480 research outputs found
Design Integrity and Immunity Checking: A New Look at Layout Verification and Design Rule Checking
A program implementing a novel approach to layout verification is presented. The approach uses topological and device information to eliminate most false and unchecked errors. This technique, coupled with a hierarchical front end to eliminated redundant checks, is appropriate for layout verification of VLSI designs. Design rules appropriate for this technique, some usage rules in the context of structured design, and a discussion of the future of design rule checking are also presented
Parametrized Complexity of Weak Odd Domination Problems
Given a graph , a subset of vertices is a weak odd
dominated (WOD) set if there exists such that
every vertex in has an odd number of neighbours in . denotes
the size of the largest WOD set, and the size of the smallest
non-WOD set. The maximum of and , denoted
, plays a crucial role in quantum cryptography. In particular
deciding, given a graph and , whether is of
practical interest in the design of graph-based quantum secret sharing schemes.
The decision problems associated with the quantities , and
are known to be NP-Complete. In this paper, we consider the
approximation of these quantities and the parameterized complexity of the
corresponding problems. We mainly prove the fixed-parameter intractability
(W-hardness) of these problems. Regarding the approximation, we show that
, and admit a constant factor approximation
algorithm, and that and have no polynomial approximation
scheme unless P=NP.Comment: 16 pages, 5 figure
Reducing the linewidth of a diode laser below 30 Hz by stabilization to a reference cavity with finesse above 10^5
An extended cavity diode laser operating in the Littrow configuration
emitting near 657 nm is stabilized via its injection current to a reference
cavity with a finesse of more than 10^5 and a corresponding resonance linewidth
of 14 kHz. The laser linewidth is reduced from a few MHz to a value below 30
Hz. The compact and robust setup appears ideal for a portable optical frequency
standard using the Calcium intercombination line.Comment: 8 pages, 4 figures on 3 additional pages, corrected version,
submitted to Optics Letter
Introduction : performing the state
Seeking to expand the domain of the political beyond normative understandings of the state, the articles in this special edition examine the performative aspects of governance and state-making in Southeast Asia. Combining historical and contemporary case studies, this collection brings together four examples of performative statecraft from Burma/Myanmar, Thailand, and Indonesia. The collection coheres around the analytical optic of performance, with particular emphasis on the performative repertoires developed by religious militas and non-state security groups. This analytical optic allows the contributors to gauge how such non-state groups conceive and engage with the state and its institutions, and to provide fresh insights on the performative aspects of state-making processes
Carrier-envelope-offset dynamics and stabilization of femtosecond pulses
Abstract. : We analyze and stabilize fluctuations of the relative phase between the carrier and the envelope of a mode-locked laser. Mechanisms generating fluctuations of the carrier-envelope-offset (CEO) phase are experimentally identified in lasers with and without prisms for dispersion compensation. One mechanism is amplitude-to-phase coupling via self-steepening. This mechanism translates power changes into variations of the CEO phase. A similar but much stronger effect is caused by beam-pointing variations in lasers with intracavity prisms. Both mechanisms convert power noise of the laser into phase noise and can be used to externally control or stabilize the CEO frequency by adjusting the pump power. Our measurements are well explained by a theoretical model. This investigation allowed us to obtain an unsurpassed stabilization of the CEO phase to 0.02rad rms for a frequency range from 0.01Hz to 10kHz. We extend the discussion to pulse-amplification schemes and show that beam-pointing variations are also expected to have a strong influence on the CEO phase of amplified pulses. We discuss methods to reduce or avoid CEO noise by suitable design of the dispersion-compensation scheme, both in oscillators and in amplifier
Salisapiliaceae – a new family of oomycetes from marsh grass litter of southeastern North America
Several filamentous oomycete species of the genus Halophytophthora have recently been described from marine environments, mostly from subtropical and tropical ecosystems. During a survey of oomycetes from leaf litter of Spartina alterniflora in salt marshes of southeastern Georgia, isolates of four taxa were recovered that bore similarity to some members of Halophytophthora but were highly divergent from isolates of Halophytophthora s.str. based on a combined sequence analysis of two nuclear loci. In phylogenetic analyses, these isolates were placed basal to a monophyletic group comprised of Pythium of the Pythiaceae and the Peronosporaceae. Sequence and morphology of these taxa diverged from the type species Halophytophthora vesicula, which was placed within the Peronosporaceae with maximum support. As a consequence a new family, the Salisapiliaceae, and a new genus, Salisapilia, are described to accommodate the newly discovered species, along with one species previously classified within Halophytophthora. Morphological features that separate these taxa from Halophytophthora are a smaller hyphal diameter, oospore production, lack of vesicle formation during sporulation, and a plug of hyaline material at the sporangial apex that is displaced during zoospore release. Our findings offer a first glance at the presumably much higher diversity of oomycetes in estuarine environments, of which ecological significance requires further exploration
Optimization of cw sodium laser guide star efficiency
Context: Sodium laser guide stars (LGS) are about to enter a new range of
laser powers. Previous theoretical and numerical methods are inadequate for
accurate computations of the return flux and hence for the design of the
next-generation LGS systems.
Aims: We numerically optimize the cw (continuous wave) laser format, in
particular the light polarization and spectrum.
Methods: Using Bloch equations, we simulate the mesospheric sodium atoms,
including Doppler broadening, saturation, collisional relaxation, Larmor
precession, and recoil, taking into account all 24 sodium hyperfine states and
on the order of 100 velocity groups.
Results: LGS return flux is limited by "three evils": Larmor precession due
to the geomagnetic field, atomic recoil due to radiation pressure, and
transition saturation. We study their impacts and show that the return flux can
be boosted by repumping (simultaneous excitation of the sodium D2a and D2b
lines with 10-20% of the laser power in the latter).
Conclusions: We strongly recommend the use of circularly polarized lasers and
repumping. As a rule of thumb, the bandwidth of laser radiation in MHz (at each
line) should approximately equal the launched laser power in Watts divided by
six, assuming a diffraction-limited spot size.Comment: 15 pages, 12 figures, to be published in Astronomy & Astrophysics,
AA/2009/1310
Open Problems in Parameterized and Exact Computation - IWPEC 2006
In September 2006, the Second International Workshop on Parameterized and
Exact Computation was held in Zürich, Switzerland, as part of ALGO 2006. At the
end of IWPEC 2006, a problem session was held. (Most of) the problems mentioned
at this problem session, and some other problems, contributed by the participants of
IWPEC 2006 are listed here
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