Molecules participating in insect immunity of Sarcophaga peregrina

Pricking the body wall of Sarcophaga peregrina (flesh fly) larvae with a needle activated the immune system of this insect and induced various immune molecules, including antibacterial proteins, in the hemolymph. In this review, I summarize and discuss the functions of these immune molecules, with particular emphasis on the dual roles of some of these molecules in defense and development.     

in situ FTIR Spectroscopic Characterization of Electroactive Species

A spectroelectrochemical technique based on the Fourier Transform Infrared Reflection Absorption Spectroscopic (FTIR-RAS) method is described, whereby high resolution in situ vibrational spectra of electrogenerated reaction intermediates (including radicals) and species adsorbed on electrode surfaces are obtained. Theoretical and experimental aspects of the method in a single reflection mode are discussed. Details of the cell design and the optimization of the operational parameters for running the FT-IR spectrometer in the RAS mode are also described. Apart from the potential of this technique to identify adsorbed species through their vibrational spectra, it can also be used to determine the orientation of the adsorbed species on the electrode surface by making use of surface selection rules. Using this technique, it has been possible to record the spectra of molecules adsorbed from aqueous and non aqueous media on metal and carbon electrodes. It has been possible to distinguish the vibrational spectra of adsorbed molecules from those in the bulk. Various systems covering a wide range of molecules have been studied and the potential of the technique as a method for the characterization of the electrode-electrolyte interface has been demonstrated.     

Kinetics of the fluorescence of poly(N-vinylcarbazole) and poly(N-vinylcarbazole) with 2,4,7-trinitrofluorenone in the solid state

The fluorescence decay time measurements by the stroboscopic method have been made on films of amorphous poly(N-vinylcarbazole) (PVCA) and PVCA doped with 2,4,7-trinitrofluorenone (TNF). The obtained lifetimes of two excimer species have at 77 K and at 300 K values of about 43 ns and 9 ns, which are similar to other measurements. The kinetics of excimer fluorescence and energy transfer in PVCA films are described by a simple model of the Stern-Volmer type. It assumes the fast migration of localized singlet excitons and their trapping in two species of excimer traps.We propose a modified kinetic model for films of PVCA with TNF. In this model we assume besides the exciton migration and trapping on excimer and impurity traps also the direct energy transfer from two excimer species to charge transfer complexes of PVCA with TNF by the Förster dipole-dipole mechanism. The estimated critical distance of this transfer are about 10 Å.     

Development of a laser-based Raman scattering system for identifying and quantifying major gas species

The construction of a laser-based Raman scattering system for identifying major gas species and quantifying their partial pressures is described. The system incorporates a pulsed laser to minimize the background luminescence. The results obtained at room temperature for N₂ at (365·80·5) nm and for O₂ at (355·80·5) nm are presented.     

The reaction of acetylene with Ni(100) and Ni(110) surfaces at room temperature

Ultraviolet photoemission spectroscopy using hv = 21.2 eV and filtered 40.8 eV radiation as well as temperature programmed thermal desorption spectroscopy are used to investigate the chemical reaction of acetylene with Ni(100) and Ni(110) surfaces at room temperature. Striking crystallographic effects and several coexisting phases are observed and found to be coverage and temperature dependent. A methodology is described and used to predict the relative energy levels for a variety of adsorbed hydrocarbon fragments on Ni surfaces. Such levels together with the thermal desorption spectra are used to identify the observed species. In particular, CH and CCH species are isolated on Ni(100) and Ni(110) surfaces, respectively, via low temperature adsorption and subsequent pulsed sample warming experiments. The room temperature adsorption phases are deduced using these ionization levels together with those of chemisorbcd acetylene, atomic hydrogen and carbon. At room temperature on Ni(100), H, C, CH and C₂H₂ species form together below 2 L exposure while CH species form thereafter, up to a saturation exposure of ~10 L. On Ni(110), H and CCH species form below 1.5 L exposure followed by the formation of CH₂ and likely CH species. The relative stabilities of these species at elevated temperatures is: C₂H₂ < CCH ? CH < CH₂. A model for the bonding of acetylene and its reaction to form CCH species on Ni(110) is proposed.     

In vivo magnetic resonance microscopy of brain structure in unanesthetized flies

We present near-cellular-resolution magnetic resonance (MR) images of an unanesthetized animal, the blowfly Sarcophaga bullata. Immobilized flies were inserted into a home-built gradient probe in a 14.1-T magnet, and images of voxel size (20-40 microm)(3)--comparable to the diameter of many neuronal cell bodies in the fly's brain--were obtained in several hours. Use of applied field gradients on the order of 60 G/cm allowed minimally distorted images to be produced, despite significant susceptibility differences across the specimen. The images we obtained have exceptional contrast-to-noise levels; comparison with histology-based anatomical information shows that the MR microscopy faithfully represents patterns of nervous tissue and allows distinct brain regions to be clearly identified. Even at the highest resolutions we explored, morphological detail was pronounced in the apparent absence of instabilities or movement-related artifacts frequently observed during imaging of live animal specimens. This work demonstrates that the challenges of noninvasive in vivo MR microscopy can be overcome in a system amenable to studies of brain structure and physiology.     

Laser-induced fluorescence detection of hydroxyl (OH) radical by femtosecond excitation

The development of a laser-induced fluorescence detection scheme for probing combustion-relevant species using a high-repetition-rate ultrafast laser is described. A femtosecond laser system with a 1 kHz repetition rate is used to induce fluorescence, following two-photon excitation (TPE), from hydroxyl (OH) radicals that are present in premixed laminar flames. The experimental TPE and one-photon fluorescence spectra resulting from broadband excitation into the (0,0) band of the OH A(2)∑(+)-X(2)Π system are compared to simulated spectra. Additionally, the effects of non-transform-limited femtosecond pulses on TPE efficiency is investigated.     

Solutions to a reduced Poisson-Nernst-Planck system and determination of reaction rates

We study a reduced Poisson-Nernst-Planck (PNP) system for a charged spherical solute immersed in a solvent with multiple ionic or molecular species that are electrostatically neutralized in the far field. Some of these species are assumed to be in equilibrium. The concentrations of such species are described by the Boltzmann distributions that are further linearized. Others are assumed to be reactive, meaning that their concentrations vanish when in contact with the charged solute. We present both semi-analytical solutions and numerical iterative solutions to the underlying reduced PNP system, and calculate the reaction rate for the reactive species. We give a rigorous analysis on the convergence of our simple iteration algorithm. Our numerical results show the strong dependence of the reaction rates of the reactive species on the magnitude of its far field concentration as well as on the ionic strength of all the chemical species. We also find non-monotonicity of electrostatic potential in certain parameter regimes. The results for the reactive system and those for the non-reactive system are compared to show the significant differences between the two cases. Our approach provides a means of solving a PNP system which in general does not have a closed-form solution even with a special geometrical symmetry. Our findings can also be used to test other numerical methods in large-scale computational modeling of electro-diffusion in biological systems.     

The vapour-phase ultra-violet photoelectron spectroscopy of metal halides at elevated temperatures

Simple UV photoelectron spectrometers capable of operation with gaseous samples at temperatures up to 1000 K are described. He(I) spectra of halides of thallium, mercury, tin, lead and caesium are reported. Comparison of the spectra of the Group IVB MX₂ species with those of the TIX and HgX₂ species suggests a new assignment of the former spectra.     

表面放电光泵浦XeF(C-A)激光数值模拟

 采用数值方法模拟表面放电光泵浦XeF(C-A)激光形成过程,分析反应粒子、气体温度、腔内损失、耦合透过率、XeF₂压力对激光输出的影响,数值计算结果与自行研制的表面放电光泵浦XeF(C-A)激光器的实验结果吻合较好。     

Surface-science aspects of plasma-assisted etching

Plasma-assisted etching methods have been used in the manufacture of integrated circuits for more than 10 years and yet the surface-science aspects of this technology are poorly understood. The chemistry must be such that the reactive species generated in the plasma react with the surface being etched to form a volatile product. The chemistry is usually dominated by atoms, molecular radicals and low-energy (20–500 eV) positive ions. In microstructure fabrication, the positive ions are accelerated from the plasma towards the etched surface arriving essentially at normal incidence. Thus, the bottom surface of a very small feature being etched is subjected to both energetic ions and reactive neutral species, whereas the sidewalls of the feature are exposed to reactive neutral species only. The role of the energetic ions is primarily to accelerate the reaction between the neutral species and the etched surface (i.e., accelerate the etch rate), thereby reducing the steady-state top-monolayer coverage of the etching species on the etched surface. On the sidewalls, however, the reacting-species coverage is a saturation coverage. The present understanding of some of the surface-science aspects of this complex environment will be summarized, often using the Si-F system as an example, and some phenomena which are not well understood will be described.     

Mid-IR difference frequency laser-based sensors for ambient CH4, CO, and N2O monitoring

A new mid-infrared sensor platform is described, which combines difference frequency generation (DFG)-based tunable laser sources with simple direct absorption spectroscopy. DFG lasers operating in the 3–5 micron window are tuned to access a variety of species in the C–H, N–O, and C–O stretch regions. The sensors are capable of sub-ppb detection of key greenhouse gas species as well as common pollutants and tracer species. Specific examples of sensor data obtained for methane, nitrous oxide, and carbon monoxide are presented, including relevant time series data and associated Allan Variances. The platform provides a cost-effective alternative to other laser-based approaches in some cases, performing at similar or superior levels. Emphasis on achieving key performance metrics driven by World Meteorological Organization guidelines for Global Air Watch program and other applications is highlighted.     

Femtosecond two-photon LIF imaging of atomic species using a frequency-quadrupled Ti:sapphire laser

Femtosecond (fs)-duration laser pulses are well suited for two-photon laser-induced-fluorescence (TPLIF) imaging of key atomic species such as H, N, and O in gas-phase reacting flows. Ultrashort pulses enable efficient nonlinear excitation, while reducing interfering photochemical processes. Furthermore, amplified fs lasers enable high-repetition-rate imaging (typically 1–10 kHz) for capturing the dynamics of turbulent flow fields. However, two-dimensional (2D), single-laser-shot fs-TPLIF imaging of the above species is challenging in most practical flow fields because of the limited ultraviolet pulse energy available in commercial optical parametric amplifier (OPA)-based tunable laser sources. In this work, we report the development of an efficient, fs frequency-quadrupling unit [i.e., fourth-harmonic generator (FHG)] with overall conversion efficiency more than six times greater than that of commercial OPA-based systems. The development, characterization, and application of the fs-FHG system for 2D imaging of H atoms in flames are described in detail. The potential application of the same laser system for 2D imaging of N and O atoms is also discussed.     

Temperature-compensated,high-resolution infrared absorption spectroscopy: Application to carbon monoxide

The analytic basis is presented for an optical absorption technique on CO suitable for a single line-of-sight determination of average gaseous species number density in the presence of concentration, pressure and temperature gradients and of particulate loading. The technique depends on the use of high-resolution IR (tunable diode laser) spectroscopy. The method requires the construction of functions of molecular line strengths that are nearly temperature independent. A method for constructing these functions is described.     

Lineshapes in quasi-elastic scattering from species hopping between non-equivalent surface sites

We present an analytic model applied to quasi-elastic scattering from an adsorbed surface species undergoing jump diffusion between adsorption sites described by a Bravais lattice combined with a basis of multiple points. The model allows for hops between adsorption sites which are both symmetrically and energetically inequivalent. We give results for 1-D hopping, which are applicable to a species jumping between the top and bridge sites along the [11?0] direction on an fcc-(110) surface or for jumps along a step edge. In 2-D, results for hopping between fcc and hcp hollow sites and between the bridge sites of an fcc-(111) surface are presented. These examples give characteristic signatures which will allow these forms of motion to be recognized in experimental data and will enable the underlying physical parameters to be extracted by comparison with the analytical forms derived here.     

国产枸杞属植物的红外指纹图谱无损快速鉴别研究

用傅里叶变换红外光谱法 (FTIR)无损快速鉴别了国产 10种枸杞。结果表明 :按其形态学分类的7种枸杞和 3变种枸杞与红外指纹图谱有一定的相关性 ,也有一些差异。这 10种枸杞的红外光谱各自均有自己的特征吸收 ,可方便地给以鉴别和区分 ,同时还进一步表明了枸杞中的化学组分之间的差异 ,为枸杞品种优良的宏观质控提供了一个快速、直观、方便、可行的方法     

Auditory temporal integration in the rhesus macaque (Macaca mulatta).

Temporal integration for pure tones was examined in two rhesus macaques. The subjects were required to respond to a brief sound (a tone burst) that deviated from a previous series of sounds (noise bursts) on a trial (a deviant-stimulus detection paradigm). Psychometric functions and thresholds were determined from correct detections (hit proportions) alone, and from d' scores. Two models describing the decline in threshold as a function of stimulus duration, one a power function the other an exponential, were tested against the data. When the decline (slope) in threshold per log stimulus duration is used as a rate measure, our results yield a lower estimate of temporal integration rate in rhesus than did a previous study [Clack, J. Acoust. Soc. Am. 40, 1140-1146 (1966)]. Both studies, however, gave slope estimates of integration rate that were higher than in most other species. Comparison of the models using data from several species, revealed that the exponential, but not the power model, could account for two sources of variation in threshold measurement. One source is due to the range across threshold as a function of duration (the linear rate component), and is described by the constant of proportionality Ik in the model. The other source of variation arises from the rate of decline within this range (the nonlinear rate component), and is described by the time constant tau. In terms of this model, differences in rate estimates between Clack's study and ours (and between rhesus and other species) are primarily due to the linear component. The nonlinear rate component was about equal for our study and Clack's (tau = approximately 150 ms): a time constant that is just slightly larger (indicating a rate of temporal integration slightly slower) than for most other species examined.     

A two-dimensional multispecies fluid model of the plasma in an ACplasma display panel

A time dependent, two-dimensional model for simulating the plasma evolution in an AC plasma display panel (AC-PDP) is described. Reaction-convection (mobility)-diffusion equations for charged particles and excited heavy neutral species are solved along with Poisson's equation, a radiation transport equation, a surface charge buildup equation, and an external L-R-C circuit equation using a fully implicit numerical method. Electron-driven rate coefficients are computed with a 0-D Boltzmann solver in the local field approximation. For studying the particle dynamics in pure helium, we consider a reduced model in which radiation transport is ignored and the excited species manifold is collapsed to composite metastable and excited states. The model predictions of breakdown voltage are quite sensitive to the value of the secondary electron emission coefficient assumed and the uncertainties in the electron-driven reaction rates. An initial comparison between the model predictions and I-V measurements from a specially constructed helium-filled panel is made with qualitatively similar behavior. The lack of quantitative agreement can be explained by a combination of uncertainties in the model input data and uncertainty in the initial surface charge state in the experiments     

Dicopper peroxo complexes: low temperature stopped-flow reaction kinetics of [(BQPA)CuI]+ and [(Me2-TMPA)CuI]+

In the last 20 years, the reaction of many different CuI complexes and with dioxygen has been described. There is quite a big variety in their coordination geometry and most of them have been characterized by X-ray crystallography. Beyond structural information, stopped-flow kinetics experiments have provided additional mechanistic insights. In the particular systems [(BQPA)CuI]+ and [(Me2-TMPA)CuI]+ a new equilibrium between the two species trans-mu-1,2-peroxo and bis-mu-oxo is demonstrated. In the case of [(BQPA)CuI]+ the two species are in an equilibrium, presumably via the transient superoxo species. The reaction of [(Me2-TMPA)CuI]+ with dioxygen leads to the parallel formation of both species. The kinetically preferred trans-mu-peroxo species is then isomerised to the thermodynamically more stable bis-mu-oxo species.     

Single-port optical access for spectroscopic measurements in industrial flue gas ducts

An in situ optical access to industrial-scale flue-gas ducts under high pressure has been designed and realised. The system is used here for the determination, by excimer-laser-induced fragmentation fluorescence (ELIF), of alkali species released from the combustion of coal in a pressurised circulating fluidised bed (PCFB) combustor. However, it could be applied to the detection of other species in a variety of industrial plants. The essential feature of the design is the access for the light source and collection of signal via the same, single window. The set-up is compact, robust and durable, having been tested under realistic flue-gas conditions for periods of up to two weeks in the PCFB pilot plant. The main features of the access are described and examples of data collected are presented to demonstrate its capabilities. Received: 3 August 1998 / Revised version: 16 February 1999 / Published online: 26 May 1999