46 research outputs found
Relativistic treatment of harmonics from impurity systems in quantum wires
Within a one particle approximation of the Dirac equation we investigate a
defect system in a quantum wire. We demonstrate that by minimally coupling a
laser field of frequency omega to such an impurity system, one may generate
harmonics of multiples of the driving frequency. In a multiple defect system
one may employ the distance between the defects in order to tune the cut-off
frequency.Comment: 9 pages Latex, 8 eps figures, section added, numerics improve
Particles-vortex interactions and flow visualization in He4
Recent experiments have demonstrated a remarkable progress in implementing
and use of the Particle Image Velocimetry (PIV) and particle tracking
techniques for the study of turbulence in He4. However, an interpretation of
the experimental data in the superfluid phase requires understanding how the
motion of tracer particles is affected by the two components, the viscous
normal fluid and the inviscid superfluid. Of a particular importance is the
problem of particle interactions with quantized vortex lines which may not only
strongly affect the particle motion, but, under certain conditions, may even
trap particles on quantized vortex cores. The article reviews recent
theoretical, numerical, and experimental results in this rapidly developing
area of research, putting critically together recent results, and solving
apparent inconsistencies. Also discussed is a closely related technique of
detection of quantized vortices negative ion bubbles in He4.Comment: To appear in the J Low Temperature Physic
Pervasive gaps in Amazonian ecological research
Biodiversity loss is one of the main challenges of our time, and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space. While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes, vast areas of the tropics remain understudied. In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity, but it remains among the least known forests in America and is often underrepresented in biodiversity databases. To worsen this situation, human-induced modifications may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge, it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost
A large diversity of hydrated minerals formed from interaction with hydrothermal fluids in Noctis Labyrinthus Mars
International audienc
Recommendations for ECG diagnostic coding
The Oxford dictionary defines code as "a body of laws so related to each
other as to avoid inconsistency and overlapping". It is obvious that natural
language with its high degree of ambiguity does not qualify as a code in the
sense of this definition. Everyday experiences provide ample evidence that
natural language, because of its richness and lack of uniqueness, is subject to
multiple interpretations and thus not suitable for conveying ideas or data in
an unequivocal, uniform and concise manner. For this reason codes have
been developed and used in several areas of medicine [1-3] to describe,
document, and transmit qualitative medical data. It is rather surprising that
electrocardiography has been able to exist for so long without any formalized
language to describe its findings. Increased use of electrocardiograms in epidemiology,
large scale electrocardiographic studies and last but not least computerized
EeG interpretation have provided incentives to develop codes. Initial
efforts in this direction [4-6] were primarily guided by loc al needs for
improved storage, retrieval and handling of information; without major
modifications they do not, however, satisfy all the requirements one expects
from an EeG code today. Nevertheless, the experience gained in the use of
these early EeG codes provides an important source of information on which to build specifications for a new or expanded code. It is significant that several
members of this working group have been extensive users of the Booth-Hull
code [4] and the Utrecht coding system [5]