10,251 research outputs found
Decoherence of a single-ion qubit immersed in a spin-polarized atomic bath
We report on the immersion of a spin-qubit encoded in a single trapped ion
into a spin-polarized neutral atom environment, which possesses both continuous
(motional) and discrete (spin) degrees of freedom. The environment offers the
possibility of a precise microscopic description, which allows us to understand
dynamics and decoherence from first principles. We observe the spin dynamics of
the qubit and measure the decoherence times (T1 and T2), which are determined
by the spin-exchange interaction as well as by an unexpectedly strong
spin-nonconserving coupling mechanism
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"If We Don't Produce, Bring Another:" Work Organization and Tomato Worker Health.
Objectives: Specific work processes and management structures that contribute to high rates of occupational illness and injury in agricultural industries are not well described in academic literature. This qualitative study of work organization in the U.S. fresh tomato industry investigates how work processes and management structures impact tomato workers' occupational health. Methods: After conducting literature review and key informant interviews, semi-structured interviews and focus groups were conducted with 36 individuals with experience working in the U.S. fresh tomato industry. Interviews and focus groups were audio-recorded, transcribed, coded, and analyzed using a modified grounded theory approach. Results: These data indicate that participants endured income insecurity and hazardous supervisory practices, including wage theft, retaliation, intimidation, and humiliation, that put them at risk of preventable illness and injury. Support from workers' organizations and health-conscious supervisory practices helped mitigate some of these occupational hazards. Conclusion: Participants' adverse work experiences may be considered sequelae of workers' lack of job control and positions of socioeconomic structural vulnerability. Other aspects of tomato work organization, including health-conscious supervisory practices and the involvement of workers' organizations, indicate that modifying work organization to better safeguard health is possible. Such modifications present compelling opportunities for employers, employees, organizations, community and government leaders, and health care professionals to help create healthier occupational environments for tomato workers
Lessons Learned from Case Histories Performance of Earth Dams, Embankments, and Natural Slopes
Polaritons and Pairing Phenomena in Bose--Hubbard Mixtures
Motivated by recent experiments on cold atomic gases in ultra high finesse
optical cavities, we consider the problem of a two-band Bose--Hubbard model
coupled to quantum light. Photoexcitation promotes carriers between the bands
and we study the non-trivial interplay between Mott insulating behavior and
superfluidity. The model displays a global U(1) X U(1) symmetry which supports
the coexistence of Mott insulating and superfluid phases, and yields a rich
phase diagram with multicritical points. This symmetry property is shared by
several other problems of current experimental interest, including
two-component Bose gases in optical lattices, and the bosonic BEC-BCS crossover
problem for atom-molecule mixtures induced by a Feshbach resonance. We
corroborate our findings by numerical simulations.Comment: 4 pages, 3 figure
The Roles of Symbols in Neural-based AI: They are Not What You Think!
We propose that symbols are first and foremost external communication tools
used between intelligent agents that allow knowledge to be transferred in a
more efficient and effective manner than having to experience the world
directly. But, they are also used internally within an agent through a form of
self-communication to help formulate, describe and justify subsymbolic patterns
of neural activity that truly implement thinking. Symbols, and our languages
that make use of them, not only allow us to explain our thinking to others and
ourselves, but also provide beneficial constraints (inductive bias) on learning
about the world. In this paper we present relevant insights from neuroscience
and cognitive science, about how the human brain represents symbols and the
concepts they refer to, and how today's artificial neural networks can do the
same. We then present a novel neuro-symbolic hypothesis and a plausible
architecture for intelligent agents that combines subsymbolic representations
for symbols and concepts for learning and reasoning. Our hypothesis and
associated architecture imply that symbols will remain critical to the future
of intelligent systems NOT because they are the fundamental building blocks of
thought, but because they are characterizations of subsymbolic processes that
constitute thought.Comment: 28 page
Functional Stability of Transfemoral Amputee Gait Using the 3R80 and Total Knee 2000 Prosthetic Knee Units
Prosthetic knee designs have become extremely sophisticated compared to early constant friction single axis mechanisms. Today, prosthetists and physicians have a wide variety of components to choose from for their transfemoral amputee patients. Unfortunately, there are little quantitative data comparing the performance of different types of prosthetic components, and prosthetic prescription is often based on empirical knowledge and experience, rather than objective comparison of prosthetic designs. This study used gait analysis to objectively evaluate the stability characteristics of two types of prosthetic knee designs, the polycentric Total Knee 2000 (Ossur, Aliso Viejo, CA) and the single axis 3R80 stance control knee (Otto Bock Healthcare, Minneapolis, MN). Five healthy, active transfemoral amputees participated in this study by completing two gait analysis sessions, one with the Total Knee 2000 and one with the 3R80. At the end of each session, subjects were asked to complete a questionnaire for comparison of their subjective preferences with the objective biomechanical measures from the gait analysis. Kinematic and kinetic gait data were collected. Stride and temporal parameters (i.e., velocity, cadence, stride length, step length, stance and swing phase durations, and single and double support durations), joint angles and moments were computed from the Vicon data. A within subjects statistical analysis was then conducted, using repeated measures ANOVA, to determine if there were significant differences in performance between the two knee designs. The stride and temporal parameters computed in this study indicated that the Total Knee 2000 demonstrated a high degree of overall stability compared to the 3R80. The differences in inherent mechanical stability in the Total Knee 2000 and the 3R80 resulted in different calculated hip moments. The corresponding required hip moments indicated that the relative stability of the two knee designs changed throughout the gait cycle due to the polycentric nature of the Total Knee 2000. Specifically, the Total Knee 2000 was found to be less stable than the 3R80 in early stance and more stable than the 3R80 in mid- and late-stance. In addition to the biomechanical evidence of increased stability with the Total Knee 2000, the responses to the subjective questionnaires indicated that most subjects felt more stable and more confident bearing weight on the Total Knee 2000 than the 3R80
Self-Modification of Policy and Utility Function in Rational Agents
Any agent that is part of the environment it interacts with and has versatile
actuators (such as arms and fingers), will in principle have the ability to
self-modify -- for example by changing its own source code. As we continue to
create more and more intelligent agents, chances increase that they will learn
about this ability. The question is: will they want to use it? For example,
highly intelligent systems may find ways to change their goals to something
more easily achievable, thereby `escaping' the control of their designers. In
an important paper, Omohundro (2008) argued that goal preservation is a
fundamental drive of any intelligent system, since a goal is more likely to be
achieved if future versions of the agent strive towards the same goal. In this
paper, we formalise this argument in general reinforcement learning, and
explore situations where it fails. Our conclusion is that the self-modification
possibility is harmless if and only if the value function of the agent
anticipates the consequences of self-modifications and use the current utility
function when evaluating the future.Comment: Artificial General Intelligence (AGI) 201
The Starburst in the Central Kiloparsec of Markarian 231
We present VLBA observations at 0.33 and 0.61 GHz, and VLA observations
between 5 and 22 GHz, of subkiloparsec scale radio emission from Mrk 231. In
addition to jet components clearly associated with the AGN, we also find a
smooth extended component of size 100 - 1000 pc most probably related to the
purported massive star forming disk in Mrk 231. The diffuse radio emission from
the disk is found to have a steep spectrum at high frequencies, characteristic
of optically thin synchrotron emission. The required relativistic particle
density in the disk can be produced by a star formation rate of 220 Msolar/yr
in the central kiloparsec. At low frequencies the disk is absorbed, most likely
by ionized gas with an emission measure of 8 x 10^5 pc cm-6. We have also
identified 4 candidate radio supernovae that, if confirmed, represent direct
evidence for ongoing star formation in the central kiloparsec.Comment: in press at ApJ for v. 519 July 1999, 14 page LaTeX document includes
6 postscript figure
Regulation by vitamin D metabolites of messenger ribonucleic acid for preproparathyroid hormone in isolated bovine parathyroid cells.
Fe XVII X-ray Line Ratios for Accurate Astrophysical Plasma Diagnostics
New laboratory measurements using an Electron Beam Ion Trap (EBIT) and an
x-ray microcalorimeter are presented for the n=3 to n=2 Fe XVII emission lines
in the 15 {\AA} to 17 {\AA} range, along with new theoretical predictions for a
variety of electron energy distributions. This work improves upon our earlier
work on these lines by providing measurements at more electron impact energies
(seven values from 846 to 1185 eV), performing an in situ determination of the
x-ray window transmission, taking steps to minimize the ion impurity
concentrations, correcting the electron energies for space charge shifts, and
estimating the residual electron energy uncertainties. The results for the
3C/3D and 3s/3C line ratios are generally in agreement with the closest theory
to within 10%, and in agreement with previous measurements from an independent
group to within 20%. Better consistency between the two experimental groups is
obtained at the lowest electron energies by using theory to interpolate, taking
into account the significantly different electron energy distributions.
Evidence for resonance collision effects in the spectra is discussed.
Renormalized values for the absolute cross sections of the 3C and 3D lines are
obtained by combining previously published results, and shown to be in
agreement with the predictions of converged R-matrix theory. This work
establishes consistency between results from independent laboratories and
improves the reliability of these lines for astrophysical diagnostics. Factors
that should be taken into account for accurate diagnostics are discussed,
including electron energy distribution, polarization, absorption/scattering,
and line blends.Comment: 29 pages, including 7 figure
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