Simulations of early universe phase transitions and gravitational waves

Upcoming space based gravitational wave observatories like the Laser Interferometer Space Antenna (LISA) will provide a new window into early universe physics. While the results from ground-based detectors have largely concerned astrophysical objects such as black holes and neutron stars, future space-based gravitational wave observatories will be able to observe far earlier times in the history of the universe than are directly accessible through the electromagnetic spectrum. LISA in particular will be sensitive to the detection of a stochastic gravitational wave background from a first-order cosmological phase transition around the electroweak scale. In cosmological phase transitions, an e↵ective scalar field passes from a false vacuum state to the true vacuum. If the transition is first-order, this occurs through the nucleation of bubbles of the true vacuum. These bubbles expand and, upon collision, produce gravitational waves. The focus of this thesis is to better characterise the gravitational wave signal from a first-order phase transition using numerical simulations. Within this thesis, I study both vacuum and thermal first-order phase transitions. In a vacuum phase transition, bubble walls accelerate to ultra-relativistic speeds. In this case, the gradients in the scalar field during bubble collisions form the dominant source of gravitational waves. I perform full 3D classical lattice field theory simulations, compute the gravitational wave signature and compare it to previously used techniques such as the envelope approximation. I further extend this work to investigate whether the shape of the e↵ective potential of the scalar field can a↵ect the final gravitational wave signal. In thermal phase transitions, the bubbles of the true vacuum nucleate in the presence of a relativistic plasma. As the bubbles expand, friction between the outward propagating bubble wall and the plasma causes shells of fluid to form around the bubble wall. The dominant source of gravitational waves from thermal transitions is shear-stress that remains in the fluid after the transition completes. While simulations of weak and intermediate strength phase transitions have been conducted, I perform the first 3D simulations of a strongly first-order phase transition and provide results for the generation of vorticity, formation of heated droplets, and the e↵ect that this has on the gravitational wave signal

Vorticity, Kinetic Energy, and Suppressed Gravitational-Wave Production in Strong First-Order Phase Transitions

We have performed the first three-dimensional simulations of strong first-order thermal phase transitions in the early universe. For deflagrations, we find that the rotational component of the fluid velocity increases as the transition strength is increased. For detonations, however, the rotational velocity component remains constant and small. We also find that the efficiency with which kinetic energy is transferred to the fluid falls below theoretical expectations as we increase the transition strength. The probable origin of the kinetic energy deficit is the formation of reheated droplets of the metastable phase during the collision, slowing the bubble walls. The rate of increase in the gravitational wave energy density for deflagrations in strong transitions is suppressed compared to that predicted in earlier work. This is largely accounted for by the reduction in kinetic energy. Current modeling therefore substantially overestimates the gravitational wave signal for strong transitions with deflagrations, in the most extreme case by a factor of 10(3). Detonations are less affected.Peer reviewe

Gravitational waves from vacuum first-order phase transitions. II. From thin to thick walls

In a vacuum first-order phase transition, gravitational waves are generated from collision of bubbles of the true vacuum. The spectrum from such collisions takes the form of a broken power law. We consider a toy model for such a phase transition, where the dynamics of the scalar field depends on a single parameter (lambda) over bar, which controls how thin the bubble wall is at nucleation and how close to degenerate the vacua are relative to the barrier. We extend on our previous work by performing a series of simulations with a range of (lambda) over bar. The peak of the gravitational-wave power spectrum varies by up to a factor of 1.3, which is probably an unobservable effect. We find that the UV power law in the gravitational-wave spectrum becomes steeper as (lambda) over bar -> 0, varying between k(-1.4) and k(-2.2) for the (lambda) over bar. considered. This provides some evidence that the form of the underlying effective potential of a vacuum first-order phase transition could be determined from the gravitational-wave spectrum it produces.Peer reviewe

Inverse folding for antibody sequence design using deep learning

We consider the problem of antibody sequence design given 3D structural information. Building on previous work, we propose a fine-tuned inverse folding model that is specifically optimised for antibody structures and outperforms generic protein models on sequence recovery and structure robustness when applied on antibodies, with notable improvement on the hypervariable CDR-H3 loop. We study the canonical conformations of complementarity-determining regions and find improved encoding of these loops into known clusters. Finally, we consider the applications of our model to drug discovery and binder design and evaluate the quality of proposed sequences using physics-based methods.Comment: 2023 ICML Workshop on Computational Biology, model weights available at https://zenodo.org/record/816469

A window on reality: perceiving edited moving images

Edited moving images entertain, inform, and coerce us throughout our daily lives, yet until recently, the way people perceive movies has received little psychological attention. We review the history of empirical investigations into movie perception and the recent explosion of new research on the subject using methods such as behavioral experiments, functional magnetic resonance imagery (fMRI) eye tracking, and statistical corpus analysis. The Hollywood style of moviemaking, which permeates a wide range of visual media, has evolved formal conventions that are compatible with the natural dynamics of attention and humans’ assumptions about continuity of space, time, and action. Identifying how people overcome the sensory differences between movies and reality provides an insight into how the same cognitive processes are used to perceive continuity in the real world

East Bay Coalition for the Homeless: Branding Study and Marketing Strategy

There are a number of potential positioning strategies. The two which make the most sense for the EBCH are to “position the EBCH away from others in the category” and to “position the EBCH as unique.” These strategies have the advantage of setting the EBCH apart from the other organizations that address homelessness. Occupying its own “position” in the minds of potential and current donors is not only an effective communications/marketing strategy but also a less costly one because it avoids head-to-head competition and comparisons

Study protocol : E-freeze-freezing of embryos in assisted conception: A randomised controlled trial evaluating the clinical and cost effectiveness of a policy of freezing embryos followed by thawed frozen embryo transfer compared with a policy of fresh embryo transfer, in women undergoing in vitro fertilisation

Acknowledgements The E-Freeze Collaborators Group contributed to the overall design of the E-Freeze trial. Funding The trial is approved and funded by the National Institute of Health Research (NIHR) Health Technology Assessment (HTA) programme. Availability of data and materials Applications for data sharing should be made to the NPEU CTU, using [email protected], with an accompanying protocol for the intended use of the data. This will be reviewed by the Trial Steering Committee if still operational or Data Sharing Committee/Data Controller. If approved, a Data Sharing Agreement will be compiled laying out the conditions to which the requestor must abide. Protocol E-Freeze Protocol, Version 2.0 (18/01/2017). Author notes All authors contributed equally to this work.Peer reviewedPublisher PD

Development of a Training Knowledge Management System for the SERVIR Global Network

No abstract availabl

Physiological, hyaluronan-selected intracytoplasmic sperm injection for infertility treatment (HABSelect): a parallel, two-group, randomised trial

Background Sperm selection strategies aimed at improving success rates of intracytoplasmic sperm injection (ICSI) include binding to hyaluronic acid (herein termed hyaluronan). Hyaluronan-selected sperm have reduced levels of DNA damage and aneuploidy. Use of hyaluronan-based sperm selection for ICSI (so-called physiological ICSI [PICSI]) is reported to reduce the proportion of pregnancies that end in miscarriage. However, the effect of PICSI on livebirth rates is uncertain. We aimed to investigate the efficacy of PICSI versus standard ICSI for improving livebirth rates among couples undergoing fertility treatment. Methods This parallel, two-group, randomised trial included couples undergoing an ICSI procedure with fresh embryo transfer at 16 assisted conception units in the UK. Eligible women (aged 18–43 years) had a body-mass index of 19–35 kg/m2 and a follicle-stimulating hormone (FSH) concentration of 3·0–20·0 mIU/mL or, if no FSH measurement was available, an anti-müllerian hormone concentration of at least 1·5 pmol/L. Eligible men (aged 18–55 years) had not had a vasovasostomy or been treated for cancer in the 24 months before recruitment and were able, after at least 3 days of sexual abstinence, to produce freshly ejaculated sperm for the treatment cycle. Couples were randomly assigned (1:1) with an online system to receive either PICSI or a standard ICSI procedure. The primary outcome was full-term (?37 weeks' gestational age) livebirth, which was assessed in all eligible couples who completed follow-up. This trial is registered, number ISRCTN99214271. Findings Between Feb 1, 2014, and Aug 31, 2016, 2772 couples were randomly assigned to receive PICSI (n=1387) or ICSI (n=1385), of whom 2752 (1381 in the PICSI group and 1371 in the ICSI group) were included in the primary analysis. The term livebirth rate did not differ significantly between PICSI (27·4% [379/1381]) and ICSI (25·2% [346/1371]) groups (odds ratio 1·12, 95% CI 0·95–1·34; p=0·18). There were 56 serious adverse events in total, including 31 in the PICSI group and 25 in the ICSI group; most were congenital abnormalities and none were attributed to treatment. Interpretation Compared with ICSI, PICSI does not significantly improve term livebirth rates. The wider use of PICSI, therefore, is not recommended at present

Movement Timing and Invariance Arise from Several Geometries

Human movements show several prominent features; movement duration is nearly independent of movement size (the isochrony principle), instantaneous speed depends on movement curvature (captured by the 2/3 power law), and complex movements are composed of simpler elements (movement compositionality). No existing theory can successfully account for all of these features, and the nature of the underlying motion primitives is still unknown. Also unknown is how the brain selects movement duration. Here we present a new theory of movement timing based on geometrical invariance. We propose that movement duration and compositionality arise from cooperation among Euclidian, equi-affine and full affine geometries. Each geometry posses a canonical measure of distance along curves, an invariant arc-length parameter. We suggest that for continuous movements, the actual movement duration reflects a particular tensorial mixture of these canonical parameters. Near geometrical singularities, specific combinations are selected to compensate for time expansion or compression in individual parameters. The theory was mathematically formulated using Cartan's moving frame method. Its predictions were tested on three data sets: drawings of elliptical curves, locomotion and drawing trajectories of complex figural forms (cloverleaves, lemniscates and limaçons, with varying ratios between the sizes of the large versus the small loops). Our theory accounted well for the kinematic and temporal features of these movements, in most cases better than the constrained Minimum Jerk model, even when taking into account the number of estimated free parameters. During both drawing and locomotion equi-affine geometry was the most dominant geometry, with affine geometry second most important during drawing; Euclidian geometry was second most important during locomotion. We further discuss the implications of this theory: the origin of the dominance of equi-affine geometry, the possibility that the brain uses different mixtures of these geometries to encode movement duration and speed, and the ontogeny of such representations