Recent Advancements

With progressive development of the computer technology, substanhal advancement has been made in the area of developing models to simplify the air-stripping tower design 

Thom and Byers (35) discussed the design and construction issues that can lead to the inaccurate model predictions compared to field observations in that liquid distribution, packing materials, fouling, chemical reaction, and end effects were of great importance. 

Another limitation and restriction of these models are the data reliability of the Henry s law constants. It is very important that accurate Henry s law constants shall be available for modeling an air stripper as all design parameters and costs are strongly sensitive to the Henry s law constants (22). For many common VOCs, the constants are available in books as well as the literature. For uncommon contaminants, the constants may be looked up in an extensive database by Sander (36) or predicted by using quantitative structure-activity relationship (QSAR) model for Henry s law constant (37). However, if the data are absent or data reliability is of question, pilot testing or laboratory measurement of the Henry s law constant is recommended (38). 

Volatile compounds exhibit high activity coefficients in water and are easily evaporated. The countercurrent air stripper provides a large wetted surface area for mass transfer in a compact unit. Although routine maintenance is required, the components of the air stripper should have long service lives. The air stripper is capable of removing large numbers of volatile compounds at relatively low cost. 

The design of an air stripping tower is essentially similar to that of the conventional cooling tower (12). There are two basic types of tower configuration crosscurrent and countercurrent, with the former being more common at the present time. 

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One of the more recent advances in XPS is the development of photoelectron microscopy [ ]. By either focusing the incident x-ray beam, or by using electrostatic lenses to image a small spot on the sample, spatially-resolved XPS has become feasible. The limits to the spatial resolution are currently of the order of 1 pm, but are expected to improve. This teclmique has many teclmological applications. For example, the chemical makeup of micromechanical and microelectronic devices can be monitored on the scale of the device dimensions. 

Some recent advances in stimulated desorption were made with the use of femtosecond lasers. For example, it was shown by using a femtosecond laser to initiate the desorption of CO from Cu while probing the surface with SHG, that the entire process is completed in less than 325 fs [90]. The mechanism for this kind of laser-induced desorption has been temied desorption induced by multiple electronic transitions (DIMET) [91]. Note that the mechanism must involve a multiphoton process, as a single photon at the laser frequency has insufScient energy to directly induce desorption. DIMET is a modification of the MGR mechanism in which each photon excites the adsorbate to a higher vibrational level, until a suflBcient amount of vibrational energy has been amassed so that the particle can escape the surface. 

Hase W L 1998 Some recent advances and remaining questions regarding unimolecular rate theory Acc. Chem. Res. 31 659-65... 

Marowsky G and Smirnov V N (eds) 1992 Coherent Raman Spectroscopy Recent Advances (Berlin Springer)... 

Many of the fiindamental physical and chemical processes at surfaces and interfaces occur on extremely fast time scales. For example, atomic and molecular motions take place on time scales as short as 100 fs, while surface electronic states may have lifetimes as short as 10 fs. With the dramatic recent advances in laser tecluiology, however, such time scales have become increasingly accessible. Surface nonlinear optics provides an attractive approach to capture such events directly in the time domain. Some examples of application of the method include probing the dynamics of melting on the time scale of phonon vibrations [82], photoisomerization of molecules [88], molecular dynamics of adsorbates [89, 90], interfacial solvent dynamics [91], transient band-flattening in semiconductors [92] and laser-induced desorption [93]. A review article discussing such time-resolved studies in metals can be found in... 

Reider G A and Heinz T F 1995 Second-order nonlinear optical effects at surfaces and interfaces recent advances Photonio Probes of Surfaoes ed P Halevi (Amsterdam Elsevier) pp 413-78... 

It is interesting to note the analogy of developments in light microscopy during the last few decades. The confocal microscope as a scaiming beam microscope exceeds by far the nomial fluorescence light microscope in resolution and detection level. Very recent advances in evanescent wave and interference microscopy seem to promise to provide even higher resolution (B1.18). 

Hansma H G, Sinsheimer R L, Groppe J, Bruice T C, Elings V, Gurley G, Bezanilla M, Mastrangelo I A, Hough P V C and Hansma P K 1993 Recent advances in atomic force microscopy of DMA Scanning 15 296... 

Yoshizawa H, Chen Y L and Israelachvili J N 1993 Recent advances in molecular level understanding of adhesion, friction and lubrication Wear 6B 161-6... 

However, recent advances in teclmiques will ensure fiirther diversification and complexification of solved surface structures. The present maturity of teclmiques will thus iucreasmgly allow the analysis of structures chosen for their practical interest rather than for their simplicity. 

Powell M J D 1971 Recent advances in unconstrained optimization Math. Prog. 1 26... 

Floudas C and Pardalos P M 1991 Recent Advances in Giobai Optimization (Princeton, NJ Princeton University Press)... 

Ausman K D, Benedetto A F, Samuelsand D A and Weisman R B 1998 Recent Advances in the Chemistry of Fuiierenes and Reiated Materiais(The Eiectrochemicai Society Proceedings Series) vol 6, ed K M Kadish and R S Ruoff (Pennington, NJ The Electrochemical Society) p 281... 

Schemes for classifying surfactants are based upon physical properties or upon functionality. Charge is tire most prevalent physical property used in classifying surfactants. Surfactants are charged or uncharged, ionic or nonionic. Charged surfactants are furtlier classified as to whetlier tire amphipatliic portion is anionic, cationic or zwitterionic. Anotlier physical classification scheme is based upon overall size and molecular weight. Copolymeric nonionic surfactants may reach sizes corresponding to 10 000-20 000 Daltons. Physical state is anotlier important physical property, as surfactants may be obtained as crystalline solids, amoriDhous pastes or liquids under standard conditions. The number of tailgroups in a surfactant has recently become an important parameter. Many surfactants have eitlier one or two hydrocarbon tailgroups, and recent advances in surfactant science include even more complex assemblies [7, 8 and 9].

To use direct dynamics for the study of non-adiabatic systems it is necessary to be able to efficiently and accurately calculate electronic wave functions for excited states. In recent years, density functional theory (DFT) has been gaining ground over traditional Hartree-Fock based SCF calculations for the treatment of the ground state of large molecules. Recent advances mean that so-called time-dependent DFT methods are now also being applied to excited states. Even so, at present, the best general methods for the treatment of the photochemistry of polyatomic organic molecules are MCSCF methods, of which the CASSCF method is particularly powerful. 

In this chapter, recent advances in the theory of conical intersections for molecules with an odd number of electrons are reviewed. Section II presents the mathematical basis for these developments, which exploits a degenerate perturbation theory previously used to describe conical intersections in nonrelativistic systems [11,12] and Mead s analysis of the noncrossing rule in molecules with an odd number of electrons [2], Section III presents numerical illustrations of the ideas developed in Section n. Section IV summarizes and discusses directions for future work. 

M A 1997. Recent Advances in Ligand Design Methods. In Lipkowitz K B and D B Boyd itors) Reviews in Computational Chemistry Volume 11. New York, VCH Publishers, pp. 1-66. 

Gresho, P. M., Lee, R. L. and Sani, R. L., 1980. On the time-dependent solution of the incompressible Navier-Stokes equations in two and three dimensions. In Recent Advances in Numerical Methods in fluids, Ch. 2, Pineridge Press, Swansea, pp. 27-75. 

Recent Advances in Density Functional Theory D. P. Chong, Ed., World Scientihc, Singapore (1995). 

The study of organic semiconductors and conductors is highly iaterdisciplinary, involving the fields of chemistry, soHd-state physics, engineering, and biology. This article provides a treatment of the theoretical aspects of organic semiconductors as well as an overview of recent advances ia the field and the uses of these materials based on their conductive and optical properties. 

J. Coleby in C. Hanson, ed.. Recent Advances in Eiquid—Eiquid Extraction, Pergamon Press, Oxford, UK, 1971. 

Recent advances in Eischer-Tropsch technology at Sasol include the demonstration of the slurry-bed Eischer-Tropsch process and the new generation Sasol Advanced Synthol (SAS) Reactor, which is a classical fluidized-bed reactor design. The slurry-bed reactor is considered a superior alternative to the Arge tubular fixed-bed reactor. Commercial implementation of a slurry-bed design requires development of efficient catalyst separation techniques. Sasol has developed proprietary technology that provides satisfactory separation of wax and soHd catalyst, and a commercial-scale reactor is being commissioned in the first half of 1993. 

F. Molesky in Recent Advances in Flame Retardamy of Polymeric Materials, Stamford, Coim., 1990 F. Molesky, "The Use of Magnesium Hydroxide for Flame Retarded Low Smoke Polypropylene," Polyolefins IHInternational Conference, Feb. 24,1991, Houston, Tex. 

D. Paul, "A New Phosphate Plasticizer for Low Smoke Wire and Cable AppHcations," paper presented at 3rd Annual BCC Conference on Recent advances in Flame Retardany of Polymeric Materials, Stamford, Conn., May 19—21,1992. 

E. D. Wed and A. M. Aaronson, "Phosphoms Flame Retardants— Some Effects on Smoke and Combustion Products," lecture at University of Detroit Polymer Conference on Recent Advances in Combustion and Smoke Retardance of Polymers, Mich., May 1976. 

Kinetic as weU as thermodynamic problems are encountered in fluorination. The rate of reaction must be decelerated so that the energy Hberated may be absorbed or carried away without degrading the molecular stmcture. The most recent advances in direct fluorination ate the LaMar process (18—20) and the Exfluot process (21—24), which is practiced commercially by 3M. 

S. B. Alpert and D. F. Spencer, Methanol and Eiquid Fuels From Coal—Recent Advances, Electric Power Research Institute, Palo Alto, Calif., 1987. 

J. P. Hanrahan, Recent Advances in Einimal Nutrition, Butterworths, London, 1986, pp. 125—138. 

J. Scott, ed.. Membrane and Ultrafiltration Technology 1980, Recent Advances, Chemical Technology Review No. 147, Noyes Data Corp., Park Ridge, N.J.,... 

P. W. Lenz, Recent Advances in Fiquid Crystalline Polymers, Elsevier Apphed Science Pubhshets, Denmark, 1983. 

T. Hogen-Esch andj. Smid, eds.. Recent Advances in Anionic Polymerisation, Elsevier, New York, 1987. 

E. N. Cogswell, ia L. L. Chapoy, Recent Advances in Eiquid Cystalline Polymers, Elseviei, New Yoik, 1985. 

Future Developments. The most recent advance in detergent alkylation is the development of a soHd catalyst system. UOP and Compania Espanola de Petroleos SA (CEPSA) have disclosed the joint development of a fixed-bed heterogeneous aromatic alkylation catalyst system for the production of LAB. Petresa, a subsidiary of CEPSA, has announced plans for the constmction of a 75,000 t/yr LAB plant in Quebec, Canada, that will use the UOP / -paraffin dehydrogenation process and the new fixed-bed alkylation process (85). 

B. V. Voia, P. R. Pujado, T. Imai, and T. R. Fritsch, Recent Advances in the Production of Detergent Olefins and Pinear Alkylbenyenes, Society of Chemical Industry, University of Cambridge, England, Mar. 26—28, 1990. 

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