Carrier lifetime and exciton saturation in a strain-balanced InGaAs/InAsP multiple-quantum-well

The bleaching of the n = 1 heavy-hole and light-hole exciton absorption has been studied at room temperature and zero bias in a strain-balanced InGaAs/InAsP multiple quantum well. Pump-probe spectroscopy was used to measure the decay of the light-hole absorption saturation, giving a hole lifetime of only 280 ps. As only 16 meV separates the light- and heavy-hole bands, the short escape time can be explained by thermalization between these bands followed by thermionic emission over the heavy-hole barrier. The saturation density was estimated to be 1 × 1016 cm-3; this is much lower than expected for tensile-strained wells where both heavy and light holes have large in-plane masses. © 1998 American Institute of Physics.

Regional differences in oxygen saturation in retinal arterioles and venules

BACKGROUND: Retinal vessel oxygenation saturation measurements have been the focus of much attention in recent years as a potential diagnostic parameter in a number of ocular and systemic pathologies. This interest has been heightened by the ability to measure oxygen saturation in vivo using a photographic technique. METHODS: Retinal vessel oxygenation in venules and arterioles of 279 retinal vessels of 12 healthy Caucasian participants (mean age: 30 SD (+/- 6) years) were measured consecutively three times to evaluate short-term variation in oxygen saturation and regional variability of retinal vessel oxygen saturation using dual-wavelength technology (Oxymetry Modul, Imedos, Germany). All subjects underwent standard optometric assessment including non-contact intra-ocular pressure assessment as well as having their systemic blood pressure measured. RESULTS: Vessels were grouped as either near-macula or peripheral, depending on their location. Peripheral arterioles and venules exhibited significantly lower oxygen saturation compared to their near-macula counterparts (arterioles: 94.7% (SD 3.9) vs. 99.7% (SD 3.2); venules: 65.1% (SD 7.2) vs. 90.3% (SD 6.7)). Both arterioles and venules, main branches, and those feeding and draining the retina near the macula and periphery showed low short-term variability of oxygen saturation (arterioles: COV 1.2-1.8%; venules: COV 2.9-4.9%). CONCLUSIONS: Retinal arterioles and venules exhibit low short-term variation of oxygen saturation in healthy subjects. Regional differences in oxygen saturation could be a potential useful marker for risk stratification and diagnostic purposes of area-specific retinal pathology such as age-related macula degeneration and diabetic maculopathy.

Analysis of nocturnal oxygen saturation recordings using kernel entropy to assist in sleep apnea-hypopnea diagnosis

In this study, a new entropy measure known as kernel entropy (KerEnt), which quantifies the irregularity in a series, was applied to nocturnal oxygen saturation (SaO 2) recordings. A total of 96 subjects suspected of suffering from sleep apnea-hypopnea syndrome (SAHS) took part in the study: 32 SAHS-negative and 64 SAHS-positive subjects. Their SaO 2 signals were separately processed by means of KerEnt. Our results show that a higher degree of irregularity is associated to SAHS-positive subjects. Statistical analysis revealed significant differences between the KerEnt values of SAHS-negative and SAHS-positive groups. The diagnostic utility of this parameter was studied by means of receiver operating characteristic (ROC) analysis. A classification accuracy of 81.25% (81.25% sensitivity and 81.25% specificity) was achieved. Repeated apneas during sleep increase irregularity in SaO 2 data. This effect can be measured by KerEnt in order to detect SAHS. This non-linear measure can provide useful information for the development of alternative diagnostic techniques in order to reduce the demand for conventional polysomnography (PSG). © 2011 IEEE.

ProxiMAX randomisation:a new technology for non-degenerate saturation mutagenesis of contiguous codons

Back in 2003, we published ‘MAX’ randomisation, a process of non-degenerate saturation mutagenesis using exactly 20 codons (one for each amino acid) or else any required subset of those 20 codons. ‘MAX’ randomisation saturates codons located in isolated positions within a protein, as might be required in enzyme engineering, or else on one face of an alpha-helix, as in zinc finger engineering. Since that time, we have been asked for an equivalent process that can saturate multiple, contiguous codons in a non-degenerate manner. We have now developed ‘ProxiMAX’ randomisation, which does just that: generating DNA cassettes for saturation mutagenesis without degeneracy or bias. Offering an alternative to trinucleotide phosphoramidite chemistry, ProxiMAX randomisation uses nothing more sophisticated than unmodified oligonucleotides and standard molecular biology reagents. Thus it requires no specialised chemistry, reagents nor equipment and simply relies on a process of saturation cycling comprising ligation, amplification and digestion for each cycle. The process can encode both unbiased representation of selected amino acids or else encode them in pre-defined ratios. Each saturated position can be defined independently of the others. We demonstrate accurate saturation of up to 11 contiguous codons. As such, ProxiMAX randomisation is particularly relevant to antibody engineering.

ProxiMAX Randomisation:a new technology for non-degenerate saturation mutagenesis of contiguous codons

ProxiMAX randomisation achieves saturation mutagenesis of contiguous codons without degeneracy or bias. Offering an alternative to trinucleotide phosphoramidite chemistry, it uses nothing more sophisticated than unmodified oligonucleotides and standard molecular biology reagents and as such, requires no specialised chemistry, reagents nor equipment. When particular residues are known to affect protein activity/specificity, their combinatorial replacement with all 20 amino acids, or a subset thereof, can provide a rapid route to generating proteins with desirable characteristics. Conventionally, saturation mutagenesis replaced key codons with degenerate ones. Although simple to perform, that procedure resulted in unnecessarily large libraries, termination codons and inherent uneven amino acid representation. ProxiMAX randomisation is an enzyme-based technique that can encode unbiased representation of all or selected amino acids or else can provide required codons in pre-defined ratios. Each saturated position can be defined independently of the others. ProxiMAX randomisation is achieved via saturation cycling: an iterative process comprising blunt end ligation, amplification and digestion with a Type IIS restriction enzyme. We demonstrate both unbiased saturation of a short 6-mer peptide and saturation of a hypervariable region of a scfv antibody fragment, where 11 contiguous codons are saturated with selected codons, in pre-defined ratios. As such, ProxiMAX randomisation is particularly relevant to antibody engineering. The development of ProxiMAX randomisation from concept to reality is described.

ProxiMAX randomisation:a new technology for non-degenerate saturation mutagenesis of contiguous codons

Back in 2003, we published ‘MAX’ randomisation, a process of non-degenerate saturation mutagenesis using exactly 20 codons (one for each amino acid) or else any required subset of those 20 codons. ‘MAX’ randomisation saturates codons located in isolated positions within a protein, as might be required in enzyme engineering, or else on one face of an alpha-helix, as in zinc finger engineering. Since that time, we have been asked for an equivalent process that can saturate multiple, contiguous codons in a non-degenerate manner. We have now developed ‘ProxiMAX’ randomisation, which does just that: generating DNA cassettes for saturation mutagenesis without degeneracy or bias. Offering an alternative to trinucleotide phosphoramidite chemistry, ProxiMAX randomisation uses nothing more sophisticated than unmodified oligonucleotides and standard molecular biology reagents. Thus it requires no specialised chemistry, reagents nor equipment and simply relies on a process of saturation cycling comprising ligation, amplification and digestion for each cycle. The process can encode both unbiased representation of selected amino acids or else encode them in pre-defined ratios. Each saturated position can be defined independently of the others. We demonstrate accurate saturation of up to 11 contiguous codons. As such, ProxiMAX randomisation is particularly relevant to antibody engineering.

The impact of flash intensity on retinal vessel oxygen saturation measurements using dual wavelength oximetry

PURPOSE. To establish the optimal flash settings for retinal vessel oxygen saturation parameters using dual-wavelength imaging in a multiethnic group. METHODS. Twelve healthy young subjects (mean age 32 years [SD 7]; three Mediterranean, two South Asian, and seven Caucasian individuals) underwent retinal vessel oxygen saturation measurements using dual-wavelength oximetry, noncontact tonometry, and manual sphygmomanometry. In order to evaluate the impact of flash intensity, we obtained three images (fundus camera angle 30°, ONH centered) per flash setting. Flash settings of the fundus camera were increased in steps of 2 (initial setting of 6 and the final of 22), which reflect logarithmic increasing intensities from 13.5 to 214 Watt seconds (Ws). RESULTS. Flash settings below 27 Ws were too low to obtain saturation measurements, whereas flash settings of more than 214 Ws resulted in overexposed images. Retinal arteriolar and venular oxygen saturation was comparable at flash settings of 27 to 76 Ws (arterioles' range: 85%-92%; venules' range: 45%-53%). Higher flash settings lead to increased saturation measurements in both retinal arterioles (up to 110%) and venules (up to 92%), with a more pronounced increase in venules. CONCLUSIONS. Flash intensity has a significant impact on retinal vessel oxygen saturation measurements using dual-wavelength retinal oximetry. High flash intensities lead to supranormal oxygen saturation measurements with a magnified effect in retinal venules compared with arteries. In addition to even retinal illumination, the correct flash setting is of paramount importance for clinical acquisition of images in retinal oximetry. We recommend flash settings between 27 to 76 Ws. © 2013 The Association for Research in Vision and Ophthalmology, Inc.

Percent in a Nutshell …

Ironically, the “learning of percent” is one of the most problematic aspects of school mathematics. In our view, these difficulties are not associated with the arithmetic aspects of the “percent problems”, but mostly with two methodological issues: firstly, providing students with a simple and accurate understanding of the rationale behind the use of percent, and secondly - overcoming the psychological complexities of the fluent and comprehensive understanding by the students of the sometimes specific wordings of “percent problems”. Before we talk about percent, it is necessary to acquaint students with a much more fundamental and important (regrettably, not covered by the school syllabus) classical concepts of quantitative and qualitative comparison of values, to give students the opportunity to learn the relevant standard terminology and become accustomed to conventional turns of speech. Further, it makes sense to briefly touch on the issue (important in its own right) of different representations of numbers. Percent is just one of the technical, but common forms of data representation: p% = p × % = p × 0.01 = p × 1/100 = p/100 = p × 10-2 "Percent problems” are involved in just two cases: I. The ratio of a variation m to the standard M II. The relative deviation of a variation m from the standard M The hardest and most essential in each specific "percent problem” is not the routine arithmetic actions involved, but the ability to figure out, to clearly understand which of the variables involved in the problem instructions is the standard and which is the variation. And in the first place, this is what teachers need to patiently and persistently teach their students. As a matter of fact, most primary school pupils are not yet quite ready for the lexical specificity of “percent problems”. ....Math teachers should closely, hand in hand with their students, carry out a linguistic analysis of the wording of each problem ... Schoolchildren must firmly understand that a comparison of objects is only meaningful when we speak about properties which can be objectively expressed in terms of actual numerical characteristics. In our opinion, an adequate acquisition of the teaching unit on percent cannot be achieved in primary school due to objective psychological specificities related to this age and because of the level of general training of students. Yet, if we want to make this topic truly accessible and practically useful, it should be taught in high school. A final question to the reader (quickly, please): What is greater: % of e or e% of Pi

Experimental data of CO2, CO3, Omega calcite saturation, pH values, alpha and epsilon fractionation factors, and Dd18O calctite-water

The oxygen isotopic composition (d18O) of calcium carbonate of planktonic calcifying organisms is a key tool for reconstructing both past seawater temperature and salinity. The calibration of paloeceanographic proxies relies in general on empirical relationships derived from field experiments on extant species. Laboratory experiments have more often than not revealed that variables other than the target parameter influence the proxy signal, which makes proxy calibration a challenging task. Understanding these secondary or "vital" effects is crucial for increasing proxy accuracy. We present data from laboratory experiments showing that oxygen isotope fractionation during calcification in the coccolithophore Calcidiscus leptoporus and the calcareous dinoflagellate Thoracosphaera heimii is dependent on carbonate chemistry of seawater in addition to its dependence on temperature. A similar result has previously been reported for planktonic foraminifera, supporting the idea that the [CO3]2- effect on d18O is universal for unicellular calcifying planktonic organisms. The slopes of the d18O/[CO3]2- relationships range between -0.0243 per mil/(µmol/kg) (calcareous dinoflagellate T. heimii) and the previously published -0.0022 per mil/(µmol/kg) (non-symbiotic planktonic foramifera Orbulina universa), while C. leptoporus has a slope of -0.0048 per mil/(µmol/kg). We present a simple conceptual model, based on the contribution of d18O-enriched [HCO3]- to the [CO3]2- pool in the calcifying vesicle, which can explain the [CO3]2- effect on d18O for the different unicellular calcifiers. This approach provides a new insight into biological fractionation in calcifying organisms. The large range in d18O/[CO3]2- slopes should possibly be explored as a means for paleoreconstruction of surface [CO3]2-, particularly through comparison of the response in ecologically similar planktonic organisms.

Effets de la nitroglycérine intraveineuse sur la saturation cérébrale hémisphérique pendant la chirurgie cardiaque à haut risque

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Effets de la nitroglycérine intraveineuse sur la saturation cérébrale hémisphérique pendant la chirurgie cardiaque à haut risque

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Seawater carbonate chemistry and sperm swimming speed of the polychaete Galeolaria caespitosa in lab experiment

The rapidity of ocean acidification intensifies selection pressure for resilient phenotypes, particularly during sensitive early life stages. The scope for selection is greater in species with greater within-species variation in responses to changing environments, thus enhancing the potential for adaptation. We investigated among-male variation in sperm swimming responses (percent motility and swimming speeds) of the serpulid polychaete Galeolaria caespitosa to near- (delta pH 0.3) and far-future ocean acidification (delta pH 0.5). Responses of sperm swimming to acidification varied significantly among males and were overall negative. Robust sperm swimming behavior under near-future ocean acidification in some males may ameliorate climate change impacts, if traits associated with robustness are heritable, and thereby enhance the potential for adaptation to far-future conditions. Reduced sperm swimming in the majority of male G. caespitosa may decrease their fertilization success in a high CO2 future ocean. Resultant changes in offspring production could affect recruitment success and population fitness downstream.

Seawater carbonate chemistry and sperm swimming speed, fertilization success of the Australasian sea urchin Heliocidaris erythrogramma in lab experiment

Background: Climate change will lead to intense selection on many organisms, particularly during susceptible early life stages. To date, most studies on the likely biotic effects of climate change have focused on the mean responses of pooled groups of animals. Consequently, the extent to which inter-individual variation mediates different selection responses has not been tested. Investigating this variation is important, since some individuals may be preadapted to future climate scenarios. Methodology/Principal Findings: We examined the effect of CO2-induced pH changes ("ocean acidification") in sperm swimming behaviour on the fertilization success of the Australasian sea urchin Heliocidaris erythrogramma, focusing on the responses of separate individuals and pairs. Acidification significantly decreased the proportion of motile sperm but had no effect on sperm swimming speed. Subsequent fertilization experiments showed strong inter-individual variation in responses to ocean acidification, ranging from a 44% decrease to a 14% increase in fertilization success. This was partly explained by the significant relationship between decreases in percent sperm motility and fertilization success at delta pH = 0.3, but not at delta pH = 0.5. Conclusions and Significance: The effects of ocean acidification on reproductive success varied markedly between individuals. Our results suggest that some individuals will exhibit enhanced fertilization success in acidified oceans, supporting the concept of 'winners' and 'losers' of climate change at an individual level. If these differences are heritable it is likely that ocean acidification will lead to selection against susceptible phenotypes as well as to rapid fixation of alleles that allow reproduction under more acidic conditions. This selection may ameliorate the biotic effects of climate change if taxa have sufficient extant genetic variation upon which selection can act.