Variable Number Of Particles Research Articles

Enhancing non-newtonian fluid modeling: A novel extension of the cross flow curve model

A number of viscosity and flow curve models can be used to numerically investigate the non-Newtonian behavior of fluids. Although particle size, grain size distribution and concentration play a crucial role in determining the viscosity and flow behavior of suspensions and colloidal systems, they are either ignored or considered indirectly in almost all models. We present a mathematical extension of the widely used Cross flow curve model to account for the effect of concentration and particle size in modeling viscosity and flow curves. In particular, this study takes into account a variable total number of individual particles in unit volume, which is assumed to be constant in other models. The proposed extension allows the flow curve to model suspensions that are typically shear-thinning but can also be Newtonian, or shear-thickening for at different shear rates and concentrations. These considerations provide insight into studying and designing suspensions, colloidal systems, and other complex fluid–solid interactions.

Maxillary sinus lift augmentation: A randomized clinical trial with histological data comparing deproteinized bovine bone grafting vs graftless procedure with a 5-12-year follow-up.

Different protocols and procedures for sinus lift and implant placement are available, generally involving the use of grafts to increase the tissue volume and/or prevent the Schneiderian membrane from collapsing. Among xenografts, deproteinised bovine bone graft (DBBP) is frequently used in sinus lift procedures. Leaving an ungrafted space following membrane elevation has proven to have a bony regenerative potential as well. This study aimed to compare the clinical and histological features of sinus lift surgery performed with or without biomaterials. Patients with severe maxillary posterior atrophy (residual bone height 2-6 mm and residual crest thickness ≥4 mm), and in need of sinus lift surgery to allow the placement of three implants were enrolled and randomly divided into two groups. They underwent sinus lifts with DBBP (control) or with a graftless technique (test) and immediate placement of two implants (a mesial and distal one). After 6 months, a bone sample was retrieved from the area between the previously inserted fixtures, and a third, central implant was placed. The collected bone samples were analyzed morphologically and histomorphometrically. The patients were provided with prosthetic restorations after 6 months and followed up for 5-12 years. Ten patients were enrolled in the test and nine in the control group. The 6-month follow-up showed in the control group an average augmentation of 10.31 mm (±2.12), while in the test group it was 8.5 mm (±1.41) and a success rate of 96.3% in the control and 86.7% in the test group (p > 0.05). The histological analysis evidenced the presence of new bone tissue surrounded by immature osteoid matrix in the test group, and a variable number of DBBP particles surrounded by an immature woven bone matrix in the control group. The results of the present trial indicate that, with residual bone height of 2-6 mm and residual crest thickness ≥4 mm, sinus lift surgery with or without biomaterials followed by implant restoration, produces similar clinical and histological outcomes.

Conformally Invariant Gravity and Gravitating Mirages

The action of an ideal fluid in Euler variables with a variable number of particles is used for the phenomenological description of the processes of particle creation in strong external fields. It has been demonstrated that the conformal invariance of the creation law imposes quite strict restrictions on the possible types of sources. It is shown that combinations with the particle number density in the creation law can be interpreted as dark matter within the framework of this model.

Magnetocalorical Effect and Phase Separation: Theory and Perspectives

Abstract—The problem of the magnetic phase separation effect on the magnitude of the magnetocaloric effect is considered. A general thermodynamic generalized Landau theory with a variable particle number is proposed, which allows simple and consistent treatment of the first order phase transition between the magnetically ordered and disordered phases, taking into account the phase separation. The calculation of the magnetic susceptibility and entropy of phases involved in the phase separation was considered. It is shown that the magnetic susceptibility of the magnetically ordered (disordered) phase participating in the phase separation is negative (positive) in the vicinity of the tricritic point, which can result in the inversion of the sign of the magnetocaloric effect.

Creation rate of Dirac particles at a point source

Only recently has it been possible to construct a self-adjoint Hamiltonian that involves the creation of Dirac particles at a point source in 3d space. Its definition makes use of an interior-boundary condition. Here, we develop for this Hamiltonian a corresponding theory of the Bohmian configuration. That is, we (non-rigorously) construct a Markov jump process in the configuration space of a variable number of particles that is -distributed at every time t and follows Bohmian trajectories between the jumps. The jumps correspond to particle creation or annihilation events and occur either to or from a configuration with a particle located at the source. The process is the natural analog of Bell’s jump process, and a central piece in its construction is the determination of the rate of particle creation. The construction requires an analysis of the asymptotic behavior of the Bohmian trajectories near the source. We find that the particle reaches the source with radial speed 0, but orbits around the source infinitely many times in finite time before absorption (or after emission).

An expectation-maximization algorithm for positron emission particle tracking.

We develop a new algorithm for the tracking of radioactive particles using Positron Emission Particle Tracking (PEPT). The algorithm relies on the maximization of the likelihood of a simple Gaussian mixture model of the lines of response associated with positron annihilation. The model includes a component that accounts for spurious lines caused by scattering and random coincidence, and it treats the relative activity of particles as well as their positions as parameters to be inferred. Values of these parameters that approximately maximize the likelihood are computed by the application of an expectation-maximization algorithm. A generalization of the model that includes the particle velocities and accelerations as additional parameters takes advantage of the information contained in the exact timing of positron annihilations to reconstruct pieces of trajectories rather than fixed positions, with clear benefits. We test the algorithm on both simulated and experimental data. The results show the algorithm to be highly effective for the simultaneous tracking of many particles (up to 80 in one test). It provides estimates of particle positions that are easily mapped to entire trajectories and handles a variable number of particles in the field of view. The ability to track a large number of particles robustly offers the possibility of a dramatic expansion of the scope of PEPT.

Supervised learning of few dirty bosons with variable particle number

We investigate the supervised machine learning of few interacting bosons in optical speckle disorder via artificial neural networks. The learning curve shows an approximately universal power-law scaling for different particle numbers and for different interaction strengths. We introduce a network architecture that can be trained and tested on heterogeneous datasets including different particle numbers. This network provides accurate predictions for all system sizes included in the training set and, by design, is suitable to attempt extrapolations to (computationally challenging) larger sizes. Notably, a novel transfer-learning strategy is implemented, whereby the learning of the larger systems is substantially accelerated and made consistently accurate by including in the training set many small-size instances.

Newton’s Second Law of a particle with variable mass

We approach the question of the movement of a particle with variable mass observed from an inertial frame. We consider two different situations: (i) a particle whose intrinsic mass value varies over time; (ii) the center of mass (CM) of a set of particles with constant mass but with a variable number of particles belonging to it. We show that Newton’s Second Law distinguishes the case in which the intrinsic mass of the particle varies over time from systems composed of particles, with constant mass, whose total mass varies over time. In the first case, we study the consequences of the equation of motion of a particle with variable mass is not covariant in inertial references under Galilean transformations. We also show that the equation that drives the dynamics of the CM of a system with variable number of particles preserves the equivalence of all inertial frames under the Galilean transformations. We verify the non-conservation of the linear momentum vector of the CM of a set of free particles during the time that one particle leaves or comes into the system.

Hamiltonians without ultraviolet divergence for quantum field theories

We propose a way of defining Hamiltonians for quantum field theories without any renormalization procedure. The resulting Hamiltonians, called IBC Hamiltonians, are mathematically well defined (and in particular, ultraviolet finite) without an ultraviolet cutoff such as smearing out the particles over a nonzero radius; rather, the particles are assigned radius zero. These Hamiltonians agree with those obtained through renormalization whenever both are known to exist. We describe explicit examples of IBC Hamiltonians. Their definition, which is best expressed in the particle–position representation of the wave function, involves a kind of boundary condition on the wave function, which we call an interior–boundary condition (IBC). The relevant configuration space is one of a variable number of particles, and the relevant boundary consists of the configurations with two or more particles at the same location. The IBC relates the value (or derivative) of the wave function at a boundary point to the value of the wave function at an interior point (here, in a sector of configuration space corresponding to a lesser number of particles).

Born’s rule for arbitrary Cauchy surfaces

Suppose that particle detectors are placed along a Cauchy surface $\Sigma$ in Minkowski space-time, and consider a quantum theory with fixed or variable number of particles (i.e., using Fock space or a subspace thereof). It is straightforward to guess what Born's rule should look like for this setting: The probability distribution of the detected configuration on $\Sigma$ has density $|\psi_\Sigma|^2$, where $\psi_\Sigma$ is a suitable wave function on $\Sigma$, and the operation $|\cdot|^2$ is suitably interpreted. We call this statement the "curved Born rule." Since in any one Lorentz frame, the appropriate measurement postulates referring to constant-$t$ hyperplanes should determine the probabilities of the outcomes of any conceivable experiment, they should also imply the curved Born rule. This is what we are concerned with here: deriving Born's rule for $\Sigma$ from Born's rule in one Lorentz frame (along with a collapse rule). We describe two ways of defining an idealized detection process, and prove for one of them that the probability distribution coincides with $|\psi_\Sigma|^2$. For this result, we need two hypotheses on the time evolution: that there is no interaction faster than light, and that there is no propagation faster than light. The wave function $\psi_\Sigma$ can be obtained from the Tomonaga--Schwinger equation, or from a multi-time wave function by inserting configurations on $\Sigma$. Thus, our result establishes in particular how multi-time wave functions are related to detection probabilities.

Fast GPU simulation of reinforced concrete at the scale of reinforcement ribs by the discrete element method

The paper presents the development of the GPU-based discrete element method (DEM) code for simulating damage and fracture of cohesive solids with application to reinforced concrete at the scale of reinforcement ribs. The solid volume of concrete and steel is modelled by bonded spherical particles. Very fine discretization, containing more than million particles, is applied to describe the 3D reinforcement bar geometry at the scale of ribs and to investigate cracking behaviour of concrete near the reinforcement bar. The numerical model is validated by using experimental results of the double pull-out test. Influence of the discretization scale to the numerical solution is evaluated by using the reinforcement strain profiles and the cracking patterns. The developed GPU-based DEM algorithm efficiently handles interaction of particles, does not require any atomic operation and allows performing fast damage and fracture simulations with large number of particles. The performance measured on GPU is compared with that attained on different CPUs for varying number of particles. The high value of the Cundall number (particle number multiplied by time steps computed per second) equal to 4.3E+07 is measured on NVIDIA® Tesla™ P100 GPU in the case of 1858560 particles.

Numerical convergence of simulations of galaxy formation: the abundance and internal structure of cold dark matter haloes

ABSTRACT We study the impact of numerical parameters on the properties of cold dark matter haloes formed in collisionless cosmological simulations. We quantify convergence in the median spherically averaged circular velocity profiles for haloes of widely varying particle number, as well as in the statistics of their structural scaling relations and mass functions. In agreement with prior work focused on single haloes, our results suggest that cosmological simulations yield robust halo properties for a wide range of gravitational softening parameters, ϵ, provided: (1) ϵ is not larger than a ‘convergence radius’, rconv, which is dictated by two-body relaxation and determined by particle number, and (2) a sufficient number of time-steps are taken to accurately resolve particle orbits with short dynamical times. Provided these conditions are met, median circular velocity profiles converge to within ≈10 per cent for radii beyond which the local two-body relaxation time-scale exceeds the Hubble time by a factor $\kappa \equiv t_{\rm relax}/t_{\rm H}\rm{\,\, \buildrel\gt \over \sim \,\,}0.177$, with better convergence attained for higher κ. We provide analytic estimates of rconv that build on previous attempts in two ways: first, by highlighting its explicit (but weak) softening-dependence and, second, by providing a simpler criterion in which rconv is determined entirely by the mean inter-particle spacing, l, for example better than 10 per cent convergence in circular velocity for $r\rm{\,\, \buildrel\gt \over \sim \,\,}0.05\, l$. We show how these analytic criteria can be used to assess convergence in structural scaling relations for dark matter haloes as a function of their mass or maximum circular speed.

Double hybrid Kalman filtering for state estimation of dynamical systems

In this paper authors present a new approaches to the hybrid Kalman filtering and modified hybrid Kalman filtering, with the changed order of methods inside (Unscented Kalman Filter and Extended Kalman Filter). For these algorithms, the modification based on double use of Hybrid Kalman Filters (Excented and Unscented) has been proposed. This new modification has been checked for Hybrid Kalman Particle Filters too, for the variable number of particles. Based on the obtained results, one can see that duplication of hybrid filters can improve the estimation quality.

Recent results of HESR original stochastic cooling tanks at COSY

The High Energy Storage Ring (HESR) of the FAIR project at GSI Darmstadt will be very important for different scientific programs due to the modularized start version of FAIR. Stochastic cooling together with barrier bucket operation will be the key component to fulfil the requirements of the different experiments. First pickup and first kicker of the HESR stochastic cooling system have been installed into the COSY accelerator at FZ Juelich. COSY is well suited to test the performance of the HESR stochastic cooling hardware at different energies and variable particle numbers. The novel dedicated HESR-structures were already success-fully tested at the Nuclotron in Dubna for longitudinal cooling and during a beam test in 2017 for transverse cooling at COSY. The results of the last stochastic cooling beam time will be presented as well as the first use of GaN based amplifiers in a stochastic cooling system. The HESR needs fast transmission-lines between PU and KI. Beside air-filled coax-lines, optical hollow fibre-lines are very attractive. First results with such a hollow fibre used for the transverse signal path will be presented.

Enhanced Control and Reproducibility of Non-Neutral Plasmas

The simultaneous control of the density and particle number of non-neutral plasmas confined in Penning-Malmberg traps is demonstrated. Control is achieved by setting the plasma's density by applying a rotating electric field while simultaneously fixing its axial potential via evaporative cooling. This novel method is particularly useful for stabilizing positron plasmas, as the procedures used to collect positrons from radioactive sources typically yield plasmas with variable densities and particle numbers; it also simplifies optimization studies that require plasma parameter scans. The reproducibility achieved by applying this technique to the positron and electron plasmas used by the ALPHA antihydrogen experiment at CERN, combined with other developments, contributed to a 10-fold increase in the antiatom trapping rate.

Gradient approximated exchange energy functionals with improved performances for two-dimensional quantum dot systems

Semilocal exchange-correlation functionals are frequently used to accurately describe the complex many-electron effects of two-dimensional quantum systems. Most of these functionals are designed using the reduced density gradient as the main ingredient. A semilocal functional for the exchange and the corresponding enhancement factor is constructed using the inhomogeneity parameter of the generalized gradient approximations by analyzing the small and large-density gradient expansion of the exchange hole. This exchange functional significantly reduces the error compared to the existing gradient approximations. Performance of the proposed semilocal functional is demonstrated by considering parabolic and Gaussian quantum dots with varying particle number and confinement strength. The results are also compared with that of the exact exchange formalism by considering it as the standard.

International Conference on Gravitation Cosmology and Continuum Mechanics (dedicated to the centenary of Kirill Petrovich Staniukovich)

International Conference on Gravitation Cosmology and Continuum Mechanics (dedicated to the centenary of Kirill Petrovich Staniukovich)

Using Lidar, in-situ measurements and Trajectory Analysis to observe air pollution in Beijing, 2014

We present combined Mie lidar, ozone lidar and wide-range particle spectrometer observations that were carried out in Beijing, north China during two periods—one haze period before the Asia-Pacific Economic Cooperation (APEC) meeting and one moderate pollution period during the meeting in 2014. High extinction coefficient, moderate ozone concentration and variable particle number concentration were obtained throughout the first haze observation period. The mean extinction coefficients in the two pollution periods were 0.52 km-1 and 0.23 km -1 , respectively, at 532 nm. The ozone concentration during the first haze phase was more various with higher average value of 49 ppb compared to that in the second pollution observations (32 ppb). The comparison of aerosols and ozone in different heights indicate different pollution sources and complicated ozone process of generation and disappearance. The four-day back trajectories from a HYSPLIT model indicate that the air masses in the lower boundary layer were advected from the densely populated south regions of China and the long pollution transportation passing through northern China.

Environmental Nanoparticles Are Significantly over-Expressed in Acute Myeloid Leukemia: a Novel Pathogenetic Cofactor?

Background: Continuing growth in the incidence of leukemia suggests a possible environmental etiology correlated to the increase of environmental pollution. Recently, environmental particulate pollution (EPP) has been declared by IARC a Class I carcinogenic agent; it looks reasonable to presume that not only chemicals like benzene and its derivatives, but also other components like EPP could be worth of study. No specific researches have up to now focused the role of EPP on acute myeloid leukemia; we thus have identified a suitable instrumentation and protocol to show the presence and composition of particulate matter in blood samples of patients affected by acute myeloid leukemia patients and in healthy controls.Methods: 38 peripheral blood samples (19 acute myeloid leukemia, 19 healthy controls) were analyzed by means of an Environmental Scanning Electron Microscopy (ESEM) coupled with an Energy Dispersive Spectroscopy (EDS) a sensor capable of identifying the composition of micro- and nano-particles of exogenous nature in pathological tissues (applied for the first time in the current study on blood samples). The results were statistically treated with unpaired two-tailed Student's t-test, MANOVA and Principal Component Analysis.Results: A consistent quantity of micron-, submicron- and nano-sized foreign bodies (from 20 micron down to 100nm) was documented in 18/19 AML cases, whereas they were absent or rare in the controls. The particles appeared as singlet and aggregates (ranging from 5 to 20micron), either in close contact with blood elements or interacting with plasma. Some reacted with blood proteins thus forming composite clusters. A total of 141 aggregates (median 8, range 0-18) in AML, compared to a total of 12 aggregates in controls (median 1, range 0-3) were counted. The aggregate analysis showed variable sizes and number of particles, with a total of 5394 particles in leukemia cases compared to a total of 207 in controls. The total numbers of aggregates and particles were statistically different between cases and controls (MANOVA, P<0.001 e P=0.009 respectively). Aggregates were then analyzed with EDS, identifying their elemental composition. The particles mostly contained highly reactive metals, and appeared not biocompatible and not biodegradable. In particular, micro- and nano-sized particulates were segregated in organic-inorganic clusters, with statistically higher frequency of a subgroup of elements in AML samples (Si, P=0.03; Al, P=0.03; Fe, P=0.002; Ti, P=0.04, Cu, P=0.02, respectively). The analyses of the chemical spectra in some cases allowed to recognize and identify the source of the contamination.Conclusion: In conclusion, we demonstrated the exposure of a subset of AML patients to environmental contaminants, with invasive character in the human body, not biocompatible and biopersistent. AML, as well as myelodysplastic syndromes, are derived from precursor cells critical in innate immunity, that submicronic particles could have triggered. New etiopathogenic hypotheses involving an interaction among sub-micron and nanosized particles with blood components are under evaluation. DisclosuresNo relevant conflicts of interest to declare.

Haze observations by simultaneous lidar and WPS in Beijing before and during APEC, 2014

We present combined Mie lidar, ozone lidar and wide-range particle spectrometer observations which were carried out in Beijing, north China during two periods—one haze period before the Asia-Pacific Economic Cooperation (APEC) meeting and one moderate pollution period during the meeting in 2014. High extinction coefficient, moderate ozone concentration and variable particle number concentration were obtained throughout the first haze observation period. The mean extinction coefficients in the two pollution periods were 0.52 and 0.23 km-1, respectively, at 532 nm. The ozone concentration during the first haze phase was more various with a higher average value of 49 ppb compared with that in the second pollution observations (32 ppb). Compared with the same metrological condition occurring at the end of October, the sharply decreased aerosol extinction coefficient and ozone concentration show the effectiveness of the emission-cutting measures implemented during APEC in November. The comparison of aerosols and ozone in different heights indicate different pollution sources and the complicated ozone process of generation and disappearance. The correlation between the scattering coefficient and particle number concentrations of various diameter depended on the ambient humidity. Especially the particle number concentration (500 nm–1 µm) contributed most to PM2.5 concentration. The four-day back trajectories from a Hybrid Single-particle Lagrangian Integrated Trajectory (HYSPLIT) model indicate that the air masses in the lower boundary layer before and during APEC were advected from the densely populated south regions of China and the long pollution transportation passing through northern China.