1,583 research outputs found
Positronium collisions with rare-gas atoms
We calculate elastic scattering of positronium (Ps) by the Xe atom using the
recently developed pseudopotential method [I. I. Fabrikant and G. F. Gribakin,
Phys. Rev. A 90, 052717 (2014)] and review general features of Ps scattering
from heavier rare-gas atoms: Ar, Kr, and Xe. The total scattering cross section
is dominated by two contributions: elastic scattering and Ps ionization
(breakup). To calculate the Ps ionization cross sections we use the
binary-encounter method for Ps collisions with an atomic target. Our results
for the ionization cross section agree well with previous calculations carried
out in the impulse approximation. Our total Ps-Xe cross section, when plotted
as a function of the projectile velocity, exhibits similarity with the
electron-Xe cross section for the collision velocities higher than 0.8 a.u.,
and agrees very well with the measurements at Ps velocities above 0.5 a.u.Comment: 7 pages, 7 figures, submitted to J. Phys.
Holonomy groups of pseudo-quaternionic-K\"ahlerian manifolds of non-zero scalar curvature
The holonomy group of a pseudo-quaternionic-K\"ahlerian manifold of
signature with non-zero scalar curvature is contained in
\Sp(1)\cdot\Sp(r,s) and it contains \Sp(1). It is proved that either is
irreducible, or and preserves an isotropic subspace of dimension
, in the last case, there are only two possibilities for the connected
component of the identity of such . This gives the classification of
possible connected holonomy groups of pseudo-quaternionic-K\"ahlerian manifolds
of non-zero scalar curvature.Comment: 7 pages; Dedicated to Dmitri Vladimirovich Alekseevsky at the
occasion of his 70th birthda
Evolution of thymopoietic microenvironments
In vertebrates, the development of lymphocytes from undifferentiated haematopoietic precursors takes place in so-called primary lymphoid organs, such as the thymus. Therein, lymphocytes undergo a complex differentiation and selection process that culminates in the generation of a pool of mature T cells that collectively express a self-tolerant repertoire of somatically diversified antigen receptors. Throughout this entire process, the microenvironment of the thymus in large parts dictates the sequence and outcome of the lymphopoietic activity. In vertebrates, direct genetic evidence in some species and circumstantial evidence in others suggest that the formation of a functional thymic microenvironment is controlled by members of the Foxn1/4 family of transcription factors. In teleost fishes, both Foxn1 and Foxn4 contribute to thymopoietic activity, whereas Foxn1 is both necessary and sufficient in the mammalian thymus. The evolutionary history of Foxn1/4 genes suggests that an ancient Foxn4 gene lineage gave rise to the Foxn1 genes in early vertebrates, raising the question of the thymopoietic capacity of the ancestor common to all vertebrates. Recent attempts to reconstruct the early events in the evolution of thymopoietic tissues by replacement of the mouse Foxn1 gene by Foxn1-like genes isolated from various chordate species suggest a plausible scenario. It appears that the primordial thymus was a bi-potent lymphoid organ, supporting both B cell and T cell development; however, during the course of vertebrate, evolution B cell development was gradually diminished converting the thymus into a site specialized in T cell development
Critical impact of vegetation physiology on the continental hydrologic cycle in response to increasing CO2
Predicting how increasing atmospheric CO2 will affect the hydrologic cycle is of utmost importance for a range of applications ranging from ecological services to human life and activities. A typical perspective is that hydrologic change is driven by precipitation and radiation changes due to climate change, and that the land surface will adjust. Using Earth system models with decoupled surface (vegetation physiology) and atmospheric (radiative) CO2 responses, we here show that the CO2 physiological response has a dominant role in evapotranspiration and evaporative fraction changes and has a major effect on long-term runoff compared with radiative or precipitation changes due to increased atmospheric CO2. This major effect is true for most hydrological stress variables over the largest fraction of the globe, except for soil moisture, which exhibits a more nonlinear response. This highlights the key role of vegetation in controlling future terrestrial hydrologic response and emphasizes that the carbon and water cycles are intimately coupled over land
Holonomy algebras of pseudo-quaternionic-K\"ahlerian manifolds of signature
Possible holonomy algebras of pseudo-quaternionic-K\"ahlerian manifolds of
signature are classified. Using this, a new proof of the classification
of simply connected pseudo-quaternionic-K\"ahlerian symmetric spaces of
signature is obtained.Comment: 16 page
Argyres-Seiberg duality and the Higgs branch
We demonstrate the agreement between the Higgs branches of two N=2 theories
proposed by Argyres and Seiberg to be S-dual, namely the SU(3) gauge theory
with six quarks, and the SU(2) gauge theory with one pair of quarks coupled to
the superconformal theory with E_6 flavor symmetry. In mathematical terms, we
demonstrate the equivalence between a hyperkaehler quotient of a linear space
and another hyperkaehler quotient involving the minimal nilpotent orbit of E_6,
modulo the identification of the twistor lines.Comment: 27 pages; v2: published versio
Hypermultiplets and Topological Strings
The c-map relates classical hypermultiplet moduli spaces in compactifications
of type II strings on a Calabi-Yau threefold to vector multiplet moduli spaces
via a further compactification on a circle. We give an off-shell description of
the c-map in N=2 superspace. The superspace Lagrangian for the hypermultiplets
is a single function directly related to the prepotential of special geometry,
and can therefore be computed using topological string theory. Similarly, a
class of higher derivative terms for hypermultiplets can be computed from the
higher genus topological string amplitudes. Our results provide a framework for
studying quantum corrections to the hypermultiplet moduli space, as well as for
understanding the black hole wave-function as a function of the hypermultiplet
moduli.Comment: 21 pages, references adde
Characterizing the metabolic effects of the selective inhibition of gut microbial β-glucuronidases in mice
The hydrolysis of xenobiotic glucuronides by gut bacterial glucuronidases reactivates previously detoxified compounds resulting in severe gut toxicity for the host. Selective bacterial β-glucuronidase inhibitors can mitigate this toxicity but their impact on wider host metabolic processes has not been studied. To investigate this the inhibitor 4-(8-(piperazin-1-yl)-1,2,3,4-tetrahydro-[1,2,3]triazino[4′,5′:4,5]thieno[2,3-c]isoquinolin-5-yl)morpholine (UNC10201652, Inh 9) was administered to mice to selectively inhibit a narrow range of bacterial β-glucuronidases in the gut. The metabolomic profiles of the intestinal contents, biofluids, and several tissues involved in the enterohepatic circulation were measured and compared to control animals. No biochemical perturbations were observed in the plasma, liver or gall bladder. In contrast, the metabolite profiles of urine, colon contents, feces and gut wall were altered compared to the controls. Changes were largely restricted to compounds derived from gut microbial metabolism. This work establishes that inhibitors targeted towards bacterial β-glucuronidases modulate the functionality of the intestinal microbiota without adversely impacting the host metabolic system
Full phase stabilization of a Yb:fiber femtosecond frequency comb via high-bandwidth transducers
We present full phase stabilization of an amplified Yb:fiber femtosecond
frequency comb using an intra-cavity electro-optic modulator and an
acousto-optic modulator. These transducers provide high servo bandwidths of 580
kHz and 250 kHz for frep and fceo, producing a robust and low phase noise fiber
frequency comb. The comb was self-referenced with an f - 2f interferometer and
phase locked to an ultra-stable optical reference used for the JILA Sr optical
clock at 698 nm, exhibiting 0.21 rad and 0.47 rad of integrated phase errors
(over 1 mHz - 1 MHz) respectively. Alternatively, the comb was locked to two
optical references at 698 nm and 1064 nm, obtaining 0.43 rad and 0.14 rad of
integrated phase errors respectively
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