1,385 research outputs found
Constraining compressed versions of MUED and MSSM using soft tracks at the LHC
A compressed spectrum is an anticipated hideout for many beyond standard
model scenarios. Such a spectrum naturally arises in the minimal universal
extra dimension framework and also in supersymmetric scenarios. Low
leptons and jets are characteristic features of such situations. Hence, a
monojet with has been the conventional signal at the Large Hadron
Collider (LHC). However, we stress that inclusion of -binned track
observables from such soft objects provide very efficient discrimination of new
physics signals against various SM backgrounds. We consider two benchmark
points each for minimal universal extra dimension (MUED) and minimal
supersymmetric standard model (MSSM) scenarios. We perform a detailed cut-based
and multivariate analysis (MVA) to show that the new physics parameter space
can be probed in the ongoing run of LHC at 13 TeV center-of-mass energy with an
integrated luminosity 20-50 fb. When studied in conjunction with
the dark matter relic density constraint assuming standard cosmology, we find
that compressed MUED (with ) can be already excluded from the
existing data. Also, MVA turns out to be a better technique than regular
cut-based analysis since tracks provide uncorrelated observables which would
extract more information from an event.Comment: 26 pages, 7 figures. Minor modifications in the text, references
added, accepted for publication in JHE
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Transient expression in Nicotiana benthamiana for rapid functional analysis of genes involved in non-photochemical quenching and carotenoid biosynthesis.
Plants must switch rapidly between light harvesting and photoprotection in response to environmental fluctuations in light intensity. This switch can lead to losses in absorbed energy usage, as photoprotective energy dissipation mechanisms can take minutes to hours to fully relax. One possible way to improve photosynthesis is to engineer these energy dissipation mechanisms (measured as non-photochemical quenching of chlorophyll a fluorescence, NPQ) to induce and relax more quickly, resulting in smaller losses under dynamic light conditions. Previous studies aimed at understanding the enzymes involved in the regulation of NPQ have relied primarily on labor-intensive and time-consuming generation of stable transgenic lines and mutant populations - approaches limited to organisms amenable to genetic manipulation and mapping. To enable rapid functional testing of NPQ-related genes from diverse organisms, we performed Agrobacterium tumefaciens-mediated transient expression assays in Nicotiana benthamiana to test if NPQ kinetics could be modified in fully expanded leaves. By expressing Arabidopsis thaliana genes known to be involved in NPQ, we confirmed the viability of this method for studying dynamic photosynthetic processes. Subsequently, we used naturally occurring variation in photosystem II subunit S, a modulator of NPQ in plants, to explore how differences in amino acid sequence affect NPQ capacity and kinetics. Finally, we functionally characterized four predicted carotenoid biosynthesis genes from the marine algae Nannochloropsis oceanica and Thalassiosira pseudonana and examined the effect of their expression on NPQ in N. benthamiana. This method offers a powerful alternative to traditional gene characterization methods by providing a fast and easy platform for assessing gene function in planta
A novel oligoribonuclease of Escherichia coli. I. Isolation and properties
A new ribonuclease has been isolated from Escherichia coli. The enzyme is present in the 100,000 times g supernatant fraction and has been purified over 200-fold. Studies of the enzyme reveal that: 1. The enzyme shows a marked preference for oligoribonucleotides; indeed, the reaction rate is inversely proportional to the chain length of the substrate. The enzyme does not attack polynucleotides even at high concentrations of enzyme and has no detectable DNase activity. 2. The enzyme is stimulated strongly by Mn2+, less strongly by Mg2+, and not at all by Ca2+ and monovalent cations. 3. The enzyme is purified free of RNase I, RNase II, RNase III, polynucleotide phosphorylase, and other known ribonucleases of E. coli. The enzyme displays identical properties when isolated from mutants of E. coli that are deficient in the above ribonucleases. 4. The enzyme has a marked thermostability, a point of further distinction from RNase II
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Vibronic mixing enables ultrafast energy flow in light-harvesting complex II.
Since the discovery of quantum beats in the two-dimensional electronic spectra of photosynthetic pigment-protein complexes over a decade ago, the origin and mechanistic function of these beats in photosynthetic light-harvesting has been extensively debated. The current consensus is that these long-lived oscillatory features likely result from electronic-vibrational mixing, however, it remains uncertain if such mixing significantly influences energy transport. Here, we examine the interplay between the electronic and nuclear degrees of freedom (DoF) during the excitation energy transfer (EET) dynamics of light-harvesting complex II (LHCII) with two-dimensional electronic-vibrational spectroscopy. Particularly, we show the involvement of the nuclear DoF during EET through the participation of higher-lying vibronic chlorophyll states and assign observed oscillatory features to specific EET pathways, demonstrating a significant step in mapping evolution from energy to physical space. These frequencies correspond to known vibrational modes of chlorophyll, suggesting that electronic-vibrational mixing facilitates rapid EET over moderately size energy gaps
The Effect Of Stellar Pulsation Cycles On Dust Formation: A Temporal Study Of Mid-infrared Spectrum Of O-rich AGB Star, T Cep
Pulsation is believed to be the driving mechanism behind mass loss and dust formation around AGB stars. We present a temporal study of T Cep, a long-period Mira variable, which was observed seven times during a 16 month period spanning a single pulsation cycle. The observed spectral dust features change over the pulsation cycle of this Mira. In general, the overall apparent changes in spectral features can be attributed to changes in the dust temperature, resulting from the intrinsic pulsation cycle of the central star. However, not all feature changes are so easily explained. In particular, the classic interpretation of the broad complex features cannot be attributed to a simple mixture of alumina and glassy silicate. The peak features at 9.7, 10.8, 11.3, 13.1 μm are better explained by crystalline silicate or mixtures of crystalline silicate and alumina
Two anthranilate synthase genes in Arabidopsis: defense-related regulation of the tryptophan pathway.
Multidrug-Resistant Shigella dysenteriae Type 1: Forerunners of a New Epidemic Strain in Eastern India?
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A Sec14 domain protein is required for photoautotrophic growth and chloroplast vesicle formation in Arabidopsis thaliana.
In eukaryotic photosynthetic organisms, the conversion of solar into chemical energy occurs in thylakoid membranes in the chloroplast. How thylakoid membranes are formed and maintained is poorly understood. However, previous observations of vesicles adjacent to the stromal side of the inner envelope membrane of the chloroplast suggest a possible role of membrane transport via vesicle trafficking from the inner envelope to the thylakoids. Here we show that the model plant Arabidopsis thaliana has a chloroplast-localized Sec14-like protein (CPSFL1) that is necessary for photoautotrophic growth and vesicle formation at the inner envelope membrane of the chloroplast. The cpsfl1 mutants are seedling lethal, show a defect in thylakoid structure, and lack chloroplast vesicles. Sec14 domain proteins are found only in eukaryotes and have been well characterized in yeast, where they regulate vesicle budding at the trans-Golgi network. Like the yeast Sec14p, CPSFL1 binds phosphatidylinositol phosphates (PIPs) and phosphatidic acid (PA) and acts as a phosphatidylinositol transfer protein in vitro, and expression of Arabidopsis CPSFL1 can complement the yeast sec14 mutation. CPSFL1 can transfer PIP into PA-rich membrane bilayers in vitro, suggesting that CPSFL1 potentially facilitates vesicle formation by trafficking PA and/or PIP, known regulators of membrane trafficking between organellar subcompartments. These results underscore the role of vesicles in thylakoid biogenesis and/or maintenance. CPSFL1 appears to be an example of a eukaryotic cytosolic protein that has been coopted for a function in the chloroplast, an organelle derived from endosymbiosis of a cyanobacterium
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