Retrograde Solubility of Methylammonium Lead Iodide in γ-Butyrolactone Does Not Enhance the Uniformity of Continuously Coated Films.

Halide perovskite thin films can be the centerpiece of high-performance solar cells, light-emitting diodes, and other optoelectronic devices if the films are of high uniformity and relatively free of pinholes and other defects. A common strategy to form dense films from solution has been to generate a high density of nuclei by rapidly increasing supersaturation, for example, by timely application of an antisolvent or forced convection. In this work, we examine the role of retrograde solubility, wherein solubility decreases with increasing temperature, as a means of increasing the nucleation density and film coverage of slot-die-coated methylammonium lead iodide (MAPbI3) from γ-butyrolactone (GBL) solution. Coverage was investigated as a function of the substrate temperature and the presence and temperature of an air knife. Results were considered within the framework of the dimensionless modified Biot number, which quantifies the interplay between evaporation and horizontal diffusion. Moderate temperatures and a heated air knife improved film coverage and morphology by enhanced nucleation up to ∼80 °C. However, despite the dense nucleation enabled by retrograde solubility, slow evaporation as a result of the low vapor pressure of GBL, combined with Ostwald ripening at high temperatures, prevented the deposition of void-free, device-quality films. This work has provided a more detailed understanding of the interplay between perovskite processing, solvent parameters, and film morphology and ultimately indicates the obstacles to forming dense, uniform films from solvents with high boiling points even in the presence of rapid nucleation.

Examining optimism and flourishing as protective factors of suicidality across the adult lifespan: A cross-sectional investigation in three Spanish age groups.

We examined optimism and flourishing as unique protective predictors of suicidality (viz., suicidal ideation and suicidal behaviors) in a cross-sectional study of young adults (18-35 years), middle-aged adults (36-55 years), and older adults (≥56 years). Young adults were found to have higher levels of suicidal ideation and suicidal behaviors compared to middle-aged and older adults. Controlling for depressive symptoms, the results of conducting regression analyses consistently implicated flourishing as a distinct predictor of lower suicidal ideation and suicidal behaviors in young adults and middle-aged adults. However, for older adults, only optimism was found to be a unique predictor of lower suicidal ideation and suicidal behaviors. Implications of the present findings for understanding the differential role of optimism and flourishing in accounting for suicidality across the adult lifespan are discussed.

Predicting the Dynamics and Steady-State Shape of Cylindrical Newtonian Filaments on Solid Substrates.

The spreading of liquid filaments on solid surfaces is of paramount importance to a wide range of applications including ink-jet printing, coating, and direct ink writing (DIW). However, there is a considerable lack of experimental, numerical, and theoretical studies on the spreading of filaments on solid substrates. In this work, we studied the dynamics of spreading of Newtonian filaments via experiment, numerical simulations, and theoretical analysis. More specifically, we used a novel experimental setup to validate a 2D moving mesh computational fluid dynamics (CFD) model. The CFD model is used to determine the effect of processing and fluid parameters on the dynamics of filament spreading. We experimentally showed that for a Newtonian filament, the same spreading dynamics and final shape are obtained when the initial radius is constant, independent of the magnitude in printing parameters. In other words, the only important parameter on the spreading of filaments is the initial filament radius. Using a numerical model, we showed that the initial filament radius manifests itself in two important dimensionless parameters, Bond number, Bo, and viscous timescale, τµ. Furthermore, the results clearly show that the dynamics of spreading are governed by the static advancing contact angle, θs. These three parameters determine a master spreading curve that can be used to predict the spreading of cylindrical filaments on flat substrates. Finally, we developed a theoretical model that was parameterized using experimental data to correlate the steady-state shape of filaments with Bo and θs. These results are particularly applicable for predicting and controlling the dynamics of filaments in DIW and other extrusion-based processes.

Quasi-2D Model to Predict Solid Microstructure in Drying Thin Films.

The microstructure of solid coatings produced by solution processing is highly dependent on the coupling between growth, solute diffusion, and solvent evaporation. Here, a quasi-2D numerical model coupling drying and solidification is used to predict the transient lateral growth of two adjacent nuclei growing toward each other. Lateral gradients of the solute and solvent influence the evolution of film thickness and solid growth rate. The important process parameters and solvent properties are captured by the dimensionless Peclet number (Pe) and the Biot number (Bi), modified by an aspect ratio defined by the film thickness and distance between nuclei. By variation of Pe and Bi, the evaporation dynamics and aspect ratio are shown to largely determine the coating quality. These findings are applied to drying thin films of crystallizing halide perovskites, demonstrating a convenient process map for capturing the relationship between the modified Bi and well-defined coating regimes, which may be generalized for any solution-processed thin film coating systems.

Influence of central sidechain on self-assembly of glycine-x-glycine peptides.

Low molecular weight gelators (LMWGs) are the subject of intense research for a range of biomedical and engineering applications. Peptides are a special class of LMWG, which offer infinite sequence possibilities and, therefore, engineered properties. This work examines the propensity of the GxG peptide family, where x denotes a guest residue, to self-assemble into fibril networks via changes in pH and ethanol concentration. These triggers for gelation are motivated by recent work on GHG and GAG, which unexpectedly self-assemble into centimeter long fibril networks with unique rheological properties. The propensity of GxG peptides to self-assemble, and the physical and chemical properties of the self-assembled structures are characterized by microscopy, spectroscopy, rheology, and X-ray diffraction. Interestingly, we show that the number, length, size, and morphology of the crystalline self-assembled aggregates depend significantly on the x-residue chemistry and the solution conditions, i.e. pH, temperature, peptide concentration, etc. The different x-residues allow us to probe the importance of different peptide interactions, e.g. π-π stacking, hydrogen bonding, and hydrophobicity, on the formation of fibrils. We conclude that fibril formation requires π-π stacking interactions in pure water, while hydrogen bonding can form fibrils in the presence of ethanol-water solutions. These results validate and support theoretical arguments on the propensity for self-assembly and leads to a better understanding of the relationship between peptide chemistry and fibril self-assembly. Overall, GxG peptides constitute a unique family of peptides, whose characterization will aid in advancing our understanding of self-assembly driving forces for fibril formation in peptide systems.

Highly stable petroleum pitches provide access to the deep glassy state.

Differential scanning calorimetry (DSC) was used to study the fast aging behavior of two petroleum pitch materials despite being only three to five years old. We observe that these highly aromatic pitches with broad distributions of both molecular weight and aromaticity exhibit large enthalpic relaxation endotherms in initial DSC heating scans, and 20-32 °C reductions in the fictive temperature and 0.35-0.87 of θK, which are indicative of aged glasses similar to ultrastable glasses and 20 MA aged amber. Quantifying the degree of thermodynamic stability relative to the Kauzmann temperature vs. the aging time demonstrates that these materials age just as quickly as low fragility metallic glasses. Additionally, we observe that pitches age faster than polymers reported in the literature when compared using down-jump experiments. We hypothesize that the fraction of higher aromaticity of pitch molecules plays a crucial role in faster dynamics. The unique aging behavior and the ability to produce pitches in bulk quantities using pilot-scale equipment, while being possible to tailor their molecular composition, make them a useful material for studying complex aging dynamics in the deep glassy state.

The Impact of Stressful Life Events on Suicidal Ideation in Gender Dysphoria: A Moderator Effect of Perceived Social Support.

Factors associated with suicidal ideation in the gender dysphoria population are not completely understood. This high-risk population is more likely to suffer stressful events such as assault or employment discrimination. This study aimed to determine the association of stressful events and social support on suicidal ideation in gender dysphoria and to analyze the moderator effect of social support in relation to stressful events and suicidal ideation. A cross-sectional design was used in a clinical sample attending a public gender identity unit in Spain that consisted of 204 individuals (51.7% birth-assigned males and 48.3% birth-assigned females), aged between 13 and 59 (M = 27.95 years, SD = 9.58). A Structured Clinical Interview, a list of 16 stressful events, and a functional social support questionnaire (Duke-UNC-11) were used during the initial visits to the unit. The data were collected between 2011 and 2012. A total of 50.1% of the sample have had suicidal ideation. The following stressful events were associated with suicidal ideation: homelessness, eviction from home, and having suffered from physical or verbal aggression. Also, there was an inverse relation between perceived social support and suicidal ideation. There was a statistically significant interaction between a specific stressful event (eviction) and perceived social support. The study suggests that the promotion of safer environments could be related to lower suicidal ideation and that networks that provide social support could buffer the association between specific stressful events and suicidal ideation.

Concentration Dependence of a Hydrogel Phase Formed by the Deprotonation of the Imidazole Side Chain of Glycylhistidylglycine.

Upon deprotonation of its imidazole group at ∼pH 6, the unblocked tripeptide glycylhistidylglycine (GHG) self-assembles into very long crystalline fibrils on a 10-1000 µm scale which are capable of forming a volume spanning network, that is, hydrogel. The critical peptide concentration for self-assembly at a pH of 6 lies between 50 and 60 mM. The fraction of peptides that self-assemble into fibrils depends on the concentration of deprotonated GHG. While IR spectra seem to indicate the formation of fibrils with standard amyloid fibril ß-sheet structures, vibrational circular dichroism spectra show a strongly enhanced amide I' signal, suggesting that the formed fibrils exhibit significant chirality. The fibril chirality appears to be a function of peptide concentration. Rheological measurements reveal that the rate of gelation is concentration-dependent and that there is an optimum gel strength at intermediate peptide concentrations of ca. 175 mM. This paper outlines the unique properties of the GHG gel phase which is underlain by a surprisingly dense fibril network with an exceptionally strong modulus that make them potential additives for biomedical applications.

The effect of pyrolysis on the chemical, thermal and rheological properties of pitch.

Pitch-based carbon fibers are of considerable interest as high-performance materials. There are reports over the last several decades detailing (i) methods of improving pitch-based carbon fiber performance, and (ii) reducing the cost of production via novel processing techniques. However, there remain considerable challenges in producing high-performance pitch-based carbon fibers consistently on an industrial scale. This is arguably due to the difficulty of scaling the melt-spinning process to compensate for variability in pitch feedstock quality and a lack of understanding of processing-structure-performance relationships. This work focuses on the early stages of heat treatment (pyrolysis) of isotropic pitch and its effect on the chemical, thermal, and rheological properties of the pitch, which help determine its processability. More specifically, we quantify significant changes in chemical structure, Mw, Tg, Ts, and shear and extensional rheology as a function of pyrolysis time at 400 °C. The extensional rheology, in particular, shows that the 'stretchability' of the pitch samples strongly depends on pyrolysis severity, and is important for characterizing 'drawability'. Using a novel analysis of the uniaxial stretching kinematics, we show an isothermal 'drawability window' that allows for the largest axial and radial Hencky strains at constant rate. We hypothesize that this extensional drawability window could facilitate the successful processing of pitch into high quality fiber, minimizing the trial-and-error approach currently used in the field.

The impact of thermal history on the structure of glycylalanylglycine ethanol/water gels.

This work revisits several open questions regarding the mechanisms of GAG fibril formation and structure as a function of temperature. The authors recently hypothesized that there is a solubility limit of GAG in ethanol/water that induces self-assembly. In other words, not all peptides can participate in fibrillization and some fraction is still soluble in solution. We show via FTIR spectroscopy that, indeed, free peptides are still present in solution after fibril formation, strongly supporting the solubility model. Furthermore, previous work showed GAG self-assembled into right-handed (phase I) or left-handed (phase II) chiral structures depending on temperature. In this study, we analyze the crystalline structure of phase I and II gels via WAXS and SAXS to compare their crystalline structures and order. Rheological measurements were used to investigate the response of the fibrillar network to temperature. They reveal that the ability of the peptide to self-assemble depends on the solubility at a given temperature and not on thermal history. Furthermore, the gel softening point, the linear viscoelastic gel microstructure, and relaxation spectrum are very similar between phase I and phase II. Overall, the temperature only affects the chirality of the fibrils and the formation kinetics.

The tripeptide GHG as an unexpected hydrogelator triggered by imidazole deprotonation.

The tripeptide glycyl-histidyl-glycine (GHG) self-assembles into long, crystalline fibrils forming a strong hydrogel (G'∼ 50 kPa) above a critical concentration of 40 mM upon the deprotonation of its imidazole group. Spectroscopic data reveal a mixture of helically twisted ß-sheets and monomers to coexist in the gel phase.

Optimism and gratitude on suicide risk in Spanish adults: Evidence for doubling up or doubling down?

OBJECTIVE: The present study examines the role of optimism and gratitude as predictors of suicide risk, namely depressive symptoms and suicide ideation. Beyond their expected predictive role, optimism and gratitude were also hypothesized to interact together to predict both suicide risk outcomes. METHODS: A sample of 1,013 Spanish adults (521 females) participated in this study. The average age was 39.63 years old (standard deviation = 16.19; range 16-82). RESULTS: Results indicated that the optimism × gratitude interaction term significantly augmented the prediction of both depressive symptoms and suicide ideation. Specifically, pessimists presented with a higher risk of suicide, but the effect was weaker among those individuals with higher levels of gratitude. Alternatively, optimists with high gratitude showed the highest amount of protection from suicide risk. CONCLUSIONS: Our findings are the first to show how optimism and gratitude might interact as a positive psychological variable to confer greater personal resources in protecting individuals against suicide risk.

An improved method of delivering a sclerosing agent for the treatment of malignant pleural effusion.

BACKGROUND: Malignant pleural effusion (MPE) is a devastating sequela associated with cancer. Talc pleurodesis is a common treatment strategy for MPE but has been estimated to be unsuccessful in up to 20-50% of patients. Clinical failure of talc pleurodesis is thought to be due to poor dispersion. This monograph reports the development of a foam delivery system designed to more effectively coat the pleural cavity. METHODS: C57BL/6 mice were injected with Lewis lung carcinoma (LL/2) cells intrapleurally to induce MPE. The mice then received either normal saline (NS) control, foam control (F), talc slurry (TS, 2 mg/g) or talc foam (TF, 2 mg/g). Airspace volume was evaluated by CT, lungs/pleura were collected, and percent fibrosis was determined. RESULTS: The TF group had significantly better survival than the TS group (21 vs 13.5 days, p < 0.0001). The average effusion volume was less in the talc groups compared to the control group (140 vs 628 µL, p < 0.001). TF induced significant lung fibrosis (p < 0.01), similar to TS. On CT, TF significantly (p < 0.05) reduced loss of right lung volume (by 30-40%) compared to the control group. This was not seen with TS (p > 0.05). CONCLUSIONS: This report describes using a novel talc foam delivery system for the treatment of MPE. In the LL/2 model, mice treated with the TF had better survival outcomes and less reduction of lung volume than mice treated with the standard of care TS. These data provide support for translational efforts to move talc foam from animal models into clinical trials.

Exploring the thermal reversibility and tunability of a low molecular weight gelator using vibrational and electronic spectroscopy and rheology.

Cationic glycylalanylglycine (GAG) self-assembles into a gel in a 55 mol% ethanol/45 mol% water mixture. The gel exhibits a network of crystalline fibrils grown to lengths on a 10-4-10-5 m scale (Farrel et al., Soft Matter, 2016, 12, 6096-6110). Rheological data are indicative of a rather strong gel with storage moduli in the 10 kPa regime. Spectroscopic data revealed the existence of two gel phases; one forms below T = 15 °C (phase I) while the other one forms in a temperature range between 15 °C and the melting temperature of ca. 35 °C (phase II). We explored the reformation of the cationic GAG gel in 55 mol% ethanol/45 mol% water after thermal annealing by spectroscopic and rheological means. Our data reveal that even a short residence time of 5 minutes in the sol phase at 50 °C produced a delay of the gelation process and a gel of lesser strength. These observations suggest that the residence time at the annealing temperature can be used to adjust the strength of both gel phases. Our spectroscopic data show that the annealing process does not change the chirality of peptide fibrils in the two gel phases and that the initial aggregation state of the reformation process is by far more ordered for phase I than it is for phase II. In the gel phases of GAG/ethanol/water mixtures, ethanol seems to function as a sort of catalyst that enables the self-assembly of the peptide in spite of its low intrinsic propensity for aggregation.

Relating Chain Conformations to Extensional Stress in Entangled Polymer Melts.

Nonlinear extensional flows are common in polymer processing, but they remain challenging theoretically because dramatic stretching of chains deforms the entanglement network far from equilibrium. Here, we present coarse-grained simulations of extensional flows in entangled polymer melts for Rouse-Weissenberg numbers Wi_{R}=0.06-52 and Hencky strains 뵳6. Simulations reproduce experimental trends in extensional viscosity with time, rate, and molecular weight. Studies of molecular structure reveal an elongation and thinning of the confining tube with increasing Wi_{R}. The rising stress is quantitatively consistent with the decreasing entropy of chains at the equilibrium entanglement length. Molecular weight dependent trends in viscosity are related to a crossover from the Newtonian limit to a high rate limit that scales differently with chain length.

The evolution of crystalline structures during gel spinning of ultra-high molecular weight polyethylene fibers.

Most studies are focused on the final mechanical properties of the fiber and the processing window required to achieve high moduli and tensile strength. Several studies have alluded to the fact that the crystalline morphologies developed during gel spinning and post-drawing are very important in determining the final mechanical properties. However, it is surprising to know that no clear correlation exists between the crystalline structure and initial, evolving, and final mechanical properties. In an attempt to define structure-property relationships, we have developed novel tools to quantify the effect of processing on crystalline structure evolution. We examine through controlled gel-spinning and SAXS analysis the effect of flow kinematics on the development of crystalline structures. Direct correlations are made between polymer solution relaxation time, extension rates, crystallization time and gel-spun crystalline morphologies. We report direct evidence of flow induced crystallization, which approaches an asymptotic crystallization rate at high Weissenberg numbers. For Wi < 1, the crystalline structure is only slightly affected by equilibrium. For Wi > 1, the crystalline structure is highly anisotropic due to chain orientation/stretch during spinning. Fibers spun at different Weissenberg numbers are drawn to low draw ratios at constant temperature to measure the initial structure evolution. A qualitative SAXS analysis clearly shows similar evolution of different starting structures with the formation of more straight chain crystals upon drawing. However, there remain quantitative differences between the length of straight chain crystals and the size and distribution of lamellar domains depending on the starting structure.

[Effect of an intervention based on virtual reality on motor development and postural control in children with Down Syndrome]. / Efecto de una intervención basada en realidad virtual sobre las habi lidades motrices básicas y control postural de niños con Síndrome de Down.

There are few studies on the effect of a virtual reality-based intervention on motor development and postural control in children with Down Syndrome (DS). OBJECTIVE: To determine the effect of a virtual reality-based intervention on motor development and postural control in children with DS. PATIENTS AND METHOD: Study with a quantitative approach, with a quasi-experimental design, which included 16 children with DS randomly assigned to an experimental group (GWBB, n = 9) and con trol group (GC, n = 7). Postural control was evaluated by the center of pressure displacement and motor development with TGMD-2. The intervention program was carried out for five weeks, two times per week. The data were subjected to statistical analysis, the Shapiro Wilk test for the sample distribution, and the Student's T-test for the comparison of group means. RESULTS: Significant chan ges were observed in the TGMD-2 Test and its manipulation subtest (p <0.01) respectively. In the rest of the tests, there was an improvement, but no significant differences were observed. CONCLUSION: A virtual reality-based intervention was effective in GWBB, providing low-impact exercises to improve postural control and thus leading to improved motor skills in children with DS.

Direct observation of active material interactions in flowable electrodes using X-ray tomography.

Understanding electrical percolation and charging mechanisms in electrochemically active biphasic flowable electrodes is critical for enabling scalable deionization (desalination) and energy storage. Flowable electrodes are dynamic material systems which store charge (remove ions) and have the ability to flow. This flow process can induce structural changes in the underlying material arrangement and result in transient and non-uniform material properties. Carbon-based suspensions are opaque, multi-phase, and three dimensional, and thus prior characterization of the structural properties has been limited to indirect methods (electrochemical and rheology). Herein, a range of mixed electronic and ionically conducting suspensions are evaluated to determine their static structure, function, and properties, utilizing synchrotron radiation X-ray tomographic microscopy (SRXTM). The high brilliance of the synchrotron light enables deconvolution of the liquid and solid phases. Reconstruction of the solid phase reveals agglomeration cluster volumes between 10 µm3 and 103µm3 (1 pL) for low loaded samples (5 wt% carbon). The largest agglomeration cluster in the low loaded sample (5 wt%) occupied only 3% of the reconstructed volume whereas samples loaded with 10 wt% activated carbon demonstrated electrically connected clusters that occupied 22% of the imaged region. The highly loaded samples (20 wt%) demonstrated clusters of the order of a microliter, which accounted for 63-85% of the imaged region. These results demonstrate a capability for discerning the structural properties of biphasic systems utilizing SRXTM techniques, and show that discontinuity in the carbon particle networks induces decreased material utilization in low-loaded flowable electrodes.

Multiple Cracks Propagate Simultaneously in Polymer Liquids in Tension.

Understanding the mechanism of fracture is essential for material and process design. While the initiation of fracture in brittle solids is generally associated with the preexistence of material imperfections, the mechanism for initiation of fracture in viscoelastic fluids, e.g., polymer melts and solutions, remains an open question. We use high speed imaging to visualize crack propagation in entangled polymer liquid filaments under tension. The images reveal the simultaneous propagation of multiple cracks. The critical stress and strain for the onset of crack propagation are found to be highly reproducible functions of the stretch rate, while the position of initiation is completely random. The reproducibility of conditions for fracture points to a mechanism for crack initiation that depends on the dynamic state of the material alone, while the crack profiles reveal the mechanism of energy dissipation during crack propagation.

Gender Dysphoria and Social Anxiety: An Exploratory Study in Spain.

INTRODUCTION: Social anxiety in gender dysphoria is still under investigation. AIM: To determine the prevalence and associated factors of social anxiety in a sample of individuals with gender dysphoria. METHODS: A cross-sectional design was used in a clinical sample attending a public gender identity unit in Spain. The sample consisted of 210 individuals (48% trans female and 52% trans male). MAIN OUTCOME MEASURES: Mini-International Neuropsychiatric Interview (MINI) for diagnosis of social anxiety disorder, Structured Clinical Interview, Exposure to Violence Questionnaire (EVQ), Beck Depression Inventory (BDI-II), and Functional Social Support Questionnaire (Duke-UNC-11). RESULTS: Of the total sample, 31.4% had social anxiety disorder. Social anxiety disorder was highly correlated with age (r = -0.181; CI = 0.061-0.264; P = .009) and depression (r = 0.345; CI = 0.213-0.468; P < .001); it is strongly associated to current cannabis use (relative risk [RR] = 1.251; CI = 1.070-1.463; P = .001) and lifetime suicidal ideation (RR = 1.902; CI 1.286-2.814; P < .001). Moreover, it is significantly associated to lifetime nonsuicidal self-injury (RR = 1.188; CI 1.018-1.386; P = .011), nationality (RR = 7.792; CI 1.059-57.392; P = .013), perceived violence at school during childhood and adolescence (r = 0.169; CI = 0.036-0.303; P = .014), unemployment (RR = 1.333; CI 1.02-1.742; P = .021), and hospitalization of parents in childhood (RR = 1.146; CI = 1.003-4.419; P = .046). Using multivariable analysis, the highly significant variables within the model were depression score (odds ratio [OR] = 1.083; CI = 1.045-1.123; P < .001) and current cannabis use (OR = 3.873; CI = 1.534-9.779, P = .004), also age (OR = 0.948; CI = 0.909-0.989; P = .012), hospitalization of parents during childhood (OR = 2.618; CI = 1.107-6.189; P = .028), and nationality (OR = 9.427; CI = 1.065-83.457; P = .044) were associated with social anxiety disorder. CONCLUSION: This study highlights the necessity of implementing actions to prevent and treat social anxiety in this high-risk population.