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Geometry, supertransfer, and optimality in the light harvesting of purple bacteria
, Article Journal of Physical Chemistry Letters ; Volume 7, Issue 19 , 2016 , Pages 3804-3811 ; 19487185 (ISSN) ; Kassal, I ; Sharif University of Technology
American Chemical Society
2016
Abstract
The remarkable rotational symmetry of the photosynthetic antenna complexes of purple bacteria has long been thought to enhance their light harvesting and excitation energy transport. We study the role of symmetry by modeling hypothetical antennas whose symmetry is broken by altering the orientations of the bacteriochlorophyll pigments. We find that in both LH2 and LH1 complexes, symmetry increases energy transfer rates by enabling the cooperative, coherent process of supertransfer. The enhancement is particularly pronounced in the LH1 complex, whose natural geometry outperforms the average randomized geometry by 5.5 standard deviations, the most significant coherence-related enhancement...
Distinguishing the roles of energy funnelling and delocalization in photosynthetic light harvesting
, Article Physical Chemistry Chemical Physics ; Volume 18, Issue 10 , 2016 , Pages 7459-7467 ; 14639076 (ISSN) ; Kassal, I ; Sharif University of Technology
Royal Society of Chemistry
2016
Abstract
Photosynthetic complexes improve the transfer of excitation energy from peripheral antennas to reaction centers in several ways. In particular, a downward energy funnel can direct excitons in the right direction, while coherent excitonic delocalization can enhance transfer rates through the cooperative phenomenon of supertransfer. However, isolating the role of purely coherent effects is difficult because any change to the delocalization also changes the energy landscape. Here, we show that the relative importance of the two processes can be determined by comparing the natural light-harvesting apparatus with counterfactual models in which the delocalization and the energy landscape are...
Distillation of free entanglement from bound entangled states using weak measurements
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 88, Issue 6 , 2013 ; ISSN: 10502947 ; Rezakhani, A. T ; Sharif University of Technology
2013
Abstract
We propose a scheme for distillation of free bipartite entanglement from bipartite bound entangled states. The crucial element of our scheme is an ancillary system that is coupled to the initial bound entangled state via appropriate weak measurements. We show that in this protocol free entanglement can be always generated with nonzero probability by using a single copy of the bound entangled state. We also derive a lower bound on the entanglement cost of the protocol and conclude that, on average, applying weaker measurements results in relatively higher values of free entanglement as well as lower costs
Temperature effects on quantum cloning of states and entanglement
, Article Physics Letters, Section A: General, Atomic and Solid State Physics ; Volume 373, Issue 8-9 , 2009 , Pages 821-825 ; 03759601 (ISSN) ; Rezakhani, A. T ; Sharif University of Technology
2009
Abstract
Performances of the symmetric universal and phase-covariant cloning transformations and entanglement cloners - qubit case - are investigated when the initial state of the hardware or the original state to be cloned is weakly coupled to a thermal environment. Different behaviors of each of these transformations are analyzed and contrasted with the ideal cases. © 2009 Elsevier B.V. All rights reserved
Bound entanglement in quantum phase transitions
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 81, Issue 4 , 2010 ; 10502947 (ISSN) ; Alipour, S ; Rezakhani, A. T ; Sharif University of Technology
2010
Abstract
We investigate quantum phase transitions in which a change in the type of entanglement from bound entanglement to either free entanglement or separability may occur. In particular, we present a theoretical method to construct a class of quantum spin-chain Hamiltonians that exhibit this type of quantum criticality. Given parameter-dependent two-site reduced density matrices (with prescribed entanglement properties), we lay out a reverse construction for a compatible pure state for the whole system, as well as a class of Hamiltonians for which this pure state is a ground state. This construction is illustrated through several examples
Oxidation of 1,4-dihydropyridines under mild and heterogeneous conditions using solid acids
, Article Journal of the Iranian Chemical Society ; Volume 3, Issue 1 , 2006 , Pages 73-80 ; 1735207X (ISSN) ; Bagherzadeh, M ; Niknam, K ; Shirini, F ; Mohammadpoor Baltork, I ; Ghorbani Choghamarani, A ; Baghbanzadeh, M ; Sharif University of Technology
Iranian Chemical Society
2006
Abstract
A combination of solid acids, including Oxone®, HIO3, H 5IO6, and polystyrenesulfonic acid and sodium nitrite, in the presence of wet SiO2 were used as an effective oxidizing agents for the oxidation of dihydropyridines to their corresponding pyridine derivatives under mild and heterogeneous conditions in good to excellent yields
Investigating the rheological properties of nanofluids of water/hybrid nanostructure of spherical silica/MWCNT
, Article Thermochimica Acta ; Volume 578 , 20 February , 2014 , Pages 53-58 ; ISSN: 00406031 ; Rashidi, A ; Soleimanisalim, A. H ; Rashtchian, D ; Sharif University of Technology
2014
Abstract
Regarding the importance of rheological properties of water based drilling fluids, the effects of silica nanospheres, multiwall carbon nanotubes (MWCNTs) and two types of their hybrid, i.e. H1 (80 wt.% silica nanosphere/20 wt.% MWCNT) and H2 (50 wt.% silica nanosphere/50 wt.% MWCNT) on the viscosity and density of distilled water were investigated. According to the results, viscosity and density of the nanofluids increased with the concentration, while they were reduced by increasing the temperature. At high concentrations, the least increase in the viscosity of distilled water by adding the nanomaterials is related to H2 (8.2% increase at 1.0 wt.%). Likewise, the optimum operating...
Synthesis of spherical silica/multiwall carbon nanotubes hybrid nanostructures and investigation of thermal conductivity of related nanofluids
, Article Thermochimica Acta ; Volume 549 , 2012 , Pages 87-94 ; 00406031 (ISSN) ; Rashidi, A ; Rashtchian, D ; Lotfi, R ; Amrollahi, A ; Sharif University of Technology
2012
Abstract
In this study, a hybrid of silica nanosphere/multiwall carbon nanotube (MWCNT) has been synthesized by wet chemical method at room temperature. The effect of MWCNTs, silica nanospheres and hybrid nanostructures (80% silica nanosphere/20% MWCNT and 50% silica nanosphere/50% MWCNT) on the thermal conductivity of distilled water has been investigated. SDBS was used as the dispersant to stabilize nanomaterials in the aqueous suspension and its concentration was 1.5 times of the concentration of nanomaterials. As results show, by increasing the concentration of nanomaterials, effective thermal conductivity of nanofluids increased. The most and the least enhancement in the effective thermal...
The Role of Quantum Coherence and Geometry on the Excitonic Energy Transfer in Photosynthetic Structures
, M.Sc. Thesis Sharif University of Technology ; Karimipour, Vahid (Supervisor) ; Rezakhani, Ali (Supervisor)
Abstract
It has been of great interest to know whether quantum effects can play an essential role in the biological processes. Considering that quantum features, such as coherence and entanglement,can be harnessed to perform quantum information processing tasks, which are believed to be hard classically, the question is whether nature has also exploited these features in order to enhance the performance of biological systems. Although the presence of warm and wet environment around the biological systems results in the rapid destruction of quantum effects, recent experiments reported the existence of quantum coherence in light-harvesting complexes of some photosynthetic systems.This coherence lasts...
Preparation of Nanofluid by Using Hybrid Nanostructures and Investigation of Thermal and Rheological Properties and Using it in the Petroleum Fluids
, M.Sc. Thesis Sharif University of Technology ; Rashtchian , Davood (Supervisor) ; Rashidi, Alimorad (Supervisor) ; Lotfi, Roghayeh (Co-Advisor)
Abstract
In this study, thermal and rheological properties of nanofluids of water/carbon nanotubes, water/spherical silica nanoparticles and water/hybrid nanoparticles (hybrid of carbon nanotubes and spherical silica nanoparticles) have been investigated. To do so, carbon nanotubes have been synthesized by CCVD process and spherical silica nanoparticles and hybrid nanoparticles by wet chemical method. After synthesis of nanomaterials, nanofluids have been prepared by using SDBS as a dispersant with the concentration of 1.5 times of concentration of nanomaterials and then thermal conductivity, kinematic viscosity, dynamic viscosity and density of nanofluids have been investigated. As the results show,...
Probability of missed detection as a criterion for receiver placement in MIMO PCL
, Article IEEE National Radar Conference - Proceedings, 7 May 2012 through 11 May 2012, Atlanta, GA ; 2012 , Pages 0924-0927 ; 10975659 (ISSN) ; 9781467306584 (ISBN) ; Chitgarha, M. M ; Radmard, M ; Nayebi, M. M ; Sharif University of Technology
IEEE
2012
Abstract
Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar
An efficient method for the ring opening of epoxides with aromatic amines by Sb(III) chloride under microwave irradiation
, Article Journal of Chemical Research ; Issue 4 , 2008 , Pages 220-221 ; 03082342 (ISSN) ; Hashemi, M. M ; Mottaghi, M. M ; Foroughi, M. M ; Sharif University of Technology
2008
Abstract
SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity
Resource allocation for uav-enabled integrated sensing and communication (isac) via multi-objective optimization
, Article ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings ; Volume 2023-June , 2023 ; 15206149 (ISSN); 978-172816327-7 (ISBN) ; Naghsh, M. M ; Karbasi, M ; Nayebi, M. M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2023
Abstract
In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit...
MIMO radar signal design to improve the MIMO ambiguity function via maximizing its peak
, Article Signal Processing ; Volume 118 , 2016 , Pages 139-152 ; 01651684 (ISSN) ; Radmard, M ; Nazari Majd, M ; Karbasi, S. M ; Nayebi, M. M ; Sharif University of Technology
Elsevier
2016
Abstract
One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function...
Detection-localization tradeoff in MIMO radars
, Article Radioengineering ; Volume 26, Issue 2 , 2017 , Pages 581-587 ; 12102512 (ISSN) ; Radmard, M ; Chitgarha, M. M ; Bastani, M. H ; Nayebi, M. M ; Sharif University of Technology
2017
Abstract
Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance...
Antenna placement and power allocation optimization in MIMO detection
, Article IEEE Transactions on Aerospace and Electronic Systems ; Vol. 50, Issue 2 , April , 2014 , pp. 1468-1478 ; Chitgarha, M. M ; Majd, M. N ; Nayebi, M. M ; Sharif University of Technology
2014
Abstract
It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive...
Ambiguity function of MIMO radar with widely separated antennas
, Article Proceedings International Radar Symposium ; 16 -18 June , 2014 ; ISSN: 21555753 ; Chitgarha, M. M ; Nazari Majd, M ; Nayebi, M. M ; Sharif University of Technology
2014
Abstract
There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas
Choosing the position of the receiver in a MISO passive radar system
, Article European Microwave Week 2012: "Space for Microwaves", EuMW 2012, Conference Proceedings - 9th European Radar Conference, EuRAD 2012 ; 2012 , Pages 318-321 ; 9782874870293 (ISBN) ; Majd, M. N ; Radmard, M ; Nayebi, M. M ; Sharif University of Technology
2012
Abstract
By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only...
Adaptive filtering techniques in passive radar
, Article Proceedings International Radar Symposium, Dresden ; Volume 2 , June , 2013 , Pages 1067-1078 ; 21555753 (ISSN) ; 9783954042234 (ISBN) ; Radmard, M ; Majd, M. N ; Nayebi, M. M ; Sharif University of Technology
2013
Abstract
One of the most important obstacles in passive radar applications is removing the direct signal from the target channel. Otherwise, week echoes from the targets in the target channel would be ignored due to the limited dynamic range of the system. One of the most effective techniques in this field is using adaptive filters. In this paper various adaptive filters are introduced and their performances are shown and compared
Ambiguity function based receiver placement in multi-site radar
, Article 2016 CIE International Conference on Radar, RADAR 2016, 10 October 2016 through 13 October 2016 ; 2017 ; 9781509048281 (ISBN) ; Chitgarha, M. M ; Nazari Majd, M ; Nayebi, M. M ; Sharif University of Technology
2017
Abstract
It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite...