419 research outputs found
Complementarity of dark matter detectors in light of the neutrino background
Direct detection dark matter experiments looking for WIMP-nucleus elastic
scattering will soon be sensitive to an irreducible background from neutrinos
which will drastically affect their discovery potential. Here we explore how
the neutrino background will affect future ton-scale experiments considering
both spin-dependent and spin-independent interactions. We show that combining
data from experiments using different targets can improve the dark matter
discovery potential due to target complementarity. We find that in the context
of spin-dependent interactions, combining results from several targets can
greatly enhance the subtraction of the neutrino background for WIMP masses
below 10 GeV/c and therefore probe dark matter models to lower
cross-sections. In the context of target complementarity, we also explore how
one can tune the relative exposures of different target materials to optimize
the WIMP discovery potential.Comment: 13 pages, 12 figures, 3 table
Locoregional hyperthermia of deep-seated tumours applied with capacitive and radiative systems. A simulation study
Background: Locoregional hyperthermia is applied to deep-seated tumours in the pelvic region. Two very different heating techniques are often applied: capacitive and radiative heating. In this paper, numerical simulations are applied to compare the performance of both techniques in heating of deep-seated tumours. Methods: Phantom simulations were performed for small (30 × 20 × 50 cm 3 ) and large (45 × 30 × 50 cm 3 ), homogeneous fatless and inhomogeneous fat-muscle, tissue-equivalent phantoms with a central or eccentric target region. Radiative heating was simulated with the 70 MHz AMC-4 system and capacitive heating was simulated at 13.56 MHz. Simulations were performed for small fatless, small (i.e. fat layer typically 3 cm) patients with cervix, prostate, bladder and rectum cancer. Temperature distributions were simulated using constant hyperthermic-level perfusion values with tissue constraints of 44 °C and compared for both heating techniques. Results: For the small homogeneous phantom, similar target heating was predicted with radiative and capacitive heating. For the large homogeneous phantom, most effective target heating was predicted with capacitive heating. For inhomogeneous phantoms, hot spots in the fat layer limit adequate capacitive heating, and simulated target temperatures with radiative heating were 2–4 °C higher. Patient simulations predicted therapeutic target temperatures with capacitive heating for fatless patients, but radiative heating was more robust for all tumour sites and patient sizes, yielding target temperatures 1–3 °C higher than those predicted for capacitive heating. Conclusion: Generally, radiative locoregional heating yields more favourable simulated temperature distributions for deep-seated pelvic tumours, compared with capacitive heating. Therapeutic temperatures are predicted for capacitive heating in patients with (almost) no fat
The Cosmic Stellar Birth and Death Rates
The cosmic stellar birth rate can be measured by standard astronomical
techniques. It can also be probed via the cosmic stellar death rate, though
until recently, this was much less precise. However, recent results based on
measured supernova rates, and importantly, also on the attendant diffuse fluxes
of neutrinos and gamma rays, have become competitive, and a concordant history
of stellar birth and death is emerging. The neutrino flux from all past
core-collapse supernovae, while faint, is realistically within reach of
detection in Super-Kamiokande, and a useful limit has already been set. I will
discuss predictions for this flux, the prospects for neutrino detection, the
implications for understanding core-collapse supernovae, and a new limit on the
contribution of type-Ia supernovae to the diffuse gamma-ray background.Comment: Accepted for publication in New Astronomy Reviews (invited talk at
"Astronomy with Radioactivities V", Clemson Univ., Sept. 2005). 9 pages, 5
figure
Bounds on Cross-sections and Lifetimes for Dark Matter Annihilation and Decay into Charged Leptons from Gamma-ray Observations of Dwarf Galaxies
We provide conservative bounds on the dark matter cross-section and lifetime
from final state radiation produced by annihilation or decay into charged
leptons, either directly or via an intermediate particle . Our analysis
utilizes the experimental gamma-ray flux upper limits from four Milky Way dwarf
satellites: HESS observations of Sagittarius and VERITAS observations of Draco,
Ursa Minor, and Willman 1. Using 90% confidence level lower limits on the
integrals over the dark matter distributions, we find that these constraints
are largely unable to rule out dark matter annihilations or decays as an
explanation of the PAMELA and ATIC/PPB-BETS excesses. However, if there is an
additional Sommerfeld enhancement in dwarfs, which have a velocity dispersion
~10 to 20 times lower than that of the local Galactic halo, then the
cross-sections for dark matter annihilating through 's required to
explain the excesses are very close to the cross-section upper bounds from
Willman 1. Dark matter annihilation directly into 's is also marginally
ruled out by Willman 1 as an explanation of the excesses, and the required
cross-section is only a factor of a few below the upper bound from Draco.
Finally, we make predictions for the gamma-ray flux expected from the dwarf
galaxy Segue 1 for the Fermi Gamma-ray Space Telescope. We find that for a
sizeable fraction of the parameter space in which dark matter annihilation into
charged leptons explains the PAMELA excess, Fermi has good prospects for
detecting a gamma-ray signal from Segue 1 after one year of observation.Comment: 11 pages, 4 figures. References added. Final published versio
Nurses\u27 Alumnae Association Bulletin, September 1958
Committee Reports
Digest of Alumnae Meetings
Graduation Awards - 1957
List of Wrong Addresses
Marriages
Necrology
New Arrivals
Physical Advances at Jefferson
President\u27s Message
School of Nursing Repor
Tumor control in ion beam radiotherapy with different ions in the presence of hypoxia: an oxygen enhancement ratio model based on the microdosimetric kinetic model
Angular Correlations of the MeV Cosmic Gamma Ray Background
The measured cosmic gamma ray background (CGB) spectrum at MeV energies is in
reasonable agreement with the predicted contribution from type Ia supernovae
(SNIa). But the characteristic features in the SNIa gamma ray spectrum,
weakened by integration over source redshifts, are hard to measure, and
additionally the contributions from other sources in the MeV range are
uncertain, so that the SNIa origin of the MeV CGB remains unproven. Since
different CGB sources have different clustering properties and redshift
distributions, by combining the CGB spectrum and angular correlation
measurements, the contributions to the CGB could be identified and separated.
The SNIa CGB large-scale structure follows that of galaxies. Its rms
fluctuation at degree scales has a characteristic energy dependence, ranging
from to order of unity and can be measured to several percent
precision by proposed future satellites such as the Advanced Compton Telescope.
With the identification of the SNIa contribution, the SNIa rate could be
measured unambiguously as a function of redshift up to , by combining
both the spectrum and angular correlation measurements, yielding new
constraints on the star formation rate to even higher redshifts. Finally, we
show that the gamma ray and neutrino backgrounds from supernovae should be
closely connected, allowing an important consistency test from the measured
data. Identification of the astrophysical contributions to the CGB would allow
much greater sensitivity to an isotropic high-redshift CGB contribution arising
in extra dimension or dark matter models.Comment: 6 pages, 3 figures. ApJ, (2004), 614, 3
- …