372 research outputs found
Paper Session I-A - Starlab Overview
Stariab, a test bed designed to be flown on NASA\u27s Space Shuttle, will be used to conduct a series of acquisition, tracking, and pointing (ATP) experiments that are relevant to the Strategic Defense Initiative (SDI) Mission. In the primary experiment, Stariab will acquire, track, and precisely point a laser beam at an instrumented 4-stage booster rocket known as Starbird. Simultaneously, booster plume data will be collected at a variety of wavelengths and at resolutions never before achieved in space. Stariab will also be used to demonstrate advanced adaptive optics techniques using a booster plume source, rapid optical retargeting, and laser communications from space to below the ocean\u27s surface. In addition, Stariab will be used to collect data on earthspace backgrounds and on adaptive optics systems used to compensate for atmospheric turbulence
Scales and hierarchies in warped compactifications and brane worlds
Warped compactifications with branes provide a new approach to the hierarchy
problem and generate a diversity of four-dimensional thresholds. We investigate
the relationships between these scales, which fall into two classes.
Geometrical scales, such as thresholds for Kaluza-Klein, excited string, and
black hole production, are generically determined soley by the spacetime
geometry. Dynamical scales, notably the scale of supersymmetry breaking and
moduli masses, depend on other details of the model. We illustrate these
relationships in a class of solutions of type IIB string theory with imaginary
self-dual fluxes. After identifying the geometrical scales and the resulting
hierarchy, we determine the gravitino and moduli masses through explicit
dimensional reduction, and estimate their value to be near the four-dimensional
Planck scale. In the process we obtain expressions for the superpotential and
Kahler potential, including the effects of warping. We identify matter living
on certain branes to be effectively sequestered from the supersymmetry breaking
fluxes: specifically, such "visible sector" fields receive no tree-level masses
from the supersymmetry breaking. However, loop corrections are expected to
generate masses, at the phenomenologically viable TeV scale.Comment: 33 pages, LaTeX. v2: reference added v3: reference added, typos
correcte
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The metabolome regulates the epigenetic landscape during naive-to-primed human embryonic stem cell transition.
For nearly a century developmental biologists have recognized that cells from embryos can differ in their potential to differentiate into distinct cell types. Recently, it has been recognized that embryonic stem cells derived from both mice and humans exhibit two stable yet epigenetically distinct states of pluripotency: naive and primed. We now show that nicotinamide N-methyltransferase (NNMT) and the metabolic state regulate pluripotency in human embryonic stem cells (hESCs). Â Specifically, in naive hESCs, NNMT and its enzymatic product 1-methylnicotinamide are highly upregulated, and NNMT is required for low S-adenosyl methionine (SAM) levels and the H3K27me3 repressive state. NNMT consumes SAM in naive cells, making it unavailable for histone methylation that represses Wnt and activates the HIF pathway in primed hESCs. These data support the hypothesis that the metabolome regulates the epigenetic landscape of the earliest steps in human development
Brane/flux annihilation transitions and nonperturbative moduli stabilization
By extending the calculation of Kahler moduli stabilization to account for an
embiggened antibrane, we reevaluate brane/flux annihilation in a warped throat
with one stabilized Kahler modulus. We find that depending on the relative size
of various fluxes three things can occur: the decay process proceeds
unhindered, the anti-D3-branes are forbidden to decay classically, or the
entire space decompactifies. Additionally, we show that the Kahler modulus
receives a contribution from the collective 3-brane tension. This allows for a
significant change in compactified volume during the transition and possibly
mitigates some fine tuning otherwise required to achieve large volume.Comment: 25 pages, 6 figures, LaTeX. v2: references adde
Discrimination of low missing energy look-alikes at the LHC
The problem of discriminating possible scenarios of TeV scale new physics
with large missing energy signature at the Large Hadron Collider (LHC) has
received some attention in the recent past. We consider the complementary, and
yet unexplored, case of theories predicting much softer missing energy spectra.
As there is enough scope for such models to fake each other by having similar
final states at the LHC, we have outlined a systematic method based on a
combination of different kinematic features which can be used to distinguish
among different possibilities. These features often trace back to the
underlying mass spectrum and the spins of the new particles present in these
models. As examples of "low missing energy look-alikes", we consider
Supersymmetry with R-parity violation, Universal Extra Dimensions with both
KK-parity conserved and KK-parity violated and the Littlest Higgs model with
T-parity violated by the Wess-Zumino-Witten anomaly term. Through detailed
Monte Carlo analysis of the four and higher lepton final states predicted by
these models, we show that the models in their minimal forms may be
distinguished at the LHC, while non-minimal variations can always leave scope
for further confusion. We find that, for strongly interacting new particle
mass-scale ~600 GeV (1 TeV), the simplest versions of the different theories
can be discriminated at the LHC running at sqrt{s}=14 TeV within an integrated
luminosity of 5 (30) fb^{-1}.Comment: 40 pages, 10 figures; v2: Further discussions, analysis and one
figure added, ordering of certain sections changed, minor modifications in
the abstract, version as published in JHE
Morality and progress:IR narratives on international revisionism and the status quo
Scholars debate the ambitions and policies of todayâs ârising powersâ and the extent to which they are revising or upholding the international status quo. While elements of the relevant literature provide valuable insight, this article argues that the concepts of revisionism and the status quo within mainstream International Relations (IR) have always constituted deeply rooted, autobiographical narratives of a traditionally Western-dominated discipline. As âordering narrativesâ of morality and progress, they constrain and organize debate so that revisionism is typically conceived not merely as disruption, but as disruption from the non-West amidst a fundamentally moral Western order that represents civilizational progress. This often makes them inherently problematic and unreliable descriptors of the actors and behaviours they are designed to explain. After exploring the formations and development of these concepts throughout the IR tradition, the analysis is directed towards narratives around the contemporary âriseâ of China. Both scholarly and wider political narratives typically tell the story of revisionist challenges China presents to a US/Western-led status quo, promoting unduly binary divisions between the West and non-West, and tensions and suspicions in the international realm. The aim must be to develop a new language and logic that recognize the contingent, autobiographical nature of ârevisionistâ and âstatus quoâ actors and behaviours
Reduced purine biosynthesis in humans after their divergence from Neandertals
We analyze the metabolomes of humans, chimpanzees, and macaques in muscle, kidney and three different regions of the brain. Although several compounds in amino acid metabolism occur at either higher or lower concentrations in humans than in the other primates, metabolites downstream of adenylosuccinate lyase, which catalyzes two reactions in purine synthesis, occur at lower concentrations in humans. This enzyme carries an amino acid substitution that is present in all humans today but absent in Neandertals. By introducing the modern human substitution into the genomes of mice, as well as the ancestral, Neandertal-like substitution into the genomes of human cells, we show that this amino acid substitution contributes to much or all of the reduction of de novo synthesis of purines in humans
Interaction, Emotion, and Collective Identities
[Excerpt] This chapter poses the question: How do emotional aspects of social interaction affect the emergence and salience of collective identities? I assume that social interaction inherently involves an implicit or explicit joint taskânamely to accomplish some result that can only be produced with others. The most fundamental âtaskâ of social interaction can be construed as the coordination and alignment of behavior, such that actors successfully conclude the interact ion episode. Essential to this task is a working consensus about definitions of self and other in the social situation, i.e., consensual self-other identities. A central component of my argument is that social interaction has emotional effects that vary with the success of actors at accomplishing this fundamental task. This paper theorizes the conditions under which emotional effects of social interaction promote collective identities that bridge or transcend self-other role identities
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