Use of spectroscopically-acquired spin echoes typically involves Fourier transformation of the right side of the echo while largely neglecting the left side. For sufficiently long echo times, the left side may have enough spectral resolution to offer some utility. Since the acquisition of this side is “free”, we deemed it worthy of attention and investigated the spectral properties and information content of this data.
Materials and methods
Theoretical expressions for left- and right-side spectra were derived assuming Lorentzian frequency distributions. For left-side spectra, three regimes were identified based upon the relative magnitudes of reversible and irreversible transverse relaxation rates, R2′ and R2, respectively. Point-resolved spectroscopy (PRESS) data from muscle, fat deposit and bone marrow were acquired at 1.5 T to test aspects of the theoretical expressions.
Results
For muscle water or methylene marrow resonances, left-side signals were substantially or moderately larger than right-side signals but were similar in magnitude for muscle choline and creatine resonances. Left- versus right-side spectral-peak amplitude ratios depend sensitively on the relative values of R2 and R2′, which can be estimated given this ratio and a right-side linewidth measurement.
Conclusion
Left-side spectra can be used to augment signal-to-noise and to estimate spectral R2 and R2′ values under some circumstances.
This article reports a CdO nanocomposite successfully synthesized by a chemical route assisted microwave irradiation technique. Sodium dodecyl benzene sulfonate (SDBS) is a good surfactant and it is used in forming the nanocomposite. The microwave irradiation technique is simple and less time consuming for preparing a nanocomposite. The obtained products were characterized by different techniques such as X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis DRS, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), room temperature photoluminescence (PL), and DC electrical conductivity. The grain size determined by the XRD pattern was found to be 20–40 nm. The lattice fringes and nanocomposite morphology particle size were obtained by TEM. The room temperature PL spectra reveal blue and red emissions. The calculated average electrical conductivity was around 5.1 × 10−8 to 2.02 × 10−8 S/cm.
Functional radiation absorbent materials (RAMs) can transform incident microwave energy into heat energy, hence being essential to impede reflections of microwaves generated by modern radars in military, aerospace, and commercial applications. For such applications, use of composites is imperative to maintain an optimum bandwidth, enhance the magnetoelectric functional activity, ensure a flexible design, and reduce weight, which can be achieved by tuning the volume fractions of such materials. Use of ferrites is widely recommended for microwave (MW) suppression due to their appropriate magnetodielectric characteristics. This review first describes the requirements for an ideal MW absorber and accurate measurements for quantification of MW absorption. Then, the significance, applications, approaches, and experimental developments of magnetodielectric polymer composite RAMs are presented. Moreover, such composites facilitate exploration of nanoscale functional properties to achieve efficient RAMs. The permeability and permittivity at microwave frequencies, magnetic properties induced by unique elemental doping mechanisms, as well as physical and chemical properties of these composites are also presented. The resonance-dependent absorption condition for different families of magnetic ferrites, as well as the dependence of their magnetic properties on the resonant frequency and their absorption bandwidth (spinels up to 30 GHz, hexaferrites 1 GHz to 100 GHz), are presented for applications. Furthermore, magnetodielectric composites decorated with carbon fillers (carbon nanotubes/multiwall carbon nanotubes, graphene, reduced graphene oxide, etc.) with enhanced microwave absorption properties are discussed. Additionally, core–shell magnetodielectric materials are also discussed in detail. Finally, this review highlights the importance of magnetodielectric polymer composites decorated with conducting materials and core–shell magnetodielectric materials as effective broadband RAMs achieving the primary application requirement of broadband absorption of at least ?10 dB with reduced thickness. 相似文献
Ab initio molecular dynamics studies have been carried out on the room temperature ionic liquid, 1,n-butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and supercritical carbon dioxide mixture at room temperature and experimental density. Partial radial distribution functions
(RDF) for different sites have been computed to see the organization of CO2 molecules around the ionic liquid. Several partial RDFs around the carbon atom of CO2 molecule are compared to find out that the CO2 has specific interaction with a carbon atom present in the imidazolium ring. The CO2 is also found to be very well organized around the terminal carbon atom of the butyl chain. The partial RDFs for the oxygen
atoms around oxygen and carbon atoms of the CO2 suggests that there is very good organization of CO2 molecules around themselves even in the [bmim][PF6]-CO2 mixture. The instantaneous quadrupole moment tensor has been calculated for the anion and the cation. The ensemble average
of diagonal components of quadrupole moment tensor of the cation have finite values, whereas the off-diagonal components of
the cation and both the diagonal and off-diagonal components of the anion have the value of zero with a large standard deviation.
The CPMD studies performed on CO2 clusters reveals the greater tendency of the clusters with more CO2 units, to deviate from the linear geometry. 相似文献
Zinc sulphide thin films were deposited by the pulse plating technique using AR grade Zinc sulphate and sodium thiosulphate
precursors. The pH of the deposition bath was adjusted to 2. The duty cycle was varied in the range of 20–60%. Total deposition
time was kept constant as 60 min in all the cases. X-ray diffraction studies indicated the formation of single phase cubic
zinc sulphide films. After heat treatment the crystal structure transformed to hexagonal structure. Optical absorption measurements
indicated a band gap values in the range of 3.6–4.0 eV as the duty cycle decreased. EDAX studies yielded a composition of
the films deposited at 50% duty cycle is Zn = 48%, S = 52%. XPS studies indicated the formation of ZnS. The Zn 2p and S 3p
peaks are observed. AFM studies indicated a rms value of surface roughness of 55 nm for the films deposited at a duty cycle
of 60%. 相似文献
To provide a comprehensive understanding of the field effect in silicon nanowire (SiNW) sensors, we take a systematic approach to fine tune the distance of a charge layer by controlling the hybridization sites of DNA to the SiNW preimmobilized with peptide nucleic acid (PNA) capture probes. Six target DNAs of the same length, but differentiated successively by three bases in the complementary segment, are hybridized to the PNA. Fluorescent images show that the hybridization occurs exclusively on the SiNW surface between the target DNAs and the PNA. However, the field-effect response of the SiNW sensor decreases as the DNA (charge layer) moves away from the SiNW surface. Theoretical analysis shows that the field effect of the SiNW sensor relies primarily on the location of the charge layer. A maximum of 102% change in resistance is estimated based on the shortest distance of the DNA charge layer (4.7 A) to the SiNW surface. 相似文献
Electrical transport studies on graphene have been focused mainly on the linear dispersion region around the Fermi level and, in particular, on the effects associated with the quasiparticles in graphene behaving as relativistic particles known as Dirac fermions. However, some theoretical work has suggested that several features of electron transport in graphene are better described by conventional semiconductor physics. Here we use scanning photocurrent microscopy to explore the impact of electrical contacts and sheet edges on charge transport through graphene devices. The photocurrent distribution reveals the presence of potential steps that act as transport barriers at the metal contacts. Modulations in the electrical potential within the graphene sheets are also observed. Moreover, we find that the transition from the p- to n-type regime induced by electrostatic gating does not occur homogeneously within the sheets. Instead, at low carrier densities we observe the formation of p-type conducting edges surrounding a central n-type channel. 相似文献
CdTe crystals were uniaxially compressed along several crystallographic axes at temperatures from 773 to 1353 K. The applied
stress ranged from 14 to 74% of the critical resolved shear stress (CRSS) measured in the authors’ laboratory. The deformed
specimens were annealed without applying stress at temperatures from 573 to 1073 K. No twins were observed after the above
operations. Dense slip bands were observed on most of the compressed specimens. Secondary slip systems were activated in some
experiments. CdTe crystals were sheared along {111}<112> at 1073 K with a load of 40% CRSS. Slip bands, but no twins, were
observed. Synchrotron x-ray topography was used to study in situ the effect of stress on crystal deformation. CdTe specimens
were uniaxially stressed in tension along <112> at 293 to 673 K. When the load reached ~50% of the CRSS, the topograph began
to distort, indicating the beginning of plastic deformation. No twins were observed on the stressed specimens. 相似文献