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We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from theGaiaspace mission data release 3 (DR3). The sample comprises a total of 397 members, with 305 (~77%) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 (~58%) are hydrogen-rich sdBs, 65 are sdOBs (~21%), 32 are sdOs (~11%), and 30 are He-sdO/Bs (~10%). Among them, 48 (~16%) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90% complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in theGaiacolour-magnitude diagram. The remaining sources in the sample include cataclysmic variables, blue horizontal branch stars, hot white dwarfs, and MS stars. We derived the mid-plane densityρ0and scale height hzfor the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech2). The best-fit values areρ0= 5.17 ± 0.33 × 10−7stars pc−3and hz= 281 ± 62 pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases toρ0= 6.15−0.53+1.16× 10−7stars pc−3. This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates.
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Quality Control Metrics to Assess MoS2 Sputtered Films for Tribological Applications
Abstract Pure molybdenum disulfide (MoS2) solid lubricant coatings could attain densities comparable to doped films (and the associated benefits to wear rate and environmental stability) through manipulation of the microstructure via deposition parameters. Unfortunately, pure films can exhibit highly variable microstructures and mechanical properties due to processes that are not controlled during deposition (i.e., batch-to-batch variation). This work focuses on developing a relationship between density, hardness, friction, and wear for pure sputtered MoS2coatings. Results show that dense films (ρ = 4.5 g/cm3) exhibit a 100 × lower wear rate compared to porous coatings (ρ = 3.04–3.55 g/cm3). The tribological performance of high density pure MoS2coatings is shown to surpass that of established composite coatings, achieving a wear rate 2 × (k = 5.74 × 10–8mm3/Nm) lower than composite MoS2/Sb2O3/Au in inert environments.
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- PAR ID:
- 10370503
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Tribology Letters
- Volume:
- 70
- Issue:
- 4
- ISSN:
- 1023-8883
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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