PubMed Health⌕ Search

Biomedical subjects

A Fasolino

Publications and source records attributed to A Fasolino.

At least 19 recordsLinked to original sources
PubMed2002

Microscopic two-dimensional lattice model of dimer granular compaction with friction.

We study by Monte Carlo simulation the compaction dynamics of hard dimers in two dimensions under the action of gravity, subjected to vertical and horizontal shaking, considering also the case in which a friction force acts for horizontal displacements of the dimers. These forces are modeled by introducing effective probabilities for all kinds of moves of the particles. We analyze the dynamics for different values of the time tau during which the shaking is applied to the system and for different intensities of the forces. It turns out that the density evolution in time follows a stretched exponential behavior if tau is not very large, while a power law tail develops for larger values of tau. Moreover, in the absence of friction, a critical value tau(*) exists, which signals the crossover between two different regimes: for tau tau(*) it reaches logarithmically a maximal saturation value. Such behavior smears out when a finite friction force is present. In this situation the dynamics is slower and lower asymptotic densities are attained. In particular, for significant friction forces, the final density decreases linearly with the friction coefficient. We also compare the frictionless single tap dynamics to the sequential tapping dynamics, observing in the latter case an inverse logarithmic behavior of the density evolution, as found in the experiments.

Journal Article↗
PubMed2002

One-dimensional scattering in K-hollandite: theory and experiment.

This work comprises calculations using the Frenkel-Kontorova and double-chain models, which led to new results explaining the experimental diffraction pattern of K-hollandite. The use of a deformable host chain and a Lennard-Jones-like interchain interaction gives the best results. From these calculations, it can also be concluded that the guest as well as the host are deformed and that the system is pinned. The inclusion of Debye-Waller factors as fitting parameters is also discussed, with the conclusion they should not be used in the case of the double-chain model.

Journal Article↗
PubMed2002

[Value and significance of cystoscopy during laparoscopic hysterectomy].

The purpose of our study is to identify the ureteral and vesical lesions that may occur in the course of total laparoscopic hysterectomy using intraoperative cystoscopy. After the patient has been placed in dorsolithotomic position, we used a Hourcabie manipulator, a 10 mm umbilical trochar and two 5-mm suprapubics. Total hysterectomy is carried out and after closing the vagina 5 ml of stain in a physiological solution are injected into the vein to carry out cystoscopy. Analysis refers to the first 120 patients from 1998 to 1999 treated with laparoscopic hysterectomy. No material or vesical intraoperative lesions were found in any of the patients with the exception of a vesical lesion which was sutured during laparoscopy. Even with the cystoscopic finding normal, 2 fistulas were observed 20 and 25 days after the operation, so the negativity of the cystoscopy excludes certainly immediate complications but not late ones. Furthermore, not all surgeons carry out intraoperative cystoscopy, so the data available are scanty.

Cystoscopy↗
PubMed2002

[The use of Foley's catheter and suturing to control abdominal wall haemorrhage provoked by the trochar. Comparative study].

Lesions of the abdominal vessels are becoming more frequent owing to the increase in the number of laparoscopies carried out with trochars: they occur in fact in 2% of cases. A study has been carried out to compare the effectiveness of 2 methods for stopping haemorrhage: the use of a Foley catheter and suturing with a Reverdin needle. Abdominal haemorrhages take place as a result of lesions during introduction of accessory trochars in the superficial, circumflex and deep epigastric vessels. Six patients were treated with Foley's catheter while 13 were treated with Reverdin's needle under visual control, maintaining the same operative route, something that is not possible with the Foley catheter. Patients treated with suturing were discharged within 24 hours without irritation or pain.

Abdominal Wall↗
PubMed2001

Breakdown of a conservation law in incommensurate systems.

We show that invariance properties of the Lagrangian of an incommensurate system, as described by the Frenkel-Kontorova model, imply the existence of a generalized angular momentum that is an integral of motion if the system remains floating. The behavior of this quantity can therefore monitor the character of the system as floating (when it is conserved) or locked (when it is not). We find that, during the dynamics, the nonlinear couplings of our model cause parametric phonon excitations that lead to the appearance of Umklapp terms and to a sudden deviation of the generalized momentum from a constant value, signaling a dynamical transition from a floating to a pinned state. We point out that this transition is related but does not coincide with the onset of sliding friction, which can take place when the system is still floating.

Journal Article↗
PubMed2001

[Evaluation of oocyte maturity in patients undergoing ICSI and R-FSH treatment].

BACKGROUND: This study compares embryo quality, fertilisation rate and pregnancy rates after ICSI related with the quality of oocytes achieved after r-FSH stimulation. METHODS: We evaluated 955 oocytes from patients following r-FSH and 643 oocytes from patients stimulated with ultrapure urinary FSH. The oocytes were divided into: a) normal oocytes; b) ooctyes with extra cytoplasmatic abnormalities (dark zona pellucida, wide perivitelline space); c) oocytes with cytoplasmatic abnormalities (dark cytoplasm, granular cytoplasm, retractile body), d) oocytes with shape abnormalities; e) oocytes with double abnormalities; f) oocytes with triple abnormalities. The embryos were divided into: A) even and homogeneous blastomeres without fragmentation; B) even and homogeneous blastomeres with <20% fragmentation; C) uneven and non-homogeneous blastomeres with 20-50% fragmentation; D) uneven and non homogeneous blastomere with >50% fragmentation. RESULTS: 40.9% of oocytes from patients treated with r-FSH have a normal morphology vs 35.2% of control groups (p<0.04). Abnormalities have a similar frequency in the two groups, except for the presence of three combined abnormalities (7.7 vs 5.4%; p<0.04). Fertilisation rate, cleavage rate, oocyte quality and pregnancy rate do not appear to be influenced by oocyte morphology and the type of FSH used for stimulation. CONCLUSIONS: The administration of r-FSH allows a large number of oocytes to be rescued, with a high incidence of normal morphology. The fertilisation rate and the quality of embryos obtained from oocytes with structural abnormalities are similar to those observed in morphologically normal oocytes. Even the probability of pregnancy is similar in the two groups.

Adult↗
PubMed2001

[Extraumbilical insertion of the laparoscope in abdominal adhesion].

Palmer s point must be considered a safe alternative site to insert the Verres needle and the primary trocar. It s possible, also, to perform adhesiolysis by this way before to insert the bigger trocar in umbilical site. Our experience shows that this technique can avoid intestinal, omental, injury if the trocar was inserted directly using the umbilical site: that in patients with previous surgery.

Abdomen↗
PubMed2000

Spontaneous formation and stability of small GaP fullerenes

We report the spontaneous formation of a GaP fullerene cage in ab initio molecular dynamics simulations starting from a bulk fragment. A systematic study of the geometric and electronic properties of neutral and ionized GaP clusters suggests the stability of heterofullerenes formed by a compound with zinc blende bulk structure. We find that GaP fullerenes up to 28 atoms have high symmetry, closed electronic shells, large highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps, and do not dissociate when ionized. We compare our results for GaP with those obtained by other groups for the corresponding BN clusters.

Journal Article↗
PubMed2000

Onset of sliding friction in incommensurate systems

We study the dynamics of an incommensurate chain sliding on a periodic lattice, modeled by the Frenkel-Kontorova Hamiltonian with initial kinetic energy, without damping and driving terms. We show that the onset of friction is due to a novel type of dissipative parametric resonances, involving several resonant phonons which are driven by the (dissipationless) coupling of the center of mass motion to the phonons with the wave vector related to the modulating potential. We establish quantitative estimates for their existence in finite systems and point out the analogy with the induction phenomenon in Fermi-Ulam-Pasta lattices.

Journal Article↗