The emergence of femtosecond diffractive imaging with X-ray lasers has enabled pioneering structural studies of isolated particles, such as viruses, at nanometer length scales. However, the issue of ...missing low frequency data significantly limits the potential of X-ray lasers to reveal sub-nanometer details of micrometer-sized samples. We have developed a new technique of dark-field coherent diffractive imaging to simultaneously overcome the missing data issue and enable us to harness the unique contrast mechanisms available in dark-field microscopy. Images of airborne particulate matter (soot) up to two microns in length were obtained using single-shot diffraction patterns obtained at the Linac Coherent Light Source, four times the size of objects previously imaged in similar experiments. This technique opens the door to femtosecond diffractive imaging of a wide range of micrometer-sized materials that exhibit irreproducible complexity down to the nanoscale, including airborne particulate matter, small cells, bacteria and gold-labeled biological samples.
The T-cell repertoire found in the periphery is thought to be shaped by two developmental events in the thymus that involve the antigen receptors of T lymphocytes. First, interactions between T cells ...and major histocompatibility complex (MHC) molecules select a T-cell repertoire skewed towards recognition of antigens in the context of self-MHC molecules. In addition, T cells that react strongly to self-MHC molecules are eliminated by a process called self-tolerance. We have recently described transgenic mice expressing the alpha beta T-cell receptor from the cytotoxic T lymphocyte 2C (ref. 11). The clone 2C was derived from a BALB.B (H-2b) anti-BALB/c (H-2d) mixed lymphocyte culture and is specific for the Ld class I MHC antigen. In transgenic H-2b mice, a large fraction of T cells in the periphery expressed the 2C T-cell receptor. These T cells were predominantly CD4-CD8+ and were able to specifically lyse target cells bearing Ld. We now report that in the periphery of transgenic mice expressing Ld, functional T cells bearing the 2C T-cell receptor were deleted. This elimination of autoreactive T cells appears to take place at or before the CD4+CD8+ stage in thymocyte development. In addition, we report that in H-2s mice, a non-autoreactive target haplotype, large numbers of CD8+ T cells bearing the 2C T-cell receptor were not found, providing strong evidence for the positive selection of the 2C T-cell receptor specificity by H-2b molecules.
Mali VP, Robless PA, Aw M, Loh DL, Quak SH, Prabhakaran K. Unusual shunt for symptomatic portal vein thrombosis after liver transplantation – Clatworthy revisited.
: PV thrombosis is not an uncommon ...occurrence following pediatric LT. Symptomatic PHT following PV thrombosis is treated medically, surgical portosystemic shunting (mesorex, splenorenal, and mesocaval) being reserved for refractory cases. A 10‐yr‐old boy suffered recurrent malena and hemorrhagic shock because of chronic PV thrombosis following LT nine yr ago (1999). Extensive work‐up failed to localize the bleeding source. The liver function remained normal. Initial attempts at surgical shunts failed owing to thrombosis (mesocaval 2001, splenorenal, inferior mesenteric‐left renal vein, splenic‐left external iliac vein 2008). In this situation, we performed a Clatworthy shunt by anastomosing the divided lower end of the LCIV to the side of SMV. There was a single, large caliber anastomosis. Post‐operatively, the malena stopped completely, and clinically, there was no lower limb edema or encephalopathy. Doppler USG revealed persistence of hepatopetal flow within the portal collaterals. Follow‐up at two yr reveals stable hepatic function with a patent shunt. To the best of our knowledge, we are not aware of a Clatworthy shunt being performed in a transplant setting. We reviewed the literature pertaining to this shunt in non‐transplant patients with PHT.
ABSTRACT The Spartan Infrared Camera provides tip-tilt corrected imaging for the SOAR Telescope in the 900-2500 nm spectral range with four 2048 × 2048 HAWAII-2 detectors. The camera has two plate ...scales: high-resolution ( 40 mas pixel - 1 ) for future diffraction-limited sampling in the H and K bands and wide-field ( 66 mas pixel - 1 ) to cover a 5′ × 5′ field, over which tip-tilt correction is substantial. The design is described in detail. Except for CaF2 field-flattening lenses, the optics are aluminum mirrors to thermally match the aluminum cryogenic-optical box in which the optics mount. The design minimizes the tilt of the optics as the instrument rotates on the Nasmyth port of the telescope. Two components of the gravitational torque on an optic are eliminated by symmetry, and the third component is minimized by balancing the optic. The optics (including the off-axis aspherical mirrors) were aligned with precise metrology. For the detector assembly, Henein pivots are used to provide frictionless, thermally compliant, lubricant-free, and thermally conducting rotation of the detectors. The heat load is 14 W for an ambient temperature of 10°C. Cooling down takes 40 hr. An activated-charcoal getter controls permeation through the large Viton O-ring for at least nine months. We present maps of the image distortion, which amount to tens of pixels at the greatest. The wavelength of the narrowband filters shift with position in the sky. The measured Strehl ratio of the camera itself is 0.81-0.84 at λ1650 nm. The width of the best K-band image was 260 mas in unexceptional seeing measured after tuning the telescope and before moving the telescope. Since images are normally taken after pointing the telescope to a different field, this supports the idea that the image quality could be improved by better control of the focus and the shape of the primary mirror. The instrument has proved to be capable of producing images that can be stitched together to measure faint, extended features and to produce photometry that agree internally to better than 0.01 mag and are well calibrated to 2MASS stars in the range of 12 < K < 16.
We present a range of steady-state photoionization simulations, corresponding to different assumed shell geometries and compositions, of the unseen postulated rapidly expanding outer shell to the ...Crab Nebula. The properties of the shell are constrained by the mass that must lie within it, and by limits to the intensities of hydrogen recombination lines. In all cases the photoionization models predict very strong emissions from high ionization lines that will not be emitted by the Crab's filaments, alleviating problems with detecting these lines in the presence of light scattered from brighter parts of the Crab. The near-NIR NeVI lambda7.652 mu m line is a particularly good case; it should be dramatically brighter than the optical lines commonly used in searches. The C IV lambda1549 doublet is predicted to be the strongest absorption line from the shell, which is in agreement with Hubble Space Telescope observations. We show that the cooling timescale for the outer shell is much longer than the age of the Crab, due to the low density. This means that the temperature of the shell will actually "remember" its initial conditions. However, the recombination time is much shorter than the age of the Crab, so the predicted level of ionization should approximate the real ionization. In any case, it is clear that IR observations present the best opportunity to detect the outer shell and so guide future models that will constrain early events in the original explosion.
To investigate the role of bcl-2 in lymphohematopoiesis, a long-term bone marrow reconstitution system was established. Transplantation of 1,000 c-Kit+ Sca-1+ and lineage markers negative cells from ...bcl-2-l-mouse bone marrow resulted in long-term reconstitution of nonlymphoid cells. However, T cells were totally absent and B-lymphocyte development was severely impaired at a very early stage of differentiation in the chimeric mouse. On the other hand, transplantation of day 14 fetal liver cells from bcl-2-l-mice resulted in generation of both T and B cells in the recipient, albeit transiently. These data suggest that bcl-2 plays a critical role in the development of lymphoid progenitor cells from the hematopoietic stem cell (HSC), but is not essential for the development of nonlymphoid cells and the self-renewal of HSC. In addition, lymphopoiesis from fetal liver HSC appears to be less dependent on bcl-2 than adult bone marrow HSC.
This report describes three cases of significant lower gastro-intestinal haemorrhage caused by a bleeding Meckel's diverticulum. In the first two cases a pre-operative technetium-pertechnetate or ...Meckel's scan was negative or inconclusive, and in the third case no Meckel's scan was carried out. The diagnosis was established at laparoscopy in all three cases and in each case the diverticulum was excised extracorporeally.
Abstract In mammals, the circadian oscillators that drive daily behavioral and endocrine rhythms are located in the hypothalamic suprachiasmatic nucleus (SCN). While the SCN is anatomically ...well-situated to receive and transmit temporal cues to the rest of the brain and periphery, there are many holes in our understanding of how this temporal regulation occurs. Unanswered questions include how cell autonomous circadian oscillations within the SCN remain synchronized to each other as well as communicate temporal information to downstream targets. In recent years, it has become clear that neuropeptides are critically involved in circadian timekeeping. One such neuropeptide, vasoactive intestinal peptide (VIP), defines a cell population within the SCN and is likely used as a signaling molecule by these neurons. Converging lines of evidence suggest that the loss of VIP or its receptor has a major influence on the ability of the SCN neurons to generate circadian oscillations as well as synchronize these cellular oscillations. VIP, acting through the VPAC2 receptor, exerts these effects in the SCN by activating intracellular signaling pathways and, consequently, modulating synaptic transmission and intrinsic membrane currents. Anatomical evidence suggests that these VIP expressing neurons connect both directly and indirectly to endocrine and other output targets. Striking similarities exist between the role of VIP in mammals and the role of Pigment Dispersing Factor (PDF), a functionally related neuropeptide, in the Drosophila circadian system. Work in both mammals and insects suggests that further research into neuropeptide function is necessary to understand how circadian oscillators work as a coordinated system to impose a temporal structure on physiological processes within the organism.
The cell-positional incidence of both spontaneous and damage-induced apoptosis of epithelial cells was assessed in longitudinal sections of the crypts of small intestine and colon of BDF1 mice. This ...was compared, using immunohistochemistry, with the pattern of expression of bcl-2, a suppressor of apoptosis. In the small intestine, apoptosis was maximal around cell position 4 from the base of the crypt; this closely corresponds to the position considered to contain the stem cells. In the colon, however, apoptosis was not confined to the area considered to harbour the stem cells (position 1 and 2). Instead, apoptosis was attenuated and distributed along the length of the crypt. Some cells at the base of murine colonic crypts expressed bcl-2 protein, whereas bcl-2 was absent in the crypts of the small intestine. Most pertinently, bcl-2 was absent from small intestinal crypt cells at positions 4-5 (the stem cell region). The importance of the expression of bcl-2 to the attenuation of apoptosis in stem cells was confirmed by analysis of the levels of both spontaneous and induced apoptosis in homozygously bcl-2 null C57BL/6 mice: in colonic crypts the level of spontaneous apoptosis rose significantly, and selectively at the base of the crypt, in comparison with crypts from wild-type animals. In contrast, there was no rise in spontaneous apoptosis in the small intestinal crypts from the bcl-2 null animals. Analysis of sections of human colon and small intestine also showed that expression of bcl-2 was confined to the base of the colonic crypt. The attenuation of apoptosis by bcl-2 in the region of the stem cells of the colonic crypts may dispose these to neoplastic transformation. Indeed, analysis of human carcinomas revealed expression of bcl-2, which in some samples was reciprocal with the expression of p53.
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