Eccentric Placement Research Articles

Effect on the physical field of the die during the backward extrusion process of magnesium alloy wheel

The eccentric placement of billets reduces the service life of the dies, and at the same time causes the scrapping of the wheel blanks. However, for axisymmetric forgings, eccentric placement is unavoidable. In this study, the mutual effects between the billet and the die during backward extrusion of magnesium (Mg) alloy wheels are analyzed by physical and numerical simulations, focusing on the effects on the physical field of the die. There were dangerous points in the design of the combined die structure and the lower mating surface of the female die and the bottom die were prone to stress concentration during the filling process of the Mg wheel, which led to the cracking of the die. The eccentric extrusion of the wheel resulted in a slope in the filling height of the rim, and it had a great effect on the physical field and microstructure distribution at the same time, which in turn affected the physical field distribution of the wheel die, resulting in uneven load distribution at the lower rim of the die and reducing the life of the combined die. The combined die structure optimization solution can process the female die into a curved surface along the fracture surface and at the same time process a hollow circular table to cooperate with the bottom die and the female die.

Analyzing heat transfer and entropy generation in catheterized, stenosed arteries

A frequent cardiovascular condition that reduces blood flow is arterial stenosis. Tangent stress pressure, produced by a stenotic blood artery, diminishes the arterial side and results in an aneurysm. We explored the dynamics of entropy generation in blood stream via arteries observing mild overlapping stenosis, using a Prandtl fluid and focusing on the eccentric placement of catheters to enhance patient comfort. The governing equations assume conditions of mild stenosis and low Reynolds number, and applied the homotopy perturbation method. Several critical physical aspects are characterized, including velocity, temperature, impedance, entropy generation, wall shear stress, the Bejan number, and flow streamlines. The results show that a rise in the catheter radius tends to elevate impedance levels, whereas an increase in eccentricity, amplitude ratio, and inner cylinder speed leads to a decrease. These behaviors may serve to optimize catheter placement to minimize patient discomfort during medical interventions.

Effect of structural support size and position on depressed tibial plateau fractures: A finite element analysis

ObjectiveStructural support for depressed tibial plateau fractures is receiving increasing attention. Currently, there has been little biomechanical evaluation of structural support. This work aimed to investigate the effect of structural support size and position on fracture fixation stability. MethodsA split-depressed tibial plateau fracture model was created according to the fracture map. Cortical screws combined with structural filler were used for fracture fixation. The filler diameter was set to small, medium and large, and the filler position was set to the center and offset by 1, 2 and 3 mm to study the effect of position and size on stability. ResultsThe maximum stress on the implant in all scenarios occurs at the lower contact surface between the anterior screw and the filler. Increased support size resulted in increased mean maximum screw stress, depressed fragment axial displacement and separated fragment transverse displacement (screw stress: 266.6 ± 37.7 MPa vs. 266.7 ± 51.0 MPa vs. 273.8 ± 41.5 MPa; depressed displacement: 0.123 ± 0.036 mm vs. 0.133 ± 0.049 mm vs. 0.158 ± 0.050 mm; separated displacement: 0.402 ± 0.031 mm VS 0.412 ± 0.047 mm VS 0.437 ± 0.049 mm). The larger the offset of the support position was, the larger the peak screw stress and the larger the reduction loss of depressed and separated fragment reduction, regardless of the support size. The medium support combined with the central position presented the minimum of peak stress and reduction loss. Cortical bone was below 2 % and trabecular strain was below 10 % for all scenarios. ConclusionCentral placement of structural support provides superior stability for the treatment of depressed tibial plateau fractures compared to the eccentric placement. When a support is placed centrally, optimal stability is achieved when the diameter matches the diameter of the depressed region. Thus, the utilization of equal-diameter fillers to provide central support appears to be an ideal selection for depressed tibial plateau fractures.

Association of Periprosthetic Fibula Fracture With Knotless Suture Button (TightRope) Fixation for Ankle Syndesmosis in Elite Athletes

Background: Suture button fixation is frequently used to stabilize the distal tibiofibular syndesmosis in athletes sustaining an isolated ligamentous syndesmosis injury. Purpose: To report on a series of periprosthetic fibula fractures adjacent to the lateral suture button after a subsequent unrelated ankle injury or progressive stress injury after initial ankle syndesmosis stabilization using the knotless TightRope (Arthrex). Study Design: Case series; Level of evidence, 4. Methods: Eight elite athletes with periprosthetic fibula fractures and stress injuries around the lateral suture buttons were evaluated. In all athletes, the knotless TightRope had been used to stabilize an isolated ligamentous ankle syndesmotic injury, after which all patients recovered and returned to professional sports at their preinjury level. The athletes subsequently developed an acute fibula fracture or a fibula stress fracture related to the 3.7-mm drill hole in the fibula adjacent to the lateral suture buttons after a mean of 14.1 months (range, 5-29 months). The management of these complications was analyzed. Results: Five athletes sustained a periprosthetic fibula fracture in the form of undisplaced spiral Weber B injuries after a subsequent, unrelated injury. Poor healing response was noted with initial nonoperative treatment for the first 2 athletes, and surgical intervention was performed with successful union of the fracture and return to sports. The subsequent 3 athletes had early surgery with uneventful recovery. Another 3 athletes developed stress injuries adjacent to the fibula suture button without a history of acute trauma. In 2 of the 3 athletes, the position of lateral suture buttons was in the anterior third of the fibula. Initial nonoperative management yielded poor healing response, and subsequent surgical intervention was required to enable healing and return to sports. Conclusion: Nonoperative management of fractures adjacent to the fibula suture button of a knotless TightRope may lead to a delay in union. Therefore, early surgical intervention should be considered in elite athletes, whose return-to-sports time is critical. Care is needed to ensure that the fibula hole for the suture button is centrally located because the eccentric placement of the fibula hole in the anterior third of the fibula may contribute to the development of a stress reaction or stress fracture. Surgical intervention for a periprosthetic fibula stress fracture leads to satisfactory resolution of symptoms.

Influence of drilling mud pulsations on well cleanout efficiency

Purpose. Determination of the influence of the non-stationary flow regime of the drilling mud on the efficiency of cleaning the wellbore in the annulus from drill cuttings. Methodology. The study on the carrying capacity of the drilling mud in a laboratory installation is carried out by simulating the process of its pulsations at different frequencies. The choice of the studied frequencies was made on the basis of previous studies. The evaluation of the influence of factors on the efficiency of rock removal was carried out using Latin experimental plans, which allowed us to evaluate the influence of the selected factors with a minimum number of experiments without losing the quality of the result. Findings. The influence of factors (mud flow rates, eccentric placement of the drill string, plastic viscosity of the drilling mud, pulsation frequency, rotation of the drill string) on the efficiency of cuttings removal along the annular space of the wellbore is analyzed. Three factors with the best interaction were found, which made it possible to build dependencies of their influence on the efficiency of rock removal on the surface. The effect of changing the frequency of pulsations of the drilling mud has been studied, and graphical dependences of their influence on the decrease in the volume of rock particles in the annular space have been obtained. Originality. Based on the results of experimental studies, the effectiveness of the impact of drilling mud pulsations on cleaning the well from rock particles has been proven. Practical value. The effectiveness of the use of drilling mud pulsations for hydrotransportation of cuttings along the horizontal section of the wellbore has been confirmed.

Experiments on the dynamics of aspirating cantilevered pipes concurrently subjected to reverse external axial flow

The dynamics of a hanging cantilevered pipe conveying fluid upwards (i.e. aspirating fluid) and concurrently subjected to a partially confined (annular) reverse external flow over its upper portion has been investigated experimentally in the present parametric study. The influence of annular confinement, pipe length, eccentric placement of the outer wall of the annulus relative to the central pipe, and a constriction at the inlet or outlet of the outer rigid casing on the system was examined for different external/internal flow velocity ratios, particularly Uo/Ui = 0.015 – 0.80. This study is primarily motivated by its application in solution-mined caverns, specifically for the hydrocarbon storage mode. Two different dynamical behaviours were observed; therefore, the results were categorized into two groups: low Uo/Ui (0.015 – 0.06) and high Uo/Ui (0.20 – 0.80). First-mode flutter was found to be the mode of instability of the aspirating pipe, for all flow velocity ratios, followed by the development of mixed-mode motions at higher flow velocities, for all configurations of the system. Even though the bifurcation diagram trends remained qualitatively unaltered for almost all cases, the onset of instability, amplitude of oscillations, and excitation of mixed-mode motions were affected, suggesting sensitivity of the system to small geometrical variations. The nature of the oscillatory motions appeared to generally be near-intermittent and disordered, with minor variations for different parameters.

Evaluation of flexural strengthening methods for beams with simulated deterioration using spike-anchored FRP externally bonded sheets and near-surface-mounted strips

• 20 beams were tested to evaluate FRP flexural strengthening techniques. • Specimens were detailed to mimic the common deterioration of bridge beams. • The effect of FRP spike anchor arrangements were evaluated. • Results show that more FRP spike anchors may not translate to superior performance. • Unsymmetrical steel and NSM reinforcement layouts were considered. In consideration of past research on both externally bonded and near-surface-mounted (NSM) fiber-reinforced polymer (FRP) reinforcement for the strengthening of deteriorated reinforced concrete elements, additional work is needed to investigate the application of FRP for flexural strengthening in specific scenarios and for specific member types. Furthermore, the need exists for guidance regarding reliable anchorage of externally bonded sheets for flexural strengthening. An experimental investigation was conducted on 20 reinforced concrete beam specimens with details and simulated deterioration patterns representative of the beams of in-service adjacent box beam bridges. Special focus was placed on the effective arrangement of FRP spike anchors for externally bonded FRP, unsymmetrical deterioration of steel reinforcement, and the eccentric placement of NSM strips. The results show that spike anchors located only at the ends of the externally bonded FRP sheets provided superior performance compared to anchors placed at multiple locations along the sheets. Moreover, the eccentricity of reinforcement did not play a significant role in the effectiveness of the strengthening systems. The test results also highlight the importance of bond on the performance of members strengthened with NSM reinforcement. Overall, the findings extend beyond adjacent box beam bridges and have a wide applicability to other flexural members.

Deep liquid tanks in seismic response control of asymmetric high-rise buildings

The present work investigates the usefulness of installing deep liquid storage tanks (DLTs) on the roof of high-rise buildings with plan irregularity. The aim is to assess the damping efficiencies of DLTs in reducing responses of high-rise buildings with plan irregularity, considering the effect of their placement and direction of the external excitation. A DLT has a higher liquid depth to tank length ratio as compared to the traditional tuned liquid dampers (TLDs). A 70 m tall, 20-storey reinforced concrete framed building with asymmetry in plan is considered for the numerical assessment. The system coupling facility of ANSYS Workbench is utilized to study the structure-fluid coupled dynamics. ANSYS Transient Structural module solves the structure part using the finite element analysis (FEA), whereas, ANSYS (FLUENT) uses the finite volume method (FVM) to solve the fluid part. The authors [1] developed a practical framework to demonstrate the efficacy of DLTs for symmetrical building, which is extended in the present study for asymmetric building. In this paper, the validity of the framework is presented through an equivalent tuned mass damper (TMD) analogy. It is observed that for an asymmetric high-rise building, eccentric placement of DLT gives better response reduction, both in terms of peak roof displacement and acceleration.

"Screw First" Technique to Get Past Nail-Jig Mismatch in Proximal Femoral Nailing.

Proximal femoral nailing is the gold standard of surgical treatment for unstable intertrochanteric hip fractures. One of the intraoperative complications encountered in this procedure is the nail-jig mismatch due to causes such as manufacturing errors and fatigue deformation of sleeves or jig. Nail-jig mismatch leads to eccentric placement of guidewire within the screw slots of PFN and subsequent difficulty in reaming and screw insertion. The potential complications of this include guide wire deformation, breakage, nail damage and screw malposition. We propose a simple and effective technique to tackle this complication, called as "Screw first" technique. The principle of this technique is to utilize screws as guide wire sleeves to effectively centralize the guidewire position within nail slots. On identifying a mismatch by the eccentric position of guidewire, a long screw is first inserted partially till its shaft engages into the screw slot allowing subsequent insertion of a guidewire which assumes a centralized position, thus bypassing the mismatch of jig. Following this, the usual steps of reaming and final screw insertion are undertaken. This method is effective, simple, quick and requires no special instrumentation.

Adjustable sound insulation frequency band through the combination of membrane-type acoustic metamaterial array

Membrane-type acoustic metamaterials are thin films or plates composed of periodic units with small additional mass. A large number of studies have shown that these metamaterials exhibit tunable anti-resonance, and their transmission loss values are much higher than the corresponding quality laws. At present, most researches on membrane-type acoustic metamaterials focus on the unit cell, and the sound insulation frequency band can only be adjusted by adjusting the structural parameters and material parameters. In this paper, two kinds of acoustic metamaterials with different structures are designed, which are the center placement of the mass and the eccentric placement of the mass.The two structures have different sound insulation characteristics. By designing different array combinations of acoustic metamaterials, the sound insulation peaks of different frequency bands are obtained. This paper studies the corresponding combination law, and effectively realizes the adjustable sound insulation frequency band.

Biomechanical Comparison of Different Volar Screw Placements for Horizontal Oblique Scaphoid Fractures

Recently, some surgeons reported that most scaphoid waist fractures were horizontal oblique and not transverse in orientation. Therefore, this cadaveric study aimed to biomechanically compare fixation strength between central and eccentric screw placements for the volar fixation of this most common scaphoid waist fracture. Eight matched pairs of fresh-frozen forearm cadaver specimens were prepared for testing and randomly assigned to two groups: group I specimens were fixed by screws in a central placement, and group II specimens were fixed by screws in an eccentric placement. Horizontal oblique osteotomy was performed along the scaphoid waist. Then, each specimen was placed under the increasing load of a pneumatically driven plunger. We recorded stiffness, load to failure, and failure mechanisms between the central and eccentric screw placement groups. Stiffness was higher in central screw placement (74.1 N/mm) than in eccentric screw placement (29.39 N/mm). The median loads to failure in groups I and II were 54.14 and 26.22 N, respectively. In this biomechanical model, we demonstrated that central screw placement is superior to eccentric placement in terms of fixation strength. However, further clinical investigation is warranted to evaluate whether the different screw placements for volar approach of horizontal oblique scaphoid fractures affect the clinical outcomes.

Study on the lateral growth of the diamond in the substrate holder and the effect of temperature gradient on the large-area diamond surface morphology

The study of the distance between the substrate edge and the substrate holder cavity edge on the growth quality was further carried out. The results showed that the substrate edge quality decreased with the increase in the distance from the substrate edge to the substrate holder cavity edge, and the lateral growth rate significantly increased. Therefore, a three-step growth method was proposed. After 68 h of growth, the substrate size grew from 3.57 mm × 3.63 mm × 1.01 mm to 6.13 mm × 6.04 mm × 2.52 mm, but at the end of the third step, the quality and the morphology of the substrate became poor. Two experiments were carried out to verify the influence of eccentric placement and the substrate holder cavity edge on the substrate morphology. The results showed that the influence of the substrate holder cavity edge on the substrate edge quality was more significant than that of eccentric placement. Because of the lateral growth, the substrate edge will inevitably be closer to the cavity edge during the growth, and its temperature gradient will increase. Therefore, an improved substrate holder was designed, and the simulation results showed that the new substrate holder could effectively guarantee the uniformity of the temperature gradient on the large-scale substrate surface.

The Utility of a Plain Film Arthrogram to Confirm Acute Liner Dissociation in the Setting of Primary Total Hip Arthroplasty

Acute Liner dissociation is a well-documented, but uncommon complication of total hip arthroplasty, yet the journey to diagnosis remains undefined. This clinical case report outlines the use of plain film arthrogram for diagnosis in a 53-year-old female who presented to the ED following a fall, describing symptoms of increasing groin pain, reduced range of movement, difficulty weight-bearing and a grinding sensation in her left hip, all on a background of total hip replacement two years ago. Examination revealed impaired flexion, rotation and abduction while AP pelvic X-ray confirmed mild eccentric placement of the femoral head, and lateral X-ray proved joint enlocation. An arthrogram of the left hip was performed the following day with injection of 4mls of iodinated contrast injected into the joint. Inferior dissociation of the liner from the shell was evident. The femoral head and liner were replaced two days later, and the liner was found to have shearing and gross plastic deformation at the rim. The patient reported immediate relief from the groin pain and was discharged on the fourth day postoperatively. This shows how plain film imaging fails in diagnosing acute liner dissociation dynamic fluoroscopic tests, post-arthrography CT and metal artifact reduction sequence magnetic resonance imaging (MARS MRI) have previously been proposed despite their associated wait-time, radiation exposure and financial costs. This case report highlights the role of plain film arthrography as a low risk and low-cost diagnostic tool. The report also suggests the incorporation of radio-dense markers in liners to facilitate the use of arthrography when diagnosing dissociation, also raising awareness of prevention and recognition in what may be an under-reported complication of hip arthroplasty.

Well washing process modelling

The study of the influence of technical and technological factors on the efficiency of well flushing was car-ried out under experimental conditions. The analysis of existing experimental installations is performed with the help of which it is possible to assess the influence of technical and technological factors on the process of well flushing. The laboratory facility for modeling the well flushing process was designed using similarity criteria ob-tained in accordance with the basic provisions of the theory of dimensions. The developed installation allows you to model and study the influence of many factors on the well flushing process due to its compact overall dimen-sions and ease of conducting experiments, namely: the eccentric placement of the drill string; the type of flushing fluid (rheological properties); the size of the rock fraction; the frequency of pulsations to create a pulsating char-acter of the fluid movement; rotation of the drill string; longitudinal movement of the drill string. The main factors of influence and the range of their changes on the efficiency of sludge transportation are determined on the basis of previous studies. An experiment plan is constructed to study the significance of factors on the quality of sludge removal from the well bore using the «Taguchi» plan. Data processing was performed in the software «Mathcad Prime». Variations in factors lead to an improvement in the quality of well flushing, by reducing the area of sludge settling in the wellbore. The flow rate of the washing liquid has the most positive effect on the removal of sludge. The size of the rock fraction and the longitudinal movement of the drill string has the least impact. Pulsa-tion of the washing liquid has a significant impact on the quality of sludge removal, which is a significant and interesting factor from the point of view of further scientific research.

CFD modelling of the hydrodynamics in a filtration unit with rotating membranes

Membrane BioReactor (MBR) is a commonly used technology in wastewater treatment; however, fouling is the main drawback of MBR. Grundfos proposes a system that splits the technology into two parts: the biological tank and the membrane system. The latter rotates to decrease and mitigate the fouling. This paper evaluates two membrane configurations, a central and eccentric axis. The shear stress profile in a single rotating membrane was obtained through CFD modelling with different operating conditions that show that an increasing TSS or angular velocity causes an increment in the shear stress over the membrane surface. Additionally, based on the CFD results and empirical correlations, a factor α used to determine the shear stress for non-Newtonian fluids was calculated in order to predict the behavior for central and eccentric placement configuration MBRs. The velocity profile in a wagon of 36 membranes was obtained from CFD simulations, where it was evident that eccentric placement is the best option since it reduces the dead zones and increases the shear stress, which helps reduce fouling.

TO A QUESTION OF DETERMINATION OF HYDRAULIC RADIUS OF A BACKFILL FLOW FOR THE EXCENTRATIVE PLACEMENT OF PIPES IN DRILLING BORE

The processes of displacement of drilling clay backfill flow from the intertubular space formed by internal surface of external and external surfaces of inner tubes are considered. In case of eccentric placement of pipes it is proposed in the form of a cross-section of the flow of a backfill to take the area limited from the outside by the Pascal's snail, and from the inside - the outer surface of the inner pipe at the first time.
 The formulas for determining areas of the cross section of the flow and the stagnant zone, the perimeter and the hydraulic radius of the section ofthe flow for the eccentric placement of the pipes in the bore are proposed. The dimensionless parameter α is introduced as the ratio of the centripetal distance to difference between internal radius of outer pipe and outer radius of inner tube. It was found that with increasing of α cross-sectional area and their hydraulic radii are increasing, and the area of stagnant zones decreases according to parabolic laws.It is established that with the growth of α velocity of the backfill flow decreases according to parabolic laws and their values are in good agreement with the experimental data.

Steady and Pulsating Flow Past a Heated Rectangular Cylinder(s) in a Channel

In the present study, the effect of laminar steady (, ) and pulsating flow (4 Hz and amplitude 0.4) is numerically studied over a centrally located heated rectangular cylinder of varying aspect ratio ( to 8) in a confined channel using finite volume method. To study the influence of channel walls at a fix distance, eccentric placement of the highest aspect ratio cylinder(s) with two gap ratios () of 5 and 0.5 is done. Isotherms and streamlines of the flow are presented along with lift and drag coefficients. Further, fast Fourier transform (FFT) spectral analysis is performed to evaluate the vortex shedding frequency of the flow upon interaction with the cylinder(s). For single cylinder at the center position in the channel, natural vortex shedding and “lock-on” shedding occurs for lower-aspect-ratio cylinder under steady and pulsating flow, respectively. An increase in aspect ratio has a suppressing effect on the vortex shedding with a substantial decrease in the heat transfer over the cylinder. Placing two cylinders () at a geometrically symmetrical eccentric location of shows an extra peak at half of the flow inlet frequency in FFT spectral curve that possibly confirms the lock-on shedding with increased heat transfer over the cylinder.

Enhancement and Intensity Inhomogeneity Correction of Diffusion-Weighted MR Images of Neonatal and Infantile Brain Using Dynamic Stochastic Resonance

Imaging of infantile/neonatal brain mandates tailored radio frequency coils (RF coils) to achieve a homogeneous field over a small region of interest (ROI). Most centers, however, perform pediatric imaging using adult RF coils only as procurement of tailored pediatric coils might prove quite expensive. This practice may not scientifically justified, whereas the image post-processing techniques reduces the deleterious effects of magnetic field inhomogeneity due to a small ROI being scanned in a large RF coil. Further, the eccentric placement of ROI within the RF coil perpetuates the field inhomogeneity within the scanned region. Hence, the structures closer to the coil appear brighter than those farther away giving rise to a ‘shading artefact’. The effect even more accentuates in weak signal sequences like diffusion-weighted imaging (DWI). The proposed method significantly removes shading artefact of real DWI and synthetic T1 and T2 weighted magnetic resonance images. Dynamic stochastic resonance (DSR) intelligently uses the coefficient of discrete cosine transform of an image for brightness normalization and image enhancement simultaneously. The quality of the output image depends on the bistability parameters associated with the dynamic equation. Particle swarm optimization (PSO) tunes these bistability parameters for the entropy minimization of different group of tissues individually. The proposed algorithm outperforms the post processing based homomorphic filtering, local entropy minimization with spline model and multiplicative intrinsic component optimization methods. The proposed PSO based DSR approach may be helpful in accurate diagnosis.

Influence of Eccentrically Located Drilling String in the Well Bore Over Cleaning Capabilities of a Wellbore

It has been analyzed solution to the problem of definition eccentric location of the drill string in the hole using analytical studies and modern systems of mathematical computer modeling. Practical implementation of technological problem solution was represented as calculated parameters of the formation and changes in the area of stagnant zones in the cross section of the annular space hole in certain baseline characteristics of the process of washing. As a result, studies have found that at lower eccentric placement of both direct and deformed drill string in the well drilling mud flow looks like sickle core flow. The maximum speed of mud while inside the nucleus, and the minimum - in the contact zones flexible pipe and the borehole wall. This change dependencies hydraulic pressure loss pumping mud pump flow rate and distribution of nuclei along the axis of the drill string at its eccentric location in the borehole. It has been determined the conditions of dead mud zones formation in the annular space and offered solutions to solve this problem.

Cytological diagnosis of metastatic malignant melanoma by fine-needle aspiration biopsy.

Despite increased surveillance and public awareness, the incidence of melanoma is increasing. Frequently, fine-needle aspiration is employed for the diagnosis of metastatic disease, and aspirated material is used for cytogenetic and molecular studies to guide treatment options. The pairing of a significant diagnosis with the numerous morphologic variants of melanoma can make the cytologic evaluation disquieting. We present selected examples of our experiences and a brief review of the literature to provide cytodiagnostic clues for this malignancy. The clinical history is foremost, although the fine-needle aspiration (FNA) of metastatic melanoma can provide a diagnosis before identification of the primary lesion in up to 20% of cases. If a history of melanoma is assured, negative results in sampling of pulmonary and subcutaneous nodules should be suspected as false negatives. The smearing pattern usually features poorly cohesive cells. Frankly malignant, spindled, and epithelioid cell shapes are most common, and cytoplasmic vacuoles, if sought on Romanowsky-stained specimens, can usually be found. The telltale feature of melanin production, although diagnostic, is only present in 50% of cases. Finally, eccentric placement of nuclei, nucleoli, and nuclear pseudoinclusions are accessory features for the cytologic interpretation of melanoma. Numerous morphologic patterns of melanoma are potentially seen, but a stepwise approach to diagnosis usually produces a successful result.