Response regulator proteins are important components of the two-component signal transduction systems, and essential in transferring the signal delivered from the sensor histidine kinase and eliciting an adaptive response. Phosphorylation and dephosphorylation of the response regulator proteins determine the direction of the signal transduction process. The phosphorylation and dephosphorylation sites of the response regulator proteins play an important role in exerting their function. Here we studied some key residues of response regulator RR468 from Thermotoga maritima. Site-directed mutagenesis experiments were performed to the key sites M55 and K85, which are located in loop b3-a3 and loop b4-a4, respectively. The structure and dynamics feature of the two mutants were investigated with liquid nuclear magnetic resonance (NMR) spectroscopy. The results of functional experiments demonstrated that the two residues could affect the phosphorylation and dephosphorylation processes.

NMR is a frequently used technique for measuring crosslink density of rubbers. In this work, three commonly used proton NMR methods for measuring crosslink density of rubbers[i.e., ¹H double-quantum (DQ) NMR, ¹H Hahn echo and ¹H CPMG echo] were compared. Different approaches showed different results, and the origin of such discrepancy was discussed. The echo time dependence of the crosslink density measured with the CPMG echo method was studied. The ways to improve theCPMG echo-based measurements are discussed.

Halogen bond, as hydrogen bond, is a non-covalent bond. Dynamic nuclear polarization (DNP) technique has been used previously to study hydrogen bonds-mediated intermolecular interactions. However, no study has been carried out so far to study the halogen bond-mediated intermolecular interactions with DNP. In this work, ¹⁹F DNP polarization efficiency of the halogen bonds existing in supramolecular assembling by 4-OH-TEMPO and 1,4-diiodotetrafluorobenzene (DITFB) was studied on a home-made DNP system. The formation of intermolecular halogen bonds appeared to increase ¹⁹F DNP polarization efficiency, suggesting that the spin-spin interactions among electrons were weakened by the halogen bonds, resulting in an increased T_2e and a larger saturation factor.

All solid state lithium-ion batteries have the advantages of high safety, long cycle life and high energy density, as compared with the conventional lithium-ion batteries, and have been attracting more and more research interest. Solid electrolyte is a crucial component of all solid state lithium-ion batteries, which largely determine the performance of the batteries. In this work, a polymer-lithium-ceramics complex was designed and synthesized. The structure and dynamics of the polymer-ceramic interface was studied with solid-state NMR techniques.

Magnetic resonance imaging (MRI) is a noninvasive intraocular tumor detection method without ionizing radiation. However, resolution limitation and motion artifacts are difficult to overcome in the imaging process. Conventional scanning methods inevitably introduce motion artifacts, or require the subjects to cooperate for accurate eye fixation, increasing the difficulty of imaging and giving the subject uncomfortable experiences. In this work, a new MRI method based on super-resolution theory is proposed, which uses a specialized orbit coil to scan a series of dynamic images of the eyeball, such that the acquisition resolution in different directions is complementary. High-resolution eyeball images with minimal motion artifacts could then be obtained after pre-processing, registration, super-resolution reconstruction and other operations. The study showed that the method proposed can be used to obtain clear eyeball images without the requirement of eye fixation.

The ¹H NMR fingerprint of Eucommia ulmoides acquired with a CPMG pulse sequence was analyzed with the complete reduction to amplitude-frequency table (CRAFT) approach. The signals of target compounds were extracted without chemical separation and purification. Quantitative analysis showed that the average concentration of pinoresinol glucoside (PDG) in Eucommia ulmoides got from Guiyang medical plant garden was 0.275 6% with a relative standard deviation (RSD) of 1.69%. The results were consistent with those obtained by high performance liquid chromatography (average content of 0.269 6% and RSD of 0.65%). NMR fingerprint and multivariate statistical analysis also revealed that there existed significant differences between Hunan and Guizhou Eucommia ulmoides Oliver.

To discriminate R and S flavanone glycoside using NMR, the mixture of R and S naringenin 7-O-glycoside was first isolated from Gleditsia sinensis. ¹H and ¹³C NMR data of the mixture were recorded with ¹H NMR, ¹³C NMR, ¹H-¹H COSY, ¹H-¹³C HSQC and ¹H-¹³C HMBC in DMSO-d₆ solution. The two diastereomers were then separated with chiral chromatographic isolation, with their absolute configurations determined by circular dichroism. To avoid the disturbance of protons from glucose residues to dihydroflavonoid, ¹H NMR spectra were acquired for pure R and S naringenin 7-O-glycoside and their mixture in CD₃CN. The two diastereomers showed the largest proton chemical shift differences at the end group of glucose residue (H-1") with a chemical shift difference of 9.4 Hz. The OH-5 proton showed a chemical shift difference of 5.8 Hz. The chemical shift of the three protons on ring C were all influenced by configuration.

The radiofrequency circuit of traditional miniature rubidium atomic frequency standard (RAFS) uses saturated output, which can stabilize the amplitude, but not the waveform, of the radiofrequency signal. This would lead to insufficient microwave power stability. In this study, an improved circuit for stabilizing power amplitude in miniature rubidium atomic frequency standard was described. The circuit took the bias voltage of step recovery diode (SRD) as a reference to achieve automatic gain control (AGC) through controlling the gain of the variable gain amplifier (VGA). This scheme controlled both the amplitude and the waveform of the radiofrequency signal. The results showed that this scheme can effectively improve power stability of the microwave signal in miniature rubidium atomic frequency standard.

Progresses have been made in the development of digitalized and miniaturized rubidium atomic frequency standard (RAFS). In the traditional RAFS circuits, the 6 840 MHz microwave signal is mixed with the 5.312 5 MHz signal generated by the frequency synthesizer to obtain 6 834.687 5 MHz microwave signal, which is used to excite rubidium atom transition. Early RAFS frequency synthesizer used a large number of discrete analog devices, and showed disadvantages such as low degree of digitization, complicated parameter optimization and large physical size. The direct digital synthesizer (DDS) scheme used currently generates the 5.312 5 MHz signal directly, but often needs to multiply the 10 MHz signal. It has the disadvantages of low spectral purity and high phase noise. This paper introduces a digital frequency synthesizer solution that generates the 5.312 5 MHz signal. The design eliminates the need for a 10 MHz multiplier circuit when using a DDS device. It has the advantages of high spectral purity, low phase noise and adjustable output frequency/phase.

A magnetic resonance imaging receiver design based on NI PXIe-7966R is proposed, with which the magnetic resonance signals are sampled directly and down-converted digitally, the raw data are uploaded and the magnetic resonance image are restored. The system-level digital signal processing (DSP) development tools offered by NI LabVIEW field programmable gate array (FPGA) was used for FPGA function modeling, simulation and automatic code generation of hardware description language (HDL). It was very flexible during the digital down conversion (DDC) designing. The sampling rate of this module was 50 Mbps, and the receiver bandwidth could be varied between 100 Hz and 1 MHz. The experimental results showed that the receiver design is a high performance magnetic resonance receiver solution.

The accuracy of gradient pulse waveform affects image quality significantly in magnetic resonance imaging (MRI). Recording and analyzing the waveform of gradient pulse helps to make rapid and accurate diagnosis of spectrometer gradient hardware and/or pulse sequence. Using the virtual instrument software LabVIEW to control the high speed data acquisition card DAQ-2005, a multi-channel acquisition scheme was designed to collect the gradient outputs from a custom-made spectrometer. The collected waveforms were post-processed (i.e., histogram statistical analysis, data filtering and difference calculation) to obtain feature points containing time and amplitude information. Experiments were carried out to validate the method, which is an auxiliary test method for the development of spectrometer and pulses sequence.

An unilateral nuclear magnetic resonance (UMR) sensor was designed to measure wood moisture nondestructively. The sensor consisted of a unilateral magnet, an anti-eddy current module, a radiofrequency (RF) coil and an impedance matching and tuning circuit. The sensor produced a static magnetic field of 71.1 mT (resonant frequency:3.027 MHz) in a 50 mm×50 mm plane locating 75 mm above the sensor's surface. Preliminary nondestructive measurement of wood moisture was carried out with the sensor. The moisture distribution in the radical direction of a cylindrical wood sample was scanned. Variations in transverse relaxation time (T₂) from the bark to core were obtained. Evaporation of moisture during wood drying was also measured with the UMR sensor. Experimental results showed that:the peak of long T₂ component in the T₂ spectrum moved to left and the peak integral area decreased gradually during drying. The integral area was proportional to the moisture content of the sample. The work presents a portable UMR device for wood research which may potentially be used for nondestructive moisture measurement on living trees in situ.

An automatically-controlled olfactometer that can be used in the magnetic resonance imaging environment was designed and built in this study. The overall system design was in accordance with the general requirements of stimulator and aimed to show improvement over an existing olfactometer in the laboratory. The device included two parts:the control system and the gas transportation system. The control system used LabVIEW platform-based software and adopted a virtual apparatus scheme. It was capable of providing man-machine interaction controlling stimulus sequence and gas paths according to the applications. The gas delivery system consisted of 4 variable gas paths and 1 constant gas path, through which clean air was transmitted to three gas-washing bottles filled with liquids having different odors. The fluctuation of gas flow measured by a Honeywell AWM43600 airflow sensor was within 0.3%, and the switching response time between different branches was about 1.07 s. Founctional magnetic resonance imaging (fMRI) experiments on olfaction were performed on 8 subjects with the stimulation device, providing odors of ethanol, pyridine and isoamyl acetate. The fMRI results demonstrated thalamus, amygdala, piriform cortex, orbital frontal cortex activations upon olfactory stimulation. It was concluded that the olfactometer built can deliver quantitative olfactory stimulus and meet the requirements for olfactory fMRI experiments.

Magnetic resonance imaging (MRI) is a practical technique for non-invasive temperature measurement. Thermo-sensitive MRI contrast agents, which cause temperature-dependent changes in magnetic resonance parameters of water molecules (i.e., relaxation, signal intensity and chemical shift) have been widely applied to MRI thermometry. This paper gives an overview of the types, principle, research status and application prospects of thermo-sensitive MRI contrast agent.