1,749 research outputs found
Penentuan Kandungan Pigmen Klorofil Pada Lamun Jenis Halophila Ovalis Di Perairan Malalayang
Tumbuhan di dunia beraneka ragam. Ada yang di darat dan ada yang di laut. Lamun Halophila ovalis merupakan tumbuhan laut yang berbentuk oval dan hidup pada substrat berpasir dan pasir bercampur lumpur. Lamun ini mengandung pigmen terlihat pada hasil analisis spektrofotometer pada ekstrak pigmen total lamun dan pemisahan pigmen lewat uji Kromatografi Lapis Tipis (KLT). Dalam proses ekstraksi digunakan pelarut aseton untuk penggerusan dan petroleum eter sebagai pemisah larutan. Pada kurva spektrofotometer terlihat dua puncak yaitu pada panjang gelombang 428 nm dan 660 nm terlihat masih adanya pencampuran pigmen. Berdasarkan hal tersebut maka dilakukan pemisahan pigmen lewat KLT dan terdapat tiga lapisan yaitu lapisan pertama berwarna kuning teridentifikasi adalah pigmen karotenoid dengan nilai Rf 0,93, lapisan kedua berwarna hijau adalah klorofil a dengan nilai rata-rata Rf 0,96 dan lapisan ketiga berwarna kelabu yang teridentifikasi adalah feofitin a dengan nilai Rf 0,97
Optical Spectroscopy and Nebular Oxygen Abundances of the Spitzer/SINGS Galaxies
We present intermediate-resolution optical spectrophotometry of 65 galaxies
obtained in support of the Spitzer Infrared Nearby Galaxies Survey (SINGS). For
each galaxy we obtain a nuclear, circumnuclear, and semi-integrated optical
spectrum designed to coincide spatially with mid- and far-infrared spectroscopy
from the Spitzer Space Telescope. We make the reduced, spectrophotometrically
calibrated one-dimensional spectra, as well as measurements of the fluxes and
equivalent widths of the strong nebular emission lines, publically available.
We use optical emission-line ratios measured on all three spatial scales to
classify the sample into star-forming, active galactic nuclei (AGN), and
galaxies with a mixture of star formation and nuclear activity. We find that
the relative fraction of the sample classified as star-forming versus AGN is a
strong function of the integrated light enclosed by the spectroscopic aperture.
We supplement our observations with a large database of nebular emission-line
measurements of individual HII regions in the SINGS galaxies culled from the
literature. We use these ancillary data to conduct a detailed analysis of the
radial abundance gradients and average HII-region abundances of a large
fraction of the sample. We combine these results with our new integrated
spectra to estimate the central and characteristic (globally-averaged)
gas-phase oxygen abundances of all 75 SINGS galaxies. We conclude with an
in-depth discussion of the absolute uncertainty in the nebular oxygen abundance
scale.Comment: ApJS, in press; 52 emulateapj pages, 12 figures, and two appendices;
v2: final abundances revised due to minor error; conclusions unchange
A Preference for a Sexual Signal Keeps Females Safe
Predation is generally thought to constrain sexual selection by female choice and limit the evolution of conspicuous sexual signals. Under high predation risk, females usually become less choosy, because they reduce their exposure to their predators by reducing the extent of their mate searching. However, predation need not weaken sexual selection if, under high predation risk, females exhibit stronger preferences for males that use conspicuous signals that help females avoid their predators. We tested this prediction in the fiddler crab Uca terpsichores by increasing females' perceived predation risk from crab-eating birds and measuring the attractiveness of a courtship signal that females use to find mates. The sexual signal is an arching mound of sand that males build at the openings of their burrows to which they attract females for mating. We found that the greater the risk, the more attractive were males with those structures. The benefits of mate preferences for sexual signals are usually thought to be linked to males' reproductive contributions to females or their young. Our study provides the first evidence that a female preference for a sexual signal can yield direct survival benefits by keeping females safe as they search for mates
Hydrochorous Seed Dispersal in Riparian Forests Altered by Urbanization
While riparian habitat alterations from urban stream syndrome are known to affect vegetation establishment and survival, the degree to which riparian seed delivery by hydrochory is affected by urbanization is unclear. We hypothesized that (1) there would be a reduction in the overall number of seeds deposited by streams as watershed urbanization increased; and (2) in the most urbanized watersheds, seeds deposited by water would be predominantly from species with traits favoring dispersal in general, including tall stature and high seed production, and favoring deposition by water in particular, including large seed size and the presence of a dispersal appendage. Nine riparian forests, selected using a stratified random approach, were studied along a gradient of watershed impervious surface area (1â41%) in the Portland, Oregon, USA , metropolitan region. Seeds deposited by water were collected using turf traps four times over a 15âmonth period that spanned both wet and dry seasonal conditions. Along the urbanization gradient of increasing total impervious area, there was a significant decrease in the total number of seeds deposited by hydrochory (adjusted R 2 = 0.74; P \u3c 0.01). Deposition of seeds from shadeâtolerant and native taxa by water decreased as surrounding urbanization increased (adjusted R 2 = 0.57; P \u3c 0.05). Deposition of nonânative seeds increased as urban development within 500 m from the riparian area increased (adjusted R 2 = 0.79, P \u3c 0.01). The findings demonstrate that seed dispersal patterns in riparian areas are altered by urbanization. During higher rainfall seasons, flashy hydrology and stream bank scour appear to alter seed delivery in highly urban watersheds. While the urban stream syndrome contributes to altered dispersal, other urbanization pressures that affect source populations, such as vegetation removal, also limit seed delivery to riparian sites. Overall, our results suggest that urbanization can limit the regeneration processes that maintain vegetation communities in riparian forests
Neutrino Quasielastic Scattering on Nuclear Targets: Parametrizing Transverse Enhancement (Meson Exchange Currents)
We present a parametrization of the observed enhancement in the transverse
electron quasielastic (QE) response function for nucleons bound in carbon as a
function of the square of the four momentum transfer () in terms of a
correction to the magnetic form factors of bound nucleons. The parametrization
should also be applicable to the transverse cross section in neutrino
scattering. If the transverse enhancement originates from meson exchange
currents (MEC), then it is theoretically expected that any enhancement in the
longitudinal or axial contributions is small. We present the predictions of the
"Transverse Enhancement" model (which is based on electron scattering data
only) for the differential and total QE cross sections
for nucleons bound in carbon. The dependence of the transverse
enhancement is observed to resolve much of the long standing discrepancy in the
QE total cross sections and differential distributions between low energy and
high energy neutrino experiments on nuclear targets.Comment: Revised Version- July 21, 2011: 17 pages, 20 Figures. To be published
in Eur. Phys. J.
Effects of Surface Geology on Seismic Ground Motion Deduced from Ambient-Noise Measurements in the Town of Avellino, Irpinia Region (Italy)
The effects of surface geology on ground motion
provide an important tool in seismic hazard studies. It is well
known that the presence of soft sediments can cause amplification
of the ground motion at the surface, particularly when there is a
sharp impedance contrast at shallow depth. The town of Avellino is
located in an area characterised by high seismicity in Italy, about
30 km from the epicentre of the 23 November 1980, Irpinia
earthquake (M = 6.9). No earthquake recordings are available in
the area. The local geology is characterised by strong heterogeneity,
with impedance contrasts at depth. We present the results
from seismic noise measurements carried out in the urban area of
Avellino to evaluate the effects of local geology on the seismic
ground motion. We computed the horizontal-to-vertical (H/V)
noise spectral ratios at 16 selected sites in this urban area for which
drilling data are available within the first 40 m of depth. A Rayleigh
wave inversion technique using the peak frequencies of the
noise H/V spectral ratios is then presented for estimating Vs
models, assuming that the thicknesses of the shallow soil layers are
known. The results show a good correspondence between experimental
and theoretical peak frequencies, which are interpreted in
terms of sediment resonance. For one site, which is characterised
by a broad peak in the horizontal-to-vertical spectral-ratio curve,
simple one-dimensional modelling is not representative of the
resonance effects. Consistent variations in peak amplitudes are seen
among the sites. A site classification based on shear-wave velocity
characteristics, in terms of Vs30, cannot explain these data. The
differences observed are better correlated to the impedance contrast
between the sediments and basement. A more detailed investigation
of the physical parameters of the subsoil structure, together with
earthquake data, are desirable for future research, to confirm these
data in terms of site response
Radiative capture and electromagnetic dissociation involving loosely bound nuclei: the B example
Electromagnetic processes in loosely bound nuclei are investigated using an
analytical model. In particular, electromagnetic dissociation of B is
studied and the results of our analytical model are compared to numerical
calculations based on a three-body picture of the B bound state. The
calculation of energy spectra is shown to be strongly model dependent. This is
demonstrated by investigating the sensitivity to the rms intercluster distance,
the few-body behavior, and the effects of final state interaction. In contrast,
the fraction of the energy spectrum which can be attributed to E1 transitions
is found to be almost model independent at small relative energies. This
finding is of great importance for astrophysical applications as it provides us
with a new tool to extract the E1 component from measured energy spectra. An
additional, and independent, method is also proposed as it is demonstrated how
two sets of experimental data, obtained with different beam energy and/or
minimum impact parameter, can be used to extract the E1 component.Comment: Submitted to Phys. Rev. C. 10 pages, 7 figure
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