Design definition study of a lift/cruise fan technology V/STOL airplane: Summary

A two-engine three-fan V/STOL airplane was designed to fulfill naval operational requirements. A multimission airplane was developed from study of specific point designs. Based on the multimission concept, airplanes were designed to demonstrate and develop the technology and operational procedures for this class of aircraft. Use of interconnected variable pitch fans led to a good balance between high thrust with responsive control and efficient thrust at cruise speeds. The airplanes and their characteristics are presented

Geometrical phase driven predissociation: Lifetimes of 2^2 A' levels of H_3

We discuss the role of the geometrical phase in predissociation dynamics of vibrational states near a conical intersection of two electronic potential surfaces of a D_{3h} molecule. For quantitative description of the predissociation driven by the coupling near a conical intersection, we developed a method for calculating lifetimes and positions of vibrational predissociated states (Feshbach resonances) for X_3 molecule. The method takes into account the two coupled three-body potential energy surfaces, which are degenerate at the intersection. As an example, we apply the method to obtain lifetimes and positions of resonances of predissociated vibrational levels of the 2^2 A' electronic state of the H_3 molecule. The three-body recombination rate coefficient for the H+H+H -> H_2+H process is estimated.Comment: 4 pages, 4 figure

Theory of dissociative recombination of highly-symmetric polyatomic ions

A general first-principles theory of dissociative recombination is developed for highly-symmetric molecular ions and applied to H$_3$O$^{+}$ and CH$_3^+$, which play an important role in astrophysical, combustion, and laboratory plasma environments. The theoretical cross-sections obtained for the dissociative recombination of the two ions are in good agreement with existing experimental data from storage ring experiments

Wave packet dynamics of potassium dimers attached to helium nanodroplets

The dynamics of vibrational wave packets excited in K$_2$ dimers attached to superfluid helium nanodroplets is investigated by means of femtosecond pump-probe spectroscopy. The employed resonant three-photon-ionization scheme is studied in a wide wavelength range and different pathways leading to K$^+_2$-formation are identified. While the wave packet dynamics of the electronic ground state is not influenced by the helium environment, perturbations of the electronically excited states are observed. The latter reveal a strong time dependence on the timescale 3-8 ps which directly reflects the dynamics of desorption of K$_2$ off the helium droplets

Empirically testing <i>Tonnetz</i>, voice-leading, and spectral models of perceived triadic distance

We compare three contrasting models of the perceived distance between root-position major and minor chords and test them against new empirical data. The models include a recent psychoacoustic model called spectral pitch class distance, and two well-established music theoretical models – Tonnetz distance and voice-leading distance. To allow a principled challenge, in the context of these data, of the assumptions behind each of the models, we compare them with a simple “benchmark” model that simply counts the number of common tones between chords. Spectral pitch class and Tonnetz have the highest correlations with the experimental data and each other, and perform significantly better than the benchmark. The voice-leading model performs worse than the benchmark. We suggest that spectral pitch class distance provides a psychoacoustic explanation for perceived harmonic distance and its music theory representation, the Tonnetz. Scores and MIDI files of the stimuli, the experimental data, and the computational models are available in the online supplement

Evaluating Primary Blast Effects In Vitro

Exposure to blast events can cause severe trauma to vital organs such as the lungs, ears, and brain. Understanding the mechanisms behind such blast-induced injuries is of great importance considering the recent trend towards the use of explosives in modern warfare and terrorist related incidents. To fully understand blast-induced injury, we must first be able to replicate such blast events in a controlled environment using a reproducible method. In this technique using shock tube equipment, shock waves at a range of pressures can be propagated over live cells grown in 2D, and markers of cell viability can be immediately analyzed using a redox indicator assay and the fluorescent imaging of live and dead cells. This method demonstrated that increasing the peak blast overpressure to 127 kPa can stimulate a significant drop in cell viability when compared to untreated controls. Test samples are not limited to adherent cells, but can include cell suspensions, whole-body and tissue samples, through minor modifications to the shock tube setup. Replicating the exact conditions that tissues and cells experience when exposed to a genuine blast event is difficult. Techniques such as the one presented in this article can help to define damage thresholds and identify the transcriptional and epigenetic changes within cells that arise from shock wave exposure

Interpretation of the angular dependence of the de Haas-van Alphen effect in MgB_2

We present detailed results for the amplitude and field dependence of the de Haas-van Alphen (dHvA) signal arising from the electron-like $\pi$ sheet of Fermi surface in MgB_2. Our data and analysis show that the dip in dHvA amplitude when the field is close to the basal plane is caused by a beat between two very similar dHvA frequencies and not a spin-zero effect as previously assumed. Our results imply that the Stoner enhancement factors in MgB_2 are small on both the Sigma and Pi sheets.Comment: 4 pages with figures. Submitted to PR

Optimal Topological Test for Degeneracies of Real Hamiltonians

We consider adiabatic transport of eigenstates of real Hamiltonians around loops in parameter space. It is demonstrated that loops that map to nontrivial loops in the space of eigenbases must encircle degeneracies. Examples from Jahn-Teller theory are presented to illustrate the test. We show furthermore that the proposed test is optimal.Comment: Minor corrections, accepted in Phys. Rev. Let

Structure factor and thermodynamics of rigid dendrimers in solution

The ''polymer reference interaction site model'' (PRISM) integral equation theory is used to determine the structure factor of rigid dendrimers in solution. The theory is quite successful in reproducing experimental structure factors for various dendrimer concentrations. In addition, the structure factor at vanishing scattering vector is calculated via the compressibility equation using scaled particle theory and fundamental measure theory. The results as predicted by both theories are systematically smaller than the experimental and PRISM data for platelike dendrimers.Comment: 7 pages, 5 figures, submitte

Peierls transition in the quantum spin-Peierls model

We use the density matrix renormalization group method to investigate the role of longitudinal quantized phonons on the Peierls transition in the spin-Peierls model. For both the XY and Heisenberg spin-Peierls model we show that the staggered phonon order parameter scales as $\sqrt{\lambda}$ (and the dimerized bond order scales as $\lambda$) as $\lambda \to 0$ (where $\lambda$ is the electron-phonon interaction). This result is true for both linear and cyclic chains. Thus, we conclude that the Peierls transition occurs at $\lambda=0$ in these models. Moreover, for the XY spin-Peierls model we show that the quantum predictions for the bond order follow the classical prediction as a function of inverse chain size for small $\lambda$. We therefore conclude that the zero $\lambda$ phase transition is of the mean-field type