9,297 research outputs found
Detection of Operator Performance Breakdown as an Automation Triggering Mechanism
Performance breakdown (PB) has been anecdotally described as a state where the human operator "loses control of context" and "cannot maintain required task performance." Preventing such a decline in performance is critical to assure the safety and reliability of human-integrated systems, and therefore PB could be useful as a point at which automation can be applied to support human performance. However, PB has never been scientifically defined or empirically demonstrated. Moreover, there is no validated objective way of detecting such a state or the transition to that state. The purpose of this work is: 1) to empirically demonstrate a PB state, and 2) to develop an objective way of detecting such a state. This paper defines PB and proposes an objective method for its detection. A human-in-the-loop study was conducted: 1) to demonstrate PB by increasing workload until the subject reported being in a state of PB, and 2) to identify possible parameters of a detection method for objectively identifying the subjectively-reported PB point, and 3) to determine if the parameters are idiosyncratic to an individual/context or are more generally applicable. In the experiment, fifteen participants were asked to manage three concurrent tasks (one primary and two secondary) for 18 minutes. The difficulty of the primary task was manipulated over time to induce PB while the difficulty of the secondary tasks remained static. The participants' task performance data was collected. Three hypotheses were constructed: 1) increasing workload will induce subjectively-identified PB, 2) there exists criteria that identifies the threshold parameters that best matches the subjectively-identified PB point, and 3) the criteria for choosing the threshold parameters is consistent across individuals. The results show that increasing workload can induce subjectively-identified PB, although it might not be generalizable-only 12 out of 15 participants declared PB. The PB detection method based on signal detection analysis was applied to the performance data and the results showed that PB can be identified using the method, particularly when the values of the parameters for the detection method were calibrated individually
A Multi-level Algorithm for Quantum-impurity Models
A continuous-time path integral Quantum Monte Carlo method using the
directed-loop algorithm is developed to simulate the Anderson single-impurity
model in the occupation number basis. Although the method suffers from a sign
problem at low temperatures, the new algorithm has many advantages over
conventional algorithms. For example, the model can be easily simulated in the
Kondo limit without time discretization errors. Further, many observables
including the impurity susceptibility and a variety of fermionic observables
can be calculated efficiently. Finally the new approach allows us to explore a
general technique, called the multi-level algorithm, to solve the sign problem.
We find that the multi-level algorithm is able to generate an exponentially
large number of configurations with an effort that grows as a polynomial in
inverse temperature such that configurations with a positive sign dominate over
those with negative signs. Our algorithm can be easily generalized to other
multi-impurity problems.Comment: 9 pages, 8 figure
On the Sign Problem in the Hirsch-Fye Algorithm for Impurity Problems
We show that there is no fermion sign problem in the Hirsch and Fye algorithm
for the single-impurity Anderson model. Beyond the particle-hole symmetric case
for which a simple proof exists, this has been known only empirically. Here we
prove the nonexistence of a sign problem for the general case by showing that
each spin trace for a given Ising configuration is separately positive. We
further use this insight to analyze under what conditions orbitally degenerate
Anderson models or the two-impurity Anderson model develop a sign.Comment: 2 pages, no figure; published versio
Human microglial cells synthesize albumin in brain
Albumin has been implicated in Alzheimer's disease since it can bind to and transport amyloid beta, the causative agent; albumin is also a potent inhibitor of amyloid beta polymerization. In a pilot phase study of Human Brain Proteome Project, we found evidence that albumin may be synthesized in immortalized human microglial cells, human primary microglial cells, and human fetal and adult brain tissues. We also found the synthesis and secretion is enhanced upon microglial activation by Amyloid [beta]~1-42~, lipopolysaccharide treatment or human Alzheimer's brain
Occlusal reduction of unilateral molars influences change of stress-related hormones in rats
In order to investigate the change of stress-related hormones by dental occlusal reduction, we ground molars in Sprague-Dawley (SD) rats and evaluated the effect on hormone levels. Thirteen and 18 weeks after occlusal reduction, cortisol concentration was increased 2.75 and 2.17 fold respectively, whereas corticosterone concentration was slightly elevated by 31.2% and 13.5%, respectively. Body weight was slightly decreased, but feed and water intake, and blood chemistry were the same in the experimental group as in the control group. Our results suggest that unilateral molar occlusal reduction may influence cortisol and corticosterone levels and the endocrine system, leading to hormone imbalance through the body.
Chemical composition-dependent hygroscopic behavior of individual ambient aerosol particles collected at a coastal site
This study investigated the hygroscopic behavior of individual ambient aerosol particles collected at a coastal site of Jeju Island, South Korea. The size of the particles changes along with the phase transitions during humidification and dehydration processes, and the chemical compositions of the particles were determined by optical microscopy and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDX), respectively. Of the 39 particles analyzed, 24 were aged sea spray aerosols (SSAs), with diverse mixing ratios of Cl− and NO3-.
The ambient SSAs exhibited multiple deliquescence and efflorescence transitions that were dominantly influenced by NaCl, NaNO3, MgCl2, Mg(NO3)2, and organic species covering the surface of the aged SSAs. For Cl-rich SSAs with X(Na,Mg)Cl>0.4, although
some particles showed very slow water uptake at low relative humidity levels (RH ≃30 %), two major transitions were observed during the humidification process. The first was at RH ≃63.8 %, regardless of their chemical compositions, which is the mutual deliquescence relative humidity (MDRH) level; and the second was at RH 67.5 % to 73.5 %, depending on their chemical compositions, which are the final deliquescence relative humidity (DRH) levels. During the dehydration process, the Cl-rich SSAs showed single-stage efflorescence at RH 33.0 % to 50.5 %, due to simultaneous heterogeneous crystallization of inorganic salts. For Cl-depleted SSAs with X(Na,Mg)Cl<0.4, two prompt deliquescence transitions were observed during the humidification process. The first was at MDRH 63.8 %, and the second was at RH 65.4 % to 72.9 %. The mutual deliquescence transition was more distinguishable for Cl-depleted SSAs. During the dehydration process, step-wise transitions were observed at efflorescence RH levels (ERH 24.6 % to 46.0 % and 17.9 % to 30.5 %), depending on their chemical compositions.
Additionally, aged mineral particles showed partial or complete phase changes with varying RH due to the presence of SSAs and/or NO3- species. In contrast, non-reacted mineral and Fe-rich particles maintained
their size during the entire hygroscopic process. The mixture particles of organic and ammonium sulfate (AS) exhibited lower deliquescence and efflorescence RH levels compared to pure AS salt, highlighting the impact of organic species on the hygroscopic behavior of AS. These findings emphasize the complexity of atmospheric aerosols and the importance of considering their composition and mixing state when modeling their hygroscopic behavior and subsequent atmospheric impacts.</p
Quantum transport through a DNA wire in a dissipative environment
Electronic transport through DNA wires in the presence of a strong
dissipative environment is investigated. We show that new bath-induced
electronic states are formed within the bandgap. These states show up in the
linear conductance spectrum as a temperature dependent background and lead to a
crossover from tunneling to thermal activated behavior with increasing
temperature. Depending on the strength of the electron-bath coupling, the
conductance at the Fermi level can show a weak exponential or even an algebraic
length dependence. Our results suggest a new environmental-induced transport
mechanism. This might be relevant for the understanding of molecular conduction
experiments in liquid solution, like those recently performed on poly(GC)
oligomers in a water buffer (B. Xu et al., Nano Lett 4, 1105 (2004)).Comment: 5 pages, 3 figure
Reduction of high reset currents in unipolar resistance switching Pt/SrTiOx/Pt capacitors using acceptor doping
The high reset current, IR, in unipolar resistance switching is an important
issue which should be resolved for practical applications in nonvolatile
memories. We showed that,during the forming and set processes, the compliance
current, Icomp, can work as a crucial parameter to reduce IR. Doping with Co or
Mn can significantly reduce the leakage current in capacitors made using SrTiOx
film, opening a larger operation window for Icomp. By decreasing Icomp with
acceptor doping, we could reduce IR in SrTiOx films by a factor of
approximately 20. Our work suggests that the decrease of Icomp by carrier
doping could be a viable alternative for reducing IR in unipolar resistance
switching.Comment: 14 pages, 3 figure
Effect of synthesis conditions on formation pathways of metal organic framework (MOF-5) Crystals
Metal Organic Frameworks (MOFs) represent a class of nanoporous crystalline materials with far reaching potential in gas storage, catalysis, and medical devices. We investigated the effects of synthesis process parameters on production of MOF-5 from terephthalic acid and zinc nitrate in diethylformamide. Under favorable synthesis conditions, we systematically mapped a solid formation diagram in terms of time and temperature for both stirred and unstirred conditions. The synthesis of MOF-5 has been previously reported as a straightforward reaction progressing from precursor compounds in solution directly to the final MOF-5 solid phase product. However, we show that the solid phase formation process is far more complex, invariably transferring through metastable intermediate crystalline phases before the final MOF-5 phase is reached, providing new insights into the formation pathways of MOFs. We also identify process parameters suitable for scale-up and continuous manufacturing of high purity MOF-5
Scanned Potential Microscopy of Edge and Bulk Currents in the Quantum Hall Regime
Using an atomic force microscope as a local voltmeter, we measure the Hall
voltage profile in a 2D electron gas in the quantum Hall (QH) regime. We
observe a linear profile in the bulk of the sample in the transition regions
between QH plateaus and a distinctly nonlinear profile on the plateaus. In
addition, localized voltage drops are observed at the sample edges in the
transition regions. We interpret these results in terms of theories of edge and
bulk currents in the QH regime.Comment: 4 pages, 5 figure
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