Effect of native fissures on the mechanical behaviour of rock under uniaxial compression

U stijeni uglavnom postoje različite mikro-pukotine, pukotine (duboke), pore, spojevi i druga oštećenja. Ta oštećenja utječu na mehanička svojstva stijene. Kako bi se razjasnilo djelovanje izvornih pukotina na deformacije i oštećenja stijene, provedeno je laboratorijsko istraživanje uporabom napukle stijene dolomita, a mjerenje brzine akustičkog vala i ispitivanje stupnja apsorpcije vode provedena su kako bi se ustanovila brzina vala i postojeća poroznost uzoraka stijene. Napravljen je niz ispitivanja jednoosne tlačne čvrstoće primjenom Rock Mechanics Rigidity Servo Testing System (sustava ispitivanja čvrstoće stijena) te su se analizirale karakteristike čvrstoće i deformacije i načini stvaranja oštećenja stijene. Rezultati ispitivanja pokazuju da su brzina vala, jednoosna tlačna čvrstoća i modul elastičnosti u korelaciji s otvorenom poroznošću primjenom negativnih odnosa logaritma, a koeficijent korelacije se kreće od 0,699 do 0,848. Kad naprezanje dostigne približno 50 % jednoosne tlačne čvrstoće, znatno se poveća broj akustičkih emisija; kad naprezanje dostigne 10 MPa, počinje se javljati unutarnje oštećenje uzorka. Analiza morfologije uzoraka nakon oštećenja pokazuje da su kod jednoosnog tlaka ispitivanog dolomita moguća tri načina nastajanja oštećenja, t.j. vlak, miješano vlak-smik i smik. Načini oštećenja su usko povezani s početnim stanjem raspodjele pukotina u stijeni. Dobiveni zaključci ovog istraživanja predstavljaju važnu referencu za analizu stabilnosti napukle stijene.Rock generally contains various micro-cracks, fissures, pores, joints, and other defects. These defects affect the mechanical properties of rock. In order to clarify the influence of native fissures on rock deformation and failure modes, a laboratory study was carried out using the fissured dolomite, and acoustic wave velocity measurement and natural water absorption tests were conducted to determine the wave velocity and open porosity of the rock specimens. A series of uniaxial compression tests were conducted using the Rock Mechanics Rigidity Servo Testing System, and the strength and deformation characteristics and failure modes of the rock were analysed. The test results show that wave velocity, uniaxial compressive strength, and elastic modulus correlate well with open porosity by negative logarithm relations, and the correlation coefficients range from 0,699 to 0,848. When the stress reaches approximately 50 % of the uniaxial compressive strength, the number of acoustic emission increases substantially; when the stress reaches 10 MPa, the internal damage of the specimens begins to occur. The analysis of the post-failure morphology of the specimens suggest that three types of failure modes, i.e., tension, tension-shear mixed, and shear failures, are possible under uniaxial compression for the tested dolomite. The failure modes are closely related to the initial state of the fissure distribution in the rock. The conclusions obtained in this study provide significant reference for the stability analysis of fractured rock in rock engineering

Antimicrobial susceptibility, variation and relative expression of relative genes of Salmonella screened from different quinolone and fluoroquinolones

Objective To study the mutation and expression of genes of Salmonella when screened by different concentrations of quinolone and fluoroquinolones during propagation and their relation with antibiotic resistance. Methods Salmonella strain was cultured in broth medium and screened on nutrition plate with different concentration of quinolone and fluoroquinolones. Antimicrobial susceptibility of the screened subculture was tested by broth microdilution method, mutation of genes in quinolone resistance-determining region (QRDR) was detected using polymerase chain reaction (PCR) and DNA sequencing method, and expression level of the encoding genes of multi-drug associated efflux pump AcrAB-TolC was detected by real-time qPCR. Results Antibiotic resistance level of the subcultures screened from LB plate with quinolone and fluoroquinolones inducement increased in different extents. Mutation of Asp87Tyr in gyrA in QRDR was detected from the fifth to the seventh generation of nalidixic acid screened strains. Mutation of Asp87Asn in gyrA in QRDR was detected from the fourth to the seventh generation of ciprofloxacin screened strains. No amino acid mutation was detected from gyrA in the first to the seventh generation of gatifloxacin, levofloxacin and delafloxacin screened strains. Compared to the expression level of the multi-drug efflux pump AcrAB-TolC encoding genes of the original strain, those of the screened strains had significantly (P<0.05) increased resistance. No significant difference was detected among the expression level of AcrAB-TolC encoding genes in the seventh generation of screened strains. The ratio of the minimal inhibitory concentrations (MICs) of the screened strains and that of Salmonella Typhimurium (ATCC 14028s), gene variation and relative expression level of acrAB-tolC of Salmonella significantly positive correlated with subculture generation and antibiotic concentration. Conclusion Under the selective pressure of antibiotics, Salmonella strain could adapt the stress environment through QRDR mutation and increase the expression level of multi-drug efflux pump AcrAB-TolC. When the next generation fluoroquinolone was used, the mutation frequency of QRDR decreased. After subcultured several times, the expression level of acrAB-tolC of the screened strains increased, however, no significant difference was detected among the expression level, which avoided the antibiotic resistance of Salmonella to be further increased

Toxin-Encoding Genes and Drug Susceptibility of Staphylococcus aureus from Vegetables Consumed Raw

Objective: To investigate the toxin-encoding genes and antibiotic susceptibility of Staphylococcus aureus isolates from retail vegetables consumed raw. Methods: The 27 S. aureus isolates from tomato, lettuce, spinach and cabbage collected from supermarkets, farmers’ markets and vendors in Xi’an, Baoji, Hanzhong and Yan’an of Shaanxi province were identified by PCR amplification of the nuc gene, the prevalence of 19 toxin-encoding genes and 12 antibiotic resistance encoding genes in these isolates was evaluated, and the antibiotic susceptibility to 14 antibiotics was determined by the agar dilution method. Results: Seventeen of these isolates were identified as methicillin-susceptible S. aureus (MSSA) and the remaining 10 isolates were identified as oxacillin-susceptible methicillin-resistant S. aureus (OS-MRSA). A total of eight toxin-encoding genes were detected in the 27 isolates, and the detection rate (29.6%, 8/27) of sec was highest. In addition, 51.9% (14/27) of these isolates carried at least one toxin-encoding gene, and nine toxin-encoding gene profiles were totally identified. Seven antibiotic resistance genes including blaZ, mecA, ermC, tetK, dfrG, dfrK, and aac(6’)/aph(2”) were detected. The isolates were all susceptible to oxacillin, rifampicin and vancomycin. Resistance to amoxicillin/clavulanate was most commonly detected, followed by trimethoprim/sulfamethoxazole, ampicillin, erythromycin, cefoxitin, ciprofloxacin, ceftriaxone, gentamicin, amikacin, tetracycline and chloramphenicol. Twenty-four (88.9%) isolates were resistant to three or more antibiotics. Conclusion: OS-MRSA is prevalent in vegetables consumed raw in Shaanxi province, and it has multiple antibiotic resistances and carries multiple toxin-encoding gens, posing a potential food safety hazard

Robust cross-linked Na3V2(PO4)2F3 full sodium-ion batteries

Sodium-ion batteries (SIBs) have rapidly risen to the forefront of energy storage systems as a promising supplementary for Lithium-ion batteries (LIBs). Na3V2(PO4)2F3 (NVPF) as a common cathode of SIBs, features the merits of high operating voltage, small volume change and favorable specific energy density. However, it suffers from poor cycling stability and rate performance induced by its low intrinsic conductivity. Herein, we propose an ingenious strategy targeting superior SIBs through cross-linked NVPF with multi-dimensional nanocarbon frameworks composed of amorphous carbon and carbon nanotubes (NVPF@C@CNTs). This rational design ensures favorable particle size for shortened sodium ion transmission pathway as well as improved electronic transfer network, thus leading to enhanced charge transfer kinetics and superior cycling stability. Benefited from this unique structure, significantly improved electrochemical properties are obtained, including high specific capacity (126.9 mAh g−1 at 1 C, 1 C = 128 mA g−1) and remarkably improved long-term cycling stability with 93.9% capacity retention after 1000 cycles at 20 C. The energy density of 286.8 Wh kg−1 can be reached for full cells with hard carbon as anode (NVPF@C@CNTs//HC). Additionally, the electrochemical performance of the full cell at high temperature is also investigated (95.3 mAh g−1 after 100 cycles at 1 C at 50 oC). Such nanoscale dual-carbon networks engineering and thorough discussion of ion diffusion kinetics might make contributions to accelerating the process of phosphate cathodes in SIBs for large-scale energy storages

Childhood Sexual Abuse and the Development of Recurrent Major Depression in Chinese Women

Background Our prior study in Han Chinese women has shown that women with a history of childhood sexual abuse (CSA) are at increased risk for developing major depression (MD). Would this relationship be found in our whole data set? Method Three levels of CSA (non-genital, genital, and intercourse) were assessed by self-report in two groups of Han Chinese women: 6017 clinically ascertained with recurrent MD and 5983 matched controls. Diagnostic and other risk factor information was assessed at personal interview. Odds ratios (ORs) were calculated by logistic regression. Results We confirmed earlier results by replicating prior analyses in 3,950 new recurrent MD cases. There were no significant differences between the two data sets. Any form of CSA was significantly associated with recurrent MD (OR 4.06, 95% confidence interval (CI) [3.19–5.24]). This association strengthened with increasing CSA severity: non-genital (OR 2.21, 95% CI 1.58–3.15), genital (OR 5.24, 95% CI 3.52–8.15) and intercourse (OR 10.65, 95% CI 5.56–23.71). Among the depressed women, those with CSA had an earlier age of onset, longer depressive episodes. Recurrent MD patients those with CSA had an increased risk for dysthymia (OR 1.60, 95%CI 1.11–2.27) and phobia (OR 1.41, 95%CI 1.09–1.80). Any form of CSA was significantly associated with suicidal ideation or attempt (OR 1.50, 95% CI 1.20–1.89) and feelings of worthlessness or guilt (OR 1.41, 95% CI 1.02–2.02). Intercourse (OR 3.47, 95%CI 1.66–8.22), use of force and threats (OR 1.95, 95%CI 1.05–3.82) and how strongly the victims were affected at the time (OR 1.39, 95%CI 1.20–1.64) were significantly associated with recurrent MD

Associations of Educational Attainment, Occupation, Social Class and Major Depressive Disorder among Han Chinese Women

Background The prevalence of major depressive disorder (MDD) is higher in those with low levels of educational attainment, the unemployed and those with low social status. However the extent to which these factors cause MDD is unclear. Most of the available data comes from studies in developed countries, and these findings may not extrapolate to developing countries. Examining the relationship between MDD and socio economic status in China is likely to add to the debate because of the radical economic and social changes occurring in China over the last 30 years. Principal findings We report results from 3,639 Chinese women with recurrent MDD and 3,800 controls. Highly significant odds ratios (ORs) were observed between MDD and full time employment (OR = 0.36, 95% CI = 0.25–0.46, logP = 78), social status (OR = 0.83, 95% CI = 0.77–0.87, logP = 13.3) and education attainment (OR = 0.90, 95% CI = 0.86–0.90, logP = 6.8). We found a monotonic relationship between increasing age and increasing levels of educational attainment. Those with only primary school education have significantly more episodes of MDD (mean 6.5, P-value = 0.009) and have a clinically more severe disorder, while those with higher educational attainment are likely to manifest more comorbid anxiety disorders. Conclusions In China lower socioeconomic position is associated with increased rates of MDD, as it is elsewhere in the world. Significantly more episodes of MDD occur among those with lower educational attainment (rather than longer episodes of disease), consistent with the hypothesis that the lower socioeconomic position increases the likelihood of developing MDD. The phenomenology of MDD varies according to the degree of educational attainment: higher educational attainment not only appears to protect against MDD but alters its presentation, to a more anxious phenotype