The role of interplanetary scattering in western hemisphere large solar energetic particle events

Using high-sensitivity instruments on the ACE spacecraft, we have examined the intensities of O and Fe in 14 large solar energetic particle events whose parent activity was in the solar western hemisphere. Sampling the intensities at low (~273 keV nucleon to the -1) and high (~12 MeV nucleon to the -1) energies, we find that at the same kinetic energy per nucleon, the Fe/O ratio decreases with time, as has been reported previously. This behavior is seen in more than 70% of the cases during the rise to maximum intensity and continues in most cases into the decay phase. We find that for most events if we compare the Fe intensity with the O intensity at a higher kinetic energy per nucleon, the two time-intensity profiles are strikingly similar. Examining alternate scenarios that could produce this behavior, we conclude that for events showing this behavior the most likely explanation is that the Fe and O share similar injection profiles near the Sun, and that scattering in the interplanetary medium dominates the profiles observed at 1 AU

Statistical interaction modeling of bovine herd behaviors

While there has been interest in modeling the group behavior of herds or flocks, much of this work has focused on simulating their collective spatial motion patterns which have not accounted for individuality in the herd and instead assume a homogenized role for all members or sub-groups of the herd. Animal behavior experts have noted that domestic animals exhibit behaviors that are indicative of social hierarchy: leader/follower type behaviors are present as well as dominance and subordination, aggression and rank order, and specific social affiliations may also exist. Both wild and domestic cattle are social species, and group behaviors are likely to be influenced by the expression of specific social interactions. In this paper, Global Positioning System coordinate fixes gathered from a herd of beef cows tracked in open fields over several days at a time are utilized to learn a model that focuses on the interactions within the herd as well as its overall movement. Using these data in this way explores the validity of existing group behavior models against actual herding behaviors. Domain knowledge, location geography and human observations, are utilized to explain the causes of these deviations from this idealized behavior

The application of ultrasonic NDT techniques in tribology

The use of ultrasonic reflection is emerging as a technique for studying tribological contacts. Ultrasonic waves can be transmitted non-destructively through machine components and their behaviour at an interface describes the characteristics of that contact. This paper is a review of the current state of understanding of the mechanisms of ultrasonic reflection at interfaces, and how this has been used to investigate the processes of dry rough surface contact and lubricated contact. The review extends to cover how ultrasound has been used to study the tribological function of certain engineering machine elements

The mixing of interplanetary magnetic field lines: A significant transport effect in studies of the energy spectra of impulsive flares

Using instrumentation on board the ACE spacecraft we describe short-time scale (~3 hour) variations observed in the arrival profiles of ~20 keV nucleon^(–1) to ~2 MeV nucleon^(–1) ions from impulsive solar flares. These variations occurred simultaneously across all energies and were generally not in coincidence with any local magnetic field or plasma signature. These features appear to be caused by the convection of magnetic flux tubes past the observer that are alternately filled and devoid of flare ions even though they had a common flare source at the Sun. In these particle events we therefore have a means to observe and measure the mixing of the interplanetary magnetic field due to random walk. In a survey of 25 impulsive flares observed at ACE between 1997 November and 1999 July these features had an average time scale of 3.2 hours, corresponding to a length of ~0.03 AU. The changing magnetic connection to the flare site sometimes lead to an incomplete observation of a flare at 1 AU; thus the field-line mixing is an important effect in studies of impulsive flare energy spectra

Seed populations for large solar particle events of cycle 23

Using high-resolution mass spectrometers on board the Advanced Composition Explorer (ACE), we surveyed the event-averaged ~0.1-60 MeV/nuc heavy ion elemental composition in 64 large solar energetic particle (LSEP) events of cycle 23. Our results show the following: (1) The rare isotope ^3He is greatly enhanced over the corona or the solar wind values in 46% of the events. (2) The Fe/O ratio decreases with increasing energy up to ~10 MeV/nuc in ~92% of the events and up to ~60 MeV/nuc in ~64% of the events. (3) Heavy ion abundances from C-Fe exhibit systematic M/g-dependent enhancements that are remarkably similar to those seen in ^3He-rich SEP events and CME-driven interplanetary (IP) shock events. Taken together, these results confirm the role of shocks in energizing particles up to ~60 MeV/nuc in the majority of large SEP events of cycle 23, but also show that the seed population is not dominated by ions originating from the ambient corona or the thermal solar wind, as previously believed. Rather, it appears that the source material for CME-associated large SEP events originates predominantly from a suprathermal population with a heavy ion enrichment pattern that is organized according to the ion's mass-per-charge ratio. These new results indicate that current LSEP models must include the routine production of this dynamic suprathermal seed population as a critical pre-cursor to the CME shock acceleration process

LArPix: Demonstration of low-power 3D pixelated charge readout for liquid argon time projection chambers

We report the demonstration of a low-power pixelated readout system designed for three-dimensional ionization charge detection and digital readout of liquid argon time projection chambers (LArTPCs). Unambiguous 3D charge readout was achieved using a custom-designed system-on-a-chip ASIC (LArPix) to uniquely instrument each pad in a pixelated array of charge-collection pads. The LArPix ASIC, manufactured in 180 nm bulk CMOS, provides 32 channels of charge-sensitive amplification with self-triggered digitization and multiplexed readout at temperatures from 80 K to 300 K. Using an 832-channel LArPix-based readout system with 3 mm spacing between pads, we demonstrated low-noise ($<$500 e$^-$ RMS equivalent noise charge) and very low-power ($<$100 $\mu$W/channel) ionization signal detection and readout. The readout was used to successfully measure the three-dimensional ionization distributions of cosmic rays passing through a LArTPC, free from the ambiguities of existing projective techniques. The system design relies on standard printed circuit board manufacturing techniques, enabling scalable and low-cost production of large-area readout systems using common commercial facilities. This demonstration overcomes a critical technical obstacle for operation of LArTPCs in high-occupancy environments, such as the near detector site of the Deep Underground Neutrino Experiment (DUNE).Comment: 19 pages, 10 figures, 1 ancillary animation. V3 includes minor revisions based on referee comment

Individual differences in the nature of conditioned behavior across a conditioned stimulus: adaptation and application of a model

Pavlovian conditioning procedures produce marked individual differences in the form of conditioned behavior. For example, when rats are given conditioning trials in which the temporary insertion of a lever into an operant chamber (the conditioned stimulus, CS) is paired with the delivery of food (the unconditioned stimulus, US), they exhibit knowledge of the leverfood relationship in different ways. For some rats (known as sign-trackers) interactions with the lever dominate, while for others (goal-trackers) approaching the food well dominates. A formal model of Pavlovian conditioning (HeiDI) attributes such individual differences in behavior to variations in the perceived salience of the CS and US. An application of the model in which the perceived salience of the CS declines (i.e., adapts) across its duration, predicts changes in these individual differences within the presentation of the CS: The sign-tracking bias is predicted to decline and goal-tracking bias is predicted to increase across the presentation of a lever. The accuracy of these predictions was confirmed though analysis of archival data from female and male rats

Elaboration of a model of Pavlovian learning and performance: HeiDI

The model elaborated here adapts the influential pooled error term, first described by Allan R. Wagner and his colleague Robert A. Rescorla, to govern the formation of reciprocal associations between any pair of stimuli that are presented on a given trial. In the context of Pavlovian conditioning, these stimuli include various conditioned and unconditioned stimuli. This elaboration enables the model to deal with cue competition phenomena, including the relative validity effect, and evidence implicating separate error terms and attentional processes in association formation. The model also includes a performance rule, which provides a natural basis for (individual) variation in the strength and nature of conditioned behaviors that are observed in Pavlovian conditioning procedures. The new model thereby begins to address theoretical and empirical issues that were apparent when the Rescorla-Wagner model was first described, together with research inspired by the model over ensuing 50 years