2,581 research outputs found
High accuracy measure of atomic polarizability in an optical lattice clock
Despite being a canonical example of quantum mechanical perturbation theory,
as well as one of the earliest observed spectroscopic shifts, the Stark effect
contributes the largest source of uncertainty in a modern optical atomic clock
through blackbody radiation. By employing an ultracold, trapped atomic ensemble
and high stability optical clock, we characterize the quadratic Stark effect
with unprecedented precision. We report the ytterbium optical clock's
sensitivity to electric fields (such as blackbody radiation) as the
differential static polarizability of the ground and excited clock levels:
36.2612(7) kHz (kV/cm)^{-2}. The clock's fractional uncertainty due to room
temperature blackbody radiation is reduced an order of magnitude to 3 \times
10^{-17}.Comment: 5 pages, 3 figures, 2 table
An atomic clock with instability
Atomic clocks have been transformational in science and technology, leading
to innovations such as global positioning, advanced communications, and tests
of fundamental constant variation. Next-generation optical atomic clocks can
extend the capability of these timekeepers, where researchers have long aspired
toward measurement precision at 1 part in . This milestone will
enable a second revolution of new timing applications such as relativistic
geodesy, enhanced Earth- and space-based navigation and telescopy, and new
tests on physics beyond the Standard Model. Here, we describe the development
and operation of two optical lattice clocks, both utilizing spin-polarized,
ultracold atomic ytterbium. A measurement comparing these systems demonstrates
an unprecedented atomic clock instability of after
only hours of averaging
The Spin Glass Transition : Exponents and Dynamics
Numerical simulations on Ising Spin Glasses show that spin glass transitions
do not obey the usual universality rules which hold at canonical second order
transitions. On the other hand the dynamics at the approach to the transition
appear to take up a universal form for all spin glasses. The implications for
the fundamental physics of transitions in complex systems are addressed.Comment: 4 pages (Latex) with 3 figures (postscript), accepted for publication
in Physica
Effect of Dilution on Microstructure and Wear Resistance of a Fe-Based Hardfacing Alloy with a High Amount of Carbide-Forming Elements
Hardfacing is a widely diffused technique adopted to increase service life of parts for heavy-duty applications. Even though
hardfacing alloys feature optimized chemistry and microstructure for specific service conditions, dilution with substrate modifies
the resulting properties along a significant fraction of the deposit thickness. In particular, C and B diffusion to the substrate alters
hypereutectic alloys reducing the carbide-forming ability andmodifying the solidification sequence. In the present paper, the effect
of dilution on a hypereutectic Fe-C-B based alloy containing Cr and Mo was investigated. The effect of dilution on the reference
alloy was studied by producing laboratory castings with an increased amount of Fe, up to 50 mass %. The obtained results were
compared with the dilution of the hardfacing alloy cast on steel substrates. The microstructural evolution was analyzed by XRD
(X-ray diffraction), differential scanning calorimetry (DSC), optical microscopy (OM), and scanning electron microscopy (SEM),
whereas mechanical behaviour was evaluated by hardness measurements and wear resistance by pin-on-disc tests
Optical Lattice Induced Light Shifts in an Yb Atomic Clock
We present an experimental study of the lattice induced light shifts on the
1S_0-3P_0 optical clock transition (v_clock~518 THz) in neutral ytterbium. The
``magic'' frequency, v_magic, for the 174Yb isotope was determined to be 394
799 475(35)MHz, which leads to a first order light shift uncertainty of 0.38 Hz
on the 518 THz clock transition. Also investigated were the hyperpolarizability
shifts due to the nearby 6s6p 3P_0 - 6s8p 3P_0, 6s8p 3P_2, and 6s5f 3F_2
two-photon resonances at 759.708 nm, 754.23 nm, and 764.95 nm respectively. By
tuning the lattice frequency over the two-photon resonances and measuring the
corresponding clock transition shifts, the hyperpolarizability shift was
estimated to be 170(33) mHz for a linear polarized, 50 uK deep, lattice at the
magic wavelength. In addition, we have confirmed that a circularly polarized
lattice eliminates the J=0 - J=0 two-photon resonance. These results indicate
that the differential polarizability and hyperpolarizability frequency shift
uncertainties in a Yb lattice clock could be held to well below 10^-17.Comment: Accepted to PR
Applying a transdisciplinary mixed methods research design to explore sustainable diets in rural South Africa
This article describes a conceptual framework for exploring sustainable diets, using a case study example of ongoing research in the Vaalharts region, a rural setting in South Africa. A qualitative research approach is followed with an integrated transdisciplinary mixed methods research design with multiple concurrent components employed during two sequential phases. A successful application of the framework is achieved through a collaborative team effort of researchers with qualitative and quantitative research expertise transcending different disciplines, as well as participation of community members throughout the research process. We demonstrate that transdisciplinary mixed methods research designs are essential to gain a better understanding of the complex concept of sustainable diets
Extending the Role of Analogies in the Teaching of Physics
Research in physics teaching has supported the use of analogies as an effective instructional tool that can be used to facilitate students’ understanding of physics concepts. The effectiveness of analogies lies in that they allow students to form cognitive links between what they already know and what they are learning, harmoniously integrating, in this way, the new physics concepts into their existing knowledge. In this paper, it is suggested that analogies could be extended to provide physics teachers with a diagnostic form of assessment that can reveal both the misconceptions their students may hold, the prior knowledge upon which such misconceptions are based, as well as knowledge sources that can be productively used in the teaching process. This suggestion arises from the findings of a cross-age study in which students, from five different age groups, were asked to make predictions about a range of situations they had not previously encountered (novel situations) and explain the reasons that led them to make those predictions
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