970 research outputs found
Homodyned and Heterodyned Vibrational Sum Frequency Generation Spectroscopy of Electrochemical Interfaces
Since its development in the 1980s the second-order nonlinear optical technique of
vibrational sum frequency generation spectroscopy (SFG) evolved into a versatile
tool to detect and characterize molecules at interfaces. To obtain complete
information on the moleculesâ absolute orientation and to disentangle the
interference of a possible non-resonant substrateâs response which distorts the
spectral line shape, however, phase-resolved measurements need to be applied.
In such heterodyned SFG experiments the signal pulse which is generated by
the nonlinear interaction between two incoming short pulses and a sample
subsequently interferes with a so called local oscillator (LO) pulse. To yield
accurate results, relative phase stability between the signal and LO as well as
a precise control of their individual timings must be warranted. The simultaneous
fulfillment of this two requirements so far have restricted heterodyned
SFG experiments to the study of solid/air and liquid/air interfaces. This thesis
presents a way to overcome these limitations by integrating a timing control
scheme into a collinear high accuracy phase-resolved SFG spectrometer. The
versatility of this approach is tested at the solid/liquid interface and extended
to potential dependent measurements since among others understanding of
electrochemical processes at the electrode/electrolyte interface will be critical
in the development of more efficient batteries and fuel cells to tackle the challenges
presented by the climate crisis. The obtained heterodyned SFG spectra
allow an insight into the parameters that influence the non-resonant substrateâs
response, such as an applied potential bias and the presence of specifically and
non-specifically adsorbed ions and molecules. In addition a method is presented
how to use phase-resolved SFG spectra to determine the phase of the
local field Fresnel factors, which so far had to be modeled. The heterodyned
spectra are compared to their homodyned analogs to discuss which new information
in fact can be obtained and what limits still need to be overcome.Eine verbreitete Methode zur Charakterisierung von molekularen Prozessen an
GrenzflÀchen ist die Summenfrequenz(SFG)-Schwingungsspektroskopie, die
auf einem nichtlinearen optischen Effekt zweiter Ordnung beruht. Die ursprĂŒngliche
Methode detektiert die IntensitÀt des SFG Signals. Dabei gehen jedoch
Informationen ĂŒber die absolute Orientierung der MolekĂŒle an der GrenzflĂ€che
verloren. AuĂerdem kann ein nichtresonanter Beitrag des unterliegenden Substrats
durch Interferenz die Linienform des Spektrums beeinflussen, was die
Interpretation erschwert. Daher wurde unter Zuhilfenahme eines lokalen Oszillator
(LO) Pulses die phasenaufgelöste SFG-Spektroskopie entwickelt. Zur
GewÀhrleistung einer akkuraten Phasenauflösung muss eine konstante Phasenbeziehung
zwischen Signal und LO vorherrschen. AuĂerdem verlangt die Methode
eine prÀzise Kontrolle der individuellen Pulszeiten. Die gleichzeitige Einhaltung
beider Voraussetzungen ist experimentell aufwendig, was bisher einen
Einsatz ĂŒber die GrenzflĂ€chen fest/gasförimg und flĂŒssig/gasförmig hinaus
verhinderte. Die vorliegende Arbeit erweitert den Einsatzbereich auch auf
die fest/flĂŒssig GrenzflĂ€che und erlaubt damit auch phasenaufgelöste in situ
Messungen elektrochemischer Prozesse an der ElektrodenoberflÀche. Das VerstÀndnis
dieser Prozesse ist ein wichtiger Schritt zur Entwicklung effektiverer
Batterien und Elektroden fĂŒr Brennstoffzellen, wichtige Bestandteile zur EindĂ€mmung
des Klimawandels. Zur Realisierung solcher Messungen wird ein
Schema zur Pulszeitkontrolle vorgestellt und in ein kollineares hoch prÀzises
phasenaufgelöstes SFG-Spektrometer eingefĂŒhrt. Die entstandenen phasenaufgelösten
SFG-Spektren erlauben einen Einblick in die AbhÀngigkeit des nichtresonanten
SFG Beitrags des Substrat von Faktoren wie einer angelegten elektrischen
Spannung und der Anwesenheit gebundener/ungebundener MolekĂŒle
/Ionen an der SubstratgrenzflÀche. Desweiteren wird eine Methode vorgestellt,
die es erlaubt die Phase der lokalen Feldfaktoren zu bestimmen, die
bisher nur theoretisch berechnet werden konnte. Die phasenaufgelösten SFG-Spektren
werden mit herkömmlichen SFG-Spektren verglichen um den zusÀtzlichen
Informationsgewinn herauszuarbeiten, aber auch um noch offene Fragen
zu erkennen
Approaching religion through linguistics: methodological thoughts on a linguistic analysis of 'religion' in political communication
The constructions of âreligionâ in general language are seldom themselves in the focus of empirical research. Aiming to retrieve the inherent knowledge that lies within these constructions, this article suggests a term-based textual analysis to focus on the linguistic use of âreligionâ. This method invites us to question the unity of texts through an analysis of textual semantics. It offers the chance to ask about the formation of the concept. The article initially shows how this approach differs from comparative and policy-oriented studies by differentiating between criticism and critique. It then develops the idea of a term-based textual analysis. Using examples from the policy field of foreign aid, the text illustrates how much inherent knowledge there is in the usage of âreligionâ in political communication and calls for a general reconsideration of the way âreligionâ is approached in empirical research
Making Plans for Commercial Aquaculture in the North Central Region
Aquaculture is not a new concept. Japanese, Chinese, Romans, Egyptians, and Mayan Indians farmed fish for food and recreation prior to 2000 BC. Ponds were constructed and fish were raised much in the same manner as fish are raised today. Both freshwater and saltwater fish are currently raised commercially throughout the world. Other related aquatic products raised commercially are shrimp, crayfish, oysters, clams, worms, crickets, frogs, and some plants. Aquaculture is the general term used to describe the propagation and rearing of aquatic animals and plants in controlled or selected environments. Although aquaculture is increasing in popularity in this country, the vast majority of fisheries food products eaten in the United States are imported or are captured wild stocks from natural waters
Trout Culture in the North Central Region
Trout have been raised in the United States for about 150 years. Initially, trout were raised to replace wild stocks that were declining because of over fishing, loss of habitat and pollution. United States trout farming began in the North Central Region with the establishment of Ackleyâs Farm near Cleveland, OH. This farm was run by Theodatus Garlick, M.D., and H.A. Ackley, M.D., who developed ways to spawn brook trout and incubate the eggs in glass jars. Today, trout are still raised in the North Central Region in state, federal and private fish farms to stock lakes, ponds and streams. Trout are also raised and sold through fee fishing operations and as food fish through restaurants and supermarkets. Rainbow trout are the most commonly raised trout followed by brook and brown trout. Private commercial trout farms range from small owner/operator farms to large farms with many employees
Feeding Tilapia in Intensive Recirculating Systems
There are many species of tilapia, but only a few are widely cultured around the world. In the United States the most commonly cultured species of tilapia are the Nile (nilotica), Blue (aurea), Mozambique (mossambicus), Hornorum (hornorum), and hybrids such as the Taiwanese and Florida red. Choosing a species to culture depends largely on customer preference, legal status, growth rate and cold tolerance. Tilapia are well suited for culturing in ponds, cages, tanks, or raceways. Using ponds is the most popular method in the southern United States due to longer growing seasons. In the southern most parts of Texas and in Florida water temperatures can remain warm enough for year-round growth. In the cooler, temperate regions of the North and Midwest, tank culture is favored
Shifting gear: new agendas in the sociological study of religion
Editorial for the special issue on the new agendas in the sociological study of religio
Letters between F. W. Garling and William Kerr
Letters concerning a student position at the Utah Agricultural College
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