Dual propagation inversion of truncated signals

Fourier transforms occur in a variety of chemical systems and processes. A few examples include obtaining spectral information from correlation functions, energy relaxation processes, spectral densities obtained from force autocorrelation functions, etc. In this article, a new functional transform, named the dual propagation inversion (DPI) is introduced. The DPI functional transform can be applied to a variety of problems in chemistry, such as Fourier transforms of time correlation functions, energy relaxation processes, rate theory, etc. The present illustrative application is to generating the frequency representation of a discrete, truncated time-domain signal. The DPI result is compared with the traditional Fourier transform applied to the same truncated time signal. For both noise-free and noise-corrupted time-truncated signals, the DPI spectrum is found to be more accurate, particularly as the signal is more severely truncated. In the DPI, the distributed-approximating-functional free propagator is used to propagate and denoise the signal simultaneously. Received: 30 January 2000 / Accepted: 6 July 2000 / Published online: 23 November 2000     

Charge-Transfer Complex Doped Photothermal Hydrogels for Discriminating Circularly Polarized Near-Infrared Light

Hydrogels behave as potential candidates to investigate circularly polarized light (CP)-matter interaction, which however suffer from small sensitivity towards circular polarization. Here we report a general protocol to build hydrogels from π-conjugated amino acids with coassembled charge-transfer (CT) complexes, covering a wide scope of donors and acceptors, which were incorporated into stable hydrogel matrices. CT complexes formed block coassemblies with gelators, induced the emergence of macroscopic chiral helices, where efficient chirality transfer occurs to realize tunable Cotton effects from visible light to NIR-I region depending on the structures of CT pairs. The hybrid hydrogels showed tunable photothermal performances with excellent heating-cooling cycling durability. Circularly polarized NIR light selectively triggered gel-solution phase transition at different timescales. Left- and right-CP illumination generates up to 2.5 folds difference in gel collapse time that allows for direct discrimination by naked eyes.     

High‐Throughput Bioassays using “Dip‐and‐Go” Multiplexed Electrospray Mass Spectrometry

A multiplexed system based on inductive nanoelectrospray mass spectrometry (nESI‐MS) has been developed for high‐throughput screening (HTS) bioassays. This system combines inductive nESI and field amplification micro‐electrophoresis to achieve a “dip‐and‐go” sample loading and purification strategy that enables nESI‐MS based HTS assays in 96‐well microtiter plates. The combination of inductive nESI and micro‐electrophoresis makes it possible to perform efficient in situ separations and clean‐up of biological samples. The sensitivity of the system is such that quantitative analysis of peptides from 1–10 000 nm can be performed in a biological matrix. A prototype of the automation system has been developed to handle 12 samples (one row of a microtiter plate) at a time. The sample loading and electrophoretic clean‐up of biosamples can be done in parallel within 20 s followed by MS analysis at a rate of 1.3 to 3.5 s per sample. The system was used successfully for the quantitative analysis of BACE1‐catalyzed peptide hydrolysis, a prototypical HTS assay of relevance to drug discovery. IC₅₀ values for this system were in agreement with LC‐MS but recorded in times more than an order of magnitude shorter.     

Helical secondary structures and supramolecular tilted chirality in N-terminal aryl amino acids with diversified optical activities

Helix structures at atomic/molecular level have not been found in self-assembled peptide seque nce with less than three residues.As β-sheet supramolecular secondary structures have been discovered in solidstate amino acids,we here report the conjugation of simple N-terminal aryl protecting group could give rise to helical supramolecular secondary structures in solid-state,which determines the optical activities of the adjacent aryl groups.The carboxylic acid-involved asymmetric H-bonds in N-te rminal aryl amino acids induce the emergence of super-helical structures of amino acid residues and aryl groups.In most cases,supramolecular tilted chirality of aryl groups is opposite to that of amino acid sequences,of which handedness and helical pitch are determined by the H-bond modalities.Determining correlation between supramolecular tilted chirality of aryl segments and their chiroptical activities is firstly unveiled,which was verified by the computational results based on density functional theory.Most aryl amino acids self-assembled by nanoprecipitation method via crystallization induced self-assembly into rigid one-dimensional microstructures with ultra-high Young's modulus.This study reveals the generic existence of chiral supramolecular structure s in aggregated amino acid derivatives and gives an in-depth investigation into the structural-property relationships,which could guide the rational design and screening of chiroptical supramolecular materials.     

Rapid determination of isocitrate dehydrogenase mutation status of human gliomas by extraction nanoelectrospray using a miniature mass spectrometer

Analytical and Bioanalytical Chemistry - Isocitrate dehydrogenase (IDH) I and II mutations in gliomas cause an abnormal accumulation of 2-hydroxyglutarate (2-HG) in these tumor cells. These...     

Semiparametric estimation in regression with missing covariates using single-index models

We investigate semiparametric estimation of regression coefficients through generalized estimating equations with single-index models when some covariates are missing at random. Existing popular semiparametric estimators may run into difficulties when some selection probabilities are small or the dimension of the covariates is not low. We propose a new simple parameter estimator using a kernel-assisted estimator for the augmentation by a single-index model without using the inverse of selection probabilities. We show that under certain conditions the proposed estimator is as efficient as the existing methods based on standard kernel smoothing, which are often practically infeasible in the case of multiple covariates. A simulation study and a real data example are presented to illustrate the proposed method. The numerical results show that the proposed estimator avoids some numerical issues caused by estimated small selection probabilities that are needed in other estimators.

     

Multi-wavelength photonic band gaps based on quasi-periodically poled lithium niobate ordered in Fibonacci sequences

We demonstrate a quasi-periodic structure exhibiting multiple photonic band gaps （PBGs） based on sub- micron-period poled lithium niobate （LN）. The structure consists of two building blocks, each containing a pair of antiparallel poled domains, arranged as a Fibonacci sequence. The gap wavelengths are analyzed with the Fibonacci sequence parameters such as the quasiperiodic indices and the average lattice parameter. The transmission properties are investigated by a traditional 4×4 matrix method. It has also been proved that the gap depth can be tuned by the lengths of poled domains.     

Electro-optic Solc-type flat-top bandpass filter based on periodically poled lithium niobate

Based on the spectrum waveform similarity (SWS) rule we discovered in periodically poled lithium niobate (PPLN), a compact tunable flat-top bandpass filter is proposed theoretically, from which the bandwidth of the flat-top waveform can be obtained. For practical application, tunable flat-top filter can be easily achieved by selecting appropriate electric field along the transverse direction of PPLN. The tolerance analysis for this kind of tunable flat-top bandpass filter is also presented.     

水相乙基化GC-AFS测定环境及生物样品中甲基汞

介绍基于水相乙基化和气相色谱（ＧＣ）－原子荧光（ＡＦＳ）的甲基汞分析法。水溶液中甲基汞与四乙基硼化钠反应生成甲乙基汞，由氮气吹扫捕集于Ｔｅｎａｘ管，然后由ＧＣ＿ＡＦＳ测定。应用于环境及生物样品，检测限为０５ｐｇＨｇ。     

Chiroptical Helices of N-Terminal Aryl Amino Acids through Orthogonal Noncovalent Interactions

In the solid state, amino acids (alanine and phenylglycine) with appended pyrene segments self-assembled into α-helix-like structures by asymmetrical H-bonds between carboxylic acid and amide segments, further inducing supramolecular tilted chirality of the achiral pyrenes. These structures bind melamine and electron-deficient units through H-bond and charge-transfer interactions, respectively. Charge-transfer interactions enhance the dissymmetry g-factor of absorption (g_abs; up to 1.4×10⁻²) with an extended Cotton effect active region (from 250 to 600 nm). Incorporating melamine inverts the handedness of circularly polarized luminescence and boosts the dissymmetry g-factor (g_lum). Melamine also induces macroscopic chirality at the nanoscale, whereby the 2D lamellar structures are transformed into 1D helices at the nanoscale, leading to giant tubular structures at the microscale.