Burst-like Growth Research Articles

Robustness and Universality in Organelle Size Control.

One of the grand challenges in cellular biophysics is understanding the precision with which cells assemble and maintain subcellular structures. Organelle sizes, for example, must be flexible enough to allow cells to grow or shrink them as environments demand yet be maintained within homeostatic limits. Despite identification of molecular factors that regulate organelle sizes we lack insight into the quantitative principles underlying organelle size control. Here we show experimentally that cells can robustly control average fluctuations in organelle size. By demonstrating that organelle sizes obey a universal scaling relationship we predict theoretically, our framework suggests that organelles grow in random bursts from a limiting pool of building blocks. Burstlike growth provides a general biophysical mechanism by which cells can maintain on average reliable yet plastic organelle sizes.

Transition from the “Burst-Like Growth” to the Normal Growth Kinetics in Free-Growing Helium Crystals

Transition from the “Burst-Like Growth” to the Normal Growth Kinetics in Free-Growing Helium Crystals

Observation of the “Burst-Like Growth” Mode on 4He Crystals Nucleated in a Metastable Liquid

On crystals containing growth defects, the “burst-like growth” mode, i.e., a sharp acceleration of the growth of facets, has been implemented. This has confirmed the hypothesis that the same physical mechanisms are responsible for the transition of facets in the state of anomalously rapid growth at high and low temperatures. It has been found that the transition from the fast to slow kinetics of crystal facet growth is stepwise. It has been established that the relaxation of the kinetic coefficient of growth is similar to the relaxation of the elastic moduli of the crystal after the fast growth stage. The kinetic coefficients of crystal growth at fast and slow growth stages have been determined.

The Effect of the Interphase Kinetics on the Motion of a Quantum Crystal in Superfluid Liquid

The fall of a quantum crystal in the state of "burst-like growth" in a superfluid liquid is considered. The experimental data of the pressure variation in the container during the fall of a crystal are discussed. The model of the motion of the crystal is suggested taking the interface dynamics into account. The results for the numerical simulation of the fall of a crystal are consistent with the experimental data. We find a significant effect of the liquid-crystal interface kinetics on the hydrodynamics of the liquid flow encircling a crystal.

Anomaly of the internal friction in the helium crystals grown in the burstlike growth mode

The internal friction in the crystals grown in two modes, namely, slow and anomalously fast (burst-like growth) modes, is measured in the temperature range 0.49-0.75K at a frequency of about 75kHz. An additional contribution to the damping decrement and softening of the dynamic modulus are detected, and their relaxation to equilibrium values at a time constant of about 3ms is observed. Possible origins of this effect are discussed.

Anomaly of the internal friction in helium-4 crystals prepared with the burst-like growth method

Abstract The internal friction is measured in the 4 He crystals prepared with the conventional and burst-like methods at temperature 0.65 K and frequency 75 kHz. It is observed that the crystals, grown too rapidly, have an excess damping and smaller dynamic elastic modulus. The magnitude of the effect enhances as the initial overpressure increases. The contribution to the excess damping vanishes at the critical overpressure 3.5 mbar separating the regions of the normal and anomalous crystal growth at the corresponding temperature. Corrections to the modulus and decrement relax with the time constant of about 3 ms. The regime of the burst-like growth may result in the crystals with the internal state different from that of equilibrium crystals.

Possible burst-like facet growth mode at high temperatures

A decade ago, a burst-like growth mode of c-facets of 4He crystals growing at mK temperatures, characterized by the alternation of time intervals during which the facet does not advance with the intervals of its fast advancement, was found [J.P. Ruutu, P.J. Hakonen, A.V. Babkin, A.Y. Parshin, J.S. Penttilä, J.P. Saramäki, G. Tvalashvili, Phys. Rev. Lett. 76 (1996) 4187]. We investigate the possibility that a similar facet growth mode exists for facets at high growth temperatures. We have applied the digital laser interferometry for monitoring facet kinetics of spherical copper selenide single crystals during their growth at constant volume growth rate around 800 K. Our analysis of directly measured (1 1 1) facet advancement curves has revealed that they consist of time intervals during which the facet does not advance vertically alternating with the time intervals of enhanced growth, resembling the burst-like facet growth mode. The results are discussed in terms of the enhancement of the local supersaturation induced by the existence of nucleation barrier.

The Giant Growth of the Facets of 4He Crystal

Below the first and second roughening transitions the facets of a helium crystal demonstrate two qualitatively different regimes of growth. At small deviations from the equilibrium a crystal grows slowly via surface defects such as screw dislocations and Frank-Reed sources. The second regime is observed at high overpressurizations. A single crystal goes over into new state with the growth rates by several orders of the magnitude higher than the previous ones. The transition occurs simultaneously in both the basal and lateral facets. The time of formation of an anomalous state decreases drastically with the increase of the overpressurization and lies within the range of 0.1–200 ms. An average overpressurization. Dp0 above which the anomalous state appears increases monotonically with the growth of temperature. The measurements of the facet growth rate immediately after a transition show that it reaches magnitudes up to ∼ 5 m/s at ∼ 20 mbar. Impurities of 3He with a concentration of 180 ppm retard the formation of the fast phase, namely, a boundary Dp0(T) shifts to higher values. The features of this phenomenon (phase diagram, effect of impurity) are similar to the “burst-like growth” observed in the range of 2–250 mK at the (0001) facet without dislocations. Possibly, kinematical multiplication of steps plays a significant role in these effects, yielding a qualitatively new channel for the growth of an ideal facet.

Determinants of Dual Secretagogue Drive of Burst-Like Growth Hormone Secretion in Premenopausal Women Studied under a Selective Estradiol Clamp

The present study tests the hypothesis that estradiol (E(2)), compared with placebo (Pl), amplifies combined-secretagogue stimulation of GH secretion in premenopausal women studied at comparable IGF-I and testosterone concentrations. To this end, 13 women underwent GnRH agonist-induced gonadal down-regulation followed by graded transdermal addback of E(2) or Pl and randomly ordered iv infusions of saline or paired secretagogues on separate morning fasting. GH secretion was assessed by frequent blood sampling, immunochemiluminometry, and variable-waveform deconvolution analysis. Two-way ANOVA revealed that specific secretagogue combination (P < 0.001), E(2) status (P = 0.012), and their interaction (P = 0.038) jointly determined GH secretory-burst mass. Compared with Pl, the E(2)-clamped milieu elevated mean fasting GH concentrations (P = 0.032), the mass of GH secreted in bursts (P = 0.037), and maximal stimulation by paired l-arginine/GH-releasing peptide (GHRP)-2 (P = 0.028). E(2) also markedly accelerated the initial release of GH induced by GHRH/GHRP-2 (P < 0.001) and l-arginine/GHRH (P < 0.01). By linear regression analysis, E(2) concentrations positively forecast 41% of intersubject variability in GH secretion stimulated by combined l-arginine/GHRP-2 (P = 0.018), whereas abdominal visceral-fat mass negatively predicted 49% of that due to l-arginine/GHRH (P = 0.012). These data indicate that pulsatile GH secretion in young women studied at constant IGF-I and testosterone concentrations is dictated 3-fold jointly by secretagogue pair, E(2) availability, and intraabdominal adiposity. Moreover, the rapidity of GH release is controlled 2-fold jointly by E(2) and GHRH.

Contributions of Gender and Systemic Estradiol and Testosterone Concentrations to Maximal Secretagogue Drive of Burst-Like Growth Hormone Secretion in Healthy Middle-Aged and Older Adults

To test whether concentrations of estradiol and testosterone predict GH responses to mechanistically distinct secretagogues in healthy older adults, we studied 16 volunteers (n = 10 men, n = 6 women, age 49-72 yr) in each of six randomly ordered sessions as follows: 1) saline; 2) l-arginine; 3) aerobic exercise; 4) GHRH; 5) GH-releasing peptide (GHRP)-2; and 6) somatostatin-induced rebound. Statistical comparisons disclosed that stimulus type (P < 0.001) and the interaction between gender and stimulus type (P = 0.023) determine GH secretion. In women, each secretagogue, except exercise and somatostatin-induced rebound, stimulated GH secretion by 2.6- to 6.4-fold over saline/rest (P < 0.023). In men, somatostatin-induced rebound drove GH secretion by 4.6-fold (P = 0.004), exercise by 16-fold (P < 0.001), and other secretagogues by 18- to 109-fold over saline/rest (each P < 0.001). Gender comparisons disclosed greater GH secretion in men than women after somatostatin-induced rebound (P = 0.008) and GHRP-2 injection (P < 0.001) and conversely greater GH secretion in women than men after saline (P = 0.013). Regression analysis showed that individual concentrations of estradiol (r = 0.80, P = 0.002) and testosterone (r = 0.63, P = 0.008) and their combination (r = 0.86, P < 0.001) strongly predict responses to GHRP-2 only. We conclude that among healthy middle-aged and older adults, the action of GHRP is uniquely determined by gender and physiological concentrations of testosterone and estradiol.

Observation of spontaneous magnetization jumps in manganites

For certain combinations of temperature and magnetic field, the evolution with time of the magnetization of some phase-separated manganese oxides exhibits a unique steplike feature. This jump in the magnetization is proposed to correspond to a burstlike growth of the ferromagnetic fraction at the expense of the antiferromagnetic component, driven by the evolution of the strains at the interfaces between the two kinds of domains. These results bear a striking similarity with the phenomenon of an ``incubation time'' encountered in standard martensitic transformations.

Facet growth of 4He crystals at mK temperatures.

We have investigated growth of c facets in good quality helium crystals with screw dislocation densities $0--20{\mathrm{cm}}^{\ensuremath{-}2}$ along the c axis. Three distinct regimes of growth were observed. One of them can be explained by spiral growth provided that kinetic energy of moving steps and their tendency to localization at large driving forces are taken into account. In the absence of screw dislocations we find burstlike growth unless the speed is less than 0.5 nm/s, in which case anomalous, intrinsic growth of facets is detected.

Thin‐Foil Phase Transformations of Tetragonal ZrO2 in a ZrO2‐8 wt% Y2O3 Alloy

Tetragonal zirconia (t‐ZrO2) grains in an annealed ZrO2 8 wt% Y2O3 alloy transformed to orthorhombic (o) or monoclinic (m) symmetry by stresses induced by localized electron beam heating in the transmission electron microscope. Different transformation mechanisms were observed, depending on foil thickness and orientation of individual grains. In thicker grains (≥150 nm), the transformation proceeded by a burst‐like growth of m laths, and this is believed to approximate bulk behavior. In thinner grains near the edge of the foil, usually those with a [100], orientation perpendicular to the thin‐foil surface, “continuous” growth of an o or m phase with an antiphase‐boundary‐containing microstructure was observed. The o phase is believed to be a high‐pressure poly‐morph of ZrO2, which forms (paradoxically) as a thin‐foil artifact because it is less dense than t‐ZrO2, but more dense than m‐ZrO2. In some very thin grains, the t→m transformation was thermoelastic. Furthermore, a mottled structure often occurred just before the t→m or t→o transformation, which is attributed to surface transformation. Aside from the lath formation, the observed transformation modes are a result of the reduced constraints in thin foils.