13,303 research outputs found
Photon correlation spectroscopy as a witness for quantum coherence
The development of spectroscopic techniques able to detect and verify quantum
coherence is a goal of increasing importance given the rapid progress of new
quantum technologies, the advances in the field of quantum thermodynamics, and
the emergence of new questions in chemistry and biology regarding the possible
relevance of quantum coherence in biochemical processes. Ideally, these tools
should be able to detect and verify the presence of quantum coherence in both
the transient dynamics and the steady state of driven-dissipative systems, such
as light-harvesting complexes driven by thermal photons in natural conditions.
This requirement poses a challenge for standard laser spectroscopy methods.
Here, we propose photon correlation measurements as a new tool to analyse
quantum dynamics in molecular aggregates in driven-dissipative situations. We
show that the photon correlation statistics on the light emitted by a molecular
dimer model can signal the presence of coherent dynamics. Deviations from the
counting statistics of independent emitters constitute a direct fingerprint of
quantum coherence in the steady state. Furthermore, the analysis of frequency
resolved photon correlations can signal the presence of coherent dynamics even
in the absence of steady state coherence, providing direct spectroscopic access
to the much sought-after site energies in molecular aggregates
The destruction of the silver pipes from Ur: a new proposal
Este artigo propõe que os tubos de prata encontrados no CemitĂ©rio Real de Ur (ca. 2450 a.C.) foram intencionalmente tornados imprĂłprios para uso apĂłs terem sido usados para tocar mĂşsica durante a procissĂŁo funerária que levou ao sepultamento do falecido na Sepultura Privada 333. Com base em evidĂŞncias arqueolĂłgicas e cuneiformes da Mesopotâmia, assim como breves observações comparativas, sugere-se que a razĂŁo para isto foi para que os espĂritos que viviam dentro deste instrumento de sopro nĂŁo pudessem, em algum momento no futuro, perturbar os vivos.This paper proposes that the silver pipes found in the Royal Cemetery of Ur (ca. 2450 BCE) were intentionally made unfit for use after having been used to play music during the funerary procession that led to the burial of the deceased in Private Grave 333. Based on Mesopotamian archaeological and cuneiform evidence, as well as brief comparative observations, it is suggested the reason for this was so that the spirits living inside this wind instrument could not at some point in the future disturb the living
Downsizing implementation and financial performance
In the present study we explore the relationship between downsizing decisions and corporate financial
performance after top management has decided to downsize. Our focus is on the financial consequences
arising from the amount of downsizing and the use of disengagement incentives. For this purpose, we use
a sample of downsizing announcements in the Spanish press from 1995 up to 2001. Although the results
show that the amount of downsizing is not significantly related to post-downsizing profitability, the
evidence provided supports the finding that the use of disengagement incentives (which motivate workers
to leave the organization) is negatively related to firm performance. Our analysis helps to understand the
role that strategic downsizing decisions play in explaining observed variance in the performance of
downsized firms. Thus, it advances scholarly organizational research by reinforcing the concept that
corporate performance is not only contingent on strategies, but also influenced by the means through
which these strategies are implemented
Does downsizing improve organizational performance? An analysis of Spanish manufacturing firms
The objective of this study is to examine the effect of downsizing on corporate performance, considering
a sample of manufacturing firms drawn from the Spanish Survey of Business Strategies during the 1993-
2005 period. No significant differences in post-downsizing performance arise between companies which
downsize and those that do not. Likewise, we find that substantial workforce reductions through
collective dismissals do not either lead to improved performance levels. Downsizing, therefore, may not
be a way for managers to increase performance, particularly in a context like the Spanish one, where the
labour market is characterized by a high protection of employees’ rights and substantial contract
termination costs
Degenerate parametric oscillation in quantum membrane optomechanics
The promise of innovative applications has triggered the development of many
modern technologies capable of exploiting quantum effects. But in addition to
future applications, such quantum technologies have already provided us with
the possibility of accessing quantum-mechanical scenarios that seemed
unreachable just a few decades ago. With this spirit, in this work we show that
modern optomechanical setups are mature enough to implement one of the most
elusive models in the field of open system dynamics: degenerate parametric
oscillation. The possibility of implementing it in nonlinear optical resonators
was the main motivation for introducing such model in the eighties, which
rapidly became a paradigm for the study of dissipative phase transitions whose
corresponding spontaneously broken symmetry is discrete. However, it was found
that the intrinsic multimode nature of optical cavities makes it impossible to
experimentally study the model all the way through its phase transition. In
contrast, here we show that this long-awaited model can be implemented in the
motion of a mechanical object dispersively coupled to the light contained in a
cavity, when the latter is properly driven with multi-chromatic laser light. We
focus on membranes as the mechanical element, showing that the main signatures
of the degenerate parametric oscillation model can be studied in
state-of-the-art setups, thus opening the possibility of studying spontaneous
symmetry breaking and enhanced metrology in one of the cleanest dissipative
phase transitions.Comment: We welcome comments, suggestions, and (constructive) criticis
Almost separating and almost secure frameproof codes over q-ary alphabets
The final publication is available at Springer via http://dx.doi.org/10.1007/s10623-015-0060-zIn this paper we discuss some variations of the notion of separating code for alphabets of arbitrary size. We show how the original definition can be relaxed in two different ways, namely almost separating and almost secure frameproof codes, yielding two different concepts. The new definitions enable us to obtain codes of higher rate, at the expense of satisfying the separating property partially. These new definitions become useful when complete separation is only required with high probability, rather than unconditionally. We also show how the codes proposed can be used to improve the rate of existing constructions of families of fingerprinting codes.Peer ReviewedPostprint (author's final draft
Recursive linear estimation for discrete time systems in the presence of different multiplicative observation noises
This paper describes a design for a least mean square error estimator in discrete time systems where the components of the state vector, in measurement equation, are corrupted by different multiplicative noises in addition to observation noise. We show how known results can be considered a particular case of the algorithm stated in this paperState estimation, multiplicative noise, uncertain observations
Glory revealed in disk-integrated photometry of Venus
Context. Reflected light from a spatially unresolved planet yields unique
insight into the overall optical properties of the planet cover. Glories are
optical phenomena caused by light that is backscattered within spherical
droplets following a narrow distribution of sizes; they are well known on Earth
as localised features above liquid clouds. Aims. Here we report the first
evidence for a glory in the disk-integrated photometry of Venus and, in turn,
of any planet. Methods. We used previously published phase curves of the planet
that were reproduced over the full range of phase angles with model predictions
based on a realistic description of the Venus atmosphere. We assumed that the
optical properties of the planet as a whole can be described by a uniform and
stable cloud cover, an assumption that agrees well with observational evidence.
Results. We specifically show that the measured phase curves mimic the
scattering properties of the Venus upper-cloud micron-sized aerosols, also at
the small phase angles at which the glory occurs, and that the glory contrast
is consistent with what is expected after multiple scattering of photons. In
the optical, the planet appears to be brighter at phase angles of 11-13 deg
than at full illumination; it undergoes a maximum dimming of up to 10 percent
at phases in between. Conclusions. Glories might potentially indicate spherical
droplets and, thus, extant liquid clouds in the atmospheres of exoplanets. A
prospective detection will require exquisite photometry at the small
planet-star separations of the glory phase angles.Comment: In press. Astronomy & Astrophysics. Letter to the Editor; 201
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