2,116 research outputs found
Systematic Study of High-pT Direct Photon Production with the PHENIX Experiment at RHIC
When studying the initial state and evolution of the matter created in
relativistic heavy ion collisions, high-pT direct photons are a powerful probe.
They are created in initial hard processes and in parton fragmentation, and
possibly in interactions of partons with the hot and dense medium. We present
systematic measurements of high-pT direct photon production in \sqrt{s_{NN}} =
200 GeV p+p and Au+Au collisions. The nuclear modification factor of direct
photons is shown for 5 < pT < 18 GeV/c, and at very high transverse momenta it
seems to be below unity in the most central Au+Au collisions.Comment: 4 pages, 4 figures. Invited parallel talk at The 19th International
Conference On Ultra relativistic Nucleus-Nucleus Collisions (Quark Matter
2006), Shanghai China, Nov. 14-20, 200
Nematic superconductivity stabilized by density wave fluctuations: Possible application to twisted bilayer graphene
Nematic superconductors possess unconventional superconducting order
parameters that spontaneously break rotational symmetry of the underlying
crystal. In this work we propose a mechanism for nematic superconductivity
stabilized by strong density wave fluctuations in two dimensions. While the
weak-coupling theory finds the fully gapped chiral state to be energetically
stable, we show that strong density wave fluctuations result in an additional
contribution to the free energy of a superconductor with multicomponent order
parameters, which generally favors nematic superconductivity. Our theory shades
light on the recent observation of rotational symmetry breaking in the
superconducting state of twisted bilayer graphene
Study on Voltage Controller of Self-Excited Induction Generator Using Controlled Shunt Capacitor, SVC Magnetic Energy Recovery Switch
Reactive compensation is required to maintain terminal voltage of induction generator under varying load and speed operation. A new variable shunt capacitor, which is called SVC magnetic energy recovery switch (SVC MERS), is proposed. The operation principle, characteristics of injected current, operating range of reactive compensation of SVC MERS in star and delta configuration were investigated. Application for induction generator voltage controller, which is required leading reactive compensator, is suitable for SVC MERS. Small scale experiments were conducted to verify the proposed system performance to control induction generator voltage in variable load and speed conditions. The advantage of this device is simple control with low switching frequency. Moreover in delta configuration, the SVC MERS current is low means downsizing of heatsink can be achieved. Keywords : Voltage controller, induction generator, reactive compensation, SVC MER
Trial of Fast Neutral Particles and Neutron Measurement by a Synthetic Diamond Radiation Detector
Magic of high order van Hove singularity
We introduce a new type of van Hove singularity in two dimensions, where a
saddle point in momentum space is changed from second-order to high-order.
Correspondingly, the density of states near such ``high-order van Hove
singularity'' is significantly enhanced from logarithmic to power-law
divergence, which promises stronger electron correlation effects. High-order
van Hove singularity can be generally achieved by tuning the band structure
with a single parameter in moir\'e superlattices, such as twisted bilayer
graphene by tuning twist angle or applying pressure, and trilayer graphene by
applying vertical electric field.Comment: 8 pages and 4 figures, figs. 1, 2 and 3 updated and Supplemental
Material adde
Rotational modulation of X-ray emission in Orion Nebula young stars
We investigate the spatial distribution of X-ray emitting plasma in a sample
of young Orion Nebula Cluster stars by modulation of their X-ray light-curves
due to stellar rotation. The study, part of the Chandra Orion Ultradeep Project
(COUP), is made possible by the exceptional length of the observation: 10 days
of ACIS integration during a time span of 13 days, yielding a total of 1616
detected sources in the 17x17 arcmin field of view. We here focus on a
subsample of 233 X-ray-bright stars with known rotational periods. We search
for X-ray modulation using the Lomb Normalized Periodogram method.
X-ray modulation related to the rotation period is detected in at least 23
stars with periods between 2 and 12 days and relative amplitudes ranging from
20% to 70%. In 16 cases, the X-ray modulation period is similar to the stellar
rotation period while in seven cases it is about half that value, possibly due
to the presence of X-ray emitting structures at opposite stellar longitudes.
These results constitute the largest sample of low mass stars in which X-ray
rotational modulation has been observed. The detection of rotational modulation
indicates that the X-ray emitting regions are distributed inhomogeneneously in
longitude and do not extend to distances significantly larger than the stellar
radius. Modulation is observed in stars with saturated activity levels
(L_X/L_bol ~ 10^(-3)) showing that saturation is not due to the filling of the
stellar surface with X-ray emitting regions.Comment: 41 pages, 15 figures, ApJS in press. Figure 15 (34 panels) is an
on-line only figure and is not included. A pdf file which includes figure 15
as well as full resolution versions of figure 10 and 11 is available at:
http://www.astropa.unipa.it/~ettoref/COUP_RotMod.pd
Tetramerisation of a frustrated spin-1/2 chain
We investigate a model of a frustrated spin-1/2 Heisenberg chain coupled to
adiabatic phonons with a general form of magnetoelastic coupling. For large
enough frustration and lattice coupling a new tetramerised phase with three
different bond lengths is found. We argue that the zig-zag spin-1/2 chain
LiVO might be a good candidate to observe such a phase
Hard X-ray PHA System for Study on Energetic Electron Tail Formation in ECRH Plasma of Heliotron J
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