Differential Absorption Experiment Research Articles

Bleeding or no bleeding? Anti‐endothelial alphaVbeta3 antibodies as a major cause of intracranial haemorrhage in fetal–neonatal alloimmune thrombocytopenia

Fetal/neonatal alloimmune thrombocytopenia (FNAIT) is a severe bleeding disorder which can result in intracranial haemorrhage (ICH), leading to death or neurological sequelae. In Caucasians, maternal anti‐HPA‐1a antibodies (abs) are responsible for the majority of FNAIT cases. However, the correlation between fetal platelet counts and risk of bleeding is loose. ICH was also observed in FNAIT cases with platelet counts within reference ranges. These observations question the exclusive role of thrombocytopenia in ICH. Recently, we observed stronger binding of anti‐HPA‐1a antibodies from mothers with ICH‐positive (+ICH) FNAIT to endothelial cell‐derived αvβ3 when compared to anti‐HPA‐1a from ‐ICH. Differential absorption experiments demonstrated that anti‐HPA‐1a is not a single antibody entity. Sera from immunized women may contain three different subspecificities: anti‐β3, anti‐αIIbβ3 and anti‐αvβ3. Anti‐β3 appears to be the dominant subtype of anti‐HPA‐1a. However, anti‐αvβ3 was only found in +ICH sera, and only the anti‐αvβ3, but not anti‐β3 subtype, induced apoptosis and disturbed tube formation of endothelial cells in vitro. Therefore, we believe that this anti‐HPA‐1a subtype plays a significant role in the development of ICH. Together with other subtypes, anti‐αvβ3 may trigger bleeding in a threshold model of FNAIT/ICH, where bleeding occurs if yet undefined levels of anti‐endothelial (loss of integrity) and/or antiplatelet (low platelet count) activities are achieved. Thus, defining anti‐HPA‐1a subtypes may have significant potential in the prediction of ICH. With upcoming nation‐wide screening programmes, detection of anti‐HPA‐1a subtypes could prove helpful to allocate treatment to appropriate (at‐risk) cases, especially in countries with restricted resources.

The molecular mechanism of dual emission in terpyridine transition metal complexes—ultrafast investigations of photoinduced dynamics

Temperature dependent luminescence experiments are combined with femtosecond time-resolved transient absorption spectroscopy to decipher the photoinduced excited-state relaxation pathway in mononuclear Fe, Ru and Os terpyridine complexes bearing a conjugated chromophore within the ligand framework. The herein presented complexes constitute a class of coordination compounds, which overcome the poor emission properties commonly observed for most terpyridine transition metal complexes. As reported earlier, the complexes reveal dual emission at room temperature stemming from ligand centered and metal-to-ligand charge-transfer states. The molecular mechanism of the room temperature dual luminescence is addressed experimentally in this contribution. The experimental results indicate an ultrafast branching reaction within the excited-state manifold upon photoexcitation of the ligand-centered S(1) state. This branching occurs from a "hot" excited state geometry close to the Franck-Condon point of absorption and within ∼100 fs, i.e. the temporal resolution of our experimental setup. The combination of ultrafast differential absorption experiments and temperature-dependent luminescence data allows not only to draw conclusions about the molecular mechanism underlying the observed dual emission but also to construct quantitative Jablonski diagrams and, thereby, to detail the excited-state topology determining the remarkable luminescence properties of the systems at hand.

1s [formula omitted]2p Terahertz transitions of the 1s paraexciton in Cu 2O

In a cw differential absorption experiment, we examined infrared transitions of excitons in Cu 2O. We find a clear transition which is assigned to induced 1s para → 2p para absorption. Line shape and intensity of induced absorption are analysed as a function of temperature and excitation conditions.

The Buckland Park MF radar: routine observation scheme and velocity comparisons

Abstract. This paper describes the routine observations scheme implemented for the Buckland Park medium frequency (BPMF) radar. These observations are rare among current MF/HF radar observations in that they are made using a relatively narrow transmit polar diagram. The flexibility of the radar allows a number of analyses to be performed simultaneously. The analyses described include the full correlation analysis (FCA), spatial correlation analysis (SCA), hybrid Doppler interferometry (HDI) and imaging Doppler interferometry (IDI) for observations of mesospheric dynamics and the temporal and spatial characteristics of their scatterers, the differential absorption experiment (DAE) for the estimation of electron densities and collision frequencies, and meteor analysis for estimation of meteor height, time and angle of arrival (AOA) distributions. Intercomparisons between wind velocities estimated using the FCA with SCA, HDI and IDI techniques are presented. The FCA velocities exhibit the well-known "triangle size effect" (TSE), whereby the wind velocity is underestimated at smaller antenna spacings. Although the SCA, IDI and HDI techniques were not applied concurrently, comparisons using FCA as a reference suggest these techniques produce velocities in good agreement.

Infrared absorption by excitons in Cu2O

AbstractIn a differential absorption experiment the induced infrared transitions from the excitonic 1s to the 2p levels in Cu2O have been investigated. Intermediate densities of 1s excitons were created by cw‐laser excitation while the interexcitonic 1s to 2p transitions were probed simultaneously, using Fourier spectroscopy. Our data give evidence for a surprisingly large splitting of the 2p level (≈3.7 meV) the origin of which is a matter of speculation. An analysis of lineshape and width of the transitions results in a ratio of the effective masses m1s/m2p which deviates from the literature value.

Differential absorption measurements of mesospheric and lower thermospheric electron densities using the Buckland Park MF radar

The differential absorption experiment (DAE) was first proposed in the 1950s for the estimation of mesospheric and lower thermospheric electron density using MF/HF radars. The technique was used extensively until the late 1970s, when interest in the technique declined, due to experimental limitations and questions regarding the assumptions of the technique. This paper describes the application of the DAE within the online observations of the Buckland Park MF (BPMF) radar. The experimental limitations of the technique for the BPMF radar are discussed, with particular attention paid to effects of complex gain differences between receiving channels used to decompose the linearly received signals into circular components. Hourly and monthly averaged midday DAE electron densities are presented, revealing good agreement with IRI model estimates. Monthly averaged midnight DAE electron densities are also presented, revealing good qualitative agreement with the IRI model estimates.

Screening and characterization of specific anti-lipopolysaccharide antibodies in Belgian blood donors by enzyme-linked immunosorbent assays.

The goal of this project was to find and collect high concentrations of endotoxin-specific antibodies for therapeutic IgG- or IgM-enriched preparations. Various enzyme-linked immunosorbent assays (ELISAs) were developed to perform longitudinal studies of the serological response to a large panel of smooth and rough purified lipopolysaccharide (LPS) extracts in a population of healthy blood donors. To accomplish this, 1612 human serum samples from volunteer blood donors collected by seven different blood banks in Belgium were screened and specific IgM and IgG activities were measured. Approximately 17% of the donors had anti-LPS concentrations higher than 40 mg L-1. Of these, 10.9% had anti-smooth LPS antibodies, 3.7% had anti-rough LPS antibodies and 2.8% were found to be positive towards both types of LPS. The mean anti-LPS antibody concentration was 8 mg L-1 for rough LPS and 14 mg L-1 for smooth LPS. Age- and sex-related distributions of the activities indicated that the greatest prevalence of high anti-LPS concentration was in women aged 40-49 years and in men older than 60 years. Differential absorption experiments showed that the pooled serum of selected blood donors contained a mixture of specific and cross-reacting antibodies. We detected predominantly anti-LPS activities due to the IgG1 and IgG2 subclasses. The range of specificities to different LPS was increased by the pooling of selected sera. It was concluded that pools of naturally occurring specific anti-LPS immunoglobulin antibodies may be obtained in Belgium by screening blood donors using ELISAs that we have developed.

Structure in the lowest absorption feature of CdSe quantum dots

We use transient differential absorption experiments to investigate the ‘‘single dot’’ absorption line shape of CdSe quantum dots. We observe both a narrow (full width half maximum ∼5 meV) and a broad (∼50 meV) bleach component within the inhomogeneously broadened first absorption line of our samples. We deduce the single dot absorption line shape which is most consistent with the experimental results. This line shape, which contains structure in the lowest quantum dot absorption feature, explains the large ‘‘Stokes’’ shift seen in the full band edge luminescence of CdSe quantum dots. We discuss the structure within the context of several competing models. The data appear inconsistent with models which use surface states to explain the anomalous emission behavior of II–VI quantum dots. Instead they imply that exciton fine structure is observed in our samples.

Dephasing processes in II–VI quantum dots

AbstractThe loss of phase coherence in II–VI quantum dots is investigated using experimental methods working both in the frequency and in the time domain. Femtosecond differential absorption experiments reveal narrow resonances at very early times after excitation and low excitation densities for CdSe quantum dots. A substructure is detected and explained by transitions from the series of confined hole states. By nondegenerate four‐wave mixing experiments (NDFWM) the dephasing time is determined for CdS quantum dots with radii larger than the Bohr radius. Temperature and excitation intensity dependent dephasing times between ≈︁ 20 fs and some 100 fs are measured and attributed to electron‐hole pair–phonon coupling and carrier–carrier scattering.

Properties of Human Anti‐Lipopolysaccharide Gamma Globulin: Specificity and Protective Effects

Blood donated to the Natal Blood Transfusion Service was screened by an enzyme-linked immunosorbent assay (ELISA) for anti-lipopolysaccharide (anti-LPS) antibodies. Plasma units with high concentrations (greater than 40 micrograms/ml) of anti-LPS IgG were pooled and fractionated to obtain a gamma globulin (lot LG-1). The binding of LG-1 antibodies to LPS prepared from 14 bacterial species and strains was found to be the highest to LPS from Shigella flexneri, Salmonella abortus equi and Salmonella typhimurium and intermediate with Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enteritidis and Escherichia coli 026:B6. Differential absorption experiments showed that LG-1 contained a mixture of specific and cross-reacting antibodies. A large proportion of antibodies binding to Sh. flexneri LPS were mainly specific, while those binding to S. typhimurium and the other Salmonella species tested were largely cross-reactive. There was little correlation between the spectrum of activity of the LG-1 antibodies and the incidence of gram-negative bacteria in blood cultures taken from hospital patients in an area covered by the Transfusion Service. Mice treated with LG-1 prior to inoculation with P. aeruginosa were significantly protected against morbidity and mortality compared to controls.

Comparisons between time variations in D-region winds and electron densities at Saskatoon, Canada (52°N; 106°W)

A partial reflection radiowave system (2.2 MHz) has been used at Saskatoon, Canada (52°N, 106°W; L = 4.4) to obtain electron densities (~65–85 km) by the differential absorption experiment, and winds (52–118 km) by the spaced antenna drifts experiment. These data have been compared during the winter (December–March) of 1974/75, eleven selected days during January and February of 1976, and during 10 days in each of the four seasons of 1976. There is consistent evidence for a correspondence between increasing ionization and decreasing northward or increasing southward winds, during winter months. This is consistent with the hypothesis that nitric oxide (NO), created during magnetic storms by the associated auroral activity, contributes to electron density variability by way of circulation changes and atmospheric waves. It has not been possible to distinguish between a latitude gradient of NO or isolated accumulations of this minor constituent.

Experimental investigations of ionospheric/stratospheric coupling in southern mid-latitudes—2. Comparison of mesospheric electron densities and drifts with stratospheric temperatures and winds

Simultaneous measurements in time and place (Christchurch, N.Z., 44°S, 172°E) of 1. (a) mesospheric electron densities (deduced from the differential absorption experiment), 2. (b) mesospheric winds (deduced from partial reflection drifts), 3. (c) temperatures near 40 km (deduced from Nimbus 4 SCR channel A radiance), and 4. (d) lower stratosphere temperatures (from balloon radiosondes), were compared for evidence of stratospheric/mesospheric coupling. In the period under investigation (June–September, 1972) coupling was only apparent in a short period during July.

Nature of cold-reactive antibodies to lymphocyte surface determinants in systemic lupus erythematosus.

Antilymphocyte antibodies in serum from patients with systemic lupus erythematosus (SLE), as detected by microcytotoxicity and indirect immunofluorescence, were predominantly cold reactive and of the IgM class. These IgM antibodies were most active at 4 degrees C. IgG antibodies were infrequent, and were only minimally lymphocytotoxic. Most sera were cytotoxic for autologous lymphocytes and were equally reactive with normal and SLE lymphocytes, as well as with B- and T-cell preparations. Separate T- and B-cell specificities, which appeared not to be related to HL-A determinants, were identified by differential absorption experiments. The functional significance of these antilymphocyte antibodies is discussed.

Electron Precipitation at an Auroral Latitude – Saskatoon, L = 4.4. II. Fluxes of Precipitating Electrons

Measurements of ambient electron densities have been made by the differential absorption experiment, on a number of aurorally disturbed nights in 1971. The measured values of the intensity of the green line (5577 Å) emission, and of the ambient electron densities, are then compared with theoretical estimates of these two variables. An exponential energy spectrum is used in the calculation, and fluxes of precipitated electrons (> 40 keV) and values for the e folding energies (E0) thereby become available. Comparisons of mean values with satellite measurements made under similar magnetic conditions, show good agreement. Calculations are also made for two specific nights, (January 26–28, 1971). Characteristic energies are typically 5 keV during the maximum of the magnetic and photometric disturbances, and increase to values of 10–15 keV near sunrise when the ionospheric disturbance (< 90 km) is greatest. The calculation is shown to be sensitive to changes in characteristic energy of the spectrum.

Differential Phase Shift of Partially Reflected Radio Waves

The addition of phase difference measurements to differential absorption experiments is shown to be both feasible and desirable. The phase information can provide a more sensitive measurement of electron density above about 75 km. The differential phase shift is only weakly dependent on collision frequency in this range, and so an accurate collision frequency profile is not a prerequisite. The differential phase shift and differential absorption measurements taken together can provide both electron density and collision frequency data from about 70 to 90 km.

Seasonal variations of electron densities below 100 km at mid-latitudes—I Differential absorption measurements

The differential absorption experiment (D.A.E.) for measuring electron densities in the lower ionosphere, using partial reflections, is examined. A model of the scattering process which invokes sharply bounded horizontally stratified irregularities is found to be more satisfactory than one based on volume scattering. The ratio of calculated reflection coefficients for the two magneto-ionic components, R x R o , is found to be insensitive to the geometry of reflecting boundaries and the fractional changes in electron concentration, ΔN N , provided the refractive index n tends to unity; but is affected by the propagation angle with respect to the magnetic field. The nature of irregularities in the lower ionosphere is discussed, and it is concluded that perturbations in collision frequency, Δv v , are not significant for the calculation of R x R o . Models of collision frequency profile, v( h) for three seasons are derived from meteorological data. Differences in probable collision frequencies between northern and southern hemispheres are examined. The sensitivity of the method, to changes in assumed v( h), is then discussed. The capability of the D.A.E. to produce electron density profiles of good height resolution and accuracy is evaluated. Errors involved in the assumption of v( h) and the measurement of the amplitude ratio of the received magneto-ionic components, R x R o , are discussed.

Coments on the theory of the Differential Absorption Experiment

Modification to theory of differential absorption experiment involving Fresnel reflection coefficient of ionospheric irregularities

THE TOXICITY OF HUMAN SERUM FOR THE GUINEA PIG

FROM THE FOREGOING STUDY THERE ARE INDICATIONS: 1. Of toxicity in all fresh human serum for the guinea pig; this toxicity tends to disappear after 48 hours after bleeding, and its manifestations are strikingly similar to those of the heterophilic antibody in immune rabbit serum. 2. Of an increased toxicity in the serum of antisera-treated human cases; this is usually coexistant with the production of other antibodies; it tends likewise to disappear in time after treatment; differential absorption experiments indicate that its character is heterophilic, and its manifestations differ from those of anaphylaxis in that certain circulatory effects-hemorrhage and increased edema in the lungs and distension of the right heart-are added to the usual findings in true anaphylactic deaths.