1,429 research outputs found
The scientific case for renewed human activities on the Moon
It is over 30 years since the last human being stood on the lunar surface and this long hiatus in human exploration has been to the detriment of lunar and planetary science. The primary scientific importance of the Moon lies in the record it preserves of the early evolution of a terrestrial planet, and of the near-Earth cosmic environment in the first billion years or so of Solar System history. This record may not be preserved anywhere else; gaining proper access to it will require a human presence. Moreover, while this will primarily be a task for the geosciences, the astronomical and biological sciences would also benefit from a renewed human presence on the Moon, and especially from the establishment of a permanently occupied scientific outpost
The peritoneal tumour microenvironment of high-grade serous ovarian cancer
High-grade serous ovarian cancer (HGSC) disseminates early and extensively throughout the peritoneal space, causing multiple lesions that are a major clinical problem. The aim of this study was to investigate the cellular composition of peritoneal tumour deposits in patient biopsies and their evolution in mouse models using immunohistochemistry, intravital microscopy, confocal microscopy, and 3D modelling. Tumour deposits from the omentum of HGSC patients contained a prominent leukocyte infiltrate of CD3(+) T cells and CD68(+) macrophages, with occasional neutrophils. Alpha-smooth muscle actin(+) (α-SMA(+) ) pericytes and/or fibroblasts surrounded these well-vascularized tumour deposits. Using the murine bowel mesentery as an accessible mouse peritoneal tissue that could be easily imaged, and two different transplantable models, we found multiple microscopic tumour deposits after i.p. injection of malignant cells. Attachment to the peritoneal surface was rapid (6-48 h) with an extensive CD45(+) leukocyte infiltrate visible by 48 h. This infiltrate persisted until end point and in the syngeneic murine ID8 model, it primarily consisted of CD3(+) T lymphocytes and CD68(+) macrophages with α-SMA(+) cells also involved from the earliest stages. A majority of tumour deposits developed above existing mesenteric blood vessels, but in avascular spaces new blood vessels tracked towards the tumour deposits by 2-3 weeks in the IGROV-1 xenografts and 6 weeks in the ID8 syngeneic model; a vigorous convoluted blood supply was established by end point. Inhibition of tumour cell cytokine production by stable expression of shRNA to CXCR4 in IGROV-1 cells did not influence the attachment of cells to the mesentery but delayed neovascularization and reduced tumour deposit size. We conclude that the multiple peritoneal tumour deposits found in HGSC patients can be modelled in the mouse. The techniques described here may be useful for assessing treatments that target the disseminated stage of this disease
Nonrelativistic double photoeffect on lithiumlike ions at high energies
The total cross section for double ionization of lithiumlike ions by a
high-energy photon is calculated in leading order of the nonrelativistic
perturbation theory. The partial contributions due to simultaneous and
sequential emissions of two electrons are taken into account. The cross section
under consideration is shown to be related to those for double photoeffect on
the ground and excited 2^{1,3}S states of heliumlike ions. The double-to-single
ionization ratio is equal to R = 0.288/Z^2 for lithiumlike ions with moderate
nuclear charge numbers Z. However, even for the lightest three-electron targets
such as Li and Be^+, analytical predictions are found to be in good agreement
with the numerical calculations performed within the framework of different
rather involved approaches.Comment: 12 pages, 2 figures. to be published in Physics Letters
Triple oxygen isotopic composition of the high-<sup>3</sup>He/<sup>4</sup>He mantle
Measurements of Xe isotope ratios in ocean island basalts (OIB) suggest that Earth’s mantle accreted heterogeneously, and that compositional remnants of accretion are sampled by modern, high-3He/4He OIB associated with the Icelandic and Samoan plumes. If so, the high-3He/4He source may also have a distinct oxygen isotopic composition from the rest of the mantle. Here, we test if the major elements of the high-3He/4He source preserve any evidence of heterogeneous accretion using measurements of three oxygen isotopes on olivine from a variety of high-3He/4He OIB locations. To high precision, the Δ17O value of high-3He/4He olivines from Hawaii, Pitcairn, Baffin Island and Samoa, are indistinguishable from bulk mantle olivine (Δ17OBulk Mantle − Δ17OHigh 3He/4He olivine = −0.002 ± 0.004 (2 × SEM)‰). Thus, there is no resolvable oxygen isotope evidence for heterogeneous accretion in the high-3He/4He source. Modelling of mixing processes indicates that if an early-forming, oxygen-isotope distinct mantle did exist, either the anomaly was extremely small, or the anomaly was homogenised away by later mantle convection.
The δ18O values of olivine with the highest 3He/4He ratios from a variety of OIB locations have a relatively uniform composition (∼5‰). This composition is intermediate to values associated with the depleted MORB mantle and the average mantle. Similarly, δ18O values of olivine from high-3He/4He OIB correlate with radiogenic isotope ratios of He, Sr, and Nd. Combined, this suggests that magmatic oxygen is sourced from the same mantle as other, more incompatible elements and that the intermediate δ18O value is a feature of the high-3He/4He mantle source. The processes responsible for the δ18O signature of high-3He/4He mantle are not certain, but δ18O–87Sr/86Sr correlations indicate that it may be connected to a predominance of a HIMU-like (high U/Pb) component or other moderate δ18O components recycled into the high-3He/4He source
Charged hydrogenic problem in a magnetic field: Non-commutative translations, unitary transformations, and coherent states
An operator formalism is developed for a description of charged electron-hole
complexes in magnetic fields. A novel unitary transformation of the Hamiltonian
that allows one to partially separate the center-of-mass and internal motions
is proposed. We study the operator algebra that leads to the appearance of new
effective particles, electrons and holes with modified interparticle
interactions, and their coherent states in magnetic fields. The developed
formalism is used for studying a two-dimensional negatively charged
magnetoexciton . It is shown that Fano-resonances are present in the
spectra of internal transitions, indicating the existence of
three-particle quasi-bound states embedded in the continuum of higher Landau
levels.Comment: 9 pages + 2 figures, accepted in PRB, a couple of typos correcte
Distribution of and hydrographic controls on ferromanganese crusts: Tropic Seamount, Atlantic
Hydrogenetic ferromanganese crusts are likely to be exploited as resources for critical metals in the near future, yet the processes controlling where and how they grow are poorly understood. Using detailed mapping of seafloor outcrop and well constrained hydrographic modelling alongside scanning electron microscope imagery of samples from the Tropic Seamount, a star-shaped guyot located in the Tropical East Atlantic, we investigate the relationship between currents, ferromanganese crustal texture and the locations and intensity of crustal erosion. Here, we report the distribution of FeMn crusts and explore factors controlling their growth and erosion. We find that just over 35% of the summit plateau of the guyot exposes some form of ferromanganese crust mineralisation, with the rest variably covered by plains of mobile sediment and slim cliff exposures of carbonate. The steep flanks of the guyot largely expose ferromanganese crust both in situ and as debris flows. The strongest currents are located on the upper flanks of the guyot, the central part of its eastern limb, and across the summit plateau. Three categories of surface morphologies are identified; from pristine botryoidal surfaces to flat areas that have been completely polished by the erosive action of currents and sediment. The relationship between the outcrop of crusts, their erosional states and the hydrographic current regime to which they are exposed is complicated. There is a general correlation between the degree of erosion and location across the seamount, with the least eroded being found on the flanks below 2000 m water depth and the most heavily eroded crusts largely restricted to the summit area. Furthermore, the pristine samples all reside in areas that rarely experience current magnitudes over 0.2 m/s, suggesting that above this the currents have the ability to erode ferromanganese crust. However, there is a strong overlap between the measured current magnitudes at the locations of partially and completely eroded crusts, as well as partial overlap with the current magnitudes measured at pristine crust locations. This complexity is likely due to the presence of cliffs and plateaus increasing current magnitudes and turbidity at a scale smaller than the model resolution
Nonequilibrium Evolution of Correlation Functions: A Canonical Approach
We study nonequilibrium evolution in a self-interacting quantum field theory
invariant under space translation only by using a canonical approach based on
the recently developed Liouville-von Neumann formalism. The method is first
used to obtain the correlation functions both in and beyond the Hartree
approximation, for the quantum mechanical analog of the model. The
technique involves representing the Hamiltonian in a Fock basis of annihilation
and creation operators. By separating it into a solvable Gaussian part
involving quadratic terms and a perturbation of quartic terms, it is possible
to find the improved vacuum state to any desired order. The correlation
functions for the field theory are then investigated in the Hartree
approximation and those beyond the Hartree approximation are obtained by
finding the improved vacuum state corrected up to . These
correlation functions take into account next-to-leading and
next-to-next-to-leading order effects in the coupling constant. We also use the
Heisenberg formalism to obtain the time evolution equations for the equal-time,
connected correlation functions beyond the leading order. These equations are
derived by including the connected 4-point functions in the hierarchy. The
resulting coupled set of equations form a part of infinite hierarchy of coupled
equations relating the various connected n-point functions. The connection with
other approaches based on the path integral formalism is established and the
physical implications of the set of equations are discussed with particular
emphasis on thermalization.Comment: Revtex, 32 pages; substantial new material dealing with
non-equilibrium evolution beyond Hartree approx. based on the LvN formalism,
has been adde
Guidelines for incorporating scientific knowledge and practice on rare diseases into higher education: neuronal ceroid lipofuscinoses as a model disorder model disorder.
This article addresses the educational issues associated with rare diseases (RD) and in particular the Neuronal
Ceroid Lipofuscinoses (NCLs, or CLN diseases) in the curricula of Health Sciences and Professional's Training
Programs. Our aim is to develop guidelines for improving scientific knowledge and practice in higher education
and continuous learning programs.
Rare diseases (RD) are collectively common in the general populationwith 1 in 17 people affected by a RDin their
lifetime. Inherited defects in genes involved in metabolism are the commonest group of RD with over 8000
known inborn errors of metabolism. The majority of these diseases are neurodegenerative including the NCLs.
Any professional training program on NCL must take into account the medical, social and economic burdens
related to RDs. To address these challenges and find solutions to themit is necessary that individuals in the government
and administrative authorities, academia, teaching hospitals and medical schools, the pharmaceutical
industry, investment community and patient advocacy groups all work together to achieve these goals.
The logistical issues of including RD lectures in university curricula and in continuing medical education should
reflect its complex nature. To evaluate the state of education in the RD field, a summary should be periodically up
dated in order to assess the progress achieved in each country that signed up to the international conventions
addressing RD issues in society. It is anticipated that auditing current practice will lead to higher standards and
provide a framework for those educators involved in establishing RD teaching programs world-wide.publishedVersio
Onset of magnetism in B2 transition metals aluminides
Ab initio calculation results for the electronic structure of disordered bcc
Fe(x)Al(1-x) (0.4<x<0.75), Co(x)Al(1-x) and Ni(x)Al(1-x) (x=0.4; 0.5; 0.6)
alloys near the 1:1 stoichiometry, as well as of the ordered B2 (FeAl, CoAl,
NiAl) phases with point defects are presented. The calculations were performed
using the coherent potential approximation within the Korringa-Kohn-Rostoker
method (KKR-CPA) for the disordered case and the tight-binding linear
muffin-tin orbital (TB-LMTO) method for the intermetallic compounds. We studied
in particular the onset of magnetism in Fe-Al and Co-Al systems as a function
of the defect structure. We found the appearance of large local magnetic
moments associated with the transition metal (TM) antisite defect in FeAl and
CoAl compounds, in agreement with the experimental findings. Moreover, we found
that any vacancies on both sublattices enhance the magnetic moments via
reducing the charge transfer to a TM atom. Disordered Fe-Al alloys are
ferromagnetically ordered for the whole range of composition studied, whereas
Co-Al becomes magnetic only for Co concentration >0.5.Comment: 11 pages with 9 embedded postscript figures, to be published in
Phys.Rev.
Two lectures on color superconductivity
The first lecture provides an introduction to the physics of color
superconductivity in cold dense quark matter. The main color superconducting
phases are briefly described and their properties are listed. The second
lecture covers recent developments in studies of color superconducting phases
in neutral and beta-equilibrated matter. The properties of gapless color
superconducting phases are discussed.Comment: 56 pages, 9 figures. Minor corrections and references added. Lectures
delivered at the IARD 2004 conference, Saas Fee, Switzerland, June 12 - 19,
2004, and at the Helmholtz International Summer School and Workshop on Hot
points in Astrophysics and Cosmology, JINR, Dubna, Russia, August 2 - 13,
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