2,527 research outputs found
Topology counts: force distributions in circular spring networks
Filamentous polymer networks govern the mechanical properties of many
biological materials. Force distributions within these networks are typically
highly inhomogeneous and, although the importance of force distributions for
structural properties is well recognized, they are far from being understood
quantitatively. Using a combination of probabilistic and graph-theoretical
techniques we derive force distributions in a model system consisting of
ensembles of random linear spring networks on a circle. We show that
characteristic quantities, such as mean and variance of the force supported by
individual springs, can be derived explicitly in terms of only two parameters:
(i) average connectivity and (ii) number of nodes. Our analysis shows that a
classical mean-field approach fails to capture these characteristic quantities
correctly. In contrast, we demonstrate that network topology is a crucial
determinant of force distributions in an elastic spring network.Comment: 5 pages, 4 figures. Missing labels in Fig. 4 added. Reference fixe
Quantum key distribution using non-classical photon number correlations in macroscopic light pulses
We propose a new scheme for quantum key distribution using macroscopic
non-classical pulses of light having of the order 10^6 photons per pulse.
Sub-shot-noise quantum correlation between the two polarization modes in a
pulse gives the necessary sensitivity to eavesdropping that ensures the
security of the protocol. We consider pulses of two-mode squeezed light
generated by a type-II seeded parametric amplification process. We analyze the
security of the system in terms of the effect of an eavesdropper on the bit
error rates for the legitimate parties in the key distribution system. We also
consider the effects of imperfect detectors and lossy channels on the security
of the scheme.Comment: Modifications:added new eavesdropping attack, added more references
Submitted to Physical Review A [email protected]
Recommended from our members
Topology determines force distributions in one-dimensional random spring networks
Networks of elastic fibers are ubiquitous in biological systems and often provide mechanical stability to cells and tissues. Fiber-reinforced materials are also common in technology. An important characteristic of such materials is their resistance to failure under load. Rupture occurs when fibers break under excessive force and when that failure propagates. Therefore, it is crucial to understand force distributions. Force distributions within such networks are typically highly inhomogeneous and are not well understood. Here we construct a simple one-dimensional model system with periodic boundary conditions by randomly placing linear springs on a circle. We consider ensembles of such networks that consist of N nodes and have an average degree of connectivity z but vary in topology. Using a graph-theoretical approach that accounts for the full topology of each network in the ensemble, we show that, surprisingly, the force distributions can be fully characterized in terms of the parameters (N,z). Despite the universal properties of such (N,z) ensembles, our analysis further reveals that a classical mean-field approach fails to capture force distributions correctly. We demonstrate that network topology is a crucial determinant of force distributions in elastic spring networks
Recommended from our members
Topology Counts: Force Distributions in Circular Spring Networks
Filamentous polymer networks govern the mechanical properties of many biological materials. Force distributions within these networks are typically highly inhomogeneous, and, although the importance of force distributions for structural properties is well recognized, they are far from being understood quantitatively. Using a combination of probabilistic and graph-theoretical techniques, we derive force distributions in a model system consisting of ensembles of random linear spring networks on a circle. We show that characteristic quantities, such as the mean and variance of the force supported by individual springs, can be derived explicitly in terms of only two parameters: (i) average connectivity and (ii) number of nodes. Our analysis shows that a classical mean-field approach fails to capture these characteristic quantities correctly. In contrast, we demonstrate that network topology is a crucial determinant of force distributions in an elastic spring network. Our results for 1D linear spring networks readily generalize to arbitrary dimensions
Production of a Fermi gas of atoms in an optical lattice
We prepare a degenerate Fermi gas of potassium atoms by sympathetic cooling
with rubidium atoms in a one-dimensional optical lattice. In a tight lattice we
observe a change of the density of states of the system, which is a signature
of quasi two dimensional confinement. We also find that the dipolar
oscillations of the Fermi gas along the tight lattice are almost completely
suppressed.Comment: 4 pages, 4 figures, revised versio
Ion detection in the photoionization of a Rb Bose-Einstein condensate
Two-photon ionization of Rubidium atoms in a magneto-optical trap and a
Bose-Einstein condensate (BEC) is experimentally investigated. Using 100 ns
laser pulses, we detect single ions photoionized from the condenstate with a
35(10)% efficiency. The measurements are performed using a quartz cell with
external electrodes, allowing large optical access for BECs and optical
lattices.Comment: 14 pages, 7 figure
Orbitally Driven Spin Pairing in the 3D Non-Magnetic Mott Insulator BaVS3: Evidence from Single Crystal Studies
Static electrical and magnetic properties of single crystal BaVS_3 were
measured over the structural (T_S=240K), metal-insulator (T_MI=69K), and
suspected orbital ordering (T_X=30K) transitions. The resistivity is almost
isotropic both in the metallic and insulating states. An anomaly in the
magnetic anisotropy at T_X signals a phase transition to an ordered low-T
state. The results are interpreted in terms of orbital ordering and spin
pairing within the lowest crystal field quasi-doublet. The disordered insulator
at T_X<T<T_MI is described as a classical liquid of non-magnetic pairs.Comment: 4 pages, 5 figures, revtex, epsf, and multicol style. Problem with
figures fixed. To appear in Phys. Rev. B Rap. Com
- …