691 research outputs found
Simple analysis of off-axis solenoid fields using the scalar magnetostatic potential: application to a Zeeman-slower for cold atoms
In a region free of currents, magnetostatics can be described by the Laplace
equation of a scalar magnetic potential, and one can apply the same methods
commonly used in electrostatics. Here we show how to calculate the general
vector field inside a real (finite) solenoid, using only the magnitude of the
field along the symmetry axis. Our method does not require integration or
knowledge of the current distribution, and is presented through practical
examples, including a non-uniform finite solenoid used to produce cold atomic
beams via laser cooling. These examples allow educators to discuss the
non-trivial calculation of fields off-axis using concepts familiar to most
students, while offering the opportunity to introduce important advancements of
current modern research.Comment: 6 pages. Accepted in the American Journal of Physic
An analytical solution for the critical number of particles for stable bose-einstein condensation under the influence of an anisotropic potential
We have considered a Bose gas in an anisotropic potential. Applying the the Gross-Pitaevskii Equation (GPE) for a confined dilute atomic gas, we have used the methods of optimized perturbation theory and self-similar root approximants, to obtain an analytical formula for the critical number of particles as a function of the anisotropy parameter for the potential. The spectrum of the GPE is also discussed.CNPQCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES
Biomass Burning Aerosol Absorption Measurements with MODIS Using the Critical Reflectance Method
This research uses the critical reflectance technique, a space-based remote sensing method, to measure the spatial distribution of aerosol absorption properties over land. Choosing two regions dominated by biomass burning aerosols, a series of sensitivity studies were undertaken to analyze the potential limitations of this method for the type of aerosol to be encountered in the selected study areas, and to show that the retrieved results are relatively insensitive to uncertainties in the assumptions used in the retrieval of smoke aerosol. The critical reflectance technique is then applied to Moderate Resolution Imaging Spectrometer (MODIS) data to retrieve the spectral aerosol single scattering albedo (SSA) in South African and South American 35 biomass burning events. The retrieved results were validated with collocated Aerosol Robotic Network (AERONET) retrievals. One standard deviation of mean MODIS retrievals match AERONET products to within 0.03, the magnitude of the AERONET uncertainty. The overlap of the two retrievals increases to 88%, allowing for measurement variance in the MODIS retrievals as well. The ensemble average of MODIS-derived SSA for the Amazon forest station is 0.92 at 670 nm, and 0.84-0.89 for the southern African savanna stations. The critical reflectance technique allows evaluation of the spatial variability of SSA, and shows that SSA in South America exhibits higher spatial variation than in South Africa. The accuracy of the retrieved aerosol SSA from MODIS data indicates that this product can help to better understand 44 how aerosols affect the regional and global climate
Single nucleotide polymorphisms from Theobroma cacao expressed sequence tags associated with witches' broom disease in cacao
In order to increase the efficiency of cacao tree resistance to witches¿ broom disease, which is caused by Moniliophthora perniciosa (Tricholomataceae), we looked for molecular markers that could help in the selection of resistant cacao genotypes. Among the different markers useful for developing marker-assisted selection, single nucleotide polymorphisms (SNPs) constitute the most common type of sequence difference between alleles and can be easily detected by in silico analysis from expressed sequence tag libraries. We report the first detection and analysis of SNPs from cacao-M. perniciosa interaction expressed sequence tags, using bioinformatics. Selection based on analysis of these SNPs should be useful for developing cacao varieties resistant to this devastating disease. (Résumé d'auteur
Bose-Einstein Condensation on Curved Manifolds
Here we describe a weakly interacting Bose gas on a curved manifold, which is
embedded in the three-dimensional Euclidean space.~To this end we start by
considering a harmonic trap in the normal direction of the manifold, which
confines the three-dimensional Bose gas in the vicinity of its
surface.~Following the notion of dimensional reduction as outlined in
[L.~Salasnich et al., Phys.~Rev.~A {\bf 65}, 043614 (2002)], we assume a large
enough trap frequency so that the normal degree of freedom of the condensate
wave function can be approximately integrated out. In this way we obtain an
effective condensate wave function on the quasi-two-dimensional surface of the
curved manifold, where the thickness of the cloud is determined
self-consistently. For the particular case when the manifold is a sphere, our
equilibrium results show how the chemical potential and the thickness of the
cloud increase with the interaction strength.~Furthermore, we determine within
a linear stability analysis the low-lying collective excitations together with
their eigenfrequencies, which turn out to reveal an instability for attractive
interactions.Comment: 33 pages, 6 figure
Entropy of a Turbulent Bose-Einstein Condensate
Quantum turbulence deals with the phenomenon of turbulence in quantum fluids,
such as superfluid helium and trapped Bose-Einstein condensates (BECs).
Although much progress has been made in understanding quantum turbulence,
several fundamental questions remain to be answered. In this work, we
investigated the entropy of a trapped BEC in several regimes, including
equilibrium, small excitations, the onset of turbulence, and a turbulent state.
We considered the time evolution when the system is perturbed and let to evolve
after the external excitation is turned off. We derived an expression for the
entropy consistent with the accessible experimental data, that is, using the
assumption that the momentum distribution is well-known. We related the
excitation amplitude to different stages of the perturbed system, and we found
distinct features of the entropy in each of them. In particular, we observed a
sudden increase in the entropy following the establishment of a particle
cascade. We argue that entropy and related quantities can be used to
investigate and characterize quantum turbulence.Comment: 14 pages, 5 figure
Working in a tourism company: experience at Dixo´s Oporto Apartments
The present report is part of the curricular internship of the Master’s degree in
Intercultural Studies for Business, from the Porto Accounting and Business School
(Instituto Superior de Contabilidade e Administração do Porto). This internship took
place at the tourism field related company, Dixo’s Oporto Apartments.
Globalization has been increasing at unprecedented rates and with that, the
limits and the borders between countries and nations have been reducing. As a result,
there has been a marked increase in the need for intercultural communication as it
becomes reality and people depend more on this type of communication.
The tourism sector is no exception from the inevitable changes imposed by
globalization, and it too depends on intercultural communication. Cities such as Porto
with a great flux of tourism rely on the finest quality services delivered by leading
professionals. High standards can only be achieved by those who are used to
intercultural communication and are familiarized with concepts such as globalization
and interculturality.
The purpose of this report is to describe and understand, at the most precise level
the activities carried out during the internship based on the concepts and knowledge
learnt during the master’s degree.O presente relatório insere-se no âmbito do estágio curricular do Mestrado em
Estudos Interculturais para Negócio, no Instituto Superior de Contabilidade e
Administração do Porto (ISCAP). O estágio decorreu na empresa Dixo’s Oporto
Apartments que se insere na área do Turismo.
A globalização tem vindo a crescer a níveis nunca previstos e, com isso, os
limites e as fronteiras entre países e nações vêm diminuindo. Com isso, a comunicação
intercultural tem crescido assim como o crescimento da comunicação entre diferentes
culturas, uma constante e as pessoas dependem cada vez mais desse tipo de
comunicação sendo uma realidade óbvia atualmente.
O turismo vive desse tipo de comunicação e da globalização. Cidades como o
Porto, com grande fluxo turístico, contam com serviços de qualidade prestados por
profissionais formados por excelência. Padrões elevados só podem ser alcançados por
aqueles que estão acostumados a comunicação intercultural e familiarizados com
conceitos como globalização e interculturalidade.
O objetivo deste relatório é descrever e compreender da forma mais precisa as
atividades desenvolvidas durante o estágio com base nos conceitos e conhecimentos
aprendidos durante o mestrado
Momentum distribution of Vinen turbulence in trapped atomic Bose-Einstein condensates
The decay of multicharged vortices in trapped Bose-Einstein condensates may
lead to a disordered vortex state consistent with the Vinen regime of
turbulence, characterized by an absence of large-scale flow and an
incompressible kinetic energy spectrum . In this work, we
study numerically the dynamics of a three-dimensional harmonically trapped
Bose-Einstein condensate excited to a Vinen regime of turbulence through the
decay of two doubly-charged vortices. First, we study the momentum distribution
and observe the emergence of a power-law behavior
consistent with the coexistence of wave turbulence. We also study the kinetic
energy and particle fluxes, which allows us to identify a direct particle
cascade associated with the turbulent stage.Comment: 5 pages, 2 figure
Remote sensing the vertical profile of cloud droplet effective radius, thermodynamic phase, and temperature
International audienceCloud-aerosol interaction is no longer simply a radiative problem, but one affecting the water cycle, the weather, and the total energy balance including the spatial and temporal distribution of latent heat release. Information on the vertical distribution of cloud droplet microphysics and thermodynamic phase as a function of temperature or height, can be correlated with details of the aerosol field to provide insight on how these particles are affecting cloud properties and its consequences to cloud lifetime, precipitation, water cycle, and general energy balance. Unfortunately, today's experimental methods still lack the observational tools that can characterize the true evolution of the cloud microphysical, spatial and temporal structure in the cloud droplet scale, and then link these characteristics to environmental factors and properties of the cloud condensation nuclei. Here we propose and demonstrate a new experimental approach (the cloud scanner instrument) that provides the microphysical information missed in current experiments and remote sensing options. Cloud scanner measurements can be performed from aircraft, ground, or satellite by scanning the side of the clouds from the base to the top, providing us with the unique opportunity of obtaining snapshots of the cloud droplet microphysical and thermodynamic states as a function of height and brightness temperature in clouds at several development stages. The brightness temperature profile of the cloud side can be directly associated with the thermodynamic phase of the droplets to provide information on the glaciation temperature as a function of different ambient conditions, aerosol concentration, and type. An aircraft prototype of the cloud scanner was built and flew in a field campaign in Brazil. The CLAIM-3D (3-Dimensional Cloud Aerosol Interaction Mission) satellite concept proposed here combines several techniques to simultaneously measure the vertical profile of cloud microphysics, thermodynamic phase, brightness temperature, and aerosol amount and type in the neighborhood of the clouds. The wide wavelength range, and the use of mutli-angle polarization measurements proposed for this mission allow us to estimate the availability and characteristics of aerosol particles acting as cloud condensation nuclei, and their effects on the cloud microphysical structure. These results can provide unprecedented details on the response of cloud droplet microphysics to natural and anthropogenic aerosols in the size scale where the interaction really happens
- …