1,569 research outputs found
Evolution-guided functional analyses reveal diverse antiviral specificities encoded by IFIT1 genes in mammals.
IFIT (interferon-induced with tetratricopeptide repeats) proteins are critical mediators of mammalian innate antiviral immunity. Mouse IFIT1 selectively inhibits viruses that lack 2'O-methylation of their mRNA 5' caps. Surprisingly, human IFIT1 does not share this antiviral specificity. Here, we resolve this discrepancy by demonstrating that human and mouse IFIT1 have evolved distinct functions using a combination of evolutionary, genetic and virological analyses. First, we show that human IFIT1 and mouse IFIT1 (renamed IFIT1B) are not orthologs, but are paralogs that diverged >100 mya. Second, using a yeast genetic assay, we show that IFIT1 and IFIT1B proteins differ in their ability to be suppressed by a cap 2'O-methyltransferase. Finally, we demonstrate that IFIT1 and IFIT1B have divergent antiviral specificities, including the discovery that only IFIT1 proteins inhibit a virus encoding a cap 2'O-methyltransferase. These functional data, combined with widespread turnover of mammalian IFIT genes, reveal dramatic species-specific differences in IFIT-mediated antiviral repertoires
Mathematical models of bipolar disorder
We use limit cycle oscillators to model bipolar II disorder, which is characterized by alternating hypomanic and depressive episodes and afflicts about 1% of the United States adult population. We consider two non-linear oscillator models of a single bipolar patient. In both frameworks, we begin with an untreated individual and examine the mathematical effects and resulting biological consequences of treatment. We also briefly consider the dynamics of interacting bipolar II individuals using weakly-coupled, weakly-damped harmonic oscillators. We discuss how the proposed models can be used as a framework for refined models that incorporate additional biological data. We conclude with a discussion of possible generalizations of our work, as there are several biologically-motivated extensions that can be readily incorporated into the series of models presented here
Integrating Informational Text and STEM: An Innovative and Necessary Curricular Approach
Recent standards-based reforms call for the use of a variety of informational texts at the elementary level. Informational texts are essential for implementing integrated problem-based science, technology, engineering, and mathematics (STEM) learning in elementary classrooms. Additionally, integrated STEM projects support the use of informational texts as students conduct research, design solutions, and communicate their results, thereby providing real-world applications of informational text. Elementary teachers need encouragement and support in order to increase the use of informational texts that assist in implementing effective STEM lessons. The authors provide strategies for melding informational texts with problem- and project-based learning in STEM
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Development of a high gradient magnetic separator using high temperature superconductors
This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). High-gradient magnetic separation (HGMS) is an application of superconducting magnet technology to the process of magnetic separation of solids from other solids, liquids, or gases. The production of both high magnetic fields and large field gradients using superconducting magnet technology has made it possible to separate a previously unreachable but large family of paramagnetic materials. It is possible to separate more than half of the elements in the periodic table using this method. Because HGMS is a physical separation process, no additional or mixed waste is generated. This project sought to develop a high-gradient magnetic separator using a high-temperature superconducting magnet
Electron-Positron Jets from a Critically Magnetized Black Hole
The curved spacetime surrounding a rotating black hole dramatically alters
the structure of nearby electromagnetic fields. The Wald field which is an
asymptotically uniform magnetic field aligned with the angular momentum of the
hole provides a convenient starting point to analyze the effects of radiative
corrections on electrodynamics in curved spacetime. Since the curvature of the
spacetime is small on the scale of the electron's Compton wavelength, the tools
of quantum field theory in flat spacetime are reliable and show that a rotating
black hole immersed in a magnetic field approaching the quantum critical value
of ~G cm is unstable. Specifically, a maximally rotating
three-solar-mass black hole immersed in a magnetic field of ~G would be a copious producer of electron-positron pairs with a
luminosity of erg s.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Simulation of Ultra-High Energy Photon Propagation in the Geomagnetic Field
The identification of primary photons or specifying stringent limits on the
photon flux is of major importance for understanding the origin of ultra-high
energy (UHE) cosmic rays. We present a new Monte Carlo program allowing
detailed studies of conversion and cascading of UHE photons in the geomagnetic
field. The program named PRESHOWER can be used both as an independent tool or
together with a shower simulation code. With the stand-alone version of the
code it is possible to investigate various properties of the particle cascade
induced by UHE photons interacting in the Earth's magnetic field before
entering the Earth's atmosphere. Combining this program with an extensive air
shower simulation code such as CORSIKA offers the possibility of investigating
signatures of photon-initiated showers. In particular, features can be studied
that help to discern such showers from the ones induced by hadrons. As an
illustration, calculations for the conditions of the southern part of the
Pierre Auger Observatory are presented.Comment: 41 pages, 9 figures, added references in introduction, corrected
energy in row 1 of Table 3, extended caption of Table
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Priority ranking of safety-related systems for structural enhancement assessment at Savannah River Site
In order to extend the service life of safety related structures and systems in a logical manner, a Structural Enhancement Program was initiated to evaluate the structural integrity of eight (8) systems, namely: Cooling Water System, Emergency Cooling System, Moderator Recovery System supplementary Safety System, Water Removal System, Service Raw Water System, Service Clarified Water System, and River Water System. Since the level of importance of each system to reactor operations varies from one system to another, the scope of structural integrity evaluation for each system should be prioritized accordingly. This paper presents the assessment of system priority for structural evaluation based on a ranking methodology and specifies the level of structural evaluation consistent with the established priority. The effort was undertaken by a five-member panel representing four (4) major disciplines, including. structures, reactor engineering/operations, risk management and materials. The above systems were divided into a total of thirty-five (35) subsystem. These subsystems were then ranked with six (6) attributes, namely: Safety Classification, Degradation Mechanisms, Difficulty of Replacement, Failure Mode, Radiation Dose to Workers and Consequence of Failure. Each attribute was assigned a set of consequences or events with corresponding weighting scores. The results of the ranking process yielded two groups of subsystems, categorized as Priority I and II subsystems. The level of structural assessment was then formulated accordingly. The prioritized approach will allow more efficient allocation of resources, so that the Structural Enhancement Program can be implemented in a cost-effective and efficient manner
Unstable states in QED of strong magnetic fields
We question the use of stable asymptotic scattering states in QED of strong
magnetic fields. To correctly describe excited Landau states and photons above
the pair creation threshold the asymptotic fields are chosen as generalized
Licht fields. In this way the off-shell behavior of unstable particles is
automatically taken into account, and the resonant divergences that occur in
scattering cross sections in the presence of a strong external magnetic field
are avoided. While in a limiting case the conventional electron propagator with
Breit-Wigner form is obtained, in this formalism it is also possible to
calculate -matrix elements with external unstable particles.Comment: Revtex, 7 pages. To appear in Phys. Rev. D53(2
Very-high-energy gamma radiation associated with the unshocked wind of the Crab pulsar
We show that the relativistic wind in the Crab pulsar, which is commonly
thought to be invisible in the region upstream of the termination shock at R <
0.1 pc, in fact could be directly observed through its inverse Compton gamm-ray
emission. The search for such specific component of radiation in the gamma-ray
spectrum of the Crab can provide unique information about the unshocked pulsar
wind that is not accessible at other wavelengths.Comment: 11 pages, 11 figures, to appear in one of the April issues of MNRA
X-ray Phase-Resolved Spectroscopy of PSRs B0531+21, B1509-58, and B0540-69 with RXTE
The Rossi X-ray Timing Explorer ({\sl RXTE}) has made hundreds of
observations on three famous young pulsars (PSRs) B0531+21 (Crab), B1509-58,
and B0540-69. Using the archive {\sl RXTE} data, we have studied the
phase-resolved spectral properties of these pulsars in details. The variation
of the X-ray spectrum with phase of PSR B0531+21 is confirmed here much more
precisely and more details are revealed than the previous studies: the spectrum
softens from the beginning of the first pulse, turns to harden right at the
pulse peak and becomes the hardest at the bottom of the bridge, softens
gradually until the second peak, and then softens rapidly. Different from the
previous studies, we found that the spectrum of PSR B1509-58 is significantly
harder in the center of the pulse, which is also in contrast to that of PSR
B0531+21. The variation of the X-ray spectrum of PSR B0540-69 seems similar to
that of PSR B1509-58, but with a lower significance. Using the about 10 years
of data span, we also studied the real time evolution of the spectra of these
pulsars, and no significant evolution has been detected. We have discussed
about the constraints of these results on theoretical models of pulsar X-ray
emission.Comment: 42 pages, 24 figure
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