ABSTRACT
Carbon enhanced metal poor (CEMP)-no stars, a subset of CEMP stars ($\rm C/Fe\ge 0.7$ and $\rm Fe/H\lesssim -1$) have been discovered in ultra-faint dwarf (UFD) galaxies, with $M_{\rm ...vir}\approx 10^8{\, \mathrm{ M}_\odot }$ and $M_{\ast }\approx 10^3-10^4{\, \mathrm{ M}_\odot }$ at z = 0, as well as in the halo of the Milky Way (MW). These CEMP-no stars are local fossils that may reflect the properties of the first (Pop III) and second (Pop II) generation of stars. However, cosmological simulations have struggled to reproduce the observed level of carbon enhancement of the known CEMP-no stars. Here, we present new cosmological hydrodynamic zoom-in simulations of isolated UFDs that achieve a gas mass resolution of $m_{\rm gas}\approx 60{\, \mathrm{ M}_\odot }$. We include enrichment from Pop III faint supernovae (SNe), with ESN = 0.6 × 1051 erg, to understand the origin of CEMP-no stars. We confirm that Pop III and Pop II stars are mainly responsible for the formation of CEMP and C-normal stars, respectively. New to this study, we find that a majority of CEMP-no stars in the observed UFDs and the MW halo can be explained by Pop III SNe with normal explosion energy (ESN = 1.2 × 1051 erg) and Pop II enrichment, but faint SNe might also be needed to produce CEMP-no stars with $\rm C/Fe\gtrsim 2$, corresponding to the absolute carbon abundance of $\rm A(C)\gtrsim 6.0$. Furthermore, we find that while we create CEMP-no stars with high carbon ratio $\rm C/Fe\approx 3-4$, by adopting faint SNe, it is still challenging to reproduce CEMP-no stars with extreme level of carbon abundance of $\rm A(C)\approx 7.0-7.5$, observed both in the MW halo and UFDs.
•Formability and springback in cold forming of peak-aged 7075 aluminum alloy sheets.•Anisotropic hardening under loading path changes were modeled.•Improved formability and lowered springback with ...heat-treated 7075 aluminum alloy sheets.•The analysis on Formability prediction using MK model by considering serrated flow.
High strength aluminum alloys have drawn much attention as the requirement for lightweight vehicle design increases in the automotive industry. However, inferior formability due to higher strength poses a technical hurdle against successful application of high strength aluminum sheets in automotive components. In this study, the mechanical properties of 7075 aluminum alloy sheet after W-temper heat treatment, which consists of solution heat treatment and subsequent quenching, are investigated. Detailed experimental and numerical studies are conducted on the anisotropy, non-proportional deformation behavior, and corresponding constitutive modeling in comparison with the corresponding characteristics of peak aged T6 heat-treated as-received alloy sheets. Based on the experimentally characterized mechanical properties and associated constitutive laws, the formability and springback of the W-tempered sheet are analyzed using the Marciniak–Kuczyinski forming limit diagram and U-draw bending springback simulations, respectively, by employing the Yld2000-2d anisotropic yield function and distortional hardening-based homogeneous anisotropic hardening model. Additionally, the improved constitutive modeling of the W-tempered 7075 aluminum sheets due to the effect of serrated flow characteristics on the hardening and frictional behaviors is discussed.
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Abstract
We investigate how patchy reionization affects the star formation history (SFH) and stellar metallicity of ultrafaint dwarf galaxies (UFDs). Patchy reionization refers to varying ultraviolet ...background strengths depending on a galaxy’s environment. Recent observations highlight the significance of this effect on UFDs, as UFDs can have different SFHs depending on their relative position with respect to their host halo during the period of reionization. However, most cosmological hydrodynamic simulations do not consider environmental factors such as patchy reionization, and the effect of reionization is typically applied homogeneously. Using a novel approach to implement patchy reionization, we show how SFHs of simulated UFDs can change. Our cosmological hydrodynamic zoom-in simulations focus on UFD analogs with
M
vir
∼ 10
9
M
⊙
,
M
*
≲ 10
5
M
⊙
at
z
= 0. We find that patchy reionization can weaken the effect of reionization by 2 orders of magnitude up to
z
= 3, enabling late star formation in half of the simulated UFDs, with quenching times ∼460 Myr later than those with homogeneous reionization. We also show that halo merger and mass assembly can affect the SFHs of simulated UFDs, in addition to patchy reionization. The average stellar iron-to-hydrogen ratio, Fe/H, of the simulated UFDs with patchy reionization increases by 0.22–0.42 dex. Finally, our findings suggest that patchy reionization could be responsible for the extended SFHs of Magellanic UFDs compared to non-Magellanic UFDs.
Abstract
We present analysis of the proper-motion (PM) field of the red clump stars in the Large Magellanic Cloud (LMC) disk using the Gaia Early Data Release 3 catalog. Using a kinematic model based ...on old stars with 3D velocity measurements, we construct the residual PM field by subtracting the center-of-mass motion and internal rotation motion components. The residual PM field reveals asymmetric patterns, including larger residual PMs in the southern disk. Comparisons of the observed residual PM field with those of five numerical simulations of an LMC analog that is subject to the tidal fields of the Milky Way and the Small Magellanic Cloud (SMC) show that the present-day LMC is not in dynamical equilibrium. We find that both the observed level of disk heating (PM residual rms of 0.057 ± 0.002 mas yr
−1
) and kinematic asymmetry are not reproduced by Milky Way tides or if the SMC impact parameter is larger than the size of the LMC disk. This measured level of disk heating provides a novel and important method to validate numerical simulations of the LMC–SMC interaction history. Our results alone put constraints on an impact parameter ≲10 kpc and impact timing <250 Myr. When adopting the impact timing constraint of ∼140–160 Myr ago from previous studies, our results suggest that the most recent SMC encounter must have occurred with an impact parameter of ∼5 kpc. We also find consistent radial trends in the kinematically and geometrically derived disk inclination and line-of-node position angles, indicating a common origin.
We investigated the effect of different spray-coating parameters on the electro-optical properties of Ag nanowires (NWs). Highly transparent and conductive Ag NW⁻graphene oxide (GO) hybrid electrodes ...were fabricated by using the spray-coating technique. The Ag NW percolation network was modified with GO and this led to a reduced sheet resistance of the Ag NW⁻GO electrode as the result of a decrease in the inter-nanowire contact resistance. Although electrical conductivity and optical transmittance of the Ag NW electrodes have a trade-off relationship, Ag NW⁻GO hybrid electrodes exhibited significantly improved sheet resistance and slightly decreased transmittance compared to Ag NW electrodes. Ag NW⁻GO hybrid electrodes were integrated into smart windows based on polymer-dispersed liquid crystals (PDLCs) for the first time. Experimental results showed that the electro-optical properties of the PDLCs based on Ag NW⁻GO electrodes were superior when compared to those of PDLCs based on only Ag NW electrodes. This study revealed that the hybrid Ag NW⁻GO electrode is a promising material for manufacturing the large-area flexible indium tin oxide (ITO)-free PDLCs.
Both the impacts of two types of El Niño on the western North Pacific (WNP) tropical cyclone (TC) activity and the seasonality in the relationship between genesis potential index (GPI) and El ...Niño–Southern Oscillation (ENSO) are investigated. The ENSO-induced GPI change over the northwestern (southeastern) part of the WNP is mostly attributed to the relative humidity (absolute vorticity) term, revealing a distinct meridional and zonal asymmetry in summer and fall, respectively. The seasonal change in ENSO (background states) from summer to fall is responsible for the seasonal change in GPI anomalies south of 20°N (over the northeastern part of the WNP). The downdraft induced by the strong upper-level convergence in the eastern Pacific (EP)-type El Niño and both the northwestward-shifted relative vorticity and northward-extended convection over the southeastern part of the WNP in the central Pacific (CP)-type El Niño lead to distinct TC impacts over East Asia (EA). The southward movement of genesis location of TCs and increased westward-moving TCs account for the enhanced strong typhoon activity for the EP-type El Niño in summer. In fall the downdraft and anomalous anticyclonic steering flows over the western part of the WNP remarkably decrease TC impacts over EA. The enhanced moist static energy and midlevel upward motion over the eastern part of the WNP under the northern off-equatorial sea surface temperature warming as well as longer passage of TCs toward EA are responsible for the enhanced typhoon activity for the CP-type El Niño. It is thus important to consider the seasonality and El Niño pattern diversity to explore the El Niño–induced TC impacts over EA.
The 2013 subseasonal asymmetry in tropical cyclone (TC) genesis over the western North Pacific (WNP) was investigated by using the 1979–2013 RSMC best track dataset. The genesis frequency of the 2013 ...WNP TCs between June–August (summer) and September–November (fall) manifested an abnormal temporal asymmetry: fewer typhoons (more tropical storms) in summer and more typhoons (normal tropical storms) in fall. The 2013 active summer-tropical storm genesis arose from both a failure of eastward extension of monsoon confluence region, especially in August and a lack of moisture supply for TC genesis over the eastern part of WNP, and consequently from fewer probability to reach typhoon intensity due to the westward movement of favorable location for genesis. Thereafter, the eastward extension of monsoon shear line in September and the establishment of monsoon gyre in October induced the eastward movement of favorable location for genesis which increased probability to reach typhoon intensity. The relative contribution of mid-level relative humidity to the positive GPI change played a major role in favorable condition for typhoon genesis in September (45.2%) and October (50.9%). The monsoon gyre pattern played a leading role in the most active fall-typhoon in 2013 contributing to the highest number of October-typhoon. The eastward-migration of convection mainly contributed to the subseasonal shift of TC genesis location following eastward movement of local SST warming from summer to fall under the La Nina-like neutral state. The enhanced active boreal summer intraseasonal oscillation (BSISO) in fall provided more favorable conditions for TC genesis showing about twice as many TCs occurred regarding BSISO in fall than those in summer. This spatiotemporal asymmetry in the large-scale circulations and moisture conditions between summer and fall accounted for the subseasonal shift of genesis location of TCs, and consequently for the active summer-tropical storm genesis and the active fall-typhoon genesis in 2013.
The hole expansion formability of W-tempered aluminum 7075 sheet, which is prepared by solution heat treatment and rapid cooling, is investigated comparatively with the peak aged T6 tempered alloy. ...The W temper heat treatment has been known to be a potential application to cold forming of high strength aluminum including 7075 alloy as an alternative to the warm or hot forming process. The hole expansion tests are designed with a conical punch and the holes are fabricated using wire-cut and punching. Basic mechanical properties and microstructure analyses are performed to study the effect of the strength and ductility in tension on the hole expansion ratios of specimens with different tempers and hole conditions. From the experimental study, the following conclusions are mainly reached. (1) The W-tempered sheets show much improved HER than T6 tempered sheets; i.e., 31 (T6) vs. 58% (W) for wire-cut hole and 19 (T6) vs. 57% (W) for punched hole. (2) The HER of W-tempered sheets show very similar HER values between wire-cut and punched hole specimens, which has not been commonly reported. (3) The initiation of cracks at hole edges is different depending on hole preparation; i.e., RD or TD (wire-cut T6 and wire-cut and punched W) vs. RD, DD, and TD (punched T6). (4) The KAM map validates the cause of lower HER of punched specimen attributes to earlier crack initiation by prior plastic deformation during punching, but the strengthening of shear affected zone has limited effect on HER. (5) The HERs of T6 and W tempered sheets are well correlated to the yield strength, ultimate tensile strength, and total elongation. However, the effect of post uniform elongation on HER is not correlated to the existing report.
Graphical Abstract
Abstract
We present a detailed analysis of the structure of the Local Group flocculent spiral galaxy M33, as measured using the Panchromatic Hubble Andromeda Treasury Triangulum Extended Region ...(PHATTER) survey. Leveraging the multiwavelength coverage of PHATTER, we find that the oldest populations are dominated by a smooth exponential disk with two distinct spiral arms and a classical central bar—completely distinct from what is seen in broadband optical imaging, and the first-ever confirmation of a bar in M33. We estimate a bar extent of ∼1 kpc. The two spiral arms are asymmetric in orientation and strength, and likely represent the innermost impact of the recent tidal interaction responsible for M33's warp at larger scales. The flocculent multiarmed morphology for which M33 is known is only visible in the young upper main-sequence population, which closely tracks the morphology of the interstellar medium. We investigate the stability of M33's disk, finding
Q
∼ 1 over the majority of the disk. We fit multiple components to the old stellar density distribution and find that, when considering recent stellar kinematics, M33's bulk structure favors the inclusion of an accreted halo component, modeled as a broken power law. The best-fit halo has an outer power-law index of −3 and accurately describes observational evidence of M33's stellar halo from both resolved stellar spectroscopy in the disk and its stellar populations at large radius. Integrating this profile yields a total halo stellar mass of ∼5 × 10
8
M
⊙
, for a stellar halo mass fraction of 16%, most of which resides in the innermost 2.5 kpc.
We present the Bayesian Extinction And Stellar Tool (BEAST), a probabilistic approach to modeling the dust extinguished photometric spectral energy distribution of an individual star while accounting ...for observational uncertainties common to large resolved star surveys. Given a set of photometric measurements and an observational uncertainty model, the BEAST infers the physical properties of the stellar source using stellar evolution and atmosphere models and constrains the line of sight extinction using a newly developed mixture model that encompasses the full range of dust extinction curves seen in the Local Group. The BEAST is specifically formulated for use with large multi-band surveys of resolved stellar populations. Our approach accounts for measurement uncertainties and any covariance between them due to stellar crowding (both systematic biases and uncertainties in the bias) and absolute flux calibration, thereby incorporating the full information content of the measurement. We illustrate the accuracy and precision possible with the BEAST using data from the Panchromatic Hubble Andromeda Treasury. While the BEAST has been developed for this survey, it can be easily applied to similar existing and planned resolved star surveys.
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