Search

This work explains how the presence of a Type-IV singularity (a mild singularity) can influence the dynamics of a bouncing universe. In particular, we examine the bounce cosmology that appears with a Type-IV singularity in the context of a ghost-free Gauss–Bonnet theory of gravity. Depending on the time of occurrence of the Type-IV singularity, three different cases may arise— when the singularity occurs before the bounce, after the bounce, or at the instant of the bounce. However, in all of these cases, we find that in the case when the singularity “globally” affects the spacetime, the scalar power spectrum becomes red-tilted, and the tensor-to-scalar ratio is too large to be consistent with the observational data. Based on these findings, we investigate a different bouncing scenario which also appears with a Type-IV singularity, and wherein the singularity affects the spacetime “locally” around the time when it occurs. As a result, and unlike the previous scenario, the perturbation modes in the second bouncing scenario are likely to be generated far away from the bounce in the deep contracting phase. This finally results in the simultaneous compatibility of the observable quantities with the Planck data and ensures the viability of the bounce model where the Type-IV singularity has local effects on the spacetime around the time of the singularity., This work was supported in part by MINECO (Spain), project PID2019-104397GB-I00 (SDO). This work was partially supported by the program Unidad de Excelencia Maria de Maeztu CEX2020-001058-M. This research was also supported in part by the International Centre for Theoretical Sciences (ICTS) for the online program-Physics of the Early Universe (code: ICTS/peu2022/1) (TP).

This Special issue contains top-tier physics-related and mathematical research, among other topics, written by scholars who are well-known in their field [...]

This issue of featured papers from 2020 is related to the study of symmetry phenomena in various different fields, but mainly in theoretical physics [...]

With continually growing adoption of FPGA based designs, and more features and capabilities available in FPGAs, board and system level test applications can - and should - take advantage of FPGA embedded instrumentation. Such FPGA assisted tests not only improve manufacturing test but also allow extensive testing in the field to address issues such as no-fault-found syndrome by enabling the detection of environment-induced defects or latent defects (related to bad solder joint quality, aging, etc.). In this paper we are briefly reviewing different types of FPGA embedded instruments before specifically addressing synthetic instrumentation and focusing on example use cases. We will be discussing design for test considerations, quality of test and diagnostics, savings in test time and test cost, and levels of automation previously not associated with functional and performance / stress test development.

Nowadays, increasing demand for High-Performance Systems produces significant growth in usage of Field Programmable Gate Arrays (FPGAs) for different applications thanks to their flexibility and high level of parallelism. Such systems rely on complex multi-layer Printed Circuit Board Assemblies (PCBA)with a few dozens of hidden layers, stacked microvias and high-density interconnects. Along with creating new test challenges, the increasing PCBA complexity elevates the criticality of defects in various subsystems. One of such sub-systems is a Power-Delivery-Network (PDN) with operating margin progressively reduced due to increasingly strict requirements of High-Performance applications. As a consequence, Marginal Defects and process variations in a PDN may create latent problems that will manifest in a particular condition thus compromising the overall system performance and causing malfunctions. In this paper we propose a new FPGA-based non-intrusive method to detect Marginal Defects in a PCBA PDN. The method is based on a monitoring circuit that measures signal delays caused by PDN variations and thus detects relevant anomalies. Additional ad-hoc PDN stress circuits have been developed to validate the measurement technique. Experimental results demonstrating the consistency of the proposed approach are obtained by comparing stress and non-stress scenarios.

One of reasons for arising the statistical ambiguity is using in the course of reasoning laws which have probabilistic, but not logical justification. Carl Hempel supposed that one can avoid the statistical ambiguity if we will use in the probabilistic reasoning maximal specific probabilistic laws. In the present work we deal with laws of the form \(\varphi \Rightarrow \psi \), where \(\varphi \) and \(\psi \) are arbitrary propositional formulas. Given a probability on the set of formulas we define the notion of a maximal specific probabilistic law. Further, we define a prediction operator as an inference with the help of maximal specific laws and prove that applying the prediction operator to some consistent set of formulas we obtain a consistent set of consequences.

Every mission-critical system goes through extensive functionality and stress tests after being manufactured. But these tests alone do not guarantee correct system behavior in the field. A contemporary high-performance system board is a complex 3D object that may contain a few dozens of hidden layers, stacked micro-vias, high density interconnect, with all above not contributing to ease of test and reliability. Today, data transmission rates on the board may be reaching multi-gigabit ranges on a single channel. Even small changes in high-speed transmission line's impedance caused by system degradation may result in system performance issues and increased error rates due to small delays, intermittent faults and other sporadic stability issues observed in certain operation modes, at certain workloads or manifesting in a seemingly stochastic manner. Diagnosing the root cause of such faulty behavior (defects) in the field is extremely difficult. Differently from Intermittent Faults, Marginal Defects are permanent imperfections, which do not have a temporary or periodic effect. In a way, they are similar to parametric variations, pushing the system (or more specifically, the assembled board) very close or slightly beyond its specified operating margins. As a remedy, high-speed signals are normally fine-tuned or even calibrated to deliver pitch perfect timing even in case of now-ubiquitous DDR3 memories. As a negative side, the calibration mechanism may mask Marginal Defects out until the operating window shrinks to unbearable size and system starts to fail. Self-test and various built-in monitors are often used to monitor system health status, predict and prepare for possible failures. In this paper, we will present methodology aimed at overcoming described above challenges and successfully monitor high-speed data transmission interface health. The methodology is based on observation of signal sampling delays deviation and method described in the previous paper [1].

We discuss various theories of modified gravity which aim to describe the whole evolution of the universe, from early-time inflation via radiation/matter dominance and finally to the dark energy era. Such unified evolution may be described in frames of the same modified gravity. Special attention is paid to F(R) gravity where R is scalar curvature and modified Gauss- Bonnet gravity. The modified gravity solves the problem of universe acceleration without the need to introduce inflation or unknown dark fluid. The explicit models of such F(R) gravity are presented where quantum gravity effects may also be taken into account. The possible generalizations of modified gravity to non-local gravity, string-inspired gravity, and teleparallel gravity are briefly discussed. A number of applications such as the qualitative change of mass-radius relation in neutron stars or the anti-evaporation effect in multiple-horizon black holes are mentioned.

We outline the main stages of Maksimova’s investigation and present in details her results published between 1972 and 1979 and concerning the study of pretabularity and interpolation properties in superintuitionisitc logics and in normal extensions of the logic S4.

Partial equilibrium logic (PEL) is a new nonmonotonic reasoning formalism closely aligned with logic programming under well-founded and partial stable model semantics. In particular it provides a logical foundation for these semantics as well as an extension of the basic syntax of logic programs. In this paper we describe PEL, study some of its logical properties and examine its behaviour on disjunctive and nested logic programs. In addition we consider computational features of PEL and study different approaches to its computation.

This chapter aims to investigate connections between Belnap’s useful four valued logic and Nelson’s constructive logic with strong negation and the role of adding logical constants to the language. We consider the paraconsistent Nelson’s logic and its expansions obtained by adding to it logical constant’s corresponding to truth values of Belnap’s useful four-valued logic.

This paper studies a new approach for board-level test based on synthesizable embedded instruments implementted on FPGA. This very recent methodology utilizes programmable logic devices (FPGA) that are usually available on modern PCBs to a large extent. The purpose of an embedded instrument is to carry out a vast portion of test application related procedures, perform measurement and configuration of system components thus minimizing the usage of external test equipment. By replacing traditional test and measurement equipment with embedded synthetic instruments it is possible not only to achieve the significant reduction of test costs but also facilitate high-speed and at-speed testing. We detail the motivation and classify the FPGA-based instrumentation into different categories based on the implementation and application domains. Experimental results show the efficiency of this approach.

Based on the formulation of the reconstruction for the k-essence model, which was recently proposed in [1], we explicitly construct cosmological model to unifying the late-time acceleration and the inflation in the early universe.

This paper is devoted to logical aspects of two closely related semantics for logic programs: the partial stable model semantics of Przymusinski [20] and the well-founded semantics of Van Gelder, Ross and Schlipf [24]. For many years the following problem remained open: Which (non-modal) logic can be regarded as yielding an adequate foundation for these semantics in the sense that its minimal models (appropriately defined) coincide with the partial stable models of a logic program? Initial work on this problem was undertaken by Cabalar [5] who proposed a frame-based semantics for a suitable logic which he called HT 2. Preliminary axiomatics of HT 2 was presented in [6]. In this paper we analyse HT 2 frames and identify them as structures of a logic N * having intuitionistic positive connectives and Routley negation and give a natural axiomatics for HT 2. We define a notion of minimal, total HT 2 model which we call partial equilibrium model . We show that for logic programs these models coincide with partial stable models, and we propose the resulting partial equilibrium logic as a logical foundation for partial stable and well-founded semantics. Finally, we discuss the strong equivalence for theories and programs in partial equilibrium logic.

The nonmonotonic formalism of partial equilibrium logic (PEL) has recently been proposed as a logical foundation for the partial stable and well-founded semantics of logic programs [1,2]. We study certain logical properties of PEL and some techniques to compute partial equilibrium models.

A formalism called partial equilibrium logic (PEL) has recently been proposed as a logical foundation for the well-founded semantics (WFS) of logic programs. In PEL one defines a class of minimal models, called partial equilibrium models, in a non-classical logic, HT2. On logic programs partial equilibrium models coincide with Przymusinski’s partial stable (p-stable) models, so that PEL can be seen as a way to extend WFS and p-stable semantics to arbitrary propositional theories. We study several extensions of PEL with strong negation and compare these with previous systems extending WFS with explicit negation, notably WSFX [10] and p-stable models with “classical” negation [11].

In [4] a nonmonotonic formalism called partial equilibrium logic (PEL) was proposed as a logical foundation for the well-founded semantics (WFS) of logic programs. PEL consists in defining a class of minimal models, called partial equilibrium (p-equilibrium), inside a non-classical logic called HT2. In [4] it was shown that, on normal logic programs, p-equilibrium models coincide with Przymusinki’s partial stable (p-stable) models. This paper begins showing that this coincidence still holds for the more general class of disjunctive programs, so that PEL can be seen as a way to extend WFS and p-stable semantics to arbitrary propositional theories. We also study here the problem of strong equivalence for various subclasses of p-equilibrium models, investigate transformation rules and nonmonotonic inference, and consider a reduction of PEL to equilibrium logic. In addition we examine the behaviour of PEL on nested logic programs and its complexity in the general case.

A contemporary high-performance system board is a complex 3D object that may contain dozens of hidden layers, stacked microvias, high density interconnect, with all of the above not contributing to the ease of test and reliability. High-speed signals are normally fine-tuned or even calibrated to deliver pitch perfect timing even in the case of now-ubiquitous DDR3 memories. Today, data transmission rates on the board may be reaching multigigabit ranges on a single channel. Such defects like dewetting, cold solder, head-in-pillow, voiding/crack in micro-via or excessive solder voids may result in system performance issues, increased error rates, intermittent faults and other sporadic stability issues observed in certain operation modes, at certain workloads or manifesting in a seemingly stochastic manner. In this work, we present a methodology aiming at systematic discovery of marginal defects, timing related faults and stability issues in board assembly's DDR3/4 data bus as part of the end-of-line testing in volume production environment. The methodology presented in this paper is based on an extended DDR memory controller in which we have converted the bus calibration mechanism into a fine-grain diagnostic instrument, which instead of masking marginal discrepancies (the normal case) would unveil and report them.

High-performance communication interfaces in modern complex electronic systems bring new challenges for board-level manufacturing test. Various means of calibration and error-correction that are incorporated into high-speed protocols tend to hide manufacturing flaws thus making comprehensive testing be an extremely hard task. Links transmitting at gigabit rates are especially susceptible to so-called marginal defects. Marginal defect often escape detection by commonly used test methods as they manifest themselves only under certain conditions that may sporadically occur during device operation in the field. As a result, undetected marginal defects badly affect system stability and reduce its overall operating margin. In this paper, we present a novel embedded instrumentation toolbox intended for use in volume production environments to screen out outliers and marginal devices. The paper focuses on instruments for testing marginal defects on High-Speed Serial Links and DDR3/4 interfaces.

A string-inspired effective theory of gravity, containing Gauss-Bonnet invariant interacting with a scalar field, is considered in view of obtaining cosmological dark energy solutions. A Lagrange multiplier is inserted into the action in order to achieve the cosmological reconstruction by selecting suitable forms of couplings and potentials. Several cosmological exact solutions (including dark energy of quintessence, phantom or Little Rip type) are derived in presence and in absence of the Lagrange multiplier showing the difference in the two dynamical approaches. In the models that we consider, the Lagrange multiplier behaves as a sort of dust fluid that realizes the transitions between matter dominated and dark energy epochs. The relation between Lagrange multipliers and Noether symmetries is discussed., Comment: 14 pages, expanded version to appear in PRD