263 research outputs found
Reconstruction of the human foetal pelvis: a study of its development
This work:- The Reconstruction of the Early
Foetal Pelvis, with a View to a Studyof its
Development, was undertaken at the suggestion of
Professor Cunningham and Dr. Waterston and was carried
out in the Laboratory of the Anatomy Department. It
seemed possible that, by this means of investigation,
something of interest might be added to the already
known facts about this region of the embryo. That,
by supplementing the work done by other methods - particularly the study of sections serially by the
microscope - a fuller and more perfect knowledge
might be had of this interesting region.
Special attention was to be directed to the
hard parts, the general shape of the pelvis, and any
peculiarities in this or in its constituent elements,
seemed to be a very interesting field for research;
and, I think I may say, that the results obtained have
fully borne this out.
Whilst the bony (or, really, cartilaginous) pelvis was the main point of investigation, it seemed
to nie that to reconstruct a model, with the viscera
in situ, might prove instructive; this, particularly
to study the topography of the viscera at this early
stage with thieir general form and arrangement. A stud
of these in their natural size is of course very
difficult and well nigh impossible. Very beautiful
models of the tail end of the early embryo have been
reconstructed by Professor Keibel cf Freiburg. They
do not, however, give a good impression of the topography of the viscera,as organs are only in many cases
shown in section, and their limits and relations to the
hard parts not made clear.
If suitable material were to be had (and I regret
that it was not - indeed, there was a great scarcity
for one reason and another - everybody seemed to wish
his specimens for private museums), it was hoped that
something might be done on the development Of the
urethra in the male. I particularly desired to
investigate the sexual characters of the hard parts
and to discover whether there were any differences
between male and female at this early period. Unfortunately I have been unable to do so since all my
specimens have turned out males.
However, with the measurements fully recorded
(in one pelvis from a foetus eleven to twelve weeks
old) cf this male pelvis, some future workers may be
more fortunate with his material and be able to prove
that there are or there are not sexual differences at
this age.
Professor Arthur Thomson (Journal of Anatomy and
Physiology, Vol. XXXIII, 1899) has shown that as early
as four months there are distinct differences between
the pelvis of the two sexes, as distinct as in the adult.
its method of investigation was by means of dissection,
a much more risky method (as he admits) when dealing,
as he had to do, with small and delicate parts. However, the results in the various specimens were uniform
and there does seem to be a difference as early, at any
rate, as four months.
Reconstruction, as a method of investigation in
Embryology, did not, it would seem, at first receive
the attention it merited. Its value is not apparent
in many cases at first sight and so the method has,
until comparatively recently, been neglected; except
perhaps by those under the immediate influence and
direction cf the originator, Professor His.
When we consider, however, it is clear that this
method must be of great service in dealing with very
early embryos when we wish to study the form and make
measurements cf these embryos or any particular organ.
By magnifying the structure and modelling it in its
enlarged form we can not only make more accurate
observations as to the form and size of any structure
at any age, but also study the development of that
structure from its first appearance up to the stage
when it can be studied accurately in its natural
condition.
A study of serial sections cf a structure has,
of course, its own particular value and much may be
made out by the aid of the microscope and other aids
even as to the form of the structure. This indeed
was what this did in his earliest reconstruction
models - models which are famous. He studied a
complete series of sections of an embryo so carefully
that he was able to model the embryo freely in wax
or clay. This, to his with his great powers cf observation, must have been a very difficult task and
it is not, as Professor Peter Thompson says, for the
ordinary man. One may be allowed to doubt whether
such models were, in their finer points, strictly
accurate. For myself I have studied these serial
sections pretty closely and have often been amazed
at the appearance after reconstruction. Taking the
cartilaginous pelvis as an example it seems to me
well nigh impossible to form an accurate idea of such
a structure with its many processes and fossae, or
what are the correct shape and dimensions of such
processes and fossae, by a mere study of sections.
In any case, in such a study, the investigator alone
would have the mental picture complete, which he could
give to others by description; but where we can reconstruct a model we have a visual picture for all to
study from.
The value cf this method therefore lies mainly
in this, that, where we wish to study form, at any
particular stage in a developing structure, we have
an accurate, enlarged, visual image of the structure
so that we can handle it and measure it and note the
relations cf one part to another.
So much for the advantages of this method of
investigation. That are its disadvantages? The
most important is that it consumes much time; though
after working at it for some time one gets along
much more rapidly than at first. There is always,
of course, much of interest in the work; but in
certain parts the procedure is very tedious and a
good. deal of patience is required to keep steadily
at the work from day to day.
The other disadvantage, or rather difficulty, is
that there is a good deal of risk in certain parts of
the technique. Everything must work smoothly during
the process until the sections are safely mounted.
For example, the tissue must be in good order for
cutting so that the sections will be complete; the
microtome must therefore also be cutting well;
draughts have to be avoided when handling the sections
for fear of mixing them; the sections must stick well
to the slides; etc. But after all,these difficulties
can be overcome by careful technique, so that there
is nothing much to be said against the method,
nothing that will weigh against the advantages, for
time is required in all methods of investigation
A next-generation inverse-geometry spallation-driven ultracold neutron source
The physics model of a next-generation spallation-driven high-current
ultracold neutron (UCN) source capable of delivering an extracted UCN rate of
around an-order-of-magnitude higher than the strongest proposed sources, and
around three-orders-of-magnitude higher than existing sources, is presented.
This UCN-current-optimized source would dramatically improve cutting-edge UCN
measurements that are currently statistically limited. A novel "Inverse
Geometry" design is used with 40 L of superfluid He (He-II), which acts as
a converter of cold neutrons (CNs) to UCNs, cooled with state-of-the-art
sub-cooled cryogenic technology to 1.6 K. Our design is optimized for a
100 W maximum heat load constraint on the He-II and its vessel. In our
geometry, the spallation target is wrapped symmetrically around the UCN
converter to permit raster scanning the proton beam over a relatively large
volume of tungsten spallation target to reduce the demand on the cooling
requirements, which makes it reasonable to assume that water edge-cooling only
is sufficient. Our design is refined in several steps to reach
s under our other restriction of 1 MW maximum
available proton beam power. We then study effects of the He-II scattering
kernel as well as reductions in due to pressurization to reach
s. Finally, we provide a design for the UCN
extraction system that takes into account the required He-II heat transport
properties and implementation of a He-II containment foil that allows UCN
transmission. We estimate a total useful UCN current from our source of
s from a 18 cm diameter guide 5 m from the source.
Under a conservative "no return" approximation, this rate can produce an
extracted density of cm in 1000~L external experimental
volumes with a Ni (335 neV) cut-off potential.Comment: Submitted to Journal of Applied Physic
The epigenetic clock is correlated with physical and cognitive fitness in the Lothian Birth Cohort 1936
Background: The DNA methylation-based 'epigenetic clock' correlates strongly with chronological age, but it is currently unclear what drives individual differences. We examine cross-sectional and longitudinal associations between the epigenetic clock and four mortality-linked markers of physical and mental fitness: lung function, walking speed, grip strength and cognitive ability. Methods: DNA methylation-based age acceleration (residuals of the epigenetic clock estimate regressed on chronological age) were estimated in the Lothian Birth Cohort 1936 at ages 70 (n=920), 73 (n=299) and 76 (n=273) years. General cognitive ability, walking speed, lung function and grip strength were measured concurrently. Cross-sectional correlations between age acceleration and the fitness variables were calculated. Longitudinal change in the epigenetic clock estimates and the fitness variables were assessed via linear mixed models and latent growth curves. Epigenetic age acceleration at age 70 was used as a predictor of longitudinal change in fitness. Epigenome-wide association studies (EWASs) were conducted on the four fitness measures. Results: Cross-sectional correlations were significant between greater age acceleration and poorer performance on the lung function, cognition and grip strength measures (r range: -0.07 to -0.05, P range: 9.7 x 10 to 0.024). All of the fitness variables declined over time but age acceleration did not correlate with subsequent change over 6 years. There were no EWAS hits for the fitness traits. Conclusions: Markers of physical and mental fitness are associated with the epigenetic clock (lower abilities associated with age acceleration). However, age acceleration does not associate with decline in these measures, at least over a relatively short follow-up
Representation in Westminster in the 1990s : The ghost of Edmund Burke
Why are 'trustee' notions of representation still invoked in the UK House of Commons in the 1990s? In answering this question this article analyses the premises of Burkean theory and the arguments that these premises are of little relevance in the late twentieth century. Despite these dismissals of trusteeship, Burkean ideas are still articulated in the Commons some 200 years after they were first voiced. The idea of trusteeship can prove extremely useful to justify the actions of representatives when those actions conflict with constituency 'opinion', party policy or the wishes of interest groups. Examples of the occasions when Burkean notions have been invoked in the 1990s are provided
Measurement of the half-life of the T= mirror decay of Ne and its implication on physics beyond the standard model
The superallowed mixed mirror decay
of Ne to F is excellently suited for high precision studies of
the weak interaction. However, there is some disagreement on the value of the
half-life. In a new measurement we have determined this quantity to be
= s, which differs
from the previous world average by 3 standard deviations. The impact of this
measurement on limits for physics beyond the standard model such as the
presence of tensor currents is discussed.Comment: 5 pages, 3 figures, 1 tabl
Search for the Neutron Decay n X+ where X is a dark matter particle
In a recent paper submitted to Physical Review Letters, Fornal and Grinstein
have suggested that the discrepancy between two different methods of neutron
lifetime measurements, the beam and bottle methods can be explained by a
previously unobserved dark matter decay mode, n X+ where X
is a dark matter particle. We have performed a search for this decay mode over
the allowed range of energies of the monoenergetic gamma ray for X to be a dark
matter particle. We exclude the possibility of a sufficiently strong branch to
explain the lifetime discrepancy with greater than 4 sigma confidence.Comment: 6 pages 3 figure
Status of the UCNτ experiment
The neutron is the simplest nuclear system that can be used to probe the structure of the weak interaction and search for physics beyond the standard model. Measurements of neutron lifetime and β-decay correlation coefficients with precisions of 0.02% and 0.1%, respectively, would allow for stringent constraints on new physics. The UCNτ experiment uses an asymmetric magneto-gravitational UCN trap with in situ counting of surviving neutrons to measure the neutron lifetime, τ_n = 877.7s (0.7s)_(stat) (+0.4/−0.2s)_(sys). We discuss the recent result from UCNτ, the status of ongoing data collection and analysis, and the path toward a 0.25 s measurement of the neutron lifetime with UCNτ
A boron-coated CCD camera for direct detection of Ultracold Neutrons (UCN)
A new boron-coated CCD camera is described for direct detection of ultracold
neutrons (UCN) through the capture reactions B
(n,0)Li (6%) and B(n,1)Li (94%).
The experiments, which extend earlier works using a boron-coated ZnS:Ag
scintillator, are based on direct detections of the neutron-capture byproducts
in silicon. The high position resolution, energy resolution and particle ID
performance of a scientific CCD allows for observation and identification of
all the byproducts , Li and (electron recoils). A
signal-to-noise improvement on the order of 10 over the indirect method has
been achieved. Sub-pixel position resolution of a few microns is demonstrated.
The technology can also be used to build UCN detectors with an area on the
order of 1 m. The combination of micrometer scale spatial resolution, few
electrons ionization thresholds and large area paves the way to new research
avenues including quantum physics of UCN and high-resolution neutron imaging
and spectroscopy.Comment: 10 pages, 8 figure
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