On April 1st, 2019, the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO), joined by the Advanced Virgo detector, began the third observing run, a year-long dedicated search for ...gravitational radiation. The LIGO detectors have achieved a higher duty cycle and greater sensitivity to gravitational waves than ever before, with LIGO Hanford achieving angle-averaged sensitivity to binary neutron star coalescences to a distance of 111 Mpc, and LIGO Livingston to 134 Mpc with duty factors of 74.6% and 77.0% respectively. The improvement in sensitivity and stability is a result of several upgrades to the detectors, including doubled intracavity power, the addition of an in-vacuum optical parametric oscillator for squeezed-light injection, replacement of core optics and end reaction masses, and installation of acoustic mode dampers. This paper explores the purposes behind these upgrades, and explains to the best of our knowledge the noise currently limiting the sensitivity of each detector.
The measurement of minuscule forces and displacements with ever greater precision is inhibited by the Heisenberg uncertainty principle, which imposes a limit to the precision with which the position ...of an object can be measured continuously, known as the standard quantum limit
. When light is used as the probe, the standard quantum limit arises from the balance between the uncertainties of the photon radiation pressure applied to the object and of the photon number in the photoelectric detection. The only way to surpass the standard quantum limit is by introducing correlations between the position/momentum uncertainty of the object and the photon number/phase uncertainty of the light that it reflects
. Here we confirm experimentally the theoretical prediction
that this type of quantum correlation is naturally produced in the Laser Interferometer Gravitational-wave Observatory (LIGO). We characterize and compare noise spectra taken without squeezing and with squeezed vacuum states injected at varying quadrature angles. After subtracting classical noise, our measurements show that the quantum mechanical uncertainties in the phases of the 200-kilowatt laser beams and in the positions of the 40-kilogram mirrors of the Advanced LIGO detectors yield a joint quantum uncertainty that is a factor of 1.4 (3 decibels) below the standard quantum limit. We anticipate that the use of quantum correlations will improve not only the observation of gravitational waves, but also more broadly future quantum noise-limited measurements.
The Advanced LIGO detectors have recently completed their second observation run successfully. The run lasted for approximately 10 months and led to multiple new discoveries. The sensitivity to ...gravitational waves was partially limited by laser noise. Here, we utilize auxiliary sensors that witness these correlated noise sources, and use them for noise subtraction in the time domain data. This noise and line removal is particularly significant for the LIGO Hanford Observatory, where the improvement in sensitivity is greater than 20%. Consequently, we were also able to improve the astrophysical estimation for the location, masses, spins, and orbital parameters of the gravitational wave progenitors.
Quantum noise imposes a fundamental limitation on the sensitivity of interferometric gravitational-wave detectors like LIGO, manifesting as shot noise and quantum radiation pressure noise. Here, we ...present the first realization of frequency-dependent squeezing in full-scale gravitational-wave detectors, resulting in the reduction of both shot noise and quantum radiation pressure noise, with broadband detector enhancement from tens of hertz to several kilohertz. In the LIGO Hanford detector, squeezing reduced the detector noise amplitude by a factor of 1.6 (4.0 dB) near 1 kHz; in the Livingston detector, the noise reduction was a factor of 1.9 (5.8 dB). These improvements directly impact LIGO’s scientific output for high-frequency sources (e.g., binary neutron star postmerger physics). The improved low-frequency sensitivity, which boosted the detector range by 15%–18% with respect to no squeezing, corresponds to an increase in the astrophysical detection rate of up to 65%. Frequency-dependent squeezing was enabled by the addition of a 300-meter-long filter cavity to each detector as part of the LIGO A+ upgrade.
Abstract To review research examining the influence of “connectedness” on adolescent sexual and reproductive health (ASRH). Connectedness, or bonding, refers to the emotional attachment and ...commitment a child makes to social relationships in the family, peer group, school, community, or culture. A systematic review of behavioral research (1985–2007) was conducted. Inclusion criteria included examination of the association between a connectedness sub-construct and an ASRH outcome, use of multivariate analyses, sample size of ≥100, and publication in a peer-reviewed journal. Results were coded as protective, risk, or no association, and as longitudinal, or cross sectional. Findings from at least two longitudinal studies for a given outcome with consistent associations were considered sufficient evidence for a protective or risk association. Eight connectedness sub-constructs were reviewed: family connectedness (90 studies), parent–adolescent general communication (16 studies), parent–adolescent sexuality communication (58 studies), parental monitoring (61 studies), peer connectedness (nine studies), partner connectedness (12 studies), school connectedness (18 studies), and community connectedness (four studies). There was sufficient evidence to support a protective association with ASRH outcomes for family connectedness, general and sexuality-specific parent–adolescent communication, parental monitoring, partner connectedness, and school connectedness. Sufficient evidence of a risk association was identified for the parent overcontrol sub-construct of parental monitoring. Connectedness can be a protective factor for ASRH outcomes, and efforts to strengthen young people's pro-social relationships are a promising target for approaches to promote ASRH. Further study regarding specific sub-constructs as well as their combined influence is needed.
The G-rich single-stranded DNA at the 3′ end of human telomeres can self-fold into G-quaduplex (GQ). However, telomere lengthening by telomerase or the recombination-based alternative lengthening of ...telomere (ALT) mechanism requires protein loading on the overhang. Using single-molecule fluorescence spectroscopy, we discovered that lengthening the telomeric overhang also increased the rate of dynamic exchanges between structural conformations. Overhangs with five to seven TTAGGG repeats, compared with four repeats, showed much greater dynamics and accessibility to telomerase binding and activity and loading of the ALT-associated proteins RAD51, WRN, and BLM. Although the eight repeats are highly dynamic, they can fold into two GQs, which limited protein accessibility. In contrast, the telomere-specific protein POT1 is unique in that it binds independently of repeat number. Our results suggest that the telomeric overhang length and dynamics may contribute to the regulation of telomere extension via telomerase action and the ALT mechanism.
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•Telomeric overhang exhibits dynamic behavior when greater than four TTAGGG repeats•Four and eight repeats yield low accessibility to WRN, BLM, Rad51, and telomerase•Five to seven repeats yield increased accessibility to loading of the same proteins•POT1 binds all repeat lengths proficiently, suggesting an active disruption of GQ
The possible G-quadruplex formation at the end of human telomeres may hinder loading of proteins. Hwang et al. show that the length of TTAGGG repeats modulates accessibility of telomerase and the alternative lengthening of telomere (ALT)-associated proteins.
ABSTRACT
BACKGROUND
Whereas dating violence among high school students has been linked with sexual risk‐taking and substance use, this association has been understudied among early adolescents. We ...estimated the prevalence of physical and nonphysical dating violence in a sample of middle school students and examined associations between dating violence, sexual, and substance use behaviors.
METHODS
Logistic regression models for clustered data from 7th grade students attending 10 Texas urban middle schools were used to examine cross‐sectional associations between dating violence victimization and risk behaviors.
RESULTS
The sample (N = 950) was 48.5% African American, 36.0% Hispanic, 55.7% female, mean age 13.1 years (SD 0.64). About 1 in 5 reported physical dating violence victimization, 48.1% reported nonphysical victimization, and 52.6% reported any victimization. Adjusted logistic regression analyses indicated that physical, nonphysical, and any victimization was associated with ever having sex, ever using alcohol, and ever using drugs.
CONCLUSIONS
Over 50% of sampled middle school students had experienced dating violence, which may be associated with early sexual initiation and substance use. Middle school interventions that prevent dating violence are needed.
Abstract
Dominance hierarchies can provide many benefits to individuals, such as access to resources or mates, depending on their ranks. In some species, rank can emerge as a product of a group’s ...history of social interactions. However, it can be difficult to determine whether social history is critical to rank in observation-based studies. Here, we investigated rank dynamics in three captive groups of monk parakeets (Myiopsitta monachus). We used experimental social perturbations to test whether social history shapes rank emergence in these groups. Using targeted removals and reintroductions, we tested whether differently ranked individuals could re-take their ranks in hierarchies after reintroduction following their removal period from the group. We performed perturbations that consisted of an 8-day removal and an 8-day reintroduction period of 15 differently ranked focal birds. We found that no focal birds could regain their previous rank immediately following reintroduction and that the top-ranked birds showed greater relative rank loss than middle/low-ranked birds. We also found that morphology, specifically bodyweight, was unassociated with rank. Combined with previous results, this experiment supports the hypothesis that rank in monk parakeet dominance hierarchies is more likely to be an emergent outcome of past interactions and memory rather than based on individual characteristics. Gaining a better understanding of how individuals achieve and maintain rank can give insight into the role of cognition on rank acquisition, as rank position can have significant biological effects on individuals in hierarchically structured groups.
Dominance rank can influence many aspects of an individual’s biology, but the factors that determine rank can vary widely across species. We manipulated group membership to determine whether rank is the product of a group’s social history (memory of past interactions) in captive monk parakeets. After reintroducing removed individuals, no removed bird could immediately re-take their rank, and bodyweight did not correlate with rank. Our results provide support that social history shapes rank in monk parakeets.
Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the ...optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher-order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15 538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electrostatic actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nN was required to maintain the acoustic mode at its minimum amplitude.
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