Coexistence of antiferrodistortive and ferroelectric distortions at the PbTiO3_3 (001) surface

The c(2$\times$2) reconstruction of (001) PbTiO$_3$ surfaces is studied by means of first principles calculations for paraelectric (non-polar) and ferroelectric ([001] polarized) films. Analysis of the atomic displacements in the near-surface region shows how the surface modifies the antiferrodistortive (AFD) instability and its interaction with ferroelectric (FE) distortions. The effect of the surface is found to be termination dependent. The AFD instability is suppressed at the TiO$_2$ termination while it is strongly enhanced, relative to the bulk, at the PbO termination resulting in a c(2x2) surface reconstruction which is in excellent agreement with experiments. We find that, in contrast to bulk PbTiO$_3$, in-plane ferroelectricity at the PbO termination does not suppress the AFD instability. The AFD and the in-plane FE distortions are instead concurrently enhanced at the PbO termination. This leads to a novel surface phase with coexisting FE and AFD distortions which is not found in PbTiO$_3$ bulk

The relationship between dose and serotonin transporter occupancy of antidepressants-a systematic review

Contains fulltext : 252198.pdf (Publisher’s version ) (Open Access)Brain imaging techniques enable the visualization of serotonin transporter (SERT) occupancy as a measure of the proportion of SERT blocked by an antidepressant at a given dose. We aimed to systematically review the evidence on the relationship between antidepressant dose and SERT occupancy. We searched PubMed and Embase (last search 20 May 2021) for human in vivo, within-subject PET, or SPECT studies measuring SERT occupancy at any dose of any antidepressant with highly selective radioligands ([(11)C]-DASB, [(123)I]-ADAM, and [(11)C]-MADAM). We summarized and visualized the dose-occupancy relationship for antidepressants across studies, overlaying the plots with a curve based on predicted values of a standard 2-parameter Michaelis-Menten model fitted using the observed data. We included seventeen studies of 10 different SSRIs, SNRIs, and serotonin modulators comprising a total of 294 participants, involving 309 unique occupancy measures. Overall, following the Michaelis-Menten equation, SERT occupancy increased with a higher dose in a hyperbolic relationship, with occupancy increasing rapidly at lower doses and reaching a plateau at approximately 80% at the usual minimum recommended dose. All the studies were small, only a few investigated the same antidepressant, dose, and brain region, and few reported information on factors that may influence SERT occupancy. The hyperbolic dose-occupancy relationship may provide mechanistic insight of relevance to the limited clinical benefit of dose-escalation in antidepressant treatment and the potential emergence of withdrawal symptoms. The evidence is limited by non-transparent reporting, lack of standardized methods, small sample sizes, and short treatment duration. Future studies should standardize the imaging and reporting procedures, measure occupancy at lower antidepressant doses, and investigate the moderators of the dose-occupancy relationship

Surface reconstruction and ferroelectricity in PbTiO3_3 thin films

Surface and ferroelectric properties of PbTiO$_3$ thin films are investigated using an interatomic potential approach with parameters computed from first-principles calculations. We show that a model developed for the bulk describes properly the surface properties of PbTiO$_3$. In particular, the antiferrodistortive surface reconstruction, recently observed from X-ray scattering, is correctly reproduced as a result of the change in the balance of long-range Coulombic and short-range interactions at the surface. The effects of the surface reconstruction on the ferroelectric properties of ultrathin films are investigated. Under the imposed open-circuit electrical boundary conditions, the model gives a critical thickness for ferroelectricity of 4 unit cells. The surface layer, which forms the antiferrodistortive reconstruction, participates in the ferroelectricity. A decrease in the tetragonality of the films leads to the stabilization of a phase with non-vanishing in-plane polarization. A peculiar effect of the surface reconstruction on the in-plane polarization profile is found.Comment: 6 pages, 5 figure

Den danske dyrkningsjords tilstand og kvalitet - konsekvenser af trafik og jordbearbejdning

Et alsidigt sædskifte og/eller tilførsel af organisk stof til jorden giver en god jordkvalitet (her defineret som en gunstig jordstruktur). Ensidige driftsformer kan i sig selv give anledning til en dårlig jordkvalitet. Jordpakning via trafik på jorden kan eliminere de gode effekter af et godt sædskifte og tilførsel af organisk stof. Trafik på jorden og i endnu højere grad intensiv jordbearbejdning øger risikoen for, at jordens lermineraler dispergeres til vandfasen. Dette kan give tilslemning og skorpedannelse på jorden og indebærer endvidere en risiko for nedvaskning af de vigtige lermineraler fra dyrkningslaget. Der bør foretages undersøgelser af omfanget af denne proces med de i dag anvendte bearbejdningsteknikker. Komprimering af jorden under normal bearbejdningsdybde via pløjning med hjulet i furebunden og via kørsel med meget tunge maskiner er i dag en realitet for stort set hele den danske landbrugsjord. Det anbefales stærkt, at landbruget overgår til pløjesystemer med alle fire hjul ’på land’ (’on-land’ pløjning). Det anbefales ligeledes, at belastningen (vægten) ved kørsel på forårs- og efterårsvåd jord ikke overstiger 6 tons på enkelt-aksel og 8-10 tons på boogi-aksel. Anvendelse af bæltekøretøjer er muligvis en løsning på pakningsproblemet. Det forudsætter dog, at de anvendte maskiner giver anledning til reelt meget lave marktryk (<50 kPa) over hele trædefladen. Der bør gennemføres flere undersøgelser af, hvorvidt de i dag tilgængelige bæltekøretøjer opfylder disse kriterier ved alle arbejdsoperationer

Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films

X-ray photoelectron diffraction is used to directly probe the intra-cell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab-initio calculations, unambiguously demonstrate non-centro-symmetry in films a few unit cells thick, imply that films as thin as 3 unit cells still preserve a ferroelectric polar distortion, and also show that there is no thick paraelectric dead layer at the surface

Island dynamics and anisotropy during vapor phase epitaxy of m-plane GaN

Using in situ grazing-incidence x-ray scattering, we have measured the diffuse scattering from islands that form during layer-by-layer growth of GaN by metal-organic vapor phase epitaxy on the (101⎯⎯0)(101¯0)(101¯0) m-plane surface. The diffuse scattering is extended in the (0001)(0001)(0001) in-plane direction in reciprocal space, indicating a strong anisotropy with islands elongated along [12⎯⎯10][12¯10] [12¯10] and closely spaced along [0001][0001][0001]. This is confirmed by atomic force microscopy of a quenched sample. Islands were characterized as a function of growth rate F and temperature. The island spacing along [0001][0001][0001] observed during the growth of the first monolayer obeys a power-law dependence on growth rate F−nF−nF−n, with an exponent n=0.25±0.02n=0.25±0.02n=0.25±0.02. The results are in agreement with recent kinetic Monte Carlo simulations, indicating that elongated islands result from the dominant anisotropy in step edge energy and not from surface diffusion anisotropy. The observed power-law exponent can be explained using a simple steady-state model, which gives n = 1/4

The predictive validity of the Strengths and Difficulties Questionnaire in preschool age to identify mental disorders in preadolescence

The Strengths and Difficulties Questionnaire (SDQ) is a brief, widely used instrument to screen for mental health problems in children and adolescents. The SDQ predictive algorithms developed for the SDQ, synthesize information from multiple informants regarding psychiatric symptoms and their impact on daily life. This study aimed to explore the validity of the SDQ predictive algorithms used in preschool age to predict mental disorders in preadolescence. The study population comprises 1176 children from the Copenhagen Child Cohort 2000 (CCC2000) assessed at age 5-7 years by the SDQ and reassessed at 11-12 years with the Development and Well Being Assessment (DAWBA) for evaluation of ICD-10 mental disorders. Odds Ratios (ORs), sensitivities, specificities, positive predictive values (PPVs) and negative predictive values (NPVs) were calculated for the SDQ predictive algorithms regarding ICD-10 diagnoses of hyperkinetic-inattentive-, behavioural- and emotional disorders. Significant ORs ranging from 2.3-36.5 were found for the SDQ predictive algorithms in relation to the corresponding diagnoses. The highest ORs were found for hyperkinetic and inattentive disorders, and the lowest for emotional disorders. Sensitivities ranging from 4.5-47.4, specificities ranging from 83.0-99.5, PPVs ranging from 5.0-45.5 and NPVs ranging from 90.6-99.0 were found for the SDQ predictive algorithms in relation to the diagnoses. The results support that the SDQ predictive algorithms are useful for screening at preschool-age to identify children at an increased risk of mental disorders in preadolescence. However, early screening with the SDQ predictive algorithms cannot stand alone, and repeated assessments of children are needed to identify, especially internalizing, mental health problems

Fluorescent carbon dioxide indicators

Over the last decade, fluorescence has become the dominant tool in biotechnology and medical imaging. These exciting advances have been underpinned by the advances in time-resolved techniques and instrumentation, probe design, chemical / biochemical sensing, coupled with our furthered knowledge in biology. Complementary volumes 9 and 10, Advanced Concepts of Fluorescence Sensing: Small Molecule Sensing and Advanced Concepts of Fluorescence Sensing: Macromolecular Sensing, aim to summarize the current state of the art in fluorescent sensing. For this reason, Drs. Geddes and Lakowicz have invited chapters, encompassing a broad range of fluorescence sensing techniques. Some chapters deal with small molecule sensors, such as for anions, cations, and CO2, while others summarize recent advances in protein-based and macromolecular sensors. The Editors have, however, not included DNA or RNA based sensing in this volume, as this were reviewed in Volume 7 and is to be the subject of a more detailed volume in the near future

The actin-bundling protein Fascin is overexpressed in inflammatory bowel disease and may be important in tissue repair

&lt;b&gt;Background&lt;/b&gt; Fascin is associated with increased cell motility in colorectal tumours but is absent from the normal colonic epithelium. We examined the expression of fascin in inflammatory bowel disease (IBD) and its location at regions undergoing restitution and regeneration. Tissue repair is essential for disease remission and we sought to determine the effects of therapeutic modalities on fascin expression and function using an in vitro model.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Methods&lt;/b&gt; Immunohistochemistry was performed on colonic tissue from IBD patients to determine changes in fascin expression and distribution. A human colorectal epithelial cell line was treated with 5-aminosalicylate (a common treatment for IBD), or sodium butyrate to determine the effect on fascin expression and cell motility.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Results&lt;/b&gt; Fascin overexpression was observed in both ulcerative colitis and Crohn's colitis and expression correlated with disease severity. Immunoreactivity was more intense and widespread in Crohn's compared to ulcerative colitis. Interestingly, highly expressing foci were consistently observed at the edges of ulcers where flattened, motile epithelial cells are actively involved in restitution, and also in areas of mucosal regeneration. 5-aminosalicylate reduced fascin expression in colorectal epithelial cells and inhibited their motility. Conversely, sodium butyrate increased fascin expression and stimulated cell motility in the same cells.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Conclusions&lt;/b&gt; Our data shows that fascin is overexpressed in inflammatory bowel disease and its location is indicative of a role in tissue repair. Our in vitro studies show that different therapeutic modalities may have converse effects on fascin expression and may have significant consequences for disease remission and the clinical management of IBD