Coherent Phonon-Induced Modulation of Charge Transfer in 2D Hybrid Perovskites

Electron–phonon interactions play an essential role in charge transport and transfer processes in semiconductors. For most structures, tailoring electron–phonon interactions for specific functionality remains elusive. Here, it is shown that, in hybrid perovskites, coherent phonon modes can be used to manipulate charge transfer. In the 2D double perovskite, (AE2T)₂AgBiI₈ (AE2T: 5,5“-diylbis(amino-ethyl)-(2,2”-(2)thiophene)), the valence band maximum derived from the [Ag_0.5Bi_0.5I₄]^2– framework lies in close proximity to the AE2T-derived HOMO level, thereby forming a type-II heterostructure. During transient absorption spectroscopy, pulsed excitation creates sustained coherent phonon modes, which periodically modulate the associated electronic levels. Thus, the energy offset at the organic–inorganic interface also oscillates periodically, providing a unique opportunity for modulation of interfacial charge transfer. Density-functional theory corroborates the mechanism and identifies specific phonon modes as likely drivers of the coherent charge transfer. These observations are a striking example of how electron–phonon interactions can be used to manipulate fundamentally important charge and energy transfer processes in hybrid perovskites.     

Diagnostic performance of edited 2HG MR spectroscopy of central glioma in the clinical environment

Magnetic Resonance Materials in Physics, Biology and Medicine - Oncometabolite D-2-hydroxyglutarate (2HG) is pooled in isocitrate dehydrogenase (IDH)-mutant glioma cells. Detecting 2HG by MR...     

Honest confidence regions and optimality in high-dimensional precision matrix estimation

We propose methodology for estimation of sparse precision matrices and statistical inference for their low-dimensional parameters in a high-dimensional setting where the number of parameters p can be much larger than the sample size. We show that the novel estimator achieves minimax rates in supremum norm and the low-dimensional components of the estimator have a Gaussian limiting distribution. These results hold uniformly over the class of precision matrices with row sparsity of small order \(\sqrt{n}/\log p\) and spectrum uniformly bounded, under a sub-Gaussian tail assumption on the margins of the true underlying distribution. Consequently, our results lead to uniformly valid confidence regions for low-dimensional parameters of the precision matrix. Thresholding the estimator leads to variable selection without imposing irrepresentability conditions. The performance of the method is demonstrated in a simulation study and on real data.     

Anisotropic Materials for Skeletal‐Muscle‐Tissue Engineering

Repair of damaged skeletal‐muscle tissue is limited by the regenerative capacity of the native tissue. Current clinical approaches are not optimal for the treatment of large volumetric skeletal‐muscle loss. As an alternative, tissue engineering represents a promising approach for the functional restoration of damaged muscle tissue. A typical tissue‐engineering process involves the design and fabrication of a scaffold that closely mimics the native skeletal‐muscle extracellular matrix (ECM), allowing organization of cells into a physiologically relevant 3D architecture. In particular, anisotropic materials that mimic the morphology of the native skeletal‐muscle ECM, can be fabricated using various biocompatible materials to guide cell alignment, elongation, proliferation, and differentiation into myotubes. Here, an overview of fundamental concepts associated with muscle‐tissue engineering and the current status of muscle‐tissue‐engineering approaches is provided. Recent advances in the development of anisotropic scaffolds with micro‐ or nanoscale features are reviewed, and how scaffold topographical, mechanical, and biochemical cues correlate to observed cellular function and phenotype development is examined. Finally, some recent developments in both the design and utility of anisotropic materials in skeletal‐muscle‐tissue engineering are highlighted, along with their potential impact on future research and clinical applications.     

Multi-view Superpixel Stereo in Urban Environments

Urban environments possess many regularities which can be efficiently exploited for 3D dense reconstruction from multiple widely separated views. We present an approach utilizing properties of piecewise planarity and restricted number of plane orientations to suppress reconstruction and matching ambiguities causing failures of standard dense stereo methods. We formulate the problem of the 3D reconstruction in MRF framework built on an image pre-segmented into superpixels. Using this representation, we propose novel photometric and superpixel boundary consistency terms explicitly derived from superpixels and show that they overcome many difficulties of standard pixel-based formulations and handle favorably problematic scenarios containing many repetitive structures and no or low textured regions. We demonstrate our approach on several wide-baseline scenes demonstrating superior performance compared to previously proposed methods.     

Towards capacity and profit optimization of video-on-demand services in a peer-assisted IPTV platform

This paper studies the conditions under which peer-to-peer (P2P) technology may be beneficial in providing IPTV services over typical network architectures. It has three major contributions. First, we contrast two network models used to study the performance of such a system: a commonly used logical “Internet as a cloud” model and a “physical” model that reflects the characteristics of the underlying network. Specifically, we show that the cloud model overlooks important architectural aspects of the network and may drastically overstate the benefits of P2P technology. Second, we propose an algorithm called Zebra that pre-stripes content across multiple peers during idle hours to speed up P2P content delivery in an IPTV environment with limited upload bandwidth. We also perform simulations to measure Zebra’s effectiveness at reducing load on the content server during peak hours. Third, we provide a cost-benefit analysis of P2P video content delivery, focusing on the profit trade-offs for different pricing/incentive models rather than purely on capacity maximization. In particular, we find that under high volume of video demand, a P2P built-in incentive model performs better than any other model, while the conventional no-P2P model generates more profits when the request rate is low. The flat-reward model generally falls in between the usage-based model and the built-in model in terms of profitability except for low request rates. We also find that built-in and flat-reward models are more profitable than the usage-based model for a wide range of subscriber community sizes. Funding for J. Rahe’s research has been provided by AT&T Labs, the State of California under the MICR Oprogram, and by the Toshiba Corporation. Zhen Xiao is partially supported by China MOST project (2006BAH02A10).     

System approach to modeling of liver glucose metabolism with physiologically interpreted model parameters outgoing from [18F]FDG concentrations measured by PET

New mathematical models from physiologically interpreted parameters capable of evaluating glucose metabolism within the liver and/or the whole body were developed. The group of pigs in a fasting state and the group of pigs with euglycemic supraphysiological hyperinsulinemia were scanned by positron emission tomography after a single dose of [(18)F]FDG tracer. Simultaneously frequent sampling of the dynamic data of [(18)F]FDG plasma concentration in artery, portal vein and hepatic vein was obtained. A system approach to the liver and/or the whole-body system by the tools of linear dynamic sysztem theory was used. Three kinds of structural models, single input and single output or multiple outputs and multiple inputs and single output, were identified. Differences between the group of fasting pigs and the group of pigs in euglycemic supraphysiological hyperinsulinemia were identified by estimated parameters of the structural models. The suitability of the structural mathematical models for the estimation of physiologically interpreted parameters from PET was validated.     

Studies on the Extraction of Manganese from Sea Nodule Residue as Ferrosilicomanganese

Most of the extraction processes developed for the polymetallic sea nodules concentrated mainly on the recovery of strategically important metals viz. Cu, Ni and Co. The residue generated in such processes is quite high enough to upset the environmental balance for industrial scale operation. The economics of the process too cannot be favourable if manganese in the residue is not recovered. In this study an attempt has been made to utilize this residue, containing appreciable amount of manganese (about 20%) for producing ferrosilicomanganese, an important ferroalloy primarily used for deoxidation in the steel industry, through smelting process. In order to have an alloy of standard grade, the residue is enriched in its manganese content, by blending it with ferromanganese slag. Bench scale studies indicate that it is possible to produce ferrosilicomanganese, of the grade required by the steel industry, by reduction smelting of the sea nodule residue with ferromanganese slag. Metal recovery, however, was less because of metal entrapment.     

X-Ray absorption study of CeO2 and Ce/V mixed oxide thin films obtained by sol-gel deposition

CeO₂ and Ce/V mixed oxide thin films prepared by sol-gel deposition and annealed in an air or argon atmosphere have been studied by chronocoulometry and by XAFS (X-ray absorption fine structure). Multielectron photoexcitations (MPE), well known to pervade XAFS spectra of Ce making the analysis of structural parameters unreliable, are removed with the help of the atomic absorption background, determined on simple Ce compounds. Distinct MPE estimates for Ce³⁺ and Ce⁴⁺ ions are used. In the analysis of the recovered pure XAFS signal, the degree of disorder is found to depend on the Ce/V molar ratio and on the heating atmosphere. The disorder correlates with charge capacity of films, both increasing with vanadium content and V⁴⁺/V⁵⁺ molar ratio.