Rotor/wing aerodynamic interactions in hover

An experimental and theoretical investigation of rotor/wing aerodynamic interactions in hover is described. The experimental investigation consisted of both a large-scale and small-scale test. A 0.658-scale, V-22 rotor and wing was used in the large-scale test. Wind download, wing surface pressure, rotor performance, and rotor downwash data from the large-scale test are presented. A small-scale experiment was conducted to determine how changes in the rotor/wing geometry affected the aerodynamic interactions. These geometry variations included the distance between the rotor and wing, wing incidence angle, and configurations both with the rotor axis at the tip of the wing (tilt rotor configuration) and with the rotor axis at the center of the wing (compound helicopter configuration). A wing with boundary-layer control was also tested to evaluate the effect of leading and trailing edge upper surface blowing on the wing download. A computationally efficient, semi-empirical theory was developed to predict the download on the wing. Finally, correlations between the theoretical predictions and test data are presented

Reduction of tilt rotor download using circulation control

The effect of boundary layer control blowing on the download of a wing in the wake of a hovering rotor was measured in a small scale experiment. The objective was to evaluate the potential of boundary layer control blowing for reducing tilt rotor download. Variations were made in rotor thrust coefficient, blowing pressure ratio, and blowing slot height. The effect of these parameter variations on the wing download and wing surface pressures is presented. The boundary layer control blowing caused reductions in the wing download of 25 to 55 percent

Widely tunable femtosecond solitonic radiation in photonic crystal fiber cladding

We report on a means to generate tunable ultrashort optical pulses. We demonstrate that dispersive waves generated by solitons within the small-core features of a photonic crystal fiber cladding can be used to obtain femtosecond pulses tunable over an octave-wide spectral range. The generation process is highly efficient and occurs at the relatively low laser powers available from a simple Ti:sapphire laser oscillator. The described phenomenon is general and will play an important role in other systems where solitons are known to exist.Peer reviewed: YesNRC publication: N

Mosquitoes Collected In South And East Kalimantan

Pengumpulan nyamuk dalam waktu singkat di sembilan tempat di Kalimantan Timur dan Selatan menghasilkan 57 species dari 11 genera. Species yang terbanyak dikumpulkan ialah dari genus Culex 27 percent Mansonia 16 percent. Anopheles 16 percent, Aedes 12 percent, Armigeres 7 percent, Mimomia 7 percent, Uranotaenia 7 percent, Hodgesia. Tripteroides, Heizmania dan Culiseta masing-masing 2 percent

Healthier prisons: The role of a prison visitors' centre

Since the inception of the prison as a ‘setting’ for health promotion, there has been a focus on how the health of those men and women who spend ‘time inside’ can at least be maintained and if possible, enhanced, during their prison sentence. This paper presents findings from a mainly qualitative evaluation of a prison visitors' centre in the UK. It reports experiences of prisoners' families, prisoners, prison staff, the local community and the ways in which the visitors' centre has contributed positively to their health and well-being. In addition, key stakeholders were interviewed to ascertain the role this visitors' centre has in policy frameworks related to re-offending. The findings from this evaluation underscore how the visitors' centre improved the quality of visits, and contributed towards the maintenance of family ties through the help and support it provides for families and prisoners. The paper concludes by suggesting that visitors' centres are an essential part of a modern prison service helping to address the government's health inequalities agenda

High harmonic generation in a gas-filled hollow-core photonic crystal fiber

High harmonic generation (HHG) of intense infrared laser radiation (Ferray et al., J. Phys. B: At. Mol. Opt. Phys. 21:L31, 1988; McPherson et al., J. Opt. Soc. Am. B 4:595, 1987) enables coherent vacuum-UV (VUV) to soft-X-ray sources. In the usual setup, energetic femtosecond laser pulses are strongly focused into a gas jet, restricting the interaction length to the Rayleigh range of the focus. The average photon flux is limited by the low conversion efficiency and the low average power of the complex laser amplifier systems (Keller, Nature 424:831, 2003; Südmeyer et al., Nat. Photonics 2:599, 2008; Röser et al., Opt. Lett. 30:2754, 2005; Eidam et al., IEEE J. Sel. Top. Quantum Electron. 15:187, 2009) which typically operate at kilohertz repetition rates. This represents a severe limitation for many experiments using the harmonic radiation in fields such as metrology or high-resolution imaging. Driving HHG with novel high-power diode-pumped multi-megahertz laser systems has the potential to significantly increase the average photon flux. However, the higher average power comes at the expense of lower pulse energies because the repetition rate is increased by more than a thousand times, and efficient HHG is not possible in the usual geometry. So far, two promising techniques for HHG at lower pulse energies were developed: external build-up cavities (Gohle et al., Nature 436:234, 2005; Jones et al., Phys. Rev. Lett. 94:193, 2005) and resonant field enhancement in nanostructured targets (Kim et al., Nature 453:757, 2008). Here we present a third technique, which has advantages in terms of ease of HHG light extraction, transverse beam quality, and the possibility to substantially increase conversion efficiency by phase-matching (Paul et al., Nature 421:51, 2003; Ren et al., Opt. Express 16:17052, 2008; Serebryannikov et al., Phys. Rev. E (Stat. Nonlinear Soft Matter Phys.) 70:66611, 2004; Serebryannikov et al., Opt. Lett. 33:977, 2008; Zhang et al., Nat. Phys. 3:270, 2007). The interaction between the laser pulses and the gas occurs in a Kagome-type Hollow-Core Photonic Crystal Fiber (HC-PCF) (Benabid et al., Science 298:399, 2002), which reduces the detection threshold for HHG to only 200nJ. This novel type of fiber guides nearly all of the light in the hollow core (Couny et al., Science 318:1118, 2007), preventing damage even at intensities required for HHG. Our fiber guided 30-fs pulses with a pulse energy of more than 10μJ, which is more than five times higher than for any other photonic crystal fiber (Hensley et al., Conference on Lasers and Electro-Optics (CLEO), IEEE Press, New York, 2008

High-efficiency cross-phase modulation in a gas-filled waveguide

Strong cross-Kerr nonlinearities have been long sought after for quantum information applications. Recent work has shown that they are intrinsically unreliable in traveling-wave configurations: cavity configurations avoid this, but require knowledge of both the nonlinearity and the loss. Here we present a detailed systematic study of cross-phase modulation and absorption in an Rb vapor confined within a hollow-core photonic crystal fiber. Using a two-photon transition, we observe phase modulations of up to pi rad with a signal power of 25 mu W, corresponding to a nonlinear Kerr coefficient, n(2), of 0.8 x 10(-6) cm(2)/W, or 1.3 x 10(-6) rad per photon

Magnetic-Field-Induced Antiferromagnetism in Two-Dimensional Hubbard Model: Analysis of CeRhIn5_5

We propose the mechanism for the magnetic-field-induced antiferromagnetic (AFM) state in a two-dimensional Hubbard model in the vicinity of the AFM quantum critical point (QCP), using the fluctuation-exchange (FLEX) approximation by taking the Zeeman energy due to the magnetic field $B$ into account. In the vicinity of the QCP, we find that the AFM correlation perpendicular to $B$ is enhanced, whereas that parallel to $B$ is reduced. This fact means that the finite magnetic field increases $T_N$, with the AFM order perpendicular to $B$. The increment in $T_N$ can be understood in terms of the reduction of both quantum and thermal fluctuations due to the magnetic field, which is caused by the self-energy effect within the FLEX approximation. The present study naturally explains the increment in $T_N$ in CeRhIn_5 under the magnetic field found recently.Comment: 5 page

Life events and hemodynamic stress reactivity in the middle-aged and elderly

Recent versions of the reactivity hypothesis, which consider it to be the product of stress exposure and exaggerated haemodynamic reactions to stress that confers cardiovascular disease risk, assume that reactivity is independent of the experience of stressful life events. This assumption was tested in two substantial cohorts, one middle-aged and one elderly. Participants had to indicate from a list of major stressful life events up to six they had experienced in the previous two years. They were also asked to rate how disruptive and stressful they were, at the time of occurrence and now. Blood pressure and pulse rate were measured at rest and in response to acute mental stress. Those who rated the events as highly disruptive at the time of exposure and currently exhibited blunted systolic blood pressure reactions to acute stress. The present results suggest that acute stress reactivity may not be independent of stressful life events experience

Engineering photon-photon interactions within rubidium-filled waveguides

Strong photon-photon interactions are a required ingredient for deterministic two-photon optical quantum logic gates. Multiphoton transitions in dense atomic vapors have been shown to be a promising avenue for producing such interactions. The strength of a multiphoton interaction can be enhanced by conducting the interaction in highly confined geometries such as small-cross-section optical waveguides. We demonstrate, both experimentally and theoretically, that the strength of such interactions scale only with the optical mode diameter, d, not d² as might be initially expected. This weakening of the interaction arises from atomic motion inside the waveguides. We create an interaction between two optical signals, at 780 and 776 nm, using the 5S₁⁄₂ → 5D₅⁄₂ two-photon transition in rubidium vapor within a range of hollow-core fibers with different core sizes. The interaction strength is characterized by observing the absorption and phase shift induced on the 780-nm beam, which is in close agreement with theoretical modeling that accounts for the atomic motion inside the fibers. These observations demonstrate that transit-time effects upon multiphoton transitions are of key importance when engineering photon-photon interactions within small-cross-section waveguides that might otherwise be thought to lead to enhanced optical nonlinearity through increased intensities.C. Perrella, P.S. Light, S. Afshar Vahid, F. Benabid, and A.N. Luite