The Promise and Challenge of Stochastic Computing Alaghi, Armin; Qian, Weikang; Hayes, John P.
IEEE transactions on computer-aided design of integrated circuits and systems,
08/2018, Letnik:
37, Številka:
8
Journal Article
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Stochastic computing (SC) is an unconventional method of computation that treats data as probabilities. Typically, each bit of an <inline-formula> <tex-math notation="LaTeX">{N} ...</tex-math></inline-formula>-bit stochastic number (SN) <inline-formula> <tex-math notation="LaTeX">{X} </tex-math></inline-formula> is randomly chosen to be 1 with some probability <inline-formula> <tex-math notation="LaTeX">p_{X} </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">{X} </tex-math></inline-formula> is generated and processed by conventional logic circuits. For instance, a single AND gate performs multiplication. The value X of an SN is measured by the density of 1 s in it, an information-coding scheme also found in biological neural systems. SC has uses in massively parallel systems and is very tolerant of soft errors. Its drawbacks include low accuracy, slow processing, and complex design needs. Its ability to efficiently perform tasks like communication decoding and neural network inference has rekindled interest in the field. Many challenges remain to be overcome, however, before SC becomes widespread. In this paper, we discuss the evolution of SC, mostly focusing on recent developments. We highlight the main challenges and discuss potential methods of overcoming them.
Here, I present a database of >160 finite fault models for all earthquakes of M 7.5 and above since 1990, created using a consistent modeling approach. The use of a common approach facilitates easier ...comparisons between models, and reduces uncertainties that arise when comparing models generated by different authors, data sets and modeling techniques.
I use this database to verify published scaling relationships, and for the first time show a clear and intriguing relationship between maximum potency (the product of slip and area) and average potency for a given earthquake. This relationship implies that earthquakes do not reach the potential size given by the tectonic load of a fault (sometimes called “moment deficit,” calculated via a plate rate over time since the last earthquake, multiplied by geodetic fault coupling). Instead, average potency (or slip) scales with but is less than maximum potency (dictated by tectonic loading). Importantly, this relationship facilitates a more accurate assessment of maximum earthquake size for a given fault segment, and thus has implications for long-term hazard assessments. The relationship also suggests earthquake cycles may not completely reset after a large earthquake, and thus repeat rates of such events may appear shorter than is expected from tectonic loading. This in turn may help explain the phenomenon of “earthquake super-cycles” observed in some global subduction zones.
•A new database of teleseismic finite fault models for all M7.5+ earthquakes since 1990 is presented.•A linear relationship between maximum potency and average potency of an earthquake is discovered.•Potency relationship has implications for earthquake hazard assessment and earthquake cycles.
The July 2019 Ridgecrest, California, earthquake sequence produced cross‐fault ruptures from a Mw6.4 left‐lateral foreshock and a Mw7.1 right‐lateral mainshock. We use interferometric synthetic ...aperture radar and satellite optical imagery to characterize the surface displacements and subsurface fault slip characteristics of the sequence. We document ~46 km of surface rupture and peak slip values of ~5 m associated with the Mw7.1 and evidence that the two ruptures crossed each other. We additionally document evidence of triggered creep along 20–25 km of the central Garlock fault. Static stress change analysis shows that the foreshock sequence systematically promoted slip at the Mw7.1 hypocenter. Moreover, we find static stress changes promoted slip on the Garlock fault only in locations where we document surface creep, strongly indicating that the Garlock fault is sensitive to static stress changes. A potential rupture of the Garlock fault where slip was promoted could produce a Mw6.7–7.0 earthquake.
Key Points
We document kinematics of the July 2019 Ridgecrest earthquake sequence, including crossing surface ruptures
The 34‐hr foreshock sequence systematically increased stresses and encouraged rupture of the Mw7.1 mainshock
The sequence triggered aseismic slip on the central Garlock fault that correlates strongly to static stress changes
Subduction zones are home to the most seismically active faults on the planet. The shallow megathrust interfaces of subduction zones host Earth's largest earthquakes and are likely the only faults ...capable of magnitude 9+ ruptures. Despite these facts, our knowledge of subduction zone geometry-which likely plays a key role in determining the spatial extent and ultimately the size of subduction zone earthquakes-is incomplete. We calculated the three-dimensional geometries of all seismically active global subduction zones. The resulting model, called Slab2, provides a uniform geometrical analysis of all currently subducting slabs.
We describe and present a new model of global subduction zone geometries, called Slab1.0. An extension of previous efforts to constrain the two‐dimensional non‐planar geometry of subduction zones ...around the focus of large earthquakes, Slab1.0 describes the detailed, non‐planar, three‐dimensional geometry of approximately 85% of subduction zones worldwide. While the model focuses on the detailed form of each slab from their trenches through the seismogenic zone, where it combines data sets from active source and passive seismology, it also continues to the limits of their seismic extent in the upper‐mid mantle, providing a uniform approach to the definition of the entire seismically active slab geometry. Examples are shown for two well‐constrained global locations; models for many other regions are available and can be freely downloaded in several formats from our new Slab1.0 website, http://on.doi.gov/d9ARbS. We describe improvements in our two‐dimensional geometry constraint inversion, including the use of ‘average’ active source seismic data profiles in the shallow trench regions where data are otherwise lacking, derived from the interpolation between other active source seismic data along‐strike in the same subduction zone. We include several analyses of the uncertainty and robustness of our three‐dimensional interpolation methods. In addition, we use the filtered, subduction‐related earthquake data sets compiled to build Slab1.0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far, concluding that the width of these seismogenic zones is on average 30% larger than previous studies have suggested.
Key Points
Introduces a new set of detailed 3D global subduction zone models
Focuses on the shallow seismogenic zone (unrepresented in previous models)
Allows for improved finite‐fault, seismic and tsunami hazard calculations
Quantum Circuit Simulation covers the fundamentals of linear algebra and introduces basic concepts of quantum physics needed to understand quantum circuits and algorithms. It requires only basic ...familiarity with algebra, graph algorithms and computer engineering. After introducing necessary background, the authors describe key simulation techniques that have so far been scattered throughout the research literature in physics, computer science, and computer engineering. Quantum Circuit Simulation also illustrates the development of software for quantum simulation by example of the QuIDDPro package, which is freely available and can be used by students of quantum information as a `quantum calculator.`
Posttraumatic stress disorder (PTSD) is a prominent mental health problem in veteran and community populations. There is accumulating evidence to suggest that aerobic exercise may serve as an ...effective treatment option for individuals with PTSD. The purpose of this review is to summarize the existing literature exploring aerobic exercise and PTSD and briefly discuss potential mechanisms of PTSD symptom reduction. A search of electronic databases and reference sections of relevant articles published through October 1, 2018 revealed 19 relevant studies that examined aerobic exercise and PTSD symptomatology. A narrative review of extant studies provides encouraging evidence that aerobic exercise interventions alone or as an adjunct to standard treatment may positively impact PTSD symptoms. Potential mechanisms by which aerobic exercise could exert a positive impact in PTSD include exposure and desensitization to internal arousal cues, enhanced cognitive function, exercise-induced neuroplasticity, normalization of hypothalamic pituitary axis (HPA) function, and reductions in inflammatory markers. Randomized clinical trials and translational neuroscience approaches are required to clarify the efficacy of exercise intervention for PTSD and elucidate potential mechanisms of exercise-induced PTSD symptom reduction.
In recent years, neuroimaging techniques such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) have played a significant role in elucidating the neural ...underpinnings of posttraumatic stress disorder (PTSD). However, a detailed understanding of the neural regions implicated in the disorder remains incomplete because of considerable variability in findings across studies. The aim of this meta-analysis was to identify consistent patterns of neural activity across neuroimaging study designs in PTSD to improve understanding of the neurocircuitry of PTSD.
We conducted a literature search for PET and fMRI studies of PTSD that were published before February 2011. The article search resulted in 79 functional neuroimaging PTSD studies. Data from 26 PTSD peer-reviewed neuroimaging articles reporting results from 342 adult patients and 342 adult controls were included. Peak activation coordinates from selected articles were used to generate activation likelihood estimate maps separately for symptom provocation and cognitive-emotional studies of PTSD. A separate meta-analysis examined the coupling between ventromedial prefrontal cortex and amygdala activity in patients.
Results demonstrated that the regions most consistently hyperactivated in PTSD patients included mid- and dorsal anterior cingulate cortex, and when ROI studies were included, bilateral amygdala. By contrast, widespread hypoactivity was observed in PTSD including the ventromedial prefrontal cortex and the inferior frontal gyrus. Furthermore, decreased ventromedial prefrontal cortex activity was associated with increased amygdala activity.
These results provide evidence for a neurocircuitry model of PTSD that emphasizes alteration in neural networks important for salience detection and emotion regulation.
In earthquake dynamics there are two end member models of rupture: propagating cracks and self‐healing pulses. These arise due to different properties of faults and have implications for seismic ...hazard; rupture mode controls near‐field strong ground motions. Past studies favor the pulse‐like mode of rupture; however, due to a variety of limitations, it has proven difficult to systematically establish their kinematic properties. Here we synthesize observations from a database of >150 rupture models of earthquakes spanning M7–M9 processed in a uniform manner and show the magnitude scaling properties of these slip pulses indicates self‐similarity. Further, we find that large and very large events are statistically distinguishable relatively early (at ~15 s) in the rupture process. This suggests that with dense regional geophysical networks strong ground motions from a large rupture can be identified before their onset across the source region.
Key Points
A catalog of large earthquake finite fault models favors rupture propagating as a self‐similar slip pulse
We establish the moment scaling properties of kinematic slip pulse parameters such as rise time and pulse width
Self‐similarity implies weak determinism, earthquakes are statistically different early on in the rupture; this has implications for early warning
Type I CRISPR systems feature a sequential dsDNA target searching and degradation process, by crRNA-displaying Cascade and nuclease-helicase fusion enzyme Cas3, respectively. Here we present two ...cryo-EM snapshots of the Thermobifida fusca type I-E Cascade: (1) unwinding 11 bp of dsDNA at the seed-sequence region to scout for sequence complementarity, and (2) further unwinding of the entire protospacer to form a full R-loop. These structures provide the much-needed temporal and spatial resolution to resolve key mechanistic steps leading to Cas3 recruitment. In the early steps, PAM recognition causes severe DNA bending, leading to spontaneous DNA unwinding to form a seed-bubble. The full R-loop formation triggers conformational changes in Cascade, licensing Cas3 to bind. The same process also generates a bulge in the non-target DNA strand, enabling its handover to Cas3 for cleavage. The combination of both negative and positive checkpoints ensures stringent yet efficient target degradation in type I CRISPR-Cas systems.
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•Snapshot of a seed crRNA-DNA duplex formation—an important R-loop intermediate•PAM recognition bends dsDNA, leading to DNA melting and seed-bubble formation•Full R-loop formation by Cascade triggers conformational changes, licensing Cas3 binding•Full R-loop formation triggers non-target strand bulge, enabling Cas3 nicking
Cryo-EM structures of type I CRISPR-Cas system resolve the mechanisms governing the PAM-dependent R-loop formation, Cas3 recruitment, and substrate handover processes.
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