97 research outputs found
Acoustic CO2 Gas Sensor Based on Phase Difference Measurement
In this research, an acoustic sensor has been successfully built to measure the concentration of CO2 gas in a mixture of gases (N2 and CO2). The nitrogen and carbon dioxide gases used are ultra-high purity (UHP) gas. The measurement parameter used is the speed of sound by utilizing the phase shift between ultrasonic wave signals that are sent and received continuously. The acoustic method in this research is by using the speaker as an ultrasonic wave transmitter, and the microphone as an ultrasonic wave receiver emitted by the speaker on the gas medium. This acoustic phase shift method is very sensitive to be used to determine the speed of sound on a gas medium. From the sensor testing, the sensor has good linearity in detecting changes in CO2 concentration in the gas mixture. The sensor test results have been validated theoretically and obtained an RMS error of 3.36 (3.36% with a maximum concentration of 100%), this proves that the work of the sensor is in accordance with the theory. In addition to theoretical validation, the work of the sensor has also been validated by looking at the direct relationship between sensor input and output through the inverse function, and an RMS error of 3.51 (3.51% with a maximum concentration of 100%) is obtained. From the overall results obtained, the acoustic CO2 gas sensor that is built can detect changes in CO2 concentrations in the gas mixture accurately, fabrication of the sensor is easy to do, and the costs required in the manufacturing process are cheap
Electromodulated photoinduced absorption : A new spectroscopy in π- conjugated polymer/C60 blends
Optical Science, Engineering and Instrumentation '97, 1997, San Diego, CA, United StatesMartin Liess, Paul A. Lane, Zakya H. Kafafi, M. Hamaguchi, Masanori Ozaki, Katsumi Yoshino, and Z. Valy Vardeny "Electromodulated photoinduced absorption: a new spectroscopy in π-conjugated polymer/C60 blends", Proc. SPIE 3142, Fullerenes and Photonics IV, (1 November 1997). DOI: https://doi.org/10.1117/12.29335
Two-photon absorption spectra of luminescent conducting polymers measured over wide spectral range
Optical Science, Engineering and Instrumentation '97, 1997, San Diego, CA, United StatesRon K. Meyer, Martin Liess, Robert E. Benner, Werner Gellermann, Z. Valy Vardeny, Masanori Ozaki, Katsumi Yoshino, Yi Wei Ding, and Thomas J. Barton "Two-photon absorption spectra of luminescent conducting polymers measured over wide spectral range", Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997). DOI: https://doi.org/10.1117/12.27927
A theoretical investigation of the low lying electronic structure of poly(p-phenylene vinylene)
The two-state molecular orbital model of the one-dimensional phenyl-based
semiconductors is applied to poly(p-phenylene vinylene). The energies of the
low-lying excited states are calculated using the density matrix
renormalization group method. Calculations of both the exciton size and the
charge gap show that there are both Bu and Ag excitonic levels below the band
threshold. The energy of the 1Bu exciton extrapolates to 2.60 eV in the limit
of infinite polymers, while the energy of the 2Ag exciton extrapolates to 2.94
eV. The calculated binding energy of the 1Bu exciton is 0.9 eV for a 13
phenylene unit chain and 0.6 eV for an infinite polymer. This is expected to
decrease due to solvation effects. The lowest triplet state is calculated to be
at ca. 1.6 eV, with the triplet-triplet gap being ca. 1.6 eV. A comparison
between theory, and two-photon absorption and electroabsorption is made,
leading to a consistent picture of the essential states responsible for most of
the third-order nonlinear optical properties. An interpretation of the
experimental nonlinear optical spectroscopies suggests an energy difference of
ca. 0.4 eV between the vertical energy and ca. 0.8 eV between the relaxed
energy, of the 1Bu exciton and the band gap, respectively.Comment: LaTeX, 19 pages, 7 eps figures included using epsf. To appear in
Physical Review B, 199
Theory of excited state absorptions in phenylene-based -conjugated polymers
Within a rigid-band correlated electron model for oligomers of
poly-(paraphenylene) (PPP) and poly-(paraphenylenevinylene) (PPV), we show that
there exist two fundamentally different classes of two-photon A states in
these systems to which photoinduced absorption (PA) can occur. At relatively
lower energies there occur A states which are superpositions of one
electron - one hole (1e--1h) and two electron -- two hole (2e--2h) excitations,
that are both comprised of the highest delocalized valence band and the lowest
delocalized conduction band states only. The dominant PA is to one specific
member of this class of states (the mA). In addition to the above class of
A states, PA can also occur to a higher energy kA state whose 2e--2h
component is {\em different} and has significant contributions from excitations
involving both delocalized and localized bands. Our calculated scaled energies
of the mA and the kA agree reasonably well to the experimentally
observed low and high energy PAs in PPV. The calculated relative intensities of
the two PAs are also in qualitative agreement with experiment. In the case of
ladder-type PPP and its oligomers, we predict from our theoretical work a new
intense PA at an energy considerably lower than the region where PA have been
observed currently. Based on earlier work that showed that efficient
charge--carrier generation occurs upon excitation to odd--parity states that
involve both delocalized and localized bands, we speculate that it is the
characteristic electronic nature of the kA that leads to charge generation
subsequent to excitation to this state, as found experimentally.Comment: Revtex4 style, 2 figures inserted in the text, three tables, 10 page
Linear and nonlinear optical properties of the conjugated polymers PPV and MEH-PPV
We have used absorption and electroabsorption spectroscopy to investigate the electronic structure of poly(para-phenylene vinylene) (PPV) and poly (2-methoxy, 5-(2'-(ethyl)hexyloxy)-p-phenylene vinylene) (MEH-PPV). In particular we examine the often used assumption that the electronic structure of PPV and its dialkoxy substituted derivatives are essentially the same. The absorption spectrum of PPV consists of three peaks, while that of MEH-PPV has four peaks. We discuss the controversial origin of the extra peak as well as evidence for Davydov splitting effects in the absorption spectrum of PPV. The analysis of the nonlinear spectra shows further differences between the two materials. First, the binding energy of the 1B(u) exciton for PPV is some 0.1 eV higher than for MEH-PPV. Second, the peak value of Im{chi((3))(-omega;0,0,omega)} for PPV is approximately 40 times higher than that of MEH-PPV. We also found that the sum-over-states modeling of the electroabsorption spectra indicates that the transition dipole moment between the mA(g) and nB(u) states is of opposite sign in the two polymers. [S0163-1829(99)02523-0]
Do drivers of biodiversity change differ in importance across marine and terrestrial systems — Or is it just different research communities' perspectives?
Cross-system studies on the response of different ecosystems to global change will support our understanding of ecological changes. Synoptic views on the planet's two main realms, the marine and terrestrial, however, are rare, owing to the development of rather disparate research communities.We combined questionnaires and a literature review to investigate howthe importance of anthropogenic drivers of biodiversity change differs amongmarine and terrestrial systems and whether differences perceived by marine vs. terrestrial researchers are reflected by the scientific literature. This included asking marine and terrestrial researchers to rate the relevance of different drivers of global change for either marine or terrestrial biodiversity. Land use and the associated loss of natural habitatswere rated as most important in the terrestrial realm,while the exploitation of the sea by fishing was rated as most important in the marine realm. The relevance of chemicals, climate change and the increasing atmospheric concentration of CO2 were rated differently for marine and terrestrial biodiversity respectively. Yet, our literature review provided less evidence for such differences leading to the conclusion that while the history of the use of land and sea differs, impacts of global change are likely to become increasingly similar
Toward refined environmental scenarios for ecological risk assessment of down-the-drain chemicals in freshwater environments
Current regulatory practice for chemical risk assessment suffers from the lack of realism in conventional frameworks. Despite significant advances in exposure and ecological effect modeling, the implementation of novel approaches as high-tier options for prospective regulatory risk assessment remains limited, particularly among general chemicals such as down-the-drain ingredients. While reviewing the current state of the art in environmental exposure and ecological effect modeling, we propose a scenario-based framework that enables a better integration of exposure and effect assessments in a tiered approach. Global- to catchment-scale spatially explicit exposure models can be used to identify areas of higher exposure and to generate ecologically relevant exposure information for input into effect models. Numerous examples of mechanistic ecological effect models demonstrate that it is technically feasible to extrapolate from individual-level effects to effects at higher levels of biological organization and from laboratory to environmental conditions. However, the data required to parameterize effect models that can embrace the complexity of ecosystems are large and require a targeted approach. Experimental efforts should, therefore, focus on vulnerable species and/or traits and ecological conditions of relevance. We outline key research needs to address the challenges that currently hinder the practical application of advanced model-based approaches to risk assessment of down-the-drain chemicals
Scientific Opinion addressing the state of the science on risk assessment of plant protection products for in-soil organisms
Following a request from EFSA, the Panel on Plant Protection Products and their Residues developed an opinion on the science behind the risk assessment of plant protection products for in-soil organisms. The current risk assessment scheme is reviewed, taking into account new regulatory frameworks and scientific developments. Proposals are made for specific protection goals for in-soil organisms being key drivers for relevant ecosystem services in agricultural landscapes such as nutrient cycling, soil structure, pest control and biodiversity. Considering the time-scales and biological processes related to the dispersal of the majority of in-soil organisms compared to terrestrial non-target arthropods living above soil, the Panel proposes that in-soil environmental risk assessments are made at in- and off-field scale considering field boundary levels. A new testing strategy which takes into account the relevant exposure routes for in-soil organisms and the potential direct and indirect effects is proposed. In order to address species recovery and long-term impacts of PPPs, the use of population models is also proposed
Design neuer Sensoren unter Berücksichtigung von Strukturaspekten
This work is a contribution to sensor science and engineering. A
mathematical method is introduced to examine sensor structures and examples
of application of this method are given. One of them is the analysis of the
retinal receptive field structure.
The main focus is chapter 4 that presents 4 novel or significantly improved
sensor principles, which are based on improved structures. They are
- Gas sensors based on the electric field induced migration of chemisorbed
gas ions on a sensitive thin film (patent DE 10041263).
- Gas sensors based on the effect that the Seebeck voltage between
thermocouples with at least one chemical sensitive material depends on the
gas environment of that material.
- Gas detectors based on photo induced ionisation (PID) where the motion of
space charges is controlled by an electric field (patent DE18928903, DE
19838759).
- Multidimensional motion sensors that are based on self-mixing of
scattered Laser light with the light wave in the cavity of the generating
laser diode (patents WO0237124, EP1261877, CN1408064T, US2003016365,
EP1261877, WO0237410, US2003160155, WO03032138, WO0237411A1, CN1416554T,
EP1334464, US2003006367, WO03102717, US6707027, US2002104957, WO2004021158)
In chapter 5 a categorization scheme for sensor structures is presented.
The scheme is used to discuss different structural improvements of sensors,
in particular those presented in chapter 4.Vorwort und Zusammenfassung
Im Hauptteil der vorliegenden Arbeit (Kapitel 4) werden vier verschiedene
neu entwickelte oder wesentlich verbesserte Sensorprinzipien vorgestellt.
Die Stärke dieser Sensorprinzipien ist deren Struktur, die zu einer
verbesserten Nachweisgrenze oder Stabilität führt.
Die Struktur eines Sensors (Kapitel 2)
Um die Wirkung der Sensorstruktur algemeingültig zu diskutieren wird im
zweiten Kapitel ein Modell entwickelt, das Eigenschaften von Sensoren auf
deren Struktur zurückführt.
Dabei werden alle Sensoreigenschaften allgemein von einer einfachen
Gleichung generiert und daraus Schlussfolgerungen für die Eigenschaften der
Sensorstruktur gezogen.
Es zeigt sich, wie sich der Effekt struktureller Maßnahmen in der
Nachweisgrenze niederschlägt, und sich mit der verbesserten Nachweisgrenze
die Messunsicherheit (als Funktion aller Eingangsgrößen) parallel
verschiebt.
Strukturanalyse eines Sensors am Beispiel der Retina (Kapitel 3)
Im dritten Kapitel wird das Modell beispielhaft auf das Auge höherer
Säugetiere angewandt. In der Einleitung werden die bekannten biologischen
Fakten für Ingenieure und Physiker verständlich eingeführt.
Darauf folgt eine mathematischen Strukturanalyse der Retina (und
Leiterstrukturen allgemein), die als Sensorsystem betrachtet wird. Es zeigt
sich, wie die Schwächen der Komponenten (Nervenzellen) der Retina durch
deren Struktur kompensiert werden.
Sensoren mit verbesserter Struktur (Kapitel 4)
1. Gasmessung mit Hilfe gasempfindlicher Thermopaare
Bekannt ist der Gebrauch von Thermopaaren zur Messung von
Temperaturunterschieden. In dieser Arbeit wird eine bisher unbekannt
gewesene Methode vorgestellt, mit der bei einem konstanten
Temperaturunterschied eine Gaskonzentration gemessen wird. Dabei spielt die
Abhängigkeit der differentiellen Thermospannung von der Ladungsträgerdichte
in sensitiven Materialien eine Rolle.
2. Elektromigration von chemisorbierten Ionen auf einem halbleitenden Film
Sensoren basierend auf Widerstandsänderungen von gasempfindlichen Filmen
sind seit längerem im Gebrauch. Neu ist, deren aufgrund von Migration
veränderliches Widerstandsprofil in Ort und Zeit zu messen und damit
Sensoren zu bauen, die unempfindlicher gegen Alterung sind.
3. Modulation von Ionenbewegungen mit Hilfe eines zusätzlichen Gitters im
Photoionisationdetektor
Zwar sind sowohl Photoionisationsdetektoren (PID's) als auch das
Modulationsprinzip an sich bekannt, jedoch ist bis dahin noch kein
modulierter PID vorgestellt worden. Entscheidend an der hier eingeführten
Innovation ist die Methode, den Photoionisationsstrom zu modulieren, jedoch
dem Leckstrom und den äußeren Photostrom an der Kathode unmoduliert zu
lassen. Das führt zu einer 20-fachen Verbesserung der Nachweisgrenze.
4. Laserdiodeneigenmischung zur mehrdimensionalen Bewegungsmessung
Die Rückwirkung von in die Quelle zurückgestreutem Laserlicht war bisher
als Störeffekt bekannt. Um diesen Effekt in einem Bewegungssensor nutzen zu
können, mussten Probleme wie Richtungserkennung und Miniaturisierung gelöst
werden.
Kapitel 5 befasst sich mit Strukturverbesserungen der im vorherigen Kapitel
genannten und weiteren Sensoren. Dazu wird eine Strukturschreibweise
vorgestellt. Kapitel 6 enthält eine Zusammenfassung und einen Ausblick
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