Cusp Length Research Articles

Interfacial Dynamics Around a Swirling Roller in the Presence of Oppositely Imposed Horizontal Crossflows

Abstract The behavior of interfacial dynamics around a swirling circular drum is reported in the presence of horizontal crossflows of gaseous phase. A constant submergence ratio of the rotary drum is considered throughout this work. Forward and reverse crossflows are defined based on the direction of rotation of drum. A clockwise rotation is imposed on the drum and the rotation direction remains fixed throughout the present investigation. The pattern of film flow and cusp entrainment is observed thoroughly by considering rotational speed (ω) and strength of crossflow as influencing parameters. Strength of crossflow of gaseous phase is calibrated using flow Reynolds number based on roller diameter (Reflow=ρgUD/μg). Subsequently, we characterized the coated film thickness (h*=h/D) and cusp width (H*=H/D) by varying ω and Reflow. Furthermore, efforts are made to observe the influence of gravitational pull (calibrated using Archimedes number, Ar) and viscous drag (determined using Morton number, Mo) on interfacial morphology. The interfacial structures respond more to the rotational inertia compared to crossflow with the continuous increase of Mo. Again, the trailing end of cusp gets widened for the case of forward crossflow, whereas the cusp growth is obstructed in the presence of reverse crossflow, which is visualized using velocity vectors. We have also predicted appropriate correlations for film thickness (h*), cusp width (H*), and steady cusp length (θs*) in the presence of forward as well as reverse crossflow of air stream. Lastly, a theoretical framework is also developed to estimate film thickness and cusp width for both cases of crossflows and this framework agrees well with the simulated predictions.

Left Main Protection During Transcatheter Aortic Valve Replacement With a Balloon-Expandable Valve.

Coronary obstruction during transcatheter aortic valve replacement (TAVR) is a rare, yet life-threatening, complication. The routine use of left main (LM) protection with or without stent placement in high-risk patients remains controversial. The aim of this study was to evaluate the outcomes of LM protection during TAVR and identify anatomic factors associated with need for stent placement. We retrospectively reviewed all TAVR cases (native and valve-in-valve) performed in our institution between 2014 and 2019 and identified patients who underwent LM protection with a coronary wire, balloon, and/or stent during the procedure. We compared the pre-TAVR computed tomography aortic root characteristics, procedural data, short-, and long-term outcomes among the patients who eventually received an LM stent and those who did not. Among 1925 TAVR patients, 41 (2.1%) underwent LM protection, and 10 of them (25%) had eventually a stent placed in the LM for threatened obstruction after valve deployment. In the native TAVR group (n = 35), 8 patients underwent LM stenting. A larger TAVR prosthesis, larger annular circumference (83.8 vs 76.1​mm; P = .038), lower ratio of sinotubular junction diameter to prosthesis size (1.02 vs 1.11; P = .032), and longer left coronary cusp (15.1 vs 13.9​mm; P = .18) were associated with higher incidence of LM stenting. In the valve-in-valve TAVR group (n = 6), 5 patients had a valve-to-coronary distance of less than 4​mm, and 2 of them received an LM stent. Both stent and nonstent groups had excellent outcomes with no major adverse cardiovascular events or coronary obstruction at 30​days. After a median follow-up of 351​days, 4 patients died (9.7%) (1 in the stent and 3 in the nonstent group), without any cases of late coronary obstruction or percutaneous coronary intervention in either group. LM protection with a coronary guidewire, balloon, or stent is a safe and effective method of coronary protection during TAVR in appropriately selected high-risk patients. Annular circumference, prosthesis size, left coronary cusp length, LM ostial height, and ratio of sinotubular junction to prosthesis size are important predictors of stent deployment.

The effect of seal bag storage on dimensional stability of alginate impression material

Background: The dimensional stability of alginate impression material is very important for obtaining an accurate cast. Seal bag storage is one way to maintain dimensional stability of the impression material. Objectives: This research aims to compare the dimensional stability of alginate impressions between imprESSIX Color Change (Alginate A), Algeniux Normal Set Major (Alginate B), and Aroma Fine Plus Normal Set (Alginate C). The alginate impressions were stored in seal bags for 0 min, 10 min, 3h, 24h, 72h, 120h, and 168h. Method: Sixty-three gypsum cast samples were obtained from a master die using 3 different alginate impression materials. The alginate impressions were stored in separate seal bags for each of the seven different time intervals, then the samples were poured with gypsum type III. The buccal cusp length from right first molar to left first molar was measured for each gypsum cast sample using calipers and compared with the master die. The data were analyzed with two-way ANOVA followed by post hoc LSD test. Results: The distance between the mesial buccal cusps of the right and left first molar was 52.280 mm for the master die. Gypsum cast samples of alginate A and B showed shorter lengths compared to master die, but the difference was not significant ( p >0.05). A significant difference in dimensional stability was observed for alginate C ( p <0.05) after 120h (52.080 mm) and 168h (52.057 mm). Conclusion: Dimensional stability of alginate impression was influenced by alginate composition and seal bag storage time. Seal bag storage could hold the dimensional stability of alginate A and B up to 168h, but for alginate C, the stability only lasted for 72h.

Bicuspid aortic valves: Diagnostic accuracy of standard axial 64-slice chest CT compared to aortic valve image plane ECG-gated cardiac CT

ObjectivesTo assess the diagnostic accuracy of standard axial 64-slice chest CT compared to aortic valve image plane ECG-gated cardiac CT for bicuspid aortic valves. Materials and methodsThe standard axial chest CT scans of 20 patients with known bicuspid aortic valves were blindly, randomly analyzed for (i) the appearance of the valve cusps, (ii) the largest aortic sinus area, (iii) the longest aortic cusp length, (iv) the thickest aortic valve cusp and (v) valve calcification. A second blinded reader independently analyzed the appearance of the valve cusps. Forty-two age- and sex-matched patients with known tricuspid aortic valves were used as controls. Retrospectively ECG-gated cardiac CT multiphase reconstructions of the aortic valve were used as the gold-standard. ResultsFourteen (21%) scans were scored as unevaluable (7 bicuspid, 7 tricuspid). Of the remainder, there were 13 evaluable bicuspid valves, ten of which showed an aortic valve line sign, while the remaining three showed a normal Mercedes-Benz appearance owing to fused valve cusps. The 35 evaluable tricuspid aortic valves all showed a normal Mercedes-Benz appearance (P=0.001). Kappa analysis=0.62 indicating good interobserver agreement for the aortic valve cusp appearance. Aortic sinus areas, aortic cusp lengths and aortic cusp thicknesses of ≥3.8cm2, 3.2cm and 1.6mm respectively on standard axial chest CT best distinguished bicuspid from tricuspid aortic valves (P<0.0001 for all). Of evaluable scans, the sensitivity, specificity, positive and negative predictive values of standard axial chest CT in diagnosing bicuspid aortic valves was 77% (CI 0.54–1.0), 100%, 100% and 70% respectively. ConclusionThe aortic valve is evaluable in approximately 80% of standard chest 64-slice CT scans. Bicuspid aortic valves may be diagnosed on evaluable scans with good diagnostic accuracy. An aortic valve line sign, enlarged aortic sinuses and elongated, thickened valve cusps are specific CT features.

Influence of resin-based composite restoration technique and endodontic access on cuspal deflection and cervical microleakage scores

ObjectivesTo assess cuspal deflection and cervical microleakage of mesio-occlusal-distal cavities in standardised premolar teeth restored incrementally with resin-based composite (RBC) placed horizontally or obliquely and with endodontic access cavities (with and without gutta percha and epoxy resin sealer obturation). Materials and methodsThirty-two teeth were allocated to four groups (n=8) and RBC restored in eight horizontal (Group A) or oblique increments (Groups B–D) using a quartz-tungsten-halogen light curing unit. The dependent variable for Groups B–D was endodontic access (none (Group B), obturated without (Group C) and with gutta percha and epoxy resin sealer (Group D)). Cuspal deflections were recorded post-irradiation using a twin channel deflection measuring gauge. Following restoration, the teeth were thermocycled, immersed in fuchsin dye, sectioned and examined for cervical microleakage. ResultsTukey's post hoc tests identified a significant decrease in total cuspal deflection for the horizontal (p=0.015) compared with the oblique placement technique. No significant difference in total cuspal deflection was evident between Groups B and D restored teeth (p>0.318) or in cervical microleakage score between Groups A and D (p=0.575). SignificanceDeformation is proportional to the cubed power of the length of a uniform cantilever beam and although a crude approximation of cuspal deformation, the reduction in the effective cusp length therefore significantly reduced the deflection in the MOD cavities when the horizontal rather than the oblique incremental restoration technique was employed.

Computed tomography-based evaluation of aortic annulus, prosthesis size and impact on early residual aortic regurgitation after transcatheter aortic valve implantation

Computed tomography (CT) is an increasingly utilized method for the evaluation of patient suitability for transcatheter aortic valve implantation (TAVI). The aim of this study was to analyse the role of CT in the choice of prosthesis and the prevention of residual aortic regurgitation (RAR). From November 2007 to September 2010, 115 patients (median age 81 years, inter-quantile range (IQR) 76-85; median ejection fraction 55%, IQR 45-60; median logistic EuroSCORE 19.7, IQR 11.0-32.1) undergoing TAVI were evaluated with a pre-procedural CT. An aortic complex was evaluated with multi-planar reconstructions, and we defined significant early RAR as RAR ≥ 2, and prosthesis/annulus mismatch (PAM) as the ratio between prosthesis size and mean annular size. All analyses were conducted for the whole sample and then separately for the two types of prosthesis implanted. An Edwards-SAPIEN(®) prosthesis was implanted in 62 patients (54.7%), and a Medtronic CoreValve(®) in 52 (45.2%). Aortic annulus minimum and maximum diameters were 22.6 ± 2.1 and 26.0 ± 2.3 mm, respectively. The aortic annulus diameter and the length of the free edge of the aortic cusps were linearly related to a 1:1 ratio (P < 0.0001). Significant RAR (34 patients, 30%) appeared directly related to the annulus diameters (particularly maximum and medium diameters, P = 0.0003 and P = 0.0010, respectively) and cusp length (P = 0.0007) but inversely correlated with PAM (P = 0.0006). Prosthesis/annulus oversizing was associated with a reduction in RAR, with a cut-off of 7% as the limit below which RAR increases; moreover, we observed different cut-off values for the Edwards and CoreValve prostheses, although statistical significance was not reached for the CoreValve (respectively, 2% with P < 0.0001, 11% with P = 0.16). No association was found between PAM and possible PAM-related complications. CT evaluation prior to TAVI showed that RAR was directly correlated with aortic root dimensions (particularly maximum and medium annulus diameters and cusp lengths) and inversely correlated with PAM. Oversizing the prosthesis by at least 7% reduces the risk of RAR. CT is an essential and invaluable tool in the assessment of patients undergoing TAVI.

Generation of dense multicharged ion flows from an ECR plasma confined in a quasi-gas-dynamic magnetic cusp trap

The possibility of generating dense multicharged ion beams with a current density as high as ∼1 A/cm2 from an ECR plasma confined in a quasi-gas-dynamic cusp trap is studied both theoretically and experimentally. The most important advantages of this type of ion source are that the plasma in the cusp is stabile against MHD perturbations and that a trap intended to operate at fairly high pump-field frequencies (above 30 GHz) is relatively inexpensive. A theoretical model of confinement of a high-density nonequilibrium ECR plasma (Te ≫ Ti) in an open magnetic trap is proposed and results are presented from model experiments with an ∼30-cm-long cusp trap (here, by the cusp length is meant the volume of a paraxial magnetic tube divided by the area of its cross sections in magnetic mirrors) pumped by a pulsed microwave field with a frequency of 37.5 GHz and power of 100 kW. The possibility of achieving a quasi-gas-dynamic regime of plasma confinement of an ECR plasma in a cusp trap is demonstrated. Ion beams with a average ion charge number of 2–4 (depending on the sort of working gas) and current densities unprecedented for ECR sources are obtained. Good agreement between theoretical and experimental results makes it possible to reliably predict the ion beam parameters that can be achieved at even higher microwave frequencies.

Understanding how the liquid-metal ion source works

There is some interesting physics in how the liquid-metal ion source (LMIS) works. This short review describes our current understanding, covering the following topics. Distinction between the real Taylor-Gilbert cone and Taylor's mathematical cone. Thermodynamic origin of the pressure-difference formula. Shape of an operating LMIS: the cusp-on-a-cone as expected shape and as an electrically driven vena contracta. Onset behaviour and Taylor's slender-body formula. Ion energy distributions, and interpretation in terms of surface processes and space-charge. Swanson's proof that the emission mechanism is field evaporation. Predicting the low-current Ga LMIS apex radius as 1.5 nm. The low-current Ga LMIS as a device driven by a negative pressure of order 40 atm. Re-examination of Mair's formula for LMIS current/voltage characteristics, and the role of space-charge. Cusp length as a function of emission current: theory and modelling. Emitter stability and control mechanisms: space-charge stabilisation, inertial/geometrical stabilisation, pressure-change destabilisation. Secondary emission phenomena: electrons, neutrals and photons. The high-temperature anomaly in the ion energy distribution, and a possible explanation. Instability and the formation of microdroplets and nanodroplets. Numerical modelling of basic LMIS behaviour: current/voltage characteristics for sources with and without viscous drag; modelling of cusp length and limiting half-angle; modelling of time-dependent effects. Current research tasks.

Modelling the link between emission current and LMIS cusp length

This paper presents new modelling results on the relationship between emission current and cusp length, for gallium and indium liquid-metal ion sources. The work is based on an improved version of the LMIS modelling program developed by Forbes and Ljepojevic, and achieves enhanced computational speed by means of parallel processing. Good agreement is found between the results derived from numerical simulation and experiment.

An analytical calculation of LMIS cusp length

A simple analytical formula is derived for the length of the liquid cusp of an operating liquid-metal ion source. This is a slightly revised version of a formula previously presented. The derivation involves electrostatic field models, and assumptions about the importance of space-charge effects and about the uniformity of hydrostatic pressure just below the ion emission threshold. Physical implications of this formula are discussed. It is suggested that an important aspect of this analytical treatment is the contribution it makes to transparency of physical argument about the mechanisms of ion source operation.

Preliminary field observations on beach cusp formation and characteristics on tidally and morphodynamically distinct beaches on the Nigerian coast

Between November, 1984 and December, 1986 observations of cusps were made on some tidally and morphodynamically distinct beaches on the Nigerian coast with a view to assess their origin, conditions for formation, distribution, dimensional and textural characteristics. No conclusive evidence can be forwarded at present with respect to their origin. Nevertheless, after formation, subsequent development and destruction are effected by swash action. Field examination of most of the commonly cited cusp-dependent parameters indicates cusp existence and extinction to be primarily controlled by foreshore slope. Two levels of cusps were typical of the coarse to medium-grained, reflective and microtidal beaches of Badagry and Victoria. The lower-level cusps were consistently absent on the above beaches when mid-tide level slope exceeded 13° and 15°, respectively. On the contrary, the fine-grained, mesotidal and largely dissipative beach at Ibeno depicted only a single set of cusps which were consistently extinct on slopes less than 3°. Cusps were most prevalent during calm coastal condition (November–January) and on foreshore segments depicting reflective beach-state. The regularity of cusp spacing was noted to improve with increase in beach reflectivity. The coarser beaches showed higher cusp relief while cusp length was longer on the fine-grained beach. In general, the spacing, slope, grain-size statistics and permeability of cusps noted in this study conform with those of earlier investigators on other beaches. Temporal changes in dimensional characteristics of cusps are considered essential for evaluating the potentials of cusps as signatures of beach and surf-zone morphodynamics. The above defines the direction of further studies.