Groove Shape Research Articles

Investigation of the Interfacial Characteristics and Mechanical Properties of Duplex Stainless Steel/Low-Alloy Steel Clad Rebar

In this work, duplex stainless steel/low-alloy steel-clad rebars were fabricated using metal deposition and hot rolling. The interfacial characteristics of the rebar, such as element diffusion and phase composition, were investigated using an optical microscope and a scanning electron microscope with an energy-dispersive spectrometer. The mechanical properties of the rebar were evaluated by tensile and bending tests. The results show that the rebar interface is composed of a carburized layer on the duplex stainless steel side and a decarburized layer on the low-alloy steel side; they also show that the rebar exhibits good mechanical properties, with 435 MPa of yield strength, 630 MPa of tensile strength, and a 24.8% percentage elongation. The reduction in the cladding thickness at the rebar’s transverse rib root was studied using the ABAQUS software. The results show that the cladding thickness is reduced due to the effect of the groove shape during the rolling process. The rebar’s transverse rib root cracked after bending due to the thinning of the cladding and brittle fractures in the interfacial martensite layer.

Continuous coaxial nozzle designs for improved powder focusing in direct laser metal deposition

Direct Laser Metal Deposition (DLMD) is a type of Additive Manufacturing (AM) that deposits blown metallic powders from a nozzle onto a substrate. These powders are then simultaneously fused together by a high powered (0.1–1 kW, often ND:YAG) laser to form a deposited layer. Out of the various nozzle designs Continuous Coaxial nozzles provide the most even spray profile due to their annular profile. This is at the cost of a reduction in spray focusing. In this paper, the authors use full factorial analysis of simulated gas-powder nozzle flows to determine the impact of inlet pressure (1–10 kPa), powder inlet angle (0° – 25°), powder inlet offset (0–10 mm offset from the centerline), and internal groove shape (no grooves, straight grooves, tapered grooves) on nozzle focusing and powder velocity. It was determined that 1 mm wide straight grooves provided the best focusing, with powder concentrations reaching from 0.3 to 0.45 kg/m3 and particle cloud diameters reaching as low as 6 mm. CFD simulations showed that straight grooves drastically reduce tangential particle velocity components, forcing powders to point towards the nozzle's focal point. A second batch of designs with a smaller nozzle angle (from 17° to 12°) focused on examining other groove geometries, including wider straight grooves and helical grooves. These simulations confirmed that narrow, straight grooves with uniform thickness provide improved powder focusing by controlling powder exit trajectories. In addition, helical grooves with steeper helical angles reduced the powder spray divergence. Finally, one control and the two best performing designs from each batch were manufactured and tested in a lab setting to experimentally observe the overall spray profile. Both the simulations and experiments showed an improvement in nozzle focusing with the addition of straight nozzle grooves, with experimental results showing a 17–18 % decrease in the spray width compared to the control nozzle.

Numerical Investigation of the Flexural Performance of Slender CFST Beams with Varied Shapes of External Stiffeners

The concrete-filled steel tube (CFST) beams are recommended for adopting in the modern composite structure since it achieves a higher load capacity and ductility behaviour than the conventional structural members. Using CFST beams with slender steel cross-section led to reduce the overall cost of the structures compared to those with compact cross-sections; however, it is more likable to buckle under the compression stress. Therefore, providing external stiffeners along the four sides of CFST beams expected to reduce the overall self-weight also can provide more stiffening to the steel’s section that led to improve the loading capacity. In this study, a finite element (FE) method was adopted for numerically investigated the flexural performance of the square CFST beams stiffened with different shapes of external grooves that provided along the beam’s sides. The FE software named ABAQUS was adopted for this purpose where the original model of CFST beam analysed and verified with the corresponding tested specimen. After that, additional CFST model have been built and analysed to investigate further parameters including the effects of varied tube’s thickness, steel yielding strength, concrete compressive strength and different external grooves shape (V-shaped, U-shaped, C-shaped, double V-shaped). The results established from the numerical analyses showed that the ultimate bending capacity (Mu) of the stiffened CFST models was generally enhanced by increasing their concrete strength, steel yield strength and tube’s thickness but in varied percentages. For example, increasing the tube thickness from 1.5 mm to 3.0 mm achieved an improvement in Mu values of about 72.3\%. while fewer improvement percentages have been recorded of about 11.9\% when only the core concrete strength increased from 25 MPa to 55 MPa. Furthermore, the shape and number of grooves have positive impact on the bending capacity of stiffened CFST models, where using U-shape, C-shape and V-shape external grooves were led to improve the Mu value of about 2.8\%, 10.7\%, and 11.1\%, respectively. Thus, the energy absorption of these models was improved accordingly.

Analysis of pressure at transition zone of valve plate of radial piston pump

In present studies focuses on the characteristics of flow-pressure of piston cylinder barrel and silencing groove chambers near the transition zone of valve plate of a fixed displacement radial piston pump. The designing of silencing groove of valve plate of the pump is carried out with appropriate geometrical configuration, compute the orifice area of piston kidney over the silencing grooves and manifolds, the interaction area make a key role in fluid flow interaction. The pressure and flow of pump is analyzed in consideration the silencing groove as separate control volume from manifold, each silencing groove chamber is connected to the both end of the manifold chamber, the shape of the silencing groove is an asymmetric tetrahedron. The radial piston pump is modelled in simulation with consideration of five pump pistons barrel, analyses the pressures near at transition zone with different bridge angle. The flows interaction of pump piston cylinder barrel with silencing groove chamber and manifold chamber are also carried out. The overall pump volumetric efficiency, flow and pressure fluctuation of radial piston pump are analyzed to optimize the pump.

A new species of tick, Ixodes (Ixodes) mojavensis (Acari: Ixodidae), from the Amargosa Valley of California

Ixodes (Ixodes) mojavensis, n. sp. (Acari: Ixodidae), is described from all parasitic stages collected from the endangered vole Microtus californicus scirpensis Bailey, 1900 (Rodentia: Cricetidae), Mus musculus L. 1758 (Rodentia: Muridae), and Reithrodontomys megalotis (Baird; 1857) (Rodentia: Cricetidae) in the Amargosa Valley of California. When first collected in 2014, this tick was tentatively identified as Ixodes minor Neumann, 1902 because the nucleotide similarity between its 16S rDNA sequence and a homologous GenBank sequence from an I. minor from the eastern U.S. was 99.51%. Nevertheless, adults of I. mojavensis differ morphologically from I. minor by hypostomal dentition, absence of a spur on palpal segment I, and punctation patterns; nymphs by the shapes of basis capituli, auriculae, cervical grooves and external files of hypostomal denticles; and larvae by the length of idiosomal setae and hypostomal dentition. DNA sequencing of fragments of 4 different genes, 12S rDNA, 16S rDNA, cytochrome c oxidase subunit I (COI), and intergenic transcribed spacer 2 (ITS2) of I. mojavensis and of closely related species of Ixodes shows that the mitochondrial gene sequences of the new tick species are almost identical to the I. minor homologous genes. Phylogenetically, the two species do not cluster in mutually exclusive monophyletic clades. However, ITS2 sequences of I. mojavensis and I. minor diverge deeply (≥ 5.74% maximum likelihood divergence) and are as different as homologous genes from other recognized species. The discrepancy between the two sets of genes is suggestive of past mitochondrial introgression or incomplete mitochondrial lineage sorting.

Impact of grooved cylinder on heat transfer by natural convection in cylindrical geometry

The current study reports a numerical analysis of a two-dimensional steady-state natural convection heat transfer from grooved heated cylinder for laminar flow regime. Two groove shapes are investigated in this work: circular and triangular groove. Simulations were carried out by varying the groove location, radius ratio f from 0.1 to 1, and the Rayleigh number over the range [103–106]. The thermal and dynamic behaviors are carefully analyzed and compared to the case of non-grooved cylinder (model 0). It is found that the heat transfer rate rises up with the increase of Rayleigh number. In addition, the groove locations φ = −90, and 80° provide the lowest heat transfer rate. A decrease of 9.4% in the heat transfer rate is detected for the case of triangular groove with f = 0.7 and Ra = 105. On the other hand, the highest heat transfer rate is provided at a position φ = −45° and 45° for f > 0.65. For these last groove locations, lower f present optimal configurations to accumulate heat on the cylinder. In fact, circular grooved cylinder with f = 0.1 decreases the heat loss by 9.3% and 12.4% for the locations φ = −45° and 45°, respectively compared to model 0. These results would be useful for engineering applications that are interested in the accumulation or transfer of heat through cylindrical ducts.

High-accuracy in the classification of butchery cut marks and crocodile tooth marks using machine learning methods and computer vision algorithms

Some researchers using traditional taphonomic criteria (groove shape and presence/absence of microstriations) have cast some doubts about the potential equifinality presented by crocodile tooth marks and stone tool butchery cut marks. Other researchers have argued that multivariate methods can efficiently separate both types of marks. Differentiating both taphonomic agents is crucial for determining the earliest evidence of carcass processing by hominins. Here, we use an updated machine learning approach (discarding artificially bootstrapping the original imbalanced samples) to show that microscopic features shaped as categorical variables, corresponding to intrinsic properties of mark structure, can accurately discriminate both types of bone modifications. We also implement new deep-learning methods that objectively achieve the highest accuracy in differentiating cut marks from crocodile tooth scores (99% of testing sets). The present study shows that there are precise ways of differentiating both taphonomic agents, and this invites taphonomists to apply them to controversial paleontological and archaeological specimens.

Microstructure anomaly during welding and its influence on the mechanical properties of dissimilar weldments of P92 martensitic steel and AISI 304L austenitic stainless steel

In this investigation, microstructural characteristics, mechanical properties, and residual stress magnitude of dissimilar weld joints (DWJs) between creep strength enhanced ferritic-martensitic (CSEF) P92 steel and austenitic stainless steel (ASS) 304L has been investigated. The Thermanit MTS 616 (P92 filler) filler metal was employed to prepare P92/304L SS DWJs. The groove geometry also plays a crucial role in DWJs, so the conventional V-groove and narrow shape groove geometry was adopted for P92/304L SS DWJs. The microstructure characterization was performed using optical microscope (OM), scanning electron microscope (SEM), and filed emission SEM (FESEM). The microstructural examination showed the formation of the δ-ferrite grains and unmixed zone (UZ) at the weld interface. The martensitic microstructure produced after welding is brittle due to quenched martensite and the dissolution of precipitates. Thus, the post-weld heat treatment (PWHT) known as tempering was carried out at 760 °C for the period of 2 h to get tempered martensitic microstructure. The ultimate tensile strength (UTS) of the as-weld (AW) and PWHT tensile specimen of the P92/304L SS DWJs was 660 MPa and 643 MPa, respectively for V-groove geometry specimens and 640 MPa and 609 MPa, respectively for narrow groove geometry specimens. The tensile fracture was experienced at 304L base metal, and the UTS value of DWJs was very close to the UTS of the 304L SS. The average microhardness value of the martensitic weld metal (352HV0.5) and coarse-grain heat-affected zone (CGHAZ, 366HV0.5), fine grain HAZ (FGHAZ, 320HV0.5) in the AW state was beyond the maximum permissible hardness value of 265HV0.5, as per the A335/A335M − 15a standard. The hardness value beyond 265HV0.5 indicates the undesirable brittle martensitic microstructure. After PWHT, the micro-hardness value of the CGHAZ (235HV0.5), FGHAZ (215HV0.5), and inter-critical HAZ (ICHAZ, 201HV0.5) was below the maximum allowable value of 265HV0.5 for P92 material because of the tempering of the quenched martensite. However, the Charpy test result concluded that the problem associated with the martensitic P92 filler is to obtain an acceptable value of the impact toughness of weld metal in AW state. The Charpy impact toughness of weld metal for P92/304L SS DWJs in AW condition was 10 J (V-groove geometry) and 37 J (narrow groove geometry), while for PWHT condition, it was 188 J (V-groove geometry) and 150 J (narrow groove geometry). The impact toughness of the P92 filler weld was below the minimum requirement of 47 J (EN ISO 3580:2017) in AW state. However, the impact toughness of the welds made by using P92 filler metal met the minimum requirement of 47 J (EN ISO 3580:2017) after PWHT due to the tempering of the martensite. The residual stress analysis using deep hole drilling (DHD) technique revealed the existence of the compressive residual stresses in the weld metal and P92 HAZ in as-weld and PWHT condition. The compressive stress was dominant because of the martensitic phase transformation.

Experimental thermodynamic analysis of automotive turbochargers using fluid film bearings with different groove shapes

Experimental thermodynamic analysis of automotive turbochargers using fluid film bearings with different groove shapes

Drug design and DNA structural research inspired by the Neidle laboratory: DNA minor groove binding and transcription factor inhibition by thiophene diamidines

The understanding of sequence-specific DNA minor groove interactions has recently made major steps forward and as a result, the goal of development of compounds that target the minor groove is an active research area. In an effort to develop biologically active minor groove agents, we are preparing and exploring the DNA interactions of diverse diamidine derivatives with a 5′-GAATTC-3′ binding site using a powerful array of methods including, biosensor-SPR methods, and X-ray crystallography. The benzimidazole-thiophene module provides an excellent minor groove recognition component. A central thiophene in a benzimidazole-thiophene-phenyl aromatic system provides essentially optimum curvature for matching the shape of the minor groove. Comparison of that structure to one with the benzimidazole replaced with an indole shows that the two structures are very similar, but have some interesting and important differences in electrostatic potential maps, the DNA minor groove binding structure based on x-ray crystallographic analysis, and inhibition of the major groove binding PU.1 transcription factor complex. The binding KD for both compounds is under 10 nM and both form amidine H-bonds to DNA bases. They both have bifurcated H-bonds from the benzimidazole or indole groups to bases at the center of the -AATT- binding site. Analysis of the comparative results provides an excellent understanding of how thiophene compounds recognize the minor groove and can act as transcription factor inhibitors.

Erosion wear resistance mechanism of erosion ripples

Erosion ripples widely exist on natural and industrial surfaces suffering gas–solid flow erosion. During the steady state of erosion ripples formation, the material removal and plastic flow rate of the material basically reach a dynamic equilibrium. In this state, the erosion rate of the surface material is steady and at a low level. In this paper, the relationship between erosion ripples and the erosion characteristics of surface materials was explored by experimental and simulation methods. Under the conditions of air pressures of 0.3, 0.4 and 0.5 MPa and erosion angles of 30°, 40° and 50°, several erosion ripples were prepared on the surface of 1060 aluminium alloy samples by sandblasting. According to the obtained morphological parameters and orthogonal test design, rippled samples with rectangular, triangular and semicircular groove sections were designed. The effect of morphology parameters on the erosion resistance of the sample was analysed by a sandblasting test. The results showed that the rippled samples have lower erosion rates than the plate sample. The cross-sectional shape of grooves is the most obviously affected factor. The velocity distribution and surface pressure distribution on the surface of rippled and plate samples were analysed by FLUENT software, and the results showed that the low-speed reflow vortex will be formed in grooves of erosion ripples that can change the near-wall flow field conditions. The differential pressure generated on two sides of the ridge between adjacent grooves, as well as the area decrease of erosion caused by the “shaded effect,” may be the cause of the erosion resistance. The results of this study can provide new insight into the active erosive wear resistance method of mechanical components.

Bending stiffness prediction to mass timber panel-concrete composite floors with notched connections

Mass timber panel-concrete composite floors consist of bottom timber panels, a top concrete layer, and a connection system in between. Notched connections made by filling concrete into the grooves cut on timber are one of the most structurally effective and cost-saving solutions to connect concrete topping to mass timber panels. However, the notched connections are not standardized due to various shapes of grooves and reinforcing techniques, and design guidelines are inadequate in terms of effective measures to achieve high composite efficiencies in notch-connected composite floors. This study developed an empirical formula to determine the shear stiffness of notched connections based on numerical modeling. The proposed formula was verified by comparing the predicted floor bending stiffness using the discrete bond composite beam model with the test results. A parametric study was then carried out to study the effects of geometry factors, including notch depth, timber shear length, number of notches, and thickness of concrete, on the overall bending stiffness of the composite floor. It has been found that the maximum composite efficiency in a mass timber panel-concrete composite floor can be achieved through optimizing the number, size, and locations of notches. The analytical and numerical investigations on the composite floors also demonstrate that in a certain range the thickness ratio between concrete and timber has little impact on the composite floor bending stiffness.

Horizontal Chimney Effect

Abstract An analysis of natural convection in horizontal slots has been carried out. It is demonstrated that a proper combination of heating and groove patterns can create a net horizontal fluid movement, which we refer to as the horizontal chimney effect. Groove shapes that can be easily manufactured as well as heating patterns that can be easily created using heating wires were considered. It has been shown that both patterns must be properly tuned. The direction of the net horizontal flow can be changed by changing the relative positions of the patterns. Changes of groove geometry can change the flow rate by up to 100%. Simultaneous use of grooves and heating at both plates can nearly double the system effectiveness. The strength of the flow increases with reduction of the Prandtl number.

Influence of Fluid Film Bearings with Different Axial Groove Shapes on Automotive Turbochargers: An Experimental Study

Most commercial automotive turbochargers (TC) employ semi-floating ring bearings (SFRB) with axial groove shapes. In order to bring some insights into the role played by the axial groove geometry on the dynamics of TC, this work deals with an experimental study of the rotordynamic behavior of a stock automotive turbocharger operating on SFRB with two different groove shapes, which have the same volume and width, and with the same number of grooves. The rotating machine behavior has been evaluated under different operating conditions using a test bench specially designed to analyze turbochargers. Rotordynamic (RD) characteristics of automotive turbochargers are estimated to evaluate the influence of the axial groove geometry on the machine vibratory behavior. Frequency spectra and orbital plots of the rotor are obtained from accelerometers and proximity probes mounted on the turbocharger. The comparative analysis of the vibrational behavior of automotive turbochargers running on different supporting systems allows the identification of the role played by the axial grooves on the machine rotordynamic performance. The experimental results rendered in this work permit to classify the influence of the axial groove geometry on the turbocharger rotordynamic behavior for several speed and flow conditions.

Flow Control Mechanism of Blade Tip Bionic Grooves and Their Influence on Aerodynamic Performance and Noise of Multi-Blade Centrifugal Fan

To improve the aerodynamic performance and reduce the noise of multi-blade centrifugal fans used in air conditioners, a bionic groove structure was introduced into the blade tip design, inspired by the drag reduction characteristics of mantis shrimp. In this paper, the numerical method was used to investigate the effects of a blade tip bionic groove on the aerodynamic performance and noise characteristics of a multi-blade centrifugal fan. Firstly, the basic design parameters, such as groove width, groove depth, groove center distance, and groove number, were selected to define the shape of the blade tip bionic groove. Then, the effect of the design parameters on the aerodynamic performance of the multi-blade centrifugal fan was studied. Finally, the multi-blade centrifugal fan models with different groove shapes, such as rectangular bionic grooves, circular bionic grooves, and triangular bionic grooves, were established to compare the influence of blade tip groove structures on the aerodynamic performance of the multi-blade centrifugal fan. Through analysis of the aerodynamic performance and noise characteristics of the multi-blade centrifugal fan and the flow fields in the fan impeller, the flow control mechanism of the blade tip bionic groove was revealed. The results showed that the triangular bionic groove on the blade tip had a certain noise reduction effect, although the structural parameters of the bionic groove had little effect on the aerodynamic performance of the multi-blade centrifugal fan. This is because the triangular bionic groove structure can effectively inhibit the vortex shedding at the trailing edge of blade and reduce the flow separation in the impeller passages. As a result, the velocity distribution at the impeller tip became more uniform and the intensity of the tip vortex and the shedding vortex was weakened. Correspondingly, the noise of multi-blade centrifugal fan was also reduced to some extent.

Texturing design of WC-Co through laser parameter selection to improve lubricant retention ability of cutting tools

Laser Surface Texturing (LST) is widely used to modify hard material surfaces improving their physic-chemical and mechanical properties. This technology is particularly relevant for tungsten carbides, a material that requires high complexity methods when other micro-machining processes are used. LST allows innovative cutting tool designs that improve the machining behavior and enlarge the cutting tool lifetime.This research analyses the influence of LST parameters on the track dimensions, roughness, microstructure, hardness, and lubricant retention ability of the modified surfaces. Twelve combinations of energy density of pulse and scanning speed created different geometrical patterns on WC-Co surfaces. LST parameters were related to specific shape and dimensions of the linear grooves. Energy density was proven as the most influential parameter for dimensional characteristics and roughness values. Specific channel morphologies increased the lubricant expansion area up to 50%, leading the lubricant to a linear track direction. Low scanning speed and high energy density also increased the surface hardness up to 20%. The surface composition was also modified. The thermal effect of the laser treatments and the non-protective atmosphere increased the oxygen on the surface and modified the WC-Co microstructure. However, the thermal affected zone is considerably low compared to other texturing processes.

Influence of bionic texture coronary stent on hemodynamics after implantation

To explore the influence of bionic texture coronary stents on hemodynamics, a type of bioabsorbable polylactic acid coronary stents was designed, for which a finite element analysis method was used to carry out simulation analysis on blood flow field after the implantation of bionic texture stents with three different shapes (rectangle, triangle and trapezoid), thus revealing the influence of groove shape and size on hemodynamics, and identifying the optimal solution of bionic texture groove. The results showed that the influence of bionic texture grooves of different shapes and sizes on the lower wall shear stress region had a certain regularity. Specifically, the improvement effect of grooves above 0.06 mm on blood flow characteristics was poor, and the effect of grooves below 0.06 mm was good. Furthermore, the smaller the size is, the better the improvement effect is, and the 0.02 mm triangular groove had the best improvement effect. Based on the results of this study, it is expected that bionic texture stents have provided a new method for reducing in-stent restenosis.

Improving the electrical performance of a carbon fiber reinforced polymer bipolar plate using a resin squeeze-out preprocess

Carbon fiber reinforced polymer (CFRP) is attracting attention as a bipolar plate (BP) material for proton-exchange membrane fuel cells (PEMFCs) due to its high specific stiffness, strength and chemical resistance. However, the low electrical conductivity of CFRP acts as an obstacle in its application, and various studies have been conducted to improve its areal specific resistance (ASR). In particular, the electrical performance of channel-shaped BPs has been dramatically reduced because the resin flow of CFRP was blocked by the groove shape. In this study, the electrical conductivity of a channel-shaped CFRP BP was improved by a preprocess of resin squeezing out. Resin squeeze-out conditions were determined based on the resin viscosity and degree of cure (DoC). Using the resin squeeze-out process, extra resin was removed, and the carbon fiber volume fraction increased by inducing proper resin flow. The mechanical properties and electrical performance of the CFRP BPs were evaluated according to a 2025 Department of Energy (DOE) technical target. Through the optimal resin squeeze-out process, the electrical and mechanical properties of the channel-shaped CFRP BP were improved to satisfy the 2025 DOE target.

Aesthetic reconstruction of the scar contracture deformity in chin and neck with expanded flaps based on the "MRIS" principle

Objective: The surgical reconstruction strategy for scar contracture deformity in chin and neck was explored, aiming to obtain better aesthetic outcome. Methods: A retrospective observational study was conducted. From December 2017 to April 2021, 34 patients with scar contracture deformity in chin and neck after burns were hospitalized in the Department of Plastic Surgery of the First Affiliated Hospital of Army Medical University (the Third Military Medical University), aged 12-54 years, including 13 males and 21 females, 4 cases with chin affected only, 7 cases with neck affected only, and 23 cases with both chin and neck affected. The scar areas were 48-252 cm2. All the patients were treated by operation with expanded flaps, following the "MRIS" principle of matching of the color and thickness of the repair flaps (match), reconstructing of the aesthetic features of subunits (reconstruction), design of incision according to the plastic principle (incision), and prevention of the surgical incision scar (scar). The rectangular or kidney shaped skin and soft tissue expander (hereinafter referred to as the expander) with rated capacity of 80-400 mL was embedded in the first stage, which was routinely expanded to 3-5 times of the rated capacity of the expander. In the second stage, scar resection and expanded flap excision were performed to repair the secondary wound, and the flap donor site was sutured directly. The expansion ratio of the expander (with average value being calculated), the type of flaps used, the reconstruction of local aesthetic morphology, the appearance of postoperative incision, the survival of flap, and the situation of donor and recipient sites observed during follow-up were recorded. Results: Among the 34 patients, the average expansion ratio of the implanted expander was 3.82 times of the rated capacity of the expander. Three cases were repaired by the expanded local pedicled flap only, 19 cases by the expanded shoulder and/or chest perforator pedicled flap only, 10 cases by the expanded local pedicled flap combined with the expanded shoulder and/or chest perforator pedicled flap, and 2 cases by the expanded local pedicled flap combined with the expanded free flap of the second intercostal perforator of internal thoracic artery. After scar resection, the shapes of lower lip and chin-lip groove were reconstructed in 10 cases, chin process reconstruction and chin lengthening were performed in 16 cases, and the cervico-mental angle and mandibular margin contour were reconstructed in 28 cases. The surgical incision was concealed, most of which were located at the natural junction or turning point of the chin and neck subunits. The vertical incision of neck was Z-shaped or fishtail-shaped. All the expanded flaps in 34 patients survived after operation, of which 8 patients had minor necrosis at the edge or tip of the expanded flaps 1-3 days after operation and healed after dressing change. During the follow-up of 3-18 months, little difference in color and thickness between the expanded flap and the skin of chin and neck was observed, and the aesthetic shape of chin and neck was significantly improved, with mild scar hyperplasia of surgical incision. Conclusions: Reconstruction of scar contracture deformity in chin and neck by using expanded flaps based on the "MRIS" principle is beneficial to improve the quality of surgery and achieve better aesthetic outcome.

Flow visualization of non-contacting mechanical seals with bidirectional rotation

Abstract Non-contacting mechanical seals are used as a shaft seal in a turbomachinery. A few micrometers thin lubrication film is formed by grooves on the seals. Various groove shapes were presented, and most of these grooves were designed for unidirectional rotation. However, reverse rotation occurs accidentally in the turbomachinery. In this study, the performance of two type unidirectional grooves was investigated by measuring the pressure in a chamber which means sealed fluid pressure and visualizing the flow in the lubrication film with bidirectional rotation. The measurement results of pressure under forward rotation showed that the pressures fluctuated as rotational speeds increased by hydrodynamic pressure. By contrast, under reverse rotation, the amount of fluctuation was smaller and almost not changed with increasing rotational speeds. In addition, the flow visualization results showed the increase of pressure drop areas and occurrence of gas phase. This indicates the decrease in load capacity and film stiffness. In contrast, the discharging flow from inner to outer side or the breakage of the film were confirmed and prevented fluid leaking. In summary, the results showed the degradation of lubrication characteristics though the no degradation of a sealing performance.