9,561 research outputs found
Experiment K-6-17. Structural changes and cell turnover in the rats small intestine induced by spaceflight
The purpose of this project was to test the hypothesis that the generalized, whole body decrease in synthetic activity associated with microgravity conditions of space flight as evidenced by negative nitrogen balance and muscle atrophy (Nicogossian and Parker, 1982; Oganov, 1981), as well as inhibited lymphocyte proliferation (Bechler and Cogoli, 1986), would be evident in cells characterized by a rapid rate of turnover. As a model, researchers chose to study the turnover of mucosal cells lining the jejunum of the small intestine, since these cells are among the most rapidly proliferating in the body. Under normal conditions, epithelial cells that line the small intestine are continually produced in the crypts of Lieberkuhn. These cells migrate out of the crypts onto intestinal villi, are progressively pushed up the villus as new crypt cells are formed, and ultimately reach the tip of villi where they are then descquamated. In rats, the entire process, from initial proliferation in crypts to desquamation, takes approximately 2 days (Cairnie et al., 1965; Lipkin, 1973). In this study, researchers determined the mitotic index for mucosal cells lining the proximal, middle, and distal regions of the jejunum in rats from three treatment groups (synchronous control, vivarium control and flight), and measured the depth of the crypts of Lieberkuhn and the length of villi present in each of the three jejunal regions sampled
A new quantity for studies of dijet azimuthal decorrelations
We introduce a new measurable quantity, , for studies of the
rapidity and transverse momentum dependence of dijet azimuthal decorrelations
in hadron-hadron collisions. In pQCD, is computed as a ratio
of three-jet and dijet cross sections in which the parton distribution
functions cancel to a large extent. At the leading order, is
proportional to , and the transverse momentum dependence of can
therefore be exploited to determine . We compute the NLO pQCD theory
predictions and non-perturbative corrections for at the LHC
and the Tevatron and investigate the corresponding uncertainties. From this, we
estimate the theory uncertainties for determinations based on
at both colliders. The potential of
measurements for tuning Monte Carlo event generators is also demonstrated.Comment: 20 pages, 11 figures, 1 table, submitted to JHE
A Framework to Manage the Complex Organisation of Collaborating: Its Application to Autonomous Systems
In this paper we present an analysis of the complexities of large group
collaboration and its application to develop detailed requirements for
collaboration schema for Autonomous Systems (AS). These requirements flow from
our development of a framework for collaboration that provides a basis for
designing, supporting and managing complex collaborative systems that can be
applied and tested in various real world settings. We present the concepts of
"collaborative flow" and "working as one" as descriptive expressions of what
good collaborative teamwork can be in such scenarios. The paper considers the
application of the framework within different scenarios and discuses the
utility of the framework in modelling and supporting collaboration in complex
organisational structures
Effects of spaceflight on the proliferation of jejunal mucosal cells
The purpose of this project was to test the hypothesis that the generalized, whole body decrease in synthetic activity due to microgravity conditions encountered during spaceflight would be demonstrable in cells and tissues characterized by a rapid rate of turnover. Jejunal mucosal cells were chosen as a model since these cells are among the most rapidly proliferating in the body. Accordingly, the percentage of mitotic cells present in the crypts of Lieberkuhn in each of 5 rats flown on the COSMOS 2044 mission were compared to the percentage of mitotic cells present in the crypts in rats included in each of 3 ground control groups (i.e., vivarium, synchronous and caudal-elevated). No significant difference (p greater than .05) was detected in mitotic indices between the flight and vivarium group. Although the ability of jejunal mucosal cells to divide by mitosis was not impaired in flight group, there was, however, a reduction in the length of villi and depth of crypts. The concommitant reduction in villus length and crypth depth in the flight group probably reflects changes in connective tissue components within the core of villi
Cold Molecule Spectroscopy for Constraining the Evolution of the Fine Structure Constant
We report precise measurements of ground-state, -doublet microwave
transitions in the hydroxyl radical molecule (OH). Utilizing slow, cold
molecules produced by a Stark decelerator we have improved over the precision
of the previous best measurement by twenty-five-fold for the F' = 2 F = 2
transition, yielding (1 667 358 996 4) Hz, and by ten-fold for the F' = 1
F = 1 transition, yielding (1 665 401 803 12) Hz. Comparing these
laboratory frequencies to those from OH megamasers in interstellar space will
allow a sensitivity of 1 ppm for over
years.Comment: This version corrects minor typos in the Zeeman shift discussio
Spin susceptibility of neutron matter at zero temperature
The Auxiliary Field Diffusion Monte Carlo method is applied to compute the
spin susceptibility and the compressibility of neutron matter at zero
temperature. Results are given for realistic interactions which include both a
two-body potential of the Argonne type and the Urbana IX three-body potential.
Simulations have been carried out for about 60 neutrons. We find an overall
reduction of the spin susceptibilty by about a factor 3 with respect to the
Pauli susceptibility for a wide range of densities. Results for the
compressibility of neutron matter are also presented and compared with other
available estimates obtained for semirealistic nucleon-nucleon interactions by
using other techniques
A Self-Consistent Approach to Neutral-Current Processes in Supernova Cores
The problem of neutral-current processes (neutrino scattering, pair emission,
pair absorption, axion emission, \etc) in a nuclear medium can be separated
into an expression representing the phase space of the weakly interacting
probe, and a set of dynamic structure functions of the medium. For a
non-relativistic medium we reduce the description to two structure functions
S_A(\o) and S_V(\o) of the energy transfer, representing the axial-vector
and vector interactions. is well determined by the single-nucleon
approximation while may be dominated by multiply interacting nucleons.
Unless the shape of S_A(\o) changes dramatically at high densities,
scattering processes always dominate over pair processes for neutrino transport
or the emission of right-handed states. Because the emission of right-handed
neutrinos and axions is controlled by the same medium response functions, a
consistent constraint on their properties from consideration of supernova
cooling should use the same structure functions for both neutrino transport and
exotic cooling mechanisms.Comment: 33 pages, Te
Magneto-electrostatic trapping of ground state OH molecules
We report the magnetic confinement of neutral, ground state hydroxyl radicals
(OH) at a density of cm and temperature of 30
mK. An adjustable electric field of sufficient magnitude to polarize the OH is
superimposed on the trap in either a quadrupole or homogenous field geometry.
The OH is confined by an overall potential established via molecular state
mixing induced by the combined electric and magnetic fields acting on the
molecule's electric dipole and magnetic dipole moments, respectively. An
effective molecular Hamiltonian including Stark and Zeeman terms has been
constructed to describe single molecule dynamics inside the trap. Monte Carlo
simulation using this Hamiltonian accurately models the observed trap dynamics
in various trap configurations. Confinement of cold polar molecules in a
magnetic trap, leaving large, adjustable electric fields for control, is an
important step towards the study of low energy dipole-dipole collisions.Comment: 4 pages, 4 figure
Understanding the impact of exposure to adverse socioeconomic conditions on chronic stress from a complexity science perspective
Background: Chronic stress increases chronic disease risk and may underlie the association between exposure to adverse socioeconomic conditions and adverse health outcomes. The relationship between exposure to such conditions and chronic stress is complex due to feedback loops between stressor exposure and psychological processes, encompassing different temporal (acute stress response to repeated exposure over the life course) and spatial (biological/psychological/social) scales. We examined the mechanisms underlying the relationship between exposure to adverse socioeconomic conditions and chronic stress from a complexity science perspective, focusing on amplifying feedback loops across different scales. Methods: We developed a causal loop diagram (CLD) to interpret available evidence from this perspective. The CLD was drafted by an interdisciplinary group of researchers. Evidence from literature was used to confirm/contest the variables and causal links included in the conceptual framework and refine their conceptualisation. Our findings were evaluated by eight independent researchers. Results: Adverse socioeconomic conditions imply an accumulation of stressors and increase the likelihood of exposure to uncontrollable childhood and life course stressors. Repetition of such stressors may activate mechanisms that can affect coping resources and coping strategies and stimulate appraisal of subsequent stressors as uncontrollable. We identified five feedback loops describing these mechanisms: (1) progressive deterioration of access to coping resources because of repeated insolvability of stressors; (2) perception of stressors as uncontrollable due to learned helplessness; (3) tax on cognitive bandwidth caused by stress; (4) stimulation of problem avoidance to provide relief from the stress response and free up cognitive bandwidth; and (5) susceptibility to appraising stimuli as stressors against a background of stress. Conclusions: Taking a complexity science perspective reveals that exposure to adverse socioeconomic conditions implies recurrent stressor exposure which impacts chronic stress via amplifying feedback loops that together could be conceptualised as one vicious cycle. This means that in order for individual-level psychological interventions to be effective, the context of exposure to adverse socioeconomic conditions also needs to be addressed
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