1,954 research outputs found
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 studentsâ 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 studentâs approach with the same kind of representation across the two topics.
Additionally, the participantsâ 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 ââqualitativeââ 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
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
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
The Upper Extremity Functional Index (UEFI). Cross-cultural adaptation, reliability, and validity of the italian version
SUMMARY
Introduction. The Italian version of the Upper Extremity Functional Index (UEFI) may
help assess shoulder function in patients with shoulder problems, especially athletes.
Objective. Translate and cross-culturally adapt UEFI into Italian; verify
UEFI validity and reliability in professional and amateur athletes
with upper limb musculoskeletal disorders, shoulder, in particular.
Methods. This study was conducted with 150 participants with musculoskeletal
disorders of the upper limb. UEFI, the short version of the Disability of the
Arm, Shoulder and Hand scale (Quick DASH), the Shoulder Pain and Disability
Index, and the Short Form-36 Health Survey (SF-36) were administered.
Acceptability was assessed in terms of refusal rate, rates of missing responses,
and administration time; test-retest reliability was assessed with intraclass
correlation coefficient (ICC); internal consistency was assessed with Cronbachâs
alpha coefficient, and validity was assessed by Pearsonâs correlation coefficients.
Results. Cronbachâs alpha coefficients for the UEFI on test and retest were
α = 0.979 and α = 0.985, respectively. The average measure ICC was 0.917.
The UEFI score demonstrated strong negative correlations with SPADI
total score (-0.636), Quick DASH score (-0.685), and SF-36 score (-0.327).
Conclusions. The Italian version of UEFI is acceptable, valid, and reliable
WS-PGRADE/gUSE in European Projects
Besides core project partners, the SCI-BUS project also supported several external user communities in developing and setting up customized science gateways. The focus was on large communities typically represented by other European research projects. However, smaller local efforts with the potential of generalizing the solution to wider communities were also supported. This chapter gives an overview of support activities related to user communities external to the SCI-BUS project. A generic overview of such activities is provided followed by the detailed description of three gateways developed in collaboration with European projects: the agINFRA Science Gateway for Workflows for agricultural research, the VERCE Science Gateway for seismology, and the DRIHM Science Gateway for weather research and forecasting
Assortativity Decreases the Robustness of Interdependent Networks
It was recently recognized that interdependencies among different networks
can play a crucial role in triggering cascading failures and hence system-wide
disasters. A recent model shows how pairs of interdependent networks can
exhibit an abrupt percolation transition as failures accumulate. We report on
the effects of topology on failure propagation for a model system consisting of
two interdependent networks. We find that the internal node correlations in
each of the two interdependent networks significantly changes the critical
density of failures that triggers the total disruption of the two-network
system. Specifically, we find that the assortativity (i.e. the likelihood of
nodes with similar degree to be connected) within a single network decreases
the robustness of the entire system. The results of this study on the influence
of assortativity may provide insights into ways of improving the robustness of
network architecture, and thus enhances the level of protection of critical
infrastructures
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 27:512â520, 1968; Maroudas, Lubrication and wear in joints. Sector, London, 1969) and takes into account the fluid transport across the articular cartilage using Darcyâs 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 33:1415â1422, 2000). The analytical integration allows the closed form description of the synovial fluid film force and the calculation of the unsteady gap thickness
Non equilibrium effects in fragmentation
We study, using molecular dynamics techniques, how boundary conditions affect
the process of fragmentation of finite, highly excited, Lennard-Jones systems.
We analyze the behavior of the caloric curves (CC), the associated thermal
response functions (TRF) and cluster mass distributions for constrained and
unconstrained hot drops. It is shown that the resulting CC's for the
constrained case differ from the one in the unconstrained case, mainly in the
presence of a ``vapor branch''. This branch is absent in the free expanding
case even at high energies . This effect is traced to the role played by the
collective expansion motion. On the other hand, we found that the recently
proposed characteristic features of a first order phase transition taking place
in a finite isolated system, i.e. abnormally large kinetic energy fluctuations
and a negative branch in the TRF, are present for the constrained (dilute) as
well the unconstrained case. The microscopic origin of this behavior is also
analyzed.Comment: 21 pages, 11 figure
Spinodal decomposition of expanding nuclear matter and multifragmentation
Density fluctuations of expanding nuclear matter are studied within a
mean-field model in which fluctuations are generated by an external stochastic
field. Fluctuations develop about a mean one-body phase-space density
corresponding to a hydrodinamic motion that describes a slow expansion of the
system. A fluctuation-dissipation relation suitable for a uniformly expanding
medium is obtained and used to constrain the strength of the stochastic field.
The distribution of the liquid domains in the spinodal decomposition is
derived. Comparison of the related distribution of the fragment size with
experimental data on the nuclear multifragmentation is quite satisfactory.Comment: 19 RevTex4 pages, 6 eps figures, to appear in Phys. Rev.
Thermal and electromagnetic properties of 166-Er and 167-Er
The primary gamma-ray spectra of 166-Er and 167-Er are deduced from the
(3-He,alpha gamma) and (3-He,3-He' gamma) reaction, respectively, enabling a
simultaneous extraction of the level density and the gamma-ray strength
function. Entropy, temperature and heat capacity are deduced from the level
density within the micro-canonical and the canonical ensemble, displaying
signals of a phase-like transition from the pair-correlated ground state to an
uncorrelated state at Tc=0.5 MeV. The gamma-ray strength function displays a
bump around E-gamma=3 MeV, interpreted as the pygmy resonance.Comment: 21 pages including 2 tables and 11 figure
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