Blood oxygenation can be measured using magnetic resonance using the paramagnetic effect of deoxy-haemoglobin, which decreases the \(\textit{T}_{2}\) relaxation time of blood. This \(\textit{T}_{2}\) contrast has been well characterised at the \(\textit{B}_{{0}}\) fields used in MRI (1.5 T and above). However, few studies have characterised this effect at lower magnetic fields. Here, the feasibility of blood oximetry at low field based on \(\textit{T}_{2}\) changes that are within a physiological relevant range is explored. This study could be used for specifying requirements for construction of a monitoring device based on low field permanent magnet systems.
Methods
A continuous flow circuit was used to control parameters such as oxygen saturation and temperature in a sample of blood. It flowed through a variable field magnet, where CPMG experiments were performed to measure its \(\textit{T}_{2}\). In addition, the oxygen saturation was monitored by an optical sensor for comparison with the \(\textit{T}_{2}\) changes.
Results
These results show that at low \(\textit{B}_{{0}}\) fields, the change in blood \(\textit{T}_{2}\) due to oxygenation is small, but still detectable. The data measured at low fields are also in agreement with theoretical models for the oxy-deoxy \(\textit{T}_{2}\) effect.
Conclusion
\(\textit{T}_{2}\) changes in blood due to oxygenation were observed at fields as low as 0.1 T. These results suggest that low field NMR relaxometry devices around 0.3 T could be designed to detect changes in blood oxygenation.
A detailed RFLP map was used to determine the chromosomal locations and subgenomic distributions of cotton (Gossypium) genes/QTLs that confer resistance to the bacterial blight pathogen, Xanthomonas campestris pv. malvacearum (Xcm). Genetic mapping generally corroborated classic predictions regarding the number and dosage effects of genes conferring Xcm resistance. One recessive allele (b6) was a noteworthy exception to the genetic dominance of most plant resistance alleles. This recessive allele appeared to uncover additional QTLs from both resistant and ostensibly susceptible genotypes, some of which corresponded in location to resistance (R)-genes effective against other Xcm races. One putatively "defeated" resistance allele (B3) reduced severity of Xcm damage by "virulent" races. Among the six resistance genes derived from tetraploid cottons, five (83%) mapped to D-subgenome chromosomes-if each subgenome were equally likely to evolve new R-gene alleles, this level of bias would occur in only about 1.6% of cases. Possible explanations of this bias include biogeographic factors, differences in evolutionary rates between subgenomes, gene conversion or other intergenomic exchanges that escaped detection by genetic mapping, or other factors. A significant D-subgenome bias of Xcm resistance genes may suggest that polyploid formation has offered novel avenues for phenotypic response to selection. 相似文献
This paper is the first part of a two-part series. It proves a number of direct relationships between the Fourier transform and the simple genetic algorithm. (For a binary representation, the Walsh transform is the Fourier transform). The results are of a theoretical nature and are based on the analysis of mutation and crossover. The Fourier transform of the mixing matrix is shown to be sparse. An explicit formula is given for the spectrum of the differential of the mixing transformation. By using the Fourier representation and the fast Fourier transform, one generation of the infinite population simple genetic algorithm can be computed in time O(cllog2(3)), where c is arity of the alphabet and l is the string length. This is in contrast to the time of O(c3l) for the algorithm as represented in the standard basis. There are two orthogonal decompositions of population space that are invariant under mixing. The sequel to this paper will apply the basic theoretical results obtained here to inverse problems and asymptotic behavior. 相似文献
This paper continues the development, begun in Part I, of the relationship between the simple genetic algorithm and the Walsh transform. The mixing scheme (comprised of crossover and mutation) is essentially "triangularized" when expressed in terms of the Walsh basis. This leads to a formulation of the inverse of the expected next generation operator. The fixed points of the mixing scheme are also determined, and a formula is obtained giving the fixed point corresponding to any starting population. Geiringer's theorem follows from these results in the special case corresponding to zero mutation. 相似文献
The temperature distributions produced within semi-infinite and finite-thickness media heated by a moving laser beam with a Gaussian power-density profile are examined by use of a time-domain method. Convective losses, described by Newton's law of cooling, from the medium surfaces are included. Various medium absorption models are considered. The solutions are given as single integrals with respect to time of simple functions. The resulting expressions have been used to examine the role of surface losses in information storage and medical applications. The role of convective losses in optical recording systems is found to be insignificant. However, for medical applications, combined convective and evaporative surface losses represent an important surface-heat-loss mechanism. 相似文献
BACKGROUND: Clinical manifestations and course of sickle-cell anemia are variable. Knowledge about the factors, possibly geographic, that influence prognosis are still scanty. POPULATION AND METHODS: Data of hospitalization and management of children with sickle-cell disease were studied during two years (1992-1993) in the Pediatric Unit of Libreville Hospital. They concerned 205 admissions of 171 children and 131 outpatients. RESULTS: The main causes of hospitalization were: acute anemia (36 cases before the age of 5 years); painful crisis whose frequency increased with age (23% before 5 years, 35% between 5 and 10, 42% after 10 years); infections, essentially pulmonary occurring early, and bone infections at any age. Eight children died (because a complication of their disease). Among the 131 outpatients, half were detected because pyrexia, anemia and/or more often "hand-foot syndrome". More than 60% had hepatomegaly, one third still had splenomegaly after five years of age and more than one third was icteric. More than half children older than ten years had growth disorders. Mean hemoglobin level was 7 g/dL. 21 of the 83 tested children for HBsAg were positive and only one out of 79 was positive for HIV. CONCLUSIONS: Clinical manifestations and course of sickle-cell anemia in our patients are similar to those reported in Congolese children. Genetic and environmental factors may be responsible for differences with children from other, in particular French, cohorts. 相似文献
Previous work has demonstrated that the use of structured abstracts can lead to greater completeness and clarity of information,
making it easier for researchers to extract information about a study. In academic year 2007/08, Durham University’s Computer Science Department revised the format of
the project report that final year students were required to write, from a ‘traditional dissertation’ format, using a conventional
abstract, to that of a 20-page technical paper, together with a structured abstract. This study set out to determine whether
inexperienced authors (students writing their final project reports for computing topics) find it easier to produce good abstracts, in terms of completeness and clarity, when using a structured form rather than a conventional form. We performed
a controlled quasi-experiment in which a set of ‘judges’ each assessed one conventional and one structured abstract for its
completeness and clarity. These abstracts were drawn from those produced by four cohorts of final year students: two preceding
the change, and the two following. The assessments were performed using a form of checklist that is similar to those used
for previous experimental studies. We used 40 abstracts (10 per cohort) and 20 student ‘judges’ to perform the evaluation.
Scored on a scale of 0.1–1.0, the mean for completeness increased from 0.37 to 0.61 when using a structured form. For clarity,
using a scale of 1–10, the mean score increased from 5.1 to 7.2. For a minimum goal of scoring 50% for both completeness and
clarity, only 3 from 19 conventional abstracts achieved this level, while only 3 from 20 structured abstracts failed to reach
it. We conclude that the use of a structured form for organising the material of an abstract can assist inexperienced authors
with writing technical abstracts that are clearer and more complete than those produced without the framework provided by
such a mechanism. 相似文献
Refinement algebras are abstract algebras for reasoning about programs in a total correctness framework. We extend a reduct of von Wright’s demonic refinement algebra with two operators for modelling enabledness and termination of programs. We show how the operators can be used for expressing relations between programs and apply the algebra to reasoning about action systems. 相似文献