629 research outputs found
Sedimentología de los yesos del sector central de la Depresión del Duero
En el sector central de la Depresión del Duero afloran sedimentosneógenos, terrígenos, carbonatados y yesíferos. En los depósitos yesiferos se han diferenciado facies de yeso primario, secundario y retrabajado que junto a las facies carbonatadas se ordenan en secuencias y megasecuencias positivas y negativas. Las megasecuencias se interpretan como retracciones o expansiones del sistema lacustre. Se relacionan las secuencias con los modelos paleogeográficos establecidos y se analizan los factores que controlaron la evolución de los depósitos yesíferos en el tiempo
A detailed two-dimensional stellar population study of M32
We present Two-Dimensional Spectroscopy of the 9x12 arcsec^2 central region
of M32 obtained with the 2D_FIS fibre spectrograph installed at the William
Herschel Telescope. From these spectra line strength maps have been
reconstructed for about 20 absorption lines, mostly belonging to the Lick
system. We find good agreement with long-slit line strength profiles in the
literature. In contrast with previous studies, indices were azimuthally
averaged along continuum isophotes of M32. A remarkable result is that no
gradients are presented in the spectral indices. So, we have fitted the mean
values of each spectral index and central colours to the models of Vazdekis et
al. (1996) and Worthey (1994), finding that an intermediate age (~4 Gyr) and
metallicity similar to solar (Z=0.02) are the best fitted values for the
innermost region of M32.Comment: accepted in MNRA
Short-timescale Fluctuations in the Difference Light Curves of QSO 0957+561A,B: Microlensing or Noise?
From optical R band data of the double quasar QSO 0957+561A,B, we made two
new difference light curves (about 330 days of overlap between the time-shifted
light curve for the A image and the magnitude-shifted light curve for the B
image). We observed noisy behaviours around the zero line and no
short-timescale events (with a duration of months), where the term event refers
to a prominent feature that may be due to microlensing or another source of
variability. Only one event lasting two weeks and rising - 33 mmag was found.
Measured constraints on the possible microlensing variability can be used to
obtain information on the granularity of the dark matter in the main lensing
galaxy and the size of the source. In addition, one can also test the ability
of the observational noise to cause the rms averages and the local features of
the difference signals. We focused on this last issue. The combined
photometries were related to a process consisting of an intrinsic signal plus a
Gaussian observational noise. The intrinsic signal has been assumed to be
either a smooth function (polynomial) or a smooth function plus a stationary
noise process or a correlated stationary process. Using these three pictures
without microlensing, we derived some models totally consistent with the
observations. We finally discussed the sensitivity of our telescope (at Teide
Observatory) to several classes of microlensing variability.Comment: MNRAS, in press (LaTeX, 14 pages, 22 eps figures
El paleógeno del sector suroccidental de la Cuenca del Duero: nueva división estratigráfica y controles sobre su sedimentación
Como resultado de un detallado trabajo cartográfico, estratigráfico y
sedimentológico, se propone la división del Paleógeno del sector suroccidental
de la Cuenca del Duero en cuatro U.T.S. limitadas por discordancias. Estas
D.T.S., que abarcan desde el tránsito Cretácico superior-Paleoceno hasta el
Oligoceno, incluyen distintas unidades litoestratigráficas que sonreordenadas,
modificando la sucesión estratigrática propuesta por los autores anteriores.
Se asigna a la U.T.S. Me una edad Cretácico superior-Paleoceno. Se
individualiza el Eoceno inferior (U.T.S. PI) en la zona de Salamanca. Se
reinterpreta la relación existente entre los materiales del Eoceno mediosuperior
y los del Eoceno superior-Oligoceno considerándolos en tránsito
por lo que se asignan a una única U.T.S. (UT.S. P2, Eoceno medio Oligoceno
inferior). Se incluyen en la U.T.S. P3 (Oligoceno superior) los
sedimentos arcósicos anterionnente considerados como Vatlesienses. Así
mismo, se considera que gran parte de los materiales asignados al mioceno
inferior son sedimentos paleógenos afectados por un proceso de alteración
de edad Miocena, lo que implica una variación en la extensión y límites de
la cuenca neógena en su extremo SO.
Se analiza la evolución de las distintas U.T.S. deduciendo un carácter
tectónico para las megasecuencias propuestas relacionado con el progresivo
levantamiento de las áreas fuente. El clima muestra un tránsito desde
condiciones tropicales sin estaciones contrastadas (U,T.S. MC) hasta un
clima mediterráneo árido (U.T.S. P3) con una estación seca muy marcada
y una corta estación húmeda caracterizada por violentas avenidas.
[ABSTRACT]
A Paleogene four-fold stratigraphical division is proposed here
as result fram the detailed studies carried out during the elaboration
of 22 sheets of the Geological Map of Spain (E. 1 :50.000).
This units (T.S.U.) are limited by regional discordances and they
have a Upper Cretaceous to Oligocene ages.
The previous stratigraphical schemes are rearranged due to the
different stratigraphical relations observed between the lithostratigraphical
units proposed by other workers (Jiménez, 1970; Corrochano, 1977;
Alonso, 1981...).
An Upper Cretaceous-Paleocene age is assumed to T.S.U. MC
which is mainly composed by siliciclastic sediments strongly silicified
forming a FU megasequence. It is intcrpretated as braided streams
that flowed downslope filling paleovalleys erodcd onto Paleozoic
materiaIs. Mineralogical features point to a tropical climate.
Lower Eocene (T.S.U. P I ) is identified in the Salamanca area,
where ir was considered as lacking. It is composed by arkosic
sediments forming a CU megasequence. Fossil faunas of this T.S.U.
record a subtropical clima te. It is observed a transition from high
sinuosity streams to braided ones.
T.S.U. P2 (Middle Eocene-Lower Oligocene) is composed of
two lithostratigraphical units previously considered as bounded by
a discordance (Alonso, 1981).It has a subarkosic to lithic nature and
forms a CU megasequence. This unit records a subtropical climate
with short arid periods and is interpretated as braided streams
showing an increasing stability and enviromental energy to the topo
T.S. U. P3 (Upper Oligocene) is composed by arkosic sediments
previously considered of Vallesian (Middle to Upper Miocene) age.
They form a CU megasequence that records braided streams prograding
basinwardfrom higher arcas. Palinological associations and pedological
features indicate an arid mediterranean climate with long arid
periods and a short rainy season with strong floods.
We consider that most of Lower Miocene sediments are of
Paleogene age. They are afected by a widespread alteration profile
developed along Lower Miocene that masked its more significative
features.
Sedimentological analysis of T.S.U. shows that its megasequentiality
is related to the rates of tectonical uplift of source arcas whereas a
distensive regime developed in the sedimentation basin
A Large Brightness Enhancement of the QSO 0957+561 A Component
We report an increase of more than 0.2 mag in the optical brightness of the
leading image (A) of the gravitational lens Q0957+561, detected during the
09/2000 -- 06/2001 monitoring campaign (2001 observing season). The brightening
is similar to or even greater than the largest change ever detected during the
20 years of monitoring of this system. We discuss two different provisional
explanations to this event: intrinsic source variability or microlensing
(either short timescale microlensing or cessation of the historical
microlensing). An exhaustive photometric monitoring of Q0957+561 is needed
until summer of 2002 and during 2003 to discriminate between these
possibilities.Comment: 13 pages including 3 figures and 1 table. Accepted for publication in
ApJ Let
Spectroscopy of the Lens Galaxy of Q0957+561A,B. Implications of a possible central massive dark object
We present new long-slit William Herschel Telescope spectroscopic
observations of the lens galaxy G1 associated with the double-imaged QSO
0957+561A,B. The obtained central stellar velocity dispersion, sigma_l = 310
+/- 20 km/s, is in reasonable agreement with other measurements of this
dynamical parameter. Using all updated measurements of the stellar velocity
dispersion in the internal region of the galaxy (at angular separations < 1".5)
and a simple isotropic model, we discuss the mass of a possible central massive
dark object. It is found that the data of Falco et al. (1997) suggest the
existence of an extremely massive object of (0.5-2.1) x 10E10/h M_\odot (80%
confidence level), whereas the inclusion of very recent data (Tonry & Franx
1998, and this paper) substantially changes the results: the compact central
mass must be 6 x10E9/h M_\odot at the 90% confidence level. We note that,
taking into account all the available dynamical data, a compact nucleus with a
mass of 10E9/h M_\odot (best fit) cannot be ruled out.Comment: 20 pages, 10 figures ApJ, in pres
Luxación esternoclavicular posterior: a propósito de un caso y revisión de la literatura
La luxación esternoclavicular posterior es una patología poco frecuente. Se presenta sobre todo en
varones jóvenes asociada a traumatismos de alta energía. Puede presentar complicaciones potencialmente letales por
compresión de estructuras mediastínicas, por lo que es necesario su reducción urgente. El diagnóstico radiográfico
puede ser difícil debido a la superposición de estructuras, siendo de gran utilidad la TC para determinar el tipo y grado
de desplazamiento, así como la relación anatómica con las estructuras mediastínicas. Se presenta el caso de un
paciente varón, de 23 años de edad, que presentó una luxación esternoclavicular posterior traumática aguda tras accidente
de tráfico en el que se consiguió la reducción cerrada mediante manipulación bajo anestesia general y posterior
inmovilización antiálgica durante 3 semanas, sin objetivarse inestabilidad esternoclavicular posterior que obligase
a más procedimientos. Se realiza una revisión de la literatura médica al respecto de esta patología.Posterior sternoclavicular dislocation is a rare disease. It occurs mainly in young men associated with
high-energy trauma. It can be life-threatening due to compression of mediastinal structures, so its reduction is
urgently needed. The radiographic diagnosis can be difficult because of overlapping structures, CT is very helpful to
determine the type and degree of displacement and the anatomic relationship with the mediastinal structures. We present
the case of a male patient, aged 23, with an acute traumatic posterior sternoclavicular dislocation after accident,
in which closed reduction was achieved by manipulation under general anesthesia, followed by analgesic immobilization
for 3 weeks resulting in sternoclavicular healing without instability, so no more procedures were needed. A literature
review is presented regarding to this case
New VR magnification ratios of QSO 0957+561
We present VR magnification ratios of QSO 0957+561, which are inferred from
the GLITP light curves of Q0957+561A and new frames taken with the 2.56m Nordic
Optical Telescope about 14 months after the GLITP monitoring. From two
photometric approaches and a reasonable range for the time delay in the system
(415-430 days), we do not obtain achromatic optical continuum ratios, but
ratios depending on the wavelength. These new measurements are consistent with
differential extinction in the lens galaxy, the Lyman limit system, the damped
Ly-alpha system, or the host galaxy of the QSO. The possible values for the
differential extinction and the ratio of total to selective extinction in the V
band are reasonable. Moreover, crude probability arguments suggest that the ray
paths of the two components cross a similar dusty environment, including a
network of compact dust clouds and compact dust voids. As an alternative (in
fact, the usual interpretation of the old ratios), we also try to explain the
new ratios as caused by gravitational microlensing in the deflector. From
magnification maps for each of the gravitationally lensed images, using
different fractions of the surface mass density represented by the microlenses,
as well as different sizes and profiles of the V-band and R-band sources,
several synthetic distributions of V-band and R-band ratios are derived. In
some gravitational scenarios, there is an apparent disagreement between the
observed pair of ratios and the simulated distributions. However, several
microlensing pictures work well. To decide between either extinction, or
microlensing, or a mixed scenario (extinction + microlensing), new
observational and interpretation efforts are required.Comment: PS and PDF versions are created from the LaTeX file and 5 EPS
figures, two additional figues (Figs. 6 and 7) in JPEG format, scheduled for
the ApJ 20 January 2005 issu
Scientific Basis for the Potential Use of Melatonin in Bone Diseases: Osteoporosis and Adolescent Idiopathic Scoliosis
The objective of this paper was to analyze the data supporting the possible role of melatonin on bone metabolism and its repercussion in the etiology and treatment of bone pathologies such as the osteoporosis and the adolescent idiopathic scoliosis (AIS). Melatonin may prevent bone degradation and promote bone formation through mechanisms involving both melatonin receptor-mediated and receptor-independent actions. The three principal mechanisms of melatonin effects on bone function could be: (a) the promotion of the osteoblast differentiation and activity; (b) an increase in the osteoprotegerin expression by osteoblasts, thereby preventing the differentiation of osteoclasts; (c) scavenging of free radicals generated by osteoclast activity and responsible for bone resorption. A variety of in vitro and in vivo experimental studies, although with some controversial results, point toward a possible role of melatonin deficits in the etiology of osteoporosis and AIS and open a new field related to the possible therapeutic use of melatonin in these bone diseases
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