Physical Sciences and Mathematics Commons^™

Studies Of A Dirhodium Tetraphosphine Catalyst For Hydroformylation And Aldehyde-Water Shift Catalysis, Aaron Rider Barnum

LSU Doctoral Dissertations

Research into the dirhodium tetraphosphine catalyst precursor [rac-Rh2(nbd)2(et,ph-P4)](BF4)2 shows it is capable of forming a highly active and regioselective hydroformylation catalyst in situ when using an acetone or acetone/water solvent. Hydroformylation experiments (using 1-hexene), FT-IR studies, and acid-base studies were performed to better understand the various complexes of the dirhodium catalyst cycle. These studies lead to the newly proposed catalyst mechanism when performed in an acetone/water solution, using the monocationic [rac-Rh2(H)(µ-CO)2(CO) (et,ph-P4)]+ as the proposed active catalyst complex for hydroformylation. For the conversion of 1-hexene to heptanal, it is capable of performing an initial rate of 30 turnovers per min, …

A Global Diatom Database- Abundance, Biovolume And Biomass In The World Ocean, K. Leblanc, J. Aristegui, L. Armand, P. Assmy, B. Becker, A. Bode, E. Breton, V. Cornet, J. Gibson, M. P. Gosselin, H. Marshall

Biological Sciences Faculty Publications

Phytoplankton identification and abundance data are now commonly feeding plankton distribution databases worldwide. This study is a first attempt to compile the largest possible body of data available from different databases as well as from individual published or unpublished datasets regarding diatom distribution in the world ocean. The data obtained originate from time series studies as well as spatial studies. This effort is supported by the Marine Ecosystem Model Inter-Comparison Project (MAREMIP), which aims at building consistent datasets for the main plankton functional types (PFTs) in order to help validate biogeochemical ocean models by using carbon (C) biomass derived from …

Plane And Simple: Planar Tetracoordinate Carbon Centers In Small Moleculesw, Chad Crigger, Bernard K. Wittmaack, Marina Tawfik, Gabriel Merino, Kelling J. Donald

Chemistry Faculty Publications

A class of neutral 18-electron molecules with planar tetracoordinate carbon (ptC) centers is introduced. We show computationally that when n = 3 the neutral singlet molecule C(BeH)_n(BH₂)_4-n and other isoelectronic (18-valence electron) molecules of main group elements collapse from locally tetrahedral arrangements at the C-center to (near) planar tetracoordinate structures. For C(BeH)₃BH₂ and C(CH₃)(BH₂)Li₂, for example, the tetrahedral type conformation is not even a minimum on the potential energy surface at the B3PW91, MP2(full), or CCSD levels of theory. The Mg analogue C(MgH)₃BH_{2 …}

Cbe5e− (E = Al, Ga, In, Tl): Planar Pentacoordinate Carbon In Heptaatomic Clusters, Abril C. Castro, Gerarso Martinez-Guajardo, Thomas Johnson, Jesus M. Ugalde, Yan-Bo Wu, Jose M. Mercero, Thomas Heine, Kelling J. Donald, Gabriel Merino

Chemistry Faculty Publications

A series of clusters with the general formula CBe₅E^- (E = Al, Ga, In, Tl) are theoretically shown to have a planar pentacoordinate carbon atom. The structures show a simple and rigid topological framework—a planar EBe4 ring surrounding a C center, with one of the ring Be–Be bonds capped in-plane by a fifth Be atom. The system is stabilized by a network of multicenter σ bonds in which the central C atom is the acceptor, and π systems as well by which the C atom donates charge to the Be and E atoms that encircle it.

On Fundamental Groups Of Quotient Spaces, Jack S. Calcut, Robert E. Gompf, John D. Mccarthy

Faculty & Staff Scholarship

In classical covering space theory, a covering map induces an injection of fundamental groups. This paper reveals a dual property for certain quotient maps having connected fibers, with applications to orbit spaces of vector fields and leaf spaces in general.

Slab Waveguide Sensor Based On Amplified Phase Change Due To Multiple Total Internal Reflections, Sofyan A. Taya, Taher M. El-Agez

Turkish Journal of Physics

We present theoretically an optical slab waveguide sensor based on amplified phase change due to multiple total internal reflections (TIRs). Compared with the conventional waveguide sensors, the proposed approach provides higher sensitivity. In this sensor, we adopt the change in the ellipsometric total phase change \Delta as the measuring probe of changes in the refractive index (RI) of the cladding. The change in \Delta is calculated for large number of alternating total reflections. Numerical calculations show that \Delta is strongly dependent on the RI variations of the cladding. Moreover, theoretical simulations show that the resolution of this sensor is predicted …

Morphological And Optical Properties Of Vacuum Evaporated Zno Thin Films, Farzana Chowdhury, S. M. Firoz Hasan, M. Sahabul Alam

Turkish Journal of Physics

ZnO thin films were deposited onto chemically and ultrasonically cleaned glass substrates by thermal evaporation in vacuum (\sim 10^{-6} mbar). The thickness of the films was measured by frequency shift of quartz crystal. The optical properties of the films have been ascertained by UV-VIS-NIR spectrophotometry in the photon wavelength range of 300--2500 nm. The effect of substrate temperature on the optical properties of the films has been investigated, where all film thickness was kept fixed at 100 \pm 10 nm. The optical transmittance spectra reveal a maximum transmittance of 88% at room temperature around photon wavelength of 2350 nm. Band …

Structural And Optical Studies On La Doped Cds Nanocrystalline Films, Kusumanjali Dehmukh, Mimi Mukherjee, Shashi Bhushan

Turkish Journal of Physics

This paper reports the synthesis of pure and lanthanum (La) doped nanocrystalline CdS semiconducting films on the glass substrate by means of chemical bath deposition (CBD), with Cd(CH_3COO)_2 as Cadmium (Cd) ion source, (NH_2)_2CS as sulphur (S) ion source and Thioglycerol as capping agent. Long, rod like structures is observed in SEM micrographs of the films. XRD studies show the existence of both hexagonal and cubic phases. Increase in FWHM is observed for smaller particle due to nanocrystalline effect. UV-VIS absorption studies show shift of absorption edge towards lower wavelength side. Corresponding change in band gap energy results in shift …

The Composition Dependence Of The Optical Band Gap In Ge Doped Se-Te Glassy Alloy, Mainika Kapoor, Nagesh Thakur

Turkish Journal of Physics

Bulk glasses with the chemical composition (Se_{80}Te_{20})_{100-x}Ge_x (x = 0, 2, 4, 6) have been prepared from high purity constituent elements. Fragments of the bulk glasses are used to deposit thin films by vacuum thermal evaporation and compositional dependence of the optical and physical properties have been studied. It has been found that optical absorption is due to indirect transition and the optical band gap E_g increases with increasing Ge content in Se-Te glassy alloy. The relationship between the E_g and chemical composition is discussed in terms of cohesive energy and co-ordination number.

Specific Heat Of Ytterbium Iron Garnet Yb_3fe_5o_{12} At Low Temperatures, Abdelmalek Boumali, Oumhani Derar

Turkish Journal of Physics

The state of the Yb^{3+} ion of the ytterbium iron garnet (Yb_3Fe_5O_{12}) is suitable for the development of theoretical models with rather good approximations. Using the theory of two-level paramagnetic ions, the total and magnetic specific heat at low temperatures has been calculated. The influence of tensors g and G on the specific heat of YbIG has been examined. A comparison has been made of our results and those obtained with a model based on of the approximation of Weiss Molecular-Field (WMF) and experimental data.

Characterization Of Analog Modulation Of Algaas Lasers And The Induced Intensity Noise, Moustafa Ahmed, Nour Zaki El-Sayed, Hameeda Ibrahim, Kamal Abdelhady

Turkish Journal of Physics

The dynamics of AlGaAs laser diodes under analog intensity modulation are characterized and the associated intensity noise is evaluated. The study is based on numerical solution of the stochastic rate equations of semiconductor lasers. Based on the shape of the modulated laser signal, the modulation dynamics are classified into eight distinct types. Four types are characterized by continuous periodic signals, and three types have periodic pulsing signals. These signals happen to have period doubling or superposed by sub-peaks from the relaxation oscillations of the laser. The last type is chaos, in which the signal is irregular and non-uniform. The noise …

Equations Of State For Amorphous And Crystalline Nickel By Means Of Molecular Dynamics Method, Soner Özgen, Levent Sonğur, İzzet Kara

Turkish Journal of Physics

There are few theoretical studies on the equation of state (EOS) for amorphous materials while much work has been carried out for crystalline systems. In this study, the EOSs for both crystal- and amorphous-structured nickel are obtained by using an anisotropic molecular dynamics method based on the Voter-Chen formalism of embedded atom method. In order to achieve the EOSs, polynomial curve fitting method has been applied to the data obtained from molecular dynamics simulations carried assuming isothermal and isobaric conditions. Isothermal bulk modulus and their pressure derivatives for both amorphous and crystal structures have also been calculated. The results are …

Monochromatization Effect Kinetic Model For Penning Gas Mixtures Emission Mechanisms, Catalina Ciobotaru, Geavit Musa

Turkish Journal of Physics

The monochromatization effect (M-effect), which consists in the reduction of an electronegative-electropositive gas mixtures discharge emission spectrum to only a few or a single line, was largely explained in our previous published papers together with their generation mechanisms, namely the polar ion-ion recombination and the energy resonance condition. This paper presents a kinetic model for the M-effect based on the radiative and collisional processes which appear between 1s_2, 1s_3, 1s_4 and 1s_5 Paschen levels, in Penning gas mixtures, where this effect was observed to be the most powerful.

The Differential Transform Method For Solving Heat-Like And Wave-Like Equations With Variable Coefficients, Khatereh Tabatabaei, Ercan Çeli̇k, Raziyeh Tabatabaei

Turkish Journal of Physics

In this article, Differential transform method is presented for solving heat-like and wave-like equations with variable coefficients. We applied these methods to six examples. This powerful method gives an exact solution. These examples are prepared to show the efficiency and simplicity of the method.

Coupled-Channels Analysis Of K^+ Scattering From ^6li, Ahmed Aly Ebrahim

Turkish Journal of Physics

Differential cross sections for the elastic and inelastic scattering of K^+ at 715 MeV/c from ^6Li are analysed by applying the Watanabe superposition model to the real potential with a phenomenological imaginary potential. The optical potential of ^6Li is calculated in terms of alpha-particle and deuteron or triton and helion optical potentials. The calculated cross sections are consistent with the triton-helion model.

Resonant Electron Transfer And L-Shell Excitation For _{26}Fe^{19+} And _{30}Zn^{23+} Ions, Hassan Ramadan

Turkish Journal of Physics

Resonant transfer and excitation (RTE) involving simultaneous electron capture and projectile L-shell excitation has been calculated for Fe^{19+} and Zn^{23+} ions, in charge states ranging from nitrogen-like to oxygen-like incident on molecular hydrogen over an energy range 0--250 MeV. By the same way the calculations have been performed with helium over an energy range 0--300 MeV. The calculations are carried out using the angular momentum average (AMA) scheme in the isolated resonance approximation (IRA). This method was previously used to calculate RTE cross sections for N-like P^{8+} and Ca^{13+}, where the results are found to agree with the present calculations. …

The Impact Of Hyperfine Interaction On The Charge Radius Of Protons, Majid Amirfakhrian

Turkish Journal of Physics

In this paper, the wave function of a Proton has been calculated via solving the Dirac equation for a three-particle system. Then, the charge radius of the proton was measured. Isospin-Isospin interaction was added to the system as a perturbation factor, and the variation of the charge radius of Proton was considered. Finally, the spin-spin and spin-isospin interactions on the charge radius of the Proton were calculated based on this method.

Bianchi-V Cosmological Models With Viscous Fluid And Constant Deceleration Parameter In General Relativity, Sharad Kandalkar, Pramod Khade, Mohini Gaikwad

Turkish Journal of Physics

In this paper we discuss the variation law for Hubble's parameter, average scale factor in spatially homogenous anisotropic Bianchi Type V space-time that yields a constant value deceleration parameter. Using the law of variation for Hubble's parameter, exact solutions of Einstein's field equations are obtained for Bianchi-V space time filled with viscous fluid in two different cases where the universe exhibits power law and exponential expansion. We investigate a number of solutions with constant and time varying cosmological constant together with variable and constant bulk viscosity. We find that the constant value of deceleration parameter is reasonable for the present …

A Fresh Look At Thermal Field Emission From Tungsten Tip, Ahmed Abdurrahman Ahmed Al-Tabbakh

Turkish Journal of Physics

Electron emission from clean tungsten tips has been investigated at different temperatures and applied electric field. Emission mechanism is analyzed on the basis of the Fowler-Nordheim (FN) model and a parameter extraction model based on elimination of field enhancement factor. The suggested extraction model of the physical and geometrical parameters is found fairly adequate to resolving the apparently confusing behavior of these parameters and shedding light on the emission mechanism. The observed linear FN plots at low temperatures confirm the predominating effect of the applied field on the electron emission. At elevated temperatures, emission is found to fall in the …

A New Karren Feature: Hummocky Karren, Lukas Plan, Christa Renetzeder, Rudolf Pavuza, Wilfried Körner

International Journal of Speleology

Karren are small-scale landforms on karst surfaces and many types have been described so far. Here we present an apparently new feature which was found on the Hochschwab karst massive in the Northern Calcareous Alps of Austria. So far only few outcrops each having less than 1 m² within a very restricted area have been found. Morphometric analysis reveals that the karren consist of a randomly distributed, dispersed assemblage of small hummocks and depressions in between. The mean distance between neighbouring hummocks is 4 to 5 cm and the mean height is 0.85 cm. Longitudinal sections are gently sinuous. The …

Cycles Of Electronic Health Records Adaptation By Physicians: How Do The Positive And Negative Experience With The Ehr System Affect Physicians' Ehr Adaptation Process?, Cherie Noteboom, Dhundy Bastola, Sajda Qureshi

Research & Publications

The integration of EHR in IT infrastructures supporting organizations enable improved access and recording of patient data, enhanced ability to make improved decisions, improved quality and reduced errors in patient care. Despite these benefits, there are mixed results as to the use of EHR. The literature suggests that the reasons for the limited use relate to policy, financial and usability considerations, but it does not provide an understanding of reasons for physicians’ limited interaction and adaptation of EHR.

Following an analysis of qualitative data, collected in a case study at a hospital using interviews, this research explains how physicians interact …

Multi-Party Multi-Period Supply Chain Coordination, Thin Yin Leong, Michelle Lee Fong Cheong

Research Collection School Of Computing and Information Systems

We apply combinatorial auction as a coordination mechanism to smooth demands placed on suppliers' limited production capacities, allowing several manufacturers to share common suppliers effectively. Products are bidders bidding for parts from suppliers, consuming their capacities in different time periods. The fourth party logistic (4PL) provider acts as the auctioneer to coordinate bids and perform price iterations. We leverage on the strong links between the Lagrangian relaxation method and combinatorial auction, where the Lagrange multipliers serve as the supply capacity reserve prices, to balance the demand and supply of capacities. To prevent cyclic behaviour and to increase convergence speed, we …

A Sentiment Analysis Of Singapore Presidential Election 2011 Using Twitter Data With Census Correction, Murphy Junyu Choy, Michelle Lee Fong Cheong, Nang Laik Ma, Ping Shung Koo

Research Collection School Of Computing and Information Systems

Sentiment analysis is a new area in text analytics where it focuses on the analysis and understanding of the human emotions from the text patterns. This new form of analysis has been widely adopted in customer relationship management especially in the context of complaint management. However, sentiment analysis using Twitter data has remained extremely difficult to manage due to sampling biasness. In this paper, we will discuss about the application of reweighting techniques in conjunction with online sentiment divisions to predict the vote percentage that individual presidential candidate in Singapore will receive in the Presidential Election 2011. There will be …

Robust Local Search For Solving Rcpsp/Max With Durational Uncertainty, Na Fu, Hoong Chuin Lau, Pradeep Varakantham, Fei Xiao

Research Collection School Of Computing and Information Systems

Scheduling problems in manufacturing, logistics and project management have frequently been modeled using the framework of Resource Constrained Project Scheduling Problems with minimum and maximum time lags (RCPSP/max). Due to the importance of these problems, providing scalable solution schedules for RCPSP/max problems is a topic of extensive research. However, all existing methods for solving RCPSP/max assume that durations of activities are known with certainty, an assumption that does not hold in real world scheduling problems where unexpected external events such as manpower availability, weather changes, etc. lead to delays or advances in completion of activities. Thus, in this paper, our …

Consumer-Driven Innovation Management, Arcot Desai Narasimhalu, Shekhar Mitra

Research Collection School Of Computing and Information Systems

The evolution of human society leads to increased affluence and prosperity of certain populations, sometimes at the expense of well-established markets. Market leaders in products and services tend to be so focused on their current customer base that they are caught off guard with the changes in markets created by the evolution. These changes often go unnoticed until it is too late. The change in customer base often requires the repositioning of products and services through innovations, which address new and emerging markets. Some of these changes could potentially result in tectonic market shifts that force innovation managers to involve …

Who Is Retweeting The Tweeters? Modeling, Originating, And Promoting Behaviors In The Twitter Network, Achananuparp Palakorn, Ee Peng Lim, Jing Jiang, Tuan Anh Hoang

Research Collection School Of Computing and Information Systems

Real-time microblogging systems such as Twitter offer users an easy and lightweight means to exchange information. Instead of writing formal and lengthy messages, microbloggers prefer to frequently broadcast several short messages to be read by other users. Only when messages are interesting, are they propagated further by the readers. In this article, we examine user behavior relevant to information propagation through microblogging. We specifically use retweeting activities among Twitter users to define and model originating and promoting behavior. We propose a basic model for measuring the two behaviors, a mutual dependency model, which considers the mutual relationships between the two …

Mantle Flow And Lithosphere-Asthenosphere Coupling Beneath The Southwestern Edge Of The North American Craton: Constraints From Shear-Wave Splitting Measurements, Hesham A. Refayee

Doctoral Dissertations

"High-quality broadband seismic data recorded by the USArray and other stations in the southwestern United States provide a unique opportunity to test different models of anisotropy-forming mechanisms in the vicinity of a cratonic edge. Systematic spatial variations of anisotropic characteristics are revealed by 3027 pairs of splitting parameters measured at 547 broadband seismic stations. The western and southern edges of the North American craton show edge-parallel fast directions with larger-than-normal splitting times, and the continental interior is characterized by smaller splitting times spatially consistent fast directions that are mostly parallel to the absolute plate motion direction of North America. Except …

N-Acetyl-L-Cysteine Amide Protects Retinal Pigment Epithelium Against Methamphetamine-Induced Oxidative Stress, Nuran Ercal, Joshua W. Carey, Shakila Tobwala, Xinsheng Zhang, Atrayee Banerjee, Eylem Y. Pinarci, Humeyra Karacal

Chemistry Faculty Research & Creative Works

Methamphetamine (METH), a highly addictive drug used worldwide, induces oxidative stress in various animal organs. Recent animal studies indicate that methamphetamine also induces oxidative stress in the retina, which is an em- bryonic extension of the forebrain. The aim of this study, therefore, was to evaluate the pro- tecttive effects of N-acetylcysteine amide (NACA) against oxidative stress induced by METH in retinal pigment epithelium (RPE) cells. Our stud- ies showed that NACA protected against METH- induced oxidative stress in retinal pigment epithelial cells. Although METH significantly de- creased glutathione (GSH) levels and increased reactive oxygen species (ROS) and malondial- dehyde …

Noncanonical Reactions Of Flavoenzymes, Pablo Sobrado

Chemistry Faculty Research & Creative Works

Enzymes containing flavin cofactors are predominantly involved in redox reactions in numerous cellular processes where the protein environment modulates the chemical reactivity of the flavin to either transfer one or two electrons. Some flavoenzymes catalyze reactions with no net redox change. In these reactions, the protein environment modulates the reactivity of the flavin to perform novel chemistries. Recent mechanistic and structural data supporting novel flavin functionalities in reactions catalyzed by chorismate synthase, type II isopentenyl diphosphate isomerase, UDP-galactopyranose mutase, and alkyl-dihydroxyacetone phosphate synthase are presented in this review. In these enzymes, the flavin plays either a direct role in acid/base …

Ace - A Model Centered Reu Program Standing On The Three Legs Of Cse: Analysis, Computation And Experiment, Hong P. Liu, Andrei Ludu

Publications

Enhancing REU (research experience for undergraduates) has become a popular strategy for many selective universities to enhance quality of undergraduate education and recruit gifted new students. The university that the authors are affiliated has set REU as one of the major outcomes for our QEP (quality enhancement program) for next 5 years. This paper presents a model centered REU program entitled as ACE standing for Analysis, Computation and Experiment. As a work in progress, the program is planned to run for the next 5 years and to serve for 20-30 undergraduate students who are gifted in mathematics and computing annually. …