1,518 research outputs found
An experiment to detect gravity at sub-mm scale with high-Q mechanical oscillators
Silicon double paddle oscillators are well suited for the detection of weak
forces because of their high Q factor (about 10^5 at room temperature). We
describe an experiment aimed at the detection of gravitational forces between
masses at sub-mm distance using such an oscillator. Gravitational excitation is
produced by a rotating aluminium disk with platinum segments. The force
sensitivity of this apparatus is about 10 fN at room temperature for 1000 s
averaging time at room temperature. The current limitations to detection of the
gravitational force are mentioned.Comment: 19 pages, to appear in Proceedings of the Tenth Marcel Grossmann
Meeting on General Relativity, edited by M. Novello, S. Perez-Bergliaffa and
R. Ruffini, World Scientific. Revision: portable format and revised figure
Properties of KCoAs and Alloys with Fe and Ru: Density Functional Calculations
Electronic structure calculations are presented for KCoAs and alloys
with KFeAs and KRuAs. These materials show electronic
structures characteristic of coherent alloys, with a similar Fermi surface
structure to that of the Fe-based superconductors, when the electron count
is near six per transition metal. However, they are less magnetic than the
corresponding Fe compounds. These results are discussed in relation to
superconductivity.Comment: 5 page
From Few to Many: Observing the Formation of a Fermi Sea One Atom at a Time
Knowing when a physical system has reached sufficient size for its
macroscopic properties to be well described by many-body theory is difficult.
We investigate the crossover from few to many-body physics by studying quasi
one-dimensional systems of ultracold atoms consisting of a single impurity
interacting with an increasing number of identical fermions. We measure the
interaction energy of such a system as a function of the number of majority
atoms for different strengths of the interparticle interaction. As we increase
the number of majority atoms one by one we observe the fast convergence of the
normalized interaction energy towards a many-body limit calculated for a single
impurity immersed in a Fermi sea of majority particles.Comment: 9 pages, 5 figure
Pairing in few-fermion systems with attractive interactions
We have studied quasi one-dimensional few-particle systems consisting of one
to six ultracold fermionic atoms in two different spin states with attractive
interactions. We probe the system by deforming the trapping potential and by
observing the tunneling of particles out of the trap. For even particle numbers
we observe a tunneling behavior which deviates from uncorrelated
single-particle tunneling indicating the existence of pair correlations in the
system. From the tunneling timescales we infer the differences in interaction
energies of systems with different number of particles which show a strong
odd-even effect, similar to the one observed for neutron separation experiments
in nuclei.Comment: 9 pages, 6 figure
Coherent molecule formation in anharmonic potentials near confinement-induced resonances
We perform a theoretical and experimental study of a system of two ultracold
atoms with tunable interaction in an elongated trapping potential. We show that
the coupling of center-of-mass and relative motion due to an anharmonicity of
the trapping potential leads to a coherent coupling of a state of an unbound
atom pair and a molecule with a center of mass excitation. By performing the
experiment with exactly two particles we exclude three-body losses and can
therefore directly observe coherent molecule formation. We find quantitative
agreement between our theory of inelastic confinement-induced resonances and
the experimental results. This shows that the effects of center-of-mass to
relative motion coupling can have a significant impact on the physics of
quasi-1D quantum systems.Comment: 7 pages, 4 figure
Quick X-ray microtomography using a laser-driven betatron source
Laser-driven X-ray sources are an emerging alternative to conventional X-ray
tubes and synchrotron sources. We present results on microtomographic X-ray
imaging of a cancellous human bone sample using synchrotron-like betatron
radiation. The source is driven by a 100-TW-class titanium-sapphire laser
system and delivers over X-ray photons per second. Compared to earlier
studies, the acquisition time for an entire tomographic dataset has been
reduced by more than an order of magnitude. Additionally, the reconstruction
quality benefits from the use of statistical iterative reconstruction
techniques. Depending on the desired resolution, tomographies are thereby
acquired within minutes, which is an important milestone towards real-life
applications of laser-plasma X-ray sources
Collisional stability of a three-component degenerate Fermi gas
We report on the creation of a degenerate Fermi gas consisting of a balanced
mixture of atoms in three different hyperfine states of Li. This new system
consists of three distinguishable Fermions with different and tunable
interparticle scattering lengths , and . We are able
to prepare samples containing atoms in each state at a
temperature of about nK, which corresponds to . We
investigated the collisional stability of the gas for magnetic fields between 0
and 600 G and found a prominent loss feature at 130 G. From lifetime
measurements we determined three-body loss coefficients, which vary over nearly
three orders of magnitude
COMPARISON OF PROLIFERATING CELL NUCLEAR ANTIGEN (PCNA) STAINING AND BRDURD-LABELING INDEX UNDER DIFFERENT PROLIFERATIVE CONDITIONS IN-VITRO BY FLOW-CYTOMETRY
PC10 is a monoclonal antibody against proliferating cell nuclear antigen (PCNA). The staining pattern in immunochemistry depends on fixation and detergent extraction treatment. The aim of this study was to validate the flow cytometric PCNA assay against Bromodeoxyuridine-labelling index (BrdUrd-LI) under different proliferative conditions in vitro. Expression of PCNA in methanol fixed cells with, and without, prior detergent extraction with EDTA/Triton was compared to BrdUrd-labelling index in NIH-3T3 fibroblasts and human Caski tumour cells in exponential phase and under confluent conditions. Serum stimulation and serum starvation conditions were studied. The results for BrdUrd-LI and PCNA-index after extraction showed good correlation for 3T3 fibroblasts and for Caski cells, with some differences for serum withdrawn Caski cells. There was no correlation between the number of cells that were positive for PCNA without extraction and BrdUrd-LI. Spheroid cells with G(1)-DNA-content showed an almost synchronous recruitment and progression through the cell cycle after trypsination and replating. Tightly bound PCNA paralleled this synchronicity whereas total PCNA did not change significantly. The results demonstrate that immunochemical detection of non-extractable PCNA-index gives similar results as compared with BrdUrd-labelling index under different proliferative conditions in vitro for different monolayer cell lines, whereas without extraction PCNA does not correlate with BrdUrd-LI in these fast growing cell lines due to its long half-life. PCNA expression parallels the progression through the cell cycle in V79 spheroids, a primitive model of tumour growth
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