8,864 research outputs found
Neutron Shielding Effectiveness of Multifunctional Composite Materials
Composite materials offer a greater degree of flexibility in design and engineering of specialized space vehicle shielding applications compared to aluminum. A new design for shielding materials has been developed by including specific neutron absorbers and conductive materials into the composite structure. In this research, the neutron shielding capability of two types of custom-designed nanocomposite materials are compared to that of T6061 aluminum
Proton electron elastic scattering and the proton charge radius
It is suggested that proton elastic scattering on atomic electrons allows a
precise measurement of the proton charge radius. Very small values of
transferred momenta (up to four order of magnitude smaller than the ones
presently available) can be reached with high probability.Comment: 4 pages, 4 figure
G0 electronics and data acquisition (forward-angle measurements)
The G0 parity-violation experiment at Jefferson Lab (Newport News, VA) is designed to determine the contribution of strange/anti-strange quark pairs to the intrinsic properties of the proton. In the forward-angle part of the experiment, the asymmetry in the cross-section was measured for elastic scattering by counting the recoil protons corresponding to the two beam-helicity states. Due to the high accuracy required to measure the few-part-per-million asymmetry, the G0 experiment was based on a custom experimental setup with its own associated electronics and data acquisition (DAQ) system. Highly specialized time-encoding electronics provided time-of-flight spectra for each detector for each helicity state. More conventional electronics, processing only a small fraction of the events, was used for monitoring (mainly FastBus). The time-encoding electronics and the DAQ system have been designed to handle events from the 128 detector pairs at a mean rate of 2 MHz per detector pair with low deadtime and with minimal helicity-correlated systematic errors. In this paper, we outline the general architecture and the main features of the electronics and the DAQ system dedicated to G0 forward-angle measurements
Strategic planning in small and medium-sized companies in the architecture sector in Portugal
Architecture today presents a highly competitive and turbulent market. This scenario of
instability and competition has reinforced the importance of strategy and, consequently,
strategic planning. The existing literature indicates that strategic planning allows
companies to achieve a better strategic positioning, performance and profitability. This
exploratory study aims to investigate in the architecture sector the importance given to
strategy, the way strategic planning is used and, finally, what are the main obstacles that
discourage its adoption. Through a set of 12 semi-structured interviews with different
micro, small and medium-sized architecture studios, this research points to a limited use
of strategic planning. This result is explained, on the one hand, by the lack of knowledge
of strategic planning methodologies and by the fact that often financial success and
market share are seen by owner-managers as secondary to other objectives, such as their
intellectual satisfaction and artistic recognition of their work. The volatility of the
construction sector and the small size of most architectural firms also seem to contribute
to their low usage. The results of this dissertation may be of interest to owners/managers
of Architecture firms and also to Architecture universities.Nos dias de hoje, o mercado da arquitetura é caracterizado por ser altamente competitivo
e turbulento. Este cenário de instabilidade e concorrência reforça a importância da
estratégia e, consequentemente, do planeamento estratégico. A literatura existente indica
que o planeamento estratégico permite às empresas conseguir um melhor posicionamento
de mercado, um melhor desempenho e rentabilidade. Este estudo exploratório tem como
objetivo investigar no setor da arquitetura, a importância atribuída ao planeamento
estratégico, a extensão e o modo com que é utilizado e, finalmente, quais os principais
obstáculos que limitam a sua utilização. Através de um conjunto de 12 entrevistas
semiestruturadas a diferentes micro, pequenas e médias empresas de arquitetura, esta
investigação sugere uma utilização limitada do planeamento estratégico. Este resultado é
explicado, por um lado, pela falta de conhecimento no sector das mais valias e
metodologias do planeamento estratégico e pelo facto de muitas vezes o sucesso
financeiro ser visto pelos donos-gestores como secundário em relação a outros objetivos,
tais como a sua satisfação intelectual e o reconhecimento artístico do seu trabalho. A
volatilidade do sector da construção e a pequena dimensão da maioria das empresas de
arquitetura também parecem contribuir para a sua baixa utilização. Os resultados desta
dissertação podem ser do interesse dos gerentes de empresas de arquitetura e também das
universidades do sector
Sharp transition for single polarons in the one-dimensional Su-Schrieffer-Heeger model
We study a single polaron in the Su-Schrieffer-Heeger (SSH) model using four
different techniques (three numerical and one analytical). Polarons show a
smooth crossover from weak to strong coupling, as a function of the
electron-phonon coupling strength , in all models where this coupling
depends only on phonon momentum . In the SSH model the coupling also depends
on the electron momentum ; we find it has a sharp transition, at a critical
coupling strength , between states with zero and nonzero momentum of
the ground state. All other properties of the polaron are also singular at
, except the average number of phonons in the polaronic
cloud. This result is representative of all polarons with coupling depending on
and , and will have important experimental consequences (eg., in ARPES
and conductivity experiments)
On an intriguing distributional identity
For a continuous random variable X with support equal to (a, b), with c.d.f. F, and g: Ω1 → Ω2 a continuous, strictly increasing function, such that Ω1∩Ω2⊇(a, b), but otherwise arbitrary, we establish that the random variables F(X) − F(g(X)) and F(g−1(X)) − F(X) have the same distribution. Further developments, accompanied by illustrations and observations, address as well the equidistribution identity U − ψ(U) = dψ−1(U) − U for U ∼ U(0, 1), where ψ is a continuous, strictly increasing and onto function, but otherwise arbitrary. Finally, we expand on applications with connections to variance reduction techniques, the discrepancy between distributions, and a risk identity in predictive density estimation
Human macrophages and osteoclasts resorb β-tricalcium phosphate in vitro but not mouse macrophages
β-TCP is a resorbable bony biomaterial but its biodegradation mechanisms in vivo remains unclear. Osteoclast can resorb β-TCP but a role for macrophages has also been suggested by in vivo studies. However no in vitro study has clearly evidenced the action of macrophages in the resorption process. We prepared flat β-TCP tablets with a smooth surface to investigate the in vitro capability of murine (RAW 264.7) and human macrophage cells (PBMCs) to resorb the biomaterial. In parallel, these cells were differentiated into multinucleated osteoclasts with M-CSF and RANK-L. The action of these cells was evaluated by scanning electron microscopy and Raman microspectroscopy after a 21 day culture on the tablets. Human macrophages and osteoclasts derived from PBMCs appeared able to resorb β-TCP by forming resorption pits at the surface of the flat tablets. RAW macrophages were unable to resorb β-TCP but they exhibited this possibility when they have been differentiated into osteoclasts. These cells can engulf β-TCP grains in their cytoplasm as evidenced by light and TEM microscopy with production of carbonic anhydrase (revealed by the immunogold technique in TEM). The resorbed areas were characterized by severe degradation of the grains showing speckled and stick-like aspects indicating a chemical corrosion. The effect was maximal at the grain boundaries which have a slightly different chemical composition. Changes in the Raman spectrum were observed between the resorbed and un-resorbed β-TCP suggesting crystal modifications. In contrast, un-differentiated murine macrophages were not able to chemically attack β-TCP and no resorption pit was observed. RAW cell is not a representative model of the macrophage-biomaterial interactions that occur in human. This in vitro study evidences that both human osteoclasts and macrophages represent active cell populations capable to resorb β-TCP
IMLI: An Incremental Framework for MaxSAT-Based Learning of Interpretable Classification Rules
The wide adoption of machine learning in the critical domains such as medical
diagnosis, law, education had propelled the need for interpretable techniques
due to the need for end users to understand the reasoning behind decisions due
to learning systems. The computational intractability of interpretable learning
led practitioners to design heuristic techniques, which fail to provide sound
handles to tradeoff accuracy and interpretability.
Motivated by the success of MaxSAT solvers over the past decade, recently
MaxSAT-based approach, called MLIC, was proposed that seeks to reduce the
problem of learning interpretable rules expressed in Conjunctive Normal Form
(CNF) to a MaxSAT query. While MLIC was shown to achieve accuracy similar to
that of other state of the art black-box classifiers while generating small
interpretable CNF formulas, the runtime performance of MLIC is significantly
lagging and renders approach unusable in practice. In this context, authors
raised the question: Is it possible to achieve the best of both worlds, i.e., a
sound framework for interpretable learning that can take advantage of MaxSAT
solvers while scaling to real-world instances?
In this paper, we take a step towards answering the above question in
affirmation. We propose IMLI: an incremental approach to MaxSAT based framework
that achieves scalable runtime performance via partition-based training
methodology. Extensive experiments on benchmarks arising from UCI repository
demonstrate that IMLI achieves up to three orders of magnitude runtime
improvement without loss of accuracy and interpretability.Comment: 10 pages, published in the proceedings of AAAI/ACM Conference on AI,
Ethics, and Society (AIES 2019
QED radiative corrections to virtual Compton scattering
The QED radiative corrections to virtual Compton scattering (reaction e p \to e p \gamma$ reaction how the observables are modified due to these first order QED radiative corrections. We show results for both unpolarized and polarized observables of the virtual Compton scattering in the low energy region (where one is sensitive to the generalized polarizabilities of the nucleon), as well as for the deeply virtual Compton scattering
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