17,971 research outputs found
Rat ß-glucuronidase as a reporter protein for the analysis of the plant secretory pathway.
No full textE. coli β-glucuronidase, a cytosolic enzyme, was found not to be a good reporter enzyme for secretion studies in plants. In this study, we chose to test and adapt an animal β-glucuronidase as a better reporter protein for the secretory pathway of plants. We modified rat β-glucuronidase to obtain secreted and vacuolar variants. Five different C-termini were produced: the original C-terminus of the rat enzyme, a 19 codon deletion (Δ19), a 15 codon deletion (Δ15) and fusions of the Δ19 or Δ15 termini with the last 6 or 7 codons of the vacuolar sorting determinant of tobacco chitinase A, respectively. The signal sequence of the rat β-glucuronidase polypeptide was replaced by the sequence encoding the signal peptide of tobacco chitinase A. In a transient expression system, the best enzymatic activity was found with β-glucuronidase having the 15 codons deletion, therefore Δ15 (secRGUS) and Δ15 + Chi (RGUS-Chi) were further evaluated and their efficiency of secretion or vacuolar targeting were tested under different conditions. To determine the correct targeting of reporter genes, we compared the localization of β-glucuronidase and of an endogenous marker, α-mannosidase. Treating cells with drugs that specifically affect different aspects of the secretory pathway also tested the validity of RGUS-based reporters. A non-specific inhibitor such as cytochalasin D and a wide range inhibitor such as BFA were compared with specific inhibitors such as wortmannin and bafilomycin A1. Finally, monensin and NH4Cl were used to evaluate the role of vacuolar pH in correct RGUS-Chi targeting. The two new reporter proteins proved to be good tools for our studies in the transient expression system in tobacco protoplasts and for further applications. © 2007 Società Botanica Italiana
Interleaved configurations of percutaneous epidural stimulation enhanced overground stepping in a person with chronic paraplegia
No full textDescending motor signals are disrupted after complete spinal cord injury (SCI) resulting in loss of standing and walking. We previously restored standing and trunk control in a person with a T3 complete SCI following implantation of percutaneous spinal cord epidural stimulation (SCES). We, hereby, present a step-by-step procedure on configuring the SCES leads to initiate rhythmic lower limb activation (rhythmic-SCES) resulting in independent overground stepping in parallel bars and using a standard walker. Initially, SCES was examined in supine lying at 2 Hz before initiating stepping-like activity in parallel bars using 20 or 30 Hz; however, single lead configuration (+2, −5) resulted in lower limb adduction and crossing of limbs, impairing the initiation of overground stepping. After 6 months, interleaving the original rhythmic-SCES with an additional configuration (−12, +15) on the opposite lead, resulted in a decrease of the extensive adduction tone and allowed the participant to initiate overground stepping up to 16 consecutive steps. The current paradigm suggests that interleaving two rhythmic-SCES configurations may improve the excitability of the spinal circuitry to better interpret the residual descending supraspinal signals with the ascending proprioceptive inputs, resulting in a stepping-like motor behavior after complete SCI
Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of meson decays to J/ψη and J/ψη′
No full textFirst evidence of the B 0 → J / ψ ω decay is found and the B s 0 → J / ψ η and B s 0 → J / ψ η ′ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb -1 collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The branching fractions of these decays are measured relative to that of the B 0 → J / ψ ρ 0 decay:frac(B (B 0 → J / ψ ω), B (B 0 → J / ψ ρ 0)) = 0.89 ± 0.19 (stat) - 0.13 + 0.07 (syst),frac(B (B s 0 → J / ψ η), B (B 0 → J / ψ ρ 0)) = 14.0 ± 1.2 (stat) - 1.5 + 1.1 (syst) - 1.0 + 1.1 (frac(f d, f s)),frac(B (B s 0 → J / ψ η ′), B (B 0 → J / ψ ρ 0)) = 12.7 ± 1.1 (stat) - 1.3 + 0.5 (syst) - 0.9 + 1.0 (frac(f d, f s)), where the last uncertainty is due to the knowledge of f d / f s, the ratio of b-quark hadronization factors that accounts for the different production rate of B 0 and B s 0 mesons. The ratio of the branching fractions of B s 0 → J / ψ η ′ and B s 0 → J / ψ η decays is measured to befrac(B (B s 0 → J / ψ η ′), B (B s 0 → J / ψ η)) = 0.90 ± 0.09 (stat) - 0.02 + 0.06 (syst)
Measurement of the branching fraction
No full textThe B
0
s
→ J/ψK
0
S
branching fraction is measured in a data sample corresponding to 0.41 fb−1
of integrated luminosity collected with the LHCb detector at the LHC. This channel is sensitive to
the penguin contributions affecting the sin 2β measurement from B
0
→ J/ψK
0
S
. The time-integrated
branching fraction is measured to be B(B
0
s
→ J/ψK
0
S
) = (1.83±0.28)×10−5
. This is the most precise
measurement to date
The developmental morphology of Leea guineensis. II. Floral development
No full textPT: J; CR: BENNEK C, 1958, BOT JB SYST, V77, P423 BUGNON F, 1953, PUBLICATION U DIJON, V11 CRONQUIST A, 1981, INTEGRATED SYSTEM CL CRONQUIST A, 1988, EVOLUTION CLASSIFICA DAHLGREN RMT, 1980, BOTANICAL J LINNEAN, V80, P91 ERDTMAN G, 1966, POLLEN MORPHOLOGY PL, V1 GAGNEPAIN MF, 1910, B SOC BOT FR, V57, P331 GERRATH JM, 1988, ASPECTS FLORAL DEV, P121 GERRATH JM, 1988, CAN J BOT, V66, P1334 GERRATH JM, 1988, CAN J BOT, V66, P209 GERRATH JM, 1988, THESIS U GUELPH GUEL GERRATH JM, 1989, CAN J BOT, V67, P1356 GERRATH JM, 1989, CAN J BOT, V67, P2371 GERRATH JM, 1989, CAN J BOT, V67, P803 HEYWOOD VH, 1978, FLOWERING PLANTS WOR LACROIX CR, 1990, BOT GAZ, V151, P204 LATIFF A, 1984, 4 U KEB COLL WORK PA, P33 MEDAN D, 1988, ASPECTS FLORAL DEV, P133 NAIR NC, 1957, WILD BOT NOT, V110, P160 NAIR NC, 1968, J INDIAN BOT SOC, V47, P193 POSLUSZNY U, 1980, CAN J BOT, V58, P2491 POSLUSZNY U, 1986, CAN J BOT, V64, P1620 RISDALE CE, 1974, BLUMEA, V22, P57 SATTLER R, 1973, ORGANOGENESIS FLOWER SMITH AC, 1985, FLORA VITIENSIS NOVA, V3, P712 SUSSENGUTH K, 1953, NATURLICHEN PFLANZ D, V20, P372 TARNAVSCHI IT, 1968, POLLEN SPORES, V10, P221 TOELKEN H, 1983, FLOWERING PLANTS AUS, P227 WILD H, 1966, FLORA ZAMBESIACA 2, V2, P492; NR: 29; TC: 6; J9: BOT GAZ; PG: 11; GA: DU901Source type: Electronic(1
Direct Numerical Simulations of Turbulent Mixing Layers Between Two Fluids of Large Density Difference
No full textIn numerous practical applications, shear layers exist between fluids of strongly differing densities. At high Atwood numbers, the large variations in density introduce important effects that have recently been observed in other flows (e.g., Livescu and Ristorcelli, J. Fluid Mech., 605:145–180, 2008). To investigate the inertial variable density effects on the instability growth and structure of mixing layers, we perform very large Direct Numerical Simulations of planar mixing layers between two miscible fluids, each with different density. The DNS domain sizes accommodate large extents of mode pairings, based on the most unstable modes obtained from linear stability analysis. The results display the overall statistical effects on the turbulence and mixing, as well as the structural differences that occur as Atwood number is varied. In particular, significant asymmetries are introduced by the differences in the densities of the mixing layer streams
Measurement of the ratio of prompt χ c to J / ψ production in pp collisions at √s = 7 TeV
No full textThe prompt production of charmonium χ c and J / ψ states is studied in proton-proton collisions at a centre-of-mass energy of √s = 7 TeV at the Large Hadron Collider. The χ c and J / ψ mesons are identified through their decays χ c → J / ψ γ and J / ψ → μ + μ - using 36 pb - 1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for χ c and J / ψ, σ (χ c → J / ψ γ) / σ (J / ψ), is determined as a function of the J / ψ transverse momentum in the range 2 < p T J / ψ < 15 GeV / c. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low p T J / ψ region
Stimuli-responsive Photoluminescent and Structural Properties of MIL-53(Al) Metal-Organic Framework
No full textThe term "metal-organic frameworks" (MOFs) refers to a novel family of crystalline microporous materials that have vast surfaces with customizable functions such as the ability to separate and purify gases [1]. Coordination bonds between organic moieties and metals or metal oxides provide these materials their structural integrity [2]. MOFs may have a flexible structure, which can result in the unusual breathing phenomenon or gate-opening effect: as external stimuli like pressure, temperature, solvents, or gas molecules are added to or removed from MOFs, the pore diameter of the material changes [3]. The class of MOFs that exhibits breathing phenomena has enormous potential in green and renewable energy as media of gas storage, chemical sensors, drug delivery systems, and is therefore at the center of attention of both fundamental and applied research [4].
This framework, MIL-53(M) series, with M = Al, Sc, Cr, Fe, and Ga, is a prototypical family of flexible MOFs, exhibiting a reversible, structural transition (breathing) from large pore (LP) to narrow pore (NP) configurations upon hydration-dehydration, respectively. Generally, the structure of MIL-53(M), is composed of connections of corner-sharing MO4(OH)2 octahedra connected by 1,4-benzenedicarboxylic (BDC) acids. The channels of as- synthetized MIL-53 are filled with disordered BDC and H2O molecules, revealing the NP form of MIL-53 (Al, Cr), which is produced hydrothermally and is referred to as MIL-53 as. The hydrogen-bond interactions between the oxygen atoms of the carboxylic group and the 2-hydroxo group, as well as the hydrogen atoms of the water molecules, are what give rise to this NP structure [5]. Due to the lack of contact, the MIL-53 develops a LP kind of porous structure when dehydrated at high temperatures. Temperature changes, in addition to guest molecules, can cause the framework transition, which results in the dehydration-rehydration cycle. MIL-53 has been demonstrated to exhibit both the LP and NP forms at high and low temperatures (>300 K and 300 K), respectively. The framework transition takes place through two different mechanisms in the absence of van der Waals force interactions between the adsorbent and the adsorbate: (1) twisted benzene groups of benzenedicarboxylate (BDC) ligands, also known as " π-flipping," and (2) distortion mode from the corner- sharing octahedral MO6 (M = Al, Cr) clusters [6].
This work focuses on photophysical characteristics of MIL-53(Al) that includes important properties: it is stable, highly active, and well suited for CO2/CH4 separation, to exhibit good adsorption behavior of organic dyes [7], and to be fluorescent sensors for Fe3+ [8]. Additionally, Al carboxylate-based MOFs were demonstrated to be photoresponsive and to exhibit photocatalytic activity towards RhB degradation and CO2 reduction [9]. Herein, we investigated the photoluminescence (PL) and structural properties of MIL-53(Al) under different stimuli, such as temperature and mechanical pressure, and based on which, selectivity and reusability tests of this material are also performed under different heating-cooling cycles, respectively.
EXPERIMENTAL RESULTS
We prepared different pellets of MIL-53(Al)-activated powder using mechanical hydraulic press with the pressure ranging from 0.044 to 0.22 GPa and then analyzed their PL properties comparing with the powder samples. Time-resolved PL spectra were carried out under a tunable laser excitation, provided by an optical parametric oscillator (VIBRANT OPOTEK) pumped by the third harmonic (3.49 eV) of a Nd:YAG laser (pulse width 5 ns, repetition rate 10 Hz). The emitted light was analyzed by a monochromator equipped with a grating of 150 lines/mm and blaze wavelength 300 nm,and acquired by an intensified CCD camera driven by a delay generator (PIMAX Princeton Instruments) setting the acquisition time window, TW, and the delay, TD, with
respect to the arrival of laser pulses. All the emission spectra were detected with a bandwidth of 10 nm and corrected for the monochromator dispersion.
We demonstrated that under UV excitation at 305 nm, MIL-53(Al) exhibits two emission bands, both decaying in a ns timescale. The first band is centered at 393 nm and is associated with an Intra-ligand charge transfer mechanism of the BDC linkers; the second is peaked at 452 nm and is related to LMCT transition. When subjected to temperature changes, this luminescent MOF exhibits a unique Ratiometric fluorescence behavior. As shown in Figure 1, the emission at 393 nm is quenched when the sample is heated up to 400 K. It is worth noting that this thermochromic response exhibits reversible relationship of emission intensity with respect to temperature which is shown to be reproducible. Moreover, under higher mechanical stress MIL-53(Al) displays turn-on behavior in PL emission intensity, which also restored towards the original intensity once after the removal of stress, hence offering a thrilling avenue for the application in mechanically deformed-based luminescent sensors.
Figure 1 – PL emission spectra of MIL-53(Al) powder recorded under UV excitation at 300 to 400K (in left) and, in right PL emission spectra of MIL-53(Al) powder + pellets pressed at pressure, P = 0.12 to 0.22 GPa
In conclusion, the reported results evidence the stimuli-responsive properties of MIL-53(Al) and are relevant in the development of MOFs based sensors.
REFERENCES
[1] Lee, J.; Farha, O.K.; Roberts, J.; Scheidt, K.A.; Nguyen, S.T.; Hupp, J.T. “Metal-organic framework materials as catalysts”. Chem. Soc. Rev., 38, 1450–1459 (2009)
[2] Mueller, U.; Schubert, M.; Teich, F.; Puetter, H.; Schierle-Arndt, K.; Pastré, J. “Metal-organic frameworks—Prospective industrial applications”. J. Mater. Chem., 16, 626–636, (2006)
[3] Beurroies, I.; Boulhout, M.; Llewellyn, P.L.; Kuchta, B.; Férey, G.; Serre, C.; Denoyel, R. “Using pressure to provoke the structural transition of metal-organic frameworks”. Angew. Chem. Int. Ed., 49, 7526–7529 (2010)
[4] Khan, N.A.; Hasan, Z.; Jhung, S.H. “Adsorptive removal of hazardous materials using metal-organic frameworks (MOFs): A review”. J. Hazard. Mater., 244–245, 444–456 (2013)
[5] Kolokolov, D.I.; Jobic, H.; Stepanov, A.G.; Guillerm, V.; Devic, T.; Serre, C.; Férey, G. “Dynamics of benzene rings in MIL-53(Cr) and MIL-47(V) frameworks studies by 2H NMR spectroscopy”. Angew. Chem. Int. Ed., 49, 4791–4794 (2010) [6] Alhamami, M.; Doan, H.; Cheng, C.-H. “A Review on Breathing Behaviors of Metal-Organic-Frameworks (MOFs) for Gas Adsorption”. Materials, 7, 3198-3250 (2014)
[7] Z.H. Li, Y.N. Wu, J. Li, Y.M. Zhang, X. Zou, F.T. Li, “The Metal–Organic Framework MIL-53(Al) Constructed from Multiple Metal Sources: Alumina, Aluminum Hydroxide, and Boehmite”. Chem. Eur. J., 21, 6913–6920 (2015)
[8] C.X. Yang, H.B. Ren, X.P. Yan, “Fluorescent Metal–Organic Framework MIL-53(Al) for Highly Selective and Sensitive Detection of Fe3+ in Aqueous Solution”. Anal. Chem., 85, 7441–7446 (2013)
[9] Y. An, H. Li, Y. Liu, B. Huang, Q. Sun, Y. Dai, X. Qin, X. Zhang, “Photoelectrical, photophysical and photocatalytic properties of Al based MOFs: MIL-53(Al) and MIL-53-NH2(Al)”. J. of S.S Chem., 233, 194-198 (2016
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Self-similar regimes in Unstably Stratified Homogeneous Turbulence
No full textUnstably stratified homogeneous turbulence develops at late time a self-similar dynamics characterized by an exponential growth of turbulent quantities. It is believed from recent theoretical studies that different growth rates are possible, depending on the initial distribution of energy at large scales. In order to confirm these predictions, we run both highly resolved direct numerical simulations and a spectral model based on an eddy-damped quasi-normal closure. In addition to confirming the influence of initial conditions, our study sheds light on the anisotropic structures of the self-similar regimes
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