494 research outputs found
Dwarf satellite galaxies in the modified dynamics
In the modified dynamics (MOND) the inner workings of dwarf satellites can be
greatly affected by their mother galaxy-over and beyond its tidal effects.
Because of MOND's nonlinearity a system's internal dynamics can be altered by
an external field in which it is immersed (even when this field, by itself, is
constant in space). As a result, the size and velocity dispersion of the
satellite vary as the external field varies along its orbit. A notable outcome
of this is a substantial increase in the dwarf's vulnerability to eventual
tidal disruption-rather higher than Newtonian dynamics (with a dark-matter
halo) would lead us to expect for a satellite with given observed parameters.Comment: 15 pages with 5 embedded figures; Astrophysical J in press Corrected
error in names of author
MOND and the Universal Rotation Curve: similar phenomenologies
The Modified Newtonian Dynamics (MOND) and the Universal Rotation Curve (URC)
are two ways to describe the general properties of rotation curves, with very
different approaches concerning dark matter and gravity. Phenomenological
similarities between the two approaches are studied by looking for properties
predicted in one framework that are also reproducible in the other one. First,
we looked for the analogous of the URC within the MOND framework. Modifying in
an observationally-based way the baryonic contribution Vbar to the rotation
curve predicted by the URC, and applying the MOND formulas to this Vbar, leads
to a "MOND URC" whose properties are remarkably similar to the URC. Second, it
is shown that the URC predicts a tight mass discrepancy - acceleration
relation, which is a natural outcome of MOND. With the choice of Vbar that
minimises the differences between the URC and the "MOND URC" the relation is
almost identical to the observational one. This similarity between the
observational properties of MOND and the URC has no implications about the
validity of MOND as a theory of gravity, but it shows that it can reproduce in
detail the phenomenology of disk galaxies' rotation curves, as described by the
URC. MOND and the URC, even though they are based on totally different
assumptions, are found to have very similar behaviours and to be able to
reproduce each other's properties fairly well, even with the simple assumptions
made on the luminosity dependence of the baryonic contribution to the rotation
curve.Comment: Accepted for publication in ApJ. 8 pages, 5 figure
On the gravitational potential of modified Newtonian dynamics
Producción CientíficaThe mathematical structure of the Poisson equation of Modified Newtonian Dynamics
(MOND) is studied. The appropriate setting turns out to be an Orlicz-Sobolev
space whose Orlicz function is related to Milgrom’s μ-function, where there exists
existence and uniqueness of weak solutions. Since these do not have in principle
much regularity, a further study is performed where the gravitational field is not
too large, where MOND is most relevant. In that case the field turns out to be
H¨older continuous. Quasilinear MOND is also analyzed
Constraining Lyman-alpha spatial offsets at from VANDELS slit spectroscopy
We constrain the distribution of spatially offset Lyman-alpha emission
(Ly) relative to rest-frame ultraviolet emission in high
redshift () Lyman-break galaxies (LBGs) exhibiting Ly emission
from VANDELS, a VLT/VIMOS slit-spectroscopic survey of the CANDELS Ultra Deep
Survey and Chandra Deep Field South fields (
total). Because slit spectroscopy compresses two-dimensional spatial
information into one spatial dimension, we use Bayesian inference to recover
the underlying Ly spatial offset distribution. We model the
distribution using a 2D circular Gaussian, defined by a single parameter
, the standard deviation expressed in polar
coordinates. Over the entire redshift range of our sample (), we find
kpc ( conf.),
corresponding to arcsec at . We also find that
decreases significantly with redshift. Because
Ly spatial offsets can cause slit-losses, the decrease in
with redshift can partially explain the increase
in the fraction of Ly emitters observed in the literature over this
same interval, although uncertainties are still too large to reach a strong
conclusion. If continues to decrease into the
reionization epoch, then the decrease in Ly transmission from galaxies
observed during this epoch might require an even higher neutral hydrogen
fraction than what is currently inferred. Conversely, if spatial offsets
increase with the increasing opacity of the IGM, slit losses may explain some
of the drop in Ly transmission observed at . Spatially resolved
observations of Ly and UV continuum at are needed to settle the
issue.Comment: Submitted to MNRA
Recommended from our members
A phase II study of temozolomide vs. procarbazine in patients with glioblastoma multiforme at first relapse.
A randomized, multicentre, open-label, phase II study compared temozolomide (TMZ), an oral second-generation alkylating agent, and procarbazine (PCB) in 225 patients with glioblastoma multiforme at first relapse. Primary objectives were to determine progression-free survival (PFS) at 6 months and safety for TMZ and PCB in adult patients who failed conventional treatment. Secondary objectives were to assess overall survival and health-related quality of life (HRQL). TMZ was given orally at 200 mg/m(2)/day or 150 mg/m(2)/day (prior chemotherapy) for 5 days, repeated every 28 days. PCB was given orally at 150 mg/m(2)/day or 125 mg/m(2)/day (prior chemotherapy) for 28 days, repeated every 56 days. HRQL was assessed using the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30 [+3]) and the Brain Cancer Module 20 (BCM20). The 6-month PFS rate for patients who received TMZ was 21%, which met the protocol objective. The 6-month PFS rate for those who received PCB was 8% (P = 0.008, for the comparison). Overall PFS significantly improved with TMZ, with a median PFS of 12.4 weeks in the TMZ group and 8.32 weeks in the PCB group (P = 0.0063). The 6-month overall survival rate for TMZ patients was 60% vs. 44% for PCB patients (P = 0.019). Freedom from disease progression was associated with maintenance of HRQL, regardless of treatment received. TMZ had an acceptable safety profile; most adverse events were mild or moderate in severity
Dyspnea in Patients Receiving Radical Radiotherapy for Non-Small Cell Lung Cancer: A Prospective Study
Background and Purpose: Dyspnea is an important symptomatic endpoint for
assessment of radiation-induced lung injury (RILI) following radical radiotherapy in
locally advanced disease, which remains the mainstay of treatment at the time of
significant advances in therapy including combination treatments with immunotherapy
and chemotherapy and the use of local ablative radiotherapy techniques. We investigated
the relationship between dose-volume parameters and subjective changes in dyspnea as
a measure of RILI and the relationship to spirometry.
Material and Methods: Eighty patients receiving radical radiotherapy for non-small cell
lung cancer were prospectively assessed for dyspnea using two patient-completed tools:
EORTC QLQ-LC13 dyspnea quality of life assessment and dyspnea visual analogue scale
(VAS). Global quality of life, spirometry and radiation pneumonitis grade were also
assessed. Comparisons were made with lung dose-volume parameters.
Results: The median survival of the cohort was 26 months. In the evaluable group of 59
patients there were positive correlations between lung dose-volume parameters and a
change in dyspnea quality of life scale at 3 months (V30 p=0.017; V40 p=0.026; V50
p=0.049; mean lung dose p=0.05), and a change in dyspnea VAS at 6 months (V30
p=0.05; V40 p=0.026; V50 p=0.028) after radiotherapy. Lung dose-volume parameters
predicted a 10% increase in dyspnea quality of life score at 3 months (V40; p=0.041, V50;
p=0.037) and dyspnea VAS score at 6 months (V40; p=0.027) post-treatment.
Conclusions: Worsening of dyspnea is an important symptom of RILI. We demonstrate a
relationship between lung dose-volume parameters and a 10% worsening of subjectiv
Radiosurgery for pituitary adenomas: evaluation of its efficacy and safety
<p>Abstract</p> <p>Object</p> <p>To assess the effects of radiosurgery (RS) on the radiological and hormonal control and its toxicity in the treatment of pituitary adenomas.</p> <p>Methods</p> <p>Retrospective analysis of 42 patients out of the first 48 consecutive patients with pituitary adenomas treated with RS between 1999 and 2008 with a 6 months minimum follow-up. RS was delivered with Gamma Knife as a primary or adjuvant treatment. There were 14 patients with non-secretory adenomas and, among functioning adenomas, 9 were prolactinomas, 9 were adrenocorticotropic hormone-secreting and 10 were growth hormone-secreting tumors. Hormonal control was defined as hormonal response (decline of more than 50% from the pre-RS levels) and hormonal normalization. Radiological control was defined as stasis or shrinkage of the tumor. Hypopituitarism and visual deficit were the morbidity outcomes. Hypopituitarism was defined as the initiation of any hormone replacement therapy and visual deficit as loss of visual acuity or visual field after RS.</p> <p>Results</p> <p>The median follow-up was 42 months (6-109 months). The median dose was 12,5 Gy (9 - 15 Gy) and 20 Gy (12 - 28 Gy) for non-secretory and secretory adenomas, respectively. Tumor growth was controlled in 98% (41 in 42) of the cases and tumor shrinkage ocurred in 10% (4 in 42) of the cases. The 3-year actuarial rate of hormonal control and normalization were 62,4% and 37,6%, respectively, and the 5-year actuarial rate were 81,2% and 55,4%, respectively. The median latency period for hormonal control and normalization was, respectively, 15 and 18 months. On univariate analysis, there were no relationships between median dose or tumoral volume and hormonal control or normalization. There were no patients with visual deficit and 1 patient had hypopituitarism after RS.</p> <p>Conclusions</p> <p>RS is an effective and safe therapeutic option in the management of selected patients with pituitary adenomas. The short latency of the radiation response, the highly acceptable radiological and hormonal control and absence of complications at this early follow-up are consistent with literature.</p
Galactic kinematics with modified Newtonian dynamics
We look for observational signatures that could discriminate between
Newtonian and modified Newtonian (MOND) dynamics in the Milky Way, in view of
the advent of large astrometric and spectroscopic surveys. Indeed, a typical
signature of MOND is an apparent disk of "phantom" dark matter, which is
uniquely correlated with the visible disk-density distribution. Due to this
phantom dark disk, Newtonian models with a spherical halo have different
signatures from MOND models close to the Galactic plane. The models can thus be
differentiated by measuring dynamically (within Newtonian dynamics) the disk
surface density at the solar radius, the radial mass gradient within the disk,
or the velocity ellipsoid tilt angle above the Galactic plane. Using the most
realistic possible baryonic mass model for the Milky Way, we predict that, if
MOND applies, the local surface density measured by a Newtonist will be
approximately 78 Msun/pc2 within 1.1 kpc of the Galactic plane, the dynamically
measured disk scale-length will be enhanced by a factor of 1.25 with respect to
the visible disk scale-length, and the local vertical tilt of the velocity
ellipsoid at 1 kpc above the plane will be approximately 6 degrees. None of
these tests can be conclusive for the present-day accuracy of Milky Way data,
but they will be of prime interest with the advent of large surveys such as
GAIA.Comment: 5 page
Infiltrative growth pattern of prostate cancer is associated with lower uptake on PSMA PET and reduced diffusion restriction on mpMRI
Purpose: Recently, a significant association was shown between novel growth patterns on histopathology of prostate cancer (PCa) and prostate-specific membrane antigen (PSMA) uptake on [68Ga]PSMA-PET. It is the aim of this study to evaluate the association between these growth patterns and ADC (mm2/1000 s) values in comparison to [68Ga]PSMA uptake on PET/MRI.
Methods: We retrospectively evaluated patients who underwent [68Ga]PSMA PET/MRI for staging or biopsy guidance, followed by radical prostatectomy at our institution between 07/2016 and 01/2020. The dominant lesion per patient was selected based on histopathology and correlated to PET/MRI in a multidisciplinary meeting, and quantified using SUVmax for PSMA uptake and ADCmean for diffusion restriction. PCa growth pattern was classified as expansive (EXP) or infiltrative (INF) according to its properties of forming a tumoral mass or infiltrating diffusely between benign glands by two independent pathologists. Furthermore, the corresponding WHO2016 ISUP tumor grade was evaluated. The t test was used to compare means, Pearson's test for categorical correlation, Cohen's kappa test for interrater agreement, and ROC curve to determine the best cutoff.
Results: Sixty-two patients were included (mean PSA 11.7 ± 12.5). The interrater agreement between both pathologists was almost perfect with κ = 0.81. While 25 lesions had an EXP-growth with an ADCmean of 0.777 ± 0.109, 37 showed an INF-growth with a significantly higher ADCmean of 1.079 ± 0.262 (p < 0.001). We also observed a significant difference regarding PSMA SUVmax for the EXP-growth (19.2 ± 10.9) versus the INF-growth (9.4 ± 6.2, p < 0.001). Within the lesions encompassing the EXP- or the INF-growth, no significant correlation between the ISUP groups and ADCmean could be observed (p = 0.982 and p = 0.861, respectively).
Conclusion: PCa with INF-growth showed significantly lower SUVmax and higher ADCmean values compared to PCa with EXP-growth. Within the growth groups, ADCmean values were independent from ISUP grading.
Keywords: Diffusion-weighted imaging; MRI; PSMA PET/MRI; Prostate cancer; Radical prostatectom
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