Quantum Fluxes at the Inner Horizon of a Spinning Black Hole

Rotating or charged classical black holes in isolation possess a special surface in their interior, the Cauchy horizon, beyond which the evolution of spacetime (based on the equations of General Relativity) ceases to be deterministic. In this Letter, we study the effect of a quantum massless scalar field on the Cauchy horizon inside a rotating (Kerr) black hole that is evaporating via the emission of Hawking radiation (corresponding to the field being in the Unruh state). We calculate the flux components (in Eddington coordinates) of the renormalized stress-energy tensor of the field on the Cauchy horizon, as functions of the black hole spin and of the polar angle. We find that these flux components are generically nonvanishing. Furthermore, we find that the flux components change sign as these parameters vary. The signs of the fluxes are important, as they provide an indication of whether the Cauchy horizon expands or crushes (when backreaction is taken into account). Regardless of these signs, our results imply that the flux components generically diverge on the Cauchy horizon when expressed in coordinates which are regular there. This is the first time that irregularity of the Cauchy horizon under a semiclassical effect is conclusively shown for (four-dimensional) spinning black holes.

Filling gaps in trustworthy development of AI

[Figure: see text].

P4Pi

High level, network programming languages, like P4, enable students to gain hands-on experience in the structure of a switch or router. Students can implement the packet processing pipeline themselves, without prior knowledge of circuit design. However, when choosing a P4 programmable target for use in the classroom, instructors face a lack of options. On the one hand, software solutions, such as the behavioral model (BMv2) switch, are overly simplified and offer low performance. On the other hand, existing hardware solutions are closed source and expensive.

In this paper, we present P4Pi, a new, low-cost, open-source hardware platform intended for networking education. P4Pi allows students to design and deploy P4-based network devices using the Raspberry Pi board, which has a price tag of less than many academic textbooks. We describe the high-level design of the P4Pi platform, offer some suggestions for how P4Pi could be used in the classroom, and present some additional use-cases for applications and functionality that could be developed using P4Pi.

An Artifact Evaluation of NDP

Artifact badging aims to rank the quality of submitted research artifacts and promote reproducibility. However, artifact badging may not indicate inherent design and evaluation limitations.

This work explores current limits in artifact badging using a performance-based evaluation of the NDP artifact. We evaluate the NDP artifact beyond the Reusable badge's level, investigating the effect of aspects such as packet size and random-number seed on throughput and flow completion time.

Our evaluation demonstrates that while the NDP artifact is reusable, it is not robust, and we identify architectural, implementation and evaluation limitations.

Thoughts about Artifact Badging

Reproducibility: the extent to which consistent results are obtained when an experiment is repeated, is important as a means to validate experimental results, promote integrity of research, and accelerate follow up work. Commitment to artifact reviewing and badging seeks to promote reproducibility and rank the quality of submitted artifacts.

However, as illustrated in this issue, the current badging scheme, with its focus upon an artifact being reusable, may not identify limitations of architecture, implementation, or evaluation.

We propose that to improve the insight into artifact reproducibility, the depth and nature of artifact evaluation must move beyond simply considering if an artifact is reusable. Artifact evaluation should consider the methods of that evaluation alongside the varying of inputs to that evaluation. To achieve this, we suggest an extension to the scope of artifact badging, and describe both approaches and best practice arising in other communities. We seek to promote conversation and make a call to action intended to strengthen the scientific method within our domain.

Quantum Fluxes at the Inner Horizon of a Spherical Charged Black Hole

In an ongoing effort to explore quantum effects on the interior geometry of black holes, we explicitly compute the semiclassical flux components ⟨T_{uu}⟩_{ren} and ⟨T_{vv}⟩_{ren} (u and v being the standard Eddington coordinates) of the renormalized stress-energy tensor for a minimally coupled massless quantum scalar field, in the vicinity of the inner horizon (IH) of a Reissner-Nordström black hole. These two flux components seem to dominate the effect of backreaction in the IH vicinity, and furthermore, their regularization procedure reveals remarkable simplicity. We consider the Hartle-Hawking and Unruh quantum states, the latter corresponding to an evaporating black hole. In both quantum states, we compute ⟨T_{uu}⟩_{ren} and ⟨T_{vv}⟩_{ren} in the IH vicinity for a wide range of Q/M values. We find that both ⟨T_{uu}⟩_{ren} and ⟨T_{vv}⟩_{ren} attain finite asymptotic values at the IH. Depending on Q/M, these asymptotic values are found to be either positive or negative (or vanishing in between). Note that having a nonvanishing ⟨T_{vv}⟩_{ren} at the IH implies the formation of a curvature singularity on its ingoing section, the Cauchy horizon. Motivated by these findings, we also take initial steps in the exploration of the backreaction effect of these semiclassical fluxes on the near-IH geometry.

From photons to big-data applications: terminating terabits

Computer architectures have entered a watershed as the quantity of network data generated by user applications exceeds the data-processing capacity of any individual computer end-system. It will become impossible to scale existing computer systems while a gap grows between the quantity of networked data and the capacity for per system data processing. Despite this, the growth in demand in both task variety and task complexity continues unabated. Networked computer systems provide a fertile environment in which new applications develop. As networked computer systems become akin to infrastructure, any limitation upon the growth in capacity and capabilities becomes an important constraint of concern to all computer users. Considering a networked computer system capable of processing terabits per second, as a benchmark for scalability, we critique the state of the art in commodity computing, and propose a wholesale reconsideration in the design of computer architectures and their attendant ecosystem. Our proposal seeks to reduce costs, save power and increase performance in a multi-scale approach that has potential application from nanoscale to data-centre-scale computers.

Genome-scan analysis for quantitative trait loci in an F2 tilapia hybrid

We searched for genetic linkage between DNA markers and quantitative trait loci (QTLs) for innate immunity, response to stress, biochemical parameters of blood, and fish size in an F2 population derived from an interspecific tilapia hybrid (Oreochromis mossambicusx O. aureus). A family of 114 fish was scanned for 40 polymorphic microsatellite DNA markers and two polymorphic genes, covering approximately 80% of the tilapia genome. These fish had previously been phenotyped for seven immune-response traits and six blood parameters. Critical values for significance were P <0.05 with the false discovery rate (FDR) controlled at 40%. The genome-scan analysis resulted in 35 significant marker-trait associations, involving 26 markers in 16 linkage groups. In a second experiment, nine markers were re-sampled in a second family of 79 fish of the same species hybrid. Seven markers (GM180, GM553, MHC-I, UNH848, UNH868, UNH898 and UNH925) in five linkage groups (LG 1, 3, 4, 22 and 23) were associated with stress response traits. An additional six markers (GM47, GM552, UNH208, UNH881, UNH952, UNH998) in five linkage groups (LG 4, 16, 19, 20 and 23) were verified for their associations with immune response traits, by linkage to several different traits. The portion of variance explained by each QTL was 11% on average, with a maximum of 29%. The average additive effect of QTLs was 0.2 standard deviation units of stress response traits and fish size, with a maximum of 0.33. In three linkage groups (LG 1, 3 and 23) markers were associated with stress response, body weight and sex determination, confirming the location of QTLs reported by several other studies.