Static Configuration Research Articles

Comparison of Flammability of Low-GWP Refrigerants Using 1.76-m3 Combustion Chamber

ABSTRACT The transition to low global-warming potential (GWP) refrigerants is ongoing. Since a large part of Low-GWP refrigerants is combustible, fundamental flammability parameters have been studied. However, the combustion behavior of accidentally released refrigerants is not fully understood. In this study, we studied the relationship between the flammability parameters such as lower flammability limit (LFL), the fundamental burning velocity (FBV) and the combustion behaviors of Low-GWP refrigerants including R290 (C3H8), R152a (CH3CHF2), R143a (CH3CF3), R142b (CH3CClF2), R41 (CH3F), and R32 (CH2F2). We conducted tests using three experimental configurations: static configuration, laminar and turbulent flow configuration simulating realistic refrigerant leak. Under static conditions, the burning velocities for R290, R152a (CH3CHF2), and R32 were measured in a 1.76 m3 combustion chamber. The measured values of burning velocities were in a good agreement with available literature data. Laminar refrigerant leak was studied for R290, R152a, R41(CH3F), R142b (CH3CClF2), and R32 in a 1.76 m3 combustion chamber. Flammability of turbulent flow leak of R290, R152a, R143a (CH3CF3), and R32 was analyzed using a 237 L plastic container. Experiments simulating laminar and turbulent flow refrigerant leak demonstrated a positive correlation between LFL and the time before ignition. The refrigerant concentration at ignition agreed with LFL. It was found that the combustion behavior of refrigerants under leak conditions corresponds two types of flame propagation. The first type corresponds to a flame which rapidly spreads horizontally on the floor surface from the ignition source. The second type corresponds to flame kernel irregularly appearing around the continuous spark source. The approximate boundary between two types of combustion behavior corresponds to R152a (FBV = 23.6 cm/s, unsupported flame propagation) and R143a（FBV = 7.1cm/s, combustion supported by the continuous ignition source). This result is consistent with ASHRAE 34, ISO 817 and the GHS classification revised in 2017 adopting the burning velocity of 10 cm/s as a boundary between “highly flammable” and “lower flammable” refrigerants.

Cisco Packet Tracer Simulation as Effective Pedagogy in Computer Networking Course

The Computer Networking course commonly taught in mixed mode involving lecture and practical session whereas beside face-to-face theory session, students need to experience hands-on activities in order to appreciate the technology and contents. Nevertheless the abstraction in Computer Networking course such as the complexity in TCP/IP network layering, the connection and configuration of client and server’s framework, differences in static and dynamic IP address configuration had imposed a great challenge for students to understand and grab the main concept of computer networking technology. As such, an approach of using computer network simulation and visualization tool in teaching and learning Computer Networking course is seen beneficial for educators and students. In this research, computer network simulation software of CISCO Packet Tracer was utilized in Computer Networking (MTN3023) course. Students (N=55) were exposed to CISCO Packet Tracer on which they developed Wide Area Network (WAN) that consists of configuration activities of Personal Computer (PC), Servers and Switches according to CISCO standard. Subsequently, student’s feedback and their insight on the effectiveness of CISCO packet Tracer in learning computer networking were probed using questionnaire. All the feedbacks were investigating statistically using SPSS 16.0. From the analysis, the descriptive results shown that all students were agreed (N=32 : Strongly Agree; N=23 : Agree) that CISCO Packet Tracer had successfully help them to understand several key concepts of computer networking and at the same quash some abstractions they faced in the course. In a nutshell, CISCO Packet Tracer as a simulation and visualization tool had been proven to be an effective software in supporting the teaching and learning of computer networking course.

Application of a Priori Hyper-Reduction to the Nonlinear Dynamic Finite Element Simulation of a Rolling Car Tire

Abstract The a priori multi-expansion modal (MEM) hyper-reduction method for nonlinear structural dynamics finite element (FE) problems is described, extended, and applied to the dynamic nonlinear FE simulation of a car tire rolling over a rough road surface, including geometrical, material, follower force, and contact nonlinearities. Rather than using time-domain training simulation data, a priori calculated static nonlinear contact configurations and eigenmodes are used as a reduction basis and to perform the hyper-reduction element sampling. The hyper-reduction element sampling is performed by solving an L1 optimization problem subject to a set of equality constraints. This yields a reduced set of elements with an a priori known cardinality, which depends on the amount of constraints taken into consideration and the reduction basis dimension. It is shown that care has to be taken during the hyper-reduction process when considering distributed contact constraints, as is the case for, e.g., a tire rolling over a rough road surface. Large speedup factors can be obtained while still retaining a relatively high accuracy, making application of the MEM method suitable to, for instance, industrial design optimization cases.

Evaluation of Steel Stairwell Dynamic Characteristics, Under Few Mass Configurations Using Ambient Vibration Method

Application of external mass on existing emergency steel stairwell in this study has altered the natural frequency when the resonance threshold has been reached and allows disruption to the human comfort feeling. Ambient vibration testing and modal analysis were carried out on 6 meter height of emergency steel stairway portal frame by using 1 Hz of tri-axial seismometer sensor and open source software of GEOPSY as the processing tool. The stairwell platforms were subjected by cumulative ascending static mass configurations of 300 kg, 600 kg and 900 kg. Identification of the predominant first mode frequency, f1, and mode shapes were made with specified empirical filtering protocols were applied. Fourier Amplitude Spectra (FAS) was used to transform the ambient vibration time series, when the first predominant frequency under bare frame (BF) condition shows at 8.32 Hz. f1 decreased linearly to 7.35 Hz (BF+300kg), 6.77 Hz (BF+600kg) and 6.23 Hz (BF+900 kg), when the masses were increased. In addition, at these frequencies’ ranges, bad human subjective experiences could be triggered as recommended by previous researchers between 8 to 5 Hz. Besides, the deflection shapes from the first mode frequency was also illustrated at higher deflection amplitude to one of the portal frame’s column which resisting two stairwell platforms. These amplitudes are higher when f1 is decreasing. It can be concluded that, ambient vibration approach has efficiently evaluated the dynamic characteristics and its influence against the structure-person interaction on existing steel stairwell portal frame in this study. Further strengthening work on the steel frame could decrease the reductions percentages of the predominant frequencies, deflection amplitudes and even increase the human comfort level when using the stairwell, especially during building evacuation procedure.

On instabilities of stationary scalar field configurations supported by reflecting compact stars

We study instabilities of the system composed of stationary scalar fields and asymptotically flat horizonless reflecting compact stars. In the probe limit, we obtain bounds on the scalar field frequency. Below this bound, stationary hairy stars are expected to suffer from nonlinear instabilities under massless field perturbations. In other words, we prove that stationary scalar hairy stars are unstable for scalar fields with small frequency.

Effect of symmetrical broken wires damage on mechanical characteristics of stay cable

Broken wires are a common damage in stay cables due to aging and harsh environment. However, the analytical method to study the effect of broken wires on the mechanical characteristics of stay cables is still limited. Therefore, based on the microstructural mechanical model of damaged multi-wire cable, this paper proposes an analytical method for the static and dynamic characteristics of cables with broken wires. The broken wire damage is equalised to the axial stiffness reduction in the end-sliding region and recovery region of the broken wire. Governing equations for static configuration and in-plane free vibration of damaged multi-wire cable are then established. Cables with different physical parameters are studied to research the effect of broken wire damage on the static and dynamic characteristics. The results reveal that an increase in the number of symmetrical broken wires linearly decreases the horizontal component of cable tension in piecewise, linearly increases the sag and decreases the in-plane natural vibration frequency in piecewise. Besides, the cable sag is sensitive to the location of broken wire damage, while the horizontal component of cable tension and natural frequency are not sensitive to the location of the broken wire damage. Under the same broken wire damage, the closer the damage is to the support, the greater the sag is. When the broken wire percentage reaches 18.9% at the mid-span, the relative reduction in horizontal component of cable tension is 1.7%, the relative increase in sag is 1.7% and the relative decrease in the in-plane natural vibration frequency is about 0.85% for 100 m long cable. Meanwhile, broken wire damage hardly alters the static characteristics of the initial slack cable with an aspect ratio greater than 1.002. However, the effect of the broken wire on the static characteristics of the initial taut cable nonlinearly increases with a decreasing aspect ratio. Moreover, the effect of broken wire damage on this cable's static characteristics nonlinearly decreases when the cable length increases. Hence, broken wire damage remarkably influences the static characteristics of short cable.

Three dimensional black strings: instabilities and asymptotic charges

Three-dimensional Einstein gravity coupled to zero, one and two forms is solved in terms of a polyhomogeneous asymptotic expansion, generalising stationary black string solutions. From first order terms we obtain, in closed form, a new solution evolving from the stationary black string structure to a geometry developing a singularity in the future. This new solution itself may be extended to more general ones. Taking into account subleading terms of the asymptotic expansion, both singularities in the past and the future occur. This demonstrates the unstable character of the stationary black string: tiny perturbations generated by terms breaking the rotational invariance of the stationary black string configurations lead to cosmological-like singularities. The symmetry algebra of the conserved charges also is determined: it is a finite dimensional one. In the general case the surface charge associated to energy is not integrable. However we identify a sub-class of solutions, admitting asymptotic symplectic symmetries and as a consequence conserved charges that appear to be integrable.

Thermodynamics-based retention maps to guide column choices for comprehensive multi-dimensional gas chromatography

Comprehensive two-dimensional gas chromatography (GC × GC) provides enhanced separation power over its one-dimensional counterpart – gas chromatography (GC). This enhancement is achieved by the inclusion of a secondary column, the choice of which is a major determinant on the quality of the ultimate separation. When developing and optimizing a new GC × GC method, the choices of stationary phase chemistries, geometries and configurations (which phase serves in which dimension) are of fundamental importance, and must often be addressed even before the manipulation of instrumental conditions. These choices are often made using educated guesses, literature searches, or trial and error. Thermodynamic models of GC separations; however, provide a fast and easy means of acquiring information for guiding these choices. By using characteristic thermodynamic parameters (characteristic temperatures, Tchar, and characteristic thermal constants, θchar), we demonstrate the generation of maps that can inform the choices of column chemistries, phase ratios and configurations for GC × GC separations.

Electromagnetic effects on complexity factor for static cylindrical system

This paper investigates the phenomenon of complexity factor for static charged anisotropic cylindrical configuration. We formulate some basic equations such as Einstein–Maxwell field equations, Tolman–Opphenheimer–Volkoff equation and mass equation. Further, the orthogonal splitting of the Riemann tensor is used to obtain the structure scalars that lead to the complexity factor. Finally, we investigate some theoretical models with vanishing complexity condition. It is found that the complexity of the system increases for α ≤ 1 in the presence of the electromagnetic field.

Nonequilibrium approach to holographic superconductors using gradient flow

We study a charged scalar field in a bulk $3+1$-dimensional anti--de Sitter (AdS) spacetime with a planar black hole background metric. Through the $\mathrm{AdS}/\mathrm{CFT}$ correspondence this is equivalent to a strongly coupled field theory in $2+1$ dimensions describing a superconductor. We use the gradient flow method and solve the flow equations numerically between two fixed points: a vacuum solution and a hairy black hole solution. We study the corresponding flow on the boundary between a normal metal phase and a superconducting phase. We show how the gradient flow moves fields between two fixed points in a way that minimizes the free energy of the system. At the fixed points of the flow the $\mathrm{AdS}/\mathrm{CFT}$ correspondence provides an equivalence between the Euclidean on-shell action in the bulk and the free energy of the boundary, but it does not tell us about fields away from equilibrium. However, we can formally link static off-shell configurations in the bulk and in the boundary at the same point along the flow. For quasistatic evolution at least, it may be reasonable to think of this link as an extension of the $\mathrm{AdS}/\mathrm{CFT}$ correspondence.

Rotating charged AdS solutions in quadratic f(T) gravity

We present a class of asymptotically anti-de Sitter charged rotating black hole solutions in f(T) gravity in N-dimensions, where f(T)=T+alpha T^{2}. These solutions are nontrivial extensions of the solutions presented in Lemos (Phys Lett B 353:46–51. arXiv:gr-qc/9404041, 1995) and Awad (Class Quantum Gravity 20:2827–2834. arXiv:hep-th/0209238, 2003) in the context of general relativity. They are characterized by cylindrical, toroidal or flat horizons, depending on global identifications. The static charged black hole configurations obtained in Awad et al. (JHEP 07:136. arXiv:1706.01773, 2017) are recovered as special cases when the rotation parameters vanish. Similar to Awad et al. (JHEP 07:136. arXiv:1706.01773, 2017) the static black holes solutions have two different electric multipole terms in the potential with related moments. Furthermore, these solutions have milder singularities compared to their general relativity counterparts. Using the conserved charges expressions obtained in Ulhoa and Spaniol (Int J Mod Phys D 22:1350069. arXiv:1303.3144, 2013) and Maluf and Ulhoa (Gen Relativ Grav 41:1233–1247. arXiv:0810.1934, 2009) we calculate the total mass/energy and the angular momentum of these solutions.

Boundary conditions for General Relativity in three-dimensional spacetimes, integrable systems and the KdV/mKdV hierarchies

We present a new set of boundary conditions for General Relativity on AdS3, where the dynamics of the boundary degrees of freedom are described by two independent left and right members of the Gardner hierarchy of integrable equations, also known as the “mixed KdV-mKdV” hierarchy. This integrable system has the very special property that simultaneously combines both, the Korteweg-de Vries (KdV) and modified Korteweg-de Vries (mKdV) hierarchies in a single integrable structure. This relationship between gravitation in three-dimensional spacetimes and two-dimensional integrable systems is based on an extension of the recently introduced “soft hairy boundary conditions” on AdS3, where the chemical potentials are now allowed to depend locally on the dynamical fields and their spatial derivatives. The complete integrable structure of the Gardner system, i.e., the phase space, the Poisson brackets and the infinite number of commuting conserved charges, are directly obtained from the asymptotic analysis and the conserved surface integrals in the gravitational theory. These boundary conditions have the particular property that they can also be interpreted as being defined in the near horizon region of spacetimes with event horizons. Black hole solutions are then naturally accommodated within our boundary conditions, and are described by static configurations associated to the corresponding member of the Gardner hierarchy. The thermodynamic properties of the black holes in the ensembles defined by our boundary conditions are also discussed. Finally, we show that our results can be naturally extended to the case of a vanishing cosmological constant, and the integrable system turns out to be precisely the same as in the case of AdS3.

Interfacial polyconvex energy-enhanced evolutionary model for shape memory alloys

A sharp-interface model describing static equilibrium configurations of shape memory alloys by means of interfacial polyconvex energy density introduced by Šilhavý and extended to a quasistatic situation by Knüpfer and Kružík is computationally tested. Elastic properties of variants of martensite and the austenite are described by polyconvex energy density functions. Volume fractions of particular variants are modeled by a map of bounded variation. In addition, energy stored in martensite–martensite and austenite–martensite interfaces is measured by an interface-polyconvex function. It is assumed that transformations between material variants are accompanied by energy dissipation, which, in our case, is positively one-homogeneous giving rise to a rate-independent model. Various two-dimensional computational examples are presented and the computer code used is made available for download.

Accurate Binding Energies for Lithium Polysulfides and Assessment of Density Functionals for Lithium–Sulfur Battery Research

Lithium–sulfur batteries have high theoretical energy density, but a better knowledge of their intimate structural details will be helpful in improving their conductivity and long-term cycling behavior. In order to identify the stationary configurations of lithium polysulfides (Li2Sn, 2 ≤ n ≤ 8) formed in the charging and discharging processes of the lithium–sulfur batteries, ab initio molecular dynamics was employed to sample the configuration space of Li2Sn, followed by optimization of structures by CCSD(T)-F12b/aug-cc-pVDZ. Using the optimized stationary points, we have created the LiSAE38 benchmark database of atomization energies (AEs) of 38 lithium polysulfide isomers by using the higher-level WMS and W3X-L methods. In addition, the performances of 39 density functionals have been assessed against the benchmark AEs and the relative stabilities of Li2Sn isomers. On the basis of the assessments with the def2-QZVP basis set, the PW6B95, B97-1, B3LYP-D3, TPSS, and DSD-PBEP86 density functionals are the ...

An embodied, platform-invariant architecture for connecting high-level spatial commands to platform articulation

In contexts such as teleoperation, robot reprogramming, human–robot-interaction, and neural prosthetics, conveying movement commands to a robotic platform is often a limiting factor. Currently, many applications rely on joint-angle-by-joint-angle prescriptions. This inherently requires a large number of parameters to be specified by the user that scales with the number of degrees of freedom on a platform, creating high bandwidth requirements for interfaces. This paper presents an efficient representation of high-level, spatial commands that specifies many joint angles with relatively few parameters based on a spatial architecture that is judged favorably by human viewers. In particular, a general method for labeling connected platform linkages, generating a databank of user-specified poses, and mapping between high-level spatial commands and specific platform static configurations are presented. Thus, this architecture is “platform-invariant” where the same high-level, spatial command can be executed on any platform. This has the advantage that our commands have meaning for human movers as well. In order to achieve this, we draw inspiration from Laban/Bartenieff Movement Studies, an embodied taxonomy for movement description. The architecture is demonstrated through implementation on 26 spatial directions for a Rethink Robotics Baxter, an Aldebaran NAO, and a KUKA youBot. User studies are conducted to validate the claims of the proposed framework.

Extra dimensions’ influence on the equilibrium and radial stability of strange quark stars

We analyze the influence of extra dimensions on the static equilibrium configurations and stability against radial perturbations. For this purpose, we solve stellar structure equations and radial perturbation equations, both modified for a $d$-dimensional spacetime ($d\geq4$) considering that spacetime outside the object is described by a Schwarzschild-Tangherlini metric. These equations are integrated considering a MIT bag model equation of state extended for $d\geq4$. We show that the spacetime dimension influences both the structure and stability of compact objects. For an interval of central energy densities $\rho_{cd}\,G_d$ and total masses $MG_d/(d-3)$, we show that the stars gain more stability when the dimension is increased. In addition, the maximum value of $M{G_d}/(d-3)$ and the zero eigenfrequency of oscillation are found with the same value of $\rho_{cd}\,G_d$; i.e., the peak value of $M{G_d}/(d-3)$ marks the onset of instability. This indicates that the necessary and sufficient conditions to recognize regions constructed by stable and unstable equilibrium configurations against radial perturbations are, respectively, $dM/d\rho_{cd}>0$ and $dM/d\rho_{cd}<0$. We obtain that some physical parameter of the compact object in a $d$-dimensional spacetime, such as the radius and the mass, depend of the normalization. Finally, within the Newtonian framework, the results show that compact objects with adiabatic index $\Gamma_1\geq2(d-2)/(d-1)$ are stable against small radial perturbations.

Capture of an external anion beam into a linear Paul trap

We describe a linear Paul trap and high-voltage platform specifically designed for the trapping of a large and pure sample of anions from an external keV-energy beam. Capture and confinement in a static configuration of DC potentials was found to occur by transfer of axial to radial ion momentum due to elastic and inelastic collisions. Stability diagrams both in transmission and capture mode were recorded. The trapping efficiency was observed to be very sensitive to the axial potentials relative to the beam energy. Several 104 oxygen anions were loaded from a 2 keV primary beam and confined for several 100 s. Identification of trapped O− ions and contaminants was achieved by selective laser photodetachment.

A parameter-free particle swarm optimization algorithm using performance classifiers

This paper presents an investigation into the short-term versus long-term performance of various particle swarm optimization (PSO) control parameter configurations. While evidence suggests that the best PSO parameter values to employ are time-dependent, this paper provides an in-depth examination of a small set of parameter values to provide a more concrete quantification of the performance degradation observed with specific control parameter configurations over time. Given that the short-term performance is not necessarily indicative of long-term performance, this paper proposes that machine learning techniques be used to build predictive models based on two easily-observable landscape characteristics. Finally, using the predictive models as a basis, this paper also proposes a parameter-free PSO algorithm, which performs on par with other top-performing PSO variants, namely the three best performing static PSO configurations, particle swarm optimization with time-varying acceleration coefficients (PSO-TVAC), and particle swarm optimization with improved random constants (PSO-iRC).

QCD 3 on the world sheet

In this article, we apply the world sheet approach developed in earlier work to QCD in 1+2 dimensions. The starting point is a field theory on the world sheet that reproduces the planar graphs of QCD parametrized by the light cone variables. We study the ground state of this model using a variational approximation, and show that it consists of a set graphs infinitely dense on the world sheet. The energy of this new ground state is lower than that of the empty world sheet, signaling a phase transition. Also, a finite mass is generated in the originally massless theory. Finally, we consider a particular set of time dependent fluctuations about the static ground state configuration, which result in the formation of a string on the world sheet.

Existence of static spherically-symmetric objects in action-dependent Lagrangian theories

We study static symmetric solutions in the context of a gravitational theory based on a action-dependent Lagrangian. Such theory has been designed as a setup to implement dissipative effects into the traditional principle of least action. Dissipation appears therefore from the first principles and has a purely geometric origin. An interesting feature of this theory is the existence of a coupling four-vector $\lambda_{\mu}$, which in an expanding background is related to cosmological bulk viscosity. General Relativity is recovered with a vanishing $\lambda_{\mu}$. We analyse the existence of equilibrium solutions of static configurations aiming to describe astrophysical objects. We find out that the existence of static spherically symmetric configurations occurs only in the particular scenario with vanishing $\lambda_t$, $\lambda_r$ and $\lambda_{\phi}$ components i.e, $\lambda_{\mu}=\{0,0,\lambda_{\theta},0\}$. Thus, the component $\lambda_{\theta}$ is the unique available parameter of the theory in the astrophysical context. This result severely constrains the existence of this sort of gravitational theories. We proceed then verifying the impact of $\lambda_{\theta}$ on the stability and the mass-radius configurations for a reasonable equation of state for the cold dense matter inside compact stars. We further investigate the relativistic spherical collapse in order to track the structure of geometrical singularities appearing in the theory.