bluuebunny/crossref_metadata_2025 huggingface dataset:
Streak interactions and breakdown in boundary layer flows
Authors: Brandt Luca , de Lange H. C.
Published: February 2008

The objective of this paper is to show that the interaction of streamwise velocity streaks of finite length can lead to turbulent breakdown in the flat-plate boundary layer flow. The work is motivated by previous numerical and experimental studies of transitional flows where the high-frequency oscillations leading to turbulence are seen to form in the region of strongest shear induced by streaks in relative motion. Therefore, a model for the interaction of steady and unsteady (i.e., slowly moving in the spanwise direction) spanwise periodic streaks is proposed. The interaction of two subsequent streaks is investigated for varying collision parameters. In particular, the relative spanwise position and angle are considered. The results show that the interaction is able to produce both a symmetric and asymmetric breakdown without the need for additional random noise from the main stream. Velocity structures characteristic of both scenarios are analyzed. Hairpin and Λ vortices are found in the case of symmetric collision between a low-speed region and an incoming high-speed streak, when a region of strong wall-normal shear is induced. Alternatively, when the incoming high-momentum fluid is misaligned with the low-speed streak in front, single quasi-streamwise vortices are identified. Despite the different symmetry at the breakdown, the detrimental interaction involves for both cases the tail of a low-speed region and the head of a high-speed streak. Further, the breakdown appears in both scenarios as an instability of three-dimensional shear layers formed between the two streaks. The streak interaction scenario is suggested to be of relevance for turbulence production in wall-bounded flows.
Magnetic properties of Fe on vicinal Pt(111)
Authors: Cheng Ruihua , Bader S. D. , Fradin F. Y.
Published: February 2008

A magnetic system such as Fe∕Pt shows strong magnetic anisotropy due to the contribution of the interface. Pt is known to be nearly ferromagnetic and can have an induced magnetic moment when it is in proximity to 3d ferromagnetic atoms. Both the magnetic moment and the magnetic anisotropy of the materials are enhanced on the step surface due to the symmetry breaking by the introduction of atomic steps on vicinal substrate. In order to study the effect of step-induced anisotropy, we investigate the magnetic properties of Fe grown on a curved Pt(111) single crystal that provides a continuous gradient in step density. Fe grown on high vicinal angle surfaces has larger values of both the saturation magnetization Ms and coercivity HC compared with the flat surface. The atomic steps of the vicinal surface greatly affect the magnetic properties of ultrathin Fe films. The anisotropy of Fe on the curved Pt(111) surface is related to the step density of the substrate.
Divalent manganese in A-position of perovskite cell: X-ray absorption finite structure study of La0.6Sr0.4−xMnTixO3 manganites
Authors: Ulyanov A. N. , Yang D. S. , Chau N. , Yu S. C. , Yoo S. I.
Published: February 2008

Local structure and magnetic properties of Ti doped A-site deficient La0.6Sr0.4−xMnTixO3+δ manganites (0.15⩾x⩾0) have been studied. The compositions belong to rhombohedral R3¯c phase. Segregation of (La0.6Sr0.4−xMny)(Mn1−y−zTix)O3+δ phase and fallout of (z∕3)Mn3O4 oxide was observed with x increase. Some amount (y) of Mn, being in divalent valence state, occupies the A(=La,Sr)-position of perovskite cell. Samples with x=0 and 0.05 are ferromagnetic with Curie temperature TC=350 and 172K, respectively. Samples with x=0.1 and 0.15 are in spin(cluster)-glass states at low temperatures.
Structure, ferroelectric properties, and magnetic properties of the La-doped bismuth ferrite
Authors: Cheng Z. X. , Li A. H. , Wang X. L. , Dou S. X. , Ozawa K. , Kimura H. , Zhang S. J. , Shrout T. R.
Published: February 2008

Bi 1 − x La x Fe O 3 ceramics with x=0, 0.1, 0.2, and 0.3 have been synthesized by solid state reaction, starting from metal oxides. A series of structure transformations is found to depend upon the doping level. Below 10% La doping, Bi1−xLaxFeO3 maintains the rhombohedral structure of BiFeO3. However, for Bi0.8La0.2FeO3 and Bi0.7La0.3FeO3, the structures change to the orthorhombic and tetragonal, respectively. La doping significantly reduces electric leakage and leads to successful observation of electrical polarization hysteresis loops. Doping with La also enhances the ferromagnetic moment, due to the broken cycloid spin structure caused by the changes in the crystalline structure.
A generic approach to nanocables via nanochannel-confined sequential electrodeposition
Authors: Yang Dachi , Meng Guowen , Xu Qiaoling , Zhao Xianglong , Liu Jianxiong , Kong Mingguang , Chu Zhaoqin , Zhu Xiaoguang , Zhang Lide
Published: February 2008

We have exploited a generic method for nanocables, consisting of two materials that can be obtained via electrodeposition, by first electrodepositing the cable “shells” on the interior walls of nanochannels inside anodic aluminum oxide template with one planar surface side coated with a thin meshlike Au layer and then filling the cavities inside the shells by electrodeposition again to achieve the cable “cores.” The method has been demonstrated for the nanocables of Cu-Bi (Cu shell and Bi core) and Bi-Cu (Bi shell and Cu core). Nanocables of other two materials with tunable shell thickness and inner core diameter can be achieved by modulating the Au-layer thickness, and might have potential in the future nanotechnology.
Thin Newtonian film flow down a porous inclined plane: Stability analysis
Authors: Sadiq I. Mohammed Rizwan , Usha R.
Published: February 2008

The flow of a thin Newtonian fluid layer on a porous inclined plane is considered. Applying the long-wave theory, a nonlinear evolution equation for the thickness of the film is obtained. It is assumed that the flow through the porous medium is governed by Darcy’s law. The critical conditions for the onset of instability of a fluid layer flowing down an inclined porous wall, when the characteristic length scale of the pore space is much smaller than the depth of the fluid layer above, are obtained. The results of the linear stability analysis reveal that the film flow system on a porous inclined plane is more unstable than that on a rigid inclined plane and that increasing the permeability of the porous medium enhances the destabilizing effect. A weakly nonlinear stability analysis by the method of multiple scales shows that there is a range of wave numbers with a supercritical bifurcation, and a range of larger wave numbers with a subcritical bifurcation. Numerical solution of the evolution equation in a periodic domain indicates the existence of permanent finite-amplitude waves of different kinds in the supercritical stable region. The long-time waveforms are either time-independent waves of permanent form that propagate or time-dependent modes that oscillate slightly in the amplitude. The presence of the porous substrate promotes this oscillatory behavior. The results show that the shape and amplitude of the waves are influenced by the permeability of the porous medium.
Resonant pumping in a multilayer impedance pump
Authors: Loumes L. , Avrahami I. , Gharib M.
Published: February 2008

This paper introduces the concept of multilayer impedance pump, a novel pumping mechanism inspired by the embryonic heart structure. The pump is a composite two-layer fluid-filled elastic tube featuring a thick gelatinous internal. Pumping is based on the impedance pumping mechanism. In an impedance pump, elastic waves are generated upon external periodic compressions of the elastic tube. These waves propagate along the tube’s walls, reflect at the tube’s extremities, and drive the flow in a preferential direction. The originality in the multilayer impedance pump design relies on the use of the thick internal gelatinous layer to amplify the elastic waves responsible for the pumping. As a consequence, only small excitations are needed to produce significant flow. This fully coupled fluid-structure interaction problem is solved for the flow and the structure using the finite element method over a relevant range of frequencies of excitation. Results show that the multilayer impedance pump is a complex system that exhibits a resonant response. Flow output and inner wall motion are maximal when the pump is actuated at the resonant frequency. The wave interaction mechanism present in an impedance pump is described here in details for the case of a multilayer impedance pump. Using energy balance for the passive portion of the elastic tube, we show that the elastic tube itself works as a pump and that at resonance maximum energy transmission between the elastic tube and the fluid occurs. Finally, the pump is especially suitable for many biomedical applications.
Theoretical radiative properties between states of the triplet manifold of NH radical
Authors: Owono Owono L. C. , Ben Abdallah D. , Jaidane N. , Ben Lakhdar Z.
Published: February 2008

Ab initio transition dipole moments between states of the triplet manifold of NH radical are determined at the complete active space self-consistent field, followed by the internally contracted multireference singles plus doubles configuration interaction level of theory with a modified aug-cc-pVTZ basis set that accounts for valence-Rydberg interactions. This enables the computation of various radiative characteristics such as Einstein coefficients, radiative lifetimes, and oscillator strengths. These properties concern as well valence and Rydberg states. For the valence states, only the (0, 0) band of the AΠ3-XΣ−3 transition has received some important amount of attention. Data for the other transitions are rather scarce and sometimes inexistent. The results obtained in this work show good agreement with the available experimental data in comparison to other theoretical numbers reported in the literature.
Characterization of electrical and structural properties of strained-Si-on-insulator layers
Authors: Choi Chel-Jong , Jung Won-Jin , Jun Myung-Sim , Jang Moon-Gyu , Lee Seong-Jae , Park June , Seong Maeng-Je , Jung Myung-Ho , Cho Won-Ju
Published: February 2008

The electrical and structural properties of strained-Si-on-insulator (sSOI) wafers were investigated. The strain, calculated from two-dimensional reciprocal space mapping, was found to be 0.78%, which is comparable to that of fully relaxed Si1−xGex film with Ge concentration of 20.6at.%. Based on the Raman peak shift combined with measured value of strain, the strain shift coefficient is extracted to be −736cm−1. The pseudo-metal-oxide-semiconductor field-effect transistor measurements, employed to characterize the electrical properties of sSOI wafers, showed that both electron and hole mobilities are enhanced by strain. The enhancement factor of electron mobility is larger than that of hole mobility.
Mobility of thin AlAs quantum wells: Theory compared to experiment
Authors: Gold A.
Published: February 2008

For interface-roughness scattering and for zero temperatures, we compare theoretical results for the transport properties of the electron gas present in thin AlAs quantum wells with experimental results for a well of width L=45Å. The importance of a density dependent effective mass is discussed. For the mobility, reasonable agreement between theory and experiment is obtained by taking into account multiple scattering effects, which lead to a metal-insulator transition. We predict the single-particle relaxation time. With a density dependent effective mass, the calculated critical electron density of the metal-insulator transition is found to be in good agreement with the experimental value.
Effects of interface states on the transport properties of all-oxide La0.8Sr0.2CoO3∕SrTi0.99Nb0.01O3 p-n heterojunctions
Authors: Bruno F. Y. , Garcia-Barriocanal J. , Torija M. , Rivera A. , Sefrioui Z. , Leighton C. , Leon C. , Santamaria J.
Published: February 2008

Electrical transport properties of heteroepitaxial p-n junctions made of La0.8Sr0.2CoO3 and SrTi0.99Nb0.01O3 were studied. Junctions display highly rectifying current-voltage characteristics over a wide temperature range (20–300K). Two distinct transport mechanisms are identified: tunneling assisted by interface states at T<130K and diffusion/recombination at higher temperatures. Capacitance-voltage characteristics are used to determine the junction built-in potential at different frequencies. A capacitance relaxation is found due to charge trapping at interface states. Interface states, which deeply affect transport, are discussed in connection to charge-transfer processes related to the polarity mismatch at the interface.
Flux pinning in YBa2Cu3O7−δ thin film samples linked to stacking fault density
Authors: Wang J. , Kwon J. H. , Yoon J. , Wang H. , Haugan T. J. , Baca F. J. , Pierce N. A. , Barnes P. N.
Published: February 2008

In this paper, we report a strong correlation between the stacking fault (SF) density and the critical current density of YBa2Cu3O7−δ (YBCO) thin films in applied field (Jcin-field). We found that the Jcin-field (H∥c) increases as a clear linear dependence of the density of SF identified in the as-grown samples deposited on both SrTiO3 (STO) and LaAlO3 substrates. Detailed microstructural studies including cross-section transmission electron microscopy (TEM) and high resolution TEM were conducted for all the films deposited on STO substrates. This work suggests that the YBCO SF density plays an important role in the YBCO in-field transport performance.
Defect band structure investigation of postbreakdown SiO2
Authors: Xu Mingzhen , Tan Changhua
Published: February 2008

The defect band structure and properties of postbreakdown SiO2 have been investigated by the variation method of Harrison. The breakdown path of SiO2 can be considered as a one-dimensional linear chain of defects between electrodes. The first soft breakdown occurs when the ratio of the distance between defects to the defect radius locally reaches a critical value of about 8, and hard breakdown occurs when the ratio is about 3.4. The ratio and the Weibull slope are recisymmetrical. Thus, the type and properties of oxide breakdown paths can be determined and analyzed when the Weibull slope is known.
Near-field optical trapping with an ultrashort pulsed laser beam
Authors: Kuriakose Smitha , Morrish Dru , Gan Xiaosong , Chon James W. M. , Dholakia Kishan , Gu Min
Published: February 2008

We report the focused evanescent optical trapping of nonfluorescent and fluorescent dielectric microspheres using a femtosecond laser. The experiment confirms that the trapping efficiency increases with the size of the particles. As a result, a pulsed laser has been used to trap particles in the Mie regime and to excite whispering gallery modes in them. The excitation of whispering gallery modes in a near-field femtosecond trap shows a significant suppression of the two-photon fluorescence background with an improvement of the photon storage factor by 46%, as compared to far-field two-photon excitation.
Water relations and mineral nutrition of closely related woody plant species on desert dunes and interdunes
Authors: Grigg Alasdair M. , Veneklaas Erik J. , Lambers Hans
Published: February 2008

Vegetation on dunes and interdunes in hot, subtropical deserts is profoundly influenced by the temporal and spatial variation in availability of water and nutrients in the landscape. We hypothesised that water is more available to plants on the dunes but that nutrients are in greater concentrations on the interdunes in the Great Sandy Desert, Western Australia. During the course of 2 years, we examined water relations and photosynthesis of six dominant woody species throughout each season, in addition to foliar δ13C, δ15N and nutrient composition. In general, stomatal conductance (gs) was greater and leaf water potential (ΨL) less negative for dune species than for closely related species on the interdunes. The largest tree species in the landscape, Corymbia chippendalei ((D.J.Carr & S.G.M.Carr) K.D.Hill & L.A.S.Johnson), occurred only on the dunes, and maintained moderate gs values year round, ranging between 240 mmol H2O m–2 s–1 in the wet season and 160 mmol H2O m–2 s–1 in the middle of the dry season. It also displayed a relatively stable ΨL, between –0.3 and –0.5 MPa at predawn, and between –1.3 and –1.6 MPa at midday throughout the year, unlike the closely related species on the interdunes, Eucalyptus victrix (L.A.S.Johnson & K.D.Hill), which always displayed significantly lower ΨL values (0.2–1.1 MPa more negative). The two Grevillea species displayed ΨL values within a similar range as for C. chippendalei, while the Acacia species exhibited consistently more negative values, especially late in the dry season. Considerable reductions in gs occurred at this time for all species, except C. chippendalei. Rates of photosynthesis (A) followed the trends in gs, yet δ13C values varied little between related species in the dune and interdune habitats. Mineral nutrient concentrations in soil and foliage tended to be greater in the interdunes. Average N : P ratio in foliage was 28 : 1, indicating P was more limiting than N. Soil depth and texture, in conjunction with their effects on water availability and root growth, were considered to be the most influential factors affecting plant distribution in the Great Sandy Desert. It is concluded that dunes hold relatively more water than adjacent interdunes, sustaining more favourable water status in deep-rooted species from this habitat, further into the dry season. Conversely, species on the interdunes must be more desiccation tolerant and develop root systems with greater ability to penetrate conglomerated lateritic gravel layers in order to access water where and when it is available.
Cytogenetical and cytotaxonomical analysis of some Brazilian species of Eleocharis (Cyperaceae)
Authors: Maximiano da Silva Carlos Roberto , González-Elizondo Maria Socorro , Rego Letícia do Nascimento Andrade de Almeida , Torezan José Marcelo Domingues , Vanzela André Luís Laforga
Published: February 2008

Karyotype analysis of 21 samples of 11 species of Eleocharis (Cyperaceae) from 10 localities in Brazil, showed the presence of chromosomes without primary constrictions and parallel movement of chromatids at metaphase–anaphase transition. Only the terminal nucleolar constrictions (satellites) were visualised. The chromosome numbers varied from 2n = 6 in E. subarticulata to 2n = 54 in E. acutangula, but the chromosome basic number x = 5 was confirmed. Generally, C-CMA3+ bands appear mostly in the extremities of the chromosomes, associated to NOR, and interstitial C-CMA3 bands were found only in E. geniculata and E. acutangula. C-DAPI+ bands were not found. Fluorescence in situ hybridisation (FISH) with the 45S rDNA probe was performed in five species. The results showed from four to eight hybridisation signals, always terminal. The analysed species include representatives of the following three subgenera of Eleocharis that occur in Brazil: Limnochloa, Scirpidium and Eleocharis. Species from the subgenus Limnochloa have small and numerous chromosomes. The remaining species, belonging to subgenera Eleocharis and Scirpidium, possess fewer and larger chromosomes. In subgenus Eleocharis, karyotypes of the section Eleocharis were differentiated by symploidy, agmatoploidy and polyploidy, whereas species of the section Eleogenus were all polyploids. Polyploidy seems to be the most frequent event in the karyotype differentiation in Eleocharis, but changes in the chromosome size and repetitive DNA sites were also observed.
RETRACTED: Solvent molecules bridge the mechanical unfolding transition state of a protein
Authors: Dougan Lorna , Feng Gang , Lu Hui , Fernandez Julio M.
Published: February 2008

We demonstrate a combination of single molecule force spectroscopy and solvent substitution that captures the presence of solvent molecules in the transition state structure. We measure the effect of solvent substitution on the rate of unfolding of the I27 titin module, placed under a constant stretching force. From the force dependency of the unfolding rate, we determine Δ
x
u
, the distance to the transition state. Unfolding the I27 protein in water gives a Δ
x
u
= 2.5 Å, a distance that compares well to the size of a water molecule. Although the height of the activation energy barrier to unfolding is greatly increased in both glycerol and deuterium oxide solutions, Δ
x
u
depends on the size of the solvent molecules. Upon replacement of water by increasing amounts of the larger glycerol molecules, Δ
x
u
increases rapidly and plateaus at its maximum value of 4.4 Å. In contrast, replacement of water by the similarly sized deuterium oxide does not change the value of Δ
x
u
. From these results we estimate that six to eight water molecules form part of the unfolding transition state structure of the I27 protein, and that the presence of just one glycerol molecule in the transition state is enough to lengthen Δ
x
u
. Our results show that solvent composition is important for the mechanical function of proteins. Furthermore, given that solvent composition is actively regulated
in vivo
, it may represent an important modulatory pathway for the regulation of tissue elasticity and other important functions in cellular mechanics.
Structural insights into an equilibrium folding intermediate of an archaeal ankyrin repeat protein
Authors: Löw Christian , Weininger Ulrich , Neumann Piotr , Klepsch Mirjam , Lilie Hauke , Stubbs Milton T. , Balbach Jochen
Published: February 2008

Repeat proteins are widespread in nature, with many of them functioning as binding molecules in protein–protein recognition. Their simple structural architecture is used in biotechnology for generating proteins with high affinities to target proteins. Recent folding studies of ankyrin repeat (AR) proteins revealed a new mechanism of protein folding. The formation of an intermediate state is rate limiting in the folding reaction, suggesting a scaffold function of this transient state for intrinsically less stable ARs. To investigate a possible common mechanism of AR folding, we studied the structure and folding of a new thermophilic AR protein (tANK) identified in the archaeonThermoplasma volcanium. The x-ray structure of the evolutionary much older tANK revealed high homology to the human CDK inhibitor p19INK4d, whose sequence was used for homology search. As for p19INK4d, equilibrium and kinetic folding analyses classify tANK to the family of sequential three-state folding proteins, with an unusual fast equilibrium between native and intermediate state. Under equilibrium conditions, the intermediate can be populated to >90%, allowing characterization on a residue-by-residue level using NMR spectroscopy. These data clearly show that the three C-terminal ARs are natively folded in the intermediate state, whereas native cross-peaks for the rest of the molecule are missing. Therefore, the formation of a stable folding unit consisting of three ARs is the necessary rate-limiting step before AR 1 and 2 can assemble to form the native state.
Assessing the solvent-dependent surface area of unfolded proteins using an ensemble model
Authors: Gong Haipeng , Rose George D.
Published: February 2008

We present a physically rigorous method to calculate solvent-dependent accessible surface areas (ASAs) of amino acid residues in unfolded proteins. ASA values will be larger in a good solvent, where solute–solvent interactions dominate and promote chain extension. Conversely, they will be smaller in a poor solvent, where solute–solute interactions dominate and promote chain collapse. In the method described here, these solvent-dependent effects are modeled by Boltzmann-weighting a simulated ensemble for solvent quality—good or poor. Solvent quality is parameterized as intramolecular hydrogen bond strength, using a “hydrogen bond dial” that can be varied from “off” to “high” (i.e., from 0 to −6 kcal/mol per hydrogen bond). When plotted as a function of hydrogen bond strength, the Boltzmann-weighted distribution of conformers describes a sigmoidal curve, with a transition midpoint near 1.5 kcal/mol per hydrogen bond. ASA tables for the 20 residues are provided under good solvent conditions and at this transition midpoint. For the backbone, these midpoint ASA values are found to be in good agreement with the earlier estimate of unfolded state ASA given by the mean of Creamer's upper and lower bounds [Creamer TP,
et al.
(1997)
Biochemistry
36:2832–2835], a gratifying result in that cosolvents of experimental interest, such as urea (good solvent) and trimethylamine
N
-oxide (poor solvent), are known to affect the backbone predominantly. Unanticipated results from our simulations predict that a significant population of three-residue, hydrogen-bonded turns (inverse γ-turns) will be detectable in blocked polyalanyl heptamers in poor solvent—an experimentally verifiable conjecture.
Shear stress regulates aquaporin-5 and airway epithelial barrier function
Authors: Sidhaye Venkataramana K. , Schweitzer Kelly S. , Caterina Michael J. , Shimoda Larissa , King Landon S.
Published: February 2008

As the interface with the outside world, the airway epithelial barrier is critical to lung defense. Because of respiratory efforts, the airways are exposed to shear stress; however, little is known regarding the effects of shear on epithelial function. We report that low-level shear stress enhances epithelial barrier function, an effect that requires serial activation of the transient receptor potential vanilloid (TRPV) 4 and L-type voltage-gated calcium channel (VGCC) and an increase in intracellular calcium. These changes lead to a selective decrease in aquaporin-5 (AQP5) abundance because of protein internalization and degradation. To determine whether AQP5 plays a role in mediating the shear effects on paracellular permeability, we overexpressed hAQP5 in 16HBE cells, an airway epithelial cell line without endogenous AQP5. We found that AQP5 expression was needed for shear-induced barrier enhancement. These findings have direct relevance to the regulation of epithelial barrier function, membrane permeability, and water homeostasis in the respiratory epithelia.
Whole-genome comparison of disease and carriage strains provides insights into virulence evolution in
Neisseria meningitidis
Authors: Schoen Christoph , Blom Jochen , Claus Heike , Schramm-Glück Anja , Brandt Petra , Müller Tobias , Goesmann Alexander , Joseph Biju , Konietzny Sebastian , Kurzai Oliver , Schmitt Corinna , Friedrich Torben , Linke Burkhard , Vogel Ulrich , Frosch Matthias
Published: February 2008

Neisseria meningitidis
is a leading cause of infectious childhood mortality worldwide. Most research efforts have hitherto focused on disease isolates belonging to only a few hypervirulent clonal lineages. However, up to 10% of the healthy human population is temporarily colonized by genetically diverse strains mostly with little or no pathogenic potential. Currently, little is known about the biology of carriage strains and their evolutionary relationship with disease isolates. The expression of a polysaccharide capsule is the only trait that has been convincingly linked to the pathogenic potential of
N. meningitidis
. To gain insight into the evolution of virulence traits in this species, whole-genome sequences of three meningococcal carriage isolates were obtained. Gene content comparisons with the available genome sequences from three disease isolates indicate that there is no core pathogenome in
N. meningitidis
. A comparison of the chromosome structure suggests that a filamentous prophage has mediated large chromosomal rearrangements and the translocation of some candidate virulence genes. Interspecific comparison of the available
Neisseria
genome sequences and dot blot hybridizations further indicate that the insertion sequence IS
1655
is restricted only to
N. meningitidis
; its low sequence diversity is an indicator of an evolutionarily recent population bottleneck. A genome-based phylogenetic reconstruction provides evidence that
N. meningitidis
has emerged as an unencapsulated human commensal from a common ancestor with
Neisseria gonorrhoeae
and
Neisseria lactamica
and consecutively acquired the genes responsible for capsule synthesis via horizontal gene transfer.
Serum levels of immunoglobulin E and the subsequent risk of pre‐eclampsia: a population‐based study
Authors: ESKILD ANNE , IL NILSEN TOM , JEANSSON STIG , JENUM PÅL A. , VATTEN LARS J.
Published: February 2008

Objective. Women with allergy may be at increased risk of developing preeclampsia. We assessed serum levels of immunoglobulin E (IgE) in the first and second trimester, and changes in concentration between trimesters, in relation to risk of preeclampsia. Materials and Methods. Population based case‐control study within a cohort of 29,948 pregnant women. We included 154 preeclampsia cases with preterm delivery (before week 37) and 190 cases with delivery at term. As controls, 392 women without preeclampsia were randomly selected. Levels of IgE were in sera from the first and second trimester were measured and women who later developed preeclampsia were compared to controls with respect to IgE levels. Results. Comparing the highest to the lowest quartile of IgE in the first trimester, the odds ratio for preterm preeclampsia was 1.7 (95% CI, 0.9–3.1), and in the second trimester, the odds ratio was 1.5 (95% CI, 0.8–2.9) for the highest compared to the lowest quartile of IgE. Change in IgE between trimesters was not associated with preeclampsia risk. Conclusion. There was a weak, however, not significant association between high levels of IgE in the first and second trimester and subsequent risk of preterm preeclampsia.
Spectral analysis of fetal heart rate variability for fetal surveillance: review of the literature
Authors: VAN LAAR J.O.E.H. , PORATH M.M. , PETERS C.H.L. , OEI S.G.
Published: February 2008

Background. Cardiotocography has a poor diagnostic value in detecting fetal acidosis. Spectral analysis of fetal heart rate variability can be used to monitor the fetal autonomic nervous system. Objective. To determine the value of spectral analysis for fetal surveillance. Methods. A systematic search was performed in the electronic databases CENTRAL (the Cochrane Library; 2007, Issue 3), PUBMED and EMBASE up to May 2007. Articles that described spectral analysis of human fetal heart rate variability and compared the energy in spectral bands with blood‐gas values obtained by funipuncture or from the umbilical cord immediately postpartum were included. Results. Six studies met the inclusion criteria. The included studies were heterogeneous, various methods of spectral analysis and different frequency bands were used and the outcome measures varied. Five out of six studies showed a decrease in spectral energy in the low frequency (LF) band in case of fetal distress. An extremely low LF power had a sensitivity of 97.5% and a specificity of 86.1% to detect fetal distress. Conclusions. Spectral analysis could be a promising method for fetal surveillance. Larger prospective studies are needed to determine the exact diagnostic value of spectral analysis. For further research, standardisation of spectral analysis is recommended. Studies should focus on real time monitoring.
Midwives’ and obstetricians’ knowledge and management of women presenting with decreased fetal movements
Authors: HEAZELL ALEXANDER E.P. , GREEN MATTHEW , WRIGHT CAROLINE , FLENADY VICKI , FREDERIK FRØEN J.
Published: February 2008

Background. Maternal perception of decreased fetal movements (DFM) affects 5–15% of pregnancies. DFM is associated with intra‐uterine fetal death (IUFD) and intra‐uterine growth restriction (IUGR). It has been proposed that maternal perception of DFM may be used as a screening tool for IUFD or IUGR. However, this proposal is complicated by variations in definitions and management of DFM. Hypothesis. We hypothesised that uncertainties in the definition and management of women presenting with DFM leads to variation in clinical practice. Methods. A postal questionnaire was sent to midwives and consultant obstetricians in the UK. Results. The majority of respondents enquired about the presence of fetal movements after 28 weeks gestation. There was little agreement on a definition of DFM, with a maternal perception of decreased movements for 24 h gaining the greatest acceptance. Few practitioners used formal fetal movement counting, with the majority of respondents stating they were ineffective in the prevention of IUGR or IUFD and led to increased intervention. There was large variation in the knowledge of associations with DFM and management of women presenting with DFM. Conclusions. There were wide variations in the practice of obstetricians and midwives with regard to women presenting with DFM; many aspects of practice were not based on the available evidence. The variation in practice may result from a lack of robust evidence on which to base the provision of care. Further research is needed to provide and disseminate evidence to direct the management of women presenting with DFM.
Advance provision of emergency contraceptive pills reduces treatment delay: a randomised controlled trial among Swedish teenage girls
Authors: EKSTRAND MARIA , LARSSON MARGARETA , DARJ ELISABETH , TYDÉN TANJA
Published: February 2008

Objective. To evaluate an intervention involving advance provision of emergency contraceptive pills (ECP) to Swedish teenage girls. Material and methods. Some 420 girls aged 15–19, requesting ECP at a local youth clinic were randomly assigned to intervention group (IG) (n = 214) or control group (CG) (n = 206). Both groups received ECP on request. The IG received one extra dose of ECP, condoms and an information leaflet regarding ECP and condom use. Main outcome measures were differences between IG and CG regarding ECP use, time span between unprotected intercourse and ECP intake, contraceptive use, and sexual risk taking. Questionnaires were completed at the initial visit, and the girls were followed up by structured telephone interviews 3 and 6 months later. Results. At the 3‐month follow‐up, girls in the IG were almost twice as likely to have used ECP compared to girls in the CG (IG: 24.0%, CG: 13%, p = 0.02), and they used it sooner after unprotected intercourse (mean time IG: 13.61 h, CG: 25.47 h, p = 0.007). Significant differences persisted 6 months after the intervention (ECP use IG: 31%, CG: 19%, p = 0.01; and mean time IG: 15.59 h, CG: 26.38 h, p = 0.006). No significant differences were found in the use of regular hormonal contraceptives or condoms at either follow‐up. About 40% of the girls in both groups had risked pregnancy during the follow‐up period, but only half of these had used ECP. Conclusions. This intervention shortened the time interval from unprotected intercourse to pill intake without jeopardising contraceptive use and without increasing sexual risk taking.
A Multicenter Qualitative Study on Preventing Hospital-Acquired Urinary Tract Infection in US Hospitals
Authors: Saint Sanjay , Kowalski Christine P. , Forman Jane , Damschroder Laura , Hofer Timothy P. , Kaufman Samuel R. , Creswell John W. , Krein Sarah L.
Published: February 2008

Objective.

Although urinary tract infection (UTI) is the most common hospital-acquired infection, there is little information about why hospitals use or do not use a range of available preventive practices. We thus conducted a multicenter study to understand better how US hospitals approach the prevention of hospital-acquired UTI.

Methods.

This research is part of a larger study employing both quantitative and qualitative methods. The qualitative phase consisted of 38 semistructured phone interviews with key personnel at 14 purposefully sampled US hospitals and 39 in-person interviews at 5 of those 14 hospitals, to identify recurrent and unifying themes that characterize how hospitals have addressed hospital-acquired UTI.

Results.

Four recurrent themes emerged from our study data. First, although preventing hospital-acquired UTI was a low priority for most hospitals, there was substantial recognition of the value of early removal of a urinary catheter for patients. Second, those hospitals that made UTI prevention a high priority also focused on noninfectious complications and had committed advocates, or “champions,” who facilitated prevention activities. Third, hospital-specific pilot studies were important in deciding whether or not to use devices such as antimicrobial-impregnated catheters. Finally, external forces, such as public reporting, influenced UTI surveillance and infection prevention activities.

Conclusions.

Clinicians and policy makers can use our findings to develop initiatives that, for example, use a champion to promote the removal of unnecessary urinary catheters or exploit external forces, such public reporting, to enhance patient safety.
Regulation and Targeting of the Fission Yeast Formin cdc12p in Cytokinesis
Authors: Yonetani Ann , Lustig Raymond J. , Moseley James B. , Takeda Tetsuya , Goode Bruce L. , Chang Fred
Published: February 2008

Formins are conserved actin nucleators which promote the assembly of actin filaments for the formation of diverse actin structures. In fission yeast Schizosaccharomyces pombe, the formin cdc12p is required specifically in assembly of the actin-based contractile ring during cytokinesis. Here, using a mutational analysis of cdc12p, we identify regions of cdc12p responsible for ring assembly and localization. Profilin-binding residues of the FH1 domain regulate actin assembly and processive barbed-end capping by the FH2 domain. Studies using photobleaching (FRAP) and sensitivity to latrunculin A treatment show that profilin binding modulates the rapid dynamics of actin and cdc12p within the ring in vivo. Visualized by functional GFP-fusion constructs expressed from the endogenous promoter, cdc12p appears in a small number of cytoplasmic motile spot structures that deliver the formin to the ring assembly site, without detectable formation of an intermediate band of “nodes.” The FH3/DID region directs interphase spot localization, while an N-terminal region and the FH1-FH2 domains of cdc12p can target its localization to the ring. Mutations in putative DID and DAD regions do not alter regulation, suggesting that cdc12p is not regulated by a canonical autoinhibition mechanism. Our findings provide insights into the regulation of formin activity and the mechanisms of contractile ring dynamics and assembly.
The Gene for the P-Subunit of Glycine Decarboxylase from the C4 SpeciesFlaveria trinervia: Analysis of Transcriptional Control in TransgenicFlaveria bidentis(C4) and Arabidopsis (C3)
Authors: Engelmann Sascha , Wiludda Christian , Burscheidt Janet , Gowik Udo , Schlue Ute , Koczor Maria , Streubel Monika , Cossu Roberto , Bauwe Hermann , Westhoff Peter
Published: February 2008

Glycine decarboxylase (GDC) plays an important role in the photorespiratory metabolism of plants. GDC is composed of four subunits (P, H, L, and T) with the P-subunit (GLDP) serving as the actual decarboxylating unit. In C3 plants, GDC can be found in all photosynthetic cells, whereas in leaves of C3-C4 intermediate and C4 species its occurrence is restricted to bundle-sheath cells. The specific expression of GLDP in bundle-sheath cells might have constituted a biochemical starting point for the evolution of C4 photosynthesis. To understand the molecular mechanisms responsible for restricting GLDP expression to bundle-sheath cells, we performed a functional analysis of the GLDPA promoter from the C4 species Flaveria trinervia. Expression of a promoter-reporter gene fusion in transgenic plants of the transformable C4 species Flaveria bidentis (C4) showed that 1,571 bp of the GLDPA 5′ flanking region contain all the necessary information for the specific expression in bundle-sheath cells and vascular bundles. Interestingly, we found that the GLDPA promoter of F. trinervia exhibits a C4-like spatial activity also in the C3 plant Arabidopsis (Arabidopsis thaliana), indicating that a mechanism for bundle-sheath-specific expression is also present in this C3 species. Using transgenic Arabidopsis, promoter deletion studies identified two regions in the GLDPA promoter, one conferring repression of gene expression in mesophyll cells and one functioning as a general transcriptional enhancer. Subsequent analyses in transgenic F. bidentis confirmed that these two segments fulfill the same function also in the C4 context.
Sequence Variation of MicroRNAs and Their Binding Sites in Arabidopsis
Authors: Ehrenreich Ian M. , Purugganan Michael D.
Published: February 2008

Major differences exist between plants and animals both in the extent of microRNA (miRNA)-based gene regulation and the sequence complementarity requirements for miRNA-messenger RNA pairing. Whether these differences affect how these sites evolve at the molecular level is unknown. To determine the extent of sequence variation at miRNAs and their targets in a plant species, we resequenced 16 miRNA families (66 miRNAs in total) and all 52 of the characterized binding sites for these miRNAs in the plant model Arabidopsis (Arabidopsis thaliana), accounting for around 50% of the known miRNAs and binding sites in this species. As has been shown previously in humans, we find that both miRNAs and their target binding sites have very low nucleotide variation and divergence compared to their flanking sequences in Arabidopsis, indicating strong purifying selection on these sites in this species. Sequence data flanking the mature miRNAs, however, exhibit normal levels of polymorphism for the accessions in this study and, in some cases, nonneutral evolution or subtle effects on predicted pre-miRNA secondary structure, suggesting that there is raw material for the differential function of miRNA alleles. Overall, our results show that despite differences in the architecture of miRNA-based regulation, miRNAs and their targets are similarly constrained in both plants and animals.
Side chain burial and hydrophobic core packing in protein folding transition states
Authors: Farber Patrick J. , Mittermaier Anthony
Published: February 2008

A critical step in the folding pathway of globular proteins is the formation of a tightly packed hydrophobic core. Several mutational studies have addressed the question of whether tight packing interactions are present during the rate‐limiting step of folding. In some of these investigations, substituted side chains have been assumed to form native‐like interactions in the transition state when the folding rates of mutant proteins correlate with their native‐state stabilities. Alternatively, it has been argued that side chains participate in nonspecific hydrophobic collapse when the folding rates of mutant proteins correlate with side‐chain hydrophobicity. In a reanalysis of published data, we have found that folding rates often correlate similarly well, or poorly, with both native‐state stability and side‐chain hydrophobicity, and it is therefore not possible to select an appropriate transition state model based on these one‐parameter correlations. We show that this ambiguity can be resolved using a two‐parameter model in which side chain burial and the formation of all other native‐like interactions can occur asynchronously. Notably, the model agrees well with experimental data, even for positions where the one‐parameter correlations are poor. We find that many side chains experience a previously unrecognized type of transition state environment in which specific, native‐like interactions are formed, but hydrophobic burial dominates. Implications of these results to the design and analysis of protein folding studies are discussed.
Thermochemical Behavior of Gallium in Weapons‐Material‐Derived Mixed‐Oxide Light Water Reactor (LWR) Fuel
Authors: Besmann Theodore M.
Published: February 2008

The use of weapons‐derived plutonium in light water reactor (LWR) fuel must consider the effects of up to 1 mass% of gallium that is used in weapons plutonium alloy. The potential effects of this residual gallium have been examined for 5% PuO2‐95% UO2 from a thermochemical standpoint. The state and effect of gallium in the fuel are predicted, based on the oxygen potential of the fuel and the effects of burn‐up. The possibility of vapor‐phase transport of gallium to the fuel clad and potential interaction with the clad also is assessed.
Chemical Vapor Deposition of B13C2 from BCl3‐CH4‐H2‐Argon Mixtures
Authors: Moss Thomas S. , Lackey W. Jack , More Karren L.
Published: February 2008

The deposition of boron carbide (B13C2) onto graphite substrates was accomplished by using a hot‐wall chemical vapor deposition (CVD) reactor at a pressure of 10.1 kPa in the temperature range of 1000°–1400°C. A modified impinging‐jet geometry was used to simplify the mass‐transfer analysis. Coatings were characterized using X‐ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The surface morphology was composed of well‐defined facets, the size of which was dependent on the growth rate and deposition time, as would be expected from a competitive growth mechanism. TEM micrographs of the coating showed long, columnar grains that emanated from a narrow nucleation zone. The growth rate could be adequately described by a first‐order kinetic expression, with respect to the bulk gas phase boron chloride (BCl3) concentration. The activation energy of the kinetic expression was estimated to be 93.1 kJ/mol. It was proposed that the deposition was limited by the adsorption of (BCl3) onto the substrate surface.
Alkaline Corrosion Resistance of Anodized Aluminum Coated with Zirconium Oxide by a Sol‐Gel Process
Authors: Hirai Shinji , Shimakage Kazuyoshi , Aizawa Shougo , Wada Kenji
Published: February 2008

To improve the alkaline corrosion resistance of aluminum, composite films were prepared that consisted of a porous layer of anodically grown aluminum oxide filled with zirconium oxide, with a zirconium oxide coating layer that was deposited thereon via the sol—gel process, using a dip‐coating technique. The alkaline corrosion resistance of these composite films was extremely improved when this coating layer was placed on an anodic oxide film. Comparisons of the composite film and conventional anodic oxide film showed that the alkaline corrosion resistance of the composite film was increased by a factor of 24–50. Because these composite films, which have high corrosion resistance, indicated a vibration phenomenon of voltage in the duration time curve of the electromotive force measurement, the composite film had a self‐repairing action for alkaline corrosion.
Healing of Lithographically Introduced Cracks in Glass and Glass‐Containing Ceramics
Authors: Ackler Harold D.
Published: February 2008

The morphological evolution of lithographically defined cracklike flaws in glass and glass‐containing ceramics was studied at elevated temperatures. The systems studied have glass contents from 100 to approximately 0.5 vol%, providing insight to the contribution of viscous flow of the glass to crack healing over a range of glass contents spanning many industrial ceramics. Healing behavior is found to be controlled by viscous flow of glass in all cases except the lowest glass content, for which significant mass transport is only accomplished by diffusional mechanisms. This implies a change of mechanism below some critical glass content.
Novel Spray‐Pyrolysis Deposition of Cuprous Oxide Thin Films
Authors: Kosugi Tsuyoshi , Kaneko Shoji
Published: February 2008

Spray pyrolysis of aqueous solutions that include copper(II) acetate, glucose, and 2‐propanol was studied for the formation of cuprous oxide (Cu2O) thin films on glass substrates. The deposition conditions, based on the phase relations of the films, were investigated in terms of solution concentration and substrate temperature. Also, the formation process was kinetically discussed. The Cu2O thin film obtained here was composed of rounded grains ∼50 nm in size with a surface roughness of ∼30 nm. This film was reddish yellow and showed indirect and direct bandgap energies of 1.95 and 2.60 eV, respectively. Furthermore, the film exhibited p‐type conduction, with a resistivity of ∼100 Omegacm.