10,467 research outputs found
The evaluation of the rolling moments induced by wraparound fins
A possible reason is suggested for the induced rolling moments occurring on wraparound-fin configurations in subsonic flight at zero angle of attack. The subsonic potential flow over the configuration at zero incidence is solved numerically. The body is simulated by a distribution of sources along its axis, and the fins are described by a vortex-lattice method. It is shown that rolling moments can be induced on the antisymmetric fins by the radial flow generated at the base of the configuration, either over the converging separated wake, or over the diverging plume of a rocket motor
Macroscopic loop formation in circular DNA denaturation
The statistical mechanics of DNA denaturation under fixed linking number is
qualitatively different from that of the unconstrained DNA. Quantitatively
different melting scenarios are reached from two alternative assumptions,
namely, that the denatured loops are formed in expense of 1) overtwist, 2)
supercoils. Recent work has shown that the supercoiling mechanism results in a
BEC-like picture where a macroscopic loop appears at Tc and grows steadily with
temperature, while the nature of the denatured phase for the overtwisting case
has not been studied. By extending an earlier result, we show here that a
macroscopic loop appears in the overtwisting scenario as well. We calculate its
size as a function of temperature and show that the fraction of the total sum
of microscopic loops decreases above Tc, with a cusp at the critical point.Comment: 5 pages, 3 figures, submitted for publicatio
Quantum random walks without walking
Quantum random walks have received much interest due to their non-intuitive
dynamics, which may hold the key to a new generation of quantum algorithms.
What remains a major challenge is a physical realization that is experimentally
viable and not limited to special connectivity criteria. We present a scheme
for walking on arbitrarily complex graphs, which can be realized using a
variety of quantum systems such as a BEC trapped inside an optical lattice.
This scheme is particularly elegant since the walker is not required to
physically step between the nodes; only flipping coins is sufficient.Comment: 12 manuscript pages, 3 figure
From metropolis to metropolis-based region: the case of Tel-Aviv
The decreasing importance of metropolitan areas in the distribution of population and economic activity within many nations of the developed world raises questions about the emergence of agglomeration diseconomies and about the changes in urban spatial structure. Here we explore the thesis that an emerging metropolitan area based region (MBR), comprising the metropolis and a surrounding territory, is gradually replacing the metropolis. Using data covering the last 22 years for the metropolis of Tel-Aviv (Israel) and its surrounding territory, various indicators are estimated. These include national and regional deconcentration (both measured in terms of population and employment), as well as centrality, dependence, attractiveness and integration (measured in terms of employment). The main results of the analysis include the following: the need to view metropolitan stagnation and deconcentration within the wider context of the MBR; employment deconcentration occurring at a slower rate than population deconcentration, leading to increasing levels of employment centrality within the MBR; the process of consolidation within the MBR and a strengthening of its economic role within the nation.
Development of flying qualities criteria for single pilot instrument flight operations
Flying qualities criteria for Single Pilot Instrument Flight Rule (SPIFR) operations were investigated. The ARA aircraft was modified and adapted for SPIFR operations. Aircraft configurations to be flight-tested were chosen and matched on the ARA in-flight simulator, implementing modern control theory algorithms. Mission planning and experimental matrix design were completed. Microprocessor software for the onboard data acquisition system was debugged and flight-tested. Flight-path reconstruction procedure and the associated FORTRAN program were developed. Algorithms associated with the statistical analysis of flight test results and the SPIFR flying qualities criteria deduction are discussed
Fast Structuring of Radio Networks for Multi-Message Communications
We introduce collision free layerings as a powerful way to structure radio
networks. These layerings can replace hard-to-compute BFS-trees in many
contexts while having an efficient randomized distributed construction. We
demonstrate their versatility by using them to provide near optimal distributed
algorithms for several multi-message communication primitives.
Designing efficient communication primitives for radio networks has a rich
history that began 25 years ago when Bar-Yehuda et al. introduced fast
randomized algorithms for broadcasting and for constructing BFS-trees. Their
BFS-tree construction time was rounds, where is the network
diameter and is the number of nodes. Since then, the complexity of a
broadcast has been resolved to be rounds. On the other hand, BFS-trees have been used as a crucial building
block for many communication primitives and their construction time remained a
bottleneck for these primitives.
We introduce collision free layerings that can be used in place of BFS-trees
and we give a randomized construction of these layerings that runs in nearly
broadcast time, that is, w.h.p. in rounds for any constant . We then use these
layerings to obtain: (1) A randomized algorithm for gathering messages
running w.h.p. in rounds. (2) A randomized -message
broadcast algorithm running w.h.p. in rounds. These
algorithms are optimal up to the small difference in the additive
poly-logarithmic term between and . Moreover, they imply the
first optimal round randomized gossip algorithm
Valence fuctuation and magnetic ordering in EuNi2(P1-xGex)2 single crystals
Unusual phases and phase transitions are seen at the magnetic-nonmagnetic
boundary in Ce, Eu and Yb-based compounds. EuNiP is a very unusual
valence fluctuating Eu system, because at low temperatures the Eu valence stays
close to 2.5 instead of approaching an integer value. Eu valence and thus the
magnetic property in this system can be tuned by Ge substitution in P site as
EuNiGe is known to exhibit antiferromagnetc (AFM) ordering of
divalent Eu moments with = 30 K. We have grown
EuNi(PGe) (0.0 0.5) single crystals and
studied their magnetic, thermodynamic and transport properties. Increasing Ge
doping to 0.4 results in a well-defined AFM ordered state with = 12
K for = 0.5. Moreover, the reduced value of magnetic entropy for = 0.5
at suggests the presence of valance fluctuation/ Kondo effect in this
compound. Interestingly, the specific heat exhibits an enhanced Sommerfeld
coefficient upon Ge doping. Subsequently, electronic structure calculations
lead to a non-integral valence in EuNiP but a stable divalent Eu
state in EuNiGe which is in good agreement with experimental results.Comment: 7 pages, 8 figure
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