Biomedical subjects

A Parola

Publications and source records attributed to A Parola.

At least 19 recordsLinked to original sources

PubMed2006

Dynamical arrest and replica symmetry breaking in attractive colloids.

Within the replica symmetry breaking framework developed by Mézard and Parisi we investigate the occurrence of structural glass transitions in a model of fluid characterized by hard sphere repulsion together with short-range attraction. This model is appropriate for the description of a class of colloidal suspensions. The transition line in the density-temperature plane displays a reentrant behavior, in agreement with mode coupling theory and recent molecular dynamics simulations. Quantitative differences are found, together with the absence of the predicted glass-glass transition at high density. We also perform a systematic study of the pure hard-sphere fluid in order to ascertain the accuracy of the adopted method and the convergence of the numerical procedure.

Journal Article↗

PubMed2004

Microscopic approach to critical phenomena at interfaces: an application to complete wetting in the Ising model.

We study how the formalism of the hierarchical reference theory (HRT) can be extended to inhomogeneous systems. HRT is a liquid-state theory which implements the basic ideas of the Wilson momentum-shell renormalization group (RG) to microscopic Hamiltonians. In the case of homogeneous systems, HRT provides accurate results even in the critical region, where it reproduces scaling and nonclassical critical exponents. We applied the HRT to study wetting critical phenomena in a planar geometry. Our formalism avoids the explicit definition of effective surface Hamiltonians but leads, close to the wetting transition, to the same renormalization group equation already studied by RG techiques. However, HRT also provides information on the nonuniversal quantities because it does not require any preliminary coarse graining procedure. A simple approximation to the infinite HRT set of equations is discussed. The HRT evolution equation for the surface free energy is numerically integrated in a semi-infinite three-dimensional Ising model and the complete wetting phase transition is analyzed. A renormalization of the adsorption critical amplitude and of the wetting parameter is observed. Our results are compared to available Monte Carlo simulations.

Journal Article↗

PubMed2004

Particle thermophoresis in liquids.

We present a microscopic description of thermophoretic phenomena in dilute suspensions of spherical colloids. The specific particle/solvent interfacial interactions generate a force density field F on the surrounding fluid which in turn gives rise to an "effective force" on the colloid. In our approach, such a force turns out to be solely related to the non-conservative anisotropic contribution to F brought forth by the thermal gradient. By adopting a Smoluchowski picture of colloid motion, we find a general expression for the Soret coefficient S(T), which we apply to the specific cases of neutral colloids in pure solvent and of Debye-Hückel systems. For the latter, our result for S(T) agrees with those obtained by previous hydrodynamic approaches.

Journal Article↗

PubMed2003

Modulational instability and complex dynamics of confined matter-wave solitons.

We study the formation of bright solitons in a Bose-Einstein condensate of 7Li atoms induced by a sudden change in the sign of the scattering length from positive to negative, as reported in a recent experiment [Nature (London) 417, 150 (2002)]]. The numerical simulations are performed by using the Gross-Pitaevskii equation with a dissipative three-body term. We show that a number of bright solitons is produced and this can be interpreted in terms of the modulational instability of the time-dependent macroscopic wave function of the Bose condensate. In particular, we derive a simple formula for the number of solitons that is in good agreement with the numerical results. We find that during the motion of the soliton train in an axial harmonic potential the number of solitonic peaks changes in time and the density of individual peaks shows an intermittent behavior.

Journal Article↗

PubMed2003

Phase diagram of symmetric binary mixtures at equimolar and nonequimolar concentrations: a systematic investigation.

We consider symmetric binary mixtures consisting of spherical particles with equal diameters interacting via a hard-core plus attractive tail potential with strengths epsilon(ij), i,j=1,2, such that epsilon(11)=epsilon(22)>epsilon(12). The phase diagram of the system at all densities and concentrations is investigated as a function of the unlike-to-like interaction ratio delta=epsilon(12)/epsilon(11) by means of the hierarchical reference theory. The results are related to those of previous investigations performed at equimolar concentration, as well as to the topology of the mean-field critical lines. As delta is increased in the interval 0<delta<1, we find first a regime where the phase diagram at equal species concentration displays a tricritical point, then one where both a tricritical and a liquid-vapor critical point are present. We did not find any clear evidence of the critical end point topology predicted by mean-field theory as delta approaches 1, at least up to delta=0.8, which is the largest value of delta investigated here. Particular attention was paid to the description of the critical-plus-tricritical point regime in the whole density-concentration plane. In this situation, the phase diagram shows, in a certain temperature interval, a coexistence region that encloses an island of homogeneous, one-phase fluid.

Journal Article↗

PubMed2002

Hierarchical reference theory study of the lattice restricted primitive model.

A three dimensional model of point charges, named lattice restricted primitive model (LRPM), is investigated by using the hierachical reference theory of fluids. This approach, which generalizes the momentum renormalization group technique, is shown to capture the physics of the model and provides a quantitative description of the phase diagram. The comparison with recent numerical simulations and with other theoretical approaches is discussed both for the LRPM and for the Blume-Capel model, which can be seen as a screened version of LRPM. The nonuniversal crossover region close to the tricritical point is also discussed.

Journal Article↗

PubMed2002

Superconductivity in the two-dimensional t-J model.

Using computational techniques, it is shown that pairing is a robust property of hole-doped antiferromagnetic insulators. In one dimension and for two-leg ladder systems, a BCS-like variational wave function with long-bond spin singlets and a Jastrow factor provides an accurate representation of the ground state of the t-J model, even though strong quantum fluctuations destroy the off-diagonal superconducting long-range order in this case. However, in two dimensions it is argued-and numerically confirmed using several techniques, especially quantum Monte Carlo-that quantum fluctuations are not strong enough to suppress superconductivity.

Journal Article↗

PubMed2001

Resonating valence bond wave functions for strongly frustrated spin systems.

The resonating-valence-bond (RVB) theory for two-dimensional quantum antiferromagnets is shown to be the correct paradigm for large enough "quantum frustration." This scenario, proposed a long time ago but never confirmed by microscopic calculations, is strongly supported by a new type of variational wave function, which is extremely close to the exact ground state of the J(1)-J(2) Heisenberg model for 0.4 less than approximately J(2)/J(1) less than approximately 0.5. This wave function is proposed to represent the generic spin-half RVB ground state in spin liquids.

Journal Article↗

PubMed2001

Construction of an effective Hamiltonian for a three-dimensional Ising universality class.

The asymptotic and preasymptotic critical behavior in fluids, mixtures, and uniaxial magnets is believed to be described by an effective straight phi(4) scalar field theory with suitable, nonuniversal, coupling constants. The critical parameters as well as the extent of crossovers and corrections to the leading critical behavior in physical systems, crucially depends on the choice of these couplings. Here we propose a new method for deriving the effective scalar field theory appropriate to a microscopic model in this universality class. Use is made of the hierarchical reference theory, which implements the basic ideas of Wilson momentum space renormalization group to microscopic Hamiltonians. The effective low-energy field theory is then analyzed by the minimal subtraction scheme of Schloms and Dohm. We discuss the application of this method to the three-dimensional Ising model and to the liquid-vapor phase transition. We make comparison with high-temperature expansion results and with experimental data for rare gas.

Journal Article↗

PubMed2001

Frequency and mortality of acute lung injury and acute respiratory distress syndrome after pulmonary resection for bronchogenic carcinoma.

OBJECTIVE: We reviewed the frequency and mortality of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) in our population of patients submitted to pulmonary resection for primary bronchogenic carcinoma. METHODS: From January 1993 to December 1999, a total of 1221 patients received pulmonary resection for primary bronchogenic carcinoma. Of these, 27 met the criteria of post-operative ALI/ARDS. There were 24 men and three women with a mean age of 64 years (range 45--79). Pre-operatively, predicted mean of PaO(2), PaCO(2) and %FEV1 were 72 mmHg (57--86), 37 mmHg (33--42) and 80% (37--114), respectively. Associated cardiac risk factors were present in eight patients. Three patients (11%) had pre-operative radiotherapy. Surgical-pathologic staging included 14 patients at Stage I, 8 patients at Stage II, four patients at Stage IIIa and one patient at Stage IIIb. RESULTS: ALI/ARDS occurred in 2.2% of our operated lung cancer patients. ALI was diagnosed in 10 patients and ARDS in 17 patients. The mean time of presentation following surgery was 4 days (range 1--10) and 6 days (1--13) for ALI and ARDS, respectively. According to the type of operation, the frequency was highest following right pneumonectomy (4.5%), followed by sublobar resection (3.2%), left pneumonectomy (3%), bilobectomy (2.4%), and lobectomy (2%). The frequency following extended operations was 4%. No differences were found between the ALI/ARDS group and the total population of resected lung cancer patients (control group) with respect to sex, mean age, pre-operative blood gases, %FEV1, surgical--pathologic staging and the use of pre-operative radiotherapy. Four patients with ALI (40%) and 10 patients with ARDS (59%) died. Mortality was highest following right pneumonectomy, extended operations and sublobar resections. Hospital mortality of the total population of operated lung cancer patients in the same period was 2.8% (34 patients). ALI/ARDS accounted for 41% of our hospital mortality. CONCLUSIONS: (1) ALI/ARDS is a severe complication following resection for primary bronchogenic carcinoma. (2) We did not detect any significant difference between the ALI/ARDS group and the control group regarding age, pre-operative lung function, staging and pre-operative radiotherapy. (3) ALI/ARDS is associated with high mortality, the highest mortality rates having been observed following right pneumonectomy and extended operation; it currently represents our leading cause of death following pulmonary resection for lung carcinoma. (4) ALI/ARDS may also occur after sublobar resections with an associated high mortality rate.

Carcinoma, Bronchogenic↗

PubMed2001

Fungal infections in lung transplantation. Incidence, risk factors and prognostic significance.

BACKGROUND AND AIM OF THE WORK: Fungal infections are frequent following lung transplantation and are associated with high mortality and morbidity. The study aims at 1) reporting our experience with fungal infections after lung transplantation; 2) identifying statistically significant correlations between the occurrence of fungal infections and bacterial infections, cytomegalovirus disease, rejection and steroid therapy; 3) assessing whether the presence of fungal infection has an impact on long-term survival. METHODS: 60 lung transplant recipients were studied with respect to incidence, pattern of presentation and median time to presentation of fungal infection after the transplant. Correlation analysis of the variables of interest was undertaken in 30 patients who had a minimum follow-up of 1 year following transplant. RESULTS: The prevalence of fungal infection was 44%; severe infections occurred in 5 patients (11%). The presence of Candida preoperatively was not associated with an increased risk of fungal infection. In a logistic regression analysis, a significant correlation was found between the occurrence of fungal infection and the following variables: respiratory bacterial infections (p = 0.0003), cytomegalovirus disease (p = 0.00001) and steroid therapy (p = 0.04). No statistically significant difference was found between patients who experienced a fungal infection and those who did not, either in univariate or multivariate survival analysis (p = 0.08). CONCLUSIONS: 1) fungal infections are frequent in lung transplant recipients and may be severe in more than 10% of the cases; 2) the presence of fungi preoperatively is not a contraindication to transplantation: an antifungal prophylaxis is probably indicated in such cases postoperatively; we recommend the use of the less nephrotoxic liposomal Amphotericin B by aerosol route; 3) a statistically significant association exists between fungal infections and both steroid therapy and CMV disease; this suggests that a similar antifungal prophylaxis is indicated in these clinical circumstances; 4) the presence of fungal infection is not an independent prognostic factor of long-term survival.

Adolescent↗

PubMed1999

The seagull wing self retaining prosthesis in the surgical treatment of pectus excavatum.

BACKGROUND: Between June 1958 and June 1996 we operated many patients affected by pectus excavatum with an original surgical technique. In this study we evaluated the durability of the results. METHODS EXPERIMENTAL DESIGN: Retrospective study with a mean follow-up time of 15.8 years/pt, and 60% complete. SETTING: private and institutional practice. PATIENTS OR PARTICIPANTS: 357 patients (253 males and 104 females, mean age = 18.2+/-5.1 years) affected by pectus excavatum. The grade of PE (Chin classification) was I in 76 patients, II in 165 and III in the remaining 116. Most of the patients required operation for aesthetic reasons only (339 patients; 95%). INTERVENTION: the surgical technique consisted of a double transversal sternotomy at the level of the lowest and highest part of the depression associated with a longitudinal sternotomy. A wedge resection of the ribs was then performed and the sternum was fixed using an original stainless steel strut prosthesis moulded into a seagull wing. The strut was removed 12 months postimplantation. RESULTS: There were no operative deaths. Four patients (1.2%) had sternal wound infection, which was successfully treated. From the aesthetic point of view, the postoperative results were excellent in 262 patients (73.4%), good in 82 (22.9%) and poor in 13 (3.6%). All subjective symptoms, when present, disappeared after surgery. CONCLUSIONS: The seagull wing prosthesis appears to be safe, easy to implant and to remove, and comfortable for the patient. This technique has shown good long-term results independently of type of deformity and patient age.

Adolescent↗

PubMed1999

Resection for bronchogenic carcinoma in the elderly.

BACKGROUND: The aim of this report was to assess postoperative complications, mortality and long term survival of surgical therapy for non small cell lung cancer in patients aged 70 years or more. Results and the significance of various prognostic factors were analysed. METHODS: At Thoracic Surgery Department of Torino, from January 1980 to December 1997, 258 patients aged 70 years or more were operated on for lung cancer. For the first 11 years of the series, more restrictive selection criteria were adopted (clinical stage I or II lung cancer, absence of major concomitant disease or previous malignancy in the last 5 years); 60 patients were operated in this period. After 1990, such criteria were no longer considered mandatory; since then 198 patients have been operated. Clinical data are reviewed in the search for predictors of mortality and morbidity and survival data are analysed. RESULTS: Overall postoperative mortality was 3.1% and morbidity was 39.1%. Pneumonectomy resulted in higher rate of mortality (9.1%, p 0.03). Complications proved to be more frequent in patients with concomitant disease (55.5%). Multivariate analysis on survival showed the importance of stage (5 years survival was 73.6% in stage I, 23% in stage II, 8.9% in stage IIIa) and type of selection (57% for the highly selected, 40% for the others). CONCLUSIONS: Selection criteria have the same impact on survival as stage in surgical treatment of lung cancer in the elderly. This factor should be analysed in series covering a long period of time. Low mortality and acceptable long term survival from this study confirmed that surgery is worthwhile in elderly patients.

Aged↗

PubMed1998