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Thermal degradation of formamidinium based lead halide perovskites into sym-triazine and hydrogen cyanide observed by coupled thermogravimetry-mass spectrometry analysis
Get PDFThe thermal stability and decomposition products of formamidinium, a widely used organic cation in perovskite solar cell formulation, were investigated. The thermal degradation experiments of formamidinium-based perovskites and their halide precursors were carried out under helium atmosphere and vacuum at a constant heating rate of 20 degrees C min(-1). In addition, pulsed heating steps were employed under illumination/dark conditions to simulate a more realistic working temperature condition for photovoltaic devices. The identification of gas decomposition products was based on the quadrupole mass spectrometry technique. The released amounts of sym-triazine, formamidine, and hydrogen cyanide (HCN) were observed to highly depend on the temperature. For the experimental conditions used in this study, sym-triazine was obtained as the thermal product of degradation at temperatures above 95 degrees C. Below this temperature, only formamidine and HCN generation routes were observed. The energy pathways of formamidinium thermal degradation under photovoltaic working temperature conditions were further assessed by density functional theory calculations. The results indicated that formamidinium was more resilient to thermal degradation and the release of irreversible decomposition products compared to methylammonium because of a larger enthalpy and activation energy obtained for the decomposition reactions. The HCN instantaneous concentration observed during the low temperature heating tests and the estimations of the maximum release of HCN achievable per meter-square of an FA based perovskite based solar cell were compared to acute exposure guideline levels of airborne HCN concentration.journal articl
Synthesis and helical supramolecular organization of discotic liquid crystalline dibenzo[hi,st]ovalene
Get PDFDibenzo[hi,st]ovalene (DBOV) has emerged as a new polycyclic aromatic hydrocarbon (PAH) with intriguing optical properties with strong red emission. Nevertheless, DBOV derivatives thus far synthesized either had mesityl groups that hinder the pi-pi stacking of the aromatic cores or showed low solubility, and the self-assembly of DBOVs has not been investigated. In this work, two 3,4,5-tris(dodecyloxy)phenyl (TDOP) groups are introduced at the meso-positions of DBOV in order to enhance its solubility without compromising the intermolecular interactions. The obtained DBOV-TDOP forms at elevated temperatures a discotic liquid crystalline phase. Due to pi-pi-stacking interactions as well as local phase separation between the aromatic cores and the flexible alkoxy side chains, the DBOV-TDOP molecules self-assemble into columnar stacks. In the low temperature phase, the space demanding TDOP substituents induce a rotation of the discs towards each other leading to an exceptionally long helical pitch within the columnar structures. Moreover, scanning tunnelling microscopy (STM) elucidates intriguing self-assembly of DBOV-TDOP at the interface of highly oriented pyrolytic graphite (HOPG) and 1-phenyloctane (PO). Individual molecules are visualized by STM, revealing that the alkyl chains protrude from the surface into the solution and suggesting that a self-assembled bilayer film structure is predominantly formed.journal articl
Substrate stiffness affects particle distribution pattern in a drying suspension droplet
Get PDFThe complexities involved in achieving a tailor-made evaporative deposition pattern have remained a challenge. Here, we show that the morphological pattern of drying suspension droplets can be altered by varying substrate elastic modulus E: We find that the particle spot diameter and spacing between the particles scale with substrate stiffness as ds E 0: 15 and s E 1: 23; respectively. We show that the larger spot diameter and spacing between particles on a softer substrate are attributed to a higher energy barrier U associated with stronger pinning of the contact line. The particle deposition pattern is characterized in terms of deposition index, Id; whose value is 0.75 for centralized (multilayer) and uniform (monolayer) deposition patterns observed for stiffer and softer substrates, respectively. The outcome of the present study may find applications in biochemical characterization and analysis of micro-/nanoparticles.journal articl
The role of robotics and AI in technologically mediated human evolution: a constructive proposal
Get PDFThis paper proposes that existing computational modeling research programs may be combined into platforms for the information of public policy. The main idea is that computational models at select levels of organization may be integrated in natural terms describing biological cognition, thereby normalizing a platform for predictive simulations able to account for both human and environmental costs associated with different action plans and institutional arrangements over short and long time spans while minimizing computational requirements. Building from established research programs, the proposal aims to take advantage of current momentum in the direction of the integration of the cognitive with social and natural sciences, reduce start-up costs and increase speed of development. These are all important upshots given rising unease over the potential for AI and related technologies to shape the world going forward.journal articl
Methylphenidate modifies reward cue responses in adults with ADHD: An fMRI study
Get PDFAttention deficit hyperactivity disorder (ADHD) has been associated with neural hyposensitivity to reward-predicting cues. Methylphenidate is widely used in the management of the disorder's symptoms, but its effects on reward sensitivity in ADHD are unknown. The current study used fMRI to measure striatal responses to reward-predicting cues in adults with ADHD on and off methylphenidate and a control group, during a classical conditioning task. Responses to cued reward were also explored. Larger differences in the ventral striatum activation to reward cues versus non-reward cues were observed when the ADHD participants were on methylphenidate compared to placebo. In response to cued-reward outcome, an exploratory analysis showed methylphenidate reduced the BOLD time-series correlation between the dorsal striatum and dorsal medial prefrontal cortex. Methylphenidate's therapeutic effects may be mediated by altering reward processing in individuals with ADHD.journal articl
Voltage Imaging with ANNINE Dyes and Two-Photon Microscopy
Get PDFVoltage imaging is a tried and tested tool for revealing changes in neuronal membrane voltage at high temporal and spatial resolution in vitro and in vivo. However, single-photon in vivo voltage imaging using cameras and synthetic dyes does not allow depth resolution in highly scattering tissue such as the mammalian brain and risks introducing artifacts due to phototoxicity and bleaching. In contrast, voltage imaging with synthetic electrochromic dyes and two-photon excitation near the red spectral edge of absorption circumvents these challenges, allowing depth-resolved measurement of voltage changes at high spatial and temporal resolution in scattering tissue with negligible phototoxicity and bleaching.
Here, we describe how to image voltage using two-photon microscopy and the voltage-sensitive dyes ANNINE-6 and ANNINE-6plus. The key advantages of these dyes are that the voltage response is linear, the temporal resolution is essentially limited by the imaging speed, and phototoxicity and bleaching can be neglected when an excitation wavelength close to the red spectral edge of absorption is chosen. We report how to image membrane voltage of dissociated cells in culture. We provide protocols for imaging average membrane voltage in vitro (in brain slices) and in anesthetized and awake animals. Finally, we describe the labeling of single neurons in vivo and how to measure supra- and sub-threshold voltage changes in their dendrites in the awake animal. Voltage can be imaged from internally labeled cells for at least 2 weeks after a single electroporation. Dendritic voltage imaging can be combined with electrical recording, calcium imaging, and/or pharmacology.boo
Evolution of Termite Symbiosis Informed by Transcriptome-Based Phylogenies
Get PDFTermitidae comprises approximately 80% of all termite species [1] that play dominant decomposer roles in tropical ecosystems [2, 3]. Two major events during termite evolution were the loss of cellulolytic gut protozoans in the ancestor of Termitidae and the subsequent gain in the termitid subfamily Macrotermitinae of fungal symbionts cultivated externally in "combs" constructed within the nest [4, 5]. How these symbiotic transitions occurred remains unresolved. Phylogenetic analyses of mitochondrial data previously suggested that Macrotermitinae is the earliest branching termitid lineage, followed soon after by Sphaerotermitinae [6], which cultivates bacterial symbionts on combs inside its nests [7]. This has led to the hypothesis that comb building was an important evolutionary step in the loss of gut protozoa in ancestral termitids [8]. We sequenced genomes and transcriptomes of 55 termite species and reconstructed phylogenetic trees from up to 4,065 orthologous genes of 68 species. We found strong support for a novel sister-group relationship between the bacterial comb-building Sphaerotermitinae and fungus comb-building Macrotermitinae. This key finding indicates that comb building is a derived trait within Termitidae and that the creation of a comb-like "external rumen" involving bacteria or fungi may not have driven the loss of protozoa from ancestral termitids, as previously hypothesized. Instead, associations with gut prokaryotic symbionts, combined with dietary shifts from wood to other plant-based substrates, may have played a more important role in this symbiotic transition. Our phylogenetic tree provides a platform for future studies of comparative termite evolution and the evolution of symbiosis in this taxon.journal articl
Skin Friction Measurements of Systematically-Varied Roughness: Probing the Role of Roughness Amplitude and Skewness
Get PDFSkin-friction, roughness functions and predictive correlations are presented for random roughness that has a Gaussian power spectral density distribution of surface elevations. The root-mean-square (rms) roughness height and the skewness of the probability density function are parametrically varied to investigate the role of these parameters in generating the friction at the wall. Results are presented for all roughness regimes, from hydraulically-smooth to fully-rough. Negative skewness (pits) had a much smaller influence on drag than positive skewness (peaks). Predictive engineering correlations for the equivalent sandgrain roughness height indicate that the rms roughess height and skewness are important scaling parameters. However, the scaling does not appear to be universal as different correlations are needed for surface roughness with positive, negative and zero skewness. Most surfaces collapse to a single roughness function in the transitionally-rough regime similar to the one developed by Nikuradase (1933) for uniform sand-grain roughness. The exceptions are the wavy surface (low effective slope) and the surface with high positive skewness.journal articl
The underestimated giants: operant conditioning, visual discrimination and long-term memory in giant tortoises
Get PDFRelatively little is known about cognition in turtles, and most studies have focused on aquatic animals. Almost nothing is known about the giant land tortoises. These are visual animals that travel large distances in the wild, interact with each other and with their environment, and live extremely long lives. Here, we show that Galapagos and Seychelle tortoises, housed in a zoo environment, readily underwent operant conditioning and we provide evidence that they learned faster when trained in the presence of a group rather than individually. The animals readily learned to distinguish colors in a two-choice discrimination task. However, since each animal was assigned its own individual colour for this task, the presence of the group had no obvious effect on the speed of learning. When tested 95 days after the initial training, all animals remembered the operant task. When tested in the discrimination task, most animals relearned the task up to three times faster than naive animals. Remarkably, animals that were tested 9 years after the initial training still retained the operant conditioning. As animals remembered the operant task, but needed to relearn the discrimination task constitutes the first evidence for a differentiation between implicit and explicit memory in tortoises. Our study is a first step towards a wider appreciation of the cognitive abilities of these unique animals.journal articl
Transcriptomic profiling of the mussel Mytilus trossulus with a special emphasis on integrin-like genes during development
Get PDFThis study is based on the Illumina RNA-sequencing data obtained for a de novo assembly of the transcriptome from early developmental stages and some tissues and cells of the adult mussel Mytilus trossulus (Mytilidae, Mollusca) using the Trinity program. A total of 200,079 contigs were obtained, and compared to the NCBI database using BLAST to search for sequence similarity. The number of annotated contigs under the GO term 3 categories was estimated to reach 19.96%. The BUSCO analysis determined a level of 99.2% completeness for the assembled transcriptome. The main findings include evidence that the mussel ? integrin-like protein sequences are very similar to the ? integrin-like proteins so far sequenced for all classes of Mollusca, while the highest similarity is observed between mussel and oyster (Crasostrea gigas) ? integrin-like proteins. Our transcriptome dataset contributes to the genetic databases of non-model animals such as bivalves and represents the first characterization of expressed sequences during early development of the mollusc M. trossulus from the Sea of Japan including the identification of candidate genes involved in cell adhesion.journal articl