bluuebunny/crossref_metadata_2025 huggingface dataset:
Elemental analysis with the helium ion microscope
Authors: Sijbrandij Sybren , Thompson Bill , Notte John , Ward Bill W. , Economou Nicholas P.
Published: December 2008

The newly developed helium ion microscope is an instrument well suited to high resolution surface specific imaging with several unique contrast mechanisms. In addition to its imaging capabilities, the focused helium ion beam (subnanometer in size) has recently been used for elemental analysis. The scattering probability, angular distribution, and recoil energy combine to provide valuable information about the specimen being analyzed.
Nanomodified surfaces and guidance of nerve cell processes
Authors: Johansson Fredrik , Hällström Waldemar , Gustavsson Per , Wallman Lars , Prinz Christelle , Montelius Lars , Kanje Martin
Published: December 2008

Axonal growth and guidance were studied on different micro- and nanostructured surfaces. Nanoimprinted grooves in a polymer, epitaxial III/V nanowires, porous silicon patterns, and chemically altered surfaces were all shown to induce axonal guidance. Neurons were also found to be able to attach and grow on gallium phosphide nanowires without compromising cell survival. The results are important for the construction of a new generation of neuroelectrical interfaces, including high spatial resolution electrodes. The advantages of the different nanostructured surfaces are discussed.
Effect of microstructure on deprotection kinetics in photoresist
Authors: Fryer David S. , Singh Vivek , Bollepalli Srinivas B. , Granovsky Alex A.
Published: December 2008

This article describes the result of predictions based on a novel continuum model for the effect of microstructure on deprotection reaction kinetics during postexposure bake (PEB). The effect of neighboring blocking groups is incorporated in a continuum PEB model. Provided blocking groups with neighbors react at a slower rate than isolated blocking groups, an up to 8% improvement in latent image contrast is predicted. In addition, a first principles calculation of the equilibrium structure for poly(methyl methacrylate-co-t-butyl methyl methacrylate) copolymer with acid present is reported. Hybrid quantum mechanics/molecular mechanics (QC/MM) results indicate that a strong hydrogen bond forms between blocked and unblocked neighbor sites in the presence of acid. The QC/MM prediction provides evidence confirming the rate constant for deprotection reaction with a neighboring blocked site is reduced relative to isolated blocking groups. The new PEB model form is shown to improve the fit to kinetic Fourier transform infrared data over conventional deprotection kinetics for those resists that contain carboxyl group deprotection chemistry. The new model also explains the difference in reaction rate between resists with otherwise identical deprotection chemistry by altering only neighboring blocked site content. Finally, a 50% greater lithographic advantage in development rate contrast is demonstrated for microstructure with increased neighboring blocked sites.
Protection and reduction of surface oxidation of Mo∕Si multilayers for extreme ultraviolet lithography projection optics by control of hydrocarbon gas atmosphere
Authors: Niibe Masahito , Koida Keigo , Kakutani Yukinobu
Published: December 2008

To protect the surface oxidation of Mo∕Si multilayer films by extreme ultraviolet (EUV) irradiation under a vacuum atmosphere with residual water, two experiments were carried out. One consisted of examining the oxidation protection effect for isopropyl alcohol (IPA) and n-decane gases. The reflectivity change of the Ru-capped multilayer film by EUV irradiation was investigated under a vacuum atmosphere with residual water vapor at a pressure of 1.3×10−5Pa, and, in addition, each hydrocarbon (HC) gas was introduced by changing its pressure. A protective effect against oxidation was observed in both gases when introduced at a pressure in the order of 10−6Pa. For IPA, no remarkable decrease in the reflectivity was observed even when the introductory pressure was raised to the order of 10−4Pa. However, for n-decane, the reflectivity decreased remarkably when pressure in the order of 10−5Pa was introduced. The other experiment consisted of examining the reduction effect of the oxidized surface by EUV irradiation when introducing HC gas. Ru- and Si-capped multilayers were once oxidized by EUV irradiation under a water vapor atmosphere. However, for the Ru-capped multilayer, the reflectivity was recovered when EUV was irradiated in the presence of ethanol gas at a pressure of 3.8×10−5Pa. The oxide layer of the Ru cap was reduced at this time.
Neutral particle proximity lithography: Noncontact nanoscale printing without charge-related artifacts
Authors: Craver Barry , Nounu Hatem , Wasson James , Wolfe John C.
Published: December 2008

The authors present neutral particle proximity lithography, a high resolution, parallel exposure technique where a broad beam of energetic neutral particles floods a stencil mask and transmitted beamlets transfer the mask pattern to resist on a substrate. It preserves the advantages of nanoscale penumbra, diffraction, and resist scattering of ion beam lithography (IBL) yet is intrinsically immune to charge accumulation on the mask and substrate. In a series of direct comparisons, involving insulating substrates, large proximity gaps, and ultrasmall features, the authors show that the use of neutral particles provides a simple method for completely eliminating the charging artifacts of IBL. They demonstrate the ability to print 8nm mask features with 5nm pattern fidelity. Exposure times are about 200s in poly(methyl methacrylate) resist.
Effect of oxygen on growth and properties of diamond thin film deposited at low surface temperature
Authors: Das D. , Singh Raj N. , Barney I. T. , Jackson A. G. , Mukhopadhyay S. M.
Published: December 2008

Polycrystalline diamond thin films are grown on a p-type Si (100) single crystal substrate at a low surface deposition temperature of 455°C using a microwave plasma enhanced chemical vapor deposition process in an Ar-rich Ar∕H2∕CH4 plasma containing different oxygen levels from 0% to 0.75%. The surface deposition temperatures are measured and monitored by an IR thermometer capable of working in a plasma environment without any interference from the plasma emissions. The lower surface deposition temperature at high microwave power of 1300W and higher gas pressure of 95torr is achieved by active cooling of the substrate from the backside using a specially designed cooling stage. An enhanced growth rate from 0.19to0.63μm∕h is observed with varying oxygen from 0% to 0.75% in the plasma. Diamond grain size also increased from 0.69μm for the sample with no oxygen to 1.74μm for the sample with 0.75% oxygen. The diamond films are characterized using x-ray diffraction, environmental scanning electron microscopy field emission gun, Raman spectroscopy, and x-ray photoelectron spectroscopy. The enhanced growth rate is correlated with the enhanced atomic hydrogen to C2 ratio with increasing oxygen concentration in the plasma, which is measured by an in situ optical emission spectroscopy.
Epitaxial cubic HfN diffusion barriers deposited on Si (001) by using a TiN buffer layer
Authors: Araujo Roy A. , Zhang Xinghang , Wang Haiyan
Published: December 2008

Cubic HfN (B1-NaCl) thin films were grown epitaxially on Si(001) substrates by using a TiN (B1-NaCl) buffer layer as thin as ∼10nm. The HfN∕TiN stacks were deposited by pulsed laser deposition with an overall thickness below 60nm. Detailed microstructural characterizations include x-ray diffraction, transmission electron microscopy (TEM), and high resolution TEM. The electrical resistivity measured by four-point probe is as low as 70μΩcm at room temperature. Preliminary Cu diffusion tests show a good diffusion barrier property with a diffusion depth (2Dτ) of 2–3nm after annealing at 500°C for 30min in vacuum.
Effects of mask absorber structures on the extreme ultraviolet lithography
Authors: Seo Hwan-Seok , Lee Dong-Gun , Kim Hoon , Huh Sungmin , Ahn Byung-Sup , Han Hakseung , Kim Dongwan , Kim Seong-Sue , Cho Han-Ku , Gullikson Eric M.
Published: December 2008

In this paper, the authors present the results of an investigation of the dependence of mask absorber thickness on the extreme ultraviolet lithography (EUVL) and suggest a new mask structure to minimize shadowing effects. For this purpose, several patterned masks with various TaN absorber thicknesses are fabricated using in-house Ru-capped EUVL mask blanks. According to the simulation using practical refractive indices, which are obtained at EUV wavelengths, the absorber thickness can be reduced to that of out-of-phase (ΔΦ=180°) ranges without loss of image contrast and normalized image log slope. Thickness to meet out-of-phase in real mask can be obtained by comparing field spectrum intensity ratio using the EUV coherent scattering microscopy (CSM). 52.4nm in thickness is close to ΔΦ=180° for TaN absorber since it shows the highest 1st/0th order intensity ratio as well as the best resolution in the microfield exposure tool (MET) test. When we apply 40-nm-thick TaN instead of 80-nm-thick TaN, the amounts of H-V bias reduction in wafer scale correspond to 80% (2.46–0.48nm) by CSM and 70% (2.23–0.65nm) by MET test results. Considering the fact that H-V bias in the MET is similar with that of simulation using the resist model, the degree of H-V bias in the alpha demo tool (ADT) is supposed to be much higher than that of MET due to its higher incident angle (θ=6°). Our final goal is to develop a thin absorber EUVL mask which has a low H-V bias, high EUV printability and DUV contrast, and sufficient optical density at the border. To achieve this, blind layer treatment and integration with anti-reflective coating layer are in progress.
Stability of HSQ nanolines defined by e-beam lithography for Si nanowire field effect transistors
Authors: Regonda Suresh , Aryal Mukti , Hu Wenchuang (Walter)
Published: December 2008

Multiple instability states, e.g., grouped collapse, single collapse, wavy, and grouped wavy states, have been observed in hydrogen silses quioxane (HSQ) nanolines defined by electron beam lithography (EBL). Experimental data show that the critical aspect ratio of the HSQ lines dramatically increase when the line pitch reduced to sub-100-nm, which is opposite to theoretical models for capillary forces and swelling strain. Such contradiction can be well explained only if Young’s modulus is considered as a significantly varying factor. Further, experimental data show a dramatic decrease in swelling strain and increase in oxygen contents in HSQ with increasing EBL dose, indicating that it is the change in Young’s modulus rather than the capillary force or swelling strain that dominates the instability behaviors at the nanoscale. Stable high aspect ratio HSQ nanolines over metal pads were used to make working Si nanowire transistors on Si on insulator substrates. 12–14nm HSQ lines with aspect ratios of 11–14 have been obtained. Fabricated field effect transistors using back-gate configuration has shown expected performance towards biosensing applications.
Relief and trench formation on chalcogenide thin films using electron beams
Authors: Hoffman G. B. , Liu W.-C. , Zhou W. , Sooryakumar R. , Boolchand P. , Reano R. M.
Published: December 2008

Electron beam irradiation of amorphous GeSe4 thin films reveals formation of reliefs and trenches as a function of electron beam dose. Mounds as high as 115nm are observed at low electron beam dose and trenches as deep as 180nm at high dose. The geometry of trench and mound formation is examined as a function of electron beam dose, film thickness, conductive overlayer thickness, exposure count, and beam step size. Thicker films are found to more likely form trenches than thinner ones. Physical mechanisms for trench and mound formation are proposed. Both types of deformations provide a route toward the direct write of optical waveguides, gratings, and waveguide-cavity coupled structures onto thin films of chalcogenide glass.
Improved field emission properties from polycrystalline indium oxide-coated single-walled carbon nanotubes
Authors: Lee Jungwoo , Lee Wonjoo , Sim Kijo , Han Sung-Hwan , Yi Whikun
Published: December 2008

The field emission (FE) characteristics of indium oxide (In2O3)-coated single-walled carbon nanotubes (SWCNTs) were studied. Scanning electron microscopy, x-ray diffractometer, and UV/visible spectroscopy confirmed that In2O3 exists as a polycrystalline cubic bixbyite structure on the surface of SWCNTs. The turn-on field of pristine SWCNTs decreased from 3.82to3.27V∕μm for In2O3-coated SWCNTs with optimal coating thickness. The maximum emission current density reached 3.5mA∕cm2, five times higher than that of pristine SWCNTs (0.68mA∕cm2) at an electric field of 7V∕μm. To explain the higher FE current density of In2O3-coated SWCNTs, Fowler–Nordheim plots were used with some assumptions.
Spatial scaling metrics of mask-induced line-edge roughness
Authors: Naulleau Patrick P. , Gallatin Gregg
Published: December 2008

Mask contributors to line-edge roughness (LER) have recently been shown to be an issue of concern for both the accuracy of current resist evaluation tests as well the ultimate LER requirements for the 22nm production node. Problems arise from mask absorber LER as well as mask multilayer roughness leading to random phase variations in the reflected beam. Not only do these mask contributors effect the total measured LER in resist but they also have an impact on LER spatial scaling characteristics such as power spectral density and the related descriptors of correlation length and roughness exponent. Understanding how these metrics respond to mask effects may lead to an experimental mechanism for evaluating the importance of mask contributors to observed LER in resist. Here the authors present a detailed study of mask-induced LER spatial characteristics. The authors further describe the influence of illumination conditions and defocus on the metrics and compare the results to those expected from intrinsic resist LER. The results show power spectral density analysis to be a promising technique for distinguishing mask and resist contributors to LER.
High-aspect-ratio plasma-induced nanotextured poly(dimethylsiloxane) surfaces with enhanced protein adsorption capacity
Authors: Vlachopoulou M. E. , Petrou P. S. , Kakabakos S. E. , Tserepi A. , Gogolides E.
Published: December 2008

The use of SF6 plasma-nanotextured poly(dimethylsiloxane) (PDMS) substrates of columnarlike surface topography as templates for protein adsorption is presented. Fresh and aged plasma-nanostructured surfaces are investigated, since ageing affects surface wettability, a critical parameter in protein adsorption. It is found that protein adsorption on such substrates increases with plasma treatment duration and surface ageing. An enhancement (up to ten times) in adsorption of biotinylated bovine serum albumin is observed on aged nanostructured PDMS substrates compared to untreated ones. Good spot homogeneity is obtained on surfaces treated for up to 6min. The use of optimized plasma-nanostructured surfaces as substrates for protein microarrays of intense and uniform spots is demonstrated.
Nanometer-level alignment to a substrate-embedded coordinate system
Authors: Moon Euclid E. , Smith Henry I.
Published: December 2008

The authors describe a method that uses infrared (IR) radiation to detect alignment on the nanometer level between grating marks on the front side of a template and a checkerboard-type mark on the back side of an IR-transparent, double-side-polished substrate. The mark can cover the entire substrate back side. No alignment marks are required on the front of the substrate. A back-side-specific mark is utilized with λ=1065nm illumination to detect alignment within σ=0.4nm.
Optical antennas: A boost for infrared detection
Authors: Li Huifeng , Cheng Xing
Published: December 2008

Optical antennas that operate at infrared wavelengths are studied for their potential application in enhancing the sensitivity of infrared detectors. Huge enhancement of infrared intensity can be achieved at the gap region of dipole and bowtie aperture antennas. The intensity enhancement is found to increase monotonically with a narrower gap size. The infrared radiation is also found to be concentrated above and below the antenna plane at the gap region, which allows for easy integration of the optical antennas with infrared detectors. The advantages of the infrared antennas, such as strong field enhancement and easy fabrication, may present a viable solution toward achieving highly sensitive and highly compact uncooled infrared detectors to impact numerous infrared technologies.
Focused ion beam fabrication of metallic nanostructures on end faces of optical fibers for chemical sensing applications
Authors: Dhawan A. , Muth J. F. , Leonard D. N. , Gerhold M. D. , Gleeson J. , Vo-Dinh T. , Russell P. E.
Published: December 2008

Focused ion beam (FIB) fabrication of fiber optic sensors, mainly chemical sensors, which are based on plasmonics-active nanostructures formed on the cleaved tips of optical fibers, is reported. The nanostructures fabricated included nanoholes in optically thick metallic films as well as metallic nanopillars and nanorods. The sensing mechanism is based on detecting shifts in surface plasmon resonances (SPRs) associated with nanoholes in metallic films and localized SPRs of metallic nanopillars and nanorods, when the refractive index of the medium surrounding the nanostructures is changed. These sensors can be employed for the detection of chemical agents in air as well as liquid media surrounding the sensors. FIB milling was employed to fabricate ordered arrays of nanoholes in optically thick (100–240nm) metallic films deposited on cleaved end faces of multimode, four-mode, and single-mode optical fibers. Separately, metallic nanorods and nanopillars were formed by first depositing a metallic (gold or silver) film on tips of optical fibers, which was followed by FIB milling large area patterns to form freestanding nanorods and nanopillars. Utilizing FIB allows engineering nanostructure geometries, i.e., nanostructure shapes and sizes that are chosen based on the plasmon resonances associated with them. Formation of periodic arrays of nanoholes provides a means of tuning plasmon resonance peaks, associated with extraordinary transmission of light through the array of nanoholes in the metallic films, based on periodicity and shape of the nanoholes as well as on refractive index changes to form sensitive chemical sensors.
Directed assembly of asymmetric ternary block copolymer-homopolymer blends using symmetric block copolymer into checkerboard trimming chemical pattern
Authors: Kang Huiman , Craig Gordon S. W. , Nealey Paul F.
Published: December 2008

Here, the authors studied the directed assembly of the asymmetric ternary blends, composed of polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) and the corresponding PS and PMMA homopolymers, on a checkerboard chemical pattern which was fabricated by e-beam lithography, controlling the periodicity (LS), length (D), and spacing of the exposed lines or dashed lines in the chemical pattern. The checkerboard chemical pattern, which cannot be generated with typical self-assembled block copolymer morphologies, consists of either offset, parallel, dashed lines, or alternating lines and dashed lines, and is used in the fabrication of dynamic random access memory. The degree of perfection and domain uniformity of the assembled block copolymer thin films on the complex pattern were a function of the commensurability of the volume fraction of PS in the blend (ϕS) with the fraction of area on the pattern wet by PS (FS), as well as the volume fraction of homopolymer in the blend (ϕH). The best assembly occurred ϕS and FS were commensurate, and ϕH was optimized for the given blend and pattern.
Study of 193nm photoresist degradation during short time fluorocarbon plasma exposure III. Effect of fluorocarbon film and initial surface condition on photoresist degradation
Authors: Sumiya M. , Bruce R. , Engelmann S. , Weilnboeck F. , Oehrlein G. S.
Published: December 2008

The effect of fluorocarbon film and surface pretreatments on roughness formation of 193nm photoresist (PR) during short time fluorocarbon plasma exposure was investigated. The present work complements two earlier reports by this group on surface modifications of 193nm PR during plasma etching. The authors employed a shutter approach to minimize initial plasma transient effects on processing of PR surfaces. Surface chemical conditions after plasma etching were observed by x-ray photoelectron spectroscopy. The authors investigated the effect of deposited fluorocarbon film and pretreatments using several gas chemistries on PR roughening. Pretreated samples exhibited smaller roughness after plasma etching as compared to specimens processed without pretreatment. Three main mechanisms were identified for surface roughness reduction after pretreatment: (a) the formation of a fluorinated surface layer—having a large amount of fluorine on the PR surface at the beginning of the etch reduces PR surface roughening, (b) the improvement of durability of the PR under plasma exposure by removal of the ester group, and (c) a rapid fluorination and a reduction in the PR etch rate during the initial etch period due to the formation of a protective film on the top of the PR. The authors conclude from this work that the initial surface chemical state is an important factor that determines the degree of surface roughness formation for 193nm PR during the initial etch period.
The replication of three dimensional structures using UV curable nanoimprint lithography
Authors: Mohamed K. , Alkaisi M. M. , Blaikie R. J.
Published: December 2008

The study investigates the use of ultraviolet nanoimprint lithography (UV-NIL) for patterning three dimensional (3D) structures. Generating the 3D structures is a challenging task especially on an insulating substrate such as quartz. These transparent molds are essential for the UV-NIL process. The 3D profiles were created on the negative tone photoresist, Microresist ma-N2403 using a Raith150 electron beam lithography (EBL) tool in a single step variable dose controlled exposure. The developed 3D resist profiles subsequently were utilized as the 3D masking layer. The 3D patterns were transferred into the quartz mold substrates by a single-step reactive ion etching (RIE). The replication of the 3D mold structure by using the UV-NIL technique requires a two-step imprint process. The master mold profile was replicated onto a Microresist Ormocomp US-S4 resist on the first imprint to become the soft mold. The cured Ormocomp soft mold, subsequently was used as a mold for replicating the 3D pattern structures on the Microresist mr-UVCur06 resist in the second imprint step to create a positive replica of the original mold. A test pattern of a 3D pyramid-shaped array with multilevel features was successfully been replicated using this technique. The replicated 3D pattern on the resist could be utilised as the final 3D masking layer for the pattern transfer onto final substrate using RIE.
Exploration of etch step interactions in the dual patterning process for process modeling
Authors: Melvin Lawrence S. , Ward Brian S. , Song Hua , Rhie Sang Uhk , Lucas Kevin D. , Wiaux Vincent , Verhaegen Staf , Maenhoudt Mireille
Published: December 2008

Double patterning is a manufacturing process targeted for the 22nm half pitch manufacturing node that harbors strong potential for reaching high volume manufacturing. The double patterning process requires twice as many manufacturing steps for a device layer as are required for a traditional single reticle device layer. However, the double patterning process does have a direct interaction between the individually processed layers at the final etch processing step. Current optical proximity correction process modeling capabilities can be designed to account for the interactions between these two processes. However, it is unclear at this time whether or not real process differences are present due to an interaction between the two patterns in double patterning. It is also not certain if proximity effects play a role in the process. This study will use currently available data from the IMEC double patterning process to determine if there is a significant interaction between the photoresist and hardmask patterns during substrate etch, and if there is a significant interaction, a discussion of how a process model could be constructed to capture this effect.
Hybrid high resolution lithography (e-beam/deep ultraviolet) and etch process for the fabrication of stacked nanowire metal oxide semiconductor field effect transistors
Authors: Pauliac-Vaujour S. , Comboroure C. , Vizioz C. , Barnola S. , Brianceau P. , Alvaro V. Maffini , Dupré C. , Ernst T.
Published: December 2008

This article highlights some aspects associated with the fabrication of stacked nanowire metal oxide semiconductor field effect transistors (MOSFETs) and more precisely the active area conception. These novel architectures, with gate-all-around or independent gates (ΦFET), are promising solutions to improve electrostatic control with high on-current (Ion) and to reduce power consumption for sub-32-nm transistors. Their fabrication is highly complex regarding lithography and etching. For this study, stacked nanowires were achieved by using hybrid lithography (e-beam/deep ultraviolet) combined with anisotropic and isotropic etchings of a Si∕SiGe multilayer to form suspended silicon nanowires. Therefore, we needed high aspect ratio resist features in order to perform the anisotropic etch of the Si∕SiGe multilayer (thickness: 250nm). For this purpose, we compared two ways to pattern the sub-32-nm silicon stacked nanowires. On one hand, a resist trimming was performed on thick large critical dimension patterns before etching. On the other hand, an amorphous carbon hard mask combined with a thin oxide capping layer was added on our structure to suppress resist thickness limitations and extend high resolution lithography capabilities. The best results so far were obtained using the first of these two techniques, which yielded 25nm stacked nanowire MOSFETs.
Nanofabrication of super-high-aspect-ratio structures in hydrogen silsesquioxane from direct-write e-beam lithography and hot development
Authors: Ocola L. E. , Tirumala V. R.
Published: December 2008

Super-high-aspect-ratio structures (>10) in hydrogen silsesquioxane resist using direct write electron beam lithography at 100kV and hot development and rinse are reported. Posts of 100nm in width and 1.2μm tall have been successfully fabricated without the need of supercritical drying. Hot rinse solution with isopropyl alcohol has been used to reduce surface tension effects during drying. Dose absorption effects have been observed and modeled using known Monte Carlo models. These results indicate that for e-beam exposures of thick negative resists (>1μm), the bottom of the structures will have less cross-link density and therefore will be less stiff than the top. These results will have impact in the design of high-aspect-ratio structures that can be used in microelectromechanical system devices and high-aspect-ratio Fresnel zone plates.
The effect of thin metal overlayers on the electron beam exposure of polymethyl methacrylate
Authors: Samantaray C. B. , Hastings J. T.
Published: December 2008

Here, the authors consider the effect of thin metal coatings on the contrast, clearing dose, and resolution of polymethyl methacrylate (PMMA) electron beam resist. They present processes suitable for deposition, exposure through, and removal of 5-nm-thick Al, Cr, and Cu layers. Contrast and clearing dose were determined by exposing large features and resolution was assessed using single pixel lines at beam energies from 2to30keV. In all cases the presence of the metal layer increases the clearing dose. They obtained a minimum linewidth of 40nm from the single pixel patterns. Both the experimental results and Monte Carlo simulations of the point spread function (PSF) support the feasibility of direct writing of sub-40-nm patterns despite of additional forward electron scattering. Applying thin metal coatings on resist provides an alternative to conductive polymers for charge reduction and an excellent foundation for fiducial grids used in spatial-phase locked electron beam lithography.
Polyfluoroorganoboron-Oxygen Compounds. 7. Studies of Conversion of [(C6HnF5-n)B(OMe)3]- Into [(C6HnF5-n)2B(OMe)2]- (n = 0, 1)
Authors: Adonin Nicolai Yu. , Bardin Vadim V. , Frohn Hermann-Josef
Published: December 2008

Conversion of salts Li[(C6HnF5-n)B(OMe)3] (n = 0, 1) into (Li·DME)[(C6HnF5-n)2B(OMe)2] was studied in dichloromethane-DME solution. The observed rate constants k decrease from (21.4 ± 0.9) × 10-3 l mol-1 s-1 (Li[C6F5B(OMe)3]) over (6.99 ± 0.11) × 10-3 l mol-1 s-1 (Li[(2,3,5,6-C6HF4)B(OMe)3]) to (2.94 ± 0.05) × 10-3 l mol-1 s-1 (Li[(2,3,4,6-C6HF4)B(OMe)3]), while Li[(2,3,4,5-C6HF4)B(OMe)3] does not undergo any transformation. Hydrolysis of (Li·DME)[(C6HnF5-n)2B(OMe)2] leads to corresponding borinic acids, whereas treatment of them with aqueous solution of M[HF2] (M = Bu4N, K) acidified with HF results in M[(C6HnF5-n)2BF2] in high yields.
HFPO Trimer-Based Alkyl Triflate, a Novel Building Block for Fluorous Chemistry. Preparation, Reactions and 19F gCOSY Analysis
Authors: Kysilka Ondřej , Rybáčková Markéta , Skalický Martin , Kvíčalová Magdalena , Cvačka Josef , Kvíčala Jaroslav
Published: December 2008

Triflate 4, CF3(CF2)2O-CF(CF3)CF2O-CF(CF3)CH2-OTf (RFOCH2OTf), of the HFPO trimer-based alcohol 3 (RFOCH2OH) is a novel highly fluorinated building block for fluorous chemistry. In analogy to similar polyfluorinated triflates with methylene spacer, its reactivity is limited to strong and soft nucleophiles. Whereas reactions with cyanide anion, phenolate anion, enolate of diethyl malonate or lithium salt of benzaldehyde bis(phenylsulfanyl)acetal were unsuccessful, the corresponding imidazole 5, iodide 6 or azide 7 were prepared in good yields. Reaction of imidazole 5 with (perfluorohexyl)methyl triflate (9) afforded highly fluorinated non-crystalline imidazolium salt 8, TfO-RFOCH2-(C3H3N2)+-CH2C6F13-n, which could be employed as fluorous ionic liquid or intermediate for fluorous carbenes. Complete assignment of complex 19F NMR spectra of all compounds employed was accomplished using 19F gCOSY NMR method.
Use of Cyclic α,β-Unsaturated Trifluoromethyl Sulfones in Diels-Alder Reactions and Michael Additions
Authors: Billard Thierry , Langlois Bernard R. , Essers Michael , Haufe Günter
Published: December 2008

Vinylic trifluoromethyl triflones, in particular cyclic ones, constitute potentially valuable building-blocks for further syntheses. Their uses in Diels-Alder cycloadditions as dienophiles or dienes led only to moderate yields of expected products. However, under fluoride activation, they afforded unexpected tricycle compounds.
A note on the bias of genetic distances in linkage maps based on small samples for backcrosses and intercrosses with complete dominance
Authors: Hühn Manfred , Piepho Hans-Peter
Published: December 2008

This paper investigates the bias (the difference between the expectation (mean) of an estimator and its true value) of genetic distances for small samples. Exact results on this bias have not received much attention in genetic mapping literature. We show that bias drops quickly with increasing sample size for both a backcross population and an F2in coupling. By contrast, bias may be substantial even for larger sample size for an F2when markers are in repulsion. It is concluded that Karlin’s map function should be used with care when mapping is done using an F2population. The same note of caution applies to other map functions such as Haldane’s and Kosambi’s. Finite-sample bias of these latter functions cannot be assessed because of the nonexistence of an expected value, but their median bias is similar to that of Karlin’s function.
Sport-specific assessment of lactate threshold and aerobic capacity throughout a collegiate hockey season
Authors: Durocher John J. , Leetun Darin T. , Carter Jason R.
Published: December 2008

The purpose of this study was to examine lactate threshold (LT) and maximal aerobic capacity with a sport-specific skating protocol throughout a competitive season in collegiate hockey players. We hypothesized that maximal aerobic capacity and skating velocity at LT would increase as the season progressed. Sixteen Division I college hockey players performed a graded exercise skating protocol to fatigue at 3 different times (pre-, mid-, and postseason). Subjects skated for 80 s during each stage, followed by 40 s of rest to allow for blood lactate sampling. Velocity at LT was similar during preseason (4.44 ± 0.08 m·s–1) and postseason (4.52 ± 0.05 m·s–1) testing, but was significantly elevated at midseason (4.70 ± 0.08 m·s–1; p < 0.01), compared with preseason. In contrast, LT as a percentage of maximal heart rate (HRmax) was unchanged throughout the season. HRmax remained constant throughout the season, at approximately 190 beats·min–1. Preseason maximal aerobic capacity (48.7 ± 0.8 mL·kg–1·min–1) was significantly higher than that at postseason (45.0 ± 1.1 mL·kg–1·min–1; p < 0.01). In conclusion, skating velocity at LT improved from pre- to midseason, but this adaptation was not maintained at postseason. Additionally, maximal aerobic capacity was reduced from pre- to postseason. These findings suggest a need for aerobic training throughout the college hockey season.
Skeletal muscle capillarization and oxidative metabolism in healthy smokers
Authors: Wüst Rob C.I. , Jaspers Richard T. , van der Laarse Willem J. , Degens Hans
Published: December 2008

We investigated whether the lower fatigue resistance in smokers than in nonsmokers is caused by a compromised muscle oxidative metabolism. Using calibrated histochemistry, we found no differences in succinate dehydrogenase (SDH) activity, myoglobin concentration, or capillarization in sections of the vastus lateralis muscle between smokers and nonsmokers. The relationship between fatigue resistance and SDH activity in nonsmokers (r = 0.93; p = 0.02) is absent in smokers. This indicates that the lower muscle fatigue resistance of smokers can likely be attributed to causes other than differences in oxidative metabolism and capillarization.
Shake table testing of museum display cases
Authors: Neurohr Theresa , McClure Ghyslaine
Published: December 2008

Throughout history, objects of art have been damaged and sometimes destroyed in earthquakes. Research was undertaken to investigate the seismic vulnerability of art objects exhibited on display cases, and museum floor motions representative of Montreal seismic hazards were simulated for that purpose. Particular attention was paid to the effects on art object seismic vulnerability of support conditions, modified floor surfaces, sliding and rocking responses of unrestrained display cases, floor elevations, art object mass, and the dynamic properties of the display cases. Seismic vulnerability of art objects was evaluated based on the seismic response of the display cases at the level of art object display. Display cases were investigated experimentally using shake table testing. Floor contact conditions and elevation had a crucial effect on the unrestrained display cases, causing them to slide or rock vigorously. As a result of experimental analysis, recommendations and (or) simple mitigation techniques are provided to reduce the seismic vulnerability of art objects exhibited on these display cases.
Development of chloride binding capacity in cement pastes and influence of the pH of hydration products
Authors: Song H. W. , Lee C. H. , Jung M. S. , Ann K. Y.
Published: December 2008

This study deals with the chloride binding capacity of cementitious materials. The binding capacities of ordinary Portland cement (OPC), 30% pulverized fuel ash (PFA), 60% ground granulated blast furnace slag (GGBS), and 10% silica fume (SF) pastes were monitored for 150 d using the water extraction method and the pH of the suspension (ground sample in distilled water) was simultaneously measured at 150 d. Results show that the binding capacity always increased with time, irrespective of binder, and the order of binding capacity with binders was 60% GGBS > 30% PFA > OPC > 10% SF. The pH of suspensions increased with time up to about 10 d, presumably due to a leaching out of alkalis, and then kept a certain value that was dependent on binder type. It was also found that an increase in the concentration of hydroxyl ions, derived from the pH of the suspension, resulted in a decrease in the mole ratio of free chloride to hydroxyl ions, reflecting the lower risk of steel corrosion.
Individual safety and health outcomes in the construction industry
Authors: McCabe Brenda , Loughlin Catherine , Munteanu Ramona , Tucker Sean , Lam Andrew
Published: December 2008

Between 2004 and 2006, 911 self-administered questionnaires were collected from 84 nonresidential Ontario construction sites. Each questionnaire contained 105 questions and took approximately 15 min to complete. This paper presents one study from that research project that seeks to understand the relationship among worker demographics, worker safety attitudes, and worker health and safety outcomes (e.g., worker well-being and accidents). The participants had an average age of 38.3 years with 15.1 years experience in the industry. Short job tenure, age, experience, and job position were highly related to safety outcomes. Apprentices experienced more accidents, whereas supervisors reported more work-related psychological symptoms. Among the situational factors, higher work pressure, high interpersonal conflict, and low-quality leadership were most strongly associated with work-related health outcomes and accidents. Regression models were developed with a maximum adjusted coefficient of determination of 0.28. A graphical means of modeling the data was demonstrated in the form of a Bayesian belief network.
The influence of sterols on the conformation of recombinant mitochondrial porin in detergent
Authors: Bay Denice C. , O’Neil Joe D. , Court Deborah A.
Published: December 2008

Mitochondrial porins (voltage-dependent anion-selective channels, VDAC) are key contributors to cellular metabolism. When isolated from mitochondria porins copurify with sterols, and some isolated forms of the protein require sterol for insertion into artificial membranes. Nonetheless, the contributions of sterols to the folded state of mitochondrial porin are not understood. Recently, with the goal of high-resolution structural studies, several laboratories have developed methods for folding recombinant porins at high concentration in detergent. In the present study, recombinant Neurospora crassa porin solubilized in detergent–sterol mixtures was examined. Sterols do not significantly alter the secondary structure of porin in lauryl dimethylamine oxide, nor in a mixture of sodium dodecylsulfate and dodecylmaltopyranoside. However, as detected by near-UV circular dichroism spectropolarimetry and fluorescence spectroscopy, the environments surrounding the aromatic amino acids in the detergent–sterol solubilized protein are measurably different from those in detergent alone. Furthermore, the effects are different in the presence of ergosterol, the native sterol in fungal mitochondria, and cholesterol. While these influences on the tertiary arrangement of detergent-solubilized porin are subtle, they may contribute to the generation of a form of the protein competent for insertion into the artificial bilayers used for electrophysiological analyses, and should be considered in future structural studies of porin.
Beneficial effect of 3,4,5,6-tetrahydroxyxanthone on dyslipidemia in apolipoprotein E-deficient mice
Authors: Xiao Hong-Bo , Sun Zhi-Liang , Lu Xiang-Yang , Li Da-Zhi , Xu Jian-Ping , Hu Ya-Ping
Published: December 2008

Previous investigations have shown that decreased expression of angiopoietin-like protein 3 (Angptl3) is protective against dyslipidemia in atherosclerosis. The present study was conducted to test the effect of 3,4,5,6-tetrahydroxyxanthone, a xanthone compound, on dyslipidemia in apolipoprotein E-deficient (ApoE−/−) mice. Forty mice were randomly divided into 4 groups (n = 10): control group (C57BL/6J mice), ApoE−/−mice group, and two groups of ApoE−/−mice treated with 3,4,5,6-tetrahydroxyxanthone (10 or 30 mg/kg per day). Eight weeks after treatment, lipid levels in the blood and liver, expression of hepatic Angptl3, and adipose tissue lipoprotein lipase (LPL) were determined. Treatment with 3,4,5,6-tetrahydroxyxanthone (10 or 30 mg/kg) significantly decreased plasma and hepatic total cholesterol and triglyceride concentrations, increased plasma high-density lipoprotein cholesterol, and significantly downregulated expression of Angptl3 mRNA and protein concomitantly with upregulated expression of LPL mRNA. In addition, T0901317 (a liver X receptor ligand) caused elevated expression of hepatic Angptl3 mRNA and protein, and the effect of T0901317 was also abrogated by 3,4,5,6-tetrahydroxyxanthone in vivo and in vitro. The present results suggest that the beneficial effect of 3,4,5,6-tetrahydroxyxanthone on dyslipidemia may be related to reduced expression of Angptl3.
Choline produces antiarrhythmic actions in animal models by cardiac M3 receptors: improvement of intracellular Ca2+ handling as a common mechanism
Authors: Liu Yan , Sun Hong-li , Li Dan-lu , Wang Li-yan , Gao Yang , Wang Yu-ping , Du Zhi-min , Lu Yan-jie , Yang Bao-feng
Published: December 2008

It is well known that choline has protective effects on ischemic arrhythmias. We designed the present study to evaluate the antiarrhythmic effects of choline and to detect its related mechanisms in aconitine-induced rat and ouabain-induced guinea pig models of arrhythmia. Laser scanning confocal microscopy and patch-clamp technique were utilized to study the action of choline on intracellular calcium concentration and L-type calcium current (ICa-L) of cardiac myocytes. M3 receptor antagonist 4-DAMP (4-diphenylacetoxy-N-methylpiperidine-methiodide) was applied preliminarily to evaluate the role of the M3 receptor. Choline significantly increased the survival time of arrhythmic rats and guinea pigs, delayed the onset of arrhythmias and ventricular tachycardia, and decreased the arrhythmia score. The overload of intracellular Ca2+ induced by aconitine or ouabain was reduced in isolated myocytes pretreated with choline. Choline reduced the increased density of ICa-L induced by aconitine or ouabain. Moreover, the beneficial effects of choline were reversed by 4-DAMP. Choline produced antiarrhythmic actions on arrhythmia models by stimulating the cardiac M3 receptor. The mechanism may be related to the improvement of Ca2+ handling.
Breeding habitat preference and nest success of Red-necked Phalaropes on Niglintgak Island, Northwest Territories
Authors: Walpole Bree , Nol Erica , Johnston Vicky
Published: December 2008

Red-necked Phalaropes ( Phalaropus lobatus (L., 1758)) breed throughout arctic and subarctic wetlands. These wetlands provide Red-necked Phalaropes dense graminoid habitat that shelters and conceals nests, and freshwater ponds where phalaropes engage in social interactions and feed on small aquatic invertebrates. We studied breeding habitat preference of Red-necked Phalaropes at multiple scales and determined which, if any, nest-site characteristics influenced hatching success. Red-necked Phalaropes avoided habitat at the meso (home range) scale containing large areas of mud and shrub cover, and selected sites with greater cover of graminoids, aquatic emergents, and open water than that available in the environment. At the micro (nest) scale, phalaropes chose sites dominated by graminoids and water. In 2005, concealed nests experienced higher daily nest survival than exposed nests. In 2006, 40% of nests were destroyed during a summer storm surge and we detected no differences in habitat characteristics between the remaining successful and unsuccessful nests. We suggest that annual differences in the adaptive value of nest-site selection depend on the relative abundance of mammalian and avian predators. A habitat model using data at the meso scale correctly identified phalarope habitat and has the potential to be used broadly across the western Arctic.
Diet of two insectivorous bats, Myotis lucifugus and Myotis keenii, in relation to arthropod abundance in a temperate Pacific Northwest rainforest environment
Authors: Burles D. W. , Brigham R. M. , Ring R. A. , Reimchen T. E.
Published: December 2008

We assessed the diet of two morphologically similar bats ( Myotis lucifugus (LeConte, 1831) and Myotis keenii (Merriam, 1895)), which both used hydrothermally heated nursery roosts at Gandll K’in Gwaayaay (Hotspring Island), Haida Gwaii (Queen Charlotte Islands), British Columbia, in 1998 and 1999. Our purpose was to determine if they fed opportunistically or actively selected prey, and whether they partitioned prey resources. We determined diet by analyzing feces collected from captured bats and compared it with the relative abundance of insects captured in light traps. Myotis lucifugus fed mainly on lepidopterans, medium-sized to large dipterans, neuropterans, and hymenopterans, while M. keenii fed on lepidopterans, arachnids, medium-sized to large dipterans, and neuropterans. We found that both species were selecting prey, although selection may have been more a function of prey size than particular taxa. Arachnids occurred in feces of both species, implying that both were capable of gleaning prey from surfaces, although only M. keenii regularly fed on spiders. We concluded from the preponderance of flying insects in the diet of M. lucifugus that it was primarily aerial hawking prey, while we took the frequent occurrence of both flying insects and spiders in the diet of M. keenii to indicate that it was both aerial hawking and gleaning prey. Weather conditions between years affected relative abundance of insects and bat diet, with species diversity being lower in light-trap samples and diet of M. lucifugus in 1999, which was cooler and wetter than in 1998. Species diversity in the diet of M. keenii was higher in 1999. Similarities in diet indicated that some interspecific competition was occurring, although this competition was likely minimized by their different foraging strategies.
MULTIBAND MODEL OF CUPRATE SUPERCONDUCTIVITY
Authors: KRISTOFFEL NIKOLAI , RUBIN PAVEL , ÖRD TEET
Published: December 2008

A minimal model for the description of cuprate superconductor characteristics on doping scale (hole and electron) is developed. The leading interband pairing channel couples an itinerant band and defect states created by doping. Bare gaps between them are supposed and become closed by extended doping. Band overlap conditions determine special points in the phase diagram. Nodal and antinodal momentum regions are distinguished. Illustrative calculations have been made using a mean-field pair-transfer multiband Hamiltonian and corresponding free-energy expansions. The results are self-consistent and demonstrate that the elaborated approach is able to reproduce characteristic features of cuprate superconductors as, e.g., the doping dependence of Tc, superconducting gaps and pseudogaps, supercarrier density and effective mass, coherence length and penetration depth, critical magnetic fields and some other properties. Interband pairing scheme is suggested to be an essential aspect of cuprate superconductivity.