152 research outputs found
Demonstration of a Transportable 1 Hz-Linewidth Laser
We present the setup and test of a transportable clock laser at 698 nm for a
strontium lattice clock. A master-slave diode laser system is stabilized to a
rigidly mounted optical reference cavity. The setup was transported by truck
over 400 km from Braunschweig to D\"usseldorf, where the cavity-stabilized
laser was compared to a stationary clock laser for the interrogation of
ytterbium (578 nm). Only minor realignments were necessary after the transport.
The lasers were compared by a Ti:Sapphire frequency comb used as a transfer
oscillator. The thus generated virtual beat showed a combined linewidth below 1
Hz (at 1156 nm). The transport back to Braunschweig did not degrade the laser
performance, as was shown by interrogating the strontium clock transition.Comment: 3 pages, 4 figure
The photon propagator in compact QED_{2+1}: the effect of wrapping Dirac strings
We discuss the influence of closed Dirac strings on the photon propagator in
the Landau gauge emerging from a study of the compact U(1) gauge model in 2+1
dimensions. This gauge also minimizes the total length of the Dirac strings.
Closed Dirac strings are stable against local gauge-fixing algorithms only due
to the torus boundary conditions of the lattice. We demonstrate that these
left-over Dirac strings are responsible for the previously observed unphysical
behavior of the propagator of space-like photons (D_T) in the deconfinement
(high temperature) phase. We show how one can monitor the number N_3 of thermal
Dirac strings which allows to separate the propagator measurements into N_3
sectors. The propagator in N_3 \neq 0 sectors is characterized by a non--zero
mass and an anomalous dimension similarly to the confinement phase. Both mass
squared and anomalous dimension are found to be proportional to N_3.
Consequently, in the N_3=0 sector the unphysical behavior of the D_T photon
propagator is cured and the deviation from the free massless propagator
disappears.Comment: 13 pages, 13 figures, 1 tabl
Pharmacophore elements of the TIPP class of delta opioid receptor antagonists
A series of tri-and tetrapeptides sharing the amino-terminal dipeptide unit Tyr-Tic, found in the high-affinity delta opioid receptor antagonist Tyr-Tic-Phe-Phe (TIPP), was prepared and evaluated in receptor binding assays to explore the role(s) of the phenylalanine residues in positions 3 and 4. It was found that aromaticity of residues 3 and 4 is not required for high affinity, a lipophilic side chain in either location being sufficient, as evidenced by the high delta receptor binding affinities observed for the tetrapeptide Tyr-Tic-Ala-Leu and the tripeptide Tyr-Tic-Leu. These results support the suggestion of Temussi et al. [Biochem. Biophys. Res. Commun., 198 (1994) 933] that the aromatic side chain of the Tic residue corresponds to the aromatic side chain found in residues 3 or 4 in other delta-selective peptide series.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43172/1/10989_2004_Article_BF00126275.pd
A Model Driven Approach to the Analysis of Timeliness Properties
Abstract. The need for a design language that is rigorous but accessible and intuitive is often at odds with the formal and mathematical nature of languages used for analysis. UML and Petri Nets are a good example of this dichotomy. UML is a widely accepted modelling language capable of modelling the structural and behavioural aspects of a system. However UML lacks the mathematical foundation that is required for rigorous analysis. Petri Nets on the other hand have a strong mathematical base that is well suited for analysis of a system but lacks the appeal and ease-of-use of UML. Design in UML languages such as Sequence Diagrams and analysis in Petri Nets require on one hand some expertise in potentially two incompatible systems and their tools, and on the other a seamless transition from one system to the other. One way of addressing this impediment is to focus the software development mainly on the design language system and to facilitate the transition to the formal analysis by means of a combination of automation and tool support. The aim of this paper is to present a transformation system, which takes UML Sequence Diagrams augmented with time constraints and generates semantically equivalent Petri Nets that preserve the timing requirements. A case study on a small network is used in order to illustrate the proposed approach and in particular the design, the transformation and the analysis processes.
Recommended from our members
Track A Basic Science
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd
Study of the lineshape of the chi(c1) (3872) state
A study of the lineshape of the chi(c1) (3872) state is made using a data sample corresponding to an integrated luminosity of 3 fb(-1) collected in pp collisions at center-of-mass energies of 7 and 8 TeV with the LHCb detector. Candidate chi(c1)(3872) and psi(2S) mesons from b-hadron decays are selected in the J/psi pi(+)pi(-) decay mode. Describing the lineshape with a Breit-Wigner function, the mass splitting between the chi(c1 )(3872) and psi(2S) states, Delta m, and the width of the chi(c1 )(3872) state, Gamma(Bw), are determined to be (Delta m=185.598 +/- 0.067 +/- 0.068 Mev,)(Gamma BW=1.39 +/- 0.24 +/- 0.10 Mev,) where the first uncertainty is statistical and the second systematic. Using a Flatte-inspired model, the mode and full width at half maximum of the lineshape are determined to be (mode=3871.69+0.00+0.05 MeV.)(FWHM=0.22-0.04+0.13+0.07+0.11-0.06-0.13 MeV, ) An investigation of the analytic structure of the Flatte amplitude reveals a pole structure, which is compatible with a quasibound D-0(D) over bar*(0) state but a quasivirtual state is still allowed at the level of 2 standard deviations
Measurement of the CKM angle in and decays with
A measurement of -violating observables is performed using the decays
and , where the meson is
reconstructed in one of the self-conjugate three-body final states and (commonly denoted ). The decays are analysed in bins of the -decay phase space, leading
to a measurement that is independent of the modelling of the -decay
amplitude. The observables are interpreted in terms of the CKM angle .
Using a data sample corresponding to an integrated luminosity of
collected in proton-proton collisions at centre-of-mass
energies of , , and with the LHCb experiment,
is measured to be . The hadronic
parameters , , , and ,
which are the ratios and strong-phase differences of the suppressed and
favoured decays, are also reported
Helium identification with LHCb
The identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using pp collision data at â(s) = 13 TeV recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of 5.5 fb-1. A total of around 105 helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately 50% with a corresponding background rejection rate of up to O(10^12). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei
Measurement of forward charged hadron flow harmonics in peripheral PbPb collisions at âsNN = 5.02 TeV with the LHCb detector
Flow harmonic coefficients,
v
n
, which are the key to studying the hydrodynamics of the quark-gluon plasma (QGP) created in heavy-ion collisions, have been measured in various collision systems and kinematic regions and using various particle species. The study of flow harmonics in a wide pseudorapidity range is particularly valuable to understand the temperature dependence of the shear viscosity to entropy density ratio of the QGP. This paper presents the first LHCb results of the second- and the third-order flow harmonic coefficients of charged hadrons as a function of transverse momentum in the forward region, corresponding to pseudorapidities between 2.0 and 4.9, using the data collected from PbPb collisions in 2018 at a center-of-mass energy of 5.02
TeV
. The coefficients measured using the two-particle angular correlation analysis method are smaller than the central-pseudorapidity measurements at ALICE and ATLAS from the same collision system but share similar features
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