12,595 research outputs found
Variational Monte Carlo and Configurational Interaction Studies of and its Fragments
The molecule and its fragments are studied using Configuration
Interaction (CI) and Variational Monte Carlo (VMC) techniques, within the
Hubbard model. Using benzene as a test case, we compare the results of the
approximate calculations with exact calculations. The fragments of
studied are pyracylene, fluoranthene and corannulene. The energies, bond
orders, spin-spin and charge-correlation functions of these systems are
obtained for various values of the Hubbard parameter, . The analysis of bond
orders and correlation functions of these individual molecules allow us to
visualise pyracylene as a naphthalene unit with two ethylenic moieties and
fluoranthene as weakly bridged benzene and naphthalene units. Corannulene is
the largest fragment of that we have studied. The hexagon-hexagon(h-h)
bond orders are slightly larger than those of the hexagon-pentagon bonds(h-p),
a feature also found in other fragments. We also find bonds between two
co-ordinated carbon sites to be stronger than bonds involving three coordinated
carbon sites. In , the h-h bonds are stronger than in corannulene and
the h-p bonds weaker than in corannulene for all correlation strengths.
Introducing bond alternation in the buckyball enhances this difference.Comment: 42 pages, 5 figures available on request, to appear in J. Phys. Che
Interfacing a high performance disk array file server to a Gigabit LAN
Our previous prototype, RAID-1, identified several bottlenecks in typical file server architectures. The most important bottleneck was the lack of a high-bandwidth path between disk, memory, and the network. Workstation servers, such as the Sun-4/280, have very slow access to peripherals on busses far from the CPU. For the RAID-2 system, we addressed this problem by designing a crossbar interconnect, Xbus board, that provides a 40MB/s path between disk, memory, and the network interfaces. However, this interconnect does not provide the system CPU with low latency access to control the various interfaces. To provide a high data rate to clients on the network, we were forced to carefully and efficiently design the network software. A block diagram of the system hardware architecture is given. In the following subsections, we describe pieces of the RAID-2 file server hardware that had a significant impact on the design of the network interface
Optical fiber taper coupling and high-resolution wavelength tuning of microdisk resonators at cryogenic temperatures
A system for studying microcavity resonators at cryogenic temperatures (~10
K) through evanescent coupling via optical fiber taper waveguides is reported,
and efficient fiber coupling to AlGaAs microdisk cavities with embedded quantum
dots is demonstrated. As an immediate application of this tool, we study
high-resolution tuning of microdisk cavities through nitrogen gas adsorption,
as first discussed by Mosor, et al. By proper regulation of the nitrogen gas
flow and delivery of the gas to the sample surface, continuous tuning can be
achieved with modest gas flows, and overall wavelength shifts as large as 4 nm
are achieved.Comment: 4 pages, 4 figure
Numerical computations of swirling recirculating flow
Swirling, recirculating, nonreacting flows were computed using a 2D elliptic program consisting of three tasks. The computations in Task 1 and 2 were made using an independent analysis for the two coaxial swirling flows. The Task 2 computations were made using the measured profiles of the mixing region. In Task 3, a modified 2D elliptic program was employed to include the effects of interaction between the inner and outer streams
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