2,037 research outputs found
The \u3cem\u3elet-7\u3c/em\u3e MicroRNA Family Members \u3cem\u3emir\u3c/em\u3e-48, \u3cem\u3emir\u3c/em\u3e-84, and mir-241 Function Together to Regulate Developmental Timing in \u3cem\u3eCaenorhabditis elegans\u3c/em\u3e
The microRNA let-7 is a critical regulator of developmental timing events at the larval-to-adult transition in C. elegans. Recently, microRNAs with sequence similarity to let-7 have been identified. We find that doubly mutant animals lacking the let-7 family microRNA genes mir-48 and mir-84 exhibit retarded molting behavior and retarded adult gene expression in the hypodermis. Triply mutant animals lacking mir-48, mir-84, and mir-241 exhibit repetition of L2-stage events in addition to retarded adult-stage events. mir-48, mir-84, and mir-241 function together to control the L2-to-L3 transition, likely by base pairing to complementary sites in the hbl-1 3′ UTR and downregulating hbl-1 activity. Genetic analysis indicates that mir-48, mir-84, and mir-241 specify the timing of the L2-to-L3 transition in parallel to the heterochronic genes lin-28 and lin-46. These results indicate that let-7 family microRNAs function in combination to affect both early and late developmental timing decisions
Chemical weathering of new pyroclastic deposits from Mt. Merapi (Java), Indonesia.
The Java Island, Indonesia with abundant amount of pyroclastic deposits is located in the very active and dynamic Pacific Ring of Fires. Studying the geochemical weathering indices of these pyroclastic deposits is important to get a clear picture about weathering profiles on deposits resulting from the eruption of Mt. Merapi. Immediately after the first phase of the eruption (March to June 2006), moist and leached pyroclastic deposits were collected. These pyroclastic deposits were found to be composed of volcanic glass, plagioclase feldspar in various proportions, orthopyroxene, clinopyroxene, olivine, amphibole and titanomagnetite. The total elemental composition of the bulk samples (including trace elements and heavy metals) was determined by wet chemical methods and X-ray fluorescence (XRF) analyses. Weathering of the pyroclastic deposits was studied using various weathering indices. The Ruxton ratio, weathering index of Parker, Vought resudual index and chemical index of weathering of moist pyroclastic deposits were lower than those of the leached samples, but the alteration indices (chemical and plagioclase) were slightly higher in the moist compared to the leached pyroclastic deposits
Do ultrafast exciton-polaron decoherence dynamics govern photocarrier generation efficiencies in polymer solar cells?
All-organic-based photovoltaic solar cells have attracted considerable
attention because of their low-cost processing and short energy payback time.
In such systems the primary dissociation of an optical excitation into a pair
of photocarriers has been recently shown to be extremely rapid and efficient,
but the physical reason for this remains unclear. Here, two-dimensional
photocurrent excitation spectroscopy, a novel non-linear optical spectroscopy,
is used to probe the ultrafast coherent decay of photoexcitations into
charge-producing states in a polymer:fullerene based solar cell. The
two-dimensional photocurrent spectra are interpreted by introducing a
theoretical model for the description of the coupling of the electronic states
of the system to an external environment and to the applied laser fields. The
experimental data show no cross-peaks in the two-dimensional photocurrent
spectra, as predicted by the model for coherence times between the exciton and
the photocurrent producing states of 20\,fs or less
Present-Day Descendants of z=3 Ly-{\alpha} Emitting Galaxies in the Millennium-II Halo Merger Trees
Using the Millennium-II Simulation dark matter sub-halo merger histories, we
created mock catalogs of Lyman Alpha Emitting (LAE) galaxies at z=3.1 to study
the properties of their descendants. Several models were created by selecting
the sub-halos to match the number density and typical dark matter mass
determined from observations of these galaxies. We used mass-based and
age-based selection criteria to study their effects on descendant populations
at z~2, 1 and 0. For the models that best represent LAEs at z=3.1, the z=0
descendants have a median dark matter halo mass of 10^12.7 M_Sun, with a wide
scatter in masses (50% between 10^11.8 and 10^13.7 M_Sun). Our study
differentiated between central and satellite sub-halos and found that ~55% of
z=0 descendants are central sub-halos with M_Median~10^12 M_Sun. This confirms
that central z=0 descendants of z=3.1 LAEs have halo masses typical of L* type
galaxies. The satellite sub-halos reside in group/cluster environments with
dark matter masses around 10^14 M_Sun. The median descendant mass is robust to
various methods of age determination, but it could vary by a factor of 5 due to
current observational uncertainties in the clustering of LAEs used to determine
their typical z=3.1 dark matter mass.Comment: Accepted for publication in Ap
Reducing errors by increasing the error rate: MLP Acoustic Modeling for Broadcast News Transcription
We describe some aspects of a Broadcast News recognition system based on hybrid HMM/MLP acoustic modeling. These include the use of novel 'modulation spectrogram' features which are combined with conventional models at the posterior probability level, some experiments with nonlinear segment normalization, and an investigation of the interaction of model size and training set size for an multilayer perceptron (MLP) acoustic classifier. We also report preliminary results of incorporating gender-dependence into this system
Most \u3cem\u3eCaenorhabditis elegans\u3c/em\u3e MicroRNAs are Individually Not Essential for Development or Viability
MicroRNAs (miRNAs), a large class of short noncoding RNAs found in many plants and animals, often act to post-transcriptionally inhibit gene expression. We report the generation of deletion mutations in 87 miRNA genes in Caenorhabditis elegans, expanding the number of mutated miRNA genes to 95, or 83% of known C. elegans miRNAs. We find that the majority of miRNAs are not essential for the viability or development of C. elegans, and mutations in most miRNA genes do not result in grossly abnormal phenotypes. These observations are consistent with the hypothesis that there is significant functional redundancy among miRNAs or among gene pathways regulated by miRNAs. This study represents the first comprehensive genetic analysis of miRNA function in any organism and provides a unique, permanent resource for the systematic study of miRNAs
The Next Generation Virgo cluster Survey. V. modelling the dynamics of M87 with the Made-to-Measure method
We study the dynamics of the giant elliptical galaxy M87 from the central to
the outermost regions with the made-to-measure (M2M) method. We use a new
catalogue of 922 globular cluster line-of- sight velocities extending to a
projected radius of 180 kpc (equivalent to 25 M87 effective radii), and SAURON
integral field unit data within the central 2.4 kpc. 263 globular clusters,
mainly located beyond 40 kpc, are newly observed by the Next Generation Virgo
Survey (NGVS). For the M2M modelling, the gravitational potential is taken as a
combination of a luminous matter potential with a constant stellar
mass-to-light ratio and a dark matter potential modelled as a logarithmic
potential. Our best dynamical model returns a stellar mass-to-light ratio in
the I band of M/LI = 6.0(+ -0.3) M_sun/L_sun with a dark matter potential scale
velocity of 591(+ -50) km/s and scale radius of 42(+ -10) kpc. We determine the
total mass of M87 within 180 kpc to be (1.5 + - 0.2) 10^13 M_sun. The mass
within 40 kpc is smaller than previous estimates determined using globular
cluster kinematics that did not extend beyond 45 kpc. With our new globular
cluster velocities at much larger radii, we see that globular clusters around
40 kpc show an anomalously large velocity dispersion which affected previous
results. The mass we derived is in good agreement with that inferred from ROSAT
X-ray observation out to 180 kpc. Within 30 kpc our mass is also consistent
with that inferred from Chandra and XMM-Newton X-ray observations, while within
120 kpc it is about 20% smaller. The model velocity dispersion anisotropy beta
parameter for the globular clusters in M87 is small, varying from -0.2 at the
centre to 0.2 at 40 kpc, and gradually decreasing to zero at 120 kpc.Comment: 20 pages, 16 figures, Accepted by Ap
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