3,944 research outputs found
Trace Element Composition of Stream Sediments an Integrating Factor for Water Quality
Bottom sediments, suspended sediments, and water were sampled along 130 miles of the Buffalo River in northern Arkansas. The water and acid extracts of the suspended sediments and the minus 95 mesh fraction of the bottom sediments were analyzed by atomic absorption spectrometry. All samples were analyzed for Na, K, Mg, Ca, Zn, Cd, Cu, Pb, Fe, Co, Cr, Ni, and Mn. Selected bottom samples also were analyzed by As, Hg, and Zr. Zr was determined by x-ray fluorescence. Li and Sr were determined for selected water and suspended sediment samples. There is a general decrease downstream in Fe, Cu, Cr, Ni, Mn, Pb, K, and Na in the bottom sediments as the drainage area increases in carbonate rock and decreases in shale. The elements Mg, Ca, Zn, and Cd increase in bottom sediments downstream. The values for these elements in the water, especially the major elements, also correspond closely with the geology of the region. Tributaries are sites of abrupt rise and fall of metal values, within a few miles, from background to anomalously high values to background, especially tributaries draining Zn and Pb mineralized areas. The bottom sediments are mainly quartz and chert grains. These grains apparently are coated with hydrous iron oxide which acts as a sorbent for many of the elements and is a dominant transport mechanism for acid extractable Co, Cr, Ni, Cu, Mn, and K. Other acid extractable metals, particularly Mg, Ca, Zn, Cd, and Pb, are mostly in clastic grains. Graphic representation of the Langmuir equation for Mn is consistent with adsorption of Mn by iron in both bottom sediments and suspended sediments. On the basis of the volume of water collected, all the elements except Fe are more concentrated in the water than in the suspended sediments. Fe concentration of the suspended sediments increases with increasing flow because the suspended load is increased. The Mn/Fe ratio of the suspended sediments is approximately equal to or greater than that of the bottom sediments. The Mn/Fe ratio of suspended sediments relative to that of the bottom sediments increases downstream, possibly because of an autocatalytic effect of Mn precipitation. The relationship between sediment and water concentrations is not clear from the data because of the restricted concentration ranges for some elements in the suspended sediment and water. The sediment from the Buffalo River can be used to estimate grossly the concentration of elements in the water
Exact solutions for interacting boson systems under rotation
We study a class of interacting, harmonically trapped boson systems at
angular momentum L. The Hamiltonian leaves a L-dimensional subspace invariant,
and this permits an explicit solution of several eigenstates and energies for a
wide class of two-body interactionsComment: 8 pages, error corrected (concerns generalization of subspace
structure
Regional Brain Activation During Meditation Shows Time and Practice Effects: An Exploratory FMRI Studyâ€
Meditation involves attentional regulation and may lead to increased activity in brain regions associated with attention such as dorsal lateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC). Using functional magnetic resonance imaging, we examined whether DLPFC and ACC were activated during meditation. Subjects who meditate were recruited and scanned on a 3.0 Tesla scanner. Subjects meditated for four sessions of 12 min and performed four sessions of a 6 min control task. Individual and group t-maps were generated of overall meditation response versus control response and late meditation response versus early meditation response for each subject and time courses were plotted. For the overall group (n = 13), and using an overall brain analysis, there were no statistically significant regional activations of interest using conservative thresholds. A region of interest analysis of the entire group time courses of DLPFC and ACC were statistically more active throughout meditation in comparison to the control task. Moreover, dividing the cohort into short (n = 8) and long-term (n = 5) practitioners (>10 years) revealed that the time courses of long-term practitioners had significantly more consistent and sustained activation in the DLPFC and the ACC during meditation versus control in comparison to short-term practitioners. The regional brain activations in the more practised subjects may correlate with better sustained attention and attentional error monitoring. In summary, brain regions associated with attention vary over the time of a meditation session and may differ between long- and short-term meditation practitioners
Bostonia: The Boston University Alumni Magazine. Volume 10
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
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
Composite Fermions, Edge Currents and the Fractional Quantum Hall Effect
We present a theory of composite fermion edge states and their transport
properties in the fractional and integer quantum Hall regimes. We show that the
effective electro-chemical potentials of composite fermions at the edges of a
Hall bar differ, in general, from those of electrons. An expression for the
difference is given. Composite fermion edge states of three different types are
identified. Two of the three types have no analog in previous theories of the
integer or fractional quantum Hall effect. The third type includes the usual
integer edge states. The direction of propagation of the edge states agrees
with experiment. The present theory yields the observed quantized Hall
conductances at Landau level filling fractions p/(mp+-1), for m=0,2,4, p=
1,2,3,... It explains the results of experiments that involve conduction across
smooth potential barriers and through adiabatic constrictions, and of
experiments that involve selective population and detection of fractional edge
channels. The relationship between the present work and Hartree theories of
composite fermion edge structure is discussed.Comment: 19 pages + 6 figures. Self-unpacking uuencoded postscript. To appear
in Physical Review B. Revised version has more details in the Appendix and a
discussion of one more experiment in Section
The effect of cigarette smoke exposure on the development of inflammation in lungs, gut and joints of TNFΔARE mice
The inflammatory cytokine TNF-alpha is a central mediator in many immune-mediated diseases, such as Crohn's disease (CD), spondyloarthritis (SpA) and chronic obstructive pulmonary disease (COPD). Epidemiologic studies have shown that cigarette smoking (CS) is a prominent common risk factor in these TNF-dependent diseases. We exposed TNF Delta ARE mice; in which a systemic TNF-alpha overexpression leads to the development of inflammation; to 2 or 4 weeks of air or CS. We investigated the effect of deregulated TNF expression on CS-induced pulmonary inflammation and the effect of CS exposure on the initiation and progression of gut and joint inflammation. Upon 2 weeks of CS exposure, inflammation in lungs of TNF Delta ARE mice was significantly aggravated. However, upon 4 weeks of CS-exposure, this aggravation was no longer observed. TNF Delta ARE mice have no increases in CD4+ and CD8+ T cells and a diminished neutrophil response in the lungs after 4 weeks of CS exposure. In the gut and joints of TNF Delta ARE mice, 2 or 4 weeks of CS exposure did not modulate the development of inflammation. In conclusion, CS exposure does not modulate gut and joint inflammation in TNF Delta ARE mice. The lung responses towards CS in TNF Delta ARE mice however depend on the duration of CS exposure
Macrophage-derived human resistin is induced in multiple helminth infections and promotes inflammatory monocytes and increased parasite burden.
Parasitic helminth infections can be associated with lifelong morbidity such as immune-mediated organ failure. A better understanding of the host immune response to helminths could provide new avenues to promote parasite clearance and/or alleviate infection-associated morbidity. Murine resistin-like molecules (RELM) exhibit pleiotropic functions following helminth infection including modulating the host immune response; however, the relevance of human RELM proteins in helminth infection is unknown. To examine the function of human resistin (hResistin), we utilized transgenic mice expressing the human resistin gene (hRetnTg+). Following infection with the helminth Nippostrongylus brasiliensis (Nb), hResistin expression was significantly upregulated in infected tissue. Compared to control hRetnTg- mice, hRetnTg+ mice suffered from exacerbated Nb-induced inflammation characterized by weight loss and increased infiltration of inflammatory monocytes in the lung, along with elevated Nb egg burdens and delayed parasite expulsion. Genome-wide transcriptional profiling of the infected tissue revealed that hResistin promoted expression of proinflammatory cytokines and genes downstream of toll-like receptor signaling. Moreover, hResistin preferentially bound lung monocytes, and exogenous treatment of mice with recombinant hResistin promoted monocyte recruitment and proinflammatory cytokine expression. In human studies, increased serum resistin was associated with higher parasite load in individuals infected with soil-transmitted helminths or filarial nematode Wuchereria bancrofti, and was positively correlated with proinflammatory cytokines. Together, these studies identify human resistin as a detrimental factor induced by multiple helminth infections, where it promotes proinflammatory cytokines and impedes parasite clearance. Targeting the resistin/proinflammatory cytokine immune axis may provide new diagnostic or treatment strategies for helminth infection and associated immune-mediated pathology
Centrifugally driven relativistic dynamics on curved trajectories
Motion of test particles along rotating curved trajectories is considered.
The problem is studied both in the laboratory and the rotating frames of
reference. It is assumed that the system rotates with the constant angular
velocity . The solutions are found and analyzed for the case
when the form of the trajectory is given by an Archimedes spiral. It is found
that particles can reach infinity while they move along these trajectories and
the physical interpretation of their behaviour is given. The analogy of this
idealized study with the motion of particles along the curved rotating magnetic
field lines in the pulsar magnetosphere is pointed out. We discuss further
physical development (the conserved total energy case, when )
and astrophysical applications (the acceleration of particles in active
galactic nuclei) of this theory.Comment: 13 pages, 3 figures, to appear in the vol.35 (July issue) of the
"General Relativity and Gravitation
Extension to order of the high-temperature expansions for the spin-1/2 Ising model on the simple-cubic and the body-centered-cubic lattices
Using a renormalized linked-cluster-expansion method, we have extended to
order the high-temperature series for the susceptibility
and the second-moment correlation length of the spin-1/2 Ising models on
the sc and the bcc lattices. A study of these expansions yields updated direct
estimates of universal parameters, such as exponents and amplitude ratios,
which characterize the critical behavior of and . Our best
estimates for the inverse critical temperatures are
and . For the
susceptibility exponent we get and for the correlation
length exponent we get .
The ratio of the critical amplitudes of above and below the critical
temperature is estimated to be . The analogous ratio for
is estimated to be . For the correction-to-scaling
amplitude ratio we obtain .Comment: Misprints corrected, 8 pages, latex, no figure
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