7,106 research outputs found
X-ray Dichroism and the Pseudogap Phase of Cuprates
A recent polarized x-ray absorption experiment on the high temperature
cuprate superconductor Bi2Sr2CaCu2O8 indicates the presence of broken parity
symmetry below the temperature, T*, where a pseudogap appears in photoemission.
We critically analyze the x-ray data, and conclude that a parity-breaking
signal of the kind suggested is unlikely based on the crystal structures
reported in the literature. Possible other origins of the observed dichroism
signal are discussed. We propose x-ray scattering experiments that can be done
in order to determine whether such alternative interpretations are valid or
not.Comment: final version to be published in Phys Rev B: some calculational
details added, clarification of XNLD contamination and biaxiality, more
discussion on possible space groups and previous optics result
Tackling territorial fragilities: does visitors' engagement matter? The active involvement during local food festivals
Questo studio propone un modello esplorativo che esamina il coinvolgimento dei visitatori durante la partecipazione a eventi locali di tipo gastronomico realizzati in destinazioni periferiche di piccole dimensioni. È stato intervistato un campione di 70 visitatori partecipanti a un noto evento ripetuto annualmente nel comune di Castellalto in Abruzzo e, attraverso l’applicazione di tre costrutti latenti mutuati dalla teoria dell’economia dell’esperienza, è stato testato il coinvolgimento attivo e passivo dei partecipanti sulle loro percezioni complessive. L’applicazione di un modello di equazione strutturale rivela che le percezioni generali dei visitatori sono positivamente influenzate dal loro coinvolgimento attivo durante l’evento, dove i fattori determinanti più rilevanti sono quelli legati alla dimensione edonica ed emotiva. Si discutono le relative implicazioni di policy.This study proposes an explorative model examining the visitors’ involvement during the participation to local food festivals held in small-sized peripheral destinations. A sample of 70 visitors attending to a popular event repeated annually in the municipality of Castellalto in Abruzzo region was surveyed and, through the application of three latent constructs borrowed by the experience economy theory, the active and passive involvement of event’s participants were tested on their overall perceptions. The application of a structural equation model reveals that the visitors’ overall perceptions are positively influenced by their active involvement during the event, where the most relevant determinants are those related to the hedonic and emotional dimension. The related policy implications are discussed.Este estudio propone un modelo exploratorio que examina la participación de los visitantes durante su participación en eventos gastronómicos locales llevados en pequeños destinos periféricos. Se entrevistó a una selección de 70 visitantes que participaban en un evento muy conocido que se repite anualmente en el municipio de Castellalto en Abruzzo y, mediante la aplicación de tres construcciones latentes tomadas de la teoría de la economía de la experiencia, se puso a prueba la participación activa y pasiva de los participantes en el evento sobre sus percepciones generales. La aplicación de un modelo de ecuación estructural revela que las percepciones globales de los visitantes están influenciadas positivamente por su participación activa durante el evento, donde los factores determinantes más relevantes son los relacionados con la dimensión hedónica y emocional. Se discuten las relativas implicaciones políticas
On the nature of the magnetic ground-state wave function of V_2O_3
After a brief historical introduction, we dwell on two recent experiments in
the low-temperature, monoclinic phase of V_2O_3: K-edge resonant x-ray
scattering and non-reciprocal linear dichroism, whose interpretations are in
conflict, as they require incompatible magnetic space groups. Such a conflict
is critically reviewed, in the light of the present literature, and new
experimental tests are suggested, in order to determine unambiguously the
magnetic group. We then focus on the correlated, non-local nature of the
ground-state wave function, that is at the basis of some drawbacks of the LDA+U
approach: we singled out the physical mechanism that makes LDA+U unreliable,
and indicate the way out for a possible remedy. Finally we explain, by means of
a symmetry argument related to the molecular wave function, why the magnetic
moment lies in the glide plane, even in the absence of any local symmetry at
vanadium sites.Comment: 7 pages, 1 figur
The age structure of stellar populations in the solar vicinity. Clues of a two-phase formation history of the Milky Way disk
We analyze high quality abundances data of solar neighborhood stars and show
that there are two distinct regimes of [alpha/Fe] versus age which we identify
as the epochs of the thick and thin disk formation. A tight correlation between
metallicity and [alpha/Fe] versus age is clearly identifiable on thick disk
stars, implying that this population formed from a well mixed ISM, over a time
scale of 4-5 Gyr. Thick disk stars vertical velocity dispersion correlate with
age, with the youngest objects having as small scale heights as those of thin
disk stars. A natural consequence of these two results is that a vertical
metallicity gradient is expected in this population. We suggest that the thick
disk set the initial conditions for the formation of the inner thin disk. This
provides also an explanation of the apparent coincidence between the step in
metallicity at 7-10 kpc in the thin disk and the confinment of the thick disk
at about R<10 kpc. We suggest that the outer thin disk developped outside the
influence of the thick disk, but also that the high alpha-enrichment of the
outer regions may originate from a primordial pollution by the gas expelled
from the thick disk. Local metal-poor thin disk stars, whose properties are
best explained by an origin in the outer disk, are shown to be as old as the
youngest thick disk (9-10 Gyr), implying that the outer thin disk started to
form while the thick disk formation was still on-going in the inner Galaxy. We
point out that, given the tight age-abundance relations in the thick disk, an
inside-out process would give rise to a radial gradient in abundances in this
population which is not observed. Finally, we argue that the data discussed
here leave little room for radial migration, either to have contaminated the
solar vicinity, or, to have redistributed stars in significant proportion
across the solar annulus.Comment: Accepted in A&A, Revised version with new figures and extended
discussio
The Milky Way as a High Redshift Galaxy: The Importance of Thick Disk Formation in Galaxies
We compare the star-formation history and dynamics of the Milky Way (MW) with
the properties of distant disk galaxies. During the first ~4 Gyr of its
evolution, the MW formed stars with a high star-formation intensity (SFI),
Sigma_SFR~0.6 Msun/yr/kpc2 and as a result, generated outflows and high
turbulence in its interstellar medium. This intense phase of star formation
corresponds to the formation of the thick disk. The formation of the thick disk
is a crucial phase which enables the MW to have formed approximately half of
its total stellar mass by z~1 which is similar to "MW progenitor galaxies"
selected by abundance matching. This agreement suggests that the formation of
the thick disk may be a generic evolutionary phase in disk galaxies. Using a
simple energy injection-kinetic energy relationship between the 1-D velocity
dispersion and SFI, we can reproduce the average perpendicular dispersion in
stellar velocities of the MW with age. This relationship, its inferred
evolution, and required efficiency are consistent with observations of galaxies
from z~0-3. The high turbulence generated by intense star formation naturally
resulted in a thick disk, a chemically well-mixed ISM, and is the mechanism
that links the evolution of MW to the observed characteristics of distant disk
galaxies.Comment: 5 pages, 4 figures; accepted to ApJ Letter
Are Coworkers in the Italian Peripheral Areas Performing Better? A Counterfactual Analysis
Coworking spaces are “serendipity accelerators” designed to host creative people and
entrepreneurs. While recent literature has started exploring the indirect effects of coworking spaces
on the local context, little is still known on how coworking spaces may directly affect the coworkers’
economic performance and wellbeing. Using a novel dataset based on a survey of 326 CWs working in
the Italian coworking spaces in 2018, this paper explores the potential economic impact for coworkers,
depending on whether a coworking space is localized in a peripheral or an urban area. Through a
propensity-score matching approach, we found that being located in a peripheral area for coworkers
may represent an opportunity to earn more than working in an urban center. The same holds for the
organization coworkers belong to
Interplay between topology and dynamics in the World Trade Web
We present an empirical analysis of the network formed by the trade
relationships between all world countries, or World Trade Web (WTW). Each
(directed) link is weighted by the amount of wealth flowing between two
countries, and each country is characterized by the value of its Gross Domestic
Product (GDP). By analysing a set of year-by-year data covering the time
interval 1950-2000, we show that the dynamics of all GDP values and the
evolution of the WTW (trade flow and topology) are tightly coupled. The
probability that two countries are connected depends on their GDP values,
supporting recent theoretical models relating network topology to the presence
of a `hidden' variable (or fitness). On the other hand, the topology is shown
to determine the GDP values due to the exchange between countries. This leads
us to a new framework where the fitness value is a dynamical variable
determining, and at the same time depending on, network topology in a
continuous feedback.Comment: Proceedings of the 5th conference on Applications of Physics in
Financial Analysis (APFA5), 29 June - 1 July 2006, Torino (ITALY
Applications of physical methods in high-frequency futures markets
In the present work we demonstrate the application of different physical
methods to high-frequency or tick-by-tick financial time series data. In
particular, we calculate the Hurst exponent and inverse statistics for the
price time series taken from a range of futures indices. Additionally, we show
that in a limit order book the relaxation times of an imbalanced book state
with more demand or supply can be described by stretched exponential laws
analogous to those seen in many physical systems.Comment: 14 Pages and 10 figures. Proceeding to the SPIE conference, 4 - 7
December 2007 Australian National Univ. Canberra, ACT, Australi
When the Milky Way turned off the lights: APOGEE provides evidence of star formation quenching in our Galaxy
Quenching, the cessation of star formation, is one of the most significant
events in the life cycle of galaxies. We show here the first evidence that the
Milky Way experienced a generalised quenching of its star formation at the end
of its thick disk formation 9 Gyr ago. Elemental abundances of stars
studied as part of the APOGEE survey reveal indeed that in less than 2
Gyr the star formation rate in our Galaxy dropped by an order-of-magnitude.
Because of the tight correlation between age and alpha abundance, this event
reflects in the dearth of stars along the inner disk sequence in the
[Fe/H]-[/Fe] plane. Before this phase, which lasted about 1.5 Gyr, the
Milky Way was actively forming stars. Afterwards, the star formation resumed at
a much lower level to form the thin disk. These events are very well matched by
the latest observation of MW-type progenitors at high redshifts. In late type
galaxies, quenching is believed to be related to a long and secular exhaustion
of gas. In our Galaxy, it occurred on a much shorter time scale, while the
chemical continuity before and after the quenching indicates that it was not
due to the exhaustion of the gas. While quenching is generally associated with
spheroids, our results show that it also occurs in galaxies like the Milky Way,
possibly when they are undergoing a morphological transition from thick to thin
disks. Given the demographics of late type galaxies in the local universe, in
which classical bulges are rare, we suggest further that this may hold true
generally in galaxies with mass lower than or approximately , where
quenching could be directly a consequence of thick disk formation. We emphasize
that the quenching phase in the Milky Way could be contemporaneous with, and
related to, the formation of the bar. We sketch a scenario on how a strong bar
may inhibit star formation.Comment: 17 pages, 8 figures. Published versio
Propagation of UHECRs in cosmological backgrounds: some results from SimProp
Ultra-High-Energy Cosmic Ray (UHECR) nuclei propagating in cosmological
radiation backgrounds produce secondary particles detectable at Earth. SimProp
is a one dimensional code for extragalactic propagation of UHECR nuclei,
inspired by the kinetic approach of Aloisio et al. As in this approach, only a
subset of nuclei and nuclear channels are used as representative. We discuss
the validation of the code and present applications to UHECR experimental
results. In particular we present the expected fluxes of neutrinos produced in
some astrophysical scenario.Comment: Poster presented by A. Di Matteo at the 33rd International Cosmic Ray
Conference, Rio De Janeiro (Brasil) July 2-9 201
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