Maximum Amplitude Research Articles

Surface plasmon resonance photonic crystal fiber biosensor: Utilizing silver-phosphorene nanoribbons for Near-IR detection

In recent years, the utilization of two-dimensional materials in photonic crystal fiber structures has developed the capabilities of biosensors in biological and biochemical applications. A photonic crystal fiber biosensor based on surface plasmon resonance with silver and phosphorene layers is proposed in this paper. Phosphorene helps with the prevention of oxidation of the silver layer used as a plasmonic active metal. The sensor performance can be optimized by changing the structural parameters. The maximum wavelength sensitivity obtained was 1800 nm/RIU in the dynamic index range of 1.39–1.45, and the proposed sensor also showed the maximum amplitude sensitivity of 268 RIU−1 with an analyte refractive index of 1.40. The performance of the proposed sensor was analyzed using the finite element method. The results show that using phosphorene may open a new window for the study of online biomolecular interaction.

Numerical analysis of the effects of pores on propagating guided waves

The present numerical study aims to analyze the effect of pores on propagating guided waves while outlining the relevance of pore formation and its significance to structural properties. The primary focus of this study was on the pores present in planar carbon fiber-reinforced polymer (CFRP) parts. The wavefield data were generated by applying the elastodynamic finite integration technique (EFIT) solver AE3D, allowing for a systematic analysis based on fully controllable configurations and noise-free data. An isotropic material model was used to simplify the modeling of the anisotropic CFRP by assuming the averaged quasi-isotropic properties of the CFRP in all directions. More than 220 specimens containing single pores or four basic configurations of pore accumulations were modeled and analyzed in terms of their effect on the out-of-plane component of the propagating guided waves. Analysis of the guided wavefield data focused on the direction-dependent maximum amplitude differences and deviations in the wavefield energy. Mode- and wavenumber-specific amplitude loss along the centerline was analyzed using a matrix pencil algorithm. Finally, principal component analysis (PCA) was conducted to examine deviations caused by the presence of pores. Analysis of the wavefield effects of the pores for each specific configuration showed good differentiation between the considered pore volume groups. At the same time, the effects of the pores were shown to be significantly dependent on the pore configuration in terms of orientation and morphological properties. Associated with this, the intersecting outcome ranges for different pore volume groups were evident when all the pore configurations were considered simultaneously.

Evaluation of clopidogrel response in healthy cats using a novel viscoelastic test and thromboelastography.

Cats with cardiomyopathy face an increased risk of arterial thromboembolism (ATE). Although clopidogrel is frequently utilized to mitigate this risk, feline responses to this therapy exhibit variability. This study evaluated 2 viscoelastic devices, thromboelastography (TEG) and Viscoelastic Coagulation Monitor (VCM), for monitoring clopidogrel in cats in comparison to light transmission aggregometry (LTA). Twenty-eight healthy cats received clopidogrel for 7 days. Blood was collected at baseline and after treatment for analysis by TEG, VCM, and LTA. On LTA, maximum amplitude, slope, and area under the curve (AUC) significantly decreased after treatment (p < 0.0001). On VCM, maximum clot firmness (MCF) significantly increased after treatment (p = 0.002). On TEG, R-time significantly prolonged (p = 0.024), while K and alpha angle significantly changed (p = 0.0002 and p = 0.0014, respectively). There was a moderate negative correlation between TEG R-time and LTA AUC (r = -0.39, p = 0.042). Eight cats were identified as non-responders to clopidogrel. Of the 8 non-responders, 6 (75%) had shortened R time after treatment. VCM appeared to be less discriminatory in identifying non-responders. LTA remained the gold standard of monitoring clopidogrel treatment in cats. Unexpected changes on VCM and TEG were likely related to high interindividual and assay variability and increased sensitivity of feline platelets. R-time on TEG may have potential utility for point-of-care monitoring of clopidogrel response in cats.

The role of adipose tissue cell elements in the regulation of the nitroxidergic system and possible ways of pharmacological modulation

Endothelial dysfunction is characterized by a decrease in the bioavailability of the vasodilator – nitric oxide (NO), and an increase in the level of vasoconstrictor substances. This imbalance leads to vasoconstriction, leukocyte attachment and inflammatory reactions in the vascular wall, atherosclerosis and thrombosis. The aim: to evaluate the role of adipose tissue elements in the regulation of parameters of the nitroxidergic system under hypoxia conditions. Materials and methods. The studies were carried out on 30 adult white male Wistar rats. All animals were randomly assigned and divided into groups: a control group (15 rats), type 2 diabetes mellitus (T2DM) was induced in the animals of the second group (15 rats). Isolated fragments of the popliteal arteries (PA) and intrapulmonary artery (IPA) were cleared of perivascular adipose tissue (PVAT-) or left uncleaned (PVAT+) and cut into rings. The simulation of acute hypoxia with further study of medical agents were performed. Results. The PA and IPA with PVAT responded to acute hypoxia with vasoconstriction – an increase in the amplitude of contraction in the first and second phases, and after removing PVAT, they responded with a decrease in the maximum amplitude of contraction by 3.4 times in the 1st phase and an increase in amplitude by 1.8 times in the 2nd phase. Perfusion with Angiolin reduced 2nd phase of HV of the PA and IPA. Adding a combination of Thiotriazoline and L-arginine (1:4) to a solution for perfusion of fragments of arteries of animals with T2DM, causes a significant increase in constrictor reactions in both the 1st and 2nd phases of HV, regardless of presence of perivascular adipose tissue. Conclusions. The presence of PVAT affects the HV of arteries, both in normal and in T2DM. The possibilities of ways of pharmacological modulation of the nitroxidergic system depending on the state of PVAT were determined.

Simulation of large plausible tsunami scenarios associated with the 2019 Durres (Albania) earthquake source and adjacent seismogenic zones

We present an analysis of the hazards of potential earthquake-generated tsunamis along the Albanian–Adriatic coast. The study adopts a case study approach to model plausible tsunamigenic events associated with the 2019 Mw 6.4 Durres (Albania) earthquake source zone. The approach combines current findings on regional tectonics and scenario-based calculations of potential tsunami impacts. The study’s goal is to analyse the propagation of tsunami waves generated by identified seismogenic sources (namely ALCS002 [Lushnje] and ALCS018 [Shijak]) and determine the tsunami risk assessment for Durres City on the Albanian–Adriatic coast. The sources can generate earthquakes with maximum moment magnitudes of Mw 7.5 and Mw 6.8, which are likely to trigger tsunamis that could cause significant impacts in the region. The modelling is performed deterministically with the NAMI DANCE numerical code, including scenarios associated with the largest plausible earthquake. The model integrates bathymetry and topography datasets of large and medium resolutions. Each tsunami scenario simulation is based on the solution of the non-linear shallow water equations used to generate maximum positive wave amplitudes (water elevation), travel time, and tsunami inundation maps. In Durres City, modelling indicates that medium-sized waves could reach up to 2.5 m inland, posing a significant danger to the city’s low-lying areas. The most substantial tsunami waves are expected to impact the area within the first 10 to 20 min. Combining inundation maps and information on exposed assets allows for identifying areas where damages can be expected. In terms of human impact, a preliminary analysis shows that the study area is prone to tsunami threat, with more than 138,000 inhabitants living in vulnerable urban areas of Durres City by 2036. The model’s capacity to capture details related to the presence of buildings is limited due to constraints posed by the resolution of bathymetry and topography datasets available during this study. If refined with high-resolution bathymetry and topography datasets, our results can be considered a backbone for exposure and resilience assessment features to be integrated into preparedness or new urban development plans.

Electrocochleography-Based Tonotopic Map: II. Frequency-to-Place Mismatch Impacts Speech-Perception Outcomes in Cochlear Implant Recipients.

Modern cochlear implants (CIs) use varying-length electrode arrays inserted at varying insertion angles within variably sized cochleae. Thus, there exists an opportunity to enhance CI performance, particularly in postlinguistic adults, by optimizing the frequency-to-place allocation for electrical stimulation, thereby minimizing the need for central adaptation and plasticity. There has been interest in applying Greenwood or Stakhovskaya et al. function (describing the tonotopic map) to postoperative imaging of electrodes to improve frequency allocation and place coding. Acoustically-evoked electrocochleography (ECochG) allows for electrophysiologic best-frequency (BF) determination of CI electrodes and the potential for creating a personalized frequency allocation function. The objective of this study was to investigate the correlation between early speech-perception performance and frequency-to-place mismatch. This retrospective study included 50 patients who received a slim perimodiolar electrode array. Following electrode insertion, five acoustic pure-tone stimuli ranging from 0.25 to 2 kHz were presented, and electrophysiological measurements were collected across all 22 electrode contacts. Cochlear microphonic tuning curves were subsequently generated for each stimulus frequency to ascertain the BF electrode or the location corresponding to the maximum response amplitude. Subsequently, we calculated the difference between the stimulus frequency and the patient's CI map's actual frequency allocation at each BF electrode, reflecting the frequency-to-place mismatch. BF electrocochleography-total response (BF-ECochG-TR), a measure of cochlear health, was also evaluated for each subject to control for the known impact of this measure on performance. Our findings showed a moderate correlation (r = 0.51; 95% confidence interval: 0.23 to 0.76) between the cumulative frequency-to-place mismatch, as determined using the ECochG-derived BF map (utilizing 500, 1000, and 2000 Hz), and 3-month performance on consonant-nucleus-consonant words (N = 38). Larger positive mismatches, shifted basal from the BF map, led to enhanced speech perception. Incorporating BF-ECochG-TR, total mismatch, and their interaction in a multivariate model explained 62% of the variance in consonant-nucleus-consonant word scores at 3 months. BF-ECochG-TR as a standalone predictor tended to overestimate performance for subjects with larger negative total mismatches and underestimated the performance for those with larger positive total mismatches. Neither cochlear diameter, number of cochlear turns, nor apical insertion angle accounted for the variability in total mismatch. Comparison of ECochG-BF derived tonotopic electrode maps to the frequency allocation tables reveals substantial mismatch, explaining 26.0% of the variability in CI performance in quiet. Closer examination of the mismatch shows that basally shifted maps at high frequencies demonstrate superior performance at 3 months compared with those with apically shifted maps (toward Greenwood and Stakhovskaya et al.). The implications of these results suggest that electrophysiological-based frequency reallocation might lead to enhanced speech-perception performance, especially when compared with conventional manufacturer maps or anatomic-based mapping strategies. Future research, exploring the prospective use of ECochG-based mapping techniques for frequency allocation is underway.

Prothrombin and activated partial thromboplastin times, thromboelastography, hematocrit, and platelet count in a feline hemorrhage/over-resuscitation model using lactated Ringer's solution or 6% tetrastarch 130/0.4.

To describe and compare prothrombin time (PT), activated partial thromboplastin time (aPTT), thromboelastography (TEG), HCT, and platelet count measurements in a hemorrhage/over-resuscitation model. Randomized crossover study. University teaching hospital. Six cats. Anesthetized cats underwent 3 treatments at 2-month intervals. The treatments were as follows: NHR-no controlled hemorrhage and sham resuscitation; LRS-controlled hemorrhage and lactated Ringer's solution (LRS) for resuscitation; and Voluven-controlled hemorrhage and 6% tetrastarch 130/0.4 for resuscitation. The LRS and Voluven were administered at 60 and 20mL/kg/h, respectively, for 120minutes. Blood samples were drawn for PT, aPTT, TEG, HCT, and platelet count measurements at a healthy check (T - 7d), after controlled hemorrhage (T0), at 60 and 120minutes of resuscitation (T60 and T120), and at 24hours after completion of resuscitation (T24h). Data were analyzed using a general linear mixed model approach (significance was P<0.05). Total median blood loss (controlled hemorrhage and blood sampling from T0 to T120) at T120 was 11.4, 31.0, and 30.8mL/kg for NHR, LRS, and Voluven, respectively. PT and aPTT during LRS and Voluven were prolonged at T60 and T120 compared to NHR (P<0.001). On TEG, the reaction time, kinetic time, and alpha-angle were within reference intervals for cats at all time points in all treatments, while maximum amplitude was less than the reference interval (40mm) at T0, T60, and T120 during Voluven and at T60 and T120 during LRS compared to NHR (both P<0.001). The HCT and platelet count were significantly lower at T60 and T120 during LRS and Voluven compared to NHR (P<0.001). Hypocoagulopathy was observed during hemorrhage and liberal fluid resuscitation. Prolongation of PT and aPPT and decreased clot strength may have been caused by hemodilution and platelet loss.

Мікроциркуляція та варіабельність серцевого ритму при хронічній ішемічній хворобі серця і COVID-19

COVID-19 is associated with a wide range of negative effects on the cardiovascular system. The aim of our study was to investigate the impact of COVID-19 on the interdependence of changes in the microcirculation system and heart rate variability in patients with chronic coronary artery disease (CAD). An ECG study was performed in 12-lead leads, as well as 24-hour Holter ECG monitoring and laser Doppler flowmetry (LDF). Patients were divided into 3 groups. Group 1 included patients with coronary artery disease (n = 32), group 2 - with coronary artery disease in combination with COVID-19 (n = 35), and group 3 - with COVID-19 (n = 35). The control group consisted of 30 conditionally healthy individuals. All subjects were determined: microcirculation index, capillary blood flow reserve of the occlusion test, as well as nitroglycerin test and wavelet transform indicators (the relationship between the frequency and amplitude of microcirculatory oscillations, which are divided into endothelial, neurogenic, myogenic, respiratory and cardiac mechanisms of microcirculation regulation). The deterioration of endothelial function, as measured by the maximum amplitude of endothelial flux motions, should be noted, and a decrease in the endotheliumdependent and endothelium-independent components of microcirculation regulation. The capillary blood flow reserve of the occlusion test in patients with CAD in combination with COVID-19 was lower than in patients with CAD (group 1) and COVID-19 (group 3). In patients of the study groups, the total heart rate variability decreased, parasympathetic activity was weakened, and the QT interval duration and its variability increased compared with controls. These changes were most pronounced in patients with coronary artery disease in combination with COVID-19 in terms of the standard deviation of all intervals, the parasympathetic component of regulation, and both characteristics of the QT interval. Thus, patients with chronic CAD and concomitant COVID-19, along with endothelial dysfunction and worsening venous outflow, showed signs of autonomic dysregulation and increased QT interval duration and variability. Additional consideration of the characteristics of the microcirculatory bed, heart rate variability and QT interval is advisable in the examination system of such patients.

Middle to Late Holocene lake level variations recorded by shoreline tufa of Longmu Co Lake, northwestern Tibet Plateau

Tufa deposits have significant potential for reconstructing past lake-level fluctuations. Here, we conducted U-Th dating of tufa deposits exposed along the shoreline of Longmu Co Lake in the northwestern Tibetan Plateau to reconstruct its water level history during the middle-late Holocene. Our data demonstrate that Longmu Co Lake reached its highest level (61 m above the present level) at around 7.4 ka in response to the strengthened Indian Summer Monsoon and increased glacial meltwater; its lake level subsequently decreased due to solar insolation-induced decline in summer monsoon and glacial meltwater. Moreover, we find that the lake level experienced an abrupt decline at ~2.2 ka with a maximum amplitude of 13 m, probably owing to the rapid cooling of the local climate. The δ18O and δ13C of Longmu Co tufa also show a covariance trend, which supports the regional climate change reflected by the lake level fluctuation of Longmu Co. Additionally, we observed an inverse correlation between initial δ234U content in tufa and lake level variation, suggesting that initial calcium δ234U can serve as a proxy for reconstructing environmental changes. Our study therefore implies that lake tufa as a reliable archive for accurately reconstructing lake level changes.

The Impact of Sex on Antiplatelet and Anticoagulant Thromboprophylaxis in Patients With Peripheral Artery Disease Post-revascularization.

The aim of this prospective study was to (1) objectively quantify the impact of sex on platelet function in patients with peripheral artery disease (PAD) taking antiplatelet and anticoagulant medications and (2) to develop and test a personalized, iterative algorithm that personalizes thromboprophylaxis that incorporates platelet function testing. Women with PAD have worse outcomes as compared with their male counterparts despite having lower risk factors. This health disparity may be mitigated by personalizing thromboprophylaxis regimens. Patients undergoing revascularization were enrolled. Serial thromboelastography (TEG) and TEG with platelet mapping (TEG-PM) were performed up to 6 months postoperatively to determine objective coagulation profiles. In a subset of patients, the Antiplatelet Coagulation Exactness (ACE) algorithm was implemented, where patients were iteratively evaluated with TEG and given antiplatelet medications to maintain platelet inhibition at >29%. Statistical analysis was performed using unpaired t test, analysis of variance, and Fisher exact test. One hundred eighty-one patients met the study criteria. Fifty-eight (32%) patients were females and 123 (68%) were males. In the Aspirin cohort, females showed significantly greater clot strength as maximum amplitude - arachidonic acid (MA AA ) and significantly lower platelet inhibition than males: (37.26 vs 32.38, P <0.01) and (52.95% vs 61.65%, P <0.05), respectively. In the Clopidogrel cohort, females showed higher Maximum Amplitude - Adenosine Diphosphate (MA ADP ) (42.58 vs 40.35, P = not significant [NS]) compared with males. Females on dual antiplatelet therapy had higher MA ADP (39.74 vs 35.07, P =NS) and lower platelet inhibition (45.25% vs 54.99%, P= NS) than males. The incidence of thrombosis of the revascularized segment, defined as thrombotic event, was objectively identified on an arterial duplex. Women showed significantly higher thrombotic events than men (22.95% vs 10.57%, P< 0.05) on the same medication. In our pilot study, implementation of the ACE algorithm led to a significant decrease in the thrombosis rate (3%), including nonthrombotic events for females, versus the historic thrombotic rate (22%) from our institution. Women with PAD exhibited higher platelet reactivity, clot strength, and reduced platelet inhibition in response to antiplatelet therapy. The use of the ACE algorithm to tailor antiplatelet medication in patients with PAD post-revascularization, resulted in a significant decrease in thrombotic event rates. This may serve as an opportune way to mitigate outcome sex-specific disparities caused by inadequate thromboprophylaxis in women.

Mathieu–Hill Equation Stability Analysis for Trapped Ions: Anharmonic Corrections for Nonlinear Electrodynamic Traps

The stability properties of the Hill equation are discussed, especially those of the Mathieu equation that characterize ion motion in electrodynamic traps. The solutions of the Mathieu-Hill equation for a trapped ion are characterized by employing the Floquet theory and Hill’s method solution, which yields an infinite system of linear and homogeneous equations whose coefficients are recursively determined. Stability is discussed for parameters a and q that are real. Characteristic curves are introduced naturally by the Sturm–Liouville problem for the well-known even and odd Mathieu equations cem(z,q) and sem(z,q). In the case of a Paul trap, the stable solution corresponds to a superposition of harmonic motions. The maximum amplitude of stable oscillations for ideal conditions (taken into consideration) is derived. We illustrate the stability diagram for a combined (Paul and Penning) trap and represent the frontiers of the stability domains for both axial and radial motion, where the former is described by the canonical Mathieu equation. Anharmonic corrections for nonlinear Paul traps are discussed within the frame of perturbation theory, while the frontiers of the modified stability domains are determined as a function of the chosen perturbation parameter and we demonstrate they are shifted towards negative values of the a parameter. The applications of the results include but are not restricted to 2D and 3D ion traps used for different applications such as mass spectrometry (including nanoparticles), high resolution atomic spectroscopy and quantum engineering applications, among which we mention optical atomic clocks and quantum frequency metrology.

Harnessing flow-induced vibrations for energy harvesting: Experimental and numerical insights using piezoelectric transducer.

Flow-induced vibrations (FIV) were considered as unwanted vibrations analogous to noise. However, in a recent trend, the energy of these vibrations can be harvested and converted to electrical power. In this study, the potential of FIV as a source of renewable energy is highlighted through experimental and numerical analyses. The experimental study was conducted on an elastically mounted circular cylinder using helical and leaf springs in the wind tunnel. The Reynolds number (Re) varied between 2300-16000. The motion of the cylinder was restricted in all directions except the transverse direction. The micro-electromechanical system (MEMS) was mounted on the leaf spring to harvest the mechanical energy. Numerical simulations were also performed with SST k-ω turbulence model to supplement the experiments and were found to be in good agreement with the experimental results. The flow separation and vortex shedding induce aerodynamic forces in the cylinder causing it to vibrate. 2S vortex shedding pattern was observed in all of the cases in this study. The maximum dimensionless amplitude of vibration (A/D) obtained was 0.084 and 0.068 experimentally and numerically, respectively. The results showed that the region of interest is the lock-in region where maximum amplitude of vibration is observed and, therefore, the maximum power output. The piezoelectric voltage and power output were recorded for different reduced velocities (Ur = 1-10) at different resistance values in the circuit. It was observed that as the amplitude of oscillation of the cylinder increases, the voltage and power output of the MEMS increases due to high strain in piezoelectric transducer. The maximum output voltage of 0.6V was observed at Ur = 4.95 for an open circuit, i.e., for a circuit with the resistance value of infinity. As the resistance value reduced, a drop in voltage output was observed. Maximum power of 10.5μW was recorded at Ur = 4.95 for a circuit resistance of 100Ω.

Single-Station Back-Azimuth Determination with the Receiver Function Rotation Technique Validated by the Locations of Earthquakes, Impacts, and Explosions

Abstract The success of seismometer installations on the ocean floor, polar regions, remote continental areas, and even other planets’ surfaces has sparked renewed interest in determining the location via the azimuthal direction of a seismic event recorded by a single station, also known as the back azimuth (BAZ). However, classical algorithms for the BAZ estimate, like principal component and polarization analyses based on P-wave particle motions, are prone to ambiguities of 180°. Motivated by the sensor orientation correction techniques used for ocean-bottom seismometers and land stations for known event locations, we explore a receiver function rotation (RFR) method to determine the BAZ for events recorded by a single station. It is a parameter search over a range of horizontal component rotation angles from 0° to 360°. The fundamental feature of the method is that the direct P wave in the radial receiver function (RF) will have the maximum amplitude when the rotation from the ZNE system (vertical, north–south, and east–west) to ZRT (vertical, radial, and tangential) is aligned with the BAZ of the incoming P wave. Hence, the largest amplitude at zero time of the ensemble of RFs computed for different horizontal component rotations shows the optimal BAZ, which is consequently free of the 180° ambiguities. The technique’s performance is validated using the well-documented location of the 2017 Democratic People’s Republic of Korea nuclear explosion and over 1200 cataloged earthquakes on the two permanent stations in Australia. We further benchmark the RFR algorithm by the locations of two ground-truth Martian impact events documented by the orbital camera and recorded by InSight’s seismometer. Our method helps enhance the reliability of BAZ estimation as a complementary scheme to other methods. It can be used in remote areas on Earth and on the future missions to the Moon and other planets.

Currents’-Physical-Component-Based Reactive Power Compensation Optimization in Three-Phase, Four-Wire Systems

In this paper, we aim to address the limited capacity of compensation devices by enhancing their utilization rate by applying the currents’ physical component (CPC) theory for reactive power optimization in three-phase four-wire systems. When reactive currents cannot be fully compensated for, we propose using CPC theory to generate reference currents for the compensation devices. Weight coefficients associated with different reactive current components are introduced, enabling flexible combinations of these independent current components. The maximum output amplitude of the three-phase current from the compensation device serves as a constraint condition, allowing for the calculation of reference currents under various compensation targets. Additionally, a reactive current optimization compensation scheme focusing on loss reduction is selected. The simulated annealing–particle swarm optimization (SA-PSO) hybrid algorithm is employed to solve the optimization mathematical model. The discussed calculations, current waveforms, and voltage waveforms are generated using the constructed mathematical model and then used for a theoretical explanation. The simulation verifies the feasibility of the proposed method.

EVALUATION OF THE SCATTER OF LIQUID LAUNCH VEHICLE POGO OSCILLATION AMPLITUDES DUE TO THE INFLUENCE OF THE SCATTER OF INTERNAL FACTORS

Almost all liquid launch vehicle developers faced the problem of ensuring stability in relation to POGO oscillations. The level of POGO amplitudes oscillations of the launch vehicle can be significantly affected by the scatter of internal factors. The study aims to create a mathematical model that can determine the range of POGO amplitudes in liquid launch vehicles. This will be demonstrated through the example of the Dnipro launch vehicle, which is affected by a variety of internal factors that cause its POGO amplitudes to vary. We developed the non-linear non-stationary mathematical model of POGO oscillations of the prototype of the Dnipro space launch vehicle. The model is built by taking into account the two lower vibration modes of the LV structure, two lower oscillation modes of the oxidizer feedline, and the first oscillation mode of the fuel feedline of the propulsion system. Modeling of dynamic processes was conducted in a combination of four liquid rocket engines based on the schematic of the staged rocket engine. The simulation takes into account cavitation phenomena in the engine pumps and delay times in the gas generators’ chambers. We have developed a method for determining the scatter of the POGO oscillations caused by the action of internal factors, which is based on the use of the LP uniformly distributed sequences. As internal factors, the frequencies, decrements, and shapes of LV structural oscillation modes, the values of pressurization of the propellant tanks, and the engines’ specific thrust impulses were considered. Based on the results of the calculations, the dependence of the POGO amplitudes in two regions of LV instability was determined, and the lower and upper enveloping curves for the POGO amplitudes were constructed. It is shown that the maximum POGO amplitudes oscillations in the first region of instability lie in the range from 0.23 g to 0.72 g and in the second region of instability — from 0 g to 0.60 g. Variants of combinations of internal factors, which provided the largest and smallest values of POGO amplitudes, were analyzed. This made it possible to determine the internal factors, the scatter of which has the greatest effect on the POGO amplitudes scatter: frequency, decrement, shape coefficients of oscillations of the oxidizer feedlines and the LV 1st mode structural longitudinal oscillations in the payload cross-section.

Effect of body position on transesophageal atrial pacing in dogs

ObjectiveTo evaluate the effect of body position on transesophageal atrial pacing (TEAP) in dogs. Study designProspective, experimental trial. AnimalsA total of eight mixed-breed dogs, median body mass 25 kg (range 11–31 kg). MethodsTEAP was performed using a 6 Fr (2 mm) pacing catheter introduced transorally and positioned in the lower esophagus in left lateral recumbency. The catheter was withdrawn in 5 mm increments until successful TEAP. The minimum pacing threshold (MPT) was determined at each 5 mm increment until atrial capture could not be achieved at a maximal pulse amplitude of 40 mA. The zone of capture (ZOC) was the total distance over which TEAP was achieved. The same process was repeated in right lateral, ventral and dorsal recumbency. A linear mixed model was used to assess the impact of body position on TEAP and ZOC. ResultsTEAP was achieved in all body positions. There was significant random effect of individual dogs on ZOC (p = 0.048) but not on MPT (p = 0.109). MPT was 11.56 ± 8.65 mA (mean ± SD), 8.43 ± 2.29 mA, 10.63 ± 6.91 mA and 10 ± 7.44 mA for dorsal, left and right lateral, and ventral recumbency, respectively. ZOC was 5.12 ± 2.08 cm, 6.35 ± 2.41 cm, 5.94 ± 3.23 cm and 5.31 ± 2.2 cm for dorsal, left lateral and right lateral, and ventral recumbency, respectively. Neither ZOC (p = 0.363) nor MPT (p = 0.716) varied significantly between body positions. Conclusions and clinical relevanceTEAP can be performed successfully in all body positions in dogs. Body position did not significantly influence MPT or ZOC values for TEAP. Further studies are needed to compare the efficacy of TEAP with the efficacy of standard pharmacological therapy for management of bradycardia during general anesthesia in dogs.

Sensitivity enhancement in erbium-doped fiber laser intra-cavity SPR sensor

To enhance sensitivity of fiber-based surface plasmon resonance (SPR) sensor for refractive index detection, we propose a concept of fiber laser intra-cavity SPR sensor that is constructed by placing a hollow fiber-based SPR sensor in an erbium-doped fiber laser cavity. The hollow fiber-based SPR sensor is firstly designed and optimized to achieve maximum amplitude sensitivity of 65.576 RIU−1 in a detection range of 1.6–1.61 at the operation wavelength of 1530 nm, and then placed in the erbium-doped fiber laser cavity to form the fiber laser intra-cavity SPR sensing system. The relationships between the detection sensitivity, pump power, and SPR sensor length of the laser intra-cavity SPR sensor are investigated in detail by using three-level rate equations, and the numerical results demonstrate that the sensitivity is enhanced 82 times, achieves 5375.627 RIU−1 when the fiber-based SPR sensor is placed in the laser cavity, and can be further enhanced by tuning the pump power to close to threshold value. The work described here demonstrates a possible solution to enhance the sensitivity by combining the fiber-based SPR sensor and the fiber laser.

Interaction of ultrasonically driven bubble with a soft tissue-like boundary

This study investigates the size-dependent dynamics of bubbles and their interaction with soft boundaries under various ultrasound (US) conditions. We found that bubble behavior is influenced by size, with smaller bubbles displaying reduced inertial motion in similar ultrasound environments. Detailed analyses of three bubble sizes (1.5 µm, 15 µm, and 150 µm) next to a soft 1 kPa boundary revealed distinct patterns in radial oscillation, bubble center displacement, and boundary deflection for different ultrasound frequencies (5 kHz − 4 MHz). The smallest bubble maintained a spherical shape, while the largest experienced significant shape changes, indicative of impending jet formation. Investigating interactions at various frequencies highlighted the collapse tendency of the larger bubbles, showcasing maximum radial amplitude, displacement, and bubble wall velocity around its natural frequency. The presence of a soft boundary minimally affected radial amplitude and velocity, while the bubble displacement was contingent on the soft boundary modulus. Furthermore, boundary responses demonstrated that softer boundaries experienced less stress during bubble oscillations, exhibiting sharper peaks at resonance frequencies for larger bubbles. These findings provide valuable insights into optimizing ultrasound conditions for a variety of applications, highlighting the influence of bubble size and boundary properties on outcomes.

Dynamic model of the functional parameter degradation changes in radio-electronic systems with two non-stationary random components corresponding to two types of noise

Problem statement. The processes of aging and degradation caused by the influence of environmental conditions, leading to changes in the functional parameters of radio-electronic systems, negatively affect the output characteristics and reduce the period of operation. The currently existing model of changes in radio-electronic system parameters, used for individual forecasting by extrapolation, includes only one random component representing various types of noise. At the same time, practical studies shows that the maximum amplitudes of different types of noise change at different rates. Therefore, for a more complete representation of the process of electromagnetic parameter changes over time, it is necessary to develop a model that takes into account this effect. The article discusses this problem using the example of the linear stabilizer output voltage. Goal. The main goal of the research presented in this article is to develop a model of functional parameter degradation that takes into account changes in maximum amplitudes of various types of noise in order to increase the accuracy of individual forecasting and the potential period of the device operation. Results. A generalized model of the electromagnetic parameter changes of the radio-electronic systems with two nonstationary random components characterizing various types of noise is presented. A software implementation of the presented model successfully verified on experimental data. Practical significance. The extended model of the functional parameter changes in radio-electronic systems can be used both in individual forecasting by extrapolation, and in the development of systems with a long period of operation, as well as devices intended for autonomous use. The prospects of using the presented model to simulate changes in functional parameters and determine the possibilities of compensating these changes are shown on the example of a frequency synthesizer with an automatic output power control system.

Photonic crystal fiber based on graphene surface plasmon resonance for high-sensitivity terahertz refractive index sensing

A photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) with a graphene coating on the cladding is designed for refractive index (RI) detection in the range of 0.3–0.5 THz, especially for liquid bioanalytical sensing. The adjustability of the graphene chemical potential (E f ) enables dynamic tuning of the loss spectra over a wide frequency range with a tuning sensitivity of 570 GHz/eV at the SPR frequency. According to the analysis by the finite element method (FEM), the highest wavelength sensitivity and maximum amplitude sensitivity of 4254.11 µm/RIU and 25.62RIU−1 (n a =1.34) are achieved in the RI range of 1.15–1.35, respectively, together with a resolution of 5.93×10−5RIU. The graphene PCF-SPR sensor boasting high-sensitivity detection in a wide RI range has broad application prospects in multiple fields.