1,721,079 research outputs found
Spatiotemporal bounded noises and transitions induced by them in solutions of the real Ginzburg-Landau model
No full textIn this work, we introduce two spatiotemporal colored bounded noises, based on the zero-dimensional Cai-Lin and Tsallis-Borland noises. Then we study and characterize the dependence of the defined stochastic processes on both a temporal correlation parameter τ and a spatial coupling parameter λ. In particular, we found that varying λ may induce a transition of the distribution of the noise from bimodality to unimodality. With the aim of investigating the role played by bounded noises in nonlinear dynamical systems, we analyze the behavior of the real Ginzburg-Landau time-varying model additively perturbed by such noises. The observed phase transition phenomenology is quite different from that observed when the perturbations are unbounded. In particular, we observed an inverse order-to-disorder transition and a reentrant transition, with dependence on the specific type of bounded noise
Cellular polarization: Interaction between extrinsic bounded noises and the wave-pinning mechanism
No full textCell polarization (cued or uncued) is a fundamental mechanism in cell biology. As an alternative to the classical Turing bifurcation, it has been proposed that the onset of cell polarity might arise by means of the well-known phenomenon of wave-pinning [ Gamba et al. Proc. Natl. Acad. Sci. USA 102 16927 (2005)]. A particularly simple and elegant deterministic model of cell polarization based on the wave-pinning mechanism has been proposed by Edelstein-Keshet and coworkers [ Biophys. J. 94 3684 (2008)]. This model consists of a small biomolecular network where an active membrane-bound factor interconverts into its inactive form that freely diffuses in the cell cytosol. However, biomolecular networks do communicate with other networks as well as with the external world. Thus, their dynamics must be considered as perturbed by extrinsic noises. These noises may have both a spatial and a temporal correlation, and in any case they must be bounded to preserve the biological meaningfulness of the perturbed parameters. Here we numerically show that the inclusion of external spatiotemporal bounded parametric perturbations in the above wave-pinning-based model of cellular polarization may sometimes destroy the polarized state. The polarization loss depends on both the extent of temporal and spatial correlations and on the kind of noise employed. For example, an increase of the spatial correlation of the noise induces an increase of the probability of cell polarization. However, if the noise is spatially homogeneous then the polarization is lost in the majority of cases. These phenomena are independent of the type of noise. Conversely, an increase of the temporal autocorrelation of the noise induces an effect that depends on the model of noise
Spatio-temporal sine-Wiener bounded noise and its effect on Ginzburg–Landau model
No full textn this work we introduce a spatio-temporal bounded noise derived by the sine-Wiener noise and by the spatially colored unbounded noise proposed by García-Ojalvo, Sancho, and Ramírez-Piscina (GSR noise). We characterize the behavior of the equilibrium distribution of this novel noise by showing its dependence on both the temporal and the spatial autocorrelation lengths. In particular, we show that the distribution experiences a stochastic transition from bimodality to trimodality.
Then, we employ the noise here defined to study the emergence of phase transitions in the real Ginzburg–Landau model. Various phenomena are evidenced by means of numerical simulations, among which reentrant transitions, as well as differences in the response of the system to “equivalent” GSR additive noise perturbations
Bounded noise induced first-order phase transitions in a baseline non-spatial model of gene transcription
No full textIn this work we consider, from a statistical mechanics point of view, the effects of bounded stochastic perturbations of the protein decay rate for a bistable biomolecular network module. Namely, we consider the perturbations of the protein decay/binding rate constant (DBRC) in a circuit modeling the positive feedback of a transcription factor (TF) on its own synthesis. The DBRC models both the spontaneous degradation of the TF and its linking to other unknown biomolecular factors or drugs. We show that bounded perturbations of the DBRC preserve the positivity of the parameter value (and also its limited variation), and induce effects of interest. First, the noise amplitude induces a first-order phase transition. This is of interest since the system in study has neither spatial components nor it is composed by multiple interacting networks. In particular, we observe that the system passes from two to a unique stochastic attractor, and vice-versa. This behavior is different from noise-induced transitions (also termed phenomenological bifurcations), where a unique stochastic attractor changes its shape depending on the values of a parameter. Moreover, we observe irreversible jumps as a consequence of the above-mentioned phase transition. We show that the illustrated mechanism holds for general models with the same deterministic hysteresis bifurcation structure. Finally, we illustrate the possible implications of our findings to the intracellular pharmacodynamics of drugs delivered in continuous infusion. (C) 2017 Elsevier B.V. All rights reserved
Chronic Venous Ulceration of the lower limbs and Thrombosis.
No full textChronic venous ulceration is a major complication of chronic venous disorder with important implications in terms of mor- bidity and social expenditure. Venous thrombosis and throm- bophilia are widespread conditions, often associated with venous ulcers of the lower limbs. This link has not yet been widely described in the literature and aim of this work was to analyze the relationship between these two conditions review- ing the current literature. PubMed, Scopus and ScienceDirect databases were searched for articles using the terms: throm- bophilia, venous ulceration, chronic venous disorders and the significant full text were downloaded and analyzed. From the literature review, a description of the most common throm- bofilic abnormalities found in literature and the relation- ship with CVU was given. Conditions such as antithrombin deficiency, protein C deficiency, protein S deficiency, factor V Leiden, hyperhomocystinaemia, prothrombin G20210A mutation, antiphospholipid antibodies, elevated factor VIII levels, elevated factor XI levels, plasminogen activator inhibi- tor type 1 mutations, cancer, obesity, pregnancy and trauma through current literature were statistically linked to the presence of chronic venous ulceration. The main conclusion to be drawn from the available literature is that patients with chronic venous ulceration of the lower limbs appear to have a prevalence of thrombophilia and/or thromboembolic events that is much higher than in the general populatio
The phlebological surgery in elderly patients
No full textThe pathogenesis of the lower limbs varicose veins in the elderly patients is the same one as in the juvenile and adult age. What changes is the severity of the clinical picture, because the disease is a chronic pathology and it is aggravated with the passing of the years in absence of prophylaxis and missed or inadequate therapy.
Equally the surgical operations on the superficial venous system of the elderly patients from a technical point of view are the same that are practiced in other ages of life. What changes is the anaesthesiological risk, which is increased, because other chronic pathologies are frequently associated with the old ones.
Currently both the use of techniques of peripheral anesthesia, as the blocks of the lower limbs nervous trunks, and the introduction of poor toxic anesthetics for the heart in therapeutical practice allow in an inci¬sive way to submit elderly people to surgical procedures.
Above all the out-patient hemodynamic surgery of the superficial chronic venous insufficiency, which requires a careful and meticulous instrumental investigation aimed surgical gestures, but simple, effective, of brief duration, has convinced many surgeons of the possibility to operate on the varicose patients of a more and more advance age.
On the other hand the rapid postoperative mobiliza¬tion of those sick, in absence of immediate complica¬tions, means that they can be discharged from the hospital on the same day of the operation.
This undoubtedly involves positive reflexes on the sanitary expense and it increases at the same time the compliance in terms of motivation and acceptance of the proposed procedure.
The elderly patient, perhaps more than the younger adult, once informed of the new anaesthesiological and surgical techniques, gladly gives his consent to the inter¬vention, pleased to return to his own house and tquickly return to his daily occupations.
How much I dictate you is translated in our experi¬ence, that is carried out near the Phlebological Center of the Siena University, in a progressive increase in the last 5 years both in absolute terms (223) and percen¬tages (12%) of the number of subjects older than sixty¬five years old that have been submitted to surgical operations for the venous disease.
Of all 223 patients, males are 68 and females are 155; 144of them have an age between 66 and 70 years, 73 belonging to the eighty years of life and 6 subject to the ninty. All patients have been operated in Day Hospi¬tal admission. No mortality has been found. Local post-operative complications was encountered in 1,8% of the cases
Angiosome-targeted revascularisation in diabetic foot ulcers.
No full textPeripheral vascular disease is a common complication of type 2 diabetes and is often more severe and diffuse than in non-diabetic individuals with a higher risk of major amputations in the lower limbs. Diabetic foot revascularisation using both traditional bypass surgery and endovascular therapy are often burdened by the failure and the inevitable subsequent massive amputation. In this study, we examined the clinical response of diabetic patients with critical limb ischaemia and extended ischaemic wounds, treated with a new angiosome-based revascularisation technique. In a 3-year period, nine diabetic patients with imminent amputation threatening and foot ulcers with no feasible arterial revascularisation options were treated by the angiosome- based surgical technique by means of deep vein arterialisation. The postoperative tcPO2 evaluation showed a mean increase in the cutaneous oxygen tension in all patients treated. The overall survival rates were 88·88%, 88·88% and 77·77% at 12, 24 and 36 months, respectively. Limb salvage was 100% at 1year and steady at 88·88% thereafter. Surgical deep venous arterialisation might be considered as an extreme alternative to attempt tissue preservation in limbs unfit for conventional arterial revascularisations. This technique would give advantages to the patients in terms of better compliance to the minor amputations and thus avoiding major limb amputation
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