A method to construct exponential families by representation theory

In this paper, we give a method to construct "good" exponential families systematically by representation theory. More precisely, we consider a homogeneous space $G/H$ as a sample space and construct an exponential family invariant under the transformation group $G$ by using a representation of $G$. The method generates widely used exponential families such as normal, gamma, Bernoulli, categorical, Wishart, von Mises, Fisher-Bingham and hyperboloid distributions

Low Temperature Properties of Antiferromagnets on the Kagome Lattice

Thermodynamic properties of antiferromagnets on the kagome lattice at low temperatures are studied for classical Heisenberg spin systems. In pure Heisenberg model, a coplanar structure is chosen by the entropy effect but it has been turned out to be disorder. Namely, it is not the √-structure in spite of the previous conjectures. The properties are also compared with those of quantum spin systems

Optical Absorption, Charge Separation and Recombination Dynamics in Pb and Sn/Pb Cocktail Perovskite Solar Cells and Their Relationships to the Photovoltaic Properties

Due to the unique characteristics such as simple low-temperature preparation method and high efficiency with a record of over 20%, organometal trihalide perovskite (CH3NH3PbI3)-based solid-state hybrid solar cells have attracted an increasing interest since 2012 when it was reported. During the last several years, some of the fundamental photophysical properties of perovskite related to the high photovoltaic performance have been investigated. Optical absorption, charge separation and recombination are very important factors influencing the perovskite solar cell performance. In this chapter, our recent results of optical absorption, charge separation (electron and hole injection) and charge recombination dynamics at each interface in perovskite solar cells, and their relationships to photovoltaic properties will be introduced. Our results suggest that charge recombination is a key factor in improving the performance of the perovskite solar cells

Very low-density lipoprotein-apoprotein CI is increased in diabetic nephropathy: Comparison with apoprotein CIII

Very low-density lipoprotein-apoprotein CI is increased in diabetic nephropathy: Comparison with apoprotein CIII.BackgroundRecent studies have suggested that apoprotein (apo) CI in very low-density lipoprotein (VLDL) plays an important role in causing hypertriglyceridemia independent of apo CIII, which is associated with coronary heart disease (CHD). Because the incidence of CHD is increased in diabetic patients and is even higher when diabetic nephropathy is developed, we measured apo CI levels in VLDL from type 2 diabetic patients, with various degree of nephropathy, and compared the results with those for healthy controls or nondiabetic patients with chronic renal failure (CRF).MethodsThis study enrolled healthy control subjects, type 2 diabetic patients with normoalbuminuria, microalbuminuria, overt proteinuria, and CRF on hemodialysis and nondiabetic hemodialyis patients. VLDL (density <1.006) was separated by ultracentrifugation. Then the apo CI, CIII, and B concentrations in VLDL were measured by enzyme-linked immunosorbent assay (ELISA).ResultsThe apo CI, CIII, and B concentrations in VLDL were respectively 3-, 2-, and 2-fold higher, respectively, in diabetic patients with overt proteinuria than in controls. Hemodialysis patients with diabetic nephropathy had levels of apo CI, CIII, and B in VLDL that were 2.6-, 2.7- and 2-fold higher, respectively, than those in controls. Nondiabetic hemodialysis patients also had a 2.7-fold higher level of VLDL apo CIII, whereas VLDL apo CI and VLDL apo B were not significantly increased. VLDL apo CI was significantly correlated with VLDL apo B independently of VLDL apo CIII level.ConclusionAn increase of VLDL apo CIII is a prominent feature of dyslipidemia in CRF patients, regardless of whether they are diabetic or nondiabetic, whereas an increase of VLDL apo CI is more specific to diabetic nephropathy and is closely associated with an increase of VLDL particle numbers, a new risk factor for CHD

Slow hot carrier cooling in cesium lead iodide perovskites

Lead halide perovskites are attracting a great deal of interest for optoelectronic applications such as solar cells, LEDs, and lasers because of their unique properties. In solar cells, heat dissipation by hot carriers results in a major energy loss channel responsible for the Shockley–Queisser efficiency limit. Hot carrier solar cells offer the possibility to overcome this limit and achieve energy conversion efficiency as high as 66% by extracting hot carriers. Therefore, fundamental studies on hot carrier relaxation dynamics in lead halide perovskites are important. Here, we elucidated the hot carrier cooling dynamics in all-inorganic cesium lead iodide (CsPbI3) perovskite using transient absorption spectroscopy. We observe that the hot carrier cooling rate in CsPbI3 decreases as the fluence of the pump light increases and the cooling is as slow as a few 10 ps when the photoexcited carrier density is 7 × 1018 cm−3, which is attributed to phonon bottleneck for high photoexcited carrier densities. Our findings suggest that CsPbI3 has a potential for hot carrier solar cell applications

Investigation of Interfacial Charge Transfer in Solution Processed Cs2SnI6 Thin Films

Cesium tin halide based perovskite Cs2SnI6 has been subjected to in-depth investigations owing to its potentiality toward the realization of environment benign Pb free and stable solar cells. In spite of the fact that Cs2SnI6 has been successfully utilized as an efficient hole transport material owing to its p-type semiconducting nature, however, the nature of the majority carrier is still under debate. Therefore, intrinsic properties of Cs2SnI6 have been investigated in detail to explore its potentiality as light absorber along with facile electron and hole transport. A high absorption coefficient (5 × 104 cm–1) at 700 nm indicates the penetration depth of 700 nm light to be 0.2 μm, which is comparable to conventional Pb based solar cells. Preparation of pure and CsI impurity free dense thin films with controllable thicknesses of Cs2SnI6 by the solution processable method has been reported to be difficult owing to its poor solubility. An amicable solution to circumvent such problems of Cs2SnI6 has been provided utilizing spray-coating in combination with spin-coating. The presence of two emission peaks at 710 and 885 nm in the prepared Cs2SnI6 thin films indicated coexistence of quantum dot and bulk parts which were further supported by transmission electron microscopy (TEM) investigations. Time-resolved photoluminescence (PL) and transient absorption spectroscopy (TAS) were employed to investigate the excitation carrier lifetime, which revealed fast decay kinetics in the picoseconds (ps) to nanoseconds (ns) time domains. Time-resolved microwave photoconductivity decay (MPCD) measurement provided the mobile charge carrier lifetime exceeding 300 ns, which was also in agreement with the nanosecond transient absorption spectroscopy (ns-TAS) indicating slow charge decay lasting up to 20 μs. TA assisted interfacial charge transfer investigations utilizing Cs2SnI6 in combination with n-type PCBM and p-type P3HT exhibited both intrinsic electron and hole transport

Solution‐Processed Air‐Stable Copper Bismuth Iodide for Photovoltaics

Bismuth‐based solar cells have been under intensive interest as an efficient non‐toxic absorber in photovoltaics. Within this new family of semiconductors, we herein report a new, long‐term stable copper bismuth iodide (CuBiI4). A solutionprocessed method under air atmosphere is used to prepare the material. The adopted HI‐assisted dimethylacetamide (DMA) co‐solvent can completely dissolve CuI and BiI3 powders with high concentration compared with other organic solvents. Moreover, the high vapor pressure of tributyl phosphate, selected for the solvent vapor annealing (SVA), enables complete low‐temperature (≤70°C) film preparation, resulting in a stable, uniform, dense CuBiI4 film. The average grain size increases with the precursor concentration, greatly improving the photoluminescence lifetime and hall mobility; a carrier lifetime of 3.03 ns as well as an appreciable hall mobility of 110 cm2V−1s−1 were obtained. XRD illustrates that the crystal structure is cubic (space group Fd3m) and favored in the [111] direction. Moreover, the photovoltaic performance of CuBiI4 was also investigated. A wide bandgap (2.67 eV) solar cell with 0.82% power conversion efficiency is presented, which exhibits excellent long‐term stability over 1008 h under ambient conditions. This air‐stable material may give an application in future tandem solar cells as a stable short‐wavelength light absorber