Showing papers by "Instituto Politécnico Nacional published in 2005"

The bactericidal effect of silver nanoparticles

Abstract: Nanotechnology is expected to open new avenues to fight and prevent disease using atomic scale tailoring of materials. Among the most promising nanomaterials with antibacterial properties are metallic nanoparticles, which exhibit increased chemical activity due to their large surface to volume ratios and crystallographic surface structure. The study of bactericidal nanomaterials is particularly timely considering the recent increase of new resistant strains of bacteria to the most potent antibiotics. This has promoted research in the well known activity of silver ions and silver-based compounds, including silver nanoparticles. The present work studies the effect of silver nanoparticles in the range of 1-100 nm on Gram-negative bacteria using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). Our results indicate that the bactericidal properties of the nanoparticles are size dependent, since the only nanoparticles that present a direct interaction with the bacteria preferentially have a diameter of approximately 1-10 nm.

The golden code: a 2/spl times/2 full-rate space-time code with nonvanishing determinants

Abstract: In this paper, the Golden code for a 2/spl times/2 multiple-input multiple-output (MIMO) system is presented. This is a full-rate 2/spl times/2 linear dispersion algebraic space-time code with unprecedented performance based on the Golden number 1+/spl radic/5/2.

Solving Multiobjective Optimization Problems Using an Artificial Immune System

Abstract: In this paper, we propose an algorithm based on the clonal selection principle to solve multiobjective optimization problems (either constrained or unconstrained). The proposed approach uses Pareto dominance and feasibility to identify solutions that deserve to be cloned, and uses two types of mutation: uniform mutation is applied to the clones produced and non-uniform mutation is applied to the ?not so good? antibodies (which are represented by binary strings that encode the decision variables of the problem to be solved). We also use a secondary (or external) population that stores the nondominated solutions found along the search process. Such secondary population constitutes the elitist mechanism of our approach and it allows it to move towards the true Pareto front of a problem over time. Our approach is compared with three other algorithms that are representative of the state-of-the-art in evolutionary multiobjective optimization. For our comparative study, three metrics are adopted and graphical comparisons with respect to the true Pareto front of each problem are also included. Results indicate that the proposed approach is a viable alternative to solve multiobjective optimization problems.

Supply chain flexibility and firm performance

Abstract: Purpose – To explore the relationship between the dimensions of supply chain flexibility and firm performance in a sample of automotive suppliers.Design/methodology/approach – Empirical survey of a representative sample of 126 Spanish automotive suppliers during the months of September and October 2003. Data gathered through a mail survey to purchasing managers by using a structured questionnaire. Spearman correlation coefficients were used to analyse the relationship between the different supply chain flexibility dimensions, between supply chain flexibility dimensions and firm performance dimensions, and between supply chain flexibility dimensions and environmental uncertainty dimensions. A multivariate analysis studied the determinants of supply chain flexibility.Findings – The research has found a positive relation between a superior performance in flexibility capabilities and firm performance, although flexibility dimensions are not equally important for firm performance. On the other hand, the result...

Phosphate starvation induces a determinate developmental program in the roots of Arabidopsis thaliana.

Abstract: When growing under limiting phosphate (P) conditions, Arabidopsis thaliana plants show dramatic changes in root architecture, including a reduction in primary root length, increased formation of lateral roots and greater formation of root hairs. Here we report that primary root growth inhibition by low P is caused by a shift from an indeterminate to a determinate developmental program. In the primary root, the low P-induced determinate growth program initiates with a reduction of cell elongation followed by the progressive loss of meristematic cells. At later stages, cell proliferation ceases and cell differentiation takes place at the former cell elongation and meristematic regions of the primary root. In low P, not only the primary but also almost all mature lateral roots enter the determinate developmental program. Kinetic studies of expression of the cell cycle marker CycB1;1:uidA and the quiescent center (QC) identity marker QC46:GUS showed that in low P conditions, reduction in proliferation in the primary root was preceded by alterations in the QC. These results suggest that in Arabidopsis, P limitation can induce a determinate root developmental program that plays an important role in altering root system architecture and that the QC could act as a sensor of environmental signals.

Controlling Two-Center Interference in Molecular High Harmonic Generation

Abstract: We experimentally investigate the process of intramolecular quantum interference in high-order harmonic generation in impulsively aligned CO2 molecules. The recombination interference effect is clearly seen through the order dependence of the harmonic yield in an aligned sample. The experimental results can be well modeled assuming that the effective de Broglie wavelength of the returning electron wave is not significantly altered by the Coulomb field of the molecular ion. We demonstrate that such interference effects can be effectively controlled by changing the ellipticity of the driving laser field.

Reduced intellectual development in children with prenatal lead exposure.

Abstract: ObjectiveLow-level postnatal lead exposure is associated with poor intellectual development in children, although effects of prenatal exposure are less well studied. We hypothesized that prenatal l...

Cassini radar views the surface of Titan

Abstract: The Cassini Titan Radar Mapper imaged about 1% of Titan's surface at a resolution of ∼0.5 kilometer, and larger areas of the globe in lower resolution modes. The images reveal a complex surface, with areas of low relief and a variety of geologic features suggestive of dome-like volcanic constructs, flows, and sinuous channels. The surface appears to be young, with few impact craters. Scattering and dielectric properties are consistent with porous ice or organics. Dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons.

Methods for modeling and supporting innovation processes in SMEs

Abstract: Purpose – Sets out to investigate business modeling techniques (BMTs) which can be used to support and improve innovation processes within small and medium‐sized enterprises (SMEs).Design/methodology/approach – Based on a literature review, different analysis perspectives on innovation processes are identified and discussed, and some firm needs and problems are pointed out. The importance of BMTs to firms is further tested by an empirical study whose initial results are reported. Finally, by matching problems and techniques characterized by the same ontology, the BMTs most suitable to address SME needs are identified and their role within the innovation process discussed.Findings – The main result of the paper is the identification of the problems facing SMEs in innovation processes and the possible support offered by BMTs. Though methods and models alone do not assure the success in the innovation development process (IDP), they are enabling factors and can support the creation of strategies, reasoning, ...

A theoretical model for the margination of particles within blood vessels.

Abstract: The margination of a particle circulating in the blood stream has been analyzed. The contribution of buoyancy, hemodynamic forces, van der Waals, electrostatic and steric interactions between the circulating particle and the endothelium lining the vasculature has been considered. For practical applications, the contribution of buoyancy, hemodynamic forces and van der Waals interactions should be only taken into account, whilst the effect of electrostatic and steric repulsion becomes important only at very short distances from the endothelium (1–10 nm). The margination speed and the time for margination t s have been estimated as a function of the density of the particle relative to blood Δ ρ, the Hamaker constant A and radius R of the particle. A critical radius R c exists for which the margination time t s has a maximum, which is influenced by both Δ ρ and A: the critical radius decreases as the relative density increases and the Hamaker constant decreases. Therefore, particles used for drug delivery should have a radius smaller than the critical value (in the range of 100 nm) to facilitate margination and interaction with the endothelium. While particles used as nanoharvesting agents in proteomics or genomics analysis should have a radius close to the critical value to minimize margination and increase their circulation time.

An Auxin Transport Independent Pathway Is Involved in Phosphate Stress-Induced Root Architectural Alterations in Arabidopsis. Identification of BIG as a Mediator of Auxin in Pericycle Cell Activation

Abstract: Arabidopsis (Arabidopsis thaliana) plants display a number of root developmental responses to low phosphate availability, including primary root growth inhibition, greater formation of lateral roots, and increased root hair elongation. To gain insight into the regulatory mechanisms by which phosphorus (P) availability alters postembryonic root development, we performed a mutant screen to identify genetic determinants involved in the response to P deprivation. Three low phosphate-resistant root lines (lpr1-1 to lpr1-3) were isolated because of their reduced lateral root formation in low P conditions. Genetic and molecular analyses revealed that all lpr1 mutants were allelic to BIG, which is required for normal auxin transport in Arabidopsis. Detailed characterization of lateral root primordia (LRP) development in wild-type and lpr1 mutants revealed that BIG is required for pericycle cell activation to form LRP in both high (1 mm) and low (1 μm) P conditions, but not for the low P-induced alterations in primary root growth, lateral root emergence, and root hair elongation. Exogenously supplied auxin restored normal lateral root formation in lpr1 mutants in the two P treatments. Treatment of wild-type Arabidopsis seedlings with brefeldin A, a fungal metabolite that blocks auxin transport, phenocopies the root developmental alterations observed in lpr1 mutants in both high and low P conditions, suggesting that BIG participates in vesicular targeting of auxin transporters. Taken together, our results show that auxin transport and BIG function have fundamental roles in pericycle cell activation to form LRP and promote root hair elongation. The mechanism that activates root system architectural alterations in response to P deprivation, however, seems to be independent of auxin transport and BIG.

Physicians' attitudes and adverse drug reaction reporting : a case-control study in Portugal.

Abstract: Objectives: Voluntary adverse drug reaction (ADR) reporting is fundamental to medical drug safety surveillance; however, substantial under-reporting exists and is the main limitation of the system. This study sought to identify the knowledge-and attitude-related factors associated with ADR reporting by physicians in Northern Portugal. Methods: Case-control study covering a population of National Health Service medical practitioners. The 88 cases comprised physicians who had reported at least one ADR to the drug surveillance unit from the year 2000 to the date of enrolment in the study. The 771 controls were randomly selected from among the remaining physicians. All interviews were conducted using a self-administered questionnaire. Knowledge and attitudes regarding spontaneous ADR reporting were based on Inman’s ‘seven deadly sins’. Agreement with the questions included in the questionnaire was measured using a horizontal, continuous visual analogue scale, which was unnumbered. Recorded answers were read in a range from zero (total disagreement) to ten (total agreement). We used logistic regression to determine the ADR reporting adjusted odds ratio (ORadj) for a change in exposure corresponding to the interquartile range for each attitude. Results: A total of 397 questionnaires were received from 731 eligible practitioners (54.3%). Physicians who worked in primary versus hospital care (ORadj 7.74 [95% CI 1.85, 32.30]) and in general medicine (ORadj 1.05 [95% CI 0.30, 3.69]) versus medical specialities were more likely to report ADRs. In contrast, physicians working in the medical-surgical/surgical fields were significantly less likely to report ADRs compared with medical specialists (ORadj 0.10 [95% CI 0.02, 0.46]). Attitudes to ADRs were strongly associated with reporting probability. Hence, an interquartile decrease in any of the following attitudes increased the probability of reporting by: (i) 87% (p < 0.05) for complacency (the belief that really serious ADRs are well documented by the time a drug is marketed); (ii) 109% (p < 0.01) for insecurity (the belief that it is nearly impossible to determine whether a drug is responsible for a particular adverse reaction); (iii) 143% (p < 0.001) for diffidence (the belief that one would only report an ADR if one were sure that it was related to the use of a particular drug); (iv) 220% (p < 0.001) for indifference (the belief that the one case an individual doctor might see could not contribute to medical knowledge); and (v) 71% (p < 0.05) for ignorance (the belief that it is only necessary to report serious or unexpected ADRs). Conclusion: This study shows that there are attitudes strongly associated with under-reporting. The implementation of purpose-designed educational interventions based on the attitudes identified in this study may serve to improve reporting substantially.

Grid Impedance Estimation via Excitation of $LCL$ -Filter Resonance

Abstract: Inverters adopted in distributed power generation, active filter, and uninterruptible power supply are often connected to the grid through an inductance-capacitor-inductance (LCL) filter. The impedance of the LCL filter has a typical frequency characteristic with a resonance peak. Hence, the LCL filter has to be damped in order to avoid instability. However, the resonance of the LCL filter can be also excited in a controlled way in order to individuate the resonance frequency in the spectrum (using for example the fast Fourier transform). This paper proposes to use a controlled excitation in measuring the grid impedance, since this one influences also the resonance frequency. This paper will address some possible limits, some solutions, and some implementation issues (e.g., how to obtain a controlled resonance in the filter without damaging the system) in order to use the resonant peak for grid impedance detection. The analysis is validated both by simulations and experimental results.

Sugar and ABA responsiveness of a minimal RBCS light‐responsive unit is mediated by direct binding of ABI4

Abstract: *Summary Photosynthesis-associated nuclear genes (PhANGs) are able to respond to multiple environmental and developmental signals, including light, sugars and abscisic acid (ABA). PhANGs have been extensively studied at the level of transcriptional regulation and several cis-acting elements important for light responsiveness have been identified in their promoter sequences. However, the regulatory elements involved in sugar and ABA regulation of PhANGs have not been completely characterized. Using conserved modular arrangement 5 (CMA5), a previously characterized minimal light-responsive unit, we show that in Arabidopsis thaliana this unit responds not only positively to light signals, but also negatively to sugars and ABA. The latter responses were found to be impaired in the abi4 mutant, indicating that ABSCISIC ACID INSENSITIVE-4 (ABI4) is a regulator involved in sugar and ABA repression of this minimal regulatory unit. Furthermore, we report a new sequence element conserved in several rbcS promoters, herewith named S-box, which is important for the sugar and ABA responsiveness of CMA5. This sequence corresponds to a putative ABI4-binding site, which is in fact bound by the Arabidopsis ABI4 protein in vitro. The S-box is closely associated with the G-box present in CMA5, and this association is conserved in the promoters of several RBCS genes. This phylogenetically conserved promoter feature probably reflects a common regulatory mechanism and identifies a point of convergence between light- and sugar-signaling pathways.

Calcium Channels and Ca2+ Fluctuations in Sperm Physiology

Abstract: Generating new life in animals by sexual reproduction depends on adequate communication between mature and competent male and female gametes. Ion channels are instrumental in the dialogue between sperm, its environment, and the egg. The ability of sperm to swim to the egg and fertilize it is modulated by ion permeability changes induced by environmental cues and components of the egg outer layer. Ca(2+) is probably the key messenger in this information exchange. It is therefore not surprising that different Ca(2+)-permeable channels are distinctly localized in these tiny specialized cells. New approaches to measure sperm currents, intracellular Ca(2+), membrane potential, and intracellular pH with fluorescent probes, patch-clamp recordings, sequence information, and heterologous expression are revealing how sperm channels participate in fertilization. Certain sperm ion channels are turning out to be unique, making them attractive targets for contraception and for the discovery of novel signaling complexes.

Smart Sensor Network for Air Quality Monitoring Applications

Abstract: The work presents a network for indoor and outdoor air quality monitoring whose nodes include tin dioxide sensor arrays connected to an acquisition and control system with WiFi communication capabilities. To increase the gas concentration measurement accuracy and to prevent false alarms, two gas sensor-influencing quantities, temperature and humidity, are also measured. Advanced processing based on multi-input single-output neural networks is implemented at the network sensing nodes in order to obtain temperature and humidity compensated gas concentration values. Anomalous operation of network nodes and power consumption are also discussed

Characterisation of phenolic extracts from olive pulp and olive pomace by electrospray mass spectrometry

Abstract: Methanol extracts of olive pomace (two-phase olive oil extraction) and olive pulp were analysed by reverse phase HPLC and the eluted fractions were characterised by electrospray ionisation mass spectrometry. This technique allowed the identification of some common phenolic compounds, namely, verbascoside, rutin, caffeoyl-quinic acid, luteolin-4-glucoside and 11-methyl-oleoside. Hydroxytyrosol-1 � - β-glucoside, luteolin-7-rutinoside and oleoside were also detected. Moreover, this technique enabled the identification, for the first time in Olea europaea tissues, of two oleoside derivatives, 6 � -β-glucopyranosyl- oleoside and 6 � -β-rhamnopyranosyl-oleoside, and of 10-hydroxy-oleuropein. Also, an oleuropein glucoside that had previously been identified in olive leaves was now detected in olive fruit, both in olive pulp and olive pomace. With the exception of oleoside and oleuropein, the majority of phenolic compounds were found to occur in equivalent amounts in olive pulp and olive pomace. Oleoside was the main phenolic compound in olive pulp (31.6mgg −1 ) but was reduced to 3.6mgg −1 in olive pomace, and oleuropein (2.7mgg −1 in the pulp) almost disappeared (<0.1mgg −1 in the pomace). Both these phenolic compounds were degraded during the olive oil extraction process.  2004 Society of Chemical Industry

Towards a catalog of aspect-oriented refactorings

Abstract: In this paper, we present a collection of aspect-oriented refactorings covering both the extraction of aspects from object-oriented legacy code and the subsequent tidying up of the resulting aspects. In some cases, this tidying up entails the replacement of the original implementation with a different, centralized design, made possible by modularization. The collection of refactorings includes the extraction of common code in various aspects into abstract superaspects. We review the traditional object-oriented code smells in the light of aspect-orientation and propose some new smells for the detection of crosscutting concerns. In addition, we propose a new code smell that is specific to aspects.

A multiyear dynamic approach for transmission expansion planning and long-term marginal costs computation

Abstract: This paper presents a multicriteria formulation for multiyear dynamic transmission expansion planning problems. This formulation considers three criteria: investment costs, operation costs, and the expected energy not supplied. The solution algorithm adopts an interactive decision-making approach that starts at a nondominated solution of the problem. This solution is identified transforming two of the three criteria in constraints specifying aspiration levels and using afterwards simulated annealing to deal with the integer nature of investment decisions. After obtaining this first solution, the decision maker can alter the aspiration levels and run the application again to obtain a new solution. Once an expansion plan is accepted, the algorithm computes long-term marginal costs, reflecting both investment and operation costs. These costs are more stable than short-term ones and inherently address the revenue reconciliation problem well known in short-term approaches. The developed algorithm is tested using a case study based on the Portuguese 400/220/150-kV transmission network.

Thermodynamics of rate-independent plasticity

Abstract: We show that the singular dissipative potential of the phenomenological rate-independent plasticity can be obtained by homogenization of a micro-model with quadratic dissipation. The essential ingredient making this reduction possible is a rugged energy landscape at the micro-scale, generating under external loading a regular cascade of subcritical bifurcations. Such landscape may appear as a result of a sufficiently strong pinning or jamming of defects, leading to elastic micro-metastability. The rate-independent plastic deformation emerges in this description as a continuous succession of infinitesimal viscous events; the limiting procedure presumes the elimination of small time and length scales. We present an explicit example of a simple viscoelastic mass-spring system whose macroscopic dissipative behavior is plastic, rate independent.

Vocal Communication in a Fission-Fusion Society: Do Spider Monkeys Stay in Touch With Close Associates?

Abstract: In fission-fusion societies, in which animals from the same group may spend long periods of time apart from each other, individuals could use long-distance vocalizations to maintain contact with others. This could be achieved with vocalizations that simply carried information about the caller's identity and location. I explored this possibility using observations and experiments from a 3-year field study of spider monkeys (Ateles geoffroyi) in Punta Laguna, Mexico, analyzing the use of the species' most frequent vocalization, the whinny. By following 2 subgroups simultaneously, I found that subgroups that were within the active space of the whinny approached each other more often than subgroups that were farther apart. Individual adults in these subgroups also emitted more whinnies when they were within hearing range of another subgroup than when farther apart. I used a paired playback design to determine whether whinnies could influence the behavior of close associates as opposed to nonassociated individuals. Although nonassociates were as likely as close associates to respond vocally to playbacks of whinnies, only a close associate ever approached the speaker. Collectively, the results suggest that whinnies are used by spider monkeys to achieve flexibility in spacing while maintaining specific social relationships.