684 research outputs found
Stable Expression of Gal/GalNAc Lectin of Entamoeba Histolytica in Transgenic Chloroplasts and Immunogenicity in Mice Towards Vaccine Development for Amoebiasis
Chloroplast genetic engineering offers several advantages, including high levels of transgene expression, transgene containment via maternal inheritance and multigene engineering in a single transformation event. Entamoeba histolytica infects 50 million people, causing about 100 000 deaths annually, but there is no approved vaccine against this pathogen. LecA, a potential target for blocking amoebiasis, was expressed for the first time in transgenic plants. Stable transgene integration into chloroplast genomes and homoplasmy were confirmed by polymerase chain reaction and Southern blot analyses. LecA expression was evaluated by Western blots and quantified by enzyme-linked immunosorbent assay (up to 6.3% of total soluble protein or 2.3 mg LecA/g leaf tissue). Subcutaneous immunization of mice with crude extract of transgenic leaves resulted in higher immunoglobulin G titres (up to 1 : 10 000) than in previous reports. An average yield of 24 mg of LecA per plant should produce 29 million doses of vaccine antigen per acre of transgenic plants. Such high levels of expression and immunogenicity should facilitate the development of a less expensive amoebiasis vaccine
Probabilistic approaches for modeling text structure and their application to text-to-text generation
Since the early days of generation research, it has been acknowledged that modeling the global structure of a document is crucial for producing coherent, readable output. However, traditional knowledge-intensive approaches have been of limited utility in addressing this problem since they cannot be effectively scaled to operate in domain-independent, large-scale applications. Due to this difficulty, existing text-to-text generation systems rarely rely on such structural information when producing an output text. Consequently, texts generated by these methods do not match the quality of those written by humans – they are often fraught with severe coherence violations and disfluencies.
In this chapter, I will present probabilistic models of document structure that can be effectively learned from raw document collections. This feature distinguishes these new models from traditional knowledge intensive approaches used in symbolic concept-to-text generation. Our results demonstrate that these probabilistic models can be directly applied to content organization, and suggest that these models can prove useful in an even broader range of text-to-text applications than we have considered here.National Science Foundation (U.S.) (CAREER grant IIS- 0448168)Microsoft Research. New Faculty Fellowshi
Radio Bursts Associated with Flare and Ejecta in the 13 July 2004 Event
We investigate coronal transients associated with a GOES M6.7 class flare and
a coronal mass ejection (CME) on 13 July 2004. During the rising phase of the
flare, a filament eruption, loop expansion, a Moreton wave, and an ejecta were
observed. An EIT wave was detected later on. The main features in the radio
dynamic spectrum were a frequency-drifting continuum and two type II bursts.
Our analysis shows that if the first type II burst was formed in the low
corona, the burst heights and speed are close to the projected distances and
speed of the Moreton wave (a chromospheric shock wave signature). The
frequency-drifting radio continuum, starting above 1 GHz, was formed almost two
minutes prior to any shock features becoming visible, and a fast-expanding
piston (visible as the continuum) could have launched another shock wave. A
possible scenario is that a flare blast overtook the earlier transient, and
ignited the first type II burst. The second type II burst may have been formed
by the same shock, but only if the shock was propagating at a constant speed.
This interpretation also requires that the shock-producing regions were located
at different parts of the propagating structure, or that the shock was passing
through regions with highly different atmospheric densities. This complex
event, with a multitude of radio features and transients at other wavelengths,
presents evidence for both blast-wave-related and CME-related radio emissions.Comment: 14 pages, 6 figures; Solar Physics Topical Issue, in pres
Large-scale Bright Fronts in the Solar Corona: A Review of "EIT waves"
``EIT waves" are large-scale coronal bright fronts (CBFs) that were first
observed in 195 \AA\ images obtained using the Extreme-ultraviolet Imaging
Telescope (EIT) onboard the \emph{Solar and Heliospheric Observatory (SOHO)}.
Commonly called ``EIT waves", CBFs typically appear as diffuse fronts that
propagate pseudo-radially across the solar disk at velocities of 100--700 km
s with front widths of 50-100 Mm. As their speed is greater than the
quiet coronal sound speed (200 km s) and comparable to the
local Alfv\'{e}n speed (1000 km s), they were initially
interpreted as fast-mode magnetoacoustic waves ().
Their propagation is now known to be modified by regions where the magnetosonic
sound speed varies, such as active regions and coronal holes, but there is also
evidence for stationary CBFs at coronal hole boundaries. The latter has led to
the suggestion that they may be a manifestation of a processes such as Joule
heating or magnetic reconnection, rather than a wave-related phenomena. While
the general morphological and kinematic properties of CBFs and their
association with coronal mass ejections have now been well described, there are
many questions regarding their excitation and propagation. In particular, the
theoretical interpretation of these enigmatic events as magnetohydrodynamic
waves or due to changes in magnetic topology remains the topic of much debate.Comment: 34 pages, 19 figure
Coronal Shock Waves, EUV waves, and Their Relation to CMEs. I. Reconciliation of "EIT waves", Type II Radio Bursts, and Leading Edges of CMEs
We show examples of excitation of coronal waves by flare-related abrupt
eruptions of magnetic rope structures. The waves presumably rapidly steepened
into shocks and freely propagated afterwards like decelerating blast waves that
showed up as Moreton waves and EUV waves. We propose a simple quantitative
description for such shock waves to reconcile their observed propagation with
drift rates of metric type II bursts and kinematics of leading edges of coronal
mass ejections (CMEs). Taking account of different plasma density falloffs for
propagation of a wave up and along the solar surface, we demonstrate a close
correspondence between drift rates of type II bursts and speeds of EUV waves,
Moreton waves, and CMEs observed in a few known events.Comment: 30 pages, 15 figures. Solar Physics, published online. The final
publication is available at http://www.springerlink.co
Emergence of Skyrme crystal in Gross-Neveu and 't Hooft models at finite density
We study two-dimensional, large field theoretic models (Gross-Neveu
model, 't Hooft model) at finite baryon density near the chiral limit. The same
mechanism which leads to massless baryons in these models induces a breakdown
of translational invariance at any finite density. In the chiral limit baryonic
matter is characterized by a spatially varying chiral angle with a wave number
depending only on the density. For small bare quark masses a sine-Gordon kink
chain is obtained which may be regarded as simplest realization of the Skyrme
crystal for nuclear matter. Characteristic differences between confining and
non-confining models are pointed out.Comment: 27 pages, 11 figures, added reference, corrected sig
On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode
A major, albeit serendipitous, discovery of the SOlar and Heliospheric
Observatory mission was the observation by the Extreme Ultraviolet Telescope
(EIT) of large-scale Extreme Ultraviolet (EUV) intensity fronts propagating
over a significant fraction of the Sun's surface. These so-called EIT or EUV
waves are associated with eruptive phenomena and have been studied intensely.
However, their wave nature has been challenged by non-wave (or pseudo-wave)
interpretations and the subject remains under debate. A string of recent solar
missions has provided a wealth of detailed EUV observations of these waves
bringing us closer to resolving their nature. With this review, we gather the
current state-of-art knowledge in the field and synthesize it into a picture of
an EUV wave driven by the lateral expansion of the CME. This picture can
account for both wave and pseudo-wave interpretations of the observations, thus
resolving the controversy over the nature of EUV waves to a large degree but
not completely. We close with a discussion of several remaining open questions
in the field of EUV waves research.Comment: Solar Physics, Special Issue "The Sun in 360",2012, accepted for
publicatio
TDP-43 in the hypoglossal nucleus identifies amyotrophic lateral sclerosis in behavioral variant frontotemporal dementia
The hypoglossal nucleus was recently identified as a key brain region in which the presence of TDP-43 pathology could accurately discriminate TDP-43 proteinopathy cases with clinical amyotrophic lateral sclerosis (ALS). The objective of the present study was to assess the hypoglossal nucleus in behavioral variant frontotemporal dementia (bvFTD), and determine whether TDP-43 in this region is associated with clinical ALS. Twenty-nine cases with neuropathological FTLD-TDP and clinical bvFTD that had not been previously assessed for hypoglossal TDP-43 pathology were included in this study. Of these 29 cases, 41% (n = 12) had a dual diagnosis of bvFTD-ALS at presentation, all 100% (n = 12) of which demonstrated hypoglossal TDP-43 pathology. Of the 59% (n = 17) cohort that presented with pure bvFTD, 35% (n = 6) were identified with hypoglossal TDP-43 pathology. Review of the case files of all pure bvFTD cases revealed evidence of possible or probable ALS in 5 of the 6 hypoglossal-positive cases (83%) towards the end of disease, and this was absent from all cases without such pathology. In conclusion, the present study validates grading the presence of TDP-43 in the hypoglossal nucleus for the pathological identification of bvFTD cases with clinical ALS, and extends this to include the identification of cases with possible ALS at end-stage
The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets
This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics
Interstellar MHD Turbulence and Star Formation
This chapter reviews the nature of turbulence in the Galactic interstellar
medium (ISM) and its connections to the star formation (SF) process. The ISM is
turbulent, magnetized, self-gravitating, and is subject to heating and cooling
processes that control its thermodynamic behavior. The turbulence in the warm
and hot ionized components of the ISM appears to be trans- or subsonic, and
thus to behave nearly incompressibly. However, the neutral warm and cold
components are highly compressible, as a consequence of both thermal
instability in the atomic gas and of moderately-to-strongly supersonic motions
in the roughly isothermal cold atomic and molecular components. Within this
context, we discuss: i) the production and statistical distribution of
turbulent density fluctuations in both isothermal and polytropic media; ii) the
nature of the clumps produced by thermal instability, noting that, contrary to
classical ideas, they in general accrete mass from their environment; iii) the
density-magnetic field correlation (or lack thereof) in turbulent density
fluctuations, as a consequence of the superposition of the different wave modes
in the turbulent flow; iv) the evolution of the mass-to-magnetic flux ratio
(MFR) in density fluctuations as they are built up by dynamic compressions; v)
the formation of cold, dense clouds aided by thermal instability; vi) the
expectation that star-forming molecular clouds are likely to be undergoing
global gravitational contraction, rather than being near equilibrium, and vii)
the regulation of the star formation rate (SFR) in such gravitationally
contracting clouds by stellar feedback which, rather than keeping the clouds
from collapsing, evaporates and diperses them while they collapse.Comment: 43 pages. Invited chapter for the book "Magnetic Fields in Diffuse
Media", edited by Elisabete de Gouveia dal Pino and Alex Lazarian. Revised as
per referee's recommendation
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