6,148 research outputs found
Applying the proto-theory of design to explain and modify the parameter analysis method of conceptual design
This article reports on the outcomes of applying the notions provided by the reconstructed proto-theory of design, based on Aristotle’s remarks, to the parameter analysis (PA) method of conceptual design. Two research questions are addressed: (1) What further clarification and explanation to the approach of PA is provided by the proto-theory? (2) Which conclusions can be drawn from the study of an empirically derived
design approach through the proto-theory regarding usefulness, validity and range of that theory? An overview of PA and an application example illustrate its present model and unique characteristics. Then, seven features of the proto-theory are explained and demonstrated through geometrical problem solving and analogies are drawn between these features and the corresponding ideas in modern design thinking.
Historical and current uses of the terms analysis and synthesis in design are also outlined and contrasted, showing that caution should be exercised when applying them. Consequences regarding the design moves, process and strategy of PA allow proposing modifications to its model, while demonstrating how the ancient method of analysis can contribute to better understanding of contemporary design-theoretic issues
HYBRID SYSTEMS: COLD ATOMS COUPLED TO MICRO MECHANICAL OSCILLATORS
Micro mechanical oscillators can serve as probes in precision measurements, as transducersto mediate photon-phonon interactions, and when functionalized with magneticmaterial, as tools to manipulate spins in quantum systems. This dissertationincludes two projects where the interactions between cold atoms and mechanical oscillatorsare studied.In one of the experiments, we have manipulated the Zeeman state of magneticallytrapped Rubidium atoms with a magnetic micro cantilever [1]. The results show aspatially localized effect produced by the cantilever that agrees with Landau-Zenertheory. In the future, such a scalable system with highly localized interactions andthe potential for single-spin sensitivity could be useful for applications in quantuminformation science or quantum simulation.In a second experiment, work is in progress to couple a sample of optically trappedRubidium atoms to a levitated nanosphere via an optical lattice [2]. This couplingenables the cooling of the center-of-mass motion of the nanosphere by laser coolingthe atoms. In this system, the atoms are trapped in the optical lattice while thesphere is levitated in a separate vacuum chamber by a single-beam optical tweezer.Theoretical analysis of such a system has determined that cooling the center-of-massmotion of the sphere to its quantum ground state is possible, even when starting atroom temperature, due to the excellent environmental decoupling achievable in thissetup. Nanospheres cooled to the quantum regime can provide new tests of quantumbehavior at mesoscopic scales and have novel applications in precision sensing
Social dynamics in conferences: analyses of data from the Live Social Semantics application
Popularity and spread of online social networking in recent years has given a great momentum to the study of dynamics and patterns of social interactions. However, these studies have often been confined to the online world, neglecting its interdependencies with the offline world. This is mainly due to the lack of real data that spans across this divide. The Live Social Semantics application is a novel platform that dissolves this divide, by collecting and integrating data about people from (a) their online social networks and tagging activities from popular social networking sites, (b) their publications and co-authorship networks from semantic repositories, and (c) their real-world face-to-face contacts with other attendees collected via a network of wearable active sensors. This paper investigates the data collected by this application during its deployment at three major conferences, where it was used by more than 400 people. Our analyses show the robustness of the patterns of contacts at various conferences, and the influence of various personal properties (e.g. seniority, conference attendance) on social networking patterns
Evolution and excitation conditions of outflows in high-mass star-forming regions
Theoretical models suggest that massive stars form via disk-mediated
accretion, with bipolar outflows playing a fundamental role. A recent study
toward massive molecular outflows has revealed a decrease of the SiO line
intensity as the object evolves. The present study aims at characterizing the
variation of the molecular outflow properties with time, and at studying the
SiO excitation conditions in outflows associated with massive YSOs. We used the
IRAM30m telescope to map 14 massive star-forming regions in the SiO(2-1),
SiO(5-4) and HCO+(1-0) outflow lines, and in several dense gas and hot core
tracers. Hi-GAL data was used to improve the spectral energy distributions and
the L/M ratio, which is believed to be a good indicator of the evolutionary
stage of the YSO. We detect SiO and HCO+ outflow emission in all the sources,
and bipolar structures in six of them. The outflow parameters are similar to
those found toward other massive YSOs. We find an increase of the HCO+ outflow
energetics as the object evolve, and a decrease of the SiO abundance with time,
from 10^(-8) to 10^(-9). The SiO(5-4) to (2-1) line ratio is found to be low at
the ambient gas velocity, and increases as we move to high velocities,
indicating that the excitation conditions of the SiO change with the velocity
of the gas (with larger densities and/or temperatures for the high-velocity gas
component). The properties of the SiO and HCO+ outflow emission suggest a
scenario in which SiO is largely enhanced in the first evolutionary stages,
probably due to strong shocks produced by the protostellar jet. As the object
evolves, the power of the jet would decrease and so does the SiO abundance.
During this process, however, the material surrounding the protostar would have
been been swept up by the jet, and the outflow activity, traced by entrained
molecular material (HCO+), would increase with time.Comment: 31 pages, 10 figures and 5 tables (plus 2 figures and 3 tables in the
appendix). Accepted for publication in A&A. [Abstract modified to fit the
arXiv requirements.
Cronologia absoluta para as ocupações do neolítico final e do calcolítico inicial do Povoado Pré-histórico de Leceia (Oerias)
Cronologia absoluta para o campaniforme da Estremadura e do sudoeste de Portugal
Separata de "O Arqueólogo Português"Mais de vinte datas de radiocarbono são actualmente conhecidas para contextos
campaniformes na Estemadura e no Sul de Portugal. Por outro lado, escavações
recentes isolaram contextos campaniformes bem definidos, que foram
datados. Estes dados permitem novas interpretações para o fenómeno campaniforme,
bem como o estabelecimento de uma cronologia mais precisa para o
mesmo.At present twenty radiocarbon dates are knoun for bell beakers in Estremadura
and the soutb of Portugal. 0n the other hand, recent archaeological digging
allowed to isolate well defined bell beaker contexts, wbich were radiocarbono dated
these new data allow new interpretations for the bell beaker phenomenon,
as a more precise chronology for the different pottery styles
Physical properties of high-mass clumps in different stages of evolution
(Abridged) Aims. To investigate the first stages of the process of high-mass
star formation, we selected a sample of massive clumps previously observed with
the SEST at 1.2 mm and with the ATNF ATCA at 1.3 cm. We want to characterize
the physical conditions in such sources, and test whether their properties
depend on the evolutionary stage of the clump.
Methods. With ATCA we observed the selected sources in the NH3(1,1) and (2,2)
transitions and in the 22 GHz H2O maser line. Ammonia lines are a good
temperature probe that allow us to accurately determine the mass and the
column-, volume-, and surface densities of the clumps. We also collected all
data available to construct the spectral energy distribution of the individual
clumps and to determine if star formation is already occurring, through
observations of its most common signposts, thus putting constraints on the
evolutionary stage of the source. We fitted the spectral energy distribution
between 1.2 mm and 70 microns with a modified black body to derive the dust
temperature and independently determine the mass.
Results. The clumps are cold (T~10-30 K), massive (M~10^2-10^3 Mo), and dense
(n(H2)>~10^5 cm^-3) and they have high column densities (N(H2)~10^23 cm^-2).
All clumps appear to be potentially able to form high-mass stars. The most
massive clumps appear to be gravitationally unstable, if the only sources of
support against collapse are turbulence and thermal pressure, which possibly
indicates that the magnetic field is important in stabilizing them.
Conclusions. After investigating how the average properties depend on the
evolutionary phase of the source, we find that the temperature and central
density progressively increase with time. Sources likely hosting a ZAMS star
show a steeper radial dependence of the volume density and tend to be more
compact than starless clumps.Comment: Published in A&A, Vol. 556, A1
A study on subarcsecond scales of the ammonia and continuum emission toward the G16.59-0.05 high-mass star-forming region
We wish to investigate the structure, velocity field, and stellar content of
the G16.59-0.05 high-mass star-forming region, where previous studies have
established the presence of two almost perpendicular (NE-SW and SE-NW), massive
outflows, and a rotating disk traced by methanol maser emission. We performed
Very Large Array observations of the radio continuum and ammonia line emission,
complemented by COMICS/Subaru and Hi-GAL/Herschel images in the mid- and
far-infrared (IR). Our centimeter continuum maps reveal a collimated radio jet
that is oriented E-W and centered on the methanol maser disk, placed at the SE
border of a compact molecular core. The spectral index of the jet is negative,
indicating non-thermal emission over most of the jet, except the peak close to
the maser disk, where thermal free-free emission is observed. We find that the
ammonia emission presents a bipolar structure consistent (on a smaller scale)
in direction and velocity with that of the NE-SW bipolar outflow detected in
previous CO observations. After analyzing our previous N2H+(1-0) observations
again, we conclude that two scenarios are possible. In one case both the radio
jet and the ammonia emission would trace the root of the large-scale CO bipolar
outflow. The different orientation of the jet and the ammonia flow could be
explained by precession and/or a non-isotropic density distribution around the
star. In the other case, the N2H+(1-0) and ammonia bipolarity is interpreted as
two overlapping clumps moving with different velocities along the line of
sight. The ammonia gas also seems to undergo rotation consistent with the maser
disk. Our IR images complemented by archival data allow us to derive a
bolometric luminosity of about 10^4 L_sun and to conclude that most of the
luminosity is due to the young stellar object associated with the maser disk.Comment: 11 pages, 12 figures, published in Astronomy and Astrophysic
A duna consolidada de Oitavos, a Oeste de Cascais, região de Lisboa : a sua datação pelo método do radiocarbono
A duna consolidada de Oitavos, atribuída ao Quaternário, situa-se junto ao litoral, a oeste de Cascais. Apresenta-se o programa de
datações pelo radiocarbono que permitiu a datação dessa duna e discute-se a fiabilidade das datas obtidas. Processaram-se
amostras de Helix provenientes não só da duna de Oitavos, mas também da duna consolidada de Magoito, localizada cerca de 16
km para norte e já devidamente datada por aquele método de datação absoluta, e ainda amostras de um contexto arqueológico
da Encosta de Sant'Ana (Baixa da cidade de Lisboa), com o objectivo de aferir a validade das datações de Oitavos sobre Helix.
Também o paleossolo existente na base da duna de Oitavos foi objecto de datação. Determinou-se assim uma data de elevada
fiabilidade para a geração da duna de Oitavos, indicando que esta se terá formado no intervalo 33-30 ka BP, provavelmente
durante o interestadial que precede a fase final do OIS 3
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