32 research outputs found
Adaptive modulations of martensites
Modulated phases occur in numerous functional materials like giant
ferroelectrics and magnetic shape memory alloys. To understand the origin of
these phases, we review and generalize the concept of adaptive martensite. As a
starting point, we investigate the coexistence of austenite, adaptive 14M phase
and tetragonal martensite in Ni-Mn-Ga magnetic shape memory alloy epitaxial
films. The modulated martensite can be constructed from nanotwinned variants of
a tetragonal martensite phase. By combining the concept of adaptive martensite
with branching of twin variants, we can explain key features of modulated
phases from a microscopic view. This includes phase stability, the sequence of
6M-10M-NM intermartensitic transitions, and magnetocrystalline anisotropy.Comment: 4 pages manuscript, 8 pages supplemen
Modulated Martensite: Why it forms and why it deforms easily
Diffusionless phase transitions are at the core of the multifunctionality of
(magnetic) shape memory alloys, ferroelectrics and multiferroics. Giant strain
effects under external fields are obtained in low symmetric modulated
martensitic phases. We outline the origin of modulated phases, their connection
with tetragonal martensite and consequences for their functional properties by
analysing the martensitic microstructure of epitaxial Ni-Mn-Ga films from the
atomic to macroscale. Geometrical constraints at an austenite-martensite phase
boundary act down to the atomic scale. Hence a martensitic microstructure of
nanotwinned tetragonal martensite can form. Coarsening of twin variants can
reduce twin boundary energy, a process we could follow from the atomic to the
millimetre scale. Coarsening is a fractal process, proceeding in discrete steps
by doubling twin periodicity. The collective defect energy results in a
substantial hysteresis, which allows retaining modulated martensite as a
metastable phase at room temperature. In this metastable state elastic energy
is released by the formation of a 'twins within twins' microstructure which can
be observed from the nanometre to millimetre scale. This hierarchical twinning
results in mesoscopic twin boundaries which are diffuse, in contrast to the
common atomically sharp twin boundaries of tetragonal martensite. We suggest
that observed extraordinarily high mobility of such mesoscopic twin boundaries
originates from their diffuse nature which renders pinning by atomistic point
defects ineffective.Comment: 34 pages, 8 figure
Universality of Temperature Dependence of Twinning Stress in Ni-Mn-Ga 10M Martensite and Effect of Crystal Quality
Decreased Apoptosis in the Ileum and Ileal Peyer's Patches: a Feature after Infection with Rabbit Enteropathogenic Escherichia coli O103
Significant changes occur in intestinal epithelial cells after infection with enteropathogenic Escherichia coli (EPEC). However, it is unclear whether this pathogen alters rates of apoptosis. By using a naturally occurring weaned rabbit infection model, we determined physiological levels of apoptosis in rabbit ileum and ileal Peyer's patches (PP) and compared them to those found after infection with adherent rabbit EPEC (REPEC O103). Various REPEC O103 strains were first tested in vitro for characteristic virulence features. Rabbits were then inoculated with the REPEC O103 strains that infected cultured cells the most efficiently. After experimental infection, intestinal samples were examined by light and electron microscopy. Simultaneously, ileal apoptosis was assessed by using terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) and caspase 3 assays and by apoptotic cell counts based on morphology (hematoxylin-and-eosin staining). The highest physiological apoptotic indices were measured in PP germinal centers (median = 14.7%), followed by PP domed villi (8.1%), tips of absorptive villi (3.8%), and ileal crypt regions (0.5%). Severe infection with REPEC O103 resulted in a significant decrease in apoptosis in PP germinal centers (determined by TUNEL assay; P = 0.01), in the tips of ileal absorptive villi (determined by H&E staining; P = 0.04), and in whole ileal cell lysates (determined by caspase 3 assay; P = 0.001). We concluded that REPEC O103 does not promote apoptosis. Furthermore, we cannot rule out the possibility that REPEC O103, in fact, decreases apoptotic levels in the rabbit ileum
Morphology of segmented filamentous bacteria and their patterns of contact with the follicle-associated epithelium of the mouse terminal ileum: Implications for the relationship with the immune system
Recent evidence indicates that segmented filamentous bacteria (SFB), “Candidatus Arthromitus”, play a unique role in different aspects of the maturation of the immune system, including T cell responses. Thus, it seems particularly relevant in this moment to shortly review the information on these bacteria and their relationship with the immune system, and to actively investigate their morphological aspects. We distinguished a developmental form from a vegetative form of these organisms. These different forms have distinct roles in the life cycle: the developmental form permits a rapid growth of the organisms while the vegetative form permits the attachment of SFB to the follicular epithelium. We have also given special attention to the modes of contact between SFB and the epithelial cells of the terminal ileum to better understand the unique relationship between these bacteria and the immune system
First-principles investigation of phonon softenings and lattice instabilities in the shape-memory system Ni
Antimicrobial resistance in European isolates of Pseudomonas aeruginosa
Pseudomonas aeruginosa is responsible for a substantial fraction of hospital infections. Twenty-five European university hospitals submitted a total of 1411 Pseudomonas aeruginosa isolates for susceptibility testing during 1997 and 1998. The isolates showed highest susceptibility to amikacin (87.5%), meropenem (87.3%) and piperacillin/tazobactam (86.8%). Susceptibility to ciprofloxacin was 73.2%. There was no clear geographical distribution of resistance, although isolates from northwestern Europe tended to be more susceptible than those from southeastern Europe. Isolates that were resistant to one class of antibiotics were also often resistant to at least one other class of antibiotics. Imipenem-resistant isolates were generally not clonally related