2,231 research outputs found
Interferometer-Type Structures for Guided Atoms
We experimentally demonstrate interferometer-type guiding structures for
neutral atoms based on dipole potentials created by micro-fabricated optical
systems. As a central element we use an array of atom waveguides being formed
by focusing a red-detuned laser beam with an array of cylindrical microlenses.
Combining two of these arrays, we realize X-shaped beam splitters and more
complex systems like the geometries for Mach-Zehnder and Michelson-type
interferometers for atoms.Comment: 4 pages, 6 figure
Macrophage migration inhibitory factor downregulation: a novel mechanism of resistance to anti-angiogenic therapy.
Anti-angiogenic therapies for cancer such as VEGF neutralizing antibody bevacizumab have limited durability. While mechanisms of resistance remain undefined, it is likely that acquired resistance to anti-angiogenic therapy will involve alterations of the tumor microenvironment. We confirmed increased tumor-associated macrophages in bevacizumab-resistant glioblastoma patient specimens and two novel glioblastoma xenograft models of bevacizumab resistance. Microarray analysis suggested downregulated macrophage migration inhibitory factor (MIF) to be the most pertinent mediator of increased macrophages. Bevacizumab-resistant patient glioblastomas and both novel xenograft models of resistance had less MIF than bevacizumab-naive tumors, and harbored more M2/protumoral macrophages that specifically localized to the tumor edge. Xenografts expressing MIF-shRNA grew more rapidly with greater angiogenesis and had macrophages localizing to the tumor edge which were more prevalent and proliferative, and displayed M2 polarization, whereas bevacizumab-resistant xenografts transduced to upregulate MIF exhibited the opposite changes. Bone marrow-derived macrophage were polarized to an M2 phenotype in the presence of condition-media derived from bevacizumab-resistant xenograft-derived cells, while recombinant MIF drove M1 polarization. Media from macrophages exposed to bevacizumab-resistant tumor cell conditioned media increased glioma cell proliferation compared with media from macrophages exposed to bevacizumab-responsive tumor cell media, suggesting that macrophage polarization in bevacizumab-resistant xenografts is the source of their aggressive biology and results from a secreted factor. Two mechanisms of bevacizumab-induced MIF reduction were identified: (1) bevacizumab bound MIF and blocked MIF-induced M1 polarization of macrophages; and (2) VEGF increased glioma MIF production in a VEGFR2-dependent manner, suggesting that bevacizumab-induced VEGF depletion would downregulate MIF. Site-directed biopsies revealed enriched MIF and VEGF at the enhancing edge in bevacizumab-naive patients. This MIF enrichment was lost in bevacizumab-resistant glioblastomas, driving a tumor edge M1-to-M2 transition. Thus, bevacizumab resistance is driven by reduced MIF at the tumor edge causing proliferative expansion of M2 macrophages, which in turn promotes tumor growth
Influence of Rb, Cs and Ba on Superconductivity of Magnesium Diboride
Magnesium diboride has been thermally treated in the presence of Rb, Cs, and
Ba. Magnetic susceptibility shows onsets of superconductivity in the resulting
samples at 52K (Rb), 58K (Cs) and 45K (Ba). Room-temperature 11B NMR indicates
to cubic symmetry of the electric field gradient at boron site for the samples
reacted with Rb and Cs, in contrast to the axial symmetry in the initial MgB2
and in the sample treated with Ba.Comment: 3 pages (twocolumn), 2 figure
Double-impulse magnetic focusing of launched cold atoms.
We have theoretically investigated three-dimensional focusing of a launched cloud of cold atoms using a pair of magnetic lens pulses (the alternate-gradient method). Individual lenses focus radially and defocus axially or vice versa. The performance of the two possible pulse sequences are compared and found to be ideal for loading both 'pancake' and 'sausage' shaped magnetic/optical microtraps. It is shown that focusing aberrations are considerably smaller for double-impulse magnetic lenses compared to single-impulse magnetic lenses. An analysis of clouds focused by the double-impulse technique is presented
High pressure investigation of the heavy-fermion antiferromagnet U_3Ni_5Al_19
Measurements of magnetic susceptibility, specific heat, and electrical
resistivity at applied pressures up to 55 kbar have been carried out on single
crystals of the heavy-fermion antiferromagnet U_3Ni_5Al_19, which crystallizes
in the Gd_3Ni_5Al_19 orthorhombic structure with two inequivalent U sites. At
ambient pressure, a logarithmic T-dependence of the specific heat and T-linear
electrical resistivity below 5 K indicates non-Fermi liquid (NFL) behavior in
the presence of bulk antiferromagnetic order at T_N=23 K. Electrical
resistivity measurements reveal a crossover from non-Fermi liquid to Fermi
liquid behavior at intermediate pressures between 46 kbar and 51 kbar, followed
by a return to NFL T^{3/2} behavior at higher pressures. These results provide
evidence for an ambient pressure quantum critical point and an additional
antiferromagnetic instability at P_c=60 kbar.Comment: 12 pages, 5 figure
Next-to-next-to-leading order fits to CCFR'97 data and infrared renormalons
We briefly summarize the outcomes of our recent improved fits to the
experimental data of CCFR collaboration for structure function of deep-inelastic scattering at the next-to-next-to-leading order. Special
attention is paid to the extraction of and the parameter of the
infrared renormalon model for -correction at different orders of
perturbation theory. The results can be of interest for planning similar
studies using possible future data of Neutrino Factories.Comment: 3 pages, presented at WG3 of 4th NuFact'02 Workshop, London 1-6 July,
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On the Slow Roll Expansion for Brane Inflation
One possibility for identifying the inflaton in the framework of string
theory is that it is a -brane modulus. This option involves a specific,
non-canonical form of the kinetic energy -- the Dirac-Born-Infeld action. This
note investigates the applicability of the slow roll approximation in
inflationary models of this type. To this end the slow roll expansion of
Liddle, Parsons and Barrow is derived for the case of the DBI action. The
resulting slow roll conditions augment the standard ones valid in the case of
canonical kinetic terms. It is also shown that in DBI models inflation does not
require that the potential dominate the energy density.Comment: References adde
Superconductivity and Quantum Criticality in CeCoIn_5
Electrical resistivity measurements on a single crystal of the heavy-fermion
superconductor CeCoIn_5 at pressures to 4.2 GPa reveal a strong crossover in
transport properties near P^* \approx 1.6 GPa, where T_c is a maximum. The
temperature-pressure phase diagram constructed from these data provides a
natural connection to cuprate physics, including the possible existence of a
pseudogap.Comment: 4 pages, 4 figure
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