304 research outputs found
Preparation of an ultra-cold sample of ammonia molecules for precision measurements
We present experiments in which an ultra-cold sample of ammonia molecules is
released from an electrostatic trap and recaptured after a variable time. It is
shown that, by performing adiabatic cooling before releasing the molecules and
adiabatic re-compression after they are recaptured, we are able to observe
molecules even after more than 10 ms of free expansion. A coherent measurement
performed during this time will have a statistical uncertainty that decreases
approximately as the inverse of the square root of the expansion time. This
offers interesting prospects for high-resolution spectroscopy and precision
tests of fundamental physics theories
Loading Stark-decelerated molecules into electrostatic quadrupole traps
Beams of neutral polar molecules in a low-field seeking quantum state can be
slowed down using a Stark decelerator, and can subsequently be loaded and
confined in electrostatic quadrupole traps. The efficiency of the trap loading
process is determined by the ability to couple the decelerated packet of
molecules into the trap without loss of molecules and without heating. We
discuss the inherent difficulties to obtain ideal trap loading, and describe
and compare different trap loading strategies. A new "split-endcap" quadrupole
trap design is presented that enables improved trap loading efficiencies. This
is experimentally verified by comparing the trapping of OH radicals using the
conventional and the new quadrupole trap designs
Impacts of Problem-Based Instruction on Students’ Beliefs about Physics and Learning Physics
To help prepare students to address future challenges in Science, Technology, Engineering, and Mathematics (STEM), they need to develop 21st-century skills. These skills are mediated by their beliefs about the nature of scientific knowledge and practices, or epistemological beliefs. One approach shown to support students’ development of these beliefs and skills is problem-based instruction (PBI), which encourages collaborative self-directed learning while working on open-ended problems. We used a mixed-method qualitative approach to examine how implementing PBI in a physics course taught at a Dutch university affected students’ beliefs about physics and learning physics. Analysis of the responses to the course surveys (41–74% response rates) from the first implementation indicated students appreciated opportunities for social interactions with peers and use of scientific equipment with PBI but found difficulties connecting to the Internet given the COVID-19 restrictions. The Colorado Learning Attitudes towards Science Survey (CLASS), a validated survey on epistemological beliefs about physics and learning physics, was completed by a second cohort of students in a subsequent implementation of PBI for the same course; analysis of the students’ pre- and post-responses (28% response rate) showed a slight shift towards more expert-like perspectives despite challenges (e.g., access to lab). Findings from this study may inform teachers with an interest in supporting the development of students’ epistemological beliefs about STEM and the implementation of PBI in undergraduate STEM courses.</p
Elements in Tap Water. Part 3. Effect of Sample Volume and Stagnation Time on the Concentration of the Element.
Abstract not availableJRC.H-Institute for environment and sustainability (Ispra
Mass and Shape Determination of Optically Levitated Nanoparticles
When introducing a nanoparticle into an optical trap, its mass and shape are
not immediately apparent. We combine a charge-based mass measurement with a
shape determination method based on light scattering and an analysis of the
damping rate anisotropy, all on the same set of silica nanoparticles, trapped
using optical tweezers in vacuum. These methods have previously only been used
separately, and the mass determination method has not been applied to
asymmetric particles before. We demonstrate that the combination of these
classification techniques is required to distinguish particles with similar
mass but different shape, and vice versa. The ability to identify these
parameters is a key step for a range of experiments on precision measurements
and sensing using optically levitated nanoparticles
Optical pumping of trapped neutral molecules by blackbody radiation
Optical pumping by blackbody radiation is a feature shared by all polar
molecules and fundamentally limits the time that these molecules can be kept in
a single quantum state in a trap. To demonstrate and quantify this, we have
monitored the optical pumping of electrostatically trapped OH and OD radicals
by room-temperature blackbody radiation. Transfer of these molecules to
rotationally excited states by blackbody radiation at 295 K limits the
trapping time for OH and OD in the state to
2.8 s and 7.1 s, respectively.Comment: corrected small mistakes; added journal reference
Molecular enhancement factors for P, T-violating eEDM in BaCH and YbCH symmetric top molecules
High-precision tests of fundamental symmetries are looking for the parity-
(P), time-reversal- (T) violating electric dipole moment of the electron (eEDM)
as proof of physics beyond the Standard Model. Particularly, in polyatomic
molecules, the complex vibrational and rotational structure gives the
possibility to reach high enhancement of the P, T-odd effects in moderate
electric fields. Additionally, it is possible to increase the statistical
sensitivity by using laser cooling. In this work, we calculate the P, T-odd
electronic structure parameters and for the
promising candidates BaCH and YbCH for the interpretation of future
experiments. We employ high-accuracy relativistic coupled cluster methods and
systematically evaluate the uncertainties of our computational approach.
Compared to other Ba- and Yb-containing molecules, BaCH and YbCH
exhibit larger and associated to increased
covalent character of the M--C bond. The calculated values are and for , and
~kHz and ~kHz for , in BaCH
and YbCH, respectively. The robust, accurate, and cost-effective
computational scheme reported in this work makes our results suitable for
extracting the relevant fundamental properties from future measurements and
also can be used to explore other polyatomic molecules sensitive to various
violations of fundamental symmetries
Mesoscopic Interference for Metric and Curvature (MIMAC) & Gravitational Wave Detection
A compact detector for space-time metric and curvature is highly desirable.
Here we show that quantum spatial superpositions of mesoscopic objects, of the
type which would in principle become possible with a combination of state of
the art techniques and taking into account the known sources of decoherence,
could be exploited to create such a detector. By using Stern-Gerlach (SG)
interferometry with masses much larger than atoms, where the interferometric
signal is extracted by measuring spins, we show that accelerations as low as
or better, as well as the
frame dragging effects caused by the Earth, could be sensed. Constructing such
an apparatus to be non-symmetric would also enable the direct detection of
curvature and gravitational waves (GWs). The GW sensitivity scales differently
from the stray acceleration sensitivity, a unique feature of MIMAC. We have
identified mitigation mechanisms for the known sources of noise, namely Gravity
Gradient Noise (GGN), uncertainty principle and electro-magnetic forces. Hence
it could potentially lead to a meter sized, orientable and vibrational noise
(thermal/seismic) resilient detector of mid (ground based) and low (space
based) frequency GWs from massive binaries (the predicted regimes are similar
to those targeted by atom interferometers and LISA).Comment: 29 pages, 3 figure
Electrostatic trapping of metastable NH molecules
We report on the Stark deceleration and electrostatic trapping of NH
() radicals. In the trap, the molecules are excited on the
spin-forbidden transition and detected via
their subsequent fluorescence to the ground state. The 1/e
trapping time is 1.4 0.1 s, from which a lower limit of 2.7 s for the
radiative lifetime of the state is deduced. The spectral
profile of the molecules in the trapping field is measured to probe their
spatial distribution. Electrostatic trapping of metastable NH followed by
optical pumping of the trapped molecules to the electronic ground state is an
important step towards accumulation of these radicals in a magnetic trap.Comment: replaced with final version, added journal referenc
Cash for Corollas: When Stimulus Reduces Spending
MacroeconomicsThe 2009 Cash for Clunkers program aimed to stimulate consumer spending in the new automobile industry, which was experiencing disproportionate reductions in demand and employment during the Great Recession. Exploiting program eligibility criteria in a regression discontinuity design, we show nearly 60 percent of the subsidies went to households who would have purchased during the two-month program anyway; the rest accelerated sales by no more than eight months. Moreover, the program’s fuel efficiency restrictions shifted purchases toward vehicles that cost on average $5,000 less. On net, Cash for Clunkers significantly reduced total new vehicle spending over the ten month perio
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