Lossless state detection of single neutral atoms

We introduce lossless state detection of trapped neutral atoms based on cavity-enhanced fluorescence. In an experiment with a single 87Rb atom, a hyperfine-state-detection fidelity of 99.4% is achieved in 85  μs. The quantum bit is interrogated many hundreds of times without loss of the atom while a result is obtained in every readout attempt. The fidelity proves robust against atomic frequency shifts induced by the trapping potential. Our scheme does not require strong coupling between the atom and cavity and can be generalized to other systems with an optically accessible quantum bit.

Emission properties and photon statistics of a single quantum dot laser

A theoretical description for a single quantum-dot emitter in a microcavity is developed.We analyze for increasing steady-state pump rate the transition from the strong-coupling regime with photon antibunching to the weak-coupling regime with coherent emission. It is demonstrated how Coulomb interaction of excited carriers and excitation-induced dephasing can strongly modify the emission properties. Our theoretical investigations are based on a direct solution of the Liouville-von Neumann equation for the coupled carrier-photon system. We include multiple carrier excitations in the quantum dot, their Coulomb interaction, as well as excitation-induced dephasing and screening. Similarities and differences to atomic systems are discussed and results in the regime of recent experiments are interpreted.

No evidence for DNA and early cytogenetic damage in bystander cells after heavy-ion microirradiation at two facilities

The occurrence of bystander effects has challenged the evaluation of risk for heavy ions, mainly in the context of space exploration and the increasing application of carbon ions in radiotherapy. In the present study, we addressed whether heavy-ion-induced DNA and cytogenetic damage is detectable in bystander cells. The formation of gamma-H2AX foci, sister chromatid exchanges and micronuclei were used as markers of damage to DNA. Normal human fibroblasts were exposed to low fluences of carbon and uranium ions, and alternatively single cells were targeted with heavy ions using the GSI microbeam. We did not observe a significant increase in the bystander formation of gamma-H2AX foci, sister chromatid exchanges or micronuclei. In addition, we performed for the first time parallel experiments at two microbeam facilities (GSI, JAEA) using the same cell line, culture conditions and irradiation protocols. No significant enhancement of the micronucleus frequencies in bystander cells was detected after targeted carbon-ion irradiation, confirming the results. Details regarding the history, culture conditions or support of the cells might be affecting the detection of bystander effects. On the other hand, the potential X-ray- and heavy-ion-induced bystander effects investigated herein clearly do not exceed the experimental error and thus are either lacking or are less pronounced than the effects reported in the literature for similar end points after alpha-particle and X-ray exposure.

Correlation between mitotic delay and aberration burden, and their role for the analysis of chromosomal damage

The aim was to investigate further the relationship between radiation-induced mitotic delay and the expression of chromosome damage in V79 cells. Recently published data on the time-course of chromosome aberrations in V79 first-cycle metaphases after exposure to 10.4 MeV u(-1) Ar ions (LET = 1226 keV microm(-1)) were supplemented and reanalysed. A statistical analysis of the distribution of aberrations among cells was performed. Furthermore, cells were grouped into subpopulations carrying 0, 1 -2, 3-4, 5- 6 and 7 or more aberrations. Then, based on the mitotic index, the flux of each subgroup through the first mitosis was determined and the average entrance time to mitosis was estimated. For comparison, the flux of aberrant V79 cells generated by X-irradiation was analysed. Analysis of the Ar ion data revealed that the flux of each subpopulation through the first mitosis is strongly affected by its aberration burden, i.e. a positive correlation between the mitotic delay and the number of aberrations carried by a cell was observed. The distribution of aberrations among cells could be well described by Neyman-type A statistics; the corresponding fit parameters also reflect the damage-dependent mitotic delay. Interestingly, comparison of the flux of Ar ion and X-ray-irradiated V79 cells through mitosis revealed (1) that a direct correlation exists between the number of aberrations carried by a cell and its average entrance time to mitosis, and (2) that this effect is independent of the linear energy transfer. The role of these observations for radiation cytogenetics is discussed.

Cell cycle arrest and aberration yield in normal human fibroblasts. II: Effects of 11 MeV u−1C ions and 9.9 MeV u−1Ni ions

PURPOSE

To investigate further the relationship between high linear energy transfer (LET) induced cell cycle arrests and the yield of chromosome aberrations observable in normal human fibroblasts at the first post-irradiation mitosis.

MATERIALS AND METHODS

Normal human fibroblasts (AG01,522C) were exposed in G0/G1 to either 11 MeV u(-1) C ions (LET = 153.5 keV microm(-1)) or 9.9 MeV u(-1) Ni ions (LET = 2,455 keV microm(-1)), subcultured in medium containing 5-Bromo-2'-deoxyuridine (BrdU) and at multiple time-points post-irradiation the yield of chromosomal damage, the mitotic index and the cumulative BrdU-labelling index were determined. Furthermore, a mathematical approach was used to analyse the entire cell population.

RESULTS

Following high LET exposure normal fibroblasts suffer a transient delay into S-phase and into mitosis as well as a prolonged, probably permanent cell cycle arrest in the initial G0/G1-phase. Cells that reach the first mitosis at early times carried less aberrations than those collected at later times indicating a relationship between cell cycle delay and the number of aberrations. However, with respect to the whole cell population, only a few aberrant fibroblasts are able to progress to the first mitosis. For all endpoints studied the relative biological effectiveness (RBE) of C ions is in the range of 2 - 4, while for Ni ions RBE < 1 is estimated. In contrast, when compared on a per particle basis Ni ions with the higher ionization density were found to be more effective.

CONCLUSIONS

Detailed analysis of the data demonstrates that the number of fibroblasts at risk for neoplastic transformation is significantly reduced by a chronic cell cycle arrest in the initial G0/G1-phase and, for the first time, the LET-dependence of this effect has been shown.

Cell cycle arrest and aberration yield in normal human fibroblasts. I. Effects of X‐rays and 195 MeV u−1C ions

PURPOSE

To examine the relationship between cell proliferation and the expression of chromosomal damage in normal human skin fibroblasts after X-ray and particle irradiation.

MATERIALS AND METHODS

Confluent G0/G1 AG1522B cells were exposed to X-rays or 195MeV u(-1) C ions with a linear energy transfer of 16.6 keV microm(-1) in the dose range 1-4 Gy. Directly after irradiation, cells were reseeded at a low density in medium containing 5-bromo-2'-deoxyuridine. At multiple time points post-irradiation, the cumulative BrdU-labelling index, mitotic index and aberration frequency were measured. Based on these data, the total amount of damage induced within the entire cell population was estimated by means of mathematical analysis.

RESULTS

Both types of radiation exposure exert a pronounced effect on the cell cycle progression of fibroblasts. They result in delayed entry of cells into S-phase and into the first mitosis, and cause a dramatic reduction in mitotic activity. Measurement of chromosomal damage in first-cycle cells at multiple time points post-irradiation shows that the frequencies of aberrant cells and aberrations increase with time up to twofold for the lower doses. However, for the higher doses, this effect is less pronounced or even disappears. When the data for the whole cell population are analysed, it becomes evident that only a few damaged fibroblasts can progress to the first mitosis, a response attributable at least in part to a long-term arrest of injured cells in the initial G0/G1-phase. As observed in other investigations, the effectiveness of 195 MeV u(-1) C ions was similar or slightly higher than X-rays for all endpoints studied leading to a relative biological effectiveness in the range 1.0-1.4.

CONCLUSIONS

Cell cycle arrests affect the aberration yield observable in normal human fibroblasts at mitosis. The data obtained for the cell population as a whole reveal that injured cells are rapidly removed from the mitotically active population through a chronic cell cycle arrest, which is consistent with other studies that indicate that this response is a specific strategy of fibroblasts to minimize the fixation and propagation of genetic alterations.

Critical Behavior of a Trapped Interacting Bose Gas

The phase transition of Bose-Einstein condensation was studied in the critical regime, where fluctuations extend far beyond the length scale of thermal de Broglie waves. We used matter-wave interference to measure the correlation length of these critical fluctuations as a function of temperature. Observations of the diverging behavior of the correlation length above the critical temperature enabled us to determine the critical exponent of the correlation length for a trapped, weakly interacting Bose gas to be nu = 0.67 +/- 0.13. This measurement has direct implications for the understanding of second-order phase transitions.

Cytogenetic effects of low-dose radiation with different LET in human peripheral blood lymphocytes

Chromosome damage and the spectrum of aberrations induced by low doses of gamma-irradiation, X-rays and accelerated carbon ions (195 MeV/u, LET 16.6 keV/microm) in peripheral blood lymphocytes of four donors were studied. G0-lymphocytes were exposed to 1-100 cGy, stimulated by PHA, and analyzed for chromosome aberrations at 48 h post-irradiation by the metaphase method. A complex nonlinear dose-effect dependence was observed over the range of 1 to 50 cGy. At 1-7 cGy, the cells showed the highest radiosensitivity per unit dose (hypersensitivity, HRS), which was mainly due to chromatid-type aberration. According to the classical theory of aberration formation, chromatid-type aberrations should not be induced by irradiation of unstimulated lymphocytes. With increasing dose, the frequency of aberrations decreased significantly, and in some cases it even reached the control level. At above 50 cGy the dose-effect curves became linear. In this dose range, the frequency of chromatid aberrations remained at a low constant level, while the chromosome-type aberrations increased linearly with dose. The high yield of chromatid-type aberrations observed in our experiments at low doses confirms the idea that the molecular mechanisms which underlie the HRS phenotype may differ from the classical mechanisms of radiation-induced aberration formation. The data presented, as well as recent literature data on bystander effects and genetic instability expressed as chromatid-type aberrations on a chromosomal level, are discussed with respect to possible common mechanisms underlying all low-dose phenomena.

Prediction of dose response for radiation induced exchange aberrations taking cell cycle delays into account

Chromosomal aberrations (CAs) are regarded as one of the most sensitive biological indicators of genetic alterations. The aberration frequency is routinely determined in the first metaphase. Yet, the data interpretation can be complicated due to radiation induced mitotic delays. To investigate the effect of delays on CA frequency in the first mitosis, human lymphocytes were irradiated with X rays and Giemsa detectable CAs were measured at different sampling times. Besides, a computer simulation was performed reproducing the main effects under investigation, that is, CA induction and cell progression through the mitotic cycle. The CA formation model takes into account the structural organisation of interphase chromosomes in a lymphocyte nucleus, DNA double-strand break (DSB) induction and their rejoining/misrejoining. Lymphocyte transition through the cell cycle was simulated by a Monte Carlo technique. The delay was proposed to result from DNA DSBs. The predicted ratios of first/second/third cycle metaphases agree with the experimental data for control and irradiated samples. Both experimental and calculated CA frequencies in the first mitosis were nearly time-independent. This was proposed to result from de-synchronisation of the lymphocyte population.

Infektionsepidemiologische Daten von Blutspendern 2003–2004

The Robert Koch Institute collects and evaluates data on the prevalence and incidence of HIV, hepatitis C (HCV), hepatitis B (HBV) and syphilis infections among blood and plasma donors in Germany in accordance with Article 22 of the Transfusion Act. This surveillance permits an assessment of the occurrence of infections in the blood donor population and consequently the safety of the collected donations. This report includes data from all blood donation services in Germany for 2003 and 2004. Altogether 7.09 million and 6.37 million donations or blood samples from prospective donors were screened in 2003 and 2004, respectively. In 2003 the prevalence rates of the relevant infections (per 100,000 donations) were 8.2 for HIV, 99.3 for HCV, 158.9 for HBV and 34.4 for syphilis. In 2003 the rates of seroconversion (per 100,000 donations) were 0.8 for HIV, 1.2 for HCV, 1.0 for HBV and 1.5 for syphilis in 2003. In 2004 the prevalence rates (per 100,000 donations) were 4.8 for HIV, 85.3 for HCV, 156.3 for HBV and 36.8 for syphilis. In 2004 the rates of seroconversion (per 100,000 donations) were 0.9 for HIV, 1.3 for HCV, 0.6 for HBV and 2.0 for syphilis. The analysis showed a very low incidence of infections with a decreasing trend for HCV infections and an increase in HIV and syphilis infections. The latter needs to be monitored carefully and possible causes evaluated. The quality of the reported data has improved compared to previous years. Still, some problems remain with the differentiation of the data according to sex, age and interdonation interval as well as reporting by individual blood donation centres as required by the Transfusion Act.

Human immunodeficiency virus, hepatitis C and hepatitis B infections among blood donors in Germany 2000-2002: risk of virus transmission and the impact of nucleic acid amplification testing

Blood and plasma donations in Germany are collected by several institutions, namely the German Red Cross, community and hospital-based blood services, private blood centres, commercial plasma donation sites and transfusion services of the army. All blood donation centres are required to report quarterly data on infection markers to the Robert Koch Institute, thus providing current and accurate epidemiological data. The prevalence and incidence of relevant viral infections are low in the blood donor population in Germany, with a decreasing trend for hepatitis C infections in new and repeat donors since 1997. The implementation of mandatory nucleic acid amplification technique (NAT) testing for hepatitis C virus (HCV) in 1999 has markedly improved transfusion safety. HIV-NAT became mandatory in 2004 but was done voluntarily by the majority of the blood donation services before then. The potential benefit of hepatitis B virus (HBV) minipool NAT is not as clear because chronic HBV carriers with very low virus levels might donate unidentified. The residual risk of an infectious window period donation inadvertently entering the blood supply can be estimated using a mathematic model which multiplies the incidence rate by the number of days during which an infection may be present but not detectable, i.e. the length of the window period. The risk of an undetected infection without NAT testing was estimated to be 1 in 2,770,000 for HIV, 1 in 670,000 for HCV and 1 in 230,000 for HBV in 2001/2002. This contrasts with 1 in 5,540,000 for HIV, 1 in 4,400,000 for HCV and 1 in 620,000 for HBV with minipool NAT testing. This demonstrates that NAT testing can further reduce the already very small risk of infectious donations entering the blood supply.

Human immunodeficiency virus, hepatitis C and hepatitis B infections among blood donors in Germany 2000-2002: risk of virus transmission and the impact of nucleic acid amplification testing

Blood and plasma donations in Germany are collected by several institutions, namely the German Red Cross, community and hospital-based blood services, private blood centres, commercial plasma donation sites and transfusion services of the army. All blood donation centres are required to report quarterly data on infection markers to the Robert Koch Institute, thus providing current and accurate epidemiological data. The prevalence and incidence of relevant viral infections are low in the blood donor population in Germany, with a decreasing trend for hepatitis C infections in new and repeat donors since 1997. The implementation of mandatory nucleic acid amplification technique (NAT) testing for hepatitis C virus (HCV) in 1999 has markedly improved transfusion safety. HIV-NAT became mandatory in 2004 but was done voluntarily by the majority of the blood donation services before then. The potential benefit of hepatitis B virus (HBV) minipool NAT is not as clear because chronic HBV carriers with very low virus levels might donate unidentified. The residual risk of an infectious window period donation inadvertently entering the blood supply can be estimated using a mathematic model which multiplies the incidence rate by the number of days during which an infection may be present but not detectable, i.e. the length of the window period. The risk of an undetected infection without NAT testing was estimated to be 1 in 2 770 000 for HIV, 1 in 670 000 for HCV and 1 in 230 000 for HBV in 2001/2002. This contrasts with 1 in 5 540 000 for HIV, 1 in 4 400 000 for HCV and 1 in 620 000 for HBV with minipool NAT testing. This demonstrates that NAT testing can further reduce the already very small risk of infectious donations entering the blood supply.

Chromosome aberration yields and apoptosis in human lymphocytes irradiated with Fe-ions of differing LET

In the present paper the relationship between cell cycle delays induced by Fe-ions of differing LET and the aberration yield observable in human lymphocytes at mitosis was examined. Cells of the same donor were irradiated with 990 MeV/n Fe-ions (LET=155 keV/micrometers), 200 MeV/n Fe-ions (LET=440 keV/micrometers) and X-rays and aberrations were measured in first cycle mitoses harvested at different times after 48-84 h in culture and in prematurely condensed G2-cells (PCCs) collected at 48 h using calyculin A. Analysis of the time-course of chromosomal damage in first cycle metaphases revealed that the aberration frequency was similar after X-ray irradiation, but increased two and seven fold after exposure to 990 and 200 MeV/n Fe-ions, respectively. Consequently, RBEs derived from late sampling times were significantly higher than those obtained at early times. The PCC-data suggest that the delayed entry of heavily damaged cells into mitosis results especially from a prolonged arrest in G2. Preliminary data obtained for 4.1 MeV/n Cr-ions (LET=3160 keV/micrometers) revealed, that these delays are even more pronounced for low energy Fe-like particles. Additionally, for the different radiation qualities, BrdU-labeling indices and apoptotic indices were determined at several time-points. Only the exposure to low energy Fe-like particles affected the entry of lymphocytes into S-phase and generated a significant apoptotic response indicating that under this particular exposure condition a large proportion of heavily damaged cells is rapidly eliminated from the cell population. The significance of this observation for the estimation of the health risk associated with space radiation remains to be elucidated.

Bericht des Robert Koch-Instituts zu den Meldungen nach � 22 Transfusionsgesetz f�r die Jahre 2001 und 2002

The Robert Koch Institute collects and evaluates data on the prevalence and incidence of HIV, hepatitis C (HCV), hepatitis B (HBV) and syphilis infections among blood and plasma donors in Germany according to Article 22 of the Transfusion Act. The surveillance permits an assessment of the occurrence of infections in the blood donor population and consequently the safety of the collected donations. This report includes data from all blood donation services in Germany for 2001 and 2002. Altogether 5.71 million and 6.63 million donations or blood samples from prospective donors were screened in 2001 and 2002, respectively. The analysis showed a very low incidence of infections with a decreasing trend for HCV infections since 1997 but a slight increase in HIV infections in 2001-2002 compared to 1999-2000. The prevalence of the relevant infections/100,000 donations was 4.7 for HIV, 94.7 for HCV, 159.0 for HBV and 33.4 for syphilis in 2001. The rate of seroconversions/100,000 donations was 0.5 for HIV, 1.6 for HCV, 1.4 for HBV and 1.6 for syphilis in 2001. In 2002 the prevalence/100,000 donations was 7.5 for HIV, 97.4 for HCV, 164.1 for HBV and 31.9 for syphilis. The rate of sero-conversions/100,000 donations in that year was 0.7 for HIV, 1.5 for HCV, 1.2 for HBV and 1.9 for syphilis. The quality of the reported data has improved significantly compared to previous years. Still, some problems remained with the differentiation of the data according to sex, age and interval between donations and the reporting by individual blood donation centres as required by the Transfusion Act.

Cytogenetic effects of densely ionising radiation in human lymphocytes: impact of cell cycle delays

The classical cytogenetic assay to estimate the dose to which an individual has been exposed relies on the measurement of chromosome aberrations in lymphocytes at the first post-irradiation mitosis 48 h after in vitro stimulation. However, evidence is accumulating that this protocol results in an underestimation of the cytogenetic effects of high LET radiation due to a selective delay of damaged cells. To address this issue, human lymphocytes were irradiated with C-ions (25-mm extended Bragg peak, LET: 60-85 keV/ micro m) and aberrations were measured in cells reaching the first mitosis after 48, 60, 72 and 84 h and in G2-phase cells collected after 48 h by calyculin A induced premature chromosome condensation (PCC). The results were compared with recently published data on the effects of X-rays and 200 MeV/u Fe-ions (LET: 440 keV/ micro m) on lymphocytes of the same donor (Ritter et al., 2002a). The experiments show clearly that the aberration yield rises in first-generation metaphase (M1) with culture time and that this effect increases with LET. Obviously, severely damaged cells suffer a prolonged arrest in G2. The mitotic delay has a profound effect on the RBE: RBE values estimated from the PCC data were about two times higher than those obtained by conventional metaphase analysis at 48 h. Altogether, these observations argue against the use of single sampling times to quantify high LET induced chromosomal damage in metaphase cells.