214 research outputs found
The Mutual Interaction Between Population III Stars and Self-Annihilating Dark Matter
We use cosmological simulations of high-redshift minihalos to investigate the
effect of dark matter annihilation (DMA) on the collapse of primordial gas. We
numerically investigate the evolution of the gas as it assembles in a
Population III stellar disk. We find that when DMA effects are neglected, the
disk undergoes multiple fragmentation events beginning at ~ 500 yr after the
appearance of the first protostar. On the other hand, DMA heating and
ionization of the gas speeds the initial collapse of gas to protostellar
densities and also affects the stability of the developing disk against
fragmentation, depending on the DM distribution. We compare the evolution when
we model the DM density with an analytical DM profile which remains centrally
peaked, and when we simulate the DM profile using N-body particles (the 'live'
DM halo). When utilizing the analytical DM profile, DMA suppresses disk
fragmentation for ~ 3500 yr after the first protostar forms, in agreement with
earlier work. However, when using a 'live' DM halo, the central DM density peak
is gradually flattened due to the mutual interaction between the DM and the
rotating gaseous disk, reducing the effects of DMA on the gas, and enabling
secondary protostars of mass ~ 1 M_sol to be formed within ~ 900 yr. These
simulations demonstrate that DMA is ineffective in suppressing gas collapse and
subsequent fragmentation, rendering the formation of long-lived dark stars
unlikely. However, DMA effects may still be significant in the early collapse
and disk formation phase of primordial gas evolution.Comment: 17 pages, 11 figures, to appear in MNRA
Complications After Systematic, Random, and Image-guided Prostate Biopsy
Prostate biopsy (PB) represents the gold standard method to confirm the presence of cancer. In addition to traditional random or systematic approaches, a magnetic resonance imaging (MRI)-guided technique has been introduced recently.
OBJECTIVE:
To perform a systematic review of complications after transrectal ultrasound (TRUS)-guided, transperineal, and MRI-guided PB.
EVIDENCE ACQUISITION:
We performed a systematic literature search of Web of Science, Embase, and Scopus databases up to October 2015, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Complications and mortality following random, systematic, and image-guided PBs were reviewed. Eighty-five references were included.
EVIDENCE SYNTHESIS:
The most frequent complication after PB was minor and self-limiting bleeding (hematuria and hematospermia), regardless of the biopsy approach. Occurrence of rectal bleeding was comparable for traditional TRUS-guided and image-guided PBs. Almost 25% of patients experienced lower urinary tract symptoms, but only a few had urinary retention, with higher rates after a transperineal approach. Temporary erectile dysfunction was not negligible, with a return to baseline after 1-6 mo. The incidence of infective complications is increasing, with higher rates among men with medical comorbidities and older age. Transperineal and in-bore MRI-targeted biopsy may reduce the risk of severe infectious complications. Mortality after PB is uncommon, regardless of biopsy technique.
CONCLUSIONS:
Complications after PB are frequent but often self-limiting. The incidence of hospitalization due to severe infections is continuously increasing. The patient's general health status, risk factors, and likelihood of antimicrobial resistance should be carefully appraised before scheduling a PB.
PATIENT SUMMARY:
We reviewed the variety and incidence of complications after prostate biopsy. Even if frequent, complications seldom represent a problem for the patient. The most troublesome complications are infections. To minimize this risk, the patient's medical condition should be carefully evaluated before biopsy
Effect of Population III Multiplicity on Dark Star Formation
We numerically study the mutual interaction between dark matter (DM) and
Population III (Pop III) stellar systems in order to explore the possibility of
Pop III dark stars within this physical scenario. We perform a cosmological
simulation, initialized at z ~ 100, which follows the evolution of gas and DM.
We analyze the formation of the first minihalo at z ~ 20 and the subsequent
collapse of the gas to densities of 10^12 cm^-3. We then use this simulation to
initialize a set of smaller-scale `cut-out' simulations in which we further
refine the DM to have spatial resolution similar to that of the gas. We test
multiple DM density profiles, and we employ the sink particle method to
represent the accreting star-forming region. We find that, for a range of DM
configurations, the motion of the Pop III star-disk system serves to separate
the positions of the protostars with respect to the DM density peak, such that
there is insufficient DM to influence the formation and evolution of the
protostars for more than ~ 5000 years. In addition, the star-disk system causes
gravitational scattering of the central DM to lower densities, further
decreasing the influence of DM over time. Any DM-powered phase of Pop III stars
will thus be very short-lived for the typical multiple system, and DM will not
serve to significantly prolong the life of Pop III stars.Comment: 16 pages, 11 figures, to appear in MNRA
Systematic Review of Complications of Prostate Biopsy
AbstractContextProstate biopsy is commonly performed for cancer detection and management. The benefits and risks of prostate biopsy are germane to ongoing debates about prostate cancer screening and treatment.ObjectiveTo perform a systematic review of complications from prostate biopsy.Evidence acquisitionA literature search was performed using PubMed and Embase, supplemented with additional references. Articles were reviewed for data on the following complications: hematuria, rectal bleeding, hematospermia, infection, pain, lower urinary tract symptoms (LUTS), urinary retention, erectile dysfunction, and mortality.Evidence synthesisAfter biopsy, hematuria and hematospermia are common but typically mild and self-limiting. Severe rectal bleeding is uncommon. Despite antimicrobial prophylaxis, infectious complications are increasing over time and are the most common reason for hospitalization after biopsy. Pain may occur at several stages of prostate biopsy and can be mitigated by anesthetic agents and anxiety-reduction techniques. Up to 25% of men have transient LUTS after biopsy, and <2% have frank urinary retention, with slightly higher rates reported after transperineal template biopsy. Biopsy-related mortality is rare.ConclusionsPreparation for biopsy should include antimicrobial prophylaxis and pain management. Prostate biopsy is frequently associated with minor bleeding and urinary symptoms that usually do not require intervention. Infectious complications can be serious, requiring prompt management and continued work into preventative strategies
Diagnostic accuracy of magnetic resonance imaging targeted biopsy techniques compared to transrectal ultrasound guided biopsy of the prostate: a systematic review and meta-analysis
Background: Multiparametric MRI localizes cancer in the prostate, allowing for MRI guided biopsy (MRI-GB) 43 alongside transrectal ultrasound-guided systematic biopsy (TRUS-GB). Three MRI-GB approaches exist; visual estimation (COG-TB); fusion software-assisted (FUS-TB) and MRI âin-boreâ biopsy (IB-TB). It is unknown whether any of these are superior. We conducted a systematic review and meta-analysis to address three questions. First, whether MRI-GB is superior to TRUS-GB at detecting clinically significant PCa (csPCa). Second, whether MRI-GB is superior to TRUS-GB at avoiding detection of insignificant PCa. Third, whether any MRI-GB strategy is superior at detecting csPCa. Methods: A systematic literature review from 2015 to 2019 was performed in accordance with the START recommendations. Studies reporting PCa detection rates, employing MRI-GB and TRUS-GB were included and evaluated using the QUADAS-2 checklist. 1553 studies were found, of which 43 were included in the meta-analysis. Results: For csPCa, MRI-GB was superior in detection to TRUS-GB (0.83 vs. 0.63 [p = 0.02]). MRI-GB was superior in detection to TRUS-GB at avoiding detection of insignificant PCa. No MRI-GB technique was superior at detecting csPCa (IB-TB 0.87; COG TB 0.81; FUS-TB 0.81, [p = 0.55]). There was significant heterogeneity observed between the included studies. Conclusions: In patients with suspected PCa on MRI, MRI-GB offers superior rates of csPCa detection and reduces detection of insignificant PCa compared to TRUS-GB. No individual MRI-GB technique was found to be better in csPCa detection. Prospective adequately powered randomized controlled trials are required
Stellar black holes at the dawn of the universe
It is well established that between 380000 and 1 billion years after the Big
Bang the Inter Galactic Medium (IGM) underwent a "phase transformation" from
cold and fully neutral to warm (~10^4 K) and ionized. Whether this phase
transformation was fully driven and completed by photoionization by young hot
stars is a question of topical interest in cosmology. AIMS. We propose here
that besides the ultraviolet radiation from massive stars, feedback from
accreting black holes in high-mass X-ray binaries (BH-HMXBs) was an additional,
important source of heating and reionization of the IGM in regions of low gas
density at large distances from star-forming galaxies. METHODS. We use current
theoretical models on the formation and evolution of primitive massive stars of
low metallicity, and the observations of compact stellar remnants in the near
and distant universe, to infer that a significant fraction of the first
generations of massive stars end up as BH-HMXBs. The total number of energetic
ionizing photons from an accreting stellar black hole in an HMXB is comparable
to the total number of ionizing photons of its progenitor star. However, the
X-ray photons emitted by the accreting black hole are capable of producing
several secondary ionizations and the ionizing power of the resulting black
hole could be greater than that of its progenitor. Feedback by the large
populations of BH-HMXBs heats the IGM to temperatures of ~10^4 K and maintains
it ionized on large distance scales. BH-HMXBs determine the early thermal
history of the universe and mantain it as ionized over large volumes of space
in regions of low density. This has a direct impact on the properties of the
faintest galaxies at high redshifts, the smallest dwarf galaxies in the local
universe, and on the existing and future surveys at radio wavelengths of atomic
hydrogen in the early universe.Comment: 7 pages, 2 figures, accepted to be published in Astronomy and
Astrophysic
Top 100 Urology Influences on Twitter: Is Social Media Influence Associated with Academic Impact?
Introduction: The purpose of this cross-sectional study is to identify and describe the top 100 urology influencers on the social media platform Twitter. Furthermore, we aim to correlate each individual\u27s Twitter influence with academic impact in urology.
Materials and Methods: Twitter influence scores for the topic search âurologyâ were collected in April 2022 using the Right Relevance software, which accounts for the individual\u27s connections (followers/following) to other influencers in urology as well as engagement (likes, retweets, and views) on the platform. The top 100 personal accounts with the highest computed scores were linked to individualsâ names, all-time h-index, geographic location, specialty, sex, and board certification. We examined the Pearson correlation coefficient between influence rank and h-index.
Results: We identified the top 100 Twitter influencers on the topic of âurology.â The majority are from the United States (63%), male (85%), and are practicing urologists (93%). Ninety-three percent (93%) of U.S. urology influencers are board certified. Only 22 out of the 50 states are represented. The second most common country is the United Kingdom with 11 urology influencers. The median all-time h-index is 41.5 (IQR: 27 â 55.5). There is a weak positive coefficient (r=0.26) between the influence rank and h-index (p=0.021).
Conclusions: The top Twitter influencers in urology are mostly Board-certified U.S. urologists. Collectively, influencers have a relatively greater academic impact compared to the average urologist, although there is a weak positive correlation between Twitter influence and h-index among top Twitter influencers
Rotation Speed of the First Stars
We estimate the rotation speed of Population III (Pop III) stars within a
minihalo at z ~ 20 using a smoothed particle hydrodynamics (SPH) simulation,
beginning from cosmological initial conditions. We follow the evolution of the
primordial gas up to densities of 10^12 cm^-3. Representing the growing
hydrostatic cores with accreting sink particles, we measure the velocities and
angular momenta of all particles that fall onto these protostellar regions.
This allows us to record the angular momentum of the sinks and estimate the
rotational velocity of the Pop III stars expected to form within them. The
rotation rate has important implications for the evolution of the star, the
fate encountered at the end of its life, and the potential for triggering a
gamma-ray burst (GRB). We find that there is sufficient angular momentum to
yield rapidly rotating stars (> 1000 km s^-1, or near break-up speeds). This
indicates that Pop III stars likely experienced strong rotational mixing,
impacting their structure and nucleosynthetic yields. A subset of them was also
likely to result in hypernova explosions, and possibly GRBs.Comment: 14 pages, 7 figures, accepted for publication in MNRA
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