bluuebunny/crossref_metadata_2025 huggingface dataset:
Depolarization, Bacterial Membrane Composition, and the Antimicrobial Action of Ceragenins
Authors: Epand Raquel F. , Pollard Jake E. , Wright Jonathan O. , Savage Paul B. , Epand Richard M.
Published: June 2010

Ceragenins are cholic acid-derived antimicrobial agents that mimic the activity of endogenous antimicrobial peptides. Ceragenins target bacterial membranes, yet the consequences of these interactions have not been fully elucidated. The role of the outer membrane in allowing access of the ceragenins to the cytoplasmic membrane of Gram-negative bacteria was studied using the ML-35p mutant strain of
Escherichia coli
that has been engineered to allow independent monitoring of small-molecule flux across the inner and outer membranes. The ceragenins CSA-8, CSA-13, and CSA-54 permeabilize the outer membrane of this bacterium, suggesting that the outer membrane does not play a major role in preventing the access of these agents to the cytoplasmic membrane. However, only the most potent of these ceragenins, CSA-13, was able to permeabilize the inner membrane. Interestingly, neither CSA-8 nor CSA-54 caused inner membrane permeabilization over a 30-min period, even at concentrations well above those required for bacterial toxicity. To further assess the role of membrane interactions, we measured membrane depolarization in Gram-positive bacteria with different membrane lipid compositions, as well as in Gram-negative bacteria. We found greatly increased membrane depolarization at the minimal bactericidal concentration of the ceragenins for bacterial species containing a high concentration of phosphatidylethanolamine or uncharged lipids in their cytoplasmic membranes. Although membrane lipid composition affected bactericidal efficiency, membrane depolarization was sufficient to cause lethality, providing that agents could access the cytoplasmic membrane. Consequently, we propose that in targeting bacterial cytoplasmic membranes, focus be placed on membrane depolarization as an indicator of potency.
Pharmacokinetic/Pharmacodynamic Investigation of Colistin against
Pseudomonas aeruginosa
Using an
In Vitro
Model
Authors: Bergen Phillip J. , Bulitta Jurgen B. , Forrest Alan , Tsuji Brian T. , Li Jian , Nation Roger L.
Published: June 2010

Colistin plays a key role in treatment of serious infections by
Pseudomonas aeruginosa
. The aims of this study were to (i) identify the pharmacokinetic/pharmacodynamic (PK/PD) index (i.e., the area under the unbound concentration-time curve to MIC ratio [ƒAUC/MIC], the unbound maximal concentration to MIC ratio [ƒ
C
max
/MIC], or the cumulative percentage of a 24-h period that unbound concentrations exceed the MIC [ƒ
T
>MIC
]) that best predicts colistin efficacy and (ii) determine the values for the predictive PK/PD index required to achieve various magnitudes of killing effect. Studies were conducted in a one-compartment
in vitro
PK/PD model for 24 h using
P. aeruginosa
ATCC 27853, PAO1, and the multidrug-resistant mucoid clinical isolate 19056 muc. Six intermittent dosing intervals, with a range of ƒ
C
max
colistin concentrations, and two continuous infusion regimens were examined. PK/PD indices varied from 0.06 to 18 for targeted ƒ
C
max
/MIC, 0.36 to 312 for ƒAUC/MIC, and 0 to 100% for ƒ
T
>MIC
. A Hill-type model was fit to killing effect data, which were expressed as the log
10
ratio of the area under the CFU/ml curve for treated regimens versus control. With ƒ
C
max
values equal to or above the MIC, rapid killing was observed following the first dose; substantial regrowth occurred by 24 h with most regimens. The overall killing effect was best correlated with ƒAUC/MIC (
R
2
= 0.931) compared to ƒ
C
max
/MIC (
R
2
= 0.868) and ƒ
T
>MIC
(
R
2
= 0.785). The magnitudes of ƒAUC/MIC required for 1- and 2-log
10
reductions in the area under the CFU/ml curve relative to growth control were 22.6 and 30.4, 27.1 and 35.7, and 5.04 and 6.81 for ATCC 27853, PAO1, and 19056 muc, respectively. The PK/PD targets identified will assist in designing optimal dosing strategies for colistin.
Oral Treatment Options for Ambulatory Patients with Urinary Tract Infections Caused by Extended-Spectrum-β-Lactamase-Producing
Escherichia coli
Authors: Auer Simon , Wojna Alexandra , Hell Markus
Published: June 2010

An increase in extended-spectrum-β-lactamase (ESBL)-producing
Escherichia coli
has been observed in outpatient settings. Consequently, 100 ESBL-positive
E. coli
isolates from ambulatory patients with clinically confirmed urinary tract infections were collected by a single laboratory between October 2004 and January 2008. Antimicrobial susceptibility testing was carried out using the oral antibiotics fosfomycin, pivmecillinam, and nitrofurantoin and the parenteral antibiotic ertapenem. Susceptibility rates indicate that fosfomycin (97%), nitrofurantoin (94%), and pivmecillinam (85%) could be considered important oral treatment options.
Synergy of Caspofungin with Human Polymorphonuclear Granulocytes for Killing
Candida albicans
Authors: Tullio Vivian , Mandras Narcisa , Scalas Daniela , Allizond Valeria , Banche Giuliana , Roana Janira , Greco Deborah , Castagno Franco , Cuffini Anna Maria , Carlone Nicola A.
Published: June 2010

The influence of caspofungin on polymorphonuclear leukocyte (PMN) phagocytosis and intracellular killing of
Candida albicans
was investigated. Caspofungin, at all of the concentrations tested (2, 3.2, and 8 μg/ml), significantly increased intracellular killing by PMNs through its direct action on both yeast cells and PMNs, indicating the potential ability of caspofungin to synergize with phagocytes for candidal killing. Caspofungin may therefore constitute an effective therapeutic option for the treatment of invasive fungal infections, including those refractory to conventional treatment with azole agents.
Immunization with theHaemophilus ducreyiHemoglobin Receptor HgbA with Adjuvant Monophosphoryl Lipid A Protects Swine from a Homologous but Not a Heterologous Challenge
Authors: Fusco William G. , Afonina Galyna , Nepluev Igor , Cholon Deborah M. , Choudhary Neelima , Routh Patricia A. , Almond Glenn W. , Orndorff Paul E. , Staats Herman , Hobbs Marcia M. , Leduc Isabelle , Elkins Christopher
Published: June 2010

Haemophilus ducreyi, the etiological agent of chancroid, has a strict requirement for heme, which it acquires from its only natural host, humans. Previously, we showed that a vaccine preparation containing the native hemoglobin receptor HgbA purified fromH. ducreyiclass I strain 35000HP (nHgbAI) and administered with Freund's adjuvant provided complete protection against a homologous challenge. In the current study, we investigated whether nHgbAIdispensed with monophosphoryl lipid A (MPL), an adjuvant approved for use in humans, offered protection against a challenge withH. ducreyistrain 35000HP expressing either class I or class II HgbA (35000HPhgbAIand 35000HPhgbAII, respectively). Pigs immunized with the nHgbAI/MPL vaccine were protected against a challenge from homologousH. ducreyistrain 35000HPhgbAIbut not heterologous strain 35000HPhgbAII, as evidenced by the isolation of only strain 35000HPhgbAIIfrom nHgbAI-immunized pigs. Furthermore, histological analysis of the lesions showed striking differences between mock-immunized and nHgbAI-immunized animals challenged with strains 35000HPhgbAIbut not those challenged with strain 35000HPhgbAII. Mock-immunized pigs were not protected from a challenge by either strain. The enzyme-linked immunosorbent assay (ELISA) activity of the nHgbAI/MPL antiserum was lower than the activity of antiserum from animals immunized with the nHgbAI/Freund's vaccine; however, anti-nHgbAIfrom both studies bound whole cells of 35000HPhgbAIbetter than 35000HPhgbAIIand partially blocked hemoglobin binding to nHgbAI. In conclusion, despite eliciting lower antibody ELISA activity than the nHgbAI/Freund's, the nHgbAI/MPL vaccine provided protection against a challenge with homologous but not heterologousH. ducreyi, suggesting that a bivalent HgbA vaccine may be needed.
Transcellular Passage of
Neisseria meningitidis
across a Polarized Respiratory Epithelium
Authors: Sutherland Thomas C. , Quattroni Paola , Exley Rachel M. , Tang Christoph M.
Published: June 2010

Neisseria meningitidis
is a major cause of sepsis and meningitis but is also a common commensal, present in the nasopharynx of between 8 and 20% of healthy individuals. During carriage, the bacterium is found on the surface of the nasopharyngeal epithelium and in deeper tissues, while to develop disease the meningococcus must spread across the respiratory epithelium and enter the systemic circulation. Therefore, investigating the pathways by which
N. meningitidis
crosses the epithelial barrier is relevant for understanding carriage and disease but has been hindered by the lack of appropriate models. Here, we have established a physiologically relevant model of the upper respiratory epithelial cell barrier to investigate the mechanisms responsible for traversal of
N. meningitidis.
Calu-3 human respiratory epithelial cells were grown on permeable cell culture membranes to form polarized monolayers of cells joined by tight junctions. We show that the meningococcus crosses the epithelial cell barrier by a transcellular route; traversal of the layer did not disrupt its integrity, and bacteria were detected within the cells of the monolayer. We demonstrate that successful traversal of the epithelial cell barrier by
N. meningitidis
requires expression of its type 4 pili (Tfp) and capsule and is dependent on the host cell microtubule network. The Calu-3 model should be suitable for dissecting the pathogenesis of infections caused by other respiratory pathogens, as well as the meningococcus.
Identification and Characterization of a New Ferric Enterobactin Receptor, CfrB, in
Campylobacter
Authors: Xu Fuzhou , Zeng Ximin , Haigh Richard D. , Ketley Julian M. , Lin Jun
Published: June 2010

The ferric enterobactin (FeEnt) receptor CfrA is present in the majority of
Campylobacter jejuni
isolates and is responsible for high-affinity iron acquisition. Our recent work and that of others strongly suggested the existence of another FeEnt uptake system in
Campylobacter
. Here we have identified and characterized a new FeEnt receptor (designated CfrB) using both
in vitro
and
in vivo
systems. CfrB, a homolog of
C. jejuni
NCTC 11168 Cj0444, shares approximately 34% of amino acid identity with CfrA. Alignment of complete CfrB sequences showed that the CfrB is highly conserved in
Campylobacter
. Immunoblotting analysis using CfrB-specific antiserum demonstrated that CfrB was dramatically induced under iron-restricted conditions and was produced in the majority of
Campylobacter coli
(41 out of 45) and in some
C. jejuni
(8 out of 32) primary strains from various sources and from geographically diverse areas. All of the CfrB-producing
C. coli
strains also produced CfrA, which was rarely observed in the tested
C. jejuni
strains. Isogenic
cfrB
,
cfrA
, and
cfrA cfrB
double mutants were constructed in 43 diverse
Campylobacter
strains. Growth promotion assays using these mutants demonstrated that CfrB has a major role in FeEnt iron acquisition in
C. coli
. Chicken colonization experiments indicated that inactivation of the
cfrB
gene alone greatly reduced and even abolished
Campylobacter
colonization of the intestines. A growth assay using CfrB-specific antiserum strongly suggested that specific CfrB antibodies could block the function of CfrB and diminish FeEnt-mediated growth promotion under iron-restricted conditions. Together, this work reveals the complexity of FeEnt systems in the two closely related
Campylobacter
species and demonstrates the important role of the new FeEnt receptor CfrB in
Campylobacter
iron acquisition and
in vivo
colonization.
Relatedness of
Vibrio cholerae
O1/O139 Isolates from Patients and Their Household Contacts, Determined by Multilocus Variable-Number Tandem-Repeat Analysis
Authors: Kendall Emily A. , Chowdhury Fahima , Begum Yasmin , Khan Ashraful I. , Li Shan , Thierer James H. , Bailey Jason , Kreisel Kristen , Tacket Carol O. , LaRocque Regina C. , Harris Jason B. , Ryan Edward T. , Qadri Firdausi , Calderwood Stephen B. , Stine O. Colin
Published: June 2010

The genetic relatedness of
Vibrio cholerae
O1/O139 isolates obtained from 100 patients and 146 of their household contacts in Dhaka, Bangladesh, between 2002 and 2005 was assessed by multilocus variable-number tandem-repeat analysis. Isolate genotypes were analyzed at five loci containing tandem repeats. Across the population, as well as within households, isolates with identical genotypes were clustered in time. Isolates from individuals within the same household were more likely to have similar or identical genotypes than were isolates from different households, but even within a household, isolates from different individuals often had different genotypes. When household contacts were sampled regularly for 3 weeks after the illness of the household index patient, isolates with genotypes related to the index patient appeared in contacts, on average, ∼3 days after the index patient, while isolates with unrelated genotypes appeared in contacts ∼6 days after. Limited data revealed that multiple isolates from the same individual collected within days of each other or even from a single stool sample may have identical, similar, or unrelated genotypes as well. Our results demonstrate that genetically related
V. cholerae
strains cluster in local outbreaks but also suggest that multiple distinct strains of
V. cholerae
O1 may circulate simultaneously within a household.
The effect of real-time gait retraining on hip kinematics, pain and function in subjects with patellofemoral pain syndrome
Authors: Noehren B , Scholz J , Davis I
Published: June 2010

Background

Patellofemoral pain syndrome (PFPS) is the most common overuse injury in runners. Recent research suggests that hip mechanics play a role in the development of this syndrome. Currently, there are no treatments that directly address the atypical mechanics associated with this injury.

Objective

The purpose of this study was to determine whether gait retraining using real-time feedback improves hip mechanics and reduces pain in subjects with PFPS.

Methods

Ten runners with PFPS participated in this study. Real-time kinematic feedback of hip adduction (HADD) during stance was provided to the subjects as they ran on a treadmill. Subjects completed a total of eight training sessions. Feedback was gradually removed over the last four sessions. Variables of interest included peak HADD, hip internal rotation (HIR), contralateral pelvic drop, as well as pain on a verbal analogue scale and the lower-extremity function index. We also assessed HADD, HIR and contralateral pelvic drop during a single leg squat. Comparisons of variables of interest were made between the initial, final and 1-month follow-up visit.

Results

Following the gait retraining, there was a significant reduction in HADD and contralateral pelvic drop while running. Although not statistically significant, HIR decreased by 23% following gait retraining. The 18% reduction in HADD during a single leg squat was very close to significant. There were also significant improvements in pain and function. Subjects were able to maintain their improvements in running mechanics, pain and function at a 1-month follow-up. An unexpected benefit of the retraining was an 18% and 20% reduction in instantaneous and average vertical load rates, respectively.

Conclusions

Gait retraining in individuals with PFPS resulted in a significant improvement of hip mechanics that was associated with a reduction in pain and improvements in function. These results suggest that interventions for PFPS should focus on addressing the underlying mechanics associated with this injury. The reduction in vertical load rates may be protective for the knee and reduce the risk for other running-related injuries.
Descriptive profile of scapulothoracic position, strength and flexibility variables in adolescent elite tennis players
Authors: Cools Ann M , Johansson Fredrik R , Cambier Dirk C , Velde Annemie Vande , Palmans Tanneke , Witvrouw Erik E
Published: June 2010

Study design

Descriptive study, cross-sectional design.

Background

Tennis requires repetitive overhead movement patterns that can lead to upper extremity injury. The scapula plays a vital role in injury-free playing. Scapular dysfunction has been associated with shoulder injury in the overhead athlete.

Objectives

The purpose of this study was to describe variables regarding scapular position, muscle strength and flexibility in young elite tennis players.

Methods

Thirty-five adolescent Swedish elite tennis players (19 boys, aged 13.6 (±1.4) years, 16 girls, aged 12.6 (±1.3) years), selected on the basis of their national ranking, underwent a clinical screening protocol consisting of: scapular upward rotation at several angles of arm elevation; isometric scapular muscle strength; and anthropometric measurement of pectoralis minor (PM) length.

Results

The players showed significantly more scapular upward rotation on their dominant side (p<0.001). For both genders, upper trapezius (p=0.003) and serratus anterior (p=0.01) strength was significantly greater on the dominant side, whereas middle and lower trapezius strength showed no side differences. PM was shorter on the dominant side (p<0.001), and in the female players (p=0.006) compared with the boys.

Conclusion

These results indicate some sports-related adaptations of young tennis players on their dominant side at the scapulothoracic level to exposure to their sport. These data may assist the clinician in the prevention and rehabilitation of sport-specific injuries in adolescent tennis players.
QUARK–DIQUARK SYSTEMATICS OF BARYONS AND THE SU(6) SYMMETRY FOR LIGHT STATES
Authors: ANISOVICH A. V. , ANISOVICH V. V. , MATVEEV M. A. , NIKONOV V. A. , SARANTSEV A. V. , VULFS T. O.
Published: June 2010

We continue our attempts to systematize baryons, which are composed of light quarks (q = u, d), as quark–diquark systems. The notion of two diquarks is used: (i) [Formula: see text], with the spin SD = 1 and isospin ID = 1 and (ii) [Formula: see text], with SD = 0 and ID = 0. Here we try to resolve the problem of the low-lying [Formula: see text] states: in the last experiments the lightest state is observed at ≳2200 MeV , not at 1900–2000 MeV as it has been stated 20 years ago. We are looking for different systematization variants with the forbidden low-lying [Formula: see text] states in the mass region ≲2000 MeV . We see that the inclusion of the SU(6) constraints on [Formula: see text] states with angular momentum L = 1 results in a shift of the lightest [Formula: see text] isobar to ~2300 MeV . The scheme with the SU(6) constraints for low-lying [Formula: see text] and [Formula: see text] states (with L = 0, 1) is presented in detail.
STUDY ON THE NONCOMMUTATIVE REPRESENTATIONS OF GALILEAN GENERATORS
Authors: KUMAR SARMISTHA (CHAUDHURI) , SAMANTA SAURAV
Published: June 2010

The representations of Galilean generators are constructed on a space where both position and momentum coordinates are noncommutating operators. A dynamical model invariant under noncommutative phase space transformations is constructed. The Dirac brackets of this model reproduce the original noncommutative algebra. Also, the generators in terms of noncommutative phase-space variables are abstracted from this model in a consistent manner. Finally, the role of Jacobi identities is emphasized to produce the noncommuting structure that occurs when an electron is subjected to a constant magnetic field and Berry curvature.
A FAST RANDOMIZED HOUGH TRANSFORM FOR CIRCLE/CIRCULAR ARC RECOGNITION
Authors: CHIU SHIH-HSUAN , LIAW JIUN-JIAN , LIN KUO-HUNG
Published: June 2010

The main drawbacks of the Hough transform (HT) are the heavy requirement of computation and storage. To improve the drawbacks of the HT, the randomized Hough transform (RHT) was proposed. But the RHT is not suitable for detecting the pattern with the complex image because the probability is too low. In this paper, we propose a fast randomized Hough transform for circle/circular arc detection. We pick one point at random to be the seed point. Then, we propose a checking rule to confirm if the seed point is on the true circle. Compared with the previous techniques, the proposed method requires less computational time and is more suitable for complex images. In the experiments, synthetic and real images are used to show the effect of the proposed method.
REVERSIBLE JPEG-BASED HIDING METHOD WITH HIGH HIDING-RATIO
Authors: CHEN LEE SHU-TENG , LIN SIAN-JHENG , LIN JA-CHEN
Published: June 2010

The stego-images generated by many existing hiding techniques are not economic in size, and hence need compression. Unfortunately, compression usually destroys the secret content hidden inside. To solve this dilemma, some hiding methods based on compression code (rather than the image itself) are reported. This paper proposes a high-capacity and high-hiding-ratio "reversible" steganography method based on JPEG-compression code. In the proposed method, the JPEG compression code of an image is used as the cover media. An 8×8 hiding-capacity table is firstly evaluated, which is then utilized to modify the quantization table attached to the given JPEG code. The two quantization tables (modified and original) together can map the DCT coefficients of each block to some larger DCT coefficients, with secret data hidden inside these larger DCT coefficients. In the decoding process, after lossless extraction of the hidden secret data, the proposed method can also recover the original JPEG-compression code. Experimental results show that our method outperforms other JPEG-based hiding methods (reversible or not) regarding both hiding-ratio and stego-image's quality.
AN INFEASIBLE ELITIST BASED PARTICLE SWARM OPTIMIZATION FOR CONSTRAINED MULTIOBJECTIVE OPTIMIZATION AND ITS CONVERGENCE
Authors: WEI JINGXUAN , WANG YUPING
Published: June 2010

In this paper, an infeasible elitist based particle swarm optimization is proposed for solving constrained optimization problems. Firstly, an infeasible elitist preservation strategy is proposed, which keeps some infeasible solutions with smaller rank values at the early stage of evolution regardless of how large the constraint violations are, and keep some infeasible solutions with smaller constraint violations and rank values at the later stage of evolution. In this manner, the true Pareto front will be found easier. Secondly, in order to find a set of diversity and uniformly distributed Pareto optimal solutions, a new crowding distance function is designed. It can assign large function values not only for the particles located in the sparse regions of the objective space but also for the crowded particles located near to the boundary of the Pareto front as well. Thirdly, a new mutation operator with two phases is proposed. In the first phase, the particles whose constraint violations are less than the threshold value will be used to compute the total force, then the force will be used as a mutation direction, being helpful to find the better solutions along this direction. In order to guarantee the convergence of the algorithm, the second phase of mutation is proposed. Finally, the convergence of the algorithm is proved. The comparative study shows that the proposed algorithm can generate widespread and uniformly distributed Pareto fronts and outperforms those compared algorithms.
FEATURE SELECTION AND EXTRACTION USING AN UNSUPERVISED BIOLOGICALLY-SUGGESTED APPROXIMATION TO GEBELEIN'S MAXIMAL CORRELATION
Authors: KURSUN OLCAY , FAVOROV OLEG V.
Published: June 2010

Feature selection and extraction are critical steps in many areas where pattern recognition techniques are applied. Feature selection and extraction are based on identifying and maximizing dependency relations. Gebelein's Maximal Correlation (GMC) is the most general form of dependence in that it does not make any statistical assumptions concerning the nature of the dependencies. Unfortunately, benefiting from such a useful measure in practice is generally impossible as there are only a few cases for which explicit formulae are available to calculate it. In this paper, we point out a parallel between GMC and the SINBAD algorithms, developed originally as a model of feature extraction for neurons in the cerebral cortex. We use SINBAD as a robust approximation to GMC to perform feature selection and extraction on a number of artificial and real datasets. We show that SINBAD estimates of GMC compare favorably to other well known feature selection and extraction methods based on mutual information, kernel canonical correlation analysis and principal component analysis.
VALUATION OF COMPOUND OPTION WHEN THE UNDERLYING ASSET IS NON-TRADABLE
Authors: LIU YU-HONG
Published: June 2010

After Geske (1979), compound options — options on options — have been employed in many fields in which real options are applied. The formula for a compound option is convenient to use in real project investment, but it has one drawback — the assets that underlie the compound options are usually non-tradable. This article addresses this issue and proposes two new compound option pricing formulae to overcome this drawback.
THE SHOCK CURVE APPROACH TO THE RIEMANN PROBLEM FOR 2 × 2 HYPERBOLIC SYSTEMS OF CONSERVATION LAWS
Authors: OHWA HIROKI
Published: June 2010

We consider the Riemann problem for 2 × 2 hyperbolic systems of conservation laws in one space variable. Our main assumptions are that the product of non-diagonal elements within the Fréchet derivative (Jacobian) of the flux is positive, and that the system is genuinely nonlinear. The first assumption implies that the system is strictly hyperbolic, but we do not require a convexity-like condition such as the Smoller–Johnson condition. By using the shock curve approach, we show that those two assumptions are sufficient to establish the uniqueness of self-similar solutions satisfying the Lax entropy conditions at discontinuities.
DIOPHANTINE APPROXIMATION IN IMAGINARY QUADRATIC FIELDS
Authors: VULAKH L. YA.
Published: June 2010

Let H3 be the upper half-space model of the three-dimensional hyperbolic space. For certain cocompact Fuchsian subgroups Γ of an extended Bianchi group Bd, the extremality of the axis of hyperbolic F ∈ Γ in H3 with respect to Γ implies its extremality with respect to Bd. This reduction is used to obtain sharp lower bounds for the Hurwitz constants and lower bounds for the highest limit points in the Markov spectra of Bd for some d < 1000. In particular, such bounds are found for all non-Euclidean class one imaginary quadratic fields. The Hurwitz constants for the imaginary quadratic fields with discriminants -120 and -132 are given. The second minima are also indicated for these fields.
HERMITIAN POINTS IN MARKOV SPECTRA
Authors: VULAKH L. YA
Published: June 2010

Let Hn be the upper half-space model of the n-dimensional hyperbolic space. For n=3, Hermitian points in the Markov spectrum of the extended Bianchi group Bd are introduced for any d. If ν is a Hermitian point in the spectrum, then there is a set of extremal geodesics in H3 with diameter 1/ν, which depends on one continuous parameter. It is shown that ν2 ≤ |D|/24 for any imaginary quadratic field with discriminant D, whose ideal-class group contains no cyclic subgroup of order 4, and in many other cases. Similarly, in the case of n = 4, if ν is a Hermitian point in the Markov spectrum for SV(Z4), some discrete group of isometries of H4, then the corresponding set of extremal geodesics depends on two continuous parameters.
ADDITIVE BASES IN ABELIAN GROUPS
Authors: LEV VSEVOLOD F. , MUZYCHUK MIKHAIL E. , PINCHASI ROM
Published: June 2010

Let G be a finite, non-trivial Abelian group of exponent m, and suppose that B1,…, Bk are generating subsets of G. We prove that if k > 2m ln log2 |G|, then the multiset union B1 ∪ Bk forms an additive basis of G; that is, for every g ∈ G, there exist A1 ⊆ B1,…, Ak ⊆ Bk such that [Formula: see text]. This generalizes a result of Alon, Linial and Meshulam on the additive bases conjecture.

As another step towards proving the conjecture, in the case where B1,…, Bk are finite subsets of a vector space, we obtain lower-bound estimates for the number of distinct values, attained by the sums of the form [Formula: see text], where Ai vary over all subsets of Bi for each i = 1,…, k.

Finally, we establish a surprising relation between the additive bases conjecture and the problem of covering the vertices of a unit cube by translates of a lattice, and present a reformulation of (the strong form of) the conjecture in terms of coverings.
RAMANUJAN'S CUBIC CONTINUED FRACTION AND RAMANUJAN TYPE CONGRUENCES FOR A CERTAIN PARTITION FUNCTION
Authors: CHAN HEI-CHI
Published: June 2010

In this paper, we study the divisibility of the function a(n) defined by [Formula: see text]. In particular, we prove certain "Ramanujan type congruences" for a(n) modulo powers of 3.
SUR UN CRITÈRE DE BÁEZ-DUARTE POUR L'HYPOTHÈSE DE RIEMANN
Authors: BALAZARD MICHEL , DE ROTON ANNE
Published: June 2010

Define en(t) = {t/n}. Let dN denote the distance in L2(0, ∞; t-2dt) between the indicator function of [1, ∞[ and the vector space generated by e1,…, eN. A theorem of Báez-Duarte states that the Riemann hypothesis (RH) holds if and only if dN → 0 when N → ∞. Assuming RH, we prove the estimate [Formula: see text]
Combining relations for information extraction from free text
Authors: Maslennikov Mstislav , Chua Tat-Seng
Published: June 2010

Relations between entities of the same semantic type tend to be sparse in free texts. Therefore, combining relations is the key to effective information extraction (IE) on free text datasets with a small set of training samples. Previous approaches to bootstrapping for IE used different types of relations, such as dependency or co-occurrence, and faced the problems of paraphrasing and misalignment of instances. To cope with these problems, we propose a framework that integrates several types of relations. After extracting candidate entities, our framework evaluates relations between them at the phrasal, dependency, semantic frame, and discourse levels. For each of these levels, we build a classifier that outputs a score for relation instances. In order to integrate these scores, we propose three strategies: (1) integrate evaluation scores from each relation classifier; (2) incorporate the elimination of negatively labeled instances in a previous strategy; and (3) add cascading of extracted relations into strategy (2). Our framework improves the state-of-art results for supervised systems by 8%, 15%, 3%, and 5% on MUC4 (terrorism); MUC6 (management succession); ACE RDC 2003 (news, general types); and ACE RDC 2003 (news, specific types) domains respectively.
A Synthesis-Oriented VHDL Course
Authors: d’Amore Roberto
Published: June 2010

This article proposes a VHDL language course that establishes a strong correlation between the language statements and their use in circuit synthesis. Two course modules are described: a basic module that contains the essential concepts of the language, sufficient for students to describe medium complexity circuits, followed by a second module with more complex language concepts. The benefits of correlated laboratory tasks which use simulation and synthesis tools are discussed. Evaluation content, student test scores, and student feedback are presented. Suggestions for improving and modifying the course are given.
The directed circular arrangement problem
Authors: Naor Joseph (Seffi) , Schwartz Roy
Published: June 2010

We consider the problem of embedding a directed graph onto evenly spaced points on a circle while minimizing the total weighted edge length. We present the first poly-logarithmic approximation factor algorithm for this problem which yields an approximation factor of
O
(log
n
log log
n
), thus improving the previous
Õ
(√
n
) approximation factor. In order to achieve this, we introduce a new problem which we call the
directed penalized linear arrangement
. This problem generalizes both the directed feedback edge set problem and the directed linear arrangement problem. We present an
O
(log
n
log log
n
)-approximation factor algorithm for this newly defined problem. Our solution uses two distinct directed metrics (“right” and “left”) which together yield a lower bound on the value of an optimal solution. In addition, we define a sequence of new directed spreading metrics that are used for applying the algorithm recursively on smaller subgraphs. The new spreading metrics allow us to define an asymmetric region growing procedure that accounts simultaneously for both incoming and outgoing edges. To the best of our knowledge, this is the first time that a region growing procedure is defined in directed graphs that allows for such an accounting.
Competitive weighted throughput analysis of greedy protocols on DAGs
Authors: Gordon Eyal , Rosén Adi
Published: June 2010

The combination of the buffer sizes of routers deployed in the Internet, and the Internet traffic itself, leads routinely to the dropping of packets. Motivated by this, we are interested in the problem of maximizing the throughput of protocols that control packet networks. Moreover, we are interested in a setting where different packets have different priorities (or weights), thus taking into account Quality-of-Service considerations.

We first extend the Competitive Network Throughput (CNT) model introduced by Aiello et al. [2003] to the weighted packets case. We analyze the performance of online, local-control protocols by their competitive ratio, in the face of arbitrary traffic, using as a measure the total weight of the packets that arrive to their destinations, rather than being dropped en-route. We prove that on Directed Acyclic Graphs (DAGs), any greedy protocol is competitive, with competitive ratio independent of the weights of the packets. Here we mean by a “greedy protocol” a protocol that not only does not leave a resource idle unnecessarily, but also prefers packets with higher weight over those with lower weight. We give two independent upper bounds on the competitive ratio of general greedy protocols on DAGs. We further give lower bounds that show that our upper bounds cannot be improved (other than constant factors) in the general case. Both our upper and lower bounds apply also to the unweighted case, and they improve the results given in Aiello et al. [2003] for that case. We thus give tight (up to constant factors) upper and lower bounds for both the unweighted and weighted cases.

In the course of proving our upper bounds we prove a lemma that gives upper bounds on the delivery times of packets by any greedy protocol on general DAGs (without buffer size considerations). We believe that this lemma may be of independent interest and may find additional applications.
Adaptive sampling strategies for quickselects
Authors: Martínez Conrado , Panario Daniel , Viola Alfredo
Published: June 2010

Quickselect with median-of-3 is largely used in practice and its behavior is fairly well understood. However, the following natural adaptive variant, which we call
proportion-from-3
, had not been previously analyzed: “choose as pivot the smallest of the sample if the relative rank of the sought element is below 1/3, the largest if the relative rank is above 2/3, and the median if the relative rank is between 1/3 and 2/3.” We first analyze the average number of comparisons made when using proportion-from-2 and then for proportion-from-3. We also analyze ν-find, a generalization of proportion-from-3 with interval breakpoints at ν and 1-ν. We show that there exists an optimal value of ν and we also provide the range of values of ν where ν-find outperforms median-of-3. Then, we consider the average total cost of these strategies, which takes into account the cost of both comparisons and exchanges. Our results strongly suggest that a suitable implementation of ν-find could be the method of choice in a practical setting. We also study the behavior of proportion-from-
s
with
s
>3 and in particular we show that proportion-from-
s
-like strategies are optimal when
s
→∞.
Fostering IPv6 migration through network quality differentials
Authors: Guérin Roch , Hosanagar Kartik
Published: June 2010

Although IPv6 has been the next generation Internet protocol for nearly 15 years, new evidences indicate that transitioning from IPv4 to IPv6 is about to become a more pressing issue. This paper attempts to quantify if and how such a transition may unfold. The focus is on "connectivity quality," e.g., as measured by users' experience when accessing content, as a possible incentive (or disincentive) for migrating to IPv6, and on "translation costs" (between IPv6 and IPv4) that Internet Service Providers will incur during this transition. The paper develops a simple model that captures some of the underlying interactions, and highlights the ambiguous role of translation gateways that can either help or discourage IPv6 adoption. The paper is an initial foray in the complex and often puzzling issue of migrating the current Internet to a new version with which it is incompatible.
An argument for increasing TCP's initial congestion window
Authors: Dukkipati Nandita , Refice Tiziana , Cheng Yuchung , Chu Jerry , Herbert Tom , Agarwal Amit , Jain Arvind , Sutin Natalia
Published: June 2010

TCP flows start with an initial congestion window of at most four segments or approximately 4KB of data. Because most Web transactions are short-lived, the initial congestion window is a critical TCP parameter in determining how quickly flows can finish. While the global network access speeds increased dramatically on average in the past decade, the standard value of TCP's initial congestion window has remained unchanged.

In this paper, we propose to increase TCP's initial congestion window to at least ten segments (about 15KB). Through large-scale Internet experiments, we quantify the latency benefits and costs of using a larger window, as functions of network bandwidth, round-trip time (RTT), bandwidth-delay product (BDP), and nature of applications. We show that the average latency of HTTP responses improved by approximately 10% with the largest benefits being demonstrated in high RTT and BDP networks. The latency of low bandwidth networks also improved by a significant amount in our experiments. The average retransmission rate increased by a modest 0.5%, with most of the increase coming from applications that effectively circumvent TCP's slow start algorithm by using multiple concurrent connections. Based on the results from our experiments, we believe the initial congestion window should be at least ten segments and the same be investigated for standardization by the IETF.
Towards understanding bugs in open source router software
Authors: Yin Zuoning , Caesar Matthew , Zhou Yuanyuan
Published: June 2010

Software errors and vulnerabilities in core Internet routers have led to several high-profile attacks on the Internet infrastructure and numerous outages. Building an understanding of bugs in open-source router software is a first step towards addressing these problems. In this paper, we study router bugs found in two widely-used open-source router implementations. We evaluate the root cause of bugs, ease of diagnosis and detectability, ease of prevention and avoidance, and their effect on network behavior.
A "Gen 2" RFID monitor based on the USRP
Authors: Buettner Michael , Wetherall David
Published: June 2010

We have developed a low cost software radio based platform for monitoring EPC Gen 2 RFID traffic. The Gen 2 standard allows for a range of PHY layer configurations and does not specify exactly how to compose protocol messages to inventory tags. This has made it difficult to know how well the standard works, and how it is implemented in practice. Our platform provides much needed visibility into Gen 2 systems by capturing reader transmissions using the USRP2 and decoding them in real-time using software we have developed and released to the public. In essence, our platform delivers much of the functionality of expensive (< $50,000) conformance testing products, with greater extensibility at a small fraction of the cost. In this paper, we present the design and implementation of the platform and evaluate its effectiveness, showing that it has better than 99% accuracy up to 3 meters. We then use the platform to study a commercial RFID reader, showing how the Gen 2 standard is realized, and indicate avenues for research at both the PHY and MAC layers.
FIE
Authors: Crowcroft Jon
Published: June 2010

There are so many initiatives to look at the Internet's Future http://www.future-internet.eu/, http://www.nets-find.net/ and similar programs in pretty every any other geo-political arena, anyone would think that there was some tremendous threat like global warming, about to bring about its immediate demise, and that this would bring civilisation crashing down around our ears.

The Internet has a great future behind it, of course. However, my thesis is that the Future Internet is about as relevant as Anthropogenic Global Warming (AGW), in the way it is being used to support various inappropriate activities. Remember that the start of all this was not the exhaustion of IPv4 address space, or the incredibly slow convergence time of BGP routes, or the problem of scaling router memory for FIBs. It was the US research community reacting to a minor (as in parochial) temporary problem of funding in Communications due to slow down within NSF and differing agendas within DARPA.

It is not necessary to invoke all the hype and hysteria - it is both necessary and sufficient to talk about sustainable energy See for example David Mackay's Without Hot Air book, at http://www.withouthotair.com/, and good technical communications research, development, deployment and operations.

To continue the analogy between FI and AGW, what we really do not need is yet more climatologists with dodgy data curation methodologies (or ethnographers studying Internet governance).

What we do need is some solid engineering, to address a number of problems the Internet has. However, this is in fact happening, and would not stop happening if the entire Future Internet flagship was kidnapped by aliens. "We don't need no" government agency doing top down dictats about what to do when. It won't work and it will be a massive waste of time, energy and other resources - i.e. like AGW, it will be a load of hot air:)

On the other hand, there are a number of deeper lessons from the Internet Architecture which might prove useful in other domains, and in the bulk of this opinion piece, I give examples of these, applying the Postel and End-to-end principles to transport, energy, government information/vices.
A continued fraction type method to find a rational number in a given closed interval whose denominator is minimal
Authors: Murakami Hiroshi
Published: June 2010

We show a fast algorithm to find a rational number in a given real interval whose denominator is minimal. The algorithm is similar to the regular continued fraction expansion for a real number.
A vector-quantization approach to coding systems
Authors: Porat Moshe
Published: June 2010

The increasing amount of information transmitted over communication channels has to be handled efficiently to avoid congestion and delays in the network service. In this work, an algebraic approach to data coding and transmission is proposed. One of its basic assumptions is that in many situations the information could be decomposed into basic components or vectors, which represent a significant part of the data. To illustrate the capabilities of the proposed approach, a coding system based on vector quantization is investigated. This approach is based on the observation that in most systems, events of recent history of the stream can be used to represent future vectors of the data. Our conclusion is that the proposed algebraic approach could be efficient in presently used coding systems.
Advanced applications of the holonomic systems approach
Authors: Koutschan Christoph
Published: June 2010

The holonomic systems approach was proposed in the early 1990s by Doron Zeilberger. It laid a foundation for the algorithmic treatment of holonomic function identities. Frédéric Chyzak later extended this framework by introducing the closely related notion of ∂-finite functions and by placing their manipulation on solid algorithmic grounds. For practical purposes it is convenient to take advantage of both concepts which is not too much of a restriction: The class of functions that are holonomic and ∂-finite contains many elementary functions (such as rational functions, algebraic functions, logarithms, exponentials, sine function, etc.) as well as a multitude of special functions (like classical orthogonal polynomials, elliptic integrals, Airy, Bessel, and Kelvin functions, etc.). In short, it is composed of functions that can be characterized by sufficiently many partial differential and difference equations, both linear and with polynomial coefficients. An important ingredient is the ability to execute closure properties algorithmically, for example addition, multiplication, and certain substitutions. But the central technique is called creative telescoping which allows to deal with summation and integration problems in a completely automatized fashion.

Part of this thesis is our Mathematica package HolonomicFunctions in which the above mentioned algorithms are implemented, including more basic functionality such as noncommutative operator algebras, the computation of Gröbner bases in them, and finding rational solutions of parameterized systems of linear differential or difference equations.

Besides standard applications like proving special function identities, the focus of this thesis is on three advanced applications that are interesting in their own right as well as for their computational challenge. First, we contributed to translating Takayama's algorithm into a new context, in order to apply it to an until then open problem, the proof of Ira Gessel's lattice path conjecture. The computations that completed the proof were of a nontrivial size and have been performed with our software. Second, investigating basis functions in finite element methods, we were able to extend the existing algorithms in a way that allowed us to derive various relations which generated a considerable speed-up in the subsequent numerical simulations, in this case of the propagation of electromagnetic waves. The third application concerns a computer proof of the enumeration formula for totally symmetric plane partitions, also known as Stembridge's theorem. To make the underlying computations feasible we employed a new approach for finding creative telescoping operators.