Improved Spin Dependent Limits from the PICASSO Dark Matter Search Experiment

The PICASSO experiment reports an improved limit for the existence of cold dark matter WIMPs interacting via spin-dependent interactions with nuclei. The experiment is installed in the Sudbury Neutrino Observatory at a depth of 2070 m. With superheated C4F10 droplets as the active material, and an exposure of 1.98±0.19 kgd, no evidence for a WIMP signal was found. For a WIMP mass of 29 GeV/c2, limits on the spin-dependent cross section on protons of σp = 1.31 pb and on neutrons of σn = 21.5 pb have been obtained at 90% C.L. In both cases, some new parameter space in the region of WIMP masses below 20 GeV/c2 has now been ruled out. The results of these measurements are also presented in terms of limits on the effective WIMP-proton and neutron coupling strengths ap and an

Neutron-gamma discrimination by pulse analysis with superheated drop detector

Superheated drop detector (SDD) consisting of drops of superheated liquid of halocarbon is irradiated to neutrons and gamma-rays from 252Cf fission neutron source and 137Cs gamma source separately. The analysis of pulse height of the signals in the neutron and gamma-ray sensitive temperature provides strong information on the identification of neutron and gamma-ray induced events.Comment: 19 pages with 8 figures, Accepted in Nucl. Instrum. Meth.

Choroid plexus in the central canal of the spinal cord causing recurrent syringomyelia

Background Syringomyelia is a fluid filled cavitation within the substance of the spinal cord. This condition usually follows a primary pathology that disrupts the normal CSF circulation or disturbs the microcirculation and cytoarchitecture of the spinal cord parenchyma. However, an aetiology of recurrent syringomyelia resulted from an ectopic choroid plexus (CP) has not been discussed. Ectopic CP rests may be found within the central nervous system. Although there has been a single report, describing ectopic intramedullary spinal cord CP, to our knowledge, extra-cranial non-malignant CP in the central canal of the spinal cord has not been reported. Case Description We report CP in the central canal of the spinal cord in a 23-year-old male patient who had developmental delay and diabetes mellitus type I who presented with dissociated sensory changes and muscle wastage predominantly on the right upper and lower limbs. MRI demonstrated a multi-loculated spinal cord syringomyelia stretching from cervical (C3) to the conus medullaris causing recurrent neurological deficits. Central canal spinal cord lesion's biopsy revealed CP. Decompression and syringo-subarachnoid shunt insertion stabilised the patient’s neurology. Conclusion Our illustrative case reveals the presence of CP in the central canal of the spinal cord that may suggest a role in the aetiology of recurrent syringomyelia. While management poses a challenge to neurosurgeons, prompt decompression and shunting of the syringomyelia remains a favourable approach with acceptable outcomes. Further investigation into the pathophysiology of central canal CP ectopic causing recurrent syringomyelia and its correlation with spinal cord development may help future treatments

Reconstructing WIMP properties with neutrino detectors

If the dark matter of the Universe is constituted by weakly interacting massive particles (WIMP), they would accumulate in the core of astrophysical objects as the Sun and annihilate into particles of the Standard Model. High-energy neutrinos would be produced in the annihilations, both directly and via the subsequent decay of leptons, quarks and bosons. While Cherenkov neutrino detectors/telescopes can only count the number of neutrinos above some threshold energy, we study how, by exploiting their energy resolution, large magnetized iron calorimeter and, possibly, liquid argon and totally active scintillator detectors, planned for future long baseline neutrino experiments, have the capability of reconstructing the neutrino spectrum and might provide information on the dark matter properties. In particular, for a given value of the WIMP mass, we show that a future iron calorimeter could break the degeneracy between the WIMP-proton cross section and the annihilation branching ratios, present for Cherenkov detectors, and constrain their values with good accuracy.Comment: 4 pp, 2 figs; revised version accepted for publication with further discussions and reference

Dark matter search experiment with CaF2(Eu) scintillator at Kamioka Observatory

We report recent results of a WIMP dark matter search experiment using 310g of CaF2(Eu) scintillator at Kamioka Observatory. We chose a highly radio-pure crystal, PMTs and radiation shields, so that the background rate decreased considerably. We derived limits on the spin dependent WIMP-proton and WIMP-neutron coupling coefficients, a_p and a_n. The limits excluded a part of the parameter space allowed by the annual modulation observation of the DAMA NaI experiment.Comment: 11 pages, 4 figure

Cholinergic Enhancement of Cell Proliferation in the Postnatal Neurogenic Niche of the Mammalian Spinal Cord

The region surrounding the central canal (CC) of the spinal cord is a highly plastic area, defined as a postnatal neurogenic niche. Within this region are ependymal cells which can proliferate and differentiate to form new astrocytes and oligodendrocytes following injury and cerebrospinal fluid contacting cells (CSFcCs). The specific environmental conditions, including the modulation by neurotransmitters that influence these cells and their ability to proliferate, are unknown. Here we show that acetylcholine promotes the proliferation of ependymal cells in mice under both in vitro and in vivo conditions. Using whole cell patch clamp in acute spinal cord slices, acetylcholine directly depolarised ependymal cells and CSFcCs. Antagonism by specific nicotinic acetylcholine receptor (nAChR) antagonists or potentiation by the α7*nAChR modulator PNU 120596 revealed that both α7*nAChRs and non-α7*nAChRs mediated the cholinergic responses. Using the nucleoside analogue EdU (5-ethynyl-2'-deoxyuridine) as a marker of cell proliferation, application of α7*nAChR modulators in spinal cord cultures or in vivo induced proliferation in the CC region, producing Sox-2 expressing ependymal cells. Proliferation also increased in the white and grey matter. PNU 120596 administration also increased the proportion of cells co-expressing oligodendrocyte markers. Thus, variation in the availability of acetylcholine can modulate the rate of proliferation of cells in the ependymal cell layer and white 1 and grey matter through α7*nAChRs. This study highlights the need for further investigation into how neurotransmitters regulate the response of the spinal cord to injury or during aging

The adult spinal cord harbors a population of GFAP-positive progenitors with limited self-renewal potential

Adult neural stem cells (aNSCs) of the forebrain are GFAP-expressing cells that are intercalated within ependymal cells of the subventricular zone (SVZ). Cells showing NSCs characteristics in vitro can also be isolated from the periaqueductal region in the adult spinal cord (SC), but contradicting results exist concerning their glial versus ependymal identity. We used an induci- ble transgenic mouse line (hGFAP-CreERT2) to conditionally label GFAP-expressing cells in the adult SVZ and SC periaque- duct, and directly and systematically compared their self-renewal and multipotential properties in vitro. We demonstrate that a population of GFAP1 cells that share the morphology and the antigenic properties of SVZ-NSCs mostly reside in the dorsal aspect of the central canal (CC) throughout the spinal cord. These cells are non-proliferative in the intact spinal cord, but incorporate the S-phase marker EdU following spinal cord injury. Multipotent, clonal YFP-expressing neurospheres (i.e., deriv- ing from recombined GFAP-expressing cells) were successfully obtained from both the intact and injured spinal cord. These spheres however showed limited self-renewal properties when compared with SVZ-neurospheres, even after spinal cord injury. Altogether, these results demonstrate that significant differences exist in NSCs lineages between neurogenic and non- neurogenic regions of the adult CNS. Thus, although we confirm that a population of multipotent GFAP1 cells co-exists alongside with multipotent ependymal cells within the adult SC, we identify these cells as multipotent progenitors showing limited self-renewal properties

Simulation of Special Bubble Detectors for PICASSO

The PICASSO project is a cold dark matter (CDM) search experiment relying on the superheated droplet technique. The detectors use superheated freon liquid droplets (active material) dispersed and trapped in a polymerized gel. This detection technique is based on the phase transition of superheated droplets at about room temperature and ambient pressure. The phase transition is induced by nuclear recoils when an atomic nucleus in the droplets interacts with incoming subatomic particles. This includes CDM particles candidate as the neutralino (a yet-to-discover particle predicted in extensions of the Standard Model of particle physics). Simulations performed to understand the detector response to neutrons and alpha particles are presented along with corresponding data obtained at the Montreal Laboratory.Comment: 13 pages, 4 figures. To appear in the Proceedings of the 14th International Conference on Solid State Dosimetry, June 27 - July 2 2004, Yale University, New Haven, CT, US