Fabric-based jamming phase diagram for frictional granular materials.

A jamming phase diagram maps the phase states of granular materials to their intensive properties such as shear stress and density (or packing fraction). We investigate how different phases in a jamming phase diagram of granular materials are related to their fabric structure via three-dimensional discrete element method simulations. Constant-volume quasi-static simple shear tests ensuring uniform shear strain field are conducted on bi-disperse spherical frictional particles. Specimens with different initial solid fractions are sheared until reaching steady state at a large shear strain (200%). The jamming threshold in terms of stress, non-rattler fraction, and coordination numbers (Z's) of different contact networks is discussed. The evolution of fabric anisotropy (F) of each contact network during shearing is also examined. By plotting the fabric data in the F-Z space, a unique critical fabric surface (CFS) becomes apparent across all specimens, irrespective of their initial phase states. Through the correlation of this CFS with fabric signals corresponding to jamming transitions, we introduce a novel jamming phase diagram in the fabric F-Z space, offering a convenient approach to distinguish the various phases of granular materials solely through the direct observation of geometrical arrangements of particles. This jamming phase diagram underscores the importance of the microstructure underlying the conventional jamming phenomenon and introduces a novel standpoint for interpreting the phase transitions of granular materials that have been exposed to processes such as compaction, shearing, and other complex loading histories.

Photochromism and Photomagnetism in Two Ni(II) Complexes Based on a Photoactive 2,4,6-Tris-2-Pyridyl-1,3,5-Triazine Ligand.

It is still challenging to construct novel photochromic and photomagnetic materials in the field of molecular materials. Herein, the 2,4,6-tris-2-pyridyl-1,3,5-triazine (TPTz) molecule was found to display photochromic properties under room temperature light irradiation. Two mononuclear structures, [Ni(H2O)(TPTz)(C2O4)]·2H2O (1; C2O42- = oxalate) [Ni(H2O)(TPTz)(C2O4)]·0.5H2O (2), and one chain compound [Ni(TPTz)(H2-HEDP)]·2H2O (3; HEDP = hydroxyethylidene diphosphonate) were obtained by assembling TPTz with polydentate O-ligands (oxalate and phosphonate) and the paramagnetic Ni2+ ions. The electron-transfer (ET)-dominated photochromism was observable in 1 and 2 after light irradiation with the photogeneration of relatively stable radicals, and the resultant photochromism was demonstrated via UV-vis, photoluminescence, X-ray photoelectron spectra, electron paramagnetic resonance spectra, and molecular orbital calculations. Due to the denser stacking interactions between the adjacent organic molecules, 2 exhibited a faster photochromic rate than 1. Compared with 1 and 2, compound 3 did not show photochromic behavior, which was deciphered by the theoretical calculations for all of the compounds. Importantly, the magnetic couplings appeared between photogenerated radicals and paramagnetic Ni2+ ions, resulting in a scarcely photomagnetic phenomenon of 1 and 2 in the Ni-based electron transfer photochromic materials. This work enriches the available kind of ligands for the design of ET photochromic materials, putting forward a method to tune the electron transfer photochromic efficiency in the molecular materials.

Determination of the two-compartment model parameters of exhaled HCN by fast negative photoionization mass spectrometry.

Breath exhaled hydrogen cyanide (HCN) has been identified to be associated with several respiratory diseases. Accurately distinguishing the concentration and release rate of different HCN sources is of great value in clinical research. However, there are still significant challenges due to the high adsorption and low concentration characteristics of exhaled HCN. In this study, a two-compartment kinetic model method based on negative photoionization mass spectrometry was developed to simultaneously determine the kinetic parameters including concentrations and release rates in the airways and alveoli. The influences of the sampling line diameter, length, and temperature on the response time of the sampling system were studied and optimized, achieving a response time of 0.2 s. The negative influence of oral cavity-released HCN was reduced by employing a strategy based on anatomical lung volume calculation. The calibration for HCN in the dynamic range of 0.5-100 ppbv and limit of detection (LOD) at 0.3 ppbv were achieved. Subsequently, the experiments of smoking, short-term passive smoking, and intake of bitter almonds were performed to examine the influences of endogenous and exogenous factors on the dynamic parameters of the model method. The results indicate that compared with steady-state concentration measurements, the kinetic parameters obtained using this model method can accurately and significantly reflect the changes in different HCN sources, highlighting its potential for HCN-related disease research.

Antigen-loaded flagellate bacteria for enhanced adaptive immune response by intradermal injection.

Since the skin limits the distribution of intradermal vaccines, a large number of dendritic cells in the skin cannot be fully utilized to elicit a more effective immune response. Here, we loaded the antigen to the surface of the flagellate bacteria that was modified by cationic polymer, thus creating antigen-loaded flagellate bacteria (denoted as 'FB-Ag') to overcome the skin barrier and perform the active delivery of antigen in the skin. The FB-Ag showed fast speed (∼0.2 µm s-1) and strong dendritic cell activation capabilities in the skin model in vitro. In vivo, the FB-Ag promoted the spread of antigen in the skin through active movement, increased the contact between Intradermal dendritic cells and antigen, and effectively activated the internal dendritic cells in the skin. In a mouse of pulmonary metastatic melanoma and in mice bearing subcutaneous melanoma tumor, the FB-Ag effectively increased antigen-specific therapeutic efficacy and produced long-lasting immune memory. More importantly, the FB-Ag also enhanced the level of COVID-19 specific antibodies in the serum and the number of memory B cells in the spleen of mice. The movement of antigen-loaded flagellate bacteria to overcome intradermal constraints may enhance the activation of intradermal dendritic cells, providing new ideas for developing intradermal vaccines.

Online Detection of HCN in Humid Exhaled Air by Gas Flow-Assisted Negative Photoionization Mass Spectrometry.

Hydrogen cyanide (HCN) is a well-known toxic compound in many fields. The trace amount of endogenous HCN in human exhalation has been associated with the presence of Pseudomonas aeruginosa (PA) infection in cystic fibrosis (CF) patients. Online monitoring of HCN profile is promising to screen PA infection rapidly and accurately. In this study, a gas flow-assisted negative photoionization (NPI) mass spectrometry method was developed for monitoring the single-exhalation HCN profile. The sensitivity could be optimized by introducing helium to eliminate the humidity influence and reduce the low mass cutoff effect, with improvements of a factor 150 observed. By employing a purging gas procedure and minimizing the length of the sample line, the residual and response time were greatly reduced. The limit of detection (LOD) of 0.3 ppbv and time resolution of 0.5 s were achieved. HCN profiles of exhalations from different volunteers before or after gargling with water were detected to show the performance of the method. All profiles showed a sharp peak and a stable end-tidal plateau, representing the concentration of oral cavity and end-tidal gas, respectively. The HCN concentration based on the plateau of the profile showed better reproducibility and accuracy, which indicates this method has potential application in the detection of PA infection in CF patients.

Rapid Determination of Ethyl Carbamate in Chinese Liquor via a Direct Injection Mass Spectrometry with Time-Resolved Flash-Thermal-Vaporization and Acetone-Assisted High-Pressure Photoionization Strategy.

Ethyl carbamate (EC), a carcinogenic compound, is naturally produced in fermented foods and alcoholic beverages. Rapid and accurate measurement of EC is necessary and important for quality control and safety evaluation of Chinese liquor, a traditionally distilled spirit with the highest consumption in China, but it remains a great challenge. In this work, a direct injection mass spectrometry (DIMS) with time-resolved flash-thermal-vaporization (TRFTV) and acetone-assisted high-pressure photoionization (HPPI) strategy has been developed. EC was rapidly separated from the main matrix components, ethyl acetate (EA) and ethanol, by the TRFTV sampling strategy due to the retention time difference of these three compounds with large boiling point differences on the inner wall of a poly(tetrafluoroethylene) (PTFE) tube. Therefore, the matrix effect of EA and ethanol was effectively eliminated. The acetone-assisted HPPI source was developed for efficient ionization of EC through a photoionization-induced proton transfer reaction between EC molecules and protonated acetone ions. The accurate quantitative analysis of EC in liquor was achieved by introducing an internal standard method (ISM) using deuterated EC (d5-EC). As a result, the limit of detection (LOD) for EC was 8.88 µg/L with the analysis time of only 2 min, and the recoveries ranged from 92.3 to 113.1%. Finally, the prominent capability of the developed system was demonstrated by rapid determination of trace EC in Chinese liquors with different flavor types, exhibiting wide potential applications in online quality control and safety evaluation of not only Chinese liquors but also other liquor and alcoholic beverages.

Influence of Pseudopotential Well Depth on the Performance of Hybrid Linear Ion Trap/Time-of-Flight Mass Spectrometry Driven by Square and Sinusoidal Waveform.

Quadrupole devices are widely used as ion analyzers and ion guides, which are usually driven by a sinusoidal waveform. Recently, these devices driven by a digital waveform have attracted much attention. Driven by different rf waveforms, the pseudopotential well depth of quadrupole devices is significantly different, which will affect their performance. However, there is a lack of comprehensive view on the performance differences of quadrupole devices or hybrid instrument driven by different rf waveforms. In this paper, the differences in mass range, resolution, sensitivity, and ion fragmentation of LIT/TOFMS driven by square and sinusoidal waveforms were investigated. Compared with the sinusoidal mode, the square mode had a wider mass range and better mass resolution. Toluene was used to study the difference in sensitivity and ion fragmentation between the two modes. The results showed that the sensitivity of the square mode was 1.7-2.5 times that of the sinusoidal mode at different ion densities. According to the sensitivity differences, it was inferred that the ion-trapping efficiency and ion capacity of LIT in the square mode were 2.0 times and 1.7 times those in sinusoidal mode. It was found that the square mode behaved "softer" and presented less fragmentation, and the proportion of fragment ions in the sinusoidal mode can reach 3.2 times that in the square mode at high ion density. Therefore, LIT/TOFMS driven by a square waveform shows greater potential in the application of the complex matrix system with a wide mass range.

Instance segmentation using semi-supervised learning for fire recognition.

Fire disaster brings enormous danger to the safety of human life and property, and it is important to identify the fire situation in time through image processing technology. The current instance segmentation algorithms suffer from problems such as inadequate fire images and annotations, low recognition accuracy, and slow inference speed for fire recognition tasks. In this paper, we propose a semi-supervised learning-based fire instance segmentation method based on deep learning image processing technology. We used a lightweight version of the SOLOv2 network and optimized the network structure to improve accuracy. We propose a semi-supervised learning method based on fire features. To reduce the negative impact of error pseudo-labels on the model training, the pseudo-labels are matched by the color and morphological features of flames and smoke at the pseudo-label generation stage, and some images are screened for strong image enhancement before entering the next round of training for the student model. We further exploit the potential of the model with a limited dataset and improve the model accuracy without affecting the inference efficiency of the model. Experiments show that our proposed algorithm can successfully improve the accuracy of fire instance segmentation with good inference speed.

A Strategy for Simultaneously Improving Resolution and Sensitivity of Hybrid Quadrupole Ion Trap/Time-of-Flight Mass Spectrometry Using Square Waveform Phase Modulation.

The hybrid quadrupole ion trap/time-of-flight mass spectrometry (QIT/TOFMS) device is popular because of its advantages of high sensitivity, high resolution, and MS/MS capability. However, the analytical performance of QIT/TOFMS is severely limited by the parameters of the ion trap, as QIT is typically used as a TOF pulser because the ion initial distributions of space, velocity, and angle change dynamically with the phase angle of rf voltage. In this work, a square waveform phase modulation strategy was proposed to eliminate the influence of the rf phase angle, and the dependence of QIT/TOFMS performance on the phase angle was studied. It was found that the mass resolution and signal intensity showed a "W" trend with the increase of the ion extraction phase angle from 0° to 360°, where the best resolution and sensitivity were obtained at 0°, 180°, and 360° while the worst resolution and sensitivity were obtained at 90° and 270°. Moreover, the optimum phase angle was independent of m/z. As a result, the mass resolution for m/z 106, 164, and 258 was improved by 162%, 160%, and 210% respectively, while the signal intensities for m/z 106, 164, and 258 were enhanced by 25 ± 1, 10 ± 1, and 21 ± 1 fold, respectively, and a limit of detection down to 0.015 ppbv for m/z 164 was obtained. The experiment results indicated that the square waveform phase modulation strategy could be used to simultaneously improve the resolution and sensitivity of QIT/TOFMS.

High Mass Resolution Multireflection Time-of-Flight Secondary Ion Mass Spectrometer.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is popular because of its advantages of parallel m/z detection and less damage for unknown or rare samples compared to sector field instruments. However, the mass resolving power of conventional TOF-SIMS is limited by its relatively large energy spread and primary ion pulse width. In this work, a high mass resolution multireflection time-of-flight secondary ion mass spectrometer (MR-TOF-SIMS) was designed and constructed. Compared with conventional TOF-SIMS, the ion flight path of the MR-TOF-SIMS was extended from meters to subkilometers, and the mass resolving power reached to 87000 after an 80 cycles flight. A pair of symmetrically arranged ion orthogonal injection/ejection deflectors, which could eliminate the influence of fringing field and remove ions with a large energy spread, were proposed to further improve the mass resolving power in fewer flight cycles. A zircon standard sample sputtered by a 10 keV O2- beam was used to demonstrate the performance of the MR-TOF-SIMS instrument. As a result, the mass resolving power was up to 30000 only after 22 flight cycles. The 92Zr+ peak was significantly separated from the mass interference peaks of 91ZrH+, 90ZrH2+, 13CC6H7+, and C7H8+. The mass accuracies of Zr ions and their hydrides were better than 1.2 ppm. An ion transmission efficiency over 40% was achieved after 115 cycles.

Rapid and highly sensitive measurement of trimethylamine in seawater using dynamic purge-release and dopant-assisted atmospheric pressure photoionization mass spectrometry.

Trimethylamine (TMA) is ubiquitous in the marine systems and may affect atmospheric chemistry as a precursor and strong stabilizer of atmospheric secondary aerosol, influencing cloud formation. Rapid and accurate measurement of the concentration of TMA in seawater is challenging due to their polarity, aqueous solubility, volatility and existence at low concentrations in marine environments. In this study, a dopant-assisted atmospheric pressure photoionization time-of-flight mass spectrometry (DA-APPI-TOFMS) coupled with a dynamic purge-release method was developed for rapid and sensitive analysis of TMA in seawater. A novel three-zones ionization source has been developed for improving the ionization efficiency of analyte molecules and minimizing the influence of high-humidity of the sample gas, which allowed direct analysis of high-humidity (RH> 90%) gas samples from microbubble purging process by the mass spectrometer. At atmospheric pressure, the three-zones ionization source allows the use of high-speed purge gas to quickly purge all organic amines dissolved in the water into the gas phase, ensuring quantitative accuracy. The limit of quantification (LOQ) for TMA down to 0.1 µg L-1 was obtained in less than 2 min by consuming only 2 mL seawater sample. This method was applied for the determination of the concentrations of TMA in the coastal seawater to validate its practicability and reliability for analysis of trace amines in marine environments.