bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonexponential T2* decay in white matter
Authors: van Gelderen Peter , de Zwart Jacco A. , Lee Jongho , Sati Pascal , Reich Daniel S. , Duyn Jeff H.
Published: May 2011

Visualizing myelin in human brain may help the study of diseases such as multiple sclerosis. Previous studies based on T1 and T2 relaxation contrast have suggested the presence of a distinct water pool that may report directly on local myelin content. Recent work indicates that T2* contrast may offer particular advantages over T1 and T2 contrast, especially at high field. However, the complex mechanism underlying T2* relaxation may render interpretation difficult. To address this issue, T2* relaxation behavior in human brain was studied at 3 and 7 T. Multiple gradient echoes covering most of the decay curve were analyzed for deviations from mono‐exponential behavior. The data confirm the previous finding of a distinct rapidly relaxing signal component (T2* ∼ 6 ms), tentatively attributed to myelin water. However, in extension to previous findings, this rapidly relaxing component displayed a substantial resonance frequency shift, reaching 36 Hz in the corpus callosum at 7 T. The component's fractional amplitude and frequency shift appeared to depend on both field strength and fiber orientation, consistent with a mechanism originating from magnetic susceptibility effects. The findings suggest that T2* contrast at high field may be uniquely sensitive to tissue myelin content and that proper interpretation will require modeling of susceptibility‐induced resonance frequency shifts. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
A symmetric mixed finite element method for nearly incompressible elasticity based on biorthogonal systems
Authors: Lamichhane Bishnu P. , Stephan Ernst P.
Published: May 2011

We present a symmetric version of the nonsymmetric mixed finite element method presented in (Lamichhane, ANZIAM J 50 (2008), C324–C338) for nearly incompressible elasticity. The displacement–pressure formulation of linear elasticity is discretized using a Petrov–Galerkin discretization for the pressure equation in (Lamichhane, ANZIAM J 50 (2008), C324–C338) leading to a non‐symmetric saddle point problem. A new three‐field formulation is introduced to obtain a symmetric saddle point problem which allows us to use a biorthogonal system. Working with a biorthogonal system, we can statically condense out all auxiliary variables from the saddle point problem arriving at a symmetric and positive‐definite system based only on the displacement. We also derive a residual based error estimator for the mixed formulation of the problem. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2012
The impact of no Child Left Behind on student achievement
Authors: Dee Thomas S. , Jacob Brian
Published: May 2011

The No Child Left Behind (NCLB) Act compelled states to design school accountability systems based on annual student assessments. The effect of this federal legislation on the distribution of student achievement is a highly controversial but centrally important question. This study presents evidence on whether NCLB has influenced student achievement based on an analysis of state‐level panel data on student test scores from the National Assessment of Educational Progress (NAEP). The impact of NCLB is identified using a comparative interrupted time series analysis that relies on comparisons of the test‐score changes across states that already had school accountability policies in place prior to NCLB and those that did not. Our results indicate that NCLB generated statistically significant increases in the average math performance of fourth graders (effect size 5 0.23 by 2007) as well as improvements at the lower and top percentiles. There is also evidence of improvements in eighth‐grade math achievement, particularly among traditionally low‐achieving groups and at the lower percentiles. However, we find no evidence that NCLB increased fourth‐grade reading achievement. © 2011 by the Association for Public Policy Analysis and Management.
Physical properties of lignin‐based polypropylene blends
Authors: Chen Feng , Dai Honghu , Dong Xiaoli , Yang Jintao , Zhong Mingqiang
Published: May 2011

The alkylation of kraft lignin with bromododecane was carried out to improve the compatibility with polypropylene (PP). The feasibility of PP/alkylated lignin composite was studied. It was found that the lignin could serve as fire retardant and toughening agent for PP matrix. Moreover, the higher lignin portion of the composites exhibited obvious damping effect. Although scanning electron micrographic observations indicated that PP‐lignin adhesion was improved by the alkylation, additional benefits were only obtained from impact behavior. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers
Effect of the resin/hardener ratio on curing, structure and glass transition temperature of nanofilled epoxies
Authors: Bignotti Fabio , Pandini Stefano , Baldi Francesco , De Santis Riccardo
Published: May 2011

The curing reaction, structure, and glass transition behavior of epoxy‐clay nanocomposites prepared using several different resin/hardener ratios were investigated. Nonisothermal DSC experiments evidenced that the incorporation of the organoclay did not induce appreciable changes in the curing enthalpy, but determined a slight acceleration of the curing reaction, without modifying the activation energy. TEM and SEM analyses of the nanocomposite resins showed the presence of micrometric aggregates for all the resin/hardener ratios investigated, even though these materials showed good optical clarity and their WAXD analyses did not evidence any organoclay peak. In addition, the higher the hardener content, the lower the tendency toward exfoliation and the broader the distribution of the interlamellar distances. The degree of cross‐linking of cured resins was evaluated both from measurements of the elastic modulus in the rubbery plateau and from solvent sorption experiments. A maximum in cross‐link density was observed near the stoichiometric composition. Both modulus and sorption experiments suggested that filler‐matrix adhesion increased with increasing the resin/hardener ratio, a trend that was confirmed also by glass transition temperature data. An analysis of ethyl acetate sorption curves evidenced that a gradual transition from Fickian to Case II diffusion occurred as the resin/hardener ratio was raised and that the organoclay promoted deviation from the Fickian behavior. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers
The effect of electric field parameters on the resistivity and induced percolation time of carbon black‐filled polystyrene composites
Authors: Tang Lina , Yan Xiaohu , Kontopoulou Marianna , Docoslis Aristides
Published: May 2011

The present work examines the influence of externally applied alternating current (AC) electric fields on the formation of electrically conducting structures in carbon black/polystyrene (CB/PS) composites. It is shown that AC electric fields are capable of producing electrically conducting composites at filler concentrations substantially lower than the composite's percolation threshold by causing filler attraction and alignment into columnar structures with orientation normal to the electrode surface. The times required for the insulator‐to‐conductor transition (termed “percolation times”) in these CB/thermoplastic composites are measured as a function of important process parameters, such as applied voltage, electric field frequency, and filler concentration. The percolation times are shown to be inversely proportional to both the square root of the applied field intensity and to the power of 0.3 of the filler concentration, while they appear to be independent of AC field frequencies in the range 10 Hz to 10 KHz. These empirical scaling laws can be used as a guide for the selection of experimental conditions in future studies on electrified composites or for the selection of processing parameters in composites manufacturing. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers
Fetal RHD genotype detection from circulating cell‐free fetal DNA in maternal plasma in non‐sensitized RhD negative women
Authors: Bombard Allan T. , Akolekar Ranjit , Farkas Daniel H. , VanAgtmael Anna L. , Aquino Frank , Oeth Paul , Nicolaides Kypros H.
Published: May 2011

Objective

To examine the performance of the SensiGene Fetal RHD Genotyping Laboratory Developed Test (RHD Genotyping LDT) using circulating cell‐free fetal DNA (ccff DNA) extracted from maternal plasma.

Methods

ccff DNA was extracted from maternal blood from non‐sensitized women with singleton pregnancies in two cohorts, one with a serotype reference (11–13 weeks' gestation) and one with the reference source (6–30 weeks' gestation). The presence of three RHD exon sequences (exons 4, 5, 7), the psi‐pseudogene, three Y‐chromosome sequences (SRY, DBY and TTTY2), and the X/Y‐chromosome TGIF gene control were determined using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry—the RHD Genotyping LDT.

Results

The cohort with a serotype RhD reference showed correct classification in 201 of 207 patients, a test accuracy of 97.1%, with a sensitivity and specificity for prediction of RhD serotype of 97.2 and 96.8%, respectively. The cohort with a genotype RHD reference showed correct classification in 198 of 199 patients, indicating a test accuracy of 99.5% with a sensitivity and specificity for prediction of RHD genotype of 100.0 and 98.3%, respectively.

Conclusion

Fetal RHD genotyping can accurately be determined using ccff DNA in the first and second trimesters of pregnancy. Copyright © 2011 John Wiley & Sons, Ltd.
Preparation of polybenzimidazole/functionalized carbon nanotube nanocomposite films for use as protective coatings
Authors: Zhang Li , Ni Qing‐Qing , Shiga Akihiko , Natsuki Toshiaki , Fu Yaqin
Published: May 2011

Functionalized multi‐walled carbon nanotubes (MWCNTs) via microwave‐induced polymerization modification route, and polybenzimidazole (PBI) nanocomposite films containing 0.1‐5 wt% functionalized MWCNTs were successfully synthesized. The functionalized MWCNTs were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and X‐ray photoelectron spectroscopy (XPS). The results verify that the polymer was successfully grafted to the MWCNTs with a polymer layer that was several nanometers thick. The TGA results showed that the quantity of the attached polymer reached approximately 9.4 wt%. The mechanical properties of the nanocomposite films were measured by tensile test and dynamic mechanical analysis (DMA). The tensile test results indicated that the Young's modulus increased by about 43.9% at 2 wt% CNT loading, and further modulus growth was observed at higher filler loading. The DMA studies indicated that the nanocomposite films had a higher storage modulus than pure PBI film in the temperature range of 30‐300°C, and the storage modulus was maintained above 0.82 GPa. Simulation results confirmed that the PBI nanocomposite films had desirable mechanical properties for use as a protective coating. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.
Stabilizer thickness profiles in polyethylene pipes transporting drinking water disinfected by bleach
Authors: Colin X. , Verdu J. , Rabaud B.
Published: May 2011

Polyethylene connection pipes of wall thickness ranging from 3.0 to 4.5 mm, used for 0, 5, 9, 12, and 18 years in the French network of drinking water disinfected by bleach, have been analyzed. The stabilizer thickness profiles reveal that bleach destroys the stabilizer in a superficial layer of about 0.5 mm depth at the water–polymer interface. In the rest of the wall, stabilizer is lost by physical processes, i.e., transport by diffusion into the bulk, extraction at the water–polymer interface, and evaporation at the polymer–air interface. The whole loss kinetics is governed by extraction and evaporation. The classical scheme for evaporation–diffusion process has been used to model physical loss processes, but with boundary conditions different from the literature ones. Concerning chemical aspects, some mechanisms proposed in the literature are criticized. The identification of the bleach reactive species remains an open question. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.
CO2‐derived latent nitrogen nucleophiles for controlled cross‐linking of brominated poly(isobutylene‐co‐isoprene)
Authors: Faba Michael A.J. , Parent J. Scott , Whitney Ralph A.
Published: May 2011

New methods for preparing thermoset elastomer products from brominated poly(isobutylene‐co‐isoprene) (BIIR) are described, wherein control of cross‐linking dynamics is gained using latent forms of ammonia, primary amines, and cyclic amidines. BIIR cross‐linking by repeated alkylation of standard nitrogen nucleophiles is too rapid at standard polymer processing temperatures, whereas CO2‐derived salts are shown to be sufficiently inactive under these conditions to support conventional BIIR compounding. Examples include the carbonate, bicarbonate and carbamate salts of ammonia; carbamate and carbamate esters of hexadecyl amine; and the bicarbonate salt of 1,8‐diazabicyclo[5.4.1]undec‐7‐ene. Thermal decomposition of these latent curatives releases CO2 and the desired nucleophile to support high cross‐linking rates and yields at standard cure temperatures. Thermogravimetric analysis of salt decomposition, rheological measurements of cross‐link density, and spectroscopic analysis of polymer dehydrohalogenation products are used to define the relationship between latent nucleophile activation and BIIR cure dynamics. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.
Micellar polymerization, characterization, and viscoelasticity of combined thermally insensitive terpolyacrylamides
Authors: Rodríguez Fátima Pérez , Jiménez‐Regalado Enrique J.
Published: May 2011

Polymer chains consisting of water‐soluble polyacrylamides and N‐isopropylacrylamide (NIPAM), hydrophobically modified with low amounts of N,N‐dialkylacrylamides (N,N‐dioctylacrylamide) have been prepared via free radical micellar polymerization, using a hydrophobic initiator derived from 4,4′‐azobis(4‐cyanopentanoic acid) containing a long linear chain of 16 (C16) carbon atoms. This procedure resulted in polyacrylamides containing hydrophobic groups along the chain as well as at the chain ends. These polymers are named “combined associative polymers” and include within their structure a water‐soluble monomer (acrylamide), a thermosensitive monomer (NIPAM) and a hydrophobic monomer. The polymers were characterized by different techniques, also studying the effect of adding a surfactant anion such as sodium dodecylsulfate. The viscoelastic properties as a function of temperature of these associative polymers were investigated using steady‐flow and oscillatory experiments considering the relaxation time (TR) and the plateau modulus (G0). The effect of concentration of acrylamide and NIPAM on the viscosity of the associative polymer solutions was investigated. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
The preparation of 3,6‐bis(3‐hexylthien‐2‐yl)‐s‐tetrazine and its conjugated polymers
Authors: Ding Jianfu , Li Zhao , Cui Zhe , Robertson Gilles P. , Song Naiheng , Du Xiaomei , Scoles Ludmila
Published: May 2011

We demonstrated, for the first time, that 3,6‐bis(3‐hexylthien‐2‐yl)‐s‐tetrazine (TTz) with hexyl group at the 3‐position of thiophene rings can be prepared using a modified sulfur‐assisted Pinner synthesis. Although the hexyl group creates large steric hindrance to the tetrazine ring formation reaction, and the reaction under a traditional condition only produces trace amount of the target product, the yield of this reaction under a modified reaction condition using anhydrous hydrazine at 68 °C can reach 65%. Two new copolymers of the resulting TTz and hexyl‐ or 2‐ethylhexyl‐substituted cyclepentadithiophene have been prepared. The polymers show a broader light absorption in film than in solution attributing to the large distribution of effective conjugation length of polymer chain due to the existence of both cis‐ and trans‐orientations of the 3‐hexylthiophene units in the planar polymer chain in solid state. Although the polymers show a narrow band gap and a deep HOMO level, which are desirable for generating an efficient light absorption and a larger open circuit voltage (Voc) of the resulting solar cell devices, the device performance is not as good as expected. It is attributed to the random distribution of the cis‐ and trans‐conformations along the polymer chain. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.
Unequal siblings: Adverse characteristics of naphtalene‐based hoveyda‐type second generation initiators in ring opening metathesis polymerization
Authors: Leitgeb Anita , Szadkowska Anna , Michalak Michal , Barbasiewicz Michał , Grela Karol , Slugovc Christian
Published: May 2011

A family of four different Hoveyda‐type initiators bearing a π‐extended carbene ligand was characterized regarding the activity in ring opening metathesis polymerization. One of the initiators shows high activity at ambient temperature, similar to the second generation Hoveyda–Grubbs catalyst and is even suited for the controlled polymerization of certain norbornene derivatives. The other family members exhibit a pronounced latency at room temperature, and polymerization can be triggered by heat. The scope of these initiators in the thermally triggered polymerizations of norbornene derivatives in general and dicyclopentadiene in particular was disclosed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.
Research progress in toughening modification of poly(lactic acid)
Authors: Liu Hongzhi , Zhang Jinwen
Published: May 2011

Renewable poly(lactic acid) (PLA) exhibits high strength and stiffness. PLA is fully biodegradable and has received great interest. However, the inherent brittleness of PLA largely impedes its wide applications. In this article, the recent progress in PLA toughening using various routes including plasticization, copolymerization, and melt blending with flexible polymers, was reviewed in detail. PLA toughening, particularly modification of impact toughness through melt blending, was emphasized in this review. Reactive blending was shown to be especially effective in achieving high impact strength. The relationship between composition, morphology, and mechanical properties were summarized. Toughening mechanisms were also discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011.
Light scattering and transmission studies of nanofiller particulate size, matrix cavitation, and high strain interfacial dewetting behavior in silica‐elastomer composites
Authors: Tunnicliffe Lewis B. , Thomas Alan G. , Busfield James J. C.
Published: May 2011

The effect of silica nanofiller surface chemistry on compounded particle size and high strain particle dewetting in a semitransparent nanosilica‐filled elastomer composite was determined using backscattered visible light and transmitted light, respectively. The integrated intensities of backscattered light from the samples were collected at various visible wavelengths for thin‐film composites using ultraviolet–visible spectrometer with an integrating sphere. The data revealed strong Rayleigh‐type scattering from compounded filler particles. Size information was extracted and found to broadly correlate with scanning electron microscopy image analysis of fracture surface. Incorporation of a siloxane surface treatment chemical during compounding resulted in a reduced average filler particle size in the cured composite. On extension of the samples, an optical transition was observed only in the filled composites. At high strains, the semi transparent samples displayed an abrupt drop in transparency becoming opaque. This was quantified using a simple light transmission‐sample extension technique. Strain‐induced crystallization was discounted as the cause for the transition by X‐ray diffraction analysis. The onset yield stress for the optical transition was found to be filler surface‐chemistry‐dependent with the siloxane‐treated filler exhibiting a greatly increased onset stress value. These observations were discussed and rationalized in terms of filler particle–matrix dewetting and cavitation at high strains. Matrix–filler dewetting was distinguished from matrix cavitation by comparison with Beer–Lambert behavior derived from unstrained samples. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011.
Preoperative serum levels of early prostate cancer antigen (EPCA) predict prostate cancer progression in patients undergoing radical prostatectomy
Authors: Zhao Zhigang , Ma Wenjing , Zeng Guohua , Qi Defeng , Ou Lili , Liang Yeping
Published: May 2011

BACKGROUND

Early prostate cancer antigen (EPCA) has been shown a prostate cancer (PCa)‐associated nuclear matrix protein, however, its serum status and prognostic power in patients with PCa are unknown. The goals of this study are to measure preoperative serum EPCA levels in a cohort of PCa patients who were treated with radical prostatectomy (RP), and to investigate whether serum EPCA levels would independently predict cancer prognosis after the surgery.

METHODS

The study group consisted of 109 consecutive patients with clinically localized PCa who were candidates for RP. Serum EPCA levels were measured by ELISA prior to the surgery, and were correlated with pathologic parameters and clinical outcomes postoperatively.

RESULTS

A total of 106 patients underwent RP. Preoperative mean serum EPCA level in RP patients (15.84 ± 3.63 ng/ml) was significantly higher than that in healthy subjects (4.62 ± 1.15 ng/ml) (P < 0.001), but serum EPCA levels in the both groups were statistically lower than the levels in patients with PCa metastatic to regional lymph nodes (27.83 ± 6.22 ng/ml) and metastatic to bone (28.50 ± 6.67 ng/ml) (all P's < 0.001). In patients who progressed during follow‐up, preoperative serum mean EPCA levels were higher in those with aggressive disease progression (27.64 ± 5.48 ng/ml) compared with nonaggressive disease progression (18.15 ± 4.63 ng/ml; P < 0.001). In pre‐ and postoperative multivariate analyses, preoperative serum EPCA level was an independent predictor for disease progression (Hazards Ratio = 5.016, P < 0.001 and Hazards Ratio = 4.305, P < 0.001, respectively).

CONCLUSIONS

Preoperative serum EPCA level is significantly elevated in localized PCa patients with metastatic disease and strongly predicts cancer progression postoperatively. Prostate 72:270–279, 2012. © 2011 Wiley Periodicals, Inc.
Androgens repress expression of the f‐box protein Skp2 via p107 dependent and independent mechanisms in LNCaP prostate cancer cells
Authors: Jiang Jingting , Pan Yunqian , Regan Kevin M. , Wu Changping , Zhang Xueguang , Tindall Donald J. , Huang Haojie
Published: May 2011

BACKGROUND

Androgens control homeostasis of the normal prostate and growth of prostate cancer (PCa) through the androgen receptor (AR) by regulating gene networks involving in cell proliferation, differentiation, and survival. We demonstrated previously that expression of Skp2, a key protein regulating cell entry into the S phase, is inhibited by androgens in an AR‐dependent manner (Oncogene, 2004; 23(12): 2161–2176). However, the underlying mechanism of this regulation is unknown.

METHODS

Using the LNCaP PCa cell line as a working model, the effect of androgens on the expression of Skp2 was examined by Western and Northern blot analyses. Cell cycle was measured by fluorescence‐activated cell sorting (FACS). Gene transfection was performed by electroporation to manipulate the expression levels of proteins studied.

RESULTS

At physiological levels androgens markedly repressed Skp2 expression but slightly induced Skp2 expression at subphysiological levels. Androgens modestly decreased the stability of the Skp2 protein. Androgenic repression of Skp2 expression was completely abolished by E1A‐mediated inactivation of pocket proteins including RB, p130, and p107. Moreover, ectopic expression of p107 inhibited Skp2 expression, and silencing of p107 partially blocked androgenic repression of Skp2.

CONCLUSIONS

Our data indicate that androgens repress Skp2 expression via p107‐dependent and ‐independent pathways in PCa cells. These regulatory mechanisms may be targeted for the development of new therapeutics of androgen‐refractory PCa. Prostate 72:225–232, 2012. © 2011 Wiley Periodicals, Inc.
Microstructure characterization of ball‐milled Ni50Co50 alloy by Rietveld method
Authors: Loudjani Nadia , Bensebaa Nadia , Alleg Safia , Djebbari Chaffia , Greneche Jean Marc
Published: May 2011

A nanostructured Ni50Co50 mixture was prepared by high‐energy ball milling in a planetary ball mill (Frisch P7) under an argon atmosphere. Scanning electron microscopy and X‐ray diffraction (XRD) have been used to study the morphology of the powder particles, microstructure, and structure evolution. Detailed analysis of the XRD patterns was performed by the MAUD program, which is based on the Rietveld method. It reveals the complete vanishing of the Co peaks after 3 h of milling, indicating the allotropic transformation of Co from hcp to fcc structure. The reciprocal dissolution of the elemental Ni and Co powders leads to the formation of a heterogeneous solid solution with two structures: fcc‐Ni(Co) and fcc‐Co(Ni) with relative fractions of about 76 and 20%, respectively, after 24 h of milling. Microstructural parameters such as lattice parameter, crystallite size, microstrains, dislocation density, and stacking faults have been deduced from the best Rietveld refinements. The formation kinetics of nanostructured Ni50Co50 mixture can be described by a lower Avrami parameter, n, close to 0.34.
Physisorption of cis‐ and trans‐decalin on Pt4 clusters from density functional theory calculations
Authors: Yu Shengping , Zeng Qun , Yang Shengyong , Yang Mingli
Published: May 2011

The adsorption of cis‐ and trans‐decalin on Pt4 clusters was investigated using density functional theory calculations. A number of low‐lying Pt4–decalin isomers were identified with an extensive structure screening. Typical physisorption of trans‐ and cis‐decalins on Pt4 surfaces was noted. The geometrical and electronic properties of Pt4 clusters are subjected to minor changes upon decalin adsorption. The rhombus Pt4 structures are found in most of the low‐lying isomers, while the tetrahedral and square Pt4 appear in a few individuals. Trans‐ and cis‐decalins behave similarly in the adsorption although the Pt4–trans‐decalin complexes are slightly more stable than the corresponding Pt4–cis‐decalin isomers. Three main adsorption patterns distinguished with the number and circumstance of Pt atom(s) and H atoms in decalin are characterized among the low‐lying isomers. The revealed Pt4–decalin interaction patterns could be useful for future study of dehydrogenation and cracking reactions of cycloalkanes catalyzed by Pt nanoclusters.
A CASSCF/CASPT2 study on the low‐lying electronic states of the CH3SS and its cation
Authors: Song Ming‐Xing , Zhao Zeng‐Xia , Zhang Wei , Bai Fu‐Quan , Zhang Hong‐Xing , Sun Chia‐Chung
Published: May 2011

Complete active space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) calculations with contracted ANO‐RCC basis set were performed for low‐lying electronic states of CH3SS and its cation in Cs symmetry. For the ground state X2A″ of CH3SS, the calculated S‐S stretching mode is in good agreement with experimental reports. The electron transitions of CH3SS+, X1A′ → 11A″, X1A′ → 21A′, and X1A′ → 21A″, are predicted at 1.055, 3.247, and 3.841 eV. Moreover, the calculated adiabatic and vertical ionization potential and adiabatic affinity are in reasonable agreement with the experimental data. The CASSCF/CASPT2 potential energy curves (PECs) were calculated for S2‐loss dissociation from the X2A″, 12A′, and 22A″ states. The electronic states of the CH3 radical and S2 molecule as the dissociation products were carefully determined by checking energies and geometries of the asymptote products. The S2‐loss PEC for CH3SS indicate that S2‐loss dissociation occurs from the X2A″ state leading to CH3 (12A″) + S2 (X3Σ), the 12A′ and 22A″ leading to CH3 (12A″) + S2 (1Δg). © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012.
A benchmark quantum Monte Carlo study of the ground state chromium dimer
Authors: Hongo Kenta , Maezono Ryo
Published: May 2011

We report calculations of the ground state energy and binding curve of the chromium dimer using the variational and diffusion quantum Monte Carlo (VMC and DMC) methods. We examined various single‐determinant and multideterminant wavefunctions multiplied by a Jastrow factor as a trial/guiding wavefunction for VMC/DMC. The molecular orbitals in the single determinants were calculated using restricted or unrestricted Hartree–Fock or density functional theory (DFT) calculations where five commonly used local (SVWN5), semilocal (PW91 and BLYP), and hybrid (B1LYP and B3LYP) functionals were examined. The multideterminant expansions were obtained from the generalized valence bond and (truncated) unrestricted configuration interaction with single and double excitations (UCISD) methods. We also examined a UCISD wavefunction in which UCISD expansions were added to the UB3LYP single‐determinant reference, and their coefficients were optimized at the VMC level. In addition to the wavefunction dependence, the effects of pseudopotentials and backflow transformation were also investigated. The UB3LYP single‐determinant and multideterminant wavefunctions were found to give the variationally best DMC energies within the framework of single‐determinant and multideterminants, respectively, though both the DMC energies were higher than twice the DMC atomic energy. Some of the VMC binding curves show a flat or quite shallow well bottom, which gets recovered deeper by DMC. All the DMC binding curves have a minimum indicating a bound state, but the unrestricted ones overestimate the equilibrium bond length. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012
Product channels in the reaction of the CH3SO radical with NO2: DFT and ab initio studies
Authors: Lesar Antonija
Published: May 2011

The stationary points involved in the CH3SO + NO2 radical‐radical reaction were examined at the B3LYP/6‐311++G(2df,2pd) and CCSD/cc‐pVDZ levels of theory. Singlet potential energy surface was calculated using the CCSD(T)/aug‐cc‐pVTZ//CCSD/CC‐pVDZ single‐point calculations and the CBS‐QB3 composite method. The association between radicals is confirmed to be a barrierless process and resulted in the two low‐energy intermediates, CH3S(O)NO2 and CH3S(O)ONO. The CH3S(O)ONO intermediate decomposes directly to the CH3SO2 + NO products with the NO bond dissociation energy of 7.9 kcal mol−1. Although the dissociation of the CS bond in the CH3SO2 requires an energy of 16.3 kcal mol−1, the formation of final CH3 + SO2 + NO products is very likely, because their energy level is by 3.4 kcal mol−1 still lower relative to that of the reactants. The formation of the CH2SO + HONO products from CH3S(O)ONO can proceed through the three‐center transition state, but it is not important due to significant barrier well above the energy level of reactants. Eventually, CH2SO + HONO may be generated in the direct H‐abstraction from CH3SO radical by NO2. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011
Phase transitions for random walk asymptotics on free products of groups
Authors: Candellero Elisabetta , Gilch Lorenz A.
Published: May 2011

Suppose we are given finitely generated groups Γ1,…,Γm equipped with irreducible random walks. Thereby we assume that the expansions of the corresponding Green functions at their radii of convergence contain only logarithmic or algebraic terms as singular terms up to sufficiently large order (except for some degenerate cases). We consider transient random walks on the free product Γ1* … *Γm and give a complete classification of the possible asymptotic behaviour of the corresponding n‐step return probabilities. They either inherit a law of the form ϱnδn log n from one of the free factors Γi or obey a ϱnδn−3/2‐law, where ϱ < 1 is the corresponding spectral radius and δ is the period of the random walk. In addition, we determine the full range of the asymptotic behaviour in the case of nearest neighbour random walks on free products of the form
\documentclass{article} \usepackage{amsmath, amsthm, amssymb, amsfonts}\pagestyle{empty}\begin{document} $\mathbb{Z}^{d_1}\ast \ldots \ast \mathbb{Z}^{d_m}$ \end{document}. Moreover, we characterize the possible phase transitions of the non‐exponential types n log n in the case Γ1 * Γ2. © 2011 Wiley Periodicals, Inc. Random Struct. Alg., 2012
Surface modification of vitreoretinal surgical instruments with layer‐by‐layer films
Authors: Valentin‐Rodriguez Celimar , Tezel Tongalp H. , Ivanisevic Albena
Published: May 2011

Commercially available vitreoretinal surgical forceps were modified with layer‐by‐layer (LbL) films designed to render them the ability to specifically adhere human the inner limiting membrane. Surgical forceps with two different geometries were etched, polished, and silanized before deposition of the films composed of poly (allylamine hydrochloride), poly (styrene sulfonate), and cationic gold nanoparticles. Stability and integrity of the LbL films was scrutinized by exposing the modified forceps to commercial disinfectant Cidex‐OPA and then placing the instruments in a physiological‐like HEPES buffer (pH 7.4, 5 mM, 154 mM NaCl). Surface topography analysis with scanning electron microscopy revealed that the geometry of the surgical instrument may affect the integrity of the film. Analysis of the HEPES buffer with inductively coupled plasma mass spectrometry demonstrated that gold nanoparticles did not leach from the LbL film after 60 min. SCANNING 33:397–401, 2011. © 2011 Wiley Periodicals, Inc.
Discovering AODV‐based multipath routes in wireless ad hoc networks
Authors: Li Gang , Sun Hongmei
Published: May 2011

Multipath extension of ad hoc on‐demand distance vector (AODV) protocol can provide reliable and adaptable routes in mobile ad hoc networks. In this paper, we propose an AODV‐based acyclic multipath routing method, which uses a dynamic hop count to discover loop‐free multipath routes. The advantage of our method is that it allows a node to add a route entry with a hop count that is larger than its current hop count. This increases the possibility to find more loop‐free route backups. To evaluate the performance, we present the simulation at the end of the paper and compare it with ad hoc on‐demand multipath distance vector (AOMDV) protocol and others. Copyright © 2011 John Wiley & Sons, Ltd.
Security analysis of an ultra‐lightweight RFID authentication protocol—SLMAP*
Authors: Erguler Imran , Unsal Cihan , Anarim Emin , Saldamli Gokay
Published: May 2011

Computational constraints mostly driven by the cost concerns of radio frequency identification tags only permit to have security schemes that are simple combinations of elementary operations rather than the bullet proven yet computationally intensive cryptographic primitives. As ultra‐lightweight authentication protocols use only basic bitwise and arithmetic operations such as XOR, OR, and addition modulo powers of 2, they are considered as a class of these schemes. Because most of the early proposed ultra‐lightweight authentication protocols are easily broken, it turned out that designing such protocols is a much deeper task than presumed. This study analyzes a modified version of the stable lightweight mutual authentication protocol denoted by SLMAP*. After exploiting an unnoticed flaw in its design rationale, it is shown that some of the freshly produced variables can be assigned to different values for the reader and the tag that presumably causes a desynchronization vulnerability. Copyright © 2011 John Wiley & Sons, Ltd.
Hybrid Nanomotor: A Catalytically/Magnetically Powered Adaptive Nanowire Swimmer
Authors: Gao Wei , Manesh Kalayil Manian , Hua Joe , Sattayasamitsathit Sirilak , Wang Joseph
Published: May 2011

A synthetic hybrid nanomotor, which combines chemically powered propulsion and magnetically driven locomotion, is described. The new catalytic–magnetic nanomotor consists of a flexible multisegment Pt‐Au‐Agflex‐Ni nanowire, with the Pt‐Au and Au‐Agflex‐Ni portions responsible for the catalytic and magnetic propulsion modes, respectively. The experimental data and theoretical considerations indicate that the hybrid design only minimally compromises the individual propulsion modes. Rapid and convenient switching from the catalytic to the magnetic mode is illustrated. The resulting catalytic–magnetic adaptive nanomotor can address the fuel depletion and salt limitation common to chemically powered motors by switching to magnetic propulsion. Reversal of the motion direction is also achieved upon applying the magnetic field. Such use of two sources to power a hybrid device offers a broader scope of operation and holds considerable promise for designing adaptive nanovehicles that reconfigure their operation in response to environmental changes or unexpected events.
One‐Step High‐Yield Aqueous Synthesis of Size‐Tunable Multispiked Gold Nanoparticles
Authors: Sau Tapan K. , Rogach Andrey L. , Döblinger Markus , Feldmann Jochen
Published: May 2011

Multispiked gold nanoparticles are required in large quantities for many fundamental studies and applications like (bio)sensing, but their preparation in high yield by the bottom‐up chemical synthetic method is challenging. A water‐based, non‐‘seed‐mediated’, straightforward method for the synthesis of gold nanoparticles with well‐developed surface spikes is reported here. The yield of multispiked gold particles is very high (>90%). The method allows the tuning of the number and size of the spikes and the overall size of the particles, and hence the localized surface plasmon resonances of the particles over the broad spectral range in the visible and near‐infrared. A mechanism for the evolution of twinned, sharp‐tipped surface protrusions has been proposed based on systematic spectrophotometric and transmission electron microscopic studies, which were employed to elucidate the morphological features, structure, chemical composition, and optical properties of the multispiked gold nanoparticles.
Quantification of Uptake and Localization of Bovine Serum Albumin‐Stabilized Single‐Wall Carbon Nanotubes in Different Human Cell Types
Authors: Holt Brian D. , Dahl Kris Noel , Islam Mohammad F.
Published: May 2011

Single‐wall carbon nanotubes (SWCNTs) possess many unique, inherent properties that make them attractive materials for application in medical and biological technologies. Development of concentrated SWCNT dispersions of isolated nanotubes that retain SWCNTs' inherent properties with minimal negative cellular effects is essential to fully realize the potential of SWCNTs in biotechnology. It is shown that bovine serum albumin (BSA), a common and well‐characterized model blood serum protein, can individually disperse SWCNTs at concentrations of up to 0.3 mg mL−1 while retaining SWCNTs' optical properties. Uptake into human mesenchymal stem cells (hMSC) and HeLa cells is quantified, revealing strikingly high concentrations of 86 ± 33 × 106 and 21 ± 13 × 106 SWCNTs per cell, respectively, without any apparent acute deleterious cellular effects. Through high‐resolution confocal Raman spectroscopy and imaging, it is established that SWCNT–BSAs are preferentially localized intracellularly, especially in the cytoplasm of both hMSCs and HeLa cells. The uptake and localization results demonstrate the efficacy of BSA as a biocompatible dispersant and a mediator of bioactivity. BSA is widely available and inexpensive, which make these concentrated, highly‐dispersed, noncovalently modified SWCNT–BSAs suitable for the development of SWCNT‐based biotechnologies.
Self‐Aligned Sub‐10‐nm Nanogap Electrode Array for Large‐Scale Integration
Authors: Gao Pingqi , Zhang Qing , Li Hong , Chan‐Park Mary B.
Published: May 2011

A novel approach to creating a gap on the nanometer scale between two adjacent electrodes of the same or different metals is described. The gap size can be well controlled through sidewall coverage in a self‐aligned manner and it can be tuned from 60 nm down to 5 nm with high reproducibility. This technique is fully compatible with traditional microfabrication technology and it is easily implemented to fabricate a nanogap electrode array for integration purposes. An array of short‐channel single‐walled carbon nanotube field‐effect transistors is demonstrated.
Effect of physico‐chemical properties of tropical starches and hydrocolloids on rice gels texture and noodles water retention ability
Authors: Qazi Ihsan Mabood , Kumar Rakshit Sudip , Tran Thierry
Published: May 2011

The links between the physico‐chemical properties of rice flour (RF), cassava (CS), sago (SS), canna (CaS), sweet potato (SPS), and mung bean (MS) starches, and the gelling properties of rice flour blends with these starches in different proportions (0, 20, 40, 60, 80, and 100% pure starches) and with xanthan (XG) and carrageenan (CG) gums were studied. Water retention ability of starches and hydrocolloids blends in noodle systems during drying at 40°C was also investigated. The mean granule diameter and AM content values of RF, CS, SPS, SS, CaS, and MS were in the range of 12.8–41.0 µm and 21.9–39.4%, respectively. Thermal properties showed significant differences (p < 0.05) between the starches in terms of gelatinization temperature and enthalpy, as well as retrogradation tendency. Different starches produced gels with a wide range of textural properties. Results confirmed the role of AM content in determining the gel strength, and indicated a possible role of retrogradation in increasing the dissipation of mechanical energy during compression and relaxation tests, which can have an effect on mouth feel. Blends of RF with other starches and hydrocolloids generally improved the characteristics of RF‐based gels, by increasing gel strength. In particular, the use of MS markedly increased the strength of RF‐based gels. Addition of hydrocolloids significantly reduced the drying rate of noodles, although overall water retention ability was reduced only to a limited extent. This may be used to produce starch‐based products, especially noodles, in a range of desired characteristics.
Activin/Nodal Signaling Controls Divergent Transcriptional Networks in Human Embryonic Stem Cells and in Endoderm Progenitors
Authors: Brown Stephanie , Teo Adrian , Pauklin Siim , Hannan Nicholas , Cho Candy H.-H. , Lim Bing , Vardy Leah , Dunn N. Ray , Trotter Matthew , Pedersen Roger , Vallier Ludovic
Published: May 2011

Activin/Nodal signaling is necessary to maintain pluripotency of human embryonic stem cells (hESCs) and to induce their differentiation toward endoderm. However, the mechanisms by which Activin/Nodal signaling achieves these opposite functions remain unclear. To unravel these mechanisms, we examined the transcriptional network controlled in hESCs by Smad2 and Smad3, which represent the direct effectors of Activin/Nodal signaling. These analyses reveal that Smad2/3 participate in the control of the core transcriptional network characterizing pluripotency, which includes Oct-4, Nanog, FoxD3, Dppa4, Tert, Myc, and UTF1. In addition, similar experiments performed on endoderm cells confirm that a broad part of the transcriptional network directing differentiation is downstream of Smad2/3. Therefore, Activin/Nodal signaling appears to control divergent transcriptional networks in hESCs and in endoderm. Importantly, we observed an overlap between the transcriptional network downstream of Nanog and Smad2/3 in hESCs; whereas, functional studies showed that both factors cooperate to control the expression of pluripotency genes. Therefore, the effect of Activin/Nodal signaling on pluripotency and differentiation could be dictated by tissue specific Smad2/3 partners such as Nanog, explaining the mechanisms by which signaling pathways can orchestrate divergent cell fate decisions.
Bone Marrow Stromal Cells Produce Long-Term Pain Relief in Rat Models of Persistent Pain
Authors: Guo Wei , Wang Hu , Zou Shiping , Gu Ming , Watanabe Mineo , Wei Feng , Dubner Ronald , Huang George T.-J. , Ren Ke
Published: May 2011

Chronic pain conditions are difficult to treat and are major health problems. Bone marrow stromal cells (BMSCs) have generated considerable interest as a candidate for cell-based therapy. BMSCs are readily accessible and are easy to isolate and expand ex vivo. Clinical studies show that direct injection of BMSCs does not produce unwanted side effects and is well tolerated and safe. Here, we show that a single systemic (intravenous) or local injection (into the lesion site) of rat primary BMSCs reversed pain hypersensitivity in rats after injury and that the effect lasted until the conclusion of the study at 22 weeks. The pain hypersensitivity was rekindled by naloxone hydrochloride, an opioid receptor antagonist that acts peripherally and centrally, when tested at 1–5 weeks after BMSC infusion. In contrast, naloxone methiodide, a peripherally acting opioid receptor antagonist, only rekindled hyperalgesia in the first 3 weeks of BMSC treatment. Focal downregulation of brainstem mu opioid receptors by RNA interference (RNAi) reversed the effect of BMSCs, when RNAi was introduced at 5- but not 1-week after BMSC transplantation. Thus, BMSCs produced long-term relief of pain and this effect involved activation of peripheral and central opioid receptors in distinct time domains. The findings prompt studies to elucidate the cellular mechanisms of the BMSC-induced pain relieving effect and translate these observations into clinical settings.
Association of fetal cranial shape with shoulder dystocia
Authors: Belfort M. A. , White G. L. , Vermeulen F. M.
Published: May 2011

Objective

To evaluate whether fetal cranial shape is related to shoulder dystocia.

Methods

We compared shoulder dystocia cases (n = 18) with controls (normal vaginal deliveries, n = 18) in a retrospective matched‐pairs observational study. Subjects were matched for known maternal and fetal risk factors and then evaluated for fetal biometric differences, which were measured by ultrasound near delivery. We tested multivariable risk models to predict shoulder dystocia by logistic regression.

Results

Cases had a smaller estimated occipitofrontal diameter (OFD) (P = 0.02) and a larger biparietal diameter/estimated OFD ratio (P = 0.003). A multivariable model including estimated fetal weight, estimated OFD, maternal weight and diabetes mellitus had sensitivity and specificity of 86% and 95%, respectively, and positive and negative likelihood ratios of 18.9 and 0.15, respectively. Estimated OFD significantly increased the predictive value of the model.

Conclusion

A small estimated OFD is a risk factor for shoulder dystocia in the presence of other significant risk factors. A multivariable model including estimated OFD can predict shoulder dystocia in a clinically useful range. Copyright © 2012 ISUOG. Published by John Wiley & Sons, Ltd.