pinecone/core-2020-05-10-deduplication huggingface dataset:
On angular momentum balance for particle systems with periodic boundary
  conditions

The well-known issue with the absence of conservation of angular momentum in
classical particle systems with periodic boundary conditions is addressed. It
is shown that conventional theory based on Noether's theorem fails to explain
the simplest possible example, notably jumps of angular momentum in the case of
single particle moving in a periodic cell. It is suggested to consider the
periodic cell as an open system, exchanging mass, momentum, angular momentum,
and energy with surrounding cells. Then the behavior of the cell is described
by balance laws rather than conservation laws. It is shown using the law of
angular momentum balance that the variation of the angular momentum in systems
with periodic boundary conditions is a consequence of (i) the non-zero flux of
angular momentum through the boundaries and (ii) torque acting on the cell due
to the interactions between particles in the cell with images in the
neighboring cells. Two simple examples demonstrating both phenomena are
presented.Comment: Keywords: angular momentum, periodic boundary conditions, open
  systems, balance laws, conservation laws, Noether theore
Modelling and simulation of acrylic bone cement injection and curing
  within the framework of vertebroplasty

The minimal invasive procedure of vertebroplasty is a surgical technique to
treat compression fractures of vertebral bodies. During the treatment, liquid
bone cement gets injected into the affected vertebral body and therein cures to
a solid. In order to investigate the treatment and the impact of injected bone
cement, an integrated modelling and simulation framework has been developed.
The framework includes (i) the generation of microstructural computer models
based on microCT images of human cancellous bone, (ii) computational fluid
dynamics (CFD) simulations of bone cement injection into the trabecular
structure and (iii) non-linear finite element (FE) simulations of the
subsequent bone cement curing. A detailed description of the material behaviour
of acrylic bone cements is provide d for both simulation stages. A non-linear
process-depending fluid flow model is chosen to represent the bone cement
behaviour during injection. The bone cements phase change from a highly viscous
fluid to a solid is described by a non-linear viscoelastic material model with
curing dependent properties. To take into account the distinctive temperature
dependence of acrylic bone cements, both material models are formulated in a
thermo-mechanically coupled manner. Moreover, the corresponding microstructural
CFD- and FE-simulations are performed using thermo-mechanically coupled
solvers. An application of the presented modelling and simulation framework to
a sample of human cancellous bone demonstrates the capabilities of the
presented approach.Comment: 26 pages, 16 figures, ZAMM - Zeitschrift f\"ur angewandte Mathematik
  und Mechanik (2015
When is natural convection completely passive?

This is the peer reviewed version of the following article: KAY, A., 2016. When is natural convection completely passive? Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, 96(3), pp.279-303, which has been published in final form at http://dx.doi.org/10.1002/zamm.201400177. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Momentum and energy equations for vertical  flow, including viscous dissipation and pressure work, are derived and shown to require that the cross-section mean density is taken as the reference density for calculation of buoyancy forces under the Boussinesq approximation. Solutions are obtained for flow between parallel plane walls, with and without the pressure work as an explicit term in the energy equation. Both walls are at the same temperature, so there is no thermal forcing, but solutions are obtained for all admissible values of dynamic pressure gradient. The passive convection condition, whereby the \ud
flow is driven entirely by buoyancy forces resulting from heat generated by the \ud
flow's own viscous dissipation, is found on one branch of the dual solutions.\ud
However, while theoretically possible, passive convection is not physically realisable with any real fluid
Energy conservation and dissipation properties of time-integration methods for nonsmooth elastodynamics with contact

International audienceThis article is devoted to the study of the conservation and the dissi-pation properties of the mechanical energy of several time–integration methods dedicated to the elasto–dynamics with unilateral contact. Given that the direct application of the standard schemes as the Newmark schemes or the generalized– α schemes leads to energy blow-up, we study two schemes dedicated to the time–integration of nonsmooth systems with contact: the Moreau–Jean scheme and the nonsmooth generalized–α scheme. The energy conservation and dissi-pation properties of the Moreau–Jean is firstly shown. In a second step, the nonsmooth generalized–α scheme is studied by adapting the previous works of Krenk and Høgsberg in the context of unilateral contact. Finally, the known properties of the Newmark and the Hilber–Hughes–Taylor (HHT) scheme in the unconstrained case are extended without any further assumptions to the case with contact
Convection-adapted BEM-based FEM

We present a new discretization method for homogeneous
convection-diffusion-reaction boundary value problems in 3D that is a
non-standard finite element method with PDE-harmonic shape functions on
polyhedral elements. The element stiffness matrices are constructed by means of
local boundary element techniques. Our method, which we refer to as a BEM-based
FEM, can therefore be considered a local Trefftz method with element-wise
(locally) PDE-harmonic shape functions. The Dirichlet boundary data for these
shape functions is chosen according to a convection-adapted procedure which
solves projections of the PDE onto the edges and faces of the elements. This
improves the stability of the discretization method for convection-dominated
problems both when compared to a standard FEM and to previous BEM-based FEM
approaches, as we demonstrate in several numerical experiments
A quaternion-based model for optimal control of the SkySails airborne
  wind energy system

Airborne wind energy systems are capable of extracting energy from higher
wind speeds at higher altitudes. The configuration considered in this paper is
based on a tethered kite flown in a pumping orbit. This pumping cycle generates
energy by winching out at high tether forces and driving a generator while
flying figures-of-eight, or lemniscates, as crosswind pattern. Then, the tether
is reeled in while keeping the kite at a neutral position, thus leaving a net
amount of generated energy. In order to achieve an economic operation,
optimization of pumping cycles is of great interest.
  In this paper, first the principles of airborne wind energy will be briefly
revisited. The first contribution is a singularity-free model for the tethered
kite dynamics in quaternion representation, where the model is derived from
first principles. The second contribution is an optimal control formulation and
numerical results for complete pumping cycles. Based on the developed model,
the setup of the optimal control problem (OCP) is described in detail along
with its numerical solution based on the direct multiple shooting method in the
CasADi optimization environment. Optimization results for a pumping cycle
consisting of six lemniscates show that the approach is capable to find an
optimal orbit in a few minutes of computation time. For this optimal orbit, the
power output is increased by a factor of two compared to a sophisticated
initial guess for the considered test scenario.Comment: 18 pages, 14 figures, submitted to Journal of Applied Mathematics and
  Mechanics (ZAMM
Irreducible decomposition of strain gradient tensor in isotropic strain
  gradient elasticity

In isotropic strain gradient elasticity, we decompose the strain gradient
tensor into its irreducible pieces under the n-dimensional orthogonal group
O(n). Using the Young tableau method for traceless tensors, four irreducible
pieces (n>2), which are canonical, are obtained. In three dimensions, the
strain gradient tensor can be decomposed into four irreducible pieces with
7+5+3+3 independent components whereas in two dimensions, the strain gradient
tensor can be decomposed into three irreducible pieces with 2+2+2 independent
components. The knowledge of these irreducible pieces is extremely useful when
setting up constitutive relations and strain energy
An improved return-mapping scheme for nonsmooth yield surfaces: PART I -
  the Haigh-Westergaard coordinates

The paper is devoted to the numerical solution of elastoplastic constitutive
initial value problems. An improved form of the implicit return-mapping scheme
for nonsmooth yield surfaces is proposed that systematically builds on a
subdifferential formulation of the flow rule. The main advantage of this
approach is that the treatment of singular points, such as apices or edges at
which the flow direction is multivalued involves only a uniquely defined set of
non-linear equations, similarly to smooth yield surfaces. This paper (PART I)
is focused on isotropic models containing: $a)$ yield surfaces with one or two
apices (singular points) laying on the hydrostatic axis; $b)$ plastic
pseudo-potentials that are independent of the Lode angle; $c)$ nonlinear
isotropic hardening (optionally). It is shown that for some models the improved
integration scheme also enables to a priori decide about a type of the return
and investigate existence, uniqueness and semismoothness of discretized
constitutive operators in implicit form. Further, the semismooth Newton method
is introduced to solve incremental boundary-value problems. The paper also
contains numerical examples related to slope stability with available Matlab
implementation.Comment: 25 pages, 10 figure
Optimal Control for a Class of Infinite Dimensional Systems Involving an
  $L^\infty$-term in the Cost Functional

An optimal control problem with a time-parameter is considered. The
functional to be optimized includes the maximum over time-horizon reached by a
function of the state variable, and so an $L^\infty$-term. In addition to the
classical control function, the time at which this maximum is reached is
considered as a free parameter. The problem couples the behavior of the state
and the control, with this time-parameter. A change of variable is introduced
to derive first and second-order optimality conditions. This allows the
implementation of a Newton method. Numerical simulations are developed, for
selected ordinary differential equations and a partial differential equation,
which illustrate the influence of the additional parameter and the original
motivation.Comment: 21 pages, 8 figure
Subdifferential-based implicit return-mapping operators in Mohr-Coulomb
  plasticity

The paper is devoted to a constitutive solution, limit load analysis and
Newton-like methods in elastoplastic problems containing the Mohr-Coulomb yield
criterion. Within the constitutive problem, we introduce a self-contained
derivation of the implicit return-mapping solution scheme using a recent
subdifferential-based treatment. Unlike conventional techniques based on
Koiter's rules, the presented scheme a priori detects a position of the unknown
stress tensor on the yield surface even if the constitutive solution cannot be
found in closed form. This fact eliminates blind guesswork from the scheme,
enables to analyze properties of the constitutive operator, and simplifies
construction of the consistent tangent operator which is important for the
semismooth Newton method applied on the incremental boundary value
elastoplastic problem. The incremental problem in Mohr-Coulomb plasticity is
combined with the limit load analysis. Beside a conventional direct method of
the incremental limit analysis, a recent indirect one is introduced and its
advantages are described. The paper contains 2D and 3D numerical experiments on
slope stability with publicly available Matlab implementations.Comment: 26 pages, 10 figure
Stress intensity factor for multiple inclined or curved cracks problem in circular positions in plane elasticity

The problems of multiple inclined or curved cracks in circular positions is treated by using the hypersingular integral equation method. The cracks center are placed at the edge of a virtual circle with radius R. The first crack is fixed on the x-axis while the second crack is located on the boundary of a circle with the varying angle, θ. A system of hypersingular integral equations is formulated and solved numerically for the stress intensity factor (SIF). Numerical examples demonstrate the effect of interaction between two cracks in circular positions are given. It is found that, the severity at the second crack tips are significant when the ratio length of the second to the first crack is small and it is placed at a small angle of θ
A study of sliding motion of a solid body on a rough surface with
  asymmetric friction

Recent studies show interest in materials with asymmetric friction forces. We
investigate terminal motion of a solid body with circular contact area. We
assume that friction forces are asymmetric orthotropic. Two cases of pressure
distribution are analyzed: Hertz and Boussinesq laws. Equations for friction
force and moment are formulated and solved for these cases. Numer- ical results
show significant impact of the asymmetry of friction on the motion. Our results
can be used for more accurate prediction of contact behavior of bodies made
from new materials with asymmetric surface textures.Comment: 13 pages, 3 tables, 2 figures, preprin
Effective transient behaviour of inclusions in diffusion problems

This paper is concerned with the effective transport properties of
heterogeneous media in which there is a high contrast between the phase
diffusivities. In this case the transient response of the slow phase induces a
memory effect at the macroscopic scale, which needs to be included in a
macroscopic continuum description. This paper focuses on the slow phase, which
we take as a dispersion of inclusions of arbitrary shape. We revisit the linear
diffusion problem in such inclusions in order to identify the structure of the
effective (average) inclusion response to a chemical load applied on the
inclusion boundary. We identify a chemical creep function (similar to the creep
function of viscoelasticity), from which we construct estimates with a reduced
number of relaxation modes. The proposed estimates admit an equivalent
representation based on a finite number of internal variables. These estimates
allow us to predict the average inclusion response under arbitrary time-varying
boundary conditions at very low computational cost. A heuristic generalisation
to concentration-dependent diffusion coefficient is also presented. The
proposed estimates for the effective transient response of an inclusion can
serve as a building block for the formulation of multi-inclusion homogenisation
schemes.Comment: 24 pages, 9 figures. Submitted to ZAMM (under review
Comparative study on the growth of juvenile Galapagos giant tortoises (Geochelone nigra) at the Charles Darwin Research Station (Galapagos Islands, Ecuador) and Zoo Zurich (Zurich, Switzerland)

In this study, the growth rates of a group of Galapagos giant tortoises raised in their natural habitat at the Charles Darwin Research Station (CDRS; Galapagos Islands, Ecuador) and a group of captive-bred specimens (Zoo Zurich, Zurich, Switzerland) were compared for the ﬁrst time. A great discrepancy in growth rates was observed after the ﬁrst year. When the animals were 4 years old, the carapace \ud
in the Zurich specimens was approximately twice as long as that in the CDRS tortoises, and the Zurich animals weighed approximately 10 times more than the CDRS animals. The zoo diet was modiﬁed by a reduction in nutrients and an increase in ﬁber to produce a more natural growth rate
Nutrition of captive lowland anoa (Bubalus depressicornis): a study on ingesta passage, intake, digestibility, and a diet survey

Members of the Bovini genus are classified as grazers. Smaller species of ruminants are not expected to be able to digest particularly fibrous diets and are more often classified as intermediate feeders or browsers. Anoas (Bubalus spp.) are interesting in this respect as they are the smallest representatives of the Bovini, being only 10-20% of the body weight of other species of the same genus. A feeding trial was carried out with four lowland anoas (Bubalus depressicornis) at London Zoo, investigating diet digestibility by total fecal collection and passage rates by the simultaneous administration of a fluid (Co-EDTA) and a particle (Cr-mordanted fibre <2 mm) marker. The diet consisted of legume hay, dairy cow pellets, browse, fruits, and vegetables. The achieved digestibility coefficients averaged 70±4% for dry matter and 57±7% for cell walls (NDF). Mean retention times for the total gastrointestinal tract were 25±4.1 hr for fluid and 39±6.7 hr for particles, respectively. The ratio of forestomach particle:fluid retention was 2.14±0.40. Additional information regarding anoa diets in captivity was collected through a survey targeting all institutions that have anoas in their collection currently. Suitability of the provided diet was evaluated using the ratio of unstructured:structured feeds (unstructured feeds pellets, grains, produce; structured feeds=roughage, browse) on a dry matter basis and an assumed complete consumption of offered unstructured diet items, with only the remaining intake capacity being met by structured items. The use of this ratio reliably predicted one facility that reported chronic diet-related problems. As other ruminants, anoas should receive a diet with restricted amounts of concentrates and fruits. The comparatively high fibre digestibility and the high selective particle retention in the forestomach suggest a classification of an intermediate/grazing ruminant
Fiber digestibility in juvenile Galapagos tortoises (Geochelone nigra) and implications for the development of captive animals

Digestive strategies have been recognized to be a key factor for healthy growth in juvenile Galapagos giant tortoises (Geochelone nigra). The aim of present study was to investigate digestive coefficients with special regard to fiber fractions. Four captive bred Galapagos giant tortoises 4-5 years of age were fed a controlled diet for 32 days. The diet consisted of 77% hay, 15% tortoise pellets, and 8% apples on a dry matter basis. On a dry matter basis diet analysis showed: 95.7% organic matter, 11.3% crude protein, 20.5% crude fiber, 22.6% acid detergent fiber, 5.0% acid detergent lignin, and 17.6% cellulose. Based on total fecal collection during 7 days average dry matter digestibilities were calculated: 65% for dry matter, 67% for organic matter, 63% for crude protein, 55% for crude fiber, 49% for acid detergent fiber, 41% for acid detergent lignin, 54% for cellulose. An increase in crude fiber content resulted in a reduced digestibility in comparative evaluations of data for different tortoise species, and in a comparison of tortoises and mammalian hindgut fermenters. Compared to some mammalian hindgut-fermenting herbivore species (domestic horses, Asian elephants, Indian rhinoceroses) on a diet of hay and concentrates, the juvenile Galapagos giant tortoises showed a digestion of similar efficiency. If a reduction in dietary digestibility is warranted in juvenile Galapagos giant tortoises, it is concluded that dietary fiber levels should be increased and it is proposed that crude fiber levels of 30-40% on a dry matter basis should be achieved
Female Social Dominance in Two Eulemur Species With Different Social Organizations

Female social dominance is rare in mammals, but common in lemurs. We investigated social dominance in two Eulemur species; the polygynous crowned lemur (E. coronatus) and the monogamous red-bellied lemur (E. rubriventer), using four and two social groups, respectively. We collected data on agonistic interactions and two types of affiliative behavior (grooming and maintaining spatial proximity). We used a combination of focal watches of individuals, instantaneous scan-sampling of groups, and all-occurrence of some behaviors in groups. We found that overall rates of agonistic interactions were higher in E. coronatus, and they also had more decided intersexual agonistic interactions than E. rubriventer. However, in both species the females won the vast majority of these agonistic interactions. E. coronatus females were groomed more often by males than vice versa, whereas no sex differences in grooming were observed in E. rubriventer. We found that males were responsible for maintaining spatial proximity in E. coronatus whereas in E. rubriventer, females were responsible. In one group of E. coronatus, the male was overweight and dominant to the female and this is the first observation of male dominance in a lemur species typically described as female dominant. We suggest that body weights in captivity be monitored for maintaining normal dominance relationships. Overall, agonistic behaviors were consistent with clear female social dominance in both E. coronatus and E. rubriventer. The affiliative behaviors also provided clear evidence for female dominance E. coronatus, but not for E. rubriventer
Differences in fecal particle size between free-ranging and captive individuals of two browser species

Data from captive animals indicated that browsing (BR) ruminants have larger fecal particles-indicative of lesser chewing efficiency-than grazers (GR). To answer whether this reflects fundamental differences between the animal groups, or different reactions of basically similar organisms to diets fed in captivity, we compared mean fecal particle size (MPS) in a GR and a BR ruminant (aurox Bos primigenius taurus, giraffe Giraffa camelopardalis) and a GR and a BR hindgut fermenter (Przewalski's horse Equus ferus przewalskii, lowland tapir Tapirus terrestris), both from captivity and from the wild. As would be expected owing to a proportion of finely ground, pelleted feeds in captive diets, MPS was smaller in captive than free-ranging GR. In contrast, MPS was drastically higher in captive than in free-ranging BR of either digestion type. Thus, the difference in MPS between GR and BR was much more pronounced among captive than free-ranging animals. The results indicate that BR teeth have adapted to their natural diet so that in the wild, they achieve a particle size reduction similar to that of GR. However, although GR teeth seem equally adapted to food ingested in captivity, the BR teeth seem less well suited to efficiently chew captive diets. In the case of ruminants, less efficient particle size reduction could contribute to potential clinical problems like "rumen blockage" and bezoar formation. Comparisons of MPS between free-ranging and captive animals might offer indications for the physical suitability of zoo diets