103 research outputs found
Charge symmetry breaking in light hypernuclei
Charge symmetry breaking (CSB) is particularly strong in the A=4 mirror
hypernuclei H--He. Recent four-body no-core shell
model calculations that confront this CSB by introducing -
mixing to leading-order chiral effective field theory hyperon-nucleon
potentials are reviewed, and a shell-model approach to CSB in p-shell
hypernuclei is outlined.Comment: presented by A. Gal at the 12th International Seminar on Nuclear
Physics, Sant'Angelo d'Ischia, May 15-19 2017; prepared for J. Phys. Conf.;
v2 -- slightly expanded versio
Calculations of nuclear quasi-bound states based on chiral meson-baryon amplitudes
In-medium scattering amplitudes developed within a new chirally
motivated coupled-channel model due to Cieply and Smejkal that fits the recent
SIDDHARTA kaonic hydrogen 1s level shift and width are used to construct
nuclear potentials for calculations of nuclear quasi-bound states. The
strong energy and density dependence of scattering amplitudes at and near
threshold leads to potential depths MeV.
Self-consistent calculations of all nuclear quasi-bound states, including
excited states, are reported. Model dependence, polarization effects, the role
of p-wave interactions, and two-nucleon absorption modes
are discussed. The absorption widths are comparable or even
larger than the corresponding binding energies for all nuclear
quasi-bound states, exceeding considerably the level spacing. This discourages
search for nuclear quasi-bound states in any but lightest nuclear
systems.Comment: 12 pages, 11 figure
Ab initio nuclear response functions for dark matter searches
We study the process of dark matter particles scattering off He with
nuclear wave functions computed using an ab initio many-body framework. We
employ realistic nuclear interactions from chiral effective field theory at
next-to-next-to-leading order (NNLO) and develop an ab initio scheme to compute
a general set of different nuclear response functions. In particular, we then
perform an accompanying uncertainty quantification on these quantities and
study error propagation to physical observables. We find a rich structure of
allowed nuclear responses with significant uncertainties for certain
spin-dependent interactions. The approach and results that are presented in
this Paper establish a new framework for nuclear structure calculations and
uncertainty quantification in the context of direct and (certain) indirect
searches for dark matter.Comment: version accepted for publication in Phys. Rev. D; figures revised
(incl. corrected labels); discussion of results extende
Hypernuclear No-Core Shell Model
We extend the No-Core Shell Model (NCSM) methodology to incorporate
strangeness degrees of freedom and apply it to single- hypernuclei.
After discussing the transformation of the hyperon-nucleon (YN) interaction
into Harmonic-Oscillator (HO) basis and the Similarity Renormalization Group
transformation applied to it to improve model-space convergence, we present two
complementary formulations of the NCSM, one that uses relative Jacobi
coordinates and symmetry-adapted basis states to fully exploit the symmetries
of the hypernuclear Hamiltonian, and one working in a Slater determinant basis
of HO states where antisymmetrization and computation of matrix elements is
simple and to which an importance-truncation scheme can be applied. For the
Jacobi-coordinate formulation, we give an iterative procedure for the
construction of the antisymmetric basis for arbitrary particle number and
present the formulae used to embed two- and three-baryon interactions into the
many-body space. For the Slater-determinant formulation, we discuss the
conversion of the YN interaction matrix elements from relative to
single-particle coordinates, the importance-truncation scheme that tailors the
model space to the description of the low-lying spectrum, and the role of the
redundant center-of-mass degrees of freedom. We conclude with a validation of
both formulations in the four-body system, giving converged ground-state
energies for a chiral Hamiltonian, and present a short survey of the
hyper-helium isotopes.Comment: 17 pages, 8 figures; accepted versio
In-medium antikaon and eta-meson interactions and bound states
The role played by subthreshold meson-baryon dynamics is demonstrated in
kaonic-atom, Kbar-nuclear and eta-nuclear bound-state calculations within
in-medium models of Kbar-N and eta-N interactions. New analyses of kaonic atom
data reveal appreciable multi-nucleon contributions. Calculations of
eta-nuclear bound states show, in particular, that the eta-N scattering length
is not a useful indicator of whether or not eta mesons bind in nuclei nor of
the widths anticipated for such states.Comment: invited talk at the Second International Symposium on Mesic Nuclei,
Cracow, Sept.22-24 2013, matches published versio
Ab Initio Description of p-Shell Hypernuclei
We present the first ab initio calculations for p-shell single-Lambda
hypernuclei. For the solution of the many-baryon problem, we develop two
variants of the no-core shell model with explicit and ,
, hyperons including - conversion,
optionally supplemented by a similarity renormalization group transformation to
accelerate model-space convergence. In addition to state-of-the-art chiral two-
and three-nucleon interactions, we use leading-order chiral hyperon-nucleon
interactions and a recent meson-exchange hyperon-nucleon interaction. We
validate the approach for s-shell hypernuclei and apply it to p-shell
hypernuclei, in particular to Li, Be and
C. We show that the chiral hyperon-nucleon interactions provide
ground-state and excitation energies that agree with experiment within the
cutoff dependence. At the same time we demonstrate that hypernuclear
spectroscopy provides tight constraints on the hyperon-nucleon interactions and
we discuss the impact of induced hyperon-nucleon-nucleon interactions.Comment: 6 pages, 4 figure
Rapid Electrochemical Detection and Identification of Microbiological and Chemical Contaminants for Manned Spaceflight Project
Microbial control in the spacecraft environment is a daunting task, especially in the presence of human crew members. Currently, assessing the potential crew health risk associated with a microbial contamination event requires return of representative environmental samples that are analyzed in a ground-based laboratory. It is therefore not currently possible to quickly identify microbes during spaceflight. This project addresses the unmet need for spaceflight-compatible microbial identification technology. The electrochemical detection and identification platform is expected to provide a sensitive, specific, and rapid sample-to-answer capability for in-flight microbial monitoring that can distinguish between related microorganisms (pathogens and non-pathogens) as well as chemical contaminants. This will dramatically enhance our ability to monitor the spacecraft environment and the health risk to the crew. Further, the project is expected to eliminate the need for sample return while significantly reducing crew time required for detection of multiple targets. Initial work will focus on the optimization of bacterial detection and identification. The platform is designed to release nucleic acids (DNA and RNA) from microorganisms without the use of harmful chemicals. Bacterial DNA or RNA is captured by bacteria-specific probe molecules that are bound to a microelectrode, and that capture event can generate a small change in the electrical current (Lam, et al. 2012. Anal. Chem. 84(1): 21-5.). This current is measured, and a determination is made whether a given microbe is present in the sample analyzed. Chemical detection can be accomplished by directly applying a sample to the microelectrode and measuring the resulting current change. This rapid microbial and chemical detection device is designed to be a low-cost, low-power platform anticipated to be operated independently of an external power source, characteristics optimal for manned spaceflight and areas where power and computing resources are scarce
Development of colorimetric solid Phase Extraction (C-SPE) for in-flight Monitoring of spacecraft Water Supplies
Although having recently been extremely successful gathering data on the surface of Mars, robotic missions are not an effective substitute for the insight and knowledge about our solar system that can be gained though first-hand exploration. Earlier this year, President Bush presented a ''new course'' for the U.S. space program that shifts NASA's focus to the development of new manned space vehicles to the return of humans to the moon. Re-establishing the human presence on the moon will eventually lead to humans permanently living and working in space and also serve as a possible launch point for missions into deeper space. There are several obstacles to the realization of these goals, most notably the lack of life support and environmental regeneration and monitoring hardware capable of functioning on long duration spaceflight. In the case of the latter, past experience on the International Space Station (ISS), Mir, and the Space Shuttle has strongly underscored the need to develop broad spectrum in-flight chemical sensors that: (1) meet current environmental monitoring requirements on ISS as well as projected requirements for future missions, and (2) enable the in-situ acquisition and analysis of analytical data in order to further define on-orbit monitoring requirements. Additionally, systems must be designed to account for factors unique to on-orbit deployment such as crew time availability, payload restrictions, material consumption, and effective operation in microgravity. This dissertation focuses on the development, ground testing, and microgravity flight demonstration of Colorimetric Solid Phase Extraction (C-SPE) as a candidate technology to meet the near- and long-term water quality monitoring needs of NASA. The introduction will elaborate further on the operational and design requirements for on-orbit water quality monitoring systems by discussing some of the characteristics of an ''ideal'' system. A description of C-SPE and how the individual components of the platform are combined to satisfy many of these requirements is then presented, along with a literature review on the applications of C-SPE and similar sorption-spectrophotometric techniques. Finally, a brief overview of diffuse reflection spectroscopy and the Kubelka-Munk function, which are used to quantify analytes via C-SPE, is presented
Nuclear physics uncertainties in light hypernuclei
The energy levels of light hypernuclei are experimentally accessible observables that contain valuable information about the interaction between hyperons and nucleons. In this work we study strangeness S=-1 systems HΛ3,4 and HeΛ4,5 using the ab initio no-core shell model (NCSM) with realistic interactions obtained from chiral effective field theory (χEFT). In particular, we quantify the finite precision of theoretical predictions that can be attributed to nuclear physics uncertainties. We study both the convergence of the solution of the many-body problem (method uncertainty) and the regulator and calibration-data dependence of the nuclear χEFT Hamiltonian (model uncertainty). For the former, we implement infrared correction formulas and extrapolate finite-space NCSM results to infinite model space. We then use Bayesian parameter estimation to quantify the resulting method uncertainties. For the latter, we employ a family of 42 realistic Hamiltonians and measure the standard deviation of predictions while keeping the leading-order hyperon-nucleon interaction fixed. Following this procedure we find that model uncertainties of ground-state Λ separation energies amount to ≈20(100)keV in HΛ3(HΛ4,He) and ≈400keV in HeΛ5. Method uncertainties are comparable in magnitude for the HΛ4,He 1+ excited states and HeΛ5, which are computed in limited model spaces, but otherwise are much smaller. This knowledge of expected theoretical precision is crucial for the use of binding energies of light hypernuclei to infer the elusive hyperon-nucleon interaction
Liquid Metering Centrifuge Sticks (LMCS): A Centrifugal Approach to Metering Known Sample Volumes for Colorimetric Solid Phase Extraction (C-SPE)
Phase separation is one of the most significant obstacles encountered during the development of analytical methods for water quality monitoring in spacecraft environments. Removing air bubbles from water samples prior to analysis is a routine task on earth; however, in the absence of gravity, this routine task becomes extremely difficult. This paper details the development and initial ground testing of liquid metering centrifuge sticks (LMCS), devices designed to collect and meter a known volume of bubble-free water in microgravity. The LMCS uses centrifugal force to eliminate entrapped air and reproducibly meter liquid sample volumes for analysis with Colorimetric Solid Phase Extraction (C-SPE). C-SPE is a sorption-spectrophotometric platform that is being developed as a potential spacecraft water quality monitoring system. C-SPE utilizes solid phase extraction membranes impregnated with analyte-specific colorimetric reagents to concentrate and complex target analytes in spacecraft water samples. The mass of analyte extracted from the water sample is determined using diffuse reflectance (DR) data collected from the membrane surface and an analyte-specific calibration curve. The analyte concentration can then be calculated from the mass of extracted analyte and the volume of the sample analyzed. Previous flight experiments conducted in microgravity conditions aboard the NASA KC-135 aircraft demonstrated that the inability to collect and meter a known volume of water using a syringe was a limiting factor in the accuracy of C-SPE measurements. Herein, results obtained from ground based C-SPE experiments using ionic silver as a test analyte and either the LMCS or syringes for sample metering are compared to evaluate the performance of the LMCS. These results indicate very good agreement between the two sample metering methods and clearly illustrate the potential of utilizing centrifugal forces to achieve phase separation and metering of water samples in microgravity
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