776 research outputs found
Analysis and Comparison of new Downlink Technologies for Earth Observation Satellites
New generation of Earth observation sensors are creating an increasing amount of data which has to be delivered from space-to-ground. Additionally, many applications require timely availability of this sensor data. As new link technologies have been made available in the last years and data rate requirements are still increasing a revise of the conventional direct-downlink technology at X-band frequencies is essential. This work aims in a trade-off of the available direct-downlink technologies for satellites in low, polar orbits. Generally, there are two approaches to fulfill the requirement of timely delivery of a huge amount of data from space-to-ground. This is either increasing space-to-ground contact time resulting in a more complex ground station network or increasing carrier frequency whereas link reliability is limited by atmospheric effects. In this work different approaches like using K-band or utilizing ground station network with additional locations are compared against each other
Superconducting phase diagram of the filled skuterrudite PrOs4Sb12
We present new measurements of the specific heat of the heavy fermion
superconductor PrOs4Sb12, on a sample which exhibits two sharp distinct
anomalies at Tc1= 1.89K and Tc2= 1.72K. They are used to draw a precise
magnetic field-temperature superconducting phase diagram of PrOs4Sb12 down to
350 mK.
We discuss the superconducting phase diagram of PrOs4Sb12 and its possible
relation with an unconventional superconducting order parameter. We give a
detailed analysis of Hc2(T), which shows paramagnetic limitation (a support for
even parity pairing) and multiband effects
Controlled Photographic Images for Visual Search Experiments with Quantified Contextual Priors
Direct observation of the quantum critical point in heavy fermion CeRhSi
We report on muon spin rotation studies of the noncentrosymmetric heavy
fermion antiferromagnet CeRhSi. A drastic and monotonic suppression of the
internal fields, at the lowest measured temperature, was observed upon an
increase of external pressure. Our data suggest that the ordered moments are
gradually quenched with increasing pressure, in a manner different from the
pressure dependence of the N\'eel temperature. At \unit{23.6}{kbar}, the
ordered magnetic moments are fully suppressed via a second-order phase
transition, and is zero. Thus, we directly observed the quantum
critical point at \unit{23.6}{kbar} hidden inside the superconducting phase
of CeRhSi
Pressure cycle of superconducting Cs0.8Fe2Se2: a transport study
We report measurements of the temperature and pressure dependence of the
electrical resistivity of single crystalline iron-based chalcogenide
Cs0.8Fe2Se2. In this material superconductivity Tc~30K develops from a normal
state with extremely large resistivity. At ambient pressure a large "hump" in
the resistivity is observed around 200K. Under pressure, the resistivity
decreases by two orders of magnitude, concomitant with a sudden Tc suppression
around p~8GPa. Even at 9GPa a metallic resistivity state is not recovered, and
the {\rho}(T) "hump" is still detected. A comparison of the data measured upon
increasing and decreasing the external pressure leads us to suggest that
superconductivity is not related to this hump
The Polarized H and D Atomic Beam Source for ANKE at COSY-J\"ulich
A polarized atomic beam source was developed for the polarized internal
storage-cell gas target at the magnet spectrometer ANKE of COSY-J\"ulich. The
intensities of the beams injected into the storage cell, measured with a
compression tube, are hydrogen atoms/s (two hyperfine
states) and deuterium atoms/s (three hyperfine states). For
the hydrogen beam the achieved vector polarizations are . For the deuterium beam, the obtained combinations of vector
and tensor () polarizations are (with a
constant ), and or (both with vanishing ). The paper includes a detailed
technical description of the apparatus and of the investigations performed
during the development.Comment: 18 pages, 26 figures, 4 table
Memory spaces – cooperative learning between physical and virtual mobility
Die Corona-Pandemie hat weltweit zu Bemühungen geführt, neue und innovative Konzepte für die digitale Lehre zu schaffen. Kern unserer Überlegungen ist ein im Wintersemester 2018/2019 an der Universität Greifswald und der Staatlichen Universität St. Petersburg durchgeführtes kooperatives Projektseminar, in dem Studierende gemeinsam an deutsch- und russischsprachigen Erinnerungsdiskursen zu gemeinsamen Erinnerungsorten im kollektiven Gedächtnis der russischen und der deutschen Gesellschaft gearbeitet haben. Ausgehend von einer Annäherung an das Konzept der Erinnerungsorte wird im vorliegenden Beitrag das damalige Kooperationsprojekt vorgestellt, das parallele Arbeitsphasen an den beiden Standorten mit Exkursionen von Studierendengruppen an den jeweils anderen Standort verbunden hat. Den Beitrag runden Überlegungen dazu ab, wie ein solches Seminar im Sinne einer Förderung virtueller akademischer Mobilität fruchtbar gemacht werden kann. The Corona pandemic has led to worldwide efforts to create new and innovative concepts for digital learning. In this article, we present a project oriented seminar that took place at the University of Greifswald and St. Petersburg State University in the winter semester of 2018. In this project seminar students of both universities worked on memory spaces that are at the same time a part of the collective memory of both German- and Russian-speaking discourse communities. After giving an outline on the concept of memory spaces, this article presents the project, which combined parallel work at the two participating universities with study visits of student groups from each university to the partner university. We end with reflections on how such seminars can serve as a basis for virtual academic mobility
Heavy Meson Production in NN Collisions with Polarized Beam and Target -- A new facility for COSY
The study of near--threshold meson production in pp and pd collisions
involving polarized beams and polarized targets offers the rare opportunity to
gain insight into short--range features of the nucleon--nucleon interaction.
The Cooler Synchrotron COSY at FZ--J\"ulich is a unique environment to perform
such studies. Measurements of polarization observables require a cylindrically
symmetrical detector, capable to measure the momenta and the directions of
outgoing charged hadrons. The wide energy range of COSY leads to momenta of
outgoing protons to be detected in a single meson production reaction between
300 and 2500 MeV/c. Scattering angles of protons to be covered extend to about
in the laboratory system. An azimuthal angular coverage of the
device around 98% seems technically achievable. The required magnetic
spectrometer could consist of a superconducting toroid, providing fields around
3 T.Comment: 6 pages, 1 figure, submitted to Czechoslovak Journal of Physic
Egalitarian despots: hierarchy steepness, reciprocity and the grooming-trade model in wild chimpanzees (Pan troglodytes)
Biological-markets theory models the action of natural selection as a marketplace in which animals are viewed as traders with commodities to offer and exchange. Studies of female Old World monkeys have suggested that grooming might be employed as a commodity to be reciprocated or traded for alternative services, yet previous tests of this grooming-trade model in wild adult male chimpanzees (Pan troglodytes) have yielded mixed results. Here we provide the strongest test of the model to date for male chimpanzees: we use data drawn from two social groups (communities) of chimpanzees from different populations, and give explicit consideration to variation in dominance hierarchy steepness as such variation results in differing conditions for biological markets. First, analysis of data from published accounts of other chimpanzee communities, together with our own data, showed that hierarchy steepness varied considerably within and across communities and that the number of adult males in a community aged 20-30 years predicted hierarchy steepness. The two communities in which we tested predictions of the grooming-trade model lay at opposite extremes of this distribution. Second, in accord with the grooming-trade model, we found evidence that male chimpanzees trade grooming for agonistic support where hierarchies are steep (despotic) and consequent effective support is a rank-related commodity, but not where hierarchies are shallow (egalitarian). However, we also found that grooming was reciprocated regardless of hierarchy steepness. Our findings also hint at the possibility of agonistic competition, or at least exclusion, in relation to grooming opportunities compromising the free market envisioned by Biological Markets theory. Our results build on previous findings across chimpanzee communities to emphasise the importance of reciprocal grooming exchanges among adult male chimpanzees, which can be understood in a biological markets framework if grooming by or with particular individuals is a valuable commodity
Variation in the Meaning of Alarm Calls in Verreaux’s and Coquerel’s Sifakas (Propithecus verreauxi, P. coquereli)
The comprehension and usage of primate alarm calls appear to be influenced by social learning. Thus, alarm calls provide flexible behavioral mechanisms that may allow animals to develop appropriate responses to locally present predators. To study this potential flexibility, we compared the usage and function of 3 alarm calls common to 2 closely related sifaka species (Propithecus verreauxi and P. coquereli), in each of 2 different populations with different sets of predators. Playback studies revealed that both species in both of their respective populations emitted roaring barks in response to raptors, and playbacks of this call elicited a specific anti-raptor response (look up and climb down). However, in Verreaux’s sifakas, tchi-faks elicited anti-terrestrial predator responses (look down, climb up) in the population with a higher potential predation threat by terrestrial predators, whereas tchi-faks in the other population were associated with nonspecific flight responses. In both populations of Coquerel’s sifakas, tchi-fak playbacks elicited anti-terrestrial predator responses. More strikingly, Verreaux’s sifakas exhibited anti-terrestrial predator responses after playbacks of growls in the population with a higher threat of predation by terrestrial predators, whereas Coquerel’s sifakas in the raptor-dominated habitat seemed to associate growls with a threat by raptors; the 2 other populations of each species associated a mild disturbance with growls. We interpret this differential comprehension and usage of alarm calls as the result of social learning processes that caused changes in signal content in response to changes in the set of predators to which these populations have been exposed since they last shared a common ancestor
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