Deep physical neural networks trained with backpropagation.

Deep-learning models have become pervasive tools in science and engineering. However, their energy requirements now increasingly limit their scalability1. Deep-learning accelerators2-9 aim to perform deep learning energy-efficiently, usually targeting the inference phase and often by exploiting physical substrates beyond conventional electronics. Approaches so far10-22 have been unable to apply the backpropagation algorithm to train unconventional novel hardware in situ. The advantages of backpropagation have made it the de facto training method for large-scale neural networks, so this deficiency constitutes a major impediment. Here we introduce a hybrid in situ-in silico algorithm, called physics-aware training, that applies backpropagation to train controllable physical systems. Just as deep learning realizes computations with deep neural networks made from layers of mathematical functions, our approach allows us to train deep physical neural networks made from layers of controllable physical systems, even when the physical layers lack any mathematical isomorphism to conventional artificial neural network layers. To demonstrate the universality of our approach, we train diverse physical neural networks based on optics, mechanics and electronics to experimentally perform audio and image classification tasks. Physics-aware training combines the scalability of backpropagation with the automatic mitigation of imperfections and noise achievable with in situ algorithms. Physical neural networks have the potential to perform machine learning faster and more energy-efficiently than conventional electronic processors and, more broadly, can endow physical systems with automatically designed physical functionalities, for example, for robotics23-26, materials27-29 and smart sensors30-32.

Reported outcome measures in complex fracture elbow dislocations: a systematic review.

BACKGROUND: Complex elbow fracture dislocations, dislocation with fracture of one or several surrounding bony stabilizers, are difficult to manage and associated with poor outcomes. While many studies have explored treatment strategies but a lack of standardization of patient-reported outcome measures (PROMs) makes cross-study comparison difficult. In this systematic review, we aim to describe what injury patterns, measured outcomes, and associated complications are reported in the complex elbow fracture dislocation literature to provide outcome reporting recommendations that will facilitate improved future cross-study comparison. METHODS: A systematic review was performed per Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines. We queried PubMed/MEDLINE, Embase, Web of Science, and Cochrane databases to identify articles published between 2010 and 2022 reporting on adult patients who had a complex elbow fracture dislocation. Pathologic fractures were excluded. A bias assessment using the methodological index for nonrandomized studies criteria was conducted. For each article, patient demographics, injury pattern, outcome measures, and complications were recorded. RESULTS: Ninety-one studies reporting on 3664 elbows (3654 patients) with an elbow fracture and dislocation (weighted mean age 44 years, follow-up of 30 months, 41% female) were evaluated. Of these, the injury pattern was described in 3378 elbows and included 2951 (87%) terrible triad injuries and 72 (2%) transolecranon fracture-dislocations. The three most commonly reported classification systems were: Mason classification for radial head fractures, Regan and Morrey coronoid classification for coronoid fractures, and O'Driscoll classification for coronoid fractures. Range of motion was reported in 87 (96%) studies with most reporting flexion (n = 70), extension (n = 62), pronation (n = 68), or supination (n = 67). Strength was reported in 11 (12%) studies. PROMs were reported in 83 (91%) studies with an average of 2.6 outcomes per study. There were 14 outcome scores including the Mayo Elbow Performance Score (n = 69 [83%]), the Disabilities of Arm, Shoulder and Hand (DASH) score (n = 28 [34%]), the visual analog scale for pain (n = 27 [33%]), QuickDASH score (n = 13 [15.7%]), and Oxford Elbow score (n = 5 [6.0%]). No significance was found between the number of PROMs used per article and the year of publication (P = .313), study type (P = .689), complex fracture pattern (P = .211), or number of elbows included (P = .152). CONCLUSION: There is great heterogeneity in reported PROMs in the complex elbow fracture dislocation literature. Although there is no gold standard PROM for assessing complex elbow fracture dislocations, we recommend the use of at least the Mayo Elbow Performance Score and DASH outcomes measures as well as visual analog scale pain rating scale in future studies to facilitate cross-study comparisons.

The Effect of Socioeconomic Status on Clinical Outcomes and Implant Survivorship After Primary Anatomic and Reverse Total Shoulder Arthroplasty.

BACKGROUND: Low socioeconomic status has been shown to contribute to poor outcomes in patients undergoing joint replacement surgery. However, there is a paucity of studies investigating shoulder arthroplasty. The purpose of this study was to evaluate the effect of socioeconomic status on baseline and postoperative outcome scores and implant survivorship after anatomic and reverse primary total shoulder arthroplasty (TSA). METHODS: A retrospective review of a prospectively-collected single-institution database was performed to identify patients who underwent primary TSA. Zip codes were collected and converted to Area Deprivation Index (ADI) scores. We performed a correlation analysis between national ADI scores and preoperative, postoperative, and pre- to postoperative improvement in range of motion, shoulder strength, and functional outcome scores in patients with minimum 2-year follow-up. Patients were additionally grouped into groups according to their national ADI. Achievement of the MCID, SCB, and PASS and revision-free survivorship were compared between groups. RESULTS: A total of 1,148 procedures including 415 anatomic and 733 reverse total shoulder arthroplasties with a mean age of 64 ± 8.2 and 69.9 ± 8.0 years, respectively, were included. The mean follow-up was 6.3 ± 3.6 years for anatomic and 4.9 ± 2.7 years for reverse TSA. We identified a weak negative correlation between national ADI and most functional outcome scores and range of motion preoperatively (R range 0.07 to 0.16), postoperatively (R range 0.09 to 0.14), and pre- to postoperative improvement (R range 0.01 to 0.17). Thus, greater area deprivation was weakly associated with poorer function preoperatively, poorer final outcomes and poorer improvement in outcomes. There was no difference in the proportion of each ADI group achieving MCID, SCB, and PASS in the anatomic TSA cohort. However, in the reverse TSA cohort, the proportion of patients achieving MCID, SCB, and PASS decreased with greater deprivation. There was no difference in survivorship between ADI groups . CONCLUSIONS: We found a negative effect of low socioeconomic status on baseline and postoperative patient outcomes and range-of-motion; however, the correlations were relatively weak. Patients that reside in socioeconomically deprived areas have poorer functional outcomes before and after TSA and achieve less improvement from surgery. We should strive to identify modifiable factors to improve the success of TSA in socioeconomically deprived areas.

Engineering a Kerr-Based Deterministic Cubic Phase Gate via Gaussian Operations.

We propose a deterministic, measurement-free implementation of a cubic phase gate for continuous-variable quantum information processing. In our scheme, the applications of displacement and squeezing operations allow us to engineer the effective evolution of the quantum state propagating through an optical Kerr nonlinearity. Under appropriate conditions, we show that the input state evolves according to a cubic phase Hamiltonian, and we find that the cubic phase gate error decreases inverse quartically with the amount of quadrature squeezing, even in the presence of linear loss. We also show how our scheme can be adapted to deterministically generate a nonclassical approximate cubic phase state with high fidelity using a ratio of native nonlinearity to linear loss of only 10^{-4}, indicating that our approach may be experimentally viable in the near term even on all-optical platforms, e.g., using quantum solitons in pulsed nonlinear nanophotonics.

Several new directions for ultrafast fiber lasers [Invited].

Ultrafast fiber lasers have the potential to make applications of ultrashort pulses widespread - techniques not only for scientists, but also for doctors, manufacturing engineers, and more. Today, this potential is only realized in refractive surgery and some femtosecond micromachining. The existing market for ultrafast lasers remains dominated by solid-state lasers, primarily Ti:sapphire, due to their superior performance. Recent advances show routes to ultrafast fiber sources that provide performance and capabilities equal to, and in some cases beyond, those of Ti:sapphire, in compact, versatile, low-cost devices. In this paper, we discuss the prospects for future ultrafast fiber lasers built on new kinds of pulse generation that capitalize on nonlinear dynamics. We focus primarily on three promising directions: mode-locked oscillators that use nonlinearity to enhance performance; systems that use nonlinear pulse propagation to achieve ultrashort pulses without a mode-locked oscillator; and multimode fiber lasers that exploit nonlinearities in space and time to obtain unparalleled control over an electric field.

Self-seeded, multi-megawatt, Mamyshev oscillator.

We demonstrate a fiber oscillator that achieves 3 MW peak power, is easily started, and is environmentally stable. The Mamyshev oscillator delivers 190-nJ pulses that can be compressed externally to 35 fs duration. Accurate numerical modeling of the gain medium provides insight into the behavior and performance of the device.

Kerr self-cleaning of femtosecond-pulsed beams in graded-index multimode fiber.

We observe a nonlinear spatial self-cleaning process for femtosecond pulses in graded-index (GRIN) multimode fiber (MMF). Pulses with ∼80 fs duration at 1030 nm are launched into GRIN MMF with 62.5 µm core. The near-field beam profile at the output end of the fiber evolves from a speckled pattern to a centered, bell-shaped transverse structure with increasing pulse energy. The experimental observations agree well with numerical simulations, which show that the Kerr nonlinearity underlies the process. This self-cleaning process may find applications in ultrafast pulse generation and beam-combining.

Observation of multimode solitons in few-mode fiber.

We experimentally isolate and directly observe multimode solitons in few-mode graded-index fiber. We rely on Raman frequency shifts to spectrally isolate these multimode solitons. By varying the input energy and modal composition of the launched pulse, we observe a continuous variation of multimode solitons with different spatiotemporal properties. They exhibit an energy-volume relation that is distinct from those of single-mode and fully spatiotemporal solitons.

Ultrafast fiber lasers based on self-similar pulse evolution: a review of current progress.

Self-similar fiber oscillators are a relatively new class of mode-locked lasers. In these lasers, the self-similar evolution of a chirped parabolic pulse in normally-dispersive passive, active, or dispersion-decreasing fiber (DDF) is critical. In active (gain) fiber and DDF, the novel role of local nonlinear attraction makes the oscillators fundamentally different from any mode-locked lasers considered previously. In order to reconcile the spectral and temporal expansion of a pulse in the self-similar segment with the self-consistency required by a laser cavity's periodic boundary condition, several techniques have been applied. The result is a diverse range of fiber oscillators which demonstrate the exciting new design possibilities based on the self-similar model. Here, we review recent progress on self-similar oscillators both in passive and active fiber, and extensions of self-similar evolution for surpassing the limits of rare-earth gain media. We discuss some key remaining research questions and important future directions. Self-similar oscillators are capable of exceptional performance among ultrashort pulsed fiber lasers, and may be of key interest in the development of future ultrashort pulsed fiber lasers for medical imaging applications, as well as for low-noise fiber-based frequency combs. Their uniqueness among mode-locked lasers motivates study into their properties and behaviors and raises questions about how to understand mode-locked lasers more generally.

Spatiotemporal dynamics of multimode optical solitons.

As optical fiber communications and fiber lasers approach fundamental limits there is considerable interest in multimode fibers. In nonlinear science, they represent an exciting environment for complex nonlinear waves. As in single-mode fiber, solitons may be particularly important. Multimode solitons consist of synchronized, non-dispersive pulses in multiple spatial modes, which interact via the Kerr nonlinearity of the fiber. They are expected to exhibit novel spatiotemporal characteristics, dynamics and, like single-mode solitons, may provide a convenient intuitive tool for understanding more complex nonlinear phenomena in multimode fibers. Here we explore experimentally and numerically basic properties and spatiotemporal behaviors of these solitons: their formation, fission, and Raman dynamics.