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Shaped ultrafast laser pulses were used to study and control the ionization dynamics of electronically excited pyrazine in a pump and probe experiment. For pump pulses created without feedback from the product signal, the ion growth curve (the parent ion signal as a function of pump/probe delay) was described quantitatively by the classical rate equations for internal conversion of the S2 and S1 states. Very different, non-classical behavior was observed when a genetic algorithm (GA) employing phase-only modulationwas used to minimize the ion signal at some pre-determined target time, T. Two qualitatively different control mechanisms were identified for early (T < 1.5 ps) and late (T > 1.5 ps) target times. In the former case, the ion signalwas largely suppressed for t < T,while for t » T, the ion signal produced by the GA-optimized pulse and a transform limited (TL) pulse coalesced. In contrast, for T > 1.5 ps, the ion growth curve followed the classical rate equations for t < T, while for t » T, the quantum yield for the GA-optimized pulse was much smaller than for a TL pulse. We interpret the first type of behavior as an indication that the wave packet produced by the pump laser is localized in a region of the S2 potential energy surface where the vertical ionization energy exceeds the probe photon energy, whereas the second type of behavior may be described by a reduced absorption cross section for S0 → S2 followed by incoherent decay of the excited molecules. Amplitude modulation observed in the spectrum of the shaped pulse may have contributed to the control mechanism, although this possibility is mitigated by the very small focal volume of the probe laser. [ABSTRACT FROM AUTHOR]

We show how the spatial phase of a focused laser beam may be used as a tool for controlling the branching ratio of a chemical reaction. Guoy discovered [Acad. Sci., Paris, C. R. 110, 1250 (1890)] that when an electromagnetic wave passes through a focus its phase increases by π. In a coherent control scheme involving the absorption of n photons of frequency ωm and m photons of frequency ωn, the overall phase shift produced by the Gouy phase is (n-m)π. At any given point in space, this phase shift is identical for all reaction products. Nevertheless, if the yields for different reaction channels have different intensity dependencies, the Gouy phase produces a net phase lag between the products that varies with the axial coordinate of the laser focus. We obtain here analytical and numerical values of this phase as the laser focus is scanned across the diameter of the molecular beam, taking into account the Rayleigh range and astigmatism of the laser beam and saturation of the transition. We also show that the modulation depth of the interference pattern may be increased by optimizing the relative intensities of the two fields. [ABSTRACT FROM AUTHOR]

We explore the possibility of using an intense laser beam to focus a molecular beam onto a surface to create nanowires. We show that with a grazing angle of incidence between the laser and molecular beams, it is possible to use available technology to create wires < 50 nm wide and > 100 µm long with a 100 W continuous wave laser. Narrower and longer features could be created with higher power lasers. This technique is very general, and may be used to deposit any atom or molecule onto an arbitrary substrate, so long as the particles may be entrained in a molecular beam and have an adequate sticking probability. The effects of spherical and chromatic aberration and laser mode structure on the focusing properties of the molecular lens are examined in detail, and design criteria for building a practical device are discussed. [ABSTRACT FROM AUTHOR]

Examines the Rydberg electronic states of hydrogen chloride through the deperturbation of Hamiltonian calculations. Description of the deperturbation scheme; Results of hydrogen chloride spectrum deperturbation; Description of intensity anomalies and photodissociation dynamics.

Studies a semiclassical model of the angular distribution of the photofragments of predissociating molecules. Neglect of exit channel effects; Comparison of the model with velocity-aligned Doppler spectra of CI atoms.

We have used the method of coherent phase modulation, first proposed by Brumer and Shapiro for controlling the rates of chemical reactions, to measure the refractive index of a gas in the vacuum ultraviolet. In these experiments we populated a Rydberg state of HCl or CO by simultaneous absorption of one VUV photon and three UV photons. Molecular ions were generated by absorption of an additional UV photon and detected with a time-of-flight mass spectrometer. The phase difference for the UV and VUV beams was altered by passing them through a cell containing either H2 or Ar. By varying the pressure in the cell we could control this phase difference and thereby modulate the ion signal. From the modulation frequency of the signal it was possible to determine the difference between the refractive indices of the gas at the UV and VUV wavelengths. Using reliable refractive indices in the UV, we extracted from our data values for the VUV indices. These values are in quantitative agreement with a calculation that uses dipole oscillator strengths constructed using constrained oscillator strength methods, taking into account the dispersion resulting from individual rotational transitions. The experimental method can be used very close to an optical transition of the refractive medium, provided that the refractive index does not vary appreciably across the bandwidth of the VUV laser. [ABSTRACT FROM AUTHOR]

Amplified spontaneous emission (ASE) is a process which competes with laser-induced fluorescence (LIF) in three level systems. This was demonstrated in the case of oxygen atoms, for which both ASE and LIF were observed at 845 nm. Ground state oxygen atoms were generated by photodissociating O2, SO2, and NO2 in a pump and probe experiment. Both nascent and thermalized O(3Pj‘) atoms were measured using two-photon LIF at 226 nm. The fine structure populations deduced from the 845 nm (3p3Pj’→3s3S) emission were considerably hotter than the distributions obtained from the 130 nm (3s3S→2p3P) transition. A kinetic model is developed showing that the distributions observed at 845 are distorted by ASE, which selectively depletes the populations of atoms originating from more highly populated multiplet levels. [ABSTRACT FROM AUTHOR]

The fine structure population of O(3P) produced in the photodissociation of O2 at 157 nm was measured in a pump-and-probe experiment. The population of the ground state (J=2) was found to be 93%, with only 6% in the J=1 level and 1% in J=0. The predominance of J=2 is consistent with direct dissociation on the B 3Σ-u potential energy surface. Based on available information in the literature we rule out excitation of the 3Πu state and curve crossing to the 5Πu state as possible origins of the population with J<2. We infer that the populations of J<2 is due to nonadiabatic transitions at large distances. Two mechanisms consistent with the data are a Demkov-type interaction, which is caused by coupling by the radial kinetic energy operator. [ABSTRACT FROM AUTHOR]

The technique of resonantly enhanced multiphoton ionization with time-of-flight mass resolution has been used to measure the two-photon absorption spectrum of HBr. We have analyzed 37 bands and assigned them to transitions to the valence, ion-pair state and to Rydberg states belonging to the sσ, pσ, dσ, pπ, dπ, and dδ manifolds. Our results are in excellent agreement with the earlier work of Ginter, Ginter, and Tilford. In addition, we have analyzed twelve new electronic states as well as numerous bands of vibrationally excited levels of previously known electronic states. Strong mixing was observed among the 0+ states. [ABSTRACT FROM AUTHOR]

The vibrational relaxation of SiF4 and C6F5H in an Ar bath was measured as a function of initial energy using the method of time-resolved optoacoustics. SiF4 was found to relax nonexponentially, with a rate constant which varied approximately as the vibrational energy raised to the 3/2 power. This behavior is similar to that observed earlier for SF6+Ar below the bottleneck. In contrast, C6F5H was observed to decay exponentially, as expected for a large molecule in the quasicontinuum. These two types of behavior are discussed in the context of previously proposed propensity rules for the vibrational relaxation of highly excited molecules. [ABSTRACT FROM AUTHOR]

The branching ratio was measured for the production of O(3P) in the photodissociation of CO2 at 157 nm. A gas mixture consisting of CO2, H2, and Ar was irradiated with an F2 excimer laser, while the relative concentration of O(3P) was monitored continuously using atomic resonance fluorescence. The O(1D) product was removed by either reacting with H2 or by being quenched by CO2. At a high H2/CO2 ratio a residual O(3P) signal persisted which was due to the nascent photofragments of CO2. A Stern–Volmer analysis indicated that the fraction of O(3P) produced is 5.9%. Control experiments using O2 and N2O as precursor molecules confirmed this interpretation of the data. A mechanism is proposed based on curve crossing from the 1B2 to the 3B2 potential energy surfaces of CO2. Since the 1B2 state is bent, a substantial fraction of the absorbed energy is initially in bending motion, resulting in a long-lived chaotic trajectory which has many opportunities to cross over to the triplet surface. A similar model proposed by Tully to explain the quenching of O(1D) by CO is in qualitative agreement with our data. [ABSTRACT FROM AUTHOR]

The acoustic waves generated by a relaxing gas have a shape which depends on the ratio of the relaxation rate to the acoustic propagation rate. It is shown how the relaxation time constant can be extracted from this waveform for a variety of relaxation rate laws, using a Green’s function to solve the linearized wave equation. The accuracy of the method is confirmed by measuring the relaxation rate constants for OCS diluted in Ar and He. These, plus a previous measurement of the relaxation rates of highly excited SF6 and C6F5H in Ar, are in good agreement with the literature. [ABSTRACT FROM AUTHOR]

The method of time-resolved optoacoustics was used to measure the time constant τ for the vibrational relaxation of SF6 by Ar as a function of the average initial excitation 〈〈E〉〉0. It was found that pτ=210±30 μs Torr for <>0 between 4000 and 19 000 cm-1, implying nearly pure exponential decay. The average amount of energy change per collision varies linearly with <>, having a value of -8 cm-1/collision at 19 000 cm-1. Below 4000 cm-1 pτ increases, approaching the low energy value obtained from IR fluorescence measurements. [ABSTRACT FROM AUTHOR]

The reaction of O(3P)+H2, D2, and HD was studied by the flash photolysis-resonance fluorescence method. The rate constants kXY(T) were measured over the temperature ranges 297–471 K for XY=H2, 422–472 K for D2, and 422–473 K for HD. Above 400 K kH2 are in excellent agreement with earlier flow measurements, but below this temperature most of the flow data are systematically lower. A small deviation from the Arrhenius function was observed for kH2 at 297 K. Our measurements of kD2 are in excellent agreement with the results of Westenberg and deHaas and differ from those Clyne and Thrush. The measured values of kHD equal the arithmetic mean of kH2 and kD2 within experimental error. A detailed comparison is made between the present results and the CEQB calculations of Bowman, Wagner, Walch, and Dunning and the ICVT/LAG calculations of Garrett and Truhlar. Good overall agreement is obtained with both theories. [ABSTRACT FROM AUTHOR]

The article explores the declining growth of the U.S. economy despite continuous technological innovation in the 21st century and the dependence of productivity growth on innovation and the rate of increase in physical and human capital.

A numerical model was used to predict effects of different liquid manure storage designs and management practices on manure temperature ( T m ). Manure storage designs included various tank diameters, proportion of the storage above-ground, addition of a roof, and floating covers (synthetic or straw). Manure management practices included the frequency of manure removal, manure agitation, and the depth of manure remaining after removal. Results showed that smaller diameter tanks with a greater depth had lower peak T m . There was no appreciable effect on T m from constructing a storage tank above-ground vs in-ground. Adding a roof decreased peak T m for spring manure removal, but not autumn removal. Floating synthetic covers with high solar absorptivity (i.e. dark colour) greatly increased peak T m , whereas straw covers had the opposite effect—decreasing peak T m . Removing manure twice per year (spring and autumn) or once annually in spring led to shallower manure depth in summer and greater peak T m ; in contrast, once annual autumn removal had greater depth and lower peak T m in summer. Manure agitation during the warm season increased peak T m substantially for autumn manure removal, and slightly for spring removal. Leaving less manure in storage after spring removal led to a more rapid increase in T m and a higher peak T m in summer. Overall, the study highlights that manure storage design and management practices can greatly affect T m , with peak T m being increased or decreased up to 8°C in some scenarios. These findings emphasize that T m is dynamic and that air temperature is an overly simplistic surrogate for T m . Thus, it is important that studies examining greenhouse gas emissions from liquid manure also measure manure temperature. Insights from the study may guide future research linking liquid manure storage design and management to T m and related effects on greenhouse gases such as methane. [ABSTRACT FROM AUTHOR]

Discusses the ultraviolet photodissociation dynamics of 2-chloro-1, 1-diffluoroethylene. Product state population having a Boltzmann-like distribution; Agreement with a simple phase-space model; Nonstatistical state distribution of HCl produced in the photodissociation of vinyl chloride and dichloroethylene.

An explanation is proposed for the qualitatively different types of behavior that have been reported for the vibrational relaxation of highly excited diatomic and polyatomic molecules. It is argued that all of the diatomic molecules that have been studied in bulk relax adiabatically at room temperature. In contrast, large polyatomic molecules have low frequency modes which act at ‘‘doorway’’ modes for the rest of the molecules, producing an impulsive relaxation mechanism. The theoretical work of Nesbitt and Hynes showed that impulsive collisions result in an exponential decay of the average vibrational energy of a Morse oscillator, whereas adiabatic collisions produce nonexponential power law behavior. We propose that this result explains a large body of data for the vibrational relaxation of small and large molecules. [ABSTRACT FROM AUTHOR]

Certain ions such as Na+ and Cl- can accumulate in recirculating greenhouse nutrient solutions and can reach levels that are damaging to crops. An option for the treatment of this problem is phytodesalinization with Na+ and Cl- hyperaccumulating plants that could be added to existing water treatment technologies such as constructed wetlands (CWs). Two microcosm experiments were conducted to evaluate eight plant species including Atriplexprostrata L. (triangle orache), Distichlis spicata (L.) Greene (salt grass), Juncus torreyi Coville. (Torrey's rush), Phragmites australis (Cav.) Trin. ex Steud. (common reed), Spartina alterniflora Loisel. (smooth cordgrass), Schoenoplectus tabernae-montani (C.C. Gmel.) Palla (softstem bulrush), Typha angustifolia L. (narrow leaf cattail), and Typha latifolia L. (broad leaf cattail) for their Na+ and Cl- accumulation potential. An initial (indoor) experiment determined that J. torreyi, S. tabernaemontani, T. angustifolia, and T. latifolia were the best candidates for phytodesalinization because they had the highest Na+ and Cl- tissue contents after exposure to Na+ and Cl--rich nutrient solutions. A second (outdoor) experiment quantified the Na+ and Cl+ ion uptake (grams of each ion accumulated per m² of microcosm). J. torreyi, S. tabernaemontani, T. angustifolia, and T. latifolia accumulated 5.8,3.9, 8.3, and 9.2 g ⋅m-2 of Na+ and 25.7,18.2,31.6, and 27.2 g ⋅m-2 of Cl-, respectively. Of the eight species, T. latifolia and S. tabernaemontani showed the greatest potential to accumulate Na+ and Cl- in a CW environment, whereas A. alterniflora, D. spicata, and P. australis showed the least potential. [ABSTRACT FROM AUTHOR]

Abstract: Manure slurry storage systems are possible sources of methane (CH4) and nitrous oxide (N2O), both of which are strong greenhouse gases (GHG). The most commonly used methods to measure these emissions rely on chamber techniques deployed at discrete intervals (i.e. non-continuously). Due to long-term and diurnal variations in GHG emissions, discrete sampling may yield biased estimates when integrating fluxes over time. This research quantified the effect of sampling interval and the ‘time-of-day’ of sample collection on total emission estimates from discrete sampling compared to continuous monitoring, and characterized temporal flux variations in relation to environmental conditions. Methane and N2O emissions were measured continuously over the 6mo warm storage season in 2010 from 6 pilot-scale dairy manure slurry storage tanks using flow-through steady state chambers. Discrete sampling was simulated by extracting data from hourly flux time series at 13 sampling intervals ranging from 1 to 21d. For each sampling interval, 24 datasets were generated, one for each hour of the day. When there were high rates of CH4 ebullition, and crusts did not completely cover the surface, diurnal flux variations were linked with the diurnal surface temperature (T 0) cycle, whereby bubbles that accumulated at the surface overnight burst after sunrise. With complete manure surface crusting, episodic and unpredictable flux events were more common. Diurnal variation in N2O emissions was strongly linked with variation in T 0 when crusts >2mo old were present. For CH4, sampling between 1800 and 0800h at intervals ≤7d yielded ±10% deviation between discrete and continuous monitoring with a frequency of 96%. The frequency of achieving ±10% deviation for N2O was 50% when sampling at ∼2000h. If sampling during these times is not possible, manual measurements should be made in early morning (before 0900h) and late afternoon (after 1700h). [Copyright &y& Elsevier]

We demonstrate strong coupling between molecular excited states and surface plasmon modes of a slit array in a thin metal film. The coupling manifests itself as an anticrossing behavior of the two newly formed polaritons. As the coupling strength grows, a new mode emerges, which is attributed to long-range molecular interactions mediated by the plasmonic field. The new, molecular-like mode repels the polariton states, and leads to an opening of energy gaps both below and above the asymptotic free molecule energy. [ABSTRACT FROM AUTHOR]

This paper examines 'asset stripping' which is said to occur particularly in matrilineal societies when young widows are stripped of their late husband's possessions. Contrary to many scholars who see asset stripping as a recent phenomenon and who believe that recent moves by traditional Owambo leaders to protect widows is a product of enlightenment induced by contemporary human rights activism, this paper shows that 'asset stripping' has deep historical roots and was a subject of contention even in the earliest mission accounts of over a century ago. Moreover, the historical records show that leaders, both traditional and Church, have long tried to improve the situation for widows, but have not achieved the success they desired. The relative failure of these legal innovations to protect widows is described and analysed. The problem is a structural one exacerbated by recent State efforts at gender equity. Finally, given the historical structural nature of the issue, questions are raised about the current proclivity to use rapid assessment techniques. [ABSTRACT FROM AUTHOR]

This article presents information about several books and films related to Namibia. The film "Le Malentendu Colonial (Colonial Misunderstanding)" is produced and directed by Jean-Marie Teno. Teno examines colonialism on the basis of Christian evangelization in the film. The book "Histories of Namibia: Living through the Liberation Struggle" has been written by Colin Leys and Susan Brown. The book focuses on the liberation struggle in Namibia.

The direct and indirect moral regulation of its citizens, subjects and denizens is one of the key — albeit under-acknowledged — activities of states, especially in Africa. Using Namibia, a former German colony and then a League of Nations mandate as a case study, the author of this paper examines what the administration regarded as the most potent medium for influencing peoples' behaviour, namely film or motion pictures. Of all the so-called mass media, film was held to have the greatest capacity to impact people's values. Censorship was strongly nuanced in terms of age, gender and race and, with hindsight, was draconian. While appearing exceptional it was very clearly part of an emergent international system of moral regulation with a nexus in the League of Nations. Part of the problem from a colonial perspective was that Europeans believed that by allowing the colonized to view the back regions of European behaviour, it would undermine white prestige and this caused a moral panic. Ironically, despite the almost magical value attributed to cinema, its use for development and moral upliftment was relatively minor. The more intriguing question is why settlers were so intrigued by the impact of the cinema? Part of the answer is that the censors' certificate at the start of the film show was a ritual imprimatur signifying that they were in control of technology and reinforced and inscribed population categories. Each certificate in turn served to amplify the need for more censorship in order to maintain the settler fantasy world of a stable social situation. [ABSTRACT FROM AUTHOR]

Pastoralists have long been recurrent figures in visual images and other representations of Africa and Africans. Whether seen in positive or negative terms, pastoralists have provided means for thinking about and imaging cultural difference and identity, with considerable continuity in representational forms and themes. As popular visual media proliferated and changed over the past two centuries--from postcards, trade cards, and live shows to Hollywood films and video games--African pastoralists have continued to appear in each new form, often replicating the types and stereotypes of Euroamerican understandings even as they register new and varied circumstances. The proliferation and reverberation of similar images through diverse visual media is one way these images have come to seem "natural" and to develop such remarkable persistence [Kratz 2002]. Using cases drawn from eastern and southern Africa, this collection of articles considers the multifaceted processes of representation involved in imaging African pastoralists. It invites attention to how such representations are produced in diverse visual media and through interconnections among visual and verbal media, examining the range of actors, interactions, and mediations involved in crafting representations of African pastoralists at different times and in different places. [ABSTRACT FROM AUTHOR]

Focuses on theoretical and experimental advances in the active control of the dynamics of atoms and molecules. Elements of control methodology; Conditions for control of quantum dynamics; Information on interference-induced control in intense fields; Control of dynamics-inverse scattering duality.

Studies the impact of the second world war on Namibia. Role of Nazism in Namibia; Establishment of a system for recruiting black volunteers to serve in the South African Defence Force (SDF); Operation of the recruitment system; Conclusions.

Opinion. Presents the author's view on the article `Quality Change in the CPI,' by Charles Hulten. Comments on the first and second conclusions of Hulten about the major sources of both upward and downward bias in the CPI; Problems with Hulten's analysis; Appropriate framework for Hulten's analysis; Views on Hulten's interpretation of the CPI bias; Criticism of Hulten's conclusions.

Comments on David Ranson's article `Monetary Policy, Market Prices, and Supply-Side Forecasting' on monetary policy, inflation and the economy. Applicability of Ranson's model; Forecasting real gross national product (GNP) with the short-term interest rate; Pinpointing forecasting errors; Views on migration model for explaining GNP's response to interest rate changes.

Focuses on attempts by Donald Bain in the 1920s and 1930s to establish policies protecting the San people in South Africa. Reasons why Bain's efforts to protect the Sans failed; Arguments raised by Bain justifying the need to establish reserves for the Sans; Empathy of the South African mass media for Bain's campaigns.

The multiplet state distribution of oxygen atoms produced in the photodissociation of SO2 was measured in a pump-and-probe experiment. An ArF laser was used to dissociate the parent molecule, while the O(3P) product was detected by two-photon laser-induced fluorescence under collisionless conditions. The multiplet populations were found to be 59.2%±5.0%, 29.5%±3.2%, and 11.4%±3.3% for J=2, 1, and 0, respectively. These results are indistinguishable from the statistical distribution of 5:3:1. [ABSTRACT FROM AUTHOR]

Lenzi et al’s comments on the number of photons absorbed by sulfur hexafluoride, and the subsequent transfer of energy to argon atoms are answered. It is suggested that the optoacoustic and the IR absorption measurements should be complimentary to each other.(AIP) [ABSTRACT FROM AUTHOR]

The electric field of a light wave accumulates a π phase shift as it passes through a focus. We show here how this effect, known as the Gouy phase, may be used to control the branching ratio of a unimolecular reaction when the products are formed with different numbers of photons. We demonstrate this control method for the ionization and dissociation of vinyl chloride, using absorption of 177 and 532 nm photons to induce a pair of interfering paths. Excellent agreement between the observed and calculated phase shift as a function of the axial coordinate of the laser focus indicates that fragmentation occurs via a ladder switching mechanism. The axial dependence of the modulation depth is evidence of loss of coherence at higher internal temperatures of the molecule. [ABSTRACT FROM AUTHOR]

Pairs of 80 fs, 800 nm laser pulses were used to ablate Si, Cu, and CaF2 in air. The spectrally resolved plasma emission was measured as a function of laser fluence and pulse delay. After an initial dip, the fluorescence was found to increase monotonically with pulse delay, reaching a plateau after some tens of picoseconds, depending on the material and fluence. The enhancement ratio (defined as the ratio of the fluorescence produced by the pulse pair to that produced by a single pulse of the same total fluence) reaches a maximum value of 6 and 11 at a fluence of ∼6 J/cm2 for Si and Cu, respectively, and declines to a value below 2 at higher fluences. In contrast, the enhancement for CaF2 increases slowly from zero near threshold to a broad maximum value of 2 near 50 J/cm2. Using reflectivity and atomic force microscopy measurements as diagnostics, we interpret the Si and Cu behavior in terms of a two phase mechanism, in which the first pulse melts the surface of the crystal and the second pulse ablates the resulting liquid film. A qualitatively different mechanism initiated by multiphoton absorption is involved in CaF2 ablation. [ABSTRACT FROM AUTHOR]

The rate constant for the reaction of O(3P)+D2 was measured over the temperature range 343 to 446 K using the laser photolysis–resonance fluorescence technique. The results can be fit well with a two-parameter Arrhenius function and are in excellent agreement with the previous measurements of Presser and Gordon and with the recent high temperature measurements of Michael. The data are also in very good agreement with the theoretical calculations of Joseph et al. and of Bowman et al. and demonstrate that tunneling makes a significant contribution to the rate coefficient over the entire range of temperatures studied in this experiment. The Arrhenius behavior of the rate constant supports the conclusions of Robie et al. in their study of the intramolecular isotope effect in O(3P)+HD, where it was found that tunneling plays a major role at low temperatures. [ABSTRACT FROM AUTHOR]

The two-photon spectra of HCl and DCl were studied using the technique of resonantly enhanced multiphoton ionization. Rovibrational bands were observed for the X 1Σ+→V 1Σ+, E 1Σ+, F 1Δ2, d 3Π1, f 3Δ2, and g 3Σ- transitions. The results are compared with the single photon spectra of Ginter, Douglas, and co-workers and with the molecular orbital calculations of Bettendorf et al. [ABSTRACT FROM AUTHOR]

Vibrational energy transfer from SF6 to N2O was studied by using a pulsed CO2 laser for multiphoton excitation of SF6 and monitoring the 4.5 μm emission from N2O(v3=1). The initial average energy of SF6 was selected by varying the fluence of the laser. The vibrational temperature of the ν2 mode of N2O was determined by measuring the attenuation of the fluorescence with a cold gas filter. The vibrational temperature of the ν3 mode was estimated by equating the SF6 and N2O(ν3) vibrational temperatures at the fluorescence maximum. The principal finding of this study is that N2O(ν2) is preferentially excited. While the mode specificity of the VV transfer declines with energy, it is greater than expected statistically. We also observed that the relaxation of ν2 is an order of magnitude slower than the relaxation of ν3. A kinetic model which accounts for most of the observations shows that VV transfer from SF6 to N2O occurs from high lying states of SF6 while the decay of N2O occurs by back transfer to the discrete levels of SF6. The slow relaxation of the bending mode of N2O indicates the existence of a bottleneck in VV transfer between N2O(ν2) and the discrete levels of SF6, which may be caused by a mechanism involving long-range attractive forces. [ABSTRACT FROM AUTHOR]

A numerical model was developed to determine the year-round temperature distribution within liquid manure storages, which is relevant for modelling temperature-dependent greenhouse gas and ammonia emissions. The model considers net short and long-wave radiation, heat conduction through walls and floor, surface convective heat transfer, evaporative heat loss, and manure loading. The model was implemented and validated for a circular concrete storage tank (40 m diameter; 2.5 m depth) on a dairy farm in Ontario, Canada, where it is assumed that heat transfer occurs in horizontal and vertical directions, and is symmetric in the angular direction. Annual root mean square error (RMSE), Nash–Sutcliffe model efficiency, coefficient of determination, and average bias between model estimates and measured values were 2.4 °C, 0.91, 0.95, and 0.12 °C, respectively. The model performed best in summer and autumn (lowest RMSE), which are the most important seasons for modelling temperature, as both temperature and manure volume are highest, leading to the greatest opportunity for gaseous emissions. A sensitivity analysis indicated that the most significant parameters were solar absorptivity, manure depth, incoming manure temperature, emissivity, and wind-speed. For every unit increase in depth (m), incoming manure temperature (°C), or wind-speed (m s −1 ), the peak summer temperature changed by −7.3, 0.3, or −2.4 °C, respectively. Parameters with little effect on temperature were the manure solids content and thermal conductivity of soil around the sides and the bottom of the tank. Results show that heat transfer is primarily 1-dimensional, and a simplified 1-D model would be sufficient for future applications. [ABSTRACT FROM AUTHOR]

Coherent control of the ionization of HCl was achieved by simulataneous 3+1 and 1+1 multiphoton excitation in a molecular beam machine, using either three 336 nm photons or one 112 nm photon to resonantly excite the intermediate j 3Σ-(Ω=0+) state. The phase difference between the two laser beams was continuously varied by passing the radiation through a cell containing either Ar or H2 gas. [ABSTRACT FROM AUTHOR]

SummaryTwo experiments assessed the effect of current and elevated levels of ultravioletB (UV-B) radiation on forage crop production. The effect of current levels of UV-B radiation was assessed by comparing the growth of eight cultivars of four legume and four grass species for three growing seasons (1994–96) under simulated sward conditions in the field. An exclusion system using cellulose diacetate or polyester covers provided comparable growing conditions for the plants, except for the presence or absence of ambient UV-B radiation, respectively. The second experiment studied the effect of elevated levels of UV-B on eight cultivars of two legume and two grass species in the greenhouse under simulated sward conditions. Natural lighting with sufficient supplemental light was used to provide ideal growing conditions for a 16-h day length. Separate sets of UV lights were installed to provide UV-B levels at approximately the same intensity as would be found in mid summer, and 33% and 66% more than this value. A fourth treatment consisted of removing UV-B radiation by using a polyester filter. Plant production was measured in both experiments. In 1994, field herbage yields from all young grass and legume seedlings were not significantly affected by the exclusion of ambient UV-B radiation, with the exception of alfalfa. Intra-specific variations with alfalfa yields were found for reduced levels of UV-B radiation. In general, these trends persisted as stands matured during two post seeding years. In the second experiment, no significant differences were observed for all tested species with increasing levels of UV-B radiation, except with some alfalfa cultivars and one birdsfoot trefoil cultivar. Collectively, these results demonstrate that in the northern latitudes young and mature plants of the studied species are resistant to current and potentially higher levels of solar UV-B radiation, with the exception of some alfalfa cultivars. The yield of these cultivars increased under enhanced levels of UV-B radiation in the greenhouse and decreased when UV-B was excluded in the field. [ABSTRACT FROM AUTHOR]