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Desenvolvimento de Ensaio Não Destrutivo baseado no Ruído Magnético de Barkhausen para caracterização de tensões elásticas e deformações plásticas em aços.; Development of Non-Destructive Test based on Magnetic Barkhausen noise for characterization of stress and elastic plastic deformation in steels.

Franco Grijalba, Freddy Armando
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 30/04/2010 PT
Relevância na Pesquisa
66.03%
Neste trabalho se estuda a aplicação de um método de Ensaio Não Destrutivo, baseado no Ruído Magnético de Barkhausen (RMB), na medição de falhas superficiais em aços. O RMB é gerado por abruptas mudanças na magnetização de materiais quando submetidos a campos magnéticos variáveis. Essas mudanças são afetadas pela microestrutura e a presença e distribuição de tensões elásticas (compressão e tração). Inicialmente apresenta-se um estudo de medições de tensões produzidas por flexão, e perfis de dureza, via RMB. Analisa-se a influência de parâmetros de medição e analise dos sinais, na qualidade do diagnostico. Analisou-se a sensibilidade dos sinais de RMB na medição de tensão a parâmetros tais como direção de laminação da chapa, intensidade e frequência de campo magnético de excitação. Nos estudos da aplicação do RMB em medições de dureza, se usaram amostras de ensaio Jominy, com variação contínua de dureza. Utilizou-se dois tipos de materiais e foram feitas medidas de dureza HRC, RMB e análise metalográfica. O comportamento de diferentes parâmetros dos sinais de RMB se correlacionou com as medições de Dureza e as micrografias obtidas. As amplitudes do RMB mostraram ser inversamente proporcionais aos níveis de dureza. Também se apresenta uma nova tecnologia para inspeção de superfícies...

Comparação de métodos não-destrutivos de cubagem de árvores em pé visando à determinação da biomassa; Comparison of non-destructive methods of wood volume determination of standing trees for biomass determination

Nicoletti, Marcos Felipe
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 06/10/2011 PT
Relevância na Pesquisa
56.09%
As florestas são vistas como excelentes acumuladoras de biomassa e carbono da atmosfera, contribuindo para a redução do efeito estufa. Para ter conhecimento da biomassa acumulada nas árvores é necessário realizar determinadas técnicas para levantar o volume de madeira dos povoamentos. Desta forma, objetiva-se neste trabalho estudar a qualidade das medidas de cubagem da árvore em pé através de dendrômetros ópticos de medição do tronco visando à determinação da biomassa de árvores sem amostragem destrutiva. O trabalho foi desenvolvido na Estação Experimental de Itatinga/SP que pertence a Universidade de São Paulo (ESALQ-USP). Foram amostradas 175 árvores em três parcelas de Eucalyptus grandis. O diâmetro do fuste das árvores em pé foi mensurado com os dendrômetros (Criterion 400 e RC3H) em distâncias de 0,1; 0,4; 0,7; 1,0; 1,3; 2,0 m e a partir deste de metro em metro ao longo do tronco até os 8 m de altura. Após a cubagem em pé foi derrubada a árvore e seccionada para pesagem do tronco, sendo que o diâmetro foi obtido com auxílio de suta e da trena nas mesmas posições em que se realizou a cubagem não destrutiva. De posse dos diâmetros foram calculados o volume por secção e por árvore individual através da fórmula de Smalian para posterior comparação dos métodos. Depois de seccionado o tronco...

Mediação de tensões em bielas utilizando interferometria laser; Stress measurement in rods using laser interferometry

Bruno Filipe Vaz
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 09/08/2012 PT
Relevância na Pesquisa
56.01%
Bielas falham quando submetidas a esforços que ultrapassam seu limite de escoamento. Esses elementos são projetados para suportar tanto esforços em tração quanto em compressão, embora os últimos sejam mais intensos. Para a criação de novas bielas, engenheiros fazem uso de análises de elementos finitos para validar seus desenhos, mas mesmo assim os desenhos atuais dessas peças seguem os modelos desenvolvidos décadas atrás. A validação das análises computacionais dos modelos é feita através de ensaios destrutivos ou medições e análises do produto em uso regular. Engenheiros de desenvolvimento e de testes seriam muito beneficiados por uma ferramenta de ensaios não destrutivos que possibilitassem validar resultados obtidos numericamente rapidamente e a um custo menor que os ensaios tradicionais. A obtenção de campos de tensão pode ser feita através de diversos métodos, dentre os quais se destaca como o mais amplamente utilizado o uso de strain-gauges. Este trabalho avalia o uso do método de medição de tensões em bielas por interferência de padrões de spekle, também conhecido como Eletronic Speckle Pattern Interferometry (ESPI). As tensões medidas na região plana da alma da biela são comparadas com resultados de elementos finitos. Essa região corresponde à porção interior da alma...

Non-destructive measurement of metabolites and tissue pH in the kidney by 31P nuclear magnetic resonance.

Sehr, P. A.; Bore, P. J.; Papatheofanis, J.; Radda, G. K.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1979 EN
Relevância na Pesquisa
55.86%
Phosphorus nuclear magnetic resonance (31P NMR) can be used as a non-destructive method for the simultaneous observation of the major phosphate-containing metabolites (ATP, ADP, nucleotide monophosphate, Pi, sugar phosphate) and intracellular pH in isolated rat kidney. The time course of changes in these metabolites and in cellular pH in the ischaemic kidney are examined at two temperatures and in the presence of different flushing media. ATP is rapidly depleted while the pH change is slower and shows biphasic behaviour. Pi production and total nucleotide (ATP and ADP) depletion also occur on the same time-scale as the tissue acidification. The relation of these observations to tissue viability is discussed and the possibility of extending the measurements to human organs is considered.

Infrared Thermography for Temperature Measurement and Non-Destructive Testing

Usamentiaga, Rubèn; Venegas, Pablo; Guerediaga, Jon; Vega, Laura; Molleda, Julio; Bulnes, Francisco G.
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 10/07/2014 EN
Relevância na Pesquisa
46.07%
The intensity of the infrared radiation emitted by objects is mainly a function of their temperature. In infrared thermography, this feature is used for multiple purposes: as a health indicator in medical applications, as a sign of malfunction in mechanical and electrical maintenance or as an indicator of heat loss in buildings. This paper presents a review of infrared thermography especially focused on two applications: temperature measurement and non-destructive testing, two of the main fields where infrared thermography-based sensors are used. A general introduction to infrared thermography and the common procedures for temperature measurement and non-destructive testing are presented. Furthermore, developments in these fields and recent advances are reviewed.

A rapid non-destructive method for root dentin moisture measurements: In vitro pilot study

Komabayashi, Takashi; Zhu, Qiang; Jiang, Jin; Safavi, Kamran E.; Spångberg, Larz S.W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
55.86%
Dentin moisture content is important in adhesive bonding and structural strength research. However, there is no rapid method available to assess dentin moisture without sample destruction. This study examined the use of a digital grain moisture meter to measure root dentin moisture in vitro. Extracted mandibular single rooted teeth were sectioned at the CEJ. The moisture of the root dentin was measured at six measuring modes for different grains and repeated five times. Dentin weight changes before and after drying were measured to obtain control values. The control values were compared with machine readings. In conclusion, (1) Each non-destructive measurement took less than 30 seconds. (2) 24 hours storage at 37°C and 100 % humidity did not restore dentin moisture. (3) Five grain modes had a high validity, and could be used for dentin moisture measurements.

Ultrasonic calibration and certification of V1 and V2 type reference standard blocks for use in Non-Destructive Testing

Maggi, Luís Eduardo; Silva, Cristiane Evelise Ribeiro da; Alvarenga, André Victor; Costa-Félix, Rodrigo Pereira Barretto da
Fonte: Inmetro - Instituto Nacional de Metrologia, Qualidade e Tecnologia Publicador: Inmetro - Instituto Nacional de Metrologia, Qualidade e Tecnologia
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.98%
6 p. : il.; Ultrasonic Non-Destructive Testing (US-NDT) has many industrial applications,such as flaws detection, welding integrity evaluation and solid material thickness measurement.To evaluate the instrumentation conditions, before a measurement begins, a “calibration” should be carried out with the aid of a reference standard block (RSB). Types V1 (ISO 2400) and V2 (ISO 7963) are the most widely used in US-NDT. Due their characteristics, V1 and V2 RSB can be classified as Reference Material, so that they can be certified, resulting in a Certified Reference Material (CRM). This paper describes technical aspects of a V1 and V2 RSB certification, based on ISO 2400, ISO 7963, EN 12223 and EN 27963. According the certification protocol established at Inmetro’s Laboratory of Ultrasound, RSB relevant dimensions were determined through calibration. Ultrasound velocity was assessed by using a scope and a signal generator at 5 MHz. Uncertainties were determined including measurement accuracy under repeatability conditions. A complete uncertainty budget was determined for both parameters. Within the specimens used, velocities were in accordance with specifications 5920 ± 30 m/s).

Non-destructive measurement of grapevine water potential using near infrared spectroscopy

De Bei, R.; Cozzolino, D.; Sullivan, W.; Cynkar, W.; Fuentes, S.; Dambergs, R.; Pech, J.; Tyerman, S.
Fonte: Australian Society of Viticulture and Oenology Publicador: Australian Society of Viticulture and Oenology
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
55.94%
BACKGROUND AND AIMS: Near infrared (NIR) spectroscopy techniques are not only used for a variety of physical and chemical analyses in the food industry, but also in remote sensing studies as tools to predict plant water status. In this study, NIR spectroscopy was evaluated as a method to estimate water potential of grapevines. METHODS AND RESULTS: Cabernet Sauvignon, Chardonnay and Shiraz leaves were scanned using an Integrated Spectronic (300–1100 nm) or an ASD FieldSpec® 3 (Analytical Spectral Devices, Boulder, Colorado, USA) (350–1850 nm) spectrophotometer and then measured to obtain midday leaf water potential using a pressure chamber. On the same shoot, the leaf adjacent the one used for midday leaf water potential measurement was used to measure midday stem water potential. Calibrations were built and NIR showed good prediction ability (standard error in cross validation (SECV) <0.24 MPa) for stem water potential for each of the three grapevine varieties. The best calibration was obtained for the prediction of stem water potential in Shiraz (R = 0.92 and a SECV = 0.09 MPa). CONCLUSION: Differences in the NIR spectra were related to the leaf surface from which the spectra were collected, and this had an effect on the accuracy of the calibration results for water potential. We demonstrated that NIR can be used as a simple and rapid method to detect grapevine water status. SIGNIFICANCE OF THE STUDY: Grapevine water potential can be measured using NIR spectroscopy. The advantages of this new approach are speed and low cost of analysis. It may be possible for NIR to be used as a non-destructive...

Non-destructive quantification of cereal roots in soil using high-resolution X-ray tomography

Flavel, R.; Guppy, C.; Tighe, M.; Watt, M.; McNeill, A.; Young, I.
Fonte: Oxford Univ Press Publicador: Oxford Univ Press
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
65.95%
One key constraint to further understanding plant root development is the inability to observe root growth in situ due to the opaque nature of soil. Of the present non-destructive techniques, computed tomography (CT) is best able to capture the complexities of the edaphic environment. This study compared the accuracy and impact of X-ray CT measurement of in situ root systems with standard technology (soil core washing and WinRhizo analysis) in the context of treatments that differed in the vertical placement of phosphorus fertilizers within the soil profile. Although root lengths quantified using WinRhizo were 8% higher than that observed in the same plants using CT, measurements of root length by the two methodologies were highly correlated. Comparison of scanned and unscanned plants revealed no effect of repeated scanning on plant growth and CT was not able to detect any changes in roots between phosphorus treatments that was observed using WinRhizo. Overall, the CT technique was found to be fast, safe, and able to detect roots at high spatial resolutions. The potential drawbacks of CT relate to the software to digitally segment roots from soil and air, which will improve significantly as automated segmentation algorithms are developed. The combination of very fast scans and automated segmentation will allow CT methodology to realize its potential as a high-throughput technique for the quantification of roots in soils.; Richard J. Flavel...

Non-destructive measurement of the plutonium content of high-active liquid waste

ZSIGRAI JOZSEF; LE TERRIER Arnaud; CASTELEYN Karin; DUHAMEL Georges; MADDISON Andrew; DECAILLON Jean-Gary; BOSKO Andey
Fonte: Publications Office of the European Union Publicador: Publications Office of the European Union
Tipo: Articles in periodicals and books Formato: Online
ENG
Relevância na Pesquisa
56.01%
To verify that all Pu in a reprocessing plant is accounted for, IAEA inspectors need a method for measuring Pu in high-active liquid waste (HALW) remaining after reprocessing of spent fuel. Some of the Pu in HALW is attached to undissolved residues. However, constraints at the IAEA on-site laboratory do not allow use of common destructive methods to measure Pu in the residues. The non-destructive method presented here is based on X-ray fluorescence (XRF) measurement combined with stirring the particles. Tests with known amounts of Uranium in simulated HALW were done using a miniature stirrer installed into a modified sample changer. During these tests the hardware parameters have been optimized. Furthermore, it was shown that the XRF peaks of undissolved residues can be seen by stirring the synthetic HALW. The optimal stirrer speed has been determined and the shielding effect of the particles has been quantified. Hot tests with real HALW are planned to be done in the EURATOM on-site lab in La Hague, France, in co-operation with the French support programme. The planned implementation of the method at the IAEA laboratory will enable the verification of the total Pu content of HALW.; JRC.E.7-Nuclear Safeguards and Forensics

Studies of Irradiation Embrittlement of Model Alloys by Thermoelectric Measurements and Positron Annihilation Spectroscopy

ACOSTA IBORRA BEATRIZ; ZEMAN Andrej; DEBARBERIS LUIGI
Fonte: Slovenian Society for Non-destructive Testing Publicador: Slovenian Society for Non-destructive Testing
Tipo: Contributions to Conferences Formato: Printed
ENG
Relevância na Pesquisa
46.05%
One of the basic mechanisms of radiation embrittlement of steels and welds is due to matrix damage. Embrittlement results in a raise in the ductile-to-brittle transition temperature, which is normally used as indicator of the degradation status of the material. Other methods different than mechanical tests can be used to follow embrittlement like small punch test, non-destructive measurements of thermo-electric and magnetic properties, positron annihilation spectroscopy (PAS) measurements, etc. As regards assessment of reactor pressure vessel's radiation embrittlement, a need exists for correlation not only between the microstructural changes and the non-destructive techniques (NDT) results, but also bewteen the non-destructive evaluation (NDE) outcomes and the mechanical behaviour or level of embrittlement. At the JRC-IE the measurement of thermoelectric voltage using a specially developed non-destructive method (STEAM) to assess the embrittlement state of materials is regularly performed. The positron annihilation spectroscopy in lifetime setup (PAS-LT) is used for study the microstructural changes of matrix due to embrittlement process. Both techniques, STEAM and PAS, have been applied to test a numb er of complex model alloys with different chemical composition...

Non-destructive measurement of chlorophyll b: a ratios and identification of photosynthetic pathways in grasses by reflectance spectroscopy

Siebke, Katharina; Ball, Marilyn
Fonte: CSIRO Publishing Publicador: CSIRO Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
55.86%
Equations for non-destructive determination of chlorophyll b:a ratios in grasses were developed from reflectance spectra of intact leaves of barley (Hordeum vulgare L.) and two barley mutants: clorina f2, which lacks chlorophyll b and clorina f104, which

Estimativa da área foliar em diferentes estados fenológicos baseada em descritores alométricos de rosas de corte cv 'Red Naomi'

Costa, P. M.; Poças, I.; Alves, S.; Pereira, M.; Carvalho, S. M. P.; Cunha, M.
Fonte: Universidade Católica Portuguesa Publicador: Universidade Católica Portuguesa
Tipo: Artigo de Revista Científica
Publicado em //2014 POR
Relevância na Pesquisa
55.86%
A number of models for estimating leaf area (LA) are available in the literature, but these were frequently developed for a specific phase of the production (generally the harvest). This study aimed at estimating the LA in different phenological stages using non-destructive allometric measurements of cut rose cv 'Red Naomi' grown in soilless system. A statistical model was developed based on the following allometric measures: leaf length (LL), leaf width (LW), leaf position (LP), number of leaflets (NL) and different combinations of these parameters. The estimated model based on 176 leaves obtained from 20 stalks harvested at different developmental stages explained 92% of the LA variance (R2 = 0.92, n = 176, p < 0.000).This model includes the numerical position of the leaf on the stem (PRFn), ln (LL*LW) and NL as parameters, and the mean absolute difference between measured and estimated LA was less than 11%. It is concluded that the obtained model shows a high accuracy and reliability in the LA estimation in very diverse situations of crop phenology.

Non-destructive measurement of electron spins in a quantum dot

Meunier, T.; Vink, I. T.; van Beveren, L. H. Willems; Koppens, F. H. L.; Tranitz, H. P.; Wegscheider, W.; Kouwenhoven, L. P.; Vandersypen, L. M. K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/03/2006
Relevância na Pesquisa
66.02%
We propose and implement a non-destructive measurement that distinguishes between two-electron spin states in a quantum dot. In contrast to earlier experiments with quantum dots, the spins are left behind in the state corresponding to the measurement outcome. By measuring the spin states twice within a time shorter than the relaxation time, T1, correlations between consecutive measurements are observed. They disappear as the wait time between measurements become comparable to T1. The correlation between the post-measurement state and the measurement outcome is measured to be ~90% on average.; Comment: 5 pages, 5 figures

Non-destructive state detection for quantum logic spectroscopy of molecular ions

Wolf, Fabian; Wan, Yong; Heip, Jan C.; Gebert, Florian; Shi, Chunyan; Schmidt, Piet O.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.99%
Laser spectroscopy of cold and trapped molecular ions is a powerful tool for fundamental physics, including the determination of fundamental constants, the laboratory test for their possible variation, and the search for a possible electric dipole moment of the electron. Optical clocks based on molecular ions sensitive to some of these effects are expected to achieve uncertainties approaching the $10^{-18}$ level. While the complexity of molecular structure facilitates these applications, the absence of cycling transitions poses a challenge for direct laser cooling, quantum state control, and detection. Previously employed state detection techniques based on photo-dissociation or chemical reactions are destructive and therefore inefficient. Here we experimentally demonstrate non-destructive state detection of a single trapped molecular ion through its strong Coulomb coupling to a well-controlled co-trapped atomic ion. An algorithm based on a state-dependent optical dipole force(ODF) changes the internal state of the atom conditioned on the internal state of the molecule. We show that individual states in the molecule can be distinguished by their coupling strength to the ODF and observe black-body radiation-induced quantum jumps between rotational states. Using the detuning dependence of the state detection signal...

Inhomogeneous Light Shift Effects on Atomic Quantum State Evolution in Non-Destructive Measurements

Windpassinger, Patrick; Oblak, Daniel; Hoff, Ulrich Busk; Appel, Juergen; Kjaergaard, Niels; Polzik, Eugene S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
55.88%
Various parameters of a trapped collection of cold and ultracold atoms can be determined non--destructively by measuring the phase shift of an off--resonant probe beam, caused by the state dependent index of refraction of the atoms. The dispersive light--atom interaction, however, gives rise to a differential light shift (AC Stark shift) between the atomic states which, for a nonuniform probe intensity distribution, causes an inhomogeneous dephasing between the atoms. In this paper, we investigate the effects of this inhomogeneous light shift in non--destructive measurement schemes. We interpret our experimental data on dispersively probed Rabi oscillations and Ramsey fringes in terms of a simple light shift model which is shown to describe the observed behavior well. Furthermore, we show that by using spin echo techniques, the inhomogeneous phase shift distribution between the two clock levels can be reversed.; Comment: 9 pages, 7 figures, updated introduction and reference list

Non-destructive measurement of the transition probability in a Sr optical lattice clock

Lodewyck, Jerome; Westergaard, Philip G.; Lemonde, Pierre
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/02/2009
Relevância na Pesquisa
55.94%
We present the experimental demonstration of non-destructive probing of the 1S0-3P0 clock transition probability in an optical lattice clock with 87Sr atoms. It is based on the phase shift induced by the atoms on a weak off-resonant laser beam. The method we propose is a differential measurement of this phase shift on two modulation sidebands with opposite detuning with respect to the 1S0-1P1 transition, allowing a detection limited by the photon shot noise. We have measured an atomic population of 10^4 atoms with a signal to noise ratio of 100 per cycle, while keeping more than 95% of the atoms in the optical lattice with a depth of 0.1 mK. The method proves simple and robust enough to be operated as part of the whole clock setup. This detection scheme enables us to reuse atoms for subsequent clock state interrogations, dramatically reducing the loading time and thereby improving the clock frequency stability.; Comment: 4 pages, 5 figures

Optical Spin Initialization and Non-Destructive Measurement in a Quantum Dot Molecule

Kim, Danny; Economou, Sophia E.; Badescu, Stefan C.; Scheibner, Michael; Bracker, Allan S.; Bashkansky, Mark; Reinecke, Thomas L.; Gammon, Daniel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.94%
The spin of an electron in a self-assembled InAs/GaAs quantum dot molecule is optically prepared and measured through the trion triplet states. A longitudinal magnetic field is used to tune two of the trion states into resonance, forming a superposition state through asymmetric spin exchange. As a result, spin-flip Raman transitions can be used for optical spin initialization, while separate trion states enable cycling transitions for non-destructive measurement. With two-laser transmission spectroscopy we demonstrate both operations simultaneously, something not previously accomplished in a single quantum dot.; Comment: Accepted for publication in Phys. Rev. Lett

Non-destructive, dynamic detectors for Bose-Einstein condensates

Lye, J. E.; Hope, J. J.; Close, J. D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/02/2003
Relevância na Pesquisa
46.01%
We propose and analyze a series of non-destructive, dynamic detectors for Bose-Einstein condensates based on photo-detectors operating at the shot noise limit. These detectors are compatible with real time feedback to the condensate. The signal to noise ratio of different detection schemes are compared subject to the constraint of minimal heating due to photon absorption and spontaneous emission. This constraint leads to different optimal operating points for interference-based schemes. We find the somewhat counter-intuitive result that without the presence of a cavity, interferometry causes as much destruction as absorption for optically thin clouds. For optically thick clouds, cavity-free interferometry is superior to absorption, but it still cannot be made arbitrarily non-destructive . We propose a cavity-based measurement of atomic density which can in principle be made arbitrarily non-destructive for a given signal to noise ratio.

Limit to non-destructive optical detection of atoms

Hope, J. J.; Close, J. D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/08/2003
Relevância na Pesquisa
55.93%
All optical techniques used to probe the properties of Bose-Einstein condensates have been based on dispersion and absorption that can be described by a two-level atom. Both phenomena lead to spontaneous emission that is destructive. Recently, both were shown to lead to the same limit to the signal to noise ratio for a given destruction. We generalise this result to show that no single-pass optical technique using classical light, based on any number of lasers or coherences between any number of levels, can exceed the limit imposed by the two-level atom. This puts significant restrictions on potential non-destructive measurement schemes.; Comment: 4 pages, 1 figure