1,269 research outputs found
Observation of the 1S0 - 3P0 clock transition in 27Al+
We report for the first time, laser spectroscopy of the 1S0 - 3P0 clock
transition in 27Al+. A single aluminum ion and a single beryllium ion are
simultaneously confined in a linear Paul trap, coupled by their mutual Coulomb
repulsion. This coupling allows the beryllium ion to sympathetically cool the
aluminum ion, and also enables transfer of the aluminum's electronic state to
the beryllium's hyperfine state, which can be measured with high fidelity.
These techniques are applied to a measurement of the clock transition
frequency, \nu = 1 121 015 393 207 851(8) Hz. They are also used to measure the
lifetime of the metastable clock state, \tau = 20.6 +/- 1.4 s, the ground state
1S0 g-factor, g_S = -0.00079248(14), and the excited state 3P0 g-factor, g_P =
-0.00197686(21), in units of the Bohr magneton.Comment: 4 pages, 2 figures; updated author lis
Anisotropy of the Seebeck Coefficient in the Cuprate Superconductor YBaCuO: Fermi-Surface Reconstruction by Bidirectional Charge Order
The Seebeck coefficient of the cuprate YBaCuO was
measured in magnetic fields large enough to suppress superconductivity, at hole
dopings and , for heat currents along the and
directions of the orthorhombic crystal structure. For both directions,
decreases and becomes negative at low temperature, a signature that the Fermi
surface undergoes a reconstruction due to broken translational symmetry. Above
a clear threshold field, a strong new feature appears in , for
conduction along the axis only. We attribute this feature to the onset of
3D-coherent unidirectional charge-density-wave modulations seen by x-ray
diffraction, also along the axis only. Because these modulations have a
sharp onset temperature well below the temperature where starts to drop
towards negative values, we infer that they are not the cause of Fermi-surface
reconstruction. Instead, the reconstruction must be caused by the quasi-2D
bidirectional modulations that develop at significantly higher temperature.Comment: 7 pages, 5 figure
The Changing Climate of the Arctic
The first and strongest signs of global-scale climate change exist in the high latitudes of the planet. Evidence is now accumulating that the Arctic is warming, and responses are being observed across physical, biological, and social systems. The impact of climate change on oceanographic, sea-ice, and atmospheric processes is demonstrated in observational studies that highlight changes in temperature and salinity, which influence global oceanic circulation, also known as thermohaline circulation, as well as a continued decline in sea-ice extent and thickness, which influences communication between oceanic and atmospheric processes. Perspectives from Inuvialuit community representatives who have witnessed the effects of climate change underline the rapidity with which such changes have occurred in the North. An analysis of potential future impacts of climate change on marine and terrestrial ecosystems underscores the need for the establishment of effective adaptation strategies in the Arctic. Initiatives that link scientific knowledge and research with traditional knowledge are recommended to aid Canadaâs northern communities in developing such strategies.Les premiers signes et les signes les plus rĂ©vĂ©lateurs attestant du changement climatique qui sâexerce Ă lâĂ©chelle planĂ©taire se manifestent dans les hautes latitudes du globe. Il existe de plus en plus de preuves que lâArctique se rĂ©chauffe, et diverses rĂ©actions sâobservent tant au sein des systĂšmes physiques et biologiques que sociaux. Les incidences du changement climatique sur les processus ocĂ©anographiques, la glace de mer et les processus atmosphĂ©riques sâavĂšrent Ă©videntes dans le cadre dâĂ©tudes dâobservation qui mettent lâaccent sur les changements de tempĂ©rature et de salinitĂ©, changements qui exercent une influence sur la circulation ocĂ©anique mondiale â Ă©galement appelĂ©e circulation thermohaline â ainsi que sur le dĂ©clin constant de lâĂ©tendue et de lâĂ©paisseur de glace de mer, ce qui influence la communication entre les processus ocĂ©aniques et les processus atmosphĂ©riques. Les perspectives de certains Inuvialuits qui ont Ă©tĂ© tĂ©moins des effets du changement climatique font mention de la rapiditĂ© avec laquelle ces changements se produisent dans le Nord. Lâanalyse des incidences Ă©ventuelles du changement climatique sur les Ă©cosystĂšmes marin et terrestre fait ressortir la nĂ©cessitĂ© de mettre en oeuvre des stratĂ©gies dâadaptation efficaces dans lâArctique. Des initiatives reliant les recherches et connaissances scientifiques aux connaissances traditionnelles sont recommandĂ©es afin de venir en aide aux collectivitĂ©s du Nord canadien pour que celles-ci puissent aboutir Ă de telles stratĂ©gies
Hyperpolarizability and operational magic wavelength in an optical lattice clock
Optical clocks benefit from tight atomic confinement enabling extended
interrogation times as well as Doppler- and recoil-free operation. However,
these benefits come at the cost of frequency shifts that, if not properly
controlled, may degrade clock accuracy. Numerous theoretical studies have
predicted optical lattice clock frequency shifts that scale nonlinearly with
trap depth. To experimentally observe and constrain these shifts in an
Yb optical lattice clock, we construct a lattice enhancement cavity
that exaggerates the light shifts. We observe an atomic temperature that is
proportional to the optical trap depth, fundamentally altering the scaling of
trap-induced light shifts and simplifying their parametrization. We identify an
"operational" magic wavelength where frequency shifts are insensitive to
changes in trap depth. These measurements and scaling analysis constitute an
essential systematic characterization for clock operation at the
level and beyond.Comment: 5 + 2 pages, 3 figures, added supplementa
Mechanism of cell death induced by spermine and amine oxidase in mouse melanoma cells
Polyamines such as spermine, spermidine and putrescine are necessary for cell proliferation and are detected at higher concentrations in most tumor tissues, compared to normal tissues. The amine oxidase enzymes can generate cytotoxic products such as hydrogen peroxide and aldehydes from these polyamines. This study investigates the mechanisms of cell death in B16-F0 mouse melanoma tumor cells exposed to bovine serum amine oxidase and exogenous spermine. The bovine serum amine oxidase/spermine enzymatic system induced inhibition of cell proliferation in B16-F0 melanoma cells and cell death by both apoptotic and necrotic processes. Bovine serum amine oxidase or spermine, alone, did not induce cytotoxicity or cell death by apoptosis, indicating that the enzymatic reaction products were responsible. Catalase and NAD-dependent aldehyde dehydrogenase, inhibitors of hydrogen peroxide and aldehydes, respectively, decreased cell death by apoptosis and necrosis. This further confirms that the cytotoxic products are responsible for causing cell death. Use of inhibitors of different caspases showed that melanoma cells were sensitive to processes involving caspase-3 and -9, but were insensitive to caspase-6. Bovine serum amine oxidase in the presence of spermine could be useful as a promising new tool for anticancer treatment by the selective generation of toxic compounds from polyamines in tumors
TESS and CHEOPS discover two warm sub-Neptunes transiting the bright K-dwarf HDâ15906
We report the discovery of two warm sub-Neptunes transiting the bright (G = 9.5 mag) K-dwarf HDâ15906 (TOIâ461, TICâ4646810). This star was observed by the Transiting Exoplanet Survey Satellite (TESS) in sectors 4 and 31, revealing two small transiting planets. The inner planet, HDâ15906âb, was detected with an unambiguous period but the outer planet, HDâ15906âc, showed only two transits separated by ⌠734 d, leading to 36 possible values of its period. We performed follow-up observations with the CHaracterising ExOPlanet Satellite (CHEOPS) to confirm the true period of HDâ15906âc and improve the radius precision of the two planets. From TESS, CHEOPS, and additional ground-based photometry, we find that HDâ15906âb has a radius of 2.24 ± 0.08 Râ and a period of 10.924709 ± 0.000032 d, whilst HDâ15906âc has a radius of 2.93+0.07â0.06 Râ and a period of 21.583298+0.000052â0.000055 d. Assuming zero bond albedo and full day-night heat redistribution, the inner and outer planet have equilibrium temperatures of 668 ± 13 K and 532 ± 10 K, respectively. The HDâ15906 system has become one of only six multiplanet systems with two warm (âČ 700 K) sub-Neptune sized planets transiting a bright star (G †10 mag). It is an excellent target for detailed characterization studies to constrain the composition of sub-Neptune planets and test theories of planet formation and evolution
Design, Fabrication, and Experimental Demonstration of Junction Surface Ion Traps
We present the design, fabrication, and experimental implementation of
surface ion traps with Y-shaped junctions. The traps are designed to minimize
the pseudopotential variations in the junction region at the symmetric
intersection of three linear segments. We experimentally demonstrate robust
linear and junction shuttling with greater than one million round-trip shuttles
without ion loss. By minimizing the direct line of sight between trapped ions
and dielectric surfaces, negligible day-to-day and trap-to-trap variations are
observed. In addition to high-fidelity single-ion shuttling, multiple-ion
chains survive splitting, ion-position swapping, and recombining routines. The
development of two-dimensional trapping structures is an important milestone
for ion-trap quantum computing and quantum simulations.Comment: 9 pages, 6 figure
Comparison of low--energy resonances in 15N(alpha,gamma)19F and 15O(alpha,gamma)19Ne and related uncertainties
A disagreement between two determinations of Gamma_alpha of the astro-
physically relevant level at E_x=4.378 MeV in 19F has been stated in two recent
papers by Wilmes et al. and de Oliveira et al. In this work the uncertainties
of both papers are discussed in detail, and we adopt the value
Gamma_alpha=(1.5^{+1.5}_{-0.8})10^-9eV for the 4.378 MeV state. In addition,
the validity and the uncertainties of the usual approximations for mirror
nuclei Gamma_gamma(19F) approx Gamma_gamma(19Ne), theta^2_alpha(19F) approx
theta^2_alpha(19Ne) are discussed, together with the resulting uncertainties on
the resonance strengths in 19Ne and on the 15O(alpha,gamma)19Ne rate.Comment: 9 pages, Latex, To appear in Phys. Rev.
New insight into the low-energy He spectrum
The spectrum of He was studied by means of the He(,)He
reaction at a lab energy of 25 MeV/n and small center of mass (c.m.) angles.
Energy and angular correlations were obtained for the He decay products by
complete kinematical reconstruction. The data do not show narrow states at
1.3 and 2.4 MeV reported before for He. The lowest resonant
state of He is found at about 2 MeV with a width of 2 MeV and is
identified as . The observed angular correlation pattern is uniquely
explained by the interference of the resonance with a virtual state
(limit on the scattering length is obtained as fm), and with
the resonance at energy MeV.Comment: 5 pages, 4 figures, 2 table
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