101 research outputs found
Multifunctional performance of carbon nanotubes and graphene nanoplatelets reinforced PEEK composites enabled via FFF additive manufacturing
The study is focused on multifunctional performance of carbon nanotubes (CNT) and Graphene nanoplatelets (GNP) reinforced PEEK composites enabled via fused filament fabrication (FFF) additive manufacturing (AM) utilizing in-house nanoengineered filaments. Thermo-physical, mechanical and wear characteristics of electro-conductive PEEK nanocomposites are reported. The coefficient of thermal expansion (CTE) is found to decrease by 26% and 18% with the incorporation of 5 wt% GNP and 3 wt% CNT into PEEK polymer, respectively. The decrease in CTE provides better dimensional stability to resulting nanocomposite structures. Due to uniform dispersion of CNT and GNP in the PEEK matrix, the crystallization temperature and degree of crystallinity are both increased. The 3D printed PEEK nanocomposites reveal interfacial voids between the beads and intra-bead pores and thus exhibit lower density compared to that of the 3D printed neat PEEK. Young's and storage moduli are found to increase by 20% and 66% for 3 wt% CNT loading and by 23% and 72% for 5 wt% GNP loading respectively. However, the PEEK nanocomposites exhibit similar tensile strength to that of neat PEEK. The coefficient of friction obtained from fretting wear tests is found to decrease by 67% and 56% for 1 wt% CNT and 3 wt% GNP loaded PEEK nanocomposites, respectively and the decrease is attributed to reduced hardness and increased porosity. Multifunctional performance of carbon nanostructures reinforced AM-enabled PEEK composites demonstrated here makes them suitable for a range of applications such as orthopedics, oil and gas, automotive, electronics and space
Average Lattice Symmetry and Nanoscale Structural Correlations in Magnetoresistive Manganites
We report x-ray scattering studies of nanoscale structural correlations in
the paramagnetic phases of the perovskite manganites
La(CaSr)MnO,
LaSrMnO, and NdSrMnO. We find
that these correlations are present in the orthorhombic phase in
La(CaSr)MnO, but they disappear
abruptly at the orthorhombic-to-rhombohedral transition in this compound. The
orthorhombic phase exhibits increased electrical resistivity and reduced
ferromagnetic coupling, in agreement with the association of the nanoscale
correlations with insulating regions. In contrast, the correlations were not
detected in the two other compounds, which exhibit rhombohedral and tetragonal
phases. Based on these results, as well as on previously published work, we
propose that the local structure of the paramagnetic phase correlates strongly
with the average lattice symmetry, and that the nanoscale correlations are an
important factor distinguishing the insulating and the metallic phases in these
compounds.Comment: a note on recent experimental work, and a new reference adde
Decay of Classical Chaotic Systems - the Case of the Bunimovich Stadium
The escape of an ensemble of particles from the Bunimovich stadium via a
small hole has been studied numerically. The decay probability starts out
exponentially but has an algebraic tail. The weight of the algebraic decay
tends to zero for vanishing hole size. This behaviour is explained by the slow
transport of the particles close to the marginally stable bouncing ball orbits.
It is contrasted with the decay function of the corresponding quantum system.Comment: 16 pages, RevTex, 3 figures are available upon request from
[email protected], to be published in Phys.Rev.
Modelling of strain effects in manganite films
Thickness dependence and strain effects in films of
perovskites are analyzed in the colossal magnetoresistance regime. The
calculations are based on a generalization of a variational approach previously
proposed for the study of manganite bulk. It is found that a reduction in the
thickness of the film causes a decrease of critical temperature and
magnetization, and an increase of resistivity at low temperatures. The strain
is introduced through the modifications of in-plane and out-of-plane electron
hopping amplitudes due to substrate-induced distortions of the film unit cell.
The strain effects on the transition temperature and transport properties are
in good agreement with experimental data only if the dependence of the hopping
matrix elements on the bond angle is properly taken into account.
Finally variations of the electron-phonon coupling linked to the presence of
strain turn out important in influencing the balance of coexisting phases in
the filmComment: 7 figures. To be published on Physical Review
Resultant pressure distribution pattern along the basilar membrane in the spiral shaped cochlea
Cochlea is an important auditory organ in the inner ear. In most mammals, it
is coiled as a spiral. Whether this specific shape influences hearing is still
an open problem. By employing a three dimensional fluid model of the cochlea
with an idealized geometry, the influence of the spiral geometry of the cochlea
is examined. We obtain solutions of the model through a conformal
transformation in a long-wave approximation. Our results show that the net
pressure acting on the basilar membrane is not uniform along its spanwise
direction. Also, it is shown that the location of the maximum of the spanwise
pressure difference in the axial direction has a mode dependence. In the
simplest pattern, the present result is consistent with the previous theory
based on the WKB-like approximation [D. Manoussaki, Phys. Rev. Lett. 96,
088701(2006)]. In this mode, the pressure difference in the spanwise direction
is a monotonic function of the distance from the apex and the normal velocity
across the channel width is zero. Thus in the lowest order approximation, we
can neglect the existance of the Reissner's membrane in the upper channel.
However, higher responsive modes show different behavior and, thus, the real
maximum is expected to be located not exactly at the apex, but at a position
determined by the spiral geometry of the cochlea and the width of the cochlear
duct. In these modes, the spanwise normal velocities are not zero. Thus, it
indicates that one should take into account of the detailed geometry of the
cochlear duct for a more quantitative result. The present result clearly
demonstrates that not only the spiral geometry, but also the geometry of the
cochlear duct play decisive roles in distributing the wave energy.Comment: 21 pages. (to appear in J. Biol. Phys.
Histological Alterations Found in the Ureter During Organ Preservation and Early Phases of Renal Transplantation
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
School-based prevention for adolescent Internet addiction: prevention is the key. A systematic literature review
Adolescents’ media use represents a normative need for information, communication, recreation and functionality, yet problematic Internet use has increased. Given the arguably alarming prevalence rates worldwide and the increasingly problematic use of gaming and social media, the need for an integration of prevention efforts appears to be timely. The aim of this systematic literature review is (i) to identify school-based prevention programmes or protocols for Internet Addiction targeting adolescents within the school context and to examine the programmes’ effectiveness, and (ii) to highlight strengths, limitations, and best practices to inform the design of new initiatives, by capitalizing on these studies’ recommendations. The findings of the reviewed studies to date presented mixed outcomes and are in need of further empirical evidence. The current review identified the following needs to be addressed in future designs to: (i) define the clinical status of Internet Addiction more precisely, (ii) use more current psychometrically robust assessment tools for the measurement of effectiveness (based on the most recent empirical developments), (iii) reconsider the main outcome of Internet time reduction as it appears to be problematic, (iv) build methodologically sound evidence-based prevention programmes, (v) focus on skill enhancement and the use of protective and harm-reducing factors, and (vi) include IA as one of the risk behaviours in multi-risk behaviour interventions. These appear to be crucial factors in addressing future research designs and the formulation of new prevention initiatives. Validated findings could then inform promising strategies for IA and gaming prevention in public policy and education
Cytokine gene expression and molecular detection of Mycobacterium avium subspecies paratuberculosisin organs of experimentally infected mice
Plantas e constituintes químicos empregados em Odontologia: revisão de estudos etnofarmacológicos e de avaliação da atividade antimicrobiana in vitro em patógenos orais
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