240 research outputs found
An index-based framework for assessing patterns and trends in river fragmentation and flow regulation by global dams at multiple scales
The global number of dam constructions has increased dramatically over the
past six decades and is forecast to continue to rise, particularly in less
industrialized regions. Identifying development pathways that can deliver the
benefits of new infrastructure while also maintaining healthy and productive
river systems is a great challenge that requires understanding the
multifaceted impacts of dams at a range of scales. New approaches and advanced
methodologies are needed to improve predictions of how future dam construction
will affect biodiversity, ecosystem functioning, and fluvial geomorphology
worldwide, helping to frame a global strategy to achieve sustainable dam
development. Here, we respond to this need by applying a graph-based river
routing model to simultaneously assess flow regulation and fragmentation by
dams at multiple scales using data at high spatial resolution. We calculated
the cumulative impact of a set of 6374 large existing dams and 3377 planned or
proposed dams on river connectivity and river flow at basin and subbasin
scales by fusing two novel indicators to create a holistic dam impact matrix
for the period 1930–2030. Static network descriptors such as basin area or
channel length are of limited use in hierarchically nested and dynamic river
systems, so we developed the river fragmentation index and the river
regulation index, which are based on river volume. These indicators are less
sensitive to the effects of network configuration, offering increased
comparability among studies with disparate hydrographies as well as across
scales. Our results indicate that, on a global basis, 48% of river volume is
moderately to severely impacted by either flow regulation, fragmentation, or
both. Assuming completion of all dams planned and under construction in our
future scenario, this number would nearly double to 93%, largely due to major
dam construction in the Amazon Basin. We provide evidence for the importance
of considering small to medium sized dams and for the need to include
waterfalls to establish a baseline of natural fragmentation. Our versatile
framework can serve as a component of river fragmentation and connectivity
assessments; as a standardized, easily replicable monitoring framework at
global and basin scales; and as part of regional dam planning and management
strategies
О необходимости прослеживания Балейско-Дарасунского разлома в пределах Борщевочного кряжа
In this paper we present the development of a compact, thermo-optically stable and vibration and mechanical shock resistant mounting technique by soldering of optical components. Based on this technique a new generation of laser sources for aerospace applications is designed. In these laser systems solder technique replaces the glued and bolted connections between optical component, mount and base plate. Alignment precision in the arc second range and realization of long term stability of every single part in the laser system is the main challenge. At the Fraunhofer Institute for Laser Technology ILT a soldering and mounting technique has been developed for high precision packaging. The specified environmental boundary conditions (e.g. a temperature range of -40 °C to +50 °C) and the required degrees of freedom for the alignment of the components have been taken into account for this technique. In general the advantage of soldering compared to gluing is that there is no outgassing. In addition no flux is needed in our special process. The joining process allows multiple alignments by remelting the solder. The alignment is done in the liquid phase of the solder by a 6 axis manipulator with a step width in the nm range and a tilt in the arc second range. In a next step the optical components have to pass the environmental tests. The total misalignment of the component to its adapter after the thermal cycle tests is less than 10 arc seconds. The mechanical stability tests regarding shear, vibration and shock behavior are well within the requirements
Некоторые результаты применения метода геометрического анализа дизъюнктов для поисков смещенного крыла пласта в Прокопьевском районе Кузбасса
In this paper we present the development of a compact, thermo-optically stable and vibration and mechanical shock resistant mounting technique by soldering of optical components. Based on this technique, new generations of laser pump sources for aerospace applications are designed. In these laser systems the used soldering technique replaces the glued connection between the optical component and its join partner. The main challenges are the alignment accuracy in the arc second range and the realization of the long term stability of every single part in the laser system (e.g. resonator mirrors)
Моделирование уравнений проекционного осциллографирования на машине "ЭМУ-10"
The passive-alignment-packaging technique presented in this work provides a method for mounting tolerance-insensitive optical components e.g. non-linear crystals by means of mechanical stops. The requested tolerances for the angle deviation are ±100 µrad and for the position tolerance ±100 µm. Only the angle tolerances were investigated, because they are more critical. The measurements were carried out with an autocollimator. Fused silica components were used for test series. A solder investigation was carried out. Different types of solder were tested. Due to good solderability on air and low induced stress in optical components, Sn based solders were indicated as the most suitable solders. In addition several concepts of reflow soldering configuration were realized. In the first iteration a system with only the alignment of the yaw angle was implemented. The deviation for all materials after the thermal and mechanical cycling was within the tolerances. The solderability of BBO and LBO crystals was investigated and concepts for mounting were developed
Evidence of the evolved nature of the B[e] star MWC 137
The evolutionary phase of B[e] stars is difficult to establish due to the un certainties in their fundamental parameters. For instance, possible classications for the Galactic B[e] starMWC 137 include pre- main-sequence and post-main-sequence phases, with a large range in luminosity. Our goal is to clarify the evolutionary stage of this peculiar object, and to study the CO molecular component of its circumstellar medium. To this purpose, we modeled the CO molecular bands using high-resolution K-band spectra. We nd that MWC137 is surrounded by a detached cool (T = 1900100 K) and dense (N = (31)1021 cm2) ring of CO gas orbiting the star with a rotational velocity, projected to the line of sight, of 84 2 kms1. We also nd that the molec- ular gas is enriched in the isotope 13C, excluding the classication of the star as a Herbig Be. The observed isotopic abundance ratio (12C=13C = 25 2) derived from our modeling is compatible with a proto-PN, main-sequence or supergiant evolutionary phase. However, based on some observable characteristics of MWC137, we propose that the supergiant scenario seems to be the most plausible. Hence, we suggest that MWC137 could be in an extremely short-lived phase, evolving from a B[e] supergiant to a blue supergiant with a bipolar ring nebula.Fil: Muratore, M. F.. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Astrofísica de La Plata; ArgentinaFil: Kraus, M.. Astronomický ústav; República ChecaFil: Oksala, M. E.. Astronomický ústav; República ChecaFil: Arias, María Laura. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Astrofísica de La Plata; ArgentinaFil: Cidale, Lydia Sonia. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Astrofísica de La Plata; ArgentinaFil: Borges Fernandes, M.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Liermann, A.. Leibniz-Institut für Astrophysik Potsdam; Alemani
Evidence of the evolved nature of the B[e] star MWC 137
The evolutionary phase of B[e] stars is difficult to establish due to the uncertainties in their fundamental parameters. For instance, possible classifications for the Galactic B[e] star MWC 137 include pre-main-sequence and post-main-sequence phases, with a large range in luminosity. Our goal is to clarify the evolutionary stage of this peculiar object, and to study the CO molecular component of its circumstellar medium. To this purpose, we modeled the CO molecular bands using high-resolution K-band spectra. We find that MWC 137 is surrounded by a detached cool (T = 1900 ± 100 K) and dense (N = (3 ± 1) × 1021 cm-2) ring of CO gas orbiting the star with a rotational velocity, projected to the line of sight, of 84 ± 2 km s-1. We also find that the molecular gas is enriched in the isotope 13C, excluding the classification of the star as a Herbig Be. The observed isotopic abundance ratio (12C/13C = 25 ± 2) derived from our modeling is compatible with a proto-planetary nebula, main-sequence, or supergiant evolutionary phase. However, based on some observable characteristics of MWC 137, we propose that the supergiant scenario seems to be the most plausible. Hence, we suggest that MWC 137 could be in an extremely short-lived phase, evolving from a B[e] supergiant to a blue supergiant with a bipolar ring nebula.Facultad de Ciencias Astronómicas y Geofísica
Hausdorff spectrum of harmonic measure
For every non-elementary hyperbolic group, we show that for every random walk
with finitely supported admissible step distribution, the associated entropy
equals the drift times the logarithmic volume growth if and only if the
corresponding harmonic measure is comparable with Hausdorfff measure on the
boundary. Moreover, we introduce one parameter family of probability measures
which interpolates a Patterson-Sullivan measure and the harmonic measure, and
establish a formula of Hausdorff spectrum (multifractal spectrum) of the
harmonic measure. We also give some finitary versions of dimensional properties
of the harmonic measure
The sudden appearance of CO emission in LHA 115-S 65
Molecular emission has been detected in several Magellanic Cloud B[e]
supergiants. In this Letter, we report on the detection of CO band head
emission in the B[e] supergiant LHA 115-S 65, and present a K-band
near-infrared spectrum obtained with the Spectrograph for INtegral Field
Observation in the Near-Infrared (SINFONI; R=4500) on the ESO VLT UT4
telescope. The observed molecular band head emission in S 65 is quite
surprising in light of a previous non-detection by McGregor et al. 1989, as
well as a high resolution (R=50000) Gemini/Phoenix spectrum of this star taken
nine months earlier showing no emission. Based on analysis of the optical
spectrum by Kraus et al. 2010, we suspect that the sudden appearance of
molecular emission could be due to density build up in an outflowing viscous
disk, as seen for Be stars. This new discovery, combined with variability in
two other similar evolved massive stars, indicates an evolutionary link between
B[e] supergiants and LBVs.Comment: Letter accepted for publication in MNRAS. 5 pages, 2 figures, 1 tabl
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