212 research outputs found
Equilibrium and nonequilibrium fluctuations at the interface between two fluid phases
We have performed small-angle light-scattering measurements of the static
structure factor of a critical binary mixture undergoing diffusive partial
remixing. An uncommon scattering geometry integrates the structure factor over
the sample thickness, allowing different regions of the concentration profile
to be probed simultaneously. Our experiment shows the existence of interface
capillary waves throughout the macroscopic evolution to an equilibrium
interface, and allows to derive the time evolution of surface tension.
Interfacial properties are shown to attain their equilibrium values quickly
compared to the system's macroscopic equilibration time.Comment: 10 pages, 5 figures, submitted to PR
Shear-induced quench of long-range correlations in a liquid mixture
A static correlation function of concentration fluctuations in a (dilute)
binary liquid mixture subjected to both a concentration gradient and uniform
shear flow is investigated within the framework of fluctuating hydrodynamics.
It is shown that a well-known long-range correlation at
large wave numbers crosses over to a weaker divergent one for wave numbers
satisfying , while an asymptotic shear-controlled
power-law dependence is confirmed at much smaller wave numbers given by , where , , and are the
mass concentration, the rate of the shear, the mass diffusivity and the
kinematic viscosity of the mixture, respectively. The result will provide for
the first time the possibility to observe the shear-induced suppression of a
long-range correlation experimentally by using, for example, a low-angle light
scattering technique.Comment: 8pages, 2figure
A schlieren method for ultra-low angle light scattering measurements
We describe a self calibrating optical technique that allows to perform
absolute measurements of scattering cross sections for the light scattered at
extremely small angles. Very good performances are obtained by using a very
simple optical layout similar to that used for the schlieren method, a
technique traditionally used for mapping local refraction index changes. The
scattered intensity distribution is recovered by a statistical analysis of the
random interference of the light scattered in a half-plane of the scattering
wave vectors and the main transmitted beam. High quality data can be obtained
by proper statistical accumulation of scattered intensity frames, and the
static stray light contributions can be eliminated rigorously. The
potentialities of the method are tested in a scattering experiment from non
equilibrium fluctuations during a free diffusion experiment. Contributions of
light scattered from length scales as long as Lambda=1 mm can be accurately
determined.Comment: 7 pages, 3 figure
Real-Time Wavelet-transform spectrum analyzer for the investigation of 1/f^\alpha noise
A wavelet transform spectrum analyzer operating in real time within the
frequency range 3X10^(-5) - 1.3X10^5 Hz has been implemented on a low-cost
Digital Signal Processing board operating at 150MHz. The wavelet decomposition
of the signal allows to efficiently process non-stationary signals dominated by
large amplitude events fairly well localized in time, thus providing the
natural tool to analyze processes characterized by 1/f^alpha power spectrum.
The parallel architecture of the DSP allows the real-time processing of the
wavelet transform of the signal sampled at 0.3MHz. The bandwidth is about
220dB, almost ten decades. The power spectrum of the scattered intensity is
processed in real time from the mean square value of the wavelet coefficients
within each frequency band. The performances of the spectrum analyzer have been
investigated by performing Dynamic Light Scattering experiments on colloidal
suspensions and by comparing the measured spectra with the correlation
functions data obtained with a traditional multi tau correlator. In order to
asses the potentialities of the spectrum analyzer in the investigation of
processes involving a wide range of timescales, we have performed measurements
on a model system where fluctuations in the scattered intensities are generated
by the number fluctuations in a dilute colloidal suspension illuminated by a
wide beam. This system is characterized by a power-law spectrum with exponent
-3/2 in the scattered intensity fluctuations. The spectrum analyzer allows to
recover the power spectrum with a dynamic range spanning about 8 decades. The
advantages of wavelet analysis versus correlation analysis in the investigation
of processes characterized by a wide distribution of time scales and
non-stationary processes are briefly discussed.Comment: 12 pages, 6 figure
Fractal fronts of diffusion in microgravity
Spatial scale invariance represents a remarkable feature of natural phenomena. A ubiquitous example is represented by miscible liquid phases undergoing diffusion. Theory and simulations predict that in the absence of gravity diffusion is characterized by long-ranged algebraic correlations. Experimental evidence of scale invariance generated by diffusion has been limited, because on Earth the development of long-range correlations is suppressed by gravity. Here we report experimental results obtained in microgravity during the flight of the FOTON M3 satellite. We find that during a diffusion process a dilute polymer solution exhibits scale-invariant concentration fluctuations with sizes ranging up to millimetres, and relaxation times as large as 1,000 s. The scale invariance is limited only by the finite size of the sample, in agreement with recent theoretical predictions. The presence of such fluctuations could possibly impact the growth of materials in microgravity
Better postpartal performance in dairy cows supplemented with rumen-protected methionine compared with choline during the peripartal period
The onset of lactation in dairy cows is characterized by high output of methylated compounds in milk when sources of methyl group are in short supply. Methionine and choline (CHOL) are key methyl donors and their availability during this time may be limiting for milk production, hepatic lipid metabolism, and immune function. Supplementing rumen-protected Met and CHOL may improve overall performance and health of transition cows. The objective of this study was to evaluate the effect of supplemental rumen-protected Met and CHOL on performance and health of transition cows. Eighty-one multiparous Holstein cows were used in a randomized, complete, unbalanced block design with 2×2 factorial arrangement of Met (Smartamine M, Adisseo NA, Alpharetta, GA) and CHOL (ReaShure, Balchem Inc., New Hampton, NY) inclusion (with or without). Treatments (20 to 21 cows each) were control (CON), CON+Met (SMA), CON+CHOL (REA), and CON+Met+CHOL (MIX). From -50 to -21d before expected calving, all cows received the same diet (1.40Mcal of NEL/kg of DM) with no Met or CHOL. From -21d to calving, cows received the same close-up diet (1.52Mcal of NEL/kg of DM) and were assigned randomly to treatments (CON, SMA, REA, or MIX) supplied as top dresses. From calving to 30 DIM, cows were fed the same postpartal diet (1.71Mcal of NEL/kg of DM) and continued to receive the same treatments through 30 DIM. The Met supplementation was adjusted daily at 0.08% DM of diet and REA was supplemented at 60g/d. Incidence of clinical ketosis and retained placenta tended to be lower in Met-supplemented cows. Supplementation of Met (SMA, MIX) led to greater DMI compared with other treatments (CON, REA) in both close-up (14.3 vs. 13.2kg/d, SEM 0.3) and first 30d postpartum (19.2 vs. 17.2kg/d, SEM 0.6). Cows supplemented with Met (SMA, MIX) had greater yields of milk (44.2 vs. 40.4kg/d, SEM 1.2), ECM (44.6 vs. 40.5kg/d, SEM 1.0), and FCM (44.6 vs. 40.8kg/d, SEM 1.0) compared with other (CON, REA) treatments. Milk fat content did not differ in response to Met or CHOL. However, milk protein content was greater in Met-supplemented (3.32% vs. 3.14%, SEM 0.04%) but not CHOL-supplemented (3.27 vs. 3.19%, SEM 0.04%) cows. Supplemental CHOL led to greater blood glucose and insulin concentrations with lower glucose:insulin ratio. No Met or CHOL effects were detected for blood fatty acids or BHB, but a Met × time effect was observed for fatty acids due to higher concentrations on d 20. Results from the present study indicate that peripartal supplementation of rumen-protected Met but not CHOL has positive effects on cow performance
Rumen-protected methionine compared with rumen-protected choline improves immunometabolic status in dairy cows during the peripartal period.
The immunometabolic status of peripartal cows is altered due to changes in liver function, inflammation, and oxidative stress. Nutritional management during this physiological state can affect the biological components of immunometabolism. The objectives of this study were to measure concentrations of biomarkers in plasma, liver tissue, and milk, and also polymorphonuclear leukocyte function to assess the immunometabolic status of cows supplemented with rumen-protected methionine (Met) or choline (CHOL). Forty-eight multiparous Holstein cows were used in a randomized complete block design with 2×2 factorial arrangement of Met (Smartamine M, Adisseo NA, Alpharetta, GA) and CHOL (ReaShure, Balchem Inc., New Hampton, NY) level (with or without). Treatments (12 cows each) were control (CON), no Met or CHOL; CON and Met (SMA); CON and CHOL (REA); and CON and Met and CHOL (MIX). From -50 to -21d before expected calving, all cows received the same diet [1.40Mcal of net energy for lactation (NEL)/kg of DM] with no Met or CHOL. From -21d to calving, cows received the same close-up diet (1.52Mcal of NEL/kg of DM) and were assigned randomly to each treatment. From calving to 30d, cows were on the same postpartal diet (1.71Mcal of NEL/kg of DM) and continued to receive the same treatments until 30d. The Met supplementation was adjusted daily at 0.08% DM of diet, and CHOL was supplemented at 60g/cow per day. Liver (-10, 7, 21, and 30d) and blood (-10, 4, 8, 20, and 30d) samples were harvested for biomarker analyses. Neutrophil and monocyte phagocytosis and oxidative burst were assessed at d 1, 4, 14, and 28d. The Met-supplemented cows tended to have greater plasma paraoxonase. Greater plasma albumin and IL-6 as well as a tendency for lower haptoglobin were detected in Met- but not CHOL-supplemented cows. Similarly, cows fed Met compared with CHOL had greater concentrations of total and reduced glutathione (a potent intracellular antioxidant) in liver tissue. Upon a pathogen challenge in vitro, blood polymorphonuclear leukocyte phagocytosis capacity and oxidative burst activity were greater in Met-supplemented cows. Overall, liver and blood biomarker analyses revealed favorable changes in liver function, inflammation status, and immune response in Met-supplemented cows
EasyPrimer: user-friendly tool for pan-PCR/HRM primers design. Development of an HRM protocol on wzi gene for fast Klebsiella pneumoniae typing
In this work we present EasyPrimer, a user-friendly online tool developed to assist pan-PCR and High Resolution Melting (HRM) primer design. The tool finds the most suitable regions for primer design in a gene alignment and returns a clear graphical representation of their positions on the consensus sequence. EasyPrimer is particularly useful in difficult contexts, e.g. on gene alignments of hundreds of sequences and/or on highly variable genes. HRM analysis is an emerging method for fast and cost saving bacterial typing and an HRM scheme of six primer pairs on five Multi-Locus Sequence Type (MLST) genes is already available for Klebsiella pneumoniae. We validated the tool designing a scheme of two HRM primer pairs on the hypervariable gene wzi of Klebsiella pneumoniae and compared the two schemes. The wzi scheme resulted to have a discriminatory power comparable to the HRM MLST scheme, using only one third of primer pairs. Then we successfully used the wzi HRM primer scheme to reconstruct a Klebsiella pneumoniae nosocomial outbreak in few hours. The use of hypervariable genes reduces the number of HRM primer pairs required for bacterial typing allowing to perform cost saving, large-scale surveillance programs
Dynamics of fluctuations in a fluid below the onset of Rayleigh-B\'enard convection
We present experimental data and their theoretical interpretation for the
decay rates of temperature fluctuations in a thin layer of a fluid heated from
below and confined between parallel horizontal plates. The measurements were
made with the mean temperature of the layer corresponding to the critical
isochore of sulfur hexafluoride above but near the critical point where
fluctuations are exceptionally strong. They cover a wide range of temperature
gradients below the onset of Rayleigh-B\'enard convection, and span wave
numbers on both sides of the critical value for this onset. The decay rates
were determined from experimental shadowgraph images of the fluctuations at
several camera exposure times. We present a theoretical expression for an
exposure-time-dependent structure factor which is needed for the data analysis.
As the onset of convection is approached, the data reveal the critical
slowing-down associated with the bifurcation. Theoretical predictions for the
decay rates as a function of the wave number and temperature gradient are
presented and compared with the experimental data. Quantitative agreement is
obtained if allowance is made for some uncertainty in the small spacing between
the plates, and when an empirical estimate is employed for the influence of
symmetric deviations from the Oberbeck-Boussinesq approximation which are to be
expected in a fluid with its density at the mean temperature located on the
critical isochore.Comment: 13 pages, 10 figures, 52 reference
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