Temporal Structures in Positron Spectra and Charge-Sign Effects in Galactic Cosmic Rays

We present the precision measurements of 11 years of daily cosmic positron fluxes in the rigidity range from 1.00 to 41.9 GV based on 3.4×10^{6} positrons collected with the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station. The positron fluxes show distinctly different time variations from the electron fluxes at short and long timescales. A hysteresis between the electron fluxes and the positron fluxes is observed with a significance greater than 5σ at rigidities below 8.5 GV. On the contrary, the positron fluxes and the proton fluxes show similar time variation. Remarkably, we found that positron fluxes are modulated more than proton fluxes with a significance greater than 5σ for rigidities below 7 GV. These continuous daily positron fluxes, together with AMS daily electron, proton, and helium fluxes over an 11-year solar cycle, provide unique input to the understanding of both the charge-sign and mass dependencies of cosmic rays in the heliosphere.

Properties of Cosmic-Ray Sulfur and Determination of the Composition of Primary Cosmic-Ray Carbon, Neon, Magnesium, and Sulfur: Ten-Year Results from the Alpha Magnetic Spectrometer

We report the properties of primary cosmic-ray sulfur (S) in the rigidity range 2.15 GV to 3.0 TV based on 0.38×10^{6} sulfur nuclei collected by the Alpha Magnetic Spectrometer experiment (AMS). We observed that above 90 GV the rigidity dependence of the S flux is identical to the rigidity dependence of Ne-Mg-Si fluxes, which is different from the rigidity dependence of the He-C-O-Fe fluxes. We found that, similar to N, Na, and Al cosmic rays, over the entire rigidity range, the traditional primary cosmic rays S, Ne, Mg, and C all have sizeable secondary components, and the S, Ne, and Mg fluxes are well described by the weighted sum of the primary silicon flux and the secondary fluorine flux, and the C flux is well described by the weighted sum of the primary oxygen flux and the secondary boron flux. The primary and secondary contributions of the traditional primary cosmic-ray fluxes of C, Ne, Mg, and S (even Z elements) are distinctly different from the primary and secondary contributions of the N, Na, and Al (odd Z elements) fluxes. The abundance ratio at the source for S/Si is 0.167±0.006, for Ne/Si is 0.833±0.025, for Mg/Si is 0.994±0.029, and for C/O is 0.836±0.025. These values are determined independent of cosmic-ray propagation.

Temporal Structures in Electron Spectra and Charge Sign Effects in Galactic Cosmic Rays

We present the precision measurements of 11 years of daily cosmic electron fluxes in the rigidity interval from 1.00 to 41.9 GV based on 2.0×10^{8} electrons collected with the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station. The electron fluxes exhibit variations on multiple timescales. Recurrent electron flux variations with periods of 27 days, 13.5 days, and 9 days are observed. We find that the electron fluxes show distinctly different time variations from the proton fluxes. Remarkably, a hysteresis between the electron flux and the proton flux is observed with a significance of greater than 6σ at rigidities below 8.5 GV. Furthermore, significant structures in the electron-proton hysteresis are observed corresponding to sharp structures in both fluxes. This continuous daily electron data provide unique input to the understanding of the charge sign dependence of cosmic rays over an 11-year solar cycle.

82 VIABILITY OF SHEEP-SKIN FIBROBLASTS AFTER SLOW FREEZING

Both tissue and cell cryopreservation can be applied for biodiversity conservation. The proper preservation of tissues and cells from a wide range of animals of different species is of paramount importance, because these cell samples could be used to reintroduce lost genes back into the breeding pool by somatic cell cloning. The aim of this work was to investigate the effect of different cooling rates on viability of frozen–thawed sheep fibroblasts for conservation of biodiversity so that it might be used in the future to provide nuclear donors (Table 1). Skin samples collected from 10 adult sheep were cut on small pieces (1 × 1 mm), placed into culture Petri dishes containing DMEM supplemented with 20% (v/v) fetal bovine serum (FBS), and covered with coverslips followed by incubation at 5% CO2, 95% relative humidity, and 37°C. During culture, fibroblasts left skin samples and proliferated. Culture medium was changed every 4 days. After 21 to 22 days of incubation, a fibroblast monolayer was observed, culture medium was removed, and cells were incubated for 7 to 10 min in presence of Dulbecco’s phosphate buffered saline + 0.25% trypsin. Dissociated fibroblasts were washed with DMEM by centrifugation at 300g for 10 min. For cryoconservation, fibroblast samples were then diluted at a concentration of 2 × 106 cells mL–1 in DMEM + 20% FBS and 10% dimethyl sulfoxide or 10% ethylene glycol and placed into 0.25-mL plastic straws or 2-mL cryovials. Straws were sealed with modeling clay and maintained at +5°C for 120 min before freezing. Cryopreservation of fibroblasts was carried out by 2 procedures: (1) straws were frozen in programmable freezer Kryo Planer 360-3,5 using the following freezing regimen: +5°C to –40°C at –1°C min–1, –40°C to –85°C at –4°C min–1, and then plunged into liquid nitrogen; (2) cryovials were placed in a Styrofoam box and loaded into a freezer at –70°C for 24 h, and then samples were plunged into liquid nitrogen for storage. Samples were thawed for 1 min in a 37°C water bath. Frozen–thawed samples were diluted with DMEM (1 : 5) and centrifuged at 300g for 7 to 10 min. Supernatants were removed, and cells were diluted with DMEM at a concentration of 2 × 106 cells mL–1. Viability of frozen–thawed fibroblast samples was detected using the Trypan Blue staining method. The values obtained (Table 1) are expressed as mean standard error of the mean (SEM). Statistical analysis was done using Student’s test. Results indicated that there was a significant difference in viability between fresh and cryopreserved fibroblasts. However, there were no differences between the cooling procedures. Importantly, our data suggest that the use of 1.5-M ethylene glycol reduced the toxic elements contained in the cryopreservation solution while maintaining a similar ability to produce viable fibroblasts after cryoconservation. Table 1.Effect of 2 cryoprotectant agent (CPA) on the viability of frozen–thawed ovine fibroblasts

Differential underacetylation of histones H2A, H3 and H4 on the inactive X chromosome in human female cells

It has previously been shown that the acetylated forms of histone H4 are depleted or absent in both constitutive, centric heterochromatin and in the facultative heterochromatin of the inactive X chromosome (Xi) in female cells. By immunostaining of metaphase chromosomes from human lymphocytes with antibodies to the acetylated isoforms of histones H2A and H3, we now show that these histones too are underacetylated in both Xi and centric heterochromatin. Xi shows two prominent regions of residual H3 acetylation, one encompassing the pseudoautosomal region at the end of the short arm and one at about Xq22. Both these regions have been shown previously to be sites of residual H4 acetylation. H2A acetylation on Xi is higher overall than that of H3 or H4 and is particularly high around the pseudoautosomal region, but not at Xq22. The results suggest that the acetylated isoforms of H3 and H4 have at least some effects on chromosomal structure and function that are not shared by acetylated H2A.

Characterization of bacterial growth on solid medium with image analysis

Alkaliphilic bacterial strains producing the enzyme cyclodextrin glucanotransferase were cultivated on solid agar medium containing an indicator system detecting the enzyme. The growth of the colony and the surrounding diffusion zone, due to the enzyme, were measured by the image analysis during the cultivation. It was possible to differentiate between relatively similar clones by observing quantitatively the changes at and around the colony. Optimal experimental conditions for such measurements are discussed. The image analysis technique provides a potential tool for characterizing microbes grown on solid media.