431 research outputs found
Report on the 2012 Proficiency Test on pyrrolizidine alkaloids in honey and hay
The purpose of this proficiency test was to investigate the current measurement capacities of testing laboratories for pyrrolizidine alkaloids in honey and plant materials. The scheme consisted of two parts: Benchmarking performance of laboratories against known estimates of pyrrolizidine alkaloids in the samples and checking for methodological differences while measuring naturally contaminated materials.
Twenty-eight laboratories expressed their will to participate and analysed multiple analytes in several test samples of honey and plant material.
The analysis of spiked honey showed no statistical differences between determining a common sum parameter for alkaloids and individual determination. A significant difference has been found however for of naturally contaminated materials. Individual alkaloid determination showed significantly lower results, possibly because of the presence of substances contributing to the sum parameter that were not in the scopes of the methods applied as well as lack of standard materials available on the market.
Satisfactory performance for all of analytes has been achieved by more than half of participants analysing for both: sum parameter, and alkaloids analysed individually.JRC.D.5-Standards for Food Bioscienc
Engineering long-range molecular potentials by external drive
We report the engineering of molecular potentials at large interatomic
distances. The molecular states are generated by off-resonant optical coupling
to a highly excited, long-range Rydberg molecular potential. The coupling
produces a potential well in the low-lying molecular potential, which supports
a bound state. The depth of the potential well, and thus the binding energy of
the molecule, can be tuned by the coupling parameters. We characterize these
molecules and find good agreement with a theoretical model based on the
coupling of the two involved adiabatic potential energy curves. Our results
open numerous possibilities to create long-range molecules between ultracold
ground state atoms and to use them for ultracold chemistry and applications
such as Feshbach resonances, Efimov physics or the study of halo molecules
Griffiths Phase in a Facilitated Rydberg Gas at Low Temperature
The spread of excitations by Rydberg facilitation bears many similarities to
epidemics. Such systems can be modeled with Monte-Carlo simulations of
classical rate equations to great accuracy as a result of high dephasing. In
this paper, we analyze the dynamics of a Rydberg many-body system in the
facilitation regime in the limits of high and low temperatures. While in the
high-temperature limit a homogeneous mean-field behaviour is recovered,
characteristic effects of heterogeneity can be seen in a frozen gas. At large
temperatures the system displays an absorbing-state phase transition and, in
the presence of an additional loss channel, self-organized criticality. In a
frozen or low-temperature gas, excitations are constrained to a network
resembling an Erd\"os-Renyi graph. We show that the absorbing-state phase
transition is replaced with an extended Griffiths phase, which we accurately
describe by a susceptible-infected-susceptible model on the Erd\"os-Renyi
network taking into account Rydberg blockade. Furthermore, we expand upon an
existing macroscopic Langevin equation to more accurately describe the density
of Rydberg atoms in the frozen and finite temperature regimes.Comment: 14 pages, 11 figure
Experimental realization of a 3D long-range random hopping model
Randomness and disorder have strong impact on transport processes in quantum
systems and give rise to phenomena such as Anderson localization [1-3],
many-body localization [4] or glassy dynamics [5]. Their characteristics
thereby depend on the strength and type of disorder. An important class are
hopping models, where particles or excitations move through a system which has
randomized couplings. This includes, e.g., spin glasses [5], coupled optical
waveguides [6], or NV center arrays [7]. They are also key to understand
excitation transport in molecular and biological systems, such as light
harvesting complexes [8]. In many of those systems, the microscopic coupling
mechanism is provided by the dipole-dipole interaction. Rydberg systems [9] are
therefore a natural candidate to study random hopping models. Here, we
experimentally study a three-dimensional many-body Rydberg system with random
dipole-dipole couplings. We measure the spectrum of the many-body system and
find good agreement with an effective spin model. We also find spectroscopic
signatures of a localization-delocalization transition. Our results pave the
way to study transport processes and localization phenomena in random hopping
models in detail. The inclusion of strong correlations is experimentally
straightforward and will allow to study the interplay between random hopping
and localization in strongly interacting systems.Comment: 7 pages, 4 figure
Experimental study of a drop "evolution" under conditions of its free fall on a heated surface
Time dependences of distilled water drop diameter were obtained experimentally after its falling on a heated copper substrate from a height of 0.09 m. The temperature of the solid surface ( Tw ) varied from 333 to 413 K in steps of 20 K. The effect on the drop dynamics after falling and the maximum ratio of the spreading diameter to the drop diameter in flight ( [beta]max ) were determined
Экологическая безопасность на территории Обь-Томского междуречья для устойчивого развития территории
Automated information system for the classification of data from XML documents
The article presents the developed automated information system that solves the task of structuring information obtained from the xml file and storing it in the database. Also, this AIS allows to change the information and upload it to the formats xls and xml
Обзор и назначение экономических информационных систем
ObjectivesThis study was designed to develop a technique to selectively increase the sympathetic tone to the heart by cardiac sympathetic nerve stimulation (SNS).BackgroundAccess to the cardiac sympathetic neurons may allow modulating the adrenergic tone of the heart while avoiding systemic side effects.MethodsCardiac sympathetic nerves course within neural sleeves along the subclavian artery. Because of this proximity, transvascular SNS was attempted with electrode catheters inside the subclavian artery in 16 pigs.ResultsRight/left (R-/L-) SNS (20 Hz) during ventricular pacing at 200/min evoked a >100% increase of left ventricular systolic pressure (baseline: 51 ± 1 mm Hg; L-SNS: 118 ± 26 mm Hg; R-SNS: 116 ± 33 mm Hg; p < 0.001) while systemic vascular resistance remained unchanged. There was a sigmoid dose-response curve with rapid on- and offset of the effect during SNS initiation/cessation. Positive inotropic effects persisted for 12 h of continued SNS (n = 4). Besides positive dromotropic effects, L-SNS/R-SNS yielded a 41% and 77% sinus rate increase, respectively.ConclusionsThe neural adrenergic tone to the heart can be selectively increased by catheter stimulation of cardiac efferent sympathetic nerves
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