arXiv subjects

Noa Zilberman

Publications and source records attributed to Noa Zilberman.

23 records · Page 2Linked to original sources

arXiv2017

The rotational shear in pre-collapse cores of massive stars

We evolve stellar models to study the rotational profiles of the pre-explosion cores of single massive stars that are progenitors of core collapse supernovae (CCSNe), and find large rotational shear above the iron core that might play an important role in the jet feedback explosion mechanism by amplifying magnetic fields before and after collapse. Initial masses of 15 Mo and 30 Mo and various values of the initial rotation velocity are considered, as well as a reduced mass-loss rate along the evolution and the effect of core-envelope coupling through magnetic fields. We find that the rotation profiles just before core collapse differ between models, but share the following properties. (1) There are narrow zones of very large rotational shear adjacent to convective zones. (2) The rotation rate of the inner core is slower than required to form a Keplerian accretion disk. (3) The outer part of the core and the envelope have non-negligible specific angular momentum compared to the last stable orbit around a black hole (BH). Our results suggest the feasibility of magnetic field amplification which might aid a jet-driven explosion leaving behind a neutron star. Alternatively, if the inner core fails in exploding the star, an accretion disk from the outer parts of the core might form and lead to a jet-driven CCSN which leaves behind a BH.

astro-ph.SR↗

arXiv2017

Extending programs with debug-related features, with application to hardware development

The capacity and programmability of reconfigurable hardware such as FPGAs has improved steadily over the years, but they do not readily provide any mechanisms for monitoring or debugging running programs. Such mechanisms need to be written into the program itself. This is done using ad hoc methods and primitive tools when compared to CPU programming. This complicates the programming and debugging of reconfigurable hardware. We introduce Program-hosted Directability (PhD), the extension of programs to interpret direction commands at runtime to enable debugging, monitoring and profiling. Normally in hardware development such features are fixed at compile time. We present a language of directing commands, specify its semantics in terms of a simple controller that is embedded with programs, and implement a prototype for directing network programs running in hardware. We show that this approach affords significant flexibility with low impact on hardware utilisation and performance.

cs.PL↗

arXiv2016

Prototyping RISC Based, Reconfigurable Networking Applications in Open Source

In the last decade we have witnessed a rapid growth in data center systems, requiring new and highly complex networking devices. The need to refresh networking infrastructure whenever new protocols or functions are introduced, and the increasing costs that this entails, are of a concern to all data center providers. New generations of Systems on Chip (SoC), integrating microprocessors and higher bandwidth interfaces, are an emerging solution to this problem. These devices permit entirely new systems and architectures that can obviate the replacement of existing networking devices while enabling seamless functionality change. In this work, we explore open source, RISC based, SoC architectures with high performance networking capabilities. The prototype architectures are implemented on the NetFPGA-SUME platform. Beyond details of the architecture, we also describe the hardware implementation and the porting of operating systems to the platform. The platform can be exploited for the development of practical networking appliances, and we provide use case examples.

cs.AR↗

arXiv2016

Setting the Foundations for PoP-Based Internet Evolution Models

Developing an evolution model of the Internet has been a long standing research challenge. Such a model can improve the design and placement of communication infrastructure, reducing costs and improving users' quality of experience. While communication infrastructure is tightly coupled to geographical locations, Internet modelling and forecasting in the last decade used network elements that are only loosely bounded to any geographical location. In this paper we set the foundations for developing an evolution model of the Internet based on the Point of Presence (PoP) level. As PoPs have a strong geographical grip they can better represent the evolution of the Internet. We annotate the PoP topologies of the Internet with geographical, economic and demographic information to achieve an understanding of the dynamics of the Internet's structure, in order to identify the constitutive laws of Internet evolution. We identify GDP as the strongest indicator on the country level, and the size of the TV market as the strongest indicator on the US metropolitan level. Finally, we draw attention to the limitations of developing a world-wide evolution model.

cs.NI↗

arXiv2010

A Study of Geolocation Databases

The geographical location of Internet IP addresses has an importance both for academic research and commercial applications. Thus, both commercial and academic databases and tools are available for mapping IP addresses to geographic locations. Evaluating the accuracy of these mapping services is complex since obtaining diverse large scale ground truth is very hard. In this work we evaluate mapping services using an algorithm that groups IP addresses to PoPs, based on structure and delay. This way we are able to group close to 100,000 IP addresses world wide into groups that are known to share a geo-location with high confidence. We provide insight into the strength and weaknesses of IP geolocation databases, and discuss their accuracy and encountered anomalies.

cs.NI↗