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This paper investigates an attitude control method for the CubeSat using a moving mass actuator to solve the problem of the strong aerodynamic disturbance in low Earth orbit. The rotational and translational equations are derived for the CubeSat with three moving masses, and their dynamic effects are analyzed. A magnetorquer is used to prevent the underactuation of the attitude control system. The movement of moving masses is slowed down by using a discrete double-loop Proportion Integral Differential control method, thereby reducing the fast time-varying additional disturbance. A nonlinear observer is used for the precise estimation of the slow time-varying disturbance. Notably, the ideal attitude control torque is allocated to two actuators by using the proposed control allocation algorithm. Numerical simulation indicates that the attitude convergence accuracy is up to ±0.1° despite the uncertain dynamics, unknown disturbances, and dynamic effects. The results verify the feasibility of the proposed control method. [ABSTRACT FROM AUTHOR]

In this paper, an improved strong tracking unscented Kalman filter based on multiplicative modified Rodrigues parameters (MRPs) is proposed for satellite attitude estimation. The multiplicative MRPs are superior to additive MRPs in terms of attitude representation, especially when attitude angles are large. By minimizing the loss function in Wahba’s problem, a novel method of weighted average for MRPs is derived to replace the simple procedure. The generation of Sigma points, update of state variables, and calculation of covariance matrices are all different from the existing literature to maintain the multiplicative property of MRPs. Simulation results by raw telemetry data from the on-orbit CubeSat Enlai-1 demonstrate the excellent performance of the proposed filter under large attitude angles. [ABSTRACT FROM AUTHOR]

There are three problems in applying central difference Kalman filter (CDKF) to attitude estimation of low‐cost satellite: (1) the negative definiteness and asymmetry of the covariance matrix caused by limited computing power and storage space of the onboard microprocessor may result in calculation divergence, (2) the system model uncertainty including model mismatch and state mutation caused by environmental disturbances from inside and outside the satellite will lead to filter divergence, (3) the addition operation on quaternions violates the normalization constraint, while enforced unitization will introduce approximation errors. To solve the above problems, this article proposes the multiplicative quaternion square root strong tracking CDKF (MQSRSTCDKF), in which three improvements to basic CDKF are made: (1) square roots of covariance matrices are adopted for information propagation in place of covariance matrices themselves, which always guarantees the symmetry and positive definiteness of covariance matrices, (2) multiple fading factors are employed to adjust square root of the covariance matrix of predicted state variables, and then adjust the gain matrix to make the filter attach more weight to sensor measurements than to corrupt state predictions caused by model uncertainties, (3) multiplication operation on quaternions is conducted instead of the addition one, which makes the normalization constraint on quaternions naturally satisfied without enforced unitization. Numerical simulation based on raw telemetry data from the on‐orbit CubeSat NJUST‐1 shows that MQSRSTCDKF has higher attitude estimation accuracy, faster convergence speed, and stronger robustness to filter divergence and calculation divergence than basic CDKF. [ABSTRACT FROM AUTHOR]

In this work, we mainly investigate the consistency and strong convergence rate for the nearest neighbor density estimator based on φ -mixing random samples. The weak consistency, complete consistency, the rates of complete consistency and strong consistency for the nearest neighbor estimator of density function based on φ -mixing random samples are established. The results obtained in the article extend some corresponding ones for independent samples. [ABSTRACT FROM AUTHOR]

This paper addressed a strongly nonlinear problem caused by status mutation in CubeSat attitude estimation system. The multiple fading factors are employed to make different state channels have separate adjustment ability, which enhances the tracking performance for status mutation. The second-order difference transformation is adopted to improve the approximation accuracy of state posterior mean and covariance. Therefore, a multiple fading second-order central difference Kalman filter (MFSCDKF) is formed for CubeSat attitude estimation system in the presence of status mutation. Compared with the single fading factor first-order central difference Kalman filter, the proposed one can improve tracking performance and estimation accuracy simultaneously. Simulation results based on real telemetry data from the on-orbit CubeSat NJUST-1 verify the effectiveness of the proposed MFSCDKF. [ABSTRACT FROM AUTHOR]

This paper investigates an attitude control technique for a low Earth orbit nanosatellite with moving masses based on the active use of aerodynamic forces. A speed-adaptive dynamic surface control scheme is designed to comprehensively solve the practical problems of aerodynamic model error, the dynamic effect of movement, stroke limitation, and slow convergence. Multiple constraints are imposed on the inputs to reduce the fast-varying dynamic effect of the masses to be negligible. Other slow-varying disturbances are precisely estimated by a nonlinear observer. In particular, to resolve the contradiction between the overshoot and the attitude convergence speed, a novel adaptive law is designed based on the smooth hyperbolic tangent function to adjust the convergence parameter within the given boundary. Moreover, considering the actual physical limitation, hard constraints are imposed on two actuators. Finally, by using the Lyapunov approach, it is proven that, despite uncertain dynamics, unknown disturbances and input constraints, the attitude error can be adjusted to be arbitrarily small by choosing the proper parameters. A semi-physical simulation platform is built to verify the feasibility of the moving mass actuator and the effectiveness and robustness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

In this paper, the complete moment convergence for arrays of rowwise negatively superadditive dependent (NSD, for short) random variables is established. As applications, the complete convergence and the Marcinkiewicz-Zygmund type strong law of large numbers for arrays of rowwise NSD random variables are also obtained. Finally, a numerical simulation is carried out to verify the validity of theoretical results. The results obtained in the paper extend the corresponding ones in the literature. [ABSTRACT FROM AUTHOR]

Thiophenol (PhSH) is toxic to the environment and biological systems although it is an indispensable material in the synthetic processes of chemical products. In this work, we designed and synthesized a malonitrile-based colorimetric and deep-red emission fluorescent dosimeter specifically for thiophenol detection by switching on the intramolecular charge transfer process. The 2,4-dinitrobenzene moiety in the probe could be cleaved by thiophenol, which led to strong deep-red fluorescence increase at 645 nm (50-fold) with a low detection limit of 9 nM. The maximum plateau of emission intensity was reached in about 30 min after the addition of thiophenol. Simultaneously, the presence of thiophenol could result in a prominent color change from orange to blue. Furthermore, the dosimeter could quantitatively sense thiophenol spiked in water samples and successfully visualize thiophenol in living SH-SY5Y cells. [ABSTRACT FROM AUTHOR]

• A deep-red emission fluorescent probe (DRP-Cys) for Cys based on a hemicyanine scaffold was developed. • A tailed malononitrile group could chromatically shift excitation/emission wavelengths to the deep-red emission range. • The probe could detect Cys with an ultrafast response time of about 1 min and a low limit of detection of 10 nM • The probe was also successfully applied for visualizing endogenous Cys in living HeLa cells and mice. It is still challenging how to selectively and sensitively detect cysteine in living systems which plays crucial roles in many physiological and biological processes. Here, we developed a deep-red emission fluorescent probe (DRP-Cys) for Cys based on a hemicyanine scaffold. A tailed malononitrile group could chromatically shift excitation/emission wavelengths to avoid the limitations such as photo-damage or auto-fluorescence in biological samples. Compared with other amino acids, Cys could trigger the Michael addition reaction to release a dramatic enhancement in fluorescence centering at around 645 nm in DMSO aqueous solution under physiological conditions with an ultrafast response time of about 1 min and a low limit of detection of 10 nM which significantly benefited from the introduction of the malononitrile moiety. The probe was also successfully applied for visualizing endogenous Cys in living HeLa cells and mice with low cytotoxicity and good cell-membrane permeability. [ABSTRACT FROM AUTHOR]

It is challenging to simultaneously discriminate two or three biothiols from each other due to their structural similarities as well as reactions sites. The development of multiple-signal fluorescent probes would be a promising way to overcome this issue. Herein, a two-separated-emission fluorescent probe for biothiols was developed based on the combination of nitrobenzofurazan (NBD) and phenanthroimidazole fluorophores linked by a facile ether bond. In the presence of Cys and Hcy, the probe in DMF–H2O demonstrates two separate fluorescence emissions at 480 and 550 nm upon excitation of two independent wavelengths. However, addition of GSH to the probe only leads to blue fluorescence at 480 nm. This difference can be reasonably ascribed to the fact that the NBD–GSH intermediate, unlike NBD–Cys/Hcy, cannot undergo an intramolecular cyclization–rearrangement reaction. The probe exhibits a rapid response with low limits of detection (14.7 nM for Cys, 14.4 nM for Hcy, and 13.4 nM for GSH) with large concentration ranges of 0–100 μM for Cys/Hcy and 0–200 μM for GSH. Furthermore, the probe is successfully applied to simultaneously distinguish endogenous Cys, Hcy, and GSH in living HeLa cells and zebrafish models. [ABSTRACT FROM AUTHOR]

Zn2+ plays fundamental roles in cellular metabolism and apoptosis, as well as neurotransmission. However, how to fast detect Zn2+ in biology is still challenging and meaningful. In this study, we rationally synthesized a simple OFF–ON fluorescent probe for fast detection of Zn2+ based on intramolecular charge transfer and chelation-enhanced fluorescence. Addition of Zn2+ into the probe induced a significant fluorescence enhancement with a bathochromic shift of 55 nm. Moreover, the probe demonstrated excellent sensitivity (detection limit = 0.072 μM) and outstanding selectivity toward Zn2+ and an ultra-fast response rate of two seconds. The recognition mechanism of the probe toward Zn2+ was fully confirmed by HRMS and 1H NMR spectra, as well as TDDFT calculations. Furthermore, the probe could rapidly visualize Zn2+ in living cells and zebrafish models in bioimaging experiments with low cytotoxicity and good biocompatibility. [ABSTRACT FROM AUTHOR]

Hydrazine is carcinogenic and highly toxic so that it can lead to serious environmental contamination and serious health risks although it has been extensively used as an effective propellant and an important reactive base in industry. Thus, the development of two-emission NIR fluorescent probes for rapid detection of hydrazine with high selectivity and sensitivity is of significance and of great challenge in both biological and environmental sciences. Here, we report a two-emission colorimetric fluorescent probe for the specific detection of hydrazine based on hydrazinolysis reaction under physiological conditions. In the presence of hydrazine, the probe showed an extremely remarkable fluorescence enhancement at 627 nm compared to the decrease at 814 nm excited at different wavelength in aqueous solution. This distinct difference of two emission intensities is suitable for detection of low concentration hydrazine with a detection limit of 0.38 ppb. Addition of hydrazine resulted in a remarkable color change from blue-green to red observed by the naked eye. Kinetic study indicated a fast response of the probe toward hydrazine in minutes. Furthermore, the probe can bioimage hydrazine in living HeLa cells and mice with low cytotoxicity and excellent biocompatibility. [ABSTRACT FROM AUTHOR]

The trinuclear NiII cluster [Ni3(bpca)2(bpy)2(H2O)4](NO3)4 ·H2O ( 1) (bpca- = anion of bis(2-pyridylcarbonyl)amine, bpy = 2, 2′-bipyridine) was isolated. Single crystal X-ray diffraction analysis showed that three crystallographically independent NiII ions are located in a six-coordinate distorted octahedral environment, bridged by the organic spacer bpca-. The crystal lattice is stabilized by hydrogen bonds, which are linking the Ni3 cations and NO3- anions into a three-dimensional framework. Variable-temperature magnetic susceptibility for complex 1 in the range 2-300 K indicates the presence of weak antiferromagnetic interactions in the Ni3 unit with J = -0.67 cm-1. [ABSTRACT FROM AUTHOR]

The title compound, [MnCl2(C24H20N6)], has been synthesized and characterized based on the multifunctional ligand 2,5-bis(2,2′-bipyridyl-6-yl)-3,4-diazahexa-2,4-diene ( L). The MnII centre is five-coordinate with an approximately square-pyramidal geometry. The L ligand acts as a tridendate chelating ligand. The mononuclear molecules are bridged into a one-dimensional chain by two C-H...Cl hydrogen bonds. These chains are assembled into a two-dimensional layer through π-π stacking interactions between adjacent uncoordinated bipyridyl groups. Furthermore, a three-dimensional supramolecular framework is attained through π-π stacking interactions between adjacent coordinated bipyridyl groups. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel chiral dinuclear Cu(II) cluster has been synthesized and characterized. [•] The two Cu ions in complex 1 are sitting in a distorted octahedral arrangement. [•] Inversion crystallographic symmetry gives dimers as either Λ or Δ isomers. [•] Magnetic susceptibility measurements indicate the presence of ferromagnetic Cu⋯Cu exchange. [ABSTRACT FROM AUTHOR]

The title compound, {[Cd4(C5H2N2O4)(C5HN2O4)2(C10H8N2)2(H2O)]·2H2O} n, crystallized in the monoclinic space group P21/ n and displays a three-dimensional architecture. The asymmetric unit is composed of four crystallographically independent CdII centres, two triply deprotonated pyrazole-3,5-dicarboxylic acid molecules, one doubly deprotonated pyrazole-3,5-dicarboxylic acid molecule, two 2,2′-bipyridine ligands, one coordinated water molecule and two interstitial water molecules. Interestingly, the CdII centers exhibit two different coordination numbers. Two CdII centres adopt a distorted octahedral arrangement and a third a trigonal-prismatic geometry, though they are all hexacoordinated. However, the fourth CdII center is heptacoordinated and displays a pentagonal-bipyramidal geometry. The three anionic ligands adopt μ3-, μ4- and μ5-bridging modes, first linking CdII centers into a one-dimensional wave-like band, then into a wave-like layer and finally into a three-dimensional coordination framework, which is stabilized by hydrogen bonds. [ABSTRACT FROM AUTHOR]

Abstract: A novel tetranuclear mixed-valence manganese(II/III) cluster [Mn4(hmp)6(N3)4] (1) where hmp is the anion of 2-hydroxymethylpyridine, was obtained by the reaction of manganese perchlorate with hmpH and NaN3 in acetonitrile. Complex 1 was characterized by chemical analysis, IR spectroscopy, single crystal X-ray diffraction and variable-temperature magnetic susceptibility studies. Complex 1 crystallizes in triclinic system with space group Pī consisting of mixed-valence Mn ions whose coordination geometry can be described as distorted octahedron. The magnetic properties were studied in the temperature range of 1.9–300K and the results show that mixed-valence Mn ions are ferromagnetically coupled in the cluster leading to an S =9 ground state. [Copyright &y& Elsevier]

Three new heterospin complexes derived from trans-oxamido-bridged copper(II) binuclear units [Cu2(oxen), oxen = N,N-bis(2-aminoethyl)oxamide] and pyridine-substituted nitronyl nitroxides (o-, m-, and p-PYNN) were synthesized and characterized structurally and magnetically. Complexes 1 and 2 are four-spin complexes. Interestingly, it is found that in complex 3, the Cu(II) ions and m-PYNN units are arranged to form 1D double-stranded helical chains, which to the best of our knowledge is the first example of a metal nitronyl nitroxide complex with such a 1D helical structure. The temperature dependencies of the magnetic susceptibilities of 1 and 2 were fitted to the four-spin model with the Hamiltonian Ĥ = -2JŜCu1ŜCu2 - 2j(ŜCu1Ŝrad1 - ŜCu2srad2), leading to J = -150.5 cm-1 and j = 47.2 cm-1 for complex 1 and J = -191.7 cm-1 and j = -18.9 cm-1 for complex 2. The temperature dependence of the magnetic susceptibility of complex 3 was approximately simulated with a simple model composed of a dimer of Cu(II) ions and two m-PYNN molecules. The best fitting leads to the values of J = -183.0 cm-1 and zJ' = -0.55 cm-1 for the magnetic exchange of two Cu(II) ions through the oxamide bridge and that between the dimer of Cu(II) ions and two m-PYNN molecules, respectively. The antiferromagnetic exchange of oxamido-bridged Cu(II) ions in complexes 1-3 is strong. The strength of such antiferromagnetic interactions is also similar for the three complexes. [ABSTRACT FROM AUTHOR]

• The article reports an ultrafast far-red fluorescent probe (Cou-DNBS) for biothiols with a large Stokes shift of 131 nm. • The probe was constructed by fusing an additional benzene ring. • The probe showed ultrafast response to biothiols, emitting a strong red fluorescence at 617 nm on excitation at 480 nm. • The probe was successfully employed to visualize biothiol fluctuations in living cells damaged by oxidative stress and mice. Intracellular biothiols are correlated with many diseases such as nerve disorder and Parkinson's disease likely due to a redox imbalance. In this work, we designed an ultrafast fluorescent probe (Cou-DNBS) for biothiols with a large Stokes shift (131 nm). The probe was constructed through linking the 2,4-dinitrobenzenesulfonyl moiety as the specially recognizing biothiols site to an iminocoumarin fluorophore Cou-NH obtained by fusing an additional benzene ring. The presence of biothiols could ultrafast perform a significant fluorescence emission at 617 nm upon the excitation of 480 with the low limits of detection (2.5 nM for Cys, 1.7 nM for Hcy and 0.84 nM for GSH). HRMS spectra as well as theoretical calculations further evidenced the rationale of recognition mechanism. Furthermore, the probe can successfully visualize endogenous biothiol recovery in living cells damaged by H 2 O 2. [ABSTRACT FROM AUTHOR]

• A simple dual-emission fluorescent biothiol probe was designed and synthesized. • The probe could discriminate cysteine from homocysteine and glutathione in both blue and green channels. • The probe could be successfully applied for visualizing biothiols in living HeLa cells and zebrafish. Cellular biothiols function crucially and differently in physiological and pathological processes. However, it is still challenging to detect and discriminate thiols within a single one molecule, especially for cysteine (Cys) and homocysteine (Hcy). In this study, a simple two-emission turn-on fluorescent biothiol probe (ICN-NBD) was rationally designed and synthesized through a facile ether bond linking 7-nitro-1,2,3-benzoxadiazole (NBD) and phenanthroimidazole containing a cyano tail. The probe in the presence of Cys elicited two fluorescence responses at 470 nm and 550 nm under excitation at 365 nm and 480 nm, respectively, because of the concomitant generation of both the fluorophore and NBD- N -Cys. In contrast, addition of Hcy and glutathione (GSH) could result in only a blue fluorescence enhancement at 470 nm. which was reasonably attributed to rearrangement from NBD- S -Hcy/GSH to NBD- N -Hcy/GSH as a result of geometrical constraints or solvent effects. Therefore, the fluorescent probe with the NBD scaffold could detect biothiols and simultaneously discriminate Cys from Hcy/GSH in both blue and green channels. The probe has been successfully applied for visualizing biothiols in living cells and zebrafish. [ABSTRACT FROM AUTHOR]