Constant Deceleration Research Articles

Dynamics of tilted Bianchi type-III cosmological model in f(R, T) gravity

Tilted Bianchi type-III cosmological model filled with perfect fluid is investigated in f(R, T) theory of gravity, where R is the Ricci scalar and T is the trace of stress energy momentum tensor. Here we study the class of $$f(R, T) = R + 2f(T)$$ . To decipher the solutions of field equations, we used time power-law form of a metric potential C, i.e. $$ C=t^m$$ , where m is a positive constant, which yields constant deceleration parameter. The solution of field equations represent an expanding model of the Universe. The physical behavior of the model are discussed by using some physical parameters.

Fondasi Ontologi Mullȃ Sadrȃ: Sebuah Tinjauan Filsafat

Because a movement is an achievement of new actuality and perfection through motion, every movement is inevitably a strengthening process and causes the movement of something more perfect. Here we need to distinguish two points, one, the process of refinement of a motion and the other is the process of refinement of a moving subject. The moving agent can be constant reaching perfection through movement but the speed of the process can be that the speed of the improvement process increases or decreases or remains. Constant speed and deceleration do not conflict with the process of refinement in a movement. Examples of the process of moving an apple to be sweeter speed more sweetness decreases but still at each time sweeter than before even though the change is slowing down. Consequently, assuming that in a motion, the motion causes a refinement process for the moving agent does not conflict with assuming a reduced speed of the process

Effect of water and rock composition on re-strengthening of cohesive faults during the deceleration phase of seismic slip pulses

The elastic strain energy release rate and seismic waves emitted during earthquakes are controlled by the on-fault temporal evolution of the shear stress during rupture propagation. High velocity friction experiments highlighted that shear stress on the fault surface evolves rapidly during seismic slip pulses. This temporal evolution of shear stress is controlled by both fault weakening at seismic slip initiation and re-strengthening rate towards the end of slip. While numerous studies focused on fault weakening, less attention was given to co-seismic re-strengthening processes. Here we performed 53 friction experiments (normal stress ≤30 MPa, slip-rate ≤6.5 ms−1) imposing constant slip acceleration and deceleration (7.8 ms−2), on cohesive Carrara marble (99% calcite) and micro-gabbro (silicate-built rock) under dry, vacuum and water pressurized conditions. Microstructural observations showed that micro-gabbro accommodated seismic slip by bulk melting of the sliding surfaces, whereas Carrara marble by coupled decarbonation and grain-size dependent crystal plastic processes. Under room humidity conditions and low imposed power density (i.e., product of normal stress per slip rate), re-strengthening rate during the deceleration stage was up to ∼ 17 times faster in marble than in micrograbbro. In the latter, the re-strengthening rate increased slightly with the power density. The presence of water enhanced further this trend. On the contrary, in marbles the re-strengthening rate decreased drastically with power density and in the presence of water. Our experimental observations highlighted the first order importance of the mineralogy and rheology of the slip zone materials and, to a second order, of the presence of water in controlling co-seismic re-strengthening of faults during seismic slip deceleration.

Can the inerter be a successful shock-absorber? The case of a ball-screw inerter with a variable thread lead

This paper investigates an application of a ball-screw inerter for mitigation of impact loadings. The problem of impact absorption is to provide a minimum reaction force that optimally decelerates and eventually stops an impacting object within the available absorber stroke. It significantly differs from vibration mitigation problems which are typical application of inerters. The paper demonstrates that the optimum absorption can be achieved by fully passive means. For known values of the object mass and inerter parameters, the obtained solution is independent of the impact velocity. The optimum passive absorption is achieved by employing a variable thread lead. As a result, two force components emerge, the typical inertance-related force and a damping-like term, and sum up to provide the optimum constant deceleration force. This result is relatively unique: conventional absorbers do not provide a constant force even with complex active control systems. Finally, an optimization problem is formulated to reduce the influence of process uncertainties (range of possible mass values, unknown friction). The results are verified and analyzed in a numerical example.

One-loop quantum gravitational backreaction on the local Hubble rate

We determine corrections to the Hubble rate due to graviton loops in a cosmological background spacetime of constant deceleration parameter. The corrections are gauge-invariant, based on a recent proposal for all-order gauge-invariant observables in perturbative quantum gravity. We find explicit expressions for the cases of matter- and radiation-dominated eras and slow-roll inflation with vanishing second slow-roll parameter. Interestingly, in the latter case the corrections can be described by a quantum-corrected first slow-roll parameter, which brings the spacetime closer to de Sitter space.

A New Class of Bianchi Type-I Cosmological Model in Self-Creation Theory

Bianchi type-I cosmological model has been studied in the self-creation theory of gravitation. A new class of exact solutions has been obtained by considering the model yields a constant deceleration parameter. The physical and geometrical properties of the obtained model are discussed. Also, we study the thermodynamic quantities (Entropy, Enthalpy, Gibbs energy and Helmholtz energy) of the universe with help of the scalar field $$\phi$$ .

An experimental investigation of interfacial instability in separated blood

Experiments are done with separated human blood decelerated at constant rates to determine the maximum deceleration rate while avoiding remixing of the layers, which have different densities and viscosities. The deceleration rate affects both the stability and separation of particles through sedimentation. The velocity at onset of instability for a constant deceleration rate is experimentally determined for a 12‐cm‐diameter disk. Parameters of cell pack thickness, plasma thickness, and total thickness are investigated experimentally, and the only statistically significant parameter to affect stability is rate of deceleration. The data describe a correlation separating regions of stability and instability. To understand stability in decelerating flow of separated blood plasma and cells, the equations of motion are solved for a two‐layer fluid flow with a moving boundary and free surface. Inclusion of non‐Newtonian rheology of blood predicts large discontinuities in the shear rate, which is proposed as the cause of the interfacial instabilities. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1376–1386, 2019

Simulation platform for constant deceleration braking system based on Simulink

ABSTRACTBased on the idea of nodal cavity method, the simulation platform of constant deceleration braking system is built in Simulink. According to JKMD 4.5 × 4 mine hoist and its matching E141A constant deceleration braking system, the simulation platform parameters are set up. Finally, given the deceleration value, the safety braking simulation is carried out. The simulation platform is verified by simulation, which provides technical support for the further study of dynamic characteristics of safe braking and the design of reliable braking system.

A stable flat universe with variable cosmological constant in f(R, T) gravity

In this paper, a general FRW cosmological model has been constructed in f(R,T) gravity reconstruction with variable cosmological constant. A number of solutions to the field equations has been generated by utilizing a form for the Hubble parameter that leads to Berman’s law of constant deceleration parameter q = m − 1. The possible decelerating and accelerating solutions have been investigated. For (q > 0) we get a stable flat decelerating radiation-dominated universe at q = 1. For (q < 0) we get a stable accelerating solution describing a flat universe with positive energy density and negative cosmological constant. Nonconventional mechanisms that are expected to address the late-time acceleration with negative cosmological constant have been discussed.

Relationship between magnetic field and anisotropy parameter in gravitation theories

The magnetized strange quark matter (MSQM) solutions are obtained for a Marder type universe using constant deceleration parameter. The exact solutions of field equations are obtained for f(R,[Formula: see text]T) = R + 2f(T) model given by [T. Harko et al., Phys. Rev. D 84, 024020 (2011)] with cosmological term. Also, we have obtained General Relativity (GR) solutions for MSQM distributions. For [Formula: see text], we get the dark energy model, i.e. [Formula: see text], [Formula: see text] and [Formula: see text]. However, for [Formula: see text], we find the cosmological constant [Formula: see text] as negative in f(R,[Formula: see text]T) theory and GR. These results agree with [S. Aygün et al., Astrophys. Space Sci. 361, 380 (2016); C. Aktaş and S. Aygün, Chinese J. Phys. 55, 71 (2017); P. K. Sahoo et al., Mod. Phys. Lett. A 32, 1750105 (2017)] in f(R,[Formula: see text]T) theory. The physical consequences of our obtained models are discussed at the end.

Ricci dark energy model with bulk viscosity

In order to explore the possibility of bulk viscosity as a possible candidate of dark energy to explain the accelerating universe, we investigate the dissipative processes in the holographic Ricci dark energy (HRDE) model within the framework of the standard Eckart theory of relativistic thermodynamics. We assume that the flat Friedmann-Robertson-Walker universe is filled with pressureless dark matter and viscous HRDE. We obtain the exact solutions of non-viscous and viscous HRDE models, respectively. We plot the evolution of the scale factor and deceleration parameter to observe the transition phase in the viscous case. We also discuss two geometrical diagnostics, namely the statefinder and Om to discriminate from other existing dark energy models. In the non-viscous HRDE model, the power-law form of expansion is obtained which gives the constant deceleration parameter and statefinder pair. It does not show phase transition. In the viscous HRDE model, we consider all possible forms of bulk viscous coefficient (with constant or general form of viscous terms) and discuss the cosmological evolution in detail. We obtain the exponential expansion of the scale factor which gives the time-dependent deceleration parameter and statefinder pair. The model shows the transition from the decelerated phase to the accelerated phase depending on the values of the viscous term. It starts to accelerate in the past for large values of the viscous term. The trajectory of the statefinder pair shows that for small values of the viscous term, the trajectory is curved and starts from quintessence in early time and approaches to $\Lambda$ CDM model in late time. It is also observed that for large values of the viscous term, it behaves like the Chaplygin gas in early time but approaches to $\Lambda$ CDM model in late time. We also plot the trajectory of the deceleration parameter, statefinder pair and Om with the model parameter to observe the evolutionary behavior of the universe. It also shows a similar behavior except for the fact that it only behaves as quintessence in the past but approaches to $\Lambda$ CDM or the steady state model in late time. The results of viscous HRDE models show that the recent acceleration is well explained with the viscous term.

Modeling of the temperature regime and stress state in the thermal sensitive pad-disk brake system

An analytical–numerical nonlinear model to investigate temperature fields and thermal stresses in a pad and a disk for a single braking with a constant deceleration has been proposed. For this purpose, the boundary-value heat conduction problem for a tribosystem strip–semi-space has been formulated, which takes into account the temperature dependence of the thermophysical properties of materials. The solution to this problem has been obtained by a partial linearization through the Kirchhoff substitution, and next with a subsequent use of the method of linearizing parameters. Knowing the distribution of temperature fields in the elements of a friction pair, the thermal stresses have been established within the theory of thermal bending of plates. In this case, the temperature dependence of the Young’s modulus, Poisson’s ratio, and linear thermal expansion of the pad and disk materials have been additionally taken into account. The numerical analysis has been performed for a friction pair consisting of a titanium alloy pad and a steel disk.

Dynamic Responses of a Four-Span Continuous Plate Structure Subjected to Moving Cars With Time-Varying Speeds

This paper presents an experimental and theoretical study of vibration of a four-span continuous plate with two rails on top and four extra supports excited by one or two moving model cars, which is meant to represent vehicle–track–bridge dynamic interaction. Measured natural frequencies of the plate structure are used to update the finite element (FE) model of the structure. Four laser displacement transducers are placed on the ground to measure the displacements of the plate. A laser-Doppler vibrometer is used to measure the real-time speed of the moving cars, which reveals that the speeds decrease with time at a small and almost constant deceleration which can affect the structural dynamic response. A fascinating experiment is the use of two cars connected in series, which is very rare and has never been done on a multispan structure. Vibration of the plate structure excited by two moving cars separated at a distance is also measured and exhibits interesting dynamic behavior too. A theoretical model of the whole structure is constructed and an iterative method is developed to determine the dynamic response. The numerical and the experimental results are found to agree very well, in particular when deceleration is considered in the theoretical model.

A fuel-optimal driving strategy for a single vehicle with CVT

The efficiency of the continuously variable transmission (CVT) is within 70∼95%, so the effects on the fuel consumption cannot be ignored. In this paper, we first analyze the quantitative relationship between the running states of inertial combustion engine with CVT and the fuel consumption, and then propose a fuel-optimal driving strategy for a vehicle with CVT. In the strategy, the vehicle speed and acceleration, the engine torque and speed, and the CVT ratio in the processes of acceleration, uniform motion and deceleration are calculated. The numerical results show that when the driving distance is less than a critical value, this vehicle experiences an acceleration–deceleration process, otherwise this vehicle experiences an acceleration–constant–deceleration process. The results can provide a fuel-optimal strategy for a vehicle under different driving distance, which can be used to the human driving guidance, the driving assistance system and the autonomous vehicles.

Dynamic response of an infinite beam resting on a Winkler foundation to a load moving on its surface with variable speed

The problem of the dynamic response of an infinite beam resting on a Winkler foundation to a load moving on its surface with variable speed is solved here analytically/numerically under conditions of plane strain. The beam is linearly elastic with viscous damping and obeys the theory of Bernoulli-Euler. The elastic foundation is characterized by its spring constant and hysteretic damping coefficient. The moving point load has an amplitude harmonically varying with time and moves with constant acceleration or deceleration along the top beam surface. The problem is solved by first applying the Fourier transform with respect to the horizontal coordinate x and the Laplace transform with respect to time t to reduce the governing equation of motion of the beam to an algebraic one, which is solved analytically. The transformed beam deflection solution is inverted numerically after some simplifying analytical manipulations to produce the time domain beam response. Parametric studies are conducted in order to assess the effects of the various parameters on the response of the beam, especially those of acceleration and deceleration. Comparisons with the case of a finite beam are also done in order to assess the effect of the beam length.

Viscous cosmology in new holographic dark energy model and the cosmic acceleration

In this work, we study a flat Friedmann–Robertson–Walker universe filled with dark matter and viscous new holographic dark energy. We present four possible solutions of the model depending on the choice of the viscous term. We obtain the evolution of the cosmological quantities such as scale factor, deceleration parameter and transition redshift to observe the effect of viscosity in the evolution. We also emphasis upon the two independent geometrical diagnostics for our model, namely the statefinder and the Om diagnostics. In the first case we study new holographic dark energy model without viscous and obtain power-law expansion of the universe which gives constant deceleration parameter and statefinder parameters. In the limit of the parameter, the model approaches to Lambda CDM model. In new holographic dark energy model with viscous, the bulk viscous coefficient is assumed as zeta =zeta _{0}+zeta _{1}H, where zeta _{0} and zeta _{1} are constants, and H is the Hubble parameter. In this model, we obtain all possible solutions with viscous term and analyze the expansion history of the universe. We draw the evolution graphs of the scale factor and deceleration parameter. It is observed that the universe transits from deceleration to acceleration for small values of zeta in late time. However, it accelerates very fast from the beginning for large values of zeta . By illustrating the evolutionary trajectories in r-s and r-q planes, we find that our model behaves as an quintessence like for small values of viscous coefficient and a Chaplygin gas like for large values of bulk viscous coefficient at early stage. However, model has close resemblance to that of the Lambda CDM cosmology in late time. The Om has positive and negative curvatures for phantom and quintessence models, respectively depending on zeta . Our study shows that the bulk viscosity plays very important role in the expansion history of the universe.

Tilted Bianchi type-I wet dark fluid model in Saez and Ballester theory

Tilted Bianchi-I wet dark fluid cosmological model is investigated in Saez and Ballester scalar theory of gravitation. Background cosmologies are obtained for a constant deceleration parameter. We consider a linear relationship between the shear scalar and the expansion scalar. We have discussed some physical and geometrical properties of the models. In our models, equation of state of the dark energy is observed to behave like a cosmological constant at late times.

On mathematical analysis for bianchi type–I string cosmological model in modified theory of relativity

The present paper deals with a spatially homogenous Bianchi Type- I massive string cosmological model with bulk viscosity and decaying vacuum energy density. The Einstein’s field equations are solved by applying a special law of variation of Hubble parameter that yields a constant deceleration parameter. Assuming the constant deceleration parameter negative and suitable form of decaying vacuum energy density, an accelerating model of the universe is derived in the presence of string scenario. The strings eventually disappear from the universe for sufficiently large-times. The physical and geometric properties of the models are also discussed.

Miniaturization of physics system in Sr optical clock

The compactness and robustness of the vacuum setup are the major limitations to develop transportable and space-borne optical clocks. The first step in the engineering challenge is to reduce volume and weight with respect to a stationary system. In this paper, we present the realization of a miniaturized vacuum system by building two anti-Helmholtz coils inside the vacuum magneto-optical-trap (MOT) chamber. The built-in coils are specially designed to minimize the distance between the coils, and in this way it is possible to reduce the current needed to realize a typical magnetic gradient of 40 Gs/cm required for blue MOT. When the MOT coil current is 2 A, an axial magnetic field gradient of 43 Gs/cm is obtained in the center of the MOT, which is enough for the first stage Doppler cooling. This novel design allows us to reduce size, weight and power consumption with respect to a traditional laser cooling apparatus, and simultaneously avoid complicating the water cooling equipment. Our vacuum system has a size of 60 cm×20 cm×15 cm, about 1/10 of the original system in the laboratory. In addition, the circularly polarized Zeeman slowing laser is sent to counter propagating atomic beam, and atoms at a few hundred meters per second are now routinely slowed down to velocities of tens of meters per second. As a result, about 16.4% of the atoms are actually trapped into the blue MOT. The final temperature of the blue MOT is approximately 10.6 mK, and the internal diameter is 1.5 mm by observing the expansion of the atoms from the MOT. The populations of cold atoms finally trapped in the MOT are 1.6×106 of 88Sr and 1.5×105 of 87Sr. The 1S0 → 1P1 transition used for the blue MOT is not perfectly closed due to the decay channel of the 5p1P1 → 4d1D2, and a part of atoms are stored in the 3P2 and 3P0 states. To prevent the atoms from losing, 707 and 679 nm repumping lasers are employed to recycle these atoms in the 3P1 state, and then the atoms decay to the ground state 1S0. Now the typical number of loaded atoms dramatically increases by 5 times compared with before. The slowing efficiency of Zeeman slower is also optimized for the operation with deceleration related to the parameter of magnet length, which uses more effectively available magnetic field distribution, in contrast to the usual constant deceleration mode. Our future work will focus on constructing a Zeeman slower combined with permanent magnets or an electric magnet for better tuning of the magnetic field.

Cosmological parametrizations and their scalar field descendants

In literature, there exist numerous cosmological solutions based upon some specific scheme of parametrization of cosmological parameters. Our present work is an attempt to reconstruct the field potentials in case of (non)phantom fields for different models resulting from parametrization of a(t) , H(t) and q(t) in the framework of Friedmann Robertson Walker (FRW) geometry. In addition we carry out similar procedure to reconstruct the field potentials for tachyonic field for the same models. In this note, we reconstructed the field potentials for some known models e.g. constant deceleration parameter model, linearly varying deceleration parameter model and a model based on a specific parametrization of Hubble parameter. The procedure adopted here shows that in principle, the scalar field potentials for quintessence, phantom and tachyonic fields can be reconstructed for any scheme of parametrization of cosmological parameters a(t),q(t),H(t),w(t),ρ(t) or p(t) .