1,096 research outputs found
A Stellar Population Gradient in VII Zw 403 - Implications for the Formation of Blue Compact Dwarf Galaxies
We present evidence for the existence of an old stellar halo in the Blue
Compact Dwarf galaxy VII Zw 403. VII Zw 403 is the first Blue Compact Dwarf
galaxy for which a clear spatial segregation of the resolved stellar content
into a "core-halo" structure is detected. Multicolor HST/WFPC2 observations
indicate that active star formation occurs in the central region, but is
strikingly absent at large radii. Instead, a globular-cluster-like red giant
branch suggests the presence of an old (> 10 Gyr) and metal poor
(=-1.92) stellar population in the halo. While the vast majority of
Blue Compact Dwarf galaxies has been recognized to possess halos of red color
in ground-based surface photometry, our observations of VII Zw 403 establish
for the first time a direct correspondence between a red halo color and the
presence of old, red giant stars. If the halos of Blue Compact Dwarf galaxies
are all home to such ancient stellar populations, then the fossil record
conflicts with delayed-formation scenarios for dwarfs.Comment: Accepted for publication in the Ap
BVR photometry of the resolved dwarf galaxy Ho IX
We present BVR CCD photometry down to limiting magnitude B=23.5 mag for 232
starlike objects and 11 diffuse objects in a 5.4' x 5.4' field of Ho IX. The
galaxy is a gas-rich irregular dwarf galaxy possibly very close to M 81, which
makes it especially interesting in the context of the evolution of satellite
galaxies and the accretion of dwarf galaxies. Investigations of Ho IX were
hampered by relatively large contradictions in the magnitude scale between
earlier studies. With our new photometry we resolved these discrepancies. The
color magnitude diagram (CMD) of Ho IX is fairly typical of a star-forming
dwarf irregular, consistent with earlier results. Distance estimates from our
new CMD are consistent with Ho IX being very close to M 81 and therefore being
a definite member of the M 81 group, apparently in very close physical
proximity to M 81.Comment: 9 pages, 8 figures, uses aa.cls, A&A in pres
Self-tuning laser speckle contrast analysis based on multiple exposure times with enhanced temporal resolution
Laser Speckle Contrast Analysis (LASCA) was introduced in 1981. Since then, several enhancements were applied to it. Nowadays, thetechnique can provide relatively high accuracy as well as high temporal and spatial resolution during the examination of ocular or cerebraltissues. However, in the case of skin, the results are highly affected by the intensive scattering on the skin surface, as the scattering onthe non-moving parts of the sample lead to the detrimental decrease of the accuracy. We present a LASCA method based on the use ofmultiple exposure times, combined with the switching-mode control of the light intensity and a special sampling technique to achieve nearto real-time measurement of the skin perfusion. The system based on our method is able to automatically handle the destructive effect ofthe skin surface and re-tune itself according to the changes of the sample, while it provides full-field perfusion maps with high accuracy,without the need of any precalibrations
MScMS-II: an innovative IR-based indoor coordinate measuring system for large-scale metrology applications
According to the current great interest concerning large-scale metrology applications in many different fields of manufacturing industry, technologies and techniques for dimensional measurement have recently shown a substantial improvement. Ease-of-use, logistic and economic issues, as well as metrological performance are assuming a more and more important role among system requirements. This paper describes the architecture and the working principles of a novel infrared (IR) optical-based system, designed to perform low-cost and easy indoor coordinate measurements of large-size objects. The system consists of a distributed network-based layout, whose modularity allows fitting differently sized and shaped working volumes by adequately increasing the number of sensing units. Differently from existing spatially distributed metrological instruments, the remote sensor devices are intended to provide embedded data elaboration capabilities, in order to share the overall computational load. The overall system functionalities, including distributed layout configuration, network self-calibration, 3D point localization, and measurement data elaboration, are discussed. A preliminary metrological characterization of system performance, based on experimental testing, is also presente
Modeling Supply Networks and Business Cycles as Unstable Transport Phenomena
Physical concepts developed to describe instabilities in traffic flows can be
generalized in a way that allows one to understand the well-known instability
of supply chains (the so-called ``bullwhip effect''). That is, small variations
in the consumption rate can cause large variations in the production rate of
companies generating the requested product. Interestingly, the resulting
oscillations have characteristic frequencies which are considerably lower than
the variations in the consumption rate. This suggests that instabilities of
supply chains may be the reason for the existence of business cycles. At the
same time, we establish some link to queuing theory and between micro- and
macroeconomics.Comment: For related work see http://www.helbing.or
A hierarchical system for effective coordination of available-to-promise logic mechanisms
The FORS Deep Field: Field selection, photometric observations and photometric catalog
The FORS Deep Field project is a multi-colour, multi-object spectroscopic
investigation of an approx. 7 times 7 region near the south galactic pole based
mostly on observations carried out with the FORS instruments attached to the
VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this
study is to improve our understanding of the formation and evolution of
galaxies in the young Universe. In this paper the field selection, the
photometric observations, and the data reduction are described. The source
detection and photometry of objects in the FORS Deep Field is discussed in
detail. A combined B and I selected UBgRIJKs photometric catalog of 8753
objects in the FDF is presented and its properties are briefly discussed. The
formal 50% completeness limits for point sources, derived from the co-added
images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57 in U, B, g, R,
I, J and Ks (Vega-system), respectively. A comparison of the number counts in
the FORS Deep Field to those derived in other deep field surveys shows very
good agreement.Comment: 15 pages, 11 figures (included), accepted for publication in A&
The Stellar Content of NGC 6789, A Blue Compact Dwarf Galaxy in the Local Void
We find that NGC6789 is the most nearby example of a Blue Compact Dwarf
galaxy known to date. With the help of WFPC2 aboard the Hubble Space Telescope,
we resolve NGC6789 into over 15,000 point sources in the V and I bands. The
young stars of NGC6789 are found exclusively near the center of the galaxy. The
red giant population identified at large galacticentric radii yields a distance
of about 3.6 Mpc, a stellar metallicity [Fe/H] of about -2, and a minimum age
of about 1 Gyr. Despite its isolated location in the Local Void,its low
metallicity, and its active star formation, the properties of NGC6789 are
clearly not those of a galaxy in formation.Comment: 8 pages, 4 figures, ApJL Accepte
Enhancements on multi-exposure LASCA to reveal information of speed distribution
Laser Speckle Contrast Analysis (LASCA) has been proven to be a highly useful tool for the full-field determination of the blood perfusion of a variety of tissues. Some of the major advantages of this technique are its relatively high spatial and temporal resolution as well as its good or excellent accordance to Doppler systems. However, traditionally it is only able to report a single characteristic speed regarding to the actual range of interest. This might be misleading if multiple characteristic speeds are present (e. g. tremor and perfusion in skin) or if several kinds of tissues are mixed (e. g. parenchyma and vessels in brain). Here we present two relatively simple extensions of LASCA for these problems. The application of multiple autocorrelation functions (combined with the usage of multiple exposure times) can help in the separation of multiple characteristic speeds. We also present a useful method for the separation of information those originate from a mixture of different tissues. The latter method can be also implemented to single-exposure systems
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