1,385 research outputs found
New paradoxical games based on Brownian ratchets
Based on Brownian ratchets, a counter-intuitive phenomenon has recently
emerged -- namely, that two losing games can yield, when combined, a
paradoxical tendency to win. A restriction of this phenomenon is that the rules
depend on the current capital of the player. Here we present new games where
all the rules depend only on the history of the game and not on the capital.
This new history-dependent structure significantly increases the parameter
space for which the effect operates.Comment: 4 pages, 3 eps figures, revte
Minimal Brownian Ratchet: An Exactly Solvable Model
We develop an exactly-solvable three-state discrete-time minimal Brownian
ratchet (MBR), where the transition probabilities between states are
asymmetric. By solving the master equations we obtain the steady-state
probabilities. Generally the steady-state solution does not display detailed
balance, giving rise to an induced directional motion in the MBR. For a reduced
two-dimensional parameter space we find the null-curve on which the net current
vanishes and detailed balance holds. A system on this curve is said to be
balanced. On the null-curve, an additional source of external random noise is
introduced to show that a directional motion can be induced under the zero
overall driving force. We also indicate the off-balance behavior with biased
random noise.Comment: 4 pages, 4 figures, RevTex source, General solution added. To be
appeared in Phys. Rev. Let
Non-interference for deterministic interactive programs
We consider the problem of defining an appropriate notion of non-interference (NI) for deterministic interactive programs. Previous work on the security of interactive programs by O'Neill, Clarkson and Chong (CSFW 2006) builds on earlier ideas due to Wittbold and Johnson (Symposium on Security and Privacy 1990), and argues for a notion of NI defined in terms of strategies modelling the behaviour of users. We show that, for deterministic interactive programs, it is not necessary to consider strategies and that a simple stream model of the users' behaviour is sufficient. The key technical result is that, for deterministic programs, stream-based NI implies the apparently more general strategy-based NI (in fact we consider a wider class of strategies than those of O'Neill et al). We give our results in terms of a simple notion of Input-Output Labelled Transition System, thus allowing application of the results to a large class of deterministic interactive programming languages
A Preliminary Discussion of the Kinematics of BHB and RR Lyrae Stars near the North Galactic Pole
The radial velocity dispersion of 67 RR Lyrae variable and blue horizontal
branch (BHB) stars that are more than 4 kpc above the galactic plane at the
North Galactic Pole is 110 km/sec and shows no trend with Z (the height above
the galactic plane). Nine stars with Z < 4 kpc show a smaller velocity
dispersion (40 +/-9 km/sec) as is to be expected if they mostly belong to a
population with a flatter distribution. Both RR Lyrae stars and BHB stars show
evidence of stream motion; the most significant is in fields RR2 and RR3 where
24 stars in the range 4.0 < Z < 11.0 kpc have a mean radial velocity of -59 +/-
16 km/sec. Three halo stars in field RR 2 appear to be part of a moving group
with a common radial velocity of -90 km/sec. The streaming phenomenon therefore
occurs over a range of spatial scales. The BHB and RR Lyrae stars in our sample
both have a similar range of metallicity (-1.2 < [Fe/H] < -2.2). Proper motions
of BHB stars in fields SA 57 (NGP) and the Anticenter field (RR 7) (both of
which lie close to the meridional plane of the Galaxy) show that the stars that
have Z 4 kpc have a Galactic V motion that is
< -200 km/sec and which is characteristic of the halo. Thus the stars that have
a flatter distribution are really halo stars and not members of the metal-weak
thick-disk.Comment: Accepted for publication in the March 1996 AJ. 15 pages, AASTeX V4.0
latex format (including figures), 2 eps figures, 2 separate AASTeX V4.0 latex
table
A novel interferometric liquid refractometer
We describe a novel form of liquid refractometer in which the optical length of a cavity containing the liquid is monitored interferometrically
Channelled spectrum liquid refractometer
We describe an experimental demonstration of a novel technique for liquid refractometry. A channeled spectrum is produced from an optical beam generated by a diode laser operating below threshold by intercepting half of the beam with a liquid cell. The spectrum is analyzed using a grating and a linear CCD array and provides information on the refractive index of the liquid. The experimental results show that accuracies of better than 0.3% in the index may be obtained with the present method
The impacts of feral boar on woodland flora and fauna in Great Britain
Mayle, B., Harmer, R., Kewitt, A., Peace, A., Straw, N., Williams, D., Upson, M
Highly thermostable carboxylic acid reductases generated by ancestral sequence reconstruction (article)
This is the final version. Available on open access from Nature Research via the DOI in this recordThe research data supporting this publication are openly available in ORE at https://doi.org/10.24378/exe.2003Carboxylic acid reductases (CARs) are biocatalysts of industrial importance. Their properties, especially their poor stability, render them sub-optimal for use in a bioindustrial pipeline. Here, we employed ancestral sequence reconstruction (ASR) – a burgeoning engineering tool that can identify stabilizing but enzymatically neutral mutations throughout a protein. We used a three-algorithm approach to reconstruct functional ancestors of the Mycobacterial and Nocardial CAR1 orthologues. Ancestral CARs (AncCARs) were confirmed to be CAR enzymes with a preference for aromatic carboxylic acids. Ancestors also showed varied tolerances to solvents, pH and in vivo-like salt concentrations. Compared to well-studied extant CARs, AncCARs had a Tm up to 35 °C higher, with half-lives up to nine times longer than the greatest previously observed. Using ancestral reconstruction we have expanded the existing CAR toolbox with three new thermostable CAR enzymes, providing access to the high temperature biosynthesis of aldehydes to drive new applications in biocatalysis.Glaxosmithkline Research & Development Lt
Quantum field theory on quantum graphs and application to their conductance
We construct a bosonic quantum field on a general quantum graph. Consistency
of the construction leads to the calculation of the total scattering matrix of
the graph. This matrix is equivalent to the one already proposed using
generalized star product approach. We give several examples and show how they
generalize some of the scattering matrices computed in the mathematical or
condensed matter physics litterature.
Then, we apply the construction for the calculation of the conductance of
graphs, within a small distance approximation. The consistency of the
approximation is proved by direct comparison with the exact calculation for the
`tadpole' graph.Comment: 32 pages; misprints in tree graph corrected; proofs of consistency
and unitarity adde
Quantum random walks with history dependence
We introduce a multi-coin discrete quantum random walk where the amplitude
for a coin flip depends upon previous tosses. Although the corresponding
classical random walk is unbiased, a bias can be introduced into the quantum
walk by varying the history dependence. By mixing the biased random walk with
an unbiased one, the direction of the bias can be reversed leading to a new
quantum version of Parrondo's paradox.Comment: 8 pages, 6 figures, RevTe
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