Medium manganese steel grades heat treated with the quench and partition (Q&P) treatment have shown promising results of strength and formability, but the number of studies on high aluminum medium ...manganese Q&P steels still remains rather limited. Consequently, this study investigates the mechanical properties, behavior and microstructures of a low carbon-high aluminum medium manganese (3%) steel after intercritical annealing and subsequent Q&P heat treatments with varying heat treatment parameters. Samples that were intercritically annealed above 760 °C showed an ultimate tensile strength (UTS) of around 1500 MPa with uniform elongation values of approximately 10%. On the other hand, the samples annealed at 740 °C showed somewhat lower UTS values (in the range of 1000 … 1200 MPa) but much higher uniform and total elongations, i.e., considerably improved formability. However, the stress-strain curves of the samples annealed at 740 °C showed rather severe serrations that can be connected to the dynamic strain aging (DSA) phenomena, which limits the usability of the steel especially in applications where good surface quality of the deformed (sheet) is required. Therefore, the main focus of this article is on the samples annealed at temperatures close to A1, where DSA serrations tend to appear. The evidence gathered from these investigations leads to the conjecture that the DSA serrations are due to the free carbon and nitrogen originating from the dissolution of M(C,N) and M2(C,N) type carbides, which were formed during the intercritical annealing at temperatures producing less than 50% of the austenite phase. Other reasons for the occurrence of DSA in the current test materials can be the scarcity of martensite and the morphology of the retained austenite.
•DSA serrations were observed in the stress-strain curve of samples intercritically annealed at 740°C (40% of austenite).•Carbides of type M(C,N) and M2(C,N) were observed at the ferritic grain boundaries in the samples that exhibited jerky flow.•Evidence gathered from investigations leads to the conjecture that serrated flow might be due to the interaction of moving dislocations and carbon/nitrogen interstitials.•Unstable TRIP effect might be contributing to the jerky flow.
Abstract Background Neuroimaging studies of attention-deficit/hyperactivity disorder (ADHD) have most commonly reported volumetric abnormalities in the basal ganglia, cerebellum, and prefrontal ...cortices. Few studies have examined the relationship between ADHD symptomatology and brain structure in population-based samples. Herein, we investigate the relationship between dimensional measures of ADHD symptomatology, brain structure, and reaction time variability—an index of lapses in attention. We also test for associations between brain structural correlates of ADHD symptomatology and maps of dopaminergic gene expression. Methods Psychopathology and imaging data were available for 1,538 youths. Parent ratings of ADHD symptoms were obtained using the Development and Well-Being Assessment (DAWBA) and the Strengths and Difficulties Questionnaire (SDQ). Self-reports of ADHD symptomatology were assessed using the youth version of the SDQ. Reaction time variability was available in a subset of participants. For each measure, whole brain voxel-wise regressions with gray matter volume (GMV) were calculated. Results Parent ratings of ADHD symptoms (DAWBA and SDQ), adolescent self-reports of ADHD symptoms on the SDQ, and reaction time variability were each negatively associated with GMV in an overlapping region of the ventromedial prefrontal cortex (vmPFC). Maps of DRD1 and DRD2 gene expression were associated with brain structural correlates of ADHD symptomatology. Conclusions This is the first study to reveal relations between vmPFC structure and multi-informant measures of ADHD symptomatology in a large population-based sample of adolescents. Our results indicate that vmPFC structure is a biomarker for ADHD symptomatology. These findings extend previous research implicating the default mode network and dopaminergic dysfunction in ADHD.
Though adolescence is a time of emerging sex differences in emotions, sex-related differences in the anatomy of the maturing brain has been under-explored over this period. The aim of this study was ...to investigate whether puberty and sexual differentiation in brain maturation could explain emotional differences between girls and boys during adolescence. We adapted a dedicated longitudinal pipeline to process structural and diffusion images from 335 typically developing adolescents between 14 and 16 years. We used voxel-based and Regions of Interest approaches to explore sex and puberty effects on brain and behavioral changes during adolescence. Sexual differences in brain maturation were characterized by amygdala and hippocampal volume increase in boys and decrease in girls. These changes were mediating the sexual differences in positive emotional regulation as illustrated by positive attributes increase in boys and decrease in girls. Moreover, the differential maturation rates between the limbic system and the prefrontal cortex highlighted the delayed maturation in boys compared to girls. This is the first study to show the sex effects on the differential cortico/subcortical maturation rates and the interaction between sex and puberty in the limbic system maturation related to positive attributes, reported as being protective from emotional disorders.
Neuroimaging findings have been reported in regions of the brain associated with emotion in both adults and adolescents with depression, but few studies have investigated whether such brain ...alterations can be detected in adolescents with subthreshold depression, a condition at risk for major depressive disorder. In this study, we searched for differences in brain structure at age 14 years in adolescents with subthreshold depression and their relation to depression at age 16 years.
High-resolution structural magnetic resonance imaging was used to assess adolescents with self-reported subthreshold depression (n = 119) and healthy control adolescents (n = 461), all recruited from a community-based sample. Regional gray and white matter volumes were compared across groups using whole-brain voxel-based morphometry. The relationship between subthreshold depression at baseline and depression outcome was explored using causal mediation analyses to search for mediating effects of regional brain volumes.
Adolescents with subthreshold depression had smaller gray matter volume in the ventromedial prefrontal and rostral anterior cingulate cortices and caudates, and smaller white matter volumes in the anterior limb of internal capsules, left forceps minor, and right cingulum. In girls, but not in boys, the relation between subthreshold depression at baseline and high depression score at follow-up was mediated by medial-prefrontal gray matter volume.
Subthreshold depression in early adolescence might be associated with smaller gray and white matter volumes in regions of the frontal-striatal-limbic affective circuit, and the occurrence of depression in girls with subthreshold depression might be influenced by medial-prefrontal gray matter volume. However, these findings should be interpreted with caution because of the limitations of the clinical assessment methods.
Abstract The serotonin 5-HT1A receptor is a putative drug development target in disorders with cognitive and in particular memory deficits. However, previous human positron emission tomography (PET) ...studies on 5-HT1A receptor binding and memory functions have yielded discrepant results. We explored the association between verbal memory and 5-HT1A receptor binding in 24 healthy subjects (14 male, 10 female, aged 18–41 years). The cognitive tests included the Wechsler Memory Scale-Revised (WMS-R), Wechsler Adult Intelligence Scale-Revised (WAIS-R) and Wisconsin Card Sorting Test (WCST). 5-HT1A receptor binding was measured with PET and the radioligand carbonyl -11 CWAY-100635, which was quantified with the gold standard method based on kinetic modeling using arterial blood samples. We found that global 5-HT1A receptor binding was positively correlated with measures of verbal memory, such that subjects who had higher receptor binding tended to have better verbal memory than subjects who had lower receptor binding. Regional analyses suggested significant correlations in multiple neocortical brain regions and the raphe nuclei. We did not find significant correlations between 5-HT1A receptor binding and executive functions as measured with WCST. We conclude that neocortical as well as raphe 5-HT1A receptors are involved in verbal memory function in man.
This study examines the effects of puberty and sex on the intrinsic functional connectivity (iFC) of brain networks, with a focus on the default-mode network (DMN). Consistently implicated in ...depressive disorders, the DMN's function may interact with puberty and sex in the development of these disorders, whose onsets peak in adolescence, and which show strong sex disproportionality (females > males). The main question concerns how the DMN evolves with puberty as a function of sex. These effects are expected to involve within- and between-network iFC, particularly, the salience and the central-executive networks, consistent with the Triple-Network Model. Resting-state scans of an adolescent community sample (n = 304, male/female: 157/147; mean/std age: 14.6/0.41 years), from the IMAGEN database, were analyzed using the AFNI software suite and a data reduction strategy for the effects of puberty and sex. Three midline regions (medial prefrontal, pregenual anterior cingulate, and posterior cingulate), within the DMN and consistently implicated in mood disorders, were selected as seeds. Within- and between-network clusters of the DMN iFC changed with pubertal maturation differently in boys and girls (puberty-X-sex). Specifically, pubertal maturation predicted weaker iFC in girls and stronger iFC in boys. Finally, iFC was stronger in boys than girls independently of puberty. Brain-behavior associations indicated that lower connectivity of the anterior cingulate seed predicted higher internalizing symptoms at 2-year follow-up. In conclusion, weaker iFC of the anterior DMN may signal disconnections among circuits supporting mood regulation, conferring risk for internalizing disorders.
Most psychopathological disorders develop in adolescence. The biological basis for this development is poorly understood. To enhance diagnostic characterization and develop improved targeted ...interventions, it is critical to identify behavioural symptom groups that share neural substrates. We ran analyses to find relationships between behavioural symptoms and neuroimaging measures of brain structure and function in adolescence. We found two symptom groups, consisting of anxiety/depression and executive dysfunction symptoms, respectively, that correlated with distinct sets of brain regions and inter-regional connections, measured by structural and functional neuroimaging modalities. We found that the neural correlates of these symptom groups were present before behavioural symptoms had developed. These neural correlates showed case-control differences in corresponding psychiatric disorders, depression and attention deficit hyperactivity disorder in independent clinical samples. By characterizing behavioural symptom groups based on shared neural mechanisms, our results provide a framework for developing a classification system for psychiatric illness that is based on quantitative neurobehavioural measures.
Adult-onset schizophrenia has repeatedly been associated with disturbances in the temporal lobes and alterations in cortical folding, which are thought to reflect neurodevelopmental impairment. ...Early-onset schizophrenia (EOS; onset before 18 years) is considered to involve even more pronounced neurodevelopmental deviance across a wide range of brain structural measures. We hypothesized that overall alteration of cortical folding also applies to EOS, and EOS involves prominent structural aberrations in superior temporal and collateral sulci.
Magnetic resonance T1 images of 51 patients with EOS and 59 healthy participants were investigated. A fully automated method was applied to the images to extract, label, and measure the sulcus area in the whole cortex. Cortical folding was assessed by computing global sulcal indices (the ratio between total sulcal area and total outer cortex area) for each hemisphere and local sulcal indices (the ratio between the area of labeled sulcus and total outer cortex area in the corresponding hemisphere) for superior temporal and collateral sulci.
Relative to healthy individuals, patients with EOS had significantly lower global sulcal indices in both hemispheres and a lower local sulcal index in the left collateral sulcus.
Reduced hemispheric sulcation appears to be a feature of schizophrenia, irrespective of age at onset. Structural aberration involving the left collateral sulcus may contribute to neurobiological substrate of EOS.
Genetic factors and socioeconomic status (SES) inequalities play a large role in educational attainment, and both have been associated with variations in brain structure and cognition. However, ...genetics and SES are correlated, and no prior study has assessed their neural associations independently. Here we used a polygenic score for educational attainment (EduYears-PGS), as well as SES, in a longitudinal study of 551 adolescents to tease apart genetic and environmental associations with brain development and cognition. Subjects received a structural MRI scan at ages 14 and 19. At both time points, they performed three working memory (WM) tasks. SES and EduYears-PGS were correlated (r = 0.27) and had both common and independent associations with brain structure and cognition. Specifically, lower SES was related to less total cortical surface area and lower WM. EduYears-PGS was also related to total cortical surface area, but in addition had a regional association with surface area in the right parietal lobe, a region related to nonverbal cognitive functions, including mathematics, spatial cognition, and WM. SES, but not EduYears-PGS, was related to a change in total cortical surface area from age 14 to 19. This study demonstrates a regional association of EduYears-PGS and the independent prediction of SES with cognitive function and brain development. It suggests that the SES inequalities, in particular parental education, are related to global aspects of cortical development, and exert a persistent influence on brain development during adolescence.
Conventional time and frequency domain measures of heart rate variability (HRV) are strongly influenced by anesthetic drugs, and are therefore not able to detect subtle changes in HRV, even during ...light anesthesia. Approximate entropy of R-R intervals is an HRV measure that has a tendency to decrease during anesthesia, but it is severely compromised by low-frequency variations of the signal. However, the negative effect of the low-frequency variations can be eliminated by differentiating the R-R interval tachogram before analysis. We designed this study to investigate characteristics of a novel HRV measure, named δ entropy (dEn), during deepening anesthesia.
Eight healthy subjects were anesthetized with sevoflurane and 8 with propofol in a stepwise manner using 3 escalating concentrations (2%, 3%, and 4% end-tidal concentration and 7.4 ± 1.7, 12.3 ± 2.6, and 18.3 ± 5.0 μg/mL plasma concentration, respectively) at 30-minute intervals. A third group of 8 subjects received a supramaximal IV dose of glycopyrrolate without anesthesia to examine the effect of cardiac vagal activity on dEn. We computed dEn at baseline, during each step of anesthesia and during the anticholinergic blockade.
The dEn decreased along with deepening levels of sevoflurane and propofol anesthesia up to 33% (95% confidence interval CI 21%-44%) and 38% (95% CI 28%-48%), respectively. At each anesthesia level, dEn differed significantly (P < 0.05) from that measured at the preceding level, similarly in both the sevoflurane and propofol groups. Parasympathetic blockade by glycopyrrolate was found to decrease dEn by 17% (95% CI 6%-28%).
The dEn is a novel HRV measure able to detect subtle sympathetic- and parasympathetic-mediated alterations in HRV both during deepening levels of sevoflurane and propofol anesthesia and during exceedingly deep anesthesia.
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