41 research outputs found
Learning in Cooperative Multiagent Systems Using Cognitive and Machine Models
Developing effective Multi-Agent Systems (MAS) is critical for many
applications requiring collaboration and coordination with humans. Despite the
rapid advance of Multi-Agent Deep Reinforcement Learning (MADRL) in cooperative
MAS, one major challenge is the simultaneous learning and interaction of
independent agents in dynamic environments in the presence of stochastic
rewards. State-of-the-art MADRL models struggle to perform well in Coordinated
Multi-agent Object Transportation Problems (CMOTPs), wherein agents must
coordinate with each other and learn from stochastic rewards. In contrast,
humans often learn rapidly to adapt to nonstationary environments that require
coordination among people. In this paper, motivated by the demonstrated ability
of cognitive models based on Instance-Based Learning Theory (IBLT) to capture
human decisions in many dynamic decision making tasks, we propose three
variants of Multi-Agent IBL models (MAIBL). The idea of these MAIBL algorithms
is to combine the cognitive mechanisms of IBLT and the techniques of MADRL
models to deal with coordination MAS in stochastic environments from the
perspective of independent learners. We demonstrate that the MAIBL models
exhibit faster learning and achieve better coordination in a dynamic CMOTP task
with various settings of stochastic rewards compared to current MADRL models.
We discuss the benefits of integrating cognitive insights into MADRL models.Comment: 22 pages, 5 figures, 2 table
Geometric characterizations for strong minima with applications to nuclear norm minimization problems
In this paper, we introduce several geometric characterizations for strong
minima of optimization problems. Applying these results to nuclear norm
minimization problems allows us to obtain new necessary and sufficient
quantitative conditions for this important property. Our characterizations for
strong minima are weaker than the Restricted Injectivity and Nondegenerate
Source Condition, which are usually used to identify solution uniqueness of
nuclear norm minimization problems. Consequently, we obtain the minimum (tight)
bound on the number of measurements for (strong) exact recovery of low-rank
matrices.Comment: 41 page
An Inertial Block Majorization Minimization Framework for Nonsmooth Nonconvex Optimization
In this paper, we introduce TITAN, a novel inerTIal block majorizaTion
minimizAtioN framework for non-smooth non-convex optimization problems. To the
best of our knowledge, TITAN is the first framework of block-coordinate update
method that relies on the majorization-minimization framework while embedding
inertial force to each step of the block updates. The inertial force is
obtained via an extrapolation operator that subsumes heavy-ball and
Nesterov-type accelerations for block proximal gradient methods as special
cases. By choosing various surrogate functions, such as proximal, Lipschitz
gradient, Bregman, quadratic, and composite surrogate functions, and by varying
the extrapolation operator, TITAN produces a rich set of inertial
block-coordinate update methods. We study sub-sequential convergence as well as
global convergence for the generated sequence of TITAN. We illustrate the
effectiveness of TITAN on two important machine learning problems, namely
sparse non-negative matrix factorization and matrix completion.Comment: 32 page
Thermal effect on magnetoexciton energy spectra in monolayer transition metal dichalcogenides
It is widely comprehended that temperature may cause phonon-exciton
scattering, enhancing the energy level's linewidth and leading to some spectrum
shifts. However, in the present paper, we suggest a different mechanism that
allows the thermal motion of the exciton's center of mass (c.m.) to affect the
magnetoexciton energies in monolayer dichalcogenides (TMDCs). By the nontrivial
but precise separation of the c.m. motion from an exciton in a monolayer TMDC
with a magnetic field, we obtain an equation for the relative motion containing
a motional Stark term proportional to the c.m. pseudomomentum, related to the
temperature of the exciton gas but neglected in the previous studies. Solving
the Schr\"odinger equation without omitting the motional Stark potential at
room temperature shows approximately a few meV thermal-magnetic shifts in the
exciton energies, significant enough for experimental detection. Moreover, this
thermal effect causes a change in exciton radius and diamagnetic coefficient
and enhances the exciton lifetime as a consequence. Surprisingly, the
thermoinduced motional Stark potential breaks the system's SO(2) symmetry,
conducting new peaks in the exciton absorption spectra at room temperature
besides those of the states. This mechanism could be extended for other
magnetoquasiparticles such as trions and biexcitons.Comment: 8 pages, 4 figures, 3 tables for main manuscript; 20 pages, 6
figures, 6 tables for supplementary. Published on Physical Review
Retrieval of material properties of monolayer transition-metal dichalcogenides from magnetoexciton energy spectra
Reduced exciton mass, polarizability, and dielectric constant of the
surrounding medium are essential properties for semiconduction materials, and
they can be extracted recently from the magnetoexciton energies. However, the
acceptable accuracy of the previously suggested method requires very high
magnetic intensity. Therefore, in the present paper, we propose an alternative
method of extracting these material properties from recently available
experimental magnetoexciton s-state energies in monolayer transition-metal
dichalcogenides (TMDCs). The method is based on the high sensitivity of exciton
energies to the material parameters in the Rytova-Keldysh model. It allows us
to vary the considered material parameters to get the best fit of the
theoretical calculation to the experimental exciton energies for the ,
, and states. This procedure gives values of the exciton reduced mass
and 2D polarizability. Then, the experimental magnetoexciton spectra compared
to the theoretical calculation gives also the average dielectric constant.
Concrete applications are presented only for monolayers WSe and WS from
the recently available experimental data. However, the presented approach is
universal and can be applied to other monolayer TMDCs. The mentioned fitting
procedure requires a fast and effective method of solving the Schr\"{o}dinger
of an exciton in monolayer TMDCs with a magnetic field. Therefore, we also
develop such a method in this study for highly accurate magnetoexciton
energies.Comment: 8 pages, 4 figures, 4 table
Performance analysis of multihop full-duplex NOMA systems with imperfect interference cancellation and near-field path-loss
Outage probability (OP) and potential throughput (PT) of multihop full-duplex (FD)
nonorthogonal multiple access (NOMA) systems are addressed in the present paper. More precisely,
two metrics are derived in the closed-form expressions under the impact of both imperfect successive
interference cancellation (SIC) and imperfect self-interference cancellation. Moreover, to model short
transmission distance from the transmit and receive antennae at relays, the near-field path-loss is
taken into consideration. Additionally, the impact of the total transmit power on the performance
of these metrics is rigorously derived. Furthermore, the mathematical framework of the baseline
systems is provided too. Computer-based simulations via the Monte Carlo method are given to
verify the accuracy of the proposed framework, confirm our findings, and highlight the benefits of
the proposed systems compared with the baseline one.Web of Science231art. no. 52
Awareness and preparedness of healthcare workers against the first wave of the COVID-19 pandemic: A cross-sectional survey across 57 countries.
BACKGROUND: Since the COVID-19 pandemic began, there have been concerns related to the preparedness of healthcare workers (HCWs). This study aimed to describe the level of awareness and preparedness of hospital HCWs at the time of the first wave. METHODS: This multinational, multicenter, cross-sectional survey was conducted among hospital HCWs from February to May 2020. We used a hierarchical logistic regression multivariate analysis to adjust the influence of variables based on awareness and preparedness. We then used association rule mining to identify relationships between HCW confidence in handling suspected COVID-19 patients and prior COVID-19 case-management training. RESULTS: We surveyed 24,653 HCWs from 371 hospitals across 57 countries and received 17,302 responses from 70.2% HCWs overall. The median COVID-19 preparedness score was 11.0 (interquartile range [IQR] = 6.0-14.0) and the median awareness score was 29.6 (IQR = 26.6-32.6). HCWs at COVID-19 designated facilities with previous outbreak experience, or HCWs who were trained for dealing with the SARS-CoV-2 outbreak, had significantly higher levels of preparedness and awareness (p<0.001). Association rule mining suggests that nurses and doctors who had a 'great-extent-of-confidence' in handling suspected COVID-19 patients had participated in COVID-19 training courses. Male participants (mean difference = 0.34; 95% CI = 0.22, 0.46; p<0.001) and nurses (mean difference = 0.67; 95% CI = 0.53, 0.81; p<0.001) had higher preparedness scores compared to women participants and doctors. INTERPRETATION: There was an unsurprising high level of awareness and preparedness among HCWs who participated in COVID-19 training courses. However, disparity existed along the lines of gender and type of HCW. It is unknown whether the difference in COVID-19 preparedness that we detected early in the pandemic may have translated into disproportionate SARS-CoV-2 burden of disease by gender or HCW type