777 research outputs found
Quantum reflection of atoms from a solid surface at normal incidence
We observed quantum reflection of ultracold atoms from the attractive
potential of a solid surface. Extremely dilute Bose-Einstein condensates of
^{23}Na, with peak density 10^{11}-10^{12}atoms/cm^3, confined in a weak
gravito-magnetic trap were normally incident on a silicon surface. Reflection
probabilities of up to 20 % were observed for incident velocities of 1-8 mm/s.
The velocity dependence agrees qualitatively with the prediction for quantum
reflection from the attractive Casimir-Polder potential. Atoms confined in a
harmonic trap divided in half by a solid surface exhibited extended lifetime
due to quantum reflection from the surface, implying a reflection probability
above 50 %.Comment: To appear in Phys. Rev. Lett. (December 2004)5 pages, 4 figure
Dynamical Instability of a Doubly Quantized Vortex in a Bose-Einstein condensate
Doubly quantized vortices were topologically imprinted in Na
condensates, and their time evolution was observed using a tomographic imaging
technique. The decay into two singly quantized vortices was characterized and
attributed to dynamical instability. The time scale of the splitting process
was found to be longer at higher atom density.Comment: 5 pages, 4 figure
Psychological Safety and Norm Clarity in Software Engineering Teams
In the software engineering industry today, companies primarily conduct their
work in teams. To increase organizational productivity, it is thus crucial to
know the factors that affect team effectiveness. Two team-related concepts that
have gained prominence lately are psychological safety and team norms. Still,
few studies exist that explore these in a software engineering context.
Therefore, with the aim of extending the knowledge of these concepts, we
examined if psychological safety and team norm clarity associate positively
with software developers' self-assessed team performance and job satisfaction,
two important elements of effectiveness.
We collected industry survey data from practitioners (N = 217) in 38
development teams working for five different organizations. The result of
multiple linear regression analyses indicates that both psychological safety
and team norm clarity predict team members' self-assessed performance and job
satisfaction. The findings also suggest that clarity of norms is a stronger
(30\% and 71\% stronger, respectively) predictor than psychological safety.
This research highlights the need to examine, in more detail, the
relationship between social norms and software development. The findings of
this study could serve as an empirical baseline for such, future work.Comment: Submitted to CHASE'201
Recommended from our members
The Observations Of The X-Ray Source Hz Herculis-Hercules X-1
NASAESASRCAstronom
Fifty Years of IMF Variation: The Intermediate-Mass Stars
I track the history of star count estimates of the Milky Way field star and
open cluster IMFs, concentrating on the neglected mass range from 1 to 15
M. The prevalent belief in a universal IMF appears to be without
basis for this mass range. Two recent estimates of the field star IMF using
different methods and samples give values of the average logarithmic slope
between -1.7 and -2.1 in the mass range 1.1 to 4 M. Two
older estimates between 2 and 15 M disagree severely; the field IMF
in this range is essentially unknown from star counts. Variations in
among open cluster IMFs in this mass range have not decreased despite numerous
detailed studies, even for studies using homogeneous data and reduction
procedures and including only clusters with a significant mass range. These
cluster variations \textit{might} be due to the combined effects of sampling,
systematic errors, stellar evolution uncertainties, dynamical evolution, and
unresolved binaries. If so, then the cluster data are consistent with a
universal IMF, but are also consistent with sizeable variations. The cluster
data do not allow an estimate of an average IMF or because the average
depends on the choice of weighting procedure and other effects. If the spread
in cluster IMFs is in excess of the effects listed above, real IMF variations
must occur that do not depend much on physical conditions explored so far. The
complexity of the star formation process seen in observations and simulations
suggests that large realization-to-realization differences might be expected,
in which case an individual cluster IMF would be in part the product of
evolutionary contingency in star formation, and the function of interest is the
probability distribution of IMF parameters.Comment: 18 pages, including 4 figures: invited talk presented at the
conference on "IMF@50: The Stellar Initial Mass Function Fifty Years Later"
held at Abbazia di Spineto, Siena, Italy, May 2004; to be published by Kluwer
Academic Publishers, edited by E. Corbelli, F. Palla, and H. Zinnecke
High LET, passive space radiation dosimetry and spectrometry
The development of high linear energy transfer (LET), passive radiation dosimetry and spectrometry is needed for the purpose of accurate determination of equivalent doses and assessment of health risks to astronauts on long duration missions. Progress in the following research areas is summerized: intercomparisons of cosmic ray equivalent dose and LET spectra measurements between STS missions and between astronauts; increases LET spectra measurement accuracy with ATAS; space radiation measurements for intercomparisons of passive (PNTD, TLD, TRND, Emulsion) and active (TEPC, RME-111) dosimeters; interaction of cosmic ray particles with nuclei in matter; radiation measurements after long duration space exposures; ground based dosimeter calibrations; neutron detector calibrations; radiation measurements on Soviet/Russian spacecraft; space radiation measurements under thin shielding; and space radiation
Towards quantum magnetism with ultracold atoms
22nd International Conference on Atomic PhysicsAt ICAP we presented the efforts and progress at MIT towards using ultracold atoms for the realization of various forms of quantum magnetism. These efforts include a study of fermions with strong repulsive interactions in which we obtained evidence for a phase transition to itinerant ferromagnetism, the characterization of cold atom systems by noise measurements, and a new adiabatic gradient demagnetization cooling scheme which has enabled us to realize temperatures of less than 350 picokelvin and spin temperatures of less than 50 picokelvin in optical lattices. These are the lowest temperatures ever measured in any physical system
Velocity Dispersion of Dissolving OB Associations Affected by External Pressure of Formation Environment
This paper presents a possible way to understand dissolution of OB
associations (or groups). Assuming rapid escape of parental cloud gas from
associations, we show that the shadow of the formation environment for
associations can be partially imprinted on the velocity dispersion at their
dissolution. This conclusion is not surprising as long as associations are
formed in a multiphase interstellar medium, because the external pressure
should suppress expansion caused by the internal motion of the parental clouds.
Our model predicts a few km s as the internal velocity dispersion.
Observationally, the internal velocity dispersion is km s which
is smaller than our prediction. This suggests that the dissipation of internal
energy happens before the formation of OB associations.Comment: 6 pages. AJ accepte
Identification of red high proper-motion objects in Tycho-2 and 2MASS catalogues using Virtual Observatory tools
Aims: With available Virtual Observatory tools, we looked for new M dwarfs in
the solar neighbourhood and M giants with high tangential velocities. Methods:
From an all-sky cross-match between the optical Tycho-2 and the near-infrared
2MASS catalogues, we selected objects with proper motions >50mas/yr and very
red V-Ks colours. For the most interesting targets, we collected
multi-wavelength photometry, constructed spectral energy distributions,
estimated effective temperatures and surface gravities from fits to atmospheric
models, performed time-series analysis of ASAS V-band light curves, and
assigned spectral types from low-resolution spectroscopy obtained with CAFOS at
the 2.2m Calar Alto telescope. Results: We got a sample of 59 bright red high
proper-motion objects, including fifty red giants, four red dwarfs, and five
objects reported in this work for the first time. The five new stars have
magnitudes V~10.8-11.3mag, reduced proper motions midway between known dwarfs
and giants, near-infrared colours typical of giants, and effective temperatures
Teff~2900-3400K. From our time-series analysis, we discovered a long secondary
period in Ruber 4 and an extremely long primary period in Ruber 6. With the
CAFOS spectra, we confirmed the red giant nature of Ruber 7 and 8, the last of
which seems to be one of the brightest metal-poor M giants ever identified.Comment: Accepted in Astronomy & Astrophysic
- …