2,175 research outputs found
Assemblage Composition and Vertical Distributions of Deep-Sea Anglerfishes (Suborder: Ceratioidei) of the Northern Gulf of Mexico
The bathypelagic zone, despite being the largest cumulative ecosystem on the planet, represents the largest data gap in biological oceanography. In a deep environment with no solar light and pressures so high that survival is impossible for most marine organisms, some species have been able to adapt and overcome these challenges to radiate into diverse and successful taxa. Among the most notable of these successful taxa are the deep-sea anglerfishes (Lophiiformes: Ceratioidei). Ceratioid anglerfishes possess unique adaptations such as a symbiotic bioluminescent lure (females) and extreme dwarfism (males) that make them a particularly interesting group to study. Despite this research attractiveness, low sample sizes in ichthyological questions preclude detailed characterizations of fundamental assemblage properties, such as faunal composition, sex ratios, and vertical distributions in specific water bodies; i.e., most of what we know is compiled from sparse data across all oceans.
Ceratioids were collected in the Gulf of Mexico (GoM) as a part of an extensive pelagic survey following the Deepwater Horizon oil spill. Using high-speed rope trawls and a multiple opening and closing net system, ceratioids were collected day and night throughout the northern GoM. The faunal composition of females, males, and larvae were analyzed separately by life stage/sex and by family to gain insight into assemblage structure and vertical distribution.
A total of 1726 ceratioids were collected, representing all 11 families in the suborder. The assemblage was dominated numerically by females of the family Ceratiidae, in particular the species Cryptopsaras couesii. Males and larval numbers were dominated by the family Linophrynidae. The type of net used affected the taxon and size of specimens captured. Four patterns of vertical distributions were identified: 1) primarily epipelagic distribution with a rapid descent to great depth; 2) primarily mesopelagic residence; 3) a wide, “spanner” vertical distribution independent of solar cycle; and, 4) a primarily bathypelagic distribution. Larvae, particularly Linophrynidae larvae, best typified Pattern 1, the family Ceratiidae typified Pattern 2, the linophrynid species Haplophryne mollis typified Pattern 3, and males of many taxa typified Pattern 4. Vertical distribution patterns were not strictly related to taxon, sex, or life stage; for example, females within the same family (e.g., Linophrynidae) often displayed different patterns. This study demonstrates that ceratioid anglerfishes are not only among the most successful fish taxa of the bathypelagic zone, they also occupy one of the largest depth ranges among all taxa
From Solar to Stellar Brightness Variations: The Effect of Metallicity
Context. Comparison studies of Sun-like stars with the Sun suggest an
anomalously low photometric variability of the Sun compared to Sun-like stars
with similar magnetic activity. Comprehensive understanding of stellar
variability is needed, to find a physical reasoning for this observation. Aims.
We investigate the effect of metallicity and effective temperature on the
photometric brightness change of Sun-like stars seen at different inclinations.
The considered range of fundamental stellar parameters is sufficiently small so
the stars, investigated here, still count as Sun-like or even as solar twins.
Methods. To model the brightness change of stars with solar magnetic activity,
we extend a well established model of solar brightness variations, SATIRE
(which stands for Spectral And Total Irradiance Reconstruction), which is based
on solar spectra, to stars with different fundamental parameters. For that we
calculate stellar spectra for different metallicities and effective temperature
using the radiative transfer code ATLAS9. Results. We show that even a small
change (e.g. within the observational error range) of metallicity or effective
temperature significantly affects the photometric brightness change compared to
the Sun. We find that for Sun-like stars, the amplitude of the brightness
variations obtained for Str\"omgren (b + y)/2 reaches a local minimum for
fundamental stellar parameters close to the solar metallicity and effective
temperature. Moreover, our results show that the effect of inclination
decreases for metallicity values greater than the solar metallicity. Overall,
we find that an exact determination of fundamental stellar parameters is
crucially important for understanding stellar brightness changes.Comment: 12 pages, 12 figures, accepted in A&
Corrosion Study of AA2024-T3 by Scanning Kelvin Probe Force Microscopy and In Situ Atomic Force Microscopy Scratching
The localized corrosion of AA2024-T3, and the behavior of intermetallic particles in particular, were studied using different capabilities of the atomic force microscope (AFM). The role of intermetallic particles in determining the locations and rates of localized corrosion was determined using scanning Kelvin probe force microscopy in air after exposure to chloride solutions. Al-Cu-Mg particles, which have a noble Volta potential in air because of an altered surface film, are actively dissolved in chloride solution after a certain induction time. Al-Cu-(Fe, Mn) particles are heterogeneous in nature and exhibit nonuniform dissolution in chloride solution as well as trenching of the matrix around the particles. Light scratching of the surface by rastering with the AFM tip in contact mode in chloride solution results in accelerated dissolution of both pure Al and alloy 2024-T3. The abrasion associated with contact AFM in situ resulted in the immediate dissolution of the Al-Cu-Mg particles because of a destabilization of the surface film.This work was supported by the Air Force Office of Scientific Research under contact no. F49620-96-1-0479, Major H. De Long, Administrator. P. S. was partially supported by the Swiss National Foundation of Research
The role of the Fraunhofer lines in solar brightness variability
The solar brightness varies on timescales from minutes to decades. A clear
identification of the physical processes behind such variations is needed for
developing and improving physics-based models of solar brightness variability
and reconstructing solar brightness in the past. This is, in turn, important
for better understanding the solar-terrestrial and solar-stellar connections.
We estimate the relative contributions of the continuum, molecular, and
atomic lines to the solar brightness variations on different timescales.
Our approach is based on the assumption that variability of the solar
brightness on timescales greater than a day is driven by the evolution of the
solar surface magnetic field. We calculated the solar brightness variations
employing the solar disc area coverage of magnetic features deduced from the
MDI/SOHO observations. The brightness contrasts of magnetic features relative
to the quiet Sun were calculated with a non-LTE radiative transfer code as
functions of disc position and wavelength. By consecutive elimination of
molecular and atomic lines from the radiative transfer calculations, we
assessed the role of these lines in producing solar brightness variability.
We show that the variations in Fraunhofer lines define the amplitude of the
solar brightness variability on timescales greater than a day and even the
phase of the total solar irradiance variability over the 11-year cycle. We also
demonstrate that molecular lines make substantial contribution to solar
brightness variability on the 11-year activity cycle and centennial timescales.
In particular, our model indicates that roughly a quarter of the total solar
irradiance variability over the 11-year cycle originates in molecular lines.
The maximum of the absolute spectral brightness variability on timescales
greater than a day is associated with the CN violet system between 380 and 390
nm.Comment: 9 pages, 4 figures, accepted for publication in
Astronomy&Astrophysic
A New Approach for the Study of Chemical Mechanical Polishing
The process of chemical mechanical polishing (CMP) can be studied using in situ atomic force microscopy (AFM) by intentionally using a high tip/sample interaction force. The nominal removal rate ofAl during AFM scratching is studied under a range of conditions including varying tip/sample force, solution pH, and electrode potential. This approach should be useful for CMP process development and furthering the fundamental understanding of CMP mechanisms
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