2,258 research outputs found
Hunting for CDF Multi-Muon "Ghost" Events at Collider and Fixed-Target Experiments
In 2008 the CDF collaboration discovered a large excess of events containing
two or more muons, at least one of which seemed to have been produced outside
the beam pipe. We investigate whether similar "ghost" events could (and should)
have been seen in already completed experiments. The CDF di-muon data can be
reproduced by a simple model where a relatively light X particle undergoes
four-body decay. This model predicts a large number of ghost events in Fermilab
fixed-target experiments E772, E789 and E866, applying the cuts optimized for
analyses of Drell-Yan events. A correct description of events with more than
two muons requires a more complicated model, where two X particles are produced
from a very broad resonance Y. This model can be tested in fixed-target
experiments only if the cut on the angles, or rapidities, of the muons can be
relaxed. Either way, the UA1 experiment at the CERN ppbar collider should have
observed O(100) ghost events.Comment: 15 pages, 9 figure
Towards Compensable SLAs
In Cooperative Information Systems, service level agreements (SLA) can be used to describe the rights and obligations of parties involved in the transaction (typically the service consumer and the service provider); amongst other information, SLA could define guarantees associated with the idea of service level objectives (SLOs) that normally represent key performance indicators of either the consumer or the provider. in case the guarantee is under-fulfilled or over-fulfilled SLAs could also define some compensations (i.e. penalties or rewards). in such a context, during the last years there have been important steps towards the automation of the management of SLAs, however the formalization of compensations in SLAs still remains as an important challenge. in this paper we aim to provide a characterization model to create SLAs with compensations; specifically, the main contributions are twofold: (i) the conceptualization of the Compensation Function to express consistently penalties and rewards and (ii) a model for Compensable Guarantees that associate SLOs with Compensation Functions. This formalization models aims to establish a foundation to elaborate tools that could provide an automated support to the modeling and analysis of SLAs with compensations. Additionally, in order to validate our approach, we model and analyze a set of guarantee terms from three real world examples of SLAs and our formalization proves to be useful for detecting mistakes that are ty
Mobile quantum gravity sensor with unprecedented stability
Changes of surface gravity on Earth are of great interest in geodesy, earth sciences and natural resource exploration. They are indicative of Earth system's mass redistributions and vertical surface motion, and are usually measured with falling corner-cube- and superconducting gravimeters (FCCG and SCG). Here we report on absolute gravity measurements with a mobile quantum gravimeter based on atom interferometry. The measurements were conducted in Germany and Sweden over periods of several days with simultaneous SCG and FCCG comparisons. They show the best-reported performance of mobile atomic gravimeters to date with an accuracy of 39nm/s2, long-term stability of 0.5nm/s2 and short-term noise of 96nm/s2/√Hz. These measurements highlight the unique properties of atomic sensors. The achieved level of performance in a transportable instrument enables new applications in geodesy and related fields, such as continuous absolute gravity monitoring with a single instrument under rough environmental conditions.Peer Reviewe
Supporting Compensations with WS-greement
During the last years the use of service level agreements
(SLA) is rising uncontrollably to describe the rights and obligations of
parties involved in service provisioning (typically the service consumer
and the service provider); amongst other information, SLA could de ne
guarantees associated with the idea of service level objectives (SLOs)
that normally represent key performance indicators of either the consumer
or the provider. In case the guarantee is under or over ful lled
SLAs could also de ne some compensations (i.e. penalties or rewards). In
such a context, there have been important steps towards the automation
of the analysis of SLAs. One of these steps is a characterization model of
SLAs with compensations proposed by the authors in a previous work;
and another step is the standardisation e ort in the SLAs notation made
by WS{Agreement. However, real-world SLAs includes complex concepts
that must be considered, namely: (i) SLA terms that specify compensations
without an explicit SLO; and (ii) a limit for the compensations.
In this paper we extend our prior characterization model considering
these complex concepts. Speci cally, (i) we provide up to ve real-world
scenarios whose SLAs incorporate aforementioned new concepts; (ii) we
extend our model for compensable guarantees considering terms without
an explicit SLO; and (iii) we provide a novel WS{Agreement-based syntax
to model SLAs with compensations considering these concepts. These
contributions aim to establish a foundation to elaborate tools that could
provide an automated support to the modelling and analysis of SLAs
with compensations.Junta de Andalucía P12--TIC--1867Ministerio de Economía y Competitividad BELI (TIN2015-70560-R
Noseleaf Dynamics during Pulse Emission in Horseshoe Bats
Horseshoe bats emit their biosonar pulses nasally and diffract the outgoing ultrasonic waves by conspicuous structures that surrounded the nostrils. Here, we report quantitative experimental data on the motion of a prominent component of these structures, the anterior leaf, using synchronized laser Doppler vibrometry and acoustic recordings in the greater horseshoe bat (Rhinolophus ferrumequinum). The vibrometry data has demonstrated non-random motion patterns in the anterior leaf. In these patterns, the outer rim of the walls of the anterior leaf twitches forward and inwards to decrease the aperture of the noseleaf and increase the curvature of its surfaces. Noseleaf displacements were correlated with the emitted ultrasonic pulses. After their onset, the inward displacements increased monotonically towards their maximum value which was always reached within the duration of the biosonar pulse, typically towards its end. In other words, the anterior leaf’s surfaces were moving inwards during most of the pulse. Non-random motions were not present in all recorded pulse trains, but could apparently be switched on or off. Such switches happened between sequences of consecutive pulses but were never observed between individual pulses within a sequence. The amplitudes of the emitted biosonar pulse and accompanying noseleaf movement were not correlated in the analyzed data set. The measured velocities of the noseleaf surface were too small to induce Doppler shifts of a magnitude with a likely significance. However, the displacement amplitudes were significant in comparison with the overall size of the anterior leaf and the sound wavelengths. These results indicate the possibility that horseshoe bats use dynamic sensing principles on the emission side of their biosonar system. Given the already available evidence that such mechanisms exist for biosonar reception, it may be hypothesized that time-variant mechanisms play a pervasive role in the biosonar sensing of horseshoe bats
Observation of mesoscopic crystalline structures in a two-dimensional Rydberg gas
The ability to control and tune interactions in ultracold atomic gases has
paved the way towards the realization of new phases of matter. Whereas
experiments have so far achieved a high degree of control over short-ranged
interactions, the realization of long-range interactions would open up a whole
new realm of many-body physics and has become a central focus of research.
Rydberg atoms are very well-suited to achieve this goal, as the van der Waals
forces between them are many orders of magnitude larger than for ground state
atoms. Consequently, the mere laser excitation of ultracold gases can cause
strongly correlated many-body states to emerge directly when atoms are
transferred to Rydberg states. A key example are quantum crystals, composed of
coherent superpositions of different spatially ordered configurations of
collective excitations. Here we report on the direct measurement of strong
correlations in a laser excited two-dimensional atomic Mott insulator using
high-resolution, in-situ Rydberg atom imaging. The observations reveal the
emergence of spatially ordered excitation patterns in the high-density
components of the prepared many-body state. They have random orientation, but
well defined geometry, forming mesoscopic crystals of collective excitations
delocalised throughout the gas. Our experiment demonstrates the potential of
Rydberg gases to realise exotic phases of matter, thereby laying the basis for
quantum simulations of long-range interacting quantum magnets.Comment: 10 pages, 7 figure
A comparative study of fragment screening methods on the p38α kinase: new methods, new insights
The stress-activated kinase p38α was used to evaluate a fragment-based drug discovery approach using the BioFocus fragment library. Compounds were screened by surface plasmon resonance (SPR) on a Biacore(™) T100 against p38α and two selectivity targets. A sub-set of our library was the focus of detailed follow-up analyses that included hit confirmation, affinity determination on 24 confirmed, selective hits and competition assays of these hits with respect to a known ATP binding site inhibitor. In addition, functional activity against p38α was assessed in a biochemical assay using a mobility shift platform (LC3000, Caliper LifeSciences). A selection of fragments was also evaluated using fluorescence lifetime (FLEXYTE(™)) and microscale thermophoresis (Nanotemper) technologies. A good correlation between the data for the different assays was found. Crystal structures were solved for four of the small molecules complexed to p38α. Interestingly, as determined both by X-ray analysis and SPR competition experiments, three of the complexes involved the fragment at the ATP binding site, while the fourth compound bound in a distal site that may offer potential as a novel drug target site. A first round of optimization around the remotely bound fragment has led to the identification of a series of triazole-containing compounds. This approach could form the basis for developing novel and active p38α inhibitors. More broadly, it illustrates the power of combining a range of biophysical and biochemical techniques to the discovery of fragments that facilitate the development of novel modulators of kinase and other drug targets. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10822-011-9454-9) contains supplementary material, which is available to authorized users
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