1,403 research outputs found
Probing sunspots with two-skip time-distance helioseismology
Previous helioseismology of sunspots has been sensitive to both the
structural and magnetic aspects of sunspot structure. We aim to develop a
technique that is insensitive to the magnetic component so the two aspects can
be more readily separated. We study waves reflected almost vertically from the
underside of a sunspot. Time-distance helioseismology was used to measure
travel times for the waves. Ray theory and a detailed sunspot model were used
to calculate travel times for comparison. It is shown that these large distance
waves are insensitive to the magnetic field in the sunspot. The largest travel
time differences for any solar phenomena are observed. With sufficient modeling
effort, these should lead to better understanding of sunspot structure
Inversions of synthetic umbral flashes: effects of the scanning time on the inferred atmospheres
The use of instruments that record narrow band images at selected wavelengths
is a common approach in solar observations. They allow the scanning of a
spectral line by sampling the Stokes profiles with 2D images at each line
position, but require a compromise between spectral resolution and temporal
cadence. We evaluate the impact of the time-dependent acquisition of different
wavelengths on the inversion of spectropolarimetric profiles from chromospheric
lines during umbral flashes. Simulations of non-linear wave propagation in a
sunspot were performed with the code MANCHA. Synthetic Stokes parameters in the
Ca II 8542 A line in NLTE were computed for an umbral flash using the code
NICOLE. Artificial profiles with the same wavelength coverage and temporal
cadence from reported observations were constructed and inverted. The inferred
atmospheric stratifications were compared with the original models. The
inferred atmospheres provide a reasonable characterization of the thermodynamic
properties of the atmosphere during most of the phases of the umbral flash.
Only at the early stages of the flash, when the shock wave reaches the
formation height of the line, the Stokes profiles present apparent wavelength
shifts and other spurious deformations. These features are misinterpreted by
the inversion code, which can return unrealistic atmospheric models from a good
fit of the Stokes profiles. The misguided results include flashed atmospheres
with strong downflows, even though the simulation exhibits upflows during the
umbral flash, and large variations in the magnetic field strength. Our analyses
validate the inversion of Stokes profiles acquired by sequentially scanning
certain selected wavelengths of a line profile, even in the case of
rapidly-changing events such as umbral flashes. However, the inversions are
unreliable during a short period at the development phase of the flash.Comment: Accepted for publication in A&
Affective uplift during video game play:A naturalistic case study
Do video games affect playersâ well-being? In this case study, we examined 162,325 intensive longitudinal in-game mood reports from 67,328 play sessions of 8,695 players of the popular game PowerWash Simulator. We compared playersâ moods at the beginning of play session with their moods during play, and found that the average player reported 0.034 [0.032, 0.036] visual analog scale (VAS; 0-1) units greater mood during than at the beginning of play sessions. Moreover, we predict that 72.1% [70.8%, 73.5%] of similar players experience this affective uplift during play, and that the bulk of it happens during the first 15 minutes of play. We do not know whether these results indicate causal effects or to what extent they generalize to other games or player populations. Yet, these results based on in-game subjective reports from players of a popular commercially available game suggest good external validity, and as such offer a promising glimpse of the scientific value of transparent industry-academia collaborations in understanding the psychological roles of popular digital entertainment
Realistic model atmosphere and revised abundances of the coolest Ap star HD101065
Among the known Ap stars, HD101065 is probably one of the most interesting
objects, demonstrating very rich spectra of rare-earth elements (REE). Strongly
peculiar photometric parameters of this star that can not be fully reproduced
by any modern theoretical calculations, even those accounting for realistic
chemistry of its atmosphere. In this study we investigate a role of missing REE
line opacity and construct a self-consistent atmospheric model based on
accurate abundance and chemical stratification analysis. We employed the
LLmodels stellar model atmosphere code together with DDAFit and SynthMag
software packages to derive homogeneous and stratified abundances for 52
chemical elements and to construct a self-consistent model of HD101065
atmosphere. The opacity in REE lines is accounted for in details, by using
up-to-date extensive theoretical calculations. We show that REE elements play a
key role in the radiative energy balance in the atmosphere of HD101065, leading
to the strong suppression of the Balmer jump and energy redistribution very
different from that of normal stars. Introducing new line lists of REEs allowed
us to reproduce, for the first time, spectral energy distribution of HD101065
and achieve a better agreement between the unusually small observed Str\"omgren
c1 index and the model predictions. Using combined photometric and
spectroscopic approaches and based on the iterative procedure of abundance and
stratification analysis we find effective temperature of HD101065 to be
Teff=6400K.Comment: Accepted by A&A, 13 pages (3 of Online Material), 10 figures, 4
table
Small-scale dynamo in cool main sequence stars. II. The effect of metallicity
All cool main sequence stars including our Sun are thought to have magnetic
fields. Observations of the Sun revealed that even in quiet regions small-scale
turbulent magnetic fields are present. Simulations further showed that such
magnetic fields affect the subsurface and photospheric structure, and thus the
radiative transfer and emergent flux. Since small-scale turbulent magnetic
fields on other stars cannot be directly observed, it is imperative to study
their effects on the near surface layers numerically. Until recently
comprehensive three-dimensional simulations capturing the effect of small-scale
turbulent magnetic fields only exists for the solar case. A series of
investigations extending SSD simulations for other stars has been started. Here
we aim to examine small-scale turbulent magnetic fields in stars of solar
effective temperature but different metallicity. We investigate the properties
of three-dimensional simulations of the magneto-convection in boxes covering
the upper convection zone and photosphere carried out with the MURaM code for
metallicity values of with and without a
small-scale-dynamo. We find that small-scale turbulent magnetic fields enhanced
by a small-scale turbulent dynamo noticeably affect the subsurface dynamics and
significantly change the flow velocities in the photosphere. Moreover,
significantly stronger magnetic field strengths are present in the convection
zone for low metallicity. Whereas, at the optical surface the averaged vertical
magnetic field ranges from 64G for M/H = 0.5 to 85G for M/H = -1.0.Comment: 13 pages, 18 figures, submitted to A&
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Does taking a short break from social media have a positive effect on well-being? Evidence from three preregistered field experiments
Concerns about the consequences of social media use on well-being has led to the practice of taking a brief hiatus from social media platforms, a practice known as âdigital detoxing.â These brief âdigital detoxesâ are becoming increasingly popular in the hope that the newly found time, previously spent on social media, would be used for other, theoretically more rewarding, activities. In this paper, we test this proposition. Participants in three preregistered field experiments (ntot = 600) were randomly assigned to receiving each of two conditions on each of two different days: a normal-use day or an abstinence day. Outcomes (social relatedness, positive and negative affect, day satisfaction) were measured on each of the two evenings of the study. Results did not show that abstaining from social media has positive effects on daily well-being (in terms of social relatedness, positive and negative affect, day satisfaction) as suggested by the extant literature. Participants reported similar well-being on days when they used social media and days when they did not. Evidence indicated that abstinence from social media had no measurable positive effect on well-being, and some models showed significant deficits in social relatedness and satisfaction with oneâs day. We discuss implications of the study of social media hiatus and the value of programmatic research grounded in preregistered experimental designs
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Selective agents in the adaptive radiation of Hebridean sticklebacks
Question: What selective agents underpin the adaptive radiation of threespine sticklebacks (Gasterosteus aculeatus) on the Outer Hebridean island of North Uist?
Hypothesis: The chief agents of selection for lateral plate number and pelvic score are predatory trout, the availability of dissolved ions, or an interaction of both.
Methods: Adult threespine sticklebacks were collected from 26 lochs on North Uist. Fish were killed, stained, and scored for lateral plate number and pelvic score. We also measured the pH and concentration of dissolved calcium and phosphorous of each loch. We assessed the abundance of predatory trout in a subset of lochs by âfly fishingâ using a lure that mimicked the appearance of sticklebacks.
Results: Dissolved calcium and phosphorous predicted stickleback lateral plate number and pelvic score, while trout abundance failed to predict either. Attack rates by trout on stickleback lures were higher in lochs with higher numbers of trout, with high water clarity, and at higher water temperatures. Our findings implicate a role for the bioavailability of dissolved ions in selection for reduced lateral plate number and pelvic score evolution, with indirect evidence for an effect of trout predation on the adaptive radiation of stickleback populations on North Uist
Optimal precision and accuracy in 4Pi-STORM using dynamic spline PSF models
Coherent fluorescence imaging with two objective lenses (4Pi detection) enables single-molecule localization microscopy with sub-10 nm spatial resolution in three dimensions. Despite its outstanding sensitivity, wider application of this technique has been hindered by complex instrumentation and the challenging nature of the data analysis. Here we report the development of a 4Pi-STORM microscope, which obtains optimal resolution and accuracy by modeling the 4Pi point spread function (PSF) dynamically while also using a simpler optical design. Dynamic spline PSF models incorporate fluctuations in the modulation phase of the experimentally determined PSF, capturing the temporal evolution of the optical system. Our method reaches the theoretical limits for precision and minimizes phase-wrapping artifacts by making full use of the information content of the data. 4Pi-STORM achieves a near-isotropic three-dimensional localization precision of 2â3 nm, and we demonstrate its capa-bilities by investigating protein and nucleic acid organization in primary neurons and mammalian mitochondria
The AMANDA Neutrino Telescope: Principle of Operation and First Results
AMANDA is a high-energy neutrino telescope presently under construction at
the geographical South Pole. In the Antarctic summer 1995/96, an array of 80
optical modules (OMs) arranged on 4 strings (AMANDA-B4) was deployed at depths
between 1.5 and 2 km. In this paper we describe the design and performance of
the AMANDA-B4 prototype, based on data collected between February and November
1996. Monte Carlo simulations of the detector response to down-going
atmospheric muon tracks show that the global behavior of the detector is
understood. We describe the data analysis method and present first results on
atmospheric muon reconstruction and separation of neutrino candidates. The
AMANDA array was upgraded with 216 OMs on 6 new strings in 1996/97
(AMANDA-B10), and 122 additional OMs on 3 strings in 1997/98.Comment: 36 pages, 23 figures, submitted to Astroparticle Physic
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