602 research outputs found
Feasibility of UV lasing without inversion in mercury vapor
We investigate the feasibility of UV lasing without inversion at a wavelength
of nm utilizing interacting dark resonances in mercury vapor. Our
theoretical analysis starts with radiation damped optical Bloch equations for
all relevant 13 atomic levels. These master equations are generalized by
considering technical phase noise of the driving lasers. From the Doppler
broadened complex susceptibility we obtain the stationary output power from
semiclassical laser theory. The finite overlap of the driving Gaussian laser
beams defines an ellipsoidal inhomogeneous gain distribution. Therefore, we
evaluate the intra-cavity field inside a ring laser self-consistently with
Fourier optics. This analysis confirms the feasibility of UV lasing and reveals
its dependence on experimental parameters.Comment: changes were made according to reviewer comments (accepted for
publication in JOSA B
A Minimalist Approach to Type-Agnostic Detection of Quadrics in Point Clouds
This paper proposes a segmentation-free, automatic and efficient procedure to
detect general geometric quadric forms in point clouds, where clutter and
occlusions are inevitable. Our everyday world is dominated by man-made objects
which are designed using 3D primitives (such as planes, cones, spheres,
cylinders, etc.). These objects are also omnipresent in industrial
environments. This gives rise to the possibility of abstracting 3D scenes
through primitives, thereby positions these geometric forms as an integral part
of perception and high level 3D scene understanding.
As opposed to state-of-the-art, where a tailored algorithm treats each
primitive type separately, we propose to encapsulate all types in a single
robust detection procedure. At the center of our approach lies a closed form 3D
quadric fit, operating in both primal & dual spaces and requiring as low as 4
oriented-points. Around this fit, we design a novel, local null-space voting
strategy to reduce the 4-point case to 3. Voting is coupled with the famous
RANSAC and makes our algorithm orders of magnitude faster than its conventional
counterparts. This is the first method capable of performing a generic
cross-type multi-object primitive detection in difficult scenes. Results on
synthetic and real datasets support the validity of our method.Comment: Accepted for publication at CVPR 201
ECoG high gamma activity reveals distinct cortical representations of lyrics passages, harmonic and timbre-related changes in a rock song
Listening to music moves our minds and moods, stirring interest in its neural underpinnings. A multitude of compositional features drives the appeal of natural music. How such original music, where a composer's opus is not manipulated for experimental purposes, engages a listener's brain has not been studied until recently. Here, we report an in-depth analysis of two electrocorticographic (ECoG) data sets obtained over the left hemisphere in ten patients during presentation of either a rock song or a read-out narrative. First, the time courses of five acoustic features (intensity, presence/absence of vocals with lyrics, spectral centroid, harmonic change, and pulse clarity) were extracted from the audio tracks and found to be correlated with each other to varying degrees. In a second step, we uncovered the specific impact of each musical feature on ECoG high-gamma power (70–170 Hz) by calculating partial correlations to remove the influence of the other four features. In the music condition, the onset and offset of vocal lyrics in ongoing instrumental music was consistently identified within the group as the dominant driver for ECoG high-gamma power changes over temporal auditory areas, while concurrently subject-individual activation spots were identified for sound intensity, timbral, and harmonic features. The distinct cortical activations to vocal speech-related content embedded in instrumental music directly demonstrate that song integrated in instrumental music represents a distinct dimension in complex music. In contrast, in the speech condition, the full sound envelope was reflected in the high gamma response rather than the onset or offset of the vocal lyrics. This demonstrates how the contributions of stimulus features that modulate the brain response differ across the two examples of a full-length natural stimulus, which suggests a context-dependent feature selection in the processing of complex auditory stimuli
Design Principles for Systematic Search Systems: A Holistic Synthesis of a Rigorous Multi-cycle Design Science Research Journey
Rigorous systematic literature searches are often described as complex, error-prone and time-consuming because of a prevailing lack of adequate technological assistance. Nonetheless, one of the first steps when conducting a rigorous literature review is finding an appropriate literature sample. The quality of this literature sample is an important factor for the overall quality of the literature review. This article investigates how to design innovative IT systems that effectively facilitate systematic literature searches. Applying the design science research paradigm, the research method consists of multiple design cycles of artifact development, evaluation, and refinement. In doing so, six design principles are derived that intend to increase the comprehensiveness, precision, and reproducibility of systematic literature searches. The results could be helpful for research and practice. The derived design knowledge builds a foundation for future research on systematic search systems and enables new methodological contributions. The results could also guide the development of innovative search systems and features that, eventually, increase the quality and efficiency of information accumulation in different contexts
A Good Beginning Makes a Good Ending: Incipient Sources of Knowledge in Design Science Research
Design science research (DSR) focuses on providing innovative solution knowledge to complex and hitherto unsolved problems. Identifying both relevant problems and unique solutions require in-depth understanding of the problem domain and potential solution technologies. Incipient sources of knowledge provide the means to find such important design problems, evaluate their relevance, and create innovative, tentative designs to tackle these problems. However, current DSR literature provides little guidance for identification, selection, and consumption of incipient knowledge. In this paper, we, therefore, set out to identify and analyze the incipient sources of knowledge in DSR with the help of a comprehensive literature review. Our work could thereby serve as a starting point for further exploration of the nature of design science knowledge and help to create novel guidelines and research processes that guide the selection and utilization of incipient DSR knowledge sources
Generic Primitive Detection in Point Clouds Using Novel Minimal Quadric Fits
We present a novel and effective method for detecting 3D primitives in
cluttered, unorganized point clouds, without axillary segmentation or type
specification. We consider the quadric surfaces for encapsulating the basic
building blocks of our environments - planes, spheres, ellipsoids, cones or
cylinders, in a unified fashion. Moreover, quadrics allow us to model higher
degree of freedom shapes, such as hyperboloids or paraboloids that could be
used in non-rigid settings.
We begin by contributing two novel quadric fits targeting 3D point sets that
are endowed with tangent space information. Based upon the idea of aligning the
quadric gradients with the surface normals, our first formulation is exact and
requires as low as four oriented points. The second fit approximates the first,
and reduces the computational effort. We theoretically analyze these fits with
rigor, and give algebraic and geometric arguments. Next, by re-parameterizing
the solution, we devise a new local Hough voting scheme on the null-space
coefficients that is combined with RANSAC, reducing the complexity from
to (three points). To the best of our knowledge, this is the
first method capable of performing a generic cross-type multi-object primitive
detection in difficult scenes without segmentation. Our extensive qualitative
and quantitative results show that our method is efficient and flexible, as
well as being accurate.Comment: Submitted to IEEE Transactions on Pattern Analysis and Machine
Intelligence (T-PAMI). arXiv admin note: substantial text overlap with
arXiv:1803.0719
Comment on Transverse Charge Density and the Radius of the Proton
The charge radius of the proton is typically determined from electron-proton
scattering by extracting the proton's electric form factor and then making use
of the derivative of that form factor at zero four-momentum transfer.
Unfortunately, experimentally, one cannot measure to zero four-momentum
transfer and thus extrapolation is often required. In the work of Alexander
Gramolin and Rebecca Russell, they present a novel method that does not use the
slope and found a radius of the proton that contradicts many other recent
results. Our analysis of their paper discusses some issues with this method and
we show that by simply changing the binning of the data and/or including an
additional set of data the results change dramatically.Comment: 6 pages, 1 figur
Combined influence of ectoine and salt: spectroscopic and numerical evidence for compensating effects on aqueous solutions
Ectoine is an important osmolyte, which allows microorganisms to survive in
extreme environmental salinity. The hygroscopic effects of ectoine in pure
water can be explained by a strong water binding behavior whereas a study on
the effects of ectoine in salty solution is yet missing. We provide Raman
spectroscopic evidence that the influence of ectoine and NaCl are opposing and
completely independent of each other. The effect can be explained by the
formation of strongly hydrogen-bonded water molecules around ectoine which
compensate the influence of the salt on the water dynamics. The mechanism is
corroborated by first principles calculations and broadens our understanding
of zwitterionic osmolytes in aqueous solution. Our findings allow us to
provide a possible explanation for the relatively high osmolyte concentrations
in halotolerant bacteria
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