bluuebunny/crossref_metadata_2025 huggingface dataset:
Annealing effect on the carrier transport in (2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene): C60 bulk heterojunction
Authors: Shi Quanmin , Hou Yanbing , Liu Xiaojun , Feng Zhihui
Published: October 2008

Using time-of-flight technique, the annealing effect on the carrier transport in (2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and MEH-PPV:C60 bulk heterojunction (BHJ) is investigated. Hole mobility drops evidently for the annealed samples compared to the as prepared sample. By analyzing the temperature dependence of field dependent mobility in the Gaussian disorder model, the drop of hole mobility can be attributed to the large value of both positional disorder and energetic disorder, which are 4.47 and 0.132 eV, respectively. However, hole mobility is enhanced for the samples annealed after preparing Al electrodes. Although electron mobility is measurable for the as prepared MEH-PPV:C60 devices, it is below the measurable range as long as the devices experience thermal treatment. The morphology of the annealed samples is investigated by scanning electron microscope and atomic force microscopy. The results manifest that the enhancement of the efficiency for the annealed MEH-PPV:C60 BHJ solar cells cannot be attributed to the improvement of carrier transport properties, but results from the changes in morphology.
Structural, magnetic, and optical properties of Co- and Gd-implanted ZnO(0001) substrates
Authors: Ney V. , Ye S. , Kammermeier T. , Ney A. , Zhou H. , Fallert J. , Kalt H. , Lo F.-Y. , Melnikov A. , Wieck A. D.
Published: October 2008

ZnO(0001) substrates were ion implanted with 100 keV of Co and 300 keV of Gd at different fluences ranging from 5×1013–1×1015/cm2. The resulting Co:ZnO and Gd:ZnO samples were analyzed with respect to their structural, magnetic, and optical properties. The effect of annealing at 350 °C on the structure and the resulting magnetic and optical properties were investigated as well. For Co:ZnO hardly any changes were observable, neither in the structural nor in the magnetic properties, even though the existence of substitutional Co2+ in the ZnO lattice could be shown by means of low temperature photoluminescence especially for Zn-annealed samples. For the much larger Gd ion the implantation leads to a changed crystal structure, which leads to a ferromagneticlike behavior for higher implantation doses, which could even be enhanced by annealing in vacuum. Ferromagnetic behavior in annealed Gd:ZnO is corroborated by ferromagnetic resonance measurements at low temperatures. The distinct behavior of Gd- and Co-implanted ZnO highlights the importance of defects in the understanding of the magnetic properties in dilute magnetic semiconductors.
A quantitative study of the effect of surface texture on plasticity induced surface roughness and dislocation density of crystalline materials
Authors: Zamiri Amir R. , Pourboghrat Farhang , Bieler Thomas R.
Published: October 2008

Microscale simulations are used to study the effects of the surface texture and plastic deformation on surface roughness and dislocation density, which are important parameters controlling some surface physical properties such as electron work function (EWF) and phonon emission of crystalline materials. The results of the simulations on superconducting niobium show that the intensity and the components of the surface texture have significant effects on the plasticity induced surface roughness and dislocation density. A weak surface texture develops a rough surface after plastic deformation, which is due to the different plastic “shear rates and directions” behavior in the grains with different orientations. Some grains with specific orientation experience more plastic deformation, and therefore develop an intragrain surface roughness due to the development of microtexture and inhomogeneous plastic deformation inside the grain. Due to an inhomogeneous plastic deformation, the dislocation density not only is different in the grains with different orientations but also is inhomogeneous within a grain. Therefore, it may be possible to design surface texture to obtain optimal EWF and minimal electron emission and control surface roughness and dislocation density in polycrystalline materials.
Microstructure, electrical and magnetic properties of Ce-doped BiFeO3 thin films
Authors: Quan Zuci , Liu Wei , Hu Hao , Xu Sheng , Sebo Bobby , Fang Guojia , Li Meiya , Zhao Xingzhong
Published: October 2008

Bi 1 − x Ce x FeO 3 (x=0, 0.05, 0.1, 0.15, and 0.20) (BCFO) thin films were deposited on Pt/TiN/Si3N4/Si and fluorine-doped SnO2 glass substrates by sol-gel technique, respectively. The effect of Ce doping on the microstructure, electrical and magnetic properties of BCFO films was studied. Compared to counterparts of BiFeO3 (BFO) film, the fitted Bi 4f7/2, Bi 4f5/2, Fe 2p3/2, Fe 2p1/2, and O 1s peaks for Bi0.8Ce0.2FeO3 film shift toward higher binding energy regions by amounts of 0.33, 0.29, 0.43, 0.58, and 0.49 eV, respectively. Raman redshifts of 2–4 cm−1 and shorter phonon lifetimes for the Bi0.8Ce0.2FeO3 film might be related to anharmonic interactions among Bi–O, Ce–O, (Bi, Ce)–O, and Fe–O bonds in the distorted oxygen octahedron. Compared to the pure counterparts, the dielectric and ferroelectric properties of the Bi0.8Ce0.2FeO3 film are improved due to the decreased oxygen vacancies by the stabilized oxygen octahedron. Current density values for the BFO and Bi0.8Ce0.2FeO3 film capacitors are 9.89×10−4 and 5.86×10−5 A/cm2 at 10 V, respectively. The current density–applied voltage characteristics indicate that the main conduction mechanism for the BCFO capacitors is the interface-controlled Schottky emission. Both the in-plane and out-of-plane magnetization–magnetic field hysteresis loops reveal that the saturation magnetization values of the BCFO films increase with increasing the Ce concentration. The enhanced magnetic properties for the BCFO films might be attributed to the presence of Fe2+ caused by oxygen vacancies, the suppressed spiral spin structure, and/or the increased canting angle induced by Ce doping.
Strain optimization in ultrathin body transistors with silicon-germanium source and drain stressors
Authors: Madan Anuj , Samudra Ganesh , Yeo Yee-Chia
Published: October 2008

The potential of Si1−xGex source and drain strained silicon p-channel transistors is investigated for ultrathin body silicon-on-insulator (SOI) substrates. We used process simulations to quantify and understand the role of device design parameters such as raised source and drain, source and drain length, and recess depth in the context of SOI transistors. Simultaneous strain calculations were performed with the process flow to capture not only lattice mismatch, but all process induced strain. Germanium condensation technique was found suitable for enhancing strain in ultrathin body transistors by increasing germanium concentration and driving germanium deeper into the source and drain. The scalability of germanium condensation process is discussed.
Activation volume for nanocrystal growth in amorphous Nd9Fe85B6
Authors: Wu Wei , Guo Defeng , Li Wei , Li Lanlan , Sun Hongyu , Zhang Xiangyi , Li Xiaohong , Liu Baoting
Published: October 2008

We have measured the pressure dependence of the growth of α-Fe and Nd2Fe14B nanocrystals in amorphous Nd9Fe85B6 up to 6 GPa at a temperature of 923 K, yielding an activation volume of ΔV∗=(0.76±0.04) and (0.57±0.05)Ω for atomic diffusion in the growth process of α-Fe and Nd2Fe14B nanocrystals, respectively, where Ω is the mean atomic volume of the alloy. This demonstrates that the growth of nanocrystals is dependent on atomic diffusion mediated by vacancy-type thermal defects. Atomic processes of the growth of nanocrystals are discussed.
Surface electronic properties of clean and S-terminated InSb(001) and (111)B
Authors: King P. D. C. , Veal T. D. , Lowe M. J. , McConville C. F.
Published: October 2008

The electronic properties of clean and sulfur-terminated surfaces of InSb(001) and (111)B are investigated using x-ray photoemission spectroscopy and high-resolution electron energy loss spectroscopy. The clean surfaces exhibit upward band bending (electron depletion) consistent with the charge neutrality level in InSb lying at the valence band maximum. The surface Fermi level to valence band maximum separation is increased for the S terminated compared with the clean surface, leading to flat bands and downward band bending (electron accumulation) for the (001) and (111)B surfaces, respectively. This is discussed in terms of compensation of native acceptor surface states.
Exact computation and large angular momentum asymptotics of 3nj symbols: Semiclassical disentangling of spin networks
Authors: Anderson Roger W. , Aquilanti Vincenzo , da Silva Ferreira Cristiane
Published: October 2008

Spin networks, namely, the 3nj symbols of quantum angular momentum theory and their generalizations to groups other than SU(2) and to quantum groups, permeate many areas of pure and applied science. The issues of their computation and characterization for large values of their entries are a challenge for diverse fields, such as spectroscopy and quantum chemistry, molecular and condensed matter physics, quantum computing, and the geometry of space time. Here we record progress both in their efficient calculation and in the study of the large j asymptotics. For the 9j symbol, a prototypical entangled network, we present and extensively check numerically formulas that illustrate the passage to the semiclassical limit, manifesting both the occurrence of disentangling and the discrete-continuum transition.
The influence of growth temperature and annealing on the magnetization depth profiles across ferromagnetic/semiconductor interfaces
Authors: Park S. , Fitzsimmons M. R. , Majkrzak C. F. , Schultz B. D. , Palmstrøm C. J.
Published: October 2008

The magnetization depth profiles of three FeCo/GaAs samples grown at different temperatures and measured before and after annealing were obtained using polarized neutron reflectometry. Prior to annealing, the sample grown at 95 °C had the thickest magnetically degraded interfacial region between the FeCo film and the GaAs substrate. For the sample grown at −15 °C, the magnetic interface was sharp. For all samples, annealing promoted thicker interfacial regions with suppressed magnetization and distinct boundaries with the adjoining (FeCo or GaAs) material. Thus, the magnetic structure of the FeCo/GaAs interfacial region was very sensitive to the conditions of growth and annealing.
Visual observation of dissociation of methane hydrate crystals in a glass micro model: Production and transfer of methane
Authors: Katsuki Daisuke , Ohmura Ryo , Ebinuma Takao , Narita Hideo
Published: October 2008

Dissociation of methane hydrate crystals in pore space caused by temperature increase or depressurization, which is one of the main concerns in developing techniques to exploit natural gases in clathrate hydrate in sediments, was observed by using a glass mimic of sediments. Hydrate crystals were formed at a system temperature of T=274.0 K and system pressure of p=12.5 MPa or T=279.6 K and p=10.1 MPa and then decomposed by increasing the system temperature to 289 or 290 K, respectively. Two experimental runs of depressurization were also conducted. Hydrate crystals formed at T=282.9 K and p=10.1 MPa or T=274.0 K and p=12.5 MPa were decomposed by depressurization to 1.7 or 0.5 MPa at a system temperature of 285.5 or 274.3 K. The glass mimic of sediments (glass micromodel) was composed of a quartz glass plate on which straight microchannels were carved and another quartz glass plate covering the microchannels. The microchannels were approximately rectangular in cross section with a top width of 1.0×102 μm and were arranged in a grid pattern at regular intervals of 2.0×102 μm. Methane gas released from dissociating methane hydrate crystals was commonly observed to form slugs that completely occupy the pores in all experiment runs. The mechanism of the dissociation of the methane hydrate crystals was discussed considering the heat and mass transfer of methane around the dissociating methane hydrate crystals.
Lorentz-force dependence of the critical current for SmBCO coated conductor
Authors: Oh Sangjun , Lee Chulhee , Cho Kyuhwan , Lee Sangmoo , Youm Dojun
Published: October 2008

Angular dependence of the critical current in a varying Lorentz-force configuration for a SmBCO coated conductor has been studied. Near the transition temperature, the angular dependence of the critical current in a varying Lorentz-force configuration was quite similar to the result of a constant Lorentz-force measurement. As the temperature is lowered and as the field is aligned along the ab-plane, the critical current measured in a varying Lorentz-force configuration becomes larger than the constant Lorentz-force measurement. We found that the field dependence of the critical current and n-value can be described by the same pinning model, the Kramer model including thermal activation, reported for constant Lorentz-force measurements of various ReBCO (Re, rare earth, Sm, or Y) thin films [S. Oh et al., J. Appl. Phys. 102, 043904 (2007)]. As a possible reason, the Lorentz force acting on segments of twisted vortex lines due to collective pinning or by thermal excitations is discussed. It is further argued that the difference in the critical current for the varying and constant Lorentz-force measurements can be understood as mainly due to a variation in the pinning force, if we interpret the Lorentz force on twisted vortex lines as a scalar product between the applied field and current.
A density functional theory–based study of the electronic structures and properties of cage like metal doped silicon clusters
Authors: Bandyopadhyay Debashis
Published: October 2008

Ab initio electronic-structure calculations were performed by using density functional theory with polarized basis set (LanL2DZ) within the spin polarized generalized gradient approximation for metal (M=Ti,Zr,Hf) doped Sin clusters where n varies from 9 to 20. In the first step of the calculation, geometrical optimizations of the nanoclusters have been done. In the next step, these optimized geometries have been used to calculate the binding energy (BE) and HOMO-LUMO gap (ΔEg) of the clusters. In order to check the stability of the clusters, the second order energy differences of the optimized geometries have been calculated. To study the optical behavior of the clusters, IR and Raman spectra calculation have been done. Further calculations on cation and anion clusters have been done to obtain their ionization potential (IP), electron affinity (EA), and chemical potential.
A simple model of the positive ion sheath in front of a plane probe in weakly ionized electropositive plasmas
Authors: Crespo R. Morales , Palop J. I. Fernández , Hernández M. A. , Lucena-Polonio M. V. , Ballesteros J.
Published: October 2008

This paper describes the positive ion sheath in front of a plane probe in weakly ionized electropositive plasmas. The results obtained are the potential profile in front of the probe and the probe positive ion current to voltage characteristic curves that have been analytically fitted as a function of the probe potential and the plasma ionization rate. Finally, the floating potential for an argon plasma has been calculated by considering a parametrization of the model obtained from the fitted characteristics.
Electric energy generation in single track-etched nanopores
Authors: Xie Yanbo , Wang Xinwei , Xue Jianming , Jin Ke , Chen Long , Wang Yugang
Published: October 2008

We investigated the efficiency of electrical power generation in single track-etched nanopores by measuring the streaming currents and conductance. Experimental results indicate that both the efficiency and output power depend on the electrolyte concentration and the dimension of the pore. The highest efficiency of 5% was obtained in nanopores with small radii of 31 nm. The surface property of the track-etched nanopores was found very important to the kinetic-electric behaviors in the pores, especially when the electrolyte concentration was low.
Lattice-Boltzmann simulation of finite Reynolds number buoyancy-driven bubbly flows in periodic and wall-bounded domains
Authors: Yin Xiaolong , Koch Donald L.
Published: October 2008

A lattice-Boltzmann method is used to probe the structure and average properties of suspensions of monodisperse, spherical, noncoalescing bubbles rising due to buoyancy with Reynolds numbers based on the bubble terminal velocities of 5.4 and 20. Unbounded suspensions subject to periodic boundary conditions exhibit a microstructure with a strong tendency toward horizontal alignment of bubble pairs even at volume fractions of as high as 0.2. This microstructure leads to a mean rise velocity whose dependence on the bubble volume fraction is not well fitted by a standard power-law function. Simulations with bounding vertical walls exhibit a deficit of bubbles near each wall and a peak of volume fraction approximately one bubble diameter from the wall. We attribute this structure to the effects of a repulsive wall-induced force and a lift force associated with the liquid flow driven by the variation in the buoyancy force with horizontal position. Weaker peaks of bubble volume fraction extend into the bulk of the suspension and these peaks are separated by a distance equal to the peak in the pair distribution function for bubble pairs in an unbounded fluid. This suggests that the layering is a result of hydrodynamic bubble-bubble interactions.
Time dependence of magnetization reversal influenced by current in perpendicularly magnetized Co/Pt thin film
Authors: Xie K. X. , Lin W. W. , Sun H. C. , Nie Y. , Sang H.
Published: October 2008

We have investigated thermally activated magnetization reversal influenced by the current in a Co/Pt thin film with perpendicular magnetic anisotropy at room temperature by measuring the extraordinary Hall effect. The magnetization could reverse in a fixed magnetic field lower than the coercive field as increasing the current, which depends on the current-sweep rate. The characteristic current for zero net magnetization is small for a low current-sweep rate and a high fixed field. Magnetization reversal becomes fast for a high current-sweep rate and a high fixed field. With the constant current, the magnetization reversal is fast for a large current and a high fixed field. The magnitude of the propagation field HP∗ reduces more than 70 Oe when the current density J reaches 1.25×105 A/cm2, which is mainly on account of the sample temperature rise due to current-induced Joule heating. Also, the effective field HI associated with spin transfer and momentum transfer perhaps has a contribution to magnetization reversal through thermal activation in a multidomain macroscopic thin film. The results show that the Joule heating and current associated effective field can reduce the activation energy barriers and speed up magnetization reversal besides the applied magnetic field.
Cross-talk compensation in atomic force microscopy
Authors: Onal Cagdas D. , Sümer Bilsay , Sitti Metin
Published: October 2008

In this work, calibration and correction of cross-talk in atomic force microscopy (AFM) is demonstrated. Several reasons and effects of this inherent problem on experimental results are discussed. We propose a general procedure that can be used on most AFM systems to compensate for cross-talk on the cantilever bending and twisting signals. The method utilizes two initial experiments on a flat surface to achieve an affine transformation between the measured signals and the actual signals. Using this transformation directly on the voltage signals allows us to remove the detrimental effects of cross-talk on AFM-based force measurement experiments. The achieved transformation matrix can be turned into a simple circuit and applied online, by users who have access to the raw signals in the AFM head. As a case study, a lateral deflection based mechanical characterization test for a poly(methyl methacrylate) microfiber that is suspended on a trench is investigated in terms of the effectiveness of the cross-talk compensation.
Native defects and their effects on properties of sputtered InN films
Authors: Kuo Dong-Hau , Shih Chun-Hung
Published: October 2008

The concept of defect chemistry is applied to investigate the native defects in the InN films prepared by radio frequency magnetron sputtering. Growth temperature and pressure ranged from 150 to 300 °C and from 0.005 to 0.07 torr, respectively, for the purpose of changing the defects and the related properties. InN is expected to form Frenkel defects, indium vacancies, and interstitials. Other major defects for the nitrogen-rich InN films include nitrogen-on-indium antisites and nitrogen interstitials at higher nitrogen pressure, as supported by the results of x-ray photoelectron spectroscopy. Structure, composition, and electrical properties coincide with defect types and density.
Hydrogenation of Mg film and Mg nanoblade array on Ti coated Si substrates
Authors: He Yuping , Zhao Yiping , Huang Liwei , Wang Howard , Composto Russell J.
Published: October 2008

The hydrogenation of Mg film and Mg nanoblade array fabricated on Ti coated Si substrates has been studied and compared. The nanoblades start to absorb hydrogen at a temperature between 250 and 300°C, which is much lower than 350°C for Mg film. However, the saturated total hydrogen uptake in nanoblades is less than half of that in the film, resulting from MgO formation by air exposure. The nanoblade morphology with large surface area and small hydrogen diffusion length, and the catalytic effect of Ti layer, are two main reasons for the nanoblade hydrogenation behavior.
Sr induced striped surface reconstructions formed on Si(111)
Authors: Teys S. , Olshanetsky B. , Zhachuk R. , Pereira S. , Norga G.
Published: October 2008

Surface structures induced by submonolayer Sr adsorption on Si(111) surface were investigated by scanning tunneling microscopy (STM). Depending on the sample temperature and Sr coverage the following reconstructions on Si(111) surface could be directly resolved: 3×2, n×1 (n=5,7,9), 23×13, 43×43, and 3×2 with increasing Sr coverage. The 3×2 and 23×13 striped structures cover large surface areas and are found to have stripe-to-stripe separations of 1.00 and 1.34nm, respectively. The surface structures and respective rotational and antiphase domains reported here can explain all the previously suggested reconstructions except 2×1, which was not found. It is also demonstrated that diffraction data may lead to ambiguous results regarding the structure periodicity, when structural antiphase domains with sizes below the coherence length are present, highlighting the importance of complementary real space STM analysis.
Surface scattering in metallic nanowires
Authors: Chen Xi , Victora R. H.
Published: October 2008

Electronic transport with surface scattering in metallic nanowires is studied theoretically based on an atomistic tight-binding approach. It is shown that the mean free path (MFP) strongly depends on the size of the wire and the scattering potential at the surface. In the weak scattering regime, the MFP grows with the wire diameter in an oscillatory manner. A perturbation theory is developed to explain this finite size effect. For narrow wires with small roughness, we show that the surface can be the dominant source of scattering and increases the resistivity well above the bulk value, which will adversely impact the future application of nanowire.
Two-dimensional photonic crystals with anisotropic unit cells imprinted from poly(dimethylsiloxane) membranes under elastic deformation
Authors: Zhu Xuelian , Zhang Ying , Chandra Dinesh , Cheng Shih-Chieh , Kikkawa James M. , Yang Shu
Published: October 2008

We study structural symmetries of two-dimensional (2D) photonic crystals with anisotropic unit cells, including square- and rectangular-lattices with orientationally modulated elliptic motifs, and a compound structure consisting of circles with sixfold rotational symmetry and elliptical lines with twofold symmetry, which are created through elastic deformation of a single elastomeric membrane with circular pores. We then investigate the photonic bandgap (PBG) properties of the corresponding 2D Si posts and their tolerance to the structural deviation. We find that in the compound structure the overall PBGs are dominated by the sublattice with a higher symmetry, while the total symmetry is determined by the one with a lower symmetry.
Ge dangling bonds at the (100)Ge/GeO2 interface and the viscoelastic properties of GeO2
Authors: Houssa M. , Pourtois G. , Caymax M. , Meuris M. , Heyns M. M. , Afanas’ev V. V. , Stesmans A.
Published: October 2008

The electronic energy band structure of a (100)Ge/GeO2 interface with a Ge3≡Ge• center (Ge dangling bond) is calculated using the density functional theory. The defect level associated with this dangling bond is found to lie near the middle of the Ge band gap. Consequently, the Ge dangling bond at this interface should be paramagnetic when the Fermi level is near the midgap, and it should thus be observed by electron spin resonance (ESR), which appears to be in contradiction with the results reported by [Afanas’ev et al., Appl. Phys. Lett. 87, 032107 (2005)]. We point out that the density of Ge3≡Ge• centers at the (100)Ge/GeO2 interface is possibly at/below the ESR detection limit due to the viscoelastic properties of GeO2, owing to a better stress relaxation at/near the interface, compared to its silicon counterpart.
Oxygen vacancy induced re-entrant spin glass behavior in multiferroic ErMnO3 thin films
Authors: Jang S. Y. , Lee D. , Lee J.-H. , Noh T. W. , Jo Y. , Jung M.-H. , Chung J.-S.
Published: October 2008

Epitaxial thin films of hexagonal ErMnO3 fabricated on Pt(111)/Al2O3(0001) and yttria-stabilized zirconia(111) substrates exhibited both ferroelectric character and magnetic ordering at low temperatures. As the temperature was reduced, the ErMnO3 films first showed antiferromagnetism. At lower temperatures, the films deposited at lower oxygen partial pressures exhibited spin glass behavior. This re-entrant spin glass behavior was attributed to competition between an antiferromagnetic interaction in the hexagonal geometry and a ferromagnetic interaction caused by a change in Mn valence induced by excess electrons from the oxygen vacancies.
Direct hydrogen gas generation by using InGaN epilayers as working electrodes
Authors: Li J. , Lin J. Y. , Jiang H. X.
Published: October 2008

We report on the growth and exploitation of InGaN epilayers as a photoelectrochemical cell (PEC) material for direct generation of hydrogen by splitting water using photoelectrochemical hydrolysis. Under white light illumination, a drastic dependence of the photocurrent density on the In content was observed. Direct hydrogen gas generation by splitting water was accomplished using an n-type InxGa1−xN epilayer with a relatively high In content (x∼0.4) as a working electrode. This demonstration of hydrogen generation by water splitting accomplished using InGaN based PEC is highly encouraging.
Photoinduced magnetic softening of perpendicularly magnetized L1-FePt granular films
Authors: Xu Z. , Liu X. D. , Gao R. X. , Chen Z. F. , Lai T. S. , Hu H. N. , Zhou S. M. , Bai X. J. , Du J.
Published: October 2008

Ultrafast spin dynamics has for the first time been studied in perpendicular magnetized granular films. For FePt continuous films and FePt–MgO and FePt–Ag granular films with femtosecond laser excitations, the coercivity HC and the saturation Kerr rotation θKS are dramatically reduced, accompanied by a sharp increase in the reflectivity R. Afterward, these physical quantities are slowly recovered. The changes in HC, θKS, and R are all different among FePt, FePt–MgO, and FePt–Ag films. The difference is caused by different film thicknesses and in particular by the surface plasmon resonance of metallic nanoparticles.
Highly luminescent surface-passivated ZnS:Mn nanoparticles by a simple one-step synthesis
Authors: Jung Dae-Ryong , Son Dongyeon , Kim Jongmin , Kim Chunjoong , Park Byungwoo
Published: October 2008

Highly luminescent surface-passivated ZnS:Mn nanoparticles were synthesized straightforwardly by a simple liquid-solid-solution method. Compared to the pristine Mn-doped zinc sulfide nanocrystals (quantum efficiency: ∼19%), the Li-added ZnS:Mn exhibited significantly enhanced luminescence properties (quantum efficiency: ∼43%). The surface passivation was investigated by x-ray photoelectron spectroscopy, transmission electron microscopy, and by the change in the radiative/nonradiative recombination rates. The photoluminescence enhancement is due to the formation of an effective passivation layer induced by lithium, and consequent suppression of the nonradiative recombination transitions.
NMR studies of a channel protein without membranes: Structure and dynamics of water-solubilized KcsA
Authors: Ma Dejian , Tillman Tommy S. , Tang Pei , Meirovitch Eva , Eckenhoff Roderic , Carnini Anna , Xu Yan
Published: October 2008

Structural studies of polytopic membrane proteins are often hampered by the vagaries of these proteins in membrane mimetic environments and by the difficulties in handling them with conventional techniques. Designing and creating water-soluble analogues with preserved native structures offer an attractive alternative. We report here solution NMR studies of WSK3, a water-soluble analogue of the potassium channel KcsA. The WSK3 NMR structure (PDB ID code
2K1E
) resembles the KcsA crystal structures, validating the approach. By more stringent comparison criteria, however, the introduction of several charged residues aimed at improving water solubility seems to have led to the possible formations of a few salt bridges and hydrogen bonds not present in the native structure, resulting in slight differences in the structure of WSK3 relative to KcsA. NMR dynamics measurements show that WSK3 is highly flexible in the absence of a lipid environment. Reduced spectral density mapping and model-free analyses reveal dynamic characteristics consistent with an isotropically tumbling tetramer experiencing slow (nanosecond) motions with unusually low local ordering. An altered hydrogen-bond network near the selectivity filter and the pore helix, and the intrinsically dynamic nature of the selectivity filter, support the notion that this region is crucial for slow inactivation. Our results have implications not only for the design of water-soluble analogues of membrane proteins but also for our understanding of the basic determinants of intrinsic protein structure and dynamics.
Kinase requirements in human cells: III. Altered kinase requirements inVHL−/− cancer cells detected in a pilot synthetic lethal screen
Authors: Bommi-Reddy Archana , Almeciga Ingrid , Sawyer Jacqueline , Geisen Christoph , Li Wenliang , Harlow Ed , Kaelin William G. , Grueneberg Dorre A.
Published: October 2008

Clear cell renal carcinomas are the most common form of kidney cancer and frequently are linked to biallelic inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene. TheVHLgene product, pVHL, has multiple functions including directing the polyubiquitylation of the HIF transcription factor. We screened 100 shRNA vectors, directed against 88 kinases, for their ability to inhibit the viability ofVHL−/− renal carcinoma cells preferentially compared with isogenic cells in which pVHL function was restored. shRNAs for “hits” identified in the primary screen were interrogated in secondary screens that included shRNA titration studies. Multiple shRNAs againstCDK6,MET, andMAP2K1(also known asMEK1) preferentially inhibited the viability of 786-O and RCC4VHL−/− cells compared with their wild-type pVHL-reconstituted counterparts. The sensitivity of pVHL-proficient cells to these shRNAs was not restored upon HIF activation, suggesting that loss of an hypoxia-inducible factor (HIF)-independent pVHL function formed the basis for selectivity. A small-molecule Cdk4/6 inhibitor displayed enhanced activity againstVHL−/− renal carcinoma cells, suggesting that in some cases hits from shRNA screens such as described here might translate into therapeutic targets.
Kinase requirements in human cells: IV. Differential kinase requirements in cervical and renal human tumor cell lines
Authors: Grueneberg Dorre A. , Li Wenliang , Davies Joan E. , Sawyer Jacqueline , Pearlberg Joseph , Harlow Ed
Published: October 2008

Functional differences among human cells have been difficult to identify by standard biochemical methods. Loss-of-function shRNA screens provide an unbiased method to compare protein requirements across cell lines. In previous work, we have studied kinase requirements in two settings, either among a panel of cells from numerous tissues or between two cell lines that differ only by the expression of a chosen oncoprotein or tumor suppressor protein. Here we examine the patterns of kinase requirements between two unrelated cells, the cervical carcinoma cell line HeLa and the renal carcinoma cell line 786-O. By using time courses of cell proliferation after shRNA transduction and by introducing different levels of the shRNAs, we were able to carefully compare the kinase requirements. These comparisons identified 10 kinases that were required in HeLa but not 786-O, and 5 kinases that were required in 786-O but not HeLa. The patterns of growth inhibition due to particular sets of shRNAs in a tumor cell line were shown to be similar in some but not all cell lines derived from the same tissue-specific cancer type. Differential kinase requirements promise to be useful in distinguishing important cell-to-cell functional variations and may lead to the identification of fingerprints for different physiological cell states.
Loss of ephrin-A5 function disrupts lens fiber cell packing and leads to cataract
Authors: Cooper Margaret A. , Son Alexander I. , Komlos Daniel , Sun Yuhai , Kleiman Norman J. , Zhou Renping
Published: October 2008

Cell–cell interactions organize lens fiber cells into highly ordered structures to maintain transparency. However, signals regulating such interactions have not been well characterized. We report here that ephrin-A5, a ligand of the Eph receptor tyrosine kinases, plays a key role in lens fiber cell shape and cell–cell interactions. Lens fiber cells in mice lacking ephrin-A5 function appear rounded and irregular in cross-section, in contrast to their normal hexagonal appearance in WT lenses. Cataracts eventually develop in 87% of ephrin-A5 KO mice. We further demonstrate that ephrin-A5 interacts with the EphA2 receptor to regulate the adherens junction complex by enhancing recruitment of β-catenin to N-cadherin. These results indicate that the Eph receptors and their ligands are critical regulators of lens development and maintenance.
Twin births, sex of children and maternal risk of endometrial cancer: A cohort study in Norway
Authors: ALBREKTSEN GRETHE , HEUCH IVAR , THORESEN STEINAR , KVÅLE GUNNAR
Published: October 2008

Objective. To explore whether twin births and sex of children influenced maternal risk of endometrial cancer, possibly with effect modification by age. Design. Population‐based prospective study. Study population. A total of 1,094,017 parous Norwegian women aged 30–74 years, including 3,356 endometrial cancer cases. Among the 27,158 mothers of twins, 101 cases occurred. Methods. Incidence rate ratios (IRR) with 95% confidence intervals (CI) were calculated in Poisson regression analyses of person‐years at risk. Results. Women ever having experienced a twin birth had an overall higher risk of endometrial cancer than women with singleton births only (IRR=1.26, 95% CI=1.03–1.53). Women with twin boys appeared to be the main contributor to the overall elevated risk (IRR=1.57, 95% CI=1.15–2.14). The risk estimates for women with twin girls or sex‐nonconcordant twins were close to unity (IRR of 1.09 and 1.12, respectively). However, age‐specific analyses revealed an elevated risk also in women with twin girls, but only before age 55 years (IRR=1.92, 95% CI=1.27–2.89); a lower risk was seen at older ages (IRR=0.41, 95% CI=0.19–0.92). The risk estimates for twin boys and sex‐nonconcordant twins were consistently observed across age groups. The effect modification by age was statistically significant (p = 0.0024). No association was found with sex of children in singleton mothers. Conclusion. Mothers of twin boys had a significantly higher risk of endometrial cancer than women with singleton births only, whereas women with twin girls had an elevated risk before age 55 years. No significant association was seen with sex‐noncordant twins, neither overall nor within age groups.
Domestic violence prior to and during pregnancy among Pakistani women
Authors: KARMALIANI ROZINA , IRFAN FARHANA , BANN CARLA M. , MCCLURE ELIZABETH M. , MOSS NANCY , PASHA OMRANA , GOLDENBERG ROBERT L.
Published: October 2008

Objective. Abuse of women has been associated with adverse pregnancy outcomes. Data about abuse from developing countries are scarce, especially from Muslim societies. Our objective was to investigate domestic violence before and during pregnancy among women in an urban area of Pakistan. Design. Population‐based cohort study. Setting. An urban community in Hyderabad, Pakistan. Population. Thousand three hundred and twenty‐four pregnant women at 20–26 weeks gestation. Methods. Socio‐demographic and reproductive history data were obtained through structured interviews. We used a modified World Health Organization screening instrument to assess women's experience of domestic violence. Measures. Physical, sexual, and verbal abuse and demographic characteristics. Results. The majority of women had received some schooling and in most households the husbands were employed; by Pakistani standards, they were middle class. Young maternal age, having an unemployed husband and one with other wives/partners, and having had a prior pregnancy were significant predictors of abuse. In the six months prior to and/or during pregnancy, 51% reported experiencing verbal, physical or sexual abuse. Twenty percent reported physical or sexual abuse alone. Sixteen percent of women considered suicide as a response to the abuse. Conclusions. Domestic violence is common among urban Pakistani women of reproductive age, suggesting a need for universal screening during antenatal care, and for support and referral. Further research is needed to determine factors that place women at greatest risk, and to assess the impact of domestic violence on pregnancy outcomes.
The Stockholm classification of stillbirth
Authors: VARLI INGELA HULTHÉN , PETERSSON KARIN , BOTTINGA ROGER , BREMME KATARINA , HOFSJÖ ALEXANDRA , HOLM MARIA , HOLSTE CAROLA , KUBLICKAS MARIUS , NORMAN MARGARETA , PILO CHRISTINA , ROOS NATHALIE , SUNDBERG ANDERS , WOLFF KERSTIN , PAPADOGIANNAKIS NIKOS
Published: October 2008

Objective. To design and validate a classification system for audit groups working with stillbirth. The classification includes well‐defined primary and associated conditions related to fetal death. Design. Descriptive. Setting. All delivery wards in Stockholm. Population. Stillbirths from 22 completed weeks in Stockholm, Sweden. Methods. Parallel to audit work, the Stockholm stillbirth group has developed a classification of conditions related to stillbirth. The classification has been validated. Main outcome measure. The classification and the results of the validation are presented. Result. The classification with 17 groups identifying underlying conditions related to stillbirth (primary diagnoses) and associated factors which may have contributed to the death (associated diagnoses) is described. The conditions are subdivided into definite, probable and possible relation to the death. An evaluation of 382 cases of stillbirth during 2002–2005 resulted in 382 primary diagnoses and 132 associated diagnoses. The most common conditions identified were intrauterine growth restriction/placental insufficiency (23%), infection (19%), malformations/chromosomal abnormalities (12%). The ‘unexplained’ group together with the ‘unknown’ group comprised 18%. Validation was done by reclassification of 95 cases from 2005 by six investigators. The overall agreement regarding primary diagnosis was substantial (kappa=0.70). Conclusions. The Stockholm classification of stillbirth consists of 17 diagnostic groups allowing one primary diagnosis and if needed, associated diagnoses. Diagnoses are subdivided according to definite, probable and possible relation to stillbirth. Validation showed high degree of agreement regarding primary diagnosis. The classification can provide a useful tool for clinicians and audit groups when discussing cause and underlying conditions of fetal death.
Differences in heparan sulfate production in cervical fibroblast cultures from women undergoing term and preterm delivery
Authors: ÅKERUD ANNA , DUBICKE AURELIJA , SENNSTRÖM MARIA , EKMAN‐ORDEBERG GUNVOR , MALMSTRÖM ANDERS
Published: October 2008

Objective. An extensive remodeling of the human cervical connective tissue occurs throughout pregnancy, with a decrease in the total concentration of collagen and proteoglycans. We hypothesized that the profound changes in proteoglycan production in the cervix would be seen in corresponding cervical fibroblasts as well. Methods. Cervical biopsies were obtained from five non‐pregnant women, five women undergoing elective Cesarean section, six women directly after spontaneous term parturition and four directly after spontaneous preterm parturition. By explant technique, fibroblasts were cultured from the biopsies. Subcultures of the primary fibroblasts were treated with antibodies to heparan sulfate proteoglycans and labeled with radioactive sulfate. The labeled proteoglycans were purified by ion‐exchange chromatography and separated by gel electrophoresis. Results. Proteoglycan production was reduced by 50% in fibroblasts obtained from term and preterm women. In comparison to equivalent control cultures from non‐pregnant women, this decline was significant. Production of the proteoglycans biglycan and perlecan was similar in term partal and preterm partal cell cultures. Biglycan production was significantly reduced (by 40%) and perlecan production was significantly induced (by 60%) compared to control cultures. Fibroblast cultures established from women with preterm delivery had significantly higher production of heparan sulfate proteoglycans than those obtained from non‐pregnant donors. Heparan sulfate proteoglycans were localized to cell membranes and intracellular compartments. Conclusions. The changes in proteoglycan production in the human pregnant cervix can also be seen in corresponding cervical fibroblasts. Term partal and preterm partal cells differed from their non‐pregnant counterpart, which suggests a role for proteoglycans in cervical ripening.
Mid‐trimester serum relaxin concentrations and post‐partum pelvic floor dysfunction
Authors: HARVEY MARIE‐ANDRÉE , JOHNSTON SHAWNA L. , DAVIES GREGORY A.L.
Published: October 2008

Objectives. To compare mid‐trimester serum relaxin concentration (SRC) in primiparous women with or without pelvic floor dysfunction (PFD – stress urinary incontinence (SUI), genital prolapse). Design. Nested observational cohort study. Setting. Urogynecology clinic of affiliated University hospital. Population. Primiparous women one to four years post‐partum, who had, at time of index pregnancy, participated in a prospective observational study looking at mid‐trimester serum relaxin and preterm delivery. Methods. Relaxin had been obtained during the index pregnancy at 24 and 28 weeks. Primiparous women who had not given birth to a subsequent child were contacted and asked to return for a single visit assessing pelvic floor function. Main outcome measures. Pelvic Organ Prolapse Quantification system (POPQ) and Urogenital Distress Inventory (UDI‐6). Results. Fifty women participated, of whom 40 delivered vaginally. Seventeen (34%) women had prolapse and 23 (46%) had stress incontinence. Relaxin was slightly higher (not significantly) in women with PFD than in those without. Relaxin concentration declined significantly more rapidly from 24 to 28 weeks in incontinent women, after adjusting for baseline and obstetrical factors. Conclusions. In contrast to previous reports, mid‐gestation relaxin tended to be higher and fall significantly faster in women with PFD. Acknowledging relaxin's effects on collagen turnover, our findings explore the association between childbirth and PFD.
First trimester uterine artery Doppler in women with previous pre‐eclampsia
Authors: PREFUMO FEDERICO , FRATELLI NICOLA , GANAPATHY RAMESH , BHIDE AMAR , FRUSCA TIZIANA , THILAGANATHAN BASKARAN
Published: October 2008

Objective. To assess the role of first trimester uterine artery Doppler in pregnancies previously complicated by pre‐eclampsia. Design and setting. Case‐control study in two tertiary referral hospitals. Sample. A total of 56 singleton pregnancies in women with a previous pregnancy complicated by pre‐eclampsia (Group 1). For each case, two parous controls (Group 2) and two nulliparous controls (Group 3) with normal pregnancy outcome were matched. Methods. Doppler examination of the uterine arteries at 11–14 weeks’ gestation. Main outcome measures. Mean uterine artery resistance index (UtARI) and notching. Pregnancy outcome. Results. UtARI did not vary significantly between the three groups (0.73, 0.70 and 0.71, respectively). Women in Group 1 had a significantly higher prevalence of uterine artery notching than those in Group 2 (73 vs 57%, p = 0.04). In Group 1, the UtARI and prevalence of notching was not significantly increased when pregnancies were subsequently complicated by pre‐eclampsia (p = 0.60 and 0.61, respectively). However, in 12 pregnancies requiring delivery before 37 weeks due to pre‐eclampsia, fetal growth restriction, abruption or intrauterine fetal death, the UtARI was significantly higher than in the 44 pregnancies with normal outcome (p = 0.04). A combination of UtARI and notching showed sensitivities up to 75% and negative predictive values up to 88% for adverse outcome before 37 weeks. Conclusions. In pregnancies following a previous gestation complicated by pre‐eclampsia, first trimester uterine artery Doppler findings are similar to those observed in nulliparous women. In these high‐risk women, a combination of UtARI and notching can predict the risk of adverse outcome before 37 weeks.
Second trimester neutrophil gelatinase‐associated lipocalin as a potential prediagnostic marker of preeclampsia
Authors: D'ANNA ROSARIO , BAVIERA GIOVANNI , GIORDANO DOMENICO , TODARELLO GIOVANNA , CORRADO FRANCESCO , BUEMI MICHELE
Published: October 2008

Neutrophil gelatinase‐associated lipocalin (NGAL) concentrations, a product of neutrophils, were investigated in normal and preeclamptic pregnancies. Prospectively collected data and late second trimester (24–26 weeks) serum samples from 48 women who subsequently developed preeclampsia (PE) and 96 control women with uncomplicated pregnancies were compared. Serum NGAL values, as determined by quantitative sandwich enzyme immunoassay, were significantly increased in the preeclamptic compared to the control women: 76.9 ng/ml (interquartile range 39.7–96.5) versus 16.0 ng/ml (interquartile range 11.2–24.4) (p<0.001), and were positively correlated to blood pressure and proteinuria, showing a high sensitivity (75%) and specificity (94.5%). The results suggest that serum NGAL might be involved in the pathophysiology of PE and could be a marker for this syndrome.