Bounds on Expected Black Hole Spins in Inspiraling Binaries

As a first step towards understanding the angular momentum evolution history of black holes in merging black-hole/neutron-star binaries, we perform population synthesis calculations to track the distribution of accretion histories of compact objects in such binaries. We find that there are three distinct processes which can possibly contribute to the black-hole spin magnitude: a birth spin for the black hole, imparted at either (i) the collapse of a massive progenitor star to a black hole or (ii) the accretion-induced collapse of a neutron star to a black hole; and (iii) an accretion spin-up when the already formed black hole [via (i) or (ii)] goes through an accretion episode (through an accretion disk or a common-envelope phase). Our results show that, with regard to accretion-induced spinup in merging BH-NS binaries [method (iii) above], only {\em accretion episodes associated with common-envelope phases and hypercritical accretion rates} occur in the formation history of merging black hole/neutron star binaries. Lacking unambiguous experimental information about BH birth spins [i.e., regarding the results of processes (i) and (ii)], we choose two fiducial values for the BH birth angular momentum parameter a=J/M^2, consistent with observations of (i) NS birth spins (a roughly 0) and (ii) X-ray binaries (a=0.5). Using these two fiducial values and a conservative upper bound on the specific angular momentum of accreted matter, we discuss the expected range of black hole spins in the binaries of interest. We conclude with comments on the significance of these results for ground-based gravitational-wave searches of inspiral signals from black hole binaries.Comment: Submitted to ApJ. (v1) Uses emulateapj.cls. 5 figures. (v2): corrected reference list and uses smaller figures (v3): Includes changes in response to referee comments, including new discussion of XRBs. Figures merged, so only 3 figures (v4) Minor typo correction, plus updated abstract posted onlin

Akt-dependent Pp2a activity is required for epidermal barrier formation during late embryonic development

Acquisition of epidermal barrier function occurs late in mouse gestation. Several days before birth a wave of barrier acquisition sweeps across murine fetal skin, converging on dorsal and ventral midlines. We investigated the molecular pathways active during epidermal barrier formation. Akt signaling increased as the barrier wave crossed epidermis and Jun was transiently dephosphorylated. Inhibitor experiments on embryonic explants showed that the dephosphorylation of Jun was dependent on both Akt and protein phosphatase 2A (Pp2a). Inhibition of Pp2a and Akt signaling also caused defects in epidermal barrier formation. These data are compatible with a model for developmental barrier acquisition mediated by Pp2a regulation of Jun dephosphorylation, downstream of Akt signaling. Support for this model was provided by siRNA-mediated knockdown of Ppp2r2a (Pr55α or B55α), a regulatory subunit of Pp2a expressed in an Akt-dependent manner in epidermis during barrier formation. Ppp2r2a reduction caused significant increase in Jun phosphorylation and interfered with the acquisition of barrier function, with barrier acquisition being restored by inhibition of Jun phosphorylation. Our data provide strong evidence that Ppp2r2a is a regulatory subunit of Pp2a that targets this phosphatase to Jun, and that Pp2a action is necessary for barrier formation. We therefore describe a novel Akt-dependent Pp2a activity that acts at least partly through Jun to affect initial barrier formation during late embryonic epidermal development

Management Jobs in the Insurance Industry: Organizational Deskilling and Rising Pay Inequality

The attention of both the research community and the popular press has begun to shift from a traditional focus on production jobs and toward management positions in part because of a perception that a fundamental change is underway in the management ranks. Unlike the temporary layoffs of production workers that were historically driven by business cycles, the changes in management job security seem to be permanent and, in large measure, driven by development inside the firm. The most important of these forces appear to be changes in the structure of management and in the organization of work processes. The authors use a unique set of data to examine the structure of management jobs among a sample of companies and observe how those jobs have changed over time. They examine changes in the skill requirements of jobs by functional area and by level in the organization, changes in the "shape" of the organization chart - the distribution of employees across management job titles - and changes in compensation for these jobs. The data were obtained from Hay Associates, and it included the internal organization of management jobs for 11 life insurance companies. The authors see a sharp expansion in the proportion of line workers, absolute declines in the number of top management positions, and only modest growth in the number of middle managers and supervisors. As a result the organization chart has changed dramatically in these companies, becoming considerably flatter. The "span of control" has increased for every level of the organization and especially for first level management. If the widening of the supervisory span of control resulted from taking decision making and responsibility from supervisors and pushing it down to line workers, it does not seem to have increased the average skill requirements of the exempt line workers. Skill requirements for the other levels rose over the period, especially for top management positions. Overall, the average level of skill in the sample fell substantially between 1986 and 1992 (even though skills rose in two of the four levels) because of a sharp shift in the distribution of employment away from management and toward line positions. The authors suggest that the best description of these patterns is that they represent upskilling of individual jobs and deskilling of organizations. Regarding compensation, none of the levels experienced increases in skill that were statically significant, but top managers received a large (28 percent) increase in pay, middle managers received a modest (10 percent) increase, and the lower two levels received virtually no increases. One conclusion is that earnings inequality is increasing substantially inside these firms in a manner that is not attributable to any increase in skill, and the dividing line for that growth in inequality is no longer exempt/nonexempt but supervisor/manager. A possible explanation for the rising inequality in compensation is that it helps offset change in the probability of promotion. The fact that the span of control is increasing and organizational chart flattening means that the probability of the average worker being promoted is declining. The decline in the probability of promotion might reduce the incentives to work hard. Increases in the compensation of top jobs increase the return to securing a promotion and may offset some of the effect produced by the decline in the probability of promotion. Another explanation is that top mangers are in "better positions to legislate their own pay increases." If true, this sample may actually underrepresent the true extent of income inequality because it consists of companies using an external consultant to help set compensation where internal consistency is an important characteristic of the pay system. These results suggest that "management" as a career will remain attractive, albeit less certain in terms of promotion prospects. Shifts to team-based approaches and the elimination of functional designations would suggest a greater need for generalists than specialists. As technology such as expert systems reduces the need for large units of "experts," the manger's skill will be in recognizing when an expert needs to be called. Leadership skills and the ability to adapt to a changing environment are two qualities that will be sought in the future. Fortunately, these skills will also be useful to team members who are not selected for promotion to mangers. Increasing income inequality may lead to distrust within the organization, though this may be offset by the technical tracks that allow highly skilled non-managers to earn equivalent levels of pay. The fact that insurance companies are relatively unique in facing no major industry-specific shocks from the outside environment suggests that these results should translate well to organizations in other industries.

Coating thermal noise for arbitrary shaped beams

Advanced LIGO's sensitivity will be limited by coating noise. Though this noise depends on beam shape, and though nongaussian beams are being seriously considered for advanced LIGO, no published analysis exists to compare the quantitative thermal noise improvement alternate beams offer. In this paper, we derive and discuss a simple integral which completely characterizes the dependence of coating thermal noise on shape. The derivation used applies equally well, with minor modifications, to all other forms of thermal noise in the low-frequency limit.Comment: 3 pages. Originally performed in August 2004. Submitted to CQG. (v2) : Corrections from referee and other

Effect of FSH on testicular morphology and spermatogenesis in gonadotrophin-deficient hypogonadal mice lacking androgen receptors

Follicle stimulating hormone (FSH) and androgen act to stimulate and maintain spermatogenesis. FSH acts directly on the Sertoli cells to stimulate germ cell number and acts indirectly to increase androgen production by the Leydig cells. In order to differentiate between the direct effects of FSH on spermatogenesis and those mediated indirectly through androgen action we have crossed hypogonadal (hpg) mice which lack gonadotrophins with mice lacking androgen receptors (AR) either ubiquitously (ARKO) or specifically on the Sertoli cells (SCARKO). These hpg.ARKO and hpg.SCARKO mice were treated with recombinant FSH for 7 days and testicular morphology and cell numbers assessed. In untreated hpg and hpg.SCARKO mice germ cell development was limited and did not progress beyond the pachytene stage. In hpg.ARKO mice testes were smaller with fewer Sertoli cells and germ cells compared to hpg mice. Treatment with FSH had no effect on Sertoli cell number but significantly increased germ cell numbers in all groups. In hpg mice FSH increased numbers of spermatogonia and spermatocytes and induced round spermatid formation. In hpg.SCARKO and hpg.ARKO mice, in contrast, only spermatogonial and spermatocyte numbers were increased with no formation of spermatids. Leydig cell numbers were increased by FSH in hpg and hpg.SCARKO mice but not in hpg.ARKO mice. Results show that in rodents 1) FSH acts to stimulate spermatogenesis through an increase in spermatogonial number and subsequent entry of these cells into meiosis, 2) FSH has no direct effect on the completion of meiosis and 3) FSH effects on Leydig cell number are mediated through interstitial ARs

Androgen-induced rhox homeobox genes modulate the expression of AR-regulated genes

Rhox5, the founding member of the reproductive homeobox on the X chromosome (Rhox) gene cluster, encodes a homeodomain-containing transcription factor that is selectively expressed in Sertoli cells, where it promotes the survival of male germ cells. To identify Rhox5-regulated genes, we generated 15P-1 Sertoli cell clones expressing physiological levels of Rhox5 from a stably transfected expression vector. Microarray analysis identified many genes altered in expression in response to Rhox5, including those encoding proteins controlling cell cycle regulation, apoptosis, metabolism, and cell-cell interactions. Fifteen of these Rhox5-regulated genes were chosen for further analysis. Analysis of Rhox5-null male mice indicated that at least 9 of these are Rhox5-regulated in the testes in vivo. Many of them have distinct postnatal expression patterns and are regulated by Rhox5 at different postnatal time points. Most of them are expressed in Sertoli cells, indicating that they are candidates to be directly regulated by Rhox5. Transfection analysis with expression vectors encoding different mouse and human Rhox family members revealed that the regulatory response of a subset of these Rhox5-regulated genes is both conserved and redundant. Given that Rhox5 depends on AR for expression in Sertoli cells, we examined whether some Rhox5-regulated genes are also regulated by androgen receptor (AR). We provide several lines of evidence that this is the case, leading us to propose that RHOX5 serves as a key intermediate transcription factor that directs some of the actions of AR in the testes

The dependence of test-mass thermal noises on beam shape in gravitational-wave interferometers

In second-generation, ground-based interferometric gravitational-wave detectors such as Advanced LIGO, the dominant noise at frequencies $f \sim 40$ Hz to $\sim 200$ Hz is expected to be due to thermal fluctuations in the mirrors' substrates and coatings which induce random fluctuations in the shape of the mirror face. The laser-light beam averages over these fluctuations; the larger the beam and the flatter its light-power distribution, the better the averaging and the lower the resulting thermal noise. In semi-infinite mirrors, scaling laws for the influence of beam shape on the four dominant types of thermal noise (coating Brownian, coating thermoelastic, substrate Brownian, and substrate thermoelastic) have been suggested by various researchers and derived with varying degrees of rigour. Because these scaling laws are important tools for current research on optimizing the beam shape, it is important to firm up our understanding of them. This paper (1) gives a summary of the prior work and of gaps in the prior analyses, (2) gives a unified and rigorous derivation of all four scaling laws, and (3) explores, relying on work by J. Agresti, deviations from the scaling laws due to finite mirror size.Comment: 25 pages, 10 figures, submitted to Class. Quantum Gra

Explaining LIGO's observations via isolated binary evolution with natal kicks

We compare binary evolution models with different assumptions about black-hole natal kicks to the first gravitational-wave observations performed by the LIGO detectors. Our comparisons attempt to reconcile merger rate, masses, spins, and spin-orbit misalignments of all current observations with state-of-the-art formation scenarios of binary black holes formed in isolation. We estimate that black holes (BHs) should receive natal kicks at birth of the order of $\sigma\simeq 200$ (50) km/s if tidal processes do (not) realign stellar spins. Our estimate is driven by two simple factors. The natal kick dispersion $\sigma$ is bounded from above because large kicks disrupt too many binaries (reducing the merger rate below the observed value). Conversely, the natal kick distribution is bounded from below because modest kicks are needed to produce a range of spin-orbit misalignments. A distribution of misalignments increases our models' compatibility with LIGO's observations, if all BHs are likely to have natal spins. Unlike related work which adopts a concrete BH natal spin prescription, we explore a range of possible BH natal spin distributions. Within the context of our models, for all of the choices of $\sigma$ used here and within the context of one simple fiducial parameterized spin distribution, observations favor low BH natal spin.Comment: 19 pages, 14 figures, as published in PR

Multiband gravitational-wave event rates and stellar physics

Joint gravitational-wave detections of stellar-mass black-hole binaries by ground- and space-based observatories will provide unprecedented opportunities for fundamental physics and astronomy. We present a semianalytic method to estimate multiband event rates by combining selection effects of ground-based interferometers (like LIGO/Virgo) and space missions (like LISA). We forecast the expected number of multiband detections first by using information from current LIGO/Virgo data, and then through population synthesis simulations of binary stars. We estimate that few to tens of LISA detections can be used to predict mergers detectable on the ground. Conversely, hundreds of events could potentially be extracted from the LISA data stream using prior information from ground detections. In general, the merger signal of binaries observable by LISA is strong enough to be unambiguously identified by both current and future ground-based detectors. Therefore third-generation detectors will not increase the number of multiband detections compared to LIGO/Virgo. We use population synthesis simulations of isolated binary stars to explore some of the stellar physics that could be constrained with multiband events, and we show that specific formation pathways might be overrepresented in multiband events compared to ground-only detections.Comment: 17 pages, 11 figures. Database and python code available at https://github.com/dgerosa/spops - Published in PR

Double Compact Objects III: Gravitational Wave Detection Rates

The unprecedented range of second-generation gravitational-wave (GW) observatories calls for refining the predictions of potential sources and detection rates. The coalescence of double compact objects (DCOs)---i.e., neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black hole-black hole (BH-BH) binary systems---is the most promising source of GWs for these detectors. We compute detection rates of coalescing DCOs in second-generation GW detectors using the latest models for their cosmological evolution, and implementing inspiral-merger-ringdown (IMR) gravitational waveform models in our signal-to-noise ratio calculations. We find that: (1) the inclusion of the merger/ringdown portion of the signal does not significantly affect rates for NS-NS and BH-NS systems, but it boosts rates by a factor $\sim 1.5$ for BH-BH systems; (2) in almost all of our models BH-BH systems yield by far the largest rates, followed by NS-NS and BH-NS systems, respectively, and (3) a majority of the detectable BH-BH systems were formed in the early Universe in low-metallicity environments. We make predictions for the distributions of detected binaries and discuss what the first GW detections will teach us about the astrophysics underlying binary formation and evolution.Comment: published in ApJ, 19 pages, 11 figure