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Biomedical subjects

Angel Sánchez

Publications and source records attributed to Angel Sánchez.

At least 19 recordsLinked to original sources
PubMed2006

Time scales in evolutionary dynamics.

Evolutionary game theory has traditionally assumed that all individuals in a population interact with each other between reproduction events. We show that eliminating this restriction by explicitly considering the time scales of interaction and selection leads to dramatic changes in the outcome of evolution. Examples include the selection of the inefficient strategy in the Harmony and Stag-Hunt games, and the disappearance of the coexistence state in the Snowdrift game. Our results hold for any population size and in more general situations with additional factors influencing fitness.

Biological Evolution↗
PubMed2006

Inhomogeneous soliton ratchets under two ac forces.

We extend our previous work on soliton ratchet devices [L. Morales-Molina, Eur. Phys. J. B 37, 79 (2004)] to consider the joint effect of two ac forces including nonharmonic drivings, as proposed for particle ratchets by Savele'v [Europhys. Lett. 67, 179 (2004); Phys. Rev. E 70, 066109 (2004)]. Current reversals due to the interplay between the phases, frequencies, and amplitudes of the harmonics are obtained. An analysis of the effect of the damping coefficient on the dynamics is presented. We show that solitons give rise to nontrivial differences in the phenomenology reported for particle systems that arise from their extended character. A comparison with soliton ratchets in homogeneous systems with biharmonic forces is also presented. This ratchet device may be an ideal candidate for Josephson junction ratchets with intrinsic large damping.

Journal Article↗
PubMed2006

[Percutaneous treatment of bifurcation lesions by crush T stenting: immediate and medium-term outcomes].

INTRODUCTION AND OBJECTIVES: Percutaneous coronary intervention for coronary bifurcations is usually associated with a low success rate, a high rate of complications, and a more frequent need for target lesion revascularization. The aim of this prospective study was to evaluate immediate and medium-term clinical and angiographic outcomes after the application of crush T stenting. METHODS: This approach to bifurcation stenting follows the same steps as modified T stenting. The only difference is that the side branch stent protrudes 3-4 mm into the main vessel from the carina. The aim is to ensure that the circumference of the side branch ostium is covered by the stent strut. RESULTS: Between December 2003 and February 2005, 82 patients were included in the study. The lesion involved the left main coronary artery in 53% of patients, the left anterior descending or diagonal coronary artery in 29%, the circumflex or marginal branch in 11%, and the right coronary artery or the posterior or posterolateral descending branch in 7%. Angiographic and clinical success was obtained in 100% and 96.4% of cases, respectively. Final dilatation was performed using a kissing balloon in 87%. Overall, 100% of patients were followed up clinically for 12 months and 77% were followed up angiographically for a mean of 8.7 (3.3) months. Target lesion revascularization was performed in 9 patients (10.8%). CONCLUSIONS: Treatment of coronary bifurcation lesions using the crush T stenting technique is safe and effective. It reduces both the restenosis rate and the major adverse cardiac event rate at one year.

Angioplasty, Balloon, Coronary↗
PubMed2006

Soliton ratchets in homogeneous nonlinear Klein-Gordon systems.

We study in detail the ratchetlike dynamics of topological solitons in homogeneous nonlinear Klein-Gordon systems driven by a biharmonic force. By using a collective coordinate approach with two degrees of freedom, namely the center of the soliton, X(t), and its width, l(t), we show, first, that energy is inhomogeneously pumped into the system, generating as result a directed motion; and, second, that the breaking of the time shift symmetry gives rise to a resonance mechanism that takes place whenever the width l(t) oscillates with at least one frequency of the external ac force. In addition, we show that for the appearance of soliton ratchets, it is also necessary to break the time-reversal symmetry. We analyze in detail the effects of dissipation in the system, calculating the average velocity of the soliton as a function of the ac force and the damping. We find current reversal phenomena depending on the parameter choice and discuss the important role played by the phases of the ac force. Our analytical calculations are confirmed by numerical simulations of the full partial differential equations of the sine-Gordon and phi4 systems, which are seen to exhibit the same qualitative behavior. Our results show features similar to those obtained in recent experimental work on dissipation induced symmetry breaking.

Journal Article↗
PubMed2006

On the discrete Peyrard-Bishop model of DNA: stationary solutions and stability.

As a first step in the search of an analytical study of mechanical denaturation of DNA in terms of the sequence, we study stable, stationary solutions in the discrete, finite, and homogeneous Peyrard-Bishop DNA model. We find and classify all the stationary solutions of the model, as well as analytic approximations of them, both in the continuum and in the discrete limits. Our results explain the structure of the solutions reported by Theodorakopoulos et al. [Phys. Rev. Lett. 93, 258101 (2004)] and provide a way to proceed to the analysis of the generalized version of the model incorporating the genetic information.

Computer Simulation↗
PubMed2005

Ratchet behavior in nonlinear Klein-Gordon systems with pointlike inhomogeneities.

We investigate the ratchet dynamics of nonlinear Klein-Gordon kinks in a periodic, asymmetric lattice of pointlike inhomogeneities. We explain the underlying rectification mechanism within a collective coordinate framework, which shows that such a system behaves as a rocking ratchet for point particles. Careful attention is given to the kink width dynamics and its role in the transport. We also analyze the robustness of our kink rocking ratchet in the presence of noise. We show that the noise activates unidirectional motion in a parameter range where such motion is not observed in the noiseless case. This is subsequently corroborated by the collective variable theory. An explanation for this phenomenon is given.

Journal Article↗
PubMed2005

Altruism may arise from individual selection.

The fact that humans cooperate with non-kin in large groups, or with people they will never meet again, is a long-standing evolutionary puzzle. Altruism, the capacity to perform costly acts that confer benefits on others, is at the core of cooperative behavior. Behavioral experiments show that humans have a predisposition to cooperate with others and to punish non-cooperators at personal cost (so-called strong reciprocity) which, according to standard evolutionary game theory arguments, cannot arise from selection acting on individuals. This has led to the suggestion of group and cultural selection as the only mechanisms that can explain the evolutionary origin of human altruism. We introduce an agent-based model inspired on the Ultimatum Game, that allows us to go beyond the limitations of standard evolutionary game theory and show that individual selection can indeed give rise to strong reciprocity. Our results are consistent with the existence of neural correlates of fairness and in good agreement with observations on humans and monkeys.

Altruism↗
PubMed2005

Length scale competition in nonlinear Klein-Gordon models: a collective coordinate approach.

Working within the framework of nonlinear Klein-Gordon models as a paradigmatic example, we show that length scale competition, an instability of solitons subjected to perturbations of an specific length, can be understood by means of a collective coordinate approach in terms of soliton position and width. As a consequence, we provide a natural explanation of the phenomenon in much simpler terms than any previous treatment of the problem. Our technique allows us to study the existence of length scale competition in most soliton bearing nonlinear models and can be extended to coherent structures with more degrees of freedom.

Algorithms↗
PubMed2005

[Pulmonary hemorrhage after abciximab. Risk factors and the role of protamine].

Large clinical trials have demonstrated the clinical effectiveness of therapy with inhibitors of the platelet surface-membrane glycoprotein IIb-IIIa receptor in a broad range of patients with ischemic heart disease. Abciximab, a platelet glycoprotein IIb-IIIa receptor blocker, is associated with improved long-term prognosis in patients who require angioplasty and stent placement. Severe bleeding from abciximab use is an uncommon event. We describe a patient with severe pulmonary hemorrhage after treatment with abciximab, and discuss predisposing factors and protamine infusion in this potentially fatal complication.

Abciximab↗
PubMed2004

Equilibrium roughening transition in a one-dimensional modified sine-Gordon model.

We present a modified version of the one-dimensional sine-Gordon model that exhibits a thermodynamic, roughening phase transition, in analogy with the two-dimensional usual sine-Gordon model. The model is suited to study the crystalline growth over an impenetrable substrate and to describe the wetting transition of a liquid that forms layers. We use the transfer integral technique to write down the pseudo-Schro dinger equation for the model, which allows us to obtain some analytical insight, and to compute numerically the free energy from the exact transfer operator. We compare the results with Monte Carlo simulations of the model, finding a perfect agreement between both procedures. We thus establish that the model shows a phase transition between a low-temperature flat phase with intriguing nontrivial properties and a high-temperature rough one. The fact that the model is one-dimensional and that it has a true phase transition makes it an ideal framework for further studies of roughening phase transitions.

Journal Article↗
PubMed2004

Nonlinear excitations in DNA: aperiodic models versus actual genome sequences.

We study the effects of the genetic sequence on the propagation of nonlinear excitations in simple models of DNA in which we incorporate actual data from the human genome. We show that kink propagation requires forces over a certain threshold, a phenomenon already found for aperiodic sequences [F. Domínguez-Adame et al., Phys. Rev. E 52, 2183 (1995)]. For forces below threshold, the final stop positions are highly dependent on the specific sequence. Contrary to the conjecture advanced by Domínguez-Adame and co-workers, we find no evidence supporting the dependence of the kink dynamics on the information content of the genetic sequences considered. We discuss possible reasons for that result as well as its practical consequences. Physically, the results of our model are consistent with the stick-slip dynamics of the unzipping process observed in experiments. We also show that the effective potential, a collective coordinate formalism introduced by Salerno and Kivshar [Phys. Lett. A 193, 263 (1994)], is a useful tool to identify key regions in DNA that control the dynamical behavior of large segments. As a side result, we extend the previous studies on aperiodic sequences by analyzing the effect of the initial position of the kink, leading to further insight on the phenomenology observed in such systems.

Base Pairing↗
PubMed2003

Internal mode mechanism for collective energy transport in extended systems.

We study directed energy transport in homogeneous nonlinear extended systems in the presence of homogeneous ac forces and dissipation. We show that the mechanism responsible for unidirectional motion of topological excitations is the coupling of their internal and translation degrees of freedom. Our results lead to a selection rule for the existence of such motion based on resonances that explain earlier symmetry analysis of this phenomenon. The direction of motion is found to depend both on the initial and the relative phases of the two harmonic drivings, even in the presence of noise.

Journal Article↗
PubMed2003

Apparent phase transitions in finite one-dimensional sine-Gordon lattices.

We study the one-dimensional sine-Gordon model as a prototype of roughening phenomena. In spite of the fact that it has been recently proven that this model cannot have any phase transition [J. A. Cuesta and A. Sánchez, J. Phys. A 35, 2373 (2002)], Langevin as well as Monte Carlo simulations strongly suggest the existence of a finite temperature separating a flat from a rough phase. We explain this result by means of the transfer operator formalism and show as a consequence that sine-Gordon lattices of any practically achievable size will exhibit this apparent phase transition at unexpectedly large temperatures.

Journal Article↗
PubMed2003

Antibodies to centromere antigens measured by an automated enzyme immunoassay.

BACKGROUND: Anticentromere antibodies (ACA) are frequently observed in patients with Raynaud's phenomenon and in the CREST syndrome, a subclass of systemic sclerosis. Likewise, ACA are also found in other autoimmune and non-autoimmune diseases. The objective of the present study was to evaluate the clinical utility of the measurement of antibodies to the best characterized centromere antigen (CENP-B) protein by an enzyme-linked immunosorbent assay (ELISA) that uses human recombinant CENP-B antigen and compare it with indirect immunofluorescence assay (IFA) on HEp-2 cells. METHODS: We have analyzed 128 sera samples from patients with the following diseases: systemic lupus erythematosus (SLE, n = 53), mixed connective tissue disease (n = 1), primary Sjögren syndrome (n = 10), primary Raynaud's phenomenon (n = 10), primary systemic sclerosis (n = 7), polymyositis/dermatomyositis (n = 3), rheumatoid arthritis (n = 9), cutaneous lupus (n = 5), primary biliary cirrhosis (n = 9), chronic autoimmune hepatitis (n = 5) and ANA-positive non-autoimmune diseases (n = 16). RESULTS: The ELISA evaluated shows a good concordance with IFA, with the advantage of being an automatable quantitative technique. CONCLUSIONS: Measurement of anticentromere antibodies by this ELISA using human recombinant antigen is a useful alternative for the autoimmune laboratory checking for diseases associated with anticentromere antibodies.

Autoantibodies↗
PubMed2002

Clinical evaluation of a new automated anti-dsDNA fluorescent immunoassay.

The measurement of anti-double-stranded DNA (anti-dsDNA) antibodies is a useful tool for the diagnosis and the follow-up of systemic lupus erythematosus (SLE). Anti-dsDNA antibodies are involved in the pathogenesis of lupus nephritis and they are, specially the high-avidity antibodies, the most specific antibodies associated with SLE nephritis and active SLE. The aim of the present study was to assess the clinical utility of an enzyme-linked immunosorbent assay (EUSA) that utilizes a circular double-stranded plasmid DNA as a nucleic acid source, adapted to an automated fluorescence immunoassay (EliA dsDNA, Pharmacia, Freiburg, Germany). Also, we compared this method with other immunoassays used in clinical laboratories. We have measured anti-dsDNA antibodies in the serum of 179 patients with a positive result for antinuclear antibodies (ANA). Seventy six sera were from SLE patients (14 men and 62 women), and the other 103 sera (from 20 men and 83 women) constituted the control group. This latter group includes nine Sjogren's syndrome patients, six patients with rheumatoid arthritis and 88 with various other diseases, including connective tissue diseases (n=34), hepatopathies (n= 17; 11 primary biliary cirrhosis and 6 autoimmune hepatitis), and 37 patients with nonautoimmune diseases (viral hepatitis, renal disease, diabetes, exanthema and hypertension). Methods used were "EliA dsDNA" (Pharmacia, Germany), "Varelisa dsDNA" (Pharmacia, Germany), Farr (Amersham, UK) and Chritidia luciliae immunofluorescence test (Vitro-Immun, Germany). We assessed sensitivity, specificity, positive predictive value and negative predictive value in the clinical study, and kappa index and scatter plots in the comparative study. The results show a low concordance between methods (kappa < 0.6). The evaluated EliA method shows a very good specificity for SLE (93.2%) and a good sensitivity for active SLE (70.8%).

Antibodies, Antinuclear↗