1,455 research outputs found
Glacier changes in the Bavarian Alps from 1989/90 to 2006/07
The five glaciers in Bavaria which today cover a total area of less than one square kilometer were frequently monitored by geodetic methods from the mid of the 20th century. In this paper, the record is extended by new surveys in 1999 and 2006. The glaciers show a prolonged surface lowering, which is intensified compared to the 1980s and reaches maximum rates from 1999-2006. Moreover, the ice thickness of four glaciers was determined in 2006 and 2007 by geophysical field techniques and allows the calculation of ice volumes. First simple extrapolations of observed volume losses indicate that the two Berchtesgaden glaciers and Südlicher Schneeferner could disappear by 2016, while the ice of Nördlicher Schneeferner endures until 2027. Ice thicknesses and surface changes are visualized in five annexed maps.Die fünf bayerischen Gletscher, die heute insgesamt eine Fläche von weniger als einem Quadratkilometer bedecken, wurden seit der Mitte des 20. Jahrhunderts regelmäßig geodätisch aufgenommen. Diese Reihe wird hier um zwei Neuvermessungen in den Jahren 1999 und 2006 erweitert. Alle Gletscher zeigen in dem Zeitraum eine fortgesetzte Erniedrigung ihrer Oberfläche, die im Vergleich zu den 1980er Jahren verstärkt ist und in der Periode 1999-2006 Maximalwerte aufzeigt. Außerdem wurden in den Jahren 2006 und 2007 die Eisdicken von vier Gletschern durch geophysikalische Messungen bestimmt, was erstmalig die Ermittlung des verbleibenden Eisvolumens erlaubt. Erste einfache Extrapolationen der beobachteten Volumenverluste in die Zukunft deuten an, dass die beiden Gletscher in den Berchtesgadener Alpen sowie der Südliche Schneeferner bis zum Jahr 2016 verschwinden könnten, während der Nördliche Schneeferner noch bis 2027 überdauern würde. Eisdicken und Oberflächenänderungen werden anhand von fünf Karten im Anhang verdeutlicht
Magnetization study on the field-induced quantum critical point in YbRh_2Si_2
We study the field-induced quantum critical point (QCP) in YbRhSi by
low-temperature magnetization, , and magnetic Gr\"uneisen ratio,
, measurements and compare the results with previous thermal
expansion, , and critical Gr\"uneisen ratio, , data
on YbRh(SiGe). In the latter case, a slightly
negative chemical pressure has been used to tune the system towards its
zero-field QCP. The magnetization derivative is far more singular than
thermal expansion, reflecting a strongly temperature dependent pressure
derivative of the field at constant entropy,
(: molar volume), which saturates at T/GPa for .
The line , previously observed in Hall- and thermodynamic
measurements, separates regimes in - phase space of stronger
) and weaker ) divergent .Comment: 4 Pages, 3 Figures, submitted to Proceedings of ICM 2009 (Karlsruhe
Electron Spin Resonance of the Yb 4f moment in Yb(Rh1-xCox)2Si2
[published in Phys. Rev. B 85, 035119 (2012)] The evolution of spin dynamics
from the quantum critical system YbRh2Si2 to the stable trivalent Yb system
YbCo2Si2 was investigated by Electron Spin Resonance (ESR) spectroscopy. While
the Kondo temperature changes by one order of magnitude, all compositions of
the single crystalline series Yb(Rh1-xCox)2Si2 show well defined ESR spectra
with a clear Yb3+ character for temperatures below \approx 20 K. With
increasing Co-content the ESR g-factor along the c-direction strongly increases
indicating a continuous change of the ground state wave function and, thus, a
continuous change of the crystal electric field. The linewidth presents a
complex dependence on the Co-content and is discussed in terms of the Co-doping
dependence of the Kondo interaction, the magnetic anisotropy and the influence
of ferromagnetic correlations between the 4f states. The results provide
evidence that, for low Co-doping, the Kondo interaction allows narrow ESR
spectra despite the presence of a large magnetic anisotropy, whereas at high
Co-concentrations, the linewidth is controlled by ferromagnetic correlations. A
pronounced broadening due to critical correlations at low temperatures is only
observed at the highest Co-content. This might be related to the presence of
incommensurate magnetic fluctuations.Comment: 8 pages, 8 Figure
Ferromagnetic quantum critical fluctuations in YbRh_2(Si_{0.95}Ge_{0.05})_2
The bulk magnetic susceptibility of
YbRh(SiGe) has been investigated %by ac-and
dc-magnetometry at low temperatures and close to the field-induced quantum
critical point at T. For T a Curie-Weiss law with a
negative Weiss temperature is observed at temperatures below 0.3 K. Outside
this region, the susceptibility indicates ferromagnetic quantum critical
fluctuations: above 0.3 K, while at low temperatures
the Pauli susceptibility follows and scales with
the coefficient of the term in the electrical resistivity. The
Sommerfeld-Wilson ratio is highly enhanced and increases up to 30 close to the
critical field.Comment: Physical Review Letters, to be publishe
Who students interact with? A social network analysis perspective on the use of Twitter in language learning
This paper reports student interaction patterns and self-reported results of using Twitter microblogging environment. The study employs longitudinal probabilistic social network analysis (SNA) to identify the patterns and trends of network dynamics. It is building on earlier works that explore associations of student achievement records with the observed network measures. It integrates gender as an additional variable and reports some relation with interaction patterns. Additionally, the paper reports the results of a questionnaire that enables further discussion on the communication patterns
Divergence of the Magnetic Gr\"{u}neisen Ratio at the Field-Induced Quantum Critical Point in YbRhSi
The heavy fermion compound YbRhSi is studied by low-temperature
magnetization and specific-heat measurements at magnetic fields
close to the quantum critical point ( T, ). Upon
approaching the instability, is more singular than , leading to a
divergence of the magnetic Gr\"uneisen ratio .
Within the Fermi liquid regime, with
and T which is consistent with
scaling behavior of the specific-heat coefficient in
YbRh(SiGe). The field-dependence of indicates
an inflection point of the entropy as a function of magnetic field upon passing
the line previously observed in Hall- and thermodynamic
measurements.Comment: 4 pages, 3 Figure
Anisotropic electron spin resonance of YbIr2Si2
A series of electron spin resonance (ESR) experiments were performed on a
single crystal of the heavy fermion metal YbIr2Si2 to map out the anisotropy of
the ESR-intensity I_ESR which is governed by the microwave field component of
the g-factor. The temperature dependencies of I_ESR(T) and g(T) were measured
for different orientations and compared within the range 2.6K \le T \le 16K.
The analysis of the intensity dependence on the crystal orientation with
respect to both the direction of the microwave field and the static magnetic
field revealed remarkable features: The intensity variation with respect to the
direction of the microwave field was found to be one order of magnitude smaller
than expected from the g-factor anisotropy. Furthermore, we observed a weak
basal plane anisotropy of the ESR parameters which we interpret to be an
intrinsic sample property.Comment: 10 pages, 5 figure
Tunable Graphene Antennas for Selective Enhancement of THz-Emission
In this paper, we will introduce THz graphene antennas that strongly enhance
the emission rate of quantum systems at specific frequencies. The tunability of
these antennas can be used to selectively enhance individual spectral features.
We will show as an example that any weak transition in the spectrum of coronene
can become the dominant contribution. This selective and tunable enhancement
establishes a new class of graphene-based THz devices, which will find
applications in sensors, novel light sources, spectroscopy, and quantum
communication devices
Temperature- and Magnetic-Field-Dependent Optical Properties of Heavy Quasiparticles in YbIr2Si2
We report the temperature- and magnetic-field-dependent optical conductivity
spectra of the heavy electron metal YbIrSi. Upon cooling below the
Kondo temperature (), we observed a typical charge dynamics that is
expected for a formation of a coherent heavy quasiparticle state. We obtained a
good fitting of the Drude weight of the heavy quasiparticles by applying a
modified Drude formula with a photon energy dependence of the quasiparticle
scattering rate that shows a similar power-law behavior as the temperature
dependence of the electrical resistivity. By applying a magnetic field of 6T
below , we found a weakening of the effective dynamical mass
enhancement by about 12% in agreement with the expected decrease of the
-conduction electron hybridization on magnetic field.Comment: 5 pages, 4 figures. to be published in Journal of the Physical
Society of Japan Vol. 79 (2010) No. 1
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