Hole Height Research Articles

Optimal Selection of Active Jet Parameters for a Ducted Tail Wing Aimed at Improving Aerodynamic Performance

The foldable tail of the box-type launch vehicle poses a risk of mechanical jamming during the launch process, which is not conducive to the smooth completion of the flight mission. The integrated nonfolding ducted tail proposed in this article can solve the problem of storing the tail in the launch box. Moreover, traditional mechanical control surfaces have been eliminated, and active jet control has been adopted to control the pitch direction of the flight attitude, which can improve the structural reliability of the tail wing. By studying the effects of parameters such as momentum coefficient, jet hole position, jet hole height, and jet angle on improving the aerodynamic performance of ducted tail wing, relatively good jet parameters are selected. Research has found that compared with jet hole height and jet angle, momentum coefficient and jet hole position are more effective in improving the aerodynamic performance of ducted tail wings. Under a trailing edge jet, a relatively good jet condition occurs when the jet hole height is equal to0.25% of the aerodynamic chord length, and the jet angle is equal to 0°. At this time, with the increase of the jet momentum coefficient, the effect of increasing the lift of the ducted tail wing is the best. Finally, a comparative analysis is conducted on the lift and drag characteristics between the ducted tail wing and traditional tail wing, and it is found that the ducted tail wing can generate lift at a 0° attack angle and will not stall in the high attack angle range of 12°~22°, with broad application prospects.

Vitrectomy combined with inverted internal limiting membrane flap insertion or single-layered flap covering technique for highly myopic macular holes with macular retinoschisis.

To investigate the anatomical and visual outcomes of inverted internal limiting membrane (i-ILM) flap insertion versus single-layered i-ILM flap covering in highly myopic macular holes (HMMHs) associated with macular retinoschisis (MRS). A retrospective study compared 23G vitrectomy with i-ILM flap insertion (30 eyes) or covering (31 eyes) in HMMH patients. Pre- and postoperative optical coherence tomography images and best-corrected visual acuity (BCVA) were evaluated. Macular hole schisis (MHS) was classified into three types based on the extent of outer layer schisis. Regression analysis identified predictors of closure rate and postoperative BCVA. The baseline data of the two groups were matched, including BCVA, axial length, and minimum linear diameter, except for a higher hole height in insertion group (P=0.038). After a mean follow-up of 11.7 months, type I closure rates were 83.3% (25/30) in the insertion group and 90.3% (28/31) in the covering group (P=0.335), respectively. The intact external limiting membrane in the covering group (7/28) was higher compared to the insertion group (1/28) finally (P=0.026). Final BCVA improved significantly in both groups (P<0.001), the BCVA was better in closed HMMHs in the covering group (P=0.011). Multivariate linear regression analysis revealed that preoperative BCVA (β=0.386, P=0.001) and MHS stage (β=0.309, P=0.004) were independent predictive factors for the final BCVA. The single-layered i-ILM flap covering favored foveal structure recovery and provided a better visual prognosis in closed HMMHs compared with insertion. The preoperative BCVA and MHS stage were independent predictors of visual outcomes in patients with HMMHs.

Factors influencing the reliability of measurements in eyes with full-thickness macular holes: are we measuring incorrectly?

PurposeThe calliper function is used for manual measurements of full thickness macular holes (FTMHs). We aimed to investigate whether a reproducible difference could be detected beyond interobserver variability between two...

Numerical Study on the Axial Compression Behavior of Composite Columns with High-Strength Concrete-Filled Steel Tube and Honeycombed Steel Web Subjected to Freeze–Thaw Cycles

To investigate the axial compression behavior of composite columns with high-strength concrete-filled steel tube flanges and honeycombed steel web (STHHC) under load during freeze–thaw cycles, 48 full-scale composite column specimens were designed with different parameters: the restraint effect coefficient (ξ), concrete strength (fcu), number of freeze–thaw cycles (nd), slenderness ratio (λ), space–height ratio (s/hw), and hole–height ratio (d/hw). The finite element models of STHHC composite columns were simulated using ABAQUS finite element software (Version: 2021). The modeling method’s rationality was verified by comparing simulation results with experimental outcomes. Based on the finite element model, a parametric analysis of the composite columns under freeze–thaw cycles was conducted, analyzing their failure modes and load-bearing processes. The results indicate that the bearing capacity of the STHHC increased with increases in ξ and fcu, and decreased with a rise in λ. In contrast, the influence of s/hw and d/hw on the ultimate bearing capacity of the composite columns was relatively minor. An equation for calculating the axial bearing capacity of the STHHC composite columns under freeze–thaw cycles was derived using statistical regression methods and considering the impact of different parameters on the axial compressive performance of the composite columns, laying the foundation for the promotion and application of this type of composite column in practical engineering projects.

The impact of preoperative parameters on postoperative foveal displacement in idiopathic macular hole

This study examined the effect of vitrectomy combined with internal limiting membrane (ILM) peeling on foveal displacement in 42 eyes with idiopathic macular hole (IMH). A retrospective analysis was conducted to measure various macular hole parameters before surgery, including basal diameter, minimum diameter, hole height, and areas affected by traction such as macular hole area (MHA), macular hole cystoid space area (MHCSA), macular hole retinal area (MHRA), and total area (TA). The results showed a postoperative shift of the fovea towards the optic disc in all cases. Notably, the extent of foveal displacement was significantly linked to the preoperative basal diameter (rs = 0.405, P = 0.008) but not to other preoperative parameters or postoperative visual acuity. Furthermore, the study found that the temporal side of the macular hole was more affected by traction than the nasal side preoperatively, leading to greater postoperative displacement (All P < 0.05).

Prediction of foveal microstructure and visual outcomes following surgery for idiopathic macular hole: An assessment using spectral-domain optical coherence tomography.

To evaluate the efficacy of two novel indices, the hole closure index (HCI) and the hole healing index (HHI), in predicting both the anatomic outcome and postoperative visual acuity following surgical intervention for idiopathic macular holes. A total of 38 patients diagnosed with idiopathic macular hole (IMH) were included. All patients underwent standard surgical treatment, including vitrectomy, internal limiting membrane (ILM) peeling, and gas tamponade. Preoperative and postoperative spectral-domain optical coherence tomography (SD-OCT) was utilized to assess the anatomical status of the macular hole (MH). The maximum distance between the tips of the external limiting membrane (ELM) was designated as the hole size (HS). HHI, calculated as the ratio of hole height to HS, and HCI, calculated as the ratio of hole height to the average of minimum diameter and base diameter, were determined. Postoperative reconstruction of ELM and ellipsoid zone (EZ) was evaluated, along with analysis of best-corrected visual acuity (BCVA) on a logarithm of the minimum angle of resolution (logMAR) scale. Regression analysis was performed to evaluate the relationship between anatomical outcomes, postoperative visual acuity, and optical coherence tomography (OCT) parameters. Receiver operating characteristic (ROC) curves were generated for both HHI and HCI. Regression analyses revealed significant correlations between HCI and the restoration of ELM and EZ at 6 months after surgery (P = 0.002 and P = 0.014, respectively). In addition, a significant correlation was found between HHI and postoperative BCVA better than logMAR 0.52 also at 6 months after surgery (P = 0.033). The area under the ROC curve (AUC) for HCI based on ELM and EZ reconstruction was high, with values of 0.942 and 0.842, respectively. AUC for HHI, determined by ROC curve analysis of postoperative BCVA, was 0.704. In conclusion, our findings indicate that HCI may be the most accurate predictor of type 1 closure, while HHI could be considered a potential predictor of postoperative visual acuity.

Numerical investigation on oil leakage and migration from the accidental hole of tank wall in oil terminal of pipeline transportation system

As a crucial component of the oil transportation system, the oil terminal (or oil tank farm) may often pose some serious threats and damage to the ecological environment and production safety for the oil leakage. An effective emergency management strategy is particularly significant, involving the accurate assessment of leakage time, oil migration path, volume distribution, etc. Therefore, the volume of fluid (VOF) and liquid phase leakage model were applied to investigate the migration and distribution characteristic after the accidental hole occurs in the tank wall, and influence factors including height and diameter of the hole were considered in our study. Results show that the lower the leaking hole position is, the faster the horizontal injection rate of the leakage hole, the increase of the accumulation area of the oil on the ground, and the difference in the overall pressure value at the leakage hole is nearly four times. Under different leakage diameters, the oil spill is symmetrical. The larger the leakage diameter, the higher the amount of oil leakage and the initial leakage speed, the maximum speed is 1.5 times the minimum speed, causing harm to safety and environmental pollution. These results can quickly locate the leakage location of the tank and provide valuable references for emergency management of the oil pipeline transportation system.

Shear behavior of web huge rectangular opening RC beams

Abstract Opening in the web of reinforced concrete (RC) beams will destroy the integrity of the beam and weaken the mechanical properties of the RC beam, such as the bearing capacity and stiffness. The three-point loading test and finite element analysis were carried out on 10 RC beams with a huge rectangular opening in the web. The effects of stirrups around the holes on the shear properties of RC opening beams, such as bearing capacity, deformation capacity, and stirrup strain, were studied, and the shear transfer mechanism of RC beams at the openings was explained by using the strut-and-tie model. The finite element test results are consistent with the actual test results, as shown by the results. When the hole width is small, the reinforcement of stirrups at the hole side can significantly improve the shear capacity of the specimen, but it can also cause chord shear failure. When the hole height is small, with the strengthening of the chord stirrup, the ultimate bearing capacity of the specimen increases, but it can still result in hole-side shear failure. The curve of stiffness degradation is approximately logarithmic. Moreover, according to the finite element stress vector diagram, the shear transfer mechanism of the perforated beam based on the strut-and-tie model has been proved.

In-Depth Analysis of Preoperative OCT Markers as Prognostic Factors for Lamellar Macular Holes and Epiretinal Membrane Foveoschisis

To identify preoperative OCT markers that correlate with postoperative visual acuity (VA) changes in eyes with lamellar macular hole (LMH) and epiretinal membrane foveoschisis (ERMF) after pars plana vitrectomy (PPV). Cross-sectional retrospective study. Patients seen at the Wilmer Eye Institute between 2011 and 2021 with an International Classification of Diseases, Ninth Revision, or International Classification of Diseases, 10th Revision, code for "macular hole" that underwent PPV, and demonstrated all OCT criteria present for either LMH or ERMF based on the Hubschman etal (2020) classification. OCT markers including hole dimensions, retinal layer continuity, and ellipsoid zone (EZ) convexity and pixelated intensity were quantified. Visual acuity immediately before PPV and at the last follow-up date available were both recorded. Preoperative OCT variables that are correlated with postoperative changes in VA. Forty-two eyes from 42 patients with LMH (n= 11) and ERMF (n= 31) that underwent PPV were identified. Visual acuity in the ERMF cohort significantly improved at last follow-up compared with preoperative VA (P < 0.001), whereas VA in the LMH cohort did not (P= 0.14). In the LMH cohort, retinal layer continuity at the hole edge was positively correlated with change in VA at final follow-up, whereas hole height was negatively correlated with VA. In the ERMF cohort, preoperative VA was negatively correlated with change in VA at final follow-up. Retinal layer continuity at the hole and hole height are novel preoperative markers that predict postoperative VA change in LMH. After identifying the type of macular lesion, surgeons should consider using these preoperative OCT markers when counseling patients on potential postoperative VA outcomes and when managing patient expectations. The authors have no proprietary or commercial interest in any materials discussed in this article.

Research on thermal performance and pressure loss of a new perforated-folded baffle solar air collector

In order to further improve the heat collection performance of solar air heaters and reduce internal pressure. This study establishes a collector with perforated baffle based on baffled collector. The model was simulated using CFD software. Fit and analyze the efficiency of the collector with the hole-opened rate (the ratio of the opening area to the baffle area). The results show that compared with non-perforated baffle collectors, perforated baffle collectors have lower pressure loss, higher collection efficiency, lower heat dissipation coefficient of about 37.58%, and higher heat transfer coefficient of about 10.51%. When the hole height is 30 mm, the hole diameter is 80 mm, and the hole-opened rate is 0.24, the coupling between heat collection efficiency and pressure loss is the best, which is 64.11% and 4.32 Pa, respectively. The heat collection efficiency decreases with the increase of porosity, and the fitting degree R 2 = 0.98. The deviation of fitting curve (between turbulence intensity and hole-opened rate) is less than 10%. Nusselt number increases gradually with the increase of Reynolds number. Fitting correlation between Nusselt number and Reynolds number, and fitting degree is 0.9985. Perforated-folded baffle collector provides theoretical basis for improving the solar thermal utilization rate.

Numerical Simulation Study of Basement Water Discharge Pressure Relief Method under Rainstorm Conditions

The development and expansion of underground space has led to a continuous increase in both the occupied area and the burial depth of underground basements. Meanwhile, due to the inaccurate estimation of groundwater buoyancy, more and more anti-floating problems of underground basement caused by rainstorm have emerged. Combined with the principles of unsaturated seepage theory, this article uses Flac3d 6.0 software to conduct simulations on the influence of various significant factors on the effect of the water discharge pressure relief method, a novel approach to reduce buoyancy. The numerical results show that the water discharge pressure relief method can ensure the stability of the basement under rainstorm conditions compared with the basement without drainage holes. In order to improve the anti-floating efficiency of the water discharge pressure relief method in preventing floating, it is recommended to initially decrease the height and spacing of the drainage holes and follow by increasing the aperture of the drainage holes. The recommended spacing of the drainage holes is between 2 m and 3 m. The height of the drainage holes should be between 1 m and 1.5 m, and the aperture of the drainage holes should be no smaller than 100 mm. Furthermore, the water head of the basement floor is proportional to the permeability of the lower backfill and cushion, and it is not significantly influenced by the upper backfill soil when its permeability is within a low range. Finally, in order to achieve a satisfactory anti-floating effect, it can be attempted to reduce the longitudinal width of the lower backfill soil or moderately increase the thickness of the cushion.

Performance Analysis of Boiling Drying Granulator Cutting Spraying Assisted Wind Field

Through computational fluid dynamics (CFD) analysis, the research focused on the influence of fish-scale hole structure and porosity on the airflow uniformity within a cutting and spraying form fluidized bed drying granulator. By optimizing the airflow distribution through simulation calculations, the overall performance of the granulator was improved, leading to enhanced drying efficiency and reduced energy consumption. Furthermore, a comprehensive understanding of the complex airflow patterns and turbulence characteristics within the granulator was gained, facilitating the identification of factors impacting airflow uniformity, such as the structural design and opening rates of the fish-scale hole structure. This knowledge contributed to the development of effective process control and optimization strategies. The research findings demonstrated that the best internal airflow uniformity was achieved when the fish-scale holes had a width of 21mm, a hole height of 3mm, and an overall porosity of 8.4%, or a width of 24mm, a hole height of 2.5mm, and an overall porosity of 8.0%. These results provide guidance for achieving better product outcomes in industrial applications.

Simultaneously improved hole injection and current uniformity in 293 nm AlGaN-based deep ultraviolet light-emitting diodes

Insufficient hole injection and current nonuniformity caused by the nature of the p-AlGaN hole injection layer (HIL) are two issues impeding the advances in the optical and electrical properties of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs). To simultaneously improve the hole injection efficiency and current uniformity, an Al-linearly-decreasing AlGaN PN junction (ALD AlGaN PN junction) is proposed to replace the conventional p-AlGaN HIL with a constant Al component. The barrier height for holes at the interface between the p-type electron blocking layer (p-EBL) and HIL as well as the hole concentration and resistance in the p-AlGaN HIL can be modulated at the same time by the proposed ALD AlGaN PN junction. As a result, the hole injection efficiency is enhanced due to the reduced barrier height at the p-EBL/HIL interface and the polarization-induced three-dimensional hole gas (3DHG) induced in the proposed ALD AlGaN PN junction HIL. In addition, the lateral current uniformity is improved by the properly regulated resistance in the p-AlGaN HIL, which can be ascribed to the additional barrier for holes in the valence band because of the incorporated ALD AlGaN PN junction. The proposed DUV LED with ALD AlGaN PN junction exhibits enhanced EQE by a factor of 39.2% at 100 A/cm2 and simultaneously improved current uniformity in the active region. This designed ALD AlGaN PN junction structure provides a promising strategy for achieving high-performance DUV LEDs.

Study on Bending Performance of Tightly Spliced Truss-Reinforced Plate-Honeycomb Flat Beam

The tightly spliced truss-reinforced plate-honeycomb flat beam is a novel type of composite beam, with the advantages of high rigidity, high bearing capacity, and ease of construction. In this study, on the basis of the performance in bending tests, the numerical analysis method is used to study the influence of the honeycomb hole–height ratio, and section height on the bearing capacity of the honeycomb composite flat beam. On this basis, the simplified method to calculate the ultimate bending capacity of the new honeycomb composite flat beam was proposed. The research results show the failure modes of the specimens are mainly divided into two states, including the deflection exceeding the limit and the concrete flange plate separating from the steel beam. The tightly spliced truss-reinforced plate-honeycomb flat beams have good ductility, of which the average value reaches 8.2. The simplified method proposed in this article for calculating this type of honeycomb composite beam has an error of less than 10% in terms of bending bearing capacity, which has advantages over the double T-shaped steel method. The calculation method and design suggestions proposed in this study provide a basis for the research and application of this type of composite flat beam.

Experimental investigation on mechanical behavior of T-type perfobond rid shear connectors under combined shear and tension

The stress of shear connectors becomes more complicated as the span length of steel-concrete composite bridges increases. To bear the great shear and uplift forces, a T-type perfobond rib (T-type PBL) shear connector with sufficient stiffness and ductility is proposed. While the shear behavior of T-type PBL connectors has been evaluated in previous studies, its mechanical performance under combined shear and tension is not well understood due to the particular shape and numerous impact factors. Therefore, one pull-out test considering pure tension and seven modified push-out tests considering combined shear and tension were carried out to investigate the failure mode, bearing capacity, and load-slip behavior of T-type PBL connectors under combined actions. The pull-out test was performed to determine the tensile resistance, followed by a series of modified push-out tests with constant horizontal tension to investigate the structural behaviors. Additionally, the effects of the rib height, flange width, and hole numbers were evaluated. Based on the test results, conical failure surfaces formed from the flange of the T-type PBL to the concrete surface for all specimens, and the concrete failure angle was approximately 32°. The bearing capacity of the specimen improved by 26% when the perfobond rib height increased from 100 mm to 120 mm, but the flange width barely had any effect. The capacity of 1-hole specimen dropped by 20% while 2-hole specimen increased by 8% compared to the standard specimen, which may relate to the distance between adjacent holes. Increasing the rib height by 25% and 50% reduced the initial relative slip (S90) by 30% and 32%, respectively, indicating the improvement in initial stiffness. Generally, the pull-out resistance of the T-type PBL shear connector was enhanced by increasing the flange width, rib height, and number of holes. An evaluation equation considering the hole number and hole spacing was suggested for the bearing capacity of T-type PBL shear connectors under the combined actions. The validity was verified by test results, with a calculated-to-test-result ratio of 1.12 and standard deviation of 0.15. This study could enhance the understanding of the behavior of T-type PBL connectors under the combined actions, and promote the potential application in long-span composite bridge decks.

Assessment of influences of needle lift and hole height on string cavitation in liquid injection

This work uses an improved cavitation model to comprehensively study the impacts of needle lift and hole height on the dynamics of in-nozzle string cavitation. The numerical models can provide a satisfying prediction on internal string cavitation and multiphase vortex flow features in liquid nozzles. Results indicate that the driving mechanism behind the string cavitation inception was the vortex evolution, and the stronger the vortex flow, the stronger the string cavitation. Moreover, the string cavitation patterns were remarkably different under various hole heights due to the evolution characteristics of in-hole longitudinal vortices; specifically, there was an in-nozzle large scale well-organized longitudinal vortices at higher hole heights, while the interaction between the two weaker counter-rotating vortices at lower hole heights resulted in there was no continuous longitudinal vortex inside the nozzles. Furthermore, the quantitative comparison of the inner string cavitation at all of the examined cases under different needle lifts and hole heights shows that appropriately reducing the maximum needle lift of the injector and simultaneously increasing the hole height of nozzles were conducive to inducing the string cavitation on the premise of the large enough flow velocity.

Seismic behavior of precast shear wall with novel bundled connections

Recently, precast shear walls have been investigated in the civil engineering field because of saving material resources and shortening the construction period. The type of connection between precast shear wall panels is critical to its seismic behavior. This paper puts forward a new type of connection for upper and lower precast shear walls. Vertical reinforcement bars in the lower precast shear walls are bundled and extended into the preformed holes of the upper precast shear wall. Then the preformed holes are filled with high-performance grouting materials. Experiments of eight full-scale specimens under cycling loading were carried out to discuss the seismic behavior of precast shear walls with the proposed connections. Results indicate that the proposed precast shear walls have no less than cast-in-place shear wall seismic performance with full hysteresis curve. The initial cracks occur near the top of the preformed holes and develop into the main crack, and staggering the height of preformed holes can prevent the development of cracks. Shortening the height of preformed holes does not deteriorate the seismic performance of the precast shear walls considering the welding of vertical reinforcement bars, while cracks near the top of preformed holes develop more. The principle of the works can provide a basis for the promotion of the novel connection in precast structures in the trend of building industrialization.

Overlying strata failure mechanism and gas migration law in close distance outburst coal seams: A case study

In the mining process of close distance outburst coal seams, a large amount of gas is desorbed and discharged into the atmosphere causing the waste of coal bed gas resource and seriously damaging the ecological environment. In this study, taking Anshun coal mine as engineering background, physical simulation combined with digital speckle technology, numerical simulation and analytical geometry theory are adopted to investigate the overlying strata failure mechanism and gas migration law in close distance outburst coal seams for providing the solutions with effective extraction and efficient utilization of coal bed gas. The results show that the mining-induced cracks play the guiding role for the migration of pressure-relieving gas, and the enrichment space for the gas migration can be observed as dynamic change state before fully mining. Most importantly, the directional long drilling section extraction technology (DLD-SET) is proposed in this study, which can cover the extraction pipeline to the whole life cycle of mining operations, and adjust the height of the final hole according to the propulsion distance and industrial comparison test was carried out. It can significantly increase the amount of gas extraction and improve the power generation efficiency compared to the traditional technology. This study provides the potential measures for green mining and low-carbon production of gas in close distance outburst coal seams by considering economic and environmental benefits.

Shear performance and failure process of perfobond connector in steel-UHPC composite structures

Nowadays, the application of Ultra-High Performance Concrete (UHPC) provides innovative concepts for structural designs of composite structures. Perfobond connectors (PBLs) with excellent shear capacity and fatigue performance may fully use the superiority of UHPC and thus are increasingly adopted in various novel steel-UHPC composite structures. However, the shear behavior and failure modes of PBLs embedded in UHPC slabs still need to be clarified. Therefore, this paper aims to evaluate the shear performance and further propose an equation for the shear capacity of UHPC PBLs. Firstly, six standard push-out tests taking the hole diameter, hole height, and whether perforated rebar was used as the parameters were performed. Subsequently, a detailed finite element (FE) model for the push-out test was established and validated by the test results, which took the fracture of perforated rebars into account by introducing the LW fracture criterion. Further, a parametric study was carried out to clarify the effects of dowel area, rebar sectional area, and hole shape. The results showed that benefiting from the high rigidity of UHPC, the PBLs with perforated rebars presented a slip-hardening behavior and excellent ductility. The slip corresponding to the rebar fracture grew with the rebar and hole diameter. Besides, the shear stiffness markedly rose with the hole diameter and height, while the effect of perforated rebars on shear stiffness was relatively small. Finally, the shear capacity equations for long-hole PBLs embedded in UHPC were proposed. The calculated results matched well with the 80 numerical and 21 collected experimental results.

PREDICTION OF MACULAR HOLE SIZE PROGRESSION BASED ON BASELINE OPTICAL COHERENCE TOMOGRAPHY FINDINGS.

To quantify the rate of idiopathic macular hole progression from presentation and identify factors that may influence stratification and urgency for surgical listing based on the initial optical coherence tomography scans. The minimal linear diameter (MLD), base diameter (BD), and hole height on nasal and temporal sides of idiopathic macular hole were measured on spectral domain optical coherence tomographies, on initial presentation and just before surgery. Mean hole height, hole height asymmetry (absolute difference between nasal and temporal height), MLD/BD, and MLD change per day (MLD/day) were calculated for each patient. Multivariable linear regression analysis with MLD/day as the dependent variable was performed to identify significant risk factors for MLD progression. Minimal linear diameter was grouped to quintiles: 1: ≤290 µ m, 2: >290 µ m and ≤385 µ m, 3: >385 µ m and ≤490 µ m, 4: >490 µ m and ≤623 µ m, and 5: >623 µ m. In 161 eyes (157 patients), we report significant associations with MLD/day: 1) MLD/BD ( P = 0.039) (i.e., wide BD relative to MLD lead to faster progression of MLD), 2) hole height asymmetry ( P = 0.006) (larger absolute difference between nasal and temporal hole height lead to faster progression), and 3) days between scans ( P < 0.001) (longer duration between scans had reduced MLD/day, indicating more rapid increase initially then plateaux), and relative to MLD Quintile 1, MLD Quintile 3 ( P = 0.002) and MLD Quintile 4 ( P = 0,008), and MLD Quintile 5 ( P < 0.001) all lead to a reduced MLD/day rate on multivariable regression. In addition to finding that the previously reported initial smaller MLD is a risk factor for rapid MLD progression, we report two novel findings, large hole height asymmetry and a low MLD/BD (wide base relative to MLD), that represent significant risk factors. These factors should be taken into consideration on presentation to stratify timing of surgery.