8,623 research outputs found
Type II superconductivity in SrPd2Ge2
Previous investigations have shown that SrPd2Ge2, a compound isostructural
with "122" iron pnictides but iron- and pnictogen-free, is a conventional
superconductor with a single s-wave energy gap and a strongly three-dimensional
electronic structure. In this work we reveal the Abrikosov vortex lattice
formed in SrPd2Ge2 when exposed to magnetic field by means of scanning
tunneling microscopy and spectroscopy. Moreover, by examining the differential
conductance spectra across a vortex and estimating the upper and lower critical
magnetic fields by tunneling spectroscopy and local magnetization measurements,
we show that SrPd2Ge2 is a strong type II superconductor with \kappa >>
sqrt(2). Also, we compare the differential conductance spectra in various
magnetic fields to the pair breaking model of Maki - de Gennes for dirty limit
type II superconductor in the gapless region. This way we demonstrate that the
type II superconductivity is induced by the sample being in the dirty limit,
while in the clean limit it would be a type I superconductor with \kappa\ <<
sqrt(2), in concordance with our previous study (T. Kim et al., Phys. Rev. B
85, (2012)).Comment: 9 pages, 4 figure
Strangeness in Neutron Stars
It is generally agreed on that the tremendous densities reached in the
centers of neutron stars provide a high-pressure environment in which several
intriguing particles processes may compete with each other. These range from
the generation of hyperons to quark deconfinement to the formation of kaon
condensates and H-matter. There are theoretical suggestions of even more exotic
processes inside neutron stars, such as the formation of absolutely stable
strange quark matter. In the latter event, neutron stars would be largely
composed of strange quark matter possibly enveloped in a thin nuclear crust.
This paper gives a brief overview of these striking physical possibilities with
an emphasis on the role played by strangeness in neutron star matter, which
constitutes compressed baryonic matter at ultra-high baryon number density but
low temperature which is no accessible to relativistic heavy ion collision
experiments.Comment: 16 pages, 5 figures, 3 tables; Accepted for publication in the
Proceedings of the International Workshop on Astronomy and Relativistic
Astrophysics (IWARA) 2005, Int. J. Mod. Phys.
Evaluation of Reservoir Inflows Using Semi-Distributed Hydrological Modeling Techniques: Application to the Esil and Moildy Rivers' Catchments in Kazakhstan
[EN] This study explores the potential application of the HBV model for simulating water inflow into the Astana reservoir in Kazakhstan. The Astana reservoir, with an area of 60.9 km2 and a capacity of 411 million m3, serves as a vital hydrotechnical structure for the regulation of long-term water resources. Positioned on the Esil River, this reservoir plays a crucial role in providing drinking water to Astana, the capital city of the Republic of Kazakhstan. This study presents a concise overview of the HBV model and includes hydrometeorological data as well as information from a digital elevation model constructed from altitude maps of the catchment areas of the Esil and Moildy rivers. To simulate the runoff from both rivers, the GAP optimization algorithm was employed. Model parameters were calibrated for the period spanning 1975 to 2020. The effectiveness of the model was evaluated using the Nash-Sutcliffe criterion, which confirms a strong correlation between the simulated runoff dynamics and observed data. This study's outcomes reveal the efficiency of the selected optimal parameters, particularly for the 2020-2022 timeframe, during which the HBV model's parameters were validated. Overall, the quality metrics achieved during both the calibration and validation periods are satisfactory, affirming the model's suitability for short-term runoff forecasts, especially during flood events. Furthermore, the model proves valuable for assessing potential shifts in river runoff patterns under the influence of climate change.Serikbay, NT.; Tillakarim, TA.; Rodrigo-Ilarri, J.; Rodrigo-Clavero, M.; Duskayev, KK. (2023). Evaluation of Reservoir Inflows Using Semi-Distributed Hydrological Modeling Techniques: Application to the Esil and Moildy Rivers' Catchments in Kazakhstan. Water. 15(16). https://doi.org/10.3390/w15162967151
Demonstration experiments for solid state physics using a table top mechanical Stirling refrigerator
Liquid free cryogenic devices are acquiring importance in basic science and
engineering. But they can also lead to improvements in teaching low temperature
an solid state physics to graduate students and specialists. Most of the
devices are relatively expensive, but small sized equipment is slowly becoming
available. Here, we have designed several simple experiments which can be
performed using a small Stirling refrigerator. We discuss the measurement of
the critical current and temperature of a bulk YBa2Cu3O(7-d) (YBCO) sample, the
observation of the levitation of a magnet over a YBCO disk when cooled below
the critical temperature and the observation of a phase transition using ac
calorimetry. The equipment can be easily handled by students, and also used to
teach the principles of liquid free cooling
Evidence for conventional superconductivity in SrPd2Ge2
Electronic structure of SrPd2Ge2 single crystals is studied by angle-resolved
photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STS) and
band-structure calculations within the local-density approximation (LDA). The
STS measurements show single s-wave superconducting energy gap \Delta(0) = 0.5
meV. Photon-energy dependence of the observed Fermi surface reveals a strongly
three-dimensional character of the corresponding electronic bands. By comparing
the experimentally measured and calculated Fermi velocities a renormalization
factor of 0.95 is obtained, which is much smaller than typical values reported
in Fe-based superconductors. We ascribe such an unusually low band
renormalization to the different orbital character of the conduction electrons
and using ARPES and STS data argue that SrPd2Ge2 is likely to be a conventional
superconductor, which makes it clearly distinct from isostructural iron
pnictide superconductors of the "122" family.Comment: submitted to PR
Dimensionally regularized box and phase-space integrals involving gluons and massive quarks
The basic box and phase space integrals needed to compute at second order the three-jet decay rate of the Z-boson into massive quarks are presented in this paper. Dimensional Regularization is used to regularize the infrared divergences that appear in intermediate steps. Finally, the cancellation of these divergences among the virtual and the real contributions is showed explicitly
Charge asymmetry in hadroproduction of heavy quarks
A sizeable difference in the differential production cross section of top and
antitop quarks, respectively, is predicted for hadronically produced heavy
quarks. It is of order and arises from the interference between
charge odd and even amplitudes respectively. For the TEVATRON it amounts to
approximately 5-10% in the region where the cross section is large and could
therefore be measured in the next round of experiments. At the LHC the
asymmetry can be studied by selecting appropriately chosen kinematical regions.Comment: LaTeX, 5pp, 5 figures, uses revtex. The complete paper, including
figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/ Final version as
published in Phys.Rev.Let
Charge asymmetries of top quarks at hadron colliders revisited
A sizeable difference in the differential production cross section of top-
compared to antitop-quark production, denoted charge asymmetry, has been
observed at the Tevatron. The experimental results seem to exceed the theory
predictions based on the Standard Model by a significant amount and have
triggered a large number of suggestions for "new physics". In the present paper
the Standard Model predictions for Tevatron and LHC experiments are revisited.
This includes a reanalysis of electromagnetic as well as weak corrections,
leading to a shift of the asymmetry by roughly a factor 1.1 when compared to
the results of the first papers on this subject. The impact of cuts on the
transverse momentum of the top-antitop system is studied. Restricting the ttbar
system to a transverse momentum less than 20 GeV leads to an enhancement of the
asymmetries by factors between 1.3 and 1.5, indicating the importance of an
improved understanding of the -momentum distribution. Predictions for
similar measurements at the LHC are presented, demonstrating the sensitivity of
the large rapidity region both to the Standard Model contribution and effects
from "new physics".Comment: 23 pages. Final version to appear in JHE
Four-Loop Decoupling Relations for the Strong Coupling
We compute the matching relation for the strong coupling constant within the
framework of QCD up to four-loop order. This allows a consistent five-loop
running (once the function is available to this order) taking into
account threshold effects. As a side product we obtain the effective coupling
of a Higgs boson to gluons with five-loop accuracy.Comment: 11 page
Failure of hydrogenation in protecting polycyclic aromatic hydrocarbons from fragmentation
A recent study of soft X-ray absorption in native and hydrogenated coronene
cations, CH , led to the conclusion that additional
hydrogen atoms protect (interstellar) Polycyclic Aromatic Hydrocarbon (PAH)
molecules from fragmentation [Reitsma et al., Phys. Rev. Lett. 113, 053002
(2014)]. The present experiment with collisions between fast (30-200 eV) He
atoms and pyrene (CH, , 6, and 16) and simulations
without reference to the excitation method suggests the opposite. We find that
the absolute carbon-backbone fragmentation cross section does not decrease but
increases with the degree of hydrogenation for pyrene molecules.Comment: 10 pages, 5 figure
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