bluuebunny/crossref_metadata_2025 huggingface dataset:
Experience versus effort: what explains dynamic heterogeneity with respect to age?
Authors: Mauck Robert A. , Huntington Charles E. , Doherty Jr Paul F.
Published: April 2012

Age‐related patterns of survival and reproduction have been explained by accumulated experience (‘experience hypothesis’), increased effort (‘effort hypothesis’), and intrinsic differences in phenotypes (‘selection hypothesis’). We examined the experience and effort hypotheses using a 40‐year data set in a population of Leach's storm‐petrels Oceanodroma leucorhoa, long‐lived seabirds for which the effect of phenotypic variation has been previously demonstrated. Age was quantified by time since recruitment (‘breeding age’). The best model of adult survival included a positive effect of breeding age (1, 2, 3+ years), sex (male > female), and year. Among‐individuals variation (fixed heterogeneity) accounted for 31.6% of the variance in annual reproductive success. We further examined within‐individual patterns in reproductive success (dynamic heterogeneity) in the subset of individuals with at least five breeding attempts. Three distinct phases characterized reproductive success – early increase, long asymptotic peak, late decline. No effect of early reproductive output on longevity was found, however, early success was positively correlated with lifetime reproductive success. Reproductive success was lower earlier than later in life. Among the few natally philopatric individuals in the population, age of first breeding had no effect on longevity, lifetime reproductive success, or early reproductive success. No support for the effort hypothesis was found in this population. Instead, age‐specific patterns of survival and reproduction in these birds are best explained by the experience hypothesis over and above the effect of intrinsic differences among individuals.
No evidence for the small‐island effect in avian communities on islands of an inundated lake
Authors: Wang Yanping , Zhang Meng , Wang Siyu , Ding Zhifeng , Zhang Jingcheng , Sun Jiji , Li Peng , Ding Ping
Published: April 2012

The small‐island effect (SIE), i.e. the hypothesis that species richness on islands below a certain threshold area varies independently of area, has become more and more part of the theoretical framework of biogeography and biodiversity research. However, existing SIE studies are extraordinarily biased taxonomically: plants and other animal taxonomic groups are predominantly studied, while birds are almost completely overlooked. Furthermore, previous methods for the detection of SIE are flawed in one or another way, including not accounting for model complexity, not comparing all relevant models, not including islands with no species, and ignoring the effects of logarithmic data transformations and habitat diversity in generating SIE. Therefore, the existence and the prevalence of the SIE may be dubious. In this study, after controlling for all these methodological shortcomings in detecting the SIE, we test for the existence of the SIE using bird data collected on islands in the Thousand Island Lake, China. We used the line‐transect method to survey bird occupancy and abundance on 42 islands from 2007 to 2011. We used three broad sets of analyses, regression‐based analyses, path analyses and null model analyses, to overcome potential methodological problems in detecting the SIE. We found no evidence for an SIE in avian communities in the Thousand Island Lake. Model selection based on AICc identified the simple power model without SIE as the most parsimonious model. In contrast, there was little support for the three breakpoint regression models with SIE. Path analyses and null model analyses also did not detect an SIE. We conclude that, for the robust detection of SIE, future study should carefully take all these methodological pitfalls into account.
Regulated Intramembrane Cleavage of the EGF Receptor
Authors: Liao Hong‐Jun , Carpenter Graham
Published: April 2012

Following the addition of EGF or ionomycin to A431 cells, protease activity mediates cleavage of the EGF receptor producing a 60 kDa fragment that includes the intracellular domain (ICD). This fragment is located in both membrane and nuclear fractions. On the basis of sensitivity to chemical inhibitors and overexpression of cDNAs, the rhomboid intramembrane proteases, not γ‐secretase proteases, are identified as responsible for the cleavage event. Agonist‐initiated cleavage occurs slowly over 3–24 h. Inhibition of calpain protease activity significantly increased the detectable level of ICD fragment.
Structural features of the C‐terminus from the human neurokinin‐1 receptor
Authors: Orel Mikhail , Padrós Esteve , Manyosa Joan
Published: April 2012

The neurokinin‐1 receptor (NK1R) is a G‐protein coupled receptor found in the central and peripheral nervous systems of vertebrates, and is responsible for many physiological processes. The C‐terminus domain seems to be essential for coupling to the corresponding G‐protein and β‐arrestin, and is important for receptor desensitization, internalization and recycling. We have focused our study on expression of the human NK1R (hNK1R) C‐terminus in Escherichia coli, and its purification and characterization, in order to elucidate its structural properties. CD and Fourier transform infrared spectroscopy showed that the hNK1R C‐terminus, rather than having a random structure, has well‐defined secondary‐structure patterns. The presence of three tyrosine residues in the primary sequence of the hNK1R C‐terminus facilitated the use of UV and fluorescence spectroscopy techniques which revealed tyrosine fluorescence and UV absorption at anomalous wavelengths. In their entirety, the results show that the hNK1R C‐terminus has clearly defined secondary (25%α‐helix, 27% unordered structure and 48%β‐sheets and β‐turns) and tertiary structures which, it is believed, are tightly related to its multiple functions.
Synthesis and Biological Evaluation of Triazole Derivatives as Potential Antifungal Agent
Authors: Chai Xiaoyun , Yang Guang , Zhang Jun , Yu Shichong , Zou Yan , Wu Qiuye , Zhang Dazhi , Jiang Yuanying , Cao Yongbing , Sun Qingyan
Published: April 2012

A series of triazole antifungal agents with piperidine side chains were designed and synthesized. Results of preliminary antifungal tests against eight human pathogenic fungi in vitro showed that all the title compounds exhibited excellent activities with broad spectrum. Moreover, a molecular model for the binding between compound 12 and the active site of CACYP51 was provided based on the computational docking results. The side chain of the compound 12 is oriented into substrate access channel 2 (FG loop) and forms hydrophobic and van der waals interactions with surrounding hydrophobic residues. The phenyl group of the side chain can interact with the phenyl group of Phe380 through the formation of π‐π face‐to‐edge interaction.
Leptin action on nonneuronal cells in the CNS: potential clinical applications
Authors: Pan Weihong , Hsuchou Hung , Jayaram Bhavaani , Khan Reas S. , Huang Eagle Yi‐Kung , Wu Xiaojun , Chen Chu , Kastin Abba J.
Published: April 2012

Leptin, an adipocyte‐derived cytokine, crosses the blood–brain barrier to act on many regions of the central nervous system (CNS). It participates in the regulation of energy balance, inflammatory processes, immune regulation, synaptic formation, memory condensation, and neurotrophic activities. This review focuses on the newly identified actions of leptin on astrocytes. We first summarize the distribution of leptin receptors in the brain, with a focus on the hypothalamus, where the leptin receptor is known to mediate essential feeding suppression activities, and on the hippocampus, where leptin facilitates memory, reduces neurodegeneration, and plays a dual role in seizures. We will then discuss regulation of the nonneuronal leptin system in obesity. Its relationship with neuronal leptin signaling is illustrated by in vitro assays in primary astrocyte culture and by in vivo studies on mice after pretreatment with a glial metabolic inhibitor or after cell‐specific deletion of intracellular signaling leptin receptors. Overall, the glial leptin system shows robust regulation and plays an essential role in obesity. Strategies to manipulate this nonneuronal leptin signaling may have major clinical impact.
Microemulsion Synthesis, Characterization of Highly Visible Light Responsive Rare Earth‐Doped Bi2O3
Authors: Wu Shuxing , Fang Jianzhang , Xu Xiaoxin , Liu Zhang , Zhu Ximiao , Xu Weicheng
Published: April 2012

In this paper, Bi2O3 and rare earth (La, Ce)‐doped Bi2O3 visible‐light‐driven photocatalysts were prepared in a Triton X‐100/n‐hexanol/cyclohexane/water reverse microemulsion. The resulting materials were characterized by X‐ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface area, photoluminescence spectra (PLS) and UV–Vis diffuse reflectance spectroscopy. The XRD patterns of the as‐prepared catalysts calcined at 500°C exhibited only the characteristic peaks of monoclinic α‐Bi2O3. PLS analysis implied that the separation efficiency for electron‐hole has been enhanced when Bi2O3 was doped with rare earth. UV–Vis diffuse reflectance spectroscopy measurements presented an extension of light absorption into the visible region. The photocatalytic activity of the samples was evaluated by degradation of methyl orange (MO) and 2,4‐dichlorophenol (2,4‐DCP). The results displayed that the photocatalytic activity of rare earth‐doped Bi2O3 was higher than that of dopant‐free Bi2O3. The optimal dopant amount of La or Ce was 1.0 mol%. And the mechanisms of influence on the photocatalytic activity of the catalysts were discussed.
Scale Issues in the Development of Future Precipitation Scenarios
Authors: Schoof Justin T.
Published: April 2012

Many of the processes that govern precipitation occurrence and intensity occur at spatial and temporal scales that remain unresolved by the current generation of climate models. The resulting mismatch between the information reliably provided by such models and the needs of researchers assessing impacts associated with changes in precipitation has led to the development of downscaling techniques. In this paper, the need for downscaling is demonstrated by describing (1) the difference between real‐world precipitation‐governing processes and their representation in climate models and (2) the differences between theoretical expectations of precipitation changes at large and small scales in a warmer world. With a primary focus on empirical‐statistical downscaling, the general strategy for developing regional scenarios is described along with outstanding issues that are likely to shape the next decade of downscaling research.
A Monte Carlo study comparing PIV, ULS and DWLS in the estimation of dichotomous confirmatory factor analysis
Authors: Nestler Steffen
Published: April 2012

We conducted a Monte Carlo study to investigate the performance of the polychoric instrumental variable estimator (PIV) in comparison to unweighted least squares (ULS) and diagonally weighted least squares (DWLS) in the estimation of a confirmatory factor analysis model with dichotomous indicators. The simulation involved 144 conditions (1,000 replications per condition) that were defined by a combination of (a) two types of latent factor models, (b) four sample sizes (100, 250, 500, 1,000), (c) three factor loadings (low, moderate, strong), (d) three levels of non‐normality (normal, moderately, and extremely non‐normal), and (e) whether the factor model was correctly specified or misspecified. The results showed that when the model was correctly specified, PIV produced estimates that were as accurate as ULS and DWLS. Furthermore, the simulation showed that PIV was more robust to structural misspecifications than ULS and DWLS.
Single motor unit activity in human extraocular muscles during the vestibulo‐ocular reflex
Authors: Weber Konrad P. , Rosengren Sally M. , Michels Rike , Sturm Veit , Straumann Dominik , Landau Klara
Published: April 2012

Key points

While the eye movements have been well characterized during the vestibulo‐ocular reflex, the corresponding motor unit activity in human eye muscles is not well understood.

The present study describes the first single motor unit recordings during the vestibulo‐ocular reflex in human eye muscles.

Simultaneous needle and surface recordings identified the inferior oblique as the eye muscle of origin of the ocular vestibular evoked myogenic potential (oVEMP), thus validating the physiological basis of this clinical test of otolith function.

The results demonstrate short‐latency vestibulo‐ocular projections from the otoliths to individual eye muscles.

Single motor unit activity of eye muscles provides a window into neural activity of the ocular motor nuclei in humans.

Abstract  Motor unit activity in human eye muscles during the vestibulo‐ocular reflex (VOR) is not well understood, since the associated head and eye movements normally preclude single unit recordings. Therefore we recorded single motor unit activity following bursts of skull vibration and sound, two vestibular otolith stimuli that elicit only small head and eye movements. Inferior oblique (IO) and inferior rectus (IR) muscle activity was measured in healthy humans with concentric needle electrodes. Vibration elicited highly synchronous, short‐latency bursts of motor unit activity in the IO (latency: 10.5 ms) and IR (14.5 ms) muscles. The activation patterns of the two muscles were similar, but reciprocal, with delayed activation of the IR muscle. Sound produced short‐latency excitation of the IO muscle (13.3 ms) in the eye contralateral to the stimulus. Simultaneous needle and surface recordings identified the IO as the muscle of origin of the vestibular evoked myogenic potential (oVEMP) thus validating the physiological basis of this recently developed clinical test of otolith function. Single extraocular motor unit recordings provide a window into neural activity in humans that can normally only be examined using animal models and help identify the pathways of the translational VOR from otoliths to individual eye muscles.
Transmission Error in Synchronous Belt With Resonance Under Installation Tension
Authors: Kagotani Masanori , Ueda Hiroyuki
Published: April 2012

Synchronous belt drives generate resonance on the belt spans between the driving and driven pulleys when the transverse natural frequency of the belt, matches the meshing frequency of the belt tooth and the pulley tooth. The resonance of the belt spans affects the accuracy of rotation transmission. In the present study, the mechanisms generating the transmission error in synchronous belt drives under installation tension and a pulley speed ratio of 1:1 are investigated theoretically and experimentally for the case in which the belt spans generate first mode vibration due to resonance. In addition, the change in the shaft load caused by resonance is examined. The calculated and experimental transmission errors show good agreement, and so the validity of our analysis is confirmed. Transmission error is generated by the difference in displacement between the upper and lower belt spans due to the convex or concave shape, the difference in the amount of belt climbing at the beginning and end of meshing, and the generation of torque due to the moment of inertia on the driven side. The transmission error has a period of 1/2 of one pitch of the pulley, and the generated change in the shaft load, which is the sum of the displacement due to the convex or concave shape of the upper and lower spans and the sum of the belt climbing at the beginning and end of meshing, has a period of one pitch of the pulley.
Studying the Dynamics of SLP-76, Nck, and Vav1 Multimolecular Complex Formation in Live Human Cells with Triple-Color FRET
Authors: Pauker Maor H. , Hassan Nirit , Noy Elad , Reicher Barak , Barda-Saad Mira
Published: April 2012

The formation of a multiprotein complex in response to T cell activation is monitored in live cells.
Differential β-Arrestin–Dependent Conformational Signaling and Cellular Responses Revealed by Angiotensin Analogs
Authors: Zimmerman Brandon , Beautrait Alexandre , Aguila Benjamin , Charles Ricardo , Escher Emanuel , Claing Audrey , Bouvier Michel , Laporte Stéphane A.
Published: April 2012

Distinct conformational changes induced in β-arrestin determine whether angiotensin II analogs enhance β-arrestin–dependent proliferation or migration.
Front-Loaded Linezolid Regimens Result in Increased Killing and Suppression of the Accessory Gene Regulator System of Staphylococcus aureus
Authors: Tsuji Brian T. , Brown Tanya , Parasrampuria Ridhi , Brazeau Daniel A. , Forrest Alan , Kelchlin Pamela A. , Holden Patricia N. , Peloquin Charles A. , Hanna Debra , Bulitta Jurgen B.
Published: April 2012

Front loading is a strategy used to optimize the pharmacodynamic profile of an antibiotic through the administration of high doses early in therapy for a short duration. Our aims were to evaluate the impact of front loading of linezolid regimens on bacterial killing and suppression of resistance and on RNAIII, the effector molecule of the accessory gene regulator system (encoded by
agr
) in methicillin-resistant
Staphylococcus aureus
(MRSA). Time-killing experiments over 48 h were utilized for linezolid against four strains of MRSA: USA100, USA300, USA400, and ATCC 29213. A hollow-fiber infection model simulated traditional and front-loaded human therapeutic regimens of linezolid versus USA300 at 10
6
CFU/ml over 240 h. Over 48 h in time-kill experiments, linezolid displayed bacteriostatic activity, with reductions of >1 log
10
CFU/ml for all strains. Front-loaded regimens that were administered over 5 days, 1,200 mg every 12 h (q12h) (total, 10 doses) and 2,400 mg q12h (total, 10 doses) followed by 300 mg q12h thereafter, resulted in sustained bactericidal activity, with reductions of the area under the CFU curve of −6.15 and −6.03, respectively, reaching undetectable limits at the 10-day study endpoint. All regimens displayed a reduction in RNAIII relative expression at 24 h and 240 h compared with that of the growth control. Monte Carlo simulations predicted a <1.27× increase in the fractional decreases in platelets for all front-loaded regimens versus the 600 mg q12h regimen, except for the highest-dose front-loaded regimen. Front-loading strategies for linezolid are promising and may be of utility in severe MRSA infections, where early aggressive therapy is necessary.
The Posttranslocational Chaperone Lipoprotein PrsA Is Involved in both Glycopeptide and Oxacillin Resistance in Staphylococcus aureus
Authors: Jousselin Ambre , Renzoni Adriana , Andrey Diego O. , Monod Antoinette , Lew Daniel P. , Kelley William L.
Published: April 2012

Understanding in detail the factors which permit
Staphylococcus aureus
to counteract cell wall-active antibiotics is a prerequisite to elaborating effective strategies to prolong the usefulness of these drugs and define new targets for pharmacological intervention. Methicillin-resistant
S. aureus
(MRSA) strains are major pathogens of hospital-acquired and community-acquired infections and are most often treated with glycopeptides (vancomycin and teicoplanin) because of their resistance to most penicillins and a limited arsenal of clinically proven alternatives. In this study, we examined PrsA, a lipid-anchored protein of the parvulin PPIase family (peptidyl-prolyl
cis/trans
isomerase) found ubiquitously in all Gram-positive species, in which it assists posttranslocational folding at the outer surface of the cytoplasmic membrane. We show by both genetic and biochemical assays that
prsA
is directly regulated by the VraRS two-component sentinel system of cell wall stress. Disruption of
prsA
is tolerated by
S. aureus
, and its loss results in no detectable overt macroscopic changes in cell wall architecture or growth rate under nonstressed growth conditions. Disruption of
prsA
leads, however, to notable alterations in the sensitivity to glycopeptides and dramatically decreases the resistance of COL (MRSA) to oxacillin. Quantitative transcriptional analysis reveals that
prsA
and
vraR
are coordinately upregulated in a panel of stable laboratory and clinical glycopeptide-intermediate
S. aureus
(GISA) strains compared to their susceptible parents. Collectively, our results point to a role for
prsA
as a facultative facilitator of protein secretion or extracellular folding and provide a framework for understanding why
prsA
is a key element of the VraRS-mediated cell wall stress response.
Fhb, a Novel Factor H-Binding Surface Protein, Contributes to the Antiphagocytic Ability and Virulence of Streptococcus suis
Authors: Pian Yaya , Gan Shuzhen , Wang Shujie , Guo Jie , Wang Pingping , Zheng Yuling , Cai Xuehui , Jiang Yongqiang , Yuan Yuan
Published: April 2012

Streptococcus suisserotype 2 is a Gram-positive bacterium that causes sepsis and meningitis in piglets and humans. The mechanisms ofS. suisserotype 2 invasive disease are not well understood. The surface proteins of pathogens usually play important roles in infection and bacterium-host interactions. Here, we identified a novel surface protein that contributed significantly to the virulence ofS. suisserotype 2 in a piglet infection model. This protein showed little similarity to other reported proteins and exhibited strong binding activity to human factor H (hFH). It was designated Fhb (factor H-binding protein). Thefhbgenes found inS. suisserotypes 1, 2, 4, 7, and 9 exhibited molecular polymorphism. Fhb possessed two proline-rich repeat sequences and XPZ domains, and one repeat sequence exhibited a high homology to Bac, an IgA-binding protein ofStreptococcus agalactiae. Evidence strongly indicated thatfhb-deficient mutants had diminished phagocytosis resistance in bactericidal assays. In addition, Fhb plays important roles in complement-mediated immunity by interacting with hFH. These findings indicated that Fhb is a crucial surface protein contributing to the virulence ofS. suis, with important functions in evading innate immune defenses by interaction with host complement regulatory factor hFH.
Complete Genomic Sequence of Chinese Virulent Duck Enteritis Virus
Authors: Wu Ying , Cheng Anchun , Wang Mingshu , Yang Qiao , Zhu Dekang , Jia Renyong , Chen Shun , Zhou Yi , Wang Xiaoyu , Chen Xiaoyue
Published: April 2012

The Chinese virulent (CHv) strain of duck enteritis virus (DEV) has a genome of approximately 162,175 nucleotides with a GC content of 44.89%. Here we report the complete genomic sequence and annotation of DEV CHv, which offer an effective platform for providing authentic research experiences to novice scientists. In addition, knowledge of this virus will extend our general knowledge of DEV and will be useful for further studies of the mechanisms of virus replication and pathogenesis.
Paleoclimate effects and geographic barriers shape regional population genetic structure of blackbrush (Coleogyne ramosissima: Rosaceae)
Authors: Richardson Bryce A. , Meyer Susan E.
Published: April 2012

Coleogyne ramosissima Torr. (blackbrush) is a dominant xerophytic shrub species in the ecotone between the warm and cold deserts of interior western North America. Amplified fragment length polymorphisms (AFLPs) were used to survey genetic diversity and population genetic structure at 14 collection sites across the species range. Analysis revealed significant population differentiation (FST= 0.103, p < 0.0001) and reasonably high levels of genetic diversity (expected heterozygosity; HE= 0.26), a surprising result for a putative paleoendemic species. Model-based Bayesian clustering, principal coordinates analysis, and neighbor-joining analysis all produced support for the existence of two metapopulations, the first centered on the Mojave Desert and the second on the Colorado Plateau. These genetic data, coupled with information from Late Pleistocene and Holocene packrat (genus Neotoma Say and Ord, 1825) middens, illustrate a demographic history in which eastern and western distributions were disjunct during the Last Glacial Maximum and remained so through the Holocene, forming the present-day metapopulations in the Mojave Desert and Colorado Plateau. This strong regional genetic differentiation has implications for population persistence and migration in response to future climate change, as well as for shrubland restoration following anthropogenic disturbances such as annual grass invasion and wildfire.
HOMOCLINIC INTERACTIONS NEAR A TRIPLE-ZERO DEGENERACY IN CHUA'S EQUATION
Authors: ALGABA ANTONIO , MERINO MANUEL , RODRÍGUEZ-LUIS ALEJANDRO J.
Published: April 2012

In this work, we consider some degeneracies of homoclinic and heteroclinic connections organized by the triple-zero degeneracy, in Chua's equation. This allows us to numerically study the homoclinic-heteroclinic transition exhibited by the curve of Takens–Bogdanov bifurcations as it passes through the triple-zero degeneracy. Several codimension-two degenerate homoclinic and heteroclinic connections organized by the triple-zero bifurcation are involved in this transitional homoclinic-heteroclinic mechanism. In particular, we point out that the existence of a curve of T-points and a curve of Belyakov points (its equilibrium passes from saddle to saddle-focus) is necessary for this process to occur. Closed curves of homoclinic connections with different pulses are also found.
INTERTWINED BASINS OF ATTRACTION
Authors: DING CHANGMING
Published: April 2012

This paper deals with intertwined basins of attraction for dynamical systems in a metric space. After giving a general definition of intertwining property, which is preserved by a topological equivalence between dynamical systems, we present a sufficient condition to guarantee the existence of intertwined basins for dynamical systems in ℝn.
ON THE STUDY OF BIFURCATIONS IN DELAY-DIFFERENTIAL EQUATIONS: A FREQUENCY-DOMAIN APPROACH
Authors: GENTILE FRANCO S. , MOIOLA JORGE L. , PAOLINI EDUARDO E.
Published: April 2012

An improved version of a frequency-domain approach to study bifurcations in delay-differential equations is presented. The proposed methodology provides information about the frequency, amplitude, and stability of the orbit emerging from Hopf bifurcation. We apply this method to different schemes of the delayed van der Pol oscillator. The time-delay dependence can appear intrinsically because of the system dynamics or can be intentionally introduced in a feedback loop. Also, a discussion about system controllability and observability is given for a proper and rigorous application of the frequency domain technique. Collateral findings involving some types of static bifurcations are included for completeness.
MULTIRESONANCE AND ENHANCED SYNCHRONIZATION IN STOCHASTICALLY COUPLED RATCHETS
Authors: NANA NBENDJO B. R. , VINCENT U. E. , MCCLINTOCK PETER V. E.
Published: April 2012

We investigate the dynamics and synchronization of two inertia ratchets interacting indirectly through a stochastic dynamical environment. We examine resonant oscillations in their synchronous and asynchronous modes; and we determine the effects of the interaction with the environment on the system's response and synchronization. We show the occurrence of noise-induced multiresonance and noise-enhanced synchronization emerging from the ratchets' interaction with the noisy environment. The simultaneous quenching of the chaotic regimes, and the domain of gain parameters for efficient control, are identified. It is shown that optimal transport can be achieved, implying that an inertia ratchet can take advantage of its noisy environment to enhance its rich dynamical and transport properties.
HIGHLY ACCURATE DOUBLET GENERATOR FOR MEMRISTOR-BASED ANALOG MEMORY
Authors: YANG CHANGJU , SAH MAHESHWAR PRASAD , ADHIKARI SHYAM PRASAD , PARK DONGSUN , KIM HYONGSUK
Published: April 2012

A novel doublet generator circuit for memristor-based analog memories or artificial synapses is presented. In memristor-based analog memories or artificial synapses, the read-out pulses cause a drifting problem in the programmed resistance of the memristor. Use of doublet pulse is known to be an efficient solution for preventing resistance variation in memristors. Switching speed and area similarity between the positive and the negative cycles of doublet are two extremely important factors in designing a doublet generator. In this paper, a fast and highly accurate doublet generator where the difference between the positive and negative cycles of pulses is less than 0.012% is proposed.
ν-CLASSES
Authors: VARSAIE S.
Published: April 2012

ν-classes are supergeometric generalization of the Chern classes. Associated to each superline bundle over supermanifold [Formula: see text], ν-class is an element of the second cohomology group of M with coefficients in ℤ[ν] with ν2 = 1.
Upscaling permeability to unstructured grids using the multipoint flux approximation
Authors: Manchuk John G. , Mlacnik Martin J. , Deutsch Clayton V.
Published: April 2012

Grids used for flow simulation are often at a much coarser scale than that of grids for geological modelling due to computational demand. Unstructured grids offer increased flexibility for the flow grid design; however, solving the flow equations and upscaling from high resolution geological grids to the coarse flow grid is more complex than using coarse regular grids. The multipoint flux approximation (MPFA) is one technique applied to discretize the flow equations on unstructured grids. This paper develops an upscaling technique that uses the MPFA method to solve the flow equations on the fine- and coarse-scale grids. Unlike most cases where the fine-scale grid is regular or structured, this work utilizes a high resolution triangular grid that conforms to the coarse-scale grid. The triangular grid is generated using the coarse-scale interaction regions as constraints. Upscaling leads to transmissibility matrices of the coarse-scale interaction regions. Two different types of local boundary conditions for the MPFA upscaling approach are developed, including linear varying pressures and pressures computed by solving the flow equations around the element boundary. The method is tested using flow simulation on several cases. Results are comparable with flow using a high resolution regular grid.
Layered fluvial reservoirs with internal fluid cross flow: a well-connected family of well test pressure transient responses
Authors: Corbett Patrick W. M. , Hamdi Hamidreza , Gurav Hemant
Published: April 2012

A new well testing response from lateral cross flow within layers is described. The response occurs when there is extremely low effective vertical permeability in the system at the larger scale. Low vertical permeability actually accentuates the layering and reduces vertical cross flow whilst enhancing lateral cross flow from within-layer heterogeneities. The response is investigated using numerical simulation of flow in end-member models of complex and geologically realistic architecture in high net-to-gross fluvial systems. This ‘ramp’ response is shown to form one member of a family of well test pressure transient responses. The other members of the family include previously-described negative geoskin and geochoke. The use of well test data to characterize these particular types of layered fluvial reservoirs is an important step in the static-dynamic integration of geological and reservoir engineering models.
Gas-driven subcritical crack propagation during the conversion of oil to gas
Authors: Fan Z. Q. , Jin Z.-H. , Johnson S. E.
Published: April 2012

In this paper, we investigate subcritical propagation of an initially oil-filled, sub-horizontal microcrack driven by the excess fluid pressure associated with the conversion of oil to gas in a petroleum source rock under continuous burial. The crack propagation distance and propagation duration (the time required for the crack to propagate during conversion of all oil to gas), as well as the excess pressure inside the crack, are determined using a finite difference scheme that couples linear elastic fracture mechanics, oil–gas transformation kinetics and an equation of state for the gas. The effects of the source-rock temperature at the initial depth of the microcrack and fracture properties of the source rock are also considered. Our numerical results show that higher burial rates significantly reduce the crack propagation duration. However, the influence of the geothermal gradient on the propagation duration and distance is only marginal. Similar to the results for the oil-driven crack propagation during kerogen–oil conversion, the duration of gas-driven crack propagation is also governed by transformation kinetics because the subcritical crack propagation rate is much faster than the oil–gas conversion rate.
Could gas hydrate in fine-grained sediments be a precursor for some shale gas deposits?
Authors: Max M.D. , Johnson A.H.
Published: April 2012

Many of the original muddy marine sediments that have compacted to become gas shale could have been in a depositional environment suitable for the formation of natural gas hydrate (NGH), which concentrates gas by a factor of 164 (at STP). Dispersed biogenic NGH in fine-grained continental slope sediments today occurs in sections as thick as 250 m and contains enormous amounts of methane. Concentrated NGH can completely fill porosity in more permeable sediments. Formation of NGH in the early diagenetic history of shale gas sediments may have been the first step in the gas concentration process. NGH that formed in ancient gas shale sediments could have persisted and held the natural gas in place during lithification so long as hydrate remained stable. It is possible that the concentrated gas was held in place until the packing of the clay minerals effectively reduced permeability to a point that the gas released from naturally converting hydrate could not migrate easily. Because NGH creates open porosity upon conversion, a very large part of this gas could have been trapped in the shales before dissociation of the NGH to its component water and gas was completed. An implication for shale gas exploration is that high gas concentrations may not be confined to organic-rich shales but may also be found in any shales that once contained substantial gas hydrates. These include grey shales with lower organic content and more siliceous shales, which respond well to fracking.
Basement structure of southern Tunisia as determined from the analysis of gravity data: implications for petroleum exploration
Authors: Gabtni Hakim , Jallouli Chokri , Mickus Kevin L. , Dhaoui Mohamed , Turki Mohamed Moncef , Jaffal Mohammed , Keating Pierre
Published: April 2012

Gravity data were analysed in the Ghadames Basin and surrounding regions in southern Tunisia in order to determine the basement structure of the region and its relationship to petroleum exploration in relatively unexplored basins. The analysis included the construction of regional Bouguer gravity anomaly and horizontal gravity gradient maps. These maps indicate that the Ghadames Basin is not a simple sag basin but consists of a series of sub-basins and uplifts. The northern boundary of the basin which we call the Telemzan–Ghadames transition zone is marked by a NE-trending high amplitude gravity gradient anomaly which decreases in amplitude toward the east and breaks into a series of north–south- and east–west-trending anomalies implying a more structurally complex region. When the known petroleum fields are overlain on to the gravity gradient anomaly maps, the fields mostly occur along or next to linear alignments of horizontal gravity gradient maxima. We interpret the correlation of the petroleum fields and horizontal gravity gradient maxima to indicate that the basement was involved in forming the petroleum traps. This study illustrates that a regional gravity analysis can be useful in determining where additional exploration can be applied in relatively unexplored basins.
The price of anarchy in network creation games
Authors: Demaine Erik D. , Hajiaghayi Mohammadtaghi , Mahini Hamid , Zadimoghaddam Morteza
Published: April 2012

We study Nash equilibria in the setting of network creation games introduced recently by Fabrikant, Luthra, Maneva, Papadimitriou, and Shenker. In this game we have a set of selfish node players, each creating some incident links, and the goal is to minimize α times the cost of the created links plus sum of the distances to all other players. Fabrikant et al. proved an upper bound
O
(√α) on the price of anarchy: the relative cost of the lack of coordination. Albers, Eilts, Even-Dar, Mansour, and Roditty show that the price of anarchy is constant for α =
O
(√
n
) and for α ≥ 12
n
⌈ lg
n
⌉, and that the price of anarchy is 15(1+(min{α
2
/
n
,
n
2
/α})
1/3
) for any α. The latter bound shows the first sublinear worst-case bound,
O
(
n
1/3
), for all α. But no better bound is known for α between ω(√
n
) and
o
(
n
lg
n
).

Yet α ≈
n
is perhaps the most interesting range, for it corresponds to considering the average distance (instead of the sum of distances) to other nodes to be roughly on par with link creation (effectively dividing α by
n
). In this article, we prove the first
o
(
n
ε
) upper bound for general α, namely 2

O
(√ lg
n
)

. We also prove a constant upper bound for α =
O
(
n
1-ε
) for any fixed ε > 0, substantially reducing the range of α for which constant bounds have not been obtained. Along the way, we also improve the constant upper bound by Albers et al. (with the lead constant of
15
) to
6
for α < (
n
/2)
1/2
and to
4
for α < (
n
/2)
1/3
. Next we consider the bilateral network variant of Corbo and Parkes, in which links can be created only with the consent of both endpoints and the link price is shared equally by the two. Corbo and Parkes show an upper bound of
O
(√α) and a lower bound of Ω(lgα) for α ≤
n
. In this article, we show that in fact the upper bound
O
(√α) is tight for α ≤
n
, by proving a matching lower bound of Ω(√α). For α >
n
, we prove that the price of anarchy is Θ(
n
/√ α).

Finally we introduce a variant of both network creation games, in which each player desires to minimize α times the cost of its created links plus the maximum distance (instead of the sum of distances) to the other players. This variant of the problem is naturally motivated by considering the worst case instead of the average case. Interestingly, for the original (unilateral) game, we show that the price of anarchy is at most
2
for α ≥
n
,
O
(min {4

√lg
n

, (
n
/α)
1/3
}) for 2√ lg
n
≤ α ≤
n
, and
O
(
n
2/α
) for α < 2√ lg
n
.

For the bilateral game, we prove matching upper and lower bounds of Θ(
n
/α + 1) for α ≤
n
, and an upper bound of
2
for α >
n
.
On the query complexity of testing orientations for being Eulerian
Authors: Fischer Eldar , Lachish Oded , Matsliah Arie , Newman Ilan , Yahalom Orly
Published: April 2012

We consider testing directed graphs Eulerianity in the orientation model introduced in Halevy et al. [2005]. Despite the local nature of the Eulerian property, it turns out to be significantly harder to test than other properties studied in the orientation model. We show a nonconstant lower bound on the query complexity of 2-sided tests and a linear lower bound on the query complexity of 1-sided tests for this property. On the positive side, we give several 1-sided and 2-sided tests, including a sublinear query complexity 2-sided test, for general graphs. For special classes of graphs, including bounded-degree graphs and expander graphs, we provide improved results. In particular, we give a 2-sided test with constant query complexity for dense graphs, as well as for expander graphs with a constant expansion parameter.
On the hardness of losing weight
Authors: Krokhin Andrei , Marx Dániel
Published: April 2012

We study the complexity of local search for the Boolean constraint satisfaction problem (CSP), in the following form: given a CSP instance, that is, a collection of constraints, and a solution to it, the question is whether there is a better (lighter, i.e., having strictly less Hamming weight) solution within a given distance from the initial solution. We classify the complexity, both classical and parameterized, of such problems by a Schaefer-style dichotomy result, that is, with a restricted set of allowed types of constraints. Our results show that there is a considerable amount of such problems that are NP-hard, but fixed-parameter tractable when parameterized by the distance.
Nominal Unification from a Higher-Order Perspective
Authors: Levy Jordi , Villaret Mateu
Published: April 2012

Nominal logic is an extension of first-order logic with equality, name-binding, renaming via name-swapping and freshness of names. Contrarily to lambda-terms, in nominal terms, bindable names, called atoms, and instantiable variables are considered as distinct entities. Moreover, atoms are capturable by instantiations, breaking a fundamental principle of the lambda-calculus. Despite these differences, nominal unification can be seen from a higher-order perspective. From this view, we show that nominal unification can be quadratically reduced to a particular fragment of higher-order unification problems: higher-order pattern unification. We also prove that the translation preserves most generality of unifiers.
Simplification Rules for Intuitionistic Propositional Tableaux
Authors: Ferrari Mauro , Fiorentini Camillo , Fiorino Guido
Published: April 2012

The implementation of a logic requires, besides the definition of a calculus and a decision procedure, the development of techniques to reduce the search space. In this article we introduce some simplification rules for Intuitionistic propositional logic that try to replace a formula with an equi-satisfiable “simpler” one with the aim to reduce the search space. Our results are proved via semantical techniques based on Kripke models. We also provide an empirical evaluation of their impact on implementations.
No User Left Behind
Authors: Poor G. Michael , Leventhal Laura M. , Barnes Julie , Hutchings Duke R. , Albee Paul , Campbell Laura
Published: April 2012

Usability and accessibility have become increasingly important in computing curricula. This article briefly reviews how these concepts may be included in existing courses. The authors conducted a survey of student attitudes toward these issues at the start and end of a usability engineering course that included a group project with an accessibility component. Results of the survey indicate that students’ awareness of issues related to usability and accessibility are increased after taking the course and completing the project. Our work and results are potentially valuable to CS educators in three ways: (1) They validate the usefulness of the survey instrument in assessing pedagogies in usability engineering, (2) They provide useful insights into the attitudes of CS majors relative to the important topics of usability and accessibility, and (3) They point to possible benefits of including usability and accessibility topics into CS curricula.
Design for symbiosis
Authors: Menell Peter S.
Published: April 2012

Promoting more harmonious paths for technological innovators and expressive creators in the Internet age.
Programming the global brain
Authors: Bernstein Abraham , Klein Mark , Malone Thomas W.
Published: April 2012

Considering how we can improve our understanding and utilization of the emerging human-computer network constituting the global brain.
Puzzled: Designs on square grids
Authors: Winkler Peter
Published: April 2012

Welcome to, as usual, three new puzzles. However, unlike previous columns, where solutions to two were known (and included in the related Solutions and Sources in the next issue), this time expect to see solutions to all three in June.
ACM's 2012 general election
Authors: Segal Gerald
Published: April 2012

Meet the candidates who introduce their plans---and stands---for the Association.

Please take this opportunity to vote.
Markovian trees subject to catastrophes
Authors: Hautphenne Sophie , Latouche Guy , Nguyen Giang T.
Published: April 2012

We consider multi-type Markovian branching processes subject to catastrophes which kill random numbers of living individuals at random epochs. It is well known that the criteria for extinction of such a process is related to the conditional growth rate of the population, given the history of the process of catastrophes, and that it is usually hard to evaluate. We give a simple characterization in the case when all individuals have the same probability of surviving a catastrophe, and we determine upper and lower bounds in the case where survival depends on the type of the individual. The upper bound appears to be often much tighter than the lower bound.
A fluid introduction to brownian motion & stochastic integration (abstract only)
Authors: Ramaswami V.
Published: April 2012

This presentation provides an introduction to Brownian motion and stochastic integrals using linear fluid flows on finite state Markov chains. Many numerical examples are presented setting the stage for the development of algorithms for stochastic integration via the well-studied and easily understood fluid flow models driven by finite state Markov chains.
A network of fluid models and its application in MANETs (abstract only)
Authors: Sonenberg Nikki , Taylor Peter G.
Published: April 2012

Ad hoc mobile networks are peer-to-peer systems whose successful operation depends on the nodes contributing the resources of their device. Nodes rely on portable energy sources, for example batteries, to transmit to each other. For the network to function, either the nodes willingly cooperate or their behaviour is influenced by an incentive mechanism.

Building on work by Latouche and Taylor (2009) and assuming finite capacity buffers, we model each user's battery energy and credit balance as fluids, with the rate of increase or decrease of the fluid modulated by the network call occupancy. This results in a network of stochastic fluid models, which we analyse using a reduced-load approach. We study the resources required to ensure the network can maintain itself without having to drop calls and investigate the design of a credit incentive mechanism to discourage uncooperative behaviour in the sharing of resources.
A new paradigm for priority patient selection (abstract only)
Authors: Stanford David , Taylor Peter G. , Ziedins Ilze
Published: April 2012

The central purpose of this work is to bridge the gap between two aspects of health care systems: 1) Key Performance Indicators (KPIs) for delay in access to care for patient classes, with differing levels of acuity or urgency, specify the fraction of patients needing to be seen by some key time point. 2) Patient classes present themselves for care, and consume health care resources, in a fashion that is totally independent of the KPIs. Rather, they present in a manner determined by the prevalence of the medical condition, at a rate that may vary over time. Treatment times will likewise be determined by medical need and current practice. There is no reason to expect the resulting system performance will adhere to the specified KPIs. The present work presents a new paradigm for priority assignment that enables one to fine-tune the system in order to achieve the delay targets, assuming sufficient capacity exists for at least one such arrangement.