Identifying and eliminating false positives in thermal-assisted photocatalysis.

We discovered that employing inappropriate calibration curves for activity evaluation resulted in false positive results. Specifically, an artificial efficiency of hydrogen production is exaggerated by up to 2.2-fold if the calibration curves are misused, leading to considerably high false positive results. Our study highlights the importance of utilizing the correct calibration curve to ensure a true performance, and is beneficial for fostering advancements in the development of thermal-assisted photocatalysis.

Influence of tuberculosis knowledge on acceptance of preventive treatment and the moderating role of tuberculosis stigma among China's general population: cross-sectional analysis.

BACKGROUND: Preventive treatment of tuberculosis infection (TBI) is considered a crucial strategy to prevent and control tuberculosis (TB). However, the acceptance and completion rates of preventive therapy for TBI are still far from optimistic. Evidence is mounting that TB knowledge and stigma may have a substantial effect on acceptance of TBI treatment. This study aimed to explore the effect of stigma on the relationship between the level of TB knowledge and acceptance of TBI treatment. METHODS: 7017 general population were included in the study. We adjusted for the covariates at the individual. Stepwise logistic regression was used to examine the moderating role of TB stigma and also explore the association between TB knowledge and acceptance of TBI treatment. RESULTS: The acceptance rate of TBI treatment among the respondents was 84.38% (n = 5921). Among respondents, a significant positive correlation between acceptance of TBI treatment and TB knowledge (OR = 1.096,95%CI = 1.073,1.118). Additionally, the association between TB knowledge and acceptance of TBI treatment was found to be moderated by TB stigma. In other words, TB stigma was found to weaken the impact of TB knowledge on acceptance of TBI treatment (OR = 0.994,95%CI = 0.991,0.996). CONCLUSION: The findings of the study indicated that having a high level of awareness about TB can enhance the general population's acceptability of TBI treatment. TB stigma moderated this association; it weakened the relationship between TB knowledge and individuals' willingness to accept TBI treatment. To mitigate TB stigma and enhance the intention of individuals with TBI to accept preventive therapy, it is imperative to enhance TB-related health education.

Large-Scale Synthesis of High-Loading Single Metallic Atom Catalysts by a Metal Coordination Route.

Single atom catalyst (SAC) is one of the most efficient and versatile catalysts with well-defined active sites. However, its facile and large-scale preparation, the prerequisite of industrial applications, has been very challenging. This dilemma originates from the Gibbs-Thomson effect, which renders it rather difficult to achieve high single atom loading (< 3 mol%). Further, most synthesizing procedures are quite complex, resulting in significant mass loss and thus low yields. Herein, a novel metal coordination route is developed to address these issues simultaneously, which is realized owing to the rapid complexation between ligands (e.g., biuret) and metal ions in aqueous solutions and subsequent in situ polymerization of the formed complexes to yield SACs. The whole preparation process involves only one heating step operated in air without any special protecting atmospheres, showing general applicability for diverse transition metals. Take Cu SAC for an example, a record yield of up to 3.565 kg in one pot and an ultrahigh metal loading 16.03 mol% on carbon nitride (Cu/CN) are approached. The as-prepared SACs are demonstrated to possess high activity, outstanding selectivity, and robust cyclicity for CO2 photoreduction to HCOOH. This research explores a robust route toward cost-effective, massive production of SACs for potential industrial applications.

Developing and validating the nurse-patient relationship scale (NPRS) in China.

BACKGROUND: Poor nurse-patient relationship poses an obstacle to care delivery, jeopardizing patient experience and patient care outcomes. Measuring nurse-patient relationship is challenging given its multi-dimensional nature and a lack of well-established scales. PURPOSE: This study aimed to develop a multi-dimensional scale measuring nurse-patient relationship in China. METHODS: A preliminary scale was constructed based on the existing literature and Delphi consultations with 12 nursing experts. The face validity of the scale was tested through a survey of 45 clinical nurses. This was followed by a validation study on 620 clinical nurses. Cronbach's α, content validity and known-group validity of the scale were assessed. The study sample was further divided into two for Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA), respectively, to assess the construct validity of the scale. RESULTS: The Nurse-Patient Relationship Scale (NPRS) containing 23 items was developed and validated, measuring five dimensions: nursing behavior, nurse understanding and respect for patient, patient misunderstanding and mistrust in nurse, communication with patient, and interaction with patient. The Cronbach's α of the NPRS ranged from 0.725 to 0.932, indicating high internal consistency. The CFA showed excellent fitness of data into the five-factor structure: χ2/df = 2.431, GFI = 0.933, TLI = 0.923, CFI = 0.939, IFI = 0.923, RMSEA = 0.070. Good content and construct validity are demonstrated through expert consensus and psychometric tests. CONCLUSION: The NPRS is a valid tool measuring nurse-patient relationship in China.

Realizing ampere-level CO2 electrolysis at low voltage over a woven network of few-atom-layer ultralong silverene nanobelts with ultrahigh aspect ratio by pairing with formaldehyde oxidation.

The development of advanced multi-functional electrocatalysts and their industrial operation on paired electrocatalysis systems presents a promising avenue for the gradual penetration of renewable energy into practical production. Herein, a self-supported conductive network of silverene nanobelts (Ag-ene NBs) was delicately assembled (Ag-NB-NWs), in which ultralong and few-atom-layer Ag-ene NBs with a high edge-to-facet ratio were interconnected, serving as "superreactors" for electron transfer and mass transport during the reaction. Such superstructures as electrocatalysts delivered an unparalleled performance toward the CO2-to-CO conversion with exclusively high faradaic efficiency (FE) and partial current densities of up to 1 A cm-2. Remarkably, the membrane electrode assembly (MEA) cell with Ag-NB-NWs as the cathode was capable of ultrastable and continuous operation for over 240 h at 0.4 A with ∼100% selectivity. More importantly, by further using Ag-NB-NWs as a bifunctional electrocatalyst, a record-low voltage overall CO2 electrolysis system coupling cathodic CO2 reduction with anodic formaldehyde oxidation in MEA cell was performed to achieve concurrent feed gas generation and formate production, substantially improving electrochemical techno-economic feasibility.

Boosting CO2 piezo-reduction via metal-support interactions in Au/ZnO based catalysts.

Confronting the challenge of climate change necessitates innovative approaches for the reduction of CO2 emissions. Metal-support interaction has been widely demonstrated to enable greatly improved performances in thermal-catalytic, photocatalytic and electrocatalytic CO2 reduction. However, its applicability and specifically its role in the emerging piezo-electrocatalytic CO2 reduction are unknown, severely hampering the utilizations of piezo-electrocatalysis in CO2 conversion. Herein, by adopting Au particles supported on ZnO (Au/ZnO) as a paradigm, it is found that the metal-support interaction can remarkably improve the separation and transfer of piezo-carriers and enhance CO2 adsorption. As a result, Au/ZnO demonstrates a substantially boosted activity for piezo-electrocatalytic CO2 reduction and the optimal sample exhibits a 37.3% increase in CO yield compared to the pristine ZnO. The integration of metal-support interactions opens a new avenue to the design of advanced piezo-electrocatalysts for CO2 reduction.

Emotional labour and turnover intention among nurses in China: Mediating effects of nurse-patient relationship and self-rated health.

AIM: This study tested the mediating role of the nurse-patient relationship and self-rated health in the effect of emotional labour on turnover intention among nurses in China. BACKGROUND: The underlying mechanism behind the effect of emotional labour on turnover intention remains inadequately understood. INTRODUCTION: Nurses with a high level of emotional labour are predisposed to experiencing poor health and tension in their relationships with patients, which may increase turnover intention. METHODS: A cross-sectional survey of 527 nurses in a public tertiary hospital in Qiqihar, located in China's Heilongjiang province, was conducted. Emotional labour and turnover intention were assessed using existing validated scales containing multiple items, while the nurse-patient relationship and self-rated health were assessed using single items, respectively. Baron and Kenny's causal steps and the Karlson/Holm/Breen method were adopted to test the mediating effects of the nurse-patient relationship and self-rated health in the association between emotional labour and turnover intention after adjusting for variations in sociodemographic and job characteristics. RESULTS: Emotional labour was positively associated with turnover intention. Self-rated poor health and a disharmonious nurse-patient relationship partially mediated the positive effect of emotional labour on turnover intention. CONCLUSIONS: Emotional labour significantly affects the turnover intention of nurses working in public tertiary hospitals in China, and this effect is partially mediated by self-rated health and the nurse-patient relationship. IMPLICATIONS FOR NURSING PRACTICE AND NURSING POLICY: Giving more attention to nurses' negative emotions and work attitudes is crucial. Developing comprehensive strategies for enhancing nurses' emotional management ability, promoting their physical and psychological well-being, and improving nurse-patient relationship to reduce nurses' turnover.

Factors influencing nurse fatigue during COVID-19: regression vs. fuzzy-set qualitative comparative analysis.

Background: Nurses during COVID-19 who face significant stress and high infection risk are prone to fatigue, affecting their health and quality of patient care. A cross- sectional study of 270 nurses who went to epidemic area to support anti-epidemic was carried out via online survey during the COVID-19 pandemic on November 2021. Methods: A web-based cross-sectional survey of 270 nurses in China who traveled to Heihe City in Heilongjiang Province to combat the novel coronavirus epidemic. The researchers collected information on sociodemographic variables, anxiety, transition shock, professionalism, collaboration, hours of work per day, and fatigue. Regression and fuzzy-set Quality Comparative Analysis (fsQCA) evaluated the factors' impact on the nurses' fatigue. Results: Regression analysis showed that the psychological variables significant for fatigue, transition shock (ß = 0.687, p < 0.001) and anxiety (ß = 0.757, p < 0.001) were positively associated with fatigue, professionalism (ß = -0.216, p < 0.001) was negatively associated with fatigue, and among the work-related variables, cooperation (ß = -0.262, p < 0.001) was negatively related to fatigue. FsQCA analysis showed that combined effects of work hours, anxiety, and nurses' educational status caused most of the fatigue (raw coverage = 0.482, consistency = 0.896). Conclusion: This study provides two main findings, the one is the greater transition shock experienced during COVID-19 in a new environment, low levels of professionalism, anxiety, and poor nursing teamwork situations lead anti-epidemic nurses to increased fatigue. Second, the fsQCA results showed that anxiety is sufficient for fatigue and that nurses' educational status, daily working hours, and anxiety are the most effective combination of factors.

Anxiety and Insomnia Mediate the Association of Fear of Infection and Fatigue: A Cross-Sectional Survey of Nurses Deployed to a COVID-19 Epicenter in China.

Background: This study aimed to test the mediating role of anxiety and insomnia in the association between fear of infection and fatigue. Methods: A cross-sectional questionnaire survey was conducted on the nurses deployed to Heihe. A serial multiple mediation model was established to determine the role of anxiety and insomnia in the association between fear of infection and fatigue. Findings: Over half (53.0%) of the study participants reported experiencing fear of infection despite stringent personal protection measures. The scores of anxiety (11.87±5.19), insomnia (16.33±5.95), and fatigue (45.94±12.93) were moderately correlated, with a Pearson correlation coefficient ranging from 0.501 to 0.579. Anxiety, either alone or in combination with insomnia, mediated the association between fear of infection and fatigue. Conclusion: The findings suggest that anxiety and insomnia play a mediating role in the relationship between fear of infection and fatigue. These results emphasize the importance of implementing targeted mental health interventions and work arrangements to address the well-being of healthcare professionals.

Band Position-Independent Piezo-Electrocatalysis for Ultrahigh CO2 Conversion.

Piezo-electrocatalysis as an emerging mechano-to-chemistry energy conversion technique opens multiple innovative opportunities and draws great interest over the past decade. However, the two potential mechanisms in piezo-electrocatalysis, i.e., screening charge effect and energy band theory, generally coexist in the most piezoelectrics, making the essential mechanism remain controversial. Here, for the first time, the two mechanisms in piezo-electrocatalytic CO2 reduction reaction (PECRR) is distinguished through a narrow-bandgap piezo-electrocatalyst strategy using MoS2 nanoflakes as demo. With conduction band of -0.12 eV, the MoS2 nanoflakes are unsatisfied for CO2 -to-CO redox potential of -0.53 eV, yet they achieve an ultrahigh CO yield of ≈543.1 µmol g-1  h-1 in PECRR. Potential band position shifts under vibration are still unsatisfied with CO2 -to-CO potential verified by theoretical investigation and piezo-photocatalytic experiment, further indicating that the mechanism of piezo-electrocatalysis is independent of band position. Besides, MoS2 nanoflakes exhibit unexpected intense "breathing" effect under vibration and enable the naked-eye-visible inhalation of CO2 gas, independently achieving the complete carbon cycle chain from CO2 capture to conversion. The CO2 inhalation and conversion processes in PECRR are revealed by a self-designed in situ reaction cell. This work brings new insights into the essential mechanism and surface reaction evolution of piezo-electrocatalysis.

Air pollution and refraining from visiting health facilities: a cross-sectional study of domestic migrants in China.

BACKGROUND: Local environmental factors are associated with health and healthcare-seeking behaviors. However, there is a paucity in the literature documenting the link between air pollution and healthcare-seeking behaviors. This study aimed to address the gap in the literature through a cross-sectional study of domestic migrants in China. METHODS: Data were extracted from the 2017 China Migrants Dynamic Survey (n = 10,051) and linked to the official air pollution indicators measured by particulate matter (PM2.5 and PM10) and air quality index (AQI) in the residential municipalities (n = 310) of the study participants over the survey period. Probit regression models were established to determine the association between air pollution and refraining from visiting health facilities after adjustment for variations in the predisposing, enabling and needs factors. Thermal inversion intensity was adopted as an instrumental variable to overcome potential endogeneity. RESULTS: One unit (µg/m3) increase in monthly average PM2.5 was associated with 1.8% increase in the probability of refraining from visiting health facilities. The direction and significance of the link remained unchanged when PM2.5 was replaced by AQI or PM10. Higher probability of refraining from visiting health facilities was also associated with overwork (ß = 0.066, p = 0.041) and good self-related health (ß = 0.171, p = 0.006); whereas, lower probability of refraining from visiting health facilities was associated with short-distance (inter-county) migration (ß=-0.085, p = 0.048), exposure to health education (ß=-0.142, p < 0.001), a high sense of local belonging (ß=-0.082, p = 0.018), and having hypertension/diabetes (ß=-0.169, p = 0.005). CONCLUSION: Air pollution is a significant predictor of refraining from visiting health facilities in domestic migrants in China.

Bedtime procrastination in the relationship between self-control and depressive symptoms in medical students: From the perspective of sex differences.

BACKGROUND: Depressive symptoms typically exhibit sex differences among medical students and are associated with bedtime procrastination (BP) and self-control. However, it remains unclear whether sex differences exist in the relationship between these variables. METHODS: A cross-sectional observational study was conducted among 402 medical students from a public university in China. Students' depressive symptoms, BP, and trait self-control were assessed using the Chinese version of the Beck Depression Inventory (BDI)-II, the Bedtime Procrastination Scale, and the Self-control Scale, respectively. Applying a BDI cutoff value of 14, 364 valid participants were divided into non-depressed (<14) and depressed (≥14) groups. RESULTS: Binary logistic regression revealed that BP was an independent predictor of the prevalence of depressive symptoms in women only. Hierarchical regression showed that high BP levels were independently positively correlated to more depressive symptoms only in non-depressed women. In contrast, low self-control levels were independently negatively correlated to more depressive symptoms in non-depressed and depressed female students. Furthermore, structural equation modeling reflected the mediating role of BP between self-control and depressive symptoms in the non-depressed female group only. CONCLUSIONS: Sex differences exist in the effect of BP on depressive symptoms as well as the relationship between self-control and depressive symptoms among Chinese medical students. As a moderator, sex regulates the mediating effect of BP on the relationship between self-control and depressive symptoms in the non-depressed group. These findings provide a sex-specific perspective for targeted prevention and intervention of depressive symptoms among high-risk medical students, especially during the non-depressed period.

Inhibitory regulation of purple sweet potato polysaccharide on the hepatotoxicity of tri-(2,3-dibromopropyl) isocyanate.

Tri-(2,3-dibromopropyl) isocyanate (TBC), a new emerged persistent organic pollutant, is widely used in fields of flame retardant, textile, rubber and plastic with strong hepatotoxicity. Purple Sweet Potato Polysaccharide (PSPP) has antioxidant and hepatoprotective effects. This study aims to answer the scientific question whether PSPP has a protective effect on TBC induced liver injury. The effect of PSPP on the apoptosis of HepG2 cells was detected by MTT assay, the morphological changes were observed by morphological observation, and the apoptosis rate was determined by flow cytometry. The apoptotic genes were detected by qPCR assay, the relevant protein express was detected by western blot. The correlation between proteins and genes in the apoptosis pathway of HepG2 cells was calculated. To further reveal the apoptosis mechanism of TBC hepatotoxicity in vivo, 19 target genes and 14 apoptotic related proteins of inhibiting apoptosis via death receptor and mitochondria were discussed, all the above results proved that PSPP had protective effect on liver injury induced by TBC. This study not only provided a scientific basis for clarifying the mechanism of TBC hepatotoxicity and the protective effect of PSPP, but also generated the new point and method in terms of the prevention in advance and early intervention of diseases caused by environmental pollution.

miRNA profiling in intrauterine exosomes of pregnant cattle on day 7.

Intrauterine exosomes have been identified to be involved in the embryo development and implantation. The aim of this study was to explore the role of miRNAs in intrauterine exosomes in bovine pregnancy. Intrauterine exosomes were collected from uterine flushing fluids of three donor and three recipient Xianan cows 7 days after fertilization. Intrauterine exosomes miRNAs were extracted and the exosomal miRNAs expression levels were analyzed. Sixty miRNAs differed significantly in their amounts between donors and recipients (p-value < 0.05, |log2(FoldChange)| > 1). Twenty-two miRNAs were upregulated and 38 downregulated in the group of donor cows. The bta-miR-184 was the most significant (P Benjamini-Hochberg < 0.001). A total of 9,775 target genes were predicted using the 60 miRNAs. GO and KEGG analysis showed that the target genes were enriched in several biological processes or pathways associated with embryo implantation and endometrial development, such as cell adhesion, cell junction, focal adhesion, and Rap1 signaling pathway. Our findings suggest that, in cattle early pregnancy stage, these differently expressed miRNAs in intrauterine exosomes involved in embryo implantation and endometrial development, which may exert a significant effect and influence the uterine microenvironment for embryo implantation. These results could provide reference for screening and exploring the intrauterine exosomal miRNA affecting embryo implantation.

Copy number variation of the USP16 gene and its association with milk traits in Chinese Holstein cattle.

Copy number variations (CNVs) were similar to single nucleotide polymorphisms (SNPs) and insertion-deletion (InDel), regarded as genetic variations in many species. CNV is defined as the variable change of DNA segment length compared with the reference genome, including gains or losses from 50 bp to several mega bases. The functions of USP16 gene are diverse, such as regulating the cell cycle, DNA damage, histone H2A deubiquitination or mitotic nuclear division. To analyze the relationship between CNV of USP16 gene and milk traits in Chinese Holstein, we used qPCR to detect the individuals of Chinese Holstein (n = 180). The results showed that the effect of USP16 gene CNV on daily milk yield and fat percentage had significant difference (p < 0.05). The gain was the advantage type in daily milk yield and the loss was the advantage type in fat percentage. Therefore, CNV of USP16 gene is an important factor of milk traits in Chinese Holstein. Meanwhile, it may be used as a molecular marker for assisted selection of milk traits in Chinese Holstein, which provides a theoretical basis for the genetic improvement of cow breeds in China.

A molecular marker of milk composition traits in NCAM2 gene of Chinese Holstein.

The aim of this study was to detect the novel copy number variation (CNV) locus of NCAM2 gene in Chinese Holstein, and to analyze the effect of the novel CNV locus in NCAM2 gene on milk composition traits. The novel CNV locus of NCAM2 gene in 310 Chinese Holstein was detected by real-time quantitative fluorescent PCR (qPCR) and association analysis was performed between the novel CNV locus in NCAM2 gene and milk composition traits in Chinese Holstein. There are three CNV types of NCAM2 gene in Chinese Holstein: gain (increased copy number), median (normal copy number) and loss (deleted copy number). Statistical analysis revealed that there was a significant association between CNV types and milk fat rate (p < 0.05). Moreover, we also discovered that the milk production and milk protein rate of gain type is higher than that of loss type, but that of mediate type is lower than that of loss type. However, in terms of somatic cell score, loss type is higher than that of gain type, but that of mediate type is lower than that of gain type. These observations suggested that gain type can be used as a candidate molecular genetic marker of milk fat rate.HighlightsThe CNVs of the NCAM2 gene were detected and validated in Chinese Holstein.The type of CNV was successfully implemented using qPCR.The statistical analysis indicated that the CNV of the NCAM2 gene are significantly associated with milk fat rate.

The Interactions Between Antibiotic Resistance Genes and Heavy Metal Pollution Under Co-Selective Pressure Influenced the Bio-Enzyme Activity.

The spread of antibiotic resistance genes (ARGs) has brought potential risks to public health. However, the interactions between heavy metals and ARGs, as well as their potential effect on bio-enzyme activity under the pressure of co-selectivity in soil still remain poorly understood. In this work, the distribution characteristics and the co-selective relationship of 28 ARGs and eight heavy metals in soil in a dairy farm were visualized via the geographic information system (GIS) technique. Eight kinds of heavy metals were detected by an atomic fluorescence spectrometer and atomic absorption spectrophotometer, which were further evaluated via the single factor pollution index value. The GIS analysis showed that arsenic (As) was the key element responsible for soil pollution, which was found to be positively related to soil depths. The top three comprehensive scores of ARGs ranked the orders of sul2 > tetX > blaTEM, indicating the high potential of risk caused by these genes in the soil environment. In addition, the functional predications performed with the 16 SrDNA sequencing data based on the KEGG database indicated that the sulfonamides in soil involved multiple pathways, especially the metabolism, transport and catabolism, and membrane transport processes. This suggested that most bio-enzymes were found to be expressed in low activities in different pathways. Significant correlations were observed between the heavy metals and ARGs (p < 0.05), particularly between the ARGs and As, Cu, Ni, Pb, and Zn (p < 0.01). This study offers deep insights into the potential interactions between heavy metals and ARGs in soil and provides guidance for the fabrication of enzyme-based smart materials for soil remediation in dairy farms.

Co and Pt Dual-Single-Atoms with Oxygen-Coordinated Co-O-Pt Dimer Sites for Ultrahigh Photocatalytic Hydrogen Evolution Efficiency.

The platinum single-atom-catalyst is verified as a very successful route to approach the size limit of Pt catalysts, while how to further improve the catalytic efficiency of Pt is a fundamental scientific question and is challenging because the size issue of Pt is approached at the ultimate ceiling as single atoms. Here, a new route for further improving Pt catalytic efficiency by cobalt (Co) and Pt dual-single-atoms on titanium dioxide (TiO2 ) surfaces, which contains a fraction of nonbonding oxygen-coordinated Co-O-Pt dimers, is reported. These Co-Pt dimer sites originate from loading high-density Pt single-atoms and Co single-atoms, with them anchoring randomly on the TiO2 substrate. This dual-single-atom catalyst yields 13.4% dimer sites and exhibits an ultrahigh and stable photocatalytic activity with a rate of 43.467 mmol g-1 h-1 and external quantum efficiency of ≈83.4% at 365 nm. This activity far exceeds those of equal amounts of Pt single-atom and typical Pt clustered catalysts by 1.92 and 1.64 times, respectively. The enhancement mechanism relies on the oxygen-coordinated Co-O-Pt dimer coupling, which can mutually optimize the electronic states of both Pt and Co sites to weaken H* binding. Namely, the "mute" Co single-atom is activated by Pt single-atom and the activity of the Pt atom is further enhanced through the dimer interaction. This strategy of nonbonding interactive dimer sites and the oxygen-mediated catalytic mechanisms provide emerging rich opportunities for greatly improving the catalytic efficiency and developing novel catalysts with creating new electronic states.

Support of modified Archimedes' law theory in granular media.

We study the resistance force of cylindrical objects penetrating quasi-statically into granular media experimentally and numerically. Simulations are validated against experiments. In contrast to previous studies, we find in both experiments and simulations that the force-depth relation consists of three regimes, rather than just two: transient and steady-state. The three regimes are driven by different dynamics: an initial matter compression, a developing stagnant zone, and an increase in steady-state force with a fully developed stagnant zone. By simulations, we explored the effects of a wide range of parameters on the penetration dynamics. We find that the initial packing fraction, the inter-granular sliding friction coefficient, and the grain shape (aspect ratio) have a significant effect on the gradient Kφ of the force-depth relation in the steady-state regime, while the rolling friction coefficient noticeably affects only the initial compression regime. Conversely, Kφ is not sensitive to the following grain properties: size, size distribution, shear modulus, density, and coefficient of restitution. From the stress fields observed in the simulations, we determine the internal friction angles φ, using the Mohr-Coulomb yield criterion, and use these results to test the recently-proposed modified Archimedes' law theory. We find excellent agreement, with the results of all the simulations falling very close to the predicted curve of φ vs. Kφ. We also examine the extreme case of frictionless spheres and find that, although no stagnant zone develops during penetration into such media, the value of their internal friction angle, φ = 9° ± 1°, also falls squarely on the theoretical curve. Finally, we use the modified Archimedes' law theory and an expression for the time-dependent growth of the stagnant zone to propose an explicit constitutive relation that fits excellently the force-depth curve throughout the entire penetration process.

Archimedes' law explains penetration of solids into granular media.

Understanding the response of granular matter to intrusion of solid objects is key to modelling many aspects of behaviour of granular matter, including plastic flow. Here we report a general model for such a quasistatic process. Using a range of experiments, we first show that the relation between the penetration depth and the force resisting it, transiently nonlinear and then linear, is scalable to a universal form. We show that the gradient of the steady-state part, K ϕ , depends only on the medium's internal friction angle, ϕ, and that it is nonlinear in µ = tan ϕ, in contrast to an existing conjecture. We further show that the intrusion of any convex solid shape satisfies a modified Archimedes' law and use this to: relate the zero-depth intercept of the linear part to K ϕ and the intruder's cross-section; explain the curve's nonlinear part in terms of the stagnant zone's development.