Emission Counts Research Articles

Cracking mechanism and strength criteria evaluation of granite affected by intermediate principal stresses subjected to unloading stress state

Extensive true-triaxial unloading tests are conducted on rectangular Miluo granite specimens to investigate their crack propagation behavior and peak unloading strength properties. Experimental results demonstrate that their failure mode transforms from shear to slabbing with the increase in intermediate principal stresses σ2. Under a lower value of σ2, the dominant failure mode represented by the macro shear band is composed of several meso-extensional cracks parallel to the maximum principal stress σ1, and the fracturing process indicates intensive dislocation and slide owing to the normal force acting on extensional cracks. However, the increase in σ2 exacerbates the extensional cracks and further propagates them toward the end of the specimen along the direction of σ1, if σ3 is unloaded to 0. This is primarily due to the enhanced ability to resist mutual slide and squeeze among extensional cracks in the shear band, and the promotion of crack initiation and propagation in the unloading direction (σ3) owing to the provided free surface. The transformation of the cracking mode is revealed via three-dimensional combined finite/discrete element modeling, scanning electron microscope observations, and acoustic emission signal feature (average frequency, rise angle, Acoustic emission (AE) counts, and accumulated AE energy) analysis. The peak unloading strength exhibits an initial increase followed by a decrease as a function of σ2. Four rock-strength criteria are employed to evaluate the true-triaxial data with emphasis on predictability in practical applications and accuracy between best-fitting functions (experimental data) and theoretical (predicted) solutions. It is demonstrated that modified the Wiebols–Cook criterion and modified Lade criterion cannot accurately estimate the unloading strength throughout the true-triaxial data. Although the Mogi 1971 criterion fits the experimental data (higher correlation coefficients) well, it cannot be correlated to strength parameters (cohesion and internal frictional angle). Hence, it fails to predict the real strength values if complex true-triaxial unloading tests are not performed. The linear Mogi criterion is recommended for predicting the true-triaxial unloading strength of granite.

A Study on the Mechanical Properties and Bursting Liability of Coal-Rock Composites with Seam Partings

Geological tectonic movements, as well as complex and varying coal-forming conditions, have led to the formation of rock partings in most coal seams. Consequently, the coal in coal-rock composites is characterised by different mechanical properties than those of pure coal. Uniaxial compression tests were performed in this study to determine the mechanical properties and bursting liability of specimens of coal-rock composites (hereinafter referred to as “composites”) with rock partings with different dip angles θ and thicknesses D. The results showed that as θ increased, the failure mode of the composite changed from tensile and splitting failure to slip and shear failure, which was accompanied by a decrease in the brittleness of the composite and an increase in its ductility as well as a decrease in the extent of fragmentation of the coal in the composite. Additionally, as θ increased, the uniaxial compressive strength σu, elastic modulus E, and bursting energy index Ke of the composite decreased. The rock parting in the composite was the key area in which elastic energy accumulated. As D increased, σu, E, and Ke of the composite increased. In addition, as D increased, the ductility of the composite decreased, and the brittleness and extent of coal fragmentation in the composite increased. Notably, the curve for the cumulative acoustic emission (AE) counts of the composite corresponding to the stress-strain curve could be divided into four regimes: pore compaction and closure, a slowly ascending linear elastic section, prepeak steady crack propagation, and peak unsteady crack propagation. The experimental results were used to propose two technologies for controlling the stability of coal-rock composites to effectively ensure safe and efficient production at working faces.

Mechanical properties of rock salt under combined creep and fatigue

The mechanical performance of rock salt under combined creep and fatigue plays a critical role in the long-term stability and serviceability of underground compressed air energy storage (CAES). In the present study, laboratory tests were performed to investigate the impact of simultaneous creep and fatigue on the hysteresis behavior, deformability, progressive damage, cycling life, and fracture mechanism of rock salt. The strain-time curves undergo a three-phase (transient, steady-state and tertiary phase) S-shaped evolution, which is similar to that observed in pure creep or fatigue tests. It has been demonstrated that the presence of a stress dwelling period does not change the geometric similarity of the cumulative deformation curve, but may accelerate the accumulation rate of inelastic deformation, leading to a reduction in the cycling life of rock salt. The consistency between acoustic emission (AE) counting rate and the volumetric deformation indicates that micro-cracks are primarily generated during the loading period and grow stably during the stress dwelling period in rock salt within a single loading cycle. The cumulative cyclic damage and time-dependent damage in rock salt promote each other, which results in a notable positive interaction between them. The life of rock salt specimens can be reasonably predicted by employing a nonlinear cumulative damage rule that incorporates an interaction term. The logarithm of the deformation rate in the steady-state phase is linearly correlated with the logarithm of the creep or fatigue life, regardless of the loading history, and serves as an alternative approach for predicting the life of rock salt. It seems that the typical failure pattern tends to transform from multiple shearing to axial splitting as the creep load fraction increases. For rock salt in the combined creep and fatigue test, a mixed microcosmic intergranular and transgranular fracture was observed using a scanning electron microscope.

Single germanium vacancy centers in nanodiamonds with bulk-like spectral stability

Motivated by the success of group IV color centers in nanodiamonds (NDs) for hybrid technology requiring a single photon source, the authors study single germanium-vacancy (GeV−) centers in NDs at room temperature with size ranging from 10 to 50 nm and with remarkable spectral properties. The authors characterize their zero-phonon line, study their internal population dynamics, and compare their emission properties in the framework of a three level model with intensity dependent de-shelving. Furthermore, the authors characterize their lifetime, polarization, and brightness. The authors find a maximum photon emission count rate of 1.6 MHz at saturation. The authors also report a polarization visibility of 92% from the fluorescence light, which potentially makes GeV− centers good candidates for quantum key distribution requiring polarized single photons. The authors show that GeV− centers in NDs presented in this work have a comparable spectral stability compared to their bulk counterpart, which is needed for future applications using nanodiamonds.

The strength characteristics and progressive failure mechanism of soft rock-coal combination samples with consideration given to interface effects

The coal-measure rock masses of China's Ordos Basin are mainly composed of typical soft rock with low strength, which bear loads together with the coal seams during coal mining activities. Accurately determining the mechanical behaviors of combination soft rock and coal masses can provide a basis for underground coal engineering designs. First, uniaxial compression tests were conducted on medium sandstone samples, coal samples, and coal-rock combination samples. It was observed that the peak axial strain, uniaxial compressive strength, stress-strain curve shape, and elastic modulus of the combination samples were closer to those of the coal samples, indicating that the mechanical characteristics of soft rock-coal combination samples were mainly affected by the coal. Then, using the static equilibrium and deformation continuous conditions, along with the Griffith strength criterion, the ultimate compressive strength of materials at different positions in a combination model was analyzed. The results revealed that the interface constraint effects had reduced the strength of the sandstone near the interface and improved that of the coal near the interface. The interface constraint effects were verified by comparing the generalized Poisson's ratio of materials at different positions with those of the standard coal and sandstone samples. Finally, based on the final failure modes, and the temporal characteristics of the acoustic emission (AE) count rate and peak frequency, the progressive failure mechanism of the soft rock-coal combination samples was studied. This failure process was found to be characterized by the synergistic failure of the material and structure. Furthermore, the effect of coal-rock height ratio on the strength of materials at different positions was discussed, which interpreted the experimental results observed in the previous related studies, namely, with the increase in the rock-coal height ratio, the strength of the combination samples had increased, and the impact tendency had been significantly enhanced.

Experimental Study on Shear Behavior and Acoustic Emission Characteristics of Nonpersistent Joints

The shear behavior of rock discontinuities controls the stability of rock masses to a great extent. In this paper, laboratory shear tests were performed on rock-like materials with different cracks to study the effect of nonpersistent joints on the shear behavior of rock masses. The results show that the variation trends of the shear stress-displacement curves of specimens with different cracks are generally similar and have the same stage characteristics. When the crack length is relatively short, the elastic stage is prolonged, the peak shear strength decreases, and the shear displacement corresponding to the peak shear strength and the residual shear strength increases with the increase of the crack length. When the crack length is relatively long, the elastic stage is shortened, the peak shear strength decreases, and the shear displacement corresponding to the peak shear strength increases with the increase of the crack length. The peak shear stress gradually decreases with the increase of the crack length. The shear strength of the specimens with unilateral cracks is much higher than that of the specimens with bilateral cracks. The shear strength of the specimens is affected not only by the crack length but also by the crack distribution. The acoustic emission (AE) count peak occurs when the shear stress drops sharply and has an inverse “S”-type variation trend with the increase of the crack length. The inclination angle of the fracture decreases, the roughness of the fracture surface decreases, and the proportion of the wear area on the fracture surface increases gradually with the increase of the crack length. The AE source decreases with the increase of the crack length, and their locations are obviously asymmetric. This work can greatly contribute to the insight into the shear failure mechanism of rock discontinuities with nonpersistent joints.

Description of the uEMEP_v5 downscaling approach for the EMEP MSC-W chemistry transport model

Abstract. A description of the new air quality downscaling model – the urban EMEP (uEMEP) and its combination with the EMEP MSC-W model (European Monitoring and Evaluation Programme Meteorological Synthesising Centre West) – is presented. uEMEP is based on well-known Gaussian modelling principles. The uniqueness of the system is in its combination with the EMEP MSC-W model and the “local fraction” calculation contained within it. This allows the uEMEP model to be imbedded in the EMEP MSC-W model and downscaling can be carried out anywhere within the EMEP model domain, without any double counting of emissions, if appropriate proxy data are available that describe the spatial distribution of the emissions. This makes the model suitable for high-resolution calculations, down to 50 m, over entire countries. An example application, the Norwegian air quality forecasting and assessment system, is described where the entire country is modelled at a resolution of between 250 and 50 m. The model is validated against all available monitoring data, including traffic sites, in Norway. The results of the validation show good results for NO2, which has the best known emissions, and moderately good for PM10 and PM2.5. In Norway, the largest contributor to PM, even in cities, is long-range transport followed by road dust and domestic heating emissions. These contributors to PM are more difficult to quantify than NOx exhaust emission from traffic, which is the major contributor to NO2 concentrations. In addition to the validation results, a number of verification and sensitivity results are summarised. One verification showed that single annual mean calculations with a rotationally symmetric dispersion kernel give very similar results to the average of an entire year of hourly calculations, reducing the runtime for annual means by 4 orders of magnitude. The uEMEP model, in combination with EMEP MSC-W model, provides a new tool for assessing local-scale concentrations and exposure over large regions in a consistent and homogenous way and is suitable for large-scale policy applications.

The Effects of Laurel Volatile Oil (Laurusnobilis L.) on In Vitro Ruminal Gas Production of Methane Emission, Organic Acids and Protozoa Counts Alfalfa Herbage

The aim of the present in vitro study was to investigate the effects of laurel volatile oil, (Laurusnobilis L.) on ruminal gas production, methane emission, organic acids and protozoa counts of Alfalfa herbage. The components of laurel volatile oil were analysed. The effects of the addition of laurel volatile oil, at levels of 0, 50, 100 and 200 mg/L (L0, L50, L100 and L200), to the rumen fluid on in vitroruminal digestion were determined using byin vitro gas produc-tion technique. The addition of 50 mg/L of laurel volatile oil decreased total gas and methane production (ml), organic matter digestion (OMD), and metabolic energy (ME) values. On the other hand, the addition of this oil at levels of 100 mg/L and 200 mg/L was observed not to alter the in vitro total gas, methane (ml), ME and OMD values (P

Failure Behavior of Hot-Dry-Rock (HDR) in Enhanced Geothermal Systems: Macro to Micro Scale Effects

Evaluations of the mechanical properties and failure modes of granite at high temperatures are important issues for underground projects such as enhanced geothermal systems and nuclear waste disposal. This paper presents the results of laboratory experiments that investigated the physico-mechanical failure behavior of granites at high temperatures. The results allowed several important conclusions to be drawn. Both the uniaxial compressive strength (UCS) and tangent modulus decrease with increasing temperature. Specifically, the UCS-temperature curve can be divided into three sections: a section (20-200°C) where UCS shows a slight decrease, a section (200-300°C) where the UCS decreases significantly, and a third section (300-500°C) where the rate of UCS decrease stabilizes. However, in the entire temperature range from 20 to 500°C, the tangent modulus decreases exponentially. The number of acoustic emission (AE) counts decrease and the counts occur less frequently at higher temperatures. Individual grains are surrounded by a large number of microcracks at 200°C and the crack length increased significantly when heating to 300°C. Specifically, the length of micro-cracks in the granite at 300 °C could be 10 times longer okthan that at 200°C. Quenching or injecting cold water into HDRs would further weaken the rock and induce thermal damage to the rock structure. The strength of rock would be further quench-weakened by 10%, 20% and 30% at 200°C, 300°C and 500°C, respectively. Therefore, in Enhanced/Engineered Geothermal Systems (EGS), quenching is much more destructive than normal thermal stress.

Adjustment of the Life Cycle Inventory in Life Cycle Assessment for the Flexible Integration into Energy Systems Analysis

With an increasing share of renewable energy technologies in our energy systems, the integration of not only direct emission (from the use phase), but also the total life cycle emissions (including emissions during resource extraction, production, etc.) becomes more important in order to draw meaningful conclusions from Energy Systems Analysis (ESA). While the benefit of integrating Life Cycle Assessment (LCA) into ESA is acknowledged, methodologically sound integration lacks resonance in practice, partly because the dimension of the implications is not yet fully understood. This study proposes an easy-to-implement procedure for the integration of LCA results in ESA based on existing theoretical approaches. The need for a methodologically sound integration, including the avoidance of double counting of emissions, is demonstrated on the use case of Passivated Emitter and Rear Cell photovoltaic technology. The difference in Global Warming Potential of 19% between direct and LCA based emissions shows the significance for the integration of the total emissions into energy systems analysis and the potential double counting of 75% of the life cycle emissions for the use case supports the need for avoidance of double counting.

Acoustic Emission Experimental Research of the Damage Characteristics of Raw Coal under Different Loading and Unloading Rates

In this study, triaxial load failure experiments of coal samples under different strain rates and different confining pressure unloading rates were carried out using an RTX-1000 rock triaxial apparatus, and the acoustic emission characteristic parameters of a Micro-II acoustic emission imaging acquisition instrument were used to study the acoustic emission characteristics and damage deformation law of coals under different conditions. Damage models were constructed on the basis of the characteristic parameters to analyze the damage law of coal samples. Experimental results show that the acoustic emission (AE) counts and AE energy of the coal samples decrease, but the peak AE counts and peak AE energy increase with the increase in strain rates. The cumulative AE counts decrease from 9902 times to 6899 times, the peak counts increase from 209 times to 431 times, the cumulative AE energy decreases from 6986 aJ to 3786 aJ, and the peak AE energy increases from 129 aJ to 312 aJ. The overall level of the AE count rates and the AE energy of the coal samples decrease, but the peak AE counts and peak AE energy increase with the increase in unloading rates. The cumulative AE counts decrease from 18,689 times to 16,842 times, the peak AE count rates increase from 245 times/s to 535 times/s, the cumulative AE energy decreases from 9846 aJ to 7430 aJ, and the peak energy increases from 257 aJ to 587 aJ. The damage models are constructed on the basis of AE counts, and the comparative experimental and theoretical curves are analyzed to obtain a higher fitness close to 1. The damage threshold increases from 0.30 to 0.50 and from 0.34 to 0.55, and the damage amount increases from 0.50 to 0.60 and from 0.34 to 0.62 with the increase in strain rates and unloading rates. The research results have practical significance for revealing the mechanism of disaster occurrence in actual engineering excavation and proposing engineering measures to prevent coal rock damage and disaster occurrence.

Acoustic Emission at the Crack Tip during Cooling of a Moisture-Saturated Composite

The effect of low temperature on the properties of moisture-saturated glass-fiber-reinforced plastic KAST-B was investigated by studying acoustic emission. During cooling of dried and moisture-saturated specimens with surface defects, the rms acoustic emission and the acoustic emission count rate remain within the background noise. It was determined for the first time that, if water is localized in a crack in the glass-fiber-reinforced plastic, then its cooling leads to an intense acoustic emission. It was assumed that this emission is caused by local damages of the polymer matrix because of the increase in the internal stresses as water turns to ice.

Experiment and peridynamic simulation on cracking behavior of red sandstone containing a single non-straight fissure under uniaxial compression

It is widely accepted that the strength, deformability, and failure behaviors of rock material are strongly influenced by widespread natural fissures. Research focusing on the crack initiation, propagation, and coalescence behavior in fissured rock material is important to ensure the reliability and predictability of rock engineering. However, the types and forms of pre-existing fissures are complex and variable; thus, mechanical experiments have rarely been conducted on rock samples containing non-straight prefabricated open fissures. In this research, the strength, deformability, and failure behaviors of sandstone samples containing a single non-straight fissure were systematically investigated by a series of uniaxial compression experiments and numerical simulations. First, the influence of the fissure angle (α) on the strength and deformation characteristics of red sandstone containing a single non-straight fissure was evaluated. Then, the ordinary state-based peridynamics model was used to investigate the fracture behavior of red sandstone specimens with respect to various α values. The results indicate that for α = 0°–15° and 75°–90°, tensile cracks first initiated from the convex points of the prefabricated fissure, and the crack initiation position transferred from the convex point to the tip of the prefabricated fissure for α = 30°–60°. In addition, for the α = 0°–90°, the cracks initiated in the form of tensile cracks, and the ultimate failure modes were mixed tensile and shear failure. Secondary cracks always appeared in the form of shear crack. Moreover, for α ≥ 75°, fewer cracks were initiated before the peak strength was reached; afterward, the crack initiations were more prolific, and more acoustic emission counts were observed.

Mechanical, acoustic, and fracture behaviors of yellow sandstone specimens under triaxial monotonic and cyclic loading

The mechanical, acoustic, and fracture behaviors of sandstone play important roles in design and stability analysis in rock engineering applications. In this research, a series of triaxial monotonic and cyclic tests was conducted on yellow sandstone. The results of triaxial monotonic experiments were used to analyze the influence of the confining pressure on the mechanical parameters of the sandstone. The strength and deformation parameters depended strongly on the confining pressure. The triaxial strength of the sandstone specimens under cyclic loading was approximately equal to that under monotonic loading, whereas the fatigue loading led to a reduction in triaxial strength. Under lower deviatoric stress levels, the specimen was highly resistant to fatigue loading; however, higher deviatoric stress level lead to fatigue failure of the specimen even though after large cycle numbers. The influence of the cycle number on the deformation and crack damage parameters of the sandstone was also investigated. The internal damage of the sandstone specimens were characterized on basis of the recorded P-wave velocity and acoustic emission (AE) counts during triaxial monotonic loading, and the effect of the cycle number on the AE behaviors was explored under triaxial cyclic loading. Finally, the fractured yellow sandstone specimens were further analyzed by using X-ray micro computerized tomography (CT) scanning. The internal fracture characteristics of the sandstone specimens were investigated by cross-section analysis and three-dimentional (3D) reconstruction of the CT scanning, which revealed the fracture mechanism of the sandstone.

Dynamic fracturing process of fissured rock under abrupt unloading condition: A numerical study

Unloading can cause many geotechnical disasters, e.g., the rock burst. The underlying mechanism of rock failure is the propagation and coalescence of cracks. To get insight into rock unloading failure, the discretized virtual internal bond (DVIB) model in conjunction with element partition method (EPM) is used to simulate the dynamic fracturing process under unloading conditions. At first, the samples with the single flaw are simulated under unloading conditions. It is found that the fracturing pattern exhibits the tensile-shear transition with the initial stress level increasing. When the flaw inclination is closer to 45 degree or the flaw is longer, shear cracks are more likely to occur. Then, the unloading failure process of rock with multiple flaws are simulated. It is found that the inclination of the parallel flaws has remarkable influence on the unloading failure of rock. When the inclination angle is about 45 degree, the rock is easier to fail. For the rock with multiple randomized flaws, the amount of flaws has slight influence on acoustic emission counts. However, the configuration of randomized flaws can significantly affect the fracture process and failure patterns. These findings can improve understanding of rock burst and provide valuable references for the prediction of unloading failure of rock.

Effect of some dopants on temperature of high-temperature phase transitions of Na0.5Bi0.5TiO3-0.06BaTiO3 lead-free relaxor ferroelectrics ceramics seen via acoustic emission

Na0.5Bi0.5TiO3-0.06BaTiO3 relaxor ferroelectrics ceramic samples doped with 1 wt% of CuO, Fe2O3, Sb2O3, La2O3 and Ta2O5 were investigated by means of dielectric and acoustic emission methods in the high-temperature range. Dielectric constants exhibited a wide and smeared maximum at the temperature Tm, accompanied by acoustic emission sharp bursts, but the dielectric constants exhibited no anomaly when further transiting into cubic paraelectric phase at the temperature Tp, accompanied by acoustic emission sharp bursts, too. Based on acoustic emission data the shifts of these two temperatures, Tm and Tp, in dependence on a wt% of the incorporated ions as well as the acoustic emission count rate distribution in dependence on the incorporated ions radii were plotted and discussed.

Study on failure mechanical characteristics and damage constitutive model of sandstone with different numbers of holes

Abstract The existence of holes in rock is one of the key factors for the instability of underground rock mass engineering. Combined with acoustic emission equipment, uniaxial compression tests of rock specimens with different numbers of holes in the rock were carried out. The results show that with the number of holes increases, the value of peak strength and elastic modulus of the rock decrease. The acoustic emission (AE) counts gone through stable, slow increase, a sudden increase and towards zero four stages and there are corresponding to the initial compaction stage, elastic stages, strain hardening stage and post-peak strain softening stage of the stress-strain curves approximately. Based on the AE events, damage variables of rocks were obtained. The damage evolution process of rock can also be divided into three parts, including stable damage stage, slowly increasing damage stage and sharply increasing damage stage. According to Duncan model, the damage variable is introduced to obtain the rock damage constitutive model. No matter it is the pre-peak initial compaction stage, the linear elasticity stage, the strain hardening stage or the post-peak strain softening stage, the fitting curves are in good agreement with the test curves. It also illustrates the rationality of the damage constitutive model.

Online Acoustic Emission Monitoring of Cyclic Ball Indentation Testing - Correlation with Hysteresis Area Response

Fatigue has been one of the most researched subjects as most of the critical component failures are traced to fatigue. While fatigue data generation for design purposes is carried out using ASTM or equivalent standard specimens, the use of miniature or small specimens to estimate the fatigue properties is considered as a tool for extending the remaining life of in-service components. Cyclic automated ball indentation (Cyclic ABI) is one of the non-conventional test techniques used for fatigue performance assessment of pristine and in-service damaged materials. This method uses compression-compression cyclic loading of a flat specimen using a tungsten carbide spherical indenter; continuous monitoring of load-displacement (measured close to the indentation location) data provides an idea about the fatigue life of the material. Apart from this, hysteresis in load-displacement is used as an indicative energy parameter to detect fatigue failure in an Inconel 617 alloy using an off-line data analysis. To ensure on-line tracking of failure events, a specially tuned, miniature acoustic emission (AE) sensor was used during cyclic indentation testing. The AE parameters were extracted in the format of counts, absolute energy; the result processed in terms of cumulative counts, cumulative energy as well as first derivative of acoustic emission counts vs. fatigue cycles was used to cross-correlate failure events with other sensor responses. The failure cycles identified from AE were found to be in good agreement with the hysteresis area under the load-displacement curves, as well as extensometer displacement during cyclic loading.

Photon Counting Statistics of a Microwave Cavity Coupled with Double Quantum Dots

The statistical properties of photon emission counting, especially the waiting time distributions (WTDs) and large deviation statistics, of a cavity coupled with the system of double quantum dots (DQDs) driven by an external microwave field were investigated with the particle-number-resolved master equation. The results show that the decay rate of the WTDs of the cavity for short and long time limits can be effectively tuned by the driving external field Rabi frequency, the frequency of the cavity photon, and the detuning between the microwave driving frequency and the energy-splitting of the DQDs. The photon emission energy current will flow from the thermal reservoir to the system of the DQDs when the average photon number of the cavity in a steady state is larger than that of the thermal reservoir; otherwise, the photon emission energy current will flow in the opposite direction. This also demonstrates that the effect of the DQDs can be replaced a thermal reservoir when the rate difference of a photon absorbed and emitted by DQDs is larger than zero; otherwise, it is irreplaceable. The results deepen our understanding of the statistical properties of photon emission counting. It has a promising application in the construction of nanostructured devices of photon emission on demand and of optoelectronic devices.

Quantification of bacteria in water using PLS analysis of emission spectra of fluorescence and excitation-emission matrices

Bacterial contamination of drinking water is a considerable concern for public health. Tryptophan-like fluorescence (TLF) has been widely suggested to enable fast and inexpensive monitoring and quantification of bacterial contamination of water. Typically, TLF is determined at a certain excitation (ex)/emission (em) wavelengths pair. The aim of this study was to assess fluorescence spectroscopy supported with partial least squares (PLS) algorithms as a tool for a rapid evaluation of the microbial quality of water, by comparing the use of a single ex/em wavelengths pair, of the spectrum of emission obtained at a single excitation wavelength to that of whole excitation-emission matrices (EEMs). For that, laboratory-grown Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa were studied as the model systems, as well as 90 groundwater samples from 6 different wells in Israel. The groundwater samples were characterized for fluorescence emission, coliforms, fecal coliforms, fecal streptococci and heterotrophic plate counts. The PLS analysis of emission spectra and, especially, of EEMs was capable of meaningfully reducing the detection limit of microorganisms in model systems, as compared with the single ex/em wavelengths pair-based determination commonly used, reaching a detection threshold as low as 10 CFU/ml. Use of PLS-analyzed EEMs becomes beneficial also in terms of correlation and similarity between the actual and predicted bacterial concentrations. Similarly, improved detection of bacteria was also achieved in groundwater samples. Furthermore, at a level of >104 CFU/ml, use of EEMs coupled with PLS enabled discrimination between E. coli, B. subtilis and P. aeruginosa.