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  • 1
    Online Resource
    Online Resource
    Dark Matter Deficient Galaxies Produced via High-velocity Galaxy Collisions in High-resolution Numerical Simulations
    American Astronomical Society ; 2020
    In:  The Astrophysical Journal Vol. 899, No. 1 ( 2020-08-01), p. 25-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 899, No. 1 ( 2020-08-01), p. 25-
    Abstract: The recent discovery of diffuse dwarf galaxies that are deficient in dark matter appears to challenge the current paradigm of structure formation in our universe. We describe numerical experiments to determine if so-called dark matter deficient galaxies (DMDGs) could be produced when two gas-rich, dwarf-sized galaxies collide with a high relative velocity of ∼300 km s −1 . Using idealized high-resolution simulations with both mesh-based and particle-based gravito-hydrodynamics codes, we find that DMDGs can form as high-velocity galaxy collisions and separate dark matter from the warm disk gas, which subsequently is compressed by shock and tidal interaction to form stars. Then using the large simulated universe Il lustris TNG, we discover a number of high-velocity galaxy collision events in which DMDGs are expected to form. However, we did not find evidence that these types of collisions actually produced DMDGs in the TNG100-1 run. We argue that the resolution of the numerical experiment is critical to realizing the “collision-induced” DMDG formation scenario. Our results demonstrate one of many routes in which galaxies could form with unconventional dark matter fractions.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/aba434
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2020
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    SSG: 16,12
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  • 2
    Online Resource
    Online Resource
    Growth of a Massive Black Hole in a Dense Star Cluster Via Tidal Disruption Accretion
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 943, No. 2 ( 2023-02-01), p. 77-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 943, No. 2 ( 2023-02-01), p. 77-
    Abstract: Stars that are tidally disrupted by a massive black hole (MBH) may contribute significantly to the growth of the MBH, especially in dense nuclear star clusters. Yet, this tidal disruption accretion (TDA) of stars onto the MBH has largely been overlooked compared to the gas accretion (GA) channel in most numerical experiments until now. In this work, we implement a black hole growth channel via TDA in the high-resolution adaptive mesh refinement code Enzo to investigate its influence on an MBH seed’s early evolution. We find that an MBH seed grows rapidly from 10 3 to ≳10 6 M ⊙ in 200 Myr in some of the tested simulations. Compared to an MBH seed that grows only via GA, TDA can enhance the MBH’s growth rate by more than 1 order of magnitude. However, as predicted, TDA mainly helps the early growth of the MBH (from 10 3–4 to ≲10 5 M ⊙ ) while the later evolution is generally dominated by GA. We also observe that the star formation near the MBH is suppressed when TDA is the most active, sometimes with a visible cavity in gas (of size ∼ a few pc) created in the vicinity of the MBH. It is because the MBH may grow expeditiously with both GA and TDA, and the massive MBH could consume its neighboring gas faster than being replenished by gas inflows. Our study demonstrates the need to consider different channels of black hole accretion that may provide clues for the existence of supermassive black holes at high redshifts.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/aca75d
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 3
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    Online Resource
    Calibration of a star formation and feedback model for cosmological simulations with enzo
    Oxford University Press (OUP) ; 2020
    In:  Monthly Notices of the Royal Astronomical Society Vol. 497, No. 4 ( 2020-10-01), p. 5203-5219
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 497, No. 4 ( 2020-10-01), p. 5203-5219
    Abstract: We introduce a new methodology for efficiently tuning sub-grid models of star formation and supernovae feedback in cosmological simulations and at the same time understanding their physical implications. Based on a set of 71 zoom simulations of a Milky Way (MW)-sized halo, we explore the feasibility of calibrating a widely used star formation and feedback model in the enzo simulation code. We propose a novel way to match observations, using functional fits to the observed baryon makeup over a wide range of halo masses. The model MW galaxy is calibrated using three parameters: the star formation efficiency (f*), the efficiency of thermal energy from stellar feedback (ϵ), and the region into which feedback is injected (r  and s). We find that changing the amount of feedback energy affects the baryon content most significantly. We then identify two sets of feedback parameter values that are both able to reproduce the baryonic properties for haloes between $10^{10}\, \mathrm{M_\odot }$ and $10^{12}\, \mathrm{M_\odot }$. We can potentially improve the agreement by incorporating more parameters or physics. If we choose to focus on one property at a time, we can obtain a more realistic halo baryon makeup. Contrasting both star formation criteria and the corresponding combination of optimal feedback parameters, we also highlight that feedback effects can be complementary: to match the same baryonic properties, with a relatively higher gas-to-stars conversion efficiency, the feedback strength required is lower, and vice versa. Lastly, we demonstrate that chaotic variance in the code can cause deviations of approximately 10 per cent and 25 per cent in the stellar and baryon mass in simulations evolved from identical initial conditions.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/staa2318
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2020
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 4
    Online Resource
    Online Resource
    Machine-guided exploration and calibration of astrophysical simulations
    Oxford University Press (OUP) ; 2022
    In:  Monthly Notices of the Royal Astronomical Society Vol. 515, No. 1 ( 2022-07-19), p. 693-705
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 515, No. 1 ( 2022-07-19), p. 693-705
    Abstract: We apply a novel method with machine learning to calibrate sub-grid models within numerical simulation codes to achieve convergence with observations and between different codes. It utilizes active learning and neural density estimators. The hyper parameters of the machine are calibrated with a well-defined projectile motion problem. Then, using a set of 22 cosmological zoom simulations, we tune the parameters of a popular star formation and feedback model within Enzo to match observations. The parameters that are adjusted include the star formation efficiency, coupling of thermal energy from stellar feedback, and volume into which the energy is deposited. This number translates to a factor of more than three improvements over manual calibration. Despite using fewer simulations, we obtain a better agreement to the observed baryon makeup of a Milky Way (MW)-sized halo. Switching to a different strategy, we improve the consistency of the recommended parameters from the machine. Given the success of the calibration, we then apply the technique to reconcile metal transport between grid-based and particle-based simulation codes using an isolated galaxy. It is an improvement over manual exploration while hinting at a less-known relation between the diffusion coefficient and the metal mass in the halo region. The exploration and calibration of the parameters of the sub-grid models with a machine learning approach is concluded to be versatile and directly applicable to different problems.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stac1614
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2022
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 5
    Online Resource
    Online Resource
    Leveraging social networking sites for disease surveillance and public sensing: the case of the 2013 avian influenza A(H7N9) outbreak in China
    World Health Organization, Western Pacific Regional Office ; 2015
    In:  Western Pacific Surveillance and Response Journal Vol. 6, No. 2 ( 2015-06-30), p. 66-72
    Details
    In: Western Pacific Surveillance and Response Journal, World Health Organization, Western Pacific Regional Office, Vol. 6, No. 2 ( 2015-06-30), p. 66-72
    Type of Medium: Online Resource
    ISSN: 2094-7321 , 2094-7313
    URL: Issue
    URL: Journal
    URL: Article
    DOI: 10.5365/wpsar.2015.6.2
    DOI: 10.5365/wpsar
    DOI: 10.5365/wpsar.2015.6.1.013
    Language: Unknown
    Publisher: World Health Organization, Western Pacific Regional Office
    Publication Date: 2015
    detail.hit.zdb_id: 2592503-9
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  • 6
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    Online Resource
    Evolving beyond z =0: insights about the future of stars and the intergalactic medium
    Oxford University Press (OUP) ; 2021
    In:  Monthly Notices of the Royal Astronomical Society Vol. 507, No. 4 ( 2021-09-16), p. 5432-5450
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 507, No. 4 ( 2021-09-16), p. 5432-5450
    Abstract: We present results from seven cosmological simulations that have been extended beyond the present era as far as redshift z ≈ −0.99 or $t\approx 96.0\, {\rm Gyr}$, using the Enzo simulation code. We adopt the calibrated star formation and feedback prescriptions from our previous work on reproducing the Milky Way with Enzo, with modifications to the simulation code, chemistry, and cooling library. We then consider the future behaviour of the halo mass function (HMF), the equation of state (EOS) of the IGM, and the cosmic star formation history (SFH). Consistent with previous work, we find a freeze out in the HMF at z ≈ −0.6 or $t\approx 28.1\, {\rm Gyr}$. The evolution of the EOS of the IGM presents an interesting case study of the cosmological coincidence problem, where there is a sharp decline in the IGM temperature immediately after z = 0. For the SFH, the simulations produce a peak and a subsequent decline into the future. However, we do find a turnaround in the SFH after z ≈ −0.98 or $t\approx 82.4\, {\rm Gyr}$ in some simulations, which we attribute to limitations of the criteria used for star formation. By integrating the SFH in time up to z ≈ −0.92 or $t\approx 55.1\, {\rm Gyr}$, the simulation with the best spatial resolution predicts an asymptotic total stellar mass that is very close to that obtained from extrapolating the fit of the observed SFR. Lastly, we investigate the future evolution of the partition of baryons within a Milky Way-sized galaxy, using both a zoom and a box simulation. Despite vastly different resolutions, these simulations predict individual haloes containing an equal fraction of baryons in stars and gas at the time of freeze out.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stab2473
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 7
    Online Resource
    Online Resource
    The fate of baryons in counterfactual universes
    Oxford University Press (OUP) ; 2022
    In:  Monthly Notices of the Royal Astronomical Society Vol. 517, No. 1 ( 2022-10-04), p. 59-75
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 517, No. 1 ( 2022-10-04), p. 59-75
    Abstract: We present results from nine simulations that compare the standard Lambda cold dark matter cosmology (ΛCDM) with counterfactual universes, for approximately $100\, {\rm Gyr}$ using the Enzo simulation code. We vary the value of Λ and the fluctuation amplitude to explore the effect on the evolution of the halo mass function (HMF), the intergalactic medium (IGM), and the star formation history (SFH). The distinct peak in star formation rate density (SFRD) and its subsequent decline are both affected by the interplay between gravitational attraction and the accelerating effects of Λ. The IGM cools down more rapidly in models with a larger Λ and also with a lower σ8, reflecting the reduced SFRD associated with these changes – although changing σ8 is not degenerate with changing Λ, either regarding the thermal history of the IGM or the SFH. However, these induced changes to the IGM or ionizing background have little impact on the calculated SFRD. We provide fits for the evolution of the SFRD in these different universes, which we integrate over time to derive an asymptotic star formation efficiency. Together with Weinberg’s uniform prior on Λ, the estimated probability of observers experiencing a value of Λ no greater than the observed value is 13 per cent, substantially larger than some alternative estimates. Within the Enzo model framework, then, observer selection within a multiverse is able to account statistically for the small value of the cosmological constant, although Λ in our universe does appear to be at the low end of the predicted range.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stac2669
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2022
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 8
    Online Resource
    Online Resource
    How Metals Are Transported in and out of a Galactic Disk: Dependence on the Hydrodynamic Schemes in Numerical Simulations
    American Astronomical Society ; 2021
    In:  The Astrophysical Journal Vol. 917, No. 1 ( 2021-08-01), p. 12-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 917, No. 1 ( 2021-08-01), p. 12-
    Abstract: Metallicity is a fundamental probe for understanding the baryon physics in a galaxy. Since metals are intricately associated with radiative cooling, star formation, and stellar feedback, reproducing the observed metal distribution through numerical experiments will provide a prominent way to examine our understanding of galactic baryon physics. In this study, we analyze the dependence of the galactic metal distribution on numerical schemes and quantify the differences in metal mixing among modern galaxy simulation codes (the mesh-based code Enzo and the particle-based codes Gadget-2 and Gizmo-PSPH ). In particular, we examine different stellar feedback strengths and an explicit metal diffusion scheme in particle-based codes, as a way to alleviate the well-known discrepancy in metal transport between mesh-based and particle-based simulations. We demonstrate that a sufficient number of gas particles are needed in the gas halo to properly investigate the metal distribution therein. Including an explicit metal diffusion scheme does not significantly affect the metal distribution in the galactic disk but does change the amount of low-metallicity gas in a hot diffuse halo. We also find that the spatial distribution of metals depends strongly on how the stellar feedback is modeled. We demonstrate that the previously reported discrepancy in metals between mesh-based and particle-based simulations can be mitigated with our proposed prescription, enabling these simulations to be reliably utilized in the study of metals in galactic halos and the circumgalactic medium.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/abffd0
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 9
    Online Resource
    Online Resource
    Viral Dynamics and Immune Correlates of Coronavirus Disease 2019 (COVID-19) Severity
    Oxford University Press (OUP) ; 2021
    In:  Clinical Infectious Diseases Vol. 73, No. 9 ( 2021-11-02), p. e2932-e2942
    Details
    In: Clinical Infectious Diseases, Oxford University Press (OUP), Vol. 73, No. 9 ( 2021-11-02), p. e2932-e2942
    Abstract: Key knowledge gaps remain in the understanding of viral dynamics and immune response of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. Methods We evaluated these characteristics and established their association with clinical severity in a prospective observational cohort study of 100 patients with PCR-confirmed SARS-CoV-2 infection (mean age, 46 years; 56% male; 38% with comorbidities). Respiratory samples (n = 74) were collected for viral culture, serum samples for measurement of IgM/IgG levels (n = 30), and plasma samples for levels of inflammatory cytokines and chemokines (n = 81). Disease severity was correlated with results from viral culture, serologic testing, and immune markers. Results Fifty-seven (57%) patients developed viral pneumonia, of whom 20 (20%) required supplemental oxygen, including 12 (12%) with invasive mechanical ventilation. Viral culture from respiratory samples was positive for 19 of 74 patients (26%). No virus was isolated when the PCR cycle threshold (Ct) value was & gt;30 or & gt;14 days after symptom onset. Seroconversion occurred at a median (IQR) of 12.5 (9–18) days for IgM and 15.0 (12–20) days for IgG; 54/62 patients (87.1%) sampled at day 14 or later seroconverted. Severe infections were associated with earlier seroconversion and higher peak IgM and IgG levels. Levels of IP-10, HGF, IL-6, MCP-1, MIP-1α, IL-12p70, IL-18, VEGF-A, PDGF-BB, and IL-1RA significantly correlated with disease severity. Conclusions We found virus viability was associated with lower PCR Ct value in early illness. A stronger antibody response was associated with disease severity. The overactive proinflammatory immune signatures offer targets for host-directed immunotherapy, which should be evaluated in randomized controlled trials.
    Type of Medium: Online Resource
    ISSN: 1058-4838 , 1537-6591
    URL: Article
    DOI: 10.1093/cid/ciaa1280
    RVK:
    XA 10000
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2002229-3
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  • 10
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    Online Resource
    GARFIELD-AF: risk profiles, treatment patterns and 2-year outcomes in patients with atrial fibrillation in Germany, Austria and Switzerland (DACH) compared to 32 countries in other regions worldwide
    Springer Science and Business Media LLC ; 2023
    In:  Clinical Research in Cardiology Vol. 112, No. 6 ( 2023-06), p. 759-771
    Details
    In: Clinical Research in Cardiology, Springer Science and Business Media LLC, Vol. 112, No. 6 ( 2023-06), p. 759-771
    Type of Medium: Online Resource
    ISSN: 1861-0684 , 1861-0692
    URL: Article
    DOI: 10.1007/s00392-022-02079-y
    RVK:
    XA 37040
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
    detail.hit.zdb_id: 2218331-0
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