High purity bright single photon source.

Using cavity-enhanced non-degenerate parametric down-conversion, we have built a frequency tunable source of heralded single photons with a narrow bandwidth of 8 MHz, making it compatible with atomic quantum memories. The photon state is 70% pure single photon as characterized by a tomographic measurement and reconstruction of the quantum state, revealing a clearly negative Wigner function. Furthermore, it has a spectral brightness of ~1,500 photons/s per MHz bandwidth, making it one of the brightest single photon sources available. We also investigate the correlation function of the down-converted fields using a combination of two very distinct detection methods; photon counting and homodyne measurement.

Effects of electric field reduction in visual display units on skin symptoms.

OBJECTIVES: This study investigated the facial skin complaints of office workers before and after the static electric fields of a visual display unit were reduced. METHODS: On the basis of a screening survey of 4556 office workers in 11 companies, 120 of 227 subjects reporting facial skin complaints were randomly selected to this double blind intervention study. Antistatic measures were used to reduce the static electric fields of the visual display unit in the intervention group but not in the control group, which worked with a visual display unit resembling that of the intervention group. Electric fields, dust concentration, health complaints, and psychological behavior tests were recorded before and after the intervention. RESULTS: The intervention group reported statistically significantly fewer facial skin complaints than the control group. In the intervention group, among those with an office dust concentration of >58 microg/m3, a median reduction of 1.5 skin index points (scale 0-8) was achieved, whereas there was no change in the control group. In the regression model "group category" was still a significant variable after control for background factors. In addition, further linear regression analyses indicated that several static electric field parameters were predictors of the skin complaint reduction. CONCLUSIONS: This field trial indicates that removing static electric fields from visual display units can probably help reduce the facial skin complaints of workers in offices with high dust concentrations.

Chromosomal aberrations in lymphocytes of employees in transformer and generator production exposed to electromagnetic fields and mineral oil.

The objective was to study the risk of cytogenetic damage among high voltage laboratory workers exposed to electromagnetic fields and mineral oil. This is a cross sectional study of 24 exposed and 24 matched controls in a Norwegian transformer factory. The exposure group included employees in the high voltage laboratory and in the generator soldering department. Electric and magnetic fields and oil mist and vapor were measured. Blood samples were analyzed for chromosomal aberrations in cultured lymphocytes. In addition to conventional cultures, the lymphocytes were also treated with hydroxyurea and caffeine. This procedure inhibits DNA synthesis and repair in vitro, revealing in vivo genotoxic lesions that are repaired during conventional culturing. In conventional cultures, the exposure group and the controls showed similar values for all cytogenetic parameters. In the DNA synthesis- and repair-inhibited cultures, generator welders showed no differences compared to controls. Among high voltage laboratory testers, compared to the controls, the median number of chromatid breaks was doubled (5 vs. 2.5 per 50 cells; P<0.05) the median number of chromosome breaks was 2 vs. 0.5 (P>0.05) and the median number of aberrant cells was 5 vs. 3.5 (P<0.05). Further analysis of the inhibited culture data from this and a previous study indicated that years of exposure and smoking increase the risk of aberrations. We conclude that there was no increase in cytogenetic damage among exposed workers compared to controls in the conventional lymphocyte assay. In inhibited cultures, however, there were indications that electromagnetic fields in combination with mineral oil exposure may produce chromosomal aberrations.

Why arguments based on photon energy may be highly misleading for power line frequency electromagnetic fields.

When evaluating possible mechanisms by which low frequency electromagnetic fields may have a biological effect, arguments based on photon energy have often been used in a misleading way. For visible light the concept of photons has proved to be very useful in explaining experimental findings. However, the concept of photons cannot be used without major modifications in describing phenomena related to near field problems at power frequency (50 or 60 Hz) electric and magnetic fields. For this regime, the photon description is very complex. A very high number of highly coherent photons must be used in a quantum electrodynamic description of low frequency electromagnetic field phenomena. Thus, one-photon interaction descriptions must be replaced by multiple-photon interaction formalism. However, at low frequencies, a classical electromagnetic field description is far more useful than quantum electrodynamics. There is in principle no difference in how much energy an electron can pick up from a low frequency electric field as compared to from a high frequency photon. Thus, the total gain in energy is not limited to the energy carried by a single photon, which is E = hv, where h is Planck's constant and (v) is the frequency of the radiation. However, the time scale of the primary event in a mechanism of action is very different for ionizing radiation compared to power line frequency fields. The advice is to consider the time scale given by the inverse of the frequency of the fields, rather than photon energy, when one use physics as a guidance in evaluating possible mechanisms for biological effects from low frequency electromagnetic fields.

Deflection of cosmic radiation near power lines--a theoretical approach.

The purpose of this work is to determine if, and to what extent, cosmic radiation can be deflected by power lines. As an alternative to experimental measurements, a computer program was developed to simulate particle trajectories. Starting from given initial values, the cosmic particles' trajectories through the electromagnetic field surrounding power lines are simulated. Particular efforts have been made to choose initial values that represent the actual physical condition of the cosmic radiation at ground level. The results show an average decrease in the particle flux density in an area below a power line and a corresponding increased flux between 12 m and 35 m on either side of the center of the power line. The average shift in flux density is, however, extremely small (less than 0.15% for low energy electrons alone, and less than 0.01% for total particle flux density) and probably not measurable with existing detector technology. The calculated particle deflection is far too small to be of any possible health significance.

Exposure of children to residential magnetic fields in Norway: is proximity to power lines an adequate predictor of exposure?

The aim of this work was to study the exposure to magnetic fields of children living at different distances from a power line and to evaluate how well theoretical calculations compared with actual exposure. Personal exposure instruments were carried for 24 h by 65 schoolchildren living 28-325 m from a 300 kV transmission line; the current load was 200-700 A. About half of the children attended a school far from the power line, whereas the other half attended a school located about 25 m from the line. Exposure to magnetic fields was analyzed for three categories of location: at home, at school, and at all other places. Time spent in bed was analyzed separately. The results indicated that children who lived close to a power line had a higher magnetic field exposure than other children. The power line was the most important source of exposure when the magnetic field due to the line was greater than about 0.2 microT. Exposure at school influenced the 24 h time-weighted average results considerably in those cases where the distance between home and power line was very different from the distance between school and power line. The calculated magnetic field, based on line configuration, current load, and distance between home and power line, corresponded reasonably well with the measured field. However, the correlation depends on whether home only or 24 h exposure is used in the analysis and on which school the children attended. The calculated magnetic field seems to be a reasonably good predictor of actual exposure and could be used in epidemiological studies, at least in Norway, where the electrical system normally results in less ground current than in most other countries.

Incidence of breast cancer in Norwegian female radio and telegraph operators.

Exposure to electromagnetic fields may cause breast cancer in women if it increases susceptibility to sex-hormone-related cancer by diminishing the pineal gland's production of melatonin. We have studied breast cancer incidence in female radio and telegraph operators with potential exposure to light at night, radio frequency (405 kHz-25 MHz), and, to some extent, extremely low frequency fields (50 Hz). We linked the Norwegian Telecom cohort of female radio and telegraph operators working at sea to the Cancer Registry of Norway to study incident cases of breast cancer. The cohort consisted of 2,619 women who were certified to work as radio and telegraph operators between 1920 and 1980. Cancer incidence was analyzed on the basis of the standardized incidence ratio (SIR), with the Norwegian female population as the comparison group. The incidence of all cancers was close to unity (SIR = 1.2). An excess risk was seen for breast cancer (SIR = 1.5). Analysis of a nested case-control study within the cohort showed an association between breast cancer in women aged 50+ years and shift work. In a model with adjustment for age, calendar year, and year of first birth, the rate ratio for breast cancer associated with being a radio and telegraph operator--in comparison with all Norwegian women born 1935 or later--analyzed with Poisson regression, was 1.5 after adjustment for fertility factors. These results support a possible association between work as a radio and telegraph operator and breast cancer. Future epidemiologic studies on breast cancer in women aged 50 and over, should address possible disturbances of chronobiological parameters by environmental factors.

High-voltage overhead power lines in epidemiology: patterns of time variations in current load and magnetic fields.

In epidemiological studies of electromagnetic fields and health effects, exposure classification is crucial. There is no generally accepted biophysical interaction mechanism, but many studies are based on the hypothesis of a causal relationship with the strength of magnetic field. Some definition of the magnitude of exposure must be used, e.g., mean magnetic flux density, the integral of magnetic flux and time, or a peak value. Magnetic fields around a particular power line depend on the current load. The aim of the present study was to follow variations in line current load in the power supply system of the largest Norwegian city on a yearly, monthly, daily and diurnal basis. Fairly large variations in load were found, but increases in consumption were not necessarily reflected in current load on high voltage lines. The correlation between outdoor temperature and current load varied widely, depending on the type of power station feeding the line in question. The registered time variations are large enough to interfere with epidemiological classification of residences and testing of epidemiological hypotheses.

Skin symptoms after the reduction of electric fields from visual display units.

OBJECTIVES: The objective of this work was to determine whether facial skin symptoms are reduced by decreasing static and low-frequency electric fields produced by visual display units. METHODS: The electric fields were reduced by electric-conducting screen filters. Twenty subjects took part in the study while working at their ordinary jobs, first two weeks without any filter, then two weeks with an inactive filter and two weeks with an active filter (or in reversed order). The inasctive filters were identical to the active ones except that the ground cable was cut. Measurements showed that the inactive filters reduced the static electric fields nonsignificantly less than the active filters. For extremely low-frequency fields the difference was greater, and the active filters reduced the very low-frequency fields significantly more than the inactive ones. RESULTS: Most symptoms were less pronounced with active filters than with inactive filters. The differences were small, and for one symptom only, tingling, pricking or itching, the result was statistically significant. The recorded physical and psychosocial factors did not explain the reduction with the use of active filters. Days with a long period spent near a visual display unit resulted in significantly more pronounced symptoms than days with short time. The findings registered by a dermatologist did not reveal any consistent difference between the two periods with filters. CONCLUSION: The results weakly support the hypothesis that skin symptoms can be reduced by a reduction of electric fields.

[Low frequency electromagnetic fields in the working environment--exposure and health effects. Elevated risk of cancer, reproductive hazards or other unwanted health effects?]. / Lavfrekvente elektromagnetiske felter i arbeidsmiljøet--eksponeringsforhold og helseeffekter. Er det økt risiko for kreft, reproduksjonsskader eller andre uønskede virkninger på helsen?

The authors describe the physical properties of low frequency electromagnetic fields and occupational exposure to such fields in different working environments. They discuss possible health effects reported in the literature. It is concluded that there seems to be elevated risk of leukemia and brain tumours among persons employed in "electrical work", though there is insufficient evidence that the fields are responsible. No conclusion can be drawn as to risk of adverse outcome of pregnancy. When this is technically and economically feasible, exposure to low frequency electromagnetic fields should be kept to a minimum.

Leukemia and brain tumors in Norwegian railway workers, a nested case-control study.

In an attempt to assess whether exposure to electromagnetic fields on Norwegian railways induces brain tumors or leukemia, the authors conducted a nested case-control study of railway workers based on incident cases from the Cancer Registry of Norway in a cohort of 13,030 male Norwegian railway workers who had worked on either electric or non-electric railways. The cohort comprised railway line, outdoor station, and electricity workers. The case series comprised 39 men with brain tumors and 52 men with leukemia (follow-up, 1958-1990). Each case was matched on age with four or five controls selected from the same cohort. The exposure of each study subject to electric and magnetic fields was evaluated from cumulative exposure measures based on present measurements and historical data. Limited information on potential confounders such as creosote, solvents, and herbicides was also collected; information on whether the subject had smoked was obtained by interviews with the subjects or work colleagues. The case-control analysis showed that men employed on electric railways, compared with non-electric ones, had an odds ratio for leukemia of 0.70 (adjusted for smoking) and an odds ratio for brain tumor of 0.87. No significant trend was shown for exposure to either magnetic or electric fields. These results do not support an association between exposure to 16 2/3-Hertz electric or magnetic fields and the risk for leukemia or brain tumors.

Chromosome aberrations in lymphocytes of high-voltage laboratory cable splicers exposed to electromagnetic fields.

Thirteen high-voltage laboratory employees and 20 referents participated in a cross-sectional, matched-pairs study of cytogenetic damage. During cable testing the workers were exposed to static, alternating, or pulsed electric and magnetic fields. The alternating magnetic field levels of 50 Hz were 5-10 microT, occasionally much higher. Chromosome aberrations, sister chromatid exchanges, and aneuploidy were studied in peripheral blood lymphocytes. In addition, chromosome aberrations were investigated in lymphocyte cultures treated with hydroxyurea and caffeine, to inhibit deoxyribonucleic acid synthesis and repair. Among seven smoking laboratory employees the mean number of chromosome breaks/200 cells was 2.3, as compared with 0.7 for the job-matched referents. The comparable figures for inhibited cultures were 12.0 versus 6.0. No increase was detected in nonsmokers with either method. The other genetic parameters showed no differences between the exposed workers and the referents. The results support, to some extent, the hypothesis of an increased risk of genotoxic effects among high-voltage laboratory workers.

Characterization of anti-cerebroside sulfate antisera using a theoretical model to analyse liposome immune lysis data.

Antisera to the acidic glycolipid cerebroside sulfate (sulfogalactosyl ceramide) were raised in rabbits by several different methods. Reactivity with cerebroside sulfate was detected from complement-mediated lysis of liposomes composed of phosphatidylcholine/cholesterol/cerebroside sulfate and containing the spin label tempocholine chloride as a marker substance. Both cholesterol rich particles and lipid bilayer liposomes containing phosphatidylcholine and cholesterol were effective carriers for cerebroside sulfate, in combination with methylated bovine serum albumin for intravenous immunization, and with Freunds complete adjuvant for subcutaneous immunization. The antisera raised by the different methods were characterized with respect to their cross reactivity with other lipids and the relative concn of specific antibodies and their affinities for cerebroside sulfate using a theoretical model developed earlier [Vistnes A. I. (1984) J. Immun. Meth. 68, 251] for analysis of data from immune lysis of liposomes. Differences in these properties, both of which can affect antibody titer, could be detected for antisera raised by different methods and obtained at different times after immunization. Some of the antisera also reacted non-specifically to varying degrees with other anionic lipids indicating that the anti-cerebroside sulfate antibodies could bind non-specifically to anionic lipids by electrostatic interactions. This suggested that basic amino acid residues may be an important part of the antibody receptor binding site for the glycolipid head group. An important implication of this result is that antibodies raised against anionic glycolipids should be tested for non-specific binding to anionic phospholipids.

Factors affecting surface expression of glycolipids: influence of lipid environment and ceramide composition on antibody recognition of cerebroside sulfate in liposomes.

The reactivity of the acidic glycolipid cerebroside sulfate (CBS) with antibody was studied as a function of its lipid environment in vesicles and of its ceramide composition. The lipid environment was varied by using phosphatidylcholine of varying chain length with cholesterol in a phosphatidylcholine:cholesterol:cerebroside sulfate molar ratio to glycolipid of 1:0.75:0.1. The ceramide structure of CBS was varied by using synthetic forms containing palmitic acid, lignoceric acid, or the corresponding alpha-hydroxy fatty acids. Reactivity with antibody was determined by measuring complement-mediated lysis of the vesicles containing a spin-label marker, tempocholine chloride. The data were analyzed by a theoretical model which gives relative values for the dissociation constant and concentration of antibodies within the antiserum which are able to bind to the glycolipid. If the phosphatidylcholine chain length was increased, increasing the bilayer thickness, only a small population of high-affinity antibodies were able to bind to cerebroside sulfate, suggesting decreased surface exposure of the glycosyl head group. A larger population of lower affinity antibodies were able to bind to it in a shorter chain length phosphatidylcholine environment. However, if the chain length of the cerebroside sulfate was increased, it could be recognized by more antibodies of lower affinity than the short chain length form, suggesting that an increase in chain length of the glycolipid increased surface exposure. Hydroxylation of the fatty acid inhibited antibody binding; only a smaller population of higher affinity antibodies was able to bind to the hydroxy fatty acid forms.(ABSTRACT TRUNCATED AT 250 WORDS)

A new method of evaluating complement mediated lysis of liposomes.

Immune lysis of liposomes has been utilized in immunoassays for detection of specific antibodies. Membrane immunoassays which have sensitivities comparable with those of radioimmunoassays are easy and rapid to perform. Information obtained so far has been limited by the fact that the method is based on empirical relationships. The present paper describes a simple theoretical model for analysing membrane immunoassay data. According to the model, relative dissociation constants for the antibody-antigen reaction and relative concentrations of high affinity antibodies for different antisera may be determined. Furthermore, the analysis yields the percentage of antibody bound to antigen under certain conditions. The method is also useful in the search for optimum experimental conditions in membrane immunoassay measurements.

Spin membrane immunoassay for use in meningococcal serology.

A modified and improved spin membrane immunoassay has been developed for detecting complement-activating antibodies to Neisseria meningitidis capsular polysaccharide antigens. The polysaccharides were incorporated in the membranes of large unilamellar vesicles prepared by the reverse-phase evaporation method and filled with the water-soluble spin label tempocholine chloride. Upon addition of group-specific antisera and complement, the lipid membrane was damaged and the spin label leaked out. This process was monitored by electron spin resonance spectroscopy. A satisfactory assay was developed for polysaccharides of group A and C, whereas in the case of the B system the assay was more labile. The method is rapid and has a sensitivity comparable to that of radioimmunoassay. When studying paired sera from five recruits vaccinated with an A + C polysaccharide vaccine, significant rises in titers to both A and C polysaccharides were observed in all the postvaccination sera.

Magnetization hysteresis electron paramagnetic resonance. A new null phase insensitive saturation transfer EPR technique with high sensitivity to slow motion.

In electron paramagnetic resonance (EPR) nonlinear phenomena with respect to magnetic-field modulation are often studied by out-of-phase spectra recordings. The existence of a nonzero out-of-phase signal implies that the EPR signal is phase shifted relative to the modulation signal. This phase shift is called a magnetization hysteresis. The hysteresis angle varies during a sweep through the resonance conditions for a free radical. By recording this variation, a magnetization hysteresis (MH) spectrum results. In practice, a MH spectrum is computer calculated from two EPR spectra detected with a 90 degree difference in phase setting. There is no need for a careful null-phase calibration like that in traditional analysis of nonlinearities. The MH spectra calculated from second harmonic EPR spectra of spin labels were highly dependent on the rotational correlation time. The technique can therefore be used to study slow molecular motion. In the present work MH spectra and Hemminga and deJager's magnitude saturation transfer EPR spectra (Hemminga, M. A., and P. A. deJager, 1981, J. Magn. Reson., 43:324-327) have been analyzed to define parameters that can describe variations in the rotational correlation time. A novel modification of the sample holder and temperature regulation equipment is described.

Free radicals and aging. Electron spin resonance studies on neuronal lipopigments and cells grown in vitro.

Electron spin resonance (ESR) spectroscopy has been used in an attempt to observe free radicals which may be connected to the aging processes. Isolated lipofuscin particles from the human brain, which may act as traps for reactive ESR centers, have been studied. The lipopigments exhibit ESR signals which were attributed to metal ions. Both high-spin ferric iron and copper (II) complexes were observed. The copper resonance showed axial symmetry and the observed ESR parameters (A parallel = 185 gauss, g parallel = 2.25 and g perpendicular = 2.066) indicate that the copper ions are of the "non-blue" type (so-called "type 2"). The data suggest that the copper ions might be ligated to two nitrogen and two oxygen atoms. Ceroid particles from the brains of dogs with end-stage "canine ceroid lipofuscinosis" yield similar resonances involving metal complexes. The concentration of the copper ions in the lipopigments seems to increase slightly towards the end stage of life. Retinal pigment epithelial cells from the eyes of dogs with canine ceroid lipofuscinosis were grown in vitro and examined with ESR when the cells reached confluency and then after being maintained confluent for 2 weeks. The spectra indicate an accumulation of metal ions due to this "aging". Phase-contrast microscopy reveals an increase in perinuclear dense bodies during the time in confluency. A weak ESR signal, compatible with an "oxygen-centered" radical, was also found to increase slightly during the "aging" period.

A spin label method for measuring internal volumes in liposomes or cells, applied to Ca-dependent fusion of negatively charged vesicles.

A new spin label - broadening agent system for measuring trapped volumes of vesicles or cells is described. The method seems to be more advantageous than existing procedures when volumes of highly negatively charged vesicles are to be determined. The membrane permeable spin label is TEMPONE (2,2,6,6-tetramethyl piperidone-N-oxyl), and the nonpermeable broadening agent is chromium oxalate (K3Cr(C2O4)3). Absolute values for the trapped volumes down to 0.1% in 0.1 ml can be measured with an accuracy of about +/- (1-10%). The method is used to study the final volume of fused phosphatidylserine vesicles as a function of the temperature at which the Ca-induced fusion takes place.