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Biomedical subjects

A Fasolino

Publications and source records attributed to A Fasolino.

At least 19 recordsLinked to original sources
PubMed2007

Quantum surface diffusion of vibrationally excited molecular dimers.

We consider the thermally activated quantum diffusion of a molecular dimer in a periodic surface potential by means of a time-dependent wave packet method. We show that the potential energy surface resulting from the interplay of intradimer and dimer-surface interactions can lead to resonant states and predict high tunneling probabilities at specific, below barrier, energies that depend also on the initial vibrational state of the dimer. For soft molecular bonds, we show that the chaotic dynamical regime of classical dimers is mirrored, in the quantum case, by the tunneling induced mixing of vibrational states. The knowledge of the transmission coefficient is used to formulate an approximate description of quantum thermal diffusion by defining an effective temperature-dependent activation energy that can be compared to the classical case.

Journal Article↗
PubMed2006

Logarithmic relaxation due to minimization of interactions in the Burridge-Knopoff model.

The time evolution of macroscopic quantities describing the relaxation of complex systems often contains a domain with logarithmic time dependence. This logarithmic behavior at the macroscopic level is often associated with strongly interacting elements at the microscopic level, whose interactions depend significantly on their history. In this paper we show that stress relaxation in the Burridge-Knopoff (BK) model of multicontact friction behaves logarithmically, when the model is in, or close to, the solitary state where the elements move independently. For this regime we present an automaton that allows us to follow the decay of stress relaxation over the entire range where it behaves logarithmically in time. We show that our model can be mapped onto a system of noninteracting elements subject to a uniform distribution of forces, for which logarithmic stress relaxation is derived analytically.

Journal Article↗
PubMed2006

Solvent-driven formation of bolaamphiphilic vesicles.

We show that a spontaneous bending of single-layer bolaamphiphiles results from the frustration due to the competition between core-core and tail-solvent interactions. We find that spherical vesicles are stable under rather general assumptions on these interactions described within the Flory-Huggins theory. We consider also the deformation of the vesicles in an external magnetic field that has been recently experimentally observed.

Magnetics↗
PubMed2005

Transition to strictly solitary motion in the Burridge-Knopoff model of multicontact friction.

We show that, in the continuous 1D Burridge-Knopoff model of multicontact friction, motion occurs via stick-slip sliding on a finite length rather than in avalanches, excluding the occurrence of self-organized criticality. We present strong numerical evidence that a transition from collective to strictly solitary motion occurs at a critical value of the interblock interactions. The solitary motion corresponds to successive stick-slip motion of one block between immobile neighbors, repeated periodically in time. This state persists also with open boundary conditions and moderate temperature.

Journal Article↗
PubMed2005

Modeling the phase diagram of carbon.

We determined the phase diagram involving diamond, graphite, and liquid carbon using a recently developed semiempirical potential. Using accurate free-energy calculations, we computed the solid-solid and solid-liquid phase boundaries for pressures and temperatures up to 400 GPa and 12 000 K, respectively. The graphite-diamond transition line that we computed is in good agreement with experimental data, confirming the accuracy of the employed empirical potential. On the basis of the computed slope of the graphite melting line, we rule out the hotly debated liquid-liquid phase transition of carbon. Our simulations allow us to give accurate estimates of the location of the diamond melting curve and of the graphite-diamond-liquid triple point.

Journal Article↗
PubMed2004

Recombinant human LH supplementation versus recombinant human FSH (rFSH) step-up protocol during controlled ovarian stimulation in normogonadotrophic women with initial inadequate ovarian response to rFSH. A multicentre, prospective, randomized controlled trial.

BACKGROUND: In approximately 12-14% of young normogonadotrophic women treated with a depot GnRH agonist long protocol, the initial ovarian response to recombinant human FSH (rFSH) can be suboptimal. We have tested the hypothesis that these women may benefit from recombinant human LH (rLH) supplementation in a multicentre, prospective, randomized trial compared with patients treated with an rFSH step-up protocol. METHODS: A total of 260 young normogonadotrophic women undergoing controlled ovarian stimulation with a GnRH agonist long protocol for IVF/ICSI were enrolled. The starting dose of rFSH was 225 IU. One hundred and thirty patients with serum estradiol levels <180 pg/ml and with at least six follicles with a mean diameter >5 mm but none >10 mm on both day 5 and day 8 of stimulation were randomly allocated to two groups. From the eighth day of stimulation, women in group A (n=65) received 150 IU of rLH in addition to rFSH, while those in group B (n=65) had an increase of 150 IU in the daily dose of rFSH (step-up protocol). One hundred and thirty normally responding women continued monotherapy with rFSH and served as a further control population (group C). RESULTS: The mean number of cumulus-oocyte complexes retrieved in group A (9.0+/-4.3) was significantly higher (P<0.01) compared with group B (rFSH 6.1+/-2.6) but significantly lower compared with group C (10.49+/-3.7, P<0.05). Implantation and pregnancy rates were significantly lower (P<0.05) in the rFSH step-up group (10.5 and 29.3% respectively) when compared with normal responders (18.1 and 47.3% respectively). CONCLUSIONS: rLH supplementation is more effective than increasing the dose of rFSH in terms of ovarian outcome in patients with an initial inadequate ovarian response to rFSH alone.

Adolescent↗
PubMed2003

[Laparoscopic conservative treatment of ovarian dermoid cysts].

Two methods for the laparoscopic dissection of dermoid ovarian cysts, less than 10 cm, in 55 fertile women, are compared. Water dissection was performed in 23 patients and bipolar scissors were used in 32 patients, creating a rhomb on the surface of the ovary, just to obtain a good traction for atraumatic dissection. The mean surgical time, complications and hospital stay have been compared. Operative laparoscopy is the technique of choice to remove most, if not all, ovarian dermoid cysts. It is suggested to use particular strategies in order to safely and easily dissect in toto the cysts.

Adolescent↗
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↗