A comparative CFD investigation of helical wire-wrapped 7, 19 and 37 fuel pin bundles and its extendibility to 217 pin bundle

Preliminary investigations of sodium flow and temperature distributions in heat generating fuel pin bundles with helical spacer wires have been carried out. Towards this, the 3D conservation equations of mass, momentum and energy have been solved using a commercial computational fluid dynamics (CFD) code. Turbulence has been accounted through the use of high Reynolds number version of standard k– model, with uniform mesh density respecting wall function requirements. The geometric details of the bundle and the heat flux in are similar to that of the Indian Prototype Fast Breeder Reactor (PFBR) that is currently under construction. The mixing characteristics of the flow among the peripheral and central zones are compared for 7, 19 and 37 fuel pin bundles and the characteristics are extended to a 217 pin bundle. The friction factors of the pin bundles obtained from the present study is seen to agree well with the values derived from experimental correlations. It is found that the normalized outlet velocities in the peripheral and central zones are nearly equal to 1.1–0.9, respectively which is in good agreement with the published hydraulic experimental measurements of 1.1–0.85 for a 91 pin bundle. The axial velocity is the maximum in the peripheral zone where spacer wires are located and minimum in the zones which are diametrically opposite to the respective zone of maximum velocity. The sodium temperature is higher in the zones where the flow area and mass flow rates are less due to the presence of the spacer wires though the axial velocity is higher there. It is the minimum in the peripheral zones where the circumferential flow is larger. Based on the flow and temperature distributions obtained for 19 and 37 pin bundles, a preliminary extrapolation procedure has been established for estimating the temperatures of peripheral and central zones of 217 pin bundle.     

Hash message authentication codes for securing data in wireless body area networks

There are numerous medical applications for the growing use of wireless body area networks (WBANs), including remote patient health monitoring, early illness detection, and computer-assisted rehabilitation. WBAN links many sensor nodes implanted or affixed to the human body to monitor physiological data. WBAN technology has the potential to benefit medical healthcare systems tremendously. However, the gathering and transferring sensitive physiological data in an unprotected environment raises severe security and privacy concerns. The limited resources and broadcast transmission of a WBAN pose grave safety issues in biomedical applications. Keeping sensitive patient data safe during broadcasts is critical in the healthcare business. As a result of the massive memory and processing requirements required by traditional public or private key architectures, tiny sensor nodes cannot use them. WBAN sensor nodes can communicate securely using the KHMAC key-agreement technique proposed in this article. Measurements and confirmations of shared physiological parameters at the transmitter and recipient sensors are key to the proposed protocol KHMAC before communication is established. The proposed KHMAC protocol enables sensors to use their prior session knowledge for secure communication within a predetermined time window. This will shorten the time it takes to establish a shared key, prevent the retransmission of extracted characteristics in the medium and eavesdropping attacks, and preserve the unpredictability of the key. Both the feature extraction and key agreement stages will be shown to have higher precision and lower error rates with KHMAC's proposed key management methodology. The proposed protocol is proven to be more energy and memory efficient than existing key agreement systems.     

TEA-CBRP: Distributed cluster head election in MANET by using AHP

Mobile Ad hoc Network consists of a set of mobile nodes that are communicating in a wireless channel. In this network, the number of nodes and their mobility have an impact on the routing performance. In order to improve the routing performance of large scale Mobile Ad Hoc Networks, clustering is one of the solution. When clustering is implemented, an unconditional cooperation among the intra cluster and inter cluster nodes is necessary. In the event where a malicious or selfish node is elected as a cluster head, the routing performance gets significantly affected. In this paper, the key decision factors such as the trust value, remaining energy, and the time of availability of the mobile node is explored to elect a cluster head. Further, these three decision factors are incorporated into the Analytical Hierarchy Process technique in order to elect the most cooperative node as the cluster head. An enhancement to the existing Cluster based Routing Protocol, is proposed in this paper and then enhanced work, is termed as Trust Energy Availability based Cluster Based Routing Protocol. A network based on the proposed protocol is simulated. The important routing performance parameters such as packet delivery ratio, end to end latency, routing packet overhead, and the number of times cluster head changes are discussed for the simulated network and the results are compared with AODV and CBRP routing protocols. The simulation results have shown that the proposed cluster based routing protocol improves the network performance by eliminating malicious and selfish nodes from being elected as cluster head.     

Turbulent flow simulation in a wire-wrap rod bundle of an LMFBR

The pressure drop and heat transfer characteristics of wire-wrapped 19-pin rod bundles in a nuclear reactor subassembly of liquid metal cooled fast breeder reactor (LMFBR) have been investigated through three-dimensional turbulent flow simulations. The predicted results of eddy viscosity based turbulence models (k-?, k-ω) and the Reynolds stress model are compared with those of experimental correlations for friction factor and Nusselt number. The Re is varied between 50,000 and 150,000 and the ratio of helical pitch of wire wrap to the rod diameter is varied from 15 to 45. All the three turbulence models considered yield similar results. The friction factor increases with reduction in the wire-wrap pitch while the heat transfer coefficient remains almost unaltered. However, reduction in the wire-wrap pitch also enhances the transverse flow velocity in the cross-sectional plane as well as the local turbulence intensity, thereby improving the thermal mixing of coolant. Consequently, the presence of wire wrap reduces temperature variation within each section of the subassembly. The associated reduction in differential thermal expansion of rods is expected to improve the structural integrity of the fuel subassembly.     

Effect of steam distillate extracts of selected resistant cultivated and wild rices on behavior of leaffolderCnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae)

Rice plant volatiles extracted as steam distillates significantly affected the behavior of the rice leaffolder,Cnaphalocrocis medinalis (Guenée). Leaffolder moths laid significantly fewer eggs on TN1 rice plants treated with extracts of resistant wild species of rice,Oryza officinalis andOryza punctata, than on TN1 plants treated with extracts of resistant cultivated rices. Extracts ofO. officinalis andO. punctata adversely affected egg hatchability.O. officinalis andO. punctata extracts were more toxic to first-instar larvae than extracts of other resistant varieties. Leaf area consumed by the larvae was reduced on TN1 plants treated withO. officinalis andO. punctata extracts compared with that on plants treated with extracts of resistant cultivated rice varieties.     

Box counting–based multifractal analysis of network to detect Domain Name Server attack

Domain Name Server (DNS) is a type of server used to maintain and process the IP addresses of all the domains in the Internet. It works by responding with corresponding IP addresses when a client requests with a domain name. The DNS can be attacked by redirecting all the incoming traffic to a fake server by returning fake IP address when requested by a client. In this work, a novel work has been employed to detect DNS attack using box‐counting method (BCM)–based multifractal analysis. A set of network features are selected and rules are created using CISCO's Flowspec model, and those features are analysed using BCM technique to find the attack in the network traffic. To the best of our knowledge, this is the first work that implements Flowspec‐based monitoring of DNS attack using fractal analysis.     

Effect of fluorine doping on the structural,optical and electrical properties of spray deposited cadmium stannate thin films

Cadmium stannate (Cd₂SnO₄) thin films were coated on Corning 1737 glass substrates at 540 °C by spray pyrolysis technique, from the aqueous solution of cadmium acetate and tin (II) chloride precursors. Fluorine doped Cd₂SnO₄ (F: Cd₂SnO₄) thin films were prepared by adding ammonium fluoride in the range of 0–5 wt% of the total weight of cadmium acetate and tin (II) chloride in the spray solution. Thickness of the prepared films is about 300 nm. X-ray diffraction analysis of the Cd₂SnO₄ and 3 wt% F: Cd₂SnO₄ films shows the signature for the growth along (222) direction. Scanning electron micrographs showed that fluorine doping effectively modifies the surface morphology of Cd₂SnO₄ films. Average optical transmittance in the visible region (500–850 nm) for Cd₂SnO₄ is ~79% and it is increased to ~83% for 1 wt% doping concentration of the NH₄F in the solution. Fluorescence spectra of F: Cd₂SnO₄ (1 wt% and 3 wt%) exhibit peak at 601 nm. F: Cd₂SnO₄ film (1 wt%) shows mobility of ~42 cm²/V s, carrier concentration of ~9.5×10¹⁹ cm^?3 and resistivity of ~1.5×10^?3 Ω cm.     

HotSpot: a dynamic compact thermal model at the processor-architecture level

This paper describes a thermal-modeling approach that is easy to use and computationally efficient for modeling thermal effects and thermal-management techniques at the processor architecture level. Our approach is based on modeling thermal behavior of the microprocessor die and its package as a circuit of thermal resistances and capacitances that correspond to functional blocks at the architecture level. This yields a simple compact model, yet heat dissipation within all major functional blocks and the heat flow among blocks and through the package are accounted for. The model is parameterized, boundary- and initial-conditions independent, and is derived by a structure assembly approach. The architecture community has demonstrated growing interest in thermal management, but currently lacks a way to model on-chip temperatures in a tractable way. Our model can be used for initial exploration of the design space at the architecture level. The model can easily be integrated into popular power/performance simulators, can be used to determine how thermal stress is correlated to the architecture, and how architecture-level design decisions influence thermal behavior and related effects.