Frequency Sweep Research Articles

Numerical simulation of RHIC polarized proton run 17 spin flipper experiments

RHIC nine-magnet spin flipper has been operated successfully during RHIC polarized proton Run 17, with 97% spin flip efficiency achieved. The results show the importance of mirror resonance removal, small spin tune spread, and proper spin flipper driving tune sweep speed. Detailed spin tracking simulations, based on a Lorentz force and Thomas-BMT differential equation numerical solver code for accuracy, have been carried out to understand the experimental results. Agreement within measurement accuracy is obtained at injection energy, 23.8 GeV. It is not as tight at 255 GeV, reasons for that are exposed. These measurements and numerical studies allow to determine the sensitivity of spin-flip efficiency to the dispersion slopes at the two Siberian snakes and to the ac dipole frequency sweep speed. They also provide guidance for future developments at BNL’s electron-ion collider. Published by the American Physical Society 2024

Modeling the Impact of Proactive Community Case Management on Reducing Confirmed Malaria Cases in Sub-Saharan African Countries.

Malaria continues to be a major source of morbidity and mortality in sub-Saharan Africa. Timely, accurate, and effective case management is critical to malaria control. Proactive community case management (ProCCM) is a new strategy in which a community health worker "sweeps" a village, visiting households at defined intervals to proactively provide diagnostic testing and treatment if indicated. Pilot experiments have shown the potential of ProCCM for controlling malaria transmission; identifying the best strategy for administering ProCCM in terms of interval timings and number of sweeps could lead to further reductions in malaria infections. We developed an agent-based simulation to model malaria transmission and the impact of various ProCCM strategies. The model was validated using symptomatic prevalence data from a ProCCM pilot study in Senegal. Various ProCCM strategies were tested to evaluate the potential for reducing parasitologically confirmed symptomatic malaria cases in the Senegal setting. We found that weekly ProCCM sweeps during a 21-week transmission season could reduce cases by 36.3% per year compared with no sweeps. Alternatively, two initial fortnightly sweeps, seven weekly sweeps, and finally four fortnightly sweeps (13 sweeps total) could reduce confirmed malaria cases by 30.5% per year while reducing the number of diagnostic tests and corresponding costs by about 33%. Under a highly seasonal transmission setting, starting the sweeps early with longer duration and higher frequency would increase the impact of ProCCM, though with diminishing returns. The model is flexible and allows decision-makers to evaluate implementation strategies incorporating sweep frequency, time of year, and available budget.

Numerical and Experimental Study on Dummy Blade with Underplatform Damper

To confirm the variation in damping ratio offered by dry friction dampers against structural vibration stress, this study developed a blade vibration response test system for capturing damping characteristic curves through both frequency sweep excitation and damping-freevibration methods. The damping-free vibration method demonstrates high efficiency, allowing for the acquisition of a complete damping ratio characteristic curve in a single experiment. Experimental findings indicate that the two contact surfaces on the triangular prism damper produce distinct damping effects, closely aligning with the predicted damping characteristic curves. The peak damping ratio was found to be independent of the centrifugal load of the damper; dampers with varying contact areas produce approximately similar damping characteristics; and the damping effect shows a positive correlation with the root extension length.

Comparison of thermal, rheological properties of Finnish Pinus sp. and Brazilian Eucalyptus sp. black liquors and their impact on recovery units

Black liquor (BL) is the major bioproduct and biomass fuel in pulp mill processes. However, the high viscosity of BL makes it a challenging material to work with, resulting in issues with evaporators and heat exchangers during its transport and processing. The thermal and rheological properties of BLs from Pinus sp. (PBL) and Eucalyptus sp. (EBL) were studied. FTIR spectra revealed the presence of the characteristic functional groups and the chemical composition in liquors. TGA/DTG curves showed three characteristic degradation stages related to evaporation of water, pyrolysis of organic groups, and condensation of char. Rheologically, liquors are classified as non-Newtonian and with comportment pseudoplastic. Their rheological dynamic shear properties included a linear viscoelastic region up to 1% shear strain, while frequency sweeps showed that storage modulus (Gʹ) > loss modulus (Gʹʹ), thus confirming the solid-like behavior of both BLs. The rheological study demonstrated that increasing the temperature and oscillatory deformations of PBL and EBL decreased their degree of viscoelasticity, which could favor their pumping and handling within the pulp mill, as well as the droplet formation and swelling characteristics in the recovery furnace.

Pulse duration, frequency band, and sweep direction effects on crosstalk in wideband backscattering measurements.

Multiple broadband transducers are typically used to cover both a wide frequency range and fill in gaps resulting from sampling with multiple narrowband echosounders. Synchronized operation of these echosounders is preferred in many cases. Simultaneous operation of multiple broadband echosounders, even when using non-overlapping primary bands, can result in cross-channel interferences caused by nonlinear generation of sound and can contaminate backscattered signal. Decreasing the transmit power of channels with lower frequencies has been demonstrated as an effective technique for reducing the level of crosstalk. Reducing the transmit power inherently decreases the signal energy. Hence, the reduction in crosstalk also reduces signal-to-noise ratio and consequently observation range. Increasing the broadband pulse duration is an alternative to compensate for the reduced signal energy from lower transmit power. This paper examines the effects of increasing pulse duration on crosstalk through numerical modeling and field experiments. Raising the transmit power amplifies the higher-harmonic level more than the main band, while extending the pulse duration increases the levels of both main-band and higher harmonics the same amount. Additionally, the study explores the influence of frequency band and sweep direction on crosstalk.

The effect of starch types on extensional, linear and nonlinear rheological properties of starch cracker dough

Cracker is a popular snack, and their quality depends on the rheological properties of the dough during production. This study focused on the impact of different starch types (tapioca, corn, and potato) used in the same amount (30 g) on the rheology of starch cracker dough. Various rheological tests were conducted to assess the dough's properties. Linear viscoelastic properties were determined using oscillatory frequency and temperature sweep tests, while the nonlinear viscoelastic behavior was characterized through stress relaxation and creep recovery tests. Extensional rheological behavior was also examined. Additionally, the textural and thermal properties of the dough were monitored to understand starch gelatinization and its interactions with other components. In the linear viscoelastic region, no significant differences were found between different dough formulations. However, in the nonlinear viscoelastic region, the potato starch-containing formulation exhibited different viscoelastic and textural properties. Biaxial extensional rheological behaviors showed no significant variations between formulations. The temperature sweep test data from differential scanning calorimetry measurements were consistent with temperature sweep data. In summary, this study provides valuable insights into how different starches influence the rheological behavior of starch cracker dough, considering various degrees of deformation and temperature. These findings have implications for cracker production parameters.

Modeling and Evaluation of a Multi-Stable Hybrid Energy Harvester

This article develops a multi-stable hybrid energy harvester (MSHEH) which consists of a piezoelectric energy harvester (PEH) and an electromagnetic energy harvester (EMEH). By tuning two parameters, the MSHEH can achieve a mono-stable, bi-stable, and tri-stable state, respectively. A numerical procedure is developed to compute the EMEH’s transduction factor. The obtained result is validated experimentally. Using the equivalent magnetic 2-point dipole theory, the restoring force model of the magnetic spring is established. The obtained model is verified experimentally. The energy harvesting performances of the MSHEH under the four different configurations (linear, mono-stable, bi-stable and tri-stable) subjected to frequency sweep excitations are evaluated by simulation and validated by experiment. The comparative analysis focuses on power output, accumulated harvested energy, and effective energy-harvesting bandwidth. The optimum load resistances are investigated by Pareto front optimizations. The following key findings are obtained. When subjected to high-level frequency sweep excitation, the tri-stable configuration exhibits the widest frequency bandwidth and the highest total accumulated harvested energy. When subjected to low-level frequency sweep excitation, the bi-stable configuration is more efficient in energy harvesting. The best performance trade-off between the PEH and EMEH can be achieved by selecting the optimum load resistances properly.

Performance Evaluation and Modification Mechanism Analysis of High-Viscosity Modified Asphalt

Abstract High-viscosity modified asphalt (HVMA) has important application potential in pavement engineering, such as porous asphalt pavements and ultrathin overlays. To comprehensively study and evaluate the overall performance of HVMA, five HVMA samples were prepared using modifier with dosages of 6 %, 9 %, 12 %, 15 %, and 18 %, respectively. The basic physical properties of HVMA were evaluated according to standard physical asphalt performance tests. The overall rheological properties of HVMA were assessed using temperature sweep tests, frequency sweep tests, and multiple stress creep recovery tests. Fluorescence microscopy was employed to analyze the microscopic characteristics and the modification mechanism of HVMA. The results show that the high-viscosity modifier could improve the overall rheological properties of HVMA at both high and low temperatures, with approximately 9 % determined as the optimal dosage. HVMA had better performance than matrix asphalt in high-temperature rutting resistance, permanent deformation resistance, temperature sensitivity, and elastic characteristics. At an appropriate dosage of the high-viscosity modifier, the modifier absorbed the light components in the asphalt, causing them to swell and dissolve. As a result, the modifier could be uniformly dispersed in the asphalt, thereby significantly improving the high-temperature stability of HVMA. The results of this paper may be helpful to the mechanism research and application of HVMA.

Formulation and characterization of ionically crosslinked gellan gum hydrogels using trilysine at low temperatures for antibody delivery

Research of the nontraditional polysaccharide gellan gum (GG) is a growing space for the development of novel drug delivery systems due to its tunable physic-mechanical properties, biocompatibility, and stability in a wide range of environments. Unfortunately, high temperature crosslinking is often required, representing a limiting factor for the incorporation of thermosensitive therapeutic agents. Here, we demonstrated that GG can be crosslinked at a low temperature (38 °C) using a simple fabrication process that utilizes trilysine as an alternative to traditional mono- or divalent ion crosslinkers. While elevated temperature mixing is still required to form a clear GG solution, crosslinking of 0.5 – 1 % GG (w/v) in the presence of trilysine (0.03 % - 0.05 % w/v) was achieved at 38 °C resulting in hydrogels with suitable working formulations to facilitate syringe loading. Low injection forces (< 20 N), and biocompatibility was evaluated with normal human dermal fibroblast (cell viability > 90 %). Frequency sweep showed a transition from purely liquid-like behavior to gel-like behavior with increased trilysine concentration. A temperature dependent behavior was lost with higher trilysine concentrations, indicating stable hydrogel formation. NMR results suggest that trilysine participates in gelation via both ionic interactions between the primary amines of trilysine and the carboxylate residues of glucuronic acid and hydrogen bonding. Released studies showed that GG hydrogels can entrap and provide sustained release of IgG in relation to the crosslinker, and antibody concentration used, with a burst release within the first 24 h (∼80 % cumulative released) followed by a sustained released for up to 5 days. Overall, findings demonstrate a promising nontoxic injectable hydrogel that requires lower crosslinking temperatures, is simple to manufacture and serves as a carrier of thermosensitive therapeutic agents.

Preload Influence on the Dynamic Properties of a Polyurethane Elastomeric Foam.

Polymeric foams are widely used in engineering applications for vibration attenuation. The foams usually work preloaded and it is known that the dynamic properties and attenuation ability of these polymers depend on the preload. In this paper, experimental characterization of a polyurethane elastomeric foam is performed in a frequency range between 1 and 60 Hz, a temperature range between -60 and 30 °C and a preload range between 2 and 12 N, using a Dynamic Mechanical Analyzer. When going from the minimum to the maximum preload, results show the linear viscoelastic range increases 57%. In the frequency sweeps, the storage modulus increases 58% on average, while the loss factor remains unaffected by preload. Moreover, the glassy transition temperature of the material decreases for greater preloads. From the curve-fitting of a four-parameter fractional derivative model using the experimental data, a seven-parameter mathematical model is developed, reducing the number of parameters needed to describe the influence of frequency and preload on the dynamic properties of the material. Hence, it has been established that the relaxation time, relaxed modulus and unrelaxed modulus depend on the exponential of the squared prestress. In contrast, the fractional parameter does not depend on preload for the range under study.

Unveiling the Impact of Gelation Temperature on the Rheological and Microstructural Properties of Type A Gelatin Hydrogels.

Gelatin-based hydrogels have garnered significant attention in the fields of drug delivery systems and tissue engineering owing to their biodegradability, biocompatibility, elasticity, flexibility and nontoxic nature. However, there is a lack of information regarding type-A-gelatin-based hydrogels. In this sense, the main aim of this work was the evaluation of the properties of type-A-gelatin-based hydrogel achieved using two different gelation temperatures (4 °C and 20 °C). Thus, the main novelty of this study lies in the analysis of the impact of gelation time on the rheological and microstructural properties of type-A-gelatin-based hydrogels. Moreover, the addition of a drug was also analyzed in order to evaluate the hydrogels' behavior as a drug delivery system. For this purpose, rheological (strain, frequency sweep tests and flow curves) and microstructural (SEM) characterizations were carried out. The results demonstrated that lowering the gelation temperature improved the rheological properties of the systems, obtaining hydrogels with an elastic modulus of 20 kPa when processing at 4 °C. On the other hand, the increase in the gelation temperature improved the critical strain of the systems at low temperatures. In conclusion, this work showed the feasibility of producing hydrogels with potential application in drug delivery with different properties, varying the testing temperature and incorporating tetracycline into their formulation.

Recovering the properties of aged bitumen using bio-rejuvenators derived from municipal wastes

Ageing of bitumen leads to significant performance deterioration of asphalt pavements and leads to material properties that are not conducive to recycling. Aiming to maximise the reusability of bitumen, this study investigated the feasibility of rejuvenating aged bitumen using bio-based rejuvenators synthesised from municipal wastes. Two bio-rejuvenators were used in this study, namely Rej-A which was a crude polymer with bio-waste pyrolysis dense fractions and Rej-B which was a filtered pyrolysis wax further derived from Rej-A. The bio-rejuvenators, virgin, aged, and rejuvenated bitumen were characterised using a comprehensive testing programme of gas chromatography and mass spectrometry (GC-MS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), multiple stress creep and recovery (MSCR), linear amplitude sweep (LAS), and frequency sweep tests. It was observed that both bio-rejuvenators produced in this study can effectively recover the rheological properties of aged bitumen, improving its fatigue performance, e.g. the fatigue lives (at 15 % strain level) of Rej-A and Rej-B rejuvenated bitumen were 5.4 times and 3.0 times of that for aged bitumen when the dosage was 14 %. The rejuvenated bitumen was more sensitive to strain while less sensitive to temperature compared with virgin bitumen. Overall, Rej-A outperformed Rej-B in recovering the properties of aged bitumen. However, Rej-A was thermally unstable, undergoing 15.6 % mass loss when heated to 160 °C.

Synthesis and Characterization of Triticale Starch-Based Hydrogel for pH Responsive Controlled Diffusion.

Considering the FAO perspectives for agriculture toward 2030, many natural sources will be no longer profitable for the synthesis of many biomaterials. Triticale (X Triticosecale Wittmack) is a cereal crop synthesized to withstand those marginal conditions; however, it is primarily used as fodder worldwide. We reported for the first time the synthesis of a natural anionic hydrogel with gastrointestinal pH stimulus-response as a new alternative of smart material, based on Eronga triticale starch as sustainable biomass, using citrate (pK a ∼3.1, 4.7, and 6.4) as cross-linking agent. The scanning electron microscopy and X-ray diffraction exhibited A and B-type starch granules, and semicrystallinity A-type. The presence of the anionic sensing group (COOH) was verified by infrared spectroscopy, the interactions by hydrogen bonds between starch and glycerol and esterification between starch and citric acid were identified by 1H NMR spectra, and through thermal analysis hydrogels exhibited four endothermic curves (179-319 °C, ∼0.711-39 kJ/mol E a). The results showed that the slight addition of glycerol increases the thermal stability, but a higher amount of glycerol decreases the intermolecular forces affecting the thermal stability contrary, the mechanical properties could be benefited. The rheological analyses showed viscoelastic tendency (G' > G″) with high stability (Tanδ < 1) in frequency, time, and strain sweeps. Gastrointestinal pH sensitivity (∼2-7.8) was verified (α ≤ 0.01) following Fick's diffusive parameters, which resulted in a tendency to gradually release BSA with increasing pH ∼3-7 by anomalous and case-II diffusion, showing greater release at pH ∼7.8/3.5 h (80-96%). We aim to expand the biomaterials area focusing on triticale starch due to its limited reported investigations, low-cost, green modification, and its rheological performance as plastic.

Fatigue performance analysis of fine aggregate matrix using a newly designed experimental strategy and viscoelastic continuum damage theory

Fine aggregate matrix (FAM), as the matrix phase in asphalt concrete (AC), significantly affects the fatigue behavior of AC. To accurately assess the mechanical properties of FAM, a newly designed experimental strategy for FAM testing was developed, and the viscoelastic continuum damage theory (VECD) theory was applied to analyze FAM’s fatigue cracking characteristics. In this study, a dumbbell-shaped geometry for dynamic shear rheometer testing was designed and verified through the FE-aided method. Subsequently, three AC mixtures’ FAM specimens with this special geometry were fabricated for the frequency sweep and linear amplitude sweep tests. Results showed that the specially designed specimens effectively capture the viscoelastic and fatigue properties of FAM with high replicability. Analyses based on the VECD theory indicated that FAM of porous asphalt (FAM(PA13)), featuring a higher asphalt content, exhibits a significant reduction in pseudo stiffness with increasing damage at the initial stage, but the reduction rate diminishes as damage progresses when compared to the other two FAMs. It was speculated that the higher aggregate content in FAM of dense-graded AC mixture (FAM(AC20) induces stress concentrations in the asphalt mastic near the protrusion areas of aggregates, thereby rendering the sample more susceptible to damage. The proposed methods will be readily extended to characterize other mechanical properties of FAM.

Examining the rheological and adhesion performance of asphalt: Insights into the influence of SARA components

The role of chemical components is pivotal in determining the rheological and adhesion performance of asphalt binders. In this study, the saturate, aromatic, resin, and asphaltene (SARA) components were directly blended with the original asphalt in specific proportions, enabling a direct assessment of their influence on critical asphalt properties. Various tests, including frequency sweep, temperature sweep, and multiple stress creep and recovery tests, were conducted, followed by the utilization of master curves to analyze the rheological properties of SARA-doped asphalt. Additionally, binder bond strength tests were performed to evaluate the adhesion properties of SARA-doped asphalt binders. The research outcomes revealed that the complex modulus, rutting factor, creep and recovery behaviors increased with higher asphaltene and resin proportions, while diminishing with elevated saturate and aromatic proportions. Analysis of the Glover–Rowe (G-R) parameter variation indicated that increasing the proportion of aromatic and saturate components can enhance cracking resistance, with the aromatic component playing a particularly significant role in this enhancement. Furthermore, augmenting the proportion of heavy components was found to enhance the adhesion performance between asphalt and commonly used aggregates. Notably, the pattern of interfacial failure transitioned from cohesive failure to adhesive failure gradually with rising proportions of heavy components.

Metamaterial Microwave Sensor for Glucose Level Measurement Based on Strip Line with Complementary Split Ring Resonator

This research focuses on investigating glucose meters utilizing metamaterial microwave sensors. The metamaterial microwave sensor is designed with a strip line loaded with a complementary split ring. The sensor is designed to conduct Ansys high‐frequency structure simulator and uses conductor material coated on a hydrocarbon ceramic laminate (Roger RO4232) substrate, with a sweep frequency range of 1–6 GHz. The signal of the metamaterial microwave sensor depends on the change in glucose permittivity and conductivity when the glucose concentration changes. The research involves designing a simulation model to explore the impact of complementary split ring size on the sensor's response to changes in glucose permittivity. Additionally, experiments are conducted using the proposed sensor to measure glucose concentration in solution, aiming to analyze trends in sensor response to varying concentrations of glucose and evaluate its sensitivity to changes in glucose concentration. The experimental results indicate that the metamaterial microwave sensor is able to respond to variations in glucose level, a sensitivity of the proposed sensor is 0.0345 dB (mg dL−1)−1 in range of 0–110 mg dL−1 with R2 0.9628.

Rheological behaviors of the multi-wall carbon nanotubes/polyethylene composites prepared by a master batch method

In this work, the rheological properties of four multi-wall carbon nanotubes (MWCNTs)/polyethylene (PE) composites containing 1 wt.% (mPEC1), 3 wt.% (mPEC3), 5 wt.% (mPEC5), and 10 wt.% (mPEC10) MWCNTs prepared by the masterbatch method were investigated and compared with those of the pure PE. The rheological investigation includes strain sweeping, frequency sweeping, stress relaxation behavior, yield stress, characteristic relaxation time, temperature effect on linear viscoelastic behavior, and gel behavior. It is mainly found that (1) the MWCNTs-MWCNTs interaction resulting in MWCNTs network structure in the PE matrix and the MWCNTs-PE interfacial interaction increase the storage and loss moduli of the MWCNTs/PE composite in comparison with those of pure PE; (2) the time-temperature equivalence principle is applicable only for pure PE and mPEC1; (3) for gel behavior of MWCNTs/PE composite at 160–180 °C, the φ g value decreases with the increase of temperature and the highest S g value is obtained at 170 °C.

High strength induced wide band gap formations in additively manufactured cubic metamaterial

Strength and band gap are the two basic physical features of the cubic metamaterial. How to design band gap characteristics with high strength of structure is the key for the further industrial application in vibration control of the cubic metamaterial. Here a cubic metamaterial is designed by optimal selection of crystal orientation angle to obtain wide band gaps with high strength. The prototype samples were fabricated using advanced additive manufacturing technology to tensile-pressure experiments and sine frequency sweep experiment, thereby demonstrating the validity of the obtained results. Results indicated that the normalized bandwidth of simple cubic (SC) metamaterials is 0.47 and the ultimate strength is 25.99 MPa. The normalized bandwidth is increased by 3.1 times and 47 times higher than that of the metamaterials of face-centered cubic (FCC) and body-centered cubic (BCC). Its ultimate strength is increased by 3.5 times and 6.7 times. The static simulation results revealed that the maximum mises stress values of SC, FCC, and BCC metamaterials were 1.71, 10.49, and 31.40 MPa respectively. The attenuation amplitude of the elastic wave measured by experiment is 80 dB, which is consistent with the simulation results. The bandwidths of cubic metamaterials exhibit a positive correlation with their strength. The variation in crystal orientation angles plays a crucial role in elucidating the underlying mechanism behind the positive correlation between the strength and the band gap. The further buckling analysis of SC metamaterial with high strength and wide bandgap characteristics reveals that the negative Poisson’s ratio structure experiences a reduction in bandwidth and strength as buckling deformation intensifies.

Comparative analysis of several short-term aging simulation methods and their impact on long-term aging performance of asphalt binders

The aging of the asphalt pavement is an essential factor to consider when constructing a road. Several methods, such as the Thin Film Oven Test (TFOT) and Rolling Thin Film Oven Test (RTFOT), have been used to simulate the short-term aging of asphalt binders. Based on the wide use of polymer-modified asphalt binder and the idea of research facilitation, 5 hours of Pressure Aging Vessel (5 h PAV) was proposed as an alternative to previous short-term aging methods of asphalt binders. However, the efficacy of this technique still needs to be wholly explored in all aspects and requires advanced research. The frequency sweep, temperature sweep, and Multiple Stress Creep Recovery tests were performed to evaluate the high-temperature performance of asphalt binders under aging conditions. In addition, the relaxation test was carried out to determine the low-temperature stress relaxation change and the fatigue cracking resistance of asphalt binders. The Chemical test explored the chemical change of asphalt binders under different aging conditions. The findings revealed that, in the case of neat asphalt binders N50, N70, and N90, the maximum disparity between the aging conditions of TFOT and 5 h PAV was found to be below 6 %. However, the difference between the aging conditions of 5 h PAV and RTFOT was observed to be approximately 20 %. Then, 5 h PAV can be highly recommended as an alternative to replacing TFOT. For SBS and high viscosity-modified asphalt binders HVMA-I and HVMA-II, the maximum gap between 5 h PAV and TFOT was estimated to be approximately 19.71 %. However, the gap between 5 h PAV and RTFOT was estimated to be less than 7 %. Then, 5 h PAV can be an alternative to replace RTFOT for modified asphalt binders if necessary. This study offers a thorough explanation and dispels doubts regarding the suitability of the 5-hour PAV as an alternative for simulating the short-term aging of asphalt binders, thereby enhancing research facilitation. Furthermore, the research delineates the impact of various short-term aging simulation methods on the long-term aging properties of asphalt binders, including the variation rates between them.

Characteristics of the Alfvénic activity during the current quench in ASDEX Upgrade

ASDEX Upgrade has developed multiple massive gas injection (MGI) scenarios to investigate runaway electron (RE) dynamics. During the current quench of the MGI induced disruptions, Alfvénic activity is observed in the 300–800 kHz range. With the help of a mode tracing algorithm based on Fourier spectrograms, mode behaviour was classified for 180 discharges. The modes have been identified as global Alfvén eigenmodes using linear gyrokinetic MHD simulations. Changes in the Alfvén continuum during the quench are proposed as explanation for the strong frequency sweep observed. A systematic statistical analysis shows no significant connection of the mode characteristics to the dynamics of the subsequent runaway electron beams. In our studies, the appearance and amplitude of the modes does not seem to affect the potential subsequent runaway beam. Beyond the scope of the 180 investigated dedicated RE experiments, the Alfvénic activity is also observed in natural disruptions with no RE beam forming.