Effect of attack angle on the electromagnetic wave transmission characteristics in the hypersonic plasma sheath of a re-entry vehicle

The attack angle may greatly affect the hypersonic plasma sheaths around the re-entry vehicle,thereby affecting the transmission characteristics of electromagnetic(EM)waves in the sheaths.In this paper,we propose an integrated three-dimensional(3D)model with various attack angles and realistic flying conditions of radio attenuation measurement C-II(RAM C-II)re-entry tasks for analyzing the effect of the attack angle on the transmission characteristics of EM waves in the sheaths.It is shown that the electron density and collision frequency of the sheath on the windward side can be increased by an order of magnitude with the increase of the attack angle.Meanwhile,the thickness of the sheath on the leeward side is increased where the electron density and collision frequency are reduced.The EM waves are mainly reflected on the windward plasma sheath due to the cutoff effect,and the radio-frequency(RF)blackout is mitigated if the antenna is positioned on the leeward side.Thus,by planning the trajectory properly and installing the antenna accordingly during the re-entry,it is possible to provide an approach for mitigation of the RF blackout problem to an extent.

A Flexible-Segment-Model-Based Dynamics Calculation Method for Free Hanging Marine Risers in Re-Entry

In re-entry, the drilling riser hanging to the holding vessel takes on a free hanging state, waiting to be moved from the initial random position to the wellhead. For the re-entry, dynamics calculation is often done to predict the riser motion or evaluate the structural safety. A dynamics calculation method based on Flexible Segment Model （FSM） is proposed for free hanging marine risers. In FSM, a riser is discretized into a series of flexible segments. For each flexible segment, its deflection feature and external forces are analyzed independently. For the whole riser, the nonlinear governing equations are listed according to the moment equilibrium at nodes. For the solution of the nonlinear equations, a linearization iteration scheme is provided in the paper. Owing to its flexibility, each segment can match a long part of the riser body, which enables that good results can be obtained even with a small number of segments. Moreover, the linearization iteration scheme can avoid widely used Newton-Rapson iteration scheme in which the calculation stability is influenced by the initial points. The FSM-based dynamics calculation is timesaving and stable, so suitable for the shape prediction or real-time control of free hanging marine risers.

Vasoactive-Ventilation-Renal Score Predicts Cardiac Care Unit Length of Stay in Patients Undergoing Re-Entry Sternotomy: A Derivation Study

Background: The vasoactive-ventilation-renal (VVR) score includes pulmonary and renal dysfunctions not previously addressed by the vasoactive inotrope score (VIS) and may be a better predictor of cardiac care unit (CCU) length of stay (LOS) in patients undergoing re-entry sternotomy (defined as no earlier than 30 days after previous sternotomy) for congenital heart disease (CHD). Methods: Patients undergoing re-entry sternotomy for CHD from August 1, 2009 to June 30, 2016 were studied retrospectively. A total of 96 patients undergoing 133 re-entry procedures were identified. VVR scores were calculated on CCU admission post-procedure (at 0 hour), 24-hour, and 48-hour after admission to the CCU. The response variable was CCU LOS.? Recursive partition analysis identified variables predicting LOS. Results: 133 re-entry sternotomies in 96 patients made up the samples of the database;11 samples were removed due to incomplete data or placement on ECMO. Of the initial 25 features, 5 were removed for near zero variance and 3 categorical features were removed for non-information. Covariance analysis did not demonstrate any significant correlation amongst the remaining features. Initial recursive tree regression using ANOVA, cross validation and conditional predictive p-value (cp) = 0.01 produced 3 trees. The tree with lowest cross validation error was selected. The resulting 2 split trees with ventilator days less than 20 days and VVR score at 48 hours greater than 23 identified three CCU LOS groups with mean CCU LOS of 77.6, 55.1, and 9.5 days. Conclusions: Recursive partition analysis identified ventilator days greater than 20 days and the sub-population VVR at 48 hours as predictive of CCU LOS in patients undergoing re-entry sternotomy for CHD.

Re-Entry of Space Objects from Low Eccentricity Orbits

This paper deals with the re-entry predictions of the space objects from the low eccentric orbit. Any re-entering object re-enters the Earth’s atmosphere with a high orbital velocity. Due to the aerodynamic heating the object tends to break into multiple fragments which later pose a great risk hazard to the population. Here a satellite is considered as the space object for which the re-entry prediction is made. This prediction is made with a package where the trajectory path, the time of re-entry and the survival rate of the fragments is done. The prediction is done using DRAMA 2.0—ESA’s Debris Risk Assessment and Mitigation Analysis Tool suite, MATLAB and Numerical Prediction of Orbital Events software. The predicted re-entry time of OSIRIS 3U was found to be on 7th March 2019, 7:25 (UTC), whereas the actual re-entry time was on 7th March 2019, 7:03 (UTC). The trajectory path found was 51.5699 deg. (Lat), −86.5738 deg. (Long.) with an altitude of 168.643 km. But the actual trajectory was 51.76 deg. (Lat), −89.01deg. (Long.) with an altitude of 143.5 km.

Re-entry rocket basic flow characteristics and thermal environment of different retro-propulsion modes

During the supersonic re-entry of multi-nozzle heavy rockets into the atmosphere,the basic flow state becomes increasingly complex due to the coupling effect between the retropropulsion plumes and the freestream.A numerical method using the hybrid Reynolds-Averaged Navier-Stokes and Large Eddy Simulation(RES)method and discrete coordinate method is developed to accurately estimate the thermal environment.In addition,finite rate chemical kinetics is used to calculate the afterburning reactions.The numerical results agree well with wind tunnel data,which confirms the validity and accuracy of the numerical method.Computations are conducted for the heavy carrier rocket re-entry from 53.1 km to 39.5 km altitude with 180°angle of attack by using three different Supersonic Retro-Propulsion(SRP)modes.The numerical results reveal that these three SRP flow fields are all Short Penetration Models(SPM).As the re-entry altitudes decrease,both the plume-plume interaction and the plume-freestream interaction become weaker.The highest temperatures in the plume shear layers of the three SRP modes increase by 8.36%,7.33%and 6.92%respectively after considering afterburning reactions,and all occur at a reentry altitude of 39.5 km.As the rocket re-enters the atmosphere,the maximum heat flux on the rocket base plate of three SRP modes stabilizes at 290,170 and 200 kW/m^(2) respectively,but the maximum heat flux on the side wall increases significantly.When the altitude declines to 39.5 km,the extreme heat flux of the three modes increase by 84.16%,49.45%and 62.97%respectively compared to that at 53.1 km.

Design of longitudinal predictive re-entry guidance law based on variable universe fuzzy-PI composite control

This paper studies the longitudinal predictive re-entry guidance law based on the variable universe fuzzy- PI composite control to overcome the inaccuracy of the reference trajectory re-entry guidance for reentry vehicles. The variable universe fuzzy controller is used to obtain a satisfactory dynamic response when the downrange error is large, and the PI controller is utilized to eliminate the steady state error when the downrange error is small. Simulation results show that the proposed guidance law is very robust to the initial errors and can achieve better accuracy, and is also able to handle the effect of the stochastic errors in re-entry processes.

Aerodynamics of ducted re-entry vehicles

Ballistic parameter plays a major role in determining the re-entry trajectory.Lower ballistic coefficient offers an optimal re-entry,wherein the vehicle decelerates higher up in the atmosphere thereby decreasing the imposed aerothermal loads.The current computational study proposes an add-on,to the existing Orion-based re-entry vehicle:a duct circumventing the capsule from the shoulder to the base,to improve the aerocapture ability of the re-entry vehicle.The design cases are categorised based on a non-dimensional parameter termed the Annular Area Ratio(AAR).Dragand ballistic coefficient of the Ducted Re-entry Vehicles(DRVs)at various Mach numbers are evaluated and compared with those of the baseline model.The results show that the proposed design increases the drag for all the AARs considered in the subsonic regime.In the supersonic regime,ducted models of higher AAR are more promising with the increase in Mach number.DRVs also exhibit lower ballistic coefficients than their baseline counterparts.

Dynamic stability characterization of re-entry modules at hypersonic mach numbers

At the time of re-entry modules entering into the atmosphere from space,a small perturbation introduces dynamic oscillations on the vehicle because of their extreme traveling speed.The dynamic stability characteristics of re-entry modules at hypersonic Mach numbers is of considerable relevance to their initial design.In the present paper,the dynamic stability of blunt cone model about 10◦is examined with wide range of design parameters such as nose bluntness,semi-vertex angle and center of rotation through theoretical and experimental methods.Theoretical approximations are made over a model based on the standard Newtonian theory.Experiments are conducted at 0.25m hypersonic wind tunnel at M=8.3 and the following trends are observed from the experimental analysis.Interestingly,the incremental higher nose bluntness,semi-vertex angle and center of rotation reduce the dynamic stability.At higher hypersonic Mach numbers(M>10),dynamic stability characteristics of the re-entry module are insensitive to the free stream Mach number.However,it is observed that the dynamic stability is increased in proportion to the vibration amplitude at hypersonic speeds.

Treatment of Supraventricular Arrhythmias by Transcatheter Radiofrequency Ablation： The Experience of the Electrophysiology Unit of the University Hospital

TC-RF （transcatheter radiofrequency） ablation has an important role in the treatment ofSVA （supraventricular arrhythmias）. The indication to TC-RF ablation is usually made to improve the patient＇s quality of life through the elimination of the arrhythmic substrate. The objective of this study is to make a brief review of the literature and to report the Electrophysiology Unit experience of the Cardiovascular Department of the University Hospital of Trieste. From the study, it can be found that about one thousand of patients are visited annually in the Cardiovascular Department of the University Hospital of Trieste （1,019 ± 71/year over the past five years）. The acute success rate of atrial fibrillation and flutter ablation procedures was respectively 93.9% and 97.9% with a relapse rate of 30% and 10% at 12 month. Accessory pathways and nodal atrio ventricular re-entry tachycardia ablation procedures had an acute success rate of respectively 91.1% and 96.6% with a relapse rate of 10% at 12 months. The overall complication rate was 5%. Catheter ablation is an effective therapy for SVA treatment. It can often be definitive, and it is generally superior to drug therapy, with a low complication rate. The improvement in patients＇ quality of life is associated with a reduced need for access to health services.

Trajectory shaping guidance law based on virtual angle with terminal constraints

A trajectory shaping guidance law based on virtua angle （TSGLBVA） is proposed for a re-entry vehicle with the constraints of terminal impact angles and their time derivatives. In the view of differential properties of the maneuvering trajectory, a virtual angle and a virtual radius are defined. Also, the shaping trajectory of the vehicle is established by the polynomials of the virtual angle. Then, four optimized parameters are selected according to the theorem of parameters transformation presented in this paper. Finally, a convergent variant of the Nelder-Mead algorithm is adopted to obtain the reference trajectory, and a trajectory feedback tracking guidance law is designed. The simulation results demonstrate that the TSGLBVA ensures the re-entry vehicle to impact a target precisely from a specified direction with smal terminal load factor command, as well as to obtain a maximum or constrained terminal velocity according to various requirements.

Aortic Sinus of Valsalva Aneurysm Isolation by Radiofrequency Ablation in Outflow Tract Ventricular Tachycardia

Idiopathic monomorphic ventricular tachycardia and premature ventricular complexes (PVCs) commonly arise from the right and left ventricular outflow tracts (VOT). Their mechanism is most commonly triggered activity from delayed after-depolarizations and successful ablation is performed at the site of earliest endocardial activation. Re-entrant mechanisms have been rarely described. We report a case of an otherwise healthy patient who ultimately underwent six electro-physiology studies (EPS) and suffered numerous implantable cardiac defibrillator (ICD) discharges prior to the successful radiofrequency ablation (RFA) of two idiopathic VOT tachycardias. During the sixth EPS, a proximal aortogram demonstrated a left aortic sinus of valsalva (LASV) aneurysm. Subsequntly, a novel and successful RFA strategy of aneurysm isolation was undertaken. The presence of multiple clinical or inducible VT morphologies and the characterization of a VT as re-entrant should raise concerns that a complex arrhythmogenic substrate is present and defining the anatomy with angiography or an alternative imaging modality is essential in achieving a successful ablation strategy.

Subintimal recanalization for non-acute occlusion of intracranial vertebral artery in an emergency endovascular procedure:A case report

BACKGROUND Endovascular recanalization of non-acute intracranial artery occlusion is technically difficult,particularly when the microwire enters the subintima.Although the subintimal tracking and re-entry technique has been well established in the endovascular treatment of coronary artery occlusion,there is limited experience with its use in intracranial occlusion due to anatomical variations and a lack of dedicated devices.CASE SUMMARY A 74-year-old man was admitted to the hospital two days after experiencing acute weakness in both lower extremities,poor speech,and dizziness.After admission,imaging revealed acute ischemic stroke and non-acute occlusion of bilateral intracranial vertebral arteries(ICVAs).On the fourth day of admission,the patient's condition deteriorated and an emergency endovascular recanalization of the left ICVA was performed.During this procedure,a microwire was advanced in the subintima of the vessel wall and successfully reentered the distal true lumen.Two stents were implanted in the subintima.The patient's Modified Rankin Scale was 1 at three months postoperatively.CONCLUSION We present a technical case of subintimal recanalization for non-acute ICVA occlusion in an emergency endovascular procedure.However,we emphasize the necessity for caution when applying the subintimal tracking approach in intracranial occlusion due to the significant dangers involved.

Surrogate-assisted differential evolution using manifold learning-based sampling for highdimensional expensive constrained optimization problems

To address the challenges of high-dimensional constrained optimization problems with expensive simulation models,a Surrogate-Assisted Differential Evolution using Manifold Learning-based Sampling(SADE-MLS)is proposed.In SADE-MLS,differential evolution operators are executed to generate numerous high-dimensional candidate points.To alleviate the curse of dimensionality,a Manifold Learning-based Sampling(MLS)mechanism is developed to explore the high-dimensional design space effectively.In MLS,the intrinsic dimensionality of the candidate points is determined by a maximum likelihood estimator.Then,the candidate points are mapped into a low-dimensional space using the dimensionality reduction technique,which can avoid significant information loss during dimensionality reduction.Thus,Kriging surrogates are constructed in the low-dimensional space to predict the responses of the mapped candidate points.The candidate points with high constrained expected improvement values are selected for global exploration.Moreover,the local search process assisted by radial basis function and differential evolution is performed to exploit the design space efficiently.Several numerical benchmarks are tested to compare SADE-MLS with other algorithms.Finally,SADE-MLS is successfully applied to a solid rocket motor multidisciplinary optimization problem and a re-entry vehicle aerodynamic optimization problem,with the total impulse and lift to drag ratio being increased by 32.7%and 35.5%,respec-tively.The optimization results demonstrate the practicality and effectiveness of the proposed method in real engineering practices.

Kinetic comparative study on aerodynamic characteristics of hypersonic reentry vehicle from near-continuous flow to free molecular flow

A scaled model of the X38-like configuration was simulated under hypersonic conditions for the direct simulation Monte Carlo method and the unified gas kinetic scheme.The inflow conditions considered several flow regimes,from the near-continuum through the slip-transitional to the free molecular regime.Flow fields and surface properties were compared in detail between these two methods.Not only the density and temperature contours distribution but also the surface pressure,heat flux,friction distribution,both kinetic methods give fairly consistent results.Aerodynamics of the model were also achieved and compared.The results provided by both methods agreed with each other very well.The effects of the Knudsen number and angle of attack were assessed.It is meaningful to carry out comparative studies and accelerate both methods to further progress.

Intimate partner violence against women. Does violence decrease after the entry of the alleged offender into the criminal justice system?

Intimate partner violence(IPV)is simultaneously assumed as a serious crime and a major public health issue,having recurrences as one of its main characteristics and,consequently,re-entries of some alleged offenders in the criminal justice system(CJS).The main goal of this study is to assess if in cases of female victims of IPV,violence decreases after the first entry of the alleged offender in the CJS.A retrospective study was performed based on the analysis of police reports of alleged cases of IPV during a 4-year period.The final sample(n=1488)was divided into two groups according to the number of entries in the CJS(single or multiple)followed by a comparative approach.Results suggest that violence decreases after the first entry of alleged offenders in the CJS.Re-entries were found in only 15.5%of the cases but they were accountable for 3.3 times more crimes on average.Besides,victims of recidivism presented more injuries and required more medical care.Thus,a small group of alleged offenders seems to be more violent and accountable for most of the IPV crimes registered in the CJS suggesting that regardless of legal sanctions aiming to deter violence,these measures may not be enough for a certain group of offenders.This study sustains the need for a predictive model to quantify the risk of repeated IPV cases within the Portuguese population.