Aerosol formation in CO2 capture plants - molecular dynamics simulation

Carbon dioxide capture is becoming a major concern not only from the perspective of traditional sour gas sweetening but also because of adverse effects of CO2 on climate change. The most conventional method to eliminate CO2 is carried out in a post-combustion CO2 capture (PCCC) column using aqueous monoethanolamine (MEA) as a solvent. Numerous reports have manifested significant amount of solvent losses due to formation of aerosols in PCCC columns. This research provides insights into formation mechanisms of aerosols or particulate matter (PM) at a molecular level by emphasizing interaction parameters between participating components. Molecular dynamics (MD) simulations were performed using GROMACS software. Five different systems under ordinary PCCC conditions were considered each of which has unique configuration of components. MD simulations revealed evolution and development of molecular clusters that formed PM which consisted of all gaseous MEA, SO2, major portion of CO2, and water vapor. Furthermore, quantitative analysis of the molecular clusters was carried out in terms of CO2 molecules. Nucleation rates of PM were in the order of 10-30 cm-3s-1. Also, formed aerosol particles were structurally examined using radial distribution functions (RDF) and determining pair potentials between the molecules. It was found that MEA in vapor phase contributes to PM formation. Furthermore, strong attraction potential between water and CO2 and MEA imply that the presence of water in vapor phase might be one of the key factors that forms and sustains PM. Taken together, the results are first of the efforts to understand PM (aerosol) formation in a typical PCCC column based on molecular simulations, and based on the findings of the study, certain practical suggestions were offered to avoid formation of PM

Modulation of Electrical Stimulation of Isolated Adrenal Chromaffin Cells is Achieved by Changing the Interphase Interval in Bipolar Pulses with Phase Durations between 3 and 50 ns

Deep brain stimulation (DBS) is an approved method to treat numerous neurological disorders including epilepsy, dystonia, and Parkinson’s disease. DBS involves implanting electrodes into specific regions of the brain to deliver electrical pulses to modulate neurological activity. Risks and potential side effects associated with this invasive method generally include infections, and hemorrhages. Non-invasive techniques such as transcranial magnetic stimulation (TMS) in which electromagnetic coils stimulate nerve cells via magnetic fields and transcranial direct current stimulation (tDCS) which stimulates brain tissue via constant current application between two electrodes are also in clinical use. However, these electrostimulation methods have either limited penetration depth or low spatial resolution. To achieve the combined benefits of invasive and non-invasive electrostimulation techniques, our group has been investigating the potential for a novel bioelectric stimulus, nanosecond duration electric pulses (NEPs). NEPs have the potential to achieve both deep and focused electrical stimulation non-invasively via antennas, and thus without the need for implanted electrodes. One way to achieve this remote electrostimulation is based on a recent finding of complete cancellation of biological effects of NEPs with the application of a second pulse of opposite polarity, a process termed bipolar pulse cancellation. The combination of the bipolar pulse cancellation effects and electric field superposition allows possible application in deep tissues by a cancellation of cancellation or CANCAN effect, leaving surrounding tissue unaffected by delivered pulses. CANCAN achieves a single biologically-effective unipolar NEP resulting in focused stimulation without the risks associated with invasive DBS. To study effects of NEPs and application of bipolar pulse cancellation we utilized bovine adrenal chromaffin cells in our studies. Chromaffin cells were chosen as a cell model for their similarities with sympathetic neurons in that they release the catecholamine epinephrine and norepinephrine (Epi and NEpi) via the Ca2+-dependent process of exocytosis. The major finding is that a single 5 ns electric pulse causes membrane depolarization and Ca2+ influx via voltage-gated calcium channels (VGCCs). Recently, we found that a single unipolar pulse that was only 2 ns in duration caused Ca2+ influx via VGCCs that can be totally abolished when another 2 ns unipolar pulse with opposite polarity is applied afterwards. The resulting pulse with two opposite phases one after another is called a bipolar pulse. The cancelling effect disappears as the interval between the two phases of the bipolar pulse increases beyond 30 ns. Furthermore, it was found that increasing the pulse duration to 150 ns caused only the portion of Ca2+ influx attributable to membrane permeabilization to be cancelled, not that due to VGCC activation. This clearly demonstrates that bipolar pulse cancellation effects have a narrow window where they are manifested. Thus, the goal of the present study was to further identify bipolar pulse exposure parameters that cancel increases in [Ca2+]i in chromaffin cells mediated by influx of Ca2+ via VGCCs. To achieve this goal, we employed a combination of experimental and theoretical calculations, such as Accelerated Membrane Discharge (AMD) model and 1) identified threshold voltage amplitudes for single unipolar pulses with durations ranging from 3 to 50 ns, 2) determined whether bipolar cancellation can be achieved throughout the range of these durations, and 3) assessed whether the minimal interphase interval required to cancel the bipolar cancellation changes with pulse duration. The goals were achieved by exposing single isolated bovine adrenal chromaffin cells to external electric fields delivered from bipolar pulsers generated by pulsers by FID GmbH and applied via handmade tungsten rod electrodes. Changes of [Ca2+]i were assessed through rise of fluorescence levels of Calcium Green-1 dye recorded on electron multiplying CCD iXon Ultra 897 camera with the help of Leica Application software. Analysis of the recorded traces was performed by a custom MATLAB application developed during the thesis. Our results demonstrate an exponential decrease in unipolar pulse threshold voltage required to elicit a response in the cells with the increase of pulse duration from 3 to 50 ns. Meanwhile, symmetrical bipolar cancellation at the threshold voltage can only be achieved for pulse durations ranging from 3 to 12 ns. By 25 ns the effects elicited by a unipolar pulse were only partially attenuated by a symmetrical bipolar pulse, and bipolar pulse cancellation was completely lost when the pulse duration was increased to 50 ns. Furthermore, by increasing the interphase interval to only 4 ns the bipolar cancellation was started to wane down. This cancellation effect was found to be inversely dependent on the pulse duration, where for a shorter duration pulse of 3 ns, an 8 ns interphase interval was enough to mostly cancel the bipolar cancellation, and for longer duration pulses of 12 ns, a 4 ns interphase interval was sufficient. We have also found that some cells would react to a bipolar stimulus with very a small initial increase in [Ca2+]i, usually leading to a full blown response that was delayed by a few seconds. One of the most plausible mechanisms to explain bipolar pulse cancellation is the AMD hypothesis, which was successfully used to model bipolar cancellation for 2 ns pulses with variable interphase intervals. AMD assumes that the cell membrane acts as a capacitor that is being charged and discharged by the application and interruption of the external electric field, respectively. Since bipolar pulses have both positive and negative phases, the cell membrane voltage would become positively charged during the positive cycle and then brought back to the resting state with the negative cycle resulting in a very short time the membrane stays at a critical voltage for electropermeabilization. The AMD model was able to correctly model bipolar cancellation of Ca2+ responses for symmetrical bipolar pulses with a duration of 3 to 12 ns, and attenuation of the effects of unipolar pulses for symmetrical bipolar pulses of 25 to 50 ns. However, AMD was not able to model Ca2+ responses when the interphase intervals were introduced. To address these discrepancies, we developed an expanded AMD model which utilizes recorded experimental pulses and allows varying the membrane charging constant to see if AMD could still explain cancellation in pulses with very small interphase intervals. When the membrane charging constant was changed for the second phase, AMD showed a significantly better fit for our experimental results. In summary, our results show the exponential relationship between unipolar pulse amplitude and duration for eliciting a cellular response. The results also show a window where bipolar pulse cancellation is manifested, and minimal interphase intervals required to abolish it with the change of pulse duration. This bipolar cancellation window is crucial for the future development of remote electrostimulation applications based on the CANCAN effect

Eliciting New Wikipedia Users' Interests via Automatically Mined Questionnaires: For a Warm Welcome, Not a Cold Start

Every day, thousands of users sign up as new Wikipedia contributors. Once joined, these users have to decide which articles to contribute to, which users to seek out and learn from or collaborate with, etc. Any such task is a hard and potentially frustrating one given the sheer size of Wikipedia. Supporting newcomers in their first steps by recommending articles they would enjoy editing or editors they would enjoy collaborating with is thus a promising route toward converting them into long-term contributors. Standard recommender systems, however, rely on users' histories of previous interactions with the platform. As such, these systems cannot make high-quality recommendations to newcomers without any previous interactions -- the so-called cold-start problem. The present paper addresses the cold-start problem on Wikipedia by developing a method for automatically building short questionnaires that, when completed by a newly registered Wikipedia user, can be used for a variety of purposes, including article recommendations that can help new editors get started. Our questionnaires are constructed based on the text of Wikipedia articles as well as the history of contributions by the already onboarded Wikipedia editors. We assess the quality of our questionnaire-based recommendations in an offline evaluation using historical data, as well as an online evaluation with hundreds of real Wikipedia newcomers, concluding that our method provides cohesive, human-readable questions that perform well against several baselines. By addressing the cold-start problem, this work can help with the sustainable growth and maintenance of Wikipedia's diverse editor community.Comment: Accepted at the 13th International AAAI Conference on Web and Social Media (ICWSM-2019

Prevention of complications after surgery to remove the radicular cyst

To date, in terms of prevalence among benign tumors and other formations of the jaws, cysts are in the first place. A radicular cyst is a cavity formation filled with fluid and having a membrane. In maxillofacial surgery and surgical dentistry, cyst removal surgery is one of the most common surgical interventions.In the structure of dental diseases, patients with odontogenic cysts and cyst-like benign formations occupy a certain place, and their number does not tend to decrease. Key words: radicular cyst, cystectomy, osteoplastic material, bioplast dent, orthopantomogram