702 research outputs found
Strong diamagnetic response and specific heat anomaly above T_c in underdoped La_(2-x)Sr_xCuO_4
By measuring AC susceptibility using a very low amplitude of the AC field (<1
mG) it is shown that underdoped samples of La_(2-x)Sr_xCuO_4 (LASCO), are
diamagnetic in a temperature region above T_c up to a temperature T^*. This
behavior is only observed with AC fields along the c-axis whereas for fields in
the ab-plane no diamagnetism above Tc was detected. The diamagnetism is almost
frequency independent in the frequency range 0.1-10 kHz. At T* a broad step
anomaly in the specific heat is inferred through measurements of the elastic
constant c33. We suggest that the observed diamagnetism and the anomaly in the
elastic constant are associated with the existence of phase incoherent Cooper
pairs between Tc and T*.Comment: 5 pages 7 figures, to appear in Phys. rev
Evidence for suppressed metallicity on the surface of La2-xSrxCuO4 and Nd2-xCexCuO4
Hard X-ray Photoemission spectroscopy (PES) of copper core electronic states,
with a probing depth of 60 \AA, is used to show that the Zhang-Rice
singlet feature is present in LaCuO but is absent in NdCuO.
Hole- and electron doping in LaSrCuO (LSCO) and
NdCeCuO (NCCO) result in new well-screened features which are
missing in soft X-ray PES. Impurity Anderson model calculations establish
metallic screening as its origin, which is strongly suppressed within 15
of the surface. Complemented with X-ray absorption spectroscopy,
the small chemical-potential shift in core levels ( eV) are shown to
be consistent with modifications of valence and conduction band states spanning
the band gap ( eV) upon hole- and electron-doping in LSCO and NCCO.Comment: 4 pages, 4 figure
A Note on Computations of D-brane Superpotential
We develop some computational methods for the integrals over the 3-chains on
the compact Calabi-Yau 3-folds that plays a prominent role in the analysis of
the topological B-model in the context of the open mirror symmetry. We discuss
such 3-chain integrals in two approaches. In the first approach, we provide a
systematic algorithm to obtain the inhomogeneous Picard-Fuchs equations. In the
second approach, we discuss the analytic continuation of the period integral to
compute the 3-chain integral directly. The latter direct integration method is
applicable for both on-shell and off-shell formalisms.Comment: 61 pages, 5 figures; v2: typos corrected, minor changes, references
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Thermodynamic and Transport Properties of CeMg2Cu9 under Pressure
We report the transport and thermodynamic properties under hydrostatic
pressure in the antiferromagnetic Kondo compound CeMg2Cu9 with a
two-dimensional arrangement of Ce atoms. Magnetic specific heat Cmag(T) shows a
Schottky-type anomaly around 30 K originating from the crystal electric field
(CEF) splitting of the 4f state with the first excited level at \Delta_{1}/kB =
58 K and the second excited level at \Delta_{2}/kB = 136 K from the ground
state.
Electric resistivity shows a two-peaks structure due to the Kondo effect on
each CEF level around T_{1}^{max} = 3 K and T_{2}^{max} = 40 K. These peaks
merge around 1.9 GPa with compression. With increasing pressure, Neel
temperature TN initially increases and then change to decrease. TN finally
disappears at the quantum critical point Pc = 2.4 GPa.Comment: 10 pages, 6 figure
Development and characterization of the readout system for POLARBEAR-2
POLARBEAR-2 is a next-generation receiver for precision measurements of the
polarization of the cosmic microwave background (Cosmic Microwave Background
(CMB)). Scheduled to deploy in early 2015, it will observe alongside the
existing POLARBEAR-1 receiver, on a new telescope in the Simons Array on Cerro
Toco in the Atacama desert of Chile. For increased sensitivity, it will feature
a larger area focal plane, with a total of 7,588 polarization sensitive
antenna-coupled Transition Edge Sensor (TES) bolometers, with a design
sensitivity of 4.1 uKrt(s). The focal plane will be cooled to 250 milliKelvin,
and the bolometers will be read-out with 40x frequency domain multiplexing,
with 36 optical bolometers on a single SQUID amplifier, along with 2 dark
bolometers and 2 calibration resistors. To increase the multiplexing factor
from 8x for POLARBEAR-1 to 40x for POLARBEAR-2 requires additional bandwidth
for SQUID readout and well-defined frequency channel spacing. Extending to
these higher frequencies requires new components and design for the LC filters
which define channel spacing. The LC filters are cold resonant circuits with an
inductor and capacitor in series with each bolometer, and stray inductance in
the wiring and equivalent series resistance from the capacitors can affect
bolometer operation. We present results from characterizing these new readout
components. Integration of the readout system is being done first on a small
scale, to ensure that the readout system does not affect bolometer sensitivity
or stability, and to validate the overall system before expansion into the full
receiver. We present the status of readout integration, and the initial results
and status of components for the full array.Comment: Presented at SPIE Astronomical Telescopes and Instrumentation 2014:
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for
Astronomy VII. Published in Proceedings of SPIE Volume 915
Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504
Several exoplanets have recently been imaged at wide separations of >10 AU
from their parent stars. These span a limited range of ages (<50 Myr) and
atmospheric properties, with temperatures of 800--1800 K and very red colors (J
- H > 0.5 mag), implying thick cloud covers. Furthermore, substantial model
uncertainties exist at these young ages due to the unknown initial conditions
at formation, which can lead to an order of magnitude of uncertainty in the
modeled planet mass. Here, we report the direct imaging discovery of a Jovian
exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS
survey. The system is older than all other known directly-imaged planets; as a
result, its estimated mass remains in the planetary regime independent of
uncertainties related to choices of initial conditions in the exoplanet
modeling. Using the most common exoplanet cooling model, and given the system
age of 160 [+350, -60] Myr, GJ 504 b has an estimated mass of 4 [+4.5, -1.0]
Jupiter masses, among the lowest of directly imaged planets. Its projected
separation of 43.5 AU exceeds the typical outer boundary of ~30 AU predicted
for the core accretion mechanism. GJ 504 b is also significantly cooler (510
[+30, -20] K) and has a bluer color (J-H = -0.23 mag) than previously imaged
exoplanets, suggesting a largely cloud-free atmosphere accessible to
spectroscopic characterization. Thus, it has the potential of providing novel
insights into the origins of giant planets, as well as their atmospheric
properties.Comment: 20 pages, 12 figures, Accepted for publication in ApJ. Minor updates
from the version
Improved Study of the Antiprotonic Helium Hyperfine Structure
We report the initial results from a systematic study of the hyperfine (HF)
structure of antiprotonic helium (n,l) = (37,~35) carried out at the Antiproton
Decelerator (AD) at CERN. We performed a laser-microwave-laser resonance
spectroscopy using a continuous wave (cw) pulse-amplified laser system and
microwave cavity to measure the HF transition frequencies. Improvements in the
spectral linewidth and stability of our laser system have increased the
precision of these measurements by a factor of five and reduced the line width
by a factor of three compared to our previous results. A comparison of the
experimentally measured transition frequencies with three body QED calculations
can be used to determine the antiproton spin magnetic moment, leading towards a
test of CPT invariance.Comment: 14 pages 9 figure
A novel immunoscintigraphy technique using metabolizable linker with angiotensin II treatment
Immunoscintigraphy is a tumour imaging technique that can have specificity, but high background radioactivity makes it difficult to obtain tumour imaging soon after the injection of radioconjugate. The aim of this study is to see whether clear tumour images can be obtained soon after injection of a radiolabelled reagent using a new linker with antibody fragments (Fab), in conditions of induced hypertension in mice. Fab fragments of a murine monoclonal antibody against human osteosarcoma were labelled with radioiodinated 3′-iodohippuryl N-ɛ-maleoyl-L-lysine (HML) and were injected intravenously to tumour-bearing mice. Angiotensin II was administered for 4 h before and for 1 h after the injection of radiolabelled Fab. Kidney uptake of 125I-labelled-HML-Fab was much lower than that of 125I-labelled-Fab radioiodinated by the chloramine-T method, and the radioactivity of tumour was increased approximately two-fold by angiotensin II treatment at 3 h after injection, indicating high tumour-to-normal tissue ratios. A clear tumour image was obtained with 131I-labelled-HML-Fab at 3 h post-injection. The use of HML as a radiolabelling reagent, combined with angiotensin II treatment, efficiently improved tumour targeting and enabled the imaging of tumours. These results suggest the feasibility of PET scan using antibody fragment labelled with 18F-fluorine substitute for radioiodine. © 1999 Cancer Research Campaig
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