Size and albedo of Kuiper belt object 55636 from a stellar occultation.

The Kuiper belt is a collection of small bodies (Kuiper belt objects, KBOs) that lie beyond the orbit of Neptune and which are believed to have formed contemporaneously with the planets. Their small size and great distance make them difficult to study. KBO 55636 (2002 TX(300)) is a member of the water-ice-rich Haumea KBO collisional family. The Haumea family are among the most highly reflective objects in the Solar System. Dynamical calculations indicate that the collision that created KBO 55636 occurred at least 1 Gyr ago. Here we report observations of a multi-chord stellar occultation by KBO 55636, which occurred on 9 October 2009 ut. We find that it has a mean radius of 143 +/- 5 km (assuming a circular solution). Allowing for possible elliptical shapes, we find a geometric albedo of in the V photometric band, which establishes that KBO 55636 is smaller than previously thought and that, like its parent body, it is highly reflective. The dynamical age implies either that KBO 55636 has an active resurfacing mechanism, or that fresh water-ice in the outer Solar System can persist for gigayear timescales.

Charon's radius and atmospheric constraints from observations of a stellar occultation.

The physical characteristics of Pluto and its moon, Charon, provide insight into the evolution of the outer Solar System. Although previous measurements have constrained the masses of these bodies, their radii and densities have remained uncertain. The observation of a stellar occultation by Charon in 1980 established a lower limit on its radius of 600 km (ref. 3) (later refined to 601.5 km; ref. 4) and suggested a possible atmosphere. Subsequent, mutual event modelling yielded a range of 600-650 km (ref. 5), corresponding to a density of 1.56 +/- 0.22 g cm(-3) (refs 2, 5). Here we report multiple-station observations of a stellar occultation by Charon. From these data, we find a mean radius of 606 +/- 8 km, a bulk density of 1.72 +/- 0.15 g cm(-3), and rock-mass fraction 0.63 +/- 0.05. We do not detect a significant atmosphere and place 3sigma upper limits on atmospheric number densities for candidate gases. These results seem to be consistent with collisional formation for the Pluto-Charon system in which the precursor objects may have been differentiated, and they leave open the possibility of atmospheric retention by the largest objects in the outer Solar System.

The recent expansion of Pluto's atmosphere.

Stellar occultations--the passing of a relatively nearby body in front of a background star--can be used to probe the atmosphere of the closer body with a spatial resolution of a few kilometres (ref. 1). Such observations can yield the scale height, temperature profile, and other information about the structure of the occulting atmosphere. Occultation data acquired for Pluto's atmosphere in 1988 revealed a nearly isothermal atmosphere above a radius of approximately 1,215 km. Below this level, the data could be interpreted as indicating either an extinction layer or the onset of a large thermal gradient, calling into question the fundamental structure of this atmosphere. Another question is to what extent Pluto's atmosphere might be collapsing as it recedes from the Sun (passing perihelion in 1989 in its 248-year orbital period), owing to the extreme sensitivity of the equilibrium surface pressure to the surface temperature. Here we report observations at a variety of visible and infrared wavelengths of an occultation of a star by Pluto in August 2002. These data reveal evidence for extinction in Pluto's atmosphere and show that it has indeed changed, having expanded rather than collapsed, since 1988.

Ovarian and breast cytotoxic T lymphocytes can recognize peptides from the amino enhancer of split protein of the Notch complex.

In this study we investigated recognition by ovarian tumor associated lymphocyte (OVTAL), and breast tumor associated lymphocytes (BRTAL), of peptides corresponding to the sequence 125-135 of the Aminoenhancer of split (AES) protein. Three of these peptides designated as G75:AES1/2 (128-135), G60: AES1/2 (127-137) and G61: AES1/2 (125-133) correspond to the wildtype AES sequence, while the fourth G76:GPLTPLPV, AES1/2 (128-135) corresponds to a variant sequence of the peptide G75 with the N-terminal Leu substituted to glycine. These sequences were chosen for study because mass-spectrometric analysis (MS) of a CTL active HPLC peptide fraction eluted from immunoaffinity precipitated HLA-A2 molecule, revealed: (a) the presence of an ion with a mass-to-charge ratio (m/z) of 793 which was more abundant than other ions of similar masses; (b) the tentatively reconstituted sequence of the ion 793 matched the sequence of peptide G76. We found that AES peptides G75 (128-135) and G76 (128-135) (L128G) reconstituted CTL recognition at concentrations ranging between 200-500 nM. These concentrations are lower than concentrations reported to activate effector function of CTL recognizing other epithelial tumor Ag. Furthermore, analysis with cloned CD8+ T cells indicated that G75 and G76 were not cross-reactive specificities, suggesting a key role for the N-terminal residues of the variant peptide in dictating specificities. Since the AES proteins are part of a set of transcriptional repressors encoded by the Enhancer of split [E(spl)] genes, and since these repressors are activated to suppress cell differentiation in response to Notch receptors signalling, the AES peptides may represent a novel class of self-antigens that deserve further consideration as tumor Ag in epithelial cancers.

Dark CO2-fixation and diurnal malic acid fluctuations in the submerged-aquatic Isoetes storkii.

In the leaves (but not corms) of the submerged aquatic Isoetes storkii malic acid concentration fluctuated from 22 µeg g FW-1 in the evening to 171 µeg g FW-1 in the morning. Associated with this was a change in titratable acidity of 152 µeg g FW-1 between morning and evening. 14C carbon was fixed in both the light and the dark, though the amount of carbon fixed in the light was more than that fixed in the dark. Autoradiographs show 88% of 14CO2 fixed in the dark is recovered after 1 h, in malic acid and the remainder in one other unidentified product, whereas these two products contain less than 15% of the 14C fixed after 1 h exposure to 14CO2 in the light. It is suggested that CAM metabolism in this aquatic species may be related to the low availability of CO2 for photosynthesis during the day in its aquatic environment and that this metabolic pathway may prove common in the genus Isoetes.

A flexible low cost signal averager.

A 2 channel signal averager based on the KIM-1 microcomputer module is described which can be easily assembled for under $500. Number of samples per pass can be set to 128 or 256 and sample time is variable from 1 msec to 256 msec. Averaged data can be displayed on an oscilloscope, output slowly for use of a chart recorder, or stored on a low cost audio cassette recorder for later analysis. Simply adding additional memory (for less than $100) allows it to be expanded to 8 channels.