250 research outputs found
Past climate changes facilitated homoploid speciation in three mountain spiny fescues (Festuca, Poaceae)
Apart from the overwhelming cases of allopolyploidization, the impact of speciation through homoploid hybridization is becoming more relevant than previously thought. Much less is known, however, about the impact of climate changes as a driven factor of speciation. To investigate these issues, we selected Festuca picoeuropeana, an hypothetical natural hybrid between the diploid species F. eskia and F. gautieri that occurs in two different mountain ranges (Cantabrian Mountains and Pyrenees) separated by more than 400 km. To unravel the outcomes of this mode of speciation and the impact of climate during speciation we used a multidisciplinary approach combining genome size and chromosome counts, data from an extensive nuclear genotypic analysis, plastid sequences and ecological niche models (ENM). Our results show that the same homoploid hybrid was originated independently in the two mountain ranges, being currently isolated from both parents and producing viable seeds. Parental species had the opportunity to contact as early as 21000 years ago although niche divergence occurs nowadays as result of a climate-driven shift. A high degree of niche divergence was observed between the hybrid and its parents and no recent introgression or backcrossed hybrids were detected, supporting the current presence of reproductive isolation barriers between these species
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV
Mid-rapidity transverse mass spectra and multiplicity densities of charged
and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC.
The spectra are exponential in transverse mass, with an inverse slope of about
280 MeV in central collisions. The multiplicity densities for these particles
scale with the negative hadron pseudo-rapidity density. The charged kaon to
pion ratios are and
for the most central collisions. The ratio is lower than the same
ratio observed at the SPS while the is higher than the SPS result.
Both ratios are enhanced by about 50% relative to p+p and +p
collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
Azimuthal anisotropy: the higher harmonics
We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 4 pages, 6 figures, contribution to the Quark Matter 2004 proceeding
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
The energy dependence of angular correlations inferred from mean- fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of angular
correlations inferred from event-wise mean transverse momentum
fluctuations in heavy ion collisions. We compare our large-acceptance
measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to
SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure
suggests that the principal source of $p_t$ correlations and fluctuations is
minijets (minimum-bias parton fragments). We observe a dramatic increase in
correlations and fluctuations from SPS to RHIC energies, increasing linearly
with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related
fluctuations near 10 GeV.Comment: 10 pages, 4 figure
All-optical switching and strong coupling using tunable whispering-gallery-mode microresonators
We review our recent work on tunable, ultrahigh quality factor
whispering-gallery-mode bottle microresonators and highlight their applications
in nonlinear optics and in quantum optics experiments. Our resonators combine
ultra-high quality factors of up to Q = 3.6 \times 10^8, a small mode volume,
and near-lossless fiber coupling, with a simple and customizable mode structure
enabling full tunability. We study, theoretically and experimentally, nonlinear
all-optical switching via the Kerr effect when the resonator is operated in an
add-drop configuration. This allows us to optically route a single-wavelength
cw optical signal between two fiber ports with high efficiency. Finally, we
report on progress towards strong coupling of single rubidium atoms to an
ultra-high Q mode of an actively stabilized bottle microresonator.Comment: 20 pages, 24 figures. Accepted for publication in Applied Physics B.
Changes according to referee suggestions: minor corrections to some figures
and captions, clarification of some points in the text, added references,
added new paragraph with results on atom-resonator interactio
Strange Resonance Production in p+p and Au+Au Collisions at RHIC Energies
Resonance yields and spectra from elementary p+p and Au+Au collisions at
200 GeV from the STAR experiment at RHIC are presented
and discussed in terms of chemical and thermal freeze-out conditions. Thermal
models do not adequately describe the yields of the resonance production in
central Au+Au collisions. The approach to include elastic hadronic interactions
between chemical freeze-out and thermal freeze-out suggests a time of 5 fm/c.Comment: 4 pages, 7 figures, proceedings of the Quark Matter 2004, in Oakland,
California, to be published in Journal of Physics G: Nuclear and Particle
Physic
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