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Author(s): Jeremy B. Clark [1]; Florent Lecocq [1]; Raymond W. Simmonds [1]; Jos Aumentado [1]; John D. Teufel (corresponding author) [1] Quantum fluctuations of the electromagnetic vacuum produce measurable physical [...]

Structural fluctuations of a protein are essential for the function of native proteins and for protein folding. To understand how the main chain in the native state of a protein fluctuates on different time scales, we examined the rotational correlation functions (RCFs), C(t), of the backbone N-H bonds and of the dihedral angles [gamma] built on four consecutive [C.sup.[alpha]] atoms. Using molecular dynamics simulations of a model [alpha]/[beta] protein (VA3) in its native state, we demonstrate that these RCFs decay as stretched exponentials, In [C(t)][approximately equal to][D.sub.[alpha]][t.sup.[alpha]] with a constant [D.sub.[alpha]] and an exponent [alpha] (0 anomalous diffusion | model-free approach | power law | free-energy landscape doi/ 10.1073/pnas.1013674107

Laser vibrometry (LV) is originally a laser-based, line-of-sight measurement technique dedicated to the analysis of surface vibrations. It was lately adapted at TU Graz for monitoring the stability of an air-methane flame (Giuliani, et al., 2006, ASME Turbo Expo, ASME Paper No. GT2006-90413). This paper reports on the mapping of density fluctuations measured with LV in a premixed air-methane flame (free jet; swirl stabilized) with a forced flow modulation (quarter-wave resonator; amplification with a siren). In order to correlate the density fluctuations with the jet aerodynamics and turbulent flame shape, stereoscopic particle image velocimetry and high-speed schlieren visualizations were used. This paper addresses issues regarding the estimate of density fluctuations, the transform from line-of-sight to local measurement with tomographic methods, and the potential of the method for detailed description of thermoacoustic couplings. One emphasized application of LV is its ability to perform precise and low-cost benchmark stability tests on a combustor during the design phase (time-resolved measurement, high frequency and phase resolution on the 5 Hz-20 kHz range with the present equipment and settings, near-constant spectral sensitivity over a large bandwidth, and no seeding required; measurement possible over the whole combustion volume). [DOI: 10.1115/1.3159373]

The next generation nuclear power/advanced gas reactor (NGNP/AGR) fuel development and qualification program included the design, installation, and testing of a 6-in. diameter nuclear fuel particle coater to demonstrate quality tri-structural isotropic (TRISO) fuel production on a small industrial scale. Scale-up from the laboratory-scale coater faced challenges associated with an increase in the kernel charge mass, kernel diameter, and a redesign of the gas distributor to achieve adequate fluidization throughout the deposition of the four TRISO coating layers. TRISO coatings are applied at very high temperatures in atmospheres of dense particulate clouds, corrosive gases, and hydrogen concentrations over 45% by volume. The severe environment, stringent product and process requirements, and the fragility of partially-formed coatings limit the insertion of probes or instruments into the coater vessel during operation. Pressure instrumentation were installed on the gas inlet line and exhaust line of the 6-in. coater to monitor the bed differential pressure and internal pressure fluctuations emanating from the fuel bed as a result of bed and gas 'bubble' movements. These instruments are external to the particle bed and provide a glimpse into the dynamics of fuel particle bed during the coating process and data that could be used to help ascertain the adequacy of fluidization and, potentially, the dominant fluidization regimes. Pressure fluctuation and differential pressure data are not presently useful as process control instruments, but data suggest a link between the pressure signal structure and some measurable product attributes that could be exploited to get an early estimate of the attribute values. [DOI: 10.1115/1.3126772] Keywords: pressure fluctuations, Hurst exponent, spouted bed, particle properties

The hydrodynamic pressure field is important for the design and safety of steeply sloping stepped spillways, which are typically designed for considerably lower maximum specific discharges than smooth spillways. The hydraulic performance of stepped spillways at high velocities may compromise its use due to major concern with safety against cavitation damage. Hydraulic model investigations were conducted in different large-size stepped chutes to characterize the nonaerated flow region which is potentially prone to cavitation damage and the pressure field acting on the step faces. The clear water depths and energy dissipation in the developing flow region are described in terms of integral measures of the turbulent boundary layer. Expressions for the location of and the flow depth at the inception point of air entrainment are derived. Pressure distributions on the horizontal and vertical faces of the step along the spillway are presented. Measurements indicated a different behavior of the pressure field in the aerated and nonaerated flow region. The mean and fluctuating pressure coefficients along the spillway are approximated by a regression function. The vertical face near the outer step edge close to the inception point of air entrainment is identified as a critical region for predicting cavitation inception in flow over stepped spillways. From the analysis of the pressure fluctuations in that region a maximum velocity of 15 m/s is proposed as a criterion to avoid extreme negative pressures in typical prototype steeply sloping stepped spillways, eventually leading to the occurrence of cavitation in the nonaerated flow. DOI: 10.1061/(ASCE)HY. 1943-7900.0000118 CE Database subject headings: Spillway; Dams; Air entrainment; Cavitation; Hydrodynamic pressure.

Competing populations in shared spaces with nonrenewable resources do not necessarily wage a battle for dominance at the cost of extinction of the less-fit strain if there are fitness advantages to the presence of the other strain. We report on the use of nanofabricated habitat landscapes to study the population dynamics of competing wild type and a growth advantage in stationary phase (GASP) mutant strains of Escherichia coil in a sealed and heterogeneous nutrient environment. Although GASP mutants are competitors with wild-type bacteria, we find that the 2 strains cooperate to maximize fitness (long-term total productivity) via spatial segregation: despite their very close genomic kinship, wild-type populations associate with wild-type populations and GASP populations with GASP populations. Thus, wild-type and GASP strains avoid each other locally, yet fitness is enhanced for both strains globally. This computation of fitness enhancement emerges from the local interaction among cells but maximizes global densities. At present we do not understand how fluctuations in both spatial and temporal dimensions lead to the emergent computation and how multilevel aggregates produce this collective adaptation. biophysics | competition | ecology | microbiology

Fluctuations in the abundance of molecules in the living cell may affect its growth and well being. For regulatory molecules (e.g., signaling proteins or transcription factors), fluctuations in their expression can affect the levels of downstream targets in a network. Here, we develop an analytic framework to investigate the phenomenon of noise correlation in molecular networks. Specifically, we focus on the metabolic network, which is highly inter-linked, and noise properties may constrain its structure and function. Motivated by the analogy between the dynamics of a linear metabolic pathway and that of the exactly soluble linear queuing network or, alternatively, a mass transfer system, we derive a plethora of results concerning fluctuations in the abundance of intermediate metabolites in various common motifs of the metabolic network. For all but one case examined, we find the steadystate fluctuation in different nodes of the pathways to be effectively uncorrelated. Consequently, fluctuations in enzyme levels only affect local properties and do not propagate elsewhere into metabolic networks, and intermediate metabolites can be freely shared by different reactions. Our approach may be applicable to study metabolic networks with more complex topologies or protein signaling networks that are governed by similar biochemical reactions. Possible implications for bioinformatic analysis of metabolomic data are discussed. noise correlation | biochemical networks | nonequilibrium steady-state

Fluctuations in the natural environment introduce variability into the biological systems that exist within them. In this paper, we develop a model for the influence of random fluctuations in the environment on a simple epidemiological system. The model describes the infection of a dynamic host population by an environmentally sensitive pathogen and is based on the infection of sugar beet plants by the endoparasitic slime-mold vector Polymyxa betae. The infection process is switched on only when the temperature is above a critical value. We discuss some of the problems inherent in modeling such a system and analyze the resulting model by using asymptotic techniques to generate closed-form solutions for the mean and variance of the net amount of new inoculum produced within a season. In this way, the variance of temperature profile can be linked with that of the inoculum produced in a season and hence the risk of disease. We also examine the connection between the model developed in this paper and discrete Markov-chain models for weather.

Experiments are performed to study the effect of cavity geometry and Mach number on the characteristics of compressible rectangular cavity flows. The study indicates that the corresponding length-to-depth ratio for the open- and transitional-type cavities increases with higher freestream Mach number. The depth-to-incoming boundary-layer thickness ratio is another important parameter to define the type of the cavity flow. The upstream influence region is minimized with the presence of a cavity, and larger downstream influence region is observed for the transitional-closed- and closed-type cavities. The distributions of surface pressure fluctuations show similar trend as those of static pressure distributions. The amplitude of surface pressure fluctuations increases toward the rear face for an open-type cavity, whereas a minor peak near the middle of the cavity floor is observed for a closed-type cavity. A transitional-type cavity induces more intense surface pressure fluctuations at the cavity floor. Higher levels of pressure fluctuations near the rear face are observed at higher Mach numbers for the transitional-and open-type cavities.

Byline: Milan M. Airkovic (1) Keywords: arrow of time; anthropic principle; entropy; philosophy of cosmology Abstract: A modern assessment of the classical Boltzmann-Schuetz argument for large-scale entropy fluctuations as the origin of our observable cosmological domain is given.The emphasis is put on the central implication of this picture which flatly contradicts the weak anthropic principle as an epistemological statement about the universe. Therefore, to associate this picture with the anthropic principle as it is usually done is unwarranted. In particular, Feynman's criticism of theanthropic principle based on the entropy-fluctuation picture is a product of this semantic confusion. Author Affiliation: (1) Astronomical Observatory of Belgrade, Volgina 7, 11160, Belgrade, Serbia, Yugoslavia Article History: Registration Date: 12/10/2004

An experimental investigation was conducted to study the transonic flow past convex corners. The mean surface pressure indicated strong--viscous interactions, and the interaction region increased with the freestream Mach number and the convex-corner angle. Unsteadiness of the interaction was characterized by an intermittent region and a local peak pressure fluctuation. The peak pressure fluctuations and the tentative boundary between the attached and separated flows could be scaled with the convex-corner angle and a second-order freestream Mach number ([M.sup.2.sub.[infinity]][eta]).

The distribution function in a classical gas at equilibrium is determined by correlations among local momenta fluctuations. External observers may be able to determine distribution when special conditions pertain to Brownian particles.

The correlation functions of the fluctuations of vibrational frequencies of azide ions and carbon monoxide in proteins are determined directly from stimulated photon echoes generated with femtosecond infrared pulses. The asymmetric stretching vibration of azide bound to carbonic anhydrase II exhibits a pronounced evolution of its vibrational frequency distribution on the time scale of a few picoseconds, which is attributed to modifications of the ligand structure through interactions with the nearby Thr-199. When azide is bound in hemoglobin, a more complex evolution of the protein structure is required to interchange the different ligand configurations, as evidenced by the much slower relaxation of the frequency distribution in this case. The time evolution of the distribution of frequencies of carbon monoxide bound in hemoglobin occurs on the [approximately equal to]10-ps time scale and is very nonexponential. The correlation functions of the frequency fluctuations determine the evolution of the protein structure local to the probe and the extent to which the probe can navigate those parts of the energy landscape where the structural configurations are able to modify the local potential energy function of the probe.

D'Alembert's variational principle and Noether's theorem to the existence of conservation laws were used to derive conservation laws for dynamic systems with variable mass, which is exclusively nonconservative in the general instance. The terms that describe the mass variation expand Noether's identity in such instances. A conservation law exists if Noether's identity is satisfied.

Four kinds of routinely employed variational functionals were used to formulate the inequality principles of the kineto-static contact problem of two elastic bodies in the common relative motion. This incremental frictional contact problem involved Hu-Washizu and Hellinger-Reissner functionals. The functional of Hu-Washizu can be used to obtain the associated principles based on the Reissner potential energy and complementary energy functionals.

Seasonally varying spectral and cross-spectral calculations are carried out on multiyear time series of vertically and zonally averaged daily zonal wind fields to describe the seasonal cycle of the 40-50-day oscillation of atmospheric angular momentum. Intraseasonal variability (including 40-50-day fluctuations) of global momentum is largest in late boreal winter and smallest in boreal autumn; however, the 40-50-day spectral peak is most pronounced in boreal summer when lower-frequency intraseasonal variance is depressed. The 40-50-day spectral peak in global momentum is much less pronounced and apparently is restricted to a narrower frequency band, than corresponding peaks in zonal wind spectra from individual tropical rawinsonde stations. Contributions to global momentum fluctuations from three near-equal-area latitude bands (tropics, Northern Hemisphere, and Southern Hemisphere) are compared, confirming that intraseasonal momentum fluctuations are tropical in origin. The variance of extratropical momentum at this time scale is about an order of magnitude less than the tropical momentum variability. Coherent tropical-extratropical interactions are found principally in boreal winter, with the highest coherence between the tropics and Northern Hemisphere. The corresponding phase difference between tropical and Northern Hemisphere momentum is suggestive of poleward propagation of momentum out of the tropics.

Finite fluctuations in particle number can offer a general pattern-forming mechanism in non-equilibrium growth, according to research into the formation of complex patterns in non-equilibrium systems. Inevitable fluctuation effects in a finite density process have been found to lead to a significant change in its large-scale properties, an unexpected result. It would be difficult to use the calculational machinery of equilibrium statistical methods to study these systems.

When a person attempts to produce from memory a given spatial or temporal interval, there is inevitably some error associated with the estimate. The time course of this error was measured in a series of experiments where subjects repeatedly attempted to replicate given target intervals. Sequences of the errors in both spatial and temporal replications were found to fluctuate as 1/f noises. 1/f noise is encountered in a wide variety of physical systems and is theorized to be a characteristic signature of complexity., Of the types of activity that characterize physical systems, perhaps the most ubiquitous and puzzling is the appearance of 1/f noise, a form of temporal fluctuation that has a power [...]

A study is conducted to investigate the temperature field in a turbulent flume. The effect of the Prandtl number on the convention velocity of temperature fluctuations in a turbulent boundary layer is considered and the effect of the Prandtl number on the connection between the velocity and the temperature fluctuations is highlighted.

The effect of stochastic fluctuations in the zonal-mean velocity field on the energy dispersion of planetary stationary waves is considered, using the nondivergent, barotropic vorticity equation. It is found that for small noise levels, the oscillatory structure of the solutions is not altered. However, for noise levels comparable to or larger than those observed in the circulation at 500 mb, the marginal density functions of the solution process in the subpolar region cluster near zero. This indicates that fluctuations in the velocity field inhibit the poleward dispersion of stationary wave energy. This localization phenomenon appears whether the ensemble average of the mean zonal flow is superrotation or has a simple two-jet structure.

By exploiting the symmetry of randomness, three mathematicians have revealed the geometric underpinnings of Brownian motion If you could watch an individual air molecule, you would see a dance that [...]

Author(s): Sébastien Balibar [1] On page 172 of this issue, Hertlein et al . [1] present the first direct evidence for a force, known as the 'critical Casimir force', that [...]

M. Hamm Lim and assoc conducted a study of the fluctuations in the vibrational frequencies of small molecules and ions in proteins using the three-pulse stimulated echo technique. Vibration frequencies are likely to be mostly sensitive to their local environment. Thus, experimental results offer an insight into the microscopic protein structure changes around their probe molecules and could pave the way to a much enhanced understanding of protein substrate interactions.