Using gravitational-wave standard sirens

Gravitational waves (GWs) from supermassive binary black hole (BBH) inspirals are potentially powerful standard sirens (the GW analog to standard candles) (Schutz 1986, 2002). Because these systems are well-modeled, the space-based GW observatory LISA will be able to measure the luminosity distance (but not the redshift) to some distant massive BBH systems with 1-10% accuracy. This accuracy is largely limited by pointing error: GW sources generally are poorly localized on the sky. Localizing the binary independently (e.g., through association with an electromagnetic counterpart) greatly reduces this positional error. An electromagnetic counterpart may also allow determination of the event's redshift. In this case, BBH coalescence would constitute an extremely precise (better than 1%) standard candle visible to high redshift. In practice, gravitational lensing degrades this precision, though the candle remains precise enough to provide useful information about the distance-redshift relation. Even if very rare, these GW standard sirens would complement, and increase confidence in, other standard candles.Comment: 10 pages, 8 figures. ApJ, in pres

Cis-regulatory basis of sister cell type divergence in the vertebrate retina

Multicellular organisms evolved via repeated functional divergence of transcriptionally related sister cell types, but the mechanisms underlying sister cell type divergence are not well understood. Here, we study a canonical pair of sister cell types, retinal photoreceptors and bipolar cells, to identify the ke

A PRELIMINARY FEASIBILITY FOR ESTABLISHING A MULTI-SPECIES MEAT PROCESSING PLANT IN SOUTHWESTERN NORTH DAKOTA

The number of small commodity livestock slaughter plants in the Upper Northern Plains region continues to decline. Significant factors contributing to this decline include: 1) pressure to consolidate, thereby capturing economies of scale; 2) relatively stringent federal inspection specifications, along with; 3) HACCP (Hazardous Analysis Critical Control Points) requirements. At the same time, consumer demand (markets) for specialty, selected, and exotic meats appears to be growing. For example, the recent market successes in Europe evidenced by the North American Bison Cooperative based in New Rockford, North Dakota. Several alternative livestock producer groups have emerged which include lamb, ratite, elk, deer, goat, poultry, rabbit, specialty beef, and organic livestock. These groups have expressed a need for slaughter and processing facilities to meet market demand. The economic question which then becomes foremost to developing a viable business enterprise is: "What is the critical threshold volume (CTV) of product required to succeed in terms of economic profit?" Specialty livestock is relatively new and production volume small in comparison to established commodity livestock such as cattle or hogs. This fact led researchers to consider the preliminary feasibility of a multi-species processing facility as a means of addressing the expressed need.multi-species, specialty meats, specialty livestock, alternative livestock, economies of scale, HACCP (Hazardous Analysis Critical Control Points), slaughter plants, processing plants, Community/Rural/Urban Development, Agribusiness,

Sleep, aging, and lifespan in Drosophila

<p>Abstract</p> <p>Background</p> <p>Epidemiological studies in humans suggest that a decrease in daily sleep duration is associated with reduced lifespan, but this issue remains controversial. Other studies in humans also show that both sleep quantity and sleep quality decrease with age. <it>Drosophila melanogaster </it>is a useful model to study aging and sleep, and inheriting mutations affecting the potassium current Shaker results in flies that sleep less and have a shorter lifespan. However, whether the link between short sleep and reduced longevity exists also in wild-type flies is unknown. Similarly, it is unknown whether such a link depends on sleep amount per se, rather than on other factors such as waking activity. Also, sleep quality has been shown to decrease in old flies, but it remains unclear whether aging-related sleep fragmentation is a generalized phenomenon.</p> <p>Results</p> <p>We compared 3 short sleeping mutant lines (<it>Hk</it>¹, <it>Hk</it>^{<it>Y </it>}and <it>Hk</it>²) carrying a mutation in Hyperkinetic, which codes for the beta subunit of the Shaker channel, to wild-type siblings throughout their entire lifespan (all flies kept at 20°C). <it>Hk</it>¹and <it>Hk</it>^{<it>Y </it>}mutants were short sleeping relative to wild-type controls from day 3 after eclosure, and <it>Hk</it>²flies became short sleepers about two weeks later. All 3 <it>Hk </it>mutant lines had reduced lifespan relative to wild-type flies. Total sleep time showed a trend to increase in all lines with age, but the effect was most pronounced in <it>Hk</it>¹and <it>Hk</it>^{<it>Y </it>}flies. In both mutant and wild-type lines sleep quality did not decay with age, but the strong preference for sleep at night declined starting in "middle age". Using Cox regression analysis we found that in <it>Hk</it>¹and <it>Hk</it>^{<it>Y </it>}mutants and their control lines there was a negative relationship between total sleep amount during the first 2 and 4 weeks of age and hazard (individual risk of death), while no association was found in <it>Hk</it>²flies and their wild-type controls. <it>Hk</it>¹and <it>Hk</it>^{<it>Y </it>}mutants and their control lines also showed an association between total daily wake activity over the first 2 and 4 weeks of age and hazard. However, when both sleep duration and wake activity were used in the same regression, the effects of activity were much reduced, while most of the sleep effects remained significant. Finally, <it>Hk</it>¹flies and wild-type siblings were also tested at 25°C, and results were similar to those at 20°C. Namely, <it>Hk</it>¹mutants were short sleeping, hyperactive, and short lived relative to controls, and sleep quality in both groups did not decrease with age.</p> <p>Conclusions</p> <p>Different <it>Hk </it>mutations affect the sleep phenotype, and do so in an age-dependent manner. In 4 of the 6 lines tested sleep associates significantly with lifespan variation even after any effect of activity is removed, but activity does not associate significantly with lifespan after the effects of sleep are removed. Thus, in addition to environmental factors and genetic background, sleep may also affect longevity. Sleep quality does not necessarily decay as flies age, suggesting that aging-related sleep fragmentation may also depend on many factors, including genetic background and rearing conditions.</p

Gravitational Waves from Stellar Collapse: Correlations to Explosion Asymmetries

The collapse of massive stars not only produces observable outbursts across the entire electromagnetic spectrum but, for Galactic (or near-Galactic) supernovae, detectable signals for ground-based neutrino and gravitational wave detectors. Gravitational waves and neutrinos provide the only means to study the actual engine behind the optical outbursts: the collapsed stellar core. While the neutrinos are most sensitive to details of the equation of state, gravitational waves provide a means to study the mass asymmetries in this central core. We present gravitational wave signals from a series of 3-dimensional core-collapse simulations with asymmetries derived from initial perturbations caused by pre-collapse convection, core rotation, and low-mode convection in the explosion engine itself. A Galactic supernovae will allow us to differentiate these different sources of asymmetry. Combining this signal with other observations of the supernova, from neutrinos to gamma-rays to the compact remnant, dramatically increases the predictive power of the gravitational wave signal. We conclude with a discussion of the gravitational wave signal arising from collapsars, the leading engine for long-duration gamma-ray bursts.Comment: 36 pages including 14 figures, accepted by Ap

Base Dependent DNA-carbon Nanotube Interactions: Activation Enthalpies and Assembly-disassembly Control

We quantify the base dependent interactions between single stranded DNA and single walled carbon nanotubes (SWNTs) in solution. DNA/SWNT hybrids hold the promise of applications ranging from nanoscale electronics and assembly of nanotube based materials, to drug delivery and DNA sequencing. These applications require control over the hybrid assembly and disassembly. Our analytical assay reveals the order of nucleobase binding strengths with SWNTs as G>C>A>T. Furthermore, time dependent fixed temperature experiments that probe the kinetics of the dissociation process provide values for the equilibrium constants and dissociation enthalpies that underlie the microscopic interactions. Quantifying the base dependency of hybrid stability shows how insight into the energetics of the component interactions facilitates control over hybrid assembly and disassembly.Engineering and Applied SciencesMolecular and Cellular BiologyPhysic

Approximating the inspiral of test bodies into Kerr black holes

We present a new approximate method for constructing gravitational radiation driven inspirals of test-bodies orbiting Kerr black holes. Such orbits can be fully described by a semi-latus rectum $p$, an eccentricity $e$, and an inclination angle $\iota$; or, by an energy $E$, an angular momentum component $L_z$, and a third constant $Q$. Our scheme uses expressions that are exact (within an adiabatic approximation) for the rates of change ($\dot{p}$, $\dot{e}$, $\dot{\iota}$) as linear combinations of the fluxes ($\dot{E}$, $\dot{L_z}$, $\dot{Q}$), but uses quadrupole-order formulae for these fluxes. This scheme thus encodes the exact orbital dynamics, augmenting it with approximate radiation reaction. Comparing inspiral trajectories, we find that this approximation agrees well with numerical results for the special cases of eccentric equatorial and circular inclined orbits, far more accurate than corresponding weak-field formulae for ($\dot{p}$, $\dot{e}$, $\dot{\iota}$). We use this technique to study the inspiral of a test-body in inclined, eccentric Kerr orbits. Our results should be useful tools for constructing approximate waveforms that can be used to study data analysis problems for the future LISA gravitational-wave observatory, in lieu of waveforms from more rigorous techniques that are currently under development.Comment: 15 pages, 5 figures, submitted to PR

Consequences of gravitational radiation recoil

Coalescing binary black holes experience an impulsive kick due to anisotropic emission of gravitational waves. We discuss the dynamical consequences of the recoil accompanying massive black hole mergers. Recoil velocities are sufficient to eject most coalescing black holes from dwarf galaxies and globular clusters, which may explain the apparent absence of massive black holes in these systems. Ejection from giant elliptical galaxies would be rare, but coalescing black holes are displaced from the center and fall back on a time scale of order the half-mass crossing time. Displacement of the black holes transfers energy to the stars in the nucleus and can convert a steep density cusp into a core. Radiation recoil calls into question models that grow supermassive black holes from hierarchical mergers of stellar-mass precursors.Comment: 5 pages, 4 figures, emulateapj style; minor changes made; accepted to ApJ Letter