409 research outputs found
Impact of COVID 19 on Library Services in US Pharmacy Programs
The COVID 19 pandemic resulted in many academic libraries closing physical spaces and the reduction of personnel due to quarantine measures. The potential reduction in library services could have a negative impact on research by pharmacy facult
Hippocampus and retrosplenial cortex combine path integration signals for successful navigation
The current study used fMRI in humans to examine goal-directed navigation in an open field environment. We designed a task that required participants to encode survey-level spatial information and subsequently navigate to a goal location in either first person, third person, or survey perspectives. Critically, no distinguishing landmarks or goal location markers were present in the environment, thereby requiring participants to rely on path integration mechanisms for successful navigation. We focused our analysis on mechanisms related to navigation and mechanisms tracking linear distance to the goal location. Successful navigation required translation of encoded survey-level map information for orientation and implementation of a planned route to the goal. Our results demonstrate that successful first and third person navigation trials recruited the anterior hippocampus more than trials when the goal location was not successfully reached. When examining only successful trials, the retrosplenial and posterior parietal cortices were recruited for goal-directed navigation in both first person and third person perspectives. Unique to first person perspective navigation, the hippocampus was recruited to path integrate self-motion cues with location computations toward the goal location. Last, our results demonstrate that the hippocampus supports goal-directed navigation by actively tracking proximity to the goal throughout navigation. When using path integration mechanisms in first person and third person perspective navigation, the posterior hippocampus was more strongly recruited as participants approach the goal. These findings provide critical insight into the neural mechanisms by which we are able to use map-level representations of our environment to reach our navigational goals
One-neutron knockout from Ni
The single-particle structure of Ni and level structure of Ni
were investigated with the \mbox{Be (Ni,Ni+)} reaction at 73 MeV/nucleon. An inclusive cross
section of 41.4(12) mb was obtained for the reaction, compared to a theoretical
prediction of 85.4 mb, hence only 48(2)% of the theoretical cross section is
exhausted. This reduction in the observed spectroscopic strength is consistent
with that found for lighter well-bound nuclei. One-neutron removal
spectroscopic factors of 0.58(11) to the ground state and 3.7(2) to all excited
states of Ni were deduced.Comment: Phys. Rev. C, accepte
Production cross sections from 82Se fragmentation as indications of shell effects in neutron-rich isotopes close to the drip-line
Production cross sections for neutron-rich nuclei from the fragmentation of a
82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions
of 126 neutron-rich isotopes of elements 11 <= Z <= 32 were scanned using an
experimental approach of varying the target thickness. Production cross
sections with beryllium and tungsten targets were determined for a large number
of nuclei including several isotopes first observed in this work. These are the
most neutron-rich nuclides of the elements 22 <= Z <= 25 (64Ti, 67V, 69Cr,
72Mn). One event was registered consistent with 70Cr, and another one with
75Fe. The production cross sections are correlated with Qg systematics to
reveal trends in the data. The results presented here confirm our previous
result from a similar measurement using a 76Ge beam, and can be explained with
a shell model that predicts a subshell closure at N = 34 around Z = 20. This is
demonstrated by systematic trends and calculations with the Abrasion-Ablation
model that are sensitive to separation energies.Comment: 13 pages, 11 figures, accepted to Phys.Rev.
Measurement of the Gamow-Teller Strength Distribution in 58Co via the 58Ni(t,3He) reaction at 115 MeV/nucleon
Electron capture and beta decay play important roles in the evolution of
pre-supernovae stars and their eventual core collapse. These rates are normally
predicted through shell-model calculations. Experimentally determined strength
distributions from charge-exchange reactions are needed to test modern
shell-model calculations. We report on the measurement of the Gamow-Teller
strength distribution in 58Co from the 58Ni(t,3He) reaction with a secondary
triton beam of an intensity of ~10^6 pps at 115 MeV/nucleon and a resolution of
\~250 keV. Previous measurements with the 58Ni(n,p) and the 58Ni(d,2He)
reactions were inconsistent with each other. Our results support the latter. We
also compare the results to predictions of large-scale shell model calculations
using the KB3G and GXPF1 interactions and investigate the impact of differences
between the various experiments and theories in terms of the weak rates in the
stellar environment. Finally, the systematic uncertainties in the normalization
of the strength distribution extracted from 58Ni(3He,t) are described and turn
out to be non-negligible due to large interferences between the dL=0, dS=1
Gamow-Teller amplitude and the dL=2, dS=1 amplitude.Comment: 14 pages, 8 figure
New Cl(p,)Ar reaction rate for astrophysical rp-process calculations
The Cl(p,)Ar reaction rate is of potential importance
in the rp-process powering type I X-ray bursts. Recently Clement et al.
\cite{CBB04} presented new data on excitation energies for low lying proton
unbound states in Ar obtained with a new method developed at the
National Superconducting Cyclotron Laboratory. We use their data, together with
a direct capture model and a USD shell model calculation to derive a new
reaction rate for use in astrophysical model calculations. In particular, we
take into account capture on the first excited state in Cl, and also
present a realistic estimate of the remaining uncertainties. We find that the
Cl(p,)Ar reaction rate is dominated entirely by capture
on the first excited state in Cl over the whole temperature range
relevant in X-ray bursts. In the temperature range from 0.2 to 1 GK the rate is
up to a factor of 70 larger than the previously recommended rate based on shell
model calculations only. The uncertainty is now reduced from up to a factor of
1000 to a factor of 3 at 0.3-0.7 GK and a factor of 6 at 1.5 GK.Comment: To be published in Phys. Rev.
Single-particle spectroscopy of rare isotope beams: Calculations beyond the eikonal approximation
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