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

Excitonic Funneling in Extended Dendrimers with Non-Linear and Random Potentials

The mean first passage time (MFPT) for photoexcitations diffusion in a funneling potential of artificial tree-like light-harvesting antennae (phenylacetylene dendrimers with generation-dependent segment lengths) is computed. Effects of the non-linearity of the realistic funneling potential and slow random solvent fluctuations considerably slow down the center-bound diffusion beyond a temperature-dependent optimal size. Diffusion on a disordered Cayley tree with a linear potential is investigated analytically. At low temperatures we predict a phase in which the MFPT is dominated by a few paths.Comment: 4 pages, 4 figures, To be published in Phys. Rev. Let

Disorder and Funneling Effects on Exciton Migration in Tree-Like Dendrimers

The center-bound excitonic diffusion on dendrimers subjected to several types of non-homogeneous funneling potentials, is considered. We first study the mean-first passage time (MFPT) for diffusion in a linear potential with different types of correlated and uncorrelated random perturbations. Increasing the funneling force, there is a transition from a phase in which the MFPT grows exponentially with the number of generations $g$, to one in which it does so linearly. Overall the disorder slows down the diffusion, but the effect is much more pronounced in the exponential compared to the linear phase. When the disorder gives rise to uncorrelated random forces there is, in addition, a transition as the temperature $T$ is lowered. This is a transition from a high-$T$ regime in which all paths contribute to the MFPT to a low-$T$ regime in which only a few of them do. We further explore the funneling within a realistic non-linear potential for extended dendrimers in which the dependence of the lowest excitonic energy level on the segment length was derived using the Time-Dependent Hatree-Fock approximation. Under this potential the MFPT grows initially linearly with $g$ but crosses-over, beyond a molecular-specific and $T$-dependent optimal size, to an exponential increase. Finally we consider geometrical disorder in the form of a small concentration of long connections as in the {\it small world} model. Beyond a critical concentration of connections the MFPT decreases significantly and it changes to a power-law or to a logarithmic scaling with $g$, depending on the strength of the funneling force.Comment: 13 pages, 9 figure

Single Stranded DNA Translocation Through A Nanopore: A Master Equation Approach

We study voltage driven translocation of a single stranded (ss) DNA through a membrane channel. Our model, based on a master equation (ME) approach, investigates the probability density function (pdf) of the translocation times, and shows that it can be either double or mono-peaked, depending on the system parameters. We show that the most probable translocation time is proportional to the polymer length, and inversely proportional to the first or second power of the voltage, depending on the initial conditions. The model recovers experimental observations on hetro-polymers when using their properties inside the pore, such as stiffness and polymer-pore interaction.Comment: 7 pages submitted to PR

On the joint residence time of N independent two-dimensional Brownian motions

We study the behavior of several joint residence times of N independent Brownian particles in a disc of radius $R$ in two dimensions. We consider: (i) the time T_N(t) spent by all N particles simultaneously in the disc within the time interval [0,t]; (ii) the time T_N^{(m)}(t) which at least m out of N particles spend together in the disc within the time interval [0,t]; and (iii) the time {\tilde T}_N^{(m)}(t) which exactly m out of N particles spend together in the disc within the time interval [0,t]. We obtain very simple exact expressions for the expectations of these three residence times in the limit t\to\infty.Comment: 8 page

An Open Pilot Study of Training Hostile Interpretation Bias to Treat Disruptive Mood Dysregulation Disorder

Objective: Irritability in disruptive mood dysregulation disorder (DMDD) may be associated with a biased tendency to judge ambiguous facial expressions as angry. We conducted three experiments to explore this bias as a treatment target. We tested: 1) whether youth with DMDD express this bias; 2) whether judgment of ambiguous faces can be altered in healthy youth by training; and 3) whether such training in youth with DMDD is associated with reduced irritability and associated changes in brain function. Methods: Participants in all experiments made happy versus angry judgments of faces that varied along a happy to angry continuum. These judgments were used to quantify a “balance point,” the facial expression at which a participant's judgment switches from predominantly happy to predominantly angry. We first compared balance points in youth with DMDD (n = 63) versus healthy youth (n = 26). We then conducted a double-blind, randomized controlled trial of active versus sham balance-point training in 19 healthy youth. Finally, we piloted open, active balance-point training in 14 youth with DMDD, with 10 completing an implicit functional MRI (fMRI) face-emotion processing task. Results: Relative to healthy youth, DMDD youth manifested a shifted balance point, expressed as a tendency to classify ambiguous faces as angry rather than happy. In both healthy and DMDD youth, active training is associated with a shift in balance point toward more happy judgments. In DMDD, evidence suggests that active training may be associated with decreased irritability and changes in activation in the lateral orbitofrontal cortex. Conclusions:These results set the stage for further research on computer-based treatment targeting interpretation bias of angry faces in DMDD. Such treatment may decrease irritability and alter neural responses to subtle expressions of happiness and anger

The cognitive and emotional effects of cognitive bias modification in interpretations in behaviorally inhibited youth

Cognitive bias modification (CBM) procedures follow from the view that interpretive biases play an important role in the development and maintenance of anxiety. As such, understanding the link between interpretive biases and anxiety in youth at risk for anxiety (e.g., behaviorally inhibited children) could elucidate the mechanisms involved in the development of pediatric anxiety. However, to date, the majority of CBM-I work only studies adult populations. The present article presents the results of a CBM study examining effects of positive interpretive bias modification on mood, stress vulnerability, and threat-related attention bias in a group of behaviorally inhibited children (n = 45). Despite successful modification of interpretive bias in the at-risk youth, minimal effects on stress vulnerability or threat-related attention bias were found. The current findings highlight the need for continued research on cognitive biases in anxiety

Interpretation of ambiguous situations: evidence for a dissociation between social and physical threat in Williams syndrome

There is increasing evidence that Williams syndrome (WS) is associated with elevated anxiety that is non-social in nature, including generalised anxiety and fears. To date very little research has examined the cognitive processes associated with this anxiety. In the present research, attentional bias for non-social threatening images in WS was examined using a dot-probe paradigm. Participants were 16 individuals with WS aged between 13 and 34 years and two groups of typically developing controls matched to the WS group on chronological age and attentional control ability respectively. The WS group exhibited a significant attention bias towards threatening images. In contrast, no bias was found for group matched on attentional control and a slight bias away from threat was found in the chronological age matched group. The results are contrasted with recent findings suggesting that individuals with WS do not show an attention bias for threatening faces and discussed in relation to neuroimaging research showing elevated amygdala activation in response to threatening non-social scenes in WS

Nitrogen-vacancy singlet manifold ionization energy

The singlet states of the negatively-charged nitrogen-vacancy centers in diamond play a key role in its optical spin control and readout. In this work, the hitherto unknown ionization energy of the singlet is measured experimentally and found to be between 1.91-2.25 eV. This is obtained by analyzing photoluminescence measurements incorporating spin control and NV charge state differentiation, along with simulations based on the nitrogen-vacancy's master equation. This work establishes a protocol for a more accurate estimate of this ionization energy, which can possibly lead to improved read-out methods