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C Zannoni

Publications and source records attributed to C Zannoni.

At least 19 recordsLinked to original sources
PubMed2006

External field-induced switching in nematic elastomers: a Monte Carlo study.

We present a Monte Carlo study of external field-induced switching in nematic elastomers, employing a coarse-grained shearable lattice model. In large enough systems a full-wavelength Fréedericksz effect is observed --as opposed to the half-wavelength effect seen in ordinary nematics-- that clearly reflects in simulated polarized light textures, as well as in deuterium magnetic resonance spectra. The reorientation of mesogenic units is accompanied by pronounced shear deformations.

Journal Article↗
PubMed2006

Memory effects in nematics with quenched disorder.

We present a combined experimental and Monte Carlo study of a nematic phase in the presence of quenched disorder. The turbidity of a nematic liquid crystal embedded in a porous polymer membrane is measured under different applied field conditions for field-cooled and zero-field-cooled samples. We find that a significant permanent alignment of the nematic can be induced by fields as low as 0.1 V/microm applied during the isotropic to nematic transition. An analogous effect and dependence on sample history is found by studying the order parameter of a sprinkled disorder Lebwohl-Lasher spin model, indicating that dilute quenched randomness is sufficient to produce memory effects in nematics. The large memory induced by field cooling appears to be written in the system during the transition as a result of the field action on freely oriented nematic nuclei. At lower temperature the nuclei consolidate into permanent nematic textures developed from the interaction with quenched disorder.

Journal Article↗
PubMed2006

An empowerment-based educational program improves psychological well-being and health-related quality of life in Type 1 diabetes.

Educational programs are reported to improve metabolic control and well-being in Type 1 diabetes mellitus (DM), but the effects of newly- structured interventions, aimed at promoting empowerment in educated patients in active selfcare, have received little attention. Ninety patients with Type 1 DM in intensive insulin treatment were invited to an empowerment-based educational intervention. Changes in quality of life and psychological well-being in the 54 patients participating in the program (median age, 44 yr) were compared with those measured in patients who refused. The following questionnaires were administered at baseline and 12 months later: Psychological General Well-Being (PGWB), Medical Outcome Survey Short-Form 36 (SF-36), and Well-Being Enquiry for Diabetics (WED). Baseline values were indicative of moderate, but significant, psychological distress in the whole cohort. At follow-up, the experimental group had a better metabolic control {glycosylated hemoglobin, -0.4% [time x treatment analysis of variance (ANOVA), p = 0.005 vs controls]}, and a general improvement in comprehensive indices and most scales of PGWB and SF-36. Vitality (p = 0.042) and Social Functioning (p = 0.039) were no longer different from population norm. Similarly, the Symptoms (p = 0.005), Discomfort (p = 0.043) and Impact scales (p = 0.032) of WED, reflecting physical functioning, diabetes-related worries and familial relationships, role functioning and social network, improved significantly in treated patients. An educational empowerment-based intervention significantly improves the psychosocial aspects of diabetes and quality of life also in patients in active and effective self-care. Repeated educational interventions are the way towards a normal life with Type 1 DM.

Adolescent↗
PubMed2005

Nematics with quenched disorder: pinning out the origin of memory.

Memory effects and glassy behavior have been repeatedly observed in disordered nematic liquid crystals but the connection between these effects and the system topology remained unrevealed. We present an analysis of the local and global topology of the nematic ordering in the presence of quenched disorder and we show that nematics with quenched disorder can be mapped into a system of pinned defect lines and that the memory of the system stems from the pinning of these strings.

Journal Article↗
PubMed2005

High-resolution 3D scaffold model for engineered tissue fabrication using a rapid prototyping technique.

Rapid prototyping, automatic image processing (computer-aided design (CAD)) and computer-aided manufacturing techniques are opening new and interesting prospects for medical devices and tissue engineering, especially for hard tissues such as bone. The development of a bone high-resolution scaffold prototype using these techniques is described. The results testify to the fidelity existing between microtomographic reconstruction and CAD. Furthermore, stereolithographic manufacturing of this scaffold, which possesses a high degree of similarity to the starting model as monitored by morphological evaluations (mean diameter 569 +/- 147 microm), represents a promising result for regenerative medicine applications.

Bone Substitutes↗
PubMed2004

Non-alcoholic fatty liver and insulin resistance: a cause-effect relationship?

The role of insulin resistance in non-alcoholic fatty liver disease is suggested by laboratory data (hyperinsulinemia and decreased sensitivity to endogenous and exogenous insulin). The clinical association with features of the metabolic syndrome, particularly in the most aggressive stages of the disease, further confirms a causative role. Fat accumulation in the liver may stem either from genetic defects, primarily responsible for insulin resistance, or excessive calorie intake and visceral obesity, and is mediated by adipocytokines (leptin, adiponectin, tumour necrosis factor-alpha). Progression of fatty liver to steatohepatitis may be the result of an imbalance between pro-inflammatory and anti-inflammatory cytokines, triggering the formation of reactive oxygen species and intrahepatic lipid peroxidation. This process may also be promoted or accelerated by pro-oxidant xenobiotics or environmental factors. Insulin resistance provides a target for specific treatment of non-alcoholic fatty liver, and insulin-sensitising agents (metformin or thiazolidinediones) as well as lifestyle changes to reduce visceral adiposity are the most promising therapeutic options. Future trials need to be performed in order to test the long-term effectiveness of these treatments on the basis of clinically relevant histological outcomes.

Adipose Tissue↗
PubMed2003

Computer simulations of hard pear-shaped particles.

We report results obtained from Monte Carlo simulations investigating mesophase formation in two model systems of hard pear-shaped particles. The first model considered is a hard variant of the truncated Stone-expansion model previously shown to form nematic and smectic mesophases when embedded within a 12-6 Gay-Berne-like potential [R. Berardi, M. Ricci, and C. Zannoni, ChemPhysChem 7, 443 (2001)]. When stripped of its attractive interactions, however, this system is found to lose its liquid crystalline phases. For particles of length to breadth ratio k=3, glassy behavior is seen at high pressures, whereas for k=5 several bi- layerlike domains are seen, with high intradomain order but little interdomain orientational correlation. For the second model, which uses a parametric shape parameter based on the generalized Gay-Berne formalism, results are presented for particles with elongation k=3, 4, and 5. Here, the systems with k=3 and 4 fail to display orientationally ordered phases, but the system with k=5 shows isotropic, nematic and, unusual for a hard-particle model, interdigitated smectic A2 phases.

Journal Article↗
PubMed2003

Structures and transitions in thin hybrid nematic films: a Monte Carlo study.

We confirm by Monte Carlo simulations of a Lebwohl-Lasher lattice spin model the existence of a biaxially ordered nonbent structure in a liquid-crystalline cell subject to opposing boundary conditions. We report on the observation of the bending transition from the biaxial to the bent-director structure when the temperature of the system is lowered. The structural transition is monitored both by the change of the order parameters and by heat capacity. We discuss the thickness dependence of the transition temperature by means of wetting-induced phenomena and elastic deformations. We propose the correspondence to the phenomenological description, which agrees well without any fitting parameters.

Journal Article↗
PubMed2003

Nematics with dispersed polymer fibrils: a Monte Carlo study of the external-field-induced switching.

We present a Monte Carlo study of molecular ordering in nematics with dispersed regular and random arrays of straight and distorted polymer fibrils. We focus on the collective molecular reorientation--the switching--resulting from the competing aligning effects of fibrils and of a progressively applied transversal external field, and for straight fibrils identify structural Fréedericksz and saturation transitions. The role of fibril topography in the switching is monitored by simulating electric capacitance Slightly distorted fibrils are shown to give a sharper switching at a lower threshold.

Journal Article↗
PubMed2002

Topological defects in schlieren textures of biaxial and uniaxial nematics.

Monte Carlo and theoretical studies of thin 3D films of biaxial and uniaxial nematics with tangential boundary conditions show distinct differences in structure and evolution of topological defects. In the uniaxial films, defects of strength k=+/-1 are point defects that bear no bulk singularity and disappear by annihilation with each other. In the biaxial films, k=+/-1 defects are true singular bulk disclinations that split into pairs of k=+/-1/2 lines; the latter disappear by annihilation processes of the type +1/2-1/2=0. These observed differences are of relevance for the current debate on the existence of biaxial phases.

Journal Article↗
PubMed2002

Nematics with quenched disorder: how long will it take to heal?

Nematics with quenched disorder have been repeatedly predicted to form glass phases. Here we present turbidity experiments and computer simulations aimed at studying glass key features such as dynamics and history dependence in randomly perturbed nematics. Electric field-cooling alignment has been employed to prepare samples in suitably oriented starting states. Remarkable remnant order and slow dynamics are found both by experiment and simulations, indicating that random disorder can, by itself, induce a nematic glass state even without perturber restructuring.

Journal Article↗
PubMed2002

Polymer network-induced ordering in a nematogenic liquid: a Monte Carlo study.

In this Monte Carlo study we investigate molecular ordering in a nematogenic liquid with dispersed polymer networks. The polymer network fibers are assumed to have rough surface morphology resulting in a partial randomness in anchoring conditions, while the fiber direction is assumed to be well defined. In particular, we focus on the loss of long-range aligning capability of the network when the degree of disorder in anchoring is increased. This process is monitored by calculating relevant order parameters and the corresponding 2H nuclear magnetic resonance spectra, showing that the aligning ability of the network is lost only for completely disordering anchoring conditions. Moreover, above the nematic-isotropic transition temperature surface-induced paranematic order is detected. In addition, for perfectly smooth fiber surfaces with homeotropic anchoring conditions topological line defects can be observed.

Journal Article↗
PubMed2001

HIDE: a new hybrid environment for the design of custom-made hip prosthesis.

This technical note describes a new software environment (HIPCOM design environment, HIDE) for the design of custom-made total hip replacements. These devices are frequently designed using general-purpose mechanical computer-aided design (CAD) programs using a set of bone contours extracted from the computer tomography (CT) images as anatomical reference. On the contrary, the HIDE system was developed to let the operator directly design the stem shape onto the CT images in a single-step operation. The operator can directly import CT data in DICOM format or use special functions to reconvert to a digital stack, the CT images printed on a radiological film. Once the stack of CT images is loaded, the operator can design the implant shape by imposing control sections directly on the CT images. The interpolation of these control sections produces the basic 3D shape of the custom-made stem. The shape is then exported to the CAD-computer-aided manufacturing (CAM) program to refine the design and to generate the part program to manufacture the implant with a CNC tooling machine. Using HIDE, the duration of design steps it affected was reduced by more than 50% with respect to the standard method in use at the manufacturer site. HIDE also improved the accuracy and the repeatability of the whole procedure. The learning curve became flat after only ten cases. These good results were achieved because of the integration of the vectorial description of the prosthetic component with the raster description of the CT data that allowed the designer to use all details available in the CT images.

Computer-Aided Design↗
PubMed2001

Border-tracing algorithm implementation for the femoral geometry reconstruction.

In some orthopaedic applications such as the design of custom-made hip prostheses, reconstruction of the bone morphology is a fundamental step. Different methods are available to extract the geometry of the femoral medullary canal from computed tomography (CT) images. In this research, an automatic procedure (border-tracing method) for the extraction of bone contours was implemented and validated. A composite replica of the human femur was scanned and the CT images processed using three different methods, a manual procedure; the border-tracing algorithm; and a threshold-based method. The resulting contours were used to estimate the accuracy of the implemented procedure. The two software techniques were more accurate than the manual procedure. Then, these two procedures were applied to an in vivo CT data set in order to determine to most critical region for repeatability. Only for the images located in this region, the repeatability measurement was carried out for six in vivo CT data sets to evaluate the inter-femur repeatability. The border-tracing method was found to achieve the highest repeatability.

Algorithms↗
PubMed2000

Nematics with quenched disorder: what is left when long range order Is disrupted?

It is now generally accepted that even low amounts of quenched disorder disrupt long-range order in anisotropic systems with continuous symmetry. However, very little is known on the key item of the nature of the residual order, if any, and particularly if this has quasi-long-range or truly-short-range character. Here we address this problem both experimentally for the nematic 6CB in dilute aerosils and with computer simulations. We find that the residual order is short ranged and scales with disorder density in agreement with the Imry-Ma argument.

Journal Article↗
PubMed2000

Dynamical and field effects in polymer-dispersed liquid crystals: monte carlo simulations of NMR spectra

We analyze the dynamical aspects of molecular ordering in nematic droplets with radial and bipolar boundary conditions-as encountered in polymer-dispersed liquid crystals-by calculating and interpreting the corresponding 2H NMR spectra. In particular, we focus on effects of molecular motion such as fluctuations of molecular long axes and translational diffusion, and on external field ordering effects. As in our previous paper [Phys. Rev. E 60, 4219 (1999)], where field effects were not considered, equilibrium configurations inside nematic droplets are obtained from Monte Carlo simulations of the Lebwohl-Lasher lattice spin model.

Journal Article↗