Functional Envelope Research Articles

Effect of Charge Localization on the Effective Hyperfine Interaction in Organic Semiconducting Polymers.

Hyperfine interaction (HFI), originating from the coupling between spins of charge carriers and nuclei, has been demonstrated to strongly influence the spin dynamics of localized charges in organic semiconductors. Nevertheless, the role of charge localization on the HFI strength in organic thin films has not yet been experimentally investigated. In this study, the statistical relation hypothesis that the effective HFI of holes in regioregular poly(3-hexylthiophene) (P3HT) is proportional to 1/N^{0.5} has been examined, where N is the number of the random nuclear spins within the envelope of the hole wave function. First, by studying magnetoconductance in hole-only devices made by isotope-labeled P3HT we verify that HFI is indeed the dominant spin interaction in P3HT. Second, assuming that holes delocalize fully over the P3HT polycrystalline domain, the strength of HFI is experimentally demonstrated to be proportional to 1/N^{0.52} in excellent agreement with the statistical relation. Third, the HFI of electrons in P3HT is about 3 times stronger than that of holes due to the stronger localization of the electrons. Finally, the effective HFI in organic light emitting diodes is found to be a superposition of effective electron and hole HFI. Such a statistical relation may be generally applied to other semiconducting polymers. This Letter may provide great benefits for organic optoelectronics, chemical reaction kinetics, and magnetoreception in biology.

Chaotic behaviors of one dimensional wave equations with van der Pol nonlinear boundary conditions

For one-dimensional linear wave equations with van der Pol boundary conditions, there have existed several different ways in the literature to characterize the complexity of their solutions. In this paper, we give a new way to characterize the dynamical behaviors of the systems, including almost equicontinuity and Devaney chaos. In order to do this, we consider a one-dimensional system (I, f) and its functional envelope (L1(I,I),Hf) and show that Hf is weakly mixing if and only if f is; Hf is Devaney chaotic if f is weakly mixing; Hf is almost equicontinuous if f has an attracting 2-period orbit. Those abstract results have their own significance and can be applied to the linear wave equations with van der Pol boundary conditions.

A tribute to Ulrich Heber (1930-2016) for his contribution to photosynthesis research: understanding the interplay between photosynthetic primary reactions, metabolism and the environment.

The dynamic and efficient coordination of primary photosynthetic reactions with leaf energization and metabolism under a wide range of environmental conditions is a fundamental property of plants involving processes at all functional levels. The present historical perspective covers 60years of research aiming to understand the underlying mechanisms, linking major breakthroughs to current progress. It centers on the contributions of Ulrich Heber who had pioneered novel concepts, fundamental methods, and mechanistic understanding of photosynthesis. An important first step was the development of non-aqueous preparation of chloroplasts allowing the investigation of chloroplast metabolites ex vivo (meaning that the obtained results reflect the in vivo situation). Later on, intact chloroplasts, retaining their functional envelope membranes, were isolated in aqueous media to investigate compartmentation and exchange of metabolites between chloroplasts and external medium. These studies elucidated metabolic interaction between chloroplasts and cytoplasm during photosynthesis. Experiments with isolated intact chloroplasts clarified that oxygenation of ribulose-1.5-bisphosphate generates glycolate in photorespiration. The development of non-invasive optical methods enabled researchers identifying mechanisms that balance electron flow in the photosynthetic electron transport system avoiding its over-reduction. Recording chlorophyll a (Chl a) fluorescence allowed one to monitor, among other parameters, thermal energy dissipation by means of 'nonphotochemical quenching' of the excited state of Chl a. Furthermore, studies both in vivo and in vitro led to basic understanding of the biochemical mechanisms of freezing damage and frost tolerance of plant leaves, to SO2 tolerance of tree leaves and dehydrating lichens and mosses.

A new nonconvex approach to low-rank matrix completion with application to image inpainting

The problem of recovering a low-rank matrix from partial entries, known as low-rank matrix completion, has been extensively investigated in recent years. It can be viewed as a special case of the affine constrained rank minimization problem which is NP-hard in general and is computationally hard to solve in practice. One widely studied approach is to replace the matrix rank function by its nuclear-norm, which leads to the convex nuclear-norm minimization problem solved efficiently by many popular convex optimization algorithms. In this paper, we propose a new nonconvex approach to better approximate the rank function. The new approximation function is actually the Moreau envelope of the rank function (MER) which has an explicit expression. The new approximation problem of low-rank matrix completion based on MER can be converted to an optimization problem with two variables. We then adapt the proximal alternating minimization algorithm to solve it. The convergence (rate) of the proposed algorithm is proved and its accelerated version is also developed. Numerical experiments on completion of low-rank random matrices and standard image inpainting problems have shown that our algorithms have better performance than some state-of-art methods.

Damaged RC beams strengthened with GFRP

In recent years one of the most important duty of civil engineers is to define methods of rehabilitation both for historic and modern structures. Reinforced concrete is a relatively modern material of construction and it is often damaged both with cracking due to loading or corrosion of reinforcement. In this paper undamaged and damaged reinforced concrete (RC) beams have been experimentally analyzed under bending loading with and without strengthening by near surface mounted (NSM) glass fiber reinforced polymer (GFRP) rod. A nondestructive method of control based on vibration tests has been utilized during the experiments on RC beams: experimental vibration tests have been carried out on RC beams without and with strengthening by GFRP rod assuming free-free ends and hinged ends. In the paper the envelope of Frequency Response functions (FRFs) obtained by the dynamic experimental tests are shown and the changes of natural frequency values are correlated to the damage degree of beam elements. A comparison of experimental and theoretical results is shown and discussed.

Robust PCA Using Matrix Factorization for Background/Foreground Separation

Background/foreground separation has become an inevitable step in numerous image/video processing applications, such as image/video inpainting, anomaly detection, motion segmentation, augmented reality, and so on. Recent low-rank based approaches, such as robust principal component analysis separating a data matrix into a low-rank matrix with a sparse matrix, have achieved encouraging performance. However, these approaches usually need relatively high computation cost, mainly due to calculation of full or partial singular value decomposition of large matrices. On the other hand, the nuclear norm is widely exploited as a convex surrogate of the original rank function, while it is not a tighter envelope of the original rank function. To address these above-mentioned issues, this paper proposes a fast background/foreground separation algorithm in which the low-rank constraint is solved by a matrix factorization scheme, thus heavily reducing the computation cost. We further adopt two non-convex low-rank approximations to improve the robustness and flexibility of the traditional nuclear norm. In comparison with the state-of-the-art low-rank reconstruction methods, experimental results on challenging data sets, which contain different real data sets, show our superior performance in both image clarity and computation efficiency.

Interband Absorption and Photoluminescence in the Cylindrical Layered CdS/HgS/CdS Heterostructure

Within the approximation of an isotropic effective mass, the one-particle states of charge carriers in the layered CdS/HgS/CdS heterostructure are considered. It is shown that under conditions in which the strong-quantization regime is realized in the HgS layer, the spatial localization of charge carriers is realized there with the maximum probability. The energy spectrum and envelopes of the wave functions of the electron and hole states are computed in the structure under consideration. The interband optical absorption is computed, when the system is a layered cylindrical quantum dot and when there is a free motion of the charge carriers along the symmetry axis. For the same cases, the photoluminescence spectrum is also considered.

Martingale Optimal Transport with Stopping

We solve the martingale optimal transport problem for cost functionals represented by optimal stopping problems. The measure-valued martingale approach developed in [A. M. G. Cox and S. Kallblad, SIAM J. Control Optim., 55 (2017), pp. 3409--3436] allows us to obtain an equivalent infinite dimensional controller-stopper problem. We use the stochastic Perron's method and characterize the finite dimensional approximation as a viscosity solution to the corresponding HJB equation. It turns out that this solution is the concave envelope of the cost function with respect to the atoms of the terminal law. We demonstrate the results by finding explicit solutions for a class of cost functions.

Functional envelope of a non-autonomous discrete system

Abstract Let (X, F = {fn}n =0 ∞) be a non-autonomous discrete system by a compact metric space X and continuous maps fn : X → X, n = 0, 1, ....We introduce functional envelope (S(X), G = {Gn}n =0 ∞), of (X, F = {fn}n =0 ∞), where S(X) is the space of all continuous self maps of X and the map Gn : S(X) → S(X) is defined by Gn(ϕ) = Fn ∘ ϕ, Fn = fn ∘ fn-1 ∘ . . . ∘ f1 ∘ f0. The paper mainly deals with the connection between the properties of a system and the properties of its functional envelope.

Mapping physical problems on fractals onto boundary value problems within continuum framework

In this Letter, we emphasize that methods of fractal homogenization should take into account a loop structure of the fractal, as well as its connectivity and geodesic metric. The fractal attributes can be quantified by a set of dimension numbers. Accordingly, physical problems on fractals can be mapped onto the boundary values problems in the fractional-dimensional space with metric induced by the fractal topology. The solutions of these problems represent analytical envelopes of non-analytical functions defined on the fractal. Some examples are briefly discussed. The interplay between effects of fractal connectivity, loop structure, and mass distributions on electromagnetic fields in fractal media is highlighted. The effects of fractal connectivity, geodesic metric, and loop structure are outlined.

Proof of concept simulator demonstration of a physics based self-preserving flight envelope protection algorithm

This article discusses the development of an adaptive protection algorithm which is based on a physical approach, with the purpose to keep a closed loop aircraft with manual control laws within the actual safe flight envelope, even in the presence of failures or disturbances. Adaptive estimation of the flight envelope guarantees that not only flap changes, but also damage (e.g. icing) and external disturbances such as wind can be taken into account. This method is robust with respect to uncertainties in the estimates for the aerodynamic properties. This updated information makes the flight control laws more self-preserving and prevents loss of control in flight. This development can extend the functional envelope of the nominal law and reduce the need to switch from nominal to alternate law in the presence of certain failures. This algorithm has been applied on a simulation model of a medium range passenger aircraft and the setup has been implemented and evaluated in the DLR Robotic Motion Simulator at the German Aerospace Center as a proof of concept demonstration.

Functional envelope for model-free sufficient dimension reduction

In this article, we introduce the functional envelope for sufficient dimension reduction and regression with functional and longitudinal data. Functional sufficient dimension reduction methods, especially the inverse regression estimation family of methods, usually involve solving generalized eigenvalue problems and inverting the infinite-dimensional covariance operator. With the notion of functional envelope, essentially a special type of sufficient dimension reduction subspace, we develop a generic method to circumvent the difficulties in solving the generalized eigenvalue problems and inverting the covariance directly. We derive the geometric characteristics of the functional envelope and establish the asymptotic properties of related functional envelope estimators under mild conditions. The functional envelope estimators have shown promising performance in extensive simulation studies and real data analysis.

On the lower semicontinuous envelope of functionals defined on polyhedral chains

In this note we prove an explicit formula for the lower semicontinuous envelope of some functionals defined on real polyhedral chains. More precisely, denoting by H:R→[0,∞) an even, subadditive, and lower semicontinuous function with H(0)=0, and by ΦH the functional induced by H on polyhedral m-chains, namely ΦH(P)≔∑i=1NH(θi)Hm(σi),for every P=∑i=1Nθi〚σi〛∈Pm(Rn),we prove that the lower semicontinuous envelope of ΦH coincides on rectifiable m-currents with the H-mass MH(R)≔∫EH(θ(x))dHm(x) for every R=〚E,τ,θ〛∈Rm(Rn).

Characterization of 4 Million Micro-Bump Interconnections at 7.6- $\mu \text{m}$ Pitch for 3-D Stacked 16 Million Pixel Image Sensor

We developed and reported on a 3-D stacked CMOS image sensor (CIS) with a massive number of micro-bump interconnections placed at a narrow pitch between silicon substrates that pushes the envelope of CIS functions. The resistances of the interconnections were measured to be less than one hundredth of an ohm per bump with a test structure. There were, however, a small number of defective micro bumps with much higher impedance among the four million interconnections of the sensor. We developed a method for distinguishing defective interconnections from other defects and evaluated all interconnection resistances in a short amount of time with additional circuits in the CIS with reduced variable factors by using a modified current flow mode. This method makes it possible not only to identify defective interconnections but also to measure their impedances with less fluctuation.

Convex and concave envelopes: Revisited and new perspectives

We discuss two approaches to approximate the convex and concave envelopes of bilinear functions over hypercubes. The first approach is based on a semidefinite program. The second approach considers some predefined cover sets of a hypercube and leads to a linear program. Then we establish a connection between the convex envelope of a bilinear function and the concave envelope of a piecewise linear function. Numerical experiments are conducted to compare the two approaches. As an extension, a novel approach is discussed.

Type W Human Endogenous Retrovirus (HERV-W) Integrations and Their Mobilization by L1 Machinery: Contribution to the Human Transcriptome and Impact on the Host Physiopathology

Human Endogenous Retroviruses (HERVs) are ancient infection relics constituting ~8% of our DNA. While HERVs’ genomic characterization is still ongoing, impressive amounts of data have been obtained regarding their general expression across tissues. Among HERVs, one of the most studied is the W group, which is the sole HERV group specifically mobilized by the long interspersed element-1 (LINE-1) machinery, providing a source of novel insertions by retrotransposition of HERV-W processed pseudogenes, and comprising a member encoding a functional envelope protein coopted for human placentation. The HERV-W group has been intensively investigated for its putative role in several diseases, such as cancer, inflammation, and autoimmunity. Despite major interest in the link between HERV-W expression and human pathogenesis, no conclusive correlation has been demonstrated so far. In general, (i) the absence of a proper identification of the specific HERV-W sequences expressed in a given condition; and (ii) the lack of studies attempting to connect the various observations in the same experimental conditions are the major problems preventing the definitive assessment of the HERV-W impact on human physiopathology. In this review, we summarize the current knowledge on the HERV-W group presence within the human genome and its expression in physiological tissues as well as in the main pathological contexts.

Characteristic measurement for femtosecond laser pulses using a GaAs PIN photodiode as a two-photon photovoltaic receiver

Photodiodes that exhibit a two-photon absorption effect within the spectral communication band region can be useful for building an ultra-compact autocorrelator for the characteristic inspection of optical pulses. In this work, we develop an autocorrelator for measuring the temporal profile of pulses at 1550 nm from an erbium-doped fiber laser based on the two-photon photovoltaic (TPP) effect in a GaAs PIN photodiode. The temporal envelope of the autocorrelation function contains two symmetrical temporal side lobes due to the third order dispersion of the laser pulses. Moreover, the joint time-frequency distribution of the dispersive pulses and the dissimilar two-photon response spectrum of GaAs and Si result in different delays for the appearance of the temporal side lobes. Compared with Si, GaAs displays a greater sensitivity for pulse shape reconstruction at 1550 nm, benefiting from the higher signal-to-noise ratio of the side lobes and the more centralized waveform of the autocorrelation trace. We also measure the pulse width using the GaAs PIN photodiode, and the resolution of the measured full width at half maximum of the TPP autocorrelation trace is 0.89 fs, which is consistent with a conventional second-harmonic generation crystal autocorrelator. The GaAs PIN photodiode is shown to be highly suitable for real-time second-order autocorrelation measurements of femtosecond optical pulses. It is used both for the generation and detection of the autocorrelation signal, allowing the construction of a compact and inexpensive intensity autocorrelator.

Study of the role of plant nuclear envelope and lamina-like components in nuclear and chromatin organisation using 3D imaging

The linker of nucleoskeleton and cytoskeleton (LINC) complex is an evolutionarily well-conserved protein bridge connecting the cytoplasmic and nuclear compartments across the nuclear membrane. While recent data supports its function in nuclear morphology and meiosis, its implication for chromatin organisation has been less studied in plants. The first aim of this work was to develop NucleusJ a simple and user-friendly ImageJ plugin dedicated to the characterisation of nuclear morphology and chromatin organisation in 3D. NucleusJ quantifies 15 parameters including shape and size of nuclei as well as intra-nuclear objects and their position within the nucleus. A step-by-step documentation is available for self-training, together with data sets of nuclei with different nuclear organisation. Several improvements are ongoing to release a new version of this plugin. In a second part of this work, 3D imaging methods have been used to investigate nuclear morphology and chromatin organisation in interphase nuclei of the plant model Arabidopsis thaliana in which heterochromatin domains cluster in conspicuous chromatin regions called chromocentres. Chromocentres form a repressive chromatin environment contributing to the transcriptional silencing of repeated sequences a general mechanism needed for genome stability. Quantitative measurements of 3D position of chromocentres in the nucleus indicate that most chromocentres are situated in close proximity to the periphery of the nucleus but that this distance can be altered according to nuclear volume or in specific mutants affecting the LINC complex. Finally, the LINC complex is proposed to contribute at the proper chromatin organisation and positioning since its alteration is associated with the release of transcriptional silencing as well as decompaction of heterochromatic sequences. The last part of this work takes advantage of available genomic sequences and RNA-seq data to explore the evolution of NE proteins in plants and propose a minimal requirement to built the simplest functional nuclear envelope. Altogether, work achieved in this thesis associate genetics, molecular biology, bioinformatics and imaging to better understand the contribution of the nuclear envelope in nuclear morphology and chromatin organisation and suggests the functional implication of the LINC complex in these processes.

MIP formulation improvement for large scale security constrained unit commitment with configuration based combined cycle modeling

As a part of the day-ahead market clearing process, Midcontinent Independent System Operator (MISO) solves one of the largest and most challenging Security Constrained Unit Commitment (SCUC) models. Better computational performance of SCUC models not only improves the market efficiency but also facilitates future market developments. This paper introduces recent developments in SCUC formulation with configuration based combined cycle modeling in MISO, which include the improvement on constraints associated with binary variables, the improvement of formulation on piecewise linear incremental energy curve (PWL) and reduction of non-zeros by aggregating variables (AGG). Furthermore, mathematical proof shows that the proposed enhanced locally ideal PWL model is the convex envelope of the PWL cost function. To illustrate the effectiveness of the proposed formulation, numerical results and analysis based on MISO system are presented.

Analysis of cracked RC beams under vibration

Among the methods of monitoring of integrity, vibration analysis is more convenient as non-destructive testing (NDT) method. Many aspects regarding the vibration monitoring of the structural integrity of damaged RC elements have not been completely analysed in literature. The correlation between the development of the crack pattern on concrete surface under bending loadings, as well as the width and depth of cracks, and the variation of dynamic parameters on a structural element is an important aspects that has to be more investigated. This paper deals with cracked RC beams controlled by NDT based on natural vibration, which may be correlated to damage degree due to cracking of concrete under severe state of loading. An experimental investigation on the assessment of RC beams in different scale under loading has been done through dynamic tests in different constraint conditions of edges measuring frequency values and frequency variation. Envelope of Frequency Response Functions (FRFs) are shown and the changes of natural frequency values are related to the damage degree of RC beams subjected to static tests. Finally, a comparison between data obtained by finite element analysis and experimental results is shown.