190 research outputs found
Enhanced dynamic nuclear polarization via swept microwave frequency combs
Dynamic Nuclear Polarization (DNP) has enabled enormous gains in magnetic
resonance signals and led to vastly accelerated NMR/MRI imaging and
spectroscopy. Unlike conventional cw-techniques, DNP methods that exploit the
full electron spectrum are appealing since they allow direct participation of
all electrons in the hyperpolarization process. Such methods typically entail
sweeps of microwave radiation over the broad electron linewidth to excite DNP,
but are often inefficient because the sweeps, constrained by adiabaticity
requirements, are slow. In this paper we develop a technique to overcome the
DNP bottlenecks set by the slow sweeps, employing a swept microwave frequency
comb that increases the effective number of polarization transfer events while
respecting adiabaticity constraints. This allows a multiplicative gain in DNP
enhancement, scaling with the number of comb frequencies and limited only by
the hyperfine-mediated electron linewidth. We demonstrate the technique for the
optical hyperpolarization of 13C nuclei in powdered microdiamonds at low
fields, increasing the DNP enhancement from 30 to 100 measured with respect to
the thermal signal at 7T. For low concentrations of broad linewidth electron
radicals, e.g. TEMPO, these multiplicative gains could exceed an order of
magnitude.Comment: Contains supplementary inf
Supernovae and their host galaxies - IV. The distribution of supernovae relative to spiral arms
Using a sample of 215 supernovae (SNe), we analyze their positions relative
to the spiral arms of their host galaxies, distinguishing grand-design (GD)
spirals from non-GD (NGD) galaxies. We find that: (1) in GD galaxies, an offset
exists between the positions of Ia and core-collapse (CC) SNe relative to the
peaks of arms, while in NGD galaxies the positions show no such shifts; (2) in
GD galaxies, the positions of CC SNe relative to the peaks of arms are
correlated with the radial distance from the galaxy nucleus. Inside (outside)
the corotation radius, CC SNe are found closer to the inner (outer) edge. No
such correlation is observed for SNe in NGD galaxies nor for SNe Ia in either
galaxy class; (3) in GD galaxies, SNe Ibc occur closer to the leading edges of
the arms than do SNe II, while in NGD galaxies they are more concentrated
towards the peaks of arms. In both samples of hosts, the distributions of SNe
Ia relative to the arms have broader wings. These observations suggest that
shocks in spiral arms of GD galaxies trigger star formation in the leading
edges of arms affecting the distributions of CC SNe (known to have short-lived
progenitors). The closer locations of SNe Ibc vs. SNe II relative to the
leading edges of the arms supports the belief that SNe Ibc have more massive
progenitors. SNe Ia having less massive and older progenitors, have more time
to drift away from the leading edge of the spiral arms.Comment: 19 pages, 10 figures, 11 tables, resubmitted to MNRAS after
addressing referee's comment
Supernovae and their host galaxies - II. The relative frequencies of supernovae types in spirals
We present an analysis of the relative frequencies of different supernova
(SN) types in spirals with various morphologies and in barred or unbarred
galaxies. We use a well-defined and homogeneous sample of spiral host galaxies
of 692 SNe from the Sloan Digital Sky Survey in different stages of
galaxy-galaxy interaction and activity classes of nucleus. We propose that the
underlying mechanisms shaping the number ratios of SNe types can be interpreted
within the framework of interaction-induced star formation, in addition to the
known relations between morphologies and stellar populations. We find a strong
trend in behaviour of the NIa/NCC ratio depending on host morphology, such that
early spirals include more Type Ia SNe. The NIbc/NII ratio is higher in a broad
bin of early-type hosts. The NIa/NCC ratio is nearly constant when changing
from normal, perturbed to interacting galaxies, then declines in merging
galaxies, whereas it jumps to the highest value in post-merging/remnant
galaxies. In contrast, the NIbc/NII ratio jumps to the highest value in merging
galaxies and slightly declines in post-merging/remnant subsample. The
interpretation is that the star formation rates and morphologies of galaxies,
which are strongly affected in the final stages of interaction, have an impact
on the number ratios of SNe types. The NIa/NCC (NIbc/NII) ratio increases
(decreases) from star-forming to active galactic nuclei (AGN) classes of
galaxies. These variations are consistent with the scenario of an
interaction-triggered starburst evolving into AGN during the later stages of
interaction, accompanied with the change of star formation and transformation
of the galaxy morphology into an earlier type.Comment: 14 pages, 9 figures, 16 tables, online dat
Relative frequencies of supernovae versus properties of spiral hosts
In this work, we present an analysis of SNe number ratios in spiral galaxies
with different morphological subtypes, luminosities, sSFR, and metallicities,
to provide important information about the physical properties of the
progenitor populations.Comment: 2 pages, 1 figur
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Room temperature "optical nanodiamond hyperpolarizer": Physics, design, and operation.
Dynamic Nuclear Polarization (DNP) is a powerful suite of techniques that deliver multifold signal enhancements in nuclear magnetic resonance (NMR) and MRI. The generated athermal spin states can also be exploited for quantum sensing and as probes for many-body physics. Typical DNP methods require the use of cryogens, large magnetic fields, and high power microwave excitation, which are expensive and unwieldy. Nanodiamond particles, rich in Nitrogen-Vacancy (NV) centers, have attracted attention as alternative DNP agents because they can potentially be optically hyperpolarized at room temperature. Here, unraveling new physics underlying an optical DNP mechanism first introduced by Ajoy et al. [Sci. Adv. 4, eaar5492 (2018)], we report the realization of a miniature "optical nanodiamond hyperpolarizer," where 13C nuclei within the diamond particles are hyperpolarized via the NV centers. The device occupies a compact footprint and operates at room temperature. Instrumental requirements are very modest: low polarizing fields, low optical and microwave irradiation powers, and convenient frequency ranges that enable miniaturization. We obtain the best reported optical 13C hyperpolarization in diamond particles exceeding 720 times of the thermal 7 T value (0.86% bulk polarization), corresponding to a ten-million-fold gain in averaging time to detect them by NMR. In addition, the hyperpolarization signal can be background-suppressed by over two-orders of magnitude, retained for multiple-minute long periods at low fields, and deployed efficiently even to 13C enriched particles. Besides applications in quantum sensing and bright-contrast MRI imaging, this work opens possibilities for low-cost room-temperature DNP platforms that relay the 13C polarization to liquids in contact with the high surface-area particles
Proton structure corrections to electronic and muonic hydrogen hyperfine splitting
We present a precise determination of the polarizability and other proton
structure dependent contributions to the hydrogen hyperfine splitting, based
heavily on the most recent published data on proton spin dependent structure
functions from the EG1 experiment at the Jefferson Laboratory. As a result, the
total calculated hyperfine splitting now has a standard deviation slightly
under 1 part-per-million, and is about 1 standard deviation away from the
measured value. We also present results for muonic hydrogen hyperfine
splitting, taking care to ensure the compatibility of the recoil and
polarizability terms.Comment: 9 pages, 1 figur
Evaluating matrix elements relevant to some Lorenz violating operators
Carlson, Carone and Lebed have derived the Feynman rules for a consistent
formulation of noncommutative QCD. The results they obtained were used to
constrain the noncommutativity parameter in Lorentz violating noncommutative
field theories. However, their constraint depended upon an estimate of the
matrix element of the quark level operator (gamma.p - m) in a nucleon. In this
paper we calculate the matrix element of (gamma.p - m), using a variety of
confinement potential models. Our results are within an order of magnitude
agreement with the estimate made by Carlson et al. The constraints placed on
the noncommutativity parameter were very strong, and are still quite severe
even if weakened by an order of magnitude.Comment: 4 pages, 3 figures, RevTex, minor change
Field Theory in Noncommutative Minkowski Superspace
There is much discussion of scenarios where the space-time coordinates x^\mu
are noncommutative. The discussion has been extended to include nontrivial
anticommutation relations among spinor coordinates in superspace. A number of
authors have studied field theoretical consequences of the deformation of N=1
superspace arising from nonanticommutativity of coordinates \theta, while
leaving \bar{theta}'s anticommuting. This is possible in Euclidean superspace
only. In this note we present a way to extend the discussion by making both
\theta and \bar{theta} coordinates non-anticommuting in Minkowski superspace.
We present a consistent algebra for the supercoordinates, find a star-product,
and give the Wess-Zumino Lagrangian L_{WZ} within our model. It has two extra
terms due to non(anti)commutativity. The Lagrangian in Minkowski superspace is
always manifestly Hermitian and for L_{WZ} it preserves Lorentz invariance.Comment: 8 pages, added references, two-column format, published in PR
Wide dynamic range magnetic field cycler: Harnessing quantum control at low and high fields
We describe the construction of a fast field cycling device capable of
sweeping a 4-order-of-magnitude range of magnetic fields, from ~1mT to 7T, in
under 700ms. Central to this system is a high-speed sample shuttling mechanism
between a superconducting magnet and a magnetic shield, with the capability to
access arbitrary fields in between with high resolution. Our instrument serves
as a versatile platform to harness the inherent dichotomy of spin dynamics on
offer at low and high fields - in particular, the low anisotropy, fast spin
manipulation, and rapid entanglement growth at low field as well as the long
spin lifetimes, spin specific control, and efficient inductive measurement
possible at high fields. Exploiting these complementary capabilities in a
single device open up applications in a host of problems in quantum control,
sensing, and information storage, besides in nuclear hypepolarization,
relaxometry and imaging. In particular, in this paper, we focus on the ability
of the device to enable low-field hyperpolarization of 13C nuclei in diamond
via optically pumped electronic spins associated with Nitrogen Vacancy (NV)
defect centers
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