ORCID Profile
0000-0002-5416-7098
Current Organisations
Australian National University
,
Agencia Aragonesa para la Investigacion y Desarrollo
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Publisher: American Physical Society (APS)
Date: 11-05-2015
Publisher: American Physical Society (APS)
Date: 10-03-2015
Publisher: Cold Spring Harbor Laboratory
Date: 06-06-2017
DOI: 10.1101/121368
Abstract: Optimal stomatal theory is an evolutionary model proposing that leaves trade-off Carbon (C) for water to maximise C assimilation ( A ) and minimise transpiration ( E ), thereby generating a marginal water cost of carbon gain (λ) that remains constant over short temporal scales. The circadian clock is a molecular timer of metabolism that controls A and stomatal conductance ( g s ), amongst other processes, in a broad array of plant species. Here, we test whether circadian regulation contributes towards achieving optimal stomatal behaviour. We subjected bean ( Phaseolus vulgaris ) and cotton ( Gossypium hirsutum ) canopies to fixed, continuous environmental conditions of photosynthetically active radiation, temperature and vapour pressure deficit over 48 hours. We observed a significant and self-sustained circadian oscillation in A and in stomatal conductance ( g s ) which also led to a circadian oscillation in λ . The lack of constant marginal water cost indicates that circadian regulation does not directly lead to optimal stomatal behaviour. However, the temporal pattern in gas exchange, indicative of either maximizing A or of minimizing E , depending upon time of day, indicates that circadian regulation could contribute towards optimizing stomatal responses. More broadly, our results add to the emerging field of plant circadian ecology and show that molecular controls may partially explain leaf-level patterns observed in the field.
Publisher: American Physical Society (APS)
Date: 14-09-2007
Publisher: World Scientific Pub Co Pte Lt
Date: 02-2017
DOI: 10.1142/S0219749917500095
Abstract: Amplification of quantum states is inevitably accompanied with the introduction of noise at the output. For protocols that are probabilistic with heralded success, noiseless linear lification in theory may still be possible. When the protocol is successful, it can lead to an output that is a noiselessly lified copy of the input. When the protocol is unsuccessful, the output state is degraded and is usually discarded. Probabilistic protocols may improve the performance of some quantum information protocols, but not for metrology if the whole statistics is taken into consideration. We calculate the precision limits on estimating the phase of coherent states using a noiseless linear lifier by computing its quantum Fisher information and we show that on average, the noiseless linear lifier does not improve the phase estimate. We also discuss the case where abstention from measurement can reduce the cost for estimation.
Publisher: Oxford University Press (OUP)
Date: 20-10-2016
Publisher: Springer Science and Business Media LLC
Date: 20-07-2023
DOI: 10.1038/S41598-023-38572-1
Abstract: The maximum amount of entanglement achievable under passive transformations by continuous-variable states is called the entanglement potential. Recent work has demonstrated that the entanglement potential is upper-bounded by a simple function of the squeezing of formation, and that certain classes of two-mode Gaussian states can indeed saturate this bound, though saturability in the general case remains an open problem. In this study, we introduce a larger class of states that we prove saturates the bound, and we conjecture that all two-mode Gaussian states can be passively transformed into this class, meaning that for all two-mode Gaussian states, entanglement potential is equivalent to squeezing of formation. We provide an explicit algorithm for the passive transformations and perform extensive numerical testing of our claim, which seeks to unite the resource theories of two characteristic quantum properties of continuous-variable systems.
Publisher: IEEE
Date: 06-2007
Publisher: WORLD SCIENTIFIC
Date: 08-2005
Publisher: Wiley
Date: 30-03-2017
DOI: 10.1111/PCE.12909
Abstract: There is increasing evidence that the circadian clock is a significant driver of photosynthesis that becomes apparent when environmental cues are experimentally held constant. We studied whether the composition of photosynthetic pigments is under circadian regulation, and whether pigment oscillations lead to rhythmic changes in photochemical efficiency. To address these questions, we maintained canopies of bean and cotton, after an entrainment phase, under constant (light or darkness) conditions for 30-48 h. Photosynthesis and quantum yield peaked at subjective noon, and non-photochemical quenching peaked at night. These oscillations were not associated with parallel changes in carbohydrate content or xanthophyll cycle activity. We observed robust oscillations of Chl a/b during constant light in both species, and also under constant darkness in bean, peaking when it would have been night during the entrainment (subjective nights). These oscillations could be attributed to the synthesis and/or degradation of trimeric light-harvesting complex II (reflected by the rhythmic changes in Chl a/b), with the antenna size minimal at night and maximal around subjective noon. Considering together the oscillations of pigments and photochemistry, the observed pattern of changes is counterintuitive if we assume that the plant strategy is to avoid photodamage, but consistent with a strategy where non-stressed plants maximize photosynthesis.
Publisher: IOP Publishing
Date: 09-05-2013
Publisher: Elsevier BV
Date: 09-2012
DOI: 10.1016/J.PLANTSCI.2012.05.009
Abstract: Mesophyll diffusion conductance to CO(2) is a key photosynthetic trait that has been studied intensively in the past years. The intention of the present review is to update knowledge of g(m), and highlight the important unknown and controversial aspects that require future work. The photosynthetic limitation imposed by mesophyll conductance is large, and under certain conditions can be the most significant photosynthetic limitation. New evidence shows that anatomical traits, such as cell wall thickness and chloroplast distribution are amongst the stronger determinants of mesophyll conductance, although rapid variations in response to environmental changes might be regulated by other factors such as aquaporin conductance. Gaps in knowledge that should be research priorities for the near future include: how different is mesophyll conductance among phylogenetically distant groups and how has it evolved? Can mesophyll conductance be uncoupled from regulation of the water path? What are the main drivers of mesophyll conductance? The need for mechanistic and phenomenological models of mesophyll conductance and its incorporation in process-based photosynthesis models is also highlighted.
Publisher: AIP Publishing LLC
Date: 2014
DOI: 10.1063/1.4903110
Publisher: IEEE
Date: 08-2011
Publisher: IOP Publishing
Date: 19-11-2019
Publisher: The Optical Society
Date: 10-06-2016
Publisher: American Physical Society (APS)
Date: 19-08-2020
Publisher: American Physical Society (APS)
Date: 28-04-2016
Publisher: Springer International Publishing
Date: 2020
Publisher: American Physical Society (APS)
Date: 18-06-2008
Publisher: IEEE
Date: 05-2013
Publisher: Elsevier BV
Date: 11-2012
Publisher: World Scientific Pub Co Pte Lt
Date: 12-2006
DOI: 10.1142/S0219749906002365
Abstract: We consider a variant of the BB84 protocol for quantum cryptography, the prototype of tomographically incomplete protocols, where the key is generated by one-way communication rather than the usual two-way communication. Our analysis, backed by numerical evidence, establishes thresholds for eavesdropping attacks on the raw data and on the generated key at quantum bit error rates of 10% and 6.15%, respectively. Both thresholds are lower than the threshold for unconditional security in the standard BB84 protocol.
Publisher: Oxford University Press (OUP)
Date: 15-04-2016
Abstract: Atmospheric carbon dioxide (CO2) concentrations are expected to increase throughout this century, potentially fostering tree growth. A wealth of studies have examined the variation in CO2 responses across tree species, but the extent of intraspecific variation in response to elevated CO2 (eCO2) has, so far, been examined in in idual studies and syntheses of published work are currently lacking. We conducted a meta-analysis on the effects of eCO2 on tree growth (height, stem biomass and stem volume) and photosynthesis across genotypes to examine whether there is genetic variation in growth responses to eCO2 and to understand their dependence on photosynthesis. We additionally examined the interaction between the responses to eCO2 and ozone (O3), another global change agent. Most of the published studies so far have been conducted in juveniles and in Populus spp., although the patterns observed were not species dependent. All but one study reported significant genetic variation in stem biomass, and the magnitude of intraspecific variation in response to eCO2 was similar in magnitude to previous analyses on interspecific variation. Growth at eCO2 was predictable from growth at ambient CO2 (R(2) = 0.60), and relative rankings of genotype performance were preserved across CO2 levels, indicating no significant interaction between genotypic and environmental effects. The growth response to eCO2 was not correlated with the response of photosynthesis (P > 0.1), and while we observed 57.7% average increases in leaf photosynthesis, stem biomass and volume increased by 36 and 38.5%, respectively, and height only increased by 9.5%, suggesting a predominant role for carbon allocation in ultimately driving the response to eCO2 Finally, best-performing genotypes under eCO2 also responded better under eCO2 and elevated O3 Further research needs include widening the study of intraspecific variation beyond the genus Populus and examining the interaction between eCO2 and other environmental stressors. We conclude that significant potential to foster CO2-induced productivity gains through tree breeding exists, that these programs could be based upon best-performing genotypes under ambient conditions and that they would benefit from an increased understanding on the controls of allocation.
Publisher: Bentham Science Publishers Ltd.
Date: 11-2005
Publisher: Springer Science and Business Media LLC
Date: 17-02-2020
Publisher: AIP Publishing
Date: 06-06-2011
DOI: 10.1063/1.3597793
Abstract: We present a random number generation scheme that uses broadband measurements of the vacuum field contained in the radio-frequency sidebands of a single-mode laser. Even though the measurements may contain technical noise, we show that suitable algorithms can transform the digitized photocurrents into a string of random numbers that can be made arbitrarily correlated with a subset of the quantum fluctuations (high quantum correlation regime) or arbitrarily immune to environmental fluctuations (high environmental immunity). We demonstrate up to 2 Gbps of real time random number generation that were verified using standard randomness tests.
Publisher: American Physical Society (APS)
Date: 18-05-2020
Publisher: Springer Science and Business Media LLC
Date: 12-08-2019
Publisher: IEEE
Date: 06-2013
Publisher: American Physical Society (APS)
Date: 23-11-2020
Publisher: IOP Publishing
Date: 15-09-2006
Publisher: IOP Publishing
Date: 03-01-2014
Publisher: Springer Science and Business Media LLC
Date: 16-03-2014
Publisher: American Physical Society (APS)
Date: 05-07-2016
Publisher: Springer Science and Business Media LLC
Date: 05-08-2012
DOI: 10.1038/NPHYS2376
Publisher: Wiley
Date: 12-04-2022
DOI: 10.1111/NPH.18113
Abstract: We compiled hydrogen and oxygen stable isotope compositions (δ 2 H and δ 18 O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ 2 H was more closely correlated with δ 2 H of xylem water or atmospheric vapour, whereas leaf water δ 18 O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ 2 H of meteoric waters relative to the extent of leaf water evaporative enrichment compared with δ 18 O. We next expressed leaf water as isotopic enrichment above xylem water (Δ 2 H and Δ 18 O) to remove the impact of xylem water isotopic variation. For Δ 2 H, leaf water still correlated with atmospheric vapour, whereas Δ 18 O showed no such correlation. This was explained by covariance between air relative humidity and the Δ 18 O of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that 2 H and 18 O in leaf water do indeed reflect the balance of environmental drivers differently our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water.
Publisher: IOP Publishing
Date: 24-11-2014
Publisher: Informa UK Limited
Date: 12-2006
Publisher: American Physical Society (APS)
Date: 14-06-2021
Publisher: World Scientific Pub Co Pte Lt
Date: 04-2014
DOI: 10.1142/S0219749914500166
Abstract: Secure communication protocols are often formulated in a paradigm where the message is encoded in measurement outcomes. In this work, we propose a rather unexplored framework in which the message is encoded in measurement settings rather than in their outcomes. In particular, we study two different variants of such secure communication protocols in which the message alphabet corresponds to measurement settings of mutually unbiased bases.
Publisher: American Physical Society (APS)
Date: 11-09-2019
Publisher: SPIE
Date: 18-11-2014
DOI: 10.1117/12.2071884
Publisher: Elsevier BV
Date: 10-2003
Publisher: Elsevier BV
Date: 05-2017
Publisher: IEEE
Date: 05-2013
Publisher: Springer Science and Business Media LLC
Date: 05-04-2008
DOI: 10.1007/S00442-008-1030-1
Abstract: The (13)C isotopic signature (C stable isotope ratio delta(13)C) of CO(2) respired from forest ecosystems and their particular compartments are known to be influenced by temporal changes in environmental conditions affecting C isotope fractionation during photosynthesis. Whereas most studies have assessed temporal variation in delta(13)C of ecosystem-respired CO(2) on a day-to-day scale, not much information is available on its diel dynamics. We investigated environmental and physiological controls over potential temporal changes in delta(13)C of respired CO(2) by following the short-term dynamics of the (13)C signature from newly assimilated organic matter pools in the needles, via phloem-transported organic matter in twigs and trunks, to trunk-, soil- and ecosystem-respired CO(2). We found a strong 24-h periodicity in delta(13)C of organic matter in leaf and twig phloem sap, which was strongly d ened as carbohydrates were transported down the trunk. Periodicity reappeared in the delta(13)C of trunk-respired CO(2), which seemed to originate from apparent respiratory fractionation rather than from changes in delta(13)C of the organic substrate. The diel patterns of delta(13)C in soil-respired CO(2) are partly explained by soil temperature and moisture and are probably due to changes in the relative contribution of heterotrophic and autotrophic CO(2) fluxes to total soil efflux in response to environmental conditions. Our study shows that direct relations between delta(13)C of recent assimilates and respired CO(2) may not be present on a diel time scale, and other factors lead to short-term variations in delta(13)C of ecosystem-emitted CO(2). On the one hand, these variations complicate ecosystem CO(2) flux partitioning, but on the other hand they provide new insights into metabolic processes underlying respiratory CO(2) emission.
Publisher: MDPI AG
Date: 26-07-2023
DOI: 10.3390/E25081122
Abstract: This work compares the performance of single- and two-qubit probes for estimating several phase rotations simultaneously under the action of different noisy channels. We compute the quantum limits for this simultaneous estimation using collective and in idual measurements by evaluating the Holevo and Nagaoka–Hayashi Cramér-Rao bounds, respectively. Several quantum noise channels are considered, namely the decohering channel, the litude d ing channel, and the phase d ing channel. For each channel, we find the optimal single- and two-qubit probes. Where possible we demonstrate an explicit measurement strategy that saturates the appropriate bound and we investigate how closely the Holevo bound can be approached through collective measurements on multiple copies of the same probe. We find that under the action of the considered channels, two-qubit probes show enhanced parameter estimation capabilities over single-qubit probes for almost all non-identity channels, i.e., the achievable precision with a single-qubit probe degrades faster with increasing exposure to the noisy environment than that of the two-qubit probe. However, in sufficiently noisy channels, we show that it is possible for single-qubit probes to outperform maximally entangled two-qubit probes. This work shows that, in order to reach the ultimate precision limits allowed by quantum mechanics, entanglement is required in both the state preparation and state measurement stages. It is hoped the tutorial-esque nature of this paper will make it easily accessible.
Publisher: IEEE
Date: 06-2013
Publisher: Wiley
Date: 25-06-2013
DOI: 10.1111/NPH.12382
Abstract: The role of the circadian clock in controlling the metabolism of entire trees has seldom been considered. We tested whether the clock influences nocturnal whole‐tree water use. Whole‐tree chambers allowed the control of environmental variables (temperature, relative humidity). Night‐time stomatal conductance ( g s ) and sap flow ( Q ) were monitored in 6‐ to 8‐m‐tall E ucalyptus globulus trees during nights when environmental variables were kept constant, and also when conditions varied with time. Artificial neural networks were used to quantify the relative importance of circadian regulation of g s and Q . Under a constant environment, g s and Q declined from 0 to 6 h after dusk, but increased from 6 to 12 h after dusk. While the initial decline could be attributed to multiple processes, the subsequent increase is most consistent with circadian regulation of g s and Q . We conclude that endogenous regulation of g s is an important driver of night‐time Q under natural environmental variability. The proportion of nocturnal Q variation associated with circadian regulation (23–56%) was comparable to that attributed to vapor pressure deficit variation (25–58%). This study contributes to our understanding of the linkages between molecular and cellular processes related to circadian regulation, and whole‐tree processes related to ecosystem gas exchange in the field.
Publisher: Springer Science and Business Media LLC
Date: 30-11-2013
Publisher: Springer Science and Business Media LLC
Date: 26-06-2018
DOI: 10.1038/NCOMMS13222
Abstract: The no-cloning theorem states that an unknown quantum state cannot be cloned exactly and deterministically due to the linearity of quantum mechanics. Associated with this theorem is the quantitative no-cloning limit that sets an upper bound to the quality of the generated clones. However, this limit can be circumvented by abandoning determinism and using probabilistic methods. Here, we report an experimental demonstration of probabilistic cloning of arbitrary coherent states that clearly surpasses the no-cloning limit. Our scheme is based on a hybrid linear lifier that combines an ideal deterministic linear lifier with a heralded measurement-based noiseless lifier. We demonstrate the production of up to five clones with the fidelity of each clone clearly exceeding the corresponding no-cloning limit. Moreover, since successful cloning events are heralded, our scheme has the potential to be adopted in quantum repeater, teleportation and computing applications.
Publisher: IEEE
Date: 05-2013
Publisher: Elsevier BV
Date: 05-2017
No related grants have been discovered for Syed Assad.