Evaluation of Mechanical Fatigue Damage Accumulation in Metal Matrix Composites Using Ultrasonic Surface Waves

This study demonstrates that an in situ nondestructive, ultrasonic surface wave technique can successfully detect the onset and extent of matrix cracking fatigue damage in a titanium metal matrix composite (MMC). A quasi-isotropic [0/±45/90]s SCS-6/Timetal®21S MMC material was used for room temperature fatigue tests and the resultant matrix cracking damage was ultrasonically monitored in situ as a function of cycle count. Damage accumulation in the material was successfully correlated with decreases in ultrasonic pitch catch amplitude and verified through the use of immersion ultrasonic C-scans and metallographic techniques. Damage initiation and progression was tracked through the use of complementary nondestructive and destructive techniques. The in situ surface wave data show that the higher the fatigue stress level, the more quickly damage occurs; conversely, the lower the stress level, the slower the damage initiation. The in situ surface wave technique proved to be more sensitive to the accumulating damage than standard load-displacement modulus measurements. The surface wave technique also indicated a change in material properties after only one fatigue cycle. The data acquired show that a better understanding of damage initiation and accumulation can be gained using the in situ surface wave technique in comparison to current load-displacement modulus measurements

Single shot, temporally and spatially resolved measurements of fast electron dynamics using a chirped optical probe

A new approach to rear surface optical probing is presented that permits multiple, time-resolved 2D measurements to be made during a single, ultra-intense ( > 1018 W cm−2) laser-plasma interaction. The diagnostic is capable of resolving rapid changes in target reflectivity which can be used to infer valuable information on fast electron transport and plasma formation at the target rear surface. Initial results from the Astra-Gemini laser are presented, with rapid radial sheath expansion together with detailed filamentary features being observed to evolve during single shots

Fast electron transport patterns in intense laser-irradiated solids diagnosed by modeling measured multi-MeV proton beams

The measured spatial-intensity distribution of the beam of protons accelerated from the rear side of a solid target irradiated by an intense (>10 Wcm) laser pulse provides a diagnostic of the two-dimensional fast electron density profile at the target rear surface and thus the fast electron beam transport pattern within the target. An analytical model is developed, accounting for rear-surface fast electron sheath dynamics, ionization and projection of the resulting beam of protons. The sensitivity of the spatial-intensity distribution of the proton beam to the fast electron density distribution is investigated. An annular fast electron beam transport pattern with filamentary structure is inferred for the case of a thick diamond target irradiated at a peak laser intensity of 6 × 10 Wcm

Divergent Mitochondrial Biogenesis Responses in Human Cardiomyopathy

Background—Mitochondria are key players in the development and progression of heart failure (HF). Mitochondrial (mt) dysfunction leads to diminished energy production and increased cell death contributing to the progression of left ventricular failure. The fundamental mechanisms that underlie mt dysfunction in HF have not been fully elucidated. Methods and Results—To characterize mt morphology, biogenesis, and genomic integrity in human HF, we investigated left ventricular tissue from nonfailing hearts and end-stage ischemic (ICM) or dilated (DCM) cardiomyopathic hearts. Although mt dysfunction was present in both types of cardiomyopathy, mt were smaller and increased in number in DCM compared with ICM or nonfailing hearts. mt volume density and mtDNA copy number was increased by ≈2-fold (P<0.001) in DCM hearts in comparison with ICM hearts. These changes were accompanied by an increase in the expression of mtDNA-encoded genes in DCM versus no change in ICM. mtDNA repair and antioxidant genes were reduced in failing hearts, suggestive of a defective repair and protection system, which may account for the 4.1-fold increase in mtDNA deletion mutations in DCM (P<0.05 versus nonfailing hearts, P<0.05 versus ICM). Conclusions—In DCM, mt dysfunction is associated with mtDNA damage and deletions, which could be a consequence of mutating stress coupled with a peroxisome proliferator-activated receptor γ coactivator 1α–dependent stimulus for mt biogenesis. However, this maladaptive compensatory response contributes to additional oxidative damage. Thus, our findings support further investigations into novel mechanisms and therapeutic strategies for mt dysfunction in DCM

Induced photon correlations through the overlap of two four-wave mixing processes in integrated cavities

Induced photon correlations are directly demonstrated by exploring two coupled nonlinear processes in an integrated device. Using orthogonally polarized modes within an integrated microring cavity, phase matching of two different nonlinear four-wave mixing processes is achieved simultaneously, wherein both processes share one target frequency mode, while their other frequency modes differ. The overlap of these modes leads to the coupling of both nonlinear processes, producing photon correlations. The nature of this process is confirmed by means of time- and power-dependent photon correlation measurements. These findings are relevant to the fundamental understanding of spontaneous parametric effects as well as single-photon-induced processes, and their effect on optical quantum state generation and control

Arbitrary Phase Access for Stable Fiber Interferometers

Well-controlled yet practical systems that give access to interference effects are critical for established and new functionalities in ultrafast signal processing, quantum photonics, optical coherence characterization, etc. Optical fiber systems constitute a central platform for such technologies. However, harnessing optical interference in a versatile and stable manner remains technologically costly and challenging. Here, degrees of freedom native to optical fibers, i.e., polarization and frequency, are used to demonstrate an easily deployable technique for the retrieval and stabilization of the relative phase in fiber interferometric systems. The scheme gives access (without intricate device isolation) to &lt;1.3 × 10−3 π rad error signal Allan deviation across 1 ms to 1.2 h integration times for all tested phases, ranging from 0 to 2π. More importantly, the phase-independence of this stability is shown across the full 2π range, granting access to arbitrary phase settings, central for, e.g., performing quantum projection measurements and coherent pulse recombination. Furthermore, the scheme is characterized with attenuated optical reference signals and single-photon detectors, and extended functionality is demonstrated through the use of pulsed reference signals (allowing time-multiplexing of both main and reference signals). Finally, the scheme is used to demonstrate radiofrequency-controlled interference of high-dimensional time-bin entangled states. © 2021 The Authors. Laser & Photonics Reviews published by Wiley-VCH Gmb

Influence of laser polarization on collective electron dynamics in ultraintense laser-foil interactions

The collective response of electrons in an ultrathin foil target irradiated by an ultraintense laser pulse is investigated experimentally and via 3D particle-in-cell simulations. It is shown that if the target is sufficiently thin that the laser induces significant radiation pressure, but not thin enough to become relativistically transparent to the laser light, the resulting relativistic electron beam is elliptical, with the major axis of the ellipse directed along the laser polarization axis. When the target thickness is decreased such that it becomes relativistically transparent early in the interaction with the laser pulse, diffraction of the transmitted laser light occurs through a so called 'relativistic plasma aperture', inducing structure in the spatial-intensity profile of the beam of energetic electrons. It is shown that the electron beam profile can be modified by variation of the target thickness and degree of ellipticity in the laser polarization