2,527 research outputs found
Sexually Transmitted Disease and Male Infertility: A Systematic Review
Context Theoretically, sexually transmitted diseases (STDs) have the potential to disrupt male fertility; however, the topic remains controversial. Objective To describe the possible association between STDs and male infertility and to explore possible pathophysiologic mechanisms. Evidence acquisition We performed a systematic literature review in accordance with the PRISMA guidelines. PubMed, Embase, and the Cochrane Library were searched for articles published before January 1, 2016, using the MeSH terms for a variety of STDs and infertility. The search was restricted to human studies performed in men and published in English. Studies were included if they contained original data on a possible association or a cause-and-effect relationship between STD and male infertility. Studies were considered only if they included an appropriate control group and/or comprehensive laboratory data. Due to heterogeneity in the literature, a qualitative analysis was performed. Evidence synthesis Relevant studies on Chlamydia trachomatis, genital mycoplasmas, Neisseria gonorrhoeae, Trichomonas vaginalis, and viral infections were identified. For all pathogens, the studies were contradictory and generally of limited quality. In studies confirming an association, there was a tendency for authors to perform multiple analyses without appropriate corrections and to subsequently focus solely on outcomes that seemed to suggest a positive association; however, the body of literature that does not confirm an association between STDs and male infertility is also of inadequate quality. The data regarding possible pathophysiologic mechanisms are inconclusive. Conclusions There may be an association between STDs and male infertility of unknown genesis and possibly with different pathogenic mechanisms for different pathogens. Alternatively, some STDs may cause male infertility, whereas others may not; however, there is hardly a strong correlation. High-quality studies of the subject are needed. Patient summary Sexually transmitted diseases may cause male infertility through unknown mechanisms; however, from the available research, we cannot be sure that there is an association, and more studies are needed
The aging male: investigation, treatment and monitoring of late-onset hypogonadism in males
Androgen deficiency in the aging male has become a topic of increasing interest and debate throughout the world. The demographics clearly demonstrate the increasing percentage of the population that is in the older age groups. The data also support the concept that testosterone falls progressively with age and that a significant percentage of men over the age of 60 years have serum testosterone levels that are below the lower limits of young adults (age 20-30 years) men. The principal questions raised by these observations are whether older hypogonadal men will benefit from testosterone treatment and what will be the risks associated with such intervention. The past decade has brought evidence of benefit of androgen treatment on multiple target organs of hypogonadal men and recent studies show short-term beneficial effects of testosterone in older men that are similar to those in younger men. Long-term data on the effects of testosterone treatment in the older population are limited and specific risk data on the prostate and cardiovascular systems are needed. Answers to key questions of functional benefits that may retard frailty of the elderly are not yet available. The recommendations described below were prepared for the International Society of Andrology (ISA) and the International Society for the Study of the Aging Male (ISSAM) following a panel discussion with active participation from the audience sponsored by the ISA on the topic at the 4th ISSAM Congress in Prague in February 2004.peer-reviewe
On the normalisation of the cosmic star formation history
Strong constraints on the cosmic star formation history (SFH) have recently
been established using ultraviolet and far-infrared measurements, refining the
results of numerous measurements over the past decade. Taken together, the most
recent and robust data indicate a compellingly consistent picture of the SFH
out to redshift z~6, with especially tight constraints for z<~1. We fit these
data with simple analytical forms, and derive conservative bands to indicate
possible variations from the best fits. Since the z<~1 SFH data are quite
precise, we investigate the sequence of assumptions and corrections that
together affect the SFH normalisation, to test their accuracy, both in this
redshift range and beyond. As lower limits on this normalisation, we consider
the evolution in stellar mass density, metal mass density, and supernova rate
density, finding it unlikely that the SFH normalisation is much lower than
indicated by our direct fit. Additionally, predictions from the SFH for
supernova type Ia rate densities tentatively suggests delay times of ~3 Gyr. As
a corresponding upper limit on the SFH normalisation, we consider the
Super-Kamiokande (SK) limit on the electron antineutrino flux from past
core-collapse supernovae, which applies primarily to z<~1. We find consistency
with the SFH only if the neutrino temperatures from SN events are relatively
modest. Constraints on the assumed initial mass function (IMF) also become
apparent. The traditional Salpeter IMF, assumed for convenience by many
authors, is known to be a poor representation at low stellar masses (<~ 1 solar
mass), and we show that recently favoured IMFs are also constrained. In
particular, somewhat shallow, or top-heavy, IMFs may be preferred, although
they cannot be too top-heavy. (Abridged)Comment: 15 pages, 8 figures, accepted for publication in ApJ, major revisions
following referee's comment
The Stellar Initial Mass Function in the Galactic Center
Massive stars define the upper limits of the star formation process, dominate
the energetics of their local environs, and significantly affect the chemical
evolution of galaxies. Their role in starburst galaxies and the early Universe
is likely to be important, but we still do not know the maximum mass that a
star can possess, i.e.``the upper mass cutoff.'' I will discuss results from a
program to measure the upper mass cutoff and IMF slope in the Galactic Center.
The results suggest that the IMF in the Galactic center may deviate
significantly from the Salpeter value, and that there may be an upper mass
cutoff to the initial mass function of 150 Msun.Comment: To be published in the IMF@50 conference proceeding
The scale-free character of the cluster mass function and the universality of the stellar IMF
Our recent determination of a Salpeter slope for the IMF in the field of 30
Doradus (Selman and Melnick 2005) appears to be in conflict with simple
probabilistic counting arguments advanced in the past to support observational
claims of a steeper IMF in the LMC field. In this paper we re-examine these
arguments and show by explicit construction that, contrary to these claims, the
field IMF is expected to be exactly the same as the stellar IMF of the clusters
out of which the field was presumably formed. We show that the current data on
the mass distribution of clusters themselves is in excellent agreement with our
model, and is consistent with a single spectrum {\it by number of stars} of the
type with beta between -1.8 and -2.2 down to the smallest clusters
without any preferred mass scale for cluster formation. We also use the random
sampling model to estimate the statistics of the maximal mass star in clusters,
and confirm the discrepancy with observations found by Weidner and Kroupa
(2006). We argue that rather than signaling the violation of the random
sampling model these observations reflect the gravitationally unstable nature
of systems with one very large mass star. We stress the importance of the
random sampling model as a \emph{null hypothesis} whose violation would signal
the presence of interesting physics.Comment: 9 pages emulateap
Universal Negative Poisson Ratio of Self Avoiding Fixed Connectivity Membranes
We determine the Poisson ratio of self-avoiding fixed-connectivity membranes,
modeled as impenetrable plaquettes, to be sigma=-0.37(6), in statistical
agreement with the Poisson ratio of phantom fixed-connectivity membranes
sigma=-0.32(4). Together with the equality of critical exponents, this result
implies a unique universality class for fixed-connectivity membranes. Our
findings thus establish that physical fixed-connectivity membranes provide a
wide class of auxetic (negative Poisson ratio) materials with significant
potential applications in materials science.Comment: 4 pages, 3 figures, LaTeX (revtex) Published version - title changed,
one figure improved and one reference change
Molecular clouds under the influence of massive stars in the Galactic HII region G353.2+0.9
The Galactic HII region G353.2+0.9 is excited by the massive open cluster
Pismis-24. By analyzing (sub-)mm molecular-line and -continuum we study the
detailed morphology of the gas and dust, as well as their physical parameters
and their variation across the PDR. We observed various molecules and
transitions to derive the physical properties of the molecular gas through line
ratios, and both LTE and non-LTE analyses. The physical properties of the gas
were derived with a Bayesian approach for the non-LTE analysis. Based on the
continuum data at 870 micron, we derived the dust mass and the column density
of H2, and thus the molecular abundances. The total mass of the gas in the
region is ca. 2000 Mo, while that of the dust is ca. 21 Mo. A velocity gradient
in the region suggests that the expansion of the ionized gas is pushing the
molecular gas away from the observer. We unambiguously identify the ionization
front, at the location of which we detect an increase in gas density and
temperature. We find at least 14 clumps at different positions and LSR
velocities. We derive kinetic temperatures in the ranges 11-45 K (CS) and 20-45
K (CN). The H2 number density is typically around 1e5 cm^-3 from CS and few 1e5
cm^-3 from CN, with maxima above 1e6 cm^-3. The abundances of the molecules
observed vary across the region, and appear to be higher in regions further
away from the ionization front.Comment: 14 pages, 11 figures. Accepted for publication in Astronomy and
Astrophysic
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