bluuebunny/crossref_metadata_2025 huggingface dataset:
Dietary practices and nutritional status of 0–24-month-old children from Brazilian Amazonia
Authors: Castro TG , Baraldi LG , Muniz PT , Cardoso MA
Published: March 2009

Objective

To assess the nutritional status and dietary practices of 0–24-month-old children living in Brazilian Amazonia.

Design

Cross-sectional study. Information on children’s dietary intakes was obtained from diet history data. Weight and length were measured for anthropometric evaluation. Fe status was assessed using fasting venous blood samples; Hb, serum ferritin and soluble transferrin receptor concentrations were measured.

Setting

The towns of Assis Brasil and Acrelândia in the state of Acre, north-west Brazil.

Subjects

A total of sixty-nine randomly selected 0–24-month-old children.

Results

Of these children, 40·3 % were anaemic, 63·1 % were Fe-deficient, 28·1 % had Fe-deficiency anaemia and 11·6 % were stunted. Breast-feeding was initiated by 97·1 % of mothers, followed by early feeding with complementary foods. The dietary pattern reflected a high intake of carbohydrate-rich foods and cow’s milk, with irregular intakes of fruit, vegetables and meat. All infants and 92·3 % of toddlers were at risk of inadequate Fe intakes. Fe from animal foods contributed on average 0·5 % and 14·3 % to total dietary Fe intake among infants and toddlers, respectively.

Conclusions

Poor nutritional status and inadequate feeding practices in this study population reinforce the importance of exclusive breast-feeding during the first 6 months of life. Greater emphasis is required to improve the bioavailability of dietary Fe during complementary feeding practices.
Northern Hemisphere tropical cyclone activity
Authors: Maue Ryan N.
Published: March 2009

Recent historical Northern Hemisphere (NH) tropical cyclone (TC) inactivity is compared with strikingly large observed variability during the past three decades. Yearly totals of the combined active‐basin NH accumulated cyclone energy (ACE) are highly correlated with boreal spring sea‐surface temperature (SST) in the North Pacific Ocean and are representative of an evolving dual‐gyre, trans‐hemispheric correlation pattern throughout the calendar year. The observed offsetting nature of Eastern Pacific and North Atlantic basin ACE during the past three decades and a strong dependence of combined Pacific TC activity upon the El Niño‐Southern Oscillation reflect the interrelated modulation of overall NH integrated TC energy by large‐scale modes of climate variability. Thus, the quiescent period of overall integrated NH TC ACE continuing throughout 2008 is not unexpected in the context of previous periods of colder Pacific SSTs.
Solar cycle variability of Mars dayside exospheric temperatures: Model evaluation of underlying thermal balances
Authors: Bougher S. W. , McDunn T. M. , Zoldak K. A. , Forbes J. M.
Published: March 2009

The response of the Mars dayside exospheric temperatures to short and long term solar flux changes was recently established. Characterization of the relative importance of various thermospheric heating and cooling mechanisms for maintaining these Mars exospheric temperatures requires the systematic application of modern global dynamical models that capture both lower and upper atmosphere thermal and dynamical processes. Coupled Mars General Circulation Model (MGCM) plus Mars Thermospheric General Circulation Model (MTGCM) simulations are utilized for this study, closely matching conditions during Mars Global Surveyor drag measurements. Simulations confirm the major balance of EUV heating and thermal heat conduction at dayside exospheric altitudes. However, the influence of variable Martian global winds is significant and must be carefully considered when investigating the global regulation of Mars exospheric temperatures over the solar cycle and Martian seasons. Finally, the present MGCM‐MTGCM heating and cooling processes suggests that an EUV‐UV heating efficiency of 19% yields net heating in accord with MGS exospheric temperatures.
Mudslide‐caused ecosystem degradation following Wenchuan earthquake 2008
Authors: Ren Diandong , Wang Jiahu , Fu Rong , Karoly David J. , Hong Yang , Leslie Lance M. , Fu Congbin , Huang Gang
Published: March 2009

We have applied a scalable and extensible geo‐fluid model (SEGMENT) that considers soil mechanics, vegetation transpiration and root mechanical reinforcement, and hydrological processes to simulate two dimensional maps of the landslides occurrence following the 2008 Wenchuan earthquake. Modeled locations and areas generally agree with observations. The model suggests that the potential energy of earth was lowered by 1.52 × 1015 J by these landslides. With this, the vegetation destroyed transfer ∼235 Tg C to the dead respiring pool and transforms 5.54 × 10−2 Tg N into unavailable sediments pools and the atmosphere. The cumulative CO2 release to the atmosphere over the coming decades is comparable to that caused by hurricane Katrina 2005 (∼105 Tg) and equivalent to ∼2% of current annual carbon emissions from global fossil fuel combustion. The nitrogen loss is twice as much as that released by the 2007 California Fire (∼2.5 × 10−2 Tg). A significant proportion of the nitrogen loss (14%) is in the form of nitrous oxide, which can affect the atmospheric ozone layer.
Baseline uncertainties in biomass burning emission models resulting from spatial error in satellite active fire location data
Authors: Hyer Edward J. , Reid Jeffrey S.
Published: March 2009

Global and regional‐scale estimates of biomass burning emissions rely on satellite data products with varying spatial resolution. In heterogeneous landscapes, moderate‐resolution fire location data may not capture fine‐scale variation in fuel type, leading to both random and systematic error in emissions. Using 120‐meter land cover data for the Amazon basin, we estimate the probability of accurate classification of individual fires at 88% for MODIS and 74% for GOES. Classification error limits the ability of emission models to reproduce patterns of emissions, and can only be reduced by innovative use of current satellite data or ancillary data. Emissions biases caused by spatial error vary with regional distribution of fire types. For regional‐scale studies in the Amazon Basin, we estimate emissions biases of +3% to +19% for MODIS and +6% to +39% for GOES. The difference between these two systems is an important consideration for multi‐sensor fire applications.
Solar cycle minimum measurements of the solar extreme ultraviolet spectral irradiance on 14 April 2008
Authors: Chamberlin Phillip C. , Woods Thomas N. , Crotser David A. , Eparvier Francis G. , Hock Rachel A. , Woodraska Donald L.
Published: March 2009

NASA sounding rocket 36.240 was launched from White Sands Missile Range in New Mexico on 14 April 2008. The primary instrument in this payload was the prototype extreme ultraviolet (EUV) Variability Experiment (EVE). The Multiple EUV Grating Spectrograph (MEGS) channels of EVE measure the solar irradiance from 6 to 106 nm at 0.1 nm spectral resolution. While the main purpose of this rocket flight is to provide the fifth underflight calibration for the Solar EUV Experiment (SEE), the importance of this rocket observation is the first observation of the solar EUV irradiance at high spectral resolution during solar cycle minimum conditions. The higher spectral resolution measurements will help resolve outstanding concerns about the previous solar soft X‐ray irradiance results made with broadband photometers shortward of 27 nm, and the measurements provide the most accurate reference for the solar cycle minimum as part of the international Whole Heliosphere Interval (WHI) campaign.
Evidence for wave coupling in type III emissions
Authors: Henri P. , Briand C. , Mangeney A. , Bale S. D. , Califano F. , Goetz K. , Kaiser M.
Published: March 2009

Using new capabilities of waveform analyses provided by the S/WAVES instruments onboard the two STEREO spacecraft, we present for the first time a complete set of direct evidence for three‐wave coupling occurring during a type III emission and involving two Langmuir waves and an ion acoustic wave. Information on the Doppler‐shifted frequencies and especially the phases of the waves are used in order to check first the conservation of momentum and energy, through Fourier analyses, and second the phase locking between the waves, through bicoherence analyses. Wavelet analyses allow us to resolve for the first time the coupling regions, in which spatial length is estimated to be 18 ± 5 km. The wave packets travel at comparable speed, and the characteristic available interaction time is about 1 s. Interpretations of the phase coupling and evaluation of the growth rate of the waves tend to favor the parametric decay, at least in the observational events considered in this work.
Lithospheric mantle duplex beneath the central Mojave Desert revealed by xenoliths from Dish Hill, California
Authors: Luffi Peter , Saleeby Jason B. , Lee Cin‐Ty A. , Ducea Mihai N.
Published: March 2009

Low‐angle subduction of oceanic lithosphere may be an important process in modifying continental lithosphere. A classic example is the underthrusting of the Farallon plate beneath North America during the Laramide orogeny. To assess the relevance of this process to the evolution and composition of continental lithosphere, the mantle stratigraphy beneath the Mojave Desert was constrained using ultramafic xenoliths hosted in Plio‐Pleistocene cinder cones. Whole‐rock chemistry, clinopyroxene trace element and Nd isotope data, in combination with geothermometry and surface heat flow, indicate kilometer‐scale compositional layering. The shallow parts are depleted in radiogenic Nd (ɛNd = −13 to −6.4) and are interpreted to be ancient continental mantle that escaped tectonic erosion by low‐angle subduction. The deeper samples are enriched in radiogenic Nd (ɛNd = +5.7 to +16.1) and reveal two superposed mantle slices of recent origin. Within each slice, compositions range from fertile lherzolites at the top to harzburgites at the bottom: the latter formed by 25–28% low‐pressure melt depletion and the former formed by refertilization of harzburgites by mid‐ocean‐ridge‐basalt‐like liquids. The superposition and internal compositional zonation of the slices preclude recent fertilization by Cenozoic extension‐related magmas. The above observations imply that the lower Mojavian lithosphere represents tectonically subcreted and imbricated lithosphere having an oceanic protolith. If so, the lherzolitic domains may be related to melting and refertilization beneath mid‐ocean ridges. The present Mojavian lithosphere is thus a composite of a shallow section of the original North American lithosphere underlain by Farallon oceanic lithosphere accreted during low‐angle subduction.
The European heat wave 2003: Early indicators from multisensoral microwave remote sensing?
Authors: Loew Alexander , Holmes Thomas , de Jeu Richard
Published: March 2009

An extreme heat wave affected large parts of Europe in 2003 with severe socioeconomic impacts. The extreme warm weather conditions lasted over a couple of months with positive temperature anomalies of 5°C for large parts of Europe. Simulations of the event using regional climate models revealed that a pronounced precipitation deficit in the beginning of the year, together with an early onset of the vegetation, resulted in a severe deficit of the soil water content. This amplified the course of the heat wave due to an increasing sensible heat flux from the land surface. The monitoring of temporal and spatial dynamics of soil water content can be accomplished using remote‐sensing‐based techniques. The present paper addresses the question whether there have been early indicators for the low soil water content using either physically based land surface modeling or remote‐sensing‐based monitoring techniques. The course of the spring surface soil moisture evolution is investigated using observations from two different microwave remote sensing sensors. An intercomparison of the high‐resolution data from the European ENVISAT satellite and coarse resolution data from the AMSR‐E mission is made. Remote‐sensing‐derived soil moisture products are compared against the results from a deterministic land surface model. The model enables to relate the year 2003 anomalies to a long‐term (30 years) climatology. The year 2003 remote sensing derived soil moisture dynamics is compared against a multiyear climatology. The results reveal a negative surface soil moisture anomaly in 2003. The results indicate that there was in general potential to monitor the spatial and temporal dimensions of the low surface soil water content early in 2003 using remote sensing techniques. Both remote sensing data sets indicate a consistent soil moisture decrease in early 2003. A good agreement between the observed surface soil moisture and soil moisture simulations from a land surface process model was found. An outlook to the use of remote‐sensing‐based soil moisture estimates for large‐scale monitoring of surface soil moisture trends is given.
Low‐frequency electromagnetic modeling of conductive obstacles buried in subsoil as coupled ellipsoids
Authors: Bréard Arnaud , Perrusson Gaële , Lesselier Dominique
Published: March 2009

The electromagnetic characterization of one or more conductive obstacles buried in a conductive subsoil from low‐frequency data (induction regime) is expected to benefit from a fast yet fairly accurate solution of the direct problem associated to it. Here, an approximate model is proposed to that effect. It is based on the localized nonlinear approximation, coupling between obstacles (whenever two or more) being approached via the Lax‐Foldy theory of multiple diffraction. The obstacles are modeled as generic ellipsoids, with spheres as the limit case. The exact primary field due to an electrical loop (or a magnetic dipole) is calculated, and its low‐frequency expansion is introduced. A semianalytical solution of the direct problem is developed from the exact field formulation, analytical solutions being proposed in the most simple cases of either sources or configurations. The model is validated by comparison with numerical experimentations carried out by tools available from the CIVA platform and by the FEKO code. Limits of the model are explored also, notably about the retrieval of the pertinent geometric and electric parameters of an ellipsoid buried in a half‐space from sparse data collected above it.
Direct Evidence for Central Proinflammatory Mechanisms in Rats with Experimental Acute Liver Failure: Protective Effect of Hypothermia
Authors: Jiang Wenlei , Desjardins Paul , Butterworth Roger F
Published: March 2009

It has been proposed that proinflammatory mechanisms are involved in the pathogenesis of brain edema in acute liver failure (ALF). The aim of this study was to assess the contribution of cerebral inflammation to the neurologic complications of ALF and to assess the antiinflammatory effect of mild hypothermia. Upregulation of CD11b/c immunoreactivity, consistent with microglial activation, was observed in the brains of ALF rats at coma stages of encephalopathy. Interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) mRNAs were increased two to threefold in the brains of ALF rats compared with that in sham-operated controls. The magnitude of increased expression of proinflammatory cytokines in the brain was correlated with the progression of encephalopathy and the onset of brain edema. Significant increases in IL-1β, IL-6, and TNF-α levels were also found in the sera and cerebrospinal fluid (CSF) of these animals. Mild hypothermia delayed the onset of encephalopathy, prevented brain edema, and concomitantly attenuated plasma, brain, and CSF proinflammatory cytokines. These results show that experimental ALF leads to increases in brain production of proinflammatory cytokines, and afford the first direct evidence that central inflammatory mechanisms play a role in the pathogenesis of the cerebral complications of ALF. Antiinflammatory agents could be beneficial in the management of these complications.
Metal-Carbon Bonds in Enzymes and Cofactors
Authors: Kraeutler Bernhard , Matthews Rowena G , Thauer Rudolf K , Lindahl Paul A , Camps Juan C Fontecilla , Peters John W , Brunold Thomas , Rivera Mario , Karlin Kenneth D , Sosa-Torres Martha E , Hille Russ , Kraeutler Bernhard , Matthews Rowena G , Thauer Rudolf K , Lindahl Paul A , Camps Juan C Fontecilla , Peters John W , Brunold Thomas , Rivera Mario , Karlin Kenneth D , Sosa-Torres Martha E , Hille Russ
Published: March 2009

This title will not be available to purchase from us after 31st December 2014. Please send any queries to booksales@rsc.org

The occurrence of a wide variety of metal-carbon bonds in living organisms, ranging from bacteria to humans, is only recently recognized. Of course, the historical examples are the B12 coenzymes containing cobalt-carbon bonds, but now such bonds are also known for nickel, iron, copper, and other transition metal ions. There is no other comparable book; MILS-6, written by 17 experts, summarizes the most recent insights into this fascinating topic.
Nickel-Alkyl Bond Formation in the Active Site of Methyl-Coenzyme M Reductase
Authors: Jaun Bernhard , Thauer Rudolf K.
Published: March 2009

Methyl-coenzyme M reductase (MCR) catalyzes the methane-forming step in methanogenic archaea and most probably also the methane-oxidizing step in methanotrophic archaea. The enzyme contains coenzyme F430 as prosthetic group. F430 is a nickel porphinoid that has to be in the reduced Ni(I) state for the enzyme to be active. The presently discussed catalytic mechanisms of MCR can in principle be divided into two basic models. In one model the key intermediate features a methyl-Ni(III) species being either formed in a nucleophilic substitution reaction or in an oxidative addition reaction. In the other model first the thioether sulfur of methyl-coenzyme M binds to the Ni(I), which subsequently results in the release of the methyl group as methyl radical leaving behind a Ni(II)-sulfur bond. The experimental evidence for and against a methyl-nickel intermediate is reviewed.
Carbon Monoxide as Intrinsic Ligand to Iron in the Active Site of [Fe]-Hydrogenase
Authors: Shima Seigo , Thauer Rudolf K. , Ermler Ulrich
Published: March 2009

Structural and spectroscopic studies on [Fe]-hydrogenase revealed an active site mononuclear low spin iron coordinated by the Cys176 sulfur, two CO, and the sp2 hybridized nitrogen of a 2-pyridinol compound with back bonding properties similar to those of cyanide. Thus, [Fe]-hydrogenases are endowed with an iron-ligation pattern related to that found in the active site of [NiFe]- and [FeFe]-hydrogenases although the three hydrogenases and the enzymes involved in their posttranslational maturation have evolved independently and although CO and cyanide ligands are not found in any other metallo-enzymes. Obviously, low-spin iron complexed with thiolate(s), CO, and cyanide or a cyanide functional analogue plays an essential role in H2 activation.
The Dual Role of Heme as Cofactor and Substrate in the Biosynthesis of Carbon Monoxide
Authors: Rivera Mario , Rodríguez Juan C.
Published: March 2009

Carbon monoxide (CO) is a ubiquitous molecule in the atmosphere. The metabolism of mammalian, plastidic, and bacterial cells also produces CO as a byproduct of the catalytic cycle of heme degradation carried out by the enzyme heme oxygenase (HO). The biological role of CO spans the range from toxic to cytoprotective, depending on concentration. CO generated by the catalytic activity of HO is now known to function in several important physiological processes, including vasodilation, apoptosis, inflammation, and possibly neurotransmission. Consequently, understanding the details of the reaction that leads to the formation of this important gaseous molecule from heme has become an important aspect in the study of the chemistry and biochemistry of HO, which utilizes heme in the dual capacity of substrate and cofactor. In this chapter, a summary, and when appropriate, discussion of the current understanding of the structural, dynamical, and reactive properties that allow HO to breakdown heme into iron, biliverdin, and CO is presented.
Copper-Carbon Bonds in Mechanistic and Structural Probing of Proteins as well as in Situations where Copper is a Catalytic or Receptor Site
Authors: Lucas Heather R. , Karlin Kenneth D.
Published: March 2009

While copper-carbon bonds are well appreciated in organometallic synthetic chemistry, such occurrences are less known in biological settings. By far, the greatest incidence of copper-carbon moieties is in bioinorganic research aimed at probing copper protein active site structure and mechanism; for example, carbon monoxide (CO) binding as a surrogate for O2. Using infrared (IR) spectroscopy, CO coordination to cuprous sites has proven to be an extremely useful tool for determining active site copper ligation (e.g., donor atom number and type). The coupled (hemocyanin, tyrosinase, catechol oxidase) and non-coupled (peptidylglycine α-hydroxylating monooxygenase, dopamine β-monooxygenase) binuclear copper proteins as well as the heme-copper oxidases (HCOs) have been studied extensively via this method. In addition, environmental changes within the vicinity of the active site have been determined based on shifts in the CO stretching frequencies, such as for copper amine oxidases, nitrite reductases and again in the binuclear proteins and HCOs. In many situations, spectroscopic monitoring has provided kinetic and thermodynamic data on CuI-CO formation and CO dissociation from copper(I); recently, processes occurring on a femtosecond timescale have been reported. Copper-cyano moieties have also been useful for obtaining insights into the active site structure and mechanisms of copper-zinc superoxide dismutase, azurin, nitrous oxide reductase, and multi-copper oxidases. Cyanide is a good ligand for both copper(I) and copper(II), therefore multiple physical-spectroscopic techniques can be applied. A more obvious occurrence of a “Cu-C” moiety was recently described for a CO dehydrogenase which contains a novel molybdenum-copper catalytic site. A bacterial copper chaperone (CusF) was recently established to have a novel d-π interaction comprised of copper(I) with the arene containing side-chain of a tryptophan amino acid residue. Meanwhile, good evidence exists that a plant receptor site (ETR1) utilizes copper(I) to sense ethylene, a growth hormone. A copper olfactory receptor has also been suggested. All of the above mentioned occurrences or uses of carbon-containing substrates and/or probes are reviewed and discussed within the framework of copper proteins and other relevant systems.
The Reaction Mechanism of the Molybdenum Hydroxylase Xanthine Oxidoreductase: Evidence Against the Formation of Intermediates Having Metal-Carbon Bonds
Authors: Hille Russ
Published: March 2009

ENDOR spectra of the catalytically relevant “very rapid” Mo(V) species generated in the course of the reaction of xanthine oxidoreductase with substrate have been examined by two different groups. While the data themselves are virtually identical, the analysis has been variously interpreted as supporting or refuting the existence of a molybdenum-carbon bond in the signal-giving species. While the basis for this difference in interpretation has now been generally agreed upon – the Mo-C distance in the signal-giving species is now understood to be too long to represent a direct Mo-C bond – independent information concerning the structure of the signal-giving species is highly desirable. Recently, several X-ray crystal structures of catalytically relevant complexes of the enzyme with several substrates and inhibitors have been reported. Taken together, these structures strongly and unambiguously support the interpretation that the intermediate giving rise to the “very rapid” EPR signal, as well as the Mo(IV) intermediate that precedes it in the reaction mechanism, has product coordinated to the active site molybdenum via the catalytically introduced hydroxyl group in a simple “end-on” fashion, with no metal-carbon bond character to the complex. The manner in which product is bound and its orientation within the active site provide important clues as to the specific catalytic roles of active sites in accelerating the reaction rate.
Computational Studies of Bioorganometallic Enzymes and Cofactors
Authors: Liptak Matthew D. , Van Heuvelen Katherine M. , Brunold* Thomas C.
Published: March 2009

Because of their complex geometric and electronic structures, the active sites and cofactors of bioorganometallic enzymes, which are characterized by their metal–carbon bonds, pose a major challenge for computational chemists. However, recent progress in computer technology and theoretical chemistry, along with insights gained from mechanistic, spectroscopic, and X-ray crystallographic studies, have established an excellent foundation for the successful completion of computational studies aimed at elucidating the electronic structures and catalytic cycles of these species. This chapter briefly reviews the most popular computational approaches employed in theoretical studies of bioorganometallic species and summarizes important information obtained from computational studies of (i) the enzymatic formation and cleavage of the Co–C bond of coenzyme B12; (ii) the catalytic cycle of methyl-coenzyme M reductase and its nickel-containing cofactor F430; (iii) the polynuclear active-site clusters of the bifunctional enzyme carbon monoxide dehydrogenase/acetyl-coenzyme A synthase; and (iv) the magnetic properties of the active-site cluster of Fe-only hydrogenases.
Correlation of the energy product with evolution of the nanostructure in the Y,Dy,Nd–(Fe, Co)–B magnetic alloy
Authors: Wu Y. Q. , Tang W. , Kramer M. J. , Dennis K. W. , Oster N. , McCallum R. W. , Anderson I. E.
Published: March 2009

The devitrification behavior of nanocrystalline MRE2(Fe,Co)14B+ZrC (MRE=Nd+Y+Dy) was studied using differential scanning calorimetry (DSC), synchrotron high temperature x-ray diffraction, and analytical transmission electron microscopy (TEM) techniques. Alloy ribbons were melt spun at 25 m/s to obtain an amorphous structure. Optimum hard magnetic properties (Br=7.2 kG, Hc=12.7 kOe and (BH)max=10.8 MG Oe) were obtained in ribbons annealed at 750 °C for 15 min. A reduced annealing temperature of 638 °C and holding time from 0 to 11 min were chosen based on DSC analysis. Large changes in both microstructure and hard magnetic properties were found in a narrow window of annealing time, 4.5–6 min, resulting in a dramatic increase in energy product, remanence and coercivity: 0.96 MG Oe, 5.2 kG, 2.7 kOe to 5.7 MG Oe, 7.2 kG, 8.5 kOe for (BH)max, Br and Hc, respectively. Energy dispersive x-ray spectroscopy and energy filtered TEM analyses indicate that Zr- and C-rich particles (∼5 nm) and thin grain boundary layers (1–2 nm thick) are formed surrounding 2-14-1 hard phase grains when the annealing time is over 6 min. Further annealing resulted in a more distinct hard phase surrounded by a nonmagnetic grain boundary phase ∼1 nm in thickness. The thin grain boundary layer phase starts to disappear with annealing time over 11 min. The partitioning behavior of various elements at different annealing conditions appears to be associated with significant changes in magnetic properties, leading to an improved optimum microstructure.
Microstructure and magnetic properties of perpendicular media with reduced grain size
Authors: Yuan Hua , Laughlin David E.
Published: March 2009

A new approach to control the grain size of Co alloy oxide perpendicular media by means of Ar-ion etching is presented. Ar plasma was applied to the surface of a continuous Ru1 layer, on top of which a granular Ru2+SiO2 layer was subsequently deposited. It was found that etching time and high Ar-ion energy have a significant effect on the surface roughness of the seedlayer, which in turn have a great effect on microstructure and magnetic properties of the media. A granular Ru2+SiO2 layer with mean grain size of 3.9±0.7 nm was obtained, and its oxide boundary thickness decreased with the decreasing Ru grain size. As a result, the mean grain size of the magnetic layer was greatly reduced to 5.3±0.8 nm from 7.6±1.3 nm of a controlled sample without Ar-ion etching. The coercivity (Hc) of the media is 2.7 kOe, while Hc of the controlled sample is 4.8 kOe. The small CoPt grain size, the possible oxidization of metal grains, and the resultant increasing c-axis dispersion of the magnetic layer can explain the decreasing Hc and remanent magnetization (Mr) and increasing (Hn−Hc) values of the perpendicular MH loops.
Anomalous magnetism and charge transport in dielectric La1−xCaxMnO3 (x≤xMIT∼0.22)
Authors: Glushkov V. V. , Anisimov M. A. , Bozhko A. D. , Chernobrovkin A. L. , Demishev S. V. , Ivanov V. Yu. , Privezentzev R. V. , Semeno A. V. , Sluchanko N. E. , Mukovskii Ya. M.
Published: March 2009

A study of the charge transport, magnetization, and high frequency (ω/2π=60 GHz) electron spin resonance (ESR) has been carried out on La1−xCaxMnO3 single crystals corresponding to the dielectric side of the concentration driven metal-insulator transition (x≤xMIT∼0.22). For x=0.22 the onset of ferromagnetism below the Curie temperature TC≈183 K was found to induce crossover from holelike (T>TC) to electronlike (T<TC) conductivity. The activation behavior of resistivity and Seebeck coefficients with the respective activation energies Eaρ∼123 meV and EaS∼32 meV was detected in the paramagnetic state of x=0.22 compound for T>TC. A large enhancement of the Hall effect, which is accompanied by the increase in Hall mobility to the values of μH∼−20 cm2/V s, was observed at intermediate temperatures 150 K<TTC was shown to evolve into an intricate two-mode ESR spectrum with irregular fine structure characterizing the ferromagnetic insulating (FI) state formed below TC. The anomalies of charge transport and magnetic properties found in FI state seem to be associated with the peculiarities of strongly disordered state with phase separation (ferromagnetic metallic domains embedded in the insulating matrix of La1−xCaxMnO3).
Magnetic properties of exchange biased Co/CoO elongated nanoring arrays
Authors: Tripathy D. , Adeyeye A. O.
Published: March 2009

We present a systematic study of the magnetic properties of exchange biased Co(25 nm)/CoO(tCoO)/Cu(2 nm) elongated nanoring arrays. The reversal mechanism in the exchange biased nanorings is directly compared to that of unbiased nanorings of identical geometry at varying temperatures. We observe that along the field cooling direction, the exchange biased nanorings exhibit reversal via shifted vortex states with enhanced magnitudes of onion→vortex and vortex→reverse onion transition fields. The magnitude of exchange bias field is also found to be strongly dependent on the CoO layer thickness tCoO, and decreases monotonically with increasing tCoO. Due to the interplay between the exchange and Zeeman energies, the exchange bias field could also be varied by adjusting the field cooling strength.
Analysis and comparison for rotor eddy current losses of permanent magnet synchronous generator according to dc and ac load conditions
Authors: Jang Seok-Myeong , Kim Hyun-Kyu , Choi Jang-Young , Ko Kyoung-Jin
Published: March 2009

This paper presents an analytical procedure for the calculation of the eddy current losses of permanent magnet synchronous generator (PMSG). The dc and ac loading effects on the eddy current is examined through the suggested analytical procedure that considers the radial and tangential flux density waveform through a phase current harmonic analysis. The corresponding test results are also presented to quantify and compare those loading effects on the eddy current. The results verified the suggested analytical procedures and show that the rotor eddy current losses for PMSG with the dc loads turned out to be more significant than those with the ac loads.
An isolated line-shape model based on the Keilson and Storer function for velocity changes. I. Theoretical approaches
Authors: Tran H. , Hartmann J.-M.
Published: March 2009

This paper presents new results for the modeling of isolated line shapes from the Doppler to the collisional regime, thus including the effects of confinement (Dicke narrowing) and of the speed dependence of collisional parameters. They are obtained within a classical description of the time evolution of the autocorrelation function of the optical transition moment, combined with the use of the Keilson and Storer model for the changes in the radiator translational velocity. A purely numerical solution to the subsequent differential equations, which uses discretized grids for the radiating-molecule velocity vector, is first described. An alternative approach, using projections onto generalized Laguerre polynomials (for the velocity modulus) and spherical harmonics (for the velocity orientation), is also presented. A first test of these approaches is made in the particular case of the Q(1) Raman line of the fundamental band of pure H2 at room temperature (others will be presented in paper II). It is shown that the two models lead to exactly the same results, as expected, and to satisfactory agreement with measured values of the linewidth at various densities.
Theory of the motion at the band crossing points in bulk semiconductor crystals and in inversion layers
Authors: Esseni David , Palestri Pierpaolo
Published: March 2009

This paper presents an original investigation of the motion at the band crossing points in the energy dispersion of either bulk crystals or inversion layers. In particular, by using a formalism based on the time dependent Schrödinger equation, we address the quite elusive topic of the belonging of the carriers to the bands that are degenerate at the crossing point. This problem is relevant and delicate for the semiclassical transport modeling in numerically calculated band structures; however, its clarification demands a full-quantum transport treatment. We here propose analytical derivations and numerical calculations clearly demonstrating that, in a given band structure, the motion of the carriers at the band crossing points is entirely governed by the overlap integrals between the eigenfunctions of the Hamiltonian that has produced the same band structure. Our formulation of the problem is quite general and we apply it to the silicon conduction band calculated by means of the nonlocal pseudopotential method, to the hole inversion layers described by a quantized k⋅p approach, and to the electron inversion layers described by the effective mass approximation method. In all the physical systems, our results underline the crucial role played by the abovementioned overlap integrals.
Equilibrium properties of a grafted polyelectrolyte with explicit counterions
Authors: Jayasree Kandiledath , Ranjith P. , Rao Madan , Kumar P. B. Sunil
Published: March 2009

We study the equilibrium conformations of a grafted polyelectrolyte (PE) in the presence of explicit counterions (CIs) using Monte Carlo simulations. The interplay between attractive Lennard-Jones interactions (parametrized by ϵ) and electrostatics (parametrized by A=q2lB/a, where q is the CI valency, lB is the Bjerrum length, and a is the monomer diameter) results in a variety of conformations, characterized as extended (E), pearls with m beads (Pm), sausage (S), and globular (G). For large ϵ, we observe a transition from G→P2→P3→…→S→G with increasing A, i.e., a change from poor to good, to re-entrant poor solvent, whereas, at lower ϵ, the sequence of transitions is E→S→G. The conformation changes are directly related to the nature of binding of CI onto the PE. The transition between S→G is continuous and associated with critical fluctuations in the shape driven by fluctuations in the fraction of condensed CI.
Laser-driven accelerators by colliding pulses injection: A review of simulation and experimental results
Authors: Malka V. , Faure J. , Rechatin C. , Ben-Ismail A. , Lim J. K. , Davoine X. , Lefebvre E.
Published: March 2009

A review of recent simulation and experimental studies of the colliding pulse injection scheme is presented. One dimensional particle in cell simulations show that when the colliding pulses have parallel polarizations, the dominant effects that have to be considered for modeling electron injection in plasma waves are (i) stochastic heating and (ii) wakefield inhibition at the collision. With cross polarized pulses, injection of an electron beam is still possible because stochastic heating still occurs. However, it is found numerically that the injection threshold is higher in this case. The simulations also underline the possibility of tuning the electron beam parameters by modifying the injection laser pulse. Experiments (i) validate these scenarios and show that stable and high quality electron beams are produced when two counterpropagating laser pulses collide in an underdense plasma and (ii) confirm very clearly the existence of a threshold for injection, which is higher with cross polarized pulses than with parallel polarized pulses.
Node-to-node pinning control of complex networks
Authors: Porfiri Maurizio , Fiorilli Francesca
Published: March 2009

In this paper, we study pinning controllability of oscillator networks. We present necessary conditions for network pinning controllability based on the spectral properties of the oscillator network and the individual oscillator dynamics. We define a performance metric for pinning-control systems based on the location of pinned sites, the pinning-control gains, and the network topology. We show that for any network structure, uniform pinning of all the network nodes maximizes the pinning-control performance. We propose the node-to-node pinning-control strategy to optimize the control performance while avoiding to simultaneously control all the network sites. In this novel strategy, the pinning-control action rapidly switches from one node to another with the goal of taming the oscillator network dynamics to the desired trajectory. We illustrate our findings through numerical simulations on networks of Rössler oscillators.
Water-mediated interactions between hydrophobic and ionic species in cylindrical nanopores
Authors: Vaitheeswaran S. , Reddy G. , Thirumalai D.
Published: March 2009

We use Metropolis Monte Carlo and umbrella sampling to calculate the free energies of interaction of two methane molecules and their charged derivatives in cylindrical water-filled pores. Confinement strongly alters the interactions between the nonpolar solutes and completely eliminates the solvent separated minimum (SSM) that is seen in bulk water. The free energy profiles show that the methane molecules are either in contact or at separations corresponding to the diameter and the length of the cylindrical pore. Analytic calculations that estimate the entropy of the solutes, which are solvated at the pore surface, qualitatively explain the shape of the free energy profiles. Adding charges of opposite sign and magnitude 0.4e or e (where e is the electronic charge) to the methane molecules decreases their tendency for surface solvation and restores the SSM. We show that confinement induced ion-pair formation occurs whenever lB/D∼O(1), where lB is the Bjerrum length and D is the pore diameter. The extent of stabilization of the SSM increases with ion charge density as long as lB/D<1. In pores with D≤1.2 nm, in which the water is strongly layered, increasing the charge magnitude from 0.4e to e reduces the stability of the SSM. As a result, ion-pair formation that occurs with negligible probability in the bulk is promoted. In larger diameter pores that can accommodate a complete hydration layer around the solutes, the stability of the SSM is enhanced.
Numerical solution of boundary-integral equations for molecular electrostatics
Authors: Bardhan Jaydeep P.
Published: March 2009

Numerous molecular processes, such as ion permeation through channel proteins, are governed by relatively small changes in energetics. As a result, theoretical investigations of these processes require accurate numerical methods. In the present paper, we evaluate the accuracy of two approaches to simulating boundary-integral equations for continuum models of the electrostatics of solvation. The analysis emphasizes boundary-element method simulations of the integral-equation formulation known as the apparent-surface-charge (ASC) method or polarizable-continuum model (PCM). In many numerical implementations of the ASC/PCM model, one forces the integral equation to be satisfied exactly at a set of discrete points on the boundary. We demonstrate in this paper that this approach to discretization, known as point collocation, is significantly less accurate than an alternative approach known as qualocation. Furthermore, the qualocation method offers this improvement in accuracy without increasing simulation time. Numerical examples demonstrate that electrostatic part of the solvation free energy, when calculated using the collocation and qualocation methods, can differ significantly; for a polypeptide, the answers can differ by as much as 10 kcal/mol (approximately 4% of the total electrostatic contribution to solvation). The applicability of the qualocation discretization to other integral-equation formulations is also discussed, and two equivalences between integral-equation methods are derived.
Self-mixing interferometry in vertical-cavity surface-emitting lasers for nanomechanical cantilever sensing
Authors: Larsson David , Greve Anders , Hvam Jørn M. , Boisen Anja , Yvind Kresten
Published: March 2009

We have experimentally investigated self-mixing interference produced by the feedback of light from a polymer micrometer-sized cantilever into a vertical-cavity surface-emitting laser for sensing applications. In particular we have investigated how the visibility of the optical output power and the junction voltage depends on the laser injection current and the distance to the cantilever. The highest power visibility obtained from cantilevers without reflective coatings was ∼60%, resulting in a very high sensitivity of 45 mV/nm with a noise floor below 1.2 mV. Different detection schemes are discussed.
Tb nanoparticles doped Nd–Fe–B sintered permanent magnet with enhanced coercivity
Authors: Yue M. , Liu W. Q. , Zhang D. T. , Jian Z. G. , Cao A. L. , Zhang J. X.
Published: March 2009

The microstructure and magnetic properties were studied for the sintered Nd–Fe–B permanent magnet doped with terbium (Tb) nanoparticles. Investigation shows that Tb is enriched as Tb2Fe14B and/or (Nd,Tb)2Fe14B phase in the surface region of the Nd2Fe14B matrix grains indicated by the remarkable enhancement in the magnetocrystalline anisotropy field of the magnet. Furthermore, the Tb-rich grain surface region with high crystal anisotropy increases the nucleation field of reverse domains in the demagnetization process. As a result, the magnet doped with a small amount of Tb nanoparticles possesses enhanced coercivity without sacrificing its magnetization.
A comparison of methods for preparing enriched populations of bovine spermatogonia
Authors: Herrid Muren , Davey Rhonda J. , Hutton Keryn , Colditz Ian G. , Hill Jonathan R.
Published: March 2009

The objective of the present study was to identify an efficient and practical enrichment method for bovine type A spermatogonia. Four different enrichment methods were compared: differential plating on laminin- or Datura stramonium agglutinin (DSA)-coated flasks, percoll-gradient isolation, magnetic-activated cell sorting (MACS) and fluorescence-activated cell sorting (FACS). The isolated cells were characterised with Dolichos biflorus agglutinin (DBA) lectin staining for type A spermatogonia and vimentin-antibody staining for Sertoli cells. A 2 × 2 factorial design was used to investigate the enrichment efficiency on laminin and DSA. In the laminin-enrichment groups, 2 h incubation in plates coated with 20 μg mL–1 laminin yielded a 3.3-fold increase in DBA-positive cells in the adherent fraction, while overnight incubation in flasks coated with 20 μg mL–1 DSA produced a 3.6-fold increase in the non-adherent fraction. However, the greatest enrichment (5.3-fold) of DBA-positive cells was obtained after 2 h incubation in control flasks (coated with bovine serum albumin). Percoll-gradient centrifugation yielded a 3-fold increase in DBA-positive cells. MACS results showed a 3.5- to 5-fold enrichment while FACS produced a 4-fold increase in DBA-positive cells. It is concluded that differential plating is a better method of recovering large numbers of type A spermatogonia for germ cell transplantation, while MACS or FACS can provide highly enriched viable type A spermatogonia for in vitro culture. Further, the combination of differential plating and other enrichment techniques may increase the purification efficiency of type A spermatogonia.
Control of bull sperm cell volume during epididymal maturation
Authors: Sahin Evrim , Petrunkina Anna M. , Waberski Dagmar , Harrison Robin A. P. , Töpfer-Petersen Edda
Published: March 2009

Mature spermatozoa have a mechanism by which they can reduce cellular swelling caused by hypo-osmotic stress. The development of this ability during epididymal maturation in the bull was investigated. Caput and cauda sperm preparations were exposed to various osmotic stresses at 38°C and measurements of cell volume made by electronic cell sizing. (1) Epididymal spermatozoa recovered and incubated in a medium isotonic with caudal epididymal plasma (360 mOsm kg–1) showed better viability and better volume regulatory ability than those incubated in a medium isotonic with seminal plasma (300 mOsm kg–1) or in seminal plasma itself. (2) Preparations of both caput and cauda spermatozoa, isolated in a medium isotonic with caudal epididymal plasma, contained two volumetric subpopulations, unrelated to the presence or absence of attached cytoplasmic droplets. (3) The cell volume of both subpopulations of caput spermatozoa was always greater than that of the corresponding cauda spermatozoa subpopulations. (4) After exposure to hypotonic challenge, both caput and cauda spermatozoa were able to reduce their relative volumes, demonstrating that both immature and mature cells are able to express regulatory volume decrease under physiological conditions. (5) When spermatozoa were incubated in chloride- or sodium-free media, although two subpopulations remained present, the volume of the caput sperm populations decreased to that of their counterparts in cauda sperm preparations. It is concluded that immature caput spermatozoa are capable of regulating their volume in a similar fashion to mature cauda spermatozoa but are less able to control their isotonic volume, probably due to poorly controlled sodium and chloride ion transport.