Maximum Amplitude Values Research Articles

Interpretable AI forecasting for numerical relativity waveforms of quasicircular, spinning, nonprecessing binary black hole mergers

We present a deep-learning artificial intelligence model (AI) that is capable of learning and forecasting the late-inspiral, merger and ringdown of numerical relativity waveforms that describe quasicircular, spinning, nonprecessing binary black hole mergers. We used theNRHybSur3dq8 surrogate model to produce train, validation and test sets of $\ensuremath{\ell}=|m|=2$ waveforms that cover the parameter space of binary black hole mergers with mass ratios $q\ensuremath{\le}8$ and individual spins $|{s}_{{1,2}}^{z}|\ensuremath{\le}0.8$. These waveforms cover the time range $t\ensuremath{\in}[\ensuremath{-}5000\text{ }\text{ }\mathrm{M},130\text{ }\text{ }\mathrm{M}]$, where $t=0M$ marks the merger event, defined as the maximum value of the waveform amplitude. We harnessed the ThetaGPU supercomputer at the Argonne Leadership Computing Facility to train our AI model using a training set of 1.5 million waveforms. We used 16 NVIDIA DGX A100 nodes, each consisting of 8 NVIDIA A100 Tensor Core GPUs and 2 AMD Rome CPUs, to fully train our model within 3.5 h. Our findings show that artificial intelligence can accurately forecast the dynamical evolution of numerical relativity waveforms in the time range $t\ensuremath{\in}[\ensuremath{-}100\text{ }\text{ }\mathrm{M},130\text{ }\text{ }\mathrm{M}]$. Sampling a test set of 190,000 waveforms, we find that the average overlap between target and predicted waveforms is $\ensuremath{\gtrsim}99%$ over the entire parameter space under consideration. We also combined scientific visualization and accelerated computing to identify what components of our model take in knowledge from the early and late-time waveform evolution to accurately forecast the latter part of numerical relativity waveforms. This work aims to accelerate the creation of scalable, computationally efficient and interpretable artificial intelligence models for gravitational wave astrophysics.

Analysis of electrical discharge machining gap phenomena on porous cemented carbides in water and oil by acoustic emission

Porous cemented carbides are porous alloys consisting of fine tungsten carbide particles bonded by a metal binder, and are superior to porous ceramics in thermal conductivity and electrical conductivity. Porous cemented carbides are expected to be applied to functional mold components with excellent gas release properties. However, the machining characteristics of porous cemented carbides in electrical discharge machining (EDM), one of the effective machining methods, have not been clarified. In the previous report, we investigated the effect of porous cemented carbide on the EDMed surface properties of single pulse and continuous discharge surfaces and the composition of the melted and resolidified layer, and the machining mechanism discussed. In this study, single pulse and continuous EDM tests were conducted on cemented carbide and porous cemented carbides in oil and water. The distance between electrodes during EDM was measured using a digital displacement sensor, and AE waves generated during EDM were analyzed using an AE sensor, and gap phenomena of porous cemented carbide were discussed. Using this method, the distance between electrodes during discharge was larger on the EDMed surface than on the polished surface in oil, but smaller on the EDMed surface than on the polished surface in water. Furthermore, regardless of the working fluid, the maximum amplitude value was higher for single pulse discharge on the EDMed surface than for single pulse discharge on the polished surface.

Machine learning approach to hydrocarbon zone prediction from seismic attributes over “GEM” field, Niger-Delta, Nigeria

A computer programme (in Python language) was developed for the generation and performance assessment of predictive models, capable of combining relevant seismic attributes for reliable hydrocarbon zone prediction ahead of drilling. It attempts to resolve the problem of making accurate and efficient interpretations from a large database of derived seismic attributes. The research utilized post-stack 3D seismic volume for the delineation of structures and the generation of seismic attributes. Six faults were identified across the mapped horizons. Five seismic attributes were generated and exported from 3D seismic data as numerical values for machine learning analysis. The binary cross-entropy classification metric was used to evaluate the performance of the developed predictive models while an individual seismic attribute (Maximum Amplitude and Extract value) map was used to validate the predictive models. A correlation of well depth-to-top of selected horizons with the seismic depth slice surface was used for further model validation. The Multi-Layer Perceptron (MLP) model results enhanced the visibility of the other five hydrocarbon prediction zones. The MLP predictive model map gave higher precision of the predicted hydrocarbon zones over the Self-Organising Map (SOM) predictive model, thus reinforcing the confidence level of the former.   Â

COMPUTER SIMULATION IN THE PROBLEMS OF STABILITY OF THIN-WALLED RODS OF AN OPEN PROFILE WITH SHAPE IMPERFECTIONS

The presented numerical methodology is based on the finite element method (FEM) and computational procedures of the NASTRAN software package. It allows to investigate the influence of geometric imperfections in the shape of thin-walled rods of open profile on the critical values of the load, the shape of the stability loss and the stress-strain state. It has been developed an algorithm for computer modeling of initial imperfections in the shape of thin-walled rods, which is implemented in the NASTRAN software package using a neutral NASTRAN PC file and a specially developed program written in FORTRAN language and adapted to this software package. Geometric imperfections of the rods can be represented as their form of loss of stability or the form of deformation from the action of the load with the possibility of varying the maximum value of the imperfections amplitude. Computational procedures for solving the Lanczos stability problem and the geometrically nonlinear static problem by the Newton-Rafson method can be used to model imperfections. The program developed by the authors allows to form new nodal coordinates of a finite-element model of rods and to visualize geometric imperfections in a given scale. The article provides a step-by-step description of finite-element construction models of thin-walled rod of open profile with an ideal surface and taking into account the imperfection of the form, which is presented as the first form of loss of rod stability from longitudinal load applied with eccentricity. With the help of the FEMAP NASTRAN preprocessor is forming the geometry of the middle surface of an ideal rod, and setting the mechanical characteristics of the material, boundary conditions and load. The middle surface of the rod is fed as a set of flat quadrangular finite elements with six degrees of freedom in the node. In the article, a linear calculation of the stability by the Lanzosch method is performed to obtain the form of rod geometric imperfection. Setting the maximum amplitude of imperfections was performed using the program developed by the authors. Using the Newton-Rafson method, the geometrically nonlinear problem of rod statics with a given shape imperfection is solved, the critical value of the longitudinal load is determined, and the corresponding form of the rod stability loss is obtained. The presented numerical technique and the developed algorithm of computer modeling of shape imperfections allow to investigate in nonlinear formulation the stability of open profile thin-walled rods taking into account geometric imperfections of different amplitude as different forms of rod deformation, including the form of stability loss, to assess the impact of imperfections on the critical value of the load, the form of stability loss and stress-strain state. The presented algorithm and numerical technique can be used to study the stability of such thin-walled structural elements as shells, plates and others.

It is time for TEG in pediatric trauma: unveiling meaningful alterations in children who undergo massive transfusion.

BackgroundHemorrhage is the leading cause of preventable death in pediatric trauma patients. In adults, goal-directed thrombelastography (TEG) has been shown to reduce mortality when used to guide massive transfusion (MT) resuscitation. There remains a paucity of data on the utility of TEG in directing resuscitation of pediatric trauma patients. We hypothesize that abnormalities on admission TEG will differ in pediatric trauma patients who undergo MT, compared to those who do not.MethodsPediatric patients (≤ 18 years) who were highest level trauma activations at two trauma centers from 2015 to 2018 were analyzed. We included patients who had admission TEGs and excluded those who did not. Patients were stratified into two groups: those who received MT (> 40 cc/kg total blood product within 6 h of admission) and those who did not. We defined TEG abnormalities based on each institution’s normative values and compared TEG abnormalities between the groups.ResultsOf 117 children included, 39 had MT. MT patients had higher injury severity scores (30 vs. 23, p = 0.0004), lactates levels (7.0 vs. 3.5, p < 0.001), base deficit levels ( − 12.2 vs. − 5.8, p < 0.001), and INR values (1.8 vs. 1.3, p < 0.001). MT patients had significantly shortened alpha-angles (35.9% vs. 15.4%, p = 0.023), maximum amplitude (MA) values (43.6% vs. 10.3%, p < 0.001), and significantly lower platelet counts (165 vs. 281, p < 0.001) compared to those who did not receive MT. There was no difference in the trends in R-time, LY30 (lysis or shutdown), or fibrinogen concentration between the groups. Logistic regression identified a decreased MA as a significant predictor for MT [OR 3.68 (CI 1.29–10.52)]ConclusionsPediatric trauma patients who undergo MT are more likely to have lower alpha-angles and MA values, as well as lower platelet counts. These findings support the use of TEG to identify hemorrhaging pediatric trauma patients, who may benefit from cryoprecipitate and/or platelet transfusions. TEG provides real-time information on coagulation status, which may expedite the delivery of specific blood products during trauma resuscitation.Level of evidence: Level IIIType of study: Retrospective comparative study.

Dynamic Behavior of Air Void during the Discharge of Cohesive Powder in a Hopper Using a Rubber Air Spring

An unstable discharge rate occurs during dry fine powder discharge from a hopper because of the significant two-phase solid/gas interactions that occur in powder flows. In addition, the air bubble phenomenon may occur in a silo during fine powder discharge. In this study, we conducted experiments using a semi-conical dual-structure hopper, and examined the effects on the hopper internal flow structure, cavity fluid pressure, pressure inside the airtight cavity section, and the powder discharge rate when changes are made in the position of the supplied air injection port and the solenoid valve open/close timing. From the experimental results, it was confirmed that an appropriate pressure supply port position exists, and the change in expansion/contraction of the flexible container due to air vibration is determined by the balance between the amount of air inserted and the amount of air discharged, and does not affect the presence or absence of powder so much. Furthermore, as the pressure value in the airtight void is directly related to the change in the expansion and contraction of the flexible container, the maximum amplitude value of the pressure in the airtight void can be kept high and constant at the time of opening and closing the solenoid valve.

Tourniquet use in primary total knee arthroplasty is associated with a hypercoagulable status: a prospective thromboelastography trial.

Prospective study. The main purpose of this study was to investigate whether the use of a tourniquet changes the blood coagulation state following primary total knee arthroplasty (TKA) by means of conventional coagulation tests and thromboelastography (TEG) analyses. A total of 154 patients who underwent primary unilateral TKA from January 2018 to October 2020 were enrolled. Seventy-nine patients were randomized into a tourniquet group, and 75 were randomized into a no-tourniquet group. Demographic data, surgical time, intra-operative blood loss, transfusion rate, and wound complications were collected. Complete blood count, conventional coagulation tests, and TEG were performed the day before surgery, oneday after surgery, threedays after surgery, and sevendays after surgery. Lower extremity Doppler ultrasound was performed the day before surgery and sevendays after surgery. The baseline characteristics of the patients were similar between the two groups. Hidden blood loss, transfusion rate, and wound complications were similar between the two groups, but the intra-operative blood loss of the tourniquet group was lower than that of the no-tourniquet group. The calculated total blood loss of the tourniquet group was higher than that of the no-tourniquet group. In terms of conventional coagulation tests and TEG, the tourniquet group had higher values of fibrin degradation products, D-dimer, maximum amplitude, and coagulation index (p < 0.001). The incidence of deep vein thrombosis (DVT) in the tourniquet group was higher than that in the no-tourniquet group (21.5% compared with 8%; p = 0.019). The application of a tourniquet during TKA significantly increases the amount of calculated total blood loss and does not decrease the post-operative transfusion rate. Using a tourniquet in routine TKA exacerbates the early post-operative hypercoagulable status together with a higher incidence of below-knee asymptomatic DVT observed via conventional coagulation tests, TEG, and ultrasonic Doppler.

Changes in regional wet heatwave in Eurasia during summer (1979–2017)

Wet heatwaves can have more impact on human health than hot dry heatwaves. However, changes in these have received little scientific attention. Using the ECMWF Reanalysis v5 reanalysis dataset, wet-bulb temperatures (T w) were used to investigate the spatial-temporal variation of wet heatwaves in Eurasia for 1979–2017. Wet heatwaves were defined as three day or longer periods when T w was above the 90th percentile of the summer distribution and characterized by amplitude, duration and frequency. Maximum values of amplitude, close to 31 °C, occur in the Indus–Ganges plain, the lower Yangtze valley, and the coasts of the Persian Gulf and Red Sea. Significant positive trends in the frequency and amplitude of wet heatwaves have occurred over most of Eurasia though with regional variations. Changes in heatwave amplitude (HWA) are largely driven by changes in summer mean T w. For Eurasia as a whole, increases in temperature contribute more than six times the impact of changes in relative humidity (RH) to changes in T w HWA. Changes in T w have a strong dependence on climatological RH with an increase in RH of 1% causing a T w increase of 0.2 °C in arid regions, and only increasing T w by 0.1 °C in humid regions. During T w heatwaves in Europe, parts of Tibet, India, East Asia and parts of the Arabian Peninsula both temperature and humidity contribute to the increase in T w, with temperature the dominant driver. During wet heatwaves in part of Russia, changes in humidity are weak and the increase in T w is mainly caused by an increase in temperature. In the Mediterranean and Central Asia, RH has fallen reducing the increase in T w from general warming.

Influence of Tool Holder Types on Vibration in Rough Milling of AZ91D Magnesium Alloy.

The article presents the results of an analysis of the influence of the technological parameters related to tool holder types on the vibrations occurring during the milling of AZ91D magnesium alloy. Magnesium alloys are very low-density materials and, therefore, are increasingly being considered as replacement materials for the more commonly used aluminium alloys. The tool used in the study was a carbide end mill with TiAlN coating, clamped in three different types of tool holder: ER collet, heat shrink, and Tendo E hydraulic. The milling tests used straight toolpaths at varied cutting speeds and feed per tooth values. Based on the vibration displacement and acceleration signals recorded during the machining tests, the following were analysed: maximum value, amplitude, and root mean square (RMS) value of the vibrations. As part of the study, composite multiscale entropy (CMSE) analysis was also performed, describing the level of disorderliness of the obtained vibration signals. The increase in machining parameters caused an increase in the values characterising the displacement and acceleration of the vibrations. It was noted that multiscale entropy might be an important parameter describing the vibration signal (both displacement and acceleration).

Multi-channel transcranial temporally interfering stimulation (tTIS): application to living mice brain

Objective. Transcranial temporally interfering stimulation (tTIS) is a noninvasive neuromodulation method, which has been reported to be able to affect the activity of small neuronal populations. To pinpoint smaller regions of the brain, a multi-channel tTIS strategy is proposed with larger numbers of electrodes and multiple sets of interfering fields. Approach. First, a computational model is adopted to prove the concept of multi-channel tTIS theoretically. Besides, animal experiments are implemented to activate motor cortex neurons in living mice and different frequencies are attempted. Finally, to better understand the envelope modulation properties of the two applied fields, tissue phantom measurement is conducted. Main results. The focality of six-channel (six electrode pairs) tTIS is increased by 46.7% and 70.2% respectively, compared with that of single-channel tTIS when maximal amplitude value drops by 3 dB and 6 dB in a numerical computation experiment. Furthermore, the focality of multi-channel tTIS is less sensitive to the electrode position. Confirmed with the myoelectricity signal, the movement frequencies of the contralateral forepaw are consistent with the corresponding difference frequencies. What is more, compared to single-channel (one electrode pair) tTIS with multi-channel (three electrode pairs) tTIS, the intensity of multi-channel tTIS stimulation is decreased by 28.5% on average in animal experiments. The c-fos-positive neurons of the target region are significantly higher than that of the non-target region. Results of the modulated envelope distribute around the whole region and its amplitude reaches a maximum at the interfering region. Significance. Both computational modeling and animal experiment validate the feasibility of the proposed multi-channel tTIS strategy and confirm that it can enhance focality and reduce scalp sensation.

Spring oscillator as case based learning (CBL) device

This research aims to: (1) develop and find out the feasibility of a spring oscillator practicum; and (2) practice the spring oscillator tool developed. The research method was the research & development method with the ADDIE development model. The study was conducted at SMAN 1 Indramayu in July-August 2019. The instrument was developed using a laser distance sensor type VL53lX as a distance gauge, a vibrator made from a coil as a spring and LCD system shaker and a laptop to display the results of the experiment. The control system uses Arduino Nano. The study was conducted in March-May 2019 at the Physics Laboratory, FMIPA, Jakarta State University. The experimental results of measuring the spring constant get an average value of 6.527 N / m. The second experiment obtained an average value of the natural frequency of the system at 1.672 Hz. The third experiment obtained a maximum amplitude value of 4.8 cm and a period of 0.59 s. The results of expert validation from media experts, and material experts were 85.16% and 90.04%, respectively. The trial of practicum tools was carried out at SMAN 1 Indramayu, West Java, as many as 20 students with a percentage of 86.66% achievement. Based on the data it is concluded that the spring oscillator practicum tool developed is suitable for use as a learning medium.

CO2 artificial pneumothorax on coagulation and fibrinolysis during thoracoscopic esophagectomy.

Background:CO2 artificial pneumothorax creates a sufficient operative field for thoracoscopic esophagectomy. However, it has potential complications and continuous CO2 insufflation may impede coagulation and fibrinolysis. We sought to compare the effects of CO2 artificial pneumothorax on perioperative coagulation and fibrinolysis during thoracoscopic esophagectomy.Methods:We investigated patients who underwent thoracoscopic esophagectomy with (group P, n = 24) or without CO2 artificial pneumothorax (group N, n = 24). The following parameters of coagulation–fibrinolysis function: intraoperative bleeding volume; serum levels of tissue plasminogen activator (t-PA), plasminogen activator inhibitor (PAI-1), thromboelastogram (TEG), D-Dimer; and arterial blood gas levels were compared with two groups.Results:Group P showed higher levels of PaCO2, reaction time (R) value and kinetics (K) value, but significantly lower pH value, alpha (α) angle and Maximum Amplitude (MA) value at 60 minutes after the initiation of CO2 artificial pneumothorax than group N ((P < .05, all). The t-PA level after CO2 insufflation for 60 minutes was significantly higher in group P than in group N (P < .05), but preoperative levels were gradually restored on cessation of CO2 insufflation for 30 min (P > .05). There was no significant difference in D-dimer.Conclusion:CO2 artificial pneumothorax during thoracoscopic esophagectomy had a substantial impact on coagulation and fibrinolysis, inducing significant derangements in pH and PaCO2.Trial registration:The study was registered at the Chinese clinical trial registry (ChiCTR1800019004)

Coagulation Effect of Sugammadex as Determined by Thromboelastography in a Randomized Controlled Study of Surgical Patients.

Introduction: Sugammadex has been shown to be associated with prolongation of prothrombin time and activated partial thromboplastin time. However, it is not known whether it could be associated with enhancing postoperative hypocoagulation. The objective of this study was to analyze the effect of 4 mg/kg of sugammadex on thromboelastography (TEG) parameters in surgical patients.Methods: After Institutional Review Board approval, a prospective double-blinded randomized controlled study was conducted between September 2016 and April 2017. Sixty adult patients scheduled for laparoscopic abdominal surgery were randomly allocated to receive either sugammadex 4 mg/kg (sugammadex group) or pyridostigmine 0.15 mg/kg in combination with glycopyrrolate 0.4 mg (control group) to reverse rocuronium-induced neuromuscular blockade at the completion of surgery. Blood samples were collected three time points; After the final suture of surgery (baseline) (T1), and at 10 min (T2) and 1 h (T3) after administration of the study drug. Whole blood was analyzed by TEG using TEG 5000 (Hemonetics Corp, Braintree, MA, USA). The primary endpoints were comparison of coagulation time (K, time to 20 mm clot amplitude), R (reaction time), alpha angle, and maximal amplitude (MA) between two groups.Results: Coagulation time was significantly prolonged in sugammadex group after 10 min of the study drug administration compared to control group (mean value 1.3 ± 0.4 vs. 1.5 ± 0.4, P = 0.03). However, R, alpha angle and MA value were not different between two groups.Conclusions: Sugammadex 4 mg/kg showed an increase in coagulation time in surgical patients. Physician should aware the potential enhancement of hypocoagulation by sugammadex in the setting of high risk of postoperative bleeding.

Experimental study on the tension of cables and motion of tunnel element for an immersed tunnel element under wind, current and wave

The tension of cables and motion response significantly affect safety of an immersed tunnel element in the immersion process. To investigate those, a hydrodynamic scale-model test was carried out and the model experiments was conducted under wind, current and wave loads simultaneously. The immersion standby (the process that the position of the immersed tunnel element should be located before the immersion process) and immersion process conditions have been conducted and illustrated. At the immersion standby conditions, the maximum force of the cables and motion is much larger at the side of incoming wind, wave and current, the maximum force of Element-6 (6 cables directly tie on the element) is larger than for Pontoon-8 (8 cables tie on pontoon of the element), and the flexible connection can reduce the maximum force of the mooring cables and motion of element (i.e. sway is expecting to decrease approximate 40%). The maximum force of the mooring cables increases with the increase of current speed, wave height, and water depth. The motion of immersed tunnel element increases with increase of wave height and water depth, and the current speed had little effect on it. At the immersion process condition, the maximum force of the cables decrease with the increase of immersion depth, and dramatically increase with the increase of wave height (i.e. the tension of cable F4 of pontoons at wave height of 1.5 m (83.3t) is approximately four times that at wave height of 0.8 m). The current speed has no much effect on the maximum force of the cables. The weight has little effect on the maximum force of the mooring cables, and the maximum force of hoisting cables increase with the increase of weight. The maximum value of six-freedom motion amplitude of the immersed tunnel element decreases with the increase of immersion depth, increase with the increase of current speed and wave height (i.e. the roll motion at wave height of 1.5 m is two times that at wave height of 0.8 m). The weight has little effect on the maximum motion amplitude of the immersed tunnel element. The results are significant for the immersion safety of element in engineering practical construction process.

Orthogonal Optimal Design Method for Spiral Coil EMAT Considering Lift-off Effect: A Case Study

This paper provided a method to improve the conversion efficiency and lessen the lift-off effect of spiral coil electromagnetic acoustic transducer (EMAT) for some specific situations, for example, irregular sample surface, online inspection and varying coating. Moreover, a new evaluation method for the performance of EMAT is proposed. To study the effect of the structural parameters on the performance of EMAT, the orthogonal test method with five factors and four levels is employed. Consequently, the degree of five factors on the lift-off performance and the theoretical maximum value of amplitude are obtained. The results show almost all factors have an obvious impact on the theoretical maximum value of amplitude, while only the magnet-to-coil distance can affect the lift-off performance effectively. The experiment results well agree with the numerical results, in which the improvement of the lift-off performance and the theoretical maximum value of amplitude is 31.94% and 78.79% respectively. In addition, the conversion efficiency of EMAT is increased by 125% when the lift-off is 1 mm. These imply the performance of spiral coil electromagnetic acoustic transducer is improved dramatically and the detectable lift-off is increased as well.

Application of Butterworth high pass filter as an approximation of Wood Anderson seismometer frequency response to earthquake signal recording

The method for generating maximum amplitude and signal to noise ratio values by using second order high pass Butterworth filter on local seismic magnitude scale calculations is proposed. The test data are signals from local earthquake that have been occurred in Sunda Strait on April 8th 2012. Based on the experimental results, a 8 Hz cutoff frequency and a gain of 2200 of second order Butterworth high pass filter as an approach to simulating the frequency response of Wood Anderson seismometer can provide maximum amplitude value, SNR, and the magnitude better than simulated Wood Anderson frequency response.

Measures of anticoagulation and coagulopathy in pediatric cardiac extracorporeal membrane oxygenation patients.

Pediatric cardiac Extracorporeal Membrane Oxygenation (ECMO) is effective, however, bleeding and clotting issues continue to cause significant morbidity and mortality. The objective of this study was to assess the correlation between measures of anticoagulation, the heparin dose in pediatric cardiac ECMO patients as well as to assess covert coagulopathy as measured by thromboelastography (TEG). Retrospective study of cardiac ECMO patients in a large, academic referral center using anticoagulation data during the ECMO support. Five hundred and eighty-four sets of anticoagulation tests and 343 TEG from 100 patients with median age of 26 days were reviewed. ECMO was post-surgical for congenital heart disease in 94% with resuscitation (ECPR) in 38% of the cases. Mean duration of support was 6.3 days. Overall survival to discharge was 35%. There was low but statistically significant correlation between individual anticoagulation measures and low correlation between Anti-Xa levels and heparin dose. There was no correlation between PTT and heparin dose. 343 TEG with Heparinase were reviewed to assess covert coagulopathy which was present in 25% of these. The coagulopathy noted was pro-hemorrhagic in almost all of the cases with high values of reaction time and kinetics and low values for angle and maximum amplitude. Coagulation monitoring on ECMO may benefit from addition of Heparinase TEG to diagnose covert coagulopathy which can contribute to significant hemorrhagic complications. There is a need for a prospective, thromboelastography guided intervention trial to reduce coagulopathy related morbidity and mortality in ECMO.

Simulation of the Field in the Vicinity of Caustics of Ordinary and Extraordinary Waves during Ionospheric Propagation

The caustic structure of the electromagnetic field is mathematically modeled, when it appears near the ground surface during the decimeter radio wave propagation in the ionospheric plasma. The caustic structures of the fields of the ordinary and extraordinary waves are compared. The influence of the extraordinary wave on the amplitude structure of the ordinary wave field is also estimated in the vicinity of the caustic. The wave fields calculated with the help of the caustic approximation and with the help of the irregular ray approximation are compared. It is suggested to estimate the maximum value of the field amplitude in the vicinity of the caustic on the basis of the ray approximation.

Role of Thromboelastography as an Early Predictor of Disseminated Intravascular Coagulation in Patients with Septic Shock.

(1) Background: The currently proposed criteria for diagnosing overt disseminated intravascular coagulation (DIC) are not suitable for early detection of DIC. Thromboelastography (TEG) rapidly provides a comprehensive assessment of the entire coagulation process and is helpful as a guide for correcting consumptive coagulopathy in sepsis-induced DIC. This study aimed to investigate the role of TEG in the prediction of DIC in patients with septic shock. (2) Methods: TEG was conducted prospectively in 1294 patients with septic shock at the emergency department (ED) between January 2016 and December 2019. After exclusion of 405 patients with “do not attempt resuscitation” orders, those refusing enrollment, and those developing septic shock after ED presentation, 889 patients were included. DIC was defined as an International Society on Thrombosis and Hemostasis score ≥ 5 points within 24 h. (3) Results: Of the 889 patients with septic shock (mean age 65.6 ± 12.7 years, 58.6% male), 158 (17.8%) developed DIC. TEG values, except lysis after 30 min, were significantly different between the DIC and non-DIC groups. Among the TEG values, the maximal amplitude (MA) had the highest discriminating power for DIC, with an area under the curve of 0.814. An MA < 60 indicated DIC with 79% sensitivity, 73% specificity, and 94% negative predictive value. Based on multivariable analysis, MA < 60 was an independent predictor of DIC (odds ratio 5.616 (95% confidence interval: 3.213–9.818)). (4) Conclusions: In patients with septic shock, the MA value in TEG could be a valuable tool for early prediction of DIC.

Comparative analysis of techniques for the limitation of compensation currents in multifunctional grid-tied inverters

Multifunctional grid-tied inverters (MFGTIs) are capable of not only injecting the energy generated by renewable energy sources into the ac grid, but also performing other distinct tasks that include reactive power and harmonic compensation, as well as voltage support. For this purpose, reference currents must be generated to separate the current components associated with the energy injection and disturbance compensation. However, the inverter power capacity may not be high enough so that it is possible to perform both functions simultaneously. Thus, it is necessary to ensure that the primary objective regarding the injection of active power is accomplished, also limiting the capacity to mitigate power quality disturbances in terms of the maximum amplitude or rms value of the ac current. In this context, this work analyzes four control strategies for the limitation of currents in MFGTIs considering key aspects such as performance and power quality indices at the point of common coupling (PCC). Both simulation and experimental results are presented and thoroughly discussed so that it is possible to establish a fair comparison among the assessed approaches used to limit the power processed by the inverter according to the rated capacity and improve the grid power quality.