56,791 research outputs found
Beam-beam observations in the RHIC
The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory
has been in operation since 2000. Over the past decade, the luminosity in the
polarized proton (p-p) operations has increased by more than one order of
magnitude. The maximum total beam-beam tune shift with two collisions has
reached 0.018. The beam-beam interaction leads to large tune spread, emittance
growth, and short beam and luminosity lifetimes. In this article, we review the
beam-beam observations during the previous RHIC p-p runs. The mechanism for
particle loss is presented. The intra-beam scattering (IBS) contributions to
emittance and bunch length growths are calculated and compared with the
measurements. Finally, we will discuss current limits in the RHIC p-p
operations and their solutions.Comment: 7 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects
in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201
A biologically active peptide in the skin of lampreys (Eudontomyzon danfordi vladykovi). [Translation from: Z.Naturforsch. (B), 26(10), 1021-1023, 1971. ]
In recent years interest in the production and description of kinin-type substances has been greatly intensified. So, for example, bradykinin, phyllokinin, physalaemin, ranatensin and caerulein could be extracted from the skin of amphibians as well as. eledoisin out of the salivary glands of Eledon moschata. An examination of lampreys seemed to us particularly profitable in the search for the incidence of further kinins. Ammocoetes of different sizes and also adults of both sexes of the species Eudontomyzon danfordi vladykovi were studied in this research. This species is found in many tributaries of the Danube. Skin extracts were tested on on isolated rat uterus, rat duodenum, guinea pig ileum and rabbit jejunum, further tests were done in order to determine a peptide character of the biologically active substance
Mechanistic Links Between the Sedimentary Redox Cycle and Marine Acid-Base Chemistry
The redox state of Earth's surface is controlled on geological timescales by the flow of electrons through the sedimentary rock cycle, mediated largely by the weathering and burial of CāSāFe phases. These processes buffer atmospheric pOā. At the same time, COā influxes and carbonate burial control seawater acidābase chemistry and climate over long timescales via the carbonateāsilicate cycle. However, these two systems are mechanistically linked and impact each other via charge balance in the hydrosphere. Here, we use a lowāorder Earth system model to interrogate a subset of these connections, with a focus on changes that occur during perturbations to electron flow through the sedimentary rock cycle. We show that the net oxidation or reduction of the Earth's surface can play an important role in controlling acidābase processes in the oceans and thus climate, and suggest that these links should be more fully integrated into interpretive frameworks aimed at understanding Earth system evolution throughout Precambrian and Phanerozoic time
Lipschitz-continuity of the integrated density of states for Gaussian random potentials
The integrated density of states of a Schroedinger operator with random
potential given by a homogeneous Gaussian field whose covariance function is
continuous, compactly supported and has positive mean, is locally uniformly
Lipschitz-continuous. This is proven using a Wegner estimate
Geochemical support for a climbing habit within the Paleozoic seed fern genus Medullosa
A long-standing problem in paleobotany is the accurate identification of the growth habits and statures of fossil plants. Tissue-specific analysis of stable carbon isotope ratios in plant fossils can provide an independent perspective on this issue. Lignin, a fundamental biopolymer providing structural support in plant tissues and the second most abundant organic material in plants, is ^(13)C depleted by several parts per thousand, averaging 4.1ā°, relative to other plant constructional materials (e.g. cellulose). With this isotopic difference, the biochemical structural composition of ancient plants (and inferred stature) can be interrogated using microscale in situ isotope analysis between different tissues in fossils. We applied this technique to a well-preserved specimen of the Late Paleozoic seed plant Medullosa, an extinct genus with a variety of growth habits that includes several enigmatic yet abundant small-stemmed species widely found in calcium carbonate concretions (ācoal ballsā) in the Pennsylvanian coal beds of Iowa, USA. It remains unclear which of the medullosans were freestanding, and recent analysis of the medullosan vascular system has shown that this system provided little structural support to the whole plant. The leading hypothesis for small-stemmed medullosan specimens predicts that cortical tissues could have provided additional structural support, but only if they were lignified. The expected isotopic difference between lignified tissue and unlignified tissue is smaller than that expected from pure extracts, for the simple reason that even woody tissues maximally contain 40% lignin (by mass). This reduces the expected maximum difference between weakly and heavily lignified tissues by 60%, down to ~0.5ā°ā2ā°. Analysis of the medullosan stem reveals a consistent difference in isotope ratios of 0.7ā°ā1.0ā° between lignified xylem and cortical tissues. This implies low abundances of lignin (between 0% and 11%) within the cortex. This inferred structural biochemistry supports hypotheses that the peripheral portions of these medullosan stems were not biomechanically reinforced to permit the plants to grow as freestanding, arborescent trees. A number of climbing or scandent medullosans have been identified in the fossil record, and this mode of growth has been suggested to be common within the group on the basis of observations from comparative biomechanics, hydraulics, and development. Finally, this mode of growth is common in several clades of stem group seed plants, including Lyginopteris and Callistophyton, along with Medullosa. This study provides further support for ideas that place a great portion of early seed plant diversity under the canopy, rather than forming it
Statistics of some atmospheric turbulence records relevant to aircraft response calculations
Methods for characterizing atmospheric turbulence are described. The methods illustrated include maximum likelihood estimation of the integral scale and intensity of records obeying the von Karman transverse power spectral form, constrained least-squares estimation of the parameters of a parametric representation of autocorrelation functions, estimation of the power spectra density of the instantaneous variance of a record with temporally fluctuating variance, and estimation of the probability density functions of various turbulence components. Descriptions of the computer programs used in the computations are given, and a full listing of these programs is included
Herschel-PACS imaging of protostars in the HH 1ā2 outflow complex
We present 70 and 160 Ī¼m Herschel science demonstration images of a field in the Orion A molecular cloud that contains the prototypical Herbig-Haro objects HH 1 and 2, obtained with the Photodetector Array Camera and Spectrometer (PACS). These observations demonstrate Herschelās unprecedented ability to study the rich population of protostars in the Orion molecular clouds
at the wavelengths where they emit most of their luminosity. The four protostars previously identified by Spitzer 3.6ā40 Ī¼m imaging and spectroscopy are detected in the 70 Ī¼m band, and three are clearly detected at 160 Ī¼m. We measure photometry of the protostars in the PACS bands and assemble their spectral energy distributions (SEDs) from 1 to 870 Ī¼m with these data, Spitzer spectra and
photometry, 2MASS data, and APEX sub-mm data. The SEDs are fit to models generated with radiative transfer codes. From these fits we can constrain the fundamental properties of the protostars. We find luminosities in the range 12ā84 L_ā and envelope densities spanning over two orders of magnitude. This implies that the four protostars have a wide range of envelope infall rates and evolutionary
states: two have dense, infalling envelopes, while the other two have only residual envelopes. We also show the highly irregular and filamentary structure of the cold dust and gas surrounding the protostars as traced at 160 Ī¼m
An orbital window into the ancient Sun's mass
Models of the Sun's long-term evolution suggest that its luminosity was
substantially reduced 2-4 billion years ago, which is inconsistent with
substantial evidence for warm and wet conditions in the geological records of
both ancient Earth and Mars. Typical solutions to this so-called "faint young
Sun paradox" consider changes in the atmospheric composition of Earth and Mars,
and while attractive, geological verification of these ideas is generally
lacking-particularly for Mars. One possible underexplored solution to the faint
young Sun paradox is that the Sun has simply lost a few percent of its mass
during its lifetime. If correct, this would slow, or potentially even offset
the increase in luminosity expected from a constant-mass model. However, this
hypothesis is challenging to test. Here, we propose a novel observational proxy
of the Sun's ancient mass that may be readily measured from accumulation
patterns in sedimentary rocks on Earth and Mars. We show that the orbital
parameters of the Solar system planets undergo quasi-cyclic oscillations at a
frequency, given by secular mode g_2-g_5, that scales approximately linearly
with the Sun's mass. Thus by examining the cadence of sediment accumulation in
ancient basins, it is possible distinguish between the cases of a constant mass
Sun and a more massive ancient Sun to a precision of greater than about 1 per
cent. This approach provides an avenue toward verification, or of
falsification, of the massive early Sun hypothesis.Comment: 7 pages, 4 Figures. Accepted to The Astrophysical Journal Letter
A Corollary for Nonsmooth Systems
In this note, two generalized corollaries to the LaSalle-Yoshizawa Theorem
are presented for nonautonomous systems described by nonlinear differential
equations with discontinuous right-hand sides. Lyapunov-based analysis methods
are developed using differential inclusions to achieve asymptotic convergence
when the candidate Lyapunov derivative is upper bounded by a negative
semi-definite function
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