bluuebunny/crossref_metadata_2025 huggingface dataset:
Association of
Helicobacter pylori
Antioxidant Activities with Host Colonization Proficiency
Authors: Olczak Adriana A. , Seyler, Richard W. , Olson Jonathan W. , Maier Robert J.
Published: December 2002

To assess the importance of two separate antioxidant activities in
Helicobacter pylori
, we tested the abilities of strains with mutations in either
tpx
(encoding thiolperoxidase) or
ahpC
(encoding alkyl hydroperoxide reductase [AhpC]) to colonize the stomachs of mice. The
tpx
strain was clearly more sensitive than the parent strain to both oxygen and cumene hydroperoxide. The strain colonized only 5% of the inoculated mice. Two different classes of oxygen-sensitive
ahpC
mutants in the type strain (ATCC 43504) were recently described (A. A. Olczak, J. W. Olson, and R. J. Maier, J. Bacteriol. 184:3186-3193, 2002). The same two classes of mutants were recovered upon
ahpC
mutagenesis of the mouse-adapted strain, SS1. Neither of these mutants was able to colonize mouse stomachs, whereas 78% of the mice inoculated with the parent strain became
H. pylori
positive.
Biodefense-Driven Murine Model of Pneumonic Melioidosis
Authors: Jeddeloh J. A. , Fritz D. L. , Waag D. M. , Hartings J. M. , Andrews G. P.
Published: December 2002

A whole-body mouse model of pneumonic melioidosis was established for future evaluation of biodefense vaccine candidates. The aerosol 50% lethal doses of
Burkholderia pseudomallei
strain 1026b for BALB/c and C57BL/6 mice and the times to death, dissemination in organs, and tissue loads after exposure of the mice to low- and high-dose aerosols are reported. In addition,
rpsL
mutant backgrounds were attenuated in this acute model of disease.
Interaction of Pulmonary Surfactant Protein C with CD14 and Lipopolysaccharide
Authors: Augusto Luis A. , Synguelakis Monique , Johansson Jan , Pedron Thierry , Girard Robert , Chaby Richard
Published: December 2002

In addition to their effects on alveolar surface tension, some components of lung surfactant also have immunological functions. We found recently that the hydrophobic lung surfactant protein SP-C specifically binds to the lipid A region of lipopolysaccharide (LPS). In this study, we show that SP-C also interacts with CD14. Four observations showed cross talk between the three molecules SP-C, LPS, and CD14. (i) Like LBP, SP-C allows the binding of a fluorescent LPS to cells expressing CD14 (the other surfactant components were ineffective). (ii) Recombinant radiolabeled CD14 and SP-C (or a synthetic analog of SP-C) interact in a dose-dependent manner. (iii) LPS blocks the binding of radiolabeled CD14 to SP-C-coated wells. (iv) SP-C enhances the binding of radiolabeled CD14 to LPS-coated wells. These results, obtained with native murine SP-C and with three synthetic analogs, suggest that LPS and CD14 interact with the same region of SP-C and that binding of SP-C modifies the conformation of CD14 or the accessibility of its LPS-binding site, allowing it to bind LPS. This ability of SP-C to interact with the pattern recognition molecule CD14 extends the possible immunological targets of SP-C to a large panel of microorganisms that can enter the airways.
Effects of Tumor Necrosis Factor Alpha on Dendritic Cell Accumulation in Lymph Nodes Draining the Immunization Site and the Impact on the Anticryptococcal Cell-Mediated Immune Response
Authors: Bauman Sean K. , Huffnagle Gary B. , Murphy Juneann W.
Published: December 2002

Cell-mediated immune (CMI) responses and tumor necrosis factor alpha (TNF-α) have been shown to be essential in acquired protection againstCryptococcus neoformans. Induction of a protective anticryptococcal CMI response includes increases in dendritic cells (DC) and activated CD4+T cells in draining lymph nodes (DLN). During the expression phase, activated CD4+T cells accumulate at a peripheral site where cryptococcal antigen is injected, resulting in a classical delayed-type hypersensitivity (DTH) reaction. Induction of a nonprotective anticryptococcal CMI response results in no significant increases in the numbers of DC or activated CD4+T cells in DLN. This study focuses on examining the role of TNF-α in induction of protective and nonprotective anticryptococcal CMI responses. We found that neutralization of TNF-α at the time of immunization with the protective immunogen (i) reduces the numbers of Langerhans cells, myeloid and lymphoid DC, and activated CD4+T cells in DLN and (ii) diminishes the total numbers of cells, the numbers of activated CD4+T cells, and amount of gamma interferon at the DTH reaction site. Although TNF-α neutralization during induction of the nonprotective CMI response had little effect on cellular and cytokine parameters measured, it did cause a reduction in footpad swelling when mice received challenge in the footpad. Our findings show that TNF-α functions during induction of the protective CMI response by influencing the accumulation of all three DC subsets into DLN. Without antigen stimulated DC in DLN, activated CD4+T cells are not induced and thus not available for the expression phase of the CMI response.
Both Family 1 and Family 2 PspA Proteins Can Inhibit Complement Deposition and Confer Virulence to a Capsular Serotype 3 Strain of
Streptococcus pneumoniae
Authors: Ren Bing , Szalai Alexander J. , Thomas Orlanda , Hollingshead Susan K. , Briles David E.
Published: December 2002

Pneumococcal surface protein A (PspA), a virulence factor of
Streptococcus pneumoniae
, is exceptionally diverse, being classified into two major families which are over 50% divergent by sequence analysis. A family 1 PspA from strain WU2 was previously shown to impede the clearance of pneumococci from mouse blood and to interfere with complement deposition on the bacterial surface. To determine whether a family 2 PspA can perform the same role as family 1 PspA, the family 1 PspA (from strain WU2) was replaced with a family 2 PspA (from strain TIGR4) by molecular genetic methods to make an isogenic pair of strains expressing different PspA proteins. Surface binding of lactoferrin and interference with C3 deposition by the two types of PspA proteins were determined by flow cytometry, and virulence was assessed in a mouse bacteremia model. Although the family 2 PspA appeared to bind less human lactoferrin than did the family 1 PspA, both PspA proteins could interfere with complement deposition on the pneumococcal surface and could provide full virulence in the mouse infection model. A mutant form of the family 2 PspA with a deletion within the choline-binding region was also produced. Pneumococci with this mutant PspA failed to bind human lactoferrin even though the PspA was present on the pneumococcal surface. The mutant PspA only partially interfered with complement deposition and moderately attenuated virulence. These results suggest that family 1 and family 2 PspA proteins play similar roles in virulence and that surface accessibility of PspA is important for their function.
Role ofBordetellaO Antigen in Respiratory Tract Infection
Authors: Burns Valorie C. , Pishko Elizabeth J. , Preston Andrew , Maskell Duncan J. , Harvill Eric T.
Published: December 2002

Lipopolysaccharide (LPS), as the major surface molecule of gram-negative bacteria, interacts with the host in complex ways, both inducing and protecting against aspects of inflammatory and adaptive immunity. The membrane-distal repeated carbohydrate structure of LPS, the O antigen, can prevent antibody functions and may vary as a mechanism of immune evasion. Genes of thewbmlocus are required for the assembly of O antigen on the animal pathogenBordetella bronchisepticaand the human pathogenB. parapertussis. However, the important human pathogenB. pertussislacks these genes and a number of in vitro and in vivo characteristics associated with O antigen in other organisms. To determine the specific functions of O antigen in these closely relatedBordetellasubspecies, we comparedwbmdeletion (Δwbm) mutants ofB. bronchisepticaandB. parapertussisin a variety of assays relevant to natural respiratory tract infection. Complement was not activated or depleted by wild-type bordetellae expressing O antigen, but both Δwbmmutants activated complement and were highly sensitive to complement-mediated killing in vitro. Although the O-antigen structures appear to be substantially similar, the two mutants differed strikingly in their defects within the respiratory tract. TheB. parapertussisΔwbmmutant was severely defective in colonization of the tracheas and lungs of mice, while theB. bronchisepticaΔwbmmutant showed almost no defect. While in vitro characteristics such as serum resistance may be attributable to O antigen directly, the role of O antigen during infection appears to be more complex, possibly involving factors differing among the closely related bordetellae or different interactions between each one and its host.
Magnesium in stroke treatment
Authors: Muir K W
Published: December 2002

Magnesium is involved in multiple physiological processes that may be relevant to cerebral ischaemia, including antagonism of glutamate release, NMDA receptor blockade, calcium channel antagonism, and maintenance of cerebral blood flow. Systemically administered magnesium at doses that double physiological serum concentration significantly reduces infarct volume in animal models of stroke, with a window of up to six hours after onset and favourable dose-response characteristics when compared with previously tested neuroprotective agents. Small clinical trials have reported benefit, but results are not statistically significant in systematic review. A large ongoing trial (IMAGES) will report in 2003–4 and further trials are planned.
Managing liver failure
Authors: Kelly D A
Published: December 2002

Liver disease is rare in childhood, but important new developments have altered the natural history and outcome. It is important that clinicians are aware of these diseases and their management. Acute liver failure is most often due to viral hepatitis, paracetamol overdose, or inherited metabolic liver disease. The clinical presentation includes jaundice, coagulopathy, and encephalopathy. Early diagnosis is necessary to prevent complications such as cerebral oedema, gastrointestinal bleeding, and renal failure. Early supportive management, in particular intravenous N-acetylcysteine, may be effective but liver transplantation is usually the definitive treatment and thus early referral to a specialist unit for liver transplantation is mandatory. Chronic liver failure may be due to unresolved neonatal liver disease, either inherited biliary hypoplasia or extrahepatic biliary atresia, while in older children, autoimmune liver disease or cystic fibrosis are the commonest causes. Treatment includes specific medication, nutritional support, and liver transplantation, which now has a 90% survival with good quality life.
Costs of waiting for gall bladder surgery
Authors: Somasekar K , Shankar P J , Foster M E , Lewis M H
Published: December 2002

Laparoscopic cholecystectomy is one of the most commonly awaited general surgical procedures in the UK. However, many patients awaiting a cholecystectomy are admitted with recurrent gallstone related symptoms while on the waiting list, resulting in significant morbidity. The aim of this study was to quantify this problem, and also to analyse the cost implications of these admissions for the NHS. A retrospective study was performed of all patients who underwent an elective cholecystectomy by three consultants in a district general hospital between January 1999 and January 2000. The demographic details, indications for surgery, details of the emergency admissions while on the waiting list, and the treatment given during these episodes were recorded. One hundred and fifty six patients were included in the study, of which 122 (78%) were females. The mean (SD) age of the patients was 54 (5) years. The mean waiting time for surgery in these patients was 12 (3) months. Thirty seven patients (23.7%) were admitted as an emergency due to gallstone related symptoms and complications while awaiting surgery. There were 47 episodes of admissions in total, of which 32 were for biliary colic, 13 were for acute cholecystitis, and two were for acute pancreatitis. In addition to routine blood tests, 20 abdominal radiographs, 10 chest radiographs, three endoscopic retrograde cholangiopancreatography tests, five ultrasonograms, and one computed tomogram were carried out in these patients. The mean duration of each episode of admission was three days. The cost of treatment per episode was £946 and the total cost of treating the 37 patients was calculated to be £44 462. Performing early laparoscopic cholecystectomy for acute cholecystitis may help to reduce costs by preventing recurrent emergency admissions in these patients. Further studies to identify risk factors associated with recurrent symptoms and complications in patients with gallstone disease may help to prioritise them for early surgery.
Cardiac involvement in HIV infected people in Yaounde, Cameroon
Authors: Nzuobontane D , Blackett K N , Kuaban C
Published: December 2002

Objective

To study the cardiac abnormalities in HIV infected patients in relation to the clinical stage of the disease and the immunological status of the patients.

Methods

A total 75 consecutive patients tested for HIV on the basis of clinical suspicion of the disease from July to September 1996 at the University Hospital Centre, Yaounde, Cameroon were recruited. The patients were classified into AIDS, HIV positive non-AIDS, and HIV negative according to clinical findings and outcome of ELISA and western blot testing. Every patient underwent a clinical examination, two dimensional and M-mode echocardiography, and blood lymphocyte typing.

Results

Dilated cardiomyopathy occurred in 7/30 (23.33%) AIDS patients, 1/24 (4.17%) HIV positive non-AIDS patient, but in none of the HIV negative patients. Other echocardiographic abnormalities included pericardial separation, effusion, thickening, and mitral valve prolapse. Although these abnormalities were more frequent in HIV infected patients, the differences did not reach levels of statistical significance. Dilated cardiomyopathy occurred in six (31.58%) of the patients with a CD4 cell count ≤100/mm3 and two (6.06%) in those with absolute CD4 counts >100/mm3 (χ2 = 4.02, p = 0.03).

Conclusions

Cardiovascular abnormalities are frequent in African HIV infected patients but clinically discrete. Low CD4 cell counts are associated with dilated cardiomyopathy. These abnormalities should be expected with greater frequency in cardiological clinical practice as management of opportunistic infections improves in a situation of continued high disease prevalence in Africa.
Thoracoscopic sympathectomy for palmar hyperhidrosis and Raynaud’s phenomenon of the upper limb and excessive facial blushing: a five year experience
Authors: Rajesh Y S , Pratap C P , Woodyer A B
Published: December 2002

Primary hyperhidrosis of the palms, face, and axillae has a strong negative impact on social and professional life. A retrospective analysis of 40 laparoscopic transaxillary thoracic sympathectomies performed in a district general hospital over a five year period was undertaken in order to determine the effectiveness of this procedure. A postal questionnaire was sent to all patients to assess the benefit from the operation; postoperative pain and time off work were collated. Immediate failure was noted in three patients, of whom two later underwent successful reoperation. Recurrence was noted in three patients (8%). Though immediate complications were minimal, the major long term postoperative morbidity was compensatory hyperhidrosis on the back, chest, and thigh (77%) along with gustatory sweating over the face (22%). Thoracoscopic sympathectomy is a safe, effective, and minimally invasive surgical treatment for hyperhidrosis, Raynaud’s phenomenon of the upper limb, and excessive facial blushing; however, the chance of long term compensatory hyperhidrosis is high.
Polyarteritis nodosa presenting as a pyrexia of unknown origin
Authors: Henderson J , Cohen J , Jackson J , Wiselka M
Published: December 2002

A case of an 18 year old woman is reported who presented with a pyrexia of unknown origin having returned from a trip to India. She initially had constitutional symptoms only, which rapidly progressed to a multisystem disorder. The difficulty in making the diagnosis of polyarteritis nodosa, especially with the possible differential diagnosis of infection after her recent travel, is discussed. The discussion reviews the condition of polyarteritis nodosa and analyses the diagnostic difficulties in this case.
Thyrotoxic periodic paralysis in a white woman
Authors: Dixon A N , Jones R
Published: December 2002

A 24 year old white woman presented with sudden onset of flaccid quadriparesis and hypokalaemia. She was later found to be thyrotoxic. Paralysis resolved with potassium supplements, and after initiation of antithyroid medication she had no further episodes of hypokalaemic paralysis. To the best of the authors’ knowledge, and after a Medline search, thyrotoxic periodic paralysis has not been described previously in a white woman.
EUCLIDEAN GIBBS STATES OF QUANTUM LATTICE SYSTEMS
Authors: ALBEVERIO S. , KONDRATIEV YU. , KOZITSKY YU. , RÖCKNER M.
Published: December 2002

An approach to the description of the Gibbs states of lattice models of interacting quantum anharmonic oscillators, based on integration in infinite dimensional spaces, is described in a systematic way. Its main feature is the representation of the local Gibbs states by means of certain probability measures (local Euclidean Gibbs measures). This makes it possible to employ the machinery of conditional probability distributions, known in classical statistical physics, and to define the Gibbs state of the whole system as a solution of the equilibrium (Dobrushin–Lanford–Ruelle) equation. With the help of this representation the Gibbs states are extended to a certain class of unbounded multiplication operators, which includes the order parameter and the fluctuation operators describing the long range ordering and the critical point respectively. It is shown that the local Gibbs states converge, when the mass of the particle tends to infinity, to the states of the corresponding classical model. A lattice approximation technique, which allows one to prove for the local Gibbs states analogs of known correlation inequalities, is developed. As a result, certain new inequalities are derived. By means of them, a number of statements describing physical properties of the model are proved. Among them are: the existence of the long-range order for low temperatures and large values of the particle mass; the suppression of the critical point behavior for small values of the mass and for all temperatures; the uniqueness of the Euclidean Gibbs states for all temperatures and for the values of the mass less than a certain threshold value, dependent on the temperature.
WZW BRANES AND GERBES
Authors: GAWȨDZKI KRZYSZTOF , REIS NUNO
Published: December 2002

We reconsider the role that bundle gerbes play in the formulation of the WZW model on closed and open surfaces. In particular, we show how an analysis of bundle gerbes on groups covered by SU(N) permits to determine the spectrum of symmetric branes in the boundary version of the WZW model with such groups as the target. We also describe a simple relation between the open string amplitudes in the WZW models based on simply connected groups and in their simple-current orbifolds.
MODULI SPACES OF FRAMED SHEAVES ON CERTAIN RULED SURFACES OVER ELLIPTIC CURVES
Authors: NEVINS THOMAS A.
Published: December 2002

Fix a ruled surface S obtained as the projective completion of a line bundle L on a complex elliptic curve C; we study the moduli problem of parametrizing certain pairs consisting of a sheaf ℰ on S and a map of ℰ to a fixed reference sheaf on S. We prove that the full moduli stack for this problem is representable by a scheme in some cases. Moreover, the moduli stack admits an action by the group C*, and we determine its fixed-point set, which leads to explicit formulas for the rational homology of the moduli space.
UNIQUENESS POLYNOMIALS FOR COMPLEX MEROMORPHIC FUNCTIONS
Authors: AN TA THI HOAI , WANG JULIE TZU-YUEH
Published: December 2002

A polynomial P(X) in [Formula: see text] is called a strong uniqueness polynomial for meromorphic functions if whenever there exist two non-constant meromorphic functions f and g and a complex non-zero constant c such that P(f) = cP(g), then we must have f = g. In this paper, we give a necessary and sufficient condition for a polynomial to be a strong uniqueness polynomial for meromorphic functions under the assumption that P(X) is injective on the roots of P′(X) = 0.
PION AND ρ MESON OBSERVABLES IN A NAMBU–JONA-LASINIO MODEL INCLUDING A TENSOR INTERACTION
Authors: JAMINON M. , RUIVO M. C. , DE SOUSA C. A.
Published: December 2002

We calculate the low energy π π scattering lengths [Formula: see text] and [Formula: see text], the coupling of the ρ to the pion gρ π π, the total width of the ρ, the low q2 behavior of the pion electromagnetic form factor, and the pion scalar form factor within a chiral SU(2) f NJL-type Lagrangian where the spin 1 ρ meson is generated from a four-quark tensor interaction. Such a simple model avoids the mathematical complication related to π - a1 mixing. Two types of regularization are discussed, mainly affecting the values of [Formula: see text] and [Formula: see text]. We find rather good agreement with data. The ρ meson described in this way does not account for the meson vector dominance model: it does not contribute to the [Formula: see text] scattering lengths, and the charge radius of the pion is mainly ascribed to the bare photon quark coupling. Even if the shape of the electromagnetic form factor is well reproduced, the strong increase near the ρ pole does not account for the ρ→ππ decay but only reflects the [Formula: see text] structure of the ρ.
FRIEDMANN–ROBERTSON–WALKER BRANE COSMOLOGICAL EQUATIONS FROM THE FIVE-DIMENSIONAL BULk (A)dS BLACK HOLE
Authors: NOJIRI SHIN'ICHI , ODINTSOV SERGEI D. , OGUSHI SACHIKO
Published: December 2002

In the first part of this work we review the equations of motion for the brane presented in Friedmann–Robertson–Walker (FRW) form, when the bulk is five-dimensional (A)dS Black Hole. The spacelike (timelike) FRW brane equations are considered from the point of view of their representation in the form similar to two-dimensional CFT entropy, the so-called Cardy–Verlinde (CV) formula. The following five-dimensional gravities are reviewed: Einstein, Einstein–Maxwell and Einstein with brane quantum corrections. The second part of the work is devoted to the study of FRW brane equations and their representation in CV form, brane induced matter and brane cosmology in Einstein–Gauss–Bonnet (GB) gravity. In particular, we focus on the inflationary brane cosmology. The energy conditions for brane matter are also analyzed. We show that for some values of GB coupling constant (bulk is AdS BH) the brane matter is not CFT. Its energy density and pressure are not always positive. The appearance of logarithmic corrections in brane cosmology is discussed.
FORM FACTORS FOR B→πlν DECAY IN A MODEL CONSTRAINED BY CHIRAL SYMMETRY AND QUARK MODEL
Authors: RIAZUDDIN  , AL-AITHAN T. A. , GILANI AMJAD HUSSAIN SHAH
Published: December 2002

The form factors for the B→π transition are evaluated in the entire momentum transfer range by using the constraints obtained in the framework combining the heavy quark expansion and chiral symmetry for light quarks and the quark model. In particular, we calculate the valence quark contribution and show that it together with the equal time commutator contribution give to the form factors a pole behavior with the heavy (B-meson in our case) mass as the pole mass. This is in addition to the usual vector meson B*-pole diagram for B→πlν in the above framework. We discuss the predictions in our model, which provide an estimate of |Vub|2.
AN ANALYTICAL MODEL FOR PREDICTING EFFECTIVE MAGNETOSTRICTION OF MAGNETOSTRICTIVE COMPOSITES
Authors: FENG XUE , FANG DAINING , HWANG KEH-CHIH
Published: December 2002

An extended double-inclusion model is developed to predict effective magnetostriction of the composites that consist of magnetostrictive particles and a nonmagnetostrictive matrix. The explicit formulas accounting for the inter-particle interaction and matrix-particle interaction under the external magnetic field are obtained for an elastically transverse isotropic magnetostrictive medium. It is shown that the magnetostriction of magnetostrictive composites depends not only on both the volume fraction of the particles and the material properties, but also on shapes and orientations of the ellipsoidal reinforced particles. To demonstrate the applicability of the model, the calculated results are compared both to the available experimental results and to the predictions calculated from other models.
THE EFFECT OF OXYGEN ON THE FORMATION OF MANGANESE SILICIDE
Authors: HOU Q. R. , WANG Z. M. , HE Y. J.
Published: December 2002

The behavior of oxygen impurities during thermal annealing of manganese-silicon diffusion couples and reactive deposition of MnSi 1.7 films has been studied. Samples were prepared by reactive deposition or thermal evaporation of manganese on silicon (100) substrates, which were then annealed in vacuum. The investigation techniques included depth profiling using Auger electron spectroscopy and electrical resistance measurements. The oxygen contamination originated from the preparation chamber or exposing the sample to air before thermal annealing. The oxygen diffused into the manganese film and blocked the silicide formation. For reactive deposition of the MnSi 1.7 films, the competition between silicide formation and oxygen diffusion resulted in the formation of silicide films with oxygen concentration of about 5 at% or the diffusion of oxygen in the manganese film with oxygen concentration of about 35 at%. The presence of a higher concentration of oxygen in the manganese layer prevented any silicide formation.
FLUCTUATION CONDUCTIVITY OF POLYCRYSTALLINE YbBa2Cu3O7 -δ SUPERCONDUCTORS
Authors: RODRIGUES P. , JURELO A. R. , DIAS F. T.
Published: December 2002

We have studied the effect of superconducting fluctuations on the electrical conductivity of granular samples of YbBa 2 Cu 3 O 7 -δ superconductors. Two different polycrystalline samples were prepared for this study. Special attention is taken above T c , where Gaussian and critical regimes are observed. Far from T c , we can observe the regime dominated by Gaussian fluctuations, with exponent approximately [Formula: see text], which is the predicted one for homogeneous 3D fluctuations. Inside the critical region, we have observed two power-law regimes: one of them is consistent with predictions for the 3D-XY universality class, with exponent [Formula: see text]. Below T c , in the approach to the zero resistance state, our results show a power-law behavior with critical exponents s1 = 2.6 ± 0.2 and s2 = 4.2 ± 0.3. We have previously shown that this corresponds to a phase transition from a paracoherent to a coherent state of the granular array.
TWO GROUPS ASSOCIATED WITH QUADRATIC PISOT UNITS
Authors: FROUGNY CHRISTIANE , SAKAROVITCH JACQUES
Published: December 2002

In a previous work, we have investigated an automata-theoretic property of numeration systems associated with quadratic Pisot units that yields, for every such number θ, a certain group Gθ.

In this paper, we characterize a cross-section of a congruence γθ of ℤ4 that had arisen when constructing Gθ. This allows us to completely describe the quotient Hθ of ℤ4 by γθ, that becomes then a second group associated with θ. Moreover, the cross-section thus described is very similar to the symbolic dynamical system associated, by a theorem of Parry, with the two numeration systems attached to θ.

The proof is combinatorial, and based upon rewriting techniques.

Résumé: Dans un article précédent, nous avions associé à chaque nombre de Pisot quadratique unitaire θ un certain groupe Gθ par le biais de la construction d'un automate qui réalise le passage entre les représentations des entiers dans deux systèmes de numération naturellement attachés à θ.

Dans cet article, nous donnons une caractérisation d'un ensemble de représentants pour une congruence γθ de ℤ4 qui avait été utilisée pour la définition de Gθ. Cette caractérisation permet la description complète du quotient Hθ de ℤ4 par γθ, autre groupe associé à θ. Elle est d'autre part remarquablement similaire à la description, donnée par un théorème de Parry, du système dynamique symbolique associé aux deux systèmes de numération attachés à θ.

La preuve est combinatoire et utilise les techniques des systèmes de réécriture.
PROPERTIES OF COMMUTATIVE ASSOCIATION SCHEMES DERIVED BY FGLM TECHNIQUES
Authors: MARTÍNEZ-MORO EDGAR
Published: December 2002

Association schemes are combinatorial objects that allow us solve problems in several branches of mathematics. They have been used in the study of permutation groups and graphs and also in the design of experiments, coding theory, partition designs etc. In this paper we show some techniques for computing properties of association schemes. The main framework arises from the fact that we can characterize completely the Bose–Mesner algebra in terms of a zero-dimensional ideal. A Gröbner basis of this ideal can be easily derived without the use of Buchberger algorithm in an efficient way. From this statement, some nice relations arise between the treatment of zero-dimensional ideals by reordering techniques (FGLM techniques) and some properties of the schemes such as P-polynomiality, and minimal generators of the algebra.
HOLONOMY EMBEDDING OF ARBITRARY STABLE SEMIGROUPS
Authors: ELSTON GILLIAN Z. , NEHANIV CHRYSTOPHER L.
Published: December 2002

We show how the Rhodes expansion Ŝ of any stable semigroup S embeds into the cascade integral (a natural generalization of the wreath product) of permutation-reset transformation semigroups with zero adjoined. The permutation groups involved are exactly the Schützenberger groups of the [Formula: see text]-classes of S. Since S ←← Ŝ is an aperiodic map via which all subgroups of S lift to Ŝ, this results in a strong Krohn–Rhodes–Zeiger decomposition for the entire class of stable semigroups. This class includes all semigroups that are finite, torsion, finite [Formula: see text]-above, compact Hausdorff, or relatively free profinite, as well as many other semigroups. Even if S is not stable, one can expand it using Henckell's expansion and then apply our embedding. This gives a simplified proof of the Holonomy Embedding theorem for all semigroups.
GRAPH PRODUCTS AND CANNON PAIRS
Authors: LOEFFLER JOSEPH , MEIER JOHN , WORTHINGTON JAMES
Published: December 2002

A pair (G, A) consisting of a group G and a finite generating set A is a Cannon pair if the language of all geodesics in the associated Cayley graph is regular. We prove that the Cannon pair property is preserved by graph products and indicate applications of this result to the geodesic and spherical growth series of graph products.
LOW-DIMENSIONAL MODELING AND NUMERICAL SIMULATION OF TRANSITION IN SIMPLE SHEAR FLOWS
Authors: Rempfer Dietmar
Published: December 2002

▪ Abstract  This review describes some of the important developments in the numerical investigation of transition to turbulence in wall-bounded and free shear flows during the past decade. The evolution of numerical techniques and models as well as the advances in our theoretical understanding of the physics of laminar-turbulent transition that were achieved using these tools are described. For wall-bounded flows, particular emphasis is placed on investigations studying various scenarios of “bypass transition” in flows that are asymptotically stable. A brief review of investigations into receptivity and control of transitional flows is included.
STABILITY AND TRANSITION OF THREE-DIMENSIONAL BOUNDARY LAYERS
Authors: Saric William S. , Reed Helen L. , White Edward B.
Published: December 2002

▪ Abstract  The recent progress in three-dimensional boundary-layer stability and transition is reviewed. The material focuses on the crossflow instability that leads to transition on swept wings and rotating disks. Following a brief overview of instability mechanisms and the crossflow problem, a summary of the important findings of the 1990s is given.
AERODYNAMICS OFSMALLVEHICLES
Authors: Mueller Thomas J. , DeLaurier James D.
Published: December 2002

▪ Abstract  In this review we describe the aerodynamic problems that must be addressed in order to design a successful small aerial vehicle. The effects of Reynolds number and aspect ratio (AR) on the design and performance of fixed-wing vehicles are described. The boundary-layer behavior on airfoils is especially important in the design of vehicles in this flight regime. The results of a number of experimental boundary-layer studies, including the influence of laminar separation bubbles, are discussed. Several examples of small unmanned aerial vehicles (UAVs) in this regime are described. Also, a brief survey of analytical models for oscillating and flapping-wing propulsion is presented. These range from the earliest examples where quasi-steady, attached flow is assumed, to those that account for the unsteady shed vortex wake as well as flow separation and aeroelastic behavior of a flapping wing. Experiments that complemented the analysis and led to the design of a successful ornithopter are also described.
LEVEL SET METHODS FOR FLUID INTERFACES
Authors: Sethian J. A. , Smereka Peter
Published: December 2002

▪ Abstract  We provide an overview of level set methods, introduced by Osher and Sethian, for computing the solution to fluid-interface problems. These are computational techniques that rely on an implicit formulation of the interface, represented through a time-dependent initial-value partial-differential equation. We discuss the essential ideas behind the techniques, the coupling of these techniques to finite-difference methods for incompressible and compressible flow, and a collection of applications including two-phase flow, ship hydrodynamics, and ink-jet-printhead design.
RAPID GRANULAR FLOWS
Authors: Goldhirsch Isaac
Published: December 2002

▪ Abstract  The recent avalanche of research activity in the field of granular matter has yielded much progress. The use of state-of-the-art (and other) computational and experimental methods has led to the discovery of new states and patterns and enabled detailed tests of theories and models. The application of statistical mechanical methods and phenomenology has contributed to the understanding of the microscopic a nd macroscopic properties of granular systems. Some previously open problems seem to be solved. Fluidized granular systems (rapid granular flows), recently referred to as granular gases, are often modeled by hydrodynamic equations of motion, some of which are based on systematic expansions applied to the pertinent Boltzmann equation. The undeniable success of granular hydrodynamics is somewhat surprising in view of the lack of scale separation in these systems and the neglect of certain correlations in most derivations of the hydrodynamic equations. Microstructures have been recognized as key features of granular gases; explanations for their existence have been proposed, and many of their properties elucidated. Granular-gas multistability can often be traced back to microstructure dynamics. In spite of these and other impressive advances, this field still poses serious challenges.
SHELL MODELS OF ENERGY CASCADE IN TURBULENCE
Authors: Biferale Luca
Published: December 2002

▪ Abstract  We review the most important theoretical and numerical results obtained in the realm of shell models for the energy-turbulent cascade. We mainly focus here on those results that had or will have some impact on the fluid-dynamics community. In particular, we address the problem of small-scale intermittency by discussing energy–helicity interactions, energy-dissipation multifractality, and universality of intermittency, i.e., independence of anomalous scaling exponents from large-scale forcing and boundary conditions. A multifractal-based description of multiscale and multitime correlation functions in turbulence is also presented. Finally, we also briefly review the analytical difficulties, and hopes, of calculating anomalous exponents.
PARTICLE-TURBULENCE INTERACTIONS IN ATMOSPHERIC CLOUDS
Authors: Shaw Raymond A.
Published: December 2002

▪ Abstract  Turbulence is ubiquitous in atmospheric clouds, which have enormous turbulence Reynolds numbers owing to the large range of spatial scales present. Indeed, the ratio of energy-containing and dissipative length scales is on the order of 105 for a typical convective cloud, with a corresponding large-eddy Reynolds number on the order of 106 to 107. A characteristic trait of high-Reynolds-number turbulence is strong intermittency in energy dissipation, Lagrangian acceleration, and scalar gradients at small scales. Microscale properties of clouds are determined to a great extent by thermodynamic and fluid-mechanical interactions between droplets and the surrounding air, all of which take place at small spatial scales. Furthermore, these microscale properties of clouds affect the efficiency with which clouds produce rain as well as the nature of their interaction with atmospheric radiation and chemical species. It is expected, therefore, that fine-scale turbulence is of direct importance to the evolution of, for example, the droplet size distribution in a cloud. In general, there are two levels of interaction that are considered in this review: (a) the growth of cloud droplets by condensation and (b) the growth of large drops through the collision and coalescence of cloud droplets. Recent research suggests that the influence of fine-scale turbulence on the condensation process may be limited, although several possible mechanisms have not been studied in detail in the laboratory or the field. There is a growing consensus, however, that the collision rate and collision efficiency of cloud droplets can be increased by turbulence-particle interactions. Adding strength to this notion is the growing experimental evidence for droplet clustering at centimeter scales and below, most likely due to strong fluid accelerations in turbulent clouds. Both types of interaction, condensation and collision-coalescence, remain open areas of research with many possible implications for the physics of atmospheric clouds.
BIFURCATING AND BLOOMING JETS
Authors: Reynolds W. C. , Parekh D. E. , Juvet P. J. D. , Lee M. J. D.
Published: December 2002

▪ Abstract  It is classically assumed that the far field of a round turbulent jet discharging into quiescent fluid has a unique behavior characterized only by its momentum flux. However, there is now considerable evidence that different discharge conditions at the jet nozzle exit can give rise to very different far-field flows. Perhaps the most striking examples of these are the bifurcating and blooming jets produced by appropriate combinations of controlled axial and circumferential excitations at the nozzle exit. With the right excitations, a jet can be made to divide into two separate jets (bifurcating jet), each of which carries half the axial momentum and spreads in a manner similar to a single jet. Trifurcating jets can also be produced. Other excitations can produce blooming jets, in which the jet explodes into a shower of vortex rings, producing a far-field flow that is quite unlike a normal unexcited jet. Bifurcating and blooming jets exhibit much greater mixing than normal jets, suggesting possible applications in flow control. This article summarizes our work on bifurcating and blooming jets, which began with our discovery of them in the early 1980s and continued through the mid- 1990s. One of us (D.E.P.) continued exploration of flow control using excited jets, first at the McDonnell Douglas Corporation, and more recently at the Georgia Institute of Technology. The key to flow control is the manipulation of the large vortical structures in the near field of the jet. Ultimately this work, and that of others, led to full-scale testing of jet engine exhaust mixing control. There it was shown that the jet temperature downstream of the engine can be very significantly reduced by application of well-designed and easily implemented excitation at the engine discharge, thereby solving problems encountered during ground operations. Related jet control work by other investigators is included in this review.
THE FLOW OF HUMAN CROWDS
Authors: Hughes Roger L.
Published: December 2002

▪ Abstract  The modern study of a crowd as a flowing continuum is a recent development. Distinct from a classical fluid because of the property that a crowd has the capacity to think, interesting new physical ideas are involved in its study. An appealing property of a crowd in motion is that the nonlinear, time-dependent, simultaneous equations representing a crowd are conformably mappable. This property makes many interesting applications analytically tractable. In this review examples are given in which the theory has been used to provide possible assistance in the annual Muslim Hajj, to understand the Battle of Agincourt, and, surprisingly, to locate barriers that actually increase the flow of pedestrians above that when there are no barriers present. Modern developments may help prevent some of the approximately two thousand deaths that annually occur in accidents owing to crowding.The field of crowd motion, that is, the field of “thinking fluids,” is an intriguing area of research with great promise.
MIXING EFFICIENCY IN STRATIFIED SHEAR FLOWS
Authors: Peltier W. R. , Caulfield C. P.
Published: December 2002

▪ Abstract  The issue of the physical mechanism(s) that control the efficiency with which the density field in stably stratified fluid is mixed by turbulent processes has remained enigmatic. Similarly enigmatic has been an explanation of the numerical value of ∼0.2, which is observed to characterize this efficiency experimentally. We review recent work on the turbulence transition in stratified parallel flows that demonstrates that this value is not only numerically predictable but also that it is expected to be a nonmonotonic function of the Richardson number that characterizes preturbulent stratification strength. This value of the mixing efficiency appears to be characteristic of the late-time behavior of the turbulent flow that develops after an initially laminar shear flow has undergone the transition to turbulence through an intermediate instability of Kelvin-Helmholtz type.
FLOW ANDDISPERSION INURBANAREAS
Authors: Britter R. E. , Hanna S. R.
Published: December 2002

▪ Abstract  Increasing urbanization and concern about sustainability and quality of life issues have produced considerable interest in flow and dispersion in urban areas. We address this subject at four scales: regional, city, neighborhood, and street. The flow is one over and through a complex array of structures. Most of the local fluid mechanical processes are understood; how these combine and what is the most appropriate framework to study and quantify the result is less clear. Extensive and structured experimental databases have been compiled recently in several laboratories. A number of major field experiments in urban areas have been completed very recently and more are planned. These have aided understanding as well as model development and evaluation.
INSTABILITIES IN FLUIDIZED BEDS
Authors: Sundaresan Sankaran
Published: December 2002

▪ Abstract  This paper reviews recent advances in our understanding of the origin and hierarchy of organized flow structures in fluidized beds, distinction between bubbling and nonbubbling systems, and stages of bubble evolution. Experimental data and theory suggest that, at high particle concentrations, the particle-phase pressure arising from flow-induced velocity fluctuations decreases with increasing concentration of particles. This, in turn, implies that nonhydrodynamic stresses must be present to impart stability to a uniformly fluidized bed at very high particle concentrations. There is ample evidence to support an argument that, in commonly encountered gas-fluidized beds, yield stresses associated with enduring particle networks are present in the window of stable bed expansion, where the particles are essentially immobile until bubbling commences. However, some recent data on gas-fluidized beds of agglomerates of cohesive particles suggest that there exists a window of bed expansion where the bed does manifest a smooth appearance to the naked eye and the particles are mobile; at higher gas velocities the bed bubbles visibly. The mechanics of such beds remain to be fully explained.
WATER-WAVE IMPACT ON WALLS
Authors: Peregrine D. H.
Published: December 2002

▪ Abstract  The more violent impacts of water waves on walls create velocities and pressures having magnitudes much larger than those associated with the propagation of ordinary waves under gravity. Insight into these effects has been gained by irrotational-flow computations and by investigating the role of entrained and trapped air in wave impacts. This review focuses on the results of theoretical work, making particular note of the value of considering pressure impulse, and highlights the aspects that are poorly understood.
MATERIAL INSTABILITY IN COMPLEX FLUIDS
Authors: Goddard J. D.
Published: December 2002

▪ Abstract  A review is given of the stability of complex fluids subject to homogeneous states of shearing, a research field that is scarcely two decades old. For the benefit of fluid mechanicians, a brief, somewhat historical overview is presented of material instability in elastoplastic solids, where one finds a considerable body of experiment and a rich source of theoretical concepts including Hadamard instability, strain localization, and nonlocal constitutive models. A survey is then given of recent theoretical and experimental studies of instability with shear banding in various complex fluids, including micellar solutions, particulate suspensions, and rapidly sheared granular media. Various stability analyses are encapsulated in a mathematical dynamical-systems model for constitutive equations of the rate-type, and a general linear-stability theory is given for viscoelastic fluids in unbounded homogeneous shear flows. A general form of (Kelvin) wave-vector stretching is shown to play a key role in the growth of Fourier modes, as illustrated by recent computations for granular shear flow. The Fourier description also provides an explicit representation of higher-gradient (nonlocal) effects as higher-order powers of wave number.
TEXTBOOK MULTIGRID EFFICIENCY FOR FLUID SIMULATIONS
Authors: Thomas James L. , Diskin Boris , Brandt Achi
Published: December 2002

▪ Abstract  Recent advances in achieving textbook multigrid efficiency for fluid simulations are presented. Textbook multigrid efficiency is defined as attaining the solution to the governing system of equations in a computational work that is a small multiple of the operation counts associated with discretizing the system. Strategies are reviewed to attain this efficiency by exploiting the factorizability properties inherent to a range of fluid simulations, including the compressible Navier-Stokes equations. Factorizability is used to separate the elliptic and hyperbolic factors contributing to the target system; each of the factors can then be treated individually and optimally. Boundary regions and discontinuities are addressed with separate (local) treatments. New formulations and recent calculations demonstrating the attainment of textbook efficiency for aerodynamic simulations are shown.
MECHANISMS ON TRANSVERSE MOTIONS IN TURBULENT WALL FLOWS
Authors: Karniadakis G.E. , Choi Kwing-So
Published: December 2002

▪ Abstract  Drag reduction in wall-bounded flows can be achieved by transverse motions imposed by passive means, e.g., riblets, or by external forcing, such as wall oscillation or transverse traveling-wave excitation. In this article, we review possible physical mechanisms responsible for turbulent drag reduction and corresponding near-wall flow modification.