8,880 research outputs found
Lick Spectral Indices for Super Metal-rich Stars
The Lick Fe5015, Fe5270, Fe5335, Mgb and Mg2 indices are presented for 139
candidate SMR stars of different luminosity class studied in Malagnini et al.
(2000). Evidence is found for a standard (i.e. [Mg/Fe]~0) Mg vs. Fe relative
abundance. Both the Worthey et al. (1994) and Buzzoni et al. (1992, 1994)
fitting functions are found to suitably match the data at super-solar
metallicity regimes. See http://www.merate.mi.astro.it/~eps/home.html for
further details.Comment: 16 pages with 11 figures (Aastex format). To appear in the Nov. '01
issue of the PAS
Ultrafast Momentum Imaging of Pseudospin-Flip Excitations in Graphene
The pseudospin of Dirac electrons in graphene manifests itself in a peculiar
momentum anisotropy for photo-excited electron-hole pairs. These interband
excitations are in fact forbidden along the direction of the light
polarization, and are maximum perpendicular to it. Here, we use time- and
angle-resolved photoemission spectroscopy to investigate the resulting
unconventional hot carrier dynamics, sampling carrier distributions as a
function of energy and in-plane momentum. We first show that the
rapidly-established quasi-thermal electron distribution initially exhibits an
azimuth-dependent temperature, consistent with relaxation through collinear
electron-electron scattering. Azimuthal thermalization is found to occur only
at longer time delays, at a rate that depends on the substrate and the static
doping level. Further, we observe pronounced differences in the electron and
hole dynamics in n-doped samples. By simulating the Coulomb- and
phonon-mediated carrier dynamics we are able to disentangle the influence of
excitation fluence, screening, and doping, and develop a microscopic picture of
the carrier dynamics in photo-excited graphene. Our results clarify new aspects
of hot carrier dynamics that are unique to Dirac materials, with relevance for
photo-control experiments and optoelectronic device applications.Comment: 23 pages, 12 figure
Tracking primary thermalization events in graphene with photoemission at extreme timescales
Direct and inverse Auger scattering are amongst the primary processes that
mediate the thermalization of hot carriers in semiconductors. These two
processes involve the annihilation or generation of an electron-hole pair by
exchanging energy with a third carrier, which is either accelerated or
decelerated. Inverse Auger scattering is generally suppressed, as the
decelerated carriers must have excess energies higher than the band gap itself.
In graphene, which is gapless, inverse Auger scattering is instead predicted to
be dominant at the earliest time delays. Here, femtosecond
extreme-ultraviolet pulses are used to detect this imbalance, tracking both the
number of excited electrons and their kinetic energy with time- and
angle-resolved photoemission spectroscopy. Over a time window of approximately
25 fs after absorption of the pump pulse, we observe an increase in conduction
band carrier density and a simultaneous decrease of the average carrier kinetic
energy, revealing that relaxation is in fact dominated by inverse Auger
scattering. Measurements of carrier scattering at extreme timescales by
photoemission will serve as a guide to ultrafast control of electronic
properties in solids for PetaHertz electronics.Comment: 16 pages, 8 figure
On the behavior of site effects in central Mexico (the Mexican volcanic belt – MVB), based on records of shallow earthquakes that occurred in the zone between 1998 and 2011
The Mexican volcanic belt (MVB) is a seismogenic zone that transects the
central part of Mexico with an east–west orientation. The seismic risk and
hazard of this seismogenic zone has not been studied in detail due to the
scarcity of instrumental data as well as because seismicity in the
continental regime of central Mexico is not too frequent. However, it is
known that there are precedents of large earthquakes (<i>M</i><sub>w</sub> > 6.0)
that have taken place in this zone. The valley of Mexico City (VM) is the
sole zone, within the MVB, that has been studied in detail. Studies have
mainly focused on the ground amplification during large events such as the
1985 subduction earthquake that occurred off coast of Michoacán. The
purpose of this article is to analyze the behavior of site effects in the MVB
zone based on records of shallow earthquakes (data not reported before) that
occurred in the zone between 1998 and 2011. We present a general overview of
site effects in the MVB, a classification of the stations in order to reduce
the uncertainty in the data when obtaining attenuation parameters in future
works, as well as some comparisons between the information presented here and
that presented in previous studies.
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A regional evaluation of site effects and Fourier acceleration spectrum
(FAS) shape was estimated based on 80 records of 22 shallow earthquakes
within the MVB zone. Data of 25 stations were analyzed. Site effects were
estimated by using the horizontal-to-vertical spectral ratio (HVSR)
methodology. The results show that seismic waves are less amplified in the
northeast sites of the MVB with respect to the rest of the zone and that it
is possible to classify two groups of stations: (1) stations with negligible
site amplification (NSA) and (2) stations with significant site amplification
(SSA). Most of the sites in the first group showed small (<3)
amplifications while the second group showed amplifications ranging from 4
to 6.5 at frequencies of about 0.35, 0.75, 15 and 23 Hz. With these groups
of stations, average levels of amplification were contrasted for the first
time with those caused by the subduction zone earthquakes. With respect to
the FAS shapes, most of them showed similarities at similar epicentral
distances. Finally, some variations of site effects were found when compared
to those obtained in previous studies on different seismicity regions. These
variations were attributed to the location of the source.
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These aspects help to advance the understanding about the amplification
behavior and of the expected seismic risk on central Mexico due to large
earthquakes within the MVB seismogenic zone
Quantitative Measurement of Marine and Fungal Biofilm Dynamics: Insights into Ecological and Biomedical Implications
The formation of biofilms by marine and fungal organisms, including four marine Vibrio isolates and fungal isolates of Candida and Rhodotorula, represents complex ecosystems with significant implications for ecology and biomedicine. This study aimed to enhance the understanding of biofilm dynamics through accurate and comprehensive measurement techniques. Following inoculation and growth in liquid media, biofilms were developed in 96-well microplates and stained with crystal violet. The stained biofilms were then solubilized with isopropanol, and optical density measurements were used to quantify the absorbance relative to biofilm concentration. Notably, optical density readings indicated an increased amount of fungal biofilm formation when compared to marine bacterial biofilms, with statistical significance (p\u3c0.05). This finding underscores the differential biofilm formation capacities among marine and fungal isolates, highlighting the importance of advanced quantitative techniques in revealing the structure, function, and ecological significance of biofilms. The study suggests potential applications in environmental and health-related fields and calls for further research into the molecular mechanisms underlying biofilm resilience and pathogenicity.
Keywords: Biofilms, Marine Vibrio, Candida, Rhodotorula, Crystal Violet, Optical Density, Comparative Analysi
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