Showing papers on "Artifact (error) published in 1981"

A Framework for Spectral Artifact Corrections in X-Ray CT

Abstract: The spectral artifact problem in X-ray computed tomography (CI) is well known. Many techniques have been suggested to correct for this problem, including linearization methods, iterative methods, and dual spectrum methods.

Fluid dynamic factors in tracheal pressure measurement.

Abstract: Because tracheal pressure measurement generally involves the use of a cannula or an endotracheal tube, fluid dynamic factors may cause a considerable artifact. We present a theoretical explanation ...

Opto-isolated stimulators used for electrically evoked BSER: some observations on electrical artifact.

Abstract: This lab uses optically isolated voltage controlled constant current stimulators in its animal ex­ periments. The stimulators are an \"in house\" design and are normally used in conjuction with the D/A output on our Nova computer; in most of our work a 100 μ5 per phase biphasic pulse is used. The prin­ cipal advantages of these stimulators in the research environment are 1) ability to produce a relatively high isolated current — up to 17.2 mA peak to peak into a 10 kfl load (with an overall dynamic range of 85 dB) , 2) ability to take any shape waveform and produce a constant current output of the same shape, 3) simplicity of design and construction, 4) relatively low artifact operation in electrically stimulated BSER experiments, and 5) a high output impedance — approximately 10 Meg.

Fact or artifact: an analysis of artifact in high-resolution computed tomographic scanning of the sella.

Abstract: Computed tomography (CT) artifacts within the sella turcica, associated with the bones of the skull base, were identified and examined by use of a human skull phantom immersed in water. These artifacts were identified in 63% of 27 clinical high-resolution CT scans performed on patients with suspected sellar or parasellar pathology. Intrasellar artifacts may be minimized or eliminated by careful choice of scanning plane. Identification and elimination of intrasellar CT artifacts are necessary for accurate interpretation of sellar image.

Range ambiguities in real‐time ultrasound

Abstract: The frequent occurrence of low-level artifactual echoes in normally echo-free areas of real-time images is shown to be due to a range-ambiguity effect caused by the fast frame rate of real-time equipment. The experimental data demonstrates the range-ambiguous echoes to be present in linear array and mechanical sector scanner real-time images. Several suggestions are made to reduce the effect of the artifact in real-time images. A set of real-time acceptance tests that utilize this artifact are proposed.

On Artifact Density and Shovel Probes

Abstract: (but not necessarily) in a relationship of domination/subordination. Thus my intention was simply to make a few remarks concerning the possibility of comparability of transitions in systems of agricultural production between societies differing in technological and economic complexity that are analyzable on a synchronic axis and of the historical stages that can be reconstructed in the agriculture of a single society. There is one last point I would like to comment upon. It has to do with the unequal access to the literature that we have in peripheral countries, which is one more aspect of the difficulty ofdoing certain kinds of research and of the preference for other kinds of study. I have been unable to examine the papers mentioned by Andrianov in his comment or by Gunda (CA 21:323-24) in his, because the journals and books they mention are not available in Venezuelan libraries. Precisely one of the achievements of a publication like CA is that it enables researchers from distant places and working in very different cultural contexts to come into contact and engage in fruitful dialogue.

New Method for Describing and Analyzing Artifact Shape

Abstract: A simple, yet objective and replicable method for recording a number of variables of the two-dimensional morphology of artifacts is presented and described. This method permits precise quantification of variables such as artifact shape and area, retouch length along the perimeter of chipped stone tools, measures of convexity or concavity, area and location of cortex, etc. Moreover, it allows for direct comparisons among varied artifact assemblages.

Pathogen Reduction in Closed Aquaculture Systems by UV Radiation: Fact or Artifact?

Abstract: Differential equations were used to set a theoretical upper limit for the efficacy of UV radiation in 3 hypothetical aquaculture systems: (a) a plug-flow system, (b) an idealized closed system with no influx of pathogens, and (c) a conventional closed system in which the influx of pathogens is continuous. The equations demonstrate that, in a conventional closed system, the mass of pathogens never reaches zero even if the UV sterilizer is 100 % effective. This suggests that agents such a s UV radiation, which do not form persistent residuals, may be incapable of preventing the spread of waterborne pathogens in systems that are recirculated. Use of UV radiation in aquaculture is most effective in sterilization of raw water supplies and discharges lnto receiving waters, both of which are singlepass applications.

Visually evoked cortical potentials accompanying blinks.

Abstract: Visual activity is initiated whenever there is a change in the light falling on the retinal receptors. In the present experiment, visually evoked cortical potentials, elicited by the light transients that accompany blinking, were recorded with an electrode array that minimized artifact pickup. Although these evoked potentials were roughly similar to those obtained by more conventional recording procedures, specific waveform features were observed.

Measuring Sleep by Wrist Actigraph.

Abstract: : Results from the first year of our contract (1978-79) indicated that sleep can be identified from recordings of wrist activity, eliminating the need for costly EEG or unreliable observational sleep recognition procedures. In the current contract year we have explored alternative activity transducers, transducer placements, and orientations. Results indicate that a crystal transducer is superior to alternative activity transducers, and it responds adequately in any orientation. We have also demonstrated that wrist activity measures are superior to head or ankle measures. We have investigated methods of artifact rejection and digital preprocessing in converting analog activity data to a digital activity score. A simple digital filtering technique was effective in cancelling 60 Hz electrical noise, a persistent artifact in our analog data. A method of enhancing as well as compressing activity data by summing changes in activity over a 2-second data epoch yields the best discrimination between sleep and wake. A computer program to recognize sleep from the digital activity score is being refined. Once an optimal algorithm for retrospective sleep recognition has been derived, its success in prospectively recognizing sleep from wrist activity will be evaluated. A portable model of a wearable prototype digital actigraphic recorder has also been manufactured. (Author)

Real-time detection of the eipleptic precursor

Abstract: The application of microprocessor instrumentation to a clinical EEG problem, detection of a waveform known to be associated with the epileptic fit, is examined. Reasons are advanced for the relative failure of earlier attempts to use the matched filter method and it is shown that a considerable degree of success can be achieved by the use of a simple algorithm. 'Muscle artifact', however, remains a difficult problem requiring further research.

Emmetropization: a vision-dependent phe-

Abstract: in an extensive reviewof many studies a, genera foundl tendenc for yneonatal refraction tos be more variable than thoseof older children I.n addition, by employing a cor-rection for the artifact of retinoscopy similar to thatused here h,e found that neonates probably havesome functional hyperopia a thas thety declinesgrow, a result simila to oursr. Mohindr and aHeld

An impedance plethysmographic apparatus and a method of removing cardiac artifact

Abstract: An impedance plethysmographic apparatus for monitor­ ing respiration of a patient by measuring an impedance signal generated by changes occurring in the patient's chest has filter elements (30, 36) for removing cardiac artifact from the impedance signal caused by cardiac activity in the chest. The filter elements (30, 36) produces an output signal dependent only upon respiration activity in the patient's chest by removing any signals from said output caused by cardiac activity which is substantially periodic in character. There is also disclosed a method of removing cardiac artifact during monitoring of a patient's respiration using impedance plethysmography.

Response to Gredler on the Birthday Effect—Fact or Artifact:

Abstract: A recent article by Gilbert R. Gredler that appeared in the Journal of Learning Disabilities (1980;13:239-242) was a reaction to DiPasquale and others (1980) regarding birthdate and achievement behavior in children. In his article, Gredler makes a number of statements which I would like to review, presenting contrasting points of view. Gredler begins by noting that there are destructive aspects of Gesellian Psychology in that maturational psychologists have been able to transmit their beliefs into changes of school practices. He notes that when people wish to debate their views in journals and conventions, no harm is done. It is dangerous when society begins to accept these beliefs and act on them. Gredler also seems to be saying that there is something inherently destructive in Gesellian Psychology and I would have assumed that the remainder of his article would have dealt fully with these destructive aspects. However, as is often the case with critics of the Gesellian Psychology, the remainder of the article deals only with the notion of maturity as it relates to achievement. This is where Gredler, as well as others who criticize Gesell, make critical errors. Those of us who believe in developmental placement proposed by the Gesell Institute are the first to admit that if we look only at achievement behavior in children, young children can often achieve and do well in academics of school. As a matter of fact, there are in the literature on developmental placement, two child characters that express this achievement behavior. They can be found in \"One Piece of the Puzzle\" (Carll & Richard 1977). These characters do quite well academically. They are of superior intellect. Other things being equal, children of superior intellect have a better chance of doing well in school academically, but the two characters described do not do well in many other facets of their lives. Socially, they are in a great deal of trouble. We are told in education that the \"whole child\" comes to school. The whole child is to be educated. Many philosophies that I have reviewed over my years in education as a teacher, counselor, psychologist, and administrator, suggest that the Gesell Institute approach is one of the few philosophies which allows us to look at the whole child. In discussing maturational psychology, Ilg and Ames (1965) talk about total school readiness, not simply readiness for academic work. When Ilg and Ames talk about overall school readiness for a child, they wish to see the child totally ready for school rather than simply be ready for cognitive or academic tasks. The children mentioned above do quite well academically, but socially are inept and in many ways dysfunctional. I imagine that Gredler would be quite content with a child who does well academically, but is experiencing social difficulties, including at times, substantial degrees of stress. These pressures often cause other psychological problems to develop in the child, but I imagine we are to set these aside because the child is doing well academically. There are children who are not young socially, but have not attained maturation in fine-motor development. The children experience difficulties in the second or third grade when cursive writing is begun. I assume that Gredler would tell us that as long as a child is reading and doing arithmetic at and above grade levels, we can put him or her in a remedial handwriting program. We could use the label \"disgraphic\" or another to explain the problems in handwriting, when all that may have been needed was time to develop more fine skills. There are children whose large motor skills are not developed. These children will have a difficult time with locomotion. The schools also take care of these children by having adaptive or remedial physical education programs and placing the children in these programs when their large-motor behavior is not smooth and graceful. Will Gredler tell us that as long as the child is doing well academically, this is fine? Finally, there are those children who are in a total way much younger developmentally than their birthday age. Despite everything else, they will likely experience failure in many different aspects of their school life and totally as a person. It would be a different matter, as Gredler suggests, if the Gesellian Philosophy were incorrect and harmful, and if he were to show totally how it were. We would waste the children's time with \"play\" rather than to get them into \"work.\" I suggest there are many reasons why their developmental approach is appropriate and necessary. Also, I agree with Gredler's example that changes in teaching also are necessary. But, I believe that the approach offered by the developmental placement program of Gesell is part of the two-pronged approach needed. I hope that if Gredler responds that his response will be directed toward a more complete picture of the Gesellian Philosophy rather than the fractionalized one in his current article.