bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Management Phenomena in Foil Gas Thrust Bearings
Authors: Dykas Brian , Prahl Joseph , DellaCorte Christopher , Bruckner Robert
Published: September 2008

Thrust foil gas bearings operate at high speeds on a very thin fluid film which experiences high shear. Shear induced viscous losses result in localized heating which must be managed to prevent thermal distortions and failure. The current work examines the need for thermal management in thrust foil bearings as evidenced by reduced performance in uncooled bearings. Measured bearing power loss is a few hundred watts from twenty-five to fifty-five krpm (89–196 m/s runner surface velocity based on mean bearing diameter). Modeling of the thrust runner demonstrates a potential for stress-induced running surface deformations greater than the gas film thickness (>10 μm), and radial temperature gradients in the bearing foils can exceed a few degrees Celcius per millimeter. Air flow forced through the foil structure achieves improvements in bearing load capacity and demonstrates a need for increased understanding of the thermal environment in these bearings.
The Blade Strength and the Dynamic Characteristics of High Speed Micro-Turbines
Authors: Kuang Jao Hwa , Chen Hsuan-Sheng , Hung Tsung-Pin
Published: September 2008

The effects of centrifugal force and operating temperature on the stress and creep deformation of rotating micro-turbo rotors are studied in this work. The thermal-mechanical- creep coupled finite element model provided in the MARC package is employed. The variation of stresses and creep strain distributions in turbo blades made of different materials, e.g. stainless steel (A304L), Ti-alloy (Ti-2411) and two ceramics (SiC and SiN3) are analyzed and compared. The effect of rotating speed on the natural frequencies of the micro-turbine with different turbo-blade materials are also evaluated and compared in this study. Numerical results indicate that the strength and dynamic behavior of the micro-turbo rotor is very sensitive to the material of turbo blade.
LHD 8 Propulsion Machinery Control System Design and Integration
Authors: Tolotta Vincent P. , Harris Howard
Published: September 2008

The LHD 8 machinery plant represents a significant departure from previous LHD class ships with a propulsion system that combines an LM2500+ and electric motor per shaft. The propulsion system integrates the first US Navy application of this gas turbine engine ultimately with the ship service electric plant. This complex system affords many advantages to the ship designers with respect to reconfigurability, survivability and maneuvering. However the design challenges the ability of the Machinery Control System (MCS) to maximize the effectiveness of this complex machinery plant. The MCS is a software-based distributed system utilizing a high bandwidth network. The system relies on the VME platform for control processing, data acquisition and operator control. The MCS design and architecture is presented. Decisions concerning network capabilities, distribution of control, and processing are considered. The impact of electric plant complexities upon the propulsion system requirements will also be addressed. The MCS architecture solution will describe LM2500+ integration issues with an electric motor.
Aerodynamic Instability Effects on Compressor Blade Failure: A Root Cause Failure Analysis
Authors: Simmons Harold R. , Brun Klaus , Cheruvu Sastry
Published: September 2008

Diagnosing the root cause of compressor blade failures by high cycle fatigue (HCF) is elusive for gas turbines with a long history of successful operation; long operating times preclude design, fabrication, and material defect issues that are usually associated with short term failures. Long exposure time might implicate erosion or corrosion issues for compressor failures. An investigation of 3rd stage stator vane and 4th stage rotor blade failure in a Frame 7 gas turbine revealed that aerodynamic excitations associated with mild compressor instability (undetected by installed sensors) was the most probable cause. A Blade Vibration Audit (BVA) approach exploits information collected and compared from independent sources: 1) Fracture mode details and expected failure stress levels estimated in metallurgical examination; 2) Aerodynamic excitations due to internal airfoil wakes, rotating stall, and flutter applied to vibratory stress response data obtained by modal testing to estimate relative operating stress levels; 3) Design margins deduced from successful operating experience, which establish a base line for comparison with the excitation sources considered likely. Diagnosis of HCF failure causes must produce results that match observations of the specific failures in three ways: 1) The airfoils must be in resonance for sufficient time for fatigue to occur, 2) The vibratory stress must be greater at the failure location than elsewhere, and 3) The causal effect must significantly increase the stress at the failure location to be more than elsewhere. The analysis showed that the 3rd stator vane failed at 2/3 span, which led to 4th blade failure due to subsequent adverse aerodynamic excitation and impact damage. The most likely cause of the 3rd stator vane failure was a combination of resonant excitation from excessive wakes of the downstream rotor blades and flutter associated with mild intermittent surge.
Safety and Efficacy of Enfuvirtide in Combination with Darunavir-Ritonavir and an Optimized Background Regimen in Treatment-Experienced Human Immunodeficiency Virus-Infected Patients: the Below the Level of Quantification Study
Authors: DeJesus Edwin , Gottlieb Michael S. , Gathe Joseph C. , Greenberg Michael L. , Guittari Carol Jean , Zolopa Andrew R.
Published: September 2008

Enfuvirtide is the first fusion and entry inhibitor approved for use for the treatment of human immunodeficiency virus (HIV) type 1 infection and as such represents a novel class of agents. For the population of patients experienced with three antiretroviral classes, enfuvirtide provides an additional option for treatment. This prospective, open-label, 24-week, single-arm trial assessed the efficacy and safety of enfuvirtide (90 mg injected subcutaneously twice daily) in combination with darunavir-ritonavir (600/100 mg administered orally twice daily) in triple-antiretroviral-class-experienced adults failing their current regimen. The primary efficacy endpoint was the proportion of participants with plasma HIV RNA loads of <50 copies/ml. Other virological and immunological measures were also evaluated, as were the effects of the baseline viral coreceptor tropism and darunavir phenotype sensitivity scores on the outcomes. At week 24, 60.3%, 72.5%, and 84.0% of 131 participants achieved viral loads of <50 copies/ml and <400 copies/ml and a change from the baseline load of ≥1 log
10
copies/ml, respectively. A baseline viral load of ≤5 log
10
copies/ml was a significant predictor of achieving a viral load of <50 copies/ml at 24 weeks; however, neither background genotype sensitivity nor darunavir phenotype sensitivity was a significant predictor of the achievement of viral loads of <50 copies/ml. Although these findings are limited by the relatively small numbers of participants with darunavir susceptibility changes of ≥10-fold, they suggest that combining enfuvirtide and darunavir-ritonavir with an optimized background regimen in triple-class experienced participants naïve to these agents can result in positive virological and immunological responses regardless of most baseline parameters.
Antifungal Activities of Human Beta-Defensins HBD-1 to HBD-3 and Their C-Terminal Analogs Phd1 to Phd3
Authors: Krishnakumari Viswanatha , Rangaraj Nandini , Nagaraj Ramakrishnan
Published: September 2008

The activities of defensins HBD-1, HBD-2, and HBD-3 and their C-terminal analogs Phd1, Phd2, and Phd3 againstCandida albicanswere investigated. Phd1 to Phd3 showed lower-level activities than HBD-1 to HBD-3, although metabolic inhibitors did not render Phd1 to Phd3 inactive. Their activities were also less salt sensitive than those of HBD-1 to HBD-3. Confocal microscope images indicated that the initial site of action was the fungal membrane.
Piperacillin-Tazobactam Penetration into Human Pancreatic Juice
Authors: Bertazzoni Minelli Elisa , Benini Anna , Franco Luigina , Bassi Claudio , Pederzoli Paolo
Published: September 2008

Piperacillin-tazobactam was administered as a single dose (4.5 g intravenous) to five patients with stabilized external pancreatic fistula. The penetration into pancreatic juice was prompt, and inhibitory concentrations were achieved and maintained for different periods (0.5 to 6 h) according to bacterial susceptibility and patients' characteristics. Piperacillin and tazobactam showed superimposable pharmacokinetics in both serum and pancreatic juice.
Plasmodium vivaxResistance to Chloroquine in Madagascar: Clinical Efficacy and Polymorphisms inpvmdr1andpvcrt-oGenes
Authors: Barnadas Céline , Ratsimbasoa Arsène , Tichit Magali , Bouchier Christiane , Jahevitra Martial , Picot Stéphane , Ménard Didier
Published: September 2008

No data were available concerningPlasmodium vivaxresistance to chloroquine (CQ) in Madagascar. We investigated the therapeutic efficacy of CQ inP. vivaxmalaria, the prevalence of mutations in thepvcrt-oandpvmdr1genes before treatment, and the association between mutant parasites and the clinical response of the patients to CQ treatment. Clinical isolates were collected at six sentinel sites located in the three epidemiological strata for malaria throughout Madagascar in 2006. Patients were enrolled, treated, and followed up according to the WHO 2001 guidelines forP. vivaxinfections. Sequencing was used to analyze polymorphisms of thepvcrt-o(exons 1 to 6) andpvmdr1genes. The treatment failure rate, after adjustment for genotyping, was estimated at 5.1% for the 105 patients included, ranging from zero in the South to 14.8% in the foothills of the Central Highlands. All samples were wild type forpvcrt-obut mutant for thepvmdr1gene. Ten nonsynonymous mutations were found in thepvmdr1gene, including five new mutations, four of which were present at low frequencies (1.3% to 7.5%) while the S513R mutation was present at a much higher frequency (96.3%). The other five mutations, including Y976F, had been described before and had frequencies of 97.8% to 100%. Our findings suggest that CQ-resistantP. vivaxisolates are present in Madagascar, particularly in the foothills of the Central Highlands. The 976Ypvmdr1mutation was found not to be useful for monitoring CQ resistance. Further efforts are required to develop suitable tools for monitoring drug resistance inP. vivaxmalaria.
Tet 42, a Novel Tetracycline Resistance Determinant Isolated from Deep Terrestrial Subsurface Bacteria
Authors: Brown Mindy G. , Mitchell Elizabeth H. , Balkwill David L.
Published: September 2008

Tet 42, a novel tetracycline resistance determinant from deep subsurface bacteria, was characterized and found to have a 30% sequence similarity to TetA(Z). The protein is a putative efflux pump that shares characteristics with previously characterized pumps, including a divergently transcribed TetR repressor, a conserved GxxSDRxGRR motif, and transmembrane domains.
Protection of Wild-Type and Severe Combined Immunodeficiency Mice against an Intranasal Challenge by Passive Immunization with Monoclonal Antibodies to theChlamydia trachomatisMouse Pneumonitis Major Outer Membrane Protein
Authors: Pal Sukumar , Bravo Jose , Peterson Ellena M. , de la Maza Luis M.
Published: September 2008

Monoclonal antibodies (MAbs) to theChlamydia trachomatismouse pneumonitis (MoPn) major outer membrane protein (MOMP) were characterized for their ability to neutralize the infectivity of this organism in vitro and in vivo. One of the MAbs (MoPn-23) recognizes a nonlinear epitope in the MOMP, MAb MoPn-40 binds to a linear epitope in the variable domain 1 (VD1), and MAb MoPn-32 recognizes the chlamydial lipopolysaccharide. MAb MoPn-23 neutralized 50% of the infectivity ofChlamydia, as measured in vitro by using HAK (FcγIII−) and HeLa-229 (FcγIII+) cells at a concentration 100 times lower than MAb MoPn-40. MAb MoPn-32 had no neutralizing ability. In comparison to the control normal mouse immunoglobulin G, passive immunization of BALB/c mice with MAb MoPn-23 resulted in a highly significant protection against an intranasal (i.n.) challenge as determined by the change in body weight, the weight of the lungs, and the yield ofChlamydiainclusion-forming units (IFU) from the lungs. Passive immunization with MAb MoPn-40 resulted in a lower degree of protection, and MAb MoPn-32 afforded no protection. MAb MoPn-23 was also tested for its ability to protect wild-type (WT) and severe combined immunodeficient (SCID) C.B-17 mice against an i.n. challenge. Protection based on total body weight, lung weight, and yield ofChlamydiaIFU was as effective in SCID as in WT C.B-17 mice. In conclusion, antibodies to MOMP can protect mice against a chlamydial infection in the presence or absence of T and B cells.
Vibrio choleraeFlagellins Induce Toll-Like Receptor 5-Mediated Interleukin-8 Production through Mitogen-Activated Protein Kinase and NF-κB Activation
Authors: Harrison Lisa M. , Rallabhandi Prasad , Michalski Jane , Zhou Xin , Steyert Susan R. , Vogel Stefanie N. , Kaper James B.
Published: September 2008

Vaccine reactogenicity has complicated the development of safe and effective live, oral cholera vaccines. Δctx Vibrio choleraemutants have been shown to induce inflammatory diarrhea in volunteers and interleukin-8 (IL-8) production in cultured intestinal epithelial cells. Bacterial flagellins are known to induce IL-8 production through Toll-like receptor 5 (TLR5). Since theV. choleraegenome encodes five distinct flagellin proteins, FlaA to FlaE, with homology to conserved TLR5 recognition regions ofSalmonellaFliC, we hypothesized thatV. choleraeflagellins may contribute to IL-8 induction through TLR5 and mitogen-activated protein kinase (MAPK) signaling. Each purified recombinantV. choleraeflagellin induced IL-8 production in T84 intestinal epithelial cells and also induced nuclear factor kappa B (NF-κB) activation in HEK293T/TLR5 transfectants, which was blocked by cotransfection with a TLR5 dominant-negative construct, demonstrating TLR5 specificity. Supernatants derived from ΔflaACand ΔflaEDBmutants induced IL-8 production in HT-29 intestinal epithelial cells and in HEK293T cells overexpressing TLR5, whereas ΔflaABCDEsupernatants induced significantly less IL-8 production, demonstrating the contribution of multiple flagellins in IL-8 induction. NF-κB activation by ΔflaABCDEsupernatants was partially restored byflaAorflaACcomplementation. Western analysis confirmed the presence ofV. choleraeflagellins in culture supernatants. Purified recombinantV. choleraeFlaA activated the MAPKs p38, c-jun N-terminal kinase (JNK), and extracellular regulated kinase (ERK) in T84 cells. FlaA-induced IL-8 production in T84 cells was inhibited by the p38 inhibitor in combination with either the JNK or ERK inhibitors. Collectively, these data suggest thatV. choleraeflagellins are present in culture supernatants and can induce TLR5- and MAPK-dependent IL-8 secretion in host cells.
A NEWMAN–PENROSE CALCULATOR FOR INSTANTON METRICS
Authors: BIRKANDAN TOLGA
Published: September 2008

We present a Maple11+GRTensorII based symbolic calculator for instanton metrics using Newman–Penrose formalism. Gravitational instantons are exact solutions of Einstein's vacuum field equations with Euclidean signature. The Newman–Penrose formalism, which supplies a toolbox for studying the exact solutions of Einstein's field equations, was adopted to the instanton case and our code translates it for the computational use.
FOURTH ORDER SYMPLECTIC INTEGRATION WITH REDUCED PHASE ERROR
Authors: VAN DE VYVER HANS
Published: September 2008

In this paper we introduce a symplectic explicit RKN method for Hamiltonian systems with periodical solutions. The method has algebraic order four and phase-lag order six at a cost of four function evaluations per step. Numerical experiments show the relevance of the developed algorithm. It is found that the new method is much more efficient than the standard symplectic fourth-order method.
ELASTIC PROPERTIES OF TRANSITION METAL DIOXIDES: XO2 (X = Ru, Rh, Os, andIr)
Authors: LI YANLING , ZENG ZHI
Published: September 2008

The elastic properties of rutile transition metal dioxides XO2 ( X = Ru , Rh , Os , and Ir ) are investigated using first-principles calculations based on density functional theory. Elastic constants, bulk modulus, shear modulus, and Young's modulus as well as Possion ratio are given. OsO 2 and IrO 2 show strong incompressibility. The hardness estimated for these dioxides shows that they are not superhard solids. The obtained Debye temperatures are comparative to those of transition metal dinitrides or diborides.
THE ALLOCATION OF SURPLUS BY MARKETS: A FRAMEWORK FOR ANALYSIS
Authors: GARRIDO NICOLÁS
Published: September 2008

The aim of this paper is to present algorithmic specifications of institutions as an alternative to the pervasive gradient institutions used in mainstream economics. A framework to evaluate the performance of the institutions is proposed using instruments from landscape theory. The problem of how a simple market allocates surplus is studied as an example of application of the framework.
A neural-network-based context-aware handoff algorithm for multimedia computing
Authors: Lin Tsungnan , Wang Chiapin , Lin Po-Chiang
Published: September 2008

The access of multimedia computing in wireless networks is concerned with the performance of handoff because of the irretrievable property of real-time data delivery. To lessen throughput degradation incurred by unnecessary handoffs or handoff latencies leading to media disruption perceived by users, this paper presents a link quality based handoff algorithm. Neural networks are used to learn the cross-layer correlation between the link quality estimator such as packet success rate and the corresponding context metric indictors, for example, the transmitting packet length, received signal strength, and signal to noise ratio. Based on a pre-processed learning of link quality profile, neural networks make essential handoff decisions efficiently with the evaluations of link quality instead of the comparisons between relative signal strength. The experiment and simulation results show that the proposed algorithm improves the user perceived qualities in a transmission scenario of VoIP applications by minimizing both the number of lost packets and unnecessary handoffs.
Towards attention-centered interfaces
Authors: Franke Ingmar S. , Pannasch Sebastian , Helmert Jens R. , Rieger Robert , Groh Rainer , Velichkovsky Boris M.
Published: September 2008

The established method of representing three-dimensional space on a two-dimensional surface involves camera based, point of regard systems, comparable in design to the early “camera obscura”. However, geometrical limitations of such models lead to distortions of perspective when projected. This research investigated the influence of single- versus multi-perspectives on aesthetic choices within one image. A clear perceptual bias towards multi-perspective images was found, additionally supported by an eye tracking study. We propose that human users are more attracted by multi-perspective images, which emphasise the “semantic foci” of the scene, than by those being synthesized statically with only one geometrical prospect.
Exploring large-scale peer-to-peer live streaming topologies
Authors: Wu Chuan , Li Baochun , Zhao Shuqiao
Published: September 2008

Real-world live peer-to-peer (P2P) streaming applications have been successfully deployed in the Internet, delivering live multimedia content to millions of users at any given time. With relative simplicity in design with respect to peer selection and topology construction protocols and without much algorithmic sophistication, current-generation live P2P streaming applications are able to provide users with adequately satisfying viewing experiences. That said, little existing research has provided sufficient insights on the time-varying internal characteristics of peer-to-peer topologies in live streaming. This article presents
Magellan
, our collaborative work with UUSee Inc., Beijing, China, for exploring and charting graph theoretical properties of practical P2P streaming topologies, gaining important insights in their topological dynamics over a long period of time.

With more than 120 GB worth of traces starting September 2006 from a commercially deployed P2P live streaming system that represents UUSee's core product, we have completed a thorough and in-depth investigation of the topological properties in large-scale live P2P streaming, as well as their evolutionary behavior over time, for example, at different times of the day and in flash crowd scenarios. We seek to explore real-world P2P streaming topologies with respect to their graph theoretical metrics, such as the degree, clustering coefficient, and reciprocity. In addition, we compare our findings with results from existing studies on topological properties of P2P file sharing applications, and present new and unique observations specific to streaming. We have observed that live P2P streaming sessions demonstrate excellent scalability, a high level of reciprocity, a clustering phenomenon in each ISP, and a degree distribution that does
not
follow the power-law distribution.
Video game design using an eye-movement-dependent model of visual attention
Authors: Jie Li , Clark James J.
Published: September 2008

Eye movements can be used to infer the allocation of covert attention. In this article, we propose to model the allocation of attention in a task-dependent manner based on different eye movement conditions, specifically fixation and pursuit. We show that the image complexity at eye fixation points during fixation, and the pursuit direction during pursuit are significant factors in attention allocation. Results of the study are applied to the design of an interactive computer game. Real-time eye movement information is taken as one of inputs for the game. The utility of such eye information for controlling game difficulty is shown.
Predictive real-time perceptual compression based on eye-gaze-position analysis
Authors: Komogortsev Oleg V. , Khan Javed I.
Published: September 2008

This article designs a real-time perceptual compression system (RTPCS) based on eye-gaze-position analysis. Our results indicate that the eye-gaze-position containment metric provides more efficient and effective evaluation of an RTPCS than the eye fixation containment. The presented RTPCS is designed for a network communication scenario with a feedback loop delay. The proposed RTPCS uses human visual system properties to compensate for the delay and to provide high ratios of multimedia compression.
Adaptive work-stealing with parallelism feedback
Authors: Agrawal Kunal , Leiserson Charles E. , He Yuxiong , Hsu Wen Jing
Published: September 2008

Multiprocessor scheduling in a shared multiprogramming environment can be structured as two-level scheduling, where a kernel-level job scheduler allots processors to jobs and a user-level thread scheduler schedules the work of a job on its allotted processors. We present a randomized work-stealing thread scheduler for fork-join multithreaded jobs that provides continual parallelism feedback to the job scheduler in the form of requests for processors. Our A-STEAL algorithm is appropriate for large parallel servers where many jobs share a common multiprocessor resource and in which the number of processors available to a particular job may vary during the job's execution. Assuming that the job scheduler never allots a job more processors than requested by the job's thread scheduler, A-STEAL guarantees that the job completes in near-optimal time while utilizing at least a constant fraction of the allotted processors.

We model the job scheduler as the thread scheduler's adversary, challenging the thread scheduler to be robust to the operating environment as well as to the job scheduler's administrative policies. For example, the job scheduler might make a large number of processors available exactly when the job has little use for them. To analyze the performance of our adaptive thread scheduler under this stringent adversarial assumption, we introduce a new technique called
trim analysis,
which allows us to prove that our thread scheduler performs poorly on no more than a small number of time steps, exhibiting near-optimal behavior on the vast majority.

More precisely, suppose that a job has work
T
1
and span
T
∞
. On a machine with
P
processors, A-STEAL completes the job in an expected duration of
O
(
T
1
/
P˜
+
T
∞
+
L
lg
P
) time steps, where
L
is the length of a scheduling quantum, and
P˜
denotes the
O
(
T
∞
+
L
lg
P
)-trimmed availability. This quantity is the average of the processor availability over all time steps except the
O
(
T
∞
+
L
lg
P
) time steps that have the highest processor availability. When the job's parallelism dominates the trimmed availability, that is,
P˜
<
T
1
/
T
∞
, the job achieves nearly perfect linear speedup. Conversely, when the trimmed mean dominates the parallelism, the asymptotic running time of the job is nearly the length of its span, which is optimal.

We measured the performance of A-STEAL on a simulated multiprocessor system using synthetic workloads. For jobs with sufficient parallelism, our experiments confirm that A-STEAL provides almost perfect linear speedup across a variety of processor availability profiles. We compared A-STEAL with the ABP algorithm, an adaptive work-stealing thread scheduler developed by Arora et al. [1998] which does not employ parallelism feedback. On moderately to heavily loaded machines with large numbers of processors, A-STEAL typically completed jobs more than twice as quickly as ABP, despite being allotted the same number or fewer processors on every step, while wasting only 10% of the processor cycles wasted by ABP.
Prep students for irreversible software trends
Authors: CACM Staff
Published: September 2008

Stephen J. Andriole and Eric Roberts debated how to educate the next generation of technology professionals in the Viewpoint Point/Counterpoint "Technology Curriculum for the Early 21st Century" (July 2008). Here, they offer their final words on each other's thoughts, beginning with Andriole.
Green computing
Authors: Kurp Patrick
Published: September 2008

Are you ready for a personal energy meter?
Searching the deep web
Authors: Wright Alex
Published: September 2008

While the Semantic Web may be a long time coming, Deep Web search strategies offer the promise of a semantic Web.
Code spelunking redux
Authors: Neville-Neil George V.
Published: September 2008

Is it getting any easier to understand other people's code?
The topology of dark networks
Authors: Xu Jennifer , Chen Hsinchun
Published: September 2008

Knowing the structure of criminal and terrorist networks could provide the technical insight needed to disrupt their activities.
Scene completion using millions of photographs
Authors: Hays James , Efros Alexei A.
Published: September 2008

What can you do with a million images? In this paper, we present a new image completion algorithm powered by a huge database of photographs gathered from the Web. The algorithm patches up holes in images by finding similar image regions in the database that are not only seamless, but also semantically valid. Our chief insight is that while the space of images is effectively infinite, the space of semantically differentiable scenes is actually not that large. For many image completion tasks, we are able to find similar scenes which contain image fragments that will convincingly complete the image. Our algorithm is entirely data driven, requiring no annotations or labeling by the user. Unlike existing image completion methods, our algorithm can generate a diverse set of image completions and we allow users to select among them. We demonstrate the superiority of our algorithm over existing image completion approaches.
An inspiring legacy
Authors: Hoffmann Leah
Published: September 2008

Admired and respected by his students and colleagues, Randy Pausch will be remembered as a devoted teacher and innovative researcher.
Polymorphism and page tables
Authors: Jones Mark P.
Published: September 2008

With features that include lightweight syntax, expressive type systems, and deep semantic foundations, functional languages are now being used to develop an increasingly broad range of complex, real-world applications. In the area of systems software, however, where performance and interaction with low-level aspects of hardware are central concerns, many practitioners still eschew the advantages of higher-level languages for the potentially unsafe but predictable behavior of traditional imperative languages like C. It is ironic that critical applications such as operating systems kernels, device drivers, and VMMs - where a single bug could compromise the reliability or security of a whole system - are among the least likely to benefit from the abstractions and safety guarantees of modern language designs.

Over the last few years, our group has been investigating the potential for using Haskell to develop realistic operating systems that can boot and run on bare metal. The House system, developed primarily by Thomas Hallgren and Andrew Tolmach, demonstrates that it is indeed possible to construct systems software in a functional language. But House still relies on a layer of runtime support primitives - some written using unsafe Haskell primitives and others written in C - to provide services ranging from garbage collection to control of the page table structures used by the hardware memory management unit. We would like to replace as much of this layer as possible with code written in a functional language without compromising on type or memory safety.

Our experiences with House have led us to believe that a new functional language is required to reflect the needs of the systems domain more directly. Interestingly, however, we have concluded that this does not require fundamental new language design. In this invited talk, I will give an update on the current status of our project and I will describe how we are leveraging familiar components of the Haskell type system - including polymorphism, kinds, qualified types and improvement - to capture more precise details of effect usage, data representation, and termination. I will also discuss the challenges of writing and compiling performance-sensitive code written in a functional style. It was once considered radical to use C in place of assembly language to construct systems software. Is it possible that functional languages might one day become as commonplace in this application domain as C is today?
FLUX
Authors: Cheney James
Published: September 2008

XML database query languages have been studied extensively, but XML database updates have received relatively little attention, and pose many challenges to language design. We are developing an XML update language called FLUX, which stands for FunctionaL Updates for XML, drawing upon ideas from functional programming languages. In prior work, we have introduced a core language for FLUX with a clear operational semantics and a sound, decidable static type system based on regular expression types.

Our initial proposal had several limitations. First, it lacked support for recursive types or update procedures. Second, although a high-level source language can easily be translated to the core language, it is difficult to propagate meaningful type errors from the core language back to the source. Third, certain updates are wellformed yet contain
path errors
, or "dead" subexpressions which never do any useful work. It would be useful to detect path errors, since they often represent errors or optimization opportunities.

In this paper, we address all three limitations. Specifically, we present an improved, sound type system that handles recursion. We also formalize a source update language and give a translation to the core language that
preserves
and
reflects
typability. We also develop a
path-error analysis
(a form of dead-code analysis) for updates.
A type-preserving compiler in Haskell
Authors: Guillemette Louis-Julien , Monnier Stefan
Published: September 2008

There has been a lot of interest of late for programming languages that incorporate features from dependent type systems and proof assistants, in order to capture important invariants of the program in the types. This allows type-based program verification and is a promising compromise between plain old types and full blown Hoare logic proofs. The introduction of GADTs in GHC (and more recently type families) made such dependent typing available in an industry-quality implementation, making it possible to consider its use in large scale programs.

We have undertaken the construction of a complete compiler for System
F
, whose main property is that the GHC type checker verifies mechanically that each phase of the compiler properly preserves types. Our particular focus is on "types rather than proofs": reasonably few annotations that do not overwhelm the actual code.

We believe it should be possible to write such a type-preserving compiler with an amount of extra code comparable to what is necessary for typical typed intermediate languages, but with the advantage of static checking. We will show in this paper the remaining hurdles to reach this goal.
Generic discrimination
Authors: Henglein Fritz
Published: September 2008

We introduce the notion of
discrimination
as a generalization of both sorting and partitioning and show that worst-case linear-time discrimination functions (discriminators) can be defined
generically
, by (co-)induction on an expressive language of
order denotations
. The generic definition yields discriminators that generalize both distributive sorting and multiset discrimination. The generic discriminator can be coded compactly using list comprehensions, with order denotations specified using Generalized Algebraic Data Types (GADTs). A GADT-free combinator formulation of discriminators is also given.

We give some examples of the uses of discriminators, including a new most-significant-digit lexicographic sorting algorithm.

Discriminators generalize binary comparison functions: They operate on
n
arguments at a time, but do not expose more information than the underlying equivalence, respectively ordering relation on the arguments. We argue that primitive types with equality (such as references in ML) and ordered types (such as the machine integer type), should expose their equality, respectively standard ordering relation, as discriminators: Having
only
a binary equality test on a type requires Θ(
n
2
) time to find all the occurrences of an element in a list of length
n
, for each element in the list, even if the equality test takes only constant time. A discriminator accomplishes this in linear time. Likewise, having only a (constant-time) comparison function requires Θ(
n
log
n
) time to sort a list of
n
elements. A discriminator can do this in linear time.
Experience report
Authors: Convey Christian , Fredricks Andrew , Gagner Christopher , Maxwell Douglas , Hamel Lutz
Published: September 2008

We investigated the relative merits of C++ and Erlang in the implementation of a parallel acoustic ray tracing algorithm for the U.S. Navy. We found a much smaller learning curve and better debugging environment for parallel Erlang than for pthreads-based C++ programming. Our C++ implementation outperformed the Erlang program by at least 12x. Attempts to use Erlang on the IBM Cell BE microprocessor were frustrated by Erlang's memory footprint.
Typed closure conversion preserves observational equivalence
Authors: Ahmed Amal , Blume Matthias
Published: September 2008

Language-based security relies on the assumption that all potential attacks are bound by the rules of the language in question. When programs are compiled into a different language, this is true only if the translation process preserves observational equivalence.

We investigate the problem of fully abstract compilation, i.e., compilation that both
preserves
and
reflects
observational equivalence. In particular, we prove that typed closure conversion for the polymorphic »-calculus with existential and recursive types is fully abstract. Our proof uses operational techniques in the form of a step-indexed logical relation and construction of certain
wrapper
terms that "back-translate" from target values to source values.

Although typed closure conversion has been assumed to be fully abstract, we are not aware of any previous result that actually proves this.
Write it recursively
Authors: Morihata Akimasa , Matsuzaki Kiminori , Takeichi Masato
Published: September 2008

Optimal path queries
are queries to obtain an optimal path specified by a given criterion of optimality. There have been many studies to give efficient algorithms for classes of optimal path problem. In this paper, we propose a generic framework for optimal path queries. We offer a domain-specific language to describe optimal path queries, together with an algorithm to find an optimal path specified in our language. One of the most distinct features of our framework is the use of recursive functions to specify queries. Recursive functions reinforce expressiveness of our language so that we can describe many problems including known ones; thus, we need not learn existing results. Moreover, we can derive an efficient querying algorithm from the description of a query written in recursive functions. Our algorithm is a generalization of existing algorithms, and answers a query in O(
n
log
n
) time on a graph of O(
n
) size. We also explain our implementation of an optimal path querying system, and report some experimental results.
Space profiling for parallel functional programs
Authors: Spoonhower Daniel , Blelloch Guy E. , Harper Robert , Gibbons Phillip B.
Published: September 2008

This paper presents a semantic space profiler for parallel functional programs. Building on previous work in sequential profiling, our tools help programmers to relate runtime resource use back to program source code. Unlike many profiling tools, our profiler is based on a cost semantics. This provides a means to reason about performance without requiring a detailed understanding of the compiler or runtime system. It also provides a specification for language implementers. This is critical in that it enables us to separate cleanly the performance of the application from that of the language implementation.

Some aspects of the implementation can have significant effects on performance. Our cost semantics enables programmers to understand the impact of different scheduling policies while hiding many of the details of their implementations. We show applications where the choice of scheduling policy has asymptotic effects on space use. We explain these use patterns through a demonstration of our tools. We also validate our methodology by observing similar performance in our implementation of a parallel extension of Standard ML.
Pattern minimization problems over recursive data types
Authors: Krauss Alexander
Published: September 2008

In the context of program verification in an interactive theorem prover, we study the problem of transforming function definitions with ML-style (possibly overlapping) pattern matching into minimal sets of independent equations. Since independent equations are valid unconditionally, they are better suited for the equational proof style using induction and rewriting, which is often found in proofs in theorem provers or on paper.

We relate the problem to the well-known minimization problem for propositional DNF formulas and show that it is £
P
/2-complete. We then develop a concrete algorithm to compute minimal patterns, which naturally generalizes the standard Quine-McCluskey procedure to the domain of term patterns.
Deciding
k
CFA is complete for EXPTIME
Authors: Van Horn David , Mairson Harry G.
Published: September 2008

We give an exact characterization of the computational complexity of the
k
CFA hierarchy. For any
k
> 0, we prove that the control flow decision problem is complete for deterministic exponential time. This theorem validates empirical observations that such control flow analysis is intractable. It also provides more general insight into the complexity of abstract interpretation.
Flask
Authors: Mainland Geoffrey , Morrisett Greg , Welsh Matt
Published: September 2008

Severely resource-constrained devices present a confounding challenge to the functional programmer: we are used to having powerful abstraction facilities at our fingertips, but how can we make use of these tools on a device with an 8- or 16-bit CPU and at most tens of kilobytes of RAM? Motivated by this challenge, we have developed Flask, a domain specific language embedded in Haskell that brings the power of functional programming to sensor networks, collections of highly resource-constrained devices. Flask consists of a staging mechanism that cleanly separates node-level code from the meta-language used to generate node-level code fragments; syntactic support for embedding standard sensor network code; a restricted subset of Haskell that runs on sensor networks and constrains program space and time consumption; a higher-level "data stream" combinator library for quickly constructing sensor network programs; and an extensible runtime that provides commonly-used services.

We demonstrate Flask through several small code examples as well as a compiler that generates node-level code to execute a network-wide query specified in a SQL-like language. We show how using Flask ensures constraints on space and time behavior. Through microbenchmarks and measurements on physical hardware, we demonstrate that Flask produces programs that are efficient in terms of CPU and memory usage and that can run effectively on existing sensor network hardware.
Experience report
Authors: Nanavati Ravi
Published: September 2008

Bluespec is a hardware-design tools startup whose core technology is developed using Haskell. Haskell is an unusual choice for a startup because it adds technical risk to the inherent business risk. In the years since Bluespec's founding, we have discovered that Haskell's purity is an unexpected match for the development needs of a startup. Based on Bluespec's experience, we conclude that pure programming languages can be the source of a competitive advantage for startup software companies.
Functional netlists
Authors: Park Sungwoo , Kim Jinha , Im Hyeonseung
Published: September 2008

In efforts to overcome the complexity of the syntax and the lack of formal semantics of conventional hardware description languages, a number of functional hardware description languages have been developed. Like conventional hardware description languages, however, functional hardware description languages eventually convert all source programs into netlists, which describe wire connections in hardware circuits at the lowest level and conceal all high-level descriptions written into source programs.

We develop a variant of the lambda calculus, called
l
λ (linear lambda), which may serve as a high-level substitute for netlists. In order to support higher-order functions,
l
λ uses a linear type system which enforces the linear use of variables of function type. The translation of
l
λ into structural descriptions of hardware circuits is sound and complete in the sense that it maps expressions only to realizable hardware circuits and that every realizable hardware circuit has a corresponding expression in
l
λ. To illustrate the use of
l
λ as a high-level substitute for netlists, we design a simple hardware description language that extends
l
λ with polymorphism, and use it to implement a Fast Fourier Transform circuit.
Quotient lenses
Authors: Foster J. Nathan , Pilkiewicz Alexandre , Pierce Benjamin C.
Published: September 2008

There are now a number of BIDIRECTIONAL PROGRAMMING LANGUAGES, where every program can be read both as a forward transformation mapping one data structure to another and as a reverse transformation mapping an edited output back to a correspondingly edited input. Besides parsimony - the two related transformations are described by just one expression - such languages are attractive because they promise strong behavioral laws about how the two transformations fit together - e.g., their composition is the identity function. It has repeatedly been observed, however, that such laws are actually a bit too strong: in practice, we do not want them "on the nose," but only up to some equivalence, allowing inessential details, such as whitespace, to be modified after a round trip. Some bidirectional languages loosen their laws in this way, but only for specific, baked-in equivalences.

In this work, we propose a general theory of QUOTIENT LENSES - bidirectional transformations that are well behaved modulo equivalence relations controlled by the programmer. Semantically, quotient lenses are a natural refinement of LENSES, which we have studied in previous work. At the level of syntax, we present a rich set of constructs for programming with CANONIZERS and for quotienting lenses by canonizers. We track equivalences explicitly, with the type of every quotient lens specifying the equivalences it respects.

We have implemented quotient lenses as a refinement of the bidirectional string processing language Boomerang. We present a number of useful primitive canonizers for strings, and give a simple extension of Boomerang's regular-expression-based type system to statically typecheck quotient lenses. The resulting language is an expressive tool for transforming real-world, ad-hoc data formats. We demonstrate the power of our notation by developing an extended example based on the UniProt genome database format and illustrate the generality of our approach by showing how uses of quotienting in other bidirectional languages can be translated into our notation.
A brief response to J. A. Cohen's joint review
Authors: Grätzer George
Published: September 2008

Would not call this a rebuttal. I agree with most everything the reviewer writes, and I thank him for his effort. Nevertheless, as the author of the two books under review, I see some things differently.
Review of applied combinatorics on words
Authors: Lothaire M.
Published: September 2008

Text manipulations play an important part in various kinds of computations. The subject of text manipulations, is a well developed subject in computer science. The book deals with algorithms, and theoretical properties of texts. Most of algorithms are expressed in pseudo code. They are accompanied by their proofs of correctness, and complexity analysis. Some of them are explained with discussions containing examples, and diagrams. The stress is on combinatorial properties. The book is a part of a series on encyclopedia of mathematics.