387 research outputs found
The effect of dairy cow breed on milk production, cow traffic and milking characteristics in a pasture-based automatic milking system
peer-reviewedDespite the increasing frequency of integrated automatic milking (AM) and pasture-based systems, there is limited knowledge available on the suitability of different dairy cow breeds to these systems. Thus, the objective of this experiment was to establish the performance of three breeds in a pasture-based AM system with respect to milk production, cow traffic and milking characteristics. The breeds examined were Holstein Friesian (HF), Jersey x HF (JEX) and Norwegian Red x HF (NRX), all of which have been previously identified as being compatible with conventional milking pasture-based systems. The experiment was conducted in mid-lactation and variables measured included milking frequency, -interval, -outcome and -characteristics, milk yield/milking and per day, wait time/visit and per day, return time/visit and the daily distribution of milking events. Data were statistically analysed using least squares means mixed procedure models, while the proportion of different milking events were analysed using the logistics procedure. While there were no significant differences between breeds for milking frequency, or milk production, significant differences did exist for proportion of successful and failed milkings events, with NRX cows recording the highest and lowest proportions, respectively. JEX also recorded a significantly shorter dead time/quarter at 17.6 s/milking compared to the HF and NRX breeds at 28.5 and 27.7 s/milking, respectively. Significant differences also existed with regard to cow traffic, with the NRX breed returning from pasture more quickly and waiting a shorter time both per visit and per day in the pre-milking yard. The distribution of milking events differed between the breeds examined, with the JEX cows recording less milkings in the hour after the pre-selection gate changes of 0000 h and 1600 h. JEX also recorded a significantly greater proportion of milkings than the NRX and HF cows during the hours at which the lowest proportion of total milking events were recorded (0400–0600 h). For the optimisation of the AM system it is important to have an even distribution of milkings throughout the day. Based on the evidence from the current experiment, this may be best achieved by a mixed breed herd rather than a single breed herd. However, the performance of the examined breeds should also be analysed in the context of the whole AM farm system, over an entire lactation, taking into consideration the range of variables that contribute to a profitable farm system
Comparing Apples and Oranges?: Next Generation Sequencing and Its Impact on Microbiome Analysis
peer-reviewedRapid advancements in sequencing technologies along with falling costs present widespread
opportunities for microbiome studies across a vast and diverse array of environments. These
impressive technological developments have been accompanied by a considerable growth in
the number ofmethodological variables, including sampling, storage, DNA extraction, primer
pairs, sequencing technology, chemistry version, read length, insert size, and analysis pipelines,
amongst others. This increase in variability threatens to compromise both the reproducibility
and the comparability of studies conducted. Here we perform the first reported study
comparing both amplicon and shotgun sequencing for the three leading next-generation
sequencing technologies. These were applied to six human stool samples using Illumina
HiSeq, MiSeq and Ion PGM shotgun sequencing, as well as amplicon sequencing across two
variable 16S rRNA gene regions. Notably, we found that the factor responsible for the greatest
variance inmicrobiota composition was the chosen methodology rather than the natural
inter-individual variance, which is commonly one of the most significant drivers in microbiome
studies. Amplicon sequencing suffered from this to a large extent, and this issue was particularly
apparent when the 16S rRNA V1-V2 region amplicons were sequenced withMiSeq.
Somewhat surprisingly, the choice of taxonomic binning software for shotgun sequences
proved to be of crucial importance with even greater discriminatory power than sequencing
technology and choice of amplicon. Optimal N50 assembly values for the HiSeq was obtained
for 10million reads per sample, whereas the applied MiSeq and PGM sequencing depths
proved less sufficient for shotgun sequencing of stool samples. The latter technologies, on
the other hand, provide a better basis for functional gene categorisation, possibly due to their
longer read lengths. Hence, in addition to highlighting methodological biases, this study demonstrates
the risks associated with comparing data generated using different strategies. We
also recommend that laboratories with particular interests in certain microbes should optimise
their protocols to accurately detect these taxa using different techniques.This publication has emanated from research supported in part by a research grant from Science Foundation Ireland (SFI) under Grant Number SFI/12/RC/2273 and 11/PI/1137 and by FP7 funded CFMATTERS (Cystic Fibrosis Microbiome-determined Antibiotic Therapy Trial in Exacerbations: Results Stratified, Grant Agreement no. 603038)
A quantum-mechanical Maxwell's demon
A Maxwell's demon is a device that gets information and trades it in for
thermodynamic advantage, in apparent (but not actual) contradiction to the
second law of thermodynamics. Quantum-mechanical versions of Maxwell's demon
exhibit features that classical versions do not: in particular, a device that
gets information about a quantum system disturbs it in the process. In
addition, the information produced by quantum measurement acts as an additional
source of thermodynamic inefficiency. This paper investigates the properties of
quantum-mechanical Maxwell's demons, and proposes experimentally realizable
models of such devices.Comment: 13 pages, Te
Measurement of conditional phase shifts for quantum logic
Measurements of the birefringence of a single atom strongly coupled to a
high-finesse optical resonator are reported, with nonlinear phase shifts
observed for intracavity photon number much less than one. A proposal to
utilize the measured conditional phase shifts for implementing quantum logic
via a quantum-phase gate (QPG) is considered. Within the context of a simple
model for the field transformation, the parameters of the "truth table" for the
QPG are determined.Comment: 4 pages in Postscript format, including 4 figures (attached as
uuencoded version of a gzip-file
Neighborhoods of trees in circular orderings
In phylogenetics, a common strategy used to construct an evolutionary tree for a set of species X is to search in the space of all such trees for one that optimizes some given score function (such as the minimum evolution, parsimony or likelihood score). As this can be computationally intensive, it was recently proposed to restrict such searches to the set of all those trees that are compatible with some circular ordering of the set X. To inform the design of efficient algorithms to perform such searches, it is therefore of interest to find bounds for the number of trees compatible with a fixed ordering in the neighborhood of a tree that is determined by certain tree operations commonly used to search for trees: the nearest neighbor interchange (nni), the subtree prune and regraft (spr) and the tree bisection and reconnection (tbr) operations. We show that the size of such a neighborhood of a binary tree associated with the nni operation is independent of the tree’s topology, but that this is not the case for the spr and tbr operations. We also give tight upper and lower bounds for the size of the neighborhood of a binary tree for the spr and tbr operations and characterize those trees for which these bounds are attained
KP line solitons and Tamari lattices
The KP-II equation possesses a class of line soliton solutions which can be
qualitatively described via a tropical approximation as a chain of rooted
binary trees, except at "critical" events where a transition to a different
rooted binary tree takes place. We prove that these correspond to maximal
chains in Tamari lattices (which are poset structures on associahedra). We
further derive results that allow to compute details of the evolution,
including the critical events. Moreover, we present some insights into the
structure of the more general line soliton solutions. All this yields a
characterization of possible evolutions of line soliton patterns on a shallow
fluid surface (provided that the KP-II approximation applies).Comment: 49 pages, 36 figures, second version: section 4 expande
Approximate Quantum Fourier Transform and Decoherence
We discuss the advantages of using the approximate quantum Fourier transform
(AQFT) in algorithms which involve periodicity estimations. We analyse quantum
networks performing AQFT in the presence of decoherence and show that extensive
approximations can be made before the accuracy of AQFT (as compared with
regular quantum Fourier transform) is compromised. We show that for some
computations an approximation may imply a better performance.Comment: 14 pages, 10 fig. (8 *.eps files). More information on
http://eve.physics.ox.ac.uk/QChome.html
http://www.physics.helsinki.fi/~kasuomin
http://www.physics.helsinki.fi/~kira/group.htm
A geometric theory of non-local two-qubit operations
We study non-local two-qubit operations from a geometric perspective. By
applying a Cartan decomposition to su(4), we find that the geometric structure
of non-local gates is a 3-Torus. We derive the invariants for local
transformations, and connect these local invariants to the coordinates of the
3-Torus. Since different points on the 3-Torus may correspond to the same local
equivalence class, we use the Weyl group theory to reduce the symmetry. We show
that the local equivalence classes of two-qubit gates are in one-to-one
correspondence with the points in a tetrahedron except on the base. We then
study the properties of perfect entanglers, that is, the two-qubit operations
that can generate maximally entangled states from some initially separable
states. We provide criteria to determine whether a given two-qubit gate is a
perfect entangler and establish a geometric description of perfect entanglers
by making use of the tetrahedral representation of non-local gates. We find
that exactly half the non-local gates are perfect entanglers. We also
investigate the non-local operations generated by a given Hamiltonian. We first
study the gates that can be directly generated by a Hamiltonian. Then we
explicitly construct a quantum circuit that contains at most three non-local
gates generated by a two-body interaction Hamiltonian, together with at most
four local gates generated by single qubit terms. We prove that such a quantum
circuit can simulate any arbitrary two-qubit gate exactly, and hence it
provides an efficient implementation of universal quantum computation and
simulation.Comment: 22 pages, 6 figure
Polarization state of a biphoton: quantum ternary logic
Polarization state of biphoton light generated via collinear
frequency-degenerate spontaneous parametric down-conversion is considered. A
biphoton is described by a three-component polarization vector, its arbitrary
transformations relating to the SU(3) group. A subset of such transformations,
available with retardation plates, is realized experimentally. In particular,
two independent orthogonally polarized beams of type-I biphotons are
transformed into a beam of type-II biphotons. Polarized biphotons are suggested
as ternary analogs of two-state quantum systems (qubits)
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