929 research outputs found
Electroweak Bioenantioselection
This paper reviews evidence for the view that biomolecular
chirality was determined not by chance but by the electroweak
interaction. Other influences (such as the Earth\u27s magnetic and
gravitational fields, or circularly polarized light) are either falsely
chiral or else even-handed on a time and space average, leaving
the weak interaction as the only consistent universal chiral influence.
Electroweak bioenantioselection could occur either through
p-radiolysis or through the small parity-violating energy differences
(PVED) between enantiomers. The PVED produces an electroweak
enantiomeric excess of only 10-17, but this can be amplified
to homochirality within 104 years by the powerful Kondepudi
mechanism. Calculations of the PVED show that the natural
L-amino acids are more stable than their »unnatural« n-enantiomers,
and natural n-glyceraldehyde and D-deoxyribose are also
PVED-stabilized. The PVED can also explain the observed 1%
excess of l(-)-quartz, which, through pre-biotic mineral catalysis,
could increase the electroweak enantiomeric excess to 10-4
Implementation of measurement reduction for the variational quantum eigensolver
One limitation of the variational quantum eigensolver algorithm is the large number of measurement steps required to estimate different terms in the Hamiltonian of interest. Unitary partitioning reduces this overhead by transforming the problem Hamiltonian into one containing fewer terms. We explore two different circuit constructions of the transformation required - one built by a sequence of rotations and the other built by a linear combination of unitaries (LCU). To assess performance, we simulated chemical Hamiltonians and studied the ground states of H2 and LiH. Both implementations are successful even in the presence of noise. The sequence-of-rotations realization offers the greatest benefit to calculations, whereas the probabilistic nature of LCU reduces its effectiveness. This work also demonstrates an experimental implementation of LCU on quantum hardware
A comparison of the Bravyi-Kitaev and Jordan-Wigner transformations for the quantum simulation of quantum chemistry
The ability to perform classically intractable electronic structure
calculations is often cited as one of the principal applications of quantum
computing. A great deal of theoretical algorithmic development has been
performed in support of this goal. Most techniques require a scheme for mapping
electronic states and operations to states of and operations upon qubits. The
two most commonly used techniques for this are the Jordan-Wigner transformation
and the Bravyi-Kitaev transformation. However, comparisons of these schemes
have previously been limited to individual small molecules. In this paper we
discuss resource implications for the use of the Bravyi-Kitaev mapping scheme,
specifically with regard to the number of quantum gates required for
simulation. We consider both small systems which may be simulatable on
near-future quantum devices, and systems sufficiently large for classical
simulation to be intractable. We use 86 molecular systems to demonstrate that
the use of the Bravyi-Kitaev transformation is typically at least approximately
as efficient as the canonical Jordan-Wigner transformation, and results in
substantially reduced gate count estimates when performing limited circuit
optimisations.Comment: 46 pages, 11 figure
Using Hierarchical Data Mining to Characterize Performance of Wireless System Configurations
This paper presents a statistical framework for assessing wireless systems
performance using hierarchical data mining techniques. We consider WCDMA
(wideband code division multiple access) systems with two-branch STTD (space
time transmit diversity) and 1/2 rate convolutional coding (forward error
correction codes). Monte Carlo simulation estimates the bit error probability
(BEP) of the system across a wide range of signal-to-noise ratios (SNRs). A
performance database of simulation runs is collected over a targeted space of
system configurations. This database is then mined to obtain regions of the
configuration space that exhibit acceptable average performance. The shape of
the mined regions illustrates the joint influence of configuration parameters
on system performance. The role of data mining in this application is to
provide explainable and statistically valid design conclusions. The research
issue is to define statistically meaningful aggregation of data in a manner
that permits efficient and effective data mining algorithms. We achieve a good
compromise between these goals and help establish the applicability of data
mining for characterizing wireless systems performance
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Consumer attitudes towards production diseases in intensive production systems
Many members of the public and important stakeholders operating at the upper end of the
food chain, may be unfamiliar with how food is produced, including within modern animal
production systems. The intensification of production is becoming increasingly common in
modern farming. However, intensive systems are particularly susceptible to production diseases,
with potentially negative consequences for farm animal welfare (FAW). Previous
research has demonstrated that the public are concerned about FAW, yet there has been little
research into attitudes towards production diseases, and their approval of interventions
to reduce these. This research explores the public’s attitudes towards, and preferences for,
FAW interventions in five European countries (Finland, Germany, Poland, Spain and the
UK). An online survey was conducted for broilers (n = 789), layers (n = 790) and pigs (n =
751). Data were analysed by means of Kruskal-Wallis ANOVA, exploratory factor analysis
and structural equation modelling. The results suggest that the public have concerns regarding
intensive production systems, in relation to FAW, naturalness and the use of antibiotics.
The most preferred interventions were the most “proactive” interventions, namely improved
housing and hygiene measures. The least preferred interventions were medicine-based,
which raised humane animal care and food safety concerns amongst respondents. The
results highlighted the influence of the identified concerns, perceived risks and benefits on
attitudes and subsequent behavioural intention, and the importance of supply chain stakeholders
addressing these concerns in the subsequent communications with the public
Ordering of Trotterization: impact on errors in quantum simulation of electronic structure
Trotter–Suzuki decompositions are frequently used in the quantum simulation of quantum chemistry. They transform the evolution operator into a form implementable on a quantum device, while incurring an error—the Trotter error. The Trotter error can be made arbitrarily small by increasing the Trotter number. However, this increases the length of the quantum circuits required, which may be impractical. It is therefore desirable to find methods of reducing the Trotter error through alternate means. The Trotter error is dependent on the order in which individual term unitaries are applied. Due to the factorial growth in the number of possible orderings with respect to the number of terms, finding an optimal strategy for ordering Trotter sequences is difficult. In this paper, we propose three ordering strategies, and assess their impact on the Trotter error incurred. Initially, we exhaustively examine the possible orderings for molecular hydrogen in a STO-3G basis. We demonstrate how the optimal ordering scheme depends on the compatibility graph of the Hamiltonian, and show how it varies with increasing bond length. We then use 44 molecular Hamiltonians to evaluate two strategies based on coloring their incompatibility graphs, while considering the properties of the obtained colorings. We find that the Trotter error for most for systems involving heavy atoms, using a reference magnitude ordering, is less than 1 kcal/mol. Relative to this, the difference between ordering schemes can be substantial, being approximately on the order of millihartrees. The coloring-based ordering schemes are reasonably promising—particularly for systems involving heavy atoms—however further work is required to increase dependence on the magnitude of terms. Finally, we consider ordering strategies based on the norm of the Trotter error operator, including an iterative method for generating the new error operator terms added upon insertion of a term into an ordered Hamiltonian
BSML: A Binding Schema Markup Language for Data Interchange in Problem Solving Environments (PSEs)
We describe a binding schema markup language (BSML) for describing data
interchange between scientific codes. Such a facility is an important
constituent of scientific problem solving environments (PSEs). BSML is designed
to integrate with a PSE or application composition system that views model
specification and execution as a problem of managing semistructured data. The
data interchange problem is addressed by three techniques for processing
semistructured data: validation, binding, and conversion. We present BSML and
describe its application to a PSE for wireless communications system design
Unitary partitioning and the contextual subspace variational quantum eigensolver
The contextual subspace variational quantum eigensolver (CS-VQE) is a hybrid quantum-classical algorithm that approximates the ground-state energy of a given qubit Hamiltonian. It achieves this by separating the Hamiltonian into contextual and noncontextual parts. The ground-state energy is approximated by classically solving the noncontextual problem, followed by solving the contextual problem using VQE, constrained by the noncontextual solution. In general, computation of the contextual correction needs fewer qubits and measurements compared with solving the full Hamiltonian via traditional VQE. We simulate CS-VQE on different tapered molecular Hamiltonians and apply the unitary partitioning measurement reduction strategy to further reduce the number of measurements required to obtain the contextual correction. Our results indicate that CS-VQE combined with measurement reduction is a promising approach to allow feasible eigenvalue computations on noisy intermediate-scale quantum devices. We also provide a modification to the CS-VQE algorithm; the CS-VQE algorithm previously could cause an exponential increase in Hamiltonian terms but with this modification now at worst will scale quadratically
Phosphatase activity and organic phosphorus turnover on a high Arctic glacier
Arctic glacier surfaces harbour abundant microbial communities consisting mainly of heterotrophic and photoautotrophic bacteria. The microbes must cope with low concentrations of nutrients and with the fact that both the dissolved and debris-bound nutrient pools are dominated by organic phases. Here we provide evidence that phosphorus (P) is deficient in the supraglacial environment on a Svalbard glacier, we quantify the enzymatic activity of phosphatases in the system and we estimate the contribution of the microbes to the cycling of the dominant organic P in the supraglacial environment. Incubation of cryoconite debris revealed significant phosphatase activity in the samples (19–67 nmol MUP g<sup>&minus;1</sup> h<sup>&minus;1</sup>). It was inhibited by inorganic P during incubations and had its optimum at around 30&deg;C. The phosphatase activity measured at near-in situ temperature and substrate concentration suggests that the available dissolved organic P can be turned over by microbes within ~3–11 h on the glacier surface. By contrast, the amount of potentially bioavailable debris-bound organic P is sufficient for a whole ablation season. However, it is apparent that some of this potentially bioavailable debris-bound P is not accessible to the microbes
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