542 research outputs found
Multistable alignment states in nematic liquid crystal filled wells
Two distinct, stable alignment states have been observed for a nematic liquid crystal confined in a layer with thickness of 12 μm and in square wells with sides of length between 20 and 80 μm. The director lies in the plane of the layer and line defects occur in two corners of the squares. The positions of the defects determine whether the director orientation is across the diagonal or is parallel to two opposite edges of the square. The device is multistable because both the diagonal and parallel states are stable when rotated by multiples of 90° in plane
Interferometric method for determining the sum of the flexoelectric coefficients (e1+e3) in an ionic nematic material
The time-dependent periodic distortion profile in a nematic liquid crystal phase grating has been measured from the displacement of tilt fringes in a Mach-Zehnder interferometer. A 0.2 Hz squarewave voltage was applied to alternate stripe electrodes in an interdigitated electrode geometry. The time-dependent distortion profile is asymmetric with respect to the polarity of the applied voltage and decays with time during each half period due to ionic shielding. This asymmetry in the response allows the determination of the sum of the flexoelectric coefficients (e1+e3) using nematic continuum theory since the device geometry does not possess inherent asymmetry
Substrate specificity and the effect of calcium on Trypanosomabrucei metacaspase 2
Metacaspases are cysteine peptidases found only in yeast, plants and lower eukaryotes, including the protozoa. To investigate the extended substrate specificity and effects of Ca<sup>2+</sup> on the activation of these enzymes, detailed kinetic, biochemical and structural analyses were carried out on metacaspase 2 from Trypanosoma brucei (TbMCA2). These results reveal that TbMCA2 has an unambiguous preference for basic amino acids at the P<sub>1</sub> position of peptide substrates and that this is most probably a result of hydrogen bonding from the P<sub>1</sub> residue to Asp95 and Asp211 in TbMCA2. In addition, TbMCA2 also has a preference for charged residues at the P<sub>2</sub> and P<sub>3</sub>positions and for small residues at the prime side of a peptide substrate. Studies into the effects of Ca<sup>2+</sup> on the enzyme revealed the presence of two Ca<sup>2+</sup> binding sites and a reversible structural modification of the enzyme upon Ca<sup>2+</sup> binding. In addition, the concentration of Ca<sup>2+</sup> used for activation of TbMCA2 was found to produce a differential effect on the activity of TbMCA2, but only when a series of peptides that differed in P<sub>2</sub> were examined, suggesting that Ca<sup>2+</sup>activation of TbMCA2 has a structural effect on the enzyme in the vicinity of the S2 binding pocket. Collectively, these data give new insights into the substrate specificity and Ca<sup>2+</sup> activation of TbMCA2. This provides important functional details and leads to a better understanding of metacaspases, which are known to play an important role in trypanosomes and make attractive drug targets due to their absence in humans
Deformation of a nearly hemispherical conducting drop due to an electric field: theory and experiment
We consider, both theoretically and experimentally, the deformation due to an electric field of a pinned nearly-hemispherical static sessile drop of an ionic fluid with a high conductivity resting on the lower substrate of a parallel plate capacitor. Using both numerical and asymptotic approaches we find solutions to the coupled electrostatic and augmented Young–Laplace equations which agree very well with the experimental results. Our asymptotic solution for the drop interface extends previous work in two ways, namely to drops that have zero-field contact angles that are not exactly π/2 and to higher order in the applied electric field, and provides useful predictive equations for the changes in the height, contact angle and pressure as functions of the zero-field contact angle, drop radius, surface tension and applied electric field. The asymptotic solution requires some numerical computations, and so a surprisingly accurate approximate analytical asymptotic solution is also obtained
VLTI/MIDI 10 micron interferometry of the forming massive star W33A
We report on resolved interferometric observations with VLTI/MIDI of the
massive young stellar object (MYSO) W33A. The MIDI observations deliver
spectrally dispersed visibilities with values between 0.03 and 0.06, for a
baseline of 45m over the wavelength range 8-13 micron. The visibilities
indicate that W33A has a FWHM size of approximately 120AU (0.030'') at 8 micron
which increases to 240AU at 13 micron, scales previously unexplored among
MYSOs. This observed trend is consistent with the temperature falling off with
distance. 1D dust radiative transfer models are simultaneously fit to the
visibility spectrum, the strong silicate feature and the shape of the mid
infrared spectral energy distribution (SED). For any powerlaw density
distribution, we find that the sizes (as implied by the visibilities) and the
stellar luminosity are incompatible. A reduction to a third of W33A's
previously adopted luminosity is required to match the visibilities; such a
reduction is consistent with new high resolution 70 micron data from Spitzer's
MIPSGAL survey. We obtain best fits for models with shallow dust density
distributions of r^(-0.5) and r^(-1.0) and for increased optical depth in the
silicate feature produced by decreasing the ISM ratio of graphite to silicates
and using optical grain properties by Ossenkopf et al. (1992).Comment: 4 pages, 4 figures. Accepted for ApJ letter
The circumburst environment of a FRED GRB: study of the prompt emission and X-ray/optical afterglow of GRB 051111
We report a multi-wavelength analysis of the prompt emission and early
afterglow of GRB051111 and discuss its properties in the context of current
fireball models. The detection of GRB051111 by the Burst Alert Telescope
on-board Swift triggered early BVRi' observations with the 2-m robotic Faulkes
Telescope North in Hawaii, as well as X-ray observations with the Swift X-Ray
Telescope. The prompt gamma-ray emission shows a classical FRED profile. The
optical afterglow light curves are fitted with a broken power law, with
alpha_1=0.35 to alpha_2=1.35 and a break time around 12 minutes after the GRB.
Although contemporaneous X-ray observations were not taken, a power law
connection between the gamma-ray tail of the FRED temporal profile and the late
XRT flux decay is feasible. Alternatively, if the X-ray afterglow tracks the
optical decay, this would represent one of the first GRBs for which the
canonical steep-shallow-normal decay typical of early X-ray afterglows has been
monitored optically. We present a detailed analysis of the intrinsic
extinction, elemental abundances and spectral energy distribution. From the
absorption measured in the low X-ray band we find possible evidence for an
overabundance of some alpha elements such as oxygen, [O/Zn]=0.7+/-0.3, or,
alternatively, for a significant presence of molecular gas. The IR-to-X-ray
Spectral Energy Distribution measured at 80 minutes after the burst is
consistent with the cooling break lying between the optical and X-ray bands.
Extensive modelling of the intrinsic extinction suggests dust with big grains
or grey extinction profiles. The early optical break is due either to an energy
injection episode or, less probably, to a stratified wind environment for the
circumburst medium.Comment: accepted to A&A on Nov. 10 (14 pages, 8 figures
Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B
Aims. The aim of this paper is to study deuterated water in the solar-type
protostars NGC1333 IRAS4A and IRAS4B, to compare their HDO abundance
distribution with other star-forming regions, and to constrain their HDO/H2O
ratios. Methods. Using the Herschel/HIFI instrument as well as ground-based
telescopes, we observed several HDO lines covering a large excitation range
(Eup/k=22-168 K) towards these protostars and an outflow position. Non-LTE
radiative transfer codes were then used to determine the HDO abundance profiles
in these sources. Results. The HDO fundamental line profiles show a very broad
component, tracing the molecular outflows, in addition to a narrower emission
component and a narrow absorbing component. In the protostellar envelope of
NGC1333 IRAS4A, the HDO inner (T>100 K) and outer (T<100 K) abundances with
respect to H2 are estimated at 7.5x10^{-9} and 1.2x10^{-11}, respectively,
whereas, in NGC1333 IRAS4B, they are 1.0x10^{-8} and 1.2x10^{-10},
respectively. Similarly to the low-mass protostar IRAS16293-2422, an absorbing
outer layer with an enhanced abundance of deuterated water is required to
reproduce the absorbing components seen in the fundamental lines at 465 and 894
GHz in both sources. This water-rich layer is probably extended enough to
encompass the two sources as well as parts of the outflows. In the outflows
emanating from NGC1333 IRAS4A, the HDO column density is estimated at about
(2-4)x10^{13} cm^{-2}, leading to an abundance of about (0.7-1.9)x10^{-9}. An
HDO/H2O ratio between 7x10^{-4} and 9x10^{-2} is derived in the outflows. In
the warm inner regions of these two sources, we estimate the HDO/H2O ratios at
about 1x10^{-4}-4x10^{-3}. This ratio seems higher (a few %) in the cold
envelope of IRAS4A, whose possible origin is discussed in relation to formation
processes of HDO and H2O.Comment: 16 pages, 13 figure
Weak-anchoring effects in a thin pinned ridge of nematic liquid crystal
A theoretical investigation of weak-anchoring effects in a thin
two-dimensional pinned static ridge of nematic liquid crystal resting on a flat
solid substrate in an atmosphere of passive gas is performed. Specifically, we
solve a reduced version of the general system of governing equations recently
derived by Cousins et al. [Proc. Roy. Soc. A}, 478(2259):20210849, 2022] valid
for a symmetric thin ridge under the one-constant approximation of the
Frank--Oseen bulk elastic energy with pinned contact lines to determine the
shape of the ridge and the behaviour of the director within it. Numerical
investigations covering a wide range of parameter values indicate that the
energetically-preferred solutions can be classified in terms of the
Jenkins--Barratt--Barbero--Barberi critical thickness into five qualitatively
different types of solution. In particular, the theoretical results suggest
that anchoring breaking occurs close to the contact lines. The theoretical
predictions are supported by the results of physical experiments for a ridge of
the nematic 4'-pentyl-4-biphenylcarbonitrile (5CB). In particular, these
experiments show that the homeotropic anchoring at the gas--nematic interface
is broken close to the contact lines by the stronger rubbed planar anchoring at
the nematic--substrate interface. A comparison between the experimental values
of and the theoretical predictions for the effective refractive index of the
ridge gives a first estimate of the anchoring strength of an interface between
air and 5CB to be at a temperature
of C
Exogenous phytase and xylanase exhibit opposing effects on real-time gizzard pH in broiler chickens
1. The current study was conducted to evaluate the influence of high phytase doses and xylanase, individually and in combination, on performance, blood inositol and real time gastric pH in broilers fed wheat-based diets. 2. In a 42 d experiment, a total of 576 male Ross 308 broiler chicks were allocated to four dietary treatments. Treatments consisted of a 2 × 2 factorial arrangement, with 500 or 2500 FTU/kg phytase and 0 or 16000 BXU/kg xylanase, fed in two phases (starter 0–21; grower 21–42 d). Heidelberg pH capsules were administered to eight birds from each treatment group, pre and post diet phase change, with readings captured over a 5.5 h period. 3. At 21 and 42 d, birds fed 500 FTU/kg phytase without xylanase had on average 127g and 223 g lower weight gain than all other treatments, respectively (P<0.05). At 21 d, FCR was reduced (P<0.01) by 2500 FTU/kg phytase or xylanase, however, 42 d FCR was unaffected by enzyme treatment. Inositol content of plasma was twice that of the erythrocyte (P<0.001), with 2500 FTU/kg phytase tending to increase (P=0.07) inositol content in both blood fractions. 4. Across all treatments, capsule readings ranged from pH 0.54 to 4.84 in the gizzard of broilers. Addition of 2500 FTU/kg phytase to the grower diet reduced (P<0.05) average gizzard pH from 2.89 to 1.69, whilst feeding xylanase increased (P<0.001)gizzard pH from 2.04 to 2.40. In contrast, digital probe measurements showed no effect of xylanase on gizzard pH, while addition of 2500 FTU/kg phytase increased (P=0.05) pH compared to 500 FTU/kg phytase with or without xylanase. 5. These findings suggested that xylanase and high phytase doses have opposite effects on real-time gastric pH, while similarly improving performance of broilers
Exogenous phytase and xylanase exhibit opposing effects on real-time gizzard pH in broiler chickens
1. The current study was conducted to evaluate the influence of high phytase doses and xylanase, individually and in combination, on performance, blood inositol and real time gastric pH in broilers fed wheat-based diets. 2. In a 42 d experiment, a total of 576 male Ross 308 broiler chicks were allocated to four dietary treatments. Treatments consisted of a 2 × 2 factorial arrangement, with 500 or 2500 FTU/kg phytase and 0 or 16000 BXU/kg xylanase, fed in two phases (starter 0–21; grower 21–42 d). Heidelberg pH capsules were administered to eight birds from each treatment group, pre and post diet phase change, with readings captured over a 5.5 h period. 3. At 21 and 42 d, birds fed 500 FTU/kg phytase without xylanase had on average 127g and 223 g lower weight gain than all other treatments, respectively (P<0.05). At 21 d, FCR was reduced (P<0.01) by 2500 FTU/kg phytase or xylanase, however, 42 d FCR was unaffected by enzyme treatment. Inositol content of plasma was twice that of the erythrocyte (P<0.001), with 2500 FTU/kg phytase tending to increase (P=0.07) inositol content in both blood fractions. 4. Across all treatments, capsule readings ranged from pH 0.54 to 4.84 in the gizzard of broilers. Addition of 2500 FTU/kg phytase to the grower diet reduced (P<0.05) average gizzard pH from 2.89 to 1.69, whilst feeding xylanase increased (P<0.001)gizzard pH from 2.04 to 2.40. In contrast, digital probe measurements showed no effect of xylanase on gizzard pH, while addition of 2500 FTU/kg phytase increased (P=0.05) pH compared to 500 FTU/kg phytase with or without xylanase. 5. These findings suggested that xylanase and high phytase doses have opposite effects on real-time gastric pH, while similarly improving performance of broilers
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