Niemeier Lattices in the Free Fermionic Heterotic-String Formulation

The spinor-vector duality was discovered in free fermionic constructions of the heterotic-string in four dimensions. It played a key role in the construction of heterotic-string models with an anomaly free extra $Z^\prime$ symmetry that may remain unbroken down to low energy scales. A generic signature of the low scale string derived $Z^\prime$ model is via di-photon excess that may be within reach of the LHC. A fascinating possibility is that the spinor-vector duality symmetry is rooted in the structure of the heterotic-string compactifications to two dimensions. The two dimensional heterotic-string theories are in turn related to the so-called moonshine symmetries that underlie the two dimensional compactifications. In this paper we embark on exploration of this connection by the free fermionic formulation to classify the symmetries of the two dimensional heterotic-string theories. We use two complementary approaches in our classification. The first utilises a construction which is akin to the one used in the spinor-vector duality. Underlying this method is the triality property of $SO(8)$ representations. In the second approach we use the free fermionic tools to classify the twenty four dimensional Niemeier lattices.Comment: 22 pages. Standard LaTex. 1 figure. Title changed in journal. Minor corrections. Published versio

Non-Tachyonic Semi-Realistic Non-Supersymmetric Heterotic String Vacua

The heterotic--string models in the free fermionic formulation gave rise to some of the most realistic string models to date, which possess N=1 spacetime supersymmetry. Lack of evidence for supersymmetry at the LHC instigated recent interest in non-supersymmetric heterotic-string vacua. We explore what may be learned in this context from the quasi--realistic free fermionic models. We show that constructions with a low number of families give rise to proliferation of a priori tachyon producing sectors, compared to the non--realistic examples, which typically may contain only one such sector. The reason being that in the realistic cases the internal six dimensional space is fragmented into smaller units. We present one example of a quasi--realistic, non--supersymmetric, non--tachyonic, heterotic--string vacuum and compare the structure of its massless spectrum to the corresponding supersymmetric vacuum. While in some sectors supersymmetry is broken explicitly, i.e. the bosonic and fermionic sectors produce massless and massive states, other sectors, and in particular those leading to the chiral families, continue to exhibit fermi-bose degeneracy. In these sectors the massless spectrum, as compared to the supersymmetric cases, will only differ in some local or global U(1) charges. We discuss the conditions for obtaining $n_b=n_f$ at the massless level in these models. Our example model contains an anomalous U(1) symmetry, which generates a tadpole diagram at one loop-order in string perturbation theory. We speculate that this tadpole diagram may cancel the corresponding diagram generated by the one-loop non-vanishing vacuum energy and that in this respect the supersymmetric and non-supersymmetric vacua should be regarded on equal footing. Finally we discuss vacua that contain two supersymmetry generating sectors.Comment: 31 pages. 10 tables. Minor corrections. Tables are amended. Published versio

How immersive virtual reality methods may meet the criteria of the National Academy of Neuropsychology and American Academy of Clinical Neuropsychology:A software review of the Virtual Reality Everyday Assessment Lab (VR-EAL)

International audienceClinical tools involving immersive virtual reality (VR) may bring several advantages to cognitive neuroscience and neuropsychology. However, there are some technical and methodological pitfalls. The American Academy of Clinical Neuropsychology (AACN) and the National Academy of Neuropsychology (NAN) raised 8 key issues pertaining to Computerized Neuropsychological Assessment Devices. These issues pertain to: (1) the safety and effectivity; (2) the identity of the end-user; (3) the technical hardware and software features; (4) privacy and data security; (5) the psychometric properties; (6) examinee issues; (7) the use of reporting services; and (8) the reliability of the responses and results. The VR Everyday Assessment Lab (VR-EAL) is the first immersive VR neuropsychological battery with enhanced ecological validity for the assessment of everyday cognitive functions by offering a pleasant testing experience without inducing cybersickness. The VR-EAL meets the criteria of the NAN and AACN, addresses the methodological pitfalls, and brings advantages for neuropsychological testing. However, there are still shortcomings of the VR-EAL, which should be addressed. Future iterations should strive to improve the embodiment illusion in VR-EAL and the creation of an open access VR software library should be attempted. The discussed studies demonstrate the utility of VR methods in cognitive neuroscience and neuropsychology

A Multifidelity deep operator network approach to closure for multiscale systems

Projection-based reduced order models (PROMs) have shown promise in representing the behavior of multiscale systems using a small set of generalized (or latent) variables. Despite their success, PROMs can be susceptible to inaccuracies, even instabilities, due to the improper accounting of the interaction between the resolved and unresolved scales of the multiscale system (known as the closure problem). In the current work, we interpret closure as a multifidelity problem and use a multifidelity deep operator network (DeepONet) framework to address it. In addition, to enhance the stability and accuracy of the multifidelity-based closure, we employ the recently developed "in-the-loop" training approach from the literature on coupling physics and machine learning models. The resulting approach is tested on shock advection for the one-dimensional viscous Burgers equation and vortex merging using the two-dimensional Navier-Stokes equations. The numerical experiments show significant improvement of the predictive ability of the closure-corrected PROM over the un-corrected one both in the interpolative and the extrapolative regimes.Comment: 24 pages, 21 figure

A systematic review and meta-analysis of systemic intraoperative anticoagulation during arteriovenous access formation for dialysis

Purpose: Surgical arteriovenous fistula (AVF) or graft (AVG) is preferred to a central venous catheter for dialysis access. Surgical access may suffer thrombosis early after placement and systemic anticoagulation during surgical access formation may increase patency rates but would be expected to increase bleeding-related complications. A systematic review and meta-analysis of randomised controlled trials was conducted to examine the impact of systemic anticoagulation on access surgery perioperative bleeding and patency rates. Methods: We included randomised controlled trials testing systemic anticoagulation during access formation versus a control group without systemic anticoagulation reporting bleeding complications and access patency. Medline, Embase, CENTRAL and CINAHL were searched up to March 2015. Risk of bias was assessed using the Cochrane risk of bias tool and the Jadad score. Meta-analysis was performed using Cochrane Revman ® software. Results: Searches identified 445 reports of which four randomised studies involving 411 participants were included. Three studies pertained to AVF only and one included both AVF and AVG. Systemic anticoagulation led to increased bleeding events in all access [four trials; risk ratio (RR) 7.18; confidence interval (CI), 2.41 to 21.38; p < 0.001]. Patency was not improved for all access (four trials; RR, 0.64; CI, 0.37 to 1.09; p = 0.10) but was improved when AVF analysed alone (three trials; RR, 0.57; CI, 0.33 to 0.97; p = 0.04). Conclusions: The use of intraoperative systemic anticoagulation during access formation is associated with a highly significant increased risk of bleeding-related complications. A significant improvement in AVF patency was seen, though not when AVF and AVG were analysed together