6,586 research outputs found
The effect of configuration on strength, durability, and handle of Kevlar fabric-based materials
Five Kevlar based laminates and three Kevlar based coated materials were designed, hand made, and tested against comparative conventional Dacron based materials for strength, peel, tear, puncture, creases, and handle. Emphasis was placed on evaluating geometric orientation of constituents, use of elastomeric film in place of high modulus films, and the use of flying thread loom bias reinforcement of Kevlar yarns. Whereas, the performance of the Kevlar laminates was severely degraded by crease effects, significant gains in overall performance factors were shown for the coated Kevlar materials
Renormalization Group Flow of Quantum Gravity in the Einstein-Hilbert Truncation
The exact renormalization group equation for pure quantum gravity is used to
derive the non-perturbative \Fbeta-functions for the dimensionless Newton
constant and cosmological constant on the theory space spanned by the
Einstein-Hilbert truncation. The resulting coupled differential equations are
evaluated for a sharp cutoff function. The features of these flow equations are
compared to those found when using a smooth cutoff. The system of equations
with sharp cutoff is then solved numerically, deriving the complete
renormalization group flow of the Einstein-Hilbert truncation in . The
resulting renormalization group trajectories are classified and their physical
relevance is discussed. The non-trivial fixed point which, if present in the
exact theory, might render Quantum Einstein Gravity nonperturbatively
renormalizable is investigated for various spacetime dimensionalities.Comment: 58 pages, latex, 24 figure
Density-functional theory investigation of oxygen adsorption at Pd(11N)(N=3,5,7) vicinal surfaces
We present a density-functional theory study addressing the on-surface
adsorption of oxygen at the Pd(11N) (N =3,5,7) vicinal surfaces, which exhibit
(111) steps and (100) terraces of increasing width. We find the binding to be
predominantly governed by the local coordination at the adsorption site. This
leads to very similar bonding properties at the threefold step sites of all
three vicinal surfaces, while the binding at the central fourfold hollow site
in the four atomic row terrace of Pd(117) is already very little disturbed by
the presence of the neighboring steps.Comment: 9 pages including 4 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Nonperturbative renomalization group for Einstein gravity with matter
we investigate the exact renormalization group (RG) in Einstein gravity
coupled to N-component scalar field, working in the effective average action
formalism and background field method. The truncated evolution equation is
obtained for the Newtonian and cosmological constants. We have shown that
screening or antiscreening behaviour of the gravitational coupling depends
cricially on the choice of scalar-gravitational and the number of scalar
fields.Comment: 7 pages, LaTeX, a few typos correcte
On the Possibility of Quantum Gravity Effects at Astrophysical Scales
The nonperturbative renormalization group flow of Quantum Einstein Gravity
(QEG) is reviewed. It is argued that at large distances there could be strong
renormalization effects, including a scale dependence of Newton's constant,
which mimic the presence of dark matter at galactic and cosmological scales.Comment: LaTeX, 18 pages, 4 figures. Invited contribution to the Int. J. Mod.
Phys. D special issue on dark matter and dark energ
Effective Average Action of Chern-Simons Field Theory
The renormalization of the Chern-Simons parameter is investigated by using an
exact and manifestly gauge invariant evolution equation for the scale-dependent
effective average action.Comment: 14 pages, late
Magnetic field dependence of hole levels in self-assembled InAs quantum dots
Recent magneto-transport experiments of holes in InGaAs quantum dots [D.
Reuter, P. Kailuweit, A.D. Wieck, U. Zeitler, O. Wibbelhoff, C. Meier, A.
Lorke, and J.C. Maan, Phys. Rev. Lett. 94, 026808 (2005)] are interpreted by
employing a multi-band kp Hamiltonian, which considers the interaction between
heavy hole and light hole subbands explicitely. No need of invoking an
incomplete energy shell filling is required within this model. The crucial role
we ascribe to the heavy hole-light hole interaction is further supported by
one-band local-spin-density functional calculations, which show that Coulomb
interactions do not induce any incomplete hole shell filling and therefore
cannot account for the experimental magnetic field dispersion.Comment: 5 pages with 3 figures and one table. The paper has been submitted to
Phys.Rev.
Sex ratio conflict and worker production in eusocial hymenoptera.
The best known of the conflicts occurring in eusocial Hymenoptera is queen-worker conflict over sex ratio. So far, sex ratio theory has mostly focused on optimal investment in the production of male versus female sexuals, neglecting the investment in workers. Increased investment in workers decreases immediate sexual productivity but increases expected future colony productivity. Thus, an important issue is to determine the queen's and workers' optimal investment in each of the three castes (workers, female sexuals, and male sexuals), taking into account a possible trade-off between production of female sexuals and workers (both castes developing from diploid female eggs). Here, we construct a simple and general kin selection model that allows us to calculate the evolutionarily stable investments in the three castes, while varying the identity of the party controlling resource allocation (relative investment in workers, female sexuals, and male sexuals). Our model shows that queens and workers favor the investment in workers that maximizes lifetime colony productivity of sexual males and females, whatever the colony kin structure. However, worker production is predicted to be at this optimum only if one of the two parties has complete control over resource allocation, a situation that is evolutionarily unstable because it strongly selects the other party to manipulate sex allocation in its favor. Queens are selected to force workers to raise all the males by limiting the number of eggs they lay, whereas workers should respond to egg limitation by raising a greater proportion of the female eggs into sexual females rather than workers as a means to attain a more female-biased sex allocation. This tug-of-war between queens and workers leads to a stable equilibrium where sex allocation is between the queen and worker optima and the investment in workers is below both parties' optimum. Our model further shows that, under most conditions, female larvae are in strong conflict with queens and workers over their developmental fate because they value their own reproduction more than that of siblings. With the help of our model, we also investigate how variation in queen number and number of matings per queen affect the level of conflict between queens, workers, and larvae and ultimately the allocation of resource in the three castes. Finally, we make predictions that allow us to test which party is in control of sex allocation and caste determination
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