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Anode-supported solid oxide fuel cells ͑SOFCs͒ with Niϩyttria-stabilized zirconia ͑YSZ͒ anode, YSZ-samaria-doped ceria ͑SDC͒ bilayer electrolyte, and Sr-doped LaCoO 3 ͑LSC͒ϩSDC cathode were fabricated. Fuel used consisted of H 2 diluted with He, N 2 , H 2 O, or CO 2 , mixtures of H 2 and CO, and mixtures of CO and CO 2 . Cell performance was measured at 800°C with the above-mentioned fuel gas mixtures and air as oxidant. For a given concentration of the diluent, cell performance was higher with He as the diluent than with N 2 as the diluent. Mass transport through porous Ni-YSZ anode for H 2 -H 2 O, CO-CO 2 binary systems, and H 2 -H 2 O-diluent gas ternary systems was analyzed using multicomponent gas diffusion theory. At high concentrations of diluent, the maximum achievable current density was limited by the anodic concentration polarization. From this measured limiting current density, the corresponding effective gas diffusivity was estimated. Highest effective diffusivity was estimated for fuel gas mixtures containing H 2 -H 2 O-He mixtures ͑ϳ0.55 cm 2 /s͒, and the lowest for CO-CO 2 mixtures ͑ϳ0.07 cm 2 /s͒. The lowest performance was observed with CO-CO 2 mixture as a fuel, which in part was attributed to the lowest effective diffusivity of the fuels tested and higher activation polarization. Recent work has demonstrated that anode-supported solid oxide fuel cells ͑SOFCs͒ exhibit high performance at intermediate temperatures. Maximum power densities as high as 1.8-1.9 W/cm 2 have been reported at 800°C for anode-supported single cells. [1][2][3][4] In a typical anode-supported SOFC, the anode support is a Ni-yttriastabilized zirconia ͑YSZ͒ cermet between ϳ0.5 and 2 mm thick. The electrolyte is a thin ͑ϳ10 m͒, dense YSZ film supported on a porous anode substrate. The cathode is usually a porous mixture of strontium-doped manganite, La 1Ϫx Sr x MnO 3Ϫ␦ ͑LSM͒, and YSZ, [1][2][3] or a porous mixture of strontium-doped cobaltite, La 1Ϫx Sr x CoO 3Ϫ␦ ͑LSC͒, and Sm-doped CeO 2 ͑SDC͒.4 In addition, single-phase, mixed ionic-electronic conductors ͑MIEC͒ materials have also been used in high-performance fuel cells. The use of thin electrolyte film results in a relatively low ohmic contribution to the total cell resistance, which makes it possible to operate anode-supported SOFCs at 800°C or lower and thereby realize the benefits of a lower temperature operation, such as the use of inexpensive metallic interconnect. One of the potential benefits of SOFCs over low-temperature fuel cells, such as proton exchange membranes ͑PEMs͒ is fuel flexibility, because SOFCs can potentially operate on various fuels including hydrogen, carbon monoxide, methane, and other hydrocarbon fuels without the problem of CO poisoning. Recent work has also shown that it may be possible to operate SOFCs directly on a number of hydrocarbon fuels, without the necessity of reforming.5-8 However, in anode-supported SOFCs, significant losses may occur due to the resistance to the transport of fuel gas through a relatively thick anode, and especial...

Gradient-echo MRI has revealed anisotropic magnetic susceptibility in the brain white matter. This magnetic susceptibility anisotropy can be measured and characterized with susceptibility tensor imaging (STI). In this study, a method of fiber tractography based on STI is proposed and demonstrated in the mouse brain. STI experiments of perfusion-fixed mouse brains were conducted at 7.0 T. The magnetic susceptibility tensor was calculated for each voxel with regularization and decomposed into its eigensystem. The major eigenvector is found to be aligned with the underlying fiber orientation. Following the orientation of the major eigenvector, we are able to map distinctive fiber pathways in 3D. As a comparison, diffusion tensor imaging (DTI) and DTI fiber tractography were also conducted on the same specimens. The relationship between STI and DTI fiber tracts was explored with similarities and differences identified. It is anticipated that the proposed method of STI tractography may provide a new way to study white matter fiber architecture. As STI tractography is based on physical principles that are fundamentally different from DTI, it may also be valuable for the ongoing validation of DTI tractography.

Anode-supported solid oxide fuel cells with a thin film of yttria-stabilized zirconia (YSZ) as the electrolyte were fabricated. The cells were operated directly on pure methanol and on an equivolume mixture of ethanol and water over a range of temperatures. Power density achieved with methanol was between 0.6 W/cm2 at 650°C and 1.3 W/cm2 at 800°C, and with normalethanol+normalwater between 0.3 W/cm2 at 650°C and 0.8 W/cm2 at 800°C. Results were compared with tests on humidified hydrogen as a fuel. No carbon deposition on the Ni-YSZ anode was observed with either methanol or an equivolume solution of ethanol and water as fuels. Differences in performance with different fuels were attributed to differences in anode polarization. © 2001 The Electrochemical Society. All rights reserved.

Prenatal ethanol exposure is the leading preventable cause of congenital mental disability. Whereas a diagnosis of fetal alcohol syndrome (FAS) requires identification of a specific pattern of craniofacial dysmorphology, most individuals with behavioral and neurological sequelae of heavy prenatal ethanol exposure do not exhibit these defining facial characteristics. Here, a novel integration of MRI and dense surface modeling-based shape analysis was applied to characterize concurrent face-brain phenotypes in C57Bl/6J fetuses exposed to ethanol on gestational day (GD)7 or GD8.5. The facial phenotype resulting from ethanol exposure depended upon stage of insult and was predictive of unique patterns of corresponding brain abnormalities. Ethanol exposure on GD7 produced a constellation of dysmorphic facial features characteristic of human FAS, including severe midfacial hypoplasia, shortening of the palpebral fissures, an elongated upper lip, and deficient philtrum. In contrast, ethanol exposure on GD8.5 caused mild midfacial hypoplasia and palpebral fissure shortening, a shortened upper lip, and a preserved philtrum. These distinct, stage-specific facial phenotypes were associated with unique volumetric and shape abnormalities of the septal region, pituitary, and olfactory bulbs. By demonstrating that early prenatal ethanol exposure can cause more than one temporally-specific pattern of defects, these findings illustrate the need for an expansion of current diagnostic criteria to better capture the full range of facial and brain dysmorphology in fetal alcohol spectrum disorders.

The relative utility of 3D, microscopic resolution assessments of fixed mouse myocardial structure via diffusion tensor imaging is demonstrated in this study. Isotropic 100-m resolution fiber orientation mapping within 5.5°accuracy was achieved in 9.1 hr scan time. Preliminary characterization of the diffusion tensor primary eigenvector reveals a smooth and largely linear angular rotation across the left ventricular wall. Moreover, a higher level of structural hierarchy is evident from the organized secondary and tertiary eigenvector fields. These findings are consistent with the known myocardial fiber and laminar structures reported in the literature and suggest an essential role of diffusion tensor microscopy in developing quantitative atlases for studying the structure-function relationships of mouse hearts. The fiber anatomy of the myocardium is known to have a profound impact on the electrical and mechanical properties of both normal and diseased hearts (1,2). Precise knowledge of the tissue fiber structure will contribute significantly in elucidating the complex structure-function relationships of the organ, especially in biomedical engineering studies based on the so-called "morphologically accurate" modeling. Advances in molecular biology have provided unprecedented opportunities to use versatile small animal (e.g., mouse) platforms (3-6) for studying genotypes and phenotypes of myocardial development, damage, or repair associated with specific pathologies. Due to the small size of the mouse heart (with overall volume typically less than 250 mm 3 ), an efficient means to accurately and quantitatively characterize the tissue fiber structure at high or microscopic-resolution would be of great benefit.Most early studies of myocardial fiber structures were based on conventional histological techniques (7-11), which are not only destructive, but also labor-intensive. By probing the tissue microstructure via its influence on the diffusion of water, MR diffusion tensor imaging (DTI) (12) has been advanced as a promising nondestructive alternative to characterize the structure of ordered tissues such as the brain white matter (13-15), myocardium (16 -22), other musculature (23), and cartilage (24). The underlying hypothesis in DTI is that the direction of fastest water diffusion coincides with the local tissue fiber orientation. Reports show evidence that validates a direct correlation between fiber orientations measured by DTI and conventional histology for freshly excised (16), perfused (17), and fixed myocardium (18).In 3D space, the generalized diffusion tensor is a symmetric, second-order 3 ϫ 3 matrix. A complete solution to the six independent parameters, plus an extra term for the diffusion-independent magnetization, requires that the DTI dataset consists of a minimum of seven images. The tradeoffs between scan time and the image signal-to-noise ratio (SNR), aggravated by the nature of diffusion sensitization (i.e., via signal attenuation) and the inadvertent T 2 weighting during the diffusion encoding gr...

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Methane was oxidatively coupled to ethylene with an ethylene yield up to 85 percent and a total C(2) hydrocarbon yield up to 88 percent in a gas recycle high-temperature (800 degrees C) electrocatalytic or catalytic reactor where the recycled gas passes continuously through a molecular sieve trap in the recycle loop. Oxygen is supplied either electrocatalytically by means of the solid electrolyte support of the silver-based catalyst or in the gas phase. The C(2) products are obtained by subsequent heating of the molecular sieve trap. The selectivity to ethylene is up to 88 percent for methane conversion up to 97 percent.