374 research outputs found
Calibration in process monitoring by using unsegmented continuous-flow systems
An overview is presented of the different aspects of the role of
analytical chemistry in process monitoring and control. On-line
monitoring is currently the most attractive option in this area,
especially with unsegmented-flow techniques. In addition to
allowing automation of these systems, the variety of ways in which
calibration and recalibration can be performed allows their
adaptation to any situation by using extremely simple, home-made
manifolds. The most relevant designs are presented and critically
discussed in this paper
Non-critically squeezed light via spontaneous rotational symmetry breaking
We theoretically address squeezed light generation through the spontaneous
breaking of the rotational invariance occuring in a type I degenerate optical
parametric oscillator (DOPO) pumped above threshold. We show that a DOPO with
spherical mirrors, in which the signal and idler fields correspond to first
order Laguerre-Gauss modes, produces a perfectly squeezed vacuum with the shape
of a Hermite-Gauss mode, within the linearized theory. This occurs at any
pumping level above threshold, hence the phenomenon is non-critical.
Imperfections of the rotational symmetry, due e.g. to cavity anisotropy, are
shown to have a small impact, hence the result is not singular.Comment: 4 pages, 1 figure, replaced with resubmitted versio
Sequential automatic on-line determination of aquiculture nutrients: phosphate and nitrate
A continuous-flow method for the determination of nitrate and
phosphate in water is proposed. The method is based on insertion of
reagents and sample solutions into a single channel through a
programmable switching valve. The method depends upon heteropolyacid
with phosphate and on the modified Griess reaction for
nitrate, and permits the determination of PO-34 in the range 1-20 μg/ml and NO-3 between 5 and 100 μg/ml, the achievable
sampling frequency being 45/hour. The two analytes can be
determined in N/P ratios between 0.25 and 100. The method has
been applied to the determination of nitrate and phosphate in the
sea-water used in fish farms
Flow injection analysis of water. Part 2: Integrated system for automatic multideterrnination
This paper describes an integrated flow injection (FI) system for the determination of ammonia, sulphate and Fe(II)/Fe(III) which can work unattended for long periods. The system was designed for the determination of individual analytes in long series of samples. Each batch of samples requires manual selection of parameters and units, such as wavelength for monitoring, preconcentration column, loops and switching of three valves to select the carrier, reagents and eluent. The system then works automatically
Espectroscopia. fundamento de la resonancia magnética nuclear
Presentamos una introducción al fenómeno de la espectroscopia, su significado y los principios físicos básicos involucrados en el proceso de absorción y emisión de radiación que posee una capacidad suficiente para perturbar las condiciones de equilibrio de un átomo. Explicamos el principio de operación de un espectrómetro sencillo y analizamos la espectroscopia de resonancia magnética nuclear (RMN) una de las herramientas más poderosas con que cuenta la Medicina moderna para detectar ciertos desequilibrios en la estructura y configuración molecular.AbstractWe present an introduction to the phenomenon of spectroscopy.Its meaning and the basic physical principles involve the process of absorption and emission of radiation that possess enough capacity to perturb the conditions of equilibrium of an atom. We explain the principle of operation of a simple spectrometer and analyze the spectroscopy of nuclear magnetic resonance (NMR). It is one of the most powerful tools available to modern medicine to detect certain imbalances in the structure and molecular configuration
Flow-injection analysis for on-line monitoring of nutrients (ammonia and nitrite) in aquaculture
This article describes photometric flow injection (FI) methods for
the determination of ammonia and nitrite in aquaculture. The
methods are based on the use of normal and reversed FI approaches
and show the potential of this technique for monitoring the input
and output streams of small tanks at young fish-breeding farms.
The methods meet the requirements of fish hatcheries, particularly in
terms of the high sampling rate allowable (40/h)
Unsegmented flow approach for on-line monitoring of pH, conductivity, dissolved oxygen and determination of nitrite and ammonia in aquaculture
A fully automated flow system for on-line monitoring of
analytes/parameters of interest in aquaculture is described. The
approach has been optimized for the photometric determination of
nitrite and ammonia and the continuous monitoring of pH,
conductivity and dissolved oxygen, but these analytes/parameters
are readily changeable as required. The system has been tested by
monitoring these species in the input and output sea water streams
of tanks at a fish breeding farm and also by monitoring water
containing high concentrations of fish feed
Theory of quantum fluctuations of optical dissipative structures and its application to the squeezing properties of bright cavity solitons
We present a method for the study of quantum fluctuations of dissipative
structures forming in nonlinear optical cavities, which we illustrate in the
case of a degenerate, type I optical parametric oscillator. The method consists
in (i) taking into account explicitly, through a collective variable
description, the drift of the dissipative structure caused by the quantum
noise, and (ii) expanding the remaining -internal- fluctuations in the
biorthonormal basis associated to the linear operator governing the evolution
of fluctuations in the linearized Langevin equations. We obtain general
expressions for the squeezing and intensity fluctuations spectra. Then we
theoretically study the squeezing properties of a special dissipative
structure, namely, the bright cavity soliton. After reviewing our previous
result that in the linear approximation there is a perfectly squeezed mode
irrespectively of the values of the system parameters, we consider squeezing at
the bifurcation points, and the squeezing detection with a plane--wave local
oscillator field, taking also into account the effect of the detector size on
the level of detectable squeezing.Comment: 10 figure
- …