218 research outputs found
Aberration features in directional dark matter detection
The motion of the Earth around the Sun causes an annual change in the
magnitude and direction of the arrival velocity of dark matter particles on
Earth, in a way analogous to aberration of stellar light. In directional
detectors, aberration of weakly interacting massive particles (WIMPs) modulates
the pattern of nuclear recoil directions in a way that depends on the orbital
velocity of the Earth and the local galactic distribution of WIMP velocities.
Knowing the former, WIMP aberration can give information on the latter, besides
being a curious way of confirming the revolution of the Earth and the
extraterrestrial provenance of WIMPs. While observing the full aberration
pattern requires extremely large exposures, we claim that the annual variation
of the mean recoil direction or of the event counts over specific solid angles
may be detectable with moderately large exposures. For example, integrated
counts over Galactic hemispheres separated by planes perpendicular to Earth's
orbit would modulate annually, resulting in Galactic Hemisphere Annual
Modulations (GHAM) with amplitudes larger than the usual non-directional annual
modulation.Comment: 24 pages, 46 figures, addition of new section 7 on anisotropic models
and Fig. 1
Ring-like features in directional dark matter detection
pre-printWe discuss a novel dark matter signature relevant for directional detection of Weakly Interacting Massive Particles (WIMPs). For heavy enough WIMPs and low enough recoil energies, the maximum of the recoil rate is not in the direction of the average WIMP arrival direction but in a ring around it at an angular radius that increases with the WIMP mass and can approach 90â—¦ at very low energies. The ring is easier to detect for smaller WIMP velocity dispersion and larger average WIMP velocities relative to the detector. In principle the ring could be used as an additional indication of the WIMP mass range
Channeling in direct dark matter detection I: channeling fraction in NaI (Tl) crystals
The channeling of the ion recoiling after a collision with a WIMP changes the
ionization signal in direct detection experiments, producing a larger signal
than otherwise expected. We give estimates of the fraction of channeled
recoiling ions in NaI (Tl) crystals using analytic models produced since the
1960's and 70's to describe channeling and blocking effects. We find that the
channeling fraction of recoiling lattice nuclei is smaller than that of ions
that are injected into the crystal and that it is strongly temperature
dependent.Comment: 37 pages, 35 figures, Accepted for publication in JCAP on 27 October
2010, Minor revisions: added an appendix, updated references, updated Fig. 9,
corrected a few typo
Channeling Effects in Direct Dark Matter Detectors
The channeling of the ion recoiling after a collision with a WIMP changes the
ionization signal in direct detection experiments, producing a larger signal
than otherwise expected. We give estimates of the fraction of channeled
recoiling ions in NaI (Tl), Si and Ge crystals using analytic models produced
since the 1960's and 70's to describe channeling and blocking effects. We find
that the channeling fraction of recoiling lattice nuclei is smaller than that
of ions that are injected into the crystal and that it is strongly temperature
dependent.Comment: 8 pages, 12 figures, To appear in the Proceedings of the sixth
International Workshop on the Dark Side of the Universe (DSU2010) Leon,
Guanajuato, Mexico 1-6 June 201
Daily modulation due to channeling in direct dark matter crystalline detectors
The channeling of the ion recoiling after a collision with a WIMP in direct
dark matter crystalline detectors produces a larger scintillation or ionization
signal than otherwise expected. Channeling is a directional effect which
depends on the velocity distribution of WIMPs in the dark halo of our Galaxy
and could lead to a daily modulation of the signal. Here we compute upper
bounds to the expected amplitude of daily modulation due to channeling using
channeling fractions that we obtained with analytic models in prior work. After
developing the general formalism, we examine the possibility of finding a daily
modulation due to channeling in the data already collected by the DAMA/NaI and
DAMA/LIBRA experiments. We find that even the largest daily modulation
amplitudes (of the order of 10% in some instances) would not be observable for
WIMPs in the standard halo in the 13 years of data taken by the DAMA
collaboration. For these to be observable the DAMA total rate should be 1/40 of
what it is or the total DAMA exposure should be 40 times larger. The daily
modulation due to channeling will be difficult to measure in future
experiments. We find it could be observed for light WIMPs in solid Ne, assuming
no background.Comment: 29 pages, 15 figures. v3: version accepted by PRD. Minor corrections
made, corrected Eq. 12 and 13 and Figs. 2, 3.a, and 4.a, corrected Eqs. 27-38
by a factor of 2, added the observability condition for solid N
Channeling in solid Xe, Ar and Ne direct dark matter detectors
The channeling of the ion recoiling after a collision with a WIMP changes the
ionization signal in direct detection experiments, producing a larger
scintillation or ionization signal than otherwise expected. We give estimates
of the fraction of channeled recoiling ions in solid Xe, Ar and Ne crystals
using analytic models produced since the 1960's and 70's to describe channeling
and blocking effects.Comment: 17 pages, 25 figures, the structure of the paper is modified and some
important equations, explanations and references are added, Fig 7 is adde
The translatome of neuronal cell bodies, dendrites,and axons
To form synaptic connections and store information, neurons continuously remodel their proteomes. The impressive length of dendrites and axons imposes logistical challenges to maintain synaptic proteins at locations remote from the transcription source (the nucleus). The discovery of thousands of messenger RNAs (mRNAs) near synapses suggested that neurons overcome distance and gain autonomy by producing proteins locally. It is not generally known, however, if, how, and when localized mRNAs are translated into protein. To investigate the translational landscape in neuronal subregions, we performed simultaneous RNA sequencing (RNA-seq) and ribosome sequencing (Ribo-seq) from microdissected rodent brain slices to identify and quantify the transcriptome and translatome in cell bodies (somata) as well as dendrites and axons (neuropil). Thousands of transcripts were differentially translated between somatic and synaptic regions, with many scaffold and signaling molecules displaying increased translation levels in the neuropil. Most translational changes between compartments could be accounted for by differences in RNA abundance. Pervasive translational regulation was observed in both somata and neuropil influenced by specific mRNA features (e.g., untranslated region [UTR] length, RNA-binding protein [RBP] motifs, and upstream open reading frames [uORFs]). For over 800 mRNAs, the dominant source of translation was the neuropil. We constructed a searchable and interactive database for exploring mRNA transcripts and their translation levels in the somata and neuropil [MPI Brain Research, The mRNA translation landscape in the synaptic neuropil. https://public.brain.mpg.de/dashapps/localseq/ Accessed 5 October 2021]. Overall, our findings emphasize the substantial contribution of local translation to maintaining synaptic protein levels and indicate that on-site translational control is an important mechanism to control synaptic strength
Constitutive Overexpression of Muscarinic Receptors Leads to Vagal Hyperreactivity
BACKGROUND: Alterations in muscarinic receptor expression and acetylcholinesterase (AchE) activity have been observed in tissues from Sudden Infant Death Syndrome (SIDS). Vagal overactivity has been proposed as a possible cause of SIDS as well as of vasovagal syncopes. The aim of the present study was to seek whether muscarinic receptor overexpression may be the underlying mechanism of vagal hyperreactivity. Rabbits with marked vagal pauses following injection of phenylephrine were selected and crossed to obtain a vagal hyperreactive strain. The density of cardiac muscarinic receptors and acetylcholinesterase (AchE) gene expression were assessed. Blood markers of the observed cardiac abnormalities were also sought. METHODOLOGY/PRINCIPAL FINDINGS: Cardiac muscarinic M(2) and M(3) receptors were overexpressed in hyperreactive rabbits compared to control animals (2.3-fold and 2.5-fold, respectively) and the severity of the phenylephrine-induced bradycardia was correlated with their densities. A similar overexpression of M(2) receptors was observed in peripheral mononuclear white blood cells, suggesting that cardiac M(2) receptor expression can be inferred with high confidence from measurements in blood cells. Sequencing of the coding fragment of the M(2) receptor gene revealed a single nucleotide mutation in 83% of hyperreactive animals, possibly contributing for the transcript overexpression. Significant increases in AchE expression and activity were also assessed (AchE mRNA amplification ratio of 3.6 versus normal rabbits). This phenomenon might represent a compensatory consequence of muscarinic receptors overexpression. Alterations in M(2) receptor and AchE expression occurred between the 5th and the 7th week of age, a critical period also characterized by a higher mortality rate of hyperreactive rabbits (52% in H rabbits versus 13% in normal rabbits) and preceeded the appearance of functional disorders. CONCLUSIONS/SIGNIFICANCE: The results suggest that cardiac muscarinic receptor overexpression plays a critical role in the development of vagal hyperreactivity, whereas AchE hyperactivity appears as a compensatory consequence of it. Since similar vagal disorders were observed recently by us in SIDS, muscarinic receptor overexpression could become a marker of risk of vasovagal syncopes and SIDS
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