Effect of Hole Density and Confining Pressure on Mechanical Behavior of Porous Specimens:An Insight from Discrete Element Modeling

Hole-like defects are very common in natural rock or coal mass,and play an important role in the failure and mechanical behaviors of rock or coal mass.In this research,multi-holed coal specimens are constructed numerically and calibrated based on UDEC-GBM models.Then,the strength,deformation and failure behavior of the porous specimens are analyzed,with consideration of hole density(P)and confining pressure(σ_(3)).The simulation results are highly consistent with those available experiment results,and show that the compressive strength decreases exponentially with the increasing hole density.The strength loss is mainly caused by the reduction of cohesion when P<P_(cr)(critical hole density)and the reduction of frictional angle when P>P_(cr).Also,the increasing hole density linearly reduces the tangent and secant modulus and causes greater nonlinear deformation of multi-holed specimens.Finally,the failure patterns,coalescence mechanism and damage behavior of the multi-holed specimens are revealed based on the analysis of mesoscopic displacement fields and stress distribution around holes.This research promotes a better understanding of the effects of hole density and confining pressure on the failure and mechanical behavior of porous geomaterials.

Determination of Electrical Conductivity of Cadaver Skeletal Muscle: A Promising Method for the Estimation of Late Postmortem Interval

The electrical conductivity(EC)of extracted muscle fluid has been extensively used to evaluate meat freshness and shelf life in the field of food sanitation for decades.The opposite of freshness is the corruption that increases with time.Based on the freshness/corruption principle,we investigated the relationship between long postmortem intervals(PMIs)and EC in cadaver skeletal muscle.EC values of extracted fluid from rat muscles were measured at different PMIs for 10 days.The results indicate that there was a significant correlation between PMI and EC,and the data fit well to the cubic polynomial regression equation y=‑0.01x3+0.264x2‑13.657x+1769.148(R2=0.925).In addition,the EC of different dilutions of these muscle extracts showed strict quadratic correlation(R2=1)with the dilution ratios,suggesting that EC can be measured with very small quantities of muscle sample.Our study suggests that determination of the EC of cadaver skeletal muscle extracts may be a useful method for estimating long PMIs.

Determining the Electrical Conductivity of Rat Cadaveric Liver,Spleen,and Kidney to Estimate Early Postmortem Interval

Previous research has found that electrical conductivity(EC),an important index to predict meat freshness and shelflife,is very promising for estimating the late postmortem interval(PMI).However,whether it has potential use in the early PMI has not been fully studied yet.To test this possibility in the present study,EC of three internal organs of rat liver,spleen,and kidney were determined within 24 postmortem hows,and then,EC changes at different PMIs were carefully analyzed.The overall results showed that EC of liver and spleen increased significantly with PMI while EC of kidney had minor changes during the same period.Specifically,significant linear positive correlations between EC of liver and spleen and PMI were found and the coefficients of their regression functions were R^(2)=0.98 and R^(2)=0.95,respectively.It can be concluded that determination of EC in certain internal organs such as liver and spleen may be a potential tool in the early PMI estimation.However,more researches on its influencing factors are needed to facilitate its final use in practice.

A GQD-based composite film as photon down-converter in CNT/Si solar cells

Graphene quantum dots (GQDs), have unique quantum confinement effects, tunable bandgap and luminescence property, with a wide range of potential applications such as optoelectronic and biomedical areas. However, GQDs usually have a strong tendency toward aggregation especially in making solid films, which will degrade their optoelectronic properties, for example, causing undesired fluorescence quenching. Here, we designed a composite film by embedding GQDs in a polyvinyl pyrrolidone (PVP) matrix through hydrogen bonding with well-preserved fluorescence, with a small addition of acid for compensating the poor conductivity of PVP. As a multifunctional solid coating on carbon nanotube/silicon (CNT/Si) solar cells, the photon down-conversion by GQDs and the PVP anti-reflection layer for visible light lead to enhanced external quantum efficiency (by 12.34% in the ultraviolet (UV) range) and cell efficiency (up to 14.94%). Such advanced optical managing enabled by low-cost, carbon-based quantum dots, as demonstrated in our results, can be applied to more versatile optoelectronic and photovoltaic devices based on perovskites, organic and other materials.

High-efficiency CNT-Si solar cells based on a collaborative system enabled by oxide penetration

Carbon nanotube-silicon(CNT-Si)solar cells represent one of the alternative photovoltaic techniques with potential for low cost and high efficiency.Here,we report a method to improve solar cell performance by depositing conventional transitional metal oxides such as WO_(3)and establishing a collaborative system,in which CNTs are well-embedded within the WO_(3)layer and both of them are in close contact to Si substrate.This unique collaborative system optimizes the overall energy conversion process including the light absorption(antireflection by WO_(3)),carrier separation(forming quasi p-n junction)and charge collection(CNT conductive network throughout the oxide layer).Combining with our previous TiO_(2)-coating and HNO_(3)-doping techniques,a solar cell efficiency of>18%at an active area of 0.09 cm 2(air mass 1.5,100 mW/cm^(2))was achieved.The oxide-enhanced CNT-Si solar cells which integrate the advantages of traditional semiconductors and novel nanostructures represent a promising route toward next-generation high-performance silicon-based photovoltaics.

Comparison of “Normal” Craniocerebral Computed Tomography of Deceased and Living Individuals

To compare“normal”craniocerebral computed tomography(CT)of deceased and living individuals.Nineteen parameters of craniocerebral CT scans of 50 deceased and 50 living individuals that met specific filtering criteria were measured separately:The intensity(CT value)ratio of gray matter to white matter(GM/WM),maximum and minimum length of frontal horn of ventricle,transverse diameter of cerebral parenchyma,length of choroid plexus,maximum external diameter of body of lateral ventricle,maximum internal transverse diameter of cranium,length of cerebral longitudinal fissure,length between two calvarium,transverse and longitudinal diameter of the third and fourth ventricle,length of the cerebral longitudinal fissure,Hackman value,ventricular index(D/A),index of the somatic part of lateral ventricle(F/E),lateral ventricular body index(G/E),frontal horn index(G/A),and ventriculocranial ratio(VCR).The values of these 19 parameters for the deceased and living individuals were performed using statistical methods.There were significant statistic differences between deceased and living individuals in terms of eight craniocerebral CT parameters,including GM/WM,D/A,transverse diameter of the fourth ventricle,and length of the cerebral longitudinal fissure.The craniocerebral CT findings differ between deceased and living individuals.Knowledge of the normal postmortem craniocerebral CT parameters is key to correct postmortem craniocerebral radiopathological diagnosis.

Estimation of the Postmortem Interval Using Chromatographic Fingerprints of Volatile Organic Compounds from Muscle

Estimation of the postmortem interval(PMI)is a crucial task in the field of forensic pathology and has unfortunately not been properly resolved.In this study,we analyzed volatile organic compounds(VOCs)in rat muscle samples collected at different PMIs and studied the feasibility of muscle VOC fingerprinting as a new method for PMI estimation.In total,110 rats were sacrificed and stored at a constant temperature(25℃).Rat skeletal muscle samples were collected at 0-10‑day postmortem,and then the VOCs were determined using a method of headspace solid‑phase microextraction coupled with gas chromatography‑mass spectrometry.The correlations between the VOCs(species and quantities)and PMIs were carefully analyzed and standard muscle VOC fingerprints at 25℃were established for different PMIs.To further test the accuracy of muscle VOC fingerprinting as a method for PMI estimation,ten additional rats with known PMIs were studied.We identified 15 kinds of VOCs and the number of VOC species increased with the PMI.The total peak areas of the VOCs increased significantly with the postmortem day(adjusted R^(2)=0.96-0.97).The mean error of the VOC fingerprinting for PMI estimation was 0.5 days and the mean relative error was 8.33%.We concluded that muscle VOC fingerprinting combining the use of VOC species and peak areas is accurate and effective and could be used as an alternative approach for PMI estimation in forensic practice.Although the preliminary results are encouraging,further studies in human cadavers under real case conditions are needed.

CNT array-induced nanobubble assembly,nanodisk fabrication and enhanced spectral detection of CNT bundle density

Alignment,functionalization and detection of carbon nanotube(CNT)bundles are vital processes for utilizing this onedimensional nanomaterial in electronics.Here,we report a polymer-assisted wet shearing method to acquire super-aligned craterpatterned CNT arrays by nanobubble(NB)self-assembly with a"migrate and aggregation"mechanism and use craters to controllably mold even-sized nanodisks periodically along CNT bundles with tunable densities.This green,low-cost method can be extended to diverse substrates and fabricate different nanodisks.As an example,the Ag-nanodisk-patterned CNT arrays are utilized as substrates of surface-enhanced Raman scattering(SERS)for rhodamine 6G(R6G)and methylene blue(MB)in which a linear correlation is found between the SERS intensity and the CNT bundle density due to the periodic distribution of hot spots,enabling a spectral detection of CNT bundles and their densities by conventional dye molecules.Distinguishing from routine morphological characterization,this spectral method possesses an enhanced accuracy and a detection range of 0.1–2μm^(–1),showing its uniqueness in the detection of CNT bundle density since the intensity of traditional spectral merely relates to the quantity of CNTs,exhibiting its potential in future CNT-bundle-based electronics.