Pre-exponential Factor Research Articles

Impact of Sn Lewis Acid Sites on the Dehydration of Cyclohexanol.

The impact of Sn on the concentration and strength of acid sites in Al containing zeolites with MFI topology and their catalytic activity for the dehydration of cyclohexanol in the aqueous phase has been investigated. The materials maintain constant Al concentrations and consequently Bro̷nsted acid site (BAS) concentrations, while exhibiting an increasing concentration of Sn Lewis acid sites (LAS). The presence of water alters LAS(Sn), leading to weak BAS(Sn) that increases the concentration of water in the zeolite micropore, while leaving the rate of dehydration of cyclohexanol unchanged. The TOF increases with the concentration of BAS(Al) in close contact with framework LAS(Sn), referred to as BAS(Pair). The increase in the Arrhenius pre-exponential factor, without affecting the activation barrier (E a), leads to the hypothesis that the proximity of both sites allows for a later transition state induced by the polarization of the C-O bond, leading in turn to a higher transition entropy.

Pyrolysis characteristics of different types of tobacco and its correlation with the released aroma components under heating condition

An in-depth insight into the pyrolysis characteristics of tobacco is of great significance for the utilization of tobacco wastes. The effects of glycerol addition on the pyrolysis characteristics and distribution of aroma components of four types of tobacco was investigated in this study by using thermogravimetry and self-built rapid heating furnace capture and GC-MS analysis. Further, correlation network analysis was used to study the correlation between pyrolysis characteristics and released aroma components. It was found that the thermal weight loss behavior of different samples exhibited both commonalities and differences, the thermal weight loss process could be divided into four stages. After the application of glycerol, the overall performance of all types of tobacco leaves at stage II showed that DTGmax2 and WL2 increased, and glycerol had a relatively obvious effect on the pyrolysis characteristic parameters of flue-cured tobacco. Pyrolysis kinetic analysis based on Coats-Redfern method showed that the activation energy and pre-exponential factor of tobacco samples were decreased after the addition of glycerol. Under the heating condition, the total amount of released aroma components from each type of tobacco followed the order of burley tobacco > flue-cured tobacco >oriental tobacco > yellow sun-cured tobacco. The release amount of heterocyclic and olefins compounds from burley tobacco were higher, while flue-cured tobacco released higher contents of esters, ketones and furans compounds. The addition of glycerol promoted the release of aroma components. In terms of correlation, Tmax2 was negatively correlated with esters, aldehydes, and furans compounds, and positively correlated with DTGmax3. Tmax3 was significantly correlated with a lot of indicators, positively with acids, aldehydes, and furans compounds, but negatively with olefins and heterocyclic compounds.

An adaptive chatter detection method for micro milling based on variational mode extraction

Current chatter detection methods using variational mode decomposition (VMD) hardly select appropriate intrinsic mode functions (IMFs) for characterizing chatter in micro milling. This article introduces a novel variational mode extraction (VME) method to isolate a single IMF representing chatter. An adaptive filter reduces chatter-independent components, enabling VME to identify the desired IMF with adaptive calculations for center frequency and penalty factor. The Hilbert–Huang transform is then applied to obtain the time–frequency distribution of the obtained IMF, and various features are computed. Finally, two methods are employed: streaming feature selection considers feature interaction, and radial basis function support vector machine selects pertinent features to establish the chatter detection model. Extensive micro milling tests validate the method, achieving an average detection accuracy of 99.34%.

High sensitivity metasurface sensor for estimating the complex permittivity of ionic liquids

In this paper, a sensor based on a metasurface structure for the complex permittivity of ionic liquids is designed. The structure consists of an F4B substrate with a metal resonance pattern, and a polystyrene foam box is used to contain the ionic liquids to achieve non-contact measurements. The simulation results show that without the presence of the ionic liquids, the sensor can achieve a significant reflection spectrum depth of −37 dB at 11.2 GHz, after adding the ionic liquids, the sensor can generate different responses depending on the types of ionic liquids in the frequency range of 8–9.3 GHz. Furthermore, by employing a characteristic matrix model inversion based on the relationships between the complex permittivity, resonance frequency, and quality factor variations, the standard deviations of the real and imaginary parts of the complex permittivity for seven ionic liquids are estimated to be 0.18 and 0.3, respectively. The estimated results show a good agreement with the standard values obtained from probe measurements. The sensor designed in this paper features a small size, simple structure, and low fabrication cost. With a volume of 0.216 milliliters of the sample, it achieves a high sensitivity of 462.87 MHz/ԑ′and frequency detection resolution of 391.57 MHz/ԑ′. It demonstrates excellent discriminatory detection capability for ionic liquids, providing a new direction for the application research of metasurfaces.

On the Origins of Intrinsic Limitations of Electrocatalytic Hydrogen Evolution in Alkaline Media

AbstractElectrocatalytic hydrogen evolution reaction (HER) in alkaline media was investigated in comparative relationship to HER in acidic media. Experimentally obtained adsorption free energies for 13 d‐metals were used to study the impact of intermediate coverage on HER activity trends, and how activity trends relate to trends in activation energies and preexponential frequency factors. A mechanistic picture of water discharge and adsorbed intermediate formation was analyzed in the light of recent experimental findings with the goal of creating a more comprehensive picture of HER electrocatalysis in alkaline media.

Frequency and clinical significance of Herpes simplex virus type 1/2 reactivation in adult patients with mild to moderately severe community-acquired pneumonia: a multicentre cohort study.

This study assessed the frequency, clinical significance, and risk factors for Herpes simplex virus (HSV) reactivation in immunocompetent patients with community-acquired pneumonia (CAP). The study included adult CAP-patients who were enrolled in the CAPNETZ study between 2007 and 2017 and had a residual sputum sample available for analysis. In addition to routine diagnostics, sputum and blood samples were tested for HSV-1/2 using PCR. Demographics, comorbidities, and CRB-65 score were compared between HSV-positive and negative patients using Fisher exact or Mann Whitney test. Logistic regression analyses investigated the influence of HSV reactivation on a modified hospital recovery scale (HRS) until day 7, divided into 3 categories (no oxygen therapy, oxygen therapy, ICU admission or death). Among 245 patients, HSV-1 and HSV-2 were detected in 30 patients (12.2%, 95%CI 8.7-16.9) and 0 patients, respectively. All HSV-positive patients were hospitalized, had a CRB-65 severity score of 0-2 and survived the first 28day. In the HSV-positive group, patients had a non-significantly higher median age (70.5 versus 66years) and a higher rate of oncological comorbidities (16.7% versus 8.8%) compared to the HSV-negative group. Distribution of co-pathogens and outcome parameters did not significantly differ between both groups. In a multivariate logistic regression model, age (AOR 1.029, p = 0.012) and CRB-65 score (AOR 1.709, p = 0.048), but not HSV-1 as single or co-pathogen were independently associated with higher HRS. Our study suggests that HSV-1 reactivation is common in CAP but might not be associated with specific risk factors or a complicated disease course.

How hot are weakly-bound cluster ions in a blackbody field? Insights from master equation modeling

Measuring accurate energetics in mass spectrometry thermochemical and calorimetry experiments depends on detailed knowledge of the energetics of the ion populations. For example, in cases where blackbody infrared radiative dissociation (BIRD) kinetics are not in the rapid energy exchange (REX) limit, threshold dissociation energies obtained directly from experiment will be too low. When ions are not in the REX limit, the ion internal energy distributions can be modeled using a master equation (ME). The ME allows evaluation of ion internal energies over time with a set of rate equations that describe the transfer of energy from one energy state to another. Here, ME modeling that accounts for the radiative absorption and emission, and dissociation rate constants is performed to determine the energetics of two model systems, M2+(H2O)n with n = 24, 55, 96, 178 and H+(AlaGly)n with n = 4, 8, 16, 32, activated by a blackbody field at temperatures between 120 and 200 K. The hydrated cluster and oligopeptide sizes are chosen such that respective ions have comparable number of internal degrees-of-freedom. The effects of blackbody temperature and inherent properties, such as frequencies and infrared (IR) intensities, molecule size, and dissociation parameters (threshold dissociation energy, E0, and high-pressure pre-exponential factor, A∞) on the resulting ion effective temperatures, steady-state energy distributions, and BIRD kinetics are explored. ME results show that at low blackbody temperatures (<∼140 K), the steady-state internal energy distributions of the ion populations resemble those of Boltzmann distributions at the blackbody temperature. At higher blackbody temperatures (>∼140 K), rapid dissociation causes the steady-state internal energy distributions to equilibrate to lower energies where absorption and emission are competitive with dissociation. This results in ion effective temperatures that deviate from and are “colder” than the blackbody temperatures. The temperature where this transition occurs depends on the competition among absorption, emission, and dissociation, and is controlled by the dissociation parameters, vibrational frequencies, and IR intensities, as illustrated for M2+(H2O)n and H+(AlaGly)n. This work shows that, under certain conditions, the ion effective temperatures can deviate significantly from those of the blackbody field temperatures. ME modeling can be used to determine the energy content of ion complexes in mass spectrometry experiments to improve the accuracy of thermochemical and calorimetry measurements of weakly-bound clusters and for more confident assignments of conformations and structures in action spectroscopy.

Surface-Like Diffusion of Fast Ions in Framework Energy Materials for Li- and Na-Ion Batteries.

The rate performance, power density, and energy efficiency of electrochemical devices are often limited by ionic conductivities in electrolyte and electrode materials. Framework Prussian blue analogs and dense niobium oxides have been identified as high-rate electrodes for sodium- and lithium-ion batteries, respectively, yet the origin of the extremely high solid-state Na+/Li+ transport is not fully understood. Of critical importance is the fact that their ultra-low activation energy and anomalous pre-exponent factor cannot be satisfactorily rationalized from conventional theory of solid-state diffusion in the crystal lattice. Here, assisted by density-functional-theory calculations, we argued that the true origin is a unique surface-like diffusion mechanism of the intercalation ions. In a surface-like migration event, a mobile ion moves along the channel wall via a low coordination number and low migration barrier experiencing minimal steric hindrance. It is similar to surface diffusion in the conventional picture and contrasts with lattice diffusion from one interstitial/vacancy site to another one with high coordination number, crowded saddle-point geometry and high migration barrier. We found that the shifting from solid-state lattice diffusion to surface-like diffusion is determined by the size difference between the mobile ion and the diffusion channel, and a lowest migration energy barrier can be reached by mediating the channel size. The analogy to gas diffusion in molecular sieves shall be discussed. Additionally, the effects of defects and crystal water in Prussian blue analogs were also discussed for better understanding their rate performances in experimental scenarios.

Unifying the temperature dependent dynamics of glass formers.

Strong changes in bulk properties, such as modulus and viscosity, are observed near the glass transition temperature, Tg, of amorphous materials. For more than a century, intense efforts have been made to define a microscopic origin for these macroscopic changes in properties. Using transition state theory (TST), we delve into the atomic/molecular level picture of how microscopic localized unit relaxations, or "cage rattles," evolve to macroscopic structural relaxations above Tg. Unit motion is broken down into two populations: (1) simultaneous rearrangement occurs among a critical number of units, nα, which ranges from 1 to 4, allowing a systematic classification of glass formers, GFs, that is compared to fragility; and (2) near Tg, adjacent units provide additional free volume for rearrangement, not simultaneously, but within the "primitive" lifetime, τ1, of one unit rattling in its cage. Relaxation maps illustrate how Johari-Goldstein β-relaxations stem from the rattle of nα units. We analyzed a wide variety of glassy materials and materials with a glassy response using literature data. Our four-parameter equation fits "strong" and "weak" GFs over the entire range of temperatures and also extends to other glassy systems, such as ion-transporting polymers and ferroelectric relaxors. The role of activation entropy in boosting preexponential factors to high "unphysical" apparent frequencies is discussed. Enthalpy-entropy compensation is clearly illustrated using the TST approach.

Kinetic Study and Reaction Mechanism of the Gas-Phase Thermolysis Reaction of Methyl Derivatives of 1,2,4,5-Tetroxane.

Tetroxane derivatives are interesting drugs for antileishmaniasis and antimalaric treatments. The gas-phase thermal decomposition of 3,6,-dimethyl-1,2,4,5-tetroxane (DMT) and 3,3,6,6,-tetramethyl-1,2,4,5-tetroxane (acetone diperoxide (ACDP)) was studied at 493-543 K by direct gas chromatography by means of a flow reactor. The reaction is produced in the injector chamber at different temperatures. The resulting kinetics Arrhenius equations were calculated for both tetroxanes. Including the parent compound of the series 1,2,4,5-tetroxane (formaldehyde diperoxide (FDP)), the activation energy and frequency factors decrease linearly with the number of methyl groups. The reaction mechanisms of ACDP and 3,6,6-trimethyl-1,2,4,5-tetroxane (TMT) decomposition have been studied by means of the DFT method with the BHANDHLYP functional. Our calculations confirm that the concerted mechanism should be discarded and that only the stepwise mechanism occurs. The critical points of the singlet and triplet state potential energy surfaces (S- and T-PES) of the thermolysis reaction of both compounds have been determined. The calculated activation energies of the different steps vary linearly with the number of methyl groups of the methyl-tetroxanes series. The mechanism for the S-PES leads to a diradical O···O open structure, which leads to a C···O dissociation in the second step and the production of the first acetaldehyde/acetone molecule. This last one yields a second C···O dissociation, producing O2 and another acetone/acetaldehyde molecule. The O2 molecule is in the singlet state. A quasi-parallel mechanism for the T-PES from the open diradical to products is also found. Most of the critical points of both PES are linear with the number of methyl groups. Reaction in the triplet state is much more exothermic than the singlet state mechanism. Transitions from the singlet ground state, S0 and low-lying singlet states S1-3, to the low-lying triplet excited states, T1-4, (chemical excitation) in the family of methyl tetroxanes are also studied at the CASSCF/CASPT2 level. Two possible mechanisms are possible here: (i) from S0 to T3 by strong spin orbit coupling (SOC) and subsequent fast internal conversion to the excited T1 state and (ii) from S0 to S2 from internal conversion and subsequent S2 to T1 by SOC. From these experimental and theoretical results, the additivity effect of the methyl groups in the thermolysis reaction of the methyl tetroxane derivatives is clearly highlighted. This information will have a great impact for controlling these processes in the laboratory and chemical industries.

Spatial distribution of inadequate meal frequency and its associated factors among children aged 6-23 months in Ethiopia: Multilevel and spatial analysis.

More than two-third of global child death is occurred due to inappropriate feeding practice that happened during early childhood period. Evidence on meal frequency status among infant and young children at national level can be used to design appropriate interventions to improve the recommended feeding frequency. Therefore, this study was aimed to explore the spatial distribution and identify associated factors of inadequate meal frequency among children aged 6-23 months in Ethiopia. Secondary data analysis was conducted using the 2019 mini Ethiopian Demographic and Health Survey data. A total weighted sample of 1,532 children aged 6-23 months were included. To identify significant factors associated with of inadequate meal frequency, multilevel binary logistic regression model was fitted. Variables with p-value < 0.25 from the bi-variable model were exported to multivariable analysis. In the multivariable model, variables with p-value < 0.05 were declared as significantly associated factors and adjusted odds ratio (AOR) with its 95% confidence interval were reported. Multilevel models were compared using deviance and log-likelihood. Spatial analysis tools were utilized to visualize the distribution of inadequate meal frequency. Bernoulli model was fitted using SaTScan V.9.6 to identify most likely clusters and ArcGIS V.10.8 was used to map the hotspot areas. Ordinary least square and geographic weighted regression models were used and compared using information criteria and adjusted-R2. Local coefficients of factors associated with hotspots of inadequate meal frequency were mapped. The prevalence of inadequate meal frequency was 47.03% (95% CI: 44.54%, 49.53%) in Ethiopia. Age of the child, sex of the household head, timely initiation of breastfeeding, current breastfeeding status, number of antenatal care visit, maternal education, and region were significantly associated with inadequate meal frequency. The spatial distribution of inadequate meal frequency was showed significant variation across Ethiopia (Global Moran's I = 0.164, p-value <0.001). A total of 38 significant clusters were detected through SaTScan analysis, from these the 22 primary clusters were located in Somali and Harari. The prevalence of inadequate meal frequency was high in Ethiopia and had significant clustering patter. Significant hotspot clusters were located in Somali, northern Afar, Harari, Amhara, Gambela, and eastern South nation nationalities and peoples' region. Therefore, public health interventions which enhance breastfeeding practice, optimal number of antenatal care visits, educational empowerments should target hotspot areas to decrease inadequate meal frequency practice.

Co-pyrolysis Behavior of Coal and Biomass: Synergistic Effect and Kinetic Analysis.

Co-pyrolysis of coal and biomass is an efficient way to utilize resources. This study investigates the co-pyrolysis behavior and kinetics of coal and biomass using thermogravimetric analysis (TGA) and TG-FTIR. Co-pyrolysis of coal and biomass exhibits a synergistic effect. When the biomass is 25%, the weight loss increases, showing a positive synergistic effect. When the biomass is 50%, it exhibits a negative synergistic effect. Increasing the heating rate can promote the generation of a synergistic effect. Co-pyrolysis involves two central pyrolysis stages: stage III (250-380 °C) and stage IV (380-550 °C). Friedman, FWO, KAS, and STA methods are used to calculate the activation energy for stages III and IV. The activation energy (E α) for co-pyrolysis is higher than that for coal or biomass pyrolysis alone. A positive synergistic effect is observed in stage III, while a negative synergistic effect is noted in stage IV. The master curve method determines an accurate reaction order (n) and pre-exponential factor (A) value of Coal75-Bio25. In stage III, E α = 238.81 kJ/mol, n = 2.4, A = 1.30 × 1021 s-1. In stage IV, E α = 37 8.01 kJ/mol, n = 4.0, A = 1.10 × 1027 s-1. The kinetic parameters in stage IV are significantly higher than those in stage III. TG-FTIR is used to analyze the synergistic effect of co-pyrolysis. Compared with coal and biomass pyrolysis separately, the Coal75-Bio25 pyrolysis process releases less CO2 and more CH4. These findings support the synergistic effect of coal and biomass during co-pyrolysis.

Raman deconvolution, radiation shielding, TL effective and dielectric investigations of Dy3+ doped alumina lead borate glasses

The objective of the current investigation was to create radiation-shielding materials that possess both thermally luminous, and dielectric behaviour. Subsequently, a glass series of Al(20-x)Pb10B70:Dyx materials was fabricated (where, x ≤ 2.5 and 0 ≤ x ≤ 1.5 in increments of 0.1, 0.5, 1, 1.5, 2, and 2.5 mol %). These materials were characterized structurally (utilizing Raman, FT-IR, DTA, SEM, XRD, and EDX), thermoluminescence, and dielectric properties. The SEM and XRD analyses demonstrate vitreous behavior. The EDX analysis provides atomic weight percent values for the chemical components. The glasses' physical properties were assessed, including their molar volume (approximately 37.48 cm3 mol−1) and density (approximately 2.725 gm/cm3). The DTA analyses of glasses indicate that the changes in GTT (approximately 286 °C) and thermal stability (∼0.656) are solely attribute to Dy3+ ions. An assortment of structural vibrations of the test glass are verified through the utilization of FT-IR and Raman analyses. The evaluation of the test glasses' micro-hardness (<5.26 GPa) was conducted utilizing ultrasonic velocities. The RPE (approximately 33.17 %) and MAC (16.9 g/cm3) indicate that the shielding behavior is also function of Dy3+ ions. The TL properties are investigated within the dose range of 5, 10, and 25 kGy of gamma irradiation. The frequency factor (3.025 × 1021 S−1) and A.E. (∼1.766 eV) of the glasses evaluated. The TL behavior of glasses is also noticed as a function of Dy3+ ions. The dielectric properties of the glasses are also analysed. The dielectric parameters such as dielectric constant (7.98), dielectric loss (0.021), ac conductivity (0.671 × 10−8 Ω−1cm−1), and A.E. (1.139 eV) evaluated. The results which include structure, elastic, radiation shielding, thermoluminescence and dialectic studies of Al(20-x)Pb10B70:Dyx glasses suggesting the glasses developed are mechanical hard, TL effective, and serve as radiation shielding dielectric resource.

Influence of sodium hydrogen carbonate, ammonium dihydrogen phosphate, and lignin-based explosion inhibitors on the sensitivity of coal dust explosion

In order to prevent coal dust explosions, this study developed a targeted environmentally friendly and efficient lignin-based explosion inhibitor. The effects of NaHCO3, NH4H2PO4, and lignin-based explosion inhibitors on the sensitivity parameters of coal dust explosions were investigated using a 20 L spherical vessel and a Hartmann tube for comparison. Furthermore, the explosion inhibition mechanisms of the three inhibitors were elucidated through SEM, conductivity, In Situ FTIR, TGA-DTG/DSC, and other testing methods. The results indicate that from the perspective of explosion sensitivity, ZA-L-NP exhibits better explosion inhibition effects than NaHCO3 and NH4H2PO4. The zeolite carrier of the composite explosion inhibitor has a fine porous structure, with some materials filling the pores of the zeolite, resulting in a rough surface of ZA-L-NP. The use of ZA-L-NP for explosion suppression has a minimal impact on the turbulent combustion rate of coal dust. Its poor conductivity provides an advantage in inhibiting coal dust explosions. All three inhibitors exhibit significant inhibitory effects on the OH functional groups in coal dust, with inhibition effects decreasing in the order of ZA-L-NP, NH4H2PO4, and NaHCO3. Using classical kinetic models, the activation energy (E) and pre-exponential factor (A) of coal dust with and without added explosion inhibitors were calculated. Analysis was conducted from the perspective of kinetic parameters such as mass residual, maximum burning rate, average burning rate, flammability discrimination index, and comprehensive combustion characteristic index. It was found that the zeolite and modified lignin (L-NP) in ZA-L-NP synergistically increased the activation energy of coal dust. The research results can provide theoretical basis for the effective prevention of coal dust explosions.

Thermoluminescence characteristics of gamma-irradiated Gd:Mg doped silica glass

This study explores the characteristics of thermoluminescence (TL) yield of silica glass doped with Gd2O3 and MgO for dosimetry via sol-gel route, with varying concentrations of rare earth metal oxides, ranging from 0.1 to 0.8 mol%. Gamma irradiation was delivered using 1.25 MeV 60Co, with entrance doses of 2–10 Gy. The characterization of Gd:Mg-doped SiO2 included assessing TL dose response, sensitivity, linearity index, glow curve, and fading. It has been found that 0.2 mol% Gd:Mg-doped SiO2 shows promising TL dosimetric properties due to its high linearity, high sensitivity, and low thermal fading. In addition, it demonstrated exceptional dosimetric response across the entire dose range studied, with a coefficient of determination R2 exceeding 91%. A computerized glow curve deconvolution method was conducted to determine the kinetic parameters by using Glowfit software. The glow curves include five peaks associated with activation energies and frequency factors with values 0.88–2.42 eV and 5.58 × 106–7.22 × 1026 s−1, respectively. The 0.2 mol% Gd:Mg-doped SiO2 demonstrates minimal fading effects, retaining a significant portion of the TL signal with ∼33% of the initial signal lost over 28 days post-irradiation. The results indicate that the Gd:Mg-doped SiO2 offers a promising performance as a low-cost passive radiation dosimeters.

Vibration Study of Functionally Graded Microcantilever Beams in Fluids Based on Modified Couple Stress Theory by Considering the Physical Neutral Plane

Theoretical studies on the vibration of microcantilever beams in fluids, which are commonly used in micro- and nanoelectromechanical systems (MEMS/NEMS). When microcantilever beams are subjected to photo-thermal excitation, they show that the material properties such as the dynamic response and the one-dimensional temperature field will show significant differences from the macroscopic properties when the size appearance of the microbeam decreases to the scale below a dozen micrometers. In this paper, by correcting the scale constants of the beams, the photothermal vibration model of the microbeam is established using the physical neutral plane theory. The one-dimensional heat transfer equations and scale-corrected temperature field of the microcantilever beam under laser excitation are derived, which are solved by Galerkin’s method, based on the theory of thermoelasticity, the hydrodynamic model of the beams vibrating in incompressible liquids proposed by Sader et al. and the theory of Euler–Bernoulli beams. The equations governing the vibration of micro-cantilever beams corrected for scale effects in different fluids when subjected to photothermal excitation are obtained. The results show that the temperature field, resonant frequency, and quality factor of the microbeam will have a significant upward drift when the size of the microbeam is close to the scale parameter, and the scale effect has a non-negligible influence on the macroscopic performance parameters; the upward drift is gradually weakening when the thickness to scale ratio gradually increases. Finally, the property of the beam is almost the same as that of the theory when the thickness of the beam is 10 times the scale constant. The correction of the theory by the scale effect is insignificant.

Clostridium perfringens in central Colombia: frequency, toxin genes, and risk factors

Clostridium perfringens is an opportunistic bacterium that causes intestinal diseases in both humans and animals. This study aimed to assess the frequency of C. perfringens and the presence of toxin-encoding genes in fecal samples from individuals with or without gastrointestinal symptoms in the Department of Boyacá, Colombia. Additionally, risk factors associated with carriage and disease development were analyzed. A total of 114 stool samples were analyzed using a molecular test based on specific polymerase chain reaction (PCR) targeting 16S-rRNA and alpha toxin (cpa) genes. For individuals with a positive result for the PCR test, stool samples were cultured on Tryptose Sulfite Cycloserine (TSC) agar. Two to five colonies forming units were selected based on phenotypic characteristics, resulting in 56 bacterial isolates. These isolates were then analyzed for toxin-coding genes associated with gastrointestinal diseases. In addition, sociodemographic and clinical data from 77 individuals were also analyzed. The overall frequency of C. perfringens was 19.3% (n = 22/114). The detection frequency in 77 individuals with clinical data was 16.6% (n = 5/30) among symptomatic individuals and 21.2% (n = 10/47) among asymptomatic individuals. All 56 isolates obtained carried the cpa gene, while cpb2 was present in 10.7% (n = 6/56); cpe and cpb genes were not detected. Notably, diabetes and autoimmune diseases are significantly associated with an increased risk of C. perfringens detection (adjusted OR 8.41: 95% CI 1.32–35.89). This study highlights an elevated frequency of C. perfringens and the presence of the cpb2 gene in asymptomatic individuals compared with their symptomatic counterparts. These findings offer insights into the distribution and virulence factors of C. perfringens at a micro-geographical level. This information supports the need for developing tailored prevention strategies based on local characteristics to promote active surveillance programs based on molecular epidemiology.

Incidence and risk factors for perineal hernia after robotic abdominoperineal resection: a single-center, retrospective cohort study.

Perineal hernia (PH) is a late complication of abdominoperineal resection (APR) that may compromise a patient's quality of life. The frequency and risk factors for PH after robotic APR adopting recent rectal cancer treatment strategies remain unclear. Patients who underwent robotic APR for rectal cancer between December 2011 and June 2022 were retrospectively examined. From July 2020, pelvic reinforcement procedures, such as robotic closure of the pelvic peritoneum and levator ani muscles, were performed as prophylactic procedures for PH whenever feasible. PH was diagnosed in patients with or without symptoms using computed tomography 1 year after surgery. We examined the frequency of PH, compared characteristics between patients with PH (PH+) and without PH (PH-), and identified risk factors for PH. We evaluated 142 patients, including 53 PH+ (37.3%) and 89 PH- (62.6%). PH+ had a significantly higher rate of preoperative chemoradiotherapy (26.4% versus 10.1%, p = 0.017) and a significantly lower rate of undergoing pelvic reinforcement procedures (1.9% versus 14.0%, p = 0.017). PH+ had a lower rate of lateral lymph node dissection (47.2% versus 61.8%, p = 0.115) and a shorter operative time (340min versus 394min, p = 0.110). According to multivariate analysis, the independent risk factors for PH were preoperative chemoradiotherapy, not undergoing lateral lymph node dissection, and not undergoing a pelvic reinforcement procedure. PH after robotic APR for rectal cancer is not a rare complication under the recent treatment strategies for rectal cancer, and performing prophylactic procedures for PH should be considered.

Pyrolysis of high-density polyethylene: Degradation behaviors, kinetics, and product characteristics

Pyrolysis is a promising technology for converting plastic waste into valuable raw materials while offering a potential solution to the global plastic pollution crisis. In this study, the thermal pyrolysis of high-density polyethylene (HDPE) is investigated in a drop tube reactor under nearly isothermal conditions. The impact of reaction temperature and gas/volatile residence time on carbon conversion and product distribution is examined across a range of 500–900 °C and 3.6–32.2 s, respectively. Non-condensable gas products detected by online mass spectrometry are H2, CH4, C2H4, C2H6, C3H6, and C3H8. At elevated temperatures and prolonged residence time, H2 yield reaches as high as 8.6 wt% of the initial HDPE mass due to intensified cracking reactions of C2–C3 hydrocarbons and long-chain aliphatic compounds. Consequently, pyrolysis tars consist mainly of polycyclic aromatic hydrocarbons (PAHs) with 5–7 rings, accompanied by visible coke deposition within the reactor. HDPE decomposition to volatiles is an endothermic process and it is complete at a temperature between 492 °C and 525 °C, depending on the heating rate employed, from non-isothermal thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) measurements. The thermal degradation of HDPE pellets follows the two-dimensional nucleation growth model for conversion levels up to 0.8 with an apparent activation energy of 259–270 kJ/mol and a pre-exponential factor of 4.83 × 1017–1.37 × 1019 min−1, determined from various isoconversional methods such as Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Starink, along with Criado's master plots. These findings provide valuable insights into optimizing process parameters and refining reactor design for pyrolysis, which can be integrated with gasification and reforming processes to enhance hydrogen production on a larger scale.

Unveiling Solvent Effects on β-Scissions through Metadynamics and Mean Force Integration.

This study introduces a methodology that combines accelerated molecular dynamics and mean force integration to investigate solvent effects on chemical reaction kinetics. The newly developed methodology is applied to the β-scission of butyl acrylate (BA) dimer in polar (water) and nonpolar (xylene and BA monomer) solvents. The results show that solvation in both polar and nonpolar environments reduces the free energy barrier of activation by ∼4 kcal/mol and decreases the pre-exponential factor 2-fold. Employing a hybrid quantum mechanics/molecular mechanics approach with explicit solvent modeling, we compute kinetic rate constants that better match experimental measurements compared to previous gas-phase calculations. This methodology presents promising potential for accurately predicting kinetic rate constants in liquid-phase polymerization and depolymerization processes.