3,161 research outputs found
Neutral-cluster implantation in polymers by computer experiments
In this work we perform atomistic model potential molecular dynamics
simulations by means of state-of-the art force-fields to study the implantation
of a single Au nanocluster on a Polydimethylsiloxane substrate. All the
simulations have ben performed on realistic substrate models containing up to
4.6 millions of atoms having depths up to 90 nm and lateral dimensions up to 25
nm. We consider both entangled-melt and cross-linked Polydimethylsiloxane
amorphous structures. We show that even a single cluster impact on the
Polydimethylsiloxane substrate remarkably changes the polymer local temperature
and pressure. Moreover we observe the presence of craters created on the
polymer surface having lateral dimensions comparable to the cluster radius and
depths strongly dependent on the implantation energy. Present simulations
suggest that the substrate morphology is largely affected by the cluster impact
and that most-likely such modifications favor the the penetration of the next
impinging clusters
Dark Matter, Dark Energy and the solution of the strong CP problem
The strong CP problem was solved by Peccei & Quinn by introducing axions, a
viable candidate for Dark Matter (DM). Here the PQ approach is modified so to
yield also Dark Energy (DE). DM and DE arise, in fai proportions, from a single
scalar field, without tuning any extra parameter. In the present epoch, they
are weakly coupled. Fluctuations have a fair evolution. The model is also
fitted to the WMAP1 release, using a Markov Chain Monte Carlo technique, and
performs as well as CDM, coupled or uncoupled DE. Best--fit
cosmological parameters for different models are mostly within 2--
level. Here, the main peculiarity of the model is to favor high values of the
Hubble parameter.Comment: Proceeding of the workshop dsu2006, "The Dark Side of th Universe",
Madrid, June 20-24, 200
Surgical Strategy in Midline Tumours of the Anterior Cranial Fossa
Midline tumors of the anterior cranial fossa (ACF) are mostly represented by olfactory groove menigiomas (OGM). There are many different approaches to this complex anatomical area but only a few that allow from the beginning dural implant removal: purely endoscopic transnasal (EA), transcranial/transfrontal sinus (TFA), and combined EA-TFA (CA) approach. Despite the improvement of EA, the optimal treatment strategy for the surgical treatment of OGM is still a matter of debate. The most advocate advantages of the EA are the absence of cerebral retraction and the possibility to resect the dural implant of the tumor, thus reducing its vascularization. On the other hand, it presents several limits: an important sinonasal morbidity, the loss of olfaction as default, increased risk of postoperative CSF leakage (5-10% in referral centers), especially in anteriorly located tumors. Moreover, the EA is contraindicated in case of lateral (above the orbital floor) or anterior extension (posterior wall of frontal sinus), cerebral parenchima involvment, or in case of major nerves or artery encasement. Consequently, only little tumors extended to the tuberculum sellae or planum sphenoidalis could be safely resected through a purely EA. The TFA is performed by a bicoronal incision, creating a craniotomy on the anterior wall of the frontal sinus and drilling the posterior wall of the frontal sinus. It gives direct access to the dural attachment of the tumor and avoids any cerebral retraction. In case of bulky or far posterior tumors, the interhemispheric route is usually very effective. The TFA permits to remove OGM of any dimension, to deal with nerves of vessel encasement, and to respect meningohypophyseal arteries. The incidence of postoperative CSF leakage is minimal since the closure with the galea is of the utmost effectiveness (0% in our experience). In case of sinonasal involvement, a CA is usually preferred
The multimode covering location problem
In this paper we introduce the Multimode Covering Location Problem. This is a generalization of the Maximal Covering Location Problem that consists in locating a given number of facilities of different types with a limitation on the number of facilities sharing the same site. The problem is challenging and intrinsically much harder than its basic version. Nevertheless, it admits a constant factor approximation guarantee, which can be achieved combining two greedy algorithms. To improve the greedy solutions, we have developed a Variable Neighborhood Search approach, based on an exponential-size neighborhood. This algorithm computes good quality solutions in short computational time. The viability of the approach here proposed is also corroborated by a comparison with a Heuristic Concentration algorithm, which is presently the most effective approach to solve large instances of the Maximal Covering Location Problem
Sulla storia degli studi di frattura in Italia
History of studies of fracture is inherently intermingled with the history of technology developments.
In the beginning very little was written about. We must credit Leonardo and Galileo as the first
ones that wrote about the problem and on how to measure and foresee rupture loads. Later, nineteenth century
italian scientists distinguished themselves in attempting to establish material laws and multiple stresses
rupture criteria. A review of the works of past centuries italian scientists is presented, along with a critical
comparison with the work of other past european scientists
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