Computational aspects of helicopter trim analysis and damping levels from Floquet theory

Helicopter trim settings of periodic initial state and control inputs are investigated for convergence of Newton iteration in computing the settings sequentially and in parallel. The trim analysis uses a shooting method and a weak version of two temporal finite element methods with displacement formulation and with mixed formulation of displacements and momenta. These three methods broadly represent two main approaches of trim analysis: adaptation of initial-value and finite element boundary-value codes to periodic boundary conditions, particularly for unstable and marginally stable systems. In each method, both the sequential and in-parallel schemes are used and the resulting nonlinear algebraic equations are solved by damped Newton iteration with an optimally selected damping parameter. The impact of damped Newton iteration, including earlier-observed divergence problems in trim analysis, is demonstrated by the maximum condition number of the Jacobian matrices of the iterative scheme and by virtual elimination of divergence. The advantages of the in-parallel scheme over the conventional sequential scheme are also demonstrated

Unstable topography of biphasic surfactant monolayers

We study the conformation of a heterogeneous surfactant monolayer at a fluid-fluid interface, near a boundary between two lateral regions of differing elastic properties. The monolayer attains a conformation of shallow, steep `mesas' with a height difference of up to 10 nm. If the monolayer is progressively compressed (e.g. in a Langmuir trough), the profile develops overhangs and finally becomes unstable at a surface tension of about K(delta c_0)^2, where (delta c_0) is the difference in spontaneous curvature and K a bending stiffness. We discuss the relevance of this instability to recently observed folding behavior in lung surfactant monolayers, and to the absence of domain structures in films separating oil and water in emulsions.Comment: 7 pages, 7 figures, LaTex using epl.cls, accepted for Europhys Let

Multi-epoch intra-night optical monitoring of 8 radio-quiet BL Lac candidates

For a new sample of 8 weak-line-quasars (WLQs) we report a sensitive search in 20 intranight monitoring sessions, for blazar-like optical flux variations on hour-like and longer time scale (day/month/year$-$like). The sample consists exclusively of the WLQs that are not radio$-$loud and have either been classified as `radio-weak probable BL Lac candidates' and/or are known to have exhibited at least one episode of large, blazar$-$like optical variability. Whereas only a hint of intra$-$night variability is seen for two of these WLQs, J104833.5$+$620305.0(z = 0.219) and J133219.6$+$622715.9 (z = 3.15), statistically significant inter$-$night variability at a few per cent level is detected for three of the sources, including the radio-intermediate WLQ J133219.6$+$622715.9 (z = 3.15) and the well known bona$-$fide radio$-$quiet WLQs J121221.5$+$534128.0 (z = 3.10) and WLQ J153259.9$-$003944.1 (z = 4.62). In the rest$-$frame, this variability is intra-day and in the far$-$UV band. On the time scale of a decade, we find for three of the WLQs large brightness changes, amounting to 1.655$\pm$0.009, 0.163$\pm$0.010 and 0.144$\pm$0.018 mag, for J104833.5$+$620305.0, J123743.1$+$630144.9 and J232428.4$+$144324.4, respectively. Whereas the latter two are confirmed radio-quiet WLQs, the extragalactic nature of J104833.5$+$620305.0 remains to be well established, thanks to the absence of any feature(s) in its available optical spectra. The present study forms a part of our ongoing campaign of intranight optical monitoring of radio quiet weak-line quasars, in order to improve the understanding of this enigmatic class of Active Galactic Nuclei and to look among them for a possible tiny, elusive population of radio-quiet BL Lacs.Comment: Accepted to MNRAS. 12 pages, 1 figure, 4 Tabl

Homogeneous nucleation in associated vapors. III. Heptanoic, decanoic, and myristic acids

Homogeneous nucleation measurements have been made on heptanoic, decanoic, and myristic acid vapors, all of which exhibit small degrees of hydrogen bond association. The measured temperature dependences of the critical supersaturation are compared with predictions of the Katz–Saltsburg–Reiss theory for nucleation in associated vapors as well as the conventional Becker–Döring–Zeldovitch theory. Heptanoic acid and decanoic acid show good agreement with theory while the myristic acid critical supersaturation measurements are consistently low

Perspectives on the modern management of non-valvular atrial fi brillation

Atrial fi brillation is the most common clinical arrhythmia. The mainstay in the prevention of atrial fi brillation related stroke is oral anticoagulation. The 2 most important aspects in the management of patients with atrial fi brillation, is therefore risk stratifi cation for stroke and risk assessment for bleeding. Assessment of risk factors is in fact a dynamic process. In appropriate patients, novel anticoagulants are safe and better tolerated, and may be considered as an alternative to warfarin. In patients who are truly intolerant of, or where an absolute contra-indication to anticoagulationexists, occlusion of the left atrial appendage may be considered. Patients are to be carefully counselled with regards this therapy as currently, questions surrounding its safety and long-term effi ciency remain unanswered. This is an area of on-going research and further evidenceis awaited. Catheter ablation of atrial fi brillation is a highly effective therapy to achieve freedom of recurrent arrhythmia and relief from symptomatic atrial fi brillation. Recent systematic reviews demonstrate a low incidence of periprocedural complications with regards catheter ablation of atrial fi brillation, with acute complication rates having decreased signifi cantly in recent years. This may be attributed to increasing experience andimproved catheter technology

Accurate estimations of circumstellar and interstellar lines of quadruply ionized vanadium using the coupled cluster approach

Accurate {\it ab initio} calculations have been carried out to study the valence electron removal energies and oscillator strengths of astrophysically important electromagnetic transitions of quadruply ionized vanadium, $V^{4+}$. Many important electron correlations are considered to all-orders using the relativistic coupled-cluster theory. Calculated ionization potentials and fine structure splittings are compared with the experimental values, wherever available. To our knowledge, oscillator strengths of electric dipole transitions are predicted for the first time for most of the transitions. The transitions span in the range of ultraviolet, visible and near infrared regions and are important for astrophysical observations.Comment: Submitted in Astrophysical

Do the mildly superluminal VLBI knots exclude ultrarelativistic blazar jets?

We compute the effective values of apparent transverse velocity and flux boosting factors for the VLBI radio knots of blazar jets, by integrating over the angular distributions of these quantities across the widths of jets with finite opening angles but constant velocities. For high bulk Lorentz factors (Gamma > 10) variations across the jet can be quite large if the opening angle, omega, is even a few degrees on sub-parsec scales. The resulting apparent speeds are often much lower than those obtained from the usual analyses that ignore the finite jet opening angles. We can thus reconcile the usually observed subluminal or mildly superluminal speeds with the very high (>~ 20) Gamma factors, required by the inverse Compton origin and rapid variability of TeV fluxes, as well as by intraday radio variability. Thus it is possible to associate the VLBI radio knots directly with shocks in the ultra-relativistic main jet flow, without invoking very rapid jet deceleration on parsec scales, or extremely unlikely viewing angles.Comment: 10 pages, 1 figure, to appear in ApJ Letters, Nov. 10 2004 issu

Stochastic Analysis of a Churn-Tolerant Structured Peer-to-Peer Scheme

We present and analyze a simple and general scheme to build a churn (fault)-tolerant structured Peer-to-Peer (P2P) network. Our scheme shows how to "convert" a static network into a dynamic distributed hash table(DHT)-based P2P network such that all the good properties of the static network are guaranteed with high probability (w.h.p). Applying our scheme to a cube-connected cycles network, for example, yields a $O(\log N)$ degree connected network, in which every search succeeds in $O(\log N)$ hops w.h.p., using $O(\log N)$ messages, where $N$ is the expected stable network size. Our scheme has an constant storage overhead (the number of nodes responsible for servicing a data item) and an $O(\log N)$ overhead (messages and time) per insertion and essentially no overhead for deletions. All these bounds are essentially optimal. While DHT schemes with similar guarantees are already known in the literature, this work is new in the following aspects: (1) It presents a rigorous mathematical analysis of the scheme under a general stochastic model of churn and shows the above guarantees; (2) The theoretical analysis is complemented by a simulation-based analysis that validates the asymptotic bounds even in moderately sized networks and also studies performance under changing stable network size; (3) The presented scheme seems especially suitable for maintaining dynamic structures under churn efficiently. In particular, we show that a spanning tree of low diameter can be efficiently maintained in constant time and logarithmic number of messages per insertion or deletion w.h.p. Keywords: P2P Network, DHT Scheme, Churn, Dynamic Spanning Tree, Stochastic Analysis

Syk, a protein-tyrosine kinase, suppresses the cell motility and nuclear factor κB-mediated secretion of urokinase type plasminogen activator by inhibiting the phosphatidylinositol 3'-Kinase activity in breast cancer cells

Tumor growth and metastasis are multifaceted processes that mainly involve cell adhesion, proteolytic degradation of the extracellular matrix, and cell migration. Syk is a member of a tyrosine kinase family that is expressed mostly in hematopoietic cells. Syk is expressed in cell lines of epithelial origin, but its function in these cells remains unknown. Here we report that Syk is expressed in MCF-7 cells but not in MDA-MB-231 cells. The overexpression of wild type Syk kinase but not kinase-negative Syk suppressed cell motility and inhibited the activation of phosphatidylinositol (PI) 3'-kinase in MDA-MB-231 cells. In contrast, when Syk-specific antisense S-oligonucleotide but not the sense S-oligonucleotide was transfected to MCF-7 cells the level of PI 3'-kinase activity as well as cell motility were increased. The MDA-MB-231 cells transfected with wild type Syk cDNA followed by treatment with piceatannol, a Syk inhibitor, enhanced cell motility and PI 3'-kinase activity. Pervanadate, a phosphotyrosine phosphatase inhibitor, induced PI 3'-kinase activity and stimulated the interaction between the inhibitor of nuclear factor κBα (IκBα) and the p85α domain of PI 3'-kinase through tyrosine phosphorylation of the IκBα, which ultimately resulted in nuclear factor κB (NFκB) activation. Pervanadate had no effect on the activation of Syk in these cells. However, Syk suppressed the NFκB transcriptional activation and interaction between IκBα and PI 3'-kinase by inhibiting the tyrosine phosphorylation of IκBα. Syk, PI 3'-kinase inhibitors, and NFκB inhibitory peptide inhibited urokinase type plasminogen activator (uPA) secretion and cell motility in these cells. To our knowledge, this is the first report that Syk suppresses the cell motility and inhibits the PI 3'-kinase activity and uPA secretion by blocking NFκB activity through tyrosine phosphorylation of IκBα. These data further demonstrate a functional molecular link between Syk-regulated PI 3'-kinase activity and NFκB-mediated uPA secretion, and all of these ultimately control the motility of breast cancer cells