Optomechanical Actuation of Diamagnetically Levitated Pyrolytic Graphite

Ewall-Wice, Miriam; Yee, Steven; DeLawder, Kelly; Montgomery, Steve; Joyce, Peter; Brownell, Cody; ElBidweihy, Hatem

doi:10.1109/tmag.2019.2892332

Cited by 21 publications

(14 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…According to Eq. 1, many mechanisms recently have been proposed to explain this significant anomaly, [2,[6][7][8][9][10][11][12][13][14][15][16], such as (a) reducing the spin temperature T s , or (b) increasing the effective background radiation temperature T γ such that T γ > T CMB , or (c) reducing the Hubble parameter.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Can conformal and disformal couplings between dark sectors explain the EDGES 21-cm anomaly?

Xiao

et al. 2019

Phys. Rev. D

View full text Add to dashboard Cite

The recently announced result by EDGES points an unexpected excess in the 21 cm global brightness temperature from cosmic dawn at z ∼ 17, potentially indicating new phenomena beyond the ΛCDM model. A generic cosmological model which allows conformal and disformal couplings between dark matter and dark energy is employed to investigate the impact on the 21cm absorption signal and understand the EDGES anomaly. After exploring a wide range of parameter space for couplings, we find that the coupling effects can lead to a moderate change in the Hubble parameter while a negligible change in the spin temperature in the early Universe. Consequently, the decrease of the Hubble parameter from the mixed conformal and disformal couplings can reproduce the 21cm absorption approximately in consistent with the EDGES result at z = 17.5. However, there is still tension in corresponding parameter space between EDGES and other cosmological observations for this model. arXiv:1807.05541v2 [astro-ph.CO]

show abstract

Section: Introductionmentioning

confidence: 99%

“…Alternatively, it is possible to raise the radiation temperature by adding extra radio backgrounds in the early universe. Some examples for this attempts were given in [13,14], where extra photons are expected to be produced either by accretion of intermediate mass black holes or by light WIMPs annihilation or decay.…”

Section: Introductionmentioning

confidence: 99%

Can conformal and disformal couplings between dark sectors explain the EDGES 21-cm anomaly?

Xiao

et al. 2019

Phys. Rev. D

View full text Add to dashboard Cite

show abstract

“…In the experiment, it was shown that the graphite is attracted to the photo irradiated region. 20,25 This can be understood that the graphite minimizes the total energy by moving to the high temperature area, where the diamagnetism is smaller so that the energy cost is lower under the same magnetic field.…”

Section: Thermal Gradient Driven Motionmentioning

confidence: 99%

“…1, where the alternating pattern of magnetic poles generates a magnetic field gradient to support a diamagnetic object in a free space. 13,[18][19][20]24,25 A recent experiment performed a detailed measurement of the levitation height of a graphite piece in this geometry. 20 The same experiment also demonstrated an optical motion control in the diamagnetic levitation, where the levitating graphite is moved towards the photo irradiated spot, motivated by the photothermal change in the magnetic susceptibility.…”

Section: Introductionmentioning

confidence: 99%

Diamagnetic levitation and thermal gradient driven motion of graphite

Fujimoto

Koshino

2019

Phys. Rev. B

View full text Add to dashboard Cite

We theoretically study the diamagnetic levitation and the thermal-driven motion of graphite. Using the quantum-mechanically derived magnetic susceptibility, we compute the equilibrium position of levitating graphite over a periodic arrangement of magnets, and investigate the dependence of the levitation height on the susceptibility and the geometry. We find that the levitation height is maximized at a certain period of the magnets, and the maximum height is then linearly proportional to the susceptibility of the levitating object. We compare the ordinary AB-stacked graphite and a randomly stacked graphite, and show that the latter exhibits a large levitation length particularly in low temperatures, because of its diamagnetism inversely proportional to the temperature. Finally, we demonstrate that the temperature gradient moves the levitating object towards the high temperature side, and estimate the generated force as a function of susceptibility.

show abstract

“…Nevertheless, at the operating frequency of these new low-frequency interferometers , our limited understanding of the sky leads to incomplete models. Model-based calibration with incomplete sky models causes calibration errors that lead to image artifacts, which in turn limit the dynamic range of observations (Grobler et al 2014;Wijnholds et al 2016) and, more relevant to EoR science, contaminate the power spectrum (Barry et al 2016;Ewall-Wice et al 2016;Trott & Wayth 2017). Redundant calibration, however, allows us to escape our ignorance of the low frequency sky because it does not require modelling (Wieringa 1992).…”

Section: Introductionmentioning

confidence: 99%

The Bias and Uncertainty of Redundant and Sky-based Calibration Under Realistic Sky and Telescope Conditions

Joseph

Trott

Wayth

2018

View full text Add to dashboard Cite

The advent of a new generation of low frequency interferometers has opened a direct window into the Epoch of Reionisation (EoR). However, key to a detection of the faint 21-cm signal, and reaching the sensitivity limits of these arrays, is a detailed understanding of the instruments and their calibration. In this work we use simulations to investigate the bias and uncertainty of redundancy based calibration. Specifically, we study the influence of the flux distribution of the radio sky and the impact of antenna position offsets on the complex calibration solutions. We find that the position offsets introduce a bias into the phase component of the calibration solutions. This phase bias increases with the distance between bright radio sources and the pointing center, and with the flux density of these sources. This is potentially problematic for redundant calibration on MWA observations of EoR fields 1 and 2. EoR field 0, however, lacks such sources. We also compared the simulations with theoretical estimates for the bias and uncertainty in sky model based calibration on incomplete sky models for the redundant antenna tiles in the MWA. Our results indicate that redundant calibration outperforms sky based calibration due to the high positional precision of the MWA antenna tiles.

show abstract

Optomechanical Actuation of Diamagnetically Levitated Pyrolytic Graphite

Cited by 21 publications

References 15 publications

Can conformal and disformal couplings between dark sectors explain the EDGES 21-cm anomaly?

Can conformal and disformal couplings between dark sectors explain the EDGES 21-cm anomaly?

Diamagnetic levitation and thermal gradient driven motion of graphite

The Bias and Uncertainty of Redundant and Sky-based Calibration Under Realistic Sky and Telescope Conditions

Contact Info

Product

Resources

About