11,350 research outputs found
Nature of the low temperature ordering of Pr in PrBa_2Cu_3O_(6+x)
Theoretical model is presented to describe the anomalous ordered phase of Pr
ions in PrBa_2Cu_3O_(6+x) below T_Pr = 12-17 K. The model considers the Pr
multipole degrees of freedom and coupling between the Cu and Pr subsystems. We
identify the symmetry allowed coupling of Cu and Pr ions and conclude that only
an ab-plane Pr dipole ordering can explain the Cu spin rotation observed at
T_Pr by neutron diffraction by Boothroyd et al. [A. T. Boothroyd et al., Phys.
Rev. Lett. 78, 130 (1997)]. A substantial enhancement of the Pr ordering
temperature is shown to arise from the Cu-Pr coupling which is the key for the
anomalous magnetic behavior in PrBa_2Cu_3O_(6+x).Comment: 6 pages, 4 figure
Amplitude variations of modulated RV Tauri stars support the dust obscuration model of the RVb phenomenon
Context. RV Tauri-type variables are pulsating post-AGB stars that evolve
rapidly through the instability strip after leaving the Asymptotic Giant
Branch. Their light variability is dominated by radial pulsations. Members of
the RVb subclass show an additional variability in form of a long-term
modulation of the mean brightness, for which the most popular theories all
assume binarity and some kind of circumstellar dust. Here we address if the
amplitude modulations are consistent with the dust obscuration model. Aims. We
measure and interpret the overall changes of the mean amplitude of the
pulsations along the RVb variability. Methods. We compiled long-term
photometric data for RVb-type stars, including visual observations of the
American Association of Variable Star Observers, ground-based CCD photometry
from the OGLE and ASAS projects and ultra-precise space photometry of one star,
DF Cygni, from the Kepler space telescope. After converting all the
observations to flux units, we measure the cycle-to-cycle variations of the
pulsation amplitude and correlate them to the actual mean fluxes. Results. We
find a surprisingly uniform correlation between the pulsation amplitude and the
mean flux: they scale linearly with each other for a wide range of fluxes and
amplitudes. It means that the pulsation amplitude actually remains constant
when measured relative to the system flux level. The apparent amplitude
decrease in the faint states has long been noted in the literature but it was
always claimed to be difficult to explain with the actual models of the RVb
phenomenon. Here we show that when fluxes are used instead of magnitudes, the
amplitude attenuation is naturally explained by periodic obscuration from a
large opaque screen, one most likely corresponding to a circumbinary dusty disk
that surrounds the whole system.Comment: 8 pages, 6 figures, accepted for publication in A&
Attention modulates the processing of emotional expression triggered by foveal faces
To investigate whether the processing of emotional expression for faces presented within foveal vision is modulated by spatial attention, event-related potentials (ERPs) were recorded in response to stimulus arrays containing one fearful or neutral face at fixation, which was flanked by a pair of peripheral bilateral lines. When attention was focused on the central face, an enhanced positivity was elicited by fearful as compared to neutral faces. This effect started at 160 ms post-stimulus, and remained present for the remainder of the 700 ms analysis interval. When attention was directed away from the face towards the line pair, the initial phase of this emotional positivity remained present, but emotional expression effects beyond 220 ms post-stimulus were completely eliminated. These results demonstrate that when faces are presented foveally, the initial rapid stage of emotional expression processing is unaffected by attention. In contrast, attentional task instructions are effective in inhibiting later, more controlled stages of expression analysis
Beta-decay properties of neutron-rich Ca, Ti, and Cr isotopes
Beta-decay properties of neutron-rich Ca, Ti, and Cr isotopes are studied
within a deformed proton-neutron quasiparticle random-phase approximation. The
underlying mean field is described self-consistently from deformed Skyrme
Hartree-Fock calculations with pairing correlations. Residual spin-isospin
interactions in the particle-hole and particle-particle channels are also
included in the formalism. The energy distributions of the Gamow-Teller
strength, the beta-decay feedings, the beta-decay half-lives, and the
beta-delayed neutron emission probabilities are discussed and compared with
other theoretical results, as well as with the available experimental
information. The evolution of these nuclear beta-decay properties is
investigated in isotopic chains in a search for structural changes. A reliable
estimate of the beta-decay properties in this mass region is a valuable
information for evaluating decay rates in astrophysical scenarios.Comment: 11 pages, 12 figure
Evidence for fresh frost layer on the bare nucleus of comet Hale--Bopp at 32 AU distance
Here we report that the activity of comet Hale--Bopp ceased between late 2007
and March, 2009, at about 28 AU distance from the Sun. At that time the comet
resided at a distance from the Sun that exceeded the freeze-out distance of
regular comets by an order of magnitude. A Herschel Space Observatory PACS scan
was taken in mid-2010, in the already inactive state of the nucleus. The albedo
has been found to be surprisingly large (8.10.9%{}), which exceeds the
value known for any other comets. With re-reduction of archive HST images from
1995 and 1996, we confirm that the pre-perihelion albedo resembled that of an
ordinary comet, and was smaller by a factor of two than the post-activity
albedo. Our further observations with the Very Large Telescope (VLT) also
confirmed that the albedo increased significantly by the end of the activity.
We explain these observations by proposing gravitational redeposition of icy
grains towards the end of the activity. This is plausible for such a massive
body in a cold environment, where gas velocity is lowered to the range of the
escape velocity. These observations also show that giant comets are not just
the upscaled versions of the comets we know but can be affected by processes
that are yet to be fully identified.Comment: 7 pages, 6 figures, accepted for publication in Ap
Issues in management of artificial intelligence based projects
Now that Artificial Intelligence (AI) is gaining acceptance, it is important to examine some of the obstacles that still stand in the way of its progress. Ironically, many of these obstacles are related to management and are aggravated by the very characteristcs that make AI useful. The purpose of this paper is to heighten awareness of management issues in AI development and to focus attention on their resolution
Charlie and the CryptoFactory: Towards Secure and Trusted Manufacturing Environments
The modernisation that stems from Industry 4.0 started populating the manufacturing sector with networked devices, complex sensors, and a significant proportion of physical actuation components. However, new capabilities in networked cyber-physical systems demand more complex infrastructure and algorithms and often lead to new security flaws and operational risks that increase the attack surface area exponentially. The interconnected nature of Industry 4.0-driven operations and the pace of digital transformation mean that cyber-attacks can have far more extensive effects than ever before. Based on that, the core ideas of this paper are driven by the observation that cyber security is one of the key enablers of Industry 4.0. Having this in mind, we propose CryptoFactory – a forward looking design of a layered-based architecture that can be used as a starting point for building secure and privacy-preserving smart factories. CryptoFactory aims to change the security outlook in smart manufacturing by discussing a set of fundamental requirements and functionality that modern factories should support in order to be resistant to both internal and external attacks. To this end, CryptoFactory first focuses on how to build trust relationships between the hardware devices in the factory. Then, we look on how to use several cryptographic approaches to allow IoT devices to securely collect, store and share their data while we also touch upon the emerging topic of secure and privacy-preserving communication and collaboration between manufacturing environments and value chains. Finally, we look into the problem of how to perform privacy-preserving analytics by leveraging Trusted Execution Environments and the promising concept of Functional Encryption
- …