Fully stabilized multi-TW optical waveform synthesizer: Toward gigawatt isolated attosecond pulses

A stable 50-mJ three-channel optical waveform synthesizer is demonstrated and used to reproducibly generate a high-order harmonic supercontinuum in the soft x-ray region. This synthesizer is composed of pump pulses from a 10-Hz repetition-rate Ti:sapphire pump laser and signal and idler pulses from an infrared two-stage optical parametric amplifier driven by this pump laser. With full active stabilization of all relative time delays, relative phases, and the carrier-envelope phase, a shot-to-shot stable intense continuum harmonic spectrum is obtained around 60 eV with pulse energy above 0.24 μJ. The peak power of the soft x-ray continuum is evaluated to be beyond 1 GW with a 170-as transform limit duration. We found a characteristic delay dependence of the multicycle waveform synthesizer and established its control scheme. Compared with the one-color case, we experimentally observe an enhancement of the cutoff spectrum intensity by one to two orders of magnitude using three-color waveform synthesis.

Further Results on Exponential Stability and State Feedback Stabilization for Time Delay Singular Saturating Actuator Systems With Delay-Dependence

This paper will study the exponential stable and state feedback stabilization of time delay singular systems with saturation actuators. Some sufficient conditions for existence of controller are obtained by using the linear matrix inequalities (LMIs) and integral inequality approach (IIA). When these LMIs are feasible, an explicit expression of controller is obtained. Based on Lyapunov–Krasovskii functional (LKF) techniques, a novel exponential stabilization criterion has been also derived in terms of LMIs which can be easily solved with efficient convex optimization algorithm. Our results are less conservative than some existing ones, and the decision variables involved in this paper are less than them. Examples illustrate our results as less conservative than those reported in the literature.

Multi-Physics Driven Co-Design of 3D Multicore Architectures

The high heat flux and strong thermal coupling in the 3D ICs has limited the performance gains that would otherwise be feasible in 3D structures. The common practice of adopting worst-case design margins is in part responsible for this limitation since average-case performance would be limited by worst-case thermal design margins. The coupling between temperature and leakage power exacerbates this effect. However, worst-case thermal conditions are not the common state across the package at runtime. We argue for the co-design of the package, architecture, and power management based on the multi-physics interactions between temperature, power consumption and system performance. This approach suggests an adaptive architecture that accommodates the thermal coupling between layers and leads to increased energy efficiency over a wider operating voltage range and therefore higher performance. In this paper, we target at a 3D multicore architecture where the cores reside on one die and the last level cache (LLC) resides on the other. The DRAM stack may be stacked on top of the package (e.g., 3D) or in the same package (e.g., 2.5D). We propose a novel adaptive cache structure — the constant performance model (CPM) cache — based on voltage adaptations to temperature variations. We construct a HSPICE model for the SRAM to explore the relationship between temperature, supply voltage, and the circuit delay in the context of the LLC. This model is used to investigate, characterize, and analyze the effect of the temperature-delay dependence of the SRAM LLC configuration on the system-level performance and energy efficiency. This analysis gives rise to an intelligent scheme for dynamic voltage regulation in the LLC cache that is sensitive to the temperature of the individual cache banks. Each cache bank is thermally coupled to the associated cores and thus is sensitive to the local core-level power management. We show that this local adaptation to the temperature-delay dependence leads to a significant power reduction in the LLC cache, and improvement of system energy efficiency computed as energy per instruction (EPI). We evaluate our approach using a cycle-level, full system simulation model of a 16-core x86 homogenous microarchitecture in 16nm technology that boots a full Linux operating system and executes application binaries. The advantages of the proposed adaptive LLC structure illustrate the potential of the co-design of the package, architecture, and power management in future 3D multicore architectures.

Stability Switches and Hopf Bifurcation in a Coupled FitzHugh-Nagumo Neural System with Multiple Delays

A FitzHugh-Nagumo (FHN) neural system with multiple delays has been proposed. The number of equilibrium point is analyzed. It implies that the neural system exhibits a unique equilibrium and three ones for the different values of coupling weight by employing the saddle-node bifurcation of nontrivial equilibrium point and transcritical bifurcation of trivial one. Further, the stability of equilibrium point is studied by analyzing the corresponding characteristic equation. Some stability criteria involving the multiple delays and coupling weight are obtained. The results show that the neural system exhibits the delay-independence and delay-dependence stability. Increasing delay induces the stability switching between resting state and periodic activity in some parameter regions of coupling weight. Finally, numerical simulations are taken to support the theoretical results.

Robust Stability Analysis of Delay-Dependence for a Class of Switched Uncertain Systems with Time Delay

Some new criteria of delay-dependent stability for the switched time-delay uncertain system are deduced by employing time-switched method and the comparison theorem in this paper. The total activation time ratio of the switching law can be determined to guarantee the switched time-delay uncertain system is exponentially stable with stability margin . Finally, this method can be extended to switched interval systems with time-delay. Some examples are exploited to illustrate the proposed schemes..