1,205 research outputs found
Value added or misattributed? A multi-institution study on the educational benefit of labs for reinforcing physics content
Instructional labs are widely seen as a unique, albeit expensive, way to
teach scientific content. We measured the effectiveness of introductory lab
courses at achieving this educational goal across nine different lab courses at
three very different institutions. These institutions and courses encompassed a
broad range of student populations and instructional styles. The nine courses
studied had two key things in common: the labs aimed to reinforce the content
presented in lectures, and the labs were optional. By comparing the performance
of students who did and did not take the labs (with careful normalization for
selection effects), we found universally and precisely no added value to
learning from taking the labs as measured by course exam performance. This work
should motivate institutions and departments to reexamine the goals and conduct
of their lab courses, given their resource-intensive nature. We show why these
results make sense when looking at the comparative mental processes of students
involved in research and instructional labs, and offer alternative goals and
instructional approaches that would make lab courses more educationally
valuable.Comment: Accepted to Phys Rev PE
Correcting for Distortions due to Ionization in the STAR TPC
Physics goals of the STAR Experiment at RHIC in recent (and future) years
drive the need to operate the STAR TPC at ever higher luminosities, leading to
increased ionization levels in the TPC gas. The resulting ionic space charge
introduces field distortions in the detector which impact tracking performance.
Further complications arise from ionic charge leakage into the main TPC volume
from the high gain anode region. STAR has implemented corrections for these
distortions based on measures of luminosity, which we present here.
Additionally, we highlight a novel approach to applying the corrections on an
event-by-event basis applicable in conditions of rapidly varying ionization
sources.Comment: 6 pages, 7 figures, proceedings of the Workshop on Tracking in High
Multiplicity Environments (TIME 05) in Zurich, Switzerland, submitted to
Nucl. Instr. and Meth.
Correction of SOHO CELIAS/SEM EUV Measurements saturated by extreme solar flare events
The solar irradiance in the Extreme Ultraviolet (EUV) spectral bands has been
observed with a 15 sec cadence by the SOHO Solar EUV Monitor (SEM) since 1995.
During remarkably intense solar flares the SEM EUV measurements are saturated
in the central (zero) order channel (0.1 -- 50.0 nm) by the flare soft X-ray
and EUV flux. The first order EUV channel (26 -- 34 nm) is not saturated by the
flare flux because of its limited bandwidth, but it is sensitive to the arrival
of Solar Energetic Particles (SEP). While both channels detect nearly equal SEP
fluxes, their contributions to the count rate is sensibly negligible in the
zero order channel but must be accounted for and removed from the first channel
count rate. SEP contribution to the measured SEM signals usually follows the
EUV peak for the gradual solar flare events. Correcting the extreme solar flare
SEM EUV measurements may reveal currently unclear relations between the flare
magnitude, dynamics observed in different EUV spectral bands, and the measured
Earth atmosphere response. A simple and effective correction technique based on
analysis of SEM count-rate profiles, GOES X-ray, and GOES proton data has been
developed and used for correcting EUV measurements for the five extreme solar
flare events of July 14, 2000, October 28, November 2, November 4, 2003, and
January 20, 2005. Although none of the 2000 and 2003 flare peaks were
contaminated by the presence of SEPs, the January 20, 2005 SEPs were unusually
prompt and contaminated the peak. The estimated accuracy of the correction is
about 7.5% for large X-class events.Comment: To appear in Astron. Nachr. /A
Mode-hop-free tuning over 135 GHz of external cavity diode lasers without anti-reflection coating
We report an external cavity diode laser (ECDL), using a diode whose front
facet is not antireflection (AR) coated, that has a mode-hop-free (MHF) tuning
range greater than 135 GHz. We achieved this using a short external cavity and
by simultaneously tuning the internal and external modes of the laser. We find
that the precise location of the pivot point of the grating in our laser is
less critical than commonly believed. The general applicability of the method,
combined with the compact portable mechanical and electronic design, makes it
well suited for both research and industrial applications.Comment: 5 pages, 5 figure
Production of Aflatoxin on Damaged Corn Under Controlled Environmental Conditions
Aflatoxin B1 production by Aspergillus flavus (NRRL 6432) was determined on physically damaged corn stored at 35,25 and 20°C and at relative humidities of 97 and 92%. Production at lower relative humidities of 80 and 85% were also tested at 25°C. Production lag times were significantly different for all test conditions. Lag times ranged from 46 h at 97% relative humidity and 35°C to 173. 8 h at 20°C and 92% relative humidity. Aflatoxin B, concentration doubled every 6 to 10 hours after a level of 10 ppb had been reached. Production rate constants were not significantly different between temperatures at 97% relative humidity; however, significant differences in the production rate constant were observed between 97 and 92% relative humidities evaluated at 25°C and between 25 and 35 °C evaluated at 92% relative humidity
Measurement of the 6S-7S transition polarizablility in atomic cesium and an improved test of the standard model
The ratio of the off-diagonal hyperfine amplitude to the tensor transition
polarizability (Mhf/beta) for the 6S-7S transition in cesium has been measured.
The value of beta=27.024(43)(expt)(67)(theory)a_0^3 is then obtained using an
accurate semi-empirical value of Mhf. This is combined with a previous
measurement of parity nonconservation in atomic cesium and previous atomic
structure calculations to determine the value of the weak charge. The
uncertainties in the atomic structure calculations are updated (and reduced) in
light of new experimental tests. The result Q_W=-72.06(28)(expt) (34)(theory)
differs from the prediction of the standard model of elementary particle
physics by 2.5 sigma.Comment: 12 pages, 1 figur
Atomic wave packet dynamics in finite time-dependent optical lattices
Atomic wave packets in optical lattices which are both spatially finite and
time-dependent exhibit many striking similarities with light pulses in photonic
crystals. We analytically characterize the transmission properties of such a
potential geometry for an ideal gas in terms of a position-dependent band
structure. In particular, we find that at specific energies, wave packets at
the center of the finite lattice may be enclosed by pairs of band gaps. These
act as mirrors between which the atomic wave packet is reflected, thereby
effectively yielding a matter wave cavity. We show that long trapping times may
be obtained in such a resonator and investigate the collapse and revival
dynamics of the atomic wave packet by numerical evaluation of the Schr\"odinger
equation
Versatile transporter apparatus for experiments with optically trapped Bose-Einstein condensates
We describe a versatile and simple scheme for producing magnetically and
optically-trapped Rb-87 Bose-Einstein condensates, based on a moving-coil
transporter apparatus. The apparatus features a TOP trap that incorporates the
movable quadrupole coils used for magneto-optical trapping and long-distance
magnetic transport of atomic clouds. As a stand-alone device, this trap allows
for the stable production of condensates containing up to one million atoms. In
combination with an optical dipole trap, the TOP trap acts as a funnel for
efficient loading, after which the quadrupole coils can be retracted, thereby
maximizing optical access. The robustness of this scheme is illustrated by
realizing the superfluid-to-Mott insulator transition in a three-dimensional
optical lattice
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