246 research outputs found
Combined effects of pressure and Ru substitution on BaFe2As2
The ab-plane resistivity of Ba(Fe1-xRux)2As2 (x = 0.00, 0.09, 0.16, 0.21, and
0.28) was studied under nearly hydrostatic pressures, up to 7.4 GPa, in order
to explore the T-P phase diagram and to compare the combined effects of
iso-electronic Ru substitution and pressure. The parent compound BaFe2As2
exhibits a structural/magnetic phase transition near 134 K. At ambient
pressure, progressively increasing Ru concentration suppresses this phase
transition to lower temperatures at the approximate rate of ~5 K/% Ru and is
correlated with the emergence of superconductivity. By applying pressure to
this system, a similar behavior is seen for each concentration: the
structural/magnetic phase transition is further suppressed and
superconductivity induced and ultimately, for larger x Ru and P, suppressed. A
detailed comparison of the T-P phase diagrams for all Ru concentrations shows
that 3 GPa of pressure is roughly equivalent to 10% Ru substitution.
Furthermore, due to the sensitivity of Ba(Fe1-xRux)2As2 to pressure conditions,
the melting of the liquid media, 4 : 6 light mineral oil : n-pentane and 1 : 1
iso-pentane : n-pentane, used in this study could be readily seen in the
resistivity measurements. This feature was used to determine the freezing
curves for these media and infer their room temperature, hydrostatic limits:
3.5 and 6.5 GPa, respectively.Comment: 27 pages, 19 figure
El tratamiento de las secuelas de la encefalitis epidemica por el virus vacuna de Levaditi-Poincloux
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Excitation and relaxation dynamics in ultrafast laser irradiated optical glasses
We discuss the dynamics of ultrashort pulsed laser excitation in bulk optical silica-based glasses (fused silica and borosilicate BK7) well-above the permanent modification threshold. We indicate subsequent structural and thermomechanical energy relaxation paths that translate into positive and negative refractive index changes, compression and rarefaction zones. If fast electronic decay occurs at low excitation levels in fused silica via self-trapping of excitons, for carrier densities in the vicinity of the critical value at the incident wavelength, persistent long-living absorptive states indicate the achievement of low viscosity matter states manifesting pressure relaxation, rarefaction, void opening and compaction in the neighboring domains. An intermediate ps-long excited carrier dynamics is observed for BK7 in the range corresponding to structural expansion and rarefaction. The amount of excitation and the strength of the subsequent hydrodynamic evolution is critically dependent on the pulse time envelope, indicative of potential optimization schemes
Simultaneous measurements of nuclear spin heat capacity, temperature and relaxation in GaAs microstructures
Heat capacity of the nuclear spin system (NSS) in GaAs-based microstructures
has been shown to be much greater than expected from dipolar coupling between
nuclei, thus limiting the efficiency of NSS cooling by adiabatic
demagnetization. It was suggested that quadrupole interaction induced by some
small residual strain could provide this additional reservoir for the heat
storage. We check and validate this hypothesis by combining nuclear spin
relaxation measurements with adiabatic remagnetization and nuclear magnetic
resonance experiments, using electron spin noise spectroscopy as a unique tool
for detection of nuclear magnetization. Our results confirm and quantify the
role of the quadrupole splitting in the heat storage within NSS and provide
additional insight into fundamental, but still actively debated relation
between a mechanical strain and the resulting electric field gradients in GaAs.Comment: 11 pages, 4 figures, 1 tabl
Ageing in the musculoskeletal system
The extent of ageing in the musculoskeletal system during the life course affects the quality and length of life. Loss of bone, degraded articular cartilage, and degenerate, narrowed intervertebral discs are primary features of an ageing skeleton, and together they contribute to pain and loss of mobility. This review covers the cellular constituents that make up some key components of the musculoskeletal system and summarizes discussion from the 2015 Aarhus Regenerative Orthopaedic Symposium (AROS) (Regeneration in the Ageing Population) about how each particular cell type alters within the ageing skeletal microenvironment
High shock release in ultrafast laser irradiated metals: Scenario for material ejection
We present one-dimensional numerical simulations describing the behavior of
solid matter exposed to subpicosecond near infrared pulsed laser radiation. We
point out to the role of strong isochoric heating as a mechanism for producing
highly non-equilibrium thermodynamic states. In the case of metals, the
conditions of material ejection from the surface are discussed in a
hydrodynamic context, allowing correlation of the thermodynamic features with
ablation mechanisms. A convenient synthetic representation of the thermodynamic
processes is presented, emphasizing different competitive pathways of material
ejection. Based on the study of the relaxation and cooling processes which
constrain the system to follow original thermodynamic paths, we establish that
the metal surface can exhibit several kinds of phase evolution which can result
in phase explosion or fragmentation. An estimation of the amount of material
exceeding the specific energy required for melting is reported for copper and
aluminum and a theoretical value of the limit-size of the recast material after
ultrashort laser irradiation is determined. Ablation by mechanical
fragmentation is also analysed and compared to experimental data for aluminum
subjected to high tensile pressures and ultrafast loading rates. Spallation is
expected to occur at the rear surface of the aluminum foils and a comparison
with simulation results can determine a spall strength value related to high
strain rates
Evaluación del comportamiento a macro-fisuración por fatiga de mezclas bituminosas modificadas con polvo de neumático
The use of crumb rubber modified bitumen (CRMB) in asphalt mixes is a road engineering technology
that has become increasingly important in recent years. Given the many economic and environmental
benefits of this type of binder, the goal is to give CRMB the same level of performance as conventional polymermodified
bitumen. The appearance and propagation of cracks due to fatigue phenomena is one of the most
common distresses affecting road pavements. Since crumb rubber enhances the mechanical properties of asphalt
mixes, it can provide a viable solution for fatigue cracking. This paper presents the results of a comparative
analysis of the fatigue-cracking behavior of asphalt mixtures manufactured with crumb rubber modified bitumen
and polymer-modified bitumen.El empleo de betunes modificados con polvo de neumático usado en la fabricación
de mezclas bituminosas es una de las técnicas que mayor auge está teniendo en los últimos años en la
ingenierÃa de carreteras. Dadas sus grandes ventajas económicas y ambientales, este tipo de ligantes pretende
conseguir prestaciones similares a la de los betunes modificados con polÃmeros utilizados habitualmente.
La aparición de fisuras debido a fenómenos de fatiga es una de las patologÃas más comunes en firmes de
carretera. Debido a las mejoras de las propiedades mecánicas del betún aportadas tras la incorporación
de polvo de neumático, las mezclas fabricadas con estos ligantes se postulan como una posible solución a
dicho problema. En este artÃculo se lleva a cabo un análisis comparativo del comportamiento a fisuración
por fatiga realizado sobre mezclas bituminosas fabricadas con betún modificado con polvo de neumático y
con polÃmeros.This research was carried out within the framework
of the R + D + i project entitled Proyecto Integrado
de Investigación, Desarrollo y Demostración de
TecnologÃas para la aplicación de neumáticos fuera
de uso en firmes de carretera resistentes a la propagación
de grietas (ref. IDI-20091076), funded by the
Center for Industrial Technological Development
(CDTI) of the Ministry of Science and Innovation
in Spain
Pressure effects on superconducting properties of single-crystalline Co doped NaFeAs
Resistivity and magnetic susceptibility measurements under external pressure
were performed on single-crystals NaFe1-xCoxAs (x=0, 0.01, 0.028, 0.075,
0.109). The maximum Tc enhanced by pressure in both underdoped and optimally
doped NaFe1-xCoxAs is the same, as high as 31 K. The overdoped sample with x =
0.075 also shows a positive pressure effect on Tc, and an enhancement of Tc by
13 K is achieved under pressure of 2.3 GPa. All the superconducting samples
show large positive pressure coefficient on superconductivity, being different
from Ba(Fe1-xCox)2As2. However, the superconductivity cannot be induced by
pressure in heavily overdoped non-superconducting NaFe0.891Co0.109As. These
results provide evidence for that the electronic structure is much different
between superconducting and heavily overdoped non-superconducting NaFe1-xCoxAs,
being consistent with the observation by angle-resolved photoemission
spectroscopy.Comment: 6 pages, 6 figure
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