Strong lensing interferometry for compact binaries

We propose a possibility to improve the current precision measurements on compact binaries. When the orbital axis is almost perpendicular to our line of sight, a pulsar behind its companion can form two strong-lensing images. These images cannot be resolved, but we can use multi-wavelength interferometry to accurately determine the passage through superior conjunction. This method does not depend strongly on the stability of the pulse profile, and applies equally well to both slow and fast pulsars. We discuss the possible improvement this can bring to the bound on stochastic gravitational wave background and to determine black hole spin. We also discuss the possibility of discovering a suitable binary system by the Square Kilometer Array that our method can apply to.Comment: 5 pages, 5 figure

Variation in habitat choice and delayed reproduction: Adaptive queuing strategies or individual quality differences?

In most species, some individuals delay reproduction or occupy inferior breeding positions. The queue hypothesis tries to explain both patterns by proposing that individuals strategically delay breeding (queue) to acquire better breeding or social positions. In 1995, Ens, Weissing, and Drent addressed evolutionarily stable queuing strategies in situations with habitat heterogeneity. However, their model did not consider the non - mutually exclusive individual quality hypothesis, which suggests that some individuals delay breeding or occupy inferior breeding positions because they are poor competitors. Here we extend their model with individual differences in competitive abilities, which are probably plentiful in nature. We show that including even the smallest competitive asymmetries will result in individuals using queuing strategies completely different from those in models that assume equal competitors. Subsequently, we investigate how well our models can explain settleme! nt patterns in the wild, using a long-term study on oystercatchers. This long-lived shorebird exhibits strong variation in age of first reproduction and territory quality. We show that only models that include competitive asymmetries can explain why oystercatchers' settlement patterns depend on natal origin. We conclude that predictions from queuing models are very sensitive to assumptions about competitive asymmetries, while detecting such differences in the wild is often problematic.

Sex-specific dispersal behaviour of crawlers in the mealybug Planococcus citri

Όταν η διασπορά σχετίζεται με το φύλο είναι δυνατό να έχει σημαντικές εξελικτικές και οικο- λογικές επιπτώσεις, επηρεάζοντας τη δομή των πληθυσμών, την αναλογία φύλου καθώς και την ταχύτητα με την οποία αποικίζονται νέα ενδιαιτήματα. Στα κοκκοειδή έντομα, οι προνύμ- φες πρώτης ηλικίας (έρπουσες) θεωρούνται ως το κύριο στάδιο διασποράς. Αν και στα κοκκο- ειδή έντομα υπάρχει μορφολογικός διμορφισμός φύλου, στα περισσότερα είναι αδύνατος ο διαχωρισμός φύλου στο στάδιο των ερπουσών προνυμφών. Στην παρούσα εργασία μελετήθη- κε η διασπορά του εντόμου Planococcus citri (Risso) (Hemiptera: Coccidae) από και προς διαθέσιμα ενδιαιτήματα. Σκοπός της μελέτης ήταν να εξετάσουμε αν: (1) η συμπεριφορά δια- σποράς στις έρπουσες προνύμφες διαφέρει στα δύο φύλα και πώς επηρεάζεται από συνθήκες όπως η πυκνότητα πληθυσμού ή η αναλογία φύλου, και (2) αν τα δύο φύλα διαφέρουν ως προς την επιτυχία διασποράς σε νέο φυτό ξενιστή. Σύμφωνα με τα αποτελέσματά μας παρατηρήθη- κε ότι τα αρσενικά και θηλυκά άτομα κατά το στάδιο της έρπουσας προνύμφης δε διαφέρουν στη συμπεριφορά διασποράς όταν αυτή συμβαίνει με βαδιστική μετακίνηση. Αυτά τα εργα- στηριακά πειράματα αποτελούν ένα σημαντικό πρώτο βήμα για την κατανόηση της εξέλιξης της συμπεριφοράς διασποράς του P. citri στη φύση ενώ απαιτούνται περαιτέρω πειράματα με διαφορετικούς τρόπους διασποράς, εκτός της μετακίνησης, για να κατανοήσουμε καλύτερα τη δεδομένη συμπεριφορά του εντόμου.Sex-specific dispersal can have important evolutionary and ecological implications, influencing local population structure and sex ratio, as well as the speed at which new habitats can be colonized. In scale insects, first-instar nymphs (crawlers) are assumed to be the main dispersal stage. Although all scale insects are extremely sexually dimorphic, in most species the sexes are indistinguishable as crawlers. Here we consider the mealybug Planococcus citri (Risso), and dispersal by crawlers to or from resource patches. The aim of this study was to test if: (1) crawler dispersal behaviour differs between the sexes and how this is affected by local conditions (population density and sex ratio); and (2) there is a difference between the sexes in crawler dispersal success to a new host plant. Using two experiments, which differed in how resources were spread between dispersal sources and sinks, we show that male and female nymphs do not differ in their dispersal behaviour or in their dispersal success when dispersal is via crawler locomotion. These laboratory experiments are an important starting point for understanding the evolution of dispersal behaviour of P. citri in the field, suggesting that more attention might need to be paid to different methods of dispersal as well as crawler locomotion

Spin and orbital excitation spectrum in the Kugel-Khomskii model

We discuss spin and orbital ordering in the twofold orbital degenerate superexchange model in three dimensions relevant to perovskite transition metal oxides. We focus on the particular point on the classical phase diagram where orbital degeneracy is lifted by quantum effects exclusively. Dispersion and damping of the spin and orbital excitations are calculated at this point taking into account their mutual interaction. Interaction corrections to the mean-field order parameters are found to be small. We conclude that quasi-one-dimensional Neel spin order accompanied by the uniform d_{3z^2-r^2}-type orbital ordering is stable against quantum fluctuations.Comment: 4 pages with 3 PS figures, 1 table, RevTeX, accepted to Phys. Rev. B. Rapid Communicatio

Trimer Formation and Metal-Insulator Transition in Orbital Degenerate Systems on a Triangular Lattice

As a prototypical self-organization in the system with orbital degeneracy, we theoretically investigate trimer formation on a triangular lattice, as observed in LiVO2. From the analysis of an effective spin-orbital coupled model in the strong correlation limit, we show that the previously-proposed orbital-ordered trimer state is not the lowest-energy state for a finite Hund's-rule coupling. Instead, exploring the ground state in a wide range of parameters for a multiorbital Hubbard model, we find an instability toward a different orbital-ordered trimer state in the intermediately correlated regime in the presence of trigonal crystal field. The trimer phase appears in the competing region among a paramagnetic metal, band insulator, and Mott insulator. The underlying mechanism is nesting instability of the Fermi surface by a synergetic effect of Coulomb interactions and trigonal-field splitting. The results are compared with experiments in triangularlattice compounds, LiVX2 (X=O, S, Se) and NaVO2.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp

Dynamics of genetic rescue in inbred <i>Drosophila melanogaster</i> populations

Genetic rescue has been proposed as a management strategy to improve the fitness of genetically eroded populations by alleviating inbreeding depression. We studied the dynamics of genetic rescue in inbred populations of Drosophila. Using balancer chromosomes, we show that the force of heterosis that accompanies genetic rescue is large and allows even a recessive lethal to increase substantially in frequency in the rescued populations, particularly at stress temperatures. This indicates that deleterious alleles present in the immigrants can increase significantly in frequency in the recipient population when they are in linkage disequilibrium with genes responsible for the heterosis. In a second experiment we rescued eight inbred Drosophila populations with immigrants from two other inbred populations and observe: (i) there is a significant increase in viability both 5 and 10 generations after the rescue event, showing that the increase in fitness is not transient but persists long-term. (ii) The lower the fitness of the recipient population the larger the fitness increase. (iii) The increase in fitness depends significantly on the origin of the rescuers. The immigrants used were fixed for a conditional lethal that was mildly deleterious at 25A degrees C but lethal at 29A degrees C. By comparing fitness at 25A degrees C (the temperature during the rescue experiment) and 29A degrees C, we show that the lethal allele reached significant frequencies in most rescued populations, which upon renewed inbreeding became fixed in part of the inbred lines. In conclusion, in addition to the fitness increase genetic rescue can easily result in a substantial increase in the frequency of mildly deleterious alleles carried by the immigrants. This can endanger the rescued population greatly when it undergoes recurrent inbreeding. However, using a sufficient number of immigrants and to accompany the rescue event with the right demographic measures will overcome this problem. As such, genetic rescue still is a viable option to manage genetically eroded populations