Constrained Environments Research Articles

An Energy-Efficient Technique to Combat DOS Attacks in Delay Tolerant Networks

A delay tolerant network is a highly constrained networking environment which is low in resources such as memory, bandwidth and battery power. In opportunistic DTNs, nodes cooperatively forward packets for each other through the carry-store-and-forward paradigm. Opportunistic data forwarding can be abused by an adversary by injecting spurious packets in order to waste the resources of the network. To guard against such attacks, it is important to authenticate packets at intermediate nodes. Packet authentication in itself comes with overheads such as computation cost and energy consumption which can be exploited by an attacker to mount a denial of service attack. We propose the use of light-weight DTN-cookies to protect this vital security service from such malicious exploitation. We show through simulations that our proposed mechanisms can improve network performance and save considerable amount of power even in the presence of attackers.

Analysis of Dynamic Differential Swing Limited Logic for Low-Power Secure Applications

Low-power secure applications such as Radio Frequency IDentification (RFID) and smart cards represent extremely constrained environments in terms of power consumption and die area. This paper investigates the power, delay and security performances of the dynamic differential swing limited logic (DDSLL). A complete analysis of an advanced encryption standard (AES) S-box is conducted using a low-power (LP) 65 nm CMOS technology node. Measurements show that the DDSLL S-box has 35% less power consumption than the static CMOS S-box, with an area increase of only 12%, at the expense of a 2.5× increase in delay which remains fairly acceptable for low-power applications such as RFIDs and smart cards. Also when compared to other dynamic differential logic (DDL) styles, simulation results show that DDSLL and dynamic current mode logic (DyCML) consume the same power which is about 1.8× less that of sense amplifier based logic (SABL). The effect of process variations is also studied, measurement results show that the DDSLL style has lower variability in terms of dynamic power as the activity factor (αF) is deterministic thanks to glitch-free operation. As for security, the perceived information metric demonstrates that the DDSLL S-box has a 3× security margin compared to static CMOS. Therefore, DDSLL presents an interesting tradeoff between improved security and area constrained low-power designs.

Rethinking America's Joint Force: Strength and Credibility in a Constrained Fiscal Environment

In today's constrained fiscal environment, we must ''re- mission'' a smaller, more interdependent Joint Force with an emphasis on capability rather than capacity. America's military is primarily intended to defend the nation from attack, prevent and deter war, and when required, to win decisively in operations ranging from low-end irregular warfare through high-end conventional warfare. In this century, our nation's economic strength, values, and credible influence will play as much a role in sustaining our security and prosperity as will military power. Working closely with other departments of the government as well as with partners and allies, the Department of Defense must rely on three key stakeholders— Congress, the service chiefs, and the combatant commanders—to shape a strong and adaptive military. Rather than focusing on traditional ends, ways, and means, this article addresses the ''concept, form, and function'' our Joint Force should pursue in support of the National Security Strategy.

Ground- and Excited-State Properties of Zn(II) Tetrakis(4-tetramethylpyridyl) Pophyrin Specifically Encapsulated within a Zn(II) HKUST Metal–Organic Framework

We have examined the photophysical properties of Zn(II) tetramethylpyridyl porphyrin (ZnT4MPyP) specifically encapsulated within the cubioctahedral cavities of a ZnHKUST metal- organic framework. The encapsulated ZnT4MPyP exhibits a Soret maxima at ∼458 nm that is bathochromically shifted relative to ZnT4PyP in ethanol solution (Soret maxima centered at 440 nm). The corresponding emission spectra of the encapsulated porphyrin exhibit resolvable bands centered at 636 and 677 nm relative to a single broad emission band of the ZnT4MPyP in ethanol solution centered at 636 nm with a shoulder situated near ∼660 nm. The fluorescence lifetime of the encapsulated porphyrin is also perturbed relative to that of the free porphyrin in solution (1.88 ns for the encapsulated porphyrin relative to 1.2 ns in solution). These results are consistent with the ZnT4MPyP being in a more constrained environment in which the peripheral pyridyl groups have restricted rotational motion. The ZnT4MPyP triplet lifetime is also affected by encapsulation, giving rise to a longer lifetime (τ ≈ 3.3 ms) relative to that for the free porphyrin in solution (τ ≈ 1 ms). The triplet-state results indicate that nonplanar vibrational modes of the porphyrin leading to intersystem crossing are retained by encapsulation of the porphyrin but that either the density of vibrational states or the specific nonplanar modes coupling the singlet and triplet states may be perturbed, resulting in the longer observed lifetime.

Management of Lupus Nephritis in Constrained Environments

Management of Lupus Nephritis in Constrained Environments

A Multiattribute Sealed-Bid Procurement Auction with Multiple Budgets for Government Vendor Selection

This paper offers a new approach to government vendor selection decisions in major public procurements. A key challenge is for government purchasing agents to select vendors that deliver the best combination of desired nonprice attributes at realistic funding levels. The mechanism proposed in this paper is a multiattribute first-price, sealed-bid procurement auction. It extends traditional price-only auctions to those in which competition takes place exclusively over attribute bundles. The model is a multiattribute auction in which a set of possible budget levels is specified. This model reveals the benefits of defining a procurement alternative in terms of its value to the buyer over a range of possible expenditures, rather than as a single point in budget-value space. This new approach leads to some interesting results. In particular, it suggests that in a fiscally constrained environment, the traditional approach of eliminating dominated alternatives could lead to suboptimal decisions. Finally, an extension of the model explicitly examines the buyer's decision problem under budget uncertainty by applying a utility function assessed over the value measure.

Automated design knowledge capture and representation in single-user CAD environments

Current computer-aided design systems excel at recording the final design solution for an engineering problem; however, they are not as adept at capturing the individual designer's rationale, knowledge or the process used during the design session. Being able to access this information will give insight into the reasons why key design decisions were made which, in turn, will support engineers who have to make revisions to the product in the future. Therefore, it would be beneficial if CAD systems were able to record design knowledge automatically. The research in this paper attempts to address this issue with a system that unobtrusively captures design processes and design knowledge by logging individual designer behaviour and system interactions while a CAD system is being used; user trials generated around 700 log files that were then analysed to extract these. In addition, various CAD system-independent representations were output to give a visual and formal representation of the processes that occurred. Overall, although carried out within a constrained design environment, this early knowledge capture work demonstrates the potential for automated knowledge capture and subsequent representations within CAD environments as well as the feasibility of design information push.

Cooperative Caching in Mobile Ad Hoc Networks

Mobile ad hoc network (MANET) presents a constrained communication environment due to fundamental limitations of client’s resources, insufficient wireless bandwidth and users’ frequent mobility. MANETs have many distinct characteristics which distinguish them from other wireless networks. Due to frequent network disconnection, data availability is lower than traditional wired networks. Cooperative caching helps MANETs in alleviating the situation of non availability of data. In this paper, the authors present a scheme called global cluster cooperation (GCC) for caching in mobile ad hoc networks. In this scheme, network topology is partitioned into non-overlapping clusters based on the physical network proximity. This approach fully exploits the pull mechanism to facilitate cache sharing in a MANET. Simulation experiments show that GCC mechanism achieves significant improvements in cache hit ratio and average query latency in comparison with other caching strategies.

Deformable Motion: Squeezing into Cluttered Environments

AbstractWe present an interactive method that allows animated characters to navigate through cluttered environments. Our characters are equipped with a variety of motion skills to clear obstacles, narrow passages, and highly constrained environment features. Our control method incorporates a behavior model into well‐known, standard path planning algorithms. Our behavior model, called deformable motion, consists of a graph of motion capture fragments. The key idea of our approach is to add flexibility on motion fragments such that we can situate them into a cluttered environment via constraint‐based formulation. We demonstrate our deformable motion for realtime interactive navigation and global path planning in highly constrained virtual environments.

An efficient hyperellipsoidal clustering algorithm for resource-constrained environments

Clustering has been widely used as a fundamental data mining tool for the automated analysis of complex datasets. There has been a growing need for the use of clustering algorithms in embedded systems with restricted computational capabilities, such as wireless sensor nodes, in order to support automated knowledge extraction from such systems. Although there has been considerable research on clustering algorithms, many of the proposed methods are computationally expensive. We propose a robust clustering algorithm with low computational complexity, suitable for computationally constrained environments. Our evaluation using both synthetic and real-life datasets demonstrates lower computational complexity and comparable accuracy of our approach compared to a range of existing methods.

Fabrication of Micropatterned Hydrogels for Neural Culture Systems using Dynamic Mask Projection Photolithography

Increasingly, patterned cell culture environments are becoming a relevant technique to study cellular characteristics, and many researchers believe in the need for 3D environments to represent in vitro experiments which better mimic in vivo qualities 1-3. Studies in fields such as cancer research 4, neural engineering 5, cardiac physiology 6, and cell-matrix interaction7,8have shown cell behavior differs substantially between traditional monolayer cultures and 3D constructs.Hydrogels are used as 3D environments because of their variety, versatility and ability to tailor molecular composition through functionalization 9-12. Numerous techniques exist for creation of constructs as cell-supportive matrices, including electrospinning13, elastomer stamps14, inkjet printing15, additive photopatterning16, static photomask projection-lithography17, and dynamic mask microstereolithography18. Unfortunately, these methods involve multiple production steps and/or equipment not readily adaptable to conventional cell and tissue culture methods. The technique employed in this protocol adapts the latter two methods, using a digital micromirror device (DMD) to create dynamic photomasks for crosslinking geometrically specific poly-(ethylene glycol) (PEG) hydrogels, induced through UV initiated free radical polymerization. The resulting "2.5D" structures provide a constrained 3D environment for neural growth. We employ a dual-hydrogel approach, where PEG serves as a cell-restrictive region supplying structure to an otherwise shapeless but cell-permissive self-assembling gel made from either Puramatrix or agarose. The process is a quick simple one step fabrication which is highly reproducible and easily adapted for use with conventional cell culture methods and substrates.Whole tissue explants, such as embryonic dorsal root ganglia (DRG), can be incorporated into the dual hydrogel constructs for experimental assays such as neurite outgrowth. Additionally, dissociated cells can be encapsulated in the photocrosslinkable or self polymerizing hydrogel, or selectively adhered to the permeable support membrane using cell-restrictive photopatterning. Using the DMD, we created hydrogel constructs up to ~1mm thick, but thin film (<200 μm) PEG structures were limited by oxygen quenching of the free radical polymerization reaction. We subsequently developed a technique utilizing a layer of oil above the polymerization liquid which allowed thin PEG structure polymerization.In this protocol, we describe the expeditious creation of 3D hydrogel systems for production of microfabricated neural cell and tissue cultures. The dual hydrogel constructs demonstrated herein represent versatile in vitro models that may prove useful for studies in neuroscience involving cell survival, migration, and/or neurite growth and guidance. Moreover, as the protocol can work for many types of hydrogels and cells, the potential applications are both varied and vast.

Fabrication of Micropatterned Hydrogels for Neural Culture Systems using Dynamic Mask Projection Photolithography

Increasingly, patterned cell culture environments are becoming a relevant technique to study cellular characteristics, and many researchers believe in the need for 3D environments to represent in vitro experiments which better mimic in vivo qualities 1-3. Studies in fields such as cancer research 4, neural engineering 5, cardiac physiology 6, and cell-matrix interaction7,8have shown cell behavior differs substantially between traditional monolayer cultures and 3D constructs. Hydrogels are used as 3D environments because of their variety, versatility and ability to tailor molecular composition through functionalization 9-12. Numerous techniques exist for creation of constructs as cell-supportive matrices, including electrospinning13, elastomer stamps14, inkjet printing15, additive photopatterning16, static photomask projection-lithography17, and dynamic mask microstereolithography18. Unfortunately, these methods involve multiple production steps and/or equipment not readily adaptable to conventional cell and tissue culture methods. The technique employed in this protocol adapts the latter two methods, using a digital micromirror device (DMD) to create dynamic photomasks for crosslinking geometrically specific poly-(ethylene glycol) (PEG) hydrogels, induced through UV initiated free radical polymerization. The resulting "2.5D" structures provide a constrained 3D environment for neural growth. We employ a dual-hydrogel approach, where PEG serves as a cell-restrictive region supplying structure to an otherwise shapeless but cell-permissive self-assembling gel made from either Puramatrix or agarose. The process is a quick simple one step fabrication which is highly reproducible and easily adapted for use with conventional cell culture methods and substrates. Whole tissue explants, such as embryonic dorsal root ganglia (DRG), can be incorporated into the dual hydrogel constructs for experimental assays such as neurite outgrowth. Additionally, dissociated cells can be encapsulated in the photocrosslinkable or self polymerizing hydrogel, or selectively adhered to the permeable support membrane using cell-restrictive photopatterning. Using the DMD, we created hydrogel constructs up to ~1mm thick, but thin film (<200 μm) PEG structures were limited by oxygen quenching of the free radical polymerization reaction. We subsequently developed a technique utilizing a layer of oil above the polymerization liquid which allowed thin PEG structure polymerization. In this protocol, we describe the expeditious creation of 3D hydrogel systems for production of microfabricated neural cell and tissue cultures. The dual hydrogel constructs demonstrated herein represent versatile in vitro models that may prove useful for studies in neuroscience involving cell survival, migration, and/or neurite growth and guidance. Moreover, as the protocol can work for many types of hydrogels and cells, the potential applications are both varied and vast.

Credit scoring for microfinance: is it worth it?

ABSTRACTDue to growing competition, over‐indebtedness, and economic crises, microfinance institutions have to pursue their social and financial objectives in an increasingly constrained environment. Developing powerful risk management tools becomes more than ever crucial to survive. Therefore this paper analyzes whether microfinance institutions can benefit from credit scoring, which has been successfully adopted in retail banking. An extensive literature overview is provided, indicating a lack of quantitative evidence, in particular for markets in Eastern Europe‐Central Asia and the Middle East‐Northern Africa. Two logistic regression‐based scoring models are developed using data from a Bosnia–Herzegovinian microlender. The models are assessed in terms of stability, readability, and discriminatory power, indicating that credit scoring is not yet able to fully replace the human‐intensive microfinance credit process. However, it is recommendable to introduce credit scoring as a refinement tool in the lending process, in order to combine both statistical and human best practices. Moreover, a microlender staff can learn from credit scoring models to validate or contrast practical intuition. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Mutational Analysis of Residues in the Helical Region of the Class IIa Bacteriocin Pediocin PA-1

A 15-mer fragment that is derived from the helical region in the C-terminal half of pediocin PA-1 inhibited the activity of pediocin PA-1. Of 13 other pediocin-like (hybrid) bacteriocins, only the hybrid bacteriocin Sak/Ped was markedly inhibited by the 15-mer fragment. Sak/Ped was the only one of these bacteriocins that had a sequence (in the C-terminal helix-containing half) identical to that of the 15-mer fragment, indicating that the fragment inhibits pediocin-like bacteriocins in a sequence-dependent manner. By replacing (one at a time) all 15 residues in the fragment with Ala or Leu, five residues (K1, A2, T4, N8, and A15) were identified as being especially important for the inhibitory action of the fragment. The results suggest that the corresponding residues (K20, A21, T23, N27, and A34, respectively) in pediocin PA-1 might be involved in interactions between pediocin PA-1 and its receptor. To characterize the environment surrounding these five residues when pediocin PA-1 interacts with target cells, these residues were replaced (one at a time) with a hydrophobic large (Leu) residue, a hydrophilic charged (Asp or Arg) residue, and a small (Ala or Gly) residue. The results revealed that residues A21 and A34 are in a spatially constrained environment, since the replacement with a small (Gly) residue was the only substitution that did not markedly reduce the bacteriocin activity. The positive charge in K20 and the polar amide group in N27 appeared to interact with electronegative groups, since the replacement of these two residues with a positive (Arg) residue was well tolerated, while replacement with a negative (Asp) residue was detrimental to the bacteriocin activity. K20 was in a less constrained environment than N27, since the replacement of K20 with a large hydrophobic (Leu) residue was tolerated fairly well and to a greater extent than N27. T23 seemed to be in an environment that was not restricted with respect to size, polarity, and charge, since replacements with large (Leu) and small (Ala) hydrophobic residues and a hydrophilic negative (Asp) residue were tolerated fairly well (2- to 6-fold reduction in activity). Moreover, the replacement of T23 with a large positive (Arg) residue resulted in wild-type or better-than-wild-type activity.

Organic Zeolite Analogues Based on Multi-Component Liquid Crystals: Recognition and Transformation of Molecules within Constrained Environments.

In liquid crystals (LCs), molecules are confined in peculiar environments, where ordered alignment and certain mobility are realized at the same time. Considering these characteristics, the idea of “controlling molecular events within LC media” seems reasonable. As a suitable system for investigating this challenge, we have recently developed a new class of ionic LCs; the salts of amphiphilic carboxylic acids with 2-amino alcohols, or those of carboxylic acids with amphiphilic 2-amino alcohols, have a strong tendency to exhibit thermotropic LC phases. Because of the noncovalent nature of the interaction between molecules, one of the two components can easily be exchanged with, or transformed into, another molecule, without distorting the original LC architecture. In addition, both components are common organic molecules, and a variety of compounds are easily available. Taking advantage of these characteristics, we have succeeded in applying two-component LCs as chiral media for molecular recognition and reactions. This review presents an overview of our recent studies, together with notable reports related to this field.

Successful project delivery in complex brownfield environments

Delivering services and projects in a brownfield environment has unique challenges. Brownfield, by its very nature, involves highly constrained and dynamic environments. This requires stakeholders to work collaboratively and be creative and nimble. Effective communication between client and service provider is essential. This is because the decision-making horizons are significantly shorter and consequences are more immediate. Brownfield projects are typically organised to minimise inter-discipline interfaces, with seamless delivery from engineering through to construction. Engineering effort needs to be the right sized based on the level of complexity and risk involved to ensure the effort and cost expended is appropriate for the modification or upgrade. When planning and executing brownfield projects, the following areas require special focus: health, safety and the environment—to cope with the inherently higher risks due to live inventory, lack of space, simultaneous operations and increased personnel; interface with operations—to plan, manage and minimise disruption to production; live systems—to assess the impact/disruption to energised systems and coordinate tie-ins; production—to minimise disruption and ensure that the project is executed safely while production continues; hot work—to a minimum and where necessary contain naked flame and spark activity on site; integrity—to ensure the condition of the asset is well understood and any sub-system upgrades to accommodate the modification are identified; limited space—to accommodate temporary project facilities, minimising the impact on operations and maintenance activities; and, access—to ensure that the project is planned to lessen disruption, maximise off-site preparation and to minimise on-site construction. Systematic program management, project engineering, and a tiered engineering approach are essential to cost effective and timely delivery. For each of the eight key areas we detail some of the subtle and enabling strategies/tools that distinguish brownfield project delivery from greenfield.

Towards understanding sodium effect on USY zeolite

Samples of a commercial USY zeolite were exchanged with NaCl solution and then thermally treated under dry atmosphere. Resulting samples were evaluated by n-butane cracking, isopropylamine ( i-pam) decomposition, TG–DSC, nitrogen adsorption, and powder XRD. Activation barriers for n-butane reactions were determined as a function of sodium load in the samples. The addition of sodium chloride has a marked negative effect upon material crystallinity, but dealumination rate does not seem to be affected, which suggests framework destruction mediated by sodium does not involve aluminum atoms. As sodium was loaded, samples were less able to retain water because of loss in crystallinity as shown by XRD and volume of micropore measurements. Activity to n-butane cracking decreases monotonically with sodium load, but selectivity to cracking, dehydrogenation, and hydride transfer products remained unaltered; that shows sodium chloride effect is not selective to a particular kind of acid site. The Brønsted acid site (BAS) density measured by i-pam decomposition exhibits a volcano-like profile with sodium load; at low sodium contents there is a gain in i-pam accessibility due to structural collapse but at higher loads BAS disappearance overcomes accessibility and density of acid sites decreases. The average pore size increases with sodium load. After thermal treatment in presence of sodium chloride, gates are opened in zeolite structure, allowing n-butane and isopropylamine to reach formerly inaccessible sites; hydrocarbon conversion can occur in spatially constrained environments where stabilization effects lead to low-energy/low-entropy activated complexes and apparent activation energy shows a minimum with sodium chloride load. Sodium chloride has an effect on Y zeolite even in dry conditions at temperatures similar to those predominant in FCC regenerator.

Sensor-Mission Assignment in Constrained Environments

When a sensor network is deployed in the field it is typically required to support multiple simultaneous missions, which may start and finish at different times. Schemes that match sensor resources to mission demands thus become necessary. In this paper, we consider new sensor-assignment problems motivated by frugality, i.e., the conservation of resources, for both static and dynamic settings. In the most general setting, the problems we study are NP-hard even to approximate, and so we focus on heuristic algorithms that perform well in practice. In the static setting, we propose a greedy centralized solution and a more sophisticated solution that uses the Generalized Assignment Problem model and can be implemented in a distributed fashion. In what we call the dynamic setting, missions arrive over time and have different durations. For this setting, we give heuristic algorithms in which available sensors propose to nearby missions as they arrive. We find that the overall performance can be significantly improved if available sensors sometimes refuse to offer utility to missions they could help, making this decision based on the value of the mission, the sensor's remaining energy, and (if known) the remaining target lifetime of the network. Finally, we evaluate our solutions through simulations.

Apport de la modélisation mathématique à la décision vaccinale.: Illustrations avec les vaccinations contre la varicelle, le rotavirus et le papillomavirus

The decision to add a new vaccine to the immunization schedule is a complex and multidisciplinary process based on the risk-benefit balance and, increasingly, on the cost- effectiveness ratio. Such decisions now use mathematical models that can predict the indirect, and potentially detrimental, effects of mass vaccination on the epidemiology of the target disease. The adjunction of an economic component to the modeling process ensures that vaccination represents an efficient allocation of available financial resources in an increasingly constrained environment.

3D Real-Time Reconstruction Approach for Multimedia Sensor Networks

Multimedia sensor networks have emerged due to the tremendous technological advances in multimedia hardware miniaturization and the application potential they present. However, the time sensitive nature of multimedia data makes them very problematic to handle, especially within constrained environments. In this paper, the authors present a novel approach based on continuous 3D real time reconstruction of the monitored area dedicated for video surveillance applications. Real-time 3D reconstruction allows an important network bandwidth reduction in context to sensor nodes sending descriptive information to the fusion server instead heavy video streams. Each node has to support additional processing in order to extract this descriptive information in real-time, which results in video sensors capturing tasks, data analysis, and extraction of features needed for 3D reconstruction. In this paper, the authors focus on the design and implementation of such sensor node and validate their approach through real experimentations conducted on a real video sensor.