Solid State Physics

Contains reports on two research projects

Low Temperature Physics

Contains reports on one research project

First Long-Term Application of Squeezed States of Light in a Gravitational-Wave Observatory

We report on the first long-term application of squeezed vacuum states of light to improve the shot-noise-limited sensitivity of a gravitational-wave observatory. In particular, squeezed vacuum was applied to the German/British detector GEO600 during a period of three months from June to August 2011, when GEO600 was performing an observational run together with the French/Italian Virgo detector. In a second period squeezing application continued for about 11 months from November 2011 to October 2012. During this time, squeezed vacuum was applied for 90.2% (205.2 days total) of the time that science-quality data was acquired with GEO600. Sensitivity increase from squeezed vacuum application was observed broad-band above 400Hz. The time average of gain in sensitivity was 26% (2.0dB), determined in the frequency band from 3.7kHz to 4.0kHz. This corresponds to a factor of two increase in observed volume of the universe, for sources in the kHz region (e.g. supernovae, magnetars). We introduce three new techniques to enable stable long-term application of squeezed light, and show that the glitch-rate of the detector did not increase from squeezing application. Squeezed vacuum states of light have arrived as a permanent application, capable of increasing the astrophysical reach of gravitational-wave detectors.Comment: 4 pages, 4 figure

Cost-benefit analysis for commissioning decisions in GEO600

Gravitational wave interferometers are complex instruments, requiring years of commissioning to achieve the required sensitivities for the detection of gravitational waves, of order 10^-21 in dimensionless detector strain, in the tens of Hz to several kHz frequency band. Investigations carried out by the GEO600 detector characterisation group have shown that detector characterisation techniques are useful when planning for commissioning work. At the time of writing, GEO600 is the only large scale laser interferometer currently in operation running with a high duty factor, 70%, limited chiefly by the time spent commissioning the detector. The number of observable gravitational wave sources scales as the product of the volume of space to which the detector is sensitive and the observation time, so the goal of commissioning is to improve the detector sensitivity with the least possible detector down time. We demonstrate a method for increasing the number of sources observable by such a detector, by assessing the severity of non-astrophysical noise contaminations to efficiently guide commissioning. This method will be particularly useful in the early stages and during the initial science runs of the aLIGO and adVirgo detectors, as they are brought up to design performance.Comment: 17 pages, 17 figures, 2 table

GEO 600 and the GEO-HF upgrade program: successes and challenges

The German-British laser-interferometric gravitational wave detector GEO 600 is in its 14th year of operation since its first lock in 2001. After GEO 600 participated in science runs with other first-generation detectors, a program known as GEO-HF began in 2009. The goal was to improve the detector sensitivity at high frequencies, around 1 kHz and above, with technologically advanced yet minimally invasive upgrades. Simultaneously, the detector would record science quality data in between commissioning activities. As of early 2014, all of the planned upgrades have been carried out and sensitivity improvements of up to a factor of four at the high-frequency end of the observation band have been achieved. Besides science data collection, an experimental program is ongoing with the goal to further improve the sensitivity and evaluate future detector technologies. We summarize the results of the GEO-HF program to date and discuss its successes and challenges

Interplay between geometry and flow distribution in an airway tree

Uniform fluid flow distribution in a symmetric volume can be realized through a symmetric branched tree. It is shown here, however, that the flow partitioning can be highly sensitive to deviations from exact symmetry if inertial effects are present. This is found by direct numerical simulation of the Navier-Stokes equations in a 3D tree geometry. The flow asymmetry is quantified and found to depend on the Reynolds number. Moreover, for a given Reynolds number, we show that the flow distribution depends on the aspect ratio of the branching elements as well as their angular arrangement. Our results indicate that physiological variability should be severely restricted in order to ensure uniform fluid distribution in a tree. This study suggests that any non-uniformity in the air flow distribution in human lungs should be influenced by the respiratory conditions, rest or hard exercise

Methods for Reducing False Alarms in Searches for Compact Binary Coalescences in LIGO Data

The LIGO detectors are sensitive to a variety of noise transients of non-astrophysical origin. Instrumental glitches and environmental disturbances increase the false alarm rate in the searches for gravitational waves. Using times already identified when the interferometers produced data of questionable quality, or when the channels that monitor the interferometer indicated non-stationarity, we have developed techniques to safely and effectively veto false triggers from the compact binary coalescences (CBCs) search pipeline

Patterns of Public Participation: Opportunity Structures and Mobilization from a Cross-National Perspective

PURPOSE: The paper summarizes data from twelve countries, chosen to exhibit wide variation, on the role and place of public participation in the setting of priorities. It seeks to exhibit cross-national patterns in respect of public participation, linking those differences to institutional features of the countries concerned. DESIGN/METHODOLOGY/APPROACH: The approach is an example of case-orientated qualitative assessment of participation practices. It derives its data from the presentation of country case studies by experts on each system. The country cases are located within the historical development of democracy in each country. FINDINGS: Patterns of participation are widely variable. Participation that is effective through routinized institutional processes appears to be inversely related to contestatory participation that uses political mobilization to challenge the legitimacy of the priority setting process. No system has resolved the conceptual ambiguities that are implicit in the idea of public participation. ORIGINALITY/VALUE: The paper draws on a unique collection of country case studies in participatory practice in prioritization, supplementing existing published sources. In showing that contestatory participation plays an important role in a sub-set of these countries it makes an important contribution to the field because it broadens the debate about public participation in priority setting beyond the use of minipublics and the observation of public representatives on decision-making bodies

Parenting and the Adjustment of Children Born to Gay Fathers Through Surrogacy

Findings are presented on a study of 40 gay father families created through surrogacy and a comparison group of 55 lesbian mother families created through donor insemination with a child aged 3–9 years. Standardized interview, observational and questionnaire measures of stigmatization, quality of parent–child relationships, and children's adjustment were administered to parents, children, and teachers. Children in both family types showed high levels of adjustment with lower levels of children's internalizing problems reported by gay fathers. Irrespective of family type, children whose parents perceived greater stigmatization and children who experienced higher levels of negative parenting showed higher levels of parent-reported externalizing problems. The findings contribute to theoretical understanding of the role of family structure and family processes in child adjustment.The research was supported by a Wellcome Trust Senior Investigator Award (097857/Z/11/Z)

Gay fathers’ motivations for and feelings about surrogacy as a path to parenthood

$\textbf{STUDY QUESTION}$ Why do gay men choose to start their families through surrogacy? $\textbf{SUMMARY ANSWER}$ Most fathers chose surrogacy because they considered adoption to be a less desirable and/or accessible path to parenthood. $\textbf{WHAT IS KNOWN ALREADY}$ Little is known of gay fathers’ motivations to use surrogacy as a path to parenthood over and above other forms of family building, such as adoption, and no studies have examined fathers’ satisfaction with the surrogacy process. $\textbf{STUDY DESIGN, SIZE, DURATION}$ This study used a cross-sectional design as part of a larger investigation of parent–child relationships and child adjustment in 40 gay father surrogacy families. Multiple strategies (e.g. surrogacy agencies, social events and snowballing) were used to recruit as diverse a sample as possible. Data were obtained from 74 fathers (in 6 families only 1 father was available for interview). $\textbf{PARTICIPANTS/MATERIALS, SETTING, METHOD}$ Semi-structured interviews, lasting ~1 h, were conducted in the family home (65%) or over Skype (35%) with 74 gay fathers (35 genetic fathers, 32 non-genetic fathers and 7 fathers who did not know or did not disclose who the genetic father was), when the children were 3–9 years old. $\textbf{MAIN RESULTS AND THE ROLE OF CHANCE}$ Genetic and non-genetic fathers were just as likely to want to become parents and had similar motivations for choosing surrogacy as a path to parenthood. Most fathers ($\textit{N}$ = 55, 74%) were satisfied with surrogacy and were satisfied ($\textit{N}$ = 31. 42%) or had neutral feelings ($\textit{N}$ = 21, 28%) about their choice of who would be the genetic father. Most fathers received supportive reactions to their decision to use surrogacy from both families of origin (e.g. parents, siblings) ($\textit{N}$ = 47, 64%) and from friends ($\textit{N}$ = 63, 85%). $\textbf{LIMITATIONS, REASONS FOR CAUTION}$ Although diverse recruitment strategies were used, data were obtained from a volunteer sample. Therefore, the possibility that fathers who had a positive surrogacy experience may have been more likely to participate in the study, and therefore introduce bias, cannot be ruled out. Due to the high average annual income of the fathers in the study, findings may not generalize to gay fathers with lower incomes. $\textbf{WIDER IMPLICATIONS OF THE FINDINGS}$ It is often assumed that parents’ primary motivation for using ART is to have a genetic connection to the child. This study revealed that whilst genetic fatherhood was important for some gay fathers in surrogacy families, it was not important for all. This information will be of use to surrogacy agencies and organizations supporting men who are considering the different routes to parenthood.Wellcome Trust [097857/Z/11/Z]; Jacob's Foundation