16,521 research outputs found
On the formation of the Kepler-10 planetary system
In this paper, we investigate the conditions required for the 3 and 17 Earth
mass solid planets in the Kepler-10 system to have formed through collisions
and mergers within an initial population of embryos. By performing a large
number of N-body simulations, we show that the total mass of the initial
population had to be significantly larger than the masses of the two planets,
and that the two planets must have built-up farther away than their present
location, at a distance of at least a few au from the central star. The planets
had to grow fast enough so that they would detach themselves from the
population of remaining, less massive, cores and migrate in to their present
location. By the time the other cores migrated in, the disc's inner edge would
have moved out so that these cores cannot be detected today. We also compute
the critical core mass beyond which a massive gaseous envelope would be
accreted and show that it is larger than 17 Earth masses if the planetesimal
accretion rate onto the core is larger than 10^{-6} Earth mass per year. For a
planetesimal accretion rate between 10^{-6} and 10^{-5} Earth mass per year,
the 17 Earth mass core would not be expected to have accreted more than about 1
Earth mass of gas. The results presented in this paper suggest that a planetary
system like Kepler-10 may not be unusual, although it has probably formed in a
rather massive disc.Comment: 12 pages, accepted for publication in MNRA
Electromagnetic Imaging with Atomic Magnetometers: A Novel Approach to Security and Surveillance
We describe our research programme on the use of atomic magnetometers to
detect conductive objects via electromagnetic induction. The extreme
sensitivity of atomic magnetometers at low frequencies, up to seven orders of
magnitude higher than a coil-based system, permits deep penetration through
different media and barriers, and in various operative environments. This
eliminates the limitations usually associated with electromagnetic detection.Comment: 5 pages, 5 figure
Neutrino Emission as Diagnostics of Core-Collapse Supernovae
With myriads of detection events from a prospective Galactic core-collapse
supernova, current and future neutrino detectors will be able to sample
detailed, time-dependent neutrino fluxes and spectra. This offers enormous
possibilities for inferring supernova physics from the various phases of the
neutrino signal from the neutronization burst through the accretion and early
explosion phase to the cooling phase. The signal will constrain the time
evolution of bulk parameters of the young proto-neutron star like its mass and
radius as well as the structure of the progenitor, probe multi-dimensional
phenomena in the supernova core, and constrain thedynamics of the early
explosion phase. Aside from further astrophysical implications, supernova
neutrinos may also shed further light on the properties of matter at
supranuclear densities and on open problems in particle physics.Comment: 26 pages, 5 figures. Accepted for publication in Annual Review of
Nuclear and Particle Science, vol. 69. Non-copyedited version prepared by the
autho
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Room temperature "optical nanodiamond hyperpolarizer": Physics, design, and operation.
Dynamic Nuclear Polarization (DNP) is a powerful suite of techniques that deliver multifold signal enhancements in nuclear magnetic resonance (NMR) and MRI. The generated athermal spin states can also be exploited for quantum sensing and as probes for many-body physics. Typical DNP methods require the use of cryogens, large magnetic fields, and high power microwave excitation, which are expensive and unwieldy. Nanodiamond particles, rich in Nitrogen-Vacancy (NV) centers, have attracted attention as alternative DNP agents because they can potentially be optically hyperpolarized at room temperature. Here, unraveling new physics underlying an optical DNP mechanism first introduced by Ajoy et al. [Sci. Adv. 4, eaar5492 (2018)], we report the realization of a miniature "optical nanodiamond hyperpolarizer," where 13C nuclei within the diamond particles are hyperpolarized via the NV centers. The device occupies a compact footprint and operates at room temperature. Instrumental requirements are very modest: low polarizing fields, low optical and microwave irradiation powers, and convenient frequency ranges that enable miniaturization. We obtain the best reported optical 13C hyperpolarization in diamond particles exceeding 720 times of the thermal 7 T value (0.86% bulk polarization), corresponding to a ten-million-fold gain in averaging time to detect them by NMR. In addition, the hyperpolarization signal can be background-suppressed by over two-orders of magnitude, retained for multiple-minute long periods at low fields, and deployed efficiently even to 13C enriched particles. Besides applications in quantum sensing and bright-contrast MRI imaging, this work opens possibilities for low-cost room-temperature DNP platforms that relay the 13C polarization to liquids in contact with the high surface-area particles
Connectivity-Enforcing Hough Transform for the Robust Extraction of Line Segments
Global voting schemes based on the Hough transform (HT) have been widely used
to robustly detect lines in images. However, since the votes do not take line
connectivity into account, these methods do not deal well with cluttered
images. In opposition, the so-called local methods enforce connectivity but
lack robustness to deal with challenging situations that occur in many
realistic scenarios, e.g., when line segments cross or when long segments are
corrupted. In this paper, we address the critical limitations of the HT as a
line segment extractor by incorporating connectivity in the voting process.
This is done by only accounting for the contributions of edge points lying in
increasingly larger neighborhoods and whose position and directional content
agree with potential line segments. As a result, our method, which we call
STRAIGHT (Segment exTRAction by connectivity-enforcInG HT), extracts the
longest connected segments in each location of the image, thus also integrating
into the HT voting process the usually separate step of individual segment
extraction. The usage of the Hough space mapping and a corresponding
hierarchical implementation make our approach computationally feasible. We
present experiments that illustrate, with synthetic and real images, how
STRAIGHT succeeds in extracting complete segments in several situations where
current methods fail.Comment: Submitted for publicatio
Information Storage and Retrieval for Probe Storage using Optical Diffraction Patterns
A novel method for fast information retrieval from a probe storage device is
considered. It is shown that information can be stored and retrieved using the
optical diffraction patterns obtained by the illumination of a large array of
cantilevers by a monochromatic light source. In thermo-mechanical probe
storage, the information is stored as a sequence of indentations on the polymer
medium. To retrieve the information, the array of probes is actuated by
applying a bending force to the cantilevers. Probes positioned over
indentations experience deflection by the depth of the indentation, probes over
the flat media remain un-deflected. Thus the array of actuated probes can be
viewed as an irregular optical grating, which creates a data-dependent
diffraction pattern when illuminated by laser light. We develop a low
complexity modulation scheme, which allows the extraction of information stored
in the pattern of indentations on the media from Fourier coefficients of the
intensity of the diffraction pattern. We then derive a low-complexity maximum
likelihood sequence detection algorithm for retrieving the user information
from the Fourier coefficients. The derivation of both the modulation and the
detection schemes is based on the Fraunhofer formula for data-dependent
diffraction patterns. We show that for as long as the Fresnel number F<0.1, the
optimal channel detector derived from Fraunhofer diffraction theory does not
suffer any significant performance degradation.Comment: 14 pages, 11 figures. Version 2: minor misprints corrected,
experimental section expande
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