bluuebunny/crossref_metadata_2025 huggingface dataset:
ADP-Glucose Pyrophosphorylase, a Regulatory Enzyme for Bacterial Glycogen Synthesis
Authors: Ballicora Miguel A. , Iglesias Alberto A. , Preiss Jack
Published: June 2003

The accumulation of α-1,4-polyglucans is an important strategy to cope with transient starvation conditions in the environment. In bacteria and plants, the synthesis of glycogen and starch occurs by utilizing ADP-glucose as the glucosyl donor for elongation of the α-1,4-glucosidic chain. The main regulatory step takes place at the level of ADP-glucose synthesis, a reaction catalyzed by ADP-Glc pyrophosphorylase (PPase). Most of the ADP-Glc PPases are allosterically regulated by intermediates of the major carbon assimilatory pathway in the organism. Based on specificity for activator and inhibitor, classification of ADP-Glc PPases has been expanded into nine distinctive classes. According to predictions of the secondary structure of the ADP-Glc PPases, they seem to have a folding pattern common to other sugar nucleotide pyrophosphorylases. All the ADP-Glc PPases as well as other sugar nucleotide pyrophosphorylases appear to have evolved from a common ancestor, and later, ADP-Glc PPases developed specific regulatory properties, probably by addition of extra domains. Studies of different domains by construction of chimeric ADP-Glc PPases support this hypothesis. In addition to previous chemical modification experiments, the latest random and site-directed mutagenesis experiments with conserved amino acids revealed residues important for catalysis and regulation.
Virus Entry, Assembly, Budding, and Membrane Rafts
Authors: Chazal Nathalie , Gerlier Denis
Published: June 2003

As intracellular parasites, viruses rely heavily on the use of numerous cellular machineries for completion of their replication cycle. The recent discovery of the heterogeneous distribution of the various lipids within cell membranes has led to the proposal that sphingolipids and cholesterol tend to segregate in microdomains called membrane rafts. The involvement of membrane rafts in biosynthetic traffic, signal transduction, and endocytosis has suggested that viruses may also take advantage of rafts for completion of some steps of their replication cycle, such as entry into their cell host, assembly, and budding. In this review, we have attempted to delineate all the reliable data sustaining this hypothesis and to build some models of how rafts are used as platforms for assembly of some viruses. Indeed, if in many cases a formal proof of raft involvement in a virus replication cycle is still lacking, one can reasonably suggest that, owing to their ability to specifically attract some proteins, lipid microdomains provide a particular milieu suitable for increasing the efficiency of many protein-protein interactions which are crucial for virus infection and growth.
The necessity of intelligent agents in social simulation
Authors: Conte Rosaria
Published: June 2003

The social simulation field is here argued to show a history of growing complexity, especially at the agent level. The simulation of the emergence of Macro-social phenomena has required heterogeneous and dynamic agents, at least in the sense of agents moving in a physical and social space. In turn, the simulation of learning and evolutionary algorithms allowed for a two-way account of the Micro-Macro link. In this presentation, a third step is envisaged in this process, and a 3-layer representation is outlined: the Micro, Mental, and Macro layers. This complex representation is shown to be necessary for understanding the functioning of social institutions. The 3-layer model is briefly discussed, and specific cognitive structures, which evolved to cooperate with emerging Macro-social systems and institutions, are analysed. Finally, social intelligence is argued to receive growing attention is several fields and applications of the science of artificial, with which social simulation is interfaced or will soon be.
False reputation in social control
Authors: Paolucci Mario
Published: June 2003

A simulation study is conduced on the spread of reputation in mixed respectful-cheater population. The effects of various mechanism giving raise to false reputation are shown, together with a discussion of foreseen results. The actual results of the simulation are then presented; informational accuracy is found to be an essential condition to maintain an advantage for the norms-followers.
Searching for Mates Using 'Fast and Frugal' Heuristics: a Demographic Perspective
Authors: Billari Francesco C.
Published: June 2003

The paper deals with the search for a mate in human populations, where agents behave according to the bounded rational, 'fast and frugal' heuristics proposed by Todd (1997), which he calls Take the Next Best (TNB). The perspective is that of a demographer, and the main focus is on the macro regularities, in particular, the shape of the frequency distribution of mating time and the proportion of ever-mated, arising from the micro hypotheses. We show – both by simulation and by formal proof – that if agents behave homogeneously according to the same TNB rule the shape of the distribution is monotonically decreasing. Switching then to the hypothesis that individuals act heterogeneously, with different TNB rules, the typical shape of the union formation curve emerges. Finally, we argue that students of demography might gain important hints for their theories by simulation-based approaches and that a population-oriented focus might also be advantageous for studying the mental models for agents.
Simulating accessibility by SWARM
Authors: Bellomo Matteo , Occelli Sylvie
Published: June 2003

Extending our conventional notion of accessibility is a major topic of interest in the geographical and planning literature. This paper explores one of these possibilities. It describes individuals' action spaces and their associated accessibility by means of computer simulation. A multi-agent model is developed with the aim of providing a deeper understanding of daily life activities in a spatial setting. The SWARM software platform is used as a means to investigate the action spaces of individuals and their management strategies.
Democratic Voting in Hierarchical Structures or How to Build a Dictatorship
Authors: Galam Serge
Published: June 2003

The dynamics of voting in hierarchical structures is modelled using the very efficient tool of the real space renormalization group borrowed from the Physics of collective phenomena. Each hierarchical level elects the one just above from local cells using a majority rule voting. The process is restricted to a two party competition. For each party two critical thresholds are found in the overall support. Below the first one, the associated party is automatically self-eliminated. Above the second one the presidency is guaranteed. In between the results are probabilistic. Depending on the voting rules, these thresholds may differ drastically from one party to the other. Higher thesholds to full power may be simultaneously at 23% for the ruling party while at 77% for the competing one making the system a dictatorship. Our model could shed new light on the collapse of the eastern european communist regime of the last century.
Towards Computational Institutional Analysis: Discrete Simulation of a 3P Model
Authors: Albert Alain , Balzer Wolfgang
Published: June 2003

A 3P model (production, predation, protection) which can be game theoretically solved for two actors is generalized to n actors and studied by means of discrete simulation. The simulations confirm robust incentives for actors to produce and predate in an institution free environment, whereas protection activity is not significantly related to the ability for protection. The model is criticized for its neglect of predators predating on each other, and for its inability to reproduce real-life proportions of producers and predators and the times these spend on the three activities.
The Interplay of Power on the Horizon
Authors: Caldas José Castro , Coelho Helder
Published: June 2003

The research in multi-agent systems, like the one in economics, has paid little attention to the question of power. This is perhaps due to the fact that power is a hard topic to tackle from the methodological individualistic perspective that has influenced both disciplines. A dependence network built upon a simple concept of dependence is used as a simulation model aimed at exploring the consequences of power on a preliminary basis. Three questions are addressed: (a) in what ways the power relations impose structure upon society?; (b) how they structure groups internally?; (c) how they differentiate groups and individuals in relation to their conditions of existence?.
The "mind or no-mind" dilemma in agents behaving in a market
Authors: Terna Pietro
Published: June 2003

In computer simulation models based upon agents, what is the degree of sophistication that we have to put into the agents? Should we provide them or not with a "mind"? The answer ranges from Axelrod's simplicity principle to the use of full BDI (Beliefs, Intentions, Desires) cognitive agents. To discuss the subject we introduce here three models: one with "no-mind" agents that operate in an unstructured market, the second with "minded" agents assuring some stability to an emerging unstructured market and, finally, the third with no mind agents, that show a sophisticated outcome in a structured market. No generalised results come from this presentation, but many useful doubts.
Variable Payoffs in the Minority Game
Authors: Savit Robert , Li Yi , Vandeemen Adrian
Published: June 2003

In the standard minority game, each agent in the minority group receives the same payoff regardless of the size of the minority group. Of great interest for real social and biological systems are cases in which the payoffs to members of the minority group depend on the size of the minority group. This latter includes the fixed sum game. We find, remarkably, that the phase structure and general scaling behavior of the standard minority game persists when the payoff function depends on the size of the minority group. There is still a phase transition at the same value of z, the ratio of the dimension of the strategy space to the number of agents playing the game. We explain the persistence of the phase structure and argue that it is due to the absence of temporal cooperation in the dynamics of the minority game. We also discuss the behavior of average agent wealth and the wealth distribution in these variable payoff games.
Modeling creation vs. diffusion of structured knowledge
Authors: Carayol Nicolas
Published: June 2003

The paper is mainly dealing with the dilemma between knowledge creation incentives and knowledge diffusion. Knowledge is modeled as a structure, which is expanding through agents' creation behaviors, and becomes "locally" available to other agents once it is disclosed. An agent taken randomly at each period of the discrete time is choosing between the acquisition of an accessible piece of knowledge and the creation of one. Knowledge value being a decreasing function of the number of agents sharing it, a higher (exogenous and tunable) rate of disclosure decreases the incentives to create (in increasing the diffusion speed). Using simulations, we show that there is, for each set of values of the different parameters, a non null optimal rate of disclosure (maximizing the collective performances of the set of agents) and discuss the effect of some of the structural parameters on it.
Simulating transaction networks in housing markets
Authors: Rosenthal Leslie
Published: June 2003

Linked networks of transactors attempting to complete both the buying and selling of properties, often termed "housing chains", are conspicuous features within owner-occupied housing markets, often seen as a cause of severe delay to transaction completion. This paper introduces a bounded or limited rationality-based model of housing market transactions and examines the properties and predictions of the resultant system. Agent-based simulation is able to reproduce: a) the existence of chains of buyers and sellers observed in the housing market; b) the delays to transaction completion often noted; and c) the empirical observation that housing price series for first-time buyers and for new or vacant housing serially leads the series for existing, current owner-occupiers.
Business Applications of Social Agent-Based Simulation
Authors: Bonabeau Eric
Published: June 2003

Agent-based simulation is a powerful simulation modeling technique that has seen a number of applications in the last five years, including applications to real-world business problems. In this chapter I introduce agent-based simulation and review three applications to business problems: a theme park simulation, a stock market simulation, and a bankwide simulation.
Breaking the symmetry of a circular system of coupledharmonic oscillators
Authors: Boyd J. N. , Hudepohl R. G. , Raychowdhury P. N.
Published: June 2003

First we compute the natural frequencies of vibration of four
identical particles coupled by ideal, massless harmonic springs.
The four particles are constrained to move on a fixed circle. The
initial computations are simplified by a transformation to
symmetry coordinates. Then the symmetry of the vibrating system
is broken by changing the mass of a single particle by a very
small amount. We observe the effect of applying the symmetry
transformation to the now slightly nonsymmetric
system. We compute the new frequencies and compare them with the
frequencies of the original symmetric system of oscillators.
Results of similar calculations for 2, 3, 5, and 6 particles are given.
On an infinite series for (1+1/x)x and its application
Authors: Chen Hongwei
Published: June 2003

An infinite series for (1+1/x)x is deduced. As an application, a refinement of Carleman′s inequality is achieved.
The class of functions convex in the negative direction of the imaginary axis of order (α, β)
Authors: Lecko Adam
Published: June 2003

The aim of this paper is to present an analytic characterization of the class of functions convex in the negative direction of the imaginary axis of order (α, β). The method of the
proof is based on Julia′s lemma.
On incidence algebras and directed graphs
Authors: Joseph Ancykutty
Published: June 2003

The incidence algebra I(X, ℝ) of a locally finite poset (X, ≤) has been defined and studied by Spiegel and O′Donnell (1997). A poset (V, ≤) has a directed graph (Gv, ≤) representing it. Conversely, any directed graph G without any cycle, multiple edges, and loops is represented by a partially ordered set VG. So in this paper, we define an incidence
algebra I(G, ℤ) for (G, ≤) over ℤ, the ring of integers, by where fi(u, v) denotes the number of directed paths of length i from u to v and . When G is finite of order n, I(G, ℤ) is isomorphic to a subring of Mn(ℤ). Principal ideals Iv of (V, ≤) induce the subdigraphs 〈Iv〉 which are the principal ideals ℐv of (Gv, ≤). They generate the ideals I(ℐv, ℤ) of I(G, ℤ). These results are extended to the incidence algebra of the digraph representing a locally finite weak poset both bounded and unbounded.
On a class of even‐dimensional manifolds structured by an affine connection
Authors: Mihai I. , Oiagă A. , Rosca R.
Published: June 2003

We deal with a 2m‐dimensional Riemannian
manifold (M, g) structured by an affine connection and a vector field
𝒯, defining a 𝒯‐parallel connection. It
is proved that 𝒯 is both a torse forming vector field
and an exterior concurrent vector field. Properties of the
curvature 2‐forms are established. It is shown that M is
endowed with a conformal symplectic structure Ω and
𝒯 defines a relative conformal transformation of
Ω.
Families of (1, 2)‐symplectic metrics on full flag manifolds
Authors: Paredes Marlio
Published: June 2003

We obtain new families of (1, 2)‐symplectic invariant metrics on
the full complex flag manifolds F(n). For n ≥ 5, we
characterize n − 3 different n‐dimensional families of
(1, 2)‐symplectic invariant metrics on F(n). Each of these
families corresponds to a different class of nonintegrable
invariant almost complex structures on F(n).
Characterizing completely multiplicative functions bygeneralized Möbius functions
Authors: Laohakosol Vichian , Pabhapote Nittiya , Wechwiriyakul Nalinee
Published: June 2003

Using the generalized Möbius functions, μα, first
introduced by Hsu (1995), two characterizations of completely
multiplicative functions are given; save a minor condition they
read and fα = μ−αf.
Center conditions for a simple class of quintic systems
Authors: Volokitin Evgenii P.
Published: June 2003

We obtained center conditions for an O‐symmetric system of degree
5 for which the origin is a uniformly isochronous singular point.
A class of simple tracially AF C*‐algebras
Authors: Livingston N. E.
Published: June 2003

The concept of a tracially AF (TAF) C*‐algebra was introduced recently to aid in the classification of nuclear C*‐algebrasHere, we construct and study a broad class of inductive‐limit C*‐algebras. We give a numerical condition which, when
satisfied, ensures that the corresponding algebra in our construction has the TAF property. We further give a necessary and sufficient condition under which certain of these C*‐algebras are TAF.
C0‐continuity of the Fröbenius‐Perron semigroup
Authors: Navas Andrés , Plaza Sergio
Published: June 2003

We consider the Fröbenius‐Perron semigroup of linear operators associated to a semidynamical system defined in a topological space X endowed with a finite or a σ‐finite regular measure. We prove that if there exists a faithful invariant measure for the semidynamical system, then the Fröbenius‐Perron semigroup of linear operators is C0‐continuous in the space . We also give a geometrical condition which ensures C0‐continuity of the Fröbenius‐Perron semigroup of linear operators in the space for 1 ≤ p < ∞, as well as in the space
.
The nonexistence of rank 4 IP tensors in signature (1, 3)
Authors: Pearson Kelly Jeanne , Zhang Tan
Published: June 2003

Let V be a real vector space of dimension 4 with a nondegenerate symmetric bilinear form of signature (1, 3). We show that there exists no algebraic curvature tensor R on V so that its associated skew‐symmetric operator R(⋅) has rank 4 and constant eigenvalues on the Grassmannian of nondegenerate 2‐planes in V.
On the time‐dependent parabolic wave equation
Authors: Gorman Arthur D.
Published: June 2003

One approach to the study of wave propagation in a restricted
domain is to approximate the reduced Helmholtz equation by a
parabolic wave equation. Here we consider wave propagation in a
restricted domain modelled by a parabolic wave equation whose
properties vary both in space and in time. We develop a
Wentzel‐Kramers‐Brillouin (WKB) formalism to obtain the
asymptotic solution in noncaustic regions and modify the Lagrange
manifold formalism to obtain the asymptotic solution near
caustics. Associated wave phenomena are also considered.
Exponential inequalities for a class of operators
Authors: Heinig Hans P.
Published: June 2003

Characterizations of weight pairs are proved for which weighted
exponential‐logarithmic integral inequalities are satisfied. The
results given contain characterizations of weights for which
inequalities involving the Riemann‐Liouville and Laplace type
operators hold.
Coefficients of singularities of the biharmonic problem of Neumann type: case of the crack
Authors: Chikouche Wided , Aibèche Aissa
Published: June 2003

This paper concerns the biharmonic problem of Neumann type in a
sector V. We give a representation of the solution u of the
problem in a form of a series u = ∑α∈ECα rα ϕα, and the functions ϕα are solutions of an auxiliary problem obtained by the separation of
variables.
On Krull′s intersection theorem of fuzzy ideals
Authors: Murali V. , Makamba B. B.
Published: June 2003

We deal with Krull′s intersection theorem on the ideals of a
commutative Noetherian ring in the fuzzy setting. We first
characterise products of finitely generated fuzzy ideals in terms
of fuzzy points. Then, we study the question of uniqueness and
existence of primary decompositions of fuzzy ideals. Finally, we
use such decompositions and a form of Nakayama′s lemma to prove
the Krull intersection theorem. Fuzzy‐points method on finitely
generated fuzzy ideals plays a central role in the proofs.
Existence of periodic solutions and homoclinic orbits forthird‐order nonlinear differential equations
Authors: Motlagh O. Rabiei , Afsharnezhad Z.
Published: June 2003

The existence of periodic solutions for the third‐order
differential equation is studied. We give some conditions for
this equation in order to reduce it to a second‐order nonlinear
differential equation. We show that the existence of periodic
solutions for the second‐order equation implies the existence of
periodic solutions for the above equation. Then we use the Hopf
bifurcation theorem for the second‐order equation and obtain many
periodic solutions for it. Also we show that the above equation
has many homoclinic solutions if has a quadratic form. Finally, we compare our result to that of Mehri and Niksirat (2001).
Regularization of a unilateral obstacle problem on the boundary
Authors: Addou A. , Zahi J.
Published: June 2003

We give a regularization method for a unilateral obstacle problem with obstacle on the boundary and second member f.
Characterizations of vector‐valued weakly almost periodic functions
Authors: Zhang Chuanyi
Published: June 2003

We characterize the weak almost periodicity of a vector‐valued,
bounded, continuous function. We show that if the range of the
function is relatively weakly compact, then the relative weak
compactness of its right orbit is equivalent to that of its left
orbit. At the same time, we give the function some other
equivalent properties.
Continuous dependence of solutions in magneto‐elasticity theory
Authors: Bofill F. , Quintanilla R.
Published: June 2003

We prove continuous dependence on the intensity coefficient and
continuous dependence on the external data in the theory of
magneto‐elasticity. We do not require the Lamé coefficients to
be positive. We use logarithmic convexity arguments similar to
those of Ames and Straughan (1992) in classical thermoelasticity.
Dynamics of a class of uncertain nonlinear systems under flow‐invariance constraints
Authors: Pastravanu Octavian , Voicu Mihail
Published: June 2003

For a class of uncertain nonlinear systems (UNSs), the
flow-invariance of a time‐dependent rectangular set
(TDRS) defines individual constraints for each component of the
state‐space trajectories. It is shown that the existence of the
flow‐invariance property is equivalent to the existence of
positive solutions for some differential inequalities with
constant coefficients (derived from the state‐space equation of
the UNS). Flow‐invariance also provides basic tools for dealing
with the componentwise asymptotic stability as a special
type of asymptotic stability, where the evolution of the state
variables approaching the equilibrium point (EP){0} is separately monitored (unlike the standard asymptotic stability,
which relies on global information about the state variables,
formulated in terms of norms). The EP{0} of a given UNS is proved to be componentwise asymptotically stable if and only if the EP{0} of a differential equation with constant coefficients is asymptotically stable in the standard sense. Supplementary requirements for the individual evolution of the state variables approaching the EP{0} allow introducing the stronger concept of componentwise exponential asymptotic stability, which can be characterized by algebraic conditions. Connections with the componentwise asymptotic stability of an
uncertain linear system resulting from the linearization of a given UNS are also discussed.
Duality by reproducing kernels
Authors: Shlapunov A. , Tarkhanov N.
Published: June 2003

Let A
be a determined or overdetermined elliptic differential
operator on a smooth compact manifold X. Write 𝒮A(𝒟)
for the space of solutions of the system Au = 0 in a domain 𝒟⋐X. Using reproducing kernels related to various
Hilbert structures on subspaces of 𝒮A(𝒟), we show
explicit identifications of the dual spaces. To prove the
regularity of reproducing kernels up to the boundary of 𝒟, we
specify them as resolution operators of abstract Neumann
problems. The matter thus reduces to a regularity theorem for the
Neumann problem, a well‐known example being the
‐Neumann problem. The duality itself takes place
only for those domains 𝒟 which possess certain convexity
properties with respect to A.
New approach to the fractional derivatives
Authors: Trenčevski Kostadin
Published: June 2003

We introduce a new approach to the fractional derivatives of the
analytical functions using the Taylor series of the functions. In
order to calculate the fractional derivatives of f, it is not
sufficient to know the Taylor expansion of f, but we should
also know the constants of all consecutive integrations of f.
For example, any fractional derivative of ex is ex only if
we assume that the nth consecutive integral of ex is ex
for each positive integer n. The method of calculating the
fractional derivatives very often requires a summation of
divergent series, and thus, in this note, we first introduce a
method of such summation of series via analytical continuation of
functions.
Nonlinear variational inequalities on reflexive Banach spaces andtopological vector spaces
Authors: Liu Zeqing , Ume Jeong Sheok , Kang Shin Min
Published: June 2003

The purpose of this paper is to introduce and study a class of
nonlinear variational inequalities in reflexive Banach spaces and
topological vector spaces. Based on the KKM technique, the
solvability of this kind of nonlinear variational inequalities is
presented. The obtained results extend, improve, and unify the
results due to Browder, Carbone, Siddiqi, Ansari, Kazmi, Verma,
and others.
Induction of Apoptosis in Rat Peripheral Blood Lymphocytes by the Anticancer Drug CI‐994 (Acetyldinaline)
Authors: Graziano Michael J. , Spoon Teresa A. , Cockrell Erin A. , Rowse Paul E. , Gonzales Andrea J.
Published: June 2003

CI‐994 (acetyldinaline) is an investigational anticancer drug currently in clinical trials. In preclinical safety studies in rats and dogs, CI‐994 resulted in significant toxicity to bone marrow and lymphoid tissue. To determine if apoptosis was involved in CI‐994 toxicity, peripheral blood lymphocytes were
isolated from untreated male Wistar rats and exposed to CI‐994 (1, 3, 10, or 30 μM) in vitro for up to 24 hours. Morphological and biochemical features of apoptosis were evaluated using several techniques, and lactate dehydrogenase (LDH) release was measured as an indicator of cell necrosis. No evidence of apoptosis or necrosis was detected in lymphocytes exposed to CI‐994 for 4 hours. After 24 hours, concentration‐dependent increases in apoptosis characterized by DNA condensation, DNA fragmentation, and/or externalization of phosphatidyl serine were seen at CI‐994 concentrations as low as
1 μM and were statistically significant beginning at 10 μM. Ultrastructural analysis confirmed the presence of DNA condensation, DNA fragmentation, cell shrinkage, and membrane blebbing in cells exposed to 30 μM CI‐994. After 24 hours, the percent of maximum LDH release from lymphocytes
treated with 10 and 30 μM CI‐994 was 7% and 15%, respectively, compared with 0% in the controls. In comparison, morphological changes of apoptosis detected by fluorescent microscopy were observed in 79% of the lymphocytes at these two concentrations. Additionally, apoptosis was seen in more than 24% of lymphocytes exposed to 1 and 3 μM CI‐994, whereas maximum LDH release was less than or equal to 1% at these concentrations. These results show that apoptosis is the primary mode of cell death in rat lymphocytes exposed to CI‐994 in vitro.
High‐Pressure Biotechnology in Medicine and Pharmaceutical Science
Authors: Masson Patrick , Tonello Carole , Balny Claude
Published: June 2003

High‐pressure (HP) biotechnology is an emerging technique initially applied for food processing and more recently in pharmaceutical and medical sciences. Pressure can stabilize enzymes and modulate both their activity and specificity. HP engineering of proteins may be used for enzyme‐catalyzed synthesis of fine chemicals, pharmaceuticals, and production of modified proteins of medical or pharmaceutical interest. HP
inactivation of biological agents is expected to be applicable to sterilization of fragile biopharmaceuticals, or medical compounds. The enhanced immunogenicity of some pressure‐killed bacteria and viruses could be applied for making new vaccines. Finally, storage at subzero temperatures without freezing is another potential application of HP for cells, animal tissues, blood cells, organs for transplant, and so forth.
Interaction Between Mevalonate Pathway and Retinoic Acid‐Induced Differentiation
Authors: Gueddari-Pouzols Naima , Duriez Patrick , Chomienne Christine , Trussardi Aurélie , Jardillier Jean Claude
Published: June 2003

All trans retinoic acid (ATRA) is a potent inducer of differentiation of HL‐60 cell line. The pretreatment of the
cells by compactin, a competitive inhibitor of 3‐hydroxy‐3‐methylglutaryl (HMG) CoA reductase, during 24 hours, enhances the ATRA‐induced cell
differentiation. At 50 nM, the percentage of cell differentiation is 34.9% ± 2 and 73% ± 2.96 in the control and compactin‐treated
cells, respectively. The removal of compactin boosts the level of HMG‐CoA reductase and therefore the biosynthesis of sterol and
nonsterol isoprenoid compounds. The participation of sterol and nonsterol pathway was then investigated. The supply of an excess
of cholesterol (up to 80 μg/ml of LDL) leads to a signiﬁcant decrease of cell differentiation by ATRA from 78% ±0.1 to 54% ±2.8. A
concomitant decrease of cell growth (51% ± 6.4) was observed. The pretreatment of cells by the geranylgeranyltransferase inhibitor
(GGTI‐298) has no effect on the cell differentiation process. By contrast, the farnesyltransferase inhibitors (FTI‐II and FTI‐277)
completely abolish theATRA‐induced differentiation, thus confirming the involvement of farnesylated proteins in the differentiation
mechanism.
CD26 Immuno‐Expression and Periodontal Disease Progression
Authors: Manna P. M. L. , Costa J. E. , Gomez R. S.
Published: June 2003

Immunological mechanisms participate in the pathogenesis of human chronic inflammatory periodontal disease (CIPD). Human CD4 + lymphocytes express functionally heterogeneous profiles of cytokine production. CD26 is an integral membrane glycoprotein, that is, a marker of Th1‐like cytokine development. The purpose of the present study was to compare the immuno‐expression of CD26 receptor in periodontal sites with and without clinical attachment loss (CAL). Five patients with rapidly progressing periodontitis and one with juvenile periodontitis were investigated. Each patient presented at least one site with and without CAL. Ten sites with CAL and nine without any CAL were biopsied, followed by the immunohistochemical identification of
the CD26 receptor using the MIB‐DS2/7 antibody. The results demonstrated that the percentage of positive cells for this antigen in the periodontal sites with CAL was not significantly different from those without attachment loss. Therefore, Th1 cell impairment may not be directly involved with periodontal attachment loss.
Response of Escherichia Coli Containing Mycobacterial Carotene Genes to UV Radiation
Authors: Houssaini-Iraqui Mohamed , Khamlichi Naima , El Yamani Jamal , Rastogi Nalin
Published: June 2003

The plasmid pC5, which encodes biogenesis of lycopene in Mycobacterium aurum A
+, was partially digested by restriction endonucleases and generated fragments were cloned.
After transformation of Escherichia coli (colorless bacteria) with the plasmids so constructed, seven orange clones were detected and found to carry the same recombinant plasmid (pC51). E. coli cells containing this plasmid synthesize neurosporene and lycopene, and were more resistant to ultraviolet irradiation than non pigmented strain.
Somatic Embryogenesis, Rhizogenesis, and Morphinan Alkaloids Production in Two Species of Opium Poppy
Authors: Kassem My Abdelmajid , Jacquin Annie
Published: June 2003

A study of somatic embryogenesis and rhizogenesis and their influence on production of morphinan alkaloids on two species of opium poppy is presented. We identified the ratios of auxin and cytokinin that caused somatic embryogenesis and rhizogenesis in hypocotyl and cotyledons of Papaver somniferum album and Papaver orientale splendidissimum. The hypocotyls and
cotyledons both show somatic embryogenesis in Papaver somniferum album whereas only the cotyledons were embryogenic in Papaver orientale splendidissimum. For rhizogenesis, the most important response is on the cotyledons and leaves in these two species. Histology showed characteristic stages of somatic embryo: Globular, cotyledonous, and heart cotyledonary. High performance liquid chromatography analysis showed that the roots of both species synthesized codeine, thebaine, and papaverine.
Morphine was only detected in aerial parts of Papaver somniferum album. Codeine and thebaine were detected in the rhizogenous but no embryonic callus. These results suggest that root organogenesis is causally related to alkaloid biosynthesis.
The Thermal Stability of the Fusarium solani pisi Cutinase as a Function of pH
Authors: Petersen Steffen B. , Fojan Peter , Petersen Evamaria I. , Petersen Maria Teresa Neves
Published: June 2003

We have investigated the thermal stability of the Fusarium solani pisi cutinase as a function of pH, in the range from pH 2–12. Its highest enzymatic activity coincides with the pH‐range at which it displays its highest thermal stability. The unfolding of the enzyme as a function of pH was investigated by
microcalorimetry. The ratio between the calorimetric enthalpy
(ΔHcal) and the van′t Hoff enthalpy (ΔHv) obtained, is far from unity, indicating that cutinase does not exhibit a simple two state unfolding behaviour. The role of pH on the electrostatic contribution to the thermal stability was assessed using TITRA. We propose a molecular interpretation for the pH‐variation in enzymatic activity.
Two Novel Frame Shift, Recurrent and de novo Mutations in the ITGB2 (CD18) Gene Causing Leukocyte Adhesion Deficiency in a Highly Inbred North African Population
Authors: Fathallah D. M. , Jamal T. , Barbouche M. R. , Bejaoui M. , Hariz M. Ben , Dellagi K.
Published: June 2003

We have identiﬁed four different mutations causing leukocyte adhesion deﬁciency (LAD) in the ITGB2 gene of patients from a
highly inbred population. Two were novel single‐bp deletions (1497delG and 1920delG) causing frame shift and the two others were
the missense mutations G284S and R593C. In our study, the G284S was a recurrent mutation while the R593C occurred de
novo. We have also characterized a novel Xba1 polymorphic site located at the 5′ end of the ITGB2 locus. Family studies showed
that the 1497delG mutation segregated with this marker and the intragenic AvaII polymorphic marker, suggesting the presence of a
founder effect. The observation of a heterogeneous spectrum including de novo and recurrent mutations causing LAD in a highly
inbred population is rather unexpected. In view of the literature published on the molecular genetics of LAD and considering the
ethnic origin of the patients studied, our ﬁndings conﬁrm the heterogeneity of the mutations causing LAD and point out potential
mutational hot spots in the ITGB2 gene.
A C‐terminal Hydrophobic Region is Required for Homo‐Oligomerization of the Hepatitis E Virus Capsid (ORF2) Protein
Authors: Xiaofang Li , Zafrullah Mohammad , Ahmad Faizan , Jameel Shahid
Published: June 2003

Hepatitis E virus (HEV) is the causative agent of hepatitis E, an acute form of viral hepatitis. The open reading frame 2 (ORF2) of HEV encodes the viral capsid protein, which can self‐oligomerize into virus‐like particles. To understand the domains within this protein important for capsid biogenesis, we have carried out in vitro analyses of association and folding patterns of wild type and
mutant ORF2 proteins. When expressed in vitro or in transfected cells, the ORF2 protein assembled as dimers, trimers and higher order forms. While N‐terminal deletions upto 111 amino acids had no effect, the deletion of amino acids 585–610 led to reduced
homo‐oligomerization. This deletion also resulted in aberrant folding of the protein, as determined by its sensitivity to trypsin. This
study suggests that a C‐terminal hydrophobic region encompassing amino acids 585–610 of the ORF2 protein might be critical for
capsid biogenesis.
The Spectrum of β‐Thalassemia Mutations in the Arab Populations
Authors: Zahed Laila
Published: June 2003

The Arab countries encompass a wide region stretching from the Persian Gulf to the Atlantic Ocean. The Arab population is quite heterogeneous and has experienced various invasions and migrations throughout history. β‐thalassemia is endemic in all countries of the Arab world. Our review of the molecular basis of β‐thalassemia in various Arab countries reveals the presence of 52 mutations, which are mostly of Mediterranean and Asian origin. The distribution of mutations reflects the geographical and historical backgrounds of each region. However, no specific mutation is confined to the Arabs, although some Arab countries do
have unique mutations.
Identification of Stem Cell Units in the Terminal End Bud and Duct of the Mouse Mammary Gland
Authors: Kenney Nicholas J. , Smith Gilbert H. , Lawrence Erin , Barrett J. Carl , Salomon David S.
Published: June 2003

The mouse mammary gland may undergo cycles of proliferation, terminal differentiation, tissue remodeling, and more importantly
malignant transformation.Mammary epithelial stem cells and their progeny participate in these processes.Mammary epithelial stem
cells are multipotent, exhibit properties of self renewal (up to 7 divisions)and may exist either as long‐lived nondividing cells or as
proliferating‐differentiating cells. The focus of this study was to locate stem cells by identifying them as long‐lived, label‐retaining
mammary epithelial cells (LRCs)in growth active (developing)or growth static (aged)mammar y ducts. Initially, primary epithelial
cells were pulse labeled with either ﬂuorescent tracker dye and/or BrdU. Cells were then transplanted into cleared juvenile syngeneic
mammary fat pads and held for 5weeks or 8weeks. In this study, we demonstrate that LRCs are stem cells and their progeny
(transitional cells)ar e arranged as transitional units (TUs). Additionally, TUs are located every 250 ± 75 µm in ducts or in the
terminal end bud 200–600 µm in diameter. Molecules expressed in TUs were Zonula Occludens‐1 and α‐catenin proteins which
were signiﬁcantly detected in 75%–91% (P < 0.001)of the LRCs cells that make up the TU. These data suggest that transitional
units may be a group of label‐retaining stem cells and maybe involved in the developmental or cancer process.
In Vitro Investigations on the Toxicity and Cell Death Induced by Tamoxifen on Two Non‐Breast Cancer Cell Types
Authors: Majumdar S. K. , Valdellon J. A. , Brown K. A.
Published: June 2003

Tamoxifen, a potent anticancer agent known to interrupt the enhanced estrogen activity of malignant mammary gland cells, was recently approved by the Food and Drug Administration (FDA)for the treatment of breast cancer. In this investigation, the toxic effects of tamoxifen were evaluated through cell multiplication, and cytological, surface ultrastructural, and biochemical studies
on human cervical carcinoma cells (HeLa)and/or murine erythroleukemic (MEL)c ells (BB‐88). Tamoxifen treatment demonstrated an inhibitory effect on HeLa cell multiplication at lower concentrations and toxicity at higher concentrations and longer treatment durations. The drug also triggered morphological and biochemical changes as revealed by light microscopy, scanning electron microscopy (SEM), fluorescence microscopy, Nucleosome ELISA, and the DNA smear pattern. Cytological observations
showed nuclear condensation, cell shrinkage, multinucleation, and apoptotic bodies. Surface ultrastructure of tamoxifen treated cells examined under the SEM revealed abnormalities such as membrane blebbing, holes, and cytoplasmic extrusions, all of which are characteristics of programmed cell death (apoptosis). Redistribution of the membrane phospholipid phosphatidylserine (PS) from the protoplasmic surface of the plasma membrane to the cell surface was identified using annexin V‐enhanced green fluorescent
protein (EGFP) in tamoxifen treated MEL BB‐88 cells, a general feature of cells undergoing apoptosis. Tamoxifen treated cells demonstrated internucleosomal damages of the genomic DNA and DNA fragmentations, evidenced by an increase in free nucleosomes, and distinctive DNA smear patterns on the agarose gel.
Relating STDP to BCM
Authors: Izhikevich Eugene M. , Desai Niraj S.
Published: June 2003

We demonstrate that the BCM learning rule follows directly from STDP when pre- and postsynaptic neurons fire uncorrelated or weakly correlated Poisson spike trains, and only nearest-neighbor spike interactions are taken into account.
Learning Optimized Features for Hierarchical Models of Invariant Object Recognition
Authors: Wersing Heiko , Körner Edgar
Published: June 2003

There is an ongoing debate over the capabilities of hierarchical neural feedforward architectures for performing real-world invariant object recognition. Although a variety of hierarchical models exists, appropriate supervised and unsupervised learning methods are still an issue of intense research. We propose a feedforward model for recognition that shares components like weight sharing, pooling stages, and competitive nonlinearities with earlier approaches but focuses on new methods for learning optimal feature-detecting cells in intermediate stages of the hierarchical network. We show that principles of sparse coding, which were previously mostly applied to the initial feature detection stages, can also be employed to obtain optimized intermediate complex features. We suggest a new approach to optimize the learning of sparse features under the constraints of a weight-sharing or convolutional architecture that uses pooling operations to achieve gradual invariance in the feature hierarchy. The approach explicitly enforces symmetry constraints like translation invariance on the feature set. This leads to a dimension reduction in the search space of optimal features and allows determining more efficiently the basis representatives, which achieve a sparse decomposition of the input. We analyze the quality of the learned feature representation by investigating the recognition performance of the resulting hierarchical network on object and face databases. We show that a hierarchy with features learned on a single object data set can also be applied to face recognition without parameter changes and is competitive with other recent machine learning recognition approaches. To investigate the effect of the interplay between sparse coding and processing nonlinearities, we also consider alternative feedforward pooling nonlinearities such as presynaptic maximum selection and sum-of-squares integration. The comparison shows that a combination of strong competitive nonlinearities with sparse coding offers the best recognition performance in the difficult scenario of segmentation-free recognition in cluttered surround. We demonstrate that for both learning and recognition, a precise segmentation of the objects is not necessary.
Approximation by Fully Complex Multilayer Perceptrons
Authors: Kim Taehwan , Adalı Tülay
Published: June 2003

We investigate the approximation ability of a multi layer perceptron (MLP) network when it is extended to the complex domain. The main challenge for processing complex data with neural networks has been the lack of bounded and analytic complex nonlinear activation functions in the complex domain, as stated by Liouville's theorem. To avoid the conflict between the boundedness and the analyticity of a nonlinear complex function in the complex domain, a number of ad hoc MLPs that include using two real-valued MLPs, one processing the real part and the other processing the imaginary part, have been traditionally employed. However, since nonanalytic functions do not meet the Cauchy-Riemann conditions, they render themselves into degenerative backpropagation algorithms that compromise the efficiency of nonlinear approximation and learning in the complex vector field. A number of elementary transcendental functions (ETFs) derivable from the entire exponential functionez that are analytic are defined as fully complex activation functions and are shown to provide a parsimonious structure for processing data in the complex domain and address most of the shortcomings of the traditional approach. The introduction of ETFs, however, raises a new question in the approximation capability of this fully complex MLP. In this letter, three proofs of the approximation capability of the fully complex MLP are provided based on the characteristics of singularity among ETFs. First, the fully complex MLPs with continuous ETFs over a compact set in the complex vector field are shown to be the universal approximator of any continuous complex mappings. The complex universal approximation theorem extends to bounded measurable ETFs possessing a removable singularity. Finally, it is shown that the output of complex MLPs using ETFs with isolated and essential singularities uniformly converges to any nonlinear mapping in the deleted annulus of singularity nearest to the origin.
Comparison of Model Selection for Regression
Authors: Cherkassky Vladimir , Ma Yunqian
Published: June 2003

We discuss empirical comparison of analytical methods for model selection. Currently, there is no consensus on the best method for finite-sample estimation problems, even for the simple case of linear estimators. This article presents empirical comparisons between classical statistical methods—Akaike information criterion (AIC) and Bayesian information criterion (BIC)—and the structural risk minimization (SRM) method, basedon Vapnik-Chervonenkis (VC) theory, for regression problems. Our study is motivated by empirical comparisons in Hastie, Tibshirani, and Friedman (2001), which claims that the SRM method performs poorly for model selection and suggests that AIC yields superior predictive performance. Hence, we present empirical comparisons for various data sets and different types of estimators (linear, subset selection, and k-nearest neighbor regression). Our results demonstrate the practical advantages of VC-based model selection; it consistently outperforms AIC for all data sets. In our study, SRM and BIC methods show similar predictive performance. This discrepancy (between empirical results obtained using the same data) is caused by methodological drawbacks in Hastie et al. (2001), especially in their loose interpretation and application of SRM method. Hence, we discuss methodological issues important for meaningful comparisons and practical application of SRM method. We also point out the importance of accurate estimation of model complexity (VC-dimension) for empirical comparisons and propose a new practical estimate of model complexity for k-nearest neighbors regression.
'THE NYAMANG ARE HARD TO TOUCH': MISSION EVANGELISM AND TRADITION IN THE NUBA MOUNTAINS, SUDAN, 1933-1952
Authors: Willis Justin
Published: June 2003

In 1935 the Church Missionary Society established a station at Salara, in the western part of the Nuba Mountains of Sudan. The station received considerable financial support from the colonial administration, as well as from donors in the United Kingdom, but it was strikingly unsuccessful in its attempts to create a local Christian community, and in the early 1950s the station was abandoned by the CMS. This paper explores the circumstances of this failure, and suggests that missionary work in Salara was undermined by the missionaries' ambivalent attitudes to tradition and modernity. These attitudes derived partly from engagement with colonial officials who were chronically uncertain as to the proper policy to pursue in the Nuba Mountains, and partly from a wider uncertainty in mission attitudes that had come to emphasize the need for a distinctly African form of Christianity but yet remained profoundly suspicious of the reliability of African Christians.