Probing into the theory of impact sensitivity: propelling the understanding of phonon-vibron coupling coefficients.

The determination of impact sensitivity of energetic materials traditionally relies on expensive and safety-challenged experimental means. This has instigated a shift towards scientific computations to gain insights into and predict the impact response of energetic materials. In this study, we refine the phonon-vibron coupling coefficients ζ in energetic materials subjected to impact loading, building upon the foundation of the phonon up-pumping model. Considering the full range of interactions between high-order phonon overtones and molecular vibrational frequencies, this is a pivotal element for accurately determining phonon-vibron coupling coefficients ζ. This new coupling coefficient ζ relies exclusively on phonon and molecular vibrational frequencies within the range of 0-700 cm-1. Following a regression analysis involving ζ and impact sensitivity (H50) of 45 molecular nitroexplosives, we reassessed the numerical values of damping factors, establishing a = 2.5 and b = 35. This coefficient is found to be a secondary factor in determining sensitivity, secondary to the rate of decomposition propagation and thermodynamic factor (heat of explosion). Furthermore, the relationship between phonon-vibron coupling coefficients ζ and impact sensitivity was studied in 16 energetic crystalline materials and eight nitrogen-rich energetic salts. It was observed that as the phonon-vibron coupling coefficient increases, the tendency for reduced impact sensitivity H50 still exists.

A Method for Predicting the Melting Temperature of Ionic Compounds.

Predicting the melting temperature of materials has always been a topic of great concern. This article proposes an alternative model for determining the melting temperature of materials based on the main idea of the Lindemann melting criterion combined with the first-principles calculations of density functional theory. To verify the accuracy of the melting model, this article selected typical ionic crystals of MgO and 10 alkali metal halides as the validation objects. The calculation results indicate that the melting temperature of the MgO crystals and I-VII compounds is in good agreement with the experimental results.

Molecular Structures, Dipole Moments, and Electronic Properties of ß-HMX under External Electric Field from First-Principles Calculations.

In order to investigate the impact of an external electric field on the sensitivity of ß-HMX explosives, we employ first-principles calculations to determine the molecular structure, dipole moment, and electronic properties of both ß-HMX crystals and individual ß-HMX molecules under varying electric fields. When the external electric field is increasing along the [100], [010], and [001] crystallographic directions of ß-HMX, the calculation results indicate that an increase in the bond length (N1-N3/N1'-N3') of the triggering bond, an increase in the main Qnitro (N3, N3') value, an increase in the minimum surface electrostatic potential, and a decrease in band gap all contribute to a reduction in its stability. Among these directions, the [010] direction exhibits the highest sensitivity, which can be attributed to the significantly smaller effective mass along the [010] direction compared with the [001] and [100] directions. Moreover, the application of an external electric field along the Y direction of the coordinate system on individual ß-HMX molecules reveals that the strong polarization effect induced by the electric field enhances the decomposition of the N1-N3 bonds. In addition, due to the periodic potential energy of ß-HXM crystal, the polarization effect of ß-HMX crystal caused by an external electric field is much smaller than that of a single ß-HXM molecule.

Triggering the mechanism of the initial reaction of energetic materials under pressure based on Raman intensity analysis.

The Raman intensity and other stoichiometric calculations of nitromethane (NM) and 2-nitrimino-5-nitro-hexahydro-1,3,5-triazine (NNHT) have been made by using first-principles density functional theory. We propose a method to judge the initial reaction mechanism of NM and NNHT under pressure based on the Raman intensity. Both the resulting NM and NNHT undergo hydrogen transfer and conventional trigger bond cleavage. And the results obtained from the Raman peak intensities infer a reaction path that is not inferior to the traditional C-NO2 and N-NO2 bond cleavage, thus verifying our results.

Atomic mean square displacement study of the bond breaking mechanism of energetic materials before explosive initiation.

Understanding and predicting the bond breaking mechanism of energetic materials before explosion initiation is one of the huge challenges in explosion science. By means of the mean square displacement of the atom from the equilibrium position and theoretical bond breaking tensile change of the chemical bond, we establish a new criterion to judge whether the chemical bond is broken. Further, α-RDX is used as the verification object to verify the accuracy of this model. We obtained an initial decomposition temperature of 434-513 K for α-RDX at 0 GPa, and the initial bond breaking type was N-NO2. Finally, based on this model, we discussed in detail the breaking of chemical bonds of solid nitromethane near the detonation pressure. We think that the high temperature and high pressure caused by the shock wave may break all the chemical bonds of nitromethane near the detonation pressure.

A simulation study on the phase transition behavior of solid nitrogen under extreme conditions.

There are numerous examples of materials that exhibit interesting phenomena at extremely low temperatures, but the difficulty of obtaining absolute zero at high pressure in experiments is sometimes a hurdle to reveal the exact explanation of these low temperature phenomena. Based on the calculations of the phonon spectrum and Gibbs free energy of α-N2 and γ-N2 under different pressures, we found that solid nitrogen at 0 K showed a re-entrant phase transition under continuously increasing pressure. The extremely low temperature in this pressure range turned out to be the main external condition for inducing phase transition as well as phase reversal.

Composition and structural characteristics of compressed alkaline earth metal hydrides.

The metallization of alkaline earth metal hydrides offers a way to achieve near-room temperature superconductivity. In order to explore the metallization mechanism of these hydrides under pressure, a detailed understanding of the property changes of alkaline earth metal hydrides is required. Based on first-principles calculations, we have systematically investigated the dihydrides (XH2, X = Be, Mg, Ca, Sr, Ba) and tetrahydrides (XH4, X = Mg, Ca, Sr, Ba) of alkaline earth metals, respectively. By applying external pressure, we show that the structures of these alkaline earth metal hydrides undergo a series of phase transitions. Moreover, we investigate how the size of the bandgap decreases and eventually closes and reveal the role of electronegativity of metal elements in the critical pressure of hydride metallization. Remarkably, the hydrogen units (H6 or H8) formed in XH4 can accelerate the metallization process. The increase of the energy level difference in hydrogen units promotes the electroacoustic coupling effect, which is conducive to realization of high superconducting transition temperature (Tc). Our theoretical findings identify MgH4-I4/mmm as having potential to be a high-temperature superconductor and provide unusual ideas for the search of unknown high-temperature superconducting materials.

Electrons and phonons of the discharge products in the lithium-oxygen and lithium-sulfur batteries from first-principles calculations.

Batteries have become a ubiquitous daily necessity, which are popularly applied to mobile phones and electric vehicles according to their size. Improving the battery cycle life and storage is important, but unexpected discharge products still restrict the upper limit of batter performance such as Li2O2, LiO2, and Li2S. In this study, we calculated electrons and phonons presenting the basic energy states in crystal using the first-principles calculations. The Li2O2 and Li2S are almost insulating due to the wide bandgap from their electronic structure, and doped-active p-orbital may be one of the pathways to improve crystal conduction due to the tendency of the density of states. The LiO2 is metallic, and the electronic structure and phonons show that the discharge products have an ionic feature. In addition, the ionic crystal can produce a larger DC permittivity because it possesses macroscopic polarisation. For Li2O2 and Li2S, the Raman peak of the O-O bonding is strong, while the Raman peak of the S-ion is very weak. The enhanced Raman peak of the S-ion presents a possibility to prevent the shuttle effect in Li-S batteries.

Theoretical study on the correlation between the structure, excess energy, surface energy, electronic structure, nitro charge, and friction sensitivity of N,N'-dinitroethylenediamine (EDNA).

The sensitivity of energetic materials along different crystal directions is not the same and is anisotropic. In order to explore the difference in friction sensitivity of different surfaces, we calculated the structure, excess energy, surface energy, electronic structure, and the nitro group along (1 1 1), (1 1 0), (1 0 1), (0 1 1), (0 0 1), (0 1 0), and (1 0 0) surfaces of EDNA based on density functional theory. The analysis results showed that relative to other surfaces, the (0 0 1) surface has the shortest N-N average bond length, largest N-N average bond population, smallest excess energy and surface energy, widest band gap, and the largest nitro group charge value, which indicates that the (0 0 1) surface has the lowest friction sensitivity compared to other surfaces. Furthermore, the conclusions obtained by analyzing the excess energy are consistent with the results of the N-N bond length and bond population, band gap, and nitro charge. Therefore, we conclude that the friction sensitivity of different surfaces of EDNA can be evaluated using excess energy.

Initial Decomposition of DATB Induced by an External Electric Field.

1,3-Diamino-2,4,6-trinitrobenzene (DATB), a nitro aromatic explosive with excellent properties, can be detonated by an electric field. Using first-principles calculation, we have investigated the initial decomposition of DATB under an electric field. In the realm of electric fields, the rotation of the nitro group around the benzene ring will cause deformation of the DATB structure. Furthermore, when an electric field is applied along the [100] or [001] direction, the C4-N10/C2-N8 bonds initiate decomposition due to electron excitation. On the contrary, the electric field along the [010] direction has a weak influence on DATB. These, together with electronic structures and infrared spectroscopy, give us a visual perspective of the energy transfer and the decomposition caused by C-N bond breaking.

Berberine and folic acid co-modified pH-sensitive cascade-targeted PTX-liposomes coated with Tween 80 for treating glioma.

Chemotherapy is a conventional treatment for glioma, but its efficacy is greatly limited due to low blood-brain barrier (BBB) permeability and lack of specificity. Herein, intelligent and tumor microenvironment (TME)-responsive folic acid (FA) derivatives and mitochondria-targeting berberine (BBR) derivatives co-modified liposome coated with Tween 80 loading paclitaxel (PTX-Tween 80-BBR + FA-Lip) was constructed. Specifically speaking, liposomes modified by FA can be effectively target ed to glioma cells. BBR, due to its delocalized positive electricity and lipophilicity, can be attracted by mitochondrial membrane potential and concentrate on mitochondria to achieve mitochondrial targeting and induce cell apoptosis. By simultaneously modifying the liposome with FA and BBR to deliver drugs, leads to a good therapeutic effect of glioma through FA-based glioma targeting and BBR-based mitochondrial targeting. In addition, the surface of the liposome was coated with Tween 80 to further improve BBB penetration. All results exhibited that PTX-Tween 80-BBR + FA-Lip can observably improve the chemotherapy therapeutic efficacy through the highly specific tumor targeting and mitochondrial targeting, which can provide new ideas and methods for the targeted therapy of glioma.

Doping effects on the antibonding states and carriers of two-dimensional PC6.

The absence of a bandgap in pristine graphene severely restricts its application, and there is high demand for other novel two-dimensional (2D) materials. PC6 has recently emerged as a promising 2D material with a direct band gap and ultrahigh carrier mobility. In light of the remarkable properties of an intrinsic PC6 monolayer, it would be intriguing to find out whether a doped PC6 monolayer displays properties superior to the pure system. In this study, we have performed density functional theory calculations to understand the doping effects of both P-site and C-site substitution in PC6 and, for the first time, we discovered doping-related impurity-level anomalies in this system. We successfully explained why no donor or acceptor defect states exist in the band structures of XP-PC6 (X = C, Ge, Sn, O, S, Se, or Te). In group-IV-substituted systems, these dopant states hybridize with host states near the Fermi level rather than act as acceptors, which is deemed to be a potential way to tune the mobility of PC6. In the case of group-VI substitution, the underlying mechanism relating to doping anomalies arises from excess electrons occupying antibonding states.

The effect of pressure on the structural, electronic and vibrational properties of solid carbon dioxide phases.

The structural, electronic and vibrational properties of solid carbon dioxide phases (I, II, III, and IV) under high pressure are studied using first-principles calculations. The calculated structural parameters are in good agreement with the experimental values. The third-order Birch-Murnaghan equation of state is fitted, and the corresponding parameters are obtained. We obtained the phase boundary points of each phase and plotted the phase diagram of solid carbon dioxide. The influence of pressure on the band structure and density of states is studied. The vibrational properties of the four phases of carbon dioxide were studied in detail, and the infrared and Raman spectra of the four phases were obtained. It can be seen from the calculated spectrum that the number and frequency of vibration peaks are in good agreement with the experimental values. And, we also analyze the influence of pressure on the frequency of vibration mode.

E-Learning during COVID-19: perspectives and experiences of the faculty and students.

BACKGROUND: Aimed to corroborate students' and faculty's experiences with e-learning during the current pandemic. METHODS: A cross-sectional study was conducted from February to June 2020. Seven surveys were distributed electronically to all undergraduate students and the faculty (4 to students and 3 to teachers) at the Southern Medical University (China). Descriptive statistics and t-tests were used to analyze the data. Statistical significance was set at p < .05. RESULTS: Most students had some exposure to e-learning prior to the all e-learning regiment, contrasted with close to 90% of teachers having no or very limited experience. Students' perceptions of the most helpful e-learning activities did not change significantly overall (Week 3 vs. Week 9). Approaching 60% of students (Week 9) did find online discussion/Q&A/forum helpful, an increase from less than 30% (Week 3). Among teachers, gaps emerged (Week 9) between e-teaching activities used and their perceived effectiveness. Despite pre-recorded lectures being the most frequently used method, the least gap was associated with live-stream lectures-the least used. Over time, teacher's perceived effectiveness of e-teaching vs. in-person teaching did not differ significantly overall. When the results among students (Week 7) and teachers (Week 9) were corroborated, a slightly higher percentage of teachers viewed online teaching to be less effective than in-person teaching and a slightly higher percentage of teachers viewed online teaching as far less effective. For preferred learning modes after the resumption of in-person learning, students' preferences did not differ significantly overall (Week 3 vs. week 9). Surveys conducted in Week 9 found that a slightly higher percentage of students (~ 70%) than teachers (~ 60%) preferred some forms of hybrid learning and a lower percentage of students preferred face-to-face learning only. Approximately three quarters of teachers responded that at least 50% of course materials could be mastered by students on their own. CONCLUSIONS: Overall, the perceived effectiveness of e-learning among students and teachers has not changed significantly over time. Nor have students' preferences shifted significantly for various learning modes after the in-person learning resumed. However, informative directional trends have emerged. Our research illustrates empirically the need to corroborate students' and instructors' experiences over time to inform more holistic improvements of e-learning.

Compositions and Biological Activities of Pomegranate Peel Polyphenols Extracted by Different Solvents.

Pomegranate peel extract (PPE), which is abundant in polyphenols, holds immerse prospects for the treatment of airway infection. In this study, water and ethanol of 30%, 50%, and 80% were used to prepare PPE. A total of 18 phenols belonging to 8 categories of polyphenols were identified in PPE by HPLC-MS/MS. The PPE from the four extraction solvents possessed different antioxidant, antibacterial, and anti-inflammatory activities. Principal component analysis revealed that though total flavonoids (TFs), total polyphenols (TPs), and total tannins (TTs) were responsible for the reducing power of PPE, only TFs contributed to the effect of PPE in inhibiting lipid membrane peroxidation. TPs, TTs, and punicalagin were positively correlated with the antibacterial strength against S. aureus while TTs alone contributed to the inhibition of methicillin-resistant S. aureus, implying the crucial role of TT in suppressing bacteria. Meanwhile, TTs was associated with the prevention of IL-6 release. The PPE with higher contents of TPs, TTs, and punicalagin had a weaker capacity to decrease nitric oxide secretion. PPE of 30% ethanol gained the highest integrated score due to its stronger antioxidant, antibacterial, and anti-inflammatory activities. It is a suitable candidate for the therapy of respiratory tract infection.

Biotin and glucose co-modified multi-targeting liposomes for efficient delivery of chemotherapeutics for the treatment of glioma.

Glioma is one of the most common primary intracranial tumor, but the current treatments of glioma are far from satisfying. As the major treatment option for malignant glioma, chemotherapy has its own disadvantages, including low chemotherapeutic agents delivery across blood-brain barrier (BBB) and lack of specificity. Therefore, new approach permitting glioma targeting ability that can allow an efficient therapeutic delivery into the glioma regions is urgently required. Ligand-mediated liposomes have shown great potential for improving the efficiency of glioma treatment. In our study, the multi-targeting liposomes based on glucose and biotin were constructed for the first time. We synthesized two ligands (Glu3-Chol, Bio2-Chol), prepared three types of modified liposomes (Glu3-Lip, Bio2-Lip and Bio2 + Glu3-Lip) and evaluated the glioma-targeting ability of these liposomes which were using paclitaxel (PTX) as the model drug in vitro. Besides, the uptake mechanism of Bio2 + Glu3-Lip was investigated. PTX-loaded Bio2 + Glu3-Lip (PTX-Bio2 + Glu3-Lip) exhibited satisfactory targeting effect in Bend.3 and C6 cells in vitro, in which the cellular uptake of Bio2 + Glu3-Lip were 4.04- and 3.49-fold more than that of the uncoated liposomes (Lip). The results suggested the multi-targeting liposomes (Bio2 + Glu3-Lip) is a promising formulation for glioma, which was almost consistent with the results of in vivo imaging. In summary, we have designed and fabricated an effective delivery system to treat glioma.

Explanation for the conductivity difference of half-Heusler transparent conductors via ionization energy.

To further understand the less-studied half-Heusler transparent conductors, we have considered four 18-electron ABX compounds (TaIrGe, TaIrSn, ZrIrSb, and TiIrSb) to focus on their carrier effective masses and ionization energies. The novelty of this work lies in two aspects: (i) we discover that hole-killer defects are more likely to form in TaIrGe than in ZrIrSb, which leads to a lower concentration of the holes in TaIrGe. This is the fundamental reason for the conductivity of TaIrGe being much lower than that of ZrIrSb; (ii) we propose that the hole effective mass near the sub-valence band maximum (Sub-VBM) could be used to forecast the potential transport performance of the materials. The obtained results show that the transport performance of TaIrGe & TaIrSn is potentially more promising than that of TiIrSb and ZrIrSb. Besides, this work firstly studies the mechanical properties of the considered ABX compounds, offering strong evidence that TaIrGe, TaIrSn, ZrIrSb, and TiIrSb could be potentially flexible and ductile TCMs.

Judging the phase transition pressure of the unknown parent phase if the resulting state is known.

In high-pressure phase transition experiments, the crystal structure of the intermediate phase in some phase transitions is difficult to successfully measure due to the limitations of the experimental conditions. The absence of crystal structure data for the intermediate phase also makes it difficult to calculate the pressure point from the intermediate phase to the new phase by the traditional thermodynamic criterion in theoretical simulations. The Conch Criterion is employed by us to successfully verify the phase transition points by observing the reverse shifts of the DOS (electron density of states) curves for the new phase of Cu2S, PbS, PbSe and PbTe, which breaks through the constraints of the traditional criterion and realizes tracing the source of the phase transition in theoretical calculations.

Liposomes modified with double-branched biotin: A novel and effective way to promote breast cancer targeting.

Although active targeting liposomes with cancer-specific ligands can bind and internalize into cancer cells, only a few high-efficiency liposomes have been developed so far because traditional single branched ligand modified liposomes generally failed to deliver adequate therapeutic payload. In this paper, we broke the traditional design concept and synthesized the double branched biotin modified cholesterol (Bio2-Chol) for the first time. On this basis, different biotin density modified liposomes ((Bio-Chol)Lip, (Bio-Chol)2Lip and (Bio2-Chol)Lip) were successfully prepared and used as active targeting drug delivery systems for the treatment of breast cancer. The in vitro and in vivo breast cancer-targeting ability of these liposomes were systemically studied using paclitaxel (PTX) as the model drug. And the uptake mechanism of (Bio2-Chol)Lip was investigated. The results showed that (Bio2-Chol)Lip had the best breast cancer-targeting ability compared with naked paclitaxel, unmodified Lip, (Bio-Chol)Lip and (Bio-Chol)2Lip. In particular, the relative uptake efficiency (RE) and concentration efficiency (CE) of (Bio2-Chol)Lip were respectively enhanced by 5.61- and 5.06-fold compared to that of naked paclitaxel. Both distribution data and pharmacokinetic parameters suggested that the double branched biotin modified liposome ((Bio2-Chol)Lip) is a very promising drug delivery carrier for breast cancer.

A new criterion for the prediction of solid-state phase transition in TMDs.

The classical thermodynamic criterion for phase transition predicts whether the phase transition will occur according to whether the nth derivative of the state parameter is discontinuous, and the continuity verification of multi-order derivatives increases the difficulty and complexity of judgment for phase transition to a certain extent. Based on the reverse shifts of the DOS curves near the Fermi level, we propose a new criterion for solid-state phase transition named Conch Criterion, which has been verified in the TMD system. The new criterion can observe the occurrence of phase transition from another perspective besides the thermodynamic properties while mutually confirming the thermodynamic criterion.