Compact Cycle Research Articles

Formulation and process strategies to minimize coat damage for compaction of coated pellets in a rotary tablet press: A mechanistic view

Compaction of multiple-unit pellet system (MUPS) tablets has been extensively studied in the past few decades but with marginal success. This study aims to investigate the formulation and process strategies for minimizing pellet coat damage caused by compaction and elucidate the mechanism of damage sustained during the preparation of MUPS tablets in a rotary tablet press. Blends containing ethylcellulose-coated pellets and cushioning agent (spray dried aggregates of micronized lactose and mannitol), were compacted into MUPS tablets in a rotary tablet press. The effects of compaction pressure and dwell time on the physicomechanical properties of resultant MUPS tablets and extent of pellet coat damage were systematically examined. The coated pellets from various locations at the axial and radial peripheral surfaces and core of the MUPS tablets were excavated and assessed for their coat damage individually. Interestingly, for a MUPS tablet formulation which consolidates by plastic deformation, the tablet mechanical strength could be enhanced without exacerbating pellet coat damage by extending the dwell time in the compaction cycle during rotary tableting. However, the increase in compaction pressure led to faster drug release rate. The location of the coated pellets in the MUPS tablet also contributed to the extent of their coat damage, possibly due to uneven force distribution within the compact. To ensure viability of pellet coat integrity, the formation of a continuous percolating network of cushioning agent is critical and the applied compaction pressure should be less than the pellet crushing strength.

Fast deformation cycles in the lithosphere and catastrophic earthquakes: Was it possible to prevent the Fukushima tragedy?

Based on principles of the regional hydrogeodeformatics, we reveal the earth’s global arrhythmic deformation pulsation, which manifests itself in short-term (several months) cycles of expansion and compaction of lithosphere plates. These processes are most evident within the global Endodrainage system (GEDS), which connects the deep segments of the Earth with its surface. We show that the global principal direction of the deformation signal movement is eastward (arriving from areas where this deformation pulse is initiated). Using some examples, we demonstrate the interconnection between deformation cycles and a series of catastrophic earthquakes, as well as some natural and natural-technogenic catastrophes. The need to monitor the global “geodynamic weather” is substantiated and the principles of a monitoring system for the Earth’s deformation are discussed.

Characterization and preparation of p(U-MMA-An) interpenetrating polymer network damping and absorbing material.

P(U-MMA-ANI) interpenetrating polymer network (IPN) damping and absorbing material is successfully synthesized by PANI particles served as an absorbing agent with the microemulsion polymerization and P(U-MMA) foam IPN network structure for substrate materials with foaming way. P(U-MMA-ANI) IPN is characterized by the compression mechanical performance testing, TG-DSC, and DSC. The results verify that the P(U-MMA) IPN foam damping material has a good compressive strength and compaction cycle property, and the optimum content of PMMA was 40% (mass) with which the SEM graphs do not present the phase separation on the macro level between PMMA and PU, while the phase separation was observed on the micro level. The DTG curve indicates that because of the formation of P(U-MMA) IPN, the decomposition temperature of PMMA and the carbamate in PU increases, while that of the polyol segment in PU has almost no change. P(U-MMA-ANI) IPN foam damping and absorbing material is obtained by PANI particles served as absorbing agent in the form of filler, and PMMA in the form of micro area in substrate material. When the content of PANI was up to 2.0% (mass), the dissipation factor of composites increased, and with the increasing of frequency the dissipation factor increased in a straight line.

New insight on the restructuring and breakage of particles during uniaxial confined compression tests on aggregates of petroleum coke

With the aim of modelling the mechanical behaviour of carbon anode paste, compression tests within a rigid mould were performed on different recipes of carbon paste containing 32 to 44wt.% binder. The compression was performed by applying a series of loading/unloading cycles. The maximum load was incrementally increased at each cycle. Test results showed that a softening behaviour occurs after the hardening of the anode paste during compaction cycles. This paper attempts to explain the mechanism of this peculiar behaviour. For comparison, two cokes with different shape factors were used to prepare the paste recipes. It was observed that round particles result in less resistance to local shear stress than do the angular ones. Binder, which consists of coal tar pitch and fine coke particles, acts as a lubricant enhancing the compaction of the paste. The breakage and slippage of particles during loading were monitored using an acoustic measurement system. A creep test, performed on a carbon paste and dry aggregates, corroborates that the time-dependency, or creep, of the paste is mainly governed by the solid skeleton.

FEM simulation of the die compaction of pharmaceutical products: Influence of visco-elastic phenomena and comparison with experiments

This work studies the influence of visco-elastic behavior in the finite element method (FEM) modeling of die compaction of pharmaceutical products and how such a visco-elastic behavior may improve the agreement between experimental and simulated compression curves. The modeling of the process was conducted on a pharmaceutical excipient, microcrystalline cellulose (MCC), by using Drucker-Prager cap model coupled with creep behavior in Abaqus(®) software. The experimental data were obtained on a compaction simulator (STYLCAM 200R). The elastic deformation of the press was determined by performing experimental tests on a calibration disk and was introduced in the simulation. Numerical optimization was performed to characterize creep parameters. The use of creep behavior in the simulations clearly improved the agreement between the numerical and experimental compression curves (stresses, thickness), mainly during the unloading part of the compaction cycle. For the first time, it was possible to reproduce numerically the fact that the minimum tablet thickness is not obtained at the maximum compression stress. This study proves that creep behavior must be taken into account when modeling the compaction of pharmaceutical products using FEM methods.

The effect of punch's shape on die compaction of pharmaceutical powders

This paper investigates the compaction of pharmaceutical powders using different shapes of punches. We introduce a model of mechanical behaviour Drucker–Prager Cap (DPC), using the approach of compressible continuous media. The model parameters that are depending on the material density, were identified from experimental data and a calibration process was applied on Microcrystalline Cellulose (MCC) powder. In addition, the mathematical formulation of the boundary problem of compaction in rigid tools brings back to an optimization problem with constraint, which is solved by finite element method. The Drucker–Prager Cap model, which is implemented in Abaqus/Standard software, was employed using a user subroutine, USDFLD. Three kinds of typical pharmaceutical tablets are considered: flat-face tablet and concave face tablet with two different depths. Results of simulations of die compaction cycle as compression, decompression and ejection, reproduce the powder compaction process for the studied shaped punches. The effects of the punch's shape on the compaction process were observed on the distribution and the maximum of stress and density in the compact. Examination of the density gradient according to the shape, suggests a capping tendency, which increases with the punch depth. This study illustrates the potentiality of the FEM method, which could be used as an efficient tool to predict the density and the stress distributions into shaped compacts and to provide a diagnostic of the capping problems.

LHC phenomenology and cosmology of string-inspired intersecting D-brane models

We discuss the phenomenology and cosmology of a Standardlike Model inspired by string theory, in which the gauge fields are localized on D-branes wrapping certain compact cycles on an underlying geometry, whose intersection can give rise to chiral fermions. The energy scale associated with string physics is assumed to be near the Planck mass. To develop our program in the simplest way, we work within the construct of a minimal model with gauge-extended sector $U(3{)}_{B}\ifmmode\times\else\texttimes\fi{}Sp(1{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1{)}_{{I}_{R}}\ifmmode\times\else\texttimes\fi{}U(1{)}_{L}$. The resulting $U(1)$ content gauges the baryon number $B$, the lepton number $L$, and a third additional Abelian charge ${I}_{R}$ which acts as the third isospin component of an $SU(2{)}_{R}$. All mixing angles and gauge couplings are fixed by rotation of the $U(1)$ gauge fields to a basis diagonal in hypercharge $Y$ and in an anomaly-free linear combination of ${I}_{R}$ and $B\ensuremath{-}L$. The anomalous ${Z}^{\ensuremath{'}}$ gauge boson obtains a string scale St\"uckelberg mass via a 4D version of the Green-Schwarz mechanism. To keep the realization of the Higgs mechanism minimal, we add an extra $SU(2)$ singlet complex scalar, which acquires a VEV and gives a TeV-scale mass to the nonanomalous gauge boson ${Z}^{\ensuremath{'}\ensuremath{'}}$. The model is fully predictive and can be confronted with dijet and dilepton data from LHC8 and, eventually, LHC14. We show that ${M}_{{Z}^{\ensuremath{'}\ensuremath{'}}}\ensuremath{\approx}3--4\text{ }\text{ }\mathrm{TeV}$ saturates current limits from the CMS and ATLAS Collaborations. We also show that for ${M}_{{Z}^{\ensuremath{'}\ensuremath{'}}}\ensuremath{\lesssim}5\text{ }\text{ }\mathrm{TeV}$, LHC14 will reach discovery sensitivity $\ensuremath{\gtrsim}5\ensuremath{\sigma}$. After that, we demonstrate in all generality that ${Z}^{\ensuremath{'}\ensuremath{'}}$ milliweak interactions could play an important role in observational cosmology. Finally, we examine some phenomenological aspects of the supersymmetric extension of the D-brane construct.

Hot fluid pumping along shallow-level collisional thrusts: The Monte Rentella Shear Zone, Umbria Apennine, Italy

The characteristics of a shallow-level shear zone that is representative of the deformation in the external sectors of the Northern Apennine fold-and-thrust belt are described. The characterization involved an integrated approach using microstructural analysis of deformation fabrics, vitrinite reflectance measurements, XRD analysis on clay minerals and carbon and oxygen stable isotopes analyses. This data set provides the evidence that the thrust was active at very shallow depths (ca. less than 3 km), with maximum paleotemperatures ranging from 60° to 100–110 °C. The regime during fault activity evolved through cycles of compaction and dilation linked to transient build up of fluid overpressure and injection. The alternating cycles of fluids supply generated a fault-fracture mesh with a complex network of blocky and striped veins that formed at temperatures ranging from 150° to 200 °C, not compatible with the conditions in the host rocks. This evidence implies that the shear zone was flooded by hot fluids coming upward from diagenetic and low-grade metamorphic dehydration of clay minerals active at deeper structural levels. The fluids were thus highly channelled and focused where deformation also focused, producing a local pronounced isotopic difference between fluids and host rock.

Lode dependency in the cold die powder compaction process

The powder forming industry looks to produce parts of increasing geometrical complexity as it is seen as a very efficient production process. This offers new challenges as three-dimensional states of stress are induced. In particular, granular and porous materials respond very differently to tensile and compressive stresses. Since experiments conducted in the 1990s, little exploration of the Lode dependency of powders was carried out. The present work investigates the effect of Lode dependency through numerical simulation, aiming to establish whether it affects the outcome of a compaction cycle and whether further experimental study of the phenomenon may be justified. To this effect, a Lode dependent model was developed and implemented in a finite element code, then two case studies were carried out. The results show that there is little impact on the density contours within the components and the stress levels during the compaction. As the parts are ejected from the die, surface stress levels are affected and this is of great interest when studying the onset of defects in powder compacts.

Flux discharge cascades in various dimensions

We study the dynamics of electric flux discharge by charged particle pair or spherical string or membrane production in various dimensions. When electric flux wraps at least one compact cycle, we find that a single "pair" production event can initiate a cascading decay in real time that "shorts out" the flux and discharges many units of it. This process arises from local dynamics in the compact space, and so is invisible in the dimensionally-reduced truncation. It occurs in theories as simple as the Schwinger model on a circle, and has implications for any theory with compact dimensions and electric flux, including string theories and the string landscape.

Study of radial die-wall pressure during high speed tableting: effect of formulation variables

With high-speed compaction cycles as applied in pharmaceutical industrial presses, robust tools like radial die-wall pressure (RDWP) are required to monitor the deformation behavior of formulations under pressure and to avoid common problems such as capping. In this study, the effects of common formulation factors such as lubricant, binder, and drug loading on RDW were investigated. Compaction simulation using Presster™ was applied for five pharmaceutical fillers with different compaction behaviors. Two lubricants, two binders and paracetamol as a model drug were used. Residual die-wall (RDP) and other compaction parameters were measured. Lubricant reduced RDP for fillers with plastic/brittle behavior(s), (p < 0.05), while increased RDP for fillers with plastic/elastic behavior, (p < 0.05), leading to higher tendency for capping in the later fillers. Binder reduced RDP for the fillers, (p < 0.05), hence, decreased capping probability. By increasing drug loading for fillers with plastic/elastic behavior(s), RDP was increased, (p = 0.00001), leading to capping, especially at high compaction pressure and speed. Die-wall instrumentation was useful in investigating formulation variables and detecting capping during high speed tableting.

Compaction Behavior and Part Thickness Variation in Vacuum Infusion Molding Process

In vacuum infusion molding process (VIMP), it is difficult to manufacture a composite part with small dimensional tolerance, since the upper mold for the process is flexible. In this study, the static and cyclic compaction responses of five kinds of fabrics were experimentally studied under real VIMP conditions, with the effects of compaction pressure, compaction time, compaction cycle and number of the fabric layers. The static and cyclic compaction responses of the all fabrics follow different power law models and the resulting fiber volume fraction and relaxation factor increase with the number of layers. Although the resulting fiber volume fraction increases with the layer numbers, change of the fiber volume fraction of the composite parts with 10 layers to 100 layers of the all fabrics is less than 2.5%. The thickness of the composite part was monitored and measured using micrometer gauges, and the effects of processing parameters on the final thickness of part was investigated. The part thickness varies as a function of spatial coordinates and time during pre-filling, filling and post-filling stages in VIMP. The variation and the final value of the part thickness would be significantly affected by the processing parameters. Statistical results show that the final part thickness is equivalent to the thickness of the dry preform under the 0.08 MPa vacuum compaction pressure in VIMP. The difference between the fiber volume fraction of the final part and that of the dry preform is 2% ~ 5.7%.

Conformal aspects of Spinor–Vector duality

We present a detailed study of various aspects of Spinor–Vector duality in Heterotic string compactifications and expose its origin in terms of the internal conformal field theory. In particular, we illustrate the main features of the duality map by using simple toroidal orbifolds preserving N 4 = 1 and N 4 = 2 spacetime supersymmetries in four dimensions. We explain how the duality map arises in this context by turning on special values of the Wilson lines around the compact cycles of the manifold. We argue that in models with N 4 = 2 spacetime supersymmetry, the interpolation between the Spinor–Vector dual vacua can be continuously realized. We trace the origin of the Spinor–Vector duality map to the presence of underlying N = ( 2 , 2 ) and N = ( 4 , 4 ) SCFTs, and explicitly show that the induced spectral flow in the twisted sectors is responsible for the observed duality. The isomorphism between current algebra representations gives rise to a number of chiral character identities, reminiscent of the recently-discovered MSDS symmetry.

Evolution of Lateritic Soils Geotechnical Parameters during a Multi-Cyclic OPM Compaction and Correlation with Road Traffic

Gravel lateritic soils are intensively used in road geotechnical engineering. This material is largely representative of engineering soil all around the tropical African Countries [1,2]. Gravel lateritic soils from parts of Burkina Faso and Senegal (West Africa) are used to determine the evolution of the geotechnical parameters from one to ten cycles of modified Proctor compaction. This test procedure is non-common for geotechnical purposes and it was found suitable and finally adopted to describe how these problematic soils behave when submitted to a multi-cyclic set of Modified Proctor compactions (OPM) [3,4]. On another hand, we propose a correlation between the traffic and the cycles of compaction considered as the repeated load. From that, this work shows the generation of active fine particles, the decrease of the CBR index and also the mechanical characteristics (mainly the Young Modulus, E) that contribute at least to the main deformation of the road structure.

Colloidal Processing and Characterization of Aluminum-Doped Lanthanum Oxyapatite, La10AlSi5O26.5

Lanthanum apatite is one of the most promising materials as electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFC), those operating close to 700°C. The complexity of microstructures, composition, and geometries of SOFC devices, make it necessary to have a precise control of processing parameters to obtain the desired combination of properties. This work involves the preparation and optimization of La10AlSi5O26.5 materials by reaction sintering of the raw materials (La2O3, Al2O3, and SiO2) to be used as IT-SOFCs electrolytes. Homogeneous mixed suspensions of those ceramic oxides were prepared. A heterocoagulation process was followed for ensuring a better reactivity during sintering. All the parameters involved in the process, such as deflocculant content, particle size of the initial powders, sonication time of the mixed suspensions, compaction, and sintering cycle were optimized. The effect of all these parameters were studied and discussed. Finally, La10AlSi5O26.5 electrolytes with density values of ∼88% of the theoretical density and total conductivities of 1.7 × 10−2 S/cm at 700°C were obtained. This study opens a path for the preparation of concentrated suspensions for obtaining dense thin films.

Holographic duals of SQCD models in low dimensions

We obtain gravity duals to supersymmetric gauge theories in two and three spacetime dimensions with unquenched flavor. The supergravity solutions are generated by a set of color branes wrapping a compact cycle in a Calabi-Yau threefold, together with another set of flavor branes extended along the directions orthogonal to the cycle wrapped by the color branes. We construct supergravity backgrounds which include the backreaction induced by a smeared set of flavor branes, which act as delocalized dynamical sources of the different supergravity fields.

Failure risk in powder-compacted parts

This article addresses the occurrence of crack-related failure within the powder compaction cycle. Both tensile and shear cracks are considered together with the challenges associated with their detection. Experimental data are presented from the compaction of multi-level parts pressed from DistaloyAE powder to green densities between 6 and 7 g/cm3. This is compared with process simulation results. Both point to compact fragility and that failure is reflected in a dilation mechanism. This is contrary to expectation where a shear-type failure was expected. Simulation of the compaction and ejection of a plain cylinder were also undertaken. This highlighted the impact of punch hold down and how it may be used to achieve part integrity through control of stress excursion within the compact. The final part of the article describes, for the first time, the integration of a failure risk model within compaction simulation. As a proof of concept, this was demonstrated to highlight high-risk areas for failure within the compaction cycle.

Effect of compaction cycles on index properties of soils from Western Niger Delta,

Lateritic soils of Western Niger Delta have been classified as immature laterites. Repeated vehicular loading on soils tends to result in deterioration of soil construction qualities. In this study, lateritic soils from the Western Niger Delta were investigated to determine the effects of vehicular loading which was simulated by subjecting the soils to series of repeated laboratory compaction cycles. The engineering index properties were determined after the specified cycles. The results of the study on A-2 and A-7 soil types from the area revealed that there were different degrees of particle breakdown with increasing compaction cycles. The polynomial equation best explains the effects of compaction cycles on the percentage of fines and liquid limit. Different equations have been developed to relate the effects of compaction cycles on percent fines and liquid limit.

Structural Insights into a Circadian Oscillator

An endogenous circadian system in cyanobacteria exerts pervasive control over cellular processes, including global gene expression. Indeed, the entire chromosome undergoes daily cycles of topological changes and compaction. The biochemical machinery underlying a circadian oscillator can be reconstituted in vitro with just three cyanobacterial proteins, KaiA, KaiB, and KaiC. These proteins interact to promote conformational changes and phosphorylation events that determine the phase of the in vitro oscillation. The high-resolution structures of these proteins suggest a ratcheting mechanism by which the KaiABC oscillator ticks unidirectionally. This posttranslational oscillator may interact with transcriptional and translational feedback loops to generate the emergent circadian behavior in vivo. The conjunction of structural, biophysical, and biochemical approaches to this system reveals molecular mechanisms of biological timekeeping.

The non-uniformity of microcrystalline cellulose bilayer tablets

The material response of the constrained microcrystalline cellulose particles during the manufacture of bilayer tablets has been investigated. This work exploits the ability of a non-contact optical profilometer to elucidate both the intricate roughness detail and the inherent form of a compacted sample surface within one measurement. Thus the effects of the imposed non-uniform stress pattern that develops during the two sequential compaction cycles have been determined. The indirect measurement procedure has been able to infer the degree of particle deformation and hence the relative local porosity can be determined. The application of two compaction cycles has shown to exasperate the inhomogeneity of the localised regions of stored elastic strain energy and this is highlighted by the non-uniform and complex ejected tablet geometry. The localised stored energy release by volume expansion in the radial direction is thought to be responsible for the fracture of tablets during the ejection phase of the manufacturing process. When the magnitude of the final layer compaction stress is greater than the initial layer compaction stress the radial volume expansion can even result in the rupture of junctions between particles in the adjacent layers at the periphery of the interfacial zone. Thus the energy dissipation by volume expansion is a possible explanation for the stress concentrating crack commonly present at interfacial boundary zone within the bilayer formulations.