85 research outputs found
Results of using the global positioning system to maintain the time and frequency synchronization in the Deep Space Network
There are two hydrogen maser clocks located at each signal processing center (SPC) in the DSN. Close coordination of the time and frequency of the SPC clocks is needed to navigate spacecraft to the outer planets. A recent example was the Voyager spacecraft's encounter with Uranus in January 1986. The clocks were adjusted with the goal of minimizing time and frequency offsets between the SPCs at encounter. How time and frequency at each SPC is estimated using data acquired from the Global Positioning System Timing Receivers operating on the NBS-BIH (National Bureau of Standards-Bureau International de l'Heure) tracking schedule is described. These data are combined with other available timing receiver data to calculate the time offset estimates. The adjustment of the clocks is described. It was determined that long range hydrogen maser drift is quite predictable and adjustable within limits. This enables one to minimize time and frequency differences between the three SPCs for many months by matching the drift rates of the three standards. Data acquisition and processing techniques using a Kalman filter to make estimates of time and frequency offsets between the clocks at the SPCs and UTC(NBS) (Coordinated Universal Time realized at NBS) are described
EUV-TEC proxy to describe ionospheric variability using satellite-borne solar EUV measurements
An updated version of a proxy, termed EUV-TEC, describing the global total
primary photoionisation is calculated from satellite-borne EUV measurements
assuming a model atmosphere consisting of four major atmospheric
constituents. Regional number densities of the background atmosphere are
taken from the NRLMSISE-00 climatology. For calculation the Lambert-Beer law
is used to describe the decrease of the radiation along their way through the
atmosphere. The EUV-TEC proxy thus describes the ionospheric response to
solar EUV radiation and its variability. EUV-TEC is compared against the
global mean total electron content (TEC), a fundamental ionospheric parameter
created from vertical TEC maps derived from GPS data. Strong correlation
between these indices is found on different time scales. Results show that
the EUV-TEC proxy represents the ionsopheric variability better than the
conventional solar index F10.7 does, especially during high and moderate
solar activity
EUV-TEC - an index to describe ionospheric variability using satellite-borne solar EUV measurements: first results
Primary ionisation of major ionospheric constituents is calculated from satellite-borne solar EUV measurements. Number densities of the background atmosphere are taken from the NRLMSISE-00 climatology. From the calculated ionisation rates, an index termed EUV-TEC, which is based on the global total ionisation is calculated, and describes
the ionospheric response to solar EUV and its variability. The index is compared against global mean ionospheric total electron content (TEC) derived from GPS data. Results show that the EUV-TEC index provides a better overall representation of global TEC than conventional solar indices like F10.7 do. The EUV-TEC index may be used for scientific research, and to describe the ionospheric effects on radio communication and navigation systems
Context‐dependent dispersal determines relatedness and genetic structure in a patchy amphibian population
Dispersal is a central process in ecology and evolution with far reaching consequences for the dynamics and genetics of spatially structured populations (SSPs). Individuals can adjust their decisions to disperse according to local fitness prospects, resulting in context-dependent dispersal. By determining dispersal rate, distance, and direction, these individual-level decisions further modulate the demography, relatedness, and genetic structure of SSPs. Here, we examined how context-dependent dispersal influences the dynamics and genetics of a Great Crested Newt (Triturus cristatus) SSP. We collected capture-recapture data of 5564 individuals and genetic data of 950 individuals across a SSP in northern Germany. We added genetic data from six sites outside this SSP to assess genetic structure and gene flow at a regional level. Dispersal rates within the SSP were high but dispersal distances were short. Dispersal was context-dependent: individuals preferentially immigrated into high-quality ponds where breeding probabilities were higher. The studied SSP behaved like a patchy population, where subpopulations at each pond were demographically interdependent. High context-dependent dispersal led to weak but significant spatial genetic structure and relatedness within the SSP. At the regional level, a strong hierarchical genetic structure with very few first-generation migrants as well as low effective dispersal rates suggest the presence of independent demographic units. Overall, our study highlights the importance of habitat quality for driving context-dependent dispersal and therefore demography and genetic structure in SSPs. Limited capacity for long-distance dispersal seems to increase genetic structure within a population and leads to demographic isolation in anthropogenic landscapes.Microsatellite Genotypes: Missing values are coded "-9".
Presence/Absence Data: Missing values are coded "-".
Funding provided by: Deutsche ForschungsgemeinschaftCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001659Award Number: STE 1130/7-1Demographic Data (CMR and Presence/Absence Data):
We surveyed 33 water bodies using mark-recapture methods for the presence, demography and reproduction of crested newts between 2012 and 2014. Newts were captured during two capture sessions (cs) per year, one early (April/May) and one late (June/July) in the breeding season. Every capture session thereby consisted of three consecutive capture events in intervals of two days. Within the context of a presence/absence analysis, all sites were surveyed for one more day in late July/early August in order to detect larvae. If a pond dried out and was therefore not surveyed during a capture session, such an event was treated as a missing observation.
Newts were captured using Ortmann's funnel traps which were evenly distributed along the shoreline of a pond. The number of traps deployed per capture event varied according to pond perimeter (one trap per 10m shoreline), ranging from one to 27 traps. For individual recognition of newts during the CMR study, we used photographs of the ventral side of an individual which provides a natural marking in form of a highly variable but individually unique and stable color pattern through the time. Recaptured individuals were identified automatically by the software AmphIdent.
Microsatellite Genotypes:
Tissue samples were taken from seven sampling sites by puncturing the tails of captured great crested newts (Triturus cristatus) using micro haematocrit capillary tubes (Carl Roth, Ø 1.6 mm) and were then stored in 80% ethanol. Total genomic DNA was extracted using the sodium dodecyl sulfate (SDS)-proteinase K/ Phenol-Chloroform extraction method. Genomic DNA was stored in Tris-EDTA buffer (10 mM Tris-HCl, 0.1 mM EDTA, pH 8.0) and used for all subsequent reactions.
Each individual sample was mugenotyped for 17 microsatellite loci. Primers were combined in three multiplex mixes (Drechsler et al., 2013). 10 µl Type-it Multiplex PCRs (Qiagen) containing 1 µl of genomic DNA were performed. The PCR profile was as follows: (1) 5 min at 95°C, (2) 30 s at 94°C, (3) 90 s at an annealing temperature of 60°C, (4) 60 s at 72°C, (5) return to step 2 for 30 times, (6) 30 min at 60°C. Obtained PCR products were diluted with 50-200 μl water depending on the strength of obtained PCR products. 1 µl of each diluted multiplex reaction was added to 20 μl of Genescan 500-LIZ size standard (Applied Biosystem) and then run on an ABI 3730 96-capillary or an ABI 3130 16-capillary automated DNA-sequencer. Allele scoring of microsatellite loci was performed using Genemarker software (SoftGenetics version 1.95)
Proxies to describe ionospheric variability and heating rates of the upper atmosphere: current progress
An updated version of the EUV-TEC proxy, describing the total primary ionisation of the upper atmosphere, is calculated from satellite-borne EUV measurements. Regional number densities of the background model atmosphere consisting of four major constituents are taken from the NRLMSISE-00 climatology. Furthermore, a first estimate of a global thermospheric heating rate is calculated from the absorbed energy.
For the calculations the Lambert-Beer law is used to describe the decrease of the radiation along their way through the atmosphere. The EUV-TEC proxy is compared against the global mean total electron content (TEC), obtained from vertical TEC maps derived from GPS data. Strong correlations between these indices are found on different time scales. Results show that the EUV-TEC proxy describes the ionospheric variability better than the conventional solar index F10.7, especially at short time scales of days to weeks
Evolution of white dwarf stars with high-metallicity progenitors: the role of 22Ne diffusion
Motivated by the strong discrepancy between the main sequence turn-off age
and the white dwarf cooling age in the metal-rich open cluster NGC 6791, we
compute a grid of white dwarf evolutionary sequences that incorporates for the
first time the energy released by the processes of 22Ne sedimentation and of
carbon/oxygen phase separation upon crystallization. The grid covers the mass
range from 0.52 to 1.0 Msun, and it is appropriate for the study of white
dwarfs in metal-rich clusters. The evolutionary calculations are based on a
detailed and self-consistent treatment of the energy released from these two
processes, as well as on the employment of realistic carbon/oxygen profiles, of
relevance for an accurate evaluation of the energy released by carbon/oxygen
phase separation. We find that 22Ne sedimentation strongly delays the cooling
rate of white dwarfs stemming from progenitors with high metallicities at
moderate luminosities, whilst carbon/oxygen phase separation adds considerable
delays at low luminosities. Cooling times are sensitive to possible
uncertainties in the actual value of the diffusion coefficient of 22Ne.
Changing the diffusion coefficient by a factor of 2, leads to maximum age
differences of approx. 8-20% depending on the stellar mass. We find that the
magnitude of the delays resulting from chemical changes in the core is
consistent with the slow down in the white dwarf cooling rate that is required
to solve the age discrepancy in NGC 6791.Comment: 10 pages, 6 figures, to be published in The Astrophysical Journa
Solar activity and ionospheric response as seen from combined SolACES and SDO-EVE solar EUV spectra
Ionospheric response to solar EUV variability during late 2012 through mid 2013 is shown by the EUV-TEC proxy based on combined SolACES and SDO/EVE solar spectra. The results are compared with global TEC analyses. We found that EUV-TEC describes TEC variability better than the conventional F107 index, especially during periods of strong solar flare activity
Gravitational settling in pulsating subdwarf B stars and their progenitors
Diffusion of atoms can be important during quiescent phases of stellar
evolution. Particularly in the very thin inert envelopes of subdwarf B stars,
diffusive movements will considerably change the envelope structure and the
surface abundances on a short timescale. Also, the subdwarfs will inherit the
effects of diffusion in their direct progenitors, namely giants near the tip of
the red giant branch. This will influence the global evolution and the
pulsational properties of subdwarf B stars. We investigate the impact of
gravitational settling, thermal diffusion and concentration diffusion on the
evolution and pulsations of subdwarf B stars. Our diffusive stellar models are
compared with models evolved without diffusion. We constructed subdwarf B
models with a mass of 0.465 Msun from a 1 and 3 Msun ZAMS progenitor. The low
mass star ignited helium in an energetic flash, while the intermediate mass
star started helium fusion gently. For each progenitor type we computed series
with and without atomic diffusion. Atomic diffusion in red giants causes the
helium core mass at the onset of helium ignition to be larger. We find an
increase of 0.0015 Msun for the 1 Msun model and 0.0036 Msun for the 3 Msun
model. The effects on the red giant surface abundances are small after the
first dredge up. The evolutionary tracks of the diffusive subdwarf B models are
shifted to lower surface gravities and effective temperatures due to outward
diffusion of hydrogen. This affects both the frequencies of the excited modes
and the overall frequency spectrum. Especially the structure and pulsations of
the post-non-degenerate sdB star are drastically altered, proving that atomic
diffusion cannot be ignored in these stars.Comment: 10 pages, 6 figures, accepted for publication in A&
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