmy D.
Published: September 2006

Clostridium difficile
toxin B (TcdB) has been studied extensively by using cell-free systems and tissue culture, but, like many bacterial toxins, the
in vivo
targets of TcdB are unknown and have been difficult to elucidate with traditional animal models. In the current study, the transparent
Danio rerio
(zebrafish) embryo was used as a model for imaging of
in vivo
TcdB localization and organ-specific damage in real time. At 24 h after treatment, TcdB was found to localize at the pericardial region, and zebrafish exhibited the first signs of cardiovascular damage, including a 90% reduction in systemic blood flow and a 20% reduction in heart rate. Within 72 h of exposure to TcdB, the ventricle chamber of the heart became deformed and was unable to contract or pump blood, and the fish exhibited extensive pericardial edema. In line with the observed defects in ventricle contraction, TcdB was found to directly disrupt coordinated contractility and rhythmicity in primary cardiomyocytes. Furthermore, using a caspase-3 inhibitor, we were able to block TcdB-related cardiovascular damage and prevent zebrafish death. These findings present an insight into the
in vivo
targets of TcdB, as well as demonstrate the strength of the zebrafish embryo as a tractable model for identification of
in vivo
targets of bacterial toxins and evaluation of novel candidate therapeutics.
The cephalic neural crest exerts a critical effect on forebrain and midbrain development
Authors: Creuzet Sophie E. , Martinez Salvador , Le Douarin Nicole M.
Published: September 2006

Encephalisation is the most important characteristic in the evolutionary transition leading from protochordates to vertebrates. This event has coincided with the emergence of a transient and pluripotent structure, the neural crest (NC), which is absent in protochordates. In vertebrates, NC provides the rostral cephalic vesicles with skeletal protection and functional vascularization. The surgical extirpation of the cephalic NC, which is responsible for building up the craniofacial skeleton, results in the absence of facial skeleton together with severe defects of preotic brain development, leading to exencephaly. Here, we have analyzed the role of the NC in forebrain and midbrain development. We show that (
i
) NC cells (NCC) control
Fgf8
expression in the anterior neural ridge, which is considered the prosencephalic organizer; (
ii
) the cephalic NCC are necessary for the closure of the neural tube; and (
iii
) NCC contribute to the proper patterning of genes that are expressed in the prosencephalic and mesencephalic alar plate. Along with the development of the roof plate, NCC also concur to the patterning of the pallial and subpallial structures. We show that the NC-dependent production of FGF8 in anterior neural ridge is able to restrict
Shh
expression to the ventral prosencephalon. All together, these findings support the notion that the cephalic NC controls the formation of craniofacial structures and the development of preotic brain.
Transcriptional activation by EBV nuclear antigen 1 is essential for the expression of EBV's transforming genes
Authors: Altmann Markus , Pich Dagmar , Ruiss Romana , Wang Jindong , Sugden Bill , Hammerschmidt Wolfgang
Published: September 2006

EBV is a paradigm for human tumor viruses because, although it infects most people benignly, it also can cause a variety of cancers. Both
in vivo
and
in vitro
, EBV infects B lymphocytes in G
0
, induces them to become blasts, and can maintain their proliferation in cell culture or
in vivo
as tumors. How EBV succeeds in these contrasting cellular environments in expressing its genes that control the host has not been explained. We have genetically dissected the EBV nuclear antigen 1 (
EBNA1
) gene that is required for replication of the viral genome, to elucidate its possible role in the transcription of viral genes. Strikingly, EBNA1 is essential to drive transcription of EBV's transforming genes after infection of primary B lymphocytes.
The quantum MacMahon Master Theorem
Authors: Garoufalidis Stavros , Lê Thang T. Q. , Zeilberger Doron
Published: September 2006

We state and prove a quantum generalization of MacMahon's celebrated Master Theorem and relate it to a quantum generalization of the boson–fermion correspondence of physics.
Molecular switch for alternative conformations of the HIV-1 V3 region: Implications for phenotype conversion
Authors: Rosen Osnat , Sharon Michal , Quadt-Akabayov Sabine R. , Anglister Jacob
Published: September 2006

HIV-1 coreceptor usage plays a critical role in virus tropism and pathogenesis. A switch from CCR5- to CXCR4-using viruses occurs during the course of HIV-1 infection and correlates with subsequent disease progression. A single mutation at position 322 within the V3 loop of the HIV-1 envelope glycoprotein gp120, from a negatively to a positively charged residue, was found to be sufficient to switch an R5 virus to an X4 virus. In this study, the NMR structure of the V3 region of an R5 strain, HIV-1
JR-FL
, in complex with an HIV-1-neutralizing antibody was determined. Positively charged and negatively charged residues at positions 304 and 322, respectively, oppose each other in the β-hairpin structure, enabling a favorable electrostatic interaction that stabilizes the postulated R5 conformation. Comparison of the R5 conformation with the postulated X4 conformation of the V3 region (positively charged residue at position 322) reveals that electrostatic repulsion between residues 304 and 322 in X4 strains triggers the observed one register shift in the N-terminal strand of the V3 region. We posit that electrostatic interactions at the base of the V3 β-hairpin can modulate the conformation and thereby influence the phenotype switch. In addition, we suggest that interstrand cation-π interactions between positively charged and aromatic residues induce the switch to the X4 conformation as a result of the S306R mutation. The existence of three pairs of identical (or very similar) amino acids in the V3 C-terminal strand facilitates the switch between the R5 and X4 conformations.
Testing the importance of p27 degradation by the SCF
skp2
pathway in murine models of lung and colon cancer
Authors: Timmerbeul Inke , Garrett-Engele Carrie M. , Kossatz Uta , Chen Xueyan , Firpo Eduardo , Grünwald Viktor , Kamino Kenji , Wilkens Ludwig , Lehmann Ulrich , Buer Jan , Geffers Robert , Kubicka Stefan , Manns Michael P. , Porter Peggy L. , Roberts James M. , Malek Nisar P.
Published: September 2006

Decreased expression of the CDK inhibitor p27
kip1
in human tumors directly correlates with increased resistance to chemotherapies, increased rates of metastasis, and an overall increased rate of patient mortality. It is thought that decreased p27 expression in tumors is caused by increased proteasomal turnover, in particular activation of the pathway governed by the SCF
skp2
E3 ubiquitin protein ligase. We have directly tested the importance of the SCF
skp
-mediated degradation of p27 in tumorigenesis by analyzing the tumor susceptibility of mice that express a form of p27 that cannot be ubiquitinated and degraded by this pathway (p27T187A). In mouse models of both lung and colon cancer down-regulation of p27 promotes tumorigenesis. However, we found that preventing p27 degradation by the SCF
skp2
pathway had no impact on tumor incidence or overall survival in either tumor model. Our study unveiled a previously unrecognized role for the control of p27 mRNA abundance in the development of non-small cell lung cancers. In the colon cancer model, the frequency of intestinal adenomas was similarly unaffected by the p27T187A mutation, but, unexpectedly, we found that it inhibited progression of intestinal adenomas to carcinomas. These studies may guide the choice of clinical settings in which pharmacologic inhibitors of the Skp2 pathway might be of therapeutic value.
Ca
2+
/calmodulin-dependent protein kinase II (CaMKII) is activated by calmodulin with two bound calciums
Authors: Shifman Julia M. , Choi Mee H. , Mihalas Stefan , Mayo Stephen L. , Kennedy Mary B.
Published: September 2006

Changes in synaptic strength that underlie memory formation in the CNS are initiated by pulses of Ca
2+
flowing through NMDA-type glutamate receptors into postsynaptic spines. Differences in the duration and size of the pulses determine whether a synapse is potentiated or depressed after repetitive synaptic activity. Calmodulin (CaM) is a major Ca
2+
effector protein that binds up to four Ca
2+
ions. CaM with bound Ca
2+
can activate at least six signaling enzymes in the spine. In fluctuating cytosolic Ca
2+
, a large fraction of free CaM is bound to fewer than four Ca
2+
ions. Binding to targets increases the affinity of CaM's remaining Ca
2+
-binding sites. Thus, initial binding of CaM to a target may depend on the target's affinity for CaM with only one or two bound Ca
2+
ions. To study CaM-dependent signaling in the spine, we designed mutant CaMs that bind Ca
2+
only at the two N-terminal or two C-terminal sites by using computationally designed mutations to stabilize the inactivated Ca
2+
-binding domains in the “closed” Ca
2+
-free conformation. We have measured their interactions with CaMKII, a major Ca
2+
/CaM target that mediates initiation of long-term potentiation. We show that CaM with two Ca
2+
ions bound in its C-terminal lobe not only binds to CaMKII with low micromolar affinity but also partially activates kinase activity. Our results support the idea that competition for binding of CaM with two bound Ca
2+
ions may influence significantly the outcome of local Ca
2+
signaling in spines and, perhaps, in other signaling pathways.
A mutation in the translation initiation codon of
Gata-1
disrupts megakaryocyte maturation and causes thrombocytopenia
Authors: Majewski Ian J. , Metcalf Donald , Mielke Lisa A. , Krebs Danielle L. , Ellis Sarah , Carpinelli Marina R. , Mifsud Sandra , Di Rago Ladina , Corbin Jason , Nicola Nicos A. , Hilton Douglas J. , Alexander Warren S.
Published: September 2006

We have generated mice from a
N
-ethyl-
N
-nitrosourea mutagenesis screen that carry a mutation in the translation initiation codon of
Gata-1
, termed
Plt13
, which is equivalent to mutations found in patients with acute megakaryoblastic leukemia and Down syndrome. The
Gata-1
locus is present on the X chromosome in humans and in mice. Male mice hemizygous for the mutation (

Gata-1
Plt13

/Y) failed to produce red blood cells and died during embryogenesis at a similar stage to
Gata-1
-null animals. Female mice that carry the
Plt13
mutation are mosaic because of random inactivation of the X chromosome. Adult
Gata-1

Plt13
/+

females were not anemic, but they were thrombocytopenic and accumulated abnormal megakaryocytes without a concomitant increase in megakaryocyte progenitor cells.
Gata-1

Plt13
/+

mice contained large numbers of blast-like colony-forming cells, particularly in the fetal liver, but also in adult spleen and bone marrow, from which continuous mast cells lines were readily derived. Although the equivalent mutation to

Gata-1
Plt13

in humans results in production of GATA-1s, a short protein isoform initiated from a start codon downstream of the mutated initiation codon, Gata-1s was not detected in
Gata-1

Plt13
/+

mice.
Cognitive testing toward the future: The example of Semantic Verbal Fluency (ANIMALS)
Authors: Ardila Alfredo , Ostrosky‐Solís Feggy , Bernal Byron
Published: September 2006

We are proposing that, in the future, tests included in psychological and neuropsychological batteries should fulfil the following criteria. (1) Have a large enough normative database (“normative criterion”). Performance of subjects of different ages and different educational levels, including illiterates, should be well established. Normative data from different countries and cultural contexts should be available. (2) Know the effects of brain damage on different characteristics on the test (“clinical criterion”). (3) Know how the brain is activated when the test is performed (“experimental criterion”). (4) Know how this test correlates with other cognitive tests (“psychometric criterion”). Few contemporary tests fulfil all these criteria. A notable exception is Semantic Verbal Fluency test using the category ANIMALS. This test requires the generation of words corresponding to a specific semantic category, such as animals, fruits, vegetables, etc. Typically, the number of correct words produced in 1 minute is counted. Semantic verbal fluency taps lexical knowledge and semantic memory organization. Using regional cerebral blood flow measures, it has been reported that both frontal and temporal activation are observed while performing this test. Optimal fluency performance involves generating words within a subcategory and, when a subcategory is exhausted, switching to a new subcategory. Although different semantic categories have been used in this test, ANIMALS is the most frequent due to some significant advantages: (1) it is a clear enough semantic category across languages and cultures; (2) it is a relatively easy semantic category with only minor differences among people living in different countries, different educational systems, or belonging to different generations; and (3) it is an easy‐to‐administer, short, and common test included in different neuropsychological test batteries. It is concluded that obtaining similar information for other cognitive tests represents a huge research endeavour for psychology and neuropsychology during the 21st century.
Cross‐linguistic meta‐analysis of phonological fluency: Normal performance across cultures
Authors: Oberg Gunilla , Ramírez Maura
Published: September 2006

The Verbal Fluency test is used extensively in clinical neuropsychological assessment as well as in research protocols. The phonological fluency task can be administered to individuals of various ages and different levels of education. Diverse investigations suggest that phonological fluency can be influenced by age and education. Up to now, cross‐cultural studies comparing phonological verbal fluency in different languages are scarce, and those studies that exist do not report subjects' execution comparing the level of education and age ranges. The purpose of the present study was to analyse the influence of education, culture, and primary language on the performance of phonological verbal fluency in neurologically intact subjects from different countries. The performance of phonological fluency in high‐ and lower‐frequency letters of a sample of 926 healthy subjects living in five different countries and speaking diverse languages (Danish, English, Spanish, Hebrew), with a higher level of education (more than 10 years), was analysed. Results of the meta‐analysis suggest that level of education influenced the number of words generated, and higher‐frequency letters produced a higher number of words in all languages. As long as years of education and letter frequency within each language were considered, the number of words generated was remarkably similar across languages and across countries. However, level of education and letter frequency within each language are relevant variables, therefore norms for one type and/or set of letters may be inappropriate for another group. In summary, regardless of the primary language and the ethnic background of the examinee, phonological verbal fluency could be a useful diagnostic tool if the level of education of the subjects being evaluated is considered. More extensive investigations that analyse the influence of culture on neuropsychological tests will clarify its effects on cognitive processes.
The MMPI‐2 Gender‐Masculine and Gender‐Feminine scales: Gender roles as predictors of psychological health in clinical patients
Authors: Woo Matthew , Oei Tian P. S.
Published: September 2006

Previous research measuring various biosocial factors such as age, sex, and marital status has found them to be essentially unrelated to measures of psychological health. Recent empirical studies have revealed that personality constructs may be more significant than demographic variables in the prediction of psychological well‐being. The present study assessed the personality constructs of masculinity and femininity and hypothesized that the Gender‐Masculine (GM) scale of the MMPI‐2 would be more effective than the Gender‐Feminine (GF) scale in predicting psychological well‐being. This hypothesis stems from previous research that has indicated the dominance of the masculinity model. It is suggested that previous research supporting androgyny as a primary indicator of well‐being was influenced by the masculinity component of this gender orientation. One hundred and seventy‐seven psychiatric patients from Australia (N = 107) and Singapore (N = 70) completed the MMPI‐2. Hierarchical multiple regression revealed significantly stronger masculinity effects, with significance achieved on measures of ego strength and low self‐esteem. No significant relationship between psychological well‐being and the GF variable was found. Similarly, androgyny did not add any further variance to the model when masculinity was controlled for. Overall, the results are consistent with an interpretation that GM is a better correlate of psychological well‐being as compared to the GF scale.
A person‐centred approach to identifying acculturation groups among Chinese Canadians
Authors: Chia Ai‐Lan , Costigan Catherine L.
Published: September 2006

This study adopted a person‐centred approach to explore acculturation groups among Chinese Canadians and to examine the demographic and adjustment profiles associated with each group. A total of 234 Chinese Canadian university students completed measures assessing different aspects of their Chinese and Canadian cultural orientations. Cluster analyses identified five acculturation groups: Integrated Group, Separated Group, Assimilated Group, Integrated Group without Chinese Practices, and Marginalized Group with Chinese Practices. Three of the five groups resembled Berry's acculturation model, and the other two groups demonstrated unique constellations of cultural orientations. The differences between the current acculturation groups and Berry's acculturation strategies were due to the differentiation between internal and external domains of cultural orientation, the addition of the domain of ethnic group evaluation, which is not typically included in acculturation research, and the use of cluster analysis, which allows for varying degrees of immersion in multiple domains of acculturation. Expected differences among the five acculturation groups in terms of participants' demographic backgrounds (e.g., length of residence in Canada), language preferences, and psychological adjustment supported the validity of the cluster solution. As expected, members of the Marginalized Group with Chinese Practices, the largest single group in the current sample, reported poorer adjustment than the Assimilated Group and the Integrated Group without Chinese Practices. The results of this study highlight the value of simultaneously considering multiple domains of acculturation and argue against research methods that assume acculturation status based on background factors such as place of birth or language use. Implications of these findings for understanding the cultural adaptation of Chinese Canadians are discussed.