An experimental study of near wall flow parameters in the blade end-wall corner region

The near wall flow parameters in the blade end-wall corner region is investigated. The blade end-wall corner region was simulated by mounting an airfoil section (NACA 65-015 base profile) symmetric blades on both sides of the flat plate with semi-circular leading edge. The initial 7 cm from the leading edge of the flat plate was roughened by gluing No. 4 floor sanding paper to artificially increase the boundary layer thickness on the flat plate. The initial flow conditions of the boundary layer upstream of the corner region are expected to dictate the behavior of flow inside the corner region. Therefore, an experimental investigation was extended to study the combined effect of initial roughness and increased level of free stream turbulence on the development of a 2-D turbulent boundary layer in the absence of the blade. The measurement techniques employed in the present investigation included, the conventional pitot and pitot-static probes, wall taps, the Preston tube, piezoresistive transducer and the normal sensor hot-wire probe. The pitot and pitot-static probes were used to obtain mean velocity profile measurements within the boundary layer. The measurements of mean surface static pressure were obtained with the surface static tube and the conventional wall tap method. The wall shear vector measurements were made with a specially constructed Preston tube. The flush mounted piezoresistive type pressure transducer were employed to measure the wall pressure fluctuation field. The velocity fluctuation measurements, used in obtaining the wall pressure-velocity correlation data, were made with normal single sensor hot-wire probe. At different streamwise stations, in the blade end-wall corner region, the mean values of surface static pressure varied more on the end-wall surface in the corner region were mainly caused by the changes in the curvature of the streamlines. The magnitude of the wall shear stress in the blade end-wall corner region increased significantly in the close vicinity of the corner line. The maximum value of the wall shear stress and its location from the corner line, on both the surfaces forming the corner region, were observed to change along the corner. These observed changes in the maximum values of the wall shear stress and its location from the corner line could be associated with the stretching and attenuation of the horseshoe vortex. The wall shear stress vectors in the blade end-wall corner region were observed to be more skewed on the end-wall surface as compared to that on the blade surface. The differences in the wall shear stress directions obtained with the Preston tube and flow visualization method were within the range in which the Preston tube was found to be insensitive to the yaw angle

Supercriticality to subcriticality in dynamo transitions

Evidence from numerical simulations suggest that the nature of dynamo transition changes from supercritical to subcritical as the magnetic Prandtl number is decreased. To explore this interesting crossover we first use direct numerical simulations to investigate the hysteresis zone of a subcritical Taylor-Green dynamo. We establish that a well defined boundary exists in this hysteresis region which separates dynamo states from the purely hydrodynamic solution. We then propose simple dynamo models which show similar crossover from supercritical to subcritical dynamo transition as a function of the magnetic Prandtl number. Our models show that the change in the nature of dynamo transition is connected to the stabilizing or de-stabilizing influence of governing non-linearities.Comment: Version 3 note: Found a sign-error in an equation which propagated further. Section 4 and Fig. 3,4,5 are updated in Version 3 (final form

Dynamic Properties of Fire Sprinkler Systems

Four fire protection systems have been attached to a small building model for testing their dynamic properties. Three of the systems used CPVC (fire rated) plastic pipes while the fourth was made from schedule-40 steel pipe. The building model was securely attached to a three by three foot shake table in one of two orientations and was able to experience base accelerations along both its principle axis (longitudinal, transverse). Test procedures involved sending a sine sweep with a progressively increasing frequency at a constant acceleration value. Various recording locations provided data showing fundamental frequencies with pronounced amplification over the base input accelerations. First the buildings natural frequencies were obtained. Then each sprinkler system was tested for acceleration values at the sprinkler drops. Sprinkler drops were affixed with an accelerometer at the fitting connection and one at the sprinkler head. Comparisons are made between the fundamental frequencies of the building and the fire sprinkler system. An analytical model of the four sprinkler systems was designed on the SAP2000 computer program. The test frequency range providing clean data was from 10 Hz – 25 Hz. In this range the computer analysis identified all of the first observed fundamental frequencies. The SAP2000 Analysis also identified the distinct second fundamental frequencies obtained from testing. Large acceleration amplifications were observed at fundamental frequencies in the building and in the sprinkler systems. The largest amplification was sixty times that of the base input experienced by one of the CPVC drops. The steel sprinkler line also experienced large amplification values of up to 35 times the base level acceleration. The fire systems were filled with water to simulate a wet-system and to indicate potential failures. No failures occurred in any of the four test systems. After testing each sprinkler design multiple times it is concluded that sprinkler systems should remain functional following a seismic event. Sprinkler systems installed to NFPA-13 code (National Fire Protection codebook) standards have been proven to perform in earthquakes as well as the structures they’re attached to. Improper connectors and lack of required pipe clearances are the main factors attributed to researched fire system failures

Hardware Implementation of Efficient Elliptic Curve Scalar Multiplication using Vedic Multiplier

This paper presents an area efficient and high-speed FPGA implementation of scalar multiplication using a Vedic multiplier. Scalar multiplication is the most important operation in Elliptic Curve Cryptography(ECC), which used for public key generation and the performance of ECC greatly depends on it. The scalar multiplication is multiplying integer k with scalar P to compute  Q=kP, where k is private key and P is a base point on the Elliptic curve. The Scalar multiplication underlying finite field arithmetic operation i.e. addition multiplication, squaring and inversion to compute Q. From these finite field operations, multiplication is the most time-consuming operation, occupy more device space and it dominates the speed of Scalar multiplication. This paper presents an efficient implementation of finite field multiplication using a Vedic multiplier.  The scalar multiplier is designed over Galois Binary field GF(2233) for field size=233-bit which is secured curve according to NIST.  The performances of the proposed design are evaluated by comparing it with  Karatsuba based scalar multiplier for area and delay. The results show that the proposed scalar multiplication using Vedic multiplier has consumed 22% less area on FPGA and also has 12% less delay, than Karatsuba, based scalar multiplier. The scalar multiplier is coded in Verilog HDL, synthesize and simulated in Xilinx 13.2 ISE on Virtex6 FPGA

Barrier Properties of Graphene-Based Polymer Nanocomposites

Exfoliated graphite nanoplatelets (herein called graphene) are nanometer-thin platelets that are being extensively researched for their high stiffness, thermal conductivity, mass transfer barrier properties, and electrical conductivity towards developing a wide range of applications such as polymer nanocomposites (PNCs). These graphene-based PNCs (GPNCs) are expected to have better properties as compared to PNCs made using carbon nanotubes or nano-layered silicates. Graphene platelets are generally hydrophilic in nature hence difficult to disperse in polymers. In the work described here, surface treatment of graphene using 3-aminopropyltrimethoxysilane (APTMS), as shown by energy dispersive x-ray spectroscopy (EDS), results in more hydrophobic graphene which shows better dispersion. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images illustrate the effect of surface treatment on the dispersion of graphene into polyvinyl acetate (PVAc). Barrier properties of treated and untreated graphene in PVAc were measured by sorption tests of GPNCs in water at various filler concentrations and different platelet diameters which show that the graphene platelets form an excellent barrier against diffusion

Breast Tumor Recognition by Semantic Segmentation of Multiclass Ultrasound Images

Objectives: The main purpose of this paper is to suggest a semantic segmentation model to reduce training time in ultrasound breast cancer images. This is achieved by employing a smaller network with fewer trainable parameters, resulting in faster training while maintaining maximum accuracy. Methods: This paper proposes a modified U-Net model, which we call the V model, for the subdivision of breast tumors. The proposed V architecture is applied explicitly to ultrasound breast cancer datasets for semantic segmentation. Our proposed model achieves semantic segmentation by employing an encoder and decoder on real and mask image datasets. Findings: Therefore, developing a proposed system, namely a V-Net computer-aided diagnosis (CAD) system, is imperative. This CAD system aims to minimize human errors while enhancing accuracy and speed in the premature finding of breast tumors. The proposed model utilizes minimal layers and parameters while maintaining superior results regarding correctness, speed, and computational proficiency. Novelty: The proposed V-net model applies to analysing any medical image for detecting disease and finding more accuracy than other U-net models

BIOCOMPATIBILITY STUDIES OF SILVER DOPED HAP/ALUMINA BY SOL-GEL METHOD

Silver doped hydroxyapatite (Ag- HAP) coated of alumina having antibacterial properties is of great interest for the development of new biomedical applications. In the current study pure hydroxyapatite (HAP), 1.5wt% (0.9gm)Ag doped in hydroxyapatite (Ag-HAP) coated on alumina disk were processed and characterized. Pure HAP and Ag-HAP were synthesized using the sol-gel method. Calcium nitrate tetrahydrate Ca(NO3)2.4H2O as a source of Ca precursor, phosphorous pentaoxide (P2O5) as a source of P precursor and Silver Nitrate (AgNO3) as a source of Ag precursor were used. Samples were characterized using SEM, FTIR, ECA (in Ringer's solution) and OCA. SEM study shows the granular like Ag-HAP. The formation HAP and Ag-HAP was confirmed using FTIR and XRD. Wettability study shows that the surface of Ag-HAP is more hydrophilic as compared to pure HAP Samples. Corrosion study reveals that Ag-HAP has lesser corrosion rate as compared to HAP. There is no toxic effect of Ag-HAP as found by bacterial cell culture test