3,145 research outputs found
Carbon Dioxide Observational Platform System (CO-OPS), feasibility study
The Carbon Dioxide Observational Platform System (CO-OPS) is a near-space, geostationary, multi-user, unmanned microwave powered monitoring platform system. This systems engineering feasibility study addressed identified existing requirements such as: carbon dioxide observational data requirements, communications requirements, and eye-in-the-sky requirements of other groups like the Defense Department, the Forestry Service, and the Coast Guard. In addition, potential applications in: earth system science, space system sciences, and test and verification (satellite sensors and data management techniques) were considered. The eleven month effort is summarized. Past work and methods of gathering the required observational data were assessed and rough-order-of magnitude cost estimates have shown the CO-OPS system to be most cost effective (less than $30 million within a 10 year lifetime). It was also concluded that there are no technical, schedule, or obstacles that would prevent achieving the objectives of the total 5-year CO-OPS program
Calorimetric Investigation of CeRu2Ge2 up to 8 GPa
We have developed a calorimeter able to give a qualitative picture of the
specific heat of a sample under high pressure up to approximately 10 GPa. The
principle of ac-calorimetry was adapted to the conditions in a high pressure
clamp. The performance of this technique was successfully tested with the
measurement of the specific heat of CeRu2Ge2 in the temperature range 1.5
K<T<12 K. The phase diagram of its magnetic phases is consistent with previous
transport measurements.Comment: 5 pages, 4 figure
Anisotropic properties of MgB2 by torque magnetometry
Anisotropic properties of superconducting MgB2 obtained by torque
magnetometry are compared to theoretical predictions, concentrating on two
issues. Firstly, the angular dependence of Hc2 is shown to deviate close to Tc
from the dependence assumed by anisotropic Ginzburg-Landau theory. Secondly,
from the evaluation of torque vs angle curves it is concluded that the
anisotropy of the penetration depth gamma_lambda has to be substantially higher
at low temperature than theoretical estimates, at least in fields higher than
0.2 T.Comment: 2 p.,2 Fig., submitted to Physica C (M2S-Rio proceedings); v2: 1 ref
adde
Infrared properties of MgAlBC) single crystals in the normal and superconducting state
The reflectivity of -oriented MgAl(BC) single crystals has been measured by means of infrared
microspectroscopy for cm. An increase with doping of
the scattering rates in the and bands is observed, being more
pronounced in the C doped crystals. The -band plasma frequency also
changes with doping due to the electron doping, while the -band one is
almost unchanged. Moreover, a interband excitation, predicted
by theory, is observed at eV in the undoped sample,
and shifts to lower energies with doping. By performing theoretical calculation
of the doping dependence , the experimental observations can be
explained with the increase with electron doping of the Fermi energy of the
holes in the -band. On the other hand, the band density of
states seems not to change substantially. This points towards a reduction
driven mainly by disorder, at least for the doping level studied here. The
superconducting state has been also probed by infrared synchrotron radiation
for cm in one pure and one C-doped sample. In the
undoped sample ( = 38.5 K) a signature of the -gap only is observed.
At = 0.08 ( = 31.9 K), the presence of the contribution of the
-gap indicates dirty-limit superconductivity in both bands.Comment: 12 pages, 9 figure
Nonmagnetic impurity effects in MgB
We study nonmagnetic impurity effects in MgB using the quasiclassical
equations of superconductivity for a weak-coupling two-band model. Parameters
in the model are fixed so as to reproduce experiments on MgB as closely
as possible. The quasiparticle density of states and the specific heat are
calculated for various values of the interband impurity scattering. The density
of states changes gradually from a two-gap structure into the conventional
single-gap structure as the interband scattering increases. It is found that
the excitation threshold is not a monotonic function of the interband
scattering. Calculated results for the specific heat are in good agreements
with experiments on samples after irradiation
Specific heat of MgB_2 after irradiation
We studied the effect of disorder on the superconducting properties of
polycrystalline MgB_2 by specific-heat measurements. In the pristine state,
these measurements give a bulk confirmation of the presence of two
superconducting gaps with 2 Delta 0 / k_B T_c = 1.3 and 3.9 with nearly equal
weights. The scattering introduced by irradiation suppresses T_c and tends to
average the two gaps although less than predicted by theory. We also found that
by a suitable irradiation process by fast neutrons, a substantial bulk increase
of dH_{c2}/dT at T_c can be obtained without sacrificing more than a few
degrees in T_c. The upper critical field of the sample after irradiation
exceeds 28 T at T goes to 0 K.Comment: 11 pages text, 6 figures, accepted by Journal of Physics: Condensed
Matte
An incremental method for meaning elicitation of a domain ontology
Internet has opened the access to an overwhelming amount of data, requiring the development of new applications to automatically recognize, process and manage informationavailable in web sites or web-based applications. The standardSemantic Web architecture exploits ontologies to give a shared(and known) meaning to each web source elements.In this context, we developed MELIS (Meaning Elicitation and Lexical Integration System). MELIS couples the lexical annotation module of the MOMIS system with some components from CTXMATCH2.0, a tool for eliciting meaning from severaltypes of schemas and match them. MELIS uses the MOMIS WNEditor and CTXMATCH2.0 to support two main tasks in theMOMIS ontology generation methodology: the source annotationprocess, i.e. the operation of associating an element of a lexicaldatabase to each source element, and the extraction of lexicalrelationships among elements of different data sources
Doping dependent evolution of magnetism and superconductivity in Eu1-xKxFe2As2 (x = 0-1) and temperature dependence of lower critical field Hc1
We have synthesized the polycrystalline samples of Eu1-xKxFe2As2 (x = 0-1)
and carried out systematic characterization using x-ray diffraction, ac & dc
magnetic susceptibility, and electrical resistivity measurements. We have seen
a clear signature of the coexistence of superconducting transition (Tc = 5.5 K)
with SDW ordering in our under doped sample viz. x = 0.15. The spin density
wave transition observed in EuFe2As2 get completely suppressed at x = 0.3 and
superconductivity arises below 20 K. Superconducting transition temperature Tc
increases with increase in K content and a maximum Tc = 33 K is reached for x =
0.5, beyond which it decreases again. The doping dependent T(x) phase diagram
is extracted from the magnetic and electrical transport data. It is found that
magnetic ordering of Eu-moments coexists with superconductivity up to x = 0.6.
The isothermal magnetization data taken at 2 K for the doped samples suggest 2+
valence states of Eu ions. We also present the temperature dependence of the
lower critical field Hc1 of superconducting polycrystalline samples. The value
of Hc1(0) obtained for x = 0.3, 0.5, and 0.7 after taking the demagnetization
factor into account is 248, 385, and 250 Oe, respectively. The London
penetration depth {\lambda}(T) calculated from the lower critical field does
not show exponential behaviour at low temperature, as would be expected for a
fully gapped clean s-wave superconductor. In contrast, it shows a T2 power-law
feature down to T = 0.4 Tc, as observed in Ba1-xKxFe2As2 and BaFe2-xCoxAs2.Comment: 17 pages, 10 figure
Melis: an incremental method for the lexical annotation of domain ontologies
In this paper, we present MELIS (Meaning Elicitation and Lexical Integration System), a method and a software tool for enabling an incremental process of automatic annotation of local schemas (e.g. relational database schemas, directory trees) with lexical information. The distinguishing and original feature of MELIS is the incremental process: the higher the number of schemas which are processed, the more background/domain knowledge is cumulated in the system (a portion of domain ontology is learned at every step), the better the performance of the systems on annotating new schemas.MELIS has been tested as component of MOMIS-Ontology Builder, a framework able to create a domain ontology representing a set of selected data sources, described with a standard W3C language wherein concepts and attributes are annotated according to the lexical reference database.We describe the MELIS component within the MOMIS-Ontology Builder framework and provide some experimental results of ME LIS as a standalone tool and as a component integrated in MOMIS
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