bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation and quantification of OH radicals in the far downstream part of an atmospheric microwave plasma jet using cavity ringdown spectroscopy
Authors: Wang Chuji , Srivastava Nimisha , Dibble Theodore S.
Published: August 2009

An atmospheric argon microwave plasma jet with a plasma column 8 mm long and 1–2 mm wide is studied. Existence of hydroxyl (OH) radicals down to 28 mm away from the plasma orifice is evidenced by UV cavity ringdown spectroscopy. The measured OH (v″=0, J″=3.5) number density at 28 mm is 7.2×1012 molecule/cm3. The plasma gas flow velocity, along with the known OH lifetimes, suggests that OH radicals observed in the downstream are not the OH radicals formed in the plasma column but were formed in the downstream.
Many worlds and modality in the interpretation of quantum mechanics: An algebraic approach
Authors: Domenech G. , Freytes H. , de Ronde C.
Published: August 2009

Many world interpretations (MWIs) of quantum mechanics avoid the measurement problem by considering every term in the quantum superposition as actual. A seemingly opposed solution is proposed by modal interpretations (MIs) which state that quantum mechanics does not provide an account of what “actually is the case,” but rather deals with what “might be the case,” i.e., with possibilities. In this paper we provide an algebraic framework which allows us to analyze in depth the modal aspects of MWI. Within our general formal scheme we also provide a formal comparison between MWI and MI, in particular, we provide a formal understanding of why—even though both interpretations share the same formal structure—MI fall pray of Kochen–Specker-type contradictions while MWI escape them.
Representation of the plasma fluid equations in “Miller equilibrium” analytical flux surface geometry
Authors: Stacey W. M. , Bae Cheonho
Published: August 2009

The plasma fluid equations are represented explicitly in the magnetic flux surface coordinate system resulting from the analytical “Miller equilibrium” solution of the Grad–Shafranov equation. The magnetic geometry is characterized by the elongation, triangularity, and location of the displaced major radius of the flux surface. The resulting fluid equations can be solved directly without the necessity of first solving the Grad–Shafranov equation numerically to define the flux surface coordinates.
Drift and diffusion in periodic potentials: Upstream and downstream step times are distributed identically
Authors: Dagdug Leonardo , Berezhkovskii Alexander M.
Published: August 2009

This note deals with particles diffusing in one dimension in the presence of a periodic potential and a uniform driving force. We show that (i) the probabilities for the particle to make a step of the length L, where L is the period, in the upstream and downstream directions are independent of the periodic potential, and (ii) the distributions of the step time are independent of the step direction. These two characteristics are used to derive expressions for the effective drift velocity and diffusion coefficient.
On the mechanism of H atom production in hot filament activated H2 and CH4/H2 gas mixtures
Authors: Comerford Dane W. , Smith James A. , Ashfold Michael N. R. , Mankelevich Yuri A.
Published: August 2009

This article reports systematic measurements of the power utilization by Ta (and Re) hot filaments (HFs) operating in a poor vacuum, in pure He, N2, and H2, and in CH4/H2 gas mixtures of relevance to diamond growth by HF chemical vapor deposition, as functions of filament temperature Tfil (in the range of 1800–2700 K) and gas pressure p (in the range of 10−2–100 Torr). In the cases of H2 and the CH4/H2 gas mixtures, the power consumption studies are complemented by in situ measurements of the relative H atom densities [H] near the HF—which are seen to maximize at p∼10–20 Torr and thereafter to remain constant or, at the highest Tfil, to decline at higher p. These (and many previous) findings are rationalized by a companion theoretical analysis, which reduces the complex array of chemisorption and desorption processes that must contribute to the HF-surface mediated dissociation of H2 to a two-step mechanism involving H atom formation by dissociative adsorption at bare (S∗) sites and by desorption at hydrogenated (SH) sites on the HF surface.
Modeling of subcontinuum thermal transport across semiconductor-gas interfaces
Authors: Singh Dhruv , Guo Xiaohui , Alexeenko Alina , Murthy Jayathi Y. , Fisher Timothy S.
Published: August 2009

A physically rigorous computational algorithm is developed and applied to calculate subcontinuum thermal transport in structures containing semiconductor-gas interfaces. The solution is based on a finite volume discretization of the Boltzmann equation for gas molecules (in the gas phase) and phonons (in the semiconductor). A partial equilibrium is assumed between gas molecules and phonons at the interface of the two media, and the degree of this equilibrium is determined by the accommodation coefficients of gas molecules and phonons on either side of the interface. Energy balance is imposed to obtain a value of the interface temperature. The classic problem of temperature drop across a solid-gas interface is investigated with a simultaneous treatment of solid and gas phase properties for the first time. A range of transport regimes is studied, varying from ballistic phonon transport and free molecular flow to continuum heat transfer in both gas and solid. A reduced-order model is developed that captures the thermal resistance of the gas-solid interface. The formulation is then applied to the problem of combined gas-solid heat transfer in a two-dimensional nanoporous bed and the overall thermal resistance of the bed is characterized in terms of the governing parameters. These two examples exemplify the broad utility of the model in practical nanoscale heat transfer applications.
Experimental microwave imaging of three-dimensional targets with different inversion procedures
Authors: Chaumet P. C. , Belkebir K. , Sentenac A.
Published: August 2009

We consider an experimental microwave imaging system in which the targets are illuminated under various angles of incidence and the scattered field is measured on a sphere surrounding them. We estimate the map of relative permittivity of the objects from the scattered field with an iterative inversion procedure based on a conjugate gradient technique. We derive several formulations of the inversion algorithm and analyze their efficiency on three different targets. We observe that including a priori information on the lower and upper bounds of the permittivity of the sample leads to a spectacular improvement of the resolution of the image.
The dynamics of a viscous vortex dipole
Authors: Delbende Ivan , Rossi Maurice
Published: August 2009

The structure of a two-dimensional viscous dipole is accurately analyzed using both numerical simulations and theoretical analyses. First, a model is proposed, which computes the dipole velocity and the vortex ellipticity based on a heuristic relation between a vortex patch and a vortex with distributed vorticity profile. Second, during the stage where vortices are close to each other, a generalized self-similar solution is postulated to describe the vorticity profiles observed during the viscous spreading of the dipole. Numerical as well as theoretical considerations are given, which demonstrate the adequacy of such a hypothesis. Finally the structure of the tail that is generated behind the dipole is given in an analytical form, which favorably compares to numerical results.
Electronic and optical properties of mixed anion layered oxychalcogenide semiconductors: An ab initio study
Authors: Ramasubramanian S. , Rajagopalan M. , Kumar J. , Thangavel R.
Published: August 2009

A full potential linear augmented plane wave method within the density functional theory is used to calculate the electronic and optical properties of layered compounds of LaCuOCh (Ch=S, Se, Te) and their alloys LaCuOCh0.5Ch0.5′(Ch, Ch′=S, Se, Te). These compounds are found to be direct band gap semiconductors and may have a high p-type electrical conductivity, which can be tuned by proper alloying. The dielectric functions and optical constants—refractive index, absorption coefficient, and real part of optical conductivity of these materials—are calculated. The present study shows by changing the chalcogenides in the alternate covalent Cu–Ch layers that one can control the electrical conductivity and optical emission in these oxychalcogenide semiconductors.
Glassy steel optimized for glass-forming ability and toughness
Authors: Demetriou Marios D. , Kaltenboeck Georg , Suh Jin-Yoo , Garrett Glenn , Floyd Michael , Crewdson Chase , Hofmann Douglas C. , Kozachkov Henry , Wiest Aaron , Schramm Joseph P. , Johnson William L.
Published: August 2009

An alloy development strategy coupled with toughness assessments and ultrasonic measurements is implemented to design a series of iron-based glass-forming alloys that demonstrate improved glass-forming ability and toughness. The combination of good glass-forming ability and high toughness demonstrated by the present alloys is uncommon in Fe-based systems, and is attributed to the ability of these compositions to form stable glass configurations associated with low activation barriers for shear flow, which tend to promote plastic flow and give rise to a toughness higher than other known Fe-based bulk-glass-forming systems.
Enhancement of ballistic efficiency due to source to channel heterojunction barrier in Si metal oxide semiconductor field effect transistors
Authors: Wang W. , Tsuchiya H. , Ogawa M.
Published: August 2009

In this paper, we study the influences of a channel source-end potential profile on the ballistic transport of carriers in Si metal oxide semiconductor field effect transistors (MOSFETs) based on a quantum-corrected Monte Carlo device simulation. As a result, we found that higher ballistic efficiency is expected in MOSFETs with a heterojunction bottleneck barrier, such as Schottky source/drain MOSFETs, compared to that with the conventional p-n junction source and drain. Such a superior ballistic behavior is demonstrated due to the narrower bottleneck potential profile formed at the source-channel interface.
Vortex structure transformation of BaTiO3 nanoparticles through the gradient function
Authors: Hong L. , Soh A. K. , Liu S. Y. , Lu L.
Published: August 2009

Phase field method has been used to simulate the vortex structures in BaTiO3 (BTO) nanoparticles. Through the modulation of the gradient coefficients, vortices are found to transform in a path of monoclinic MA→orthorhombic→monoclinic MC→tetragonal. Although the gradient coefficients vary significantly, the change in gradient energy is remarkably small. The simulation results show that the rotation and magnitude reduction in polarization dipoles increase the bulk energy, which induces the vortex transformation process in BTO nanoparticles. Moreover, the existence of monoclinic phase is a necessity to start the polarization rotation as well as the vortex transformation process.
Three-dimensional velocity map imaging: Setup and resolution improvement compared to three-dimensional ion imaging
Authors: Kauczok S. , Gödecke N. , Chichinin A. I. , Veckenstedt M. , Maul C. , Gericke K.-H.
Published: August 2009

For many years the three-dimensional (3D) ion imaging technique has not benefited from the introduction of ion optics into the field of imaging in molecular dynamics. Thus, a lower resolution of kinetic energy as in comparable techniques making use of inhomogeneous electric fields was inevitable. This was basically due to the fact that a homogeneous electric field was needed in order to obtain the velocity component in the direction of the time of flight spectrometer axis. In our approach we superimpose an Einzel lens field with the homogeneous field. We use a simulation based technique to account for the distortion of the ion cloud caused by the inhomogeneous field. In order to demonstrate the gain in kinetic energy resolution compared to conventional 3D Ion Imaging, we use the spatial distribution of H+ ions emerging from the photodissociation of HCl following the two photon excitation to the V ∑1+ state. So far a figure of merit of approximately four has been achieved, which means in absolute numbers Δv/v=0.022 compared to 0.086 at v≈17 000 m/s. However, this is not a theoretical limit of the technique, but due to our rather short TOF spectrometer (15 cm). The photodissociation of HBr near 243 nm has been used to recognize and eliminate systematic deviations between the simulation and the experimentally observed distribution. The technique has also proven to be essential for the precise measurement of translationally cold distributions.
Anomalous diffusion in a generalized Langevin equation
Authors: Fa Kwok Sau
Published: August 2009

We analyze the motion of a particle governed by a generalized Langevin equation with the colored noise described by a combination of power-law and generalized Mittag–Leffler function. This colored noise generalizes the power-law correlation function and an exponential one. We obtain exact results for the relaxation function. Further, we obtain the first moments and variances of the displacement and velocity. The long-time behaviors of these quantities are also investigated. We show that normal diffusion processes can be generated by a class of these colored noises.
Direct measurement of electrical transport through single DNA molecules
Authors: Qian Jun , Liao Sicheng , Xu Song , Stroscio Michael A. , Dutta Mitra
Published: August 2009

The apparently contradictory results indicating the ability of DNA to transport charge as well as the possible charge transport mechanisms in DNA have been addressed by making scanning tunneling microscopy (STM) or current-sensing atomic force microscopy measurements using gold nanoparticle (GNP)-DNA complexes bound to a gold substrate designed to minimize nonreproducibility of the specific binding modes and configurations of the DNA-metal contacts. Using these GNP-DNA complexes but a different strand of DNA [13-base-pair poly(dA)-poly(dT) double-stranded DNA] and STM, semiconductorlike charge transport characteristics are demonstrated for DNA; importantly, several different observed I-V characteristics are correlated with different configurations of GNP-DNA complexes as well as with I-V characteristics calculated using a Landauer formalism. These joint measured and simulated I-V characteristics for the GNP-DNA complexes are consistent with charge transport in a semiconductor where the lowest unoccupied molecular orbital energy of the DNA serves as the lowest conduction band energy and the highest occupied molecular orbital energy of the DNA serves as the highest valence band energy.
Water diffusion and fracture behavior in nanoporous low-k dielectric film stacks
Authors: Li Han , Tsui Ting Y. , Vlassak Joost J.
Published: August 2009

Among various low-dielectric constant (low-k) materials under development, organosilicate glasses (OSGs) containing nanometer-size pores are leading candidates for use as intrametal dielectrics in future microelectronics technologies. In this paper, we investigate the direct impact of water diffusion on the fracture behavior of film stacks that contain porous OSG coatings. We demonstrate that exposure of the film stacks to water causes significant degradation of the interfacial adhesion energy, but that it has negligible effect on the cohesive fracture energy of the nanoporous OSG layer. Isotope tracer diffusion experiments combined with dynamic secondary ion mass spectroscopy show that water diffuses predominantly along the interfaces, and not through the porous films. This unexpected result is attributed to the hydrophilic character of the interfaces.
Enhanced reactivity of nanoenergetic materials: A first-principles molecular dynamics study based on divide-and-conquer density functional theory
Authors: Shimojo Fuyuki , Nakano Aiichiro , Kalia Rajiv K. , Vashishta Priya
Published: August 2009

Integration of nanowires and nanoparticles of energetic materials into semiconducting structures is giving birth to “nanoenergetics-on-a-chip” technology. Understanding and controlling the reactions of nanoenergetic materials pose a theoretical challenge for combining quantum-mechanical accuracy with large scales to capture nanostructural effects. Recent developments in linear-scaling density functional theory have set a stage for first-principles molecular dynamics simulation of thermite reaction at an Al∕Fe2O3 interface. Here, we report the finding of a concerted metal-oxygen flip mechanism that enhances mass diffusion and reaction rate at the interface. This mechanism leads to two-stage reactions, which may explain recent experimental observation in thermite nanowire arrays.
A superconducting transistorlike device having good input-output isolation.
Authors: Nevirkovets I. P.
Published: August 2009

A multiterminal superconducting device with the S1IS2FIS3 structure (where S, I, and F denote a superconductor, an insulator, and a ferromagnetic material) is fabricated and characterized. Introducing a thin ferromagnetic layer into the middle electrode dramatically reduces parasitic back action of the acceptor junction (S1IS2) bias current on the injector junction (S2FIS3) current-voltage characteristic as compared with that for the formerly reported quiteron, a device exploiting similar operation principle.
Surface acoustic wave generation in ZX-cut LiNbO3 superlattices using coplanar electrodes
Authors: Yudistira Didit , Benchabane Sarah , Janner Davide , Pruneri Valerio
Published: August 2009

We report on a configuration to generate surface acoustic waves (SAWs) in acoustic superlattices based on ZX-cut periodically poled lithium niobate. The coplanar electrode configuration allows inducing Rayleigh type SAWs with the elastic energy mainly concentrated in between the electrodes gap and under the crystal surface. With respect to standard interdigitated transducers using the same crystal orientation, the efficiency of the SAW generation in the proposed designs are similar, while, for the same grating period, the resonance frequency that can be achieved is two times larger.
Vortex dislocations in wake-type flow induced by spanwise disturbances
Authors: Ling Guo Can , Zhao Hong Liang
Published: August 2009

Vortex dislocations in wake-type flow induced by three types of spanwise disturbances superimposed on an upstream velocity profile are investigated by direct numerical simulations. Three distinct modes of vortex dislocations and flow transitions have been found. A local spanwise exponential decay disturbance leads to the appearance of a twisted chainlike mode of vortex dislocation. A stepped spanwise disturbance causes a streamwise periodic spotlike mode of vortex dislocation. A spanwise sinusoidal wavy disturbance with a moderate waviness causes a strong unsteadiness of wake behavior. This unsteadiness starts with a systematic periodic mode of vortex dislocation in the spanwise direction followed by the spanwise vortex shedding suppressed completely with increased time and the near wake becoming a steady shear flow. Characteristics of these modes of vortex dislocation and complex vortex linkages over the dislocation, as well as the corresponding dynamic processes related to the appearance of dislocations, are described by examining the variations of vortex lines and vorticity distribution. The nature of the vortex dislocation is demonstrated by the substantial vorticity modification of the spanwise vortex from the original spanwise direction to streamwise and vertical directions, accompanied by the appearance of noticeable vortex branching and complex vortex linking, all of which are produced at the locations with the biggest phase difference or with a frequency discontinuity between shedding cells. The effect of vortex dislocation on flow transition, either to an unsteady irregular vortex flow or suppression of the Kármán vortex shedding making the wake flow steady state, is analyzed. Distinct similarities are found in the mechanism and main flow phenomena between the present numerical results obtained in wake-type flows and the experimental-numerical results of cylinder wakes reported in previous studies.
Optical spin control in nanocrystalline magnetic nanoswitches
Authors: Echeverría-Arrondo C. , Pérez-Conde J. , Ayuela A.
Published: August 2009

We investigate the optical properties of (Cd,Mn)Te quantum dots (QDs) by looking at the excitons as a function of the Mn impurities positions and their magnetic alignments. When doped with two Mn impurities, the Mn spins, aligned initially antiparallel in the ground state, have lower energy in the parallel configuration for the optically active spin-up exciton. Hence, the photoexcitation of the QD ground state with antiparallel Mn spins induces one of them to flip and they align parallel. This suggests that (Cd,Mn)Te QDs are suitable for spin-based operations handled by light.
The epitaxial growth of indium nitride using berlinite (AlPO4) and other piezoelectric crystals of the quartz family as substrates
Authors: Moret M. , Ruffenach S. , Briot O. , Gil B. , Pauthe M.
Published: August 2009

We report the growth of indium nitride on AlPO4, which is a piezoelectric substrate, by using metal organic vapor phase epitaxy (MOVPE). The substrate we used was the as-grown (011) surface of an AlPO4 crystal grown by hydrothermal synthesis. InN growth occurs as the nonpolar M-plane. The structural, optical, and electrical properties of the epilayer are comparable with those of layers obtained by conventional growth on polar GaN MOVPE templates deposited on C-plane sapphire. We discuss the utilization of other MX–O4 oxides for growing nitrides.
Improvement of resistive switching characteristics in TiO2 thin films with embedded Pt nanocrystals
Authors: Chang Wen-Yuan , Cheng Kai-Jung , Tsai Jui-Ming , Chen Hung-Jen , Chen Frederick , Tsai Ming-Jinn , Wu Tai-Bor
Published: August 2009

We have fabricated TiO2 thin films with embedded Pt nanocrystals (Pt-NCs) and investigated the resistive switching characteristics for nonvolatile memory application. Reversible and steady bistable resistance switching behavior was observed for the Pt/TiO2/Pt capacitors with Pt-NCs embedded in the TiO2 films. Moreover, an improvement in the stability of resistance switching and retention properties was also achieved from the embedding of uniform and fine Pt-NCs.
Photovoltaic effect in the La0.67Ca0.33MnO3/LaMnO3/SrTiO3:Nb heterojunctions with variant LaMnO3 layers
Authors: Wei A. D. , Sun J. R. , Lü W. M. , Shen B. G.
Published: August 2009

Influence of LaMnO3 layer, 0–12 nm in thickness, on photovoltaic effect (PVE) has been experimentally studied for the La0.67Ca0.33MnO3/LaMnO3/SrTiO3:Nb junction. Presence of LaMnO3 causes an obvious weakening of the PVE, demonstrated by the reduction in the carrier density excited by each photon. The interfacial barrier deduced from the PVE shows a rapid growth, from ∼1.22 to ∼1.45 eV, as the layer thickness increases from 0 to 2 nm, and saturates at ∼1.5 eV above 2 nm. On the contrary, current-voltage characteristics suggest a smooth reduction in interfacial barrier with layer thickness. These results can be quantitatively understood assuming the occurrence of a notch and a spike in the conduction band edges at the interface of the junction.
Ion core structure in (N2O)n+(n=2–8) studied by infrared photodissociation spectroscopy
Authors: Inokuchi Yoshiya , Matsushima Ryoko , Kobayashi Yusuke , Ebata Takayuki
Published: August 2009

IR photodissociation (IRPD) spectra of (N2O)2+•Ar and (N2O)n+ with n=3–8 are measured in the 1000–2300 cm−1 region. The (N2O)2+•Ar ion shows an IRPD band at 1154 cm−1, which can be assigned to the out-of-phase combination of the ν1 vibrations of the N2O components in the N4O2+ ion; the positive charge is delocalized over the two N2O molecules. The geometry optimization and the vibrational analysis at the B3LYP/6-311+G∗ level show that the N4O2+ ion has a C2h structure with the oxygen ends of the N2O components bonded to each other. The IRPD spectra of the (N2O)n+(n=3–8) ions show three prominent bands at ∼1170, ∼1275, and ∼2235 cm−1. The intensity of the ∼1170 cm−1 band relative to that of the other bands decreases with increasing the cluster size. Therefore, the ∼1170 cm−1 band is ascribed to the N4O2+ dimer ion core and the ∼1275 and ∼2235 cm−1 bands are assigned to the ν1 and ν3 vibrations of solvent N2O molecules, respectively. Since the band of the N4O2+ ion core is located at almost the same position for all the (N2O)n+(n=2–8) clusters, the C2h structure of the dimer ion core does not change so largely by the solvation of N2O molecules, which is quite contrastive to the isoelectronic (CO2)n+ case.
Does Cross-Border Cooperation Empower European Regions? The Case of Interreg III-A France–Spain
Authors: Harguindéguy Jean-Baptiste , Bray Zoé
Published: August 2009

In this paper we investigate the impact of the implementation of EU programmes on substate actors, and more specifically regional ones. We focus on the case of the INTERREG cross-border initiative in France and Spain between 2000 and 2003, and whether INTERREG succeeded in empowering regional governments and local authorities as it initially claimed to. Our analysis puts to the fore that this programme has not evolved from being ‘a policy for the regions to a policy by the regions' as many expected, but that its implementation rather reveals a wide range of configurations. Indeed, the execution of INTERREG facilitated the transition from a state-centric scheme to a regionalised one only in those territories where a previous decentralisation policy had been realised at the domestic level and where a consistent regional leadership had emerged during earlier versions of INTERREG.
Miserly Thinking/Excessful Geography: From Restricted Economy to Global Financial Crisis
Authors: Doel Marcus A
Published: August 2009

Against the horizon of Earthly depletion and social exhaustion, miserly thinking is once again on the ascendancy, catching hold of critical and radical thought as well as the popular and conservative imagination. Whatever its ethicopolitical inflection, miserly thought enjoins one to conserve, constrain, and sustain. It is consumed by scarcity: specifically, the inability of the world to accommodate itself to the insatiable demands that are placed upon it. Faced with lack, miserly thought advances its ethic of restraint, the target of which is everything that would exceed the paucity of means placed at our world's disposal. Pitching itself against miserly thinking, the paper unfolds a form of thought animated by excession rather than immiseration, by a world given as excess rather than as privation. This is accomplished in four parts, the first of which dislodges the grip of miserly thinking by recourse to Georges Bataille's notion of general economy. The paper then considers arguably the best-known form of excessful thinking: Marxian political economy, as rendered by David Harvey. Nevertheless, while this successfully reveals how social formations are animated by surplus rather than by scarcity, its desire to restitute excess remains mired in miserly thinking. Consequently, the third part of the paper considers the fate of excess once it suffuses the whole of existence. With its ontology of association, Bruno Latour's actor-network theory has gone the furthest in this regard. However, this ontology runs aground upon an inconsistent excess held in reserve: plasma. The final part of the paper addresses the limitations of Latour's actor-network theory by way of Alain Badiou's ontology of subtraction. In the final analysis, the sequence of ‘lack’, ‘surplus’, and ‘association’ gives way to the constellation of ‘multiplicity’, ‘situation’, and ‘event’, which is illustrated with reference to the global financial crisis of 2008 and 2009.
Transfers and transitions: Parent–offspring conflict, genomic imprinting, and the evolution of human life history
Authors: Haig David
Published: August 2009

Human offspring are weaned earlier than the offspring of other great apes but take longer to reach nutritional independence. An analysis of human disorders of imprinted genes suggests genes of paternal origin, expressed in infants, have been selected to favor more intense suckling than genes of maternal origin. The same analysis suggests that genes of maternal origin may favor slower childhood growth but earlier sexual maturation. These observations are consistent with a hypothesis in which slow maturation was an adaptation of offspring that reduced maternal fitness, whereas early weaning was an adaptation of mothers that reduced the fitness of individual offspring.
Jacques Banchereau: On a quest for cures
Authors: Maxmen Amy
Published: August 2009

Jacques Banchereau wonders why more kids don't want to grow up to be scientists. After all, what's not to like about changing lives, relieving suffering, and giving patients in need a reason to remain hopeful?
Optical analysis of circuitry for respiratory rhythm in isolated brainstem of foetal mice
Authors: Muller Kenneth J. , Tsechpenakis Gavriil , Homma Ryota , Nicholls John G. , Cohen Lawrence B. , Eugenin Jaime
Published: August 2009

Respiratory rhythms arise from neurons situated in the ventral medulla. We are investigating their spatial and functional relationships optically by measuring changes in intracellular calcium using the fluorescent, calcium-sensitive dye Oregon Green 488 BAPTA-1 AM while simultaneously recording the regular firing of motoneurons in the phrenic nerve in isolated brainstem/spinal cord preparations of E17 to E19 mice. Responses of identified cells are associated breath by breath with inspiratory and expiratory phases of respiration and depend on CO
2
and pH levels. Optical methods including two-photon microscopy are being developed together with computational analyses. Analysis of the spatial pattern of neuronal activity associated with respiratory rhythm, including cross-correlation analysis, reveals a network distributed in the ventral medulla with intermingling of neurons that are active during separate phases of the rhythm. Our experiments, aimed at testing whether initiation of the respiratory rhythm depends on pacemaker neurons, on networks or a combination of both, suggest an important role for networks.
The potency of different serotonergic agonists in counteracting opioid evoked cardiorespiratory disturbances
Authors: Dutschmann M. , Waki H. , Manzke T. , Simms A. E. , Pickering A. E. , Richter D. W. , Paton J. F. R.
Published: August 2009

Serotonin receptor (5-HTR) agonists that target 5-HT4(a)R and 5-HT1AR can reverse μ-opioid receptor (μ-OR)-evoked respiratory depression. Here, we have tested whether such rescuing by serotonin agonists also applies to the cardiovascular system. In working heart–brainstem preparationsin situ, we have recorded phrenic nerve activity, thoracic sympathetic chain activity (SCA), vascular resistance and heart rate (HR) and in conscious rats, diaphragmatic electromyogram, arterial blood pressure (BP) and HR via radio-telemetry. In addition, the distribution of 5-HT4(a)R and 5-HT1AR in ponto-medullary cardiorespiratory networks was identified using histochemistry. Systemic administration of the μ-OR agonist fentanylin situdecreased HR, vascular resistance, SCA and phrenic nerve activity. Subsequent application of the 5-HT1AR agonist 8-OH-DPAT further enhanced bradycardia, but partially compensated the decrease in vascular resistance, sympathetic activity and restored breathing. By contrast, the 5-HT4(a)R agonist RS67333 further decreased vascular resistance, HR and sympathetic activity, but partially rescued breathing. In conscious rats, administration of remifentanyl caused severe respiratory depression, a decrease in mean BP accompanied by pronounced bradyarrhythmia. 8-OH-DPAT restored breathing and prevented the bradyarrhythmia; however, BP and HR remained below baseline. In contrast, RS67333 further suppressed cardiovascular functionsin vivoand only partially recovered breathing in some cases. The better recovery of μ-OR cardiorespiratory disturbance by 5-HT1AR than 5-HT4(a)R is supported by the finding that 5-HT1AR was more densely expressed in key brainstem nuclei for cardiorespiratory control compared with 5-HT4(a)R. We conclude that during treatment of severe pain, 5-HT1AR agonists may provide a useful tool to counteract opioid-mediated cardiorespiratory disturbances.
Alterations in cholinergic sensitivity of respiratory neurons induced by pre-natal nicotine: a mechanism for respiratory dysfunction in neonatal mice
Authors: Coddou Claudio , Bravo Eduardo , Eugenín Jaime
Published: August 2009

Nicotine may link cigarette smoking during pregnancy with sudden infant death syndrome (SIDS). Pre-natal nicotine leads to diminished ventilatory responses to hypercarbia and reduced central chemoreception in mice at post-natal days 0–3. We studied how pre-natal nicotine exposure changes the cholinergic contribution to central respiratory chemoreception in neonatal isolated brainstem–spinal cord and slice preparations.

Osmotic minipumps, implanted subcutaneously into 5–7 days pregnant mice, delivered saline or nicotine ditartrate 60 mg kg−1d−1for up to 28 days. In control preparations, acidification of the superfusion medium from pH 7.4 to 7.3 increased the frequency and reduced the amplitude of fictive respiration. In nicotine-exposed neonatal mice, the reduction in amplitude induced by acidification was reduced. In control preparations, atropine suppressed respiratory responses to acidification, while hexamethonium did not. By contrast, in nicotine-exposed preparations, hexamethonium blocked chemosensory responses but atropine did not.

Our results indicate that pre-natal nicotine exposure switches cholinergic mechanisms of central chemosensory responses from muscarinic receptors to nicotinic receptors. Modification of the cholinergic contribution to central chemoreception may produce respiratory dysfunctions, as suggested by receptor-binding studies in victims of SIDS.
Structural and functional architecture of respiratory networks in the mammalian brainstem
Authors: Smith Jeffrey C. , Abdala Ana P. L. , Rybak Ilya A. , Paton Julian F. R.
Published: August 2009

Neural circuits controlling breathing in mammals are organized within serially arrayed and functionally interacting brainstem compartments extending from the pons to the lower medulla. The core circuit components that constitute the neural machinery for generating respiratory rhythm and shaping inspiratory and expiratory motor patterns are distributed among three adjacent structural compartments in the ventrolateral medulla: the Bötzinger complex (BötC), pre-Bötzinger complex (pre-BötC) and rostral ventral respiratory group (rVRG). The respiratory rhythm and inspiratory–expiratory patterns emerge from dynamic interactions between: (i) excitatory neuron populations in the pre-BötC and rVRG active during inspiration that form inspiratory motor output; (ii) inhibitory neuron populations in the pre-BötC that provide inspiratory inhibition within the network; and (iii) inhibitory populations in the BötC active during expiration that generate expiratory inhibition. Network interactions within these compartments along with intrinsic rhythmogenic properties of pre-BötC neurons form a hierarchy of multiple oscillatory mechanisms. The functional expression of these mechanisms is controlled by multiple drives from more rostral brainstem components, including the retrotrapezoid nucleus and pons, which regulate the dynamic behaviour of the core circuitry. The emerging view is that the brainstem respiratory network has rhythmogenic capabilities at multiple hierarchical levels, which allows flexible, state-dependent expression of different rhythmogenic mechanisms under different physiological and metabolic conditions and enables a wide repertoire of respiratory behaviours.
Chemosensory pathways in the brainstem controlling cardiorespiratory activity
Authors: Spyer K. Michael , Gourine Alexander V.
Published: August 2009

Cardiorespiratory activity is controlled by a network of neurons located within the lower brainstem. The basic rhythm of breathing is generated by neuronal circuits within the medullary pre-Bötzinger complex, modulated by pontine and other inputs from cell groups within the medulla oblongata and then transmitted to bulbospinal pre-motor neurons that relay the respiratory pattern to cranial and spinal motor neurons controlling respiratory muscles. Cardiovascular sympathetic and vagal activities have characteristic discharges that are patterned by respiratory activity. This patterning ensures ventilation–perfusion matching for optimal respiratory gas exchange within the lungs. Peripheral arterial chemoreceptors and central respiratory chemoreceptors are crucial for the maintenance of cardiorespiratory homeostasis. Inputs from these receptors ensure adaptive changes in the respiratory and cardiovascular motor outputs in various environmental and physiological conditions. Many of the connections in the reflex pathway that mediates the peripheral arterial chemoreceptor input have been established. The nucleus tractus solitarii, the ventral respiratory network, pre-sympathetic circuitry and vagal pre-ganglionic neurons at the level of the medulla oblongata are integral components, although supramedullary structures also play a role in patterning autonomic outflows according to behavioural requirements. These medullary structures mediate cardiorespiratory reflexes that are initiated by the carotid and aortic bodies in response to acute changes in PO2, PCO2and pH in the arterial blood. The level of arterial PCO2is the primary factor in determining respiratory drive and although there is a significant role of the arterial chemoreceptors, the principal sensor is located either at or in close proximity to the ventral surface of the medulla. The cellular and molecular mechanisms of central chemosensitivity as well as the neural basis for the integration of central and peripheral chemosensory inputs within the medulla remain challenging issues, but ones that have some emerging answers.
Wide-field and two-photon imaging of brain activity with voltage- and calcium-sensitive dyes
Authors: Homma Ryota , Baker Bradley J. , Jin Lei , Garaschuk Olga , Konnerth Arthur , Cohen Lawrence B. , Zecevic Dejan
Published: August 2009

This review presents three examples of using voltage- or calcium-sensitive dyes to image the activity of the brain. Our aim is to discuss the advantages and disadvantages of each method with particular reference to its application to the study of the brainstem. Two of the examples use wide-field (one-photon) imaging; the third uses two-photon scanning microscopy. Because the measurements have limited signal-to-noise ratio, the paper also discusses the methodological aspects that are critical for optimizing the signal.

The three examples are the following. (i) An intracellularly injected voltage-sensitive dye was used to monitor membrane potential in the dendrites of neurons in
in vitro
preparations. These experiments were directed at understanding how individual neurons convert complex synaptic inputs into the output spike train. (ii) An extracellular, bath application of a voltage-sensitive dye was used to monitor population signals from different parts of the dorsal brainstem. We describe recordings made during respiratory activity. The population signals indicated four different regions with distinct activity correlated with inspiration. (iii) Calcium-sensitive dyes can be used to label many individual cells in the mammalian brain. This approach, combined with two-photon microscopy, made it possible to follow the spike activity in an
in vitro
brainstem preparation during fictive respiratory rhythms.

The organic voltage- and ion-sensitive dyes used today indiscriminatively stain all of the cell types in the preparation. A major effort is underway to develop fluorescent protein sensors of activity for selectively staining individual cell types.
Developmental basis of the rostro-caudal organization of the brainstem respiratory rhythm generator
Authors: Champagnat J. , Morin-Surun M. P. , Fortin G. , Thoby-Brisson M.
Published: August 2009

TheHoxgenetic network plays a key role in the anteroposterior patterning of the rhombencephalon at pre- and early-segmental stages of development of the neural tube. In the mouse, it controls development of the entire brainstem respiratory neuronal network, including the pons, the parafacial respiratory group (pFRG) and the pre-Bötzinger complex (preBötC). Inactivation ofKrox20/Egr2eliminates the pFRG activity, thereby causing life-threatening neonatal apnoeas alternating with respiration at low frequency. Another respiratory abnormality, the complete absence of breathing, is induced when neuronal synchronization fails to develop in the preBötC. The present paper summarizes data on a third type of respiratory deficits induced by alteringHoxfunction at pontine levels. Inactivation ofHoxa2, the most rostrally expressed Hox gene in the hindbrain, disturbs embryonic development of the pons and alters neonatal inspiratory shaping without affecting respiratory frequency and apnoeas. The same result is obtained by thePhox2a+/−mutation modifying the number of petrosal chemoafferent neurons, by eliminating acetylcholinesterase and by alteringHox-dependent development of the pons with retinoic acid administration at embryonic day 7.5. In addition, embryos treated with retinoic acid provide a mouse model for hyperpnoeic episodic breathing, widely reported in pre-term neonates, young girls with Rett's syndrome, patients with Joubert syndrome and adults with Cheyne–Stokes respiration. We conclude that specific respiratory deficitsin vivoare assignable to anteroposterior segments of the brainstem, suggesting that the adult respiratory neuronal network is functionally organized according to the rhombomeric,Hox-dependent segmentation of the brainstem in embryos.
Secondary 1 Program of Project P.A.T.H.S.: Process Evaluation Based on the Co-Walker Scheme
Authors: Shek Daniel T. L. , Ng Catalina S. M.
Published: August 2009

This study examined the implementation quality of the Tier 1 Program (Secondary 1 Curriculum) delivered in the second year of the Full Implementation Phase of the Project P.A.T.H.S. (Positive Adolescent Training through Holistic Social Programmes). Under the “Co-Walker Scheme”, systematic observation of curriculum units was conducted in 138 schools. Results indicated that the overall level of program adherence was high, with an average of 82.9%. The mean ratings of the program implementation quality were also high. Despite limitations, the findings of this study suggest that the implementation of the Secondary 1 Program (Tier 1 Program) of the Full Implementation Phase was of very high quality. The present findings also provide strong evidence to account for the successful and encouraging outcomes of a major positive youth development program in Hong Kong.
A 5-Year Audit of Accidental Dural Punctures, Postdural Puncture Headaches, and Failed Regional Anesthetics at a Tertiary-Care Medical Center
Authors: Singh Sukhdip , Chaudry Shagufta Y. , Phelps Amy L. , Vallejo Manuel C
Published: August 2009

Obstetric anesthesia-related complications occur as a result of labor epidural or spinal placement. The purpose of this continuous quality-improvement audit was to review the occurrence of accidental dural punctures (ADPs), postdural puncture headaches (PDPHs), and failed regional anesthetics at an academic tertiary-care medical center over a 5-year period. Obstetric anesthesia complications contained in three databases consisting of ADPs, PDPHs, and failed regional anesthetics were matched to a perinatal database, with no complications serving as controls. Of the 40,894 consecutive parturients, there were 765 documented complications. Complication rates were 0.73% (95% CI: 0.65–0.82) for ADP, 0.49% (95% CI: 0.43–0.56) for PDPH, and 0.65% (95% CI: 0.57–0.73) for failed regional anesthetic. When compared to the no complication group, factors associated with obstetric anesthesia complications included increased weight and BMI (p< 0.01), epidural block (p< 0.01), and vaginal delivery (p< 0.01).
A previously unknown zinc finger protein, DST, regulates drought and salt tolerance in rice via stomatal aperture control
Authors: Huang Xin-Yuan , Chao Dai-Yin , Gao Ji-Ping , Zhu Mei-Zhen , Shi Min , Lin Hong-Xuan
Published: August 2009

Abiotic stresses, such as drought and salinity, lead to crop growth damage and a decrease in crop yields. Stomata control CO2 uptake and optimize water use efficiency, thereby playing crucial roles in abiotic stress tolerance. Hydrogen peroxide (H2O2) is an important signal molecule that induces stomatal closure. However, the molecular pathway that regulates the H2O2 level in guard cells remains largely unknown. Here, we clone and characterize DST (drought and salt tolerance)—a previously unknown zinc finger transcription factor that negatively regulates stomatal closure by direct modulation of genes related to H2O2 homeostasis—and identify a novel pathway for the signal transduction of DST-mediated H2O2-induced stomatal closure. Loss of DST function increases stomatal closure and reduces stomatal density, consequently resulting in enhanced drought and salt tolerance in rice. These findings provide an interesting insight into the mechanism of stomata-regulated abiotic stress tolerance, and an important genetic engineering approach for improving abiotic stress tolerance in crops.
RNAi in the Red Flour Beetle (Tribolium)
Authors: Posnien Nico , Schinko Johannes , Grossmann Daniela , Shippy Teresa D. , Konopova Barbora , Bucher Gregor
Published: August 2009

INTRODUCTION

Tribolium castaneum is exceptionally amenable to gene knockdown by RNA interference (RNAi) which, in this insect, is systemic (spreading throughout the organism and to the next generation), highly penetrant, and able to phenocopy genetic null phenotypes. Hence, any gene function can be knocked down at any stage in (apparently) all tissues upon injection of double-stranded RNA (dsRNA). The RNAi effect is elicited both in the injected animal and, if female pupae or adults have been injected, transferred to the offspring. Embryonic RNAi (eRNAi) usually generates the strongest phenotypes in the injected individual, but suffers from elevated lethality caused by injection injury. Pupal RNAi (pRNAi), in which female pupae are injected and phenotypes scored in the offspring, is the easiest to perform. However, in some cases, the knockdown of a gene leads to sterility of the injected female. This problem can be circumvented in many cases by injecting adult females (aRNAi) or using eRNAi. In order to interfere with processes during metamorphosis, injection into last-stage larvae is used (lRNAi). Up to two genes in a single experiment have been successfully knocked down via RNAi. The inclusion of more than two genes usually leads to a dilution effect, which lowers phenotypic strength. This protocol describes the production of dsRNA from a polymerase chain reaction (PCR) template, injection procedures for each Tribolium life stage, and important controls for effective analysis.
Analyzing Microarray Data Using WebArray
Authors: Wang Yipeng , McClelland Michael , Xia Xiao-Qin
Published: August 2009

INTRODUCTION

WebArray is a web platform for microarray data analysis. As an analysis suite designed by bench biologists, WebArray is user-friendly for life scientists without a bioinformatics background. It is simple to use but employs powerful analysis functions. Analysis is based on files uploaded by users. For Affymetrix GeneChip data, intensity files in CEL format can be used. For two-color experiments, WebArray can recognize intensity files generated from many different software packages. WebArray provides functions for data quality control, background correction, normalization, differential analysis, and plotting on a genome map. A user-friendly aspect of WebArray is the fact that users generally do not have to change the default parameters for common experimental designs, so they are usually protected from applying the wrong statistical tools. In most cases, novice users will have no problem finding explanations for file formats or terms in the extensive help system.