As lung ultrasound (LUS) is a noninvasive, radiation-free, repeatable and portable imaging tool suitable for a point-of-care use, several recent literature reports have emphasized its role as the ideal screening tool for SARS-CoV2 pneumonia. To evaluate the actual diagnostic accuracy of LUS for this purpose, we performed a systematic comparative study between LUS and CT scan ndings in a population of 82 patients hospitalized because of COVID-19. LUS and Chest CT have been performed in all patients within 6-12 hours from the admission. The sensitivity of LUS in assessing typical CT ndings was 60%. Despite LUS detected consolidations adherent to pleural surface in all cases, it was not able to detect all the consolidations assessed at CT scan (p=0.002), showing a risk to underestimate the actual disease's extent. Moreover, only 70% of pleural surface is visible by LUS. Considering that the speci city and the positive predictive value of the same LUS signs may be lowered in a normal setting of non epidemic COVID-19 and in case of pre-existing cardio-pulmonary diseases, LUS use should not be indicated for diagnosis of COVID-19. However, it may be very useful for the assessment of pleural effusion and to guide safer uid drainage.

The pi-stacked interactions in some explosive crystal packing are discussed. Taking a typical pi-stacked explosive 2,4,6-trinitrobenzene-1,3,5-triamine (TATB) as a sample and using molecular simulations, we investigated the nature of the pi-stacked interactions versus the external mechanical stimuli causing possible slide and compression of explosives. As a result, between the neighbor layers in the TATB unit cell, the electrostatic attraction decreases with a little decrease of vdW attraction when its top layer slides, whereas the vdW attraction increases with a decrease of electrostatic attraction when TATB crystal is compressed along its c axis. Meanwhile, we studied the correlation between the pi-stacked structures and the impact sensitivities of explosives by means of three representatives including TATB with typical planar pi-stacked structures, 2,2-dinitroethylene-1,1-diamine (Fox-7) with wavelike pi-stacked structures, and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) without pi-stacked structure. The results showed that pi-stacked structures, particularly planar layers, can effectively buffer against external mechanical stimuli. That is, pi-stacked structures can partly convert the mechanical energy acting on them into their intermolecular interaction energy, to avoid the increase of the molecular vibration resulting in the explosive decomposition, the formation of hot spots, and the final detonation. This is another reason for the low mechanical sensitivity of pi-stacked explosives besides their stable conjugated molecular structures.

Low-sensitivity and high-energy explosives (LSHEs) are highly desired for their comprehensive superiority of safety and energy. Crystal packing is crucial to both the safety and energy, and therefore becomes of interest in energetic crystal engineering. This work carries out systemic analyses on the crystal packing of 11 existing LSHEs with both energy and safety close or superior to TNT. As a result, we find that the LSHE crystals wholly feature π−π stacking with the aid of intermolecular hydrogen bonding. Each LSHE molecule is πbonded with a big conjugated structure composed of all nonhydrogen atoms in the entire molecule. Intramolecular hydrogen bonding exists in most LSHE molecules with strongly active hydrogen bond (HB) donors of amino and hydroxyl groups, and various strength. These big π-conjugated structures and intramolecular HBs lead to planar molecules with high stability, settling a base of π−π stacking in crystals. With the help of intermolecular HBs, the π−π stacking holding the LSHE crystals appears in four modes. Among them, the face-to-face stacking (always offset) gives rationally the smallest steric hindrance when interlayer slide occurs in crystal, which is the reason for very low impact sensitivity. This work suggests that the planar conjugated molecular structure and intermolecular hydrogen bonding supporting the π−π stacking are necessary to the crystal engineering of LSHEs.

Molecular and crystal designs are crucial to the engineering of high-energy explosives, which are a class of substantial materials usually with high costs and high risks.Understanding their structures, properties, and performances, and the relationships among them is the basis for the design. As a continuation of a systemic analysis of the crystal packing of low-sensitivity and high-energy explosives (LSHEs) (Cryst. Growth Des. 2014, 14, 4703−4713), we present in this work another analysis of 10 existing impact-sensitive high-energy explosives (SHEs), which possess both velocities of detonation and impact sensitivity close to or higher than those of RDX. We find that SHE molecules are usually less stable than LSHE ones, due to the deficiencies of big π-conjugated molecular structures, and adequate and strong intramolecular hydrogen bonds (HBs) even though H atoms are contained. The intermolecular HBs cannot be formed sometimes in H-contained SHE crystals, and the noncovalent O•••O interactions dominate the connection of SHE molecules to build a three-dimensional network and hold crystals, generally, with the strength above intermolecular HBs. The absence of single-atom-layered stacking in SHE crystals makes the intermolecular sliding difficult or even unallowed when against impact, which leads to inefficiency of energy buffering and ease of molecular decay, hot spot formation, and final combustion or detonation. In contrast to LSHEs, SHEs are disadvantageous on dual structural levels causing their high sensitivity: molecules with low stability and crystals without HB-aided single-atom-layered stacking. It re-verifies that the intermolecular HB-aided π−π stacking is necessary for crystal engineering of LSHEs, which are highly desired currently.

A novel image-intensified charge-coupled device (ICCD) imaging system has been developed to perform 3D fluorescence tomographic imaging in the frequency-domain using near-infrared contrast agents. The imager is unique since it (i) employs a large tissue-mimicking phantom, which is shaped and sized to resemble a female breast and part of the extended chest-wall region, and (ii) enables rapid data acquisition in the frequency-domain by using a gain-modulated ICCD camera. Diffusion model predictions are compared to experimental measurements using two different referencing schemes under two different experimental conditions of perfect and imperfect uptake of fluorescent agent into a target. From these experimental measurements, three-dimensional images of fluorescent absorption were reconstructed using a computationally efficient variant of the approximate extended Kalman filter algorithm. The current work represents the first time that 3D fluorescence-enhanced optical tomographic reconstructions have been achieved from experimental measurements of the time-dependent light propagation on a clinically relevant breast-shaped tissue phantom using a gain-modulated ICCD camera.