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Mixing of Isotactic and Syndiotactic Polypropylenes in the Melt

Description: The miscibility of polypropylene (PP) melts in which the chains differ only in stereochemical composition has been investigated by two different procedures. One approach used detailed local information from a Monte Carlo simulation of a single chain, and the other approach takes this information from a rotational isomeric state model devised decades ago, for another purpose. The first approach uses PRISM theory to deduce the intermolecular packing in the polymer blend, while the second approach uses a Monte Carlo simulation of a coarse-grained representation of independent chains, expressed on a high-coordination lattice. Both approaches find a positive energy change upon mixing isotactic PP (iPP) and syndiotactic polypropylene (sPP) chains in the melt. This conclusion is qualitatively consistent with observations published recently by Muelhaupt and coworkers. The size of the energy chain on mixing is smaller in the MC/PRISM approach than in the RIS/MC simulation, with the smaller energy change being in better agreement with the experiment. The RIS/MC simulation finds no demixing for iPP and atactic polypropylene (aPP) in the melt, consistent with several experimental observations in the literature. The demixing of the iPP/sPP blend may arise from attractive interactions in the sPP melt that are disrupted when the sPP chains are diluted with aPP or iPP chains.
Date: July 14, 2000
Creator: CLANCY,THOMAS C.; PUTZ,MATHIAS; WEINHOLD,JEFFREY D.; CURRO,JOHN G. & MATTICE,WAYNE L.
Partner: UNT Libraries Government Documents Department

ABSOLUTE ASYMMETRIC SYNTHESIS. I. ON THE MECHANISM OF THEPHOTOCHEMICAL ABSOLUTE ASYMMETRIC SYNTHESIS OF HELICENES WITH CIRCULARLYPOLARIZED LIGHT. . WAVELENGTH DEPENDENCE OF THE OPTICAL YIELD OFOCTAHELICENE.

Description: The synthesis of nonracemic yields of hexa-, hepta-, octa-, and nonhelicene with circular light was observed, and the structural and wavelength dependence of the induced optical yields was examined. The results obtained, together with a detailed consideration of the mechanism of helicene synthesis from the parent diarylolefins, indicate that the induced optical activity is due to selective reaction of enantiomeric conformations of the parent cis diarylolefins by circular light.
Date: May 1, 1971
Creator: Bernstein, William J.; Calvin, Melvin & Buchardt, Ole.
Partner: UNT Libraries Government Documents Department

Capillary electrophoresis separation of neutral organic compounds, pharmaceutical drugs, proteins and peptides, enantiomers, and anions

Description: Addition of a novel anionic surfactant, namely lauryl polyoxyethylene sulfate, to an aqueous-acetonitrile electrolyte makes it possible to separate nonionic organic compounds by capillary electrophoresis. Separation is based on differences in the association between analytes and the surfactant. Highly hydrophobic compounds such as polyaromatic hydrocarbons are well separated by this new surfactant. Migration times of analytes can be readily changed over an unusually large range by varying the additive concentration and the proportion of acetonitrile in the electrolyte. Several examples are given, including the separation of four methylbenz[a]anthracene isomers and the separation of normal and deuterated acetophenone. The effect of adding this new surfactant to the acidic electrolyte was also investigated. Incorporation of cetyltrimethylammonium bromide in the electrolyte is shown to dynamically coat the capillary and reverse electroosmotic flow. Chiral recognition mechanism is studied using novel synthetic surfactants as chiral selectors, which are made from amino acids reacting with alkyl chloroformates. A satisfactory separation of both inorganic and organic anions is obtained using electrolyte solutions as high as 5 M sodium chloride using direct photometric detection. The effect of various salts on electrophoretic and electroosmotic mobility is further discussed. Several examples are given under high-salt conditions.
Date: February 12, 1999
Creator: Ding, W.L.
Partner: UNT Libraries Government Documents Department

High temperature meson propagators with domain-wall quarks.

Description: We study the chiral properties of domain-wall quarks at high temperatures on an ensemble of quenched configurations. Low lying eigenmodes of the Dirac operator are calculated and used to check the extent to which the Atiyah-Singer index theorem is obeyed on lattices with finite N{sub 5}. We calculate the connected and disconnected screening propagators for the lowest mass scalar and pseudoscalar mesons in the sectors of different topological charge and note that they behave as expected. Separating out the would-be zero eigenmodes enables us to accurately estimate the disconnected propagators with far less effort than would be needed otherwise.
Date: September 23, 1999
Creator: Lagae, J.-F. & Sinclair, D. K.
Partner: UNT Libraries Government Documents Department

A New Class of Macrocyclic Chiral Selectors for Stereochemical Analysis

Description: This report summarizes the work accomplished in the authors laboratories over the previous three years. During the funding period they have had 23 monographs published or in press, 1 book chapter, 1 patent issued and have delivered 28 invited seminars or plenary lectures on DOE sponsored research. This report covers the work that has been published (or accepted). The most notable aspect of this work involves the successful development and understanding of a new class of fused macrocyclic compounds as pseudophases and selectors in high performance separations (including high performance liquid chromatography, HPLC; capillary electrophoresis, CE; and thin layer chromatography, TLC). They have considerably extended their chiral biomarker work from amber to crude oil and coal. In the process of doing this we've developed several novel separation approaches. They finished their work on the new GSC-PLOT column which is now being used by researchers world-wide for the analysis of gases, light hydrocarbons and halocarbons. Finally, we completed basic studies on immobilizing a cyclodextrin/oligosiloxane hybrid on the wall of fused silica, as well as a basic study on the separation behavior of buckminster fullerene and higher fullerenes.
Date: March 11, 1999
Partner: UNT Libraries Government Documents Department

Residual Chiral Symmetry Breaking in Domain-Wall Fermions

Description: The authors study the effective quark mass induced by the finite separation of the domain walls in the domain-wall formulation of chiral fermion as the function of the size of the fifth dimension ($L-s$), the gauge coupling $beta$ and the physical volume $V$. They measure the mass by calculating the small eigenvalues of the hermitian domain-wall Dirac operator ($H-[rm DWF](m-0))$ in the topologically-nontrivial quenched SU(3) gauge configurations. The authors find that the induced quark mass is nearly independent of the physical volume, decays exponentially as a function of $L-s$, and has a strong dependence on the size of quantum fluctuations controlled by $beta$. The effect of the choice of the lattice gluon action is also studied.
Date: September 1, 2000
Creator: Jung, Chulwoo; Gadiyak, Valeriya; Ji, Xiangdong & Edwards, Robert G.
Partner: UNT Libraries Government Documents Department

Review of NN Interaction from Lattice QCD

Description: Historically, lattice studies of QCD have concentrated on understanding the properties and structure of an isolated hadron. Recently, there have efforts at understanding the interactions between hadrons. In this talk I will review two approaches to this problem
Date: July 1, 2000
Creator: Richards, D.
Partner: UNT Libraries Government Documents Department

Wilson Versus Clover Fermions: A Case for Improvement

Description: The authors present evidence for improvement with tadpole improved clover fermions based on an analysis of the chiral behavior of B{sub K} and the quark condensate. Also presented are a comparison of the mass splittings in the baryon octet and decuplet, a calculation of c{sub A} using standard 2-point correlation functions, and the problem of zero modes of the Dirac operator.
Date: July 14, 1998
Creator: Gupta, R.
Partner: UNT Libraries Government Documents Department

Exact Chiral Symmetry for Domain Wall Fermions with Finite L{sub s}*

Description: We show how the standard domain wall action can be simply modified to allow arbitrarily exact chiral symmetry at finite fifth dimensional extent. We note that the method can be used for both quenched and dynamical calculations. We test the method using smooth and thermalized gauge field configurations. We also make comparisons of the performance (cost) of the domain wall operator for spectroscopy compared to other methods such as the overlap-Dirac operator and find both methods are comparable in cost.
Date: October 1, 2000
Creator: Edwards, Robert G. & Heller, Urs M.
Partner: UNT Libraries Government Documents Department

A nonplanar porphyrin-based receptor molecule for chiral amine ligands

Description: A novel porphyrin-based receptor molecule for chiral amine ligands is described in which nonplanarity of the porphyrin macrocycle is used to orient the ligand and to enhance porphyrin-ligand interactions. The porphyrin macrocycle provides a versatile platform upon which to build elaborate superstructures, and this feature coupled with a rich and well-developed synthetic chemistry has led to the synthesis of many elegant models of heme protein active sites and numerous porphyrin-based receptor molecules. One design feature which is not usually considered in the design of porphyrin-based receptor molecules is nonplanarity of the porphyrin ring, although there are a few systems such as the pyridine sensitive Venus Flytrap and the chirality-memory molecule which illustrate that nonplanar porphyrin-based receptors can display unique and interesting behavior. Given the novel properties of these receptors and the continuing interest in the effects of nonplanarity on the properties of porphyrins the authors decided to investigate in more detail the potential applications of nonplanarity in the design of porphyrin-based receptors. Herein, they describe the design, synthesis, and characterization of a new kind of nonplanar porphyrin-based receptor molecule for chiral amines.
Date: March 6, 2000
Creator: MUZZI,CINZIA M.; MEDFORTH,CRAIG J.; SMITH,KEVIN M.; JIA,SONG-LING & SHELNUTT,JOHN A.
Partner: UNT Libraries Government Documents Department

Chiral Boson Theory on the Light-Front

Description: The framework for describing the quantized theory of chiral boson is discussed. It avoids the conflict with the requirement of the principle of microcausality as is found in the conventional treatment. The discussion of the Floreanini-Jackiw model and its modified version for describing the chiral boson becomes very transparent on the light-front.
Date: September 16, 1999
Creator: Srivastava, Prem P.
Partner: UNT Libraries Government Documents Department

New Constraints on Chiral Gauge Theories

Description: Recently, a new constraint on the structure of a wide class of strongly coupled field theories has been proposed. It takes the form of an inequality limiting the number of degrees of freedom in the infrared description of a theory to be no larger than the number of underlying, ultraviolet degrees of freedom. Here we apply this inequality to chiral gauge theories. For some models we find that it is always satisfied, while for others we find that the assumption of the validity of the inequality implies a strong additional restriction on the spectrum of massless composite particles.
Date: April 27, 1999
Creator: Schmaltz, Martin
Partner: UNT Libraries Government Documents Department

Final Technical Report for DOE Grant DE-FG02-03ER15473 “Molecular Level Design of Heterogeneous Chiral Catalysis”

Description: The production of enantiomerically pure chiral compounds is of great importance in the pharmaceutical industry. Although processes involving chiral catalysis and separations involving solid surfaces are known, the molecular-scale details of these processes are not well understood. This lack of understanding strongly limits the development of new chiral processes. Our collaborative research effort examines several intertwined aspects of chirality and enantioselectivity at catalytically active metal surfaces. At Carnegie Mellon, our efforts focus on the development of chirally imprinted metal powders as materials for chiral columns and the experimental and theoretical study of small chiral molecules adsorbed on well-characterized metal surfaces, both achiral and chiral. These efforts are being performed in close collaboration with our team members at the University of California Riverside and the University of Wisconsin Milwaukee.
Date: March 15, 2007
Creator: Sholl, David & Gellman, Andrew
Partner: UNT Libraries Government Documents Department

Topological susceptibility with the improved Asqtad action

Description: As a test of the chiral properties of the improved Asqtad (staggered fermion) action, we have been measuring the topological susceptibility as a function of quark masses for 2 + 1 dynamical flavors. We report preliminary results, which show reasonable agreement with leading order chiral perturbation theory for lattice spacing less than 0.1 fm. The total topological charge, however, shows strong persistence over Monte Carlo time.
Date: January 6, 2004
Creator: al., C. Bernard et
Partner: UNT Libraries Government Documents Department

Quenched Chiral Log and Light Quark Mass from Overlap Fermions

Description: We study the quenched chiral behavior of the pion with mass as low as {approx} 180 MeV. The calculation is done on a quenched lattice of size 16{sup 3} x 28 and a = 0.2 fm with 80 configurations using overlap fermions and an improved gauge action. Using an improved constrained curve fitting technique, we find that the ground state pseudoscalar mass versus bare quark mass behavior is well controlled with small statistical errors; this permits a reliable fit of the quenched chiral log effects, a determination of the chiral log parameter ({delta} = 0.26(3)), and an estimate of the renormalized mass of the light quark (m{sup {ovr MS}}({mu} = 2 GeV) = 3.7(3) MeV).
Date: June 1, 2002
Creator: Draper, Terrence; Dong, Shao-Jing; Horvath, Ivan; Lee, Frank; Liu, Keh-Fei; Mathur, Nilmani et al.
Partner: UNT Libraries Government Documents Department

Hadron production at RHIC - chemical freeze-out, effective masses and expanding matter.

Description: The properties of the strongly interacting matter produced at RHIC are investigated within a chemical and thermal equilibrium chiral SU(3) {sigma}-{omega} approach. The focus is on the freeze-out conditions, the effective masses for the produced hadrons and the expansion of the system. For the freeze-out conditions the commonly adopted noninteracting gas calculations yield temperatures and chemical potentials close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. Contrary, the chiral SU(3) model predicts temperature and density dependent effective hadron masses and effective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three different parametrizations of the model, which show different types of phase transition behavior, are investigated. They show that if a chiral phase transition occurred in those collisions, freezing of the relative hadron abundances in the symmetric phase is excluded by the data. Therefore, either very rapid chemical equilibration must occur in the broken phase, or the measured hadron ratios are the outcome of the dynamical symmetry breaking. Furthermore, the extracted chemical freeze-out parameters differ considerably from those obtained in simple noninteracting gas calculations. In particular, the three models yield up to 35 MeV lower temperatures than the free gas approximation. The in-medium masses turn out differ up to 150 MeV from their vacuum values.
Date: September 26, 2002
Creator: Zschiesche, D.; Schramm, S.; Schaffner-Bielich, J.; Stocker, H. & Greiner, W.
Partner: UNT Libraries Government Documents Department

Remark on the theoretical uncertainty in B0-Bbar0 Mixing

Description: The authors re-examine the theoretical uncertainty in the Standard Model expression for B{sup 0}-{bar B}{sup 0} mixing. They focus on lattice calculations of the ratio {xi}, needed to relate the oscillation frequency of B{sub s}{sup 0}-{bar B}{sub s}{sup 0} mixing to V{sub td}. They replace the usual linear chiral extrapolation with one that includes the logarithm that appears in chiral perturbation theory. We find a significant shift in the ratio {xi}, from the conventional 1.15 {+-} 0.05 to {xi} = 1.32 {+-} 0.10.
Date: September 19, 2002
Creator: Kronfeld, Sinead Ryan and Andreas
Partner: UNT Libraries Government Documents Department

Parameter-free effective field theory calculation for the solar proton-fusion and hep processes

Description: Spurred by the recent complete determination of the weak currents in two-nucleon systems up to {Omicron}(Q{sup 3}) in heavy-baryon chiral perturbation theory, we carry out a parameter-free calculation of the threshold S-factors for the solar pp (proton-fusion) and hep processes in an effective field theory that combines the merits of the standard nuclear physics method and systematic chiral expansion. The power of the EFT adopted here is that one can correlate in a unified formalism the weak-current matrix elements of two-, three- and four-nucleon systems. Using the tritium {beta}-decay rate as an input to fix the only unknown parameter in the theory, we can evaluate the threshold S factors with drastically improved precision; the results are S{sub pp}(0) = 3.94 x (1 {+-} 0.004) x 10{sup -25} MeV-b and S{sub hep}(0) = (8.6 {+-} 1.3) x 10{sup -20} keV-b. The dependence of the calculated S-factors on the momentum cutoff parameter {Lambda} has been examined for a physically reasonable range of {Lambda}. This dependence is found to be extremely small for the pp process, and to be within acceptable levels for the hep process, substantiating the consistency of our calculational scheme.
Date: August 1, 2002
Creator: Park, T.S.; Marcucci, L.E.; Schiavilla, R.; Viviani, M.; Kievsky, A.; Rosati, S. et al.
Partner: UNT Libraries Government Documents Department

Spin on the Lattice.

Description: I review the current status of hadronic structure computations on the lattice. I describe the basic lattice techniques and difficulties and present some of the latest lattice results; in particular recent results of the RBC group using domain wall fermions are also discussed. In conclusion, lattice computations can play an important role in understanding the hadronic structure and the fundamental properties of Quantum Chromodynamics (QCD). Although some difficulties still exist, several significant steps have been made. Advances in computer technology are expected to play a significant role in pushing these computations closer to the chiral limit and in including dynamical fermions. RBC has already begun preliminary dynamical domain wall fermion computations [49] which we expect to be pushed forward with the arrival of QCD0C. In the near future, we also expect to complete the non-perturbative renormalization of the relevant derivative operators in quenched QCD.
Date: January 7, 2003
Creator: Orginos, K.
Partner: UNT Libraries Government Documents Department