1,307 research outputs found
Two-pion interferometry for the granular sources in ultrarelativistic heavy ion collisions
We investigate the two-pion interferometry in ultrarelativistic heavy ion
collisions in the granular source model of quark-gluon plasma droplets. The
pion transverse momentum spectra and HBT radii of the granular sources agree
well with the experimental data of the GeV Au-Au and
TeV Pb-Pb most central collisions. In the granular source
model the larger initial system breakup time may lead to the larger HBT radii
, , and . However, the large droplet
transverse expansion and limited average relative emitting time of particles in
the granular source lead to small ratios of the transverse HBT radii .Comment: 4 pages, 4 figure
Induced log-concavity of equivariant matroid invariants
Inspired by the notion of equivariant log-concavity, we introduce the concept
of induced log-concavity for a sequence of representations of a finite group.
For an equivariant matroid equipped with a symmetric group action or a finite
general linear group action, we transform the problem of proving the induced
log-concavity of matroid invariants to that of proving the Schur positivity of
symmetric functions. We prove the induced log-concavity of the equivariant
Kazhdan-Lusztig polynomials of -niform matroids equipped with the action of
a finite general linear group, as well as that of the equivariant
Kazhdan-Lusztig polynomials of uniform matroids equipped with the action of a
symmetric group.
As a consequence of the former, we obtain the log-concavity of
Kazhdan-Lusztig polynomials of -niform matroids, thus providing further
positive evidence for Elias, Proudfoot and Wakefield's log-concavity conjecture
on the matroid Kazhdan-Lusztig polynomials. From the latter we obtain the
log-concavity of Kazhdan-Lusztig polynomials of uniform matroids, which was
recently proved by Xie and Zhang by using a computer algebra approach. We also
establish the induced log-concavity of the equivariant characteristic
polynomials and the equivariant inverse Kazhdan-Lusztig polynomials for
-niform matroids and uniform matroids.Comment: 36 page
Full polar cap cascade scenario: -ray and X-ray luminosities from spin-powered pulsars
We modify polar cap cascade picture to include the ICS of the higher
generation pairs. In such a ``full-cascade'' scenario, not only the
perpendicular portion of the energy of the pairs goes to high energy radiation
via SR, but the parallel portion of the energy of the pairs can also contribute
to high energy emission via ICS with the soft thermal photons from either the
full neutron star surface or the hot polar cap. An important output of such a
scenario is that the soft tail of the ICS spectrum can naturally result in a
non-thermal X-ray component which can contribute to the luminosities observed
by ROSAT and ASCA. Here we present an analytic description of such a full polar
cap cascade scenario within the framework of Harding & Muslimov acceleration
model. We present the theoretical predictions of the -ray luminosities,
the thermal and non-thermal X-ray luminosities for the known spin-powered X-ray
pulsars. Our results show that the observed different dependences of the high
energy luminosities on the pulsar spin-down luminosities, i.e., and , are well
reproduced. Our model predicts that the {\em pulsed} soft X-rays in the ROSAT
band from most of the millisecond pulsars might be of thermal origin if there
is no strong multipole field components near the surfaces of these pulsars.Comment: 23 pages, emulateapj style, final version to appear in the
Astrophysical Journa
Optical properties and charge-transfer excitations in edge-functionalized all-graphene nanojunctions
We investigate the optical properties of edge-functionalized graphene
nanosystems, focusing on the formation of junctions and charge transfer
excitons. We consider a class of graphene structures which combine the main
electronic features of graphene with the wide tunability of large polycyclic
aromatic hydrocarbons. By investigating prototypical ribbon-like systems, we
show that, upon convenient choice of functional groups, low energy excitations
with remarkable charge transfer character and large oscillator strength are
obtained. These properties can be further modulated through an appropriate
width variation, thus spanning a wide range in the low-energy region of the
UV-Vis spectra. Our results are relevant in view of designing all-graphene
optoelectronic nanodevices, which take advantage of the versatility of
molecular functionalization, together with the stability and the electronic
properties of graphene nanostructures.Comment: J. Phys. Chem. Lett. (2011), in pres
An Investigation of Willingness to Pay for Geopark Management and Conservation: A Case Study of Geotourists in the Greater China Region
Willingness to pay (WTP) for geological protection is essential for market-based geopark conservation tactic formulations. Whether geotourists are willing to pay and how much they prefer to pay might be influenced by different determinants. The present study aims to (1) investigate the probability of paying and the payment amount for geopark conservation and (2) examine how factors influence the intention and amount to pay for the upkeep of geoparks. The results suggest that geotourists would contribute financially to geological conservation and geopark management. The findings also revealed that geotourists’ intentions and payment for conservation were associated with educational background and monthly income level. In addition, geotourist attachment and satisfaction concerning visiting geoparks positively affected intention and payment. This study might provide empirical references for geopark management and conservation in the Greater China Region
Understanding the Determinants of Geologically Responsible Behaviour among Geotourists: A Multi-Destination Analysis
This study explores the drivers of geologically responsible behaviour among geotourists in three geoparks in the Greater China region: Danxiashan UNESCO Global Geopark in southern China, Hong Kong UNESCO Global Geopark, and Yehliu Geopark in northern Taiwan. On-site questionnaire surveys were conducted, collecting over 800 respondents in these geoparks, and structural equation modelling was applied for our analysis. The findings reveal that geologically responsible behaviour is positively associated with environmentally responsible attitudes, in line with some previous research. Notably, place attachment and visitor satisfaction were not directly related to geologically responsible behaviour but were positively correlated with environmentally responsible attitudes. This suggests that emotional connections to geoparks and visitor satisfaction indirectly nurture environmentally responsible attitudes, subsequently leading to geologically responsible behaviour. These results offer practical implications for geopark management practices. Providing informative guided tours and quality informational materials can enhance visitors’ geological knowledge and foster environmentally responsible attitudes. The improvement of the visitor experience, combined with the dissemination of accurate environmental knowledge and conservation messaging, can enhance visitor satisfaction, deepen attachment to geoparks, and, ultimately, encourage more geologically responsible behaviours. Understanding these relationships can assist geotourism destinations in promoting geological resources’ conservation while enhancing the visitor experience
Designing all-graphene nanojunctions by covalent functionalization
We investigated theoretically the effect of covalent edge functionalization,
with organic functional groups, on the electronic properties of graphene
nanostructures and nano-junctions. Our analysis shows that functionalization
can be designed to tune electron affinities and ionization potentials of
graphene flakes, and to control the energy alignment of frontier orbitals in
nanometer-wide graphene junctions. The stability of the proposed mechanism is
discussed with respect to the functional groups, their number as well as the
width of graphene nanostructures. The results of our work indicate that
different level alignments can be obtained and engineered in order to realize
stable all-graphene nanodevices
The WISDOM Radar: Unveiling the Subsurface Beneath the ExoMars Rover and Identifying the Best Locations for Drilling
The search for evidence of past or present life on Mars is the principal objective of the 2020 ESA-Roscosmos ExoMars Rover mission. If such evidence is to be found anywhere, it will most likely be in the subsurface, where organic molecules are shielded from the destructive effects of ionizing radiation and atmospheric oxidants. For this reason, the ExoMars Rover mission has been optimized to investigate the subsurface to identify, understand, and sample those locations where conditions for the preservation of evidence of past life are most likely to be found. The Water Ice Subsurface Deposit Observation on Mars (WISDOM) ground-penetrating radar has been designed to provide information about the nature of the shallow subsurface over depth ranging from 3 to 10 m (with a vertical resolution of up to 3 cm), depending on the dielectric properties of the regolith. This depth range is critical to understanding the geologic evolution stratigraphy and distribution and state of subsurface H2O, which provide important clues in the search for life and the identification of optimal drilling sites for investigation and sampling by the Rover's 2-m drill. WISDOM will help ensure the safety and success of drilling operations by identification of potential hazards that might interfere with retrieval of subsurface samples
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