79,055 research outputs found
Induced Magnetic Ordering by Proton Irradiation in Graphite
We provide evidence that proton irradiation of energy 2.25 MeV on
highly-oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism.
Measurements performed with a superconducting quantum interferometer device
(SQUID) and magnetic force microscopy (MFM) reveal that the magnetic ordering
is stable at room temperature.Comment: 3 Figure
Intrinsic mechanism of phase locking in two-dimensional Josephson junction networks in presence of an external magnetic field
We present numerical simulations of the dynamics of two-dimensional Josephson
junction arrays to study the mechanism of mutual phase locking. We show that in
the presence of an external magnetic field two mechanisms are playing a role in
phase locking: feedback through the external load and internal coupling between
rows due to microwave currents induced by the field. We have found the
parameter values (junction capacitance, cell loop inductance, impedance of the
external load) for which the interplay of both these mechanisms leads to the
in-phase solution. The case of unshunted arrays is discussed as well.Comment: 13 pages, incl. 6 ps figures, Subm. to Europhysics Letter
Asymptotics of Spinfoam Amplitude on Simplicial Manifold: Euclidean Theory
We study the large-j asymptotics of the Euclidean EPRL/FK spin foam amplitude
on a 4d simplicial complex with arbitrary number of simplices. We show that for
a critical configuration (j_f, g_{ve}, n_{ef}) in general, there exists a
partition of the simplicial complex into three regions: Non-degenerate region,
Type-A degenerate region and Type-B degenerate region. On both the
non-degenerate and Type-A degenerate regions, the critical configuration
implies a non-degenerate Euclidean geometry, while on the Type-B degenerate
region, the critical configuration implies a vector geometry. Furthermore we
can split the Non-degenerate and Type-A regions into sub-complexes according to
the sign of Euclidean oriented 4-simplex volume. On each sub-complex, the spin
foam amplitude at critical configuration gives a Regge action that contains a
sign factor sgn(V_4(v)) of the oriented 4-simplices volume. Therefore the Regge
action reproduced here can be viewed as a discretized Palatini action with
on-shell connection. The asymptotic formula of the spin foam amplitude is given
by a sum of the amplitudes evaluated at all possible critical configurations,
which are the products of the amplitudes associated to different type of
geometries.Comment: 27 pages, 5 figures, references adde
Detection of an exoplanet around the evolved K giant HD 66141
Aims. We have been carrying out a precise radial velocity (RV) survey for K
giants to search for and study the origin of the lowamplitude and long-periodic
RV variations.
Methods. We present high-resolution RV measurements of the K2 giant HD 66141
from December 2003 to January 2011 using the fiber-fed Bohyunsan Observatory
Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO).
Results. We find that the RV measurements for HD 66141 exhibit a periodic
variation of 480.5 +/- 0.5 days with a semi-amplitude of 146.2 +/- 2.7 m/s. The
Hipparcos photometry and bisector velocity span (BVS) do not show any obvious
correlations with RV variations. We find indeed 706.4 +/- 35.0 day variations
in equivalent width (EW) measurements of H_alpha line and 703.0 +/- 39.4 day
variations in a space-born measurements 1.25{\mu} flux of HD 66141 measured
during COBE/DIRBE experiment. We reveal that a mean value of long-period
variations is about 705 +/- 53 days and the origin is a rotation period of the
star and variability that is caused by surface inhomogeneities. For the 480 day
periods of RV variations an orbital motion is the most likely explanation.
Assuming a stellar mass of 1.1 +/- 0.1 M_Sun? for HD 66141, we obtain a minimum
mass for the planetary companion of 6.0 +/- 0.3 M_Jup with an orbital
semi-major axis of 1.2 +/- 0.1 AU and an eccentricity of 0.07 +/- 0.03.Comment: 7 pages, 10 figures, 3 tables, accepted for publisation in Astronomy
& Astrophysic
Low-amplitude and long-period radial velocity variations in giants HD 3574, 63 Cygni, and HD 216946 (Research Note)
Aims. We study the low-amplitude and long-period variations in evolved stars
using precise radial velocity measurements. Methods. The high-resolution,
fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) was used from
September 2004 to May 2014 as part of the exoplanet search program at the
Bohyunsan Optical Astronomy Observatory (BOAO). Results. We report the
detection of low-amplitude and long-period orbital radial velocity variations
in three evolved stars, HD 3574, 63 Cyg, and HD 216946. They have periods of
1061, 982, and 1382 days and semi-amplitudes of 376, 742, and 699 m/s,
respectively.Comment: 6 pages, 7 figures, 4 tables, accepted for publisation in Astronomy &
Astrophysic
Assessment of different urban traffic control strategy impacts on vehicle emissions
This paper investigates the influence of traffic signal control strategy on vehicle emissions, vehicle journey time and total throughput flow within a single isolated four-armed junction. Two pre-timed signal plans are considered, one with two-stages involving permissive-only opposing turns and the other with four-stages which has no conflicting traffic. Additionally, the increase in efficiency by utilising actuated signal timing where green time is re-optimised as flow values vary is investigated. A microscopic traffic simulation model is used to model flows and AIRE (Analysis of Instantaneous Road Emissions) microscopic emissions model is utilised to out- put emission levels from the flow data. A simple junction model shows that the two-stage signal plan is more efficient in both emis- sions and journey time. However, as the level of opposed turning vehicles and conflicting movement increases, the two-stage model moves to being the inferior signal plan choice and the four-stage plan outputs fewer emissions than the two-stage plan. A real-world example of a four-armed junction has been used in this study and from the traffic survey data and existing junction layout; it is rec- ommended that a two-stage plan is used as it produces lower amounts of emissions and shorter journey times compared to a four-stage plan. The results also show that nitrogen oxides (NOx) are the most sensitive to changes in flow followed by carbon dioxide (CO2), Black Carbon and then particulate matter (PM10)
Impact of traffic management on black carbon emissions: a microsimulation study
This paper investigates the effectiveness of traffic management tools, includ- ing traffic signal control and en-route navigation provided by variable message signs (VMS), in reducing traffic congestion and associated emissions of CO2, NOx, and black carbon. The latter is among the most significant contributors of climate change, and is associated with many serious health problems. This study combines traffic microsimulation (S-Paramics) with emission modeling (AIRE) to simulate and predict the impacts of different traffic management measures on a number traffic and environmental Key Performance Indicators (KPIs) assessed at different spatial levels. Simulation results for a real road network located in West Glasgow suggest that these traffic management tools can bring a reduction in travel delay and BC emission respectively by up to 6 % and 3 % network wide. The improvement at local levels such as junctions or corridors can be more significant. However, our results also show that the potential benefits of such interventions are strongly dependent on a number of factors, including dynamic demand profile, VMS compliance rate, and fleet composition. Extensive discussion based on the simulation results as well as managerial insights are provided to support traffic network operation and control with environmental goals. The study described by this paper was conducted under the support of the FP7-funded CARBOTRAF project
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