601 research outputs found
Multidirectional ECG Coherent Optimal Timing of Defibrillation Shocks
A method for of delivering a defibrillation shock to a heart at an optimal time to stop ventricular fibrillation which involves obtaining an electrocardiogram of a heart in at least two directions, determining a time-coherency of the electrocardiogram based upon each of the at least two directions, and computing a tracking function from the time-coherency. An optimal time to apply a defibrillation shock to the heart is determined by locating a local maximum on the tracking function. The method utilizes spacia characteristics of the ventricular fibrillation. The method can be incorporated into implantable cardioverter defibrillators utilizing existing hardware technology
The intramolecular aldol condensation of 3-oxocyclohexaneacetaldehydes: A useful tool in the synthesis of natural products
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Probing Hyperbolic and Surface Phonon-Polaritons in 2D materials using Raman Spectroscopy
The hyperbolic dispersion relation of phonon-polaritons (PhPol) provides
high-momentum states, highly directional propagation, subdiffractional
confinement, large optical density of states, and enhanced light-matter
interactions. In this work, we use Raman spectroscopy in the convenient
backscattering configuration to probe PhPol in GaSe, a 2D material presenting
two hyperbolic regions separated by a \textit{double} reststrahlen band. By
varying the incidence angle, dispersion relations are revealed. Raman spectra
calculations confirm the observation of one surface and two extraordinary
guided polaritons and matches the evolution of PhPol frequency as a function of
confinement. Resonant excitation close to the excitonic state singularly exalts
the scattering efficiency of PhPol. Raman spectroscopy of PhPol in
non-centrosymmetry 2D materials does not require any wavevector matching
strategies. Widely available, it may accelerate the development of MIR
nanophotonic devices and applications
âExtremeâ Organisms and the Problem of Generalization: Interpreting the Krogh Principle
Many biologists appeal to the so-called Krogh principle when justifying their choice of experimental organisms. The principle states that âfor a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studiedâ. Despite its popularity, the principle is often critiqued for implying unwarranted generalizations from optimal models. We argue that the Krogh principle should be interpreted in relation to the historical and scientific contexts in which it has been developed and used. We interpret the
Krogh Principle as a heuristic, i.e., as a recommendation to approach biological problems through organisms where a specific trait or physiological mechanism is expected to be most distinctively displayed or most experimentally accessible. We designate these organisms âKrogh organisms.â We clarify the differences between uses of model organisms and non-standard Krogh organisms. Among these is the use of Krogh organisms as ânegative modelsâ in biomedical research, where organisms are chosen for their dissimilarity to human physiology. Importantly, the representational scope of Krogh organisms and the generalizability of their
characteristics are not fixed or assumed but explored through experimental studies. Research on Krogh organisms is steeped in the comparative method characteristic of zoology and comparative physiology, in which studies of biological variation produce insights into general physiological constraints. Accordingly, we conclude that the Krogh principle exemplifies the advantages of studying biological variation as a strategy to produce generalizable insights
Excitonic coupling dominates the homogeneous photoluminescence excitation linewidth in semicrystalline polymeric semiconductors
We measure the homogeneous excitation linewidth of regioregular
poly(3-hexylthiophene), a model semicrystalline polymeric semiconductor, by
means of two-dimensional coherent photoluminescence excitation spectroscopy. At
a temperature of 8\,K, we find a linewidth that is always \,meV
full-width-at-half-maximum, which is a significant fraction of the total
linewidth. It displays a spectral dependence and is minimum near the 0--0
origin peak. We interpret this spectral dependence of the homogeneous
excitation linewidth within the context of a weakly coupled aggregate model.Comment: 13 pages, 4 figures, Supplementary Materia
Conference program - ALKALI ACTIVATED MATERIALS AND GEOPOLYMERS: SUSTAINABLE CONSTRUCTION MATERIALS AND CERAMICS MADE UNDER AMBIENT CONDITIONS
The origin of the E+ transition in GaAsN alloys
Optical properties of GaAsN system with nitrogen concentrations in the range
of 0.9-3.7% are studied by full-potential LAPW method in a supercell approach.
The E+ transition is identified by calculating the imaginary part of the
dielectric function. The evolution of the energy of this transition with
nitrogen concentration is studied and the origin of this transition is
identified by analyzing the contributions to the dielectric function from
different band combinations. The L_1c-derived states are shown to play an
important role in the formation of the E+ transition, which was also suggested
by recent experiments. At the same time the nitrogen-induced modification of
the first conduction band of the host compound are also found to contribute
significantly to the E+ transition. Further, the study of several model
supercells demonstrated the significant influence of the nitrogen potential on
the optical properties of the GaAsN system.Comment: 5 pages, 3 figure
Carrier thermal escape in families of InAs/InP self-assembled quantum dots
We investigate the thermal quenching of the multimodal photoluminescence from
InAs/InP (001) self-assembled quantum dots. The temperature evolution of the
photoluminescence spectra of two samples is followed from 10 K to 300 K. We
develop a coupled rate-equation model that includes the effect of carrier
thermal escape from a quantum dot to the wetting layer and to the InP matrix,
followed by transport, recapture or non-radiative recombination. Our model
reproduces the temperature dependence of the emission of each family of quantum
dots with a single set of parameters. We find that the main escape mechanism of
the carriers confined in the quantum dots is through thermal emission to the
wetting layer. The activation energy for this process is found to be close to
one-half the energy difference between that of a given family of quantum dots
and that of the wetting layer as measured by photoluminescence excitation
experiments. This indicates that electron and holes exit the InAs quantum dots
as correlated pairs
How to Choose Your Research Organism
Despite August Kroghâs famous admonition that a âconvenientâ organism exists for every biological problem, we argue that appeals to âconvenienceâ are not sufficient to capture reasoning about organism choice. Instead, we offer a detailed analysis based on empirical data and philosophical arguments for a working set of twenty criteria that interact with each other in the highly contextualized judgements that biologists make about organism choice. We propose to think of these decisions as a form of âdifferential analysisâ where researchers weigh multiple criteria for organismal choice against each other, and often utilize multidimensional refinement processes to finalize their choices. The specific details of any one case make it difficult to draw generalizations or to abstract away from specific research situations. However, this analysis of criteria for organismal choice and how these are related in practice allows us to reflect more generally on what makes a particular organism useful or âgood.
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