Добірка наукової літератури з теми "SERS Enhancement Factor"

Over the past 40 years fundamental and application research into Surface-Enhanced Raman Scattering (SERS) has been explored by academia, industry, and government laboratories. To date however, SERS has achieved little commercial success as an analytical technique. Researchers are tackling a variety of paths to help break through the commercial barrier by addressing the reproducibility in both the SERS substrates and SERS signals as well as continuing to explore the underlying mechanisms. To this end, investigators use a variety of methodologies, typically studying strongly binding analytes such as aromatic thiols and azarenes, and report SERS enhancement factor calculations. However a drawback of the traditional SERS enhancement factor calculation is that it does not yield enough information to understand substrate reproducibility, application potential with another analyte, or the driving factors behind the molecule–metal interaction. Our work at the US Army Edgewood Chemical Biological Center has focused on these questions and we have shown that thermodynamic principles play a key role in the SERS response and are an essential factor in future designs of substrates and applications. This work will discuss the advantages and disadvantages of various experimental techniques used to report SERS enhancement with planar SERS substrates and present our alternative SERS enhancement value. We will report on three types of analysis scenarios that all yield different information concerning the effectiveness of the SERS substrate, practical application of the substrate, and finally the thermodynamic properties of the substrate. We believe that through this work a greater understanding for designing substrates will be achieved, one that is based on both thermodynamic and plasmonic properties as opposed to just plasmonic properties. This new understanding and potential change in substrate design will enable more applications for SERS based methodologies including targeting molecules that are traditionally not easily detected with SERS due to the perceived weak molecule–metal interaction of substrates.

In this study, metallic nanoislands were prepared by thermal annealing of gold thin film produced by vacuum evaporation on a glass substrate to investigate the surface-enhanced Raman scattering (SERS) effect on them. The influence of the analyte on the enhancement factor of SERS was studied with riboflavin and rhodamine 6G dye. Two laser excitation sources at 532 and 633 nm wavelengths were used for SERS measurements. We found that the enhancement factors of the gold nanoisland SERS substrates were influenced by the analytes’ adsorption tendency onto their surfaces. The SERS amplification was also found to be dependent on the electronic structure of the molecules; higher enhancement factors were obtained for rhodamine 6G with 532 nm excitation, while for riboflavin the 633 nm source performed better.

Raman spectroscopy has enabled researchers to map the specific chemical makeup of surfaces, solutions, and even cells. However, the inherent insensitivity of the technique makes it difficult to use and statistically complicated. When Raman active molecules are near gold or silver nanoparticles, the Raman intensity is significantly amplified. This phenomenon is referred to as surface-enhanced Raman spectroscopy (SERS). The extent of SERS enhancement is due to a variety of factors such as nanoparticle size, shape, material, and configuration. The choice of Raman reporters and protective coatings will also influence SERS enhancement. This review provides an introduction to how these factors influence signal enhancement and how to optimize them during synthesis of SERS nanoparticles.

The SERS enhancement factor (SERS-EF) is one of the most important parameters that characterizes the ability of a given substrate to enhance the Raman signal for SERS applications. The comparison between dynamic and static substrates, however, should not be performed in sense of SERS-EF.

We present here the amplification of the surface-enhanced Raman scattering (SERS) signal of nanodisks on a gold film for SERS sensing of small molecules (thiophenol) with an excellent sensitivity. The enhancement is achieved by adding a silicon underlayer for the composition of the nanodisks. We experimentally investigated the sensitivity of the suggested Au/Si disk-shaped nanoresonators for chemical sensing by SERS. We achieved values of enhancement factors of 5 × 10 7 − 6 × 10 7 for thiophenol sensing. Moreover, we remarked that the enhancement factor (EF) values reached experimentally behave qualitatively as those evaluated with the E 4 model.

Schematic of study to optimize the SERS enhancement factor of a low cost and facile gold nanostar (AuNS)-based paper-SERS substrate through optimizing the paper materials, immobilization strategies, and SERS acquisition conditions.

: Tunability in resonance wavelength and the enhancement of the electromagnetic field intensities around the surface are two unique properties which make metal as a plasmonic material. A theoretical investigation on the LSPR and field enhancement for heterogeneous dimer–trimer metallic nanostructure by constituting Al and Au as two different plamsonic materials has been studied. Since electrons in Al exhibit free behavior for LSPR of Au, therefore, they influence the electric field magnitude generated by Au LSPR. Methods: The electromagnetic simulations reported in this paper were performed using the FDTD Solutions (version 7.5.1), a product of Lumerical Solutions Inc., Vancouver, Canada. We adopted a cubic Yee cell of 1 nm side and a time step Δt= 1.31•10-18 s, bounded by Courant condition. Results: The extinction spectrum shows LSPR peak over UV-visible region for isotropic nanostructure which shifts to NIR region for anisotropic shape nanostructure. The spherical shape hetero dimer nanostructure shows enhancement factor ~ 3.9 X 105 whereas it increases to ~ 6.2 X 106 for anisotropic shape at 610 nm. The field distribution corresponding to the trimer nanostructure reveals a large dipolar field distribution on each of the three nanoparticles, oscillating approximately in-phase. The spherical shape Al-Au-Al shows enhancement factor ~ 8.5 X 106 at 571 nm. The anisotropic shape increase the enhancement factor to ~ 2.4 X 107 at peak wavelength 700 nm i.e. tuning the plasmon wavelength towards NIR region. Conclusion: The tunability in plasmon wavelength and field enhancement factor has been evaluated for heterogeneous nanostructure over wider spectrum range i.e. DUV-Visible-NIR using Au-Al dimer and trimer nanostructure. The isotropic shape Au-Al hetero nanostructure shows larger enhancement in the UV-visible region, whereas the anisotropic shape nanostructure contributes towards the NIR region.

Over the last decades optical sensors assumed a major role in the analytical field. In particular, plasmonics, that is the branch of sensors that exploits the excitation of surface plasmons due to the collective oscillation of the electrons in the conduction band, allowed to achieve excellent results in terms of detection limits and accuracy. This kind of sensors exploits the interaction between the metal nanoparticles that possess plasmonic properties (Au, Ag, Cu) and an interacting molecules. In fact, under resonance conditions, a strong localized electric field is produced on the surface of the nanostructure, that, by the interaction with a molecule located at the interface, may amplify or attenuate its optical properties. In this thesis various methods of synthesis of substrates based on silver nanostructures, ordered or otherwise, as thin films for applications in Raman and UV-Visible (LSPR) sensors were explored. The samples were characterized in terms of chemical, physical and morphological properties and were systematically tested to assess their efficiency and quality. In the first part of the thesis, commercially available digital versatile discs (DVDs) were used to fabricate SERS easy&cheap substrates. DVDs contain a silver-coated spiral distribution of rectangular-shaped grooves (AgDVD): for the first time, they were used to produce surface-enhanced Raman scattering (SERS) substrates by electrochemical deposition of silver nanoparticles (AgNPs@AgDVD). The overall procedure only requires cheap and widely available materials and can be easily accomplished. Scanning electron microscopy images of AgNPs@AgDVD revealed that small Ag NPs (average diameter about 15 nm) are present within the valleys of AgDVD, whereas over the ridges, the Ag NPs are bigger, more densely packed and with a dendrite-like morphology somewhere. The SERS properties of these substrates were studied in terms of the enhancement factor (EF), point-to-point reproducibility and sample-to-sample repeatability. It turned out that high SERS EF and good reproducibility are both fulfilled. As for repeatability, remarkably better results than typical literature values were achieved. Such an easy&cheap preparation along with efficient SERS properties make DVD-derived SERS substrates very good candidates for the development of convenient and disposable sensing platforms. In the second part of the thesis, Ag nanostructures (Ag NSs) were grown by AC electrodeposition on Anodic Alumina Oxide (AAO) connected membranes acting as templates. Depending on the thickness of the template and on the voltage applied during the growth process, different Ag NSs with different optical properties were obtained. When ca 1 µm thick AAO membranes are used, the Ag NSs consist in Ag nanorods, at the bottom of the pores, and Ag nanotubes (Ag NTs) departing from the nanorods and filling the pores almost for the whole length. When ca 3 µm thick AAO membranes are used, the nanostructures are Ag spheroids, at the bottom of the pores, and Ag nanowires (Ag NWs) that do not reach the upper part of the alumina pores. The samples were characterized by Angle Resolved X-Ray Photoelectron Spectroscopy, Scanning Electron Microscopy measurements and UV-Vis and Raman Spectroscopies. In the case of µm thick AAO membranes, a simple NaOH etching procedure, followed by sonication in ethanol, allows one to obtain an exposed ordered array of Ag nanorods (Ag NRs), suitable for Surface Enhanced Raman Spectroscopy, while in the other case (3 µm thick AAO membranes) the sample can be used in Localized Surface Plasmon Resonance sensing. The AC electrodeposition procedure was extended to copper in order to obtain Cu NSs to be used as sacrificial anodes for the subsequent deposition of Ag. Also in this case the samples were chemically, physically and morphologically characterized and finally tested as sensors. Finally, SERS substrates were produced by electrophoretic deposition (EPD) of Ag NPs. The Ag NPs colloidal suspension was prepared by simply using [Ag(NH3)2]+ as silver source and glucose as reducing agent. This simple “green synthesis” allows to obtain an Ag NPs suspension with a good dimensional monodispersion and good optical performances. The obtained Ag NPs are characterized by a negative z-potential and therefore suitable for EPD. The stability of the suspension, obtained by this simple way, is guaranteed by the “protection” of the adsorbed gluconic acid on the Ag NPs surface, that forms during the redox reaction between the [Ag(NH3)2]+ complex and glucose. Because of the gluconic acid protection the Ag NPs maintain their original dimension even after the EPD. Moreover, molecules that bind more strongly to Ag, like thiols or amines, can easily substitute the gluconic acid adsorbed on the Ag NPs surface (weak interaction). Such samples were characterized by XPS, SEM, UV-Vis and finally tested as SERS substrates
Nel corso degli ultimi decenni la sensoristica ottica ha assunto un ruolo di primaria importanza in campo analitico. In particolare, la plasmonica, ovvero quella branca della sensoristica che sfrutta l’eccitazione dei plasmoni di superficie, dovuta all’oscillazione collettiva degli elettroni in banda di conduzione, ha permesso di raggiungere risultati eccellenti in termini di limiti di rivelabilità e accuratezza. Questo tipo di sensoristica sfrutta l’interazione tra le nanoparticelle metalliche che godono di proprietà plasmoniche (Au, Ag, Cu) e le molecole interagenti. Infatti, in condizioni di risonanza, si sviluppa sulla superficie della nanostruttura un fortissimo campo elettrico localizzato che, interagendo con una molecola posizionata all’interfaccia, può amplificare o attenuare le sue proprietà ottiche. In questo tesi sono state esplorate diverse metodiche di sintesi di substrati basati su nanostrutture di argento, ordinate e non, su film sottile per applicazioni in Sensoristica Raman e UV-Visibile (LSPR). I campioni sono stati caratterizzati dal punto di vista chimico, fisico e morfologico e sono stati testati sistematicamente per valutarne l’efficienza e la qualità. Nella prima fase della tesi sono stati preparati dei campioni su substrati di basso costo e facilmente reperibili. A tale scopo sono stati utilizzati dei DVD scrivibili disponibili in commercio, che contengono una distribuzione a spirale di scanalature di forma rettangolare ricoperte da un film sottile di Ag (AgDVD): per la prima volta sono stati usati per produrre substrati per surface-enhanced Raman scattering (SERS) tramite deposizione elettrochimica di nanoparticelle di Ag (AgNPs@AgDVD). La procedura generale richiede solo materiali economici, ampiamente disponibili e può essere facilmente realizzata. Le immagini effettuate tramite Scanning electron microscopy (SEM) mostrano che nelle valli dell’AgDVD sono presenti piccole nanoparticelle di Ag (Ag NPs, diametro medio di circa 15 nm), mentre sulle creste, le Ag NPs sono più grandi, più densamente impaccate e in alcune zone presentano una morfologia di tipo dendritico. Le proprietà SERS di questi substrati sono state studiate in termini di enhancement factor (EF), di ripetitibilità da punto a punto e di riproducibilità da campione a campione. Si è scoperto che i requisiti di alti SERS EF e di una buona riproducibilità sono entrambi soddisfatti. Per quanto riguarda la ripetibilità, sono stati raggiunti risultati di gran lunga migliori rispetto ai valori tipici riportati in letteratura. Tale preparazione easy&cheap con efficienti proprietà SERS rende i substrati SERS derivati dai DVD ottimi candidati per lo sviluppo di sensori convenienti e monouso. Nella seconda fase della tesi sono state cresciute nanostrutture di Ag (Ag NSs) mediante elettodeposizione in corrente alternata utilizzando come template delle membrane di allumina nanoporosa (AAO) direttamente connesse al substrato metallico. A seconda dello spessore del template e del voltaggio applicato durante il processo di crescita è possibile ottenere differenti Ag NSs con differenti proprietà ottiche. Quando si usano AAO da circa 1 µm di spessore, le nanostrutture che si formano sono nanobarre di Ag (Ag NRs), alla base dei pori, e nanotubi di Ag (Ag NTs) che partono dalle nanobarre e riempiono il poro in quasi tutta la sua lughezza. Quando si usano AAO da circa 3 µm di spessore, le nanostrutture che si formano sono sferoidi, alla base dei pori, e nanofili di Ag (Ag NWs) che non raggiungono la parte superiore dei pori dell’allumina. Nel caso delle AAO da circa 1 µm di spessore, un semplice trattamento di erosione in NaOH, seguito da sonicazione in etanolo, permette di ottenere una disposizione ordinata (array) di Ag NRs, adatta per il SERS, mentre nell’altro caso (per le AAO da 3 µm di spessore) i campioni possono essere utilizzati per misure di Localized Surface Plasmon Resonance sensing (LSPR). La procedura di elettrodeposizione in corrente alternata è stata estesa anche al rame al fine di ottenere Cu NSs da utilizzare come anodi sacrificali per la successiva deposizione di Ag. Anche in questo caso i campioni sono stati caratterizzati chimicamente, fisicamente e morfologicamente ed infine testati come sensori. Infine sono stati preparati dei substrati SERS tramite deposizione elettroforetica (EPD) di Ag NPs. La sospensione colloidale di Ag NPs è stata preparata utilizzando semplicemente [Ag(NH3)2]+ come precursore d'argento e glucosio come agente riducente. Questa semplice "sintesi verde" permette di ottenere una sospensione di Ag NPs con una buona monodispersione dimensionale e buone prestazioni ottiche. Le Ag NPs ottenute sono caratterizzate da un potenziale z negativo e quindi adatte per l’EPD. La stabilità della sospensione, ottenuta in questo modo semplice, è garantita dalla "protezione" offerta dall’acido gluconico adsorbito sulle Ag NPs, che si forma durante la reazione redox tra il complesso [Ag(NH3)2]+ e il glucosio. Grazie alla protezione offerta dall’acido gluconico le Ag NPs mantengono la loro dimensione originaria anche dopo l’EPD. Inoltre, le molecole che si legano più fortemente all’Ag, come tioli o ammine, possono facilmente sostituire l'acido gluconico adsorbito sulla superficie delle Ag NPs (interazione debole). Tali campioni sono stati caratterizzati tramite XPS, SEM, UV-Vis e infine sono stati testati come substrati SERS

碩士
國立臺灣師範大學
化學系
104
A series of MTAMs (microtube array membranes) were produced by the electrospinning method. After this, a piece of MTAM was used for making a SERS (Surface-Enhanced Raman Scattering) substrate by means of silver mirror reaction. Poly-L-lactic acid solution was selected as making material. The optimal conditions, including applied voltage, the distance between ejector and collector, speed of the drum, flow rate of inner/outer tube, humidity and temperature, were 5 kV, 3cm, the 100 rpm, 4/6 ml/h, 50 %, 25 ℃, respectively. On the other hand, the silver mirror reaction took place to produce colloidal silver at the surface of MTAMs. In the beginning, MTAMs were cleaned up and wetted by ammonia hydroxide. Following this, a mixing solution (v/v/v; 1/1/1) was prepared by using 0.3 M aqueous solution of glucose, 1.68 % ammonia hydroxide and 0.05 M aqueous solution of silver nitrate. Finally, the MTAMs were put into the mixed solution for occurring silver mirror reaction, in which the temperature of water bath and reaction time were set at 55 ℃ and 12 minutes, respectively. As the result, the nano-silver particles can be uniformly deposited on the surface of the MTAMs, leading to make silver-MTAMs. The sizes of the nano-silver particles on MTAMs were about 80 nm, which size was useful to induce a surface plasma resonance when a laser was used. In order to evaluate the performance of the silver-MTAMs, p-ATP (p-aminothiophenol) was selected as the test sample. The findings show that the use of silver-MTAMs a SERS enhancement factor of 104-fold was achieved; the limit detection was found to 10 ppb. It can be seen that a covalent bond might be formed between the Sulfur atom and the nano-silver particles, and as the result, the energy of C-S bond was decreased, since the energy of a C-S bond was decreased from 1088 cm-1 (Raman signal) to 1070 cm-1 (SERS signal). Based on this signal, an enhancement factor was 1.17×104.

碩士
中原大學
奈米科技碩士學位學程
101
This study used the Raman spectrometer to observe a variety of amino acid molecules (cysteine, phenylalanine, tyrosine, tryptophan) and thymine adsorbed on the surface of the silver colloids to enhance Raman scattering effect. When the amino acid molecules are mixed with silver colloids, different functional groups of the molecules will cause different orientations of the amino acid molecules when adsorbed on the surface of silver colloids, leading different Raman scattering intensity. In order to determine the functional group that causes the adsorption orientation difference, this study added aggregating agents and adjusted the pH of the solution in the experiments to investigate the adsorption of amino acid molecules on the surface of silver colloids. Calculation of the Raman enhancement factor showed that the addition of aggregating agents, such as potassium fluoride and potassium phosphate, can achieve the best enhancement of amino acid molecule surface Raman scattering effect. When the pH is in the range from 6.7 to 10, amino acid molecular mapping signals have an increased enhancement effect. In this pH range, the addition of potassium phosphate can achieve the best enhancement of surface Raman scattering effect. All experimental evidences showed that the particle size of the anionic aggregating agent, the charge number, and the pH of the solution are closely related to the enhancement of the surface Raman scattering effect.

Herein we addressed a study to determine the enhancement factor (EF) of the Raman signal reached by composite films with two main components, Ag nanoparticles and SiO2 spheres. The study involves the synthesis, structural composition and optical response by using experimental techniques and theoretical-numerical modeling. A colloid with single NPs and agglomerates of them, with a tannic acid layer on its surface, was produced. Separately, porous SiO2 spheres were obtained. A mixture of both, Ag NPs and SiO2 particles was used to produce the films by solvent evaporation method. It is shown that single or agglomerated Ag NPs are preferentially located at the interstices of the SiO2 spheres. Using discrete dipole approximation, the SERS EF has been estimated considering the agglomeration and tannic acid layer. Both, the dielectric spheres and tannic acid layer diminish the electric field intensity and therefore the SERS EF. When a Ag NP with/without a dielectric shell is touching a SiO2 sphere, the EF is as high as 1 × 103, the zones where this value is reached are smaller when the dielectric layer is present. With a cluster of 3 nude Ag NPs surrounded by SiO2 spheres an EF of 2.4 × 103 is obtained.

There is growing concern regarding the enhancement of NPOs´ efficiency as it is considered an excellent strategy to tackle the imbalance between greater social demand and the decrement of their resources, as well as the lack of credibility in the current best practices of the sector. Within a Colombian context, this paper sets out two main objectives. Firstly, an analysis of the efficiency of NPOs in reaching their social goals and, secondly an analysis of the influence of certain factors in NPOs´ efficiency. The main findings indicate that, in general terms, Colombian NPOs should make a greater effort in the efficient management of their resources. Moreover, younger entities and those with a national scope are shown to be the most interested in improving their levels of efficiency.

The enhancements in the socio-economic status of many people has come from the expansion of agricultural and industrial production. But, some of the activities associated with this expansion have adversely affected water quality. This leads to a negative impact on public health, eminence of life, and environment. This chapter sets out to explain the various factors that lead to water contamination and different mitigation techniques to manage them. We need this knowledge so as to develop suitable solutions for a broad range of environmental problems.

The issue of the status of mathematical knowledge a priori or a posteriori has been repeatedly considered by the philosophy of mathematics. At present, the development of computer technology and their enhancement of the everyday work of mathematicians have set a new light on the problem. It seems that a computer performs two main functions in mathematics: it carries out numerical calculations and it presents new areas of research. Thanks to cooperation with the computer, a mathematician can gather different data and facts concerning the issue of interest. Moreover, he or she can carry out different "tests" with the aid of a computer. For instance, one can study strange attractors, chaotic dynamics, and fractal sets. By this we may talk about a specific experimentation in mathematics. The use of this kind of testing in mathematical research results in describing it as an experimental science. The goal of the paper is to attempt to answer the questions: does mathematics really transform into experimental or quasi-experimental science and does mathematics vary from axiomatic-deductive science into empirical science?

Abstract It is a fundamental principle of criminal law that offenders are to be punished for their crimes and not for other reasons such as lifestyle or character. The legality principle enjoys widespread recognition at the point of attribution of criminal liability. In addition, it is complemented in the procedural context by the requirement that the burden lies on the state to prove that a crime was committed. Much is made of the importance of the definition of the crime, of the obligation on the state to prove the various aspects of the charge, and yet at the sentencing stage it is common for factors to be taken into consideration which seem to have little to do with an offender’s culpability for the crime at issue. This chapter sets out to examine the importance of legality at sentencing and begins with an examination of the relationship between legality and the act and culpability requirements. It then goes on to analyse the case law of the European Court of Human Rights on Article 7(1) ECHR in order to establish the scope of the human rights principle at sentencing. This provides the basis for consideration of the compatibility of important sentencing practices, notably sentence enhancements for prior convictions, the treatment of confessions, and the extent of the sentence reductions in cases of diminished culpability or responsibility. This provides the basis for broader consideration of the role of legality as a limit on punishment.

This remark says it clearly: the best teaching sets learners on their own path to discovery. Appeal to students’ hearts as well as filling their heads; it is sustenance for their professional journey. Effective, engaging, and enjoyable lessons do not happen automatically. They take effort. They demand attention to striking the right balance between content and process, to meeting the requirements of the curriculum and the distinctive needs of students. Every course is different. Every class is organic. Every group of students is distinctive. A tightly framed lesson leaves room for the unexpected and exceptional—a corollary to the apparent paradox stated earlier—structure frees you to be spontaneous. It affords room for you to weave teachable moments into the overall fabric of the lesson. Curricula and syllabi are basically fixed, general, and inflexible. Without compromising the integrity of the prescribed content, a solidly designed lesson creatively customizes classes to reflect your particular expertise, preferences, and manner. At the same time it takes into account students’ experience, strengths, and styles. Pre-reflection lesson planning—pulling it all together, in other words—is a kind of mental rehearsal. It focuses on desired changes in students, envisions the optimal conditions for creating a context for learning, and generates a strategy to intertwine process and content into a vibrant tapestry. Weaving it together calls for a self-conscious and conscientious effort. The lesson plan takes stock of the characteristics and conditions associated with you (personality, knowledge, skills, experiences, style), with students (receptivity, motivation, attitude toward the subject, style), with classroom milieu (number of students, physical environment, room temperature, acoustics), and with varied modes of instruction. It increases the likelihood of achieving greater student participation and optimizing learning. It makes teaching more stimulating and gratifying for both students and you. A lesson plan arises from pre-reflection and buttresses both reflection-in- action, and reflection-on-action. It harnesses your ingenuity to coalesce a multitude of factors—goals, themes, patterns, assignments, exercises, and enhancement materials (e.g., handouts) into a coherent and unified presentation. The lesson plan plots a path through this complex terrain by synchronizing this panoply of variables.

We present the design and fabrication of Surface-Enhanced Raman Spectroscopy substrates based on two-photon polymerization of photoresist with direct laser writing. Moreover, experimental validation and enhancement factor values are demonstrated for biosensing applications.

A highly ordered surface enhanced Raman spectroscopy substrate based on TiO2-Ag nanotubes was prepared using simple and rapid electrochemical method. Its enhancement factor was measured up to 1.5 × 109 using rhodamine 6G probe.

We applied Raman and SERS spectroscopy to obtain the fingerprint of glyphosate, a worldwide used dangerous pesticide. We corroborate the utility of gold nanoparticles to improve the Raman scattering, obtaining an enhancement factor of 105.

We have identified the long debated origin of the short-range component of surface-enhanced Raman scattering (SERS) as Ag 4 + clusters which are stabilized by co-adsorbed molecules or by low substrate temperature on rough Ag surfaces. The assignment has been supported by vibrational mode calculations which include the effects of adsorption of the cluster, image interaction with the metal, and co-adsorbed anions in the electrochemical environment. The observed modes at 73, 110, and 161 cm−1 correspond to those calculated at 75, 100 and 118, and 170 cm−1. The adsorbed clusters act as Lewis acid sites onto which other molecules such as pyridine are bonded thus leading to SERS beyond the usual electromagnetic factor which is due to macroscopic roughness. The mechanism of the added enhancement is through charge transfer excitation between the adsorbed molecules and the clusters and through HOMO—LUMO transitions within the cluster.

We have identified the long debated origin of the short-range component of surface-enhanced Raman scattering (SERS) as Ag4+ clusters which are stabilized by co-adsorbed molecules or by low substrate temperature on rough Ag surfaces. The assignment has been supported by vibrational mode calculations which include the effects of adsorption of the cluster, image interaction with the metal, and co-adsorbed anions in the electrochemical environment. The observed modes at 73, 110, and 161 cm-1 correspond to those calculated at 75, 100 and 118, and 170 cm-1. The adsorbed clusters act as Lewis acid sites onto which other molecules such as pyridine are bonded thus leading to SERS beyond the usual electromagnetic factor which is due to macroscopic roughness. The mechanism of the added enhancement is through charge transfer excitation between the adsorbed molecules and the clusters and through HOMO—LUMO transitions within the cluster.

The deck height of a tension leg platform or semi-submersible depends in large part on the expected crest height. This expected crest height is the result of the sea state, i.e. the incoming wave train, and local enhancement due to the vessels diffraction of the wave train. These local enhancements are usually determined by a combination of numerical computations and model tests. Quite often a crest enhancement factor is defined which takes into consideration these local amplification effects. Extrapolating the enhancement factor from extreme conditions to survival conditions may lead to significantly large crests and result in a very high deck elevation. Many studies, including the CresT JIP address the characteristics of the crests within a given sea state and in the absence of a vessel. This paper addresses the effect of the presence of a vessel on the crest heights, and in particular the high crests which will ultimately determine deck height. The paper is based on experimental measurements of wave elevations underneath and around various tension leg platforms and semi submersibles. The investigated sea states comprise of a series of long crested irregular waves, generated in a model basin, which describe extreme and survival conditions in the Gulf of Mexico. The crest heights underneath the vessel are measured and compared with crests which occur without the presence of the vessel. Numerical predictions of the local amplification are also made, based on 1st order diffraction analysis and the as-measured incident wave train. A narrative is provided on the differences in crest height and observed phenomena.

Prevailing data suggest that activation of factor VIII (VIII) results in the enzymatic cleavage of the molecule into two chains bound by Ca++. When Ca++ becomes critically involved is not clear. We have investigated this process by studying the relationship of thrombin activation of VIII and the EDTA enhancement of VIII antigen (VIII:Ag). VIII:Ag was assayed by a specific and sensitive (<0.7 mU/ml) ELISA using microtiter plates coated with human anti-VIII IgG and probed with a mouse monoclonal antibody to VIII:Ag. Unlike VIII activities, plasma VIII:Ag levels detected by this ELISA were found to be relatively constant during in vitro thrombin activation. However, in the presence of EDTA (at pH 7.0), the apparent VIII:Ag values were enhanced by 1.6-1.8 fold. Sera devoid of VIII activity, on the contrary, already had VIII:Ag values about 1.6-fold higher than the corresponding plasma values, and the raised serum VIII:Ag values could not be further enhanced in the presence of EDTA. Fractionation of VIII from cryoprecipitates by aminohexyl-agarose chromatography in buffers containing Ca++ and protease inhibitors revealed the heterogeneous nature of VIII molecules. The different VIII fractions showed differential responses to activation by thrombin, and VIII:Ag enhancement by EDTA. Thrombin activation studies showed that the earlier fractions were most activatable, with the thrombin activatability falling progressively with successive fractions. When EDTA enhancement of VIII:Ag was studied, the reverse was observed: the enhancement increased progressively with successive fractions. Thus, aminohexyl-agarose chromatography resulted in fractionation of VIII into a continuous spectrum of molecular forms. We postulate that the earlier eluting fractions contained mainly "native" molecules which responded maximally to thrombin and minimally to EDTA. Subsequent fractions contained mainly the "active" form of VIII which responded minimally to thrombin but maximally to EDTA. The enhancement of VIII:Ag by EDTA is likely due to the removal of Ca++ with exposure of additional antigenic determinants. Our data suggest that Ca-^ participates mainly in the conformation of "active" VIII molecules. In serum, the molecule had been degraded with maximum exposure of the antigenic determinants, so that EDTA had no further enhancement effect.