Space-time Time Research Articles

Replica wormhole and AMPS firewall

We investigate the potential for generating an AMPS firewall from the replica wormhole topology, which describes the post-Page time spacetime in the evaporation process of a black hole. Our analysis reveals that this topology gives rise to a Dirac delta force experienced by infalling particles at the event horizon, consistent with the AMPS firewall hypothesis. This force, proportional to the particle's total energy squared, is a direct consequence of the inherent Dirac delta in the Ricci scalar of the replica wormhole. We provide a regularization scheme for this force, which is crucial for obtaining physically meaningful results. Notably, our approach suggests that considering the replica wormhole resolves both the information paradox and the AMPS argument regarding the monogamy of entanglement simultaneously, yielding a more coherent framework.

Looking for Carroll particles in two time spacetime

We make an attempt to describe Carroll particles with a nonvanishing value of energy (i.e. the Carroll particles which always stay in rest) in the framework of two time physics, developed in the series of papers by I. Bars and his coauthors. In the spacetime with one additional time dimension and one additional space dimension one can localize the symmetry which exists between generalized coordinate and their conjugate momenta. Such a localization implies the introduction of the gauge fields, which in turn implies the appearance of some first-class constraints. Choosing different gauge-fixing conditions and solving the constraints one obtain different time parameters, Hamiltonians, and generally, physical systems in the standard one time spacetime. In this way such systems as nonrelativistic particle, relativistic particles, hydrogen atoms, and harmonic oscillators were described as dual systems in the framework of two time physics. Here, we find a set of gauge fixing conditions which provides as with such a parametrization of the phase-space variables in the two time world which gives the description of Carroll particle in the one time world. Besides, we construct the quantum theory of such a particle using an unexpected correspondence between our parametrization and that obtained by Bars for the hydrogen atom in 1999. Published by the American Physical Society 2024

Space-Time Correlated Sea Scattering Map Simulation Based on Statistical Model

In numerous researching fields involving sea scattering problems, the electromagnetic (EM) scattering model becomes a better alternative rather than a direct experiment due to its low cost and easy realization. Nevertheless, the EM scattering model still appears to be slow and laborious when encountering the large scene or the long time case. This letter proposes an effective and efficient approach for 3-D space-time correlated sea scattering map simulation, an important step in real clutter simulation, which is based on the statistical characteristics from the EM scattering model. Namely, this approach can give a fast simulation of the large scene or long time space-time correlated sea scattering map through the statistic characteristics of that with a small scene or short time acquired by the EM scattering model. From the comparisons of the texture feature and the statistical characteristics between the results derived from the EM model and the proposed approach, it is demonstrated that the proposed approach can give a fast and effective simulation of the 3-D space-time correlated sea scattering map.

New time-space-time optical packet switching node based on nonlinear polarization rotation of a semiconductor optical amplifier.

In this paper, we establish a simple model to analyze the semiconductor optical amplifier's (SOA) nonlinear polarization rotation (NPR) and acquire the variable curves of phase difference between TE and TM modes with bias current, pump power, probe power, and linewidth enhancement factor (LEF). The results indicate that the optical switch based on the SOA's NPR can be realized by changing the pump's optical power and the main operating parameters, such as bias current and hold beam power, and then the pump power can be determined. On this basis, a time-space-time (T-S-T) optical packet switching node is proposed, in which the SOA's NPR switch is the basic element. Then, the T-S and S-T experimental systems are set up, and the experimental results demonstrate that the proposed switch scheme can implement the optical switching function in accordance with the routing requirement. The signal-to-noise ratio (SNR) exceeds 20 dB, and the extinction ratio (ER) is more than 10 dB after being delayed and switched in the node.

Interconnect intellectual property for Network-on-Chip (NoC)

As technology scales down, the interconnect for on-chip global communication becomes the delay bottleneck. In order to provide well-controlled global wire delay and efficient global communication, a Network-on-Chip (NoC) architecture was proposed by different authors [Route packets, not wires: on-chip interconnection networks, in: Design Automation Conference, 2001, Proceedings, p. 684; Network on chip: an architecture for billion transistor era, in: Proceeding of the IEEE NorChip Conference, November 2000; Network on chip, in: Proceedings of the Conference Radio vetenskap och Kommunication, Stockholm, June 2002]. NoC uses Interconnect Intellectual Property (IIP) to connect different resources. Within an IIP, the switch has the central function. Depending on the network core of the NoC, the switch will have different architectures and implementations. This paper first briefly introduces the concept of NoC. It then studies NoC from an interconnect point of view and makes projections on future NoC parameters. At last, the IIP and its components are described, the switch is studied in more detail and a time-space-time (TST) switch designed for a circuit switched time-division multiplexing (TDM) NoC is proposed. This switch supports multicast traffic and is implemented with random access memory at the input and output. The input and output are then connected by a fully connected interconnect network.

Analysis of satellite on-board time-space-time switching networks with multiple separated space switches

Advanced satellite on-board baseband switching processors have time-space-time (T-S-T) structures which are similar to the terrestrial switching networks (Sw-Nw). Generally, the satellite systems require higher reliability than ground equipment because of more severe environment and lack of repair. This paper proposes fault-tolerant satellite on-board T-S-T Sw-Nw with multiple separated space switches instead of a single spare switch. The authors analyze the mean time to unreliable operation (MTUO), as a performance and reliability index for the T-S-T systems with multiple separated space switches as well as conventional T-S-T systems. The MTUO varies depending on the threshold level of blocking-probability and the offered traffic. In general, T-S-T Sw-Nw with multiple space switches have better performance and reliability than those with the single space switch, and their performabilities are appreciably improved, especially for one additional spare space switch. This study can be extended to analyze the performance and reliability of entire satellite communication systems including the on-board baseband Sw-Nw, Rx interfaces, and Tx interfaces.

Traffic analysis of large TST networks

The traffic performance of time-space-time (TST) switching networks built from large time-switching stages used in digital switching systems is discussed. These switching networks exhibit steep load-service characteristics and present new numerical problems for traffic performance evaluation. The precise numerical calculation of switch blocking and the amount of search effort needed to find a network path are addressed. Computational efficiency and robustness are emphasized. The approach is based on a familiar model that uses state-dependent transitions in formulating the balance equations. A comparative study with traditional methods illustrates the numerical gains to be made for switching networks of arbitrary size. >

Multichannel circuit switching-performance evaluation of switching networks

An approximate analytical method is presented for the estimation of the loss probability for single and multichannel calls in TST (time-space-time) switching networks. Two extended methods are described. The assumptions for the basic method are that: all occupation patterns of the two internal highways between a certain start and destination highway for a given number of occupied channels have the same probability, and that the state probabilities of the start and destination highway are given by a multidimensional Erlang distribution. Based on this method, the second approximation considers calls that are switched from start to destination highway. In a third method, the dependency of the states of all input and output highways is taken into account. The basic approximation has shown the best agreement with the simulation results. The other methods take into account additional properties of TST switching networks for single and multichannel connections. In order to keep the state space in a reasonable size, additional assumptions had to be used which impair the results significantly compared to the basic approximation method. >

A fast decoupled approach for optimum TDM assignment in constrained hierarchical switching systems

A three-tiered digital switching hierarchy is considered in which traffic from remote users is grouped, concentrated into time-multiplexed lines, and then transmitted to a central location for interconnection by a central space division switch. While the configuration provides efficient sharing of both transmission and switching resources, the TDM (time-division multiplexing) assignment problem for a conventional time-space-time (T-S-T) switch can become quite formidable due to the various hierarchical constraints. A time-slot assignment strategy is proposed that circumvents this problem by temporarily storing the incoming traffic at the central switch. Unlike the traditional T-S-T approach, the in-bound and out-bound assignments are entirely decoupled, which greatly simplifies the assignment process and produces a fast circuit switching capability. Necessary and sufficient conditions governing the assignability of traffic to the three-tiered switching system are stated and proved, and a block diagram of the proposed switching architecture is presented. >

Concurrent fault detection in TST switches for on-board satellite systems

The letter proposes a general fault model for a time-space-time (TST) switch and an error detection scheme. It is shown that many types of fault can be detected during normal operation of the switch by attaching a unique destination flag to the information field from each source.