Interactive manipulation of microparticles in an octagonal sonotweezer

An ultrasonic device for micro-patterning and precision manipulation of micrometre-scale particles is demonstrated. The device is formed using eight piezoelectric transducers shaped into an octagonal cavity. By exciting combinations of transducers simultaneously, with a controlled phase delay between them, different acoustic landscapes can be created, patterning micro-particles into lines, squares, and more complex shapes. When operated with all eight transducers the device can, with appropriate phase control, manipulate the two dimensional acoustic pressure gradient; it thus has the ability to position and translate a single tweezing zone to different locations on a surface in a precise and programmable manner

Low Frequency Observations of Millisecond Pulsars with the WSRT

With LOFAR beginning operation in 2008 there is huge potential for studying pulsars with high signal to noise at low frequencies. We present results of observations made with the Westerbork Synthesis Radio Telescope to revisit, with modern technology, this frequency range. Coherently dedispersed profiles of millisecond pulsars obtained simultaneously between 115-175 MHz are presented. We consider the detections and non-detections of 14 MSPs in light of previous observations and the fluxes, dispersion measures and spectral indices of these pulsars. The excellent prospects for LOFAR finding new MSPs and studying the existing systems are then discussed in light of these results.Comment: 5 pages, 5 figures, To appear in the proceedings of "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007, McGill University, Montreal, Canad

SN 1987A's Circumstellar Envelope, II: Kinematics of the Three Rings and the Diffuse Nebula

We present several different measurements of the velocities of structures within the circumstellar envelope of SN 1987A, including the inner, equatorial ring (ER), outer rings (ORs), and the diffuse nebulosity at radii < 5 pc, based on CTIO 4m and HST data. A comparison of STIS and WFPC2 [N II]6583 loci for the rings show that the ER is expanding in radius at 10.5+-0.3 km/s, with the northern OR expanding along the line of sight at about 26 km/s, and for the southern OR, about 23 km/s. Similar results are found with CTIO 4m data. Accounting for inclination, the best fit to all data show both ORs with an expansion from the SN of 26 km/s. The ratio of the ER to OR velocities is nearly equal to the ratio of ER to OR radii, so the rings are roughly homologous, all having kinematic ages corresponding to about 20,000 yr before the SN explosion. This makes previously reported, large compositional differences between the ER and ORs difficult to understand. Additionally, a grid of longslit 4m/echelle spectra centered on the SN shows two velocity components over a region roughly coextensive with the outer circumstellar envelope extending about 5 pc (20 arcsec) from the SN. One component is blueshifted and the other redshifted from the SN centroid by about 10 km/s each. These features may represent a bipolar flow expanding from the SN, in which the ORs are propelled 10-15 km/s faster than that of the surrounding envelope into which they propogate. The kinematic timescale for the entire nebula is at least about 350,000 yr. The kinematics of these various structures constrain possible models for the evolution of the progenitor and its formation of a mass loss nebula.Comment: 25 pages AASTeX text plus 12 figures. ApJ, in pres

Mitigation of Moral Hazard and Adverse Selection in Venture Capital Financing: The Influence of the Country’s Institutional Setting

A venture capitalist (VC) needs to trade off benefits and costs when attempting to mitigate agency problems in their investor-investee relationship. We argue that signals of ventures complement the VC’s capacity to screen and conduct a due diligence during the pre-investment phase, but its attractiveness may diminish in institutional settings supporting greater transparency. Similarly, whereas a VC may opt for contractual covenants to curb potential opportunism by ventures in the post-investment phase, this may only be effective in settings supportive of shareholder rights enforcement. Using an international sample of VC contracts, our study finds broad support for these conjectures. It delineates theoretical and practical implications for how investors can best deploy their capital in different institutional settings whilst nurturing their relationships with entrepreneurs

Rotation reduces convective mixing in Jupiter and other gas giants

Recent measurements of Jupiter's gravitational moments by the Juno spacecraft and seismology of Saturn's rings suggest that the primordial composition gradients in the deep interior of these planets have persisted since their formation. One possible explanation is the presence of a double-diffusive staircase below the planet's outer convection zone, which inhibits mixing across the deeper layers. However, hydrodynamic simulations have shown that these staircases are not long-lasting and can be disrupted by overshooting convection. In this paper we suggests that planetary rotation could be another factor for the longevity of primordial composition gradients. Using rotational mixing-length theory and 3D hydrodynamic simulations, we demonstrate that rotation significantly reduces both the convective velocity and the mixing of primordial composition gradients. In particular, for Jovian conditions at $t\sim10^{8}~\mathrm{yrs}$ after formation, rotation reduces the convective velocity by a factor of 6, and in turn, the kinetic energy flux available for mixing gets reduced by a factor of $6^3\sim 200$. This leads to an entrainment timescale that is more than two orders of magnitude longer than without rotation. We encourage future hydrodynamic models of Jupiter and other gas giants to include rapid rotation, because the decrease in the mixing efficiency could explain why Jupiter and Saturn are not fully mixed.Comment: Accepted for publication in the Astrophysical Journal Letter

The Lick Planet Search: Detectability and Mass Thresholds

We analyse 11 years of precise radial velocities for 76 solar type stars from the Lick survey. Eight stars in this sample have previously reported planetary-mass companions, all with mass (m sin i) less than 8 Jupiter masses (MJ). For the stars without a detected companion, we place upper limits on possible companion mass. For most stars, we can exclude companions with m sin i > 0.7 MJ (a/AU)^1/2 for orbital radii a < 5 AU. We use our results to interpret the observed masses and orbital radii of planetary-mass companions. For example, we show that the finite duration of the observations makes detection of Jupiter mass companions more and more difficult for orbital radii beyond 3 AU. Thus it is possible that the majority of solar type stars harbor Jupiter-mass companions much like our own, and if so these companions should be detectable in a few years. To search for periodicities, we adopt a "floating-mean" periodogram, which improves on the traditional Lomb-Scargle periodogram by accounting for statistical fluctuations in the mean of a sampled sinusoid. We discuss in detail the normalization of the periodogram, an issue which has been of some debate in the literature.Comment: To appear in the Astrophysical Journal (50 pages, LaTeX, including 11 figures

Photometry of SN 2002ic and Implications for the Progenitor Mass-Loss History

We present new pre-maximum and late-time optical photometry of the Type Ia/IIn supernova 2002ic. These observations are combined with the published V-band magnitudes of Hamuy et al. (2003) and the VLT spectrophotometry of Wang et al. (2004) to construct the most extensive light curve to date of this unusual supernova. The observed flux at late time is significantly higher relative to the flux at maximum than that of any other observed Type Ia supernova and continues to fade very slowly a year after explosion. Our analysis of the light curve suggests that a non-Type Ia supernova component becomes prominent $\sim20$ days after explosion. Modeling of the non-Type Ia supernova component as heating from the shock interaction of the supernova ejecta with pre-existing circumstellar material suggests the presence of a $\sim1.7 10^{15}$ cm gap or trough between the progenitor system and the surrounding circumstellar material. This gap could be due to significantly lower mass-loss $\sim15 (v_w/10 km/s)^{-1}$ years prior to explosion or evacuation of the circumstellar material by a low-density fast wind. The latter is consistent with observed properties of proto-planetary nebulae and with models of white-dwarf + asymptotic giant branch star progenitor systems with the asymptotic giant branch star in the proto-planetary nebula phase.Comment: accepted for publication in Ap

Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models

We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D hydro models: the very highly parameterized deflagration model W7, and two delayed detonation models. We find that overall both models do about equally well at fitting well observed SNe Ia near to maximum light. However, the Si II 6150 feature of W7 is systematically too fast, whereas for the delayed detonation models it is also somewhat too fast, but significantly better than that of W7. We find that a parameterized mixed model does the best job of reproducing the Si II 6150 line near maximum light and we study the differences in the models that lead to better fits to normal SNe Ia. We discuss what is required of a hydro model to fit the spectra of observed SNe Ia near maximum light.Comment: 29 pages, 14 figures, ApJ, in pres

Investigation of mechanical losses of thin silicon flexures at low temperatures

The investigation of the mechanical loss of different silicon flexures in a temperature region from 5 to 300 K is presented. The flexures have been prepared by different fabrication techniques. A lowest mechanical loss of $3\times10^{-8}$ was observed for a 130 $\mu$m thick flexure at around 10 K. While the mechanical loss follows the thermoelastic predictions down to 50 K a difference can be observed at lower temperatures for different surface treatments. This surface loss will be limiting for all applications using silicon based oscillators at low temperatures. The extraction of a surface loss parameter using different results from our measurements and other references is presented. We focused on structures that are relevant for gravitational wave detectors. The surface loss parameter $\alpha_s$ = 0.5 pm was obtained. This reveals that the surface loss of silicon is significantly lower than the surface loss of fused silica.Comment: 16 pages, 7 figure

Status Update of the Parkes Pulsar Timing Array

The Parkes Pulsar Timing Array project aims to make a direct detection of a gravitational-wave background through timing of millisecond pulsars. In this article, the main requirements for that endeavour are described and recent and ongoing progress is outlined. We demonstrate that the timing properties of millisecond pulsars are adequate and that technological progress is timely to expect a successful detection of gravitational waves within a decade, or alternatively to rule out all current predictions for gravitational wave backgrounds formed by supermassive black-hole mergers.Comment: 10 pages, 3 figures, Amaldi 8 conference proceedings, accepted by Classical & Quantum Gravit