Purdue e-Pubs Copyright (c) 2012 Purdue University All rights reserved. http://docs.lib.purdue.edu Recent documents in Purdue e-Pubs en-us Tue, 15 May 2012 04:40:47 PDT 3600 Authentication and Key Management for Advanced Metering Infrastructures Utilizing Physically Unclonable Functions 2012-2 http://docs.lib.purdue.edu/cctech/3 http://docs.lib.purdue.edu/cctech/3 Mon, 14 May 2012 06:57:54 PDT Conventional utility meters are increasingly being replaced with smart meters as smart meter based AMIs (Advanced Metering Infrastructures) provide many benefits over conventional power infrastrucutures. However, security issues pertaining to the data transmission between smart meters and utility servers have been a major concern. With large scale AMI deployments, addressing these issues is challenging. In particular, as data travels through several networks, secure end-to-end communication based on strong authentication mechanisms and a robust and scalable key management schemes are crucial for assuring the confidentiality and the integrity of this data. In this paper, we propose an approach based on PUF (physically unclonable function) technology for providing strong hardware based authentication of smart meters and efficient key management to assure the confidentiality and integrity of messages exchanged between smart meters and the utility. Our approach does not require modifications to the existing smart meter communication. We have developed a proof-of-concept implementation of the proposed approach which is also briefly discussed in the paper.

]]> Mohamed Nabeel et al. Multi-objective Optimization of Sustainable Single-Effect Water/Lithium Bromide Absorption Cycle http://docs.lib.purdue.edu/coolingpubs/177 http://docs.lib.purdue.edu/coolingpubs/177 Sat, 12 May 2012 21:46:05 PDT A rigorous mathematical approach is developed for optimization of sustainable single-effect water/ Lithium Bromide (LiBr) absorption cooling cycles. The multi-objective formulation accounts for minimization of the chiller area as well as the environmental impact associated with the operation of the absorption cycle. The environmental impact is quantified based on the global warming potential and the Eco-indicator 99, both of which follow principles of life cycle assessment. The design task is formulated as a bi-criterion non-linear programming problem, the solution of which is defined by a set of Pareto points that represent the optimal compromise between the total area of the chiller and global warming potential. These Pareto sets are obtained via the epsilon constraint method. A set of design alternatives are provided for the absorption cycles rather than a single design; the best design can be chosen from this set based on the major constraints and benefits in a given application. The proposed approach is illustrated design of a typical absorption cooling cycle.

]]> B. H. Gebreslassie et al. Intuitive Tip of the Tongue Judgments Predict Subsequent Problem Solving One Day Later http://docs.lib.purdue.edu/jps/vol4/iss2/9 http://docs.lib.purdue.edu/jps/vol4/iss2/9 Fri, 11 May 2012 20:25:54 PDT Often when failing to solve problems, individuals report some idea of the solution, but cannot explicitly access the idea. We investigated whether such intuition would relate to improvements in solving and to the manner in which a problem was solved after a 24- hour delay. On Day 1, participants attempted to solve Compound Remote Associate problems, for which they viewed three problem words (crab, sauce, pine) and tried to generate one solution word (apple) that could form a compound word with each problem word (crabapple, applesauce, pineapple). For problems they failed to solve, participants reported whether they had an intuitive sense that they might have solution related processing in the back of their mind, similar to a Tip-of-the-Tongue (TOT) experience. After an overnight delay, on Day 2 participants attempted to solve unsolved Old problems from Day 1 (mixed among New problems). Participants solved more Old problems for which they reported a TOT on Day 1 than Old problems without a TOT, demonstrating a TOT specific incubation effect. Interestingly, participants reported solving a marginally higher proportion of these TOT problems, compared to No TOT problems, with insight. Results suggest that intuitive TOT judgments are indicative of subthreshold solution related activation that can facilitate eventual problem solving, especially with insight.

]]> Azurii K. Collier et al. Is Insight Always the Same? A Protocol Analysis of Insight in Compound Remote Associate Problems http://docs.lib.purdue.edu/jps/vol4/iss2/8 http://docs.lib.purdue.edu/jps/vol4/iss2/8 Fri, 11 May 2012 20:25:53 PDT Compound Remote Associate (CRA) problems have been used to investigate insight problem solving using both behavioral and neuroimaging techniques. However, it is unclear to what extent CRA problems exhibit characteristics of insight such as impasses and restructuring. CRA problem-solving characteristics were examined in a study in which participants solved CRA problems while providing concurrent verbal protocols. The results show that solutions subjectively judged as insight by participants do exhibit some characteristics of insight. However, the results also show that there are at least two different ways in which people experience insight when solving CRA problems. Sometimes problems are solved and judged as insight when the solution is the first thing considered, but these solutions do not exhibit any characteristics of insight aside from the “Aha!” experience. In other cases, the solution is derived after a longer period of problem solving, and the solution process more closely resembles insight as it is has been traditionally defined in the literature. The results show that separating these two types of solution processes may provide a better understanding of the behavioral and neuroanatomical correlates of insight solutions.

]]> Edward A. Cranford et al. Firing the Executive: When an Analytic Approach to Problem Solving Helps and Hurts http://docs.lib.purdue.edu/jps/vol4/iss2/7 http://docs.lib.purdue.edu/jps/vol4/iss2/7 Fri, 11 May 2012 20:23:10 PDT There is a general assumption that a more controlled or more focused attentional state is beneficial for most cognitive tasks. However, there has been a growing realization that creative problem solving tasks, such as the Remote Associates Task (RAT), may benefit from a less controlled solution approach. To test this hypothesis, in a 2x2 design, we manipulated whether solvers were given the RAT before or after an implicit learning task. We also varied whether they were told to “use their gut” as part of either initial task. The results suggest that a less analytic approach engendered by a “use your gut” instruction benefits performance on the RAT for monolingual solvers. The same benefit was not found for bilingual speakers suggesting that more controlled solution processes may be needed when speakers with multiple lexicons perform this task, which relies heavily on accessing common phrases in a particular language.

]]> Daniel A. Aiello et al. Visual Attention Modulates Insight Versus Analytic Solving of Verbal Problems http://docs.lib.purdue.edu/jps/vol4/iss2/6 http://docs.lib.purdue.edu/jps/vol4/iss2/6 Fri, 11 May 2012 20:23:09 PDT Behavioral and neuroimaging findings indicate that distinct cognitive and neural processes underlie solving problems with sudden insight. Moreover, people with less focused attention sometimes perform better on tests of insight and creative problem solving. However, it remains unclear whether different states of attention, within individuals, influence the likelihood of solving problems with insight or with analysis. In this experiment, participants (N = 40) performed a baseline block of verbal problems, then performed one of two visual tasks, each emphasizing a distinct aspect of visual attention, followed by a second block of verbal problems to assess change in performance. After participants engaged in a center-focused flanker task requiring relatively focused visual attention, they reported solving more verbal problems with analytic processing. In contrast, after participants engaged in a rapid object identification task requiring attention to broad space and weak associations, they reported solving more verbal problems with insight. These results suggest that general attention mechanisms influence both visual attention task performance and verbal problem solving.

]]> Ezra Wegbreit et al. Remote Associates Test and Alpha Brain Waves http://docs.lib.purdue.edu/jps/vol4/iss2/5 http://docs.lib.purdue.edu/jps/vol4/iss2/5 Fri, 11 May 2012 20:23:07 PDT Previous studies found that performance on the remote associates test (RAT) improves after a period of incubation and that increased alpha brain waves over the right posterior brain predict the emergence of RAT insight solutions. We report an experiment that tested whether increased alpha brain waves during incubation improve RAT performance. Participants received two blocks of RAT items (RAT1 and RAT2), with the second block consisting of items that were not solved during the first block. Participants were randomly assigned to three groups, which were matched for their number of RAT1 solutions. Participants in an alpha-up neurofeedback group aimed to increase their alpha brain waves over the right posterior brain in between the two blocks, whereas participants in an alpha-down neurofeedback group aimed to decrease these same brain waves. A third group of participants did not perform neurofeedback and proceeded immediately from the first to the second block of RAT items. We found evidence for more RAT2 solutions in participants who interrupted their RAT performance with neurofeedback, especially in ones who showed high alpha brain waves during neurofeedback. These results are consistent with the notion that an alert but relaxed mental state, indexed by alpha brain waves, may aid the read out of an implicitly activated memory network of weak associates.

]]> Henk J. Haarmann et al. Testing the Cue Dependence of Problem-Solving-Induced Forgetting http://docs.lib.purdue.edu/jps/vol4/iss2/4 http://docs.lib.purdue.edu/jps/vol4/iss2/4 Fri, 11 May 2012 20:23:03 PDT Thinking and remembering can cause forgetting. In the context of remembering, retrieving one item can cause the forgetting of other items (Anderson, Bjork, & Bjork, 1994). A similar phenomenon has been observed in the context of creative problem solving—attempting to generate a target associate in the Remote Associates Test (RAT) can cause the forgetting of inappropriate associates (Storm, Angello, & Bjork, 2011). Experiment 1 examined whether this problem-solving-induced forgetting is cue dependent or cue independent by manipulating the cues used at final test. Whereas some participants were tested on the inappropriate associates using the same cues that were used during problem solving, other participants were tested using new, or independent, cues. Problem-solving-induced forgetting was observed in the same-cue condition, but not in the new-cue condition. Experiment 2 replicated the overall absence of problem-solvinginduced forgetting in the new-cue condition and found that individual differences in cue-independent forgetting did not predict problem-solving performance on a separate set of RAT problems.

]]> Benjamin C. Storm et al. Clue Insensitivity in Remote Associates Test Problem Solving http://docs.lib.purdue.edu/jps/vol4/iss2/3 http://docs.lib.purdue.edu/jps/vol4/iss2/3 Fri, 11 May 2012 20:23:02 PDT Does spreading activation from incidentally encountered hints cause incubation effects? We used Remote Associates Test (RAT) problems to examine effects of incidental clues on impasse resolution. When solution words were seen incidentally 3-sec before initially unsolved problems were retested, more problems were resolved (Experiment 1). When strong semantic associates of solutions were used as incidental clues, however, it did not improve resolution (Experiments 2 and 4). The semantic associates we used as incidental clues primed our RAT solution words in a lexical decision task, but they did not facilitate impasse resolution unless participants were explicitly instructed to use the associates as hints to the retested problems (Experiment 4). The results do not support the theory that spreading activation is a sufficient cause of incubation effects, and suggest that serendipitously encountered clues (i.e., words that are semantically related to RAT solutions) have no automatic benefit on impasse resolution in RAT problem solving.

]]> Steven M. Smith et al. Investigating Insight as Sudden Learning http://docs.lib.purdue.edu/jps/vol4/iss2/2 http://docs.lib.purdue.edu/jps/vol4/iss2/2 Fri, 11 May 2012 20:22:59 PDT Gestalt psychologists proposed two distinct learning mechanisms. Associative learning occurs gradually through the repeated co-occurrence of external stimuli or memories. Insight learning occurs suddenly when people discover new relationships within their prior knowledge as a result of reasoning or problem solving processes that re-organize or restructure that knowledge. While there has been a considerable amount of research on the type of problem solving processes described by the Gestalt psychologists, less has focused on the learning that results from these processes. This paper begins with a historical review of the Gestalt theory of insight learning. Next, the core assumptions of Gestalt insight learning theory are empirically tested with a study that investigated the relationships among problem difficulty, impasse, initial problem representations, and resolution effects. Finally, Gestalt insight learning theory is discussed in relation to modern information processing theories of comprehension and memory formation.

]]> Ivan K. Ash et al. Contents http://docs.lib.purdue.edu/jps/vol4/iss2/1 http://docs.lib.purdue.edu/jps/vol4/iss2/1 Fri, 11 May 2012 20:22:57 PDT Second-Law Analysis of Molten-Salt Thermal Energy Storage in Thermoclines http://docs.lib.purdue.edu/coolingpubs/176 http://docs.lib.purdue.edu/coolingpubs/176 Wed, 09 May 2012 21:02:58 PDT The cyclic operation of a molten-salt thermocline tank is simulated to investigate the influence of internal granule diameter and external convection losses on tank performance. Practical constraints limiting thermocline tank height are taken into account. The authors two-temperature model, developed in earlier work (Solar Energy, 84, 974–985, 2010) for the analysis of heat transfer and fluid flow in the thermocline tank, is extended to monitor entropy generation and exergy transport. Storage performance is measured in terms of first- and second-law efficiency definitions, as well as a first-law efficiency used in conjunction with an outflow temperature criterion. Reducing the diameter of the fillerbed granules improves the thermocline tank performance by sustaining higher molten-salt outflow temperatures throughout the discharge phase of the cycle, which results in greater operational efficiency. External convection losses strongly influence entropy generation inside the tank fillerbed due to the development of radial temperature gradients and increased irreversible thermal diffusion. Convection losses also result in lower tank efficiencies due to the reduction of hot molten salt available inside the tank. A comparison of the different efficiency definitions employed in this work reveal that the ad hoc outflow temperature criterion used in past studies provides an overly conservative assessment of thermocline performance.

]]> S. Flueckiger et al. Special issue: best papers of VLDB 2010 http://docs.lib.purdue.edu/ccpubs/461 http://docs.lib.purdue.edu/ccpubs/461 Wed, 09 May 2012 12:50:42 PDT This special issue of the VLDB Journal is dedicated to the best papers from the 36th International Conference on Very Large Data Bases, which took place on 13–17 September 2010 in Singapore.

The conference received 686 submissions overall. For the research tracks:

• The Core Databse Technology Trak received 280 submissions; of these, 19 were rejected without review because of formatting violations and 48 were accepted. The acceptance rate computed with respect to the reviewed papers is 18.4%.

• The infrastructure for Information Systems Track received 215 submissions; of these, 11 were rejected without review because of formatting violations and 33 were accepted. The acceptance rate computed with respect to the reviewed papers is 16.1%.

• The experiemental and Analysis Track received 15 submissions and accepted 4.

]]> Paolo Atzeni et al. Efficient Leakage-free Authentication of Trees, Graphs and Forests http://docs.lib.purdue.edu/ccpubs/460 http://docs.lib.purdue.edu/ccpubs/460 Wed, 09 May 2012 12:50:30 PDT Leakage-free authentication of trees and graphs have been studied in the literature. Such schemes have several practical applications especially in the cloud computing area. In this paper, we propose an authentication scheme that computes only one signature (optimal). Our scheme is not only super-efficient in the number of signatures it computes and in its runtime, but also is highly versatile -- it can be applied not only to trees, but also to graphs and forests (disconnected trees and graphs). While achieving such efficiency and versatility, we must also mention that our scheme achieves the desired security -- leakage-free authentication of data objects represented as trees, graphs and forests. This is achieved by another novel scheme that we have proposed in this paper -- a secure naming scheme for nodes of such data structures. Such a scheme assigns "secure names" to nodes such that these secure names can be used to verify the order between the nodes efficiently without leaking information about other nodes. As far as we know, our scheme is the first such scheme in literature that is optimal in its efficiency, supports two important security concerns -- authenticity and leakage-free (privacy-preserving/confidentiality), and is versatile in its applicability as it is to trees, graphs as well as forests. We have carried out complexity as well as experimental analysis of this scheme that corroborates its performance.

]]> Ashish Kundu et al. On practical specification and enforcement of obligations http://docs.lib.purdue.edu/ccpubs/459 http://docs.lib.purdue.edu/ccpubs/459 Wed, 09 May 2012 12:50:19 PDT Obligations are an important and indispensable part of many access control policies, such as those in DRM (Digital Rights Management) and healthcare information systems. To be able use obligations in a real-world access control system, there must exist a language for specifying obligations. However, such a language is currently lacking. XACML (eXtensible Access Control Markup Language), the current de facto standard for specifying access control policies, seems to integrate obligations as a part of it, but it treats obligations largely as black boxes, without specifying what an obligation should include and how to handle them. In this paper we examine the challenges in designing a practical approach for specifying and handling obligations, and then propose a language for specifying obligations, and an architecture for handling access control policies with these obligations, extending XACML's specification and architecture. In our design, obligations are modeled as state machines which communicate with the access control system and the outside world via events. We further implement our design into a prototype system named ExtXACML, based on SUN's XACML implementation. ExtXACML is extensible in that new obligation modules can be added into the system to handle various obligations for different applications, which shows the strong power of our design.

]]> Ninghui Li et al. Leakage-free redactable signatures http://docs.lib.purdue.edu/ccpubs/458 http://docs.lib.purdue.edu/ccpubs/458 Wed, 09 May 2012 12:50:06 PDT Redactable signatures for linear-structured data such as strings have already been studied in the literature. In this paper, we propose a formal security model for leakage-free redactable signatures (LFRS) that is general enough to address authentication of not only trees but also graphs and forests. LFRS schemes have several applications, especially in enabling secure data management in the emerging cloud computing paradigm as well as in healthcare, finance and biological applications. We have also formally defined the notion of secure names. Such secure names facilitate leakage-free verification of ordering between siblings/nodes. The paper also proposes a construction for secure names, and a construction for leakagefree redactable signatures based on the secure naming scheme. The proposed construction computes a linear number of signatures with respect to the size of the data object, and outputs only one signature that is stored, transmitted and used for authentication of any tree, graph and forest.

]]> Ashish Kundu et al. Irregularity in high-dimensional space-filling curves http://docs.lib.purdue.edu/ccpubs/457 http://docs.lib.purdue.edu/ccpubs/457 Wed, 09 May 2012 12:49:54 PDT A space-filling curve is a way of mapping the discrete multi-dimensional space into the one-dimensional space. It acts like a thread that passes through every cell element (or pixel) in the discrete multi-dimensional space so that every cell is visited exactly once. Thus, a space-filling curve imposes a linear order of the cells in the multi-dimensional space. There are numerous kinds of space-filling curves. The difference between such curves is in their way of mapping to the one-dimensional space. Selecting the appropriate curve for any application requires knowledge of the mapping scheme provided by each space-filling curve. Irregularity is proposed as a quantitative measure for the ordering quality imposed by space-filling curve mapping. The lower the irregularity the better the space-filling curve in preserving the order of the discrete multi-dimensional space. Five space-filling curves (the Sweep, Scan, Peano, Gray, and Hilbert) are analyzed with respect to irregularity. Closed formulas are developed to compute the irregularity in any dimension k for a D-dimensional space-filling curve with grid size N. A comparative study of different space-filling curves with respect to the irregularity is conducted and results are presented and discussed. We find out that for an application that is biased toward one of the dimensions, the Sweep or the Scan space-filling curves are the best choice. For high-dimensional applications, the Peano space-filling curve would be the best choice. For applications that require fairness among various dimensions, the Hilbert and Gray space-filling curves are the best choice.

]]> Mohamed Mokbel et al. A Distributed Access Control Architecture for Cloud Computing http://docs.lib.purdue.edu/ccpubs/456 http://docs.lib.purdue.edu/ccpubs/456 Wed, 09 May 2012 12:49:41 PDT The large-scale, dynamic, and heterogeneous nature of cloud computing poses numerous security challenges. But the cloud's main challenge is to provide a robust authorization mechanism that incorporates multitenancy and virtualization aspects of resources. The authors present a distributed architecture that incorporates principles from security management and software engineering and propose key requirements and a design model for the architecture.

]]> Abdulrahman Almutairi et al. A hybrid approach of OpenMP for clusters http://docs.lib.purdue.edu/ccpubs/455 http://docs.lib.purdue.edu/ccpubs/455 Wed, 09 May 2012 12:49:31 PDT We present the first fully automated compiler-runtime system that successfully translates and executes OpenMP shared-address-space programs on laboratory-size clusters, for the complete set of regular, repetitive applications in the NAS Parallel Benchmarks. We introduce a hybrid compiler-runtime translation scheme. Compared to previous work, this scheme features a new runtime data flow analysis and new compiler techniques for improving data affinity and reducing communication costs. We present and discuss the performance of our translated programs, and compare them with the performance of the MPI, HPF and UPC versions of the benchmarks. The results show that our translated programs achieve 75% of the hand-coded MPI programs, on average.

]]> Okwan Kwon et al. U-MAP: a system for usage-based schema matching and mapping http://docs.lib.purdue.edu/ccpubs/454 http://docs.lib.purdue.edu/ccpubs/454 Wed, 09 May 2012 12:49:20 PDT This demo shows how usage information buried in query logs can play a central role in data integration and data exchange. More specifically, our system U-Map uses query logs to generate correspondences between the attributes of two different schemas and the complex mapping rules to transform and restructure data records from one of these schemas to another. We introduce several novel features showing the benefit of incorporating query log analysis into these key components of data integration and data exchange systems.

]]> Hazem Elmeleegy et al. Leveraging query logs for schema mapping generation in U-MAP http://docs.lib.purdue.edu/ccpubs/453 http://docs.lib.purdue.edu/ccpubs/453 Wed, 09 May 2012 12:49:10 PDT In this paper, we introduce U-MAP, a new system for schema mapping generation. U-MAP builds upon and extends existing schema mapping techniques. However, it mitigates some key problems in this area, which have not been previously addressed. The key tenet of U-MAP is to exploit the usage information extracted from the query logs associated with the schemas being mapped. We describe our experience in applying our proposed system to realistic datasets from the retail and life sciences domains. Our results demonstrate the effectiveness and efficiency of U-MAP compared to traditional approaches.

]]> Hazem Elmeleegy et al. Instance-specific multi-objective parameter tuning based on fuzzy logic http://docs.lib.purdue.edu/ccpubs/452 http://docs.lib.purdue.edu/ccpubs/452 Wed, 09 May 2012 12:49:00 PDT

Finding good parameter values for meta-heuristics is known as the parameter setting problem. A new parameter tuning strategy, called IPTS, is proposed that is a novel instance-specific method to take the trade-off between solution quality and computational time into consideration. Two important steps in the method are an a priori statistical analysis to identify the factors that determine heuristic performance in both quality and time for a specific type of problem, and the transformation of these insights into a fuzzy inference system rule base which aims to return parameter values on the Pareto-front with respect to a decision maker’s preference.

Applied to the symmetric Travelling Salesman Problem and the meta-heuristic Guided Local Search, the approach is consistently faster than a traditional non-instance-specific parameter tuning strategy without significantly affecting solution quality; optimised for speed, computational times are shown to be on average 20 times faster while producing solutions of similar quality. A number of interesting areas for further research are discussed.

]]> Jana Ries et al. Visualization of Vapor Formation Regimes during Capillary-Fed Boiling http://docs.lib.purdue.edu/coolingpubs/175 http://docs.lib.purdue.edu/coolingpubs/175 Tue, 08 May 2012 21:57:04 PDT The current study investigates capillary-fed boiling of water from porous sintered powder wicks used in emerging high-effective-conductivity vapor chamber heat spreaders intended for management of hot spots with heat fluxes exceeding 500Wcm-2. Characterization of 1 mm thick wicks composed of 100 lm sintered copper particles is performed in a test facility which replicates the capillary feeding conditions that occur in such devices. Boiling curves are obtained for a 5 mm x 5 mm heated input area, along with high-speed in-situ visualization of the evaporation/boiling processes. Understanding the vapor formation regimes is essential to predictive modeling of the observed characteristics. Schematic representations of such regimes along the boiling curves are presented for homogeneous and modified wick structures. In general, incipience of boiling in sintered-powder wicks reduces the effective thermal resistance and, for small heat input areas, does not cause liquid starvation due to a capillary limitation. The thermal performance enhancement provided by two different augmentation methods is quantified and explained in terms of the observed vapor formation characteristics. Patterns fabricated within the sintered powder create multi-scale wicks with regions of different pore size. These patterns reduce thermal resistance throughout the boiling regime by increasing the permeability to vapor exiting the wick, as confirmed by visualization of the preferential vapor venting from the surface. At the highest heat fluxes investigated prior to dryout, a thin liquid film is observed to form in the recessed patterned areas at the base of the wick. Integration of copper-coated carbon nanotubes on to the sintered powder reduces the required superheat for boiling incipience, thus reducing the overall thermal resistance at low heat fluxes. Evaporation and boiling regime heat transfer predictions from several available correlations are compared to the current results, and are shown to corroborate the conclusions regarding vapor permeability.

]]> J. A. Weibel et al. Visualization of Vapor Formation Regimes during Capillary-Fed Boiling http://docs.lib.purdue.edu/coolingpubs/174 http://docs.lib.purdue.edu/coolingpubs/174 Tue, 08 May 2012 21:52:36 PDT The current study investigates capillary-fed boiling of water from porous sintered powder wicks used in emerging high-effective-conductivity vapor chamber heat spreaders intended for management of hot spots with heat fluxes exceeding 500Wcm-2. Characterization of 1 mm thick wicks composed of 100 lm sintered copper particles is performed in a test facility which replicates the capillary feeding conditions that occur in such devices. Boiling curves are obtained for a 5 mm x 5 mm heated input area, along with high-speed in-situ visualization of the evaporation/boiling processes. Understanding the vapor formation regimes is essential to predictive modeling of the observed characteristics. Schematic representations of such regimes along the boiling curves are presented for homogeneous and modified wick structures. In general, incipience of boiling in sintered-powder wicks reduces the effective thermal resistance and, for small heat input areas, does not cause liquid starvation due to a capillary limitation. The thermal performance enhancement provided by two different augmentation methods is quantified and explained in terms of the observed vapor formation characteristics. Patterns fabricated within the sintered powder create multi-scale wicks with regions of different pore size. These patterns reduce thermal resistance throughout the boiling regime by increasing the permeability to vapor exiting the wick, as confirmed by visualization of the preferential vapor venting from the surface. At the highest heat fluxes investigated prior to dryout, a thin liquid film is observed to form in the recessed patterned areas at the base of the wick. Integration of copper-coated carbon nanotubes on to the sintered powder reduces the required superheat for boiling incipience, thus reducing the overall thermal resistance at low heat fluxes. Evaporation and boiling regime heat transfer predictions from several available correlations are compared to the current results, and are shown to corroborate the conclusions regarding vapor permeability.

]]> J. A. Weibel et al. Flow Regime-Based Modeling of Heat Transfer and Pressure Drop in Microchannel Flow Boiling http://docs.lib.purdue.edu/coolingpubs/173 http://docs.lib.purdue.edu/coolingpubs/173 Tue, 08 May 2012 21:45:16 PDT Local heat transfer coefficients and pressure drops during boiling of the dielectric liquid fluorinert FC-77 in parallel microchannels were experimentally investigated in recent work by the authors. Detailed visu- alizations of the corresponding two-phase flow regimes were performed as a function of a wide range of operational and geometric parameters. A new transition criterion was developed for the delineation of a regime where microscale effects become important to the boiling process and a conventional, macroscale treatment becomes inadequate. A comprehensive flow regime map was developed for a wide range of channel dimensions and experimental conditions, and consisted of four distinct regions – bubbly, slug, confined annular, and alternating churn/annular/wispy-annular flow regimes. In the present work, phys- ics-based analyses of local heat transfer in each of the four regimes of the comprehensive map are formu- lated. Flow regime-based models for prediction of heat transfer coefficient in slug flow and annular/ wispy-annular flow are developed and compared to the experimental data. Also, a regime-based predic- tion of pressure drop in microchannels is presented by computing the pressure drop during each flow regime that occurs along the microchannel length. The results of this study reveal the promise of flow regime-based modeling efforts for predicting heat transfer and pressure drop in microchannel boiling.

]]> T. Harirchian et al. The Importance of Turbulence during Condensation in a Horizontal Circular Minichannel http://docs.lib.purdue.edu/coolingpubs/172 http://docs.lib.purdue.edu/coolingpubs/172 Tue, 08 May 2012 21:31:52 PDT Three-dimensional simulations of condensation of refrigerant R134a in a horizontal minichannel are presented. Mass fluxes ranging from 50kgm-2 s-1 up to 1000kgm-2 s-1 are considered in a circular minichannel of 1mm diameter, and uniform wall and vapour–liquid interface temperatures are imposed as boundary conditions. The Volume of Fluid (VOF) method is used to track the vapour–liquid interface; the effects of interfacial shear stress, gravity and surface tension are taken into account. The influence of turbulence in the condensate film is analysed and compared against the assumption of laminar condensate flow by employing different computational approaches and validating the results against experimental data. Under the assumption of laminar condensate flow, experimental heat transfer coefficient values at low mass fluxes can be predicted, but the computed heat transfer coefficient is found to be almost independent of mass flux and vapour quality. Only when turbulence in the condensate film is taken into account does the numerical model capture the influence of mass flux that is observed in the experimental measurements.

]]> E. da Riva et al. The Importance of Turbulence during Condensation in a Horizontal Circular Minichannel http://docs.lib.purdue.edu/coolingpubs/171 http://docs.lib.purdue.edu/coolingpubs/171 Tue, 08 May 2012 21:26:34 PDT Three-dimensional simulations of condensation of refrigerant R134a in a horizontal minichannel are presented. Mass fluxes ranging from 50kgm-2 s-1 up to 1000kgm-2 s-1 are considered in a circular minichannel of 1mm diameter, and uniform wall and vapour–liquid interface temperatures are imposed as boundary conditions. The Volume of Fluid (VOF) method is used to track the vapour–liquid interface; the effects of interfacial shear stress, gravity and surface tension are taken into account. The influence of turbulence in the condensate film is analysed and compared against the assumption of laminar condensate flow by employing different computational approaches and validating the results against experimental data. Under the assumption of laminar condensate flow, experimental heat transfer coefficient values at low mass fluxes can be predicted, but the computed heat transfer coefficient is found to be almost independent of mass flux and vapour quality. Only when turbulence in the condensate film is taken into account does the numerical model capture the influence of mass flux that is observed in the experimental measurements.

]]> E. da Riva et al. Carbon Nanotube Coatings for Enhanced Capillary-Fed Boiling from Porous Microstructures http://docs.lib.purdue.edu/coolingpubs/170 http://docs.lib.purdue.edu/coolingpubs/170 Tue, 08 May 2012 21:11:08 PDT Due to their high intrinsic thermal conductivity, carbon nanotubes (CNTs) have previously been incorporated into a variety of thermal management applications to improve cooling performance. Implementation of controlled CNT growth techniques and functionalization methods are applied herein to enhance boiling heat transfer from the porous capillary wicking surfaces widely used in high heat flux thermal management devices. A microwave plasma-enhanced chemical vapor deposition (MPCVD) synthesis process resulted in growth of a permeable CNT coating, and physical vapor deposition of copper over these nanotubes yielded the requisite hydrophilic wicking surface. An array of test samples was fabricated and then evaluated using an experimental test facility to determine the reduction in surface temperature resulting from CNT coating and micropatterning of the porous surfaces under two-phase heat transfer conditions with water as the working fluid. Both CNT coating and micropatterning techniques were able to provide significant performance enhancements, reducing the surface superheat up to 72% compared to baseline tests and eliminating disad- vantageous temperature overshoot corresponding to boiling incipience. Such performance gains are attributable to the formation of nanoporous cavities that increase nucleation site density and high permeability vents through which vapor can readily depart the surface under vigorous boiling conditions. The synthesis procedures developed that result in the observed enhancement can be readily incorporated into currently employed devices.

]]> J. A. Weibel et al. Detecting Inconsistencies in Private Data with Secure Function Evaluation http://docs.lib.purdue.edu/cstech/1758 http://docs.lib.purdue.edu/cstech/1758 Tue, 08 May 2012 12:36:30 PDT Nilothpal Talukder et al. vSlicer: Latency-Aware Virtual Machine Scheduling via Differentiated-Frequency CPU Slicing http://docs.lib.purdue.edu/cstech/1757 http://docs.lib.purdue.edu/cstech/1757 Tue, 08 May 2012 12:36:20 PDT Cong Xu et al. White Box Sampling in Uncertain Data Processing Enabled by Program Analysis http://docs.lib.purdue.edu/cstech/1756 http://docs.lib.purdue.edu/cstech/1756 Tue, 08 May 2012 12:36:10 PDT Tao Bao et al. CobWeb: A System for Automated In-Network Cobbling of Web Service Traffic http://docs.lib.purdue.edu/cstech/1755 http://docs.lib.purdue.edu/cstech/1755 Tue, 08 May 2012 12:35:59 PDT Hitesh Khandelwal et al. An ensemble model for collective classification that reduces learning and inference variance http://docs.lib.purdue.edu/cstech/1754 http://docs.lib.purdue.edu/cstech/1754 Tue, 08 May 2012 12:35:48 PDT Hoda Eldardiry et al. Network Similarity Decomposition (NSD): A Fast and Scalable Approach to Network Alignment http://docs.lib.purdue.edu/cstech/1753 http://docs.lib.purdue.edu/cstech/1753 Tue, 08 May 2012 12:25:45 PDT Giorgos Kollias et al. Structured Comparative Analysis of Systems Logs to Diagnose Performance Problems http://docs.lib.purdue.edu/cstech/1752 http://docs.lib.purdue.edu/cstech/1752 Tue, 08 May 2012 12:25:37 PDT Karthik Nagaraj et al. Accentuating the Positive: Atomicity Inference and Enforcement Using Correct Executions http://docs.lib.purdue.edu/cstech/1751 http://docs.lib.purdue.edu/cstech/1751 Tue, 08 May 2012 12:25:30 PDT Dasarath Weeratunge et al. The TCP Outcast Problem: Exposing Unfairness in Data Center Networks http://docs.lib.purdue.edu/cstech/1750 http://docs.lib.purdue.edu/cstech/1750 Tue, 08 May 2012 12:25:21 PDT Pawan Prakash et al. Featherweight Threads for Communication http://docs.lib.purdue.edu/cstech/1749 http://docs.lib.purdue.edu/cstech/1749 Tue, 08 May 2012 12:25:13 PDT KC Sivaramakrishnan et al. Privacy Preserving Regression Residual Analysis http://docs.lib.purdue.edu/cstech/1748 http://docs.lib.purdue.edu/cstech/1748 Tue, 08 May 2012 12:25:05 PDT John Ross Wallrabenstein et al. Network Sampling via Edge-based Node Selection with Graph Induction http://docs.lib.purdue.edu/cstech/1747 http://docs.lib.purdue.edu/cstech/1747 Tue, 08 May 2012 12:24:57 PDT Nesreen Ahmed et al. Geometric Interoperability for Resilient Manufacturing http://docs.lib.purdue.edu/cstech/1746 http://docs.lib.purdue.edu/cstech/1746 Tue, 08 May 2012 12:24:50 PDT Christoph M. Hoffmann et al. Opportunistic Flooding to Improve TCP Transmit Performance in Virtualized Clouds http://docs.lib.purdue.edu/cstech/1745 http://docs.lib.purdue.edu/cstech/1745 Tue, 08 May 2012 12:24:42 PDT Sahan Gamage et al. Leave Them Microseconds Alone: Scalable Architecture for Maintaining Packet Latency Measurements http://docs.lib.purdue.edu/cstech/1744 http://docs.lib.purdue.edu/cstech/1744 Tue, 08 May 2012 12:24:34 PDT Myungjin Lee et al. Using Past Queries for Resource Selection in Distributed Information Retrieval http://docs.lib.purdue.edu/cstech/1743 http://docs.lib.purdue.edu/cstech/1743 Tue, 08 May 2012 12:24:26 PDT Sulleyman Cetintas et al. On the Efficacy of Fine-Grained Traffic Splitting Protocols in Data Center Networks http://docs.lib.purdue.edu/cstech/1742 http://docs.lib.purdue.edu/cstech/1742 Tue, 08 May 2012 12:24:18 PDT Advait Dixit et al. Methods to Determine Node Centrality and Clustering in Graphs with Uncertain Structure http://docs.lib.purdue.edu/cstech/1741 http://docs.lib.purdue.edu/cstech/1741 Tue, 08 May 2012 12:24:10 PDT Joseph J. Pfeiffer III et al. Query Processing in Private Data Outsourcing Using Anonymization http://docs.lib.purdue.edu/cstech/1740 http://docs.lib.purdue.edu/cstech/1740 Tue, 08 May 2012 12:24:02 PDT Ahmet Erhan Nergiz et al. c-Lock: Dynamic Lock-coalescing for Latency-sensitive Distributed Locking http://docs.lib.purdue.edu/cstech/1739 http://docs.lib.purdue.edu/cstech/1739 Tue, 08 May 2012 12:23:54 PDT Adnan Hassan et al. Sparse Matrix-variate t Process Blockmodels http://docs.lib.purdue.edu/cstech/1738 http://docs.lib.purdue.edu/cstech/1738 Tue, 08 May 2012 12:23:46 PDT Zenglin Xu et al. Transactional Support in MapReduce for Speculative Parallelism http://docs.lib.purdue.edu/cstech/1737 http://docs.lib.purdue.edu/cstech/1737 Tue, 08 May 2012 08:41:47 PDT Naresh Rapolu et al. Lightweight Task Graph Inference for Distributed Applications http://docs.lib.purdue.edu/cstech/1736 http://docs.lib.purdue.edu/cstech/1736 Tue, 08 May 2012 08:41:39 PDT Bin Xin et al. vSnoop: Improving TCP Throughput in Virtualized Environments via Acknowledgement Offload http://docs.lib.purdue.edu/cstech/1735 http://docs.lib.purdue.edu/cstech/1735 Tue, 08 May 2012 08:41:31 PDT Ardalan Kangarlou et al. Analyzing Concurrency Bugs Using Dual Slicing http://docs.lib.purdue.edu/cstech/1734 http://docs.lib.purdue.edu/cstech/1734 Tue, 08 May 2012 08:41:23 PDT Dasarath Weeratunge et al. One Stack to Run Them All Reducing Concurrent Analysis to Sequential Analysis Under Priority Scheduling http://docs.lib.purdue.edu/cstech/1733 http://docs.lib.purdue.edu/cstech/1733 Tue, 08 May 2012 08:41:15 PDT Nicholas Kidd et al. Path-Sensitive Analysis Using Edge Strings http://docs.lib.purdue.edu/cstech/1732 http://docs.lib.purdue.edu/cstech/1732 Tue, 08 May 2012 08:41:08 PDT Armand Navabi et al. Isolates: Serializability Enforcement for Concurrent ML http://docs.lib.purdue.edu/cstech/1731 http://docs.lib.purdue.edu/cstech/1731 Tue, 08 May 2012 08:41:00 PDT Lukasz Ziarek et al. Composable Asynchronous Events http://docs.lib.purdue.edu/cstech/1730 http://docs.lib.purdue.edu/cstech/1730 Tue, 08 May 2012 08:40:52 PDT Lukasz Ziarek et al. FineComb: Measuring Microscopic Latencies and Losses in the Presence of Reordering http://docs.lib.purdue.edu/cstech/1729 http://docs.lib.purdue.edu/cstech/1729 Tue, 08 May 2012 08:40:44 PDT Myungjin Lee et al. Memory Indexing and its Use in Automated Debugging http://docs.lib.purdue.edu/cstech/1728 http://docs.lib.purdue.edu/cstech/1728 Tue, 08 May 2012 08:40:36 PDT William Summer et al. Revisiting Overlay Multicasting for the Cloud http://docs.lib.purdue.edu/cstech/1727 http://docs.lib.purdue.edu/cstech/1727 Tue, 08 May 2012 08:40:28 PDT Karthik Nagaraj et al. Correcting Bias in Statistical Tests for Network Classifier Evaluation http://docs.lib.purdue.edu/cstech/1726 http://docs.lib.purdue.edu/cstech/1726 Tue, 08 May 2012 08:40:20 PDT Jennifer Neville et al. Generalizations with Probability Distributions for Data Anonymization http://docs.lib.purdue.edu/cstech/1725 http://docs.lib.purdue.edu/cstech/1725 Tue, 08 May 2012 08:40:12 PDT Mehmet Ercan Nergiz et al.