A comparison of the fine-scale structure of the diurnal cycle of tropical rain and lightning

In this study, the fine-scale structure of the diurnal variability of ground-based lightning is systematically compared with satellite-based rain. At the outset, it is shown that tropical variability of lightning exhibits a prominent diurnal mode, much like rain. A comparison of the geographical distribution of the timing of the diurnal maximum shows that there is very good agreement between the two observables over continental and coastal regions throughout the tropics. Following this global tropical comparison, we focus on two regions, Borneo and equatorial South America, both of which show the interplay between oceanward and landward propagations of the phase of the diurnal maximum. Over Borneo, both rain and lightning clearly show a climatological cycle of ``breathing in'' (afternoon to early morning) and ``breathing out'' (morning to early afternoon). Over the equatorial east coast of South America, landward propagation is noticed in rain and lightning from early afternoon to early morning. Along the Pacific coast of South America, both rain and lightning show oceanward propagation. Though qualitatively consistent, over both regions the propagation is seen to extend further in rainfall. Additionally, given that lightning highlights vigorous convection, the timing of its diurnal maximum often precedes that of rainfall in the convective life cycle. (C) 2015 Elsevier B.V. All rights reserved.

Extended self-similar scaling law of multi-scale eddy structure in wall turbulence

The longitudinal fluctuating velocity of a turbulent boundary layer was measured in a water channel at a moderate Reynolds number. The extended self-similar scaling law of structure function proposed by Benzi was verified. The longitudinal fluctuating velocity, in the turbulent boundary layer was decomposed into many multi-scale eddy structures by wavelet transform. The extended self-similar scaling law of structure function for each scale eddy velocity was investigated. The conclusions are I) The statistical properties of turbulence could be self-similar not only at high Reynolds number, but also at moderate and low Reynolds number, and they could be characterized by the same set of scaling exponents xi (1)(n) = n/3 and xi (2)(n) = n/3 of the fully developed regime. 2) The range of scales where the extended self-similarity valid is much larger than the inertial range and extends far deep into the dissipation range,vith the same set of scaling exponents. 3) The extended selfsimilarity is applicable not only for homogeneous turbulence, but also for shear turbulence such as turbulent boundary layers.

Multiple SNP Markers Reveal Fine-Scale Population and Deep Phylogeographic Structure in European Anchovy (Engraulis encrasicolus L.)

10 p.

Cavity-enhanced spectroscopies for applications of remote sensing, chemical kinetics and detection of radical species

This thesis describes applications of cavity enhanced spectroscopy towards applications of remote sensing, chemical kinetics and detection of transient radical molecular species. Both direct absorption spectroscopy and cavity ring-down spectroscopy are used in this work. Frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) was utilized for measurements of spectral lineshapes of O₂ and CO₂ for obtaining laboratory reference data in support of NASA’s OCO-2 mission. FS-CRDS is highly sensitive (> 10 km absorption path length) and precise (> 10000:1 SNR), making it ideal to study subtle non-Voigt lineshape effects. In addition, these advantages of FS-CRDS were further extended for measuring kinetic isotope effects: A dual-wavelength variation of FS-CRDS was used for measuring precise D/H and ¹³C/¹²C methane isotope ratios (sigma>0.026%) for the purpose of measuring the temperature dependent kinetic isotope effects of methane oxidation with O(¹D) and OH radicals. Finally, direct absorption spectroscopic detection of the trans-DOCO radical via a frequency combs spectrometer was conducted in collaboration with professor Jun Ye at JILA/University of Colorado.

1. Ultrasonic studies of binary liquid structure in the critical region. Theory and experiment for the 2,6-lutidine/water system. 2. Hartree-Fock calculations of electric polarizabilities of some simple atoms and molecules, and their practicality. 3. Calculation of vibrational transition probabilities in collinear atom-diatom and diatom-diatom collisions with Lennard-Jones interaction

Part 1. Many interesting visual and mechanical phenomena occur in the critical region of fluids, both for the gas-liquid and liquid-liquid transitions. The precise thermodynamic and transport behavior here has some broad consequences for the molecular theory of liquids. Previous studies in this laboratory on a liquid-liquid critical mixture via ultrasonics supported a basically classical analysis of fluid behavior by M. Fixman (e. g., the free energy is assumed analytic in intensive variables in the thermodynamics)--at least when the fluid is not too close to critical. A breakdown in classical concepts is evidenced close to critical, in some well-defined ways. We have studied herein a liquid-liquid critical system of complementary nature (possessing a lower critical mixing or consolute temperature) to all previous mixtures, to look for new qualitative critical behavior. We did not find such new behavior in the ultrasonic absorption ascribable to the critical fluctuations, but we did find extra absorption due to chemical processes (yet these are related to the mixing behavior generating the lower consolute point). We rederived, corrected, and extended Fixman's analysis to interpret our experimental results in these more complex circumstances. The entire account of theory and experiment is prefaced by an extensive introduction recounting the general status of liquid state theory. The introduction provides a context for our present work, and also points out problems deserving attention. Interest in these problems was stimulated by this work but also by work in Part 3.

Part 2. Among variational theories of electronic structure, the Hartree-Fock theory has proved particularly valuable for a practical understanding of such properties as chemical binding, electric multipole moments, and X-ray scattering intensity. It also provides the most tractable method of calculating first-order properties under external or internal one-electron perturbations, either developed explicitly in orders of perturbation theory or in the fully self-consistent method. The accuracy and consistency of first-order properties are poorer than those of zero-order properties, but this is most often due to the use of explicit approximations in solving the perturbed equations, or to inadequacy of the variational basis in size or composition. We have calculated the electric polarizabilities of H₂, He, Li, Be, LiH, and N₂ by Hartree-Fock theory, using exact perturbation theory or the fully self-consistent method, as dictated by convenience. By careful studies on total basis set composition, we obtained good approximations to limiting Hartree-Fock values of polarizabilities with bases of reasonable size. The values for all species, and for each direction in the molecular cases, are within 8% of experiment, or of best theoretical values in the absence of the former. Our results support the use of unadorned Hartree-Pock theory for static polarizabilities needed in interpreting electron-molecule scattering data, collision-induced light scattering experiments, and other phenomena involving experimentally inaccessible polarizabilities.

Part 3. Numerical integration of the close-coupled scattering equations has been carried out to obtain vibrational transition probabilities for some models of the electronically adiabatic H₂-H₂ collision. All the models use a Lennard-Jones interaction potential between nearest atoms in the collision partners. We have analyzed the results for some insight into the vibrational excitation process in its dependence on the energy of collision, the nature of the vibrational binding potential, and other factors. We conclude also that replacement of earlier, simpler models of the interaction potential by the Lennard-Jones form adds very little realism for all the complication it introduces. A brief introduction precedes the presentation of our work and places it in the context of attempts to understand the collisional activation process in chemical reactions as well as some other chemical dynamics.

Extended effective medium model for refractive indices of thin films with oblique columnar structure

The refractive indices of thin films, containing dielectric and voids in an oblique columnar structure, are modeled by extended effective medium in the quasi-static limit. The dielectric function is shown to be strongly dependent on the angle of incidence and on the columnar orientation for p-polarized light. This model is applied to model ZrO2 thin films with oblique columnar structures and the computed results, with the Maxwell Garnett, the Bragg-Pippard, and the Bruggeman formalisms, have been given. (c) 2004 Elsevier B.V. All rights reserved.

Infrared absorption efficiency in AlAs/AlxGa1-xAs type-II multiple-quantum-well structure grown on (211) GaAs substrate

We have made a normal incidence high infrared absorption efficiency AlAs/Al0.55Ga0.45As multiple-quantum-well structure grown on (211) GaAs substrates by molecular beam epitaxy (MBE). A strong infrared absorption signal at 11.6 mu m due to the transition of the ground state to the first excited state, and a small signal at 6.8 mu m due to the transition from the ground state to continuum. were observed. A 45 degrees tilted incidence measurement was also performed on the same sample for the comparison with a normal incidence measurement. Both measurements provide important information about the quantum well absorption efficiency. Efficiencies which evaluate the absorption of electric components perpendicular and parallel to the well plane are eta(perpendicular to) = 25% and eta(parallel to) = 88%, respectively. The total efficiency is then deduced to be eta = 91%. It is apparent that the efficiency eta(parallel to) dominates the total quantum efficiency eta Because an electron in the (211) AlAs well has a small effective mass (m(zx)* or m(zy)*), the normal incidence absorption coefficient is expected to be higher:than that grown on (511) and (311) substrates. Thus, in the present study, we use the (211) substrate to fabricate QWIP. The experimental results indicate the potential of these novel structures for use as normal incidence infrared photodetectors.

Wide-band underwater acoustic absorption based on locally resonant unit and interpenetrating network structure

The interpenetrating network structure provides an interesting avenue to novel materials. Locally resonant phononic crystal (LRPC) exhibits excellent sound attenuation performance based on the periodical arrangement of sound wave scatters. Combining the LRPC concept and interpenetrating network glassy structure, this paper has developed a new material which can achieve a wide band underwater strong acoustic absorption. Underwater absorption coefficients of different samples were measured by the pulse tube. Measurement results show that the new material possesses excellent underwater acoustic effects in a wide frequency range. Moreover, in order to investigate impacts of locally resonant units, some defects are introduced into the sample. The experimental result and the theoretical calculation both show that locally resonant units being connected to a network structure play an important role in achieving a wide band strong acoustic absorption.

ZnO clusters encapsulated inside micropores of zeolites studied by UV Raman and laser-induced luminescence spectroscopies

Using microporous zeolites as host, sub-nanometric ZnO clusters were prepared in the micropores of the host by the incipient wetness impregnation method. A small amount of sub-nanometric ZnO clusters were introduced into the channels of HZSM-5 zeolite, whereas a large quantity of sub-nanometric ZnO clusters can be accommodated in the supercages of HY zeolite and no macrocrystalline ZnO exists on the extra surface of the HY material. The vibrations of the zeolite framework and ZnO were characterized by UV Raman spectroscopy. The optical properties of these ZnO clusters were studied by UV-visible absorption spectroscopy and laser-induced luminescence spectroscopy. It is found that there are strong host-guest interactions between the framework oxygen atoms of zeolite and ZnO clusters influencing the motions of the framework oxygen atoms. The interaction may be the reason why ZnO clusters are stabilized in the pores of zeolites. Different from bulk ZnO materials, these sub-nanometric ZnO clusters exhibit their absorption onset below 265 nm and show a purple luminescence band (centered at 410-445 nm) that possesses high quantum efficiency and quantum size effect. This purple luminescence band most likely originates from the coordinatively unsaturated Zn sites in sub-nanometric ZnO clusters. On the other hand, the differences in the pore structure between HZSM-5 and HY zeolites cause the absorption edge and the purple luminescence band of ZnO clusters in ZnO/HZSM-5 show a red shift in comparison with those of ZnO clusters in ZnO/HY.

Synthesis, electrical properties and crystal structure of a new radical-ion salt based on pi-extended bis(TTF) and a Keggin heteropolymolybdate

By electrocrystallization of 2,6-[4,5-bis(n-butylsulfanyl)-1,3-dithiol-2-ylidene]-4,8-bis(6-iodo-n-hexyloxy)-1,3,5,7-tetrathia-s-indacene (BHBDTI) and [NBu4](4)[SiMo12O40] in the mixed solvent CHCl2CH2Cl and CH3CN, the new radical-ion salt [C42H60Cl2O2S12](2)[SiMo12O40] was prepared. It was characterized by means of IR and ESR spectroscopy and X-ray diffraction. In the crystal structure, organic radical dications and silicomolybdate anions are alternatively arranged along the a axis to form a 1-D conducting layer. The organic layer consists of two isolated groups of BHBDTI divided by the (011) plane without short interatomic contacts. However, in each group, BHBDTI molecules associate with each other in a head to tail manner running along the [011] direction and face-to-face overlapping with a relative shift by approximately one TTF subunit along the long axis of the molecule and a slight shift along the short axis of the molecule with significantly short S ... S contacts. The room-temperature d.c. conductivity determined by the two-probe method is 10(-4) S cm(-1), suggesting that the compound is a semiconductor.

Pump-dump control and the related transient absorption spectroscopies

We combine theories of optimal pump-dump control and the related transient probe absorption spectroscopy in order to elucidate the relation between these two optical processes and the possibility of experimental realization. In the weak response regime, we identify the globally optimal pair of pump-dump control fields, and further propose a second-order difference detection scheme to monitor the wave packets dynamics that is jointly controlled by both the pump and dump fields. The globally optimal solution serves also as the initial input for the iterative search for the optimal control fields in the strong response regime. We use a model I-2 molecule to demonstrate numerically the pump-dump control and the detection of a highly vibrationally excited wave packet focusing dynamics on the ground X surface in both the weak and strong response regimes. The I2B surface serves as the intermediate to assist the pump-dump control and the optical detection processes. Demonstrated in the strong response regime are the optimal pair of pump-dump molecular-pi pulses that invert nearly total population onto the predefined target region within a half period of vibration motion. (C) 1999 American Institute of Physics. [S0021-9606(99)00115-4].

The active sites in different TS-1 zeolites for propylene epoxidation studied by ultraviolet resonance Raman and ultraviolet visible absorption spectroscopies

The titanium species in four kinds of titanium-containing MFI zeolites have been studied by ultraviolet (UV)-Raman and ultraviolet visible (UV-Vis) absorption spectroscopies and by the epoxidation of propylene with diluted H2O2 solution (30%). UV-Raman spectroscopy is proved to be a suitable means to estimate qualitatively the framework titanium in TS-l zeolites. Based on the comparison of the relative intensity ratio I-1125/I-380 of UV-Raman spectra, the TS-1(conv.) sample synthesized hydrothermally by the conventional procedure shows the highest amount of framework titanium. UV-Vis spectroscopy reveals that besides minor anatase. titanium species are mainly tetrahydrally coordinated into the framework for TS-l(conv.) or the Ti-ZSM-5 sample prepared by gas-solid reaction between deboronated B-ZSM-5 and TiCl4 vapor at elevated temperatures. For the TS-1(org.) and TS-1(inorg.) samples synthesized hydrothermally using tetrapropylammonium bromide (TPABr) as template and tetrabutylorthotitanite (TBOT) and TiCl3 as titanium source, respectively, the presence of mononuclear and isolated TiOx species which are proposed to bond to the zeolite extraframework is observed. In addition to the framework titanium species, these isolated TiOx species are assumed to be also active for propylene epoxidation.