3,992 research outputs found
From the chiral magnetic wave to the charge dependence of elliptic flow
The quark-gluon plasma formed in heavy ion collisions contains charged chiral
fermions evolving in an external magnetic field. At finite density of electric
charge or baryon number (resulting either from nuclear stopping or from
fluctuations), the triangle anomaly induces in the plasma the Chiral Magnetic
Wave (CMW). The CMW first induces a separation of the right and left chiral
charges along the magnetic field; the resulting dipolar axial charge density in
turn induces the oppositely directed vector charge currents leading to an
electric quadrupole moment of the quark-gluon plasma. Boosted by the strong
collective flow, the electric quadrupole moment translates into the charge
dependence of the elliptic flow coefficients, so that
(at positive net charge). Using the latest quantitative simulations of the
produced magnetic field and solving the CMW equation, we make further
quantitative estimates of the produced splitting and its centrality
dependence. We compare the results with the available experimental data.Comment: Contains 12 pages, 6 figures, written as a proceeding for the talk of
Y. Burnier at the conference "P and CP-odd Effects in Hot and Dense Matter
2012" held in BN
Ultrafast spectroscopy of propagating coherent acoustic phonons in GaN/InGaN heterostructures
We show that large amplitude, coherent acoustic phonon wavepackets can be
generated and detected in InGaN/GaN epilayers and heterostructures
in femtosecond pump-probe differential reflectivity experiments. The amplitude
of the coherent phonon increases with increasing Indium fraction and unlike
other coherent phonon oscillations, both \textit{amplitude} and \textit{period}
are strong functions of the laser probe energy. The amplitude of the
oscillation is substantially and almost instantaneously reduced when the
wavepacket reaches a GaN-sapphire interface below the surface indicating that
the phonon wavepackets are useful for imaging below the surface. A theoretical
model is proposed which fits the experiments well and helps to deduce the
strength of the phonon wavepackets. Our model shows that localized coherent
phonon wavepackets are generated by the femtosecond pump laser in the epilayer
near the surface. The wavepackets then propagate through a GaN layer changing
the local index of refraction, primarily through the Franz-Keldysh effect, and
as a result, modulate the reflectivity of the probe beam. Our model correctly
predicts the experimental dependence on probe-wavelength as well as epilayer
thickness.Comment: 11 pages, 14 figure
Optical studies of carrier and phonon dynamics in Ga_{1-x}Mn_{x}As
We present a time-resolved optical study of the dynamics of carriers and
phonons in Ga_{1-x}Mn_{x}As layers for a series of Mn and hole concentrations.
While band filling is the dominant effect in transient optical absorption in
low-temperature-grown (LT) GaAs, band gap renormalization effects become
important with increasing Mn concentration in Ga_{1-x}Mn_{x}As, as inferred
from the sign of the absorption change. We also report direct observation on
lattice vibrations in Ga1-xMnxAs layers via reflective electro-optic sampling
technique. The data show increasingly fast dephasing of LO phonon oscillations
for samples with increasing Mn and hole concentration, which can be understood
in term of phonon scattering by the holes.Comment: 13 pages, 3 figures replaced Fig.1 after finding a mistake in
previous versio
Alternating-Spin Ladders
We investigate a two-leg spin ladder system composed of alternating-spin
chains with two-different kind of spins. The fixed point properties are
discussed by using spin-wave analysis and non-linear sigma model techniques.
The model contains various massive phases, reflecting the interplay between the
bond-alternation and the spin-alternation.Comment: 6 pages, revtex, to appear in PR
Miniature micromachined quadrupole mass spectrometer array and method of making the same
The present invention provides a quadrupole mass spectrometer and an ion filter, or pole array, for use in the quadrupole mass spectrometer. The ion filter includes a thin patterned layer including a two-dimensional array of poles forming one or more quadrupoles. The patterned layer design permits the use of very short poles and with a very dense spacing of the poles, so that the ion filter may be made very small. Also provided is a method for making the ion filter and the quadrupole mass spectrometer. The method involves forming the patterned layer of the ion filter in such a way that as the poles of the patterned layer are formed, they have the relative positioning and alignment for use in a final quadrupole mass spectrometer device
KMT-2016-BLG-2052L: Microlensing Binary Composed of M Dwarfs Revealed from a Very Long Time-scale Event
We present the analysis of a binary microlensing event KMT-2016-BLG-2052, for
which the lensing-induced brightening of the source star lasted for 2 seasons.
We determine the lens mass from the combined measurements of the microlens
parallax \pie and angular Einstein radius \thetae. The measured mass
indicates that the lens is a binary composed of M dwarfs with masses of
and . The measured relative
lens-source proper motion of is smaller
than of typical Galactic lensing events, while
the estimated angular Einstein radius of \thetae\sim 1.2~{\rm mas} is
substantially greater than the typical value of .
Therefore, it turns out that the long time scale of the event is caused by the
combination of the slow and large \thetae rather than the heavy mass of
the lens. From the simulation of Galactic lensing events with very long time
scales ( days), we find that the probabilities that long
time-scale events are produced by lenses with masses and
are and 2.6\%, respectively, indicating that
events produced by heavy lenses comprise a minor fraction of long time-scale
events. The results indicate that it is essential to determine lens masses by
measuring both \pie and \thetae in order to firmly identify heavy stellar
remnants such as neutron stars and black holes.Comment: 9 pages, 11 figure
Recommended from our members
A roadmap for China to peak carbon dioxide emissions and achieve a 20% share of non-fossil fuels in primary energy by 2030
As part of its Paris Agreement commitment, China pledged to peak carbon dioxide (CO2) emissions around 2030, striving to peak earlier, and to increase the non-fossil share of primary energy to 20% by 2030. Yet by the end of 2017, China emitted 28% of the world's energy-related CO2 emissions, 76% of which were from coal use. How China can reinvent its energy economy cost-effectively while still achieving its commitments was the focus of a three-year joint research project completed in September 2016. Overall, this analysis found that if China follows a pathway in which it aggressively adopts all cost-effective energy efficiency and CO2 emission reduction technologies while also aggressively moving away from fossil fuels to renewable and other non-fossil resources, it is possible to not only meet its Paris Agreement Nationally Determined Contribution (NDC) commitments, but also to reduce its 2050 CO2 emissions to a level that is 42% below the country's 2010 CO2 emissions. While numerous barriers exist that will need to be addressed through effective policies and programs in order to realize these potential energy use and emissions reductions, there are also significant local environmental (e.g., air quality), national and global environmental (e.g., mitigation of climate change), human health, and other unquantified benefits that will be realized if this pathway is pursued in China
Chirality-Selective Excitation of Coherent Phonons in Carbon Nanotubes
Using pre-designed trains of femtosecond optical pulses, we have selectively
excited coherent phonons of the radial breathing mode of specific-chirality
single-walled carbon nanotubes within an ensemble sample. By analyzing the
initial phase of the phonon oscillations, we prove that the tube diameter
initially increases in response to ultrafast photoexcitation. Furthermore, from
excitation profiles, we demonstrate that an excitonic absorption peak of carbon
nanotubes periodically oscillates as a function of time when the tube diameter
undergoes radial breathing mode oscillations.Comment: 4 pages, 4 figure
- …