Male gender predisposes to severe sepsis and septic shock. This effect has been ascribed to higher levels of testosterone. The ESPNIC ARDS database was searched, to determine if there was evidence of ...a similar male preponderance in severe sepsis in prepubertal patients in spite of low levels of male sex hormones at this age. A total of 72 patients beyond neonatal age up to 8 years of age with sepsis were identified. The male/female (M/F) ratio was 1.7 (1.0;2.7) and differed significantly from non-septic ARDS patients in this age group n = 209; M/F = 1.0 (0.8;1.3). The highest M/F-ratio was observed in the first year of life. The gender-ratio was the same as reported in adult patients with sepsis. In infants between 1 month and 12 months of age, the ratio was 2.8 (1.2;6.1) (Chi2= 5.6; P< 0.01), in children from 1 year to 8 years of age it was 1.2 (0.7;2.2) (n.s.). In a subgroup of patients with severe sepsis or septic shock, caused by other bacteria than Neisseria meningitidis, the M/F-ratio was 2.1 (1.2;3.6) (Chi2= 4.9; P<0.05), while in patients with meningococcal sepsis (n=20) the M/F-ratio was 1.0 (0.4;2.3). In prepubertal ARDS patients with sepsis an increased frequency of male patients is found, comparable to adults. No male preponderance exists in patients with ARDS due to meningococcal septic shock. Since levels of testosterone and other sex hormones are extremely low at this age, we conclude that factors others than testosterone are involved in the male preponderance in severe sepsis.
Rapid densification of ceramics has been realized and its merits were demonstrated through multiple approaches out of which UHS and flash sintering attract recent attention. So far, however, ...scalability remains difficult. A rise in throughput and scalability is enabled by the introduction of blacklight sintering powered by novel light source technology. Intense illumination with photon energy above the bandgap (blacklight) allows high absorption efficiency and, hence, very rapid, contactless heating for all ceramics. While heating the ceramic directly with light without any furnace promises scalability, it simultaneously offers highly accurate process control. For the technology transfer to industry, attainable material quality needs to be assured. Here, we demonstrate the excellent microstructure quality of blacklight‐sintered ceramics observed with ultrahigh voltage electron microscopy revealing an option to tune nanoporosity. Moreover, we confirm that electronic, electron, oxygen, and lithium‐ion conductivities are equal to conventionally sintered ceramics. This gives the prospect of transmitting the merits of rapid densification to the scale of industrial kilns.
Functional and structural ceramics have become irreplaceable in countless high-tech applications. However, their inherent brittleness tremendously limits the application range and, despite extensive ...research efforts, particularly short cracks are hard to combat. While local plasticity carried by mobile dislocations allows desirable toughness in metals, high bond strength is widely believed to hinder dislocation-based toughening of ceramics. Here, we demonstrate the possibility to induce and engineer a dislocation microstructure in ceramics that improves the crack tip toughness even though such toughening does not occur naturally after conventional processing. With modern microscopy and simulation techniques, we reveal key ingredients for successful engineering of dislocation-based toughness at ambient temperature. For many ceramics a dislocation-based plastic zone is not impossible due to some intrinsic property (
e.g.
bond strength) but limited by an engineerable quantity,
i.e.
the dislocation density. The impact of dislocation density is demonstrated in a surface near region and suggested to be transferrable to bulk ceramics. Unexpected potential in improving mechanical performance of ceramics could be realized with novel synthesis strategies.
Dislocations are mobile at low temperatures in surprisingly many ceramics but sintering minimizes their densities. Enabling local plasticity by engineering a high dislocation density is a way to combat short cracks and toughen ceramics.
Flash sintering involves very rapid densification of ceramic powder compacts during a thermal runaway induced by an applied voltage and current. The mechanisms of fast densification are still not ...well-understood. The present study investigates the impact of high heating rates during flash sintering on densification, dislocation density and plasticity of SrTiO3. After flash sintering, a high dislocation density of almost 1014 m−2 was observed by TEM. Uniaxial compression at 1150 °C revealed very high deformation rates. It is argued that for SrTiO3, dislocations are generated and migrate during flash sintering. This becomes possible by the very high heating rates, which conserve high driving forces for sintering up to high temperatures. High driving forces of several 10 MPa are preserved up to high temperatures. Thus, the sintering stress can be above the flow stress of SrTiO3 (5 MPa), and the nucleation of dislocations occurs, paving the path for plastic flow.
This article presents an X‐ray microscopy approach for mapping deeply embedded dislocations in three dimensions using a monochromatic beam with a low divergence. Magnified images are acquired by ...inserting an X‐ray objective lens in the diffracted beam. The strain fields close to the core of dislocations give rise to scattering at angles where weak beam conditions are obtained. Analytical expressions are derived for the image contrast. While the use of the objective implies an integration over two directions in reciprocal space, scanning an aperture in the back focal plane of the microscope allows a reciprocal‐space resolution of ΔQ/Q < 5 × 10−5 in all directions, ultimately enabling high‐precision mapping of lattice strain and tilt. The approach is demonstrated on three types of samples: a multi‐scale study of a large diamond crystal in transmission, magnified section topography on a 140 µm‐thick SrTiO3 sample and a reflection study of misfit dislocations in a 120 nm‐thick BiFeO3 film epitaxially grown on a thick substrate. With optimal contrast, the half‐widths at half‐maximum of the dislocation lines are 200 nm.
An X‐ray microscopy approach for mapping deeply embedded dislocations with a resolution of currently 200 nm is presented. The technique involves scanning an aperture in the back focal plane, which allows the strain fields around dislocations to be visualised with a strain resolution better than 10−4.
Dislocation networks have been demonstrated to substantially enhance functional properties. As-sintered samples are virtually devoid of dislocations, new innovative techniques for introducing ...sufficiently high dislocation densities into polycrystalline ceramics are needed. While dislocation-based plasticity at high temperatures has been demonstrated for a large range of ceramic single crystals, plasticity in polycrystals is much less understood. Here, we demonstrate plastic strains in excess of several % based on dislocation motion in polycrystalline SrTiO
3
at ≈ 1100 °C with 3.9 µm grain size. Ultra-high voltage electron microscopy reveals an associated increase in dislocation density by three orders of magnitude. Achievable strain rates are comparable to creep-based mechanisms and much less sensitive to applied stress than observed for metals. A specialized testing protocol allows quantification of the deformability via stress exponent, activation volume and activation enthalpy giving additional quantification. In conjunction with TEM images, the mechanical data gives insight into the underlying mechanisms.
Dislocation networks have been demonstrated to substantially enhance functional properties. As-sintered samples are virtually devoid of dislocations, new innovative techniques for introducing ...sufficiently high dislocation densities into polycrystalline ceramics are needed. While dislocation-based plasticity at high temperatures has been demonstrated for a large range of ceramic single crystals, plasticity in polycrystals is much less understood. Here, we demonstrate plastic strains in excess of several % based on dislocation motion in polycrystalline SrTiO.sub.3 at almost equal to 1100 °C with 3.9 microm grain size. Ultra-high voltage electron microscopy reveals an associated increase in dislocation density by three orders of magnitude. Achievable strain rates are comparable to creep-based mechanisms and much less sensitive to applied stress than observed for metals. A specialized testing protocol allows quantification of the deformability via stress exponent, activation volume and activation enthalpy giving additional quantification. In conjunction with TEM images, the mechanical data gives insight into the underlying mechanisms.
Dislocations have been identified to modify both the functional and mechanical properties of some ceramic materials. Succinct control of dislocation‐based plasticity in ceramics will also demand ...knowledge about dislocation interaction with point defects. Here, we propose an experimental approach to modulate the dislocation‐based plasticity in single‐crystal SrTiO3 based on the concept of defect chemistry engineering, for example, by increasing the oxygen vacancy concentration via reduction treatment. With nanoindentation and bulk compression tests, we find that the dislocation‐governed plasticity is significantly modified at the nano‐/microscale, compared to the bulk scale. The increase in oxygen vacancy concentration after reduction treatment was assessed by impedance spectroscopy and is found to favor dislocation nucleation but impede dislocation motion as rationalized by the nanoindentation pop‐in and nanoindentation creep tests.
Abstract
Rapid densification of ceramics has been realized and its merits were demonstrated through multiple approaches out of which UHS and flash sintering attract recent attention. So far, however, ...scalability remains difficult. A rise in throughput and scalability is enabled by the introduction of blacklight sintering powered by novel light source technology. Intense illumination with photon energy above the bandgap (blacklight) allows high absorption efficiency and, hence, very rapid, contactless heating for all ceramics. While heating the ceramic directly with light without any furnace promises scalability, it simultaneously offers highly accurate process control. For the technology transfer to industry, attainable material quality needs to be assured. Here, we demonstrate the excellent microstructure quality of blacklight‐sintered ceramics observed with ultrahigh voltage electron microscopy revealing an option to tune nanoporosity. Moreover, we confirm that electronic, electron, oxygen, and lithium‐ion conductivities are equal to conventionally sintered ceramics. This gives the prospect of transmitting the merits of rapid densification to the scale of industrial kilns.
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