bluuebunny/crossref_metadata_2025_split huggingface dataset:
A dual beam total internal reflection fluorescence spectrometer for dynamic depth resolved measurements of biochemical liquid-solid interface binding reactions in opaque solvents
Authors: Liebmann Lars W. , Robinson John A. , Mann Kenneth G. 
Published: July 2002

The initiation of many physiologically important biochemical reactions is dependent on the binding of a molecule or molecules from solution to an appropriate solid surface such as a cell membrane. The quantitative study of dynamic interactions of molecules in solution with immobilized surfaces under physiologically relevant conditions presents a significant physical problem. Traditionally these measurements have been performed by discontinuous, nonequilibrium assays that cannot accurately model in vivo reaction mechanisms. Total internal reflection fluorescence spectroscopy (TIRFS) is an analytical technique that is based on the excitation of fluorescence by means of an exponentially decaying surface energy wave called the evanescent wave. The limited ‘‘penetration depth’’ of the evanescent wave leads to excitation of fluorescent molecules at or near the surface. This phenomena makes TIRFS uniquely qualified for the dynamic fluorescence study of liquid-solid interface binding reactions. The instrument described here permits the powerful technique of TIRFS to be used by biomedical researchers in their investigation of biochemical interface reactions. The fully automated, menu driven instrument allows the real time dynamic measurement of binding of fluorescent-labeled molecules in solution at physiologically relevant concentrations to appropriate immobilized surfaces.
The novel design of the total internal reflection element enables the study of binding from essentially opaque and highly scattering solutions such as whole blood. Measurements may be performed under static, stirred, or flow conditions. The presently described TIRFS instrument is capable of tracking a binding reaction with evanescent fields established by two identical reflecting light beams with different reflection angles. This instrumental feature allows the dynamic measurement not only of the primary binding event but also of fluctuations in the distance between the optical interface and the point of signal generation. Data from experiments involving fluorescently labeled molecules binding to cell monolayers as well as binding experiments performed in whole blood are shown to verify the instrument performance. Due to its extraordinary capabilities and its user friendly design, the developed TIRFS instrument opens up a large number of relevant but previously unmeasurable experimental systems for investigation.
Nonadiabatic unimolecular reactions. III. Dissociation mechanisms of methylnitrite and deuterated methylnitrite ions
Authors: Leyh-Nihant B. , Lorquet J. C. 
Published: July 2002

At low energies, methylnitrite ions dissociate via two channels giving rise to CH3O+NO+ or to [CH3O+]+NO fragments. Peculiar characteristics have been detected in the dissociation of energy-selected parent ions, viz., remarkably low rate constants, one of which is found to remain insensitive to an increase of the internal energy, and large isotope effect. These peculiarities are accounted for by a statistical, nonadiabatic model. Ab initio calculations, confirmed by multipolar expansions reveal that the potential energy curves which correlate to these two dissociation asymptotes cross. The crossing takes place at a large value along the reaction coordinate R, indicating a long-range interaction. Production of the CH3O+NO+ fragments results from a simple bond cleavage taking place on a single diabatic surface. On the other hand, production of [CH3O+]+NO fragments is brought about by a transition from one diabatic surface to the other. It leads to deformed methoxy ions which immediately rearrange to the much more stable H2COH+ structure. The nonadiabatic rate constant has been calculated by a statistical method. The contribution of each channel is weighted by a transmission coefficient which is equal to the nonadiabatic transition probability. Implementation of this statistical treatment requires partitioning
the set of degrees of freedom as follows: {R, y, d, v}. It is necessary to withdraw the isomerization mode y from the statistical treatment, because the equilibrium positions along this coordinate are very different in each electronic state. Physically, this means that the reaction involves tunneling from one surface to the other along the displaced degree of freedom y. The large isotope effect has a double origin: part of it (a factor of ∼9) results from tunneling along y; the remainder (an additional factor of 3) comes from the usual RRKM-like effect on the densities of states. The degrees d constitute a set of four low-energy bending modes which form a sink for the internal energy. The nonadiabatic transition probability is determined by the off-diagonal matrix element V12(Rc). Effective potential energy curves have been calculated by extending the Quack and Troe method to nonadiabatic reactions. It turns out that the excitation of the set d leads to a decrease of V12(Rc) and hence to a decrease of the nonadiabatic transmission coefficient. This accounts for the weak dependence of the rate constants kCH3O+ and kCD3O+ vs the energy (at least above a certain energy threshold).
Multiple transition states in chemical reactions: Variational transition state theory studies of the HO2 and HeH+2 systems
Authors: Song Kihyung , Chesnavich Walter J. 
Published: July 2002

The results of a microcanonical variational transition state theory study of the HO2 and HeH+2 systems are reported. The calculations were carried out using a modification of the Wardlaw–Marcus flexible transition state theory method in which the sum of states N(E,R) is calculated directly. For the HO2 system, the results obtained using the Melius–Blint
potential surface are in excellent agreement with previously reported variational transition state theory calculations of Rai and Truhlar on this system. In particular, two transition states were found for the HO2→OH+O half-reaction. However, calculations using the Lemon–Hase surface produced only one transition state. From calculations carried out on surfaces constructed by combining the two original surfaces and calculations carried out using an orbiting transition state variational model (i.e., ignoring the angular part of the potential), it is shown conclusively that the two transition states found for the Melius–Blint surface arise from the peculiar shape of the minimum reaction path for this surface. Also, the orbiting transition state calculations
suggest that phase space theory can describe this half-reaction on the Lemon–Hase surface over a large energy range provided that the potential along the minimum reaction path is used in the phase space theory calculations. Other calculations, in which the parameters of the Lemon–Hase surface were adjusted, were also carried out in order to determine the conditions necessary to support multiple transition states. The results of these calculations suggest that multiple transition states are more likely to occur when a strong bottleneck is present in the angular part of the potential, especially when the intermediate complex exists in a shallow well. These predictions were confirmed by the
results obtained for the HeH+2 system using the McLaughlin–Thompson–Joseph–Sathyamurthy surface. Two transition states were found for the HeH+2→HeH++H half-reaction and calculations using the orbiting model showed that the origin of the multiple transition
states is not the minimum reaction path as in the case of the Melius–Blint surface. Furthermore, the energy at which ‘‘transition state switching’’ occurs is in reasonable accord with the energy at which phase space theory calculations begin to diverge from the experimental data on the cross section for this system. Lifetime calculations for the pseudocomplex lying between the two transition states suggest that the observation of multiple transition states may be possible using femtosecond transition state spectroscopy. Finally, calculations on the HeH+2→He+H+2 half-reaction showed that one transition state exists for this half-reaction at low energy, while at higher energy there are no transition states.
Rigid bender analysis of van der Waals complexes: The intermolecular bending potential of a hydrogen bond
Authors: Nesbitt David J. , Lovejoy Christopher M. 
Published: July 2002

High resolution ir data on weakly bound OCOHF complexes formed in a slit supersonic expansion reveal a progression of extremely low frequency vibrational levels associated with the bending of the OCO–HF hydrogen bond. In a previous paper [J. Chem. Phys. 93, 7716 (1990)], we presented a spectroscopic analysis of the fundamental, combination and hot bands observed, corresponding to transitions between vlbend=00, 11, 20, 22, and 31, where vlbend denotes quanta of OCOHF skeletal bend excitation with l units of vibrational angular momentum. In this paper, we analyze the rotationally resolved data in terms of the rigid bender formalism of Hougen, Bunker and Johns to determine an explicit angular potential, V(θ), for the OCOHF complex in both the HF ground (vHF=0) and vibrationally excited (vHF=1) state.
The OCOHF ground state (vHF=0) potential is dominated by quartic and sextic angular terms, and thus is surprisingly shallow with respect to the bending angle. This quasilinear vibrational behavior is characterized by wide amplitude bending wave functions with zero point motion extending from −38° to +38°. In contrast, the OCOHF excited state (vHF=1) exhibits a significantly bent equilibrium geometry with a hydrogen bond bend angle of 31°±5°, corresponding to a cylindrically symmetric, noncolinear minimum in the potential. This shift in equilibrium geometry upon vHF excitation is quantitatively responsible for promoting Δvbend=0,2,... combination band vibrational modes, in analogy with Franck–Condon progressions in a bent←linear electronic transition.
The predissociation lifetimes for vHF=1 excited OCOHF vary systematically with vlbend, and can be analyzed in terms of a geometry dependent predissociation rate which increases with bending of the hydrogen bond angle. These empirical bending potentials are in qualitative agreement with, but quantitatively much shallower than predicted by previous electrostatic and ab initio calculations, and differ fundamentally from the traditional notions of a relatively stiff, linear hydrogen bond. The present results on the hydrogen bond potential surface for O=C=O---HF are consistent with statistical analyses of–C=O---H–N hydrogen bond angles obtained from x-ray crystallographic studies of proteins.
Competing C–Br and C–C bond fission following 1[n(O),π*(C=O)] excitation in bromoacetone: Conformation dependence of nonadiabaticity at a conical intersection
Authors: Kash P. W. , Waschewsky G. C. G. , Morss R. E. , Butler L. J. , Francl M. M. 
Published: July 2002

These experiments investigate the competition between C–C and C–Br bond fission in bromoacetone excited in the 1[n(O),π*(C=O)] absorption, elucidating the role of molecular conformation in influencing the probability of adiabatically traversing the conical intersection along the C–C fission reaction coordinate. In the first part of the paper, measurement of the photofragment velocity and angular distributions with a crossed laser-molecular beam time-of-flight technique identifies the primary photofragmentation channels at 308 nm. The time-of-flight spectra evidence two dissociation channels, C–Br fission and fission of one of the two C–C bonds, BrH2C–COCH3. The distribution of relative kinetic energies imparted to the C–Br fission and C–C fission fragments show dissociation is not occurring via internal conversion to the ground electronic state and allow us to identify these channels in the closely related systems of bromoacetyl- and bromopropionyl chloride.
In the second part of the work we focus on the marked conformation dependence to the branching between C–C fission and C–Br fission. Photofragment angular distribution measurements show that C–Br fission occurs primarily from the minor, anti, conformer, giving a β of 0.8, so C–C fission must dominate the competition in the gauche conformer. Noting that the dynamics of these two bond fission pathways are expected to be strongly influenced by nonadiabatic recrossing of the reaction barriers, we investigate the possible mechanisms for the conformation dependence of the nonadiabatic recrossing with low-level ab initio electronic structure calculations on the C–Br reaction coordinate and qualitative consideration of the conical intersection along the C–C reaction coordinate. The resulting model proposes that C–C bond fission cannot compete with C–Br fission in the anti conformer because the dissociation samples regions of the phase space near the conical intersection along the C–C fission reaction coordinate, where nonadiabaticity inhibits C–C fission, while from the gauche conformer C–C fission can proceed more adiabatically and dominate C–Br fission. A final experiment confirms that the branching ratio changes with the relative conformer populations in accord with this model.
On the generalized Gibbs formula and the thermodynamic solution of the Boltzmann equation
Authors: Chen M. 
Published: July 2002

The purpose of this paper is to examine the relationship between the entropy balance equation, the Gibbs formula, and the Boltzmann equation. Consider a system of a mixture of gases contained in an arbitrary region Ω with volume V, where no chemical reactions take place. Let fi be the one-particle distribution function of species i. First, suppose there exist some fi, such that the entropy density ρS, the entropy flux Js, the entropy production σ, and the Boltzmann H-function, H(t), satisfy, respectively, the entropy balance equation and the Boltzmann H-equation under appropriate boundary conditions on the surface ∂Ω of Ω. Then fi can be shown to satisfy the Boltzmann equation. Under the functional hypothesis, where fi depends on time t and the spatial coordinates r only in terms of the thermodynamic variables—particle density of species i, ρi, hydrodynamic velocity v, energy density E, stress tensor π̄i, heat flux Q′i, and mass flux Ji, and possibly the spatial derivatives of { ρi, v, E, π̄i, Qi, Ji}, the entropy balance equation together with the semipositive definiteness of the entropy production, σ≥0, then provides an alternative method of solving the Boltzmann equation. The thermodynamic variables, in turn, are governed by their corresponding evolution equations with appropriate boundary conditions.
Second, to the linear order of the spatial gradients of the temperature T, the hydrodynamic velocity v, and the ratio of the particle number ni /n, the entropy balance equation then yields a generalized Gibbs formula and a nonlinear solution of fi in terms of the thermodynamic variables, such that σ≥0. The generalized Gibbs formula is an exact one-form of the thermodynamic variables that contains the equilibrium Gibbs formula. Furthermore, if fi is linearized, it is identical to the expression given by Grad’s 13-moment method. Finally, we consider the stability problem of the evolution equations for π̄i, Q′i, and Ji.
Policing, collective action and social movement theory: the case of the Northern Ireland civil rights campaign*
Authors: Ellison Graham , Martin Greg 
Published: July 2002

ABSTRACTIn this paper we examine the relationship between social movements and the police through an analysis of the Civil Rights Movement (CRM) which emerged in the late 1960s in Northern Ireland. Following della Porta (1995) and Melucci (1996) we argue that the way in which episodes of collective action are policed can affect profoundly both levels of mobilization and the orientation of social movements. We also submit that the symbolic and representational dimensions of policing can be a significant trigger in the stimulation of identification processes and collective action. The paper concludes by questioning some of the assumptions contained within social movement theory, and their applicability to divided societies such as Northern Ireland.
Factors influencing young children’s ability to discriminate unfamiliar faces by age
Authors: George P. A. , Hole G. J. , Scaife M. 
Published: July 2002

Three experiments examined young children’s ability to discriminate between pairs of unfamiliar faces which differed in age. Apre-test found that 99% of 6-year-olds, but only 36%of 4-year-olds, could reliably decide which of two faces was the oldest. Experiment 1 attempted to identify the nature of the information used for age-processing faces. Face-pairs were presented in four different versions: Original (unmodified image); Features-only (containing only the internal face features); Skin-blur (in which the skin regions of the face were subjected to Gaussian blurring); or Overall-blur (in which the entire image was blurred). The last three versions selectively reduced specific cues to age. No significant differences in age-discrimination performance were found between these different versions, suggesting that, as with adults, children are capable of adaptively using a variety of cues in order to discriminate between faces on the basis of age. Experiments 2 and 3 investigated in more detail a phenomenon suggested by Experiment 1: That children found it easier to discriminate between faces by age that were similar in age to themselves, than between adult faces. The results suggest that children as young as 6 years can use age to discriminate between faces of all ages with a relatively high degree of accuracy, but experience most difficulty with adult faces.
Education, citizenship and difference in the South African transition: policy, politics and practice
Authors: Unterhalter Elaine 
Published: July 2002

ABSTRACTThe article looks at three approaches to analysing the relationship between education, citizenship and difference that have been evident in the transition to democracy in South Africa. First, it examines the position that education moulds good citizens and overcomes discriminatory differences, which is evident in the South African Education Policy Act. (This position is similar to that expounded in the Crick Report.) Second, it looks at the view that education is an enactment of citizenship and a celebration of difference. This is articulated in the new South African Curriculum 2005, which celebrates the school as just one of a number of learning spaces, but which is only slowly being implemented with considerable difficulty in overcoming deeply entrenched and multifaceted discriminatory views. Third, it looks at the view, articulated in the South African Constitution of 1996, that education is a relatively autonomous space and that in this particular institutional space education, difference and citizenship are in tension. While there is potential for a creative dialogue to emerge in this historically formed space, preliminary research findings indicate how difficult and diffuse the process of transformation is likely to be.
Stereotypes in cyberspace: writing an anti‐racist website
Authors: Gaine Chris 
Published: July 2002

ABSTRACTThis article deals with some of the difficulties and dilemmas of writing and producing an educational website about ‘race’ and racism (www.britkid.org). With a ‘cast’ of fictionalized characters exploring a wide range of issues relating to racism in the UK, the site is arguably closer to being a mass media product than conventional school materials, and the white, male author had to negotiate complex dilemmas about stereotyping and representation in both the initial drafts and in responding to prepublication feedback. These are explored, together with some reflections upon the relationship between research and a ‘product’ such as this.
A grand day out: towards a mode of interrogation of non‐school pedagogic sites
Authors: Dowling Paul , Brown Andrew 
Published: July 2002

ABSTRACTInterest is increasingly being taken in educational sites which extend or which are located beyond the school. These include sites associated with developing information and communications technologies and mass media organizations as well as institutions of longer standing, such as museums, galleries and so forth. In this article we shall deploy a sociological framework originally developed for the analysis of school texts to such non‐school sites. Our focus will include considerations of heritage and conservation sites in the form of castles and zoos. We contend that in operating in terms of both pedagogic and exchange relations, such sites may have something to teach as well as something to learn from schooling.
Differential regulation of metalloproteinase production, proliferation and chemotaxis of human lung fibroblasts by PDGF, Interleukin‐1β and TNF‐α
Authors: Sasaki Masahiro , Kashima Masayuki , Ito Takefumi , Watanabe Akiko , Izumiyama Noriko , Sano Masaaki , Kagaya Manabu , Shioya Takanobu , Miura Mamoru 
Published: July 2002

Fibroblast migration, proliferation, extracellular matrix protein synthesis and degradation,all of which play important roles in inflammation, are them selves induced by various growth factors and cytokines. Less is known about the interaction of these substances on lung fibroblast function in pulmonary fibrosis.The goal of this study was to investigate the effects of PDGF alone and in combination with IL–1β and TNF–α on the production of human lung fibroblast matrix metalloproteinases, proliferation, and the chemotactic response. The assay for MMPs activity against FITC labeled type I and IV collagen was based on the specificity of the enzyme cleavage of collagen. Caseinolytis and gelatinolytic activities of secreted proteinases were analyzed by zymography. Fibronectin in conditioned media was measured using human lung fibronectin enzyme immunoassay. Cell proliferation was measured by 3H‐Thymidine incorporation assay. Cell culture supernatants were tested for PGE2 content by ELISA. Chemotactic activity was measured using the modified Boyden chamber.Matrix metalloproteinase assay indicated that IL–1β, TNF–α and PDGF induced intestitial collagenase (MMP‐1) production. MMP assay also indicated that IL–1β and TNF–α had inhibitory effects on MMP‐2,9(gelatinaseA,B) production. Casein zymography confirmed that IL–1β stimulated stromlysin (matrix metalloproteinase 3; MMP–3) and gelatin zymography demonstrated that TNF–α induced MMP–9 production in human lung fibroblast, whereas PDGF alone did not. PDGF in combination with IL–1β and TNF–α induced MMP–3 and MMP–9 activity, as demonstrated by zymography. PDGF stimulated lung fibroblast proliferation in a concentration‐dependent manner, whereas IL–1β and TNF–α alone had no effect. In contrast, the proliferation of human lung fibroblasts by PDGF was inhibited in the presence of IL–1β and TNF–α, and this inhibition was not a consequence of any elevation of PGE2. PDGF stimulated fibroblast chemotaxis in a concentrationdependent manner, and this stimulation was augmented by combining PDGF with IL–1β and TNF–α.These findings suggested that PDGF differentially regulated MMPs production in combination with cytokines, and further that MMP assay and zymography had differential sensitivity for detecting MMPs. The presence of cytokines with PDGF appears to modulate the proliferation and chemotaxis of human lung fibroblasts.