1,429 research outputs found
Temperature-Dependence Studies of Photorefractive Effect in a Low Glass-Transition-Temperature Polymer Composite
The temperature dependence of the photorefractive effect in a polymer composite containing poly(9-vinycarbazole), tricresyl phosphate, buckminsterfullerene, and 4-(N,N-diethylamino)-ÎČ-nitrostyrene is presented. The photoconductive, electro-optic and photorefractive properties of the material have been studied in the temperature range of 22-61°C. An apparent increase of electro-optic modulation with temperature and its eventual saturation is observed. This behavior is attributed to the temperature activated orientational mobility of the second-order nonlinear chromophores. The polarization anisotropy between the p- and s-polarized readouts is consistent with what would be expected on the basis of directly measured effective electro-optic coefficients. By correlating the electro-optic value with the diffraction efficiency, the temperature dependence of the space-charge field is obtained and explained by temperature dependencies of the dark conductivity and the photoconductivity of the material
Applying Advanced Ground-Based Remote Sensing in the Southeast Asian Maritime Continent to Characterize Regional Proficiencies in Smoke Transport Modeling
This work describes some of the most extensive ground-based observations of the aerosol profile collected in Southeast Asia to date, highlighting the challenges in simulating these observations with amesoscale perspective. An 84-hWRFModel coupled with chemistry (WRF-Chem)mesoscale simulation of smoke particle transport at Kuching, Malaysia, in the southern Maritime Continent of Southeast Asia is evaluated relative to a unique collection of continuous ground-based lidar, sun photometer, and 4-h radiosonde profiling. The period was marked by relatively dry conditions, allowing smoke layers transported to the site unperturbed by wet deposition to be common regionally. The model depiction is reasonable overall. Core thermodynamics, including land/seabreeze structure, are well resolved. Total model smoke extinction and, by proxy, mass concentration are low relative to observation. Smoke emissions source products are likely low because of undersampling of fires in infrared sun-synchronous satellite products, which is exacerbated regionally by endemic low-level cloud cover. Differences are identified between the model mass profile and the lidar profile, particularly during periods of afternoon convective mixing. A static smoke mass injection height parameterized for this study potentially influences this result. The model does not resolve the convective mixing of aerosol particles into the lower free troposphere or the enhancement of near-surface extinction from nighttime cooling and hygroscopic effects
Interiorized Feminism and Gendered Nostalgia of The âDaughter Generationâ in Ning Ying's Perpetual Motion
This is the author's accepted manuscript. The original publication is available at http://dx.doi.org/10.1386/jcc.5.3.253_1Ning Yingâs 2006 film Wuqiong dong/Perpetual Motion can be regarded as her first attempt to explore the genre of âwomenâs filmâ. Deviating from her previous neo-realist style, this film seeks to cultivate an alternative cinematic practice through developing a heavy-handed negative aesthetics. Ning Ying interiorizes the filmic exploration of female subjectivity in an enclosed time and space, which is constantly haunted by a spectral aesthetics characterized by audio-visual allusions to loss, grave, ruins and ghosts. However, the filmâs radical content and alternative aesthetics are, ironically, packaged in prevailing consumer aesthetics and commodity fetishism on and off the silver screen. All these competing drives and accounts render the film a contested narrative constantly oscillating between avant-garde feminism and domestic melodrama, and between a register of disintegrating sisterhood and a celebrity scandal of adultery. This article examines the discursive and aesthetic innovations, contradictions and limits of Ning Yingâs cinematic feminism
Epidemiologic Features and Environmental Risk Factors of Severe Fever with Thrombocytopenia Syndrome, Xinyang, China
Background:Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease discovered in rural areas of Central China in 2009, caused by a novel bunyavirus, SFT
Gamma ray flares from Mrk421 in 2008 observed with the ARGO-YBJ detector
In 2008 the blazar Markarian 421 entered a very active phase and was one of
the brightest sources in the sky at TeV energies, showing frequent flaring
episodes. Using the data of ARGO-YBJ, a full coverage air shower detector
located at Yangbajing (4300 m a.s.l., Tibet, China), we monitored the source at
gamma ray energies E > 0.3 TeV during the whole year. The observed flux was
variable, with the strongest flares in March and June, in correlation with
X-ray enhanced activity. While during specific episodes the TeV flux could be
several times larger than the Crab Nebula one, the average emission from day 41
to 180 was almost twice the Crab level, with an integral flux of (3.6 +-0.6)
10^-11 photons cm^-2 s^-1 for energies E > 1 TeV, and decreased afterwards.
This paper concentrates on the flares occurred in the first half of June.
This period has been deeply studied from optical to 100 MeV gamma rays, and
partially up to TeV energies, since the moonlight hampered the Cherenkov
telescope observations during the most intense part of the emission. Our data
complete these observations, with the detection of a signal with a statistical
significance of 3.8 standard deviations on June 11-13, corresponding to a gamma
ray flux about 6 times larger than the Crab one above 1 TeV. The reconstructed
differential spectrum, corrected for the intergalactic absorption, can be
represented by a power law with an index alpha = -2.1 extending up to several
TeV. The spectrum slope is fully consistent with previous observations
reporting a correlation between the flux and the spectral index, suggesting
that this property is maintained in different epochs and characterizes the
source emission processes.Comment: Accepted for publication on ApJ
Observation of TeV gamma-rays from the unidentified source HESS J1841-055 with the ARGO-YBJ experiment
We report the observation of a very high energy \gamma-ray source, whose
position is coincident with HESS J1841-055. This source has been observed for
4.5 years by the ARGO-YBJ experiment from November 2007 to July 2012. Its
emission is detected with a statistical significance of 5.3 standard
deviations. Parameterizing the source shape with a two-dimensional Gaussian
function we estimate an extension \sigma=(0.40(+0.32,-0.22}) degree, consistent
with the HESS measurement. The observed energy spectrum is dN/dE =(9.0-+1.6) x
10^{-13}(E/5 TeV)^{-2.32-+0.23} photons cm^{-2} s^{-1} TeV^{-1}, in the energy
range 0.9-50 TeV. The integral \gamma-ray flux above 1 TeV is 1.3-+0.4 Crab
units, which is 3.2-+1.0 times the flux derived by HESS. The differences in the
flux determination between HESS and ARGO-YBJ, and possible counterparts at
other wavelengths are discussed.Comment: 17 pages, 4 figures, have been accepted for publication in Ap
Observation of CR Anisotropy with ARGO-YBJ
The measurement of the anisotropies of cosmic ray arrival direction provides
important informations on the propagation mechanisms and on the identification
of their sources. In this paper we report the observation of anisotropy regions
at different angular scales. In particular, the observation of a possible
anisotropy on scales between 10 and 30
suggests the presence of unknown features of the magnetic fields the charged
cosmic rays propagate through, as well as potential contributions of nearby
sources to the total flux of cosmic rays. Evidence of new weaker few-degree
excesses throughout the sky region R.A. is
reported for the first time.Comment: Talk given at 12th TAUP Conference 2011, 5-9 September 2011, Munich,
German
Proton-air cross section measurement with the ARGO-YBJ cosmic ray experiment
The proton-air cross section in the energy range 1-100 TeV has been measured
by the ARGO-YBJ cosmic ray experiment. The analysis is based on the flux
attenuation for different atmospheric depths (i.e. zenith angles) and exploits
the detector capabilities of selecting the shower development stage by means of
hit multiplicity, density and lateral profile measurements at ground. The
effects of shower fluctuations, the contribution of heavier primaries and the
uncertainties of the hadronic interaction models, have been taken into account.
The results have been used to estimate the total proton-proton cross section at
center of mass energies between 70 and 500 GeV, where no accelerator data are
currently available.Comment: 14 pages, 9 figure
Search for Gamma Ray Bursts with the Argo-YBJ Detector in Scaler Mode
We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100
GeV in coincidence with the prompt emission detected by satellites using the
Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ)
air shower detector. Thanks to its mountain location (Yangbajing, Tibet, P.R.
China, 4300 m a.s.l.), active surface (about 6700 m**2 of Resistive Plate
Chambers), and large field of view (about 2 sr, limited only by the atmospheric
absorption), the ARGO-YBJ air shower detector is particularly suitable for the
detection of unpredictable and short duration events such as GRBs. The search
is carried out using the "single particle technique", i.e. counting all the
particles hitting the detector without measurement of the energy and arrival
direction of the primary gamma rays.
Between 2004 December 17 and 2009 April 7, 81 GRBs detected by satellites
occurred within the field of view of ARGO-YBJ (zenith angle < 45 deg). It was
possible to examine 62 of these for >1 GeV counterpart in the ARGO-YBJ data
finding no statistically significant emission. With a lack of detected spectra
in this energy range fluence upper limits are profitable, especially when the
redshift is known and the correction for the extragalactic absorption can be
considered. The obtained fluence upper limits reach values as low as 10**{-5}
erg cm**{-2} in the 1-100 GeV energy region.
Besides this individual search for a higher energy counterpart, a statistical
study of the stack of all the GRBs both in time and in phase was made, looking
for a common feature in the GRB high energy emission. No significant signal has
been detected.Comment: accepted for publication in Ap
An NLO QCD analysis of inclusive cross-section and jet-production data from the ZEUS experiment
The ZEUS inclusive differential cross-section data from HERA, for charged and
neutral current processes taken with e+ and e- beams, together with
differential cross-section data on inclusive jet production in e+ p scattering
and dijet production in \gamma p scattering, have been used in a new NLO QCD
analysis to extract the parton distribution functions of the proton. The input
of jet data constrains the gluon and allows an accurate extraction of
\alpha_s(M_Z) at NLO;
\alpha_s(M_Z) = 0.1183 \pm 0.0028(exp.) \pm 0.0008(model)
An additional uncertainty from the choice of scales is estimated as \pm
0.005. This is the first extraction of \alpha_s(M_Z) from HERA data alone.Comment: 37 pages, 14 figures, to be submitted to EPJC. PDFs available at
http://durpdg.dur.ac.uk/hepdata in LHAPDFv
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