24,438 research outputs found
Impact of future HERA data on the determination of proton parton distribution functions using the ZEUS QCD fit
The high precision and large kinematic coverage of the data from the HERA-I
running period (1994-2000) have already allowed precise extractions of proton
parton distribution functions (PDFs). The HERA-II running program is now
underway and is expected to provide a substantial increase in the luminosity
collected at HERA. In this paper, a study is presented which investigates the
potential impact of future data from HERA on the proton PDF uncertainties,
within the currently planned running scenario. In addition, the effect of a
possible future measurement of the longitudinal structure function, FL, on the
gluon distribution is investigated.Comment: 5 pages, 2 figures, in proceedings of the XIII International Workshop
on Deep Inelastic Scattering - DIS 2005, Madison, Wisconsin, 200
Electrical transport properties of nanostructured ferromagnetic perovskite oxides La_0.67Ca_0.33MnO_3 and La_0.5Sr_0.5CoO_3 at low temperatures (5 K > T >0.3 K) and high magnetic field
We report a comprehensive study of the electrical and magneto-transport
properties of nanocrystals of La_0.67Ca_0.33MnO_3 (LCMO) (with size down to 15
nm) and La_0.5Sr_0.5CoO_3 (LSCO) (with size down to 35 nm) in the temperature
range 0.3 K to 5 K and magnetic fields upto 14 T. The transport,
magnetotransport and non-linear conduction (I-V curves) were analysed using the
concept of Spin Polarized Tunnelling in the presence of Coulomb blockade. The
activation energy of transport, \Delta, was used to estimate the tunnelling
distances and the inverse decay length of the tunnelling wave function (\chi)
and the height of the tunnelling barrier (\Phi_B). The magnetotransport data
were used to find out the magnetic field dependences of these tunnelling
parameters. The data taken over a large magnetic field range allowed us to
separate out the MR contributions at low temperatures arising from tunnelling
into two distinct contributions. In LCMO, at low magnetic field, the transport
and the MR are dominated by the spin polarization, while at higher magnetic
field the MR arises from the lowering of the tunnel barrier by the magnetic
field leading to an MR that does not saturate even at 14 T. In contrast, in
LSCO, which does not have substantial spin polarization, the first contribution
at low field is absent, while the second contribution related to the barrier
height persists. The idea of inter-grain tunnelling has been validated by
direct measurements of the non-linear I-V data in this temperature range and
the I-V data was found to be strongly dependent on magnetic field. We made the
important observation that a gap like feature (with magnitude ~ E_C, the
Coulomb charging energy) shows up in the conductance g(V) at low bias for the
systems with smallest nanocrystal size at lowest temperatures (T < 0.7 K). The
gap closes as the magnetic field and the temperature are increased.Comment: 13 figure
Aspects of Duality in Nodal Liquids
Starting from a microscopic t-J like model and a SU(2) spin-charge separation
ansatz, a relativistic continuum gauge lagrangian is obtained in the vicinity
of a nodal point of the Fermi surface. The excitations in the pseudogap phase
are described by topological excitations in the dual model which has a Z_2
global symmetry due to the effect of instantons. Confinement of spinon and
holons emerge from this picture. The adjoint and fundamental strings are
associated with stripes. As the spin gap decreases a local Z_2 symmetry
emerges.Comment: 15 pages revtex, no figure
Spin rings in bi-stable planar semiconductor microcavities
A unique feature of exciton-polaritons, inherited from their mixed
light-matter origin, is the strongly spin-dependent polariton-polariton
interaction, which has been predicted to result in the formation of spin rings
in real space [Shelykh et al., Phys. Rev. Lett. 100, 116401 (2008)]. Here we
experimentally demonstrate the spin bi-stability of exciton-polaritons in an
InGaAs-based semiconductor microcavity under resonant optical pumping. We
observe the formation of spin rings whose size can be finely controlled in a
spatial scale down to the micrometer range, much smaller than the spot size. We
additionally evaluate the sign and magnitude of the antiparallel polariton spin
interaction constant.Comment: 5 pages, 4 figure
Unconventional magnetism in multivalent charge-ordered YbPtGe probed by Pt- and Yb-NMR
Detailed Pt- and Yb nuclear magnetic resonance (NMR) studies
on the heterogeneous mixed valence system YbPtGe are reported. The
temperature dependence of the Pt-NMR shift indicates the
opening of an unusual magnetic gap below 200\,K. was analyzed by a
thermal activation model which yields an isotropic gap \,K. In contrast, the spin-lattice relaxation rate () does
not provide evidence for the gap. Therefore, an intermediate-valence picture is
proposed while a Kondo-insulator scenario can be excluded. Moreover,
() follows a simple metallic behavior, similar to the reference
compound YPtGe. A well resolved NMR line with small shift is assigned to
divalent Yb. This finding supports the proposed model with two sub-sets
of Yb species (di- and trivalent) located on the Yb2 and Yb1 site of the
YbPtGe lattice.Comment: Submitted in Physical Review B (Rapid Communication
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Comparing cities’ cycling patterns using online shared bicycle maps
Bicycle sharing systems are increasingly being deployed in urban areas around the world, alongside online maps that disclose the state (i.e., location, number of bicycles/number of free parking slots) of stations in each city. Recent work has demonstrated how regularly monitoring these online maps allows for a granular analysis of a city’s cycling trends; further, the literature indicates that different cities have unique spatio-temporal patterns, reducing the generalisability of any insights or models derived from a single system. In this work, we analyse 4.5 months of online bike-sharing map data from 10 cities which, combined, have 996 stations. While an aggregate comparison supports the view of cities having unique usage patterns, results of applying unsupervised learning to the temporal data shows that, instead, only the larger systems display heterogeneous behaviour, indicating that many of these systems share intrinsic similarities. We further show how these similarities are reflected in the predictability of stations’ occupancy data via a cross-city comparison of the error that a variety of approaches achieve when forecasting the number of bicycles that a station will have in the near future.We close by discussing the impact of uncovering these similarities on how future bicycle sharing systems can be designed, built, and managed.This is the accepted manuscript. The final published version is available at http://link.springer.com/article/10.1007%2Fs11116-015-9599-9
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