181,289 research outputs found
Studies of spin relaxation and molecular dynamics in liquid crystals by two-dimensional Fourier transform electron spin resonance .1. Cholestane in butoxy benzylidene-octylaniline and dynamic cage effects
No full textTwo-dimensional Fourier transform (2D-FT) electron spin resonance (ESR) studies on the rigid rodlike cholestane (CSL) spin-label in the liquid crystal solvent 4O,8 (butoxy benzylidene octylaniline) are reported. These experiments were performed over a wide temperature range: 96 degrees C to 25 degrees C covering the isotropic (I), nematic (N), smectic A (S-A) smectic B (S-B), and crystal (C) phases. It is shown that 2D-FT-ESR, especially in the form of 2D-ELDOR (two-dimensional electron-electron double resonance) provides greatly enhanced sensitivity to rotational dynamics than previous cw-ESR studies on this and related systems. This sensitivity is enhanced by obtaining a series of 2D-ELDOR spectra as a function of mixing time, T-m, yielding essentially a three-dimensional experiment. Advantage is taken of this sensitivity to study the applicability of the model of a slowly relaxing local structure (SRLS). In this model, a dynamic cage of solvent molecules, which relaxes on a slower time scale than the CSL solute, provides a local orienting potential in addition to that of the macroscopic aligning potential in the liquid crystalline phase. The theory of Polimeno and Freed for SRLS in the ESR slow motional regime is extended by utilizing the theory of Lee et al. to include 2D-FT-ESR experiments, and it serves as the basis for the analysis of the 2D-ELDOR experiments. It is shown that the SRLS model leads to significantly improved non-linear least squares fits to experiment over those obtained with the standard model of Brownian reorientation in a macroscopic aligning potential. This is most evident for the S-A phase, and the use of the SRLS model also removes the necessity of fitting with the unreasonably large CSL rotational asymmetries in the smectic phases that are required in both the cw-ESR and 2D-ELDOR fits with the standard model. The cage potential is found to vary from about k(B)T in the isotropic phase to greater than 2k(B)T in the N and S-A phases, with an abrupt drop to about 0.2k(B)T in the S-B and C phases. Concomitant with this drop at the S-A-S-B transition is an almost comparable increase in the orienting potential associated with the macroscopic alignment. This is consistent with a freezing in of the smectic structure at this transition. The cage relaxation rate given by R(c), its ''rotational diffusion coefficient,'' is of order of 10(7) s-(1) in the I and N phases. It drops somewhat in the S-A phase, but there is a greater than order of magnitude drop in R(c) for the S-B and C phases to about 10(5) s(-1). This drop is also consistent with the freezing in of the smectic structure. The rotational diffusion tensor of the CSL probe is significantly larger than R(c) which is consistent with the basic physical premise of the SRLS model. In particular, R(perpendicular to)(0) and R(parallel to)(0) are of order 10(8) s(-1) and 10(9) s(-1) respectively
Polymorphisms in Gag spacer peptide 1 confer varying levels of resistance to the HIV-1 maturation inhibitor bevirimat
No full textBackground: The maturation inhibitor bevirimat (BVM) potently inhibits human immunodeficiency virus type 1 (HIV-1) replication by blocking capsid-spacer peptide 1 (CA-SP1) cleavage. Recent clinical trials demonstrated that a significant proportion of HIV-1-infected patients do not respond to BVM. A patient’s failure to respond correlated with baseline polymorphisms at SP1 residues 6-8. Results: In this study, we demonstrate that varying levels of BVM resistance are associated with point mutations at these residues. BVM susceptibility was maintained by SP1-Q6A, -Q6H and -T8A mutations. However, an SP1-V7A mutation conferred high-level BVM resistance and SP1-V7M and T8Δ mutations conferred intermediate levels of BVM resistance. Conclusions: Future exploitation of the CA-SP1 cleavage site as an antiretroviral drug target will need to overcome the baseline variability in the SP1 region of Gag.Peer reviewe
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Chain dynamics and the simulation of electron spin resonance spectra from oriented phospholipid membranes
No full textA model previously developed for describing the dynamics of flexible alkyl chains that is based on Flory's rotational isomeric state approximation is adapted and applied to the analysis of electron spin resonance (ESR) spectra obtained from a phospholipid spin label in a macroscopically aligned phospholipid membrane, In this model, rotation around each C-C bond of the labeled alkyl chain is characterized by three inequivalent minima, with one end of the chain fixed to mimic the phospholipid headgroup, and with the dynamic effects of the nitroxide label explicitly included. This model is integrated with that for the overall rotation of the phospholipid in the mean orientational potential of the aligned membrane, and it is incorporated into the stochastic Liouville equation which describes the ESR line shape in the presence of these dynamic processes. The analysis is simplified by introducing the fact that the relatively rapid internal modes of motion can be treated by motional narrowing theory and a time scale separation can be made with respect to the much slower overall motions of the phospholipid. A series of ESR spectra from the spin label 16-PC in the lipid dimyristoylphosphatidylcholine were obtained over a range of temperatures (35-65 degrees C) in the L-alpha phase for various orientations of the normal to the bilayer plane relative to the magnetic field. Very good agreement with experiment is obtained from this model by using least squares fitting procedures for the overall motional dynamics. One finds an order parameter of [D-00(2)] that is constant throughout the phase and the perpendicular component for rotational diffusion, R-perpendicular to, that ranges from about 1-3 x 10(7)s(-1) (which corresponds to the ESR slow motional regime). Fits to the ESR spectra were also obtained from a simple but standard model wherein a single overall rotational diffusion tensor is used to describe the combined effects of internal and overall dynamics. These fits were almost as good, but they lead to a much larger R-perpendicular to approximate to 3-6 x 10(8)s(-1) and a smaller [D-00(2)] = 0.1, since these parameters now include the composite effects of both types of processes. New ESR experiments are proposed to provide more critical tests of these models
Personal Papers (MS 80-0002)
No full textHandwritten letter from Mrs. Ray Freed to Mr. R. Lee Kempner expressing thankfulness for the check towards Galveston County Jewish Welfare Association
Author, Author! Part 1
No full textThere can be no better venue for paying homage to celebrated writers than a journal devoted to wordplay. A score of such literary luminaries awaiting well-deserved recognition is concealed in the listing below. Revealing a name entails permuting the collection that results when a new letter replaces a given one in each word. To illustrate, after scrambling, the creators of Tom Sawyer and Robinson Crusoe will be exposed when W supplants G in GIANT and O does the same to R in FREED, respectively. A perfect score authorizes you to call yourself an author authority
L. Kendall, B. Mathé, T. Ross Miller With S. A. Freed, R. S. Freed & L. Williamson, Drawing Shadows to Stone. The Photography of the Jesup North Pacific Expedition, 1897-1902
No full textMauzé Marie. L. Kendall, B. Mathé, T. Ross Miller With S. A. Freed, R. S. Freed & L. Williamson, Drawing Shadows to Stone. The Photography of the Jesup North Pacific Expedition, 1897-1902. In: L'Homme, 1998, tome 38 n°148. Lignage, mariage, héritage. pp. 287-288
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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