499 research outputs found
Blood Meal as a Source of Histidine for Cattle Fed Grass Silage and Barley
Previous research has shown that cattle fed grass silage are responsive to protected amino acids (Veira et al., 1991). Methionine and lysine were suggested as the most limiting amino acids for grass silage diets. Recently, Korhonen et al. (2000) have shown that histidine is the first limiting amino acids for dairy cows fed grass silage and barley-based concentrates. However, histidine is not available in a rumen protected form and needs to be provided through dietary ingredients. Blood meal is rich in histidine. This trial was designed to determine the effect of increasing histidine supply through blood meal on N metabolism of cattle fed a grass silage and barley-based diet
Stabilisation of Quantum Computations by Symmetrisation
We propose a method for the stabilisation of quantum computations (including
quantum state storage). The method is based on the operation of projection into
, the symmetric subspace of the full state space of redundant
copies of the computer. We describe an efficient algorithm and quantum network
effecting --projection and discuss the stabilising effect of the
proposed method in the context of unitary errors generated by hardware
imprecision, and nonunitary errors arising from external environmental
interaction. Finally, limitations of the method are discussed.Comment: 20 pages LaTeX, 2 postscript figure
Changes in hemlock looper [Lepidoptera: Geometridae] pupal distribution through a 3-year outbreak cycle
La distribution des chrysalides de l’arpenteuse de la pruche, Lambdina fiscellaria, a été étudiée au cours d’un cycle épidémique d’une durée de trois ans près du Lac Princeton sur l’île d’Anticosti au Québec. Au total, 10 sapins ont été coupés et toutes les chrysalides ont été comptées sur le tronc et les branches (partie non-foliée vs foliée) de la cime inférieure, médiane et supérieure, ainsi que sur le tronc sous la cime. En condition préépidémique, les chrysalides ont principalement été trouvées sur les branches des cimes médianes et supérieures. Durant l’épidémie, la densité des chrysalides n’a pas augmenté dans ces sites de pupaison et les larves se sont surtout transformées en chrysalides sur le tronc, à partir du sol jusque dans la cime médiane, ainsi que sur les branches de la cime inférieure. Peu de chrysalides ont été trouvées sur la partie foliée des branches en période post-épidémique, la plupart étant trouvées sur la partie basale non-foliée qui apparaît comme un endroit préférentiel pour la pupaison de l'arpenteuse de la pruche. De façon à optimiser la détection des augmentations de populations dans les réseaux de surveillance, des pièges à chrysalides devraient être placés à hauteur de poitrine sur le tronc de sapins baumiers.The hemlock looper, Lambdina fiscellaria, pupal distribution was studied through a 3-year outbreak cycle near Lac Princeton on Anticosti Island in Quebec. Over the 3 years, 10 balsam fir trees were cut and all pupae were counted on the stem and branches (non-foliated vs foliated parts) of the lower, middle and upper crowns and on the stem below crown. In pre-outbreak conditions, pupae were mostly found on branches of the middle and upper crowns. During the outbreak, pupal density did not increase on these parts of the trees, since pupae were mostly found on the stem, from the ground to the middle crown, and on branches of the lower crown. Few pupae were found on the foliated portion of branches in post-outbreak conditions but most were found on the basal non-foliated part of branches, which appears to be a preferred location for hemlock looper pupation. In order to optimize detection of population increases in monitoring networks, we suggest using pupal traps at breast height on balsam fir trees
Quantum secret sharing
Secret sharing is a procedure for splitting a message into several parts so
that no subset of parts is sufficient to read the message, but the entire set
is. We show how this procedure can be implemented using GHZ states. In the
quantum case the presence of an eavesdropper will introduce errors so that his
presence can be detected. We also show how GHZ states can be used to split
quantum information into two parts so that both parts are necessary to
reconstruct the original qubit.Comment: 6 pages, revtex, revised version, to appear in Phys. Rev.
Demonstration of improved sensitivity of echo interferometers to gravitational acceleration
We have developed two configurations of an echo interferometer that rely on
standing wave excitation of a laser-cooled sample of rubidium atoms that
measures acceleration. For a two-pulse configuration, the interferometer signal
is modulated at the recoil frequency and exhibits a sinusoidal frequency chirp
as a function of pulse spacing. For a three-pulse stimulated echo
configuration, the signal is observed without recoil modulation and exhibits a
modulation at a single frequency. The three-pulse configuration is less
sensitive to effects of vibrations and magnetic field curvature leading to a
longer experimental timescale. For both configurations of the atom
interferometer (AI), we show that a measurement of acceleration with a
statistical precision of 0.5% can be realized by analyzing the shape of the
echo envelope that has a temporal duration of a few microseconds. Using the
two-pulse AI, we obtain measurements of acceleration that are statistically
precise to 6 parts per million (ppm) on a 25 ms timescale. Using the
three-pulse AI, we obtain measurements of acceleration that are statistically
precise to 0.4 ppm on a timescale of 50 ms. A further statistical enhancement
is achieved by analyzing the data across the echo envelope to improve the
statistical precision to 75 parts per billion (ppb). We discuss methods for
reducing prominent systematic effects due to a magnetized vacuum chamber and
improving the signal-to-noise ratio. Simulations of both AI configurations with
a timescale of 300 ms reached in a non-magnetic vacuum chamber suggest that an
optimized experiment with improved vibration isolation and atoms selected in
the mF = 0 state can result in measurements of g statistically precise to 0.3
pbb for the two-pulse AI and 0.6 ppb for the three-pulse AI.Comment: 17 pages, 9 figures, 3 table
A flow cell simulating a subsurface rock fracture for investigations of groundwater-derived biofilms
Laboratory scale continuous-flow-through chambers (flow cells) facilitate the observation of microbes in a controlled, fully hydrated environment, although these systems often do not simulate the environmental conditions under which microorganisms are found. We developed a flow cell that mimics a subsurface groundwater-saturated rock fracture and isamenable to confocal laser scanning microscopy while allowing for the simple removal of the attached biomass. This flow cell was used to investigate the effect of toluene, a representative contaminant for non-aqueous phase liquids, on groundwater-derived biofilms. Reduced average biofilm biomass and thickness, and diminished diversity of amplifiable 16S rRNA sequences were observed for biofilms that developed in the presence of toluene, compared to the biofilms grown in the absence of toluene. The flow cell also allowed the detection of fluorescent protein-labelled cells
Perfect quantum error correction coding in 24 laser pulses
An efficient coding circuit is given for the perfect quantum error correction
of a single qubit against arbitrary 1-qubit errors within a 5 qubit code. The
circuit presented employs a double `classical' code, i.e., one for bit flips
and one for phase shifts. An implementation of this coding circuit on an
ion-trap quantum computer is described that requires 26 laser pulses. A further
circuit is presented requiring only 24 laser pulses, making it an efficient
protection scheme against arbitrary 1-qubit errors. In addition, the
performance of two error correction schemes, one based on the quantum Zeno
effect and the other using standard methods, is compared. The quantum Zeno
error correction scheme is found to fail completely for a model of noise based
on phase-diffusion.Comment: Replacement paper: Lost two laser pulses gained one author; added
appendix with circuits easily implementable on an ion-trap compute
Two-Bit Gates are Universal for Quantum Computation
A proof is given, which relies on the commutator algebra of the unitary Lie
groups, that quantum gates operating on just two bits at a time are sufficient
to construct a general quantum circuit. The best previous result had shown the
universality of three-bit gates, by analogy to the universality of the Toffoli
three-bit gate of classical reversible computing. Two-bit quantum gates may be
implemented by magnetic resonance operations applied to a pair of electronic or
nuclear spins. A ``gearbox quantum computer'' proposed here, based on the
principles of atomic force microscopy, would permit the operation of such
two-bit gates in a physical system with very long phase breaking (i.e., quantum
phase coherence) times. Simpler versions of the gearbox computer could be used
to do experiments on Einstein-Podolsky-Rosen states and related entangled
quantum states.Comment: 21 pages, REVTeX 3.0, two .ps figures available from author upon
reques
Mesoscopic superpositions of vibronic collective states of N trapped ions
We propose a scalable procedure to generate entangled superpositions of
motional coherent states and electronic states in N trapped ions. Beyond their
fundamental importance, these states may be of interest for quantum information
processing and may be used in experimental studies of decoherence.Comment: Final version, as published in Physical Review Letters. See also
further developments and applications in quant-ph/020207
Experimental realization of the one qubit Deutsch-Jozsa algorithm in a quantum dot
We perform quantum interference experiments on a single self-assembled
semiconductor quantum dot. The presence or absence of a single exciton in the
dot provides a qubit that we control with femtosecond time resolution. We
combine a set of quantum operations to realize the single-qubit Deutsch-Jozsa
algorithm. The results show the feasibility of single qubit quantum logic in a
semiconductor quantum dot using ultrafast optical control.Comment: REVTex4, 4 pages, 3 figures. Now includes more details about the
dephasing in the quantum dots. The introduction has been reworded for
clarity. Minor readability fixe
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