Simple modification of a spin echo imaging pulse sequence generates useful spectroscopic information at 0.35 T. New images are produced that show water only, fat only, and the difference between water and fat intensity. Imaging speed, spatial resolution, and signal-to-noise ratio are comparable with ordinary imaging. The method provides new parameters for tissue characterization and improved contrast between some organs.

Magnetic resonance (MR) imaging methods with good spatial and contrast resolution are often too slow to follow the uptake of contrast agents with the desired temporal resolution. Imaging can be accelerated by skipping the acquisition of data normally taken with strong phase-encoding gradients, restricting acquisition to weak-gradient data only. If the usual procedure of substituting zeroes for the missing data is followed, blurring results. Substituting instead reference data taken before or well after contrast agent injection reduces this problem. Volunteer and patient images obtained by using such reference data show that imaging can be usefully accelerated severalfold. Cortical and medullary regions of interest and whole kidney regions were studied, and both gradient- and spin-echo images are shown. The method is believed to be compatible with other acceleration methods such as half-Fourier reconstruction and reading of more than one line of k space per excitation.

The research reported here develops an explanation for the often-noted absence of international war between democratic states. This explanation is derived from a theoretical rationale centered on universal democratic norms for reconciling competing values and interests. I argue that democratic states locked in disputes are better equipped than others with the means for diffusing conflict situations at an early stage before they have an opportunity to escalate to military violence. Not only is this explanatory logic consistent with the published findings on democracy and war, but it also entails the novel empirical proposition that disputes between democracies are more amenable than are other disputes to peaceful settlements, the hypothesis I examine here. Analyses of contemporary interstate disputes reveal that even when potentially confounding factors are controlled, democratic opponents are significantly more likely to reach peaceful settlements than other types of disputants.

NMR spectra are needlessly confusing when spinning sidebands and isotropic peaks lie on the same curve. Qualitative analysis is impossible if these spinning sidebands cannot be distinguished from isotropic peaks and quantitative measurement is frustrated whenever any sideband overlaps any other peak. Resolving a spectrum into several curves, one containing only isotropic peaks, another only first higher frequency sidebands, still another only first lower, etc., eliminates these problems. These extra curves, which can be generated by an echo technique, do not require extra acquisition time. An ordinary echo spectrum refocused after two revolutions has the same S/N ratio as each curve in a separated spectrum which is made with the same total number of acquisitions.

The efficiency of chemical exchange dependent saturation transfer (CEST) agents is largely determined by their water or proton exchange kinetics, yet methods to measure such exchange rates are variable and many are not applicable to in vivo measurements. In this work, the water exchange kinetics of two prototype paramagnetic agents (PARACEST) are compared by using data from classic NMR line-width measurements, by fitting CEST spectra to the Bloch equations modified for chemical exchange, and by a method where CEST intensity is measured as a function of applied amplitude of radiofrequency field. A relationship is derived that provides the water exchange rate from the X-intercept of a plot of steady-state CEST intensity divided by reduction in signal caused by CEST irradiation versus 1/x 1 2 , referred to here as an omega plot. Furthermore, it is shown that this relationship is independent of agent concentration. Exchange rates derived from omega plots using either high-resolution CEST NMR data or CEST data obtained by imaging agree favorably with exchange rates measured by the more commonly used Bloch fitting and linewidth methods. Thus, this new method potentially allows access to a direct measure of exchange rates in vivo, where the agent concentration is typically unknown. Magn Reson Med 63:625-632,

Molecular motions in polycarbonates and polycarbonate-like materials have been characterized by dipolar rotational spin-echo 13C NMR. The dominant motion in polycarbonate is 180°f lips about the aromatic-ring C2 axes. These flips occur over a broad range of frequencies extending to over 15 MHz. The flips are superimposed on 30°r ing oscillations about the same axes. Other main-chain motions, as measured through methyl-carbon dipolar patterns, are also significant; amplitudes of these motions are of the order of 20°. Chlorine substitution on the rings abolishes both ring and main-chain motions. Chemical modification of the links between rings also reduces motion, in some cases by preventing a fraction of the rings from flipping.

The research reported here extends investigation of the democracy-war hypothesis by focusing on the norms of dispute resolution integral to the democratic process. If we extend these norms to the international arena, then it becomes reasonable to expect democratic states to adopt compromise solutions to international problems. One implication of this logic is that democracies are likely to be more amenable than others to efforts of third parties to resolve or ameliorate interstate disputes. This hypothesis is examined in the present study. A sample of strictly interstate disputes acquired from the Alker-Sherman disaggregated conflict set provide the basis for this inquiry. Democracy is assessed for each disputant party with the composite index from the Polity II data collection. In order to control for extraneous effects on the probability of management, the author develops a baseline model consisting of prior management activity, the costs of conflict, and the power of the disputants. Because the dependent variable in this analysis is a binary indicator, the author employs probit regression to estimate the effects of democracy while partialling out the controls. The empirical results show that democracy does carry the systematic positive influence on the probability of conflict management expected of it.

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