1,117 research outputs found
BUMC Annual Report
Annual report of the Boston University Medical Center
BUMC Annual Report
Annual report of the Boston University Medical Center
Production of antihydrogen at reduced magnetic field for anti-atom trapping
We have demonstrated production of antihydrogen in a 1T solenoidal
magnetic field. This field strength is significantly smaller than that used in
the first generation experiments ATHENA (3T) and ATRAP (5T). The
motivation for using a smaller magnetic field is to facilitate trapping of
antihydrogen atoms in a neutral atom trap surrounding the production region. We
report the results of measurements with the ALPHA (Antihydrogen Laser PHysics
Apparatus) device, which can capture and cool antiprotons at 3T, and then
mix the antiprotons with positrons at 1T. We infer antihydrogen production
from the time structure of antiproton annihilations during mixing, using mixing
with heated positrons as the null experiment, as demonstrated in ATHENA.
Implications for antihydrogen trapping are discussed
Processes of ‘hummocky moraine’ formation in the Gaick, Scotland: insights into the ice-marginal dynamics of a Younger Dryas plateau icefield
Younger Dryas ice-marginal (‘hummocky’) moraines in Scotland represent valuable terrestrial archives that can be used to obtain important information on ice-marginal dynamics and glacier thermal regimes during a period of rapid climatic change. In this paper, we present detailed sedimentological studies of Younger Dryas ice-marginal moraines in the Gaick, central Scotland, the former site of a spatially restricted plateau icefield. Exposures demonstrate that moraines in the Gaick represent terrestrial ice-contact fans, with evidence of proglacial and subglacial glaciotectonization, as reported elsewhere in Scotland. The exposures also reveal the influence of local hydrogeological conditions, with pressurization of the groundwater system leading to the formation of hydrofracture fills within some moraines. Clast shape analysis shows that all the moraines contain debris consistent with transport in the subglacial traction zone. The sedimentological data, and the planform arrangement of the moraines as nested arcs or chevrons, indicate that retreat of the Younger Dryas Gaick Icefield outlets was incremental and oscillatory. This evidence strongly suggests a mainly temperate thermal regime and short glacier response times, but with narrow cold-ice zones near the margins facilitating the elevation of basal debris to the glacier surface. Analogous glaciodynamic regimes occur at modern ice-cap and plateau icefield outlets in Iceland and Norway, although there are significant differences in the nature of ice-marginal deposition. The glaciodynamic signature recorded by moraines in the Gaick has allowed us to shed new light on the ice-marginal dynamics and thermal regime of one of the most easterly Younger Dryas icefields in Scotland
Two-neutron transfer reaction mechanisms in C(He,He)C using a realistic three-body He model
The reaction mechanisms of the two-neutron transfer reaction
C(He,He) have been studied at 30 MeV at the TRIUMF ISAC-II
facility using the SHARC charged-particle detector array. Optical potential
parameters have been extracted from the analysis of the elastic scattering
angular distribution. The new potential has been applied to the study of the
transfer angular distribution to the 2 8.32 MeV state in C, using
a realistic 3-body He model and advanced shell model calculations for the
carbon structure, allowing to calculate the relative contributions of the
simultaneous and sequential two-neutron transfer. The reaction model provides a
good description of the 30 MeV data set and shows that the simultaneous process
is the dominant transfer mechanism. Sensitivity tests of optical potential
parameters show that the final results can be considerably affected by the
choice of optical potentials. A reanalysis of data measured previously at 18
MeV however, is not as well described by the same reaction model, suggesting
that one needs to include higher order effects in the reaction mechanism.Comment: 9 pages, 9 figure
BUMC Annual Report
Annual report of the Boston University Medical Center
BUMC Annual Report
Annual report of the Boston University Medical Center
Protocols for the Fabrication, Characterization, and Optimization of n-Type Thermoelectric Ceramic Oxides
The development of oxides with high figure of merit, ZT, at modest temperatures (∼300–500 °C) is desirable for ceramic-based thermoelectric generator technology. Although ZT is a compound metric with contributions from thermal conductivity (κ), Seebeck coefficient (S), and electrical conductivity (σ), it has been empirically demonstrated that the key to developing thermoelectric n-type oxides is to optimize σ of the ceramic to ∼1000 S/cm at the operating temperature. Titanate-based perovskites are a popular choice for the development of n-type oxide ceramics; however, the levels of σ required cannot be achieved without control of the ceramic quality, significant reduction of the ceramic in low P(O2) atmosphere (e.g., N2/5%H2), and the use of specific dopants and dopant mechanisms, which allow the egress of oxygen homogeneously from the lattice. Here, we discuss the processing protocols to fabricate reliable, reproducible ceramic oxides and schemes for inducing high levels of σ, thereby optimizing the power factor (PF = σS2) and ZT. The problems associated with measuring κ, σ, and S to achieve reproducible and accurate values of ZT are discussed, as are future directions which should enable further optimization. Finally, we comment on how these protocols may be applied to other systems and structures
The TRIUMF nuclear structure program and TIGRESS
The isotope separator and accelerator (ISAC) facility located at the TRIUMF laboratory in Vancouver, Canada, is one of the world\u27s most advanced isotope separator on-line-type radioactive ion beam facilities. An extensive γ-ray spectroscopy programme at ISAC is centred around two major research facilities: (i) the 8π γ-ray spectrometer for β-delayed γ-ray spectroscopy experiments with the low-energy beams from ISAC-I, and (ii) the next generation TRIUMF-ISAC gamma-ray escape suppressed spectrometer (TIGRESS) for in-beam experiments with the accelerated radioactive-ion beams. An overview of these facilities and recent results from the diverse programme of nuclear structure and fundamental interaction studies they support is presented. © 2007 Elsevier B.V. All rights reserved
The Large Enriched Germanium Experiment for Neutrinoless Double Beta Decay (LEGEND)
The observation of neutrinoless double-beta decay (0)
would show that lepton number is violated, reveal that neutrinos are Majorana
particles, and provide information on neutrino mass. A discovery-capable
experiment covering the inverted ordering region, with effective Majorana
neutrino masses of 15 - 50 meV, will require a tonne-scale experiment with
excellent energy resolution and extremely low backgrounds, at the level of
0.1 count /(FWHMtyr) in the region of the signal. The
current generation Ge experiments GERDA and the MAJORANA DEMONSTRATOR
utilizing high purity Germanium detectors with an intrinsic energy resolution
of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in
the 0 signal region of all 0
experiments. Building on this success, the LEGEND collaboration has been formed
to pursue a tonne-scale Ge experiment. The collaboration aims to develop
a phased 0 experimental program with discovery potential
at a half-life approaching or at years, using existing resources as
appropriate to expedite physics results.Comment: Proceedings of the MEDEX'17 meeting (Prague, May 29 - June 2, 2017
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