526 research outputs found
Triassic palynoevents in the circum-Arctic region
Triassic successions of the present-day Arctic contain abundant and diverse assemblages of nonmarine palynomorphs that have provided important biostratigraphic information. Dinoflagellate cyst are biostratigraphically useful in marine intervals in the Upper Triassic. Based on published records, we present a compilation of 78 last occurrences (LOs), first occurrences (FOs), and some abundance events that are anticipated to have correlation potential in the Arctic region. Palynological work has been carried out in many Arctic areas, with extensive palynological research published on the Triassic successions of the Norwegian Barents Sea and Svalbard. An updated, recent palynological zonation scheme exists for that region, integrating previous schemes and illustrating the chronostratigraphic value of palynology in the Triassic. For the Lower and Middle Triassic, good ammonoid control ties the palynological zones to the chronostratigraphic scale. Independent control is sparse, and resolution is lower in the Upper Triassic, so that palynology is commonly the only biostratigraphic discipline available for chronostratigraphic dating and correlation
Permian palynoevents in the circum-Arctic region
Permian palynofloras are recorded around the present-day Arctic and are typically dominated by taeniate and non-taeniate pollen, with intervals of spore domination. The assemblages show close similarities around the Arctic. Based on the published record, we present a compilation of 23 last occurrences (LOs), first occurrences (FOs), and some abundance events. These are anticipated to have regional correlation potential. In general, the Permian palynofloras of the Arctic have not been extensively studied, and the resolution is low due to a general lack of independent age control
Polarization control of metal-enhanced fluorescence in hybrid assemblies of photosynthetic complexes and gold nanorods
Fluorescence imaging of hybrid nanostructures composed of a bacterial light-harvesting complex LH2 and Au nanorods with controlled coupling strength is employed to study the spectral dependence of the plasmon-induced fluorescence enhancement. Perfect matching of the plasmon resonances in the nanorods with the absorption bands of the LH2 complexes facilitates a direct comparison of the enhancement factors for longitudinal and transverse plasmon frequencies of the nanorods. We find that the fluorescence enhancement due to excitation of longitudinal resonance can be up to five-fold stronger than for the transverse one. We attribute this result, which is important for designing plasmonic functional systems, to a very different distribution of the enhancement of the electric field due to the excitation of the two characteristic plasmon modes in nanorods
Comparing large lecture mechanics curricula using the Force Concept Inventory: A five thousand student study
The performance of over 5000 students in introductory calculus-based
mechanics courses at the Georgia Institute of Technology was assessed using the
Force Concept Inventory (FCI). Results from two different curricula were
compared: a traditional mechanics curriculum and the Matter & Interactions
(M&I) curriculum. Post-instruction FCI averages were significantly higher for
the traditional curriculum than for the M&I curriculum; the differences between
curricula persist after accounting for factors such as pre-instruction FCI
scores, grade point averages, and SAT scores. FCI performance on categories of
items organized by concepts was also compared; traditional averages were
significantly higher in each concept. We examined differences in student
preparation between the curricula and found that the relative fraction of
homework and lecture topics devoted to FCI force and motion concepts correlated
with the observed performance differences. Limitations of concept inventories
as instruments for evaluating curricular reforms are discussed.Comment: 21 pages, 4 figures, submitted to Am. J. Phys. arXiv admin note:
substantial text overlap with arXiv:1112.559
Forward Neutron Production at the Fermilab Main Injector
We have measured cross sections for forward neutron production from a variety
of targets using proton beams from the Fermilab Main Injector. Measurements
were performed for proton beam momenta of 58 GeV/c, 84 GeV/c, and 120 GeV/c.
The cross section dependence on the atomic weight (A) of the targets was found
to vary as where is for a beam momentum of
58 GeV/c and 0.540.05 for 120 GeV/c. The cross sections show reasonable
agreement with FLUKA and DPMJET Monte Carlos. Comparisons have also been made
with the LAQGSM Monte Carlo.Comment: Accepted for publication in Physical Review D. This version
incorporates small changes suggested by referee and small corrections in the
neutron production cross sections predicted by FLUK
Indium(II) chloride as a precursor in the synthesis of ternary (AgâInâS) and quaternary (AgâInâZnâS) nanocrystals
A new indium precursor, namely, indium(II)
chloride, was tested as a precursor in the synthesis of ternary
AgâInâS and quaternary AgâInâZnâS nanocrystals. This new
precursor, being in fact a dimer of Cl2InâInCl2 chemical structure,
is significantly more reactive than InCl3, typically used in the
preparation of these types of nanocrystals. This was evidenced by
carrying out comparative syntheses under the same reaction
conditions using these two indium precursors in combination with
the same silver (AgNO3) and zinc (zinc stearate) precursors. In
particular, the use of indium(II) chloride in combination with low
concentrations of the zinc precursor yielded spherical-shaped (D =
3.7â6.2 nm) AgâInâZnâS nanocrystals, whereas for higher
concentrations of this precursor, rodlike nanoparticles (L = 9â10
nm) were obtained. In all cases, the resulting nanocrystals were enriched in indium (In/Ag = 1.5â10.3). Enhanced indium precursor
conversion and formation of anisotropic, longitudinal nanoparticles were closely related to the presence of thiocarboxylic acid type of
ligands in the reaction mixture. These ligands were generated in situ and subsequently bound to surfacial In(III) cations in the
growing nanocrystals. The use of the new precursor of enhanced reactivity facilitated precise tuning of the photoluminescence color
of the resulting nanocrystals in the spectral range from ca. 730 to 530 nm with photoluminescence quantum yield (PLQY) varying
from 20 to 40%. The fabricated AgâInâS and AgâInâZnâS nanocrystals exhibited the longest, reported to date,
photoluminescence lifetimes of âŒ9.4 and âŒ1.4 ÎŒs, respectively. It was also demonstrated for the first time that ternary (AgâInâ
S) and quaternary (AgâInâZnâS) nanocrystals could be applied as efficient photocatalysts, active under visible light (green)
illumination, in the reaction of aldehydes reduction to alcohols
Alterations in the Interleukin-1/Interleukin-1 Receptor Antagonist Balance Modulate Cardiac Remodeling following Myocardial Infarction in the Mouse
Background
Healing after acute myocardial infarction (AMI) is characterized by an intense inflammatory response and increased Interleukin-1 (IL-1) tissue activity. Genetically engineered mice lacking the IL-1 receptor (IL-1R1-/-, not responsive to IL-1) or the IL-1 receptor antagonist (IL-1Ra, enhanced response to IL-1) have an altered IL-1/IL-1Ra balance that we hypothesize modulates infarct healing and cardiac remodeling after AMI. Methods
IL-1R1-/- and IL-1Ra-/- male mice and their correspondent wild-types (WT) were subjected to permanent coronary artery ligation or sham surgery. Infarct size (trichrome scar size), apoptotic cell death (TUNEL) and left ventricular (LV) dimensions and function (echocardiography) were measured prior to and 7 days after surgery. Results
When compared with the corresponding WT, IL-1R1-/- mice had significantly smaller infarcts (â25%), less cardiomyocyte apoptosis (â50%), and reduced LV enlargement (LV end-diastolic diameter increase [LVEDD], â20%) and dysfunction (LV ejection fraction [LVEF] decrease, â50%), whereas IL-1Ra-/- mice had significantly larger infarcts (+75%), more apoptosis (5-fold increase), and more severe LV enlargement (LVEDD increase,+30%) and dysfunction (LVEF decrease, +70%)(all P values \u3c0.05). Conclusions
An imbalance in IL-1/IL-1Ra signaling at the IL-1R1 level modulates the severity of cardiac remodeling after AMI in the mouse, with reduced IL-1R1 signaling providing protection and unopposed IL-1R1 signaling providing harm
Probing the Interstellar Medium in Early type galaxies with ISO observations
Four IRAS-detected early type galaxies were observed with ISO. With the
exception of the 15 micron image of NGC1052, the mid-IR emission from NGC1052,
NGC1155, NGC5866 and NGC6958 at 4.5, 7 and 15 microns show extended emission.
Mid-IR emission from NGC1052, NGC1155, and NGC6958 follows a de Vaucouleurs
profile. The ratio of 15/7 micron flux decreases with radius in these galaxies,
approaching the values empirically observed for purely stellar systems. In
NGC5866, the 7 and 15 micron emission is concentrated in the edge-on dust lane.
All the galaxies are detected in the [CII] line, and the S0s NGC1155 and
NGC5866 are detected in the [OI] line as well. The ISO-LWS observations of the
[CII] line are more sensitive measures of cool, neutral ISM than HI and CO by
about a factor of 10-100. Three of four early type galaxies, namely NGC1052,
NGC6958 and NGC5866, have low ratio FIR/Blue and show a lower [CII]/FIR, which
is due to a softer radiation field from old stellar populations. The low
[CII]/CO ratio in NGC5866 ([CII]/CO(1-0) < 570) confirms this scenario. We
estimate the UV radiation expected from the old stellar populations in these
galaxies and compare it to that needed to heat the gas to account for the
cooling observed [CII] and [OI] lines. In three out of four galaxies, NGC1052,
NGC5866 and NGC6958, the predicted UV radiation falls short by a factor of 2-3.
In view of the observed intrinsic scatter in the "UV-upturn" in elliptical
galaxies and its great sensitivity to age and metallicity effects, this is not
significant. However, the much larger difference (about a factor of 20) between
the UV radiation from old stars and that needed to produce the FIR lines for
NGC 1155 is strong evidence for the presence of young stars, in NGC1155.Comment: To appear in the Astrophysical Journal. Figure 1 appears as a
separate jpg figur
Search for neutral charmless B decays at LEP
A search for rare charmless decays of \Bd and \Bs mesons has been performed in the exclusive channels \Bd_{(\mathrm s)}\ra\eta\eta, \Bd_{(\mathrm s)}\ra\eta\pio and \Bd_{(\mathrm s)}\ra\pio\pio. The data sample consisted of three million hadronic \Zo decays collected by the L3 experiment at LEP from 1991 through 1994. No candidate event has been observed and the following upper limits at 90\% confidence level on the branching ratios have been set \begin{displaymath} \mathrm{Br}(\Bd\ra\eta\eta)<4.1\times 10^{-4},\,\, \mathrm{Br}(\Bs\ra\eta\eta)<1.5\times 10^{-3},\,\, \end{displaymath} \begin{displaymath} \mathrm{Br}(\Bd\ra\eta\pio)<2.5\times 10^{-4},\,\, \mathrm{Br}(\Bs\ra\eta\pio)<1.0\times 10^{-3},\,\, \end{displaymath} \begin{displaymath} \mathrm{Br}(\Bd\ra\pio\pio)<6.0\times 10^{-5},\,\, \mathrm{Br}(\Bs\ra\pio\pio)<2.1\times 10^{-4}. \end{displaymath} These are the first experimental limits on \Bd\ra\eta\eta and on the \Bs neutral charmless modes
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