850 research outputs found
Descriptive Complexity of Deterministic Polylogarithmic Time and Space
We propose logical characterizations of problems solvable in deterministic
polylogarithmic time (PolylogTime) and polylogarithmic space (PolylogSpace). We
introduce a novel two-sorted logic that separates the elements of the input
domain from the bit positions needed to address these elements. We prove that
the inflationary and partial fixed point vartiants of this logic capture
PolylogTime and PolylogSpace, respectively. In the course of proving that our
logic indeed captures PolylogTime on finite ordered structures, we introduce a
variant of random-access Turing machines that can access the relations and
functions of a structure directly. We investigate whether an explicit predicate
for the ordering of the domain is needed in our PolylogTime logic. Finally, we
present the open problem of finding an exact characterization of
order-invariant queries in PolylogTime.Comment: Submitted to the Journal of Computer and System Science
Wakeful rest alleviates interference-based forgetting
Retroactive interference (RI)—the disruptive influence of events occurring after the formation of a new memory—is one of the primary causes of forgetting. Placing individuals within an environment that postpones interference should, therefore, greatly reduce the likelihood of information being lost from memory. For example, a short period of wakeful rest should diminish interference-based forgetting. To test this hypothesis, participants took part in a foreign language learning activity and were shown English translations of 20 Icelandic words for immediate recall. Half of the participants were then given an 8-min rest before completing a similar or dissimilar interfering distractor task. The other half did not receive a rest until after the distractor task, at which point interference had already taken place. All participants were then asked to translate the Icelandic words for a second time. Results revealed that retention was significantly worse at the second recall test, but being allowed a brief rest before completing the distractor task helped reduce the amount of forgetting. Taking a short, passive break can shield new memories from RI and alleviate forgetting.ERAS Scheme, University of Wolverhampto
Transport, magnetic, thermodynamic and optical properties in Ti-doped Sr_2RuO_4
We report on electrical resistivity, magnetic susceptibility and
magnetization, on heat capacity and optical experiments in single crystals of
Sr_2Ru_(1-x)Ti_xO_4. Samples with x=0.1 and 0.2 reveal purely semiconducting
resistivity behavior along c and the charge transport is close to localization
within the ab-plane. A strong anisotropy in the magnetic susceptibility appears
at temperatures below 100 K. Moreover magnetic ordering in c-direction with a
moment of order 0.01 mu_B/f.u. occurs at low temperatures. On doping the
low-temperature linear term of the heat capacity becomes reduced significantly
and probably is dominated by spin fluctuations. Finally, the optical
conductivity reveals the anisotropic character of the dc resistance, with the
in-plane conductance roughly following a Drude-type behavior and an insulating
response along c
Frameworks for logically classifying polynomial-time optimisation problems.
We show that a logical framework, based around a fragment of existential second-order logic formerly proposed by others so as to capture the class of polynomially-bounded P-optimisation problems, cannot hope to do so, under the assumption that P ≠NP. We do this by exhibiting polynomially-bounded maximisation and minimisation problems that can be expressed in the framework but whose decision versions are NP-complete. We propose an alternative logical framework, based around inflationary fixed-point logic, and show that we can capture the above classes of optimisation problems. We use the inductive depth of an inflationary fixed-point as a means to describe the objective functions of the instances of our optimisation problems
Spontaneous symmetry breaking in a two-lane model for bidirectional overtaking traffic
First we consider a unidirectional flux \omega_bar of vehicles each of which
is characterized by its `natural' velocity v drawn from a distribution P(v).
The traffic flow is modeled as a collection of straight `world lines' in the
time-space plane, with overtaking events represented by a fixed queuing time
tau imposed on the overtaking vehicle. This geometrical model exhibits platoon
formation and allows, among many other things, for the calculation of the
effective average velocity w=\phi(v) of a vehicle of natural velocity v.
Secondly, we extend the model to two opposite lanes, A and B. We argue that the
queuing time \tau in one lane is determined by the traffic density in the
opposite lane. On the basis of reasonable additional assumptions we establish a
set of equations that couple the two lanes and can be solved numerically. It
appears that above a critical value \omega_bar_c of the control parameter
\omega_bar the symmetry between the lanes is spontaneously broken: there is a
slow lane where long platoons form behind the slowest vehicles, and a fast lane
where overtaking is easy due to the wide spacing between the platoons in the
opposite direction. A variant of the model is studied in which the spatial
vehicle density \rho_bar rather than the flux \omega_bar is the control
parameter. Unequal fluxes \omega_bar_A and \omega_bar_B in the two lanes are
also considered. The symmetry breaking phenomenon exhibited by this model, even
though no doubt hard to observe in pure form in real-life traffic, nevertheless
indicates a tendency of such traffic.Comment: 50 pages, 16 figures; extra references adde
A model for bidirectional traffic of cytoskeletal motors
We introduce a stochastic lattice gas model including two particle species
and two parallel lanes. One lane with exclusion interaction and directed motion
and the other lane without exclusion and unbiased diffusion, mimicking a
micotubule filament and the surrounding solution. For a high binding affinity
to the filament, jam-like situations dominate the system's behaviour. The
fundamental process of position exchange of two particles is approximated. In
the case of a many-particle system, we were able to identify a regime in which
the system is rather homogenous presenting only small accumulations of
particles and a regime in which an important fraction of all particles
accumulates in the same cluster. Numerical data proposes that this cluster
formation will occur at all densities for large system sizes. Coupling of
several filaments leads to an enhanced cluster formation compared to the
uncoupled system, suggesting that efficient bidirectional transport on
one-dimensional filaments relies on long-ranged interactions and track
formation.Comment: 20 pages, 9 figure
Enhancement of spin mixing conductance in La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub>/LaNiO<sub>3</sub>/SrRuO<sub>3</sub> heterostructures
Spin pumping and the effective spin-mixing conductance in heterostructures based on magnetic oxide trilayers composed of La0.7Sr0.3MnO3 (LSMO), LaNiO3 (LNO), and SrRuO3 (SRO) are investigated. The heterostructures serve as a model system for an estimation of the effective spin-mixing conductance at the different interfaces. The results show that by introducing a LNO interlayer between LSMO and SRO, the total effective spin-mixing conductance increases due to the much more favorable interface of LSMO/LNO with respect to the LSMO/SRO interface. Nevertheless, the spin current into the SRO does not decrease because of the spin diffusion length of λLNO ≈ 3.2nm in the LNO. This value is two times higher than that of SRO. The results show the potential of using oxide interfaces to tune the effective spin-mixing conductance in heterostructures and to bring novel functionalities into spintronics by implementing complex oxides
Chimeric Investigations into the Diamide Binding Site on the Lepidopteran Ryanodine Receptor
Alterations to amino acid residues G4946 and I4790, associated with resistance to diamide insecticides, suggests a location of diamide interaction within the pVSD voltage sensor-like domain of the insect ryanodine receptor (RyR). To further delineate the interaction site(s), targeted alterations were made within the same pVSD region on the diamondback moth (Plutella xylostella) RyR channel. The editing of five amino acid positions to match those found in the diamide insensitive skeletal RyR1 of humans (hRyR1) in order to generate a human−Plutella chimeric construct showed that these alterations strongly reduce diamide efficacy when introduced in combination but cause only minor reductions when introduced individually. It is concluded that the sites of diamide interaction on insect RyRs lie proximal to the voltage sensor-like domain of the RyR and that the main site of interaction is at residues K4700, Y4701, I4790 and S4919 in the S1 to S4 transmembrane domains
Diamide insecticide resistance in transgenic Drosophila and Sf9-cells expressing a full-length diamondback moth ryanodine receptor carrying an I4790M mutation
BACKGROUNDResistance to diamide insecticides in Lepidoptera is known to be caused primarily by amino acid changes on the ryanodine receptor (RyR). Recently, two new target site mutations, G4946V and I4790M, have emerged in populations of diamondback moth, Plutella xylostella, as well as in other lepidopteran species, and both mutations have been shown empirically to decrease diamide efficacy. Here, we quantify the impact of the I4790M mutation on diamide activation of the receptor, as compared to alterations at the G4946 locus.RESULTSI4790M when introduced into P. xylostella RyR expressed in an insect-derived Sf9 cell line was found to mediate just a ten-fold reduction in chlorantraniliprole efficacy (compared to 104- and 146-fold reductions for the G4946E and G4946V variants, respectively), whilst in the field its presence is associated with a ≥150-fold reduction. I4790M-mediated resistance to flubendiamide was estimated to be >24-fold. When the entire coding sequence of P. xylostella RyR was integrated into Drosophila melanogaster, the I4790M variant conferred ~4.4-fold resistance to chlorantraniliprole and 22-fold resistance to flubendiamide in the 3rd instar larvae, confirming that it imparts only a moderate level of resistance to diamide insecticides. Although the I4790M substitution appears to bear no fitness costs in terms of the flies' reproductive capacity, when assessed in a noncompetitive environment, it does, however, have potentially major impacts on mobility at both the larval and adult stages.CONCLUSIONSI4790M imparts only a moderate level of resistance to diamide insecticides and potentially confers significant fitness costs to the insect
A novel heavy-fermion state in CaCu_3Ru_4O12
We have measured susceptibility, specific heat, resistivity, and thermopower
of CaCuTiRuO and CaCuMnRuO, and
have found that CaCuRuO can be regarded as a heavy-fermion oxide
in d-electron systems. The Kondo temperature is near 200 K, and the
susceptibility (1.4 emu/Cu mol) and the electron specific heat
coefficient (28 mJ/Cu molK) are moderately enhanced. The resistivity is
proportional to at low temperatures, and satisfies the Kadowaki-Woods
relation. The heavy-fermion state comes from the interaction between the
localized moment of Cu 3d and the conduction electron of Ru 4d. An
insulator-metal transition occurs between and 4 in
CaCuTiRuO, which can be regarded as a transition from
magnetic insulator to heavy-fermion metal.Comment: 4 pages, 5 figures, submitted to J. Phys. Soc. Jp
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