Orientation of particle attachment and local isotropy in diffusion limited aggregation (DLA)

We simulate 50 off-lattice DLA clusters, one million particles each. The probability distribution of the angle of attachment of arriving particles with respect to the local radial direction is obtained numerically. For increasing cluster size, $N$, the distribution crosses over extremely accurately to a cosine, whose amplitude decreases towards zero as a power-law in $N$. From this viewpoint, asymptotically large DLA clusters are locally $isotropic$. This contradicts previous conclusions drawn from density-density correlation measurements [P. Meakin, and T. Viscek, Phys. Rev. A {\bf 32}, 685 (1985)]. We present an intuitive phenomenological model random process for our numerical findings.Comment: 10 pages, RevTex 3.0, 11-9

Residential Water Consumption: A Cross Country Analysis

Survey data from over 1,600 households in ten countries were used to analyse the determinants of residential water demand. Results show that in every country the price elasticity is negative and statistically significant. Households that do not have to pay for the water they use (volumetric water charges) consume about a third more water than similar households that do have to pay such charges. Consumers’ attitudes do not have a statistically significant effect on total water use, although they do increase the probability of households using some water saving behaviours. Volumetric water charges also have an impact on the adoption of water saving actions. Full-cost water pricing appears to be a highly effective instrument to manage residential water demand.water demand, water consumption, water pricing, Environmental Economics and Policy, Resource /Energy Economics and Policy, C21, Q25, Q50,

Dendritic Synapse Location and Neocortical Spike-Timing-Dependent Plasticity

While it has been appreciated for decades that synapse location in the dendritic tree has a powerful influence on signal processing in neurons, the role of dendritic synapse location on the induction of long-term synaptic plasticity has only recently been explored. Here, we review recent work revealing how learning rules for spike-timing-dependent plasticity (STDP) in cortical neurons vary with the spatial location of synaptic input. A common principle appears to be that proximal synapses show conventional STDP, whereas distal inputs undergo plasticity according to novel learning rules. One crucial factor determining location-dependent STDP is the backpropagating action potential, which tends to decrease in amplitude and increase in width as it propagates into the dendritic tree of cortical neurons. We discuss additional location-dependent mechanisms as well as the functional implications of heterogeneous learning rules at different dendritic locations for the organization of synaptic inputs

Toxoplasma MIC2 Is a Major Determinant of Invasion and Virulence

Like its apicomplexan kin, the obligate intracellular protozoan Toxoplasma gondii actively invades mammalian cells and uses a unique form of gliding motility. The recent identification of several transmembrane adhesive complexes, potentially capable of gripping external receptors and the sub-membrane actinomyosin motor, suggests that the parasite has multiple options for host-cell recognition and invasion. To test whether the transmembrane adhesin MIC2, together with its partner protein M2AP, participates in a major invasion pathway, we utilized a conditional expression system to introduce an anhydrotetracycline-responsive mic2 construct, allowing us to then knockout the endogenous mic2 gene. Conditional suppression of MIC2 provided the first opportunity to directly determine the role of this protein in infection. Reduced MIC2 expression resulted in mistrafficking of M2AP, markedly defective host-cell attachment and invasion, the loss of helical gliding motility, and the inability to support lethal infection in a murine model of acute toxoplasmosis. Survival of mice infected with MIC2-deficient parasites correlated with lower parasite burden in infected tissues, an attenuated inflammatory immune response, and induction of long-term protective immunity. Our findings demonstrate that the MIC2 protein complex is a major virulence determinant for Toxoplasma infection and that MIC2-deficient parasites constitute an effective live-attenuated vaccine for experimental toxoplasmosis

The impact of high speed machining on computing and automation

Machine tool technologies, especially Computer Numerical Control (CNC) High Speed Machining (HSM) have emerged as effective mechanisms for Rapid Tooling and Manufacturing applications. These new technologies are attractive for competitive manufacturing because of their technical advantages, i.e. a significant reduction in lead-time, high product accuracy, and good surface finish. However, HSM not only stimulates advancements in cutting tools and materials, it also demands increasingly sophisticated CAD/CAM software, and powerful CNC controllers that require more support technologies. This paper explores the computational requirement and impact of HSM on CNC controller, wear detection, look ahead programming, simulation, and tool management

Phase-Remapping Attack in Practical Quantum Key Distribution Systems

Quantum key distribution (QKD) can be used to generate secret keys between two distant parties. Even though QKD has been proven unconditionally secure against eavesdroppers with unlimited computation power, practical implementations of QKD may contain loopholes that may lead to the generated secret keys being compromised. In this paper, we propose a phase-remapping attack targeting two practical bidirectional QKD systems (the "plug & play" system and the Sagnac system). We showed that if the users of the systems are unaware of our attack, the final key shared between them can be compromised in some situations. Specifically, we showed that, in the case of the Bennett-Brassard 1984 (BB84) protocol with ideal single-photon sources, when the quantum bit error rate (QBER) is between 14.6% and 20%, our attack renders the final key insecure, whereas the same range of QBER values has been proved secure if the two users are unaware of our attack; also, we demonstrated three situations with realistic devices where positive key rates are obtained without the consideration of Trojan horse attacks but in fact no key can be distilled. We remark that our attack is feasible with only current technology. Therefore, it is very important to be aware of our attack in order to ensure absolute security. In finding our attack, we minimize the QBER over individual measurements described by a general POVM, which has some similarity with the standard quantum state discrimination problem.Comment: 13 pages, 8 figure

Quantum anti-Zeno effect without rotating wave approximation

In this paper, we systematically study the spontaneous decay phenomenon of a two-level system under the influences of both its environment and continuous measurements. In order to clarify some well-established conclusions about the quantum Zeno effect (QZE) and the quantum anti-Zeno effect (QAZE), we do not use the rotating wave approximation (RWA) in obtaining an effective Hamiltonian. We examine various spectral distributions by making use of our present approach in comparison with other approaches. It is found that with respect to a bare excited state even without the RWA, the QAZE can still happen for some cases, e.g., the interacting spectra of hydrogen. But for a physical excited state, which is a renormalized dressed state of the atomic state, the QAZE disappears and only the QZE remains. These discoveries inevitably show a transition from the QZE to the QAZE as the measurement interval changes.Comment: 14 pages, 8 figure

Tidally excited oscillations in hot white dwarfs

We study the flux variation in helium white dwarfs (WDs) induced by dynamical tides for a variety of WD models with effective temperatures ranging from T=10kK to T=26kK⁠. At linear order, we find the dynamical tide can significantly perturb the observed flux in hot WDs. If the temperature T≳14kK⁠, then the dynamical tide may induce a fractional change in the flux by >1 per cent when the orbital period is P_(orb) ≃ 20−60min⁠. The ratio between the flux modulation due to the dynamical tide and that due to the equilibrium tide (i.e. ellipsoidal variability) increases as the WD’s radius decreases, and it could exceed O(10) if the WD has a radius R ≲ 0.03 R_⊙. Unlike the ellipsoidal variability which is in phase with the orbital motion, the pulsation caused by the dynamical tide may have a substantial phase shift. A cold WD with T≃10kK⁠, on the other hand, is unlikely to show observable pulsations due to the dynamical tide. At shorter orbital periods, the dynamical tide may break and become highly non-linear. We approximate this regime by treating the waves as one-way travelling waves and find the flux variation is typically reduced to 0.1–1 per cent and the excess phase is ∼90° (though with large uncertainty). Even in the travelling-wave limit, the flux perturbation due to dynamical tide could still exceed the ellipsoidal variability for compact WDs with R ≲ 0.02 R_⊙. We further estimate the non-linear flux perturbations oscillating at four times the orbital frequency dominated by a self-coupled parent g-mode driving low-order daughter p modes. The non-linear flux variation could be nearly 50 per cent of the linear variation for very hot WD models with T≳26kK and 1 per cent linear flux variation. We thus predict that both the linear and non-linear flux variations due to dynamical tides are likely to have significant observational signatures