The role of complexity for digital twins of cities

We argue that theories and methods drawn from complexity science are urgently needed to guide the development and use of digital twins for cities. The theoretical framework from complexity science takes into account both the short-term and the long-term dynamics of cities and their interactions. This is the foundation for a new approach that treats cities not as large machines or logistic systems but as mutually interwoven self-organizing phenomena, which evolve, to an extent, like living systems.

Nonlinear growth and condensation in multiplex networks

Different types of interactions coexist and coevolve to shape the structure and function of a multiplex network. We propose here a general class of growth models in which the various layers of a multiplex network coevolve through a set of nonlinear preferential attachment rules. We show, both numerically and analytically, that by tuning the level of nonlinearity these models allow us to reproduce either homogeneous or heterogeneous degree distributions, together with positive or negative degree correlations across layers. In particular, we derive the condition for the appearance of a condensed state in which one node in each layer attracts an extensive fraction of all the edges.

Growing multiplex networks

We propose a modeling framework for growing multiplexes where a node can belong to different networks. We define new measures for multiplexes and we identify a number of relevant ingredients for modeling their evolution such as the coupling between the different layers and the distribution of node arrival times. The topology of the multiplex changes significantly in the different cases under consideration, with effects of the arrival time of nodes on the degree distribution, average shortest path length, and interdependence.

Transport on coupled spatial networks

Transport processes on spatial networks are representative of a broad class of real world systems which, rather than being independent, are typically interdependent. We propose a measure of utility to capture key features that arise when such systems are coupled together. The coupling is defined in a way that is not solely topological, relying on both the distribution of sources and sinks, and the method of route assignment. Using a toy model, we explore relevant cases by simulation. For certain parameter values, a picture emerges of two regimes. The first occurs when the flows go from many sources to a small number of sinks. In this case, network utility is largest when the coupling is at its maximum and the average shortest path is minimized. The second regime arises when many sources correspond to many sinks. Here, the optimal coupling no longer corresponds to the minimum average shortest path, as the congestion of traffic must also be taken into account. More generally, results indicate that coupled spatial systems can give rise to behavior that relies subtly on the interplay between the coupling and randomness in the source-sink distribution.

Effect of water soluble extract of nacre (Pinctada maxima) on alkaline phosphatase activity and Bcl-2 expression in primary cultured osteoblasts from neonatal rat calvaria

The nacre (mother of pearl) layer of the oyster Pinctada maxima shell can initiate bone formation by human osteoblasts in vivo and in vitro and is a new biomaterial that induces osteogenesis. This activity of nacre could be due to its water-soluble matrix. We examined the action of a water-soluble extract of nacre on the osteoblast phenotype of cells isolated from rat neonatal calvaria by measuring alkaline phosphatase (ALP) activity and by localization of the anti-apoptotic protein Bcl-2 by immunocytochemistry. ALP activity was increased 7% (p<0.001) by 100 microg proteins/ml extract and 20% (p<0.001) by 50 microg proteins/ml extract, but a low concentration of extract decreased the ALP activity by 8%. Cells treated with a high aspartic acid content fraction of the extract had increased ALP activity (23%, p<0.0001). Nacre extract and the fraction have no effect on the proliferation of mature osteoblasts. Immunoreactive Bcl-2 was overproduced in the cytoplasm and nuclei of osteoblasts at all stages of culture. Bcl-2 was found over the whole chromatin in quiescent and mitotic cells at the end of mitosis in the two nuclei in one cell, before cytodieresis. Bcl-2 was also found over chromosomes. Thus, nacre extract stimulates Bcl-2 production in osteoblasts, that is correlated with the cell cycle. Bcl-2 was also abundant in the nucleoli of extract-treated cells. Thus, the concentration and subcellular distribution of Bcl-2 in osteoblasts in primary cultures is influenced by nacre extract, and related to the cell cycle and the regulation of gene expression. Hence, knowledge of how water-soluble extracts of Pinctada maxima nacre act on osteoblasts in vitro may reveal the mechanisms involved in its action in vivo on bone cells and bone regeneration.

Effect of water-soluble matrix fraction extracted from the nacre of Pinctada maxima on the alkaline phosphatase activity of cultured fibroblasts

A new approach to the isolation of the water-soluble factors from nacre without any demineralization is described and examined their effect on fibroblast cells in culture. The soluble matrix in pure water from the nacre of Pinctada maxima was analysed by size-exclusion HPLC. Four fractions (SE1-SE4) of the water-soluble matrix (WSM) were further analysed by anion-exchange HPLC. The amino acid composition of the WSM showed that it is mainly composed of glycine and alanine. SE1 and SE4 had different amino acid compositions from the whole WSM. The WSM and SE4 tested on a culture of human foetus lung tissue fibroblasts increased the alkaline phosphatase (ALP) activity. SE1 caused a decrease in ALP activity. Our results support the hypothesis that WSM promotes the differentiation of cells in vitro.

Classes of small-world networks

We study the statistical properties of a variety of diverse real-world networks. We present evidence of the occurrence of three classes of small-world networks: (a) scale-free networks, characterized by a vertex connectivity distribution that decays as a power law; (b) broad-scale networks, characterized by a connectivity distribution that has a power law regime followed by a sharp cutoff; and (c) single-scale networks, characterized by a connectivity distribution with a fast decaying tail. Moreover, we note for the classes of broad-scale and single-scale networks that there are constraints limiting the addition of new links. Our results suggest that the nature of such constraints may be the controlling factor for the emergence of different classes of networks.

Self-consistent effective-medium approximations with path integrals

We study effective-medium approximations for linear composite media by means of a path integral formalism with replicas. We show how to recover the Bruggeman and Hori-Yonezawa effective-medium formulas. Using a replica-coupling ansatz, these formulas are extended into ones which have the same percolation thresholds as those of the Bethe lattice and Potts model of percolation, and critical exponents s=0 and t=2 in any space dimension d>/=2. Like the Bruggeman and Hori-Yonezawa formulas, the obtained formulas are exact to second order in the weak-contrast and dilute limits. The dimensional range of validity of the four effective-medium formulas is discussed, and it is argued that out formulas are of better relevance than the classical ones in dimensions d=3,4 for systems obeying the nodes-links-blobs picture, such as random-resistor networks.

Multifractal properties of the random resistor network

We study the multifractal spectrum of the current in the two-dimensional random resistor network at the percolation threshold. We consider two ways of applying the voltage difference: (i) two parallel bars, and (ii) two points. Our numerical results suggest that in the infinite system limit, the probability distribution behaves for small i as P(i) approximately 1/i, where i is the current. As a consequence, the moments of i of order q</=q(c)=0 do not exist and all currents of value below the most probable one have the fractal dimension of the backbone. The backbone can thus be described in terms of only (i) blobs of fractal dimension d(B) and (ii) high current carrying bonds of fractal dimension going from 1/nu to d(B).

Implication of Ile-69 and Thr-182 residues in kinetic characteristics of IRT-3 (TEM-32) beta-lactamase

The substitution of a methionine for an isoleucine at position 69 (Met69Ile), which causes inhibitor resistance to TEM-type beta-lactamases (IRT-3 and IRT-I69), altered the positions of the Asn-170 and Glu-166 side chains as well as the position of the catalytic water molecule. A novel hydrogen bond between the hydroxyl of Thr-182 and the carbonyl of Glu-64 was expected to be responsible for the increase in the catalytic activity of the IST-T182 and IRT-3 enzymes compared with those of TEM-1 and IRT-169, respectively.

Cancer in Gabon, 1984-1993: a pathology registry based relative frequency study

A pathology based cancer registry was established in 1977 in the pathology department of the faculty of health sciences of the University of Omar Bongo in Librevile, Gabon, which is the only pathology service catering to the needs of the population of approximately 1 million of Gabon. Analysis of the histologically diagnosed cancers during 1984 through 1993 revealed 1,367 male and 1,235 female cases. The leading sites in males were: skin (11.0%), liver (8.9%), non-Hodgkin's lymphoma (8.7%), prostate (7.8%), lung (6.9%), mouth (4.9%) and tongue (4.7%). The predominant sites in females were: uterine cervix (26.3%), breast (13.9%), non-Hodgkin's lymphoma (7.1%), skin (5.1%), liver (3.9%) and ovary (3.3%). Considering the little information available on cancer patterns in Africa, even relative frequency data for different periods from different sources are of considerable interest. We propose to establish population based cancer registration in Libreville (pop 400,000) where 40% of the national population lives, in the near future, which should provide reliable information on the cancer burden and patterns in Gabon.

The distribution of Ag-NORs proteins and ribosomal RNA genes in human spermatogonia: an original procedure associating silver-staining, fish and confocal microscopy

It is generally accepted that Ag-NORs proteins are associated with nucleolar components engaged in rRNA synthesis. Since conflicting results have been reported concerning the intranucleolar sites of active ribosomal genes, the relationships between the silver-stained areas and the distribution of rDNA were analyzed in human spermatogonia using confocal microscopy of fluorescent in situ hybridized preparations previously stained with silver. The fluorescent signal strictly corresponded to the silver-stained area, identified at the ultrastructural level as the fibrillar center and the surrounding dense fibrillar component. A quantitative evaluation of nucleolar activity solely based on silver-staining may be misleading, taking into account that only Ag-positive proteins located in the dense fibrillar component can be associated with transcriptional activity, while those stored in the fibrillar center are associated with non-transcribed rRNA genes.

[Properties of a cephalosporinase produced by Proteus penneri inhibited by clavulanic acid]

P. penneri produces an inducible cephalosporinase, as many Enterobacteriaceae. Nevertheless this betalactamase is susceptible to clavulanic acid which is an exception also encountered for P. vulgaris. The authors studied the enzyme produced by P. penneri 14HBC resistant to cefotaxime (MIC 16 mg/l) isolated in Spain in 1992. This betalactamase of isoelectric point 6.65 hydrolyzes first generation cephalosporins, amoxycillin and poorly ticarcillin as it occurs for all cephalosporinases. However, this enzyme hydrolyzes strongly oxyimino-cephalosporins: cefuroxime, cefotaxime, cefepime, cefpirome as it occurs with extended-spectrum betalactamases. Cephamycins and imipenem are not substrates. Clavulanic acid has a very good affinity for this betalactamase which is inactivated progressively. These properties are similar to those of the enzyme of P. vulgaris Ro104 of isoelectric point 8.3 which, contrarily to other cephalosporinases, belongs to the structural Ambler's class A.

Petroclival meningioma mimicking the presentation of a transient ischemic attack

A case of petroclival meningioma with pseudo-vascular clinical feature, documented by magnetic resonance imaging, is described. The location of the tumor and the persistent normality of the clinical examination excluded any surgical attempt. Such transient neurological symptoms in case of posterior fossa meningiomas have been seldom reported. Attempts for a physiological explanation are considered.

Torsade de pointes during loading with amiodarone

Torsade de pointes represents a potential complication of chronic amiodarone therapy. Several reports have emphasized the need for a loading dose in order to achieve therapeutic blood levels rapidly. We report a case of torsade de pointes following a single oral dose of amiodarone (1400 mg or 30 mg kg-1) administered after short intravenous loading for prevention of paroxysmal atrial flutter. Torsades de pointes were preceded and associated with marked QT prolongation and bradycardia. This report suggests that careful monitoring of patients undergoing oral amiodarone loading is necessary.

Classification of beta-lactamases from Branhamella catarrhalis in relation to penicillinases produced by other bacterial species

Branhamella catarrhalis strains resistant to commonly used penicillins, and presently isolated, produce a beta-lactamase. Most of these enzymes are chromosomally mediated, but a plasmid-mediated beta-lactamase has been described (enzyme BRO-1). With reference to isoelectric points, 7 different enzymes have been identified: 6 chromosomally mediated and 1 plasmid-mediated. Nevertheless, they have many common properties, such as being biosynthesised constitutively but with a low level of production. They have a penicillinase-type profile, and are strongly inhibited by clavulanic acid.

[Perinephretic phlegmon of pseudotumor form]

The authors report a case of perinephric phlegmon simulating a tumor. Ultrasound and CT scan were unable to provide grounds for correct diagnosis. It was only after incision of the mass and drainage of the purulent matter that a correct diagnosis could be made.

[Echocardiographic measurement of true left ventricular inotropism in patients under haemodialysis (author's transl)]

M-mode echocardiography was performed 18 to 22 hours after a haemodialysis session in 16 patients under chronic dialysis. The patients (12 men and 4 women, mean age 21 years, haematocrit 24 +/- 5%) were normotensive and had no clinical or radiological sign of heart failure. Patients with renal hypertension, diabetes or amyloidosis had been excluded from the study. Eight healthy subjects of similar age, heart rate and blood pressure were used as controls. In all 24 individuals the following parameters were calculated: end diastolic time diameter index (DTDI), end systolic time diameter index (STDI), ejection time (ET), mean velocity of circumferential fiber shortening (VCF) and ejection fraction (EF). DTDI was greater in haemodialyzed patients (31 +/- 2 mm/m2) than in controls, but STDI and ET were the same in both groups. This would explain the increase of VCF (1.68 +/- 0.1 c/sec) and EF (0.78 +/- 0.05) observed in dialyzed patients. After compression of the fistula for 3 min the differences disappeared. These results suggest that the echocardiographic measurements listed above give a better idea of the true contractile state of the left ventricle in haemodialyzed patients, disregarding load changes due to the fistula, to anaemia and to intermittent volume expansion.

Novel beta-lactamase from Branhamella catarrhalis

A strain of Branhamella catarrhalis isolated from sputum was shown to be resistant to penicillin and ampicillin. This strain produced a beta-lactamase which has been judged to be a novel enzyme, on the basis of substrat profil, isoelectric point and location of genetic determinant.

Beta-lactamases: determination of their isoelectric points

Important discrepancies in isoelectric points (pI) of beta-lactamases were observed depending on the experimental procedure used for their determination: isoelectric focusing (IEF) in sucrose density gradients or analytical IEF in thin-layer polyacrylamide gels (PA). The variations, negligable in the case of TEM-like beta-lactamases, appeared to be important in the case of cephalosporinases and are related to an artifact which appears in PA-IEF. This has been clearly shown with beta-lactamase preparations from the following bacterial strains: Pseudomonas aeruginosa NCTC 8203 (pI = 8.7), P. aeruginosa NCTC 10701 (pI = 9.4), and Proteus morganii NCTC 235 (pI = 8.3). The data previously obtained by PA-IEF were much lower.

[Microheterogeneity of R plasmid coded beta-lactamases in analytical isoelectric focusing (author's transl)]

Analytical isoelectric focusing of plasmid-coded beta-lactamases in polyacrylamide gels gives rise to several satellite bands in addition to one major active band (microheterogeneity). When the R plasmids are transferred by conjugation into 4 different bacterial species (Escherichia coli, Klebsiella pneumoniae, Salmonella typhi-murium, Proteus mirabilis) the position of the main band remains constant, but the number and position of the satellite bands are changed. Furthermore, the minimal inhibitory concentrations of several beta-lactamines are also changed when the plasmids are transferred between these different host strains. These facts suggest that the bacterial host might modify the physical structure and the activity of plasmid-determined beta-lactamases. They also suggest that identification of beta-lactamases and comparison of their isoelectric focusing patterns should always be carried out using the same bacterial host strain.

Beta-lactamases produced by a Pseudomonas aeruginosa strain highly resistant to carbenicillin

A Pseudomonas aeruginosa strain isolated at Besançon Hospital, France, proved to be highly resistant to carbenicillin and showed a high hydrolytic activity toward this antibiotic. We clearly demonstrated that two beta-lactamases were synthetized: one of them, constitutive, has its enzymatic activity directed mainly toward penicillins, and carbenicillin appears to be its best substrate (higher V(max)); thus, this beta-lactamase is a "carbenicillinase" that differs from the well-known "TEM-like" enzymes. The isoelectric point of this carbenicillinase is 5.30 +/- 0.03. The other one is an inducible cephalosporinase, very similar to the cephalosporinases usually found in these organisms. Its isoelectric point is 8.66 +/- 0.04. These two enzymes have been separated by affinity chromatography and isoelectric focusing. The kinetic constants were measured by computerized microacidimetry.

[Incidence of metabolic acidosis during status asthmaticus in adults. Physiopathological consideration]

In the course of 28 cases of status asthmaticus in adults, the authors noted the frequency of metabolic acidosis, assessed as a base deficit. This disorder, already noted by other authors, remains poorly explained. It may nevertheless be conceived that its onset is favourised by the special haemodynamic consequences of this particular form of acute respiratory insufficiency.