Solving the electrical control of magnetic coercive field paradox

The ability to tune magnetic properties of solids via electric voltages instead of external magnetic fields is a physics curiosity of great scientific and technological importance. Today, there is strong published experimental evidence of electrical control of magnetic coercive fields in composite multiferroic solids. Unfortunately, the literature indicates highly contradictory results. In some studies, an applied voltage increases the magnetic coercive field and in other studies the applied voltage decreases the coercive field of composite multiferroics. Here, we provide an elegant explanation to this paradox and we demonstrate why all reported results are in fact correct. It is shown that for a given polarity of the applied voltage, the magnetic coercive field depends on the sign of two tensor components of the multiferroic solid: magnetostrictive and piezoelectric coefficient. For a negative applied voltage, the magnetic coercive field decreases when the two material parameters have the same sign and increases when they have opposite signs, respectively. The effect of the material parameters is reversed when the same multiferroic solid is subjected to a positive applied voltage

The Extended Star Formation History of the Andromeda Spheroid at 35 Kpc on the Minor Axis

Using the HST ACS, we have obtained deep optical images reaching well below the oldest main sequence turnoff in fields on the southeast minor-axis of the Andromeda Galaxy, 35 kpc from the nucleus. These data probe the star formation history in the extended halo of Andromeda -- that region beyond 30 kpc that appears both chemically and morphologically distinct from the metal-rich, highly-disturbed inner spheroid. The present data, together with our previous data for fields at 11 and 21 kpc, do not show a simple trend toward older ages and lower metallicities, as one might expect for populations further removed from the obvious disturbances of the inner spheroid. Specifically, the mean ages and [Fe/H] values at 11 kpc, 21 kpc, and 35 kpc are 9.7 Gyr and -0.65, 11.0 Gyr and -0.87, and 10.5 Gyr and -0.98, respectively. In the best-fit model of the 35 kpc population, one third of the stars are younger than 10 Gyr, while only ~10% of the stars are truly ancient and metal-poor. The extended halo thus exhibits clear evidence of its hierarchical assembly, and the contribution from any classical halo formed via early monolithic collapse must be small.Comment: Accepted for publication in The Astrophysical Journal Letters. 4 pages, latex, 2 color figure

The Panchromatic Hubble Andromeda Treasury II. Tracing the Inner M31 Halo with Blue Horizontal Branch Stars

We attempt to constrain the shape of M31's inner stellar halo by tracing the surface density of blue horizontal branch (BHB) stars at galactocentric distances ranging from 2 kpc to 35 kpc. Our measurements make use of resolved stellar photometry from a section of the Panchromatic Hubble Andromeda Treasury (PHAT) survey, supplemented by several archival Hubble Space Telescope observations. We find that the ratio of BHB to red giant stars is relatively constant outside of 10 kpc, suggesting that the BHB is as reliable a tracer of the halo population as the red giant branch. In the inner halo, we do not expect BHB stars to be produced by the high metallicity bulge and disk, making BHB stars a good candidate to be a reliable tracer of the stellar halo to much smaller galactocentric distances. If we assume a power-law profile r^(-\alpha) for the 2-D projected surface density BHB distribution, we obtain a high-quality fit with a 2-D power-law index of \alpha=2.6^{+0.3}_{-0.2} outside of 3 kpc, which flattens to \alpha<1.2 inside of 3 kpc. This slope is consistent with previous measurements but is anchored to a radial baseline that extends much farther inward. Finally, assuming azimuthal symmetry and a constant mass-to-light ratio, the best-fitting profile yields a total halo stellar mass of 2.1^{+1.7}_{-0.4} x 10^9 M_sun. These properties are comparable with both simulations of stellar halo formation formed by satellite disruption alone, and with simulations that include some in situ formation of halo stars.Comment: 15 pages, 1 table, 5 figures, accepted for publication in Ap

Ordered groupoids and the holomorph of an inverse semigroup

We present a construction for the holomorph of an inverse semigroup, derived from the cartesian closed structure of the category of ordered groupoids. We compare the holomorph with the monoid of mappings that preserve the ternary heap operation on an inverse semigroup: for groups these two constructions coincide. We present detailed calculations for semilattices of groups and for the polycyclic monoids.Comment: 16 page

Scaling metagenome sequence assembly with probabilistic de Bruijn graphs

Deep sequencing has enabled the investigation of a wide range of environmental microbial ecosystems, but the high memory requirements for {\em de novo} assembly of short-read shotgun sequencing data from these complex populations are an increasingly large practical barrier. Here we introduce a memory-efficient graph representation with which we can analyze the k-mer connectivity of metagenomic samples. The graph representation is based on a probabilistic data structure, a Bloom filter, that allows us to efficiently store assembly graphs in as little as 4 bits per k-mer, albeit inexactly. We show that this data structure accurately represents DNA assembly graphs in low memory. We apply this data structure to the problem of partitioning assembly graphs into components as a prelude to assembly, and show that this reduces the overall memory requirements for {\em de novo} assembly of metagenomes. On one soil metagenome assembly, this approach achieves a nearly 40-fold decrease in the maximum memory requirements for assembly. This probabilistic graph representation is a significant theoretical advance in storing assembly graphs and also yields immediate leverage on metagenomic assembly

Collecting biomedical and social data in a longitudinal survey: A comparison of two approaches

The inclusion of the collection of biomeasures within social surveys, and longitudinal surveys in particular, is becoming ever more common. Combining objective measurements of health with detailed information about lifestyles and behaviour collected over long periods of time offers enormous research potential. Studies that combine an interview with the collection of biomeasures can be conducted in various ways. One model is that field interviewers make initial contact with participants, conduct the interviews and arrange follow-up visits for a nurse to collect the biomeasures. Alternatively, field interviewers can be trained to collect biomeasures, but there remain questions about whether the quality of data collected is comparable to that collected by a nurse. Other studies invite participants to visit clinics, but this can be very costly in a large-scale national study. There is no consensus on the optimal strategy for combining a social survey with the collection of biomeasures. The 1970 British Cohort Study (BCS70) is a longitudinal birth cohort study which began in 1970. The 11th sweep of the study began in 2016, when study members were aged 46, and included an interview component alongside the collection of a range of biomeasures. The first phase of fieldwork was conducted using a new approach where nurses conducted all of the data collection. Midway through fieldwork BCS70 switched to a two-stage approach where interviews were conducted by interviewers followed by a separate nurse visit. This presented a unique opportunity to evaluate the success of the two approaches

Simulator study of stall/post-stall characteristics of a fighter airplane with relaxed longitudinal static stability

A real-time piloted simulation was conducted to evaluate the high-angle-of-attack characteristics of a fighter configuration based on wind-tunnel testing of the F-16, with particular emphasis on the effects of various levels of relaxed longitudinal static stability. The aerodynamic data used in the simulation was conducted on the Langley differential maneuvering simulator, and the evaluation involved representative low-speed combat maneuvering. Results of the investigation show that the airplane with the basic control system was resistant to the classical yaw departure; however, it was susceptible to pitch departures induced by inertia coupling during rapid, large-amplitude rolls at low airspeed. The airplane also exhibited a deep-stall trim which could be flown into and from which it was difficult to recover. Control-system modifications were developed which greatly decreased the airplane susceptibility to the inertia-coupling departure and which provided a reliable means for recovering from the deep stall

A structured approach for the engineering of biochemical network models, illustrated for signalling pathways

http://dx.doi.org/10.1093/bib/bbn026Quantitative models of biochemical networks (signal transduction cascades, metabolic pathways, gene regulatory circuits) are a central component of modern systems biology. Building and managing these complex models is a major challenge that can benefit from the application of formal methods adopted from theoretical computing science. Here we provide a general introduction to the field of formal modelling, which emphasizes the intuitive biochemical basis of the modelling process, but is also accessible for an audience with a background in computing science and/or model engineering. We show how signal transduction cascades can be modelled in a modular fashion, using both a qualitative approach { Qualitative Petri nets, and quantitative approaches { Continuous Petri Nets and Ordinary Differential Equations. We review the major elementary building blocks of a cellular signalling model, discuss which critical design decisions have to be made during model building, and present ..