A [ITAL]z[/ITAL] = 5.34 Galaxy Pair in the Hubble Deep Field

Abstract— Meteoritic data strongly suggest that most chondrules reached maximum temperatures in a range of 1650–2000 K and cooled at relatively slow rates of 100–1000 K/h, implying a persistence of external energy supply. The presence of fine‐grained rims around chondrules in most unequilibrated chondrites also indicates that a significant quantity of micron‐sized dust was present in chondrule formation regions. Here, we assume that the persistent external energy source needed to explain chondrule cooling rates consists primarily of radiation from surrounding heated chondrules, fine dust, and gas after the formation event. Using an approximate one‐dimensional numerical model for the outward diffusion of thermal radiation from such a system, the scale sizes of formation regions required to yield acceptable cooling rates are determined for a range of possible chondrule, dust, and gas parameters. Results show that the inferred scale sizes depend sensitively on the number densities of micron‐sized dust and on their adopted optical properties. In the absence of dust, scale sizes > 1000 km are required for plausible maximum chondrule number densities and heated gas parameters. In the presence of dust with mass densities comparable to those of the chondrules and with absorptivities and emissivities of ∼0.01 calculated for Mie spheres with a pure mineral composition, scale sizes as small as ∼100 km are possible. If dust absorptivities and emissivities approach unity (as may occur for particles with more realistic shapes and compositions), then scale sizes as small as ×10 km are possible. Considering all uncertainties in model parameters, it is concluded that small scale sizes (10–100 km) for chondrule formation regions are allowed by the experimentally inferred cooling rates.

The rate of cross‐field plasma diffusion in the F region ionosphere is significantly increased when the magnetic field lines thread a highly conducting E region below. This reduces the lifetime of small‐scale F region electron density irregularities in the polar ionosphere where the presence of a highly conducting E region is commonplace. A simple model is developed to describe the effects of a conducting E layer on classical F region plasma diffusion. In the absence of an E region, the difference in ion and electron diffusion rates leads to a charge separation and, hence, to an electrostatic field that retards ion diffusion. When the highly conducting magnetic field lines are tied to a conducting E region, however, electrons can flow along B to reduce the ambipolar diffusion electric field, and ions can proceed perpendicular to B at a rate approaching their own (higher) diffusion velocity. It is shown that the enhanced total diffusion rate that results depends strongly on the height of the F layer and on the ratio of the E to F region Pedersen conductivities. Although the enhanced classical diffusion rate hastens the removal of irregularities once their production source is removed, it is not a strong enough damping mechanism to prevent instabilities from operating routinely in the polar ionosphere. However, the E region probably plays an important role in determining the scale size of the irregularities that are favored. E region ‘images’ may be important for low E region electron densities and small scale sizes, in which case the diffusion rate is lowered. However, if the E region conductivity is high, the presence of images only reduces the F region cross‐field plasma diffusion rate by about 25% from the ion rate. We hypothesize that the spectrum of high‐latitude plasma density irregularities is controlled at large scales (λ ≳ 10 km) by structured soft electron precipitation and classical diffusion. Smaller scale waves are produced by plasma instabilities operating on the edges of the large scale structures. The generalized instability (including the current convective process) acts to strengthen waves in the intermediate scale size (100 m ≤ λ ≤ 10 km) in regions where the geometry is appropriate or where field‐aligned currents are significant. Universal drift waves transfer energy from the intermediate scale to smaller structures but are ineffectual at large scales. The classical diffusion process described herein is applied (in conjunction with a model of irregularity production and convection) to the problem of explaining the morphology of the large scale high‐latitude irregularities in a companion paper (Kelley et al., this issue). The anomalous diffusion due to the instabilities mentioned above is also described in more detail.

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

We present results from a systematic study of star formation in local galaxy clusters using 22 micron data from the Wide-field Infrared Survey Explorer (WISE). The 69 systems in our sample are drawn from the Cluster Infall Regions Survey (CIRS), and all have robust mass determinations. The all-sky WISE data enables us to quantify the amount of star formation, as traced by 22 micron, as a function of radius well beyond R200, and investigate the dependence of total star formation rate upon cluster mass. We find that the fraction of star-forming galaxies increases with cluster radius but remains below the field value even at 3 R200. We also find that there is no strong correlation between the mass-normalized total specific star formation rate and cluster mass, indicating that the mass of the host cluster does not strongly influence the total star formation rate of cluster members.

A time dependent model of F region structure decay by “classical” cross field diffusion and electrical coupling along magnetic field lines to the E region is examined. The temporal behavior of the ion concentration fluctuations is determined by the electric field in the coupled system as well as by the initial perturbation spectra and the E region recombination rate. The formation of image structure in the E region ion concentration affects the lifetime of F layer structure in a scale size dependent way. Once an image is formed, the image amplitude and the driving F region structure amplitude decay at the same rate. At large scale sizes, λ(λ=2π/k), this rate is proportional to k² and the ratio of the temperatures in each region. At small scale sizes it depends on the E region recombination rate and the temperatures of the two regions but is only very weakly dependent on k. The background E region concentration determines the wave number beyond which the structure amplitude decay rate is almost independent of its scale size.

We present a direct comparison between the observed star formation rate functions (SFRFs) and the state-of-the-art predictions of semi-analytic models (SAMs) of galaxy formation and evolution. We use the PACS Evolutionary Probe Survey and Herschel Multi-tiered Extragalactic Survey data sets in the COSMOS and GOODS-South fields, combined with broad-band photometry from UV to sub-mm, to obtain total (IR+UV) instantaneous star formation rates (SFRs) for individual Herschel galaxies up to z ∼ 4, subtracted of possible active galactic nucleus (AGN) contamination. The comparison with model predictions shows that SAMs broadly reproduce the observed SFRFs up to z ∼ 2, when the observational errors on the SFR are taken into account. However, all the models seem to underpredict the bright end of the SFRF at z 2. The cause of this underprediction could lie in an improper modelling of several model ingredients, like too strong (AGN or stellar) feedback in the brighter objects or too low fallback of gas, caused by weak feedback and outflows at earlier epochs.

Abstract. Magnetic holes with relatively small scale sizes, detected by Cluster and TC-1 in the magnetotail plasma sheet, are studied in this paper. It is found that these magnetic holes are spatial structures and they are not magnetic depressions generated by the flapping movement of the magnetotail current sheet. Most of the magnetic holes (93%) were observed during intervals with Bz larger than Bx, i.e. they are more likely to occur in a dipolarized magnetic field topology. Our results also suggest that the occurrence of these magnetic holes might have a close relationship with the dipolarization process. The magnetic holes typically have a scale size comparable to the local proton Larmor radius and are accompanied by an electron energy flux enhancement at a 90° pitch angle, which is quite different from the previously observed isotropic electron distributions inside magnetic holes in the plasma sheet. It is also shown that most of the magnetic holes occur in marginally mirror-stable environments. Whether the plasma sheet magnetic holes are generated by the mirror instability related to ions or not, however, is unknown. Comparison of ratios, scale sizes and propagation direction of magnetic holes detected by Cluster and TC-1, suggests that magnetic holes observed in the vicinity of the TC-1 orbit (~7–12 RE) are likely to be further developed than those observed by Cluster (~7–18 RE).

Context. Observations at UV and optical wavelengths have revealed that galaxies at z ∼ 1 − 4 host star-forming regions, dubbed “clumps”, which are believed to form due to the fragmentation of gravitationally unstable, gas-rich disks. However, the detection of the parent molecular clouds that give birth to such clumps is still possible only in a minority of galaxies, mostly at z ∼ 1. Aims. We investigated the [C II] and dust morphology of a z ∼ 3.4 lensed galaxy hosting four clumps detected in the UV continuum. We aimed to observe the [C II] emission of individual clumps that, unlike the UV, is not affected by dust extinction, to probe their nature and cold gas content. Methods. We conducted ALMA observations probing scales down to ∼300 pc and detected three [C II] clumps. One (dubbed “NE”) coincides with the brightest UV clump, while the other two (“SW” and “C”) are not detected in the UV continuum. We do not detect the dust continuum. Results. We converted the [C II] luminosity of individual clumps into molecular gas mass and found Mmol ∼ 108 M⊙. By complementing it with the star formation rate (SFR) estimate from the UV continuum, we estimated the gas depletion time (tdep) of clumps and investigated their location in the Schmidt–Kennicutt plane. While the NE clump has a very short tdep = 0.16 Gyr, which is comparable with high-redshift starbursts, the SW and C clumps instead have longer tdep > 0.65 Gyr and are likely probing the initial phases of star formation. The lack of dust continuum detection is consistent with the blue UV continuum slope estimated for this galaxy (β ∼ −2.5) and it indicates that dust inhomogeneities do not significantly affect the detection of UV clumps in this target. Conclusions. We pushed the observation of the cold gas content of individual clumps up to z ∼ 3.4 and showed that the [C II] line emission is a promising tracer of molecular clouds at high redshift, allowing the detection of clumps with a large range of depletion times.

We investigate the star formation properties of dynamically relaxed galaxy clusters as a function of cluster mass for 308 low-redshift clusters drawn from the Sloan Digital Sky Survey (SDSS) C4 cluster catalog. It is important to establish if cluster star formation properties have a mass dependence before comparing clusters at different epochs, and here we use cluster velocity dispersion, σ, as a measure of cluster mass. We select clusters with no significant substructure, a subset of the full C4 sample, so that velocity dispersion is an accurate tracer of cluster mass. We find that the total stellar mass, the number of star-forming galaxies, and total star formation rate scale linearly with the number of member galaxies, with no residual dependence on cluster velocity dispersion. With the mass-dependence of cluster star formation rates established, we compare the SDSS clusters with a sample of z 0.75 clusters from the literature and find that on average (correcting for the mass growth of clusters between the two redshifts) the total Hα luminosity of the high-redshift clusters is 10 times greater than that of the low-redshift clusters. This can be explained by a decline in the Hα luminosities of individual cluster galaxies by a factor of up to ~10 since z 0.75. The magnitude of this evolution is comparable to that of field galaxies over a similar redshift interval, and thus the effect of the cluster environment on the evolution of star-forming galaxies is at most modest. Our results suggest that the physical mechanism driving the evolution of cluster star formation rates is independent of cluster mass, at least for clusters with velocity dispersion greater than 450 km s−1, and operates over a fairly long timescale such that the star formation rates of individual galaxies decline by an order of magnitude over ~7 billion years.

<p>The ESA Swarm constellation of satellites have been measuring the ionospheric electric and perturbation magnetic fields since 2013. Recently, the entire dataset of Swarm electric fields has been reprocessed into a 16Hz data product, allowing the analysis of ionospheric dynamics on sub-kilometre scales.</p><p>In combination with the on-board magnetometer data, the Swarm satellites can use the electric field measurements to determine the total electromagnetic energy into and out of the ionosphere, the Poynting flux. The 16Hz dataset allows for the capturing of much smaller scale sizes than previously considered, thus presenting the opportunity to study how much Poynting flux is missed when utilizing data across typically monitored scales (usually on the order of tens to hundreds of kilometres).</p><p>We present a statistical analysis of the Swarm A and B derived 16Hz Poynting flux, utilising various low-pass filters on the electric and magnetic field data to simulate smoothing the data to larger scale sizes. We find that by increasing the width of the low-pass filters, measured Poynting flux decreases significantly and quickly. Our results show that there is an over 50% underestimation in the total hemisphere integrated Poynting flux when observing it on scale sizes of a few hundred kilometres, compared to the raw 16Hz measurements that correspond to scales of around 0.5km. Under certain circumstances, as much as a 10% underestimation in the Poynting flux is observed by increasing scale size to only 5km. These results stress the importance observing small-scale electric and magnetic fields, as they may account for a large proportion of the ionosphere-thermosphere energy budget.</p>

Size scales over which ordinary chondrites and their parent asteroids are homogeneous in oxidation state and oxygen-isotopic composition

A large body of work has been devoted to defining and identifying clusters or communities in social and information networks, i.e., in graphs in which the nodes represent underlying social entities and the edges represent some sort of interaction between pairs of nodes. Most such research begins with the premise that a community or a cluster should be thought of as a set of nodes that has more and/or better connections between its members than to the remainder of the network. In this paper, we explore from a novel perspective several questions related to identifying meaningful communities in large social and information networks, and we come to several striking conclusions. Rather than defining a procedure to extract sets of nodes from a graph and then attempting to interpret these sets as "real" communities, we employ approximation algorithms for the graph-partitioning problem to characterize as a function of size the statistical and structural properties of partitions of graphs that could plausibly be interpreted as communities. In particular, we define the _network community profile plot_, which characterizes the "best" possible community—according to the conductance measure—over a wide range of size scales. We study over one hundred large real-world networks, ranging from traditional and online social networks, to technological and information networks and web graphs, and ranging in size from thousands up to tens of millions of nodes. Our results suggest a significantly more refined picture of community structure in large networks than has been appreciated previously. Our observations agree with previous work on small networks, but we show that large networks have a very different structure. In particular, we observe tight communities that are barely connected to the rest of the network at very small size scales (up to ≈ 100 nodes); and communities of size scale beyond ≈ 100 nodes gradually "blend into" the expander-like core of the network and thus become less "community-like," with a roughly inverse relationship between community size and optimal community quality. This observation agrees well with the so-called Dunbar number, which gives a limit to the size of a well-functioning community. However, this behavior is not explained, even at a qualitative level, by any of the commonly used network-generation models. Moreover, it is exactly the opposite of what one would expect based on intuition from expander graphs, low-dimensional or manifold-like graphs, and from small social networks that have served as test beds of community-detection algorithms. The relatively gradual increase of the network community profile plot as a function of increasing community size depends in a subtle manner on the way in which local clustering information is propagated from smaller to larger size scales in the network. We have found that a generative graph model, in which new edges are added via an iterative "forest fire" burning process, is able to produce graphs exhibiting a network community profile plot similar to what we observe in our network data sets.

We have determined the spatiotemporal characteristics of the magnetosphere‐ionosphere (M‐I) coupling using auroral imaging. Observations at fixed positions for an extended period of time are provided by a ground‐based all‐sky imager measuring the 557.7 nm auroral emissions. We report on a single event of nightside aurora (∼22 magnetic local time) preceding a substorm onset. To determine the spatiotemporal characteristics, we perform an innovative analysis of an all‐sky imager movie (19 min duration, images at 3.31 Hz) that combines a two‐dimensional spatial fast Fourier transform with a temporal correlation. We find a scale size‐dependent variability where the largest scale sizes are stable on timescales of minutes while the small scale sizes are more variable. When comparing two smaller time intervals of different types of auroral displays, we find a variation in their characteristics. The characteristics averaged over the event are in remarkable agreement with the spatiotemporal characteristics of the nightside field‐aligned currents during moderately disturbed times. Thus, two different electrodynamical parameters of the M‐I coupling show similar behavior. This gives independent support to the claim of a system behavior that uses repeatable solutions to transfer energy and momentum from the magnetosphere to the ionosphere.

Personal health monitoring is being considered the future of a sustainable health care system. Biosensing platforms are a very important component of this system. Real-time and accurate sensing is essential for the success of personal health care model. Currently, there are many efforts going on to make these sensors practical and more useful for such measurements. Implantable sensors are considered the most widely applicable and most reliable sensors for such accurate health monitoring applications. However, macroscopic (cm scale) size has proved to be a limiting factor for successful use of these systems for long time and in large numbers. This work is focused to resolve the issues related with miniaturizing these devices to a microscopic (mm scale) size scale which can minimize many practical difficulties associated with their larger counterparts currently. To accomplish this goal of miniaturization while retaining or even improving on the necessary capabilities for such sensing platforms, an integrated approach is presented which focuses on system-level miniaturization using standard fabrication procedures. First, it is shown that a completely integrated and wireless system is the best solution to achieve desired miniaturization without sacrificing the functionality of the system. Hence, design and implementation of the different components comprising the complete system needs to be done according to the requirements of the overall integrated system. This leads to the need of on-chip functional sensors, integrated wireless power supply, integrated wireless communication and integrated control system for realization of such system. In this work, different options for implementation of each of these subsystems are compared and an optimal solution is presented for each subsystem. For such complex systems, it is imperative to use a standard fabrication process which can provide the required functionality for all subsystems at smallest possible size scale. Complementary Metal Oxide Semiconductor (CMOS) process is the most appropriate of the technologies in this regard and has enabled incredible miniaturization of the computing industry. It also provides options for designing different subsystems on the same platform in a monolithic process with very high yield. This choice then leads to actual designs of subsystems in the CMOS technology using different possible methods. Careful comparison of these subsystems provides insights into different design adjustments that are made until the desired functions are achieved at the desired size scale. Integration of all these compatible subsystems in the same platform is shown to provide the smallest possible sensing platform to date. The completely wireless system can measure a host of different important analyte and can transmit the data to an external device which can use it for appropriate purpose. Results on measurements in phosphate buffer solution, blood serum and whole blood along with wireless communication in real biological tissues are provided. Specific examples of glucose and DNA sensors are presented and the use for many other relevant applications is also proposed. Finally, insights into animal model studies and future directions of the research are discussed.

Zinc sulfide multiscale aggregates can be obtained by homogeneous precipitation in a stirred reactor. Particle size distributions and morphologies are studied as a function of several operating parameters: pH, concentration in reactants (thioacetamide and zinc sulfate), temperature and stirring rate. Four size scales are observed. Stirring rate and pH have an influence respectively on the largest and the smallest size scale. Concentration in thioacetamide has an effect on the largest scales. All size scales depend on temperature.