2,033 research outputs found
Detecting Axion Stars with Radio Telescopes
When axion stars fly through an astrophysical magnetic background, the
axion-to-photon conversion may generate a large electromagnetic radiation
power. After including the interference effects of the spacially-extended
axion-star source and the macroscopic medium effects, we estimate the radiation
power when an axion star meets a neutron star. For a dense axion star with
, the radiated power is at the order of
10^{11}\,\mbox{W}\times(100\,\mu\mbox{eV}/m_a)^4\,(B/10^{10}\,\mbox{Gauss})^2
with as the axion particle mass and the strength of the neutron star
magnetic field. For axion stars occupy a large fraction of dark matter energy
density, this encounter event with a transient \mathcal{O}(0.1\,\mbox{s})
radio signal may happen in our galaxy with the averaged source distance of one
kiloparsec. The predicted spectral flux density is at the order of Jy for
a neutron star with Gauss. The existing Arecibo, GBT, JVLA and
FAST and the ongoing SKA radio telescopes have excellent discovery potential of
dense axion stars.Comment: 16 pages, 2 figure
Effect of off-diagonal exciton-phonon coupling on intramolecular singlet fission
Intramolecular singlet fission (iSF) materials provide remarkable advantages
in terms of tunable electronic structures, and quantum chemistry studies have
indicated strong electronic coupling modulation by high frequency phonon modes.
In this work, we formulate a microscopic model of iSF with simultaneous
diagonal and off-diagonal coupling to high-frequency modes. A non-perturbative
treatment, the Dirac-Frenkel time-dependent variational approach is adopted
using the multiple Davydov trial states. It is shown that both diagonal and
off-diagonal coupling can aid efficient singlet fission if excitonic coupling
is weak, and fission is only facilitated by diagonal coupling if excitonic
coupling is strong. In the presence of off-diagonal coupling, it is found that
high frequency modes create additional fission channels for rapid iSF. Results
presented here may help provide guiding principles for design of efficient
singlet fission materials by directly tuning singlet-triplet interstate
coupling
Zoomorphic amalgamation: speculative devices for alternative communication
Zoomorphic Amalgamation: Speculative Devices for Alternative Communication is a series of speculative works that assist introverts re-adapting in the extro-oriented society. The work serves as a lens to challenge and question the authority afforded to extroverts in contemporary society, and aims to provide a comprehensive understanding of introverted personality. As a person with an introverted personality, the thesis project draws upon personal experience and to reflect on the current bias and stereotype of characteristics that common to the introverts.
By integrating technological sensors and microcontrollers, the works are created to help the wearer express insecurity, at the same time providing a facsimile of confidence, relaxation, and recharging experience within the duration of wearing. Through interactive engagement the devices embody the connection between the wearer and the observer, and aim to visualize the discomfort of social interaction through forms of movement, sound, and color shift in reference to the defensive behaviors of animals and insects
Digital reflection-mode time-reversed ultrasonically encoded (TRUE) optical focusing
To achieve localized light delivery beyond turbid layers, TRUE optical focusing has been previously implemented by both analog and digital devices. The digital scheme offers a higher energy gain than the analog version. In many biological applications, the reflection-mode configuration, which uses backscattered light from the sample, is more suitable than the transmission-mode configuration. Although reflection-mode analog TRUE focusing has been demonstrated, its digital implementation has not been explored. Here, we report a reflection-mode digital TRUE focusing to concentrate light through a turbid layer. Further, by simply moving the ultrasound focus, we show the system's dynamic focusing capability
Finite-temperature time-dependent variation with multiple Davydov states
The Dirac-Frenkel time-dependent variational approach with Davydov Ans\"atze
is a sophisticated, yet efficient technique to obtain an acuurate solution to
many-body Schr\"odinger equations for energy and charge transfer dy- namics in
molecular aggregates and light-harvesting complexes. We extend this variational
approach to finite temperatures dynamics of the spin-boson model by adopting a
Monte Carlo importance sampling method. In or- der to demonstrate the
applicability of this approach, we compare real-time quantum dynamics of the
spin-boson model calculated with that from numerically exact iterative
quasiadiabatic propagator path integral (QUAPI) technique. The comparison shows
that our variational approach with the single Davydov Ans\"atze is in excellent
agreement with the QUAPI method at high temperatures, while the two differ at
low temperatures. Accuracy in dynamics calculations employing a multitude of
Davydov trial states is found to improve substantially over the single Davydov
Ansatz, especially at low temperatures. At a moderate computational cost, our
variational approach with the multiple Davydov Ansatz is shown to provide
accurate spin-boson dynamics over a wide range of temperatures and bath
spectral densities.Comment: 8 pages, 3 figure
Continuous scanning of a time-reversed ultrasonically encoded optical focus by reflection-mode digital phase conjugation
Time-reversed ultrasonically encoded (TRUE) optical focusing in turbid media was previously implemented using both analog and digital phase conjugation. The digital approach, in addition to its large energy gain, can improve the focal intensity and resolution by iterative focusing. However, performing iterative focusing at each focal position can be time-consuming. Here, we show that by gradually moving the focal position, the TRUE focal intensity is improved, as in iterative focusing at a fixed position, and can be continuously scanned to image fluorescent targets in a shorter time. In addition, our setup is, to the best of our knowledge, the first demonstration of TRUE focusing using a digital phase conjugate mirror in a reflection mode, which is more suitable for practical applications
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Recent changes to Arctic river discharge
Arctic rivers drain ~15% of the global land surface and significantly influence local communities and economies, freshwater and marine ecosystems, and global climate. However, trusted and public knowledge of pan-Arctic rivers is inadequate, especially for small rivers and across Eurasia, inhibiting understanding of the Arctic response to climate change. Here, we calculate daily streamflow in 486,493 pan-Arctic river reaches from 1984-2018 by assimilating 9.18 million river discharge estimates made from 155,710 satellite images into hydrologic model simulations. We reveal larger and more heterogenous total water export (3-17% greater) and water export acceleration (factor of 1.2-3.3 larger) than previously reported, with substantial differences across basins, ecoregions, stream orders, human regulation, and permafrost regimes. We also find significant changes in the spring freshet and summer stream intermittency. Ultimately, our results represent an updated, publicly available, and more accurate daily understanding of Arctic rivers uniquely enabled by recent advances in hydrologic modeling and remote sensing
Optimization of Hydraulic Retention Time and Biomass Concentration in Microalgae Biomass Production from Treated Sewage with a Membrane Photobioreactor
Treated sewage is a promising source of nitrogen and phosphorus in microalgae biomass production for carbon-neutral biofuel and chemical products. In this study, Chlorella vulgaris was continuously cultivated in membrane photobioreactors (MPBRs) under short hydraulic retention times (HRTs) and with different numbers of submerged membrane modules to investigate potential microalgae productivity when treated sewage was used as a nutrient source. Microalgae biomass concentrations were independent of HRT in MPBRs with one membrane module owing to microalgae biomass deposition on the membrane. Installation of an additional submerged membrane module effectively reduced deposition on the submerged membrane, resulting in increased microalgae biomass concentration and volumetric productivity. Growth kinetics suggested that HRT is the essential parameter influencing the volumetric productivity of microalgae under nutrient-limited conditions, and that optimization of the biomass concentration, which depends on the surface/volume ratio of the photobioreactor and initial light intensity, is critical to maximization of the volumetric productivity under light-limited conditions
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