8,605 research outputs found
Pinning of spiral fluxons by giant screw dislocations in YBa_2Cu_3O_7 single crystals: Josephson analog of the fishtail effect
By using a highly sensitive homemade AC magnetic susceptibility technique,
the magnetic flux penetration has been measured in YBa_2Cu_3O_7 single crystals
with giant screw dislocations (having the structure of the Archimedean spirals)
exhibiting a=3 spiral turnings, the pitch b=18.7 microns and the step height
c=1.2nm (the last parameter is responsible for creation of extended weak-link
structure around the giant defects). The magnetic field applied parallel to the
surface enters winding around the weak-link regions of the screw in the form of
the so-called spiral Josephson fluxons characterized by the temperature
dependent pitch b_f(T). For a given temperature, a stabilization of the fluxon
structure occurs when b_f(T) matches b (meaning an optimal pinning by the screw
dislocations) and manifests itself as a pronounced low-field peak in the
dependence of the susceptibility on magnetic field (applied normally to the
surface) in the form resembling the high-field (Abrikosov) fishtail effect.Comment: see also http://www.jetpletters.ac.ru/ps/1886/article_28701.shtm
Deciphering M-T diagram of shape memory Heusler alloys: reentrance, plateau and beyond
We present our recent results on temperature behaviour of magnetization
observed in Ni_47Mn_39In_14 Heusler alloys. Three regions can be distinguished
in the M-T diagram: (I) low temperature martensitic phase (with the Curie
temperature T_CM = 140 K), (II) intermediate mixed phase (with the critical
temperature T_MS = 230 K) exhibiting a reentrant like behavior (between T_CM
and T_MS) and (III) high temperature austenitic phase (with the Curie
temperature T_CA = 320 K) exhibiting a rather wide plateau region (between T_MS
and T_CA). By arguing that powerful structural transformations, causing drastic
modifications of the domain structure in alloys, would also trigger strong
fluctuations of the order parameters throughout the entire M-T diagram, we were
able to successfully fit all the data by incorporating Gaussian fluctuations
(both above and below the above three critical temperatures) into the
Ginzburg-Landau scenario
Desenvolvimento de livro interativo digital sobre sistema de integração lavoura-pecuária-floresta no polo agrícola de Paragominas no estado do Pará.
O desenvolvimento da informática e a popularização da internet expandiu o alcance de novas mídias. O conhecimento científico pode estar acessível e ao alcance das pessoas, que possuam mínimos conhecimentos de computação. O sistema de integração lavoura-pecuária-floresta (iLPF) está em fase inicial de adoção comercial e foi descrito na forma de livro interativo digital. O desenvolvimento regional foi relatado para divulgação de experiências exitosas com pecuária sustentável na Amazônia. A tecnologia é composta de uma série de princípios aplicados em torno da interação dos componentes florestais, agrícolas e pecuários do sistema. A mudança na paisagem rural é de longo prazo e pode ser descrita visualmente por meio de modelo de simulação digital, fotografia e vídeo. A síntese do conhecimento pode ser elaborada por vários tipos de modernas mídias amplamente disponíveis. O livro interativo digital foi desenvolvido tendo como base um banco de dados de fotografias e informações técnicas a respeito do polo agrícola de Paragominas. O trabalho foi inovador, sendo o primeiro livro interativo digital desenvolvido na Embrapa no Brasil
Biopolymeric matrices for structural and functional stabilization of bacteriophages
In the recent past years, bacteriophage research has experienced a renaissance due to their potential application in the pharmaceutical field, especially with the increase of bacterial resistance to antibiotics and the possibility to take part in new methods of early detection and diagnosis of bacterial infections. In that context, the structural and functional stabilization of bacteriophages using biopolymeric microporous hydrogels represents a promising research focus with a broad potential biomedical/ biopharmaceutical application. The scope of this work was to develop biopolymeric non-toxic phage-hydrogels of agar and sodium alginate, obtained at neutral pH and mild polymerization conditions, in order to offer adequate characteristics to the maintenance of phage’s lytic activity. Disc-like phage-hydrogels were prepared, with a phage and polymer concentration of 1.3x108 PFU/ml and 1.5% (w/v), respectively. Regarding the alginate hydrogels, CaCO3 (22.5 mM) and GDL (48 mM) were also included in the formulation. Agar hydrogels were prepared naturally by jellification, as a function of temperature lowering, and alginate hydrogels were prepared by internal gelation. The matrices were inoculated with a suspension of susceptible (host) bacteria and incubated at 37 ºC for 24h. Observation of bacterial lawn’s lysis demonstrated that bacteriophages kept their lytic activity, being the method of physical entrapment able to promote their stabilization. Cryo-SEM analysis revealed that both types of phage-hydrogels present interconnective microporous network, which guaranties a facilitated access of the phages to the bacteria, ensuring an efficient lysis of the host bacteria present in the surface of the hydrogels.The developed hydrogels also present appropriate physical and chemical properties for a wider variety of applications in the field of pharmaceutical sciences, such as controlled release of (macro)molecules, cell immobilization and 3D support for tissue regeneration
Manifestation of finite temperature size effects in nanogranular magnetic graphite
In addition to the double phase transition (with the Curie temperatures
T_C=300K and T_{Ct}=144K), a low-temperature anomaly in the dependence of the
magnetization is observed in the bulk magnetic graphite (with an average
granular size of L=10nm), which is attributed to manifestation of the size
effects below the quantum temperature. The best fits of the high-temperature
data (using the mean-field Curie-Weiss and Bloch expressions) produced
reasonable estimates for the model parameters, such as defects mediated
effective spin exchange energy J=12meV (which defines the intragranular Curie
temperature T_C) and proximity mediated interactions between neighboring grains
(through potential barriers created by thin layers of non-magnetic graphite)
with energy J_t=exp(-d/s)J=5.8meV (which defines the intergranular Curie
temperature T_{Ct}) with d=1.5nm and s=2nm being the intergranular distance and
characteristic length, respectively
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