Transition from ion-coupled to electron-only reconnection: Basic physics and implications for plasma turbulence

Using kinetic particle-in-cell (PIC) simulations, we simulate reconnection conditions appropriate for the magnetosheath and solar wind, i.e., plasma beta (ratio of gas pressure to magnetic pressure) greater than 1 and low magnetic shear (strong guide field). Changing the simulation domain size, we find that the ion response varies greatly. For reconnecting regions with scales comparable to the ion Larmor radius, the ions do not respond to the reconnection dynamics leading to ''electron-only'' reconnection with very large quasi-steady reconnection rates. The transition to more traditional ''ion-coupled'' reconnection is gradual as the reconnection domain size increases, with the ions becoming frozen-in in the exhaust when the magnetic island width in the normal direction reaches many ion inertial lengths. During this transition, the quasi-steady reconnection rate decreases until the ions are fully coupled, ultimately reaching an asymptotic value. The scaling of the ion outflow velocity with exhaust width during this electron-only to ion-coupled transition is found to be consistent with a theoretical model of a newly reconnected field line. In order to have a fully frozen-in ion exhaust with ion flows comparable to the reconnection Alfv\'en speed, an exhaust width of at least several ion inertial lengths is needed. In turbulent systems with reconnection occurring between magnetic bubbles associated with fluctuations, using geometric arguments we estimate that fully ion-coupled reconnection requires magnetic bubble length scales of at least several tens of ion inertial lengths

Observation of Macroscopic Structural Fluctuations in bcc Solid 4He

We report neutron diffraction studies of low density bcc and hcp solid 4He. In the bcc phase, we observed a continuous dynamical behaviour involving macroscopic structural changes of the solid. The dynamical behaviour takes place in a cell full of solid, and therefore represents a solidsolid transformation. The structural changes are consistent with a gradual rotation of macroscopic grains separated by low angle grain boundaries. We suggest that these changes are triggered by random momentary vibrations of the experimental system. An analysis of Laue diffraction patterns indicates that in some cases these structural changes, once initiated by a momentary impulse, seem to proceed at a constant rate over times approaching an hour. The energy associated with these macroscopic changes appears to be on the order of kT. Under similar conditions (temperature and pressure), these effects were absent in the hcp phase.Comment: 14 pages, 6 figure, accepted for PR

A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33

We present UBVRI photometry obtained from Mosaic images of M31 and M33 using the KPNO 4-m telescope. The survey covers 2.2 sq degrees of M31, and 0.8 sq degrees of M33, chosen so as to include all of the regions currently active in forming massive stars. The catalog contains 371,781 and 146,622 stars in M31 and M33, respectively, where every star has a counterpart (at least) in B, V, and R. We compare our photometry to previous studies. We provide cross references to the stars confirmed as members by spectroscopy, and compare the location of these to the complete set in color-magnitude diagrams. While follow-up spectroscopy is needed for many projects, we demonstrate the success of our photometry in being able to distinguish M31/M33 members from foreground Galactic stars. We also present the results of newly obtained spectroscopy, which identifies 34 newly confirmed members, including B-A supergiants, the earliest O star known in M31, and two new Luminous Blue Variable candidates whose spectra are similar to that of P Cygni.Comment: Accepted by the Astronomical Journal. A version with higher resolution figures can be found at: http://www.lowell.edu/users/massey/M3133.pdf.g

Persistent Transport Barrier on the West Florida Shelf

Analysis of drifter trajectories in the Gulf of Mexico has revealed the existence of a region on the southern portion of the West Florida Shelf (WFS) that is not visited by drifters that are released outside of the region. This so-called ``forbidden zone'' (FZ) suggests the existence of a persistent cross-shelf transport barrier on the southern portion of the WFS. In this letter a year-long record of surface currents produced by a Hybrid-Coordinate Ocean Model simulation of the WFS is used to identify Lagrangian coherent structures (LCSs), which reveal the presence of a robust and persistent cross-shelf transport barrier in approximately the same location as the boundary of the FZ. The location of the cross-shelf transport barrier undergoes a seasonal oscillation, being closer to the coast in the summer than in the winter. A month-long record of surface currents inferred from high-frequency (HF) radar measurements in a roughly 60 km $\times$ 80 km region on the WFS off Tampa Bay is also used to identify LCSs, which reveal the presence of robust transient transport barriers. While the HF-radar-derived transport barriers cannot be unambiguously linked to the boundary of the FZ, this analysis does demonstrate the feasibility of monitoring transport barriers on the WFS using a HF-radar-based measurement system. The implications of a persistent cross-shelf transport barrier on the WFS for the development of harmful algal blooms on the shoreward side of the barrier are considered.Comment: Submitted to Geophysical Research Letter

Characterization of the Prion Protein (PRP) Gene in Ten Breeds of Sheep

Transmissible Spongiform Encephalopathies (TSE\u27s) are neurodegenerative disorders characterized by a long generation time, spongy degeneration in the cerebral gray matter, neuronal loss and proliferation and hypertrophy of glial cells. An abnormal form of the prion protein (PrP) plays a major part in TSE pathogenesis and has been hypothesized to be the only component of the infectious agent. Some animals exposed to scrapie, the TSE affecting sheep and goats, seem to be resistant to development of the disease. Alleles encoding amino acid substitutions at codons 136 (A/V) and 171 (Q/R/H) have been associated with scrapie resistance. Other amino acid substitutions at codons 112 (M/T), 137 (M/T), 141 (L/F), 154 (R/H), and 211 (R/Q) have been reported but not associated with scrapie resistance. It may be possible to reduce the incidence of ovine scrapie by increasing the frequency of resistant genotypes (AA-136, RR-171, or QR-171). Thus, an important consideration is the frequency of these genotypes in different breeds of sheep. In this study, the genetic sequence for codons 104-175 was determined for at least ten animals of ten sheep breeds (n=207). Genotypes at codons 112, 136, 154, and 171 were determined. For codon 136, the frequency of the susceptible allele (V) was less than 0.20 in all breeds. In contrast, the frequency of the susceptible allele (Q) at codon 171 ranged from 0.27 (St. Croix) to 0.96 (Hampshire). In addition, a previously unreported substitution was found at codon 143 (H/R), with frequencies as high as 0.40

Validity of wrist-worn consumer products to measure heart rate and energy expenditure

Introduction: The ability to monitor physical activity throughout the day and during various activities continues to improve with the development of wrist-worn monitors. However, the accuracy of wrist-worn monitors to measure both heart rate and energy expenditure during physical activity is still unclear. The purpose of this study was to determine the accuracy of several popular wrist-worn monitors at measuring heart rate and energy expenditure. Methods: Participants wore the TomTom Cardio, Microsoft Band and Fitbit Surge on randomly assigned locations on each wrist. The maximum number of monitors per wrist was two. The criteria used for heart rate and energy expenditure were a three-lead electrocardiogram and indirect calorimetry using a metabolic cart. Participants exercised on a treadmill at 3.2, 4.8, 6.4, 8 and 9.7 km/h for 3 minutes at each speed, with no rest between speeds. Heart rate and energy expenditure were manually recorded every minute throughout the protocol. Results: Mean absolute percentage error for heart rate varied from 2.17 to 8.06% for the Fitbit Surge, from 1.01 to 7.49% for the TomTom Cardio and from 1.31 to 7.37% for the Microsoft Band. The mean absolute percentage error for energy expenditure varied from 25.4 to 61.8% for the Fitbit Surge, from 0.4 to 26.6% for the TomTom Cardio and from 1.8 to 9.4% for the Microsoft Band. Conclusion: Data from these devices may be useful in obtaining an estimate of heart rate for everyday activities and general exercise, but energy expenditure from these devices may be significantly over- or underestimated

A Model Ground State of Polyampholytes

The ground state of randomly charged polyampholytes is conjectured to have a structure similar to a necklace, made of weakly charged parts of the chain, compacting into globules, connected by highly charged stretched `strings'. We suggest a specific structure, within the necklace model, where all the neutral parts of the chain compact into globules: The longest neutral segment compacts into a globule; in the remaining part of the chain, the longest neutral segment (the 2nd longest neutral segment) compacts into a globule, then the 3rd, and so on. We investigate the size distributions of the longest neutral segments in random charge sequences, using analytical and Monte Carlo methods. We show that the length of the n-th longest neutral segment in a sequence of N monomers is proportional to N/(n^2), while the mean number of neutral segments increases as sqrt(N). The polyampholyte in the ground state within our model is found to have an average linear size proportional to sqrt(N), and an average surface area proportional to N^(2/3).Comment: 8 two-column pages. 5 eps figures. RevTex. Submitted to Phys. Rev.

A Survey of Local Group Galaxies Currently Forming Stars: III. A Search for Luminous Blue Variables and Other H-alpha Emission-Lined Stars

We describe a search for H-alpha emission-lined stars in M31, M33, and seven dwarfs in or near the Local Group (IC 10, NGC 6822, WLM, Sextans B, Sextans A, Pegasus and the Phoenix dwarf) using interference filter imaging with the KPNO and CTIO 4-m telescope and Mosaic cameras. The survey is aimed primarily at identifying new Luminous Blue Variables (LBVs) from their spectroscopic similarity to known LBVs, avoiding the bias towards photometric variability, which may require centuries to manifest itself if LBVs go through long quiescent periods. Followup spectroscopy with WIYN confirms that our survey detected a wealth of stars whose spectra are similar to the known LBVs. We "classify" the spectra of known LBVs, and compare these to the spectra of the new LBV candidates. We demonstrate spectacular spectral variability for several of the new LBV candidates, such as AM2, previously classified as a Wolf-Rayet star, which now shows FeI, FeII and Balmer emission lines but neither the NIII 4634,42 nor HeII 4686 emission that it did in 1982. Profound spectral changes are also noted for other suspected and known LBVs. Several of the LBV candidates also show >0.5 mag changes in V over the past 10-20 years. The number of known or suspected LBVs is now 24 in M31, 37 in M33, 1 in NGC 6822, and 3 in IC 10. We estimate that the total number of LBVs in M31 and M33 may be several hundred, in contrast to the 8 known historically through large-scale photometric variability. This has significant implications for the time scale of the LBV phase. We also identify a few new WRs and peculiar emission-lined objects.Comment: Accepted by the Astronomical Journal. Version with higher quality figures may be downloaded from http://www.lowell.edu/users/massey/has.pdf.g

Validity of Wrist-worn Physical Activity Monitors to Measure Heart Rate

Numerous physical activity monitors exist and are used to track and improve fitness levels. Due to the increasing popularity of these devices, newer products have been developed that measure heart rate (HR) at the wrist. Little is known about how accurate these devices are at measuring HR at the wrist and how they compare to each other. PURPOSE: To determine how accurately HR was measured by three different wrist-worn physical activity monitors. METHODS: Recreationally active men (n=9) and women (n=3) participated in this study. The average age and weight of participants was 22 ± 3 years and 73.9 ± 12 kg. TomTom Cardio (TT), Fitbit Surge (FB) and Microsoft Band (MB) physical activity monitors were used. The TT, FB, and MB were randomly assigned to the right or left wrist for each participant. The testing procedure included speeds of 2, 3, 4, 5, and 6 mph with each speed lasting three minutes. HR was measured by electrocardiography (ECG) using standard limb lead II and by the three different physical activity monitors. HR was recorded from each device every minute throughout the duration of the procedure. Pearson product moment correlations and bias between electrocardiography (ECG) and physical activity monitors with 95% limits of agreement (Bland-Altman analysis) were calculated. Repeated measures ANOVA [Speed x Device] were also calculated. Statistical significance was set at pRESULTS: At 2 mph and 3 mph, only TT HR was significantly correlated with ECG heart rate (r=0.693, p=0.012 and r=0.592, p=0.043). At 4 mph and 6 mph TT was significantly correlated with ECG (r=0.911, pCONCLUSION: With increasing speeds, physical activity monitors more accurately measure HR but individuals should be aware that these devices may overestimate HR during slower walking speeds

Studies Needed to Address Public Health Challenges of the 2009 H1N1 Influenza Pandemic: Insights from Modeling

In light of the 2009 influenza pandemic and potential future pandemics, Maria Van Kerkhove and colleagues anticipate six public health challenges and the data needed to support sound public health decision making.The authors acknowledge support from the Bill & Melinda Gates Foundation (MDVK, CF, NMF); Royal Society (CF); Medical Research Council (MDVK, CF, PJW, NMF); EU FP7 programme (NMF); UK Health Protection Agency (PJW); US National Institutes of Health Models of Infectious Disease Agent Study program through cooperative agreement 1U54GM088588 (ML); NIH Director's Pioneer Award, DP1-OD000490-01 (DS); EU FP7 grant EMPERIE 223498 (DS); the Wellcome Trust (DS); 3R01TW008246-01S1 from Fogerty International Center and RAPIDD program from Fogerty International Center with the Science & Technology Directorate, Department of Homeland Security (SR); and the Institut de Veille Sanitaire Sanitaire funded by the French Ministry of Health (J-CD). The funders played no role in the decision to submit the article or in its preparation