Compressibility Correction Research Articles

Selection Effect of Liquid Nitrogen Freeze-Thaw Cycles on Full Pore Size Distribution of Different Rank Coals.

In China, the capacity to produce coalbed methane and extract underground gas is restricted by the prevalence of low-permeability coal seams. Liquid nitrogen fracturing is a new low temperature-high-pressure anhydrous fracturing technology that uses low temperature and high frost heave forces to increase coal permeability. To better understand the liquid nitrogen fracturing effect on coal, we conduct the liquid nitrogen freeze-thaw cycle (LNCFT) experiments on different rank coals from Qinghai, Shanxi, and Shaanxi provinces. We combined the low-pressure nitrogen and carbon dioxide adsorption experiment with the non-local density functional theory model and mercury injection porosimetry with compressibility corrections to examine the full pore size distributions of untreated and water-saturated samples before and after LNCFT. The results found that LNCFT can effectively increase the pore volume (PV) and specific surface area of the water-saturated coal sample. Compared with the raw coal, the increased ratio of the full pore size PV is 70.41-100.17%. However, the scale-selective transformation effect on pores during liquid nitrogen fracturing is noticeable. Under the same conditions, LNCFT can significantly increase the pore volume of micropores (>2 nm) and macropores (>50 nm), and the increase ratios are 24.40-44.16 and 103.55-327.93%, respectively. The PV of mesopores (2-50 nm) shows a slightly increasing trend with the increase in metamorphic degree, and the increase ratio is between 8.7 and 56%. Comparing the full pore size distribution curves before and after LNCFT, it is found that the alteration of high-volatile bituminous coal (BLT coal) and anthracite (SH coal) has more significance in the range of less than 2 and 50-20,000 nm, while middle-volatile bituminous coal (YJL coal) varies between 50 and 2000 nm. Meanwhile, the ratio of micropore and mesopore PV to the total decreased gradually before and after LNCFT, while the proportion of macropores increased, indicating that small-scale pores would intersect and connect to form larger-scale pores during the fracturing. The combined effects of temperature gradient, water-ice phase transition, and heat transmission rate are the key factors that determine the impact of LNCFT on pore size distribution. Our results provide new information for enhancing the permeability of low-permeability coal seams of different ranks.

Compressibility corrections to extend a smooth local correlation-based transition model to transonic flows

AbstractThis paper presents progress towards a transition modelling capability for use in the numerical solution of the Reynolds-averaged Navier-Stokes equations that provides accurate predictions for transonic flows and is thus suitable for use in the design of wings for aircraft flying at transonic speeds. To this end, compressibility corrections are developed and investigated to extend commonly used empirical correlations to transonic flight conditions while retaining their accuracy at low speeds. A compressibility correction for Tollmien-Schlichting instabilities is developed and applied to a smooth local correlation-based transition model and a stationary crossflow instability compressibility correction is included by adding a new crossflow source term function. Two- and three-dimensional transonic transition test cases demonstrate that the Tollmien-Schlichting compressibility correction produces substantially improved agreement with the experimental transition locations, particularly for higher Reynolds number applications where the effects of flow compressibility are expected to be more significant, such as the NASA CRM-NLF wing-body configuration, while the crossflow compressibility correction prevents an inaccurate, upstream transition front. The compressibility corrections and modifications do not significantly affect the numerical behaviour of the model, which provides an efficient alternative to non-local and higher-fidelity approaches, and can be applied to other transport-equation-based transition models with low-speed empirical correlations without affecting their predictive capability in the incompressible regime.

Highly reliable and efficient encoding systems for hexadecimal polypeptide-based data storage.

Polypeptides consisting of amino acid (AA) sequences are suitable for high-density information storage. However, the lack of suitable encoding systems, which accommodate the characteristics of polypeptide synthesis, storage and sequencing, impedes the application of polypeptides for large-scale digital data storage. To address this, two reliable and highly efficient encoding systems, i.e. RaptorQ-Arithmetic-Base64-Shuffle-RS (RABSR) and RaptorQ-Arithmetic-Huffman-Rotary-Shuffle-RS (RAHRSR) systems, are developed for polypeptide data storage. The two encoding systems realized the advantages of compressing data, correcting errors of AA chain loss, correcting errors within AA chains, eliminating homopolymers, and pseudo-randomized encrypting. The coding efficiency without arithmetic compression and error correction of audios, pictures and texts by the RABSR system was 3.20, 3.12 and 3.53 Bits/AA, respectively. While that using the RAHRSR system reached 4.89, 4.80 and 6.84 Bits/AA, respectively. When implemented with redundancy for error correction and arithmetic compression to reduce redundancy, the coding efficiency of audios, pictures and texts by the RABSR system was 4.43, 4.36 and 5.22 Bits/AA, respectively. This efficiency further increased to 7.24, 7.11 and 9.82 Bits/AA by the RAHRSR system, respectively. Therefore, the developed hexadecimal polypeptide-based systems may provide a new scenario for highly reliable and highly efficient data storage.

Photonic unsupervised learning variational autoencoder for high-throughput and low-latency image transmission.

Following the explosive growth of global data, there is an ever-increasing demand for high-throughput processing in image transmission systems. However, existing methods mainly rely on electronic circuits, which severely limits the transmission throughput. Here, we propose an end-to-end all-optical variational autoencoder, named photonic encoder-decoder (PED), which maps the physical system of image transmission into an optical generative neural network. By modeling the transmission noises as the variation in optical latent space, the PED establishes a large-scale high-throughput unsupervised optical computing framework that integrates main computations in image transmission, including compression, encryption, and error correction to the optical domain. It reduces the system latency of computation by more than four orders of magnitude compared with the state-of-the-art devices and transmission error ratio by 57% than on-off keying. Our work points to the direction for a wide range of artificial intelligence-based physical system designs and next-generation communications.

Weak Signal Processing Method for Moving Target of GNSS-S Radar Based on Amplitude and Phase Self-Correction

Navigation satellite signals have the advantages of all-day, all-weather, and global coverage, and the use of navigation signals for the detection of moving targets has significant application prospects. However, the GNSS signal is very weak, and the signal power is greatly attenuated after being scattered by the target. In order to detect the echo signal, a long integration time is required. However, the movement of the target will cause the echo signal to produce unpredictable range migration and a Doppler frequency shift, which will weaken the cumulative effect of long-term integration. This paper proposes a weak signal processing method with amplitude and phase self-correction for moving target detection in the GNSS-S radar. First, the phase consistency of the echoes of a single GNSS satellite is realized by the block expansion compression and phase differential correction method to improve the coherent accumulation gain; then, multi-star joint accumulation is carried out after the signal amplitudes of multiple satellites are corrected by the improved keystone method, so as to obtain a stable echo signal track. This method can effectively improve the integral gain of the scattering signal of the moving target and realize target detection. The simulation results and field tests show that this method can effectively improve the SNR of the GNSS-S signal and can realize the detection of small moving targets such as cars with GNSS-S radar.

Finite-wing-analogy formula for compressibility correction to pressure coefficient of an underwater vehicle model at low Mach number

Wind tunnels are usually used to investigate the flows and forces associated with underwater vehicles when free-surface effects can be ignored. However, because of the large differences between air and water in density and viscosity, the freestream Mach number in a wind tunnel is much higher than that in a water tunnel or towing tank at the same Reynolds number. Therefore, compressibility correction is required for accurate measurement compatibility between wind tunnels and water tunnels or towing tanks. In the study reported here, the flows and forces associated with an underwater vehicle model at different Mach numbers were investigated by solving the Navier–Stokes equations for compressible flow numerically as virtual-wind tunnel experiments. The freestream Mach number Ma varies from 0.004 to 0.5. The distribution of the pressure coefficient on the hull and the effects of Ma on the peaks of the pressure coefficient are discussed in detail. The performances of the Prandtl–Glauert rule, the Karman–Tsien rule, and the Laitone rule for compressibility correction to the pressure coefficient of underwater vehicles are assessed. Defining the average correction factor with larger values for better correction effect, the values for these three compressibility correction formulas are 0.51, 0.38, and 0.23, respectively. A finite-wing-analogy formula to improve the compressibility correction to the pressure coefficient at low Ma is proposed. Inspired by the finite-wing correction to the lift slope of airfoils, the proposed formula offers good convergence of the pressure coefficient and highly accurate compressibility correction with an average correction factor of 0.84.

A compressible turbulence model for the dissipation rate

In this work, the ability of a Reynolds stress model to compute turbulent homogeneous shear flow with significant compressibility effects is discussed. Several studies of compressible turbulent flows carried out in the past years have shown that the pressure strain correlation is mainly responsible for the strong changes in the magnitude of the Reynolds stress anisotropies. Two recent compressible models of this term are considered in conjunction with the standard model of the dissipation rate of the turbulent kinetic energy to predict compressible homogeneous flow highly sheared are tested. It is found that deficiencies appear in the calculations even if the pressure strain model is improved by compressibility corrections. Consistent with earlier studies, this deficiency is attributed to the use of the incompressible model for turbulent dissipation. However, a compressibility correction of this equation model uncovers the main focus of the present study. This correction makes the standard coefficients of this equation depend on the turbulent gradient Mach and Mach numbers. The proposed model is tested for low and strong compressibility cases from the DNS results of Sarkar. A comparison of the proposed model predictions with the DNS results shows good qualitative agreement. Therefore, compressibility correction for the incompressible model of the turbulent dissipation rate is found to be an important issue for the compressible homogeneous turbulent shear flow.

An Investigation of Scale-Resolving Turbulence Models for Supersonic Retropropulsion Flows

Characterization of unsteady loads is critical for the development of control systems for next-generation air vehicles. Both Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) methods are prohibitively expensive, and existing Reynolds-Averaged Navier-Stokes (RANS) approaches have been shown to be inadequate in predicting both mean and unsteady loads. In recent years, scale-resolving methods, such as Partially Averaged Navier-Stokes (PANS) and Detached Eddy Simulation (DES), have been gaining acceptance and filling the gap between RANS and LES. In this study, we focus on a new variant of the PANS method, namely blended PANS or BPANS, which was shown to perform well in the incompressible regime for both wall-bounded and free shear flows. In this paper, we extend BPANS to compressible supersonic flows by adding a compressibility correction, leading to a new model called BPANS CC. The new model is tested using a well-known supersonic mixing layer case, and the results show good agreement with experimental data. The model is then used on a complex supersonic retropropulsion case and the results are in good agreement with experimental data.

An all-speed formulation using a modified γ-model for the prediction of boundary layer transition and heat transfer

• Effect of Mach number and temperature is added in the modified γ -model to find the transition onset for all speed flows. • Algebraic correlation is derived for the scaling constant of F onset1 based on the Mach number and temperature ratio. • Compressibility correction is added to the R e θ c correlation. • Effect of inlet viscosity ratio on transition and an existing correlation for it is identified to use with modified γ -model . Menter’s one-equation transition model, known to predict all types of boundary layer transition in low-speed flows, does not include the effect of Mach number and temperature, predominant at high speeds. This work uses an algebraic correlation based on a self-similar solution of compressible boundary layer equations to predict the transition onset location at all speed regimes ranging from incompressible to hypersonic speeds at different temperature ratios. Since Menter’s model is highly susceptible to inflow conditions (viscosity ratio and turbulence intensity), the modified model uses correlations related to the experimental conditions for inlet turbulence quantities. A two-dimensional in-house solver based on the finite volume method is developed for this study and validated with standard test cases (flat plate, ramp) in different speed regimes for the turbulence model and a low-speed test case for Menter’s transition model. Transition location is predicted from the heat transfer rate for high-speed flows and skin friction co-efficient for low-speed flows. Numerical results obtained from Menter’s and modified model for various test cases are compared against the experimental and DNS data. Computational results show that modified γ -model could predict the transition onset location more accurately than Menter’s model in all speed regimes.

Management of bronchomalacia in infants post-cardiac surgery using synchronized nasal DuoPAP: A novel technology.

Tracheo-bronchomalacia (TBM) is the weakness in the structural integrity of the cartilaginous ring and arch. It may occur in isolation with prematurity or secondarily in association with various congenital anomalies. Bronchomalacia is more commonly associated with congenital heart diseases. The conventional treatment options include positive pressure ventilation with or without tracheostomy, surgical correction of external compression and airway stenting. To use "synchronized" nasal Dual positive airway pressure (DuoPAP), a non-invasive mode of ventilation as an alternative treatment option for bronchomalacia to avoid complications associated with conventional treatment modalities. Prospective observational study conducted in Army Hospital Research and Referral from Jul 2019 to Dec 2020. We diagnosed seven cases of TBM post-cardiac surgery at our institute, incidence of 4.2%. Four infants were diagnosed with left sided bronchomalacia, 2 were diagnosed with right sided bronchomalacia and one with tracheomalacia. Those infants were managed by "synchronized" nasal DuoPAP, a first in ventilation technology by Fabian Therapy Evolution ventilator (Acutronic, Switzerland). All seven infants showed significant improvement with synchronized nasal DuoPAP both clinically as well as radiologically. None of the infant required tracheostomy and discharged to home successfully. The synchronized nasal DuoPAP is a low cost and effective treatment option for infants with TBM. It could be attributed to synchronization of the breaths leading to better tolerance and compliance in paediatric age group.

When the center cannot hold in conventional orthopedic and trauma treatments, things will not fall apart with linear rail system: A hospital based retrospective study

Background: Distraction osteogenesis is a method of producing unlimited quantities of living bone directly from a special osteotomy (cortico to my). Advances in methods of external fixation have made limb lengthening a feasible option achieved by distraction osteogenesis. Complex trauma cases such as failure of fractures to unite after several attempts, significant soft tissue infection, significant bone loss ab initio, the presence of significant soft tissue loss, or chronic osteomyelitis that may warrant significant bone resection are a nightmare to the surgeon the patient and the patients relations as well. The linear rail system and the Ilizarov device oppose other methods of bone gap management permits the realization of compression, distraction, bone-lengthening, and deformity correction, as such improving the quality of life of the patients, good fracture union with insignificant complications.Methods: A hospital based retrospective study conducted at The Potters Specialist Hospital Jos between January 2018 and December 2020. Patients were recruited following a perusal of the operation register. A proforma was filled which included the patient’s demographics, clinical characteristics. Clinical outcomes during the treatment such union at fracture site, length gained and complications during treatment were included in the proforma. Patient’s quality of life after the treatment was also assessed. Data was analyzed using SPSS version 23.Results: Thirty-six patients were enrolled into the study. Patients mean age was 39.36±10.64. Age group 31-40 accounted for 47.2% of those recruited. Males were 83.3% and complications of fracture management were noticed to account for 22 (61.1%) of the indications for surgery. Those who had two surgeries done during treatment were 27.8% with interval corticotomy counting as a separate surgery. Limb lengthening was done in 52.8% of the patients and the leg was found to be operated limb 75% of cases. Though 72.6% did not develop any problems, among those with problems, pin tract infection was noticed in 13.9%. Similarly, 88.9% had no complications but amongst complications noted limb length discrepancy in 5.6%. All of them had their fractures united and limb lengths equalized to an acceptable level. Regarding quality of life most patients (44.4%) rated it as good and the other 22.2% very good and when asked about the satisfaction their current health 50% said they were satisfied and another 19.4% were very satisfied.There was significant association noticed between quality of life and indications for surgery, between complication and aim of surgery and noticed between complication and length gained.Conclusion: The use of the linear rail system in the treatment of complex major limb fractures yielded satisfactory results with improved quality of life and less problems and complications.

Treatment of In-Stent Restenosis Using a Dedicated Super High-Pressure Balloon

BackgroundTreatment of in-stent restenosis (ISR) is challenging and treatment failure rate remains high. Correction of stent under-expansion and neointimal compression using the twin-layer OPN™ highly non-compliant balloon (NCB) at high pressure (>30 atm) may lead to increased luminal gain and thus better clinical outcomes. We evaluated periprocedural safety and clinical long-term outcomes after ISR treatment using the OPN™ NCB in a real-world population. MethodsFrom an ongoing registry, consecutive ISR patients treated with the OPN™ NCB at a tertiary cardiology center in Switzerland were analyzed. We evaluated procedural efficacy, periprocedural complications, target lesion/vessel failure (TLF/TVF), and major adverse cardiovascular events (MACE). ResultsTotally, 208 ISR lesions were treated in 188 patients (mean age 68 ± 13 years, 78 % males). Most lesions were moderately to heavily calcified (89 %), the majority (70.2 %) had complex lesion characteristics (AHA Type B2/C lesions) and 50.5 % were non-focal ISR lesions. After ISR treatment using high pressure pre- and post-dilatation (mean pressure 33 ± 6 atm) with the OPN™ NCB device, the rate of major complications was low (0.96 % coronary perforation, 4 % major dissections, 1.9 % no-reflow and 0.5 % acute vessel closure). At 1-year follow-up, MACE occurred in 19.7 %; 15.4 % patients had TVF; MI and stent thrombosis was found in 5.9 % and 2.1 % of all patients, respectively; and 5 patients died. ConclusionsFor ISR treatment, using the super non-compliant OPN™ balloon at very high pressures is safe. Moreover, its use might lead to a low rate of TLF/TVF during long-term follow-up, but this requires further evaluation in dedicated comparative trials.

A secure gray-scale image watermarking technique in fractional DCT domain using zig-zag scrambling

Security of watermark is a huge concern when dealing with imperceptible watermarking for copyright protection and owner identification. A novel watermarking technique that is intrinsically secure against unauthorized extraction of watermark and robust against a variety of attacks has been proposed in this paper. Semi-blind in nature, the technique employs fractional discrete cosine transform (FDCT) and zig-zag scrambling to add a layer of security while embedding watermark bits in the cover image. Transformation through multiple fractional value pairs yields robust results against attacks for every cover image. A pair out of these is chosen while embedding the watermark. The same pair is needed at the time of extraction of original watermark from a signed image. This pair of unique values adds a layer of security in the proposed technique. After dividing the cover image into sub-blocks that are non-overlapping, fuzzy entropy is used to make the selection of appropriate sub-blocks in which watermark bits are to be embedded. These blocks are first mapped in a zig-zag fashion and then, after selection of half sub-blocks, FDCT is applied on each of them. FDCT coefficients serve as training data for Kernel extreme learning machine (KELM). Used as a non-linear regression model, KELM predicts the value of a particular coefficient with the help of neighboring transform domain coefficients. Multiple scaling factors are used to control the extent to which the watermark bit modifies the predicted coefficient. Strength of these scaling factors is determined and controlled with the help of standard deviation of every selected sub-block. The technique shows perfect extraction of watermarks (Normalized correlation=1.0, Bit error ratio=0.0) against attacks like median filtering (3 × 3), Gaussian filtering, Weiner filtering, JPEG compression (Quality factor 40) and gamma correction. Even for other attacks, the extracted watermarks are not too bad in quality that they are beyond recognition.

An improved 2.75D method relating pressure distributions of 2D airfoils and 3D wings

Since the 2.75D method takes both wing sweep and taper into consideration, it can build a transformation relation for pressure distributions between a 2D airfoil and a 3D wing under the assumption of conical flow. However, it is observed that the classical 2.75D method proposed by Lock has insufficient transformation accuracy in subsonic flow regions on transonic and subsonic wings. This article proposes an improved 2.75D method to address this problem. For subsonic flow region(s), a method based on Kaman-Tsien compressibility correction is proposed; for supersonic flow region(s), the original method of enforcing an equal normal Mach number between an airfoil and the corresponding wing section is used. Lock's and the improved methods are demonstrated by test cases of transonic and subsonic wings. Results show the transformation accuracy of pressure distributions between 2D airfoils and 3D wings is dramatically improved using the proposed method. The application of these methods to the pressure distribution design for a tapered swept wing section is also demonstrated. The design optimization using the improved 2.75D method leads to a design result being more approximate to a 3D tapered swept wing with a computation effort similar to a 2D airfoil design.

Compressibility Correction to Models for Hypersonic Turbulent Boundary Layers

A compressibility correction for models is proposed, and it explicitly takes the effects of high Mach numbers and wall-cooling into account. The correction is validated by a recent set of direct numerical simulation databases with and without pressure gradient. The proposed compressibility correction is based on the correspondence between eddy viscosity in compressible and incompressible turbulence, which shows that the standard models estimate incorrect values of eddy viscosity in the near-wall region of a hypersonic turbulent boundary layer with a cold wall. For a range of Mach numbers between 2.5 and 14, and wall-to-recovery temperature ratios between 0.18 and 1, the correction collapses the eddy viscosity profiles on the incompressible data and predicts significantly improved velocity, temperature, skin friction, and wall heat transfer coefficient profiles. The present approach is independent of the eddy viscosity definition and Reynolds stress model, and it can be implemented easily in any model by modifying the closure coefficients of the production and destruction in the equation. Furthermore, the formulation is completely local and is disabled as the effects of compressibility disappear.

Hypersonic Turbulent Flow Reynolds-Averaged Navier–Stokes Simulations with Roughness and Blowing Effects

Thermal protection systems experience severe thermal load during atmospheric reentry of hypersonic vehicles. Inherent to the ablation process, roughness and blowing effects may appear, affecting the performance of the heat shield. The modeling and the simulation of these effects in the hypersonic regime are challenging and rarely compared to experimental data. In this paper, Reynolds-averaged Navier–Stokes simulations of hypersonic turbulent boundary layers with roughness and blowing wall conditions are performed on Holden’s experimental configurations (“Studies of Surface Roughness and Blowing Effects on Hypersonic Turbulent Boundary Layers over Slender Cones,” 27th Aerospace Sciences Meeting, AIAA Paper 1989-0458, 1989). Using the shear stress transport model. Four experimental configurations, characterized by different levels of turbulence compressibility, are considered. A detailed discussion is proposed about the behavior of equivalent sand grain corrections and blowing corrections in combination with turbulence compressibility corrections. The predictions of skin-friction coefficients and Stanton numbers are in good agreement with Holden’s experimental data. These results show that the combination of the Zeman compressibility correction and roughness/blowing wall corrections is promising for the simulation of hypersonic boundary layers over rough walls with blowing.

Coal Mine Personnel Safety Monitoring Technology Based on Uncooled Infrared Focal Plane Technology

In an effort to overcome the difficulty of real-time early warning via traditional infrared imaging technology caused by the complex working environment in coal mines, this paper proposes a mine early warning method based on uncooled infrared focal plane technology. The infrared thermal spectrogram of the detected object was visually displayed in a pseudo-color image with high resolution and high sensitivity, which can realize the real-time detection and early warning of personnel safety in modern mines. The multipoint compression correction algorithm based on human visual characteristics divided the response units of all acquisition units into gray intervals according to a threshold value, then the corresponding parameters were set in different intervals, and finally, each interval was compressed using a two-point correction algorithm. The volume of stored data was the sum of the calibration curve and the data from an encode table corrected by a MATLAB simulation, and the number of CPU cycles was run by a CCS 3.3 clock calculation algorithm. The results showed that when the temperature of the blackbody reached 115 °C, the nonuniformity before correction was 6.32%, and the nonuniformity after the multipoint correction of human eyes was 2.99%, which implied that the algorithm proposed in this paper had good denoising ability. The number of CPU cycles occupied by this algorithm was 18,257,363 cycles/frame with a frequency of 29.97 Hz. The sharpness of the compressed infrared images was obviously improved, and the uniformity was better. The method proposed in this paper can meet the need for modern mine personnel search and rescue, equipment supervision and dangerous area detection and other early warning requirements so as to achieve the goal of developing smart mines and ensuring safety in coal mine production.

Numerical Investigation of a Supersonic Flow in the Near Wake Region of a Cylindrical Afterbody

A computational study of a supersonic flow in the base region and the nearest wake of a cylindrical body moving at a supersonic speed have been carried out. A mathematical model of high-enthalpy flows is presented. In this case, the "prehistory" of the flow was taken into account, i.e., the configuration of the computational domain was as close as possible to the real one. The use of various turbulence models for calculating flow in the base region and the nearest wake was analyzed. The following turbulence models were considered: 1) the Spalart --- Allmaras model; 2) SST model; 3) standard k--ε model; 4) k--ε model with compressibility correction; 5) k--ε RNG (renormalized group) model; 6) k--ε Realizable model; 7) standard Reynolds Stress (RS) model; 8) RS BSL (Reynolds stress baseline) model. Based on a comparison of the calculation results with experimental data, it is shown that: 1) when calculating the flow in the base region and in the wake of the vehicle, it is very important to take into account the "prehistory" of the flow, i.e., to calculate the flow around the entire vehicle; 2) the best match was obtained using Reynolds Stress models and the k--ε RNG model

Feeding Difficulties Following Vascular Ring Repair: A Contemporary Narrative Review.

Vascular rings are congenital abnormalities of the aortic arch vascular system that compress the trachea and esophagus. A review of long-term outcomes suggests that chronic feeding difficulties can persist following surgical repair of vascular rings. Previous reports of postoperative vascular ring division outcomes indicate that chronic esophageal symptoms may persist following repair, though most available data focuses on persistent respiratory symptoms. It is therefore the aim of this article to summarize and organize recent evidence reporting the frequency, presentation, and management of feeding difficulties following vascular ring repair in pediatric patients. Pathophysiologic mechanisms for postoperative esophageal symptoms may include residual compression from an unresected diverticulum of Kommerell or delayed repair leading to chronic esophageal dysmotility despite correction of esophageal compression. Guidance on the management of feeding difficulties following vascular ring repair is limited. The authors describe success in one case with nasogastric tube feeding and interdisciplinary evaluation. Consensus regarding the management of feeding difficulty following vascular ring repair is needed.

발사체 기저 유동 해석을 위한 2-방정식 난류 모델의 압축성 보정

Explicit compressibility correction methods have been applied to two-equation RANS turbulence models for analyzing the base flow and the entire flow field of a projectile. First, supersonic base flow at a specific Mach number has been analyzed to compare performances of the various compressibility corrections. Base flows at various Mach numbers and Reynolds numbers with Ristorcelli’s compressibility correction applied to κ-ω SST model have been computed, and compared with the experimental results. Lastly, transonic flow analyses of a secant-ogive-cylinder projectile have been performed with Ristorcelli’s compressibility correction. It is found that Ristorcelli’s compressibility correction gives considerable improvement in predicting the base pressure and drag at various flow conditions.