Effects of roughness on droplet apparent contact angles on a fiber

This paper reports on our investigation of the effects of surface roughness on the equilibrium shape and apparent contact angles of a droplet deposited on a fiber. In particular, the shape of a droplet on a roughened fiber is studied via the energy minimization method implemented in the surface evolver finite element code. Sinusoidal roughness varying in both the longitudinal and radial directions is considered in the simulations to study the effects of surface roughness on the most stable shape of a droplet on a fiber (corresponding a global minimum energy state). It is found that surface roughness delays droplet shape transition from a symmetric barrel to a clamshell or an asymmetric barrel profile. A phase diagram that includes the effects of fiber roughness on droplet configurations-symmetric barrel, clamshell, and asymmetric barrel-is presented for the first time. It is also found that droplet apparent contact angle tends to decrease on rough fibers. Likewise, roughness tends to increase the force required to detach a droplet from a fiber but the effect diminishes as droplet size increases relative to the size of surface roughness. The results presented in our study have been compared with experimental data or those from prior studies whenever possible, and good agreement has been observed

Transition of amorphous to crystalline oxide film in initial oxide overgrowth on liquid metals

It is important to understand the mechanism of oxidation in the initial stage on the free surface of liquid metals. Mittemeijer and co-workers recently developed a thermodynamic model to study the oxide overgrowth on a solid metal surface. Based on this model, we have developed a thermodynamic model to analyse the thermodynamic stability of oxide overgrowth on liquid metals. The thermodynamic model calculation revealed that the amorphous oxide phase is thermodynamically preferred up to 1.3 and 0.35 nm respectively, in the initial oxide overgrowth on liquid Al and Ga at the corresponding melting point. However, the amorphous phase is thermodynamically unstable in the initial oxide overgrowth on liquid Mg. The thermodynamic stability of amorphous phase in the Al and Ga oxide systems is attributed to lower sums of surface and interfacial energies for amorphous phases, compared to that of the corresponding crystalline phases.Financial support under grant EP/H026177/1 from the EPSRC was used

A study of the phase transition in the usual statistical model for nuclear multifragmentation

We use a simplified model which is based on the same physics as inherent in most statistical models for nuclear multifragmentation. The simplified model allows exact calculations for thermodynamic properties of systems of large number of particles. This enables us to study a phase transition in the model. A first order phase transition can be tracked down. There are significant differences between this phase transition and some other well-known cases

Rare isotope production in statistical multifragmentation

Producing rare isotopes through statistical multifragmentation is investigated using the Mekjian method for exact solutions of the canonical ensemble. Both the initial fragmentation and the the sequential decay are modeled in such a way as to avoid Monte Carlo and thus provide yields for arbitrarily scarce fragments. The importance of sequential decay, exact particle-number conservation and the sensitivities to parameters such as density and temperature are explored. Recent measurements of isotope ratios from the fragmentation of different Sn isotopes are interpreted within this picture.Comment: 10 eps figure

Expert chess memory: Revisiting the chunking hypothesis

After reviewing the relevant theory on chess expertise, this paper re-examines experimentally the finding of Chase and Simon (1973a) that the differences in ability of chess players at different skill levels to copy and to recall positions are attributable to the experts' storage of thousands of chunks (patterned clusters of pieces) in long-term memory. Despite important differences in the experimental apparatus, the data of the present experiments regarding latencies and chess relations between successively placed pieces are highly correlated with those of Chase and Simon. We conclude that the 2-second inter-chunk interval used to define chunk boundaries is robust, and that chunks have psychological reality. We discuss the possible reasons why Masters in our new study used substantially larger chunks than the Master of the 1973 study, and extend the chunking theory to take account of the evidence for large retrieval structures (templates) in long-term memory

CORYNEBACTERIAL PSEUDOTUBERCULOSIS IN MICE : II. ACTIVATION OF NATURAL AND EXPERIMENTAL LATENT INFECTIONS

Latent corynebactenai infection occurs naturally in many strains of mice. It can be evoked into the active disease, pseudotuberculosis, by a single injection of 10 mg of cortisone. The cortisone effect was tested in 21 colonies, representing 11 genetically different strains of mice. Animals of the C57B1/6, DBA/2, and RIII strains were shown to be latently infected with Corynebacterium kutscheri by the fact that they developed fatal pseudotuberculosis following cortisone treatment. Virulent C. kutscheri could not be isolated from homogenates of organs obtained from latently infected animals before cortisone administration; however, these homogenates yielded small translucent colonies of avirulent organisms. Recovery of these atypical colonies was facilitated by preincubating the organ homogenates before plating. The organisms constituting such colonies differed morphologically and immunologically from C. kutscheri, but had similar biochemical properties with the exception that they lacked urease and catalase activity. Mice treated with cortisone yielded both the avirulent bacteria and virulent C. kutscheri. The latter was the predominant organism present in the organs at the height of infection. Injection of avirulent organisms into Swiss Lynch mice, which are normally free of latent corynebacteria, occasionally established a latent infection which could be converted into corynebacterial pseudotuberculosis by cortisone. Cultures of fully virulent C. kutscheri were then obtained from the lesions. Latency was produced experimentally with a streptomycin-resistant strain of virulent C. kutscheri (CKsr) derived from the stock culture. When sublethal doses of CKsr were injected into NCS mice (Institut Pasteur colony), they induced a latent infection characterized by the presence of avirulent organisms possessing the streptomycin resistance marker. These were isolated in the form of small translucent colonies from the livers of the infected animals. Administration of cortisone to these animals subsequently evoked active infection from which virulent CKsr could be obtained. Injection of the avirulent streptomycin-resistant organisms into normal NCS mice established a latent infection which could be uniformly converted into corynebacterial pseudotuberculosis by cortisone. The virulent C. kutscheri obtained from the lesions bore the genetic marker of streptomycin resistance, thus being identical with CKsr. Except for streptomycin resistance, the avirulent organisms isolated from the experimentally induced latent infections were identical with those found in the naturally occurring latent infections. These results suggest that C. kutscheri can persist in vitro in an avirulent form which is resistant to the defense mechanisms of the host, and can thus establish a latent infection. Treatment of the animal with cortisone results in the conversion of the avirulent form into virulent C. kutscheri, and of the latent infection into active corynebacterial pseudotuberculosis. The findings are discussed with regard to their relevance to infection immunity, and to the conversion of latent infection into overt disease

Cross-link governed dynamics of biopolymer networks

Cytoskeletal networks of biopolymers are cross-linked by a variety of proteins. Experiments have shown that dynamic cross-linking with physiological linker proteins leads to complex stress relaxation and enables network flow at long times. We present a model for the mechanical properties of transient networks. By a combination of simulations and analytical techniques we show that a single microscopic timescale for cross-linker unbinding leads to a broad spectrum of macroscopic relaxation times, resulting in a weak power-law dependence of the shear modulus on frequency. By performing rheological experiments, we demonstrate that our model quantitatively describes the frequency behavior of actin network cross-linked with $\alpha$-Actinin-$4$ over four decades in frequency.Comment: 4 page

Hyperuniformity, quasi-long-range correlations, and void-space constraints in maximally random jammed particle packings. I. Polydisperse spheres

Hyperuniform many-particle distributions possess a local number variance that grows more slowly than the volume of an observation window, implying that the local density is effectively homogeneous beyond a few characteristic length scales. Previous work on maximally random strictly jammed sphere packings in three dimensions has shown that these systems are hyperuniform and possess unusual quasi-long-range pair correlations, resulting in anomalous logarithmic growth in the number variance. However, recent work on maximally random jammed sphere packings with a size distribution has suggested that such quasi-long-range correlations and hyperuniformity are not universal among jammed hard-particle systems. In this paper we show that such systems are indeed hyperuniform with signature quasi-long-range correlations by characterizing the more general local-volume-fraction fluctuations. We argue that the regularity of the void space induced by the constraints of saturation and strict jamming overcomes the local inhomogeneity of the disk centers to induce hyperuniformity in the medium with a linear small-wavenumber nonanalytic behavior in the spectral density, resulting in quasi-long-range spatial correlations. A numerical and analytical analysis of the pore-size distribution for a binary MRJ system in addition to a local characterization of the n-particle loops governing the void space surrounding the inclusions is presented in support of our argument. This paper is the first part of a series of two papers considering the relationships among hyperuniformity, jamming, and regularity of the void space in hard-particle packings.Comment: 40 pages, 15 figure

Gravitationally Collapsing Shells in (2+1) Dimensions

We study gravitationally collapsing models of pressureless dust, fluids with pressure, and the generalized Chaplygin gas (GCG) shell in (2+1)-dimensional spacetimes. Various collapse scenarios are investigated under a variety of the background configurations such as anti-de Sitter(AdS) black hole, de Sitter (dS) space, flat and AdS space with a conical deficit. As with the case of a disk of dust, we find that the collapse of a dust shell coincides with the Oppenheimer-Snyder type collapse to a black hole provided the initial density is sufficiently large. We also find -- for all types of shell -- that collapse to a naked singularity is possible under a broad variety of initial conditions. For shells with pressure this singularity can occur for a finite radius of the shell. We also find that GCG shells exhibit diverse collapse scenarios, which can be easily demonstrated by an effective potential analysis.Comment: 27 pages, Latex, 11 figures, typos corrected, references added, minor amendments in introduction and conclusion introd