21,702 research outputs found
Event by Event Net Charge Fluctuations
We present analyses of event-by-event dynamical net charge fluctuations
measured in 130 and 200 GeV Au Au collisions with the STAR detector. The
dynamical net charge fluctuations are evaluated using the
observable. Dynamical fluctuations measured in Au Au collisions at 130 and 200
GeV are finite, and exceed charge conservation limits. They deviate from a
perfect 1/N scaling and provide an indication that the collision dynamics
varies with collision centrality.Comment: 6 pages, 3 figures, Proc of 19th Nuclear Dynamics Conf at
Breckenridge, Colorado, Feb 8-15, 200
BaNiF4: an electric field-switchable weak antiferromagnet
We show that in the antiferromagnetic ferroelectric BaNiF4 the
Dzyaloshinskii-Moriya interaction leads to a small canting of the magnetic
moments, away from the easy axis, resulting in a noncollinear magnetic
structure. The canting corresponds to an additional "weak" antiferromagnetic
order parameter whose orientation is determined by the polar structural
distortion and can be reversed by switching the ferroelectric polarization with
an electric field. Our results point the way to a more general coupling
mechanism between structural distortions and magnetic order parameters in
magnetoelectric multiferroics which can be exploited in the design of electric
field-switchable magnets.Comment: 4 pages, 4 figure
X-ray Isophote Shapes and the Mass of NGC 3923
We present analysis of the shape and radial mass distribution of the E4
galaxy NGC 3923 using archival X-ray data from the ROSAT PSPC and HRI. The
X-ray isophotes are significantly elongated with ellipticity e_x=0.15
(0.09-0.21) (90% confidence) for semi-major axis a\sim 10h^{-1}_70 kpc and have
position angles aligned with the optical isophotes within the estimated
uncertainties. Applying the Geometric Test for dark matter, which is
independent of the gas temperature profile, we find that the ellipticities of
the PSPC isophotes exceed those predicted if M propto L at a marginal
significance level of 85% (80%) for oblate (prolate) symmetry. Detailed
hydrostatic models of an isothermal gas yield ellipticities for the gravitating
matter, e_mass=0.35-0.66 (90% confidence), which exceed the intensity weighted
ellipticity of the R-band optical light, = 0.30 (e_R^max=0.39).
We conclude that mass density profiles with rho\sim r^{-2} are favored over
steeper profiles if the gas is essentially isothermal (which is suggested by
the PSPC spectrum) and the surface brightness in the central regions (r<~15")
is not modified substantially by a multi-phase cooling flow, magnetic fields,
or discrete sources. We argue that these effects are unlikely to be important
for NGC 3923. (The derived e_{mass} range is very insensitive to these issues.)
Our spatial analysis also indicates that the allowed contribution to the ROSAT
emission from a population of discrete sources with Sigma_x propto Sigma_R is
significantly less than that indicated by the hard spectral component measured
by ASCA.Comment: 14 pages (6 figures), To Appear in MNRA
X-ray Constraints on the Intrinsic Shape of the Lenticular Galaxy NGC 1332
We have analyzed ROSAT PSPC X-ray data of the optically elongated S0 galaxy
NGC 1332 with the purposes of constraining the intrinsic shape of its
underlying mass and presenting a detailed investigation of the uncertainties
resulting from the assumptions underlying this type of analysis. The X-ray
isophotes are elongated with ellipticity (90% confidence) for
semi-major axes 75\arcsec -90\arcsec and have orientations consistent with
the optical isophotes (ellipticity ). The spectrum is poorly
constrained by the PSPC data and cannot rule out sizeable radial temperature
gradients or an emission component due to discrete sources equal in magnitude
to the hot gas. Using (and clarifying) the "geometric test" for dark matter, we
determined that the hypothesis that mass-traces-light is not consistent with
the X-ray data at 68% confidence and marginally consistent at 90% confidence
independent of the gas temperature profile. Detailed modeling gives constraints
on the ellipticity of the underlying mass of \epsilon_{mass} = 0.47 - 0.72
(0.31 - 0.83) at 68% (90%) confidence for isothermal and polytropic models. The
total mass of the isothermal models within a=43.6 kpc (D = 20h^{-1}_{80} Mpc)
is M_{tot} = (0.38 - 1.7) \times 10^{12}M_{\sun} (90% confidence) corresponding
to total blue mass-to-light ratio \Upsilon_B = (31.9 - 143) \Upsilon_{\sun}.
Similar results are obtained when the dark matter is fit directly using the
known distributions of the stars and gas. When possible rotation of the gas and
emission from discrete sources are included flattened mass distributions are
still required, although the constraints on \epsilon_{mass}$, but not the
total mass, are substantially weakened.Comment: 45 pages (figures missing), PostScript, to appear in ApJ on January
20, 199
Metastable supersymmetry breaking in N=2 non-linear sigma-models
We perform a general study of the issue of metastability for
supersymmetry-breaking vacua in theories with N=1 and N=2 global supersymmetry.
This problem turns out to capture all the important qualitative features of the
corresponding question in theories with local supersymmetry, where
gravitational effects induce only quantitative modifications. Moreover, it
allows to directly compare the conditions arising in the N=1 and N=2 cases,
since the latter becomes particular case of the former in the rigid limit. Our
strategy consists in a systematic investigation of the danger of instability
coming from the sGoldstini scalars, whose masses are entirely due to
supersymmetry breaking mass-splitting effects. We start by reviewing the
metastability conditions arising in general N=1 non-linear sigma-models with
chiral and vector multiplets. We then turn to the case of general N=2
non-linear sigma-models with hyper and vector multiplets. We first reproduce
and clarify the known no-go theorems applying to theories with only Abelian
vector multiplets and only hyper multiplets, and then derive new results
applying to more general cases. To make the comparison with N=1 models as clear
as possible, we rely on a formulation of N=2 models where one of the
supersymmetries is manifestly realized in terms of ordinary superfields,
whereas the other is realized through non-trivial transformations. We give a
self-contained account of such a construction of N=2 theories in N=1
superspace, generalizing previous work on various aspects to reach a general
and coordinate-covariant construction. We also present a direct computation of
the supertrace of the mass matrix.Comment: 50 pages, no figures; v2 minor corrections and addition of comments
and reference
Search for Conical Emission with Three-Particle Correlations
We present preliminary STAR results on 3-particle azimuthal angle correlation
studies in Au+Au collisions at = 200 GeV. The studies are
carried out at mid-rapidity between a trigger particle with 3 4 GeV/c and two associated particles in 1 2 GeV/c. A
cumulant analysis reveals finite 3-particle azimuthal correlations, dominated
by near and away side particle correlations consistent with jet production, and
jet-flow correlations. We use a two-component model to remove underlying
background correlations. This analysis indicates the presence of the conical
emission signals in central Au+Au collisions within the model assumptions about
background composition and normalization.Comment: Proceedings for STAR talk presented at Quark Matter 2006, 4 pages 2
figures, Version 2: typos corrected, references adde
Hunting in times of change: Uncovering indigenous strategies in the Colombian amazon using a role-playing game
Despite growing industrialization, the shift to a cash economy and natural resource overexploitation, indigenous people of the Amazon region hunt and trade wildlife in order to meet their livelihood requirements. Individual strategies, shaped by the hunters' values and expectations, are changing in response to the region's economic development, but they still face the contrasting challenges of poverty and overhunting. For conservation initiatives to be implemented effectively, it is crucial to take into account people's strategies with their underlying drivers and their adaptive capabilities within a transforming socio-economic environment. To uncover hunting strategies in the Colombian Amazon and their evolution under the current transition, we co-designed a role-playing game together with the local stakeholders. The game revolves around the tension between ecological sustainability and food securityâhunters' current main concern. It simulates the mosaic of activities that indigenous people perform in the wet and dry season, while also allowing for specific hunting strategies. Socio-economic conditions change while the game unfolds, opening up to emerging alternative potential scenarios suggested by the stakeholders themselves. Do hunters give up hunting when given the opportunity of an alternative income and protein source? Do institutional changes affect their livelihoods? We played the game between October and December 2016 with 39 playersâall of them huntersâfrom 9 different communities within the Ticoya reserve. Our results show that providing alternatives would decrease overall hunting effort, but impacts are not spatially homogenous. Legalizing trade could lead to overhunting except when market rules and competition come into place. When it comes to coupled human-nature systems, the best way forward to produce socially just and resilient conservation strategies might be to trigger an adaptive process of experiential learning and scenario exploration. The use of games as âboundary objectsâ can guide stakeholders through the process, eliciting the plurality of their strategies, their drivers and how outside change affects them
Age differences in fMRI adaptation for sound identity and location
We explored age differences in auditory perception by measuring fMRI adaptation of brain activity to repetitions of sound identity (what) and location (where), using meaningful environmental sounds. In one condition, both sound identity and location were repeated allowing us to assess non-specific adaptation. In other conditions, only one feature was repeated (identity or location) to assess domain-specific adaptation. Both young and older adults showed comparable non-specific adaptation (identity and location) in bilateral temporal lobes, medial parietal cortex, and subcortical regions. However, older adults showed reduced domain-specific adaptation to location repetitions in a distributed set of regions, including frontal and parietal areas, and to identity repetition in anterior temporal cortex. We also re-analyzed data from a previously published 1-back fMRI study, in which participants responded to infrequent repetition of the identity or location of meaningful sounds. This analysis revealed age differences in domain-specific adaptation in a set of brain regions that overlapped substantially with those identified in the adaptation experiment. This converging evidence of reductions in the degree of auditory fMRI adaptation in older adults suggests that the processing of specific auditory âwhatâ and âwhereâ information is altered with age, which may influence cognitive functions that depend on this processing
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