- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Encyclopedia of Spectroscopy and Spectrometry || MRI Using Stray Fields
摘要： MRI is accomplished using gradients in the magnetic field flux density (normally referred to as the magnetic field). These gradients are generally produced in conventional imaging with the aid of sets of gradient coils. The suggestion to use the gradients that are present in the stray field of a superconducting magnet for imaging purposes was made first by Samoilenko and colleagues in 1988. The method has the advantage that these field gradients are large, of the order of 50 T m?1. This has proved to be very useful not only for the imaging of solids but also additionally for the imaging of liquids in solids, neither of which can be imaged very satisfactorily or even at all with conventional MRI techniques. The method was generalized from one spatial dimension to three by Samoilenko and Zick, working at Bruker Spectrospin, but the technique was exemplified only by proton and fluorine work in diamagnetic solids such as organic polymers. The extension to multinuclear work, even quadrupolar nuclides, was accomplished by Randall and colleagues in one-dimensional studies. They also showed that the method gave good images of diamagnetic crystalline solids, and even of paramagnetic crystalline solids. Thus now virtually any nuclide, even those with electric quadrupole moments, can be imaged in any solid, with the possible exception of ferromagnetics. Because metals conduct electricity, they are not penetrated by radiofrequency fields and therefore can be imaged only when in powder form. Distortions of the images produced by magnetic susceptibility are greatly reduced in proportion to the gradient strength.
关键词： quadrupolar nuclides,imaging,stray field,paramagnetic solids,STRAFI,MRI,diffusion,spectroscopy
更新于2025-09-10 09:29:36
-
A National Certification Scheme to Enhance Trust and Quality in the Indian Residential Solar PV Market
摘要： India has recently committed to install 100 GW of solar power by 2022, the principal component of its climate policy agenda. But the pace of solar adoption in the residential rooftop sector—the success of which is important for local job creation and sustaining political support for India’s broader climate goals—has been sluggish, notwithstanding government efforts to jumpstart the market. At the core of the residential solar market’s dysfunction is a negative spiral of low-quality solar installations and consumer distrust that fuel one another. Quality and trust are essential drivers of successful technology diffusion, and the emergence of trusted brands can drive a virtuous cycle rather than a vicious one. A promising solution to enable a virtuous cycle is a third-party certification scheme, which could instill trust in consumers by designating solar providers with a proven track record and competent technicians. India’s government should implement a voluntary, two-level certification scheme that accredits individual technicians as well as solar providers and makes the certifications publicly available. If the government can leverage best practices from around the world, avoid over-regulation, and deter corruption, then India’s residential solar market could finally take off.
关键词： Consumer Behavior,Third-party certification,Residential solar,Information asymmetry,Diffusion of Innovation,Energy in India
更新于2025-09-10 09:29:36
-
Light-Tuned DC Conductance of Anatase TiO2 Nanotubular Arrays: Features of Long-Range Charge Transport
摘要： Experimental results related to the photoactivated dc conductance of anatase TiO2 nanotubular arrays (aTNTAs) under pulsed irradiation by a laser light inside and outside the fundamental absorption band are presented. It is found that the mobility and diffusion coefficients of charge carriers in the examined aTNTA are extremely low due to a strong charge-phonon coupling, abundance of shallow traps, and hopping conductivity between adjacent nanotubes. We consider that the confining electric field appeared within the array structure due to the difference in the local concentrations of excess electrons and holes at large values of the dc conductance suppresses the drift current. In this case, the dc conductance of such aTNTAs is mainly matured by the diffusion of mobile carriers. A recurrent kinetic model for evolution of the dc conductance of aTNTAs under laser irradiation has been proposed to interpret the experimental results.
关键词： anatase nanotubes,laser irradiation,dc conductance,Urbach energy,drift current,inter-band transition,diffusion current,charge mobility
更新于2025-09-10 09:29:36
-
Tuning phototactic robots with sensorial delays
摘要： The presence of a delay between sensing and reacting to a signal can determine the long-term behavior of autonomous agents whose motion is intrinsically noisy. In a previous work [Mijalkov, McDaniel, Wehr, and Volpe, Phys. Rev. X 6, 011008 (2016)], we have shown that sensorial delay can alter the drift and the position probability distribution of an autonomous agent whose speed depends on the illumination intensity it measures. In this work, we consider an agent whose speed and rotational diffusion both depend on the illumination intensity and are subject to two independent sensorial delays. Using theory, simulations, and experiments with a phototactic robot, we study the dependence of the drift and of the probability distribution of the robot’s position on the sensorial delays. In particular, the radial drift may have a positive as well as negative sign, and the position probability density peaks in different regions, depending on the choice of the model’s parameters. This not only generalizes previous work but also explores new phenomena resulting from the interaction between the two delay variables.
关键词： autonomous agents,phototactic robot,sensorial delay,rotational diffusion,position probability distribution
更新于2025-09-10 09:29:36
-
Aberrant visual pathway development in albinism: From retina to cortex
摘要： Albinism refers to a group of genetic abnormalities in melanogenesis that are associated neuronal misrouting through the optic chiasm. We perform quantitative assessment of visual pathway structure and function in 23 persons with albinism (PWA) and 20 matched controls using optical coherence tomography (OCT), volumetric magnetic resonance imaging (MRI), diffusion tensor imaging and visual evoked potentials (VEP). PWA had a higher streamline decussation index (percentage of total tractography streamlines decussating at the chiasm) compared with controls (Z = ?2.24, p = .025), and streamline decussation index correlated weakly with inter-hemispheric asymmetry measured using VEP (r = .484, p = .042). For PWA, a significant correlation was found between foveal development index and total number of streamlines (r = .662, p < .001). Significant positive correlations were found between peri-papillary retinal nerve fibre layer thickness and optic nerve (r = .642, p < .001) and tract (r = .663, p < .001) width. Occipital pole cortical thickness was 6.88% higher (Z = ?4.10, p < .001) in PWA and was related to anterior visual pathway structures including foveal retinal pigment epithelium complex thickness (r = ?.579, p = .005), optic disc (r = .478, p = .021) and rim areas (r = .597, p = .003). We were unable to demonstrate a significant relationship between OCT-derived foveal or optic nerve measures and MRI-derived chiasm size or streamline decussation index. Our novel tractographic demonstration of altered chiasmatic decussation in PWA corresponds to VEP measured cortical asymmetry and is consistent with chiasmatic misrouting in albinism. We also demonstrate a significant relationship between retinal pigment epithelium and visual cortex thickness indicating that retinal pigmentation defects in albinism lead to downstream structural reorganisation of the visual cortex.
关键词： magnetic resonance imaging,visual pathway,diffusion tensor imaging,albinism,optical coherence tomography
更新于2025-09-10 09:29:36
-
Applied Nanophotonics || Energy transfer processes
摘要： In this chapter, we introduce the general phenomenon of excitation energy transfer, explain radiative and nonradiative types of energy transfer, and derive the basic processes of energy transfer. We look at the F?rster resonance energy transfer (FRET) in particular. We also describe Dexter energy transfer, charge transfer, exciton diffusion, and exciton dissociation. Finally, we summarize the modifications of FRET when using nanostructures with mixed dimensionalities and in different assemblies.
关键词： F?rster resonance energy transfer,nanostructures,FRET,charge transfer,exciton diffusion,energy transfer,Dexter energy transfer,exciton dissociation
更新于2025-09-10 09:29:36
-
Total image constrained diffusion tensor for spectral computed tomography reconstruction
摘要： Photon counting detector (PCD)-based spectral computed tomography (CT) is a promising imaging technique that enables high energy resolution imaging with narrow energy bins. However, the image quality is degraded because the number of photons in each energy bin is less than the number of photons in the full spectrum. To reconstruct high quality spectral CT images with narrow energy bins, we developed a total image constrained diffusion tensor (TICDT) for statistical iterative reconstruction (SIR) based on a penalized weighted least-squares (PWLS) principle, which is called “PWLS-TICDT.” Specifically, TICDT uses supplementary information from a high-quality total image as a structural prior for SIR, so that the narrow energy bin image can be enhanced, while some primary features are preserved. We also developed an alternating minimization algorithm to solve the associated objective function. We conducted qualitative and quantitative studies to validate and evaluate the PWLS-TICDT method using digital phantoms and preclinical data. Results from both numerical simulation and real PCD data studies show that the proposed PWLS-TICDT method achieves noticeable gains over competing methods in terms of suppressing noise, detecting low contrast objects, and preserving resolution. More importantly, the multi-energy images reconstructed by PWLS-TICDT method can generate more accurate basis material decomposition results than the other methods.
关键词： Photon counting detector,Image reconstruction,Diffusion tensor,Spectral CT
更新于2025-09-10 09:29:36
-
Pressureless joining of SiC ceramics at low temperature
摘要： Pressureless joining of SiC ceramics at low temperature was developed using Ti powder interlayer. Phase assemblage and microstructure of SiC joint revealed that the products after diffusion bonding mainly consisted of Ti5Si3 and TiC owing to the comparatively low joining temperature. Additionally, Si and C elements were found to be with higher penetration depth in the Ti interlayer. Benefitting from the lower proportion of the brittle Ti5Si3 phase and porosity, shear strength reached a relatively higher value of 41 MPa after joining at 1200oC for 30 min.
关键词： SiC ceramics,Shear strength,Ti powder,Diffusion bonding,Pressureless joining
更新于2025-09-10 09:29:36
-
The Rise of Ultrafast Waves
摘要： Traditionally, biochemical traveling waves are thought to propagate due to a coupling of bistable reactions with diffusion. Recent work proposes mechanisms by which cells achieve fast signaling without necessarily resorting to pure bistability or diffusion-mediated coupling.
关键词： diffusion,bistable reactions,fast signaling,biochemical traveling waves,mechanochemical feedback
更新于2025-09-10 09:29:36
-
Diffusion on the ground: Rethinking the logic of scale and access in off-grid solar in Sri Lanka
摘要： Off-grid solar photovoltaics have come to play a leading role in the current challenge of achieving the 7th Sustainable Development Goal of access to modern energy for all by 2030. In this context, the goal of achieving scale and accelerating growth in the off-grid solar market is now considered prominent and urgent. This paper presents an ethnographic account of the diffusion of Solar Home Systems (SHSs) under the Renewable Energy for Rural Economic Development (RERED) project in Sri Lanka which came to an end in 2011. Based on ethnographic data from 2012 and 2018 it shows that a successful model for the diffusion of SHSs is not necessarily or automatically the same as a successful model for lasting energy access. The paper thus challenges the assumption that accelerated growth in the off-grid solar market will lead straightforwardly to sustainable access to electricity for people in countries of the global south. Focusing on the experiences of project administrators, solar installers and owners of SHSs during and after the RERED project it provides insight into how diffusion was achieved on the ground and with what consequences after the project came to an end. It argues for a need to look at the different kinds of relations, imaginaries, ideas and practices involved in diffusion in action in order to better understand what is being achieved on the ground.
关键词： Energy access,Solar,Scalability,Diffusion,Sri Lanka
更新于2025-09-10 09:29:36