Covalently Immobilized Regenerable Immunoaffinity Layer with Orientation-Controlled Antibodies Based on Z-Domain Autodisplay

A regenerable immunoaffinity layer comprising covalently immobilized orientation-controlled antibodies was developed for use in a surface plasmon resonance (SPR) biosensor. For antibody orientation control, antibody-binding Z-domain-autodisplaying Escherichia coli (E. coli) cells and their outer membrane (OM) were utilized, and a disuccinimidyl crosslinker was employed for covalent antibody binding. To fabricate the regenerable immunoaffinity layer, capture antibodies were bound to autodisplayed Z-domains, and then treated with the crosslinker for chemical fixation to the Z-domains. Various crosslinkers, namely disuccinimidyl glutarate (DSG), disuccinimidyl suberate (DSS) and poly (ethylene glycol)-ylated bis (sulfosuccinimidyl)suberate (BS(PEG)5), were evaluated, and DSS at a concentration of 500 μM was confirmed to be optimal. The E. coli-cell-based regenerable HRP immunoassay was evaluated employing three sequential HRP treatment and regeneration steps. Then, the Oms of E. coli cells were isolated and layered on a microplate and regenerable OM-based HRP immunoassaying was evaluated. Five HRP immunoassays with four regeneration steps were found to be feasible. This regenerable, covalently immobilized, orientation-controlled OM-based immunoaffinity layer was applied to an SPR biosensor, which was capable of quantifying C-reactive protein (CRP). Five regeneration cycles were repeated using the demonstrated immunoaffinity layer with a signal difference of <10%.

Thermal Noise Decoupling of Micro-Newton Thrust Measured in a Torsion Balance

The space gravitational wave detection and drag free control requires the micro-thruster to have ultra-low thrust noise within 0.1 mHz–0.1 Hz, which brings a great challenge to calibration on the ground because it is impossible to shield any spurious couplings due to the asymmetry of torsion balance. Most thrusters dissipate heat during the test, making the rotation axis tilt and components undergo thermal drift, which is hysteretic and asymmetric for micro-Newton thrust measurement. With reference to LISA’s research and coming up with ideas inspired from proportional-integral-derivative (PID) control and multi-timescale (MTS), this paper proposes to expand the state space of temperature to be applied on the thrust prediction based on fine tree regression (FTR) and to subtract the thermal noise filtered by transfer function fitted with z-domain vector fitting (ZDVF). The results show that thrust variation of diurnal asymmetry in temperature is decoupled from 24 μN/Hz1/2 to 4.9 μN/Hz1/2 at 0.11 mHz. Additionally, 1 μN square wave modulation of electrostatic force is extracted from the ambiguous thermal drift background of positive temperature coefficient (PTC) heater. The PID-FTR validation is performed with experimental data in thermal noise decoupling, which can guide the design of thermal control and be extended to other physical quantities for noise decoupling.

A New Method for Obtaining Model-Free Viscoelastic Material Properties from Atomic Force Microscopy Experiments Using Discrete Integral Transform Techniques

Viscoelastic characterization of materials at the micro- and nanoscales is commonly performed with the aid of force-distance relationships acquired using atomic force microscopy (AFM). The general strategy for existing methods is to fit the observed material behavior to specific viscoelastic models, such as generalized viscoelastic models or power-law rheology models, among others. Here we propose a new method to invert and obtain the viscoelastic properties of a material through the use of the Z-transform, without using a model. We present the rheological viscoelastic relations in their classical derivation and their Z-domain correspondence. We illustrate the proposed technique on a model experiment involving a traditional ramp-shaped force-distance AFM curve, demonstrating good agreement between the viscoelastic characteristics extracted from the simulated experiment and the theoretical expectations. We also provide a path for calculating standard viscoelastic responses from the extracted material characteristics. The new technique based on the Z-transform is complementary to previous model-based viscoelastic analyses and can be advantageous with respect to Fourier techniques due to its generality. Additionally, it can handle the unbounded inputs traditionally used to acquire force-distance relationships in AFM, such as “ramp” functions, in which the cantilever position is displaced linearly with time for a finite period of time.

Thermal Noise Decoupling of Micro-Newton Thrust Measured in a Torsion Balance

The space gravitational wave detection and drag free control requires the micro-thruster to have very low thrust noise within 0.1mHz~100mHz, which poses a great challenge to the ground thrust test. The evaluation and decoupling of thermal noise are the difficulties in the application of torsion balance for most thrusters dissipate heat in the experiment. The research has adopted a calibration scheme of micro-Newton thrust torsion balance. On the basis of Lisa Pathfinder's former research and using ideas inspired from PID control and multi time scale (MTS) for reference, the paper proposes to expand the state space of temperature to be applied on thrust prediction based on fine tree regression (FTR), to subtract the thermal noise filtered by transfer function fitted with z-domain vector fitting (ZDVF). The results show that the thrust amplitude thrust density in diurnal temperature fluctuation is decoupled from 24&mu;N/Hz1/2 to 4.9&mu;N/Hz1/2 at 0.11mHz. And the 1&mu;N square wave modulations of electrostatic fins (ESF) is extracted from the simultaneously ambiguous background of temperature for PTC's heating and cooling. The FTR method is well demonstrated in thermal noise decoupling and can guide the design of thermal control and be extended to other physical quantities for noise decoupling.

Waypoint following dynamics of a quaternion error feedback attitude control system

Closed-loop attitude steering is a concept for implementing an attitude trajectory by using a conventional quaternion error feedback controller to track the time-varying attitude reference, rather than to simply regulate to a desired orientation. This is done by sampling the reference input and executing the maneuver as a sequence of closely spaced regulating commands that are read out from the spacecraft’s command buffer. The idea has been employed in practice to perform zero-propellant maneuvers on the International Space Station and minimum-time maneuvers on NASA’s TRACE space telescope as well as NASA’s Lunar Reconnaissance Orbiter (LRO). A challenge for operational implementation of the idea is the limited capacity of a space vehicle’s command storage buffer, which is normally not designed with attitude tracking in mind. One approach to mitigate the problem is to downsample-and-hold the attitude commands so that the attitude control system (ACS) regulates to a series of waypoints. This article explores the waypoint following dynamics of a quaternion error feedback control law for such an approach. It is shown that downsample-and-hold induces a ripple between downsamples that causes the satellite angular rate to significantly overshoot the desired limit. Analysis in the z-domain is carried out in order to understand the phenomenon. An interpolating Chebyshev-type filter is proposed that allows the desired attitude trajectory to alternatively be encoded in terms of a small set of filter coefficients. Using the interpolating filter, the continuous-time reference trajectory can be reconstructed and issued at the ACS rate but with significantly reduced memory requirements. The ACS of the LRO is used as an example to illustrate the behavior of a practical ACS.

Elucidation of the complicated scenario of primate APOBEC3 gene evolution

APOBEC3 proteins play pivotal roles in defenses against retroviruses, including HIV-1, as well as retrotransposons. Presumably due to the evolutionary arms race between the hosts and retroelements, APOBEC3 genes have rapidly evolved in primate lineages through sequence diversification, gene amplification and loss, and gene fusion. Consequently, modern primates possess a unique set or “repertoire” of APOBEC3 genes. The APOBEC3 gene repertoire of humans has been well investigated. There are three types of catalytic domains (Z domain; A3Z1, A3Z2, and A3Z3), 11 Z domains, and 7 independent genes, including 4 genes encoding double Z domains. However, the APOBEC3 gene repertoires of nonhuman primates remain largely unclear. Here, we characterize APOBEC3 gene repertoires among primates and investigated the evolutionary scenario of primate APOBEC3 genes using phylogenetic and comparative genomics approaches. In the 21 primate species investigated, we identified 145 APOBEC3 genes, including 69 double-domain type APOBEC3 genes. We further estimated the ages of the respective APOBEC3 genes and revealed that APOBEC3B, APOBEC3D, and APOBEC3F are the youngest in humans and were generated in the common ancestor of Catarrhini. Notably, invasion of the LINE1 retrotransposon peaked during the same period as the generation of these youngest APOBEC3 genes, implying that LINE1 invasion was one of the driving forces of the generation of these genes. Moreover, we found evidence suggesting that sequence diversification by gene conversions among APOBEC3 paralogs occurred in multiple primate lineages. Together, our analyses reveal the hidden diversity and the complicated evolutionary scenario of APOBEC3 genes in primates. Importance In terms of virus-host interactions and coevolution, the APOBEC3 gene family is one of the most important subjects in the field of retrovirology. APOBEC3 genes are composed of a repertoire of subclasses based on sequence similarity, and a paper by LaRue et al. provides the standard guideline for the nomenclature and genomic architecture of APOBEC3 genes. However, it has been over 10 years since this publication, and new information, including RefSeq, which we used in this study, is accumulating. Based on accumulating knowledge, APOBEC3 genes, particularly those of primates, should be refined and reannotated. This study updates knowledge of primate APOBEC3 genes and their genomic architectures. We further inferred the evolutionary scenario of primate APOBEC3 genes and the potential driving forces of APOBEC3 gene evolution. This study will be a landmark for the elucidation of the multiple aspects of APOBEC3 family genes in the future.

First result of orbit verification of Taiji-1 hall micro thruster

The Hall Micro Thrusters (HMTs) use cold gas or accelerated plasma dual mode to provide ultra-precise spacecraft altitude control. They were operated in space for the first time as part of the demonstration payloads on Chinese Academy of Science’s (CASs) Taiji-1 spacecraft since September 2019. Hall Micro Thruster Assemblies (HMTAs) were the actuators in drag-free control, and will compensate the nonconservative force for gravity wave observatories. The HMTAs meet the requirements of operating at 5–100 [Formula: see text]N of thrust with 0.7 [Formula: see text]N resolution and [Formula: see text]0.6 [Formula: see text]N/Hz[Formula: see text] (0.01–1 Hz) noise to deliver the nanometer-level precision control as fast as 30 ms measured by Gravitational Reference Sensor (GRS). A transfer function model in z-domain was fit and used to filter HMTs cathode voltage to predict GRSs thrust noise response. Simulations of a single or dual-frequency disturbance and the corresponding compensation demonstrated that HMTAs could deliver the required thrust profile expected. The capability to meet the requirements of thruster noise in drag-free control is critical for future missions because the acceleration noise on test mass directly relates to the gravity wave signa l. Preliminary in-orbit verification of Taiji-1 has showed HMTAs’ great potential in future, and the data in the experiments are presented in this paper.