818 research outputs found
Origin of gamma-ray emission in the shell of Cassiopeia A
Non-thermal X-ray emission from the shell of Cassiopeia A (Cas A) has been an
interesting subject of study, as it provides information about relativistic
electrons and their acceleration mechanisms in the shocks. Chandra X-ray
observatory revealed the detailed spectral and spatial structure of this SNR in
X-rays. The spectral analysis of Chandra X-ray data of Cas A shows unequal flux
levels for different regions of the shell, which can be attributed to different
magnetic fields in those regions. Additionally, the GeV gamma-ray emission
observed by Large Area Telescope on board Fermi Gamma Ray Space Telescope
showed that the hadronic processes are dominating in Cas A, a clear signature
of acceleration of protons. In this paper we aim to explain the GeV-TeV
gamma-ray data in the context of both leptonic and hadronic scenario. We
modeled the multi-wavelength spectrum of Cas A. We use synchrotron emission
process to explain the observed non-thermal X-ray fluxes from different regions
of the shell. These result in estimation of the model parameters, which are
then used to explain TeV gamma-ray emission spectrum. We also use hadronic
scenario to explain both GeV and TeV fluxes simultaneously. We show that a
leptonic model alone cannot explain the GeV-TeV data. Therefore, we need to
invoke a hadronic model to explain the observed GeV-TeV fluxes. We found that
although pure hadronic model is able to explain the GeV-TeV data, a
lepto-hadronic model provides the best fit to the data.Comment: Accepted in A&
Tc-Glutathione Complex (Tc -GSH) : Labelling, Chemical Characterization and Biodistribution in Rats
The chemical structure of 99mTc-GSH has been estabilished using the 99Tc
isotope.
Labeling of glutathione with technetium in the presence of stanous chloride gave a high yield
result. In a comparative study between 99Tc
and 99Tc
glutathione, the Tc-GSH complex obtained
was purified and characterized by uv, visible spectroscopy, HPLC, Biogel chromatography, mass
and NMR spectroscopy. Stoichiometric analysis showed a 2 : 1 molar ratio of GSH/Tc for the
reaction. The molecular mass assessed by mass spectroscopy was 727 Da corresponding to an
oxo(bis) glutathione technetate. NMR studies demonstrated that each glutathione molecule was
coordinated to technetium via cysteinyl sulfur and nitrogen atoms. The biodistribution of the
complex was studied in normal rats. Blood clearance was rapid during the first hour involving a
biexponential curve ( t1/2
(1) : 50 min, t1/2
(2) : 400 min ). No radioactive accumulation was found in
any specific organ except kidney and bladder. All the activity excreted was found unchanged in
urine. In conclusion, Tc-GSH displayed an anionic dimer form as GSH-Tc-GSH. We assume that the
complex is a tetradentate (2N,2S) complex containing a pentavalent technetium coordinated by two
thiol and nitrogen atoms of both GSH ligands, and an apical oxo group
Smart thinking on co-creation and engagement: Searchlight on underground built heritage
This paper aims to explore public participation for activating underground built heritage (UBH). It describes and analyses practices of stakeholdersâ engagement in different UBH assets, based on experiences gathered in the scope of the European COST Action âUnderground4valueâ. It brings together five inspiring cases from Italy, Portugal, Spain, Switzerland and the United Kingdom, in which digital and mobile technologies were used as tools to improve community experiences in UBH. Thus, the paper discusses âsmartnessâ from the perspective of people and communities around cultural assets, where âsmartnessâ becomes a new connotation and a pathway to advance (local) knowledge and know-how. Therefore, this paper takes on the challenge to define a smart city as an ecosystem for peopleâs empowerment and participation, and, in particular, to explore social tools for creating new values in heritage placemakingâwhere sharing knowledge becomes a fundamental principle.info:eu-repo/semantics/publishedVersio
RXTE Studies of Long-Term X-ray Spectral Variations in 4U 1820-30
We present the results of detailed spectral studies of the ultra-compact low
mass X-ray binary (LMXB) 4U 1820-30 carried out with the Rossi X-ray Timing
Explorer (RXTE) during 1996-7. 4U 1820-30 is an ``atoll'' source X-ray burster
(XRB) located in the globular cluster NGC 6624. It is known to have an 11
minute binary period and a ~176 day modulation in its 2--12 keV flux.
Observations were made with the PCA and HEXTE instruments on RXTE at roughly
one-month intervals to sample this long-term period and study flux-related
spectral changes. There are clear correlations between our fitted spectral
parameters and both the broad-band (2--50 keV) flux and the position in the
color-color diagram, as described by the parameter S_a introduced by Mendez et
al. (1999). In addition, we find a strong correlation between the position in
the color-color diagram and the frequencies of the kilohertz quasi-periodic
oscillations (kHz QPOs) reported by Zhang et al. (1998). This lends further
support to the notion that evidence for the last stable orbit in the accretion
disk of 4U 1820-30 has been observed. For a model consisting of Comptonization
of cool photons by hot electrons plus an additional blackbody component, we
report an abrupt change in the spectral parameters at the same accretion rate
at which the kHz QPOs disappear. For a model consisting of a multicolor disk
blackbody plus a cut-off power law, we find that the inner disk radius reaches
a minimum at the same accretion rate at which the kHz QPO frequency saturates,
as expected if the disk reaches the last stable orbit. Both models face
theoretical and observational problems when interpreted physically for this
system.Comment: 39 pages, 11 figures, accepted to the Astrophysical Journa
Measuring velocity of sound with nuclear resonant inelastic x-ray scattering
Nuclear resonant inelastic x-ray scattering is used to measure the projected
partial phonon density of states of materials. A relationship is derived
between the low-energy part of this frequency distribution function and the
sound velocity of materials. Our derivation is valid for harmonic solids with
Debye-like low-frequency dynamics. This method of sound velocity determination
is applied to elemental, composite, and impurity samples which are
representative of a wide variety of both crystalline and noncrystalline
materials. Advantages and limitations of this method are elucidated
Assessment of the Linkages and Leakages in a Cloud-Based Computing Collaboration among Construction Stakeholders
The uniqueness of the construction industry can be understood in the large volumes of information in terms of paper works, processes, and communication disseminated
daily. The voluminous information requires close coordination which cloud based systems offer. The aim of this research is to assess the linkages and leakages in a
cloud-based computing collaboration among construction stakeholders. A purposive sampling technique was used in selecting the participants of the study. A questionnaire based instrument was distributed to eighty (80) construction
stakeholder in Lagos State, Nigeria. The data collected was analyzed using SPSS v.21. Statistical tools such as frequencies, stacked bars, mean scores, factor analysis,
and analysis of variance (ANOVA) were used in the study. The result of the study revealed that construction stakeholders rarely utilize cloud-based technologies for their construction processes. Construction professionals that access cloud based technologies, do so with their smart mobile phones, laptops, and tablet. The study classified the leakages that exist in the use of cloud-based technologies as securitybased factors, cloud-based infrastructure factors, and cloud-based benefits deficiency based factors. In conclusion, the study revealed that the linkages in the use of cloudbased technologies include knowledge sharing, remote access of back-office activities and engendering collaboration among construction stakeholders. It was recommended that construction stakeholders should leverage on the benefits cloud-based technologies has to offer in todayâs competitive economy. Construction stakeholdersshould be adequately informed on the available cloud-based computing technologies and the additions it can bring into the construction process. Cloud computing technology vendors should improve on the security and privacy features of the platform for adequate protection of building data
Optical Imaging and Spectroscopic Observation of the Galactic Supernova Remnant G85.9-0.6
Optical CCD imaging with H and [SII] filters and spectroscopic
observations of the galactic supernova remnant G85.9-0.6 have been performed
for the first time. The CCD image data are taken with the 1.5m Russian-Turkish
Telescope (RTT150) at TUBITAK National Observatory (TUG) and spectral data are
taken with the Bok 2.3 m telescope on Kitt Peak, AZ.
The images are taken with narrow-band interference filters H, [SII]
and their continuum. [SII]/H ratio image is performed. The ratio
obtained from [SII]/H is found to be 0.42, indicating that the
remnant interacts with HII regions. G85.9-0.6 shows diffuse-shell morphology.
[SII] average flux ratio is calculated from the
spectra, and the electron density is obtained to be 395 . From
[OIII]/H ratio, shock velocity has been estimated, pre-shock density of
, explosion energy of ergs,
interstellar extinction of , and neutral hydrogen column density
of are reported.Comment: 20 pages, 4 tables, 4 figures. Accepted for publication in
Astrophysics & Space Scienc
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