1,721,061 research outputs found
From porous media to trabecular bone relaxation analysis: spatial variation of marrow 1H relaxation time distributions detected in vitro by quasi-continuous distribution analysis.
No full textSingle-sided NMR Analysis on Model Systems for the Evaluation of in situ Measurements on Cultural Heritage Materials
No full text
Pore-size evaluation by single-sided nuclear magnetic resonance measurements: Compensation of water self-diffusion effect on transverse relaxation
No full textThe determination of penetration depth and distribution of water at surfaces is essential to knowledge of the state of conservation of Cultural Heritage items and materials, such as frescoes, stone, brick, wood, and paper. Water can penetrate the surface of an object, coming from either an external or an internal source, and in general the moisture content of the surface region is the cause of various decay phenomena such as microfractures and disintegration. The nuclear magnetic resonance (NMR) approach can be very powerful for the evaluation of the state of fine arts materials. Not only the water saturation and?or the porosity of the material can be evaluated but also information on material pore-size distributions can be obtained by monitoring the distributions of relaxation times of the transverse (T2) and longitudinal (T1) components of the magnetization of the trapped water. The drawback is that generally the sample does not fit into standard NMR magnets, and for in situ application, single-sided NMR devices have to be used. Therefore, the standard methods to get NMR parameters are not always valid, and some alternative procedures have to be performed. For example, in strongly inhomogeneous magnetic fields due to the geometrical features of single-sided NMR devices, the transverse relaxation is greatly influenced by the molecular self-diffusion even at the shortest interpulse time available for a Carr–Purcell–Meiboom–Gill (CPMG) sequence. In this paper we show how the dephasing effect due to molecular self-diffusion can be corrected by using the “constant echo time method.” We report an attempt to recover the corrected T2 distribution in well-characterized porous materials saturated with water, with data acquired in the highly inhomogeneous magnetic field of a single-sided NMR device. The results are discussed and compared with those acquired on the same samples in the highly homogeneous magnetic field of a traditional NMR instrument
Galileo y el problema del metodo
No full textPresentamos informalmente una breve discusion de algunas de las interpretaciones mas importantes que se han avanzado acerca de las contribuciones de Galileo a conformar el llamado metodo cientifico
Investigation of the First Sorption Cycle of White Portland Cement by 1H NMR
Full text linkThis work is focused on the effects of drying/re-saturation cycles on the structure and components of White Portland Cement (WPC) samples. In particular, WPC of 0.5 water-to-cement ratio was studied by 1H Nuclear Magnetic Resonance (NMR) Relaxometry. A number of NMR sequences and different data processing methods were applied. Short (14 days of re-saturation) and long (6 months for the whole cycle) sorption cycles were investigated, using two drying methods: oven drying and drying under controlled relative humidity. The evolution during drying/re-saturation processes of interlayer space, gel pores, and bigger pores was followed by both the transverse relaxation times and the intensities of the nuclear magnetization. As a result of drying, reversible and irreversible changes in the pore structure, especially concerning the smaller porosity (interlayer and gel pores), were seen. Likewise, 1H signals in the crystalline phases of the cement were investigated by the standard Quadrature Echo method and by a more informative analysis based and a proper acquisition and processing of the longitudinal relaxation data. This analysis allowed the signal separation of 1H nuclei with higher and lower mobility (“solid” components). The NMR signal from this last component was analyzed on the basis of the Pake-Doublet theory in the time domain and two components were clearly detected, and assigned to 1H nuclei of crystalline water in Ettringite and OH groups in Portlandite. Reversible changes of the solid components of the cement samples were observed. This is a new method to deeply investigate the changes of solid components during sorption cycles
Pore-size evaluation by single-sided nuclear magnetic resonance measurements: Compensation of water self-diffusion effect on transverse relaxation
No full textThe determination of penetration depth and distribution of water at surfaces is essential to
knowledge of the state of conservation of Cultural Heritage items and materials, such as frescoes,
stone, brick, wood, and paper. Water can penetrate the surface of an object, coming from either an
external or an internal source, and in general the moisture content of the surface region is the cause
of various decay phenomena such as microfractures and disintegration. The nuclear magnetic
resonance sNMRd approach can be very powerful for the evaluation of the state of fine arts
materials. Not only the water saturation and/or the porosity of the material can be evaluated but also
information on material pore-size distributions can be obtained by monitoring the distributions of
relaxation times of the transverse sT2d and longitudinal sT1d components of the 1H magnetization of
the trapped water. The drawback is that generally the sample does not fit into standard NMR
magnets, and for in situ application, single-sided NMR devices have to be used. Therefore, the
standard methods to get NMR parameters are not always valid, and some alternative procedures
have to be performed. For example, in strongly inhomogeneous magnetic fields due to the
geometrical features of single-sided NMR devices, the transverse relaxation is greatly influenced by
the molecular self-diffusion even at the shortest interpulse time available for a Carr–Purcell–
Meiboom–Gill sCPMGd sequence. In this paper we show how the dephasing effect due to molecular
self-diffusion can be corrected by using the “constant echo time method.” We report an attempt to
recover the corrected T2 distribution in well-characterized porous materials saturated with water,
with data acquired in the highly inhomogeneous magnetic field of a single-sided NMR device. The
results are discussed and compared with those acquired on the same samples in the highly
homogeneous magnetic field of a traditional NMR instrument
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