2,424 research outputs found
Time variations in the deep underground muon flux measured by MACRO
More than 30 million of high-energy muons collected with the MACRO detector
at the underground Gran Sasso Laboratory have been used to search for flux
variations of different natures. Two kinds of studies were carried out: search
for periodic variations and for the occurrence of clusters of events. Different
analysis methods, including Lomb-Scargle spectral analysis and Scan Test
statistics have been applied to the data.Comment: 6 pages, 4 EPS figures. Talk given at the 29th ICRC, Pune, India,
3-10 August 200
A global view of the oncogenic landscape in nasopharyngeal carcinoma : an integrated analysis at the genetic and expression levels
Previous studies have reported that the tumour cells of nasopharyngeal carcinoma (NPC) exhibit recurrent chromosome abnormalities. These genetic changes are broadly assumed to lead to changes in gene expression which are important for the pathogenesis of this tumour. However, this assumption has yet to be formally tested at a global level. Therefore a genome wide analysis of chromosome copy number and gene expression was performed in tumour cells micro-dissected from the same NPC biopsies. Cellular tumour suppressor and tumour-promoting genes (TSG, TPG) and Epstein-Barr Virus (EBV)-encoded oncogenes were examined. The EBV-encoded genome maintenance protein EBNA1, along with the putative oncogenes LMP1, LMP2 and BARF1 were expressed in the majority of NPCs that were analysed. Significant downregulation of expression in an average of 76 cellular TSGs per tumour was found, whilst a per-tumour average of 88 significantly upregulated, TPGs occurred. The expression of around 60% of putative TPGs and TSGs was both up-and down-regulated in different types of cancer, suggesting that the simplistic classification of genes as TSGs or TPGs may not be entirely appropriate and that the concept of context-dependent onco-suppressors may be more extensive than previously recognised. No significant enrichment of TPGs within regions of frequent genomic gain was seen but TSGs were significantly enriched within regions of frequent genomic loss. It is suggested that loss of the FHIT gene may be a driver of NPC tumourigenesis. Notwithstanding the association of TSGs with regions of genomic loss, on a gene by gene basis and excepting homozygous deletions and high-level amplification, there is very little correlation between chromosomal copy number aberrations and expression levels of TSGs and TPGs in NPC
Nuclear Track Detectors. Searches for Exotic Particles
We used Nuclear Track Detectors (NTD) CR39 and Makrofol for many purposes: i)
Exposures at the SPS and at lower energy accelerator heavy ion beams for
calibration purposes and for fragmentation studies. ii) Searches for GUT and
Intermediate Mass Magnetic Monopoles (IMM), nuclearites, Q-balls and
strangelets in the cosmic radiation. The MACRO experiment in the Gran Sasso
underground lab, with ~1000 m^2 of CR39 detectors (plus scintillators and
streamer tubes), established an upper limit for superheavy GUT poles at the
level of 1.4x10^-16 cm^-2 s^-1 sr^-1 for 4x10^-5 <beta<1. The SLIM experiment
at the high altitude Chacaltaya lab (5230 m a.s.l.), using 427 m^2 of CR39
detectors exposed for 4.22 y, gave an upper limit for IMMs of ~1.3x10^-15 cm^-2
s^-1 sr^-1. The experiments yielded interesting upper limits also on the fluxes
of the other mentioned exotic particles. iii) Environmental studies, radiation
monitoring, neutron dosimetry.Comment: Talk given at "New Trends In High-Energy Physics" (experiment,
phenomenology, theory) Yalta, Crimea, Ukraine, September 27-October 4, 200
Time variations in the deep underground muon flux
More than 35 million high-energy muons collected with the MACRO detector at
the underground Gran Sasso Laboratory have been used to search for flux
variations of different nature. Two kinds of studies were carried out: a search
for the occurrence of clusters of events and a search for periodic variations.
Different analysis methods, including the Scan Statistics test and the
Lomb-Scargle spectral analysis have been applied to the data.Comment: 7 pages, 5 figures, accepted by EP
Experimental Bounds on Masses and Fluxes of Nontopological Solitons
We have re-analyzed the results of various experiments which were not
originally interested as searches for the Q-ball or the Fermi-ball. Based on
these analyses, in addition to the available data on Q-balls, we obtained
rather stringent bounds on flux, mass and typical energy scale of Q-balls as
well as Fermi-balls. In case these nontopological solitons are the main
component of the dark matter of the Galaxy, we found that only such solitons
with very large quantum numbers are allowed. We also estimate how sensitive
future experiments will be in the search for Q-balls and Fermi-balls.Comment: 19 pages, 7 eps figures, RevTeX, psfig.st
Confronting Spin Flavor Solutions of the Solar Neutrino Problem with current and future solar neutrino data
We show that spin flavor precession solutions to the solar neutrino problem,
although preferred by the latest solar data, are ruled out by the first results
from the KamLAND reactor experiment, at more than 3_sigma. An illustrative chi2
plot comparing these descriptions with oscillations is given.Comment: new appendix added discussing the impact of the KamLAND data. This
updates the one published in Phys.Rev.D66:093009,200
Signatures for a Cosmic Flux of Magnetic Monopoles
Any early universe phase transition occurring after inflation has the
potential to populate the universe with relic magnetic monopoles. Observations
of galactic magnetic fields, as well as observations matched with models for
extragalactic magnetic fields, lead to the conclusion that monopoles of mass
\lsim 10^{15} GeV are accelerated in these fields to relativistic velocities.
We explore the possible signatures of a cosmic flux of relativistic monopoles
impinging on the earth. The electromagnetically-induced signatures of monopoles
are reliable. The hadronically-induced signatures are highly model-dependent.
Among our findings are (i) the electromagnetic energy losses of monopoles
continuously initiate a protracted shower of small intensity; (ii) monopoles
may traverse the earth's diameter, making them a probe of the earth's interior
structure; (iii) in addition to the direct monopole Cherenkov signal presently
employed, a very attractive search strategy for monopoles is detection of their
radio-Cherenkov signal produced by the coherent charge-excess in the
shower - in fact, Cherenkov-detectors have the potential to discover a monopole
flux (or limit it) several orders of magnitude below the theoretical Parker
limit of /s/sr; (iv) it is conceivable (but not compelling)
that bound states of colored monopoles may be the primary particles initiating
the air showers observed above the GZK cutoff.Comment: 33 pages, 5 figures, revtex, to appear in Astro. Part. Phy
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