Amplitude Angle Research Articles

Eight new astrometry results of 6.7 GHz CH3OH and 22 GHz H2O masers in the Perseus arm

AbstractWe report astrometric results for seven 6.7 GHz CH3OH and one 22 GHz H2O masers in the Perseus arm with VLBA and VERA observations. Among the eight sources, we succeeded in obtaining trigonometric parallaxes for all sources, except G098.03+1.44 at 6.7 GHz band. By combining our results with previous astrometry results (Choi et al. 2014), we determined an arm width of 0.41 kpc and a pitch angle of 8.2 ± 2.5 deg for the Perseus arm. By using a large sample of the Perseus arm (26 sources), we examined the three-dimensional, non-circular motions (defined as U, V and W) of sources in the Perseus arm as a function of the distance (D) perpendicular to the arm. Interestingly, we found a weighted mean of <U > = 12.7 ± 1.2 km s−1 for 14 sources with D < 0 kpc (i.e. sources on the interior side of the arm) and <U > = −0.3 ± 1.5 km s−1 for 12 sources with D > 0 kpc (i.e. sources exterior to the arm). These findings might be the first observational indication of the ”damping phase of a spiral arm” suggested by the non-steady spiral arm model of Baba et al. (2013). The small pitch angle of the Perseus arm (< 10 deg) also supports the damping phase, based on ”pitch angle vs. arm amplitude” relation shown in Grøsbol et al. (2004).

An experimental study on the cyclic settlement of sand and cemented sand under different inclinations of the bedding angle and loading amplitudes

Although the directional dependence of soil behaviour is a subject of great interest, yet studies of its effects on cyclic settlement are lacking. Therefore, this paper investigated the macro-scale cyclic settlement under various inclinations of bedding plane (α = 0° to 90°) and different loading amplitudes (qc/qu), and to assess the degree of improvement provided by cement additions which reduce directional dependence. There was high variability in the cyclic settlement of uncemented sand according to bedding plane inclination. The difference between settlement ratios at 0° and 90° were 5.1, 29 and 55% after 100 load cycles with amplitudes of 10, 20 and 30%, respectively. Most of this difference occurred when α ≥ 60°. However, settlement variation became marginal after a large number of load cycles for all amplitudes. Sand treated with cement was improved and it showed a decrease in settlement ratio and elimination of directional dependency. With 7% cement, settlement variation with α did not exceed 12% for all loading amplitudes. However, these effects were still pronounced at lower cement contents, especially when α = 60–90°.

Anisotropic mechanical properties and constitutive relations of PTFE coated glass fibers

This paper presents the anisotropic mechanical properties and constitutive relations of PTFE (Polytetrafluoroethylene) coated glass fibers. First, the monotonous and cyclic tests are carried out, in which the effects of stress amplitude and bias angle are considered. Then, the decomposition of material strain during the cyclic tests is studied and the predicted models are also discussed. Finally, an anisotropic constitutive relation is proposed to predict the off-axial creep behaviors. Results show that the tensile behaviors of PTFE coated glass fibers are anisotropic, which is mainly related with the crimp degree of woven structure. The material deformation can be divided into three parts, elastic deformation, recoverable viscous deformation and unrecoverable viscous deformation. The bias angle and stress amplitude have significant effects on the cyclic tensile behaviors. After unloading, the total residual strain has decreased about 90% in the first 3days. The final unrecoverable strain of 45 specimen is the highest, about 30 times of that of warp specimen, or 8 times of that of weft specimens. Besides, the revised Burgers model can be used to describe the cyclic tensile behaviors. Finally, the proposed anisotropic constitutive relation can be used to predict the creep behaviors at any directions.

CONTINUOUS MONITORING OF TURNING MOBILITY IN PATIENTS WITH ALZHEIMER’S DISEASE: A PILOT STUDY

Patients with Alzheimer's Disease (AD) frequently have impairments with spatial orientation and navigation. These deficits in spatial cognition are thought to contribute to the increased risk of falls and wandering in AD, which are highly morbid conditions for these patients. Recent studies using continuous activity monitoring in cognitively-normal older adults observed that reduced spatial cognitive skills was associated with poorer turning mobility. The goal of this study was to investigate the preliminary feasibility of continuous monitoring of turning mobility in AD patients, with the broader goal of developing an objective measure of spatial cognitive skills in AD patients. We recruited four AD patients into the study. The patients wore an Opal sensor (APDM, Portland, OR) on a belt on the lower back during normal daily activity and were instructed to wear the device for 4 consecutive days. An algorithm identified periods of walking from the 3D accelerations (>10 sec) and calculated the following turning metrics that occurred while walking: 1) number of turns occurring in each 30 min period, 2) turn angle amplitudes, 3) turn durations, 4) turn velocities (mean and peak). We were able to successfully record from all 4 patients (mean age 77.3 years, 75% male, MMSE range 13–24). The number of days of use ranged from 2–5 days, and the number of hours of use ranged from 16.5–45.5 hours. Data on turning mobility were generated for all 4 patients. The only quantity that differed substantially between data from healthy older adults and the AD patients was mean turn angle which was higher in the older adults (96° vs. 75°). In this pilot study, AD patients (even with an MMSE of 13) tolerated the Opal continuous monitoring device and provided evaluable data on turning mobility. We determined that 4 days of monitoring (yielding at least 36 hours of data) would be needed to provide sufficient data for estimation of turning mobility parameters. The next steps of this study are to complete recruitment of a total of 25 patients, and evaluate whether turning mobility is associated with MMSE and spatial cognition in AD patients.

Growth and magnetooptical properties of anisotropic TbF3 single crystals

This paper investigates the Faraday effect and absorption and luminescence spectra of single-crystal TbF3 measured at 90 K and 300 K. The optical-quality single-phase TbF3 crystals (structural type β-YF3) were grown by the Bridgman technique. Faraday rotation angles were measured at remagnetization along the [100] crystallographic axis. Low temperature optical measurements were carried out along the [100] axis. “Quasi-doublet” sublevels with energy at 0 cm−1, 65 cm−1, and 190 cm−1, and also a singlet sublevel with energy at 114 cm−1 located in the ground 7F6 multiplet were determined from the low temperature luminescence spectra. The Van-Vleck behavior of the magnetic susceptibility χb can be satisfactorily explained by the magnetic mixing of wave functions belonging to the ground and first excited “quasi-doublet” sublevels at 0 and 65 cm−1, respectively. Analysis of the oscillation dependences of the rotation angle showed that the value of the natural birefringence (Δn ≈ 0.0186) remains nearly constant within the wavelength and temperature ranges under investigation. As the temperature decreases, we find significant increases in the oscillation amplitude of the rotation angle and in the Verdet constant V. The spectral dependences V(χ) are linear throughout the temperature range. The magnetooptical activity of TbF3 can be explained by means of the spin- and parity-allowed electric-dipole 4f → 5d transitions in the Tb3+ ions.

Numerical study on S-wave transmission across a rough, filled discontinuity

This paper presents a numerical simulation of S-wave propagation across a rough, filled discontinuity using the universal distinct element code (UDEC). The ability of UDEC to simulate a stress wave across a smooth and planar discontinuity filled with an elastic material is validated through comparisons with analytical solutions. Next, the effect of the plastic deformation of the fill on the wave propagation is investigated. The model is extended to further study S-wave propagation across a filled discontinuity with rough interfaces, which is described using a sawtooth. The transmission coefficient defined by the energy is used to measure the wave attenuation. Finally, a parametric study is conducted to investigate the influences of the filled thickness, asperity angle, and incident amplitude on the transmission waves and transmission coefficients. The asperity angle and filled thickness together determine the transmitted waveform and transmission coefficient. The transmitted wave may be cut off when the incident wave amplitude exceeds a threshold value. The transmission coefficient decreases with a different trend with the incident wave amplitude increasing when the asperity angle varies. Compared with planar discontinuity, a filled discontinuity with rough interfaces is more sensitive to the amplitude of the incident wave. The causes of these phenomena are analyzed in detail. In addition, the deformation of the fill material is strongly related to the wave attenuation.

Modelling and simulation of the dynamic performance of a no-till seeding assembly with a semi-active damper

In no-till seeding, one of the biggest challenges to achieve a reliable seed germination and an even plant field emergence is an extreme variation in the desired seeding depth. This is caused by the inadequate response of the seeder motion dynamics to harsh soil conditions and to high operating speeds. In order to assess and optimise the dynamic response of a no-till seeder, mathematical models were developed for simulating the vertical motion of a coulter assembly. The models included the dynamics of the coulter assembly, with the packer wheel as a passive system, and a semi-active MR (magnetorheological) damper system, which was considered to be located in-between the coulter and the packer wheel. The developed model of the coulter assembly dynamics was validated based on a correlation between the simulated and the measured impact forces and pitch angles. A root-mean-squared (RMS) error resulted from the correlation have increased from 6.84% at the lower speed of 10kmh−1 to 14.5% at the higher speed of 15kmh−1 for the impact forces, from 8.1% at the lower speed of 10kmh−1 to 13.1% at the higher speed of 15kmh−1 for the pitch angle. Conversely, there was a fall in the correlation coefficient from 0.699 to 0.681 for the impact forces and from 0.942 to 0.684 for the pitch angle between the lower speed of 10kmh−1 and the higher speed of 15kmh−1, respectively. Furthermore, all three applied hysteresis models, such as Bingham, Dahl and Bounc-Wen model, for the semi-active MR damper system behaviour demonstrated significant improvements over the passive system model. Among the models, the Bouc-Wen model produced more adequacy of the MR damper behaviour with the highest reduction of 54.1%, 63.3% and 41.2% in the amplitude of the impact forces and 52.3%, 58.2% and 38.1% in the amplitude of the pitch angles at the speeds of 10kmh−1, 12kmh−1 and 15kmh−1, respectively.

Source wavelet and local wave propagation effects on the amplitude-variation-with-offset response of thin-layer models: A physical modeling study

In target layers with thicknesses below the vertical seismic resolution as thin layers, the tuning effect/interference between the wave propagation modes may increase the challenge of doing amplitude-variation-with-offset (AVO) analysis because it is difficult to recover the primary PP amplitudes embedded in the data by further seismic data processing. Thus, we have investigated the importance of the primary PP reflections, locally P-SV converted waves, and internal multiple reflections in the amplitude response of two thin-layer seismic physical models. One model consists of a thin water layer embedded between two nylon plates, and another model with a thin acrylic layer surrounded by water. Numerical modeling using the reflectivity method was applied to analyze each wave propagation mode and the source waveform role in the experimental data. Before the experimental reflection data acquisition, we characterized two source and receiver piezoelectric transducer (PET) pairs: one with a circular plane face and the other with a semispherical face. We measured the source wavelet, its dominant frequency, and the PETs’ directivity pattern. Semispherical PETs were chosen to acquire common midpoint reflection data. Thereafter, a processing workflow was applied to remove linear events interfering with the target reflections and to correct amplitudes due to transmission losses, source/receiver directivity, and geometric spreading effects. Finally, we investigated the thin-layer targets near incidence angle amplitude and the AVO response. The results showed that the interference between the primary PP reflections and the locally converted shear waves may considerably affect the observed amplitude response. The source wavelet bandwidth appeared as a second-order effect, and the internal multiple reflections were practically negligible. These results suggested that in real data sets, it is important to investigate the wave propagation modes and source wavelet role in the amplitudes observed, before deciding the AVO analysis/inversion workflow that should be adopted.

Evaluation of Hemostatic Function with Thromboelastography in Dogs with Hypercoagulable Diseases

Thromboembolic complications are increasing in veterinary medicine. Thromboelastography (TEG) is a more comprehensive method for assessing the clotting process than standard plasma-based coagulation tests. This study compared the ability of TEG and standard coagulation tests to analyze the overall hemostatic state of dogs. The study involved 40 dogs with underlying diseases that predispose to hypercoagulability, including neoplasia, hyperadrenocorticism, immune-mediated diseases, gastrointestinal diseases, and protein-losing nephropathies and enteropathies, and 20 healthy dogs. Their overall hemostatic functional state was evaluated by TEG and routine coagulation assays, including activated partial thromboplastin time, prothrombin time, platelet count, and D-dimer concentration. TEG analysis showed significant differences in clot formation time, α angle, and maximum amplitude (MA) between diseased and control dogs (P ＜ 0.001 each). Increased MA was the most frequent abnormality on TEG and was indicative of hypercoagulability. TEG was useful in detecting hemostatic dysfunction in dogs with diseases associated with hypercoagulability. Dogs with TEG tracings indicative of hypercoagulability are likely to be in procoagulant states. Future prospective studies are needed to evaluate whether TEG tracings indicative of hypercoagulability are predictive of thrombosis in dogs.

Identificación de un patrón tromboelastográfico en niños sometidos a cirugía cardiaca con exposición prolongada a circulación extracorpórea

BackgroundPoint-of-care thromboelastography is used for guiding peri-operative haemostatic therapy. ObjectiveTo identify a thromboelastographic pattern in children with prolonged cardiopulmonary bypass exposure, and their association with age and weight. Material and methodsA cohort study of 62 patients undergoing prolonged cardiopulmonary bypass was performed. Patients with preexisting coagulopathy, use of drugs known to interfere with clotting, haematocrit >60%, weight <3kg, or hepatic disease were excluded. The thromboelastography study was conducted at the point of care. ResultsBaseline and rewarming reaction time values were 8.24±6.35 and 7.66±2.15minutes, respectively (P=.102). Baseline and rewarming angle values were 64.88±13.08 and 54.67±8.98 degrees, respectively (P<.001). Baseline and rewarming maximum amplitude values were 64.54±12.31 and 43.14±12.47mm, respectively (P=.001). The same trend was observed when the cohort was divided into patients under and over 3years of age, and patients under and over 10kg of body weight. DiscussionThis study suggests the existence of a thromboelastographic pattern independent of age or weight in patients undergoing paediatric cardiac surgery with prolonged cardiopulmonary bypass exposure, characterised by a reduction of angle and maximum amplitude values, with no change in reaction time.

Identification of a thromboelastographic pattern in children undergoing cardiac surgery with prolonged exposure to cardiopulmonary bypass

BackgroundPoint-of-care thromboelastography is used for guiding peri-operative haemostatic therapy. ObjectiveTo identify a thromboelastographic pattern in children with prolonged cardiopulmonary bypass exposure. Material and methodsA cohort study of 62 patients undergoing prolonged cardiopulmonary bypass was performed. Patients with preexisting coagulopathy, use of drugs known to interfere with clotting, hematocrit>60%, weight<3kg, or hepatic disease were excluded. The thromboelastography study was conducted at the point of care. ResultsBaseline and rewarming reaction time values were 8.24±6.35 and 7.66±2.15min, respectively (p=0.102). Baseline and rewarming angle values were 64.88±13.08 and 54.67±8.98 degrees, respectively (p<0.001). Baseline and rewarming maximum amplitude values were 64.54±12.31 and 43.14±12.47mm, respectively (p=0.001). The same trend was observed when the cohort was divided into patients under and over 3 years of age, and patients under and over 10kg of body weight. DiscussionThis study suggests the existence of a thromboelastographic pattern independent of age or weight in patients undergoing paediatric cardiac surgery with prolonged cardiopulmonary bypass exposure, characterised by a reduction of angle and maximum amplitude values, with no change in reaction time.

Effects of hemolysis and lipemia interference on kaolin-activated thromboelastography, and comparison with conventional coagulation tests

The effects of hemolysis and lipemia on thromboelastography (TEG) analysis have been scarcely evaluated in human samples, and neglected in clinical practice. We aimed to investigate the effects of in vitro mechanical hemolysis and lipemia on TEG analysis and conventional coagulation tests. Twenty-four healthy volunteers were enrolled in the study. Besides the controls, three groups with slight, moderate and severe mechanical hemolysis were constituted according to free hemoglobin (Hb) concentrations of 0.5–1.0, 2.0–6.0 and 7.0–13.0 g/L, respectively; and three groups with mild, moderate and high lipemia were established according to triglyceride concentrations of ∼6.0, ∼12.0, and ∼18.0 mmol/L, respectively. Four TEG parameters, reaction time (R), coagulation time (K), angle (α), and maximum amplitude (MA), were measured alongside conventional plasma tests including prothrombin time (PT), activated partial thromboplastin time (APTT) and fibrinogen (FIB) by mechanical method, and platelet count by optical method. Results showed that the median R and MA values at moderate and severe hemolysis and K at severe hemolysis exceeded respective reference intervals, and were considered unacceptable. Median values of TEG parameters in lipemic samples were all within reference intervals. Bias values of conventional plasma tests PT, APTT and FIB in hemolyzed or lipemic samples were all lower than the Clinical Laboratory Improvement Amendments (CLIA) allowable limits. Bias values of platelet count at moderate to severe hemolysis and lipemia exceeded the CLIA allowable limits. In conclusion, the detection of TEG was in general more affected by mechanical hemolysis than plasma coagulation tests. Pre-analytical variables should be taken into account when unexpected TEG results are obtained.

Dynamic response analysis under atmospheric disturbances for helicopters based on elastic blades

A flight dynamics model based on elastic blades for helicopters is developed. Modal shape analysis is used to describe the rotating elastic blades for the purpose of reducing the elastic degrees of freedom for blades. The analytical result is employed to predict the rotor forces and moments. The equilibrium equation of the flight dynamics model is then constructed for the elastic motion for blades and the rigid motion for other parts. The nonlinear equation is further simplified, and the gradient descent algorithm is adopted to implement the trim simulation. The trim analysis shows that the effect of blade elasticity on the accuracy of rotor forces and moments is apparent at high speed, and the proposed method presents good accuracy for trim performance. The time-domain response is realized by a combination of the Newmark method and the adaptive Runge-Kutta method. The helicopter control responses of collective pitch show that the response accuracy of the model at a yaw-and-pitch attitude is improved. Finally, the influence of blade elasticity on the helicopter dynamic response in low-altitude wind shear is investigated. An increase in blade elasticity reduces the oscillation amplitude of the yaw angle and the vertical speed by more than 70%. Compared with a rigid blade, an elastic blade reduces the vibration frequency of the angular velocity and results in a fast return of the helicopter to its stable flight.

Direct Stator Flux Vector Control Strategy for IPMSM using a Full-order State Observer

A direct stator flux vector control scheme in discrete-time domain is proposed in this paper for the interior permanent magnet synchronous motor (IPMSM) drive to remove the proportional-integral (PI) controller from the direct torque control (DTC) scheme applied to IPMSM and to obtain faster dynamic response and lower torque ripple output. The output of speed outer loop is used as the desired torque angle instead of the desired torque in the proposed scheme. The desired stator flux vector in dq coordinate is calculated with a given amplitude. The state-space equations in discrete-time for IPMSM are established, the actual stator flux vector is estimated in deadbeat manner by a full-order state observer, and then the closed-loop control is achieved by the pole placement. The stator flux error vector is utilized to calculate the reference stator voltage vector. Extracting the angle position and amplitude from the estimated stator flux vector and estimating the output torque are eliminated for the direct feedback control of the stator flux vector. The proposed scheme is comparatively investigated with a PI-SVM DTC scheme by experiment results. Experimental results show the feasibility and advantages of the proposed control scheme.

Spatial Kinetics Model of Supercavitating Vehicles Reflecting Conic‐Like Oscillation

A spatial kinetics model for supercavitating vehicles including the coupled motion of pitch, yaw, and rolling was presented. Mathematical simulations were performed to investigate dynamic performance of supercavitating vehicles. An intrinsic conic‐like oscillation in the motion of supercavitating vehicles was discovered. A lakebed experiment was carried out to validate the oscillation. Good agreement is achieved between simulation and experiment in terms of the amplitude and frequency of attitude angles. The steady phase difference between the motions in different planes is also accurately captured which is about π/2. The conic‐like oscillation is attributed to the occurrence of the tail‐slap motion in the vertical and horizontal planes and the steady phase difference.

Impact of Spasticity on Balance Control during Quiet Standing in Persons after Stroke.

Background Balance impairments, falls, and spasticity are common after stroke, but the effect of spasticity on balance control after stroke is not well understood. Methods In this cross-sectional study, twenty-seven participants with stroke were divided into two groups, based on ankle plantar flexor spasticity level. Fifteen individuals with high spasticity (Modified Ashworth Scale (MAS) score of ≥2) and 12 individuals with low spasticity (MAS score <2) completed quiet standing trials with eyes open and closed conditions. Balance control measures included centre of pressure (COP) root mean square (RMS), COP velocity, and COP mean power frequency (MPF) in anterior-posterior and mediolateral (ML) directions. Trunk sway was estimated using a wearable inertial measurement unit to measure trunk angle, trunk velocity, and trunk velocity frequency amplitude in pitch and roll directions. Results The high spasticity group demonstrated greater ML COP velocity, trunk roll velocity, trunk roll velocity frequency amplitude at 3.7 Hz, and trunk roll velocity frequency amplitude at 4.9 Hz, particularly in the eyes closed condition (spasticity by vision interaction). ML COP MPF was greater in the high spasticity group. Conclusion Individuals with high spasticity after stroke demonstrated greater impairment of balance control in the frontal plane, which was exacerbated when vision was removed.

An objective evaluation of healthy human upper extremity motions

This paper presents an investigation of quality evaluation of human upper extremity motions by introducing a new methodology. The VICON motion capturing system was applied to evaluate the kinematics of the upper extremity. The created 3D 5 DOF dynamical model in MATLAB allowed calculating additional movement’s quantitative parameters: the work done and power used during the appropriate motion. Finally, least squares method was applied to define torques by using a 3rd degrees polynomial approximation of mean torque values in the angle domain. The calculated parameters of 23 healthy participants’ motions as well as the investigated method could be used in the future in rehabilitation field to evaluate the quality of upper extremity motion of patients. The Pearson’s correlation coefficient between motion angle and angular velocity amplitudes is 0.49-0.82 and between work done and power of the movement is 0.61-0.99.

Thromboelastographic Characterization of the Activated Clotting System in Children with Sickle Cell Trait or Sickle Cell Disease

Background: Recent epidemiological evidence suggests sickle cell disease (SCD) and sickle cell trait (SCT) are risk factors for venous thromboembolism. The increased in vivo markers of thrombin generation support the notion that such patients are in a chronic hypercoagulable state. In an attempt to better understand the underlying mechanism, global hemostatic assays including thrombin generation assay (TGA) and thromboelastography (TEG) have been utilized by several groups, with inconsistent results either due to small sample size or technical differences. As opposed to the bleeding disorders, the traditional methods of TEG are not sensitive to hypercoagulability. Our group developed modified methods that prolonged the baseline TEG parameters to enhance this sensitivity. These altered TEG profiles were shown to be significantly shortened by increasing concentrations of thrombin in vitro.Objectives: Global hemostatic characterization of children with SCD or SCT by using TGA and modified TEG methods.Materials and methods: In this pilot study, we obtained hemostatic data including complete blood count with differential, reticulocyte count, fibrinogen, D-dimer, thrombin antithrombin complex and prothrombin fragment 1.2 on specimens from subjects with SCD in their usual state of health, subjects with SCT and healthy controls (NC). In addition global hemostatic assays including standard and modified thromboelastography methods as well as thrombin generation assays were performed.Results: Thirty-nine African-American subjects were recruited: 12 NC, 14 SCT and 13 SCD. The median ages for the groups were 12 (Range: 5-39), 19 (Range: 2-40) and 8 (Range: 2-14) years for NC, SCT, and SCD, respectively. Females represented 58% of the NC, 57% of the SCT subjects and 38% of the SCD subjects. In vivo markers of thrombin generation and activation of fibrinolysis including D-dimer and thrombin-antithrombin complexes were higher in SCD subjects as compared to SCT and NC (p=0.001; p=0.05 respectively). Reaction (R) time, and Kinetic (K) time with modified TEG methods was significantly shorter in SCD when compared to SCT and NC (p=0.014, p=0.038) respectively. Angle (alpha) and maximum amplitude (MA) did not show any significant differences between the groups. TGA profiles did not show any difference between the three groups either.Conclusion: The in vivo use of modified thromboelastography methods is able to detect the hypercoagulability known to occur in the sickle cell disease population but a larger sickle cell trait cohort needs to be studied to determine if this group also has hypercoagulability. Importantly, this study, the first to evaluate both TEG and TGA assays in SCD or SCT population demonstrates the importance of using whole blood to differentiate these groups as the TEG assay demonstrated differences the TGA could not detect. As SCD and SCT subjects have a highly complex physiology with not only alterations in almost all the components of the coagulation system, but also variation in the quantity and function of other blood components including white blood cells, platelets and red blood cells, TEG may prove a good tool in measuring a change in the activity of the coagulation system rather than a single baseline measurement. Our results support the need for further studies using thromboelastography in SCD and SCT population in order to better understand and triage this cohort of patients for risks of thrombotic complications. DisclosuresNo relevant conflicts of interest to declare.

Dabigatran Neutralizing Antobody, Idarucizumab, Exhibits Procoagulant and Platelet Activation Responses in Whole Blood. Potential Clinical Implications

Introduction: Idarucizumab is a humanized monoclonal antibody fragment which is capable of neutralizing Dabigatran and is currently clinically available for the control of bleeding associated with Dabigatran. Although this antibody is capable of neutralizing the anticoagulant effects of Dabigatran, its effect on the blood coagulation and platelet activation profile are not completely understood. There is limited data on the effect of Idarucizumab on the blood coagulation and platelet activation profile. The purpose of this study is to determine the effect of this antibody on blood coagulation and platelet activation profile.Materials: Idarucizumab was purchased from Brigham and Women's Hospital (Boston, MA) and was provided as a 50 mg/mL solution. Dabigatran was of synthetic origin and obtained from Sellec Chemical (Houston, TX). Whole blood from healthy volunteers was collected in plastic syringes using a sterile method for the TEG and ACT analysis. Citrated whole blood was used for the preparation of platelet rich plasma which was used in platelet aggregation studies. Such agonists as arachidonic acid, ADP, epinephrine, thrombin, and collagen were used.Methods: The TEG studies were carried on a Haemoscope 500 instrument. Native whole blood was supplemented with Idarucizumab in a concentration range of 0-10 mg/mL. Saline was used as a control. The TEG profile was measured for 15-30 minutes. Such parameters as R time, K time, angle, and max amplitude were recorded. The ACT studies were carried out in celite tubes in a concentration of 0-5 mg/mL. The agonist-induced platelet aggregation profile was studied by pre incubating platelet rich plasma with Idarucizumab at a fixed concentration of 1.0 mg/mL and studying its effect on the aggregation profile of such agonists as arachidonic acid, ADP, epinephrine, thrombin, and collagen. Both the slope and percent aggregation were measured. The effect of Idarucizumab on HIT antibodies mediated platelet aggregation was studied by pre incubating platelets with Idarucizumab and determining its effect on the HIT antibody mediated aggregation of platelets. Pooled plasma from symptomatic HIT patients was pre incubated with Idarucizumab at 1.0 mg/mL followed by the addition of HIT antibody pool in a 1:10 dilution. The aggregation profile was noted for up to an hour.Results: Idarucizumab produced a dose-dependent hypercoagulable effect in the TEG profile of native whole blood resulting in a reduction in R time and max amplitude at 35% and 45% respectively. At high concentrations, Idarucizumab produced a marked effect on the clot retraction. In the ACT studies, Idarucizumab produced a mild shortening of the ACT at a 5 mg/mL at 6%. Idarucizumab produced variable augmentation of different agonists mediated platelet aggregation. In the HIT mediated aggregation studies, Idarucizumab produced a strong augmentation of HIT antibody mediated platelet aggregation. At 1.0 ug/mL, Idarucizumab produced almost a 20% increase in platelet aggregation.Conclusions: These studies indicate that Idarucizumab produces mild procoagulant effects on whole blood coagulation process as studied by TEG and ACT. This agent also produces the augmentation of the platelet aggregation profile by various agonists including Anti-heparin platelet factor IV antibodies. These procoagulant effects of Idarucizumab may contribute to the potential hypercoagulable/prothrombotic events associated with its use. DisclosuresNo relevant conflicts of interest to declare.

Research on chain-model transition identification of magnetic dipole theory for magneto-rheological fluid

Chain formation model is very useful to characterize the magneto-rheological phenomenon and prepare good magneto-rheological fluids. The single-chain model is common to explain the process of chain formation for ferromagnetic particles under magnetic field. With the increment of magnetic field and ferromagnetic particle content, the chain will transit from the single chain to multi-chains. However, there are few literatures involved in this phenomenon. This study investigates the effect of magnetic field and ferromagnetic particles content on the transition. The static yield stresses at different magnetic fields were measured under quasi-static mode for different magneto-rheological fluid samples. The results show that the transition of chain model can be identified on two parameters including the amplitude of static yield angle, [Formula: see text], and the inclined angles distribution, [Formula: see text]. The single-chain model is only effective under low magnetic field and ferromagnetic particles below content of 30% volume. With the increment of magnetic field and ferromagnetic particles content, the transition from single chain to multiple chains will be observed, which validates that there is a transition from the single chain to multi-chains.