141 research outputs found
High-Resolution Measurements of the Dark Matter Halo of NGC 2976: Evidence for a Shallow Density Profile
We have obtained two-dimensional velocity fields of the dwarf spiral galaxy
NGC 2976 in Halpha and CO. The high spatial (~75 pc) and spectral (13 km/s and
2 km/s, respectively) resolution of these observations, along with our
multicolor optical and near-infrared imaging, allow us to measure the shape of
the density profile of the dark matter halo with good precision. We find that
the total (baryonic plus dark matter) mass distribution of NGC 2976 follows a
rho_tot ~ r^(-0.27 +/- 0.09) power law out to a radius of 1.8 kpc, assuming
that the observed radial motions provide no support. The density profile
attributed to the dark halo is even shallower, consistent with a nearly
constant density of dark matter over the entire observed region. A maximal disk
fit yields an upper limit to the K-band stellar mass-to-light ratio (M*/L_K) of
0.09^{+0.15}_{-0.08} M_sun/L_sun,K (including systematic uncertainties), with
the caveat that for M*/L_K > 0.19 M_sun/L_sun,K the dark matter density
increases with radius, which is unphysical. Assuming 0.10 M_sun/L_sun,K <
M*/L_K < 0.19 M_sun/L_sun,K, the dark matter density profile lies between
rho_dm ~ r^-0.17 and rho_dm ~ r^-0.01. Therefore, independent of any
assumptions about the stellar disk or the functional form of the density
profile, NGC 2976 does not contain a cuspy dark matter halo. We also
investigate some of the systematic effects that can hamper rotation curve
studies, and show that 1) longslit rotation curves are far more vulnerable to
systematic errors than two-dimensional velocity fields, 2) NGC 2976 contains
large radial motions at small radii, and 3) the Halpha and CO velocity fields
of NGC 2976 agree within their uncertainties. [slightly abridged]Comment: 30 pages, 4 tables, 13 figures (7 in color; Figures 1 and 3 are
low-resolution to save space). Accepted for publication in ApJ. Version with
full-resolution figures available at
http://astro.berkeley.edu/~bolatto/ngc2976rotation.ps (46 MB
The Distribution of Mass in the Orion Dwarf Galaxy
Dwarf galaxies are good candidates to investigate the nature of Dark Matter,
because their kinematics are dominated by this component down to small
galactocentric radii. We present here the results of detailed kinematic
analysis and mass modelling of the Orion dwarf galaxy, for which we derive a
high quality and high resolution rotation curve that contains negligible
non-circular motions and we correct it for the asymmetric drift. Moreover, we
leverage the proximity (D = 5.4 kpc) and convenient inclination (47{\deg}) to
produce reliable mass models of this system. We find that the Universal
Rotation Curve mass model (Freeman disk + Burkert halo + gas disk) fits the
observational data accurately. In contrast, the NFW halo + Freeman disk + gas
disk mass model is unable to reproduce the observed Rotation Curve, a common
outcome in dwarf galaxies. Finally, we attempt to fit the data with a MOdified
Newtonian Dynamics (MOND) prescription. With the present data and with the
present assumptions on distance, stellar mass, constant inclination and
reliability of the gaseous mass, the MOND "amplification" of the baryonic
component appears to be too small to mimic the required "dark component". The
Orion dwarf reveals a cored DM density distribution and a possible tension
between observations and the canonical MOND formalism.Comment: 8 pages, 9 figures, accepted for publication in MNRA
Gauge-invariant response functions of fermions coupled to a gauge field
We study a model of fermions interacting with a gauge field and calculate
gauge-invariant two-particle Green's functions or response functions. The
leading singular contributions from the self-energy correction are found to be
cancelled by those from the vertex correction for small and . As a
result, the remaining contributions are not singular enough to change the
leading order results of the random phase approximation. It is also shown that
the gauge field propagator is not renormalized up to two-loop order. We examine
the resulting gauge-invariant two-particle Green's functions for small and
, but for all ratios of and we conclude that they can
be described by Fermi liquid forms without a diverging effective mass.Comment: Plain Tex, 35 pages, 5 figures available upon request, Revised
Version (Expanded discussion), To be published in Physical Review B 50,
(1994) (December 15 issue
A proof-of-concept study on the use of a fluorescein-based 18F-tracer for pretargeted PET
BACKGROUND: Pretargeted immuno-PET tumor imaging has emerged as a valuable diagnostic strategy that combines the high specificity of antibody-antigen interaction with the high signal and image resolution offered by short-lived PET isotopes, while reducing the irradiation dose caused by traditional (89)Zr-labelled antibodies. In this work, we demonstrate proof of concept of a novel âtwo-stepâ immuno-PET pretargeting approach, based on bispecific antibodies (bsAbs) engineered to feature dual high-affinity binding activity for a fluorescein-based (18)F-PET tracer and tumor markers. RESULTS: A copper(I)-catalysed click reaction-based radiolabeling protocol was developed for the synthesis of fluorescein-derived molecule [(18)F]TPF. Binding of [(18)F]TPF on FITC-bearing bsAbs was confirmed. An in vitro autoradiography assay demonstrated that [(18)F]TPF could be used for selective imaging of EpCAM-expressing OVCAR3 cells, when pretargeted with EpCAMxFITC bsAb. The versatility of the pretargeting approach was showcased in vitro using a series of fluorescein-binding bsAbs directed at various established cancer-associated targets, including the pan-carcinoma cell surface marker EpCAM, EGFR, melanoma marker MCSP (aka CSPG4), and immune checkpoint PD-L1, offering a range of potential future applications for this pretargeting platform. CONCLUSION: A versatile pretargeting platform for PET imaging, which combines bispecific antibodies and a fluorescein-based (18)F-tracer, is presented. It is shown to selectively target EpCAM-expressing cells in vitro and its further evaluation with different bispecific antibodies demonstrates the versatility of the approach. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s41181-022-00155-2
Dissipational versus Dissipationless Galaxy Formation and the Dark Matter Content of Galaxies
We examine two extreme models for the build-up of the stellar component of
luminous elliptical galaxies. In one case, we assume the build-up of stars is
dissipational, with centrally accreted gas radiating away its orbital and
thermal energy; the dark matter halo will undergo adiabatic contraction and the
central dark matter density profile will steepen. For the second model, we
assume the central galaxy is assembled by a series of dissipationless mergers
of stellar clumps that have formed far from the nascent galaxy. In order to be
accreted, these clumps lose their orbital energy to the dark matter halo via
dynamical friction, thereby heating the central dark matter and smoothing the
dark matter density cusp. The central dark matter density profiles differ
drastically between these models. For the isolated elliptical galaxy, NGC 4494,
the central dark matter densities follow the power-laws r^(-0.2) and r^(-1.7)
for the dissipational and dissipationless models, respectively. By matching the
dissipational and dissipationless models to observations of the stellar
component of elliptical galaxies, we examine the relative contributions of
dissipational and dissipationless mergers to the formation of elliptical
galaxies and look for observational tests that will distinguish between these
models. Comparisons to strong lensing brightest cluster galaxies yield median
M*/L_B ratios of 2.1+/-0.8 and 5.2+/-1.7 at z=0.39 for the dissipational and
dissipationless models, respectively. For NGC 4494, the best-fit dissipational
and dissipationless models have M*/L_B=2.97 and 3.96. Comparisons to expected
stellar mass-to-light ratios from passive evolution and population syntheses
appear to rule out a purely dissipational formation mechanism for the central
stellar regions of giant elliptical galaxies.Comment: 15 pages, 9 figures, accepted to Ap
Experimental loophole-free violation of a Bell inequality using entangled electron spins separated by 1.3 km
For more than 80 years, the counterintuitive predictions of quantum theory
have stimulated debate about the nature of reality. In his seminal work, John
Bell proved that no theory of nature that obeys locality and realism can
reproduce all the predictions of quantum theory. Bell showed that in any local
realist theory the correlations between distant measurements satisfy an
inequality and, moreover, that this inequality can be violated according to
quantum theory. This provided a recipe for experimental tests of the
fundamental principles underlying the laws of nature. In the past decades,
numerous ingenious Bell inequality tests have been reported. However, because
of experimental limitations, all experiments to date required additional
assumptions to obtain a contradiction with local realism, resulting in
loopholes. Here we report on a Bell experiment that is free of any such
additional assumption and thus directly tests the principles underlying Bell's
inequality. We employ an event-ready scheme that enables the generation of
high-fidelity entanglement between distant electron spins. Efficient spin
readout avoids the fair sampling assumption (detection loophole), while the use
of fast random basis selection and readout combined with a spatial separation
of 1.3 km ensure the required locality conditions. We perform 245 trials
testing the CHSH-Bell inequality and find . A
null hypothesis test yields a probability of that a local-realist
model for space-like separated sites produces data with a violation at least as
large as observed, even when allowing for memory in the devices. This result
rules out large classes of local realist theories, and paves the way for
implementing device-independent quantum-secure communication and randomness
certification.Comment: Raw data will be made available after publicatio
Understanding Dwarf Galaxies in order to Understand Dark Matter
Much progress has been made in recent years by the galaxy simulation
community in making realistic galaxies, mostly by more accurately capturing the
effects of baryons on the structural evolution of dark matter halos at high
resolutions. This progress has altered theoretical expectations for galaxy
evolution within a Cold Dark Matter (CDM) model, reconciling many earlier
discrepancies between theory and observations. Despite this reconciliation, CDM
may not be an accurate model for our Universe. Much more work must be done to
understand the predictions for galaxy formation within alternative dark matter
models.Comment: Refereed contribution to the Proceedings of the Simons Symposium on
Illuminating Dark Matter, to be published by Springe
Non-minimally coupled dark matter: effective pressure and structure formation
We propose a phenomenological model in which a non-minimal coupling between
gravity and dark matter is present in order to address some of the apparent
small scales issues of \lcdm model. When described in a frame in which gravity
dynamics is given by the standard Einstein-Hilbert action, the non-minimal
coupling translates into an effective pressure for the dark matter component.
We consider some phenomenological examples and describe both background and
linear perturbations. We show that the presence of an effective pressure may
lead these scenarios to differ from \lcdm at the scales where the non-minimal
coupling (and therefore the pressure) is active. In particular two effects are
present: a pressure term for the dark matter component that is able to reduce
the growth of structures at galactic scales, possibly reconciling simulations
and observations; an effective interaction term between dark matter and baryons
that could explain observed correlations between the two components of the
cosmic fluid within Tully-Fisher analysis.Comment: 18 pages, 6 figures, references added. Published in JCA
Design, Synthesis, and Biological Evaluation of 2-Hydroxy-4-phenylthiophene-3-carbonitrile as PD-L1 Antagonist and Its Comparison to Available Small Molecular PD-L1 Inhibitors
In search of a potent small molecular PD-L1 inhibitor, we designed and synthesized a compound based on a 2-hydroxy-4-phenylthiophene-3-carbonitrile moiety. Ligand's performance was tested in vitro and compared side-by-side with a known PD-L1 antagonist with a proven bioactivity BMS1166. Subsequently, we modified both compounds to allow 18F labeling that could be used for PET imaging. Radiolabeling, which is used in drug development and diagnosis, was applied to investigate the properties of those ligands and test them against tissue sections with diverse expression levels of PD-L1. We confirmed biological activity toward hPD-L1 for this inhibitor, comparable with BMS1166, while holding enhanced pharmacological properties. </p
Design, synthesis, and biological evaluation of 2-hydroxy-4-phenylthiophene-3-carbonitrile as PD-L1 antagonist and its comparison to available small molecular PD-L1 inhibitors
In search of a potent small molecular PD-L1 inhibitor, we designed and synthesized a compound based on a 2-hydroxy-4-phenylthiophene-3-carbonitrile moiety. Ligandâs performance was tested in vitro and compared side-by-side with a known PD-L1 antagonist with a proven bioactivity BMS1166. Subsequently, we modified both compounds to allow 18F labeling that could be used for PET imaging. Radiolabeling, which is used in drug development and diagnosis, was applied to investigate the properties of those ligands and test them against tissue sections with diverse expression levels of PD-L1. We confirmed biological activity toward hPD-L1 for this inhibitor, comparable with BMS1166, while holding enhanced pharmacological properties
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