8,855 research outputs found
Human operator identification model and related computer programs
Four computer programs which provide computational assistance in the analysis of man/machine systems are reported. The programs are: (1) Modified Transfer Function Program (TF); (2) Time Varying Response Program (TVSR); (3) Optimal Simulation Program (TVOPT); and (4) Linear Identification Program (SCIDNT). The TV program converts the time domain state variable system representative to frequency domain transfer function system representation. The TVSR program computes time histories of the input/output responses of the human operator model. The TVOPT program is an optimal simulation program and is similar to TVSR in that it produces time histories of system states associated with an operator in the loop system. The differences between the two programs are presented. The SCIDNT program is an open loop identification code which operates on the simulated data from TVOPT (or TVSR) or real operator data from motion simulators
Massive stars in the hinterland of the young cluster, Westerlund 2
Accepted for publication in MNRAS, 13 July 2018. 16 pages, plus one-page table in an appendix.An unsettled question concerning the formation and distribution of massive stars is whether they must be born in massive clusters and, if found in less dense environments, whether they must have migrated there. With the advent of wide-area digital photometric surveys, it is now possible to identify massive stars away from prominent Galactic clusters without bias. In this study we consider 40 candidate OB stars found in the field around the young massive cluster, Westerlund 2, by Mohr-Smith et al.: these are located inside a box of 1.5 × 1.5 deg 2 and are selected on the basis of their extinctions and K magnitudes.We present VLT/X-shooter spectra of two of the hottest O stars, respectively 11 and 22 arcmin from the centre of Westerlund 2. They are confirmed as O4V stars, with stellar masses likely to be in excess of 40 M ·. Their radial velocities relative to the non-binary reference object, MSP 182, in Westerlund 2 are -29.4 ± 1.7 and -14.4 ± 2.2 km s -1, respectively. Using Gaia DR2 proper motions we find that between 8 and 11 early O/WR stars in the studied region (including the two VLT targets, plus WR 20c and WR 20aa) could have been ejected fromWesterlund 2 in the last one million years. This represents an efficiency of massive-star ejection of up to ~ 25 per cent. On sky, the positions of these stars and their proper motions show a near N-S alignment. We discuss the possibility that these results are a consequence of prior sub-cluster merging combining with dynamical ejection.Peer reviewe
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Adapting the International System of Units to the twenty-first century
We review the proposal of the International Committee for Weights and Measures
(Comité International des Poids et Mesures, CIPM), currently being considered by
the General Conference on Weights and Measures (Conférences Générales des Poids et
Mesures, CGPM), to revise the International System of Units (Le Système International
d’Unitès, SI). The proposal includes new definitions for four of the seven base units of
the SI, and a new form of words to present the definitions of all the units. The objective
of the proposed changes is to adopt definitions referenced to constants of nature, taken
in the widest sense, so that the definitions may be based on what are believed to be
true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and
mole are linked to exact numerical values of the mass of the international prototype of the
kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature
of water and the molar mass of carbon-12, respectively, in the new SI these units are linked
to exact numerical values of the Planck constant, the elementary charge, the Boltzmann
constant and the Avogadro constant, respectively. The new wording used expresses the
definitions in a simple and unambiguous manner without the need for the distinction
between base and derived units. The importance of relations among the fundamental
constants to the definitions, and the importance of establishing a mise en pratique for
the realization of each definition, are also discussed
Benchmark on neutron capture extracted from reactions
Direct neutron capture reactions play an important role in nuclear
astrophysics and applied physics. Since for most unstable short-lived nuclei it
is not possible to measure the cross sections, reactions
have been used as an alternative indirect tool. We analyze simultaneously
at deuteron energies and 56 MeV
and the thermal reaction at 25 meV. We include results for the
ground state and the first excited state of Ca. From the low-energy
reaction, the neutron asymptotic normalization coefficient (ANC) is
determined. Using this ANC, we extract the spectroscopic factor (SF) from the
higher energy data and the data. The SF obtained through
the 56 MeV data are less accurate but consistent with those from the
thermal capture. We show that to have a similar dependence on the single
particle parameters as in the , the (d,p) reaction should be
measured at 30 MeV.Comment: 5 pg, 4 figs, Phys. Rev. C (rapid) in pres
Deconvolution of complex G protein-coupled receptor signaling in live cells using dynamic mass redistribution measurements
Label-free biosensor technology based on dynamic mass redistribution (DMR) of cellular constituents promises to translate GPCR signaling into complex optical 'fingerprints' in real time in living cells. Here we present a strategy to map cellular mechanisms that define label-free responses, and we compare DMR technology with traditional second-messenger assays that are currently the state of the art in GPCR drug discovery. The holistic nature of DMR measurements enabled us to (i) probe GPCR functionality along all four G-protein signaling pathways, something presently beyond reach of most other assay platforms; (ii) dissect complex GPCR signaling patterns even in primary human cells with unprecedented accuracy; (iii) define heterotrimeric G proteins as triggers for the complex optical fingerprints; and (iv) disclose previously undetected features of GPCR behavior. Our results suggest that DMR technology will have a substantial impact on systems biology and systems pharmacology as well as for the discovery of drugs with novel mechanisms
Lamb Shift of 3P and 4P states and the determination of
The fine structure interval of P states in hydrogenlike systems can be
determined theoretically with high precision, because the energy levels of P
states are only slightly influenced by the structure of the nucleus. Therefore
a measurement of the fine structure may serve as an excellent test of QED in
bound systems or alternatively as a means of determining the fine structure
constant with very high precision. In this paper an improved analytic
calculation of higher-order binding corrections to the one-loop self energy of
3P and 4P states in hydrogen-like systems with low nuclear charge number is
presented. A comparison of the analytic results to the extrapolated numerical
data for high ions serves as an independent test of the analytic
evaluation. New theoretical values for the Lamb shift of the P states and for
the fine structure splittings are given.Comment: 33 pages, LaTeX, 4 tables, 4 figure
Screened self-energy correction to the 2p3/2-2s transition energy in Li-like ions
We present an ab initio calculation of the screened self-energy correction
for (1s)^2 2p3/2 and (1s)^2 2s states of Li-like ions with nuclear charge
numbers in the range Z = 12-100. The evaluation is carried out to all orders in
the nuclear-strength parameter Z \alpha. This investigation concludes our
calculations of all two-electron QED corrections for the 2p3/2-2s transition
energy in Li-like ions and thus considerably improves theoretical predictions
for this transition for high-Z ions
Electron Self Energy for the K and L Shell at Low Nuclear Charge
A nonperturbative numerical evaluation of the one-photon electron self energy
for the K- and L-shell states of hydrogenlike ions with nuclear charge numbers
Z=1 to 5 is described. Our calculation for the 1S state has a numerical
uncertainty of 0.8 Hz in atomic hydrogen, and for the L-shell states (2S and
2P) the numerical uncertainty is 1.0 Hz. The method of evaluation for the
ground state and for the excited states is described in detail. The numerical
results are compared to results based on known terms in the expansion of the
self energy in powers of (Z alpha).Comment: 21 pages, RevTeX, 5 Tables, 6 figure
The second-order electron self-energy in hydrogen-like ions
A calculation of the simplest part of the second-order electron self-energy
(loop after loop irreducible contribution) for hydrogen-like ions with nuclear
charge numbers is presented. This serves as a test for the
more complicated second-order self-energy parts (loop inside loop and crossed
loop contributions) for heavy one-electron ions. Our results are in strong
disagreement with recent calculations of Mallampalli and Sapirstein for low
values but are compatible with the two known terms of the analytical
-expansion.Comment: 13 LaTex pages, 2 figure
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