bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrolytic degradation of poly(rac‐lactide) and poly[(rac‐lactide)‐co‐glycolide] at the air–water interface
Authors: Kulkarni Amit , Reiche Juergen , Lendlein Andreas
Published: June 2007

The understanding of the simultaneous transport and chain‐scission phenomena involved in the hydrolysis of bulk‐degrading polymers requires the experimental separation of chain cleavage and water diffusion. The hydrolytic chain cleavage of poly(rac‐lactide) rac‐(PLA) and poly[(rac‐lactide)‐co‐glycolide] (PLGA) is analysed on the basis of monolayer degradation experiments combined with an improved data reduction procedure. Different, partly contradictory models of the hydrolytic degradation and erosion mechanism of PLA and PLGA, namely random chain scission and chain‐end scission, are discussed in the literature. The instantaneous linear area reduction observed for the polymer Langmuir films indicates a chain‐end scission mechanism. As monolayers of end‐capped and non‐end‐capped polymers degrade with exactly the same rate, the observed differences in the degradation kinetics of bulk samples do clearly result from differences in the water penetration into these polymers. A pronounced ‘auto‐inhibition’ effect is observed for the polymers degraded at initially high pH of the aqueous subphase in the absence of buffers. Copyright © 2007 John Wiley & Sons, Ltd.
In situ investigations of the interaction of small inorganic acidifying molecules in humidified air with polycrystalline metal surfaces by means of TM‐AFM, IRRAS, and QCM
Authors: Kleber Ch. , Hilfrich U. , Schreiner M.
Published: June 2007

Initial atmospheric corrosion of copper, silver, and iron induced by humidity and oxidizing agents was studied in situ by three highly surface‐sensitive and complementary techniques: infrared reflection‐absorption spectroscopy (IRRAS), quartz crystal microbalance (QCM), and tapping‐mode atomic force microscopy (TM‐AFM). These techniques deliver information about the change of the topography of the sample surfaces with emphasis on the shape and lateral distribution of the corrosion products grown within the first 1300–2800 min of weathering (TM‐AFM), as well as chemical (IRRAS) and kinetic (QCM) data. A completely different mechanism of the initial stages of atmospheric corrosion of the three investigated metals could be observed. A uniform growth of corrosion products was seen on the copper surface (identified by IRRAS and XPS to be cuprite‐like) during exposure to synthetic air with 80% relative humidity (RH), whereas the iron surface remained unattacked. The investigations of the silver surface exposed to humidity revealed that silver is attacked by humidity and tends to form oxide and hydroxide surface species. While an increased humidity content of the surrounding atmosphere causes higher corrosion rates on copper, on the exposed silver sample only a change in the degradation mechanism could be observed.

The addition of SO2 to the humidified air causes the growth of so‐called ‘second‐order’ features on copper, identified to be CuSO3 · xH2O‐like, which reveals the formation of a new chemical species on the investigated surface. These features are placed on top of the homogeneous formed oxide layer and tend to form well‐defined islands. In contrast to copper, on a silver surface exposed to humidity and SO2 no new chemical species are formed; nevertheless an increased corrosion rate could be observed owing to a change of the chemistry in the physisorbed water layer. Iron exposed to humidity and SO2 still remains unattacked. An iron surface is attacked only if exposed to humidity and SO2 and NO2, which show a synergistic effect by the oxidation of four‐valent sulfur‐oxygen species by NO2. Such an attack leads to the formation of pitting corrosion, which was observed in situ and time‐resolved. The pits mainly occur on predamaged surface structures, such as scratches caused from the polishing process of the samples, and therefore promote the initiation of the corrosion. The results obtained demonstrate the high potential of the surface‐sensitive methods applied for investigating the early stages of corrosion of different metals and for obtaining a better understanding of the molecular mechanisms during degradation. Copyright © 2007 John Wiley & Sons, Ltd.
Yeast vectors for the integration/expression of any sequence at the TYR1 locus
Authors: Mirisola Mario G. , Colomba Leonarda , Gallo Alessia , Amodeo Roberta , De Leo Giacomo
Published: June 2007

We have constructed new yeast vectors for targeted integration and conditional expression of any sequence at the Saccharomyces cerevisiae TYR1 locus which becomes disrupted. We show that vector integration is not neutral, causing prototrophy for tyrosine and auxotrophy for the vector's selectable marker (uracil or leucine, depending on the vector used). This feature allows a double screening of transformed yeast cells, improving the identification of colonies with the desired chromosomal structure. The GAL10 gene promoter has been added to drive conditional expression of cloned sequences. Using these vectors, chromosomal structure verification of recombinant clones is no longer necessary, since the noise of non‐homologous recombination, as well as spontaneous reversion of the selected phenotype, can easily be identified. The ability of the vector to conditionally control gene expression has been confirmed using the gene for the green fluorescent protein (GFP) as a reporter. GenBank Accession Nos EF202083–202086. Copyright © 2007 John Wiley & Sons, Ltd.
Presence of an unsuitable host diminishes the competitive superiority of an insect parasitoid: a distraction effect
Authors: Meisner Matthew , Harmon Jason P. , Ives Anthony R.
Published: June 2007

Competitive interactions between parasitoid species are traditionally evaluated when they compete for a single host species. Yet, the presence of additional host species can alter competitive interactions, even if the host is unsuitable for parasitoid development. In alfalfa of the mid‐western USA, a native parasitoid species, Praon pequodorum, was once a dominant natural enemy, but it has become rare since the introduction of another parasitoid, Aphidius ervi. Despite A. ervi's competitive superiority for their most common host, the pea aphid Acyrthosiphum pisum, P. pequodorum still persists at low densities. We performed a suite of laboratory and field studies to determine if the presence of an alternative host, the spotted alfalfa aphid Therioaphis maculata, may mitigate A. ervi's competitive superiority and facilitate P. pequodorum's persistence. We show that spotted alfalfa aphids reduce the foraging efficiency of both parasitoid species for pea aphids, despite spotted alfalfa aphids being an unsuitable host. This decrease in efficiency, however, was not symmetrical; the presence of spotted alfalfa aphids had a greater detrimental effect on A. ervi foraging for pea aphids. This might facilitate the persistence of the competitively inferior P. pequodorum. Our study suggests that indirect effects generated by the presence of alternative hosts are important for understanding parasitoid–host dynamics and overall insect community structure.
Separating Oil from Aqueous Extraction Fractions of Soybean
Authors: Lamsal B. P. , Johnson L. A.
Published: June 2007

Previous research has shown that enzyme‐assisted aqueous extraction processing (EAEP) extracts 88–90% of the total soybean oil from extruded full‐fat soy flakes into the aqueous media, which is distributed as cream (oil‐in‐water emulsion), skim, and free oil. In the present work, a simple separatory funnel procedure was effective in separating aqueous skim, cream and free oil fractions allowing mass balances and extraction and recovery efficiencies to be determined. The procedure was used to separate and compare liquid fractions extracted from full‐fat soy flour and extruded full‐fat soy flakes. EAEP extracted more oil from the extruded full‐fat soy flakes, and yielded more free oil from the resulting cream compared to unextruded full‐fat soy flour. Dry matter partitioning between fractions was similar for the two procedures. Mean oil droplet sizes in the cream and skim fractions were larger for EAEP of extruded flakes compared to non‐enzymatic AEP of unextruded flour (45 vs. 20 μm for cream; 13 vs. 5 μm for skim) making the emulsions from EAEP of extruded flakes less stable. All major soy protein subunits were present in the cream fractions, as well as other fractions, from both processes. The cream could be broken using phospholipase treatments and 70–80% of total oil in the extruded full‐fat flakes was recovered using EAEP and a phospholipase de‐emulsification procedure.
Development of Lipid Changes Related to Quality Loss During the Frozen Storage of Farmed Coho Salmon (Oncorhynchus kisutch)
Authors: Rodríguez Alicia , Losada Vanesa , Larraín M. Angélica , Quitral Vilma , Vinagre Julia , Aubourg Santiago P.
Published: June 2007

Lipid changes related to quality loss were evaluated during frozen storage of coho salmon for up to 15 months. Biochemical indices concerning lipid hydrolysis (free fatty acids, FFA) and oxidation (peroxide value, PV; thiobarbituric acid index, TBA‐i; fluorescent compounds, FR; polyene index, PI) were determined and compared to sensory (odor and taste) and endogenous antioxidant (tocopherol isomers and astaxanthin) assessments. As a result of the frozen storage, lipid hydrolysis was shown to develop according to the increase in FFA content (p < 0.05). However, most biochemical lipid oxidation indices (PV, TBA‐i and FR) led to a low degree of rancidity development (p < 0.05) when compared to other fatty fish species under similar frozen storage conditions. The PI value decreased (p < 0.05) at month 10 but then remained unchanged until the end of the experiment. Rancid odor and taste development were shown to be low throughout the experiment, according to the biochemical indices mentioned above. However, a progressive decrease (p < 0.05) in the original fresh odor and taste of salmon fish flesh occurred with increasing frozen storage time, such that fish samples had the poorest scores by month 15. Endogenous antioxidants were remarkably stable throughout the experiment and which might contribute to the oxidative stability of frozen farmed coho salmon lipids.
Identification of the molecular basis for the functional difference between flavonoid 3′‐hydroxylase and flavonoid 3′,5′‐hydroxylase
Authors: Seitz Christian , Ameres Stefanie , Forkmann Gert
Published: June 2007

Flavonoid 3′‐hydroxylase (F3′H) and flavonoid 3′,5′‐hydroxylase (F3′5′H) are cytochrome P450 enzymes and determine the B‐ring hydroxylation pattern of flavonoids by introducing hydroxyl groups at the 3′‐ or the 3′‐ and 5′‐position, respectively. Sequence identity between F3′H and F3′5′H is generally low since their divergence took place early in the evolution of higher plants. However, in the Asteraceae the family‐specific evolution of an F3′5′H from an F3′H precursor occurred, and consequently sequence identity is substantially higher. We used this phenomenon for alignment studies, in order to identify regions which could be involved in determining substrate specificity and functionality. Subsequent construction and expression of chimeric genes indicated that substrate specificity of F3′H and F3′5′H is determined near the N‐terminal end and the functional difference between these two enzymes near the C‐terminal end. The impact on function of individual amino acids located in substrate recognition site 6 (SRS6) was further tested by site‐directed mutagenesis. Most interestingly, a conservative Thr to Ser exchange at position 487 conferred additional 5′‐hydroxylation activity to recombinant Gerbera hybrida F3′H, whereas the reverse substitution transformed recombinant Osteospermum hybrida F3′5′H into an F3′H with low remaining 5′‐hydroxylation activity. Since the physicochemical properties of Thr and Ser are highly similar, the difference in size appears to be the main factor contributing to functional difference. The results further suggest that relatively few amino acids exchanges were required for the evolutionary extension of 3′‐ to 3′,5′‐hydroxylation activity.
Cytoplasmic ATPase involved in ferrous ion uptake from magnetotactic bacterium Magnetospirillum magneticum AMB‐1
Authors: Suzuki Takeyuki , Okamura Yoshiko , Arakaki Atsushi , Takeyama Haruko , Matsunaga Tadashi
Published: June 2007

A non‐magnetic mutant of Magnetospirillum magneticum AMB‐1 (NMA61), harboring a defective gene located in ORF4 (gene ID: amb4111) was generated by transposon mutagenesis. Biochemical characterization of the gene product of ORF4 revealed that it was localized in the cytoplasm and displayed ATPase activity. The ability of NMA61 to take up iron was severely compromised. Ferrous ion concentration in the medium decreased more with the wild‐type than with NMA61, while the iron content in the cytoplasmic fraction of NMA61 was much lower than the wild‐type strain. This cytoplasmic ATPase is essential for iron trafficking within M. magneticum AMB‐1.
The mitochondrial inner membrane protein Mitofilin exists as a complex with SAM50, metaxins 1 and 2, coiled‐coil‐helix coiled‐coil‐helix domain‐containing protein 3 and 6 and DnaJC11
Authors: Xie Jing , Marusich Michael F. , Souda Puneet , Whitelegge Julian , Capaldi Roderick A.
Published: June 2007

A monoclonal antibody (mAb) has been produced which reacts with human mitofilin, a mitochondrial inner membrane protein. This mAb immunocaptures its target protein in association with six other proteins, metaxins 1 and 2, SAM50, CHCHD3, CHCHD6 and DnaJC11, respectively. The first three are outer membrane proteins, CHCHD3 has been assigned to the matrix space, and the other two proteins have not been described in mitochondria previously. The functional role of this new complex is uncertain. However, a role in protein import related to maintenance of mitochondrial structure is suggested as mitofilin helps regulate mitochondrial morphology and at least four of the associated proteins (metaxins 1 and 2, SAM50 and CHCHD3) have been implicated in protein import, while DnaJC11 is a chaperone‐like protein that may have a similar role.
Uterine anomalies and pregnancy outcome following resectoscope metroplasty
Authors: Zlopaša G. , Škrablin S. , Kalafatić D. , Banović V. , Lešin J.
Published: June 2007

Objective: To compare reproductive outcome in women with uterine anomalies and women with a normal uterus, and evaluate the effect of resectoscope metroplasty. Methods: The pregnancy outcomes, past and present, of 105 women with congenital uterine anomalies were compared with those of 182 women with a normally shaped uterus. The outcomes of 25 women with septate and bicornuate uteri before and after resectoscope metroplasty were also analyzed. The χ2 and Mann‐Whitney U test were used for statistical analysis, with P < 0.05 considered statistically significant. Results: Uterine anomalies were associated with higher rates of spontaneous abortion, preterm delivery, intrauterine growth retardation, breech presentation, and cesarean delivery (P < 0.001). The highest incidence of early spontaneous abortion was noted among women with septate uteri, and the highest incidence of preterm labor was noted among women with arcuate or bicornuate uteri. Among women with arcuate uteri, significantly lower gestational age and birth‐weight were observed compared with any other type of adverse outcome. Compared with their previous pregnancies, the abortion rates were lower and delivery rates were higher in women who conceived following hysteroscopic metroplasty (P < 0.001). Conclusion: Resesctoscope metroplasty significantly improved pregnancy outcome in women with uterine anomalies.
Novel therapeutic strategies for the treatment of protein-misfolding diseases
Authors: Rochet Jean-Christophe
Published: June 2007

Most proteins in the cell adopt a compact, globular fold that determines their stability and function. Partial protein unfolding under conditions of cellular stress results in the exposure of hydrophobic regions normally buried in the interior of the native structure. Interactions involving the exposed hydrophobic surfaces of misfolded protein conformers lead to the formation of toxic aggregates, including oligomers, protofibrils and amyloid fibrils. A significant number of human disorders (e.g. Alzheimer disease, Parkinson disease, Huntington disease, amyotrophic lateral sclerosis and type II diabetes) are characterised by protein misfolding and aggregation. Over the past five years, outstanding progress has been made in the development of therapeutic strategies targeting these diseases. Three promising approaches include: (1) inhibiting protein aggregation with peptides or small molecules identified via structure-based drug design or high-throughput screening; (2) interfering with post-translational modifications that stimulate protein misfolding and aggregation; and (3) upregulating molecular chaperones or aggregate-clearance mechanisms. Ultimately, drug combinations that capitalise on more than one therapeutic strategy will constitute the most effective treatment for patients with these devastating illnesses.
A decade of GPS in Southeast Asia: Resolving Sundaland motion and boundaries
Authors: Simons W. J. F. , Socquet A. , Vigny C. , Ambrosius B. A. C. , Haji Abu S. , Promthong Chaiwat , Subarya C. , Sarsito D. A. , Matheussen S. , Morgan P. , Spakman W.
Published: June 2007

A unique GPS velocity field that spans the entire Southeast Asia region is presented. It is based on 10 years (1994–2004) of GPS data at more than 100 sites in Indonesia, Malaysia, Thailand, Myanmar, the Philippines, and Vietnam. The majority of the horizontal velocity vectors have a demonstrated global accuracy of ∼1 mm/yr (at 95% confidence level). The results have been used to (better) characterize the Sundaland block boundaries and to derive a new geokinematic model for the region. The rotation pole of the undeformed core of the Sundaland block is located at 49.0°N–94.2°E, with a clockwise rotation rate of 0.34°/Myr. With respect to both geodetically and geophysically defined Eurasia plate models, Sundaland moves eastward at a velocity of 6 ± 1 to 10 ± 1 mm/yr from south to north, respectively. Contrary to previous studies, Sundaland is shown to move independently with respect to South China, the eastern part of Java, the island of Sulawesi, and the northern tip of Borneo. The Red River fault in South China and Vietnam is still active and accommodates a strike‐slip motion of ∼2 mm/yr. Although Sundaland internal deformation is general very small (less than 7 nanostrain/yr), important accumulation of elastic deformation occurs along its boundaries with fast‐moving neighboring plates. In particular in northern Sumatra and Malaysia, inland‐pointing trench‐perpendicular residual velocities were detected prior to the megathrust earthquake of 26 December 2004. Earlier studies in Sumatra already showed this but underestimated the extent of the deformation zone, which reaches more than 600 km away from the trench. This study shows that only a regional Southeast Asia network spanning thousands of kilometers can provide a reference frame solid enough to analyze intraplate and interplate deformation in detail.
Triggering of the Hinlopen/Yermak Megaslide in relation to paleoceanography and climate history of the continental margin north of Spitsbergen
Authors: Winkelmann Daniel , Stein Ruediger
Published: June 2007

On the basis of the detailed sedimentological record of the key‐core PS66/309‐1 and a review of open literature, we present an assessment of the paleoenvironmental conditions as well as trigger mechanism of the Hinlopen/Yermak Megaslide north of Spitsbergen. The Svalbard archipelago is characterized by strong inflow of Atlantic water accompanied by rapidly falling sea level, rapidly growing Svalbard‐Barents Sea‐Ice Sheet, and associated increasing glaciotectonic activity during the time window around 30 calendar kyr B. P. of this catastrophic failure event. Thus the potential trigger mechanisms include sediment buoyancy and excess pore pressure, hydrate stability, and tectonic/glaciotectonic processes. While the common scenarios seem to fail to explain this unique submarine megaslide, we focus on glacial processes and their consequences for the regional tectonic framework. We conclude that the Hinlopen/Yermak Megaslide has been the consequence of the rapid onset of Late Weichselian glaciation resulting in a drastic sea level drop, asymmetrical ice loading, and a forebulge development leading to enhanced tectonic movements along the Hinlopen fault zone. As the final trigger we assume a strong earthquake positioned below or close to the SE Sophia Basin.
Response of the global carbon cycle to human‐induced changes in Southern Hemisphere winds
Authors: Zickfeld Kirsten , Fyfe John C. , Saenko Oleg A. , Eby Michael , Weaver Andrew J.
Published: June 2007

An Earth System model is used to explore the response of the oceanic and terrestrial carbon sinks to strengthening and poleward shifting of the extratropical Southern Hemisphere winds, which is a robust feature of climate models' response to greenhouse gas forcing through the 20th and 21st centuries. We find that under time‐varying CO2 emissions poleward intensifying Southern Hemisphere winds act on average to slightly enhance the efficacy of both the oceanic and terrestrial carbon sinks, thus providing a small negative feedback on the atmospheric CO2 concentration. Regionally, the effects of the changing winds on oceanic and terrestrial carbon uptake are more pronounced and partly of opposite sign. We further show that the magnitude and sign of global oceanic CO2 uptake is also controlled by changes in mesoscale eddy activity, which has been suggested to increase in response to intensifying Southern Hemisphere winds.
National Geophysical Data Center candidate for the World Digital Magnetic Anomaly Map
Authors: Maus S. , Sazonova T. , Hemant K. , Fairhead J. D. , Ravat Dhananjay
Published: June 2007

Marine and airborne magnetic anomaly data have been collected for more than half a century, providing global coverage of the Earth. Furthermore, the German CHAMP satellite is providing increasingly accurate information on large‐scale magnetic anomalies. The World Digital Magnetic Anomaly Map project is an international effort to integrate all available near‐surface and satellite magnetic anomaly data into a global map database. Teams of researchers were invited to produce candidate maps using a common pool of data sets. Here we present the National Geophysical Data Center (NGDC) candidate. To produce a homogeneous map, the near‐surface data were first line‐leveled and then merged by Least Squares Collocation. Long wavelengths were found to agree surprisingly well with independent satellite information. This validates our final processing step of merging the short‐wavelength part of the near‐surface data with long‐wavelength satellite magnetic anomalies.
First observations of iodine oxide from space
Authors: Saiz‐Lopez Alfonso , Chance Kelly , Liu Xiong , Kurosu Thomas P. , Sander Stanley P.
Published: June 2007

We present retrievals of IO total columns from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite instrument. We analyze data for October 2005 in the polar regions to demonstrate for the first time the capability to measure IO column abundances from space. During the period of analysis (i.e. Southern Hemisphere springtime), enhanced IO vertical columns over 3 × 1013 molecules cm−2 are observed around coastal Antarctica; by contrast during that time in the Artic region IO is consistently below the calculated instrumental detection limit for individual radiance spectra (2–4 × 1012 molecules cm−2 for slant columns). The levels reported here are in reasonably good agreement with previous ground‐based measurements at coastal Antarctica. These results also demonstrate that IO is widespread over sea‐ice covered areas in the Southern Ocean. The occurrence of elevated IO and its hitherto unrecognized spatial distribution suggest an efficient iodine activation mechanism at a synoptic scale over coastal Antarctica.
XML in Motion from Genome to Drug
Authors: Mohan C. Gopi
Published: June 2007

Information technology (IT) has emerged as a central to the solution of contemporary genomics and drug discovery problems. Researchers involved in genomics, proteomics, transcriptional profiling, high throughput structure determination, and in other sub-disciplines of bioinformatics have direct impact on this IT revolution. As the full genome sequences of many species, data from structural genomics, micro-arrays, and proteomics became available, integration of these data to a common platform require sophisticated bioinformatics tools. Organizing these data into knowledgeable databases and developing appropriate software tools for analyzing the same are going to be major challenges. XML (eXtensible Markup Language) forms the backbone of biological data representation and exchange over the internet, enabling researchers to aggregate data from various heterogeneous data resources. The present article covers a comprehensive idea of the integration of XML on particular type of biological databases mainly dealing with sequence-structure-function relationship and its application towards drug discovery. This e-medical science approach should be applied to other scientific domains and the latest trend in semantic web applications is also highlighted.
A statistical mechanics approach for scale-free networks and finite-scale networks
Authors: Bianconi Ginestra
Published: June 2007

We present a statistical mechanics approach for the description of complex networks. We first define an energy and an entropy, associated with a degree distribution, which have a geometrical interpretation. Next we evaluate the distribution that extremizes the free energy of the network. We find two important limiting cases: a scale-free degree distribution and a finite-scale degree distribution. The size of the space of allowed simple networks given these distributions is evaluated in the large network limit. Results are compared with simulations of algorithms generating these networks.
Self-assembly of β-sheet forming peptides into chiral fibrillar aggregates
Authors: Bellesia Giovanni , Shea Joan-Emma
Published: June 2007

The authors introduce a novel mid-resolution off-lattice coarse-grained model to investigate the self-assembly of β-sheet forming peptides. The model retains most of the peptide backbone degrees of freedom as well as one interaction center describing the side chains. The peptide consists of a core of alternating hydrophobic and hydrophilic residues, capped by two oppositely charged residues. Nonbonded interactions are described by Lennard-Jones and Coulombic terms. The influence of different levels of “hydrophobic” and “steric” forces between the side chains of the peptides on the thermodynamics and kinetics of aggregation was investigated using Langevin dynamics. The model is simple enough to allow the simulation of systems consisting of hundreds of peptides, while remaining realistic enough to successfully lead to the formation of chiral, ordered β tapes, ribbons, as well as higher order fibrillar aggregates.
Evolution of mushroom-type structures behind a heated cylinder
Authors: Ren Maosheng , Rindt Camilo , van Steenhoven Anton
Published: June 2007

The three-dimensional transition in the wake flow behind a heated cylinder occurs at a much lower Reynolds number than for the unheated case. The three-dimensional transition is initialized in the near-wake by the formation of Λ-shaped structures and manifests itself in the far-wake as escaping mushroom-type structures from the upper vortices. In this study, both experimental and numerical techniques are used to investigate the origin and development of these mushroom-type structures. The formation of the mushroom-type structures is associated with the occurrence of Λ-shaped vortices in the near-wake. Hot fluid between the legs and the head of the Λ-shaped structure is lifted up. This lift-up process together with the action of buoyancy pulls out hot fluid from the upper vortex cores, resulting in a mushroom-type structure, which is comprised of a so-called stem and cap. Hot fluid is continuously transported through the stem to the advancing front of the mushroom-type structure. Finally, a pinch-off phenomenon is observed of the cap, ending up as a buoyant vortex ring. An analytical model is presented for the pinch-off process.
Vorticity dynamics of a bileaflet mechanical heart valve in an axisymmetric aorta
Authors: Dasi L. P. , Ge L. , Simon H. A. , Sotiropoulos F. , Yoganathan A. P.
Published: June 2007

We present comprehensive particle image velocimetry measurements and direct numerical simulation (DNS) of physiological, pulsatile flow through a clinical quality bileaflet mechanical heart valve mounted in an idealized axisymmetric aorta geometry with a sudden expansion modeling the aortic sinus region. Instantaneous and ensemble-averaged velocity measurements as well as the associated statistics of leaflet kinematics are reported and analyzed in tandem to elucidate the structure of the velocity and vorticity fields of the ensuing flow-structure interaction. The measurements reveal that during the first half of the acceleration phase, the flow is laminar and repeatable from cycle to cycle. The valve housing shear layer rolls up into the sinus and begins to extract vorticity of opposite sign from the sinus wall. A start-up vortical structure is shed from the leaflets and is advected downstream as the leaflet shear layers become wavy and oscillatory. In the second half of flow acceleration the leaflet shear layers become unstable and break down into two von Karman-like vortex streets. The onset of vortex shedding from the valve leaflets is responsible for the growth of significant cycle-to-cycle vorticity oscillations. At peak flow, the housing and leaflet shear layers undergo secondary instabilities and break down rapidly into a chaotic, turbulent-like state with multiple small-scale vortical structures emerging in the flow. During the deceleration and closing phases all large-scale coherent flow features disappear and a chaotic small-scale vorticity field emerges, which persists even after the valve has closed. Probability density functions of the leaflet position during opening and closing phases show that the leaflet position fluctuates from cycle to cycle with larger fluctuations evident during valve closure. The DNS is carried out by prescribing the leaflet kinematics from the experimental data. The computed instantaneous vorticity fields are in very good agreement with the measurements, especially during the accelerating phase when the flow remains coherent and repeatable and instantaneous comparisons are meaningful. The computed results are analyzed to elucidate for the first time the intricate and highly three-dimensional structure of the pulsatile jet through the triple-opening orifice of the bileaflet valve and explain the rich flow phenomena documented in the two-dimensional vorticity measurements.
Precipitation of trapped relativistic electrons by amplified whistler waves in the magnetosphere
Authors: Kuo S. P. , Kuo Steven S. , Huynh James T. , Kossey Paul
Published: June 2007

Numerical study of a loss-cone negative mass instability to amplify whistler waves by energetic electrons in the radiation belts is presented. The results show that a very low intensity whistler wave can be amplified by 50keV electrons more than 25dB, consistent with the Siple experimental result [Helliwell et al., J. Geophys. Res. 85, 3360 (1980)]. The dependencies of the amplification factor on the energetic electron density and on the initial wave intensity are evaluated. It is shown that the amplification factor decreases as the initial wave intensity increases. However, this gain can still exceed 15dB for a 30dB increase of the initial wave intensity, which is needed for the purpose of precipitating MeV electrons in the radiation belts. We then show that there exists a double resonance situation, by which, as an example, a wave is simultaneously in cyclotron resonance with 50keV electrons as well as with 1.5MeV electrons; the wave is first amplified by 50keV electrons and then precipitates 1.5MeV electrons. With the aid of the cyclotron resonance, the threshold field for the commencement of chaos in the electron trajectories is reduced considerably from that for a general case. Pitch angle scattering of 1.5MeV electrons is demonstrated. The results show that a whistler wave with magnetic field amplitude of 0.08% of the background magnetic field can scatter electrons from an initial pitch angle of 86.5° to a pitch angle <50°.
Energy dissipation via electron energization in standing shear Alfvén waves
Authors: Damiano P. A. , Wright A. N. , Sydora R. D. , Samson J. C.
Published: June 2007

A two-dimensional hybrid magnetohydrodynamic-kinetic electron model in dipolar coordinates is used to study the case of a fundamental mode toroidal field line resonance (FLR) centered on an L=10 closed dipolar magnetic field line. The model is initialized via a perturbation of the azimuthal shear Alfvén velocity so that only upward field aligned currents (corresponding to downwelling electrons) are present at the ionospheric boundaries during the first half wave period. It is found that the acceleration of the electrons to carry the field aligned currents can be a significant sink of Alfvén wave energy depending on the width of the flux tube. For a FLR with an equatorial perpendicular wavelength of 0.25 RE about 20% of the wave energy is dissipated over a half cycle. This varies inversely with the width of the flux tube increasing to 40% by a width of 0.15 RE, which, unless the system is driven, can completely damp the resonance in about 2–3cycles.
Cavitation bubble behavior inside a liquid jet
Authors: Robert Etienne , Lettry Jacques , Farhat Mohamed , Monkewitz Peter A. , Avellan François
Published: June 2007

The growth and collapse of laser-induced vapor cavities inside axisymmetric free-falling liquid water jets have been studied. Bubbles of different size are generated at various distances from the jet axis and the effects on the jet interface are recorded by means of ultrafast cinematography. The configuration is characterized by two dimensionless parameters: the bubble to jet diameter ratio δ and the eccentricity coefficient ε defined as the radius of bubble generation divided by the jet radius. For high δ and ε, microjets and droplets are ejected from the liquid jet at speeds exceeding 100m∕s. The observed jet fragmentation shows similarities with experiments conducted on a liquid mercury jet hit by a pulsed proton beam, a candidate configuration for future accelerator based facilities.
Observation of the ÃA″1 state of isocyanogen
Authors: Lynch W. Bryan , Bechtel Hans A. , Steeves Adam H. , Curley John J. , Field Robert W.
Published: June 2007

The ÃA″1 state of isocyanogen, CNCN, is observed using photofragment fluorescence excitation spectroscopy in a room temperature cell and in a molecular beam. The spectra are highly congested, but progressions that correspond to the Franck-Condon active C–N–C bending vibration in the excited state are evident. Linewidth measurements indicate that the excited state lifetime is <10ps. These measurements are consistent with previous ab initio calculations, which predicted a bent excited state with a short lifetime due to predissociation. Although we do not believe that we have observed the origin band of the electronic transition, we place an upper limit of 42523cm−1 on the energy of the excited state zero point level.
Simple uniaxial pressure device for ac-susceptibility measurements suitable for closed cycle refrigerator system
Authors: Arumugam S. , Manivannan N. , Murugeswari A.
Published: June 2007

A simple design of the uniaxial pressure device for the measurement of ac-susceptibility at low temperatures using closed cycle refrigerator system is presented for the first time. This device consists of disc micrometer, spring holder attachment, uniaxial pressure cell, and the ac-susceptibility coil wound on stycast bobbin. It can work under pressure till 0.5GPa and at the temperature range of 30–300K. The performance of the system at ambient pressure is tested and calibrated with standard paramagnetic salts [Gd2O3, Er2O3, and Fe(NH4SO4)26H2O], Fe3O4, Gd metal, Dy metal, superconductor (YBa2Cu3O7), manganite (La1.85Ba0.15MnO3), and spin glass material (Pr0.8Sr0.2MnO3). The performance of the uniaxial pressure device is demonstrated by investigating the uniaxial pressure dependence of La1.85Ba0.15MnO3 single crystal with P‖c axis. The Curie temperature (Tc) decreases as a function of pressure with P‖c axis (dTc∕dP‖caxis=−11.65K∕GPa) up to 46MPa. The design is simple, is user friendly, and does not require pressure calibration. Measurement can even be made on thin and small size oriented crystals. The failure of the coil is remote under uniaxial pressure. The present setup can be used as a multipurpose uniaxial pressure device for the measurement of Hall effect and thermoelectric power with a small modification in the pressure cell.
Symmetry breaking in induced-charge electro-osmosis over polarizable spheroids
Authors: Yossifon G. , Frankel I. , Miloh T.
Published: June 2007

We study the induced-charge electro-osmotic flow around a stationary polarizable dielectric spheroid in the presence of a uniform arbitrarily oriented external electric field. A Robin-type condition connecting the respective electric potentials within the dielectric solid and the bulk electro-neutral solution is highlighted in formulating the macroscale description for the limit of thin electric double layers and low potentials. The results illustrate symmetry breaking phenomena in the ensuing flow and demonstrate qualitative differences associated with variations of the dielectric constant. We briefly discuss the potential impact of these differences on the rotation of freely suspended spheroids.
Stability of flow between two corotating disks in an enclosure
Authors: Miura Tomohito , Mizushima Jiro
Published: June 2007

Linear stability of flow between two corotating disks in an enclosure is investigated numerically, and the result is confirmed experimentally with a visualization method. The outer cylindrical boundary of the flow is assumed to be stationary, whereas the inner cylinder rotates together with the two disks. Polygonal flow patterns have been observed in previous experiments and numerical simulations performed for large Reynolds numbers of O(103)–O(105). The flow pattern was classified into two groups, one of which is asymmetric with respect to the interdisk midplane and the other has the so-called shift-and-reflect symmetry. We found that the first instability of the axisymmetric flow that is a unique solution at small Reynolds numbers is caused by a disturbance with an unexpectedly large wavenumber such as from 20 to 30 for narrow disk spacings. The resultant flow from the instability has aligned vortices along the outer boundary and possesses the shift-and-reflect symmetry always at the criticality, which is expected to develop into polygonal flows at much larger Reynolds numbers than the critical value.
Device physics and design of double-gate tunneling field-effect transistor by silicon film thickness optimization
Authors: Toh Eng-Huat , Wang Grace Huiqi , Samudra Ganesh , Yeo Yee-Chia
Published: June 2007

The device physics of the double-gate tunneling field-effect transistor (DG TFET) is explored through two dimensional device simulations. The on-state drain current Ion of the DG TFET, which is based on band-to-band tunneling, has a strong dependence on the silicon film thickness TSi and the physics governing it is detailed. It is established that band-to-band tunneling at the surface is very strong and accounts for a large part of the total drain current. However, a substantial part of the total drain current Ids is contributed by a subsurface portion of the silicon film. Detailed potential distributions show that the coupling of two gate electrodes in the DG TFET could effectively reduce the tunneling width ωT at the center of the silicon film up to an optimum TSi where maximum drain current is obtained.
Helium atom scattering study of the interaction of water with the BaF2(111) surface
Authors: Vogt Jochen
Published: June 2007

The interaction of water with the BaF2(111) single crystal surface is investigated using the helium atom scattering technique. It is found that H2O forms a long-range ordered two-dimensional (2D) phase with (1×1) translational symmetry already after an exposure of 3L (1L=10−6Torrs) at temperatures below 150K. The activation energy for desorption of the saturated 2D phase, which is assigned to a bilayer, is estimated to be 46±2kJmol−1, corresponding to a desorption temperature of 165K. The desorption of multilayers was observed at 150K, consistent with a binding energy of 42±2kJmol−1. Before completion and after desorption of the saturated 2D phase, a superstructure consistent with a disordered (3×3)R30° lattice has been observed, which is attributed to the first layer of water with a coverage of one molecule per surface unit cell, in accordance with recent theoretical studies. Desorption of this phase is observed at temperatures above 200K, consistent with an unexpectedly strong bonding of the molecules to the substrate.
H
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ion-implantation energy dependence of electronic transport properties in the MeV range in n-type silicon wafers using frequency-domain photocarrier radiometry
Authors: Wang Chinhua , Mandelis Andreas , Tolev Jordan , Burchard Bernd , Meijer Jan
Published: June 2007

Industrial n-type Si wafers (resistivity of 5–10Ωcm) were H+ ion implanted with energies between 0.75 and 2.00MeV, and the electronic transport properties of the implanted layer (recombination lifetime, carrier diffusion coefficient, and front-surface and implanted-interface recombination velocities s1 and s2) were studied using photocarrier radiometry (PCR). A quantitative fitting procedure to the diffusing photoexcited free-carrier density wave was introduced using a relatively simple two-layer PCR model in lieu of the more realistic but substantially more complicated three-layer model. The experimental trends in the transport properties of H+-implanted Si layers extracted from the PCR amplitude and phase data as functions of implantation energy corroborate a physical model of the implanted layer in which (a) overlayer damage due to the light H+ ions decreases with increased depth of implantation at higher energies, (b) the implanted region damage close to the interface is largely decoupled from the overlayer crystallinity, and (c) the concentration of implanted H+ ions decreases at higher implantation energies at the interface, thus decreasing the degree of implantation damage at the interface proper.
Potential energy of hydrogen atom motion on Pd(111) surface and in subsurface: A first principles calculation
Authors: Ozawa Nobuki , Roman Tanglaw A. , Nakanishi Hiroshi , Kasai Hideaki , Arboleda Nelson B. , Diño Wilson Agerico
Published: June 2007

We calculate the adiabatic potential energy for hydrogen atom motion on a Pd(111) surface and in a subsurface within the framework of the density functional theory in order to understand the diffusion mechanism of a hydrogen atom from the Pd(111) surface to the subsurface. According to the calculated adiabatic potential energy surface for the hydrogen atom motion up to the third atom layer, an effective diffusion path of the hydrogen atom into the Pd bulk starts from the fcc hollow site on the Pd(111) surface. Moreover, the diffusion path passes through the octahedral site between the first and the second Pd atom layers, the tetrahedral site beneath a Pd atom of the first layer or above the Pd atom of the third layer, and the octahedral site between the second and third layer.
Optical properties of Pr thin film and nanoparticle layers during hydrogen loading and deloading
Authors: Kala Shubhra , Mehta B. R.
Published: June 2007

Changes in the optical properties of Pd capped Pr thin film and nanoparticle layers prepared by vacuum evaporation and inert gas evaporation techniques, respectively, have been studied as a function of time during hydrogen loading and deloading. These samples were characterized by transmission electron microscopy, atomic force microscopy, x-ray diffraction, and spectrophotometery techniques. Absorption spectra of Pr thin film and nanoparticles samples in metal, and hydrogen loaded and deloaded states have been reported. It is observed that filling of octahedral sites in the dihydride phase results in changes in absorption coefficient values at 1.5–2.0eV and H content in the trihydride phase causes shift of the absorption edge. Enhanced surface area, loose topography, a larger number of interparticle boundaries due to small sizes, relatively loose adhesion to the substrate, and smaller structural changes in nanoparticle layers result in larger and faster changes in the optical properties during loading in comparison to thin film.
Heating-induced carrier accumulation in the optical confinement layer and the output power in broadened symmetric and narrow asymmetric waveguide laser diodes
Authors: Ryvkin Boris , Avrutin Eugene
Published: June 2007

We analyze the thermal effects in carrier accumulation (leakage) in the optical confinement layer of high-power λ=1.06μm semiconductor lasers. The experimental data for the symmetric broadened-cavity lasers are analyzed to extract the information on the current dependence of the internal loss and laser temperature. These data are used to predict the thermal behavior and output power-current dependence of a proposed asymmetric nonbroadened construction operating at the same wavelength, and a significant improvement is predicted.
Effect of Co doping on the static dielectric constant of ZnO nanoparticles
Authors: Ghosh C. K. , Chattopadhyay K. K. , Mitra M. K.
Published: June 2007

Co doped ZnO nanoparticles were synthesized by a simple rheological phase reaction-precursors method using zinc acetate, cobalt acetate, and oxalic acid for different atomic percentages of Co doping. X-ray diffraction studies confirmed the correct phase formation, and the composition were obtained from the x-ray photoelectron spectroscopic studies. Particle size was obtained from the small angle x-ray scattering studies. It was observed that the static dielectric constant, calculated from the shift of band gap energy, shows a gradual decrease with Co doping. A simple theoretical model was developed to explain the observed change of dielectric constant on the doping concentration. The model could successfully describe the dependence of the static dielectric constant on the doping concentration.
Layer thickness and angular dependence of spin transfer torque in ferromagnetic trilayers
Authors: Jalil M. B. A. , Tan S. G. , Law R. , Chung N. L.
Published: June 2007

We investigate the spin transfer torque arising from a perpendicular-to-plane current in a ferromagnetic (FM)-nonmagnetic-FM trilayer. Our analysis is based on the spin drift-diffusion model, modified for the case of noncollinear magnetization, i.e., with arbitrary angle θ between the magnetization orientation of the two FM layers. By solving the electrochemical potential and spin accumulation across the trilayer, we obtain the θ dependence of the magnetoresistance and spin transfer torque in the free FM layer. The optimal magnetization orientation θmax and the corresponding maximum torque τmax are investigated as a function of the FM layer thicknesses. Based on the analysis, we propose that (i) the free (fixed) FM layer thickness be set at approximately the transverse (longitudinal) spin relaxation lengths, and (ii) the relative FM orientation be biased at some intermediate angles instead of the conventional collinear configuration, in order to maximize the current-induced magnetization switching effect.