118 research outputs found
The effects of amoebic dysentery as encountered in British troops from 1942 to 1946
1. Amoebic Dysentery has constituted a considerable
problem during the War.
2. Large numbers of British troops suffered from Amoebic
Dysentery for the fist time in 1942 in Bengal. Most of
the patients were recent arrivals in India. 815 cases were
treated in eight months in a Hospital in Calcutta in 1942.
3. The incidence of Amoebic Dysentery was greater than
that of Bacillary Dysentery among British troops treated in
Calcutta in 1942.
4. There was a marked rise in the incidence of Amoebic
Dysentery at the time of the Monsoon, favouring a water
borne spread. Bacillary Dysentery showed a similar rise in
the Monsoon period.
5. The immediate mortality from fresh infections with
Amoebic Dysentery was low.
6. Emetine Hydrochloride injections and Carbarsone were
administered as routine treatment in 1942. The period of
observation of cases following treatment was unduly short.
The form of treatment and the short period of observation
were dicta /ted by conditions at the time.
Relapses occurred following this treatment and the
proved relapse figure of 5% within eight months is a
minimal one.
Carbarsone appeared to be of value in eradicating
Entamoeba Histolytica cysts.
Kurchi Bismuth Iodide was valueless as an Amoebicidal
agent and was of symptomatic use in relieving diarrhoea only.
7. Fifty chronic cases of Amoebiasis were treated in 1943
as the Hospital had become e Centre for the treatment of
Chronic Amoebic Dysentery.
All the cases had recieved repeated courses of Emetine
injections and it is postulated that they had experienced
relief from this treatment but had never been cured. The
unsatisfactory nature of treatment by Emine injections and
Carbarsone alone was thus displayed again.
8. Chronic Amoebic Dysentery leads to a state of
invalidism with mentalapathy, intermittent diarrhoea, weaknes
gross loss of weight and abdominal pain.
9. Sigmoidoscopy is an excellent method of assessing
progress in Chronic Ameóbiasis but stool examinations are
even more important in diagnosis. Thus 85% of cases in which
the stools were positive showed Sigmoidoscopic lesions.
It was interesting to observe the disappearance of
ulcers in three weeks in some cases of Chronic Amoebiasis
while other ulcers showed no response following Emetine
Bismuth Iodide and Chiniofon.
Sigmoidoscopy is a good test of cure but stool
examination is even more reliable.
10. Emetine Bismuth Iodide was a drug of low toxicity in
that the pulse and blood pressure were not affected
following treatment. .
11. Emetine Bismuth Iodide and Chiniofon alone cured only
42% of fifty chronic cases. This consitituted an advance
in that the patients had not been cured by Emetine injections
The result was nevertheless disappointing.
12. 125 of the cases relapsed during observation over a
period of one month, thus emphasising the importance of an
adequate period of surveillance.
13. The lack of response to Emetine Bismuth Iodide and
Chiniofon or Yatren was apparent to various workers when
chronic refractory cases from the India and Burma Theatres
returned to the United Kingdom.
14. Failure of previous methods of treatment give rise to
speculation on the causes of chronicity.
15. Hargreaves contended that secondary infection was
responsible for the failure of Chronic Amoebiasis to
respond to treatment by Amoebici dal drugs. He therefore
advocated a preliminary course of Penicillin and Sulpha-suxidine in all such cases.
A few cases were personally treated in this way in
the United Kingdom. Three cases of Chronic Colonic
Amoebiasis have progressed well to date and are still under
observation. A Haemolytic Streptococcus was cultured from
the Amoebic ulcers of one case.
16. Perusal of the researches of various workers corroborate
the importance of secondary infection in Amoebic Dysentery.
It is considered that this is the most important factor from
the therapeutic point of view. Cultures from Amoebic ulcers
on Desoxycholate and bloodfiger media from a large number of
Chronic cases would enable t e frequency of occurrence of
some of the various secondary organisms to be assessed.
17. An adequate period of surveillance after treatment of
Amoebic Dysentery is essential. Observation for three months
at least is suggested as fifty chronic cases treated in 1943
averaged two and a half months between recurrences of symptoms.
18. After witnessing the effects of this disease for four
years, one feels that no treatment, however prolonged, can
be too thorough in the eradication of the infection
Path-integral dynamics of water using curvilinear centroids
We develop a path-integral dynamics method for water that resembles centroid
molecular dynamics (CMD), except that the centroids are averages of
curvilinear, rather than cartesian, bead coordinates. The curvilinear
coordinates are used explicitly only when computing the potential of mean
force, the components of which are re-expressed in terms of cartesian
'quasi-centroids' (so-called because they are close to the cartesian
centroids). Cartesian equations of motion are obtained by making small
approximations to the quantum Boltzmann distribution. Simulations of the
infrared spectra of various water models over 150-600 K show these
approximations to be justified: for a two-dimensional OH-bond model, the
quasi-centroid molecular dynamics (QCMD) spectra lie close to the exact quantum
spectra, and almost on top of the Matsubara dynamics spectra; for gas-phase
water, the QCMD spectra are close to the exact quantum spectra; for liquid
water and ice (using the q-TIP4P/F surface), the QCMD spectra are close to the
CMD spectra at 600 K, and line up with the results of thermostatted
ring-polymer molecular dynamics and approximate quantum calculations at 300 and
150 K. The QCMD spectra show no sign of the CMD 'curvature problem' (of
erroneous red shifts and broadening). In the liquid and ice simulations, the
potential of mean force was evaluated on the fly by generalising an adiabatic
CMD algorithm to curvilinear coordinates; the full limit of adiabatic
separation needed to be taken, which made the QCMD calculations 8 times more
expensive than partially adiabatic CMD at 300 K, and 32 times at 150 K (and the
intensities may still not be converged at this temperature). The QCMD method is
probably generalisable to many other systems, provided collective
bead-coordinates can be identified that yield compact mean-field ring-polymer
distributions.Cambridge University Vice Chancellor's award
Boltzmann-conserving classical dynamics in quantum time-correlation functions: "Matsubara dynamics".
We show that a single change in the derivation of the linearized semiclassical-initial value representation (LSC-IVR or "classical Wigner approximation") results in a classical dynamics which conserves the quantum Boltzmann distribution. We rederive the (standard) LSC-IVR approach by writing the (exact) quantum time-correlation function in terms of the normal modes of a free ring-polymer (i.e., a discrete imaginary-time Feynman path), taking the limit that the number of polymer beads N → ∞, such that the lowest normal-mode frequencies take their "Matsubara" values. The change we propose is to truncate the quantum Liouvillian, not explicitly in powers of ħ(2) at ħ(0) (which gives back the standard LSC-IVR approximation), but in the normal-mode derivatives corresponding to the lowest Matsubara frequencies. The resulting "Matsubara" dynamics is inherently classical (since all terms O(ħ(2)) disappear from the Matsubara Liouvillian in the limit N → ∞) and conserves the quantum Boltzmann distribution because the Matsubara Hamiltonian is symmetric with respect to imaginary-time translation. Numerical tests show that the Matsubara approximation to the quantum time-correlation function converges with respect to the number of modes and gives better agreement than LSC-IVR with the exact quantum result. Matsubara dynamics is too computationally expensive to be applied to complex systems, but its further approximation may lead to practical methods.T.J.H.H., M.J.W., and S.C.A. acknowledge funding from the U.K. Engineering and Physical Sciences Research Council. A.M. acknowledges the European Lifelong Learning Programme (LLP) for an Erasmus student placement scholarship. T.J.H.H. also acknowledges a Research Fellowship from Jesus College, Cambridge and helpful discussions with Dr. Adam Harper.This is the author accepted manuscript. The final version is available from AIP via http://dx.doi.org/10.1063/1.491631
Atomic-scale representation and statistical learning of tensorial properties
This chapter discusses the importance of incorporating three-dimensional
symmetries in the context of statistical learning models geared towards the
interpolation of the tensorial properties of atomic-scale structures. We focus
on Gaussian process regression, and in particular on the construction of
structural representations, and the associated kernel functions, that are
endowed with the geometric covariance properties compatible with those of the
learning targets. We summarize the general formulation of such a
symmetry-adapted Gaussian process regression model, and how it can be
implemented based on a scheme that generalizes the popular smooth overlap of
atomic positions representation. We give examples of the performance of this
framework when learning the polarizability and the ground-state electron
density of a molecule
Snow property controls on modelled Ku-band altimeter estimates of first-year sea ice thickness: Case studies from the Canadian and Norwegian Arctic
Uncertainty in snow properties impacts the accuracy
of Arctic sea ice thickness estimates from radar altimetry. On firstyear sea ice (FYI), spatiotemporal variations in snow properties
can cause the Ku-band main radar scattering horizon to appear
above the snow/sea ice interface. This can increase the estimated
sea ice freeboard by several centimeters, leading to FYI thickness
overestimations. This study examines the expected changes in Kuband main scattering horizon and its impact on FYI thickness
estimates, with variations in snow temperature, salinity and
density derived from 10 naturally occurring Arctic FYI Cases
encompassing saline/non-saline, warm/cold, simple/complexly
layered snow (4 cm to 45 cm) overlying FYI (48 cm to 170 cm).
Using a semi-empirical modeling approach, snow properties from
these Cases are used to derive layer-wise brine volume and
dielectric constant estimates, to simulate the Ku-band main
scattering horizon and delays in radar propagation speed.
Differences between modeled and observed FYI thickness are
calculated to assess sources of error. Under both cold and warm
conditions, saline snow covers are shown to shift the main
scattering horizon above from the snow/sea ice interface, causing
thickness retrieval errors. Overestimates in FYI thicknesses of up
to 65% are found for warm, saline snow overlaying thin sea ice.
Our simulations exhibited a distinct shift in the main scattering
horizon when the snow layer densities became greater than 440
kg/m3
, especially under warmer snow conditions. Our simulations
suggest a mean Ku-band propagation delay for snow of 39%,
which is higher than 25%, suggested in previous studies
Machine-learning of atomic-scale properties based on physical principles
We briefly summarize the kernel regression approach, as used recently in
materials modelling, to fitting functions, particularly potential energy
surfaces, and highlight how the linear algebra framework can be used to both
predict and train from linear functionals of the potential energy, such as the
total energy and atomic forces. We then give a detailed account of the Smooth
Overlap of Atomic Positions (SOAP) representation and kernel, showing how it
arises from an abstract representation of smooth atomic densities, and how it
is related to several popular density-based representations of atomic
structure. We also discuss recent generalisations that allow fine control of
correlations between different atomic species, prediction and fitting of
tensorial properties, and also how to construct structural kernels---applicable
to comparing entire molecules or periodic systems---that go beyond an additive
combination of local environments
Approximating Matsubara dynamics using the planetary model: Tests on liquid water and ice.
Matsubara dynamics is the quantum-Boltzmann-conserving classical dynamics which remains when real-time coherences are taken out of the exact quantum Liouvillian [T. J. H. Hele et al., J. Chem. Phys. 142, 134103 (2015)]; because of a phase-term, it cannot be used as a practical method without further approximation. Recently, Smith et al. [J. Chem. Phys. 142, 244112 (2015)] developed a "planetary" model dynamics which conserves the Feynman-Kleinert (FK) approximation to the quantum-Boltzmann distribution. Here, we show that for moderately anharmonic potentials, the planetary dynamics gives a good approximation to Matsubara trajectories on the FK potential surface by decoupling the centroid trajectory from the locally harmonic Matsubara fluctuations, which reduce to a single phase-less fluctuation particle (the "planet"). We also show that the FK effective frequency can be approximated by a direct integral over these fluctuations, obviating the need to solve iterative equations. This modification, together with use of thermostatted ring-polymer molecular dynamics, allows us to test the planetary model on water (gas-phase, liquid, and ice) using the q-TIP4P/F potential surface. The "planetary" fluctuations give a poor approximation to the rotational/librational bands in the infrared spectrum, but a good approximation to the bend and stretch bands, where the fluctuation lineshape is found to be motionally narrowed by the vibrations of the centroid
Demonstration of Metabolic and Cellular Effects of Portal Vein Ligation Using Multi-Modal PET/MRI Measurements in Healthy Rat Liver.
OBJECTIVES: In the early recognition of portal vein ligation (PVL) induced tumor progression, positron emission tomography and magnetic resonance imaging (PET/MRI) could improve diagnostic accuracy of conventionally used methods. It is unknown how PVL affects metabolic patterns of tumor free hepatic tissues. The aim of this preliminary study is to evaluate the effect of PVL on glucose metabolism, using PET/MRI imaging in healthy rat liver. MATERIALS AND METHODS: Male Wistar rats (n = 30) underwent PVL. 2-deoxy-2-(18F)fluoro-D-glucose (FDG) PET/MRI imaging (nanoScan PET/MRI) and morphological/histological examination were performed before (Day 0) and 1, 2, 3, and 7 days after PVL. Dynamic PET data were collected and the standardized uptake values (SUV) for ligated and non-ligated liver lobes were calculated in relation to cardiac left ventricle (SUVVOI/SUVCLV) and mean liver SUV (SUVVOI/SUVLiver). RESULTS: PVL induced atrophy of ligated lobes, while non-ligated liver tissue showed compensatory hypertrophy. Dynamic PET scan revealed altered FDG kinetics in both ligated and non-ligated liver lobes. SUVVOI/SUVCLV significantly increased in both groups of lobes, with a maximal value at the 2nd postoperative day and returned near to the baseline 7 days after the ligation. After PVL, ligated liver lobes showed significantly higher tracer uptake compared to the non-ligated lobes (significantly higher SUVVOI/SUVLiver values were observed at postoperative day 1, 2 and 3). The homogenous tracer biodistribution observed before PVL reappeared by 7th postoperative day. CONCLUSION: The observed alterations in FDG uptake dynamics should be taken into account during the assessment of PET data until the PVL induced atrophic and regenerative processes are completed
Wind redistribution of snow impacts the Ka- and Ku-band radar signatures of Arctic sea ice
Wind-driven redistribution of snow on sea ice alters its
topography and microstructure, yet the impact of these processes on radar
signatures is poorly understood. Here, we examine the effects of snow
redistribution over Arctic sea ice on radar waveforms and backscatter
signatures obtained from a surface-based, fully polarimetric Ka- and Ku-band
radar at incidence angles between 0∘ (nadir) and 50∘.
Two wind events in November 2019 during the Multidisciplinary drifting Observatory for
the Study of Arctic Climate (MOSAiC) expedition are evaluated. During both events, changes in Ka- and
Ku-band radar waveforms and backscatter coefficients at nadir are observed,
coincident with surface topography changes measured by a terrestrial laser
scanner. At both frequencies, redistribution caused snow densification at
the surface and the uppermost layers, increasing the scattering at the
air–snow interface at nadir and its prevalence as the dominant radar scattering surface. The waveform data also detected the presence of previous
air–snow interfaces, buried beneath newly deposited snow. The additional
scattering from previous air–snow interfaces could therefore affect the
range retrieved from Ka- and Ku-band satellite altimeters. With increasing
incidence angles, the relative scattering contribution of the air–snow
interface decreases, and the snow–sea ice interface scattering increases.
Relative to pre-wind event conditions, azimuthally averaged backscatter at
nadir during the wind events increases by up to 8 dB (Ka-band) and 5 dB (Ku-band). Results show substantial backscatter variability within the scan
area at all incidence angles and polarizations, in response to increasing
wind speed and changes in wind direction. Our results show that snow
redistribution and wind compaction need to be accounted for to interpret
airborne and satellite radar measurements of snow-covered sea ice.</p
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