7,031 research outputs found
A structure marker study for Pd_2Si formation: Pd moves in epitaxial Pd_2Si
A sample with the configuration Si (111)/single crystalline Pd_2Si/polycrystalline Pd_2Si/Pd is used to study the dominant moving species during subsequent Pd_2Si formation by annealing at 275 °C. The interface between monocrystalline and polycrystalline Pd_2Si is used as a marker to monitor the dominant moving species. The result shows that Pd is the dominant moving species in the monocrystal
Trajectory sensitivity analysis of hybrid systems
The development of trajectory sensitivity analysis for hybrid systems, such as power systems, is presented in the paper. A hybrid system model which has a differential-algebraic-discrete (DAD) structure is proposed. This model forms the basis for the subsequent sensitivity analysis. Crucial to the analysis is the development of jump conditions describing the behavior of sensitivities at discrete events, such as switching and state resetting. The efficient computation of sensitivities is discussed. A number of examples are presented to illustrate various aspects of the theory. It is shown that trajectory sensitivities provide insights into system behavior which cannot be obtained from traditional simulation
Model reduction in power systems using Krylov subspace methods
This paper describes the use of Krylov subspace methods in the model reduction of power systems. Additionally, a connection between the Krylov subspace model reduction and coherency in power systems is proposed, aiming at retaining some physical relationship between the reduced and the original system
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Mental health stigma
Comparing self-reports to administrative records, we find that survey respondents are significantly more likely to under-report mental illnesses compared to other health conditions. This behavior is consistent with the existence of stigma of mental illnesses. We show that stigma can play a role in determining health-seeking behavior
Dynamic security-constrained rescheduling of power systems using trajectory sensitivities
In the deregulated environment of power systems, the transmission networks are often operated close to their maximum capacity to achieve transfer of power. Besides, the operators must operate the system to satisfy its dynamic stability constraints under credible contingencies. This paper provides a method using trajectory sensitivity to reschedule power generation to ensure system stability for a set of credible contingencies while satisfying its economic goal. System modeling issue is not a limiting concern in this method, and hence, the technique can be used as a preventive control scheme for system operators in real time
Superfluid, Mott-Insulator, and Mass-Density-Wave Phases in the One-Dimensional Extended Bose-Hubbard Model
We use the finite-size density-matrix-renormalization-group (FSDMRG) method
to obtain the phase diagram of the one-dimensional () extended
Bose-Hubbard model for density in the plane, where and
are, respectively, onsite and nearest-neighbor interactions. The phase diagram
comprises three phases: Superfluid (SF), Mott Insulator (MI) and Mass Density
Wave (MDW). For small values of and , we get a reentrant SF-MI-SF phase
transition. For intermediate values of interactions the SF phase is sandwiched
between MI and MDW phases with continuous SF-MI and SF-MDW transitions. We
show, by a detailed finite-size scaling analysis, that the MI-SF transition is
of Kosterlitz-Thouless (KT) type whereas the MDW-SF transition has both KT and
two-dimensional-Ising characters. For large values of and we get a
direct, first-order, MI-MDW transition. The MI-SF, MDW-SF and MI-MDW phase
boundaries join at a bicritical point at (.Comment: 10 pages, 15 figure
Simulation and optimization in an AGC system after deregulation
In this paper, the traditional automatic generation control (AGC) two-area system is modified to take into account the effect of bilateral contracts on the dynamics. The concept of distribution companies (DISCO) participation matrix to simulate these bilateral contracts is introduced and reflected in the two-area block diagram. Trajectory sensitivities are used to obtain optimal parameters of the system using a gradient Newton algorithm
Algorithmic Verification of Asynchronous Programs
Asynchronous programming is a ubiquitous systems programming idiom to manage
concurrent interactions with the environment. In this style, instead of waiting
for time-consuming operations to complete, the programmer makes a non-blocking
call to the operation and posts a callback task to a task buffer that is
executed later when the time-consuming operation completes. A co-operative
scheduler mediates the interaction by picking and executing callback tasks from
the task buffer to completion (and these callbacks can post further callbacks
to be executed later). Writing correct asynchronous programs is hard because
the use of callbacks, while efficient, obscures program control flow.
We provide a formal model underlying asynchronous programs and study
verification problems for this model. We show that the safety verification
problem for finite-data asynchronous programs is expspace-complete. We show
that liveness verification for finite-data asynchronous programs is decidable
and polynomial-time equivalent to Petri Net reachability. Decidability is not
obvious, since even if the data is finite-state, asynchronous programs
constitute infinite-state transition systems: both the program stack and the
task buffer of pending asynchronous calls can be potentially unbounded.
Our main technical construction is a polynomial-time semantics-preserving
reduction from asynchronous programs to Petri Nets and conversely. The
reduction allows the use of algorithmic techniques on Petri Nets to the
verification of asynchronous programs.
We also study several extensions to the basic models of asynchronous programs
that are inspired by additional capabilities provided by implementations of
asynchronous libraries, and classify the decidability and undecidability of
verification questions on these extensions.Comment: 46 pages, 9 figure
T-Cell Assays for Tuberculosis Infection: Deriving Cut-Offs for Conversions Using Reproducibility Data
Although interferon-gamma release assays (IGRA) are promising alternatives to the tuberculin skin test, interpretation of repeated testing results is hampered by lack of evidence on optimal cut-offs for conversions and reversions. A logical start is to determine the within-person variability of T-cell responses during serial testing.We performed a pilot study in India, to evaluate the short-term reproducibility of QuantiFERON-TB Gold In Tube assay (QFT) among 14 healthcare workers (HCWs) who underwent 4 serial QFT tests on day 0, 3, 9 and 12. QFT ELISA was repeated twice on the same sets of specimens. We assessed two types of reproducibility: 1) test-retest reproducibility (between-test variability), and 2) within-person reproducibility over time. Test-retest reproducibility: with dichotomous test results, extremely high concordance was noticed between two tests performed on the same sets of specimens: of the 56 samples, the test and re-test results agreed for all but 2 individuals (kappa = 0.94). Discordance was noted in subjects who had IFN-gamma values around the cut-off point, with both increases and decreases noted. With continuous IFN-gamma results, re-test results tended to produce higher estimates of IFN-gamma than the original test. Within-person reproducibility: when continuous IFN-gamma data were analyzed, the within-person reproducibility was moderate to high. While persons with negative QFT results generally stayed negative, positive results tended to vary over time. Our data showed that increases of more than 16% in the IFN-gamma levels are statistically improbable in the short-term.Conservatively assuming that long-term variability might be at least twice higher than short-term, we hypothesize that a QFT conversion requires two conditions to be met: 1) change from negative to positive result, and 2) at least 30% increase in the baseline IFN-gamma response. Larger studies are needed to confirm our preliminary findings, and determine the conversion thresholds for IGRAs
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