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The bioprinting technique with specialized tissue production allows the study of biological, physiological, and behavioral changes of cancerous and non-cancerous tissues in response to pharmacological compounds in personalized medicine. To this end, to evaluate the efficacy of anticancer drugs before entering the clinical setting, tissue engineered 3D scaffolds containing breast cancer and derived from the especially patient, similar to the original tissue architecture, can potentially be used. Despite recent advances in the manufacturing of 3D bioprinted breast cancer tissue (BCT), many studies still suffer from reproducibility primarily because of the uncertainty of the materials used in the scaffolds and lack of printing methods. In this review, we present an overview of the breast cancer environment to optimize personalized treatment by examining and identifying the physiological and biological factors that mimic BCT. We also surveyed the materials and techniques related to 3D bioprinting, i.e, 3D bioprinting systems, current strategies for fabrication of 3D bioprinting tissues, cell adhesion and migration in 3D bioprinted BCT, and 3D bioprinted breast cancer metastasis models. Finally, we emphasized on the prospective future applications of 3D bioprinted cancer models for rapid and accurate drug screening in breast cancer.

Carbon based nanomaterials have attracted attention due to their exceptional physical, chemical and biological properties, which make them promising candidates in transforming the future of various critical applications. The intense demand to develop carbon nanomaterials via environment-friendly and inexpensive synthesis strategies have been driving a significant proportion of efforts globally. Precursors utilized for the growth of carbon based nanomaterials play a crucial role toward the success of the evolving technology. Most conventional synthesis techniques employ expensive carbon feedstocks such as hydrocarbons and graphite which lead to high cost of production and hence limit their commercialization. Coal, an abundant and cheap natural resource, is considered a green and viable alternative to effectively generate carbon nanomaterials such as carbon nanotubes, nanofibers/particles/spheres, graphene, graphene oxide, graphene quantum dots and carbon dots. Our review includes recent advances in the production of various carbon based nanomaterials from various types of coal (lignite, bituminous, anthracite among others) as raw materials and outlines their potential applications in the energy, environmental and biomedical sectors.

Floating car data (FCD) refers to the motion and sensor data produced by moving vehicles on the road. Given that traffic management authorities and drivers can benefit from FCD enormously, there is an urgency to develop efficient FCD collection and dissemination techniques that scale with peak road traffic. In this paper, we present CarAgent, a message exchange protocol that periodically collects and uploads FCD to data centres with the minimal utilisation of existing mobile network resources. We also show how CarAgent can be easily extended to efficiently disseminate FCD to all vehicles in a target area using Dedicated Short Range Communication (DSRC), a recently released wireless communication standard for vehicles. We analytically derive the key performance metrics of CarAgent and validate them with simulations. We evaluate CarAgent using microscopic simulation of road traffic in real street maps while incorporating wireless protocol details of Long Term Evolution (LTE) and DSRC. Simulation results confirm that, compared to the state-of-the-art, CarAgent consumes 50% less LTE resources for FCD collection. For FCD dissemination, CarAgent consumes 45% less DSRC resources while improving the speed of dissemination significantly.

Biocompatible and photostable fluorescent probes are crucial yet challenging to develop for visualising and tracking biological functions and interactions that occur in living organisms. We synthesised biocompatible CQDs with 15% QY and tested them for cellular and scaffold imaging at variable depths. The CQDs, synthesised from collagen under controlled and benign conditions in a hydrothermal reactor, were characterised for their key physicochemical properties. The fluorescence characteristics were determined using two-photon microscopy, and based on our results we propose a mechanism for CQD luminescence by combining the carbogenic core and edge-effect contributions to the PL behaviour. The bioimaging of cells embedded in a luminescent 3D printed scaffold showed that CQDs enable imaging at depths of about 1500 μm under biomimetic conditions. Real-time videography and imaging tests showed differential visualisation of individual cells and scaffold. The excellent photostability and non-photobleaching characteristics of CQDs make them suitable for long-term whole cell and tissue imaging via multi-photon microscopy.

How to effectively delivering therapeutic agents, including γ-secretase inhibitors (GSIs), into live cells, remains a significant challenge. This study assessed the effect of Notch signaling inhibition by examining levels of the Notch1 intracellular domain (N1ICD) in cultured oral cancer cells analyzed with random stitched images (2D) and 3D visualizations using confocal microscopy and quantitative gene analysis. Substantially, we have developed a novel method to assist the delivery of γ-secretase inhibitor, DAPT, into live cells in the presence of an effective minimum concentration of Triton-X100 (0.001%) without damaging cell activity and membrane integrity assessed with cell proliferation assays. The images obtained in this study showed that DAPT alone could not block the γ-secretase inhibitor despite inhibiting cell growth. Further analysis of quantitative gene expressions of Notch signaling canonical pathway to verify the effectiveness of the novel method for delivering inhibitor into live cells, displayed deregulation of Notch1, Delta-like ligand 1 (DLL1) and hairy and enhancer of split 1 (Hes1). Our data suggest that Notch1/Hes1 signaling pathway is deactivated using DAPT with a low dose of Triton-X100 in this cancer cells. And the finding also suggests that Notch1 could be engaged by DLL1 to promote differentiation in oral cancer cells. Using this approach, we demonstrate that Triton-X100 is a promising and effective permeabilization agent to deliver γ-secretase inhibitor DAPT into live oral epithelial cells. This strategy has the potential to implicate in the treatment of cancer diseases.

Functional metastructures exhibiting unique optical properties are desirable for advancements in microfluidics, optoelectronics, nonlinear photonics, biochemical sensing, and metamaterials. Additive manufacturing techniques are expected to enable rapid prototyping of complex 3D architectonics required for such applications. We report the fabrication of highly fluorescent all-organic metastructures via carbon quantum dot assisted in-situ polymerization of acrylate and carbon dot composite resin. The polymerized structures fabricated from acrylate and carbon dot composite resin exhibit excellent linear and nonlinear optical properties due to the presence of two-photon active carbon quantum dots incorporated in the resin. By activating the two-photon process, we eliminated the need for adding two-photon absorbing toxic chemicals for initiating the polymerization process. The fabrication of functional nanostructures using acrylate and carbon dot composite resin opens the door for rapid prototyping of metastructures for various applications such as developing functional metamaterials, solid-state lighting, live monitoring of cells in cultures, fluorescent tagging and detection of counterfeiting among others.

A new model is here proposed to investigate the effects of nano-ferroliquid under the influence of low oscillating over stretchable rotating disk. The basic governing equations are formulated under the effects of magnetic field. The resulting system of partial differential equations is first reduced in non-dimensional form by using proper transformations and then reduced coupled system of differential equations is solved analytically by means of homotopy analysis method (HAM). The physical interpretation of velocity and temperature towards different emerging parameters such as particle concentration and effective magnetization parameter are discussed graphically. The physical parameters such as shear stress at wall, heat transfer rate through wall, boundary layer thickness and volume flow rate in axial direction are also presented in tabular form. Finally a comparison with the existing literature is made as a limiting case of the reported problem and found in good agreement.

Porous nitrogen-doped graphene samples were synthesized and tuned via pyrolysis of solid nitrogen precursor dimethyl-aminoterephthalate with graphene oxide as template. Our investigations show that the extent of thermal treatment, total concentration of nitrogen and the nature of nitrogen moieties play important roles in enhancing oxygen reduction reaction (ORR) and CO 2 uptake. N-doped graphene synthesized at 650 °C (NG-650) with specific BET surface area of 278 m 2 /g, exhibits enhanced CO 2 sorption capacity of 4.43 mmol/g (at 298 K, 1 bar) with exceptional selectivity (CO 2 :N 2 = 42) and cyclic regeneration stability. In contrast, nitrogen-doped graphene synthesized at 750 °C (NG-750) demonstrated excellent catalytic activity for ORR via favourable 4e − transfer, performance stability with tests conducted up to 5000 cycles, and is unaffected by methanol cross-over effect. Thus, NG-750 shows potential to replace metal-based electrodes for fuel cell application. The comparative results for ORR with non-doped and nitrogen-doped graphene electrodes showed that graphitic nitrogen sites play vital role in enhancing catalytic activity.

We characterize terahertz wireless channels for extracting data from nanoscale sensors deployed within human lungs. We discover that the inhalation and exhalation of oxygen and carbon dioxide causes periodic variation of the absorption coefficient of the terahertz channel. Channel absorption drops to its minimum near the end of inhalation, providing a window of opportunity to extract data with minimum transmission power. We propose an algorithm for nanosensors to estimate the periodic channel by observing signal-to-noise ratio of the beacons transmitted from the data sink. Using real respiration data from multiple subjects, we demonstrate that the proposed algorithm can estimate the minimum absorption interval of the periodic channel with 98.5% accuracy. Our analysis shows that by confining all data collections during the estimated low-absorption window of the periodic channel, nanosensors can reduce power consumption by six orders of magnitude. Finally, we demonstrate that for wireless communications within human lungs, 0.1–0.12 THz is the least absorbing spectrum within the terahertz band.

Internet browsing over cellular networks is a major source of power consumption in mobile devices. A device could potentially reduce its browsing power consumption by downloading a page from the browser cache of a proximate device over the short-range low-power non-cellular device-to-device (D2D) wireless link, such as Bluetooth. Using an Android-based cooperative browser prototype, this paper experimentally characterizes the power saving opportunity of such D2D cache cooperation. In particular, we model the impact of cellular network power management protocol and the dynamic components of web pages on the power saving of D2D cooperation. We find that the power saving is limited (upper bounded) by the power management parameter values of cellular networks, which could vary significantly from operator to operator. Based on previously reported cellular power management data and the data obtained from our own experiments, the upper bound can vary from as low as 15-51%. Our model also shows that the existence of dynamic components in the web page decreases the power saving further proportional to the amount of dynamic components. We validate the model with power measurement data from smartphones using real cellular networks for Internet access and Bluetooth connectivity for D2D cache access. By downloading most popular web pages and studying the distribution of their dynamic components, we find that the expected amount of dynamic component in a popular page is rather small, allowing D2D cooperation to achieve device power saving close to (95% of) its upper bound.

We study a networking scenario for 5G and beyond, called DroneCells, where miniaturized base stations (BSs) are mounted on flying drones to serve mobile users. We propose that the drones never stop, and move continuously within the cell in a way that reduces the distance between the BS and the serving users, thus potentially improving the spectral efficiency of the network. By considering the practical mobility constraints of commercial drones, we design drone mobility algorithms to improve the spectral efficiency of DroneCells. We propose a range of practically realizable heuristics with varying complexity and performance. Simulations show that, using the existing consumer drones, the proposed algorithms can readily improve spectral efficiency by 34% and the 5-percentile packet throughput by 50% compared to the scenario, where drones hover over fixed locations. More significant gains can be expected with more agile drones in the future. A surprising outcome is that the drones need to fly only at minimal speeds to achieve these gains, avoiding any negative effect on drone battery lifetime. We further demonstrate that the optimal solution provides only modest improvements over the best heuristic algorithm, which employs Game Theory to make mobility decisions for drone BSs.

It is reported that mobile users spend most of their time on texting SMS, Social Networking, Emailing, or sending instant messaging (IM), all of which involve text input. There are three primary text input modalities, soft keyboard (SK), speech to text (STT) and Swype. Each one of them engages a different set of hardware and consequently consumes different amounts of battery energy. Using high-precision power measurement hardware and systematically taking into account the user context, we characterize and compare the energy consumption of these three input modalities. We find that the length of interaction, or the message length, determines the most energy efficient modality. For short interactions, less than 14-30 characters, SK is the most energy efficient. For longer interactions, however, STT significantly outperforms both SK and Swype. When message length distributions of popular text activities are considered, STT provides near optimal energy consumption without requiring the user to predict the message length and decide between SK and STT. In terms of battery life, the choice of input modality makes significant differences. If users always choose SK for all their text activities, they will consume nearly 50% of the phone battery each day. Choosing STT over SK can save 30%-40% of the battery depending on the choice of STT software.

We consider a growing research trend of using personal mobile devices for forwarding opportunistic network data. Because personal device storage is meant to support user applications, opportunistic networks must use it in a manner that remains completely transparent to the user. One way to make a device's storage use transparent is to allow priority access to the storage to user applications, even if the storage is currently occupied by network data yet to be forwarded. This means that data given to a device waiting to be forwarded can be overwritten by application data and may, thus, be lost. In this paper we consider random access memory (RAM) as the primary storage location in a mobile device. We propose three algorithms of different sophistications to answer the question of how much data should be moved when a contact opportunity arises between two devices in such a way to first maximise the data transferred while minimising the probability that this data will be overwritten when applications claim priority access. We collect 33 h of high-resolution RAM usage traces of two real smartphones over a 3-day period under a variety of usage scenarios to evaluate and compare the performances of the proposed algorithms. Surprisingly, we find that autoregression forecasting of RAM usage cannot outperform the simplest algorithm that greedily occupies all of the RAM that is found unused at the time of contact. We show that Bayesian inference is very effective in minimising the risk of data loss in such uncertain environments and significantly outperforms the greedy approach as well as autoregression forecasting.

In this paper, a mathematical model is analyzed in order to study the natural convection boundary layer flow along an inverted cone. The shape of nanosize particles on entropy generation with based fluid is considered. Simultaneous effects of porous medium, magnetohydrodynamics, radiation and power law index effects are also taken into account. Hamilton–Crosser model is used for the effective thermal conductivity. The nonlinear coupled equations under the assumption of Boussinesq approximation are solved analytically. The calculations are performed for different governing parameters such as Prandtl number, Rayleigh number, power law index, porosity parameter, radiation parameter and magnetic parameter. The physical interpretations of obtained results are illustrated by graphs and tables. In addition, correlation of Nusselt number and skin friction corresponding to active parameters are also analyzed in this investigation.

The design and development of efficient TiO 2 -based, hybrid, nanostructured photocatalysts has recently been receiving substantial attention for environmental remediation due to their excellent physiochemical properties. This article provides an overview of the synthesis strategies and characteristics of the next-generation TiO 2 -based hybrid photocatalysts, produced in combination with polymers (e.g., polyaniline, polypyrrole, polythiophene) and carbon nanomaterials (e.g., graphene, GO, CNT, carbon quantum dots, carbon nitride). The structural aspects, nanostructure formation process, parameters affecting catalytic activity, photocatalytic mechanisms and photocatalytic applications of TiO 2 -based catalysts for efficient photocatalytic degradation of gaseous/volatile organic pollutants in water/air are reviewed. Further, current research trends, means to increase catalytic performance and future prospects of high-performance TiO 2 -based hybrid photocatalytic materials, are briefly summarized.

Multi-color emissive carbon dots (CDs) with intrinsic ternary doping were synthesized by a hydrothermal process from a single precursor, vitamin B1 derivative, thiamine pyrophosphate or ThPP. The origin of the multi-color photoluminescence was ascribed to the hybrid doping (N, S, P) in a carbon framework. The subsequent conjugation of CDs with folic acid (FA) enabled targeted bioimaging and photosensitization of the human melanoma cancer cells, SK-MEL28. The unique excitation-dependent multi-color emission of CD-FA probes allowed wide spectral resolution and targeting for amplified whole cell bioimaging including the nucleus. The photosensitization of cancer cells in the multi-color window was accomplished in a deep tissue cell culture setting. The synthesized CD-FAs showed excellent biocompatibility, photostability, and notably, their cellular targeting with enhanced uptake by folate receptor positive (FR+) cancer cells, SK-MEL28 over folate receptor negative (FR-), HEK293T ones in a co-culture model having both diseased and normal cells. The results demonstrate excellent potential for melanoma diagnostic, mapping and phototherapeutic applications with multi-spectral sensitivity.

Free-standing composite films based on graphene/polyaniline (PANI) nanostructure were synthesized for supercapacitor application. First, polyaniline nanospheres were prepared by microemulsion polymerization, followed by the incorporation of graphene oxide nanosheets by hierarchical organization. The cationic PANI nanospheres were attached to the anionic GO sheets by electrostatic interaction and hierarchical deposition of GO/PANI nanostructures on a membrane filter via targeted self-assembly. Subsequent in situ chemical reduction of GO using hydroiodic acid produced well-defined graphene/PANI nanostructures having interpenetrating network with 3D open structure. The in situ GO reduction enabled keeping the hierarchical organization intact. The flexible graphene/PANI film produced was tested as a supercapacitor electrode using voltammograms and Nyquist analysis. The electro-capacitance of the film (448 F/g) was enhanced by 60% through the synergistic combination of graphene and PANI nanostructures. About 81% capacity retention was achieved for the composite compared to 38% for PANI alone after subjecting the samples to 5000 cyclic operations.

The arsenic-iron sludge generated in most of the treatment systems around the world is discharged into the nearest watercourse, which leads to accumulative rise of arsenic and iron concentrations in water. In this study, attempts were made to use the arsenic-iron sludge in making bricks and to analyze the corresponding effects on brick properties. The water treatment plant sludge is extremely close to brick clay in chemical composition. So, the sludge could be a potential substitute for brick clay. This study involved the addition of sludge with ratios 3%, 6%, 9% and 12% of the total weight of sludge-clay mixture. The physical and chemical properties of the produced bricks were then determined and evaluated and compared to control brick made entirely from clay. Results of different tests indicated that the sludge proportion and firing temperature were the two key factors in determining the quality of bricks. The compressive strength of 3%, 6%, 9% and 12% sludge containing brick samples were found to be 14.1 MPa, 15.1 MPa, 9.4 MPa and 7.1 MPa, respectively. These results indicate that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion. Leaching characteristics of burnt bricks were determined with the variation of pH at a constant temperature. The optimum amount of sludge that could be mixed with clay to produce good bonding of clay-sludge bricks was found to be 6% (safely maximum) by weight.

Network mobility (NEMO) allows various types of in-vehicle networks (e.g., WLANs inside public transport vehicle) to be seamlessly connected to the Internet. An on-board mobile router (MR) connects the moving network to the Internet by means of high-speed cellular mobile data services. Unlike terminal mobility, where the mobile hosts (MHs) connect to the cellular base station directly, MHs in NEMO encounter an additional wireless link (MR–MH) before they get connected to the Internet. In this paper, we first note the impact of this additional wireless link on the performance of the wireless enhancements of TCP and observe that the existing TCP enhancement schemes designed for conventional terminal mobility are not equally effective in NEMO. So, we propose an extension of TCP, called on-board TCP (obTCP), to effectively address the double wireless link related issues in NEMO. We compare obTCP against a classical scheme, called snoop, known for its effectiveness in terminal mobility, and analytically demonstrate that the performance gain of obTCP over snoop increases linearly with the delays, and non-linearly with the loss probabilities in the wireless links. Finally, we extend these analyses to obtain throughput models for snoop and obTCP in NEMO. The throughput models are validated through ns-2 simulations.

The inclusion of nanomaterials into biopolymeric matrices followed by three-dimensional printing is poised to open new horizons in tissue engineering by generating customized 3D structures with optimized properties and multifunctionality. In this review, we present an overview on nanostructured ceramic, metal, carbon and polymer materials integrated with hard and soft forms of biopolymers for manufacturing both acellular and cellular 3D tissue constructs using a range of 3D-printing and bioprinting techniques. Property enhancements and emergence of new functional characteristics of biopolymeric composites with the incorporation of nanomaterials, followed by 3D printing are of particular interest. Several methods, including fused deposition modelling, stereolithography, selective laser sintering and bioprinting using droplet, laser and extrusion assisted techniques are presented. Significant modifications via surface functionalization, biodegradation of scaffolds and the cytotoxicity of nanocomposites are discussed. The results derived from in vitro and in vivo analysis of stem cells and 3D printed scaffolds, their interactions and degradations are highlighted. Advances with multiple nanomaterials are also discussed with the advantages of harnessing the potential of 3D printing to produce unique multifunctional nanocomposites for tissue engineering.

Aqueous phase exfoliation was developed for producing high-yield graphene nanosheets from expandedgraphite (EG). The process included ultrasonication with sodium dodecyl sulfate (SDS) emulsion in aque-ous phase. The high throughput exfoliation process was characterized by UV–vis spectroscopy, transmis-sion electron microscopy (TEM) and electrical impedance spectroscopy (EIS). Controlled sonicationexperiments revealed that optimum exfoliation corresponds to maxima in UV–vis spectra. TEM resultsshowed that the exfoliated graphene comprised nanoflakes having 65 layers ( 60%) and 610 layersfor 90% of the product. The potential use of this highly dispersed graphene was demonstrated by one-pot synthesis of graphene/polymer composite via in situ emulsion polymerization with styrene. The inte-grated role of SDS included adsorption and exfoliation of graphite, dispersion of graphene produced andassisting with micelle formation in emulsion. The high surface area graphene nanosheets as dispersedphase in polymeric nanocomposites showed significant improvement in thermal stability and electricalconductivity. 2013 Elsevier Inc. All rights reserved.

The reuse and recycling of waste materials are now sincerely considered to be an integral part of solid waste management in many parts of the world. In this context, a vast number of options ranging from small scale decentralized to larger scale centralized plants have been adopted. This study aimed at investigating the waste reuse schemes in Khulna city located in the southern part of Bangladesh and ranked third largest city in the country. The shops for reusable material (SRM) were mostly situated around railway, waterway, and truck station markets which provided easy transportation to further locations. For the reuses of waste materials and products, a chain system was found to collect reusable wastes under a total number of 310 identified SRM with 859 persons directly or indirectly involved in the scheme. This was a decentralized waste management system with self sufficient (autonomous) management. According to mass balance, about 38.52 tons d{sup -1} solid wastes were reused in Khulna city area, accounting for 7.65% of the total generated wastes. This study revealed that apparently a silent, systematic, smooth, and clean reuse chain has been established in Khulna city area under private initiatives, whose sustainability was confirmed over the years inmore » the country without any official or formal funds. However, proper adjustment between the higher and lower chain in the materials flow path, as well as personal hygiene training for the workers, would further improve the achievements of the established reuse scheme.« less

Oxidation of ferrous ions by iron-oxidizing bacteria facilitates adsorption of arsenic on iron and subsequent co-precipitation. Based on this technique, a novel treatment process has been developed and tested under field conditions for simultaneous iron and arsenic removal from groundwater. In this study, a biological fixed bed reactor containing coconut husk and subsequent layers of iron matrix, charcoal and sand filter combined the biological and physicochemical treatment processes in a single system. Experimental results showed that arsenic could be efficiently treated from initial concentration of 500 μg L− 1 to residual (effluent) concentrations lower than 15 μg L− 1. Simultaneous significant iron removal efficiency (over 95%) was also achieved. Microbial water quality examination confirmed absence of any contamination in the treated water. Simple and inexpensive construction using locally available materials, considerable treatment performance as well as ease of operation and maintenance present the developed system as a promising one.

When routers continue to transmit packets of a multimedia flow while inflicting a packet loss rate beyond a given threshold, they effectively transmit useless packets. Algorithms to avoid Useless Packet Transmission (UPT) over single and multiple congested links have been analysed previously in the context of a single multimedia flow sharing network links with TCP flows [Computer Communications, accepted for publication; Technical Report UNSW-CSE-TR-0215, 2002]. The main philosophy behind these algorithms is to drop all packets from a multimedia flow whenever the flow experiences a packet loss rate beyond the tolerable threshold. In this paper, we investigate UPT in the context of multiple multimedia flows. We find that previously proposed UPT avoidance algorithms lead to poor link utilisation, as they take action on each and every multimedia flow. We propose two different enhancements, RandomSelect (RS) and Least Bandwidth Select (LBS), to selectively take action on multimedia flows. Using computer simulations of MPEG-2 video, we evaluate the effectiveness of both RS and LBS under various network scenarios (e.g. single/multiple congested links, homogeneous/heterogeneous video applications, etc.). Results show that RS and LBS have similar performance with homogeneous multimedia applications. However, with heterogeneous multimedia applications, LBS yields better performance, in terms of number of video flows affected and overall intelligibility of video applications.

When packet loss rate exceeds a given threshold, received audio and video become unintelligible. A congested router transmitting multimedia packets, while inflicting a packet loss rate beyond a given threshold, effectively transmits useless packets. Useless packet transmission wastes router bandwidth when it is needed most. We propose an algorithm to avoid transmission of useless multimedia packets, and allocate the recovered bandwidth to competing TCP flows. We show that the proposed algorithm can be easily implemented in well-known WFQ and CSFQ fair packet queueing and discarding algorithms. Simulation of a 15-s MPEG-2 video clip over a congested network shows that the proposed algorithm effectively eliminates useless packet transmission, and as a result of that significantly improve throughput and file download times of concurrent TCP connections. For the simulated network, file download time is reduced by 55% for typical HTML files, 36% for typical image files, and up to 30% for typical video files. A peak-signal-to-noise-ratio (PSNR) based analysis shows that the overall intelligibility of the received video is no worse than that received without the incorporation of the proposed useless packet transmission avoidance algorithm. Our fairness analysis confirms that implementation of our algorithm into the fair algorithms (WFQ and CSFQ) does not have any adverse effect on the fairness performance of the algorithms.

We propose and analyse three different power selection schemes for slotted ALOHA random access protocol operating under multiple power levels. Through analysis and numerical examples we demonstrate that these schemes can significantly improve the performance of slotted ALOHA, in terms of throughput and stability, under heavy load. The proposed schemes are truly distributive in nature and can be easily implemented in wireless access systems without requiring any centralised control.

In this paper we describe the development and testing of an agent-based intrusion detection system for Linux platform. We take a dual-approach to intrusion detection: pre-emptory and reactionary. With the pre-emptory approach, a network-based agent is implemented to monitor all packets entering the network and detect a known attack-based on a pre-defined rule. The reactionary approach is realized through a separate host-based agent to routinely check specific log files in order to detect system anomalies caused by successful attacks. Once a possible intrusion attempt has been detected by either one of the agents, it attempts to block the attack, records the attack details in a system log file, E-mails the system administrator, displays a warning through a graphical warning window. The agents operate in the background of user applications and system software without any noticeable performance effect on them.

A number of distributed corporate intranets can be connected together using the ABR service of an ATM network to form a virtual private network. However, because the available bandwidth of the ABR connection may be occasionally reduced by the ATM network, severe congestion may occur at the gateway connecting an intranet to the ATM network. Such congestion is likely to cause packet loss at the gateway which in turn may significantly reduce the throughput of intranet applications. In order to address the above problem, we propose a novel rate-based flow control mechanism, called Host Gateway Rate Control Protocol (HG-RCP), between the gateway and the intranet hosts. The control mechanism of HG-RCP is modeled as a classical feedback control system and the control parameters are selected to guarantee the stability of the system. The performance of HG-RCP is evaluated using simulation for both limited and unlimited buffers at the gateway. Simulation results confirm that HG-RCP is very stable and fair in allocating the ABR bandwidth among the competing sources in the intranet. It is also demonstrated via simulation that HG-RCP can significantly reduce the amount of buffers required at the gateway and improve the performance of TCP/IP applications in the intranets.

Available bit rate (ABR) is an emerging asynchronous transfer mode (ATM)-based telecommunication service, which dynamically allocates bandwidth to the users according to the available bandwidth in the network. However, research shows that ABR-based connections suffer from congestion at LAN-ATM gateway when ATM network abruptly reduces the bandwidth available to the gateway. Gateway congestion may result in high packet loss. This paper proposes a gateway congestion control mechanism, which controls the rate of outgoing enterprise traffic according to the available bandwidth at the gateway. Our analysis shows how to achieve a stable system and keep the packet loss below a desired threshold. Analytical results are validated by simulation.