Biomedical subjects

Alberto Rosso

Publications and source records attributed to Alberto Rosso.

8 recordsLinked to original sources

PubMed2005

Nonequilibrium relaxation of an elastic string in a random potential.

We study the nonequilibrium motion of an elastic string in a two dimensional pinning landscape using Langevin dynamics simulations. The relaxation of a line, initially flat, is characterized by a growing length L(t) separating the equilibrated short length scales from the flat long distance geometry that keeps a memory of the initial condition. We show that, in the long time limit, L(t) has a nonalgebraic growth with a universal distribution function. The distribution function of waiting times is also calculated, and related to the previous distribution. The barrier distribution is narrow enough to justify arguments based on scaling of the typical barrier.

Journal Article↗

PubMed2005

Creep motion of an elastic string in a random potential.

We study the creep motion of an elastic string in a two-dimensional pinning landscape by means of Langevin dynamics simulations. We find that the velocity-force characteristics are well described by the creep formula predicted from phenomenological scaling arguments. We analyze the creep exponent mu and the roughness exponent zeta. Two regimes are identified: when the temperature is larger than the strength of the disorder, we find mu approximately 1/4 and zeta approximately 2/3, in agreement with the quasi-equilibrium-nucleation picture of creep motion; on the contrary, when lowering the temperature enough, the values of mu and zeta increase, showing a strong violation of the latter picture.

Journal Article↗

PubMed2004

Universal statistics of the critical depinning force of elastic systems in random media.

We study the rescaled probability distribution of the critical depinning force of an elastic system in a random medium. We put in evidence the underlying connection between the critical properties of the depinning transition and the extreme value statistics of correlated variables. The distribution is Gaussian for all periodic systems, while in the case of random manifolds there exists a family of universal functions ranging from the Gaussian to the Gumbel distribution. Both of these scenarios are a priori experimentally accessible in finite, macroscopic, disordered elastic systems.

Journal Article↗

PubMed2004

Width distribution of contact lines on a disordered substrate.

We have studied the roughness of a contact line on a disordered substrate by measuring its width distribution, which characterizes the roughness completely. The measured distribution is in excellent agreement with the distribution calculated in previous works, extended here to the case of open boundary conditions. This type of analysis, which is performed here on experimental data, provides a strong confirmation that the Joanny-de Gennes model is not sufficient to describe the dynamics of the contact line at the depinning threshold.

Journal Article↗

PubMed2003

Universal interface width distributions at the depinning threshold.

We compute the probability distribution of the interface width at the depinning threshold, using recent powerful algorithms. It confirms the universality classes found previously. In all cases, the distribution is surprisingly well approximated by a generalized Gaussian theory of independent modes which decay with a characteristic propagator G(q)=1/q(d+2zeta); zeta, the roughness exponent, is computed independently. A functional renormalization analysis explains this result and allows one to compute the small deviations, i.e., a universal kurtosis ratio, in agreement with numerics. We stress the importance of the Gaussian theory to interpret numerical data and experiments.

Journal Article↗

PubMed2003

Depinning of elastic manifolds.

We compute roughness exponents of elastic d-dimensional manifolds in (d+1)-dimensional embedding spaces at the depinning transition for d=1, em leader,4. Our numerical method is rigorously based on a Hamiltonian formulation; it allows us to determine the critical manifold in finite samples for an arbitrary convex elastic energy. For a harmonic elastic energy (Delta(2) model), we find values of the roughness exponent between the one-loop and two-loop functional renormalization group results, in good agreement with earlier cellular automaton simulations. We find that the Delta(2) model is unstable with respect both to slight stiffening and to weakening of the elastic potential. Anharmonic corrections to the elastic energy allow us to obtain the critical exponents of the quenched Kardar, Parisi, Zhang class.

Journal Article↗

PubMed2002

Lethal pulmonary complications significantly correlate with individually assessed mean lung dose in patients with hematologic malignancies treated with total body irradiation.

PURPOSE: To assess the impact of lung dose on lethal pulmonary complications (LPCs) in a single-center group of patients with hematologic malignancies treated with total body irradiation (TBI) in the conditioning regimen for bone marrow transplantation (BMT). METHODS: The mean lung dose of 101 TBI-conditioned patients was assessed by a thorough (1 SD around 2%) in vivo transit dosimetry technique. Fractionated TBI (10 Gy, 3.33 Gy/fraction, 1 fraction/d, 0.055 Gy/min) was delivered using a lateral-opposed beam technique with shielding of the lung by the arms. The median lung dose was 9.4 Gy (1 SD 0.8 Gy, range 7.8--11.4). The LPCs included idiopathic interstitial pneumonia (IIP) and non-idiopathic IP (non-IIP). RESULTS: Nine LPCs were observed. LPCs were observed in 2 (3.8%) of 52 patients in the group with a lung dose < or = 9.4 Gy and in 7 (14.3%) of 49 patients in the >9.4 Gy group. The 6-month LPC risk was 3.8% and 19.2% (p = 0.05), respectively. A multivariate analysis adjusted by the following variables: type of malignancy (acute leukemia, chronic leukemia, lymphoma, myeloma), type of BMT (allogeneic, autologous), cytomegalovirus infection, graft vs. host disease, and previously administered drugs (bleomycin, cytarabine, cyclophosphamide, nitrosoureas), revealed a significant and independent association between lung dose and LPC risk (p = 0.02; relative risk = 6.7). Of the variables analyzed, BMT type (p = 0.04; relative risk = 6.6) had a risk predictive role. CONCLUSION: The mean lung dose is an independent predictor of LPC risk in patients treated with the 3 x 3.33-Gy low-dose-rate TBI technique. Allogeneic BMT is associated with a higher risk of LPCs.

Adolescent↗

PubMed2002

Roughness at the depinning threshold for a long-range elastic string.

In this paper, we compute to high precision the roughness exponent zeta of a long-range elastic string, at the depinning threshold, in a random medium. Our numerical method exploits the analytic structure of the problem ("no-passing" theorem), but avoids direct simulation of the evolution equations. The roughness exponent has recently been studied by simulations, functional renormalization-group calculations, and by experiments (fracture of solids, liquid meniscus in 4He). Our result zeta=0.388 +/- 0.002 is significantly larger than what was stated in previous simulations, which were consistent with a one-loop renormalization-group calculation. Furthermore, the data are incompatible with the experimental results for crack propagation in solids and for a 4He contact line on a rough substrate. This implies that the experiments cannot be described by pure harmonic long-range elasticity in the quasistatic limit.

Journal Article↗