2,594 research outputs found
Scaling in the Lattice Gas Model
A good quality scaling of the cluster size distributions is obtained for the
Lattice Gas Model using the Fisher's ansatz for the scaling function. This
scaling identifies a pseudo-critical line in the phase diagram of the model
that spans the whole (subcritical to supercritical) density range. The
independent cluster hypothesis of the Fisher approach is shown to describe
correctly the thermodynamics of the lattice only far away from the critical
point.Comment: 4 pages, 3 figure
The Impact of R&D Offshoring on the Home Knowledge Production of OECD Investing Regions
This paper investigates the relationship between home and offshore R&D activities on the knowledge production of the investing home region. Debate is ongoing on whether R&D offshoring complements the R&D performed at home. In the light of increased offshoring of innovative activities to emerging countries, we explicitly focus on Brazil, Russia, India, China, Singapore and Taiwan. We suggest that complementarity should obtain, when home region and offshore R&D activities are dissimilar as well as when offshore R&D activities is about modular and less complex technologies. We ground our predictions on arguments related to geographical technological specialisation and reverse knowledge transfer from offshore locations to home regions within the more general open innovation trend. Using a theoretical framework based on the international business literature and the regional system of innovation perspective, we estimate a knowledge production function for a sample of 221 regions from 21 OECD countries with home region patent applications as the dependent variable. Our test supports our predictions on the complementarity between home region and offshore R&D.Home Region R&D; Offshore R&D; Knowledge Production; Complementarity; Emerging Countries
Isotopic composition of fragments in multifragmentation of very large nuclear systems: effects of the chemical equilibrium
Studies on the isospin of fragments resulting from the disassembly of highly
excited large thermal-like nuclear emitting sources, formed in the ^{197}Au +
^{197}Au reaction at 35 MeV/nucleon beam energy, are presented. Two different
decay systems (the quasiprojectile formed in midperipheral reactions and the
unique source coming from the incomplete fusion of projectile and target in the
most central collisions) were considered; these emitting sources have the same
initial N/Z ratio and excitation energy (E^* ~= 5--6 MeV/nucleon), but
different size. Their charge yields and isotopic content of the fragments show
different distributions. It is observed that the neutron content of
intermediate mass fragments increases with the size of the source. These
evidences are consistent with chemical equilibrium reached in the systems. This
fact is confirmed by the analysis with the statistical multifragmentation
model.Comment: 9 pages, 4 ps figure
Alkaline pretreatment of walnut shells increases pore surface hydrophilicity of derived biochars
The surface chemistry and morphology of biochars produced by pyrolysis of walnut shells affects their utility for adsorption applications. Yet, little is known about surface interactions in the pores of these materials, mostly due to the challenging nature of accessing information at this length scale in a non-destructive manner. Here, for the first time, the relative adsorption strengths of solvents comprising different functional groups to internal (pore) surfaces of walnut shells and derived biochars were investigated using low-field nuclear magnetic resonance (NMR) relaxation time measurements to non-destructively probe interactions of fluids with pore surfaces. Carbon bonding state compositions of these materials with respect to distance from the particle surface were determined using X-ray photoelectron spectroscopy coupled with ion beam etching. Alkaline pretreatment was found to increase the hydrophilicity of both walnut shells and derived biochars. It was found to increase surface interactions with hydroxyl groups, and to decrease those with methyl groups. Results were contextualised by thermogravimetric analysis, scanning electron microscopy, and previous in-situ X-ray imaging results. Taken together, results showed that alkaline pretreatment may be used to modulate responses to pyrolysis temperature of several factors that affect adsorption properties including surface hydrophilicity, particle size, porosity, pore accessibility, and surface texture
Attività preliminari per la caratterizzazione in termini di dose assorbita in acqua di una sorgente di radiazioni gamma del 60Co
Representational task formats and problem solving strategies in kinematics and work
Previous studies have reported that students employed different problem solving approaches when presented with the same task structured with different representations. In this study, we explored and compared students’ strategies as they attempted tasks from two topical areas, kinematics and work. Our participants were 19 engineering students taking a calculus-based physics course. The tasks were presented in linguistic, graphical, and symbolic forms and requested either a qualitative solution or a value. The analysis was both qualitative and quantitative in nature focusing principally on the characteristics
of the strategies employed as well as the underlying reasoning for their applications. A comparison was also made for the same student’s approach with the same kind of representation across the two topics.
Additionally, the participants’ overall strategies across the different tasks, in each topic, were considered. On the whole, we found that the students prefer manipulating equations irrespective of the representational format of the task. They rarely recognized the applicability of a ‘‘qualitative’’ approach to solve the
problem although they were aware of the concepts involved. Even when the students included visual representations in their solutions, they seldom used these representations in conjunction with the
mathematical part of the problem. Additionally, the students were not consistent in their approach for interpreting and solving problems with the same kind of representation across the two topical areas. The representational format, level of prior knowledge, and familiarity with a topic appeared to influence their
strategies, their written responses, and their ability to recognize qualitative ways to attempt a problem. The nature of the solution does not seem to impact the strategies employed to handle the problem
Statistical evolution of isotope composition of nuclear fragments
Calculations within the statistical multifragmentation model show that the
neutron content of intermediate mass fragments can increase in the region of
liquid-gas phase transition in finite nuclei. The model predicts also
inhomogeneous distributions of fragments and their isospin in the freeze-out
volume caused by an angular momentum and external long-range Coulomb field.
These effects can take place in peripheral nucleus-nucleus collisions at
intermediate energies and lead to neutron-rich isotopes produced in the
midrapidity kinematic region.Comment: 14 pages with 4 figures. GSI preprint, Darmstadt, 200
Misura della dose assorbita in acqua di una sorgente di radiazioni gamma del 60Co installata presso il Laboratorio Energia Nucleare Applicata dell’Università di Pavia
Effects of surface modifications on molecular diffusion in mesoporous catalytic materials
In this work, we use pulsed-field gradient (PFG) NMR to probe molecular diffusion of liquids inside
mesoporous structures and assess the influence of surface modifications, namely, deposition of
palladium (Pd) nanoparticles over alumina (Al2O3) surfaces and passivation of titania (TiO2) surfaces
with alkyl chains, on the diffusion pattern
Approximate Analytical Model for the Squeeze-Film Lubrication of the Human Ankle Joint with Synovial Fluid Filtrated by Articular Cartilage
The aim of this article is to propose an analytical approximate squeeze-film lubrication model of the human ankle joint for a quick assessment of the synovial pressure field and the load carrying due to the squeeze motion. The model starts from the theory of boosted lubrication for the human articular joints lubrication (Walker et al., Rheum Dis 27:512–520, 1968; Maroudas, Lubrication and wear in joints. Sector, London, 1969) and takes into account the fluid transport across the articular cartilage using Darcy’s equation to depict the synovial fluid motion through a porous cartilage matrix. The human ankle joint is assumed to be cylindrical enabling motion in the sagittal plane only. The proposed model is based on a modified Reynolds equation; its integration allows to obtain a quick assessment on the synovial pressure field showing a good agreement with those obtained numerically (Hlavacek, J Biomech 33:1415–1422, 2000). The analytical integration allows the closed form description of the synovial fluid film force and the calculation of the unsteady gap thickness
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