Method and apparatus for producing microshells

A method is described for forming hollow particles, or shells, of extremely small size. The shell material is heated to a molten temperature in the presence of a gas that is at least moderately soluble in the shell material, to form a solution of the molten shell material and the soluble gas. The solution is atomized to form a multiplicity of separate droplets that are cooled while in free fall. Cooling of a droplet from the outside traps the desolved gas and forces it to form a gas bubble at the center of the droplet which now forms a gas filled shell. The shell is reheated and then cooled in free fall, in an environment having a lower pressure than the gas pressure in the shell. This causes expansion of the shell and the formation of a shell having a small wall thickness compared to its diameter

Measuring forces between protein fibers by microscopy

We propose a general scheme for measuring the attraction between mechanically frustrated semiflexible fibers by measuring their thermal fluctuations and shape. We apply this analysis to a system of sickle hemoglobin (HbS) fibers that laterally attract one another. These fibers appear to “zip” together before reaching mechanical equilibrium due to the existence of cross-links into a dilute fiber network. We are also able to estimate the rigidities of the fibers. These rigidities are found to be consistent with sickle hemoglobin “single” fibers 20 nm in diameter, despite recent experiments indicating that fiber bundling sometimes occurs. Our estimate of the magnitude of the interfiber attraction for HbS fibers is in the range 8 ± 7 kBT/μm, or 4 ± 3 kBT/μm if the fibers are assumed, a priori to be single fibers (such an assumption is fully consistent with the data). This value is sufficient to bind the fibers, overcoming entropic effects, although extremely chemically weak. Our results are compared to models for the interfiber attraction that include depletion and van der Waals forces. This technique should also facilitate a similar analysis of other filamentous protein assembles in the future, including β-amyloid, actin, and tubulin

Tic: a Methodology for the Improvement of DHCP

Linked lists must work. In fact, few biologists would disagree with the deployment of e-business, which embodies the private principles of artificial intelligence. Our focus in this paper is not on whether lambda calcu- lus can be made cacheable, event-driven, and pervasive, but rather on proposing a method- ology for the investigation of IPv6 (Tic) [4]

Strategies towards statistically robust interpretations of in situ U–Pb zircon geochronology

Zircon U–Pb geochronology has become a keystone tool across Earth science, arguably providing the gold standard in resolving deep geological time. The development of rapid in situ analysis of zircon (via laser ablation and secondary ionization mass spectrometry) has allowed for large amounts of data to be generated in a relatively short amount of time and such large volume datasets offer the ability to address a range of geological questions that would otherwise remain intractable (e.g. detrital zircons as a sediment fingerprinting method). The ease of acquisition, while bringing benefit to the Earth science community, has also led to diverse interpretations of geochronological data. In this work we seek to refocus U–Pb zircon geochronology toward best practice by providing a robust statistically coherent workflow. We discuss a range of data filtering approaches and their inherent limitations (e.g. discordance and the reduced chi-squared; MSWD). We evaluate appropriate mechanisms to calculate the most geologically appropriate age from both 238U/206Pb and 207Pb/206Pb ratios and demonstrate the cross over position when chronometric power swaps between these ratios. As our in situ analytical techniques become progressively more precise, appropriate statistical handing of U–Pb datasets will become increasingly pertinent

SACRIFÍCIO REI, ESTADO RUANDÊS E GENOCÍDIO

Em contraste com as análises do genocídio ruandês de 1994, que privilegiam o político, este artigo sustenta que o poder e a política durante o tempo que precedeu o genocídio foram afetadas por noções ruandesas específicas de cosmologia e ontologia. Para entender esse componente “imaginário” da violência, precisamos examinar atentamente as crenças e práticas relacionadas com a instituição da realeza sagrada em Ruanda. Embora essas crenças e práticas foram oficialmente encerradas em 1931, quando o último rei de Ruanda sagrado foi deposto e substituído por seu filho educado por missionários, a sua matriz cosmológica manteve-se em tempos recentes. Isto pode ser visto na literatura popular de rua Ruandesa, que circulou amplamente nos dias que antecederam o genocídio. Nessa literatura, o então presidente Juvenal Habyarimana era comparado explicitamente a um rei ruandês. Mais importante ainda para os objetivos deste artigo, foi a comparação mais difusa, implícita, e simbólica entre Habyarimana e um rei sagrado. Em particular, alguns dos elementos-chave neste simbolismo iluminam (e mostram a importância da persistência) da imagem de como um rei (ou presidente) deveria se comportar. Como havia muitos jornalistas ruandeses reacionários (e racistas) que tinham começado a duvidar da capacidade do presidente Habyarimana de ser um “bom rei”, seu “sacrifício”’subseqüente estava, em um sentido simbólico, fortemente predestinado. Palavras-chave: simbolismo, genocídio Ruanda, realeza sagrada. KING SACRIFICE, THE RWANDAN STATE, AND GENOCIDE Christopher C. Taylor In contrast to analyses of the 1994 Rwandan genocide that privilege the political, this paper maintains that power and politics during the time preceding the genocide were embedded in and conditioned by specifically Rwandan notions of cosmology and ontology. In order to understand this “imaginary” component to the violence, we need to closely examine Rwandan beliefs and practices related to the institution of sacred kingship. Although these beliefs and practices effectively terminated in 1931 when the last sacred Rwandan king was deposed and replaced by his mission-educated son, their cosmological matrix endured well into recent times. This is seen in the popular Rwandan street literature which circulated widely in the days leading up to the genocide. In this literature, then President Juvenal Habyarimana was explicitly compared at times to a Rwandan king. More importantly for the purposes of this paper, was the more diffuse, implicit, and symbolic comparison of Habyarimana to a sacred Rwandan king. In particular, some of the key elements in this symbolism adumbrate (and show the persisting importance of) an image of what a morally positive king (or modern president) should be like. Because there were many reactionary (and racist) Rwandan journalists who had begun to doubt President Habyarimana’s adequacy as a ‘good king,’ his subsequent ‘sacrifice’ was in a strong, though symbolic sense, preordained. KEY WORD: symbolism, Rwandan genocide, sacred kingship. SACRIFICE ROI, ÉTAT RWANDAIS ET GÉNOCIDE Christopher C. Taylor Contrairement à l’analyse du génocide rwandais de 1994, où le politique est mis en avant, cet article démontre que le pouvoir et la politique, au cours de la période qui a précédé le génocide, ont été marqués par des notions rwandaises de cosmologie et d’ontologie. Afin de comprendre cette composante ‘imaginaire’ de la violence, il nous faut examiner attentivement les croyances et les pratiques liées à l’institution de la royauté sacrée au Rwanda. Même si ces croyances et ces pratiques ont été officiellement supprimées en 1931, lorsque le dernier roi sacré du Rwanda a été détrôné et remplacé par son fils élevé par des missionnaires, sa matrice cosmologique a subsisté jusqu’à une période récente. On peut le constater dans la littérature populaire du Rwanda qui circulait énormément dans les jours qui ont précédé le génocide. Dans cette littérature, le président de l’époque, Juvenal Habyarimana, était comparé de manière explicite à un roi rwandais. Ce qui est encore plus important pour nous, dans cet article, c’est cette comparaison plus diffuse, implicite et symbolique entre Habyarimana et un roi sacré. Certains éléments-clés éclairent tout particulièrement ce symbolisme (et montrent l’importance de la persistance) de l’image selon laquelle un roi (ou un président) devrait se comporter. Comme il y avait de nombreux journalistes rwandais réactionnaires (et racistes) qui doutaient des capacités du président Habyarimana d’être un ‘bon roi’, son ‘sacrifice’ ultérieur était, dans un sens très symbolique, fortement prédestiné. MOTS-CLÉS: symbolisme, génocide Rwanda, royauté sacrée. Publicação Online do Caderno CRH: http://www.cadernocrh.ufba.br   Publicação Online do Caderno CRH no Scielo: http://www.scielo.br/ccr

Shear-induced breaking of internal gravity waves

Motivated by observations of turbulence in the strongly stratified ocean thermocline, we use direct numerical simulations to investigate the interaction of a sinusoidal shear flow and a large-amplitude internal gravity wave. Despite strong nonlinearities in the flow and a lack of scale separation, we find that linear ray tracing theory is qualitatively useful in describing the early development of the flow as the wave is refracted by the shear. Consistent with the linear theory, the energy of the wave accumulates in regions of negative mean shear where we observe evidence of convective and shear instabilities. Streamwise-aligned convective rolls emerge the fastest, but their contribution to irreversible mixing is dwarfed by shear-driven billow structures that develop later. Although the wave strongly distorts the buoyancy field on which these billows develop, the mixing efficiency of the subsequent turbulence is similar to that arising from Kelvin-Helmholtz instability in a stratified shear layer. We run simulations at Reynolds numbers of 5000 and 8000, and vary the initial amplitude of the internal gravity wave. For high values of initial wave amplitude, the results are qualitatively independent of $Re$. Smaller initial wave amplitudes delay the onset of the instabilities, and allow for significant laminar diffusion of the internal wave, leading to reduced turbulent activity. We discuss the complex interaction between the mean flow, internal gravity wave and turbulence, and its implications for internal wave-driven mixing in the ocean.Comment: 27 pages, 12 figures, accepted to J. Fluid. Mec

Discovery of Molecular Gas in the Outflow and Tidal Arms around M82

We present the first fully sampled map of 12CO (1-0) emission from M82 covering the entire galaxy. Our map contains a 12 x 15 kpc^2 area. We find that extraplanar CO emission, previously reported at short distances above the galactic plane, extends to heights of up to 6 kpc above the disk. Some of this emission is associated with tidal arms seen in HI, implying either that M82 contained substantial amounts of molecular gas in the outer disk, or that molecular gas formed after the tidal features. CO emission along the direction of the outflow extends to distances of 3 kpc above and below the disk. At this distance, the line is shifted in velocity about 100 km/s, and has the same sense as the galactic outflow from the central starburst. This implies that molecular gas may be entrained into the outflow.Comment: 4 pages, 6 figures. Uses emulateapj5. Accepted by ApJ Letter

Quantifying mixing and available potential energy in vertically periodic simulations of stratified flows

Turbulent mixing exerts a significant influence on many physical processes in the ocean. In a stably stratified Boussinesq fluid, this irreversible mixing describes the conversion of available potential energy (APE) to background potential energy (BPE). In some settings the APE framework is difficult to apply and approximate measures are used to estimate irreversible mixing. For example, numerical simulations of stratified turbulence often use triply periodic domains to increase computational efficiency. In this setup however, BPE is not uniquely defined and the method of Winters et al. (1995, J. Fluid Mech., 289) cannot be directly applied to calculate the APE. We propose a new technique to calculate APE in periodic domains with a mean stratification. By defining a control volume bounded by surfaces of constant buoyancy, we can construct an appropriate background buoyancy profile $b_\ast(z,t)$ and accurately quantify diapycnal mixing in such systems. This technique also permits the accurate calculation of a finite amplitude local APE density in periodic domains. The evolution of APE is analysed in various turbulent stratified flow simulations. We show that the mean dissipation rate of buoyancy variance $\chi$ provides a good approximation to the mean diapycnal mixing rate, even in flows with significant variations in local stratification. When quantifying measures of mixing efficiency in transient flows, we find significant variation depending on whether laminar diffusion of a mean flow is included in the kinetic energy dissipation rate. We discuss how best to interpret these results in the context of quantifying diapycnal diffusivity in real oceanographic flows.Comment: 28 pages, 10 figures, accepted to J. Fluid Mec

Microlensing of the Lensed Quasar SDSS0924+0219

We analyze V, I and H band HST images and two seasons of R-band monitoring data for the gravitationally lensed quasar SDSS0924+0219. We clearly see that image D is a point-source image of the quasar at the center of its host galaxy. We can easily track the host galaxy of the quasar close to image D because microlensing has provided a natural coronograph that suppresses the flux of the quasar image by roughly an order of magnitude. We observe low amplitude, uncorrelated variability between the four quasar images due to microlensing, but no correlated variations that could be used to measure a time delay. Monte Carlo models of the microlensing variability provide estimates of the mean stellar mass in the lens galaxy (0.02 Msun < M < 1.0 Msun), the accretion disk size (the disk temperature is 5 x 10^4 K at 3.0 x 10^14 cm < rs < 1.4 x 10^15 cm), and the black hole mass (2.0 x 10^7 Msun < MBH \eta_{0.1}^{-1/2} (L/LE)^{1/2} < 3.3 x 10^8 Msun), all at 68% confidence. The black hole mass estimate based on microlensing is consistent with an estimate of MBH = 7.3 +- 2.4 x 10^7 Msun from the MgII emission line width. If we extrapolate the best-fitting light curve models into the future, we expect the the flux of images A and B to remain relatively stable and images C and D to brighten. In particular, we estimate that image D has a roughly 12% probability of brightening by a factor of two during the next year and a 45% probability of brightening by an order of magnitude over the next decade.Comment: v.2 incorporates referee's comments and corrects two errors in the original manuscript. 28 pages, 10 figures, published in Ap

Method and apparatus for generating microshells of refractory materials

A system is described for forming accurately spherical and centered fluid-filled shells, especially of high melting temperature material. Material which is to form the shells is placed in a solid form in a container, and the material is rapidly heated to a molten temperature to avoid recrystallization and the possible generation of unwanted microbubbles in the melt. Immediately after the molten shells are formed, they drop through a drop tower whose upper end is heated along a distance of at least one foot to provide time for dissipation of surface waves on the shells while they cool to a highly viscous, or just above melting temperature so that the bubble within the shell will not rise and become off centered. The rest of the tower is cryogenically cooled to cool the shell to a solid state