726 research outputs found
Van der Waals and resonance interactions between accelerated atoms in vacuum and the Unruh effect
We discuss different physical effects related to the uniform acceleration of
atoms in vacuum, in the framework of quantum electrodynamics. We first
investigate the van der Waals/Casimir-Polder dispersion and resonance
interactions between two uniformly accelerated atoms in vacuum. We show that
the atomic acceleration significantly affects the van der Waals force, yielding
a different scaling of the interaction with the interatomic distance and an
explicit time dependence of the interaction energy. We argue how these results
could allow for an indirect detection of the Unruh effect through dispersion
interactions between atoms. We then consider the resonance interaction between
two accelerated atoms, prepared in a correlated Bell-type state, and
interacting with the electromagnetic field in the vacuum state, separating
vacuum fluctuations and radiation reaction contributions, both in the
free-space and in the presence of a perfectly reflecting plate. We show that
nonthermal effects of acceleration manifest in the resonance interaction,
yielding a change of the distance dependence of the resonance interaction
energy. This suggests that the equivalence between temperature and acceleration
does not apply to all radiative properties of accelerated atoms. To further
explore this aspect, we evaluate the resonance interaction between two atoms in
non inertial motion in the coaccelerated (Rindler) frame and show that in this
case the assumption of an Unruh temperature for the field is not required for a
complete equivalence of locally inertial and coaccelerated points of views.Comment: 8 pages, Proceedings of the Eighth International Workshop DICE 2016
Spacetime - Matter - Quantum Mechanic
Bracket base remnants after orthodontic debonding
Objective: To evaluate whether the debonding procedure leads to restitutio ad integrum of the enamel surface by investigating the presence of enamel within the bracket base remnants after debonding. Materials and Methods: Sixty patients who completed orthodontic treatment with fixed appliances were included. A total of 1068 brackets were microphotographed; the brackets presenting some remnants on the base (n \u200a=\u200a 818) were selected and analyzed with ImageJ software to measure the remnant area. From this population a statistically significant sample (n \u200a=\u200a 100) was observed under a scanning electron microscope to check for the presence of enamel within the remnants. Energy dispersive x-ray spectrometry was also performed to obtain quantitative data. Results: Statistically significant differences in the remnant percentage between arches were observed for incisor and canine brackets (P < .0001 and P \u200a=\u200a .022, respectively). From a morphologic analysis of the scanning electron micrographs the bracket bases were categorized in 3 groups: group A, bases presenting a thin enamel coat (83%); group B, bases showing sizable enamel fragments (7%); group C, bases with no morphologic evidence of enamel presence (10%). Calcium presence was noted on all evaluated brackets under energy dispersive x-ray spectrometry. No significant difference was observed in the Ca/Si ratio between group A (16.21%) and group B (18.77%), whereas the Ca/Si ratio in group C (5.40%) was significantly lower than that of the other groups (P < .323 and P \u200a=\u200a .0001, respectively). Conclusion: The objective of an atraumatic debonding is not achieved yet; in some cases the damage could be clinically relevant
A transparent distributed ledger-based certificate revocation scheme for VANETs
The widespread adoption of Cooperative, Connected, and Automated Mobility (CCAM) applications requires the implementation of stringent security mechanisms to minimize the surface of cyber attacks. Authentication is an effective process for validating user identity in vehicular networks. However, authentication alone is not enough to prevent dangerous attack situations. Existing security mechanisms are not able to promptly revoke the credentials of misbehaving vehicles, thus tolerate malicious actors to remain trusted in the system for a long time. The resulting vulnerability window allows the implementation of complex attacks, thus posing a substantial impairment to the security of the vehicular ecosystem. In this paper we propose a Distributed Ledger-based Vehicular Revocation Scheme that improves the state of the art by providing a vulnerability window lower than 1 s, reducing well-behaved vehicles exposure to sophisticated and potentially dangerous attacks. The proposed scheme harnesses the advantages of the underlying Distributed Ledger Technology (DLT) to implement a privacy-aware revocation process while being fully transparent to all participating entities. Furthermore, it meets the critical message processing times defined by EU and US standards, thus closing a critical gap in the current international standards. Theoretical analysis and experimental validation demonstrate the effectiveness and efficiency of the proposed scheme, where DLT streamlines the revocation operation overhead and delivers an economically viable yet scalable solution against cyber attacks on vehicular systems
Engineering Design Education - Core Competencies
In the past, it was very common for students to come to the university to study engineering with basic design and build skills acquired through hands-on experiences acquired through play with friends, work on farms, work on cars and general tinkering. Engineering students were predominantly white males and eager to dive into design projects that could call upon skills in spatial reasoning, problem solving, working with others, and more. Currently, students who enter the university to study engineering are more diverse in race, gender, and background. The pervasiveness of computers, computer gaming, and social networking has also shifted the competencies of most incoming students. Many incoming students do not have the background and skills required to succeed in the design of solutions to engineering problems. This paper suggests there is a need to identify and better understand the basic set of core competencies that, if possessed by the student, would assure their success in the engineering education environment as well as in industry upon graduation. This paper identifies industry lists and critiques and academic efforts to catalogue core competencies and gives an example of one core competency, after being identified as being weak and remediated, showed dramatically improved student performance.This proceeding was published in the Proceedings of the 50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Paper No. AIAA 2012-1222, doi:10.2514/6.2012-1222. Posted with permission.</p
Building the capacity to solve complex health challenges in Sub-Saharan Africa : CARTAâs multidisciplinary PhD training
Objectives: To develop a curriculum (Joint Advanced Seminars- JAS) that produced PhD fellows who understood that health is an outcome of multiple determinants within complex environments and that approaches from a range of disciplines is required to address health and development within the Consortium for Advanced Research Training in Africa. We sought to attract PhD fellows, supervisors and teaching faculty from a range of disciplines into the program.
Methods: Multidisciplinary teams developed the JAS curriculum. CARTA PhD fellowships were open to academics in consortium member institutions, irrespective of primary discipline, interested in doing a PhD in public and population health. Supervisors and JAS faculty were recruited from CARTA institutions. We use routine JAS evaluation data (closed and open ended questions) collected from PhD fellows at every JAS, a survey of one CARTA cohort and an external evaluation of CARTA to assess the impact of the JAS curriculum on learning.
Results: We describe our pedagogic approach arguing its centrality to an appreciation of multiple disciplines and illustrate how it promotes working in multidisciplinary ways. CARTA has attracted PhD fellows, supervisors and JAS teaching faculty from across a range of disciplines. Evaluations indicate PhD fellows have a greater appreciation of how disciplines other than their own are important to understand health and its determinants and an appreciation and capacity to employ mixed methods research.
Conclusions: In the short-term, we have been effective in promoting an understanding of multidisciplinarity resulting in fellows using methods from beyond their discipline of origin. This curriculum has international application
Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at = 5.02 TeV
Two-particle angular correlations between unidentified charged trigger and
associated particles are measured by the ALICE detector in p-Pb collisions at a
nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum
range 0.7 5.0 GeV/ is examined,
to include correlations induced by jets originating from low
momen\-tum-transfer scatterings (minijets). The correlations expressed as
associated yield per trigger particle are obtained in the pseudorapidity range
. The near-side long-range pseudorapidity correlations observed in
high-multiplicity p-Pb collisions are subtracted from both near-side
short-range and away-side correlations in order to remove the non-jet-like
components. The yields in the jet-like peaks are found to be invariant with
event multiplicity with the exception of events with low multiplicity. This
invariance is consistent with the particles being produced via the incoherent
fragmentation of multiple parton--parton scatterings, while the yield related
to the previously observed ridge structures is not jet-related. The number of
uncorrelated sources of particle production is found to increase linearly with
multiplicity, suggesting no saturation of the number of multi-parton
interactions even in the highest multiplicity p-Pb collisions. Further, the
number scales in the intermediate multiplicity region with the number of binary
nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/161
Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider
Measurements of multi-particle azimuthal correlations (cumulants) for charged
particles in p-Pb and Pb-Pb collisions are presented. They help address the
question of whether there is evidence for global, flow-like, azimuthal
correlations in the p-Pb system. Comparisons are made to measurements from the
larger Pb-Pb system, where such evidence is established. In particular, the
second harmonic two-particle cumulants are found to decrease with multiplicity,
characteristic of a dominance of few-particle correlations in p-Pb collisions.
However, when a gap is placed to suppress such correlations,
the two-particle cumulants begin to rise at high-multiplicity, indicating the
presence of global azimuthal correlations. The Pb-Pb values are higher than the
p-Pb values at similar multiplicities. In both systems, the second harmonic
four-particle cumulants exhibit a transition from positive to negative values
when the multiplicity increases. The negative values allow for a measurement of
to be made, which is found to be higher in Pb-Pb collisions at
similar multiplicities. The second harmonic six-particle cumulants are also
found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find
which is indicative of a Bessel-Gaussian
function for the distribution. For very high-multiplicity Pb-Pb
collisions, we observe that the four- and six-particle cumulants become
consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and
Pb-Pb are measured. These are found to be similar for overlapping
multiplicities, when a gap is placed.Comment: 25 pages, 11 captioned figures, 3 tables, authors from page 20,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/87
Agricultura orgĂąnica em ĂĄreas urbanas e periurbanas com base na agroecologia.
A agricultura orgĂąnica com base na agroecologia Ă© o mote tecnolĂłgico adequado Ă realidade dos agroecossistemas urbanos. Este artigo ressalta a necessidade de se desenvolver tecnologias e insumos especĂficos. A partir de experiĂȘncias com agricultura urbana em diferentes paĂses em desenvolvimento, evidencia-se a necessidade de se buscar capacidades locais e apoio do poder pĂșblico, especialmente nas iniciativas da sociedade organizada e mobilizada para a produção agrĂcola urbana
Student Experiences of Multidisciplinarity in the Undergraduate Geography Curriculum
This paper explores the student experience of multidisciplinarity within the undergraduate Geography curriculum. It considers the drivers that have underpinned this development before considering the findings of research into student experiences in two universities in the south of England. The results suggest that most students view this development positively and recognize a number of advantages that it brings, citing expanded opportunities for learning, working with people from other disciplines, expansion of perspectives and perceived benefits to employability. However, for a minority this development is more problematic. The research points here to issues with specialist knowledge and disciplinary pedagogies, social issues within the classroom and class organization and some reservations regarding groupwork. The paper concludes with a series of recommendations
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