Could thermal fluctuations seed cosmic structure?

We examine the possibility that thermal, rather than quantum, fluctuations are responsible for seeding the structure of our universe. We find that while the thermalization condition leads to nearly Gaussian statistics, a Harrisson-Zeldovich spectrum for the primordial fluctuations can only be achieved in very special circumstances. These depend on whether the universe gets hotter or colder in time, while the modes are leaving the horizon. In the latter case we find a no-go theorem which can only be avoided if the fundamental degrees of freedom are not particle-like, such as in string gases near the Hagedorn phase transition. The former case is less forbidding, and we suggest two potentially successful ``warming universe'' scenarios. One makes use of the Phoenix universe, the other of ``phantom'' matter.Comment: minor corrections made, references added, matches the version accepted to PR

The First Magnetic Fields

We review current ideas on the origin of galactic and extragalactic magnetic fields. We begin by summarizing observations of magnetic fields at cosmological redshifts and on cosmological scales. These observations translate into constraints on the strength and scale magnetic fields must have during the early stages of galaxy formation in order to seed the galactic dynamo. We examine mechanisms for the generation of magnetic fields that operate prior during inflation and during subsequent phase transitions such as electroweak symmetry breaking and the quark-hadron phase transition. The implications of strong primordial magnetic fields for the reionization epoch as well as the first generation of stars is discussed in detail. The exotic, early-Universe mechanisms are contrasted with astrophysical processes that generate fields after recombination. For example, a Biermann-type battery can operate in a proto-galaxy during the early stages of structure formation. Moreover, magnetic fields in either an early generation of stars or active galactic nuclei can be dispersed into the intergalactic medium.Comment: Accepted for publication in Space Science Reviews. Pdf can be also downloaded from http://canopus.cnu.ac.kr/ryu/cosmic-mag1.pd

Mapping density, diversity and species-richness of the Amazon tree flora

Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution

More than 10,000 pre-Columbian earthworks are still hidden throughout Amazonia

Indigenous societies are known to have occupied the Amazon basin for more than 12,000 years, but the scale of their influence on Amazonian forests remains uncertain. We report the discovery, using LIDAR (light detection and ranging) information from across the basin, of 24 previously undetected pre-Columbian earthworks beneath the forest canopy. Modeled distribution and abundance of large-scale archaeological sites across Amazonia suggest that between 10,272 and 23,648 sites remain to be discovered and that most will be found in the southwest. We also identified 53 domesticated tree species significantly associated with earthwork occurrence probability, likely suggesting past management practices. Closed-canopy forests across Amazonia are likely to contain thousands of undiscovered archaeological sites around which pre-Columbian societies actively modified forests, a discovery that opens opportunities for better understanding the magnitude of ancient human influence on Amazonia and its current state

Frequency Augumented Clock Synchronizaion for Space-based interferometry

Recently, an increase in distributed space systems and a rise in number of nodes in such systems is observed in numerous space applications, for example space-based interferometry. Such applications pose stringent demands on time synchronization which can be challenging to achieve for satellite networks that lack an absolute time reference source, as would be the case with networks beyond Earth orbit. In this paper, we propose a new class of frequency-based and multi-domain time synchronization and ranging algorithms applicable to anchorless mobile networks of asynchronous nodes. First, the Frequency-based Pairwise Least Squares (FPLS) that estimates clock skew and relative velocity under constant pairwise velocity assumption. Second, the Combined Pairwise Least Squares (CPLS)— a two step approach where first, skew and velocity are estimated using FPLS and then its results are fed into a reformulated time domain method to estimate offset and range. The proposed methods are applied to a case study to OLFAR — a spaceborne large aperture radio interferometric array platform for observing the cosmos in the frequency range from 0.3 MHz to 30 MHz to be stationed in the Lunar orbit. The results show that the proposed methods decrease communication and computation needs and can improve the clock synchronization performance for space-based interferometry

Communications architecture for Martian surface exploration with a swarm of wind-driven rovers

This decade has seen growing interest in Mars exploration. Advances in distributed systems, miniaturization and commoditization of space electronics and innovations in communications permit us to rethink the current paradigm of relying on a few heavy, slow and expensive high-tech rovers for Mars surface exploration. In this work, we address the demanding communication needs for a mission that deploys a swarm of uncontrolled wind-driven exploration rovers onto the martian surface. The concept for these lightweight, autonomous, ellipsoid ”Tumbleweed” rovers — named after the desert plant — is not new, and was studied and validated by NASA researchers decades ago. Recently, a new plan to turn the Tumbleweed mission into reality has been proposed to the ESA open space innovation platform (OSIP). The idea is to launch approximately 90 Tumbleweeds in one transfer vehicle and release them on the martian surface to survey the northern hemisphere of Mars over a mission duration of three months. Reliable communication is one of the key challenges for this mission. The rovers’ instruments, e.g. cameras, generate large volumes of data, and many rovers need to be served simultaneously. Furthermore, the tumbling motion on the martian surface constitutes unprecedented challenges in terms of antenna pointing for planetary exploration rovers. We present a trade-off analysis between direct to Earth communication and relayed communication using satellites orbiting Mars culminating in a baseline communication architecture for the Tumbleweed mission. For this purpose we model the kinematics of the Tumbleweed rovers and relay satellites w.r.t the Earth. A numerical simulation of all potential communication links over the full mission duration is conducted. The analysis shows that direct communication to Earth is infeasible due to the rolling motion of the rover. Hence, the relayed communication scenario is proposed, as it does not require a directional antenna on the Tumbleweed rovers. Therefore, we propose a constellation of three relay satellites in a circular, Earth-facing orbital plane around Mars, which communicate with the Tumbleweed rovers using the UHF frequency band. Commercial ground stations on Earth in Ka-band are used for the relay-ground link. The proposed communications architecture is estimated to achieve a raw data throughput of ě84Mbit per Tumbleweed rover per Sol

Frequency Augumented Clock Synchronizaion for Space-based interferometry

Recently, an increase in distributed space systems and a rise in number of nodes in such systems is observed in numerous space applications, for example space-based interferometry. Such applications pose stringent demands on time synchronization which can be challenging to achieve for satellite networks that lack an absolute time reference source, as would be the case with networks beyond Earth orbit. In this paper, we propose a new class of frequency-based and multi-domain time synchronization and ranging algorithms applicable to anchorless mobile networks of asynchronous nodes. First, the Frequency-based Pairwise Least Squares (FPLS) that estimates clock skew and relative velocity under constant pairwise velocity assumption. Second, the Combined Pairwise Least Squares (CPLS)— a two step approach where first, skew and velocity are estimated using FPLS and then its results are fed into a reformulated time domain method to estimate offset and range. The proposed methods are applied to a case study to OLFAR — a spaceborne large aperture radio interferometric array platform for observing the cosmos in the frequency range from 0.3 MHz to 30 MHz to be stationed in the Lunar orbit. The results show that the proposed methods decrease communication and computation needs and can improve the clock synchronization performance for space-based interferometry.ElectronicsSignal Processing System

Communications architecture for Martian surface exploration with a swarm of wind-driven rovers

This decade has seen growing interest in Mars exploration. Advances in distributed systems, miniaturization and commoditization of space electronics and innovations in communications permit us to rethink the current paradigm of relying on a few heavy, slow and expensive high-tech rovers for Mars surface exploration. In this work, we address the demanding communication needs for a mission that deploys a swarm of uncontrolled wind-driven exploration rovers onto the martian surface. The concept for these lightweight, autonomous, ellipsoid ”Tumbleweed” rovers — named after the desert plant — is not new, and was studied and validated by NASA researchers decades ago. Recently, a new plan to turn the Tumbleweed mission into reality has been proposed to the ESA open space innovation platform (OSIP). The idea is to launch approximately 90 Tumbleweeds in one transfer vehicle and release them on the martian surface to survey the northern hemisphere of Mars over a mission duration of three months. Reliable communication is one of the key challenges for this mission. The rovers’ instruments, e.g. cameras, generate large volumes of data, and many rovers need to be served simultaneously. Furthermore, the tumbling motion on the martian surface constitutes unprecedented challenges in terms of antenna pointing for planetary exploration rovers. We present a trade-off analysis between direct to Earth communication and relayed communication using satellites orbiting Mars culminating in a baseline communication architecture for the Tumbleweed mission. For this purpose we model the kinematics of the Tumbleweed rovers and relay satellites w.r.t the Earth. A numerical simulation of all potential communication links over the full mission duration is conducted. The analysis shows that direct communication to Earth is infeasible due to the rolling motion of the rover. Hence, the relayed communication scenario is proposed, as it does not require a directional antenna on the Tumbleweed rovers. Therefore, we propose a constellation of three relay satellites in a circular, Earth-facing orbital plane around Mars, which communicate with the Tumbleweed rovers using the UHF frequency band. Commercial ground stations on Earth in Ka-band are used for the relay-ground link. The proposed communications architecture is estimated to achieve a raw data throughput of ě84Mbit per Tumbleweed rover per Sol.Signal Processing System

Systemic infection of petunia by mechanical inoculation with tomato golden mosaic virus

Aangetoond werd dat Petunia hybrida systemisch kan worden geïnfecteerd met het 'tomato golden mosaic virus' (TGMV), een virus dat behoort tot de groep van de geminivirussen. Mechanische inoculatie van petuniaplanten met TGMV gaf in de systemisch geïnfecteerde bladeren symptomen, die eerder in een aantal andere Solanaceae waren waargenomen. Daar in eerdere proeven petunia niet met TGMV kon worden geïnfecteerd en DNA-replicatie en symptoomontwikkeling wel optrad in, voor de beide genomen van het virus, transgene planten, werd gesuggereerd dat het hier een geval betrof van uitbreiding van de waardplantenreeks. De hier gepresenteerde resultaten kunnen echter tot andere conclusies leiden. Het is namelijk mogelijk, dat bepaalde F-hybriden van petunia resistenter zijn tegen het virus. Verschillen in de symptoomontwikkeling zijn echter ook niet uit te sluiten en zouden veroorzaakt kunnen worden door premunitie als gevolg van de aanwezigheid van het manteleiwit in opnieuw geïnfecteerde cellen.Peer reviewe