373 research outputs found
STM study of multiband superconductivity in NbSe2 using a superconducting tip
We present a method to produce superconducting tips to be used in Scanning
Tunneling Microscopy/Spectroscopy experiments. We use these tips to investigate
the evolution of the electronic density of states of NbSe2 from 0.3K up to its
critical temperature (7.2K). The use of a superconducting tip (Pb) as
ounterelectrode provides an enhancement of the different features related to
the DOS of NbSe2 in the tunneling conductance curves, along all the studied
thermal range. The analysis of the experimental results gives evidence of the
presence of multiband superconductivity in NbSe2.Comment: 5 pages, 5 figures, PDF fil
Point-contact spectroscopy on URuSi
Tunnel and point contact experiments have been made in a URuSi single
crystal along the c-axis. The experiments were performed changing temperature
and contact size in a low temperature scanning tunneling microscope. A
resonance develops at the Fermi level at K. This resonance splits
and becomes asymmetric when the 17.5 K phase transition is crossed. These
results are consistent with the existence of Kondo like bound states of the
U ionic configurations and the conduction electrons. Below the
transition, these configurations are split by the development of quadrupolar
ordering. The peak separation can be interpreted as a direct measurement of the
order parameter. Measurements on a policrystalline UAu_2Si_2$ sample are also
reported, with a comparative study of the behavior of both materials.Comment: 4 pages (Latex) + 2 postscript figure
Differences in code terminology and frequency of findings in meat inspection of finishing pigs in seven European countries
The overall objectives of meat inspection are to contribute to food safety, animal welfare, and animal health. In the European Union (EU), there is a request for a modernised meat inspection system that addresses these objectives in a more valid, feasible and cost-effective way than does the traditional system. One part of the modernisation deals with the coding system to register meat inspection findings. Although unified standards are set at the EU level for judgement criteria regarding fitness of meat for consumption, different national systems are in force. The question is the extent of the differences and whether there is a basis for harmonisation. To investigate this, information was gathered about the code systems in Denmark, Finland, Germany, Italy, Norway, Portugal and Spain. Moreover, meat inspection data covering pigs slaughtered in 2019 were collected. A comparison of the number of codes available, the terminology and the frequencies of the findings registered was undertaken. Codes with a similar meaning were grouped. Hereby, two lists were compiled showing the most common codes leading to total and to partial condemnation. Substantial variations in the percentage of condemned pigs and in the terms used were identified, and possible reasons behind this are discussed. Moreover, a strengths-weaknesses-opportunities-threats (SWOT)-like analysis was applied to the coding systems. Finally, the reasons for unfitness of meat given in the EU Food Inspection Regulation 2019/627 were compared to the national code lists. The results show the systems in force varied substantially, and each system had its advantages and disadvantages. The diverse terminology observed made it a challenge to compare data between countries. Development of harmonised terminology for meat inspection findings is suggested, enabling comparison of data between abattoirs, regions, and countries, while respecting the national epidemiological situation, the local food safety culture, and the trade agreements in force.Peer reviewe
Proximity effect and strong coupling superconductivity in nanostructures built with an STM
We present high resolution tunneling spectroscopy data at very low
temperatures on superconducting nanostructures of lead built with an STM. By
applying magnetic fields, superconductivity is restricted to length scales of
the order of the coherence length. We measure the tunneling conductance and
analyze the phonon structure and the low energy DOS. We demonstrate the
influence of the geometry of the system on the magnetic field dependence of the
tunneling density of states, which is gapless in a large range of fields. The
behavior of the features in the tunneling conductance associated to phonon
modes are explained within current models.Comment: 4 figures, 4 page
Scanning Tunneling Spectroscopy in MgB 2
We present extensive Scanning Tunneling Spectroscopy (STM/S) measurements at
low temperatures in the multiband superconductor MgB. We find a similar
behavior in single crystalline samples and in single grains, which clearly
shows the partial superconducting density of states of both the and
bands of this material. The superconducting gaps corresponding to both
bands are not single valued. Instead, we find a distribution of superconducting
gaps centered around 1.9mV and 7.5mV, corresponding respectively to each set of
bands. Interband scattering effects, leading to a single gap structure at 4mV
and a smaller critical temperature can be observed in some locations on the
surface. S-S junctions formed by pieces of MgB attached to the tip clearly
show the subharmonic gap structure associated with this type of junctions. We
discuss future developments and possible new effects associated with the
multiband nature of superconductivity in this compound.Comment: 11 pages, 6 figures, submitted to Physica
Scanning microscopies of superconductors at very low temperatures
We discuss basics of scanning tunneling microscopy and spectroscopy (STM/S)
of the superconducting state with normal and superconducting tips. We present a
new method to measure the local variations in the Andreev reflection amplitude
between a superconducting tip and the sample. This method is termed Scanning
Andreev Reflection Spectroscopy (SAS). We also briefly discuss vortex imaging
with STM/S under an applied current through the sample, and show the vortex
lattice as a function of the angle between the magnetic field and sample's
surface
Calibration of the length of a chain of single gold atoms
Using a scanning tunneling microscope or mechanically controllable break
junctions it has been shown that it is possible to control the formation of a
wire made of single gold atoms. In these experiments an interatomic distance
between atoms in the chain of ~3.6 Angstrom was reported which is not
consistent with recent theoretical calculations. Here, using precise
calibration procedures for both techniques, we measure length of the atomic
chains. Based on the distance between the peaks observed in the chain length
histogram we find the mean value of the inter-atomic distance before chain
rupture to be 2.6 +/- 0.2 A . This value agrees with the theoretical
calculations for the bond length. The discrepancy with the previous
experimental measurements was due to the presence of He gas, that was used to
promote the thermal contact, and which affects the value of the work function
that is commonly used to calibrate distances in scanning tunnelling microscopy
and mechanically controllable break junctions at low temperatures.Comment: 6 pages, 6 figure
Soil organisms in organic and conventional cropping systems.
Apesar do crescente interesse pela agricultura orgânica, são poucas as informações de pesquisa disponíveis sobre o assunto. Assim, num Argissolo Vermelho-Amarelo distrófico foram comparados os efeitos de sistemas de cultivo orgânico e convencional, para as culturas do tomate (Lycopersicum esculentum) e do milho (Zea mays), sobre a comunidade de organismos do solo e suas atividades. As populações de fungos,bactérias e actinomicetos, determinadas pela contagem de colônias em meio de cultura, foram semelhantes para os dois sistemas de produção. A atividade microbiana, avaliada pela evolução de CO2, manteve-se superior no sistema orgânico, sendo que em determinadas avaliações foi o dobro da evolução verificada no sistema convencional. O número de espécimes de minhoca foi praticamente dez vezes maior no sistema orgânico. Não foi observada diferença na taxa de decomposição de matéria orgânica entre os dois sistemas. De modo geral, o número de indivíduos de microartrópodos foi superior no sistema orgânico do que no sistema convencional, refletindo no maior índice de diversidade de Shannon. As maiores populações de insetos foram as da ordem Collembola, enquanto para os ácaros a maior população foi a da superfamília Oribatuloidea. Indivíduos dos grupos Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura e Symphyla foram ocasionalmente coletados e de forma similar entre os sistemas
Localized Intersections of Non-Extremal p-branes and S-branes
A class of solutions to Supergravity in 10 or 11 dimensions is presented
which extends the non-standard or semi-local intersections of Dp-branes to the
case of non-extremal p-branes. The type of non-extremal solutions involved in
the intersection is free and we provide two examples involving black-branes
and/or D-\bar{D} systems. After a rotation among the time coordinate and a
relatively transverse radial direction the solutions admit the interpretation
of an intersection among D-branes and S-branes. We speculate on the relevance
of these configurations both to study time dependent phenomena in the AdS/CFT
correspondence as well as to construct cosmological brane-world scenarios
within String Theory admitting accelerating expansion of the Universe.Comment: 31 pages, latex file; v2: typos corrected and references adde
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