Collapse Of Shell Research Articles

Silo Collapse under Granular Discharge

We investigate, at a laboratory scale, the collapse of cylindrical shells of radius R and thickness t induced by a granular discharge. We measure the critical filling height for which the structure fails upon discharge. We observe that the silos sustain filling heights significantly above an estimation obtained by coupling standard shell-buckling and granular stress distribution theories. Two effects contribute to stabilize the structure: (i) below the critical filling height, a dynamical stabilization due to granular wall friction prevents the localized shell-buckling modes to grow irreversibly; (ii) above the critical filling height, collapse occurs before the downward sliding motion of the whole granular column sets in, such that only a partial friction mobilization is at play. However, we notice also that the critical filling height is reduced as the grain size d increases. The importance of grain size contribution is controlled by the ratio d/√[Rt]. We rationalize these antagonist effects with a novel fluid-structure theory both accounting for the actual status of granular friction at the wall and the inherent shell imperfections mediated by the grains. This theory yields new scaling predictions which are compared with the experimental results.

多雪地域に建つ学校体育館の妻壁に起因する屋根型単層ラチスシェルの水平地震時鉛直応答の分析と保有耐力評価

The study deals with school gymnasium structures composed of EP roof type lattice shells, gable walls with a high rigidity and with truss arch frames. The collapse mechanisms of the structure are taken to be a horizontal structural collapse such as the member buckling collapse of the lattice shell and a vertical structural collapse such as the tensile member collapse of the gable wall. The purpose of this study is to investigate the static and the dynamic collapse by means of the both elasto-plastic analyses considering a geometric nonlinearity. The estimation method is also proposed to calculate practically the base-shear strength coefficient and the applied seismic lateral and vertical load distributions on the lattice shells, the gable walls and the truss arch frames. The study is practically useful to determine the collapse mechanism and calculate the ultimate lateral strength on the earthquake-proof design for the damage and safety limit earthquakes.

Enlarged Pore Size in Mesoporous Silica Films Templated by Pluronic F127: Use of Poloxamer Mixtures and Increased Template/SiO2 Ratios in Materials Synthesized by Evaporation-Induced Self-Assembly

Although evaporation-induced self-assembly (EISA) has proven to be a convenient method for synthesizing nanoporous silica films (and particles), accessing material structures with pore sizes larger than ca. 10 nm remains experimentally inconvenient. The use of pore swelling agents (SAs), commonly used during the hydrothermal synthesis of mesoporous silicas, results in little or no pore size expansion due to evaporation or phase separation. Moreover, diblock copolymer templates can yield large pores but are quite expensive and generally require the addition of strong organic cosolvents. Here, we hypothesized that pores templated by the Pluronic triblock polymer F127 could be successfully enlarged, without phase separation, by using a chemically similar, nonvolatile, secondary Pluronic polymer (P103) as the SA. We find pore size increased up to 15 nm for a spherical pore morphology, with a phase transition to a multilamellar vesicle (MLV)-based nanostructure occurring as the P103/F127 ratio is further increased. This MLV phase produces even larger pore sizes due to the collapse of concentric silica shells upon template removal. Remarkably, F127 alone exhibits expansion of pore size (up to ca. 16 nm) as the template/silica ratio is increased. We find appearance of the MLV phase is due to geometric packing considerations, with expansion of F127 micelle size being a result of favorable intermolecular interactions driven by the large poly(ethylene oxide) content of F127. Other Pluronic polymers with this feature also exhibit variable pore size based on the template/silica ratio, enabling the synthesis of mesoporous films with 3D pore connectivity and truly variable pore size of ca. 4.5 to almost 20 nm.

Smart polyaniline nanoparticles with thermal and photothermal sensitivity

Conductive polyaniline nanoparticles (PANI NPs) are synthesized by oxidation of aniline with persulfate in acid media, in the presence of polymeric stabilizers: polyvinilpyrrolidone (PVP), poly(N-isopropylacrylamide) (PNIPAM), and hydroxylpropylcellulose (HPC). It is observed that the size of the nanoparticles obtained depends on the polymeric stabilizer used, suggesting a mechanism where the aggregation of polyaniline molecules is arrested by adsorption of the polymeric stabilizer. Indeed, polymerization in the presence of a mixture of two polymers having different stabilizing capacity (PVP and PNIPAM) allows tuning of the size of the nanoparticles. Stabilization with biocompatible PVP, HPC and PNIPAM allows use of the nanoparticle dispersions in biological applications. The nanoparticles stabilized by thermosensitive polymers (PNIPAM and HPC) aggregate when the temperature exceeds the phase transition (coil to globule) temperature of each stabilizer (Tpt = 32 °C for PNIPAM or Tpt = 42 °C for HPC). This result suggests that an extended coil form of the polymeric stabilizer is necessary to avoid aggregation. The dispersions are reversibly restored when the temperature is lowered below Tpt. In that way, the effect could be used to separate the nanoparticles from soluble contaminants. On the other hand, the PANI NPs stabilized with PVP are unaffected by the temperature change. UV-visible spectroscopy measurements show that the nanoparticle dispersion changes their spectra with the pH of the external solution, suggesting that small molecules can easily penetrate the stabilizer shell. Near infrared radiation is absorbed by PANI NPs causing an increase of their temperature which induces the collapse of the thermosensitive polymer shell and aggregation of the NPs. The effect reveals that it is possible to locally heat the nanoparticles, a phenomenon that can be used to destroy tumor cells in cancer therapy or to dissolve protein aggregates of neurodegenerative diseases (e.g. Alzheimer). Moreover, the long range control of aggregation can be used to modulate the nanoparticle residence inside biological tissues.

Facile preparation of gold nanocages and hollow gold nanospheres via solvent thermal treatment and their surface plasmon resonance and photothermal properties

Although template etching method is one of the most common ways of preparation of hollow gold nanostructures, this approach still requires further improvements to avoid the collapse of gold shells after the cores were removed. In this work, an improved template etching method, with which hollow gold nanostructure is fabricated by etching Polystyrene (PS) cores from PS@Au core–shell nanospheres with solvent thermal treatment in N,N-Dimethylformamide (DMF), is demonstrated. When PS cores were removed by a thermal treatment process, gold nanoshells reconstruct and the collapse of the nanoshells is avoided. Gold nanocages and hollow gold nanospheres are easily obtained from the various structures of PS@Au core–shell nanospheres. These hollow nanostructures represent special near infrared (NIR) optical property and photothermal property. Compared with hollow gold nanospheres, the gold nanocages show higher temperature increase at the same particle concentration.

Dynamics of gravitational collapse and holographic entropy production

We consider the time evolution of two entropy-like quantities, the holographic entanglement entropy and causal holographic information, in a model of holographic thermalization dual to the gravitational collapse of a thin planar shell. Unlike earlier calculations valid in different limits, we perform a full treatment of the dynamics of the system, varying both the shell's equation of state and initial position. In all cases considered, we find that between an early period related to the acceleration of the shell and a late epoch of saturation towards the thermal limit, the entanglement entropy exhibits universal linear growth in time in accordance with the prediction of Liu and Suh. As intermediate steps of our analysis, we explicitly construct a coordinate system continuous at the location of an infinitely thin shell and derive matching conditions for geodesics and extremal surfaces traversing this region.

Actin-Myosin Spatial Patterns from a Simplified Isotropic Viscoelastic Model

F-actin networks are involved in cell mechanical processes ranging from motility to endocytosis. The mesoscale architecture of assemblies of individual F-actin polymers that gives rise to micrometer-scale rheological properties is poorly understood, despite numerous in vivo and vitro studies. In vitro networks have been shown to organize into spatial patterns when spatially confined, including dense spherical shells inside spherical emulsion droplets. Here we develop a simplified model of an isotropic, compressible, viscoelastic material continually assembling and disassembling. We demonstrate that spherical shells emerge naturally when the strain relaxation rate (corresponding to internal network reorganization) is slower than the disassembly rate (corresponding to F-actin depolymerization). These patterns are consistent with recent experiments, including a collapse of shells to a central high-density focus of F-actin when either assembly or disassembly is reduced with drugs. Our results demonstrate how complex spatio-temporal patterns can emerge without spatially distributed force generation, polar alignment of F-actin polymers, or spatially nonuniform regulation of F-actin by upstream biochemical networks.

Effects of the cosmological constant on cold dark matter clusters

Context. Cold dark matter inhomogeneities are considered in a homogeneous background of matter, radiation, and the cosmological constant in a flat universe. Aims. We investigate the influence of the cosmological constant on the non-linear collapse of cold dark matter clusters. Methods. For simplicity, a spherical infall model has been used to describe the collapse of non-relativistic mass shells; besides, an average distribution of density around a cluster of galaxies has been taken. Boundary conditions are imposed by the solution of the linearized equation for the growth of matter perturbations and by the cold dark matter power spectrum. Results. For an average cluster, the radii of shells and masses enclosed by them have been obtained at their zero proper acceleration (ZA) redshifts, at their turn-around (TA) redshifts and at their virialization (VIR) redshifts. According to our results at present, the shell that reaches its turn-around point shows [r TA ]0 = 6.85 Mpc and [M TA ]0 = 6.76 × 10 14 M� . The virializing shell fulfills [r TA ]0 = 4.57 [r VIR ]0 and [M TA ]0 = 1.95 [M VIR ]0. These results differ appreciably from those derived from a model with cosmological constant equal to zero in a flat universe: [r TA ( Λ= 0)]0 = 6.62 [r VIR ( Λ= 0)]0 and [M TA ( Λ= 0)]0 = 5.26 [M VIR ( Λ= 0)]0 ;t his discrepancy could be considered as a new independent proof of the existence of dark energy. The shell with zero proper acceleration presents [r ZA ]0 = 1.59 [r TA ]0 and [M ZA ]0 = 1.63 [M TA ]0. We have found that there is a limit to the mass of the average cluster, which is able to virialize; its value is {M VIR }MAX = 8.1 × 10 14 M� . As expected, we found that shells present null proper acceleration at redshift values that are smaller than 0.755. Conclusions. We have noticed that the cosmological constant imposes an upper limit for the mass enclosed by shells, which are able to reach zero proper velocity. Hence, this mass is the maximum mass of the virialized core, {M VIR }MAX. For the average cluster addressed in this work, the value is 2.34 times the mass of the virialized core at present. Shells enclosing masses M > {M VIR }MAX achieve zero proper acceleration and speed up, moving away from the virialized core, and never reach a turn-around point. Shells with M�{ M VIR }MAX show zero proper aceleration at redshifts close to that at which the universe background acceleration is null. Finally, we have found that the relation between shell proper velocities and their radii can be adjusted by a straight line at z = 0a nd from approximately 20 up to 40 Mpc; however, this line does not intercept the origin as velocities due to the Hubble flux do.

Temperature- and pH-responsive micelles with collapsible poly(N-isopropylacrylamide) headgroups.

We have studied the micelle formation and phase behavior of a series of temperature- and pH-responsive surfactants prepared by controlled radical (RAFT) polymerization. These C12NIPAMm surfactants consist of a dodecyl tail, a poly(N-isopropylacrylamide) (polyNIPAM) headgroup with average degrees of polymerization of between 7 and 96, and an ionizable carboxylate group. In the un-ionized state, these surfactants phase separate on warming toward a lower critical solution temperature (LCST), which decreases as the length of the NIPAM group is decreased. This is in agreement with the behavior of conventional nonionic poly(ethylene oxide)-based surfactants but is very different from that of polyNIPAM oligomer solutions. Small angle neutron scattering (SANS) shows that these surfactants self-assemble into micelles consisting of a nearly spherical hydrophobic core surrounded by a "hairy" polyNIPAM shell far below their LCST. Upon warming, the micelles undergo a sphere-to-rod transition induced by the collapse of the polyNIPAM shell, causing a reduction in the headgroup area. In the un-ionized state the demixing follows at the LCST, but a single charge on the free polymer end completely suppresses phase separation, allowing micelles to undergo a shape change but remain dissolved.

Design of Multi‐Stage Thermal Responsive Wettable Surface

Design of Multi‐Stage Thermal Responsive Wettable Surface

Singularity free gravitational collapse in an effective dynamical quantum spacetime

We model the gravitational collapse of heavy massive shells including its main quantum corrections. Among these corrections, quantum improvements coming from Quantum Einstein Gravity are taken into account, which provides us with an effective quantum spacetime. Likewise, we consider dynamical Hawking radiation by modeling its back-reaction once the horizons have been generated. Our results point towards a picture of gravitational collapse in which the collapsing shell reaches a minimum non-zero radius (whose value depends on the shell initial conditions) with its mass only slightly reduced. Then, there is always a rebound after which most (or all) of the mass evaporates in the form of Hawking radiation. Since the mass never concentrates in a single point, no singularity appears.

Entanglement growth during thermalization in holographic systems

We derive in detail several universal features in the time evolution of entanglement entropy and other nonlocal observables in quenched holographic systems. The quenches are such that a spatially uniform density of energy is injected at an instant in time, exciting a strongly coupled CFT which eventually equilibrates. Such quench processes are described on the gravity side by the gravitational collapse of a thin shell that results in a black hole. Various nonlocal observables have a unified description in terms of the area of extremal surfaces of different dimensions. In the large distance limit, the evolution of an extremal surface, and thus the corresponding boundary observable, is controlled by the geometry around and inside the event horizon of the black hole, allowing us to identify regimes of pre-local- equilibration quadratic growth, post-local-equilibration linear growth, a memory loss regime, and a saturation regime with behavior resembling those in phase transitions. We also discuss possible bounds on the maximal rate of entanglement growth in relativistic systems.

Holographic probes of collapsing black holes

We continue the programme of exploring the means of holographically decoding the geometry of spacetime inside a black hole using the gauge/gravity correspondence. To this end, we study the behaviour of certain extremal surfaces (focusing on those relevant for equal-time correlators and entanglement entropy in the dual CFT) in a dynamically evolving asymptotically AdS spacetime, specifically examining how deep such probes reach. To highlight the novel effects of putting the system far out of equilibrium and at finite volume, we consider spherically symmetric Vaidya-AdS, describing black hole formation by gravitational collapse of a null shell, which provides a convenient toy model of a quantum quench in the field theory. Extremal surfaces anchored on the boundary exhibit rather rich behaviour, whose features depend on dimension of both the spacetime and the surface, as well as on the anchoring region. The main common feature is that they reach inside the horizon even in the post-collapse part of the geometry. In 3-dimensional spacetime, we find that for sub-AdS-sized black holes, the entire spacetime is accessible by the restricted class of geodesics whereas in larger black holes a small region near the imploding shell cannot be reached by any boundary-anchored geodesic. In higher dimensions, the deepest reach is attained by geodesics which (despite being asymmetric) connect equal time and antipodal boundary points soon after the collapse; these can attain spacetime regions of arbitrarily high curvature and simultaneously have smallest length. Higher-dimensional surfaces can penetrate the horizon while anchored on the boundary at arbitrarily late times, but are bounded away from the singularity. We also study the details of length or area growth during thermalization. While the area of extremal surfaces increases monotonically, geodesic length is neither monotonic nor continuous.

Schizophrenic Core–Shell Microgels: Thermoregulated Core and Shell Swelling/Collapse by Combining UCST and LCST Phase Transitions

A variety of slightly cross-linked poly(2-vinylpyridine)-poly(N-isopropylacrylamide) (P2VP-PNIPAM) core-shell microgels with pH- and temperature-responsive characteristic were prepared via seeded emulsion polymerization. Negatively charged sodium 2,6-naphthalenedisulfonate (2,6-NDS) could be internalized into the inner core, followed by formation of (P2VPH(+)/SO3(2-)) supramolecular complex through the electrostatic attractive interaction in acid condition. The thermoresponsive characteristic feature of the (P2VPH(+)/SO3(2-))-PNIPAM core-shell microgels was investigated by laser light scattering and UV-vis measurement, revealing an integration of upper critical solution temperature (UCST) and lower critical solution temperature (LCST) behaviors in the temperature range of 20-55 °C. The UCST performance arised from the compromised electrostatic attractive interaction between P2VPH(+) and 2,6-NDS at elevated temperatures, while the subsequent LCST transition is correlated to the thermo-induced collapse of PNIPAM shells. The controlled release of 2,6-NDS was monitored by static fluorescence spectra as a function of temperature change. Moreover, stopped-flow equipped with a temperature-jump accessory was then employed to assess the dynamic process, suggesting a millisecond characteristic relaxation time of the 2,6-NDS diffusion process. Interestingly, the characteristic relaxation time is independent of the shell cross-link density, whereas it was significantly affected by shell thickness. We believe that these dual thermoresponsive core-shell microgels with thermotunable volume phase transition may augur promising applications in the fields of polymer science and materials, particularly for temperature-triggered release.

Nonlocal (but also nonsingular) physics at the last stages of gravitational collapse

We study the end stages of gravitational collapse of the thin shell of matter in ingoing Eddington-Finkelstein coordinates. We use the functional Schrodinger formalism to capture quantum effects in the near singularity limit. We find that that the equations of motion which govern the behavior of the collapsing shell near the classical singularity become strongly non-local. This reinforces previous arguments that quantum gravity in the strong field regime might be non-local. We managed to solve the non-local equation of motion for the dust shell case, and found an explicit form of the wavefunction describing the collapsing shell. This wavefunction and the corresponding probability density are non-singular at the origin, thus indicating that quantization should be able to rid gravity of singularities, just as it was the case with the singular Coulomb potential.

Pressure-induced drastic collapse of a high oxygen coordination shell in quartz-like α-GeO2

With the combination of a single crystal diamond anvil cell and a polycapillary half-lens, the local structural evolution around germanium in tetrahedrally networked quartz-like α-GeO2 has been investigated using extended x-ray absorption fine structure spectroscopy of up to 14 GPa by multiple-scattering analysis method. While the first shell Ge–O bond distances show a slight contraction with increasing pressure, the third shell Ge–O bond distances are found to decrease dramatically. The sluggish lengthening of the first shell Ge–O bond distances, initiated by coordination increase from fourfold to sixfold, occurs in the 7–14 GPa range just when the third shell Ge–O bond distances fall in the region of the second shell Ge–Ge bond distances. Moreover, these features are accompanied by the closing of intertetrahedral Ge–O–Ge angles and the opening of two intratetrahedral O–Ge–O angles, whose topological configuration surprisingly exhibits a helical chirality along the c axis that is opposite to the double helices of the corner-linked GeO4 tetrahedra. These results suggest that the high-pressure phase transitions in quartz and quartz-like materials could be associated with a structural instability that is driven by the drastic collapse of the next-nearest-neighbour anion shell, which is consistent with the emergence of high-symmetry anion sublattice. Our findings provide crucial insights into the densification mechanisms of quartz-like oxides, which would have broad implications for our understanding of the metastability of various post-quartz crystalline phases and pressure-induced amorphization.

Trehalose Induced Modifications in the Solvation Pattern of N-Methylacetamide

We have carried out molecular dynamics simulation to investigate the role of trehalose molecules on the change in the structural and dynamical properties of aqueous N-methylacetamide (NMA) solution. In this study, we considered six different trehalose concentrations ranging from 0 to 66%. Results are discussed in the framework of hydrophobic interactions between different methyl groups of NMA, structure of the solutions, and hydrogen bonding interactions between different solution species. We observe that the propensity of hydrophobic association through the methyl groups of NMA is essentially insensitive to trehalose concentration except for higher trehalose concentration where the hydrophobic interactions between the hydrophobic methyl groups are getting reduced. Also observed are (i) trehalose induced slight collapse of the second hydration shell of water, (ii) presence of excess water molecules near NMA, and (iii) exclusion of trehalose from NMA. Our NMA-water radial distribution function analyses followed by average number of hydrogen bonds per NMA calculations reveal that, in the hydration of NMA molecules, its carbonyl group oxygen (over amide hydrogen) is predominantly involved. As trehalose is added, we observe, in accordance with the water replacement hypothesis, the replacement of water-NMA hydrogen bonds by NMA-trehalose hydrogen bonds, keeping the average number of hydrogen bonds formed by a single NMA with different solution species essentially unchanged. Our hydrogen bond calculations further reveal that addition of trehalose replaces water-NMA hydrogen bonds by water-trehalose hydrogen bonds. And as a result, we find that the average number of hydrogen bonds formed by a water molecule remain unchanged. We also find that addition of trehalose decreases the translational motion of all the solution species sharply.

Entanglement Tsunami: Universal Scaling in Holographic Thermalization

We consider the time evolution of entanglement entropy after a global quench in a strongly coupled holographic system, whose subsequent equilibration is described in the gravity dual by the gravitational collapse of a thin shell of matter resulting in a black hole. In the limit of large regions of entanglement, the evolution of entanglement entropy is controlled by the geometry around and inside the event horizon of the black hole, resulting in regimes of pre-local-equilibration quadratic growth (in time), post-local-equilibration linear growth, a late-time regime in which the evolution does not carry memory of the size and shape of the entangled region, and a saturation regime with critical behavior resembling those in continuous phase transitions. Collectively, these regimes suggest a picture of entanglement growth in which an "entanglement tsunami" carries entanglement inward from the boundary. We also make a conjecture on the maximal rate of entanglement growth in relativistic systems.

Osmotic buckling of spherical capsules

We study the buckling of elastic spherical shells under osmotic pressure with the osmolyte concentration of the exterior solution as a control parameter. We compare our results for the bifurcation behavior with results for buckling under mechanical pressure control, that is, with an empty capsule interior. We find striking differences for the buckling states between osmotic and mechanical buckling. Mechanical pressure control always leads to fully collapsed states with opposite sides in contact, whereas uncollapsed states with a single finite dimple are generic for osmotic pressure control. For sufficiently large interior osmolyte concentrations, osmotic pressure control is qualitatively similar to buckling under volume control with the volume prescribed by the osmolyte concentrations inside and outside the shell. We present a quantitative theory which also captures the influence of shell elasticity on the relationship between osmotic pressure and volume. These findings are relevant for the control of buckled shapes in applications. We show how the osmolyte concentration can be used to control the volume of buckled shells. An accurate analytical formula is derived for the relationship between the osmotic pressure, the elastic moduli and the volume of buckled capsules. This also allows use of elastic capsules as osmotic pressure sensors or deduction of elastic properties and the internal osmolyte concentration from shape changes in response to osmotic pressure changes. We apply our findings to published experimental data on polyelectrolyte capsules.

A Crashworthy Problem on Composite Structures Using a Mathematical Approach

Abstract During the last decades the attention given to vehicle crash energy management has been centred on composite structures. The use of fibre-reinforced plastic composite materials in automotive structures, in fact, may result in many potential economic and functional benefits due to their improved properties respect to metal ones, ranging from weight reduction to increased strength and durability features. Although significant experimental work on the collapse of fibre-reinforced composite shells has been carried out, studies on the theoretical modelling of the crushing process are quite limited since the complex and brittle fracture mechanisms of composite materials. Moreover most of the studies have been directed towards the axial crush analysis, because it represents more or less the most efficient design. A mathematical approach on the failure mechanisms, pertaining to the stable mode of collapse of thin-walled composite structures subjected to axial loading, is investigated. The analysis is conducted from an energetic point of view. The main energy contributions to the absorption (bending, petal formation, circumferential delamination, friction) are identifies and then the total internal energy is equated to the work done by the external load. The total crushing process can be seen as a succession of deformation states, each responsible for a partial absorption. The minimum configuration for each impact force in the specific state of deformation, function of several variables and dependent on geometric and material parameters is obtained. A comparison between theory and experiments concerning crushing loads and total displacements is presented, showing how the proposed analytical model is effective in predicting the energy absorption capability of axially collapsing composite shells.