15 research outputs found
Some remarks on the cyclic response of non-plastic and high-plasticity natural silty soils of the Kathmandu valley (Nepal)
No full textThis note presents the results of constant-volume equivalent-undrained cyclic simple shear tests performed on saturated natural silty soils obtained from two different locations in the Kathmandu valley (Nepal) and characterized by different plasticity. Two simple shear devices were employed: the DSDSS (Double Specimen Cyclic Simple Shear) device and a modified NGI-type DSS device. The above two types of tests complemented each other and jointly covered a wide range of cyclic shear strains amplitudes. Nonlinear soil behavior (i.e. variation of shear stiffness and damping with shear strain level) and liquefaction resistance of the non-plastic silty soil were investigated. The results of the experimental investigation presented in this paper, albeit limited, increase the knowledge on the cyclic response of natural silty soils, especially those of very low plasticity, and provide first geotechnical data on the soft fluvio-lacustrine deposits of the Kathmandu Valley, responsible for site effects and liquefaction phenomena during the 2015 Mw=7.8 Gorkha earthquake
Numerical simulation of site effects in the upper aterno valley array during the aftershock sequence of the 2009 L'Aquila earthquake
No full textOn April 6th, 2009 a Mw=6.3 earthquake jolted the Abruzzo region of Central Italy, very close to the urban center of L'Aquila. Availability of high-quality recordings of the mainshock along with several aftershocks makes the seismic sequence the best recordednear-source events in Italy. In the present study, attention is devoted to the strong motion recordings of the upper Aterno River Valley array, which is part of the Italian Accelerometric Network (Rete Accelerometrica Nazionale, RAN), deployed NW of L'Aquila. These data provide a better understanding of the role played by site effects in the seismic response of the valley in epicentral area. This was accomplished by comparing recordings with the results of 1D and 2D site response analyses. The subsoil model of the Aterno Valley passing through the accelerometric stations was assumed from a previous study and was integrated with the results of dynamic tests carried out on reconstituted samples of coarse materials frequently encountered in the subsoil. First, the ground surface motion computed by assuming linear soil behavior was compared to the small-magnitude (ML=3-3.5) aftershocks recordings. It was found that 2D modeling provides a satisfactory understanding of the amplification phenomena in the array. Moreover, 2D analyses performed slightly better than 1D predictions. Based on this calibration study, further site response analyses were carried out and the computed ground motion was compared with the aftershock recordings of moderate magnitude (MW=4-5.6). In contrast, the results from these events do not show the analogous performance as obtained in the linear range. More specifically, shape of acceleration response spectra is generally satisfactorily simulated whereas discrepancies are observed in terms of PGA as well as maximum spectral amplitude. It is speculated on the possible explanations of these discrepancies
Assessment of site effects in the Kathmandu valley, Nepal, during the 2015 Mw 7.8 Gorkha earthquake sequence using 1D and 2D numerical modelling
No full textThe paper reports on the results of 1D and 2D site response analyses carried out in the Kathmandu Valley, Nepal, in order to investigate how site effects influenced the seismic response during the 2015 Mw 7.8 Gorkha earthquake sequence. The mainshock and a Mw 6.6 aftershock, for which recordings at both rock and soil sites are available, were considered. First, 1D analyses were carried out for the Pulchowk soft soil site, where a borehole was drilled. The shear wave velocity profile was defined using several 2D seismic array surveys carried out in the valley and constrained by noise measurements at Pulchowk site; the nonlinear soil behavior was characterized by means of cyclic simple shear tests carried out on undisturbed soil samples. Both equivalent and nonlinear approaches were adopted in the 1D analyses. Overall, the 1D model was capable to capture some relevant features shown by mainshock recordings such as the de-amplification of medium-to-high frequencies. On the contrary, the unusual high spectral amplification at long periods (3–6 s) recorded during the mainshock was better captured by the 2D finite element analyses carried out on a 20 km-large cross section of the entire valley, thus supporting the hypothesis of the occurrence of basin effects. The paper contributes to the understanding of site effects in Kathmandu Valley for the implementation of seismic risk mitigation strategies in the area
Some remarks on the cyclic response of nonplastic and high-plasticity natural silty soils of the Kathmandu valley (Nepal)
No full textThis note presents the results of constant-volume equivalent-undrained cyclic simple shear tests performed on saturated natural silty soils obtained from two different locations in the Kathmandu valley (Nepal) and characterized by different plasticity. Two simple shear devices were employed: the DSDSS (Double Specimen Cyclic Simple Shear) device and a modified NGI-type DSS device. The above two types of tests complemented each other and jointly covered a wide range of cyclic shear strains amplitudes. Nonlinear soil behavior (i.e. variation of shear stiffness and damping with shear strain level) and liquefaction resistance of the non-plastic silty soil were investigated. The results of the experimental investigation presented in this paper, albeit limited, increase the knowledge on the cyclic response of natural silty soils, especially those of very low plasticity, and provide first geotechnical data on the soft fluvio-lacustrine deposits of the Kathmandu Valley, responsible for site effects and liquefaction phenomena during the 2015 Mw=7.8 Gorkha earthquake
Characterisation of antibiotic-resistant psychrotrophic bacteria in raw milk
No full textDynamics of raw milk associated bacteria during cold storage of raw milk and their antibiotic resistance was reviewed, with focus on psychrotrophic bacteria. This study aimed to investigate the significance of cold storage of raw milk on antibiotic-resistant bacterial population and analyse the antibiotic resistance of the Gram-negative antibiotic-resistant psychrotrophic bacteria isolated from the cold-stored raw milk samples. Twenty-four raw milk samples, six at a time, were obtained from lorries that collected milk from Finnish farms and were stored at 4°C/4 d, 6°C/3 d and 6°C/4 d. Antibiotics representing four classes of antibiotics (gentamicin, ceftazidime, levofloxacin and trimethoprim-sulfamethoxazole) were used to determine the antibiotic resistance of mesophilic and psychrotrophic bacteria during the storage period. A representative number of antibiotic-resistant Gram-negative isolates retrieved from the cold-stored raw milk samples were identified by the phenotypic API 20 NE system and a few isolates by the 16S rDNA gene sequencing. Some of the isolates were further evaluated for their antibiotic resistance by the ATB PSE 5 and HiComb system. The initial average mesophilic counts were found below 105 CFU/mL, suggesting that the raw milk samples were of good quality. However, the mesophilic and psychrotrophic population increased when stored at 4°C/4 d, 6°C/3 d and 6°C/4 d. Gentamicin- and levofloxacin-resistant bacteria increased moderately (P < 0.05) while there was a considerable rise (P < 0.05) of ceftazidime- and trimethoprim-sulfamethoxazole-resistant population during the cold storage. Of the 50.9 % (28) of resistant isolates (total 55) identified by API 20 NE, the majority were Sphingomonas paucimobilis
(8), Pseudomonas putida (5), Sphingobacterium spiritivorum (3) and Acinetobacter baumanii (2). The analysis by ATB PSE 5 system suggested that 57.1% of the isolates (total 49) were multiresistant. This study showed that the dairy environment harbours multidrug-resistant Gramnegative psychrotrophic bacteria and the cold chain of raw milk storage amplifies the antibioticresistant psychrotrophic bacterial population
CALIBRATION OF 1-D NUMERICAL CODES SOFTWARE FOR SITE RESPONSE ANALYSES
No full textGround response analyses are used to predict surface ground motions for development of design response spectra, to evaluate dynamic stresses and strains for evaluation of earthquake hazards, and to determine the earthquake induced forces that can lead to instability of earth-retaining structures. The effects of local soil on ground motion are commonly evaluated by performing numerical analyses either in frequency or time domains.In order to evaluate the differences between frequency and time domain analysis, several analyses were conducted for homogenous stiff soil deposit with respective codes which are SHAKE and D-MOD2000. Linear and non linear analyses have been conducted. The non linear analyses with D-MOD2000 code have been carried out by using different frequencies in the Rayleigh damping formulation, i.e. fundamental and predominant frequency. For linear, PGA 0.1g is used in the analysis while for non linear PGA is scaled into three different value of 0.1, 0.3, and 0.5g.The results for both linear and non linear approach are similar. For the non linear analyses, it is shown that the curves derived using predominant frequency perform better than those using fundamental frequency. Main differences are for non linear approach where the differences between two codes are higher for higher input motion. As the calibration using predominant frequency between the two codes perform good, the respective codes are applied to evaluate soil response in Sant’ Agostino and San Carlo, in terms of PGA, due to May 20th 2012 Emilia Earthquake. There are 139 accelerometric station recorded strong motion. In this analysis, we consider one record which is in Mirandola station, the closest recording station where the Magnitude in epicentral area was 5.9 and 5.8 in Mirandola station. The recorded surface motion in Mirandola is transferred to the bedrock in 112 m depth and used as input motion for the two evaluated sites, San Carlo village and nearby municipality Sant’Agostino on 17 km distance from Mirandola station. The preliminary data presented here shows the PGA recorded in the bedrock of Mirandola station is 0.75g, while in Sant’Agostino and San Carlo is 0.92g and 0.81g
Earthquake Geotechnical Engineering aspects: the 2012 Emilia-Romagna earthquake (Italy)
No full textOn May 20, 2012 an earthquake of magnitude ML=5.9 struck the Emilia Romagna Region of Italy and a little portion of Lombardia Region. Successive earthquakes occurred on May 29, 2012 with ML=5.8 and ML=5.3. The earthquakes caused 27 deaths, of which 13 on industrial buildings. The damage was considerable. 12,000 buildings were severely damaged; big damages occurred also to monuments and cultural heritage of Italy, causing the collapse of 147 campaniles. The damage is estimated in about 5-6 billions of euro. To the damage caused to people and buildings, must be summed the indirect damage due to loss of industrial production and to the impossibility to operate for several months. The indirect damage could be bigger than the direct damage caused by the earthquake.
The resilience of the damaged cities to the damage to the industrial buildings and the lifelines was good enough, because some industries built a smart campus to start again to operate in less of one month and structural and geotechnical guidelines were edited to start with the recovering the damage industrial buildings. In the paper a damage survey is presented and linked with the ground effects. Among these, soil amplification and liquefaction phenomena are analyzed, basing on the soil properties evaluation by field and laboratory tests. Particular emphasis is devoted to the damaged suffered by the industrial buildings and to the aspects of the remedial work linked with the shallow foundation inadequacy and to the liquefaction mitigation effects
Anti-bacterial and anti-biofilm activities of arachidonic acid against the cariogenic bacterium Streptococcus mutans
No full textStreptococcus mutans is a Gram-positive, facultative anaerobic bacterium, which causes dental caries after forming biofilms on the tooth surface while producing organic acids that demineralize enamel and dentin. We observed that the polyunsaturated arachidonic acid (AA) (ω-6; 20:4) had an anti-bacterial activity against S. mutans, which prompted us to investigate its mechanism of action. The minimum inhibitory concentration (MIC) of AA on S. mutans was 25 μg/ml in the presence of 5% CO2, while it was reduced to 6.25-12.5 μg/ml in the absence of CO2 supplementation. The anti-bacterial action was due to a combination of bactericidal and bacteriostatic effects. The minimum biofilm inhibitory concentration (MBIC) was the same as the MIC, suggesting that part of the anti-biofilm effect was due to the anti-bacterial activity. Gene expression studies showed decreased expression of biofilm-related genes, suggesting that AA also has a specific anti-biofilm effect. Flow cytometric analyses using potentiometric DiOC2(3) dye, fluorescent efflux pump substrates, and live/dead SYTO 9/propidium iodide staining showed that AA leads to immediate membrane hyperpolarization, altered membrane transport and efflux pump activities, and increased membrane permeability with subsequent membrane perforation. High-resolution scanning electron microscopy (HR-SEM) showed remnants of burst bacteria. Furthermore, flow cytometric analysis using the redox probe 2',7'-dichlorofluorescein diacetate (DCFHDA) showed that AA acts as an antioxidant in a dose-dependent manner. α-Tocopherol, an antioxidant that terminates the radical chain, counteracted the anti-bacterial activity of AA, suggesting that oxidation of AA in bacteria leads to the production of cytotoxic radicals that contribute to bacterial growth arrest and death. Importantly, AA was not toxic to normal Vero epithelial cells even at 100 μg/ml, and it did not cause hemolysis of erythrocytes. In conclusion, our study shows that AA is a potentially safe drug that can be used to reduce the bacterial burden of cariogenic S. mutans.Published versionThe author(s) declare financial support was received for the research, authorship, and/or publication of this article. This study was conducted in the context of two student exchange programs. The student exchange program of MC was supported by a scholarship from the Israeli Chamber of Commerce in Hong Kong and a sponsorship from the Hong Kong Baptist University. The student exchange program of JH was supported by ShanghaiTech University
