Initial Decomposition Mechanism of NH3OH+N5- Crystal under Thermal and Shock Loading: A First-Principles Study.

NH3OH+N5- is a novel energetic material (EM) which has attracted much interest for its promising performances, including high energy density, high density, low sensitivity, and low toxicity. In this study, the initial decomposition mechanism of NH3OH+N5- crystal was investigated under thermal and shock loading by molecular dynamics simulation. First, programmed heating and constant temperature simulations were carried out by molecular dynamics simulation on the basis of density functional theory (DFT-MD). Results indicated that the initial decomposition reactions of NH3OH+N5- could be described by three reactions: proton transfer, ring-opening reaction, and cation decomposition and recombination, and three pathways of ring-opening reaction were found, including the ring-opening of N5-, HN5, and H2N6. The first two reactions are the main pathways that produce N2 molecules. Furthermore, we carried out DFT-MD simulations to study the shock decomposition behaviors of NH3OH+N5-, and three initial steps were proposed: N5-, HN5, and N6 ring-opening. The fewer N5- and HN5 ring-opening reactions were found during the shock simulation, accompanied by a significant change in the N5- bond angle. What's more, the transition states of decomposition reactions were investigated through quantum chemical calculations. The results revealed that the proton transfer reaction exhibits lower activation barriers compared to ring-opening reactions, and proton transfer would accelerate ring-opening reactions. In addition, the ring-opening reaction is the main energy-releasing reaction in the early stages of the decomposition. This work could promote the comprehension of the decomposition mechanism and energy release regularity of N5- ions.

Two Energetic Framework Materials Based on DNM-TNBI as Host Molecule: Effectively Coordinated by Different Cations.

With the demand of develop outstanding-performance energetic materials, 1-(dinitromethyl)-4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole (DNM-TNBI) emerged as a great contender (D: 9102 m ⋅ s-1; P: 37.6 GPa). However, the relatively poor thermal stability (Td: 142 °C) limits its practical application. In this study, DNM-TNBI as a host molecule to synthesize two new energetic open-framework materials by effectively coordinated with different cations. Their supramolecular structures were investigated and indicated that [DNM-TNBI2 -][2NH4 +] and [DNM-TNBI2 -][2K+] can be classified as a new energetic hydrogen-bonded ammonium framework (EHAF) and an energetic metal organic framework (EMOF). Meanwhile, their thermal stabilities are higher than that of DNM-TNBI and have satisfactory detonation performance ([DNM-TNBI2 -][2NH4 +], D: 8050 m ⋅ s-1, P: 26.4 GPa; [DNM-TNBI2 -][2K+], D: 8301 m ⋅ s-1, P: 30.8 GPa).

Investigation of dislocation and twinning behavior in HMX under high-velocity impact employing molecular dynamics simulations.

CONTEXT: Under the ReaxFF/lg force field, the multiscale shock technique (MSST) was employed to investigate the decomposition behavior of perfect, dislocated, and twinned octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) at a velocity of 11 km/s. This study aimed to analyze the changes in system temperature, bond formation and breaking, variations in the number of small molecules, and the number of clusters. The results indicated that the sensitivity of dislocated HMX was the lowest, while the sensitivity of twinned and perfect HMX was comparable. Comparing the formation and breaking of bonds in HMX during the shock process, it was found that the change in the number of bonds in dislocated HMX was similar to that in perfect HMX, whereas twinning accelerated the breaking of bonds. By analyzing the changes in small molecular fragments (CO, CO2, H, H2, H2O, N2, N2H, NH2, NO, NO2, and O) during the shock process of HMX, it was found that dislocation had a relatively minor effect on the small molecular fragments, while twinning promoted the generation of CO, H, NO, and O and accelerated the decomposition of NO. A comparison of the number, weight, and atomic ratio of clusters under perfect, dislocated, and twinned conditions revealed that under the influence of shock, the number of clusters initially increased sharply and then decreased slowly. Meanwhile, compared to the perfect and dislocated explosives, the number of clusters under the twinned structure was significantly fewer, indicating that the twinned structure could reduce cluster formation. The proportion of oxygen to carbon in the twinned HMX was lower than that in the perfect and dislocated explosives, possibly due to the higher content of small molecular fragment O in twinned HMX. METHODS: Different structures of HMX crystals were constructed, including twinned defect structure (with a supercell containing 6458 atoms), dislocation defect structure (with a supercell containing 2352 atoms), and perfect structure (also with a supercell containing 2352 atoms). The modeling of defect crystal structures was carried out using the Atomsk software. For the twinned defect structure, we first constructed a mirror symmetric structure of the original configuration and then merged these two structures together. For the dislocation defect structure, we shifted a segment of the originally ordered perfect crystal structure by a certain distance using Atomsk. Before conducting the simulations, we performed geometric optimization of the models using the conjugate gradient (CG) algorithm and carried out 10 ps of NVT and NPT simulations to equilibrate the energy, temperature, and other parameters within the system. Finally, a 50-ps MSST impact simulation was performed using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS).

Evaluating effects of climate change on the spatial distribution of an atypical cavefish Onychostoma macrolepis.

Comprehending endangered species' spatial distribution in response to global climate change (GCC) is of great importance for formulating adaptive management, conservation, and restoration plans. However, it is regrettable that previous studies mainly focused on geoclimatic species, while neglected climate-sensitive subterranean taxa to a large extent, which clearly hampered the discovery of universal principles. In view of this, taking the endemic troglophile riverine fish Onychostoma macrolepis (Bleeker, 1871) as an example, we constructed a MaxEnt (maximum-entropy) model to predict how the spatial distribution of this endangered fish would respond to future climate changes (three Global Climate Models × two Shared Socio-economic Pathways × three future time nodes) based on painstakingly collected species occurrence data and a set of bioclimatic variables, including WorldClim and ENVIREM. Model results showed that variables related to temperature rather than precipitation were more important in determining the geographic distribution of this rare and endemic fish. In addition, the suitable areas and their distribution centroids of O. macrolepis would shrink (average: 20,901.75 km2) and move toward the northeast or northwest within the study area (i.e. China). Linking our results with this species' limited dispersion potential and unique habitat requirements (i.e. karst landform is essential), we thus recommended in situ conservation to protect this relict.

Multi-aspect simulation insight on thermolysis mechanism and interaction of NTO/HMX-based plastic-bonded explosives: a new conception of the mixed explosive model.

Reactive molecular dynamics (RMDs) calculations were used to determine, for the first time, the process of thermolysis of the mixed explosives, including 3-nitro-1,2,4-triazol-5-one (NTO) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazoline (HMX). Significantly, this is the first time that a layered model for mixed explosives, which is an extreme innovation of mixed explosive models was adopted. It is shown that a large amount of NO2 in the HMX and OH groups generated by the decomposition of HNO2 has a favorable effect on the thermolysis of NTO, as further validated by a reduction in the activation energy of NTO/HMX. The amount of H2O and N2 in the resulting products increased significantly, but the amount of NH3 changed slightly. The analysis results correspond to the change in chemical bonds. Whenever there is an increase in temperature, the time for the maximum number of clusters to appear is shortened accordingly. In addition, the acidity of NTO has been considered. An independent gradient model based on Hirshfeld partition (IGMH) and atoms in molecule (AIM) analysis of NTO/HMX was implemented. The relatively strong hydrogen bonds indicate that HMX can inhibit the acidity of NTO and is beneficial for the wide application of NTO/HMX-based plastic-bonded explosives (PBXs).

Precise Electron-Withdrawing Strength Modulation of ESIPT Probes for Ultrasensitive and Specific Fluorescence Sensing.

The precise regulation of the electron-withdrawing/electron-donating strength in a probe is of great significance for the design of reaction-based fluorescent probes with specific functionalities. Here, a family of excited-state intramolecular proton transfer (ESIPT)-based probes with fluorescence turn-on sensing properties toward KMnO4 was designed by precisely modulating the electron-withdrawing strength of the substituents located at the para-position of the recognition group. It is found that -F, -CHO, and -H as the electron-withdrawing groups bound at the probe can specifically recognize KMnO4, which ensures a blue emission displayed by the reaction products. Especially with -CHO as the electron-withdrawing group, the reaction product shows the most stable fluorescence. The probe 2-(benzo[d]oxazol-2-yl)-4-formylphenyl acrylate (BOPA-CHO) demonstrated a more superior sensing performance toward KMnO4, including a low limit of detection (LOD, 0.96 nM), a rapid response (<3 s), and a rather good selectivity even in the presence of 21 interferents. Moreover, the practicality of the probe was further verified by a test pen comprising a BOPA-CHO-embedded sponge, which is capable of detecting KMnO4 solid with a naked-eye LOD of 11.62 ng. The present probe design and modulation strategy would open up a new path for the design of high-performance fluorescent probes.

Learning defense transformations for counterattacking adversarial examples.

Deep neural networks (DNNs) are vulnerable to adversarial examples with small perturbations. Adversarial defense thus has been an important means which improves the robustness of DNNs by defending against adversarial examples. Existing defense methods focus on some specific types of adversarial examples and may fail to defend well in real-world applications. In practice, we may face many types of attacks where the exact type of adversarial examples in real-world applications can be even unknown. In this paper, motivated by that adversarial examples are more likely to appear near the classification boundary and are vulnerable to some transformations, we study adversarial examples from a new perspective that whether we can defend against adversarial examples by pulling them back to the original clean distribution. We empirically verify the existence of defense affine transformations that restore adversarial examples. Relying on this, we learn defense transformations to counterattack the adversarial examples by parameterizing the affine transformations and exploiting the boundary information of DNNs. Extensive experiments on both toy and real-world data sets demonstrate the effectiveness and generalization of our defense method. The code is avaliable at https://github.com/SCUTjinchengli/DefenseTransformer.

Theoretical study on the influence of different solvents on the growth morphology of 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF).

CONTEXT: 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF) is a new energetic compound with high energy and high density, and it is an important component of propellant and melt cast explosive. In order to study the effect of solvent on the growth morphology of DNTF, the growth plane of DNTF in vacuum is predicted by attachment energy (AE) model, and then the modified attachment energy of each growth plane in different solvents is calculated by molecular dynamics simulation. The morphology of crystal in solvent is predicted by modified attachment energy (MAE) model. The factors affecting crystal growth in solvent environment are analyzed by mass density distribution, radial distribution function and diffusion coefficient. The results show that the growth morphology of crystal in solvent is not only related to the adsorption strength of solvent to crystal plane, but affected by the attraction of crystal plane to solute. The hydrogen bond plays an important role in the adsorption strength between solvent and crystal plane. The polarity of solvent has a great influence on the crystal morphology, and the interaction between the solvent with stronger polarity and the crystal plane is stronger. The morphology of DNTF in n-butanol solvent is closer to spherical, which can effectively reduce the sensitivity of DNTF. METHODS: The molecular dynamics simulation is carried out under the COMPASS force field of Materials Studio software. Gaussian software is used to calculate the electrostatic potential of DNTF at B3LYP-D3/6-311 + G (d, p) theoretical level.

Challenging the Limitations of Tetranitro Biimidazole through Introducing a gem-Dinitromethyl Scaffold.

A gem-dinitromethyl group was successfully introduced into the TNBI·2H2O structure (TNBI: 4,4',5,5'-tetranitro-2,2'-bi-1H-imidazole) to obtain 1-(dinitromethyl)-4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole (DNM-TNBI). Benefiting from the transformation of an N-H proton into a gem-dinitromethyl group, the current limitations of TNBI were well solved. More importantly, DNM-TNBI has high density (1.92 g·cm-3, 298 K), good oxygen balance (15.3%), and excellent detonation properties (Dv = 9102 m·s-1, P = 37.6 GPa), suggesting that it has great potential as an oxidizer or a high-performance energetic material.

TDDFT calculations of the PETN's ultraviolet absorption spectrum under the electric field loading.

CONTEXT: The UV(ultraviolet) absorption spectrum of PETN under different electric field loading directions(X, Y, and Z) with the value of strength range from 0.001 a.u. to 0.006 a.u. was calculated with the TDDFT(Time-dependent density functional) in this work. With the increase of electric field strength, the absorbance of PETN in the ultraviolet band decreases. To explain the action mechanism of the electric field on PETN UV(ultraviolet) absorption spectrum, we analyzed and counted the contribution rate, oscillator strength, and vertical excitation energy of the main excitation process whose contribution rate to the UV absorption spectrum is greater than 10%. The contribution of PETN to the UV spectrum in all directions without an electric field was also listed to investigate the anisotropy of PETN in the excitation process under an electric field. The hole-electron analysis showed that the electric field will enhance the charge transfer characteristics in the excitation process of PETN. To investigate the anisotropy of the response under different electric field application directions, the contribution of the UV absorption spectrum in different directions was studied. METHODS: Optimization and TDDFT calculation were performed at the level of M06-2X/def2-TZVP and PBE0/def2-TZVP respectively, with Gaussian09 program. The hole-electron analysis and UV absorption spectrum plotting were performed with Multiwfn3.8.

Editorial for the Special Issue "Materials under High Pressure".

The high-pressure-related problems of materials constitute a field at the confluence of several scientific disciplines [...].

Comprehensive theoretical study on safety performance and mechanical properties of 3-nitro-1,2,4-triazol-5-one (NTO)-based polymer-bonded explosives (PBXs) via molecular dynamics simulation.

3-nitro-1,2,4-triazol-5-one (NTO)-based polymer-bonded explosives (PBXs) have been widely used in insensitive munitions, but the main properties of NTO-based PBXs such as compatibility, safety performance, and mechanical properties are rarely reported. In this work, molecular dynamics simulation was carried out to study interface interactions of NTO-based PBXs, in which hydroxy-terminated polybutadiene (HTPB), ethylene-vinyl acetate copolymer (EVA), glycidyl azide polymer (GAP), poly-3-nitratomethyl-3-methyl oxetane (Poly-NIMMO), and ester urethane (Estane5703) are selected as binders. The binding energy analysis indicates that the order of compatibility is NTO/GAP > NTO/Estane5703 > NTO/HTPB > NTO/Poly-NIMMO > NTO/EVA. Radial distribution function analysis results show that the interface interaction is mainly the hydrogen bond between H atoms of NTO and O atoms of Estane5703, HTPB, EVA, and Poly-NIMMO or N atoms of GAP. The values of cohesive energy density verify that the safety is NTO/GAP > NTO/Poly-NIMMO > NTO/HTPB > NTO/EVA > NTO/Estane5703. Mechanical properties results show that GAP and EVA would improve the plasticity of the systems effectively. Furthermore, it can be found that the most favorable interactions occur between the NTO (1 0 0) crystal face and binders.

Intra- and Peritumoral Radiomics Model Based on Early DCE-MRI for Preoperative Prediction of Molecular Subtypes in Invasive Ductal Breast Carcinoma: A Multitask Machine Learning Study.

Purpose: The aim of this study is to investigate radiomics features extracted from the optimal peritumoral region and the intratumoral area on the early phase of dynamic contrast-enhanced MRI (DCE-MRI) for predicting molecular subtypes of invasive ductal breast carcinoma (IDBC). Methods: A total of 422 IDBC patients with immunohistochemical and fluorescence in situ hybridization results from two hospitals (Center 1: 327 cases, Center 2: 95 cases) who underwent preoperative DCE-MRI were retrospectively enrolled. After image preprocessing, radiomic features were extracted from the intratumoral area and four peritumoral regions on DCE-MRI from two centers, and selected the optimal peritumoral region. Based on the intratumoral, peritumoral radiomics features, and clinical-radiological characteristics, five radiomics models were constructed through support vector machine (SVM) in multiple classification tasks related to molecular subtypes and visualized by nomogram. The performance of radiomics models was evaluated by receiver operating characteristic curves, confusion matrix, calibration curves, and decision curve analysis. Results: A 6-mm peritumoral size was defined the optimal peritumoral region in classification tasks of hormone receptor (HR)-positive vs others, triple-negative breast cancer (TNBC) vs others, and HR-positive vs human epidermal growth factor receptor 2 (HER2)-enriched vs TNBC, and 8 mm was applied in HER2-enriched vs others. The combined clinical-radiological and radiomics models in three binary classification tasks (HR-positive vs others, HER2-enriched vs others, TNBC vs others) obtained optimal performance with AUCs of 0.838, 0.848, and 0.930 in the training cohort, respectively; 0.827, 0.813, and 0.879 in the internal test cohort, respectively; and 0.791, 0.707, and 0.852 in the external test cohort, respectively. Conclusion: Radiomics features in the intratumoral and peritumoral regions of IDBC on DCE-MRI had a potential to predict the HR-positive, HER2-enriched, and TNBC molecular subtypes preoperatively.

Genetic Diversity and Genetic Differentiation of Populations of Golden-Backed Carp (Cyprinus carpio var. Jinbei) in Traditional Rice Fields in Guizhou, China.

The aim of this study was to assess the current status of the germplasm resources of golden-backed carp (Cyprinus carpio var. Jinbei) cultured in paddy fields in Guizhou Province, China. Five populations of golden-backed carp in Liping County, Jinping County, Huangping County, Congjiang County and Duyun City in Guizhou Province were subjected to high-throughput sequencing by 2b-RAD technology, and their genetic diversity and genetic differentiation were analysed. Based on sequencing, 44,896 SNP loci were obtained, and all five population genetic diversity indicators showed low diversity. In the NJ tree, the Congjiang and Liping populations were mixed together, and the other three groups formed a cluster. A cross-validation error box plot and pong cluster plot were constructed to show the K value results. When K = 1, the cross-validation error rate was the lowest. Principal component analysis showed that the Duyun population formed a group separate from the group comprising the other four populations. The genetic differentiation index and genetic distances between the Duyun population and the remaining four populations were greater than 0.05, indicating population differentiation. The genetic diversity of the five populations of golden-backed carp in Guizhou Province was low, the genetic differentiation of the Duyun population was the most significant, and the Duyun population was separate from the other four groups.

Molecular dynamics simulation of initial thermal decomposition mechanism of DNTF.

In order to understand the thermal decomposition characteristics of 3,4-Bis(3-nitrofurazan-4-yl)furoxan (DNTF), the thermal decomposition reaction of DNTF at 300-4000 K temperature programmed and constant temperatures of 2000 K, 2500 K, 3000 K, 3500 K, and 4000 K was simulated by ab initio computational molecular dynamics method. The thermal decomposition mechanism of DNTF at different temperatures was analyzed from the aspects of product evolution, cluster, potential energy curve, and reaction path. The analysis of products shows that the initial small molecular products are NO, NO2, CO, CO2, and N2, and the final small molecular products are CO2 and N2. In the early stage, the ring-opening reaction of furoxan in DNTF structure is the main trigger reaction, and the C-C bond is broken at the initial stage of reaction. The carbon chain structure produced by decomposition forms various cluster structures in the form of C-N bond. In addition, it was found that temperature significantly affects the decomposition rate of DNTF, but does not change its initial decomposition path.

Molecular dynamics simulation of 1-methyl-4,5-dinitroimidazole (MDNI)/1-methyl-3,4,5-trinitropyrazole (MTNP) eutectic mixtures.

1-Methyl-4,5-dinitroimidazole (MDNI)/1-methyl-3,4,5-trinitropyrazole (MTNP) mixtures with different mass ratios were investigated by a combination of theory and experiment. The melting points were predicted using the relationships of specific volume versus temperature, non-bond energy versus temperature, and diffusion coefficient versus temperature, and compared with the experimental values. It was found that the melting point values obtained from the three relationships were in good agreement with the experimentally measured melting points with little error. The interactions between MDNI/MTNP were analyzed by binding energy and RDF, and the results showed that, as the temperature increased, the intermolecular interactions weakened, the binding energy decreased, and the stability of the system decreased. The comprehensive results show that mixture 4 (MDNI/MTNP = 60/40) has a low melting point value and good compatibility, and the detonation velocity and density are improved compared with TNT and MDNI, which is expected to be further applied in melt-cast explosives.

Osteoblastoma of the breast:An uncommon and easily overlooked location.

Osteoblastoma is a rare benign osseous neoplasm that accounts for 1%-3% of all primary bone tumors. Osteoblastomas can involve any part of the skeleton, but mainly occurs in the spine and other long bones, rarely in extra-skeletal areas. Extra-skeletal osteoblastomas arise from tissues outside of the bone, and only a few cases have been reported previously. To our knowledge, only one case of osteoblastoma in the breast has been described in the English literature. Here, we report another case of a breast osteoblastoma in a middle-aged woman, which was initially detected by ultrasound examination and digital mammography, and then was confirmed by histopathology. In this report, the imaging features and differential diagnosis of breast osteoblastoma are discussed.

Theoretical prediction of the trigger linkage, cage strain, and explosive sensitivity of CL-20 in the external electric fields.

In order to add safely external electric fields into the systems of the explosives with strong cage strain, the effects of the external electric fields on the strengths of trigger linkages, cage strain energies (CSEs), surface electrostatic potentials (ESPs), as well as impact and shock initiation sensitivities of CL-20 were investigated using the B3LYP and M06-2X methods with 6-311++G(2d,p) basis set. The results show that the changes of the strengths of the N-NO2 bonds are more notable than those of the bonds forming cage, and the changes involving the N-NO2 bonds attached to the five-membered ring are more significant than those attached to the six-membered ring. In most cases, the CSEs in the electric fields are stronger than those in no field. From the BDEs, the N-NO2 cleavage is the decomposition reaction pathway in detonation initiation. However, from the surface ESPs, the N-NO2 cleavage, C-N and C-C bond breaking may initiate the reactions. The global ESPs are more reasonable and reliable to estimate the impact sensitivities of the cage-shaped explosives. The changes of the bond lengths, Mulliken bond orders, nitro group charges and BDEs correlate well with the external electric field strengths. Interestingly, an abnormal result is found that the h50 values in the electric fields are larger than those in no field.

CT radiomics facilitates more accurate diagnosis of COVID-19 pneumonia: compared with CO-RADS.

BACKGROUND: Limited data was available for rapid and accurate detection of COVID-19 using CT-based machine learning model. This study aimed to investigate the value of chest CT radiomics for diagnosing COVID-19 pneumonia compared with clinical model and COVID-19 reporting and data system (CO-RADS), and develop an open-source diagnostic tool with the constructed radiomics model. METHODS: This study enrolled 115 laboratory-confirmed COVID-19 and 435 non-COVID-19 pneumonia patients (training dataset, n = 379; validation dataset, n = 131; testing dataset, n = 40). Key radiomics features extracted from chest CT images were selected to build a radiomics signature using least absolute shrinkage and selection operator (LASSO) regression. Clinical and clinico-radiomics combined models were constructed. The combined model was further validated in the viral pneumonia cohort, and compared with performance of two radiologists using CO-RADS. The diagnostic performance was assessed by receiver operating characteristics curve (ROC) analysis, calibration curve, and decision curve analysis (DCA). RESULTS: Eight radiomics features and 5 clinical variables were selected to construct the combined radiomics model, which outperformed the clinical model in diagnosing COVID-19 pneumonia with an area under the ROC (AUC) of 0.98 and good calibration in the validation cohort. The combined model also performed better in distinguishing COVID-19 from other viral pneumonia with an AUC of 0.93 compared with 0.75 (P = 0.03) for clinical model, and 0.69 (P = 0.008) or 0.82 (P = 0.15) for two trained radiologists using CO-RADS. The sensitivity and specificity of the combined model can be achieved to 0.85 and 0.90. The DCA confirmed the clinical utility of the combined model. An easy-to-use open-source diagnostic tool was developed using the combined model. CONCLUSIONS: The combined radiomics model outperformed clinical model and CO-RADS for diagnosing COVID-19 pneumonia, which can facilitate more rapid and accurate detection.