Structure of methylammonium lead iodide within mesoporous titanium dioxide: active material in high-performance perovskite solar cells.

We report the structure of methylammonium lead(II) iodide perovskite in mesoporous TiO2, as used in high-performance solar cells. Pair distribution function analysis of X-ray scattering reveals a two component nanostructure: one component with medium range crystalline order (30 atom %) and another with only local structural coherence (70 atom %). The nanostructuring correlates with a blueshift of the absorption onset and increases the photoluminescence. Our findings underscore the importance of fully characterizing and controlling the structure for improved solar cell efficiency.

Atomic structures and gram scale synthesis of three tetrahedral quantum dots.

Luminescent semiconducting quantum dots (QDs) are central to emerging technologies that range from tissue imaging to solid-state lighting. However, existing samples are heterogeneous, which has prevented atomic-resolution determination of their structures and obscured the relationship between their atomic and electronic structures. Here we report the synthesis, isolation, and structural characterization of three cadmium selenide QDs with uniform compositions (Cd35Se20(X)30(L)30, Cd56Se35(X)42(L)42, Cd84Se56(X)56(L)56; X = O2CPh, L = H2N-C4H9). Their UV-absorption spectra show a lowest energy electronic transition that decreases in energy (3.54 eV, 3.26 eV, 3.04 eV) and sharpens as the size of the QD increases (fwhm = 207 meV, 145 meV, 115 meV). The photoluminescence spectra of all three QDs are broad with large Stokes shifts characteristic of trap-luminescence. Using a combination of single-crystal X-ray diffraction and atomic pair distribution function analysis, we determine the structures of their inorganic cores, revealing a series of pyramidal nanostuctures with cadmium terminated {111} facets. Theoretical and experimental studies on these materials will open the door to a deeper fundamental understanding of structure-property relationships in quantum-confined semiconductors.

Confirmation of disordered structure of ultrasmall CdSe nanoparticles from X-ray atomic pair distribution function analysis.

The atomic pair distribution function (PDF) analysis of X-ray powder diffraction data has been used to study the structure of small and ultra-small CdSe nanoparticles. A method is described that uses a wurtzite and zinc-blende mixed phase model to account for stacking faults in CdSe particles. The mixed-phase model successfully describes the structure of nanoparticles larger than 2 nm yielding a stacking fault density of about 30%. However, for ultrasmall nanoparticles smaller than 2 nm, the models cannot fit the experimental PDF showing that the structure is significantly modified from that of larger particles and the bulk. The observation of a significant change in the average structure at ultra-small size is likely to explain the unusual properties of the ultrasmall particles such as their white light emitting ability.

Rh(III)-Catalyzed Synthesis of Substituted Isoindoles through a Direct C-H Activation/[4 + 1] Annulation and Acyl Migration Cascade of Oxadiazolones with Diazo Compounds.

A Rh(III)-catalyzed C-H bond activation for the synthesis of fused 2H-isoindole scaffolds from oxadiazolones with diazo compounds was developed. The reaction proceeded through C-H activation of oxadiazolones/[4 + 1] annulation, intramolecular cyclization, and an unusual acyl migration cascade to afford target scaffolds with good yields. These 2H-isoindole derivatives could be further transformed into intriguing drug privileged scaffolds.

Impact of Perception of Green Space for Health Promotion on Willingness to Use Parks and Actual Use among Young Urban Residents.

Promoting the use of green space is a fundamental way to improve physical and mental health and to enhance the quality of life of urban residents. In response to increasing demand for green space in cities, the impact of perception of green space for health promotion on willingness to use parks and actual use among young urban residents was investigated in this study. A total of 1135 young residents (ages 18-35) in three cities in China were surveyed by online questionnaire. A group of multiple regression models was constructed to investigate the influencing perception factors of participants' willingness to use parks and actual use. The results revealed that the young residents' perception of green space components for health promotion (green space access, types, sizes, plants, water, sensory features, microclimate environments and amenity facilities) had a greater effect on their willingness to use parks and to promote health, while it was less influential with respect to their actual park use behavior (frequency and duration). Among these variables, green space access is a critical concern for willingness to use toward parks. The disparities of perception of green space for health promotion effect on willingness to use a park and actual use provide a better understanding of the psychological factors affecting park use among young residents. The findings also provided some implications for public health policymakers, urban planners and landscape architects in designing parks to encourage visitation by young people.

Serial Mediation of Environmental Preference and Place Attachment in the Relationship between Perceived Street Walkability and Mood of the Elderly.

Urban streets are important public spaces for daily activities that play a crucial role in promoting health in the elderly. The purpose of this study was to investigate the association between perceived street walkability and mood in the elderly, and specifically, the mediating effect of environmental preference and place attachment. We surveyed a total of 269 elderly residents from six streets in Guangzhou, China. We collected assessments of the street environments, environmental preferences, place attachment, and mood status from the elderly. A serial multiple mediator model was constructed using the structural equation modeling method. The results showed that the perceived street walkability was sequentially associated first with an increased level of place attachment (ß = 0.798, SE = 0.358, p < 0.000) and then environmental preference (ß = 0.191, SE = 0.033, p = 0.038), which was in turn related to improvement of positive mood in the elderly (ß = 0.595 SE = 0.341, p < 0.000). Environmental preference alone was found to be significantly associated with positive mood (ß = 0.595, SE = 0.341, p < 0.000), while no significant effect of place attachment was found when considered individually (ß = -0.075, SE = 0.089, p = 0.395). These findings provide a greater understanding of the possible mechanism through which street environment impacts mood in the elderly. Therefore, when promoting the emotional experience of the elderly, we might consider not only physical environment factors but also psychological conditions in street environments.

Genetic architecture study of rheumatoid arthritis and juvenile idiopathic arthritis.

BACKGROUND: Rheumatoid arthritis and juvenile idiopathic arthritis are two types of autoimmune diseases with inflammation at the joints, occurring to adults and children respectively. There are phenotypic overlaps between these two types of diseases, despite the age difference in patient groups. METHODS: To systematically compare the genetic architecture of them, we conducted analyses at gene and pathway levels and constructed protein-protein-interaction network based on summary statistics of genome-wide association studies of these two diseases. We examined their difference and similarity at each level. RESULTS: We observed extensive overlap in significant SNPs and genes at the human leukocyte antigen region. In addition, several SNPs in other regions of the human genome were also significantly associated with both diseases. We found significantly associated genes enriched in 32 pathways shared by both diseases. Excluding genes in the human leukocyte antigen region, significant enrichment is present for pathways like interleukin-27 pathway and NO2-dependent interleukin-12 pathway in natural killer cells. DISCUSSION: The identification of commonly associated genes and pathways may help in finding population at risk for both diseases, as well as shed light on repositioning and designing drugs for both diseases.

Complex modeling: a strategy and software program for combining multiple information sources to solve ill posed structure and nanostructure inverse problems.

A strategy is described for regularizing ill posed structure and nanostructure scattering inverse problems (i.e. structure solution) from complex material structures. This paper describes both the philosophy and strategy of the approach, and a software implementation, DiffPy Complex Modeling Infrastructure (DiffPy-CMI).

Magnetic pair distribution function analysis of local magnetic correlations.

The analytical form of the magnetic pair distribution function (mPDF) is derived for the first time by computing the Fourier transform of the neutron scattering cross section from an arbitrary collection of magnetic moments. Similar to the atomic pair distribution function applied to the study of atomic structure, the mPDF reveals both short-range and long-range magnetic correlations directly in real space. This function is experimentally accessible and yields magnetic correlations even when they are only short-range ordered. The mPDF is evaluated for various example cases to build an intuitive understanding of how different patterns of magnetic correlations will appear in the mPDF.

Bulk metallic glass-like scattering signal in small metallic nanoparticles.

The atomic structure of Ni-Pd nanoparticles has been studied using atomic pair distribution function (PDF) analysis of X-ray total scattering data and with transmission electron microscopy (TEM). Larger nanoparticles have PDFs corresponding to the bulk face-centered cubic packing. However, the smallest nanoparticles have PDFs that strongly resemble those obtained from bulk metallic glasses (BMGs). In fact, by simply scaling the distance axis by the mean metallic radius, the curves may be collapsed onto each other and onto the PDF from a metallic glass sample. In common with a wide range of BMG materials, the intermediate range order may be fit with a damped single-frequency sine wave. When viewed in high-resolution TEM, these nanoparticles exhibit atomic fringes typical of those seen in small metallic clusters with icosahedral or decahedral order. These two seemingly contradictory results are reconciled by calculating the PDFs of models of icosahedra that would be consistent with the fringes seen in TEM. These model PDFs resemble the measured ones when significant atom-position disorder is introduced, drawing together the two diverse fields of metallic nanoparticles and BMGs and supporting the view that BMGs may contain significant icosahedral or decahedral order.

Hollandites as a new class of multiferroics.

Discovery of new complex oxides that exhibit both magnetic and ferroelectric properties is of great interest for the design of functional magnetoelectrics, in which research is driven by the technologically exciting prospect of controlling charges by magnetic fields and spins by applied voltages, for sensors, 4-state logic, and spintronics. Motivated by the notion of a tool-kit for complex oxide design, we developed a chemical synthesis strategy for single-phase multifunctional lattices. Here, we introduce a new class of multiferroic hollandite Ba-Mn-Ti oxides not apparent in nature. BaMn3Ti4O14.25, designated BMT-134, possesses the signature channel-like hollandite structure, contains Mn(4+) and Mn(3+) in a 1:1 ratio, exhibits an antiferromagnetic phase transition (TN ~ 120 K) with a weak ferromagnetic ordering at lower temperatures, ferroelectricity, a giant dielectric constant at low frequency and a stable intrinsic dielectric constant of ~200 (1-100 MHz). With evidence of correlated antiferromagnetic and ferroelectric order, the findings point to an unexplored family of structures belonging to the hollandite supergroup with multifunctional properties, and high potential for developing new magnetoelectric materials.

Pair distribution function computed tomography.

An emerging theme of modern composites and devices is the coupling of nanostructural properties of materials with their targeted arrangement at the microscale. Of the imaging techniques developed that provide insight into such designer materials and devices, those based on diffraction are particularly useful. However, to date, these have been heavily restrictive, providing information only on materials that exhibit high crystallographic ordering. Here we describe a method that uses a combination of X-ray atomic pair distribution function analysis and computed tomography to overcome this limitation. It allows the structure of nanocrystalline and amorphous materials to be identified, quantified and mapped. We demonstrate the method with a phantom object and subsequently apply it to resolving, in situ, the physicochemical states of a heterogeneous catalyst system. The method may have potential impact across a range of disciplines from materials science, biomaterials, geology, environmental science, palaeontology and cultural heritage to health.