bluuebunny/crossref_metadata_2025 huggingface dataset:
The fate and intermediary metabolism of stearic acid
Authors: Sampath Harini , Ntambi James M.
Published: November 2006

Coming from the Greek for “hard fat”, stearic acid represents one of the most abundant FA in the Western diet. Otherwise known as n‐octadecanoic acid (18∶0), stearate is either obtained in the diet or synthesized by the elongation of palmitate, the principal product of the FA synthase system in animal cells. Stearic acid has been shown to be a very poor substrate for TG synthesis, even as compared with other saturated fats such as myristate and palmitate, and in human studies stearic acid has been shown to generate a lower lipemic response than medium‐chain saturated FA. Although it has been proposed that this may be due to less efficient absorption of stearic acid in the gut, such findings have not been consistent. Along with palmitate, stearate is the major substrate for the enzyme stearoyl‐CoA desaturase, which catalyzes the conversion of stearate to oleate, the preferred substrate for the synthesis of TG and other complex lipids. In mice, targeted disruption of the stearoyl‐CoA desaturase‐1 (SCD1) gene results in the generation of a lean mouse that is resistant to diet‐induced obesity and insulin resistance. SCD1 also has been shown to be a key target of the anorexigenic hormone leptin, thus underscoring the importance of this enzyme, and consequently the cellular stearate‐to‐oleate ratio, in lipid metabolism and potentially in the treatment of obesity and related disorders.
Comparative effect of fenofibrate on hepatic desaturases in wild‐type and peroxisome proliferator‐activated receptor α‐deficient mice
Authors: Guillou Hervé , Martin Pascal , Jan Sophie , D'Andrea Sabine , Roulet Alain , Catheline Daniel , Rioux Vincent , Pineau Thierry , Legrand Philippe
Published: November 2006

In this study is presented the effect of fenofibrate, a prototypical peroxisome proliferator of the fibrate class, on wild‐type and peroxisome proliferator‐activated receptor α (PPARα)‐/‐mouse liver FA profile, desaturase mRNA levels, and activities. We established that, following peroxisome proliferator exposure, the hepatic FA profile was greatly modified. These modifications in hepatic FA content required the expression of PPARα, as they are suppressed in transgenic mice deficient in this nuclear receptor. Following peroxisome proliferator exposure, Δ6‐ and Δ5‐desaturase mRNA levels and activities were increased in wild‐type but not in PPARα‐deficient mouse liver. These results suggest the involvement of PPARα in the control of hepatic Δ6‐ and Δ5‐desaturases in mice. Their roles in minimizing long‐chain PUFA depletion in the liver during peroxisome proliferator exposure are discussed.
The bottom‐up solution to the triacylglycerol lipidome using atmospheric pressure chemical ionization mass spectrometry
Authors: Byrdwell William Craig
Published: November 2006

Presented here is an approach to representing the data from atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) of triacylglycerols (TAG) using a set of one, two, or three Critical Ratios. These Critical Rations may be used directly to provide structural information concerning the regioisomeric composition of the triacylglycerols (TAG), and about the degree of unsaturation in the TAG. An AAA‐type, or Typel, TAG has only one Critical Ratio, the ratio of the protonated molecule, [M+H]+, to the DAG fragment ion, [AA]+. The Critical Ratio for a Type I TAG is [MH]+/Σ[DAG]+, and the mass spectrum of a Type I TAG can be reproduced from only this one ratio. An ABA/AAB/BAA, or Type II, TAG has two Critical Ratios, the [MH]+/Σ[DAG]+ ratio and the [AA]+/[AB]+ ratio. The [AA]+/[AB]+ ratio for a single TAG or TAG mixture can be compared with the [AA]+/[AB]+ ratios of pure regioisomeric standards, and the percentage of each regioisomer can be estimated. The abundance of the protonated molecule and the abundances of the two [DAG]+ fragment ions can be calculated from the two Critical Ratios for a Type II TAG. To calculate the abundances, the Critical Ratios are processed through the Bottom‐Up Solution to the TAG lipidome. First, Critical Limits are calculated from the Critical Ratios, and then the Critical Ratios are classified into Cases by comparison with the Critical Limits. Once the Case classification is known, the equation for the abundance of each ion in the mass spectrum is given by the Bottom‐Up Solution. A Type III TAG has three different FA and three Critical Ratios. The [MH]+/Σ/[DAG]+ ratio is the first Critical Ratio, the [AC]+/([AB]++[BC]+) ratio is the second Critical Ratio, and the [BC]+/[AB]+ ratio is the third Critical Ratio. The second critical ratio for a Type III TAG can be compared with regioisomeric standards to provide an estimate of the percentage composition of the regioisomers. The three Critical Ratios for a Type III TAG can be processed through the Bottom‐Up Solution to calculate the four ion abundances that make up the APCI‐MS mass spectrum. The Critical Ratios constitute a reduced data set that provides more information in fewer values than the raw abundances.
Application of supercritical fluid chromatography in the quantitative analysis of minor components (carotenes, vitamin E, sterols, and squalene) from palm oil
Authors: Choo Yuen May , Ng Mei Han , Ma Ah Ngan , Chuah Cheng Hock , Hashim Mohd Ali
Published: November 2006

The application of supercritical fluid chromatography (SFC) coupled with a UV variable‐wavelength detector to isolate the minor components (carotenes, vitamin E, sterols, and squalene) in crude palm oil (CPO) and the residual oil from palm‐pressed fiber is reported. SFC is a good technique for the isolation and analysis of these compounds from the sources mentioned. The carotenes, vitamin E, sterols, and squalene were isolated in less than 20 min. The individual vitamin E isomers present in palm oil were also isolated into their respective components, α‐tocopherol, α‐tocotrienol, γ‐tocopherol, γ‐tocotrienol, and δ‐tocotrienol. Calibration of all the minor components of palm as well as the individual components of palm vitamin E was carried out and was found to be comparable to those analyzed by other established analytical methods.
A semiautomated enzymatic method for determination of nonesterified fatty acid concentration in milk and plasma
Authors: Christmass Michael A. , Mitoulas Leon R. , Hartmann Peter E. , Arthur Peter G.
Published: November 2006

An enzymatic assay for the determination of non‐esterified fatty acid concentrations in milk and plasma is described. The procedure is semiautomated for use with a plate luminometer or plate spectrophotometer and enables routine batch processing of large numbers of small samples (≤5 μL). Following the activation of nonesterified fatty acids (NEFA) by acyl‐CoA synthetase, the current assay utilizes UDP‐glucose pyrophosphorylase to link inorganic pyrophosphate to the production of NADH through the reactions catalyzed by phosphoglucomutase and glucose‐6‐phosphate 1‐dehydrogenase. With this assay sequence the formation of NADH from NEFA is complete within 50 min at 37°C. Enzymatic spectrophotometric techniques were unsuitable for NEFA determination in human milk due to the opacity of the sample. The use of the NADH‐luciferase system has overcome this problem, allowing the enzymatic determination of NEFA in human milk. Sample collection and treatment procedures for milk and plasma have been developed to prevent enzymatic lipolysis and to limit interference from enzymes present in milk. The recovery of palmitic acid added to milk and plasma samples was 94.9±2.9 and 100±4.5%, respectively. There was no difference (P=0.13) in plasma NEFA concentrations determined by the current method and a commercially available enzymatic spectrophotometric technique (Wako NEFA‐C kit). Plasma NEFA concentrations determined by gas chromatography were 28% higher compared to both the Wako NEFA‐C kit and the current method.
Effect of tetracosahexaenoic acid on the content and release of histamine, and eicosanoid production in MC/9 mouse mast cell
Authors: Ishihara Kenji , Murata Masakazu , Kaneniwa Masaki , Saito Hiroaki , Shinohara Kazuki , Maeda‐Yamamoto Mari , Kawasaki Ken‐ichi , Ooizumi Tooru
Published: November 2006

6,9,12,15,18,21‐Tetracosahexaenoic acid (24∶6n−3) was isolated from a brittle star,Ophiura sarsiLütken, at>95% purity to evaluate its physiological functions. The effects of 24∶6n−3 on the production of leukotriene (LT)‐related compounds such as LTB4, LTC4and 5‐hydroxyeicosatetraenoic acid, and the accumulation and release of histamine in an MC/9 mouse mast cell line were studied. We found that 24∶6n−3 could inhibit the antigen‐stimulated production of LT‐related compounds as well as other n−3 polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid (20∶5n−3) and docosahexaenoic acid (22∶6n−3), which are major n−3 PUFA in fish oils; 24∶6n−3 was also shown to reduce the histamine content in MC/9 cells at 25 μM (27% reduction from the control), and the effect was diminished with increase of the fatty acid concentration (up to 100 μM). These two n−3 PUFA, 20∶5n−3 and 22∶6n−3, also reduced the histamine content (16 and 20% reduction at 25 μM, respectively), whereas arachidonic acid (20∶4n−6) increased it (18% increase at 25 μM). Spontaneous‐ and antigen‐induced release of histamine was not influenced with these PUFA (at 25 μM). Ionophore‐stimulated release of histamine was suppressed by the PUFA (13,9,15, and 11% reduction with 20∶4n−6, 20∶5n−3, 22∶6n−3, and 24∶6n−3, respectively). The patterns of the effects of 24∶6n−3 on the synthesis of eicosanoids and histamine content were more similar to those of 22∶6n−3 than 20∶5n−3. From these results, 24∶6n−3 can be expected to have anti‐inflammatory activity and antiallergic activities similar to those of 22∶6n−3.
Quantitative determination of butylated hydroxyanisole, butylated hydroxytoluene, and tert‐butyl hydroquinone in oils, foods, and biological fluids by high‐performance liquid chromatography with fluorometric detection
Authors: Yankah Vivienne V. , Ushio Hideki , Ohshima Toshiaki , Koizumi Chiaki
Published: November 2006

Concentrations of synthetic antioxidants butylated hydroxyanisole, butylated hydroxytoluene, and tert‐butyl hydroquinone were quantified using a high‐performance liquid chromatograph with spectrofluorometric detector. The antioxidants were separated and eluted on a reversed‐phase column by gradient of a mixture of H2O/acetonitrile/acetic acid (66.5: 28.5∶5, by vol) and a mixture of acetonitrile/acetic acid (95∶5, vol/vol). The eluants were monitored at emission and excitation wavelengths of 310 and 280 nm, respectively. Calibration curves obtained using peak areas against concentration showed ligh coefficients of multiple determination (R2>0.99) for all antioxidants. Known concentrations of added antioxidant standards were recoverable within 98–99% from oils and over 93% from mouse blood. This method requires minimum sample extraction and purification before analysis and provides a relatively high percentage recovery. The method has been applied successfully for the measurement of antioxidant concentrations in oils, dried foods, and biological fluids.
Inhibition of the formation of amyloid β‐protein fibrils using biocompatible nanogels as artificial chaperones
Authors: Ikeda Keisuke , Okada Takuma , Sawada Shin-ichi , Akiyoshi Kazunari , Matsuzaki Katsumi
Published: November 2006

The formation of fibrils by amyloid β‐protein (Aβ) is considered as a key step in the pathology of Alzheimer's disease (AD). Inhibiting the aggregation of Aβ is a promising approach for AD therapy. In this study, we used biocompatible nanogels composed of a polysaccharide pullulan backbone with hydrophobic cholesterol moieties (cholesterol‐bearing pullulan, CHP) as artificial chaperones to inhibit the formation of Aβ‐(1–42) fibrils with marked amyloidgenic activity and cytotoxicity. The CHP‐nanogels incorporated up to 6–8 Aβ‐(1–42) molecules per particle and induced a change in the conformation of Aβ from a random coil to α‐helix‐ or β‐sheet‐rich structure. This structure was stable even after a 24‐h incubation at 37 °C and the aggregation of Aβ‐(1–42) was suppressed. Furthermore, the dissociation of the nanogels caused by the addition of methyl‐β‐cyclodextrin released monomeric Aβ molecules. Nanogels composed of amino‐group‐modified CHP (CHPNH2) with positive charges under physiological conditions had a greater inhibitory effect than CHP‐nanogels, suggesting the importance of electrostatic interactions between CHPNH2 and Aβ for inhibiting the formation of fibrils. In addition, CHPNH2 nanogels protected PC12 cells from Aβ toxicity.
The collapsin response mediator protein 1 (CRMP‐1) and the promyelocytic leukemia zinc finger protein (PLZF) bind to UDP‐N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase (GNE), the key enzyme of sialic acid biosynthesis
Authors: Weidemann Wenke , Stelzl Ulrich , Lisewski Ulrike , Bork Kaya , Wanker Erich E. , Hinderlich Stephan , Horstkorte Rüdiger
Published: November 2006

Sialic acids (Sia) are expressed as terminal sugars in many glycoconjugates. They are involved in a variety of cell–cell interactions and therefore play an important role during development and regeneration. UDP‐N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase (GNE) is the key enzyme in the de novo synthesis of Sia and it is a regulator of cell surface sialylation. Inactivation of GNE in mice results in early embryonic lethality. Mutations in the GNE gene are of clinical relevance in hereditary inclusion body myopathy, but these mutations do not necessarily decrease the enzymatic activity of GNE. In this study, we searched for novel function of the GNE protein beside its enzymatic function in the Sia biosynthesis. We here report the identification of novel GNE‐interacting proteins. Using a human prey matrix we identified four proteins interacting with GNE in a yeast two‐hybrid assay. For two of them, the collapsin response mediator protein 1 and the promyelocytic leukemia zinc finger protein, we could verify protein–protein interaction with GNE.
The pathway to excellence: the role of psychological characteristics in negotiating the challenges of musical development
Authors: MacNamara Áine , Holmes Patricia , Collins Dave
Published: November 2006

The pathway to excellence is turbulent and aspiring musicians must cope with the ‘ebb and flow’ of development if they are to realise their potential. With this in mind, internationally renowned musicians were interviewed in order to identify the challenges of each stage of musical development and the psychological characteristics that can enable aspiring musicians to sustain this developmental process. Results suggest that while certain psychological characteristics are salient throughout the career and facilitate continued development, others are especially important at key stages and critically at key transitions. This research satisfies more than academic interest, as findings should sensibly inform music educators about the skills and characteristics required by aspiring musicians at key stages during the learning process.
The effect of ‘sad’ and ‘happy’ background music on the interpretation of a story in 5 to 6-year-old children
Authors: Ziv Naomi , Goshen Maya
Published: November 2006

Children hear music in the background of a large variety of situations and activities. Throughout development, they acquire knowledge both about the syntactical norms of tonal music, and about the relationship between musical form and emotion. Five to six-year-old children heard a story, with a background ‘happy’, ‘sad’ or no melody. Results show that background music affected children's interpretation of the story: ‘happy’ background music led to positive interpretations, whereas ‘sad’ background music led to more negative interpretations of the story. The effect of ‘happy’ music was stronger than that of ‘sad’ music. Implications for education are discussed.
Tradition, authenticity and context: the case for a dynamic approach
Authors: Schippers Huib
Published: November 2006

The encounter – and sometimes confrontation – of music with various cultural backgrounds challenges many preconceptions and prejudices on music making and learning. The rise of what is now often called ‘world music’ has not only brought new sound worlds to Western ears, but digs deep into existing systems of belief. In discussing both Western classical and world music, concepts such as tradition, authenticity and context are often used with firm conviction. On closer examination, however, they are applied with ambiguous or even contradictory meaning. A cross-cultural exploration of these concepts reveals that they are not nearly as clear, stable and value-free as they may appear. A more dynamic interpretation of these terms is needed to understand contemporary realities of music making and education at all levels, and to enable teachers to apply these concepts to everyday studio and classroom practices.
General versus locoregional anesthesia in carotid surgery: A prospective randomised trial
Authors: Kasprzak  , Altmeppen  , Angerer  , Mann  , Mackh  , Töpel
Published: November 2006

Background: To evaluate the influence of anesthetic technique on perioperative neurological and cardiopulmonary complication rates in patients undergoing carotid endarterectomy. Patients and methods: 186 patients with symptomatic internal carotid artery (ICA) stenosis > 70% or asymptomatic ICA stenosis > 80% were prospectively randomized for either locoregional (LA) or general anesthesia (GA). Results: Neurological complication rates were similar in both groups (GA 2% vs. LA 2%). Cardiopulmonary complication rates were not significantly different (GA 4% vs LA 1%).There were no stroke-related deaths, but one patient from the GA group died from severe postoperative pneumonia. Thus, a significant difference in combined stroke / cardiopulmonary related death between the two groups (GA 1% vs LA 0%) could not be found. However, perioperative cardiopulmonary monitoring showed that significantly more patients operated under general anesthesia had hypertensive events, with systolic blood pressure values greater than 180 mmHg on postoperative day one. There were no differences in the number of postoperatively hypotensive episodes (systolic blood pressure values < 100 mmHg) between the two groups. Conclusions: Significant differences in the perioperative neurological and cardiopulmonary complication rates between general and locoregional anesthesia in patients undergoing carotid endarterectomy could not be observed.
Minas de Riotinto (south Spain) forest fire: Burned area assessment and fire severity mapping using Landsat 5‐TM, Envisat‐MERIS, and Terra‐MODIS postfire images
Authors: Roldán‐Zamarrón A. , Merino‐de‐Miguel S. , González‐Alonso F. , García‐Gigorro S. , Cuevas J. M.
Published: November 2006

This analysis concerns an estimation of burned area and fire severity levels in an area affected by a large wildfire that took place in the south of Spain in July 2004. Fire severity is defined in this work as the impact of fire on the vegetation. The objective was to find an efficient method for quick fire severity mapping based on remote sensing techniques that can be useful for postfire forest management. Several methods for image analysis (Linear Spectral Unmixing, Matched Filtering and Normalized Burn Ratio Index) were applied to postfire Landsat 5‐TM, Envisat‐MERIS, and Terra‐MODIS images. Maps depicting fire severity of three levels of an acceptable reliability were obtained using a small amount of field data and following a simple method of processing. Linear spectral unmixing produced the best classifications for MERIS and MODIS images, while the matched filtering technique produced the most accurate classification for the TM image. These preliminary results show that short‐term fire severity maps can be obtained by means of high‐ to medium‐resolution postfire remote sensing data, in order to evaluate the situation after a forest fire and plan forest restoration works.
Source location of the wedge‐like dispersed ring current in the morning sector during a substorm
Authors: Yamauchi M. , Brandt P. C. , Ebihara Y. , Dandouras I. , Nilsson H. , Lundin R. , Rème H. , Vallat C. , Lindquvist P.‐A. , Balogh A. , Daly P. W.
Published: November 2006

Source of wedge‐like dispersed sub‐keV ring current ions (wedge‐like structure) is investigated using Cluster CIS data. Statistics from nearly 550 traversals show that the wedge‐like structure with upper energy extending to ordinary energy of ring current is found mostly in the morning sector whereas those limited within sub‐keV range are found mostly in the noon‐to‐afternoon sector. The former is most likely the original form of the latter. With this knowledge, the Cluster traversal on 21 October 2001 turned out to be a unique observation that reveals the formation of the wedge‐like structure. Spacecraft 1 and 4 detected a wedge‐like structure of 0.1 ∼ 10 keV protons at 2350 UT, while spacecraft 3 did not detect it 10 min before in the same magnetic flux tube. With the observed electric field of less than 3 mV/m, this fact indicates that the dispersion started within half an hour. Pitch angle distributions of the wedge‐like structure is in most cases double conic‐like butterfly distributions, but the wedge‐like dispersed oxygen ions during the 21 October 2001 event flow mainly from one direction (from Northern Hemisphere) without a loss cone. With its characteristic energy of 0.05 ∼ 0.3 keV, these oxygen ions originate from the Northern Hemisphere about 20 ∼ 30 min before the observation. Both the dispersion analysis and the oxygen ion tracing suggest that the observed wedge‐like structure is formed in the late morning sector during the latest substorm that started at 2310 UT. Possible mechanisms of the morning source are discussed.
Dependence of ring current asymmetry on storm phase
Authors: Weygand James M. , McPherron Robert L.
Published: November 2006

The currents that cause magnetic storms are usually characterized by the hourly Dst and Asym indices. It is observed and expected physically that the ring current is asymmetric during the main phase of a magnetic storm and becomes symmetric in the recovery phase. We report work utilizing 1‐min resolution Sym‐H* and Asym‐H to study the time development of these currents. As an index of the degree of ring current symmetry we use the ratio (‐Sym‐H/Asym‐H). We show that this index does not behave as expected. Corrections for solar wind dynamic pressure do not change this behavior. We find that the ring current is always asymmetric. Using ∼160 magnetic storms, we have determined the median response of these indices as a function of time relative to the time of minimum Sym‐H. We find that both indices appear to contain offsets. Sym‐H* appears to be −19.7 nT too low, and Asym‐H appears to be 18.8 nT too high. We also find that in the main phase both median curves can be represented by a single exponential with nearly identical growth times: ∼6 hours. In the recovery phase double exponentials are needed to obtain reasonable fits to the median curves. The time constants for Sym‐H* (5.25 and 64.3 hours) are nearly twice as long as those for Asym‐H (2.2 and 20.9 hours). If we subtract the calculated offsets from the measured indices, we obtain a corrected ratio that behaves as expected. In the main phase the ratio is close to 1.0, implying equal Sym‐H* and Asym‐H, i.e., that either the two currents grow together or that both ground disturbances are caused by the same current. In the recovery phase the ratio increases continuously until both corrected indices approach zero and the ratio becomes meaningless. This is the expected behavior with the main phase current system being converted to a symmetric ring as the ring current decays.
Magnetic memory and coupling between spin‐canted and defect magnetism in hematite
Authors: Özdemir Özden , Dunlop David J.
Published: November 2006

Saturation isothermal remanent magnetization (SIRM) has been studied on submicron hematite powders with grain sizes between 0.12 and 0.52 μm and on 2 to 5 mm natural hematite single crystals before and after zero‐field cycling through the Morin transition (TM). SIRM cooling and warming curves for single‐domain (SD) crystals are similar to those of multidomain (MD) hematites. Both have similar remanence losses at TM (97–98% of the original SIRM), a similar defect moment below TM (2–3% of initial SIRM), and similar memory (30–40% of initial SIRM). Regardless of grain size, higher SIRM memory ratios are associated with higher defect moments below TM. In SD and MD hematites alike, room temperature magnetic memory seems to be an amplification of residual weak ferromagnetism that persists even at very low temperatures, much below TM. Applying a strong field to initially demagnetized SD and MD hematites at 20 K produced a substantial SIRM, which spontaneously increased by a factor 10–28 upon crossing the transition at TM. These observations imply that some spins do not participate in the general rotation from the ferromagnetic c plane to the antiferromagnetic c axis below TM. The defect moment of these spins serves to restore preferred directions of spins and ferromagnetic domains during zero‐field warming through the Morin transition and is thus responsible for the memory phenomenon. The existence of a weak ferromagnetic moment in antiferromagnetic hematite below TM is also indicated by colloid patterns observed by Gallon. We propose that the mechanism of memory is clusters of spins pinned magnetoelastically by lattice defects. These spins rotate only partially out of the basal plane during cooling through TM. Some basal plane anisotropy, also magnetoelastic in origin, must remain below TM in order to explain the existence of low‐temperature SIRM and also to guide spin nuclei into preferred orientations above TM on rewarming through the transition in zero field.
Humidification factors from laboratory studies of fresh smoke from biomass fuels
Authors: Day D. E. , Hand J. L. , Carrico C. M. , Engling Guenter , Malm W. C.
Published: November 2006

Measurements of smoke aerosol humidification factors were performed in a laboratory for different biomass fuel types and burn conditions. Two nephelometers simultaneously measured dry and humidified light scattering coefficients (bsp(dry) and bsp(RH), respectively), providing the first observations of the temporal evolution of the humidification factor (f(RH) = bsp(RH)/bsp(dry)) for fresh (minutes‐old) smoke. Hygroscopic characteristics of the smoke aerosols varied with fuel type and fire conditions, with the mean f(RH) ranging from 1.01 to 1.95 for fresh minutes‐old smoke for the relative humidity (RH) range of 70–94%. These f(RH) values exhibited temporal variability, with some fuels alternating from hygroscopic to nonhygroscopic within minutes. Humidograms were also obtained, demonstrating that smoke from different fuels begins to take up water at different RH values. Humidification factors for hour‐old smoke ranged from 1.10 to 1.51 for RH > 90%. Finally, light‐absorbing carbon mass measured with a multiwavelength aethalometer demonstrated different spectral responses as a function of fuel type. These laboratory experiments demonstrate the complexity of smoke hygroscopicity from young fires and are essential for understanding the radiative effects of biomass burning in the ambient atmosphere.
Moving solvated electrons with light: Nonadiabatic mixed quantum/classical molecular dynamics simulations of the relocalization of photoexcited solvated electrons in tetrahydrofuran (THF)
Authors: Bedard-Hearn Michael J. , Larsen Ross E. , Schwartz Benjamin J.
Published: November 2006

Motivated by recent ultrafast spectroscopic experiments [Martini et al., Science 293, 462 (2001)], which suggest that photoexcited solvated electrons in tetrahydrofuran (THF) can relocalize (that is, return to equilibrium in solvent cavities far from where they started), we performed a series of nonequilibrium, nonadiabatic, mixed quantum/classical molecular dynamics simulations that mimic one-photon excitation of the THF-solvated electron. We find that as photoexcited THF-solvated electrons relax to their ground states either by continuous mixing from the excited state or via nonadiabatic transitions, ∼30% of them relocalize into cavities that can be over 1nm away from where they originated, in close agreement with the experiments. A detailed investigation shows that the ability of excited THF-solvated electrons to undergo photoinduced relocalization stems from the existence of preexisting cavity traps that are an intrinsic part of the structure of liquid THF. This explains why solvated electrons can undergo photoinduced relocalization in solvents like THF but not in solvents like water, which lack the preexisting traps necessary to stabilize the excited electron in other places in the fluid. We also find that even when they do not ultimately relocalize, photoexcited solvated electrons in THF temporarily visit other sites in the fluid, explaining why the photoexcitation of THF-solvated electrons is so efficient at promoting recombination with nearby scavengers. Overall, our study shows that the defining characteristic of a liquid that permits the photoassisted relocalization of solvated electrons is the existence of nascent cavities that are attractive to an excess electron; we propose that other such liquids can be found from classical computer simulations or neutron diffraction experiments.
Particle emission from tantalum plasma produced by 532nm laser pulse ablation
Authors: Torrisi L. , Caridi F. , Picciotto A. , Margarone D. , Borrielli A.
Published: November 2006

A study of visible laser ablation of tantalum in vacuum by using 3ns Nd:YAG laser radiation at high pulse energy is reported. Nanosecond pulsed ablation, at an intensity on the order of 109W∕cm2, produces high nonisotropic emission of neutrals and ionic species. Mass quadrupole spectrometry, coupled to electrostatic ion deflection, allows estimation of the energy distributions of the emitted species within the plume as a function of the incident laser energy. Neutrals show typical Boltzmann distributions while ions show Coulomb-Boltzmann-shifted distributions depending on their charge state. Surface profiles of the craters and microscopy investigations permitted to study the ablation threshold, ablation yields, and deposition rates of thin films on silicon substrates. The multicomponent structure of the plume emission is rationalized in terms of charge state, ion and neutral equivalent temperatures, and plasma density. A special regard is given to the ion acceleration process occurring inside the plasma due to the high electrical field generated at the nonequilibrium plasma conditions. The angular distributions of the neutral and ion species are also presented and discussed.
The effect of interfacial layer properties on the performance of Hf-based gate stack devices
Authors: Bersuker G. , Park C. S. , Barnett J. , Lysaght P. S. , Kirsch P. D. , Young C. D. , Choi R. , Lee B. H. , Foran B. , van Benthem K. , Pennycook S. J. , Lenahan P. M. , Ryan J. T.
Published: November 2006

The influence of Hf-based dielectrics on the underlying SiO2 interfacial layer (IL) in high-k gate stacks is investigated. An increase in the IL dielectric constant, which correlates to an increase of the positive fixed charge density in the IL, is found to depend on the starting, pre-high-k deposition thickness of the IL. Electron energy-loss spectroscopy and electron spin resonance spectra exhibit signatures of the high-k-induced oxygen deficiency in the IL consistent with the electrical data. It is concluded that high temperature processing generates oxygen vacancies in the IL responsible for the observed trend in transistor performance.
Integrated measurement system for simultaneous functional magnetic resonance imaging and diffuse optical tomography in human brain mapping
Authors: Zhang Xiaofeng , Toronov Vladislav Y. , Webb Andrew G.
Published: November 2006

An integrated measurement system has been developed for performing simultaneous functional magnetic resonance imaging (fMRI) and diffuse optical tomography (DOT) for human brain mapping experiments. The components of this system consist of a MRI-compatible multioverlapping-channel near-infrared (NIR) optical probe, techniques for accurate and reliable coregistration of optical and fMRI results, and an optical image reconstruction algorithm with structural and physiological constraints derived from the MRI data. The optical probe is fully MRI compatible in that it produces negligible MR image distortion and does not require any modification to the MRI scanner or data acquisition protocols. This probe can be attached to virtually any part of the head without imposing limits on optical data acquisition. Coregistration of images from fMRI and optical measurements is achieved by localizing the positions of the optical fibers using MRI markers. Human studies show successful implementation of the entire system.
Electronic structure of zigzag carbon nanotubes
Authors: Tishchenko S. V.
Published: November 2006

The method of zero-range potentials is used to investigate the band structure of the one-electron spectrum of zigzag single-walled carbon nanotubes. It is shown that the formation of a narrow forbidden band in (3N,0) zigzag nanotubes is due to the influence of the curvature of their walls on the one-electron spectrum of the π electrons. Expressions are obtained for the widths of the forbidden bands (band gaps) and effective masses of (3N,0), (3N−1,0), and (3N+1,0) nanotubes as functions of their diameter.
Orientation dependence of ferroelectric and piezoelectric properties of Bi3.15Nd0.85Ti3O12 thin films on Pt(100)∕TiO2∕SiO2∕Si substrates
Authors: Hu G. D.
Published: November 2006

Bi 3.15 Nd 0.85 Ti 3 O 12 (BNT0.85) thin films with (100) [α(100)=87.8%], (117) [α(117)=77.1%], and (001) [α(001)=98.8%] preferred orientations were deposited on Pt(100)∕TiO2∕SiO2∕Si substrates using a metal organic decomposition process. The remanent polarization of (100)-predominant BNT0.85 film is about 50% and three times larger than those of (117)-preferred and (001)-oriented films, respectively, suggesting that the major polarization vector of BNT0.85 is close to the a axis rather than the c axis. This result can be further demonstrated by the piezoelectric measurements using an atomic force microscope in the piezoresponse mode.
Electroosmotic flow and mixing in microchannels with the lattice Boltzmann method
Authors: Tang G. H. , Li Zhuo , Wang J. K. , He Y. L. , Tao W. Q.
Published: November 2006

Understanding the electroosmotic flow in microchannels is of both fundamental and practical significance for the design and optimization of various microfluidic devices to control fluid motion. In this paper, a lattice Boltzmann equation, which recovers the nonlinear Poisson-Boltzmann equation, is used to solve the electric potential distribution in the electrolytes, and another lattice Boltzmann equation, which recovers the Navier-Stokes equation including the external force term, is used to solve the velocity fields. The method is validated by the electric potential distribution in the electrolytes and the pressure driven pulsating flow. Steady-state and pulsating electroosmotic flows in two-dimensional parallel uniform and nonuniform charged microchannels are studied with this lattice Boltzmann method. The simulation results show that the heterogeneous surface potential distribution and the electroosmotic pulsating flow can induce chaotic advection and thus enhance the mixing in microfluidic systems efficiently.
Phase transitions in DNA-linked nanoparticle assemblies: A decorated-lattice model
Authors: Talanquer V.
Published: November 2006

We use decorated-lattice models to explore the phase behavior of two types of DNA-linked colloidal mixtures: systems with identical nanoparticles functionalized with two different DNA strands (mixture Aab) and mixtures involving two types of particles each one functionalized with a different DNA strand (mixture Aa-Ab). The model allows us to derive the properties of the mixtures from the well-known behavior of underlying spin-n Ising models with temperature and activity dependent effective interactions. The predicted evolution of the dissolution profiles for the colloidal assemblies as a function of temperature and number of single DNA strands on a nanoparticle M is in qualitative agreement with that observed in real systems. According to our model, the temperature at which the assemblies dissolve can be expected to increase with increasing M only for concentrations of colloids below a certain threshold. For more concentrated solutions, the dissolution temperature is a decreasing function of M. Linker-mediated interactions between Aa and Ab particles in the Aa-Ab mixture render the phase separation involving disordered aggregates metastable with respect to a phase transition between a solvent-rich and an ordered phase. The stability of the DNA-linked assembly is enhanced by the ordering of the colloidal network and the ordered aggregates dissolve at higher temperatures. Our results may explain the contrasting evolution of the dissolution temperatures with increasing probe size in Aab and Aa-Ab mixtures as observed experimentally.
A new local density functional for main-group thermochemistry, transition metal bonding, thermochemical kinetics, and noncovalent interactions
Authors: Zhao Yan , Truhlar Donald G.
Published: November 2006

We present a new local density functional, called M06-L, for main-group and transition element thermochemistry, thermochemical kinetics, and noncovalent interactions. The functional is designed to capture the main dependence of the exchange-correlation energy on local spin density, spin density gradient, and spin kinetic energy density, and it is parametrized to satisfy the uniform-electron-gas limit and to have good performance for both main-group chemistry and transition metal chemistry. The M06-L functional and 14 other functionals have been comparatively assessed against 22 energetic databases. Among the tested functionals, which include the popular B3LYP, BLYP, and BP86 functionals as well as our previous M05 functional, the M06-L functional gives the best overall performance for a combination of main-group thermochemistry, thermochemical kinetics, and organometallic, inorganometallic, biological, and noncovalent interactions. It also does very well for predicting geometries and vibrational frequencies. Because of the computational advantages of local functionals, the present functional should be very useful for many applications in chemistry, especially for simulations on moderate-sized and large systems and when long time scales must be addressed.
Impurity transport in ITER-like plasmas
Authors: Fülöp T. , Weiland J.
Published: November 2006

Neoclassical impurity transport is compared with transport calculated from the reactive drift wave model of turbulent transport for an ITER-like [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)] scenario. The turbulent transport is inward for both main ions and impurities, but the impurity ion inward transport is much weaker than the main ion inward transport. The neoclassical impurity transport is outward because of temperature screening. The total impurity transport, determined by a balance between turbulent and neoclassical transport, depends sensitively on the charge number of the impurity and the ratio of the ion density and temperature scale lengths, ηi.
The inverse problem for six-dimensional codimension two nilradical lie algebras
Authors: Rawashdeh M. , Thompson G.
Published: November 2006

Ado’s theorem asserts that every real Lie Algebra g of dimension n has a faithful representation as a subalgebra of gl(p,R) for some p. The theorem offers no practical information about the size of p in relation to n and in principle p may be very large compared to n. This article is concerned with finding representations for a certain class of six-dimensional Lie algebras, specifically, real, indecomposable algebras that have a codimension two nilradical. These algebras were classified by Turkowski and comprise of 40 cases, some of which contain up to four parameters. Linear representations are found for each algebra in these classes: More precisely, a matrix Lie group is given whose Lie algebra corresponds to each algebra in Turkowski’s list and can be found by differentiating and evaluating at the identity element of the group. In addition a basis for the right-invariant vector fields that are dual to the Maurer-Cartan forms are given thereby providing an effective realization of Lie’s third theorem. The geodesic spray of the canonical symmetric connection for each of the 40 linear Lie group G is given. Thereafter the inverse problem of the calculus of variations for each of the geodesic sprays is investigated. In all cases it is determined whether the spray is of Euler-Lagrange type and in the affirmative case at least one concrete Lagrangian is written down. In none of the cases is there a Lagrangian of metric type.
The local and intermediate range structures of the five amorphous ices at 80K and ambient pressure: A Faber-Ziman and Bhatia-Thornton analysis
Authors: Bowron D. T. , Finney J. L. , Hallbrucker A. , Kohl I. , Loerting T. , Mayer E. , Soper A. K.
Published: November 2006

Using isotope substitution neutron scattering data, we present a detailed structural analysis of the short and intermediate range structures of the five known forms of amorphous ice. Two of the lower density forms—amorphous solid water and hyperquenched glassy water—have a structure very similar to each other and to low density amorphous ice, a structure which closely resembles a disordered, tetrahedrally coordinated, fully hydrogen bonded network. High density and very high density amorphous ices retain this tetrahedral organization at short range, but show significant differences beyond about 3.1Å from a typical water oxygen. The first diffraction peak in all structures is seen to be solely a function of the intermolecular organization. The short range connectivity in the two higher density forms is more homogeneous, while the hydrogen site disorder in these forms is greater. The low Q behavior of the structure factors indicates no significant density or concentration fluctuations over the length scale probed. We conclude that these three latter forms of ice are structurally distinct. Finally, the x-ray structure factors for all five amorphous systems are calculated for comparison with other studies.
Temperature-dependent bimodal size evolution of InAs quantum dots on vicinal GaAs(100) substrates
Authors: Liang S. , Zhu H. L. , Wang W.
Published: November 2006

The effects of growth temperature on the bimodal size distribution of InAs quantum dots on vicinal GaAs(100) substrates grown by metal organic chemical vapor deposition are studied. An abnormal trend of the bimodal size evolution on temperature is observed. With the increase of the growth temperature, while the density of the large dots decreases continually, that of the small dots first grows larger when temperature was below 520°C, and then exhibits a sudden decrease at 535°C. The trend is explained by taking into account the presence of multiatomic steps on the substrates. Photoluminescence (PL) studies show that quantum dots on vicinal substrates have a narrower PL linewidth, a longer emission wavelength, and a larger PL intensity than those of the dots with exact substrates.
Positron lifetimes of polycrystalline metals: A positron source correction study
Authors: McGuire S. , Keeble D. J.
Published: November 2006

Positron lifetime measurements have been made on a series of polycrystalline metals with atomic numbers varying from 13 to 82, using positron sources deposited on Ni, Al, and Kapton support foils. Bulk positron lifetimes for Al, Ni, Zr, In, and Pb are reported. The results support previous assignments of monovacancy lifetimes for Ag, Ta, and Pb. A method for obtaining the extrinsic positron lifetime components due to the radionuclide source is developed, and the experimentally determined source lifetime components are studied as a function of the sample atomic number. The Z dependence of the source foil component intensities were fitted using known expressions for positron backscatter and multiple scattering within the source sample geometry, neglecting backscatter from the foil. The foil material positron absorption coefficients were obtained and found to be comparable with the results of previous transmission experiments.
Enhanced field emission properties of thin-multiwalled carbon nanotubes: Role of SiOx coating
Authors: Moon J. S. , Alegaonkar P. S. , Han J. H. , Lee T. Y. , Yoo J. B. , Kim J. M.
Published: November 2006

We report the fabrication, characterization, and field emission properties of (silicon oxide) SiOx coated thin-multiwalled carbon nanotubes (t-MWNTs). The coated t-MWNTs show improved field emission behavior. Initially, raw t-MWNTs (diameter ∼5–8nm) were functionalized by acid treatment. Using spin on glass as a Si precursor, SiOx was coated on the nanotubes by routine chemical methods. The coated samples were characterized by high resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) techniques. The HRTEM results show that the local thickness of the coating varies from ∼1to2nm. The FTIR investigations show the formation of nanophases, such as Si–C, Si–O–C, and intercalated Si–O, at the coating/nanotube interface. The TGA reveals that the coating prevents the high-temperature oxidation and degradation of the nanotubes. The field emission characteristics of the coated, functionalized, and raw nanotubes show that the turn-on fields and current density are improved for the coated nanotubes. This improvement was attributed to the lowering of the work function and dielectric constant of the C∕SiOx interface layer and the localization of the density of states close to the Fermi energy for the coated nanotubes. The analysis of the emission stability spectra shows that the coated nanotubes have a more favorable lifetime. The observed enhancement was attributed to the protection of the nanotubes from the reactive sputter etching during the field emission process. The details of the analysis are presented.
Using neural networks to represent potential surfaces as sums of products
Authors: Manzhos Sergei , Carrington Tucker
Published: November 2006

By using exponential activation functions with a neural network (NN) method we show that it is possible to fit potentials to a sum-of-products form. The sum-of-products form is desirable because it reduces the cost of doing the quadratures required for quantum dynamics calculations. It also greatly facilitates the use of the multiconfiguration time dependent Hartree method. Unlike potfit product representation algorithm, the new NN approach does not require using a grid of points. It also produces sum-of-products potentials with fewer terms. As the number of dimensions is increased, we expect the advantages of the exponential NN idea to become more significant.
Surface contamination effects on resistance of gold nanowires
Authors: Lilley Carmen M. , Huang Qiaojian
Published: November 2006

Gold nanowires were patterned with e-beam lithography and fabricated with a gold film deposited by e-beam evaporation. The resistances of these wires were measured and found to be nonlinear with respect to surface area/volume. With x-ray photoelectron spectroscopy analysis, carbon and oxygen contaminants in the forms of C, C–O–C, and CO were found adsorbed on the gold surface. This contamination adsorbed on the surface may lead to increased resistance of nanowires.