Instabilities and coarsening of stressed crystal surfaces in aqueous solution

Strong pattern formation occurs on polished miscut surfaces of sodium chlorate (NaClO3) single crystals that are uniaxially stressed perpendicular to the step edge direction and placed in a saturated aqueous solution. The wavelength lambda of the stress-induced surface instability increased continuously in experiments up to 9 days after placed in the solution. There were three successive regimes of coarsening: (i) one-dimensional step bunching with lambda approximately t(1/4) until an undulation transition was reached, (ii) a two-dimensional coarsening mechanism with lambda approximately t(1/2), and a gradual transition to (iii) Ostwald ripening-like coarsening with lambda approximately t(1/3). The coarsening of the surface patterns towards a stable, flat surface implies the spontaneous formation of a stress-free skin on the surface of the stressed solid.     

Coarsening in a driven Ising chain with conserved dynamics

We study the low-temperature coarsening of an Ising chain subject to spin-exchange dynamics and a small driving force. This dynamical system reduces to a domain diffusion process, in which entire domains undergo nearest-neighbor hopping, except for the shortest domains-dimers-which undergo long-range hopping. This system exhibits anomalous ordering dynamics due to the existence of two characteristic length scales: the average domain length L(t) approximately t(1/2) and the average dimer hopping distance l(t) approximately square root[L(t)] approximately t(1/4). As a consequence of these two scales, the density of short domains decays as t(-5/4), instead of the t(-3/2) decay that would arise from pure domain diffusion.     

Coarsening and pearling instabilities in silver nanofractal aggregates

We investigate the morphological changes of 3D supported fractal aggregates generated through the deposition of silver clusters on graphite. The fractal relaxation, activated after their formation by perturbing them either by thermal annealing or by using a surfactant, as oxide molecules, carried by silver clusters in a subsequent deposition, shows evidence of two distinct fragmentation patterns. The post coarsening, driven by thermal heating, gives a broad asymmetrical distribution of fragments in agreement with a random process, whereas the entire silver fractal pearling fragmentation is driven by chemical adjunction of the surfactant.     

Experimental study of spinodal decomposition in a 1D conserved order parameter system

We study the zigzag instability coarsening of splay-bend walls formed in a nematic liquid crystal under external fields. The vertexes of zigzag can be considered as kinks in a one-dimensional order parameter system and the geometrical constraints associated with the necessary equal length sum of zig and zag segments impose a conserved quantity in this Cahn-Hilliard-type problem. In the late stage of coarsening, the characteristic length of the system L(t) shows a logarithmic increase in time and the dynamical scaling law holds. We then try to extract the nontrivial asymptotic scaling exponent lambda of the two-time correlation function, defined by lim( approximately [L(t)/L(t('))](-lambda). The scaling exponents with respective time references, t(')=32 and 64 s, after quench are found to be lambda approximately 2 which is larger than the value with respective time reference t(')=0, predicted by numerical simulation.     

Evolution of a stress-driven pattern in thin bilayer films: spinodal wrinkling

We report the full spectrum of the evolution of the wrinkle pattern formation in a thin bilayer film of an elastic metal on a viscoelastic polymer. Although the origin is different, the transition of an initial islandlike pattern to a labyrinthine structure without any change in the wavelength (q approximately t(0)) and the overall evolutionary process is strikingly similar to that in the spinodal system but the process is robust and takes place on a long time scale (about 10 days). The change into a mountainous topography in the late stages is accompanied by an increase in the length scale from an initial wavelength to another. This change, due to the relaxation of the confined polymer that results in a transition from elastic- to viscouslike behavior, induces wave coarsening (q approximately t(-1.04+/-0.08)) and macroscopic roughening.     

A longitudinal study of MR diffusion changes in normal appearing white matter of patients with early multiple sclerosis

BACKGROUND AND PURPOSE: The stage at which normal appearing white matter (NAWM) abnormalities first appear in multiple sclerosis (MS) is not clear. The aim of our study was to monitor water diffusion changes over time in NAWM of patients with early MS.METHODS: Out of a consecutive series of patients enrolled in a MR study on clinically isolated syndrome (CIS), we selected 19 subjects who had completed a one year follow-up. The MR scans obtained at baseline and at 12 months were reviewed according to the new criteria on the diagnosis of MS. Lesion load on T2 and T1 weighted images and the trace of the apparent diffusion coefficient in NAWM were measured both at baseline and at 12 months in patients and in 12 healthy controls.RESULTS: In three patients the diagnosis of MS was done at baseline based on MR. Thirteen patients developed MS during the study and in three patients the diagnosis remained "possible MS." TADC in NAWM in patients was significantly higher than in controls at the 12 months' follow-up but not at baseline (controls mean tADC +/- sd = 0.745 +/- 0.02 mm(2)/sec x 10(-3); patients mean tADC(12) +/- sd = 0.767 +/- 0.02 mm(2)/sec x 10(-3); p < 0.02). TADC and T2 lesion load at 12 months were significantly correlated (p < 0.01). Patients exhibiting tADC(12) above a confidence interval had a significantly greater EDSS score at the same time period (EDSS(12) +/- sd = 1.9 +/- 0.5 and = 1.1 +/- 0.4 respectively; p < 0.01).CONCLUSIONS: This study suggests that diffusion MR cannot detect alterations in NAWM of patients with a CIS suggestive of MS. After one year, when most patients develop MS, diffusion MR abnormalities in NAWM become apparent. These abnormalities are correlated with T2 lesion load and may contribute to neurological impairment.     

Characteristics of driven polymer surfaces: growth and roughness

Using a Monte Carlo simulation, the growth and roughness characteristics of polymer surfaces are studied in 2+1 dimensions. Kink-jump and reptation dynamics are used to move polymer chains under a driving field where they deposit onto an impenetrable attractive wall. Effects of field (E), chain length (L(c)), and the substrate size (L) on the growing surfaces are studied. In low field, the interface width (W) shows a crossover from one power-law growth in time (W approximately t(beta(1))) to another (W approximately t(beta(2))), before reaching its asymptotic value (W(s)), with beta(1)( approximately 0.5+/-0.1)相似文献   

Two-dimensional coarsening kinetics of reconstruction domains: GaAs(001)-beta(2 x 4)

We study the nonconserved coarsening kinetics of a reconstructed semiconductor surface. The domain size evolution is obtained in situ by time-resolved surface x-ray diffraction. The system exhibits four equivalent domain types with two nonequivalent types of domain boundaries. Small domains are prepared by molecular beam epitaxy deposition of one GaAs layer. We find the correlation lengths of the domain size distribution to depend on time as l is proportional to t(0.42+/-0.05) in the half-order reflections and l is proportional to t(0.22+/-0.05) in the quarter-order reflections. The fraction of the higher energy domain boundaries increases as lnt.     

The effect of saccharides on the post-thaw recovery of cane toad (Bufo marinus) spermatozoa

The effect of monosaccharides (glucose, fructose) and disaccharides (maltose, sucrose, trehalose) as diluents, in cryoprotective additives containing 15% (v/v) DMSO or glycerol as cryoprotectants, were investigated on the recovery of sperm motility after cryopreservation of cane toad (Bufo marinus) spermatoazoa at low (approximately 5 degrees C/min(-1)) and high cooling rates (approximately 35 degrees C/min(-1)). The results show that: 1. recovery of percentage motility was higher with slow cooling than with high cooling rates (37.0 +/- 2.5%, 15.3 +/- 1.6%, P<0.001, respectively), 2. disaccharides were more effective than monosaccharides in protecting spermatozoa with slow cooling (43.9 +/- 1.2%, 26.8 +/- 2.5%, P<0.02, respectively), 3. glycerol was more effective than DMSO with fast cooling (18.3 +/- 2.2%, 12.6 +/- 2.3%, P<0.02, respectively), 4. trehalose with glycerol was the most effective cryoprotective additive with fast cooling (31.0 +/- 3.2%, P<0.05), and 5. overall the recovery of degree (vigour) of motility (range, 1.9 - 3.2) was more resilient to cryopreservation than recovery of percentage motility (range, 8.9 - 51.5 %). Comparison of post-thaw percentage and vigour of sperm motility up to 24 minutes after activation showed disaccharides supported greater duration sperm motility than monosaccharides This result and the recovery of spermatozoa immediately after freeze-thaw, show the main effect of saccharides are as cryoprotectants and not as exogenous energy substrates.     

Fluctuation and relaxation properties of pulled fronts: A scenario for nonstandard kardar-parisi-zhang scaling

We argue that while fluctuating fronts propagating into an unstable state should be in the standard Kardar-Parisi-Zhang (KPZ) universality class when they are pushed, they should not when they are pulled: The 1/t velocity relaxation of deterministic pulled fronts makes it unlikely that the KPZ equation is their proper effective long-wavelength low-frequency theory. Simulations in 2D confirm the proposed scenario, and yield exponents beta approximately 0.29+/-0.01, zeta approximately 0.40+/-0.02 for fluctuating pulled fronts, instead of the (1+1)D KPZ values beta = 1/3, zeta = 1/2. Our value of beta is consistent with an earlier result of Riordan et al., and with a recent conjecture that the exponents are the (2+1)D KPZ values.     

Diffusive mobility of fractal aggregates over the entire Knudsen number range

We determine the effective mobility radius for fractal aggregate particles. Our method is to use static light scattering to measure the radius of gyration R(g) of the aggregates, and dynamic light scattering to measure the diffusion coefficient hence the mobility radius R(m). The range of our results can be specified by the Knudsen number Kn, which is the mean free path of the medium molecules divided by the radius of the aggregate. Our results apply to the entire range of Kn from the continuum limit (Kn=0) to the free molecular limit (Kn>1). In the continuum regime we find R(m)/R(g)=0.97+/-0.05 when the aggregate fractal dimension is D(f) approximately 2.15, and 0.70+/-0.05 when D(f) approximately 1.75. The latter result is independent of Kn for Kn < or approximately 1.3. The free molecular mobility goes as R(m)=aN(0.44+/-0.03), where a is the monomer radius and N is the number of monomers per aggregate. Since R(g) approximately aN(1/D(f)), R(m)/R(g) is not a constant when Kn is large. We find for all Kn that the functionality of R(m)/R(g) must always begin with the correct N-->1 limit, and this affects experimental observation.     

Evolution of pore and surface characteristics of silica xerogels during calcining

This paper has investigated the effect of calcining temperature (600-1000°C) on the mesopore structure and surface fractal dimension of silica xerogels derived from two-step acid-base-catalyzed TEOS (tetraethyl orthosilicate) systems. Two base contents were adopted in the base step. FE-SEM (field emission gun-scanning electron microscopy) observation and XRD (X-ray diffraction) analysis indicate that gel coarsening, agglomeration and sintering occurred successively with increasing temperature, and those prepared with higher base content exhibit easier agglomeration, lower sintering temperature and weaker crystallizability. Percent mesoporosity and surface fractal dimensions evaluation via image analysis methods shows that the mesoporosity of those prepared with lower base content increases below 700°C and decline at higher temperatures, while the surface fractal dimension appears to decrease above 800°C.     

Distinctive fluctuations in a confined geometry

Spurred by recent theoretical predictions [Phys. Rev. E 69, 035102(R) (2004)10.1103/PhysRevE.69.035102; Surf. Sci. Lett. 598, L355 (2005)10.1016/j.susc.2005.09.023], we find experimentally using STM line scans that the fluctuations of the step bounding a facet exhibit scaling properties distinct from those of isolated steps or steps on vicinal surfaces. The correlation functions go as t0.15 +/- 0.03 decidedly different from the t0.26 +/- 0.02 behavior for fluctuations of isolated steps. From the exponents, we categorize the universality, confirming the prediction that the nonlinear term of the Kardar-Parisi-Zhang equation, long known to play a central role in nonequilibrium phenomena, can also arise from the curvature or potential-asymmetry contribution to the step free energy.     

Measurement of polarization and triple-product correlations in B-->phiK* decays

We present measurements of decay amplitudes and triple-product correlations in B-->phiK* decays based on 253 fb(-1) of data recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB e(+)e(-) storage ring. The decay amplitudes for the three different helicity states are determined from the angular distributions of final-state particles. The longitudinal polarization amplitudes are found to be 0.45 +/- 0.05 +/- 0.02 for B0-->phiK(*0) and 0.52 +/- 0.08 +/- 0.03 for B+ -->phiK(*+) decays. CP- and T-odd CP-violating triple-product asymmetries are measured to be consistent with zero.     

Branching fractions and CP asymmetries in B0-->pi0pi0, B+-->pi+pi0, and B+-->K+pi0 decays and isospin analysis of the B-->pipi system

Based on a sample of 227 x 10(6) BB pairs collected by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC, we measure the branching fraction B(B0-->pi(0)pi(0))=(1.17+/-0.32+/-0.10)x10(-6), and the asymmetry Cpi(0)(pi(0))=-0.12+/-0.56+/-0.06. The B0-->pi(0)pi(0) signal has a significance of 5.0 sigma. We also measure B(B+-->pi(+)pi(0))=(5.8+/-0.6+/-0.4)x10(-6), B(B+-->K+pi(0))=(12.0+/-0.7+/-0.6)x10(-6), and the charge asymmetries Api(+)(pi(0))=-0.01+/-0.10+/-0.02 and AK+(pi(0))=0.06+/-0.06+/-0.01. Using isospin relations, we find an upper bound on the angle difference |alpha-alpha(eff)| of 35 degrees at the 90% C.L.     

A simplified measurement of hydrated crystal densities of low melting points (low transition points) by solidifications of aqueous solutions

A volume change method for measuring crystal densities is described. It allows the densities of unstable hydrated crystals at room temperature to be determined, by measurements of volume changes during the solidification of aqueous solutions. NaCl x 2H2O, KCl, MgSO4 x 12H2O and K2HPO4 x 6H2O were measured by the method and their densities (SE) are 1.61+/-0.02, 1.99+/-0.05, 1.45+/-0.01 and 1.75+/-0.02 g ml(-1) respectively. Data of NaCl x 2H2O and KCl are in good agreement with the previously reported values.     

All-fiber absolute temperature sensor using an unbalanced high-birefringence Sagnac loop

We demonstrate a highly sensitive temperature sensor based on a stress-induced high-birefringence-fiber Sagnac loop that uses a Nd-doped-fiber amplified spontaneous emission source. Relative temperature sensing is done in the spectral domain by shifts of a resonant wavelength lambda(r) and absolute temperature sensing by changes in separation between resonances Dlambda . The measured relative change of these parameters with temperature in the range 15-110 degrees C, is (1/lambda(r))(deltalambda(r)/deltaT) = -(1/Dlambda)(deltaDlambda/delta T) approximately (1/Dn)(delta Dn/deltaT)(-0.94 +/- 0.02) x 10(-3)/K, with measured fiber birefringence Dn = 8 x 10(-4) . This gives a wavelength-shift sensitivity of -1.00 nm/K at 1.065 microm and a resonance separation sensitivity of 0.006 nm/K for Dlambda = 6.8 nm . This telemetric point sensor has a loop length of 80 m, an operational bandwidth of more than 50 nm, and a temperature accuracy of better than 1 degrees C.     

Measurement of membrane hydraulic conductivity of bovine carotid artery endothelial cells using a perfusion microscope

The osmotic properties of bovine carotid artery endothelial cells (BCAECs) associated with cryobiology were investigated using a perfusion microscope. These properties include the hydraulic conductivity (Lp) and its activation energy (ELp). The response of isolated cells was observed when the extracellular concentration increased from 0.15 M to 0.5 M NaCl at three different temperatures. The transient volumes of the cell were calculated from the measurements of the projected areas with an assumption of a spherical cell. The hydraulic conductivity (Lp) and the osmotically inactive volume (Vb) of BCAECs were simultaneously determined using nonlinear regression to fit the change of cell volume estimated by water transport equations to measured cell volumes. The Lp values were 0.26 +/- 0.08, 0.12 +/- 0.02, and 0.06 +/- 0.02 m/atm/min (mean +/- SD) at 23, 11 and 4 degree C, respectively, yielding the activation energy of Lp of 47.6 kJ/mol according to the Arrhenius relationship.     

Cerebral tissue water spin-spin relaxation times in human neonates at 2.4 tesla: methodology and the effects of maturation

Using a 4-echo spin-echo sequence, cerebral T2 was measured in specific anatomic regions in eleven healthy newborn infants, whose gestational plus postnatal ages (GPAs) lay between 37 and 42 weeks. For a region in the pons, T2 was 141+/-9 ms (mean +/- standard deviation), and no significant dependence upon GPA was seen. In the thalamus mean T2 was 136+/-13 ms, and T2 demonstrated a significant negative linear dependence upon age (r = 0.690; p < 0.02). In periventricular and frontal regions, mean T2 were 217+/-33, and 228+/-32 ms respectively, and more marked negative linear correlations with age were observed (r = 0.833; p < 0.001 and r = 0.722; p < 0.02). For these regions, the rate of T2 decrease with age appeared to be related to known patterns of myelination. For the parietal region studied, mean T2 was 204+/-34 ms, no significant dependence upon GPA being seen. T2 shows promise as an objective measure of cerebral development in the perinatal period.