Lateral Slots Research Articles

Microbial composition and diversity in intraradicular biofilm formed in situ: New concepts based on next-generation sequencing.

This study aimed to characterize the taxonomic composition of intraradicular multispecies biofilms (IMB) formed in situ in a model to reproduce clinical conditions. Twelve palatal roots of maxillary molars had its canals prepared. Two roots were randomly selected to sterility control. Ten intraoral prosthetic appliances with lateral slots were fabricated. The roots were positioned in the slots with the canal access open to the oral cavity. Eight volunteers wore the appliance for 21 days, and two wore it at two different time points. One root from each appliance was removed and stored at -20°C until DNA extraction and sequencing (n=10). Biofilm was analyzed using next-generation sequencing and bioinformatics. The V4 hyper-variable region of the 16SrRNA gene was amplified and sequenced. For data analyses, the mothur pipeline was used for 16SrRNA processing, and subsequent analyses of the sequence dataset were performed in R using the Microbiome Analyst R package. The taxonomy-based analysis of bacterial communities identified 562 operational taxonomic units (OTUs), which belonged to 93 genera, 44 families, and 8 phyla. Bacterial colonization was different for each biofilm, and samples did not have the same group of bacteria. Alpha and beta diversity analysis revealed some general patterns of sample clustering. A core microbiome of prevalent OTUs and genera was identified. IMBs were heterogeneous when analyzed individually, but some diversity patterns were found after sample clustering. The experimental model seemed to reproduce the actual biofilm composition in endodontic infections, which suggests that it may be used to evaluate disinfection protocols.

Microbial composition and diversity in intraradicular biofilm formed in situ: New concepts based on next-generation sequencing.

This study aimed to characterize the taxonomic composition of intraradicular multispecies biofilms (IMBs) formed in situ in a model to reproduce clinical conditions. Twelve palatal roots of maxillary molars had its canals prepared. Two roots were randomly selected to sterility control. Ten intraoral prosthetic appliances with lateral slots were fabricated. The roots were positioned in the slots with the canal access open to the oral cavity. Eight volunteers wore the appliance for 21 days, and two wore it at two different time points. One root from each appliance was removed and stored at -20°C until DNA extraction and sequencing (n=10). Biofilm was analyzed using next-generation sequencing and bioinformatics. The V4 hyper-variable region of the 16SrRNA gene was amplified and sequenced. For data analyses, the mothur pipeline was used for 16SrRNA processing, and subsequent analyses of the sequence dataset were performed in R using the MicrobiomeAnalyst R package. The taxonomy-based analysis of bacterial communities identified 562 operational taxonomic units (OTUs), which belonged to 93 genera, 44 families, and 8 phyla. Bacterial colonization was different for each biofilm, and samples did not have the same group of bacteria. Alpha and beta diversity analysis revealed some general patterns of sample clustering. A core microbiome of prevalent OTUs and genera was identified. IMBs were heterogeneous when analyzed individually, but some diversity patterns were found after sample clustering. The experimental model seemed to reproduce the actual biofilm composition in endodontic infections, which suggests that it may be used to evaluate disinfection protocols.

Numerical investigation of flow and heat transfer in rotating trapezoidal channel with lateral slots and dimple structure

High-efficiency trailing edge cooling technology is essential for the safe and stable operation of turbine blades. In this paper, trapezoidal trailing edge channels with lateral slots are modeled, and a variety of dimples with different sizes and arrangement densities are placed on the end walls. Flow characteristics, wall heat transfer distributions and overall heat transfer performance under stationary and rotating states are numerically investigated and effects of dimple arrangement, rotation number (Ro) and channel orientation (β) are comprehensively analyzed. The results show that, under rotating state, the Coriolis force leads to the flow separation, while dimples promote the generation and development of three-dimensional spatial vortices, and effectively suppresses the expansion of separation area. Dimples greatly improve the rotating cooling performance, and there exists a critical point of arrangement density, in which the maximum heat transfer level is obtained. A 108.2% improvement in relative Nusselt number of trailing surface can be achieved by increasing rotation number in dimple channels. And the operation condition of Ro = 0.8 and β = 15° is recommended for the cooling of trapezoidal trailing edge. Compared with rotation number, the channel orientation has a stronger effect on the flow and heat transfer performances.

Effects of Channel Outlet Configuration and Dimple/Protrusion Arrangement on the Blade Trailing Edge Cooling Performance

The trailing edge regions of high-temperature gas turbine blades are subjected to extremely high thermal loads and are affected by the external wake flow during operation, thus creating great challenges in internal cooling design. With the development of cooling technology, the dimple and protrusion have attracted wide attention for its excellent performance in heat transfer enhancement and flow resistance reduction. Based on the typical internal cooling structure of the turbine blade trailing edge, trapezoidal cooling channels with lateral extraction slots are modeled in this paper. Five channel outlet configurations, i.e., no second passage (OC1), radially inward flow second passage (OC2), radially outward flow second passage (OC3), top region outflow (OC4), both sides extractions (OC5), and three dimple/protrusion arrangements (all dimple, all protrusion, dimple–protrusion staggered arrangement) are considered. Numerical investigations are carried out, within the Re range of 10,000–100,000, to analyze the flow structures, heat transfer distributions, average heat transfer and friction characteristics and overall thermal performances in detail. The results show that the OC4 and OC5 cases have high heat transfer levels in general, while the heat transfer deterioration occurs in the OC1, OC2, and OC3 cases. For different dimple/protrusion arrangements, the protrusion case produces the best overall thermal performance. In conclusion, for the design of trailing edge cooling structures with lateral slots, the outlet configurations of top region outflow and both sides extractions, and the all protrusion arrangement, are recommended.

The Whirl Cookstove: A Novel Development for Clean Biomass Burning

ABSTRACTAn innovation in cookstove design was developed through a simple change in the natural-draft air entrainment pattern. The new concept is based on the establishment of a whirl in the combustion chamber, with air being introduced only tangentially through lateral slots in the cookstove walls. The whirl configuration creates better mixing between fuel and oxidizer, more uniform burning, and a reduction in pollutant emissions. Water boiling tests revealed significant improvements with respect to the ordinary natural draft mode of operation, the so-called rocket mode, including: a 13% average increase in the thermodynamic efficiency and a decrease in total particulate emissions by 53%. In water simmering tests, the gain in thermodynamic efficiency is estimated at 24% and the reduction in particulate mass and number are 70% and 44%, respectively. The particle abatement is more significant for sizes larger than 0.5 um. A whirl retrofit can be introduced in almost any existing cookstove design and is well suited to scalable manufacturing of inexpensive stoves by casting them from an inexpensive mold.

The Richtmyer-Meshkov instability by diffracted incident shock waves and reshock

The developments of Richtmyer-Meshkov instability at gas interface subjected to a diffracted incident shock wave of low Mach number and reshock wave have been experimentally studied using the high-speed schlieren photography and laser sheet technique. The motionless and stable interface is formed in a vertical shock tube by using a downward flow of nitrogen (light gas N₂) and an upward flow of heavy gas SF₆, which meet at the desired interface location and exit from the lateral slots in the test section walls. The interaction yields of shock waves with rigid cylinder is complex, including the primary incident shock, reflected bow shock, Mach shock, slip lines originated from the triple Mach shock. The understanding of interaction of this with interface, will contribute to the knowledge of the perturbation originated from the complex flow. The planar shock wave diffracted over a cylindrical column produces local perturbation at the gas interface. It has been demonstrated that the thickness of the interface grows slowly under the incident shock wave, while spike and bubble are clearly observed upon reshock. Moreover, the interaction between the reshock wave and the boundary layer generates wall vortices, which enhances the development of Turbulence Mixing Zone (TMZ). The reflected rarefaction wave from wall-end also accelerates the development of TMZ.

Skirts and barriers for reduction of wayside noise from railway vehicles—an experimental investigation with application to the BR185 locomotive

An experimental investigation to determine the noise reduction efficiency of a number of combinations of vehicle mounted noise skirts and trackside low barriers has been carried out. A 1:4-scale mock-up of the German BR185 locomotive was built. Special care was taken to achieve a realistic representation of the wheel/rail sources, using rotating acoustic source wheels able to imitate the radiation from structural modes and acoustic rail ducts with independently adjustable vertical and lateral slots. The acoustic insertion loss (IL) equivalent to a full-scale microphone position at 25 m distance from the track was determined for the different source components separately. The total IL was obtained from sound power spectra calculated with the TWINS software. Results for the design speed ( v=120 km/h) and a case with a lower speed ( v=100 km/h) are presented to illustrate the effect of speed on the acoustic IL. The tests were performed in open-air free field conditions. The experimental procedure used in the present investigation gives detailed information on the relative contributions from different source components, which is valuable for further design studies. For the eight combinations reported here, the overall reduction achieved was in agreement with results in the literature. The IL was 2–3 dB(A) for cases with only vehicle skirts and the case with only low track barriers. The combined configurations had insertion losses of 7–13 dB(A).

Elastic buckling of plates with eccentrically positioned rectangular perforations

The conjugate load/displacement method is used to analyze square plates with perforations, and results are presented for geometries with rectangular holes offset from one or both axes of symmetry. Results are given for uniaxial and shear loading, and simply supported and fully fixed boundaries. Design guidance for the location of perforations and the effect of longitudinal or lateral slots is explained. The potential to increase the elastic critical load for an unperforated plate by the introduction of a small perforation is reported.

The behaviour and form of Psephenus herricki (DeKay) (Coieoptera: Psephenidae) in relation to water flow*

1. Psephenus herricki (DeKay) larvae were observed in aquaria and artificial streams using videomacroscopic techniques. Dye visualization was used to determine flow around the organisms.2. The highly flattened larvae of Psephenus herricki are able to withstand and/or avoid the force of flowing water in streams through a number of mechanisms. The legs are vital: if they cannot gain purchase the larvae can be dislodged by the lifting forces acting on the body. At the flow rates tested (up to 50 cm s−1), suction under the carapace is not needed to maintain position.3. Active pumping of water through lateral slots of the carapace and out from under the body posteriorly greatly reduces turbulence around the body and may act to decrease drag at high Reynolds numbers.4. An interpretation of the flattened body‐shape of Psephenus herrickilarvae as an adaptation to fast currents and/or to prevent the larvae from being removed from the substrate by a predator is of questionable ecological significance because individuals are usually found in crevices and on the undersides of stones.

The Effect of Slots on the Buckling and Postbuckling Behavior of Laminated Plates

An experimental study was conducted to evaluate the effect of lateral slots on the buckling response, the postbuckling response, and the failure characteristics of flat rectangular graphite-epoxy plates loaded in compression. The slots did not significantly affect the prebuckling and buckling behavior of the plates. The slots caused local changes in the strain distribution and out-of-plane deformations near the slot. Failure loads and modes were strongly affected by slot location. Centrally located slots did not affect the failure loads or failure modes of the plates. Slots located close to an unloaded edge of a plate reduced the postbuckling strength of the plate and affected the failure mode. For one slightly offset slot location, interaction of out-of-plane deformations with the slot tip was observed to affect the failure mode significantly without affecting the failure load.