Inserting auxeticity into graphene oxide via bottom-up strategy.

Carbon-based materials that process a wide bandgap, high mechanical performance, thermal stability and adjustable characteristics are in high demand. Auxeticity is one of the factors that helps enhances the mechanical performance. Based on this concept, two stable layered carbon-based materials, namely α-C2O and ß-C2O, are proposed. A new mechanism (multi-directional negative Poisson's ratio (NPR) effect) is induced, which is attributed to the interaction of modified pz orbitals between interfacial layers. This effect introduces high mechanical properties into materials. Besides, all layered materials are ultrawide bandgap semiconductors, which endows them comparable dielectric properties to those of diamond. Furthermore, α-BK-C2O would maintain its configuration over 2000 K, thereby guaranteeing extremely high thermodynamic stability. So far, these advantages suggested that these carbon-based layer materials could be used in nanoelectronics, especially in electromechanical devices.

Development of Megaselia scalaris at constant temperatures and its significance in estimating the time of death.

Megaselia scalaris (Schmitz, 1938) (Diptera: Phoridae) is a common insect in forensic science that is frequently found in indoor cases, particularly on corpses in closed environments. Although this species is useful for estimating the minimum postmortem interval (PMImin) in the absence of Calliphoridae, there is a lack of data on its development in China. Herein, we studied the development of M. scalaris exposed to seven constant temperatures ranging from 16 to 34 °C. The mean (± SD) developmental durations of M. scalaris from egg to adult stage at 16, 19, 22, 25, 28, 31, and 34 °C were 1486.9 ± 75.3, 823.7 ± 42.8, 448.2 ± 59.8, 417.7 ± 19.7, 297.2 ± 27.3, 272.9 ± 10.4, and 253.0 ± 5.0 h, respectively. The mean (± SE) lower developmental threshold temperature (TL) and the thermal summation constant (K) were determined by a linear model as 12.69 ± 0.3 °C and 4965.8 ± 227.9-degree hours, respectively. A nonlinear model estimated the lower developmental threshold temperature, intrinsic optimum temperature, and upper lethal developmental threshold temperature as 14.58, 21.00, and 34.15 °C, respectively. We established three development models to estimate the age of the immature insect, namely the isomegalen diagram, isomorphen diagram, and thermal summation model. In addition, a regression analysis of the relationship between body length and total development time from hatching to pupariation was performed. Our findings provide a basis for applications of M. scalaris in PMImin estimations.

Developmental Indicators of Chrysomya nigripes Aubertin under Different Constant Temperature Conditions and an Application Case for Estimating the PMImin.

Chrysomya nigripes Aubertin, 1932, is a Calliphoridae species that colonize the carcass after the bloat phase and remains for long periods. Some early sarcosaprophagous insects complete one generation of development and are no longer associated with the corpse and surrounding environment, while C. nigripes larvae and pupae remain, providing a basis for the estimation of the minimum postmortem interval (PMImin) for highly decomposed or skeletonized carcasses. However, data on the growth and development of this species are not yet complete. As a result, we studied the developmental patterns of C. nigripes at eight constant temperatures ranging from 16-37 °C and constructed various developmental models, including the isomorphen diagram, isomegalen diagram, linear thermal summation model, nonlinear thermodynamic Optim SSI model, and logistic regression model. Chrysomya nigripes could not complete the entire developmental process at 16 °C, although it could be completed at other temperatures. The mean developmental times (±SD) of C. nigripes from egg to adult at 19 °C, 22 °C, 25 °C, 28 °C, 31 °C, 34 °C, and 37 °C were 644.9 ± 36.8 h, 422.9 ± 20.1 h, 323.1 ± 13.9 h, 246.6 ± 11.2 h, 202.5 ± 1.8 h, 191.5 ± 3.8 h, and 191.8 ± 2.0 h, respectively. The thermal summation constant (K) and lower critical thermal threshold (TL) derived from the linear thermal summation models were 4083.00 ± 293.39 degree hours and 12.52 ± 0.83 °C, respectively. In addition, TL, intrinsic optimum temperature (TΦ), and upper critical thermal threshold (TH) estimated by the optimized nonlinear thermodynamic Optim SSI model were 15.76 °C, 24.88 °C, and 38.15 °C, respectively. This study provides more comprehensive developmental data of C. nigripes for PMImin estimation.

Accelerating Density Functional Calculation of Adatom Adsorption on Graphene via Machine Learning.

Graphene has attracted significant interest due to its unique properties. Herein, we built an adsorption structure selection workflow based on a density functional theory (DFT) calculation and machine learning to provide a guide for the interfacial properties of graphene. There are two main parts in our workflow. One main part is a DFT calculation routine to generate a dataset automatically. This part includes adatom random selection, modeling adsorption structures automatically, and a calculation of adsorption properties. It provides the dataset for the second main part in our workflow, which is a machine learning model. The inputs are atomic characteristics selected by feature engineering, and the network features are optimized by a genetic algorithm. The mean percentage error of our model was below 35%. Our routine is a general DFT calculation accelerating routine, which could be applied to many other problems. An attempt on graphene/magnesium composites design was carried out. Our predicting results match well with the interfacial properties calculated by DFT. This indicated that our routine presents an option for quick-design graphene-reinforced metal matrix composites.

Thick quilt may severely impact the estimation of postmortem interval using forensic entomology-based methods -two case reports.

This paper introduces two indoor cases in China, characterized by bodies lying on a mattress, covered with thick quilts and wearing clothes. There were obvious deviation in the estimated minimum postmortem interval (PMImin) of the corpses using entomological methods. Based on the forensic entomology evidence from the scene, the PMImin estimated using temperature data from the nearest weather station was longer than the actual postmortem interval (PMI) based on the police investigation and the security camera footage. The most probable cause of the errors in PMImin estimation was the hindrance in heat dissipation since the corpses were covered with thick quilts while lying on the mattress. Therefore, the heat generated by the decomposition process and larval activity was hard to lose, resulting in the rapid development of insects. These case reports emphasize the importance of temperature collection in forensic entomological investigations. Our findings call for standardized temperature acquisition procedures, including which temperature measurements (body, microenvironment or ambient temperature) should be used in forensic entomological investigations when handling similar cases.

Unexpected low thermal expansion coefficients of pentadiamond.

A new carbon allotrope, pentadiamond, was recently reported in the literature. Herein, we investigate its thermal expansion and thermoelastic properties by first principles. It is observed that the bulk modulus and hardness of pentadiamond are far less than those of diamond, but the thermal expansion of pentadiamond is lower than that of diamond in the range of 0 K to 2000 K, and even negative in the temperature range of 0-190 K. The negative thermal expansion at low temperature originates from the transverse vibrations of the edge-shared atoms in the coplanar double-pentagon. The low thermal expansion at high temperature is contributed by the strong bonds in pentadiamond. Benefiting from the low thermal expansion, the elastic constants of pentadiamond decrease very slowly with respect to temperature compared with those of diamond. The low sensitivity of thermodynamic and thermoelastic properties to temperature makes pentadiamond a promising material for high anti-thermal-shock and accurate electronic device applications.

The Postmortem Interval of Two Decedents and Two Dog Carcasses at the Same Scene Based on Forensic Entomology.

In this paper, we report the estimation of the minimum PMIs of two human corpses and two dog carcasses using entomological evidence. Corpses of an elderly couple and carcasses of four dogs were found scattered on different floors in a house. The scene was very dirty. In addition, there were 12 emaciated live dogs at the scene. The corpses had been eaten by the dogs to different degrees, but the damage was greater on the man's corpse. After forensic examination, it was concluded that both individuals died of natural causes. The minimum PMIs of the two individuals and the two dogs were estimated using entomological evidence. The minimum PMIs of the other two dogs were not estimated because of the risk of contamination with the human corpses. Different insect species were found on each of the corpses and carcasses. The minimum PMIs were estimated as about 8.75 days for the woman, 4.17 days for the man, 3.13 days for the dog found in the stairwell and about 28.80 days for the dog found in the toilet. These estimations coincided with the time the woman stopped communicating with her daughter and when the electricity consumption at the house decreased significantly.

Increased room temperature ferromagnetism in Co-doped tetrahedral perovskite niobates.

Dilute magnetic semiconductors (DMSs), such as (In, Mn)As and (Ga, Mn)As prototypes, are limited to III-V semiconductors with Curie temperatures (T c) far from room temperature, thereby hindering their wide application. Here, one kind of DMS based on perovskite niobates is reported. BaM x Nb(1-x)O3-δ (M = Fe, Co) powders are prepared by the composite-hydroxide-mediated method. The addition of M elements endows BaM x Nb(1-x)O3-δ with local ferromagnetism. The tetragonal BaCo x Nb(1-x)O3-δ nanocrystals can be obtained by Co doping, which shows strong saturation magnetization (M sat) of 2.22 emu g-1, a remnant magnetization (M r) of 0.084 emu g-1 and a small coercive field (H c) of 167.02 Oe at room temperature. The ab initio calculations indicate that Co doping could lead to a 64% local spin polarization at the Fermi level (E F) with net spin DOS of 0.89 electrons eV-1, this result shows the possibility of maintaining strong ferromagnetism at room temperature. In addition, the trade-off effect between the defect band absorption and ferromagnetic properties of BaM x Nb(1-x)O3-δ is verified experimentally and theoretically.

Solution-Based Synthesis of Layered Two-Dimensional Oxides as Broadband Emitters.

Preparing transition-metal oxides in their two-dimensional (2D) form is the key to exploring their unrevealed low-dimensional properties, such as the p-type transparent superconductivity, topological Mott insulator state, existence of the condensed 2D electron/hole gas, and strain-tunable catalysis. However, existing approaches suffer from the specific constraint techniques and precursors that limit their product types. Here, we report a solution-based method to directly synthesize KNbO2 in 2D by an out-of-the-pot growth process at low temperature, which is observed directly in real time. The developed method can also be applied to other 2D ternary oxide syntheses, including CsNbO2 and composited NaxK1-xNbO2, and it can be extended to the preparation of self-assembled nanofilms. In addition, We demonstrate the emission of broadband photoluminescence (PL, λ ∼ 350-800 nm) from as-synthesized single-crystal 2D KNbO2 sheets down to a single unit cell thickness. The ultra-broadband emission is ascribed to the self-trapped excitation state (STEs) from the in-phase distortion of the NbO6 octahedrons in 2D NbO2- layers. Beyond the broader luminescent range and the robust material thermal stability of niobates, the absence of sample size restrictions and the large aspect ratio of the 2D oxide sheets will provide opportunities in miniaturizing and advancing 2D-materials integrated optoelectronic devices.

Giant Zeeman-type spin splitting of free electron/hole states on quasi-2D perovskite niobates: a theoretical prediction.

We study the spin-orbit interaction of two-dimensional electron/hole gas (2DEGs/2DHGs) on quasi-2D potassium niobates (KNs) via first-principles calculations. The strong surface polarity changes the free surface states from 2DEGs to 2DHGs. The in-plane dipole maintained on 2D models leads to giant Zeeman-type spin splitting, as high as 566 meV for the (001)c facet KN and 1.21 eV for the (111)c facet KN. The thickness-dependent Zeeman-type spin splitting shows a linear relation with respect to 1/r, while the corresponding in-plane polarization quantum has a linear relation of 1/(2^0.5)with respect to a decrease in thickness. Interestingly, the 2DHGs with molecular-like orbital character is solely constituted by O 2p states, showing logic switchable behavior at extremely thin samples with enormous Zeeman-type splitting that can switch between insulator and conductor by opposite spin polarization.

Estimation of post-mortem interval based on insect species present on a corpse found in a suitcase.

Murderers sometimes dispose of bodies in zipped suitcases in an attempt to conceal their crimes. In these cases, the species of insects found and their succession patterns are typically different from those found on exposed corpses due to hindrances or delays in colonization. Here we report a case in which an unidentified female corpse was found in a soft-shell suitcase in a wetland area among some reeds in Guangdong, China on 13 May 2018. The suitcase was unbroken and zippers were well-sealed. The victim was a young woman, naked, and curled up in the suitcase. The insect evidence we collected include (i) pupae and empty puparia of Chrysomya nigripes (Aubertin) (Diptera: Calliphoridae) and Fannia canicularis (Linnaeus) (Diptera, Muscidae), (ii) larvae, pupae and empty puparia of Megaselia scalaris (Loew) (Diptera: Phoridae) and Hermetia illucens (Linnaeus) (Diptera: Stratiomyidae). According to this insect evidence, we estimated the PMImin as 56 days. Bhadra et al. (2014) show that larvae of Calliphora vomitoria (Linnaeus) (Diptera: Calliphoridae) and Calliphora vicina (Robineau-Desvoidy) (Diptera, Calliphoridae) can colonize carcasses concealed in zipped suitcases. Although the size of the zipper (7mm) in this case is larger than that described in Bhadra et al. (4mm), we did not find Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae), Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae), or Lucilia sericata (Meigen) (Diptera: Calliphoridae) which usually colonize fresh corpses in this area. Therefore, we deduced that the victim may have been killed in winter. After the crime was solved, the murderer confessed that he killed the victim on 5 January.

Forensic entomology application in China: Four case reports.

We present four cases that use entomological data to estimate postmortem interval (PMI). In the first case, the body was found in an outdoor environment at 26 °C and was at the fresh stage. However, the PMImin estimated using maggots collected from the corpse was more than 68 h. This was certainly an incorrect estimation because the degree of the body decomposition was light, and it may have been caused by flies invading the corpse before death occurred. In the second case, a corpse of an adult male was found in a semi-closed room, and the body was highly decomposed and mummified. In this case, we used Dermestes maculatus DeGeer (Coleoptera: Dermestidae) to successfully estimate the PMI. The third case involved a female body discovered in her room after she committed suicide by consuming excessive clozapine and alcohol. The PMImin estimated through entomological data did not match the time of death that the other evidence indicated. Thus, we speculated that clozapine and alcohol may have influenced the development of fly larvae. The fourth case occurred in the winter. The murderer killed the victim and burned and dumped the corpse. However, the burned body still attracted necrophagous insects and we successfully calculated the PMImin by using insect evidence.

Quantum confined two-dimensional electron/hole gas switching by facet orientation of perovskite oxides.

The Polar discontinuity at heterointerface and the bare surface reconstructs the electronic phase of perovskite oxides. This gives rise to confined free electrons which intrinsically transit material from band insulator to metal. However, the insulator-metal transition induced by free holes has not been investigated so far due to the challenge in obtaining free hole state in oxides. Here, we propose a simple method whereby free holes can be obtained via polar facet reorientation. In the high polarity case, free holes can be supported by the lift up of O 2p subbands, which split into three independent subbands (one heavy hole subband and two light hole subbands) due to strong quantum confinement. Results show that both of the free electron and hole states are confined in a two dimensional quantum well, subjecting to the confined energy (E - E F) and occupied density of states around the Fermi level, indicating a finite thickness for preserving the metal states.