Time-domain nuclear magnetic resonance (TD-NMR) of (1)H nuclei has been used to monitor and model changes of endodontic cement pastes during hydration, from the initial reaction period up to hours and days. The (1)H in the samples are divided into two major spin groups by fitting each free induction decay, acquired after the second pulse of an inversion recovery (I-R) pulse sequence with variable interpulse delay, by the sum of a quasi-Gaussian (signal from low mobility nuclei) and an exponential (from higher mobility nuclei). The extrapolations to zero time of the signals from the two spin groups give two sets of I-R data that have been analyzed to give quasi-continuous T(1) distributions. After about a day, two clearly solid components appear. From a day to a few days, three liquid populations are identified, one of them mainly in the low-mobility spin group, which later merge, giving a single T(1) or T(2) peak. The rapid onset of the solid components, at the cost of the liquid, and the rapid changes of the relaxation time distributions of all components are clear indicators of the amount and kinetics of reaction products formation (C-S-H gel and Portlandite) and of the C-S-H micronanoporous structure buildup and evolution. At 30 days of hydration, the very short T(1) and T(2) liquid component (T(1) congruent with 200 micros and T(2) congruent with 50 micros) can be assigned to C-S-H intralayer water (thickness of the order of fractions of a nanometer) and the remaining liquid signal to interlayer water (thickness of the order of 1 nm). Comparisons are made among a widely used commercial endodontic cement paste and two more recent commercial pastes, with additive compounds to make the hydration process faster and to increase the workability. Parameters can be extracted from the data to characterize the different kinetics and nanostructure of the pore space formed up to 30 days. The parameters are in agreement with the expected effects of the additives, so the parameters can be used to optimize the formulation of new pastes, in order to improve their therapeutic performance.
Dual-energy mammographic imaging experimental tests have been performed using a compact dichromatic imaging system based on a conventional x-ray tube, a mosaic crystal, and a 384-strip silicon detector equipped with full-custom electronics with single photon counting capability. For simulating mammal tissue, a three-component phantom, made of Plexiglass, polyethylene, and water, has been used. Images have been collected with three different pairs of x-ray energies: 16-32 keV, 18-36 keV, and 20-40 keV. A Monte Carlo simulation of the experiment has also been carried out using the MCNP-4C transport code. The Alvarez-Macovski algorithm has been applied both to experimental and simulated data to remove the contrast between two of the phantom materials so as to enhance the visibility of the third one.
Different "average" nuclear magnetic resonance relaxation times for correlation with fluid-flow permeability and irreducible water saturation in water-saturated sandstones In 1 H NMR ͑nuclear magnetic resonance͒ relaxation measurements for a set of eight hardwood and softwood samples, each free induction decay ͑FID͒ is fitted by the sum of a "solid" signal of the form A exp͓−c͑t / T S ͒ 2 ͔͓1−g͑t / T S ͒ 2 + h͑t / T S ͒ 4 ͔ plus a "liquid" signal B exp͑−t / T 2-FID ͒. Distributions of longitudinal ͑T 1 ͒ relaxation times were computed separately for the solid and liquid components, giving also the solid/liquid 1 H ratio ␣. From measurements on the samples dried, seasoned, and hydrated, the moisture content ͑liquid/solid weight ratio͒ was found to be approximately 0.50/ ␣. For each of the "seasoned" samples ͑10%-13% moisture content͒ a single T 1 peak was found for the solid and two for the liquid, with the longer liquid T 1 close to that of the solid, but with some differences exceeding perceived experimental uncertainties. None of the solid or liquid-long T 1 's is much less than 20 ms, even though liquid-short times go as low as 0.35 ms, appearing to negate simple solid-to-liquid exchange on a millisecond time scale. Data for six of the samples ͑all except for two resin-containing pine species͒ can be formally fitted by a two-site exchange model, in which cases the solid-to-liquid exchange times are a few tens of milliseconds. For our set of wood samples, each of the above three T 1 values, and also the overall liquid geometric-mean and rate-average T 1 's, as well as the liquid long-T 1 fraction, for a seasoned hardwood is longer than the corresponding value for any softwood, suggesting that relaxation parameters may provide a useful ranking of seasoned woods.
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