63 research outputs found
Quantum transport efficiency and Fourier's law
We analyze the steady-state energy transfer in a chain of coupled two-level
systems connecting two thermal reservoirs. Through an analytic treatment we
find that the energy current is independent of the system size, hence violating
Fourier's law of heat conduction. The classical diffusive behavior in Fourier's
law of heat conduction can be recovered by introducing decoherence to the
quantum systems constituting the chain. Implications of these results on energy
transfer in biological light harvesting systems, and the role of quantum
coherences and entanglement are discussed.Comment: 6 pages, 4 figure
Vibration-enhanced quantum transport
In this paper, we study the role of collective vibrational motion in the
phenomenon of electronic energy transfer (EET) along a chain of coupled
electronic dipoles with varying excitation frequencies. Previous experimental
work on EET in conjugated polymer samples has suggested that the common
structural framework of the macromolecule introduces correlations in the energy
gap fluctuations which cause coherent EET. Inspired by these results, we
present a simple model in which a driven nanomechanical resonator mode
modulates the excitation energy of coupled quantum dots and find that this can
indeed lead to an enhancement in the transport of excitations across the
quantum network. Disorder of the on-site energies is a key requirement for this
to occur. We also show that in this solid state system phase information is
partially retained in the transfer process, as experimentally demonstrated in
conjugated polymer samples. Consequently, this mechanism of vibration enhanced
quantum transport might find applications in quantum information transfer of
qubit states or entanglement.Comment: 7 pages, 6 figures, new material, included references, final
published versio
Quantum transport in quantum networks and photosynthetic complexes at the steady state
Recently, several works have analysed the efficiency of photosynthetic
complexes in a transient scenario and how that efficiency is affected by
environmental noise. Here, following a quantum master equation approach, we
study the energy and excitation transport in fully connected networks both in
general and in the particular case of the Fenna-Matthew-Olson complex. The
analysis is carried out for the steady state of the system where the excitation
energy is constantly "flowing" through the system. Steady state transport
scenarios are particularly relevant if the evolution of the quantum system is
not conditioned on the arrival of individual excitations. By adding dephasing
to the system, we analyse the possibility of noise-enhancement of the quantum
transport.Comment: 10 pages, single column, 6 figures. Accepted for publication in Plos
On
Psychiatric disorders in Iranian children and adolescents
Objective: The aim of the present study was to investigate the epidemiology of psychiatric disorders in children and adolescents in five provinces of Iran: Tehran, Shiraz, Isfahan, Tabriz and Mashhad. Method: In the present study, we selected 9,636 children and adolescents aged 6-18 years through multistage cluster random sampling method from Tehran, Shiraz, Isfahan, Tabriz and Mashhad. We instructed the clinical psychologists to complete the Strengths and Difficulties Questionnaire (SDQ) for the participants, and those who received a high score on SDQ, completed the Persian version of Kiddie-SADS-Present and Lifetime Version (K-SADS-PL). We used descriptive analysis and 95 confidence interval to investigate the relationship between scores of the K- SADS questionnaire and demographic factors . We used one-way ANOVA to test the significant differences among the disorders according to sex, age and province of residence. Results: Based on the results, oppositional defiant disorder (ODD) (4.45) had the highest prevalence of psychiatric disorders in the five provinces and substance abuse and alcohol abuse (0) had the lowest prevalence. In addition, attention deficit hyperactivity disorder (ADHD) had the most prevalence in boys (5.03) and ODD had the most prevalence in girls (4.05). Among the three age groups, 6 to 9 year olds had the highest rates of ADHD (5.69); 10 to 14 and 15 to 18 year olds had the highest rates of ODD (4.32 and 4.37 respectively). Among the five provinces, Tehran and Mashhad allocated the highest rates of ODD; Isfahan and Shiraz had the highest rates of ADHD; and Tabriz had the highest rates of social phobia. Conclusion: The current study revealed that the overall frequency of psychiatric disorders based on Kiddie- SADS-Present and Lifetime Version (K-SADS-PL) was higher than a similar study. Moreover, in this study, among the five provinces, Tehran and Mashhad allocated the highest rates of ODD; Isfahan and Shiraz had the highest rates of ADHD; and Tabriz had the highest rates of social phobia. Therefore, these percentage of psychiatric disorders in Iran lead us toward a greater use of consultation and mental health services
Cardiovascular patients in COVID-19 era, a case series, an experience from a tertiary cardiovascular center in Tehran, Iran
Different cardiovascular presentations of coronavirus disease 2019 can be seen because of the systemic involvement. Considering its new presentations, there is need for further studies regarding the mechanistic pathways involved. © 2020 The Authors. Clinical Case Reports published by John Wiley & Sons Lt
Psychiatric disorders in Iranian children and adolescents
Objective: The aim of the present study was to investigate the epidemiology of psychiatric disorders in children and adolescents in five provinces of Iran: Tehran, Shiraz, Isfahan, Tabriz and Mashhad. Method: In the present study, we selected 9,636 children and adolescents aged 6-18 years through multistage cluster random sampling method from Tehran, Shiraz, Isfahan, Tabriz and Mashhad. We instructed the clinical psychologists to complete the Strengths and Difficulties Questionnaire (SDQ) for the participants, and those who received a high score on SDQ, completed the Persian version of Kiddie-SADS-Present and Lifetime Version (K-SADS-PL). We used descriptive analysis and 95 confidence interval to investigate the relationship between scores of the K- SADS questionnaire and demographic factors . We used one-way ANOVA to test the significant differences among the disorders according to sex, age and province of residence. Results: Based on the results, oppositional defiant disorder (ODD) (4.45) had the highest prevalence of psychiatric disorders in the five provinces and substance abuse and alcohol abuse (0) had the lowest prevalence. In addition, attention deficit hyperactivity disorder (ADHD) had the most prevalence in boys (5.03) and ODD had the most prevalence in girls (4.05). Among the three age groups, 6 to 9 year olds had the highest rates of ADHD (5.69); 10 to 14 and 15 to 18 year olds had the highest rates of ODD (4.32 and 4.37 respectively). Among the five provinces, Tehran and Mashhad allocated the highest rates of ODD; Isfahan and Shiraz had the highest rates of ADHD; and Tabriz had the highest rates of social phobia. Conclusion: The current study revealed that the overall frequency of psychiatric disorders based on Kiddie- SADS-Present and Lifetime Version (K-SADS-PL) was higher than a similar study. Moreover, in this study, among the five provinces, Tehran and Mashhad allocated the highest rates of ODD; Isfahan and Shiraz had the highest rates of ADHD; and Tabriz had the highest rates of social phobia. Therefore, these percentage of psychiatric disorders in Iran lead us toward a greater use of consultation and mental health services
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