16,647 research outputs found
A preliminary study of the Soviet civil space program. Volume 1: Organization and Operations
The organization, planning, and personnel is focused of Soviet space, advantage is taken of glasnost and improved foreign relations to explore a hitherto obscure subject. The way in which the civil space program obtains approval and funding is altered. Missions must be approved before the Supreme Soviet, and public opinion is beginning to play a greater role in the legislature's budget decision. The Soviet civil space program remains a collection of disparate elements, not unified by any national, centralized space agency. An attempt was made to catalog and delineate the relationships between the components proves helpful. There is little or no coordination of independent associations' efforts, and the planning process relied on previously to set priorities and allocate resources appears to be currently inoperative or in a state of flux. The civil space program is moving in new directions: toward budget tautness, more international interactions, an emphasis on civilian over military applications, commercialization, and fiscal accountability. This study is a snapshot of a dynamic subject, but hopefully on which has highlighted the critical elements to track
Geometric phases for corotating elliptical vortex patches
We describe a geometric phase that arises when two elliptical vortex patches corotate. Using the Hamiltonian moment model of Melander, Zabusky, and Styczek [J. Fluid Mech. 167, 95–115 (1986)] we consider two corotating uniform elliptical patches evolving according to the second order truncated equations of the model. The phase is computed in the adiabatic setting of a slowly varying Hamiltonian as in the work of Hannay [J. Phys. A 18, 221–230 (1985)] and Berry [Proc. R. Soc. London, Ser. A 392, 45–57 (1984)]. We also discuss the geometry of the symplectic phase space of the model in the context of nonadiabatic phases. The adiabatic phase appears in the orientation angle of each patch—it is similiar in form and is calculated using a multiscale perturbation procedure as in the point vortex configuration of Newton [Physica D 79, 416–423 (1994)] and Shashikanth and Newton [J. Nonlinear Sci. 8, 183–214 (1998)], however, an extra factor due to the internal stucture of the patch is present. The final result depends on the initial orientation of the patches unlike the phases in the works of Hannay and Berry [J. Phys. A 18, 221–230 (1985)]; [Proc. R. Soc. London, Ser. A 392, 45–57 (1984)]. We then show that the adiabatic phase can be interpreted as the holonomy of a connection on the trivial principal fiber bundle pi:T2×S1-->S1, where T2 is identified with the product of the momentum level sets of two Kirchhoff vortex patches and S1 is diffeomorphic to the momentum level set of two point vortex motion. This two point vortex motion is the motion that the patch centroids approach in the adiabatic limit
Coins falling in water
When a coin falls in water, its trajectory is one of four types determined by
its dimensionless moment of inertia and Reynolds number Re: (A)
steady; (B) fluttering; (C) chaotic; or (D) tumbling. The dynamics induced by
the interaction of the water with the surface of the coin, however, makes the
exact landing site difficult to predict a priori. Here, we describe a carefully
designed experiment in which a coin is dropped repeatedly in water, so that we
can determine the probability density functions (pdf) associated with the
landing positions for each of the four trajectory types, all of which are
radially symmetric about the center-drop line. In the case of the steady mode,
the pdf is approximately Gaussian distributed, with variances that are small,
indicating that the coin is most likely to land at the center, right below the
point it is dropped from. For the other falling modes, the center is one of the
least likely landing sites. Indeed, the pdf's of the fluttering, chaotic and
tumbling modes are characterized by a "dip" around the center. For the tumbling
mode, the pdf is a ring configuration about the center-line, with a ring width
that depends on the dimensionless parameters and Re and height from
which the coin is dropped. For the chaotic mode, the pdf is generally a
broadband distribution spread out radially symmetrically about the center-line.
For the steady and fluttering modes, the coin never flips, so the coin lands
with the same side up as was dropped. For the chaotic mode, the probability of
heads or tails is close to 0.5. In the case of the tumbling mode, the
probability of heads or tails based on the height of the drop which determines
whether the coin flips an even or odd number of times during descent
Challenges posed by non-standard neutrino interactions in the determination of at DUNE
One of the primary objectives of Deep Underground Neutrino Experiment (DUNE)
is to discover the leptonic CP violation and to identify it's source. In this
context, we study the impact of non-standard neutrino interactions (NSIs) on
observing the CP violation signal at DUNE. We explore the impact of various
parameter degeneracies introduced by non-zero NSI and identify which of these
can influence the CP violation sensitivity and CP precision of DUNE, by
considering NSI both in data and in theory. In particular, we study how the CP
sensitivity of DUNE is affected because of the intrinsic hierarchy degeneracy
which occurs when the diagonal NSI parameter and
Bystanders, parcelling, and an absence of trust in the grooming interactions of wild male chimpanzees
The evolution of cooperation remains a central issue in socio-biology with the fundamental problem of how individuals minimize the risks of being short-changed (‘cheated’) should their behavioural investment in another not be returned. Economic decisions that individuals make during interactions may depend upon the presence of potential partners nearby, which o ers co operators a temptation to defect from the current partner. The parcelling model posits that donors subdivide services into parcels to force cooperation, and that this is contingent on opportunities for defection; that is, the presence of bystanders. Here we test this model and the e ect of bystander presence using grooming interactions of wild chimpanzees. We found that with more bystanders, initiators gave less grooming at the beginning of the bout and were more likely to abandon a grooming bout, while bouts were less likely to be reciprocated. We also found that the groomer’s initial investment was not higher among frequent groomers or stronger reciprocators, suggesting that contrary to current assumptions, grooming decisions are not based on trust, or bonds, within dyads. Our work highlights the importance of considering immediate social context and the in uence of bystanders for understanding the evolution of the behavioural strategies that produce cooperation
Evaluation of buffer-radius modelling approaches used in forest conservation and planning
Spatial modelling approaches are increasingly being used to direct forest management and conservation planning at the landscape scale. A popular approach is the use of buffer-radius methods, which create buffers around distinct forest habitat patches to assess habitat connectivity within anthropogenic landscapes. However, the effectiveness and sensitivity of such methods have rarely been evaluated. In this study, Euclidean and least-cost buffer-radius approaches were used to predict functional ecological networks within the wooded landscape of the Isle of Wight (UK). To parameterize the models, a combination of empirical evidence and expert knowledge was used relating to the dispersal ability of a model species, the wood cricket (Nemobius sylvestris Bosc.). Three scenarios were developed to assess the influence of increasing the amount of spatial and species-specific input data on the model outcomes. This revealed that the level of habitat fragmentation for the model species is likely to be underestimated when few empirical data are available. Furthermore, the least-cost buffer approach outperformed simple Euclidean buffer in predicting presence and absence for the model species. Sensitivity analyses on model performance revealed high sensitivity of the models to variation in buffer distance (i.e. maximum dispersal distance) and permeability of common landscape features such as roads, watercourses, grassland and semi-natural habitat. This indicates that when data are lacking with which to parameterize buffer-radius models, the model outcomes need to be interpreted with caution. This study also showed that if sufficient empirical data are available, least-cost buffer approaches have the potential to be a valuable tool to assist forest managers in making informed decisions. However, least-cost approaches should always be used as an indicative rather than prescriptive management tool to support forest landscape conservation and planning
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