Vacancy clustering effect on the electronic and transport properties of bilayer graphene nanoribbons.

Experimental realizations of two-dimensional materials are hardly free of structural defects such as e.g. vacancies, which, in turn, modify drastically its pristine physical defect-free properties. In this work, we explore effects due to point defect clustering on the electronic and transport properties of bilayer graphene nanoribbons, for AA and AB stacking and zigzag and armchair boundaries, by means of the tight-binding approach and scattering matrix formalism. Evident vacancy concentration signatures exhibiting a maximum amplitude and an universality regardless of the system size, stacking and boundary types, in the density of states around the zero-energy level are observed. Our results are explained via the coalescence analysis of the strong sizeable vacancy clustering effect in the system and the breaking of the inversion symmetry at high vacancy densities, demonstrating a similar density of states for two equivalent degrees of concentration disorder, below and above the maximum value.

Block copolymer nanopatterns affect cell spreading: Stem versus cancer bone cells.

Bone healing after a tumor removal can be promoted by biomaterials that enhance the bone regeneration and prevent the tumor relapse. Herein, we obtained several nanopatterns by self-assembly of polystyrene-block-poly-(2-vinylpyridine) (PS-b-P2VP) with different molecular weights and investigated the adhesion and morphology of human bone marrow mesenchymal stem cells (BMMSC) and osteosarcoma cell line (SaOS-2) on these patterns aiming to identify topography and chemistry that promote bone healing. We analyzed > 2000 cells per experimental condition using imaging software and different morphometric descriptors, namely area, perimeter, aspect ratio, circularity, surface/area, and fractal dimension of cellular contour (FDC). The obtained data were used as inputs for principal component analysis, which showed distinct response of BMMSC and SaOS-2 to the surface topography and chemistry. Among the studied substrates, micellar nanopatterns assembled from the copolymer with high molecular weight promote the adhesion and spreading of BMMSC and have an opposite effect on SaOS-2. This nanopattern is thus beneficial for bone regeneration after injury or pathology, e.g. bone fracture or tumor removal.

Antithrombotic and hemocompatible properties of nanostructured coatings assembled from block copolymers.

We describe the antithrombotic properties of nanopatterned coatings created by self-assembly of poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) with different molecular weights. By changing the assembly conditions, we obtained nanopatterns that differ by their morphology (size and shape of the nanopattern) and chemistry. The surface exposition of P2VP block allowed quaternization, i.e. introduction of positive surface charge and following electrostatic deposition of heparin. Proteins (albumin and fibrinogen) adsorption, platelet adhesion and activation, cytocompatibility, and reendothelization capacity of the coatings were assessed and discussed in a function of the nanopattern morphology and chemistry. We found that quaternization results in excellent antithrombotic and hemocompatible properties comparable to heparinization by hampering the fibrinogen adhesion and platelet activation. In the case of quaternization, this effect depends on the size of the polymer blocks, while all heparinized patterns had similar performance showing that heparin surface coverage of 40 % is enough to improve substantially the hemocompatibility.

Modulation of persistent current in graphene quantum rings.

We investigate the effect of long-range impurity potentials on the persistent current of graphene quantum rings in the presence of an uniform perpendicular magnetic field. The impurity potentials are modeled as finite regions of the ring with a definite length. We show that, due to the relativistic and massless character of the charge carriers in graphene, the effect of such non-uniform potentials on the energy spectrum and on the persistent current of the rings can be reliably modeled by assuming a non-perturbed ring and including an additional phase due to the interaction of the charge carriers with the potential. In addition, the results show the presence of localized states in the impurity regions. Moreover, we show that for the case of a potential created by a p-n-p junction, the persistent current can be modulated by controlling the voltage at the junction.

Zitterbewegung of Moiré Excitons in Twisted MoS_{2}/WSe_{2} Heterobilayers.

The moiré pattern observed in stacked noncommensurate crystal lattices, such as heterobilayers of transition metal dichalcogenides, produces a periodic modulation of their band gap. Excitons subjected to this potential landscape exhibit a band structure that gives rise to a quasiparticle dubbed the moiré exciton. In the case of MoS_{2}/WSe_{2} heterobilayers, the moiré trapping potential has honeycomb symmetry and, consequently, the moiré exciton band structure is the same as that of a Dirac-Weyl fermion, whose mass can be further tuned down to zero with a perpendicularly applied field. Here we show that, analogously to other Dirac-like particles, the moiré exciton exhibits a trembling motion, also known as Zitterbewegung, whose long timescales are compatible with current experimental techniques for exciton dynamics. This promotes the study of the dynamics of moiré excitons in van der Waals heterostructures as an advantageous solid-state platform to probe Zitterbewegung, broadly tunable by gating and interlayer twist angle.

Longitudinal Association between Late-Life Depression (LLD) and Frailty: Findings from a Prospective Cohort Study (MiMiCS-FRAIL).

OBJECTIVES: The aim of the present study was to investigate whether late-life depression (LLD) is associated with incident frailty over time. DESIGN: Prospective cohort study, one-year follow-up. SETTING: Geriatric outpatient clinic, Southwestern of Brazil. PARTICIPANTS: 181 follow-up participants aged 60 years or over. MEASUREMENTS: Depressive disorders were classified as Major Depressive disorder (MDD) or Subthreshold Depression (STD) according to DSM-5 criteria. Depressive symptoms were assessed with validated versions of 15-item Geriatric Depression Scale (GDS-15) and 9-item Patient Health Questionnaire (PHQ-9). We performed binary logistic regressions to estimate the odds ratio (OR) for frailty in LLD adjusting for multiple confounders. Participants who were frail at baseline were excluded from the analyses according to measures of frailty (FRAIL questionnaire and 36-item Frailty Index, FI-36). We also estimated the risk ratio or relative risk (RR) and the risk difference (RD) for incident frailty. RESULTS: We observed a 2 to 4-fold increased risk for incident frailty among participants with LLD. The presence of a depressive disorder was significantly associated with the onset of frailty (adjusted OR for FRAIL and FI-36: 3.07 [95% CI = 1.03 - 9.17] and 3.76 [95% CI = 1.09 - 12.97], respectively. Notably, the risk for frailty due to LLD was significantly higher with the FI-36 compared to the FRAIL (RR: 3.03 versus 2.23). RD was of 17.3% and 12.7% with the FRAIL and the FI-36, respectively. CONCLUSION: Our data support the association between LLD and incident frailty over one year among geriatric outpatients, reinforcing longitudinal evidence from population-based studies.

Gate potential-controlled current switching in graphene Y-junctions.

In this work we investigate the ballistic transport of electrons through three-terminal graphene-based devices. The system consists of a Y-shaped junction formed by three armchair-edged graphene nanoribbons with a rectangular gate potential applied to one of the output branches, whereby current control can be established by the controlling of the refractive index in graphene p-n junctions. Transport properties are obtained by using the Landauer-Büttiker formalism and the tight-binding model within the nearest-neighbor approximation, which allows the calculation of the conductance as function of the Fermi energy, the applied potential, and the system size, as well as the current density. The results demonstrate that the applied electric field can tune the current transmission between the input and two output leads and, consequently, the proposed system acts as a current switch.

Mineral and natural films change the physical-chemical properties of grapes and modulate oviposition behaviour of Ceratitis capitata Wiedemann (Diptera: Tephritidae).

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), is one of the main pests of fruit, worldwide, and the use of population suppression method with low environmental impact is an increasingly strong requirement of the consumer market. The aim of this study was to evaluate the effect of mineral and natural films on the physical-chemical properties of grapes (Vitis vinifera L.), cultivar Itália, and oviposition behaviour of C. capitata. Fruits were immersed in suspensions (100 and 200 g L-1) of mineral (kaolin Surround®WP, kaolin 607, kaolin 608, kaolin 611 and talc) and natural films (chitosan, cassava starch, potato starch and guar gum 5.0 g L-1) and distilled water (control). After drying, fruits were exposed to C. capitata pairs of males and females for 24 h in choice and non-choice tests; the number of punctures with and without eggs, eggs per fruit and behavioural response of fly to treated and untreated fruits were recorded. Results obtained in this study are promising, given the scientific evidence that films of mineral particles such as kaolin (Surround®, 607, 608 and 611) changed the firmness, luminosity, chroma and hue angle of grapes and reduced the oviposition of C. capitata. In addition, our results also showed that natural polymers do not deter C. capitata females, but rather seem to stimulate oviposition.

Effect of zitterbewegung on the propagation of wave packets in ABC-stacked multilayer graphene: an analytical and computational approach.

The time evolution of a low-energy two-dimensional Gaussian wave packet in ABC-stacked n-layer graphene (ABC-NLG) is investigated. Expectation values of the position (x, y) of center-of-mass and the total probability densities of the wave packet are calculated analytically using the Green's function method. These results are confirmed using an alternative numerical method based on the split-operator technique within the Dirac approach for ABC-NLG, which additionally allows to include external fields and potentials. The main features of the zitterbewegung (trembling motion) of wave packets in graphene are demonstrated and are found to depend not only on the wave packet width and initial pseudospin polarization, but also on the number of layers. Moreover, the analytical and numerical methods proposed here allow to investigate wave packet dynamics in graphene systems with an arbitrary number of layers and arbitrary potential landscapes.

Gap opening in graphene nanoribbons by application of simple shear strain and in-plane electric field.

The effects of shear strain and applied in plane electric field on the electronic properties of monolayer graphene nanoribbons (GNRs) are theoretically investigated. Band structures and the probability densities are calculated within the tight-binding model and the mechanical stresses submitted to the GNRs are taken into account by using the theory of linear elasticity with joint modifications in the elongation of the nearest-neighbor vectors and the modification of the hopping parameters. The energy gaps for specific widths of (semiconducting) armchair nanoribbons are verified also in the presence of either strain or field, whereas zigzag nanoribbons are metallic for any value of strain and exhibit a small gap for any value of field. However, our results demonstrate that when both strain and electric field are combined, a significant energy gap is always observed in the band structure, for any width or edge type of the ribbon. Moreover, the obtained total wave function is asymmetric along the ribbon width due to the applied electric field that pushes the electrons to one side of the ribbon and, under shear strain, a peak at the center of the ribbon in the spatial distribution is also observed owing to the preferable localization around the almost undeformed carbon bonds at ribbon center.

Development of an antibacterial nanocomposite hydrogel for human dental pulp engineering.

Hydrogel-based regenerative endodontic procedures (REPs) are considered to be very promising therapeutic strategies to reconstruct the dental pulp (DP) tissue in devitalized human teeth. However, the success of the regeneration process is limited by residual bacteria that may persist in the endodontic space after the disinfection step and contaminate the biomaterial. The aim of this work was to develop an innovative fibrin hydrogel incorporating clindamycin (CLIN)-loaded Poly (d,l) Lactic Acid (PLA) nanoparticles (NPs) to provide the hydrogel with antibacterial properties. CLIN-PLA-NPs were synthesized by a surfactant-free nanoprecipitation method and their microphysical properties were assessed by dynamic light scattering, electrophoretic mobility and scanning electron microscopy. Their antimicrobial efficacy was evaluated on Enteroccocus fæcalis by the determination of the minimal inhibitory concentration (MIC) and the minimal biofilm inhibition and eradication concentrations (MBIC and MBEC). Antibacterial properties of the nanocomposite hydrogel were verified by agar diffusion assays. NP distribution into the hydrogel and release from it were evaluated using fluorescent PLA-NPs. NP cytotoxicity was assessed on DP mesenchymal stem cells (DP-MSCs) incorporated into the hydrogel. Type I collagen synthesis was investigated after 7 days of culture by immunohistochemistry. We found that CLIN-PLA-NPs displayed a drug loading of 10 ± 2 µg per mg of PLA polymer and an entrapment efficiency of 43 ± 7%. Antibiotic loading did not affect NP size, polydispersity index and zeta potential. The MIC for Enterococcus fæcalis was 32 µg mL-1. MBIC50 and MBEC50 were 4 and 16 µg mL-1, respectively. CLIN-PLA-NPs appeared homogenously distributed throughout the hydrogel. CLIN-PLA-NP-loaded hydrogels clearly inhibited E. faecalis growth. DP-MSC viability and type I collagen synthesis within the fibrin hydrogel were not affected by CLIN-PLA-NPs. In conclusion, CLIN-PLA-NP incorporation into the fibrin hydrogel gave the latter antibacterial and antibiofilm properties without affecting cell viability and function. This formulation could help establish an aseptic environment supporting DP reconstruction and, accordingly, might be a valuable tool for REPs.

Undiagnosed depression, persistent depressive symptoms and seeking mental health care: analysis of immigrant and non-immigrant participants of the Canadian Longitudinal Study of Aging.

AIMS: Early diagnosis and treatment of depression are associated with better prognosis. We used baseline data of the Canadian Longitudinal Study on Aging (2012-2015; ages 45-85 years) to examine differences in prevalence and predictors of undiagnosed depression (UD) between immigrants and non-immigrants at baseline and persistent and/or emerging depressive symptoms (DS) 18 months later. At this second time point, we also examined if a mental health care professional (MHCP) had been consulted. METHODS: We excluded individuals with any prior mood disorder and/or current anti-depressive medication use at baseline. UD was defined as the Center for Epidemiological Studies Depression 10 score ⩾10. DS at 18 months were defined as Kessler 10 score ⩾19. The associations of interest were examined in multivariate logistic regression models. RESULTS: Our study included 4382 immigrants and 18 620 non-immigrants. The mean age (standard deviation) in immigrants was 63 (10.3) years v. 65 (10.7) years in non-immigrants and 52.1% v. 57.1% were male. Among immigrants, 12.2% had UD at baseline of whom 34.2% had persistent DS 18 months later v. 10.6% and 31.4%, respectively, among non-immigrants. Female immigrants were more likely to have UD than female non-immigrants (odds ratio 1.50, 95% confidence interval 1.25-1.80) but no difference observed for men. The risk of persistent DS and consulting an MHCP at 18 months did not differ between immigrants and non-immigrants. CONCLUSIONS: Female immigrants may particularly benefit from depression screening. Seeking mental health care in the context of DS should be encouraged.

Bactericidal nanopatterns generated by block copolymer self-assembly.

We describe the bactericidal capacity of nanopatterned surfaces created by self-assembly of block copolymers. Distinct nanotopographies were generated by spin-coating with polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) followed by solvent vapor annealing. We demonstrate that the bactericidal efficiency of the developed coatings depends on the morphology and the chemistry of the surface: cylindrical nanotopographies presenting both blocks at the surface have stronger bactericidal effect on Escherichia coli than micellar patterns with only PS exposed at the surface. The identified mechanism of bacterial death is a mechanical stress exerted by the nanostructures on the cell-wall. Moreover, the developed nanopatterns are not cytotoxic, which makes them an excellent option for coating of implantable materials and devices. The proposed approach represents an efficient tool in the fight against bacteria, which acts via compromising the bacterial wall integrity. STATEMENT OF SIGNIFICANCE: Bacterial infections represent an important risk during biomaterial implantation in surgeries due to the increase of antibiotic resistance. Bactericidal surfaces are a promising solution to avoid the use of antibiotics, but most of those systems do not allow mammalian cell survival. Nanopatterned silicon surfaces have demonstrated to be simultaneously bactericidal and allow mammalian cell culture but are made by physical methods (e.g. plasma etching) applicable to few materials and small surfaces. In this article we show that block copolymer self-assembly can be used to develop surfaces that kill bacteria (E. coli) but do not harm mammalian cells. Block copolymer self-assembly has the advantage of being applicable to many different types of substrates and large surface areas.

Current modulation in graphene p-n junctions with external fields.

In this work we describe a proposal for a graphene-based nanostructure that modulates electric current even in the absence of a gap in the band structure. The device consists of a graphene p-n junction that acts as a Veselago lens that focuses ballistic electrons on the output lead. Applying external (electric and magnetic) fields changes the position of the output focus, reducing the transmission. Such device can be applied to low power field effect transistors, which can benefit from graphene's high electronic mobility.

MSX1 is differentially expressed in the deepest impacted maxillary third molars.

An impacted third molar is one of the most common dental abnormalities. Among the reasons for impaction the most common are: insufficient space, time of eruption, improper position of the tooth bud, and genetic disruptions. To investigate if runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP2), and msh homeobox 1 (MSX1) are differently expressed depending on the position of the molar, we studied 32 patients who had been referred for surgical removal. An orthopantomogram was used to separate them according to Winter's, and Pell & Gregory's, classifications. Bone samples were harvested during the operation for gene expression assay. The Kruskal-Wallis, Dunn's post hoc, and Spearman's correlation, tests were used to assess the significance of differences. No correlations were found in expression of the genes, and no differences between expression in maxillary and mandibular third molars, nor were they expressed differently according to Winter's or Pell and Gregory's classifications or in relation to impaction of the mandibular ramus. However, MSX1 was expressed differently when account was taken of the depth of impaction in maxillary third molars (p = 0.029), but there was no difference in expression of RUNX2, BMP2, and MSX1 for the Pell and Gregory classification of depth of impaction (p > 0.05). We conclude that MSX1 is expressed differently depending on the depth of maxillary impaction phenotypes.

Magnetic field induced vortices in graphene quantum dots.

The energy spectrum and local current patterns in graphene quantum dots (QD) are investigated for different geometries in the presence of an external perpendicular magnetic field. Our results demonstrate that, for specific geometries and edge configurations, the QD exhibits vortex and anti-vortex patterns in the local current density, in close analogy to the vortex patterns observed in the probability density current of semiconductor QD, as well as in the order parameter of mesoscopic superconductors.

Ketone body supplement label claims: what supplement has been supplemented?

Background: There is a keen interest in performance-enhancing supplementation and the associated benefits, despite reports of incorrect label claims made by manufacturers and the questionable efficacy of the supplements. The use of ketone body supplements as a source of fuel during exercise and sporting performance, in particular, is of interest to sportspeople. By increasing blood ketone body levels, with an accompanying decrease in blood glucose, may indicate a state of nutritional ketosis, whereby the body no longer relies on glucose metabolism but rather the metabolism of ketone bodies. This could be beneficial for long, slow steady-state endurance exercise. Discussion: There are numerous ketone body supplements on the market manufactured in South Africa and internationally. However, unlike medicines, the sports supplementation industry is poorly regulated. Furthermore, ketone body supplementation with regard to its effects on improving exercise and athletic performance is still unconvincing. Conclusion: Within the ever-changing sports supplementation industry, ketone body supplements are being used despite controversies regarding the accuracy and scientific merit of label claims. The ingredients and their quantities, as well as the performance benefits, need to be objectively validated.

The association between portal system vein diameters and outcomes in acute pancreatitis.

BACKGROUND/OBJECTIVES: Acute pancreatitis (AP) progresses to necrotizing pancreatitis in 15% of cases. An important pathophysiological mechanism in AP is third spacing of fluids, which leads to intravascular volume depletion. This results in a reduced splanchnic circulation and reduced venous return. Non-visualisation of the portal and splenic vein on early computed tomography (CT) scan, which might be the result of smaller vein diameter due to decreased venous flow, is associated with infected necrosis and mortality in AP. This observation led us to hypothesize that smaller diameters of portal system veins (portal, splenic and superior mesenteric) are associated with increased severity of AP. METHODS: We conducted a post-hoc analysis of data from two randomized controlled trials that included patients with predicted severe and mild AP. The primary endpoint was AP-related mortality. The secondary endpoints were (infected) necrotizing pancreatitis and (persistent) organ failure. We performed additional CT measurements of portal system vein diameters and calculated their prognostic value through univariate and multivariate Poisson regression. RESULTS: Multivariate regression showed a significant inverse association between splenic vein diameter and mortality (RR 0.75 (0.59-0.97)). Furthermore, there was a significant inverse association between splenic and superior mesenteric vein diameter and (infected) necrosis. Diameters of all veins were inversely associated with organ failure and persistent organ failure. CONCLUSIONS: We observed an inverse relationship between portal system vein diameter and morbidity and an inverse relationship between splenic vein diameter and mortality in AP. Further research is needed to test whether these results can be implemented in predictive scoring systems.

Valley filtering in graphene due to substrate-induced mass potential.

The interaction of monolayer graphene with specific substrates may break its sublattice symmetry and results in unidirectional chiral states with opposite group velocities in the different Dirac cones (Zarenia et al 2012 Phys. Rev. B 86 085451). Taking advantage of this feature, we propose a valley filter based on a transversal mass kink for low energy electrons in graphene, which is obtained by assuming a defect region in the substrate that provides a change in the sign of the substrate-induced mass and thus creates a non-biased channel, perpendicular to the kink, for electron motion. By solving the time-dependent Schrödinger equation for the tight-binding Hamiltonian, we investigate the time evolution of a Gaussian wave packet propagating through such a system and obtain the transport properties of this graphene-based substrate-induced quantum point contact. Our results demonstrate that efficient valley filtering can be obtained, provided: (i) the electron energy is sufficiently low, i.e. with electrons belonging mostly to the lowest sub-band of the channel, and (ii) the channel length (width) is sufficiently long (narrow). Moreover, even though the transmission probabilities for each valley are significantly affected by impurities and defects in the channel region, the valley polarization in this system is shown to be robust against their presence.