bluuebunny/crossref_metadata_2025 huggingface dataset:
N
2
adsorption study on quartz, silver, and carbon nanotube by inductive pulse quartz crystal microbalance
Authors: Park Jang-ik , Yu Insuk , Seo Yongho
Published: March 2007

We utilize an “inductive pulse” quartz crystal microbalance method to study N2 adsorption on quartz, silver, and a single wall carbon nanotube at 77 K. This method is based on radio frequency electric pulse excitation and ring-down signal measurements of quartz crystal resonators located in an induction coil. The surface areas and adsorption strength c are estimated by the Brunauer-Emmett-Teller (BET) model. The estimated c for quartz and silver surface are about 1/5 times smaller than that measured by the conventional method. This is explained as suppression of the self-heating effect, by using our inductive pulse method. We suggest a simple theoretical estimation of self-heating effects on conventional and inductive pulse methods. For the intermediate adsorption range, we analyze our data using the generalized Frenkel-Hasley-Hill (FHH) model with fractal dimension. While the quartz and silver have fractal dimensions of about 2.2±0.1, single wall carbon nanotube has 1.2±0.1, which are explained by its strong adsorptive force.
Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. I. Structure
Authors: Enevoldsen A. D. , Hansen F. Y. , Diama A. , Criswell L. , Taub H.
Published: March 2007

The structure of a monolayer film of the branched alkane squalane (C30H62) adsorbed on graphite has been studied by neutron diffraction and molecular dynamics (MD) simulations and compared with a similar study of the n-alkane tetracosane (n-C24H52). Both molecules have 24 carbon atoms along their backbone and squalane has, in addition, six methyl side groups. Upon adsorption, there are significant differences as well as similarities in the behavior of these molecular films. Both molecules form ordered structures at low temperatures; however, while the melting point of the two-dimensional (2D) tetracosane film is roughly the same as the bulk melting point, the surface strongly stabilizes the 2D squalane film such that its melting point is 91K above its value in bulk. Therefore, squalane, like tetracosane, will be a poor lubricant in those nanoscale devices that require a fluid lubricant at room temperature. The neutron diffraction data show that the translational order in the squalane monolayer is significantly less than in the tetracosane monolayer. The authors’ MD simulations suggest that this is caused by a distortion of the squalane molecules upon adsorption on the graphite surface. When the molecules are allowed to relax on the surface, they distort such that all six methyl groups point away from the surface. This results in a reduction in the monolayer’s translational order characterized by a decrease in its coherence length and hence a broadening of the diffraction peaks. The MD simulations also show that the melting mechanism in the squalane monolayer is the same footprint reduction mechanism found in the tetracosane monolayer, where a chain melting drives the lattice melting.
Crackling noise peaks as signature of avalanche correlation
Authors: Celasco Edvige , Celasco Marcello , Eggenhöffner Roberto
Published: March 2007

Until now, all existing theories failed to explain peaks in the power noise spectra. Here we focus on the role of correlation among avalanches as the main source of the noise peaks observed. The present theory is based on first principles statistics of elementary events clustered in time-amplitude correlated avalanches. A noise spectral power master equation suitable to explain any peaked noise spectra is analytically achieved. Excellent agreement with our noise experiments in superconductors and with recent experiments in Escherichia coli, in single DNA molecule, and in single electron tunneling is reported.
Effect of stagnant-layer conductivity on the electric permittivity of concentrated colloidal suspensions
Authors: Carrique F. , Arroyo F. J. , Shilov V. N. , Cuquejo J. , Jiménez M. L. , Delgado A. V.
Published: March 2007

A long-lasting experience in the electrokinetics of suspensions has shown that the so-called standard model may be partly in error in explaining experimental data. In this model, the stagnant layer is considered nonconducting (Kσi=0), and only the diffuse layer contributes to the total surface conductivity (Kσ=Kσd). In the present work, the authors analyze the consequences of assuming a nonzero stagnant layer conductivity on the permittivity of concentrated suspensions. Using a cell model to account for the particle-particle interactions, and a well established ion adsorption isotherm on the inner region of the double layer, the authors find the frequency-dependent electric permittivity of suspensions of spherical particles with volume fractions of solids up to above 40%. It is demonstrated that the addition of Kσi significantly increases the contributions of the double layer to the polarization of the suspension: the α or concentration polarization at low (kilohertz) frequencies, and the Maxwell-Wagner-O’Konski (associated with conductivity mismatch between particle and medium) one at intermediate (megahertz) frequencies. While checking for the possibility that the results obtained in conditions of Kσi≠0 could be reproduced assuming Kσi=0 and raising Kσd to reach identical total Kσ, it is found that this is approximately possible in the calculation of the permittivity. Interestingly, this does not occur in the case of electrophoretic mobility, where the situations Kσ=Kσd and Kσ=Kσd+Kσi (for equal Kσ) can be distinguished for all frequencies. This points to the importance of using more than one electrokinetic technique to properly evaluate not only the zeta potential but other transport properties of concentrated suspensions, particularly Kσi.
Analytical saturated domain orientation textures and electromechanical properties of ferroelectric ceramics due to electric/mechanical poling
Authors: Li F. X. , Rajapakse R. K. N. D.
Published: March 2007

Saturated domain orientation textures of three types of pseudocubic (tetragonal, rhombohedral, and orthorhombic) ferroelectric ceramics after complete electric and uniaxial tension (compression) poling is studied analytically in this paper. A one-dimensional orientation distribution function (ODF) of the domain polar vectors is explicitly derived from the uniform inverse pole figures of the poling field axes on a stereographic projection with respect to the fixed crystallite coordinates. The analytical ODF is used to obtain the analytical solutions of saturated polarization and strain after electric/mechanical poling. Based on the closed form solution of the saturated domain orientation textures, the resultant intrinsic electromechanical properties of ferroelectric ceramics, which depend only on the ODF and properties of the corresponding single crystals, are obtained. The results show how the macroscopic symmetries of ferroelectric crystals change from 4mm (tetragonal), 3m (rhombohedral), and mm2 (orthorhombic) single crystals to a ∞mm (transversely isotropic) completely poled ceramic.
Anisotropy of ferroelectric and piezoelectric properties of Bi3.15Pr0.85Ti3O12 thin films on Pt(100)∕Ti∕SiO2∕Si substrates
Authors: Hu G. D. , Fan S. H. , Cheng X.
Published: March 2007

Bi 3.15 Pr 0.85 Ti 3 O 12 (BPT) thin films with (100) (α(100)=89.1%), (117) (α(117)=83.2%), and (001) (α(001)=99.7%) orientations and a c-axis-oriented (α(001)=99.9%) Bi4Ti3O12 (BT) film were deposited on Pt(100)∕TiO2∕SiO2∕Si substrates using a metal organic decomposition process. Both the values of the remanent polarization (Pr) and coercive field (Ec) of the (001)-oriented BPT film are about 50% higher than those of the BT film with the same orientation, indicating that the ferroelectric properties of BT along the c axis can be improved by doping of praseodymium. Nevertheless, the major polarization vector of BPT is still close to the a axis rather than the c axis due to the fact that the Pr values of the (100)-oriented BPT film are about one and four times larger than those of (117)- and (001)-oriented BPT films, respectively. Based on the volume fractions of (100)-, (117)-, and (001)-oriented grains in BPT films with three orientations, the Pr values of the purely (100)-, (117)-, and (001)-oriented BPT films can be predicated to be about 28.2, 11.1, and 5.3μC∕cm2, respectively. The maximum of the piezoelectric coefficient of BPT can be demonstrated to also be close to the a axis by the piezoelectric measurements using an atomic force microscope in the piezoresponse mode.
Mechanism of enhanced adhesion between hydrogenated amorphous carbon films and tungsten preimplanted steel substrates
Authors: Xu Ming , Cai Xun , Chen Qiulong , Zhao Jun , Chu Paul K.
Published: March 2007

Hydrogenated amorphous carbon (a-C:H) films have good mechanical properties but poor adhesion on substrates such as tool steels thereby limiting their applications. Film adhesion can be improved by conducting tungsten preimplantation into the steel substrates before deposition of the carbon film. The enhancement mechanism is investigated in this study by depositing the films on W plasma-preimplanted (20kV, 5×1017ionscm−2) and untreated steel substrates using mixed acetylene and argon plasmas with different flow rate ratios by means of plasma immersion ion implantation and deposition. Preimplantation creates a graded WC interface that mitigates diffusion of the dissociated carbon atoms on the surface. Compared to the films deposited on untreated steel substrates, the ones deposited on the W-implanted steel substrates exhibit improved adhesion strength, especially for the lower acetylene to argon flow rate ratios. Tungsten preimplantation is critical to the successful fabrication of a-C:H films on steel substrates. Furthermore, the flow rate ratio also has a large impact on the film properties due to the variations in the deposition rate causing different internal stress in the film. A nucleation model is proposed to explain the enhancement of the adhesion properties.
Hysteresis scaling of uniaxially anisotropic Heisenberg model
Authors: Guo Y. B. , Chen X. , Liu J.-M.
Published: March 2007

We simulate by the Monte Carlo method the dynamic hysteresis and hysteresis scaling of two-dimensional uniaxially anisotropic Heisenberg model submitted to a time-oscillating magnetic field h of frequency f and amplitude h0. It is revealed that the hysteresis area as a function of f and h0 exhibits well-defined power law behaviors over the low-f and high-f regimes as long as h0 is high enough. The power law exponents for the low-f regime depend on the uniaxially anisotropic factor K, but the exponents for the high-f regime are universal. The single-peaked hysteresis dispersions at different h0 follow both the empirical scaling approach and the single-variable scaling hypothesis, respectively, demonstrating the existence of a single characteristic time for spin reversal mode given the amplitude h0. However, the scaling may be broken when h0 is low, due to the coexistence of spin reversal and spin tilting resonances.
Field shifts and lowest order QED corrections for the ground 1S1 and 2S3 states of the helium atoms
Authors: Frolov Alexei M.
Published: March 2007

The bound state properties of the ground 1S1(L=0) state and the lowest triplet 2S3(L=0) state of the He3, He4, and He∞ helium atoms are determined to very high accuracy from the results of direct numerical computations. To compute the bound state properties of these atoms the author applied his exponential variational expansion in relative/perimetric three-body coordinates. For the ground 1S1(L=0) state and the lowest triplet 2S3(L=0) state of the He3, He4, and He∞ atoms the author also determined the lowest order QED corrections and the field component of isotopic shift (=field shift). For the 2S3(L=0) state of the He3 atom the hyperfine structure splitting is evaluated. The considered properties of the ground 1S1 state and the lowest 2S3 state in the He3 and He4 atoms are of great interest in a number of applications.
Crumpling, buckling, and cracking: Elasticity of thin sheets
Authors: Marder Michael , Deegan Robert D. , Sharon Eran
Published: March 2007

Deforming thin surfaces creates a rich set of structural and dynamical problems combining physics and geometry.
Observation of the splitting of degenerate surface plasmon polariton modes in a two-dimensional metallic nanohole array
Authors: Pang Lin , Tetz Kevin A. , Fainman Yeshaiahu
Published: March 2007

The authors report the experimental observation of the splitting of the degenerate (0,±1) surface plasmon polariton modes excited in a metallic nanohole array integrated with microfluidic channel for delivery and precise control of the index of refraction of overlaying layer. They use high-resolution wavelength and angle scans for excitation of the surface modes and a polarizer-analyzer pair to suppress the nonresonant transmission. The two resultant modes include an intense, spectrally broad low-energy mode and a weaker, much narrower bandwidth high-energy mode.
Operation of a reversed pentacene-fullerene discrete heterojunction photovoltaic device
Authors: Nanditha D. M. , Dissanayake M. , Hatton Ross A. , Curry Richard J. , Silva S. R. P.
Published: March 2007

The photoresponse of reversed bilayer organic photovoltaic device based on pentacene and C60 is examined, and the mechanism of photocurrent generation is shown to be different to that in conventional heterojunction devices, with free charge carriers generated at the electrode-organic interfaces rather than the organic heterojunction. This hypothesis is tested with silver nanoclusters incorporated at the organic heterojunction to quench excitons and facilitate recombination of free charge carriers, which shows a predicted increase in Jsc. The large Voc in this reversed cell structure is also rationalized in the context of the model proposed.
Enhancement of six-wave mixing by atomic coherence in a four-level inverted Y system
Authors: Zhang Yanpeng , Xiao Min
Published: March 2007

The authors have considered the coexisting dressed four-wave mixing (FWM) and six-wave mixing (SWM) in an open four-level inverted Y configuration. The authors also report an experimental observation of optical pumping-assisted FWM and electromagnetically induced transparency (EIT)-assisted SWM. The efficient SWM can be selected by EIT window and controlled by the coupling as well as dressed field detuning and power. Due to EIT and optical pumping assistance, the enhanced SWM signal is more than ten times lager than the coexisting FWM signal.
Creating and Characterizing Individual Molecular Bonds with a Scanning Tunneling Microscope
Authors: Day Charles
Published: March 2007

In high school chemistry experiments, it's easy to follow a chemical reaction: Mix the chemicals in a test tube, and watch for a change of color, fizzing, or some other sign of chemical transformation. But what do you do if you want to probe the spatial limits of chemistry—that is, to initiate and examine an individual chemical reaction? In a recent paper in Science, Wilson Ho of Cornell University and his graduate student Hyojune Lee provide an answer. By using a scanning tunneling microscope (STM), Ho and Lee combined atoms and molecules on a metal surface to make new molecules. But that's not all they accomplished. To confirm the chemical identity of their molecular creations, they measured the individual molecules' vibrational energies—again with the STM. “Their results are truly remarkable,” comments the University of Maryland's Ellen Williams, “not just creating the bonding, but also the single-molecule spectroscopy.”
The Composite Fermion: A Quantum Particle and Its Quantum Fluids
Authors: Jain Jainendra K.
Published: March 2007

Discovery of new particles is not usually associated with condensed matter physics, because, at one level, we already know all the particles that go into the Hamiltonian—namely, electrons and ions. But it is a most profound fact of nature—indeed the very reason why physics can make progress at many different levels—that strongly interacting particles reorganize themselves to become more weakly coupled particles of a new kind. Often they are simple bound states of the old particles. But sometimes they are fantastically complicated collective objects (for example, solitons) that nonetheless behave as legitimate particles, with well-defined charge, spin, statistics, and other properties we attribute to particles.
Andrei Sakharov and the Nuclear Danger
Authors: Drell Sidney D.
Published: March 2007

For over forty years, nuclear weapons were a major concern of Andrei Dmitrievich Sakharov. A brilliant physicist whose work was instrumental in the creation of the Soviet hydrogen bomb, Sakharov was led by his concern about the dangers of nuclear weapons and the threat of nuclear war to become a courageous activist for peace and disarmament, as well as for human rights (A 1989 talk by Sakharov is reprinted in PHYSICS TODAY, July 1999, page 22; for more on Sakharov, see PHYSICS TODAY, August 1990, which was a special issue devoted to him; also see the American Institute of Physics's Center for the History of Physics on-line exhibit on Sakharov at http://www.aip.org/history/sakharov/). In his lifetime he saw the problems and dangers associated with creating such massively destructive weapons through the highly refracting lens of the cold war. That war is over. The Soviet Union no longer exists. But great dangers remain, albeit mutated into new forms. We still face grave perils.
Do Neighbourhoods Influence the Readiness to Learn of Kindergarten Children in Vancouver? A Multilevel Analysis of Neighbourhood Effects
Authors: Oliver Lisa N , Dunn James R , Kohen Dafna E , Hertzman Clyde
Published: March 2007

A growing body of literature has examined the effects of neighbourhood characteristics on child health and well-being and the mechanisms through which such effects may operate. Research investigating neighbourhood effects on children is based on the notion that individuals and families who live in a neighbourhood collectively create a social context that influences the developing child. In this paper we investigate the relationship between individual and neighbourhood socioeconomic characteristics and kindergarten children's readiness to learn in Vancouver, Canada ( n = 3736), using multilevel modeling techniques and 1996 census data for Vancouver neighbourhoods ( n = 68). Findings suggest that although family-level characteristics carry the most weight in shaping children's readiness to learn, neighbourhood-level factors are independently associated with early developmental outcomes, particularly physical health and well-being, language and cognitive development, and communications skills and general knowledge. The strongest neighbourhood characteristics associated with readiness to learn were median income and the percentage of single-parent families. Also important were the percentage of the population who had not moved in the previous five years and the percentage of the population whose mother tongue was non-English. The latter neighbourhood characteristic was an especially strong predictor of communication skills and general knowledge. The findings suggest that neighbourhood-based policies to improve physical health and well-being, language and cognitive development, and communications skills may also meet with some success.
The Changing Structure of Ethnic Diversity and Segregation in England, 1991–2001
Authors: McCulloch Andrew
Published: March 2007

Using data from the 1991 and 2001 Censuses, I examine patterns of ethnic diversity and segregation in England's metropolitan regions. Diversity is measured using the Shannon entropy index and segregation is measured using the Theil index. Both indices can be decomposed into contributions due to region, district, and ward, which may indicate the processes responsible for patterns of ethnic diversity and segregation. The results show that ethnic diversity increased from 0.533 in 1991 to 0.731 in 2001. Between 1991 and 2001 the share of diversity contributed by Inner London and the West Midlands declined and the share contributed by Outer London and the Outer Metropolitan Area rose. Decomposition of total diversity shows that regional and district differences in ethnic diversity increased between 1991 and 2001 but differences between wards declined in importance. Within-ward diversity contributed more than 75% of total diversity at each census. Between 1991 and 2001 there was a slight increase in the overall level of segregation. Decomposition of total segregation into between-district and within-district components for each region shows that the contribution of within-district segregation to total segregation fell between 1991 and 2001. However, the contribution of between-district segregation to total segregation remained important and increased significantly in Inner London. Across the area investigated wards have on average become more ethnically diverse but there remain significant differences in diversity and segregation between regions and districts.
Cross-Sectional and Quasi-Panel Explorations of the Connection between the Built Environment and Auto Ownership
Authors: Cao Xinyu , Mokhtarian Patricia L , Handy Susan L
Published: March 2007

Auto ownership is a critical mediating link in the connection between the built environment and travel behavior: the built environment presumably influences auto ownership, which in turn impacts travel behavior. However, the way in which individual elements of the built environment affect auto-ownership choices is far from understood. Further, residential self-selection may confound the interaction between the built environment and auto ownership. And the absence of panel data impedes our understanding of the causal relationships. Using a survey of 1682 respondents in Northern California, we applied ordered probit and static-score modeling techniques to investigate the causal link from the built environment to auto ownership in both cross-sectional and quasi-panel contexts. Through variable selection in cross-sectional analysis, we found that individuals' attitudes regarding residential neighborhood and travel are more strongly associated with their auto-ownership decision than is the built environment per se. Specifically, when general preferences for various neighborhood traits were allowed to enter the model, they drove out from the model the (perceived) measure of the same trait for the neighborhood of current residence, a pattern suggesting that the observed correlation between neighborhood characteristics and auto ownership is primarily a result of self-selection. On the other hand, the quasi-panel results indicate that some built-environment elements such as outdoor spaciousness and mixed land use are causes of auto ownership (remaining even after attitudes were allowed to enter the model), but their effects are marginal. In contrast, the strong influence of sociodemographics suggests that households' auto-ownership decisions are fundamentally based on their mobility needs and purchasing power. Given the mixed findings, we do not definitively confirm a causal relationship between the built environment and auto ownership. However, we provide encouraging evidence that land-use policies designed to reduce auto ownership and use will lead to a marginal reduction in auto ownership.
Planning Guidance and Large-Store Development in the United Kingdom: The Search for ‘Flexibility’
Authors: Guy Cliff , Bennison David
Published: March 2007

An important feature of town-planning practice in Western Europe has been the attempt to control commercial-property development in order to conform with planning principles. The growth history of large stores such as hypermarkets, superstores, and retail warehouses has thus been characterised by disputes between developers and planners. In this paper we examine the responses of large-store developers to UK government planning guidance that retail developments should be of a nature and scale suited to the physical environment of town centres. This goes against some retailers' preferences for large formats which are generally unsuited to town centres. We explain these two opposed views, devoting particular attention to the retail developers' case. We then use findings from two interview surveys with selected retailers to explore how far retail developers are prepared to go in compromising their preferred models of store development in line with government policy. Finally we discuss potential effects of recent changes in government policy.
(Re)making the Other, Heterosexualising Everyday Space
Authors: Browne Kath
Published: March 2007

In this paper I develop conceptions of sexualised space as continually becoming by exploring the (re)creation of heterosexual spaces through the processes of power that hierarchise sexualities and how they are narrated. I seek to gain insights into the subtle operations of power between momentary enactments and stabilised manifestations of power. Central to this are the (invisiblised and unnamed) microlevel processes and the ‘common sense’ assumptions. In the empirical research I interrogate how twenty-eight nonheterosexual women discuss their experiences of eating in restaurant spaces to examine othering processes, rather than solely relying on categories of difference or named discriminations in theorising the (re)formation of spaces. From this it is possible to render the contingency of heterosexualised spaces visible, if reiterated and congealed in part (and para-doxically) through an absence of naming. I conclude by contending that focusing on (re)productive practices could expand our understandings of the hierarchical (re)construction of space.
Exploring the Role of Professional Associations in Collective Learning in London and New York's Advertising and Law Professional-Service-Firm Clusters
Authors: Faulconbridge James R
Published: March 2007

The value of regional economies for collective learning has been reported by numerous scholars. However, often their work has been criticised for lacking analytical clarity and failing to explore the architectures of collective learning and the role of the knowledge produced in making firms in a cluster economy successful. In this paper I engage with these problematics and investigate how collective learning is facilitated in the advertising and law professional-service-firm clusters in London and New York. I explore the role of professional associations and investigate how they mediate a collective-learning process in each city. I argue that professional associations seed urban communities of practice that emerge outside of the formal activities of professional associations. In these communities individuals with shared interests in advertising and law learn from one another and are therefore able to adapt and evolve one-another's approaches to common industry challenges. I suggest this is another form of the variation Marshall highlighted in relation to cluster-based collective learning. I also show how the collective-learning process is affected by the presence, absence, and strength of an institutional thickness. I therefore argue that a richer understanding of institutional effects is needed in relation to collective learning.
The Estimation of International Migration Flows: A General Technique Focused on the Origin-Destination Association Structure
Authors: Raymer James
Published: March 2007

The log-linear model, with an alternative parameter coding scheme, is used in this paper to obtain estimates of international migration flows in situations where the data are inadequate or missing. The alternative parameter coding scheme is particularly useful in constructing the origin-destination association stricture—a key element often required for more-accurate predictions. To illustrate the method, international migration flows between countries in the northern region of Europe during the 1999–2000 period are estimated.
The Spatial Distribution of Income Inequality in the European Union
Authors: Ezcurra Roberto , Pascual Pedro , Rapún Manuel
Published: March 2007

In this paper we examine the distribution of income inequality among the regions of the European Union from 1993 to 2000. The results obtained show that the levels of inequality vary considerably between regions. Nevertheless, we have detected a high level of positive spatial dependence in the distribution under consideration. However, 57% of the regions considered registered no statistically significant variations in the degree of income dispersion over time, though there was a reduction in 40% of them. The empirical evidence presented indicates the existence of a process of regional convergence in terms of inequality during the period considered, mainly as a result of the evolution of regions whose initial levels of inequality were relatively high. Moreover, our analysis highlights the important roles played by the national component, activity, and unemployment rates, gross domestic product per capita, and the weight of the agricultural sector in total employment in accounting for differences in the degree of income dispersion across the European regions.
Conformational flexibility in the chromatin remodeler RSC observed by electron microscopy and the orthogonal tilt reconstruction method
Authors: Leschziner Andres E. , Saha Anjanabha , Wittmeyer Jacqueline , Zhang Yongli , Bustamante Carlos , Cairns Bradley R. , Nogales Eva
Published: March 2007

Chromatin remodeling complexes (remodelers) are large, multisubunit macromolecular assemblies that use ATP hydrolysis to alter the structure and positioning of nucleosomes. The mechanisms proposed for remodeler action on nucleosomes are diverse, and require structural evaluation and insights. Previous reconstructions of remodelers using electron microscopy revealed interesting features, but also significant discrepancies, prompting new approaches. Here, we use the orthogonal tilt reconstruction method, which is well suited for heterogeneous samples, to provide a reconstruction of the yeast RSC (
r
emodel the
s
tructure of
c
hromatin) complex. Two interesting features are revealed: first, we observe a deep central cavity within RSC, displaying a remarkable surface complementarity for the nucleosome. Second, we are able to visualize two distinct RSC conformers, revealing a major conformational change in a large protein “arm,” which may shift to further envelop the nucleosome. We present a model of the RSC-nucleosome complex that rationalizes the single molecule results obtained by using optical tweezers and also discuss the mechanistic implications of our structures.
G551D and G1349D, Two CF-associated Mutations in the Signature Sequences of CFTR, Exhibit Distinct Gating Defects
Authors: Bompadre Silvia G. , Sohma Yoshiro , Li Min , Hwang Tzyh-Chang
Published: March 2007

Mutations in the gene encoding cystic fibrosis transmembrane conductance regulator (CFTR) result in cystic fibrosis (CF). CFTR is a chloride channel that is regulated by phosphorylation and gated by ATP binding and hydrolysis at its nucleotide binding domains (NBDs). G551D-CFTR, the third most common CF-associated mutation, has been characterized as having a lower open probability (Po) than wild-type (WT) channels. Patients carrying the G551D mutation present a severe clinical phenotype. On the other hand, G1349D, also a mutant with gating dysfunction, is associated with a milder clinical phenotype. Residues G551 and G1349 are located at equivalent positions in the highly conserved signature sequence of each NBD. The physiological importance of these residues lies in the fact that the signature sequence of one NBD and the Walker A and B motifs from the other NBD form the ATP-binding pocket (ABP1 and ABP2, named after the location of the Walker A motif) once the two NBDs dimerize. Our studies show distinct gating characteristics for these mutants. The G551D mutation completely eliminates the ability of ATP to increase the channel activity, and the observed activity is ∼100-fold smaller than WT-CFTR. G551D-CFTR does not respond to ADP, AMP-PNP, or changes in [Mg2+]. The low activity of G551D-CFTR likely represents the rare ATP-independent gating events seen with WT channels long after the removal of ATP. G1349D-CFTR maintains ATP dependence, albeit with a Po ∼10-fold lower than WT. Interestingly, compared to WT results, the ATP dose–response relationship of G1349D-CFTR is less steep and shows a higher apparent affinity for ATP. G1349D data could be well described by a gating model that predicts that binding of ATP at ABP1 hinders channel opening. Thus, our data provide a quantitative explanation at the single-channel level for different phenotypes presented by patients carrying these two mutations. In addition, these results support the idea that CFTR's two ABPs play distinct functional roles in gating.
Intravenous Lidocaine Infusion Facilitates Acute Rehabilitation after Laparoscopic Colectomy
Authors: Kaba Abdourahamane , Laurent Stanislas R. , Detroz Bernard J. , Sessler Daniel I. , Durieux Marcel E. , Lamy Maurice L. , Joris Jean L.
Published: March 2007

Background

Intravenous infusion of lidocaine decreases postoperative pain and speeds the return of bowel function. The authors therefore tested the hypothesis that perioperative lidocaine infusion facilitates acute rehabilitation protocol in patients undergoing laparoscopic colectomy.

Methods

Forty patients scheduled to undergo laparoscopic colectomy were randomly allocated to receive intravenous lidocaine (bolus injection of 1.5 mg/kg lidocaine at induction of anesthesia, then a continuous infusion of 2 mg.kg.h intraoperatively and 1.33 mg.kg.h for 24 h postoperatively) or an equal volume of saline. All patients received similar intensive postoperative rehabilitation. Postoperative pain scores, opioid consumption, and fatigue scores were measured. Times to first flatus, defecation, and hospital discharge were recorded. Postoperative endocrine (cortisol and catecholamines) and metabolic (leukocytes, C-reactive protein, and glucose) responses were measured for 48 h. Data (presented as median [25-75% interquartile range], lidocaine vs. saline groups) were analyzed using Mann-Whitney tests. P<0.05 was considered statistically significant.

Results

Patient demographics were similar in the two groups. Times to first flatus (17 [11-24] vs. 28 [25-33] h; P<0.001), defecation (28 [24-37] vs. 51 [41-70] h; P=0.001), and hospital discharge (2 [2-3] vs. 3 [3-4] days; P=0.001) were significantly shorter in patients who received lidocaine. Lidocaine significantly reduced opioid consumption (8 [5-18] vs. 22 [14-36] mg; P=0.005) and postoperative pain and fatigue scores. In contrast, endocrine and metabolic responses were similar in the two groups.

Conclusions

Intravenous lidocaine improves postoperative analgesia, fatigue, and bowel function after laparoscopic colectomy. These benefits are associated with a significant reduction in hospital stay.
Racial Differences in the Use of Epidural Analgesia for Labor
Authors: Glance Laurent G. , Wissler Richard . , Glantz Christopher , Osler Turner M. , Mukamel Dana B. , Dick Andrew W.
Published: March 2007

Background

There is strong evidence that pain is undertreated in black and Hispanic patients. The association between race and ethnicity and the use of epidural analgesia for labor is not well described.

Methods

Using the New York State Perinatal Database, the authors examined whether race and ethnicity were associated with the likelihood of receiving epidural analgesia for labor after adjusting for clinical characteristics, demographics, insurance coverage, and provider effect. This retrospective cohort study was based on 81,883 women admitted for childbirth between 1998 and 2003.

Results

Overall, 38.3% of the patients received epidural analgesia for labor. After adjusting for clinical risk factors, socioeconomic status, and provider fixed effects, Hispanic and black patients were less likely than non-Hispanic white patients to receive epidural analgesia: The adjusted odds ratio was 0.85 (95% CI, 0.78-0.93) for white/Hispanic and 0.78 (0.74-0.83) for blacks compared with non-Hispanic whites. Compared with patients with private insurance, patients without insurance were least likely to receive epidural analgesia (adjusted odds ratio, 0.76; 95% CI, 0.64-0.89). Black patients with private insurance had similar rates of epidural use to white/non-Hispanic patients without insurance coverage: The adjusted odds ratio was 0.66 (95% CI, 0.53-0.82) for white/non-Hispanic patients without insurance versus 0.69 (0.57-0.85) for black patients with private insurance.

Conclusion

Black and Hispanic women in labor are less likely than non-Hispanic white women to receive epidural analgesia. These differences remain after accounting for differences in insurance coverage, provider practice, and clinical characteristics.
Late Psychological Symptoms after Awareness among Consecutively Included Surgical Patients
Authors: Samuelsson Peter , Brudin Lars , Sandin Rolf H.
Published: March 2007

Background

Awareness during general anesthesia can cause late psychological symptoms. Selection bias may have affected the results in previous retrospective studies. The authors used prospective consecutive collection to recruit patients with previous awareness.

Methods

In a cohort of 2,681 consecutive patients scheduled to undergo general anesthesia, 98 considered themselves to have been aware during previous surgery. Six patients died before inclusion, and another 13 were excluded (4 cases of stroke or dementia, 7 declined to participate, and 2 could not be located). Seventy-nine patients were interviewed by telephone, and medical records were checked in uncertain cases. The interview followed a structured protocol, including seven late symptoms (anxiety, chronic fear, nightmares, flashbacks, indifference, loneliness, and lack of confidence in future life). Three persons independently assessed the interviews for classification, to determine whether awareness had occurred.

Results

Four cases were performed using regional anesthesia, and another 29 were not considered as awareness by the assessors. Therefore, the final analyses included 46 patients. Twenty (43%) had experienced pain, and 30 (65%) described acute emotional reactions during the awareness episode. Fifteen (33%) patients had experienced late psychological symptoms afterward. In 6 of those cases, the symptoms lasted for more than 2 months, and 1 patient had a diagnosis of post-traumatic stress disorder. Acute emotional reactions were significantly related to late psychological symptoms (P<0.05).

Conclusion

The method for recruiting awareness cases in studies on late psychological symptoms may affect the result. The authors found fewer and milder problems, despite a similar degree of initial problems as in previous studies.
Dreaming during Anesthesia and Anesthetic Depth in Elective Surgery Patients
Authors: Leslie Kate , Skrzypek Hannah , Paech Michael J. , Kurowski Irina , Whybrow Tracey
Published: March 2007

Background

Dreaming reported after anesthesia remains a poorly understood phenomenon. Dreaming may be related to light anesthesia and represent near-miss awareness. However, few studies have assessed the relation between dreaming and depth of anesthesia, and their results were inconclusive. Therefore, the authors tested the hypothesis that dreaming during anesthesia is associated with light anesthesia, as evidenced by higher Bispectral Index values during maintenance of anesthesia.

Methods

With approval, 300 consenting healthy patients, aged 18-50 yr, presenting for elective surgery requiring relaxant general anesthesia with a broad range of agents were studied. Patients were interviewed on emergence and 2-4 h postoperatively. The Bispectral Index was recorded from induction until the first interview. Dream content and form were also assessed.

Results

Dreaming was reported by 22% of patients on emergence. There was no difference between dreamers and nondreamers in median Bispectral Index values during maintenance (37 [23-55] vs. 38 [20-59]; P=0.68) or the time at Bispectral Index values greater than 60 (0 [0-7] vs. 0 [0-31] min; P=0.38). Dreamers tended to be younger and male, to have high home dream recall, to receive propofol maintenance or regional anesthesia, and to open their eyes sooner after surgery. Most dreams were similar to dreams of sleep and were pleasant, and the content was unrelated to surgery.

Conclusions

Dreaming during anesthesia is unrelated to the depth of anesthesia in almost all cases. Similarities with dreams of sleep suggest that anesthetic dreaming occurs during recovery, when patients are sedated or in a physiologic sleep state.
Pharmacokinetics of Ropivacaine in Patients with Chronic End-stage Liver Disease
Authors: Jokinen Mika J. , Neuvonen Pertti J. , Lindgren Leena , Höckerstedt Krister , Sjövall Jan , Breuer Olof , Askemark Yvonne , Ahonen Jouni , Olkkola Klaus T.
Published: March 2007

Background

Ropivacaine is mainly eliminated by hepatic metabolism. The authors studied the effect of chronic end-stage liver disease on the pharmacokinetics of ropivacaine.

Methods

Thirteen patients with chronic end-stage liver disease and eight healthy volunteers received a single dose of 0.6 mg/kg ropivacaine intravenously over 30 min. Ropivacaine, 3-hydroxyropivacaine, and 2',6'-pipecoloxylidide were measured in venous plasma and urine.

Results

Peak ropivacaine plasma concentrations were similar. Patients with chronic end-stage liver disease had, on average, 60% lower total (P=0.001) and 56% lower unbound plasma clearance (P=0.002), 59% higher steady state volume of distribution (P=0.03), and 4.2-fold longer half-life (P<0.001) of ropivacaine. Of the variation in total ropivacaine clearance, 69% was accounted for by variation in albumin, 57% in prealbumin, 25% in international normalized ratio of plasma thromboplastin time, and 24% in galactose half-life. The patients excreted a larger fraction of the original dose as unchanged ropivacaine (2.1% vs. 0.3%; P<0.001) and a smaller fraction as 3-hydroxyropivacaine (11% vs. 27%; P=0.001). The fraction excreted as 2',6'-pipecoloxylidide (4.7% vs. 5.0%) was similar.

Conclusions

Ropivacaine clearance is decreased in chronic end-stage liver disease. A normal dose can be considered for a single block in patients with liver impairment, because the peak plasma concentrations were essentially similar. When using a postoperative ropivacaine infusion in a patient with end-stage liver disease, the lowest effective dose should be used for the shortest possible time and the patient should be monitored closely, because systemic toxicity cannot be ruled out. Because of wide interindividual differences in pharmacokinetics in patients with liver disease, no definitive dosing instructions can be given.
A Randomized Crossover Comparison of the Effects of Propofol and Sevoflurane on Cerebral Hemodynamics during Carotid Endarterectomy
Authors: McCulloch Timothy J. , Thompson Christopher L. , Turner Martin J.
Published: March 2007

Background

Intravenous and inhalational anesthetic agents have differing effects on cerebral hemodynamics: Sevoflurane causes some vasodilation, whereas propofol does not. The authors hypothesized that these differences affect internal carotid artery pressure (ICAP) and the apparent zero flow pressure (critical closing pressure) during carotid endarterectomy. Vasodilation is expected to increase blood flow, reduce ICAP, and reduce apparent zero flow pressure.

Methods

In a randomized crossover study, the gradient between systemic arterial pressure and ICAP during carotid clamping was measured while changing between sevoflurane and propofol in 32 patients. Middle cerebral artery blood velocity, recorded by transcranial Doppler, and ICAP waveforms were analyzed to determine the apparent zero flow pressure.

Results

ICAP increased when changing from sevoflurane to propofol, causing the mean gradient between arterial pressure and ICAP to decrease by 10 mmHg (95% confidence interval, 6-14 mmHg; P<0.0001). Changing from propofol to sevoflurane had the opposite effect: The pressure gradient increased by 5 mmHg (95% confidence interval, 2-7 mmHg; P=0.002). Ipsilateral middle cerebral artery blood velocity decreased when changing from sevoflurane to propofol. Cerebral steal was detected in one patient after changing from propofol to sevoflurane. The apparent zero flow pressure (mean+/-SD) was 22+/-10 mmHg with sevoflurane and 30+/-14 mmHg with propofol (P<0.01). There was incomplete drug crossover due to the limited duration of carotid clamping.

Conclusions

Compared with sevoflurane, ipsilateral ICAP and apparent zero flow pressure are both higher with propofol. Vasodilatation associated with sevoflurane can cause cerebral steal.
Family-centered Preparation for Surgery Improves Perioperative Outcomes in Children
Authors: Kain Zeev N. , Caldwell-Andrews Alison A. , Mayes Linda C. , Weinberg Megan E. , Wang Shu-Ming , MacLaren Jill E. , Blount Ronald L.
Published: March 2007

Background

Children and parents experience significant anxiety and distress during the preoperative period. Currently available interventions are having limited efficacy. Based on an integration of the literature in both the anesthesia and psychological milieus, the authors developed a behaviorally oriented perioperative preparation program for children undergoing surgery that targets the family as a whole.

Methods

Children and their parents (n = 408) were randomly assigned to one of four groups: (1) control: received standard of care; (2) parental presence: received standard parental presence during induction of anesthesia; (3) ADVANCE: received family-centered behavioral preparation; and (4) oral midazolam. The authors assessed the effect of group assignment on preoperative anxiety levels and postoperative outcomes such as analgesic consumption and emergence delirium.

Results

Parents and children in the ADVANCE group exhibited significantly lower anxiety in the holding area as compared with all three other groups (34.4+/-16 vs. 39.7+/-15; P=0.007) and were less anxious during induction of anesthesia as compared with the control and parental presence groups (44.9+/-22 vs. 51.6+/-25 and 53.6+/-25, respectively; P=0.006). Anxiety and compliance during induction of anesthesia was similar for children in both the ADVANCE and midazolam groups (44.9+/-22 vs. 42.9+/-24; P=0.904). Children in the ADVANCE group exhibited a lower incidence of emergence delirium after surgery (P=0.038), required significantly less analgesia in the recovery room (P=0.016), and were discharged from the recovery room earlier (P=0.04) as compared with children in the three other groups.

Conclusion

The family-centered preoperative ADVANCE preparation program is effective in the reduction of preoperative anxiety and improvement in postoperative outcomes.