11,108 research outputs found
IRIS thermal balance test within ESTEC LSS
The Italian Research Interim Stage (IRIS) thermal balance test was successfully performed in the ESTEC Large Space Simulator (LSS) to qualify the thermal design and to validate the thermal mathematical model. Characteristics of the test were the complexity of the set-up required to simulate the Shuttle cargo bay and allowing IRIS mechanism actioning and operation for the first time in the new LSS facility. Details of the test are presented, and test results for IRIS and the LSS facility are described
Charge and Magnetic Flux Correlations in Chern-Simons Theory with Fermions
Charge and magnetic flux bearing operators are introduced in Chern-Simons
theory both in its pure form and when it is coupled to fermions. The magnetic
flux creation operator turns out to be the Wilson line. The euclidean
correlation functions of these operators are shown to be local and are
evaluated exactly in the pure case and through an expansion in the inverse
fermion mass whenever these are present. Physical states only occur in the
presence of fermions and consist of composite charge-magnetic flux carrying
states which are in general anyonic. The large distance behavior of the
correlation functions indicates the condensation of charge and magnetic flux.Comment: Latex, 17 page
Quantum global vortex strings in a background field
We consider quantum global vortex string correlation functions, within the
Kalb-Ramond framework, in the presence of a background field-strength tensor
and investigate the conditions under which this yields a nontrivial
contribution to those correlation functions. We show that a background field
must be supplemented to the Kalb-Ramond theory, in order to correctly describe
the quantum properties of the vortex strings. The explicit form of this
background field and the associated quantum vortex string correlation function
are derived. The complete expression for the quantum vortex creation operator
is explicitly obtained. We discuss the potential applicability of our results
in the physics of superfluids and rotating Bose-Einstein condensates.Comment: To appear in Journal of Physics A: Mathematical and Genera
Supersymmetric free-damped oscillators: Adaptive observer estimation of the Riccati parameter
A supersymmetric class of free damped oscillators with three parameters has
been obtained in 1998 by Rosu and Reyes through the factorization of the Newton
equation. The supplementary parameter is the integration constant of the
general Riccati solution. The estimation of the latter parameter is performed
here by employing the recent adaptive observer scheme of Besancon et al., but
applied in a nonstandard form in which a time-varying quantity containing the
unknown Riccati parameter is estimated first. Results of computer simulations
are presented to illustrate the good feasibility of this approach for a case in
which the estimation is not easily accomplished by other meansComment: 8 pages, 6 figure
Unlocking innovation for net zero: Constraints, enablers, and firm-level transition strategies
Transition pathways for net zero encompass seemingly insurmountable innovation challenges for the scaling of less mature technological solutions such as hydrogen, materials substitution, and electrification as well as societal challenges to increase the market acceptability of these solutions. In this article, we present a conceptual framework which provides a firm-level perspective on net-zero innovation which has four unique characteristics, i.e. it is complex, systemic, urgent, and directional. The framework shows that the input, process, and output constraints that incumbent firms face in the net-zero transition can be tackled through four firm-level innovation levers – i.e. recombinative, collaborative, integrative, and socio-cognitive capabilities – which, in concert, act as enablers for firms to address these net-zero constraints. We conclude the article by outlining the framework’s main insights for firms’ innovation strategies for net zero and the policy implications. We also propose avenues for future research on net-zero innovation
The HST Large Program on Omega Centauri. I. Multiple stellar populations at the bottom of the main sequence probed in NIR-Optical
As part of a large investigation with Hubble Space Telescope to study the
faintest stars within the globular cluster Omega Centauri, in this work we
present early results on the multiplicity of its main sequence (MS) stars,
based on deep optical and near-infrared observations. By using appropriate
color-magnitude diagrams we have identified, for the first time, the two main
stellar populations I, and II along the entire MS, from the turn-off towards
the hydrogen-burning limit. We have compared the observations with suitable
synthetic spectra of MS stars and conclude that the two MSs are consistent with
stellar populations with different metallicity, helium, and light-element
abundance. Specifically, MS-I corresponds to a metal-poor stellar population
([Fe/H]~-1.7) with Y~ 0.25 and [O/Fe]~0.30. The MS-II hosts helium-rich
(Y~0.37-0.40) stars with metallicity ranging from [Fe/H]~-1.7 to -1.4. Below
the MS knee (mF160W~19.5, our photometry reveals that each of the two main MSs
hosts stellar subpopulations with different oxygen abundances, with very O-poor
stars ([O/Fe]~-0.5) populating the MS-II. Such a complexity has never been
observed in previous studies of M-dwarfs in globular clusters. A few months
before the lunch of the James Webb Space Telescope, these results demonstrate
the power of optical and near-infrared photometry in the study of multiple
stellar populations in globular clusters.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Charge pairing, superconducting transition and supersymmetry in high-temperature cuprate superconductors
We propose a model for high-T superconductors, valid for
, that includes both the spin fluctuations of the
Cu magnetic ions and of the O doped holes. Spin-charge separation
is taken into account with the charge of the doped holes being associated to
quantum skyrmion excitations (holons) of the Cu spin background. The
holon effective interaction potential is evaluated as a function of doping,
indicating that Cooper pair formation is determined by the competition between
the spin fluctuations of the Cu background and of spins of the O
doped holes (spinons). The superconducting transition occurs when the spinon
fluctuations dominate, thereby reversing the sign of the interaction. At this
point (), the theory is supersymmetric at short distances
and, as a consequence, the leading order results are not modified by radiative
corrections. The critical doping parameter for the onset of superconductivity
at T=0 is obtained and found to be a universal constant determined by the shape
of the Fermi surface. Our theoretical values for are in good
agreement with the experiment for both LSCO and YBCO.Comment: RevTex, 4 pages, no figure
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Driving performance via exploration in changing environments: Evidence from Formula One racing
Until recently, scholars have customarily lumped multiple dimensions of environmental change into single constructs, and usually ascertained that the more the context changes, the more value firms derive from higher levels of exploration. In sync with more recent studies focusing on specific dimensions of change, in this paper we borrow theoretical elements from systems theory to examine the possibility that the reward to developing innovative product components may itself be eroded by implicit and yet burgeoning costs to fit the new component technology into existing architectures, thereby dampening system performance. Specifically, we theoretically assess how varying magnitudes of industry regulatory changes affect the optimum level of firm exploration, and propose—counter-intuitively vis-à-vis past literature—that the more radical (i.e., competence-destroying), as opposed to incremental (i.e., competence-enhancing) these changes are, the more the optimum intensity of firm exploration recedes. Based on quantitative as well as qualitative empirical analyses from the Formula One racing industry, we precisely trace the observed performance outcomes back to the underlying logic of our theory, stressing that impaired capabilities to integrate the new component in the architecture re-design, as well as time-based cognitive limitations both operate to inhibit the otherwise positive relationship between firm exploration and performance. In the end, we offer new insights to theory and practice
The State-of-the-Art HST Astro-Photometric Analysis of the core of \omega Centauri. III. The Main Sequence's Multiple Populations Galore
We take advantage of the exquisite quality of the Hubble Space Telescope
26-filter astro-photometric catalog of the core of Omega Cen presented in the
first paper of this series and the empirical differential-reddening correction
presented in the second paper in order to distill the main sequence into its
constituent populations. To this end, we restrict ourselves to the five most
useful filters: the magic "trio" of F275W, F336W, and F438W, along with F606W
and F814W. We develop a strategy for identifying color systems where different
populations stand out most distinctly, then we isolate those populations and
examine them in other filters where their sub-populations also come to light.
In this way, we have identified at least 15 sub-populations, each of which has
a distinctive fiducial curve through our 5-dimensional photometric space. We
confirm the MSa to be split into two subcomponents, and find that both the bMS
and the rMS are split into three subcomponents. Moreover, we have discovered
two additional MS groups: the MSd (which has three subcomponents) shares
similar properties with the bMS, and the MSe (which has four subcomponents),
has properties more similar to those of the rMS. We examine the fiducial curves
together and use synthetic spectra to infer relative heavy-element,
light-element, and Helium abundances for the populations. Our findings show
that the stellar populations and star formation history of Omega Cen are even
more complex than inferred previously. Finally, we provide as a supplement to
the original catalog a list that identifies for each star which population it
most likely is associated with.Comment: 22 pages, 17 figures (most in lower res), 2 tables, accepted for
publication in Ap
Multi-wavelength Hubble Space Telescope photometry of stellar populations in NGC288
We present new UV observations for NGC288, taken with the WFC3 detector on
board the Hubble Space Telescope, and combine them with existing optical data
from the archive to explore the multiple-population phenomenon in this globular
cluster (GC). The WFC3's UV filters have demonstrated an uncanny ability to
distinguish multiple populations along all photometric sequences in GCs, thanks
to their exquisite sensitivity to the atmospheric changes that are tell-tale
signs of second-generation enrichment. Optical filters, on the other hand, are
more sensitive to stellar-structure changes related to helium enhancement. By
combining both UV and optical data we can measure helium variation. We quantify
this enhancement for NGC288 and find that its variation is typical of what we
have come to expect in other clusters.Comment: 15 pages, 5 figures, accepted for publication in Ap
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